煤中固有矿物质在热解过程中对氮释放的影响

采用管式炉固定床反应器,考察了平朔煤( PS)、神木煤( SM)和阳城煤( YC)三种不同变质程度的煤种在热解过程中的HCN和NH3 释放规律,主要讨论煤中所固有的矿物质在这一过程中对氮分配的影响.结果表明:不同变质程度的煤种脱除矿物质后,均表现为热解过程中的NH3释放量减少,其减少程度与灰分的性质有关;而HCN的释放与煤中矿物质的关系却受煤变质程度的影响;同时矿物质对不同形态氮的分配也有明显的作用.     

钙及其赋存形态对煤热解过程中氮转化的影响

燃煤NO_x生成与煤中含氮物质的种类及其在热解、燃烧中的转化特性密切相关。利用酸洗—物理混合/溶液浸渍添加方法制备获得含不同赋存形态Ca的煤粉,在水平管式炉上研究了不同赋存形态Ca对煤热解过程中氮转化特性的影响。结果表明,无机形式存在的Ca会使热解后的焦氮含量升高,而有机形式存在的Ca倾向于降低热解后的焦氮含量。添加以Ca(OH)2为模型物质的无机含钙矿物会抑制煤热解过程中NH_3的生成。添加以醋酸钙为模型物质的外在或内在有机含钙矿物后,NH_3均降低而HCN生成量升高,表明有机含钙矿物会促进煤中氮向HCN的转化。与以外在矿物形式添加的醋酸钙相比,以内在矿物形式添加的醋酸钙对热解中氮转化行为的影响较小。     

基于显微组分化学键特征的宁夏庆华煤热解特性及动力学分析

通过X射线光电子能谱和傅里叶红外光谱表征宁夏宁东庆华煤不同显微组分的官能团种类、表面结构元素价态分布及化学键赋存特征。采用热重-质谱联用考察庆华煤镜质组和惰质组在不同热解温度下的失重行为和关键气体组分变化。进一步基于Coats-Redfern模型从化学键断裂特征和反应动力学角度探讨煤镜质组和惰质组的热解行为差异。结果表明,庆华煤显微组分的热解失重峰与相应化学键断裂信息能够很好地吻合。不同显微组分的热重曲线变化趋同,但相同热解温度下镜质组的失重率始终高于惰质组。快速热解阶段镜质组较惰质组表现出更大的失重率和最大失重速率。其主要原因在于镜质组的脂肪族官能团相对含量更高,快速热解阶段会发生更多的C_al—C_al断裂。不同热解温度下庆华煤显微组分三个主要热解阶段的活化能和频率因子大小次序为：快速热解阶段>快速缩合阶段>缓慢热解阶段。在快速热解阶段,镜质组和惰质组的平均活化能均约为75 kJ/mol,但镜质组的频率因子更高。     

发生炉造气过程中NO_x及前驱体生成的探讨

结合煤气发生炉的造气原理和过程,对煤氮在发生炉热解、还原、燃烧过程中的转化以及NOx与前驱体的生成进行了定性的分析。指出发生炉热解、气化过程中,煤氮一部分转化为焦油;一部分以NH3、HCN、N2形式转化为煤气;另外一部分残存于灰渣中。通过分析,说明一段式发生炉、两段式发生炉和干馏式发生炉三种炉型在气化过程中,NH3、HCN和N2的生成量基本没有差异;NH3和HCN主要来源于气化过程;而热解过程次之,但干馏式发生炉在煤的热解过程中NH3和HCN的生成量最少。     

气氛、温度对煤热解过程中NH3和HCN释放的影响

为了实现煤的洁净转化,研究煤热解过程中N转移的机理,实验在固定床反应器上采用程序升温法对云南煤在不同温度下进行了氩、甲烷、15%水蒸气/氩和15%水蒸气/甲烷气氛下的煤加氢热解研究,主要对热解过程中产生的No2主要前驱物NH3和HCN的释放规律进行了考察,实验表明云南煤热解释放的NH3随热解温度的升高而增加,但是HCN...     

