The ability to carry out pyrolysis of entire wood chips and rods instead of small particles would be of great value for mobile pyrolysis units, because of the large possible savings in grinding costs (7-9 % of total process costs). With this goal in mind, we designed and constructed a novel lab-scale ablative reactor for fast pyrolysis of entire wood chips and even wood rods, converting those directly into a high yield of bio-oil for the first time. The bio-oil yield from fast pyrolysis of wood chips (10 × 20 mm) was as high as 60 wt. %, similar to that from wood crumbles (2 × 2 mm). Additionally, the yield and composition of bio-oil from ablative pyrolysis were in the same range as those obtained from a fluidized bed reactor using < 1 mm particles, with the small differences (slightly lower yield and HHV, and higher water content) attributed to the longer vapor residence times in the ablative reactor, which promote secondary reactions. We modeled the heat transfer characteristics of this semi-batch system, and comparison with experimental measurements confirmed that radiation from the hot components does not significantly decompose the wood prior to direct contact with the hot metallic surface in ablative pyrolysis. The findings of this work have the potential to lead to new developments for small-scale, mobile pyrolysis units for the disposal of forest residues.
We pyrolyzed entire wood chips (5×15 mm) in a new ablative reactor with the goal to evaluate the possibility to minimize grinding costs before pyrolysis. The effects of the operating parameters on the product yields and composition were investigated. Our results revealed that the bio‐oil yield in the ablative reactor was favored at a moderate pyrolysis temperature of 500 °C, low initial thickness of the wood chips layer (≤5 mm), low applied pressure on the wood chips (≤0.5 bar), and with the rotation of the bowl (≥100 rpm). The temperature profile of the wood chips indicated that the ablative pyrolysis of thick layers is limited strongly by heat transfer rates. The maximum bio‐oil yield obtained was approximately 60 wt %. The bio‐oil elemental composition was determined mostly by its water content and that of char was affected primarily by the temperature. The knowledge of how operating conditions affect the ablative process can be used in the design of continuous mobile pyrolysis units in the future.
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