内部烟气循环技术在低氮燃烧器中的应用

利用计算燃烧学技术,采用数值模拟手段结合试验及实际工程应用详细研究了配套WNS锅炉的燃天然气燃烧器的燃烧特性,对燃烧器内部的压力、流速、烟气回流量、混合流场、燃烧室的直径等参数进行了分析对比,并最终确定了燃烧器及燃烧室的结构优选方案,对燃天然气燃烧器和低温燃烧设计提供理论基础数据。     

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。     

微型燃气轮机生物质气燃烧实验台设计

本研究以现有的微型燃气轮机为原型,设计了单喷嘴生物质气燃烧实验台并具体介绍了实验台的系统、重要组成模块、测量参数和方法以及实验台的主要作用。本实验台能够实现关键流动参数测量、PIV流场测量、燃烧温度场测量和尾气排放测量等。实验室条件下,对微型燃气轮机燃烧室进行研究,得出的结论可应用于燃烧室流场结构分析、喷嘴的改型、火焰稳定性、排放控制、燃料组分改变对燃烧性能的影响以及相关的燃烧技术研究。     

改烧焦炉煤气后燃气轮机燃烧室的改进

为改烧焦炉煤气,对原来燃用天然气的QD128燃气轮机燃烧室进行了改进,重新设计了能使用焦炉煤气和液体燃料的双燃料喷嘴,修改了火焰筒的头部结构,同时减少了火焰筒内壁掺混孔的进气比例.采用计算流体动力学软件Fluent对燃烧室进行了数值模拟计算,并与燃用天然气的原型燃烧室流场、温度场计算结果进行了对比分析.结果表明:燃烧室头部燃烧区存在明显的空气回流能满足稳定火焰的要求.温度场与原型燃烧室基本一致,出口截面温度场品质(OTDF、RTDF)优于原型燃烧室.     

燃气轮机燃烧室柔和燃烧热力学与燃料条件的计算分析

本文通过零维数值模拟,对基于烟气循环的不同级别燃气轮机燃烧室中实现柔和燃烧的条件进行了计算分析。结果表明燃气轮机燃烧室柔和燃烧主要受回流烟气和燃料、空气的混合物温度的影响,烟气回流起到缩短混合物点火延迟时间的作用。由于不同燃料和不同负荷条件下混合物自燃温度变化不大,柔和燃烧具有较好的燃料适应性和变负荷性能。分析还表明未完全反应的烟气不会影响柔和燃烧工况范围。     

某重型燃气轮机环型燃烧室的数值模拟

参考现有某重型燃气轮机环型燃烧室,运用FLUENT软件对其喷嘴结构及燃烧室部分进行三维数据模拟及分析,通过数值模拟分析燃烧过程速度、压力、温度等变量的分布规律,以及对燃烧室不同截面的流场分布规律的分析,特别是对主要区域各关键截面的流场分析,从而判断出燃烧室设计的合理性,为进一步优化燃烧室的结构设计、改善流场结构奠定基础.     

燃烧空气散布角对高温空气燃烧影响的数值研究

以高温空气燃烧技术为应用背景,对多股射流对炉内燃烧特性的影响进行了数值模拟,讨论了燃烧空气散布角对燃烧特性的影响。采用标准的-双方程模型计算流场,气相燃烧模型采用函数的PDF燃烧模型,采用离散坐标法模拟辐射换热过程,NOX模型为热力型NOX,燃烧室尺寸为800mm×800mm×1400mm,燃料喷口为圆形,直径为10mm,位于中心。空气喷口设计为5个等面积的圆形置于燃气喷口周围。计算结果表明,由于射流之间的相互作用,在炉膛内存在回流区。烟气的回流一方面加强了燃料和空气的混合,使温度分布更为均匀,同时改变了炉膛空间内的燃料和氧的分布,从而影响燃烧强度和NOX的局部生成。燃烧空气散布角越小,燃料、氧以及燃烧后的高温烟气等的混合越充分,燃烧越稳定,低氧区域扩大,温度分布均匀,局部高温受到抑制,局部NOX的生成减少。较大时,喷嘴布置接近于同轴射流,高温烟气的回流主要起到稳定燃烧的作用,而周向的低氧条件将不复存在,低氧燃烧将转化为强化燃烧。在15%的氧条件下,=120°时与=360°相比,NOX排放量可减少65%。研究结果对高温空气燃烧喷嘴结构设计及运行管理具有参考价值。     

