Study on correlation between speciation of nitrogen and sulfur elements and their transformation during pyrolysis of typical middle and low-rank coal in Ningdong
As a relatively ideal type of middle and low-rank coal for graded conversion,understanding the migration and transformation behavior of nitrogen and sulfur elements during the thermal conversion process of typical middle and low-rank coal in Ningdong is crucial for the control of pollutants.Currently,gasification is the main process for coal thermal conversion,with pyrolysis as the fundamental stage of gasification.Therefore,based on a deep understanding of coal quality charac-teristics,the migration and transformation patterns of sulfur and nitrogen elements contained in typical middle and low-rank coal from the Ningdong area during the pyrolysis process were investigated.The experimental results are expected not only to provide a theoretical basis for optimizing the thermal con-version process conditions and pollutant control of middle and low-rank coal in Ningdong,but also to offer basic data for pollutant control in gasification processes.Therefore,this paper focuses on Yangchangwan coal(YCW),Shangwan cleaned coal(SW)and Meihuajing coal(MHJ)from Ning-dong area as research subjects,using a fixed bed reactor to explore the release rules of HCN,NH3 and H2S during the pyrolysis of three different types of coal with varying sulfur contents.The effects of element speciation,pyrolysis temperature(300℃-900℃)and heating rate(3℃/min-10℃/min)on the migration and transformation of nitrogen and sulfur elements are investigated.The experimental results show that the release of HCN gradually increases with temperature.The release of NH3 is mainly concentrated between 500℃-900℃,with its maximum release peak at 700℃.The release of H2S is primarily concentrated between 400℃-900℃,with its maximum release peaks at 600℃ and 800℃,corresponding to the decomposition of pyrite sulfur and some unstable organic sulfur,respec-tively.Higher ash content can prevent the combination of free radicals,allowing more hydrogen-containing free radicals to combine with nitrogen-containing free radicals to form HCN.The higher the content of quaternary nitrogen,the greater the release of NH3.The higher the proportion of unstable organic sulfur in coal samples,the more H2S is released.An appropriate heating rate is con-ducive to the secondary reaction of HCN to form NH3.With the increase of heating rate,thermal hys-teresis occurs.When the heating rate is increased from 3℃/min to 10℃/min,the conversion rates of HCN,NH3 and H2S in MHJ coal all show a significant decreasing trend,with the conversion rate of HCN dropping from 4.02％to 1.28％,NH3 from 13.80％to 3.91％,and H2S from 38.33％to 26.04％.In summary,the element speciation,pyrolysis temperature and heating rate significantly impact the migration of nitrogen and sulfur elements during the pyrolysis process.Coal samples with lower ash content,quaternary nitrogen content,and unstable organic sulfur content will release fewer nitrogen and sulfur pollutants under pyrolysis conditions of 10℃/min,resulting in less environmental impact.
万方数据
维普
