Advancing Sustainable Refining: Analysis of the CDFU + KHC Wastewater Treatment Solution
1. Formation and characteristics of sour water
The continuous growth of petroleum product consumption makes pollution control in refining ever more important. Crude oil is rich in sulphides and nitrides which, after high-temperature cracking, catalytic refining, delayed coking, catalytic hydrogenation and other process steps, are converted into acid gases such as hydrogen sulphide (H₂S) and ammonia (NH₃). These gases are absorbed by water in subsequent processing, forming industrial wastewater containing sulphur, ammonia and other components — commonly known as sour water.
2. Conventional treatment processes and their limitations
The main purpose of a sour water stripper is to remove ammonia and hydrogen sulphide from sulphidic wastewater, so that it becomes stripped water with low ammonia nitrogen and sulphide content.
Both ammonia and sulphide dissolve in water and ionise:
Ammonia is more soluble in water than hydrogen sulphide, and the solubility of both decreases as the temperature rises. When hydrogen sulphide and ammonia coexist in water, they are in chemical, ionisation and phase equilibrium:
At room temperature, hydrogen sulphide and ammonia dissolve in water and exist as ions. When the temperature rises, the three equilibria expressed by equation (3) shift to the right. Sour water stripping makes use of this principle: the sour water is heated to above 140 °C, which destroys the equilibrium of hydrogen sulphide and ammonia in water and drives them from the liquid phase to the vapour phase; at the same time, steam is used to reduce the partial pressure of hydrogen sulphide and ammonia in the vapour phase, so that their content in the water is lowered.
Figure 1. Sour water reuse process in a refinery
However, the scaling problem that commonly exists in this system has a significant impact on long-term stable operation of the unit and on energy consumption control. Studies show that the foulant in stripper trays and reboilers is mainly composed of aluminium compounds, originating mainly from the suspended solids (such as coke fines) and oily sludge contained in the sour water. Conventional de-oiling equipment uses a combination of air flotation, gravity settling and membrane filtration; although it can meet treatment requirements in the short term, the membrane modules clog easily, operation and maintenance costs are high, and the performance in de-oiling and coke-fines removal cannot be reliably sustained over long-term use.
3. SINOKLE CDFU + KHC combined treatment solution
To address the above problems, SINOKLE has developed a combined decontamination flowsheet of “coarse filter + CDFU high-efficiency compact cyclonic flotation + fine filtration + KHC high-efficiency coalescing separator”. Based on the density difference between the oil, gas and water phases, the process achieves efficient separation using purely physical demulsification technology without any chemical dosing, and offers low energy consumption, a high degree of automation and excellent effluent quality; the produced water can be reused directly in the stripping unit, providing reliable support for long-term, full-load, high-quality operation of the system.
Figure 2. SINOKLE solution for refining sour wastewater treatment
CDFU (Cyclonic Dissolved gas Flotation Unit) is cyclonic dissolved gas flotation, a generation of high-efficiency cyclonic dissolved gas flotation equipment that organically combines ultra-fine bubble generation technology, cyclonic centrifugal separation technology and dissolved gas flotation separation technology. By applying dissolved gas and swirling flow to produce micro/nano bubbles, this efficient compact unit greatly improves the flotation effect while sharply reducing flotation time, and can efficiently and rapidly remove suspended solids, waste oil, emulsified oil and many other indicators from water. This efficient compact unit is suitable for treating all kinds of difficult oily (and solids-bearing) wastewater on the market.
The KHC high-efficiency coalescing de-oiler comprehensively applies Stokes' law, shallow-pool theory and the coalescence principle and, on the basis of absorbing advanced technology and concepts at home and abroad, is an optimised and improved new type of de-oiler. Through the centrifugal action of the inlet swirl it rapidly separates dispersed oil while accelerating oil droplet coalescence. A special sand-washing system is designed inside and flushes promptly according to sediment conditions, preventing blockage of the tank interior and packing and keeping treatment performance stable. It runs smoothly in petroleum, refining, power plant, oil depot and other environments.
4. Application cases
• Sour water treatment test on the overhead system of a chemical enterprise
Figure 4. Pilot equipment (pilot water flow: 3 m³/h)
Figure 5. Effluent performance
(Inlet: emulsified sour water, oil content: 5%;
effluent: oil content ≤50 mg/L; water content in recovered oil ≤0.1%)
• Coking sour water treatment unit at a Sinopec refinery
Figure 6. Equipment on site (capacity: 15 m³/h)
Figure 7. Effluent performance
Inlet wastewater oil content: ≤150,000 ppm (15%); effluent oil content: ≤50 ppm (average)
