The Improvement of Thermal Diffusion Performance in the Modified Frazier Scheme by Increasing the Column Heights at a Constant Ratio

The effects of column number and the variation of column heights on thermal diffusion along the modified Frazier scheme, has been investigated with the total sum of column heights fixed. The equations, which may be employed to predict the optimal number of columns and the optimal column-height ratio for the maximum separation, have been derived. Considerable improvement in performance is obtainable if the column-height ratio and/or column number in a modified Frazier scheme with the total sum of column heights fixed are properly assigned for a certain flow-rate operation, instead of using the conventional Frazier scheme of uniform column height with the same total sum of column heights.     

Enrichment of Heavy Water by Thermal Diffusion in the Frazier Schemes with Column Heights Varied at a Constant Increment for Improved Performance

The improvement of heavy water enrichment by thermal diffusion in the Frazier scheme with column heights varied at a constant increment and with the total sum of column heights fixed, has been investigated. The equations, which may be employed to predict the optimal column number and the optimal column-height increment for maximum separation, have been derived. Considerable improvement in heavy water enrichment is obtainable if the column number and column-height increment in a modified Frazier scheme with the total sum of column heights fixed, are property assigned under certain flow-rate operation, instead of using the conventional scheme of uniform column height.     

Thermal diffusion in the modified Frazier schemes with column heights varied at a constant increment for improved performance

The effects of column number and column-height increment on the degree of separation in the modified Frazier scheme of thermal diffusion columns with the total sum of column heights fixed, has been investigated. The equations, which may be employed to predict the optimal column number and the optimal column-height increment for the maximum separation, have been derived. Considerable improvement in performance is obtainable if the column number and column-height increment in a modified Frazier scheme with the total sum of column heights fixed, are properly assigned under a certain flow-rate operation, instead of using the conventional Frazier scheme of constant column height with the same total sum of column heights.     

Heavy water enrichment by thermal diffusion in the flat‐plate frazier scheme with column heights increased at a constant ratio for improved performance

This study investigates heavy water enrichment using the Frazier scheme of flat‐plate thermal diffusion columns with the column number adjusted and the column heights varied at a constant ratio with the total sum of column heights fixed. The equations for predicting the best number of columns and the best column‐height ratio for maximum separation are derived. Considerable improvement in performance is obtainable if the column‐height ratio and/or column number in a modified Frazier scheme are properly assigned, instead of using the conventional Frazier scheme of uniform column height with the same total sum of column heights. © 2013 Canadian Society for Chemical Engineering     

THE PROPER COLUMN NUMBER FOR BEST PERFORMANCE IN THERMAL DIFFUSION COLUMNS OF THE FRAZIER SCHEME WITH TOTAL SUM OF COLUMN HEIGHT FIXED

The effect of column number on the Frazier scheme performances with total sum of column heights fixed has been investigated. The equations that may be employed to predict the optimal number of columns (generally not integers) for the maximum performance are derived. Accordingly, the proper number of columns, which are the integers nearest to and smaller than the optimal column numbers, are obtained for practical applications. Considerable improvement in performance is obtainable if the scheme is constructed with the proper number of thermal diffusion columns, instead of using a single column, with the same total sum of column heights.     

The best performance of spiral wired thermal diffusion columns of the frazier scheme

Equations have been derived for the optimum wire angles of inclination for maximum separation, maximum production rate and minimum column height in the Frazier scheme of concentric‐tube thermal diffusion columns with a tight fitting wire spiral, having a diameter equal to the annular spacing, and wrapped on the entire inner tube. Considerable improvement in performance is obtained when a Frazier scheme is operated at the optimum corresponding wire angle of inclination, especially for the scheme of high column number.     

Effect of Changes in Operating Variables on Stage-wise and Cumulative Separation in Binary Multistage Distillation

Abstract

The progressive separation that occurs stage-wise within a multistage distillation column is characterized by the cumulative extent of separation, ζ _N ; while the contribution of individual stages, δ _N , to the overall separation is given by the difference between ζ _N for successive stages. These indexes permit the “goodness” of separation for individual stages and for the entire column to be compared on an equivalent basis. This paper examines the effects of changing operating variables of reflux ratio, feed rate, feed composition, and feed stage location on the separation obtained in a distillation column containing a fixed number of ideal stages, and how the single-stage contribution changes when these variables are altered from the design value. The calculations show that the reflux ratio (R) is probably the most important variable in determining how well a column makes a separation. Separation declines rapidly as R is reduced below the design value, as the feed rate is increased at constant boil-up rate, and as the feed concentration drops below the design value. Changing the feed stage location of ±5 stages in a 50-stage column has a minimal effect on separation at all feed compositions. δ _N clearly shows how the contribution of individual stages changes when operating variables are varied from the design values.     

