The Basic Theory On The Preparation Of Iron Coke And Characterization Of Its Structure And Property

The contradiction among China's huge steel output,shortage of high-quality coking coal resources and severe environmental problems is increasingly prominent.Therefore,it is essential to optimize the blast furnace ironmaking technology for realizing energy saving and emission reduction.Reducing the agent rate,and then improving the reaction efficiency in blast furnace stack is very significant,which has the potential in energy saving and emission reduction.Under these conditions,the researchers have put forward a new idea of developing high reactivity and high strength iron coke.However,the preparation and utilization of iron coke are facing some challenges from the poor understanding of effects of iron substances on coal pyrolysis and iron coke structure,unclear declaration of iron coke strength degradation and evolution behavior of iron coke in the blast furnace,which have the inhibiting effects on the the production and application of iron coke.According to the above problems,the influences of iron substances on coal pyrolysis and iron coke were declared initially for optimizing the addition type and amount of iron substances in the preparation of iron coke.Then the iron coke degradation mechnism was revealed by studying the change of carbon structure and metaplast?fluid phase?during thermoplastic stage of coal matrix pyrolysis,and the iron coke with high reactivity and high strength could be obtained by adding the suitable binder.Finally,the iron coke evolution behavior under alkali enrichment condition in cohesive zone of blast furnace and combustion behavior in the raceway were declared for the practical application of iron coke.The influences of iron substances on the thermoplastic properties and pyrolysis behavior of blending coal were analyzed by using Gieseler plastometer and Thermogravimetry analyzer?TGA?.Futher,the kinetic parameters were discussed.The results show that the thermoplastic behavior of blending coal decreases with the addition of different kinds of iron substances?Fe2O3?Fe3O4 and FeC2O4?.With increasing addition levels of Fe2O3,the thermoplastic behavior of blending coal declines heavily.The thermal weight loss behavior of blending coal varies with the addition of iron substances.The added iron substances can increase the apparent activation energy?E?and frequency factor?A?in the primary pyrolysis stage and secondary pyrolysis stage of coal samples,and the influence degree is ranked as Fe2O3>Fe3O4>FeC2O4.The E and A values in the main pyrolysis stage and secondary pyrolysis stage of coal samples increase with the asending of addition levels of Fe2O3.Iron coke was performed by mixing iron substances with blending coal during coking process.Then the effects of iron substances on iron coke mechnical and thermal properties were analyzed.Further,the influences of iron substances on iron coke structure were investgated by using X-ray diffraction?XRD?,Raman spectroscopy,N2adsorption and Mineral quantitative analysis method.Finally,the optimal iron mineral addition type and level for the preparation of iron coke were obtained.The results show that the addition of iron substances can reduce iron coke mechnical strength,coke strength after reaction?CSR?,aromaticity,microcrystalline size,graphitization degree,crystalline volume and carbon order degree,increase coke reactivity index?CRI?and pulverization rate.Moreover,iron substances are mainly transformed into metallic iron after coking process,and some metallic iron is converted into Fe3O4 after iron coke gasification.The iron coke mechnical strength decreases with the descending of carbon order degree and ascending of metallic iron content.The CRI increases while the CSR decreases when the crystalline volume and carbon order degree decrease,and metallic iron content increases.Further,adding 3%Fe2O3 has the most suitable effects on the properties and structure of iron coke.Thus,Fe2O3 with its level of 3%has been used as additive in the preparation of iron coke.Two-stage solvent extraction,involving acetone?light extraction?and tetrahydrofuran?heavy extraction?,was used to obtain metaplast?fluid phase?materials from zhujiao coal matrix during the thermoplastic stage of pyrolysis.The detailed components of metaplast?fluid phase?and its structure transformation during coking process were analyzed.Then the effects of Fe2O3 on thermal behavior and structure transformation of zhujiao coal and blending Coal matrix were investgated by using Gieseler plastometer,TGA,XRD,Fourier transform infrared spectroscopy?FT-IR?and Gas chromatography-mass spectrometer?GC-MS?.Finally,the iron coke strength degradation mechanism was declared.The results show that the metaplast?fluid phase?consists of monocyclic benzene compounds and unbranched alkanes with carbon atoms of 19-26.The structural transformation of the metaplast?fluid phase?in thermoplastic stage could be divided into two stages:formation and stabilization of the metaplast,and the cross-linking and re-attaching of the metaplast to coal char.The added Fe2O3inhibits the cleavage of Cal-O,Cal-S,Cal-N,Cal-Car and Cal-Cal bonds during thermoplastic stage and further reduces the production of ethylbenzene,o-xylene and unbranched alkanes with carbon atoms in 24-26,and then decreases the amount of metaplast.These result in the decrease of aromaticity and average stacking height,increase of interlayer spacing of the crystallite,aliphatic chain length and hydrocarbon-generating potential of coal matrix,further cause maximum Gieseler fluidity and plastic range decreasing,and finally result in the iron coke strength declining.The blending coal tar components were collected by a self-made tar collecting device and determined by GC-MS.Then the coal tar was clarified as the additive for the improvement of iron coke strength.Further,the effects of coal tar on iron coke properties and structure were analyzed by coke reactivity measurement device,XRD and N2 adsorption.The results show that the high-temperature decomposition products of complex polycyclic compounds and aliphatic compounds in coal tar are similar to the components of metaplast?fluid phase?.So,the coal tar has been chosen as the additive for optimizing the iron coke strength.The addition of coal tar can increase the graphitization degree,aromaticity and crystalline size,and reduce the surface area of iron coke,making the iron coke mechanical strength and CSR increase.Furthermore,the above parameters reach the best values when the coal tar addition level is 3%.Based on the above analysis,coal tar with 3%addition level has been selected as the strength optimization binder for iron coke.Furthermore,the iron coke with CRI of 40.21%and CSR of 55.86%can be obtained.The effects of alkali carbonate on ordinary coke and iron coke were analyzed comparisely by using coke reactivity measurement device,XRD,N2 adsorption and Mineral quantitative analysis method.The combustion behavior of ordinary coke and iron coke were discussed comparisely by studying their thermogravimetric behavior,combustible index,calorific value and kinetic parameters.The results show that the addition of alkali carbonate causes the decrease of iron coke average stacking height,lateral size and crystalline volume,and increase of surface area,resulting in the asending of iron coke reactivity and desending of iron coke strensth.The added alkali carbonate would transform into nepheline bearing Na or K after iron coke gasification.The influences of alkali carbonate on properties and structure of iron coke are greater than that of ordinary coke.The corresponding temperature of ignition,burn-out and maximum combustion rate of iron coke are lower than that of ordinary coke,and the maximum combustion rate,flammability index,and calorific value are relative higher.The E and A values of iron coke combustion are lower than that of ordinary coke as much as 17.179 kJ/mol and 29.374 s^-1,separately.This indicates that the iron coke has the better combustion reactivity and activity than ordinary coke.