What are the different kinds of pumps used at power plants?
Many different kinds of pumps are used in power plants to fulfill a wide range of applications. Boiler feed pumps are crucial for the operation of power plants. These pumps are typically multistage and deliver feedwater to boilers. An example of a multistage boiler feed pump can be seen in Image 1. Feedwater is then turned into steam, which is what turns the turbines generating power at the power plants.
To assist in the pumping of feedwater, boiler feed booster pumps are also present upstream of the feed pumps. The booster pumps increase the suction pressure of feedwater fulfilling the NPSH requirement of the main boiler feed pump.
Condensate pumps collect saturated water from the condenser hot well and pumps it either to a deaerating heater or back into the boiler feed pump. Condensate pumps operate at extremely low suction pressures. For this reason these pumps are often located at the lowest level of any pump in the power plant and installed in a suction can that is below ground level. The velocity of the flow entering the condensate pipe is kept to a minimum to limit frictional losses in the piping to keep the elevation difference as the only contribution to NPSH available (NPSHa).
Condenser circulating pumps deliver cool water from freshwater sources near the power plant and pump it through the condenser to condense exhaust steam from the turbine. These pumps can be either located in dry pits or wet pits.
If they are in wet pits, then they are a vertical design.
Boiler circulating pumps pump water through a boiler helping to increase the effectiveness of the boiler. The water is at the same temperature and pressure as the boiler and the pump operates at a low total head requirement only needing to overcome the friction in the tubes of the boiler. However, these pumps operate at very high temperatures and suction pressures and are welded into the boiler itself.
Heater drain pumps are necessary in power plants to pump condensate from closed heaters back into the feedwater system. Similar to condensate pumps they have very little NPSHa.
For more information on the application of pumps in power plants, refer to the HI Guideline Power Plant Pumps—Guidelines for Application and Operation and the Rotodynamic Pump Certificate training modules at www.pumps.org.