When crude oil is boiled down to make diesel, a solid matter called petroleum coke, petcoke, is left at the bottom of a refinery tank. The substance that was virtually unheard of a few years ago is fast becoming one of China’s most pressing environmental concerns.

Petcoke that is 80 percent carbon and has a low sulfur content is used extensively in the steel and aluminum industries. The high-sulfur version is used for fuel in power and cement plants. It is cheaper than coal but much dirtier, resulting in more pollution and high carbon emissions.

Petcoke gained notoriety earlier this year when a three-story mountain of the stuff was dumped on the banks of the Detroit River. The Wall Street Journal followed up with a report on the huge surplus the United States has accumulated in recent years.

At a time when most countries are looking for greener sources of energy, there did not seem to be a market for it.

Until China came calling.

U.S. Department of Energy figures show that while petcoke sales in United States have declined since 2006, China’s demand has increased. In the first half of 2013, China imported 24 million barrels from the United States, 55 percent more than in the same period last year. China accounts for about 20 percent of U.S. petcoke exports. An analysis by the consulting firm ICIS China says this increase is the result of China’s incessant desire for cheap fuel. It adds that the imports are mainly used by glass and power plants.

Researchers at Huazhong University of Science and Technology, in the central city of Wuhan, found that petroleum coke emits much more pollutants such as sulfur dioxide and nitrogen oxide than coal.

The U.S. Environmental Protection Agency takes a dim view of petcoke as an energy source, so most of it ends up in China and Mexico. In 2011, the United States became a net exporter of oil for the first time in over 60 years, mainly as result of petcoke exports.

Gina McCarthy, a commentator at energy industry news site CleanTechnica, said the United States is not necessarily immunizing itself from danger by exporting petcoke in such large amounts. In addition to the ever-growing threat of global warming, pollution from China and other Asian nations gets high in the atmosphere and crosses the Pacific to return to the United States.

Cheap Fuel

Lorne Stockman, director of the organization Oil Change International, describes petcoke as the dirtiest form of oil on the planet. It is so cheap, he said, because it is simply a byproduct of the oil industry. Oil companies do not necessarily need to sell it for much given their huge profits from gasoline and diesel. Also, transport and storage difficulties mean that companies want to get rid of it quickly.

Burning petroleum coke produces up to 10 percent more carbon dioxide than coal, he says. Carbon emissions from power plants have already had a great impact on global warming, and the increased use of petcoke is bound to exacerbate this.

While the process can be made greener through desulfurization, this will not necessarily be done because developing countries have no compulsory restriction on carbon emissions, Stockman says. To make matters worse, petcoke emissions also contribute to high levels of PM2.5 and PM10, fine particles that are harmful to human health when they reach the lungs.

Dong Xiucheng, director of the Beijing-based China University of Petroleum’s China Oil and Gas Center, said refineries are being “bled dry” to maximize profits. Use of petcoke only made sense from an economic perspective, he said, and this was why many power plants decided to use it.

Dong, however, said that use of petcoke in China was still dwarfed by the billions of tons of coal the country burns every year.

Yue Guangxi, a thermal engineering researcher at Tsinghua University, said the country’s large-scale imports of high-sulfur petcoke stemmed from a lack of domestic production. Furthermore, he added, “due to the high price of coal, it made sense for many factories to use mixing methods involving petcoke.”

The Way Forward

Han Xiaoping, chief information officer of China Energy Network, says that while the country’s power plants are burning a huge amount of petcoke, rigorous testing and appropriate emission standards could mitigate pollution problems. Of course, he added, the country’s environmental standards also need to improve.

Han said China must strive to become greener, but is aware that this would require a complete energy makeover. Further, he says, petcoke has a part to play in the country’s energy future. Upgrading and improving the energy structure is a long process, Han said, and radical reforms are impossible.

Mark Routt, an energy adviser to oil and gas consulting company KBC Advanced Technologies in Houston, in the U.S. state of Texas, said that although the United States will no longer allow extensive use of petcoke as fuel, China will continue to use it a cheap alternative to coal. Demand would also be strong from India and Latin American countries.

Stockman said China should be very concerned about its air pollution problem, which petcoke is contributing to. A huge number of Chinese coal-fired power plants are saving money by replacing cole with petroleum coke, but that savings was being offset by global warming and a host of health problems.

Stockman said he is confident China will play a leading role in the global shift toward clean energy and improving energy efficiency. In the short term, this could involve reducing imports of petroleum coke. He said that if the country cut down on imports, the market would lose its biggest buyer, putting pressure on the heavy oil refining industry.

Wang Fuchen, professor at the Clean Coal Technology Institute at the East China University of Science and Technology in Shanghai, said petcoke emissions are a severe environmental hazard. Even if 80 percent of the sulfur is removed, the remaining content is still equivalent to that of coal. Several chemical factories are investigating using petcoke to produce synthetic gas to better control sulfur emissions.

Yue, the Tsinghua researcher, is one of many advocates of this process, and said he is optimistic that the country can lead the way in desulfurization. In his view, this will put China on the path toward clean energy and off one dominated by cheap, dirty fuel.