O_2/CO_2气氛下高岭土和石灰石控制燃煤PM_1排放的试验研究

在O2/CO2气氛和不同温度下,在沉降炉中对分别添加2种吸附剂的2种典型褐煤进行了燃烧试验,研究了高岭土和石灰石对碱金属、重金属和硫的吸附以及温度对PM1排放特性的影响.结果表明:高岭土与煤中金属发生吸附反应,而石灰石吸附了大量的硫,使金属和硫由小于1μm的颗粒向大于1μm的颗粒转移;添加吸附剂后,2种煤的PM1排放均明显减少,且均在1100℃时减排效果最好.对PM1的减少率进行比较发现,A煤添加高岭土比B煤添加高岭土的效果好,而B煤添加石灰石比A煤添加石灰石的效果好.     

220MW煤粉炉PM2.5浓度排放特性的试验研究

本文采用荷电低压撞击器(ELPI),通过对二级稀释系统采样对某电厂220 MW煤粉锅炉PM2.5的浓度排放特性进行了研究。研究结果显示,煤粉锅炉所产生烟气中PM2.5粒数浓度呈较明显的双峰分布,小颗粒峰值一般在0.12μm或0.07μm,较大颗粒峰值一般在0.76μm,PM2.5粒数浓度一般为几百万粒/cm3,主要取决于由气化凝结机理形成的细模态颗粒物PM0.38,PM2.5质量浓度呈单峰分布,一般为几百mg/m3,其质量浓度主要取决于由中间模态颗粒物PM0.38~2.5;采用覆膜滤料的布袋除尘器和电袋联合除尘器对PM2.5具有较好的除尘效果,二电场电袋复合除尘器出口烟气中PM2.5最小可达200μg/m3,粒数浓度在几万粒/cm3;当除尘效果较好时,湿法脱硫装置出口烟气中PM2.5粒数浓度和质量浓度可能会有所增加。     

神华煤粉在CO2和N2高温气氛下SOx生成释放规律的研究

通过在固定反应床实验系统上,进行了不同燃烧气氛、不同氧气体积浓度、不同燃烧环境温度及不同颗粒粒径下神华煤粉的燃烧实验,在实验过程中对气体污染物SOx生成释放规律进行了研究。发现了CO2气氛下SOx呈现双峰现象,即在煤粉燃烧过程中,S元素转化成SOx的过程分为挥发分释放阶段和焦炭燃烧阶段。SOx释放过程中第一个峰的积分值占总积分值的百分比随着燃烧环境温度的升高而降低,即在较高的燃烧环境温度下SOx主要来源于无机硫化合物。在煤粉燃烧过程中,SOx生成释放曲线的2个峰值随着氧气浓度的升高而增加,SOx总生成量也略为增加;单位氧气消耗量生成的SOx(记为YSOx)随着燃烧环境温度的升高而升高;煤粉颗粒粒径对YSOx的影响规律不明显。高温1 600℃下,煤粉自固硫特性的作用下SOx的生成量与1 000℃时相当。     

湿法脱硫对660MW煤粉炉PM_(2.5)排放影响的实验研究

为研究湿法脱硫系统对电站煤粉锅炉PM2.5排放特性的影响,以一台660 MW煤粉炉为研究对象,通过两级稀释系统对PM2.5等速采样,利用低压荷电撞击器(ELPI)监测污控设备对PM2.5粒数浓度和质量浓度的影响。结果表明:锅炉产生的PM2.5粒数浓度与质量浓度均呈双峰分布;脱硫后各级PM2.5浓度均有所升高;除雾器清洗可降低PM2.5排放量而增加运行的循环浆液泵数可增加PM2.5排放量。由于脱硫浆液会形成颗粒,除雾效果不佳的湿法脱硫装置可增加PM2.5排放量。     

