Heat Balance And Thermodynamic Calculation Of Iron Production By COG In Shaft Furnace Process

With the deterioration of the environment,the concept of sustainable development has gradually become the consensus of the international community.Iron and steel industry is one of the largest carbon dioxide emission industries in the world.As the "leading" industry of iron and steel manufacturing industry,whether iron making can adapt to the requirements of urban steel plants largely determines the fate of iron and steel plants.Therefore,energy saving and emission reduction of iron making system is very important.Compared with the traditional long process of blast furnace ironmaking-converter steelmaking,the short process of direct reduction ironmaking(or steel scrap)-electric furnace steelmaking has no sintering,coking and other processes.Therefore,it has many advantages,including short process,low CO2 emission and low energy consumption.In addition,its energy saving and emission reduction advantages are also very obvious.Besides,the direct reduction iron belongs to pure iron,which is most suitable for producing pure steel in electric furnace.It can significantly increase the added value of steel and promote the supply side reform.At present,the most mature direct reduction process is gas based shaft furnace process,in which natural gas is used as primary energy.However,the development of gas based shaft furnace process is limited in China and other countries lacking natural gas,Therefore,scholars at home and abroad have done a lot of research,and the results show that coke oven gas can replace natural gas.However,due to the different composition and reduction capacity of coke oven gas and natural gas,the yield of metallic iron is different.In this paper,based on heat balance and thermodynamic calculation,the yield of metallic iron of coke oven gas used in shaft furnace process was investigated and analyzed,The results are shown as follows.(1)The consumption of coke oven gas as heat source is greater than that of reducing agent.There are two ways to replenish the heat of shaft furnace,one is "Reforming outside shaft furnace+shaft furnace reduction" process in which cracking reaction takes place in heating furnace,and the other is "Gas zero reformation+COG supplement" process in which cracking reaction takes place in shaft furnace.The yield of metallic iron is different with different ways.(2)In the process of "Reforming outside shaft furnace+shaft furnace reduction",the yield of metallic iron decreases with the increase of iron reduction temperature.At 850℃ and 900℃,the yield of metallic iron of 100mol uncracked coke oven gas is 2.352 kg/100mol GOG and 2.314 kg/100mol GOG respectively under ideal conditions.Under the actual conditions of 65%iron ore grade,350℃ top gas temperature and 100%metallization rate,they are 2.238 kg/100mol GOG and 2.205 kg/100mol GOG respectively.(3)In the process of "Gas zero reformation+COG supplement",the yield of metallic iron first increases and then decreases,and there is a peak value.At 845℃ and 900℃,the yield of metallic iron of 100mol uncracked coke oven gas are 2.629 kg/100mol GOG and 2.582 kg/100mol GOG respectively under ideal conditions.Under the actual conditions of 65%iron ore grade,350℃ top gas temperature and 100%metallization rate,at 850℃ and 900℃,the yield of metallic iron of 100mol uncracked coke oven gas are 2.497 kg/100mol GOG and 2.461 kg/100mol GOG respectively.(4)Under the two ways of heat supplement,the heat income of the heating furnace is far greater than the heat consumption,and it is more than twice of the heat consumption.Therefore,it is necessary to adopt the process of "Gas zero reformation+COG supplement",in order to provide part of the heat to the shaft furnace,so as to improve the utilization rate of coke oven gas and increase the yield of metallic iron.(5)The yield of metallic iron decreases with increasing top gas temperature.Taking the actual conditions of 65%iron grade,100%metallization rate and 850℃ iron reduction temperature as an example,when the temperature of top gas is 300℃,350℃ and 400℃,the yield of metallic iron of 100mol coke oven gas are 2.709 kg/100mol GOG,2.497 kg/100mol GOG and 2.288 kg/100mol GOG respectively under the process of "Gas zero reformation+COG supplement".(6)The yield of metallic iron increases with decreasing metallization rate of direct reduced iron.Taking the actual conditions of 65%iron grade,350℃ top gas temperature and 850℃ iron reduction temperature as an example,when the metallization rate of direct reduced iron is 100%,95%and 90%,the yield of metallic iron increases,The yield of metallic iron of 100mol coke oven gas are 2.709 kg/100mol GOG,2.740 kg/100mol GOG and 2.772 kg/100mol GOG respectively under the process of "Gas zero reformation+COG supplement".The findings from this work may provide guidelines for choosing optimal parameters for an actual shaft furnace process.It has important theoretical and practical significance for the development of China’s direct reduction process,the reduction of CO2 emissions in the iron and steel industry,and the integration and innovation of new technologies.