Major Progress in Coking Wastewater Purification: Integrated CDFU and KHC Process Effectively Tackles Acidic Water Treatment Challenges
The acidic wastewater generated during coking mainly comes from the overhead reflux drum of the fractionator, the small quench water of the coke drum and the large steam purge. Among them, the acidic water discharged from the fractionator overhead reflux drum is a continuous discharge source.
This coking acidic wastewater has the following notable characteristics:
Coking acidic water has a complex composition: high coke powder content with a small particle size distribution;
high oil content, small oil droplets and severe emulsification;
high sulfur, ammonia nitrogen and phenol levels
The necessity of effectively treating coking acidic water is mainly reflected in the following:
This industrial wastewater has poor biodegradability and is difficult to treat. If it enters the stripper directly without pretreatment, the coke powder tends to combine with waste oil under the heat of steam to form a viscous gel, plugging the valve trays inside the stripper, which not only lowers purification quality but also seriously affects stripping efficiency.
If not cleaned in time, continued operation will negatively affect the entire unit. As plugging worsens, the coking unit must shut down for cleaning, extending the production cycle and increasing operating costs. Tray plugging is related both to poor influent quality and to the limited fouling capacity of conventional trays, a phenomenon particularly prominent during long-term operation of acidic water stripping units.
Therefore, this acidic water must undergo de-oiling and coke powder removal pretreatment to ensure the stripper can effectively remove volatile components such as hydrogen sulfide, ammonia and volatile phenols.
To address the problem of a petrochemical company's coking acidic water exceeding oil and suspended solids limits, SINOKLE adopted a purely physical oil-water separation skid built around CDFU (cyclonic dissolved-air flotation) + KHC (coalescing de-oiler) as the core technology to treat the wastewater.
Figure 1. Coking acidic water treatment process flow diagram
The main advantages of this coking acidic water treatment process:
① Purely physical demulsification with excellent effect, effectively separating emulsified oil and suspended solids from the wastewater
② No chemical addition and no oily sludge generated
③ The waste oil separated by the unit has a low water content and can be re-refined, saving resources while generating revenue
④ Strong shock resistance and stable operation
⑤ Small footprint, enclosed operation, safe and environmentally friendly
In August 2023, SINOKLE completed commissioning of an additional acidic water treatment skid retrofit at the coking unit of a large petrochemical company in Henan Province. The equipment ran continuously and stably for more than half a month with good effluent quality, and the workshop conducted a 72-hour performance test of the skid to assess its ability to remove waste oil and suspended solids from the acidic water and evaluate equipment performance.
Complete coking acidic water treatment unit
During this period, the oil content of normal water draw from the fractionator overhead reflux drum was around 5%-8% with severe emulsification, and the acidic water oil content during the small steam purge exceeded 10%. After treatment by the unit, the effluent was clear and transparent with oil below 100 mg/L (de-oiling rate above 99%) and suspended solids below 10 mg/L, outperforming the technical indicators of influent oil no more than 10%, solids no more than 880 mg/L, effluent oil no more than 500 mg/L and suspended solids no more than 10 mg/L; the performance acceptance was passed.
Coking acidic water treatment performance
The acidic water treatment skid has been running continuously and stably ever since, with consistently good treatment results and strong shock resistance, keeping the effluent stably compliant even under large influent quality fluctuations. The successful implementation of this project marks an important breakthrough for SINOKLE's new acidic water treatment process in the field of acidic water treatment in the petroleum refining industry.
