Desuperheating Stations. Desuperheating stations usually consist of a
control valve station which is used to regulate the flow of desuperheating water (from
boiler feed pumps or condensate pumps discharge, depending upon the reduced pressure of
export steam) to the desuperheater. Water used for tempering must be of demineralized
water or good quality condensate to avoid mineral deposits on the desuperheater.
Desuperheaters may be of the steam or mechanically atomized type. Desuperheaters may
also be used on the boiler steam headers for main steam temperature control, depending
upon the design of the boiler.
Applications. The major uses of compressed air for power plants are for plant
service which includes boiler fuel oil atomizing, soot blowing, and instrument air
supply. The use of compressed air for fuel oil atomizing should be economically
evaluated versus steam or mechanical atomization. The use of compressed air versus
steam blowing for soot blowers should also be economically evaluated.
air dryers, see MIL-HDBK-1003/6 and NAVFAC DM-3.05, Compressed Air and Vacuum Systems.
Auxiliary Cooling Water System. A closed circulating cooling water system
fans, for air compressor jackets and aftercoolers, turbine oil coolers, generator air or
hydrogen coolers, and sample cooling coils. The system shall consist of two shell and
tube heat exchangers, two water circulating pumps, one head tank, and necessary valves
and piping. A typical auxiliary cooling water system is illustrated in Figure 35.
The auxiliary cooling water head tank is used as an expansion tank, to
provide head on the system and to provide a still volume to permit release of air from
the system. The normal operating water level of the head tank should be approximately
70 percent of the tank capacity. To provide for expansion from cold to operating
temperatures, a volume equal to approximately one percent of the volume of the system
should be provided between the normal operating level and the high water alarm. The
tank should be provided with an overflow piped to drain. The tank should be located
above the highest piece of equipment being cooled by the auxiliary cooling water system.
This will assure a positive pressure throughout the system both during normal operation
and in the shutdown mode.