- November 14, 2014
By Clive Jones, et al, Global Heat Transfer
A properly maintained heat transfer system employing food-grade heat transfer fluids will contribute to low cost operation and efficient production.
By Clive Jones, et al, Global Heat Transfer
Applications in the food and beverage industry are well suited to the use of heat transfer fluids, but improper maintenance of these fluids and their systems can cause a myriad of issues for process engineers. Not only are there serious health and safety risks for engineers working with poorly maintained thermal fluid systems, but with the food and drink industry’s strict regulations, preserving the quality of heat transfer fluid is now more important than ever. Food safety and compliance can keep company executives awake at night - and rightly so. It is clear that the consequences of breaking rules and regulations in the food industry are often catastrophic. A properly maintained heat transfer system employing food-grade heat transfer fluids will contribute to low cost operation and efficient production. How degraded heat transfer fluids erode profit Heat transfer fluids (HTFs) will degrade over time due to operating schedule, operating temperature and system flow. The processes that cause this to occur are thermal cracking and oxidation. A heat transfer fluid will begin to darken and smell pungent, as acidic carbonaceous sludge is produced. Eventually, the sludge deposits on all surfaces in the system. Inside the heater these deposits harden and permanently reduce heat transfer. One of the easiest problems to ignore is thermal cracking, the process by which HTF molecules break down due to the absence of oxygen. HTF molecules decompose to low boiling fractions known as light ends, resulting in reduced flash and fire points, and high boiling fractions known as heavy ends, which recombine to form heavier polyaromatic molecules, resulting in fouling of the heat transfer surface through carbon deposition. Thermal oxidation is the reaction of the HTF molecules when exposed to oxygen, which decompose to organic acids that are measured in terms of Total Acid Number (TAN) and Ramsbottom Carbon Residue (RCR). Carbon residue increases the formation of insoluble particles and sludge, which has the effect of fouling a heat transfer surface, causing loss of thermal efficiency and hot spots, which can become hazardous. The Ramsbottom test is adopted by the American Society for Testing and Materials as ASTM D-524-10, a standard test method for Ramsbottom Carbon Residue of petroleum products, while ASTM D664-11a is a standard test method for acid number of petroleum products. TAN is a measure of the concentration of acidity in a heat transfer fluid and is determined by quantifying the volume of an alkaline reagent, for example potassium hydroxide, which is needed to neutralise the acid. One limitation of monitoring TAN is that it provides a measure of the acids generated by both oxidation and by those acids produced as contaminants during the process. It is no surprise that acid by-products are potentially devastating to a heat transfer fluid and its system. In the worst case, the fluid will need to be replaced because the acidic by-products are corrosive to a system’s metal components and will accelerate system wear, as well as leading to concurrent increases in fluid viscosity and deposits. Oxidation is the main reason for black sludge forming, which deposits on heaters and blocks pipe work. All of these increase the risk of component failures in a system. New HTFs typically have a TAN less than 0.05. Although this does vary by fluid type - and fresh Polyalkylene Glycol (PAG) will typically have an acid number ranging between 0.1 and 0.5. - PAG is used as a high temperature, thermally stable HTF exhibiting strong resistance to oxidation. Modern PAG's can also be non-toxic and non-hazardous. Condemning limit The condemning limit for a heat transfer fluid is widely regarded to be 1.0. However, the negative system effect of rising acid by-products occurs at acid numbers in excess of 0.4. When fluids reach their condemning limit they need to be replaced. HTF replacement comes with an associated cost depending on the type of fluid selected – mineral versus semi-synthetic versus synthetic. To prevent oxidation, fluid in the expansion tank must be kept cool. If this cannot be done, consider ‘padding’ the system with inert gas like nitrogen, which is inexpensive and readily available. A line runs from a nitrogen source to an expansion tank’s head space and the gas should flow from the source through an alarmed flow meter, regulator and check valve into the expansion tank. A back-pressure control valve should be fitted to a tank’s vent line, along with a relief valve. In addition to protecting a fluid from oxidation, inert gas will prevent water from condensing in the fluid due to increased ambient temperature and dew point changes. Some heat transfer fluids contain oxidation inhibitors: sacrificial material designed to prevent the fluid from oxidising during incidental contact with air. They are not designed to replace good system design, maintenance and operation. Disposal of the old fluid will also need to be managed correctly by qualified professionals, such as Global Heat Transfer who operate in accordance with environmental regulations. Hence the replacement with new fluid involves production downtime and lost output, which can be extremely expensive if unplanned. In such cases, planned, preventative maintenance contracts should be considered. In trying to reduce the rate of degradation, manufacturers