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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. [ABSTRACT FROM AUTHOR]

A novel cogeneration system in which the combination of an organic Rankine cycle (ORC) and an absorption heat pump (AHP) are applied to recover condensate waste heat of exhaust steam from steam turbine in a direct air cooling coal-fired power plant is put forward to further improve energy utilization efficiency in the paper. The novel cogeneration mode can achieve multiple purposes of increasing power generation, improving heating load, reducing irreversible heat exchange loss of heating network and preventing from freezing for air cooling system in winter. The energy and exergy analyses have been accomplished for a 600 MW direct air cooling coal-fired power plant based on the first and second laws of thermodynamics. The generated power and heating load increase by 16.2 MW and 78,541.16 kW at 50% THA (Turbine heat acceptance) as heating flow rate is 100 kg/s in the novel cogeneration mode. The standard coal consumption rate and total exergy loss decrease by 48.98 g/kWh and 62.21 MW. The total energy and exergy efficiency respectively improve by 11.97% and 4.01%. Besides, the total exergy efficiency is increased with increasing load. The proposed scheme can provide a new method for energy conservation and icing protection of direct air cooling units in winter. • Presented a novel coupled method to improve power output and heating load. • Established thermodynamic models based on first and second law of thermodynamic. • Revealed performance advantages from qualitative and quantitative perspectives. • Improved significantly both energy and exergy efficiencies of energy utilization. [ABSTRACT FROM AUTHOR]