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ATEX centrifugal fans for sub-zero temperatures

20 January 2010

The design and supply of equipment for the oil, gas and petrochemical industries are demanding enough but it becomes all the more so when the equipment is to be installed in the sub-zero temperatures encountered north of the Arctic Circle.

GBA Flarestack at Melkoy Island, Hammerfest
GBA Flarestack at Melkoy Island, Hammerfest

The centrifugal fans supplied to GBA Flare Systems for the the Air Assisted Process Flare as part of the Elevated Flare Package on Statoil’s Snorvit LNG Project on Melkoy Island, Hammerfest, Norway had not only to meet ATEX standards but temperatures down to -35o C.

Two large centrifugal fans were required to supply air to the process flare to achieve smokeless combustion of waste gases, each fan being capable of supplying 50% of the total required air volume. In addition, a smaller purge fan was required to provide a steady supply of purge air into the riser when the combustion air fans are shut down in order to keep a minimum flow of air passing into the system and to prevent hydrocarbon gas falling back into the air riser.

Due to the potentially hazardous environment, all electrical equipment and instrumentation had to be certified for at least Zone 1 IIB T3 or better, junction boxes had to be rated to IP65 and the fans themselves and associated equipment had to satisfy the requirements of ATEX Group II Category 2.

The climatic conditions imposed their own demands. The whole package had to be suitably designed and constructed mechanically to cope with the harsh environmental conditions, notably an ambient temperature range between -20oC to +50oC and a maximum snowfall depth of 2.3 metres.

The application demanded extra thickness 43D carbon steels for all the fan fabrications which were then subject to certified low temperature impact testing. A further major requirement was the surface preparation and protective coating of these fabrications. This work all had to comply with a stringent Statoil specification that required that all corners be ground to specific radii and all welds ground to a completely smooth surface finish prior to grit blasting. The prepared surfaces were then coated with a priority four-coat paint system to a nominal DFT of 370μm. All stages of preparation and protective coating were subject to thorough scrutiny by the client prior to the issuance of acceptance and guarantee certificates.

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