The Macrokinetics Model Constructed For Coal Particles Thermal Reaction

China is one of only several countries with coal as the main source of energy in the world, so the situation of coal resources as the main energy consumption will exist for a long time. However, it's non-renewable and incidental to the many environmental problems, which have seriously hampered the sustainable development of mankind, should have gradually been worldwide attention. Pollution caused by the utilization of coal is main source of air pollution in China, thereby improving the efficiency of the utilization of coal and reducing environmental pollution caused by the utilization of coal is pressing problem. Jiaozuo anthracite, Yunfu bituminous, Xiaolongtan lignite were used in this study as the representatives of three typical Chinese coals, and coal pyrolysis and combustion/gasification mechanism and model were studied in detail, which should understand better coal pyrolysis, combustion and gasification process and reveal its nature is of great significance.First, the pyrolysis of coal was studied using a bench scale fixed bed reactor coupled with gas analyzer. The release properties of gas products during coal pyrolysis were analyzed on-line. Using the characteristics of Weibull distribution function and the nature of step function, simplified DAEM was established and this model to be amended in this chapter. The results show that the heating rate, temperature and coal type are important factors for the gas releasing characteristics during coal pyrolysis. The peak of the gas products concentration increases with the pyrolysis temperature increasing during coal pyrolysis, With increasing pyrolysis temperature, the peak of the main gas products (CO2, CO and CH4) concentration increases, and the release properties of the main gas products during coal pyrolysis due to the difference of coal type is larger distinction. Compared with simplified DAEM and modified DAEM predicting the release properties of gas products during coal pyrolysis, it was found that two DAEM were more accurate to describe the experimental results, especially to the DAEM improved in this chapter.The combustion of Chinese three typical coal chars in O2/CO2 under chemical reaction control was studied using a TG/DTG. The internal pore structure of the coal chars was investigated with the help of fractal theory, and structure parameterΨin random pore model is modified based on pore fractal feature and fractal random pore model was constructed. The results showed that coal chars combustion under O2/CO2 atmosphere at lower temperature fractal dimensions slightly change at the initial stage, and then kept stable in the middle stage before decreasing drastically. On the other hand, the effect of final pyrolysis temperature for pore structure can not be negligible, this phenomenon was mainly caused by the changes of pore structure affected by devolatilization and thermal deformation of the char. The change of parameterΨcan be divided into the following two categories,Ψis almost constant at this stage of reaction (X=0-0.7), thoughΨdecreases slightly during the initial stage of the reaction (X=0-0.3). This phenomenon is mainly caused by generation of a large number of new pores and micropore expansion. At the end of stage (X=0.7-1),Ψvalues increase remarkably. Structure evolution in particles at this stage is mainly caused by pore collapse which also makes reaction surface decrease gradually. Compared to the results calculated by five different random pore models, the prediction results of fractal random pore model and Struis model are better throughout the conversion period, especially to the prediction results of fractal random pore model.The combustion of Chinese three typical coal chars in O2/CO2 under diffusion controlled condition was studied using the thermogravimetric balance and the bench scale fixed bed. The methodology developed is based on an approximate method for decoupling partial differential mass conservation equation, and a mathematical model was created to describe the reaction rates of coal chars under diffusion controlled condition. The results show that the adsorption isotherm curves of three kinds of coal chars in the various conversions slightly distinct in shape, but they were tested against "S" shape, and its adsorption first increases and then decreases with increasing carbon conversions. The adsorption isotherms curves of coal chars prepared at various carbon conversions is diverse, it can be indicated that pore size distribution of coal chars is different at various carbon conversions. In addition, the specific surface area SBET of three typical coal combustion at high temperature has an increasing trend at the initial stage, which is mainly caused by generation of a large number of new pores and micropore expansion. The variation of the micropore volume and surface area is very similar, which mainly due to the specific surface area determined by the micropore. Compared to the results calculated by the models, the prediction results of the model improved in this chapter are better throughout the conversion period, it indicates that this model can be recommended as a quick and reasonable way to predict the reaction rates of coal chars under diffusion controlled condition.Finally, the steam gasification of coal was studied using thermogravimetric and the fluidized bed furnace. The characteristics of coal steam gasification were investigated, and modified DAEM model was used to simulate the experimental results. The results show that coal type and temperature are important factors for the gas products releasing characteristics during coal steam gasification. The change trends of the maximum gas releasing concentration during coal steam gasification is related with volatile content, the change trends of the maximum gas releasing concentration of the low volatile coal and high volatile coal is different. With increasing gasification temperature, the peak of the main gas products concentration increases and reached its peak at the shorter time. The changes of the volume fraction of gas products during coal steam gasification is also significantly different, the changes of the volume fraction of gas products during high volatile coal gasification is smaller. Modified DAEM can simulate better the characteristic of char reaction during the low volatile coal steam gasification. The results simulated by this model during the high volatile coal gasification have rather big difference with experimental results. This phenomenon may be due to the high volatile coal that makes the gasification reaction occur the phenomenon of the second peak, and the errors of simulation results are caused by it.