Challenge

The North Salt Lake (Utah) Refinery of Big West Oil LLC, a wholly owned subsidiary of Flying J Inc., needed to upgrade its wastewater treatment facilities to remain compliant with its wastewater discharge permit. The refinery had increased its throughput by more than 100% over the last 20 years without any major additions to the wastewater system. The larger wastewater flow resulted in less holding time to respond to upsets and increasing maintenance costs as a result of the refinery’s existing circular DAF unit’s age.

Solution

In 2006, refinery management decided to upgrade the 400 gpm (91 m³/hr)-treatment system. After a successful on-site pilot study, Siemens Water Technologies designed a new rectangular Folded Flow® DAF system that included an ancillary flocculation and flash mix tank. The new unit came online in May 2009.

The new design resulted in a smaller footprint that enhances separation and allows for better hydraulic loading at a higher rate for more effective removal of contaminants. The footprint is minimized by folding the effluent flow underneath the influent in the new DAF unit, allowing separation to occur over a surface area of 132 ft2 (12.3 m2) – less than a quarter of the surface area provided by the 27-ft (8.2-m) diameter circular tank. Dissolved air comes in with recycled water on the Folded Flow unit through a dispersion pipe that runs the full width of the tank – as opposed to being delivered in the middle of the tank with a dispersion tray as did the circular DAF unit.

Results

The new DAF system requires less maintenance and thus, less operator attention. It has also significantly improved the consistency and reliability of treatment. 

Comparing discharge data six months before and after the project, BOD levels in wastewater from the refinery fell by 67%, COD dropped 60%, and ammonia, BTEX and sulfate/sulfides experienced minor reductions.

This marks the first Folded Flow DAF separator to provide secondary oil/water separation in a U.S. refinery.

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