Treatment of Refinery Atmospheric/Vacuum Overhead Sour Water
SINOKLE SiC Filter + KHC Coalescing Oil Remover Process
With the global trend of inferior and heavier crude oil, refineries face increasingly severe challenges in processing. Among them, the atmospheric and vacuum distillation unit, as the 'forerunner' of the refinery, produces overhead sour water that not only has high oil content but also easily forms stable emulsions. How to efficiently and cost-effectively remove oil from overhead sour water has become a technical pain point that refining enterprises must urgently solve to achieve green, low-carbon, and long-cycle stable operation. This article deeply analyzes the 'SiC filter + KHC coalescing oil remover' combined process launched by SINOKLE, discussing its core advantages and huge economic benefits in refinery overhead water treatment.
I. Necessity and Industry Pain Points of Overhead Sour Water Treatment
The crude-oil processing first separates crude into different straight-run fractions by the boiling points of various products, then removes the non-ideal components from these fractions according to product-quality standards, or converts them through chemical reactions to generate the required components, thereby obtaining a series of qualified petroleum products. In the entire refining system, distillation is the most common and economical separation method and is also the first processing step in refining crude oil.
During the separation of crude into different fractions through pre-distillation and atmospheric/vacuum distillation, the overhead oil-gas is generally condensed and separated into oil, water, and gas in an oil-water separator. Because its condensed sewage usually contains high concentrations of sulfides, the industry calls it sour (sulfur-containing) wastewater. Normally, after stripping treatment, this wastewater is sent as purified water to downstream units for reuse.
However, in recent years, due to the inferiority and diversification of processed crude, the overhead condensate from atmospheric/vacuum units is highly prone to emulsification and oil carryover. This phenomenon not only causes the loss of high-value light oil products but also creates huge operational shocks to downstream stripping and other units, specifically in the following three core aspects:
Severe disruption of gas-liquid equilibrium:As a surface-active substance, oil is highly prone to foaming under the intense vapor-water contact inside the stripper. Large amounts of foam prevent effective mass transfer between vapor and liquid phases, not only increasing steam consumption but also causing serious operational fluctuations, greatly reducing the tower's treatment capacity.
Severe fouling of trays and reboilers:The emulsified oil in overhead water has a very complex composition; when the oil content of the wastewater is high, oil easily accumulates at key heat-transfer and mass-transfer sites such as trays and reboilers, eventually leading to equipment blockage. This not only seriously affects the unit's mass-transfer efficiency but may also cause local hot spots or even overheating, shortening the overall service life and operating cycle of the equipment.
By-product quality contamination:During stripping, if the sour water contains large amounts of hydrocarbons, black sulfur is easily produced after reaction. At the same time, oil carried in liquid ammonia also seriously affects the quality purity of the final by-product.
II. In-Depth Analysis: The Culprit of 'Emulsification' in Atmospheric/Vacuum Sour Water
To thoroughly solve the oil-removal problem of sulfur-containing wastewater, one must first understand why it is difficult to separate. The oil-in-water emulsions in overhead water can remain unseparated for a long time with persistently high oil content; the root cause lies in the physicochemical reactions at the microscopic interface.
As crude inferiority becomes more severe, the inferior heavy oil itself contains large amounts of natural surfactants (such as asphaltenes, resins, petroleum acids, etc.). In addition, various additives added during crude extraction (such as alkylbenzene sulfonic acid, fatty alcohol polyoxyethylene ether, etc.) and corrosion inhibitors added for anti-corrosion in atmospheric/vacuum distillation (such as alkaline solutions) together form large amounts of anionic surfactants in the wastewater.
These macromolecular surfactants have low hydration and can directly penetrate the water film, enter the inner Helmholtz plane to replace the water dipole layer, and produce strong characteristic adsorption with the oil-droplet surface. This adsorption causes a sharp drop in the interfacial tension at the oil-water interface. At the same time, the negative charge on the oil-droplet surface together with the anionic surfactants forms a dense Stern electric double layer, producing a high x potential (Zeta potential).
Under the high-temperature conditions of refineries, the thermal motion and diffusion of liquids are more pronounced, causing the Stern double layer to become thicker, the x potential to increase accordingly, and thus the electrostatic repulsion between oil droplets to become extremely large. More fatally, these surfactants form an oriented adsorption layer at the oil-water interface, building a stable and firm 'protective interfacial film' that tightly hinders the fusion and coalescence of oil droplets upon collision. This is the fundamental microscopic reason why the traditional gravity-settling method is helpless against such emulsions.
III. Limitations of Traditional Sour Water De-Oiling Technology
To ensure the efficiency and stability of the downstream stripping process, the industry generally requires that the oil content of sour water entering the stripper be below 50 mg/L. Currently, major refineries commonly use the large-tank gravity-settling method. This process usually sets up two large tanks in series-one as a settling tank and the other as a buffer tank. To achieve a certain separation effect, the required settling time is generally as long as 50-70 hours. This method not only requires extremely large tank capacity and footprint, but also cannot guarantee the oil-removal effect for stable emulsified oil formed by surfactants, and the floating oil generated in the tank is very difficult to collect and recover.
