Heat transfer fluids used for heating and cooling within the pharmaceutical industry have a significant impact on the operational efficiency and lifespan of processing equipment and long-term costs. Gary Lydiate, Kilfrost, discusses the importance of choosing the correct heat transfer fluid
Glycol-based heat transfer fluids
The higher heat capacity and thermal conductivity of glycol-based heat transfer fluids makes them far more efficient in terms of heat transfer than non-aqueous alternatives. This reduces overall energy consumption, lowering both carbon dioxide emissions and long-term financial costs. In addition, aqueous-based heat transfer fluids have a superior environmental profile to non-aqueous-based equivalents.
It is well understood that glycol/water mixtures (commonly referred to as antifreeze) are corrosive and the use of simple commodity chemicals, like glycols, as heat transfer fluids can lead to significant issues. These include corrosion and fouling of processing equipment, leading to increased downtime and, in some cases, expensive repairs and replacements. There are, however, heat transfer fluids, with an inhibited glycol base, formulated specifically for heating or cooling processes. Inhibited glycol/water mixtures make excellent heat transfer fluids in comparison to oil and synthetic-based fluids.
Corrosion inhibition of glycol-based heat transfer fluids has advanced dramatically over the last 20 years, with the use of toxic chromates, nitrites and borates, as well as environmentally harmful phosphates and nitrates in decline. Advanced, fully inhibited glycol-based fluids will include long-lasting organic corrosion inhibitors based on a combination of long and short chained carboxylic acid salts, heterocyclic compounds and polymeric materials.
A demanding international standard with respect to corrosion control is adhered to by reputable companies, although it still remains voluntary. The ASTM D1384-05 corrosion test standard is playing an increasingly important role, as the pharmaceutical industry begins to recognise the challenges that system corrosion can cause. The test immerses metals commonly used in heating and cooling systems in a heated and aerated glycol/water mixture. After two weeks the metals are analysed for signs of corrosion, assessing the impact of heat transfer fluids on a system.
Efficiency versus toxicity
A variety of glycol-based fluids are used within heat transfer fluid formulations. The most commonly used glycol bases are mono ethylene glycol (MEG) and mono propylene glycol (MPG). Both of these base fluids have different thermo-physical properties and, of prime consideration for the pharmaceutical industry, very different toxicity profiles.
Inhibited MEG based fluids are an excellent choice for numerous applications, but the fluid’s high toxicity means it poses a health risk when used in systems where incidental contact with items intended for human consumption is possible.
MPG based fluids are commonly used in systems within the pharmaceutical industry due to their low toxicity. However MPG is far less efficient than MEG at transferring heat energy because of its higher viscosity which leads to increases in pressure drops and often makes the attainment of efficient turbulent flow unfeasible (Figure 1). In consequence, the use of MPG based products will lead to higher overall investment and operating costs.
Figure 1
As the chart shows, below 0o C the viscosity of MPG based heat transfer fluids rises sharply, making it increasingly difficult to pump efficiently. The difference in viscosity and overall system efficiency becomes even larger as the circulating temperature of the fluid decreases. To provide the industry with an advanced lower viscosity, low toxicity, ASTM-D1384-05 rated heat transfer fluid, Kilfrost ALV has been developed.
Environmental profile
The environmental profile of heat transfer fluids is also very important, with more and more companies looking for sustainable options to replace petroleum-derived specialty chemical products, like heat transfer fluids.
Current bio-derived heat transfer fluids formulated with a sustainable chemical feedstock have struggled to make a significant impact in the glycol-based heat transfer fluid market as they offer no significant additional advantages aside from their green credentials. However, Kilfrost ALV offers better performance than existing products, whilst also making use of available bio-derived feedstocks.
With the growing demand for non-toxic heat transfer fluids, alongside the ever-increasing desire for fluids that boost system efficiency, it is not always easy to find a heat transfer fluid that meets businesses’ needs. Kilfrost ALV removes the need for compromise, providing a non-toxic heat transfer fluid which guarantees higher system efficiency than products already on the market.