基于波瓣旋流燃烧器的甲烷燃烧污染物排放特性

贫燃预混燃烧方式是抑制燃烧过程中NO_x生成的方法之一,但易出现燃烧不稳定现象.针对这一问题,试验采用波瓣旋流燃烧器,研究了当量比、预混气分级比、预混气分级形式对NO_x和CO排放规律、燃烧室声压峰值及火焰形态的影响.结果表明,随着当量比的减小,烟气中NO_x浓度减小,而CO浓度上升.旋流侧流量/波瓣内侧流量减小时,烟气中NO_x浓度降低,CO浓度增大.通过调节旋流器和波瓣外侧预混气分级比,NO_x和CO的排放浓度都有所下降,并在旋流侧流量、波瓣内侧流量、波瓣外侧流量分级比为6∶0∶4时浓度较低.燃烧室内声压峰值随当量比的减小而增大.当量比为0.60,预混气分级比为5∶0∶5时,燃烧室声压峰值最低,燃烧较为稳定.     

零碳燃料对燃气锅炉燃烧过程调控作用

利用小型化模拟炉膛开展了零碳燃料氢气对燃气锅炉燃烧过程调控作用实验研究,研究了掺氢比对炉膛内部预混火焰宏观形态、炉膛温度均匀性、炉膛污染物排放规律的影响,并总结了CO及NO_x的排放规律。实验结果表明：随着预混当量比增加,纯甲烷火焰长度逐渐缩短;对于20%掺氢火焰,随着预混程度的提高,火焰长度降低明显;不同火焰条件下,炉膛温度只由燃烧功率控制;改变燃烧条件时,处于壁面附近位置的温度变化较为平稳,而靠近火焰处温度变化较大;天然气中掺入氢气,燃烧时可以有效降低未燃CO排放;在相同预混程度下,全局当量比减小导致未燃空气增加,热量被稀释,火焰温度降低,热力型NO_x的生成降低;随着掺氢比的增加,燃烧时火焰温度升高,导致热力型NO_x排放增加。     

当量比对微型燃气轮机H2/Air燃烧特性的影响

为了探究氢气微型燃气轮机的燃烧特性,用数值模拟方法分析了6种不同当量比工况下的燃烧室内流场特性、压力损失、燃烧效率、NO_x排放和速度分布等参数。结果表明：当量比对回流区的范围影响不大,压力损失和出口速度随当量比增加逐渐增大,出口温度分布系数（OTDF）、排气温度和NO_x排放随当量比的增加先增大后减小;径向速度的分布关于燃烧室中心轴线对称;当量比小于1时,燃烧效率在99.9%以上;当量比大于1时,燃烧效率随当量比增加而降低;当量比为1时,排气温度达到2 500 K,NO_x排放达到最大值,偏离化学当量比燃烧有利于抑制NO_x的生成。     

两级浓淡燃烧室内氨-氢-空气预混旋流燃烧过程的NOx排放特性

为了掌握燃气轮机两级浓淡燃烧室内氨-氢-空气预混旋流火焰的NO_x排放特性和影响NO_x生成的动力学机制,对氨-氢-空气预混旋流燃烧过程进行了三维反应流数值模拟并开展了燃烧反应动力学特性研究．结果表明：在掺氢比为35%、压力为0.5 MPa且当量比为1.20的绝热燃烧工况下,NO_x排放可降至54×10^-6(15%O₂).H+O₂(+M)=HO₂(+M)是燃烧压力影响氨-氢燃料燃烧过程中NO_x排放的关键反应．燃烧压力的升高会促进NO与HO₂反应并转化为NO₂．对于氨-氢混合燃料而言,过高的掺氢比(60%～80%)会导致NO_x排放显著升高,而根据壁面热损失程度的不同,适当的掺氢比(35%～55%)则有利于实现较低的NO_x排放(54×10^-6～86×10^-6 (15%O₂...     

