Meanwhile, other completely different approaches involve burning coal in pure oxygen (oxyfuel), or turning it into a mixture of carbon monoxide and hydrogen, which is then burned.

BBC: Whatever happened to carbon capture?

The first well supplies oxidants (a mixture of water and air or water and oxygen), which are injected into the location where the process is actually occurring.

FORBES: Underground Coal Gasification: A Trend Worth Watching

That hydrogen and carbon monoxide mixture is then pumped into one of two NOx traps, where it strips the oxygen from the NOx, forming nitrogen, carbon dioxide and water.

FORBES: Clearing the Air