The objective of this research is to investigate the occurrence of agglomeration phenomena during fluidized bed processing of biomass fuels. These are to be ascribed to the alkali content in biomass materials that gives rise to low melting compounds in combination with SiO2, normally present in bed materials. The results obtained in a lab scale facility under operating conditions of gasification highlight that other materials may be adopted (e.g. olivine and chromite), despite they have higher density with respect to silica sand, affecting the bed fluid-dynamics. As alternative the addition of metakaolin is effective in order to delay the occurrence of bed agglomeration, as demonstrated by experiments carried out in alumina crucible at 900 °C and complemented by electronic scanning microscopy (SEM) and x-ray diffraction (XRD) analyses. The results are reported and discussed in the article, with the sake of providing further insights for contrasting the undesired agglomeration behavior in practical applications.