Effect of Storage Conditions on Moisture Sorption of Mixed Biomass Pellets

The aim of this paper was to study the moisture sorption characteristics of mixed biomass pellets. The pellets were developed using a mixture of woody (spruce or pine) and agricultural (reed canary grass or hay) biomass with a ratio of 1:1. The pellets were stored in a controlled environment until reaching the equilibrium moisture content. The temperature of the controlled environment was varied between 15 and 25 and relative humidity between 20 to 90%. The experimental results showed this temperature range had no effect on the moisture sorption isotherms. However, the equilibrium moisture content at higher relative humidity was found dependent on the type of the material and was higher for spruce-hay pellets compared to the other tested pellets. Oswin, Guggenheim-Anderson-de Boer, Henderson and Peleg models were tested for the prediction of the moisture isotherms. With a coefficient of determination varying between 0.998 and 0.995, a standard error between 0.054 and 0.071 and chi-square error ranging between 0.009 and 0.015, Oswin model was found more suitable to predict the moisture sorption isotherms of all biomass pellets. This result was further confirmed using the residuals plot, showing a more uniform distribution for Oswin model compared to the other models.