steam generating system

8/12/2019 Steam Generating System

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India Boiler dot Com

Steam Generating System

In a Water Tube Boiler, watercirculates through tubes andheat source is outside. Heat istransferred from outside the

tube to water inside the tube.Where large !uantity of steam isre!uired, at high pressure 3Water Tube type "oiler ispreferred. In power plants,normally, high pressure water4tube type boilers are used,where capacity rages from 0' to

56' t1hr, having pressure 7temperature up to &5' kg1cm2-g and 68' '( respectively.

lexibility in design is more but re!uires

stringent water !uality control sincewater side cleaning is a complicated andtime taking process.

Water Tube Boiler

If we take a complete steam generating system and break it into various subsystems, we can have a better understanding of the overall system. or this purposelet us take a steam generating system of a 9ower 9lant, which is comprised of mostof the sub4systems.

:et us follow the water route while it is being converted into steam while passingthrough various components of a steam generating system and thereby go thoughvarious sub4systems.

Feed Water System; 9roperly treated eed Water first comes to e!uipment knownas #eaerator, where dissolved /xygen gets removed. eed water is added as ma!eup "ater to the condensate, which is being circulated back to the system.

#eaeration is done by heating up the water by auxiliary steam. This is part of the

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sensible heat received in the cycle, which we can compare with a temperatureenthalpy curve.

rom the #eaerator, the feedwater goes to the Boiler Feed$ump, which pumps the feed

water at high pressure into the%vaporator &Circulating "ater' steam system(. "ut at thispoint the temperature of thewater is much less thansaturation temperature.Therefore a lot of sensible energyis still re!uired by the waterbefore it reaches the saturationtemperature and evaporationwould start.

o it is first taken inside the flue gas path where the gas is about to be released in

the atmosphere through chimney at a high temperature -and therefore having a lotof heat energy to increase the feed water temperature in an %conomi)er. Now theheated feed water enters the


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In the superheater, the temperature of steam is raised by further heating. The finaltemperature is usually controlled by water spraying through attemperator, which isplaced before the final superheater.The superheated steam then goes to the turbine, which expands in the turbinesection and rotates the turbine blade. In some power plants, where multiple

pressure turbine section is available, the expanded team, which is at lower pressureand temperature, is further brought back to the boiler section. This part is known as,e*eater and steam gets further superheated in this section before it enters the >9or :9 stage of the turbine. rom the final turbine stage, the exhaust steam -which ispartially wet now goes to the Condenser, where the latent heat is removed bycooling water circulation and the condensed water -condensate is circulated back&Condensate System( to the -eaeratorwith the help of condensate extractionpump.

It would be interesting to know that the steam enters the condenser usually attemperature of 8' to 86o( -cold steam. This is because the condenser operatesunder vacuum to extract maximum work output from the turbine. If we refer thesteam table, we can confirm this fact.

When we are discussing fired boilers, the heat source is combustion of fuel. The fuelcan be of solid, li!uid or gaseous type and the combustion takes place in an enclosedsection known as the furnace. The first thing the furnace would need is the fuel,which has to be brought from the place it is stored &Fuel system which is notshown here(. "efore it enters the furnace, the fuel might re!uire some preparation.or example, in 9ulveri*ed coal fired boiler -most commonly used for large thermalpower plant, coal has to be ground into fine talcum powder consistency andtherefore crusher and pulveri*ing mills are used. or li!uid fuel system, the fuelshould be atomi*ed -broken into fine particles to increase surface area, which is

done by steam or air atomi*er. ome li!uid fuels re!uire certain temperature toretain proper viscosity and therefore suitable heater would be there. or gaseous

fuel, however, such preparations are not re!uired and only the pressure is to bemaintained.In the furnace, fuel re!uires air and ignition temperature for combustion. The air isone thing, which is available in the nature for free. However, it is still re!uired to bebrought inside the furnace. /nce combustion takes place, the furnace gets filled withthe product of combustion, i.e. flue gas and this flue gas again is re!uired to betaken out of the system to allow entry of further air. The system which handles theair and flue gas is called #raught ystem.The draught system is generally of three types;Forced -raug*t/Where the air is being pushed into the furnace with the help of afan known as # fan, which is located before the furnace. It pushed the air, which in

turn pushes the flue gas inside the furnace till it is taken out of the system throughthe chimney.Induced -raug*t/Where the flue gas from the furnace is sucked and taken out ofthe system through the chimney. The fan used in this system is called I# fan and itis located %ust before the chimney, after the


