Valve Tray Research Articles

Combined trapezoid spray tray (CTST)—A novel tray with high separation efficiency and operation flexibility

The combined trapezoid spray tray (CTST) is a novel spray tray with unique trapezoid spatial structure. With gas-liquid co-current contact, the CTST has a lot of advantages, such as high capacity, efficiency and operation flexibility, low pressure drop, excellent anti-blockage performance, and foaming resistance. In the present work, the hydrodynamic and mass transfer performance of the CTST were investigated in a plexiglass column with air-water-carbon dioxide as an experimental system and were compared to a type of Glitsch V1 valve tray. Based on the result, the correlation equations of dry-plate and wet-plate pressure drop for the CTST were established. In terms of hydrodynamic and mass transfer performance, the CTST was superior than the Glistch V1 valve tray when the gas velocity is high. The industrial application case further validated the experiment result.

Hydrodynamic characteristics of valve tray: Computational fluid dynamic simulation and experimental studies

In order to better understand the hydrodynamics of valve trays, air-water operation in an industrial scale tower with 1.2 m of diameter, consisting of two 14% valve trays, was studied. Experimental results of clear liquid height, froth height, average liquid holdup, dry pressure drop, total pressure drop, weeping and entrainment were investigated, and empirical correlations were presented. Then, a three-dimensional computational fluid dynamics (CFD) simulation in an Eulerian framework for valve tray with ANSYS CFX software was done. The drag coefficient, which was used in the CFD simulations, was calculated from the data obtained in the experiments. The simulation results were found to be in good agreement with experimental data at this industrial scale. The objective of the work was to study the extent to which experimental and CFD simulations must be used together as a prediction and design tool for industrial trays.

Prediction of gas–liquid interfacial area in valve trays

An accurate prediction of gas–liquid interfacial area is very important for the design and optimization of column trays. However, the difference of the gas–liquid flow regimes operating at different scale trays significantly affect the interfacial area calculation. Therefore, in this study, an interfacial area model operating at small column was established using the Kolmogorov's isotropic turbulence hypothesis. According to the analyzes of the gas–liquid flow phenomena of different scale columns, an assumption that the similarity principle of flow characteristics of gas–liquid in full contact was proposed. Moreover, a new model that can be used to predict the gas–liquid interfacial area of a large column with exiting the nonideal flow was obtained through the extension of the small tray interfacial area model based on this principle. Finally, the new model was tested by comparisons with the experimental results of references. The prediction accuracy significantly improved with the maximum deviation of approximately 40%. © 2015 American Institute of Chemical Engineers AIChE J, 62: 905–915, 2016

Applied aspects for enhanced CO2 capture from reformer gas: Comparison between the performance of valve tray absorber and packed column, Part I

The CO2 capture from reformer gas is a technique to reduce greenhouse gas emissions. In this investigation, monoethanolamine (MEA) solution was employed as absorbent for the CO2 capture in valve tray column. The electrolyte NRTL and Redlich–Kwong equations were used to simulate the CO2-H2O-MEA system. The calculated results were validated by the data obtained from an industrial scale absorber. The effects of operational factors such as pressure, gas flow rate, MEA concentration, lean-MEA and inlet gas temperatures were evaluated on the performance of tray and packed columns. The optimum structured packing was determined and the appropriate conditions for achieving the maximum capacity were discussed in details. It was concluded that Mellapak Plus 452Y can provide the maximal capacity with an acceptable level of efficiency if operational pressure considered being lower than 2.5bar. When the structured column operates at pressure of 3.5bar, the Mellapak 350X is the appropriate choice to increase the absorption capacity. The reported results can be useful in industrial applications.

CFD gas–liquid simulation of oriented valve tray

Computational fluid dynamics (CFD) has recently emerged as an effective tool for the investigation of the hydraulic parameters and efficiency of tray towers. The computation domain was established for two types of oriented valves within a tray and meshed into two parts with different grid types and sizes. The volume fraction correlation concerning inter-phase momentum transfer source was fitted based on experimental data, and built in UDF for simulation. The flow pattern of oriented valve tray under different operating conditions was simulated under Eulerian–Eulerian framework with realizable k-ε model. The predicted liquid height from CFD simulation was in good agreement with the results of pressure drop and volume fraction correlations. Meanwhile, the velocity distribution and volume fraction of the two phases were demonstrated and analyzed, which are useful in design and analysis of the column trays.

