| The flue gas discharged from sintering process accounts for more than 40%of the total waste gas in the steel industry,and it is also the most serious pollution source.Due to the high dust content and complex composition of pollutants in sintering flue gas,as well as the large fluctuation of flue gas amount and pollutant content,the method of flue gas end-treatment cleaning is not only difficult in the level of technology,but also has high cost of investment and operation.Flue gas recirculation sintering is an economical and feasible emission reduction technology.The principle is to reuse directly part of the sintering flue gas,which can not only reduce the emission amount of flue gas,but also make use of flue gas heat and CO latent heat.Besides,some pollutants are degraded in flue gas recirculation sintering process,which can achieve good energy saving and emission reduction effect.However,the sintering flue gas contains a lot of steam and dust,and its O2 concentration is also low,which are unfavorable factors for sintering.At present,there are few researches on the optimization of flue gas recirculation in combination with oxygen enrichment and fuel gas injection.In this work,the integrated sintering process with oxygen enrichment and coke oven gas injection,as well as flue gas recirculation is proposed to the optimize the flue gas recirculation sintering process.The influence of oxygen enrichment and coke oven gas injection on iron ore sintering process and sinter quality were studied with numerical simulation.The main research contents and results are as follows.(1)A static process model of iron ore sintering process to study the solid fuel consumption,CO2,SO2 and flue gas emission of sintering process with flue gas recirculation,oxygen enrichment and coke oven gas injection under different process parameters.The advantages and disadvantages of flue gas recirculation,oxygen enrichment and coke oven gas injection was evaluated preliminarily.The results of model also calculation provide also the boundary conditions for the subsequent numerical simulation.(2)Gas flow,heat and mass transfers,and various physical and chemical reactions in iron ore sintering process were analyzed.Base on the conservation equations of gas flow,heat transfer,mass transfer,and considering the physical and chemical phenomena in iron ore sintering process,a transient two-dimensional mathematical model was developed to simulate the integrated sintering process.Emphases are place on mass-thermal coupling,multi-reaction coupling,water evaporation and condensation,coke powder combustion,solution loss reaction,carbonate decomposition,iron oxide reduction and oxidation,NOx formation and reduction,gas fuel combustion,mineral melting and solidification,sintering bed structure variation.The model was validated by sintering pot experiment data.The temperature profile in sintering bed was analyzed base on simulation results,and charactoristic parameters such as the highest temperature of material layer,melting zone residence time,melt quantity index,cooling index and sinter yield were obtained.The sinter yield and quality evaluation system was established based on the temperature distribution of sintering bed,and was used subsequently to analyze and evaluate various sintering processes.(3)Nunerical simulations were carried out to study the sintering processes with flue gas circulation,oxygen enrichment and coke oven gas injection respectively.The effects of flue gas circulation(recirculation position,qunatity and covering area),oxygen enrichment(oxygen injection location,oxygen concentration,injection area)and coke oven gas injection(injection location,quantity and covering area)on the temperature and composition fields of gas and solid phases in sintering bed,as well as the sinter yield and quality and NOx emissions were investigated and clarified,which also provide the foundation data and boundary conditions for the subsequent optimization of integrated sintering process.(4)The integrated sintering process with flue gas recirculation,oxygen enrichment and coke oven gas injection was optimized by considering comprehensively the waste heat utilization,sold fuel consumption,NOx emission,and quality and yield of sinter product.The optimum integrated sintering process was obtained.The quality and efficiency improvement and energy saving and emission reduction effects of the optimized process were analyzed.To sum up,aiming at the issues of low oxygen content in flue gas,insufficient waste heat utilization,poor sinter quality of the surface layer,low yield of sintering production,and environmental pollution of sintering process with merely flue gas recirculation,the proposed integrated sintering process with flue gas recirculation,oxygen enrichment and coke oven gas injection were studied by static process model and numerical simulation.Optimun integrated sintering process was finally identified.The result can be used for further development of the integrated iron ore sintering process. |
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