Strengthening Mechanism And Method Of Carbon-based Materials In The Recovery Process Of Coal-fired Flue Gas Sulfur Resources

Energy and environmental issues are major development strategy issues of concern to all countries in the world today.Energy consumption,energy demand and pollutant emissions brought about by economic development are increasingly not negligible.China uses nearly 2 billion tons of coal for power generation each year,and limestone-gypsum wet desulfurization is mostly used.At least 125 million tons of high-quality limestone are mined each year,destroying the ecological environment;by-product of low-quality gypsum 215 million tons,which is large in quantity and low in quality,difficult to use;water consumption is large,and desulfurization wastewater is difficult to discharge.The current desulfurization process will cause serious ecological problems.China is a country poor in natural sulfur resources.In 2015,it imported more than 11 million tons of sulfur,and its dependence on foreign sources was as high as 71%,and it was increasing year by year.Therefore,the development of environmentally friendly flue gas purification and high-value sulfur resource recovery technologies based on the power production process is a national strategic need.Coal-based solid carbon materials have the advantages of a wide range of sources,low production costs,and strong structural controllability.Based on the preparation of carbon-based materials in the production of coal-fired power for the recovery of sulfur resources in flue gas,it is an important development in the current sulfur resource recovery technology direction.To clarify the formation and occurrence mechanism of desulfurization products in the multi-scale structure of carbon-based materials is a prerequisite for the realization of high-value sulfur resource recovery;compared to the by-product Ca SO₄ produced by wet desulfurization,sulfur resources are more easily recovered by H₂SO₄ or elemental sulfur value.Based on the above considerations,this article first studied the mechanism of SO₂ adsorption,catalytic conversion and product occurrence in carbon-based materials.On this basis,researches were carried out on the high-value recovery paths of H₂SO₄ and sulfur.Based on the above research,it was proposed and realized the method of applied to a large-scale preparation coal-based activated coke for high-efficiency removal of SO₂and recovery of sulfur resources.In view of the fact that the existing experimental research cannot achieve single factor,quantitatively explore the problem of SO₂ adsorption by oxygen-containing functional groups.In this paper,mechanochemical methods are used to reveal the adsorption mechanism of SO₂ by oxygen-containing functional groups at the edges of carbon materials from an experimental point of view.The results show that the carboxyl functional groups at the edge of the carbon-based surface dominate the physical adsorption of SO₂,while the edge unsaturated sites dominate the chemical adsorption of SO₂.Aiming at the key issues that restrict the migration and occurrence of desulfurization products,this paper prepares model carbon materials with gradual gradation of pores,and explores the influence of pore structure configuration on the migration and occurrence of desulfurization products.The research results show that the hierarchical pore structure strengthens the migration and occurrence of desulfurization products in activated coke.This part of the research explored the influence of oxygen-containing functional groups on the SO₂ adsorption process in carbon materials from the group scale;and explored the pore structure coordination group required for the migration and occurrence of H₂SO₄ in carbon materials from the pore structure scale.The above-mentioned research work has laid a theoretical foundation for the next high-value resource utilization of coal-fired flue gas SO₂.The key to the direct and efficient recovery of the desulfurization product H₂SO₄ lies in the reasonable design of the active coke pore composition.The reason for the low efficiency of sulfuric acid regeneration and desorption in the traditional water-washing regeneration process is the single micropore distribution of activated coke.This paper proposes a hierarchical structure of activated coke pores to achieve high-efficiency desorption of sulfuric acid in desulfurized activated coke.The research results show that the hierarchical porous activated coke with equal volume of micropores and medium and large pores has the best H₂SO₄ cyclic desorption performance.After 10 cycles,it can still maintain a high sulfur capacity of 70 mg g^-1and a water washing regeneration efficiency of 90%.Combined with molecular dynamics simulation,it is proved that the self-diffusion coefficient of H₂SO₄ in medium and large pores is about twice that of micropores.In order to solve the problem of high water consumption and low acid concentration in the water washing regeneration process,this paper proposes a method of steam purging to enhance the direct desorption of