Phase feeding

Fig 18. Experimental trickle-bed system A, tube bundle for liquid flow distribution B, flow distribution packing of glass helices C, activated carbon trickle bed 1, mass flow controllers 2, gas or liquid rotameters, 3, reactor (indicating point of gas phase introduction) 4, overflow tank for the liquid phase feed 5, liquid phase hold-up tank 6, absorber pump 7, packed absorption column for saturation of the liquid phase 8, gas-liquid disengager in the liquid phase saturation circuit. (Figure from Haure et ai, 1989, with permission, 1989 American Institute of Chemical Engineers.)... 

In general all materials used to catalyze reactions of a vapor phase feed are calcined or activated at temperatures above 400 to 500 °F. This heat treatment may accomplish one or more of the following tasks. 

Hammershpj M. and Kjaer J.B. (1999). Phase feeding for laying hens effect of protein and essential amino acids on egg quality and production , ActaAgriculturaeScandinavica, Section A - Animal Science, 49, 31-41. 

Cocurrent means that the air flow and the solid phase have the same direction, see Figure 27A. Countercurrent correspond to opposite flows, see Figure 27C. In a crosscurrent system the solid phase feed and the air flow cross each other, see Figure 27B. 

The size of settlers is determined by the rate of phase disengagement, which, here, is a function of the solvent concentration of LIX 64N and the aqueous phase feed rate. The capital cost of extraction equipment is a function of the number of tanks, the size of the tanks, and the solvent inventory [9] ... 

Figure 4 is a diagram of the experimental unit. In its operation the two-phase feed of brine and methylene chloride enters the flash column. Ice slurry forms in the upper part of the column as the methylene chloride vaporizes, and the slurry is transferred by the slurry pump to the glass tee at the bottom of the separation column. In the glass tee, the ice floats into the separation column, where it is washed and removed. The brine recycles from the bottom of the separation unit to the ice generator by joining a stream of fresh feed and liquid refrigerant. 

The feed stream mixes with the feed-stage fluids prior to any separation. This assumption is good for a single-phase feed, but less satisfactory for a partially vaporized feed (11). A partially vaporized feed splits prior to mixing the feed liquid then mixes with liquid of the tray below, while vapor mixes with vapor of the tray above. Ledanois and Olivera-Fuentes (11) derived a simple correction to the x-y diagram construction to alleviate the inaccuracy. Their correction is valid where tray efficiency is high (i,e,f above 60 to 70 percent) at lower tray efficiencies, the inaccuracy is more difficult to quantify. 

The values of vy and Xp may be obtained from an adiabatic flash for a single phase feed or from the constant relative volatility estimated with the converged compositions at the feed stage and feed quality. This procedure can be reformulated for multiple feeds and side products as well as different key components. A pinch point near the feed stage occurs for nearly all binary ideal mixtures. However, for nonideal multicomponent systems, the pinch point exists in rectifying and stripping sections. 

These separations are usually carried out by pervaporation (see Section 10.5) or vapor permeation but they have also been performed using gas-phase feeds on organophihc [75] or hydrophilic membranes [76]. On organophdic membranes the permeation of the organic or less polar compound is favored, while the opposite trend is expected for hydrophilic membranes. 

As seen in Figure 13.8, hydrophilic membrane discs are hxed on a horizontal shaft and their lower parts are immersed to compartments, which are hlled with the feed and strip solutions. The remaining parts of the discs, in which aqueous phases (feed or strip) are immersed, due to rotation, are in contact with the LM phase. Mass transfer of the solute from the feed into the strip solutions occurs through the BLM phase. 

These methods for obtaining coalescence frequencies in batch systems have been extended to continuous-flow systems (C13, K13). Komasawa (K13) derived the appropriate model for flow systems assuming uniform drops present and two dispersed-phase feed streams entering the vessel, one with dye and the other without. The result is... 

