Sieve Tray Column Research Articles

CFD study on flow characteristics of sieve tray columns with circular downcomers

AbstractTo investigate the flow characteristics of sieve tray columns with circular downcomers, the Euler–Euler gas–liquid two‐phase flow model is used to simulate a three‐dimensional sieve tray column. Each phase is regarded as an interpenetrating continuum with independent transport equations. The velocity distribution, clear liquid height, and foam layer height are predicted by the model. The correlation is established for predicting the clear liquid height on the sieve tray. The results show the following: (1) The sensitivity of the clear liquid height to the gas phase load is greater than that of the liquid phase load. (2) When the gas–liquid distribution is stable, the flow on the round sieve tray column presents a piston flow pattern. (3) The average liquid holdup of the circular downcomer of the three heights all showed a slow decrease at first, and then an inflection point appeared near the height of 0.02 m, after which the liquid holdup dropped sharply. (4) The established correlation has good predictive performance for calculating the clear liquid height in the column, and the relative error between the calculated value and the actual value is less than 10%.

Modeling and Simulation of Carbon Dioxide Gas Reactive Desorption Process with Piperazine Promoted Diethanolamine Solvent in Sieve Tray Column

Carbon dioxide (CO2) is an acidic and corrosive gas, and the presence of this gas in the piping system can cause various problems in the industrial sector. Therefore, the CO2 must be separated from the gas stream. One of the CO2 gas separation processes from the gas stream is carried out in a CO2 removal unit, where a desorption unit serves as a solvent regeneration step. Therefore, this study aims to develop a rate-based model and simulation of the reactive desorption process of CO2 gas in a sieve tray column. The rate-based model in the reactive desorption process of CO2 gas is based on film theory, the liquid in the tray is assumed completely agitated due to gas bubbling, the flow pattern of gas is plug flow, and the effect of the reaction on the mass transfer follows the enhancement factor concept. The number of trays used in this study was 20. In addition, the effect of several variables, such as: desorber pressure, rich amine temperature, rich amine flow rate, and reboiler load, was also assessed on the CO2 stripping efficiency. The accuracy of our prediction model is 1.34% compared with industrial plant data. Compared with the chemical engineering simulator simulation results, the average deviation is 4%. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Experimental Study of the Influence of Different Load Changes in Inlet Gas and Solvent Flow Rate on CO2 Absorption in a Sieve Tray Column.

An experimental study was conducted in a sieve tray column. This study used a simulated flue gas consisting of 30% CO2 and 70%. A 10% mass fraction of methyl diethanolamine (MDEA) aqueous solution was used as a solvent. Three ramp-up tests were performed to investigate the effect of different load changes in inlet gas and solvent flow rate on CO2 absorption. The rate of change in gas flow rate was 0.1 Nm3/h/s, and the rate of change in MDEA aqueous solution was about 0.7 NL/h/s. It was found that different load changes in inlet gas and solvent flow rate significantly affect the CO2 volume fraction at the outlet during the transient state. The CO2 volume fraction reaches a peak value during the transient state. The effect of different load changes in inlet gas and solvent flow rate on the hydrodynamic properties of the sieve tray were also investigated. The authors studied the correlation between the performance of the absorber column for CO2 capture during the transient state and the hydrodynamic properties of the sieve tray. In addition, this paper presents an experimental investigation of the bubble-liquid interaction as a contributor to entropy generation on a sieve tray in the absorption column used for CO2 absorption during the transient state of different load changes.

Experimental evaluation of the performance of a cryogenic distillation system under offshore conditions

Cryogenic distillation is the most widely-used industrial method to produce liquid oxygen with high-purity. However, the distillation process in the sieve tray column is very sensitive to tilting and swing, which limits the application of cryogenic air-separation in marine and offshore infrastructures. In this paper, a small air-separation plant with dual-column distillation process was proposed to improve the distillation performance under the offshore conditions, and experiments were carried out under standard (no-tilting and stationary), tilting and swing conditions. A reduction factor of overall section efficiency is proposed to evaluate the influence of offshore conditions on the system performance. The results indicate that sieve tray column can maintain the distillation purity to a certain extent under offshore conditions within the range of 6° tilting and ±10° swing amplitude. Under severe tilting (6°) and swing (±10°-amplitude&11 s-period) conditions, the reduction factors were reduced to 0.592 and 0.590, respectively. Based on the experimental results, two correlations are presented to predict the reduction factor of section efficiency under different tilting angle and swing parameters, respectively, which provide engineering guidance for the design of cryogenic distillation column for offshore applications.

