氧气高炉气—固两相流的物理和数学模拟研究

发布时间：2018-05-10 09:29

本文选题：氧气高炉 + 气-固两相流　；参考：《北京科技大学》2017年博士论文

【摘要】：随着全球变暖、环境恶化及能源资源短缺等问题日益严重,各国制定了严格的环保减排政策,对于高能耗、高污染的钢铁行业来说更是面临巨大压力,其中高炉炼铁工序节能减排是减少钢铁企业能源消耗和CO2及其它污染物排放的重要途径。炉顶煤气循环-氧气鼓风高炉炼铁技术(简称氧气高炉)的节碳减排能力已经通过理论计算和高炉试验得到了验证。炉身喷吹部分脱除CO2并预热到一定温度的炉顶循环煤气是氧气高炉的关键特征之一,本文采用物理模型实验和DEM-CFD耦合数学模型相结合的方式,对氧气高炉内气-固两相流进行了研究,同时对影响氧气高炉炉身喷吹煤气分布特征的因素进行了研究,最后提出了未来高炉DEM-CFD耦合数学模型的发展方向。首先,依据相似原理搭建了缩小比例的氧气高炉二维冷态物理模型,并对不同高炉操作条件下尤其是氧气高炉不同操作条件下的气-固流动行为进行了模拟实验研究,结果表明:氧气高炉内固相流动的主要特征区域与传统高炉一致仍可分为四个流动区域;随着批重的增加,静止区形状有向矮胖方向发展趋势;在不同工艺条件下,处于活塞流动区域的炉料下降速度大致相同;随着炉身喷吹煤气量所占比例的增加,静止区有往瘦高方向发展的趋势。其次,结合多种数值模拟前处理软件,完成了对二维和三维高炉DEM-CFD耦合数学模型的前处理过程,主要包括实际高炉抽象出模型高炉、几何模型数据化处理、网格划分、模型局部特殊处理、控制方程确定等部分。再次,建立了与二维冷态模型相对应的DEM-CFD耦合数学模型,对前期已经完成的冷态模型实验进行简单地数值模拟,数值模拟结果表明:与实验结果一致,氧气高炉炉内仍分为四个流动区域;炉身喷吹煤气对于氧气高炉炉内固体炉料运动特征没有显著影响,数值模拟结果比物理实验结果更接近实际氧气高炉炉内颗粒运动状态;处于快速流动区域的颗粒所受到的压力较小,但是处于炉身块状区和炉缸死料柱两个区域的颗粒受挤压力较大,这两个区域颗粒挤压严重,透气性较差。进一步利用二维扁片氧气高炉DEM-CFD耦合数学模型分析了多影响因素下氧气高炉炉内的气-固两相流动特征,考察了炉料粒径、炉身风口尺寸及炉身喷吹煤气量与炉内总煤气量之比等参数对炉身喷吹煤气分布的影响,结果如下:随着炉内颗粒运动达到稳定状态,在高炉中心轴向会形成一个空隙率较低的煤气通道,利于上升煤气中心发展;在炉身喷吹煤气出口水平,喷吹煤气向中心的渗透距离最短,但随着向上流动,逐渐渗透到高炉中心;随着炉料粒径和鼓风动能的增加,炉身喷吹煤气可以更加深入到高炉中心;炉身喷吹煤气量与炉内总煤气量之比对优化喷吹煤气在炉内的分布有决定性作用;影响炉身喷吹煤气渗透距离的本质因素是炉身风口水平之上和之下的气体压力差,压力差越小,炉身喷吹煤气便可以更加深入到高炉中心。利用三维氧气高炉DEM-CFD耦合数学模型,分析了氧气高炉炉内气-固两相流特征,考虑了软熔带、回旋区等重要特征,通过改进耦合代码使颗粒数量更接近实际高炉,对三种炉身风口排布方式做了计算对比,提出最优配置。结果如下:三维模型可以消除二维模型中的壁面效应,软熔带以上的颗粒几乎全部处于活塞流动中;除了在风口回旋区及其附近,高炉边缘的固相体积分数均比中心大,利于煤气中心发展;固相体积分数在软熔带附近达到最大值(透气性最差),在软熔带部位气相单位高度压降达到最大,且煤气的流动方向经过软熔带后也发生了微小变化;当炉身喷吹煤气的水平速度增加到一定程度,由于其和上升煤气的强烈碰撞,其会出现向下流动的趋势,不利于充分利用;炉身风口最优的排布方式为炉身风口和炉缸风口等数量,且炉身风口处于炉缸风口两两之间,该方式可以为全炉提供更加合理的热分布。将三维模型建模思路移植到二维扁片模型中,建立了氧气高炉复杂二维DEM-CFD耦合模型,炉料粒径进一步减小,研究结果如下:复杂二维模型中,固相体积分数与三维模型相比有所提高,炉内透气性变差;炉身上部与三维模型一致出现了矿石颗粒和焦炭颗粒的分层现象,但在炉身中下部时炉料的分层现象相较于三维模型提前消失;复杂二维模型在相同的炉身喷吹煤气比例下,相较于简单二维模型,炉身水平喷吹煤气更难以达到高炉中心,边缘特征刚好相反。复杂二维模型与之前模型相比准确性得到提高。氧气高炉的DEM-CFD耦合模型未来的发展重点应该在以下几个方面:逐渐加入气-固换热、颗粒下降过程粒径变化及软熔带颗粒收缩等更接近实际高炉的模型和控制方程;更为先进的DEM-CFD耦合模型,应该考虑加入液相、气-固-液多相间反应、反应进程-颗粒参数耦合模型等。氧气高炉仿真模型的完善离不开实验室研究及工业试验研究基础数据的支持,同样也依赖于计算方法和计算机能力的改进。
[Abstract]:With the global warming, environmental deterioration and the shortage of energy resources and other problems, countries have formulated strict environmental protection and emission reduction policies for high energy consumption and high pollution iron and steel industry. Energy conservation and emission reduction in the blast furnace process is an important way to reduce energy consumption and CO2 and other pollutants in iron and steel enterprises. The carbon emission reduction capacity of the furnace top gas cycle oxygen blast furnace ironmaking technology (BF for short oxygen blast furnace) has been verified by theoretical calculation and blast furnace test. It is one of the key features of the oxygen blast furnace to remove CO2 and preheat to a certain temperature to a certain temperature. In this paper, the physical model experiment and DEM-CFD are used in this paper. Coupled with the coupled mathematical model, the gas solid two-phase flow in oxygen blast furnace is studied. At the same time, the factors affecting the distribution characteristics of gas distribution in the oxygen blast furnace body are studied. Finally, the development direction of the DEM-CFD coupling mathematical model in the future is put forward. First, according to the similar principle, a reduced proportion of oxygen blast furnace is built. A two-dimensional cold physical model was used to simulate the gas solid flow behavior under different operating conditions of the blast furnace, especially