Holding Power-Plant Draw-Off Water Below 10 mg/L With Two-Stage CDFU and KFM Media Filtration

Draw-off water from heavy-fuel-oil storage tanks at power plants is a classic hard case in industrial wastewater. It carries high oil and suspended-solids content, it is severely emulsified, it looks black, and the treated effluent has to hold oil below 10 mg/L consistently. No single treatment method can manage that combination. The process built on two-stage CDFU cyclonic dissolved air flotation plus a KFM active media filter gives a systematic answer through physical demulsification and deep filtration, and it is worth taking apart along three lines: water-quality characteristics, equipment mechanism and division of labour.

Know the opponent first

The difficulty of oil-depot draw-off water concentrates in three features. Oil content is high, and the oil arrives as a mixture of floating oil, dispersed oil and emulsified oil; gravity settling removes floating oil and is essentially ineffective against the other two. Emulsification is severe, because oil and water form a stable emulsion with droplets wrapped in an interfacial film that conventional demulsification hardly touches, and that is the core contradiction behind difficult draw-off water. Suspended solids are high and the water runs black, since large amounts of tank-bottom sediment and impurities mix in, raising the treatment load and making sensory indicators hard to meet.

The industry control target is effluent oil below 10 mg/L. Getting from black oil to clear water needs a process that genuinely tears the emulsion apart.

CDFU as a three-in-one physical demulsifier

CDFU (Cyclonic Dissolved Gas Flotation Unit) is a proprietary patented technology independently developed by SINOKLE: a new-generation, highly efficient, compact, enclosed and pressurized flotation technology at internationally advanced levels and pioneered domestically. Its design combines three technologies in one vessel.

Cyclonic centrifugal separation creates a cyclonic centrifugal force field inside the enclosed chamber, using the oil-water density difference to strengthen droplet coalescence and accelerate separation. Micro-fine bubble generation produces huge numbers of tiny bubbles that behave like countless small grippers on the oil-droplet surface, raising rise efficiency substantially. Dissolved air flotation dissolves and releases air in an enclosed pressurized environment, releasing bubbles uniformly and efficiently for rapid separation of oil, water and suspended solids.

Working together, these three achieve efficient separation of foul oil, emulsified oil and suspended solids, and the whole process is pure physical demulsification with no chemicals at all. That is the fundamental difference from the traditional chemical-dosing flotation route, and it is also why the recovered oil is worth having.

Two stages, and why not one bigger one

The two-stage arrangement is a division of labour rather than a simple series connection. The first-stage CDFU carries the main treatment load, rapidly removing large amounts of floating oil and coarse suspended solids so that the fine treatment downstream is not buried. The second-stage CDFU handles fine separation of emulsified and finely dispersed oil, taking on the hardest fraction specifically. Working in synergy, the pair treats high-oil, high-suspended-solids, high-emulsification water efficiently while avoiding the performance swing that comes from overloading a single unit.

The foul oil separated out goes to a collection tank, and because the separation is purely physical it is never contaminated by chemicals, so the recovered oil is high quality and has genuine reuse value.

KFM as the bottom line

After two-stage CDFU, residual trace oil droplets and fine suspended solids face final deep filtration in the KFM active media filter. The deep interception capability of the active media locks effluent oil content firmly below 10 mg/L, which is the difference between a process that usually works and one that reliably passes.

KFM is periodically backwashed during operation, and backwash water goes to the sludge tank for centralized treatment, so the filter keeps high efficiency over the long term. That periodic backwash detail is precisely the safeguard mechanism behind long-term stable compliance, and it is the item most often under-specified at design stage.

Against the conventional route

Against simple oil separation or chemical DAF, the differences line up clearly. Demulsification moves from chemical dosing, or a separator that cannot break emulsified oil at all, to cyclonic plus microbubble plus DAF physical demulsification. Process design moves from single-stage, load-sensitive treatment to two-stage gradient separation with deep-filtration backup. Effluent compliance moves from large fluctuation and instability to a stable figure at or below 10 mg/L. Chemical dependence disappears, so secondary pollution disappears with it. Oil recovery changes from a stream mixed with chemicals that is hard to reuse into a clean, reusable product. O&M changes from complex chemical management to an enclosed pressurized unit with a closed backwash loop.

The short version

Two-stage CDFU owns physical demulsification and gradient separation; KFM owns deep filtration and backwash regeneration. The two chains interlock and hold effluent oil from oil-depot draw-off water below 10 mg/L. Pure physical, zero chemicals, stable compliance and recoverable oil: for heavy-fuel-oil storage-tank draw-off water, that combination delivers technical reliability, operating economy and resource-recovery value in the same package.