Analysis On Metallurgical Coke From Lignite Impact On Blast Furnace Smelting

Coking coal resources are scarce,and the resources of non-coking coal,such as lean coal and anthracite,low-rank bitumite and lignite,are relatively abundant in China.From the perspective of improving the indirect reduction of ore,coke should have high reactivity.Using the high reactivity characteristics of coke prepared from lignite,the indirect reduction of ore can be increased to improve the smelting process in Blast Furnace.On the other hand,because of the low price of lignite,the application of coke with the lignite addition has important social and economic value.Thus,it is necessary to carry out systematic research on the effect of lignite treatment method and dosage on the coke performance,and further to improve the utilization value of lignite.Therefore,Lignite,semi-coke,and modified lignite were taken as the research object.The influences of different samples on coke performance and the feasibility of using lignite to prepare metallurgical coke for blast furnace have been investigated in this study.The main contents and conclusions are as follows:First,the basic properties differences of lignite,semi-coke,and hydrothermal dewatered and acid washed lignite were investigated in terms of chemical composition,morphology characteristics,and pore suructure.The results show that if a large proportion of lignite replaces coking coal,the release of volatile matter would cause serious deterioration of coke performance due to the volatile matter content of lignite over 54%.After carbonization,the volatile matter content of semi-coke are greatly reduced and the ash content and the specific surface area increases.The aromaticity of semi-coke increases due to the content of aliphatic hydrogen decreasing and that of aromatic hydrogen increasing.Hydrothermal dewatering can effectively reduce the moisture and oxygen content in lignite.With the decrease of the content of hydrophilic functional groups,the aromaticity of hydrothermal dewatered lignite also increases.Meanwhile,acid washing can effectively reduce the content of ash,alkali metals,and alkaline earth metals.During the cokeing process,with the lignite and semi-coke addition increasing,the yield of coke decreases gradually.The ash content of coke obtained by adding modified lignite decreases with the increase of modified lignite addition.Second,the comparative study on the strength of coke obtained from lignite was carried out by drum test,thermal balance,SEM,BET and polarizing microscope.The results show that the temperature interval of the thermal decomposition for lignite is overlapped with that of the fluidity for coking coal and the decomposition products abstracts the hydrogen derived from coking coal leading to the decrease of caking property.Then,the uneven degree increases,finally resulting in the decrease of the coke drum strength.At the same time,lignite has a degradation effect on the optical structure of coke.With the increase of lignite addition,the anisotropy in coke decreases,and the isotropy,silky and fragmentary tissu increase,which finally leads to the decrease of the drum strength of coke as well.Lignite has the negative effect on the carbon structure of unreacted coke.Combined with double exponential model,it reveals that there is no limiting step of gasification reaction process at the content of lignite addition above 4%.The gasification reaction enhances the permeation of CO2 further into coke,and further degrades the strength of the lignite-enriched coke after reaction.Third,the influence factors of the strength of coke with the addition of semi-coke were analyzed from the microcrystalline structure,pore structure distribution and optical structure.The results show that when the ratio of semi-coke addition is less than 6%,the coke drum strength is higher than that of the coke without the addition of semi-coke.The semi-coke can promote the growth of coke crystallites and inhibit the formation of coke pores.And,as the proportion of lignite semi-coke increases,the Lc value of coke microcrystalline stacking height increases first and then decreases.When the semi-coke ratio is less than 4%,the microcrystalline structure of coke can be improved,and the strength before and after gasification can be improved.As the lignite semi-coke ratio increases,the anisotropic tissue in the coke optical structure plays an important role on resisting external stress.In terms of the reactivity and strength,the performance of coke with the ratio of semi-coke addition less than 6%is better than that of the coke without the semi-coke addition.Forth,lignite pretreated by hydrothermal dewatering and acid washing was studied for replacing the coking coal.The results show that the hydrothermal dewatered and acid washed lignite used for coking coal blending has been found to be effective in improving the strength of coke before and after gasification.The acid washing removes the alkali metal and alkaline earth metal in the lignite,inhibits the progress of the crosslinking reaction,thereby promoting the fluidity of the macromolecular network,and further increases the adhesion between the sample particles on the basis of hydrothermal dewatering.Hydrothermal dewatered and acid washed lignite for coking coal blending has been found to be an effective way to increase the strength of coke before and after gasification and the degree of microcrystalline ordering.Combined with kinetic analysis,hydrothermal dewatering and acid washing can increase the activation energy of coke gasification reaction,thereby inhibiting gasification reaction.Finally,the coke produced by adding different samples has the characteristics of high reactivity.And,the initial reaction temperature generally shows a positive correlation with the strength after reaction.Due to the high ash content of lignite and semi-coke,the amount of blast furnace slag and the physical heat loss increases,when the sample ratio is 4%,the use of lignite reduction can save 1.42kg/tHM and semi-coke coke 1.23kg/tHM.Due to the improved performance of lignite after pretreatment,the coke reactivity and strength are also optimized,which can save fuel by 0.54kg/tHM.