1000MW超超临界塔式锅炉NO_x排放特性试验研究

对某电厂1 000MW超超临界塔式锅炉进行了燃烧优化调整试验,分析了省煤器出口O2体积分数、机组负荷、二次风配风方式、紧凑燃尽风(CCOFA)风量、分离燃尽风(SOFA)风量及磨煤机组合方式等因素对锅炉燃烧及NOx排放特性的影响.结果表明:省煤器出口O2体积分数和机组负荷对锅炉热效率和NOx排放质量浓度有较大的影响;随着省煤器出口O2体积分数的增加,NOx排放质量浓度显著上升;随着机组负荷的降低,NOx排放质量浓度先降低后升高,锅炉热效率则先升高后降低;通过设置合理的二次风配风方式、CCOFA和SOFA风量比例以及磨煤机组合方式,既可以提高锅炉热效率又可以降低NOx排放质量浓度.     

超超临界旋流燃烧锅炉低NO_x高效燃烧试验研究

针对某厂660 MW超超临界燃煤锅炉,通过变O_2体积分数、变不同层燃烧器风量分配方式、变内二次风量、变同层燃烧器风量分配方式和变燃尽风量等试验对其进行了性能优化研究。结果表明:投产后锅炉炉渣碳质量分数和CO排放体积浓度较高,但通过高O_2体积分数运行、开大内二次风量和设置合理的外二次风配风方式及燃尽风风门开度,可有效降低炉渣碳质量分数和CO排放体积浓度,其中内二次风量的影响最大;在各影响因素中,运行O_2体积分数和燃尽风量大小对NO_x排放影响最大。通过综合优化调整,锅炉性能得到明显改善,各项主要性能参数均达到或优于设计值。     

不同燃烧条件下煤粉锅炉NOx排放特性的试验研究

以1台670 t/h煤粉锅炉为对象进行了热态试验,研究了煤粉锅炉在不同燃烧条件下NOx 的排放特性.采用在线烟气分析仪对烟气成分进行分析,并通过化学分析获得了飞灰中的可燃物含量.改变二次风配风方式、炉膛出口氧量、周界风风门开度以及磨煤机组合方式等影响因素,对锅炉热效率、飞灰可燃物以及NOx排放浓度进行测量和分析,获得了可减少NOx排放并保持较高燃烧效率的合理燃烧方式:采用均等配风,炉膛出口氧量为2.25%左右,周界风风门开度为15%,采用ABC层的磨煤机组合方式.     

1000MW超超临界锅炉燃烧调整的试验研究

对某电厂1000MW燃煤锅炉进行了燃烧优化调整试验,分析了一次风配风均匀性、煤粉细度、燃烧器配风、运行中氧的体积分数以及燃尽风率对锅炉效率的影响．结果表明：对同层燃烧器外二次风采用两端和中间开度大的配风方式可以改善由于大风箱两端进风引起的沿炉膛宽度方向氧气的体积分数偏差,随着炉内氧气的体积分数增加,锅炉的热效率先提高后降低．当氧气的体积分数在3．0％左右时,锅炉热效率达到最高．随着燃尽风率的逐渐降低,锅炉热效率和NOx排放质量浓度逐渐提高．综合考虑锅炉效率、NOx排放质量浓度以及屏式过热器管壁金属温度,在额定负荷下,燃尽风率以保持在25％左右为宜,此时锅炉热效率为93．9％,NOx排放质量浓度为306．1mg／m^3．     

前后对冲旋流燃煤锅炉CO和NO_x分布规律的试验研究

针对某电厂600MW超临界机组前后对冲燃煤锅炉CO排放质量浓度较高且局部易出现峰值、沿炉膛宽度方向左右侧偏差明显、在不同O2体积分数下变化较大的现象,通过现场试验分析了O2体积分数和燃尽风风量对CO和NOx排放质量浓度的影响,提出了降低CO排放质量浓度的调整控制措施.结果表明:该电厂前后对冲旋流燃煤锅炉的CO排放质量浓度较高是由于配风不均而造成的;关小侧燃尽风二次风挡板开度及燃尽风二次风和三次风挡板开度,有利于降低CO排放质量浓度;综合考虑CO和NOx排放质量浓度的变化趋势,运行O2体积分数为3.0%时较为合适.     

