CASES & ENCLOSURES FEATURE
Figure 2: An externally- accessible HMI, allows operators to make adjustments to control programs without entering the shelter and exposing the interior to local
corrosive atmospheres
allowing operators on the ground to make adjustments to the control programs locally via a small panel (Figure 2). The active parts of the cooling system - which employs three separate cooling technologies for ultra reliability - is also accessed from the exterior. For extreme reliability, the main cooling mechanism is provided by a passive cooler (with heat exchanger mounted on the roof) boosted by a water chiller. However, a third air conditioning system is also installed as an emergency back up. Although the shelter has a door to the interior, this is locked in normal use and is there purely for access during plant shutdowns or under other special strictly controlled circumstances. Thanks to these enclosure configuration
innovations, the EPC for this upgrade project decided to install the control/safety functionality in the new style of peri shelter. As all the shelters have the same compact footprint of around 2m x 3m, they are small enough to be sited easily in existing free spaces close to the burner processes, minimising cabling. If this EPC had taken a more conventional approach to the upgrade, the project would have involved the replacement of existing satellite instrument houses - very large blast-proof buildings with large HVAC systems attached - located close to the burners deep inside the refinery. This would have been significantly more costly, and taken a lot longer to design and build. Passive cooling technology is not limited to large
Figure 3: A small passively-cooled cabinet for Ex field instrumentation in a brewery
enclosures. As an example, Figure 3 shows a small anti-static cabinet (with a heat exchanger roof/sunshade) currently being built by Intertec to house field instrumentation for location in a Zone 22 (combustible dust) area of a brewery in Mexico. A small tank holding around 80 litres of water provides cooling capability for 20W of heat dissipation, to maintain a stable operating environment for the instrumentation. Both of these enclosure examples are built using custom composite GRP materials - with internal and external GRP sheets ‘sandwiching’ embedded insulation. The exterior surface also features an advanced gelcoat which provides protection against many environmental challenges such as very high levels of UV, dust and sand abrasion.
Intertec Instrumentation
www.intertec.info
INSTRUMENTATION | MAY 2018 19
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