热水室中热质同时传递过程强化研究

发布时间：2019-05-17 02:37

【摘要】：气流床煤气化技术是煤炭清洁高效利用的核心技术,是发展现代煤化工、IGCC发电等过程工业的基础。黑水能量回收单元是气流床煤气化系统的核心过程之一,该单元运行好坏不仅影响到煤气化系统的整体效率,也严重影响和制约气化系统的安全、长周期、稳定、优质运行。本文以黑水处理关键设备-蒸发热水塔为研究对象,采用实验和理论计算相结合的手段,对蒸发热水塔中的热水室内两相直接接触的冷凝过程、不同接触方式的传热强化和各种塔内件上两相的流体力学行为进行了研究。论文主要内容如下:(1)在其他结构参数相同的情况下,孔中心距减小,固阀塔板的传热效率略有增大,但增大幅度不明显;当孔径增大50%时,固阀塔板的传热效率增大25%;当开孔率减小60%时,固阀塔板的传热效率增大20%;固阀高度增大,固阀塔板的传热效率先快速减小,后维持稳定不变;筛孔塔板的传热效率随着孔径增大50%而减小约10%,其余结构参数如孔中心距和开孔率等对筛孔塔板的传热效率的影响作用不显著。由于塔板上两相接触流型的不同,固阀塔板的传热效率均优于筛孔塔板。穿流式固阀和筛孔塔板上进行的两相直接接触冷凝过程,传热单元数与两相的流动参数间存在指数关系NTUl=a·FPb,其中,固阀塔板的拟合系数a=0.32-0.84,b=0.85-0.91,筛孔塔板的系数a=0.29-0.4,b=0.86-0.9,此模型可对工业装置的塔板设计和选型提供理论指导。(2)以散堆拉西环填料为两相接触元件,考察了两相在填料塔中的传热和传质过程。研究了两相流体流量及填料堆积高度等参数对传热效率的影响。得到描述两相间的传热单元数与流动参数的关系式如下,(?)该经验关系式与实验数据的平均偏差为2%,可较准确地快速估算填料塔内热质同时传递过程的传热单元数。(3)对不同塔板结构的固阀塔内流体流动行为开展了系统实验研究,研究结果表明,在溢流式塔板上,随着轴向高度的增大,固阀对于塔板上局部气含率的影响逐渐减小,沿着径向方向的气含率分布趋于均匀,且液相流量对于局部气含率的影响越来越显著。而在穿流式塔板上,塔板中心区域的局部气含率大于溢流式塔板,而靠近塔壁的边缘区域,局部气含率则小于溢流式塔板。两种不同结构的固阀塔板上的局部气含率均呈现出塔板中心区域大,而塔板边缘区域小的趋势。在塔板的不同轴向高度上,穿流式塔板上沿不同径向长度上气泡速度均大于溢流式塔板。对于这两种不同结构的塔板,其气泡速度的分布有相似的趋势,即中心区域的气泡速度大于塔壁附近区域;在塔板的中心区域,穿流塔板上的气液比表面积大于溢流塔板,随着径向长度的增加,穿流塔板上的气液比表面积逐渐减小,而溢流塔板上气液比表面积随径向长度的变化则无明显规律,呈现出波动性。(4)实验研究了塔板型式和结构参数对塔板压降的影响特征,得出穿流式塔板的塔板压降小于溢流式塔板。随着孔中心距和开孔率的减小,穿流式塔板的压降和清液层高度均增大,孔径的增大,则使压降和清液层高度增大;对清液层高度与塔板结构参数和操作变量进行关联,拟合值与实验测量值吻合良好。从最小能量原理出发,推导了穿流(?)式塔板上气体流过开孔面积分率的计算式(?)。由计算式可得,气体流通分率正比于气体流过阀孔的压降与漏液区、鼓泡区静态液层高度差的比值的立方根。计算结果表明,塔板上开孔区的气体流通分率随着孔中心距的减小而减小,并随着孔径和开孔率的增大而减小。且在各个塔板结构变量中,孔径对该气体流通分率参数的影响最不显著。
[Abstract]:The gas-flow bed coal gasification technology is the core technology of coal cleaning and high-efficiency utilization, and is the foundation of the development of modern coal chemical industry, IGCC power generation and other process industries. The black water energy recovery unit is one of the core processes of the air-flow bed coal gasification system. The operation of the unit not only affects the overall efficiency of the coal gasification system, but also seriously affects and restricts the safety, long-period, stable and high-quality operation of the gasification system. This paper deals with the condensation process of the two-phase direct contact of the hot water chamber in the steam-heating water tower by means of the combination of experiment and theoretical calculation, taking the key equipment of the black water treatment-the steam-heating water tower as the research object, using the combination of experiment and theoretical calculation. The heat transfer enhancement of different contact modes and the fluid mechanics behavior of two phases on the internal parts of the tower were studied. The main contents of the thesis are as follows: (1) In the case of the same structure parameters, the center distance of the hole is reduced, the heat transfer efficiency of the fixed valve tray is slightly increased, but the increase is not obvious; when the aperture is increased by 50%, the heat transfer efficiency of the fixed valve tray is increased by 25%; when the opening ratio is reduced by 60%, The heat transfer efficiency of the fixed valve tray is increased by 20%, the height of the solid valve is increased, the heat transfer efficiency of the fixed valve tray is rapidly reduced, the stability is maintained, and the heat transfer efficiency of the sieve tray tray is reduced by about 10% as the aperture is increased by 50%, The influence of the other structural parameters, such as the center distance of the hole and the opening ratio, on the heat transfer efficiency of the sieve tray tray is not significant. Since the two-phase contact flow pattern on the tray is different, the heat transfer efficiency of the fixed valve tray is better than that of the sieve tray. The two-phase direct contact condensation process is carried out on the flow-through fixed valve and the sieve plate tray, and the number of the heat transfer units and the flow parameters of the two-phase flow are the index relation NTUl = a. FPb, wherein the fitting coefficient a of the fixed valve plate