径向浓淡旋流燃烧器NOx排放和燃尽率的试验研究

在设计热功率为1 MW的热态模化实验台上,研究了带有燃尽风的径向浓淡双调风旋流燃烧器的运行特点,得到燃尽风布置的相对位置、一次风率、内二次风率、外二次风率以及二次风旋流强度对NOx生成和飞灰含碳量的影响.结果表明:旋流对冲的煤粉浓淡燃烧配合采用燃尽风(OFA)空气分级燃烧技术,对降低NOx的生成和减少飞灰含碳量非常有益;只有合理地设计和布置OFA燃烧器,才能在降低NOx生成量的同时,尽量减少飞灰含碳量;增大一次风率时,NOx的生成量先增加后减少,而飞灰含碳量先减少后增加;增加内、外二次风的旋流强度,NOx的生成量不断提高,而飞灰含碳量则呈现降低趋势.     

采用缝隙式燃烧器的W火焰锅炉燃烧调整试验研究

针对某电厂采用缝隙式燃烧器的W火焰锅炉高负荷下存在的飞灰含碳量高、屏式过热器超温严重、侧墙结渣严重、排烟温度过高及炉膛前后墙出现偏烧等问题,对锅炉的配风方式和炉膛出口氧体积分数等进行燃烧调整,并提出了相应的优化运行方式.结果表明:优化后的运行方式为中间二次风开度控制在85%,两侧二次风开度控制为90%,三次风开度减小到40%,内二次风保持原工况不变,外二次风开度增大至50%,炉膛出口氧体积分数控制在3%~3.5%,乏气缩孔开度关小至30%;优化后过热器超温问题得到解决,飞灰含碳质量分数降低了7.5%左右,排烟温度降低了8K左右,锅炉效率达到设计值,燃烧经济性显著提高,有效缓解了侧墙结渣和前后墙偏烧的程度.     

600MW对冲燃烧锅炉NO_x排放特性的数值模拟

采用数值模拟方法对某台600 MW超临界对冲燃烧锅炉不同燃尽风(OFA)风量比例和燃烧器运行组合方式时的NOx排放特性进行了研究.结果表明:在600 MW额定负荷时,随着OFA风量比例的增大,飞灰含碳量近似呈线性增加,但NO排放质量浓度明显下降;当OFA风量比例从25%增大至35%时,飞灰含碳量增加了1.22%,NO排放质量浓度下降了293mg/m3,当OFA风量比例接近30%时,飞灰含碳量和NO排放质量浓度综合指标最佳;停运上层燃烧器(运行组合方式为ACDEF)时,飞灰含碳量和NO排放质量浓度相较于停运中层燃烧器(运行组合方式为ABCDE)和下层燃烧器(运行组合方式为BCDEF)时有所下降;与停运下层燃烧器相比,停运上层燃烧器时飞灰含碳量降低了0.46%,NO排放质量浓度降低了40mg/m3.     

660 MW超超临界二次再热燃煤锅炉运行特性试验研究

针对某660 MW超超临界二次再热旋流燃烧锅炉投产后锅炉燃烧均衡性较差,锅炉热效率和一、二次再热汽温偏低,NO_x排放质量浓度偏高等问题,通过改变O₂体积分数、煤粉细度、一次风量、外二次风挡板开度、异层燃烧器风量分配方式、燃尽风直流风水平摆角和燃尽风量等参数对其进行了性能优化试验研究。结果表明：通过提高O₂体积分数运行和磨煤机动态分离器转速,以及合理设置外二次风配风方式、燃尽风直流风水平摆角及燃尽风风门开度,有效降低了灰、渣碳质量分数和CO排放浓度,提高了一、二次再热蒸汽温度。在各影响因素中,同层煤粉燃烧器外二次风风门开度和燃尽风直流风水平摆角的配置,对锅炉燃烧均衡性的影响至关重要;运行O₂体积分数和燃尽风量大小对NO_x排放影响最大。通过综合优化调整,锅炉性能得到明显改善,各项主要性能参数均达到或优于设计值。     

低NOx排放燃烧技术及燃烧优化的试验研究

介绍了煤燃烧过程中NOx生成机理和电站锅炉采用低NOx燃烧技术.通过对某电厂670 t/h锅炉进行炉膛出口氧量、一次风速、二次风配风方式、燃烧器上、下组的给粉方式、一次风煤粉浓淡比等对NOx排放量、飞灰可燃物含量和锅炉再热蒸汽温度的影响规律的试验研究.得出水平浓淡风煤粉燃烧技术能降低NOx排放量,确定了给出锅炉优化运行方式.试验结果表明燃烧优化调整是提高锅炉运行的经济性和降低NOx排放量的有效方法.     

