Bunker stem with catalytic fines and an ECA changeover ahead
During a night bunkering at Singapore, MV Kestrel receives 800 t of RMG 380 in two parcels. The bunker delivery note states sulphur 0.47% m/m. The supplier's certificate of quality gives density 989.6 kg/m³ at 15 °C, viscosity 372 cSt at 50 °C, water 0.4% V/V, Al+Si 82 mg/kg, vanadium 310 mg/kg, sodium 38 mg/kg, pour point 21 °C, CCAI 855 and total sediment potential 0.05% m/m. The ship has one fuel-oil purifier rated 1.8 m³/h, a heater able to hold 140 °C at the separator inlet, and 240 t of fuel from the same supplier already in the tanks. The next leg is nine days: six days outside any emission control area, then three days inside a 0.10% sulphur ECA where 180 t of 0.08% MGO is available. The chief engineer proposes burning the new fuel on the existing purifier settings and changing over to MGO at the ECA boundary. The charterer wants the ship kept on the cheaper high-sulphur parcel for as long as possible.
1. Which of the reported parameters are non-conformances against the usual RMG 380 specification, and what does each mean physically?
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Al+Si 82 mg/kg exceeds the ISO 8217 limit of 60 mg/kg for residual grades. These are catalytic fines: hard aluminium-silicate particles from refinery cracking units, mostly a few micrometres across. They are abrasive, they pass through filters and settle in the fuel system, and they cause liner, piston-ring and fuel-pump wear. This is the decisive number in the stem.
Other values are within the usual RMG 380 envelope but still informative: density 989.6 kg/m³ (limit 991.0) leaves little margin for separator gravity-disc setting; viscosity 372 cSt at 50 °C is within the 380 limit; water 0.4% V/V is below the 0.5% limit; sodium 38 mg/kg is low, and with vanadium 310 mg/kg points to hot-corrosion monitoring rather than an immediate problem; pour point 21 °C is not a breach but dictates storage and transfer temperatures on a cold-climate arrival. CCAI 855 is a calculated index indicating a highly aromatic fuel, so ignition quality and injection timing should be watched.
2. Evaluate the chief engineer's plan for the catalytic fines and the ECA changeover, and state what you would require instead.
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Catalytic fines. Burning a 82 mg/kg fuel on unchanged settings is not acceptable. Fines cannot be blended away or removed by settling; they are removed by the purifier by density difference, and efficiency depends on throughput, separation temperature and gravity-disc choice. With one unit rated 1.8 m³/h, halve the feed rate, run the separator at the temperature that gives the correct viscosity at the bowl (not the engine-inlet temperature), desludge more frequently, and use both purifiers in series if a second is available. Monitor the purifier sludge and the fuel-filter differential pressure, and check the piston-ring and liner wear trend afterwards.
Changeover. 0.47% sulphur complies with the global 0.50% cap but not with the 0.10% ECA limit. Changeover must be completed before the boundary, not at it: start early enough to purge the system and consume the settled high-sulphur fuel, follow the ship's written changeover procedure, and record times, tank quantities and the boundary crossing. Watch for the classic MGO problems - loss of viscosity causing pump and injector seizure, seal and leak-off pipe leaks, and thermal shock if the temperature is dropped too fast. The charterer's preference is irrelevant to the ECA limit.
3. What would you do about mixing the new parcel with the 240 t already on board, and about the pour point, before signing the bunker documents?
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Compatibility. Same supplier and same grade is not proof of compatibility. Fuels from different refinery streams can be incompatible even when each meets specification, and mixing can precipitate asphaltenes that block filters and separators within hours. Before loading, check the certificate against the previous bunker certificate and, if the source or properties differ materially, run a spot compatibility test (a simple blend test) or keep the parcels in separate tanks and change over cleanly.
Pour point. 21 °C means the fuel must be kept above roughly 30 °C in storage and heated before transfer on a cold passage; without heating, wax can block transfer lines and the purifier.
Before signing. Retain the sealed sample, verify sulphur by an independent laboratory rather than relying only on the BDN, record the time and quantity of each parcel, and enter a protest on the BDN if the Al+Si result stands. A note on the BDN costs nothing; discovering the problem after the ship has sailed costs a claim.