Coking Acidic Water Stripping Starts With De-Oiling: A CDFU Plus KHC Skid That Passed a 72-Hour Test

Acidic wastewater from delayed coking has three main sources: the overhead reflux drum of the fractionator, the small quench water of the coke drum and the large steam purge. Of the three, the acidic water discharged from the fractionator overhead reflux drum is the continuous discharge source — which means any treatment train has to handle it around the clock, not just during batch events.

What makes this stream so difficult

Coking acidic water is a troublesome combination on three fronts. Coke powder content runs high, with a small particle size distribution. Oil content is high, the droplets are small and emulsification is severe. On top of that sit high levels of sulfur, ammonia nitrogen and phenol. Each contaminant complicates the others: the fines stabilise the emulsion, the emulsion carries the fines, and neither wants to separate.

Why the stripper cannot take it raw

This industrial wastewater has poor biodegradability and is difficult to treat. Sent directly to a stripper without pretreatment, the coke powder combines with waste oil under the heat of steam and forms a viscous gel that plugs the valve trays inside the stripper. Purification quality drops, and stripping efficiency suffers with it. Left uncleaned, the damage spreads across the whole unit: as plugging worsens, the coking unit must shut down for cleaning, extending the production cycle and increasing operating costs. Tray plugging traces back 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.

De-oiling and coke powder removal before the stripper is therefore not an optional refinement. It is what allows the stripper to effectively remove the volatile components — hydrogen sulfide, ammonia and volatile phenols — that it was actually built to handle.

A purely physical skid for the job

When a petrochemical company found its coking acidic water exceeding oil and suspended solids limits, SINOKLE adopted a purely physical oil-water separation skid built around two core technologies: CDFU (cyclonic dissolved-air flotation) and KHC (coalescing de-oiler). Avoiding chemistry was a deliberate choice, and the advantages follow from it:

• Purely physical demulsification with excellent effect, effectively separating emulsified oil and suspended solids from the wastewater.
• No chemical addition and no oily sludge generated.
• The waste oil separated by the unit has a low water content and can be re-refined — saving resources while generating revenue.
• Strong shock resistance and stable operation.
• Small footprint, enclosed operation, safe and environmentally friendly.

The re-refining point deserves emphasis. In chemically dosed schemes the emulsified oil ends up in a sludge stream, mixed with coagulant flocs and unrecoverable in any useful sense. Here the separated waste oil carries a low water content and goes back for re-refining instead, which turns a disposal liability into a small revenue line — and removes the oily sludge handling cost from the operating budget at the same time.

Commissioning and the 72-hour test

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, after which 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 overall equipment performance.

The feed lived up to its reputation. Normal water draw from the fractionator overhead reflux drum carried around 5%-8% oil with severe emulsification, and during the small steam purge the acidic water oil content exceeded 10%. After treatment by the unit, the effluent ran clear and transparent, with oil below 100 mg/L — a de-oiling rate above 99% — and suspended solids below 10 mg/L. Those figures outperformed the technical indicators on record: 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.

What the result means

The acidic water treatment skid has been running continuously and stably ever since, with consistently good treatment results and strong shock resistance — the effluent stays stably compliant even under large influent quality fluctuations. That shock tolerance is not a luxury in coking service: the switch between continuous overhead draw and batch steam purge events swings the feed oil content by several multiples within hours, and a treatment step that cannot absorb the swing pushes the problem straight through to the stripper.

For a stream that used to threaten stripper trays and unit availability, a physical skid that hands the stripper clean water while recovering re-refinable waste oil changes the operating math entirely. The successful implementation also marks an important breakthrough for the SINOKLE acidic water treatment process in the field of acidic water treatment in the petroleum refining industry.