Low Pressure Heater Drain Pump. Low pressure heater drain pumps may be used
for pumping drains from the lowest pressure heater to a point in the condensate piping
downstream from the heater in lieu of returning the drains to the condenser. Pumping of
the heater drains in this fashion provides recovery of heat which would other wise be
lost to the condenser. The use of low pressure heater drain pumps can be decided by
economic evaluation. Use only one pump and provide alternate bypass control of drains
to the condenser for use when the drain pump is out of service.
High Pressure Heater Drain Pumps. High pressure heater drain pumps are
required, when high pressure heater drains are cascaded to the deaerator, in order to
overcome the elevation difference between the lowest high pressure heater and deaerator.
Use two full capacity pumps with one of the two pumps for standby use.
Deaerators. Provide at least one deaerator for the generating plant. The
deaerator usually is arranged in the cycle to float in pressure with changes in
extraction pressure (which changes with turbine load). Deaerator(s) for power plants
usually heat the condensate through a range of 50 to 75 degrees (28 to 42 degrees C).
See Section 4, Table 6; and MIL-HDBK-1003/6, for further requirements.
Deaerator Function. The primary function of the deaerator is to remove
dissolved oxygen from the condensate in excess of 0.005 cc of oxygen per liter of
condensate at all loads. In addition, the deaerator will normally perform the following
a) Heat the condensate in the last stage of condensate system prior to
the boiler feedwater system.
Receive the boiler feed pump recirculation.
Provide the boiler feed pumps with the required net positive
d) Receive water from the condensate system and provide surge capacity
in the storage tank.
e) Provide hot water for air preheating and combustion gas reheating
(if any) and/or other auxiliary heat requirements.
Receive drains from high pressure heaters.
Receive high pressure trap drains.
The deaerator functions are illustrated in Figure 33.
Deaerator Design Pressure
a) Turbine manufacturers indicate that the extraction pressure quoted
on the heat balances may vary as much as plus or minus 10 percent. Considering
operation with extraction heaters out of service, the manufacturers recommend that the