Numerical Simulation And Optimization Of Coal Gasification And Flash Ironmaking Coupling Process

Traditional long process ironmaking process includes sintering,coking,blast furnace ironmaking and other processes,which will cause serious environmental problems.At the same time,the scarce metallurgical coke resources will cause problems such as cost increase and energy consumption.After years of development,the traditional blast furnace ironmaking technology has made progress in reducing fuel consumption and improving energy utilization,but the fundamental structure with coke as the skeleton has not changed.Therefore,it is impossible to eliminate the high pollution and high energy consumption process from the source.In recent years,flash ironmaking has attracted more and more attention as a new non-blast furnace ironmaking process,which uses high-temperature reducing gas to directly reduce small-sized ore particles in the entrained flow bed,so as to obtain high-quality sponge iron in a very short time.Based on the laboratory development of flash ironmaking technology,a pilot-scale industrial application scheme,namely flash ironmaking coal gasification coupling process,was proposed in this thesis.In this scheme,the mature coal gasification process was used to prepare the reducing gas,and the coupling process was feasible to reduce the repeated conversion in the same reactor.The comprehensive utilization efficiency of energy and materials was improved at the same time.In this thesis,the possible problems that appeared in the coupling process were investigated using the thermodynamic model and numerical simulation.The main contents and conclusions are as follows:(1)The flash reduction experiments were carried out firstly in the laboratory-scale equipment.The experimental results show that the reduced iron with a 60%reduction degree can be obtained by reducing 45-100 ?m hematite particles at 1550?in the CO atmosphere,and more than 90%reduction degree can be achieved at 1450? in H2 atmosphere.By SEM-EDS,it was found that the slag and iron separated from each other when the particle temperature was close to the melting temperature,which should be attributed to the surface tension.As observed,the dense iron core was wrapped by FeO when the reductio degree was lower than 60%However,when the reduction degree was higher,the dense iron phase does not appear until 1550?,because of the high melting point and poor fluidity of the iron phase.Finally,the slag phase was repelled to the surface of the iron phase by the surface tension.The CFD numerical model based on the high-temperature reduction kinetics was established simultaneously,in which the kinetic parameters in the literature were used to predicated the experimental values,and good agreements were achieved.(2)Based on laboratory-scale flash reduction research,the pilot-scale coupling process was further investigated by the heat balance model.The optimized operation conditions were explored by investigating cases with different material ratios.The results show that the equilibrium temperature decreases continuously with decreasing oxygen/coal ratio and increasing ore/coal ratio.In some cases,the equilibrium temperature was lower than the maximum output temperature,which indicates the insufficient heat during the coupling process.With increasing ore/coal ratio,the reduction degree(R)shows a downward trend,while the utilization rate of reducing gas increases.Furthermore,the heat balance model of the molten pool was also established using a step-by-step balance and was further used to predict the ideal products.According to the specified technical indexes:liquid temperature(>1450?),metal yield(>95%),and carbon residue(<90 kg/h),the feasible operation range can be finally determined.The optimized case(mcoal=0.80,moxygen/mcoal=0.85)in the range can be determined.(3)Furthermore,the CFD numerical simulation for the coupling process was established.The simulation results show the stable turbulent structure formed by the sudden expansion structure,which mainly includes three regions:jet zone(?),reflux zone(?),and plug flow zone(?).According to the particle path analysis,the recirculation region in the flow structure has a significant effect on the residence time.The pilot-scale coupling model predicted a more than 95%reduction degree in basic case,which confirmed the feasibility of simultaneous production of reduced iron and coal gas in the single reactor.With the increase of the ore/coal ratio,the shape of the high-temperature zone gradually changed from "?" type to"?" type,and the low-temperature center appeared near the nozzle.According to the different cases,two feasible schemes are provided.The first one is to obtain high-quality sponge iron(R>99%)and high-quality syngas(?>90%)at the same time under the condition of low ore/coal ratio(<0.4);the second method is to obtain qualified primary reduced iron(R=75.57%)and syngas with higher calorific value(?=71.52%)at a high ore coal ratio(=1.6)?(4)The exergy analysis method was introduced to investigate the transition process of the key coupling process and the whole process.The exergy flow diagram of the coupling process developed by step-by-step heat balance shows that the exergy of reducing gas was transferred into reduced iron and effectively stored.Due to the irresivisble loss in the transition process,the final efficiency of the coupling process is 76.0%,which is slightly lower than 77.5%of efficiency in the pure coal gasification.However,since the loss of reduced iron in the subsequent utilization process was relatively low,the advantages of the poly-generation system can be expected after establishing the whole process based on the flash ironmaking coal gasification process.As we can see,the exergy efficiency(49.4%)of the flash ironmaking-coal gasification-power generation process is much higher than the traditional coal gasification-power generation process(44.0%),in which the value stored in reduced iron accounts for 17%of the total exergy output.The efficiency of flash ironmaking-coal gasification-methanol synthesis-power generation system was as high as 56.3%,which proved that the coupling process can utilize the reduced iron to store the exergy,to achieve the purpose of increasing system efficiency.