Sources and Treatment Challenges of High-Emulsification Acidic Wastewater in Refining

In refining and petrochemical production, high-emulsification, high-acid wastewater is a widely recognised treatment challenge. This stream has a complex composition and fluctuates widely, and treating it effectively directly affects unit stability, resource recovery and environmental compliance. To build a targeted solution, its core sources and treatment challenges must first be clarified.

1. Main sources
This wastewater mainly originates from the following key process units:

1. Crude distillation (CDU/VDU): wastewater comes mainly from the atmospheric tower overhead reflux drum and the vacuum tower overhead water seal drum. The volume generated is directly related to the bottom stripping steam, side-stream stripping steam and overhead water injection rates.

2. Fluid catalytic cracking (FCC): sources include the fractionator overhead reflux drum, the compressor outlet oil-gas separator, the compressor interstage condensate drum and the stabiliser overhead reflux drum.

3. Delayed coking: during coking, sulfur- and nitrogen-bearing compounds undergo high-temperature cracking and related reactions, generating hydrogen sulfide, ammonia and other gases. These gases are absorbed by water in subsequent steps, forming sulfur- and ammonia-bearing wastewater.

4. Hydrotreating units (including hydrotreating and hydrocracking): the mechanism is similar — sulfur and nitrogen compounds in the feedstock are converted into acid gases through reaction, which then form acidic wastewater.

2. Core treatment difficulties
Conventional methods for treating this stream typically face the following bottlenecks:

1. Severe emulsification undermines stability: the wastewater contains large amounts of emulsified oil and fine suspended solids, which not only reduce the deacidification and deammoniation efficiency of downstream stripping towers and affect the quality of recovered liquid ammonia, but also readily clog trays or packing and, in severe cases, cause unplanned unit shutdowns.

2. Complex composition and frequent fluctuation: besides oily substances, the wastewater contains high concentrations of corrosive and toxic species such as sulfides and ammonia nitrogen, and both flow rate and quality fluctuate frequently, placing stringent demands on the adaptability of the treatment system.

3. Limited effectiveness of conventional processes: conventional physical methods such as gravity settling and cyclone separation often suffer from incomplete separation and non-compliant effluent, along with easy equipment fouling and high operating and maintenance costs.

In response to these challenges, the industry is continuously exploring more efficient and stable innovative treatment processes.