烟气再循环对天然气非预混燃烧NO_x排放特性的影响

天然气在燃烧过程中生成NO_x的浓度主要受温度影响.烟气再循环不仅能降低燃烧温度,而且减小了燃烧高温区域,使污染物排放降低.为减少NO_x排放,采用一台标定功率为800,k W的非预混燃烧器进行了烟气再循环非预混燃烧试验,主要研究了燃烧负荷、过量空气系数、烟气再循环率对NO_x生成的影响.同时,采用FLUENT6.3软件模拟计算燃烧火焰温度分布和NO_x质量浓度分布.结果表明:燃烧器热负荷的增加,会使烟气中NO_x质量浓度增加;过量空气系数?在1.0~1.15之间时,有利于降低NO_x排放;烟气再循环量增加能有效降低NO_x排放,在?为1.1和1.15时、烟气再循环率为20%,时,NO_x质量浓度为40~50,mg/m3.     

低排放分级燃烧器中CH4燃烧特性

烟气回流是实现柔和燃烧的手段,为精确控制回流比例,建立了分级燃烧器,实验研究了回流比例、当量比对CH4柔和燃烧火焰形态和NO、CO排放的影响。当量比为0.8,回流比例为0.6～0.7时实现柔和燃烧,反应区分散不分层,烟气中NO和CO体积分数分别小于1.2×10-5和4×10-5;回流比例过小时发生扩散燃烧,过大时燃烧不稳定;NO排放主要在烟气发生区产生。回流比例为0.6、当量比为0.6～0.8时,射流和主流有效掺混并伴有火焰抬升,实现柔和燃烧;相同当量比时,分级燃烧的NO排放较旋流扩散低,当量比0.8时,分级燃烧相对旋流扩散减排NO达44%。     

射流喷嘴旋流强度对燃烧室回流和燃烧特性的影响研究

随着燃气轮机参数的提高和稳定低排放运行工况的拓宽,对燃烧的要求也越来越高。柔和燃烧作为一种有潜力的燃烧技术,具有温度均匀、燃烧稳定和污染物排放低等优点,而如何在燃烧室内组织流动是实现柔和燃烧的关键。采用高速射流引射掺混的方式可以较好的满足柔和燃烧产生所需的条件。预混射流喷嘴结构和布置对流场和燃烧特性有重要影响,如何选择射流喷嘴结构值得进一步研究。本文通过实验和数值模拟相结合的方式,研究了柔和燃烧器中预混射流喷嘴的旋流强度对燃烧器流动结构和燃烧排放的影响。结果表明,旋流能增强燃料/空气的掺混,低旋流作用下能使喷嘴出口掺混不均匀度ISMD下降0. 15左右;但是喷嘴旋流对燃烧室的烟气回流有减弱的作用,使回流区向喷嘴和中轴线靠近;同时,旋流会造成温度场和火焰面不均匀分布,略微拓宽燃烧工况范围并略微增加火焰的稳定性。实验结果表明喷嘴旋流进气角从0°变化到45°时,NOx排放随旋流角的增大而增加。     

燃料掺混方式对天然气柔和燃烧器燃烧性能的影响研究

燃气轮机在更高参数下的低污染排放限制和宽工况范围稳定运行的需求,对燃烧室燃烧提出了新的要求。柔和燃烧作为一种新型燃烧技术,具有燃烧稳定和污染物排放低的优势。高速射流引射掺混是实现柔和燃烧所需条件的一种可行方式。本文主要研究不同燃料掺混方式对柔和燃烧器污染物排放和稳定工作范围的影响。在前期工作基础上设计了可实现燃料不同掺混方式的天然气柔和燃烧器。在常压条件下,通过实验研究了不同当量比、不同燃料/空气掺混方式下天然气柔和燃烧器的污染物排放,并研究了不同掺混方式对燃烧贫燃极限的影响,通过OH~*自发荧光、OH平面激光诱导荧光测量和数值模拟对反应区和流场结构进行了观察和分析。实验结果表明,在相同当量比下,全预混模式下的NO_x排放最低,全预混模式下稳定燃烧的贫熄火当量比为0.57;扩散模式下NO_x排放相对高,但贫熄火当量比可低至0.15,燃烧稳定范围更宽;混合模式下污染物排放水平介于预混和扩散模式之间;非预混模式下较好的贫燃火焰稳定性得益于燃烧室头部扩散燃料周围形成的低速稳定反应区。     

