Colorado-based global specialty chemicals company Innospec has published an article on handling fuel instability of very low sulphur fuel oil (VLSFO) in their February technical bulletin :
Problems associated with VLSFO
What is Fuel instability and why is it more important than ever?
HSFO instability meant Asphaltenes dropped-out of solution causing filter blocking, tank fouling, poor combustion and increased purifier cleaning/servicing frequency. VLSFO still contains Asphaltenes from residual streams; however, it is a different animal. The majority of VLSFO components come from low cost distillate and low sulphur petrochemical streams which can be highly volatile, these can separate readily to form distillate sludge such as sticky gums, hard sediments or even polymers in storage/handling tanks, filters, pipework, purifiers and mechanical contact surfaces.
It has been shown that after-burn and dumb-bell ignition (both early and late ignition) are a high risk due to the incompatible mixture of light (paraffinic) and heavy (Asphaltenes) fractions used to achieve lower costs and 0.5% Sulphur found in VLSFO. Using the best methods for component mapping and stability monitoring we have proven the blend of two dissimilar components pose a significant risk of instability through rapid chemi-cal ageing, this makes storage/handling unpredictable with some of the effects being unavoidable on-board.
Distillate sludge blocks filters and purifiers just as residual sludge does, only this can happen rapidly for a variety of reasons including prolonged storage (>1 month), heating or co-mingling. Unfortunately, it can also happen due to an inherent instability, which leads to chemical changes in the fuel once on-board.
The true risk of distillate sludge is to ships engines. Paraffinic gums are highly adhesive and stick to contact surfaces such as injectors and fuel pumps. Once established they allow hardinorganics such as metals/cat fines to become imbedded within, creating an abrasive surface that wear down fine tolerances, or create blockages. The quick onset of injector nozzle blockage leading to poor spray pattern and ignition efficiency which will lead to greater instance of liner impingement, after- burn and post combustion fouling (soot, ash, T/C deposits).
What does this mean for combustion?
Asphaltenes have always existed within Marine Fuels, they have a high calorific value and burn readily if effectively dispersed within the fuel; if stabilised the Asphaltenes are dispersed and protected by naturally occurring resins, which keep them small enough to find sufficient oxygen and burn during combustion. By contract, VLSFO can be an overly refined product containing low cost distillate streams that strip-away protective resins causing the Asphaltenes to agglomerate to form huge complex structures, which drop out of solution. Those that are not removed during filtration or purification or develop afterward are injected into the combustion chamber but are too large to burn effectively. This is when we see ‘black’ residual deposits on liners and pistons from unburnt fuel.
The same is true of distillate sludge, only that we have seen that these tend to effect engine components far more than Asphaltenes. Once injector efficiency is reduced through nozzle blockage, early ignition or contact surface wear, this leads to poor spray pattern and further compounds poor combustion efficiency.
How do we keep ships sailing?
Fuel handling practices will need to change to face the new challenges; unfortunately, each fuel bunkering will vary significantly from region to region or even within the same port. VLSFO is still a residual fuel that requires heating due to high pour points, variable viscosity and waxy distillate components. Unfortunately heating VLSFO can lead to the rapid onset of aging, which brings us instability. There are cases where fuel has polymerised within four hours of leaving the storage tank and entering the fuel handling system (with purifier temperatures as low as 60°C!). These chemical reactions cannot be avoided even when good on-board practices are followed.
Innospec were approached by Industry to develop OctamarTM HF-10 PLUS; our expertise in the Marine, Automotive, Aviation and Refinery business uniquely places us in a position to maximise the operability of fuels.
OctamarTM HF-10 PLUS contains our famous Asphaltenes dispersant/stabiliser which has been used in over 3000 vessels world-wide to clean-up and maintain fuel tank cleanliness, and our unique distillate stabiliser/detergent and dispersant, which targets problem elements in the low quality distillate streams, preventing them from propagating into sludge or adhering to machinery contact surfaces.
This means clean tanks, filters, purifier, engines and better combustion. Our formulas have been a must-have in automotive/industrial diesels and long-term storage units for decades and we are pleased to bring it to the marine sector in these trying times.
OctamarTM HF-10 Plus chemically targets problem elements within the fuel, cleaning up Asphaltenes, distillate gums and sediments, and prevents the onset of polymerisation and oxidation.
Would you like to know more?
To find out more details please contact our technical team in your region and visit our website:
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Photo credit: Innospec
Published: 17 February, 2020
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