Condensate Storage and Transfer. About 0.5 percent of the steam flow to the
turbine is lost from the cycle. These losses occur at points such as the deaerator
continuous noncondensibles and steam vent, pump glands, valve packing leaks, continuous
boiler blowdown, and continuous water and steam samples. Demineralized water is also
required for filling the boiler/turbine generator unit system initially prior to startup
and during times of boiler or cycle maintenance and chemical cleaning. The condensate
storage and transfer equipment is illustrated in Figure 32.
Condensate Storage Tank. For normal operation, the excess or deficiency of
cycle water caused by load changes is usually handled by providing a condensate storage
tank which can accept and hold excess condensate or provide condensate makeup for cycle
water deficiency. A tank sized for twice the cycle water swell volume will usually
provide sufficient capacity for normal condensate makeup and dump requirements.
Condenser vacuum is normally used as the motive force to draw condensate from the
storage tank to the condenser through makeup control valves. Condensate dump from the
cycle to the storage tank usually is made from the condensate pump discharge
through dump control valves. For cogeneration plants, the function of condensate return
from heating and other processes is usually combined with the function of condensate
storage using a single tank.
Deionized or Demineralized Water Storage Tank. Water required for filling the
cycle or boiler either initially, for maintenance or for chemical cleaning, is usually
stored in separate tanks which contain deionized or demineralized water. The amount of
storage required is about 1,000 gallons per MW of installed electric generating capacity
which is usually divided into not less than two tanks. Provide two pumps for transfer
of water as needed from these tanks to the condensate storage/return tank. If an
evaporator is used for cycle water makeup, a similar amount of 1,000 gallons per MW
storage capacity is necessary. For additional requirements see MIL-HDBK-1003/6.
Condensate Receivers and Pumps Sizing. For sizing of condensate receivers and
associated pumps, see Section 4, Power Plant Steam Generation.
Condensate Pumps. Condenser condensate pumps are used for pumping condensate
from the turbine condenser to the deaerator through the low pressure feedwater heaters,
the steam jet air ejector, and the turbine gland steam condenser (if any). Two
condenser condensate pumps, each capable of handling full load operation, shall be
provided of either the horizontal split case or vertical can type. The vertical can
type pumps are often used because the construction and installation provides for net
positive suction head (NPSH) requirements without the use of a pit for pump location.