使用不同燃烧器对火筒式加热炉的影响分析

利用实验和数值模拟方法,分析了两种不同燃烧器对油田用火筒式加热炉内部温度场、流场以及燃烧过程中NO_x(氮氧化物)生成情况的影响。两种燃烧器功率均为700 kW,通过实验测量和数值模拟得到以下结论:在相同的功率情况下,采用强制鼓风式燃烧器的加热炉炉内具有更高的平均温度;大气式燃烧器产生的火焰偏斜严重,炉顶部容易受到烟气冲刷而产生高温区域,炉底部烟气流量较小温度较低,换热条件较差;大气式燃烧器和强制鼓风式燃烧器在加热炉炉内燃烧所排放的烟气中NO_x质量—体积浓度差别较小,分别为118.3和108.1 mg/m~3。     

MILD条件下氢-天然气混合燃烧特性及排放物分析

针对目前天然气掺氢后燃烧效率及氮氧化物排放研究较少的问题,应用组分输运模型、涡耗散概念燃烧模型和Do辐射模型,结合GRI-22化学反应机理,建立柔和燃烧模拟模型,通过与实验结果对比验证了模型的可靠性,进一步应用该模型分析不同掺氢比例对燃烧特性的影响。结果表明,随着掺氢比例增加,燃料与氧化剂的混合程度逐渐提高,混合气体的径向分量不断减小;由于反应速率和放热速率提高,燃烧器内部的温度升高,热力型氮氧化物含量增高,主要集中于燃烧器后端;燃料进口速度增大会导致燃烧器内燃烧不完全、出口处温度降低,氧气浓度升高,氮氧化物含量降低。研究发现,天然气中掺入氢气更有利于达到柔和燃烧条件。     

低NO_x燃烧器对重油低氮燃烧特性的影响

为降低燃油注汽锅炉燃烧过程中产生的氮氧化物(NO_x)含量,设计了1种适用于重油燃烧的低NOx燃烧器,在0.8 MW的卧式炉试验台上进行燃烧试验,研究了中间射流、燃烧区喷水以及烟气再循环等措施对重油燃烧特性以及NO_x生成的影响.结果表明:中间射流的速度、喷水量以及烟气再循环率对燃烧稳定性和NO_x的生成具有重要的影响,采用50 m/s的中间射流速度、25%的喷水量以及20%的烟气再循环率时实现了烟气中NOx排放从原先的865 mg/m~3(折算为φO2=3.5%)降低至508 mg/m~3(折算为φO2=3.5%),NO_x排放降低41.2%.     

小型天然气锅炉低氮燃烧技术的数值模拟和实验研究

为实现小型天然气锅炉低氮排放,针对0.2 MW天然气锅炉,开发出一种以烟气再循环和燃料预混贫氧燃烧技术为基础的小型天然气锅炉专用低氮燃烧器.对此燃烧技术的排放特性进行了数值模拟研究,分析了烟气再循环率、预混段长度以及多孔板孔径等因素对NOx排放量的影响,搭建了相应的实验台进行热态实验并对其设计合理性进行了验证.被热态实...     

烟气再循环对金属纤维表面燃烧器NO_x排放和燃烧稳定性的影响

结合全预混金属纤维表面燃烧器和外部烟气再循环燃烧技术,在350 kW卧式燃气锅炉上进行了实验研究.研究了负荷、过量空气系数和烟气再循环率对CO、NO_x排放和燃烧稳定性的影响.结果表明:负荷变化对NO_x排放无明显影响;过量空气系数越大,NO_x排放越低,但系统热效率随之降低;不采用烟气再循环技术时,NO_x排放低于30 mg/m3时过量空气系数需大于1.73,此时系统热效率低于92.1%;如采用23%的烟气再循环率,实现上述相同NO_x排放水平仅需过量空气系数大于1.3,系统热效率比无烟气再循环时高1.3%;随着烟气再循环率的增大,火焰燃烧不稳定加剧.出现炉膛震动时的烟气再循环率极限值随着负荷的增大而逐渐提高.     

