CFD Simulation of Mass Transfer Efficiency and Pressure Drop in a Structured Packed Distillation Column

The pressure drop and mass transfer efficiency for two‐phase flow in a structured packed column were simulated using a commercial CFD package, CFX version 10. The distillation of the methanol/isopropanol system was carried out in a 0.073 m diameter column, with an element composed of a ceramic structured packing and 0.053 m in height. The Height Equivalent to Theoretical Plate (HETP) value varied from 0.106–0.146 m. Pressure drop experiments were measured with an air/water system. The pressure drops at the flooding and loading points were ca. 173 and 580 Pa/m of packing, respectively. HETPs and pressure drops calculated from the Computational Fluid Dynamics (CFD) model were compared to their experimental counterparts. The average relative error between CFD predictions and the experimental data for the prediction of dry pressure drop, irrigated pressure drop and mass transfer efficiency are 20.3 %, 23 % and 9.15 %, respectively. In all cases, the CFD predictions show a good agreement with the experimental data, indicating that CFD is a reliable, cost saving and suitable technique for the design and optimization of separation processes.     

Efficiencies of Sieve Tray Distillation Columns by CFD Simulation

A 3‐D two‐fluid CFD model in the Eulerian‐Eulerian framework was developed to predict the hydrodynamics and heat and mass transfer of sieve trays. Interaction between the two phases occurs via interphase momentum and heat and mass transfer. The tray geometries are based on the large rectangular tray of Dribika and Biddulph and FRI commercial‐scale sieve tray of Yanagi and Sakata. In this work a CFD simulation is developed to give predictions of the fluid flow patterns, hydraulics, and mass transfer efficiency of distillation sieve trays including a downcomer. The main objective has been to find the extent to which CFD can be used as a design and prediction tool for real behavior, concentration and temperature distributions, and efficiencies of industrial trays. Despite the use of simple correlations for closure models, the efficiencies obtained are very close to experimental data. The results show that values of point efficiency vary with position on the tray because of variation of affecting parameters, such as velocities, temperature and concentration gradients, and interfacial area. The simulation results show that CFD can be used as a powerful tool in tray design and analysis, and can be considered as a new approach for efficiency calculations and as a new tool for testing mixing models in both phases. CFD can be used as a “virtual experiment” to simulate tray behavior under operating conditions.     

Dynamic Study of Distillation Column Operated with Tray Heat Source Combined with Reboiler

This work reports experimental tests using the distribution of energy in distillation by applying internal heat sources combined with a reboiler in order to reduce the transition time when the process is disturbed. In this way, a dynamic study was undertaken in a pilot column with ethanol and water, comparing the effects of a step disturbance in the reboiler and the same heat quantity in the intermediate tray of the column. The results showed that the use of the combined heat supply reduced the hydraulic delay in the distillation column and, consequently, the transition time. In this way, this study suggests that it is possible to use the heat distribution to control a distillation column using classical strategies and simple controllers, such as proportional-integral-derivatives (PID), and with this obtain faster responses.     

Hydrodynamics in a RDC Extractor: Single and Two‐Phase PIV Measurements and CFD Simulations

The single and two‐phase flow field of a rotating disc contactor (RDC) extraction column is simulated with the help of computational fluid dynamics (CFD). The simulations were validated by particle image velocimetry (PIV) measurements. The single phase setup was used to test different turbulence models, and a 2D and 3D grid approach. For the two‐phase simulations, a 2D computational grid and the Euler‐Euler model was used. The two‐phase PIV measurements are possible when using an iso‐optical system, where the refractive indices of both liquid phases are identical.     

Experimental Reaction Equilibrium and Kinetics of the Liquid‐phase Butyl Acrylate Synthesis Applied to Reactive Distillation Simulations

Butyl acrylate, which can be produced in liquid phase from butanol and acrylic acid, is an important precursor for varnishes and adhesives. The reaction equilibrium and the kinetics of the butyl acrylate synthesis catalyzed by acid ion exchange resins were measured and the results are used to derive formulas for the equilibrium and the kinetics which is supposedly based on a Langmuir‐Hinshelwood‐Hougen‐Watson mechanism. Because of the highly nonideal reaction mixture, both the equilibrium and the kinetics are expressed in terms of activities. The equations are used in the modeling and simulation of a butyl acrylate production plant which consists of a catalytic tube reactor and a reactive distillation column. A column that is operated in the common manner, i.e. by heating only the reboiler, leads to a reactive azeotrope over a large part of the column. However, distributing the heat flow over the whole column improves the separation and the conversion significantly.     

