Clive Jones describes common problems with heat transfer systems and thermal fluids in the food manufacturing industry. He also outlines his key recommendations to optimise safety and efficiency
Thermal fluids are used in a variety of sectors including manufacturing pharmaceuticals, cosmetics, textiles, petrochemicals and food.
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 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. 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 and certified 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.
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 is maintaining an optimum temperature of the heat transfer system.
A 10% 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.
If the temperature of the fluid rises above its recommended temperature, thermal cracking and oxidation occur at an increased rate, 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.
If the reaction stops, 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 dangerous — to solve this problem we'd use a Light Ends Removal Kit (LERK). Plant managers should also regularly sample their thermal fluid and the analysis will indicate when to remove light ends.
These samples can only be truly representative if collected when the fluid is hot and circulating in a closed system, to prevent volatiles escaping to atmosphere.
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.
Hot spots are also formed and cause the surface of the metal to burn through which can result in a thermal fluid 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.
We can work it out
Ideally, any plant using heat transfer fluids should create a robust maintenance plan such as Thermocare, that contains regular sample analysis and careful flashpoint management and thermal fluid condition maintenance, as well as site surveys and employee training.
By caring for heat transfer fluids and the health of the overall system, plant managers can prevent loss of downtime and increase site safety, while saving money on pipework maintenance, system drain down, cleanse and refill of 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. This ensures a happy relationship between system and plant.
Clive Jones is CEO of heat transfer fluid specialist, Global Heat Transfer.