Design horizontal three-phase separator

A typical horizontal three-phase separator with flooded weir is shown in Figure 3.4. The inlet nozzle (Nl) and the gas outlet nozzles (N2) are placed as close as possible to the vessel tangent line. The distance of tiie nozzle center line and the tan line is dictated by tiie mechanical limitations of the vessel however, distances in Table 3.7 can be used for initial design. 

Process pressure vessel cost. Process pressure vessels are always designed in accordance with the current ASME code. These major equipment items are always cylindrical metal shells capped with two elliptical heads, one on each end. Installation can be either vertical or horizontal. Vertical is generally a fractionation-type column with internal trays or packing, although the smaller-height vertical vessels (less than 15 ft) are mostly two-phase scrubber separators. The horizontal vessel is generally a two- or three-phase separation vessel. 

There are a number of special variants of the basic horizontal or vertical decanter for simple clarification and dewatering. Special designs are available for three-phase separation, for thickening applications, with a filtration section, for leaching, for washing, and those for operating at extra high temperature and pressure. 

Proper selection of the separator type is important. For three-phase separation, a horizontal separator is more effective than a vertical separator. Also, it is easier to design the control system for a three-phase horizontal separator. 

As the flow rates are quite high and the design needs to accommodate 7 m of slug, a horizontal three-phase flooded-weir separator has been selected. 

Fig- 2—Typical configuration of a three-phase horizontal separator. Interface level control maintains water level, weir maintains oil level. Vessels may be equipped with sand jets If sand production is a problem. jets are designed for 20 fps velocity, and produced water normally is used for backwashing. 

Fig. 3—Bucket and weir configuration for three-phase horizontal separator eliminates interface controller and uses conventional displacement fioal lo operate oil and water dump valves This design is useful if paraffin or large volumes o emulsions that would loul interlace controllers are expected.

Normally, all three-phase horizontal separators are designed and maintained to be half full of liquid. 

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