Adds structures to dispose of unwanted items and fluids.
Mods introducing new content into the game.
Furnaces, assembling machines, production chains.
They seem to be overlapping, thus causing an error on load.
What kind of error? I just fired up the latest version of Flare Stack in Factorio 0.18.6 and it ran without issue.
I re-downloaded the mod, and now it works. Go figure.