Study On Characteristics Of Reduction Degree Of Porous Medialimonite Based On Reduction Roasting

Steel material is one of the important basis for national economic development in along period of time. However, at present, our country’s high-grade iron ore resources areincreasingly scarce. The efficient pick of low-grade and hard-to-separate iron representedby limonite has become a problem that must be solved for realizing sustainabledevelopment of the economy and society in china.The traditional roasting reduction of limonite is mainly carried out in the shaft furnace,boiling furnace and rotary kiln, etc. But these devices with the shortcomings of high energyconsumption and the long restoration time cause the low quality of related technology andoverall structure of the equipment, which make the quality of reduction roasting poor,management and operation difficult, structure complex, investment high and dustcollection system complex. Based on the development projects of magnetic roasting ofInner Mongolia limonite in circulating fluidized bed, in order to understand the mechanismof reduction and the dynamic behavior of fine iron ore deeply, considering the process ofgas reduction of iron ore, this paper builds a mathematical model to simulate the behaviorof magnetic roasting of limonite, which can provide a theoretical basis for the applicationof low-grade limonite.In this paper, the kinetics of CO reduction of limonite was studied by simultaneousthermal analyzer, and the structure of limonite after dehydration was analyzed by scanningelectron microscopy. The changes of specific surface area and porosity were also measuredby specific surface area and porosity analyzer. The results show that the reaction ofmagnetization roasting for limonite is very easy to perform. Within a given range ofconditions, the reaction will depend on the ambient temperature, the concentration ofreaction gas and the size of the particles. The activation energys of the limonite aredetermined by the results of simultaneous thermal analyzer, which show that fine particleshave a lower activation energy. According SEM images of the limonite after dehydrationand the classification of BET adsorption isotherm, it can be seen that limonite has a higher porosity after dehydration, and the adsorption isotherms of limonite are more in line withthe type Ⅲ adsorption isotherm.According to the actual situation of the magnetization roasting, the dynamic modelof the gas-solid reactions include the equation of non-steady-state heat transfer equationwithin the particle, the equation of gas transmission in pores and heterogeneous chemicalkinetic equation basd on the improved random pore model describing the pore sizedistribution. The finite volume method with implicit formulation was applied to solve thecontrol equations. The relationships of reaction rate and the magnetization roasting timewere obtained by simulation with MATLAB under these conditions of differenttemperatures, different initial gas concentrations, different particle sizes and differentinitial porositys. The concentration distributions of carbon monoxide were obtained underdifferent porositys, and the concentration distributions along the radial direction of thelimonite particle were also studied under different of particle sizes and differenttemperatures. The prediction results of model are in good agreement with the experimentalresults. Increasing the reaction temperature can significantly shorten the completion timeof the reaction. The roasting reaction rate of limonite is approximately proportional to theconcentration of the reduction gas of CO. At elevated temperatures, the effective depth ofpenetration of CO is decreased. It will affect the interior transfer of reaction gas in theparticles when the particle size becomes large. It can be more conducive to the reaction ofthe limonite if the limonite has a large porosity.