Experimental Study of the Influence of Gas Flow Rate on Hydrodynamic Characteristics of Sieve Trays and Their Effect on CO2 Absorption

An experimental study was conducted in the sieve tray column to investigate the influence of gas flow rate on the hydrodynamic characteristics of the sieve tray, such as total tray pressure drop, wet tray pressure drop, dry tray pressure drop, clear liquid height, liquid holdup, and froth height. The hydrodynamic characteristics of the sieve tray were investigated for the gas/water system at different gas flow rates from 12 to 24 Nm3/h and at different pressures of 0.22, 0.24, and 0.26 MPa. In this study, a simulated waste gas was used that consisted of 30% CO2 and 70% air. The inlet volumetric flow rate of the water was 0.148 m3/h. The temperature of the inlet water was 19.5 °C. The results showed that the gas flow rate has a significant effect on the hydrodynamic characteristics of the tray. The authors investigated the effect of changing these hydrodynamic characteristics on the performance of a tray column used for CO2 capture.

Investigation of Factors Affecting the Efficiency of Carbon Dioxide Removal in a Single Perforated Sieve Tray Column

An experimental work was carried out for the recovery of carbon dioxide in monoethanolamine solution (MEA) using pilot plant of perforated sieve tray column. The effect of MEA concentration, carbon dioxide ratio in the gas phase, liquid flow rate, gas flow rate and CO2 loading in the absorption solution was investigated. The results show that the efficiency of recovery increased by increasing the concentration of MEA and better removal efficiency can be achieved by increasing the liquid flow rate and the contact time between CO2 and the absorbent and that can be happened by decreasing the air flow rate.

Development of a digital twin for a flexible air separation unit using a pressure-driven simulation approach

Currently, digitalization provides new challenges and opportunities for the process industry. A frequently used keyword in this context is digital twin. In this work, the term digital twin is defined with regard to a flexible air separation unit. Furthermore, the digital twin’s core component, a highly detailed dynamic plant model, is presented. A pressure-driven approach is used as a basis for the modeling. The focus of this work is on the distillation columns. Therefore, a pressure-driven sieve tray column model is presented using design correlations for the calculation of pressure drop and both the liquid and vapor holdup. Furthermore, two industrially relevant load change scenarios are presented and discussed. A plant shutdown is simulated until a state of cold standby is reached. Then, starting from this state a cold restart is simulated. Cold standby means that the plant remains at cryogenic temperatures. Lastly, a hazard analysis is conducted.

Simulation for Absorption of Acid Gas into Piperazine Promoted Methyl Diethanolamine Solution Using Sieve Tray Column

The removal of CO2 and H2S gas is a crucial process in the sweetening of natural gas. One of the processes for taking these gases is reactive absorption using piperazine (PZ) promoted methyl diethanolamine (MDEA) solution. The absorption process is carried out in the sieve tray column to avoid liquids distribution problems in large diameter columns. No research discusses the acid gas absorption process simulation in the MDEA-PZ system using a sieve tray column. Therefore, this research simulates the acid gas absorption process in the MDEA-PZ system using a sieve tray column with a rate based modeling approach. The development of the rate-based model is based on the Film model’s theory. The effect of the reaction on the mass transfer coefficient is expressed by the enhancement factor. The diffusion interaction of the components in the mixture is expressed by the Stefan-Maxwell equation. The research’s main objective is to observe the effect of lean amine temperature and absorber pressure on the percentage removal of CO2 and H2S. The simulation prediction results showed the highest percentage of CO2 and H2S removal when the lean amine temperature was 60°C and the absorber pressure was 35 atm.

Study of packed sieve tray column in ethanol purification using distillation process

Sieve tray becomes a popular contacting device in distillation process because of its relative simplicity and low cost. There is one way to improve the contact performance, especially mass transfer by modifying the sieve tray into packed sieve tray. This study was aimed to investigate the effect of adding packing in each tray to ethanol content on ethanol purification. This research was conducted via experiment and simulation approaches. The experiment used packed sieve tray that contained 3 cm and 5 cm bed of steel wool with 16 trays in the column, with operating pressure about 760 mmHg and performed in batch condition. The simulation used a reduced rated base model with some modifications for operation in the packed sieve tray column. It was found that the use of packed sieve tray gave better distillate in the batch distillation process than the use of sieve tray. The packed sieve tray raised distillate content about 8.89% when using 3 cm of packing and 23.31% when using 5 cm of packing when it was compared with sieve tray. The use of packed sieve tray could increase the mass transfer and reduce bubble diameter in the batch distillation process.

