Showing papers on "Mixing (process engineering) published in 1990"

Liquid-to-Gas Mass Transfer in Anaerobic Processes: Inevitable Transfer Limitations of Methane and Hydrogen in the Biomethanation Process

Abstract: Liquid-to-gas mass transfer in anaerobic processes was investigated theoretically and experimentally. By using the classical definition of kLa, the global volumetric mass transfer coefficient, theoretical development of mass balances in such processes demonstrates that the mass transfer of highly soluble gases is not limited in the usual conditions occurring in anaerobic fermentors (low-intensity mixing). Conversely, the limitation is important for poorly soluble gases, such as methane and hydrogen. The latter could be overconcentrated to as much as 80 times the value at thermodynamic equilibrium. Such overconcentrations bring into question the biological interpretations that have been deduced solely from gaseous measurements. Experimental results obtained in three different methanogenic reactors for a wide range of conditions of mixing and gas production confirmed the general existence of low mass transfer coefficients and consequently of large overconcentrations of dissolved methane and hydrogen (up to 12 and 70 times the equilibrium values, respectively). Hydrogen mass transfer coefficients were obtained from the direct measurements of dissolved and gaseous concentrations, while carbon dioxide coefficients were calculated from gas phase composition and calculation of related dissolved concentration. Methane transfer coefficients were based on calculations from the carbon dioxide coefficients. From mass balances performed on a gas bubble during its simulated growth and ascent to the surface of the liquid, the methane and carbon dioxide contents in the gas bubble appeared to be controlled by the bubble growth process, while the bubble ascent was largely responsible for a slight enrichment in hydrogen.

The effect of processing parameters on the morphology of an immiscible binary blend

Abstract: In this study an immiscible blend of polypropylene(PP) and polycarbonate (PC) was examined. Experiments were carried out in an internal mixer and the objective was to examine the influence of the time of mixing, the speed of rotation of the rotors as well as the effect of time under quiescent conditions on the size and size distribution of the minor phase. The morphology was studied by light and electron microscopy and the photographs were quantitatively analyzed by semiautomatic image analysis. The effect of the time of mixing was studied for up to 20 min at three viscosity ratios for PC dispersed in PP. The most significant particle size deformation and disintegration processes take place within the first 2 min of mixing. After 2 min very little reduction in the size of the minor phase is observed up to 20 min mixing time, although some phase size/time dependence was observed at an intermediate viscosity ratio. The influence of rotor speed was also studied and the results indicate that this blend is insensitive to changes in the speed of rotation of the rotor over a three- to fourfold range. The effect of time at 250°C under quiescent conditions was studied at 7% and 23% composition (volume fraction) for PP dispersed in PC and also for PC in PP. Coalescence coarsening was observed only for 23% PC in PP where the particle size was found to increase by 75% after approximately 90 min at temperature.

Process and apparatus for the mixing and direct emplacement of a two-component bone cement

Abstract: A process and apparatus is disclosed for the mixing and direct emplacement of a bone cement formed from two components, one liquid and one powder, comprising the steps of storing the two components separately in a multichamber container, opening the liquid phase container within one of the said chambers which is not in communication with the outside atmosphere, setting up a negative pressure within the chamber containing the powder phase, causing aspiration of the liquid into the chamber containing the powder, mixing the two phases, compacting the paste obtained, injecting the paste into a cannula and extruding the paste with direct emplacement of the cement.

Lightweight oil and gas well proppants

Abstract: A lightweight oil and gas well proppant made by simultaneously mixing and compacting a milled calcined kaolin clay powder to form green pellets and then drying, screening and sintering the pellets to form proppant pellets having a specific gravity of 3.0 or less and a conductivity of at least 4,200 millidarci-feet and preferably at least 5,100 md-ft as measured by the Stim-Lab method after 50 hours at 8,000 psi and 275° F. in the presence of deoxygenated aqueous 2% solution of KCl.

Effect of mixing on the precipitation of barium sulfate in an MSMPR reactorssss

Abstract: The effect of mixing intensity (power input) on the precipitation/crystallization of barium sulfate in a two-feedstream (sodium sulfate, barium chloride) continuous stirred-tank crystallizer with mixed product removal was investigated through experiments and companion mathematical models. Crystal growth rate and nucleation rate were very sensitive to mixing intensity, with growth rate increasing eightfold and nucleation rate decreasing 100-fold as power input per unit mass was increased from 0.001 to 0.73 m2/s3 (0 to 1,200 rpm stirrer speed). Experimental results at high feed concentration were accurately described by a model accounting for homogeneous nucleation and kinetic growth of particles as well as turbulent mass transfer to particles and turbulent micromixing of feedstreams. The principal mixing effect was due to particle mass transfer, not micromixing. Experiments at low feed concentration were more difficult to model because of a more complex nucleation mechanism and altered particle morphology.

