SCT REACTION KINETICS MODEL AND DIFFUSION FOR PULVERIZED COAL COMBUSTION IN TGA

摘要

Recently, the process of char burnout is extensively concerned. Global model used widely cannot predict the extent of char burnout at the latter burning stage. For the need of predicting the extent of burnout in the industrial Pulverized Coal (p. c.) fired furnace by making use of the experimental data from such as Thermogravimetry Analysis (TGA) and Drop Tube Furnace, the SCT model based on the Simple Collision Theory (SCT) of chemical reaction kinetics is educed, the p. c. combustion is considered as the results of strike and oxidation of oxygen molecules on the p.c. particle surface, the frequency of effective strike was determined by Boltzmann factor. Strike and oxidation occurs on the oxygen accessible specific surface area (OASA). Chemical regime controlled is at temperature below 1200 K, and molecules diffusion regime controlled is at the temperature above 1600 K, at which OASA is corresponding to the specific surface area of pore diameter wider than 38nm of p.c particles in coal-fired boiler. The OASA of p.c. particles increase with the combustion, for the particles swells, shrinks and cracks. The burning rates of calculating based on SCT model have shown good correspondence with experimental data reported. The process of p.c. combustion can be divided into four remarkable stages according to the experimental data and the characteristics of critical activation energy Ec: ignition including chemical adsorption oxygen and starting mass loss, devolatilization, char combustion and the char burnout. Ec is always the function of extent of burnout for the different stage. The curves of Ec and burning rate are plotted at different temperature according to the TGA data.