Tray Column Research Articles

Conceptual Design and Practical Challenges of Gas-Phase Catalytic Reactive Distillation/Absorption

Reactive distillation/absorption is among multifunctional reactors for process intensification. Conventionally, reactive distillation/absorption is suitable for liquid-phase catalytic reaction, with rare reports for gas-phase catalytic reaction. By reviewing the conventional reactive distillation/absorption concepts, we re-classify RD/A based on the criterion of phase state; and by analyzing the recent advances of column trays and catalyst development etc., we put forward novel conceptual design to conveniently achieve gas-phase catalytic reaction in reactive distillation/absorption process, which is termed as Gas-phase Catalytic Reactive Distillation/Absorption (GC-RD/A). The feasibility of this concept in theory and practice are analyzed from the perspective of catalyst, reactive internals and phase states. Practical challenges are presented comprehensively including equipment design, flow patterns, transport phenomena, reaction selection and operation window, and catalyst design, from fundamentals to industrial implementation.

Efficient fault detection and diagnosis of distillation column using gamma scanning

This paper presents an efficient approach for automated fault detection and diagnosis of the distillation column by analyzing the gamma intensity variations. Gamma-ray scanning is one of the most common techniques that is used in industrial radioisotopes applications. It is used to get signals that reflect the inner details of a distillation column. These signals are gamma intensity variation that comes from material density variation in the column. In the proposed approach, the signals of each distillation column are divided into frames. Each frame contains the signal of just one column tray. Therefore, the position of the defected tray can be determined exactly in the column. Discrete wavelet transform, power density spectrum, higher order statistics (HOS), area under the curve (AUC) and correlation between signals are features that are extracted to be used in artificial neural network. The proposed results prove that the selection of HOS with correlation and AUC effectively achieves the fault detection and diagnosis approach in different high noise environments.

Hydrodynamics performance and tray efficiency analysis of the novel vertical spray packing tray

Abstract Column setup has been widely utilized in the petroleum and chemistry industries. However, with the fast progress of industries and the increasingly serious energy shortage, designing a new column setup with better performance and higher capacity becomes more urgent. In order to improve column's capacity and expand operating condition, a new type of column tray named novel vertical spray packing (NVSP) tray was designed and experimented. The performances of the novel tray, including pressure drop, weeping, entrainment and tray efficiency, were tested in a plexiglass column. In addition, performances of the novel tray were compared with that of the sieve tray and the Glitsch V1 valve tray. Based on the experiment data, the mathematical correlations of pressure drop, weeping and entrainment for the novel tray were established by regression analysis method. A fundamental model of dry pressure drop of the novel tray was promoted at the form of sum mode. The results indicate that the novel tray has wider operating condition and better performance.

Hydrodynamic modeling of ionic liquids and conventional amine solvents in bubble column

The green solvent ionic liquids (ILs) are getting attention in variety of industries, because of their unique properties. Few studies explain the hydrodynamics of ILs, but the comparison with conventional amine solvents in CO2 capture process has not so far been reported. The primary target of this research is to develop a state of the art computational fluid dynamics (CFD) model that would be useful to understate hydrodynamic parameters of both ILs and conventional amine solvents in a glance. In present study, three ILs are investigated inside a 3D flat bubble column and their higher viscosities are examined vigilantly by comparison with three amine solvents. The flow pattern, liquid velocity magnitude, CO2 holdup and bubble size distribution are explained. It is reported that current CFD model may be used for higher viscous ILs and amine solvents. Compared with amine solvents, CO2 plume meandering behavior was not observed and very low gas holdup was obtain in ILs. The velocity magnitude of ILs increased with the height in bubble column, but a decreasing trend with column height was followed in the case of amine solvents. CO2 exhibited non-coalescence behavior in ILs, but coalescence and breakup phenomena were seen in amine solvents. Finally, baffled type industrial tray column is also investigated and some useful hydrodynamic aspects in the comparison of pure ionic liquid, 90%-solution of ionic liquid and 30%-solution of MEA are drawn. The experimentally validated CFD model would be useful for switching to ILs from corrosive amine solvents and further investigation of new economical ILs.

