Cat Fines Pose Growing Threat

The issue of how to deal with cat fines is becoming ever more urgent as the 2020 global sulphur cap approaches.

Ever since catalytic cracking processes were developed during the oil crisis to squeeze more product from crude stock, cat fines have been a problem in marine engines. The problem is not a new one, and it is not going away.

Recent reports from ExxonMobil and Fuel Oil Bunkering Analysis and Advisory Service (FOBAS) have found significant problems with cat fines in engines and bunker fuel respectively. Given the damage cat fines can do to engines, this is highly significant.

Cat fines are hard ceramic compounds of aluminium and silicon used as a catalyst in the crude oil refining process. They are used to enable a higher yield of distillate fuels to be extracted from the feedstock, but often get carried over into the end product used as ships’ fuel. They range from 75μm down to 1μm. They get embedded in engine components – particularly cylinder liners and piston rings – and cause abrasive wear.

Cat fine damage mainly occurs in large, low-speed main engines because the larger fuel injection components allow sizeable cat fine particles into the cylinders. Cylinder lubricating oil is minimally applied to the liner surface, and does not wash cat fines away.

Cat fine damage to medium- and high-speed engines is less frequently found, as more copious splash lubrication of cylinder liners can wash away cat fine particles, while the closer tolerance of components prevents the ingress of larger particles.

Damage caused by the ingress of cat fines can lead to significant costs, with the price of replacing just one liner estimated at US$65,000 for parts alone. This can rapidly escalate to more than US$1 million when the labour and the accompanying expenses of downtime, repair and off-hire are considered, as well as the likely event that multiple cylinders are affected.

FOBAS’s findings stemmed from a test undertaken at Fujeirah, a strategic bunkering port. This showed that a number of bunker samples delivered aluminium and silicon cat fines at levels ranging from “above 75 mg/kg up to nearly double, at 139 mg/kg.” Given that the ISO 8217 specifications for marine fuels maintain a 60 mg/kg limit for cat fines, this is bad enough. But when one considers that this ISO threshold is considered to be fairly high and that research has shown that even particles of 10µm can contribute to wear, this is alarming news. Equally, a significant discrepancy exists between ISO standards for cat fine content and the content recommended and anticipated by engine manufacturers in engine design.

Furthermore, the FOBAS analysis goes on to state that “Al+Si at 75mg/kg can be difficult to reduce but may be manageable; however Al+Si at levels up to 139 mg/kg would prove extremely difficult to bring down to acceptable levels for engine entry (<15 mg/kg). Carry over of abrasive Al+Si material at high levels may lead to damage to fuel pumps/injectors and cylinder components.”

ExxonMobil’s research involved in-depth data analysis of more than 400,000 oil samples from ExxonMobil’s MobilGard Cylinder Condition Monitoring programme. The research identified a wide range of potentially damaging engine issues facing vessel operators. It revealed that 43 per cent of vessels have an issue with cat fines.

This problem is only likely to get worse once the 2020 Global Sulphur Cap comes into effect. An increase in the use of Ultra Low Sulphur Fuel (ULSF) and a potentially greater variance in local fuel blends mean the cat fine problem has the potential to become more serious. This is due to their use in the creation of low-sulphur fuels. As Francisco Malta, director of VM Industrials (a distributor of Aderco Fuel Treatment Solutions), put it: “There seems to be a direct correlation between Ultra Low Sulphur Fuel Oil global demand and engine damage by cat fines. This is an issue as ULSFO demand is only forecast to continue to rise.”

Purification systems exist to combat cat fines. A fuel-purifier process tries to identify the cat fines before they make their way into the fuel line toward the engines, and in theory all the cat fines should be found and rejected here.

Speaking to Marine Propulsion, ExxonMobil global marketing manager Iain White indicated that he was surprised by the scale of the cat fine problem, saying: “If you’re running your purifiers properly, you shouldn’t have a problem with cat fines, so this data indicates that there are some serious problems with the skills and expertise of the crew.”

Francisco Malta takes issue with this, saying: “The reason purifiers have difficulty identifying the cat fines is because silicon and aluminium are both highly hydrophilic and when emulsified in water the purifiers cannot identify them.” Indeed, FOBAS data suggests that purifiers operate at only 60-65 per cent efficiency on average.

Once water is present and attached to the cat fines, a purifier is far less effective: even the smallest content of water in fuel is enough to trick the purifier.

All fuels contain traces of water, even if very small. With the ongoing condensation that is naturally present in fuel storage tanks, water is an unavoidable fact. Although around 96 per cent of water will sink to the bottom of the tank, the other 4 per cent remains suspended on the storage walls, ceilings and in the fuel. It is impossible to completely separate the water unless an effective de-emulsifier product is introduced when bunkering. According to Mr Malta: “The solution is to de-emulsify all water from the fuel at storage.”

Clearly, then, the answer to this problem is far from simple, but increasingly urgent as the 2020 deadline looms ever closer. In its 2016 position paper discussing the issue, the International Union of Maritime Insurers recommended a number of changes that would help reduce damage from cat fines. These included:

• Mandatory sampling and testing of fuel before use
• Improved fuel handling on board
• Improving the quality of bunkers
• Alteration of the ISO standard so as to lower the quantity of cat fines in fuel
• Charter/bunkering contracts should specify fuel less than 60 ppm
• Regular cleaning of filters, and frequent drainage of tanks
• Cleaning the settling and service tanks during drydock
• Checking the filter centrifuge capacity on specifications for new ships

Another approach is to make use of the hydrophilic nature of cat fines to offers a solution for reducing risk. Using a surfactant-based fuel treatment solution that facilitates water separation will ensure that a significant portion of the cat fines captured by water molecules in the fuel tanks can be drained off along with the water.

Allowing thorough settling of the fuel will further reduce the counts of cat fines, especially large particles. In addition, the right fuel-treatment solution will isolate contaminants, disperse agglomerations that lead to sludge, and stabilise as well as homogenise the fuel. The net effect is that the fuel enters the line cleaner for more efficient combustion, with a lower cat fine count, enabling the separator to eject remaining cat fines and contaminants more effectively.

One solution, of course, is to identifty the problem before the fuel enters the system. For this purpose, Parker Kittiwake offers a Cat Fines Test Kit. This uses a straightforward pre-mixed chemical bottle test that identifies the presence of cat fines in a representative sample of fuel oil. Engineers become able to spot these abrasive particles in the fuel oil before it enters the system – either during the bunkering of new fuel or from the settling tank when it has been stirred up during bad weather.

Whatever the chosen route to minimising the risk from cat fines, it seems certain they will be with us for years to come yet and that the best guarantees of protection against them are vigilance and precaution.

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Source: Marine Propulsion & Auxiliary Machinery

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