电子低压冲击器不同稀释比对PM2．5排放测试的影响

燃煤电厂PM2.5排放检测技术是目前研究的热点和难点,电子低压冲击器（ELPI）可以实时得到颗粒物的质量浓度,方便工程现场测试。利用ELPI对扬州第二发电厂600 Mw机组湿法脱硫后烟气进行测试研究,并分别尝试采用一级稀释器和两级稀释器两种方法进行比较,结果表明：两种稀释比测得颗粒数浓度粒径分布规律基本一致,采用两级稀释测得PM1、PM2.5、PM2.5数浓度结果均小于一级稀释;对于质量浓度,采用两级稀释测得PM1、PM2.5结果小于一级稀释,而PM2.5测量结果却大于一级稀释。     

O2/CO2气氛下考虑斯蒂芬流的碳粒燃烧模型

针对富氧燃烧中的O2/CO2气氛,考虑表面氧化反应、表面还原反应和斯蒂芬流,建立了新的碳粒燃烧理论模型.实验表明,与未考虑斯蒂芬流的模型相比,该模型的预报结果与实验值符合得更好.对斯蒂芬流影响的分析计算显示,无论斯蒂芬流存在与否,燃烧速率均随氧体积分数(20%和30%)、粒径(100～240,μm)、表面温度(1,750～1,900,K)、环境气体温度(1,200～1,400,K)的增大而增大,但由于斯蒂芬流阻碍了反应气体向颗粒表面的扩散,减缓了反应进程,因此在本文计算条件下,新模型计算得到的燃烧速率比未考虑斯蒂芬流的情况低1/4～1/3.     

煤粉粒径对燃烧过程中可吸入颗粒物排放特性的影响

采用沉降炉研究了煤粉粒径对可吸入颗粒物排放特性的影响。试验用煤种为平顶山烟煤,三种煤粉的粒径分别是100~200μm,63~100μm和小于63μm;燃烧试验在1400℃,空气气氛下进行。试验用低压撞击器(LPI)按不同粒径大小从0.03~10μm分为13级,分别采集燃烧后的可吸入颗粒物。结果显示煤粉粒径是燃烧过程中影响PM10(10μm以下颗粒物)生成的重要因素,粒径越小,生成的PM10越多;三种粒径煤粉燃烧后生成的PM10粒径分布都是相似的双峰分布,峰值点分别出现在0.1μm和4.3μm左右;通过对PM10的成分分析得知,峰值粒径在0.1μm左右的颗粒物主要含硫酸盐,峰值粒径在4.3μm左右的颗粒物主要含硅铝酸盐;随着煤粉粒径的减小,Al2O3、SiO2、Na2O、K2O、Fe2O3、CaO几种金属元素分别在PM1.0与PM1.0 中的浓度值增加很大。图3表4参8     

O2/CO2气氛下煤燃烧NOx排放特性的实验研究

利用管式电阻炉在O₂/CO₂气氛和O₂/N₂气氛下对煤粉燃烧过程中NO_x排放特性进行实验,研究在不同停留时间、炉内燃料/氧化学当量比、温度、氧浓度等因素对燃煤过程中NO_x放特性的影响,并对这两种燃烧方式下NO_x的排放特性进行对比。结果表明:在O₂/CO₂气氛下NO_x的生成量要远远低于O₂/N₂气氛下NO_x的生成量。随着停留时间的延长,NO_x沿程释放特性是先增大后减少。随着燃料/氧化学当量比的增加,NO_x排放浓度也呈现出先增加后降低的趋势。随着炉内温度的增加,2种气氛下NO_x的排放浓度均增加。随着氧浓度的提高,NO_x排放浓度增大。     

不同煤粉燃烧对一次颗粒物排放特性的影响

在实验室条件下,以沉降炉作为燃烧设备,用8级Andersen粒子撞击器分离并收集燃烧后的颗粒物,研究了3种煤粉燃烧后生成的一次颗粒物中可吸入颗粒物排放的特性.结果表明,煤粉燃烧后,PM10、PM2.5、PM1的排放量并不是煤中灰分、固定碳或挥发分的单一函数.用Rosin-Ramm ler函数对一次颗粒物的质量-粒径分布进行曲线拟合,并计算了其中PM2.5/PM10、PM1/PM2.5的值.结果显示,灰分较高的煤粉生成的PM2.5/PM10、PM1/PM2.5值较高,灰分含量低的煤粉生成的PM2.5/PM10、PM1/PM2.5值较低.但PM2.5/PM10、PM1/PM2.5的值与灰分含量并不成正相关性.分析认为,不同煤粉中组分形式和含量的不同,影响了煤粉燃烧后一次颗粒物形成的过程,造成一次颗粒物排放特性的不同.     

