Petrochemical Water Purification: Treating High-Oil and High-Salinity Wastewater

The large volumes of tracing steam condensate and process condensate generated by petrochemical plants are characterized by high temperature and good water quality, but they often carry free oil and emulsified oil droplets. If directly discharged, this condensate would cause a massive waste of thermal energy and water resources. During purification treatment, this condensate first undergoes coarse separation through an "oil collection tank + oleophilic-hydrophobic fiber bundle coalescer." Subsequently, it goes through an activated carbon filter or ceramsite filter media for deep adsorption, reducing the oil content to below 0.3 mg/L. Only after this can the water be sent to the boiler feed water system. The difficulty with this purification combination lies in the fact that the oil content in the incoming water fluctuates drastically and may carry sudden loads of heavy tar. Such conditions can very easily lead to filter media hardening and failure. Therefore, an online oil analyzer and an emergency bypass must be installed at the front end. This ensures that the boiler—the heart of the power system—is protected from oil contamination, preventing boiler tube rupture accidents.

The high-concentration sulfur- and ammonia-containing wastewater generated during oil refining and ethylene cracking is a toxic and hazardous treatment target in petrochemical water purification. For this type of wastewater, the system typically employs a single-tower or dual-tower pressurized steam stripping process. This process exploits the differences in the hydrolysis characteristics of hydrogen sulfide and ammonia under varying temperatures and pressures to drive them out of the water stage by stage. The acid gas from the top of the stripping tower is then sent to a sulfur recovery unit and converted into elemental sulfur. The key operational challenge is that this type of sour water exerts an extremely strong stress corrosion effect on the tower body and its internals. Therefore, the selection of the tower material and lining directly determines the equipment's service life. At the same time, optimizing the energy consumption of the stripping steam and achieving refined ammonia recovery are also key steps in reducing operating costs and improving efficiency.

Achieving zero liquid discharge for comprehensive wastewater is the final hurdle of the entire process. The RO concentrate often rejects ultra-high concentrations of refractory aromatic hydrocarbons, and therefore, conventional reverse osmosis membranes are highly susceptible to fouling. For this reason, the system needs to employ a combined "advanced oxidation decomplexation + specialty anti-fouling membrane" process for treatment. The evaporation crystallizer at the terminal end must be able to resist chloride ion corrosion and the coking and scaling of organic matter on heating surfaces. Therefore, selecting duplex stainless steel materials and strictly controlling the crystallization temperature and seed crystal recirculation are the core measures to ensure stable equipment operation. Currently, the overall technological trend is developing towards intelligent chemical dosing and online membrane system monitoring. This trend aims to flexibly respond to the complex and variable conditions of petrochemical incoming water, ultimately achieving a complete transformation from wastewater characterized by high oil, high salinity, and high chemical oxygen demand into reusable pure water and solid salts.