Carbonization of wood: Product analysis and energy assessment

The pyrolysis of wood blocks (65 x 35 x 35 mm) of oak (Quercus pedunculata) and of plaquettes (250 x 40 x 25 mm) of assao (Macro-samanea pedicellaris) were studied in a laboratory retort to investigate the supplementary specific energy (SSE) required to carbonize 1 kg of dry wood and indicators characterizing the retort carbonization, such as: weight and net energy efficiencies; effluents produced per kg of dry wood carbonized (condensables and non-condensables); effluents produced as a function of carbonization cycle time; and SSE consumption. The endo/exothermicity of pyrolysis reactions were estimated and the results verified later by thermal analysis using a Calvet isothermal calorimeter. The pyrolysis retort set-up was classical (with possibilities of recovery of all effluents generated) and used electrical resistors to provide the heat for carbonizing the wood. The electrical energy utilized during a complete cycle of carbonization was measured by a watt-hour meter to estimate the SSE. The carbonization process parameters (i.e. initial wood moisture, final temperatures, residence time at final temperatures, and heating rates employed) were varied and chosen to approach field carbonization conditions as would be encountered on an industrial scale. This paper reports typical results achieved with the laboratory set-up used. The results are compared with the measurements from an industrial retort-kiln.