程序升温气化过程中氮的释放规律研究

采用 U 型管反应系统研究了不同煤种在程序升温条件下在四种气氛中反应时燃料氮的释放规律.研究发现热解时主要的含氮产物为 HCN,如果煤中含有较多的氧,即使在惰性气氛下也会释放出 NO.没有检测到 NH3 的生成,证实NH3 来源于 HCN 在焦表面的二次反应.N2O 仅在有氧气氛中气化时生成,说明氧气是 N2O 生成的必要条件.气化时的总固定氮 TFN 高于热解时,且气化剂中 O2 含量越高则总固定氮 TFN 越高.     

原煤与煤焦热解气化过程氮转化特性研究

采用热重红外联用的方法,在线检测实验煤种在常压热重分析仪上气化时气体产物的释放过程.实验主要考察无烟煤的挥发分的析出、孔隙比表面积和孔容积对 N 析出与转化的影响,从反应机理上分析含 N 热解气化产物的转化规律.研究发现挥发分的析出速度对煤焦气化影响很明显,在原煤慢焦气化过程中,由于挥发分析出速度慢,形成的孔隙和孔容积较小,而且挥发分中含N量减少会导致焦炭 N 含量增加,从而使得 NH3 和 NO 的析出量增大.在快焦气化过程中,挥发分快速析出,形成的孔隙比表面积和孔容积都较大,导致活性 H 较快释放生成,所以仍然有一定浓度的 HCN 和 NH3.     

吡咯类氮在空气中燃烧的分子动力学研究

采用基于ReaxY、F反应力场的分子动力学模拟方法研究了不同温度和氧浓度条件下吡咯在空气中的燃烧机理。通过观察模拟过程中不同时间下的燃烧产物可以发现,吡咯燃烧的主要产物包括NO、NO_2、N_2、CO_2、CO和H_2O等,主要的中间体和自由基包括C_4H_4N、HNCO、C_2H_2N、C_3HN、C_3H_3N、C_4H_3N、C_3H_3、H、OH、HO_2等。随着温度的升高,吡咯的燃烧速率和生成产物的速率加快,达到平衡的时间越快。随着氧气浓度的升高,有更多的HCN及含氮中间产物转化为NO_x,使其生成量增加。     

采用详细化学反应机理研究煤富氧燃烧NO_x生成机制

本文采用详细化学反应机理,建立氧煤燃烧气固反应模型,分析煤在富氧燃烧条件下NO_x生成机制,研究不同O₂浓度和分级燃烧对NO_x排放的影响。富氧燃烧时,NO_x生成主要路径为:HCN→CN→NCO→NO和HCN→CN→NCO→HNCO→HN₂→NH→HNO→NO。初始O₂增大,挥发分和HCN析出时间提前,高的O₂初始浓度对燃料N转化率有促进作用;煤富氧分级燃烧时,主燃区还原气氛有利于NO还原为N₂,其主要还原路径如下:NO+CO→N+CO₂、NO+H→N+OH和NO+N→N₂+O,当主燃区过量空气系数SR₁从1.15减小到0.6,N最终转化率（t=1000 ms）只是从0.379减小到0.339,相对于未分级燃烧时变化了10.55%,与煤空气分级燃烧相比,煤富氧分级燃烧对N转化率影响较小。     

低温等离子体协同NH_3-SCR去除柴油机NO_x研究

为研究低温等离子体协同NH_3-SCR去除柴油机NO_x的性能与相关影响因素,实验研究了单独NH_3-SCR,单独低温等离子体以及低温等离子体协同NH_3-SCR三种系统下NO_x的去除效率,并考察了反应温度、NO_2/NO比值、O_2浓度、C_3H_6浓度、放电能量密度等因素对各系统去除NO_x的影响。实验结果表明;在合适的O_2浓度下,低温等离子体可以有效将NO部分氧化为NO_2,但过多的能量密度输入会导致副产物的大量生成同时造成能量消耗过多;提高NO_2的量对于低温工况下大幅度提高SCR还原NO_x效率有重要意义,当NO_2/NO=1时,NH_3-SCR在各温度下NO_x转化效率达到最高,继续增大NO_2的比例,NO_x的转化效率又趋于下降。利用低温等离子体辅助NH_3-SCR的协同作用可以大幅度提高低温工况下NH_3-SCR的NO_x转化效率。     