燃机电厂NOx排放过高的分析与优化研究

对燃机电厂NO_x排放过高的原因进行深入分析,对比空气湿度、机组负荷和天然气热值对燃机电厂NO_x排放的影响,据此制定有效的优化改造方案。结果显示：空气湿度较大时,机组NO_x排放降低;天然气热值较高时,NO_x的排放量相应增加。通过烟气加装脱硝装置、燃机进气喷雾加湿改造以及燃机预混旋流片改造,均能有效降低NO_x排放。     

当量比对甲烷预混低旋流燃烧的影响

通过实验和数值模拟的方法研究了甲烷/空气预混低旋流燃烧的流场结构及当量比对甲烷低旋流燃烧的影响.结果表明,甲烷/空气预混低旋流气流在喷嘴出口处扩张,形成有利于燃烧稳定的低速区;预混火焰"悬浮"于喷嘴上方,在剪切区的内侧,火焰呈W型;富燃时,随着当量比的增加,火焰的推举高度略有增加;甲烷/空气预混低旋流流场具有自相似性,无量纲轴向速度的径向分布几乎不受当量比的影响.同时,燃烧室出口的温度随着当量比的增加而增加,并且在当量比为0.8~1.4时变化较为明显,当量比超过1.4后,增加趋势变缓.     

微小定容腔内喷射正丁烷/空气着火与燃烧特性

利用微小定容腔着火及燃烧试验平台,开展了喷射进气时正丁烷/空气的热着火与燃烧特性研究.结果表明:火焰在热丝表面形成后向外传播,传播过程中火焰呈现强烈褶皱状,后期表现为多点着火;高热丝温度下,当量比为0.9～1.5时出现"着火—熄火—再着火"的现象.着火时间随热丝温度增加而缩短,缩短程度和当量比有关;低热丝温度下,着火时间随当量比增大而延长,高热丝温度下,着火时间随当量比增大先缩短后延长,这是预混气加热和化学反应影响程度不同所致.在接近贫/富燃极限工况时,热丝温度对燃烧中最大压力差Δpmax的影响不明显,其他条件下,随温度和当量比增大,Δpmax均先增大后减小.     

多孔介质燃烧器的辐射输出效率和污染物

使用双温度体积平均模型、详细化学反应机理GRI3．0，对甲烷，空气预混气在多孔介质燃烧器内的预混火焰进行模拟．分析不同当量比和质量流量下的预热效率、辐射输出效率以及污染物排放情况，并对辐射输出效率随多孔介质热物性参数的变化进行敏感性分析．结果表明，增大相间对流换热系数或减小当量比、质量流量及固相消光系数都可以提高辐射输出效率，减小当量比或质量流量可以减少污染物排放．在所有的影响因素中，当量比的影响最大，发展超贫燃燃烧技术是获得高效低污染多孔介质燃烧器的关键．     

旋流燃烧器结构对116 MW立式燃气锅炉低氮性能的影响

利用ANSYS-Fluent CFD软件,采取Realizable k-ε模型和有限速率/涡耗散模型对某116 MW立式燃气锅炉进行数值模拟,该立式锅炉有左右两个燃烧器入口。对比分析了不同旋流数(0、0.54、0.77、1.11、1.67)和左右入口空气不同旋转方向下,燃烧室内中心截面速度矢量分布、温度分布以及轴向不同截面平均温度和NO_x质量分数。结果表明：旋流空气能在炉内形成中心回流区,使得燃料与空气有效混合,燃烧扩散到整个炉膛,随着旋流数的增加,炉膛内中心回流区向入口移动,高温区域也随之向入口方向移动,且高温区域减少,炉膛内整体温度下降,出口NO_x排放从212 mg/m³降低到76 mg/m³,而当旋流数增加到1.11以上时,旋流数大小对炉膛内NO_x的生成和排放的影响将会很小。研究还发现当左入口空气为左旋,右入口空气为右旋时,该燃气锅炉不仅燃烧稳定并且具有较低的NO_x排放。     

甲烷/空气混合物在微小型钝体燃烧器中的燃烧特性

为了实现在淬熄距离以下的稳定燃烧,试验设计了两种带钝体的回热型燃烧器,研究预混甲烷在高度小于淬熄距离的燃烧室中的燃烧特性。燃烧器的燃烧室高度为2 mm,长度为20 mm,进口处安装了边长为1mm的等边三角形钝体或相同尺寸的"V"形钝体,并在上下两侧设置了预热通道。利用Fluent6.3软件对甲烷/空气在这两个燃烧器的预混燃烧做了数值模拟,确定了浓度极限和速度极限,并对稳燃机理进行了分析。与三角形钝体燃烧器相比较,"V"形钝体燃烧器的稳燃范围更大。在所给出的稳定燃烧工况下两者的燃烧效率均在99%以上,甲烷/空气的混合气体能够完全燃烧。但当进气速度较小同时当量比较大时会发生回火现象。     

