ENCLOSURES & AIR MOVERS FEATURE
HOUSING SOLUTIONS for the gas industry
Cabinets and shelters from Intertec are being used in gas projects to protect instrumentation equipment from conditions such as salt, moisture, high temperatures and even tropical cyclones. Here the company looks into the conditions faced, and how its products offer suitable protection
I
ntertec Instrumentation is supplying 120 environmental protection
cabinets to house on-line process analysis instrumentation on Shell’s Prelude floating liquefied natural gas (FLNG) vessel. The vessel, which has a length of 488m and a width of 74m, is designed to liquefy natural gas extracted from subsea wells by chilling it to -162˚C, and then store the liquid until it is offloaded to large LNG carriers. Due to enter service in 2017, the vessel will be towed to the Prelude and Concerto gas fields in the Browse Basin near Timor, about 200km off the northwest coast of Australia, where it will be permanently anchored for about 25 years. After this time it will be inspected, overhauled and possibly moved to a new location. The intended operating environment
for the FLNG vessel poses significant instrumentation protection challenges. The Browse Basin is very close to the Equator and has an average temperature of around 32˚C. Furthermore, this moist and hot environment, combined with a salt-laden atmosphere, is highly conducive to rust formation. In some of Prelude’s more confined spaces, the ambient temperature could reach more than 50˚C. The Intertec purpose-built cabinets
will be housing much of the on-line process analysis instrumentation – 90 cabinets are being used for sample conditioning systems and 30 for process analysers. Each is designed to match the instrumentation content and layout precisely in order to optimise thermal performance. According to Hans Geiger,
Intertec’s commercial director, only three of the cabinets are the same size, however the company’s specialised design and automated manufacturing capabilities enable the production of custom environmental
/ DESIGNSOLUTIONS
Each cabinet used for the Prelude floating liquefied natural gas project incorporates semi-passive cooling technology
protection products very easily.
ENVIRONMENTAL CHALLENGES Constructed from a proprietary composite material comprising sandwich walls of long-fibre glass reinforced polyester (GRP) sheets, enclosing a core of polyurethane foam, the cabinets offer a similar strength to stainless steel yet are four times lighter, explains the company – a benefit for offshore platforms and floating structures. For this application, the
cabinets have been designed to not only be capable of withstanding severe Category 5 tropical cyclones with wind speeds in excess of 157mph, but to also have a minimum service life of 25 years – with 50 years as a design aim. Additional requirements included a high degree of resistance to corrosion caused by the saline environment and the presence of
sour or acid gas, and the ability to cool electronics equipment without using explosion-proof air conditioning systems. The cabinets also offer a very low
thermal conductivity which facilitates the construction of efficient, condensation- free cooling cabinets. For this project, the external surfaces of the cabinets are further protected by a thick layer of UV-resistant gel coat. In order to meet the application’s high wind speed requirements, each cabinet is equipped with special built-in mountings – which are external to the thermally insulated parts of the enclosure – to secure the top and base to Prelude’s deck structure. All external metal components are fabricated from 316 stainless steel with a corrosion-resistant protective coating that is specified for ship use.
“Constructed from a proprietary composite material comprising
sandwich walls of long-fibre GRP sheets, enclosing a core of
polyurethane foam, the cabinets offer a similar strength to stainless steel yet are four times lighter”
COOLING TECHNOLOGY Each cabinet also incorporates semi- passive cooling technology. The internal face of the rear walls are fitted with a high efficiency heat exchanger, comprising one or more aluminium cooling plates and stainless steel coolant pipes connected to Prelude’s cold water supply system. Heat dissipated by the equipment in the cabinets is absorbed by the water and transferred to the vessel’s main water cooling system, where it is dissipated to the
environment. The size of each cabinet
depends on the power dissipation of the contained sample conditioning or process analyzer system, which ranges from 140W to 900W. Such distributed cooling provides a very efficient means of removing heat from the cabinets without requiring local air conditioning systems, which would need to be explosion proof. The semi-passive cooling system is inherently safe for use in a hazardous environment; at the cabinet level it requires little or no electrical power of its own and is virtually maintenance-free, making it ideal for long life-cycle applications. Despite the tough conditions faced, all
the passively-cooled cabinets for this project are designed to keep their internal air temperature below 35˚C.
SHELTERS Instrumentation shelters from Intertec, meanwhile, are being used to house remote control and instrumentation equipment required for a new natural gas collection project in the Middle East. Located in a coastal area, the atmosphere contains salt and chlorine as well as
DESIGN SOLUTIONS | MARCH 2014
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