Study On Minerals Phase Transformation In Coal Coking And Coke Gasification Process

Mineral composition in coals are complex.It is obvious that the content and occurance of the minerals are different between the different metamorphism degree coals. In the coal coking and coke gasification process, the mixture of minerals results in difficult analysis of the mineral transformation. However, part of the minerals has the impact on coke properties which contains coke reactivity index(CRI), coke cold strength, coke strength after reaction(CSR).The content, kind and occurance of minerals lead to the difference in the carbon solution loss reaction and coke pore wall. Therefore, it is important to analyze the content, kind and occurance of minerals and study the mineral transformation integrally.Firstly, Mineral Phase Quantitative Analysis Method and Factsage were used to investigate the content of the main minerals and phase transformation of Nantong Coal and Yonghun Coal in coal coking process. The research results showed that, the main minerals of Nantong Coal contain quartz, kaolinite, cyrite and calcite, its content, respectively, are 19.57%,46.03%,7.83% and 17.64%. The main minerals of Nantong Coke were quartz, mullite, pyrrhotite and γ-Al2O3, its content, respectively, are 35.48%, 30.03%, 7.01% and 10.12%.During the coking process of Nantong Coal, clay minerals decomposed completely, 65.24% of kaolinite decomposed to mullite, the other 17.02% decomposed to cristobalite and γ-Al2O3, the remaining decomposition product would react with other minerals in Nantong Coal and generate new minerals. 89.53% of pyrite converted into pyrrhotite. The quartz mineral content in ash increased from 19.57% to 35.48% and calcite decomposed completely. During coking process of Yonghun Coal, the transformation rule of minerals was similar with Nantong Coal.It was small difference of analysis results which were got between Mineral Phase Quantitative Analysis Method and Factsage. And they proved that Mineral Phase Quantitative Analysis Method was accurate in theory.Secondly, Mineral Phase Quantitative Analysis Method was used to analyze mineral transformation of the blending coal during coking and coke gasification process,then the effect of coking conditions on mineral transformation during coal coking and coke gasification process were researched.The research results showed that, during the blending coal coking process, kaolinite mainly decomposed to mullite and sillimanite, the other mainly decomposed to cristobalite and γ-Al2O3.Apart from that, content of anhydrite decreased a little. In the blending coal coking process, content of quartz decrease in a certain degree, anhydrite and mullite increased respectively by 0.53% and 8.95%.With the increase of temperature, content of quartz and γ-Al2O3 mullite(sillimanite) which were the decomposition product of kaolinite increased and content of minerals changed a little in the coke gasification process. With the increase of coking time, content of quartz increased gradually and content of mullite decreased in coke.In the coke gasification process, content of quartz also increased gradually and the content of sillimanite was different in a certain degree.Finally, Mineral Phase Quantitative Analysis Method and Scanning Electron Microscope were used to analyze the influence of addictive on mineral transformation during coal coking and coke gasification process. The results showed that, the addition of Ca O made the content of quartz and γ-Al2O3 mullite(sillimanite) decrease. Ca O could react with other minerals in coal and let the content of minerals bearing Ca increase. After coke gasifiation,the content of minerals did not change much before and after reaction.The content of minerals had a great difference with the increase of Ca O. The addition of Ti O2 had slight influnce on the mineral transformation during coal coking and coke gasification process. Ti O2 could transform into anatase under the temperature of 300 ℃,then crystal type of anatase changed and it transform into rutile after coke gasification. The addition of Ca O had a big effect on the microstructure of coke surface. With the increase of Ca O, the white mineral on pore surface of coke increased, transformed from particles to needle-like mineral, and finally attached itself inside the pores. After coke gasification, the white mineral was adhered to the outer wall of coke with a layered distribution. The more Ca O was added, the more intensive the layered distribution would be, and the rougher the surface of pores would be. When adding Ti O2, the white mineral in pores of coke was very small and had a messy distribution. With the increase of Ti O2, the white mineral incerased and gradually gathered together. After coke gasification, the damage degree of coke pore wall was smaller than that with Ca O or without additive.