Mixing Time in a Short Bubble Column

Mixing time measurements have been carried out in a 0.2m I.D. short bubble column (Hc/D ? 5) with different spargers and for different clear liquid height to diameter (H_C/D) ratios. Superficial gas velocity has been varied in the range of 0.01m/s to 0.1m/s. Effect of bulk fluid viscosity on the mixing time has also been studied. The circulation cell model, with two fitted parameters viz. number of circulation cells, S and the inter‐cell exchange velocity, V_e, has been used to predict and explain the variation in mixing time and the flow pattern in the short bubble column for different types of spargers.     

The optimum plate aspect ratio for the best performance in a flat-plate thermal diffusion column of the frazier scheme

The effects of plate aspect ratio on the degree of separation, production rate and plate surface area in a flat-plate thermal diffusion column of the Frazier scheme, have been investigated. Theoretical considerations show that when the thermal diffusion columns of the Frazier scheme are constructed with the best plate aspect ratio, maximum separation, maximum production rate or minimum plate surface area can be obtained. The optimum plate aspect ratio for maximum separation is obtained with given production rate and plate surface area, while that for maximum production rate is determined with the degree of separation and plate surface area fixed, and that for minimum plate surface area is estimated with known degree of separation and production rate. It is interesting that the optimum plate aspect ratio for maximum separation is exactly the same as that for minimum plate surface area. The maximum separation and maximum production rate are achieved without changing any total expenditure, while the design with minimum plate surface area results in minimizing the total expense.     

The best performance of inclined thermal diffusion columns of the frazier scheme

The equations for the best angles of inclination for maximum separation, maximum production rate and minimum column length in inclined flat-plate thermal-diffusion columns of the Frazier scheme, have been derived. Considerable improvement in performance is obtained when a Frazier scheme is operated at the best corresponding angle of inclination, especially for the schemes of high column number.     

DRY COLUMN APPROXIMATION FOR PRESSURE DROP IN SPINNING CONE COLUMNS

A rotation-related normalization of variables has been introduced, and dimensionless fundamentally based correlations have been developed, for pressure drop in a spinning cone column (SCC) in the absence of liquid flow (dry column). The pressure drop is a sum of the dynamic and the centrifugal pressure components. Under typical SCC conditions, the correlation reduces to the form of ΔP _G  = 2N _st (k _reg R o ² + k _rot ), where N _st is a number of cone sets, Ro is the Rossby number (a rotation-normalized gas flow rate), and k _reg and k _rot are empirical coefficients characterizing the flow regime and the centrifugal efficiency of the rotor, respectively. This “dry column approximation” fits the data extremely well (the variation accounted for by the correlation is 98% of the total variation). It can be used as a theoretical limit for pressure drop prediction in an SCC at low liquid loads. The pressure regimes are classified as the centrifugal (Ro < 0.2), the intermediate (0.2 < Ro < 1.0), and the dynamic regimes (Ro > 1). Based on these dimensionless boundaries, dimensional diagrams of SCC operating regimes are constructed for laboratory and commercial-scale columns. The generality of the results is discussed in terms of the applicability of the correlations to larger scale equipment, the determination of empirical coefficients, and the linkage with CFD analysis of SCCs.     

Investigation of flow parameters and efficiency of mixture separation on a structured packing

