Rashig Rings Research Articles

CALCULATION OF SPECIFIC SURFACE AREA AND POROSITY OF PACKING OF MASS-EXCHANGE COLUMN WITH MODIFIED RASHIG RINGS

New modified Rashig rings are proposed for mass transfer packing columns. Inside these rings, plate elements are attached to rods or springs in the form of rolled spirals with spiral gaps to increase the contact surface area of the phases. A formula linking the porosity and specific surface area of the packing through its geometric dimensions is obtained, allowing for the theoretical determination of one of these parameters based on the known value of the other. An example calculation of specific surface area using the derived formula for a standard Rashig ring is provided. It is demonstrated that the calculation results coincide with reference tabular values. The use of the derived formula in technological calculations of mass transfer columns allows for the theoretical determination of initial parameters (porosity or specific surface area of the packing) without the need for reference or experimental data. An analytical formula for determining the specific surface area of the proposed modified packing is derived. The ordered arrangement of this packing on the support grids of the mass transfer column apparatus is considered, with the spiral element of the modified packing having three turns with uniform spiral gap and made of thin plates. An example calculation of the specific surface area of the proposed modified Rashig ring is given for the considered packing arrangement in the column apparatus. The porosity of the modified packing is calculated using the proposed formula. A comparative analysis of the porosity and specific surface area of the proposed modified Rashig ring with a plate rolled in a spiral inside it and the standard Rashig ring is performed. The results show an increase in specific surface area of the packing in the modified ring by 1.5 times or more, from 65 to 102.7 m2/m3, with a slight decrease in porosity from 0.6 to 0.55 m3/m3. This reduces the calculated height of the packing layer in the mass transfer column apparatus and, consequently, the height and volume of the apparatus itself. The use of the new modified Rashig rings allows for a significant reduction in the total volume of packing in packing columns during extraction, absorption, desorption, and rectification processes.

Hydrodynamics of narrow-tube fixed bed reactors filled with Raschig rings

The local flow structure and pressure drop in random packings of Raschig rings are analyzed using sequential Rigid Body Dynamics (RBD) method and Computational Fluid Dynamics (CFD) simulation. Tube-to-pellet diameter ratios, N, between 3 and 6 are investigated for laminar, transitional and turbulent flow regimes (5 ≤ Rep ≤ 3,000). The computed pressure drops are in good agreement with the empirical correlation of Nemec and Levec (2005), while the Ergun equation exhibited high deviations of more than 60%, even when it is modified to explicitly account for non-sphericity of pellets. This deviation is ascribed to additional sources for eddy formation offered by Rashig rings, compared to spheres and cylinders, which cannot be counterbalanced by the usage of a higher specific surface area. The 3D results of flow structure demonstrate a large influence of packing topology on the velocity distribution: rings oriented parallel to the flow accelerate the local velocity through their axial holes, while rings oriented perpendicular to the flow provide additional space for vortex formation. The flow fields are substantially different from that found in packings of spheres and cylinders, both in terms of volume of backflow regions and velocity hotspots. This implies a higher order of local flow inhomogeneity in azimuthal and axial directions compared to spherical and cylindrical packings. Furthermore, it is found that azimuthal averaging of the 3D velocity field over the bed volume, which has been used to improve classical plug-flow pseudo-homogenous models to account for the role of tortuous velocity fields, cannot reflect the appearance of vortex regions and thereby leads to underestimation of the local axial velocity values by over 500% of the inlet velocity.

Use of numerical modeling methods in desing of combined rectification column

The article is devoted to the study of methods for modeling the operation of rectification columns using the HYSIS application software package. Such studies are very important not only for design, but also for the functioning of existing industries. The article proposes to use for combining nozzle devices in the concentration part of the column, and plate-shaped structures in the distant part of the column for more efficient and stable operation of distillation columns. To determine the hydrodynamic parameters of the operation of distillation column, a technique of determining the range of stable loads and the position of the operating point inside or outside the range of stable loads was taken. A column model was constructed using the HYSYS software package for separating gas mixtures with various contact devices: sieve trays, Rashig ring nozzles. Experiments for the same type and combined contact devices were carried out and their comparison was carried out in terms of hydraulic calculation and operating range. As a result of experiments with the use of the HYSYS software package, it was shown that the combined arrangement of contact devices can provide a stable hydraulic mode, in contrast to the use of similar contact devices.