Municipal waste thermal oxidation system

Abstract: An air-starved, batch burn, modular, municipal waste incinerator. It is designed to oxidize unsorted loads of heterogeneous materials in quantities ranging from 5 to 500 tons per 12 to 15 hours. The unique aspect of this system design is that through research in air mixing, air turbulence, and temperature control, it is possible to burn this material with a highly favorable stack emission product, without the need for bag houses, dry scrubbing, or other elaborate down stream air processing equipment. The incinerator includes a primary combustion chamber connected to a secondary combustion unit by a gas transfer tube. Solid material in the primary is oxidized--or gasified--without live flame. This flammable gas stream is vented into the secondary for ignition. Combustion gases from the primary chamber are completely burned in the secondary combustion unit as the gases pass upwardly through the air mixing ring and tangentially disposed re-ignition burners. The tangential orientation of the re-ignition burners forms a vortex of flame through which the combustion gases travel before exiting from the stack.

Recovering clean metal and particulates from metal matrix composites

Abstract: A process is described for removing all reinforcing particles contained in metal matrix composite scrap materials. This new technique involves providing a treatment vessel for holding a melt of an aluminum matrix composite to be recycled. Heating means are provided for heating the contents of the vessel to a temperature in the range of 700°-750° C. Mixing of the melt is carried out by means of a power driven vaned rotary impeller and this impeller is operated under different conditions for different stages of the process. In the first mixing stage, the impeller is operated under vortex-forming conditions and a fluxing salt is added to the melt while a gas is injected through a gas outlet beneath the surface of the melt and near the rotating impeller. This causes the salt to rapidly mix with the melt and the inlet gas, providing a uniform distribution through the melt of gas bubbles each surrounded by a layer of liquid salt. As a second stage of the treatment process, the impeller is operated at a high differential velocity between the impeller and the melt. These conditions cause collisions between the salt-coated bubbles and wetted reinforcing particles such as to de-wet the reinforcing particles and cause the reinforcing particles and salt flux to rise to the surface of the melt. The surface layer that is formed is essentially a powder which can easily be removed leaving a substantially pure metal with its chemical composition unchanged.

Method and device for direct production of nanocapsules

Abstract: The method consists of obtaining a preparation liquid by mixing at least one amphiphilic compound and one aqueous medium with an active substance which is soluble or dispersible in the amphiphilic compound or the aqueous medium, setting in motion the preparation liquid and alternately pressurizing and depressurizing the moving preparation liquid. Applications in the preparation of liposomes.

Device for conversion of chemical energy from hydrocarbons into electric energy by an electrochemical high-temperature process

Abstract: Device for the conversion of chemical energy of hydrocarbons into electric energy by plate-shaped high-temperature fuel cells, arranged like a stack around a central reaction space, on the basis of zirconium oxide as solid electrolyte, wherein gas jet pumps are provided for the transport and mixing of a part of the O2 excess and ballast gas with the gaseous oxygen carrier, as well as for the transport and mixing of a part of the fuel excess and the reaction products with the gaseous fuel, and a central perforated feed pipe and a perforated body with catalyst coating are provided such that endothermic conversion reactions are performed within the central reaction space.

Membrane drying process and system

Abstract: Enhanced air drying or other gas purifications are achieved using purge gas, rather than product gas, to facilitate permeation in membrane systems having substrates adapted to achieve radial mixing and having countercurrent flow patterns and uniform flow of gas over the surface of the membranes.

Multiphase process mixing and measuring system

Abstract: A liquid is supplied to a vessel (10) to form a pool (21) from which it discharges through a venturi. A supply pipe or pipes (12, 30) convey other liquids and/or gases from separate sources or from above the liquid pool into the venturi for mixing with the liquid. The supply pipes can extend through the pool and be perforated (22) to tend to maintain the level of the pool. Associated with the venturi are pressure sensors (40, 41) for measuring flow and a densiometer (52) permitting mass flow rate measurement of gas and liquid phases. The apparatus can be incorporated in a cartridge (60) for reception in a receptacle (61) at a subsea installation.

