Experimental study and numerical simulation of gas-particle flows with radial bias combustion and centrally fuel rich swirl burners

Numerical simulation is applied to gas-particle flows of the primary and the secondary air ducts and burner region, and of two kinds of swirl burners. The modeling results of Radial Bias Combustion (RBC) burner well agreed with the data from the three-dimensional Phase-Doppler anemometry (PDA) experiment by Li, et al. The modeling test conducted in a 1025 t/h boiler was to study the quality of aerodynamics for a Central Fuel Rich (CFR) burner, and the Internal Recirculation Zone (IRZ) was measured. In addition, gas-particle flows with a CFR burner were investigated by numerical simulation, whose results accorded with the test data fundamentally. By analyzing the distribution of gas velocity and trajectories of particles respectively, it is found that the primary air’s rigidity of CFR burner is stronger than that of RBC burner, and the primary air mixes with the secondary air later. Furthermore, high concentration region of pulverized coal exists in the burner’s central zone whose atmosphere is reduced, and trajectories of particles in IRZ of CFR burner are longer than that of RBC burner. They are favorable to coal’s ignition and the reduction of NOx emission.

Numerical investigation of gas-particle flow in the primary air pipe of a low NO_x swirl burner-The DEM-CFD method

The gas-particle flow in the primary air pipe （PAP） of a low NOx swirl burner was investigated using the computational fluid dynamics （CFD） coupled with the discrete element method （DEM）. The mathematical models were validated using the measured values obtained at the outlet of the primary pipe through a phase Doppler anemometer （PDA） system. Particles of different Stokes numbers in the primary air pipe （PAP） were investigated, and the effects of the structure of the primary air pipe and the particle-particle interaction on particle dispersion were analyzed. The results indicate that particles under the combined effects of the Venturi pipe and the spindle body are concentrated into a narrow band area and that the PAP structure can more efficiently concentrate particles with large Stokes numbers. The formed fuel rich/lean jet persists for a long distance out of the burner, thereby favoring of air-staged combustion and NOx reduction. The particle collision frequency and its fluctuation range increase as the particle Stokes number increases. The collisions among particles result in an increase of the spanwise dispersion of particles. Experimental results indicate that the models that take particle-particle collision into consideration are more able to predict particle concentration.

Numerical Simulation of Gas-particle Flows with Different Swirl Numbers in a Swirl Burner

Swirl burner design was optimized by simulating swirl gas\|particle flows with different swirl numbers at the exit of a small\|scale swirl burner for pulverized\|coal furnaces using the k\|ε\|k p model. The predicted two\|phase time\|averaged velocities and particle concentration distributions for several different cases were compared to improve the design. The effect of the swirl number on the two\|phase velocities and particle concentration was investigated. The results give the two\|phase axial and tangential time\|averaged and fluctuation velocities and particle concentrations, showing that large recirculation zones of gas and particles forms in the near\|axis region of the burner exit, but the particle concentration in the recirculating zone is very low.

Simulation of Combustion Flow of Methane Gas in a Premixed Low-Swirl Burner using a Partially Premixed Combustion Model

Because the rotational current stabilizes the flame by creating a recirculation zone,it may increase the risk of reversal.For this reason,low-spin combustion is used to stabilize the flame while preventing flashbacks.Therefore,in this study,the combustion flow of methane gas in a low-swirl burner is simulated using a partially premixed combustion model.Furthermore,the fuel flow rate is considered constant.The research parameters include swirl angle(θ=35°–47°),equivalence ratio(φ=0.6–0.9)and inlet axial flow radius(R=0.6–0.7)and effect of these parameters on temperature distribution,flame length,flame rise length,velocity field,and streamlines of the number of pollutant species are investigated.The contours of streamline,temperature distribution,and velocity distribution are also presented for analysis of flow physics.The results show that with increasing the fuel-air ratio,the strength of the axial flow decreases,and the position of the maximum flame temperature shifts toward the inlet of the reactants.The results also reveal that by increasing the swirl angle of the flow,the position of the minimum velocity value(opposite to the direction of the axis)tends towards the outlet.The results also indicate that the maximum temperature of the combustion chamber increases with increasing the swirl angle,and inθ=35°,the maximum temperature is 1711℃and inθ=41°,this value is 1812℃.Finally,by increasing the swirl angle toθ=47°,the maximum flame temperature position is found at a considerable distance from the inlet and is 1842℃.

