User's Manual for Computer Simulation and Design of the Moving-Bed Coal Gasifier. Final Report

摘要

A computer model of countercurrent moving-bed coal gasifier developed previously has been updated. This manual presents in detail how the computer program developed is used. The unique feature of the present gasifier model is the treatment of the pyrolysis of coal. A semi-empirical approach is taken in the present model to represent the pyrolysis zone of the bed. The pyrolysis reactions are represented by three simple chemical reactions: devolatilization, cracking and carbon deposition with empirically estimated reaction rate constants. The gasification reactions are assumed to be heterogeneous reactions. For fast reactions, diffusion is the rate controlling step while for slow reactions, the surface reactions within the pores of particles is the rate controlling step. Therefore, the rates of gasification reactions used in the model are composed of two terms,the reaction term and the diffusion term. The computer program developed can be used for both simulation and design. It can be used to simulate a gasifier to obtain the gas product distributions and coal conversion and calculate the required bed height for a given carbon conversion. A map of feasible operation ranges can then be constructed for the optimum design of a gasifier. Kinetic parameters for three different kinds of coal are specified in the program. However, the program users may change these parameters according to the guides listed in the manual if the coal used is different. In addition, the reaction rate equations may be replaced if better rate expressions become available. It is important that the user checks the assumptions, the simplifications and the limitations of this computer program before applying in order to assure that the applicability of the model is within the range specified. The scale-up and extrapolation from normal operating conditions should be done with caution and, if possible, verified through additional experimentations. (ERA citation 08:031054)