Investigation of the use of steam coil preheater to increase the net efficiency of thermal power plant

Abstract

Conventionally, regenerative feed water heating is used to increase the net efficiency of a thermal power plant. In this method, extracted steam from the steam turbine is used to increase feed water temperature before feed water is sent to the boiler. Increasing the number of feed water heaters or the mass flow rates of extracted steam causes the net power plant efficiency to increase. However, there is a practical limit of the number of feed water heaters. Furthermore, there is an upper limit of the mass flow rate of extracted steam for a feed water heater. Consequently, there is an upper limit of the net power plant efficiency in a conventional design of power plant that relies only on regenerative feed water heating. In this paper, it is argued that the net power plant efficiency can be increased beyond this limit by using extracted steam to increase air temperature in steam coil air preheater before air enters the boiler. Models of boiler, steam turbine, and steam coil air preheater are used to demonstrate that the net efficiency of 50-MW power plant is increased by 2.32% due to the integration of steam coil air preheater having the area of 500 m 2 .