Dixon Rings Research Articles

Hydrodynamic and Mass Transfer in the Desorption Process of CO2 Gas in a Packed-Bed Stripper

A lab-scale packed-bed stripper containing Dixon rings was used to explore the effects of the process variables on the hydrodynamics and mass-transfer in a stripper using a mixed solvent loaded CO2. The variables are the liquid flow rate, reboiler temperature, and amine concentration, and the hydrodynamic and mass-transfer data can be determined using different models. In the case of hydrodynamics, the dimensionless pressure drop at the flooding point and the total pressure drop were explored first. In the case of mass-transfer, the correlation of the mass-transfer coefficient and the parameter importance were also observed. In addition, the number of plates per meter can be compared with the Dixon rings manufacturer. Finally, the performances of a mixed solvent and monoethanolamine (MEA) solvent were also discussed.

Influence of fluid properties on the hydrodynamics and operability of a countercurrent supercritical packed column

The hydrodynamic operability and the influence of fluid properties on hydrodynamics under supercritical conditions were investigated in a 38mm diameter column packed with ¼” Dixon rings. The column was operated using 100cSt and 200cSt Poly[dimethylsiloxane] (PDMS), with supercritical CO2 at 14MPa and 333K, 328K and 323K respectively. The pressure drop, liquid hold-up, mass flow and mass fractions were measured. The column operability limits were determined for both systems over a range of liquid and supercritical fluid flow rates using the measured data. Three distinct types of inoperability were identified, namely liquid layer flooding, bubble column flooding and excessive entrainment. It was found that liquid hold-up and pressure drop are not reliable indicators of operability in supercritical systems. Further, no observable loading operating regime was found, with the column only operating in the pre-loading or inoperable (flooded/entrained) regimes. The influence of the density and dynamic viscosity on hydrodynamics was found to be complex, yet significant. Small changes in temperature caused substantial changes in fluid properties, having a significant impact on column operability. Column operability range reduced with an increase in liquid viscosity and SF density. Finally, the data are compared to available models.

Sol-gel alumina coating of wire mesh packing

Wire mesh packings have seen increasing applications to multiphase processes in recent years. Despite the high surface area, open structure and thermal and chemical resistance, wire mesh packings have a complex geometry which hinders some chemical applications, including changes of surface properties through application of a uniformly adhesive coating. In this work, the sol-gel deposition method of alumina coating ceramics was investigated for the first time on stainless steel wire mesh by using Dixon rings as example. The kinetics of deposition during the hydrolysis and polycondensation was followed for a range of initial composition of the coating such as the ratios of Al2O3 to water, acid content, polyethyleneimine binder content and the number of deposition cycles. Well-adhered alumina with a thickness up to 20 μm was successfully deposited. The molar ratios of acid to alumina and alumina to water of 0.25 and 0.01, respectively, 48 h of the aging time, 96 h of the mixing time and 2.1 g/L of polyethyleneimine binder formed a free of cracks coating of controlled thickness alumina on the Dixon rings.

Simulation of the catalyzed isotopic exchange between hydrogen and water in a trickle bed reactor

The catalytic exchange column of countercurrent trickle bed for deuterium removal from hydrogen is simulated based on experimental results along with established reaction and mass transfer models, accounting for the humidification of hydrogen in a catalyst bed filled with platinum/styrene-divinylbenzene copolymer pellets and Dixon rings. Relative deviations of less than 30% are achieved between the experimental and the simulated HD molar fractions at the column outlet. Simulation results indicate that hydrogen humidification exerts a noticeable influence on gas and liquid phase flow rates, leading to an overestimated removal percentage of deuterium when such flow rate variances are neglected. Rate limiting step for the overall gas-liquid isotopic exchange is discussed. Finally, the operation conditions are optimized using the developed model.

Removal of hydrogen sulfide from coke oven gas by catalytic oxidative absorption in a rotating packed bed

The shortage of low-sulfur coking coal will bring about an increasingly high hydrogen sulfide (H2S) in the coke oven gas (COG) in the near future. This work investigated the removal of hydrogen sulfide (H2S) from a simulated coke oven gas (COG) by catalytic oxidative absorption in a rotating packed bed (RPB). Sodium carbonate (Na2CO3) solution doped with 20mgL−1 of a commercial “888” catalyst was used as the absorbent. The removal efficiency of H2S was evaluated under various operating conditions including rotation speed of the RPB (N), liquid-gas ratio (L/G), inlet H2S concentration (cH2S,in), temperature (T) and Na2CO3 concentration (cNa2CO3) in an attempt to optimize the conditions. The results were validated by comparison with those of separate experiments conducted in a packed column comprising a high-efficiency laboratory packing of Dixon rings. The comparison results reveal that the RPB exhibited higher H2S removal efficiency than the packed column, indicating it as an efficient gas-liquid contactor with a greater potential to remove H2S from COG.

