Hi In Historic Out, The Legacy! Is the Rockefeller family really getting out of oil?

Hi In Historic Out, The Legacy! Is the Rockefeller family really getting out of oil?

There’s no doubt that the decision by the $860 million Rockefeller Brothers Fund to reinvest its fossil fuel money in clean energy represents a pretty symbolic moment.

John D Rockefeller – who founded Standard Oil in 1870  – is one of the towering figures; some would argue the father, of the international oil industry. So the news that a charitable fund bearing his name is turning its back on the stuff that made the family fortune was always going to raise a few eyebrows. The fact that the announcement was timed to coincide with the current UN Climate change summit gave it extra punch.

Standard Oil Refinery No. 1 in Cleveland, Ohio

Before we get carried away it’s worth stressing that the announcement is perhaps not quite as dramatic as some have claimed.

Indeed, whilst the tone of some headlines might imply that the Rockefeller family’s entire oil wealth is being sunk into renewable s, the reality is more low-key.  The Rockefeller Brothers Fund is one of a number of charitable funds – such as the much larger $1bn Rockefeller Foundation - all of which have heavy investments in the oil industry.  And as yet, there’s no indication that these other funds are likely to follow suit.

Nevertheless, the decision is significant as well as symbolic.

The Rockefeller Brothers Fund is now the most high profile convert to “divest-invest”, a global initiative which began life on US university campuses around a decade ago and claims to have persuaded over 181 institutions to redirect $50bn of oil investments into clean energy.

For many, the goals of the movement will no-doubt be seen as fluffy and idealistic.  And some will undoubtedly argue that any investors following this path have been duped, and are putting misplaced ethical concerns ahead of economic common sense.

But whilst most of those signing up to  “Divest-invest” will be motivated by ethical concerns, the appearance of the Rockefeller name reinforces a growing perception that hard-nosed economics is playing a role here too.

In his landmark 2006 report – Nicholas Stern, one of the most influential voices on climate change - argued that concern for the climate and economically sustainable energy policies were, far from being mutually exclusive, actually deeply entwined.  Could the blossoming interest in initiatives such as divest-invest be evidence of this phenomenon in action?

What’s more, even if you disregard concerns over climate change it’s certainly arguable that thanks to a combination of geology, geography and geopolitics the economics of fossil fuel extraction are becoming less attractive.

Perhaps it’s no real surprise that one of oil’s oldest families should be looking elsewhere for a return on its investment.

- "House rule Pituitary Demands A Perspective By Choice."

Your Hi Fluid Zone! Part 1C! Safe Sampling of Heat-Transfer Fluids!.

Your Hi Fluid Zone! Part 1C! Safe Sampling of Heat-Transfer Fluids!.

Collecting representative samples of heat-transfer fluid for routine quality checks falls short of the goal if safety or the environment is compromised. While users should consider their systems’ unique design features in consultation with their safety and health experts, incorporating the tips below can help to avoid common potential safety concerns associated with sampling these fluids, which may be at extreme temperatures. Understanding these safety issues is the first step in planning a safely conducted task.

Ergonomics;

"In Contrast We See & We Do"

Safe access to heat-transfer-fluid sample ports is a key part of an ergonomically designed station. 

Important aspects of a well-designed sampling station include the following:

• Clear standing area with unobstructed path of egress.

• Height of sample port below chest-high, to avoid upper body splash.

• Limited extent of reach required to avoid body strain.

• Space beneath sample port to allow hands-free placement of a properly labelled flush bucket.

• Non-slip, solid floor surfaces to prevent drips to a lower level.

• Globe valves in sample port are preferred for the best control of flow-rate.

Extreme temperatures;

"The Knowledge Will Empower Your Design"

Representative samples are best collected during operation, when the fluid is uniformly mixed throughout the system. Heat-transfer fluids routinely reach temperatures that can present thermal burn hazards. The following tips are for sampling hot streams:

• Review safety data sheets (SDS) for the personal protective equipment (PPE) that is required for the fluid being sampled, as well as its physical and chemical properties, and hazard information.

• Use a sample cooler to reduce fluid temperature to below 93ºC (200ºF) to protect sample composition integrity.

• Wear gloves that provide chemical and thermal protection, as well as a splash apron, eye goggles and a face shield. 

• Inspect the port area for uninsulated contact points to avoid.

• Avoid drips which may occur before, during or after collection.

• Do not remove PPE until the port and sample bottle are secured.

Splashes and spray;

Even with the proper PPE in use, initiating flow from the sample port is a transient operation that can result in splatter or spray, and efforts should be made to limit the splash potential. Since the fluid may be hot, it is important to take precautions against accidental hot-fluid contact to avoid thermal burns. Thermal burns are the single greatest safety concern to personnel working with high-temperature fluids and equipment. Use of a globe valve can provide better flow control when opening the sample port.

Think ahead to plan what actions will be taken in the event of an unexpected spray. Anticipate pressure on the line when opening the port valve, and open the valve gradually. Stand to the side so that any spray will be directed away from potential physical contact. One technique to better control the sample stream is to install a short length of small-diameter tubing on the sample valve outlet, which steadies the stream and also permits easy insertion into the neck of sample bottles.

When flushing the sample port prior to collecting the “good” sample, direct the stream into a dry bucket. Any moisture in the flush bucket can result in violent splatter of the hot heat-transfer fluid into the vicinity, if the sample stream is above the boiling point of water.

Take the time needed to sample the fluid safely. Rushing to perform this task can pose unnecessary safety risks for those collecting the fluid samples.

Spills;

"What Creates That Destroys"

By expecting the unexpected, we can prepare adequately to avoid potential spills and their consequences, or minimize their extent and impact. A well-placed sample port will be at ground level with little exposure to sewers or floor drains. A small, curbed area can help keep small releases contained. Above all, efforts should be taken to keep potential releases of organic heat-transfer fluids from drains and waterways. If a storm drain is in the area, it should be adequately covered or otherwise blocked during sample collection.

High-temperature heat-transfer fluids are commonly organic liquids, and suitable dry, absorbent media should be available in the area for response to stabilize and aid in clean-up. These fluids are also likely to be combustible, and clean-up should be performed promptly.

Some heat-transfer fluids may have unique spill clean-up and disposal methods that are directed by their manufacturers, so refer to the product SDS for specific guidance.

Finally, any fluid residues will also create a hazard by making walking surfaces, handrails, or coated structures slippery. To avoid slips and falls, and to avoid fueling a fire, these residues should also be cleaned. Oil-absorbent cloths and socks can also be used to help keep the areas clean. Additional clean-up may be done with appropriate detergents or chemical cleaners.

Inhalation;

"Find Your Depth, Discover The Surface"

Each heat-transfer fluid chemistry can be different, so learn about the unique requirements of each one from the supplier’s literature. Key concepts to avoid unnecessary exposure to fluid vapors are the following:

• Cooler fluid has lower vapor pressure, and provides less exposure.

• Stand upwind of the sample port during flushing and sampling.

• Place a lid over the sample port flush bucket when finished.

• Promptly cap and seal the sample bottle once filled.

For products containing components that have established airborne-exposure limits, consult with an industrial hygiene technician about the need for respiratory protection. In many cases, proper job planning and sample cooling may eliminate the need for respiratory protection.

Finishing the job well;

"Find Your Result, Measure Its Performance"

Now that the sample has been collected, it is ready for packaging and shipment to the laboratory for analysis. While most organic heat-transfer fluids are not regulated for transport by the U.S. Dept. of Transportation (Washington, D.C.; www.dot.gov) for sample quantities, the bottle should be packed properly so that it remains leak- and damage-free until it arrives at its destination.

Bottles should be protected against breakage. Metal containers offer the greatest resistance, and glass containers will require adequate packing materials. 

Precautions against container leakage can include the following actions:

• Ensure all seals are properly in place in the neck and mouth of the bottle.

