Study On The Catalytic Effect Of K/Ca/Fe Compunds In Coal Char Gasification

Catalytic gasification can significantly reduce reaction temperature of coal and the cost of the process.Improving the reactivity of Datong coal is an urgent problem because low reactivity severely restricts its application as coal gasification material.Datong coal samples were deashed by HCl-HF method,and deashed coal char was obtained by pyrolysis.The gasification reaction characteristic,pore structure,and carbon structure of the deashed coal char and raw coal char were studied in detail.A special attention was paid on the characteristic of K/Ca/Fe catalysts on their catalytic activity.The dispersivity of catalysts which loaded on the deashed coal char was explored by SEM-EDX.The influence factors of catalytic gasification of deashed coal char were discussed via kinetics calculation.The key findings are as follows.The ash content of coal can be removed by 85.32%via the HC1-HF method.And the proportion of aliphatic carbon and aromatic carbon in the Datong coal did not change by deashed.However,the specific surface area of coal was increased by 16%,and the pore structure became more developed.The reactivity of the deashed coal char is lower than that of the raw coal char,because the ankerite with catalytic activity in coal was removalled.However,after deashing,the coal char pores become more developed,and the carbon structure is basically unchanged,so the gasification reaction rate of TH coal char at high temperature(above 1050?)is higher than that of DT coal char.The deashed coal char is loaded by K/Ca/Fe catalysts via impregnation method,and the catalytic properties of coal char are studied by the thermogravimetric analyzer.The deashed coal char samples of loaded catalyst are pyrolyzed in a high temperature tube furnace to study the dispersivity of catalyst by SEM-EDX.The results show that K2CO3 exhibit good dispersivity,which can easily contact with char surface.To same degree,the loading amount of K2CO3 greater the higher of the catalytic activity.The catalysts of CaO and Fe(NO3)3 with poor dispersivity are less effective to char gasification,and the optimum loading amount all is 2%.Tomogeneous model,shrinkage core model and random pore model are used to fit the gasification reaction data.For the raw coal char,the fitting effect of the homogeneous model is better.However,for the deashed coal char before and after loading catalyst,random pore model can better reflect the gasification process than Homogeneous model and Shrinking core model,which indicate that the change of pore structure has a significant impact on gasification rate during the gasification process.Besides,all the catalyst in varying degrees can reduce the active energy,and the abilities on reducing the activation energy of different catalysts are as follows:3%Fe(N03)3-2%CaO>2%K2CO3>2%CaO>2%Fe(N03)3.