In a previous blog it was assumed that the operation life of a plant can be extended to 25 years. Dr Chris I Wright examines proven technologies to maximise a plant’s operating life.
Chris Wright is a research scientist whose research focuses on the use and maintenance of heat transfer fluids in manufacturing and processing, which includes food, pharmaceutical, specialist chemicals and solar sectors. (Image: Global Heat Transfer Ltd.)
It is a fact that a plant’s life can be shortened by the thermal degradation of a heat transfer fluids (HTF), which includes a wide range of mineral (e.g., BP Transcal N, Globatherm M) and synthetic-based fluids (Dowtherm A, Therminol VP-1, Globaltherm Omnitech). Knowing that a fluid will degrade and that fluid cleanliness is related to component life, it seems logical that a system’s (i.e., pump, heater, internal pipework) life can be extended by slowing fluid degradation. Eight approaches that can be used include:
1. Sampling. Improved fluid condition is associated with sustained component life and past research shows that more frequent sampling can maintain a system’s operating life.
2. Temperature. Prolonged life can be achieved by decreasing the fluid’s operating temperature. This is explained by Arrehenius’s Law which shows that decomposition rate is halved for every 10 degrees Celsius drop in temperature.
3. Dilution. Adding a percentage (up to 50% of the total volume) of virgin HTF to an existing system works to remove degradation by-products.
4. Filtration. This works remove degradation by-products from the system and avoid their potential catalytic effect on degradation of a fluid.
5. Removal of light-ends. Light-chain hydrocarbons (‘light-ends’) are a by-product of thermal degradation and can be removed through distillation by installing a temporary or permanently installed light-ends removal kit, similar to the one shown in Figure 1.
6. Recharge with a synthetic fluid. It is well known that synthetic-based HTFs maximise the ability of a plant to operate at higher temperatures due to their high thermal stability, high heat transfer efficiency and high purity as discussed in a previous blog.
7. Nitrogen blanket. Oxygen is detrimental to a HTF operating above 60 degrees Celsius and leads to the formation of acids which corrode and foul a pump and system. One way to counter this is to use a nitrogen blanket to prevent the HTF coming into contact with air whilst in the expansion tank.
8. Anti-oxidants. Another potential approach to oxidation is to use anti-oxidant additives that deplete the oxygen in a fluid.
In summary, routine sampling of a fluid is normally discussed in terms of ‘maintenance of a system’s component parts’. All of the eight approaches discussed above have been proven to be effective and can be offered as individual interventions or as part of a management plan, such as the Thermocare programme offered by Global Heat Transfer Ltd, in order to extend the life of a system’s components.
