Right, so, Carbon converts to condensed carbon in a 2:1 ratio. There is a lossless inversion of the process, getting you 2 carbon from one condensed carbon.
Except the charge of condensed carbon is actually 3 times higher, not just twice. That is of course the main incentive to convert your carbon to condensed carbon, so that is not a problem.
The problem starts when you start fueling your portable refinery with condensed carbon. It takes fifty, and that equates to the same charge as a 150 carbon. So far so clear.
But when you pick up your portable refinery, you get its current charge payed back into your inventory. In the form of carbon.
In other words, feed 50 condensed carbon into the refinery, and pick it up without doing anything, you just converted that to carbon at a ratio of 1:3. You got a full 150 carbon, instead of just 100 as you would have if you’d actually have used the refinery to properly convert it.
You can now take those 150 carbon and convert them back to 75 condensed carbon, 50% more than you had to begin with. Minus a tiny bit you needed to power the conversion.