The effect of packing on direct contact evaporation in spray column

AbstractThe direct contact evaporation in countercurrent spray column has been experimentally investigated. Two kinds of random packing were added into the column independently to study their influence on heat transfer process. Three different continuous phase flow rates (150, 200, 250 L/h) and two different dispersed flow rates (6.565, 13.13 L/h) were used in the experiment. The inlet continuous phase temperature ranged from 42 to 57 °C, and the inlet dispersed phase temperature was near its boiling point. The effect of variable factors on the optimal column height, the volumetric heat transfer coefficient, the pressure drop, and the thickness of foam layer were studied. The results showed that packing had positive effects on heat transfer, such as decreasing the optimal column height and the thickness of foam layer, increasing heat transfer coefficient. But extra pressure was also obvious. Dixon rings performed better than Raschig rings in the experiments due to their finer structure.

The effect of Dixon rings on direct contact heat transfer performance: Comparison of counter and co-current evaporation

In the experiment, direct contact evaporation in both co-current and counter-current flow were compared with pentane as dispersed phase and water as continuous phase. Dixon rings were also added into the column to enhance heat transfer in those two different contact ways. Axial temperature distribution, optimal column height and volumetric heat transfer coefficient are important parameters to evaluate heat transfer performance. The influences coming from pentane flow rate, water flow rate and inlet water temperature have also been carefully studied. Compared with co-current flow, the optimal column height decreased 15–25% and but heat transfer coefficient increased in the same scale no matter with packing or not in the counter-current condition. The optimal column height was halved and heat transfer coefficient doubled with packing when other factors were the same. Both optimal height and heat transfer coefficient would decrease with the increasing inlet water temperature. Packing in the column was an effective approach to enhance heat transfer performance especially under the condition of low water temperature as well as high water flow rate.

Process enhancement of supercritical methanol biodiesel production by packing beds

Continuous fixed bed reactors filled by three kinds of packing which were glass bead, glass spring and Dixon rings were investigated. The effect of temperature, pressure, the molar ratio of methanol to oil, flow rate, the size and shape of the packing were researched. The highest yield 90.84% of FAME was obtained by filling Dixon rings as packing with the condition of the temperature was 350°C, the pressure was 22MPa, the molar ratio of methanol to oil was 42:1. In addition, the reusability of Dixon rings was perfect. Numerical simulation was researched to provide theoretical basis for experimental results, besides the kinetics and thermodynamics behavior were investigated to explore the reaction mechanism.

Mass-Transfer Performance of CO2 Absorption with Aqueous Diethylenetriamine-Based Solutions in a Packed Column with Dixon Rings

This study investigated the absorption performance of CO2 into a diethylenetriamine (DETA)-based solution containing piperazine (PZ) or 1-(2-aminoethyl)piperazine (AEPZ) as an activator in a packed column with Dixon rings. The effects of various operation conditions such as the activator concentration, gas flow rate, liquid flow rate, CO2 partial pressure, and solution temperature on overall gas-phase volumetric mass-transfer coefficient (KGav) were explored. Results indicate that the presence of PZ in DETA solution yields a better enhancement effect on KGav than AEPZ, and, thus, a combination of 5%PZ+25%DETA solution is expected to be a promising absorbent for CO2 absorption. The results further show that KGav increases with an increase in the liquid flow rate and a decrease in CO2 partial pressure and first increases and then decreases with an increase in solution temperature. On the other hand, the gas flow rate has an insignificant effect on KGav. A simplified empirical correlation for KGav as a function of the operation parameters has been proposed, and most of the calculated values are in agreement with the experimental data with a deviation within ±15%.

Mass-Transfer Characteristics of the CO2Absorption Process in a Rotating Packed Bed

This article presents systematic investigations on the mass-transfer characteristics, including the overall gas-phase volumetric mass-transfer coefficient (KGa) and the height of mass-transfer unit (HTU), of the CO2 absorption process into a mixture of diethylenetriamine (DETA) and piperazine (PZ) solution in a rotating packed bed (RPB). The effects of operating conditions, including PZ concentration, rotation speed, liquid volumetric flow rate, gas volumetric flow rate, gas treatment capacity of packing, inlet CO2 mole fraction, temperature, CO2 loading of lean solution, and distributor specification on KGa and HTU in the RPB, were systematically studied. Also, a comparison of CO2 absorption performance between the packed column with Dixon rings packing and the RPB is presented. Results indicate that both KGa and HTU were significantly affected by rotation speed, liquid volumetric flow rate, gas volumetric flow rate, temperature, and lean CO2 loading while the PZ concentration, inlet CO2 mole fraction, a...

