Walnut shell media filtration has traditionally been used in upstream and downstream produced water treatment applications onshore. This has been largely driven by the footprint required for the flux rates traditionally applied to walnut shell filtration. At the traditional flux rates, walnut shell filters typically require a larger footprint atop a platform or FPSO than equipment such as hydrocyclones and gas flotation units. Recent developments including the incorporation of internalized backwash systems as well as increased processing capacity using reduced footprint has made media filtration using walnut shells more appealing to both onshore and offshore users and operators. In addition, there has been a trend to use tertiary treatment technologies downstream of secondary equipment such as flotation cells, due to the need to reduce hydrocarbon discharge to the environment.
One limitation in using walnut shell media is that walnut, as well as other nut shell media, are produced by, and are subject to, an agricultural season. Due to the fact that nut shell media are subject to uncontrollable environmental factors, crop yields can be sparse resulting in reduced availability. More recently, a synthetic alternative has been developed to replace nut shell media. The synthetic media is manufactured from materials that are not subject to yearly agricultural limitations. Through experimental and field testing, the following benefits have been observed in using this synthetic media:
Ability to handle greater than four to five times the amount of oil before requiring a backwash as compared to standard nut shell media
Ability to maintain feed concentrations of greater than 500 mg/L while producing effluent well under 29 ppm
Applicability to a wide range of oil API from 10-35+ and elevated temperatures greater than 90°C
This paper will highlight the performance data and results, backwash frequency, ability to remove and/or eliminate treatment equipment upstream of media filtration such as gas flotation and its combination with standard nut shell filtration. It will also highlight the potential reduction of treatment chemicals needed to enhance gas flotation and reduction or elimination of waste sludge into recoverable crude. It will also capture comparison of reduced footprint and weight as compared to full produced water treatment systems.