Effect of sepiolite bed material on gas composition and tar mitigation during C. cardunculus L. gasification

Abstract

Sepiolite, a clay mineral that is commonly used as adsorbent, is proposed as bed material for biomass gasification in a lab-scale bubbling fluidized bed. In order to compare the obtained gas composition and tar generation, silica sand has been used as reference bed material. C. cardunculus L. has been employed as biomass feedstock. The operating temperature is varied from 830 to 875°C, at constant equivalence ratio (ER) of 0.30. The gas produced with sepiolite as bed material has a slightly lower quality than the gas generated with silica sand, the lower heating value (LHV) is 0.4–1.4MJ/Nm3 lower for sepiolite than for silica sand. However, the tar generation is rather reduced in the sepiolite bed and the tar composition is also different among the bed materials: the polycyclic aromatic hydrocarbons fraction (PAH) is drastically reduced while oxygenated compounds arise in the sepiolite tests. Sepiolite properties such as surface area and morphology have been analysed by means of specific surface area (BET) and scanning electron microscopy (SEM-EDS) before and after the experiments. The fuel behaviour and the properties of sepiolite induce the adsorption of tars and molten ashes on the sepiolite surface, leading to a much better performance in terms of tar mitigation and agglomeration.