Re: That technogy already exists.
No, CHP is different. That's when you take the heat output and sell it as heat, which is incredibly efficient if you happen to have someone or something nearby that wants a lot of heat.
What the GP was talking about was "combined cycle" generation - you take the waste heat from your primary generation process, and and use it to generate yet more electricity, thus increasing your overall efficiency.
Two entirely different principles, and not entirely compatible with each other (i.e. you can't do both with the same plant, at least not without seriously compromising efficiency).