Energy and economic analysis of flue gas heat recovery systems improving the energy efficiency of gas cogeneration units

Abstract

This paper presents the results of energy and economic analyses of a gas-fired CHP plant. The analyses were carried out for three variants of technical solutions to improve the thermal efficiency of the CHP plant. The fuel combustion process involves the generation of a large amount of heat. In addition, the heat is dissipated to the surroundings through the exhaust gas with a high temperature of 300÷350 °C. Therefore, to limit heat loss, a heat recovery system is used, which removes heat from the engine body and from the hot exhaust gases through a heat exchanger, allowing the exhaust gases to be cooled to a temperature of 100÷120 °C. In addition, heat is recovered from the oil cooling process and intercoolers. The recovered heat is usually supplied to the heating water in the district heating network. For the calculations, the temperature distribution of the return water from the district heating network during the year was assumed. First, the benefits of adding an additional economizer to pre-heat district heating water were analysed, Next, a heat recovery system was simulated to cool the flue gases to lower temperatures using an absorption heat pump or a compressor heat pump.