Mechanisms Determining Softening/Melting and Reduction Properties of Lumps and Pellets
作者单位：Centre for Ironmaking Materials Research Discipline of Chemical Engineering School of Engineering Faculty of Engineering & Built Environment The University of Newcastle
会议名称：《“第十届中国钢铁年会”暨“第六届宝钢学术年会”》
会议日期：2015年
学科分类：080602[工学-钢铁冶金] 08[工学] 0806[工学-冶金工程]
基 金：BHP Billiton for financial support
关 键 词：blast furnace cohesive zone softening and melting bed properties
摘 要：Although softening/melting tests are widely used to assess ferrous material properties in the cohesive zone of a blast furnace,there is little understanding of the mechanisms causing the softened bed to densify.Quenched beds of three acid feed materials–a porous hematite goethite lump（PHGL）,a dense high silica lump（DHSL）and a high silica pellet（HSP）-were used to provide information on the role of silica and porosity on softening and melting behavior.Reduction of all three materials is topochemical,resulting in the formation of a distinct metallic iron shell and a wustite core.The efficiency of the wustite to iron reduction process is dependent on the penetration of reducing gas through the shell and the structure of the core.This is enhanced for samples with higher porosity and low silica content,which minimizes the formation of fayalite,a low melting compound formed from the reaction of silica with iron oxide.With higher levels of fayalite,the core can become sealed off from the reducing gases,leading to greater levels of wustite that must undergo direct reduction at temperatures above 1000℃.Furthermore,the presence of fayalite in significant quantities can act as a lubricant between particles,facilitating sliding and bed densification further reducing bed permeability and reduction efficiency.For the three materials tested,the higher porosity and lower silica content of the PHGL improved the low temperature reducibility of the sample relative to DHSL and HSP,leaving much less wustite for direct reduction.This study also shows that increasing the reduction rate of wustite to iron also has two other benefits.Firstly,with higher reducibility,fayalite levels decrease because iron oxide,not metallic iron,is required in its formation.Secondly,the level of exuded liquid wustite in inter-particle pores decreases which will improve cohesive zone permeability.These results suggest that as a complementary feed to basic sinter,a porous low-silica lump such as PHGL should yield better performance in a blast furnace.