Thermodynamic analysis of a novel combined heat and power system incorporating a CO2 heat pump cycle for enhancing flexibility

摘要

A novel design of combined heat and power (CHP) with improved flexibility was developed in this paper. A CO2 heat pump (HP) cycle has been adopted in the proposed CHP scheme, where the excess self-produced electricity can be converted into district heat through the HP cycle, recovering the waste energy of the exhaust steam in the meantime. The thermal performance of the proposed scheme was examined based on a 300 MW coal-fired CHP unit, compared with the conventional scheme and the scheme with an electric boiler (EB). The results indicate that while 15.0 MW of the generated power is consumed for heating on site and the total heat output remains 300.0 MW, the proposed design can reduce the minimum power output from 170.7 MW to 132.1 MW, which Is 16.3 MW less than that of the EB scheme and conduces to dispatching more renewable electricity. And the effective electric efficiency of the new scheme is 4.89 and 7.70 percentage points higher than those of the conventional scheme and EB scheme, respectively. Energy and exergy analyses were conducted to explore the decoupling and energy-saving mechanisms of the novel concept. Besides, the sensitivity of the reformative CHP system was discussed.