Fundamentals On Integration Of Coal Pyrolysis With Iron Ore Reduction Process

Catalytic pyrolysis is one of the major technologies producing liquid fuels and valuable chemicals from low-rank coal resources.The iron and steel industry is an important basic industry of the national economy.Various catalysts examined so far for coal catalytic pyrolysis still has lots of problems such as:high cost,difficult separation and recovery,etc.To solve catalyst problems and make up the shortage of high-grade iron ores,an integrated process combined coal pyrolysis with iron ore reduction was put forward.The process adopts low-grade iron ores to catalyze coal pyrolysis vapor to obtain light tar,while iron ore is reduced by the pyrolytic vapor at the same time.The distribution and formation of coal pyrolytic products catalyzed by iron ores,the mechanism of iron ore catalytic reaction,the mechanism of iron ore reduction,the technology of integration process of coal pyrolysis combined with iron ore reduction in both the fundamental and technological aspects have been investigated in this thesis.The major findings are listed as following:1.The impact on coal pyrolysis products by different iron ores were studied by Py-GC/MS.Results showed that limonite was the most effective one for promoting the formation of light aromatic hydrocarbons among four iron ores.The microstructure and physicochemical properties of iron ore showed positive correlation between the specific surface area of iron ore and the yield of light aromatic hydrocarbon.Using C19 alkanes and phenol as model compounds,it is found that deoxygenation is dominant in the pathways of formation of light aromatics considering the relation between oxygen-containing gas yield and yield of light aromatics.Results of coal effect exhibited that high oxygen content of coal has a relatively high percentage increase of light aromatics.It was indirectly validated that the catalytic effect of limonite on deoxygenation and transformation of oxygen-containing compounds in coal tar.2.The effect of operating conditions on coal pyrolysis products over iron ore catalyst was further studied by Py-GC/MS.The results showed that high temperature,high pressure in hydrogen atmosphere were beneficial to the formation of light aromatics.However,high pressure(0.1-0.9 MPa)and hydrogen atmosphere suggested no significant promotion on the limonite’s catalytic cracking.Limonite promoted the decomposition of phenols and oxygenates and formation of light aromatics.The experiments of multicycle and regeneration of limonite showed that the reduction of limonite to low valence iron increased the catalytic activity,and the limonite remained high activity after many cycles and regeneration.3.The reduction characteristics of iron oxides in pyrolytic vapor were studied on a fixed bed reactor.The effects of reduction temperature,reduction time and tar concentration on the reduction degree of ferric oxide were investigated using simulated pyrolysis gas and tar model compound as raw materials.The results showed that the reduction degree of iron oxide increases with the increase of reduction temperature and time.Pyrolysis gas only had a weaker reduction ability and addition of tar would promote the reduction of ferric oxide to cementite.Increasing the tar concentration in the pyrolytic vapor could promote the reduction process to obtain high quality iron products.The feasibility of high quality iron products attained from integration of coal pyrolysis with iron ore reduction was proved.4.Based on the results of experiments operated on Py-GC/MS and fixed bed reactor,a continuous apparatus of integration coal pyrolysis with iron ore reduction was designed and set up.The reaction conditions of coal pyrolysis were optimized.Under the optimized condition the catalytic cracking temperature and space velocity were examined.The highest light tar yield achieved was 3.78 wt%,and the content of the light tar is 85.12 wt%at pyrolysis temperature of 550℃,solid retention time of 15 min,the catalytic cracking temperature of 700℃ and space velocity of 7651 h-1.The light tar yield and content has increased by 6.70%and 29.42%,respectively,comparing with the thermal cracking under same condition.The products catalyzed by limonite showed that light tar mainly came from the cracking of heavy tar and the conversion of oxygen-containing compounds in tar.Oxygen-containing compounds during the catalytic process were analyzed to give further explanation.5.The physicochemical properties of limonite obtained from the integration of coal pyrolysis with iron ore reduction process,such as pore structure,phase composition,carbon deposition,microscopic morphology and reduction degree,were characterized.The basic reduction process was describe based on the results.Porous iron ore formed after the dehydration process was easily reduced to FexOy(y/x<1.5).Results has shown that space velocity is more significant than catalytic cracking temperature on reduction process.The reduction degree could be 24%under the optimal condition(700℃,3825 h-1),while iron ore products was composed of Fe3O4and FeO.Thermogravimetric analysis illustrated that carbonized ore had higher reactivity,which could be used as high quality raw materials for ironmaking.6.The exergy analysis diagram of integration of coal pyrolysis with iron ore reduction was established.Compared with the conventional process(separated coal pyrolysis and iron ore preheating process),the integrated process reduced the exergy loss by 10.4%.The reduced exergy loss could owe to the recovery of the physical exergy of high temperature cracking gas.Moreover,the carbonized iron ore could be applied in sinter plant.When the ratio of carbonized iron ore exceeds 50%,the heat produced from carbonized ore could be sufficient without additional coke breeze cost.