Dec 18 (Reuters) - China Shenhua Group, the country's largest coal producer, has started building a $21.4 billion facility to produce alumina from coal ash, the state Xinhua news agency said on Sunday, citing a senior company executive.

The company plans to invest 135.8 billion yuan ($21.4 billion) in the project, near Jungar coal mine in Ordos city in northern China's Inner Mongolia, Xinhua quoted Ling Wen, deputy manager of Shenhua Group, as saying.

No details were given about how the company would turn coal ash, a waste byproduct of thermal power generation, into alumina.

The project included a 6,600-megawatt power plant, an alumina plant and a gallium plant, all of which will use materials recycled from coal burning, Xinhua said.

Ordos, which is home to one-sixth of the country's coal reserves, will be able to produce 3 billion tonnes of alumina, which is used to make aluminum, according to Xinhua.