尿素合成塔气液两相流的CFD模拟

发布时间：2018-03-26 04:03

本文选题：尿素合成塔　切入点：CFD　出处：《重庆大学》2015年硕士论文

【摘要】：尿素合成塔是一种高温高压操作、气液两相共存、内置塔盘的塔式反应器,是整个尿素生产过程中的关键设备。为了强化反应效果,其内置塔盘在生产实践中被不断改进,出现了许多类型的塔盘。因为缺乏实验数据,对尿素合成塔内的气液两相流场进行基于计算流体力学(CFD)的模拟计算及分析,将在塔盘的改进、设计及操作中具有重要的理论指导意义。本文以计算流体力学(CFD)软件Fluent为平台,对尿素合成塔内的气液物流,在经过不同类型塔盘之后的两相流状态进行数值模拟分析。为此,将尿素合成塔相邻两塔板之间的反应空间可看作一个鼓泡段,气液两相以并流的方式经过塔盘进入鼓泡段。每个鼓泡段内的经过了反应平衡、物料平衡和气液平衡计算之后的物料数据,由其它计算软件提供,因此本计算中忽略鼓泡段内的化学反应。在CFD模拟中,选择Euler-Euler双流体多相流模型,采用Realizable k-ε湍流模型,对安装有平筛板和波形塔盘的尿素合成塔气液两相非定常流动分别进行了二维模拟,并采用群体平衡模型(PBM)对两种塔板的气泡大小分布规律进行了数值模拟。考察了在不同的表观气速下,合成塔内平均气含率的变化规律;又设定10组不同的气泡尺寸,研究气泡经过不同的多孔塔板后的变化及其在塔内的分布情况。结果表明:随着空塔气速的增大,鼓泡塔内的气含率与空塔气速近似成线性关系;波形塔盘中的气体分布更为均匀;在多气泡尺寸的PBM模拟中,波形塔盘的小气泡数量比例要比平筛板中的大,更有利于两相间的传质。采用与二维模拟中相同的数学模型和边界条件,对平筛板合成塔实际的三维模型做了不同进口气速下的模拟计算。结果表明:合成塔内较大气速下的气相能够较早地实现整体的分布均匀,并探索了在不同进口气速下的气含率的分布随塔高的变化规律。
[Abstract]:Urea reactor is a kind of high temperature and high pressure operation, gas-liquid two-phase coexisting, built-in tray tower reactor, is the key equipment in the whole urea production process. In order to enhance the reaction effect, its built-in tray has been continuously improved in production practice. Due to the lack of experimental data, the simulation and analysis of gas-liquid two-phase flow field in urea reactor based on computational fluid dynamics (CFD) will be improved in the tray. The design and operation are of great theoretical significance. Based on the computational fluid dynamics (CFD) software Fluent, the two-phase flow state in urea synthesis tower after passing through different types of trays is numerically simulated in this paper. The reaction space between the two adjacent trays of the urea synthesis tower can be regarded as a bubbling section. The gas-liquid two-phase flows through the tray into the bubbling section in a parallel way. The reaction equilibrium in each bubbling section is obtained. The material data after material balance and gas-liquid equilibrium calculation are provided by other calculation software, so the chemical reaction in bubble section is ignored in this calculation. In CFD simulation, the Euler-Euler two-fluid multiphase flow model is selected and the Realizable k- 蔚 turbulence model is used. Two-dimensional simulation of gas-liquid two-phase unsteady flow in urea synthesis column with flat sieve plate and corrugated tray was carried out. A population equilibrium model (PBM) was used to simulate the bubble size distribution of two kinds of trays. The variation of average gas holdup was investigated at different apparent gas velocities, and 10 groups of different bubble sizes were set up. The change of bubble and its distribution in the column after different porous trays are studied. The results show that the gas holdup in the bubble column is approximately linear with the increase of the gas velocity in the bubble tower. The gas distribution in the corrugated tray is more uniform. In the PBM simulation of multi-bubble size, the number of small bubbles in the corrugated tray is larger than that in the flat sieve plate. It is more favorable for mass transfer between two phases. The same mathematical model and boundary conditions as in two-dimensional simulation are used. The actual 3D model of flat sieve plate synthetic tower is simulated under different inlet gas velocities. The results show that the gas phase at large gas velocities in the converter can realize the uniform distribution of the whole gas earlier. The variation law of gas holdup distribution with tower height at different inlet gas velocities is also explored.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ441.41;TQ053.5

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