挥发份的均相反应等对N_2O、NO生成影响的模拟与实验研究

用模拟和实验相结合的方法研究了挥发分的均相反应、温度等因素对N2O、NO生成与分解的影响。研究发现，挥发分主要通过分解反应影响N2O的排放量，而主要通过生成反应影响NO的排放量。与高挥发分煤混合燃烧时，不仅N2O生成量降低，氮生成N20的总体转化率也下降。N2O的经时特性要经历一个从生成到分解的过程。     

煤热解挥发分还原NO的反应过程分析

采用详细的化学反应动力学机理对烟煤快速热解挥发分气体还原NO过程进行了数值模拟.根据实际反应条件确定模拟条件为0.1 MPa,1273～1573 K,煤质为准格尔烟煤。首先应用FG-DVC模型模拟得到了热解条件下的气体成分和含量,然后将该气体作为再燃燃料,选取化学当量比为0.6、1.0和1.2进行还原NO的计算.通过敏感性分析和生成速率分析,发现了控制NO生成和还原的关键步骤.只有CH_3、N_2O、NH_i、HCN和H_2CN才可以将NO还原成N_2。     

基于TGA-FTIR研究生物质热解过程中氮化物的生成

基于TGA-FTIR联用技术,考察了升温速率对生物质中氮热解转化成NH3和HCN的影响.结果表明,热解的升温速率影响生物质中氮转化的速率和转化的量,升温速率提高,NH3和HCN的生成量减小,NH3和HCN的起始释放温度及达到最大析出值的温度提高.慢速升温热解,HCN的析出与NH3的析出规律相似,但HCN的析出量明显小于NH3的析出量,生物质中氮主要以NH3的形式析出.     

燃料型NO生成的实验研究

在二维平面射流中进行了燃料型NO的实验研究,采用在甲烷中加入NH_3的方法来模拟燃料氮。实验结果表明:实验过程中生成的NO主要是燃料型NO,热力型NO和快速型NO占排放的总NO的比例很小,同时随着NH_3的增加,NO迅速增加,并且NO浓度沿轴向呈双峰分布。     

基于红外光谱研究沥青燃烧机理和有害气体成分分析

利用Rosemount气体分析仪和定碳炉搭建起固定床燃烧反应试验平台,通过红外光谱分析技术定量分析沥青及其胶浆在高升温速率条件下燃烧反应的有毒气态产物成分、及其释放规律。研究表明,在高升温速率、近等温条件下,沥青及胶浆的燃烧过程可近似分为活泼挥发组分析出燃烧、二次挥发析出结合残炭燃烧两个阶段,其主要气态产物为CO₂,CO,NO,NO₂及SO₂。沥青材料中活泼挥发组分含量是影响燃烧气态产物释放规律的关键因素之一,减少沥青材料中活泼挥发组分的含量可有效降低燃烧气态产物的生成、尤其是CO的产生。     

Spatially and temporally resolved IR-DFWM measurement of HCN released from gasification of biomass pellets