O2/CO2气氛下生物质混煤燃烧SO2排放特性的实验研究

在水平管式炉上通过在线烟气分析仪研究了O2/CO2气氛下生物质混合比例、温度、燃烧气氛及氧浓度对生物质混煤SO2排放特性的影响规律。结果表明,O2/CO2气氛下,随着生物质混合比例的增大,生物质混煤SO2释放峰值减小,SO2排放完毕的时间减少,SO2的排放量降低;随着温度的升高,生物质混煤SO2的排放量增加。O2/CO2和O2/N2气氛下随着氧浓度的增大,生物质混煤SO2的排放量均增加。相同氧浓度时,O2/CO2气氛下生物质混煤SO2的排放量略小于O2/N2气氛下的情况,其降低幅度约为5%左右。     

Explosion behavior of CH4/O2/N2/CO2 and H2/O2/N2/CO2 mixtures

In this work, the explosion behavior of stoichiometric CH₄/O₂/N₂/CO₂ and H₂/O₂/N₂/CO₂ mixtures has been studied both experimentally and theoretically at different CO₂ contents and oxygen air enrichment factors. Peak pressure, maximum rate of pressure rise and laminar burning velocity were measured from pressure time records of explosions occurring in a closed cylindrical vessel. The laminar burning velocity was also computed through CHEMKIN–PREMIX simulations.     

Hydrogen permeation through a Pd-based membrane and RWGS conversion in H2/CO2, H2/N2/CO2 and H2/H2O/CO2 mixtures

This study investigated the effect of gases such as CO₂, N₂, H₂O on hydrogen permeation through a Pd-based membrane −0.012 m² – in a bench-scale reactor. Different mixtures were chosen of H₂/CO₂, H₂/N₂/CO₂ and H₂/H₂O/CO₂ at temperatures of 593–723 K and a hydrogen partial pressure of 150 kPa. Operating conditions were determined to minimize H₂ loss due to the reverse water gas shift (RWGS) reaction. It was found that the feed flow rate had an important effect on hydrogen recovery (HR). Furthermore, an identification of the inhibition factors to permeability was determined. Additionally, under the selected conditions, the maximum hydrogen permeation was determined in pure H₂ and the H₂/CO₂ mixtures. The best operating conditions to separate hydrogen from the mixtures were identified.     

Burning velocities and kinetics of H2/NF3/N2, CH4/NF3/N2, and C3H8/NF3/N2 flames

The combustion characteristics and reaction mechanism of mixtures containing nitrogen trifluoride (NF₃) were investigated. Burning velocities for H₂/NF₃/N₂, CH₄/NF₃/N₂, and C₃H₈/NF₃/N₂ flames were determined for the first time at various equivalence ratios and N₂ mole fractions. The burning velocities of the latter two flames were similar and showed peaks at equivalence ratios of ∼1.0, while those of the H₂/NF₃/N₂ flames had the pronounced peak at low equivalence ratios where the formation of the wrinkled flames was observed. A detailed kinetic model was constructed to simulate the laminar burning velocities of H₂/NF₃/N₂ and CH₄/NF₃/N₂ flames. The model accurately reproduced the experimental results. Analyses of the reaction mechanism revealed the major reaction pathways that involve the decomposition of NF₃, the oxidation and chain-fluoridation of H₂ and CH₄, and the formation of N₂.     