基于铁基载氧体的煤化学链气化还原过程中氮元素迁移行为

采用热重-质谱-红外联用技术（TG-MS-FTIR），Ar气氛下对煤进行化学链气化实验，实时分析还原过程热解阶段和水蒸气气化反应阶段的过程中固体质量变化和生成气体成分。使用X射线光电子能谱对固相产物进行表面元素分析，探究化学链气化还原过程不同阶段固相产物中氮赋存形态的变化。研究结果表明：载氧体对化学链气化还原过程不同阶段含氮气体释放均有影响。热解阶段载氧体促进自由基的生成，加速了一次热解阶段含氮气体的释放，高温下，载氧体促使NH₃转化为HCN；气化阶段载氧体的加入使半焦的石墨化程度降低，含氮气体释放速率增加。对固相产物中氮的赋存形态而言，载氧体会抑制热解阶段吡咯型氮的分解与转化，高温下，半焦的石墨化和有序化程度降低的同时，镶嵌在煤大分子里面的质子化吡啶裸露出来，质子化吡啶含量降低，吡啶型氮和吡咯型氮的含量大大提升。     

不同变质煤热解和气化中燃料氮的转化规律

利用水平管式炉对不同变质程度煤进行了热解和气化实验,并利用傅里叶红外气体分析仪对热解和气化过程中主要含氮产物的释放规律进行了研究.结果发现,煤的变质程度对煤热解和气化过程中HCN的释放具有重要影响,而对NH3的释放影响较小.对于低变质程度煤来说,挥发分含量较高,而挥发分的深度裂解是HCN产生的主要来源.因此,低变质程度煤热解过程中转化为HCN的燃料氮份额高于高变质程度煤;对于不同变质程度煤在热解过程中转化为NH3的燃料氮份额则大致相当.对不同变质程度煤在CO2气氛条件下气化反应过程中含氮产物生成规律的研究发现,焦炭氮几乎全部转化为NO;转化为NH3的燃料氮份额有所增加;除印尼褐煤外,转化为HCN的燃料氮份额也有所增加;此外,对CO2气化过程中NO的生成机理进行分析,认为焦炭氮的直接氧化可能是NO产生的主要来源.     

煤岩显微组分分离富集物热化学反应特性

依据煤中不同类型有机质性质差异对其进行分离，进而分质利用是实现煤炭清洁高效利用的有效手段。论文利用重选法将一种低变质烟煤分质得到镜质组较原煤48.25%增加至76.02%的富镜样，惰质组较原煤43.96%增加至63.98%的富惰样，以及矿物质含量高于61.99%的富矿样。利用热重-质谱分析仪，考察了分离富集物的热解反应特性及气体逸出规律，及其燃烧和气化反应特性。结果表明，分离所得富镜样热解反应失重量及热解过程中逸出的小分子挥发分的量及组成与富惰样和富矿样均有明显差异，表明分质实现了煤中不同类型官能团的分离富集。而由分离所得富镜样、富惰样和原煤热解失重峰温基本一致则表明分质所得煤的主体官能团结构仍较为接近，但含量有明显差距。富镜、富惰与原煤的燃烧曲线整体趋势较为类似，燃烧活性差别不大。以气化反应峰值温度高低判断，富镜样气化反应活性最低，富惰样与原煤气化反应活性较为接近，富矿样气化反应活性最高。将原煤在对应热反应时的理论反应曲线与实验曲线进行对比，发现煤分质过程及煤中镜质组、惰质组和矿物质的分离与否对热解过程挥发分的逸出影响较小，但导致了其燃烧和气化反应活性有所降低。     