The effect of Dixon rings on direct contact evaporative heat transfer performance

Experimental study was conducted to investigate the effect of packing on performance of direct contact evaporative heat transfer for n-pentane and water operated in a bubble column with concurrent upward flow. The optimal column height and volumetric heat transfer coefficient with and without Dixon rings were examined and compared under the conditions of different flow velocity ratios of n-pentane to water, temperature differences between water and n-pentane and distributor apertures. It is found that packing enables optimal column height to decrease significantly. Optimal column height considerably reduces maximally by 25% under temperature difference less than 8 °C and flow velocity ratio 0.265. Volumetric heat transfer coefficient is 100–450 kW/(m3 °C) with packing while 40–150 kW/(m3 °C) without packing. Especially when the flow velocity ratio is 0.265 and 0.192, volumetric heat transfer coefficient with packing is nearly twice as much as that in bubble column without packing at the temperature difference below 8 °C. The effect of packing at temperature difference below 8 °C is more pronounced. Besides, backmixing observed in the experiment was demonstrated, and its significant influence on evaporative heat transfer performance was also analyzed.

Removal of CO2 from a submersible atmosphere by scrubbing with water—Experiments in a single column

In order to explore methods of removing CO2 from submersible habitats with sea water, gas scrubbing experiments (using tap water, and tap water with 3.5wt% sea salt) were performed in a 108mm i.d. pilot-scale column, investigating the removal efficiency of CO2 (e.g. at 2vol%) from a gaseous stream. The performance of this column fitted with 5 spray nozzles was compared with a column packed with 1/8thin. Dixon rings (packing depth=1480mm). More detailed experiments were then performed in the column packed with Dixon rings at: liquid flows from 4 to 8dm3min−1; gas flows 18 and 36Ndm3min−1, column pressures=1 and 4bar(g); column temperatures approximately 5 and 17°C. In general, CO2 removal increased as column operating pressure was increased, or fluid temperature was decreased. When approaching low gas outlet CO2 levels at the top of the column (e.g. 0.1vol%), the concentration of carbonate species in the tap water (fed into the column) restricted further improvements in the performance of the column.In experiments in a short column with Dixon rings (packing depth=180mm), using fresh water in each column, the performance of a multi-column eight chamber compact scrubber was simulated, and shown to be significantly better than a single tall column.

Preparation and characterization of hydrophobic platinum-doped carbon aerogel catalyst for hydrogen isotope separation

We report preparation of hydrophobic platinum-doped carbon aerogel (PtCA) catalyst and its characterization for catalytic exchange reactions between hydrogen isotopes. The PtCA powder was synthesized by sol-gel polymerization method, mixed with colloidal PTFE solution, and coated on Dixon rings to obtain hydrophobic catalyst. The Pt cluster size in PtCA powder was observed to vary from 3 to 5 nm for a change in resorcinol to alkali molar ratio in synthesis solution from 20 to 200. Transmission electron microscopy of powder showed that the Pt clusters were uniformally dispersed and Pt0 metallic content estimated by X-ray photoelectron spectroscopy (XPS) was found to be of ~70%. The catalytic activity was found to depend on Pt cluster size and was higher for smaller cluster size. For the smallest achieved Pt cluster size of 3 nm, catalytic activity of ~0.8 m3 (STP) s−1 m−3 was obtained for hydrogen isotope exchange in atmospheric pressure conditions.

Investigation of Mass-Transfer Performance for CO2 Absorption into Diethylenetriamine (DETA) in a Randomly Packed Column

The mass-transfer performance of CO2 absorption into aqueous diethylenetriamine (DETA) solutions was investigated in an absorption column randomly packed with Dixon rings at 303–303 K and atmospheric pressure, and compared with that of monoethanolamine (MEA), which is widely considered as a benchmark solvent for CO2 absorption. The mass-transfer performance was presented in terms of volumetric overall mass-transfer coefficient (KGav). In particular, the effects of operating parameters, such as inlet CO2 loading, solvent concentration, liquid flow rate, inert gas flow rate, and liquid temperature, were investigated and compared for both MEA and DETA. Over 40 runs of absorption experiments were carried out in this study. The results showed that KGav of DETA was found to be higher than that of MEA. Also, inlet CO2 loading, solvent concentration, liquid flow rate, and liquid inlet temperature had significant effect on KGav for both systems. However, the inert gas flow rate had an insignificant effect on KGav....

