Basics

The Process of Converting Solid Combustable Materials into Carbon Monoxide , Hydrogen and Carbon Dioxide via partial oxidation
Assuming a "pure" feedstock, it should only produce the gasses (Some ash may be produced from impurities in the charcoal, gasification of Biomass / RDF will produce ash)
Can be as simple as a Rocket Stove , or as complex as a grid scale Fluidized Bed Gassifier

Internal Links

The Wikipedia Page on Gasification
The NETL page on "DOE GASIFICATION SYSTEMS PROGRAM AND BENEFITS"
The NETL page on "MAJOR GASIFICATION SOLID BYPRODUCTS"
BTG's "Two Stage Gasification" (seems to just be gasification, and tar/lpg etc cracking to syngas?) (need to see if the "char combustor" is a gasifier burner or just a combustor as in "coal fired furnace" type thing? )
- Need to check The Wayback Machine ; this page may have changed since this original link's posting