need to focus on regular preventative maintenance plans, such as those offered by Global Heat Transfer, to minimise oxidation and thermal cracking and reduce the risk of fire due to closed flash temperatures falling below 100°C (212°F). Planned, preventative maintenance also enables manufacturers to trend the data that is collected. Regular analysis means that parameters can be plotted against time and monitored correctly. The advantage of doing so is that any changes in the status of the heat transfer fluid can be detected and interventions to correct any deviations can be planned around the manufacturer’s production schedule. Maintenance contracts can also be tailored to client needs. For instance, in any system the header tank temperature needs to remain below 60°C (140°F) during normal operation to help to reduce the extent of fluid oxidation. Hence this tank must remain cool enough to touch. However, if the system is running too hot, the rate of oxidation will increase and may require fitting a nitrogen blanket. Anti-oxidant additives A further measure that manufacturers can employ to combat oxidation is the use of smart thermal fluids that work to depress oxidation. Such fluids contain anti-oxidant additives that help to attenuate the oxidation process at higher temperatures and therefore assist in preventing the build up of sludge. The benefit is longer fluid life, which in turn implies less maintenance, less process downtime, less fluid needing to be disposed and thus less environmental waste. The use of such fluids would be extremely beneficial in helping to prevent oxidation in header tanks and may also be an interim solution to preventing further oxidation until a manufacturer has sufficient time to replace the existing fluid. A word of caution however: such fluids need to cater for food and non-food manufacturing and particular attention needs to be given to the suitability of some additives in food-grade manufacturing - something that is not new, since all thermal fluids used in food manufacturing should be approved. This is a regulatory requirement imposed by several bodies including the US Food and Drug Administration (FDA) and NSF International, but it is one that many manufacturers are entirely unaware of. Global Heat Transfer provides contracts that cater for such eventualities. Using infra-red thermography and telescopic lenses, Global Heat Transfer can monitor header tank temperature from distance. As a result, no-one has to touch the potentially burning header tank. Global Heat Transfer can also advise on measures to reduce header tank temperature and on fitting a nitrogen blanket, if needed. The last tool available to every manufacturer is the expert knowledge of engineers working in the thermal fluids sector. Educating customers is critical to help them understand how thermal fluids break down and what they can do to avoid it. Given the right expertise it is a straightforward task to mitigate the problems that thermal cracking and oxidisation can create. You simply have to be willing to take your head out of the sand and address them head on. The science and compliance of heat transfer Industry is littered with regulations that are misunderstood, poorly communicated and acted on incorrectly. There is no application where this statement is more appropriate than oil-based heat transfer, especially in food applications. Here, the Dangerous Substances and Explosive Atmospheres Regulations of 2002 (DSEAR) and ATEX both apply and, in addition, there is a regulatory need for Food Grade (FG) fluids to be used in food environments. Compliance is often seen as another piece of red tape in the way of achieving a business’ objectives. Independent testing is important, as is using a correct sampling procedure, expert analysis and planned maintenance. To get an accurate picture, thermal fluid samples must be collected at their operating temperature when the fluid is hot and circulating. Older fluid will naturally be more glutinous, so making sure that the sample is taken with the system running and at the required temperature will make for an accurate reading, ensuring the usual turbulent flow is taking place. There is a substantial difference in consistency between samples at working temperature and dormant samples, affecting the way the fuel-like light fractions mix. Where an ‘open’ sample is collected, the most volatile (lowest flash-point) specimens will automatically escape and flash off to the atmosphere, instead of being allowed to cool and condense back into the sample, where it can be decanted under laboratory conditions. Light ends consist of a homologous mix of hydrocarbons with different boiling/flash points. In the case of open samples, as the lowest flash point material has been vented off, incorrect (too high) flash point values will be returned to give an inaccurate result. Food grade fluids Food regulations are much stricter and, when using fluid-based heat transfer, the thermal fluid must be fully H1 or HT1 certified as a food grade thermal fluid by the US Food and Drug Administration (FDA) and the NSF International, respectively. If there is any possibility for oil or lubricant to come into contact with food products, a certified food grade fluid must be used to safeguard consumer health. Food grade thermal fluid is extremely important in the food processing industry; if a manufacturer was to use another type of oil this could potentially put its business at risk. Food grade thermal fluid is designed for incidental contact with food products. Failure to use food grade fluid in a food application can result in