Influence of coal type and briquetting conditions on combustion rate of biobriquette

The combustion time history of a biobriquette is divided into two stages in which volatile matter content mainly evolves and burns prior to char combustion. The volume model for the former stage and the shrinking-core reaction model for the latter stage are employed to calculate the combustion rate of the biobriquette. In this study, the influence of briquette shape, compression pressure and types of coal on the combustion rate are investigated by using the two models and experimental data. The shapes of spherical and cylindrical biobriquettes hardly influence the combustion behavior of the biobriquette (if they have same diameter and the length of cylinder is equal to its diameter). Compression pressure has no effect on the rate of the former stage but gave obvious effect on the latter stage through the density change of the biobriquette when it is under about 245 MPa. The reaction rate constant and its order vary linearly with the fuel ratio of coal briquette in the former stage. The type of coal and compression pressure have a larger influence on the rate of the latter stage due to different porosity in the ash layer. Finally, the combustion rate can be analyzed by the obtained models and semi-empirical equation.