Numerical Simulation Of Pulverized Coal Flow And Combustion Characteristics In Modern Blast Furnace Raceway

PCI(Pulverized Coal Injection) has been considered the most economic methodto reduce the coke consumption in iron-making industry. The energy consumption andproduction costs are significantly influenced by the performance of pulverized coalcombustion and gasification in blast furnace. Based on the theory of Two-Phase Flowand Foundation of Coal/Coke Combustion, a Two-Dimensional model provided byFluent which include UDF second development, was established to validate theapplication of this new model on predict combust influence under differentparameters including pulverized coal particle size, volatile content, blast temperature,blowing rate of Oxygen enrichment and coal injection rate.On the basis results of Two-dimensional computation a comprehensiveThree-Dimensional model was developed to compute gas-powder flow, regionaltemperature, gas composition distribution and pulverized coal burnout rate in aphysical blast. The results indicated that corresponding to the gas flow, the coaltrajectories have two different flow pattern:(1) a main coal plume located along thebottom of the raceway; and (2) a large-scale recirculation of the fine a particlesaround the raceway centre. This is because the large particles tend to maintain itsinitial momentum and the fine particles are easier to be affected by the turbulence andthen dispersed more widely. Combined with Energy equation, the preheated coalpowder started to release volatile after escaped from tuyere, oxygen around theparticles converted to carbon dioxide or carbon monoxide rapidly, meanwhile thevolatile&residual carbon combustion heat raised the temperature of racewaysignificantly. Besides this, an additional observation shows that fine particles showshorter preheating stages, followed by the earlier release of volatile at faster rates.This is because fine particles have higher surface area/mass ratios, leading to fastertemperature rises.By using the Control Variable Method, the effects of three key operatingconditions on coal/coke Flow-Thermal-Chemical behaviors are investigated,including blast furnace temperature, hot air oxygen enrichment and coal injection rate.The conclusion says that oxygen enriched air could not only increase the coal burnoutin the raceway but also generates more carbon monoxide, going even furtherenhanced the calorific value of blast furnace gas. Compared with hot air oxygenenrichment, the increase of blast furnace temperature and coal injection rate played alimited role in improving the coal burnout and particle temperature:(1) when the blasttemperature is higher than1300K, the final burnout of coal powder will not increasesignificantly and(2): PCI=200kg/tHM is regarded as a particular economic injectionrate, both burnout and coal injection rate performed well, under current physical conditions.Pulverized coal burnout value in this Three-dimensional model is lower thanprevious Two-Dimensional study, this is because previous calculation has not takenthe coke bed heat-absorbing effect into account.