Comparative investigation on heat pump solutions for peak shaving and heat-power decoupling in combined heat and power plants

Abstract

One pressing concern for coal-fired power plants is the retrofitting of heating supply, as central heating demand continues to rise, and carbon emission reduction becomes a priority. However, the cogeneration of heat and power leads to unwanted heat-power coupling and restricts the power peak-shaving flexibility. In this study, heat pump (HP) is used in designing highly efficient and heat-power decoupling retrofit systems. Three retrofit cases integrating absorption heat pump (AHP) and electric heat pump (EHP) are proposed. Their energy utilization efficiency, exergy efficiency, coal consumption rate of power generation with varying operating conditions, and heat-power decoupling characteristics are compared. Moreover, the techno-economic considering the repayment time and the benefits of peak shaving in the retrofit cases is investigated. A 600 MW coal-fired power plant is studied. Results show that three retrofit cases can enhance the heating capacity and achieve heat-power decoupling. The EHP-CHP system has the largest heating capacity of 1049 MW and the minimum power load of 150 MW at the heating load of 546 MW. In contrast, the AHP-CHP system can only decrease the minimum power load to 300 MW. The EHP-CHP coupled with the extracted exhaust steam system shows the highest energy utilization efficiency of 90.46 % at the maximum heating capacity, with the lowest coal consumption rate of power generation of 141.96 g (kW h)⁻¹ under 50 % THA, which is lower than the 153.27 g (kW h)⁻¹ the EHP-CHP system. However, the utilization of EHP decreases the exergy efficiency compared to AHP. The AHP-CHP system provides a maximum exergy efficiency of 36.46 % under the design heating load. In addition, the EHP-CHP coupled with the extracted exhaust steam retrofit case leads to a short repayment time of only 1.9 years. The EHP-CHP coupled with exhaust steam system proves to be a preferable energy-efficient, heat-power decoupling, and economic benefit-favorable solution.