Coalescing Plate Oil Water Separator

A coalescing plate oil water separator removes free and dispersed oil, sludge and suspended solids from industrial wastewater using a pack of closely spaced inclined plates. The plates give the oil a large surface to collect on over a short rise distance, so a compact unit does the work that an open gravity tank would need many times the footprint to match. Baldwin Industrial Systems designs and builds these separators in Australia, sizing each one to the site flow and the discharge limit it has to meet.

It is a gravity separator with an engineered plate pack, also called a CPI (coalescing or corrugated plate interceptor) separator. Oily water passes through inclined plates that bring small oil droplets together into larger ones, which rise and release as a surface oil layer, while solids drop to a sludge zone. No chemicals are dosed, and there are no moving parts in the separation chamber.

Coalescing plate separators form a core part of Baldwin’s wastewater treatment products. They prevent contamination, reduce operational downtime and help sites meet EPA discharge requirements across mining, petroleum, manufacturing, transport and utilities sectors.

Units are available for above-ground or in-ground installation, with flow capacities from 1,000 L/hr to 500,000 L/hr.

Oil separation is created by the density difference between oil and water. Left in an open tank, free oil rises slowly under gravity. The rise velocity of a droplet follows Stokes’ law: it scales with the square of the droplet diameter and the oil to water density difference, and falls as the viscosity of the water rises. Two things follow. Small droplets rise very slowly, which is why fine and emulsified oil is the hard case. Warmer, less viscous water separates faster than cold water.

Inclined plates change the geometry of the problem. A droplet only has to rise the narrow gap between two plates before it meets a collection surface, rather than climbing the full depth of a tank. The plates also pack a large projected area into a small volume, so the unit is sized on the hydraulic loading across that plate area, not on tank residence time alone.

The separation runs in four stages:

1. Flow enters the separator and passes through a bank of inclined coalescing plates.
2. Oil droplets collide and combine (coalesce), forming larger droplets.
3. As droplets grow, they rise to the surface, where the oil is collected for removal.
4. Heavier solids sink to the bottom, forming a sludge layer for periodic clean-out.

With no moving parts in the separation chamber, there is little to fail. Performance holds while flow stays inside the design envelope, and the plate pack is kept clean.

A Baldwin coalescing plate separator is sized to capture down to 20 microns and to leave an outlet free-oil content in line with your trade waste limit, depending on how the system is designed.

A coalescing plate oil water separator will only work well for your project if it is designed on the right data. When we are customising your unit, the engineers at Baldwin will ask for:

• Peak and average flow rate, including any first-flush or batch surges
• Inlet oil concentration and the target outlet limit from your trade waste agreement
• Droplet size distribution, or a design droplet to capture, where that is not known
• Oil specific gravity and operating temperature, which set the rise velocity
• Suspended solids load, which sets the desludging frequency and any need for upstream solids removal

Every system is built to suit the duty, with stainless steel used where the wastewater chemistry calls for it, and factory-tested before delivery. Optional equipment is specified for your unique project, including floating suction skimmers, feed pumps, control panels, polishing media, waste oil tanks and access platforms.

The distinction lies between free and emulsified oil. A coalescing plate separator effectively manages free and dispersed oil, common in workshops and wash bays. However, emulsified oil poses a challenge. Detergents, degreasers, and high-shear pumping keep droplets under 10 microns suspended, requiring a dissolved air flotation (DAF) system, often with coagulation and flocculation, to break the emulsion.

Many sites use both: a plate separator removes bulk free oil first, followed by DAF or media polishing to meet stringent limits. Baldwin designs and builds both systems to suit your effluent needs.

Not sure which one is right for your project? Call one of our experts on (02) 4954 0440 or send us your effluent data, and we’ll help you find the right fit.

In Australia, rules for discharging oily wastewater are set by local water authorities rather than a national standard. Generally, two main rules apply: you cannot have any visible floating oil, and total petroleum hydrocarbons (TPH) are usually limited to 30 mg/L. The specific limits for your site will be detailed in your local trade waste agreement.

• NSW: Sydney Water prohibits free oil and sets limits per agreement; Hunter Water caps TPH at 30 mg/L.
• VIC: Yarra Valley Water, Greater Western Water and South East Water set limits per agreement, no free oil layer accepted.
• QLD: Urban Utilities and Unitywater require oil pre-treatment, with limits in the acceptance criteria schedule and approval.
• SA: SA Water caps grease and oil at 100 mg/L and TPH at 30 mg/L.
• WA: Water Corporation caps TPH at 30 mg/L and emulsified oil and grease at 500 mg/L, with no free layers.
• TAS: TasWater requires oil pre-treatment, with the limit set in the agreement.
• ACT: Icon Water accepts no free oil layer and sets limits through the approval.
• NT: Power and Water sets limits per approval under its Trade Waste Code.

Each duty brings its own challenge: surfactant-heavy wash water, high solids from mining, hydrocarbon slugs at fuel depots. Baldwin sizes the separator, and any pretreatment, to the conditions on site. Common applications include:

• Mining and resources
• Petroleum depots and refineries
• Railway workshops and wash bays
• Power stations and tank farms
• Mechanical and maintenance facilities
• Petrol stations
• Stormwater and bund-water treatment

Each system is fully scalable to site flow rates and discharge requirements.

Compliance without compromise.

Baldwin has designed and built industrial wastewater equipment in Australia for more than 35 years, sizing each unit to the site. Separators are engineered and fabricated in-house, so the team that sizes the unit is the team that builds it, and custom duties are routine rather than the exception.

• Proven performance across mining, manufacturing, food, and infrastructure sectors
• Designed for safety, reliability, and low maintenance
• Supported by qualified technicians and local spare parts supply
• Backed by in-house fabrication and complete project management

A coalescing plate separator can run as a standalone unit or as one stage in a larger treatment train. Baldwin separators connect with other Baldwin systems, including clarifiers, dissolved air flotation (DAF), floating oil skimmers, filtration and polishing media, control panels, custom fabrication and RM-10 oil separators. The modular approach keeps performance consistent and servicing simple across the plant.

Speak with Baldwin Industrial Systems about a coalescing plate separator tailored to your water quality and operational goals. Explore our wastewater treatment case studies for examples of system performance, and browse resources including oil skimmers and DAF units to see how Baldwin solutions can support your site.