the loss of the manufacturer’s top tier accreditation, should EFSIS (the European Food Safety Inspection Service, part of SAI Global Insurance Services) learn that an inappropriate product is being used. High quality food grade fluid is non-hazardous, non-toxic and odourless, which means it requires no special handling and is not considered a controlled substance under United States OSHA (Occupational Safety & Health Administration), Canadian WHMIS (Workplace Hazardous Materials Information System) or other work place regulations. This certainly applies to Globaltherm’s food grade fluid, which is designed to reduce carbon build up, when operated correctly. ATEX and DSEAR From July 2003, companies in the EU must follow two ATEX directives, which have been enacted to protect employees from risk of explosion in an atmosphere where this is a hazard. The two ATEX directives consist of The ATEX 95 equipment directive 94/9/EC, intended to ensure equipment complies to help prevent the risk of explosion, and the ATEX 137 workplace directive 99/92/EC, intended to improve overall safety of staff. Employers must warn their employees where the hazardous areas and explosive atmospheres can be found. Equipment and protective systems intended to be used in zoned areas must meet ATEX requirements. Zone 0 and 20 require Category 1 marked equipment, zone 1 and 21 require Category 2 marked equipment and zone 2 and 22 require Category 3 marked equipment. Zones 0 through to 20 are at the most risk of an explosive atmosphere being present. It is important to remember that any equipment in use before July 2003 is still useable; providing a full risk assessment has been conducted confirming it is safe to use. The ATEX directive 94/9/EC allows free trade of the equipment throughout the EU. Another directive to adhere to is DSEAR, which is the UK version of ATEX. DSEAR has been implemented to help reduce the risk to employees because of dangerous substances igniting or exploding. These regulations may seem confusing but they must be adhered to in order to protect employees, so food manufacturers need to make sure they conduct regular independent testing correctly. Reducing explosion risk and damage to equipment The Abergavenny Fine Food Company discovered an oxidation issue in its thermal fluid, which was causing considerable carbon fouling of its equipment and a build up of acidity within the fluid.
For every increase of 10 degrees centigrade, the oxidation reaction rate doubles. Abergavenny’s header tank was in excess of 100 degrees centigrade and had no nitrogen blanketing system to protect the overheated fluid from the air above it. Based in Gwent, The Abergavenny Fine Food Company is a small to medium sized family business operating from 40,000 sq ft headquarters in Blaenavon and offering products across a variety of categories including snacking, ready meals, dairy and desserts. “We were having a problem with our thermal fluid - it was frequently damaging circulation pumps,” explains Paul Sanders, site engineering manager at Abergavenny Fine Foods. “We use thermal fluid as a means of indirectly heating fryer oil for our breaded party foods line. I had been in the business for a few months when, about three years ago, we got Global Heat Transfer involved. They carried out analysis of the thermal fluid in the system and found that there was a build up of carbon around the pipe work because the fluid had not been tested or maintained for a number of years,” continued Mr Sanders. DSEAR & ATEX “The carbon was coming loose and damaging the seals in the circulation pump. Global Heat Transfer put forward their recommendations to firstly clean the system, then to refill it, and finally to comply with DSEAR using monthly testing and oil analysis.” Global Heat Transfer offers expert sampling and analysis services of premium quality thermal fluids. The company services all types of heat transfer systems for clients operating across diverse industry sectors both inland and offshore. Global Heat Transfer’s 12 point test process goes further than the legislative requirements to show that flash points and corresponding auto ignition temperatures are being managed to safe levels. Flushing & cleaning A team of Global engineers drained, flushed and cleaned the system at the Abergavenny Fine Food Company using a unique combined flushing/cleaning product, Globaltherm C1, which is exclusive to Global Heat Transfer, before replacing the thermal fluid. The dual action power works to rid a heat transfer system of potentially harmful contaminants such as old/oxidised residual fluids, carbon deposits, loose debris, water and volatile light ends. Globaltherm C1 is specially formulated to remove harsh by-products of synthetic and mineral based fluids. It effectively displaces and flushes out waste, leaving behind a clean and safe operating system, ready to accept a new charge of heat transfer fluid. It is compatible with most heat transfer fluids. “Now we have the condition of thermal fluid under control, and when we carry out our monthly analysis we can pick up an issue before it starts to cause problems,” adds Paul Sanders. “We can monitor the carbon content and pick up any excess build up of carbon, as well as the acid levels, which can cause corrosion if they go over a certain level. “We can also keep an eye on the flashpoint, which was very low in this case. When I joined the company, the thermal fluid had not been analysed or changed for seven years prior to Global Heat Transfer getting involved. By that time the damage had been done from the carbon build up in the pipe work, tubes