| In the process of iron ore sintering,the alkali metals remaining in sintering products,namely sodium and potassium,could result in problems like nodulation and lining erosion in blast furnace,endangering blast furnace operation and safe production,while alkali metal species entering the flue gas could aggravate the emission of fine particles.In the field of coal combustion,the high content of sodium in Zhundong coal results in serious fouling,slagging and particulate matter emission problems in the application process.In this paper,the migration and transformation behavior of alkali metals and technological measures to alleviate the related problems were systematically studied.Firstly,small-scale sintering experiments were carried out on a self-designed volatilization-condensation platform.The law of volatilization and migration of alkali metal species during iron ore sintering with charcoal and coke breeze as solid fuel was studied.It was found that alkali metal species entering the flue gas were mainly potassium chloride,followed by sodium chloride.Alkali metal species did not release until the bed temperature reached a certain critical point,and volatilization and migration behavior mainly occurred in the combustion layer of the sintering bed.There was alkali metal deposition in the preheating layer,where the bed temperature near the flame front was higher.In the high-temperature area,some deposited particles were molten and the deposition amount was lower.When the bed height and temperature decreased,the size of alkali metal particles increased and there existed coalescence between condensed particles.The alkali metal chlorides trapped in the lower bed position promoted the chlorination and removal of alkali metals in the bed.Secondly,the effects of technical parameters on volatilization and migration behavior of alkali metals were studied.With the increase of the proportion of iron-bearing dust,the removal rate of alkali metals went up,while their content in the sinter also increased.A rising fuel ratio could promote the removal process of alkali metals,and the removal effect under charcoal condition is less as good as coke breeze condition,which resulted from the difference of chemical composition and micromorphology between the two fuels.With calcium chloride added,the alkali metal content declined significantly,and the removal effect using charcoal as fuel was better than that of coke breeze.Combined with the chlorination removal process,using biomass charcoal for the replacement of coke breeze is a prospective development direction of iron ore sintering.Finally,surface modification of kaolin by intercalation-exfoliation method combined with acid leaching was carried out.Such method could effectively peel off the original layered structure,promoting physical adsorption by improving surface area and pore volume.Besides,by dehydroxylation of exfoliation process and the leaching effect of acid treatment,active adsorption sites increased,and chemical adsorption was thus promoted.The results showed that,with regards to sodium capture capability,the kaolin sample modified by the above method was superior to kaolin modified by intercalationexfoliation and raw kaolin.The effects of combustion temperature and blending ratio on sodium retention were also discussed.The time-resolved adsorption processes of sodium chloride vapor of kaolin samples were studied by gaseous alkali adsorption experiments.Four adsorption models were applied to analyze the adsorption kinetics,rate control steps,and potential mechanism.The analysis of fusibility showed that the modification process could reduce the effect of kaolin additive on the ash fusibility.The fusion temperatures of coal ash showed an increasing tendency after a decreasing process,with the increase of kaolin dosage.The optimal mixing proportion should be determined according to parameters such as slag discharging mode during combustion. |