Performance of Appended Wire Mesh Packing in Sieve Tray Distillation Column of Ethanol-Water System

For the separation process in liquid-liquid mixture such as ethanol-water mixture, a sieve tray distillation columnis an alternatif for affordable process and maintenance. However to date, this sieve tray system is still currentlyhaving a lower Murphee efficiency and smaller interfacial area, as compared to other tray system, that is, either abubble cap or valve tray. Therefore it is of important to optimize the performance of sieve tray distillation bymeans of adding the wire mesh packing on that tray, as being the aim of the present study. This study isconducted by using a batch sieve tray distillation system, where the wire mesh packing is added on the third traythat is calculated from the top of the column, to avoid flooding inside the column. Here the resulting fermentedmolasses of containing a 10% volume of ethanol is used as a mixture distillation feed. The height of the wiremesh packing being studied is varied as 5 cm, 3 cm, and 2 cm. Our results showed that the Murphee efficiencyobtained by the variation of the packing height of 5 cm, 3 cm, 2 cm and without packing were 73.5%, 66.27%,56.86%, and 46.7% respectively, and were increased by subsequent level of the packing height. Thecorresponding hydrodynamic properties of this appended packing sieve tray distillation by means of theinterfacial area were 11.88 cm2/cm3, 0.48 cm2/cm3, and 0.32 cm2/cm3, while its pressure drop measured from thewater manometer height were 38.33 cm H2O/m, 30 cm H2O/m, 10 cm H2O/m for the packing height of 5 cm, 3cm, 2 cm height, respectively. The increasing of the performance of appended packing sieve tray distillation bymeans of the Murphee efficiency is explained by the increasing of the interfacial area for vapour-liquid than thetray itself. This preliminary study is expected to be a pioneer study of strategy to increase the performance ofconventional sieve tray distillation that is known as a kind of affordable distillation process.

Experimental study of two phase flow characteristics on the dual-flow tray

This paper addresses an experimental investigation in the hydrodynamic behavior of a new type of dual-flow fixed valve tray. Water/air system was used at atmospheric pressure and ambient temperature. The dry pressure drop, total pressure drop and clear liquid height were measured and the comparisons between different tray geometry were made. The results show that the total pressure drop and clear liquid height have the same trend, which is increased with the decreased center distance of holes, increased holes diameter and decreased open area. Correlation for clear liquid height is proposed, and the agreement of the experimental and calculated data is demonstrated in the paper.The results show that gas and liquid flow counter-currently through the tray hole area and four main hydrodynamic regimes are distinguished at different gas/liquid load. A characteristic parameter named the fraction of holes passing gas is defined and deduced. The calculated results show that the fraction of holes passing gas is reduced by the decreased center distance of holes and holes diameter, while the increased open area leads to the less fraction.

Dynamic models for safety shutdown of distillation columns

Pressure relief valves are commonly used to protect distillation columns from overpressure in emergency situations like loss of cooling. An alternative safeguarding method, which may eliminate the need for relief altogether, is safety shutdown of the energy inputs to the column. Keeping the holdup enclosed in the pressure system is especially advantageous in hazardous, corrosive or reacting systems. Furthermore, the time required for restarting operations may be shorter if the holdup is not relieved to a flare.Shutting down the heat input leads to a rapid collapse of the pressure profile and fast draining of low boiling liquid from the internals to the hot column bottom. During the dynamic draining process, the mixture's vapor pressure continuously changes and may increase considerably. The maximum pressure rise during the shutdown process must be considered in the mechanical design pressure of all connected equipment.During shutdown, the flow regime leaves the stable hydraulic operating range. Experimental data from an industrial valve tray column is analyzed. A standard hydraulic model is unable to predict the pressure dynamics. A literature sieve tray weeping model is adapted to valve trays and fitted to plant data. Simulation results show good dynamic agreement with experimental data.

Effect of path length on valve tray columns: Experimental study

Experimental measurements of hydrodynamic and interfacial area parameters are carried out over two rectangular pilot scale valve tray columns. The effect of tray path length on extrapolation between the two columns is studied and phenomenological correlations for hydrodynamic and interfacial area are proposed. Correlations are compared both to literature and to industrial results showing good agreement and a significant improvement for the prediction of industrial conditions. Discrepancies preventing an accurate description of industrial trends are highlighted through comparison between typical emulsion height profiles on both columns.

