Tech Focus: Polishing water for UAE's Shah Field
Water treatment specialist Metito on its $2.1 million ADNOC contract
ADNOC’s Shah Gas Development has enlisted the help of water treatment specialists Metito to design, engineer and supply a demineralisation and water polishing plant in a deal worth $2.1 million.
Planned to provide the development’s process plant with high-purity water for its boilers, the facility will use desalinated water supplied by a local utility agency and also stripped tail gas treatment unit (TGTU) condensate.
Discussing the purity requirements for the water Bassem Halabi, group business development director for Metito Overseas, explains: “The demineralisation system is vital to ensure the longevity and efficiency of the process plant. The product water is polished to such a high standard because it is feed to steam production from 40 barg boilers.”
A special grade of resin in the polishing unit designed to operate at high temperatures will be used to provide the required quality of water.
In order to be demineralised, filtered water is passed through a series of cation and anion exchangers. The former sees cations like calcium, magnesium and sodium exchanged for hydrogen/sodium ions in their preferential order, and the latter exchanges acids formed during a pass through the anion exchanger resin with hydroxyl/chloride ions, producing deionised water.
“In the polishing unit, condensate water is passed through a working mixed-bed ion exchanger,” Halabi explains. “The two resins are intimately mixed by agitiation with compressed air, thus arranging them side-by-side. The whole bed behaves like an infinite number of anion and cation exchangers in series, producing water of a high quality. Finally, the polished water will be collected in a demineralised water tank, and from there used for the process areas and boilers.”
The plant will be designed to process 1944 cubic metres of demineralised water per day, and 7124 cubic metres of TGTU stripped water, and is planned for completion in Q1 2012.