Two-phase vapor-liquid separators are used in many industries including oil refineries, chemical plants, refrigeration systems, natural gas and petrochemical processing plants.
Depending on the specific application and the vapor-liquid mixture being separated, two-phase vessels can be oriented vertically or horizontally. In their simplest form, they are an empty tank that’s used to reduce the velocity of a fluid on entry, thus allowing the liquid to fall to the bottom of the vessel and the vapor to rise to the top. Most separators include internal devices that assist in the separation process, such as:
• An inlet diverter – An inlet diverter includes a downcomer that directs the inlet flow below the liquid level in the tank. This has the effect of stabilizing the liquid level while preventing splattering and foaming.
• A mist eliminator – A mist eliminator removes liquid droplets entrained with the gas.
As their name indicates, liquid-liquid separators are used to separate two immiscible liquids, like oil and water. The viscosity, specific gravity and interfacial tension of the two liquids must be considered when designing this separator.
If the difference in density between the two liquids is large, separation can be achieved through gravity separation. In such instances, the heavier liquid is drawn off the bottom of the tank and the lighter liquid off the top. Otherwise, a coalescer can be used to facilitate liquid-liquid separation using plastic, polymer, wool or fiberglass as a coalescing medium.
Solid-liquid separation is normally achieved through filtration, settling or centrifugation. These types of separators utilize filters, which contain a porous medium that retains suspended solids as the mixture passes through it. Settlers are normally tanks of very basic design that facilitate the settling of solids to the bottom of the vessel by gravity.