Research On The Performance And Mechanism Of Sulfur Chemical Looping Combustion Based On Iron-based Oxygen Carrie

In the traditional process of burning sulfur to produce sulfuric acid,the size of the unit,such as SO₂/SO₃ converter,largely depends on the volume of gas treated.The oxygen carriers react with the gasified sulfur in FR,which can theoretically obtain a higher SO₂ concentration than the traditional sulfur combustion process,greatly reduce the operation cost of the equipment and reduce the emission of NOx and SOx pollutants.Therefore,the research on chemical looping combustion of sulfur has great development potential,and CLC acid making process also has broad industrial application prospects.In this paper,iron based composite oxygen carriers with different inert carriers（ZrO₂、MgAl₂O₄ and Al₂O₃）and different loading ratios were prepared by sol-gel method and characterized by XRD,H₂-TPR and SEM-EDS.The results show that Fe₂O₃/MgAl₂O₄ contains Fe₂O₃,Mg Al₂O₄ and a small amount of Al₂O₃.When the mass ratio of active component to inert carrier is 5:5,the grain size of oxygen carrier is the smallest;The H₂-TPR of Fe₂O₃/Zr O₂oxygen carrier shows three peaks,and the H₂-TPR of Fe₂O₃/MgAl₂O₃ and Fe₂O₃/Al₂O₃ has only two peaks;The three oxygen carriers with the mass ratio of active component to inert carrier of 5:5 have good pore structure and the elements in the oxygen carrier are fully loaded and evenly dispersed.In this paper,the Gibbs free energy of the reaction is calculated through the reaction module of factsage software.The results show that reaction 6Fe₂O₃+S=4Fe₃O₄+SO₂ is the main reaction of sulfur gas reducing Fe₂O₃ oxygen carrier;On the basis of Gibbs free energy,the dominant region of solid phase is obtained by using predom module.The results show that at standard atmospheric pressure,with the increase of reaction temperature,the dominant region of Fe₃O₄ and FeS₂ phase decreases,while the stable region of Fe O,Fe and FeS phase increases.High sulfur equilibrium partial pressure is conducive to the formation of FeS₂ and FeS,while low sulfur equilibrium partial pressure is conducive to the formation of Fe₃O₄,Fe O and Fe;The CLC reaction of iron-based oxygen carrier with sulfur at different temperatures was simulated by Aspen plus.The results show that when the molar ratio of Fe₂O₃ to S is 6:1,almost all sulfur will react to produce SO₂,and all Fe₂O₃ will be reduced to Fe₃O₄.This proves that it is feasible to generate high concentration SO₂ gas through chemical looping combustion reaction with sulfur as fuel and Fe₂O₃ as oxygen carrier.When the sulfur is excessive,FeS will be generated,and a small amount of S₂ will not react completely.When the oxygen carrier is excessive,the sulfur will be over oxidized to generate a small amount of SO₃（the concentration is about0.01%）.By comparing the content of S element in the samples after the reaction of Fe6Zr4 oxygen carrier and pure Fe₂O₃ with sulfur,it is found that the addition of inert carrier is conducive to increase the sulfur resistance of oxygen carrier and reduce the reaction between S and Fe₂O₃;Through the combination of three temperature zone tubular furnace and SO₂ flue gas analyzer,the changes of SO₂ concentration and conversion rate produced by the combustion of iron-based oxygen carrier and sulfur chemical looping under different working conditions were studied.It is found that when the gasification temperature of sulfur is 500℃,the temperature of reduction reaction between oxygen carrier and sulfur is 900℃,the flow rate of N₂ is 300ml/min and the molar ratio of Fe₂O₃/S is 6:1,the reaction effect of sulfur and oxygen carrier is the best.When the mass ratio of active component to inert carrier is 5:5,the SO₂ concentration and conversion produced by the reaction are higher.When the proportion of active component increases or decreases,the SO₂ concentration and conversion show a downward trend;The reduced Fe5Zr5,Fe5Mg Al5 and Fe5Al5 oxygen carriers were characterized by XRD and XPS.It was found that a small amount of FeS and FeS₂ were generated in addition to Fe₃O₄.Fe₂O₃in Fe5Mg Al5 and Fe5Al5 oxygen carriers is over reduced to Fe O and FeS₂;SEM-EDS analysis of the three oxygen carriers showed that the reduced oxygen carriers contained a small amount of sulfur,in which the sulfur content of Fe5Zr5 was the most and Fe5Al5 was the least.At the same time,the SO₂ concentration and conversion rate of the gas products of chemical looping combustion of Fe5Al5 oxygen carrier and sulfur are higher than Fe5Zr5 and Fe5Mg Al5 oxygen carrier,so Fe5Al5 oxygen carrier is more suitable for sulfur chemical looping combustion.