Research on the application of fiber liquid film technology in crude oil pretreatment

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Abstract: This paper introduces the mass transfer and separation principles of fiber liquid film pre-treatment for crude oil, and conducts industrial tests as well as studies on the adaptability of this method to crude oil. The results show that after three-stage fiber liquid membrane pretreatment, the crude oil has a salt content of <3.0 mg NaCl/L, a water content of <0.2%, calcium and iron contents of <10.0 μg/g, and a water-cut content of <150 mg/L; all these parameters meet the requirements for industrial production, making this method superior to the electrodialysis process. 1. Introduction Liquid membrane separation technology (Liquid membrane permeation, LMP) is a separation technique that utilizes the differences in the permeability of various components within a mixture to achieve separation, purification, or concentration. It represents a new type of separation method that mimics the mass transfer functions of biological membranes, addressing issues such as separation factors and selectivity. It was proposed in 1968 by Dr. Li Nianzhi, a Chinese-American from Exxon in the United States. Liquid membrane separation technology offers advantages over solid membrane separation technology in terms of high efficiency, speed, strong selectivity, and energy savings; compared to liquid-liquid extraction, it features simultaneous extraction and back-extraction, high separation and concentration factors, lower amounts of extractant required, and reduced solvent loss. Among them, the fiber liquid membrane separation technology has seen rapid development in the field of oil refining in China in recent years. 2. The mass transfer and separation principle of fiber liquid film crude oil pretreatment relies on a large number of specially hydrophilic fiber filaments as a support. By taking advantage of the difference in surface tension between the oil and water phases, a very thin layer of liquid film is formed on the surface of these fiber filaments. As the crude oil flows downward along the fiber filaments through this aqueous liquid film layer, a highly efficient mass transfer surface is created, with a short mass transfer distance; this approach avoids the problems associated with phase separation that occur in processes involving dispersed mixing for mass transfer. In crude oil, salt substances migrate toward the aqueous phase film driven by concentration differences. Water-soluble inorganic salts enter the aqueous phase film directly, while oil-soluble organic salts first react with the desalination agents on the surface of the aqueous phase film to be converted into water-soluble inorganic salts before entering the aqueous phase film, thereby achieving the desalination of crude oil. Compared with the traditional electric desalination process for crude oil, the fiber liquid membrane crude oil desalination process has the following technical advantages: it features a simple process flow, and no external electric field or demulsifier is required ； High mass transfer efficiency, with excellent results in dehydration, desalination, and calcium/iron removal ； There is little two-phase entrainment; the water content and COD value of the oil after crude oil separation are low ； High air velocity, large processing capacity ； Low operating costs and strong technical economy ； Environmentally friendly in operation, with high intrinsic safety. Figure 1 Principle flow diagram of fiber liquid membrane crude oil pretreatment. 3. Industrial trials: An industrial test unit for three-stage membrane desalination of crude oil with a capacity of 8×103 kt/a, built using the fiber liquid membrane crude oil pretreatment technology by Sinopec Changling Branch, was successfully commissioned in May 2014 and has been operating well ever since. The raw material used in this processing unit is crude oil transported via the Yichang pipeline, and its properties are shown in Table 1. Table 1: Properties of Crude Oil Transported via the Yichang Pipeline. Parameter: Density (Kg/m3); Value: 963.8. Parameter: Sulfur (m%); Value: 0.9271. Parameter: Viscosity at 100°C (mm2/s); Value: 56.3. Parameter: Nitrogen (m%); Value: 0.5558. Parameter: Resin content (m%); Value: 21.3. Parameter: Nickel (μg/g); Value: 35.5. Parameter: Asphaltenes content (m%); Value: 11.5. Parameter: Vanadium (μg/g); Value: 245.0. The desalination effect is shown in Figure 2; after being treated using a three-stage fiber liquid membrane process, the salt content in the crude oil in the industrial test unit is less than 3.0 mg NaCl/L, with an average value of only 1.5 mg NaCl/L, which meets the requirements for industrial production. Figure 2 shows the salt content of the crude oil after three-stage fiber liquid membrane pretreatment in the industrial tests, which is 3.2%. The dehydration effect is shown in Figure 3; after such pretreatment, the water content in the crude oil in the industrial test setup is less than 0.2%, meeting the requirements for industrial production. Figure 3 shows the water content in crude oil after three-stage fiber liquid membrane pretreatment in industrial tests, which is 3.3%. The demetallization effect is shown in Figure 4; the industrial test setup used the specialized KJ-FMT1 demetallizing agent. After the three-stage fiber liquid membrane pretreatment, the calcium and iron contents in the crude oil were kept below 10.0 μg/g, with a calcium removal rate of over 80% and an iron removal rate of over 70%, satisfying the requirements for industrial production. Figure 4 shows the calcium and iron contents in the crude oil after three-stage fiber liquid film pretreatment in industrial tests; these values are 3.4 respectively. The water-cutting oil content is shown in Figure 5. In the industrial test setup, the water-cutting oil content after three-stage fiber liquid film pretreatment was less than 150 mg/L, which meets the requirements for industrial production. Figure 5: Water cut and oil content of crude oil after three-stage fiber liquid film pretreatment in industrial tests. Data from industrial installations show that, after being treated with the three-stage fiber liquid film method, the crude oil meets the requirements for industrial production. Compared with the electrodialysis process, the injection of demulsifiers and an external electric field are eliminated, resulting in significantly lower operating costs ； The content of cut water oil and COD is significantly lower than that in the electrodesalination process, resulting in notable environmental benefits. 4. Adaptability study of the fiber liquid film crude oil pretreatment technology: An adaptability study was conducted on the relatively typical heavy and low-quality crude oils processed by domestic refineries. As shown in Figure 6, after three-stage fiber liquid membrane pretreatment, the water content of Ma Rui oil is 0.03% ； Salt content: 6.20 mg NaCl/L, desalination rate: 97.05% ； The cutwater oil content is 118.50 mg/L. Figure 6 shows the effect of Ma Rui oil fiber liquid film pretreatment. As shown in Figure 7, after being subjected to three-stage fiber liquid film pretreatment, the water content of Tahe crude oil remains stable at 0.2% ； The average salt content is 7.9 mg NaCl/L, with a desalination rate of over 98% ； The cutwater oil content ranged from a minimum of 6.8 mg/L to a maximum of 93.8 mg/L, with an average value of 36.9 mg/L. All indicators are superior to those of electrodesalination industrial units in the same period. Figure 7 shows the pretreatment effects of the fiber liquid film for Tarim crude oil. The results of the above experiments indicate that the fiber liquid film technology possesses significant advantages in the field of crude oil pretreatment, such as strong adaptability to different types of crude oil, excellent desalination and dewatering performance, and a low content of water-separated oil. 5. Conclusion: As crude oil becomes increasingly heavy and of lower quality, domestic refineries face more and more challenges when using electric desalination technology for crude oil. As a new type of efficient mass transfer technology, studies on the application of fiber liquid film technology in crude oil pretreatment have shown that it can effectively reduce energy consumption during the mass transfer process and minimize entrainment. It offers advantages such as lower investment costs, reduced space requirements, and lower operating expenses. Additionally, it has good adaptability to crude oil, giving it promising prospects for application. Selected Papers from the 2016 National Conference on Advanced Technologies in the Refining and Petrochemical Industry, Hunan Changling Petrochemical Technology Development Co., Ltd