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Gasification of bio-oil and bio-oil/char slurry Sakaguchi, Masakazu

Abstract

Economic utilization of biomass as a fuel has been limited by transportation cost. One suggested remedy to address the problems of processing biomass on a large scale is to pyrolyze solid biomass at numerous local sites and transport the resulting liquid or liquid/char slurry to a large centralized conversion plant. This research involves the gasification of biomass fast pyrolysis oil, so called bio-oil, and a slurry mixture of bio-oil and fast pyrolysis char into synthesis gas. Kinetics of the reaction of steam with chars was studied using a thermo-gravimetric analyzer. Slurry Char was produced by pyrolysis of an 80 wt% bio-oil/20 wt% char mixture at nominal heating rates of 100–10,000°C/s. The resulting Slurry Char was subjected to steam gasification with 10–50 mol% steam at 800–1200°C. Reactivity of the Slurry Chars increased with the pyrolysis heating rate, but was lower than that of Original Chars. Kinetic parameters were established for a power-law rate model. Some measurements were initially done of gasification in CO₂. A fluidized bed reactor, equipped with an atomization system, was constructed for gasification of bio-oil and slurry. The reactor contained either sand, or Ni-based catalyst. Experiments included gasification with pure steam and air. Effects of bed temperatures in the range 720–850°C, steam-to-carbon molar ratios of 2.0–7.5, and air ratios of 0–0.5 on gas composition and yields were tested. The carbon conversion of bio-oil to gas was found to be greater than that of slurry. The product gas composition was affected significantly by catalysis of the water-gas shift and the steam gasification. Greater yields of hydrogen and lesser yields of CO and hydrocarbons were found when catalyst was used. On a dry, inert-free basis, gases of up to 61% H₂ were obtained. The data were compared with a thermodynamic equilibrium model. The product gas yield was reasonably predictable by the model. A mass and energy balance model of steam gasification in a dual-bed gasifier-combustor revealed that energy requirements are sensitive to the steam/carbon ratio and to the recovery of latent heat in the produced gas.

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