【作者】 金渭龙；

【导师】 王亦飞；

【作者基本信息】 华东理工大学 ， 热能工程， 2014， 博士

【摘要】 本文以化学热回收两段组合式气化炉为研究对象,采用实验与数值模拟相结合的方法,对两段炉冷态实验装置内的流场特征进行了研究,并且研究了热态实验装置内二段固定床的气化反应性和显热回收效果。此外,还比较了二段水煤浆进料对原有多喷嘴对置式(OMB)气化炉气化效率的影响,并且考察了不同的操作条件对一种上吹式多喷嘴两段式(TS-OMB)气化炉工艺指标的影响。主要内容如下：1.在冷态两段炉内,随着Reynolds数和床层高度的增加二段床层的压降增加,并且空隙率越小,二段床层的压降越大。Montiller公式相比于经典的Ergun方程,能够更加准确地预测炉内的二段床层压降。当单喷嘴顶喷时,随着二段床层高度的增加,中心气速在床层上表面的冲击区内衰减越快。在轴向速度的径向分布中,中心气速最大并且衰减最快,在r=0.5R径向位置处,由于回流的存在导致轴向速度呈先增大后减小的变化趋势,管流区在喷嘴平面下方2.9D处形成。当四喷嘴对喷时,在喷嘴平面的上方和下方形成两股径向射流,径向射流的中心气速从喷嘴平面上的零值增加到最大值后,呈射流衰减变化,向下的径向射流达到管流区所需的轴向距离约为1.1D。在四喷嘴对喷的条件下,平均停留时间随着表观气速和床层压降的增加而减小。采用部分短路Gamma分布数学模型能够与停留时间密度函数的实验值吻合较好。通过模型参数的分析得出,在四喷嘴对喷的条件下炉内几乎不存在短路现象,随着表观气速的减小和床层阻力的增加,炉内气体的流型以及混合程度趋近于全混流。平推流部分的影响程度随着表观气速以及二段床层阻力的增加变得显著。2.对冷态两段炉建立了三维模型,采用Realizable κ-ε模型模拟一段气体的湍流流动,多孔介质模型模拟二段固定床。模拟结果表明,当单喷嘴顶喷时,中心气速沿轴向逐渐衰减,并在喷嘴下方2.7D处形成管流区。在射流基本段的外围近壁面处形成了与中心速度相反的回流,回流比沿着轴向位置,呈先增大后减小的变化规律。当四喷嘴对喷时,中心轴向速度在喷嘴平面的上方和下方速度呈现先增加后减小的变化趋势,最大径向速度的位置距离喷嘴平面约为0.21L。在径向射流的外围形成了回流,并且喷嘴平面上方的回流比大于喷嘴下方。相比于单喷嘴顶喷的条件,四喷嘴对喷所形成的回流更为明显。在四喷嘴对喷的条件下,随着二段床层高度的增加,中心气速在床层上表面的冲击区内衰减加快,随着一段气量的增加和喷嘴直径的减小,最大径向射流速度增加,而最大径向射流的位置基本不变。回流比和回流区域的大小随着床层高度的增加以及一段喷嘴直径的减小而显著增加。一段气量的增加,提高了炉内的回流量,但是回流比和回流区域的大小不发生改变。3.在热态两段炉内,粒径范围为15-20mm的冶金焦,其气化反应性优于10-15mm和20-25mm,与初始的一段气体相比,其二段平均有效气浓度提高了2.52%,平均低热值(LHV)增加了2.27%,CO2转化率为8.9%,最终碳转化率为32.4%。当一段氧油比最大时(1.92m3·kg-1),二段冶金焦的气化反应性最好,平均有效气浓度增加了7.43%,平均LHV增幅为5.26%,CO2转化率为18.1%,最终碳转化率为41.7%。在内蒙褐煤中添加5%的硝酸钾或者硝酸钙,均能有效地提高气化反应速率。5%硝酸钾的催化效果优于5%的硝酸钙。当添加5%的钾时,二段出口处的平均有效气浓度提升了3.43%,平均LHV提高了4.72%,CO2转化率为9.3%,二段块煤的碳转化率为85.5%。二段块煤的气化反应性随着钙添含量的增加而增加。当钙的添加量大于5%时,才能起到显著的催化作用。当二段添加8%的钙时,催化效果最为明显,平均有效气浓度提高了3.74%,平均LHV增幅4.95%,CO2转化率为9.4%,二段内蒙褐煤的碳转化率为90.8%。4.对小型的两段炉热态实验装置,建立了固定床气化反应模型,模拟结果与实验数据吻合良好。当高温合成气流通二段固定床区域时,气体速度增加,气体温度显著降低,并且合成气中C02和H20的含量减小,有效组分CO和H2增加。随着反应的进行,气化反应中心从煤层的上层逐渐向下层转移,气体组分和温度在煤层中的变化亦逐渐减小。二段煤量的减少使得块煤的升温速率增加,导致有效气浓度和气固反应速率在反应初期较高,而最终的碳转化率随着煤量的增加而降低。二段块煤粒径的减小提高了有效气浓度、气固反应速率和碳转化率,并且使得气固反应率先进行,有利于二段块煤的气化反应。一段合成气中C02和H20含量的增加,提高了二段块煤的气固反应速率和碳转化率,并且一段气体温度的升高,使得二段块煤的升温速率和气化反应温度增加,加速了脱挥发分速率和气固反应速率,有利于二段气化反应的进行。5.建立了OMB气化炉的三维模型,模拟结果与实际测量值吻合良好。研究结果表明在OMB气化炉的撞击区和径向射流区域气化反应显著。在OMB-staged气化炉中,二段额外喷入的水煤浆降低了整个气化炉内的温度,并且降低了炉内的气化反应速率和碳转化率。TS-OMB气化炉与OMB相比,有效气产率提高了31.1Nm3·h-1,冷煤气效率和碳转化率均有所提高,表明了将原有的OMB气化炉进行TS-OMB形式的改进是提高气化效率的一种潜在方式。在所提出的上吹式TS-OMB气化炉的典型工况下,出口气体温度为1353.5K,冷煤气效率达到77.47%,碳转化率为96.25%。随着二段给煤比的增加,炉膛温度和碳转化率降低,而有效气浓度和冷煤气效率均存在一个峰值。随着一段氧煤比的提高,炉膛温度和碳转化率增加,有效气浓度和冷煤气效率呈先增加后减小的趋势。随着水煤浆浓度的增加,炉膛温度、碳转化率、有效气浓度和冷煤气效率均呈现逐渐增加的趋势。更多还原

【Abstract】 Experimental research and numerical simulation are conducted to investigate the flow field characteristic in the cold-state experimental scale combined gasifier, and the gasification reactivity and heat recovery effect are also studied in a hot-state experimental scale device. Furthermore, the gasification efficiency of coal water slurry (CWS) injecting from the second stage burner in the opposed multi-burner (OMB) gasifier is assessed and compared with original OMB gasifier. Also the influence of various operating conditions on the gasification indicators in a novel updraft two-stage gasifier modified from the OMB (TS-OMB) gasifier is analyzed.1. The pressure drop of second stage fixed-bed shows an increased trend with the increase of Reynolds number and bed height. A smaller porosity for the bed layer turns to be a larger pressure drop. Compared with the classical Ergun equation, the Montiller empirical formula can predict the pressure drop in the combined gasifier more accurately. With the form of top-burner, an impacting zone is formed above the second stage fixed bed, and a faster central velocity decay in the impacting zone for a