Thank you for your suggestions! In regards to balance, with my mod 5 pieces of wood get turned into 1 solid fuel, with wood gasification, 8 pieces of wood get turned into 1 solid fuel, but I do not intends, at least for now, to change that. In regards to getting access to solid fuel too early, I don't personally see the issue, the research is at the same point as wood gasification(for comparison) and it even costs a bit more to research, as well as solid fuel being unlocked in the prerequisite research(Oil processing). As for the category of the mod, I'm still learning which category is for what kind of mod so it most likely wont be in the category that it should be in, however I will take your suggestion into consideration.
