Evaluation of drying and devolatilization in the IEA-AFBC model - and a new model proposal

摘要

Devolatilization of coal particles is a complex phenomenon involving both heat and mass transfer coupled to chemical kinetics. Since volatiles may contain up to about 50% of the total energy released during combustion, it is important to know where the volatiles are released. If the volatiles are released directly into the freeboard, f.ex when over bed feeding is used, the freeboard must be designed to give the gased sufficient residence time for burnout to occur. The purpose of this paper is to give an evaluation of the treatment of drying and devolatilization in the IEA-AFBC model. A new model, taking internal temperature gradients into account is proposed and compared to the existing model. The distribution of moisture and volatiles is based on a comparison of the time scales for drying and devolatilization to take place and the turnover time. The turnover time describes the vertical mixing rate of solids in the bed. The distribution of volatiles is calculation in subroutine VSPLIT. It is not the scope of this paper to evaluate the model for the distribution of moisture and volatiles, which is used in its present form. (AB).