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In the system schematic shown here, we are using a "alanced #raught, where theair is pushed inside the furnace by theF- fan. "ut before it goes to the furnace, theair is first taken inside the flue gas path through an 2ir $re3*eater, where the air isheated by using the residual heat of the flue gas remaining after it passes theeconomi*er. The heated combustion air increases the combustion efficiency and also

further reduces the exit gas temperature. )fter )ir 9re4heater, heated air is takeninside the furnace.Inside the furnace, after combustion takes place, tremendous amount of heat isbeing released. The schematic diagram may not represent it properly, but some ofthe superheater and reheater sections are kept in the furnace to take advantage ofthe radiation heat transfer. The hot flue gas leaves the furnace and passes throughvarious sections of uperheater, @eheater, (@ and other operationalparameters. (entral "oiler "oard is a central authority, which formulates andamends the regulations governing boilers to keep pace with technological

advancement and oversees that the stipulated rules framed by the different tateBovernments and regulations under I"@ are strictly followed by all concerned

authorities. The Indian "oilers )ct, &C20 is enacted by the parliament and administeredby the all tate Bovernments through (hief Inspector of "oilers, as the sub%ect D"oilerDcomes under the concurrent list of the constitution of India. The tate :evel @egulatory"odies under the (hief Inspector of "oilers, in every state, are solely responsible forimplementation of various regulations of the Indian "oiler @egulation -I"@ concerningall types of boilers for their manufacture, erection, operation and maintenance. #uringmanufacture and erection the (I" inspects various stages and finally issuesmanufacturing certificates in statutory formats and if any owner of a boiler intends torun it, he has to apply to the (I" with manufacturing certificates for registration of thesame. or boiler under use, (I" will inspect it once in a year in normal condition.However, in emergency the fre!uency of inspections may increase.

The tate #irectorate of (hief Inspector of "oilers also governs the !uality andcapability of personnel handling %obs of manufacturing, maintenance and operating.Welders deployed in manufacture and maintenance and repairs of pressure vesselsare also covered under such rules. The state (hief Inspector of "oilers is authori*edto conduct regular examinations for testing and certifying candidates working onboiler or a pressure vessel.

T4% I0-I20 B5I6%,S &27%0-7%0T( 2CT 899:Some of t*e significant C*anges/

T*e definition of ;boilers


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i with capacity less than 26 litres -such capacity measured from the feed checkvalve to main steam stop valveii with less than one kilogram per centimeter s!uare design gauge pressure andworking pressureor

iii in which water is heated below one hundred degree centigrade. T*e definition of ;Steam $ipeE/

In old act it is a pipe line through which steam passes from boiler to a prime moveror other user or both. /f course there were limitations to pressure or diameter -0.6kg1 cm2and 26' N".In new act, it means any pipe through which steam passes. The pressure anddiameter limitation will be there.

Introduction of t*ird party inspecting bodies besides Boiler

-irectorate/i (ompetent 9ersonii (ompetent )uthority

iii Inspecting )uthority

$eriodicity of certificate issued to boiler users after carrying out

statutory inspection.Till now the certified period to use the boilers was for twelve months whatever maybe the si*e and running condition of boilers.Now it will vary from &2 months to 8F months depending upon various factors to beoutlined by the Indian "oiler @egulation.

Stricter penal measures/

The new act has introduced heavy penalty for various offences

or running of boilers without certificate there was a fine of five hundred rupeesearlier, now it has become one lakh rupees.

In section 8# for ot*er penalties li!e

a ailing to engrave the registration numberb Illegal repairsc ails to report accidentd Tempering with safety valvese )llowing any person to go inside boiler without effective disconnectionIn old act it was a fine of five hundred rupees. Now it is revised to Gpunishable withimprisonment which may extend to two years or with fine which may extends to onelakh rupees or with both.

In section 26 for offence of tempering registration mark, the fine may extends toone lakh rupees

Water Tube $ac!aged Boiler/9ackage water tube boilers are as popular as packaged fire tube boilers. uchboilers are compact and standardi*ed for pressure and capacity. They are shopassembled having a furnace accommodated with water walls. Benerating tubes,superheater and economiser ready for transportation by road or sea. They aree!uipped with firing e!uipments, feed pumps, auxiliaries and ancillaries, oil pumps,oil heaters, draught fans, feed water regulator, soot blowers and automatic controlfor efficient performance.

