Integrated study on a novel central heating system with large-temperature-difference heat exchange based on heat-electricity-gas synergy

To achieve high-efficiency, low-carbon central heating in northern China, the integration of large-temperature-difference heat exchange processes with conventional heating system was considered a promising approach for improving exhaust steam heat recovery. In this study, a novel central heating system was proposed, where multi-heat-source cascade heating in thermal power plants was combined with a large-temperature-difference heat exchange based on heat-electricity-gas synergy in networks. As a result, the integrated system was demonstrated to enhance the overall exergy efficiency by over 20 %. To quantify improvements, a mathematical model was developed for thermodynamic analysis and system evaluation. For practical validation, a case study was conducted based on a 2 × 600 MW cogeneration unit, where the impacts of natural gas peak-shaving ratios and electric heating ratios on system performance were investigated. It was found that the primary return water temperature can be reduced to 18 °C when the large-temperature-difference heat exchange ratio was set to 0.6. Additionally, an increase of 78.5 million kWh in power generation can be achieved over the heating season, along with a decrease of the equivalent electricity from 32.8 kWh/GJ to 27.8 kWh/GJ. Moreover, the investment payback period of the novel system was 7 years, indicating fine economic feasibility.