煤热解与挥发份燃烧时SO2与NO的交互作用

为研究煤热解与挥发份燃烧过程中SO2对NO的影响，在燃烧综合实验台上研究了硫含量、煤种等因素在煤热解与挥发份燃烧过程中对SO2生成量、NO生成量等的影响。结果表明，SO2的生成对燃烧过程中NO的生成具有一定影响和作用。但不同的煤种硫的析出与氧化对NO的生成影响和作用有所不同，挥发份含量高、活化能低的煤，与NO之间的交互作用较强。铜川贫煤和宜宾无烟煤，原煤中的固有硫和添加硫总量分别达到4.34％和5．17％以上时，硫的热解和氧化过程才对NO的生成有较明显的影响；而对神木烟煤，原煤中的固有硫和添加硫总量达到2．0％时，硫的热解和氧化就对NO的生成起到了明显的作用。图10表3参6     

生物质热解过程中氮转化规律的试验研究

采用TG-FTIR联用技术在氩气氛围下研究稻草、麦秆、杨木3种生物质热解过程中4种主要的含氮组分NH3、HCN、HNCO及NO的释放特性,并考察焦炭-N的产率。结果表明:在所选取的3种生物质热解过程中,4种含氮组分的释放趋势均与TG-DTG曲线一致,热解后期(温度高于500℃)释放较少;不同生物质热解,4种含氮组分的释放规律有较大差异,且相对产量分布不同。3种生物质NH3和HCN的相对产量明显高于HNCO和NO,NH3最高,HCN次之,两者之和占70%以上。随着生物质中H/N质量比的增大,NH3的相对产量增加,HCN的相对产量先增加后减少,HCN/NH3物质的量之比逐渐减小。杨木热解过程中气相氮释放较少,燃料氮81.50%存在于焦炭中,而稻草和麦秆中大部分燃料氮随挥发分析出,焦炭氮产率分别为29.97%和33.45%。     

煤的模型化合物热解过程中HCN_NH_3的逸出规律

为了解煤燃烧过程中NOx的生成机理,在600～1400℃温度范围内,选取吡啶、吡咯为煤的含氮模型化合物,采取傅立叶红外光谱仪(Ft-Ir)和分光光度计连用方式,在等温连续式流动反应器中实验研究了模型化合物热解过程中HCN、NH3的逸出规律。结果表明：HCN是模型化合物的热解产物中的主要含氮产物;吡啶、吡咯的HCN的转换率都随着温度的升高而增大;同温度下,吡咯的HCN生成率高于吡啶的HCN生成率,吡咯的NH3生成率高于吡啶的NH3生成率。     

温度及氧煤比对煤预燃过程中NO/HCN转化的影响

为探究煤粉预燃-燃烧耦合技术的低氮机理,通过在一维管式炉上对煤粉预燃过程中温度和氧煤比对NO/HCN的转化特性进行详细研究.实验结果表明在氧煤比为0和0.1时,随着温度升高,NO的含量下降,而HCN含量上升;当氧煤比进一步升高到0.3及以上时,随温度的升高NO的含量会升高,HCN的含量先升高后降低.同时,利用NO生成与还原的总包反应的速率常数随温度的变化趋势,得出在高温低氧情况下HCN还原NO占主导地位,在高氧情况下氧化生成NO占主导地位,以此来揭示NO的不同变化趋势.     

煤质特性对快速热解中HCN释放的影响

在管式半携带半固定床反应器中，在600—1000℃范围内对6种煤质各异的原煤进行了快速热解HCN释放的研究．结果表明，热解温度、煤的灰分和氢含量对HCN的释放具有很大的影响，而煤氮向HCN的转化并不依赖于煤的含氮量．随着热解温度的升高，煤氮向HCN的转化率显著提高．原煤中氢含量越高，煤氮向HCN的转化率越高，说明热解过程中煤的供氢能力是决定HCN释放的重要因素．原煤中灰分越多，则煤氮向HCN的转化率越低，说明煤灰能够抑制HCN的生成或者能够促进HCN的分解．对原煤添加NaCl、CaCO3和二茂铁Fe(C5H5)2的热解研究表明，Na和Ca对于HCN释放的影响不明显，而Fe则显著降低了HCN的释放．     

