Challenge
A Canadian oil upgrader started experiencing poor naphtha/water separation in the overhead accumulator of their fluid coker fractionator after completing some internal modifications during turnaround. High naphtha content was found in the sour water stream, indicating poor oil/water separation, reaching concentrations of up to 25%. Water samples from the fractionator’s separator draw-off pump returned a milky appearance, indicating a tight oil-in-water emulsion.
In the fluid coker unit fractionator, heavy and light gas oil are fractionated and condensed into liquid products. The fractionator overhead system contains steam, fuel gas and naphtha. This gaseous stream passes through heat exchangers that condense the water and naphtha. The resulting gas/liquid/liquid mixture is sent to the fractionator overhead accumulator. In this horizontal drum, the fuel gas flow is separated from the two liquids as water and naphtha are also separated from one another. The fuel gas is sent to a knockout drum and eventually to an off-gas compressor, while the water is sent to the sour water processing facilities. A portion of the naphtha is recycled to the fractionator as reflux and the remaining product is sent downstream for further processing.
As a result of the contamination, the light slop (wasted naphtha to sour water) reprocessing system was overwhelmed, and the upgrader was running out of light slop storage room. The fluid coker was facing an emergency shutdown if a solution was not identified rapidly. Excessive naphtha content in the sour water also resulted in upsets and fouling in downstream sour water processing units, reducing refinery reliability, flexibility and ultimately, plant profitability.
Solution
The process technical engineer turned to Veolia to help troubleshoot and recommend a solution. Veolia reviewed the overhead accumulator system operating conditions and conducted a field experiment on the emulsified sample. Varying concentrations of demulsifier was directly injected into the emulsion sample. A small dosage of KlarAid* product resulted in rapid emulsion resolution and was therefore chosen Coker emergency shutdown averted with emulsion resolution of naphtha/water separation CASE STUDY I Hydrocarbon Processing / Oil & Gas 2 as the treatment chemistry to apply to the system. The demulsifier product was then injected directly into the accumulator drum liquid section. The demulsification effect was immediate, promoting oil and water separation in the drum. This allowed the plant to reduce light slop tank levels through reprocessing. Ultimately, the demulsifier injection point was relocated from its original position to upstream of the accumulator in order to increase overall reaction time and optimize separation. The KlarAid demulsifier continues to be utilized to manage the emulsion formation in the overhead accumulator following this event.
Result
The selected KlarAid product is a highly charged, cationic, low molecular weight liquid coagulant formulated to effectively destabilize oil-in-water emulsions. Due to the organic nature of the chemistry and low dosage, no downstream effects were expected in the condensed fractionator overhead stream, and none were observed.
Bench tests and field applications demonstrated this product can liberate enough naphtha from the sour water to form, by level, a 20-25% free naphtha layer in under 1 minute.
As the KlarAid treatment proved successful through emulsion resolution and free oil layer formation, it eliminated the need for an emergency shutdown which could have cost over $50M in lost production and maintenance.
Overall, the KlarAid demulsifier application assisted in eliminating production downtime and the need for re-routing sour water tankage volumes. The financial savings associated with the recovered naphtha were estimated by the customer to be ~$3.1 million per year in avoided production loss.