Development of a Coal Combustion Model Compliant with the CHEMKIN Format for Use in Co-Firing Analysis with Hydrogen and Low-Carbon Fuels

Abstract

We developed a simplified coal combustion model that is used in combination with detailed gas reaction models. This model aimed to develop co-firing systems for decarbonized fuels such as coal and hydrogen. The reaction mechanism was described in the CHEMKIN format. We aimed to develop a coal combustion model that is easy to handle even for experts in gas combustion. Based on the experimental results, we modified the following reaction models. (1) Determining the rate constant of NOx reduction by char in the presence of oxygen. (2) Determining the gasification reaction rate constants, especially the rate constant of the steam gasification reaction, from staged combustion experiments. (3) Adoption of a chemical structural model of char based on elemental analysis results. Char was composed of carbon; C, nitrogen; N, and hydrocarbons; CnHm. As a result of the improvement, we achieved the NOx prediction error halved. Improving the calculation accuracy of the coal burnout was most important for improving the accuracy of the gas reactions. If there was an error in the calculated coal burnout due to an error in the gasification reaction, and so forth, the amount of C, H, O, and N species in the coal released into the gas phase would change. These changed the burning conditions, for example, stoichiometric ratio, in the gas phase. As a result, the concentration of radicals such as H, O, and OH changed, causing a decrease in NOx prediction accuracy. We obtained outline of the combustion performances when decarbonized fuel such as hydrogen and coal were co-combusted.