作为分级转化比较理想的中低阶煤,认识和理解宁东典型中低阶煤在热转化过程中氮、硫元素迁移转化行为对污染物的调控至关重要。目前,煤热转化工艺多以气化为主,其中热解作为气化的基础阶段,在煤热转化过程中至关重要,因此在深入认识煤质特性的基础上,研究宁东地区典型中低阶煤所含硫、氮元素在热解过程中的迁移与转化规律,不仅有望为宁东中低阶煤的热转化工艺条件优化及污染物控制提供理论参考,也可为目前的气化工艺过程污染物调控提供基础数据。基于此,以宁东地区的羊场湾煤(YCW)、上湾精煤(SW)与梅花井煤(MHJ)为研究对象,使用固定床反应器,探究三种不同硫含量的煤在热解过程中HCN,NH3与H2S的释放规律,主要考察元素的赋存形态、热解温度(300℃~900℃)与升温速率(3℃/min~10℃/min)对氮、硫元素迁移转化的影响。结果表明:HCN的释放量随着温度升高而逐渐增加,NH3的释放主要集中在500℃~900℃,最大释放峰温为700℃,H2S的释放主要集中在400℃~900℃,最大逸出峰温为600℃和800℃(分别对应于硫铁矿硫与部分不稳定有机硫的分解);较高的灰分含量能够阻止自由基间相互结合,使更多的含氢自由基与含氮自由基结合生成HCN,季氮含量越高,NH3的释放量越大,不稳定有机硫占比越高的煤样,H2S的释放越多;适宜的升温速率有利于HCN发生二次反应生成NH3,随着升温速率增大,产生热滞后现象,当升温速率由3℃/min提高至10℃/min时,MHJ的HCN,NH3和H2S转化率均呈明显下降趋势,HCN转化率由4.02%降至1.28%,NH3转化率由13.80%降至3.91%,H2S转化率由38.33%降至26.04%。综上,元素赋存形态、热解温度与升温速率对热解过程中氮、硫元素迁移影响均较大。灰分含量、季氮含量与不稳定有机硫含量较低的煤样在10℃/min热解条件下,氮、硫污染物的释放量较低,对环境影响较小。

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, NH  and  H S 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 NH  is  mainly concentrated between 500 ℃-900 ℃, with its maximum release peak at 700 ℃.  The release of  H S 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 NH .  The higher the proportion of  unstable organic sulfur in coal samples, the more H S is released.  An appropriate heating rate is con‐ ducive to the secondary reaction of HCN to form NH .  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, NH  and H S in MHJ coal all show a significant decreasing trend, with the conversion rate of  HCN dropping from 4. 02% to 1. 28%, NH  from 13. 80% to 3. 91%, and H S 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.