Study On Maximized Utilization Of Physical And Chemical Energies In Direct Reduction Shaft Furnace

With the rapid development of global industrialization,climate change,resources and environment issues have become the biggest global challenges.Iron and steel industry is the basic industry of the national economy,but meanwhile it also account for the bulk of energy consumption,more than 60%of which is consumed by ironmaking process.Therefore,developing the green ironmaking industry is the key to achieving the energy conservation and emission reduction goals.So far,there still remains the problem of inadequate utilization of chemical energy of reducing gas in ironmaking reactor because of the unbalance between the physical and chemical energies of reducing gas,especially in direct reduction shaft furnace with hydrogen-rich gas as reducing gas,which causes greater heat requirement for endothermic reaction of hydrogen reduction.The material and heat balances results show that,compared with the gas requirement by chemical reaction,a much greater quantity of gas has to be blown into the furnace to satisfy the heat balance,leading to a high fresh gas consumption,high reduction potential of top gas,low gas utilization ratio,and high energy consumption and so on.To solve the above problem,top gas recycling processes(TGR processes)are proposed first in order to enhance the utilization of carbon and hydrogen.Secondly,a new method is proposed for modifying the shaft furnace with oxygen blowing,including direct oxygen blowing(DOB)and indirect oxygen blowing(IOB)processes.In the new process,cold oxygen is blown into the upper zone of the shaft furnace for the combustion of some gas to transform the excessive chemical energy into thermal energy,which can break the limit of demand for physical energy.As a result,the reducing gas consumption is significantly decreased,the temperature and reduction rate in the upper zone are increased.Therefore,the utilization of gas is enhanced and energy consumption is reduced essentially.At last,the new processes with both oxygen blowing and top gas recycling(OB-TGR processes)are proposed.In this dissertation,the static process model,1D kinetic model and 2D kinetic model are developed to simulate and evaluate the proposed shaft furnace processes.The results may provide the theoretical foundation for further development of such ironmaking processes.The main contents and results are as follows.(1)The static model is established to simulate the material and energy balances of each process and get the optimal processes.For the TGR processes,the simulation results show that,compared with TGR1 and TGR3 cases,the TGR2 case has the lowest reduction potential of top gas,total energy consumption and CO2 emission,and its energy utilization ratio is the highest.Therefore,TGR2 process is the optimal process.For the studied processes with oxygen blowing,the oxygen consumptions are 13.21,24.99 and 16.41 m3·tDRI-1,respectively.Because of the current technical limitations,it is difficult for DOB process to be applied in industrial production.For the IOB processes,the reduction potential of top gas,total energy consumption and CO2 emission in IOB2 case are lower than those in IOB1 case.Therefore,IOB2 process is the optimal process.For the studied OB-TGR processes,the oxygen consumptions are 35.39,19.90,and 34.22 m3·tDRI-1,respectively.In OB-TGR2 case,compared with OB-TGR1 and OB-TGR3 cases,the reduction potential of top gas,total energy consumption and CO2 emission are the lowest,and the energy utilization ratio is the highest.Therefore,OB-TGR2 process is the optimal process.(2)The 1D kinetic model is established to simulate the proposed optimal processes from the operation conditions calculated by the static model.In TGR2 case,the metallization ratio of DRI decreases by 1.96%compared with the base case.In IOB2 case,the upper reducing gas is blowing at 4.75 m in depth where the wustite reduction starts.Because of the low reduction potential of upper inlet gas,the reduction potential in the upper zone is too low for wustite reduction.As a result,the metallization ratio of DRI decreases by 15.21%compared with the base case,which can not satisfy the industrial requirement.By contrast,in OB-TGR2 case,the high temperature and high reduction potential reducing gas is blown at 3.83 m in depth,which causes high temperature and high reduction potential in the upper zone.Therefore,the kinetic condition for reduction reaction is perfectly satisfied and the reduction rate is increased.The surplus gas for wustite reduction in the top area and reduction potential of top gas decrease greatly and the metallization ratio of DRI increases.In addition,in OB-TGR2 case,the total energy consumption is the lowest and the energy utilization ratio is the highest.Therefore,OB-TGR2 process is the optimal process in the study.(3)To study the radial distribution of process parameters,the 2D kinetic model is established to simulate OB-TGR2 case with the operation conditions from both the static model and 1D kinetic model.In OB-TGR2 case,the upper reducing gas can increase the gas velocity,temperature and reduction potential in the near-wall region of upper zone.Therefore,the kinetic condition for reduction reaction is improved and the reduction rate is increased in this area.As a result,the surplus gas for wustite reduction in the top area decreases greatly,the reduction potential of top gas decreases by 8.38%,the utilization ratio of top gas increases by 3.91%,the metallization ratio increases greatly in near-wall zone and the metallization ratio of DRI increases by 1.97%.However,OB-TGR2 case not only fails to promote the gas velocity in the upper center zone,but also deteriorates the gas flow in the lower center zone.Therefore,in the central zone,both the reduction potential and the kinetic condition for reduction reaction are deteriorated.As a result,the metallization ratio of DRI at center decreases,and the metallization homogeneity of the DRI product is deteriorated.