For the first time, to the best of the authors’ knowledge, nonintrusive quantitative measurement of hydrogen cyanide (HCN) released during the devolatilization phase of straw pellets gasification is demonstrated with high spatial and temporal resolution. Mid-infrared degenerate four-wave mixing (IR-DFWM) measurements of HCN were performed by probing the interference-free P(20) line in the v₁ vibrational band at around 3?µm and the IR-DFWM signal was detected with an upconversion-based detector, providing discrimination of thermal noise and increased sensitivity. A novel single-pellet setup consisting of a multi-jet burner was used to provide hot flue gas environments with an even and well-defined temperature distribution, for single straw pellet gasification at atmospheric pressure. The environments had temperatures of 1380?K, 1540?K and 1630?K with a constant oxygen concentration of 0.5?vol%. In order to quantify the amount of HCN released during the devolatilization of straw pellets, calibration measurements were performed in well-defined HCN gas flows. Selected hot water lines were probed with IR-DFWM in the interrogated volume to obtain the instantaneous temperature, which were used to correct the temperature effect. HCN concentrations up to 1500?ppm were detected during the devolatilization stage, and the results indicate a strong temperature dependence of the HCN release.     

高浓度CO2气氛下燃煤氮、硫污染物的释放特性

采用污染物在线分析仪、气相便携红外分析仪研究了程序升温条件下改变氧化介质时煤中氮,硫的释放特性以及含硫物相的浓度变化规律,探讨了不同气氛,CO2浓度与O2浓度单独变化时对NO、SO2析出特性的影响机理.结果表明:O2/CO2燃烧气氛下NO、SO2排放峰值及总量均低于O2/N2气氛.CO2气氛下烟气中存在大量的CO,有利于NO的降解,同时也促进了烟气中其他含硫物相的形成,随着CO2浓度的增加,特别是在燃烧后期,NO、SO2的排放显著降低.O2浓度改变对NO和SO2的释放影响不同:O2浓度升高促进了SO2的析出;但是O2浓度在一定范围内增加对NO的排放并无明显影响,随着O2浓度进一步增加,NO的释放峰向低温区迁移,同时排放量降低.     

Experimental study of influence of temperature on fuel-N conversion and recycle NO reduction in oxyfuel combustion

Coal combustion in O₂/CO₂ environment was examined with a bituminous coal in which the gas-phase and char combustion stages were considered separately. The effects of temperature (1000–1300 °C) and the excess oxygen ratio λ (0.6–1.4) on the conversion of volatile-N and char-N to NOx were studied. Also, the reduction of recycle NOx by fuel-N was investigated under various conditions. The results show that fuel-N conversion to NO in O₂/CO₂ is lower than that in O₂/N₂. In O₂/CO₂ atmosphere, the volatile-N conversion ratios vary from 1–7% to 15–24% under fuel-rich and fuel-lean conditions, respectively. The char-N conversion ratios are 11–28% and 30–50% under fuel-rich and fuel-lean conditions, respectively. The influences of temperature on the conversion of volatile-N to NO under fuel-rich and fuel-lean conditions are contrary. A significant difference for char-N conversion in fuel-rich and fuel-lean conditions is observed. The experimental data of recycle NO reduction indicate that the reduction of recycle NO by gas-phase reaction can be enhanced by volatile-N addition in fuel-lean condition at high temperature, while in fuel-rich condition, the volatile-N influence cancelled out and the overall impact is small. NO/char reaction competes with the conversion of fuel-N to NO at higher temperatures.     

PbO对V_2O_5/TiO_2催化剂NH_3选择性催化还原NO的影响

基于铅在中国燃煤和MSW焚烧烟气中的特点,采用静态N_2物理吸附、NH_3化学吸附、程序升温表面反应、傅里叶变换红外光谱和催化剂活性评价的方法,研究了PbO对1 wt.%V_2O_5/TiO_2催化剂NH_3选择性催化还原NO的影响.结果表明,PbO使SCR催化剂活性降低.对于燃煤锅炉,PbO对V_2O_5/TiO_2催化剂的影响可以忽略不计;对于MSW焚烧炉,PbO是使V_2O_5/TiO_2催化剂失活的重要铅化合物.Pb覆盖在TiO_2表面上,与V活性位覆盖在TiO_2表面上的方式类似.催化剂的失活主要是由于PbO中和了催化剂表面Brφnsted酸性位的酸性,Brφnsted酸性位对于NH_3的吸附和活化起重要作用.     

