Recirculation Of Liquid Research Articles

ВЫБОР ЖИДКОСТНОКОЛЬЦЕВОГО ВАКУУМНОГО НАСОСА ДЛЯ ШАРОВОЙ МЕЛЬНИЦЫ С ВАКУУМНЫМ ОТВОДОМ

The use of powders is of interest in many industries. At the same time, the degree of grinding of materials depends on the intended purpose; in particular, in the production of paints, it is necessary to ensure a certain fineness of grinding of the pigment. The smaller the particles, the higher its hiding power. However, excessively high grinding fineness may reduce the hiding power of the pigment. It is proposed to grind the pigment in a two-section cylindrical-conical ball mill with vacuum removal of particles of a given degree of grinding. The article describes the design of the mill and shows a diagram of the line for vacuum transportation of the crushed pigment. The purpose of the work is to determine the main parameters of the vacuum line of pneumatic transport when grinding solid organic materials using a ball mill with a vacuum outlet. A method for calculating the geometric, kinematic and dynamic parameters of the developed mill and pneumatic transport line is presented. A significant reduction in energy costs for excess grinding is achieved through timely vacuum removal of crushed particles. The vacuum in the system is created and maintained by a liquid ring vacuum pump. Various options for the operation of the developed installation are described: direct grinding; additional grinding and recirculation of additional liquid generated during the operation of the liquid ring vacuum pump, which further reduces energy costs during grinding

Electrokinetic actuation of an uncharged polarizable dielectric droplet in charged hydrogel medium.

Electrokinetic transport of an uncharged nonconducting microsized liquid droplet in a charged hydrogel medium is studied. Dielectric polarization of the liquid drop under the action of an externally imposed electric field induces a non-homogeneous charge density at the droplet surface. The interactions of the induced surface charge of the droplet with the immobile charges of the hydrogel medium generates an electric force to the droplet, which actuates the drop through the charged hydrogel medium. A numerical study based on the first principle of electrokinetics is adopted. Dependence of the droplet velocity on its dielectric permittivity, bulk ionic concentration, and immobile charge density of the gel is analyzed. The surface conduction is significant in presence of charged gel, which creates a concentration polarization. The impact of the counterion saturation in the Debye layer due to the dielectric decrement of the medium is addressed. The modified Nernst-Planck equation for ion transport and the Poisson equation for the electric field is considered to take into account the dielectric polarization. A quadrupolar vortex around the uncharged droplet is observed when the gel medium is considered to be uncharged, which is similar to the induced charge electroosmosis around an uncharged dielectric colloid in free-solution. We find that the induced charge electrokinetic mechanism creates a strong recirculation of liquid within the droplet and the translational velocity of the droplet strongly depends on its size for the dielectric droplet embedded in a charged gelmedium.

Coupling Microbial Electrolysis Cell and Activated Carbon Biofilter for Source-Separated Greywater Treatment

Reclamation and reuse of wastewater are increasingly viewed as a pragmatic tool for water conservation. Greywater, which includes water from baths, washing machines, dishwashers, and kitchen sinks, is a dilute wastewater stream, making it an attractive stream for extraction of non-potable water. However, most previous studies primarily focused on passively aerated biological and physicochemical treatment processes for greywater treatment. Here, we investigated an integrated process of a microbial electrochemical cell (MEC) followed by granular activated carbon (GAC) biofilter for greywater treatment. The integrated system could achieve 99.3% removal of total chemical oxygen demand (TCOD) and 98.7% removal of the anionic surfactants (linear alkylbenzene sulphonates) from synthetic greywater at a total hydraulic residence time (HRT) of 25 h (1 day for MEC and 1 h for GAC biofilter). For one-day HRT, the maximum peak volumetric current density from MEC was 0.65 A/m3, which was comparable to that achieved at four-day HRT (0.66 A/m3). The adsorption by GAC was identified as a key mechanism for the removal of organics and surfactants. In addition, recirculation of liquid within the GAC biofilter was identified as a critical factor in achieving high-rate treatment. Although results indicated that GAC biofilter could be a standalone process for greywater, MEC can provide an opportunity for potential energy recovery from greywater. However, further studies should focus on developing high-rate MECs with higher energy recovery potential for practical operation.