Evolutional computational fluid dynamics analyses of reactive distillation columns for methyl acetate production process

The hydrodynamics of non-reactive and reactive distillation sieve tray columns are analyzed in this study. The first mentioned task was performed in order to verify the accuracy of Computational Fluid Dynamics (CFD) simulation in modeling the flow behavior of a sieve tray system. For the reactive distillation system, the studies were performed for the 25th reactive tray in the methyl acetate (MeAc) production process. Aspen Plus V9.0 simulation was carried out to determine the clear liquid height on the tray as a function of tray geometry and operating condition. The transient vapor-liquid hydrodynamics on the 25th reactive tray was simulated using CFD techniques involving the turbulence-chemistry interaction (TCI) effects. The predicted chemical products in liquid and vapor phases by Aspen Plus and CFD are of reasonable agreement. Furthermore, the CFD results can deliver more physics in determining localized distributions of the hydrodynamic parameters in the MeAc production process. Information obtained about the location and distribution of the vortex flow can be used to optimize the heat transfer and turbulence mixing.

The influence of liquid physical properties on entrainment inside a sieve tray column

Entrainment data were measured with Isopar G, n-butanol, silicone oil, water and ethylene glycol in a rectangular sieve tray column to cover relatively large ranges of liquid density (739–1095kg/m3), surface tension (19.9–60mN/m) and dynamic viscosity (0.9–48.8mPas). CO2 was used as the gas phase. Liquid flow rates ranged between 2.8 and 80m3/(hm), with gas flow factors (Fs) between 1.9 and 3.9m/s(kg/m3)0.5. The results showed a complex interaction of liquid physical properties influencing entrainment. An increased surface tension and higher liquid density resulted in fewer, but larger diameter, heavier droplets that decreased entrainment. Liquid viscosity and its combination with surface tension were shown to have a non-monotonic effect on entrainment. Liquids with relatively low viscosity and low surface tension formed higher dispersion layers with many small projected droplets, thus increasing entrainment. However, an increase in liquid viscosity beyond a critical point caused a decrease in entrainment. In general, notable deviations were observed between existing, published entrainment prediction correlations and the data generated in this study. This is most probably due to the fact that such correlations had been developed with limited liquid property variations, not covering the full spectrum of this study.

Design and development of bubble-cap tray column for continuous transesterification plant in coconut-oil-based biodiesel production

A study was carried out on production of biodiesel from coconut oil using alkali catalyzed transesterification process by two different reactive distillation columns, viz. sieve tray and bubble-cap tray column. Coconut oil with free fatty acid content of 1.2% was used for transesterification. In laboratory scale batch system, among all the variations adopted, it was found that maximum methyl esters yield of 97.7% was obtained with 6:1 molar ratio of methanol-to-oil, 1% NaOH at 60ºC reaction temperature. A continuous flow transesterification using sieve tray reactive distillation column yielded 93.75% methyl ester with 5.55 min average reaction time at 65ºC under 4:1 molar ratio (methanol-to-oil). The excess alcohol was found to be 11.4 ml. Based on performance evaluation of sieve tray reactive distillation column, a new bubble-cap tray reactive distillation column was designed and developed for continuous biodiesel production. Maximum methyl ester yield was 96.2% with 5.55 min average reaction time at 65ºC under 4:1 molar ratio. Excess alcohol was found to be 17.1 ml. Daily average electricity consumption was found to be 13.6 kWh for continuous transesterification biodiesel production and processing cost was worked out as ` 26.03. Regression analysis was employed to evaluate the effects of molar ratio and temperature on the yield of methyl esters. The R2 value was 0.87 for sieve tray reactive distillation column and 0.92 for bubble-cap reactive distillation column which confirmed the validity of the predicted model. Based on the findings from the study, it was found out that continuous transesterification was more feasible and efficient way for production of biodiesel. It was concluded that bubble-cap tray reactive distillation column was found to be an effective than sieve tray column due to its increased yield (1 time), excess alcohol recovery (1.5 times) and better fuel properties.

