Cleaning of refinery feed oil filter elements

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Cleaning of the filter elements in crude oil filters in refineries – Summary: Crude oil filters are essential equipment for the secondary processing of crude oil in refineries, but they tend to get clogged very easily over time. Using ordinary physical and chemical methods yields poor cleaning results. Through screening, a combination of high-temperature baking, ultrasonic cleaning, and cleaning agents was used for cleaning, with excellent results. Key words: Crude oil filter; Cleaning. The cleaning of the filter element used for crude oil processing. Wang Wei, Wang (Oil Refining Factory of Daqing Petroleum Company, Daqing, Heilongjiang Province 163711). Abstract: Filters for crude oil are essential equipment in oil refineries. However, over time, these filters can easily become clogged. Conventional physical and chemical cleaning methods do not yield satisfactory results. After analyzing various approaches, we combined high-temperature roasting, ultrasonic cleaning, and special cleaning solutions for cleaning the filter elements. As a result, we achieved good outcomes. Key words: Crude oil filter; Cleaning. 1. Introduction: The filters used for crude oil in the hydrogenation units of oil refineries were designed and manufactured by the American company PALL. As shown in Table 1, these filters utilize sintered mesh elements with a filtration precision of 20μm. After being used for filtering and separating crude oil for a period of 1.5 years, the surfaces inside and outside these elements, as well as the spaces between them, became covered with residues such as coke and asphaltenes, leading to severe blockages that prevented proper functioning. This situation caused the catalysts to become clogged and ineffective, significantly affecting both production volume and quality. Common cleaning methods cannot solve this problem. If the cleaning effect is not satisfactory, the filter element, which costs 2.8 million yuan, can only be discarded. Table 1 Basic Data of Filters: Number of models of sintered filters (pieces), specifications (mm), filtration flow rate, material of filter interface. Rigimesh R 203: 330φ25.4×15; flow rate: 54 gpm/ft²; thread type: 1″; material: 316L. 2. Selection of cleaning methods: Since these filters are composed of sintered mesh elements with a filtration precision of 20μm, it is not possible to clean them using ordinary physical or chemical methods. Cleaning is carried out through screening by combining high-temperature baking, ultrasonic cleaning, and cleaning agents. 3. Cleaning: The cleaning process is as follows: 3.1 Remove the filter element on-site. This cleaning must be carried out in a designated location, and the filter element needs to be removed first. During disassembly, follow the established procedures and arrange the components properly. Then check each filter element for any signs of deformation or damage; wrap them in wear-resistant cloth to ensure they are protected, and place them in specialized wooden boxes before transporting them to the cleaning facility. 3.2 Equipment and materials for cleaning filter elements: a) Cleaning furnace: capable of baking off excess oil and impurities from the filter elements at a temperature of 380°C continuously; b) CNC ultrasonic cleaner; c) Pressure-regulable spraying equipment; d) Heated cleaning tank; e) Powerful cleaning agents, high-efficiency water-based cleaning agents. Due to the intergranular corrosion of austenitic stainless steel caused by chloride ions, the strong cleaning agents and high-efficiency water-based cleaning agents used contain no chlorides. f. The cleaning water used is well water, filtered through a 5μm filtration device, with a chloride ion content of less than 20 ppm. g. The gas used is filtered through 5μm dust removal equipment. 3.3 Cleaning process a: Measure the pressure difference of the filter element before cleaning; the surface of the filter element was severely clogged before cleaning. b. Place the filter element in a furnace under nitrogen protection, raise the temperature to 380°C and maintain it for 2 hours to bake off any excess oil, dirt, and impurities on the filter element, as well as to remove carbonized particles and asphaltenes. c. Place the filter element in the ultrasonic cleaner tank filled with a strong cleaning solution, heat it to 80°C, and maintain that temperature for 1 hour. This process induces cavitation, allowing the cleaning solution to penetrate every tiny corner of the filter element, thereby reducing dirt to zero. At the same time, a Hanging piece corrosion testing method is used in the cleaning tank to determine the degree of corrosion caused by the cleaning agent on the filter element. d. Rinse the filter element from the inside and outside with filtered water for 20 seconds to wash away the cleaning agent. e. Use the filtered air for back-blowing for 20 seconds to dry out the moisture. f. Place the filter element in the tank of the ultrasonic filtration machine filled with a high-efficiency water-based cleaning agent, heat it to 80°C, and soak it for 1 hour. At the same time, conduct a Hanging piece corrosion test in the cleaning tank to determine the degree of corrosion of the filter element caused by the cleaning agent. g. Rinse the filter element with filtered water. h. Backwash the filter element with filtered water for 20 seconds. i. Blow with filtered air in the reverse direction for 20 seconds to dry out the moisture. j. Place the filter element in a cleaning oven and dry it at 50°C. k. Examine the inside, outside, and surface of each filter element under a 30x magnifying glass to check its cleanliness. 