Recombination of hydrogen-air catalyzed by Pt/C catalyst in a confined vessel at ambient temperature

Most of the previous studies have investigated the detonation and combustion characteristics of hydrogen and air mixtures, but the change process of hydrogen-air recombination reaction at ambient temperature is unclear. In this study, the variation of temperature and hydrogen conversion during the H₂-air mixture reaction catalyzed by Pt/C catalyst was examined. Experiments were carried out in a small-scale cylindrical vessel to investigate the effects of hydrogen volume fraction, catalyst mass, and inlet gas flow rate on the reaction process. The results revealed that the reaction temperature climbed as the hydrogen volume fraction increased, with a peak value achieved when the hydrogen volume fraction reached 35 vol%, and subsequently reduced as the hydrogen volume fraction increased further. The increase of the inlet gas flow rate also promoted the growth of reaction temperature. However, there was no significant linear relationship between the rise of catalyst mass and the change of reaction temperature.     

Cooling performance investigation of electronics cooling system using Al2O3–H2O nanofluid

In this study, the cooling performance of Al₂O₃–H₂O nanofluid was experimentally investigated as a much better developed alternative for the conventional coolant. For this purpose the nanofluid was passed through the custom-made copper minichannel heat sink which is normally attached with the electronic heat source. The thermal performance of the Al₂O₃–H₂O nanofluid was evaluated at different volume fraction of the nanoparticle as well as at different volume flow rate of the nanofluid. The volume fraction of the nanoparticle varied from 0.05 vol.% to 0.2 vol.% whereas the volume flow rate was increased from 0.50 L/min to 1.25 L/min. The experimental results showed that the nanofluid successfully has minimized the heat sink temperature compared to the conventional coolant. It was noticed also that the thermal entropy generation rate was reduced via using nanofluid instead of the normal water. Among the other functions of the nanofluid are to increase the frictional entropy generation rate and to drop the pressure which are insignificant compared to the normal coolant. Given the improved performance of the nanofluid, especially for high heat transportation capacity and low thermal entropy generation rate, it could be used as a better alternative coolant for the electronic cooling system instead of conventional pure water.     

太阳能驱动的膜式加热加湿系统性能实验研究

中空纤维膜加湿系统能从根本上解决空气加湿过程中气液夹带的问题.通过搭建太阳能驱动的中空纤维膜加热加湿系统试验台并在冬季进行实验测试,分析出太阳能辐射量、空气体积流量和热水体积流量对系统加热加湿性能的影响.研究发现提高太阳能辐射量和空气体积流量对系统的加湿能力和热性能系数均有积极影响,而前者的影响更为显著.为了获得最好的...     

Comparative study between parallel and counter flow configurations between air and falling film desiccant in the presence of nanoparticle suspensions

A comparative numerical study is employed to investigate the heat and mass transfer between air and falling film desiccant in parallel and counter flow configurations. Nanoparticles suspensions are added to the falling film desiccant to study heat and mass transfer enhancements. The numerical results show that the parallel flow channel provides better dehumidification and cooling processes of the air than counter flow configuration for a wide range of pertinent parameters. Low air Reynolds number enhances the dehumidification and cooling rates of the air and high air Reynolds number improves the regeneration rate of the liquid desiccant. An increase in the channel height results in enhancing the dehumidification and cooling processes of air and regeneration rate of liquid desiccant. The dehumidification and cooling rates of air are improved with an increase in the volume fraction of nanoparticles and dispersion factor. Copyright © 2003 John Wiley & Sons, Ltd.     

Modeling soot formation in turbulent kerosene/air jet diffusion flames

Soot volume fraction and number density in a turbulent diffusion flame burning kerosene/air were predicted using two approaches. The first used a conventional soot inception model based on the acetylene concentration and is referred to as the acetylene model. The second used a soot inception model based on the formation rate of three and two ring aromatics [1] and is referred to as the PAH inception model. The soot models account for inception, coagulation, surface growth, and oxidation processes. The Favre-averaged governing equations of mass, momentum, and energy in the turbulent field were solved in conjunction with the k − ε turbulence model. A recently developed detailed reaction mechanism for kerosene/air [2] was coupled to the turbulent flow field by the stretched laminar flamelet approach. A radiation heat transfer model that considered the soot, water and CO₂ levels is included. Models are validated by comparing the numerical results to the experimental results of Young et al. [3] for a turbulent jet-flame burning pre-vaporized aviation kerosene. Significant improvements in the prediction of soot volume fraction are obtained using the PAH inception model for soot inception compared to the conventional acetylene approach.     

