Heat and Power Decoupling and Energy Saving of the CHP Unit with Heat Pump Based Waste Heat Recovery System

Abstract

Combined heat and power (CHP) plants are operating under more fluctuating working conditions due to the increasingly inconsistent demands for heat and power and integration of renewable energy. This paper proposes to use an electric heat pump (EHP) to decouple heat and power and save energy by recovering waste heat from the cooling water. The thermodynamic model of the CHP unit under dynamic working conditions is established, and the dynamic EHP model based on an efficiency factor is proposed. The thermo-electric decoupling and energy-saving potential with different heat and power outputs and the heat pump DH ratio χHP are analyzed for a CHP unit as a case study. Absorption heat pump (AHP) and EHP-based waste heat recovery systems are also compared. The results indicate that the heat and power decoupling potential is bigger when χHP and the heat demand are increasing. The energy-saving effect is clearer by increasing the coefficient of performance (COP), χHP, or both. AHP and EHP can help the system obtain a certain level of heat and power decoupling and energy-saving effects, but these effects of the AHP-based system are smaller than that with EHP, especially under high heat demand and low power demand working conditions.