Effect Of Process Conditions And Additives On Removal Of Solid Phase Sulfur During Lignite Pyrolysis

Coal-burning pollution is the main type of air pollution in China.Most of the civil bulk coal was Unorganized emission,and the large amount of coal burning and scattered combustion location lead the more difficult control of pollutants.At present,government promote coal shift to gas or electric in northern area,but our country energy structure is rich coal,deficient oil and lean gas,which caused natural gas was in short supply.Inaddition,the electricity or gas for heating had the defects of high cost and low efficiency.Therefore,the use of coal-based clean fuel instead of civil bulk coal to control pollutant emission was considered to be a more effective measure.However,with the increase of environmental protection,the country has a stricter standard for the sulfur content of coal-based civil fuels,resulting in restrictions on the promotion of civil coke.In order to reduce the sulfur content in civil coke,it is of great significance to study the removal rules of sulfur during coal pyrolysis and the influence of additives on sulfur.In this paper,lignite with abundant reserves in Inner Mongolia was used to investigate the influence of sulfur removal in coal on pyrolysis process.On this basis,three desulfurization additives were introduced into lignite pyrolysis respectively,aiming to effectively reduce sulfur content in pyrolysis product semi-coke through the interaction between additives and sulfur.Meanwhile,combined with the experimental results and characterization methods such as XPS,XRD and TG-MS,the mechanism of sulfur removal in the pyrolysis process by additives was studied.The main results are as follows:（1）The best desulfurization temperature was 700℃in the middle and low temperature pyrolysis process.At this temperature,the sulfur content of lignite pyrolysis product semi-coke reached the lowest 0.98%and the corresponding total sulfur removal rate is 58.7%.There were a lot of organic thiophene and sulfone in semi-coke,accounting for 67%of the total sulfur content.Inorganic sulfur were pyrite decomposition product FeS and sulfur fixation product CaS.（2）The optimum pyrolysis heating rate was 10℃/min,at which time the sulfur content of the semi-coke is the lowest,and the influence of the heating rate on inorganic sulfur had greater than that on organic sulfur.Excessive heating rate is not conducive to sulfur removal.With larger particle size of coal,uneven heating lead to insufficient pyrolysis,which hindered the diffusion of sulfur and increased the sulfur content in the coal,the optimum condition particle size was 0.2 mm.The optimal pyrolysis residence time was 60 min,if shorter than this time,the coal pyrolysis was not sufficient and the sulfur compounds in the coal were not fully decomposed.Meanwhile,if longer than this time,the loss of volatiles was too large,which would lead the decline of the quality and yield of semi-coke.（3）The addition of P₂O₅ could obviously remove total sulfur and inorganic sulfur.When the addition amount of P₂O₅ was 3%,the total sulfur content and inorganic sulfur content reached 0.7%and 0.13%.P₂O₅ reduced sulfur by increasing the pore volume of coal and increasing the gas overflow rate.While,after addition 1%KCl,the sulfur content was 0.81%,and removal rate was63.8%.By promoting the gasification of coal to generate more CO,the auxiliary agent KCl increased the generation of COS and reduced the secondary reaction of gas phase sulfur（NH₄）₂MoO₄ promoted the decomposition of organic sulfur through the hydrogenation.