废橡胶和废纸热解过程NOx前驱体的生成

在固定床反应器中热解废橡胶和废纸,考察在不同热解终温和加热方式下NOx前驱体(HCN和NH3)的生成特性.研究结果表明,随着热解终温的升高,原料中的N转化为HCN和NH3的比例不断增加.以废橡胶为例,HCN和NH3的产率从400℃的0.5%分别增加到1000℃的7%和9%;加热方式对HCN和NH3的产率有明显的影响.实验条件下,非等温热解时,废橡胶在所有热解温度下HCN和NH3的产率均高于等温热解时的产率.     

燃煤耦合城市污泥燃烧特性与NOx生成行为模拟

利用自定义燃烧模型对煤粉与城市污泥共燃过程进行数值模拟,研究不同掺烧比例下共燃过程的燃烧特性、NO_x体积分数空间分布和生成行为等。结果表明：污泥对煤粉第一阶段燃烧有明显的促进作用,在掺烧比例≤3%时,对煤粉第二阶段燃烧也有促进作用,而在掺烧比例≥6%时有抑制作用;在燃烧器出口附近氮存在形式丰富,大部分NH₃在该区域转换为HCN,少量转换为HNO和NH₂等,而在回流区后半段,HCN体积分数明显降低,NO体积分数上升,随着燃烧反应的进行,部分NO被还原成HCN和HNO;NO_x生成行为主要集中发生在燃料燃烧的2个阶段,在第一阶段,NO的生成过程主要为NH被O和O₂氧化以及N被O₂氧化,第二阶段主要为NH被O氧化以及N被CO₂氧化;NO被CH₃还原成HCN是2个阶段中NO被还原的主要过程。     

CO_2气氛中超细煤粉热解含氮气体释放规律

在固定床反应器上进行了CO2气氛中内蒙古褐煤的热解/气化试验,对含氮气体和CO析出特性进行了连续在线测量,考察了温度、粒径和气氛等因素的影响.结果表明,气氛对于气化反应特性和含氮气体的析出特性有较大影响且在高温区更为明显;煤样与CO2的气化反应在550,℃之后显著加快.CO2气氛下煤中氮主要以NH3、HCN和N2O形式析出,而N2气氛下主要是以NH3、HCN和NO形式析出;不同粒径的煤粉热解时HCN和NH3析出曲线相似且差距不大,N2O析出量随粒径增大稍有增加.     

超细煤粉热解特性及热解反应动力学研究

采用TG-DSC分析方法对内蒙古煤和神华煤两种煤种各4个不同粒径的超细煤粉分别在5℃/min、10℃/min、20℃//min和30℃/min的升温速率下进行热解实验并采集数据分析,研究了不同煤种超细煤粉热解过程中煤粉粒径、升温速率、煤种中组分对热解过程的影响。最后根据Coats-Redfern法建立了动力学模型并计算出了相关系数。结果表明:超细煤粉的热解过程可以分为干燥脱气、半焦形成和熟化成焦(二次脱气)3个失重阶段。     

焦炭流化床燃烧条件下氧化亚氮生成过程的实验研究

在小型流化床实验台上对一种无烟煤焦炭燃烧过程中氧化亚氮的生成途径进行了实验研究,实验结果表明,在焦炭燃烧过程中HCN的氧化反应是焦炭氮向N2O转化的一条途径。同时,NO与焦炭表面的多相反应也是N2O的一条生成途径。HCN的析出是焦炭燃烧过程中进一步脱挥发份的结果,当焦炭脱挥发份过程结束后,N2O来源于NO和焦炭表面的气固多相反应。     

