Torrefaction of almond shells: Effects of torrefaction conditions on properties of solid and condensate products

Almond shells were torrefied in a fixed bed reactor and their solid and condensate products were collected for analysis. Response surface methodology was used to examine effects of torrefaction temperature (230 degrees C, 260 degrees C, and 290 degrees C) and time (60, 80, and 100 min) on mass and energy yields of solid products as well as mass yields and gross calorific values (GCVs) of condensate products. This was the first study on condensates produced during torrefaction of almond shells. Also, true density, moisture sorption isotherms, thermal stability, and elemental composition of the solid products were characterized. The mass yields of solid products drastically decreased at higher temperatures, from 85.4-92.7% at 230 degrees C to 39.4-45.3% at 290 degrees C. Also, mass yields (8.79-11.71% at 230 degrees C to 23.13-29.39% at 290 degrees C) and GCVs of condensates (2.3 +/- 0.3 to 4.3 +/- 1.0 MJ/kg at 230 degrees C to 5.6 +/- 1.0 to 7.1 +/- 1.2 MJ/kg at 290 degrees C) generally increased in value at higher temperatures and longer times. Moisture sorption isotherms of torrefied shells were measured for the first time and all torrefied shells had lower equilibrium moisture contents than raw shells. In addition, equilibrium moisture contents and GCVs of the condensates were found, for the first time, to be predicted relatively well using just the sample mass loss results. The minimum moisture contents were predicted to occur at 16.4-19.9% mass loss. Published by Elsevier B.V.