Coking Wastewater Without Chemicals: How CDFU and KHC Tackle Coal Chemical Effluent

Coal chemical plants generate few streams nastier than coking wastewater: complex, concentrated, toxic and barely biodegradable. SINOKLE answers it with something unusual in this corner of the industry — a purely physical oil-water separation solution built around CDFU (Cyclonic Dissolved Air Flotation) and the KHC coalescing oil remover, with no chemicals in the separation stage at all.

Why Coking Wastewater Fights Back

The water comes from coking, gas purification and chemical product refining, at 0.1-0.35 m3 of wastewater per ton of dry coal. Its inventory is hostile: inorganic pollutants such as ammonium, thiocyanate and cyanide ions, plus heterocyclic and polycyclic aromatic compounds — benzenes, phenols, naphthalene, pyridine — all wrapped in high salinity, high nitrogen concentration, high toxicity and poor biodegradability. Traditional gravity sedimentation needs 50-70 hours of settling for limited separation, while consuming large ground area and leaking acidic gases.

The Core Breakthrough

The CDFU cyclonic dissolved air flotation technology works on a pure physical demulsification and separation principle, optimising the internal flow field design to improve oil-water separation. It exploits the density difference among the oil, gas and water phases; compared with traditional flotation equipment, separation efficiency improves by 2-5 times. Paired with the high-precision coalescing filler of the KHC coalescing oil remover, the train removes emulsified oil droplets as small as 0.1 um and holds effluent oil stably below 10 ppm.

How the Two Units Divide the Labour

CDFU handles the bulk phase: cyclonic flow plus dissolved-gas microbubbles strip free and dispersed oil and carry fines out in one pass. KHC finishes the job on the droplets that survive — the fine emulsified fraction that decides whether effluent meets spec. Because both units separate by physics rather than chemistry, performance does not drift with dosage errors, and the recovered oil stays clean enough to re-refine rather than becoming a disposal liability.

What the Design Buys You

• Pure physical demulsification with no chemical additives — no secondary pollution at the source
• Recovered waste oil with low water content, directly re-refinable for economic return
• Fully enclosed automatic operation with no acidic gas leakage — a step change in safety and environmental performance
• Skid-mounted layout occupying only 1/3 of the area of traditional processes
• Strong shock load tolerance for the fluctuating water quality typical of coking plants

Proof at a Henan Petrochemical Plant

Where Conventional Equipment Loses Ground

Understanding why the physical route wins starts with what defeats the alternatives. Gravity basins need half a week of residence and still cannot split droplets whose surface films keep them suspended; their open surfaces also release the acidic gases that make coking plants unpopular with neighbours. Dissolved-air flotation without the cyclonic flow field wastes bubbles on water rather than oil when droplets are fine. Chemical demulsification works, but it converts a separation problem into a sludge problem and often contaminates the recovered oil, erasing the very revenue that justifies the equipment. The cyclonic geometry sidesteps all three failures: centrifugal forces multiply the effective density difference, microbubbles attach to oil films rather than clean water, and nothing foreign enters the stream.

In August 2023, SINOKLE applied the process to a coking unit sour water treatment project at a large petrochemical enterprise in Henan. The conditions were punishing: influent oil at 5%-8%, climbing above 10% during small-scale gas stripping. After treatment, effluent oil dropped below 100 mg/L, the oil removal rate exceeded 99%, and suspended solids stayed below 10 mg/L — every indicator better than the technical requirement. The equipment has run continuously and stably for more than half a year, holding compliance through large influent swings, which is the reliability test that matters most on this stream.

What It Is Worth

At a treatment scale of 50 m3/h, the recovery side alone captures nearly a thousand tons of light oil products annually, saving considerable treatment cost each year against traditional technology. The pure physical separation route avoids the secondary pollution caused by chemical additives and yields markedly better recovered-oil quality. Through technological innovation and engineering practice, the process has turned one of the industry's most difficult effluents into a recoverable resource rather than a compliance burden.

Operating Notes

Three habits keep the train at its published numbers. Watch the influent swing — the Henan case shows the unit rides out excursions, but sustained operation above the design oil fraction still deserves a check on skimming frequency. Keep the KHC packing inspection on schedule; coalescing surface condition is the one wear item that matters. And log the recovered oil quality alongside effluent oil, because a drifting water-content trend is the earliest sign that demulsification inside the train is slipping.

Selection Boundary

The physical train is not a universal answer — biological polishing still handles the dissolved organics, and streams dominated by dissolved salts need different chemistry. But for the oil-removal stage of coking wastewater, where emulsification and coke fines break conventional equipment, the CDFU + KHC combination has now cleared the hardest test available: a full-scale, continuously running plant whose influent oil swings from 5% to above 10% and still lands below 100 mg/L at the outlet. As environmental requirements tighten, more industrial wastewater scenarios are expected to adopt this physical route.