3.4 Hazard prevention measures throughout the cleaning process: a. Since high-temperature baking at 380°C is used during cleaning, temperature control must absolutely not exceed the metal’s embrittlement temperature. At the same time, nitrogen must be introduced into the furnace for protection. b. The chemicals used in cleaning contain no chloride ions, and the corrosion of metals should be kept at ≤1.0 g/m2·h. c. During shipping, care should be taken to prevent the filter element from coming into contact or collision with other metal objects, so as to avoid ferrite transfer and preserve the filter element’s corrosion resistance. Special packaging boxes are manufactured in accordance with relevant standards, and measures are taken to protect the filter elements from one another, ensuring that they remain undamaged during transportation. 3.5 Acceptance methods and standards: a) Inspection under a 30x magnifying glass: The surface of the filter element is clean both on the inside and outside; it shows its natural color and is free from damage. b. Equipment corrosion rate: Stainless steel ≤ 1 g/m2·h ； The cleaning process is determined using the hanging plate method. c. Measure the compression air filtration pressure drop of each filter element after cleaning; it should not exceed 3160 Pa (for new filter elements, it should not exceed 2763 Pa), with all pores essentially open. 4. Cleaning and Inspection 4.1 Inspection Standards a. Inspect under a 30x magnifying glass: The surface of the filter element should appear clean both on the inside and outside; it should show its original color and be free from any damage. b. Equipment corrosion rate: Stainless steel ≤ 1 g/m2·h ； The cleaning process is determined using the hanging plate method. c. Measure the compressed air filtration pressure drop of each filter element after cleaning; it should not exceed 3158 Pa (for new filter elements, it should not exceed 2763 Pa), with all pores essentially open. 4.2 Effects 4.2.1 Surface inspection: Upon examination with a 30x magnifying glass, the interior and exterior of the filter element show a clean surface; the filter element retains its original color and is free from damage. 4.2.2 Corrosion rate testing: The filtration elements used in the crude oil filters were tested using the hanging slice method, and the results met the required standards. The values were as follows: 50 filtration elements: ≤ 0.66 g/m2·h; 50 filtration elements: ≤ 0.69 g/m2·h; 50 filtration elements: ≤ 0.71 g/m2·h; 60 filtration elements: ≤ 0.73 g/m2·h; 60 filtration elements: ≤ 0.75 g/m2·h; 60 filtration elements: ≤ 0.77 g/m2·h. It can be seen that all these values are below the standard of ≤1 g/m2·h for stainless steel. 4.2.3 Permeability test: Before cleaning, 33 filters out of the 330 filters used in the crude oil filtration system were selected as samples, and their air permeability was tested using compressed air; these samples represented 10% of the total number of filters. The test results are shown in Table 2: Table 2 – Conditions before cleaning. Filter model, air flow rate, pressure difference in Pa, number of filters, percentage of filters sampled: Rigimes R: 2020 m3/hour, 4605, 1236.4; 4736, 1030.3; 4868, 1133.3. It can be seen from these sample test results that the pressure difference is greater than 3158 Pa in all cases. After cleaning the crude oil filters, each filter element was inspected under a 30x magnifying glass to ensure that its interior, exterior, and surface were clean, showing their natural color without any damage. Subsequently, the air permeability of each filter element was tested using compressed air; the results are shown in Table 3: Table 3: Conditions after cleaning. Filter model, Air flow rate, Pressure difference, Number of filter elements, Percentage of samples tested: Rigimes R: 2020 m3/hour, 2961, 1200, 60.6%; 3026: 1003, 30.3%; 3092: 309.1%. As can be seen from these test results, the pressure difference was no greater than 3158 Pa, indicating that the filters were cleaned effectively. The air permeability of each filter element exceeded 90%, confirming that this cleaning process was effective. 4.2.4 Usage Status: After cleaning, it met the required usage standards after 4 months of use; details are shown in Table 4: Table 4 Usage Status – Process parameters before cleaning vs. those to be achieved after cleaning. The backwash filter’s auxiliary line is slightly open; if it were fully closed, the switching time would be around 30 minutes, whereas the normal setting for the switching time is 2 hours. Filter clogged (the specific filtration accuracy cannot be determined). Cleaning improved the purity of the feed oil, provided better protection for the catalyst, and reduced the differential pressure in the reactor bed. After cleaning, the equipment regained its functional capability. All feeder lines are turned off, with a switching time of around 2 hours. The filtration accuracy of the filter has been restored to the original 20μm. 5. Conclusion: Through the acceptance and evaluation of the raw oil filter elements after cleaning, it was found that cleaning improved the cleanliness of the hydrogenation feed oil after filtration, provided better protection for the catalysts, and reduced the differential pressure across the reactor bed. After cleaning, the equipment regained its functional capacity; all connections were disconnected, and the switching time was around 2 hours. The filtration accuracy of the filter has been restored to the original 20μm. ”The appearance inspection of the cleaned filter element is the same as that of a new one. The filter element cleaning achieved its goal: the permeability of the filter element reached over 90%, fully restoring its flow capacity. The filtered element after cleaning fully meets the usage requirements of the original design. After cleaning, this equipment, which costs 2.8 million yuan, is restored to its original operating performance; cleaning can save 2.5 million yuan in equipment costs.