Smoke billows from the chimney of the cooling towers of a coal-fired power plant in Datong, Shanxi province. Photo: AP

A professor has recently lodged a petition to Chinese energy and environment watchdogs asking them to enhance transparency in petroleum coke use in power generation which he considers as a major source of the country's heavy smog.

In the petition presented to the National Energy Administration (NEA) and the Ministry of Environmental Protection (MEP), Shen Kui, a professor at Peking University Law School, called on the government to publish the number of on-going petroleum coke power-generation projects and explain if the use of the fuel would have correlation with smog.

The professor's call is partly a response to a document issued by the NEA and MEP in December to strictly curb the establishment of new thermal power plants burning petroleum coke, which is seen as a fuel dirtier than coal due to its high sulfur and heavy mental contents.

High in contaminants, petroleum coke is a residue produced from refining crude oil. Low-sulfur petroleum coke is widely used in metal manufacturing, while high-sulfur petroleum coke is burned to generate power and heat.

According to the document, approval for new self-supplied petroleum coke-fired thermal power plants including thermoelectric units must be suspended in the regions and cities where air pollution control is at the forefront of government agenda.

"There are some considerations behind the policy. The overtone of the policy may reflect a certain connection between smog and petroleum coke use," Shen said in an interview.

On the culmination of heavy smog in China in January, an article critical of burning petroleum coke went viral on the social media, in which the author said that China annually bought 10 million metric tons of petroleum coke from the US, where it is generally considered a waste which is detrimental to health. The article labeled petroleum coke as a low-quality, low-price industry fuel that could lead to lung cancer.

In a paper published in 2015, Wang Tao, a nonresident scholar at Carnegie-Tsinghua Center for Global Policy, pointed out that about 33 million metric tons of petroleum coke were consumed in China in 2013, with 7 million metric tons of the substance being imported from the US, the world's top petroleum coke producer and a key exporter of high-sulfur petroleum coke to China.

Petroleum coke emits 11 percent more greenhouse gases than coal, Wang wrote in the paper, adding that toxic metal and sulfur dioxide emissions of petroleum coke are higher than those of coal if burned in a regular furnace.

Shen said that making public the information about petroleum coke use in China would contribute to clearing up public fears intensified by the unsubstantiated articles, as the Chinese government is not aware of the danger of petroleum coke use.

At a press conference on January 6, Chen Jining, minister of the MEP, reiterated that coal burning and vehicle exhaust are major contributors to the creation of tiny particles in air in the Chinese large and medium-sized cities. Moreover, his answers to the reporters' questions about the government's efforts in addressing smog did not contain curbing consumption of petroleum coke.

China's new air pollution prevention and control law dictates that imports, sales and burning of petroleum coke which does not meet quality standards are not allowed. But there are debates over the government's tolerance for the petroleum coke-fired power plants equipped with desulphurization facilities.

The news conference on January 6 was held amid a record-breaking orange alert persisting in the Chinese capital for nine days. But the effort seemed to be negated by media reports which said that some factories turned a blind eye to the city government's ban on production during smoggy days.