Ask the expert: Undetected cat fines
In a new column, an expert from ExxonMobil answers questions on fuel and fuel condition. In the October issue, technical liaison manager John LaRese shares his expertise.
The fuel I bunkered is low in cat fines but recent scrape down oil samples reveal damaging levels in my engine. How can this be the case?
This issue is actually more common than you might think. In fact, we frequently receive oil samples with the exact same problem and the explanation is often very simple.
In storage cat fines tend to settle to the bottom of a storage or settling tank, which is a good thing as it generally helps minimise the damage they can cause. However, it can become a problem in rough seas, which can really stir up tank sediments. Cat fines that have settled in a storage tank may also be disturbed by the bunkering process itself, particularly when bunkering rate is high.
These situations can result in cat fines being moved from the bunker tanks to the settling tanks and through to the purifiers. When this happens, the purifiers can become overwhelmed and fail to remove them all from the fuel. They get through to the service tank and then due to their small size pass through the fine filters into the engine injection system.
The scrape down oil samples will suddenly show high levels of cat fines, which at their worst can result in severe engine damage. You’re therefore right to keep conducting scrape down tests, irrespective of the level of cat fines in the recently bunkered fuel. It is also essential that the purifiers are always operated at the lowest throughput to suit the engine load, and at the optimum temperature.
If worrying levels are found, then where possible, run two purifiers in parallel with minimum flow and keep the fuel inlet temperature at 98° C to ensure efficient purification. Your purifiers should also be cleaned at the intervals recommended by the manufacturers or more often if you suspect poor fuel quality.
It’s also important to continue to take regular scrape down oil samples to ensure that the level of cat fines entering the engine has been brought down to an acceptable level. Cat fine accumulation can be prevented by regularly cleaning tank bottoms.
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