• Do not use substitute parts for liquid seals.

• Apply tape to the outside of the tightly-sealed container cap.

• Place the bottle within a chemically compatible bag, which is then closed to prevent liquid escape into the outer package.

• Foam packing (pre-formed, or “peanuts”) can be placed around the sample container to protect it against sharp blows.

• Properly dispose of fluid collected in the sample-port flush bucket.

References;

"Your Arrival Is Here, Anticipate Your Delivery"

1. “Therminol Information Bulletin #2: In-Use Testing of Therminol Heat Transfer Fluids. Pub. #7239112C, Solutia Inc., a subsidiary of Eastman Chemical Co.

2. “Liquid Phase Design Guide” Pub. #TF-04, 5/14, Eastman Chemical Co.

Editor’s note: The content for this column was provided by Eastman Chemical Co. (Kingsport, Tenn.; www.eastman.com). Eastman and Therminol are trademarks of Eastman Chemical Co. or its subsidiaries. 

DISCLAIMER: Although the information and recommendations set forth herein are presented in good faith, Eastman Chemical Co. and its subsidiaries make no representations or warranties as to the completeness or accuracy thereof. You must make your own determination of suitability and completeness for your own use, for the protection of the environment and for the health and safety of your employees and purchasers of your products. Nothing contained herein is to be construed as a recommendation to use any product, process, equipment or formulation in conflict with any patent, and we make no representations or warranties, express or implied, that the use thereof will not infringe any patent. NO REPRESENTATIONS OR WARRANTIES, EITHER EXPRESS OR IMPLIED, OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR OF ANY OTHER NATURE ARE MADE HEREUNDER WITH RESPECT TO INFORMATION OR THE PRODUCT TO WHICH INFORMATION REFERS AND NOTHING HEREIN WAIVES ANY OF THE SELLER’S CONDITIONS OF SALE. Safety Data Sheets providing safety precautions that should be observed when handling and storing our products are available online or by request. You should obtain and review available material safety information before handling our products. If any materials mentioned are not our products, appropriate industrial hygiene and other safety precautions recommended by their manufacturers should be observed.

Your Hi Fluid Zone! Part 1B! Get the Most From High-temperature Heat-transfer-fluid Systems!.

Your Hi Fluid Zone! Part 1B! Get the Most From High-temperature Heat-transfer-fluid Systems!.

Fluid selection, system design and maintenance are the keys to achieving the best performance;

Although water and steam are the ideal media for heat transfer, there are often situations when other heat-transfer fluids are called upon to perform this function in the chemical process industries (CPI). Thus there are, at the very high-temperature end, various types of heat-transfer fluids, such as molten salts and even molten metals. At the lower end of the temperature scale we have various proprietary and non-proprietary brines, usually glycols of one kind or the other. Between these two temperature extremes, a variety of heat-transfer fluids are also available. For this discussion, the focus will be on high-temperature heat-transfer fluids; those having useful bulk-fluid-operating temperatures of approximately 70–400°C.

For high-temperature operation, heat-transfer-fluid systems have distinct advantages when compared to steam or direct-fired heating. For example, using steam for process heating to temperatures in excess of 225°C would require steam pressures upwards of 40 bars. For the same application, the use of a heat-transfer-fluid system would thus eliminate the need for costly high-pressure equipment and piping, expensive boiler-feed-water treatment, and specially trained boiler operators. And compared to direct-fired heating, the use of heat-transfer fluids allows the heater to be safely located away from the process and reduces the danger of forming hot spots in the process itself.

An engineer likely to be involved with high-temperature heat-transfer fluids should be familiar with the types of fluids available, and how to choose among them. It is also important to be aware of the design guidelines for the components of a heat-transfer-fluid system, and the problems that can arise with them.

FLUID SELECTION;

Fluid chemistry;

High-temperature heat transfer fluids can be categorized by their chemical structure into three primary types:

• Hot oils (mineral oils).

• Synthetic organic fluids.

• Silicone fluids.

Hot oils are petroleum-based and are composed of paraffinic or napthenic hydrocarbons. The bulk-fluid-operating temperature of hot oils is in the range of –25 to 315°C.

Synthetic organic fluids have aromatic ring structures and include the diphenyl-diphenyl oxide mixtures, biphenyls, terphenyls and alkylated aromatics. Depending on the specific fluid, the bulk-fluid-operating temperature range of these types is from – 60 to 400°C.

Silicone-based fluids are primarily used in specialized applications requiring process-product compatibility in case a heat-exchanger leak occurs. They find favor in food-processing industry.

Synthetic organic fluids are much more expensive than mineral oils, but are far less prone to thermal degradation; their aromatic-ring structure is more robust than the aliphatic chains of mineral oils. The thermal decomposition rate of mineral oils can be as much as six times that of synthetic-organic fluids at operating temperatures of 330°C. Silicone fluids require higher initial investment, but their thermal stability is excellent. Although they exhibit some thermally induced changes, a balanced steady-state-equilibrium composition is eventually attained, and, depending on service conditions, this can reduce or eliminate the need for adding more fluid during the operating life of the system. The fluid life can be ten years or longer.

A life-cycle-costing approach has to be adopted when choosing between synthetic fluids and mineral oils. The fact that there will be fluid loss (regardless of the fluid type) every time a pump or valve is opened for maintenance should not be overlooked. A point in favor of mineral oils is that the spent oil can be easily disposed off by blending with fuel oil for boilers.

Traditionally, mineral oils for heat-transfer applications have been manufactured by petroleum companies and distributed through lubricant dealers. Because relatively low volumes of oil are needed for heat-transfer applications, the technical support has often been found wanting; this is one of the main reasons why mineral oils stand discredited in some eyes today. In contrast, the excellent product support provided by manufacturers of synthetics has ensured a better life span for these fluids.

Fluid properties;

A good heat-transfer fluid should have many desirable attributes, including the following:

• High boiling point.

• High flash point.

• High autoignition point.

• High thermal stability.

• Good heat-transfer properties.

• High solubility for decomposed fractions.

• Low pour point and pumping limit.

• Low viscosity

• Low vapor pressure.

When evaluating alternatives, it is useful to take a look at the values of the above properties. Two of the properties — thermal stability and heat-transfer characteristics — are especially important.

Thermal stability: This is the heat-transfer fluid’s inherent ability to withstand thermal cracking, and is the primary factor in determining its maximum bulk-fluid-operating temperature. The fluid can be used up to this temperature and still maintain an acceptable level of thermal stability. Continuous use above the manufacturer’s recommend bulk-fluid-operating temperature will result in an exponential increase in fluid degradation rates.

The first step in selecting the fluid is to determine the maximum bulk-operating temperature required by the process. Most hot oils have a recommended maximum bulk fluid temperature of 280–315°C, while the synthetic organics have recommended maximum bulk-fluid temperatures between 315 and 400°C, depending on the fluid. Because aromatic compounds have a greater thermal stability than the hot oils above 315°C, synthetic fluids are strongly recommended above this temperature. For process applications requiring bulk fluid temperatures from 160 to 315°C, one can specify either synthetic or petroleum based fluids. Within this latter temperature range the relative-thermal-stability data supplied by manufacturers can be used to compare individual fluids at specific temperatures.

Heat transfer coefficients: At a given temperature, the heat-transfer coefficient of the various fluid types may differ by as much as 30%. Depending on the thermal resistance of other components in the system, a fluid with a substantial advantage in heat-transfer coefficient might allow a significant reduction in equipment sizing.

Most of the aromatic fluids reportedly have a significant advantage over hot oils in heat-transfer characteristics in the temperature range of 150 to 250°C. Above this temperature range (up to 315°C), the differences narrow somewhat, with a select number of highly refined paraffinic-napthenic white oils having a slight edge over the aromatics.

