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

Authors: Chiou, Bor-Sen; Valenzuela-Medina, Diana; Bilbao-Sainz, Cristina; Klamczynski, Artur; Avena-Bustillos, Roberto; Milczarek, Rebecca; Du, Wen-Xian; Glenn, Gregory - Greg; Orts, William

Submitted to: Industrial Crops and Products
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2016
Publication Date: 3/21/2016
Citation: Chiou, B., Valenzuela-Medina, D., Bilbao-Sainz, C., Klamczynski, A., Avena-Bustillos, R.D., Milczarek, R.R., Du, W., Glenn, G.M., Orts, W.J. 2016. Torrefaction of almond shells: effects of torrefaction conditions on properties of solid and condensate products. Industrial Crops and Products. 86:40-48.

Interpretive Summary: Torrefaction of biomass involves heating the sample under inert atmosphere at temperatures between 200-300'C for one hour or less. Most studies on torrefaction of biomass had involved different wood species. There had been very few studies focusing on nut shells, such as almond shells. In this study, we examined the torrefaction of almond shells. We characterized the effects of torrefaction temperature and time on properties of the solid and condensate products. The condensate heating values generally increased at higher temperatures and longer times. Also, raw shells had higher equilibrium moisture contents than all torrefied samples. In addition, energy yields and heating values of solid products as well as heating values of condensates could be predicted from mass loss results.

Technical Abstract: Almond shells were torrefied in a fixed bed reactor and their solid and condensate products were collected for analysis. A central composite design and response surface methodology were used to examine effects of torrefaction temperature and time on mass and energy yields of solid products as well as mass yields and gross calorific values (GCVs) of condensate products. Also, true density, moisture sorption isotherms, thermal stability, and elemental composition of the solid products were characterized by gas pycnometry, dynamic vapor sorption, thermogravimetric analysis, and elemental analysis, respectively. The mass and energy yields of the solid products depended more on temperature than on time. Also, mass yields and GCVs of condensates generally increased in value at higher temperatures and longer times. Torrefaction conditions did not have much of an effect on true density of the samples. Also, all torrefied samples had lower equilibrium moisture contents than the raw shells over the experimental relative humidity range. All moisture sorption isotherms showed good fit to the Guggenheim-Anderson-De Boer model. In addition, energy yields and GCVs of the solid products as well as GCVs of the condensates could be predicted relatively well using just the sample mass loss results.