【作者】 王振元；

【导师】 程振民；

【作者基本信息】 华东理工大学 ， 化学工程， 2014， 博士

【摘要】 石油的加氢技术是指石油馏分在氢气存在下的催化加工过程,是石油产品精制、改质和重油加工的重要手段。近年来,随着世界范围内对轻质、洁净燃油的需求越来越高,以及原油品质的逐年下降,加氢技术在炼化领域的地位也变得越来越重要。自加氢技术问世以来,对加氢催化剂的研究获得了突破性的进展,其催化活性获得了极大的提高,但加氢反应器及其内构件的发展却相对滞后,正严重制约着加氢技术的进一步发展。本文对气液两相流体在固定床加氢反应器内构件(气液分布器和冷氢箱)中的分散与混合行为进行了理论和实验研究,并力图开发出具有优异性能的新型内构件。为克服传统抽吸型气液分布器抗塔板倾斜性能不强和液体分布不均匀的缺陷,本文提出了气液分流式的液体抽吸理论,并开发了一种具有抗塔板倾斜性能的新型气液分布器。通过冷模实验研究了气液流量变化对气液分流式分布器的液体破碎性能、液体分布均匀性及阻力损失的影响,并在直径1m的加氢反应器上研究了由气液分流式分布器组成的气液分配盘的液体分布均匀性。结果表明,存在一个液体破碎雾化的临界气体流量,而且只有气体流量超过该临界值时,气液分流式分布器才能实现对液体的均匀分布,说明临界气体流量同时也是液体分布均匀与否的分界点。而当通过气液分配盘的气量超过总体临界气体流量时,其液体分布相对不均匀度可降至5%以内,实现了对液体的较为均匀的分布。另外,基于实验数据,还得到了气液分流式分布器的阻力损失与气液两相Reynolds数间的关系式。此外,本文还通过实验研究了几何结构对气液分流式分布器的液体破碎分散性能、抗塔板倾斜性能及阻力损失等流体力学性能的影响。结果表明,采用两个进气孔,且进气孔与进液孔中心间距设置为55mm时,气液分流式分布器的综合性能最优。为克服传统旋流式冷氢箱由于气液分层流动而导致的气液接触面积小和湍动程度低的缺陷,以进一步提高冷氢箱的气液和液-液混合性能,本文开发了一种具有多重旋流结构的超重力旋流式冷氢箱,并引入Froude数的概念与机械能衡算相结合,建立了描述液体利用惯性力克服重力以实现沿水平轴向作超重力旋流运动的数学模型。通过冷模实验和计算流体力学(CFD)模拟对超重力旋流式冷氢箱的气液混合性能和流体流动情况进行了研究。模拟和实验结果都表明,液体在超重力旋流式冷氢箱内实现了沿水平轴向和重力方向的多重旋流运动,极大的提高了气液间的接触面积和相互作用。将CFD模拟结果与Higbie的溶质渗透理论相结合,研究了气液流量变化对传质系数的影响,结果表明,传质系数会随着气体流量的增加而显著提高,与氧吸收实验得到的结论相吻合,说明气液两相流体在超重力旋流式冷氢箱内实现了良好的接触,液体可以充分利用气体的推动作用提高自身的湍动程度,从而有效提高了气液混合效果。此外,本文采用α-萘酚与对氨基苯磺酸重氮盐之间的串联竞争反应为测试体系,研究了操作条件对超重力旋流式冷氢箱微观混合过程的影响,并以离集指数表征微观混合性能。结果表明,离集指数随气体流量的增加而显著减小,随液体流量的增加而增大。在实验基础上,采用团聚模型获得了离集指数与微观混合时间的关系,并计算出超重力旋流式冷氢箱的微观混合时间为40～100ms,远小于自身的平均停留时间,说明液体在流出超重力旋流式冷氢箱之前已经实现了组分和温度在分子尺度上的均一性。为了更直观的研究超重力旋流式冷氢箱的混合换热能力,本文还对箱体内的气液相间和液-液相内的传热过程进行了CFD模拟。结果表明,气液换热速率会随着气体流量的增加而显著升高,与气液传质部分的模拟和实验研究结果相符。液-液混合换热过程的模拟结果表明,最大温差高达60K的三股液体,在箱体内经过旋流混合后,在出口处的最大温差下降了近97%,而温度分布的不均匀度仅为0.7K,液体在出口处获得了近乎均一的温度分布,表明超重力旋流式冷氢箱具有优异的液-液混合换热性能。更多还原

