Showing papers on "Countercurrent exchange published in 1986"

Pressure swing adsorption process

Abstract: In air separation and other gas separations employing pressure swing adsorption technology, reduced cycle times are achieved by an advantageous combination of simultaneous processing steps. The gas released upon cocurrent depressurization from higher adsorption pressure is employed simultaneously for pressure equalization and provide purge purposes. Cocurrent depressurization is also carried out at an intermediate pressure level, while countercurrent depressurization is simultaneously carried out at the opposite end of the bed being depressurized to its lower desorption pressure level.

A critical review of the flooding literature

Abstract: Countercurrent flow of a gas and a liquid in direct contact with each other is, of necessity, gravity dominated. That is, in the absence of electromagnetic force fields, thermocapillary effects, or concentration-capillary effects, countercurrent flow can be sustained only as a result of the difference in the gravitational force per unit volume on the gas and on the liquid. If the gas and liquid are simultaneously introduced into a porous medium or into a vertical or inclined pipe, the gas tends to rise relative to the liquid. If conditions allow complete separation, it is possible to maintain steady countercurrent flow in which the liquid discharges at the bottom while the gas flows out from the top. The countercurrent flow is opposed by interfacial friction between the phases, which always seems to increase monotonically as the relative countercurrent mean velocity of the phases increases. Hence, for a given geometry and liquid-gas pair, there is a maximum relative velocity that can be sustained in countercurrent flow. This point is known as the onset of flooding. Further increases in gas or liquid input ratas result in only partial delivery of the liquid out of the bottom. Eventually, if the gas velocity becomes sufficiently high, none of the liquid is delivered at the bottom, and fully cocurrent upward flow is established. If the liquid is being introduced from an upper plenum, none will penetrate into the pipe or porous medium when this second critical gas velocity is reached.

Entropy Generation in a Heat Exchanger

Abstract: The entropy generation (irreversibility) concept founded on the second law of thermodynamics may be applied in heat exchanger analysis. In this paper the quantity termed enthalpy exchange irreversibility norm (EEIN) is the measure of the internal heat exchanger irreversibilities. The behavior of EEIN as a function of the heat exchanger thermal size is discussed for an arbitrary flow arrangement and more precisely for two characteristic limiting cases: cocurrent and countercurrent heat exchangers.

Enhanced pressure swing adsorption processing

Abstract: A feed gas is passed to a pressure swing adsorption system, each bed of which undergoes a processing cycle that includes (1) pressurization (2) copurge at upper adsorption pressure, (3) countercurrent depressurization, including, in some embodiments, evacuation to a lower subatmospheric desorption pressure. By recycling effluent gas released upon copurge and countercurrent depressurization for use in the pressurization or the copurge step, the more readily adsorbable component of the feed gas is advantageously recovered at high purity and at high recovery levels. Enriched less readily adsorbable component is also recoverable as coproduct effluent at relatively high recovery levels. The process can be advantageously employed for the separation and recovery of product nitrogen from air.

Pass-through furnace for heat recovery in the heat treatment of aggregates of metallic articles or parts

Abstract: For recovery of heat, aggregates of metallic articles through which gas can flow are carried in a succession of baskets through a preheat zone, a treatment zone and a cooling zone of a heat treatment furnace and a heat transfer gas is constrained to flow vertically through the baskets in succession, beginning with the basket farthest advanced through the furnace, so far as concerns the basket in the cooling and preheat zone, the baskets having bottoms through which the gas can flow into or out of the aggregates. The heat transfer gas flows directly from the cooling zone. This may be done through the treatment zone where it may pick up additional heat. Heat may be removed from the heat transfer gas in a return circulation path outside the furnace. When the path of the basket is horizontal through the preheat and cooling zones, the flow of heat transfer gas is in transverse countercurrent to the advancement of the work, but if vertical transport of baskets is provided in the preheat and cooling zones, simple countercurrent operation can be provided with vertical flow through the baskets and aggregates. The ratio of heat capacity flow of the work to that of the heat transfer gas in the cooling and/or preheat zones is controlled to keep these heat capacity flows approximately equal and the preheat and cooling zones are so designed that the thermal exchange coefficient epsilon between the work and the heat transfer gas is consistently greater than 0.5.

A Study of the Graetz Problems in Concentric-Tube Continuous-Contact Countercurrent Separation Processes with Recycles at Both Ends

Abstract: A mathematical model for the concentric-tube square-off continuous-contact countercurrent separation process with recycles at both ends is developed to predict the concentrations of product. An analytical solution is obtained by means of the orthogonal expansion method. It has been found that only the positive eigenvalues for the enriching section and the negative eigenvalues for the stripping section are required during the calculation of the concentrations of product. Numerical results are presented for the separation of a benzene-n-heptane mixture in a concentric-tube thermal diffusion column.

