helium turbomachinery operating experience from gas turbine power plants

8112019 Helium Turbomachinery Operating Experience From Gas Turbine Power Plants

httpslidepdfcomreaderfullhelium-turbomachinery-operating-experience-from-gas-turbine-power-plants 135

Helium turbomachinery operating experience from gas turbine power plants

and test facilities

Colin F McDonald

McDonald Thermal Engineering 1730 Castellana Road La Jolla CA 92037 USA

a r t i c l e i n f o

Article history

Received 19 November 2011

Accepted 21 February 2012

Available online 27 March 2012

Keywords

Closed Brayton cycle

Helium gas turbine

Compressor

Turbine

Helium circulator

Test facilities

a b s t r a c t

The closed-cycle gas turbine pioneered and deployed in Europe is not well known in the USA Sincenuclear power plant studies currently being conducted in several countries involve the coupling of a high

temperature gas-cooled nuclear reactor with a helium closed-cycle gas turbine power conversion system

the experience gained from operated helium turbomachinery is the focus of this paper

A study done as early as 1945 foresaw the use of a helium closed-cycle gas turbine coupled with a high

temperature gas-cooled nuclear reactor and some two decades later this was investigated but not

implemented because of lack of technology readiness However the 1047297rst practical use of helium as a gas

turbine working 1047298uid was recognized for cryogenic processes and the 1047297rst two small fossil-1047297red helium

gas turbines to operate were in the USA for air liquefaction and nitrogen production facilities In the 1970rsquos

a larger helium gasturbine plant andhelium test facilities were builtand operated in Germany to establish

technology bases for a projected future high ef 1047297ciency large nuclear gas turbine power plant concept

This review paper covers the experience gained and the lessons learned from the operation of helium

gas turbine plants and related test facilities and puts these into perspective since over three decades

have passed since they were deployed An understanding of the many unexpected events encountered

and how the problems some of them serious were resolved is important to avoid them being replicated

in future helium turbomachines The valuable lessons learned in the past in many cases the hard way

particularly from the operation in Germany of the Oberhausen II 50 MWe helium gas turbine plant andthe technical know-how gained from the formidable HHV helium turbine test facility are viewed as

being germane in the context of current helium turbomachine design work being done for future high

ef 1047297ciency nuclear gas turbine plant concepts

2012 Elsevier Ltd All rights reserved

1 Introduction

While the pioneer closed-cycle gas turbine power plant oper-

ated in Switzerland in 1939 [1] the commercial deployment of this

type of prime-mover was delayed by a decade or so because of the

Second World War and the dif 1047297cult economic times that followed

it The initial success of the closed-cycle gas turbine in the 1950swas its ability to burn low-grade fuels available at the time such as

coal blast furnace gas coke-oven gas heavy oil and peat in its

external heater at modest levels of turbine inlet temperature and

operation in a combined power and heat mode The high grade

sensible heat rejection from the intercooler and precooler offered

ideal cogeneration possibilities and facilitated the use of economic

dry cooling

More than 20 or so plants were built accumulating an operating

time of about 750000 h with some of them in service for over

100000 trouble-free hours An interesting account has been

documented [2] on the construction and operation of closed cycle

gas turbine plants in Europe with emphasis on those using air as

the working 1047298uid in the closed-cycle power conversion system

The performance of early open cycle industrial gas turbines

was modest because of the component technology status in that

era With increasing technology from rapidly developing aeroen-gines being transferred to industrial gas turbines particularly

advancement in turbine inlet temperature as shown on Fig 1

which was generated in 1995 [3] and still considered to be fairly

representative today the early advantages of the externally-1047297red

closed-cycle were eclipsed Gains in turbine inlet temperature

over the years for closed-cycle gas turbines were only incremental

since they were limited by available metallic radiant heater tech-

nology The extrapolation of the closed-cycle gas turbine inlet

temperature trend on Fig 1 beyond 1995 (to say a postulated value

of 1050 C by 2012) did not materialize for fossil-1047297red plants

because of minimal advancements made in ceramic heatE-mail address kmcdona1sanrrcom

Contents lists available at SciVerse ScienceDirect

Applied Thermal Engineering

j o u r n a l h o m e p a g e w w w e l s e v i e r c o m l o c a t e a p t h e r m e n g

1359-4311$ e see front matter 2012 Elsevier Ltd All rights reserved

doi101016japplthermaleng201202041

Applied Thermal Engineering 44 (2012) 108e142



exchanger technology or for nuclear plants since no large VHTR

plants were built although the small 46 MWt AVR nuclear plant in

Germany operated successfully with a helium reactor outlet

temperature of 950 C for many years

By the late 1960rsquos it had become clear that externally-1047297red fossil

gas turbine plants could no longer compete with rapidly improving

simpler higher ef 1047297ciency more compact and lower cost open cycle

gas turbines

The coupling of a high temperature gas-cooled nuclear reactor

with a closed-cycle gas turbine power conversion system usinghelium was 1047297rst suggested by Professor Curt Keller (co-founder of

the closedBrayton cycle gas turbine with Professor Ackeret) in 1945

[1] From the technology standpoint it was clearly ahead of its time

however it did generate interest in the use of helium as an attrac-

tive working 1047298uid and this topic has been studied periodically over

the last six decades The initial deployment of fossil-1047297red helium

gas turbines in the 1960rsquos were for specialized cryogenic processes

However in this time frame it had become clear that the future of

the closed-cycle gas turbine was really tied to its coupling with

a high temperature gas-cooled nuclear reactor A 1047297rst step towards

this ambitious goal was the needed demonstration of a large

helium gas turbine plant The Oberhausen II 50 MW helium gas

turbine plant started in 1974 and was followed by a large helium

turbomachine test facility (HHV) both of these being located inGermany In the ensuing three and a half decades or so work on

nuclear gas turbines has essentially been limited to paper studies

Projecting into the future an advanced modular VHTR demon-

stration plant embodying a helium closed-cycle gas turbine power

conversion system with the potential for an ef 1047297ciency of over 50

percent could perhaps be built and become operational in circa

2025e2030

2 Closed-cycle gas turbine background

21 Fossil- 1047297red plants

At a time when practical gas turbine work was in its infancy

the basic patent for the closed-cycle gas turbine by Ackeret and

Keller (CH 468287) was registered in Bern Switzerland in July

1935 Following his work on airfoil theory [4] much credit is given

to the late Professor Keller for engineering the 1047297rst closed-cycle

gas turbine a 2 MW power plant that was built and run in Zur-

ich in 1939 This pioneering plant has been well documented

previously [1256] and only its major features are highlighted

below

The AK-36 plant shown on Fig 2 was based on a recuperated

cycle with a turbine inlet temperature of 660 C (1220 F) The

compression process was split into three sections with two stagesof intercooling Based on prevailing technology a very large number

of compressor and turbine stages were required With an external

light-oil 1047297red heater the plant demonstrated an ef 1047297ciency of over

30 percent when operating with a turbine inlet temperature of

700 C (1292 F) During the Second World War the plant operated

for about 6000 h providing electrical power for the Escher Wyss

plant facility in Zurich

This 2 Mwe pioneer plant paved the way for closed-cycle gas

turbine deployment in Europe and with air as the working 1047298uid

plants burning a variety of low-grade fuels have been documented

previously [27e9] The 14 MW Oberhausen I closed cycle gas

turbine plant operated in Germany in a combined power and heat

mode between 1960 and 1982 A view of this plant is shown on

Fig 3 and details of the operational problems encountered andhow they were resolved are discussed in a later section The last

closed-cycle gas turbine to operate commercially in Europe with

air as the working 1047298uid was the 17 MW Gelsenkirchen plant [10]

Starting in 1967 this plant was externally 1047297red with blast furnace

gas and around 10 percent light oil With axial 1047298ow turboma-

chinery an ef 1047297ciency of 30 percent was achieved and the reject

heat was used for district heating The plant proved to be very

reliable and ran for almost 100000 h

After this plant entered service it was apparent that the fossil-

1047297red closed-cycle gas turbine could no longer compete with open

cycle gas turbines however one further plant was built In 1972

a combined power and district heating plant was installed in

Vienna [2] Rated at 30 MW the Spittelau plant was the largest

closed-cycle plant using air as the working 1047298

uid Fired with heavy

Nomenclature

ANP aircraft nuclear propulsion

AGR advanced gas cooled reactor

AVR Arbeitsgemeinschaft Versuchsreaktor

BBC Brown Boveri amp Company

CAD computer aided design

CAE computer aided engineering

CFD computational 1047298uid dynamics

CHP combined heat and power

dB decibel

EVO Energieversorgung Oberhausen

FEA 1047297nite element analysis

FSV Fort St Vrain

HTGR power plant

GA general atomics

GHH Gutehoffnungeshutte Sterkrade AG

GT gas turbine

GTeHTR nuclear gas turbine

GTeMHRgas turbine modular helium reactor

GTeVHTR advanced nuclear gas turbine

HP high pressureHHT high temperature helium turbine

HHV high temperature helium test facility

HTGR high temperature gas cooled reactor

HTR high temperature reactor

IHX intermediate heat exchanger

ICR intercooled and recuperated

INL Idaho National Laboratory

ISI inservice inspection

JAEA Japanese Atomic Energy Agency

kW kilowatt

LP low pressure

MHR modular helium reactor

MW megawatt

MPa mega pascal

NGNP next generation nuclear plant

NGT nuclear gas turbine

NGTCC nuclear GT combined cycle

ODS oxide dispersion strengthened alloy

PBMR pebble bed modular reactor

PCS power conversion system

RC recuperated cycle

ST steam turbine

THTR thorium high temperature reactor

TIT turbine inlet temperatureTZM tungsten zirconium molybdenum alloy

VHTR very high temperature reactor

CF McDonald Applied Thermal Engineering 44 (2012) 108e142 109



oil the turbine inlet temperature was 720 C (1328 F) and with

a pressure ratio of 6 two stages of intercooling were used Because

of a variety of technical problems (including excessive rotor

vibration and the failure in quick succession of two blades in the

1047297rst stage of the LP turbine later determined to be due to Karman

vortices originating in the turbine inlet casing) and overriding

political issues this plant was never commissioned for commercial

operation This was a disappointment to engineers who felt at the

time it was the 1047297nest closed-cycle gas turbine ever designed and

built [2]In the 1980rsquos following the introduction of 1047298uidized bed tech-

nology for the combustion of low-grade fuels particularly coal

there was renewed interest in closed-cycle gas turbines A 5 MW

closed-cycle gas turbine burning a low-grade fuel (ie petroleum

coke in an atmospheric 1047298uidized combustor) was built by Garrett

Corporation in the USA in 1985 After evaluating different working

1047298uids [11] air was selected for overall simplicity An overall view of

this plant is shown on Fig 4 With a turbine inlet temperature of

790 C (1454 F) the plant operated well and had low emissions

[12] but was not commercialized because of signi1047297cant advance-

ments being made in the open cycle gas turbine 1047297eld and company

realignments This was the last closed-cycle gas turbine to operate

burning a low-grade fuel and essentially represented the end of an

era spanning 45 years

To the authorrsquos knowledge the last closed-cycle gas turbine

plant to operate was a natural gas-1047297red demonstration facility (as

shown on Fig 5) developed by British Gas at their Coleshill site

near Birmingham in 1995 [13] The closed loop working 1047298uid was

a composition of nitrogen and 2 oxygen The gas 1047298ow in the

circuit was provided by a turbomachine arrangement consisting

of two turbochargers but the rotating assembly did not include

an electrical generator This plant was noteworthy regarding

the use of an advanced heat source exchanger operating at

a temperature several hundred degrees Centigrade higher than inexternally-1047297red European closed-cycle gas turbine plants The

gas-1047297red heater with a thermal rating of about 1000 kWt con-

sisted of a radiant and convective section with headers formed in

a ldquoharprdquo arrangement This tubular heat exchanger was fabricated

from an oxide dispersion strengthened (ODS) alloy [14] A gas

temperature of 1070 C leaving the radiant section was achieved

with this externally 1047297red heater but by means of a bypass

system the gas temperature entering the turbine was reduced to

900 C

This project was intended to lead to a 300 MWe closed-cycle gas

turbine plant using helium as the working 1047298uid with a higher

turbine inlet temperature Due to changes in the organization at the

time testing of the small gas-1047297red facility in the UK did not

advance beyond the initial development phase This demonstration

Fig 1 Gas turbine inlet temperature trends

CF McDonald Applied Thermal Engineering 44 (2012) 108e142110



represented the end of an era of gas-1047297red closed-cycle gas turbine

activities

While valuable experience had been gained in the design

fabrication operation and maintenance of plants with air as the

working 1047298uid [2] the future of this prime-mover was seen to be

with helium and its coupling with a high temperature nuclear heat

source in the 21st century But before this ambitious venture could

be undertaken operating experience was needed with large size

helium turbomachinery in fossil-1047297red plants and in dedicated test

facilities

22 Nuclear gas turbine power plant studies

The Dragon helium cooled reactor was the pioneer HTR plant to

operate and this project took place in the UK between 1959 and

1976 [15] The DragonHTR didnot have a power conversion system

and the reject heat was dissipated in air-blast coolers Follow-on

HTR power plant designs were based on steam cycle power

conversion systems but from the early days of the HTR in the UK

nuclear gas turbine variants were recognized and design concepts

established [16]

From the mid 1960rsquos to about 1980 HTR gas turbine plant

studies in the UK USA and Germany were mainly focused on large

helium turbomachines installed in prestressed concrete reactor

vessels With machines rated between 300 and 1000 MWe the

resultant plant concepts were complex [17] In about 1980 it had

become clear that such concepts would require an extensive

development effort to establish a technically viable nuclear gas

turbine plant to satisfy demanding safety and licensing criteria

and further design innovation was necessary to identify plant

features for improved economics [18] Accordingly there was

a cessation of nuclear gas turbine plant studies in the USA and

Germany and interest reverted to earlier steam cycle HTR plant

concepts

In 1979 a new and innovative modular HTR concept based on

a pebble bed reactor core was proposed by researchers in Germany

Fig 3 Oberhausen I 14 MWe closed-cycle gas turbine utility power plant operated from 1960 to 1982 (Courtesy EVO)

Fig 2 Pioneer AK-36 2 MWe closed-cycle gas turbine with air as the working 1047298uid

operated in Switzerland in 1939 (Courtesy Escher Wyss)




[1920] Initial studies were focused on steam cycle plant concepts

in which the reactor core and major components were installed in

two separate vertical steel vessels After the Chernobyl accident in

1986 work intensi1047297ed on the modular HTR with emphasis on its

passive decay heat removal and inherent safety features While

a compact direct cycle nuclear gas turbine version of the modular

HTR was 1047297rst suggested in the USA in 1986 [21] it wasa further 1047297ve

years or so before it became accepted based to a large extent on its

potential for very high ef 1047297ciency

Evolution of the nuclear gas turbine power plant concept

spans a period of over six and half decades with intermittent

design studies undertaken by different engineering organizations

in various countries [22] In the last 20 years or so PCS paperstudies have been focused on plant layout arrangements and on

helium turbomachine design with limited sub-component

development [23] in support of various modular nuclear gas

turbine concepts

Up until about 2009 projects in different states of design

de1047297nition were being investigated in several countries and these

are summarized as follows 1) in a joint USARussia project

(GTeMHR) the design of an integrated concept (with all the PCS

components installed in a single pressure vessel) is based on

a direct ICR cycle with a vertically oriented 286 MWe helium tur-

bomachine with a turbine inlet temperature of 850 C [24] 2) the

Japanese GTeHTR300 is a distributed plant concept (the PCS

components being installed in separate pressure vessels) with

a direct recuperated cycle and embodies a horizontal 274 MWe

turbomachine with a turbine inlet temperature of 850 C [25] 3 ) i n

France the ANTARES distributed concept is of the indirect type

using an IHX and with a combined gas and steam turbine PCS has

a power output of 280 MWe with a turbine inlet temperature of

800 C [26] 4) in China a study was undertaken of the HTR e10GT

concept involving the future coupling of a small vertical 22 MWe

helium turbine with the HTR-10 pebble bed reactor it being an

integrated concept with an ICR cycle and a turbine inlet temper-

ature of 750 C [27] and 5) in South Africa design and develop-

ment activities had been underway for several years on a nuclear

gas turbine demonstration plant project (PBMR) involving the

coupling of a helium gas turbine PCS with a pebble bed reactor for

operation in about 2015 For this modular plant a distributedsystem based on an ICR cycle embodied a horizontal 165 MWe

helium turbomachine with a turbine inlet temperature of 900 C

[2829] However in 2009 work on this gas turbine demonstration

plant was terminated and the project redirected to an indirect

steam cycle cogeneration plant concept The cancellation of the

PBMR gas turbine was a disappointment since some had viewed

this demo plant as a benchmark for the eventual commercializa-

tion of modular nuclear gas turbine plants

3 Reasons for choice of helium as the working 1047298uid

Following the initial deployment of European fossil-1047297red gas

turbines with air as the working 1047298uid the demand for plants with

higher powerlevels instigated studies to evaluate other gases in the

Fig 4 Last closed-cycle gas turbine (rated at 5 MWe) burning a low-grade fuel (petroleum coke) in a 1047298uidized bed combustor operated in 1985 (Courtesy Garrett Corporation)




closed power conversion loop Performance analyses and compo-

nent design studies were undertaken for gases that included

helium nitrogen carbon dioxide various gas mixtures and

nitrogen tetroxide For terrestrial power generation considering

the size of the major components namely the turbomachine heat

exchangers casings ducts and the external fossil-1047297red heater itwas generally concluded that for plants rated up to about 30 MWe

air was the favored working 1047298uid from the standpoints of

simplicity conventionality and cost

For the nuclear gas turbine the choice of the working 1047298uid

involved considerations being given from both the reactor coolant

and power conversion system standpoints Studies by engineers

and physicists concluded that helium being neutronically neutral

and chemically inert was compatible with the reactor turboma-

chinery and heat exchangers and acceptable for plants with large

power outputs [30]