Environmental considerations;

Petroleum-based fluids offer substantial advantages in ease of handling, reprocessing, shipping and disposal as compared to the synthetic fluids. The white mineral oils, in fact, meet the U.S. Food and Drug Administration’s (Washington, D.C.) criteria for “incidental food contact.” Also, the petroleum-based fluids do not form hazardous degradation byproducts; therefore most spent hot oils can be sent to a local oil-lube recycler for disposal. The hot oils warrant no special handling precautions and require no special storage requirements. From a personnel standpoint, the hot oils are extremely user-friendly (apart from the risk of becoming burned). Most have no discernible odor, and are non-toxic both in contact with skin and after ingestion.

On the other hand, because of the aromatic chemistry, some synthetic fluids can form hazardous degradation by-products that require special precautions. Some synthetic fluids and their vapors may cause skin and eye irritation after prolonged exposure, and emit pungent odors. Since there is a wide range of chemistries available within the aromatic group, not all fluids have similar properties and environmental or personnel concerns, and regulations vary from fluid to fluid.

Most synthetic fluids are composed of a limited number of aromatic components and have a narrow boiling range, allowing easy identification of the degradation by-products or contaminants. Reprocessing synthetics via fractional distillation is an economical alternative to disposal and replacement. Most synthetic-fluid suppliers offer this service at a nominal cost. Some suppliers also offer credit for spent material, which can be traded in for a replacement charge. Because of the relatively low cost of petroleum based fluids, few suppliers offer reprocessing services for hot oils.

System design;

The main constituents of a heat transfer fluid system are:

• The heater

• Circulating pumps and piping

• The expansion tank

• Filters

• Controls and instrumentation

The heater;

The heater is the heart of the system and requires careful design to ensure a long fluid life. The most common design uses a cylindrical or box-type heating chamber with vertical tubes carring the heat-transfer fluid arrayed along the walls of the chamber. The heater design should avoid hot spots caused, for instance, by flame impingement on the tubes. The fluid should be pumped at sufficient velocities to ensure that there are no stagnant pockets. Fluid velocities should also be high enough to develop a high degree of turbulence within the tubes; this prevents film temperatures from becoming excessively high, which would be detrimental to the fluid life. Recommended velocities are in the range of 1.5–3.0 m/s, depending on the operating temperature.

Pumps and piping;

Pumps fitted with mechanical seals, sealless magnetically driven, or canned-motor pumps are the three normal options available for heat-transfer-fluid systems. The pipework should have adequate flexibility to accommodate thermal stresses. Most organic heat-transfer fluids have a propensity to leak through joints and fittings unless these are very tight. The recommended gasket is stainless steel, spiral-wound type with flexible-graphite filler. Globe valves are commonly used, but the valves should have a minimum of five solid-graphite packing rings. Control of leaks from pipework is especially important because fluid-soaked insulation poses a more serious hazard than the leaking fluid itself. An all welded system, or one that minimizes the number of flanged joints, is the best option.

Filtering;

The use of a filter in the heat-transfer-fluid circuit is usually not given the importance it deserves. Filtration reduces plugging and fouling of tubes in any heat exchangers and in the heater. Filtration also improves the longevity of system components, such as pump-shaft seals and valve stems. Filters are a must in mineral oil circuits, since these are more prone to thermal degradation, which results in the formation of carbon particles. Such filters are usually installed off the main circuit in a side-stream to prevent any inadvertent flow restriction. Cartridge filters with a 10–20-µm cutoff are usually preferred.

The expansion tank;

The expansion tank is the simplest but perhaps the most crucial piece of hardware in the heat-transfer-fluid system. The purpose of this tank is to allow for thermal expansion of the fluid, which can be as high as 25%. A properly designed and correctly installed expansion tank goes a long way in eliminating many operational problems and also increases the life of the heat-transfer fluid. The rule-of-thumb for sizing the expansion tank is that it should be one-quarter full at ambient temperature and three-quarters full at normal operating temperature. The tank size thus depends on the total system volume and the normal operating temperature. The expansion tank should be installed at the highest point in the system and connected to the suction side of the pumps that circulate the fluid through its cycle. Being located at the highest point of the loop, the expansion tank serves as a convenient place for venting any low-boiling thermal-decomposition products from the system.

Expansion-tank design;

The expansion-tank design should:

• Allow for the increase in fluid volume due to thermal expansion

• Provide a means for venting water, non-condensables and by-products of thermal degradation during start-up and operation.

The simplest type of expansion tank is the surge drum, which essentially acts as a receiver for the return fluid from the consumers and from which the circulating pump draws the fluid for pumping through the heater. This design offers no protection against thermal oxidation of the fluid; in fact oxidation is promoted due to aeration within the drum. However the surge-drum design provides excellent system-venting capabilities during start-up and extended operation.

The ideal design is the expansion tank located at the highest point in the system with a double-drop-leg piping arrangement, as shown in Figure 1. While the expansion tank should be connected to the system by a sufficiently small line during normal operation to avoid thermal recirculation, the line should handle full system flow at start-up conditions.

New systems almost always contain some water, typically left over from hydrotesting, and this water must be removed to avoid pump cavitation. The double-leg design permits this.

All organic heat-transfer fluids undergo oxidation on contact with air leading to the formation of insoluble compounds. These insolubles can cause fouling, which adversely affects heat transfer. Because the usual source of air into the system is through the expansion tank, blanketing with nitrogen should be used to prevent fluid oxidation. Nitrogen blanketing also eliminates the ingress of atmospheric moisture. Although this is the most effective method to prevent oxidation, a cold-seal-trap or baffled design can be adopted in situations where nitrogen is not readily available. Such a design is shown in Figure 2.

Controls and instrumentation;

Control systems are required for the heater and for the individual energy consumers. At the heater end, the firing mechanism should be regulated to ensure that the heat input is in accordance with the energy demand. At the individual user equipment, flow controls are typically installed. In a multiple user system, such as shown in Figure 3, controls should be provided at each user individually to ensure proper energy delivery.

Mode of operation;

Processes utilizing heat-transfer fluids can be categorized into three types: liquid-phase systems (pressurized and non-pressurized) and pressurized vapor-phase systems. Non-pressurized liquid-phase systems are generally the simplest to design and operate. Both hot oils and synthetic fluids can be used equally well in this type of system as long as the operating temperature of the heat-transfer fluid is below its boiling range. Major components in these systems consist of the heater, heat exchanger, vented-expansion tank, and circulating pump. In these types of systems, the expansion tank does not require the application of an inert gas in order to maintain a positive pressure on the circulating pump. To reduce the probability of fluid oxidation, a baffled expansion tank design can be used.

Pressurized liquid phase systems using both hot oils and synthetics are similar in design to non-pressurized systems except that an inert gas must be applied through the expansion tank when the required operating temperature of the heat-transfer fluid is above its boiling range. In this case, the pressurized inert gas (such as nitrogen) is used to keep the heat-transfer fluid in liquid state. However, with the exception of the multiphase fluids, such as the diphenyl oxide/biphenyl-type, most of the liquid-phase synthetic fluids and all of the hot oils ordinarily do not require inert gas pressurization to maintain the liquid phase at their highest recommended operating temperatures.

Pressurized vapor-phase systems use the latent heat of condensation to deliver the energy to the process consumer. Only a handful of synthetic fluids, most notably the aforementioned diphenyl oxide/biphenyl type, can be utilized in these cases. A simple vapor-phase system can be designed using hydrostatic pressure to return the condensate from the user to the vaporizer by gravity, eliminating the need for a condensate pump. More-complex systems require a flash tank, condensate return tank, and a condensate return pump.

Troubleshooting;

Preventive-maintenance analysis of high-temperature heat-transfer fluids can play a major role in maintaining production rates, minimizing unscheduled fluid-related downtime, predicting mechanical component failure and reducing overall heat-transfer-fluid costs. The importance of periodic fluid sampling to monitor the health of the heat-transfer system can never be overemphasized. The sampling frequency should be based on previous experience with the operating system. In case of a new start-up, sampling can be every three months to begin with. When the unit is operating at a temperature closer than 20°C to the upper limit, the sampling frequency should be increased.

