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Proactive monitoring for improved efficiencies

10 February 2020

Dave Dyer explains how a poorly maintained heat transfer system can lead to an equally problematic slowdown in production. He goes on to talk about how plant managers can prevent this. 

Heat transfer systems are designed to carry heat transfer fluids (HTFs) through a production line for various purposes – such as cooking or processing foods or ingredients. 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 can even crystallise into solid carbon build-ups that obstruct the system and cause uneven heat distribution which can impact the final product, resulting in under or overcooked food. Early intervention and proactive maintenance is important to help maintain the quality of thermal fluids, and therefore the condition of a system’s pipes. 

Fluid degradation
Preparation is key. Before inserting the fluid in the system it should be tested against leaking. 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, it is necessary to 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 it is necessary to use an appropriate cleaner – one which is specifically designed to remove any contaminants which could prematurely accelerate the rate of HTF degradation.

The right fluid
It is also important to choose the right fluid for the temperature of the system. 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 vital. 

Preventing exposure to oxygen is the next step in prolonging the life expectancy of a fluid. 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  pipework. As well as this, sludge can form in the expansion tank and the fluid can thicken, reducing pump efficiency and increasing operating costs.  

It is 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 is not taken.

Finally, it is good practice to prevent contamination of all kinds. Water contamination can occur during preliminary testing and 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 engineers do everything they can to slow degradation, it will still occur over time. For this reason a good preventive maintenance programme should be considered as an essential tool to help get the most out of a heat transfer system. 

Dave Dyer is technical sales engineer Global Heat Transfer.

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