Sour Water De-oiling with CDFU and KHC: A Physical Route Without Chemicals
Refinery sour water looks like a solved problem until the stripper starts fouling. The ammonia and sulphide come out easily enough with heat and steam; what does not come out is the fine coke and oily sludge that carries aluminium compounds into the trays and the reboiler, where they bake into scale. Every de-oiling upgrade in a sour water system is really an attempt to keep that material out of the tower.
Where sour water comes from
Rising petroleum product demand keeps pushing refining pollution control up the agenda, and the source of the problem sits in the crude itself. Crude oil is rich in sulphides and nitrides which, after high-temperature cracking, catalytic refining, delayed coking, catalytic hydrogenation and similar steps, convert into acid gases such as hydrogen sulphide (H2S) and ammonia (NH3). Those gases are absorbed by water in the units downstream, producing an industrial wastewater carrying sulphur, ammonia and a good deal else - the stream the industry calls sour water.
The equilibrium the stripper exploits
A sour water stripper exists to take ammonia and hydrogen sulphide out of sulphidic wastewater so that what leaves is stripped water with low ammonia nitrogen and low sulphide. Both species dissolve and ionise, and ammonia is the more soluble of the two; solubility for both falls as temperature rises. When the two coexist in water they sit in chemical, ionisation and phase equilibrium, and raising the temperature shifts those equilibria to the right. Stripping works on exactly that principle: the sour water is heated above 140 °C, which destroys the equilibrium holding hydrogen sulphide and ammonia in the liquid and drives them into the vapour phase, while steam lowers their partial pressure in the gas so that the residual content in the water falls further.
The scaling problem nobody budgets for
That heat and that chemistry make the upstream de-oiling duty unforgiving. Foulant found in stripper trays and reboilers is mainly composed of aluminium compounds, and those compounds originate in the suspended solids - coke fines above all - and the oily sludge carried in with the sour water. Conventional de-oiling relies on a combination of air flotation, gravity settling and membrane filtration. It meets the specification for a while. Then the membrane modules clog, maintenance costs climb, and the de-oiling and coke-fines removal performance stops being something the operator can rely on over a long campaign. Once the fines reach the tower, the energy penalty and the downtime follow.
The CDFU and KHC combination
The SINOKLE answer is a combined decontamination flowsheet of coarse filter, CDFU high-efficiency compact cyclonic flotation, fine filtration and KHC high-efficiency coalescing separator. It works on the density difference between the oil, gas and water phases and achieves separation by purely physical demulsification, with no chemical dosing at all. Energy consumption is low, automation is high, effluent quality is consistent, and the treated water can go straight back to the stripping unit - which is what long-term full-load operation actually requires.
CDFU stands for Cyclonic Dissolved gas Flotation Unit: cyclonic dissolved gas flotation equipment that combines ultra-fine bubble generation, cyclonic centrifugal separation and dissolved gas flotation separation in one vessel. Dissolved gas and swirling flow together produce micro and nano bubbles, which lifts the flotation effect sharply while cutting flotation time, and the unit removes suspended solids, waste oil, emulsified oil and several other indicators quickly. It suits the whole range of difficult oily and solids-bearing wastewater found in refineries and chemical plants.
The KHC high-efficiency coalescing de-oiler applies Stokes' law, shallow-pool theory and the coalescence principle, and improves on conventional de-oiler design through the centrifugal action of an inlet swirl that separates dispersed oil while accelerating droplet coalescence. A special sand-washing system inside the vessel flushes on a schedule set by the sediment load, so the tank interior and the packing do not block and performance stays flat. It runs in petroleum, refining, power plant and oil depot service without drama.
Two field cases
A sour water treatment test on the overhead system of a chemical enterprise ran on pilot equipment with a pilot water flow of 3 m³/h. The inlet was emulsified sour water at an oil content of 5%; the effluent came out at oil content ≤50 mg/L, and water content in the recovered oil stayed ≤0.1%. A coking sour water treatment unit at a Sinopec refinery, with a capacity of 15 m³/h, took inlet wastewater at oil content ≤150,000 ppm (15%) and returned effluent oil content ≤50 ppm on average.
Those figures matter less as headline numbers than as evidence about fines. A train that keeps solids out of the stripper feed is a train that keeps the reboiler clean, and a clean reboiler is where the energy saving in a sour water system is actually booked - not in the de-oiling unit itself, which is only the instrument that makes it possible.