热重-红外联用研究上湾煤中低温热解行为

利用热重-傅立叶红外联用技术(TG-FTIR)考察了粒度为3mm~6mm神东上湾煤的中低温热解行为.结果表明,130℃时上湾煤失水速率达到最大值1.1%/min~1.2%/min;以10℃/min的速率将温度从室温升高至250℃可实现煤样的充分干燥;随着热解终温的升高,失重率增加,并且出现两个热解阶段.整个热解过程中都伴随着CO2,H2O,CH4和轻质碳氢化合物(LHCs)的释放,而且其生成量都随热解温度的升高而增加;而CO的释放仅存在于终温为750℃和850℃的热解过程中.LHCs以650℃温度前的释放为主,在750℃时达到最大值38.5mg,但由于热缩聚反应的加剧,850℃时LHCs生成量明显降低.     

矿物质对高碱煤显微组分热解特性的影响

利用固定床热解炉和热重分析仪研究了沙尔湖煤显微组分的热解特性和产物产率,考察了酸洗处理对热解产物和动力学参数的影响。结果表明：经浮沉实验发现镜质组富集于S2（密度为1.4～1.5g/cm³浮选煤样）中,惰质组富集于S3（密度为>1.5g/cm³浮选煤样）中,其中S3所含硅铝酸盐类矿物显著高于S2。且碱及碱土金属（alkali and alkaline earth metals, AAEM）多以可溶性形式存在,经酸洗处理后剩余矿物质主要为石英、高岭土及硅酸盐类。在选用不同煤样进行热解特性分析发现,碱及碱土金属的存在会抑制热解主反应阶段的挥发分释放,而在二次脱气阶段,AAEM矿物质则会提高挥发分的释放速率。且在热解实验中发现,AAEM在热解中会充当煤大分子结构的交联点,降低热解焦油产率。对比不同显微组分发现,惰质组热稳定性更强,镜质组中烷烃侧链较多,芳香度较小,更易受热断裂。采用Doyle积分法确定了沙尔湖煤热解反应的动力学参数。     

简化的Solomon热解模型和旋流煤粉燃烧NO生成的数值模拟

提出一种简化的Solomon热解模型, 用于模拟煤粉燃烧NO生成数值模拟中HCN的释放.用纯双流体模型、k-ε-k_p两相湍流模型、EBU-Arrhenius燃烧模型、六热流辐射模型、双方程热解模型、简化的Solomon热解模型以及NO生成湍流反应二阶矩代数模型对旋流煤粉燃烧器内两相流动、煤粉燃烧、HCN释放以及NO生成进行了数值模拟.模拟结果与文献中实验结果的对比表明,基于简化Solomon热解模型的HCN释放模型预报结果比基于双方程热解模型的HCN释放模型预报结果好.     

Formation of HCN and NH3 during coal macerals pyrolysis and gasification with CO2

Three coal macerals with high purities were separated from Pingshuo gas coal. The formation rules of HCN and NH₃ during macerals pyrolysis and gasification were investigated. Experiments were carried out in a tubular quartz reactor at atmospheric pressure. The reactor allowed coal particles to be heated up rapidly and held for a prespecified period of time at a peak temperature. The amount of HCN and NH₃ were quantified by ion chromatography. The influence of temperature and macerals type on the formation rules of HCN and NH₃ was discussed. Results showed that the formation of HCN was mainly due to the thermal cracking of volatile, and NH₃ formed both from the thermal cracking of volatile and the cracking of nascent char. The HCN yield increased with an increase in pyrolysis temperature. For three coal macerals (liptinite, vitrinite and inertinite), the yield of HCN depended not only on their volatile contents but also nitrogen-containing functional groups, in which more pyrrole-type nitrogens would form more amount of HCN at lower temperature. The yield of NH₃ depended on the ability of forming ‘H’ radical. Under the experiment condition in this study, inertinite could convert more nitrogen into NH₃ than vitrinite and liptinite. The yield of HCN during gasification was almost the same as that during pyrolysis, the yield of NH₃ during gasification was little higher than that during pyrolysis.     

