多孔介质内煤矿低浓度瓦斯燃烧波多参数耦合时空演化机理

发布时间：2018-08-08 17:13

【摘要】：瓦斯抽采是确保煤炭安全开采的主要方式,随着煤炭产量增加,瓦斯抽采量逐年上升。煤矿瓦斯既是强温室性气体,又是优质清洁能源。然而,抽采瓦斯利用率一直很低,近60%瓦斯作为废气直接排放。大量瓦斯无法利用的主要原因是抽采瓦斯浓度低、瓦斯浓度和流量波动频繁,以致常规技术很难实现安全高效利用。多孔介质燃烧技术具有贫燃极限范围宽、燃烧效率高和污染物排放低等优点,尤其适合低浓度瓦斯利用。目前,该技术主要局限于实验室理想工况研究,针对瓦斯工程背景研究较少,且研究手段单一、研究内容不全面,亟待进一步深入研究和完善。本文采用现场测试、理论分析、实验研究和数值模拟相结合的方法,研究了多孔介质内低浓度瓦斯燃烧波多参数耦合时空演化机理。主要研究成果如下:(1)开展了煤矿瓦斯气源特性和多孔介质材料特征研究。发现瓦斯抽采地点差异显著影响着抽采瓦斯的浓度、流量及其波动强弱,瓦斯利用时工况调节方案应充分参照井下抽采管路情况制定;实验获得了Al2O3和Si C泡沫陶瓷的主要成分、孔径分布、平均孔径、密度、孔隙率等参数,可为多孔介质燃烧模型参数设置和实验数据分析提供理论依据。(2)开展了多孔介质内低浓度瓦斯驻定燃烧研究。文中提出一种在网状泡沫陶瓷中填充堆积床来实现燃烧波驻定的新型燃烧器;研究发现13mm小球堆积床内的传热特性和10PPI碳化硅泡沫陶瓷更加接近;小球堆积床可填充于泡沫陶瓷和换热管间空隙,减少空隙对多孔介质内传热的影响;新型燃烧器内驻定速度极限范围相比单一泡沫陶瓷区时缩小;随瓦斯速度增加,燃烧器出口NOx排放量先增大后减小,而CO排放量却先减小后增大,但HC排放量一直减少,且新型燃烧器HC排放量介于单一堆积床和单一泡沫陶瓷燃烧器排放量之间。(3)开展了多孔介质内低浓度瓦斯非驻定燃烧研究(向上游)。随燃烧波向上游传播,峰值温度和燃烧波传播速度都维持稳定均匀,而出口区烟气温度却逐渐降低;考虑多孔介质内弥散效应后,传播速度提高了近19.8%,更贴近实验测量值,有助于提高模型准确性;随瓦斯浓度增加,传播速度和峰值温度均提高,而瓦斯速度增加时,传播速度降低,峰值温度增高;当壁面散热强度增加时,传播速度和峰值温度均降低;随燃烧波向上游传播,CO排放量逐渐降低,而NO排放量先缓慢增加再维持稳定,且峰值温度越低,NO排放量越快达到稳定。(4)开展了多孔介质内低浓度瓦斯非驻定燃烧研究(向下游)。实验时通过二维温度测点布置,结合插值法获得了燃烧器内二维温度分布;随燃烧波向下游传播,火焰出现倾斜、破裂等不稳定现象,且火焰越靠近出口不稳定特性越明显;当瓦斯速度增加时,传播速度增大,而瓦斯浓度增大时,传播速度却减小;实验获得的二维温度分布可为数值模型中散热系数选择提供理论依据;随填充小球直径增加,传播速度逐渐增大,而随燃烧器长度增加,传播速度却逐渐减小。(5)研究了含水低浓度瓦斯燃烧特性。当含水量增大时,峰值温度和NO排放量均呈线性下降趋势,而CO排放量与含水量却呈二次函数关系;瓦斯流速为0.5m/s时,峰值气流速度增加近4.4倍,燃烧器设计时应考虑气流速度增大带来的冲击力;随含水量增大,驻定燃烧极限范围逐渐变窄,其中速度下限变化很小(0.15~0.2m/s),而速度上限明显下降;定义了峰值反应速率变化率,并以此获得了水汽显著影响和轻微影响基元反应步。(6)研究了燃烧器尺度对低浓度瓦斯燃烧特性影响。当燃烧器入口直径增大时,出口NO排放量减少,而CO排放量却增加;随燃烧器长度增大,出口NO和CO排放量均逐渐减小;燃烧器大型化时,速度极限呈现波动特征,且当量比越大速度极限波动越明显,燃烧器设计应考虑尺度对工况极限的影响。(7)研究了渐扩型燃烧器中低浓度瓦斯燃烧特性。当瓦斯浓度增加时,峰值温度呈线性增长,稳燃火焰位置向上游移动,同时,NO排放量逐渐增大,而CO排放量呈先减小后增大趋势;瓦斯预热能明显提高燃烧峰值温度,有利于稳燃火焰位置移向上游,且NO排放量也显著上升,确定入口瓦斯预热程度时,应综合衡量热效率和污染物排放。研究成果有助于完善多孔介质内燃烧波多参数耦合时空演化机理,而基于煤矿低浓度瓦斯工程背景开展的相关研究,可为多孔介质燃烧技术实际应用和燃烧器设计提供理论支撑。课题研究期间发表学术论文9篇,其中SCI检索4篇,EI检索2篇,获得省部级科技进步一等奖1项,授权国家发明专利4项,实用新型专利5项。
[Abstract]:Gas extraction is the main way to ensure the safety of coal mining. With the increase of coal production, gas extraction is increasing year by year. Coal mine gas is not only a strong greenhouse gas but also a high quality clean energy. However, the utilization rate of gas extraction is very low, nearly 60% of gas is discharged directly as exhaust gas. The main reason why a large amount of gas can not be used is to pull out the tile. Low concentration and frequent fluctuation of gas concentration and flow rate, so that conventional technology is difficult to achieve safe and efficient use. Porous medium combustion technology has the advantages of wide range of poor combustion limit, high combustion efficiency and low emission of pollutants, especially suitable for the use of low concentration gas. The study of engineering background is less, and the research means is single and the research content is not comprehensive. It is urgent to further study and improve it. In this paper, the multi parameter coupling spatio-temporal evolution mechanism of low concentration gas combustion wave in porous media is studied by means of field testing, theoretical analysis, experimental research and numerical simulation. The main research results are as follows: (1) The gas source characteristics of coal mine and the characteristics of porous media material have been studied. It is found that the difference of gas extraction location significantly affects the concentration of gas extraction, the flow and its fluctuation, and the scheme should fully refer to the conditions of the downhole extraction pipeline. The main components of Al2O3 and Si C foam ceramics are obtained by the experiment. The parameters such as diameter distribution, average pore size, density and porosity can provide theoretical basis for the parameters setting of porous medium combustion model and analysis of experimental data. (2) a study on the stationary combustion of low concentration gas in porous media was carried out. A new type of burner with filling bed in reticular foam ceramics to achieve combustion wave stationary combustion was proposed. It is found that the heat transfer characteristics in the packed bed of 13mm ball are closer to that of the 10PPI silicon carbide foam ceramics, and the small ball packed bed can be filled in the gap between the foam ceramics and the heat exchange tube, reducing the effect of the gap on the heat transfer in the porous medium, and the limit range of the stationary velocity in the new burner is smaller than that in the single foam ceramic area. The NOx emission at the outlet of the device first increased and then decreased, while the CO emission decreased first and then increased, but the HC emission decreased, and the HC emission of the