The effect of hydrogen containing fuel blends upon flashback in swirl burners

Lean premixed swirl combustion is widely used in gas turbines and many other combustion Processes due to the benefits of good flame stability and blow off limits coupled with low NO_x emissions. Although flashback is not generally a problem with natural gas combustion, there are some reports of flashback damage with existing gas turbines, whilst hydrogen enriched fuel blends, especially those derived from gasification of coal and/or biomass/industrial processes such as steel making, cause concerns in this area. Thus, this paper describes a practical experimental approach to study and reduce the effect of flashback in a compact design of generic swirl burner representative of many systems. A range of different fuel blends are investigated for flashback and blow off limits; these fuel mixes include methane, methane/hydrogen blends, pure hydrogen and coke oven gas. Swirl number effects are investigated by varying the number of inlets or the configuration of the inlets. The well known Lewis and von Elbe critical boundary velocity gradient expression is used to characterise flashback and enable comparison to be made with other available data.Two flashback phenomena are encountered here. The first one at lower swirl numbers involves flashback through the outer wall boundary layer where the crucial parameter is the critical boundary velocity gradient, G_f. Values of G_f are of similar magnitude to those reported by Lewis and von Elbe for laminar flow conditions, and it is recognised that under the turbulent flow conditions pertaining here actual gradients in the thin swirl flow boundary layer are much higher than occur under laminar flow conditions. At higher swirl numbers the central recirculation zone (CRZ) becomes enlarged and extends backwards over the fuel injector to the burner baseplate and causes flashback to occur earlier at higher velocities. This extension of the CRZ is complex, being governed by swirl number, equivalence ratio and Reynolds Number. Under these conditions flashback occurs when the cylindrical flame front surrounding the CRZ rapidly accelerates outwards to the tangential inlets and beyond, especially with hydrogen containing fuel mixes. Conversely at lower swirl numbers with a modified exhaust geometry, hence restricted CRZ, flashback occurs through the outer thin boundary layer at much lower flow rates when the hydrogen content of the fuel mix does not exceed 30%. The work demonstrates that it is possible to run premixed swirl burners with a wide range of hydrogen fuel blends so as to substantially minimise flashback behaviour, thus permitting wider used of the technology to reduce NOx emissions.     

Stabilization regimes and pollutant emissions from a dual fuel CH4/H2 and dual swirl low NOx burner

Burning hydrogen in gas turbines is a relevant technological solution to decarbonize power production and propulsion systems. However, ensuring low NOx emission and preventing flashback can be challenging with hydrogen. Stabilization regimes and pollutant emissions from partially premixed CH₄/H₂/air flames above a coaxial Dual Fuel Dual Swirl injector are investigated in a laboratory-scale combustor at atmospheric conditions for increasing hydrogen contents. The injector consists of an external annular swirler providing premixed methane/air and a central channel fed with pure hydrogen. This burner virtually removes the risk of flashback due to the late injection of hydrogen. Flame stabilization regimes, CO and NOx emissions are analyzed for different configurations of the injector and operating points. The effect of swirling the hydrogen stream is investigated together with the influence of the hydrogen injector recess, i.e. its nozzle position with respect to the backplane of the combustion chamber. It is shown that swirling the central hydrogen stream favors aerodynamically stabilized flames resulting in a low thermal stress on the injector and limited NOx emissions. The study also highlights that a small recess of the central hydrogen injector widely extends the operability range of the burner with aerodynamically stabilized flames. With a sufficient inner swirl and a small recess, flames detach from the injector rim when the hydrogen bulk velocity is large enough. In this configuration, it is found that NOx emissions remain low even for operation with pure hydrogen. Moreover, NOx emissions decrease when increasing the thermal power for a fixed equivalence ratio.     