Preferably, the fluid samples should be taken from the discharge of the main circulating pump to ensure a representative sample. Provision for safe sampling, including adequate cooling of the sample, should be provided for in the design. Many suppliers of heat-transfer fluids provide sample analysis free of charge as part of their technical support. The sample is primarily analyzed for moisture, low and high boilers, and insolubles.

Moisture;

Some amount of moisture from humid air can be sucked into the system through improperly blanketed expansion tanks. Water might also be left over in the system because of improper elimination during startup or hydrotesting, as noted above. Water can also be introduced into the system through contamination in a drum used for topping up. But water content in excess of 0.05% or the presence of free water in the sample is a strong indicator of a hardware failure in the system; for instance a pinhole in the jacket of a vessel or the tubes in a tubular-heat exchanger. Water incursion into the system can also be detected through a cracking or popping sound in the heater, or by frothing and steaming in the expansion tank. Pump cavitation may also be symptomatic of the presence of water in the system.

High and low boilers;

Presence of high- or low-boiling contaminants in the sample is suggestive of the thermal degradation of the fluid. All heat-transfer fluids gradually degrade during normal use, with the rate of degradation increasing as the fluid approaches the high end of its bulk-fluid operating temperature. High and low boilers are formed when heat-transfer fluids are heated to a high temperature and certain molecular bonds begin to break or thermally degrade. Some of the new materials that form have a lower molecular weight and typically a lower boiling point than the original fluid — these are low boilers. Other compounds resulting from thermal degradation will polymerize into higher molecular weight and higher boiling point molecules than the original fluid — these are high boilers. High and low boilers may not have the heat-transfer efficiency and thermal stability of the original heat-transfer fluid molecules.

Experience indicates that, under normal conditions, most fluids with 5% low-boiler or 10% high-boiler levels call for reprocessing or replacement to maintain heat-transfer capabilities. In the case of a dramatic increase in high- or low-boiler levels from the previous sample, and with the fluid still operating within its maximum bulk-operating temperatures, either outside contamination, heater malfunction or decreased fluid flowrate may be assumed to be the cause. A rapid increase in concentration of low and high boilers strongly indicates malfunction of the heater or the pump. Flame impingement on a heater tube can cause abnormally high film temperatures inside the tube, resulting in increased thermal degradation. A reduced circulation due to a pump problem or a flow restriction in the system can also contribute to this problem.

Insolubles;

Insoluble compounds found in the fluid are primarily pipe slag, metal fines, hard carbon and other inorganic contaminants. The presence of large amounts of carbon is another indication of thermal degradation of the fluid and is probably due to coking or sludge formation, or fluid oxidation. Coke and sludge can adversely affect a system’s heat-transfer efficiency by fouling the heat-transfer surface.

The presence of metal fines in the fluid may indicate process pump, mechanical seal, or valve wear. An insolubles level in excess of 0.05% calls for the installation of a slipstream filtration in the system. This will minimize wear on mechanical components such as pumps and valves.

Fluid reprocessing;

As discussed above, heat-transfer fluids will undergo gradual, or even accelerated, thermal degradation during normal operation. Fluids can also become contaminated because of leaks in heat exchangers. Degradation and contamination of the fluid will lead to a significant decrease in heat-transfer performance. In many cases, a full fluid change-out might be the only option to restore the system performance, but other economical alternatives should be investigated, preferably with the help of the supplier.

In the fluid-reprocessing option, the degraded or contaminated fluid is removed from the system and sent to the supplier for reprocessing. Reprocessing essentially consists of removing the low and high boilers by distillation. To avoid a total system shutdown, the reprocessing can be done in lots. Partial fluid replacement can also improve the system performance by diluting the degraded by-products or contaminants to within acceptable limits, and this option might be the economical alternative in some cases.

Collaboration with suppliers;

No one knows the heat-transfer fluid better than the supplier, and it is important to take advantage of this knowledge at every stage of the process from selection and system design to operating guidelines, troubleshooting and periodic testing. 

Typically, fluid suppliers offer the following services:

• Assistance in fluid selection and system design.

• Assistance in start-up.

• Troubleshooting during operation.

• Reprocessing of used fluid.

• Assistance in disposal of spent fluid.

• Testing and analytical services.

- "Edited by Gerald Ondrey."

THANK YOU!!!. 

Your Hi Fluid Zone! Part 1A! Maximizing Heat-Transfer Fluid Longevity.

Your Hi Fluid Zone! Part 1A! Maximizing Heat-Transfer Fluid Longevity.

Maximizing Heat-Transfer Fluid Longevity;

Proper selection, monitoring and maintenance can protect fluids and components from damage due to thermal degradation, oxidation damage and contamination;

Faced 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 & maintenance of liquid-phase heat-transfer systems, both large and small, that use an organic-based heat-transfer 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 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.

Further discussion of initial fluid selection is beyond the scope of this article, but is covered in Ref. [ 1–7 ].

Over time, the most common threats to the life of heat-transfer fluids (and sometimes the entire system) include the following: 

• Thermal degradation

• Oxidative degradation

• Process contamination

• Contamination by other materials

Each threat is discussed below, along with findings from real case studies, and practical recommendations for how to deal with these challenges.

Thermal degradation;

Regardless of the chemistry of the heat-transfer media, thermal degradation can occur whenever the heat source provides more energy than the heat-transfer media can absorb and carry away at that particular time [8 ].

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).

Figure 1 shows a simple example of the thermal degradation of a typical petroleum-based heat-transfer fluid (n-hexacosane) with ISO viscosity grade 32. In this case, the fluid is a distribution of molecules of various lengths, averaging 26 carbons long.

As shown in Figure 1, when the energy submitted to the fluid exceeds the threshold necessary to start breaking the stable covalent carbon-carbon bonds, the result is the formation of shorter hydrocarbons. The example in Figure 1 shows the scission (cracking) of a perfect straight, long-chain alkane into shorter molecules, such as dodecane (C12) and tetradecane (C14), each having a lower boiling and flashpoint and viscosity compared to the starting C26 hydrocarbon.

FIGURE 2. Excessive thermal stress often results in a breakdown 
of the heat-transfer fluid, and the carbonaceous byproducts can 
build up on the inside surfaces of pipes.

The systematic result of thermal degradation is a reduction in the overall fluid viscosity and increased volatility, which increases the risk of leakage and loss through evaporation. Thermal cracking increases the vapor pressure, lowers the flashpoint and fire point, and sometimes, reduces autoignition temperature (AIT). As the name implies, the AIT is the temperature at which the fluid vapors are hot enough to ignite spontaneously in absence of an ignition source [ 9, 10 ].

As shown in Figure 2, the problem worsens if left unaddressed. Reynolds discovered in 1883 [ 12, p. 86 ], that low-viscosity fluids offer the best heat transfer behavior in a forced-convection situation such as a typical heat transfer system. Based on these findings, one may think thermal cracking is advantageous from a thermal conductivity point of view. However, the resulting drop in viscosity is not necessarily favorable.

Safety risks;

The concern is that the associated potential reduction of the AIT of the degraded fluid can make the operation of a closed system unsafe if the operating temperature nears or exceeds the AIT. Moreover, shortened molecules are not the only species formed during thermal degradation of the fluid.

On the other hand, an open system — that is, one in which the heated fluid is constantly in contact with the atmosphere — is even less forgiving. Any drop in the heat-transfer fluid’s flashpoint and fire point (defined as the temperature at which the fluid sustains a fire for five seconds in the ASTM-D92 Cleveland Open Cup, or COC flashpoint test apparatus) could jeopardize the entire operation, considering that the fluid was likely chosen, in part, based on its fresh oil, open-cup flashpoint rating (to which a safety margin was likely added).