Hot-water and cold-water mixing device

Abstract: In a hot-water and cold-water mixing device of the type wherein a hot-water side valve element (27) and a cold-water side valve element (28) are provided for regulat­ing the flow rate of hot and cold water, the valve elements (27, 28) are so constructed as to possess a temperature regulating function attained by varying the hot water-to-­cold water mixing ratio depending on a biasing force, and also an automatic pressure regulating function to automati­cally accommodate a sudden pressure change. The water mixing device of the foregoing construction is compact in size and capable of adjusting the final water temperature reliably and speedily.

Process and apparatus for recycling aqueous fluid absorbents fines

Abstract: A process for recycling and reblending dry, difficult to hydrate polymer fines into a water-swellable fluid absorbent polymer gel is disclosed. The process requires feeding the dry polymer fines into a first mixing zone where they are subjected to spraying with water that at least partially hydrates the fines and mixing, substantially simultaneously with the water contact, at high shear such at the fines are substantial completely hydrated without agglomeration. The hydrated fines are then transported from the first zone into a second mixing zone where blending of the hydrated fines with fresh polymer gel occurs at medium shear such that a substantially uniformly blended product results. The resulting process successfully re-introduces fines into the main product stream wherein the resulting product has high aqueous fluid absorbent capacity and good particulate mechanical integrity.

Method and apparatus for cleaning semiconductor devices

Abstract: An apparatus for cleaning semiconductor devices has a mixing section for mixing a chemical solution with pure water A semiconductor substrate to be cleaned is placed on a support An ultrasonic generator applies ultrasonic vibrations to the supplied pure water The mixing section mixes a predetermined chemical solution with the pure water applied with the ultrasonic vibrations and supplies a desired pure water solution onto the semiconductor substrate

A method for the study of turbulent mixing using fluorescence spectroscopy

Abstract: The mixing of two feed streams in a reactor, one with a fluorescent tracer, the other without, results in a fluctuating concentration field, due to the turbulent flow. Fluorescence spectroscopy allows the characterization of the fluctuations at small scale and high frequencies. Measurements have been made with a spatial resolution of about 30 μm and up to a frequency of 5,000 Hz. Methods have been developed to determine the variance (intensity of segregation) and the power spectra. The spectra can be used to calculate the integral scale of the fluctuations, and in some cases the microscale and dissipation rate. Two optical setups are presented, one based on a nonfocused and the other on a focused laser beam. It is shown that only the focused system has sufficiently high laser flux density and sufficiently small measurement volume to give useful results at the desired characteristic size and frequency. As a demonstration of the method, the turbulent mixing in a continuous stirred tank reactor has been studied. Experiments were carried out in a 225 cm3 baffled reactor, stirred by a six-bladed Rushton disk turbine. The effects of stirring speed and position on the mixing were investigated.

Hydrodynamics of a gas-liquid reactor stirred with a multi-impeller system

Abstract: The behaviour of a sparged vessel agitated by two impellers is examined. Three stirrer configurations were tested: double Rushton turbine, Rushton turbine plus a pumping downward mixed flow turbine and a Rushton turbine plus a pumping upward mixed flow turbine. Hydrodynamic regimes, dissipated power and mixing time of the liquid were considered, several regimes were identified both for the bottom impeller and for the upper one

Process for hydroformylation of an olefin

Abstract: A process for hydroformylation of an olefin, which comprises reacting an olefin with carbon monoxide and hydrogen in the presence of a rhodium catalyst having a trivalent organic phosphorus compound as a ligand, wherein the hydroformylation reaction is conducted by two stage reactor systems i.e. a first stage reactor system comprising a reactor or reactors having a mixing characteristic of the liquid phase being substantially of complete mixing type, and a second stage reactor system being a reaction system of a catalyst solution circulating type and comprising a reactor or reactors having a mixing characteristic of piston flow type wherein when the mixing characteristic of the liquid phase is represented by a diffusion model, a non-dimensional number U (hereinafter referred to as a "flow mixing parameter") defined by the formula (I): U = ~L/2~ (I) wherein ~ is an average flow velocity (cm/sec), L is the length (cm) of the reaction layer, and ~ is an average diffusion coefficient (cm2/sec), is at least 0.4, a gaseous product or gas-liquid mixture discharged from the first stage reactor system, is separated into a stream containing the unreacted olefin and other stream, and a part or whole of the stream containing the unreacted olefin is supplied to the second stage reactor system.