Heat transfer modeling of non-boiling gas-liquid slug flow using a slug tracking approach

This study proposes a new set of equations for the energy balance for predicting the temperature distribution of gas-liquid slug flows using a slug tracking approach. The model proves able to work around non-physical oscillations of the temperature distribution found with a previously published set of equations for the energy balance. The main difference here is that rather than being applied to each structure (namely the liquid slug, the liquid film and the elongated bubble) individually, the temperature is assigned to the whole unit cell. Central Differencing Schemes were avoided since the problem is convection-dominant, thus preference to Upwind Differencing Schemes was given. Comparison of the new model with an experimental dataset for air-water flow in a 52-mm ID pipeline showed deviations of ±25% for the temperature and pressure gradients. An extra head loss term caused by the recirculation of liquid in the elongated bubble wake was introduced into the momentum balance, correcting an existing –20% systematic deviation found in the pressure gradient as computed by the former model. Simulations for an extended, 200-m long pipeline comparing isothermal, cooling and heating flows are also presented. These simulations demonstrate the competition of gas expansion caused by pressure drop and of gas expansion/contraction caused by mixture heating/cooling, and their consequences on the elongated bubble length increase/decrease, on the mixture acceleration/deceleration, on the coalescence rate of elongated bubbles, and on their statistic distributions.

Potentiality of municipal sludge for biological gas production at Soba Station South of Khartoum (Sudan)

Potentiality of municipal sludge for biological gas production at Soba Station South of Khartoum (Sudan)

A new look at the environmental conditions favorable to secondary ice production

Abstract. This study attempts a new identification of mechanisms of secondary ice production (SIP) based on the observation of small faceted ice crystals (hexagonal plates or columns) with typical sizes smaller than 100 µm. Due to their young age, such small ice crystals can be used as tracers for identifying the conditions for SIP. Observations reported here were conducted in oceanic tropical mesoscale convective systems (MCSs) and midlatitude frontal clouds in the temperature range from 0 to −15 ∘C and heavily seeded by aged ice particles. It was found that in both MCSs and frontal clouds, SIP was observed right above the melting layer and extended to higher altitudes with colder temperatures. The roles of six possible mechanisms to generate the SIP particles are assessed using additional observations. In most observed SIP cases, small secondary ice particles spatially correlated with liquid-phase, vertical updrafts and aged rimed ice particles. However, in many cases, neither graupel nor liquid drops were observed in the SIP regions, and therefore, the conditions for an active Hallett–Mossop process were not met. In many cases, large concentrations of small pristine ice particles were observed right above the melting layer, starting at temperatures as warm as −0.5 ∘C. It is proposed that the initiation of SIP above the melting layer is stimulated by the recirculation of large liquid drops through the melting layer with convective turbulent updrafts. After re-entering a supercooled environment above the melting layer, they impact with aged ice, freeze, and shatter. The size of the splinters generated during SIP was estimated as 10 µm or less. A principal conclusion of this work is that only the freezing-drop-shattering mechanism could be clearly supported by the airborne in situ observations.

Liquid Holdup by Gravimetric Recirculation Continuous Measurement Method. Application to Trickle Bed Reactors under Pressure at Laboratory Scale

Liquid holdup is a crucial parameter when operating catalytic trickle bed reactors related to wetting efficiency and residence time. Most of the classical methods are expensive, time-consuming, or not valid for high pressures. Liquid holdup by gravimetric recirculation (LHGR) measurement method determines the average total liquid holdup using a closed loop with total recirculation of liquid. The recirculating liquid is contained in a vessel that is weighed instantaneously with a known amount of liquid. The difference between the initial amount of liquid and the instantaneous weight gives the liquid holdup. Main benefits are the following: first, the measurement takes only the time of stabilization that at laboratory scale is 2–5 min; second, the system is ready for the next measurement without any modification (the bed is not disturbed nor modified); third, it works for high pressures; finally, it gives values comparable to those from classical techniques like RTD or conductivity methods.

Velocity Field Visualization in USP Dissolution Apparatus 3 Using Particle Image Velocimetry

