The Creation of Petroleum Coke

Tar Sands in Alberta, Canada
Veronique de Viguerie/Getty Images News/Getty Images

Petroleum coke, or petcoke, is a byproduct from the refining of crude oil. It consists mostly of carbon, with variable amounts of sulfurs and heavy metals. It has many industrial uses, including the production of batteries, steel, and aluminum. Lower-grade petcoke, which contains higher concentrations of sulfur, is used as fuel in coal-fired power plants and cement kilns. Lower-grade coal is estimated to represent 75% to 80% of all petcoke produced.

The production of petcoke in North America has increased in recent years due to the refining of crude oil originating from Canada’s tar sands region. If all the recoverable bitumen (the “proven reserves”) from tar sands was removed and refined, several billion tons of petcoke could be produced. When operating at capacity, large U.S. refineries can produce 4,000 to over 7,000 tons of petcoke per day. In 2012 the United States exported 184 million barrels (33 million metric tons) of petcoke, predominantly to China. A lot of petcoke is also produced in Canada, in close proximity to the tar sands, where bitumen is upgraded into synthetic crude oil or syncrude.  

A Troublesome Source of Atmospheric Carbon Dioxide

Bitumen’s high density, or what gives it that semi-solid consistency, is explained by the fact that it contains more carbon than conventional oil. Refining crude oil from tar sands involves the reduction of the number of carbon atoms per hydrocarbon molecule. These discarded carbon atoms eventually form petcoke. Since large volumes of tar sand crude oil are currently refined, large amounts of low-grade petcoke are produced and sold as an inexpensive fuel for coal plants. This burning of petcoke is where tar sand bitumen releases extra carbon dioxide, compared to conventional oil. Petcoke produces more CO2 per pound than almost any other energy source, making it a contributor to greenhouse gases and thus a driver of global climate change.

Not Just a Carbon Problem

Refining sulfur-rich tar sand bitumen concentrates the sulfur content in the petcoke. Compared to coal, petcoke combustion requires the use of additional pollution controls to capture much of that sulfur. In addition, heavy metals are also concentrated into the petcoke. There are concerned with the release of these metals into the air when petcoke is used as a fuel in a coal power plant. These same concentrated heavy metals can enter the environment at storage sites where large piles of petcoke are staged, uncovered. The epicenter of complaints stemming from petcoke storage seems to be in the Chicago, Illinois, area. Large piles of petcoke, each made of thousands of tons of the dusty material, sit along the Calumet River and come from an oil refinery in nearby Whiting, Indiana. These storage sites are in close proximity to residential areas in Chicago’s Southeast side, where residents complain about dust from the petcoke piles blowing into their neighborhoods. 

Indirect Effects: Keeping Coal-Fired Plants Open

The recent boom in natural gas production has been a challenge for coal-fired power stations. Many have been closed or converted to natural gas power generators. However, petcoke can be used concurrently with coal in many power plants, a practice known as co-firing. Some technical challenges associated with co-firing exist (from petcoke’s high sulfur content, for example), but the very low price of petcoke could be an important factor to keep coal plants open in an economically competitive energy environment. New life could be breathed into slated-to-close coal power plants, with for a net result elevated CO2 emissions.