Coalescing Gas Separators
Coalescing gas separators are designed specifically for the removal of mist, fogs, and dust from gas streams. These contaminants usually exist with the bulk of the particles having diameters considerably less than 10 microns; therefore, standard separators or scrubbers are not capable of effectively removing these minute particles.
Coalescing gas separators consist of a vessel combining specially constructed fiberglass coalescing elements and a separation section with either a wire mesh or vane type mist extractor. A liquid accumulation section is provided to properly collect and discharge the liquid for further processing or disposal. Coalescing takes place as the gas passes through the fiberglass in the sock-type replaceable filter elements. The fiberglass forces small particles to agglomerate (coalesce)-forming larger drops or particles. The resulting larger droplets are then removed from the gas as the stream flows through the separator section. Further removal of entrained droplets is provided by the wire mesh or vanes of the mist extractor. All separated droplets are then collected in the liquid accumulation section. Any dirt, dust, rust, and scale in the gas will be removed on the outside surface of the filter elements.
Typical application for coalescing gas separators:
Many wellstreams are encountered today that produce foam or have a tendency to foam under certain conditions. Foam can be produced either by mechanical agitation or chemical reaction. Foaming problems can be caused by changes in pressure or temperature, or the presence of minute particles of solids, surfactants from the producing formation, corrosion protection chemicals injected into the stream or any combinations of these factors. The heavier crudes tend to be more susceptible to foam formation.
Foam is a two-phase material, which can be present or created within the gas-liquid mixture as it is produced from the formation. It can be further aggravated by pressure reductions, turbulence caused by flow thru valves or piping, and temperature changes in the system. If the volume of the foam is too high or the stability of the foam is too great to allow the foam to break, the foamy fluids will pass through a separator and on into the gas line, thereby reducing the separation efficiency. The foam layer on top of the oil also interferes with the movement of liquid particles out of the gaseous phase and the release of solution gas from the oil phase.
Mechanically induced foam can usually be "broken" by mechanical means. Chemically induced foam may require chemical foam breakers as well as mechanical means. Foam separators are designed to provide increased contact surface to the foam to break up the stable foam. The use of special wire mesh foam pads and parallel plate surfaces are typical ways of providing this. The surface area must be great enough so that the rate of foam breakup will be faster than the rate of buildup. Horizontal separators are generally considered to be the best configuration for foamy production.
Waxes, Paraffins and Hydrates
Another group of problems encountered are wellstreams containing waxes, paraffins or hydrates. The only sure solution to wax or paraffin problems is to heat the wellstream above the wax or paraffin formation temperature before it enters the separator. Internals of the separator must be designed so that accumulations do not cause excessive pressure differentials, which could damage the internals. The internal construction must also allow for ease in steam cleaning, or back washing with solvents. Vane type mist extractors are usually preferred with wellstreams that have a tendency to deposit wax or paraffin. Separators cannot be designed to handle hydrates. The operating temperature of the separator must be kept above the hydrate forming range.
How It Works
Gas containing entrained liquid mist or fog, dust, rust, or scale (singly or in combination) enters the vessel through the inlet connection into the large inlet chamber ahead of the coalescing elements. This allows the gas to distribute around the coalescing elements for efficient use of the available filter surface area. Solid particulate materials are trapped by the filter element fibers as the gas and liquids pass through. The liquid mist or fog is retained by the fibers of the filter element until enough liquid accumulates to form a large drop. The gas then forces the large drops through the filter element. These large drops are then separated from the gas by gravity or by the action of the mist extractor section.
The liquid accumulates in the liquid chamber where it is removed by the action of the liquid level controller and dump valve. The gas, free from its particulate contaminants and liquids, leaves the vessel through the gas outlet.