[Majromax]

> he heat energy increases the pressure of the newly created CO2. This higher pressure is placed on one side of a turbine or a piston, and we extract useful work by moving it from a high density state to a low density state, causing it to cool in the process.

You run the hot, high-pressure gas through a turbine to give you less-hot, lower-pressure gas. You then extract as much waste heat out of that stream as you can via a heat exchanger process, to pre-heat incoming fuel/air and to recover more energy by boiling water to run through another turbine.

At the end of the process, you have a medium-temperature stream of combustion product that has high concentrations of CO2. You capture the carbon from this stream, before releasing the last bits of gas to the atmosphere.

You gain usable energy out of the process because all of the heat movement happens through a turbine (to directly generate energy) or through a heat exchanger (to recycle the heat to other more useful parts of the process).