Energy and Exergy Analysis of a New Cogeneration Heating System Based on Condensed Waste-Heat Utilization in the Direct Air Cooling Coal-Fired Power Plant

Abstract

A new cogeneration system coupled with an absorption heat transformer (AHT) to recover condensed waste heat of a direct-air-cooling coal-fired power plant is presented to reduce the energy grade mismatch between the energy-supplying side and energy-receiving side of the existing waste heat recovery system with an absorption heat pump (AHP). Thermodynamic models of two cogeneration systems, namely, the AHP and heater of the heating network (AHP-HHN) and the absorption heat transformer and heater of the heating network (AHT-HHN), are established. The performance analysis and comparison of two cogeneration systems, focusing on a 600 MW direct air-cooling coal-fired power plant, are carried out from the aspects of energy and exergy utilization. The output power and waste heat recovery ratio are increased by 14.81 MW and 51.56% in the AHT-HHN at 75% THA (turbine heat acceptance) load with a 230,000 kW heating load. The standard coal consumption rate and total exergy loss are decreased by 8.86 g/kWh and 45.54 MW. The total energy efficiency and exergy efficiency are improved by 1.33% and 1.31%, respectively. Moreover, the larger the heating load, the greater the performance difference. The new waste heat recovery scheme can further improve the energy cascade utilization level.