Question
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We have fuel performance issues when we blend low sulphur marine fuels from different sources. How can we resolve this?
Apr-2021
Answers
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Marcello Ferrara, ITW Technologies, mferrara@itwtechnologies.com
The difficulty for marine engines to keep up with the times has been severely tested by the new IMO 2020 regulations which require the use of low sulphur fuels which may create deposits and fouling inside the combustion chamber and consequently cause severe damage to the pistons, liners and pistons rings, and in the worst cases lead to a sudden stop of the engine. Additionally, all of the system upstream of the engine will suffer from fouling issues.
While lower sulphur in fuels will mean fewer harmful emissions, the loss of lubricity that sulphur brings can also make engine operations more challenging.
Distillate ageing also contributes to increasing issues. The percentage of distillate blend components in VLSFO often come from complex secondary refinery streams where much of the natural stability has been removed or weakened.
Distillate ageing is a chemical process that produces sludge in the presence of elevated temperature, oxygen, or by a catalyst present in the fuel (for instance, a metal). These processes can be prevented by the use of proprietary additives.
Unstable distillates oxidise (most commonly under elevated temperatures and pressures), forming sand-like sediments which block injector nozzles, while gums become impregnated with inorganics (catalyst fines, metals, sediments), creating a grinding paste on small tolerance contact surfaces (fuel pumps, injectors, and so on).
Long chain paraffins present in many fractions of VLSFO are also responsible for wax formation in fuels. Injector blockages and separation failures indicate aged distillate material.
The major problem when blending VLSFO comes however with asphaltene stability. It is well known in the industry that, by blending different stocks, asphaltene stability will be impacted and finally asphaltene will associate into larger molecules and precipitate. Additionally, the paraffinic matrix of the VLSFO will make asphaltene naturally unstable as it will dilute the resins that keep asphaltene in solution. These larger asphaltenic molecules require more time and oxygen than is available within one combustion cycle to burn. These unburnt residuals deposit on liners and pistons in the combustion chamber; or burn later and contribute to poor ignition and airborne emissions.
Adding proprietary chemistries for chemically rebalancing the fuel and restoring stability is king for improving fuel performance and for avoiding all of the operating issues, as asphaltenes can be kept in solution and sustain inappropriate blending.
Both ship owners and fuel suppliers have no chance of controlling the blending in that a ship can bunker at any place in the world and the fuel makers receive their feeds from any place in the world.
The problem can therefore be addressed only by enhancing asphaltene stability in situ, either while bunkering or at the fuel supplier tank.
ITW has a long track record in asphaltene stabilisation, ranging from blending incompatible stocks to getting out-of-range values of sediments back on-spec by hot filtration, as well as dissolving precipitated asphaltene and coke-like materials.
Additionally, ITW has a long track record in reducing airborne emissions in engines and in power stations firing any type of fuel oil, including the ones with very high asphaltene content.
Apr-2021
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