in the oxygen blast furnace. The results showed that the main characteristic region of the solid flow in the oxygen blast furnace could be divided into four flow regions in accordance with the conventional blast furnace. With the increase of batch weight, the static zone shape was increased. Under different technological conditions, the decreasing speed of the furnace material in the piston flow area is approximately the same. With the increase of the proportion of gas in the furnace body, the static zone has the tendency to develop in the lean direction. Secondly, combined with a variety of numerical simulation pretreatment software, the two and three dimensional blast furnace DEM-CFD coupling is completed. The pre-treatment process of the mathematical model mainly includes the actual blast furnace abstract model blast furnace, the geometric model data processing, the mesh division, the local special treatment of the model, the control equation and so on. Thirdly, the DEM-CFD coupling mathematical model corresponding to the two-dimensional cold model is established, and the cold model experiment has been completed in the earlier period. The numerical simulation results show that the oxygen blast furnace furnace is still divided into four flow areas in accordance with the experimental results, and the furnace body injection gas has no significant influence on the motion characteristics of solid charge in the oxygen blast furnace. The numerical simulation results are more close to the physical experiment results than the actual oxygen blast furnace. The pressure of the particles in the fast flow area is smaller, but the particles in the two regions of the two regions of the hearth block and the hearth die are heavily squeezed, and the two regions have serious extrusion and poor permeability. Further, the two dimensional flat sheet oxygen blast furnace DEM-CFD coupling mathematical model is used to analyze the oxygen blast furnace under the multiple influence factors. In the gas solid two phase flow characteristics, the effects of the size of the furnace material, the size of the furnace body and the ratio of the amount of gas in the furnace body and the ratio of the total gas in the furnace to the gas distribution of the furnace body are investigated. The results are as follows: with the steady state of the particle movement in the furnace, a gas channel with low void ratio will be formed in the axial direction of the blast furnace, which is beneficial to the rise of the gas. The gas center develops; in the gas outlet level of the furnace body, the penetration distance from the gas to the center is the shortest, but with the upward flow, it gradually penetrates into the center of the blast furnace; with the increase of the particle size and the kinetic energy of the blast, the furnace body can be more deep into the center of the blast furnace; the ratio of the amount of gas to the total gas in the furnace is optimized. The distribution of gas in the furnace is decisive; the essential factor affecting the penetration distance of the gas injection is the difference between the gas pressure above and below the level of the body of the furnace body. The smaller the pressure difference is, the lower the pressure difference, the gas can be further penetrated into the center of the blast furnace. The oxygen blast furnace is analyzed by the mathematical model of the DEM-CFD coupling of the three dimensional oxygen high furnace. The characteristics