Thermodynamic analysis of a novel dual expansion coal-fueled direct-fired supercritical carbon dioxide power cycle

The direct-fired supercritical CO2 power cycle not only has the potential of reaching high efficiency but also has inherent ability to capture almost all of the combustion derived CO2. A novel direct-fired supercritical CO2 power cycle layout is proposed in this paper, using the syngas produced by coal gasification as the fuel. The proposed cycle layout is specially designed to facilitate heat integration between the power cycle, the fuel conversion process and other auxiliary subsystems. Heat from the air compressor intercooler and the low temperature syngas is introduced to the regenerator to correct its imbalanced heat exchange, a typical problem of the supercritical CO2 power cycle that is caused by the abrupt physical property variation. Design considerations of the proposed cycle layout are discussed in detail. The result shows that the net efficiency is 42.1%, with near-zero CO2 emissions. The proposed cycle layout is then further modified by integrating more heat from the oxygen compressors and the syngas compressor, which reduces the hot end temperature difference of the regenerator to less than 10 °C and increases the net efficiency to 43.7%. Heat integration through novel cycle layout has been proved essential to guarantee the high efficiency of the supercritical CO2 power cycle.