higher bed height. Among the axial velocity of radial distribution, the central velocity turns to be the largest and decays fastest. In the position of r=0.5R, the axial velocity increases firstly and then decreases due the presence of recirculation flow in the furnace. The velocity has been the form of plug flow in the distance of2.9D below the burner plane. With the form of four-burner, impinging-jet flows are formed above and below the burner plane. The velocity of impinging-jet flow increases from nil to the maximum velocity, and then decays with the axial position. The distance for the downward impinging-jet flow to be plug flow is1.1D. In the condition of four-burner, the average residence time shows a decreasing tendency with the increase of superficial gas velocity and bed layer residence. The mathematical model of Gamma distribution shows good agreement with the experimental data for fitting the residence time density function. By analyzing the model parameters, almost no short-circuit is existed in the furnace. With the increase of superficial gas velocity and decrease of bed layer resistance, the flow pattern in the furnace is close to complete mixing flow. The influence of plug flow becomes more significant with the increase of superficial gas velocity and bed layer resistance.2. A3-dimensional model is established for the cold-stage two-stage gasifier, in which the Realizable k-ε model is adopted for the turbulent flowing of first stage, and a porous media model for the second stage fixed-bed. With the form of top-burner, the central velocity decays gradually with the axial position, and the plug flow is formed below the burner plane of2.7D. The recirculation flow with the opposite direction from the central is formed surrounding the jet flow, and the reflux ratio turns to be an increasing firstly and then decreasing trend. With the form of four-burner, the central velocity above and below the burner plane shows decreasing trend after first increasing. The position of maximum impingping-jet velocity is located at about0.21L. The recirculation flows are also formed surround the impinging-jet flows, in which the reflux ratio above the burner plane is much larger than that below the burner plane. The recirculation formed by four-burner is much more remarkable than that by top-burner. In the condition of four-burner, with the increase of bed layer height the velocity decays faster in the impacting zone, and the reflux ratio and recirculation zone becomes larger. With the increase of gas velocity at burner outlet, the maximum velocity of impinging-jet flow increases and then shows a faster decaying rate, while its position has almost no change. The reflux ratio and recirculation flow zone increases for a higher bed layer height and smaller burner diameter, while unchanged with the gas flow rate.3. As for the hot-state two-stage gasifier, the metallurgical coke of15-20mm shows a better gasification reactivity than10-15mm and20-25mm. Compared with the initial syngas from first stage, the average effective gas concentration (EGC) of second stage increased by2.52%,2.27%for average low heat value (LHV) and8.9%for CO2conversion. The final carbon conversion is32.4%after a three-hour reaction time. When the oxygen/diesel ratio reaches the highest (1.92m3-kg-1), the average EGC and LHV increased by7.43%and5.26%, respectively, and18.1%for the CO2conversion. The final carbon conversion of coke is41.72%. The gasification reaction rate can be improved effectively after adding5%potassium nitrate or calcium nitrate in Inner Mongolia