PetroChina Co., the country’s biggest oil company, started operating a 30 billion-yuan ($4 billion) refining and chemical complex in the northwestern province of Xinjiang to help boost the nation’s energy security, reported Bloomberg.

The Dushanzi complex is comprised of a 10 million-metric-ton-a-year refinery and a 1 million ton-a-year ethylene plant.

The complex will boost PetroChina’s refining capacity at Dushanzi to 16 million tons a year, Liu Xiaolin, an official at the plant said in July. The refinery, which began production Monday, will process high-sulfur crude oil from Kazakhstan, said PetroChina.

The Dushanzi project may generate more than 60 billion yuan in annual revenue, China National said.

China’s biggest oil companies, including China Petroleum & Chemical Corp., are competing to expand processing capacity after the government adjusted a fuel-pricing system to include crude oil costs and a profit for refiners.