The Thermal Calculation And Economical Analysis Of The Feed Pump Turbine On300MW Diregt Air-cooling Units

In order to improve the economical efficiency of operation of power plant, in addition toimproving unit efficiency, we must also pay attention to the operation and configuration ofauxiliary. Boiler feed pump is an important auxiliary equipment, it drives the working fluid tocycle. The two main driving modes of feed pumps are motor-driven mode and steam-drivenmode in China power stations, which mode is better needs for analysis because of differentevaluation criteria. For direct air cooling power plants, no matter selecting the drive mode orscheme will need to consider many actual factors, almost all the early air-cooling units chosemotor-driven mode and there’s fewer research about the application of boiler feed pumpturbine in air cooling units. With the thermal power plant unit capacity increase, motor-drivenmode will cause higher power consumption.This paper takes300MW direct air-cooling units as the research object, in order tocompare the thermal economy of motor-driven mode and steam-driven mode, we establishedthe mathematical model of comprehensive efficiency, internet net power, power consumptionrate, heat rate and coal consumption rate which can be calculated by power plants to choosedriving mode of feed pumps. For the actual situation of a power plant, we got the conclusionthat steam-driven mode has a higher thermal economy than motor-driven mode which canreduce power consumption rate and increase internet net power.Then we studied the technical and economical comparative methods of different drivingscheme, also studied the technical feature of the motor-driven scheme and three steam-drivenschemes that have different exhaust steam cooling way. Taking one project of turningmotor-driven feed pump into steam feed pump as example, in the direct air cooling scheme ofsteam feed pump, the main steam should be increased to ensure the generator powerunchanged, that will affect the cooling capacity of the air cooling condenser. On account of this, a peak cooling system should be used to increase the cooling area and reduces the backpressure. By comparing the technical conditions, initial investments and investment returns ofeach steam pump scheme, we chose the direct air cooling scheme of steam feed pump with asummer peak wet cooling system. We found that steam-driven scheme has an obviousadvantage if service life exceeds10years by using the minimum annual cost method.Finally, we studied the load change influence on feed pump parameters, and calculatedthe pump flow, head, shaft power, pump steam turbine’s steam inlet/exhaust condition, whichprovide a theoretical basis for calculation of extraction flow and the increase of the mainsteam flow.