A fundamental model for valve tray vapor cross‐flow channeling calculation

An accurate prediction of tray hydraulics is very important for large diameter trays design, and vapor cross‐flow channeling (VCFC) is one of the key points that affect the hydraulics calculation. Therefore, in this article, a theoretical analysis was first conducted to reveal that the energy of gas–liquid on the tray was closely related to its flow state. Then, a model was obtained on the basis of the principle of the lowest energy, which can be used to calculate VCFC. The model shows that the ratio of dry tray pressure drop to liquid height on a tray determines the gas distribution on the tray. Finally, the model was tested by comparisons with experimental results available in reference. The agreements are good. Furthermore, the effects of liquid load and fractional hole area on VCFC were studied. The results are consistent with the field experience summarized in literatures. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1032–1042, 2015

Predicting valve tray efficiency

Existing literature models for predicting the mass transfer efficiencies of binary hydrocarbon, distillation columns employing moving valve trays are evaluated. Only four models for predicting valve tray efficiencies exist in the open literature. All of these models use data from valve trays. The last theoretical model was published in 1972, 42 years ago. By comparison, sieve tray efficiency models are numerous and recent. Sieve tray models were developed from large databases. There are no valve tray equivalents to the fundamental mechanistic models available for sieve trays. Despite the differences between valve and sieve trays, many of the phenomena on sieve and valve trays are similar. Consequently, sieve tray models can be employed to provide estimates for valve trays. In this work, using public FRI data on round moving valves, the performance of the Chen and Chuang sieve tray mechanistic model is compared to the performance of four valve tray models. It appears that, in the absence of fundamental (and qualified) valve tray models, the sieve tray models present a potential alternative for valve tray efficiency predictions.

An experiment investigation of particle collection efficiency in a fixed valve tray washing column

The collection efficiency is one of the key parameters to evaluate the performance of washing columns, and the gas–liquid flow characteristic is an important factor affecting collection efficiency. In this work, the gas–liquid flow characteristic and its effect on collection efficiency in a fixed valve column have been investigated. The experimental results show that the fixed valve washing column is capable of generating higher gas holdup than a standard bubble column under similar situations. For different particle sizes, with increasing gas holdup, the changes of the trends in collection efficiency are different. For particles larger than 1μm, the collection efficiency increases with gas holdup while for particles finer than 1μm, the collection efficiency either decreases (0.5–1μm) or decreases initially and then increases again (0.3–0.5μm). The collection efficiency increases with liquid-to-gas ratio but decreases with bubble size, bubble velocity and particle loading. The contribution of each tray to the collection efficiency is different. A correlation is developed for predicting the collection efficiency of particles and the experimental values agree well with the predicted values.

Computational Fluid Dynamics Modeling of Hydrodynamics of a New Type of Fixed Valve Tray

A three-dimensional computational fluid dynamics (CFD) model was developed to predict the hydrodynamics of a new type of fixed valve tray. The model considered gas- and liquid-flow within the Eulerian framework in which both phases were treated as interpenetrating continuum having separate transport equations. Interphase momentum transfer term was employed for describing the interfacial forces between the two phases, and the related average gas hold-up was obtained via the regression equation from experiment data. Calculations were carried out using the commercial packages ANSYS CFX 12.0. Clear liquid height, gas hold-up, and gas and liquid velocity profiles were predicted for various combinations of weir height, gas, and liquid flow rates. The predicted clear liquid height was generally in good agreement with measurement. The information predicted by the CFD model can be used in the optimal design of industrial trays.

A Novel SiC Foam Valve Tray for Distillation Columns

The novel SiC foam valve tray was made of thin slices of SiC foam material with a high specific surface area. Hydrodynamic performances of the novel SiC foam valve tray were studied with air-water system at atmospheric pressure. These performance parameters included pressure drop, entrainment, weeping and clear liquid height. The mass transfer efficiency of the SiC foam valve tray was measured in laboratory plate column. Compared with the F1 float valve tray, the dry pressure drop was decreased about 25%, the entrainment rate was about 70% lower at high gas load, the weeping was much better, and the mass transfer efficiency was far higher. Thus, the overall performance of the novel SiC foam valve tray was better than that of F1 float valve tray.

CFD Simulation of Concap Tray Hydrodynamics

This research includes both experimental and CFD investigation in the hydrodynamic behavior of a new type of column tray introduced as “Concap” tray. The proposed column tray is used in contactor columns especially in stripping columns. The hydrodynamics of this Concap tray is investigated in a 1.2m in diameter column. Using air-water system, the experiments were performed for different liquid and vapor loads at constant ambient temperature and pressure. The clear liquid height and total pressure drop were measured. The results were compared with the experimental data of a valve tray in the same column simulator rig. The total pressure drop and clear liquid height of Concap tray were similar to a valve tray, having equal 14% open holes area. Liquid velocity distribution on the tray has been predicted by CFD and is reported.

