Keeping industry spinning

Thermal fluids are used in a variety of sectors including manufacturing pharmaceuticals, cosmetics, textiles, petrochemicals and food. Although fluid maintenance and analysis are essential operations, many plant managers don’t realise that there is a problem until the system is clogged up, shows a low flash point and is draining resources. 

Typical problem

A textile manufacturing company recently asked Global Heat Transfer to conduct some tests and analyse its heat transfer fluid. Although the fluid had just been changed, the system was acting in an abnormal way and the operations team couldn’t understand why. Reduced flow rates and a high content of sludge were occurring time and again. 

Although it seemed that all maintenance procedures were followed, in just six months the system decayed so badly that sludge had to be manually removed twice a week. 

After the sludge was taken out of the filters, the 4000L system had to be topped up with 400L of fresh heat transfer fluid. Depending on the type and volume required, this can become a huge financial burden. The operations team decided that  the problem needed to be remedied without delay. 

A sample of the fluid was taken and tested using an independent laboratory. Global Heat Transfer’s analysis of the results revealed abnormally high amounts of carbon residue. A normal system should have only 0.02% carbon residue; the sample was in excess of 3.4%.

Dangerously, the flashpoint temperature was as low as 146°C which is close to the 100°C condemnable limit of many thermal fluids. In ideal circumstances, the system should have been able to withstand flashpoints as high as 260°C. This put the safety of people and the site overall at risk, as the plant was more likely to ignite in hazardous conditions such as a fluid leak.  

Carbon residue, also known as coke, is a clear indicator of system and fluid aging. It is normally weighed and represented as a percentage of the original amount of oil. The compound is the result of a process where high molecular mixtures transform into coke-like deposits. 

High amounts of carbon in a heat transfer system can lead to fouling. Over time, carbon deposits bake inside pipework. At this stage, maintenance activities are relatively easy to conduct, as the carbon is still soft and can be flushed by using thermal cleaning products, such as the Globaltherm C1 cleaning and flushing fluid. Ideally, action should be taken when the carbon residue level is somewhere between 0.75 and 1% of total fluid weight. 

In the textiles manufacturing plant, the carbon deposits were three and a half times higher than this level. In such situations, the carbon is already hardened and cannot be easily flushed. Carbon deposits act as an insulator and thus the entire system significantly loses thermal efficiency and more energy is needed to heat it up. 

Because of the increased temperature in the system, the fluid was showing signs of serious thermal cracking and significant thermal oxidation. The tests showed a total acid number (TAN) of 0.54, which is high and, in conjunction with the accelerated carbon production, it leads to carbon residue in excess of 3%. Furthermore, thermal cracking decreases the flash point temperature which can be dangerous for operators. 

Solution

The company was advised to drain the system of heat transfer fluid and then clean the pipework to remove all carbon debris, acids and flammable by-products. 

Where carbon is hardened or baked onto the system, a simple flushing procedure is not enough. A more aggressive type of cleaner is needed and once flushing is completed, a second safety flushing must take place to ensure that there are no remaining cleaning products that can later react with the virgin heat transfer fluid. 

The moral of the story is that thermal fluid maintenance should be a priority for manufacturers in order to maintain optimum safety levels and production efficiency. By caring for heat transfer fluids and the health of the overall system, plant managers can save money on pipework maintenance, cleaning products and new heat transfer fluids. Furthermore, proactive management including dilution, filtration and light ends removal will send savings straight to the bottom line in decreased energy bills.

So if you want to keep your circulatory system healthy, make sure you do regular checks on thermal fluids and heat transfer systems as often as is appropriate.