Experimental Study On Desulfurization Characteristic And Mechanism Of Alkaliferous Industry Waste

At present,Chinese national conditions of coal as main energy determine that coal-fired thermal power occupy main position of power industry.Coal-fired pollution becomes the focus of Chinese environmental pollution,in which controlling emissions of sulfur dioxide is an important element.Fluidized bed combustion desulfurization technology and median-temperature circulating fluidized bed gas desulfurization technology are suitable to Chinese national situation because of low early equipment investment,low operating costs,simple process,etc.With Chinese economic rapid development,a large number of discharge industrial waste cause serious environmental pollution.Based on the purpose of waste governance waste and protecting environment,several kinds of alkaline industry wastes from Shandong province were selected as desulfurizer, their desulfuration performance were studied at medium-high temperature and medium temperature,microstructure and desulphurization product characteristic were investigated respectively by mercury porosimeter,XRD diffraction technology and thermo-gravimetric analytic method,desulfurization reaction mechanism at different temperature sections were studied,which provide theoretical basis for preparation of waste type desulfurization agent.Pore structures of experiment alkali waste were investigated by mercury porosimeter.The research results show that as to original samples of alkali industrial waste,pore diameter centralized distribution range are broad,medium and large sized pores are much,and porosity and specific pore volume all are large.The microscopic structures of calcined alkali industrial waste closely are related to their initial pore structure and composition.The surface free energy of original samples with large surface area are relatively larger,it sintering easily during calcined process,which results in surface area decreasing.At 850℃,Al₂O₃,Fe₂O₃ can react with CaO to form aluminate and ferrite,whose melting point are low,in addition, the melting points of CaCl₂ and NaCl are low also,aluminate,ferrite,CaCl₂ and NaCl can form liquid melt,which can make loose granular structure dense,medium and large pore reduced,but ion migration and proliferation increase,CaO lattice destruction,irregular pores form,which result in surface area,pore volume and porosity enhanced.As temperature increased,because sintering process is controlled by diffusion also,melting acceleration ion proliferation,at the same time, accelerated the sintering,which result in some holes plug or big hole form,surface area,porosity and pore volume declining.For some calcined alkali waste,whose compound content of Al₂O₃,Fe₂O₃,CaCl₂ and NaCl are low,at 850℃and 950℃, aperture concentrated distribution range widen,specific surface area,specific pore volume and porosity increase,at 1050℃,total surface area start to decrease because of sintering,the changes low of total porosity and specific pore volume have the same rule.Vulcanization reaction characteristics of five kinds of alkali industrial waste were analysed by thermo-gravimetric analysis technology in the simulated flue gas temperature at medium-high temperature,the influence of particle size,furnace temperature and SO₂ concentration on efficiention ions conversion rate were studied, the desulfurization performance of different types desulfurization agent were evaluated.The results show that some experiments alkali industrial waste such as; alkali slag,red mud,salt slurry,and so on,because of lower melting point and rich in compound and CaO forming lower melting point metal substances(such as; CaCl₂,Al₂O₃,Fe₂O₃ and NaCl),their best desulfurization reaction temperature are at 850℃.On the contrary,alkali industrial waste containing less content of above compound,such as;white clay and carbide sludge,the best desulfurization reaction temperature ranged from 900℃to 1000℃,have good high-temperature desulfurization performance.Through discussing influence of pore structure characteristics on alkali industrial waste desulfurization performance,it can be found that differences in desulfurization characteristic of experimental alkaline industrial wastes mostly caused by inner pore size and difference structure of grain.Bigger specific surface area and specific pore volume can premise condition for desulfurization reaction, but these are not sufficient condition,it also relate to inner pore size and difference structure of grain.The little pore make a significant contribution to efficiention ions conversion rate at the initial stage of reaction and lower temperature,but with time going and temperature increasing,reaction still run at low speed,and it still make contribution to the total efficiention ions conversion rate at the end reaction of stage and higher temperature.The range of effective porosity are different at different temperature,which respectively is 5～20nm at temperature ranged from 850℃to 950℃and 0.2～0.3μm at temperature ranged from 950℃to 1050℃.From 850℃to 950℃,efficiention ions conversion rate of alkaline industrial waste are higher and desulphurization reaction activity are better because calcined alkaline industrial waste owned more small holes,which result in more specific surface area and higher porosity.With reaction temperature increasing,as the result of sintering,pore structure of alkali slag,red mud and salt slurry will be seriously damaged and the porosityε,specific pore volume V_m and specific surface area S_m will be reduced evidently,so that efficiention ions conversion rate are influenced evidently, desulphurization effect be deteriorated.Compared to alkali slag,red mud and salt slurry,white clay and carbide residue have less Al₂O₃,Fe₂O₃,CaCl₂ and NaCl,so sintering is not serious during calcining decomposition and desulphurization reaction process,their pore structure change less and sinter-resistant characteristic are better with temperature increasing,So efficiention ions conversion rate get