A new crossflow rotating bed, Part 3: Stage efficiency model

Concentric-baffle rotating bed (CRB) is a novel HIGEE device, whose performance has been experimentally studied in distillation process. The CRB structure optimization has also been obtained from comparison among the several CRB variants. The CRB is a stagewise contactor, and thus, its mass transfer performance can be expressed by the overall efficiency, which can be easily used to convert theoretical stages to real stages. Therefore, the prediction of the overall efficiency is an important step in CRB design. In our study, it is found that the CRB exhibits a highly similar flow and contact pattern to the sieve tray column. Then, on this basis, a semi-theoretical model predicting the overall efficiency of the CRB is developed, which involve calculations of mass transfer coefficients, effective interfacial area, number of mass transfer units, Murphree point efficiency, and Murphree stage efficiency. The proposed model was validated by comparison of predicted efficiencies with the experimental data obtained in the optimized CRB. It shows that the proposed model can provide a good prediction in the industrially relevant operating area around the highest efficiency point, i.e. with the F-factor lower than 4.0. Further comparison shows that the proposed model can give a much better prediction than several models available in the literature, which are widely used for the tray column. The proposed model is more fundamental and only involves one adjustable empirical parameter for the average diameter of liquid droplets, but it is still a great preliminary model for the CRB and other contactors with similar gas and liquid flow regimes. The validity of the proposed model requires further testing by more data from different sources.

Rate-based modelling and simulation of distillation columns with sandwich packings

Sandwich packings are innovative column internals consisting of two layers of ordinary packing with different geometrical surface area. The layer with the high surface area, hold-up layer, has a lower flooding point as compared to another, de-entrainment layer. Sandwich packings can be operated even when the hold-up layer is flooded. In operation, different fluid dynamic regimes occur along the column. The flow in the flooded hold-up layer is comparable with that in trays. A froth regime is established above the hold-up layer, whereas a film flow develops in the remaining part of the de-entrainment layer. The proper design of sandwich packings requires a mass transfer model capable of considering all these different regimes. In this work, the rate-based concept is used to develop a mass transfer model of sandwich packings. This model employs two alternate column segments. One of them corresponds to de-entrainment layer, and here, mass transfer correlations for packed columns are applied. Another segment is related to the hold-up layer; it is described with correlations for sieve tray columns. The developed mass transfer model is validated with experimental efficiency data for sandwich packings.

The influence of gas physical properties on entrainment inside a sieve tray column

Existing entrainment prediction correlations, often used in the design of sieve tray distillation columns, have been developed mostly with air/water data. Therefore, the aim of this work was to investigate the influence of gas physical properties on entrainment, by also utilising gases with physical properties notably different from air. Air, CO2 and SF6 were passed through a rectangular sieve tray column (tray hole diameter of 6.3mm and fractional hole area of 0.156). These three gases were chosen in order to cover a large gas density range of 1.2–5.8kg/m3. Water, ethylene glycol and n-butanol were used as liquids in order to achieve the desired wide range of liquid physical properties. Tray spacing and weir height were set at 615mm and 51mm, while the liquid rate was varied from 2.9 to 80m3/(hm) to cover both the spray and froth regimes. Gas flow factors ranged between 1.9 and 4.8m/s(kg/m3)0.5. A database of over 500 experimental data points was generated in this study. The main objective was to use the experimental data to describe the effect of gas physical properties and gas-and-liquid flow rates on entrainment. The data were also used to evaluate the scope and limitations of current entrainment prediction models. Existing correlations fitted the air/water data well, but showed rather large deviation from the non-air/water data. A new approach to describe the influence of gas physical properties on entrainment is proposed. This approach utilises a variation of the Reynolds and Froude numbers along with the ratio of the gas to liquid density to correlate entrainment.

Separation of Bovine Serum Albumin by Foam Fractionation with Sieve Tray Column

A batch foam fractionation column with sieve trays was developed for enhancing the foam drainage. Effects of feeding concentration, air flow rate, number of stages, and sieve pore size on foam fractionation performances were investigated. The results indicated that the sieve trays enhanced the foam drainage effectively and improved enrichment ratio. At the liquid loading volume 490 mL, feeding concentration 0.1 g L−1, and air flow rate 300 mL min−1, the enrichment ratio reached 7.56 by using 10 stages of sieve trays with opening ratio of 38.25%, which was 1.84 times of that obtained by the control column.