Stripping Bioethanol from Fermented Molasses in A Packed Tower

<p>The high price of bioethanol is the barrier of its implementation as renewable energy sources. Therefore, efforts to reduce its price is an important factor to drive the implementation. Stripping is a way to separate bioethanol from the broth which will be cheaper than distillation process. This research was aimed to separate bioethanol from its fermented molasses. The effect of feed flow rate, air flow rate and feed temperature were investigated. A column with inside diameter of 0.1 m was used and packed with 0.02 x 0.016 m PVC rashig ring at 1 m of bed. The broth was fed from the top side and the air stripper was flown down from the bottom side. Six millimeters of the top product was collected at steady state condition for analysis of bioethanol concentration. The best experiment was the one which had feed flow rate 1,5 L/min and stripping air flow rate of 5,85 L/min. It resulted bioethanol content of 19.39% or equivalent to 38.5% stripped out of the broth.</p>

Experimental investigations of velocity fields in packed bed static mixers

Experimental investigations of velocity fields have been carried out in static mixers filled by Inzhekhim random packings of various sizes and Rashig rings. Studies have been performed on a laboratory setup by stereoscopic particle image velocimetry using a Polis multiphase flow measurement system. Experimental data have been supplemented by the results of numerical modelling of the hydrodynamics of flow, which were obtained using ANSYS Fluent software.

In-situ biogas upgrading in thermophilic granular UASB reactor: key factors affecting the hydrogen mass transfer rate

Biological biogas upgrading coupling CO2 with external H2 to form biomethane opens new avenues for sustainable biofuel production. For developing this technology, efficient H2 to liquid transfer is fundamental. This study proposes an innovative setup for in-situ biogas upgrading converting the CO2 in the biogas into CH4, via hydrogenotrophic methanogenesis. The setup consisted of a granular reactor connected to a separate chamber, where H2 was injected. Different packing materials (rashig rings and alumina ceramic sponge) were tested to increase gas-liquid mass transfer. This aspect was optimized by liquid and gas recirculation and chamber configuration. It was shown that by distributing H2 through a metallic diffuser followed by ceramic sponge in a separate chamber, having a volume of 25% of the reactor, and by applying a mild gas recirculation, CO2 content in the biogas dropped from 42 to 10% and the final biogas was upgraded from 58 to 82% CH4 content.

Evaluation of the performance of structured mixed packing and inert packing materials in toluene biotrickle-filtration

Packing materials play a key role in waste gas treatment. Organic and inert packing materials have their disadvantages, which may be minimized by mixed packing. In this study, various operating conditions were applied to evaluate the performance of structured mixed packing and inert packing materials in toluene biotricklefiltration. Four biotrickle filters were packed with structured mixed packing materials, namely, ceramic pall rings, ceramic rashig rings, and lava rock. Their toluene removal capacity was studied for 217 day using a laboratory-scale reaction under various operating conditions. The key elimination capacity (removal efficiency > 95%) ranking of the biotrickle filters was as follows: Structured mixed packing (306.20 ± 7.90 g/m3/h) > pall ring (156.71 ± 7.84 g/m3/h) > rashig ring (153.31 ± 6.14 g/m3/h) > lava rock (150.32 ± 9.19 g/m3/h). The structured mixed packing and inert packing resulted in excellent toluene-degrading biofilter performance under long-term operation. The structured mixed packing provided a more rapid startup rate and better process robustness than the inert packing did. The biotrickle filter with mixed packing materials had a high elimination capacity which makes it suitable for various real-life applications, whereas the capability of the inert packing material was more suitable for treating a steady low toluene load.

Application of artificial neural networks for simulation of experimental CO 2 absorption data in a packed column

The generalization performances of the Back Propagation Multi-Layer Perceptron (BPMLP) and the Radial Basis Function (RBF) neural networks were compared together by resorting to several sets of experimental data collected from a pilot scale packed absorption column. The experimental data were obtained from an 11 cm diameter packed tower filled with 1.8 m ¼ inch ceramic Rashig rings. The column was used for separation of carbon dioxide from air using various concentrations and flow rates of Di-Ethanol Amine (DEA) and Methyl Di-Ethanol Amine (MDEA) solutions. Two in-house efficient algorithms were employed for optimal training of both neural networks. The simulation results indicated that the RBF networks can perform more adequately than the MLP networks for filtering the noise (measurement errors) and capturing the true underlying trend which is essential for a reliable generalization performance.

Methodological analysis of gamma tomography system for large random packed columns

Gamma ray tomography experiments have been carried out to detect spatial patterns in the porosity in a 0.27 m diameter column packed with steel Rashig rings of different sizes: 12.6, 37.9, and 76 mm. using a first generation CT system (Chen et al., 1998). A fast Fourier transform tomographic reconstruction algorithm has been used to calculate the spatial variation over the column cross section. Cross-sectional gas porosity and solid holdup distribution were determinate. The values of cross-sectional average gas porosity were epsilon=0.849, 0.938 and 0.966 for the 12.6, 37.9, and 76 mm rings, respectively. Radial holdup variation within the packed bed has been determined. The variation of the circumferentially averaged gas holdup in the radial direction indicates that the porosity in the column wall region is a somewhat higher than that in the bulk region, due to the effect of the column wall.

