They exist but you're right that you can't just use the waste heat directly. You have to pump in some extra heat to make it worthwhile.
They are called co-generation power plants. The one I used to work at took the waste heat from gas turbines, added more heat with HRSGs (heat recovery steam generators) and fed it into a steam turbine. It adds a significant amount of efficiency.
They are called co-generation power plants. The one I used to work at took the waste heat from gas turbines, added more heat with HRSGs (heat recovery steam generators) and fed it into a steam turbine. It adds a significant amount of efficiency.