PurposeThe hydrodynamics in USP dissolution apparatus 3, at five different dip rates, was characterized by analyzing phase-averaged velocity fields obtained using Particle Image Velocimetry (PIV).MethodsPhase locked 2 Component-PIV (2C–PIV) measurements were recorded on a typical dissolution apparatus 3 configuration with a black painted tablet fixed at the center of the bottom porous screen of the reciprocating cylinder. A trigger mechanism was employed to capture data over 12 phase positions for each reciprocation cycle. Data were captured over a fixed number of cycles, based on dip rate, and the resultant images were post-processed to obtain phase-averaged velocity fields at each phase.ResultsFor all dip rates studied, the sinusoidal nature of the cylinder’s reciprocating motion was evident in the images. The phase positions, in which the cylinder was completely submerged, were characterized by recirculation of liquid through the cylinder, top fitting cap, vessel-cylinder annulus, and bottom fitting cap. The direction of recirculation was opposite for phase positions during the up- and downstrokes. The end positions of the up- and downstrokes were characterized by vortices below and above the cylinder respectively. Increasing dip rates led mainly to increasing velocity magnitudes while all flow characteristics, in general, were retained.ConclusionsThe hydrodynamics in typical USP dissolution apparatus 3 is characterized by cyclic phase-dependent flow fields. Specifically, the velocity field distribution within dissolution apparatus 3 is greatly influenced by the relative position of the top cap to the liquid level in the cylinder.

Performance of a cell-foam trickle-bed reactor for phenol wet oxidation: Influence of operation parameters and modelling

Abstract The homogeneous wet oxidation of phenol, catalysed by Cu(II), has been studied in a trickle-bed reactor. The reactor bed consisted of a ceramic foam made of alumina with a cell density of 20 ppi. This bed is especially suited to promote mass transfer between phases with very low pressure drop. The gas phase (oxygen at 0.6 MPa) was circulated continuously, while the liquid phase (40 mol/m 3 phenol in water) was circulated in discontinuous mode, i.e. with total recirculation of liquid. The experiments were planned to determine the influence of the main operating conditions, i.e. liquid superficial velocity (0.9–3.3 × 10 −3 m/s), Cu(II) concentration (0.41–0.945 mol/m 3 ) and temperature (110–143 °C). Temperature and liquid superficial velocity were found to have the most marked influence in phenol conversion. The use of the foam packing, particularly at high liquid superficial velocities, enhances oxygen mass transfer between phases and increases the efficiency of the process (higher phenol conversion). A mathematical model, based on conservation equations applied to the bulk liquid and liquid film, has been proposed and validated with the experimental results. It has been found that the model is able to predict the experiments within an error of ±10%.

Kinetics and mass transfer of the hydrogenation of 2-methyl-3-butyn-2-ol in a structured Pd/ZnO/Al2O3 reactor

This work presents a study of the hydrogenation of 2-methyl-3-butyn-2-ol in flow over a structured catalyst. A porous tubular metal structure is coated with a layer of ZnO/Al2O3 and impregnated with palladium. This reactor is operated with recirculation of the process liquid and continuous supply of hydrogen with co-current upward flow. A Langmuir-Hinshelwood mechanism based on noncompetitive adsorption of hydrogen and organics is used to model the experimental results. The kinetic and adsorption parameters governing the process are estimated in the kinetic regime by means of a numerical optimization procedure. The extension of the model to the mass transfer limited regime, at lower hydrogen flowrates, allows the estimation of an overall mass transfer coefficient Kov. The reaction appears to be strongly dependent on the hydrogen flowrate with estimated Kov lower than 0.25s−1 in the range of flowrates 0.1–0.5nLmin−1. The mathematical model, successfully validated, is able to accurately predict the concentration profiles of the species involved in the system at varying temperatures, in both kinetic and mass transfer limited regimes.

Convection-Enhanced Biopatterning with Recirculation of Hydrodynamically Confined Nanoliter Volumes of Reagents.

We present a new methodology for efficient and high-quality patterning of biological reagents for surface-based biological assays. The method relies on hydrodynamically confined nanoliter volumes of reagents to interact with the substrate at the micrometer-length scale. We study the interplay between diffusion, advection, and surface chemistry and present the design of a noncontact scanning microfluidic device to efficiently present reagents on surfaces. By leveraging convective flows, recirculation, and mixing of a processing liquid, this device overcomes limitations of existing biopatterning approaches, such as passive diffusion of analytes, uncontrolled wetting, and drying artifacts. We demonstrate the deposition of analytes, showing a 2- to 5-fold increase in deposition rate together with a 10-fold reduction in analyte consumption while ensuring less than 6% variation in pattern homogeneity on a standard biological substrate. In addition, we demonstrate the recirculation of a processing liquid using a microfluidic probe (MFP) in the context of a surface assay for (i) probing 12 independent areas with a single microliter of processing liquid and (ii) processing a 2 mm2 surface to create 170 antibody spots of 50 × 100 μm2 area using 1.6 μL of liquid. We observe high pattern quality, conservative usage of reagents, micrometer precision of localization and convection-enhanced fast deposition. Such a device and method may facilitate quantitative biological assays and spur the development of the next generation of protein microarrays.

