Northshore CC827494: Calcium removal from high-calcium crude at the desalter

The refinery’s 1.8 million tonnes/year crude unit processed a crude slate made up entirely of high-calcium offshore crudes. Calcium varied from about 30 ppm to more than 200 ppm with the blend. Conventional desalting did not adequately remove the oil-soluble calcium naphthenates.

The plant reported high desalter current, increased power consumption and trips. Calcium carried into atmospheric and vacuum residue and VGO was associated with FCC catalyst poisoning, particle agglomeration, riser plugging and interrupted fluidisation. Equilibrium-catalyst calcium had reached 17,660 µg/g, and fresh-catalyst make-up had increased to 3.9 kg per tonne of FCC feed.

The trial target was calcium removal above 70% across the desalter train, without modifying desalter metallurgy or mechanical equipment.

Northshore CC827494 is a water-soluble calcium-removal agent applied through desalter wash water. It reacts with oil-soluble calcium naphthenates to form a water-soluble complex that leaves with the brine. The reported program maintained high removal at neutral to weakly alkaline effluent pH.

Cestoil designed injection ahead of each stage’s wash-water static mixer on the three-stage desalter train, supported by a pretreatment aid at the crude charge pump. The team monitored inlet and outlet calcium and iron, desalter currents, effluent pH and chemical oxygen demand (COD).

Dosing began on 18 September 2008, immediately after the crude unit restarted from turnaround. Oversized metering pumps initially made precise dose control difficult. On 29 September, Cestoil installed dedicated metering pumps: 110 L/h for stages 1–2 and 170 L/h for stage 3. With all three stages dosed, the total dose was adjusted from an initial 343 ppm toward 120–215 ppm while performance and effluent quality were reviewed.

Metering-pump figures are equipment ratings, not the chemical injection rates used throughout the trial. Dose was adjusted to crude calcium and operating response.

All seven analysed days exceeded the 70% target. Mean removal was approximately 83%. At 76 ppm inlet calcium, 180 ppm of CC827494 achieved 90.4% removal, giving a reported product-dose-to-calcium ratio of approximately 2.4.

The observed range was 71.2–90.4%; the 80–90% headline in the supplied PDF does not describe every analysed day. These data reflect changing feed and treatment conditions, rather than a controlled dose-response test.

Fresh-catalyst consumption fell by 2.7 kg/t, approximately 69% from the reported endpoints. Light-product and total-liquid yields increased by 6.4 and 5.6 percentage points, respectively. The refinery attributed the gain chiefly to calcium removal, while noting that FCC equipment upgrades also contributed; the comparison does not isolate the chemical program’s share of the yield increase.

Third-stage desalter currents reportedly fell from 64–87 A to 30–50 A within a day of dosing. The plant reported lower power consumption, no trips and clear effluent water during the monitored period.

As dosing was optimised, effluent pH moved from 4.5 to 7.1–7.5, while COD decreased from 13,697 to 3,199 mg/L, approximately 77%. Calcium removal remained at 88–90% in the reported optimisation comparison. No corrosion was found in the reported evaluation.

These are annualised figures based on the refinery’s 2008 report, not a full year of measured net savings or a current price quotation. Catalyst savings are expressed per tonne of FCC feed, while chemical cost is per tonne of crude. Feed calcium, throughput, chemical prices, catalyst cost and unit changes affect the economics at another site.

Measure calcium in incoming crude receipts so treatment can follow crude-slate changes. The refinery identified delayed knowledge of cargo calcium content as a principal operating difficulty.

Use metering pumps sized for the intended dose range. Track calcium removal together with desalter currents, effluent pH and COD, and plan for calcium-bearing brine at the wastewater plant. Review equilibrium-catalyst metals, fresh-catalyst addition and FCC yields over several catalyst turnovers, accounting for feed changes and equipment upgrades.