Efforts to determine a definitive relationship between a drop in flashpoint and a drop in AIT have not proven successful. Fortunately for users, in many cases where a petroleum-based fluid exhibits a relatively low flashpoint, we have seen the AIT remained high, but this is not always the case.

The performance data shown in Table 1 demonstrate how progressive thermal degradation leads to steadily diminishing flashpoint and viscosity of the heat-transfer fluid. The gas chromatography distillation (GCD) test consists of a simulated distillation of the fluid in the laboratory. In the cited example, the initial distillation point (GCD 10%) drops over time, which again confirms the increased concentration of low-boiling components present in the fluid.

Table 1. Analysis Data showing thermal degradation of the heat-transfer fluid at a meat-processing facility
Sample date, mm/dd/yy	Flashpoint, °C (COC)*	Water content, ppm (Karl Fisher)	Viscosity at 40 °C, (centistokes, cSt)	Gas chromatoraphy distillation (GDC)**
				10% boiling, °C	90% boiling, °C	% boiling below 335°C
04/04/00	154	660	27.0	327	512	10.49
08/10/01	155	580	23.2	307	507	14.40
06/11/02	175	313	22.7	317	490	12.80
09/09/02	171	51	21.2	201	481	31.90
12/09/02	161	220	20.5	304	489	16.20
03/12/03	175	42	19.8	294	490	19.00
After startup and shutdown procedure modification of April 2003
06/11/03	169	156	23.0	310	497	15.70
New fluid properties	209	—	35.6	382	498	0.80
* COC represents analysis via the ASTM-D92 Cleveland Open Cup (COC) flashpoint test apparatus. ** GCD = gas chromatography distillation. The GCD test consists of a simulated distillation of the fluid in the laboratory. Comparison with the fresh-oil boiling curve allows for the detection of lighter and heavier molecules in the fluids.

Performance problems;

Another major consequence of thermal cracking is the formation of carbonaceous residues (Figure 2), which result from reactions of recombination. To a certain extent, these particles can be compared to soot that is produced during fuel combustion in a diesel engine, where it is documented that soot is harder than the metallic components of the engine [ 13 ].

Such unwanted carbon residues are not only abrasive toward the piping, but they also tend to stubbornly adhere and harden onto the hot surface points, forming an insulation layer inside the pipe. This occurrence often forces the user to increase the heater set temperature (increasing energy consumption) to maintain the desired operating fluid temperature.

As a general rule of thumb, Wheeler [ 14 ] reports that the widely used heat-transfer fluids based on polyalkylene glycols (PAGs) begin to experience thermal degradation near 250°C (482°F). Meanwhile, Wheeler also reports that the thermal degradation of uninhibited polyethylene glycol results in a mix of five organic acids [ 15 ]. 

The formation of these byproduct acids leads to increased corrosion over time in high-temperature systems.

Of similar importance is the fact that even systems running at temperatures that are considered to be relatively mild (for example, around 149–204°C or 300–400°F), are not exempt from the ravages that elevated temperatures can bring, in terms of the thermal cracking of the heat-transfer fluid. For example, consider a system in which the fluid experienced a change in physical properties, combined with oil-flow issues (for instance, from a defective pump, a fluid containing solids, or some piping restriction or pluggage) or a problem with the heater (for instance, the heater coil or electrical element has baked-on carbon that acts as an insulation layer forcing a higher energy demand to maintain the target fluid outlet temperature). Such factors can cause a rise in the skin-film temperature (the temperature of the fluid immediately touching the heated surface).

Any combination of the conditions mentioned above can cause the skin-film temperature to be significantly higher than the temperature of the fluid circulating in the center of the heated pipe (which is called the bulk oil temperature). The larger the gap between skin film and bulk oil temperature, the more energy the fluid tries to distribute within itself through turbulence. At some point, the fluid at the heated surface will receive more energy than it can absorb (its heat capacity), carry and release (its thermal conductivity), resulting in thermal degradation of the fluid.

Minimization strategies;

Discussed below are ways to minimize the thermal degradation of a heat-transfer fluid in open systems.

Use the right fluid for the job. By choosing a fluid with a high thermal stability, Guyer and Brownell [ 16 ] suggest that most problems associated with localized or temporary temperature excursion can be prevented. Ashman [ 17 ] also emphasizes the importance of using a heat-transfer fluid with a suitable thermal stability for the application. Hudson, Sahasranaman [ 6, 7 ] and many others acknowledge that petroleum-based fluids of pharmaceutical quality produced by a severe hydrogenation and hydrocracking process (also referred to as “white mineral oils”) tend to have greater thermal stability compared to petroleum base oils that are produced from other refining methods [ 6, 7 ].

Use appropriate venting. Venting involves the periodic release (from the fluid and the system) of the light, more highly volatile hydrocarbons that form during thermal cracking. Venting is typically carried out by circulating some of the hot fluid to the expansion reservoir, so that those molecules with a relatively high vapor pressure can naturally migrate into the gas phase above the fluid. Then, depending on the system design, the vapors are released directly into the atmosphere or sent to a collection drum or tank, although laws governing volatile organic compounds (VOCs) and other environmental trends cause most users to collect the condensed low-boilers and properly dispose of them.

Fresh fluid needs to be added periodically, to maintain the desired fluid level (to prevent pump starvation and cavitation when the system charge contracts after a shutdown). As a precautionary note, users should remember that fresh fluid must never be added directly into the hot oil stream; rather it should be added into the expansion tank or other cool reservoirs connected to the system.

Venting continuously or for extended periods is not advised, because the resulting rise in the bulk fluid temperature in the expansion tank will accelerate oxidation (discussed below).

We recommend the use of an oil-analysis program to determine the rate of generation of low-boilers during any operation. With proper venting and analysis, users can establish how often, and for how long, the fluid must be periodically vented, in order to safely operate a high temperature system with a fluid that stays in good condition (maintaining characteristics that are similar to the fresh oil for as long as possible).

Adopt proper startup and shutdown procedures. The successful startup of any heat-transfer system is important, since the faster the heat-transfer fluid reaches its desired operating temperature, the faster the facility can produce its products and begin to fulfill orders. This becomes even more important for systems that stop and start up regularly.

One may say that running the pump and the heater for a few extra hours to accommodate a slower, more-gentle startup is not cost-effective, but for many applications, such an approach pays its own dividends. For instance, by maintaining a more-gradual heating profile at startup, the fluid will be able to effectively remove heat and reduce the risk of thermal degradation, and minimizing the formation and buildup of baked-on residues. The net result will be extended planned-maintenance intervals and greater component life expectancy.

Shutdown procedures also impact system efficiency and fluid life. For instance, Stone [ 19 ] and others recommend maintaining oil circulation after the heater is turned off until it’s been cooled to 65°C (150°F). The refractory material in a furnace is designed to retain heat for as long as possible, so stopping the oil flow immediately after the heat source has been turned off provides an opportunity for the stagnant fluid to crack, forming low-boiling fractions and carbon residues. This negatively impacts the life of the fluid and the overall heater efficiency.

With regard to smaller systems such as temperature-controlled units (TCUs) or extruders, many designs have improved greatly in recent years and now maintain fluid circulation for some period of time following shutdown as a common approach.

An insufficient shutdown interval was the overall problem at the facility whose degraded fluid was shown in Table 1. After a service call, it was determined that the 249°C (480°F) system was shut down on Friday evening with only a short circulation period following shutdown. It was fired up again at 7:00 a.m. on Monday, to allow for production to start at 9:00 a.m.

A full system shutdown and cleaning was deemed impossible by the user at that time, so the fluid was left untouched, but better future practices were implemented. The last set of results in Table 1 shows that two months after the initial analysis, the rate of generation of low-boilers had diminished (as seen in the percentage boiled below 335°C). As a direct result, the facility did not add any new oil. The increase in kinematic viscosity and flashpoint, and the fact that the strainer no longer collected carbon residues in any appreciable amount, provided evidence of improvement.