The speci1047297c heat of monatomic helium is 1047297ve times that of air

and since the compressor stage temperature rise varies inversely

as speci1047297c heat (for a given limiting blade speed) it follows that

the available temperature rise per stage when operating withhelium will be only one 1047297fth that of air and this of course means

that more stages (for a given pressure ratio) are required for

a helium axial 1047298ow compressor It is fortunate that the optimi-

zation (for maximum ef 1047297ciency) of a highly recuperated and

intercooled Brayton cycle results in a relatively low pressure ratio

(ie 25e30) hence the number of compressor and turbine stages

are fairly comparable with modern industrial open cycle gas

turbines [31]

Substitution of helium for air greatly modi1047297es the turbo-

machine aerodynamic requirements because the high sonic

velocity of helium removes Mach number effects The size of the

machine is essentially dictated by the choice of blade speed there

being an incentive to use the highest possible values commensu-

rate with stress limitations to reduce the number of stages since

the stage loading factor is inversely proportional to the square of

the blade speed In general aerothermal 1047298uid dynamic and

mechanical design methodologies from air-breathing gas turbines

are applicable but the effects that the properties of helium have on

the design of a turbomachine in a high pressure closed-cycle

system are recognized and include the following

- Low molecular weight and high speci1047297c heat results in a large

number of stages (for a given pressure ratio)

- Long slender rotor (rotor dynamic stability concerns)

- Speci1047297c heat 5 times that of air gives high speci1047297c power

- High hub-to-tip ratio blading (in HP compressor)

- Small blade heights (resulting from high pressure system)

- Low aspect ratio blading (large blade chords because of high

bending stress)

- Thicker blade pro1047297les (because of high bending stress)

- Small compressor annulus taper and turbine 1047298are

- High compressor and turbine ef 1047297ciencies

- low Mach number (less than 030)

- high Reynolds numbers (gt5 106

)- clean oxide free blades (in inert helium)

- blade tip clearances minimized (machine not subjected to

severe thermal transients)

The experience gained from helium turbomachines that have

operated in the USA and Germany are covered in the following

sections

4 Pioneer La Fleur helium gas turbine

In 1960 La Fleur Enterprises in Los Angeles initiated work on an

air separation plant that involved the coupling of a closed-cycle gas

turbine with a cryogenic facility Helium was chosen as the closed

cycle working 1047298

uid since the La Fleur process for air liquefaction

Fig 5 Closed-cycle gas turbine demonstration test facility operated in the UK in 1995 with a 1000 kW natural gas- 1047297red heat source (Courtesy British gas)




required that the working 1047298uid remain gaseous throughout the

system Details of the plant and the axial 1047298ow helium turboma-

chinery have been documented previously [3233] and are only

brie1047298y discussed here This small plant is important in the context

of this paper since it was the 1047297rst fossil-1047297red helium gas turbine

ever to operate

The temperatureeentropy diagram (Fig 6) and the rather

simplistic cycle diagram (Fig 7) are pertinent to understanding

the function of this plant It was not designed to generate

electrical power instead the useful output being ldquobleed heliumrdquo

The major component was the free-running axial 1047298ow helium

turbomachine The rotating assembly consisted of a helium power

turbine compressor and refrigeration turbine mounted on the

same shaft

In the closed Brayton cycle part of the system the helium exiting

the compressor was split with about half of the mass 1047298ow passing

through the hot recuperator and then 1047298owing through the natural

gas-1047297red external heater where the temperature was further

increased before entering the power turbine Exiting the turbine

the helium then 1047298owed through the other side of the recuperator

and after a further reduction in temperature in a precooler entered

the compressor

In the cryogenic part of the cycle the temperature of the other

half of the helium bled from the compressor was reduced in an

aftercooler and then further reduced in the cold recuperator It was

then expanded in a refrigeration turbine and reached the lowest

temperature in the system The cold helium then passes through

a condenser in which the air is lique1047297ed and after passing through

the other side of the cold recuperator enters the compressor

Because the temperature of this bleed helium stream is less than

that coming from the precooler the mixed temperature at the

compressor inlet is cooler thus reducing the compressor workrequired

An overall view of the La Fleur plant is shown on Fig 8 and the

major parameters and features are given on Table 1 From the onset

of the project conservative parameters were selected to ensure

that when constructed the plant would operate reliably and meet

the process requirements since funding available for the project

was limited

With a turbine inlet temperature of 650 C (1202 F) and

a system pressure of 125 MPa (180 psia) a compressor pressure

Fig 6 Temperatureeentropy diagram of La Fleur helium gas turbine plant

Fig 7 Cycle diagram of La Fleur helium gas turbine plant




ratio of 15 was selected With modest stage loading a 16 stage axial

compressor was designed the welded rotor being shown on Fig 9

Fifty percent reaction blading was used throughout The axial

velocity was kept constant and with a low value of pressure ratio

the annulus taper was rather slight The target ef 1047297ciency for the

compressor was83 percent The blades were cast 410 stainless steel

and these were welded to forged discs since this was the lowest

cost type of construction at the timeFor the turbine a tip speed of 305 ms (1000 ftsec) was

conservatively selected the rotational speed being 19500 rpm

While not coupled to a generator to produce electrical power the

size of the constant speed free-running turbine was equivalent to

that in a machine rated in the 1000e2000 kW class A view of the

turbine rotor is given on Fig 10 The material for the investment

cast blades was Haynes 21 and these were welded to a Timken 16-

25-6 disc The turbine ef 1047297ciency goal was 85 percent

The rotor was supported on oil-lubricated bearings To avoid oil

ingress into the helium circuit the oil pump scavenge pump and

the other accessories were separately driven by electric motors As

also experienced in later closed-cycle gas turbine plants oil ingress

into the helium closed loop occurred this being traced to a poor

design of the oil seals Keeping the system leak-tight when

operating with such a low molecular weight gas was a major

challenge and this topic will be discussed later for other helium

systems operating at high pressure and temperature

In this small pioneer plant the worldrsquos 1047297rst helium turbo-

machine operated satisfactorily the major achievement being that

it proved the La Fleur cryogenic process for air liquefaction The

experience gained from this small prototype plant led to the

construction and operation of a larger fossil-1047297red helium closed-cycle gas turbine for a lique1047297ed gas cryogenic plant and this is

discussed in the following section

5 Escher Wyss helium gas turbine plant

Following the successful operation of the pioneer plant La Fleur

Corporation designed and built a cryogenic facility in Phoenix

Arizona in 1966 for the liquefaction of 90 tonsday of nitrogen The

helium turbomachine was developed and built in Zurich by Escher

Wysswho up to that date hadfabricated the majority of the closed-

cycle gas turbine plants in Europe [2] The thermodynamic cycle

(involving splitting the helium 1047298ow at the compressor exit)

resembled the aforementioned pioneer plant with the exception

that the compressor was separated into two sections to facilitate

Fig 8 Overall view of 1047297rst helium gas turbine (Courtesy La Fleur Corp)




intercooling [634] The major parameters and features of this plant

are summarized on Table 1



ratio of 20 was selected A cross-section of the turbomachine is

shown on Fig 11 The LP and HP compressors had 10 and 8 stages

respectively The compressors were designed with a degree of

reaction slightly above 100 percent based on the prevailing view by

Escher Wyss at the time that this had advantages for helium

compressors Since this philosophy was carried over into the next

much larger helium gas turbine (as covered in the following

section) the rationale for this aerothermal design decision is brie1047298y

addressed below

The degree of reaction can essentially be regarded as the ratio of

pressure rise (although accurately de1047297ned as the static enthalpy

rise) in the rotor with the total pressure rise through the combi-

nation of the rotor and stator In early British axial 1047298ow compres-

sors a value of 50 percent was adopted this enabling the same

blade pro1047297le to be used for the rotor and stator In contemporary

air-breathing gas turbines the compressor degree of reaction is not

a major design factor The effect that selected compressor rotor and

stator positioning and geometries have on the degree of reaction is

illustrated in a simple form on Fig 12 In the early years of closed-

cycle gas turbine work Escher Wyss in Switzerland advocateda degree of reaction of 100 percent or higher [35] With such

blading the gas enters and leaves the stage in an axial direction The

basic stage embodies a negative pre-whirl stator ahead of the rotor

With the stator blades acting as a nozzle it was felt that the

resulting acceleration in the stator had the effect of smoothing out

the 1047298ow providing the best possible conditions for the rotor

However such blading with high stagger and lowsolidity has a very

high relative velocity and attendant high Mach number and is not

used in machines with air as the working 1047298uid since the associated

losses would be excessive leading to low overall compressor ef 1047297-

ciency This type of stator-before-rotor high reaction arrangement

was felt to be advantageous for helium axial 1047298ow compressors to

reduce the number of stages since Mach number effects are not

encountered because the sonic velocity of helium is on the order of

three times that of air

Because of the properties of helium (ie low molecular weight

high speci1047297c heat higher adiabatic index etc) a higher number of

compressor and turbinestages for a given pressure ratio are needed

as mentioned previously An axial compressor with just over

a hundred percent reaction as in the Escher Wyss helium gas

turbine that operated in Phoenix has a greater enthalpy rise per

stage for a given tip speed this reducing the number of stages for

a given pressure ratio but the ef 1047297ciency is slightly lower Mini-

mizing the number of stages was important from the rotor dynamic

stability standpoint for the very long rotor assembly associated

Fig 9 La Fleur plant 16 stage compressor (Courtesy La Fleur Corp) Fig 10 La Fleur plant 4 stage helium turbine (Courtesy La Fleur Corp)

Table 1

Salient features of operated helium turbomachinery

Turbomachine Helium closed-cycle gas turbines Test facility Helium circulator

Facility La Fleur

gas turbine

Escher Wyss

gas turbine

Oberhausen 11

power plant

HHV

test loop

FSV HTGR

Country USA USA Germany Germany USA

Year 1962 1966 1974 1981 1976

Application Cryogenic Cryogenic CHP plant Development Nuclear plant

Heat source NG NG Coke oven gas Electrical NuclearPower MW 2 equiv 6 equiv 50 90 4

Cycle Recuperated ICR ICR Customized Steam

Compressor

Type Axial Axial Axial Axial Axial

No stages 16 10LP8HP 10LP15HP 8 1

Inlet press MPa 125 122 105285 45 473

Inlet temp C 21 22 25 820 394

Pressure ratio 15 20 27 113 102

Flow kgsec 73 11 85 212 110

In vol 1047298ow m3sec 35 55 50 107 32

Turbine

Type Axial Axial Axial Axial ST

No stages 4 9 11LP7HP 2 1

Inlet press MPa 18 23 165 50 e

Inlet temp C 650 660 750 850 e

In vol 1047298ow m3sec 30 57 67 98 e

Out vol 1047298ow m3

sec 36 85 120 104 e

Rotation speed rpm 19500 18000 55003000 3000 9550

Shaft type Single Single Twin (geared) Single Single

Generator type None None Conventional Elect motor e




with this intercooled helium axial compressor of the type shown on

Figs 11 and 13

In the high pressure helium environment a high degree of reaction leads to a rotor blading with longer chords and low aspect

ratio The larger chord length combined with low solidity results in

comparatively few compressor blades Low aspect ratio (de1047297ned as

the ratio of blade height to chord length) results in several effects

including the following 1) high stagger with wider chords results in

a greater overall machine bladed length 2) fewer blades per stage

3) relatively large area of casing and blade surface with adverse

frictional losses tending to give lower ef 1047297ciency and 4) a stiffer

blade section (also with a thicker pro1047297le) with the needed strength

to combat bending stress which can be signi1047297cant in a high pres-

suredensity helium closed-cycle system A way to partially balance

out the bending stress would be by leaning the blades and off-

setting the blade cross-section centre of gravity For the early

helium gas turbine plants a view expressed by Escher Wyss wasthat the use of high reaction blading gave the maximum attainable

head a 1047298atter pressureevolume characteristic and a better surge

margin [36] The merits of increased pressure rise per stage asso-

ciated with high reaction blading has to be put into perspective by

its lower values of ef 1047297ciency [37]

The turbine had 9 stages and a rotational speed of 18000 rpm

While not coupled with a generator the equivalent output of the

free-running turbine was on the order of 6000 kW An overall view

of the long slender rotor is shown on Fig 13 and the turbomachine

assembly being installed in a cylindrical horizontally split casing is

shown on Fig 14 The major 1047298anges had peripheral lip seals to

facilitate welding closure to ensure leak tightness

With an external gas-1047297red heater the plant operated for about

5000 h and the helium gas turbine proved to be mechanically

sound and met its speci1047297ed performance This very specialized

plant proved to be too expensive to operate for the limited market

for cryogenic 1047298uids Anticipated market growth in the late 1960sdid not materialize and while the machinery performed satisfac-

torily the customer Dye Oxygen withdrew the plant from service

As far as the helium gas turbine was concerned the plant repre-

sented a signi1047297cant milestone since the technology generated was

applied to a follow-on helium gas turbine which at this stage was

still to be fossil-1047297red but now with the long-term goal in mind of

paving the way for the eventual operation of a helium closed-cycle

gas turbine power plant with a high temperature nuclear heat

source

6 Oberhausen II helium gas turbine plant at EVO

61 Closed-Cycle gas turbine experience at EVO

With initial operation starting in 1960 the municipal energy

utility (EVO) of the city of Oberhausen in the German industrial

Ruhr area deployed a closed-cycle gas turbine plant Referred to as

Oberhausen I the plant (shown previously on Fig 3) operated in

a combined power and heat mode with an electrical output of

14 MW and the thermal heat rejection of about 20 MW was

supplied to the cityrsquos district heating system The external heater

was initially 1047297red with Bituminous coal and in 1971 a change was

made to use coke-oven gas that had become available While using

air as the working 1047298uid some of the technical dif 1047297culties experi-

enced with this plant are highlighted below simply because if they

were to occur in a future direct cycle nuclear gas turbine plant they

would be very costly and time consuming to resolve as will be

discussed in a following section

Fig 11 Cross-section view of helium gas turbine (Courtesy Escher Wyss)




In 1963 after 20000 h of operation a failure in the HP

compressor occurred [10] A rotor blade in the 1047297rst stage failed at

the root and in passing through the compressor caused extensive

damage The failure necessitated replacing the complete HP

compressor rotor assembly From a metallurgical examination of

the broken parts the failure was attributed to a small crevice at the

edge of the blade It was postulated that a corrosive action due to

impurities in the closed-loop working 1047298uid (ie air) in1047298uenced the

propagation of the crevice and blade vibration eventually caused

the failure To prevent a further failure of this kind an electric

polishing procedure was applied to the surface of the blade to

detect any imperfections

In 1967 debris from within the closed circuit caused damage to

the rotor blades and stators of several stages in the LP compressor

In 1973 further damage in the LP compressor due to blade vibration

required blading replacement During these de-blading events the

failed fragments were contained within the machine casings Using

conventional equipment the split casings of this machine were

opened and the failed parts removed by hands-on operations New

parts were then installed and the rotor assembly re-balanced The

problems were resolved and this closed-cycle gas turbine plant

with air as the working 1047298uid then performed well over the years

with high reliability [38]Rotor vibrations are mentioned here because they had caused

problems in three fossil-1047297red closed-cycle gas turbine plants using

air as the working 1047298uid namely1) in the John Brown 12 MW Plant

in Dundee where insurmountable vibration problems occurred [2]

