10 international conference on compressors and...

Turbomachinery group for cold energy concept application

1Turboalgor S.r.l., Massa Martana,

Perugia, Italy

10th INTERNATIONAL CONFERENCE ON

COMPRESSORS AND THEIR SYSTEMS

11th-13th September 2017

S. Alavi2, A. Arpi1, M. Ascani1, G. Cerri2, L. Chennaoui2, A. Manni1

2Roma Tre University, Department

of Engineering, Rome, Italy

Refrigeration Energy Consumption & Emissions

ELECTRICITY CONSUMPTION

WORLDWIDE 15 - 17%

INDUSTRIALIZED COUNTRIES 23 – 25 %

WARM COUNTRIES 40 %

WORLDWIDE EMISSIONS

4 – 5 % OF GLOBAL POLLUTANT EMISSIONS

Numerous attempts have been investigated and applied toward reducing

the electric power consumed per unit of cooling power

10th International Conference on

Compressors and their Systems

City, University of London 11th-13th September 2017

State of the art

ATTEMPTS TO SAVE POWER:

• Mainly based on thermal regeneration, which in vapour compression

cycles leads to increasing the condensate subcooling through cycle

internal processes

CONDENSER

EVAPORATOR

BL

EE

D

EV

AP

OR

AT

OR

CO

MP

RE

SS

OR




COP

SPECIFIC ENERGY

CONSUPTION

COMPRESSOR

CAPACITY

+BLEED VAPOUR

GENERATOR

+TURBOMACHINERY

BASED BOOSTER UNIT

VAPOUR COMPRESSION

REFRIGERANT PLANT

(VCRP)

COLD ENERGY PROJECT




Scientific and technical background

• Improvements that can be achieved modifying a vapour compressor refrigeration

Simple Cycle (SC), adding some devices

• Optimum sizing of the innovative devices, using economically viable technologies

Simple Cycle (SC) as a reference




Power Regenerated Cycles

Power regeneration is based on internal power cycles (IPCs) that drive compressor

to increase the pressure at the main compressor suction

1B1CEG 2B1CEG 2B2CEG




Modular approach to establish SC model(Each module corresponds to one component)

SC COMPONENTS

WF = Working Fluid

MC = Main Compressor

K = Condenser

MEV = Main Expansion Valve

EV = Evaporator

Component properties are

defined by a Set of

NonLinear Equations (NLES)

WFNLES

MCNLES

KNLES

MEVNLES

EVNLES

The SC is described by a set of independent nonlinear

equations:

SCNLES = WFNLES+MCNLES+KNLES+MEVNLES+EVNLES

Number of equations = Number of unknown variables No degree of freedom (DoF)




Power Regenerated Cycles

The overall Power Regenerated Vapour Compressor Refrigerated Cycle (PRVCRC)

is represented by an Overall NLES (ONLES):

ONLES = SCNLES U Bleed Vapour Generator NLES (BVGNLES) U

Compressor Expander Group NLES (CEGNLES)

Degrees of freedom for each jth Power Regeneration Internal Cycle are:

• SBVGj = Bleed Vapour Generator Surface

• pbj = Bleed pressure

• mbj = Bleed Mass Flow Rate

If DoFs are inside the feasibility domain, a solution can be calculated




Optimization process

Subject to the ONLES

OBJECTIVE FUNCTION: Maximize COP = Cooling Power (CP)/ Main

Compressor Power (MMC)

Search SBVGj, pbj and mbj

Some inequality constraints are restrictions

on temperatures and pressures

TURBOMACHINERY SELECTION (TS):

TS model is based on similitude concepts using the Car

Engine Turbocharger Technology (CETT) Data Base:

• DoF is compressor specific angular speed ωcs

• The modified ONLES problem that also contain

TSNLES leads to the optimizing of the PRVCRC

performance with the more suitable turbomachinery

impellers being selected




Optimization process

TURBOMACHINERY SIZING:

Nominal speed

Compressor exducer selected together with the impeller types

Expander inducer

HUB AND SHROUD PROFILES ARE KNOWN

Modify the shroud profiles of the

compressor and expander to

achieve the best performance,

minimizing the losses

1D MEAN LINE MODELLING (1D MLM) APPROACH




Turbomachinery 1D MLM

1D MLM is based on the use of channel sections

that are quasi-orthogonal to the channel centreline

Center Line

Quasi-orthogonal

Using the mass and rothalpy conservation, it is possible

to establish a set of NLES for any impeller that,

for each radius r, correlates:

𝑭𝒊 𝑴𝒂𝒔𝒔 𝑭𝒍𝒐𝒘 (𝒎),𝑹𝒂𝒅𝒊𝒖𝒔(𝒓),𝑬𝒏𝒕𝒉𝒂𝒍𝒑𝒚(𝒉),𝑷𝒓𝒆𝒔𝒔𝒖𝒓𝒆(𝒑),𝑾𝒐𝒓𝒌(𝑾),𝑪𝒉𝒂𝒏𝒏𝒆𝒍 𝑯𝒆𝒊𝒈𝒉𝒕(𝒃),𝑳𝒐𝒔𝒔(∆𝒉𝒍) =𝟎

Loss ∑ ∆hl can be calculated as an objective function, thus the following

problem can be stated:

Subject to TSNLES

OBJECTIVE FUNCTION: minimize ∑ ∆hl

Search b(rj) ∀ j = 1, Nr Solution provides the best W(r),

p(r), h(r) distributions along the

channel centreline and to

establish the shroud profiles




Turbomachinery sizing outcomes

Application of the 1D MLM provides

the profiles of the compressor and

expander impellers

Two views of machined compressor impeller Original and machined expander impellers




Theoretical and experimental results – 2B1G layout with R404a WF

The PRVCRC has been optimized taking into

consideration the use of Vd = 3 dm3/turn screw

compressor running at a synchronous speed of 3000 rpm

Optimum CP, COP, mMC

and mex versus the 1st

bleed pressure




Test Bench for 2B1G scheme

The TB consists of four essential

elements:

1. Condenser unit

2. Calorimeters section

3. Compressor-expander group (CEG)

4. Cold liquid R404a piping

The Test Bench is provided with special software that ensures the automatic

control, measured data acquisition and storage of all parameters related to the

overall operation of the refrigerating system, and more specifically of

compressor-expander group




Experimental results

Nomenclature:

CPD =Compressor Pressure Difference

EPD = Expander Pressure Difference

EMF = Expander Mass Flow

SPEED (krpm)

PO

WER

SA

VIN

G (

%)




Industrial Phase

The results obtained in the COLD ENERGY project provided the

motivation to continue both in the direction of performance

improvement and product industrialization




Cold Energy kit

Shut-Off

Valve

Electric Panel

Turbocharger

Heat

Exchangers

Lubrication

System




Turbocharger integrated in the main compressor

Already started the project to install turbocharger in the body of

compressor

With this constructive solution, reciprocating

compressor will be equipped with ECO-port

as scroll or screw compressors

ECO-port

Suction port

Turbocharger




Conclusions

• The utilization of an internal power cycle for power regeneration

purposes brings about a lowering of the power consumption per unit of

cooling power produced by a VCRP

• It has been demonstrated that the cycle and components can be

optimized up to achieve about 22-24 % of power saving

• Turbomachinery for the Expander Compressor Group can be selected

among the units available in the Car Engine Turbocharger Technology

• Modifications to the impeller profiles must be taken into consideration

• An industrial application is now being investigated and some initial

forecasts have been studied and will be demonstrated in dedicated

industrial VCRPs







THANK YOU

FOR YOUR ATTENTION

10 international conference on compressors and...

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