Laminar burning velocities and transition to unstable flames in H2/O2/N2 and C3H8/O2/N2 mixtures

Effects of positive flame stretch on laminar burning velocities, and conditions for transition to unstable flames, were studied experimentally for freely propagating spherical flames at both stable and unstable preferential-diffusion conditions. The data base involved new measurements for H₂/O₂/N₂ mixtures at values of flame stretch up to 7600 s⁻¹, and existing measurements for C₃H₈/O₂/N₂ mixtures at values of flame stretch up to 900 s⁻¹. Laminar burning velocities varied linearly with increasing Karlovitz numbers—either decreasing or increasing at stable or unstable preferential-diffusion conditions—yielding Markstein numbers that primarily varied with the fuel-equivalence ratio. Neutral preferential-diffusion conditions, however, were shifted toward the unstable side of the maximum laminar burning velocity condition that the simplest preferential-diffusion theories associate with neutral stability. All flames exhibited transition to unstable flames: unstable preferential-diffusion coditions yielded early transition to irregular flame surfaces, and stable preferential-diffusion conditions yielded delayed transition to cellular flames by hydrodynamic instability. Conditions for hydrodynamic instability transitions for H₂/O₂/N₂ mixtures were consistent with an earlier correlation due to Groff for propane/air flames, based on the predictions of Istratov and Librovich.     

High performance composite hollow fiber membranes for CO2/H2 and CO2/N2 separation

The search for a clean energy source as well as the reduction of CO₂ emissions to the atmosphere are important strategies to resolve the current energy shortage and global warming issues. We have demonstrated, for the first time, a Pebax/poly(dimethylsiloxane)/polyacrylonitrile (Pebax/PDMS/PAN) composite hollow fiber membrane not only can be used for flue gas treatment but also for hydrogen purification. The composite membranes display attractive gas separation performance with a CO₂ permeance of 481.5 GPU, CO₂/H₂ and CO₂/N₂ selectivity of 8.1 and 42.0, respectively. Minimizing the solution intrusion using the PDMS gutter layer is the key to achieving the high gas permeance while the interaction between poly(ethylene oxide) (PEO) and CO₂ accounts for the high selectivity. Effects of coating solution concentration and coating time on gas separation performance have been investigated and the results have been optimized. To the best of our knowledge, this is the first polymeric composite hollow fiber membrane for hydrogen purification. The attractive gas separation performance of the newly developed membranes may indicate good potential for industrial applications.     

Role of CO2 in the CH4 oxidation and H2 formation during fuel-rich combustion in O2/CO2 environments

The effect of CO₂ reactivity on CH₄ oxidation and H₂ formation in fuel-rich O₂/CO₂ combustion where the concentrations of reactants were high was studied by a CH₄ flat flame experiment, detailed chemical analysis, and a pulverized coal combustion experiment. In the CH₄ flat flame experiment, the residual CH₄ and formed H₂ in fuel-rich O₂/CO₂ combustion were significantly lower than those formed in air combustion, whereas the amount of CO formed in fuel-rich O₂/CO₂ combustion was noticeably higher than that in air. In addition to this experiment, calculations were performed using CHEMKIN-PRO. They generally agreed with the experimental results and showed that CO₂ reactivity, mainly expressed by the reaction CO₂ + H → CO + OH (R1), caused the differences between air and O₂/CO₂ combustion under fuel-rich condition. R1 was able to advance without oxygen. And, OH radicals were more active than H radicals in the hydrocarbon oxidation in the specific temperature range. It was shown that the role of CO₂ was to advance CH₄ oxidation during fuel-rich O₂/CO₂ combustion. Under fuel-rich combustion, H₂ was mainly produced when the hydrocarbon reacted with H radicals. However, the hydrocarbon also reacted with the OH radicals, leading to H₂O production. In fact, these hydrocarbon reactions were competitive. With increasing H/OH ratio, H₂ formed more easily; however, CO₂ reactivity reduced the H/OH ratio by converting H to OH. Moreover, the OH radicals reacted with H₂, whereas the H radicals did not reduce H₂. It was shown that OH radicals formed by CO₂ reactivity were not suitable for H₂ formation. As for pulverized coal combustion, the tendencies of CH₄, CO, and H₂ formation in pulverized coal combustion were almost the same as those in the CH₄ flat flame.     

