Optimal design and thermodynamic evaluation of supercritical CO2 oxy-coal circulating fluidized bed power generation systems

Replacing the steam Rankine cycle with the supercritical CO2 Brayton cycle (sCO2 cycle) has been demonstrated to be an effective way to improve the efficiency of oxy-coal power plants. The present work focuses on the optimal design of the sCO2 oxy-coal circulating fluidized bed (CFB) power generation systems which so far has not received much attention in the research field. A novel triple recompression sCO2 cycle and a new sCO2 oxy-coal CFB boiler configuration with medium-temperature and high-temperature flue gas recirculation have been proposed and evaluated. With the novel boiler configuration and triple recompression cycle, the system efficiency can be increased by about 1.4% points in comparison to the basic system using the basic recompression cycle and the basic boiler configuration. The influences of the cycle minimum temperature, recuperator pinch temperature difference, furnace inlet oxygen concentration, flue gas recirculation flow distribution and coal itself on the sCO2 oxy-coal CFB power generation system performances were thoroughly investigated. The results show that increasing the minimum cycle temperature and the recuperator pinch temperature difference reduces the system efficiency while increasing the oxygen concentration at the furnace inlet and reducing the proportion of the recirculating flue gas as the primary oxidizing gas can boost the system efficiency. Coal itself also has an impact on the system efficiency due to its properties affecting the cycle efficiency, boiler efficiency and auxiliary equipment power consumptions.