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

Highlights: • A new system to improve energy efficiency and flexibility of CHP plants is proposed. • Ratio of Power output can be adjusted from 46.2% to 95.0% while fully recover the waste heat. • Thermal efficiency is 87.3% and electric efficiency is 23.8–30.6%. -- Abstract: 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 co-operated 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.