The coal is there to remove oxygen from the silicon. That it also provides the heat required is just an added bonus. You could add carbon capture equipment and

The coal is there to remove oxygen from the silicon. That it also provides the heat required is just an added bonus. You could add carbon capture equipment and use nuclear or hyrdo electricity to break down the CO2 back into carbon, and this carbon could be reused instead of fresh coal which would also limit the emission of other pollutants. This is a substantial additional cost though, and the conversion of an existing plant to run this way is non-trivial.