Measurement of CO,HCN, and NO productions in atmospheric reaction induced by femtosecond laser filament

It is proved that the chemical reaction induced by femtosecond laser filament in the atmosphere produces CO, HCN, and NO, and the production CO and HCN are observed for the first time. The concentrations of the products are measured by mid-infrared tunable laser absorption spectroscopy. In the reduced pressure air, the decomposition of CO₂ is enhanced by vibration excitation induced by laser filament, resulting in the enhanced production of CO and HCN. At the same time, the CO and HCN generated from the atmosphere suffer rotation excitation induced by laser filament, enhancing their absorption spectra. It is found that NO, CO, and HCN accumulate to 134 ppm, 80 ppm, and 1.6 ppm in sealed air after sufficient reaction time. The atmospheric chemical reaction induced by laser filament opens the way to changing the air composition while maintaining environmental benefits.     

二次风率对分级进风燃烧室内湍流燃烧与NOx生成的影响

本文在分级进风燃烧室的热态实验装置上,测量了燃烧室内湍流燃烧的温度场和组分浓度场,研究了分级进风的流量比率即二次风率对燃烧及NOx生成的影响.得到了四组不同二次风率下燃烧室内气体温度和O2、CO2、CO与NO浓度的分布.     

Microscopic insight into catalytic HCN removal over the CuO surface in chemical looping combustion

Hydrogen cyanide (HCN) is well-accepted as a main nitrogen-containing precursor from fuel nitrogen to nitrogen oxides. When using coal as fuel with a CuO-based oxygen carrier in chemical looping combustion (CLC), complex heterogeneous reactions exist among the system of HCN, O₂, NO, H₂O, and CuO particles. This work performs density functional theory (DFT) calculations to systematically probe the microscopic HCN heterogeneous reactions over the CuO particle surface. The results indicate that HCN is chemisorbed on the CuO surface, and the third dissociation step within the consecutive three-step HCN dissociations (HCN*→CN*→NCO*→N*) is the rate-determining step. Namely, the CN*/NCO* radicals can be deemed as an indicator of the performance of HCN removal due to their quite higher dissociation energies. With the existence of O₂, H₂O, and NO, the reaction mechanism of HCN conversion becomes extremely complex. Both DFT calculations and kinetic analyses determine that O₂, NO, and H₂O all significantly accelerate the consumption of CN*/NCO* radicals to produce various N-containing species (NOx or NH₃) to different extents. Finally, a skeletal reaction network in a system of O₂/NO/H₂O/HCN is concluded, which clearly elucidates that CuO exhibits excellent catalytic activity toward HCN removal.     

A reactive molecular dynamics study of NO removal by nitrogen-containing species in coal pyrolysis gas

Coal splitting and staging is a promising technology to reduce nitrogen oxides (NOx) emissions from coal combustion through transforming nitrogenous pollutants into environmentally friendly gasses such as nitrogen (N₂). During this process, the nitrogenous species in pyrolysis gas play a dominant role in NOx reduction. In this research, a series of reactive force field (ReaxFF) molecular dynamics (MD) simulations are conducted to investigate the fundamental reaction mechanisms of NO removal by nitrogen-containing species (HCN and NH₃) in coal pyrolysis gas under various temperatures. The effects of temperature on the process and mechanisms of NO consumption and N₂ formation are illustrated during NO reduction with HCN and NH₃, respectively. Additionally, we compare the performance of NO reduction by HCN and NH₃ and propose control strategies for the pyrolysis and reburn processes. The study provides new insights into the mechanisms of the NO reduction with nitrogen-containing species in coal pyrolysis gas, which may help optimize the operating parameters of the splitting and staging processes to decrease NOx emissions during coal combustion.