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a (hemical processes involving exothermic reactions vi*.,

b @ecovering heat that is;

It reduces air and water pollution and lowers the flue gas temperature,reducing the maintenance of flues, fans and stacks.

#esign considerations in the selection of a waste heat boiler are;&. Heat load and temperature of the gases available for waste heat recovery for

steam generation,

2. (hemical nature and corrosiveness of the gases,

0. )vailable draught -draft,

8. Whether the gases are under pressure or suction,

6. #ust load and its nature in the gases,

5. )vailable space,

=. @e!uirement for a start4up furnace, gas preheating emergency use or addedcapacity, etc. and

F. :ocation for the outlet in the case of flue gases.

Tec*nological -evelopment in Boilers/

Super Critical Boiler;

Two factors, namely the necessity to reduce emission of (/ 2-Breen House Bas andever increasing cost of fuel have always attracted the attention of the designer. Inorder to achieve these two ob%ectives, the designers have taken steps to increasethe thermal efficiency 7 power cycle by adopting the usage of uper (ritical 9ressuresteam. ) super critical boiler is one, which operates above the critical steampressure of 22C kg1cm2-g at 0=8'(. )t this critical pressure, steam and water areat the same density, which means steam, is as compressed as water and at atemperature of 0=8'(, water can does not re!uire any latent heat to become vapourfrom fluid. When such substance is heated above the critical temperature, drysuperheated steam is produced, which is very suitable for driving turbo generators.In super critical boiler, are provided with only pre4heater and super heaters andthere is no boiler drum. )lso, the super critical pressure boilers are of once through,forced circulation type.

T*e 2dvantages of Super Critical Boiler over Sub Critical Boiler/

a The heat transfer rate is very high. -Typically, the heat transfer co4efficient insub4critical boiler is 8'' kcal1m2.hr.(, while that in super4critical boiler is 6''''

kcal1m2

.hr.(.b "y using super critical boiler, steam efficiency of power plant can be as high as

about 8' to 82.

c #ue to absence of steam4water mixture -no two4phase effect, there is veryless erosion and corrosion.

d The overall operation is very easy.

e The turbo generator connected to super critical boiler can easily attain peak4loads.

Fluidi)ed Bed Combustion;

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When air or gas is passed through an inert bed of solid particles such as sand orcrushed refractories supported on a fine mesh or grid the air will initially seek a pathof least resistance, and pass upwards through the bed.

With further increase in the velocity, the air starts bubbling through the bed and theparticle attains a state of high turbulence. Jnder such conditions, the bed assumes

the appearance of a fluid and exhibits the properties associated with a fluid andhence the name A:JI#I


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b 9revention of vitrification of ash particles causing them to be less than ashfrom fire or p.f. boilers.

c >inimal Instruments 7 (ontrols re!uired. No flame monitoring system beingnecessary for monitoring the flame of boiler furnace.

d Jnlike 9ulverised uel ired "oilers, no flame supporting and stabili*ing firing

of econdary uel such as /il is re!uired.

e High availability and reliability with poor grade coal,

f @ated parameters are obtained faster and the time taken from the instant oflighting up is !uite less.

g Wide Turn4down @atio of 8 to & is achievable, due to which rated steamconditions are maintained down to very low loads and response to loadvariations is fast.

h (oal !uality much inferior to the !uality envisaged during design and widefluctuation in !uality can often be accommodated without sacrificing thegeneration or efficiency.

i luidi*ed "ed (ombustion "oilers can be designed to burn Waste uels suchas bagasse, husk saw dust or washery middling.

% @eduction in "oiler efficiency with reduction in boiler load is much lesser ascompared with other type of boilers.

k "oiler can be comfortably operated at low loads without any support fuel dueto segmental airbox and fuel combustion bed.

l "oiler start up -cold startis fast.

m Hot start is faster due to heat retention in bed.

n oot blowers are not re!uired as it has minimum touching and slaggingpotential

o /peration is simple and generally there is lesser danger of explosion.

p :ess of maintenance due to absence of moving parts.

