Oils systems coalescing separators

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. 

For any pure chemical species, there exists a critical temperature (Tc) and pressure (Pc) immediately below which an equilibrium exists between the liquid and vapor phases (1). Above these critical points a two-phase system coalesces into a single phase referred to as a supercritical fluid. Supercritical fluids have received a great deal of attention in a number of important scientific fields. Interest is primarily a result of the ease with which the chemical potential of a supercritical fluid can be varied simply by adjustment of the system pressure. That is, one can cover an enormous range of, for example, diffusivities, viscosities, and dielectric constants while maintaining simultaneously the inherent chemical structure of the solvent (1-6). As a consequence of their unique solvating character, supercritical fluids have been used extensively for extractions, chromatographic separations, chemical reaction processes, and enhanced oil recovery (2-6). 

A significant discovery was made in the 1990s when a mixture of soy oil and com starch was passed through an excess steam jet cooker. The resulting starch dispersion contained soy oil droplets about 1 to 10 xm in diameter and the droplets did not coalesce with time, even after prolonged storage (Fanta and Eskins, 1995). The stability and lack of coalescence of the oil droplets in both hqnid dispersions and dried sohds was demonstrated, suggesting a specific starch-oil interaction (Knntson et al., 1996). Dickinson (1988) proposed that starch separates from water solntion and adsorbs onto the hydrophobic surfaces of oil droplets because water is a thermodynamically poor solvent for starch, and the adsorption of starch at the lipid-water interface leads to a redaction in the interfacial tension of the two-phase aqueous oil system. 

Coalescers are used to improve the performance of other gravity-hased separation equipment. They are specified hy the equipment vendor as an integral part of the water treating system, or they may he added as a retrofit to improve the performance of an existing system. Coalescers are particularly useful when the oil droplet size in the incoming water is small as a result of excess shearing in upstream piping or valves. 

Because of the coalescing action, these separators can separate oil droplets as small as 0.006 mm (6 microns) in diameter and produce effluent-free oil concentrations as low as 10 mg/L [27], There is a broad range of applications for tilted-plate separators. As little space is required, they can be installed to polish the effluent from existing API separators that are either overloaded or improperly designed, or they can be installed parallel with existing separators, reducing the hydraulic load and enhancing the oil removal capacity of the system. 

The SFC Oleofiltration system separates hydrocarbons from water. The technology combines a vertical-fin coalescing unit and a patented, amine-coated, oleophilic granule filtration system (the Oleofilter) into one system that can, according to the vendor, separate mechanical emulsions of hydrocarbons in water that are not treatable by conventional oil/water separators. The Oleofilter can also separate many chemical emulsions and reduce the concentrations of dissolved hydrocarbons. The technology is not commercially available. 

A third approach is emulsification. Most emulsified commercial products are the oil-in-water type, in which the oil is suspended in the form of small spheres in the water. The oil is the discontinuous or internal phase, and the water is the continuous or external phase. Stabilization of these systems is effected by surface-active compounds that prevent the oil drops from coalescing and by proportioning the two phases so that the lighter phase cannot separate to the top. In applying the emulsion ap-... 

A skim pile is a type of disposal pile. As shown in Fig. 9, flow through a scries of baffle plates creates quiescent wines that reduce the distance which a given oil droplet must rise to be separated from the main flow. Once in the quiescent zone, there is ample time for coalescence and gravity separation. Larger droplets then migrate up the underside of the baffle to an oil collection system... 

Previous and. New Hater-Treatment Trains. The previous system ofproduced-watcr treatment is shown in Fig. I. The degassed stream ol oil and water enters the frec-watcr knockout tFWKO) drums There arc two types of FWKO s in the field the old type, which is a conventional drum allowing gravity separation, and the new type, which is fitted with coalescer packs... 

Figure 183. Drums with coalescers for assisting in the separation of small amounts of entrained liquid, (a) A liquid-liquid separating drum equipped with a coalescer for the removal of small amounts of dispersed phase. In water-hydrocarbon systems, the pot may be designed for 0.5 ft/sec (Facet Enterprises, Industrial Division), (b) An oil-water separator with corrugated plate coalescers (General Electric Co.).

In such concentrated disperse systems three types of liquid films form foam films (G/L/G), water-emulsion films (O/W/O) and non-symmetric films (O/W/G). The kinetics of thinning of these films, their permeability as well as the energy barrier impeding the film rupture determine the stability of these systems. They might be subjected to internal collapse, i.e. coalescence of bubbles or droplets and increase in their average size, or to destruction as a whole, i.e. separation into their initial phases - gas, oil and water. 

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