Feature Report
Maximizing Heat-Transfer Fluid Longevity H
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Proper selection, monitoring and maintenance can protect fluids and components from damage due to thermal degradation, oxidation damage and contamination
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n-Hexocosane (C26H54) COC flash point : 215°C / 419°F Molecular weight : 366.7 grams/mole
Excess Heat
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n-Dodecane (C12H26) COC Flash Point: 71°C / 160°F Molecular weight: 170.34 grams/mole
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n-Tetradecane (C14H30) COC flash point : 99°C / 210°F Molecular weight : 198.4 grams/mole
Heavy carbonaceous residues
Gaston Arseneault Petro-Canada Lubricants, a Suncor Energy business
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aced with increased workloads and time and budget constraints that often restrict external training support, many chemical process operators are forced to get the most out of their heat transfer system with less help. This article offers recommendations for how to carry out proactive maintenance on heat-transfer fluids, to maximize their useful life and minimize problems associated with fluid degradation, such as excessive downtime for unplanned maintenance when the heat transfer system has become unsafe or is no longer able to carry heat in a reliable manner. It is useful for anyone developing or refreshing asset-care-management programs related to heat-transfer fluids and systems. Discussed below are the most common fluid-related problems encountered by heat-transfer systems and a variety of potential solutions. While individual system designs and variations in process and operating conditions make each application unique, all heat-transfer fluids share many common attributes, making these recommendations widely applicable. Ultimately, our goal is to educate those involved with the operation and maintenance of liquid-phase heat-transfer systems, both large and
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FIGURE 1. In this example with heat-transfer fluid n-hexacosane, thermal degradation occurs when excess heat drives the cracking of a straight-chain hydrocarbon (not shown is the formation of reactive free radicals, which have been omitted for clarity)
small, that use an organic-based heattransfer fluid. The organics include chemical aromatics, fluids based on petroleum derivatives, silicone or glycol, the polyalphaolefins (PAO; also referred to as API Group IV-based fluids) and more. A properly designed and operated heat-transfer system can be the biggest ally in maintaining (and even increasing) productivity while reducing overall maintenance and production costs.
It starts with smart selection
The selection of the heat-transfer fluid — whether at the system design phase, or on an ongoing basis after commissioning — should not be taken lightly. Fluid selection should not be dictated solely by the purchase price or any single physical characteristic. Rather, a variety of factors should be considered: • The potential impact on workers of a given fluid, in terms of adequate training and protection that must be implemented to address hazards related to potential exposure to the fluid, in both its vapor form (inhalation risk and mist concentration) and liquid form (skin contact). In addition to direct exposure, the choice of the fluid could impact productivity engendering additional handling
ChemiCal engineering www.Che.Com DeCember 2009
and paperwork protocols involving other internal resources within the company, such as the health and safety advisors, medical care personnel, personnel in the receiving department and so forth • Freight charges related to delivery of fresh product • Cost associated with the pickup, handling and disposal of the used oil and drums • Proven fluid performance beyond fresh oil data (for instance, if vendor data is able to demonstrate the retention of fresh oil properties after some time in service, as demonstrated by extensive oxidation and thermal stability data) • Can the current system accommodate the fluid being considered (in terms of compatibility with sealing materials, existence of a properly sized expansion reservoir, suitable match between the fluid properties and the existing hardware, such as the pump and safety-relief valve) • Miscibility with current heat-transfer fluids if partial (rather than full) changeout is needed • Documented success by the vendor in your type of application • Level of liability coverage, service and expertise the fluid maker and distributor bring to the table