FEED WATER HEATER
Feedwater heater is a power plant component used to pre-heat water delivered to a steam generating boiler.
- Low pressure feed water heaters are used in the condensate system between the condensate pump discharge and boiler feed pumps, and utilize low pressure turbine extraction or auxiliary turbine exhaust steam for heating the condensate.
- High pressure feed water heaters are used in the feed water system between the boiler feed pump discharge and the boiler, and utilize high pressure turbine extraction steam for heating the feed water.
- The condensate or feed water temperature increase for each feed water heater will be in the range of 28 to 56 degrees C with the actual value determined by turbine manufacturer‟s stage location of steam extraction nozzles.
- Depending on turbine size, some turbines offer alternate number of extraction nozzles with usually a choice of using the highest pressure extraction nozzle.
- The selection, in this case, of the total number of feed water heaters to use should be based on economic evaluation.
Low Pressure Heater(s)
Use one or more low pressure feed water heaters to raise the temperature of condensate from condensate pump discharge temperature to the de-aerator inlet temperature. The heater drains are cascaded from the higher pressure heater to the next lower pressure heater with the lowest pressure heater draining to the condenser.
High Pressure Heater(s)
Use one or more high pressure feed water heaters to raise the temperature of feed water from de-aerator outlet temperature to the required boiler economizer inlet temperature. The heater drains are cascaded from heater to heater, back to the de-aerator in a fashion similar to the heater drain system for the low pressure heaters.
(a) Fuel economy.
(b) Longer life of the boiler.
(c) Increase in steaming capacity.
- A feedwater heater is a power plant component used to pre-heat water delivered to a steam generating boiler.
- Preheating the feedwater reduces the irreversibilities involved in steam generation and therefore improves the thermodynamic efficiency of the system.
- This reduces plant operating costs and also helps to avoid thermal shock to the boiler metal when the feedwater is introduced back into the steam cycle.
- In a steam power plant (usually modeled as a modified Rankine cycle), feedwater heaters allow the feedwater to be brought up to the saturation temperature very gradually.
- This minimizes the inevitable irreversibilities associated with heat transfer to the working fluid (water).