IV. The Breakthrough: SINOKLE SiC Filter + KHC Coalescing Oil Remover Process
Facing the industry-wide challenge of high-concentration emulsified oil in overhead sour water, merely extending settling time or increasing chemicals can no longer meet the dual pursuit of environmental protection and efficiency by modern refining enterprises. Based on years of experimental exploration and industrial application in the de-oiling field [cite: 12], SINOKLE has launched a new-generation physical high-efficiency de-oiling combined process-the 'SiC filter + KHC high-efficiency coalescing oil remover' combination.
First line of defense: SiC (silicon carbide) filter-high-flux interception and primary demulsificationBecause overhead sour water usually contains mechanical impurities such as coke powder and ferrous sulfide (FeS), these fine solid particles easily adsorb at the oil-water interface, forming the so-called 'solid-stabilized emulsion' (Pickering emulsion), greatly enhancing the rigidity of the emulsion. The SINOKLE process first uses an SiC tubular/membrane filter for pretreatment. The silicon-carbide ceramic material not only has excellent high-temperature resistance and strong acid/alkali corrosion resistance, but also extremely strong hydrophilic-oleophobic properties. When sulfur-containing wastewater passes through the SiC filtration medium at high flux, it not only thoroughly intercepts micron-level suspended solids (SS), breaking the foundation of 'solid-stabilized emulsification,' but also, due to the shear force of the pores and the hydrophilic-oleophobic surface, performs a certain degree of pre-coalescence and demulsification of emulsified oil droplets, clearing obstacles for subsequent deep de-oiling.
Second line of defense: KHC coalescing oil remover-microscopic collision and phase separationThe emulsion that has passed pre-filtration and had solid impurities removed then enters the KHC high-efficiency coalescing oil remover. The equipment is filled with a polymer oleophilic modified-fiber coalescing cartridge independently developed and patented by SINOKLE. When water containing micro/nano-scale oil droplets flows through the dense coalescing bed, relying on the dual action of fluid mechanics and surface chemistry, oil droplets undergo four microscopic steps on the filter surface: 'interception - wetting - attachment - fusion.' Tiny oil droplets are captured on the extremely large inter-phase contact area and, guided by the coalescing material, break through the aforementioned 'Stern electric double layer' repulsion, rapidly colliding and fusing into large oil droplets of tens of microns or even millimeters. Subsequently, the large oil droplets rapidly float up to the oil-collection zone at the top of the equipment under buoyancy, achieving high-precision liquid-liquid separation. According to SINOKLE's industrial application data at Luoyang Petrochemical for 15 m3/h sulfur-wastewater treatment, under the extreme condition of average influent oil content as high as 15%, the effluent oil concentration remained stably below 50 mg/L, and the single-system oil-removal efficiency reached an astonishing 99.96%.
V. Excellent Technical and Economic Benefit Comparison
Introducing SINOKLE's 'SiC filter + KHC coalescing oil removal' combined process is not only a means to environmental compliance but also a 'profit point' for refineries to reduce costs and increase efficiency.
Compared with the large-tank gravity-settling method requiring a residence time of 50-70 hours, this combined process requires only 5 minutes of residence time for emulsified-oil removal. More critically, because it uses pure physical separation (no demulsifier added), the recovered light emulsified oil is unpolluted in quality and can directly enter the unit for re-refining. This completely avoids the oil-processing losses caused by poor recovered-oil quality in traditional processes.
Taking sour water with a treatment capacity of 30 m3/h (oil content 2%, annual operation 8,000 hours) as an example, if this combined process recovers 300 mg/L more light emulsified oil than the traditional gravity-settling method, just the light-oil recovery alone can generate about 430,000 RMB in direct economic benefit per year (based on light oil at 6,000 RMB/ton). Comprehensively considering the avoided light-oil processing loss (2.4 million RMB), compared with gravity settling, its annual comprehensive benefit can exceed 2.84 million RMB.
Moreover, in terms of energy reduction and system optimization, front-end high-efficiency de-oiling directly reduces the oil entering the stripper. Temperature and pH have a large effect on stripping; under normal temperature, pH 7.5, and well-controlled gas-liquid ratio, effectively combined with other desulfurization means, it can even partially replace traditional high-energy steam stripping. It is estimated that for a 30 m3/h scale, if part of the stripping load can be replaced, plus the saved stripper blockage maintenance cost (about 120,000 RMB/year), the comprehensive energy savings and direct benefits can total up to 10.56 million RMB/year
VI. Conclusion
Facing the increasingly stringent safety/environmental standards and profit-margin challenges of the refining industry, process innovations in details often bring huge butterfly effects. SINOKLE's 'SiC filter + KHC coalescing oil remover' combined technology precisely breaks the pain point of difficult separation of fine emulsified oil in overhead sour water, transforming the 'waste liquid' that originally harmed downstream equipment and caused oil-product losses into high-quality re-refined oil and compliant purified water. Its technical performance of 5-minute ultra-fast separation, constant high efficiency, and high-return payoff undoubtedly provides a scientific, reliable, and novel solution path for the quality-and-efficiency improvement of sulfur-wastewater projects in modern smart refineries.
