Pyrolysis Mechanism Of Lump Coal And Combustion Behavior Of Pulverized Coal Injection In COREX Melter Gasifier

COREX process is a smelting reduction ironmaking technology which has beenproved in industrialized production. The property and the high temperature pyrolysisbehavior of the lump coal have great influence on the fuel rate of the COREX process.The present operation status shows that the coal consumption in the COREX process ismuch higher than blast furnace process. The lump used in the COREX process isnon-coking coal which should meet the requirement of composition and particle size.However, lots of coal powder is produced during the production, transportation andscreening. Therefore, it is of great significance to make researches on the pyrolysis oflump coal, as well as the combustion of pulverized coal injection.Firstly, the pyrolysis characteristics and gas generation regularity of XLZ coal andDT coal were investigated by simultaneous thermogravimetric–mass spectrometricanalysis. Factors influencing on the pyrolysis behavior of the coal such as coal rank,heating rate, CO atmosphere were considered. In addition, the kinetics of the pyrolysisprocess was calculated according to the weight loss and gas evolution of the coal.Results show that the pyrolysis of the coal could be divided into three stages, the weightloss and weight loss rate of XLZ coal are greater than DT coal. The higher the heatingrate, the greater the weight loss rate and gas generation rate of the coal. However, thereis no significant change on the final weight loss. The CO atmosphere leads to thedecrease of the maximum weight loss rate and the delay of secondary reaction. The firstorder reaction model gives a better representation of the first stage, the one dimensionaldiffusion model is suitable for the second stage and the third order reaction model issuitable for the third stage. The second order reaction model can better describe theevolution of the gas species, and the average activation energy order of the gas speciesis CO₂>CO>CH₄>H₂>H₂O.Secondly, the high temperature pyrolysis behavior of Xinglongzhuang lump coaland Datong lump coal was studied by a self-made pyrolysis experimental apparatus.The morphology and structure characteristics of the lump coal after pyrolysis wereanalyzed, and the kinetics of the high temperature pyrolysis process of the lump coalwas calculated. Results show that the pyrolysis of the lump coal could divided into threestages, the moisture and absorbed gases are removed at the first two minutes, the mainpyrolysis of lump occurs from2to10min, and the polymerization reaction of char occurs after10min. the lump coal starts to crack during the pyrolysis, as well as largeamounts of porosity is produced. The FTIR analysis shows that the decomposition ofmain functional groups takes place before4min. As the pyrolysis temperatureincreases, the weight loss rate of the lump coal increases and the pyrolysis time isshortened. The XRD analysis shows that the carbon peak （002） and carbon peak （001）of the lump coal after pyrolysis become narrow and sharp, which indicates a highdegree of ordered carbon. The diffusion model can better describe the high temperaturepyrolysis of the lump coal, and the apparent activation energy of Xinglongzhuang coalis a little higher than that of Datong coal.Then, on the basis of similarity criterion, pulverized coal injection experimentalapparatus of the melter gasifier furnace was made to study the combustion behavior ofthe pulverized coal injection. Factors influencing combustion behavior of the coal suchas coal type, particle size, and temperature were considered. In addition, blendinginjection of bituminous coal and anthracite was carried out. Results show that thesmaller the particle size, the higher the combustion rate. The combustion rate alsoincreases with the increasing of temperature. It also shows that the combustion rate ofthe bituminous coal is higher that of the anthracite coal. Blending injection ofbituminous coal and anthracite coal with small particle size has good effect.Finally, a two-dimensional mathematical model of the tuyere zone in COREXmelting gasifier was built using CFD software to simulate the combustion behavior ofthe pulverized coal. Numerical simulation shows that the pulverized coal is quicklybrought into the tuyere zone by the pure oxygen and combustion reaction begins afterthe finish of devolatilization. The temperature is higher in the center of the tuyuer zoneand lower in the surrouding. The pyrolysis rate does not change with the increasing ofoxygen blowing rate, injection quantity, and injection angle. When the particle size ofcoal increased, the pyrolysis rate does not change at first, but when it increases to acertain degree, the pyrolysis rate decreased rapidly. The combustion rate decreasesrapidly with the increasing of oxygen blowing rate, injection quantity and particle size,and increases with the increasing of injection angle.