Chemical handling and mixing system

Abstract: A chemical handling and mixing apparatus is disclosed, consisting of a chemical loading apparatus in which bulk chemical is mixed with water into an aqueous solution or slurry and an agitation apparatus which receives the aqueous solution or slurry from the chemical loading apparatus and further mixes the solution or slurry to ensure even mixing and delivers the mixed chemical to a pump for storage or use.

Cross-linkable hot-melt adhesive and method of producing same

Abstract: A cross-linkable hot-melt adhesive is prepared by mixing an acid graft modified propylene/olefin copolymer with an epoxy cross-linking agent and a tertiary amine catalyst. The adhesive is cross-linked at an elevated temperature such as when melt mixing the components.

Use of liquid carbon dioxide as a blowing agent in the production of open-cell polyurethane foam

Abstract: A process for the production of an open cell polyurethane foam comprises the mixing of the following components at ambient temperatures in a mixing zone: a diisocyanate having a functionality of at least about 2.0, at least one hydrogen donor, at least one surfactant which is effective in forming an open cell polyurethane foam, at least one catalyst, and a blowing agent comprising a gas having a boiling point below approximately -100°F at atmospheric temperature and pressure which preferably comprises carbon dioxide. In addition, the mixture may also optionally contain water. The mixture is subjected to a pressure in said mixing zone which is sufficient to maintain the blowing agent in the liquid state at ambient temperatures. After mixing the mixture is ejected from the mixing zone to atmospheric pressure, thereby completely and instantaneously vaporizing the blowing agent to provide expansion of the mixture. The resultant foam is then cured at ambient temperatures.

Dual drum recycle asphalt drying and mixing method and apparatus

Abstract: An asphalt drum drying and mixing plant capable of using recycled pavement aggregate material includes two interacting drums, each being heated to different temperatures. A first drum is a parallel flow drying and mixing drum. The recycled material is introduced at the intake or feed end of this first drum and dried and heated to a comparatively low temperature in a first region of the first drum. A burner of relatively lower heat generation capacity furnishes heated gases. The recycled material is protected by supplying the gases through a cylindrical combustion chamber within which the fuel is completely burned such that no luminous gases enter the drum and contact the recycled material. A second, adjacent region of the parallel flow drum is the mixing region. The recycled material is transferred to the mixing region with the close control over the temperature at which the material enters the mixing region. The parallel flow drum also has an intermediate feed chute through which virgin aggregate material is added. The virgin aggregate is heated in a counterflow drum to a temperature higher than the recycled material and the temperature of the final mix is controlled by changing the temperature of the virgin material. The exhaust from the mixing region is introduced as secondary air into the counterflow drum burner assembly. From the counterflow drum all gases are passed to a cleaning system including a cyclone separator and a baghouse filter. From the cyclone separator and the baghouse filter separated material and fines are routed into the mixing region together with liquid asphalt cement.

Spray nozzle for fire control

Abstract: A spray nozzle for fire control produces a spray of gas and liquid having an oval transverse cross-section and comprises a mixing chamber having an oval transverse cross-section adapted to induce a toroidal mixing pattern in pressurized gas and liquid introduced to the mixing chamber through a plurality of inlets. In a preferred embodiment the mixing chamber is toroidal. The spray may be used in fire control systems in vehicles or other confined spaces.

Fluidised bed appts. for mixing, drying and coating bulk solids - has support tube concentrically placed around down pipe to form ring shaped aperture in mixing chamber

Abstract: In globe-shaped fluidised bed plant, bulk goods are mixed. The novelty is that a support tube is concentrically placed around the down pipe to create a ring-shaped aperture in the mixing chamber. Specifically, the mixer comprises a globular housing (1) in which the solids are mixed about the same rotary axis (2), consisting of upper (14) and lower (3) sections made of steel or glass meeting at flanges (15,16). The upper part (14) bears an collector egress unit (17) while the lower (3) section incorporates a reverser basin (4). The down tube (6) passes through the mixing chamber (13, 19) at which point the support tube (11) is affixed by ribs (24). USE/ADVANTAGE - The arrangement reduces fractured mixing of the bulk solids and prevents the formation of hard deposits within the mixer bed. The arrangement is suited for coating catalyst substrates such as are applied in the manufacture of phthalic acid anhydride. The catalyst substrates are formed as balls, cylinders, rings or rods of 5-15 mm radius.