Fast Synthesis of Biodiesel at High Throughput in Microstructured Reactors

Transesterification of cottonseed oil and methanol with KOH as the catalyst for biodiesel production was carried out in microstructured reactors at residence times of less than 1 min and high flow rates. The reaction system included a micromixer that was connected to either a stainless steel capillary (inner diameter of 0.6 mm) or a PTFE tube (inner diameter of 3 mm, packed with Dixon rings) where the reaction is supposed to take place. The influences of the type of the micromixer, the residence time, the methanol-to-oil molar ratio, the flow rate, the type of delay loop, and reaction temperatures below and above the boiling point of methanol were examined. Flow patterns under different conditions were also examined in transparent microtubes. The results indicated that multilamination micromixers exhibited higher efficiencies in biodiesel production than simple T- and J-type micromixers. A higher yield of biodiesel could be obtained at reaction temperatures above the normal boiling point of methanol. By using the stainless steel capillary as the delay loop, the yield of biodiesel reached 94.8% under the conditions of a methanol-to-oil molar ratio of 8:1, a flow rate of 2.5 mL/min, a residence time of 44 s, and a reaction temperature of 70 °C. Under such circumstances, the pressure drop was 0.8 MPa. By using the PTFE tube packed with Dixon rings as the delay loop, the yield of biodiesel reached 99.5% at the same methanol-to-oil molar ratio and reaction temperature, a flow rate of 10 mL/min, and a residence time of 17 s. The pressure drop was 0.7 MPa. Thus, very fast biodiesel production at high throughput can be achieved in microstructured reactors.

Tritium Isotope Separation by Water Distillation Column Packed with Silica-gel Beads

Tritium enrichment or depletion by water distillation was investigated using a glass column of 32 cm in height packed with silica-gel beads of 3.4mm in average diameter. The total separation factor of the silica-gel distillation column, αH-T—, was compared with those of an open column distillation tower and of a column packed with stainless-steel Dixon rings. Depletion of the tritium activity in the distillate was enhanced by isotopic exchange with water adsorbed on silica-gel beads that have a higher affinity for HTO than for H2O. The value of alphaH-T-1 of the silica-gel distillation column was about four times larger than that of a column without any packing and about two times larger than that of the Dixon-ring column. The improvement of αH-T by the silica-gel adsorbent indicated that the height of the distillation-adsorption column becomes shorter than that of the height of conventional distillation columns.

Countercurrent packed column supercritical CO 2 extraction of olive oil. Mass transfer evaluation

Experiments to determine the number of transfer units (NTU) and height of a transfer unit (HTU) of different random packings such as Raschig rings, Dixon rings, Fenske rings and glass beads in a countercurrent (CC) supercritical fluid extraction (SFE) column of 17.6 mm I.D. and 1.8-m length at 20 MPa and 313 K, with olive oil and CO 2, were performed. The extracts were collected by means of two separators, the first one operated at 10 MPa and 313 K and the second at 3 MPa and 273 K. The performance of SFE was studied by analyzing the content of vitamin E and sterols in the raffinate and in the collected extracts by HPLC equipped with a photodiode array detector. The value of HTU and the NTU were evaluated for each random packing at solvent to feed ratios from 23.14 to 41.65 kg CO 2/kg oil. Fenske rings showed the best results in terms of efficiency and performance of the CC system for the SFE of olive oil.

Concentration of sterols and tocopherols from olive oil with supercritical carbon dioxide

AbstractA process based on the use of a semicontinuous countercurrent supercritical fluid extraction has been developed to isolate and concentrate minor compounds, such as sterols and tocopherols, from olive oil. In the present work, an evaluation of the efficiency of different random packing materials (Raschig rings, Dixon rings, Fenske rings, and glass beads) to selectively separate sterols and tocopherols from olive oil has been performed. Parameters such as recovery, enrichment, and selectivity vs. TG are discussed. Considering the importance of supercritical fluid extraction as a clean processing technology and the interest in minor compounds with nutraceutical properties from olive oil, the process studied represents an alternative to the reuse of low‐quality olive oil to extract high added‐value products.

Channeling Stage Model for separative analysis of packed water distillation column

A new `Channeling Stage Model' which enables us to estimate a HETP value of a packed distillation column is proposed. An example of separative analysis by the present model is given for binary H 2O-HTO water distillation by the packed column with 3.0 and 6.0 mm φ SUS Dixon rings. The present model can explain well the effect of vapor rate on HETP of a packed column.

Experimental Study for Dynamic Behavior of Cryogenic Distillation Columns Separating H-D-T System

This paper reports on dynamic behavior of cryogenic distillation columns which has been studied with a H-D-T system (1.5 g of tritium) under single column and two-column cascade operation modes. The columns used were different in inner diameters (1 cm and 2 cm) and in size packings (3 mm Dixon rings for the larger column and 1.5 mm Dixon rings for the smaller column). For both of the columns, the experimental observations for composition distribution at the steady-state was in close agreement with calculated results of all the components. The HETP values measured were in the range from 3 to 6 cm. The dynamic variations of compositions in bottom product streams experimentally observed were well predicted by computer-aided simulation. For top product streams, the variations were significantly slow in comparison with those of the calculated results using an assumption that liquid holdups in condensers were negligible. These results indicate holdups at the condensers.