Determination of dairy wastewater treatability by bio-trickling filter packed with lava rocks – case study PEGAH dairy factory

This paper investigates the effectiveness of a biological trickling filter for the treatment of wastewaters produced by a company manufacturing dairy products. First a bio-trickling column with a height of 150 cm was packed with lava rocks from north mountain of Tehran. It operates with the recirculation of liquid through the packing. In order to startup the pilot scale, steady state condition was gained by pumping activated sludge and dairy wastewater for 23 days. Afterwards, dairy wastewater was added to liquid tank for treatment. Hydraulic retention time (HRT) of treatment decreases from 5 days to 1 day then at HRT of 12, 8, 7, 6 and 4 h. Results show that the average chemical oxygen demand (COD) decreased from 2,750 to 98 mg/L at HRT of 7 h and efficiency of TKN removal was more than 70%. The microorganisms developed in the bio-trickling filter were able to efficiently remove COD levels up to 2,750 mg/L, under aerobic conditions at pH values between 6.8 and 7.2 under low temperature condition between 10 and 13 °C.

Testing new centrifugal trays with liquid recirculation

The results of hydraulic tests of new centrifugal trays with repeated recirculation of liquid in the centrifugal elements in the water–air system. Curves were obtained for calculating the amount of liquid circulating in the centrifugal elements and the pressure drop in dry and reflux trays.

Modeling of sprays using computational fluid dynamics codes

Recently developed approaches to droplet and spray modeling in computational fluid dynamics (CFD) codes are reviewed. It is emphasized that the modeling of spray primary break-up needs to take into account the transient nature of sprays, while the modeling of droplet heating and evaporation needs to take into account a number of factors, including recirculation and finite thermal conductivity of liquid, semi-transparency of droplets and the kinetic effects. This modeling needs to take place in realistic three-dimensional enclosures, which makes it essential to find a compromise between the accuracy of the models and their CPU efficiency.

Anaerobic digestion of alfalfa silage with recirculation of process liquid

Process liquid recirculation initially stimulated one-phase anaerobic digestion of alfalfa silage in two semi-continuously fed and stirred tank reactors. Thus, with increased pH, alkalinity and stability it was possible to increase the organic loading rate to 3 g VS L −1 d −1, as compared to 2.25 g VS L −1 d −1 in a control reactor without recirculation. However, the recirculation of liquid eventually caused an accumulation of organic and inorganic substances, leading to an inhibition of hydrolysis and methanogenesis. This inhibition of microbial activity was prevented in one of the processes by replacing 50% of the recirculated process liquid with water during the second half of the operation period. A multiple linear regression model of principal components using seven input variables explained the variance in output variables nearly as well as the original model using all 23 measured input variables. The results show that it is necessary to adjust the degree of liquid recirculation to reach an optimal process.

Identification of fuzzy controller for use with a falling-film evaporator

A first-order Takagi–Sugeno fuzzy inference engine based on the use of polynomial consequents in the fuzzy rules was applied to the identification of a thermocompression evaporator. The fuzzy system obtained proved to be suitable for the description and off-line optimization of the process based on the recirculation of sugar liquid in the equipment. Only two linguistic rules were needed to successfully describe the complicated and non-linear effects of four input variables on the outlet concentration of sugar. Supervisory control of evaporation could be realized by steering only the feed of liquid to the evaporator, or the recirculation of liquid in the evaporation section.

Improvements of Ebullated-Bed Technology for Upgrading Heavy Oils

Improvements of Ebullated-Bed Technology for Upgrading Heavy Oils — Residue from heavy crude oils can be upgraded through various existing processes. Among these processes, the catalytic hydroconversion ebullated-bed process (H-Oil) has the unique feature of deeply converting heavy feedstocks with high impurity contents while operating with a long cycle time. This is accomplished through daily on-line catalyst replacement of a small portion of the catalyst bed. The ebullated-bed reactor includes an internal recirculation of the reactor liquid to ebullate the catalyst bed. The paper will present background information on the H-Oil process and discuss some of the recent improvements that have been developed for this technology. A Residence-Time Distribution (RTD) study was conducted using a radiotracer on a new laboratory bench unit of this process. This experiment quantified the reactor hydrodynamics and the liquid holdup. These parameters are critical to insure a safe extrapolation of the pilot plant results. The technology of H-Oil process was improved for heavy feedstocks. A new hot high-pressure separator design, based on R&D studies, has been developed to improve the separation of gas/liquid avoiding excessive liquid carry-over and gas carry-under. The use of this new separator in a commercial H-Oil plant operation at higher feedstock throughput results in improved operation and minimization of operating costs.

