Influence Of Dolomite On Gasification Reactivity Of Coal Char With CO₂

Coal gasification is an effective approach to accomplishing high efficient and clean utilization of coal resource. Compared with other coal gasification technologies, coal catalytic gasification technology has the advantages of lower reaction temperature, higher reaction speed. Shenmu bituminous coal was used in this text. The calcined dolomite was selected as catalyst of coal gasification. Kinetics characteristics of coal char gasification with CO2at850℃-1000℃were studied by using the thermogravimetric experimental system which was designed by ourselves.The paper first investigate into the effect of different making char temperatures, particle size and gasification temperature, results indicated that the gasification reactivity of coal char decreases with increasing char-making temperature. The effect of inside diffusion could be eliminated by choosing particle size less than0.096mm. The kinetics parameters and the gasification mechanism were calculated through model fitting method. In view of the fact that the calcined products of dolomite were CaO and MgO, it is necessary that we should undertake a study respectively on catalytic properties of CaO and MgO. The results show that:the catalytic properties of CaO were better than MgO’s; With the increasing of gasification temperature, the loading saturation level of CaO increases; However, the loading saturation level of MgO is always15%. Comparing the single and binary catalysts, the latter present the higher catalytic activity, but the best mass ratio of CaO and MgO is changed with the gasification temperature. The catalytic effect of the calcined dolomite was affected by the calcination temperatures, particle size, calcination time, the times of calcination/carbonation cycle. The further research shows that:the catalytic effect increases as the calcination temperature increasing which ranges form850℃to950℃. The reason for this phenomenon is that the higher calcination temperation is benefinal to the formation of the bigger hole, which is in favour of the gas diffusion. The size of dolomite is smaller, the catalytic effect will be better. Because the smaller catalyst has larger contact area with coal char. Though the longer calcination time is benefit for the formation of the bigger hole, it also will lead to losing the activation centers. According to the research, the optimum calcination time is2h-4h, while the proper times of the calcination/carbonation cycle is2.This study indicated that the gasification rate will increase due to the presence of the calcined dolomite product.