to maximum at 950℃and are comparatively high at 1000℃.White clay and carbide residue have good desulphurization reaction characteristics at higher temperature.How the experimental wastes affect sulfur release process were researched by coal-SO₂ control platform.The results show that different alkali industrial wastes possess of different ability of capture low-temperature and low-temperature sulfur. Calcined decomposition temperature of alkali industrial waste are lower and required time are shorter because of loose structure and more SO₂,Al₂O₃,Fe₂O₃, which make industrial waste effectively capture low temperature sulfur.Because industrial waste contain less impurity content and loose structure,they have a strong ability of capture sulfur low temperature and high temperature.At higher temperature,due to SO₂,Al₂O₃ in ash need consume more alkaline oxide,the active center of alkali industrial waste reduce,the best reaction temperature slightly is lower than that in the thermal conditions.Added red mud to limestone, low-temperature sulfurs's precipitation peak decrease and peak width become narrow,the ability of capture low-temperature sulfur rise,the performance of the desulfurization become better.Added red mud to carbide sludge and white clay, their low-temperature sulfur precipitation are in advance,but precipitation rate become lower.Desulfurization kinetic characteristics of industrial wastes were studied by equivalent ion model,and their kinetic parameter—activation energy E,chemical reaction rate constant k,product layer diffusion coefficient Ds,were calculated desulfurization mechanism of alkali industrial waste as fluidized bed combustion desulfurization agent were explored.It can be found that compared alkali industrial waste to limestone,the reaction rate constant at chemical reaction control stage and the diffusion coefficients at proliferation stage are larger,and possess of better desulfurization activity.SiO₂,Fe₂O₃,Al₂O₃ and alkali metal salt in alkaline industrial waste are beneficial to improve production layer diffusion coefficient Ds, but as reaction temperature increased,desulphurization production layer sintering be aggravated,so there will be an optimal applicable temperature range.Big specific surface area,specific pore volume and small crystal size of alkaline industrial waste also reduce relative resistances of gas and production layer surface reaction in pores,and are beneficial to reaction gas diffusion and the reaction in the entire particle.Desulfurization reaction processes of different kinds of waste compound were studied.It can be found that added Ba(OH)₂,Fe₂O₃ and MnCO₃,product layer diffusion coefficient of white clay,carbide slag and limestone are increasing,which promote their efficient ions conversion rate and makes their desulfurization reaction performance at high temperature improved.Desulfurization performance of composition of limestone and salt slurry are improved.Alkaline slurry and salt slurry exacerbated sinter of white clay and carbide slag,there into alkaline slurry is more obviously,which make desulfurization result of white clay and carbide slag reduction.Most Dicalcium silicate in red mud has been hydrated and definite intensity,during calcination and desulfurization,the influence of compounds in white clay and carbide slag,such as Al₂O₃,Fe₂O₃,on pore structure of limestone, are not as apparent as salt that in slurry and alkaline slurry,moreover,activities of hydrous dicalcium silicate and calcium aluminate in red mud are higher and create catalysis to desulfurization reaction.The desulfurization characteristics of experimental waste were studied by coal-SO₂ control platform at median temperature,and based on this,the phase composition and mineral content of desulfurization product were analyzed by XRD and thermal gravimetric,desulfurization mechanism of alkali industrial waste were explored at median temperature.It can be found that on one hand,Al₂O₃,SiO₂ and Fe₂O₃ play the role of transferring oxygen during the formation process of CaSO₄, CaSO₃ easily oxidized and form sulfate calcium,which results in proportion of CaSO₄ larger than that of CaSO₃,On the other hand,they make initial grain size of carbonate crystallization small and dispersion high,which can increase desulfurization reaction surface area,thin product thickness,reduce product layer resistance and raise the proportion of carbonate forming sulfate.If carbide slag and lime applied for median temperature flue gas desulfurizer,in order to maximize their utilization rate,it should avoid that the reaction of calcium oxide and carbon dioxide excessive consuming desulfurizer,join a certain amount of Al₂O₃,SiO₂ and Fe₂O₃ into them or choose a suitable desulfurization temperature,namely,800℃.The results of desulfurization characteristics,microporous structure,material composition,apparent morphology of alkali industry waste after rapid dry hydration were integrated,and influence mechanism of rapid dry hydration on desulfurization performance of alkali industrial waste were explored at median temperature.It can be found that desulfurization capability of experimental alkali industrial waste after hydration reaction are 1.5 to 3 times that of the calcined samples.In the course of fast-drying hydration,physical adsorbing water in the particles are evaporated to escape,and re-form median pore in the particles,in addition,calcium oxide and joined water form calcium hydroxide,augment size of particles and heating expansion will lead to particle refinement during reaction process,which are favorable for desulfurization.Silica and alumina can react with calcium oxide to form silicate and aluminate during calcined process.Silicate and aluminate react with water to form silicate hydrate and aluminate hydrate during fast-drying hydrated process,which have higher desulfurization activity.This study will promote the development of desulfurization technology and provide theoretical foundation for Preparation waste-desulfurizer and guide for engineering application.