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本文对浓淡型双调风旋流燃烧器的空气动力场和气固两相流特性进行了详细的理论分析。并在分析中分别改变二、三次风的旋流强度,以考察各射流的调节特性。从中发现:三次风旋流强度的变化是影响回流区变化的主要因素;因为采用分级送风,射流前期的混合主要是在二、三次风之间。燃烧器一次风管内装有煤粉收集器,煤粉在一次风管内被惯性分离,形成了沿圆周方向煤粉气流浓淡分股;由于一次风出口加装了稳燃环,煤粉有向中心汇集的趋势;稳燃环可实现高煤粉浓度、高温、高湍动度的着火与稳燃以及挥发份剧烈的高温裂解。同时对双调风旋流燃烧器的设计特点和降低NOx生成的机理做了一定的理论分析。 相似文献
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《动力工程学报》2020,(8)
在350 kW热态中试炉上开展一次风浓淡比(煤粉质量流量比)对一次风着火特性影响的热态实验研究。通过测量燃烧器下游主燃区不同轴向位置、径向位置处的炉膛温度、O_2体积分数、CO体积分数以及NO_x质量浓度等参数,研究浓淡比对神华烟煤与神木半焦混合燃烧时(掺混比为50%)着火特性和NO_x质量浓度的影响。结果表明:除了浓淡比为1.0,混合燃料浓侧射流着火燃烧均优于淡侧,焦炭稳定燃烧位置向炉膛上游移动,O_2消耗及燃烧产物生成也主要集中在浓侧;随着浓淡比的增加,着火距离减小,高温区燃烧稳定性增强,NO_x质量浓度大幅降低,但浓淡比为3.8和5.0时,主燃区出口中心NO_x质量浓度差值仅为20.27 mg/m~3,差距较小,推荐半焦混合燃烧的合适浓淡比为3.8~5.0。 相似文献
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气固两相双平行矩形自由射流混合特性的调查是水平浓淡煤粉燃烧技术研发过程中一项基础性工作,考察自由湍流射流的实验和理论研究进展有助于确定射流混合特性研究方法。自由湍流射流理论研究综述表明:单相自由湍流射流的理论研究可采用时间平均法和直接法。时间平均法能不同程度地满足工程需要;直接法中的有限差分法和离散涡方法可以预测大尺度涡的控制作用,包括谱方法的直接法尚难以模拟耗能涡影响。气固两相湍流射流的理论研究可采用Euler方法和Lagrangian方法。关于Euler方法中双流体模型的数学描述方法,尚存在分歧;在数值模拟伪扩散、考察颗粒变化历程等方面,Euler方法和Lagrangia方法互为优缺点;方法更适于预测拟序结构对大颗粒的快速弥散机制,发展于中国的Euler—Lagrangian方法值得关注。 相似文献
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一次风速度对煤颗粒群着火特性影响的实验研究 总被引:1,自引:0,他引:1
利用Hencken型平面携带流反应器,研究了一次风速度对两种高挥发分褐煤和一种贫煤射流着火特性的影响.实验结果表明,低雷诺数(Re=878)条件下,贫煤煤粉气流先后发生外层单颗粒着火燃烧和内层颗粒群着火燃烧,煤粉颗粒着火和燃烧轨迹十分规则.但在高雷诺数(Re=4,392)条件下,贫煤煤粉气流更难形成群燃火焰,呈现出暗红色火焰.随着一次风速度的增加,尽管煤粉颗粒的停留时间减小,但湍流强度的增加使颗粒加热速率以及挥发分析出的强化作用占主导,使得煤粉气流的着火距离减小.此外,群燃火焰在挥发分聚集到一定程度后产生,是颗粒群燃烧的特有现象,而煤种挥发分含量的增加和有效聚集有利于群燃火焰的出现. 相似文献
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燃尽风对炉内流动和燃烧过程影响的数值模拟 总被引:10,自引:0,他引:10
燃尽风作为降低锅炉NOx排放浓度的一个措施已在我国得到逐步推广应用。应用数值模拟方法,对1台600MW对冲燃烧煤粉锅炉,在满负荷下燃尽风对炉内流动、燃烧和传热过程的影响开展了研究工作。应用混合分数/概率密度函数法模拟湍流燃烧,用P-1辐射模型开展辐射传热模拟,利用拉格朗日/欧拉法处理气固两相间的动量、质量和能量交换,对挥发份的析出采用单步反应模型,采用动力/扩散反应速率模型模拟煤粉颗粒的表面燃烧。研究发现:一方面,燃尽风的应用改善了炉内气流的充满情况,延迟了煤粉燃烧过程氧气的供应,加强了炉内的还原性气氛,降低了炉内最高火焰温度,有利于降低NOx排放浓度;但另一方面。燃尽风的应用将导致煤粉燃烧效率下降。 相似文献
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运行参数对锅炉煤粉着火燃烧和飞灰含碳量影响的数值研究 总被引:6,自引:1,他引:6
为了达到锅炉的优化运行以保证煤粉气流及时着火和充分燃尽,采用IPSA两相流动模型和煤粉燃烧综合模型,在不同的一次风率和煤粉细度的工况下,对1台350MW锅炉煤粉燃烧过程进行了数值模拟,得出了炉内燃烧器区域以及出口处烟气温度场和燃烧产物的组分浓度分布。分析了一次风率和煤粉细度对煤粉着火燃烧和飞灰含碳量的影响规律,并确定了优化的运行参数。结果表明:一次风率对煤粉气流的着火影响较大,而对出口处烟气温度、氧量以及飞灰含碳量影响较小。煤粉细度对煤粉气流的着火、燃烧以及燃尽均有较大影响。图8表2参9 相似文献
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四角切向燃烧锅炉煤粉射流逆向稳燃技术的研究开发 总被引:1,自引:0,他引:1
本文首次提出并分析了四角切向燃烧锅炉煤粉射流逆向稳燃技术的设计思想。根据炉内三维湍流流场的数值模拟,优化设计了本项技术应用于焦作电厂No.3炉的燃烧器改造方案。计算结果及现场应用证实,采用煤粉射流逆向稳燃技术能够大幅度延长一次风射流中煤粉颗粒在着火初期的停留时间,改善煤粉气流的着火条件,同时能够有效地削弱炉膛出口气流的残余旋转,从而减轻烟温偏差,并能改变煤粉颗粒的切圆运动轨迹,从而缓解了炉膛燃烧器区域水冷壁的结渣与高温腐蚀。 相似文献
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《Energy》2005,30(2-4):323-336
