Much talked-about US efforts to build a coal-fired power plant with near zero emissions are now concentrated in a single project, as the costs and difficulties of the endeavour have mounted and the stakes have risen.

FutureGen, a $1.5-billion public-private venture, aims to design and test the technology required to turn coal into a gas that can be stripped of harmful emissions, then burned to produce electricity and hydrogen. It will also capture carbon dioxide - widely blamed for global warming - and store it underground forever.

Plants that burn coal, already used to produce half the electricity consumed in the United States, were poised to make a major comeback after a decade of construction of less-polluting, natural gas-fired units.

The FutureGen alliance includes US utilities and coal producers like American Electric Power Co and Peabody Energy, along with international miners Anglo American, BHP Billiton and China's largest coal-based power company, China Huaneng Group.

Coal gasification technology uses heat and pressure to convert coal or any carbon material into a synthetic gas which is burned in a turbine to generate electricity. Hot gas leaving the turbine is used to heat water to produce steam to power a steam turbine and generate more power.