Experimental and numerical investigation of low-pressure laminar premixed synthetic natural gas/O2/N2 and natural gas/H2/O2/N2 flames

The oxidation of laminar premixed natural gas flames has been studied experimentally and computationally with variable mole fractions of hydrogen (0, 20, and 60%) present in the fuel mixture. All flames were operated at low pressure (0.079 atm) and at variable overall equivalence ratios (0.74<?<1.0) with constant cold gas velocity. At the same global equivalence ratio, there is no significant effect of the replacement of natural gas by 20% of H₂. The small differences recorded for the intermediate species and combustion products are directly due to the decrease of the amount of initial carbon. However, in 60% H₂ flame, the reduction of hydrocarbon species is due both to kinetic effects and to the decrease of initial carbon mole fraction. The investigation of natural gas and natural gas/hydrogen flames at similar C/O enabled identification of the real effects of hydrogen. It was shown that the presence of hydrogen under lean conditions activated the H-abstraction reactions with H atoms rather than OH and O, as is customary in rich flames of neat hydrocarbons. It was also demonstrated that the presence of H₂ favors CO formation.     

Combustion characteristics of H2/N2 and H2/CO syngas nonpremixed flames

Turbulent nonpremixed H₂/N₂ and H₂/CO syngas flames were simulated using 3D large eddy simulations coupled with a laminar flamelet combustion model. Four different syngas fuel mixtures varying from H₂-rich to CO-rich including N₂ have been modelled. The computations solved the Large Eddy Simulation governing equations on a structured non-uniform Cartesian grid using the finite volume method, where the Smagorinsky eddy viscosity model with the localised dynamic procedure is used to model the sub-grid scale turbulence. Non-premixed combustion has been incorporated using the steady laminar flamelet model. Both instantaneous and time-averaged quantities are analysed and data were also compared to experimental data for one of the four H₂-rich flames. Results show significant differences in both unsteady and steady flame temperature and major combustion products depending on the ratio of H₂/N₂ and H₂/CO in syngas fuel mixture.     

Structural and electrochemical properties of CeO2 and mixed CeO2/SnO2 coatings

CeO₂ and mixed CeO₂/SnO₂ coatings were prepared via the sol-gel method using the aqueous-based process. The addition of SnO₂ to the mixed oxides coatings on their structural characteristics and optical properties were studied. The influence of added SnO₂ in the CeO₂ oxide coatings on the inserted/extracted charge was determined by chronocoulometric measurements. It was found that for 60 nm thick films the inserted/extracted charge was twice as large (Q = 10 mC/cm²) for films containing 17 mol% SnO₂ if compared to CeO₂.     

Experimental and modeling studies of C2H4/O2/Ar, C2H4/methylal/O2/Ar and C2H4/ethylal/O2/Ar rich flames and the effect of oxygenated additives

The addition of dimethoxymethane (DMM or methylal) and diethoxymethane (DEM or ethylal) to a rich ethylene/oxygen/argon flame has been investigated by measuring the depletion of soot precursors. Three rich premixed ethylene/oxygen/argon (with and without added methylal or ethylal) flat flames have been stabilized at low-pressure (50 mbar) on a Spalding–Botha type burner with the same equivalence ratio of 2.50. Identification and monitoring of signal intensity profiles of species within the flames have been carried out by using molecular beam mass spectrometry (M.B.M.S.). The replacement of some C₂H₄ by C₃H₈O₂ or C₅H₁₂O₂ is responsible for a decrease of the maximum mole fractions of the detected intermediate species. This phenomenon is noticeable for C₂–C₄ intermediates and becomes more effective for C₅–C₁₀ species, mainly when C₃H₈O₂ added.A new kinetic model has been elaborated and contains 546 reactions and 107 chemical species in order to simulate the three investigated flames: C₂H₄/O₂/Ar, C₂H₄/DMM/O₂/Ar and C₂H₄/DEM/O₂/Ar. The reaction mechanism well reproduces experimental mole fraction profiles of major and intermediate species, and underlines the effect of methylal and ethylal addition on species concentration profiles for these flames.