In order to elucidate the enhancement mechanisms of turbulent flame propagation, it is indispensable to examine and clarify the process of vortex–flame interaction in detail. This is because it constitutes one of the key processes in the promotion of flame propagation velocity. In this investigation, a series of large-scale organized eddies formed in the plane propane–air premixed shear flow are selected as an objective eddy field. Two devised techniques are introduced and combined with each other; one is the acoustic excitation of the shear flow, the other is the simultaneous two-directional high-speed schlieren photography. The former makes the organized eddy formation extremely regular and enables synchronized ignition with a high-speed video camera. The latter provides the opportunity to analyze two different directional views of a single propagating flame. In this study a spark-ignited flame, which is initiated at the center of a premixed organized eddy and is propagating along the axis, is optically observed and analyzed by using the proposed technique. It is shown that the propagation velocity along the axis of the eddy is promoted by the vortex bursting and is about 80% greater than that in the radial direction. It is also shown that after completing combustion in the radial direction within an organized eddy, the flame travels to the boundary regions between two adjacent eddies on the upstream and downstream sides, mainly promoted by the rolling-up motion in the coherent structure. These results suggest that there exist two kinds of vortex–flame interactions of a spark-ignited flame with coherent structure in the plane shear flow. 相似文献
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A numerical model for gas-particle flow dynamics has been combined with an NOx chemistry post-processor to predict the formation of nitric oxide in a three-dimensional, W-shaped boiler furnace burning pulverized fuel. The model includes complex interactions in gas-particle turbulent flow, heat transfer, gaseous chemical reaction, coal combustion, and NOx reaction chemistry. Because fuel nitrogen is released in proportion to burnout of pulverized coal particles, the particles are treated in a Lagrangian framework in order to track burning pulverized coal particles through the gas continuum. The results show capability of the model to describe NOx emissions under different operating conditions for full and partial loads. 相似文献
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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 NOX 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. 相似文献
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中心大速差射流浓缩煤粉方法的研究 总被引:3,自引:2,他引:3
本文提出了一种新的煤粉浓缩方法-位于一次风出口处的中心大速差射流方法,并对中心大速差射流的冷态工况进行了实验研究和数值模拟,实验和计算表明,该方法有明显的浓缩煤粉的效果,因此它不仅可以改善煤粉锅炉的燃烧稳定性及降低NOx,而且有可能解决当前煤粉浓缩燃烧技术难以解决的煤粉浓度难以控制,后期混合不好,煤粉管易堵塞和磨损以及引发炉内结焦等一系列问题。 相似文献