The Model Of Heat And Mass Transfer On Carbon Dioxide Capture From Blast Furnace Gas By Ammonia Method

To address the impact of climate change on human society,President Xi Jinping has set ambitious targets for China's carbon peak by 2030 and carbon neutral by 2060.China's steel industry is a major carbon emitter,and blast furnace gas is the most important CO₂emitter in the steel industry.CO₂capture of blast furnace gas is not only beneficial to carbon emission reduction in metallurgical industry,but also can increase the calorific value of blast furnace gas,thus bringing economic benefits.This article is to explore the method of blast furnace gas ammonia decarbonization absorption process of heat transfer,mass transfer and chemical reaction,according to the basic theory of the ammonia absorption of CO₂,the design method of blast furnace gas ammonia decarbonization absorber,based on quality,heat transfer and conservation equation,establish a method of blast furnace gas ammonia absorption tower decarburization process of heat and mass transfer mathematical model of the numerical simulation method to study the effect of related factors on decarburization process performance.Firstly,based on the double membrane theory and Henry's law,the rate and mass transfer resistance of the CO₂absorption process of water are analyzed.When ammonia and CO₂have chemical reaction,liquid film resistance can be reduced and partial pressure of CO₂gas phase equilibrium can be reduced.Therefore,the speed and limit of CO₂absorption process by ammonia method is better than physical absorption such as CO₂absorption by water.The enhancement effect of the chemical reaction on the absorption process of CO₂by ammonia method was measured by the chemical reaction enhancement factor,which could be calculated by the chemical reaction principle and kinetic data of ammonia water and CO₂.Secondly,the distribution and influencing factors of carbon flow in iron and steel enterprises are introduced,and the influence of blast furnace gas decarbonization on enterprise carbon emission is analyzed,as well as the research status of blast furnace gas decarbonization technology.A decarburizing absorber for blast furnace gas is designed for the No.1 blast furnace ironmaking system of a certain iron and steel company.In the design,the net gas handling capacity of blast furnace is 400 000Nm³/h,the CO₂inlet concentration is 20%,and the removal rate is not less than 90%.The ammonia solution with a mass fraction of 8%was selected as the absorbent,and the absorption operation was carried out under normal temperature and pressure.The bulk packing is made of polypropylene plastic with the size of 50mm,the liquid-gas ratio is 6L/m³,the diameter of the absorption tower is 10m,and the height of the packing layer is 22m.Then,according to the law of mass and heat conservation and transfer,the mathematical model of ammonia decarbonization process of blast furnace gas in absorption tower was established by analyzing the CO₂transfer and heat transfer of micro-element packing layer,including four governing equations and two boundary conditions.Fortran language was used to write the program to realize the simulation of decarburization process.The accuracy of the model is verified by comparing with relevant experimental data.Finally,based on the ammonia decarbonization absorbing tower of blast furnace gas,the distribution of CO₂concentration and gas-liquid two-phase temperature along the tower height is simulated,and the heat and mass transfer rule under the design condition is analyzed.By changing the height of the packing layer,ammonia concentration,liquid-gas ratio and inlet temperature of ammonia,the influence rule and degree of the influence on the decarbonization process were simulated and analyzed.The results show that the CO₂removal rate is 90.2%,which meets the requirements.In the range of selected parameters,the CO₂removal rate increased to different degrees with the increase of the height of the packing layer,ammonia concentration,liquid-gas ratio and ammonia inlet temperature.When the height of the packing layer increased from 14m to 22m,the removal rate increased from 76.3%to90.2%,and when the height of the packing layer was 30m,the removal rate exceeded95%.When the ammonia concentration increased from 2%to 8%,the removal rate increased from 70.2%to 90.2%,and when the ammonia concentration was 10%,the removal rate was 92.3%.When the liquid-gas ratio increased from 4L/m³to 12L/m³,the removal rate increased from 87.8%to 93.2%.In general,ammonia concentration and the height of the packing layer had great influence on the removal rate.The mathematical model of heat and mass transfer established in this study can provide theoretical basis for the application of decarbonization technology of blast furnace gas and can guide the design and optimization operation of CO₂capture system of blast furnace gas.