Formation of NOx precursors during the pyrolysis of coal and biomass. Part VIII. Effects of pressure on the formation of NH3 and HCN during the pyrolysis and gasification of Victorian brown coal in steam

Effects of pressure on the formation of HCN and NH₃ during the pyrolysis and gasification of Loy Yang brown coal in steam were investigated using a pressurised drop-tube/fixed-bed reactor. The NH₃ yield increased with increasing pressure during both pyrolysis and gasification. Increasing pressure selectively favours the formation of NH₃ at the expenses of other N-containing species. The changes in the yield of NH₃ with increasing pressure were mainly observed in the feeding periods both during pyrolysis and gasification and were closely related to the formation and subsequent cracking of soot both as a result of intensified thermal cracking of volatile precursors inside the particles and as a result of volatile-char interactions after the release of volatiles. While the corresponding HCN yield during pyrolysis showed little sensitivity to changes in pressure, the HCN yield during gasification in steam showed some increases with increasing pressure. Our data indicate that the direct hydrogenation of char-N by H radicals, favoured by the presence of steam, is the main route of NH₃ formation during pyrolysis and gasification. The direct conversion, either through hydrogenation or hydrolysis, of HCN into NH₃ on char surface during the pyrolysis and gasification of brown coal is not an important route of NH₃ formation.     

Formation of NOx and SOx precursors during the pyrolysis of coal and biomass. Part IV. Pyrolysis of a set of Australian and Chinese coals

The formation of HCN and NH₃ from the pyrolysis of a small set of Chinese and Australian coals were studied using a novel fluidised-bed/fixed-bed reactor and a fluidised-bed/tubular reactor. The fluidised-bed/fixed-bed reactor has some features of a fluidised-bed reactor and of a fixed-bed reactor, allowing the evaluation of the effects of coal properties on the formation of HCN and NH₃ to be carried out on a similar basis for a wide range of coals. The thermal cracking of volatiles was investigated in a tubular reactor in tandem with the fluidised-bed/fixed-bed reactor where the nascent volatiles were generated in situ from the pyrolysis of coal. Our experimental results indicate that, in addition to coal rank, the petrographic composition and/or geographic origin of the coal are important factors influencing the formation of HCN and NH₃ during pyrolysis. Among the few Chinese and Australian coals studied, the inertinite-rich Chinese coals tend to give more NH₃ during pyrolysis than the Australian coals of similar carbon contents. It is believed that the structure of inertinites of less caking properties favours the formation of H radicals in the pyrolysing solid over a ‘correct’ temperature range to overlap with the activation and subsequent hydrogenation of the N-containing ring systems for the formation of NH₃ in the solid. If the coal properties favour the release of coal-N as volatiles, the formation of HCN in the gas phase is more likely. Under the current experimental conditions, where volatiles may be deposited on the reactor wall, the formation and destruction of the sooty materials on the reactor wall play an important role in the formation of HCN from the cracking of volatiles.     

神木煤热解形成NOx前驱物的影响因素研究

热解是煤加工的重要基础过程，它是煤燃烧、气化的初始和伴随反应。通过固定床石英反应器研究了不同的热解方式、加热速率、气体流速和粒径对神木煤形成NO，的前驱物HCN和NH3，的影响规律，得出以下结论：终温和加热速率越高，形成的HCN和NH，的量越大；粒径的变化对HCN和NH3的影响规律不同；气体流速对HCN和NH3的形成受加热方式的影响。     

流化床煤燃烧过程不同气氛下的气态氮释放特征

利用微型流化床反应装置,结合快速过程质谱仪,在850~940℃操作温度下,研究了三种不同粒度分布烟煤和无烟煤在热解、气化和燃烧反应条件下四种主要气态氮产物HCN、NH₃、NO和NO₂的释放规律。结果表明,微型流化床可以实时检测挥发分氮和焦炭氮的动态释放序和类型,热解、气化和燃烧反应气氛的改变主要影响HCN和NH₃的释放量。热解产物的气态氮主要是来自于挥发分,燃烧反应的HCN和NH₃的释放量与温度有明显关系,而气化反应的各类气态氮释放量随温度变化波动不大。煤颗粒尺寸和温度变化对烟煤和无烟煤中各类气态氮释放量产生影响比较复杂,其中NH₃的释放特性是区分挥发分N释放和半焦N释放的重要特征。     

