Mechanism And Effect Of Al₂O₃ And CaCO₃ Compostie Additive On Sulfur Fixation Of Clean Coke During Combustion

The pollution caused by coal-burning is the main type of air pollution in China,and the level of air pollution comes from residential burning coal is very high.The combustion of domestic coal is mostly disorganized low emission,and the amount of domestic coal is so large and the venue more scattered that controlling coal-burning pollution becomes more and more difficult.The emission intensity of dust particulate matter?PM?and the sulphur oxide?SO_X?is at least 5⁸ times than that of coal-fired in power plants.Adopting the central heating,electricity or natural gas to replace the domestic coal combustion have the drawback of high cost and low efficiency.Therefore using coal-based clean fuels to substitute domestic coal for the treatment of pollution from scattering point has been considered to be a more effective method,especially in controlling emissions of SO_X and PM.This research group put forward the idea that utilizing excess coking capacity to produce clean coke for replacing domestic coal.The clean coke have characteristics of high-temperature fixing sulfur and catalytic combustion,which have resolved the technical problem that a larger SO_x emission and the higher ignition point of metallurgical coke,which makes it unsuitable for domestic fuels.Clean coke have lower particulate emissions than coal combustion,but it,like sulfur-fixation in coal combustion,has disadvantage of sulfur-fixing lower efficiency in high-temperature combustion.In this paper,a kind of high temperature sulfur-fixation phase?C₄A₃S?was introduced to clean coke in combustion process,and by adjusting the ratio of CaCO₃ and Al₂O₃ composite additives in coal-pyrolysis has greatly improved the sulfur-fixation efficiency of clean coke in combustion,and determine the best ratio of additive.Meanwhile,main influencing factors and mechanisms of sulfurfixation during the combustion of clean coke were researched by experimental results and utilizing TG-MS,XPS,SEM,XRD techniques,main results as followings:?1?When composite additives and coal co-pyrolysis,the optimum ratio of additives are as follows: n?Ca?/n?S?= 3.0,the amount of Al₂O₃ mass fraction less than 8%?n?Al?/n?S?= 1.02?,and sulfur-fixing efficiencies under the optimum ratio of Clean Coke in combustion were measured,that is to say,the range of sulfur-fixation efficiency is from 73% to 99% between 1050? and 1150?,and from 30% to 58% between 1200? and 1300?.?2?The main present forms of inorganic sulfur and organic sulfur in clean coke which prepared from single or hybrid additive and coal co-pyrolysis are respectively calcium sulfide?CaS?,sulfone sulfur of oxygen-containing and the stable-ring thiophenic sulfur,and the amount of inorganic sulfur?CaS?in clean coke account total sulfur for 13%¹8%.?3?The influence of mineral matters?plus and itself?on Coke-oven Gas components during the pyrolysis of coals is extremely large,which mainly consist of CO,CO₂ and the sulfurous gas?H₂S,COS,CS₂?.Calcium-based sulfur-fixation agent?minerals?decomposition released large of CO and CO₂,and it would also form stable calcium sulfide with sulfurous gas reaction in reductive atmosphere.However,the effect of composite additives?minerals?on hydrogen-containing gases?H₂,CH₄,H₂O?is opposite.?4?The sulfur-fixation mechanism of clean coke in combustion is that Al₂O₃ and CaCO₃ composite additives react with the sulfurous gas to form calcium sulfide and calcium oxide during the pyrolysis of coal,and react with the releasing sulfur dioxide?SO₂?during the combustion of organic sulfur in clean coke to produce calcium sulfate.The generated calcium sulfate during high-temperature combustion is wrapped by iron-silicon compound playing the role of sulfurfixation at high-temperature,or occurr the solid-state reaction with Al₂O₃ in composite additives to form an amount of high-temperature phase of calcium sulphoaluminate?C₄A₃S?,therefore improving the high-temperature sulfurfixation efficiency.The iron-silicon composite compound wrapping up calcium sulfate in sulfur-fixation products derives from decomposition of pyrite in coalpyrolysis,which was transferred to iron-silicon compound during the combustion of clean coke.