CFD and experimental studies of liquid weeping in the circular sieve tray columns

Sieve trays are widely used in fractionating devices like tray distillation towers existing in separation and purification industries. The weeping phenomenon that has a critical effect on the efficiency of tray towers was studied by a numerical model and some experiments. The experiments were carried out in a pilot scale column with the diameter of 1.22m that includes two test trays and two chimney trays. Weeping rates and some hydraulic parameters were measured in sieve trays with the hole area of 7.04%. Furthermore, the total weeping rate and weeping rate in inlet and outlet halves of the test tray were determined. It was also used an Eulerian–Eulerian computational fluid dynamics (CFD) method for the present study. The model was able to predict the dry tray pressure drop, total pressure drop, clear liquid height, froth height, and weeping rate simultaneously. Furthermore, the obtained CFD results were in a good agreement with the experimental data in terms of pressure drop and the model properly predicted several hydraulic parameters like the liquid weeping behavior along the tray.

Comparison between the design of experiments and simulation in the three-phase distillation in a sieve tray column for glycerine dehydration

Design of experiments (DOE) is a value scientific approach used to understand the processes in a better way and to determine how the inputs affect the response(s). In this work, this method has been applied to study the behavior of the three-phase distillation in a sieve tray column, through the effects of the process and geometrical variables. The experimental values were compared with predicted values obtained by simulation using the equilibrium and nonequilibrium models. Three-phase distillation has been used for glycerine dehydration using toluene as entrainer, in order to avoid the glycerol degradation by distillation at atmospheric pressure. The best conditions found were: vapor flow rate of toluene=23.5kg/h, feed flow rate=2.2kg/h and feed concentration=50wt% glycerol, using the layout L4 with fractional hole area=0.04 and weir height=70mm. The nonequilibrium model based on Eckert and Vanek's approach (2001) and Chen–Chuang's correlation (1993) have been used to estimate the binary coefficients of mass transport. The predicted values obtained by the experimental model and by the nonequilibrium model have represented the behavior of the dehydration in the sieve tray column studied. Both models underpinned the experimental results obtained for this column.

Dynamic analysis and control of sieve tray gas absorption column using MATALB and SIMULINK

The present work highlights the powerful combination of SIMULINK/MATLAB software as an effective flowsheeting tool which was used to simulate steady state, open and closed loop dynamics of a sieve tray gas absorption column. A complete mathematical model, which consists of a system of differential and algebraic equations was developed. The S-Functions were used to build user defined blocks for steady state and dynamic column models which were programmed using MATLAB and SIMULINK flowsheeting environment. As a case study, the dynamic behaviour and control of a sieve tray column to absorb ethanol from CO2 stream in a fermentation process were analysed. The linear difference equation relating the actual and equilibrium gas phase compositions was solved analytically to relate the actual gas phase composition to the liquid phase with Murphree tray efficiency as a parameter. The steady state mathematical model was found to be nonlinear (w.r.t. number of stages) due to the introduction of the Murphree tray efficiency. To avoid the solution of large linear algebraic system, a sequential steady state solution algorithm was developed and tested through the idea of tearing the recycle stream in the closed loop configuration. The number of iterations needed to achieve a given tolerance was found to be function of the Murphree tray efficiency. The open-loop dynamic analysis showed that the gas phase composition response was nonlinear with respect to the inlet gas flow rate, while it was linear with respect to inlet gas composition. The nonlinearity increased along the column height and was maximum at the top tray. On the other hand, the Murphree tray efficiency had little effect on the dynamic behaviour of the column. The controlled variable was found to exhibit fairly large overshoots due to step change in the inlet gas flow rate, while the PID controller performance was satisfactory for step change in the inlet gas composition. The closed-loop dynamic analysis showed that the controlled variable (outlet gas phase composition) had a fairly linear dynamics due to step changes in the set point.

Synthesis and Control Analysis of Gas Absorption Column using MATALB and SIMULINK

The present work highlights the powerful combination of SIMULINK/MATLAB software as an effective flowsheeting tool which was used to simulate steady state and closed loop dyanmics of a sieve tray gas absorption column. A complete mathematical model, which consists of a system of differential and algebraic equations was developed. As a case study, the dynamic behaviour and control of a sieve tray column to absorb ethanol from CO 2 stream in a fermentation process were analyzed. The nonlinearity increased along the column height and was maximum at the top tray. The controlled variable was found to exhibit fairly large overshoots due to step change in the inlet gas flow rate, while the PID controller performance was satisfactory for step change in the inlet gas composition. The closed-loop dynamic analysis showed that the controlled variable (outlet gas phase composition) had a fairly linear dynamics due to step changes in the set point.