Coalescers pressure vessels

FIGURE 3.23. Schematic of an oil/water/sediment coalescing pressure vessel. 

Pressurized Vertical-Vessel Coalescer. Pressurized influent is pumped into a vertical vessel maintained at a gauge pressure of about 30 psi (200 kPa], The vessel is fitted with coalescer cartridges. The equipment layout is compact, requiring little floor space. The main disadvantage is that for specified duty conditions, it needs a continuously operating SO-hp [40-kW pump. Any breakdown of the pump set would result in complete unit shutdown. The operating... 

Coalescer pads estimate as a fraction of the cost of the vessel. 10-30% c/s cost of pressure vessel. 

Vane eiiminators force gas flow to undergo directional changes as it passes between parallel plates. Droplets impinge on plate surfaces, coalesce and fail to a liquid collecting spot for routing to the liquid-collection section of the vessel. Vane-type eliminators are sized by their manufacturers to assure a certain minimum pressure drop. 

The DPET is designed to hold 1720 L (10.8 bbl) and operates safely at pressures up to 517 kPa (75 psi) and temperatures up to 150 C (300 T). The application of a high-voltage, dual-polarity electric potential to electrodes inside the vessel is used to coalesce and remove small droplets of water in the oil emulsion. The oil should be degassed and have a water content less than 15% before entering the vessel however, the treater does have the capability for free-water knockout. Preheated emulsion is pumped into the bottom portion of the vessel, below the electrodes, where free water generated by heating or chemical treatment may drop out. As more emulsion is... 

The DPET s electrodes are in the form of concentric cylindrical plates suspended from the top of the vessel and are connected to a high-voltage transformer such that adjacent plates are given opposite charges. As the oil passes through the electrodes, water droplets are influenced by the field to create a sinusoidal migration between plates of opposite charge. This motion serves two purposes to restrict the upward flow of the water in relation to the oil and to enhance the rate of collision of water droplets, which are distorted to form dipoles under the electric field, and thereby increase the rate of coalescence. Clean oil leaves from the top of the vessel, while water is drained out from the bottom. Instrumentation available on this unit permits pressure and temperature measurement of both the feed and vessel conditions and the treated oil and outlet water flow rates. 

The reactor vessel is usually a stirred tank. The monomer phase is subjected either to turbulent pressure fluctuations or to viscous shear forces, which break it into small droplets that assume a spherical shape under the influence of interfacial tension. These droplets undergo constant collisions (collision rate >1 s ), with some of the collisions resulting in coalescence. Eventually, a dynamic equilibrium is established, leading to a stationary mean particle size. Individual drops do not retain their unique identity, but undergo continuous breakup and coalescence instead. In some cases, an appropriate dispersant can be used to induce the formation of a protective Aim on the droplet surface. As a result, pairs of clusters of drops that tend to coalesce are broken up by the action of the stirrer before the critical coalescence period elapses. A stable state is ultimately reached in which individual drops maintain their identities over prolonged periods of time [247]. 

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