SPLIT-CYLINDER AIRLIFT REACTORS: HYDRAULICS AND HYDRODYNAMICS OF A NEW MODE OF OPERATION

Abstract An unusual mode of operation of internal-loop airlift reactors is described as being of potential use in extending the range of practicable operating volumes or turndown ratios in wastewater treatment applications. Unlike normal operation, the new mode employs an inital static liquid level that is lower than the upper edge of the draft-tube or the splitting baffle. Hydrodynamics of the operation are analyzed using fundamental principles and an equation is developed for predicting the minimum required gas flow for attaining recirculation of the liquid. The equation is proven experimentally using data for air-water in split-cylinder reactors (aspect ratio = 7; volume = 0.08 m3; riser-to-downcomer cross-sectional area ratio = 2.44; − 0.03 < hc ≤ 0.12, where hc is the dimensionless clearance between the upper edge of the baffle and the static height of gas-free liquid), Effects of the clearance hc on gas holdup in the riser and downcomer, mixing behavior and liquid circulation rate are presented. In terms of mixing characteristics, the riser behaves as a bubble column until the gas-liquid dispersion spills into the downcomer. Further increase in gas flow rate gradually increases recirculation of liquid and the characteristic oscillatory tracer response pattern of airlift reactors is obtained eventually. Gas holdup in the riser is consistently affected by the hc value although the effect is small. In contrast, the hc -value strongly affects the downcomer gas holdup. The commonly observed linear relationship between the riser and the downcomer gas holdup that applies to the normal mode or operation, breaks down for the configuration tested. The downcomer remains gas-free until a certain critical gas holdup (dependent on Ac-value) has been attained in the riser. Further increase causes a rapid increase in the downcomer holdup. Similarly, the variation of induced liquid circulation rate with gas flow velocity is different from the characteristic patterns reported for the normal mode of operation. In summary, for all the main hydrodynamic parameters tested, the behaviour of the new mode of operation differed from the previously reported characteristic behaviour of internal-loop airlift devices.

Determination of the surface area of mass transfer in a direct-flow contact-separation element with an internal central surface

UDC 66.015.23+66.71 It is established on the basis of analysis performed by the Autonomous Union TsKBN and comparison of contact gasdrying equipment that the construction of the direct-flow/centrifugal element makes it possible to increase the velocity factor of the gas in a section of the apparatus to 6 as a result of utilization of the energy of involuted gas flow [1]. It is also established that the efficiency of the element can be improved by dispersing the liquid directly in the element, i.e., on contact between the liquid and gas in a direct-flow contact-separation element with recirculation of the liquid in the element. The liquid separated in the element falls onto a plate deck, from where it proceeds again into the element for contact with the gas; excess liquid overflows onto the underlying plate. The Autonomous Union TsKBN has developed a direct-flow contact-separation element [2], in the central section of which an ejector pump is installed to disperse the liquid and reduce gas entrainment in the drops of liquid. The liquid is fed into the ejector pump from beneath, while a preliminarily involuted gas flow strips the liquid, dispersing a certain size of droplet. Liquid for the contact with the gas flow is therefore fed directly into a region of reduced pressure; this provides for an increase in liquid feed to the element as gas consumption increases. Mass exchange in the contact zone (surface area of interphase contact) depends heavily on the point of entry of the liquid phase to the contact zone, which is located at the center of the involuted gas flow in the indicated design. In centrifugal mass-exchange elements with both a central, and peripheral liquid feed, the gas breaks the liquid up into

Reducing the consumption of fresh water in the process of alginate extraction using Macrocystis pyrifera (Phaeophyta, Laminariales), by recirculating the residual liquids from the pre-extraction and precipitation

The recirculation of the residual liquid from the pre-extraction stage and precipitation using samples of Macrocystis pyrifera was studied to reduce the consumption of fresh water in the process of alginate extraction in the laboratory. An average yield of 28.44% was obtained with three recirculations in the pre-extraction stage, with a saving of 25% in the consumption of fresh water and of 56.25% in the consumption of concentrated hydrochloric acid. The consumption of fresh water was reduced by 50% with three recirculations of the residual liquid from the precipitation in the alkaline extraction stage, with an average yield of sodium alginate of 33.45%. The sodium alginates obtained had high viscosity and pH values within the maximum stability range (pH 5-9).