Finer resolution and more resilient filters can help prevent engine damage
Filter manufacturers have been challenged by the IMO sulphur cap to manage the risks introduced by new fuels, namely less stability and a higher concentration of catalytic fine amounts. These need to be filtered out to prevent engine issues.
“There are implications of using low-sulphur fuel for filtration,” says Bollfilter sales team leader Martin van Son. “Low-sulphur fuel itself is not an issue in terms of its chemical structure, but what is important are the cat fines,” he says.
These catalytic fines are hard aluminium and silicon oxide particles introduced to crude oil in the refining process to enhance low-temperature fuel cracking. Ranging in size from roughly 10-30 µm microns, these metallic particles are abrasive and can cause damage to sensitive engine parts, such as injection pumps, cylinder liners and piston rings.
“If left unchecked, this abrasive damage can lead to costly malfunctions or breakdowns,” says Mr van Son.
This is a particularly important issue for vessels running on fuels compliant with IMO’s 0.5% sulphur cap, which often contain higher concentrations of catalytic fines – 60-70 ppm – due to the different refining processes involved in their production processes.
“Disposable, fine-grade cartridges could be an operational risk”
“Automatic filtration acting as a mechanical barrier is absolutely needed,” says Mr van Son, noting that many engine manufacturers have upgraded their specifications and recommend the use of finer filtration to reduce cat fine content to a safer level of 10 ppm.
Owners have two choices when it comes to retrofitting these higher-spec filters, explains Mr van Son. The first option is to install an additional filter to operate alongside the engine’s existing filtration system; the second is to upgrade the existing filter to use finer mesh elements capable of achieving the 10 ppm cat fine level.
“Finer filtration necessitates a recalculation of flow-rate capacity, so technical expertise is needed to assess whether the existing automatic filter can maintain a reliable filtration function,” says Mr van Son.
“When that recalculation has been done, the most suitable option – either upgrade or installation of an additional filter – can be decided on,” he adds.
There are other uncertain factors, over and above cat fines, with chemical components and their reactions. “We have heard talk from refineries about waxes inside the heavy fuel oil, and asphaltites,” says Mr van Son.
“These circumstances also make an efficient automatic filter necessary. A reliable, backflushing automatic process is really important to let the flow to the engine, or to the heavy fuel oil booster system, operate correctly.”
This has led to increased request from shipping companies to retrofit cat fine filters. “Many well-known owners and shipping companies have taken the decision to upgrade,” says Mr van Son.
But, he cautions against using what he terms ‘grey-market systems’ from suppliers that may not be able to validate claims as to their product’s efficacy: “Shipowners should focus on reliable partners in filtration, with proven experience in this sector, or they risk putting the most important part of the vessel – the engine – in danger.”
Engine manufacturers and CIMAC recommend the use of 10 micro-metre (µm) filters to better cope with possible catalytic fines remaining in the line, says Alfa Laval concept development and product manager Adrien Nicolle.
“With Alfa Laval Moatti filters, we have a unique technology that allows smooth operations. We have been promoting installation of 10 µm filters as the last protection for engines; locating them in the recirculation line of fuel conditioning modules,” he says.
“Automatic filtration as a mechanical barrier is absolutely needed”
A common design for filters involves flushing air through the mesh to backwash their filtering elements. “But cold air induces thermal shock to fuels, precipitating the asphaltene in the fuel then clogging the filter elements on the clean side,” Mr Nicolle explains.
“These filters are subject to continuous hiccups which affect the vessel operation, when they are not irreversibly plugged.”
However, Alfa Laval Moatti filters use clean fluid to continuously clean the elements, preventing any thermal shock. “Our technology, thanks to continuous backflushing, is a proven way to cope with this instability, because backflushing is not triggered too late when clogging occurs, like in a sequential backflushing,” says Mr Nicolle.
Additionally, users can monitor any pressure drop and diagnose the installation, without impacting on the operation. This has led to some shipowners and managers retrofitting filters on their fleets.
Mr Nicolle thinks finer filtration and smart, self-adjusting systems are the way forward for engine safety and security. “Finer filtration means the need for ever-more resilient filters to avoid unplanned maintenance and spare consumption,” he explains.
Greater levels of connectivity enable Alfa Laval to fully integrate and co-ordinate other onboard devices, such as separators and fuel conditioning modules with the filters. Alfa Laval Moatti 290 filters are also available for traditional lubrication oil applications, for medium-speed or low-speed engines.
Man Diesel & Turbo has approved Alfa Laval’s Moatti 290 hydraulic control oil filter for its two-stroke engines. MAN’s approval came after validation tests aboard three Stena Bulk IMO II MAX vessels in 2018.
“The challenge is that the automatic filter mesh is unusually fine – 6 µm absolute,” Mr Nicolle explains. Alternative solutions for hydraulic control oil filtration now use the redundancy filter to treat the backflushed oil from the automatic filter.
The redundancy filter is a disposable cartridge and defined by the prescriber to have an even finer grade than the automatic filter. “The purpose is to be able to temporary use this filter as a treatment unit to prevent damage on the hydraulic line downstream, when tapping new oil in the system,” says Mr Nicolle.
“We believe that this disposable, fine-grade cartridge could be an operational risk for the ship,” he continues.
“If a sudden amount of pollution were to reach the filter, like when facing rough sea conditions, when the pollution settled in the oil sump is stirred back in suspension, it would likely quickly clog the cartridge,” Mr Nicolle says.
With no backflush treatment left, the main automatic filter would clog as well, and no redundancy could be achieved anymore. “The alternative we developed is to use a second stage of automatic filtration to treat the backflush – removing the need of any disposable filters,” he says.
“The redundancy filters, which are as fine a grade as specified, are then independent. Moreover, the filtering technology we use for this redundancy filter is not depth filtration and is therefore cleanable,” he adds.