Separation Using Coalescers

A eoaleseer aehieves separation of an oily phase from water on the basis of density differences between the two fluids. These systems obviously work best with non-emulsified oils. Applications historically have been in the oil and gas industry, and hence the most famous oil/water separator is the API separator (API being the abbreviation for the American Petroleum Institute). 

In this diagram the key features are A - Diffusion baffle this serves four roles. First to dissipate the velocity head, thereby improving the overall hydraulic characteristics of the separator. Next, to direct incoming flow downward and outward maximizing the use of the separator volume. Third, to reduce flow turbulence and to distribute the flow evenly over the separator s cross-sectional area. Finally, to isolate inlet turbulence from the rest of the separator. B- Internal chambers In the sediment chamber, heavy solids settle out, and concentrated slugs of oil rise to the surface. As the oily water passes through the parallel corrugated 

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Another type of gravity separator used for small amounts of oily water, the oil interceptor, is widely used both offshore and onshore. These devices work by encouraging oil particles to coalesce on the surface of plates. Once bigger oil droplets are formed they tend to float to the surface of the water faster and can be skimmed off. A corrugated plate interceptor (CPI) is shown below and demonstrates the principle involved. However there are many varieties available. Plate interceptors can typically reduce oil content to 50-150 ppm. 

A liquid-liquid separator used for removing small, usually 2% or less, quantities of one immiscible liquid from another is termed a coalescer. These units are not gravity settlers, but agglomerate the smaller liquid by passing... 

Lipids are insoluble in water and an interfacial tension therefore exists between the phases when lipids are dispersed (emulsified) in water (or vice versa). This tension in toto is very large, considering the very large interfacial area in a typical emulsion (section 3.7). Owing to the interfacial tension, the oil and water phases would quickly coalesce and separate. However, coalescence (but not creaming) is prevented by the use of emulsifiers (surface active agents) which form a film around each fat globule (or each water... 

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. 

Figure 14 shows a very interesting and an important correlation between the rate of coalescence in macroemulsions and the apparent viscosity in the flow through porous media. It was observed that a minimum in apparent viscosity for the flow of macroemulsions in porous media coincides with a minimum in phase separation time at the optimal salinity. This correlation between the phenomena occurring in the porous medium and outside the porous medium allows us to use coalescence measurements as a screening criterion for many oil recovery formulations for their possible behavior in porous media. It is. very likely that a rapidly coalescing macroemulsion may give a lower apparent viscosity for the flow in porous media (53). 

Low shear process will produce larger liquid droplets (>30 microns), and heavy/light liquids can be separated using gravity settling method. Examples of low shear process are solvent extraction, mixer settlers, steam stripping, washing process, and counter-current tower. Coalescer pad can be used to speed up the liquid/liquid separation and reduce the separator size. 

Coalescer pad is either wire mesh pad or corrugated plate pad. Materia of construction can be metal or plastic. In this section, preliminary liquid/liquid separator sizing by surge volume method or using coalescer pad will be... 

The preceding treatment relates primarily to flocculation rates, while the irreversible aging of emulsions involves the coalescence of droplets, the prelude to which is the thinning of the liquid film separating the droplets. Similar theories were developed by Spielman [54] and by Honig and co-workers [55], which added hydrodynamic considerations to basic DLVO theory. A successful experimental test of these equations was made by Bernstein and co-workers [56] (see also Ref. 57). Coalescence leads eventually to separation of bulk oil phase, and a practical measure of emulsion stability is the rate of increase of the volume of this phase, V, as a function of time. A useful equation is... 

Emulsion polymerization also has the advantages of good heat transfer and low viscosity, which follow from the presence of the aqueous phase. The resulting aqueous dispersion of polymer is called a latex. The polymer can be subsequently separated from the aqueous portion of the latex or the latter can be used directly in eventual appUcations. For example, in coatings applications-such as paints, paper coatings, floor pohshes-soft polymer particles coalesce into a continuous film with the evaporation of water after the latex has been applied to the substrate. 

Suspension polymerization of VDE in water are batch processes in autoclaves designed to limit scale formation (91). Most systems operate from 30 to 100°C and are initiated with monomer-soluble organic free-radical initiators such as diisopropyl peroxydicarbonate (92—96), tert-huty peroxypivalate (97), or / fZ-amyl peroxypivalate (98). Usually water-soluble polymers, eg, cellulose derivatives or poly(vinyl alcohol), are used as suspending agents to reduce coalescence of polymer particles. Organic solvents that may act as a reaction accelerator or chain-transfer agent are often employed. The reactor product is a slurry of suspended polymer particles, usually spheres of 30—100 pm in diameter they are separated from the water phase thoroughly washed and dried. Size and internal stmcture of beads, ie, porosity, and dispersant residues affect how the resin performs in appHcations. 

Coalescing. Sand towers or cartridge-type coalescers may be used to separate any undissolved water from the LPG. Removal of the undissolved water meets the specification moisture limit for butanes. However, this step does not produce specification propane. 

The in situ process is simpler because it requires less material handling (35) however, this process has been used only for resole resins. When phenol is used, the reaction system is initially one-phase alkylated phenols and bisphenol A present special problems. As the reaction with formaldehyde progresses at 80—100°C, the resin becomes water-insoluble and phase separation takes place. Catalysts such as hexa produce an early phase separation, whereas NaOH-based resins retain water solubiUty to a higher molecular weight. If the reaction medium contains a protective coUoid at phase separation, a resin-in-water dispersion forms. Alternatively, the protective coUoid can be added later in the reaction sequence, in which case the reaction mass may temporarily be a water-in-resin dispersion. The protective coUoid serves to assist particle formation and stabUizes the final particles against coalescence. Some examples of protective coUoids are poly(vinyl alcohol), gum arabic, and hydroxyethjlceUulose. 

Ammonia has low miscibility in mineral oils, alkylbenzenes, and polyol ester lubricants, particularly at low temperatures. A typical ammonia system uses a coalescing separator that removes all oil in droplet or aerosol form and drains it back to the compressor. Sometimes separators are equipped with some means of cooling the discharge gas to condense any oil that is discharged as a vapor. 

These include the use of coalescers, separating membranes, and electrical devices and the addition of emulsion-breakiug reagents. These last are used for treating permanent enmlsions and whl not be discussed here. 

The relatively complex form of Eq. (11-37) leads to some approximate solutions that were widely used before the modem computer solutions were available. One of these was based on the coalescence temperature. This is the point at which two separate resonances are no longer observable. It can usually be measured to 0.2 °C. The rate constant in either direction at this temperature is... 

Uintaite is not easily water wet with most surfactants. Thus, stable dispersions of uintaite are often difficult to achieve, particularly in the presence of salts, calcium, solids and other drilling fluid contaminants and/or in the presence of diesel oil. The uintaite must be readily dispersible and must remain water wet otherwise it will coalesce and be separated from the drilling fluid, along with cuttings at the shale shaker or in the circulating pits. Surfactants and emulsifiers are often used with uintaite drilling mud additives. 

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