Influence of mass air flow ratio on gas-particle flow characteristics of a swirl burner in a 29 MW pulverized coal boiler

In a gas/particle two-phase test facility, a three-component particle-dynamics anemometer was used to measure the characteristics of gas/particle two-phase flows in a 29 megawatt (MW) pulverized coal industrial boiler equipped with a new type of swirling pulverized coal burner. The distributions of three-dimensional gas/particle velocity, particle volume flux, and particle size distribution were measured under different working conditions. The mean axial velocity and the particle volume flux in the central region of the burner outlet were found to be negative. This indicated that a central recirculation zone was formed in the center of the burner. In the central recirculation zone, the absolute value of the mean axial velocity and the particle volume flux increased when the external secondary air volume increased. The size of the central reflux zone remained stable when the air volume ratio changed. Along the direction of the jet, the peak value formed by the tertiary air gradually moved toward the center of the burner. This tertiary air was mixed with the peak value formed by the air in the adiabatic combustion chamber after the cross-section of x/d = 0.7. Large particles were concentrated near the wall area, and the particle size in the recirculation zone was small.

Measurements of Non-reacting and Reacting Flow Fields of a Liquid Swirl Flame Burner

The understanding of the liquid fuel spray and flow field characteristics inside a combustor is crucial for designing a fuel efficient and low emission device.Characterisation of the flow field of a model gas turbine liquid swirl burner is performed by using a2-D particle imaging velocimetry（PIV）system.The flow field pattern of an axial flow burner with a fixed swirl intensity is compared under confined and unconfined conditions,i.e.,with and without the combustor wall.The effect of temperature on the main swirling air flow is investigated under open and non-reacting conditions.The result shows that axial and radial velocities increase as a result of decreased flow density and increased flow volume.The flow field of the main swirling flow with liquid fuel spray injection is compared to non-spray swirling flow.Introduction of liquid fuel spray changes the swirl air flow field at the burner outlet,where the radial velocity components increase for both open and confined environment.Under reacting condition,the enclosure generates a corner recirculation zone that intensifies the strength of radial velocity.The reverse flow and corner recirculation zone assists in stabilizing the flame by preheating the reactants.The flow field data can be used as validation target for swirl combustion modelling.

空气射流特征对纯氨旋流燃烧火焰影响规律

氨是理想能源,为更好利用纯氨燃料,开发适用纯氨燃料的燃烧器,通过数值模拟对某10 kWth天然气旋流燃烧器进行三维建模,并对其纯氨燃烧和氮氧化物排放性能进行计算及仿真分析,探讨空气射流特性对火焰形态、温度分布、NO生成及排放的影响规律,以优化燃烧器纯氨燃烧能力。燃烧早期,旋流对燃料和空气混合影响大,而燃烧后期湍流强度对该过程影响大。发现通过增大空气射流孔面积(由12.8 mm^(2)增至19.2 mm^(2))、增加空气射流角度(由15°增至30°)均可增强旋流强度,促进燃料和空气混合,促进氨燃料快速着火和稳定燃烧,缩短着火距离。但过大的射流角度可能导致空气和燃料出现短暂分离,推迟混合过程,延长着火距离。此外,减小射流孔面积、增大射流角度还将增强燃烧器喷嘴附近湍流强度,促进氨燃料和空气混合燃耗,产生局部高温区,导致NO生成浓度升高。经对比优化,空气射流孔面积19.2 mm^(2)、射流角度15°、射流速度19.83 m/s时纯氨燃烧器实现稳定低NO燃烧,着火距离0.024 m、火焰长度0.446 m,NO生成峰值浓度和排放浓度分别降至443×10^(-6)和37.7×10^(-6)。

