Study on a novel co-operated heat and power system for improving energy efficiency and flexibility of cogeneration plants

The power adjustment capacity of cogeneration power plants decreases while heating, which severely curtails wind power generation in northern China during winter. This article describes a new system, called the cooperated heat and power system (CoHP), which greatly increases the adjustment capacity while maintaining the maximum heat output and high thermal efficiency of cogeneration plants. The system includes a low-temperature storage tank, high-temperature storage tank, and electric heat pumps. Surplus power during valley hours is used to produce and store high- and low-temperature water; the stored water is released to increase the power output of the generator during peak hours. A model is built for simulation and analysis. The CoHP system is applied to a 300-MW water cooled cogeneration plant. Results show that the system has a power adjustment capacity of 156 MW and storage efficiency of 60.2%. Waste heat from the exhausted steam continues to be fully recovered such that the thermal efficiency has a high value of 87.3%. The electric efficiency is 26.9%, which is lower than the efficiency of the benchmark system (29.2%). The effects of the heating network temperature, temperature difference of heat transfer, and adiabatic efficiency of the compressor are also analyzed. The use of a CoHP system is an effective way of increasing both the energy efficiency and flexibility of cogeneration plants and the system can be widely applied in China.