Coal-fired Supercritical Carbon Dioxide Power Generation System: System Development And Performance Study

As a new energy conversion method with great efficiency potential and wide application prospect,supercritical carbon dioxide（sCO₂）power cycle can obtain more competitive cycle efficiency,and can be applied to a variety of heat sources,including fossil energy,nuclear energy,waste heat recovery,renewable energy and so on.The application of sCO₂ cycle power generation technology in the field of coal-fired power generation can realize the low-carbon and clean utilization of fossil energy,which is of great significance to reduce carbon emissions and meet the challenge from climate change.It can be divided into the following two directions:（1）The indirect-fired sCO₂cycle is applied to coal-fired power station instead of steam Rankine cycle to achieve higher cycle efficiency,and realizeCO₂emission reduction with CCUS（Carbon Capture,Utilization and Storage）technology;（2）The direct-fired sCO₂ cycle,which uses coal as fuel,achieves higher efficiency while achieving zero emission ofCO₂,competing with IGCC with carbon capture and storage（CCS）.Combined with the current energy situation in China,the paper mainly studied the sCO₂power cycle system for coal-fired power plants with zero carbon emission and inherent carbon capture,establishes the system model,explores the influence of system performance and system key parameters,and determines the optimal cycle parameters;establishes the exergy analysis model to quantitatively analyze the exergy destruction caused by irreversibility of each equipment and subsystem and evaluate the exergy utilization of equipment and processes in the system.The power model of 600 MWe integrated coal gasification direct-fired supercritical sCO₂power cycle system was constructed.Under the condition of 1150℃/30 MPa,The system design yields a net plant thermal efficiency of 40.67%（LHV）,with nearly 100%carbon capture.Compared with IGCC power station system with CCS,the system has advantages on the overall effiency.The effects of combustion chamber outlet temperature,turbine inlet and outlet pressure,pinch point temperature difference of regenerator and O₂ purity on the overall cycle performance are analyzed.The results show that the energy consumption of intergrated coal gasification direct-fired sCO₂poewer cycle system is mainly concentrated on the circulatingCO₂ compressor,coal synthesis gas compressor and O₂ compressor,accounting for 72.16%of the total energy consumption of the system,and ASU energy consumption also has a significant impact on the system efficiency;Compared with95 v%purity O₂,99.5 v%purity O₂ has higher system efficiency;the performance of regenerator plays an important role in the system;when the pinch temperature difference of regenerator increases from 5°C to 10°C,the net system efficiency will reduce 1.2%.Exergy analysis model of the integrated coal gasification direct-fired sCO₂ power cycle system was established.Under the condition that the inlet parameter of the turbine was 1150℃/30 MPa,exergic efficiency of the system was 29.67%.The results show that,the exergy loss of the integrated coal gasification direct-fired sCO₂ power cycle system is the sCO₂ power cycle subsystem,coal gasification subsystem,ASU subsystem and carbon capture subsystem from high to low,among which the local exergy loss rate of sCO₂ power cycle subsystem is 54.64%and the local exergy loss rate of the coal gasification subsystem is 33.82%.The model of the coal direct-fired sCO₂ cycle system was built;energy and exergy analysis was performed on the system.The following conclusions can be drawn:under the same key cycle parameters,the efficiency of coal direct-fired sCO₂ cycle can be improved by about 7.54%compared with that of the integrated coal gasification direct-fired sCO₂power cycle system.Exergic efficiency of direct-fired sCO₂ cycle system is 33.43%.Exergy loss of the system was mainly concentrated on the combustion chamber,accounting for 52.47%of the total exergy loss of the system.The model of the O₂/sCO₂ combustion coal-fired power station coupled with sCO₂recompression cycle was built to explore the system performance,analyze the influence of cycle parameters on the cycle performance;and to build a exergy analysis model,and analyze the exergic efficiency of the system,including subsystem and equipment.The results show that the main operating conditions affecting the system efficiency are the inlet temperature and pressure of the turbine.Under different inlet temperature conditions,the system efficiency increases with the pressure of the inlet of the turbine.When the pressure is lower than 25MPa,the cycle efficiency increases with the increase of the compressor outlet pressure.Between 25 MPa and 30 MPa,the cycle efficiency basically remains unchanged with the increase of pressure.Exergy loss is mainly concentrated on the recompression sCO₂ power cycle subsystem and combustion subsystem,which is mainly due to irreversible loss from combustion chamber and heat transfer through the heating surface.The exergic efficiency of the O₂/sCO₂ combustion coal-fired power station coupled with indirect recompression sCO₂ cycle is 27.41%.