“Bunker,” the Fuel for the Giant Engines in Large Cargo Ships
The world grapples with the emissions.
When pricing a container shipment, we are sometimes told rates have gone up because “bunker oil” has increased in price or that the delivery will take a few extra days because shipowners ordered their skippers to slow down to save “bunker oil.”
But what is this “bunker oil”?
The term “bunker oil” defines all types of fuel used by the shipping industry and generally speaking can be split in two categories: distillates and residuals.
Distillates are produced during fractional distillation of crude oil and generally are very close in density to diesel #2, the mainstay fuel in trucking and agriculture, but slighter denser.
Residuals are produced from the thick sludge left over at the bottom of the refinery’s fractionating column and are only a step or two removed from bitumen, the stuff used to pave roads: the most widespread types of residual bunker available have densities ranging from 500 to 700cSt at room temperature. For comparison, the densest types of diesel fuel have a density of under 35cSt at room temperature. This means that this type of bunker has to be pre-heated before it can be pumped into the fuel system.
There are also several blends of distillates and residuals, or of various residuals, whose density ranges from 300 to 400 cSt, which are sold to provide a cheap alternative to straight diesel fuel while at the same time helping to meet environmental legislation.
Pollution by maritime vessels is regulated worldwide by the International Convention for the Prevention of Pollution from Ships (MARPOL), first ratified in 1973, and regularly amended over the years, the last time in 2013.
The MARPOL protocol legislates all aspects of ship-related pollution, from emission levels to how waste from the ship latrines should be processed and disposed of (not a joke when modern cruise ships are involved).
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