New England, where the project will be located, doesn't use very much coal at all (usually less than 1% of generation recently). Mostly it's natural gas, nuclear, hydro from Canada, and renewables.

https://www.iso-ne.com/isoexpress/web/charts

On very cold winter days we do use a fair amount of oil for power generation, but that's typically limited to just a handful of days a year when we can't get enough natural gas due to pipeline constraints.

> Replacing coal plants will happen

For the US, it has already mostly happened. Coal has dropped 60% since 2008. By the time Boston Metal gets a full size steel plant built (about 5 years) coal will mostly be gone.

Over the last 12 months, renewables provided more electricity than coal or nuclear individually (not together).