Separators designed for use in the gas industry are mechanical devices, which remove liquids from the natural gas stream. Proper separator design must accomplish the following:
- Dissipate and control the energy of the inlet gas stream.
- Reduce gas and liquid velocities so that initial gravitational separation will occur.
- Allow adequate liquid retention time for the separation of entrained gases from hydrocarbon liquid streams.
- Eliminate separated liquid re-entrainment into the outlet gas phase.
- Provide adequately sized connections for inlet, gas outlet, liquid outlet, pressure safety valve, level controls, level gauge, pressure gauge, temperature gauge, drains and inspection openings.
Separators are primarily manufactured in 2 basic styles – Vertical and Horizontal.
- Vertical Separators are well suited for handling large liquid slugs, solids and surging flow conditions, in addition, vertical separators require less floor space. In standard vertical up-flow designs, the gas volume is limited due to re-entrainment because of the counter current flow of gas (up) and liquid (down). Vertical units equipped with specially designed vane mist extractors eliminate re-entrainment and have an increased gas capacity.
- Horizontal Separators are best suited for streams with: high gas / liquid ratios, constant flow and relatively low liquid surging. The gas transit time is increased in horizontal separators thus allowing gravity more time to capture liquid particles. If foaming is anticipated, predesigned de-foaming sections can be added to release entrained solution gas from the foam. Due to the large interfacial area available between phases, horizontal units are best suited for 3 phase (liquid, liquid gas) separation.
QBJ gas scrubbers are basically 2-phase separators specifically designed to handle gas streams having high gas-liquid ratios, varying flows, and liquid surging. QBJ scrubbers are designed in both the vertical and horizontal configuration.
3 PHASE SEPARATION
The design and construction of 3-phase separators are different from 2-phase separators in that the liquid retention time is increased to allow for liquid / liquid phase separation of a hydrocarbon liquid stream from a H2O liquid stream. Depending upon the service, this time will vary from 3 to 30 minutes. The horizontal configuration is best suited for liquid-liquid-gas, or three phase, separations because of the large interfacial area available between the two liquid phases. A series of weirs and liquid–liquid interface points facilitate the phase separation.
LIQUID-LIQUID PHASE SEPARATION
The design and sizing of liquid-liquid or phase separators is generally based upon a minimum retention time and a coalescing element to facilitate gravity separation. Depending on the volume and removal efficiency, coalescing vanes, mesh pads or coalescing filter elements may be specified.