Coalescing Filtration Skid

Polishing by Coalescence

The SorbiTech Coalescing Filtration Skid is the polishing stage downstream of a gravity separator. A solids pre filter protects the coalescing element, then the element merges fine dispersed oil droplets that are too small to settle in a CPI or API separator into larger drops that rise out of the water phase and are removed.

The skid takes residual oil in water from the 10 to 100 ppm range down to single digit ppm, which is the limit required for tight discharge consents, for surface water reinjection, and for protection of a downstream activated carbon polishing bed. SorbiTech fabricates the skid for permanent installation or holds rental units at the regional service centre.

Two Stage Element Architecture

A pre filter cartridge with a 5 to 25 micron rating removes the residual solids that would otherwise blind the coalescing surface and shorten its run. The coalescing element itself is a graded fibre matrix, usually glass fibre or oleophilic polymer, in which the bulk water flows through a fine pore network while dispersed oil droplets wet the fibre, migrate along it, and coalesce at the downstream face.

The coalesced drops detach into the downstream chamber, rise to the surface, and are skimmed; the polished water exits the bottom. A separator pack between the coalescer and the outlet captures any drops that fail to rise on the first pass.

Construction

The compact SorbiTech skid is built with:

• Solids pre filter housings sized for the inlet particulate load
• Coalescer and separator vessel with replaceable elements on quick release closures
• Differential pressure transmitters on the pre filter and the coalescer to time element change outs
• Inlet sample point, outlet sample point, and oil drain to a recovery vessel
• Skid frame sized for fast tie in to existing piping; lift lugs and forklift channels for site relocation

Differential Pressure and Element Replacement

The pre filter is changed at a differential pressure of 1.0 barg, and the coalescer element at 0.6 to 0.8 barg or at a measured drop in coalescence efficiency. Change out takes 30 to 60 minutes per vessel using site labour, and the spent elements are disposed of as oily waste under the local regulation.

Outlet oil in water is monitored either by laboratory sample or by an inline oil in water analyser, and the trend is the early warning that drives the element change schedule.

Design Data

• Capacity: 2 to 200 m³/h
• Inlet dispersed oil: up to 100 ppm, with pre filtered solids
• Outlet oil in water: below 5 ppm
• Operating pressure: 2 to 10 barg
• Design standard: ASME VIII for API 421 polishing duty

Element Selection by Service

• Hydrocarbon water separation: glass fibre coalescer with stainless support
• Aqueous polishing downstream of CPI: oleophilic polymer coalescer rated for refinery effluent
• Refinery sour water: 316L stainless coalescer with epoxy element seals, NACE MR0175 hardware
• Groundwater remediation with light hydrocarbons: high efficiency cartridge with surfactant tolerant media
• Solids loaded streams: stacked pleated pre filter with 5 micron rating before the coalescer

A wrongly specified coalescer in oily water service can lose 50 percent of its rated capacity within weeks. SorbiTech sizes the element from the inlet analysis and a 24 hour pilot trial on the actual stream.

Rental, Permanent, and Turnaround Service

SorbiTech holds the rental fleet pre tested and in storage so the unit arrives on site, set up, and ready to produce within 24 to 48 hours of release. The rental option suits turnarounds, commissioning campaigns, and emergency response. For permanent installation the skid sits downstream of a CPI oil water separator in a produced water treatment train delivered by SorbiTech.

Footprint and Site Integration

The skid is delivered on a single weld frame with lift lugs at the four upper corners, drag rails on the underside for skid pushing, and forklift channels along the long axis. Standard inlet and outlet flanges are ANSI 150 raised face, with options for ANSI 300 on the pressurised variants. The compact arrangement supports tie in within an 8 hour shutdown window for most refinery and field applications.

Power, instrument air, and a drain to the recovered oil header are the only utilities required. Local indication is on the skid mounted panel; remote indication to the plant DCS is a four wire termination on the supplied SorbiTech junction box.

Performance Verification and Compliance Documentation

The polishing duty is verified by inlet and outlet sampling at the start of each campaign and at scheduled intervals afterward. The lab method is ASTM D7066 or the regional equivalent for oil in water, with hydrocarbon speciation by GC FID for projects that need the breakdown by carbon chain. A SorbiTech compliance dossier covering material certificates, weld procedures, hydrotest records, and the as built P&ID is delivered with every unit. SorbiTech delivers the coalescing skid downstream of the CPI separator for produced water polishing, with rental and permanent options across the oil & gas and refining sectors.