2) multiple blade failures in the Spittelau 30 MW plant [2] and 3)

compressor blade failures in the aforementioned Oberhausen plant

As will be mentioned in a following section a further turbine blade

failure was experienced in a larger plant using helium as the

working 1047298uid

Correcting the subsequent blade failure damage to the turbo-

machine in a fossil-1047297red plant was straightforward however the

implication of such an operation in a future direct cycle nuclear gas

turbine with radioactively contaminated blading would be far more

severe This would likely require complex remote handling equip-ment and a dedicated facility for machine decontamination and

disassembly before hands-on repair could be undertaken

The Oberhausen I plant operated for about 120000 h and was

decommissioned in 1982 In about 1971 an expansion of the utilityrsquos

Fig 12 Impact of compressor blading geometry on degree of reaction (Courtesy

Escher Wyss)

Fig 13 Intercooled axial 1047298

ow helium turbomachine rotating assembly (Courtesy Escher Wyss)




capacity was needed due to increasing demand A larger fossil-1047297red

closed-cycle cogeneration plant of conventional design and still

retaining the use of air as the working 1047298uid was initially foreseen

but an emerging German development in the nuclear power plant

1047297eld resulted in a different decision being made as discussed

below

62 Relevance of the Oberhausen II helium turbine

Starting in 1972 development work sponsored by the Federal

Republic of Germany within the scope of the 4th Atomic program

was initiated on a high temperature reactor power plant with

a helium gas turbine (HHT) The reference plant design was based

on a large single-shaft intercooled helium turbine rated at

1240 MW A demonstration plant rated at 676 MW was planned

but prior to the construction of this it was necessary to test the

most important components to reduce risk Details of the two

major facilities to accomplish this have been reported previously

[39] and are summarized as follows

The Oberhausen II helium gas turbine plant was designed andbuilt to perform two major functions 1) it had to operate as

a commercial venture to provide electrical power (50 MWe) and

district heating (53 MWt) for the city of Oberhausen and 2) provide

data applicable to the nuclear gas turbine project particularly the

dynamic behavior of the overall plant and the integrity and long-

term operating experience of the major components in a helium

environment especially the turbomachine

The second facility was the HHV an experimental plant for

testing under representative conditions with respect to machine

size operating temperature pressure and mass 1047298ow of a large

helium turbomachine The facility was extensively instrumented to

gatherdata in the following areas rotorcooling system veri1047297cation

thermal insulation integrity 1047298ow characteristics blading ef 1047297ciency

acoustics rotor dynamic stability bearings dynamic and static

seals system leak tightness and metals behavior for the full

spectrum of plant operations including plant startup load change

shutdown upset conditions etc Details of the HHV facility and

testing undertaken are given in a later section

63 Oberhausen II helium gas turbine plant design

The design and construction of the plant was based on joint

efforts between EVO (plant designer and operator) GHH (turbo-

machine recuperator coolers and controls) Sulzer (helium

heater) and the University of Hannover Institute for Turboma-

chinery which contributed to the designwork and monitoring plant

performance

For the future planned nuclear gas turbine plant design values

of the temperature and pressure at the turbine inlet were 850 C

(1562 F) and 60 MPa (870 psia) respectively Attainment of this

temperature in the Oberhausen II plant could not be achieved and

750 C (1382 F) was selected based on tube material stress

considerations in the external coke-oven gas 1047297red heater An

intercooled and recuperated closed cycle was selected and themajor features of the plant are given on Table 1 The salient

parameters are given on the simpli1047297ed cycle diagram (Fig 15)

While rated at 50 MW a maximum system pressure of only

285 MPa (413 psia) was chosen so that the helium volumetric 1047298ow

(hence size of the bladed passages) would correspond to a much

larger helium turbomachine (on the order of 300 MW in fact) This

together with a rotational speed of 5500 rpm for the HP group

would result in representative stress loadings and would permit

a reasonable extrapolation to the machine size planned for the

nuclear demonstration plant

For the intercooled and recuperated cycle a compressor pressure

ratio of 27 was selected The helium mass 1047298ow rate was 85 kgs

(187 lbsec) and the circuit pressure loss was estimated at 104

percent Based on state-of-the-art component ef 1047297

ciencies and

Fig 14 Intercooled helium turbomachine with an equivalent power rating of 6000 kW installed in a split-case steel pressure vessel (Courtesy Escher Wyss)




a recuperator effectiveness of 87 percent the projected thermal

ef 1047297ciency was 326 percent gross and 313 percent net

The isometric sketch of the distributed power conversion

system shown on Fig 16 (from Ref [40]) is convenient for

describing the plant layout A decision was made [41] to install the

horizontal turbomachinery in three large steel vessels the group-

ings being as follows 1) LP compressor rotor 2) HP compressor and

HP turbine grouping and 3) LP turbine The 1047297rst two assemblies

were on a single-shaft with a rotational speed of 5500 rpm The

generator with a rotational speed of 3000 rpmis driven from the LP

turbine end The rotors were geared together but with the selected

shafting arrangement only a small amount of power was trans-

mitted through the gearbox This con1047297guration was established

so that the dynamic behavior would be the same as in the large

single-shaft reference nuclear gas turbine plant design concept

The arrangement of the three vessels can be clearly seen on Fig 17

The horizontal tubular recuperator is positioned below the

turbomachinery The tubular precoolers and intercoolers are

installed in vertical steel vessels This type of orientation of the

major components was used in some of the earlier closed-cycle

plants using air as the working 1047298uid

Power regulation was achieved by inventory control as in the

aforementioned Oberhausen I plant which meant that the system

pressure (hence mass 1047298ow) was changed as required To lower the

power output helium was extracted from the loop after the HP

compressor through a control valve into a storage vessel For

a power increase helium was returned from the storage vessel into

the system upstream of the LP compressor without the need for an

additional blower With this arrangement the turbine inlet

temperature and speed remained constant and plant ef 1047297ciency

would be essentially constant down to a very low power level [42]

To achieve rapid load changes a bypass valve was included in the

system in which helium was transferred in a line between the HP

compressor exit end and LP end of the recuperator A very rapid

change from 100 percent load to no-load operation and back was

demonstrated [43]

64 Helium turbomachinery

The major features and parameters for the turbomachine are

given on Table 2 and are summarized as follows A longitudinal

cross-section of the turbomachine is shown on Fig 18 At the left

hand end the LP compressor is installed in a spherical pressure

vessel A high degree of reaction (ie 100 percent) was selected for

this 10 stage axial compressor this practice following the experi-

ence of an earlier discussed helium turbomachine A view showing

the bladed rotor of the LP compressor installed in the pressure

vessel split casing is shown on Fig19 with an appreciation for the

size of the spherical casing being shown on Fig 20 Both the HP

compressor and HP turbine rotors are installed in a common

housing as shown in the turbomachine cross-section (Fig 21) and

Fig 15 Oberhausen II helium gas turbine cycle diagram

Fig 16 Isometric layout of Oberhausen II helium gas turbine power conversion system (Courtesy EVO)




in the view with the HP rotor assembly positioned above the

horizontal split casing (Fig 22) The 15 stage HP compressor was

again designed with 100 percent reaction blading The HP turbine

has 7 stages and operated with an inlet temperature of 750 C

(1382O F) A cross-section of the 11 stage LP turbine installed in

a separate spherical vessel is shown on Fig 23 The amount of

power transmitted in the gearbox between the HP and LP turbinesis small since at rated output the HP turbine power level is only

slightly more than is needed to drive both compressors

The rotor of the HP group is supported on two oil-lubricated

bearings For the complete rotating assembly the thrust bearing is

located at the warm end of the LP compressor The six turbo-

machine bearing housings were designed such that direct access to

the large oil bearings was possible without having to open the large

casings This was done to reduce maintenance time because the

large split casings have 1047298anges that were welded closed at the

peripheral lip seals to minimize helium leakage

Special attention was given to the design of the cooling system

for the rotor In the case of this plant with a turbine inlet

temperature of 750 C the turbine blades themselves based on the

use of an existing superalloy did not have to be internally cooledbut cooling gas bled from the HP compressor outlet 1047298owed through

the hollow shaft and was used to cool the turbine discs and the

blade root attachments and then returned downstream of the

turbine

In a closed-cycle gas turbine the powerlevel can be regulated by

means of changing the system pressure and careful attention must

be given to the design of the various sealing systems to accom-

modate pressure differentials within the system particularly

during transient operation To simulate what would be needed in

a direct cycle nuclear gas turbine (to prevent 1047297ssion products

coming into contact with the bearing lubricating oil) a system

having a separate chamber for each of the three labyrinth seals was

incorporated in the machine design Outboard of the labyrinth seals

where the shafts penetrate the casings there were two further

seals a 1047298oating ring seal and a shutdown seal to prevent external

helium leakage

65 Helium turbomachine operating experience

Various presentations papers and publications have previously

covered the over 13 year operation of the Oberhausen II helium gas

turbine plant [43e48] The experience gained with the operation

Fig 17 Overall view of Oberhausen II 50 MWe helium gas turbine power plant (Courtesy EVO)

Table 2

Oberhausen II plant helium turbomachinery

Plant design electrical power MW 50

District heating thermal supply MW 535

Plant design ef 1047297ciency at terminals 313

Thermodynamic cycle ICR

Control method Helium inventory

compressor bypass

Rotor arrangement 2 Shaft (geared together)

Helium mass 1047298ow kgsec 85

Overall pressure ratio 27

Generator ef 1047297ciency 98

Design system pressure loss 104Compressor LP HP

Inlet pressure MPa l05 l54

Inlet temperature C 25 25

Vol 1047298ow inletoutlet m3s 5040 4025

Ef 1047297ciency 870 855

Rotational speed rpm 5500 5500

Number of stages 10 15

Blade height inletoutlet mm 10385 7253

Turbine LP HP

Inlet pressure MPa 165 270


Ef 1047297ciency 900 883



Vol 1047298ow inletoutlet m3sec 92120 6792





of the large axial 1047298ow helium turbomachine is summarized asfollows

On the positive side the following were accomplished The rotor

helium buffered bearing labyrinth oil sealing system was one of the

numerous systems that worked well from the onset This was

encouraging since the external leakage of helium contaminated by

1047297ssion products and the ingress of lubricating oil into the closed

helium loop during the projected plant lifetime of 60 years are of

concern to designers of a direct cycle nuclear gas turbine plant (for

a machine with oil bearings) because of the likely long plant

downtime for cleanup and repair

With some modi1047297cations the helium puri1047297cation system

worked well with the purity level within the speci1047297cation The

helium cooling systems worked well to keep the temperatures of

the turbine discs blade root attachments and casings at speci1047297

edlevels Load change by inventory control was done routinely and

the ability to shed 100 percent of the load in a very short period by

means of the bypass valve was demonstrated The integrity of the

co-axial turbine inlet hot gas duct was proven At the end of plant

operation the major turbomachine casings were opened and there

were no signs of corrosion or erosion of the turbine or compressor

blades The coatings applied to mating metallic surfaces were

effective with no evidence of galling or self-welding in the oxygen-

free closed-loop helium environment

Experience from previously operated high temperature helium

cooled nuclear reactor power plants (with Rankine cycle steam

turbine power conversion systems) demonstrated that absolute

helium leak tightness was not attainable This was also true in the

Oberhausen II fossil-1047297red gas turbine plant where during initial

operation the helium leakage was about 45 kg per day Attention

was given to this and helium losses were reduced to the range of

5e10 kg per day principally by seal welding the major 1047298anges This

value can be compared with other closed loop helium systems as

shown below

On the negative side several unexpected problems had a majorimpact on the operation of the plant Following initial running of

the machine at 3000 rpm in preparation to synchronizing the

system the HP casing was opened for inspection revealing

damage to the labyrinth seals this being caused by shifting of

the rotor in the axial direction The labyrinth seals were replaced

and the turbine was 1047297rst synchronized with the grid on November

8 1975

Subsequent vibration problems were encountered and the HP

shaft oscillation became so large that it caused damage to the

bearings and the design value of speed and power could not be

maintained and the plant was shut down This was initially thought

to be due to thermal distortion of the rotor and a large unbalance

Fig 18 Cross-section of Oberhausen II plant helium turbomachinery rotating assembly (Courtesy EVO)

Fig 19 Oberhausen II low pressure helium compressor installed in casing (Courtesy

GHH)

Plant Helium inventory kg Leakage

kgday day

Dragon 180 020e20 010e10

AVR 240 10e30 040e12

Oberhausen II 1400 5e10 035e070

HHV 1250 25e50 020e040

FSV e Excessive leakage




Modi1047297cations to the rotor were made and the bearings replaced

but now the HP spool design speed of 5500 rpm could not be

achieved Subsequent major design and fabrication changes were

made including decreasing the bearing span by 600 mm (24 in)

giving a shorter stiffer rotor and changing the type of bearings In

restarting the plant the design speed of the HP rotor was achieved

however the power output was only 30 MW compared with the

design value of 50 MW

Fig 20 View of Oberhausen II low pressure helium compressor spherical vessel (Courtesy GHH)

Fig 21 Cross-section of Oberhausen II high pressure rotating group (Courtesy GHH)




To gain operational experience it was decided to continue

running the plant at the reduced power rating On February 5 1979

after nearly 11000 h of operation a rotor blade from the second

stage of the HP turbine failed causing damage in the remaining

stages but the high energy fragments were contained within the

thick machine casing Examination of the failed blade revealed the

defect as a crack caused by the forgingprocess on the semi-1047297nishedproduct To prevent such a failure occurring in the future an electric

polishing process applied to the blade surface before inspection

was implemented and improved crack detection methods

introduced

Acoustic loads in a closed-cycle gas turbine represent pressure

1047298uctuations propagating at the speed of sound through the helium

working 1047298uid Pressure 1047298uctuations of importance result from the

aerodynamic effects of high velocity helium impacting and

essentially being intermittently ldquocutrdquo by the blading in the

compressor and turbine Care must be taken in the design of the

plant to ensurethat these 1047298uctuating pressure waves do not induce

vibrations of a magnitude that could result in excitation-induced

fatigue failures in components in the circuit Critical vibrations

occur when resonance exists between the main frequency of

the propagating sound and the natural frequencies of the

components particularly ones that have large surface area to

thickness ratio

Measurements of sound spectrum were taken at four different

locations in the circuit The design level of power of 50 MW was not

achieved but at the 30 MW power output actually realized the

maximum recorded sound power level was 148 dB After plantshutdown there was no evidence of adverse effects on the major

components of noise induced excitation emanating from the axial

1047298ow turbomachinery The integrity of the turbine inlet hot gas duct

and insulation was con1047297rmed

The inability to reach rated power was attributed to shortcom-

ings in the helium turbomachine This included the compressors(s)

and turbine(s) blading failing to attain design values of ef 1047297ciencies

and the bleed helium mass 1047298ows for cooling and sealing being

signi1047297cantly greater than analytically estimated Based on data

taken from the well instrumented plant detailed analyses were

undertaken by specialists [4950] to calculate the losses in the

turbomachine to explain the power output de1047297ciency A summary

of the projected losses and various component ef 1047297ciencies is pre-

sented in a convenient form on Table 3

Fig 22 Oberhausen II high pressure rotor being installed (Courtesy GHH)




