Performance Analysis of Power Plant Condensers

P M V SubbaraoProfessor

Mechanical Engineering DepartmentI I T Delhi

A Device Which makes Power Plant A True Cycle..A Device Which set the limit on minimum cycle

pressure…..

T-S Diagram : Rankine Cycle with FWHs.

?,, exitcondincond pp

inCWT ,outCWT ,

?TTD

exhaustturbinep ,

hoodp

Two-Pass Surface Condenser

T-S Diagram : Rankine Cycle with FWHs.

?.steamsatcond pp

inCWT ,outCWT ,

?TTD

exhaustturbinep ,

hoodp

Thermal Processes Occurring in Condensers

• The condenser never receives pure seam from the turbine.• A mixture of steam and non-condensable gases (Air-steam

mixture) enters the condenser.• The ratio of the quantity of gas that enters the condenser to the

quantity of steam is called the relative air content.

sc

air

m

m

,

•The value of , depends on type, capacity, load and design dimensions of the condenser plant.

Variation of Steam-air Mixture Parameters

airsc mm

,

steampiinc pp ,,

steampep ,

airpep ,

satT

steameexitc TT ,,

exit

airpisteampiinc ppp ,,,

airpesteampeexitc ppp ,,,

• Using Dalon’s Law: asc ppp

sssssaaaaa TRmvpTRmvp &

622.0

s

a

s

a

s

a

m

m

R

R

p

p

622.01 c

s

pp

s

ssss

a

aaaa p

TRmv

p

TRmv

Gas laws:

Volumes and temperatures are same.

• At the entry to condenser the relative content of air is very low and partial pressure of steam is almost equal to condenser pressure.

• As air-steam mixture moves in the condenser, steam is condensed and the relative content of air increases.

• Accordingly, the partial pressure of steam drops down.• The total pressure in the bottom portion of condenser is lower than

that of the top portion.• The pressure drop from inlet to exit of condenser is called steam

exhaust resistance of a condenser.

• The partial pressure of air at the bottom of the condenser cannot be neglected.

exitcincc ppp ,,

airpesteampeexitc ppp ,,,

cairpesteampeinc pppp ,,,

• The temperature of steam is a function of condenser pressure.

• As the air-steam mixture moves through the condenser and the steam is condensed, its temperature decreases owing to decreasing partial pressure of saturated steam.

• This is due to increase in relative content of air in the mixture.

• The pressure also decreases due to resistance to flow of steam.

• The zone of intensive condensation.• The zone of cooling of air-steam mixture.

Variation of Steam Partial Pressure & Saturation Temperature

0

10

20

30

40

50

60

70

1 2 3 4 5 6

Inlet exit

Saturation Temperature, 0C

Steam Partial Pressure, kPa

Tcw,in

Tcw,out

Condenser with Air Removal Pump : A practicable Concept

ambinCW TT ,

exitCWT ,

s

a

m

m622.01

condensersat

pp

Combined Condensation & Air Pumping Action:

value.finite a tocontrolled beCan

zero. todecreasesy Continuosl : & decreasesSlowly :

sa mm

Air Pumping Action Vs Condensing Action !!!

Effect of Air Leakage on Condenser Pressure

Cooling water Inlet Temperature

10 3020 40 50

Inle

t C

onde

nser

Pre

ssur

e, m

m o

f H

g

Condenser controlling the back pressure

Air pump controlling the back pressure

Air pump controlling the back pressure

Condenser controlling the back pressure

Power Loss Due to Excess Back Pressure

What is Techno-economically Viable value of TTD ?

Condensate Depression

• The temperature of condensate is always a few degrees lower than the coincident condensing steam temperature.

• Subcooling of condensate is undesirable on two accouts:• It lowers the thermodynamic efficiency of the power

cycle.• It enhances the propensity of the condensate to

reabsorb non-condensibles.