The world grapples with the emissions.

By MC01, a frequent commenter on WOLF STREET:

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 viscosity 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 viscosity 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 viscosity 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).

Emissions in particular have long focused on sulfur oxides. As with all fossil fuels, the trend has long been towards lower and lower sulfur content. But instead of focusing on emissions themselves, the MARPOL protocol legislates the limit of sulfur in bunker oil, and in such bizarre fashion it deserves a mention.

While there exists an ISO standard for bunker oil (ISO:8217, last revised in 2017), it’s not considered binding by MARPOL, which instead relies on the International Maritime Organization (IMO) to sample bunker oil sold in several locations worldwide and coming up with a “worldwide average” which is just that. Presently the limit for this “worldwide average” is 4.5% sulfur content.

This helps explain why worldwide consumption of residual fuels (as defined by the US Department of Energy) has been steadily declining after peaking in 1991. Latest data put daily worldwide consumption at 8.3 million barrels per day, down 4 million barrels per day from the 1991 peak.

When the MARPOL protocol relating to sulfur content was being discussed, several countries expressed concerns about its standards not being strict enough. To appease them, the concept of Environmental Control Areas (ECA’s) was introduced. ECA’s are areas coinciding with the territorial waters of EU member countries, Norway, Iceland and the United States (plus US dependencies in the Caribbean) where ships must use low-sulfur fuel, meaning bunker oil with less than 1% sulfur content.

In addition, the Chinese government has unilaterally created three ECA’s: One around Hong Kong and the Pearl River Delta, one around the estuary of the Yangtze River, and one largely coinciding with the Bohai Gulf. These three ECA’s include seven of the ten busiest ports worldwide.

Starting in 2000, ships sailing through these ECA’s have to comply with another set of emission rules collectively known as Regulation 13, which limit air polluting nitrogen oxides (NOx) emissions.

Regulation 13 is divided in three Tiers: Tier I, for ships built starting January 1, 2000, Tier II for ships built starting January 1, 2011, and Tier III for ships built starting January 1, 2016.

Each Tier is further divided in categories according to engine rotation speed. Low speed engines, the kind used in the large commercial vessels, have deceptively high limits: for example Tier III defines the NOx limit for engines up to 129 rpm as 3.4g/kWh while engines in the 130-1,999 rpm class have an emission limit of 2.4g/kWh.

However these low speed engines tend to run on much “dirtier” (meaning with a high organic nitrogen content) fuels than high speed ones for economic considerations, meaning they require even more work from engine manufacturers to provide engines the shipping industry can use worldwide.

Stricter environmental legislation around the world is only part of the increasingly more challenging environment these engine manufacturers have to deal with. There are only three that make the giant low-speed two-stroke diesel engines used in the largest container ships, bulk carriers, and tankers: MAN SE of Germany, Mitsubishi Heavy Industries of Japan, and Wärtsilä of Finland. Read… The Engines of the Largest Container Ships in the World, and Challenges their Manufacturers Face

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