Charcoal Production via Multistage Pyrolysis

Interests in charcoal usage have recently been re-ignited because it is believed that charcoal is a much better fuel than wood. The conventional charcoal production consumes a large amount of energy due to the prolonged heating time and cooling time which contribute to the process completing in one to several days. Wood pyrolysis consists of both endothermic and exothermic reactions as well as the decomposition of the different components at different temperature range (hemicellulose: 200–260 °C; cellulose: 240–350 °C and lignin: 280–500 °C). In this study we propose a multistage pyrolysis which is an approach to carry out pyrolysis with multiple heating stages so as to gain certain processing benefits. We propose a three-stage approach which includes rapid stepwise heating stage to a variable target temperatures of 250 °C, 300 °C, 350 °C and 400 °C, slow and gradual heating stage to a final temperature of 400 °C and adiabatic with cooling stage. The multi-stage pyrolysis process can save 30% energy and the processing time by using a first temperature target of 300 °C and heating rate of 5 °C·min−1 to produce a fixed-carbon yield of 25.73% as opposed to the base case with a fixed-carbon yield of 23.18%.