煤粉柔和气化炉内流动特性数值模拟

基于煤粉柔和气化炉的工况特征,采用数值模拟手段研究了喷嘴位置、喷嘴孔径(射流速度)和煤粉平均粒径等对气化炉内气固流场特性、烟气回流比和颗粒平均停留时间等的影响规律。结果表明:柔和气化炉内流场分布主要受二次风喷嘴位置和射流速度的影响,二次风喷嘴位置对流场影响更大;保持一次风和二次风射流速度不变时,随着二次风喷嘴与炉膛中心距离的增加,烟气回流比和颗粒平均停留时间先增大后减小;随着二次风射流速度的增大,烟气回流比增大,而颗粒平均停留时间有所变短;随着煤粉平均粒径减小,烟气回流比变化很小,而颗粒平均停留时间显著延长。     

伞型结构气化器两相流动和传热数值模拟

采用通用有限比率模型对一种新型烟气冲击浸于水的伞型结构气化器燃烧室的流场与温度场进行了数值模拟,分析了循环烟气量对燃烧室喷嘴出口烟气速度和温度的影响;采用VOF两相流模型对烟气与水滴气液两相流动的传热进行了数值模拟,分析了喷嘴高度和液面高度对烟气冲击浸于水的伞型结构的两相流动传热的影响.结果表明:当循环烟气量为燃烧产生烟气量的50%、液面高度为75mm时,冲击效果最佳,水滴被烟气充分卷起并充满气化器,气化传热得到强化.     

重型燃气轮机燃烧室流动特性研究

为了探究燃烧室流动特性,为燃气轮机燃烧室设计改型、燃气轮机的安全稳定运行及合理的组织燃烧室流场提供参考依据,本文基于某重型燃气轮机分管型燃烧室,建立了预混燃烧模式下燃烧室三维数值仿真模型,采用数值模拟方法研究了燃烧室温度场、压力场、速度场以及主要组分浓度场的分布规律。结果表明:燃烧室旋流喷嘴下游中心区域为局部高温区,在喷嘴射流区存在低温区域,燃烧室中后部温度高于燃烧室头部温度;燃烧室头部压力较大,后部压力分布趋于均匀;燃烧室喷嘴及燃烧室头部区域,回流区域明显;旋流喷嘴附近NOx质量分数最大。     

MILD combustion for hydrogen and syngas at elevated pressures

As gas recirculation constitutes a fundamental condition for the realization of MILD combustion, it is necessary to determine gas recirculation ratio before designing MILD combustor. MILD combustion model with gas recir- culation was used in this simulation work to evaluate the effect of fuel type and pressure on threshold gas recir- culation ratio of MILD mode. Ignition delay time is also an important design parameter for gas turbine combustor, this parameter is kinetically studied to analyze the effect of pressure on MILD mixture ignition. Threshold gas re- circulation ratio of hydrogen MILD combustion changes slightly and is nearly equal to that of 10 MJ/Nm3 syngas in the pressure range of 1-19 atm, under the conditions of 298 K fresh reactant temperature and 1373 K exhaust gas temperature, indicating that MILD regime is fuel flexible. Ignition delay calculation results show that pres- sure has a negative effect on ignition delay time of 10 MJ/Nm3 syngas MILD mixture, because OH mole fraction in MILD mixture drops down as pressure increases, resulting in the delay of the oxidation process.     

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。     

天然气锅炉NOx及CO排放控制试验研究

为了响应政府业及民用天然气锅炉达到超低氮排放,要求绝大多数天然气锅炉采用低氮燃烧器+烟气再循环系统的技术路线,实施后普遍出现NO_x、CO含量偏高、炉膛振动较大等问题。借助116 MW天然气锅炉进行试验研究,研究了燃烧器燃料配比、燃烧火焰长度、助燃空气氧含量三个因素对NO_x及CO的影响,并对投入烟气再循环前后炉膛振动情况进行了检测。试验表明:燃烧器燃料内外配比对NO_x、CO生成影响较大,两者呈现相反趋势变化;燃烧火焰长度对NO_x生成影响较大,对CO含量影响较小;助燃空气氧含量对NO_x、CO生成以及锅炉振动影响较大。三种影响因素相比,助燃空气氧含量影响更为突出。     

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。     

Hydrogen combustion test in a small gas turbine

Details of the gaseous hydrogen combustion test in a can-type conventional gas-turbine combustor and the operating performance of a 275 PS (202 kW) small gas turbine are provided.Initially, experiments were conducted to determine the configuration of the hydrogen fuel nozzles on a combustor test facility. The kerosene fueled gas turbine combustor was used without modification of the original configuration and dimensions.Secondly, the operation performance of the gas turbine was investigated when the gaseous hydrogen was used as a substitute fuel for kerosene fuel. The kerosene fuel supply system was removed or rendered inoperative and a hydrogen flow metering system was newly installed. The high pressure storage cylinders were used to supply hydrogen to the fuel metering system.Data was obtained on pressure losses of the fuel nozzles, ignition performance, temperature distributions at the combustor outlet, combustion efficiency, liner wall temperature distributions, NO_x emission levels, noise levels, operating performance, etc.     

