Mechanism Of Intensified Combustion Of PCI Coal By Catalysts And Its Fundamental Research For Application In Blast Furnace

Due to the higher requirements of government on energy conservation andemission reduction for iron and steel industry as well as the cost increase of ironmaking,optimizing energy efficiency of BF become an important measure for improving thecompanies’ competiveness. Pulverized coal injection (PCI) is a primary solution foroptimizing the structure of fuels and reducing the fuels consumption. This technologycould not only benefit the cost saving for ironmaking process, but could reduce thepollution of the environment from coke making process. Thus, increasing the PCI rate isthe objective for iron and steel companies. The burnout rate of pulverized coal (PC) inthe tuyere and raceway is an especially important restriction in BF. Researchers takemany measures to enhance the PC combustion in these zones. However, there arecertain gaps for China in PCI rate when compared with international advanced levels.Catalytic combustion is an important technique for utilization of fossil fuels.Although the research of catalytic combustion on coal started late, it developed rapidlyin recent years. Depending on the features of PC combustion in BF and the generationfor unburnt char (UBC), adding an adequate additive in the PC before injection into theBF could increase the utilization efficiency of fuel, and improve the gas/liquidpermeability of charging column, leading to a higher PCI rate. The effect and adaptationof additives are the innermost core that need to be evaluated before application ofcatalytic combustion for PCI coal. The PCI additive should have these featuresincluding obvious catalytic effect, no negative on iron-making process and inexpensive.The research results of catalytic combustion mechanism of PCI coal could provide abasis for selecting the PCI additives.This paper centered on the research target of catalytic combustion-ralted issues andits foundamental application on PCI technology. A careful theoretical analysis and anumber of experiments were carried out for investigating the catalytic combusitionbehavior, oxygen reserve/transmit during catalytic combusiton process, catalyticmechanism at high temperature, and compound additives for application in PCI.Firstly, the catalytic effect of different of additives on pulverized coal combustionwas investigated by Thermal analysis (TA). The effect of heating rate on pulverized coalcombustion process was investigated, and the isoconversional and Melak method is applied to establish the pulverized coal kinetics model. Combustion characteristic andkinetic study was carried out for investigating the typical catalyst, and the experimentalphenomena was explained by the microcosmic mechanism. Two novel additives wereproposed and the catalytic mechanism was analyzed:①Due to the active compoundin the dust such as Fe2O3, CaO and its special microstructure, BOF dust is the bestsubstance for catalytic combustion in the eight iron-containing powder;②Due to thedecomposition temperature of CaO2approached the coal pyrolysis, CaO2supports thecoal combustion based on its three effects, including the released oxygen, improving thechar morphology and catalyzing char combustion.To solve the insufficiency understand of the “oxygen transmit theory”, a Firstprinciple study of CaO,-Fe2O3and its derivative-FeO on catalytic combustion basedon density functional theory (DFT) was employed. The storage/transmit oxygen lawwas proposed based on DFT, and the results showed that:①The top of Ca-O bonds ofCaO(001) surface, the oxygen vacancies of Fe2O3(0001) and Fe2O3(1102) surface, andtop of Fe atoms on FeO(001) surface are the catalytic active sites, where have strongability of adsorption of O2result in generation of active oxygen species;②The carboncluster and CO preferentially reacted with these active oxygen species, and the productscould easily desorbed from catalytsts surface;③The reduction of Fe2O3(0001) andFe2O3(1102) surface by C and CO, leading the generation of active oxygen species.Then the catalytic route and discipline of oxygen reserve/transmit were proposed, andoxidation reaction mechanism was analyzed.In order to investigate the influences of applying catalysts on PCI and BFoperations, the catalytic combustion was simulated by using a drop tube furnace (DTF),and variation of structures as well as the reactivity of unburnt chars (UBC) wereexamined. For bituminous, the relative active sequence of catalysts to the burnout ratewas: CaO> Fe2O3> MnO2. For anthracite, it as follows: Fe2O3> CaO> MnO2. Ingeneral, these three catalysts exhibited better catalytic effect on anthracite thanbituminous coal. The catalytic features can be analyzed by these aspects:①Thestructural study shows that a decrease in particle size and surface area of unburnt charsformed form catalytic combustion, implying that the chemical reactions on char particleand pore surface were enhanced greatly by catalysts;②the X-ray diffraction analysisshows that chars became more ordered with catalysts addition. Nevertheless, the TGAand kinetic study results indicates that unburnt chars formed from catalytic combustionstill have a higher reactivity than pure unburnt char, these results imply that the catalytic combustion in PCI operation facilitates the combustion process of pulverized coal inraceway, as well as the following consumption of unburnt char out of raceway.To analysis the catalytic products in the following evolution in BF, the fusion andviscosity were investigated by the FactSage software, and the effect of products on cokeproperties was discussed based on experiment. It can be found that:①Fe2O3and CaOcould decrease the liquid temperature and viscosity below the1.5%of addition in coal;②The coal combustion products has not wettability on the coke surface, however, thecatalytic combustion product could infiltrated in the coke surface;③The reactionbetween UBC and coke is slow, therefore, there was little change on the morphology ofcoke. The pore diameter increased by coal ash, however, the effect only appeared on theentrance of pores and coke surface. The catalytic product could enter into the inside ofcoke, leading to the pore diameter increase.④The reactivity of coke prepared by coalash and UBC was decreased, while the catalytic products increased the coke reactivity,and this effect of Fe2O3is more remarkable than CaO.⑤Based on this results, itshould consider the intrinsic property of PCI and control the addition.Finally, a three component additive and a four component additives weredeveloped by the expand experiment. In the three component additive, the bestproportion of Fe2O3、CaO2and CaO was presented, which has obvious effect on PCIcoal combusion. In addition, when part of Fe2O3was replaced by BOF dust, thecombustion rate was increased by8.94%at the addition content of0.6%. The softwarewas used to forecasting the effect of catalytic combustion on the properties of tuyereand raceway, such as combustion kinetics, temperature, and gas composition. A forecastabout the operating parameter of BF after adopting the technique of catalyticcombustion was presented.To sum up the above results, in this paper, author carried out an exploratoryresearch on the catalytic combustion of PCI coal, and proposed a complex additivewhich is suitable for BF. Moreover, the influence of catalytic combustion on BFoperation was analyzed. These results could give a guidance on the combustionenhancement of PCI.