Novel water purification treatment for giant gas project

Paul Boughton

Norway is famed for its strict environmental legislation, so when a water purification system was needed for a major gas field project the solution had to meet a great many requirements.

Discovered in 1997, Ormen Lange is the deepest gas field development project on the Norwegian continental shelf. Operated by Hydro, It is located 100km off the north west coast of Norway at depths of 800–1100metres. When the field comes on stream in October 2007, it will not only be a major contributor to the European gas and energy market, but also make Norway the second biggest exporter of natural gas in the world.
Arnhem-based Akzo Nobel MPP Systems has just won a contract to supply one of its innovative macro porous polymer extraction (MPPE) water purification units to remove dissolved hydrocarbons from process water at Ormen Lange.

The technology will be used to help Hydro achieve its ambitious environmental goal of zero discharge of environmentally harmful substances. As well as being used for offshore process water treatment, the technology can also be utilised for groundwater, industrial process and wastewater treatment.

In the MPPE unit, hydrocarbon-contaminated water is passed through a column packed with MPPE particles (Fig.1). An extraction liquid immobilised within the MPP matrix removes the hydrocarbons from the water in a single pass. The purified water passes out of the column directly to reuse or discharge.

Regeneration of the extraction liquid containing particles is accomplished periodically in-situ with low-pressure steam. During regeneration the hydrocarbons are removed from the particles by low-pressure steam stripping, while the immobilised non-volatile extraction liquid is retained in the pores of the polymer. After condensation of the vapour phase an organic and an aqueous phase are obtained in the gravity separator. The aqueous condensate is returned to the feed of the extraction column. The organic phase is separated for re-use or disposal (Fig.2).

The two columns allow continuous operation with simultaneous extraction and regeneration. At the end of the cycle, columns are switched: the one used for extraction is regenerated and vice versa. Flow rates from 0.5m3/h up to hundreds of cubic metres per hour can be treated economically.

There are no maximum flow rate restrictions. Removal efficiencies of 99.9999percent for wide varieties and combinations of aliphatic, aromatic, halogenated and poly aromatic hydrocarbons (PAHs) are achieved.

Akzo also claims a number of other benefits for its MPPE technology, including energy consumption between five and 50 times lower than that required for steam stripping and a no-fouling operation which is ensured by periodic in-situ steam cleaning.

The MPPE process is also very flexible, being able to treat both higher and lower flows and concentrations. For example, if the concentration rises by 50percent, effluent treatment needs only a 10percent lower flow to cope. At lower feed concentrations, higher flows can be used to meet effluent demands.

The unit itself is very compact, with a small footprint and low weight. Because of this and the fact that it is fully automated, it is ideal for process integrated applications.

Akzo also points to the fact that MPPE has undergone three months of offshore testing by the Orkney Water Technology Centre on behalf of oil and gas companies from both the USA and Europe. The removal of both dispersed and dissolved hydrocarbons and the reduction of toxicity was verified, while a four-month offshore demonstration has been executed successfully with NAM (Shell/Exxon).

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