Consult your suppliers about proposed design or operational changes.Business is booming, more production is expected from the plant, more parts must be produced, and lines need to be added. Do you need to increase the operating temperature? What about the flowrate, is it adequate? What does your heater manufacturer think of the proposed addition? Operators should get as much input as possible from their system designer. manufacturers, and parts and fluid suppliers before any major changes are implemented. Stone [18] recommends that operators should maintain an updated list of contacts and keep it handy for questions or troubleshooting help.

It is relevant to document the skin-film temperature in the current system and in the proposed operating conditions. Make certain your fluid supplier confirms your current heat-transfer fluid’s ability to handle any new operating parameters.

Maintain, inspect and perform preventative maintenance on system components. Even though liquid-phase systems commonly operate above the flashpoint of the fluid (but below its auto-ignition temperature), the risk of fire should be very low in a normal, well-designed system, especially one that is kept oil-tight, leak-free and subject to regular inspection and maintenance [ 19 ].

For any system where heat is purposely generated to raise the fluid temperature, ensuring proper operation of the heat source is critical to achieve optimum performance. Daily inspections, using a consistent checklist of items to monitor are recommended [ 18, 20 ]. For instance, fired heaters should be inspected for flame impingement, especially if the burner is oversized or cycles frequently. In the case of flame impingement, the flame (whose temperature is typically on the order of 1,093–1,650°C, or 2,000–3,000°F) subjects the oil tubes to excessive localized heat flux, which can cause tube deformation and coking (resulting from thermal degradation, as seen in Figure 2), and leakage with increased risk of fire [ 21 ].

In the case of systems equipped with immersed electrical heaters, excessive watt density, lack of fluid turbulence around the hot tubes, or insufficient flowrate often causes premature degradation of the fluid. Such degradation can be offset in part by proper fluid selection and maintenance practices [ 22, 23 ].

In any system, the oil-circulation pump can be compared to the heart, moving the fluid around. The pump should be well-maintained. Specifically, drive bearings on the electric motor and pump seals should receive proper attention. Centrifugal pumps should ideally operate at or near their best efficiency point (BEP), with bearings well-maintained and seals working properly. Finally, the expansion reservoir, piping, connections and valves should be selected and maintained appropriately, as part of a world-class maintenance program.

Meanwhile, the life blood of the operation — the fluid itself — should be tested regularly. While further discussion of the types of tests, their significance and data interpretation is beyond the scope of this article, the American Society for Testing and Materials (ASTM) Method D5372 should be followed to properly monitor the condition of heat-transfer fluids [ 24 ].

Oxidative degradation;

For the purpose of this article, we define fluid oxidation as the reaction of the heat-transfer fluid with oxygen from air. The oxidative degradation of organic compounds is extremely complex, as it involves a series of chemical reactions that result in the formation of high energy, unstable and reactive free-radicals and peroxides. One initial free-radical allows for the possibility of forming two radical species, which results in the formation of a variety of oxygen-containing species, mainly organic acids. These long-chained organic acids may be weak on their own, but as their concentration grows in the fluid, the oil eventually becomes more corrosive [ 25 ].

These acids also polymerize — often to a level that is sufficient to modify the fluid properties, causing an increase in viscosity, discoloration and eventually, precipitation as lacquer, varnish and sludge [ 26 ] such as that shown in Figure 3. The varnish formation is seldom a concern in heat transfer applications because of relatively large pipe diameters and valves with high tolerances. However, further oxidation will lead to the formation of heavier acids and sludge. Oxidation-related sludge is not very soluble in heat-transfer fluids, so it tends to adhere to metallic surfaces or settle in areas of low flow and low turbulence.

Fluids for a specific project are generally chosen based on their properties in a fresh state. Any alteration of the fluid physical properties (resulting from degradation or contamination) could negatively impact the heat absorption and dissipation capabilities of the heat-transfer media.

Such sludge also tends to settle at the bottom and the sides of the expansion tank, and can also circulate throughout the system and make its way into control valves.

FIGURE 3. These illustrations shows the type of varnish (left)

and sludge (center, right) that can result from oxidation-related 

degradation of a petroleum-based, chemical aromatic and 

polyalkylene glycol (PAG) fluid

Table 2 provides oil-analysis data for an uninhibited, chemical aromatic (synthetic), heat-transfer fluid that experienced oxidation in a large 27,000-L (7,132-gal) system in Europe. (In this context, the term “uninhibited” refers to the fact that the fluid does not contain additives such as anti-oxidants and rust-corrosion inhibitors to prevent degradation.) The acid number (AN) — as determined by ASTM D664 Method and used to quantify the level of acids in an oil sample — was increasing over time.

Table 2. OIL-ANALYSIS DATA DESCRIBING A FLUID THAT HAS EXPERIENCED oxidation (source: Petro-Canada LUBRICANTS, A SUNCOR ENERGY COMPANY).
Sample date, mm/dd/yy	Flash point (COC), °C	Water content, ppm (Karl Fisher)	Viscosity at 40°C, cSt	Acid number (AN*), mg/KOH/g	Solids (insolubles), wt.%	GCD
						10% boiling, °C	90% boiling, °C	% boiling below 335°C
05/12/04	193	301	30.4	<0.1	0.1	333	423	10.5
04/25/06	179	382	29.6	0.11	0.24	324	426	11.0
04/15/08	201	138	39.4	0.23	0.48	336	431	9.4
*Acid Number (AN) is obtained using ASTM D664 titration method, which is used to quantify the levels of acid in an oil sample.

The distillation of the fluid, represented by the GCD 10% boiling point, shows the initial boiling is at the same temperature as fresh oil, so thermal degradation does not seem to be an issue in this example. We notice the viscosity has risen by 30% over time and the end of the distillation curve (GCD 90%) is shifting toward higher temperatures, indicating the increasing presence of heavy compounds not found in the fresh oil.

An increasing amount of insoluble particles are forming, and the AN values are rising. By connecting the dots, we conclude that oil oxidation is causing an increased formation of heavy acidic polymers that will foul the low-flow areas of the system. This degraded oil, with its higher viscosity, cannot deliver the same performance capabilities as fresh oil, and in today’s context of high energy costs, any loss of efficiency is costly.

In the example discussed above, the company could not afford a shutdown to clean its system this year. Instead, operators opted for a partial fluid replacement of 50% of the entire charge this year (incurring an expenditure of roughly $175,000, excluding waste oil disposal and labor) and are planning a full drain, clean, flush and refill next year. In general, fluid oxidation imposes great cost penalties on any system; the selection of a fluid with better oxidation stability could have avoided this massive spending and offered many more years of useful life.

Minimization strategies;

Discussed below are several options that are available to avoid or minimize potential oxidative degradation.

Inert gas blanketing. 

In closed systems, the most effective way to eliminate the potential for oxidation is to install an inert gas blanket in the expansion tank headspace. Hudson [29] provides details and recommendations on how to install such systems. The basic principle relies on substituting air (which contains oxygen) with an inert gas (most often nitrogen, although carbon dioxide and argon may also be considered) in the only location where warm oil can come into contact with oxygen from air — the expansion tank headspace. Displacing oxygen that might react with the fluids virtually eliminates oxidation.

The pressure of the inert gas is maintained slightly above atmospheric pressure. Gas-blanketing systems, including the safety-relief valve, require ongoing inspection and maintenance to prevent inert gas leaks and limit unnecessary, costly gas consumption.

Choose a fluid formulated for the job. Oxidation-inhibitor additives are also available to enhance the performance of heat-transfer fluids. Most chemical aromatics sold today contain one or a few varieties of molecules and do not contain any performance enhancing additives such as antioxidants or rust and corrosion inhibitors.

