Thermodynamics, flexibility and techno-economics assessment of a novel integration of coal-fired combined heating and power generation unit and compressed air energy storage

Abstract

The new power system with increasingly high renewable energy proportion necessitates the combined heating and power (CHP) generation units to provide more flexibility. With full consideration of operation characteristics, this paper firstly proposes an advanced coal-fired CHP-CAES system consisting of a 350 MW coal-fired CHP unit and a 30 MW CAES system, which realizes more efficient energy utilization and enhances the system adjusting flexibility through thermal cycles integration and energy comprehensive utilization. The thermodynamic models and multi-dimensional performance analysis models are separately established. Based on that, the comparative study is conducted for two CHP-CAES configurations and the stand-alone CHP unit. With 80% heating load, the minimum power ratio is lowered by 11.69% rated power and the maximum power output is increased by 6.35% rated power, and 27.26 tons of coal can be saved for a single cycle compared with the stand-alone CHP unit. The results also demonstrate that the system still has superiority when the load ratio changes. Techno-economic evaluations for a typical application scene show that the dynamic payback period of the proposed system is shortened by 10.41 years compared with the reference separate CHP-CAES system. These results show that the proposed system presents better performance in energy utilization, enhancing flexibility, realizing clean and low-carbon heating as well as techno-economics. In addition, parametric analysis is implemented to find the influence of CAES parameters on the system. It is found that increasing the expander inlet temperature and air storage pressure can further enhance the system round-trip performance. Yet, the investment cost increases greatly for higher storage pressure and the payback period will be lengthened. Furthermore, the system advantages are strengthened with a CAES system of greater capacity. Nevertheless, we find that the deep coupling in the thermodynamic cycle of the two systems results in an upper capacity for the integrated CAES system, and it is nearly 35 MW for the studied system. These regularities and conclusions can provide theoretical guides and directions for the customized CAES system design with the purpose to integrate with a coal-fired CHP unit.