The plant operated for approximately 24000 h and was shut-

down and decommissioned in 1988 when the coke-oven gas supply

for the heater was no longer available A total plant operating time

of about 11500 h had been at the design turbine inlet temperature

of 750 C (1382 F) Turbomachinery related experience gained

from operation of this large helium gas turbine plant was extremely

valuable While many of the functions performed well from the

onset and others worked satisfactorily after modi1047297cations were

made serious unexpected problems were encountered

The achieved electrical power output of only 60 percent of the

design value was initially thought to be due to a grossly excessive

system pressure loss However when the data was carefully eval-uated it was found that 85 percent of the 20 MW power loss was

attributed to turbomachine related problems as delineated on

Table 3

To remedy this power de1047297ciency it was clear that a major re-

design of the turbomachinery would be required While replace-

ment of the gas turbine was not contemplated a study was

undertaken based on data from the plant and new technologies

that had become available since the initial design Based on the

1047297ndings a new turbomachine layout concept was suggested [43]

and a simplistic view of the rotor arrangement is shown on Fig 24

A more conventional single-shaft arrangement was proposed with

the two compressors and turbine having a rotational speed of

5400 rpm A gearbox was still retained to give a generator rota-

tional speed of 3000 rpm Based on prevailing technology at the

time the requirements for such a gearbox would have been moredemanding since the 50 MW from the turbine to the generator

would have to be transmitted through it This would necessitate

a larger system to pump 1047297lter and cool the bearing lubrication oil

To remedy the very large losses in the compressors and turbines

the number of stages would have to be increased In the case of the

compressors the use of lighter aerodynamically loaded higher

ef 1047297ciency stages with 50 percent reaction blading was

recommended

7 High temperature helium test facility (HHV)

71 Background

In the late 1960rsquos with large numbers of orders placed for 1047297rst

generation light water reactor nuclear power plants studies were

initiated for next generation power plants with higher ef 1047297ciency

potential Following the initial operational success of the 1047297rst three

small helium cooled HTR plants (ie Dragon in the UK Peach

Bottom I in the USA and AVR in Germany) studies on larger plants

based on the use of both Rankine steam cycle and helium closed

Brayton cycle power conversion systems were undertaken In the

early 1970rsquos emphasis was placed on nuclear gas turbine plant

designs with larger power output both in the USA (for the

HTGR eGT) and in Europe (for the HHT) Work in the USA was

limited to only paper studies [18] The much larger program in

Germany (with participation by Swiss companies for the turbo-

machine heat exchangers and cooling towers) included a well

planned development testing strategy to support the plant design

Fig 23 Cross-section of Oberhausen II low pressure helium turbine (Courtesy GHH)

Table 3

Oberhausen II helium turbine plant power losses

Componentcause Design

value

Measured Power loss

MW

Compressors

B Flow losses in inlet diffusers

and blades

Low pressure ef 1047297ciency 870 826 13

High pressure ef 1047297ciency 855 779 40

Turbines

B Blade gap and 1047298ow losses


B Pro1047297le losses due to Remachined

blades after having detected

damaged blades


BSealing leakage and cooling 1047298ows

in all turbomachines Kgsec

18 75 53

B Circuit pressure losses

(Ducting Hxrsquos etc)

102 128 26

B Miscellaneous heat losses 05

Total power loss 200 MW

Notes (1) Plant designed for electrical power output of 50 MW actual power output

measured 30 MW

(2) Power de1047297ciency of20 MW based on measurements taken and then recalculated

for the rated plant output

(3) 85 of Power loss attributed to helium turbomachinery related issues




While the reference HHT plant for eventual commercializationembodied a very large single helium gas turbine rated at 1240 MW

this was to be preceded by a nuclear demonstration plant rated at

676 MW [51] To support the design of this plant technology

generated from the following was planned 1) operational experi-

ence from the aforementioned Oberhausen II 50 MW helium gas

turbine power plant and 2) testing of components in a large high

temperature helium test facility as discussed below

72 Development facilitytesting objectives

An overall view of the HHV test facility sited in Julich in

Germany is shown on Fig 25 and since this has been reported on

previously [52] it will only be brie1047298

y covered in this section Tominimize risk and assure the performance integrity and reliability

of the nuclear demonstration plant some non-nuclear testing of

the major components especially the helium turbomachine was

deemed essential Because of the limitations of a conventional

closed-cycle helium gas turbine power plant particularly the

temperature limitations of existing fossil-1047297red and electrical

heaters a new type of test facility was foreseen

A simpli1047297ed schematic line diagram of the HHV circuit is shown

on Fig 26 The major design parameters are shown on Fig 27

together with the temperatureeentropy diagram which is conve-

nient for describing the unique relationship between the compo-

nents in the closed helium loop Starting at the lowest pressure in

Fig 24 Proposed new concept for Oberhausen II helium gas turbine rotating assembly to remedy problems encountered during operation of the 50 MWe power plant (Courtesy

EVO)

Fig 25 HHV helium turbomachinery test facility (Courtesy BBC)




the system the helium is compressed (Ae

B) its temperatureincreasing to 850 C (1562 F) before 1047298owing through the test

section (BeC) After being cooled slightly (CeD) the helium is

expanded in the turbine (DeA) down to the compressor inlet

conditions completing the loop There is no power output from the

system and without the need for an external heater the

compression heat is used to raise the helium to the maximum

system temperature in what can be described as a very large heat

pump The required compressor power is 90 MW and to supple-

ment the 45 MW generated by expansion in the turbine external

power is provided by a 45 MW synchronous electrical motor A

cooler is required to remove the compression heat that is contin-

uously put into the closed helium loop and this is done by bleeding

about 5 percent of the mass 1047298ow after the compressor cooling it

and re-introducing it into the circuit close to the turbine inlet In

addition to testing the turbomachine the facility was engineered

with a test section to accommodate other small components (eg

hot gas 1047298ow regulation valves bypass valves insulation con1047297gu-

rations and types of hot gas duct construction) With the highest

temperature in the system being at the compressor exit the facility

had the capability to provide helium at a temperature up to 1000 C

(1832 F) for short periods at the entrance to the test section

While a higher ef 1047297ciency of the planned nuclear demonstration

plant could be projected with a turbine inlet temperature in the

range 950e1000 C (1742e1832 F) this would have necessitated

either turbine blade cooling or the use of a high temperature alloy

such as Titanium Zirconium Molybdenum (TZM) At the time it was

felt that using either of these would have added cost and risk to theprojectso a conventionalnickel-basedalloyas usedin industrialgas

turbines was selected for the 850 C design value of turbine inlet

temperature this negating the needfor actual internal bladecooling

However a complex internal coolingsystemwas neededto keep the

Fig 26 Cycle diagram of HHV test loop (Courtesy BBC)

Fig 27 Salient features of HHV helium turbomachinery (Courtesy BBC)




turbine discs and blade root attachments and casings to acceptable

temperatures commensurate with prescribed stress limitations for

thelife of theturbomachine In addition a heliumsupplywas needed

to provide a buffering system for the various labyrinth seals

In a direct Brayton cycle nuclear gas turbine the turbomachine is

installed in the reactor circuit and via the hot gas duct heated

helium is transported directly from the reactor core to the turbine

From the safety licensing and reliability standpoints there are

various seals that must perform perfectly A helium buffered

labyrinth seal system is necessary to prevent bearing lubricating oil

ingress to the closed helium loop Since in the proposed HHT plant

design the drive shaft from the turbine to the generator penetrates

the reactor primary system pressure boundary two shaft seals are

needed one a dynamic seal when the shaft is rotating and a static

seal when the turbomachine is not operating Testing of these seals

in a size and operating conditions representative of the planned

commercial power plant was considered to be a licensing must

The mechanical integrity of the rotating assembly must be

assured there being two major factors necessitating testing the

machine at full speed and temperature and at high pressure

namely 1) loading the blading under representative centrifugal and

gas bending stresses and 2) to monitor vibration and con1047297rm rotor

dynamic stability For the design of the planned commercial planta knowledge of the acoustic emissions by the turbomachine and

propagation in the closed circuit was required Data from the HHV

facility would enable dynamic responses of the major components

(especially the insulation) resulting from excitation by the sound

1047297eld to be calculated

The circuit was instrumented to gather data on the effectiveness

of the hot gas duct insulation thermal expansion devices hot gas

valves helium puri1047297cation system instrumentation and the

adequacy of the coatings applied to mating metallic surfaces to

prevent galling or self-welding Details of the turbomachinery and

the experience gained from the operation of the HHV facility are

covered in the following sections

73 Helium turbomachine

A cross-section of the turbomachine is shown on Fig 28 The

single-shaft rotating assembly consists of 8 compressor stagesand 2

turbine stages and had a weighton the order of 66 tons(60000 kg)

The hub inner and outer diameters are 16 m (525 ft) and 18 m

(59 ft) respectively the blading axial length being 23 m (75 ft)The

span between the oil bearings being 57 m (187 ft) The physical

dimensions of the turbogroup shown on Fig 28 correspond to

a machine rated at about 300 MW The oil bearings operate in

a helium environment and the diameters of the labyrinths and

1047298oating ring shaft seals to prevent oil ingress are representative of

a machine rated at about 600 MW The complexity of the machine

design especially the rotor cooling system sealing system very

large casing and heat insulation have been reported previously

[53e55]

To ensure high structural integrity the rotor was constructed by

welding together the forged compressor and turbine discs The

compressor had 8 stages each having 56 rotor and 72 stator blades

The turbine had 2 stages each having 90 stator and 84 rotor blades

An appreciation for the large size of the rotating assembly can be

seen from Fig 29 The rotor blades have 1047297r-tree attachments

embodying cooling channels Since the temperature and pressure

do not vary very much along the blading in the 1047298ow direction an

intricate rotor and stator cooling system was required Channels in

both the blade roots and the spacers between adjacent blade rows

form an axial geometry for the passage of a cooling helium supplyto keep the temperature of the multiple discs below 400 C

(752 F) The design of this was a challenge since the rotor and

stator blade attachments of both the 8 stage compressor and 2

stage turbine had to be cooled Excessive leakage had to be avoided

since this would have prevented the speci1047297ed compressor

discharge temperature (ie the maximum temperature in the

circuit) from being reached

In the 1970rsquos and early 1980rsquos signi1047297cant studies were carried

out on large helium gas turbines by various organizations [56e62]

In this era there was general agreement that testing of the turbo-

machine in one form or another in non-nuclear facilities be

undertaken to resolve areas of high risk (eg seals bearings cooling

systems rotor dynamic stability compressor surge margin

dynamic response rotor burst protection etc) before installationand operation of a large gas turbine in a nuclear environment

This low risk engineering philosophy which prevailed at the time

in both Germany and the USA emphasized the importance of

Fig 28 Cross-section of HHV helium turbomachinery (Courtesy BBC)




the HHV test facility as being an important step towards the

eventual deployment of a high ef 1047297ciency nuclear gas turbine power

plant

74 Initial operation of the HHV facility

During commissioning of the plant in 1979 oil ingress into the

helium circuit from the seal system occurred twiceThe 1047297rst ingressof oil between 600 and 1200 kg (1322 and 2644 lb) was due to

a serious operatorerror and the absence of an isolation valve in the

system The oil in the circuit was partly coked and formed thick

deposits on the cold and hot surfaces of the turbomachinery and in

other parts of the closed loop including saturation of the 1047297brous

insulation The fouled metallic surfaces were cleaned mechanically

and chemically by cracking with the addition of hydrogen and

additives The second oil ingress was due to a mechanical defect in

the labyrinth seal system The quantity of oil introduced was small

and it was removed bycracking at a temperature of 600 C (1112 F)

and with the use of additives To obviate further oil ingress inci-

dents the labyrinth seal system was redesigned The buffer and

cooling helium system piping layout was modi1047297ed to positively

eliminate oil ingress due to improper valve operation and toprevent further human error

Pressure and leak detection tests of the HHV test facility at

ambient temperature showed good leak tightness for the turbo-

machine 1047298anged joints and of the main and auxiliary circuits

However at the operating temperature of 850 C (1562 F) large

helium leaks were detected The major 1047298anges had been provi-

sioned with lip seals and the 1047297rst step was to weld the closures A

large leak persisted at the front 1047298ange of the turbomachine This

was diagnosed as being caused by a non-uniform temperature

distribution during initial operation resulting in thermal stresses

creating local gaps This problem was overcome by redesign of the

cooling system with improved gas 1047298ow distribution and 1047298ow rates

to give a more uniform temperature gradient The leakage from the

system was reduced to on the order of 020e

040 percent of the

helium inventory per day this being of the same magnitude as in

other closed helium circuits as discussed in Section 65

It should be mentioned that in addition to the HHV experience

bearing oil ingress into the circuits and system loss of the working

1047298uid in other closed-cycle gas turbine plants have occurred In all of

these fossil-1047297red facilities 1047297xing leaks and removal of oil deposits

were undertaken based on conventional hands-on approaches but

nevertheless such operations were time-consuming However if a new and previously untested helium turbomachine operating in

a direct cycle nuclear gas turbine plant experienced an oil ingress

the rami1047297cations would be severe The likely use of remote

handling equipment to remove the turbomachine from the vessel

machine disassembly (including breaking the welded 1047298ange joints)

and removal of oil from the radioactively contaminated turbo-

machine blade surfaces and system insulation would be time

consuming A diagnosis of the failure would be required before

a spare turbomachine could be installed and this plant downtime

could adversely affect plant availability

75 Experience gained

Afterresolutionof the aforementionedproblems the HHVfacilitywas started in the Spring of 1981 and in an orderly manner was

brought up to full pressure and a temperature of 850 C (1562 F)

During a 60 h run the functioning of the instrumentation control

and safety systems were veri1047297ed During these tests the ability to

stop the turbomachine from full operating conditions to standstill

within 90 s was demonstrated After system depressurization the

plant was then run up again to full operating conditions with no

problems experienced The HHV facility was successfully run for

about 1100 h of which theturbomachineryoperated forabout325 h

at a temperature of 850 C The test facility was extensively instru-

mented and interpretation and analysis of the data recorded gave

positive and favorable results in the following areas

The complex rotor cooling system which was engineered to

assure that the temperature of the discs be kept below 400

C

Fig 29 HHV helium turbomachine rotating assembly (size equivalent to a 300 MWe machine) being installed in a pressure vessel (Courtesy BBC)




(752 F) was demonstrated to be effective The measured rotor

coolant 1047298ows (about 3 percent of the mass1047298ow passing through the

machine) were slightly larger than had been estimated and this

resulted in measured turbine disc temperatures lower than pre-

dicted [55]

The dynamic labyrinth shaft seal functioned well at the full

temperature and pressure conditions and met the requirement of

zero oil ingress into the helium circuit The measured rotor oscil-

lation did not have any adverse effect on the shaft sealing system

The static rotor seal (for shutdown conditions) functioned without

any problems

The compressor and turbine blading hadef 1047297ciencies higher than

predicted The structural integrity of the rotor proved to be sound

when operating at 3000 rpm under the maximum temperature and

pressure conditions The stiff rotor shaft had only slight unbalance

and thermal distortion and measured oscillations were in the range

typical of large steam turbines

Sound power spectrum measurements were taken in four

different locations in the circuit These were taken to determine the

spectrum and intensity of the sound generated and propagated by

the turbomachinery and the resultant vibration of internal

components The maximum sound power level in the helium

circuit was160 dB Numerous strain gages were placedin the circuitto determine the in1047298uence of the sound 1047297eld particularly on the

fatigue strength of the turbine inlet hot gas duct In later examining

the internal components there was no evidence of excessive

vibration of the components especially the ducting and the insu-

lation Based on the measurements and calculations it was

concluded that the fatigue strength limit of the components would

not be exceeded during the designed life of the planned commer-

cial nuclear gas turbine power plant

In a direct cycle nuclear gas turbine the hot gas duct used to

transport the helium from the reactor core to the turbineis a critical

component The hot gas duct in the HHV facility performed well

mechanically and con1047297rmed the adequacy of the thermal expan-

sion devices From the thermal standpoint the 1047297ber insulation

performed better than the metallic type

After dismantling the HHV facility there were no signs of

corrosion or erosion of the turbine or compressor blading While

the total number of hours operated was limited the coatings

applied to mating metallic surfaces to prevent galling and frictional

welding in the oxidation-free helium worked well

The helium buffer and cooling system worked well However

problems remained with the puri1047297cation of the buffer helium The

oil separation system consisting of a cyclone separator and a wire

mesh and a down stream 1047297ber 1047297lter needed further improvement

In late 1981 a decision was made to cancel the HHT project and

the HHV facility was shutdown The design and operational expe-

rience gained from the running of this facility would have been

extremely valuable had the nuclear gas turbine power plant

concept moved towards becoming a reality The identi1047297cation of

somewhat inevitable problems to be expected in such a complexturbomachine and their resolution were undertaken in a timely

and cost effective manner in the non-nuclear HHV facility This

should be noted for future nuclear gas turbine endeavors since

remedying such unexpected problems in the case of a new and

untested large helium turbomachine being operated for the 1047297rst

time using nuclear heat could result in very complex repair

Fig 30 Speci1047297

c speed-speci1047297

c diameter array for gas circulators in various gas-cooled nuclear plants




activities and extended plant downtime and indeed adding risk to

the overall success of the nuclear gas turbine concept

8 Circulators used in gas-cooled reactor plants

Circulators of different types will be needed in future helium

cooled nuclear plants these including the following 1) primary

loop circulator for possible next generation steam cycle power andcogeneration plants 2) for future indirect cycle gas turbine plants