Curl and co-workers (R15, R16, VI1) have measured coalescence frequencies in a continuous flow vessel by introducing two dispersed-phase feed streams containing different concentrations of dye. Samples removed from the vessel are analyzed by a specially designed photometer that measures the bivariate drop volume-dye concentration distribution in the dispersion (see Fig. 4). The appropriate equation for obtaining oa in this... 

Groothuis and Zuiderweg (GIO) measured coalescence frequencies for continuous-flow dispersed-phase systems by introducing two streams of dispersed phase feed with different densities such that if a drop of one stream coalesces with a drop of the other stream, the new drop will be heavier than the continuous phase. Coalescence frequencies were then estimated by measuring the change in dispersed-phase fraction heavier than water as it passes through the vessel. 

Regardless of its mechanical configuration, the extractor brings two liquid phases (feed and solvent) into intimate contact to allow transfer of solute from the feed to the solvent. The process yields two streams, the cleaned stream or raffinate and the extract or solute-laden solvent stream. Both streams will contain extraction solvent and may require further processing to remove and/or recover the solvent and solute. 

Vane vapor distributors use directional vanes to ensure vapor distribution of a vapor stream. Vane-type distributors are commonly used for distribution of high-velocity, mixed-phase feeds. Various proprietary and patented designs are in use. Both radial entry and tangential entry designs are available. Tangential entry designs are the better choice for two-phase flows. However, radial entry designs will work acceptably for most applications. 

For a mixed phase feed, that is part vapor and part liquid, at Tf and Pf, the liquid portion joins the liquid leaving the feed tray and the vapor portion joins the vapor leaving it. The amount of liquid is qF and that of the vapor is (1 - q)F. For a partially vaporized feed, q is equal to the liquid fraction (0 < 7 < 1). 

A column operator can control the column performance by manipulating the reboiler and condenser duties. Consider starting up a column with a mixed-phase feed introduced at some intermediate tray between the condenser and reboiler. With no condenser or reboiler duties, the liquid flows down the column and out as bottoms, and the vapor flows up the column and out as overhead. The column thus acts as a flash drum. 

To complete the construction of the Y-X diagram from simulation results, the feed line must be drawn. The intersection with the diagonal of a straight line drawn through the feed composition determines one point on the q-line. One other point is determined by the feed equilibrium vapor and liquid compositions at the feed tray conditions. If the feed is a saturated liquid, the equilibrium liquid composition is the same as the feed composition, and the equilibrium vapor composition is the bubble point composition on the equilibrium curve. In this case the q-line is vertical. For a saturated vapor feed, the equilibrium vapor composition is the same as the feed composition, the equilibrium liquid composition is the dew point composition, and the q-line is horizontal. For a mixed-phase feed, the c/ line slope is determined by the feed thermal condition (Section 5.2.2). Note that, for a multi-component mixture, the feed equilibrium vapor and liquid compositions from the simulation output may not lie exactly on the equilibrium curve because of the discrepancies resulting from lumping the light components in one pseudocomponent. 

L Liquid phase solvent and extract M Mixture point N Number of stages Q Liquid phase feed and raffinate R Raffinate 5 Solvent X Mole fraction A Difference point... 

Activated carbon is the most common adsorbent due to its large surface area per unit mass (300 to 1,500 m /g). The surface area per unit volume and the pore-size distribution vary depending on whether the application is for liquid- or gas-phase feed streams. Larger pore sizes are used for liquid-phase streams (30-A-diameter, as opposed to the 10-25-A-diameter carbons used for gas-phase feeds) due to the larger size of the sorbates and the slower diffusion rates for liquids. 

Membrane fouling, especially with liquid-phase feeds, causes flux decline and can reduce lifetime. 

The molecular formula of the solute may suggest the type of solvent which maybe selective for its extraction, based on probable affinities between related functional groups. Thus, to extract organic acids or alcohols from water, an ester, ether, or ketone (of sufficient molecular weight to have very limited solubility in the aqueous phase) might be chosen as the solvent. The pH of aqueous phase feeds may also be very important. The sodium or potassium salts of an organic salt may well prefer the aqueous media at pH >10, but in the acidulated form may readily extract into the organic phase if the pH is low. 

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