Heavy-Oil Tank Farm Oily Water at Power Plants: Why CDFU Plus KFM Filters Holds
The feed, described honestly
Oily wastewater from the heavy-oil tank farms of a thermal power plant is not a simple oil-on-water problem. The composition is complex, petroleum substances can reach 1,000 mg/L, suspended solids ride along, the oil is viscous and the emulsion is well developed. Discharged as it stands, or treated badly, it pollutes the receiving environment and also destabilises the plant's own water circulation system, because the same water is reused inside the site.
Three reasons the conventional train stumbles
Oil-water separation is hard, and it is hardest for the emulsified fraction, where droplets are small enough that buoyancy alone will not move them in the time a tank can offer. Conventional processes adapt poorly to high-concentration oily wastewater and are easily upset by swings in water quality. And the treatment itself generates large volumes of oily sludge and other secondary pollutants, which converts a water problem into a hazardous waste disposal bill.
What plants used before
Thermal power stations once relied on oil separation tanks, flotation and chemical flocculation, usually in that order. Oil separation tanks only remove floating oil and do very little for dispersed or emulsified oil. Flotation can lift fine droplets but needs substantial equipment investment and electrical energy. Chemical flocculation requires continuous dosing and produces large amounts of floc, which means high treatment cost and a standing risk of secondary pollution. All three share the same weaknesses: long process chains, large footprints, poor shock resistance and unstable operation.
The SINOKLE arrangement: CDFU first, KFM second
To address those shortcomings, SINOKLE (Shenzhen) Technology Co., Ltd. put together a pretreatment process for heavy-oil tank farm wastewater centred on CDFU compact cyclonic dissolved gas flotation, backed by KFM active filter media filters. The train starts with primary oil-water separation in an oil separation tank, which takes the free oil cheaply and keeps it out of the equipment downstream.
From there the wastewater enters the CDFU unit, where cyclonic centrifugal separation, dissolved gas flotation and ultra-fine bubble technology work together to break the emulsion and make oil droplets aggregate and float. CDFU effluent then passes to the KFM active filter media filters, which take out the residual fine droplets and suspended solids that flotation cannot reach. Waste oil collected through the process is recovered, and off-gas goes to a dedicated treatment system rather than to atmosphere.
What the combination delivers
- Removal and resilience. Separation is purely physical with no chemicals, oil removal runs above 95%, and the system absorbs large swings in both water quality and flow.
- No hazardous sludge. Nothing is dosed, so no oily sludge is created, which removes the secondary pollution route and its disposal cost. Recovered oil returns to the crude tank as product.
- Footprint. The integrated skid-mounted design occupies about 1/10 of the plot a conventional process needs, which matters on a site that was never planned around water treatment.
- Operation. Automation is high and the moving parts are few, so operation and maintenance stay simple and construction is quick.
- Effluent quality. After treatment, petroleum substances and suspended solids both drop below 20 mg/L on a stable basis, better than conventional discharge standards and a sound starting point for any further polishing.
The Sierra Leone reference unit
One installation worth looking at is the unit built for a heavy-oil power plant in Sierra Leone: two stages of CDFU followed by KFM active filter media filters, supplied as a single packaged train. The layout is the argument in physical form — two flotation stages to handle the emulsion, one media stage to polish what flotation leaves, all inside a battery limit that fits the plant yard.
Why the oil separation tank stays in the train
It is tempting to treat the gravity tank as legacy equipment and start the process at the flotation unit, and that shortcut is a mistake. Free oil is the cheapest oil to remove and the most expensive to carry downstream: it loads the flotation stage with a phase it was not sized for, it coats the media in the KFM filters, and it arrives in slugs whenever a tank is drained for inspection. A tank that costs a few hours of residence time removes that load at almost no operating cost, which is why the train keeps it in front rather than replacing it.
Where the design stops working
No train is unconditional, and this one is no exception. Free-oil slugs that arrive faster than the upstream tank can buffer will carry through to the flotation stage and shorten its effective capacity. Feed temperature matters, because viscous heavy oil that has cooled below its pour point will not coalesce on the schedule the design assumes. And the KFM stage needs its backwash sequence respected; a media bed that is not cleaned on schedule stops being a polisher and becomes a bypass.
What to fix in the specification
Write the inlet envelope rather than a single design point, including the maximum petroleum substance concentration and the solids load that comes with tank cleaning. Require the oil recovery route to be defined, because recovered oil with nowhere to go becomes waste again. And ask for effluent guarantees at the bottom of the expected temperature range, not at the top, because that is where every heavy-oil site actually operates in winter.