Mathematical Modeling for Coal Gasification Kinetics in Supercritical Water

Supercritical water gasification of coal is a newly clean coal technology. In this study, we established a quantitative model for the reaction kinetics of coal gasification in supercritical water. The large number of real intermediates formed during gasification were lumped using volatile and fixed carbon, and mass balance was also ensured in kinetic equation which would facilitate access to a comprehensive model considering flow and heat transfer. The model focused on the formation of the individual gaseous species (H-2, CO2, CH4, CO). Then the model was applied to fit the experimental data and kinetic parameters were estimated. It was found that predicted results of the model were in accordance with experiments. The model predicted that volatile completely 'converted into gas quickly when temperature reached above 650 degrees C, and the reforming reaction of fixed carbon became the control step of gasification. Hydrogen was mainly from volatile decomposition in the initial short stage and water gas shift reaction then contributed to the hydrogen production. Carbon reforming reaction dominated hydrogen generation after about 5 min. Methane generated from the direct decomposition of volatile and the effect of methanation reaction was negligible. Carbon monoxide was generated during the volatile decomposition and it was consumed simultaneously in water gas shift reaction with substantial carbon dioxide produced. As a result, carbon monoxide content accounted for a small percentage and hydrogen and carbon dioxide dominated the gas products of gasification.