Combinational coalescing

FIG. 15-25 Combination coalescer, settler, and membrane separator. (Courtesy of Selas Corporation of Ametica. )... 

The combination coalescer and flotation system and the dissoJvod-gas flotation sy steal require chemical additives, in addition To the continuously routing machinery, to keep the entire unit operating. These requirements are not favorable for our operating conditions. 

Secondary components of the system are a gas processing train and gas storage vessel. The gas processing train can include different components such as scrubbers, catalytic combiners, coalescers, filters and flashback arrestors. Its purpose is to remove particulate contamination, purify the gas stream, and remove excess water or other liquids. 

Feed >10% v/v, or contamination present, or ill-behaved, size as coalescence controlled. For vertical decanters, allow a total residence time that depends on density difference and interfacial surface tension. For a typical 0.5-m height of coalescent band (or a decanter of 0.7-m height), use an overflow total flow rate velocity of 1.5 (Ap/0.1)° L/s m, where the density difference is in units of Mg/m to determine the horizontal cross-sectional area. For horizontal configurations, use half of the vertical overflow velocity. Can add parallel plates or high- and low-energy combination coalescer promoters (see size increase, liquid-liquid. Section 16.11.9.2). 

Can add parallel plates or high and low energy combination coalescer promoters (see Section 9.2). 

Combinational coalescing is implemented by clustering the BIF based on data-flow dependencies. Logic operations are gathered into a cluster subject to the restriction that no sequential operations exist that both reference the outputs of operations in the cluster and produce outputs that are referenced by operations in the cluster. The algorithm is straightforward and is not described here. 

It is quite clear, first of all, that since emulsions present a large interfacial area, any reduction in interfacial tension must reduce the driving force toward coalescence and should promote stability. We have here, then, a simple thermodynamic basis for the role of emulsifying agents. Harkins [17] mentions, as an example, the case of the system paraffin oil-water. With pure liquids, the inter-facial tension was 41 dyn/cm, and this was reduced to 31 dyn/cm on making the aqueous phase 0.00 IM in oleic acid, under which conditions a reasonably stable emulsion could be formed. On neutralization by 0.001 M sodium hydroxide, the interfacial tension fell to 7.2 dyn/cm, and if also made O.OOIM in sodium chloride, it became less than 0.01 dyn/cm. With olive oil in place of the paraffin oil, the final interfacial tension was 0.002 dyn/cm. These last systems emulsified spontaneously—that is, on combining the oil and water phases, no agitation was needed for emulsification to occur. 

Emulsion Adhesives. The most widely used emulsion-based adhesive is that based upon poly(vinyl acetate)—poly(vinyl alcohol) copolymers formed by free-radical polymerization in an emulsion system. Poly(vinyl alcohol) is typically formed by hydrolysis of the poly(vinyl acetate). The properties of the emulsion are derived from the polymer employed in the polymerization as weU as from the system used to emulsify the polymer in water. The emulsion is stabilized by a combination of a surfactant plus a coUoid protection system. The protective coUoids are similar to those used paint (qv) to stabilize latex. For poly(vinyl acetate), the protective coUoids are isolated from natural gums and ceUulosic resins (carboxymethylceUulose or hydroxyethjdceUulose). The hydroHzed polymer may also be used. The physical properties of the poly(vinyl acetate) polymer can be modified by changing the co-monomer used in the polymerization. Any material which is free-radically active and participates in an emulsion polymerization can be employed. Plasticizers (qv), tackifiers, viscosity modifiers, solvents (added to coalesce the emulsion particles), fillers, humectants, and other materials are often added to the adhesive to meet specifications for the intended appHcation. Because the presence of foam in the bond line could decrease performance of the adhesion joint, agents that control the amount of air entrapped in an adhesive bond must be added. Biocides are also necessary many of the materials that are used to stabilize poly(vinyl acetate) emulsions are natural products. Poly(vinyl acetate) adhesives known as "white glue" or "carpenter s glue" are available under a number of different trade names. AppHcations are found mosdy in the area of adhesion to paper and wood (see Vinyl polymers). 

Coalescence and Phase Separation. Coalescence between adjacent drops and between drops and contactor internals is important for two reasons. It usually plays a part, in combination with breakup, in determining the equiHbrium drop si2e in a dispersion, and it can therefore affect holdup and flooding in a countercurrent extraction column. Secondly, it is an essential step in the disengagement of the phases and the control of entrainment after extraction has been completed. 

Many different combinations of surfactant and protective coUoid are used in emulsion polymerizations of vinyl acetate as stabilizers. The properties of the emulsion and the polymeric film depend to a large extent on the identity and quantity of the stabilizers. The choice of stabilizer affects the mean and distribution of particle size which affects the rheology and film formation. The stabilizer system also impacts the stabiUty of the emulsion to mechanical shear, temperature change, and compounding. Characteristics of the coalesced resin affected by the stabilizer include tack, smoothness, opacity, water resistance, and film strength (41,42). 

Although the thermodynamic aspects of acylotropy are well documented, there have been few kinetic studies of the process. The activation barrier is much higher than for prototropy and only Castells et al. (72CC709) have succeeded in observing a coalescence phenomenon in H NMR spectra. At 215 °C in 1-chloronaphthalene the methyl groups of N-phenyl-3,5-dimethylpyrazole-l-carboxamide coalesce. The mechanism of dissociation-combination explains the reversible evolution of the spectra (Scheme 9). 

Figure 15-25 shows a combination device containing coalescers and both hydrophobic and hydrophilic separating membranes. Coalescers... 

Modehng growth where deformation is significant is more difficult. It can be assumed that a critical cutoff size exists tr> which determines which combination of granule sizes are capable of coalescence, based on their inertia. When the harmonic average of sizes of two colliding... 

Foam persistence increases with rise in BW TDS because the bubbles are stabilized by the combined repelling forces of electrical charges at the steam-water interface that result from the high concentration of dissolved salts. The repulsion effect of similar charges prevents bubble thinning, bubble rupture and coalescence mechanisms from taking place. 

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