For an efficient heat transfer system, the first step is maintaining the fluid
When embarking on a long journey, drivers hope for a clear highway and smoothly flowing traffic, allowing them to reach their destination quickly and hassle-free.
Sometimes, however, problems such as broken-down vehicles or poorly planned roadworks can cause annoying slowdowns. Here, Dave Dyer, Technical Sales Engineer at thermal oil supplier, Global Heat Transfer, explains how a poorly maintained heat transfer system can lead to an equally problematic slowdown in production and how plant managers can prevent this.
Heat transfer systems carry heat transfer fluids (HTFs) through a production line for various purposes, such as cooking food or processing chemicals. These fluids are designed to be chemically and thermally stable, which leads many to believe that they require little to no maintenance.
However, under certain conditions, they can deteriorate and become more viscous and acidic or even crystallise into solid carbon build-ups that obstruct the system and cause uneven heat distribution.
This can seriously impact the final product. For example, food could be under or overcooked and chemicals could be unevenly dissolved in a solution. Luckily, early intervention and proactive maintenance can help in maintaining the quality of thermal fluids, and therefore the condition of a system’s pipes, for as long as possible.
So, what can plant managers do to maximise the potential of their heat transfer systems? Preparation is key. Before inserting the fluid in the system, this should be tested against leaking. Although not ideal, this can be done with water, which should be appropriately drained afterwards to ensure that moisture does not contaminate fluids, accelerating their degradation.
To do this, you can either eliminate residual water through gas purging or replace it altogether by using low-pressure helium leak detection instead of hydrostatic testing. However, there is always a risk that all of the water may not be eliminated and any remaining water will flash to steam and cause cavitation.
Instead you should use an appropriate cleaner, such as Globaltherm C1, that is specifically designed to remove any contaminants which, if otherwise left in the system, would prematurely accelerate the rate of HTF degradation.
It is also important to choose the right fluid for the system’s temperature. This may seem obvious, but there can be occurrences where the temperature exceeds the maximum temperature-rating of the fluid. Choosing a fluid with a good capacity to withstand these temperatures and understanding the causes of occasional overheating is paramount.
Preventing exposure to oxygen is the next step in prolonging a fluid’s life expectancy. Exposure to oxygen, otherwise known as oxidation, can lead to elevated carbon levels in the fluid and the formation of polymers or solids on the internal coating of the system’s pipework. As well as this, sludge can form in the system’s expansion tank and the fluid can thicken, reducing pump efficiency and increasing operating costs.
It’s important to remember that oxidation is not the only cause of degradation. Thermal cracking, the natural process by which thermal oils crack into smaller hydrocarbon molecules, can produce volatile by-products such as light-ends. These can reduce the flash-point of the fluid, posing a risk of fire and explosion if remedial action isn’t taken.
Finally, another rule of thumb is to try and prevent contamination of all kinds. Water contamination can occur not only during preliminary testing but also through the return of condensate collected from the system vent stream, which introduces organic acids in the system.
Fluids can also be contaminated by compounds derived from different phases of the production process, some of which might have low thermal stability and form coke deposits which overtime cause blistering and rupture.
Even if plant managers do everything they can to slow degradation, it will still occur with time. That’s why a good preventive maintenance programme is essential to get the most out of heat transfer systems. An experienced thermal fluid supplier can take and analyse samples of your thermal fluid to determine its condition and quality.
They can also provide appropriate technical interventions when needed, execute a flow test before and after the procedure to determine its level of improvement and, eventually, refill or replace the fluid when necessary.
Another major service that Global Heat Transfer provides is a comprehensive training programme. Because problems in heat transfer systems can lead to serious health and safety hazards, workers should be appropriately trained to recognise them in advance.