Here’s a simple schematic of a boiler used for power production.  It works like this:

1. The fuel goes in (in this case, it’s natural gas).
2. The fuel is burned.
3. The heat passes over a series of boiler tubes or coils filled with water.
4. The water boils into steam.
5. The steam passes through a steam turbine, causing the turbine to spin.
6. The spinning turbine is attached to a generator, which also spins.
7. The generator creates electricity.
8. The de-energized steam is returned to the boiler.  It can also be passed through a cooling tower to turn it back into water (or colder steam).

There are a million variations on this, but it’s the basic process.  Doesn’t it seem like a waste to send all of that good energy up the boiler stack?  Hmmm.  If only there was a way to capture some of that energy… Let’s take a look at how we would add cogeneration to this scenario.