Fly ash, muh man.
Either you cyclone, hot filter and wet scrub, killing your efficiency, or you eat out your moving parts with silica nanoparticles and alkali salts.
In an emergency, you do what you gotta do, but I'm more interested in building a static gassifier, cleaning the product, and compressing it as totally-not-LPG.
Big project, I'm collecting firebricks... :)
