Who says you power that thing with fossil fuels? The real way to do that is via giant nuclear reactors or reactor complexes.

Fission power can be made cheaper per MW by just making the reactors bigger. Economies of scale, the square cube law and all that. The problem with doing this in the commercial power sector is that line losses kill you on distribution. There just aren't enough customers within a reasonable distance to make monster 10 GW or 100 GW reactors viable, regardless of how cheap they might make energy.

But DACC is one of the few applications this might not be a problem for. Just build your monster reactors right next door to your monster DACC plants.