CPI (Corrugated Plate Interceptors)

Water from oil & gas production facilities and process/plant water often requires a number of options and stages to effectively treat to remove free oil and solids

. A CPI Unit can be very effective as the primary oil/solids removal device.



The corrugated plate pack in a CPI separator, used in Oily water treatment for removal of free oil, consists of number of parallel corrugated plates.
The effectiveness of this technique is subjected to various factors such as density difference, viscosity of the oil and operation conditions.
This system is typically used as a package in cases where the capacity of the wastewater is low and less space is needed.

The design of the CPI Unit depends on a number of factors including:

• Operating conditions (pressure & temperature)
• Produced water properties
• Sludge production
• Inlet oil & solids levels
• Outlet specifications
• Retention time typically +10 minutes

Process Group CPI Units are designed to remove free oil and solids (TSS) from water as a primary stage of water treatment.
These units typically include a number of elements:
• Inlet chamber to collect oil/solids slugs
• Inlet solids settling chamber
• Plate packs, removable through man-ways
• PSV’s and gas vent lines
• Solids/sludge removal outlets
• Recovered oil collection & automated removal
• Fully automated and unmanned operation

The Plate Packs are designed with specific spacing between the plates and with the plates set at designated angles to allow solids to settle and fall to the bottom while simultaneously allowing oil droplets to rise and coalesce on the underside of the plates as they rise to the water surface.
Plate Packs for CPI Units typically use either Stainless Steel materials (for high temperatures service) or polypropylene materials for lower cost and weight options.
Pressure vessel materials of construction are selected based on the process fluid and operating environment. Materials such as carbon steel (typically internally coated), stainless steel or duplex stainless steel are commonly used materials of construction. Non-metallic materials such as GRP and fiberglass are also available.

Operating Principles

Water with entrained oil and solids enters the CPI Unit and flows through an inlet distributor to reduce fluid velocity, as it flows into the inlet chamber.
This allows large oil droplets to rise and be collected in the oil collection zone prior to fluid entering the Plate Packs. The coarse solids settle and are collected in the solids sump section of the inlet chamber.
The water containing the residual oil and solids passes horizontally into the Plate Packs where the flow profile forces laminar flow along a set path through the packs, which are set at an angle to allow simultaneous rise of oil and settling of solids. This flow path provides a low velocity path for the water through the packs that allows:
• Oil droplets rise to the underside of the plates
• Oil droplets coalesce on the plate surface and travel upwards, further coalescing
• Solids settle to the top of the plates and slide to the bottom.

Advantages of CPI Units include:

• Low Spare requirement.
• Very low maintenance cost since there are no moving parts.
• Not required large space.
• High efficiency and capacity combined with compact volume.
• Can handle shock loads of flow without affecting effluent quality significantly.
• Selection can be done from large number of type of basins (RCC, Mild Steel, and Stainless Steel)


Disadvantages of CPI:

• The effluent oil concentration is higher than that of other methods
• Large surface area required
• Large volume results in dead zones en reduction of net available surface area
• Expensive oil/bottom scrapers required that are maintenance intensive
• Ineffective with small oil droplets or emulsified oil, Require long retention time to achieve efficient separation

CPI Units are suited to the following applications:

• Where water is collected from multiple, low pressure sources,
• Handles oil/solids slugs & intermittent flows,
• Common in onshore centralized Water Treatment plants,
• Settles larger oil droplets and coarse solids,
• Mostly supplied with a Pressurized Vessel, to contain and control all gas and liquid emissions
• Primary treatment stage of a Water Treatment train where multiple stages of treatment are required to ensure reliable and effective water treatment.

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