Modelling thermal behaviour of a single solid particle pyrolysing in a hot gas flow

Abstract

Pyrolysis is a first stage of the solid fuel combustion. Due to complexity of the phenomena during heating and the fuels’ variety, the analysis of their conversion and its modelling is still of importance from the cognitive and the practical point of view. In the paper the original mathematical 1D model to describe the behaviour of heated fuel particle is presented. The model accounts for the water phase transition (evaporation and condensation), and the transport of released gas and liquid products inside the particle. An in-house numerical code in FORTRAN was developed. The proposed new approach describing the devolatilization source term includes the limit pyrolysis progress function. It takes into account the proper direction of particle structure changes due to decomposition. A strong emphasis was placed on the role of transport processes of products inside the porous grain and their impact on the devolatilization time. Thus, the characteristic plateau in a temperature distribution at the level of 100oC can be predicted. The times complete conversion of the single solid particle depending on the fuel type and size were analysed and discussed. Based on the calculation results, the main differences in behaviour of heated particle between biomass and coal were outlined.