Acidic Water From Refining and Coking: Why Conventional Units Choke and Which Process Chain Holds the Line
Acidic water from refining, chemical and coking units is among the least forgiving streams an environmental engineer handles. Sulfides, ammonia nitrogen and phenols arrive in force at low pH, oil droplets are small and firmly emulsified, and every downstream unit feels the consequences when the water is poorly treated. SINOKLE has built a treatment answer around its CDFU technology that takes the stream head-on.
The stream originates across the plant: sour water strippers, coking units, catalytic crackers and acid gas treatment all contribute, and each source carries its own signature of sulfides, phenols and cyanides. Blending them into one header makes the feed worse, not better, which is why the treatment train is specified against the blended worst case rather than any single contributor.
What the water actually contains
Typical acidic water carries oil at 500-3,000 mg/L and suspended solids dominated by coke powder at 50-200 mg/L, with a high proportion of droplets below 5 μm and severe emulsification. That combination defeats ordinary gravity equipment: the oil will not rise, the solids will not settle, and conventional methods routinely fail to separate either effectively.
Why plants feel it operationally
The pain shows up in three places. High pollutant concentrations upset downstream treatment, and strippers clog easily enough to force unplanned shutdowns. Sulfides and ammonia nitrogen generate irritating odors that reach beyond the fence line and concern employees inside it. And direct discharge under any of these conditions places enormous environmental pressure on the operator, at a time when regulators are watching acidic water more closely than ever.
Single machines rarely survive this stream, and the reason is the droplet population. Free oil is easy, but the bulk of the oil sits in micron-scale droplets stabilised by naphthenic acids and sulfides, so a gravity separator exports the problem downstream rather than solving it. Breaking that population down needs size-graded treatment: coarse capture first, cyclonic flotation for the emulsified middle, and coalescing media for the polish. That is exactly what the three process combinations encode, and matching the combination to the inlet analysis is the whole art of the design.
The CDFU core and the three process combinations
The CDFU (cyclonic dissolved air flotation) unit integrates cyclonic separation, dissolved air flotation and ultrafine bubble technology. Its bubbles measure only 5-30 microns in diameter, which is what drives single-stage oil removal above 90% together with substantial suspended solids capture. Around that core, SINOKLE assembles the train to the water: high-concentration conditions take a coalescing pressure deoiler, a multi-phase cyclone filter and a KHC coalescing oil-water separator; conventional conditions run the multi-phase cyclone filter plus KHC pairing; complex conditions add a coarse filter, CDFU and fine filter ahead of the KHC high-efficiency coalescing oil-water separator.
Performance in numbers
The headline spec: inlet oil of 5,000 mg/L or less reduced to 50 mg/L or less. In a refinery project in Chad, Africa, running 20 m³/h with inlet oil of 500 ppm or less, outlet oil settled at 15 ppm or below, excluding dissolved oil. Operation is fully automatic on a PLC control system with intelligent backwashing and remote monitoring, cutting labour cost sharply. The train is shock-resistant, absorbing flow fluctuations of about plus or minus 30% while staying stable on complex feed. Economics follow the engineering: operating costs run 20%-30% below traditional gravity settling, the footprint drops by two thirds, and a 50 m³/h project recovers roughly 1,584 tons of light oil per year, revenue that funds the rest of the environmental programme.
The recovered oil is not a rounding error either. Light oil recovered from acidic water returns to the refinery's product stream after minimal handling, and at the volumes a 50 m³/h train processes, the recovery line item funds operation of the environmental system several times over. Backwashing keeps the coalescing media online without chemical cleaning, so the recovery continues at design efficiency between maintenance windows.
The Henan case: 15% oil in, on-spec out
At a Sinopec petrochemical company in Henan, the emulsified acidic water treatment project processes 15 m³/h with inlet oil as high as 150,000 ppm, which is 15% oil by fraction. Using the combined process of coarse filter plus CDFU plus fine filtration plus the KHC high-efficiency coalescing oil-water separator, outlet oil holds stably at 50 ppm or below. Few streams in the industry announce their difficulty this plainly, and the train absorbs it without drama.
SINOKLE backs the package with more than 30 patents, among them 7 invention patents and 1 PCT international patent, with ultra-micro nano bubble generation and special super-hydrophilic material modification driving the next round of gains. For industrial operators, the practical takeaway is that acidic water is not a single problem but a family of them, and the fix is a matched process chain rather than a single machine: knock out free oil, break the emulsion physically, polish with coalescing media, and automate the whole sequence so it survives the feed swings that acidic water guarantees.