HBS-LNSB Ⅲ 型旋流燃烧器回流区和着火距离的试验研究

针对某煤粉燃烧器的回流区和着火距离进行了试验研究。试验考查了中心风量、外二次风量、内二次风量以及内二次风旋流强度对回流区大小的影响规律,结果发现内二次风量的变化对回流区宽度的影响最大,中心风量对回流区与燃烧器的轴向距离影响最大。试验结果为不同煤种燃烧时的燃烧器配风选择提供依据。通过对各影响因素下煤粉着火距离的研究发现,针对着火距离短的易燃煤种,为了避免燃烧器喷口烧损,提高中心风量以及一次风速是最有效的措施。由于低负荷下炉内整体温度水平低,煤粉着火距离变长,可以适当提高易燃煤种的掺烧比例。对于着火温度较高的煤种,中心风量、内外二次风量的变化对于其着火距离均有明显的规律性,内二次风旋流强度的影响需要综合考虑旋流强度带来的风量变化的影响。不同煤种着火距离的工业试验为旋流燃烧器的配风选择提供了指导。煤种发生较大变化时应进行回流区与着火距离的工业试验,为燃烧器配风找到最优选择。

醇基燃料燃烧器的优化设计

为了强化醇基燃料的燃烧效果,降低NOx的排放量,对轻油燃烧器进行优化,设计出旋流器和烟气回流装置。采用数值模拟的方法,研究不同的旋流角度、旋流叶片的个数和回流口宽度下炉内温度分布规律及炉膛出口处NOx浓度的排放量。研究结果表明:旋流叶片角度从20°增大到60°时,火焰温度呈先降低后升高的趋势。炉膛出口处NO浓度也是先减小后增大。当旋流叶片角度成40°时,炉膛内的局部高温区面积最小,且炉膛出口处NO浓度排放量最低;旋流叶片的个数从8个增加到16个时,炉膛内火焰充满度逐渐增加,温度也不断升高,而炉膛内的高温区面积呈先减小后增大的趋势,出口处NO浓度的排放量也是先减小后增大。当旋流叶片有12个时,出口处NO浓度的排放量最低;回流口宽度从0 mm增大到30 mm时,炉膛温度逐渐降低,火焰长度也不断减小,且出口处的NO浓度排放量也减小。当回流口宽度为30 mm时,炉膛出口处NO浓度的排放量最少,且比无回流口时降低了54%。

On the Role of Electrodes in Introducing Airflow Distortion in Residential Oil Burners

Computational Fluid Dynamics (CFD) simulations of airflow through a retention head residential oil burner were carried out to study the velocity field near and around the fuel spray. The simulations revealed (as expected, based on some previous experimental measurements) the velocity flow field to be far from axisymmetric. Moreover, the center of the swirling airflow was found to be at some radial distance away from the physical centerline of the flame tube. Since it was suspected that the two electrodes just upstream of the retention ring of the burner might be responsible for this flow distortion, additional CFD simulations were then carried out for the cases of no electrodes and 4-electrodes. The results clearly show that all flow distortions (velocity deviations from axisymmetric value) vanish when no electrodes are present and that the flow distortions are reduced by a factor of 2 when two additional dummy electrodes (for a total of 4 electrodes) are included in the burner design. Furthermore, for the 4-electrode case, the eccentricity of the swirling airflow is reduced by almost a factor of 3 as compared to the base design case of 2-electrodes.

煤粉低NO_(x)旋流燃烧器结构优化及试验

对OPCC型旋流燃烧器结构优化前后(包括优化内二次风扩锥结构和增加分离环)的流动、燃烧和NO_(x)生成特性开展数值模拟及锅炉现场试验研究。模拟结果与现场试验数据一致性较好。优化后燃烧器性能改善明显,主要体现在:(1)形成较大中心回流区,卷吸更多高温烟气量,有利于改善煤粉着火和燃烧稳定性(尤其在深度调峰灵活运行下);具体表现为着火距离由优化前的0.21 m缩小至0.14 m,火焰充满度好。(2)焦炭燃尽速率显著提高,由优化前的0.02×10^(-4)kg/s升至0.11×10^(-4)kg/s。(3)高CO浓度还原性区域更集中,有利于减少燃烧器喷口区域NO_(x)的生成。(4)现场试验数据表明,优化后出口CO体积分数由优化前的300×10^(-6)降至85×10^(-6),飞灰含碳由1.97%降至0.98%,出口NO变化不明显。