! :ow operation 7 maintenance cost.

r "ottom feeding system helps in ensuring uniform bed temperature and highefficiency even when the content of fines in the coal is very high.

s (ompact design due to high heat transfer rate over a small heat transfer area

immersed in bed.

t :ow cost of steam generation. High efficiency -F64F5, use of low cost fuel,less maintenance cost, and negligible oil consumption reduce the cost ofsteam generation considerably.

u Thermally homogenous combustion, hence lower potential for local hot or coldspots.

Classification of fluidi)ed3bed boiler /

luidi*ed4bed boilers can be categori*ed into two main groups, depending on themode of operation of the fluidi*ed bed. These are;

-a )tmospheric luidi*ed "ed -)" boilers and

-b 9ressuri*ed luidi*ed "ed -9" boilers.

)tmospheric luidi*ed "ed boilers can be of two types;

-a )tmospheric "ubbling "ed boilers and

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-b )tmospheric (irculating4"ed boilers

) distinction can also be made on the basis of fluidi*ing velocity of air, which is thefundamental distinguishing feature of fluidi*ed4bed4combustion units.

2tmosp*eric Fluidi)ed Bed &2FB( boilers/

luidised bed combustion -"( is ideally suited to the burning of solid fuel or lowcalorific value waste. In the "( system, fuel is added to a fire bed -composed ofinert particles, such as sand 4 or limestone if sulphur capture is re!uired, which isLfluidisedL by blowing combustion air upwards through it. This produces highlyefficient combustion and allows the use of low4grade fuels that are not suitable forconventional combustion plant designs./perational efficiencies for )"(s are 26406, similar to conventional coal4firedplant. The atmospheric fluidised bed combustion -)"( systems run close toatmospheric pressure. There are two types of )"(s; "ubbling luidised bed combustors -""(, where combustion is in a

conventional bubbling bed and combustion efficiencies of C'4CF are achieved

and (irculating luidised bed combustors -("(, where the bed medium is

entrained and circulated with the combustion gases. ) cyclone separates the bedmaterial and returns it to the main chamber. ("(s can achieve combustionefficiencies greater than CF.

Fig. 5utline of 2FBC

Typical fuels for )"(s are coal, anthracite, petroleum coke, oil shale, biomass,shredded tyres, paper sludge, wood waste, high sulphur solid fuels, municipalsledges and industrial process waste. The ash is used as a cement aggregate or forother construction materials. It is generally inert and non4ha*ardous, althoughtesting may be performed to detect any possible ha*ardous residuals.


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2pplication of FBC

or power generation with low4grade fuel, this is an ideal technology with numerousadvantages stated before. /ld boilers can be converted into "( or retrofitting iseasily possible.

Furt*er 2dvancement in Fluidi)ed Bed Combustion Tec*nology t*e$ressuri)ed Fluidi)ed Bed &$FB( boilers/In a 9"( boiler, improvements in the design of "( technology have been made toreach higher operating efficiencies by using differential air pressures, special bedgeometries, etc 4 aiming to improve the combustion of difficult materials such ashigh sulphur solid fuels and biomass. /perating efficiencies for 9"(s are 00482,depending on fuel characteristics -i.e., ulphur content, ash content, caloric value,type of 9"( system -i.e. combined cycle versus turbo4charged, circulating versusbubbling, and peak temperature of the gas turbine. econd4generation units, whichintegrate gas and steam turbines, are expected to have efficiencies in the range of8646'.The space re!uired for repowering a conventional coal4fired power plant with 9"(

technology would be similar to that re!uired for a flue4gas scrubber unit.(onventional particulate removal from a 9"( is by cyclone, bag house and1orelectrostatic precipitator.olid waste from 9"(s -containing fuel ash, calcium sulphate and consumedsorbent can be safely used for landfill or sold as a byproduct.

4eat ,ecovery Steam Generator in $o"er $lant/The H@B MHeat @ecovery

team Benerator is a system that generates steam from a primary source of heat,

like gas turbine exhaust, or the waste Incinerators etc.

The main function of the H@B is to serve as the link between two differentthermodynamic cycles. These are; The gas turbine cycle -"rayton and

The water steam cycle -@ankine.

These two cycles conform what is called a combined cycle.