and boiler.” Acidity level Global Heat Transfer looks at a standard suite of 11 relevant tests and has found that around 80% of customers are carrying out irrelevant checks and incorrect sampling, if any at all. The three main assessments Global Heat Transfer undertakes are checking of the carbon level and amount of insoluble particulates, closed flash point and the acidity level or Total Acid Number (TAN), which is the amount of potassium hydroxide in milligrams that is needed to neutralise the acids in one gram of fluid - an indication of any oxidation or acidic contamination that may be present. If the carbon level (heavy ends) is too high it will result in system fouling which means carbon insoluble particles will stick to the system internals and eventually bake on hard if not flagged, cleaned and flushed in time. Carbon is an insulator, so a build up will ultimately reduce efficiency at the process end and result in higher running costs. The most common cause of heater coil failure is when the insulating effects of carbon fouling do not allow the thermal fluid to carry enough heat away from the burner flame. This can result in hot spots and the coil burning through, at which point the combustion triangle of ignition source, fuel and air are present. This can lead to a serious fire in the thermal oil if there are no adequate or correctly operating safety systems in place. Flashpoint The closed flash point must be managed under DSEAR legislation. Global Heat Transfer takes a hot, circulating and ‘closed’ sample as open samples allow light ends to flash off to atmosphere giving inaccurate readings, which are outside DSEAR and insurance industry requirements. Other checks include viscosity, water content, ferrous and particulate quantities, as well as open flash and fire point, which are accessed in conjunction with the other sample results. If thermal fluid samples are not collected in a representative method, artificially high flash point values will be returned. This results in the end user perceiving a lower risk from flash points than is actually correct. This has obvious and important insurance, health and safety and, with the effect of DSEAR/ATEX regulations, legislative implications. Molecular weight If the sample is taken with the system running and at normal working temperature, it is far more likely that turbulent flow is occurring, thus ensuring that a homogenous mix of fractions within the bulk fluid is sampled. Any insoluble contaminants will, for the same reason, be more likely to be suspended within the bulk fluid. Both high and low molecular weight ranges of fractions will be detected. Representative thermal fluid samples must also be collected in a closed manner. A closed sample device such as a ‘bomb’ must be used to ensure that the fluid does not pass through atmosphere. Light ends or volatiles consist of a homologous mix of hydrocarbons with different boiling/flash points. Finally, representative thermal fluid samples must be collected from a circulating system. This is again to ensure a homologous mix of hydrocarbons. Light ends will ‘pond out’ in still fluid. Paul Sanders, comments, “Boiler efficiency has improved significantly and has seen our heat-up time reduced by 50%. It is flowing more efficiently and will show a saving in pump life”. Sausage maker beats downtime with thermal fluid knowledge When James T. Blakeman suffered production downtime as a result of inconsistent cooking temperatures, it decided to call in thermal fluid specialist Global Heat Transfer. Today the company has the benefit of significantly improved cooking efficiency and reduced downtime. Founded in 1953, James T. Blakeman manufactures sausage and meat products with a strong focus on quality. It produces cooked product for the catering and ready meal markets and provides a contract cooking service for meat, fish and poultry. The company has two 40,000 square foot state-of-the-art manufacturing facilities in Newcastle-Under-Lyme, approved to the highest health, safety and hygiene standards. Blakeman distributes 12,000 tonnes of product per year and holds both Higher Level EFSIS (European Food Safety Inspection Service) and EEC-approved accreditations. The company’s product range includes fifty varieties including Cumberland, Lincolnshire, pork and coriander sausages. Despite its current position, the company had humble beginnings; growing from a mobile refreshment bar, and later a market stall founded by James Blakeman in 1954, to reach its current annual turnover of around £12m. Similarly, the foundations of Blakeman’s work with Global Heat Transfer can be found in these early days, when the entrepreneur decided the company’s first key principle would be quality, not just in the ingredients used to manufacture, but in every aspect of the business. The second key principle relates to investing in the most efficient manufacturing processes, including plant, machinery, recruitment, training and quality assurance systems. This has been demonstrated throughout the company’s history, from investment in a new manufacturing and cold storage plant, completed in 1988, to the decision to invest in a new company wide IT system in 2004, which links all of Blakeman’s operations. The roots of the company’s work with Global Heat Transfer can be found in this progressive philosophy. In 2010, Christopher Austin, the company’s health and safety advisor, was faced with inconsistent temperatures in some of the company’s ovens. This meant that thermal fluid had to be replaced far more often than necessary, with the attendant production downtime that this