Results of experimental study of the effect of initial maldistribution of structured packing irrigation on efficiency of binary mixture separation are presented in this article. The studies were carried out in the experimental distillation column with the diameter of 0.9 m using the R114 and R21 freon mixture. Experiments were performed on the structured Mellapak 350.Y packing of stainless steel 316L, containing 19 layers with the total height of 4.016 m at the ratio of mole liquid and vapor flow rates L/V = 1 and 1.7, respectively, and the pressure in the upper part of the column p_top = 3 bars. Nonuniformity at the packing inlet was generated via the blocking of some holes in the liquid distributor. Here, we present some results on efficiency of mixture separation, pressure drop on the packing, distribution of local liquid flow rate under the packing over the cross‐section and on the column wall within the range of vapor loading factor (0.69 < F_v < 1.61 Pa^0.5), as well as experimental data on distribution of local concentration of the low‐boiling component over the cross‐section and along the height of the structured packing. It is found out that significant maldistribution of mixture concentration and liquid flow rate over the cross‐section slightly changes along the height in the lower part of the column at a change in the degree of packing irrigation nonuniformity at the inlet. It is shown that efficiency of mixture separation depends considerably on the value of parameter L/V, vapor flow factor F_v, and size of the zone underirrigated by liquid at the inlet. In the studied range of liquid and vapor flow rates, the relative pressure drop on the packing does not depend on the ratio of liquid and vapor flow rates L/V and degree of irrigation maldistribution. © 2013 American Institute of Chemical Engineers AIChE J 60: 690–705, 2014     

Optimum Plate-Spacing for the Best Performance of the Enrichment of Heavy Water in Flat-Plate Thermal-Diffusion Columns of the Frazier Scheme

Abstract

The effect of plate spacing on the degree of separation and production rate for the enrichment of heavy water in flat-plate thermal diffusion columns of the Frazier scheme with fixed operating expense has been investigated. The equations for estimating optimum plate-spacing for maximum separation and for maximum production rate have been developed. Considerable improvement in performance is obtainable when thermal diffusion columns with optimum plate-spacing are employed for operation.     

Application of Statistical Analysis on the Bubble Surface Area Flux in a Column Flotation Cell

Flotation is a widely used separation process with applications from mineral separation to de-inking of recycled paper, waste water treatment, and solid remediation. In flotation column, bubble surface area flux (S_b) has been reported to describe the gas dispersion properties, and it has a strong correlation with the flotation rate constant. No information is available regarding S_b for coal flotation in column cell. This paper describes the effects of hydrodynamic parameters on S_b by means of a 2³ factorial experimental design in designed flotation column using coal slurry. The results showed that S_b increased with increasing superficial gas velocity and frother concentration, but decreased with increasing solid concentration. The main and interaction effects of operating parameters on S_b were evaluated using Yates’ analysis. The statistical model was developed to predict S_b in column flotation cell using experimental data. This paper also presents the development of the statistical model and the validation using a number of additional data sets. There is a good agreement between experimental results and predicted results from the developed model.     

Gas Separation by a Continuous Membrane Column

Abstract

The continuous membrane column provides a revolutionary new separation technique. In gaseous diffusion the continuous membrane column is used to separate as highly concentrated products both the most permeable and least permeable gases from a feed mixture of any composition. The main features of the column are countercurrent enrichment, high reflux and minimal backmixing. The new method eliminates the need for numerous interstage compressors and extensive product stream recycling found in conventional gaseous diffusion cascades.

Experiments are carried out for systems of C0₂-O₂, O₂2-N₂ (air), and CO₂-N₂ mixtures using continuous membrane columns made out of silicone rubber membrane. Also, a theoretical model is developed to interpret the experimental data. The agreement between theory and experiment is excellent. The maximum degree of separation can be achieved at total reflux. It is experimentally verified that the maximum degree of enrichment attainable by a conventional method can easily be exceeded without limit when a continuous membrane column is employed.

Finally, a comparative study has been conducted for a conventional gas permeator and a continuous membrane column.     

Performance Characteristics of Mechanical Foam-Breakers with Rotating Parts Fitted to Bubble Column

The characteristics of four mechanical foam-breakers (a six-blade turbine (F-B), a six-blade vaned disk (V-D), a two-blade paddle (T-P) and a conical rotor (C-R) having six-blades fixed internally) with rotating parts fitted to a bubble column (BC) treating various foaming liquids were examined. In the BC with different foam-breakers, the average liquid hold-up in foam, ϕ_L, was both a typical parameter reflecting the foaming intensity of the BC, and a parameter related to the difficulty or ease of foam-breaking. The value of power consumption, P_kc, for foam-breaking in the C-R was the largest amongst the foam-breakers. Furthermore, it was demonstrated that in the four foam-breakers with rotating parts a considerable amount of very small liquid droplets was entrained with the exhaust air. © 1997 SCI.     