双风道煤粉燃烧器的结构性能分析

为了有空间插入多种燃料输送管以满足燃烧多种燃料的需求,某煤粉燃烧器取消了中心风,采用了双风道结构;并且为了使高温二次风尽快地与煤风中的煤粉接触,将煤风道置于最外层;为了在操作时根据需要随时能够调节旋流度,该燃烧器净风采用万向可调的多个小喷嘴喷射,随时可以调节火焰形状,以满足窑工况变化或者熟料烧成的需要。实践证明,这种燃烧器一次风用量并非最小,性价比不高,但设计理念值得借鉴。

墙式锅炉屏式过热器低负荷热偏差特性数值模拟研究

为缓解热偏差造成的锅炉屏式过热器超温爆管现象,研究了某600 MW超临界墙式对冲燃烧锅炉屏式过热器的热偏差特性,分析了此锅炉屏过热偏差的形成机理并给出优化方案。为克服燃烧器与锅炉间巨大尺寸差异的限制,使计算结果准确体现燃烧器设计对炉内流动与热偏差分布的影响,首先提出一种分别模拟计算燃烧器与锅炉,以燃烧器出口平面计算结果作为锅炉燃烧器入口边界条件的计算方法,并提出了降低中层燃烧器风量及调整锅炉左右侧燃烧器风量的方法,以降低屏过高热偏差区域的烟气通量。结果表明:由于相邻燃烧器旋流相互作用,在炉内形成2束较为集中的烟气流,使高温烟气在流经屏过时形成左低右高的双峰形吸热分布,这是形成屏过双峰形热偏差分布的主要原因;所提出的2种风量调整方法均可有效降低屏过热偏差峰值,大幅降低屏过超温爆管的风险。

超临界煤粉锅炉炉膛出口受热面结渣特性分析

针对某600 MW超临界煤粉锅炉炉膛出口屏式过热器和末级再热器严重结渣问题,综合分析了入炉煤种结渣综合判别指数、炉内空气动力场分布、烟气还原性气氛对炉膛出口受热面结渣特性的影响。结果表明:入炉煤种结渣综合判别指数影响较大,是该锅炉受热面结渣的重要原因;而提出的入炉煤种掺烧、燃烧优化调整等运行控制方法,可为同类锅炉预防受热面结渣提供解决方案。

赤泥回转窑双旋流燃烧器掺燃甘蔗髓数值模拟

针对赤泥回转窑煤粉燃烧器在使用时导致的高煤耗问题,以寻求更节能环保的煤替代燃料,进行赤泥回转窑双旋流燃烧器掺燃甘蔗髓的数值模拟研究。应用Fluent软件,建立数值模型。考察在掺混15%(热耗替代率)的蔗髓做为部分烟煤替代燃料的条件下,对比内旋流风角度分别为20°、30°、40°时,回转窑内的速度场、温度场以及燃烧组分的分布情况。结果表明,在回转窑中掺混高挥发分蔗髓,可得到较理想的燃烧工况。随着内旋流风角度的增大,会影响蔗髓和烟煤粉的燃烧效率,促进燃料燃烧,减少CO的产生,同时导致NOx排放增加。在回转窑中,高挥发分蔗髓与低挥发分烟煤粉混燃,可产生协同效应。在一定范围内增大内旋流风角度,会促进蔗髓挥发分的释放,从而提高烟煤粉的燃烧效率。

旋流对冲锅炉燃烧器烧损试验研究

为研究托克托发电公司四期锅炉燃烧器烧损的原因,对比了同类型机组的燃烧器设计参数,并开展了热态辐射温度试验,得出了燃烧器烧损的主要原因为一次风刚性不足,并提出了解决燃烧器烧损问题的改进设计方法和燃烧调整方案。该试验研究结果可以为锅炉燃烧器的设计、改造以及燃烧调整提供参考依据。

