The exergy release mechanism and exergy analysis for coal oxidation in supercritical water atmosphere and a power generation system based on the new technology

The oxidation environment has important influence on the transformation of the energy contained in fuel and generation of pollutants. To the problem of nearly 50% exergy losses in coal oxidation at air atmosphere, this research intends to change oxidation atmosphere from air to supercritical water/oxidant and achieve efficient release of exergy in coal at about 650 degrees C with the aid of a high solubility and unique performance of heat and mass transfer of supercritical water. Therefore, firstly, based on the exergy analysis theory and the energy-utilization diagrams, the release mechanism of exergy of coal in supercritical water oxidation process is revealed. It is pointed out that supercritical water oxidation has changed the release pathways of chemical exergy, and decreased the level difference between chemical exergy and thermal energy, and more exergy is released. Meanwhile, there is also no exergy loss of physical heat transfer. As a result, supercritical water oxidation has higher exergy efficiency than conventional oxidation. Secondly, the exergy losses, level difference between chemical exergy and thermal energy as well as exergy efficiency, are quantitatively investigated. Results show that the exergy efficiency of supercritical water oxidation reactor may be as high as 80.1% and has increased by 27% relative to conventional boilers. Thirdly, based on supercritical water oxidation of coal, a concept power generation system is constructed. Exergy efficiency is calculated and exergy analysis is provided for the supercritical water oxidation power plant. Compared with conventional power plant, exergy efficiency in supercritical water oxidation plant reaches as high as 61.3% and 21% higher than that in conventional power plant. Finally, from the results obtained, it is believed that the commercial breakthrough of the supercritical water oxidation process will be possible when the corrosion and salt deposition in the reactor are solved. (C) 2016 Elsevier Ltd. All rights reserved.