Really cool! A few suggestions since it seems you're going to keep working on it:
- I would've liked to see how well I'm doing since I sometimes felt like I stopped to think for too long. Maybe something like a health bar or something similar to signify that there is actual pressure would help.
- Maybe the game could be paced even slower in the beginning. What if you let the coal required be available for the first few and gradually introduce the "split, swap, increase" mechanics?
Overall I had fun with it and the presentation was really pretty.