Numerical investigation on hydrogen-enriched methane combustion in a domestic back-pressure boiler and non-premixed burner system from flame structure and pollutants aspect

In this paper, the non-premixed hydrogen-enriched methane-air combustion was investigated numerically with the use of a CFD code. In the first part of the study, the combustion experiments were performed in a back- pressure boiler using natural gas. The intake rate of fuel was kept constant as 45 Nm³/h while the coefficient for the air excess ratio was changed between 1.2 and 1.35. After the experiments, the numerical analyses were performed. The Fluent code was utilized as the simulation instrument. The eddy dissipation combustion model was selected to be used in the numerical analyses, since it is known that this combustion model can save computational time and fairly predict the combustion flame structure and emissions. Pure methane and natural gas were taken as fuels in the numerical analyses. The obtained results from the numerical analyses were validated with the experimental flue gas temperature and emission measurements. Then, the hydrogen-enrichment of pure methane fuel was investigated numerically in such a way that the boiler capacity (432 kW) was kept constant. The coefficient for the air excess ratio was 1.2 for all the considered combustion simulation cases. The hydrogen addition ratio was 25%, 50% and 75% by mass, respectively. The thermal NO emissions and temperature distributions in the combustion chamber were obtained according to the different hydrogen-enriched methane fuel combustion cases. In addition, the emissions contained in the flue gas together with the temperature values were calculated. The obtained results from the numerical studies indicate that the hydrogen-enrichment of methane reduces the carbon emissions, while it substantially augments the formation of the thermal NO emissions. The calculated thermal NO emission value in the flue gas is 147 ppm for the pure methane combustion case, and it is 566 ppm for the combustion case with 75% by mass of hydrogen addition ratio. Therefore, it is determined that hydrogen fuel is a pollutant from the thermal NO emission aspect for the considered enrichment ratios in the studied domestic boiler-burner system.     

外二次风旋流数对燃烧室内湍流燃烧与NOx生成的影响

建立了采用分级进风方式的旋流燃烧室实验装置。在此实验装置上分别对天然气进行了湍流旋流燃烧的实验研究。在保持过量空气系数不变的条件下,测量了在不同外二次风旋流数下,燃烧室内烟气的时均温度场,O2,CO2,CO和NO浓度场的分布。由实验结果分析讨论了二次风旋流数对旋流燃烧室内湍流燃烧及NOx生成的影响。     

Experimental investigations of the influence from different operating conditions on the particle emissions from a small-scale pellets combustor

The purpose of this study is to determine how different design parameters in an idealised small-scale combustor affect the emission of particulates in the flue gas and to provide insight that can be used for design optimisation. The design parameters are the primary air factor, the total air factor and the magnitude of swirling flow in the combustion chamber. Particles from the reactor were collected from two different sampling lines, one located in the combustion zone, just above the fuel bed, and the other in the flue stack after the reactor. The measurements show that this burner gives very low emissions of particulates and CO in the flue gas. Furthermore, the concentration of particles in the flue gas is uncoupled to the concentration of particles immediately above the fuel bed, probably as a result of a well-designed secondary air supply. The variable that had the strongest effect on the total particulate emission from the combustor was the total air factor. In order to understand the qualitative differences in the flow nature between different operating conditions, CFD simulations of the flow field were also performed.     

Mathematical modeling of MILD combustion of pulverized coal

MILD (flameless) combustion is a new rapidly developing technology. The IFRF trials have demonstrated high potential of this technology also for N-containing fuels. In this work the IFRF experiments are analyzed using the CFD-based mathematical model. Both the Chemical Percolation Devolatilization (CPD) model and the char combustion intrinsic reactivity model have been adapted to Guasare coal combusted. The flow-field as well as the temperature and the oxygen fields have been accurately predicted by the CFD-based model. The predicted temperature and gas composition fields have been uniform demonstrating that slow combustion occurs in the entire furnace volume. The CFD-based predictions have highlighted the NO_x reduction potential of MILD combustion through the following mechanism. Before the coal devolatilization proceeds, the coal jet entrains a substantial amount of flue gas so that its oxygen content is typically not higher than 3-5%. The volatiles are given off in a highly sub-stoichiometric environment and their N-containing species are preferentially converted to molecular nitrogen rather than to NO. Furthermore, there exists a strong NO-reburning mechanism within the fuel jet and in the air jet downstream of the position where these two jets merge. In other words, less NO is formed from combustion of volatiles and stronger NO-reburning mechanisms exist in the MILD combustion if compared to conventional coal combustion technology.