3) shut down cooling circulators forall HTRand VHTR plants and 4)

for various circulators needed in future VHTR high temperature

process heat plant concepts The technology status of operated

helium circulators is brie1047298y addressed as follows

81 Background

It would be remiss not to mention experience gained in the past

with gas circulators and while not gas turbines they are rotating

machines that operate in the primary loop of a helium cooled

reactor With electric motor drives there are basically two types of

compressor rotor con1047297gurations namely radial and axial 1047298ow

machinesIn a single stage form the centrifugal impeller is used for high

stage pressure rise and low volume 1047298ow duties whereas the axial

type covers low pressure rise per stage and high volume 1047298ow The

selection of impeller type is very much related to the working

media type of bearings drive type rotor dynamic characteristics

and installation envelope A wide range of circulators have operated

and a well established technology base exists for both types [63] A

useful portrayal of compressor data in the form of quasi- non-

dimensional parameters (after Balje [64]) showing approximate

boundaries for operation of high ef 1047297ciency axial and radial types is

shown on Fig 30 (from Ref [65])

Both high speed axial and lower speed radial 1047298ow types are

amenable to gas oil and magnetic bearings From the onset of

modularHTR plant studies theuse of active magnetic bearings[6667]offered a solution to eliminate lubricating oil into the reactor circuit

and this tribology technology is attractive for use in submerged

rotating machinery in the next generation of HTR plants [68]

While now dated an appreciation of the main design features of

typical electric motor-driven helium circulators have been reported

previously namely an axial 1047298ow main circulator for a modular

steam cycle HTR plant [69] and a representative radial 1047298ow shut-

down cooling circulator [70]

The operating experience gained from three particular circula-

tors is brie1047298y included below because of their relevance to the

design of helium turbomachinery in future HTR plant variants

82 Axial 1047298ow helium circulator

Since all of the aforementioned predominantly European

helium gas turbines used axial 1047298ow turbomachinery it is of interest

to mention a helium axial 1047298ow circulator that operated in the USA

and to brie1047298y discuss its design parameters and features The

330 MW Fort St Vrain HTGR featured a Rankine cycle power

conversion system Four steam turbine driven helium circulators

were used to transport heat from the reactor core to the steam

generators The complete circulator assemblies were installed

vertically in the prestressed concrete reactor vessel [71e73]

A cross-section of the circulator is shown on Fig 31 with thecompressor rotor and stator visible on the left hand end of the

machine Based on early 1960rsquos technology a decision was made to

use water lubricated bearings and from the overall plant reliability

and availability standpoints this later proved to be a bad choice

Within the vertical circulator assembly there were four 1047298uid

systems namely the helium reactor coolant water lubricant in the

bearings steam for the turbine drive and high pressure water for

the auxiliary Pelton wheel drive During plant transients the pres-

sures and temperatures of these four 1047298uids oscillated considerably

and the response of the control and seal systems proved to be

inadequate and resulted in considerable water ingress from the

bearing cartridge into the reactor helium circuit The considerable

clean up time needed following repeated occurrences of this event

resulted in long periods of plant downtime and this had an adverseeffect on plant availability This together with other technical

Fig 31 Cross section of FSV helium circulator (Courtesy general Atomics)




dif 1047297culties eventually contributed to the plant being prematurely

decommissioned

On the positive side in the context of this paper the helium

circulators operated for over 250000 h and exhibited excellent

helium compressor performance good mechanical integrity and

vibration-free operation The rotating assembly showing the axial

1047298ow compressor and steam turbine rotors together with a view of

the machine assembly are given on Fig 32 The helium compressor

consists of a single stage axial rotor followed by an exit guide vane

The machine was designed for axial helium 1047298ow entering and

leaving the stage and this can be seen from the velocity triangles

shown on Fig 33 which also includes the de1047297nition of the various

aerodynamic parameters Major design parameters and features of

this helium circulator are given on Table 4 Related to an earlier

discussion on the degree of reaction for axial 1047298ow compressors the

value for this conventional single stage circulator is 78 percent All

of the major aerothermal and structural loading criteria were

within established boundaries for an axial compressor having high

ef 1047297ciency and a good surge margin

The compressor gas 1047298ow path and blading geometries were

established based on prevailing industrial gas turbine and aero-

engine design practice A low Mach number (025) a high Reynolds

number (3 106) together with a modest stage loading (ie

a temperature rise coef 1047297cient of 044) and an acceptable value of

diffusion factor (042) were some of the factors that contributed to

a helium circulator that had a high ef 1047297ciency and a good pressure

rise- 1047298ow characteristic The large rotor blade chord and thick blade

section for this single stage circulator are necessary to accommo-

date the high bending stress characteristic of operation in a high

pressure environment The solidity and blade camber were opti-

mized for minimum losses

There were essentially two reasons for including this single-

stage axial 1047298ow compressor that operated in a helium cooled

reactor although its overall con1047297guration can be regarded as a 1047297rst

and last of a kind A rotor blade from this circulator as shown onFig 34 was based on a NASA 65 series airfoil which at the time

were one of the best performing cascades for such low Mach

number and high Reynolds number applications Interestingly it

has almost the same blade height aspect ratio and solidity as would

be used in the 1047297rst stage of an LP compressor in a helium turbo-

machine rated on the order of 250 MW

The second point of interest is that the helium mass 1047298ow rate

through the single stage axial compressor (rated at 4 MWe) is

110 kgs compared with 85 kgs through the multistage compressor

in the 50 MWe Oberhausen II helium gas turbine plant However

the volumetric 1047298ow through the Oberhausen axial compressor is

higher than that through the circulator by a factor of 16 this again

pointing out that the Oberhausen II plant was designed for high

volumetric 1047298ow to simulate the much larger size of turboma-chinery that was planned at the time in Germany for use in future

projected nuclear gas turbine power plants

83 High temperature helium circulator

For future helium turbomachines embodying active magnetic

bearings a challenge in their design relates to accommodating

elevated levels of temperature in the vicinity of the electronic

components In this regard it is of interest to note that a small very

high temperature helium axial 1047298ow circulator rated at 20 kW (as

shown on Fig 35) operated for more than 15000 h in an insulation

test facility in Germany more than two decades ago [74] The

signi1047297cance of this machine is that it operated with magnetic

bearings in a high temperature helium test loop with a circulatorgas inlet temperature of 950 C (1742 F) This necessitated the use

of ceramic insulation to ensure that the temperature in the vicinity

of the magnetic bearing electronics did not exceed a temperature of

about 150 C (300 F)

This machine although a very small axial 1047298ow helium blower

performed well and has been brie1047298y mentioned here since it

represents a point of reference for future helium rotating machines

capable operating with magnetic bearings in a very high temper-

ature helium environment

84 Radial 1047298ow AGR nuclear plant gas circulators

The electric motor-driven carbon dioxide circulators rated at

about 5 MW with a total runningtimein excess of 18 million hours

Fig 32 Fort St Vrain HTGR plant helium circulator (Courtesy General Atomics) (a)

Axial 1047298ow helium compressor and steam turbine rotating assembly (b) 4 MW helium

circulator assembly




in AGR nuclear power plants in the UK have demonstrated veryhigh availability [7576] To a high degree this can be attributed to

the fact that the machines were conservatively designed and proof

tested in a non-nuclear facility at full temperature and power

under conditions that simulated all of the nuclear plant operating

modes The test facility shown on Fig 36 served two functions 1)

design veri1047297cation of the prototype machine and 2) test of all new

and refurbished machines before they were installed in nuclear

plants Engineers currently involved in the design and development

of helium turbomachinery could bene1047297t from this sound testing

protocol to minimize risk in the deployment of helium rotating

machinery in future HTRVHTR plant variants

9 Helium turbomachinery development and testing

91 On-going development activities

The various helium turbomachines discussed in previous

sections operated over a span of about two decades starting in the

early 1960s From about 1990 activities in the nuclear gas turbine

1047297eld have been focused mainly on the design of modular GTeHTR

plant concepts In support of these plant studies many signi1047297cant

helium turbomachine design advancements have been made and

attention given to what development testing would be needed In

the last decade or so limited sub-component development has

been undertaken for helium turbomachines in the 250e300 MWe

size and these are brie1047298y summarized below

In a joint USARussia effort development in support of the

GTe

MHR turbomachine has been undertaken including testing in

the following areas magnetic bearings seals and rotor dynamicsfor the vertical intercooled helium turbomachine rated at 286 MWe

[77e80]

In Japan development activities have been in progress for

several years in support of the 274 MWe helium turbomachine for

the GTeHTR300 plant concept [2581] A detailed discussion on

the aerodynamic design of the axial 1047298ow helium compressor for

this turbomachine has been published in the open literature [82]

While the design methodology used for axial compressor design in

air-breathing industrial and aircraft gas turbines is generally

applicable for a multi-stage helium compressor a decision was

made by JAEA to test a small scale compressor in a helium facility

because of the inherent and unique gas 1047298ow path and type of

blading associated with operation in a high pressure helium

environment The major goal of the test was to validate the designof the 20 stage helium axial 1047298ow compressor for the GTeHTR300

plant

An axial 1047298ow compressor in a closed-cycle helium gas turbine is

characterized by the following 1) a large number stages 2) small

blade heights 3) high hub-to-tip ratio 4) a long annulus with

small taper that tends to deteriorate aerodynamic performance as

a result of end-wall boundary layer length and secondary 1047298ow 5)

low Mach number 6) high Reynolds number and 7) blade tip

clearances that are controlled by the gap necessary in the magnetic

journal and catcher bearings While (as covered in earlier sections)

helium gas turbines have operated there is limited data in the

open literature on the performance of multi-stage axial 1047298ow

compressors operating in a high pressure closed-loop helium

environment

Fig 33 Velocity triangles for axial compressor stage




A 13rd scale 4 stage compressor was designed to simulate the

stage interaction the boundary layer growth and repeated stage

1047298ow in an actual compressor The 1047297rst four stages were designed to

be geometrically similar to the corresponding stages in the

GTe

HTR300 compressor Details of the model compressor havebeen discussed previously [81] and are summarized on Table 5

from [83]

A cross-section of the compressor test model is shown on Fig 37

A view of the 4 stage compressor rotor installed in the lower casing

is shown on Fig 38 The test facility (Fig 39) is a closed helium loop

consisting of the compressor model cooler pressure adjustment

valve and a 1047298ow measurement instrument The compressor is

driven by a 3650 kW electrical motor via a step-up gear The rota-

tional speed of 10800 rpm (three times that of the compressor in

the GTeHTR300 plant) was selected to match blade speed and

Mach number in the full size compressor

Details of the planned aerodynamic performance objectives of

the 13rd scale helium compressor test have been published

previously [84] Extensivetesting of the subscale model compressorprovided data to validate the performance of the full size

compressor for the GTeHTR300 power plant The test data and

test-calibrated CFD analyses gave added insight into the effect of

factors that impact performance including blade surface roughness

and Reynolds number

Based on advanced aerodynamic methodology and experi-

mental validation [82] there is now a sound basis for added

con1047297dence that the design goals of 90 percent polytropic ef 1047297ciency

and a design point surge margin of 20 percent are realizable in

a large multistage axial 1047298ow compressor for a future nuclear gas

turbine plant

In a similar manner a design of a one third size single stage

helium axial 1047298ow turbine has been undertaken and a cross

section of the machine is shown on Fig 40 (from Ref [81]) This

Table 4

Major features of axial 1047298ow helium circulator

Helium 1047298ow rate kgsec 110

Inlet temperature C 394

Inlet pressure MPa 473

Pressure rise KPa 965

Volumetric 1047298ow m3sec 32

Compressor type Single stage axial

Compressor drive Steam turbine

Bearing type Water lubricated

Rotational speed rpm 9550

Power MW 40

Rotor tip diameter mm 688

Rotor tip speed msec 344

Number of rotor blades 31

Number of stator blades 33

Blade height mm 114

Hub-to-tip ratio 067

Axial velocity msec 157

Flow coef 1047297cient 055

Temperature rise coef 1047297cient 044

Degree of reaction 078

Mean rotor solidity 128

Rotor aspect ratio 155

Rotor Mach number 025

Rotor diffusion factor 042

Rotor Reynolds number 3106

Speci1047297c speed 335

Speci1047297c diameter 066

Blade root thickness 15

Airfoil type NASA 65

Rotor blade chord mm 94e64

Stator blade chord mm 79

Rotor centrifugal stress MPa 125

Rotor bending stress MPa 30

Circulator(s) operating Hours gt250000

Fig 34 Rotor blade from single stage axial 1047298ow helium circulator (Courtesy General

Atomics)

Fig 35 20 kW axial 1047298ow helium circulator with magnetic bearings operated in 1985 in

an insulation test loop with a gas inlet temperature on 950

C (Courtesy BBC)




single stage scale model turbine for validity of the full size turbine

has been built and plans made to test the aerodynamic

performance

92 Nuclear gas turbine helium turbomachine testing

In planning for the 1047297rst nuclear gas turbine plant projected to

enter service perhaps in the third decade of the 21st century

a major decision has to be made as to what extent the large helium

turbomachine should be tested prior to operation on nuclear heat

Issues essentially include cost impact on schedule but the over-

riding one is risk Certainly turbomachine component testing will

be undertaken including the compressor (as discussed in the

previous section) and turbine performance seals cooling systems

hot gas valves thermal expansion devices high temperature

insulation rotor fragment containment diagnostic systems

instrumentation helium puri1047297cation system and other areas to

satisfy safety licensing reliability and availability concerns The

major point is really whether a full size or scaled-down turbo-machine be tested early in the project in a non-nuclear facility

To obviate the need for pre-nuclear testing of a large helium

turbomachine a view expressed by some is that advantage can be

taken of formidable technology bases that exist today for large

industrial gas turbines and high performance aeroengines On the

other hand it is the view of some including the author that very

complex power conversion system components especially those

subjected to severe thermal transients donrsquot always perform

exactly as predicted by analysts and designers even using sophis-

ticated computer codes This was exempli1047297ed in the case of the

turbomachine in the aforementioned Oberhausen II helium gas

turbine plant

The need for a helium turbomachine test facility goes beyond

just veri1047297

cation of the prototype machine Each newgas turbine for

commercial modular nuclear reactor plants would have to be proof

tested and validated before being transported to the reactor site

Similarly turbomachines that would be periodically removed from

the plant at say 7 year intervals during the plant operating life of 60

years for scheduled maintenance refurbishment repair or updat-ing would be again proof tested in the facility before re-entering

service

The direction that turbomachine development and testing will

take place for future helium gas turbines needs to be addressed by

the various organizations involved

Fig 36 AGR circulator test facility In the UK (Courtesy Howden)

Table 5

Major design parametersfeatures of model GTeHTR300 axial 1047298ow helium

compressor (Courtesy JAERI)

Scale of GTeHTR300 compressor 13

Helium mass 1047298ow rate (kgsec) 122

Helium volumetric 1047298ow rate (mV s) 87


Inlet pressure MPa 0883Compressor pressure ratio at design point 1156

Number of stages 4


Drive motor power kW 3650

Hub diameter mm 500

Rotor tip diameter (1st4th stage mm) 568566

Hub-to-tip ratio (1st stage) 088

Rotor tip speed (1st stage msec) 321

Number of rotorstator blades (1st stage) 7294

Rotorstator blade height (1st stage mm) 34337

Rotor stator blade c hor d l eng th (1st stage mm) 2620

Rotorstator solidity (1st stage) 119120

Rotorstator aspect ratio (1st stage) 1317


Stage loading factor 031

Reynolds number at design point 76 l05




10 Helium turbomachinery lessons learned

101 Oberhausen II gas turbine and HHV test facility

It is understandable that 1047297rst-of-a-kind complex turboma-

chinery operating with an inert low molecular weight gas such as

helium will experience unique and unexpected problems In the

operation of the two pioneering large helium turbomachines in

Germany there were many positive1047297ndings which could only have

been achieved by development testing Equally important some

negative situations were identi1047297ed many of which were remedied

In the case of the Oberhausen II helium gas turbine plant some of

the very serious problems encountered were not resolved Inves-

tigations were undertaken to rationalize the problems associated

with the large power de1047297ciency and a data base established to

ensure that the various anomalies identi1047297ed would not occur in

future large helium turbomachines

The experience gained from the operation of the Oberhausen II

helium gas turbine power plant and the HHV test facility have been

discussedin thetextand arepresentedin a summaryformon Table6

Fig 37 Cross-section of 13rd scale helium compressor test model (Courtesy JAEA)