of gas solid two phase flow in the furnace are characterized by the consideration of the important characteristics of the soft melting zone and the gyration zone. By improving the coupling code, the number of particles is closer to the actual blast furnace. The calculation and comparison of the three kinds of furnace tuyere arrangement are made and the optimal configuration is put forward. The results are as follows: the three-dimensional model can eliminate the wall effect in the two-dimensional model and the particles above the soft melting zone. In addition to the piston flow, the solid volume fraction of the blast furnace edge is larger than that of the center, which is beneficial to the development of the gas center, and the solid volume fraction reaches the maximum value near the soft melt zone (the worst gas permeability), and the maximum pressure drop of the gas phase in the soft melt zone reaches the maximum, and the flow direction of the gas passes through the flow direction. There is a slight change in the soft melt zone. When the horizontal velocity of the gas is increased to a certain extent, the downward flow trend will appear because of the strong collision with the rising gas, which is not conducive to the full use of the gas. The best arrangement way of the body of the furnace body is the number of the hearth vents and the tuyere of the hearth, and the body of the body is in the vate tuyere. 22, this method can provide more reasonable heat distribution for the whole furnace. The three-dimensional model modeling idea is transplanted into the two-dimensional flat plate model, and the complex two-dimensional DEM-CFD coupling model of the oxygen blast furnace is established. The particle size of the furnace is further reduced. The results are as follows: in the complex two-dimensional model, the solid volume fraction is improved compared with the three-dimensional model. The gas permeability in the furnace becomes worse; the upper part of the furnace body is consistent with the three dimensional model of the stratification of ore particles and coke particles, but the stratification of the furnace material is disappearing earlier than the three-dimensional model in the lower part of the furnace body, and the complex two-dimensional model is compared to the simple two-dimensional model, and the furnace body is blown by the furnace body horizontally under the same proportion of the gas blowing in the same furnace body. It is more difficult to reach the center of the blast furnace and the edge features are just opposite. The accuracy of the complex two-dimensional model is improved compared with the previous model. The future development of the DEM-CFD coupling model of the oxygen blast furnace should be in the following aspects: the gradual addition of gas to solid heat, the change of particle size and the shrinkage of the soft melting zone particles are more close to the actual height. The model and the control equation of the furnace, the more advanced DEM-CFD coupling model, the liquid phase, the gas-solid liquid multiphase reaction and the reaction process particle parameter coupling model should be considered. The improvement of the oxygen blast furnace simulation model can not be separated from the support of the laboratory research and the basic data of the industrial test research. It also depends on the calculation method and the computer. Improvement of ability.

【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TF53

【参考文献】