The Key Technology Of The Preparation Of All-hematite Oxidized Pellets By Grate-rotary Kiln

With the development of blast furnace burden structure and iron and steel short process smelting,the demand of oxidized pellets increased gradually.But the magnetite resources for production oxidized pellets are increasingly scarce,the production of oxidized pellets by hematite as raw material has gradually become a focus of attention.However,the production of pellet oxidized hematites existed high preheating temperature and calcination temperature,poor performance of calcination consolidation,high reduction expansion rate,and the rotary kiln occurred ring-forming frequently and so on.Therefore,the key technologies of the preparation of hematite pellets with grate-kiln system are researched,which will have important practical significance for the preparation of oxidized pellet with hematite.Due to the increasing shortage of magnetite resources,a few grate-kiln pelletizing production enterprises began adding hematite to produce oxidized pellets,when hematite was added to a certain extent,the green ball was burst,the powder was much produced,the compressive strength were reduced and the rotary kiln ring-forming was occurred.In this paper,the first domestic hematite grate-kiln pellet project of two million t/a as the research background,the difficulties of hematite pellets are analyzed,and the engineering application will be achieved,which will provide successful examples and practical experience for production of hematite pellets.The pelletizing performance,the drying and preheating performance and the roasting properties are studied systemly.The suitable parameters of ball forming process and drying and preheating and roasting process are determined.The preparation process of raw ball are further optimized,the key technologies of grate and kiln are researched and developed.In grate-kiln pellets production,basing on hematite pellet kiln powder more easily soft melting to cause ring-forming,and the advantages of oxygen enriched roasting,R&D and application of the new process of thermal screening for rotary kiln to reduce ring-forming first time,and the oxygen enriched roasting technology is applied.The project application of hematite grate-kiln pellet showed that,the process flow achieves intensification,the logistics transportation accumulation time is only 6.04min,the solid waste resources is used again.Studying on Optimization of thermodynamic system of grate-kiln,the process energy consumption of pellet production reduces from 37.03kgce/t to 32.86kgce/t,the binder consumption is only 10.3kg/t,the compressive strength of pellets reached 2707N/P.Comparing with the South American belt type roasting machine,the process energy consumption is much the same,but the quality of grate kiln oxidized pellets is better,and the total investment of the grate-kiln is lower 20%than the belt type roasting machine.The influence of the dosage of serpentine on the properties of hematite pellets showed that,the serpentine could be conducive to improve the performance of green ball,improve compressive strength of the preheated pellets and the roasted pellets,and decrease the reduction expansion rate of oxidized pellets.The microstructure of oxidized pellets showed that,which occurred infinite solid solution of MgO and Fe₂O₃ during the roasting process,the solid diffusion reaction was promoted,so as to improve the consolidation strength of oxidized pellets.The serpentine hematite oxidized pellets industrial test research showed that:the comprehensive cost is decreased ?35.87 per ton,the compression strength and metallurgical properties of pellets are improved.During the blast furnace with addition of serpentine pellets,the qualified rate of hot metal reach 99.97%,the ratio of first-grade products reaches 75.06%.The quality of hot metal are improved,the slag basicity increase from 1.14 to 1.15,and the w?MgO?/w?Al₂O₃?reach up to 0.58.