Static electricity is an imbalance of electric charge that builds up in/on a material. It may be generated in a circulating fluid system.
This is not a fault with the equipment, but an unfortunate and accepted occasional side effect of the method in general. There are thousands of reaction systems in the field that are pumping oil around a reactor, and only a small number have static issues.
Possible causes of static
- Generally, oil-based thermal fluids (heat transfer fluids) are not good conductors of electricity, and can therefore develop static charge. This is because, whilst in use, they are creating constant friction with the hoses, vessel jacket and the inside of the circulator (thermoregulator). Some thermal fluids are more prone to static than others.
- In some cases, the friction generated from the stirrer shaft turning in the vessel contents can also cause static, although this depends on the particular material being stirred.
- Site and environmental factors, such as power supply wiring, can also cause static.
If you do experience signs of static build-up within your system (such as erratic temperature readings), we would strongly recommend that this is discussed and reviewed with your own on-site process safety advisers, to check the earthing potential of nearby power supplies, and ensure that safe engineering practices are used to deal with static.
The two most popular methods for reducing or eliminating the risk of static build-up in a system are as follows; in most cases it is recommended to adopt both:
- The use of earthing lines, to connect all of the system components (vessel, framework, circulator etc.) to an earth line. This is often the accepted practice in process and plant installations.
- Adding an anti-static additive to the thermal fluid, which helps make the thermal fluid a better electrical conductor, and dissipates build-up of electrostatic charge. It is important to ensure that the additive is compatible with the thermal fluid in use and that its concentration is maintained, even after thermal fluid changes.