Two-Stage Purely Physical Route for Tank-Farm Cut Water: CDFU Flotation Plus HCC Polishing

Anyone who has run a refinery tank farm knows the phrase "cut water" carries a warning. The oil content is extraordinarily high - it can climb past more than 100,000 mg/L - and the emulsion is deep, so oil and water do not part company on their own. Conventional processes fight to hit discharge limits consistently, and the fight is expensive and tiring. The two-stage, purely physical separation route SINOKLE introduced for this duty is worth walking through, because it splits a very hard job into two simpler ones.

Stage One: CDFU Cyclonic Dissolved Air Flotation

CDFU draws its capability from two things: how it makes bubbles, and how it captures oil. The dissolved-air system forces air into water under pressure; a release device then drops the pressure abruptly, and the water gives up a swarm of microbubbles that are extremely fine and enormous in number. Once those bubbles are in the oily water they collide with emulsified droplets and cling to them, forming bubble-and-droplet aggregates. Because the aggregate density sits far below that of water, buoyancy lifts it to the surface quickly, where a skimming device collects the floating oil layer.

The cyclonic geometry adds a second lever. It intensifies the flow-field disturbance inside the unit, which raises the odds that bubbles and oil droplets meet at all. That is exactly what microbubble flotation needs on a heavily emulsified feed, and it is why the first stage can strip the bulk of a load measured in six figures of mg/L.

Stage Two: HCC High-Efficiency Cyclonic Coalescer

After the first pass most emulsified oil is gone, but a small population of fine droplets survives. HCC exists to deal with that remainder. Oily water entering the unit spins at high speed inside the cyclonic field, and centrifugal force drives droplets toward the centre. At the same time the water passes through coalescing media, where fine droplets wet and adsorb onto the surface, collide, and merge into larger droplets. Those larger droplets rise quickly under buoyancy and separate. It is a dual mechanism - cyclonic separation plus coalescence - and it pulls the second-stage effluent oil content down further, giving the site a defensible margin on discharge limits.

Why the Two Stages Belong Together

The stages are not simply chained in series. They divide the labour deliberately. CDFU handles the main separation of high-concentration, heavily emulsified cut water, lifting the overwhelming majority of oil and suspended solids out and sharply reducing the downstream load. HCC then applies deep coalescing separation to the fine droplets left in the flotation effluent, which is what keeps treated quality steady when the feed is not steady.

Put plainly, the first stage solves the problem of quantity and the second solves the problem of quality. Joined tightly, they form a complete removal chain that runs from oil contents on the order of 100,000 mg/L all the way to compliant discharge. Neither unit could reach that endpoint alone.

How It Compares With Established Options

• Applicable oil types. Conventional oil separation handles floating oil and free oil only, while conventional flocculation can take on emulsified oil. The CDFU+HCC combination covers emulsified oil, dissolved oil and suspended solids.
• Chemical dosing. Conventional oil separation needs no dosing but is limited; flocculation demands a large chemical dosage. The two-stage physical route uses zero chemicals.
• Secondary pollution. Flocculation leaves oily sludge and scum classified as hazardous waste. The purely physical chain leaves no secondary pollution.
• Oil recovery. Conventional routes recover only partially, or find recovery difficult. Here the recovered oil goes straight back to the crude oil tank.
• Effluent quality. Settling struggles to meet standards and flocculation fluctuates widely, while the two-stage physical train delivers effluent that meets discharge standards.

What the Split Buys the Operator

There is a practical reason the two-stage layout is easier to live with than a single heroic unit. Because the first stage absorbs the bulk load and the second works on the residual, neither has to be oversized for the worst case at every point. Feed that arrives heavier than usual is mostly handled up front, and the polishing stage keeps its margin because it is dealing with a much smaller droplet population. That is the difference between a process that meets limits on a good day and one that keeps meeting them when the tank farm is behaving badly. Sizing also becomes more forgiving, because extra margin can be bought cheaply in the first stage rather than expensively across the whole train.

Application Value in One Paragraph

Measured by process completeness, CDFU plus HCC two-stage purely physical separation treats highly oily, heavily emulsified cut water in a way that holds up: the effluent meets discharge standards and satisfies environmental requirements; recovered oil returns to the crude oil tank, turning a waste stream into a product; and the whole route runs on zero chemicals with no secondary pollution, sidestepping both the dosing bill and the hazardous-waste burden. For tank farm operators who weigh environmental compliance and resource recovery equally, that combination is about as workable as a technical option gets.