To efficiently mate the @ankine steam cycle with high4temperature gas turbines,

H@Bs are developed to operate at substantially higher flue4gas temperatures. New

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H@B designs also are re!uired to match each incremental %ump in gas4turbine si*e

as combined cycle units grow larger and larger. 9erhaps the most important

development in H@B design is the move from single to dual4pressure steam

production. This change, which enabled lower stack temperatures and thus greater

recovery of thermal energy from the gas turbine exhaust, increased thermal

efficiency of a combined4cycle plant by nearly four percentage points. :ater designshas gone one step further, from dual to triple4pressure steam production, and

yielded approximately one more percentage point gain for the overall cycle. Today,

most of the H@Bs for large combined cycle power plants are designed for triple

pressure reheat steam systems to maximi*ed efficiency.

Importance of $inc* $oint and 2pproac* $oint in 4,SG

Jnlike conventional steam generators, where the inlet gas temperatures are very

high namely adiabatic combustion temperatures of the fuel fired -&5''4&F''o(, the

gas turbine exhaust inlet gas temperature to the H@Bs is very low, on the order of

6'' 4 6F' o(. This creates a problem. We cannot arbitrarily assume an exit gas

temperature to determine the steam flow. There are a few reasons for this, such asthe low ratio of gas1steam and capacity of heat sink in the form of economi*er. ) lot

of energy is transferred to the steam before the flue gases enter the economi*er,

while in H@Bs, it could be very small due to the low inlet gas temperature. This in

turn affects the energy absorbed in economi*er and hence the H@B exit gas

temperature. Hence gas1steam profiles cannot be easily predicted.

The pinc* point is the difference between the gas temperature leaving theevaporator and the saturation temperature, while approac* pointis the differencebetween the water temperature leaving the economi*er and saturation temperature.

)pproach point is used in the si*ing of the


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difference -pinch point, approach temperature difference, stack gas temperature,reheat steam temperature, etc.

4eat Transfer and Tube FinningThe temperature differential between the flue gas, steam and water, especiallyaround the back end of the evaporators, is very poor. The situation is compoundedby the poor heat transfer coefficient on the flue gas side. Water side and steam sidecoefficients are much better as will seen in the Table below.Typical 4,SG 4eat Transfer Coefficients

Section of 4,SG

Flue Gas Water in%conomiser

Water in%vaporator

4$ Steam

Heat Transfer

(oefficient-W.m42.Q4&

6' 6'' 26''4&'''' &'''

It follows from this that tube wall temperatures tend to run !uite close to the waterand steam side temperatures.


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There are a few variants to the basic design of the H@B. These variants define thetype of H@B and the variant is determined by a specific aspect of the H@Boperation. These are as below;

Hori*ontal or ?ertical design

(irculation 4 Natural, orced, assisted (irculation or once through

upplementary fired, and )uxiliary fired.

ingle, #ual or Triple pressure levels

Horizontal or Vertical design

The vertical or the Hori*ontal design is basically the particular manufacturerLs designfeature. In the Hori*ontal design the exhaust hot gases from the primary heatsource flow in a hori*ontal direction over the exchanger tubes. In a vertical designthe gases flow in a vertical direction Mbottom to top over the exchanger tubes.Though both designs work e!ually effectively, certain countries have preference forone over the above.

?ertical designs, which have originally been developed in


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Forced Circulation/

Forced Circulation

The circulation arises from the work done by a water circulation pump.

It normally includes a drum.

T*e 2ssisted Circulationimilar to forced circulation

The circulation arises from the work done by a water circulation pump that is

only in service during the start4up of the H@". )pplies normally for vertical H@" types.

It normally includes a drum.

T*e 5nce T*roug* Flo"

The circulation arises from the weight force of the water entering the boiler ata very high point.

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It normally has no drum.

There is no recirculation taking place in the evaporator.

Supplementary3fired and 2uxilliary firedIf the heat from the primary source is not ade!uate to meet the specific plantre!uirements, then supplementary firing is re!uired in the H@B using some burnersystem. In the supplementary fired H@B heat from the primary source and fromthe burner are always available. )uxiliary firing will be re!uired if the H@B is toproduce steam for the plant even when the primary heat source is not available.9er )>< 9ower Test (ode 8.8, the H@B efficiency is defined as;%A &energy to steam"aterfluids(ex*aust gas flo" x ent*alpy D fuel

input on 64@ basisE

(ompared to an unfired H@B, the fired unit is more efficient for the followingreasons;

)ddition of auxiliary fuel reduces the effective excess air in the exhaustgases, as no air is added. The fuel utili*es only the excess oxygen in the turbineexhaust. This is opposite to what happens in a steam generator, where withincrease in excess air, the heat losses are more and thus efficiency is reduced.

