The cheapest liquid fuel on Earth must be heated before it will flow
Heavy fuel oil is so thick it has to be warmed before it can even be pumped, and it is loaded with sulfur. Those flaws make it the cheapest liquid fuel there is, which is why big ships burn it. The hidden bill is paid in public health.
Fuel oil is a family of products distilled from crude. Light molecules such as propane, gasoline and kerosene boil off early; heavier fractions like diesel and lubricating oil come out more slowly, and the heaviest residues are left at the end. Grades are numbered, and as the number rises, so do boiling point, chain length and viscosity, while price falls. Number 1 is essentially kerosene, once called coal oil or stove oil. Number 2 is home heating oil, close to truck diesel. Its old name, gas oil, recalls its early use enriching manufactured gas.
At the heavy end, number 6 oil must be stored at around 38 degrees Celsius and heated further before it can be pumped and burned. That rules it out for cars and small boats, but power plants and large ships can manage the heating equipment. It once fired boilers, steam locomotives and steamships. Coal power stations still use it to light up their boilers, a bit like kindling. When spilled, it tends to break into tarballs that sink rather than spread as a slick, and its stickiness makes underground contamination hard to clean.
Its role has shrunk. Residual oil made 16.8 percent of American electricity in 1973 but 6.2 percent a decade later, squeezed by natural gas and emissions rules. New York City estimated in 2011 that the one percent of buildings burning grades 4 and 6 produced 86 percent of all building soot, and every building using number 6 had switched by the end of 2015. Heating oil remains common in the northeastern United States, though gas and heat pumps are eroding it.
Shipping is the biggest remaining problem. Before a global sulfur cap took effect in 2020, pollution from ships was estimated to cause around 400,000 premature deaths and 14 million childhood asthma cases a year. Even afterward the estimates stand near 250,000 deaths annually. Countries on busy sea lanes suffer most; in Taiwan, shipping caused 70 percent of transport-related pollution deaths in 2015.
Source: Fuel oil
