With the shipping industry making increasing efforts to use renewable energy sources in light of IMOs greenhouse gas (GHG) strategy, many vessels are already trialling the use of biofuels on board their ships.
Biofuels do emit CO2 during combustion, but can potentially reduce GHG emissions based on the perspective of carbon cycle – CO2 release into atmosphere during biofuel combustion will be absorbed by the biomass feedstock during their growth stage. However, more importantly biofuels do not emit sulphur oxides (SOx) during their combustion, at a time when the maritime industry is clamping down on sulphur use in marine fuels. Biofuel also has advantageous as it can be used as drop-in fuel without modification of existing marine diesel engines.
The main types of biofuel candidates used in trials are:
FAME (Fatty Acid Methyl Ester)
HVO (Hydrated Vegetable Oil)
F-T Diesel (Fischer-Tropsch Diesel, a Biomass to Liquid Fuel)
At present, no regulations are in force for IMO member states regarding the use of biofuels although procedures for evaluating the CO2 reduction effect of biofuel in life cycle accounting are currently being developed by the IMO.
Some handling and safety aspects with biofuels, in particular, FAME are highlighted below:
Recommended Precautionary Measures
FAME has great affinity for water to form stable emulsion. FAME and water emulsion (fuel haziness) can generate microbiological growth which leads to excessive formation of sludge that can clog filters and affect engine performance.
All fuel storage tanks should have an effective drainage arrangement.
Regular draining of the fuel tanks to remove water.
FAME oxidizes readily to form precipitates which can clog filters, increased acidity from oxidized fuel can foul injectors.
Avoid long-tern storage.
Low Temperature Operation Issue:
FAME has a higher cloud point when compared to petroleum diesel which can potentially cause wax formation at lower temperature leading to filter clogging.
Pay attention to storage and transfer temperature and monitor for any signs of strainers or filters choking.
Microbial growth can produce sulphide reducing bacteria (SRB) causing corrosion of steel tanks.
Water can promote hydrolytic reaction, breaking down the FAME to form free fatty acids. Such species are corrosive and may attack exposed metal surfaces.
Regular draining of the fuel tanks.
Ensure water content and acid number of fuel are not elevated.
High Detergency Property & Cleaning Effect:
FAME especially in higher concentrations has a solvent/scrubbing action that cleans/removes deposits from the fuel system, resulting in clogged fuel filters.
Ensure tanks and pipes are clean before fuel change over.
Compatibility and Degeneration Effect:
FAME is less compatible with the following materials:
Metals – brass, bronze, copper, lead, tin and zinc may oxidize FAME.
Elastomers – Nitrile rubber, neoprene, chloroprene, natural rubber, styrene-butadiene rubber, butadiene rubber and others (swelling and aging of seal materials can lead to leakages and malfunctioning of equipment).
Polymers – polyethylene, polypropylene, polyurethane, polyvinylchloride (potential swelling of polymers might affect its material properties).
Recommend to check with suppliers of sub equipment on compatibility with FAME.
Consult with engine and fuel system manufacturer for suitability of the biofuel to be used onboard vessel.
If you vessel is planning on trialling the use of biofuels, Class may recommend you carry out three procedures beforehand:
(1) Request a temporary exemption from NOx emission compliance from the Flag State Administration.
(2) Consult with the engine and fuel supply systems manufacturer about the suitability of the biofuel.
(3) In principle, confirm the suitability of the biofuel usage on the vessel by evaluating the quality of the biofuel after bunkering to ensure safe and smooth fuel usage by optimising the fuel storage, handling and treatment onboard ships.
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