On the mass transfer in a sprinkled biofilter

The mass transfer from a water film to fixed fill grains (Rashig ring) has been investigated. It has been revealed that the film regime of flow is characterized by incomplete flow over the surface of Raschig rings. The mass transfer coefficient and the portion of the washed surface depending on the flow rate of water have been measured. The process of mass transfer in a freely falling film has been simulated, and a comparison between the theoretical and measured values of the mass transfer coefficient has been made.

Effective irregular ceramic ring packing for heat- and mass-exchange processes

A new effective irregular ceramic ring packing is developed for heat- and mass-exchange processes; the packing has a lower hydraulic resistance and higher efficiency as compared with tested packings, and can be used in lieu of the Rashig rings most frequently employed in industry. Laws governing variation in basic hydrodynamic and mass-exchange characteristics of the developed packing are determined, and empirical equations are proposed for calculation of the parameters in question.

Tritium recovery system for Li–Pb loop of inertial fusion reactor

The best material for a wet wall and blanket of an inertial fusion reactor is selected among Li, eutectic alloys of Li–Pb, Li–Sn and a 2LiF + BeF 2 molten salt mixture called Flibe, judging from their chemical, nuclear and heat-transfer properties. Li 0.17Pb 0.83 is found to be the most promising one because of low Li vapor pressure, moderate melting temperature, good heat-transfer properties under the condition of a KOYO-fast circulation loop operated between 300 and 500 °C. A counter-current extraction tower packed with metallic rashig rings is proposed to extract tritium generated and dissolved in the Li–Pb eutectic alloy. Mass-transfer parameters when He and Li–Pb flow counter-currently through the tower packed with the rings are determined to satisfy the two necessary conditions of a self-sufficient tritium generation rate of 1.8 MCi/day and a target tritium leak rate of 10 Ci/day. It is found that the height of a tower to achieve the 99.999% recovery is comparatively low because of the promising property of a large equilibrium pressure of tritium. In order to mitigate the disadvantage of its high density, which needs a large pumping power, a porous packing material that keeps good contact between He and Li–Pb should be developed in the future. It is found experimentally that D 2 addition in He purge gas is effective to achieve a faster rate of tritium recovery from the Li–Pb flow. The rate-determining step of tritium permeation through a steam generator is determined as a function of a Li–Pb flow rate in a stainless-steel heat-transfer tube.

Modeling Process Characteristics and Performance of Fixed and Fluidized Bed Regenerative Thermal Oxidizer

The abatement of volatile organic components (VOC) in emissions is an extremely stringent environmental problem. One of the most frequently used technologies is the regenerative thermal oxidation (RTO), because of its thermal efficiency and cost-effectiveness. In the present paper, a computational one-dimensional unsteady model, able to account for fixed as well as fluidized beds of particles, is developed, validated, and applied to realistic plant conditions. Process thermal efficiency and gas pressure drop are calculated as functions of the system geometry and operating parameters. Results of a validation against experimental data are presented first, showing very good agreement. The overall thermal efficiency is obtained as the performance index for packed beds of spheres and Rashig rings and fluidized beds of spheres, allowing a direct comparison of the two systems. The simulation results clearly show that, despite the high efficiency of gas−solid contact in fluidized beds, their thermal performances are unacceptably poor, because of the cyclic nature of the process.

Sol–gel synthesis of Au/TiO 2 thin films for photocatalytic degradation of phenol in sunlight

Thin films of Au/TiO 2 on glass substrates have been prepared by simple sol–gel dip coating method using a sol of colloidal gold doped titanium peroxide (Au/TiO 2 sol). The sol of colloidal gold and titanium peroxide forms a viscous gel after 1–3 h depending on the concentration of both colloidal gold and titania. The sol of particular viscosity range (140–2800 cps) was used to deposit the Au/TiO 2 thin films of uniform thickness on various substrates such as glass slides, glass helix and silica rashig rings. Films deposited on glass plates after drying were transparent, uniform in color as well as thickness. Optical characterization by UV–vis spectrophotometer showed a shift in optical absorption wavelength to visible region may be due to the incorporation of gold nanoparticles into titania structure. The optimum concentration of gold loading was found to be 1–2% (by weight) beyond this the gold particles disturb the gel network resulting the formation of gelatinous precipitate. Thin film photo-catalyst prepared was characterized by various techniques such as UV–vis, TG-DTA, XRD, ICP-OES and TEM. The photo-activity of the thin films was tested in sunlight using phenol as model pollutant. The kinetic study showed that the rate of decomposition of phenol using Au/TiO 2 photo-catalyst was improved by 2–2.3 times than undoped TiO 2.