Fig 38 Four stage helium compressor rotor assembly installed in lower casing (Courtesy JAEA)




102 Impact of 1047297ndings on future helium gas turbine

The long slender rotorcharacteristic of closed-cycle gas turbines

has resulted in shaft dynamic instability which in some cases has

resulted in blade vibration and failure and bearing damage This

remains perhaps the major concern in the design of large

(250e

300 MW) helium turbomachines for future nuclear gas

turbine plants With pressure ratios in the range of about 2e3 in

a helium system a combination of splitting the compressor (to

facilitate intercooling) and having a large number of compressor

and turbine stages results in a long and 1047298exible rotating assembly

andthis is exempli1047297ed by the rotorassembly shown on Fig13 With

multiple bearings (either oil lubricated or magnetic) the rotor

would likely pass through multiple bending critical speeds before

Fig 39 Helium compressor test facility (Courtesy JAEA)

Fig 40 Cross-section of single stage helium turbine test model (Courtesy JAEA)




reaching the design speed While very sophisticated computer

codes will be used in the detailed rotor dynamic analyses the real

con1047297rmation of having rotor oscillations within prescribed limits

(to avoid blade bearing and seal damage) will come from actual

testingA point to be made here is that in operated fossil-1047297red closed-

cycle gas turbine plants it was possible to remedy problems asso-

ciated with rotor vibrations and blade failures in a conventional

manner In fact in some situations the casings were opened several

times and modi1047297cations made to facilitate bearing and seal

replacement and rotor re-blading and balancing

An accurate assessment of pressure losses must be made

particularly those associated with the helium entering and leaving

the turbomachine bladed sections Minimizing the system pressure

loss is important since it directly impacts the all important quotient

of turbine expansion ratio to compressor pressure ratio and power

and plant ef 1047297ciency

Based on the operating experience from the 20 or so fossil-1047297red

closed-cycle gas turbine plants using air as the working1047298

uid it was

recognized that future very high pressure helium gas turbines

would pose problems regarding the various seals in the turbo-

machine and obtaining a zero leakage system with such a low

molecular weight gas would be dif 1047297cult and this is discussed

below

When the Oberhausen II gas turbine plant and the HHV facility

operated over 30 years ago oil lubricated bearings were used to

support the heavy rotor assemblies and helium buffered labyrinth

seals were used to prevent oil ingressinto the heliumworking1047298uid

Initial dif 1047297culties encountered in both plants were overcome by

changes made to the seal geometries and for the operating lives of

the helium turbomachines no further oil ingress events were

experienced Twoseals were required where the turbine drive shaft

penetrated the turbomachine casing namely 1) a dynamic laby-

rinth seal and 2) a static seal for shutdown conditions In both

plants these seals functioned without any problems

Labyrinth seals were also required within the helium turbo-

machines to pass the correct helium bleed 1047298ow from the

compressor discharge for cooling of the turbine discs blade root

attachments and casings The fact that the very complex rotor

cooling system in the large helium turbomachine in the HHV test

facility operated well for the test duration of about 350 h with

a turbine inlet temperature of 850 C was encouragingIn the case of the Oberhausen II gas turbine plant analysis of the

test data revealed that the labyrinth seal leakage and excessive

cooling 1047298ows were on the order of four times the design value A

possible reason for this was that damage done to the labyrinth

seals caused excessive clearances when periods of excessive rotor

oscillation and vibration occurred during early operation of the

machine

Clearly 1047298uid dynamic and thermal management of the cooling

system and 1047298ow through the various labyrinth seals will require

extensive analysis design and development testing before the

turbomachine is operated on nuclear heat for the 1047297rst time

In future heliumgas turbine designs (with turbine inlet tempera-

tureslikelyontheorderof950C)the1047298owpathgeometriesofhelium

bledfromthecompressornecessarytocoolpartsoftheturbomachinewillbemorecomplexthanthosetestedto-dateInadditiontoproviding

acooling1047298owtotheturbinebladesanddiscsbladerootattachmentsand

casingsheliummustbetransportedtotheseveralmagneticbearingsto

ensure thatthe temperatureof theirelectronic components doesnot

exceedabout150C

The importance of the points made above is evidenced when

examining the data on Table 3 where a combination of excessive

pressure losses and high bleed 1047298ows contributed to about 40

percent of the power de1047297ciency in the Oberhausen II helium

turbine plant

Retaining overall system leak tightnessin closed heliumsystems

operating at high pressure and temperature has been elusive

including experience from the Fort St Vrain HTGR plant as dis-

cussed in Section 65 New approaches in the design of the plethoraof mechanical joints must be identi1047297ed Experience to-date has

shown that having welded seals on 1047298anges while minimizing

system leakage did not eliminate it

The importance of lessons learned from the operation of the

Oberhausen II helium turbine power plant and the HHV test facility

have primarily been discussed in the context of helium turbo-

machines currently being designed in the 250e300 MWe power

range However the established test data bases could also be

applied to the possible emergence in the future of two helium

cooled reactor concepts namely 1) an advanced VHTR combined

cycle plant concept embodying a smaller helium gas turbine in the

power range of 50e80 MWe [22] and 2) the use of a direct cycle

helium gas turbine PCS in a recently proposed all ceramic fast

nuclear reactor concept [85]

Table 6

Experience gained from Oberhausen II and HHV facility

Oberhausen II 50 MW helium gas turbine power plant

Positive results

e Rotating and static seals worked well

e No ingress of bearing lubricant oil into closed circuit

e Load change by inventory control worked well

e 100 Percent load shed by means of bypass valves demonstrated

e Turbine disc and blade root cooling system con1047297rmed

e Coatings on mating surfaces prevented galling and self-welding

e After 24000 h of operation no evidence of corrosion or erosion

e Coaxial turbine hot gas inlet duct insulation and integrity con1047297rmed

e Monitoring of complete power conversion system for steady state

and transient operation undertaken

Problem areas

e Serious power output de1047297ciency (30 MW compared with design

value of 50 MW)

e Compressor(s) and turbine(s) ef 1047297ciencies several points below predicted

e Higher than estimated system pressure loss

e Rotor dynamic instability and blade vibration

e Bearings damaged and had to be replaced

e Blade failure caused extensive damage in HP turbine but retained

in casing

e Very excessive sealing and cooling 1047298ow rates

e Absolute leak tightness not attainable even with welded 1047298ange lips

HHV test facility

Positive resultse Use of heat pump approach facilitated helium temperature capability

to 1000 C

e Large oompressorturbine rotor system operated at 3000 rpm Complex

turbine disc and blade root cooling system veri1047297ed

e Dynamic and static seals met requirement of zero oxl ingress into circuit

e Structural integrity of rotating assembly veri1047297ed at temperature of 850 C

e Measured rotor oscillations within speci1047297cation

e Compressor and turbine ef 1047297ciencies higher than predicted

e Coatings on mating metallic surfaces prevented galling and self-welding

e Instrumentation control and safety systems veri1047297ed

e Seal 1047298ows within speci1047297cation

e Machine stop from operating speed to shutdown in 90 s demonstrated

e Hot gas duct insulation and thermal expansion devices worked well

e After 1100 h of operation no evidence of corrosionof erosion

Problem areas

e Before commissioning a large oil ingress into the circuit occurred due

to serious operator error and absence of an isolation valve A second oilingress occurred due to a mechanical defect in the labyrinth seal system

These were remedied and no further oil ingress was experienced for the

duration of testing

e Cooling 1047298ows slightly larger than expected but this resulted in actual

disc and blade root temperatures lower than the predicted value of

400 C

e System leak tightness demonstrated when pressurized at ambient

temperature conditions but some leakage occured at 850 C even with

the seal welding of 1047298ange(s) lips




11 New technologies

It is recognized that in the 3 to 4 decades since the operation of

the helium turbomachines covered in this paper new technologies

have emerged which negate some of the early issues An example of

this is the technology transfer from the design of modern axial 1047298ow

gas turbines (ie industrial aircraft and aeroderivatives) that fully

utilize sophisticated CAE CAD CFD and FEA design software

Air breathing aerodynamic design practice for compressors and

turbines are generally applicable but the properties of helium and

the high system pressure have a signi1047297cant impact on gas 1047298ow

paths and blade geometries With short blade heights high hub-to-

tip ratios long annulus 1047298ow path length (with resultant signi1047297cant

end-wall boundary layer growth and secondary 1047298ow) and blade tip

clearances in some cases controlled by clearances in the magnetic

catcher bearing testing of subscale model compressors and

Fig 41 Gas turbine test facility for aircraft nuclear propulsion involving the coupling of a 32 MWt air-cooled reactor with two modi 1047297ed J-47 turbojet aeroengines each rated at

a thrust of about 3000 kg operated in 1960 (Courtesy INL)

Fig 42 Mobile 350 KWe closed-cycle nuclear gas turbine power plant operated in 1961 (Courtesy US Army)




turbines will be needed While most of the operated helium tur-

bomachines discussed in this paper took place 3 or 4 decades ago it

is encouraging that the fairly recent test data and test-calibrated

CFD analysis from a subscale four stage model helium axial 1047298ow

compressor in Japan [80] gave a high degree of con1047297dence that

design goals are realizable for the full size 20 stage compressor in

the 274 MWe GTeHTR300 plant turbomachine

In the future the use of active magnetic bearings will eliminate

the issue of oil ingress however the very heavy rotor weight and

size of the journal and thrust bearings (and catcher bearings) of the

type for helium turbomachines in the 250e300 MWe power range

are way in excess of what have been demonstrated in rotating

machinery For plant designs retaining oil-lubricated bearings well

established dry gas seal technology exists particularly experience

gained from the operation of high pressure natural gas pipe line

compressors

For future nuclear helium gas turbine plants the designer has

freedom regarding meeting different frequency requirements that

exist in some countries These include use of a synchronous

machine (ie designed for 50 or 60 Hz grids) use of a gearbox drive

between the turbine and generator or the use of a frequency

converter which gives the designer an added degree of freedom

regarding the selection of speed for the rotating assemblyCompared with the past very sophisticated electronic control

systems instrumentation and diagnostic systems are available

today

12 Conclusions

In this review paper experience from operated helium turbo-

machines has been compiled based on open literature sources At

this stage in the evolution of HTR and VHTR plant concepts it is not

clear in what role form or time-frame the nuclear gas turbine will

emerge when commercialized By say the middle of the 21st

century all power plants will be operating with signi1047297cantly higher

ef 1047297ciencies to realize improved power generation costs and

reduced emissions In a nuclear gas turbine the helium turbo-machine will be a major contributor towards the achievement of

ef 1047297ciencies higher than 50 percent

While it has been 3 to 4 decades since the Oberhausen II helium

turbine power plant and the HHV high temperature helium turbine

facility operated signi1047297cant lessons were learned and the time and

effort expended to resolve the multiplicity of unexpected technical

problems encountered The remedial repair work was done under

ideal conditions namely that immediate hands-on activities were

possible This would not have been possible if the type of problems

experienced had been encountered in a new and untested helium

turbomachine operated for the 1047297rst time with a nuclear heat

source

While new technologies have emerged that negate many of the

early problems there are some uniquely inherent issues associatedwith for large helium turbines operating in a high pressure and

temperature environment and these include the following 1)

minimizing system leakage with such a low molecular weight gas

2) clearances in labyrinth seals to minimize helium bypass1047298ows 3)

the dynamic stability of long slender rotors 4) minimizing the

turbomachine inlet and outlet pressure losses 5) 1047298ow maldis-

tribution in complex ductturbomachine interfaces 6) integrity

veri1047297cation of the catcher bearings (journal and thrust) after

multiple rotor drops (following loss of the magnetic 1047297eld) during

the plant lifetime 7) assurances that high energy fragments from

a failed turbine disc are contained within the machine casing 8)

turbomachine installation and removal from a steel pressure vessel

and 9) remote handling and cleaning of a machine with turbine

blades contaminated with 1047297

ssion products

The need for a helium turbomachine test facility has been

emphasized to ensure that the integrity performance and reli-

ability of the machine before it operates the 1047297rst time on nuclear

heat Engineers currently involved in the design of helium rotating

machinery for all HTR and VHTR plant variants should take

advantage of the experience gained from the past operation of

helium turbomachinery

13 In closing-GT rsquos operated with nuclear heat

In the context of this paper it is germane to mention that two

gas turbines have actually operated using nuclear heat as brie1047298y

highlighted below

In the late 1950rsquos a program was initiated in the USA for aircraft

nuclear propulsion (ANP) While different concepts were studied

only the direct cycle air-cooled reactor reached the stage of

construction of an experimental reactor [86] A view of the large

nuclear gas turbine facility is given on Fig 41 and shows the air-

cooled and zirconiumehydride moderated reactor rated at

32 MWt coupled with two modi1047297ed J-47 turbojet engines each

rated with a thrust of about 3000 kg In this open cycle system the

high pressure compressor air was directly heated in the reactor

before expansion in the turbine and discharge to the atmosphere in

the exhaust nozzle The facility operated between 1958 and 1961 at

the Idaho reactor testing facility While perhaps possible during the

early years of the US nuclear program it is clear that such a system

would not be acceptable today from safety and environmental

considerations

The 1047297rst and indeed the only coupling of a closed-cycle gas

turbine with a nuclear reactor for power generation was under-

taken to meet the needs of the US Army In the late 1950 rsquos an RampD

program was initiated for a 350 kW trailer-mounted system to be

used in the 1047297eld by military personnel A prototype of the ML-1

plant shown on Fig 42 was 1047297rst operated in 1961 [8788]

It was based on a 33 MW light water moderated pressure tube

reactor with nitrogen as the coolant The closed-cycle gas turbine

power conversion system with nitrogen as the working 1047298uid hada turbine inlet temperature of 649 C (1200 F) and delivered

around 300 kW With changes in the Armyrsquos needs the project was

discontinued in 1965

While the experience gained from the above twounique nuclear

plants is clearly not relevant for future nuclear gas turbine power

plants that could see service in the third decade of the 21st century

these ambitious and innovative nuclear gas turbine pioneering

engineering efforts need to be recognized

Acknowledgements

The author would like to thank the following for helpful discus-

sions advice and for providing valuable comments on the initial

paper draft Prof Dr Hermann Haselbacher Hans Ulrich Frutschi DrXing Yan DrPeter Zenker Professor DavidGordon Wilson Professor

Aristide Massardo Arthur Harris DrFred Starr and DrGuido Bac-

caglini This paper has been enhanced by the inclusion of hardware

photographs and unique sketches and the author is appreciative to

all concerned with credits being duly noted

References

[1] C Keller The Escher Wyss AK Closed-Cycle Gas Turbine Its Actual Develop-ment and Future Prospects Paper Presented at ASME Meeting November 261945

[2] HU Frutschi Closed-Cycle Gas Turbines Operating Experience and FuturePotential ASME Press NY 2005

[3] CF McDonald The Nuclear Gas Turbine-Towards Realization After Half

a Century of Evolution (1995) ASME Paper 95-GT-292




[4] C Keller The Theory and Performance of Axial Flow Fans McGraw Hill BookCompany Inc NY 1937

[5] J Ackert C Keller Aerodynamic turbine with closed circuit In A Century of Turbines vols 1516 Escher Wyss News 1942e43 5e19

[6] Escher Wyss News Closed-Cycle Gas Turbines for all Fuels Coal Gas Nuclearvol 39 No 1 (1966)

[7] C Keller Closed-cycle gas turbine Escher Wyss-AK development 1945e1950Transactions of ASME (August 1950) 835e850

[8] C Keller Operating Experience and Design Features of Closed-Cycle GasTurbine Power Plants (1956) ASME Paper 56-GTP-15

[9] C Keller HU Frutschi Closed-cycle plants -conventional and nuclear designapplication operation In Sawyerrsquos Gas Turbine Engineering Handbooksecond ed vol 2 Applications (1976) pp 265e283

[10] K Bammert G Groschup Status Report on Closed-Cycle Power Plants in theFederal Republic of Germany (1976) ASME Paper 76-GT-54

