Hydrogen production by supercritical water gasification of coal: A reaction kinetic model including nitrogen and sulfur elements

Abstract

Researches on reaction kinetics and mechanism are crucial to the application of hydrogen production technology by supercritical water gasification of coal from experiment to industrialization. Based on the migration mechanisms of nitrogen and sulfur in the process, this paper developed a general model including nitrogen and sulfur to study the generation path, consumption path and reaction rate of the gasification products. The parameters of the kinetic model were obtained by fitting the experimental data of the gasification products, and the activation energy of each reaction was obtained by the Arrhenius equation. By comparing the reaction rates among the various reactions, the reaction steps for controlling the production or digestion of the product could be obtained. The main source of ammonia production was pyrolysis of coal followed by steam reforming reaction of fixed carbon. The rate of ammonia contribution from ammonia synthesis was extremely low and could be ignored. The consumption path of ammonia was the decomposition reaction of ammonia though its rate was also slow. The pyrolysis reaction of coal was the main source of hydrogen sulfide, followed by the steam reforming reaction of fixed carbon. The difference of the concentration and reactivity between organic sulfur and inorganic sulfur caused the difference in the generation source of hydrogen sulfide in early and late stage of the gasification. The kinetic model can predict not only the production of hydrogen, methane, carbon dioxide, carbon monoxide, ammonia and hydrogen sulfide under different operating conditions, but also the products for different coal types, which may provide a theoretical basis for the targeted regulation of nitrogen and sulfur elements in supercritical water.