lignite, and the catalytic effect of5%potassium nitrate is better than calcium nitrate. When adding5%potassium, the average EGC increases by3.43%, LHV by4.72%, and CO2conversion by9.3%. The final carbon conversion of Inner Mongolia lignite is85.5%after a three-hour reaction time. With the increase of calcium loading in the lump coal, the gasification reactivity becomes better. When the calcium loading is larger than5%, catalytic effect for the gasification reaction is much more significant. When the calcium loading of lump coal is8%, the average EGC is increased by3.74%, LHV by4.95%, and CO2conversion by9.4%. The final carbon conversion of8%calcium loading is90.8%.4. Based on the former hot-state experimental scale two-stage gasifier, a fixed-bed gasification reaction model is established. The simulated result shows a good agreement with the experimental data. When the high temperature syngas flows through the bed layer, the gas velocity increases and the gas temperature reduces significantly. The content of CO2+H2O in the syngas is reduced, and the effective content of CO+H2is increased due to the gasification reaction. With the proceeding of gasification reaction, the reaction zone shows a moving down trend from the upper to the bottom in the coal layer, and the varying of gas composition and temperature becomes smaller. With the decrease of coal amount in the fixed-bed, it turns to be a faster heating rate in the initial stage, which will take the lead of devolatilization and gasification reaction. The final carbon conversion decreases with the increase of coal amount. With the decrease of coal particle size, the EGC, reaction rate and carbon conversion are enhanced, as well as a leading gasification reaction, which is propitious to the gasification reaction. The gasification reaction rates and carbon conversion are also enhanced with the increase of CO2+H2O content of syngas. Furthermore, the heating rate and reaction temperature of fixed-bed coal layer are enhanced with the increase of syngas temperature, which results in a faster devolatilization rate and gasification rate, and is propitious to the second stage gasification reaction.5. A3-dimensional numerical model for an OMB gasifier is established, and the simulated results show good agreement with practical values. The gasification reaction in the impinging and impinging-jet flow zones turns to be significant in OMB gasifier. As for OMB-staged gasifier, the injecting of additional CWS in the second stage reduces the temperature in the whole furnace, resulting in a relative low reaction rate and carbon conversion. As for TS-OMB gasifier, the productivity of effective gas increases by31.1Nm3·h-1, and a slight higher cold gas efficiency (CGE) and carbon conversion compared with OMB gasifier, which shows that a two-stage modified for the gasifier is a potential way to improve the gasification efficiency. In the typical condition of updraft TS-OMB gasifier, the cold gas efficiency reaches77.47%with the outlet gas temperature of1353.5K, and final carbon conversion of96.25%. With the increase of coal distribution in the second stage, the average temperature and carbon conversion are reduced, and the EGC and CGE turn to be peak values. With the increase of oxygen/coal ratio in the first stage, the average temperature and carbon conversion are enhanced, while the EGC and CGE show decreasing trends after the increasing. With the increase of CWS concentration, the average temperature, EGC, CGE and carbon conversion are all increased, which is propitious to the gasification reaction.更多还原