Plant & Works Engineering
Fluid for thought
Published:  08 January, 2015

Thermal fluids are used in a variety of sectors including manufacturing pharmaceuticals, cosmetics, textiles, petrochemicals and food. Dr Chris Wright, head of research and development at Global Heat Transfer describes common problems with heat transfer systems and thermal fluids in the food manufacturing industry. He also outlines his key recommendations for ensuring a harmonious and healthy relationship between plant, fluid and system.

Heat transfer fluid maintenance and analysis are essential operations that need to be conducted periodically. Unfortunately, some plant managers don’t realise that there is a problem until the system is clogged up, shows a low flash point and is draining resources from the company. In fact, some food manufacturers aren't even aware of what thermal fluid they should be using to ensure compliance in the first instance.

You were made for me

In an environment where there is potential for an oil or lubricant to come into contact with food or a food preparation surface, a certified food-grade (FG) fluid should be used. This fluid must be clear, non-toxic and odourless to ensure consumer safety in the event of a leak or spillage. As you can imagine, this is an essential health and safety measure in the food processing industry.

Furthermore, FG thermal fluid is a requirement for manufacturers that want to supply to the top supermarkets and fast food chains in the UK, in compliance with the British Retail Consortium's (BRC) global standards.

Members of the BRC include Tesco, Sainsbury's, Asda, Morrisons, Waitrose, Aldi, McDonalds, KFC, Burger King and many more retail giants. Thus, compliance with the standards outlined by the BRC is a must for companies wanting to reach these distributors.

Internationally, FG thermal fluid is also a regulatory requirement imposed by the US Food and Drug Administration (FDA) and NSF International. Again, any manufacturer that wants to sell into the US food market must abide by the correct standards.

Further emphasis has been placed on FG thermal fluid since 2011, when President Obama signed the Food Safety Modernisation Act (FSMA), which made sweeping changes to US food safety laws. The most notable of these was the attitude towards food safety problems - focus was placed on preventative measures rather than reactionary.

Any manufacturer that does not use FG thermal fluid in a food application runs the risk of not only losing its top tier certification, but also footing the resulting costs when non-FG fluid comes into contact with food products. That's a bad break up in our book.

With this in mind the lack of commercial awareness is surprising. At Global Heat Transfer we still see food manufacturers who don't know what's required of them and it’s hard to argue that it’s entirely the fault of the manufacturer. More awareness of the complexities of thermal fluid could be beneficial and that’s really the responsibility of suppliers like us. Moreover, some companies still do not fully appreciate the costs they will incur if things do go wrong with their heat transfer system.

Heartbreak hotel

As well as ensuring that you are using the right kind of thermal fluid, it is essential that maintenance and analysis are both conducted regularly. A common problem in the food industry is maintaining an optimum temperature of the heat transfer system.

A ten per cent change in temperature either way is all it takes to cut the time it takes the fluid to degrade in half. Therefore, maintaining a constant temperature is intrinsically linked to maintaining a healthy system, reducing down time and decreasing the amount of costly thermal fluid changes needed.

If the temperature of the fluid rises above its recommended level, thermal cracking and oxidation occur, which can have serious consequences.

Thermal cracking is the decomposition of large oil molecules into solid carbon or "coke" and can result in one of two outcomes, neither of them good.

If the reaction stops, you are left with what we call low boilers. Lighter components created in the thermal reaction decrease the flash point and viscosity of the thermal fluid, whilst increasing its vapour pressure. The flash point is the temperature at which the vapours produced from a fluid will ignite if exposed to an ignition source. Lowering the flash point is therefore very dangerous.

To solve this problem we'd use a Light Ends Removal Kit (LERK) to help maintain a constant optimum temperature and improve system efficiency.

If the reaction continues and the smaller molecules react with one another further, it creates larger molecules than were originally present and you are left with what we call high boilers. These larger molecules increase the oil viscosity until the solubility level is exceeded and solid coke begins to build up in the system.

Over time this process leads to fouling of the system, whereby carbon residue becomes baked onto the inside of the pipes. If left, the deposits harden and acts as an insulator; thus the entire system significantly loses thermal efficiency and more energy is required to heat it up. When there is significant build-up of carbon it creates hot spots which can lead to equipment failure and even fire.

It is therefore in the interest of the manufacturer to carry out regular thermal heat transfer fluid analysis to ensure a healthy system. If the carbon deposits are identified whilst they are still soft, maintenance can be done to flush the system with thermal cleaning products, such as Globaltherm C1 cleaning and flushing fluid. Ideally, action should be taken when the carbon residue level is somewhere between 0.75 and 1.00% of total fluid weight.

We can work it out

The moral of the story here is that fluid quality and 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 sample analysis and careful flashpoint management and thermal fluid condition maintenance.

By caring for heat transfer fluids and the health of the overall system, plant managers can save money on pipework maintenance, 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 in decreased energy bills. Regular sample analysis and staff training will ensure regulatory compliance and health and safety requirements are met.

In addition, it is essential that food manufacturers choose the right kind of thermal fluid to begin with. By using FG thermal fluid you reduce the costs that come with throwing away a batch or line. Moreover, plant managers should be aware that using FG thermal fluids is a required requisite by food standards bodies such as the BRC, FDA and NSF.

So if you want to keep a healthy working relationship in your food plant, make sure you're using the correct product and do regular checks on thermal fluids and heat transfer systems as often as is appropriate.

Global Heat Transfer is a thermal fluid specialist, providing heat transfer engineering assistance and thermal fluid supplies. Services offered include sampling and analysis, 24 hour delivery of premium quality thermal fluids, system drain down / cleaning / waste management, planned maintenance programs and a broad portfolio of affiliated system design and installation services.

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