Offshore Ultrafiltration with Multi Element Vessels
Authors: Das Supriyo , Alvarez Elbir Jové , Lange Neville 
Published: April 2016

In the Oil & Gas industry, treatment of injection water into oil bearing reservoirs for secondary or tertiary oil recovery processes is commonly used to maintain the reservoir pressure and to sweep displaced oil towards the production wells. Pre-treated (usually filtered) injection water is either injected directly to the reservoir, or is fed to a Sulfate Removal Plant (SRP) for further removal of sulfates to avoid sulfate scale precipitation in the reservoir.

Ultrafiltration (UF) pretreatment is being increasingly adopted in the Oil and Gas industry as it is recognized that it provides advantages over granular media filtration. Onshore use of Ultrafiltration is widely practiced for different filtration applications such as desalination, waste water treatment or industrial water treatment (Galloway, 2004). These onshore systems are usually based on manifolding many individual Ultrafiltration membrane modules. The membrane modules and associated piping are usually low pressure design and are not suitable for offshore use because of the more demanding offshore design requirements such as ship accelerations, blast loads, piping thermal expansion, higher design pressure etc.

The Multi Element Vessel (MEV) is the heart of a new ultrafiltration system designed by Veolia and Dow Water and Process Solutions in order to overcome the shortcomings of manifolding single modules and pressure requirements for offshore applications. The MEV consists of a conventional pressure vessel with unique adaptor to house multiple ultrafiltration modules operating in parallel. The MEV can meet any required design pressure for use on offshore oil production facilities, and has reduced footprint due to better packing density and elimination of the complex piping manifolds. It provides better access and needs less maintenance.

To prove the performance advantages of the MEV a pilot unit has been in operation for more than one year at the Global Water Technology Center that Dow Water & Process Solutions has in Tarragona (Spain). The MEV pilot unit containing DOWTM Ultrafiltration OG50-1100 modules was operated side by side with DOWTM Ultrafiltration SFP-2880 single element modules. Conclusions of the one year trial with the MEV compared with Single UF modules confirmed following value proposition: –Elimination of complex piping manifold used in single element ultrafiltration whilst maintaining filtrate and backwash flow distribution.–Pressure resistant housing (&gt;15 bar) with multiple ultrafiltration modules inside operating in parallel.–No differences in transmembrane pressure and permeability and similar filtrate quality compared to single element ultrafiltration.–Sustainable operation at filtration flux of 80 L/m2h.–Optimized OG50-1100 module and Multi Element Vessel design guarantees good hydrodynamics either during operation or cleanings.–Additionally, in order to increase even more the efficiency of the UF system and thus, to achieve a further reduction in footprint, the cleaning strategy to be followed has been optimized by reducing the amount of treated UF filtrate used during the cleanings.