new burner was between the single stack bed and the single foam ceramic burner emission. (3) the study on the non stationary combustion of the low concentration gas in the porous medium (Xiang Shangyou). The peak temperature and the propagation velocity of the combustion wave are stable and uniform, but the flue gas temperature in the outlet area decreases gradually. Considering the dispersion effect in the porous media, the propagation speed increases by nearly 19.8%, which is closer to the experimental measurement value, which is helpful to improve the accuracy of the model. The propagation speed and peak temperature increase when the wall heat dissipation increases. When the wall heat dissipation increases, the propagation velocity and peak temperature decrease, and the CO emission decreases gradually with the burning wave to the upstream, while the NO emission increases slowly and then maintains stability. The faster the peak temperature is, the faster the NO emission reaches stability. (4) the low concentration in porous media is carried out. In the experiment, the two dimensional temperature distribution in the burner is obtained through the arrangement of two dimensional temperature measurement points and the interpolation method. As the combustion waves propagate downstream, the flame appears inclined and ruptured, and the more the flame is closer to the exit instability, the more obvious the propagation speed increases when the gas velocity increases. When the gas concentration increases, the propagation speed decreases, and the two-dimensional temperature distribution obtained by the experiment provides a theoretical basis for the selection of the heat dissipation factor in the numerical model. With the increase of the diameter of the filled ball, the propagation speed increases gradually, but the propagation speed decreases gradually with the increase of the burner length. (5) the characteristics of the gas burning with low water content are studied. When the water content increases, the peak temperature and the NO emission are all linearly decreasing, while the CO emission and the water content are two function relations. When the gas flow velocity is 0.5m/s, the peak air velocity increases nearly 4.4 times. The burners should consider the impact force of the air velocity increasing when the burner is designed. With the increase of water content, the limit range of the fixed combustion is gradually changed. The velocity lower limit change is very small (0.15~0.2m/s), and the velocity upper limit decreases obviously; the peak reaction rate change rate is defined, and the significant effect of water vapor and the slight influence of the basic element reaction step are obtained. (6) the effect of burner scale on the low concentration gas combustion characteristics is studied. When the inlet diameter of the burner increases, the outlet NO emissions are reduced. Less, but CO emissions increase, with the burner length increasing, the outlet NO and CO emissions gradually decrease; when the burner is large, the speed limit presents fluctuating characteristics, and the greater the limit of the equivalent ratio is, the more obvious the limit of the burner design should take into consideration. (7) the low concentration gas combustion in the diffused burner is studied. When the gas concentration increases, the peak temperature increases linearly and the position of the combustion flame moves upstream. At the same time, the NO emission increases gradually, while the CO emission decreases first and then increases. The gas preheating can obviously increase the peak temperature of the combustion, which is beneficial to the position of the combustion flame to the upstream, and the NO emission is also significantly increased, determining the entrance tile. In the preheating degree, the thermal efficiency and the emission of pollutants should be synthetically measured. The research results can help to improve the mechanism of the multi parameter coupling time and space evolution in the porous medium, and based on the related research of the coal mine low concentration gas engineering background, it can provide theoretical support for the practical application of the porous medium combustion technology and the burner design. During the study, 9 papers were published, of which 4 were retrieved by SCI, 2 by EI, 1 for the first prize in science and technology progress at the provincial level, 4 for national invention patents and 5 for utility model patents.
【学位授予单位】：中国矿业大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TD712

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