The additives that are used in heat-transfer fluids are different from the ones found in other industrial lubricants that are not subjected to such elevated temperatures. Specifically, in the case of antioxidants, some technologies combat oxidation by reacting with free radicals before they can lead to acid formation, while others attack intermediate peroxides [ 25 ].

Fluid selection is complicated by the fact that it is extremely difficult to determine the oxidation stability of a heat-transfer fluid by its technical data sheet. Even though many of the heat-transfer fluids on the market today are unadditized, their respective marketing materials often praise their fouling resistance and promote their outstanding oxidation stability. Thus, users should assess all product claims with a critical eye.

In general, systems with an enormous amount of oil tend to be more forgiving because it takes a longer time to oxidize a larger volume of fluid to a point where it raises concerns in terms of oil analysis results. In these cases, user experience, references, testimonials and competitive benchmarking studies should be evaluated in conjunction with vendor data, to assess the likely longevity of a fluid for the application at hand and avoid costly changeouts in large systems.

Compared to closed or blanketed systems, open systems allow the hot fluid to come in direct contact with air, making oxidative damage a harsh reality rather than a possibility. In these cases, the importance of choosing a robust product to maintain high productivity standards becomes even more important.

For example, an electronic company operating an open system at 175°C (350°F) was replacing its heat-transfer fluid every six months, after which time the fluid had become viscous and dark with a burnt odor. Switching to a fluid with better resistance to oxidation enabled longer service life. In fact, judging by the oil-analysis results, the oil properties still look like new after more than 24 months of service in these harsh conditions. This obviously saves the facility money in terms of time, labor and fluid purchases.

In closed systems with no inert gas blanketing, the key is to maintain the fluid temperature in the expansion tank below 65°C (150°F), if possible. The main reason is because there is a direct relationship between the temperature and the rate of oxidation. For instance, the rate of reaction between a petroleum-derived oil with oxygen (doubles for every 10°C (15°F) increase above 80°C (175°F) (with slight variations depending on the author) [28], so the higher the temperature the more severe the degradation, and this does not take into account the fact that the oxidation reaction is exponential and is accelerated by contaminants such as copper or iron particles, water and other catalysts.

Oxidation could occur in systems with a design that allows the oil to circulate through the expansion reservoir with full flow, either directly after the heater or on the return from the heat users. Such design exposes the hot fluid directly to oxygen from air, thereby acceleraing oxidation and greatly reducing fluid life.

Using the oil-analysis results, fluid oxidation can be monitored by paying close attention to acid number (AN) and gas chromatographic distillation (GCD) results.

Minimizing process contamination;

Process contamination can be extremely damaging to the heat-transfer fluid and the system components. As is often the case, logic suggests that contamination is unlikely since the pressure is greater on the fluid side, but real life experience has shown on many occasions that process material can enter the heat-transfer fluid stream. The urgency required to fix a process leak really depends on the severity, the type of contaminant (chemistry), and the heat transfer media it comes in contact with. The case of contamination by water is discussed in the next section, although water is sometimes part of the process.

For example, in the oil-and-gas industry, a natural-gas-extraction facility may experience an unintended leak of the process hydrocarbons into the heat-transfer fluid system. Being hydrocarbon-based, the heated gaseous molecules will mix very well with heat-transfer fluids of a similar chemistry, such as petroleum-based fluids, chemical aromatics and PAO Group IV synthetic fluids ([ 4 ] provides details on competing fluid types). Within a short time, the viscosity of the entire fluid charge will be greatly reduced and its overall volatility increased.

In a situation such as this one, emphasis must be put into venting the heat-transfer fluid to release those light hydrocarbons into the proper collection device in order to maintain a safe operation, and if at all safely possible, to keep the unit running until the next shutdown opportunity to repair the leak.

Another example of process contamination in the petroleum industry occurs frequently at asphalt terminals. Similar to the example discussed above, any unintended ingress of asphalt in the heat-transfer fluid circuit will mix very well with most of the fluids, since the majority are based on long hydrocarbon chains. However, the highly viscous hydrocarbon asphalt will quickly thicken the fluid.

We have seen heat-transfer fluids increase to several hundred centistokes or even become too thick to measure at 40°C (104°F), thereby ruining the fluid’s ability to transfer heat effectively. The heavy asphalt components will also coat the system internals and plug small lines, meaning a full system cleaning and flushing will eventually become necessary to restore the system to efficient operation.

In some cases, the contaminant itself may be inert to the fluid but it may still react with traces of moisture to form acidic or insoluble compounds. These byproduct contaminants can accelerate rust and cause corrosion and fluid degradation.

Depending on the process contaminants that are inadvertently leaking into the fluid system, it might be possible to detect them (qualitatively) via oil analysis, using the common elemental analysis method like Inductively Coupled Plasma – Atomic Emission Spectrometry (ICP-AES). Sometimes the contaminant can be detected indirectly after it has reacted with another compound in the fluid. In some cases regular oil analysis will not detect the process contaminant and specialized methodology and instruments are needed, such as those found in specialized research-and-development facilities.

A quantitative evaluation to determine the type and extent of the contamination generally requires sophisticated equipment (such as an electronic microscope, or gas chromatography coupled with mass spectrometry), as well as well-trained analysts who are knowledgeable about the product being tested and informed on what contaminant types to look for.

Whenever a process leak is suspected, it is advisable to reach out to your fluid supplier’s technical contact immediately and explain the situation. A sample of the fluid should be analyzed right away.

Other sources of contamination;

In addition to contamination that can arise from process materials (discussed above), heat-tranfer fluids may also become contaminated by the environment (rain or snow), condensation, foreign liquids (such as the wrong fluid put in the system), or the ingress of air. For systems where the expansion reservoir is outside and vented to the atmosphere, it is critical to have — at a minimum — an enclosed tank with a 180-deg, goose-neck pipe on the top.

This may sound very basic, but we were once called to investigate unusual noise coming from the hot oil piping at a saw mill. After assessing the noise, we climbed up to the top of the burner building to examine the expansion tank. The 12-by-12-in. steel cover normally bolted to the side of the 250-gal expansion tank was laying on the catwalk, covered by a foot of dirt, wood dust and snow and no one could remember who had been up there last. Rainwater and snow falling directly into the expansion tank from the open hole was responsible for the high water content we later measured in the fluid and the knocking noise in the piping below.

New construction or recently cleaned systems or heat exchangers are not typically flushed before commissioning. However, in systems where a full or partial cleaning was performed, traces of aggressive cleaning fluids or water-based solutions that are not removed could accelerate corrosion, fouling or create their own polymerization and insoluble residues [29]. In newly commissioned systems, aside from the typical wood debris, welding rods and rags, residual water from pressure testing is most often the culprit for startup problems. Unlike many industrial applications, water in the heat-transfer fluid is more easily detectable by operators and unforgiving because it is heated above its boiling point during service in most applications.

Entrained water will affect various fluid chemistries in different ways. In lubricating and circulation fluids based on mineral and synthetic Group IV PAO oils, prolonged exposure to water may cause the following [30]:

• Hydrolysis or precipitation of oil additives (for those oils that have them).

• Accelerated rust and corrosion of system internals.

• Accelerate degradation (oxidation).

• Cause pump cavitation and wear.

• Create a gargling noise in the expansion tank and knocking in the hot oil piping.

Based on years of examining real-life oil-analysis results, we can say that in general, water does not appear to pose immediate productivity concerns at concentrations below 500 ppm (0.05 wt.%), although we have encountered certain, more-sensitive systems where lower concentrations did have a noticeable impact. However, residual water at concentrations above 1,000 ppm (0.1 wt.%) becomes alarming and calls for investigation and removal.

In the case of mineral oils, the best practical way to remove the water from a heat-transfer fluid while the system is running involves more of a two-step process. First, vent the fluid, allowing the water vapor to migrate into the expansion tank. Once inside the expansion tank, some of the steam will have sufficient vapor pressure to leave through the vent pipe or safety-relief valve when it opens.

