Study On Gasification Reactivity Of Coal Char Catalyzed By Red Mud

China is rich in coal resources.Coal promoted the rapid social and economic development,but has also caused serious environmental pollution problems.Coal catalytic gasification technology can convert coal into series products,such as gas or liquid fuel,in order to achieve efficient and clean use of coal.In this thesis,the catalytic properties of RM and Fe/RM catalyst as well as the relationship between the reactivity and microstructure of coal char were explored,and the reaction mechanism of lignite activated char was investigated.The following three aspects were studied in a fixed bed reactor.First,the gasification reaction performance of chemical char was studied by a thermogravimetric analyzer.The effects of reaction conditions,such as reaction temperature and steam flow on the reaction performance of char-H₂O were investigated in a fixed bed reactor.The results showed that the char with 10%K₂CO₃ catalyst at 1000?exhibited the highest gasification reactivity,while the weight loss rate of char with 10%calcium keeps a similar weight loss with raw char.The degree of graphitization of char is higher,the carbon conversion rate increased gradually with the increase of temperature,and the carbon conversion rate was 65.46%at 900?.Syngas content reached the maximum value?83.42%?when the steam flow was equal to1 g/min.Second,the chemical char is gasified with steam in a fixed bed reactor at 900?with different mass ratio of Fe/RM catalyst.The reactivity,surface functional group,pore structure and carbon crystallite structure of char during different stages of gasification process were characterized by FT-IR,BET,Raman spectra.The results demonstrated that the steam gasification reactivity of char could be significantly improved using Fe1/RM2catalyst.In the process of char-Fe1/RM2-steam gasification,the active functional groups,such as methylene,carboxyl,and phenolic hydroxyl,formed on the surface of coal char interacted with Na⁺and Ca²⁺in Fe1/RM2.Therefore,new small molecular active groups or compounds were formed.The specific surface area of char firstly increases and then decreases(6.98³23.22 m²·g^-1)with char conversion,while the average pore size has an opposite trend overall?2.91¹1.25 nm?.The degree of carbon ordering is reduced first and then increased,and the relative content of amorphous carbon?0.371?is the highest when the conversion is 36%.In the initial stage of the char-Fe1/RM2 steam gasification reaction?Xc=³6%?,the char gasification reactivity was improved comprehensively,due to the increased surface active groups,the enlarged specific surface area and the decreased ordering degree of the char.In the later stage of gasification,the ordering degree of char increased,resulting in a decrease in the gasification reactivity rate of char-H₂O.Finally,the influence of lignite addition on chemical char gasification reactivity was investigated.The surface functional groups,pore structure and carbon ordering degree of char during lignite pyrolysis stage were analyzed by FT-IR,BET and Raman spectra.The catalytic performance of Fe/RM catalyst for co-gasification of char-lignite was studied.The results showed that the co-gasification rate of the mixture of char and lignite was found to be higher than the rate sum of single char and single lignite,which suggested that a synergistic effect took place due to the co-gasification.The results showed that with increasing lignite addition,the intensities of surface active functional groups increased,the total specific surface area increased first and then decreased(6.98¹4.41 m²·g^-1).The specific surface area of the pores gradually increased,and the active free radicals that were pyrolysised by lignite destroyed the stable chemical structure of the char,resulting in a decrease in the degree of carbon ordering of the char,which is significantly improved the steam gasification reactivity of char.The Fe₂O₃,K₂O and CaO existing in the RM could enhance the gasification reaction.Fe/RM catalyst significantly raised carbon conversion rate of char-lignite co-gasification.When the reaction time is 100 min,the conversion rates of Fe4RM6 and Fe4RM6K1 were increased by 10.98%and 14.08%,respectively,and the syngas content is maintained at 78%.After five cycles,the Fe4RM6catalyst still has a high reactivity with stable carbon conversion and syngas content.