【Abstract】 Catalytic hydroprocessing is a mature technology practiced in the petroleum refining industry for upgrading a variety of hydrocarbon streams ranging from straight-run naphtha to vacuum residua or even heavy crude oils. Nowadays, the hydroprocessing technology is of vital importance to the refining industry, as a result of the growing market of high value petroleum products and decreasing availability of light oils. Since the introduction of hydroprocessing technology, catalyst suppliers have made significant advances in improving the relative activities of hydroprocessing catalysts. However, the design of hydroprocessing reactors has not advanced at the same pace as the development of hydroprocessing catalysts, and the existing reactors are not capable of utilizing the benefits of the high activity catalysts. To develop novel types of internals with excellent performance, mixing and dispersion of gas and liquid for internals (gas-liquid distributor and quench box) of the fixed bed hydroprocessing reactor was investigated in this paper.To overcome shortages of the traditional gas-liquid distributor, a novel gas-liquid separated flow distributor was designed in this paper, which was supposed to show low sensitivity to the tray levelness and distribute liquid uniformly. The relationship between the breakup of liquid and the liquid distribution uniformity, and effects of operating conditions on the pressure drop of the novel distributor were studied through cold model experiments. Furthermore, the liquid distribution uniformity of a distribution tray, which was composed of37gas-liquid separated flow distributors, was investigated. Results show that, there exists a critical gas volume flow rate for the atomization of liquid. Liquid can be distributed uniformly only when the gas volume flow rate is higher than the critical value. The relative liquid distribution nonuniformity of the distribution tray is lower than5%when the gas volume flow rate is higher than the overall critical value, which reveals the uniform distribution of liquid. Besides, a brief correlation between the pressure drop of the novel distributor and Reynolds number of two phases was proposed. After that, experiments were conducted to investigate effects of geometry structures on the hydraulic performance of the gas-liquid separated flow distributor, such as sensitivity to the tray levelness, liquid breakup performance and pressure drop. Results show that, the optimal comprehensive performance of the gas-liquid separated flow distributor can be obtained, when two gas-inlet holes are drilled as well as the center distance between gas-inlet and liquid-inlet is spaced at approximately55millimeters.To enhance the gas-liquid and liquid-liquid mixing efficiency of the quench box, a novel structure based on supergravitational swirling flow was proposed, which owns multiple swirling flow structures. To reach supergravitational swirling flow, the Froude number of liquid in the horizontal swirling tube should be greater than unity. Through computational fluid dynamics (CFD) simulation and using a high-speed camera, the supergravitational swirling flow was visualized. Based on the Higbie’s penetration theory, CFD simulation was conducted to estimate the gas-liquid mass-transfer coefficient, and was compared with the oxygen absorption experiment. It shows the gas flow rate plays a key role in the gas-liquid mixing performance in the quench box. Experiments were also carried out to investigate effects of operating conditions on the pressure drop of the two-phase flow in quench box, and a correlation was proposed accordingly. Furthermore, to study effects of operating conditions on the micromixing process, cold model experiments were carried out based on the competitive and consecutive reaction between1-naphthol and diazotized sulphanilic acid, and the segregation index was used to characterize the micromixing performance. Results show that, the segregation index decreases sharply with the increase of the gas flow rate, while increases with increasing liquid flow rate. This indicates that intimate contact between gas and liquid can be realized in the novel designed quench box, while the turbulence intensity and micromixing efficiency of the liquid can be notablely improved by taking full advantage of the gas phase’s driving effect. The relationship between segregation index and micromixing time was obtained according to the incorporation model. Under the operating conditions of this work, the micromixing time was calculated to be40～100ms, which is far less than the average residence time and is of the same order of magnitude as the mechanically stirred tank. Hence, it illustrates that the composition and temperature of liquid should be perfectly homogenized at outlet of the supergravitational swirling-type quench box, and the novel quench box owns excellent liquid-liquid mixing performance.In addition, to investigate mixing and heat transfer capability of the supergravitational swirling-type quench box, gas-liquid and liquid-liquid heat transfer processes at industrial conditions were investigated through CFD simulation. Results show that, gas-liquid heat exchange rate will be increased significantly with the increase of gas flow rate, which shows the same tendency as the conclusions regarding studies of the gas-liquid mass transfer. Meanwhile, the simulation results of liquid-liquid heat transfer process show that, the maximum temperature difference of liquid at outlet of the supergravitational swirling-type quench box is lower than2K and is reduced by97%compared with that of the inlet.更多还原