In the case of PAG-based fluids, the numerous oxygen atoms in their structure produces strong hygroscopic behavior that is directly proportional to relative humidity in the environment. Wheeler [ 15 ] reports that at 50% relative humidity, pure ethylene glycol absorbs 20% water at equilibrium. This can cause serious concerns.

Lastly, operators must take steps to guard against potential contamination by airborne vapors or particles that could affect the fluid. Just think of a saw mill example, where entrained cellulose dust from the wood dust may not degrade the fluid itself, but will affect the fluid's ability to flow, which will reduce the thermal efficiency and accelerate fouling in the system [ 29 ]. Such an occurrence is more likely to happen if the expansion tank is located in a very dusty environment.

Minimization strategies;

Discussed below are a variety of techniques for minimizing contamination that can threaten heat- transfer fluids.

Investigate and fix. All cases of contamination should be investigated and fixed, and such incidents should also be reported to your fluid supplier, for advice on the potential impact on the fluid. As mentioned earlier, sometimes the contaminant can be evacuated, boiled off or it could ruin the fluid and foul the system in a short time.

Flush new constructions or recently cleaned systems before startup.Operating companies and builders seldom factor in the cost of a system flush, since they often assume the blowing of the water will be done correctly and the contractors will not leave debris in the piping. Unfortunately, discovering such contaminants after the system is running can prove to be costly down the road. While nobody needs the extra costs of flushing a new system (especially when the fluid of choice is relatively expensive, like PAGs or silicone-based fluids), it is nonetheless a good practice. With systems filled with mineral oils, circulating a virgin base oil of the same viscosity as the heat-transfer fluid of choice is a cost-effective way to remove any potential contaminants.

Keep an eye on filters and strainers.Solids collection in the oil filters or strainers should be noted in a log book and monitored closely, preferably with photos taken. The size, texture and color of the deposits all tell a story, and such residues can be sent periodically to a laboratory with sophisticated analytical equipment for accurate identification.

Keep in mind that different solids may come from more than one source, and may become discolored, so don’t jump to conclusions.

Similarly solids from the previous fluids may reside in the system for a long time before an event such as pipe work or partial fluid replacement creates enough disturbance to loosen them. We see this in cases where a used furnace is bought and commissioned without cleaning and flushing prior to the connection to the main system.

Often solids may have a familiar smell or texture that suggests an origin, but could well be something else. For example, a plant was using a heat-transfer fluid that caused valve malfunction because of deposits accumulating inside the valve spools. The black, abrasive deposits looked and felt like carbon particles (abrasive, gritty between the fingers). However, lab analysis identified the material as copper sulfide, formed by the localized chemical attack of sulfur present in the fluid’s base stock onto the copper from the brass valves.

The facility could have spent several thousands of dollars in parts and labor to upgrade all the valves to more expensive stainless steel. Instead it switched to a properly formulated fluid based on highly refined API Group II base oils containing only traces of sulfur. This replacement fluid has proven to be harmless to copper components after years of service, and has had the added benefit of extending oil changes considerably, based on oil-analysis results.

- "Edited by Suzanne Shelley."

Our Author's;

Gaston Arseneault is a senior technical advisor with Petro-Canada Lubricants, a Suncor Energy business (1310 Lakeshore Road West, Mississauga, Ontario, Canada L5J 1K2; Phone: 973-673-3164; E-mail: garseneault@suncor.com), located in the Newark, N.J., area. With the company for more than ten years, Arseneault holds an M.S. in analytical chemistry from the Université de Montréal in Canada and is a member of Society of Tribologists and Lubrication Engineers, from which he has obtained the Certified Lubrication Specialist (CLS) and Oil Monitoring Analyst (OMA I) certifications. He also holds the Machinery Lubrication Technician I certification from the International Council for Machinery Lubrication.

THANK YOU!!!.

References;

1. Guffey II, G.E., Sizing up heat transfer fluids and heaters”, Chem. Eng., Oct. 1997, pp. 126–131.

2. Shanley, A., and Kamiya, T., Heat transfer fluids: A buyers’ market, Chem. Eng., Sept. 1998, pp. 63–66.

3. Arseneault, G., Seven criteria for selecting heat transfer fluid, Processes Heating, January 2008, pp. 2–3.

4. Arseneault, G., Safe handling of heat transfer fluids, Chem. Eng. Prog., April 2008, pp. 42–47.

5. Crabb, C., A fluid market for heat transfer, Chem. Eng., April 2001, pp. 73–76.

6. Hudson, J., Choosing the heat transfer fluid, Process Heating, January 2007.

7. Sahasranaman, K., Get the most from high-temperature heat-transfer-fluid systems, Chem. Eng., March 2005, pp. 46–50.

8. Guyer E.C. and Brownell D.L., “Handbook of Applied Thermal Design,” McGraw-Hill, ISBN 0070253536, 1988, pp. 5–46.

9. Singh, J., “Heat Transfer Fluids and Systems for Process and Energy Applications,” CRC, ISBN 0824771915, 1985, p. 214.

10. Petro-Canada, “TechData: Handbook of Petroleum Product Terms,” Revised Edition 89.06, 1989.

11. Kay, J.M., and Nederman, R.M., “Fluid Mechanics and Transfer Processes”, ISBN 0521303036, 1985, p. 18.

12. Peters, M.S., “Elementary Chemical Engineering,” McGraw-Hill, 1984, p. 85.

13. Petro-Canada, “TechBulletin: The Truth About Soot,” Edition 89.06, 1989.

14. Society of Tribologists and Lubrication Engineers (STLE), “Basic Handbook of Lubrication,” 2nd ed., 2003, Section 3, p. 8.

15. Wheeler, K., Technical Insights into Unihibited Ethylene Glycol, P rocess Cooling & Equipment, July/August 2002.

16. Guyer, E.C., and Brownell, D.L., “Handbook of Applied Thermal Design,” McGraw-Hill, ISBN 0070253536, 1988, pp. 5–47.

17. Ashman, L.A., Troubleshooting problems in heat transfer systems, Process Heating, October 1988, www.process-heating.com.

18. Stone, C.D., “Eight tips to extend your thermal fluid system’s service life,” Process Heating, April 2003.

19. BP (British Petroleum), “Transcal Heat Transfer Fluids”, BP Printing, England, Document # MP59, 1979.

20. Arseneault, G., Preventative maintenance for heat transfer systems, World Pumps, April 2008, pp. 40–43.

21. Vinagayam, K., Minimizing flame impingement in fired heaters, Chem. Eng., pp. May 2007, pp. 70–73.

22. Klein, R., Immersion heaters: Selection and implementation, Chem. Eng., January 2006, pp. 44–50.

23. Arseneault, G., Preventive maintenance for heat transfer systems using electrical immersion heaters, Process Heating, November 2006, p. 12.

24. ASTM International, ASTM D5372-04: Standard Guide for Evaluation of Hydrocarbon Heat Transfer Fluid, 2004, p. 3.

25. The Lubrizol Corporation, “Ready Reference for Grease,” The Lubrizol Corp., Wickliffe, Ohio, Version 2.00, May 2007, pp. 36–37.

26. Singh, J., “Heat Transfer Fluids and Systems for Process and Energy Applications”, CRC, ISBN 0824771915, 1986, p. 179.

27. Hudson, J., The Expansion Tank, Process Heating, September 2007, accessed online at www.process-heating.com.

28. Society of Tribologists and Lubrication Engineers, Alberta Section, “Basic Handbook of Lubrication,” 2nd ed., Section 26, 2003, p. 8.

29. Guyer, E.C., and Brownell, D.L., “Handbook of Applied Thermal Design,” McGraw-Hill, New York, 1988, pp. 5–50.

30. Bloch, H.P., “Practical Lubrication for Industrial Facilities,” The Fairmount Press, 2000, pp. 464–465.