Experimental hydrodynamic study of valve trays

Valve trays column design for gas treatment still relies on empirical correlations developed on pilot units. The available correlations lead to large discrepancies and thus more experimental works are needed. The present hydrodynamic study was carried out on a Plexiglas 1.26m per 0.1905m absorption column containing four V-4 Glitsch valve trays. Water/air system was used at atmospheric pressure and ambient temperature. Liquid rate per weir unit length was varied between 3.2×10−3m3.(m.s)−1 and 24.3×10−3m3.(m.s)−1 and the kinetic gas factor between 0 and 3.5Pa0.5.The following hydrodynamic parameters were determined: tray pressure drop, valves pressure drop, clear liquid height, mean emulsion height and liquid mean hold up on the tray. Correlations for clear liquid height, liquid mean hold up and emulsion height are proposed.Emulsion profiles characterisation was possible due to video records post-processing. Four different behaviours are identified for emulsion profiles according to liquid and gas velocities.Significant behaviour changes on the hydrodynamic parameters allowed the identification of three system limits: dumping, weeping and pre-flooding. Correlations are proposed for these limits and an operational diagram is presented.

A new dry tray pressure drop model of float valve trays

An accurate prediction of the dry pressure drop is very important for consideration of valve trays and for calculations in distillation field. Therefore, in this article, a series of hydraulic experiments were first conducted to reveal that the intermediate state during the valve opening process is closely related to the dry tray pressure drop under great valve weight. Then, a rigorous force analysis was made to show that Euler number is related only to the valve's position at the balance points for a certain valve type. Third, a new model for prediction of the dry tray pressure drop—which considers for the first time the influence of the intermediate state—was developed and then simplified for the purpose of convenient utilizations. Finally, the new model and its simplified form were tested by comparisons with the experimental results. The agreements are good, with the mean deviations being <5%. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2694–2705, 2013

The Particle Removing Characteristics in a Fixed Valve Tray Column

A method of predicting the particle collection efficiency of a fixed valve tray column and the particle size distribution properties, which considers diffusion, interception, and impaction, is pres...

Flow-guided sieve-valve tray (FGS-VT) – A novel tray with improved efficiency and hydrodynamics

Flow-guided sieve tray (FGST) has been widely used as column internal for mass and energy transfer between gas and liquid, or liquid and liquid, due to its low pressure drop, high efficiency, and high capacity. But as sieve tray, improving the operation flexibility is the urgent task which has to be resolved. Flow-guided sieve-valve tray (FGS-VT) was designed to overcome the shortcoming of FGST by putting some valves onto the FGST, which do not change the original structure before the valves are open. Comparison of the hydrodynamic and mass transfer performances of FGS-VT, FGST, and Glitsch V1 valve tray was done, using air–water–oxygen system in a 0.6m diameter plexiglass column, and the mathematical model of dry-plate pressure drop for FGS-VT was established. The results showed that the FGS-VT has higher operation flexibility and tray efficiency than FGST and Glitsch V1 valve tray.

Hydrodynamic characteristic of Conical Cap tray: Experimental studies on dry and total pressure drop, weeping and entrainment

This paper addresses an experimental investigation in the hydrodynamic behavior of a new type of cap trays called Conical Cap tray (ConCap tray). The hydrodynamics of the tray was investigated in a commercial scale air–water column with an internal diameter of 1.2m. The experimental liquid loads were 29.9, 44.4, 60 and 74.4(m3/h)/m of weir length and gas flow in terms of Fs in the range of 0.2–1.5m/s(kg/m3)0.5. The dry pressure drop, total pressure drop, weeping and entrainment for the ConCap tray and a valve tray were measured and compared. Correlations for pressure drop, weeping and entrainment of the ConCap tray were provided using regression analysis method. Standard deviations of correlations, R2, are quoted. The ConCap tray was compared with a bubble cap tray using correlations. The pressure drop of the ConCap tray was less than the bubble cap and close to the valve tray. The weeping rate of the ConCap tray was less than the valve tray. Its entrainment is more than the valve tray and less than the bubble cap tray. Good turndown ratio is important characteristic of the ConCap tray which is achieved without having too much pressure drop.