Countercurrent Gas-Liquid Flow in Boiling Channels

Abstract: Countercurrent gas-liquid flow is theoretically and experimentally evaluated for a boiling system simulating a BWR core. In a single channel, flow patterns are determined from the mass balance equations and pressure drop under steady state conditions is calculated for each flow pattern using a drift flux model, where the distribution parameter and drift velocity are correlated as functions of void fraction and hydraulic diameter from void fraction data. The calculated pressure drop shows a similar trend to that of the data for the effects of bypass leak flow rate and heater power. Countercurrent behavior in three boiling channels under slow transient conditions is also predicted from the single channel characteristics and close agreement is obtained between the predicted and experimental results. The results show that steam up-flow or cocurrent up-flow easily occurs in a channel with low pressure drop, namely, with a large entry orifice, high power or low bypass leak flow rate.

Hollow fiber gas permeator with countercurrent or cocurrent flow: series solutions

Abstract: The problems in the numerical solution of boundary value problems encountered in hollow fiber binary gas permeatbrs having cocurrent or countercurrent permeate flow with axial pressure drop inside the fiber bore are discussed. A series solution technique is developed to express each product composition and the pressure ratio as a power series in terms of a dimensionless membrane area for shell side constant-pressure feed flow. Cocurrent or countercurrent rating or design problems require the solution of elther one algebraic equation, two coupled algebraic equations, or three coupled algebraic equations to determine the unknown quantities of interest. Calculated product and reject compositions, stage cuts, and closed-end pressure ratios compare quite well with those from numerical solutions for practically useful low to moderate cuts over a wide range of parameters. Cocurrent rating calculations requiring solution of only one algebraic equation are recommended for shortcut procedures since flow pattern effects are significant but not large.

Kinetics of Continuous Hydrolysis of Olive Oil by Lipase in Microporous Hydrophobic Membrane Bioreactor

Abstract: Kinetics of the continuous hydrolysis of olive oil by Candida cylindracea lipase in a microporous hydrophobic membrane bioreactor (flat membrane or hollow fiber module) was studied. A general equation for outlet conversion was derived on the assumption that flow of oil is of plug-flow type when the reversible Michaelis-Menten equation was applied in “surface phase”. The cases of first-and zero-order kinetics and the diffusion-controlled case through micropores were also analyzed as limiting cases. The theoretical considerations indicate that the flow rate of oil divided by the total membrane area, F/A, is an important operating parameter which governs the performance of the microporous hydrophobic membrane bioreactor. Analyses of batch lipolysis data reported by three research groups showed that the hydrolysis reaction of oil obeyed the first-orded reversible kinetics. Experimental data for the flat membrane bioreactor (countercurrent operation) obtained by the authors agreed with the reversible first-order kinetics in a wide range of F/A, while the data for the hollow fiber module (countercurrent operation) agreed with the reversible first-order kinetics only at higher F/A. Lower rates of hydrolysis at lower F/A seemed to be due to non-uniform flow of oil through the hollow fibers. The new concept of “equivalent droplet size” is proposed to compare the performance of the membrane bioreactor system with that of the emulsion system.

An improved adsorption process for the production of high-fructose syrup

Abstract: By applying a temperature profile to the system, the concentration of the extract product in a countercurrent adsorption separation process may be increased relative to the maximum concentration attainable under isothermal conditions. To achieve the required temperature profile in a simulated countercurrent system it is necessary to heat and cool the columns in sequence as the feed and product draw-off points are switched through the bed. The practical feasibility of operating the system in this way has been demonstrated experimentally for the separation of glucose-fructose mixtures. By maintaining a temperature difference of 30–35°C across the bed an extract product containing 28% fructose and about 1% glucose was obtained, at steady state, from a feed containing 25 wt. % of each sugar.

Novel gas-liquid-solid reactors

Abstract: Multiphase reactors involving gas, liquid, and solid phases have several important applications in the chemical industry, particularly in catalytic processes. Some of the well-known examples are: hydrogenation and oxidation of organic compounds, hydro-processing coal-derived and petroleum oils, Fischer-Tropsch synthesis, and methanation reactions. Due to the presence of three phases, the problem of reactor design is often important to achieve effective mass and heat transfer as well as a mixing pattern favorable to the particular process. The reactors are mainly of two types: (a) solid catalyst is suspended either by mechanical agitation or gas-induced agitation and (b) solid catalyst is in a fixed bed with concurrent or countercurrent feed of gas and liquid re-actants. The reactor types conventionally used in industry are: (a) mechanically agitated or bubble column slurry reactors and (b) trickle-bed or packed-bed bubble reactor. The various design and modeling aspects of these reactors have bee...