With increased steam generation, usually the exhaust gas temperature

decreases in a single pressure system. This is due to the increased ratio ofsteam1gas. In a conventional steam generator, the gas1steam ratio is nearlyconstant, while in a H@B, exhaust gas flow remains the same, while the steamgeneration increases due to auxiliary firing. The increased water flow through theeconomi*er -with gas flow remaining same can pull the gas temperature furtherdown due to the increased duty.

But in practice it *as been found t*at t*e *eat rate increases "it* auxiliaryfiring. @adiation heat pick up in the H@B designed to utili*e low grade heat is poorand thus contributes to the decrease of the overall efficiency of the power plant. It istherefore prudent to use duct firing as upplementary firing instead of auxiliary firingonly to augment power generation at the time of need.

Single -ual or Triple pressure levelsH@Bs, may have single or multiple pressure levels, to suit a specific plantre!uirement. The pressure and flow values are dictated by the downstreame!uipmentLs re!uirement. There are obvious differences in H@Bs from a coal firedor oil fired steam plant. The H@B does not have a furnace and all the heat comingfrom a Bas Turbine exhaust. Where in conventional boiler, the superheater is located

after the evaporator, in an H@B, the evaporators are located at downstream ofsuperheater and reheater. In a triple pressure H@B, there are actually three sets ofevaporators, an H9 set, an I9 and an :9 set. There are also separate sets of H9, I9and :9 economi*ers. In an conventional fired boiler, although there are H9, I9 and :9steam turbines, all the evaporation takes place at %ust one very high pressure. Thesedifferences can be traced back to heat transfer consideration, which dominates theH@B design.The temperature in the furnace of a conventional coal or oil fired steam plant isaround 2'''o(, and in the superheater and reheater region, temperatures runbetween F'' to &8''o(.It is a truism for both gas and steam turbines, that to attain the highest practicable

efficiencies, the turbine entry temperature needs to be as high as possible. teamtemperatures of most H@B units lie in the range of 8F' to 60' o(, to make use of a

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steam temperature of the order of 6''o( or more, the steam must be expandedthrough an ade!uate pressure ratio. ince the pressure in condenser is more or lessfixed, this re!uires an ade!uate steam pressure into the turbine. or an H@Be!uipped with a superheater and a reheater these days, the pressure is more than&2' bar.

Benerating steam at this pressure has a huge impact on H@B design, basicallybecause much of the heat uptake happens at the evaporator due to the higherre!uirement of latent heat. ince the saturation temperature increases with theincrease of pressure, the water side has to be raised to a very high temperature 3 tothe extent of 0'' 3 02'o(. Biven that the flue gas entering an H@B is around5''K(, and the bulk of the heat uptake occurs at around the boiling point, this wouldmean that the temperature of the flue gas going up the stack would be %ust over0''K(. In other words, about half of the available heat in the flue gas would be lostup the stack, in a H@B that produced steam at %ust one very high pressure, as in apulveri*ed fuel boiler.

This problem is overcome by installing a further set of evaporators, economi*ers andsuperheaters in the H@B, down stream of the high pressure steam. This additionalset produces steam at a much lower pressure, somewhere between 8 and &' bar,the actual value being that which corresponds to the exit pressure from the H9turbine, or if the plant is fitted with a reheater, the I9 turbine. )s the boiling point ofwater at this sort of pressure is in the range of &8'K(4&F'K( low temperature heatin the flue gases can be picked up !uite easily. In addition some superheating of the:9 steam is done with the aim of matching the temperature of the GcoldE steam fromthe H9 or I9 turbine. It is then possible to merge the steam from these two differentsystems and put them to the :9 turbine.team, for deaeration, at an even lower pressure, can also be raised using the last

vestige of heat in the flue gases. To summarise in a modern H@B steam would beraised at three different pressures with separate evaporator and pumping circuits foreach. This is in complete contrast to a pulveri*ed fuel steam plant, where all theevaporation takes place at one very high pressure. )nother difference is that

feedheaters, of the type used on conventional pulveri*ed fuel plant, using steamextracted from the turbines are not used on H@B systems. This would simply raisethe water temperature at the inlet to the economi*ers, and would reduce the amountof heat, which could be transferred from the flue gases.

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steam generating system

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