A modified approach to equilibrium modelling of coal gasification is presented, based on global thermodynamic analysis of both homogeneous and heterogeneous reactions occurring during a gasification process conducted in a circulating fluid bed reactor. The model is based on large-scale experiments (ca. 200 kg/h) with air used as a gasification agent and introduces empirical modifications governing the quasi-equilibrium state of two reactions: water-gas shift and Boudouard reaction. The model predicts the formation of the eight key gaseous species: CO, CO 2 , H 2 O, H 2 , H 2 S, N 2 , COS and CH 4 , volatile hydrocarbons represented by propane and benzene, tar represented by naphthalene, and char containing the five elements C, H, O, N, S and inorganic matter.
Thermodynamic analysis of a gasification process was conducted assuming that it is composed of two successive stages, namely: pyrolysis reaction followed by a stage of gasification reaction. This approach allows formulation the models of selected gasification processes dominating in industrial applications namely: Shell (coal), SES (coal), and DFB (dual fluid bed, biomass) gasification. It was shown that the enthalpy of fuel formation is essential for the correctness of computed results. The specific computational formula for a wide range of fuels enthalpy of formation was developed. The following categories were evaluated in terms of energy balance: total reaction enthalpy of gasification process, enthalpy of pyrolysis reaction, enthalpy of gasification reaction, heat demand for pyrolysis reaction, and heat demand for gasification reactions. The discussion of heat demand for particular stages of gasification related to the various processes was performed concluding the importance of the pyrolysis stage.
Coal plasticity is a phenomenon directly affecting the creation of coke structure. It is very much a time-and temperaturedependent transformation of the coal matrix, which allows changing the physical phase from solid to liquid-like and again into solid of different properties. The coking process, particularly in a plasticization temperature range, can be considered as a non-isothermal reaction at a constant heating rate. In this work, a macro-kinetics approach is applied that results in effective kinetic parameters, i.e. pre-exponential factor and activation energy. It is postulated in this work that the original content of metaplast (M 0) is a part of volatile matter that melts under the effect of temperature. The coal sample can melt steadily with the temperature increase, achieving the maximum fluidity (F max) when the total amount of metaplast available turns into the plastic state. Coal behaviour while it is being heated can be described by two mechanisms. Under first one, the coal turns into plastic phase starting at t 1 and ending at t max , where solidification starts. This can be considered as independent reactions model. In the second model, both plasticization and solidification reactions compete over entire range of phenomena. This can be considered as reactions in the series model. The developed models were validated against experimental data of coal fluidity delivering kinetic parameters.
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