环形套筒窑下燃烧器旋流角度对燃烧特性的影响

文章通过数值模拟方法研究了环形套筒窑下燃烧器电石气的燃烧特性,分别对燃气和一次风旋流角度对燃烧特性的影响进行了研究,分析了旋流角度对燃烧温度分布以及CO、CO_(2)、NO_(x)等燃烧产物的影响。结果表明:燃气旋流角度对提高燃料燃烧效率影响较大。燃气旋流角度的增加,燃烧火焰最高温度和燃料的燃烧速率提高,内套筒处CO浓度降低;当燃气旋流角度从30°增加到55°时,对应内套筒处的CO浓度由8929 mg/m^(3)降低至2467 mg/m^(3)。一次风旋流角度增大,对降低CO和NO_(x)生成影响不明显。

多通道逆喷旋流燃烧器不同负荷下煤粉燃烧特性研究

旋流燃烧器煤粉燃烧特性与其结构参数及运行工况密切相关,是工业煤粉锅炉的研究重点。为了研究煤粉在多通道逆喷旋流燃烧器不同负荷下的燃烧特性,以热态试验台架为基础,采用高温热电偶、烟气分析仪和高速摄像机3种手段对预燃室内的温度分布、组分浓度分布及预燃室外的火焰形态进行测量,分析不同负荷下煤粉在预燃室内、外的燃烧过程。试验结果表明:多通道逆喷旋流燃烧器在不同负荷下均可实现煤粉稳定燃烧,负荷最低可至35%;煤粉呈现“风包火、火包粉”的径向分级燃烧状态,其中低温空气层保证预燃室结构长期稳定运行,高温无氧强还原性气氛保证煤粉快速着火稳定燃烧同时抑制燃烧初期NOx生成;低负荷运行时,煤粉燃烧过程集中在预燃室内且燃烧强度较高,温度较高其峰值均值为1204℃,无氧区域较大时强还原性气氛中CO浓度较高,预燃室外无形态稳定火焰;中、高负荷运行时,预燃室内煤粉燃烧强度略低,温度较低时其峰值均值分别为1087℃、1090℃,无氧区域较小时强还原性气氛中CO浓度较低,燃烧过程延伸至预燃室外,形成稳定的旋流火焰,其直径和发散角度分别维持在750 mm和25°左右,而火焰长度则由2627 mm延伸至3216 mm。

天然气燃烧器的低氮优化及数值模拟

近年来,天然气低氮燃烧技术层出不穷,然而单一低氮技术的控制效果始终有限。为实现天然气清洁燃烧和低氮排放,设计了一种集分级燃烧、旋流燃烧和烟气再循环等低氮技术于一体的新型低氮燃烧器,以降低燃烧过程中氮氧化物的生成和排放。建立了功率14 MW的燃烧器模型并对其进行数值模拟计算,分析了不同燃烧器结构和运行参数下燃烧器出口附近温度场、速度场以及氮氧化物(NO)浓度场,探究了混合气体旋流强度和二次风出口速度等因素对低氮燃烧性能的影响,优化该燃烧器的结构和运行参数使其达到最佳低氮性能。结果表明:优化前的燃烧器可使燃气在出口截面分布均匀并与空气充分混合,出口截面NO质量浓度已经低于30 mg·m^(-3)的低氮排放标准;燃气支管数量优化为8根时,高温区的集中度和氮氧化物的排放量最低,出口截面NO质量浓度低至7.61 mg·m^(-3);一次风和燃气混合气体旋流强度S 0优化为0.6时,出口截面NO质量浓度低至5.04 mg·m^(-3),S 0越大,产生的旋流效果越好,炉膛内的烟气内循环效应越明显;二次风出口速度优化到15~30 m·s^(-1)范围内时,能形成“山”字型的氮氧化物分布特征,有效降低氮氧化物的排放,炉膛出口截面NO的平均质量浓度能够降至4.91 mg·m^(-3)。优化后的新型低氮燃烧可使NO接近零排放,为后续的实验和工程实践提供重要参考。

旋流煤粉燃烧器一次风组件装配及工装

本文对一种前后墙对冲旋流煤粉燃烧器一次风组件装配工艺进行深入研究,从产品结构和材料特性进行分析,介绍了装配注意事项,设计出专用工装,使一次风组件的装配工艺更加科学、安全和合理,产品装配精度和生产效率得到大幅提高。