The Mixed Reforming Of High Temperature Converter Gas And Coke Oven Gas

To utilize the secondary resources and waste heat more efficiently and reasonably in iron and steel industry,improve the recovery rate of waste heat and quality of byproduct gas,and reduce emissions of CO2,this paper proposed the reforming of high temperature converter gas and coke oven gas.Through the thermochemical reforming,the converter gas and coke oven gas are transformed to the product gas which is mainly composed of of H2 and CO and can be used for downstream chemical production or direct reduction process.The heat required in the reforming process comes from the high temperature converter gas,so the heat of the high temperature gas is fully utilized.In addition,the dust in the converter gas is used as catalyst in reforming.The in-situ catalytic of the dust eliminates the need for additional catalysts,reduces the production cost and does not have the problem of catalyst deactivation.First,to confirm theoretically the possibility of reforming of converter gas and coke oven gas,the thermodynamics of the reforming system was researched.Through thermodynamic equilibrium calculation and regression analysis,the influence of temperature,pressure and initial composition(ΦCOG)on CH4 conversion rate,CO2 conversion rate,H2/CO and carbon deposition rate were obtained.The results show that low pressure and high temperature are beneficial to improve the conversion rate of CH4 and CO2,and to ensure high the conversion rate of CH4 and CO2,above 850℃ under normal pressure is suitable for the reforming.Temperature and pressure have little effect on H2/CO,while ΦCOG has obvious effect on H2/CO.To compare the difference between the actual reforming process and the thermodynamic equilibrium state,we conducted experiments about the reforming of the two kinds of gas mainly investigating the effects of temperature and initial composition on the reforming at normal pressure.The experimental results show that the conversion rate of CH4 is low when the temperature is lower than 1050℃,and the conversion rate of CH4 increases obviously with the increase of temperature above 1050℃,and reaches a higher level at 1250℃.The conversion rate of CO2 also increases with the increase of temperature.When the ΦCOG is 0.5,the CO2 conversion rate reaches 50%and 75%at 1150℃ and 1250℃,respectively.H2/CO increases significantly with the increase of temperature above 1100℃.The CH4 conversion rate decreases slightly with the increase of ΦCOG,while the CO2 conversion rate and H2/CO increase significantly.It can be seen that the reforming system is not easy to reach the thermodynamic equilibrium state during the experiments.Therefore,we studied the kinetics of the main reactions in the reforming process,and obtained the reaction order,reaction rate constant,activation energy and pre-exponential factors of the main reactions.Because it is difficult to achieve thermodynamic equilibrium in the reforming experiment,it is more important to improve the kinetic conditions of the reforming reaction.The dust in the converter gas is mainly composed of Fe oxide and CaO,has a large specific surface area and is fully mixed with the gas,which may affect the reforming process significantly.Therefore,we have experimentally studied the catalytic effect of the dust on the reforming of the two kinds of gas.After the addition of converter dust,the temperature at which the CH4 conversion rate began to increase significantly decreased from 1050℃,the temperature without catalyst,to 950℃.And in the entire experimental temperature range(900-1150℃),the addition of the dust significantly improved the CH4 conversion rate.The conversion rate of CO2 is significantly higher than that without catalyst,and the difference between the two conversion rates increases with the increase of temperature.WhenΦCOG is 0.5,the dust catalysis increases the conversion rate by 9.6%and 41.6%at 900℃ and 1150℃,respectively.At the same time,the dust reduces the temperature at which H2/CO begins to rise from 1050℃ to 1000℃.The CH4-CO2 reaction is the main reaction in the reforming processes.Subsequently,we deeply studied the effect of the main components of dust on the reaction,which include the effect of Fe,Fe oxides and CaO on the CH4 decomposition reaction and C-CO2 reaction.The results show that the promotions of the substances to the decomposition of CH4 is in the following order:Fe>Fe3O4≈CaO>FeO,and the promotions to the C-CO2 reaction is in the order:Fe3O4>CaO>FeO>Fe.Subsequently,to provide further foundation for industrial application,based on the kinetic parameters obtained from the experiments,the reforming process in the flue of a 120t converter was studied by numerical simulation,which includes the effects of the ratio of coke oven gas addition(RCOG),the preheating temperature of coke oven gas,the number and flow velocity of coke oven gas inlets on the reforming.The results show that the conversion rate of CH4 decreased with the increase of RCOG.When the RCOG was less than 0.189,the conversion is close to 100%,and when the RCOG is greater than 0.189,the conversion rate decreases rapidly with the increase of the RCOG.The conversion rate of CO2 increases with the increase of RCOG when the RCOG is less than 0.316,reaches the peak when the RCOG between 0.38-0.44,and then decreases slightly.When the preheating temperature of coke oven gas increases,the conversion rates of CH4 and CO2 increase significantly.The effect of the number of coke oven gas inlets on the conversion rates of CH4 and CO2 is not obvious,but the conversion rates under 4 inlets are slightly higher than the rates under 2 or 8 inlets.The influence of the flow velocity of coke oven gas inlet on the conversion rates of CH4 and CO2 is not obvious.After the reforming,the temperature of product gas is above 900℃,which can be used to preheat coke oven gas.After preheating coke oven gas,the temperature of product gas is still higher than 700℃,and this part of the physical heat can be recovered by steam turbine power generation technology.Therefore,we proposed a converter gas treatment and physical heat recovery process combining the three processes of gas reforming,coke oven gas preheating,and physical heat power generation,and calculated the recovery rate of physical heat in this process.The results show that after adding the reforming process,the total physical heat recovery rate of converter gas is 50-60%,which is significantly higher than the rate of 2537%in the traditional steam turbine power generation process.Finally,the utilization of the product gas is discussed.The product gas can be used for chemical synthesis requiring H2/CO of less than 1.The above researches confirm the feasibility of the reforming from the theoretical and experimental aspects,prove the catalytic effect of dust in gas on reforming,obtain suitable conditions for the reforming in the converter flue,and lays a solid foundation for the reforming industrial production.