Comparison of Hydrodynamics and Mass Transfer in Airlift and Bubble Column Reactors Using CFD

Computational Fluid Dynamics (CFD) is used to compare the hydrodynamics and mass transfer of an internal airlift reactor with that of a bubble column reactor, operating with an air/water system in the homogeneous bubble flow regime. The liquid circulation velocities are significantly higher in the airlift configuration than in bubble columns, leading to significantly lower gas holdups. Within the riser of the airlift, the gas and liquid phases are virtually in plug flow, whereas in bubble columns the gas and liquid phases follow parabolic velocity distributions. When compared at the same superficial gas velocity, the volumetric mass transfer coefficient, k_La, for an airlift is significantly lower than that for a bubble column. However, when the results are compared at the same values of gas holdup, the values of k_La are practically identical.     

Effect of Structured Packing Characteristics on Styrene Monomer/Ethylbenzene Distillation Process

The application of various types of structured packings to separate styrene monomer/ethyl benzene in packed columns is presented. The investigation was conducted over a wide range of operating conditions such as packing type, pressure, and reflux ratio. Several structured packings were used for separation of styrene monomer/ethyl benzene and the optimum conditions were determined for each of them. The proper condition of separation process and appropriate parameters for achieving better efficiency was discussed. The calculated results were compared with those obtained in industrial scale. It was shown that Mellapak‐Plus 252Y and 452Y packings can provide the maximum capacity with an acceptable level of efficiency over a wide range of operating conditions.     

利用计算流体力学及计算传质的方法研究精馏塔传质效率

It has long been found that the flow pattern of the liquid phase on distillation tray is of great importance on distillation process performance. But until now, there was very few published work on quantitative investigation of this subject. By combining the computational fluid dynamics (CFD) with the mass transfer equation, a theoretical model is proposed for predicting the details of velocity and concentration distributions as well as the tray efficiency of distillation tray column. Using the proposed model, four different cases corresponding to different assumptions of liquid and vapor flowing condition for a distillation tray column were investigated. In Case I, the distributions of velocity and concentration of the incoming liquid from the downcomer and the uprising vapor from the underneath tray spacing are uniform. In Case Ⅱ, the distribution of the incoming liquid is non-uniform but the uprising vapor is uniform. In Case Ⅲ, the distribution of the incoming liquid is uniform but the uprising vapor is non-uniform.In Case IV, the distributions of both the incoming liquid and the uprising vapor are non-uniform. The details of velocity and concentration distributions on a multiple sieve tray distillation column in four different cases were simulated using the proposed model. It is found that the shape of the simulated concentration profiles of vapor and the liquid is quite different from case to case. The computed results also show that the tray efficiency is highly reduced by the maldistribution of velocity and concentration of the incoming liquid and uprising vapor. The tray efficiency for Case Ⅰ is higher than Case Ⅱ or Case Ⅲ, and that for Case Ⅳis the lowest. It also reveals that the accumulated effect of maldistribution becomes more pronounced when the number of column trays increased. The present study demonstrates that the use of computational method to predict the mass transfer efficiency for the tray column, especially for the large one, is feasible.     

用组合导向浮阀塔改造甲醇回收塔

对原有Φ14 0 0甲醇回收泡罩塔进行改造 ,利用计算机进行塔的模拟与优化 ,采用新型高效组合导向浮阀塔替代了原有塔型 ,取得了理想的效果     

Predictions for Start‐Up Processes of Reactive Distillation Column via Artificial Neural Network

The time consumed in starting up the unit with appropriate holdups can form an important part of the total distillation time, particularly for reactive distillation systems with large holdups. Also, the products formed during the start‐up time are off specification, and are not easily recycled as for traditional distillation, but must be carefully disposed of, which can be very costly. A back‐propagation algorithm artificial neural network model is presented as a tool to assess the start‐up process for a given reactive distillation system. All the data required for training and testing the artificial neural network have been generated using the CHEMCAD simulator, version 5.2–0. The values for the learning rate, momentum term, and gain term of the artificial neural network have been taken as 0.01, 0.6, and 1.0, respectively. From the case studied in this work, it can be seen that a good start‐up policy can reduce both the energy and time requirements in the start‐up phase of reactive distillation processes. Results from predictions show the time consumed in the start‐up period has an average error of 2.833 %, and a maximum error of 7.600 %, for the case studied here. The accuracy of the model will depend upon the data available and the type of model being approximated.     

