MEWAR UNIVERSITY

TOPIC :- FEEDWATER HEATER

FEEDWATER HEATER A feedwater heater is a power plant component used to

pre-heat water delivered to a steam generating boiler. In a steam power plant, feedwater heaters allow the

feedwater to be brought up to the saturation temperature very gradually.

It improves the thermodynamic efficiency of the system by reducing plant operating costs and also helps to avoid thermal shock to the boiler metal.

CYCLE EXPLANATION The energy used to heat the feedwater is usually derived from steam

extracted between the stages of the steam turbine. Therefore, the steam that would be used to perform expansion work in the turbine (and therefore generate power) is not utilized for that purpose.

The percentage of the total cycle steam mass flow used for the feedwater heater is termed the extraction fraction and must be carefully optimized for maximum power plant thermal efficiency since increasing this fraction causes a decrease in turbine power output.

TYPES OF FEEDWATER HEATERS

FWH

OPEN FWH CLOSED FWH

OPEN FEEDWATER HEATERSAn open heat exchanger is one in which extracted steam is allowed to mix with the feedwater. This kind of heater will normally require a feed pump at both the feed inlet and outlet since the pressure in the heater is between the boiler pressure and the condenser pressure.

A deaerator is a special case of the open feedwater heater which is specifically designed to remove non-condensable gases from the feedwater.

CLOSED FEEDWATER HEATERS Closed feedwater heaters are typically shell and tube heat

exchangers where the feedwater passes throughout the tubes and is heated by turbine extraction steam. These do not require separate pumps before and after the heater to boost the feedwater to the pressure of the extracted steam as with an open heater.

Many power plants incorporate a number of feedwater heaters and may use both open and closed components. Feedwater heaters are used in both fossil- and nuclear-fueled power plants.

ECONOMIZER VS FEEDWATER HEATERS An economizer serves a similar purpose to a feedwater heater, but is technically

different as it does not use cycle steam for heating. The economizer uses the lowest-temperature flue gas from the furnace to heat the water before it enters the boiler.

Most nuclear power plants do not have an economizer. However, the Combustion Engineering System 80+ nuclear plant design and its evolutionary successors, (e.g. Korea Electric Power Corporation's APR-1400) incorporate an integral feedwater economizer. This economizer preheats the steam generator feedwater at the steam generator inlet using the lowest-temperature primary coolant.

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