Development of a novel coal-fueled nearly zero emission semi-closed supercritical CO2 cycle with the net efficiency above 50 % based on the process splitting method

To realize the high efficiency and nearly zero emission for coal-fueled electric power generation plants, a novel coal-fueled semi-closed supercritical CO2 (sCO2) cycle is developed based on process splitting method, which splits the semi-closed cycle into the closed cycle formed by recycled CO2 and the open process related to other streams, i.e., fuel, oxygen and combustion products. In the proposed system, all process heat released from the open process is integrated with the efficient closed sCO2 cycle as the waste heat from the cycle cold-end is recovered for the coal-pre-drying and CO2 split from the sCO2 cycle is utilized as the agent for coal gasification to avoid the requirement of the steam generation. Furthermore, the recompression modification is also applied to the sCO2 cycle, which could save more recuperation heat to drive the closed sCO2 cycle. The effects of CO2 stream split points for gasification and recompression are also analyzed to optimize the thermodynamic performance of the overall system. Results show that for the scheme without recompression, the net efficiency reaches 48.42 % (based on lower heating value, LHV) after the adoption of low-temperature pre-drying and CO2 gasification, and the different CO2 split points from cycle hot end or cold end for gasification have little effect on the net efficiency. While, for the scheme with recompression, the net efficiency can be further improved, and the CO2 split from the top turbine for gasification is better than that from the bottom compressor. Finally, after optimizing the CO2 split point for recompression, the coal-fueled semi-closed CO2 cycle achieves a pretty high efficiency of 51.35 % (LHV).