Gasification of Wood and Torrefied Wood with Air, Oxygen, and Steam in a Fixed-Bed Pilot Plant

Abstract

In this work, the efficiency of the updraft gasification of different biomass was analyzed using a 20 kg/h pilot facility. Eucalyptus wood chips, torrefied Eucalyptus wood chips, and torrefied Spruce chips were investigated. Absolute air, mixes of air with steam, and mixes of pure oxygen with steam were used as gasification media. The direct comparison between the parental and torrefied biomass emphasizes the positive effect of this pretreatment on syngas properties and plant performances. Typically, the use of torrefied feedstock resulted in a reduction to about 1/5 of the tar load in the syngas and in 44% increment of the thermal power of the plant when compared to the performances obtained with the parental wood. The introduction of steam as co-gasifying stream was effective to avoid hot spots inside the reactive bed and to stabilize the process. Moreover, the use of steam positively affected the molar ratio of H2/CO that reached the value of 1.17 with the H2 concentration in the syngas of 39 vol %. The cold gas efficiency was 0.85 with torrefied biomass and pure oxygen with steam (0.82 when taking into account the energy for steam production), whereas the use of parental wood in similar conditions gave a value of 0.67 (net of 0.65). The treatment capacity of the plant was directly proportional to the reactivity of the feedstock as assessed by thermogravimetric analysis when the feed was reported as volumetric flow.