incurred. The use of thermal fluid as a heat transfer media is common in the food processing industry, particularly in large scale baking and frying in industrial kitchens, where the even temperatures it provides are useful in retaining taste. Fundamentally, heat transfer fluids convey the heat from one hot source to another point in the process. A heat transfer medium is required where direct heating of a process is not practically possible. James T. Blakeman decided to call in Global Heat Transfer. The solution was to supply and fit a Light Ends Removal Kit (LERK) and provide a contract to maintain the system, including removing the light ends from site and replacing old fluid. Thermal fluid with excessive light ends can build an explosive atmosphere with air in the expansion tank and in the drain tank. Replacing the oil continuously will solve this problem but can be expensive, as Blakeman discovered. A LERK is a much more cost effective and elegant solution. Global Heat Transfer’s LERK is a distillation loop modification designed to remove light ends and manage flash points, fire points and auto ignition temperatures.‚Ä®It is a totally automated system for draining off light ends and can also be used as a batch vent or regenerator.‚Ä®Installation of a LERK completely removes any future need to hire in a costly regeneration rig or replace the thermal fluid on a regular basis.‚Ä®Monitoring of flash points is a continuous process and the Global Heat Transfer LERK ensures safety at all times. Hiring a remote regeneration rig only monitors the risk for the period when the rig is hired. However, flash points are guaranteed to fall over time, which creates risk and an unsafe system, so the need to re-hire equipment at a high on-going cost will always be there.‚Ä®Furthermore, the LERK is proven to be more effective at batch venting and regeneration. “The impact was evident,” says Chris Austin. “There has been a reduction in downtime, and we have reduced costs by replacing the fluid less frequently, thanks to improved system efficiency. While we had been aware of the LERK for a number of years, for one reason or another we hadn’t yet invested in one. “Installing the LERK equipment has revolutionised the heating on our cooking plant. Global Heat Transfer provides excellent response services to every enquiry, request or problem and the process has helped enormously with our overall compliance procedures.” In fact, quality control processes have always been complete and rigorous. James T. Blakeman communicates regularly with the relevant official bodies to ensure its factories adopt the latest standards as they are introduced. The fully-integrated ‘Tropos’ computer system provides real-time, full traceability that allows the quality team to track ingredients from order to warehouse, from production to finished product. The quality control team inspects all meat on arrival at the factory, whilst an independent laboratory carries out additional weekly quality testing. Temperature control and metal detector checks complete the series of tests. The picture of the modern Blakeman’s factory, complete with state of the art technology and a philosophy focussed on quality, is a long way removed from the young James Blakeman and his market stall. However, the philosophy remains the same – an approach that has seen the company decrease downtime, advance its compliance standards and improve efficiency. Conclusion You can’t wait for a problem to arise before you implement a proactive maintenance plan. Your response will be too slow and ineffective. You’ll make operational losses and compliance losses, whilst risking the safety of your employees and racking up significant breakdown and replacement costs. Senior management needs to implement advanced risk management strategies and ensure company culture and daily routine are deeply rooted in health and safety and food regulation laws. This can truly help minimise loss, whether it‘s financial, a loss in production, property damage, or, in extreme circumstances, loss of life. Maintenance methods are not only important for hazardous purposes - when a plant is properly maintained it is also cost-effective and productive. When it comes to heat transfer fluid maintenance, you need to assess your effectiveness in terms of prevention, identification, notification, removal, and replenishment. You should enlist proactive strategies designed to reduce risks. The key to implementing these strategies is to build them into the technology you use to run your business. Preventative maintenance and clear procedures are your best friends when it comes to quickly and effectively responding to problems as they arise, and do so while maintaining customer trust and a positive reputation. The moral of the story here is that fluid safety should be a priority for food manufacturers in order to maintain optimum safety levels and production efficiency. Ideally, any plant using heat transfer fluids should create a robust maintenance plan that contains regular fluid analysis system flushing, fluid top-ups and careful flashpoint management. By caring for heat transfer fluids and the health of the overall system, plant managers can save money on pipework maintenance and energy usage, cleaning products and new heat transfer fluids. Furthermore, proactive management including dilution, filtration and light ends removal will send savings straight to the bottom line. Regular sample analysis and staff training will ensure regulatory compliance and health and safety requirements are met.Learn More
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