Effect of rank,temperatures and inherent minerals on nitrogen emissions during coal pyrolysis in a fixed bed reactor

Pyrolysis of 11 coals with carbon contents of 77–93 wt.% (daf) and corresponding demineralized samples has been studied in a fixed bed quartz reactor with a heating rate of 20 K/min to examine rank, demineralization, temperature and inherent mineral species dependences of nitrogen distribution. Nitrogen mass balances fall within 92.5–104.6%. The results indicate that the chars derived from the coals with higher rank show larger nitrogen retention. Demineralization suppresses volatile nitrogen emission during coal pyrolysis, especially for low rank coals. Coal-N conversion to tar-N reaches the asymptotic values at 600 °C. HCN yields are lower than NH₃ yields during coal pyrolysis. The trends in HCN and NH₃ emissions are very similar and the yields reach the asymptotic value at about 1200 °C. N₂ starts emitting at 600 °C, and as the temperature increases the conversion increases linearly with a corresponding reverse change of char-N. With the catalysts added, N₂ formation is prompted with the sequence of Fe>Ca>K>Ti≫Na≫Si≈Al, meanwhile, char-N decreases correspondingly. Fe, Ca, K, Na, Si and Al increase coal-N conversion to NH₃ with the sequence of Fe>Ca>K≈Na≫Si≈Al in the pyrolysis. Na addition prompts HCN formation; however, the presence of Ti and Ca decrease the HCN yields with small value. The other catalysts have no notable influence on HCN emission in the pyrolysis. Demineralization and Ti addition increase coal-N conversion to tar-N slightly whereas K, Ca, Mg, Na, Si and Al additions decrease tar-N yield weakly, other catalysts hardly influence tar nitrogen emission. N₂ emits mainly from char-N with slight contribution of volatile nitrogen. The mechanism of different N-containing species formation and catalysts influence in the pyrolysis is also discussed in the paper.     

Formation of NOx and SOx precursors during the pyrolysis of coal and biomass. Part III. Further discussion on the formation of HCN and NH3 during pyrolysis

The formation of HCN and NH₃ from the pyrolysis of coal (and biomass) is discussed based on our experimental data as well as the data in the literature, including the pyrolysis of N-containing pyrrolic and pyridinic model compounds reported in the literature. The pyrolysis of the model compounds and the thermal cracking of coal pyrolysis volatiles appear to be in good qualitative agreement in terms of the onset decomposition temperature, the main intermediates and the final N-containing product (HCN). The formation of NH₃ requires the presence of condensed phase(s) of carbonaceous materials rich in hydrogen. Direct hydrogenation of the N-sites by the H radicals generated in situ in the pyrolysing solid is the main source of NH₃ from the solid. The initiation of the N-containing heteroaromatic ring by radical(s) is the first step for the formation of both HCN and NH₃. While the thermally less stable N-containing structures are mainly responsible for the formation of HCN, the thermally more stable N-containing structures may be hydrogenated slowly by the H radicals to NH₃. The formation of NH₃ and the formation of HCN are controlled by the local availability of radicals, particularly the H radicals, in the pyrolysing solid. The increased yield of NH₃ (and HCN) with increasing heating rate can be explained by the rapid generation of the H radicals at high heating rates, favouring the formation of NH₃ (and HCN) over the combination of N-containing ring systems within the coal/char matrix. The size of the N-containing heteroaromatic ring systems and the types of substitutional groups also play important roles in the formation of HCN and NH₃.