Primary reactions of lignite-water slurry gasification under the supercritical conditions

The experimental research of lignite-water suspension gasification under the supercritical conditions of water was carried out. The conversion of lignite was studied under the pressure 24 MPa in two temperature range: 290-360 and 390-500 degrees C without and with additives. Calculation of the activation energies of the reactions of gases formations had shown that NiO-MoO3-Al2O3 had acted as a catalyst, sodium and calcium hydroxides had behaved as reactants. The general scheme of the mechanism on formation of the gas products containing H-2, CH4 and CO2 was examined. It was shown that at the subcritical temperature the gas products were formed mainly from hydrogen of coal and oxygen of mineralized water. Carbon of lignite behaves like an acid, and water is as a base at the subcritical temperature; they switch their roles at the supercritical temperature. 80% of hydrogen and oxygen of gas products were of water origin at the supercritical temperature. C, O and H conversions at initial rates of reactions with gases distribution have been synchronously analyzed for primary reactions clearing. It had found that the gasification of lignite-water suspension under the supercritical pressure had at least four types of interactions: thermal decomposition of coal, carbon oxidation by oxygen of water as well as hydrolysis and hydrocracking of coal. Oxidation of carbon was dominant for the process at the subcritical temperature on water. Hydrolysis of C-C bonds of coal was the main at the supercritical parameters of water. (C) 2016 Elsevier B.V. All rights reserved.