Multistage arrangement for countercurrent separation and methods of operating same

Abstract: A multistage arrangement for countercurrent separation of suspended solids, such as crystals, by means of hydro-cyclone groups connected in series and corresponding pumps and pump wells. For operating with relatively small expenditures with respect to apparatus under high pressures and at high temperatures within a certain, limited temperature range, the hydro-cyclone groups, the pump wells with pumps projecting into the pump wells, and the essential parts or regions of the lines are placed in a common pressure-proof and heat-insulated chamber. In addition, for removing coarser crystallizations and solid particles, an upstream classifier also accommodated in the chamber may be provided. The multistage arrangement can be used in a process for the production of terephthalic acid from dimethyl-terephthalate as the intermediate product, and in a process for the hydrogenation of coal.

Method and apparatus for drying low grade coal

Abstract: A method and apparatus for drying low-rank coals, such as lignite, where the coal is passed through a sealed vessel in a plurality of heated fluidized beds, with fluidization effected by superheated steam flowing countercurrent to the coal flow. A composite steam is exhausted from the sealed vessel and passed to a vessel where water is sprayed therein to cool the same and remove occluded solids. A first portion of the steam is then reheated and returned to the sealed vessel as fluidizing steam, while a second portion of the steam is heated and passed through heat exchange tubes in the sealed vessel to heat the fluidizing coal, with the second portion, after passage through the heat exchange tubes discharged from the system.

Ozone-producing process

Abstract: Each ozonization loop (1) which includes a compressor (2), an ozonizer (3), and a heat exchanger (8) for cooling the oxygen-ozone mixture, is associated with three cylinders (4,5,6) filled with silica gel. Each cylinder operates in succession in a cocurrent adsorption, in countercurrent desorption by a substitution gas, and in scavenging by taking off a part of the flow circulating in the loop. The scavenging flow is recovered and combined with the substitution gas. The substitution gas may be in particular impure nitrogen supplyed by an air distillation apparatus producing the necessary oxygen.

Trace Ions in Countercurrent Electrolysis in a Thin, Porous Membrane

Abstract: The transport of trace ions added to a binary electrolyte system through a porous membrane during countercurrent electrolysis has been studied both theoretically and experimentally. Theoretical models based both on the general transport equations and on the Nernst-Planck equations are presented. Experiments and calculations for the binary system NaCl-H2O with trace ions Li+ and K+ were performed. The theoretical model was able to predict the transport phenomena fairly well.

Gas separation by means of a porous membrane with cocurrent and countercurrent flows

Abstract: Methode de calcul des separateurs de gaz a membrane poreuse, utilisant la formule de Present et de Bethune comme equation de permeation de base. L'accord est bon avec des resultats experimentaux obtenus a cocourant et a contrecourant

Countercurrent heat exchanger

Abstract: In known countercurrent heat exchangers for the aeration and deaeration of stables, the foul-air guidance does not always run vertically, since the lower ends of the throughflow ducts for the foul air are curved towards one side. As a result, foreign bodies and condensation water collect in the curves. The novel countercurrent heat exchanger is to avoid obstruction by means of vertical foul-air guidance. The throughflow ducts (22) of the novel countercurrent heat exchanger serve to supply the fresh air (52) and open at their upper ends (28) into sucking-in ducts (30), each of which connects a row of throughflow ducts (22) and is laterally linked to supply-air openings (46) of the heat exchanger constructed as a chimney (10). The countercurrent heat exchanger is particularly suitable for the aeration and deaeration of stables.

The Effect of Membrane Thickness on Countercurrent Electrolysis in a Thin, Porous Membrane

Abstract: The effect of membrane thickness on countercurrent electrolysis in a porous membrane is studied and compared with the increase of convection. It was verified both theoretically and experimentally that the separation efficiency increases considerably when the membrane is made thicker. When the fluxes of ions to be separated deviate from zero, no simple relationship between the logarithm of selectivity ratio and convection could be found. Both computed and measured results showed that IgS =f(vc ) is strictly nonlinear. Results show that in the light of separation efficiency it is more useful to use higher convections than thicker membrane. This is, of course, done at the cost of increased power consumption. Therefore, in practice the most reasonable approach is a compromise between increased convection and making the membrane thicker.

Processing of high normal paraffin concentration naphtha feedstocks

Abstract: Normal paraffins present in high concentrations in light naphtha streams are separated from non-normal paraffins in a four or more bed adsorption system employing, on a cyclic basis, the processing steps of (1) cocurrent purge/adsorption, (2) cocurrent feed/adsorption, (3) countercurrent purge and (4) countercurrent displacement. A processing sequence is employed wherein the cocurrent purge/adsorption and countercurrent purge steps are carried out on a discontinuous basis, while cocurrent feed/adsorption and countercurrent displacement steps are carried out in overlapping sequence. Control means are provided to assure that the high normal paraffin-containing hydrocarbon feed gas and stripping gas are passed to the appropriate beds for said cocurrent purge/adsorption and countercurrent purge steps on a non-continuous basis, said feed gas being continuously fed to a mix drum for mixture with countercurrent purge effluent before removal for use in said cocurrent purge/adsorption step and in said cocurrent feed/adsorption step of the overall four-step process.