Optimization of pre-concentration, entrainer recycle and pressure selection for the extractive distillation of acetonitrile-water with ethylene glycol

We optimize the extractive distillation process for separating the acetonitrile – water azeotropic mixture with ethylene glycol by using a multi-objective genetic algorithm for minimizing under purity constraints the total cost, the energy consumption and the separation efficiency. For the first time we have shown the interest of five aspects by considering them simultaneously (1) the pre-concentration column has been included and (2) there is no need to set a distillate composition constraint (like being at the azeotropic composition) in the pre-concentration column. (3) The operating pressure should be lower than 1 atm because it enhances the relative volatility for 1.0-1a class system. (4) A closed loop optimization must be run, to handle the effect of impurity in the entrainer recycle since too much impurity limits the main product recovery and purity from the extractive column. (5) All three columns process must be optimized together rather than sequentially and with multiple objectives. The studied system belongs to class 1.0-1a and the impurity of the recycled entrainer has strong effect on the purity of acetonitrile product. Overall, 17 variables are optimized; column trays, all feed locations, refluxes, entrainer flow rate and all distillate products; under purity constraints for the acetonitrile and water product and for the entrainer recycle impurity. Among nearly 400 designs satisfying the purity specifications, the design case 3 shows an energy consumption and TAC reduced by more than 20% than a literature reference case, thanks to smaller entrainer flow rate, a reduction of 32 trays and lower operating pressures. The best design is a trade-off between first a feasibility governed by thermodynamics through composition profiles and relative volatility maps and second process cost and energy demands.

Hydrodynamics and flow mechanism of foam column Trays: Contact angle effect

Wettability has significant influence on fluid flow inside foam ceramics. Foam SiC valves with various wettability were prepared by a facial bottom-up strategy. Subsequently, pressure drop, weeping and gas distribution were studied. Results indicate that pressure drop decreases remarkably with increasing contact angle (CA), 43% at most; weeping rate presents a peak at CA<90°but monotonous decrease at CA>90°; gas distribution becomes more uniform with increasing CA at small F-factor but presents obvious boundary effect at large F-factor. To illustrate the CA effect, we propose a new strategy for pressure drop decomposition, introducing the fourth part called CA-induced pressure drop by modifying classical three-component strategy, which also catalyzes a new pressure drop measuring strategy. In the meanwhile, the mathematical model to predict pressure drop is proposed and shows good agreement with experiments. Moreover, process model to illustrate the mechanism is proposed based on interfacial phenomena, force analysis and flow patterns.

Intensification of the ethylbenzene production process using a column configured with a side reactor

An innovative heat-integrated column configured with a side-reactor was developed for ethylbenzene (EB) production. To achieve an economical design, the total annual cost, as an objective function, was minimized by optimizing the reactor volume, the number of side reactors, the number of column trays, the reactor side-return tray, and the column pressure. The proposed side-reactor column (SRC) configuration reduces capital, energy, and total annual costs by 13.6, 12.9, and 13.2%, respectively, compared to a conventional process for the same desired yield and purity. In addition, the multiple effect heat integration was examined on the proposed configuration for energy efficiency. The resulting heat-integrated side reactor (HI-SRC) configuration further reduces capital, energy, and total annual costs by 14.8, 53.0, and 38.3%, respectively.

CFD simulation and experimental validation of bubble cap tray hydrodynamics

Abstract In this study, numerical simulations of gas-liquid flow behavior of bubble cap tray have been done. The aim of this work is to develop a Computational Fluid Dynamic (CFD) model enable of predicting the hydrodynamic parameters of any desired system. A transient three-dimensional model in Eulerian framework with standard k-e turbulence model has been developed, ignoring mass and energy transfer equations. For this purpose a new correlation of liquid hold-up with 7.89% average error has been developed using Genetic Algorithm based on the experimental clear liquid height data. By substitution of this correlation in drag force relation, the source term has been added to the momentum equations. Simulations have been carried out over a wide range of liquid and vapor flow rates and the predicted results have been found to be in reasonable agreement with the experimental data. Velocity and pressure distributions, clear liquid height, froth height, and liquid holdup fraction in the froth region have been predicted, which are beneficial in analysis and design of the column trays.

Estimation of the efficiency of packed mass-transfer devices

The problems of assessing the effectiveness of packed mass-transfer devices in relation to distillation processes have been considered. The authors have shown that the existing dependences of determining the height equivalent to a theoretical plate cannot be used to calculate tray columns and columns with vortex packings, the contact surfaces of the phases and coefficients of mass transfer of which depend substantially on the water concentration (reflux ratio) and gas rate (vapor for distillation).