生物质快速热解气相成分析出规律

利用恒温沉降炉对秸秆、稻壳、木屑及一种烟煤煤粉在900、1000、1100℃ 3个温度进行了快速热解试验,对4种燃料在快速热解过程中气相成分析出的规律进行了研究.生物质成分中高的挥发分、氧、H/C决定了其快速热解会取得比煤粉高的气相产率,木屑的气相产物产量最多,秸秆次之,稻壳最低.4种燃料热解气相产物中的主要成分是CO、H_2、CO_2、CH_4,少量的G_2H_4、C_2H_6、NO、HCN、COS,生物质和煤粉在快速热解及短的停留时间内,其析出的氮前驱物为HCN.快速热解析出的气相成分产量及组分分布与燃料种类、热解温度、热解停留时间相关.几种物料共同的规律是随停留时间的延长,气相产物的量不断地增加,当气相产物的产量趋于平稳时,相应的气相产物的各组分趋于恒定,这一停留时间标志着热解过程的结束,相同温度条件下煤粉的热解速率要慢于3种生物质.     

Effects of Minerals on the Release of Nitrogen Species from Anthracite

Abstract

Experiments have been carried out to investigate the effects of minerals on nitrogen species emission including NO and its precursors from a high rank coal during temperature-programmed combustion by TG/EGA method at 10°C/min. Sodium was found to be an excellent catalyst for the reduction of NO and HCN evolution due to its higher catalysis of sodium on the char-NO reaction. However, iron can induce an increase of NO release. Calcium and titanium additives can be classified as inactive constituents because of their weak catalysis on HCN and NO emission. All the metallic additives can promote NH₃ emission except sodium. Parent coal has higher fractions of nitrogen release as NO and NH₃ and lower fraction of nitrogen release as HCN than demineralized coal, which can be attributed to the catalysis of indigenous minerals in parent coal.     

水蒸汽流化下煤热解气化中污染物释放与脱硫综合模型及参数识别方法研究

本文在流态化模型、热解模型、硫化氢与脱硫剂气固反应等单一过程模型基础上，建立了水蒸汽流化条件下煤热解气化过程中污染物释放与脱硫综合模型，分析了模型计算结果，并对当实验数据含有相关随机误差时的参数识别方法进行了考察，为实验装置设计和测量系统的选择提供了依据。     

Theoretical study of the effect of hydrogen radicals on the formation of HCN from pyrrole pyrolysis

As a typical fossil fuel, coal is a major contributor to nitrogen oxide (NO_x) pollution. The detailed mechanism of NO_x generation from coal pyrolysis need to be clarified. Within this research, we used density functional theory (DFT) to investigate the formation mechanism of HCN as a NO_x precursor during pyrolysis of pyrrole in the presence of hydrogen (H) radicals. Firstly, three different reaction positions for hydrogen radical attacking were compared. It was identified that hydrogen radical initially reacts with pyrrole at the location adjacent to N through a single elementary reaction step with an activation energy of 77.12 kJ/mol. Additionally, to examine the role of hydrogen radical in the pyrrole pyrolysis to form HCN, 12 subsequent reaction pathways were theoretically investigated. It was found that one of the pathway (Pathway a-4) involving hydrogen transfer followed by carbon-carbon cleavage processes is the route with the lowest energy barrier of all of the mechanisms reported, thus it plays an important role in the formation of HCN from the pyrrolic components of coal. These results further indicated that the hydrogen radicals significantly reduce the energy barrier of the pyrrole pyrolysis.     

再燃烧条件下煤粉热解过程中C、H、N释放特性

在携带流反应装置中研究了再燃条件下煤粉的热解特性,测量了煤粉在高温烟气环境中热解时的质量损失和煤中C、H、N等主要元素的释放份额,分析了煤种、热解温度、热解气氛和煤粉粒径等因素对煤中主要元素释放的影响。结果表明,在实验条件下,煤中H析出份额远大于C、N和煤的质量损失份额,C、N析出份额与煤的质量损失份额基本相同,随煤挥发分含量增加、热解环境温度升高和煤粉颗粒粒径减小,C、H、N释放份额增加,煤焦中H,C值下降。     

Mechanism study of nitric oxide reduction by light gases from typical Chinese coals