Turbulent diffusion flame sooting—Relationship to smoke-point tests

Soot volume fractions have been measured in turbulent diffusion flames issuing into still air for a range of gaseous and liquid fuels. The liquid fuels were prevaporized and all fuels had a common inlet temperature. It was found that flame widths were independent of fuel stoichiometry and were only a function of fluid mechanics. Soot quantities peaked at a height of 0.25–0.55 of flame length. Normalized radial profiles of soot volume fraction were approximately self-similar for all fuels.A characteristic soot volume fraction was defined for each fuel and found to be largely independent of residence time in the flame. The turbulent flame characteristic soot volume fraction was related to its laminar flame counterpart and was found to be predictable from the laminar flame smoke-point flow rate.     

低体积分数瓦斯发动机混合器优化

针对某型号低体积分数瓦斯发动机启机成功率低的问题开展分析与研究。基于ANSYS Workbench的Fluent模块,建立从燃料阀前到增压器前的流道三维数模,并对模型进行标定。基于该模型开展仿真计算和优化设计,并在低体积分数瓦斯发动机上进行验证。试验结果表明：改进后的导向型混合器能够在瓦斯体积分数为11%~14%的工况下,在增压器入口前可获得0.7以上的过量空气系数,启机成功率大大提高。     

NCN concentration and interfering absorption by CH2O, NH and OH in low pressure methane/air flames with and without N2O

Absorption spectra in the wavelength region around 329 nm have been recorded with the cavity ring-down technique in various low pressure (200 hPa) CH₄/air flames, two of which with N₂O (nitrous oxide) addition. NCN (cyanonitrene) absorption appears to be significant only in N₂O-enriched flames, which also reveal spectrally nearby absorption by NH. In a φ = 1.14, N₂O oxidizer volume fraction = 57.0% flame, an upper limit for the NCN mole fraction of 4.0 × 10⁻⁶ has been found. Absorption spectra have been recorded as a function of height and these clearly show the presence of CH₂O (formaldehyde) and OH as well. In CH₄/air flames, absorption by CH₂O at and near the flame front is strong enough to mask any possible absorption signal due to NCN. OH absorption spectrally coincident with the maximum NCN absorption has been observed as well. CH₂O absorption is present throughout the whole 327–331 nm range, which can severely affect the accuracy of NCN concentration measurements if both species are present in the measurement volume. This necessitates the acquisition of continuous spectra instead of absorption measurements at a few specific wavelengths. Absorption signals at wavelengths characteristic for NCN, CH₂O, NH and OH are analysed as function of height in the flame. Probabilities that these signals may be assigned unambiguously to a single species are discussed.     

In-situ studies of gas phase composition and anode surface temperature through a model DIR-SOFC steam–methane reformer at 973.15 K

A comparative study into the effects of total volume flow rate, methane ‘residency time’, methane volume flow rate, and steam-to-carbon ratio on the steam–methane reforming process was performed in a model Direct Internal Reforming SOFC (DIR-SOFC) reformer operating in steady state at a nominal temperature of 973 K. The spatial distributions of major gas species (CH₄, H₂O, CO, CO₂, and H₂) over the reformer surface were measured in-situ using Vibrational Raman Spectroscopy. Surface temperature measurements were recorded using IR thermometry. The effects of varying the intake mole fractions of methane and water were considered. The results of this work have demonstrated a strong positive correlation between the intake mole fraction of methane and the rate of the steam–methane reformation reaction. A weak negative correlation between the intake mole fraction of water and the rate of the reformation reaction was also shown.     

Experimental microchannel heat sink performance studies using nanofluids

In this study, microchannel heat sink (MCHS) performance using nanofluids as coolants is addressed. We first carried out a simple theoretical analysis that indicated more energy and lower MCHS wall temperature could be obtained under the assumption that heat transfer could be enhanced by the presence of nanoparticles. Experiments were then performed to verify the theoretical predictions. A silicon MCHS was made and CuO–H₂O mixtures without a dispersion agent were used as the coolants. The CuO particle volume fraction was in the range of 0.2 to 0.4%. It was found that nanofluid-cooled MCHS could absorb more energy than water-cooled MCHS when the flow rate was low. For high flow rates, the heat transfer was dominated by the volume flow rate and nanoparticles did not contribute to the extra heat absorption. The measured MCHS wall temperature variations agreed with the theoretical prediction for low flow rate. For high flow rate, the measured MCHS wall temperatures did not completely agree with the theoretical prediction due to the particle agglomeration and deposition. It was also found that raising the nanofluid bulk temperature could prevent the particles from being agglomerated into larger scale particle clusters. The experimental result also indicated that only slightly increase in pressure drop due to the presence of nanoparticles in MCHS operation.