- Model CPI - Corrugated Plate Interceptor



The CPI is the basic TiPSS unit mainly used for oil-water separation. The CPI holds modular-counter-current-flow plate packs executed in GRP or Stainless Steel. The CPI basin can be executed in concrete or steel. The concrete units are specifically suited to integrate with sewer systems below ground level so that a gravity flow can be used. The steel CPI can optionally be supplied with integrated oil sump and/or effluent sump or with a gas-tight cover.

  • Ballast water and tank farm waters
  • Refinery effluents and run-off
  • Petrochemical effluents and run-off
  • Airport or other large site rain run-off

  • Flow rates 50 - 10.000 m3/h
  • Oil globules cut-off diameter 30 - 60µm and larger
  • Oil removal 50 - 99%
  • residual 5 - 20 ppm free and separable oil
  • TSS removal 80-90%

  • No moving parts
  • High separation efficiency
  • Compact construction gives great economy in space and foot print
  • Low installation costs on site since units can be prefabricated
  • Minimum maintenance and operation costs
  • Uniformity in design guarantees quick delivery of unit and spares
  • Short hydraulic retention time
  • Continuous operation
  • Insensitive to weather conditions and variations in capacity, temperature and water characteristics
  • Resistant to shock and slug loads.

  • Oil globules cut off diameter: 10 – 60 μm and larger
  • Oil removal 50 – >99%
  • Residual 5 – 20 ppm slop oil
  • Tss removal 80 – >90%

  • HPI industries:
    • Produced water (oil and gas fields)
    • Ballast water and tank farm waters
    • Refinery effluents
    • CPI industries
    • Process waters
    • Petrochemical effluents
    • Textile industries
  • Food and beverage industries:
    • Edible oil refining
  • Automotive, iron & steel industries:
    • Potable & process water pre-treatment

Gravity separation is the most straightforward method of effluent treatment and is, therefore, utilised widely in industry for the separation of settling and/or flotable impurities from a carrier liquid. In the majority of cases the separators are constructed in the form of a rectangular tank.

The effectiveness of such a tank depends theoretically upon its net separation surface (A) and the amount of water to be treated (Q). The ratio Q/A is called the overflow rate. The rising or settling velocity of a discrete particle with a diameter d can be indicated by Stokes’ law:

All particles or droplets having a settling or flotation velocity Vs>Q/A are fully intercepted, while a portion of the smaller particles will be captured also in a ratio of (d/ds)² x 100%.

An enlarged separating surface can be achieved by placing various smaller planes on top of each other in the tank. If these planes are subsequently inclined in a tilted position, material separated between the plates is removed by the gravitational force. This is the principle on which the TPI corrugated plate pack is based.

In this plate pack the planes as referred to have been constructed in the shape of corrugated plates. They promote both the coalescence of the intercepted oil particles and, at the same time, their transfer through the plate pack (see fig. 1).

If settleable material is present in the liquid, such material is collected and concentrated in the troughs of the corrugations so that it will slide down in the plate pack smoothly and easily. Very small separating diameters can be obtained in the TPI system, because the disturbing factors, such as eddies and turbulences, which adversely affect large conventional separating tanks (e.g. API’s), are eliminated in the TPI.

Data are essential:

  • The type of pollutants to be intercepted
  • The separating diameter of the oil droplet
  • The difference in density between the carrier liquid (waste water) and the pollutants to be intercepted
  • The maximum amount of water to be treated
  • The water temperature
  • The sedimentation velocity
  • Origin of the oily liquid
  • Physical data, chemical analysis of carrier phase.

Subsequently the required separating area (A) is computed with:

A = Q/Vs

The required number of plate packs are determined from this separating area.

With the objective of not breaking up the oil droplets unnecessarily, the TPI system is preferably fed by gravity. The oily water flows into the interceptor through the inlet compartment which has a dual function as a sand trap (1). A double slotted baffle (2) induces incoming water to flow evenly and uniformly to the entrance of the corrugated plate pack (3). In the plate pack the oil droplets are intercepted and coalesce into large droplets. They leave the pack rapidly in counter current mode and move upwards against the liquid flow, to the surface. The separated oil builds up a floating layer (4) which is removed through a skim pipe (5).

Settleable material, if present in the aqueous phase, is similarly separated in the plate pack. It collects in the corrugated plate troughs and then slides down to the sludge compartment (6). The treated clear water leaves the plate pack at the bottom and is discharged over an adjustable weir (7).

To reduce fire hazard and odours to a minimum, the system can be covered and gas blanketed. The amounts of oily water to be treated can vary from some m3/h to many thousands m3/h. In order to effectuate quick delivery of complete plants for the required amount of waste effluent, VWS MPP Systems BV produces corrugated plate packs in various sizes for different capacities.

Many hundreds of complete, advanced wastewater treatment plants have been put into operation throughout the world.

The compact design and the high separating efficiency versus low investment and maintenance costs which are so characteristic for this gravity separator system, have proven their value in practice.

Each effluent stream has its own individual characteristics; the impurities in the aqueous phase can occur either as a dispersion, an emulsion or a solution and the particle size distribution differs from case to case. For this reason, specific process analyses and design calculations must be made for each case.

It is however fundamentally impossible to separate dissolved or emulsified components from the aqueous phase by means of gravity only.

A physical-chemical treatment, might make this possible in some instances. Our brochures on tailor-made water treatment designs provide you with more detailed information on our various physico-chemical systems.

Refinery Effluents
Refinery effluents, classified as AOC/COC (Accidentally Oil Contaminated / Continuously Oil Contaminated) effluents, originate from the following sources: oily surface run-off (rain) water, fire fighting, tank bottom-, equipment-, and desalter drains and process water. Above effluents are properly (pre-) treated via TPI gravity separator. Above streams are directed to a TPI unit to segregate sand and free and separable oil. Depending on the onsite requirements, further treatment can be carried out via a flocculation-flotation unit or subsequently a biologic polishing plant. Rain and fire fighting waters are optimally treated separately due to their large quantities and dispersed oil contamination.

Ballast Water Treatment
The ballast water is pumped from the tanker into a retention tank. Here, the first rough oil/water separation takes place.

In addition, the retention tank serves as a buffer for stabilising the variable ballast water feed. The oily waste water leaving the tank, rapidly passes through the TPI plant where the oil is removed. The ballast water is discharged into the river or sea. Complete TPI plants for the purification of ballast water can be installed in below grade concrete structures and also in mild steel vessels above-ground.

The TPI (CPI) separator can be combined with other VWS MPP Systems BV or Veolia Water Solutions & Technologies systems to improve the quality of the effluent or process water to e.g. comply with the requirements set forth by the authorities or company prescriptions:

  • screens removal of coarse material
  • CPF / TPF separation of flocculated impurities by flotation and chemical pretreatment
  • SBR batch wise operated bio reactor for the aerobic treatment of dissolved pollutants
  • PCS / MMF Walnut Shell Filters / Multi Media filters
  • MBBR/MBR Mixed Bed BioReactor or Membrane BioReactor

The VWS MPP Systems BV scope of work can be:

  • Turnkey deliveries
  • Recommendations
  • Design
  • Engineering
  • Erection
  • Installation, commissioning and start-up
  • After sales service
  • Laboratory and field research
  • Pilot plants.

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