Investigation of new control strategies for acid gas absorber columns to improve the response rates using dynamic process simulation

Increasing penetration of intermittent renewable sources of electrical energy such as wind or solar into the energy mix places an increasing demand on the flexibility of other power plant, in particular fossil fuel-based units.The suppliers of natural gas combined cycle equipment have been particularly successful in designing plants with increased ramp rates. In a recent review (Todd et al., 2014) EPRI has analysed the potential for using such equipment to improve the ramp rates of IGCC power plant. The review concluded that this was certainly possible, and identified the limiting equipment to be the acid gas removal system. Experience with such units in chemical applications has shown that at faster ramping rates than about 3%/min, the design sulfur specification cannot be maintained and a short-term sulfur breakthrough occurs. In that review it was postulated that this could be attributed to reduced solvent flow in the lower part of the column, while the hold-up required for higher load operation was being built up.Follow up work has been performed at the Technical University of Darmstadt to verify this hypothesis and propose mitigation measures. A typical tray column using a physical solvent was modeled, initially in ASPEN Plus and then in ASPEN Plus Dynamics. The dynamic model was calibrated against typical performance of industrial plant. The initial hypothesis could be verified and further refined. A number of proposals for mitigation measures were investigated and evaluated. The understanding gained by this work will be applicable also to packed columns and chemical solvents, though in the latter case the model will need to be extended to include kinetic effects.This paper describes the simulation work and a control strategy to improve the ramp rate of an acid gas removal system.

A NOVEL RP-HPLC METHOD FOR THE DETECTION AND QUANTIFICATION OF CLARITHROMYCIN OR SPIRAMYCIN IN BULK DRUG SAMPLES AND DOSAGE FORMS

&lt;p&gt;&lt;strong&gt;Objective: &lt;/strong&gt;This study was aimed at developing an HPLC method that would be suitable and sufficiently robust to analyze clarithromycin or spiramycin from bulk materials, amorphous solid dispersions as well as when included into solid dosage forms.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Methods: &lt;/strong&gt;A C&lt;sub&gt;8&lt;/sub&gt; column (250 x 4.6 mm, 5 µm) was used as stationary phase, the mobile phase consisted of 0.1 M dipotassium hydrogen orthophosphate buffer (pH 6.0) and acetonitrile in a 50:50 (% v/v) ratio. The flow rate was set to 0.5 ml/min. UV detection of 210 nm was used for clarithromycin and 232 nm for spiramycin. Ambient column and sample tray temperatures were used.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Results: &lt;/strong&gt;The method proved to be suitable for the detection of both macrolide antibiotics in bulk samples, as part of amorphous solid dispersions as well as in dosage forms. The isocratic elution was rapid. The method was validated in terms of system suitability, limits of detection (LOD), limit of quantification (LOQ), accuracy, precision, linearity, and specificity. This method showed linearity across the concentration range of 4.0–5000.0 µg/ml for both antibiotics.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Conclusion: &lt;/strong&gt;The developed method showed to be a simple and sufficiently sensitive method for the detection and quantification of either clarithromycin or spiramycin from samples that might contain even very small quantities of the antibiotics.&lt;/p&gt;

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.

Simple estimation of effective elastic constants for thin plates with regular perforations and an application to the vibration of distillation column trays

The horizontal perforated sheet metal plates are commonly used in the process industries as trays in distillation columns, important internal parts for fractionating the input liquid mixture. Normally, the operating performance of such trays is satisfactory. However, cases have been reported of abnormally high levels of tray vibration during operation at particular conditions. The trays then experienced fatigue cracking accompanied by the loosening of bolts and fixings, which led to expensive failures. The excitation of structural resonance was suspected as a component in flow-induced vibration. Using linear stress superposition, a simple but robust analytical method is developed to provide high-quality predictions for the stress and strain distributions for in-plane loaded thin perforated plates with periodic hole arrangements. This approach is built on the classical solution for the elastic stress field around a single circular hole in a large plate. The perforated plates with square penetration patterns are investigated in this article, although the same approach is applicable to any regular penetration pattern. Stress concentration factors as well as the effective elastic constants, which can be used to describe the bending properties of the perforated plates, are then verified against both the established theoretical solutions and the results from finite element simulations. Excellent agreement to both previously published physical experiments and complex modelling is observed in all cases, with small-to-medium (up to 40%) hole-area fraction. The proposed analytical method is much simpler and computationally efficient than finite element analysis. The computed effective elastic constants are used in a finite element modal analysis to estimate the free vibration frequencies of a stiffened distillation column tray example; the first 30 vibration modes are found to be almost uniformly distributed between 25 and 70 Hz, which matches the vibration frequency range reported from plant operations.

