Beijing: China has built the world's largest facility to turn excess methane gas from coal mines into electricity, which could help the communist giant reduce its emissions.

Lu'an Group, which completed the facility at Shanxi Province in north China said it would soon start operating the generator with a capacity of 30 megawatts, capable of utilising 99 per cent of methane gas discharged from the coal mine, state-run Xinhua news agency reported on Friday.

The poisonous gas is a common emission during underground mining. Normally, mines will liquify the gas into methyl alcohol if it has a concentration higher than 30 per cent; for concentrations between 10 per cent and 20 per cent, it is captured and used to fuel internal combustion engines.

However, methane concentrations lower than 10 per cent, which qualifies 81 per cent of the gas released during mining, cannot be consumed through direct combustion. The gas was also responsible for numerous explosions in the mines in recent times, causing hundreds of casualties in China.

Jia Jian, deputy head of the Methane Gas Research Institute of the company, said the new technology has helped tackle the problem of how to dispose of the waste.

The project can decompose the gas into carbon dioxide and water under temperatures more than 950 Celsius, and use the heat and steam for power generation, he said.

Jia said by recovering and utilising the gas, the project can help reduce 1.4 million tonnes of greenhouse gases and produce 200 million kilowatt-hours of electricity a year.

China's coal mines produce over 10 billion cubic metres of low-concentration methane gas each year, which causes greenhouse gas emissions equivalent to 200 million tonnes of carbon dioxide. Jia said the project of making waste profitable has a good market potential.

The demonstration facility installed at Gaohe Coal Mine has drawn interest from a number of coal mining firms, which have signed agreements predicted to reduce 15.8 million tonnes of carbon emissions.

Coal mining firms in China, the largest coal producer, are under greater pressure than ever to control carbon emissions as the government continues to step up efforts to cut emissions.

China has set an ambitious goal of reducing carbon emissions per unit of gross domestic product (GDP) by 40 to 45 per cent from the level in 2005.

By 2013, carbon emissions per unit of GDP dropped by 28.56 per cent from 2005. In the first three quarters of 2014, energy consumption per unit of GDP dropped by 4.6 per cent from a year earlier and carbon emissions were down by 5 per cent, according to data.