Discussion on the treatment technology for oily wastewater generated in electrodesalination processes in the refining and petrochemical industry
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First, let’s discuss the reasons for the generation of electrodialysis wastewater. 1. With the successive development of various oil fields and an increase in imported crude oil, refineries have a more diversified source of crude oil, resulting in more complex compositions ； 2. Meanwhile, as oil extraction progresses, the quality of crude oil declines, with an increase in heavier and lower-quality crude oil ； 3. To improve efficiency and increase the utilization rate of crude oil, major refining plants typically mix recycled heavy contaminated oil, after preliminary treatment, back into the crude oil for blending, thereby further exacerbating crude oil emulsification ； 4. The equipment operates for long periods of time, and sometimes even under overload; inadequate maintenance and operation contribute to poor demulsification performance of the electrodesalination unit. As a result, the oil-water interface level in the electrodesalination tanks remains unstable, and the oil content in the output water exceeds acceptable levels by a large margin. This not only imposes a significant burden on downstream wastewater treatment plants but also leads to the waste of large amounts of high-quality crude oil. If left unaddressed, this situation fails to meet current requirements related to energy conservation, environmental protection, and sustainable development, causing environmental and reputational damage to the enterprise.
Characteristics of existing electrodesalination oily wastewater: 1. High content of heavy oil, with a density very close to that of the wastewater, making separation difficult. 2. High oil content, which can exceed 20% in some cases. 3. Small particle size of oil droplets, leading to severe emulsification and difficulty in separation. 4. Presence of large amounts of fine suspended particles, which exacerbates the emulsification of crude oil in the wastewater. 5. It has a high salt content and high mineralization level, which causes significant corrosion to equipment, and it also tends to form scale that can lead to equipment blockages. 6. Hazardous gases such as oily sulfides and volatile phenols severely affect the health of employees in the plant area and damage the environment. Table 1: Data on oily wastewater generated by electrodialysis at a petrochemical plant in the south. Table 2: Data on the water quality after water separation via electrodialysis at a petrochemical plant in the north