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。     

Distributed swirl combustion for gas turbine application

Colorless distributed combustion (CDC) has been shown to provide significant improvement in gas turbine combustor performance. Colorless distributed combustion with swirl is investigated here to develop ultra-low emissions of NO and CO, and significantly improved pattern factor. Experimental investigations have been performed using a cylindrical geometry combustor with swirling air injection and axial hot gas exit stream from the combustor. Air was injected tangentially to impart swirl to the flow inside the combustor. The results obtained from the combustor have demonstrated very low levels of NO (∼3 PPM) and CO (∼70 PPM) emissions at an equivalence ratio of 0.7 and a high heat release intensity of 36 MW/m³-atm under non-premixed combustion. To further simulate gas turbine operating conditions, inlet air to the combustor was preheated to 600 K temperature and the combustor operated at 2 atm pressure. Results showed very low levels of CO (∼10 PPM) but the NO increased somewhat to ∼10 PPM at an equivalence ratio of 0.5 and heat release intensity of 22.5 MW/m³-atm under non-premixed combustion conditions. For premixed combustion, the combustor demonstrated low levels of both NO (5 PPM) and CO (8 PPM) at an equivalence ratio of 0.6 and a heat release intensity of 27 MW/m³-atm. Results are reported at different equivalence ratios on the emission of NO and CO, lean stability limit and OH^* chemiluminescence. These results suggest that further performance improvement can be achieved with improved fuel mixture preparation prior to the ignition of fuel at higher operational pressures using swirling combustor design for our quest to develop ultra low emission high intensity combustor for gas turbine application.     

A chemical reactor network for oxides of nitrogen emission prediction in gas turbine combustor

This study presents the use of a new chemical reactor network （CRN） model and non-uniform injectors to predict the NOx emission pollutant in gas turbine combustor. The CRN uses information from Computational Fluid Dy- namics （CFD） combustion analysis with two injectors of CH4-air mixture. The injectors of CH4-air mixture have different lean equivalence ratio, and they control fuel flow to stabilize combustion and adjust combustor＇s equiva- lence ratio, Non-uniform injector is applied to improve the burning process of the turbine combustor. The results of the new CRN for NOx prediction in the gas turbine combustor show very good agreement with the experimen- tal data from Korea Electric Power Research Institute.     

空气分级比对同轴分级燃烧室性能参数的影响

为掌握同轴分级燃烧室性能参数随空气分级比(主燃级空气流量的比值)的变化规律,以某同轴分级燃烧室为研究对象,数值分析了空气分级比对燃烧室的燃烧效率、总压损失、出口温度分布、污染物排放和绝热壁面最高温度的影响。结果表明：空气分级比主要会改变角涡位置的燃烧温度和高温烟气的停留时间;随着空气分级比的升高,燃烧室总压损失、出口温度分布系数、NO_x排放、绝热壁面最高温度逐渐升高,但燃烧效率、CO污染物排放、径向温度分布系数对空气分级比不敏感;在同轴分级燃烧室设计中,在保证燃烧稳定的前提下可采用较小的空气分级比以实现燃烧室高效、低阻、低污染燃烧。     

贫预混预蒸发燃烧室振荡燃烧特性的实验研究

针对燃用航空煤油的贫预混预蒸发模型燃烧室的振荡燃烧特性开展了实验研究。实验表明:在相同的燃烧室入口空气燃料混合物流速下,随着当量比的增加,燃烧室振荡燃烧的振荡主频从132 Hz增加到144 Hz,但燃烧室的均方根脉动压力幅值却从1 464 Pa下降到342 Pa。在当量比不变情况下,入流空气燃料混合物流速较低时,容易引发振荡燃烧现象,而当入流空气燃料混合物流速较高时,则燃烧会变得稳定。分析了整个燃烧实验装置的前4阶轴向声学模态频率,发现实验中所激励出的振荡燃烧主频和第二阶轴向声学模态频率吻合的很好。     

模型燃烧室燃烧自激振荡与音频特征的实验研究

以甲烷为燃料,在以GE燃机6B喷嘴为基础的1/3模型燃烧室中,研究了燃烧室空气流量和当量比的变化对燃烧自激振荡的压力波动的影响,以及燃烧发出的音频信号的特征。实验结果显示：在3组不同的入口空气流量工况下,随着当量比的增加,燃烧室的稳定——自激振荡——稳定工作的变化趋势保持一致;在不同的流量下,当量比=0.61的工况产生了最强烈的自激振荡,同时振荡的压力波动幅值和频率随燃烧室入口空气流量的增加而增大;通过FFT（快速傅里叶变换）计算发现,在有明显自激振荡的工况中,动态压力与音频信号的幅值均大幅超过稳定燃烧的工况,同时音频信号的一个特征频率与动态压力信号的特征频率重合。     

基于多孔介质燃烧的端部辐射器的实验研究

设计了基于多孔介质燃烧技术的端部辐射器,研究不同预混气体流速(功率)下当量比对燃烧器燃烧稳定性、多孔介质内部温度、辐射器表面温度及其均匀性、污染物排放、辐射效率等特性的影响.结果表明,燃烧器辐射表面的温度均匀性较好.最大相对温差小于3%:多孔介质燃烧器可实现最低当量比0.33的稳定可持续燃烧;小功率燃烧时.多孔介质内部温度及端部辐射表面温度都随当量比增大而增加,且流量越大增加程度越大,可据此提出实现更高辐射表面温度的方案.实验工况范围内.最大辐射效率达23%;NO<,x>排放体积分数低于25×10<'6>,在当量比大于0.45时,CO排放体积分数均低于10×10<'6>.     