[11] JL Mason Monatomic Working Gases versus Air for Closed Brayton Cycles(1985) ASME Paper 85-IGT-50

[12] JL Mason et al 5 MW Closed Cycle Gas Turbine (1984) ASME Paper 84-GT-268

[13] The British Gas Closed-Cycle Demonstrator (1995) British Gas Research ampTechnology Final Year Report

[14] F Starr ODS alloy high temperature heat exchanger prototype developmentPaper Presented at ODS 2010 Materials Workshop UCSD Jacobs Hall La JollaCalifornia Nov17e18 2010

[15] CA Rennie Achievements of the Dragon project Pergamon Press Annals of Nuclear Energy 5 (1978) 305e320

[16] SB Hosegood et al Dragon Project Engineering Studies on the Direct CycleHTR Proceedings of Conference on Nuclear Gas Turbines The British NuclearEnergy Society London April 8e9 1970 pp 161e179

[17] Nuclear Gas Turbines Proceedings of British Nuclear Society Meeting LondonApril 8-9 1972

[18] CF McDonald C Peinado ldquoThe nuclear gas Turbine-A perspective on a long-term advanced technology HTGR plant Optionrdquo ASME Paper 82-GT-289

[19] GH Lohnert et al Technical design features and essential safety-relatedfeatures of the HTR-Module Nuclear Engineering and Design 121 (1990)259e275

[20] H Reutler GH Lohnert The modular high temperature nuclear reactorNuclear Technology 62 (1983) 22e30

[21] CF McDonald Exploitation of the very high temperature capability of theMHTGR to meet National energy needs after the year 2000 IECEC Paper869006

[22] CF McDonald Power conversion system considerations for an advancednuclear gas turbine (GT-VHTR) CHHP demonstration plant concept Interna-tional Journal of Turbo amp Jet Engines 27 (2010) 179e217

[23] N Hee Cheon et al A review of helium gas turbine technology for hightemperature gas cooled reactors Nuclear Engineering and Design 29 (2007)21e30

[24] CB Baxi et al Development of the GT-MHR Turbomachine ASME PaperGT2009e59450[25] X Yan GTHTR300 design and development Nuclear Engineering and Design

222 (2003) 247e262[26] JC Gauthier et al ANTARES the HTRVHTR project of Framatome ANP

Nuclear Engineering and Design 236 (2006) 526e533[27] J Wang et al ldquoDesign features of gas turbine power conversion system for

HTR-10GT paper D05 presented at 2nd Intl Meeting on HTR TechnologyBeijing China September 21e24 2004

[28] A Koster et al ldquoPBMR Design For the Futurerdquo Nuclear engineering andDesign 222 (203) 231e245

[29] S van der Linden Closed cycle nuclear plant rated at 165 MWe and 40 percentef 1047297ciency Gas Turbine World (MarcheApril 2007) 28e32

[30] CF McDonald Large closed-cycle gas turbines Sawyerrsquos gas turbine engi-neering handbook In Selection and Applications vol II (1985) pp 81e38(Chapter 8)

[31] CF McDonald Helium and Combustion Gas Turbine Power ConversionSystems Comparison (1995) ASME Paper 95-GT-263

[32] JK La Fleur Description of an Operating Closed-Cycle Helium Gas Turbine

ASME Paper 63-AHGT-74[33] JK La Fleur The use of turbomachinery in the 1047297eld of cryogenics In

Sawyerrsquos Gas Turbine Engineering Handbook vol II (1976) 296e311[34] W Spillmann The Closed-Cycle Gas Turbine for Non-Conventional Applica-

tions ASME Paper 66-GT-8[35] K Holliger On the in1047298uence of the degree of reaction on the secondary losses

in axial 1047298ow compressors Escher Wyss News 23 (1960)[36] W Gut Comparison of the relative losses and characteristics of axial

compressor stages Escher Wyss News 23 (1959)[37] JH Horlock Axial Flow Compressors Butterworths Scienti1047297c Publications

London 1958 pp 92e93[38] G Deuster Long-term Operating Experience with Oberhausen I Closed-Cycle

Gas Turbine Power Plant (1970) ASME Paper 70-GT-73[39] G Noak Signi1047297cance of the Helium Turbine Power Plant at Oberhausen (EVO)

and the High Temperature Helium Test Facility (HHV) at Julich for theDevelopment of HTR Direct Cycle (HHT) IAEA Publication SM-20026 Vienna1970 189e200

[40] K Bammert G Deuster Layout and Present Status of the Closed-Cycle HeliumTurbine Plant Oberhausen II (1974) ASME Paper 74-GT-132

[41] P Zenker The Oberhausen 50 MW helium turbine plant Combustion 47 (2)(April 1976)

[42] K Bammert et al Operation and Control of the 50 MW Closed Cycle HeliumTurbine Plant Oberhausen (1974) ASME Paper 74-GT-13

[43] P Zenker 10 years operating experience with the Oberhausen II heliumturbo-generator plant VGB Krafswerkstechnik 68 (7) (July 1998) 616e621

[44] K Bammert G Deuster The First Operating Experiences With the OberhausenHelium Turbine Plant Paper Presented at ASME Gas Turbine Conference NewOrleans March 21e25 1976

[45] G Deuster P Zenker Operation of the Oberhausen Helium Turbine Plant

Paper Presented at ASME Gas Turbine Conference London April 1978[46] P Zenker Operating Experience of the Oberhausen Helium Turbine Plant

Paper Presented at ASME Gas Turbine Conference San Diego 1979[47] G Deuster P Zenker Further Operating Experience of the Oberhausen Helium

Turbine Plant Paper Presented at ASME Gas Turbine Conference NewOrleans 1980

[48] P Zenker Past Experience and Future Prospects of Closed-Cycle Gas TurbinesPaper Presented at ASME Gas Turbine Conference London April 18e22 1982

[49] IA Weisbrodt Summary Report on Technical Experiences from HighTemperature Helium Turbine Testing in Germany Report IAEA-TECDOC-899Vienna Nov 1994

[50] F Bentivoglio G Geffraye Validation of the CATHARE Code Against Experi-mental Data from Brayton Cycle Plants Paper C00000228 Proceedings of HTR 2006 Johannesburg October 1e4 2006

[51] E Arndt HHT-Demonstration Plant Paper Presented at European NuclearConference Hamburg May 6 1979

[52] G Hebel HHV-Anlage Erfahrungen bei Bau und Inbetriebnahme Atom-wirtschaft(5) (1982) 258e262

[53] H Haselbacher A Eierman Development of Helium Gas Turbine in NuclearField (1974) ASME Paper 74-GT-123

[54] H Haselbacher The HHT Helium Gas Turbine and HHV Plant Paper A421 5thInternational Fair and Technical Meeting of Nuclear Industry BaselSwitzerland October 3e7 1978

[55] H Haselbacher HJ Sponholz Cooling and Insulating Problems in a HighTemperature Helium Test Facility (1984) ASME Paper 84-GT-253

[56] C Keller D Schmidt The Helium Gas Turbine for Nuclear Power Plants (1967)ASME Paper 67-GT-10

[57] W Endres Large Helium Turbine for Nuclear Power Plants (1970) ASME Paper70-GT-99

[58] JN Hurst Gas turbomachinery for helium cooled reactors in Proceedings of International Conference on Nuclear Gas Turbines British Nuclear SocietyLondon April 8 1970 pp 45e50

[59] K Bammert Nuclear Gas Turbine of Large Output for HHT Plant (1974) ASMEPaper 74-GT-10

[60] CF McDonald The Nuclear Closed-Cycle Gas Turbine (GT-HTGR) e A UtilityPower Plant for the Year 2000 (1979) AIAA Paper 79e0191

[61] CF McDonald MJ Smith Turbomachinery design considerations for the

nuclear HTGR-GT power plant ASME Journal of Engineering for Power 103 (1)(January 1981) 65e77[62] CF McDonald et al Helium Turbomachine Design for GT-MHR Power Plant

(1994) ASME Paper 94-JPGC-NE-12[63] Gas Cooled Reactor Coolant Circulator and Blower Technology (1988) IAEA

Report IWGGCR17[64] OE Balje Turbomachines A Guide to Design Selection and Theory John

Wiley amp Sons NY 1981[65] CF McDonald et al Circulator DesignTechnology Evolution for Gas Cooled

Reactors (1992) ASME Paper 92-GT-79[66] J Donaldson Application of Magnetic Bearings to Helium Circulators for High

Temperature Gas Cooled Reactors (1987) IECEC Paper 879419[67] CF McDonald Active Magnetic Bearings for Rotating Machinery in Closed-

Cycle Power Plant Systems (1989) ASME Paper 89-WANE-5[68] JA Rennie CF McDonald Active Magnetic Bearings for Rotating Machinery

in Future Gas Cooled Reactor Plants Paper Presented at 4th Intl Symposiumon Magnetic Bearings ETH Zurich August 23e26 1994

[69] CF McDonald MK Nichols Helium Circulator Design Considerations forModular High Temperature Gas Cooled Power Plant (1987) ASME Paper 87-

GT-138[70] CF McDonald Shutdown Cooling Helium Circulator Design Considerations

for MHTGR Power Plant (1989) ASME Paper 89-WANE-5[71] J Yampolsky Steam Turbine Driven Circulators for High Temperature Gas

Cooled Reactors Part I Design (1972) ASME Paper 72-WANE-20[72] VJ Barbat Steam Turbine Driven Circulators for High Temperature Gas

Cooled Reactors Part II Development (1972) ASME Paper 72-WANE-21[73] L Cavallaro J Yampolsky Design and development of a steam turbine driven

circulator for high temperature gas cooled reactors Nuclear Engineering andDesign (1974) 135e147

[74] J Henssen et al Facility for fatigue testing of thermal insulation BBC Review72 (6) (1985)

[75] J Donaldson Development of Carbon Dioxide Circulators IAEA ReportIWGGCR17 (1988) pp 47e63

[76] Personal Communication from John Donaldson (April 7 2006)[77] NG Kodochigov et al Development of the GT-MHR Vertical Turbomachine

Design ASME Paper HTR2008-58309[78] CB Baxi et al ldquoRotor Scale Model Tests for Power Conversion Unit of GT-

MHR rdquo ASME Paper HTR 2008e58015




[79] NG Kodochibov et al Development of Catcher Bearings for the GT-MHR Turbomachine(Oct 18e20 2010)Proceedings of HTR 2010Paper 025Prague

[80] IV Drumov et al Studies of the Electromagnetic Suspension System for theGT-MHRTurbomachineProceedings of HTR2010Paper041 Oct18e20 (2010)

[81] T Takizuka et al RampD on the power conversion system for the gas turbinehigh temperature reactor Nuclear Engineering and Design 233 (2004)239e346

[82] X Yanet alAerodynamic design model test and CFDanalysisfor a multistageaxialhelium compressor ASME Journal of Turbomachinery 130 (3) (July2008)

[83] S Takada et al The 13rd Scale Aerodynamic Performance Test of Helium

Compressor for GTHTR300 Turbomachine of JAERI (April 20e

23 2003)ICONE11e36368 Tokyo Japan

[84] S Takada et al Program for aerodynamic performance tests of heliumcompressor model of GTHTR300 Transactions of the Atomic Energy Society of

Japan 2 (3) (2003) 291e300[85] RW Schleicher et al EM2 An Innovative Approach to US Energy Security

and Nuclear Waste Disposition Paper Presented at Nuclear Power Interna-tional Conference Orlando Florida December 15 2010

[86] RL Loftness Nuclear Power Plants Norstrand Company Inc NY 1964(Chapter 9 and 11)

[87] SA Varga et al The ML-1 Mobile Nuclear Power Plant (1961) ASME Paper61-SA-43

[88] JA Bailey et al Status of the Army Closed Brayton Cycle Gas Turbine Program(1967) ASME Paper 67-GT-13




exchanger technology or for nuclear plants since no large VHTR

plants were built although the small 46 MWt AVR nuclear plant in

Germany operated successfully with a helium reactor outlet

temperature of 950 C for many years

By the late 1960rsquos it had become clear that externally-1047297red fossil

gas turbine plants could no longer compete with rapidly improving

simpler higher ef 1047297ciency more compact and lower cost open cycle

gas turbines

The coupling of a high temperature gas-cooled nuclear reactor

with a closed-cycle gas turbine power conversion system usinghelium was 1047297rst suggested by Professor Curt Keller (co-founder of

the closedBrayton cycle gas turbine with Professor Ackeret) in 1945

[1] From the technology standpoint it was clearly ahead of its time

however it did generate interest in the use of helium as an attrac-

tive working 1047298uid and this topic has been studied periodically over

the last six decades The initial deployment of fossil-1047297red helium

gas turbines in the 1960rsquos were for specialized cryogenic processes

However in this time frame it had become clear that the future of

the closed-cycle gas turbine was really tied to its coupling with

a high temperature gas-cooled nuclear reactor A 1047297rst step towards

this ambitious goal was the needed demonstration of a large

helium gas turbine plant The Oberhausen II 50 MW helium gas

turbine plant started in 1974 and was followed by a large helium

turbomachine test facility (HHV) both of these being located inGermany In the ensuing three and a half decades or so work on

nuclear gas turbines has essentially been limited to paper studies

Projecting into the future an advanced modular VHTR demon-

stration plant embodying a helium closed-cycle gas turbine power

conversion system with the potential for an ef 1047297ciency of over 50

percent could perhaps be built and become operational in circa

2025e2030

2 Closed-cycle gas turbine background

21 Fossil- 1047297red plants

At a time when practical gas turbine work was in its infancy

the basic patent for the closed-cycle gas turbine by Ackeret and

Keller (CH 468287) was registered in Bern Switzerland in July

1935 Following his work on airfoil theory [4] much credit is given

to the late Professor Keller for engineering the 1047297rst closed-cycle

gas turbine a 2 MW power plant that was built and run in Zur-

ich in 1939 This pioneering plant has been well documented

previously [1256] and only its major features are highlighted

below

The AK-36 plant shown on Fig 2 was based on a recuperated

cycle with a turbine inlet temperature of 660 C (1220 F) The

compression process was split into three sections with two stagesof intercooling Based on prevailing technology a very large number

of compressor and turbine stages were required With an external

light-oil 1047297red heater the plant demonstrated an ef 1047297ciency of over

30 percent when operating with a turbine inlet temperature of

700 C (1292 F) During the Second World War the plant operated

for about 6000 h providing electrical power for the Escher Wyss

plant facility in Zurich

This 2 Mwe pioneer plant paved the way for closed-cycle gas

turbine deployment in Europe and with air as the working 1047298uid

plants burning a variety of low-grade fuels have been documented

previously [27e9] The 14 MW Oberhausen I closed cycle gas

turbine plant operated in Germany in a combined power and heat

mode between 1960 and 1982 A view of this plant is shown on

Fig 3 and details of the operational problems encountered andhow they were resolved are discussed in a later section The last

closed-cycle gas turbine to operate commercially in Europe with

air as the working 1047298uid was the 17 MW Gelsenkirchen plant [10]

