Three Units, One Train: Getting Oil Out of Every Power Plant Wastewater Stream

Thermal generation is the backbone of the power industry, and it produces large volumes of industrial wastewater while doing its job. Oily wastewater is the stream that causes the most trouble, because it arrives from everywhere: boiler cleaning, desulfurisation systems, turbine maintenance. Discharge it without proper treatment and the consequences range from ecological damage to straightforward breach of emission regulations, which have been tightening year after year.

The same plant, wildly different water

The difficulty is not a single pollutant but the mixture. Power plant oily wastewater typically carries crude oil and lubricating oil from equipment maintenance and pipeline cleaning; suspended solids including silt and rust; residues of the chemical reagents used in water treatment; and, in desulfurisation wastewater especially, very high salinity.

Worse, streams from different sources behave differently. Some carry oil content of only tens of ppm, while others reach hundreds of thousands of ppm. A treatment process designed around the low end will fail on the high end, and a process sized for the high end will be grossly over-built for everything else.

Conventional methods each have a known weakness. Oil-intercepting ponds occupy large areas and perform inconsistently. Flotation equipment is poor at emulsified oil. Chemical reagent routes are prone to secondary pollution. What a plant needs is something efficient, economical and stable across the whole range.

Unit one: CDFU cyclonic dissolved air flotation

The first technology combines cyclonic separation with flotation separation. Instead of relying on gravity alone, it lets wastewater complete oil-water separation inside a high-speed rotating centrifugal force field, which improves separation efficiency substantially and shortens the time required.

Unit two: KHC coalescing oil separator

The second uses a special coalescing material to make tiny oil droplets dispersed in water gradually merge into large oil beads, at which point oil and water separate readily. Against conventional equipment, the KHC coalescing oil separator handles emulsified oil far more effectively, and it suits wastewater where oil content fluctuates widely and droplet sizes are small — precisely the profile of power plant effluent.

Unit three: KFM active filter media filter

The third is a polishing stage. The KFM filter uses a specially formulated active filter media that removes suspended solids efficiently and further adsorbs residual oil. The media can be backwashed and regenerated, which keeps long-term consumable costs low.

What the combined train delivers

SINOKLE assembles the three units according to each plant's actual conditions rather than selling a fixed package.

• Wide treatment range. The train handles wastewater with oil content from tens of ppm up to hundreds of thousands of ppm.
• Results that clear the bar comfortably. Treated effluent oil content drops below 5 ppm, with a removal rate above 99%.
• Stable operation. A high degree of automation means no dedicated operator is needed on shift.
• No secondary pollution. Treatment is purely physical, with no chemical reagents added at any stage.

Two plants, two profiles

A back-pressure cogeneration project in Shaanxi Province. The oily wastewater here had an oil content as high as 500,000 ppm — that is, 50% — which makes treatment genuinely difficult. SINOKLE applied a combined filter plus KHC coalescing oil separator process. Final effluent oil content dropped below 5 ppm with a removal rate above 99%, comfortably beyond the discharge standard. A stream that would clog most conventional equipment became a routine duty.

A heavy oil power plant in Sierra Leone. This project used a three-stage CDFU + KFM treatment process with equally strong results. Inlet wastewater carried oil content below 50 mg/L and suspended solids below 80 mg/L. After treatment, effluent oil content was below 10 mg/L and suspended solids below 20 mg/L, with every indicator meeting the discharge standard.

The two cases sit at opposite ends of the concentration range, which is the point: the same three-unit architecture, arranged differently, covers both.

Why three units rather than one

No single device covers this range cleanly. Cyclonic flotation alone handles a heavy oil load but leaves fine emulsified droplets behind. A coalescing separator is excellent on emulsions but does nothing about suspended solids. Filtration polishes well but blinds quickly if it receives raw oily water. Stacking the units in the right order lets each one work where it is strongest, and that order can be reversed — filtration first where solids dominate, CDFU first where oil dominates — without changing the equipment list at all.

The same flexibility drives sizing. A plant with one dominant stream can run a two-unit train and stop there. A plant dealing with several dissimilar streams will usually need all three, with the CDFU unit taking the bulk of the oil load and the KFM filter standing as the final barrier before the water leaves the site. Deciding which of those two situations applies is really the first step of the design, and it follows from sampling the actual streams rather than from the plant's nominal capacity.

Why it matters beyond compliance

Under the dual carbon goals, green and low-carbon operation has become the main theme of the power industry, and efficient oily wastewater treatment is part of how a plant meets its social responsibility rather than a box to be ticked for the regulator. SINOKLE works on this technology base to give power plants oily wastewater treatment that holds up under real operating conditions, which is what green power development ultimately depends on.