Horizontal coalescer

Generally, vertical or horizontal coalescer-separator vessels for fuels are fabricated from carbon steel, coated internally with various linings such as epoxy resin. Applications include their use in refuelling facilities around the world, helicopter and VTOL support bases, with large capacity units used for bunkering or fuel distribution depots. 

Gravity Settlers Decanters These are tanks in which a liqmd-liquid dispersion is continuously settled and coalesced and from wriich the settled liquids are continuously withdrawn. They can be either horizontal or vertical. Figure 15-24 shows some typical horizontal decanters. For an uninstrumented decanter the height of the heavy-phase-liquid leg above the interface is balanced against the height of the hght-hquid phase above the interface, Eq. 15-50. 

An empty vessel may be employed, but horizontal baffles can be used to reduce turbulence and assist the coalescence through preferential wetting of the solid surface by the disperse phase. More elaborate methods to assist the coalescence include the use of mesh pads in the vessel or the use of an electric field to promote coalescence. Chemical additives can also be used to promote coalescence. 

Fig. 9.24 Basic phenomena of drop coalescence at a horizontal interface. The drop has to reach the interface. A thin layer of the continuous phase remains between the drop and the interface. The thin layer has to drain until it breaks up. Then the drop can flow into its homophase. Mostly, the drainage process is the time-determining step of this process. 

Large particles with a mean diameter greater than 600 Um and a density above 4000 kg m are classed as group D and whereas in Geldart B beds the bubbles tend to rise faster than the gas in the dense phase, the reverse is true of bubbles in Geldart D particle beds. Bubbles tend to coalesce horizontally rather than vertically and reach a large... 

When a drop (water) falls to a flat interface (benzene-water) the entire drop does not always join the pool (water). Sometimes a small droplet is left behind and the entire process, called partial coalescence, is repeated. This can happen several times in succession. High-speed motion pictures, taken at about 2000 frames per second, have revealed the details of the action (W3). The film (benzene) ruptures at the critical film thickness and the hole expands rapidly. Surface and gravitational forces then tend to drag the drop into the main pool (water). But the inertia of the high column of incompressible liquid above the drop tends to resist this pull. The result is a horizontal contraction of the drop into a pillar of liquid above the interface. Further pull will cause the column to be pinched through, leaving a small droplet behind. Charles and Mason (C2) have observed that two pinches and two droplets occurred in a few cases. The entire series of events required about 0.20 sec. for aniline drops at an aniline-water interface (C2, W3). 

Wallis points out that, from continuity considerations and bubble dynamics, the cocurrent flow of uniformly dispersed bubbles as a discontinuous phase in a liquid can always be made to occur in any system and for any void volume. (This is not true for countercurrent flow.) Coalescence of bubbles may occur, of course, and if this coalescence is sufiiciently rapid, a developing type of flow is observed, usually from bubble to slug flow. Because of this behavior, the particular flow pattern observed in bubble flow is quite dependent on the previous history of the two-phase mixture. This would be true for both horizontal and vertical flow. 

Fig. 1— Horizontal separator employs four basic mechanisms to liberate gaa from liquid. Inlet diverter imposes a sudden direction and momentum change on the flowstrearn, causing heavier liquids to drop out. Gravity settling section provides opportunity for smaller droplets to leave gas stream, and mist extractor coalesces remaining liquids as gas exits vessel. In addition, entrained gas escapes In liquid collection section.

Another type of separator used in certain high-gaa/low-liquid flow applications is a filter separator. These can be either horizontal or vertical in configuration. Fig. 4 shows a horizontal design. Filter tubes in the initial separation section coalesce liquid mist into larger droplets as gas passes through the tubes. A secondary section, consisting of vanes or other mist extractor elements, removes these coalesced droplets. 

Fig. 2—Muftiweil installations normaRy employ horizontal treaters Flow enters from le t on d. iwing and is coml.K-ted tn a spm.vVr o liquid-filled coalescing section on ngnc...

Fig. 3—Except lor electrodes in coalescing section, electrostatic treaters are simriar to other horizontal-type treaters.