Starting in 1967 this plant was externally 1047297red with blast furnace

gas and around 10 percent light oil With axial 1047298ow turboma-

chinery an ef 1047297ciency of 30 percent was achieved and the reject

heat was used for district heating The plant proved to be very

reliable and ran for almost 100000 h

After this plant entered service it was apparent that the fossil-

1047297red closed-cycle gas turbine could no longer compete with open

cycle gas turbines however one further plant was built In 1972

a combined power and district heating plant was installed in

Vienna [2] Rated at 30 MW the Spittelau plant was the largest

closed-cycle plant using air as the working 1047298

uid Fired with heavy

Nomenclature

ANP aircraft nuclear propulsion

AGR advanced gas cooled reactor

AVR Arbeitsgemeinschaft Versuchsreaktor

BBC Brown Boveri amp Company

CAD computer aided design

CAE computer aided engineering

CFD computational 1047298uid dynamics

CHP combined heat and power

dB decibel

EVO Energieversorgung Oberhausen

FEA 1047297nite element analysis

FSV Fort St Vrain

HTGR power plant

GA general atomics

GHH Gutehoffnungeshutte Sterkrade AG

GT gas turbine

GTeHTR nuclear gas turbine

GTeMHRgas turbine modular helium reactor

GTeVHTR advanced nuclear gas turbine

HP high pressureHHT high temperature helium turbine

HHV high temperature helium test facility

HTGR high temperature gas cooled reactor

HTR high temperature reactor

IHX intermediate heat exchanger

ICR intercooled and recuperated

INL Idaho National Laboratory

ISI inservice inspection

JAEA Japanese Atomic Energy Agency

kW kilowatt

LP low pressure

MHR modular helium reactor

MW megawatt

MPa mega pascal

NGNP next generation nuclear plant

NGT nuclear gas turbine

NGTCC nuclear GT combined cycle

ODS oxide dispersion strengthened alloy

PBMR pebble bed modular reactor

PCS power conversion system

RC recuperated cycle

ST steam turbine

THTR thorium high temperature reactor

TIT turbine inlet temperatureTZM tungsten zirconium molybdenum alloy

VHTR very high temperature reactor












































900 C











activities








facilities









established [16]













concepts
























turbine concepts





















































power outputs [30]











turbines [31]




















bending stress)











sections
















ever to operate








same shaft








the compressor
















was limited
































































addressed below





































Table 1



Facility La Fleur

gas turbine

Escher Wyss

gas turbine

Oberhausen 11

power plant

HHV

test loop

FSV HTGR


Year 1962 1966 1974 1981 1976




Compressor



Inlet press MPa 125 122 105285 45 473

Inlet temp C 21 22 25 820 394


Flow kgsec 73 11 85 212 110

In vol 1047298ow m3sec 35 55 50 107 32

Turbine




Inlet temp C 650 660 750 850 e

In vol 1047298ow m3sec 30 57 67 98 e


sec 36 85 120 104 e








Figs 11 and 13






































source



















































working 1047298uid










Escher Wyss)











below




































performance





















ciencies and








































demonstrated [43]









































turbine












helium leakage






Table 2







compressor bypass









Ef 1047297ciency 870 855




Turbine LP HP



Ef 1047297ciency 900 883








































shown below







8 1975








GHH)


kgday day

Dragon 180 020e20 010e10

AVR 240 10e30 040e12


HHV 1250 25e50 020e040



























introduced













thickness ratio



































Table 3



















recommended


71 Background

















Table 3



value

Measured Power loss

MW

Compressors


and blades



Turbines





damaged blades




18 75 53



102 128 26




measured 30 MW































EVO)

























































































[53e55]

































plant






























040 percent of the

































C









dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References


















































































































































900 C











activities








facilities









established [16]













concepts
























turbine concepts





















































power outputs [30]











turbines [31]




















bending stress)











sections
















ever to operate








same shaft








the compressor
















was limited
































































addressed below





































Table 1



Facility La Fleur

gas turbine

Escher Wyss

gas turbine

Oberhausen 11

power plant

HHV

test loop

FSV HTGR


Year 1962 1966 1974 1981 1976




Compressor



Inlet press MPa 125 122 105285 45 473

Inlet temp C 21 22 25 820 394


Flow kgsec 73 11 85 212 110

In vol 1047298ow m3sec 35 55 50 107 32

Turbine




Inlet temp C 650 660 750 850 e

In vol 1047298ow m3sec 30 57 67 98 e


sec 36 85 120 104 e








Figs 11 and 13






































source



















































working 1047298uid










Escher Wyss)











below




































performance





















ciencies and








































demonstrated [43]









































turbine












helium leakage






Table 2







compressor bypass









Ef 1047297ciency 870 855




Turbine LP HP



Ef 1047297ciency 900 883








































shown below







8 1975








GHH)


kgday day

Dragon 180 020e20 010e10

AVR 240 10e30 040e12


HHV 1250 25e50 020e040



























introduced













thickness ratio



































Table 3



















recommended


71 Background

















Table 3



value

Measured Power loss

MW

Compressors


and blades



Turbines





damaged blades




18 75 53



102 128 26




measured 30 MW































EVO)

























































































[53e55]

































plant






























040 percent of the

































C









dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References











































































































activities








facilities









established [16]













concepts
























turbine concepts





















































power outputs [30]











turbines [31]




















bending stress)











sections
















ever to operate








same shaft








the compressor
















was limited
































































addressed below





































Table 1



Facility La Fleur

gas turbine

Escher Wyss

gas turbine

Oberhausen 11

power plant

HHV

test loop

FSV HTGR


Year 1962 1966 1974 1981 1976




Compressor



Inlet press MPa 125 122 105285 45 473

Inlet temp C 21 22 25 820 394


Flow kgsec 73 11 85 212 110

In vol 1047298ow m3sec 35 55 50 107 32

Turbine




Inlet temp C 650 660 750 850 e

In vol 1047298ow m3sec 30 57 67 98 e


sec 36 85 120 104 e








Figs 11 and 13






































source



















































working 1047298uid










Escher Wyss)











below




































performance





















ciencies and








































demonstrated [43]









































turbine












helium leakage






Table 2







compressor bypass









Ef 1047297ciency 870 855




Turbine LP HP



Ef 1047297ciency 900 883








































shown below







8 1975








GHH)


kgday day

Dragon 180 020e20 010e10

AVR 240 10e30 040e12


HHV 1250 25e50 020e040



























introduced













thickness ratio



































Table 3



















recommended


71 Background

















Table 3



value

Measured Power loss

MW

Compressors


and blades



Turbines





damaged blades




18 75 53



102 128 26




measured 30 MW































EVO)

























































































[53e55]

































plant






























040 percent of the

































C









dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References

























































































































turbine concepts





















































power outputs [30]











turbines [31]




















bending stress)











sections
















ever to operate








same shaft








the compressor
















was limited
































































addressed below





































Table 1



Facility La Fleur

gas turbine

Escher Wyss

gas turbine

Oberhausen 11

power plant

HHV

test loop

FSV HTGR


Year 1962 1966 1974 1981 1976




Compressor



Inlet press MPa 125 122 105285 45 473

Inlet temp C 21 22 25 820 394


Flow kgsec 73 11 85 212 110

In vol 1047298ow m3sec 35 55 50 107 32

Turbine




Inlet temp C 650 660 750 850 e

In vol 1047298ow m3sec 30 57 67 98 e


sec 36 85 120 104 e








Figs 11 and 13






































source



















































working 1047298uid










Escher Wyss)











below




































performance





















ciencies and








































demonstrated [43]









































turbine












helium leakage






Table 2







compressor bypass









Ef 1047297ciency 870 855




Turbine LP HP



Ef 1047297ciency 900 883








































shown below







8 1975








GHH)


kgday day

Dragon 180 020e20 010e10

AVR 240 10e30 040e12


HHV 1250 25e50 020e040



























introduced













thickness ratio



































Table 3



















recommended


71 Background

















Table 3



value

Measured Power loss

MW

Compressors


and blades



Turbines





damaged blades




18 75 53



102 128 26




measured 30 MW































EVO)

























































































[53e55]

































plant






























040 percent of the

































C









dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References
























































































































power outputs [30]











turbines [31]




















bending stress)











sections
















ever to operate








same shaft








the compressor
















was limited
































































addressed below





































Table 1



Facility La Fleur

gas turbine

Escher Wyss

gas turbine

Oberhausen 11

power plant

HHV

test loop

FSV HTGR


Year 1962 1966 1974 1981 1976




Compressor



Inlet press MPa 125 122 105285 45 473

Inlet temp C 21 22 25 820 394


Flow kgsec 73 11 85 212 110

In vol 1047298ow m3sec 35 55 50 107 32

Turbine




Inlet temp C 650 660 750 850 e

In vol 1047298ow m3sec 30 57 67 98 e


sec 36 85 120 104 e








Figs 11 and 13






































source



















































working 1047298uid










Escher Wyss)











below




































performance





















ciencies and








































demonstrated [43]









































turbine












helium leakage






Table 2







compressor bypass









Ef 1047297ciency 870 855




Turbine LP HP



Ef 1047297ciency 900 883








































shown below







8 1975








GHH)


kgday day

Dragon 180 020e20 010e10

AVR 240 10e30 040e12


HHV 1250 25e50 020e040



























introduced













thickness ratio



































Table 3



















recommended


71 Background

















Table 3



value

Measured Power loss

MW

Compressors


and blades



Turbines





damaged blades




18 75 53



102 128 26




measured 30 MW































EVO)

























































































[53e55]

































plant






























040 percent of the

































C









dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References















































































































ever to operate








same shaft








the compressor
















was limited
































































addressed below





































Table 1



Facility La Fleur

gas turbine

Escher Wyss

gas turbine

Oberhausen 11

power plant

HHV

test loop

FSV HTGR


Year 1962 1966 1974 1981 1976




Compressor



Inlet press MPa 125 122 105285 45 473

Inlet temp C 21 22 25 820 394


Flow kgsec 73 11 85 212 110

In vol 1047298ow m3sec 35 55 50 107 32

Turbine




Inlet temp C 650 660 750 850 e

In vol 1047298ow m3sec 30 57 67 98 e


sec 36 85 120 104 e








Figs 11 and 13






































source



















































working 1047298uid










Escher Wyss)











below




































performance





















ciencies and








































demonstrated [43]









































turbine












helium leakage






Table 2







compressor bypass









Ef 1047297ciency 870 855




Turbine LP HP



Ef 1047297ciency 900 883








































shown below







8 1975








GHH)


kgday day

Dragon 180 020e20 010e10

AVR 240 10e30 040e12


HHV 1250 25e50 020e040



























introduced













thickness ratio



































Table 3



















recommended


71 Background

















Table 3



value

Measured Power loss

MW

Compressors


and blades



Turbines





damaged blades




18 75 53



102 128 26




measured 30 MW































EVO)

























































































[53e55]

































plant






























040 percent of the

































C









dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References


































































































































































addressed below





































Table 1



Facility La Fleur

gas turbine

Escher Wyss

gas turbine

Oberhausen 11

power plant

HHV

test loop

FSV HTGR


Year 1962 1966 1974 1981 1976




Compressor



Inlet press MPa 125 122 105285 45 473

Inlet temp C 21 22 25 820 394


Flow kgsec 73 11 85 212 110

In vol 1047298ow m3sec 35 55 50 107 32

Turbine




Inlet temp C 650 660 750 850 e

In vol 1047298ow m3sec 30 57 67 98 e


sec 36 85 120 104 e








Figs 11 and 13






































source



















































working 1047298uid










Escher Wyss)











below




































performance





















ciencies and








































demonstrated [43]









































turbine












helium leakage






Table 2







compressor bypass









Ef 1047297ciency 870 855




Turbine LP HP



Ef 1047297ciency 900 883








































shown below







8 1975








GHH)


kgday day

Dragon 180 020e20 010e10

AVR 240 10e30 040e12


HHV 1250 25e50 020e040



























introduced













thickness ratio



































Table 3



















recommended


71 Background

















Table 3



value

Measured Power loss

MW

Compressors


and blades



Turbines





damaged blades




18 75 53



102 128 26




measured 30 MW































EVO)

























































































[53e55]

































plant






























040 percent of the

































C









dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References











































































































Figs 11 and 13






































source



















































working 1047298uid










Escher Wyss)











below




































performance





















ciencies and








































demonstrated [43]









































turbine












helium leakage






Table 2







compressor bypass









Ef 1047297ciency 870 855




Turbine LP HP



Ef 1047297ciency 900 883








































shown below







8 1975








GHH)


kgday day

Dragon 180 020e20 010e10

AVR 240 10e30 040e12


HHV 1250 25e50 020e040



























introduced













thickness ratio



































Table 3



















recommended


71 Background

















Table 3



value

Measured Power loss

MW

Compressors


and blades



Turbines





damaged blades




18 75 53



102 128 26




measured 30 MW































EVO)

























































































[53e55]

































plant






























040 percent of the

































C









dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References








































































































































working 1047298uid










Escher Wyss)











below




































performance





















ciencies and








































demonstrated [43]









































turbine












helium leakage






Table 2







compressor bypass









Ef 1047297ciency 870 855




Turbine LP HP



Ef 1047297ciency 900 883








































shown below







8 1975








GHH)


kgday day

Dragon 180 020e20 010e10

AVR 240 10e30 040e12


HHV 1250 25e50 020e040



























introduced













thickness ratio



































Table 3



















recommended


71 Background

















Table 3



value

Measured Power loss

MW

Compressors


and blades



Turbines





damaged blades




18 75 53



102 128 26




measured 30 MW































EVO)

























































































[53e55]

































plant






























040 percent of the

































C









dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References















































































































below




































performance





















ciencies and








































demonstrated [43]









































turbine












helium leakage






Table 2







compressor bypass









Ef 1047297ciency 870 855




Turbine LP HP



Ef 1047297ciency 900 883








































shown below







8 1975








GHH)


kgday day

Dragon 180 020e20 010e10

AVR 240 10e30 040e12


HHV 1250 25e50 020e040



























introduced













thickness ratio



































Table 3



















recommended


71 Background

















Table 3



value

Measured Power loss

MW

Compressors


and blades



Turbines





damaged blades




18 75 53



102 128 26




measured 30 MW































EVO)

























































































[53e55]

































plant






























040 percent of the

































C









dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References













































































































































demonstrated [43]









































turbine












helium leakage






Table 2







compressor bypass









Ef 1047297ciency 870 855




Turbine LP HP



Ef 1047297ciency 900 883








































shown below







8 1975








GHH)


kgday day

Dragon 180 020e20 010e10

AVR 240 10e30 040e12


HHV 1250 25e50 020e040



























introduced













thickness ratio



































Table 3



















recommended


71 Background

















Table 3



value

Measured Power loss

MW

Compressors


and blades



Turbines





damaged blades




18 75 53



102 128 26




measured 30 MW































EVO)

























































































[53e55]

































plant






























040 percent of the

































C









dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References
































































































































turbine












helium leakage






Table 2







compressor bypass









Ef 1047297ciency 870 855




Turbine LP HP



Ef 1047297ciency 900 883








































shown below







8 1975








GHH)


kgday day

Dragon 180 020e20 010e10

AVR 240 10e30 040e12


HHV 1250 25e50 020e040



























introduced













thickness ratio



































Table 3



















recommended


71 Background

















Table 3



value

Measured Power loss

MW

Compressors


and blades



Turbines





damaged blades




18 75 53



102 128 26




measured 30 MW































EVO)

























































































[53e55]

































plant






























040 percent of the

































C









dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References










































































































































shown below







8 1975








GHH)


kgday day

Dragon 180 020e20 010e10

AVR 240 10e30 040e12


HHV 1250 25e50 020e040



























introduced













thickness ratio



































Table 3



















recommended


71 Background

















Table 3



value

Measured Power loss

MW

Compressors


and blades



Turbines





damaged blades




18 75 53



102 128 26




measured 30 MW































EVO)

























































































[53e55]

































plant






























040 percent of the

































C









dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References
































































































































introduced













thickness ratio



































Table 3



















recommended


71 Background

















Table 3



value

Measured Power loss

MW

Compressors


and blades



Turbines





damaged blades




18 75 53



102 128 26




measured 30 MW































EVO)

























































































[53e55]

































plant






























040 percent of the

































C









dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References























































































































Table 3



















recommended


71 Background

















Table 3



value

Measured Power loss

MW

Compressors


and blades



Turbines





damaged blades




18 75 53



102 128 26




measured 30 MW































EVO)

























































































[53e55]

































plant






























040 percent of the

































C









dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References


































































































































EVO)

























































































[53e55]

































plant






























040 percent of the

































C









dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References






























































































































































































[53e55]

































plant






























040 percent of the

































C









dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References












































































































plant






























040 percent of the

































C









dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References














































































































dicted [55]






any problems














































Fig 30 Speci1047297
















81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References




















































































































81 Background



























































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References











































































































decommissioned




























































about 150 C (300 F)











circulator assembly




























GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References


































































































































GTe



[77e80]













plant












environment









GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References














































































































GTe


from [83]
















and Reynolds number






turbine plant




Table 4











Power MW 40





Blade height mm 114





















Atomics)



C (Courtesy BBC)






performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References












































































































performance

























turbine plant


just veri1047297







service





Table 5








Number of stages 4



Hub diameter mm 500











































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References






































































































































(250e
































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References




























































































































uid it was





below
























machine











exceedabout150C





turbine plant


















Table 6



Positive results











Problem areas


value of 50 MW)






in casing



HHV test facility


to 1000 C













Problem areas




duration of testing



400 C







11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References










































































































11 New technologies




































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References

























































































































compressors









today

12 Conclusions



















source
















ssion products











highlighted below















considerations

















Acknowledgements








References








































































































helium turbomachinery operating experience from gas turbine power plants

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