Numerical simulations on the effect of sloshing on liquid flow maldistribution of randomly packed column

Randomly packed columns are key equipment for natural gas pre-treatment process of the FLNG (Floating Liquefied Natural Gas). It is of great importance to study on the effect of sloshing on liquid flow maldistribution at the column tray under severe sea state. A three-dimensional CFD model for randomly packed column under sloshing conditions was developed and the inter-phase drag force, porous resistance force, liquid dispersion and radial variation of volume porosity were incorporated into the volume averaged equations. Then the simulation results were validated with the experimental data. Both static and sloshing simulations have been carried out with varying angles and aspect ratios to map the distortion of liquid distribution. Quantitative analysis of liquid volume fraction, liquid velocity and maldistribution factor affected by tilt angles and aspect ratios were provided. The duration time of the dry area occupies about 40% of the period in the wall region and the total dry area occupies about 10% of the cross-sectional area. The maximum tilt angle should be less than 3° to prevent severe liquid flow maldistribution of the column with the aspect ratio of 3 (L/D=3).

Fabrication of Tunable, Stable, and Predictable Superhydrophobic Coatings on Foam Ceramic Materials

Superhydrophobic foam ceramic materials can be used as distillation column internals, and surface wettability has a remarkable influence on column trays. There are no existing methods for industrial fabrication of superhydrophobic surfaces on foam ceramic materials. This paper presents a facile method for fabricating stable superhydrophobic or hydrophobic coatings on the outside and inside of foam SiC materials with submicrometer silica particles, for dip-coating, and alkylchlorosilane, for surface reaction. Scanning electron microscopy, atomic force microscopy, dynamic light scattering methods, and Fourier transform infrared spectroscopy were employed to study the physical and chemical details. The contact angle of coatings can be tuned to 155°, 140°, 125°, and 95° by adapting coating times and particle size. Superhydrophobic surfaces presented excellent stability under various conditions. In addition, a theoretical prediction strategy by surface microscopic morphology and surface chemical composition ba...

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.

An imaging technique for characterization of fluid flow pattern on industrial-scale column sieve trays

Non-uniform flow patterns on distillation trays can result in significant losses in separation efficiency compared to conditions with straight chordal flow paths. To improve flow pattern via tray design revamps as well as for more accurate prediction of achievable separation efficiency, better understanding of the flow formation is required. This is, however, not straight forward since the evolving patterns depend on column and tray design as well as on operating conditions and may cover configurations with continuous liquid being pushed through a curtain of rising bubbles (bubble regime) or a continuous gas phase carrying the liquid as droplets (spray regime).In this study, the wire-mesh sensor technique was used to visualize flow patterns on larger trays. The technique tracks conductivity tracer pulses during their passage across the tray. A proper calibration routine was developed and a methodology is proposed to determine point liquid residence time distributions and weir-to-weir liquid velocities. Experiments were carried out in a tray column of 800mm diameter. The feasibility study included experiments at different liquid capacities and various outlet weir obstructions. Tray benchmark data at high spatio-temporal resolution were obtained, which are suitable for validation of CFD models for flow simulation of industrial-scale sieve trays.

Hydrodynamics and mass transfer performance of vapor–liquid flow of orthogonal wave tray column

In the present work, hydrodynamics and mass-transfer performance of vapor–liquid flow of orthogonal wave tray (OWT) column was studied. Dry pressure drop, operating range (capacity graph) and overall column efficiency of OWT column were investigated using pilot columns. A three-dimensional CFD model was developed within the two-phase Eulerian framework to have an insight into the two-phase flow and mass-transfer behavior of OWT. The simulated results were compared with experimental data and showed a good agreement. Hydrodynamic and mass-transfer behaviors were revealed with the aid of velocity profiles, streamlines, interfacial area density distribution and so on. The effects of vapor/liquid load (FS factor) on the Murphree tray efficiency were also studied. The simulations of OWT with different waves showed that the pressure drop, clear liquid height, froth height and Murphree tray efficiency increase with the increase of slope, and OWT with middle slope tended to have more uniform foam layer. Comparison of the liquid-phase component velocity between OWT and ripple shows that OWT has better performance in froth layer distribution and stability. The mass-transfer data showed that OWT not only had almost the same “peak efficiency” as sieve tray, but also had higher capacity and stability, it was suitable for capacity expansion.

Process design and optimization for etherification of glycerol with isobutene

Surplus glycerol from biodiesel production can be transformed to valuable fuel additives through etherification with isobutene. Our previous work has studied the kinetics and thermodynamics of this reaction. In the present work, a novel process design is proposed. An optimization problem is also formulated to minimize the cost of production of the di-tert-butyl ethers and tri-tert-butyl ether of glycerol. The resulting mixed-integer nonlinear program enables simultaneous determination of values of key decision variables including number of column trays, feed tray location of column, volume of reactor, process flowrates etc. The optimal design leads to a minimal production cost of glycerol ethers of 1.201 $/kg, which is dominated by the cost of isobutene.