What are the factors affecting the condenser performance?

 

Condenser is the main heat sink in the entire power cycle. Plant heat rate is mostly depending on condenser performance. There are two types of condenser are available in power plant , one is water cooled and another is air cooled condenser. Air cooled condenser is considered when there is water availability is less. Isentropic heat drop through the turbine depends on the inlet steam pressure & temperature and condenser vacuum. If the vacuum in condenser is lower, the work done by the turbine will be reduced.

 In case of water cooled condenser cooling water supplied to the surface condenser tube side to cool the exhaust steam from the turbine. In this process undissolved air or gasses are separated and is evacuated from the shell side by ejector or vacuum pump to maintain the vacuum and proper heat transfer with steam and tube surface. Normally it is two pass , shell and tube type heat exchanger. We need to familiarize with the following terms :

TTD- Terminal temperature difference = T3- T2

T3 – Exhaust Steam (Saturation) temperature, T2- CW outlet Temperature

TR- Temperature Difference = T2- T1

T1- CW inlet temperature

Condenser Effectiveness=  (CW temperature rise)/ (Maximum Temp Difference)

                                  

dTm=LMTD= Log mean temperature difference

CW Mass Flow Rate , m= dUA, where

d – density of water

U- velocity of water

A-condenser surface area

Q= Heat transfer rate in condenser= K.A.dTm =m.Cp .(T2-T1)  considering no other heat loss taking place in steady state condition, so

K- heat transfer coefficient of tube

A-Surface area

m- mass flow rate (CW)

Cp- specific heat of water

So.  Condenser Effectiveness is depends on CW temperature difference or ratio of temperature difference, specific heat of water, mass flow rate of cooling water, heat transfer coefficient of condenser tube and surface area of condenser tubes.

Cleanliness Factor: CF 

 Ki is initial heat transfer coefficient , this can be derived from the above formula.

                                                                Kt is heat transfer coefficient after Time t.

CF is 100% when it is new and cleaned condition. After running sometime this value will be reduced. Normally system is designed for 85% CF.

 

Fouling Factor: FF

this factor is used to predict the performance trend of the condenser

Theoretically 10mmHg reduction in vacuum generation loss of 20Kcal/kwhr  and  there is 1% of efficiency loss for 210MW unit.

 

Condenser performance can degrade due to following reason:

·         Air binding on the shell side:  This is due to poor performance of the steam ejector /vacuum pump or air ingress into the system.

·         Bio fouling : This can be avoided by proper chlorination of the CW system

·         Scaling: Proper CW quality- pH, TDS, hardness, COC, conductivity etc are to be maintained to avoid the scaling inside the tube surface.

·         Silting : Obstruction in the tubes can occurs due to silt deposition and choking of the tubes by film of cooling tower or debris carried away by cooling water.

Daily monitoring of TTD, TR, CF and FF easily will show the gradual deterioration of the parameters.

Remedies:

    ·         Online  condenser tube cleaning system will help to maintain the above parameters

·         Chemical treatment of Cooling Water and monitoring of cooling water parameters are required

·         Inspection and cleaning of water box, tubes are to be done during periodical shutdown

·         If the hard scale is formed inside the tube,, chemical cleaning is be done

·         Plugged tubes are to be replaced during shut down of the unit. It should not exceed 5% of the total tubes.

Condenser leak test is to be done during shut down to identify the leaked tube 

Secondly any air ingress point immediately is to plugged for better performance of the condenser.  Install the air leakage monitoring system,