Prediction of The Kolmogorov Entropy Derived from CT Data in a Bubble Column Operated under The Transition Regime and Ambient Pressure

The Kolmogorov entropy (KE) algorithm was successfully applied to single source γ‐ray Computed Tomography (CT) data measured by three scintillation detectors in a 0.162 m‐ID bubble column equipped with a perforated plate distributor (163 holes × ?? 1.32 · 10^–3 m). The aerated liquid height was set at 1.8 m. Dried air was used as a gas phase, while Therminol LT (ρ_L = 886 kg m^–3, μ_L = 0.88 · 10^–3 Pa s, σ = 17 · 10^–3 N m^–1) was used as a liquid phase. At ambient pressure, the superficial gas velocity, u_G, was increased stepwise with an increment of 0.01 m s^–1 up to 0.2 m s^–1. Based on the sudden changes in the KE values, the boundaries of the following five regimes were successfully identified: dispersed bubble regime (u_G < 0.02 m s^–1), first transition regime (0.02 ≤ u_G < 0.08 m s^–1), second transition regime (0.08 ≤ u_G < 0.1 m s^–1), coalesced bubble regime consisting of four regions (called 4‐region flow; 0.1 ≤ u_G < 0.12 m s^–1), and coalesced bubble regime consisting of three regions (called 3‐region flow; u_G > 0.12 m s^–1). The KE values derived from three scintillation detectors in the first transition regime were successfully correlated to both bubble frequency and bubble impact. The latter was found to be inversely proportional to the bubble Froude number. The KE model implies that the bubble size in this particular flow regime is a weak function of the orifice Reynolds number (d_b = 7.1 · 10^–3Re₀^–0.05).     

Column Dynamics for Adsorption of Bulk Binary Gas Mixtures on Activated Carbon

Abstract

Dynamics of adsorption from bulk N₂-He, CH₄-He, CO₂-He, CO₂-N₂, and CO₂-CH₄ binary mixtures were measured in a column packed with the BPL activated carbon. The data were analyzed using an adiabatic, isobaric, constant pattern model of column adsorption in conjunction with a linear driving force model for the adsorbate mass transfer. It was found that the mass transfer coefficients for adsorption of CO₂, CH₄, and N₂ were significantly lower during binary co-adsorption in the presence of each other than the corresponding pure component mass transfer coefficients in the presence of nonadsorbing helium. The reduction was more pronounced for the less strongly adsorbed species of the binary mixture. This kinetic interaction between the adsorbates could not be predicted a priori. Equilibrium isotherms for adsorption of pure N₂, CH₄, and CO₂ and for adsorption of CO₂-N₂ and CO₂-CH₄ binaries were also measured on the carbon. The isotherms obeyed the Langmuir equation.     

Adsorption Characteristics of Toluene and p‐Xylene in a Reversed‐Phase C18 Column for Simulated Moving Bed Chromatography

Abstract

The adsorption equilibria and transport properties of toluene and p‐xylene on a Eurosil 100‐30‐C₁₈ column were measured from a chromatographic response in a reversed‐phase HPLC. Moment method was applied to the effluent peaks obtained from various temperatures and eluent compositions. The adsorption equilibrium constants were obtained from the first moment analysis. On the other hand, the transport properties such as the axial dispersion coefficient and effective diffusivity were obtained from the second moment analysis. The simulated results of the simulated moving bed process using the parameters obtained from the moment analysis agreed well with the experimental results. And the separation of toluene/p‐xylene mixture could be successfully separated by the simulated moving bed process.     

Column Selection for Biomedical Analysis Supported by Column Classification Based on Four Test Parameters

This article focuses on correlating the column classification obtained from the method created at the Katholieke Universiteit Leuven (KUL), with the chromatographic resolution attained in biomedical separation. In the KUL system, each column is described with four parameters, which enables estimation of the F_KUL value characterising similarity of those parameters to the selected reference stationary phase. Thus, a ranking list based on the F_KUL value can be calculated for the chosen reference column, then correlated with the results of the column performance test. In this study, the column performance test was based on analysis of moclobemide and its two metabolites in human plasma by liquid chromatography (LC), using 18 columns. The comparative study was performed using traditional correlation of the F_KUL values with the retention parameters of the analytes describing the column performance test. In order to deepen the comparative assessment of both data sets, factor analysis (FA) was also used. The obtained results indicated that the stationary phase classes, closely related according to the KUL method, yielded comparable separation for the target substances. Therefore, the column ranking system based on the F_KUL-values could be considered supportive in the choice of the appropriate column for biomedical analysis.