sulfuric acid in the activated coke.The research results show that steam purging can directly carry out the H₂SO₄ in the activated coke in the form of sulfuric acid vapor.At the same time,due to the low regeneration temperature,the oxidation-reduction reaction of carbon and H₂SO₄ is inhibited,thereby effectively reducing carbon loss and playing the role of"active sites protection".In order to further strengthen the direct directional analysis of sulfuric acid in the activated coke,this paper explores the influence of field synergy on the direct directional analysis of sulfuric acid in the activated coke.The research results show that the microwave field-assisted regeneration of activated coke desulfurization products quickly resolve in the form of SO₂ and sulfur.The main mechanism of action is the"hot spot effect"of the selective heating of polar H₂SO₄ molecules by microwave,which strengthens the direct reduction of H₂SO₄.In addition,the microwave field has a reactivation effect on the activated coke,which improves the circulating desulfurization performance of the activated coke.The research of the above work provides a feasible method for the direct directional analysis of desulfurization products in activated coke.Carbothermal reduction of SO₂ is an important way to recover elemental sulfur.The physical and chemical structure of carbon materials has an important influence on the by-product associated pathways and sulfur selectivity.In this paper,methods such as directional control of the physical,chemical structure of carbon materials,and kinetic experiments are used to deeply analyze the key influence characteristics of the physical and chemical properties of carbon materials on the reaction process of carbothermal reduction of SO₂.The research results show that temperature and carbon-sulfur ratio have a crucial influence on the production of non-target by-products.As the degree of graphitization increases,the carbothermal reaction activity and sulfur generation selectivity decrease.The hierarchical porous activated coke with both microporous and medium-large pore structure has high reactivity and selectivity for sulfur generation.In addition,the introduction of oxygen-containing groups of the carbon material itself promotes the improvement of the reaction activity of carbothermal reduction of SO₂,but also promotes the production of non-target by-products CO and COS.The research of the above work provides theoretical guidance for realizing carbon-based materials to efficiently reduce SO₂ resources and recover sulfur.Aiming at the problem that it is difficult to synergize the reaction activity and the selectivity of sulfur generation in the low-cost carbothermic reduction of SO₂resource recovery sulfur,this paper proposes a strategy based on the catalytic component to strengthen the carbothermic reduction of SO₂ resource recovery.Using kinetic experiments and DFT theoretical calculation methods,the effect mechanism of the catalytic components on the reaction activity of the carbothermal reduction of SO₂ to sulfur and the selectivity of sulfur formation were deeply explored.The results of the study show that the appropriate ratio of calcium source loading can synergistically enhance the activity of activated coke to reduce SO₂ and the selectivity of S₂ generation(80.2%),which is far better than pure activated coke reducing agent.The mechanism of action is that the C-O-Ca structure weakens the C-O bond in the carbothermal reduction reaction intermediate,thereby reducing the energy required for the O transfer process,and making the overall carbothermal reduction SO₂reaction path easier to occur.The recovery process of calcium source supported by activated coke is simple and has good recyclability.The above research work provides a feasible scheme for the carbothermic reduction of SO₂ resource recovery technology.Finally,based on the requirement of carbon-based sulfur resource recovery process for the multi-scale structure of carbon materials,a technical route based on one-step catalytic activation of raw coal to prepare unshaped and hierarchical pore coal-based activated coke was proposed.In view of the key issues involved in its application in the sulfur resource recovery process,the SO₂ removal kinetics experiment,the water washing regeneration experiment and the technical verification of the carbothermal reduction of SO₂ resource recovery sulfur were carried out in the water washing regeneration and fixed bed reaction system.The research results show that using the inherent mineral components of raw coal,the one-step catalytic activation process can be used to prepare kilogram-level unshaped coal-based activated coke on a rotary kiln.The prepared unshaped activated coke has the characteristics of high specific surface area and hierarchical pore structure.The verification results of sulfur resource recovery technology show that the monolithic coal-based activated coke prepared by the one-step catalytic activation process has excellent SO₂ removal,water washing regeneration and SO₂ reduction performance.