How To Extend Heat Transfer Fluid Life
By: Michael R. Damiani
International Sales Manager
Radco Industries, Inc.
Published in Process Heating magazine, October 2001
By Utilizing Your Fluid Manufacture’s Product Support Services, You Can Extend the Time Between Fluid Replacements, Lower Your Fluid Make-Up Costs, And Improve System Performance
High temperature heat transfer fluid manufacturers design fluids to operate within the recommended temperature range safely and efficiently for many years with minimal required maintenance. Occasionally, a system upset will occur, drastically affecting the fluid’s heat transfer efficiency and/or thermal stability. System upsets can be caused by a wide assortment of maladies, including heat exchanger leaks, sudden temperature excursions, failed circulation pumps, the addition of a mislabeled drum of fluid to the system, etc. More commonly, over a period of time many heat transfer systems slowly lose their ability to efficiently transfer heat due the fluid’s gradual thermal and oxidative degradation. This usually leads to gradually increasing production times that even the most astute process engineer can miss. In either case, utilizing your heat transfer fluid supplier’s product support services can solve a system problem cost effectively and quickly, and more often than not, without having to drain the system and replace the whole fluid charge. Taking full advantage of a good product support program can save unit downtime, lower fluid make-up rates, and improve overall system performance. Many of these services are on a “no-cost” basis or are relatively cost-effective as compared to the cost of replacing the fluid charge and/or new fluid make-up.
Whether it is the case of a sudden system upset or the realization that the system has lost heat transfer fluid efficiency over time, the first phone call made should be to the fluid manufacturer to discuss the situation and review options. Most major fluid manufacturers offer a wide assortment of fluid support programs to aid in maximizing the fluid user’s investment. These programs usually fall under two categories- preventative maintenance services and fluid performance improvement services.
Preventative Maintenance Services- The First Step In Extending Fluid Life
Fluid Analysis: Consistent fluid analysis is by far the most important service that should be utilized by every heat transfer fluid user. This service is especially important for newly commissioned systems so that the fluid baseline analysis be established for future comparisons. Consistently taking a periodic representative system sample for analysis is invaluable in many ways- it allows both the user and the fluid manufacturer to track, or “trend” the fluid’s degradation rate (the molecular breakdown due to thermal stress) over time. Evaluating this data can give an accurate prediction of when any action, such as fluid reprocessing or replacement, is required to maintain heat transfer efficiency. An accurate forecast from sample analysis data allows more than adequate time to plan for any needed heat transfer fluid work to be completed during a scheduled shutdown or turnaround, and not on an unexpected or emergency basis. Periodically sampling the system also detects any mechanical problems such as product contamination through leaking or ruptured heat exchanger interfaces. In almost every case, the product that leaks into the heat transfer fluid is not as thermally stable or is as heat transfer efficient. Not only will this lower overall heat transfer system efficiency, in many cases the contaminant can increase the degradation rate of the heat transfer fluid. Sample analysis can catch even minute process leaks into the heat transfer system. Early detection and remedy of a process leak or other outside contamination can save major system problems and heat transfer fluid replacement costs down the road.
Most fluid manufacturers recommend that a system sample be analyzed every 6 months. Sample analysis is usually on a “no-charge” basis and many fluid manufactures will supply a sampling kit with written instructions for taking a representative sample, packaging the sample, and returning the kit to the lab. A written report and recommendation is then sent to the user with the results within a week of the lab receiving the sample. Generally, the tests performed include high/low boilers (by both gas chromatography and atmospheric boiling tests), density, moisture, acidity, residual carbon (insolubles), and fire properties (flash point, fire point, and auto-ignition temperature). Correctly interpreted, the data generated from these tests are extremely accurate in revealing overall fluid condition and level of heat transfer efficiency.
Technical/Engineering Support: In general, major fluid manufactures’ technical support teams consist of graduate engineers that not only specialize in heat transfer fluids and heat transfer theory, but most aspects of heat transfer system components, design, and system troubleshooting. Many solutions to questions and problems that seem unique and perplexing to a specific heat transfer fluid user can be readily answered with one quick phone call to the fluid manufacturer, or a plant visit by a heat transfer fluid specialist.
Advice regarding component specifications- such as fluid compatibilities, pump sizing, expansion tank sizing, seals/gaskets, and instrumentation- for specific applications, temperature ranges, and heat transfer fluids can be also quickly answered. Many heat transfer fluid manufactures also list and recommend quality suppliers of heat transfer system components, which can greatly assist in the design and equipment specification stage of a new project. Finally, most fluid manufactures’ technical support people have years of experience in solving heat transfer fluid-related problems ranging from inherent system/equipment design flaws to accelerated fluid degradation and outside contamination. These technical support teams have the experience to quickly identify the problem and recommend a solution that will correct the situation while minimizing system downtime and heat transfer fluid costs.
Fluid Improvement Services- When Something Goes Wrong Or The Fluid Needs to Be Replaced
Replacement/Reprocessing Programs: Most fluid manufacturers recommend fluid replacement when the aggregate high/low boiler (or contamination) level reaches an upper limit of 15%. Even at 10% level, a significant drop in system heat transfer efficiency occurs. If the system charge needs to be replaced either due to catastrophic system upset or from years of degradation or oxidation, a number of options are available from fluid suppliers to minimize downtime. A very common program is the “Fluid Credit Program” where the user drains the existing charge of fluid and returns it to the fluid manufacturer. The recoverable yield is determined (generally no more than 80% is given, even if the yield is higher) and the value of the yield (less a reprocessing charge) is applied against the purchase price of the new fluid cost. This type of program allows for very quick turnaround times. In just about every case, the new charge of fluid can be on-site even before the old fluid is drained from the system. This type of program is especially useful when the scheduled shutdown window is small or the change-out needs to be done on an emergency basis.
Generally, a “toll reprocessing” program is much more cost effective for system change-outs as compared to a fluid credit program. Since most high temperature heat transfer fluids have a limited number of components and a defined boiling range, manufacturers with toll reprocessing services can use fractional distillation techniques to easily separate and remove contaminants and high/low boiling degradation by-products from the heat transfer fluid product. Reprocessed fluid many times meets new fluid specifications. With this type of program, the off-spec fluid is removed from the system and returned to the fluid manufacturer for toll reprocessing. The fluid is reprocessed and the user than receives back the actual recovered yield of heat transfer fluid (in many cases the actual yield returned is greater than the maximum 80% allowed in the typical credit program).
Both types of replacement/reprocessing programs offer significant new fluid cost savings versus disposal and purchase of a completely new charge. Additional cost savings can be achieved by returning small drum quantities of material generated by leaking pumps, equipment swap outs, system vents, etc. for either credit or reprocessing.
Filtration Programs: Filtration is a cost-effective method of removing carbon (coke) and metallic particles suspended in the heat transfer fluid without draining the system and sending the fluid off-site. While permanent filters rated for high temperature duty are recommended for most heat transfer fluid systems, some fluid suppliers offer on-site filtration services with portable high temperature units. In many cases these portable units are able to filter out the carbon and particulates while the system is still in operation, eliminating system downtime.
Like all companies that use and depend on high temperature heat transfer fluids, fluid manufacturers are acutely aware of the importance of heat transfer fluids in production units (and also their relatively high cost). Service programs are offered by the manufacturers so that the user can maximize both the performance properties of the fluid and the return on the initial fluid investment. If not already familiar with the fluid support programs and services, the fluid user should ask their fluid supplier for a detailed explanation of all their programs. Chances are, one call to the fluid supplier will lead to extended fluid life and improved system performance.