Radial Thermal Conductivity in Cylindrical Beds Packed by Shaped Particles

Experimental data on radial thermal conductivity of beds formed of solid cylinders, Rashig rings, six-spoke wheels, four- and 52-hole cylindrical pellets are presented. The use of shaped particles in packed beds can significantly improve radial heat transfer. Thermal conductivity of the bed increases with the increase of the channel cross-section in the particle. The hydrodynamic approach to the description of convective radial thermal conductivity in packed beds of cylindrical particles with arbitrary number and form of channels is proposed. The approach is based on the account of mean fluid velocities around and through the hollow cylinders in the packed bed.

Effects of packing material on the biofiltration of benzene, toluene and xylene vapours

Biofiltration was used to eliminate volatile organic compounds from air streams in bench‐scale reactors inoculated with an adapted consortium. Organic and inert supports were tested on 100 days of operation. The supports were: peat, vermiculite, a mixture of vermiculite and activated carbon, tree bark and, porous glass Rashig rings. A mixture of benzene, toluene and xylene vapors with a load of 200 gC m−3 h−1 was fed to the biofilters with an empty bed residence time of 60 s. Removal efficiencies higher than 95% were obtained with the mixture of vermiculite and activated carbon, 85% for peat and bark, 80% for vermiculite and 65% for the Rashig rings. In all cases, drying problems in beds were observed after several days of operation. Water addition with or without nutrients was required to maintain and increase the performance of biofilters. In steady state operation, experiments at loads ranging from 50 to 400 gC m−3 h−1 were carried out and a maximum elimination capacity of 260 gC m−3 h−1 was obtained for vermiculite‐activated carbon support. The three xylene isomers were degraded. Observations of the supports surface by scanning electronic microscopy at the end of the biofiltration experiment showed abundant growth of fungi, which were not in the inoculum, had colonized the biofilter.

Effects of Rashig rings placed in interplate spaces and the rheological properties of the liquid phase on power consumption in a gassed reciprocating plate column

The power consumption in a gassed reciprocating plate column with Rashig rings placed in interplate spaces increases with both increasing vibration intensity and content of solid particles but decreases with increasing the superficial gas velocity, regardless of the rheological properties of the liquid phase. Under the same operating conditions, the power consumption is higher when the column is filled with a non-newtonian liquid than with distilled water.

Ammonia oxidation into nitrous oxide over Mn/Bi/Al catalyst: I. Single cooling tube experiments

The process of ammonia oxidation with air oxygen was tested on the pilot-scale using a single-tube reactor to model the unit of a multi-tubular industrial reactor. The spherical Mn/Bi/Al catalyst was loaded into the reactor tube. Experimental studies were based on the data obtained by kinetic studies and simulation of the tubular reactor. The relationship between the operation conditions and temperature regime was established by varying the process parameters over a wide range. The steady-state temperature regimes were observed at the inlet ammonia concentration equal to 4–5%. The selectivities to nitrous oxide and nitrogen oxide reached 87–88% and no more than 0.5%, respectively, at near 100% conversion of ammonia. Modeling of the pilot reactor demonstrated a good agreement between the experimental and calculated data that supports appropriateness of the reactor simulation for prediction of technological regimes for the industrial reactor. The Rashig rings loaded in the tubular reactor were found to provide stable operation regimes at the inlet ammonia concentration of 7–8%.

Radial heat transfer in packed beds of spheres, cylinders and Rashig rings: Verification of model with a linear variation of λer in the vicinity of the wall

Experimental data on the effective radial thermal conductivities and wall heat transfer coefficients of cylindrical beds formed of spheres, cylinders and Rashig rings are presented. The obtained heat transport parameters are compared with literature data. A model with a linear variation of λ er in the vicinity of the wall is proposed to the description of the radial heat transfer in the packed bed. The model allows simple correlation between the wall Nusselt number and the bed core effective radial thermal conductivity. The model is verified by experiments.

Gas holdup in a gassed reciprocating plate column with rashig rings placed in interplate spaces

AbstractThe gas holdup is studies in a gassed reciprocating plate column with the addition of the Rashig rings placed in each interplate space. The gas holdup generally increases with increasing the vibration speed, the superficial gas velocity, and the solids concentration in the range of operating conditions applied. Independently of the solids concentration, the gas holdup is correlated with the power consumption and the superficial gas velocity. The Rashig rings are shown to have more effective dispersion action than the polypropylene spheres under the same other operating conditions.