A numerical study on combustion and emission characteristics of premixed hydrogen air flames

Main challenges for micro power generators that utilize combustion process for energy production are inadequate residence time, destructive radical wall interactions and intensified heat loss which are mainly rooted from size limitation of such devices. To achieve high and uniform energy output, and bring in a solution to these challenges in an environment friendly manner without any kind of fundamental modification, effect of equivalence ratio on combustion and emission behavior of premixed hydrogen/air flames is numerically investigated in this study. For this purpose, an experimentally tested micro cylindrical combustor model is constructed and premixed hydrogen/air combustion in this model is simulated by varying equivalence ratio between 0.5 and 1.2 to find an optimal equivalence ratio with respect to drawbacks of micro power generators. Combustion and turbulence models implemented in this study are Eddy Dissipation Concept and Standard k-ε models, respectively. A detailed hydrogen/air reaction mechanism which consists of 9 species and 19 steps is employed to accurately gain insight into combustion process. Simulation results show that as the equivalence ratio decreases; centerline temperature distribution gets a lower value and the place where chemical reactions take place moves downstream. The most uniform temperature distribution is achieved between 0.8 and 1.0 equivalence ratios. The highest NO_x formation is at 0.9 equivalence ratio and its mass fraction decreases sharply when the equivalence ratio reduces from 0.9 to 0.5.     

Numerical studies on flame inclination in porous media combustors

Inclinational instability developing during propagation of a filtration combustion wave in an inert porous medium is studied using two-dimensional numerical model. Stable and unstable combustion waves are generated by varying combustion parameters such as pressure, equivalence ratio, filtration velocity, effective conductivity of porous media, pellet diameter and combustor scale. The wave propagation velocity of inclinational flame is studied and compared with flat flame. The growth and reduction of inclinational instability are analyzed at different conditions. The numerical results show that a development of inclinational instability causes essential flow non-uniformity and can result in a separation of the flame front in the multiple flame zones. The limited conductive and radiant heat transfer in the solid phase, small pellet diameter of packed bed, high inlet velocity, large combustor scale and low equivalence ratio promote the instability growth. The inclinational instability is suppressed in a reciprocal combustor.     

Flame–vortex interaction driven combustion dynamics in a backward-facing step combustor

The combustion dynamics of propane–hydrogen mixtures are investigated in an atmospheric pressure, lean, premixed backward-facing step combustor. We systematically vary the equivalence ratio, inlet temperature and fuel composition to determine the stability map of the combustor. Simultaneous pressure, velocity, heat release rate and equivalence ratio measurements and high-speed video from the experiments are used to identify and characterize several distinct operating modes. When fuel is injected far upstream from the step, the equivalence ratio entering the flame is temporally and spatially uniform, and the combustion dynamics are governed only by flame–vortex interactions. Four distinct dynamic regimes are observed depending on the operating parameters. At high but lean equivalence ratios, the flame is unstable and oscillates strongly as it is wrapped around the large unsteady wake vortex. At intermediate equivalence ratios, weakly oscillating quasi-stable flames are observed. Near the lean blowout limit, long stable flames extending from the corner of the step are formed. At atmospheric inlet temperature, the unstable mode resonates at the 1/4 wavemode of the combustor. As the inlet temperature is increased, the 5/4 wavemode of the combustor is excited at high but lean equivalence ratios, forming the high-frequency unstable flames. Higher hydrogen concentration in the fuel and higher inlet temperatures reduce the equivalence ratios at which the transitions between regimes are observed. We plot combustion dynamics maps or the response curves, that is the overall sound pressure level as a function of the equivalence ratio, for different operating conditions. We demonstrate that numerical results of strained premixed flames can be used to collapse the response curves describing the transitions among the dynamic modes onto a function of the heat release rate parameter alone, rather than a function dependent on the equivalence ratio, inlet temperature and fuel composition separately. We formulate a theory for predicting the critical values of the heat release parameter at which quasi-stable to unstable and unstable to high-frequency unstable modes take place.