The Art, Science, and Technology of Charcoal Production

TLDR

Charcoal is a renewable fuel with negligible sulfur, mercury, nitrogen, and ash, is highly reactive, easy to store, and can serve as an adsorbent or a semimetal with graphite‑like resistivity. The review seeks to consolidate knowledge on charcoal production and properties accumulated over 38 millennia. The authors synthesize existing studies on charcoal production processes, highlighting key parameters such as pressure, moisture, and gas flow that influence carbonization. Optimizing pressure, moisture, and gas flow during biomass carbonization can yield fixed‑carbon content near theoretical limits within minutes, while exothermic secondary reactions reduce tar formation and improve yield, indicating charcoal’s expanding potential as a renewable fuel, reductant, adsorbent, and soil amendment.

Abstract

In this review, we summarize the knowledge of the production and properties of charcoal that has been accumulated over the past 38 millenia. The manipulation of pressure, moisture content, and gas flow enables biomass carbonization with fixed-carbon yields that approachor attainthe theoretical limit after reaction times of a few tens of minutes. Much of the heat needed to carbonize the feed is released by vigorous, exothermic secondary reactions that reduce the formation of unwanted tars by augmenting the charcoal yield in a well-designed carbonizer. As a renewable fuel, charcoal has many attractive features: it contains virtually no sulfur or mercury and is low in nitrogen and ash; it is highly reactive yet easy to store and handle. Carbonized charcoal can be a good adsorbent with a large surface area and a semimetal with an electrical resistivity comparable to that of graphite. Recent advances in knowledge about the production and properties of charcoal presage its expanded use as a renewable fuel, reductant, adsorbent, and soil amendment.