重型燃气轮机先进低NOx燃烧技术分析

对重型燃气轮机领域中的低NOx燃烧技术进行介绍与说明,首先简要论述了重型燃气轮机燃烧室中氮氧化物的产生机理及抑制方法,其次,介绍了贫预混多喷嘴分级燃烧技术、富油/烽熄/贫油燃烧技术和贫预混低旋流燃烧技术等7种可用于重型燃气轮机燃烧室的先进低NOx燃烧技术,并详细论述了这7种低NOx燃烧技术的作用原理及应用进展,可为国内重型燃气轮机低污染燃烧室的设计与研制提供技术参考.     

Hydrogen addition effects in a confined swirl-stabilized methane-air flame

The effect of hydrogen addition in methane-air premixed flames has been examined from a swirl-stabilized combustor under confined conditions. The effect of hydrogen addition in methane-air flame has been examined over a range of conditions using a laboratory-scale premixed combustor operated at 5.81 kW. Different swirlers have been investigated to identify the role of swirl strength to the incoming mixture. The flame stability was examined for the effect of amount of hydrogen addition, combustion air flow rates and swirl strengths. This was carried out by comparing adiabatic flame temperatures at the lean flame limit. The combustion characteristics of hydrogen-enriched methane flames at constant heat load but different swirl strengths have been examined using particle image velocimetry (PIV), micro-thermocouples and OH chemiluminescence diagnostics that provided information on velocity, thermal field, and combustion generated OH species concentration in the flame, respectively. Gas analyzer was used to obtain NO_x and CO concentration at the combustor exit. The results show that the lean stability limit is extended by hydrogen addition. The stability limit can reduce at higher swirl intensity to the fuel-air mixture operating at lower adiabatic flame temperatures. The addition of hydrogen increases the NO_x emission; however, this effect can be reduced by increasing either the excess air or swirl intensity. The emissions of NO_x and CO from the premixed flame were also compared with a diffusion flame type combustor. The NO_x emissions of hydrogen-enriched methane premixed flame were found to be lower than the corresponding diffusion flame under same operating conditions for the fuel-lean case.     

Interactions for flames in a coaxial flow with a stagnation point

The possible burning structures existing in two co-flowing combustible mixtures with different compositions, and their implications to the field of turbulent combustion are examined in this study. A coaxial burner with a quartz plate was used to experimentally investigate the flames of methane/air and propane/air mixtures propagating in a coaxial flow impinging onto a stagnation surface. The possible burning structures were observed to be: (1) a single-flame (a lean or rich premixed flame); (2) a double-flame (two lean or rich premixed flames, or a rich premixed flame and a diffusion flame); and (3) a triple-flame (a rich premixed flame, a diffusion flame and a lean premixed flame). An inner (or outer) mixture, far beyond the flammability limit, can still burn if a stronger outer (or inner) flame supports it. The extinction limit of the top part of the inner hat-shaped premixed flame is nearly independent of the burning intensity of the outer flame. It was found that the inner flame has a wider flammable region than the outer flame, and that the latter has a narrower flashback region than the former. Both propane and methane flames may exhibit flame-front instability, although the former displays much more clearly than the latter. Cellular and polyhedral instabilities can exist individually or appear simultaneously in the inner flame. However, only polyhedral (stripped-pattern) instability was observed in the outer flame. Finally, the experiments were analyzed theoretically using a simple geometrical model incorporated with the numerical simulations. The predicted shapes and locations of the flames are in good agreement with the experimental observations qualitatively.     

火焰筒扩张角与旋流匹配对燃烧特性的影响

为研究旋流器流量分配对干式低排放(Dry Low Emission,DLE)燃烧室燃烧特性的影响规律,针对单头部中心分级旋流燃烧室,以天然气作为燃料,在保持旋流数不变的前提下开展两级旋流器不同空气分配比例下的试验测试和数值模拟,获得不同结构参数条件下燃烧室的综合燃烧性能以及污染物排放等变化规律。研究表明：随主燃级/预燃级旋流器流量比增大,燃烧室中心回流区变小、回流区长度变短;预燃级局部当量比的增大造成燃烧室出口CO排放增加,主燃区燃烧加剧,热力型NOx排放也增加;同时,燃烧室中心高温区域向燃烧室出口方向扩张,出口温度分布均匀性变差。     

Mechanism analysis on the pulverized coal combustion flame stability and NOx emission in a swirl burner with deep air staging

