In power generation plants, which pump is most important?
You could point to the largest pump in the system as the most important; however, the power generating system will not operate properly if any of the pump applications in the system are out of service.
Image 3 provides a simplified feedwater diagram for power generation, illustrating two primary pump applications within the feedwater cycle, which are the condensate pump and boiler feed pump applications. As noted, there may be additional pump applications required within the feed water cycle such as pressure booster pumps and heater drain pumps that return condensate from the heaters. Additionally, there are many more pump applications outside the feed water cycle that are required for proper operation.
In the simplified diagram, steam passes through the turbine generating electricity and then changes phase to liquid in the condenser. The condensed liquid collects in a hotwell where a condensate pump, which is specifically designed to pump water near its vapor pressure, starts the feedwater cycle. The pressure of the condensate is increased by the condensate pump while heaters superheat the water prior to the boiler feed pump, which further increases the pressure so the superheated water can enter the boiler where it changes phase to steam.
If you wanted to point to the largest pump as the most important, traditional power plants use large (some exceeding 50,000 horsepower [hp]) boiler feed pumps that deliver high temperature water in great volume and pressure to the boiler. These pumps are impressive to see, are highly engineered, but require specific conditions to operate reliably. One common requirement for these types of pumps is net positive suction head (NPSH) margin that limits cavitation. Therefore, it is common for systems with these large boiler feed pumps to require booster pumps in the system to raise the pressure of the superheated water prior to entering the feed pump.
For more information on pump applications in power generation refer to HI’s Pump Application Guidebook for Power Plant Pumps at pumps.org.