Coal devolatilization plays an important role in NO formation and reduction. In this study, the coal pyrolysis experiment was performed in an entrained flow reactor to obtain the light gas release characteristics. Six typical Chinese coals with volatile content ranged from 8.8% to 38.3% were studied. The pyrolysis temperature was in the range from 600 to 1200 °C. A significant rank dependence of HCN, CO and C₂H₂/C₂H₄/C₂H₆ was observed and their release for high volatile coals was higher than that for low volatile coals. The HCN–N/NH₃–N ratio ranged from 0.00 to 0.66 for anthracite coals and ranged from 1.63 to 3.90 for high volatile coals. Based on the experimental results, the effect of coal pyrolysis gas on NO reduction in a plug flow reactor at reducing atmosphere was kinetically calculated. The optimal excess air ratio(α_opt) corresponding to the maximum NO removal efficiency decreased with an increase in reduction temperature. For the light gas from the HL coal pyrolyzed at 800 °C, the α_opt decreased from 0.73 to 0.17 when the reduction temperature increased from 927 to 1327 °C. The rate of production analysis indicated that NO removal efficiency was determined by 3 competing reaction paths: NO reduction, NO formation and oxygen consumption by combustible species.     

Mechanism study on the effect of alkali metal ions on the formation of HCN as NOx precursor during coal pyrolysis

Coal, as a typical fossil fuel, is a current major contributor to the global emission of nitrogen oxides (NO_x). The NO_x formation process during coal utilisation can be described as the thermal decomposition of N-containing model compounds into NO_x precursors followed by NO_x formation. The existence of alkali metal ions, Na⁺ and K⁺, during the coal utilisation process has a significant influence on the formation of NO_x species. However, the information about this influence is currently lacking within the available literature. Within this research, the effect of Na⁺ and K⁺ on the formation mechanism of NO_x during pyrrole pyrolysis were investigated using density functional theory (DFT). A hydrogen migration occurs from the meta-position of pyrrole-N is transferred to the ortho-position, and then pyrrole-N disconnected from the ortho-position C, which makes the ring opened. Lastly, in a concerted mechanism, a long carbon bond breaking between the migrating hydrogen and the carbon, nitrogen atoms. It was found that Na⁺ and K⁺ have a catalytic effect on the internal hydrogen transfer and ring-opening of pyrrole but have an inhibitory effect on internal hydrogen isomerization and concerted decomposition reaction. It was also found that those alkali metal ions (Na⁺ and K⁺) have strong interactions with pyrrole and its derived compounds (HCN and propyne molecules), those interactions are much larger than the existing attractive interactions among HCN, propyne molecules and their complexes. Additionally, it was found that both Na⁺ and K⁺ inhibit the HCN formation step from pyrrole pyrolysis, with Na^+, has a higher inhibition effect than that of K⁺. Furthermore, the mechanisms discussed in this research may well play a role in the thermal decomposition of other coal compounds such as indole and carbazole.     

用热分析法研究煤的热解特性

采用热分析法对煤热分解进行了试验研究,探讨了影响煤热解的因素,例如,煤粉粒度对热解产物的影响;温升速率对煤热解的影响等。研究了混煤的热解特性,提出了反映煤热解特性的煤粉热解产物释放特性指数。用热解反应动力学方程研究煤的热解过程,并以平顶山煤为例,将计算数值和试验数据进行了比较,结果基本一致     

Distribution of Nitrogen Species During Vitrinite Pyrolysis and Gasification

The formation of HCN and NH₃ during pyrolysis in Ar and gasification in CO₂ and steam/Ar was investigated. Vitrinites were separated and purified from different rank coal from lignite to anthracite. Pyrolysis and gasification were carried out in the drop-tube/fixed-bed reactor at temperatures of 600–900°C. Results showed that with increase of reaction temperature the yield of HCN increased significantly during pyrolysis and gasification. Decrease of coal rank also increased the yield of HCN. Vitrinite from lower rank of coal with high volatile content released more HCN. The yield of NH₃ was the highest at 800°C during pyrolysis and gasification. And the yield of NH₃ from gasification in steam/Ar was far higher than that from gasification in CO₂, where the hydrogen radicals play a key role. Nitrogen retained in char was also investigated. The yield of char-N decreased with an increase of pyrolysis temperature. Vitrinite from lower rank coal had lower yield of char-N than that from the high rank coal.