Implementation and Operation of a Dividing‐Wall Distillation Column

The design and construction of a prototype of a dividing‐wall distillation column was possible by integrating previous knowledge in process intensification, energy savings, theoretical control properties, and closed‐loop dynamics of thermally coupled distillation sequences. In order to achieve the predicted energy savings for this class of complex distillation column, a dividing wall and a side tank were implemented in order to manipulate the internal flows associated with energy consumption. The reaction between ethanol and acetic acid was conducted within the prototype, and the experimental results indicate that a heterogeneous mixture of ethyl acetate and water is obtained as the top product. The temperature profile measured during the experimental run can be used for controlling the batch distillation column in cyclic operation mode.     

催化精馏塔内催化剂床层润湿率研究

在９０ｍ ｍ 的有机玻璃塔内,用空气－水系统,通过稳态降阶示踪法对催化精馏塔内催化剂床层的润湿特性进行研究。得到润湿率随操作参数的变化曲线,并关联了润湿率随液体流速和气体流速变化的经验关联式, 为催化剂床层润湿率的预测提供依据。     

新型规整填料及塔内件在润滑油减压塔中的应用

列举了常减压蒸馏装置润滑油型减压塔的实际操作、标定及原始设计等方面的详实数据,并通过工业时间进行了较为系统、科学地对比分析和深层次研究。同时,重点介绍了新型规整填料及塔内件在大型润滑油减压塔中的实际应用。     

高效导向筛板及填料在乙酸乙烯-乙酸甲酯精馏技改中的研究与应用

采用高效导向筛板与填料对乙酸乙烯-乙酸甲酯精馏塔进行了技改设计,技改后扩大生产能力40%,大幅度提高了分离效率,节能30%,降低原料消耗1380t/a。技改的设备投资为6万元,年增经济效益772万元。     

Identification and Control of an Industrial Binary Distillation Column: A Case Study

The challenging problem of identification and control of an industrial binary distillation column is addressed in this paper. Process identification represents an alternative to modeling and is shown to be the appropriate procedure for predictive control design. The predictive controllers based on the identified model ensure stability and high performance for a wide operating range of the industrial distillation column.     

Multiple Analysis in a Reactive Distillation Column for the Synthesis of tert‐Amyl Methyl Ether

tert‐Amyl methyl ether (TAME) is produced via reactive distillation. A simulation is set up and controlled on Aspen HYSYS v 8.0 for generating the highest purity of TAME. This simulation includes a plug‐flow reactor and a reactive distillation column. Emphasis was put on finding the optimal operating conditions of the reactive distillation column in order to get the maximum purity of TAME. The operational parameters were reflux ratio, number of reactive stages in the distillation column, and condenser pressure. The results indicated the optimal reflux ratio and condenser pressure which could be adapted to industrial scale.     

Hydrodynamics and scale-up of liquid-solid circulating fluidized beds: Similitude method vs. CFD

Hydrodynamics and scale-up of liquid-solid circulating fluidized beds (LSCFBs) are investigated using similitude method and computational fluid dynamics (CFD) technique. Similitude method is applied to establish the dynamic similarity among LSCFBs by tuning physical properties of liquids and solids, operating conditions and bed dimensions to match several scaling sets of dimensionless groups. The hydrodynamic behaviors in these constructed LSCFBs are simulated by a validated CFD model [Cheng, Y., Zhu, J., 2005. CFD modeling and simulation of hydrodynamics in liquid-solid circulating fluidized beds. Canadian Journal of Chemical Engineering 83, 177-185] and compared in terms of the axial and radial flow structures characterized by the solids fraction, particle and liquid velocities and solids mass flux. The results demonstrate that only the full set scaling parameters obtained from similitude method, i.e., five dimensionless groups together with fixed bed geometry, particle sphericity, particle size distribution as well as particle collision properties, can ensure the similarity of hydrodynamics in the fully developed region of different LSCFBs. Developing flow structures in LSCFBs are strongly influenced by some parameters such as turbulent kinetic energy at the inlet so that the proposed similitude method may not always be applicable.     

Development of a CFD Model of Bubble Column Bioreactors: Part Two – Comparison of Experimental Data and CFD Predictions

The application of computational fluid dynamics (CFD) as a tool to simulate bubble column bioreactors is investigated. A three‐dimensional model utilizing the Euler‐Euler approach is evaluated. The role of various terms, i.e., lift, drag, bubble‐induced turbulence, and volume fraction correction terms for drag, is determined. Good agreement between experimental data and simulation results was obtained by means of a single‐bubble size model provided that bubble‐induced turbulence and the reduction in drag due to the presence of other bubbles were taken into account.