Low NOx burner and air staged combustion are widely applied to control NOx emission in coal-fired power plants. The gas-solid two-phase flow, pulverized coal combustion and NOx emission characteristics of a single low NOx swirl burner in an existing coal-fired boiler was numerically simulated to analyze the mechanisms of flame stability and in-flame NOx reduction. And the detailed NOx formation and reduction model under fuel rich conditions was employed to optimize NOx emissions for the low NOx burner with air staged combustion of different burner stoichiometric ratios. The results show that the specially-designed swirl burner structures including the pulverized coal concentrator, flame stabilizing ring and baffle plate create an ignition region of high gas temperature, proper oxygen concentration and high pulverized coal concentration near the annular recirculation zone at the burner outlet for flame stability. At the same time, the annular recirculation zone is generated between the primary and secondary air jets to promote the rapid ignition and combustion of pulverized coal particles to consume oxygen, and then a reducing region is formed as fuel-rich environment to contribute to in-flame NO_X reduction. Moreover, the NOx concentration at the outlet of the combustion chamber is greatly reduced when the deep air staged combustion with the burner stoichiometric ratio of 0.75 is adopted, and the CO concentration at the outlet of the combustion chamber can be maintained simultaneously at a low level through the over-fired air injection of high velocity to enhance the mixing of the fresh air with the flue gas, which can provide the optimal solution for lower NOx emission in the existing coal-fired boilers.     

直喷汽油对反应活性控制压燃负荷拓展影响的数值模拟研究

基于三维计算流体力学软件CONVERGE,通过数值模拟的方法,基于不同的燃油总量、直喷汽油量、预混汽油油量和汽柴油喷射时刻等参数,展开了缸内直喷汽油对反应活性控制压燃(RCCI)燃烧模式高负荷拓展影响的研究。结果表明:进气压力及柴油喷射时刻会影响缸内浓度分层进而影响燃烧过程,而汽油喷射时刻影响不明显;在汽油采用进气道结合缸内直喷的混合喷射策略下,增加缸内直喷汽油量可以进一步增强缸内的混合气浓度分层,延长燃烧持续期,降低缸内的最高燃烧压力和压力升高率,实现更低的燃烧温度。仿真计算结果显示:若保证碳烟和NOx排放在限值内且油耗有所降低,可将平均有效指示压力(IMEP)拓展至1.6MPa;将IMEP拓展到1.7MPa后,增加汽油的预混比例并不能提高IMEP,但对排放略有改善,相应的压力升高率和燃烧压力提高。     

Numerical simulation of ammonia/methane/air combustion using reduced chemical kinetics models

Ammonia appears to be a potential alternative fuel that can be used as a hydrogen vector and fuel for gas turbines and internal combustion engines. Chemical mechanisms of ammonia combustion are important for the development of ammonia combustion systems, but also as a mean of investigation of harmful NOx emissions, so they can be minimized. Despite of large body of experimental and modelling work on the topic of ammonia combustion, there is still need for additional investigation of combustion kinetics.The object of this work is further numerical study of ammonia combustion chemistry under conditions resembling industrial ones. After literature review, three mechanisms of ammonia combustion that also include carbon chemistry are used for simulation of experimental premixed swirl burner with the aim of evaluating their performance. San Diego mechanism, that was also the most detailed one, proved to be the best in terms of emissions, but neither one of the models was able to accurately reproduce CO emission after equivalence ratio went beyond 0.81. It was also observed that oxygen is excessively consumed. This study contributes to the current knowledge by providing new insights in ammonia burning conditions closely resembling those in industrial applications, and consequently is expected that insights obtained will help in the design of real industrial burning systems.     

天然气锅炉分级柔和燃烧模拟研究

燃气锅炉在我国应用广泛,随着煤改气的进行,应用越来越多, NO_x排放标准也越来越严格。降低NO_x的排放有利于减少空气污染。以小型天然气柔和燃烧炉膛为研究对象,通过数值模拟的方法研究燃料分级下的柔和燃烧特性,分析在不同当量比、不同热强度条件下轴向分级对炉膛烟气中NO_x生成的影响。结果表明,给定条件下柔和燃烧分级带来的NO_x减排收益随着二级燃料量的增加而减小,当二级燃料量在15%左右的时候可以最大程度地优化温度场分布,降低燃烧峰值温度,获得比较好的NO_x控制效果。随着当量比和热强度的提高,燃料分级带来的收益也会变大。