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.     

固体热载体热解煤中氮的迁移特性

在固体热载体快速热解装置上考察了锅炉循环灰对内蒙古羊市塔烟煤热解过程中氮的迁移转化特性的影响.结果表明,在考察温度(530℃~660℃)内,在气相氮中仅含有HCN和NH3,无N2产生.循环灰对煤结构及焦油分子中氮杂环的裂解没有催化作用,与惰性石英砂作为热载体的实验结果相比,热解温度600℃时,循环灰作为热载体使气相中HCN-N和NH3-N的产率分别降低了24.53%和29.86%.并通过向惰性石英砂中添加碱性矿物质对循环灰中影响煤热解过程中气相氮释放的主要物质进行了考察.     

固体热载体煤热解过程中氮的迁移

在固体热载体煤热解实验装置上考察了石英砂、燃烧灰和气化半焦为热载体对煤热解过程中氮迁移的影响.固体热载体煤热解过程中,热解温度升高有利于煤中挥发分析出,可以促进煤中含氮官能团发生断键,利于氮的脱除.快速热解可促进煤中氮脱除生成HCN和NH3.分别以石英砂、燃烧灰和气化半焦为热载体,研究表明:热载体中矿物质可促进焦油氮分...     

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。     

含钠煤热解过程中NH_3的形成和释放

以3种煤及其相应的不同含量的加钠煤作为研究对象,考察了外加金属钠在热解过程中影响NH3生成与释放的主要因素。结果表明：外加钠在热解过程中对NH3释放的作用较大程度上取决于煤的变质程度,变质程度越低的煤影响越明显。在不同温度范围内,Na的负载量不同,对NH3的释放所起的作用也不相同。在600～800℃温度范围内,2%的钠负载量对小龙潭和神东煤NH3的形成起促进作用。当温度达到900℃时,随着添加剂量的增加,钠对NH3的形成表现为抑制趋势。     

煤中氮在热解过程中释放规律的数学模拟

以化学渗透模型(CPD)为基础构建煤的结构，以实验数据为基础，通过对煤中氮在热解阶段反应历程的描述，以及对NOx的主要前驱体HCN和NH3生成的动力学表达，建立了煤热解阶段氮释放的模型，将模型的计算结果与五种煤在管式固定床反应器中热解阶段形成HCN和NHx的测定结果进行比较，研究发现：模型能够相对准确的预测HCN形成(误差在20％以内)，但由于没有考虑惰质组的影响，对部分煤NHx的模拟误差较大(甚至超过50％)，模型也表达出在快速热解条件下随温度升高，HCN和NHx的生成量增加；随煤阶增加，HCN生成量减少；随惰质组含量增加，NHx的生成量增加的释放规律。     

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...     

矿物质对煤转化过程中含氮物迁移的影响

综述了煤本身所固有的矿物质和外来添加物在煤热解、气化过程中的作用,主要针对煤中氮的形态变化和迁移规律进行了讨论.煤中的含氮物在热解气化过程中以HCN、NH3 N2等形式释放于气相产物之中,还是以大分子杂环化合物形式残留于煤焦和焦油之中,煤中固有的矿物质和添加剂对其在各形态间的分配比例具有较大影响.含Fe、Ca等金属元素的化合物是对含氮物迁移转化存在明显作用的代表性物质,同时对Fe、Ca在煤氮催化转化生成N2中的可能机理和在氮氧化物形成之前进行其前驱体的抑制进行了分析.     

煤中矿物质对热解过程N化物的影响

通过介绍煤中N的赋存形态以及热解过程中产生的主要含氮气相物,详细的分析了矿物质对氮化物在热解过程中的作用,以及对NH_3、HCN和其他氮化物释放含量的影响,从而总结出矿物质铁在热解过程中对氮化物的影响起到积极作用。     

煤及其模型化合物快速热解过程中HCN和NH3逸出规律的研究

利用高频热解装置对褐煤、烟煤和无烟煤三种不同煤阶的煤及模型化合物吡咯、吡啶进行了热解实验,分别考察了煤热解终温为1200℃,平均升温速率为2.7,8.0,11.9,17.1,22.9℃·s-1和不同热解终温(600～1200℃)下煤及吡咯、吡啶快速热解过程中HCN和NH3的生成规律,并且对煤热解过程中HCN和NH3逸出...     

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 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.     

煤热解过程中氮的分配及存在形态的研究进展

介绍了不同热解条件下煤中氮行为研究方面的基本情况,对煤中氮的存在形态和影响氮在热解产品分配因素如煤种,温度,压力,停留时间,粒径,煤阶等作了初步探讨,并给出了ＨＣＮ和ＮＨ３可能的形成途径。     

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。     

Nitrogen chemistry in coal pyrolysis: Catalytic roles of metal cations in secondary reactions of volatile nitrogen and char nitrogen

The present review focuses on elucidating the chemistry of nitrogen release during coal pyrolysis, in particular, on making clear catalytic roles of inherent Ca and Fe ions in not only the partitioning of volatile-N to tar-N, HCN, NH₃ and N₂ but also the conversion of char-N to N₂.     

Formation of NOx and SOx precursors during the pyrolysis of coal and biomass. Part I. Effects of reactor configuration on the determined yields of HCN and NH3 during pyrolysis

The formation of HCN and NH₃ during the pyrolysis of a biomass (bagasse) and a set of rank-ordered coal samples has been studied in a novel reactor. The reactor has some features of both a drop-tube reactor and a fixed-bed reactor: the reactor allows the coal/biomass particles to be heated up rapidly as well as to be held for a pre-specified period of time at peak temperature. The experimental results obtained suggest that a considerable amount of the nitrogen in the nascent char could be converted into HCN and NH₃ if the char is held at high temperatures for long time. The formation of NH₃ from the thermal cracking of char was seen to last for more than an hour even at temperatures as high as 700–900°C. The formation of HCN went to completion much more rapidly than that of NH₃. Compared with the results in the literature from the pyrolysis of coals in a fluidised-bed reactor, the reactor configuration used in this study allows the effects of fuel rank to be studied on an unbiased basis towards the type of fuel. The yields of HCN and NH₃ from the present study decrease with increasing rank. The experimental results suggest that the differences in reactor configurations used by various researchers would account at least partially for some of the discrepancies in the literature regarding the formation of HCN and NH₃ during the pyrolysis of coals.     

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.     

Releases of NO and its precursors from coal combustion in a fixed bed

Experiments have been carried out to investigate the emissions of nitrogen species including NO and its precursors during temperature-programmed coal combustion by TG/EGA method. Experimental results show that the conversion ratio of fuel nitrogen to NO is the highest, followed by that of fuel nitrogen to HCN and the conversion ratio to NH₃ is negligibly small. Nitrogen is retained in the char and released mainly as NO at the later stages of coal combustion. HCN and NO are both primary products from coal char oxidation. Coal rank, heating rate, indigenous minerals and external additives are the major influential factors of the nitrogen species release. Higher rank coals with higher fuel ratio have higher NO releases. HCN release decreases as fuel ratio increases for most coals. The fuel nitrogen conversion to NO increases and the fuel nitrogen conversion to HCN decreases with the increase of heating rate, which may imply that the char nitrogen prefers to react with oxygen to form NO instead of HCN while coal char is combusted at higher temperatures. Different metallic additives show different effects on nitrogen species emission and the effects of indigenous minerals on nitrogen release can be qualitatively estimated by ash analyses.