Electrostatic treaters. Fig. 3 illustrates a typical horizontal elrrirostatir treater. The flow path in an electrostatic treater di- -am- - in a hi-i i/unt il hcan-r-trc.in-r. th- n il - difference is that an AC and/or DC electrostatic field is used to promote coalescence of water droplets. 

It should hr noted that the height of the coalescing section in a vertical treater does not enter into the settling equation The < ros -se< tional area of flow for upward velocity of oil is a function of vessel diameter alone In a horizontal vessel, the cross-sectional area for flow nfoil upward is a function of diarnctc-f tunes length of the coalescing section. 

Fig. 9—Graph establishes dimensional ranges of horizontal heater-treater an example problem Diameter and coalescing section dimensions must fall outside shaded area for adequate treatment tame...

Fig. 4—Plait coalescers employ plates mounted at an angle to the horizontal.

Parallel-plate interceptor. The first form of plate coalescer was the parallel-plate interceptor (PPI). This involved installing a series of plates parallel to the longitudinal axis of an API separator (a horizontal, rectangular cross-section skimmer). When viewed perpendicular to the axis of flow, the plates form a "V so that the oil sheet migrates up the underside of the coalescing plate and to the sides Sediments migrate toward the middle and down to the bottom of the separator where they are removed. 

Irnrr and retention time for droplrts to coalesce A pipe diameter is chosen that is large enough to present coalesced 1 droplets from shearing in accordance with the dispersion equation discussed in the previous installment. In effect, the unit grows a droplet distribution curve in the inlet stream that can then be treated in the tank or flume. Fig. 1 shows an ( installation using SP packs in a series of tanks Fig. 2 shows an installation in a series of compartments in a horizontal flume such as a barge bull or a pit. 

Polyurethane sponge foam. One fabricator offers a coalescer design employing an open-celled polvure-thane foam in a horizontal tank (Fig 4). 

The clean water flows horizontally through the unn and falls into the clean-water outlet chamber overflowing the adjustable water-outlet weir plates. The height of this water weir as measured from tank inside bottom decides ihc working level of the coalescer unit A sheen baffle is located just before (lie water-outlet weir. The sheen baffle captures small oil droplets that might pass undet the oil-retention baffle. The buildup of oil film at the sheen baffle is so slow that no skimming device is required This oil buildup gets hack into the separation chamber when the unit is shut down for planned maintenance purposes... 

Figure 5-51 (A) The low-field region of the one-dimensional H NMR spectrum of E. coli tRNAjVal at 27°C in H20. Resonances are identified by letters A - X. (B) NOESY spectrum of the same tRNA under similar conditions showing the imino-imino NOEs. In the lower right sector the connectivity traces of the acceptor helix and dihydrouridine helix are shown as solid and dotted lines, respectively. In the NOESY sample the two protons in peak EF are partially resolved whereas the two protons in peak T have coalesced. (C) NOESY spectrum of E. coli tRNA,Val at 32°C showing the imino and aromatic proton regions. AU-type imino protons have been connected horizontally by a dotted line to the cross-peak of their proximal C2-H or C8-H in the 7 to 9 ppm region, which has been labeled with the corresponding lower-case letter. From Hare et al.669 Courtesy of Brian Reid.

An interesting class of exact self-similar solutions (H2) can be deduced for the case where the newly formed phase density is a function of temperature only. The method involves a transformation to Lagrangian coordinates, based upon the principle of conservation of mass within the new phase. A similarity variable akin to that employed by Zener (Z2) is then introduced which immobilizes the moving boundary in the transformed space. A particular case which has been studied in detail is that of a column of liquid, initially at the saturation temperature T , in contact with a flat, horizontal plate whose temperature is suddenly increased to a large value, Tw T . Suppose that the density of nucleation sites is so great that individual bubbles coalesce immediately upon formation into a continuous vapor film of uniform thickness, which increases with time. Eventually the liquid-vapor interface becomes severely distorted, in part due to Taylor instability but the vapor film growth, before such effects become important, can be treated as a one-dimensional problem. This problem is closely related to reactor safety problems associated with fast power transients. The assumptions made are ... 

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