is a = 0.32-0.84, b = 0.85-0.91, and the coefficient a of the sieve plate tray is 0.29-0.4, b = 0.86-0.9, The model can provide theoretical guidance for the design and selection of the tray of the industrial plant. (2) The heat transfer and mass transfer process of the two-phase in the packed column were investigated in the form of two-phase contact elements. The effect of two-phase fluid flow and packing height on heat transfer efficiency was studied. The relationship between the number of heat transfer units and the flow parameters that describe the two phases is as follows (? ) The average deviation of the empirical relation and the experimental data is 2%, and the number of heat transfer units in the heat transfer process of the internal heat of the packed column can be estimated more accurately. (3) The system experiment was carried out on the fluid flow behavior in the fixed valve column of the different tower plate structure. The results show that, with the increase of the axial height, the effect of the solid valve on the partial gas content on the tray decreases gradually with the increase of the axial height. The gas-containing rate distribution in the radial direction tends to be uniform, and the effect of the liquid-phase flow on the partial gas content is becoming more and more significant. And the partial gas holdup in the central region of the tray is higher than that of the overflow tray on the flow-through tray, and the partial gas content is less than that of the overflow tray. The partial gas holdup in the fixed-valve trays of the two different structures exhibited a large central area of the tray and a small trend in the edge area of the tray. At different axial heights of the trays, the velocity of the air bubbles on the flow-through trays along different radial lengths is larger than that of the overflow tray. for the trays of the two different structures, the distribution of the bubble velocity is similar, that is, the bubble velocity in the central region is larger than that in the vicinity of the tower wall; in the central region of the tray, the gas-liquid ratio surface area on the flow-through tray is larger than that of the overflow tray, and as the radial length increases, The gas-liquid ratio surface area of the flow-through tray is gradually reduced, while the gas-liquid ratio surface area on the overflow tray decreases with the change of the radial length. (4) The influence of the tray type and the structural parameters on the pressure drop of the tray was studied, and the pressure drop of the tray in the flow-through tray was less than that of the overflow tray. As the distance of the center of the hole and the aperture ratio are reduced, the pressure drop of the through-flow tray and the height of the clear liquid layer are both increased, and the pore diameter is increased, so that the pressure drop and the height of the clear liquid layer are increased; and the height of the clear liquid layer is associated with the parameters of the tower plate structure and the operating variable, and the fitting value is in good agreement with the experimental measurement value. From the principle of minimum energy, a flow-through (? ) The calculation formula (?) of the gas flow through the opening area fraction on the tray? And the gas flow rate is proportional to the cubic root of the ratio of the pressure drop and the leakage liquid area of the gas flowing through the valve hole and the height difference of the static liquid layer of the bubbling area. The results show that the gas flow rate of the open hole in the tray decreases with the decrease of the center distance of the hole, and decreases with the increase of the aperture and the aperture ratio. And in each column plate structure variable, the influence of the pore size on the gas flow rate parameter is least significant.
【学位授予单位】：华东理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ545

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