Abstract
Tar compounds have been defined as Achilles’ heel in biomass gasification. Catalytic reforming solves problems caused by tar by converting them into H2 and CO. Most of the research has focused on secondary and tertiary tar reforming while some information on primary tar can be derived from bio-oil reforming. However, these studies use humidified N2, Ar or He as gas carrier. Therefore, in this work, three catalysts are compared for reforming 40 g/Nm3 acetic acid as main primary tar compound from biomass updraft gasification using simulated biosyngas as gas carrier. The catalysts were tested over a 72 h period between 680 and 750 °C with a gas composition of 35.0 vol% H2O, 2.3 vol% CO, 19.5 vol% CO2, 3.6 vol% CH4, 24.0 vol% H2 and 15.6 vol% N2. Olivine completely converted acetic acid, but a considerable amount of carbonaceous deposits was found on the catalyst and the catalytic activity decreased over time with 0.2 g/Nm3 hydroxyacetone measured in the last day of testing. Dolomite showed promising performances by completely converting acetic acid and accumulating carbonaceous deposits only in the low temperature part of the catalyst bed. The carbonaceous deposits could be suppressed increasing the steam content to 50.1 vol% and the temperature to 900 °C. However, the catalyst became excessively brittle. The metal-based catalyst out-performed the naturally-occurring catalysts by completely converting acetic acid with almost no carbonaceous deposits accumulation. These results are expected to help the further development of tar reformers, and the commercialisation of biomass updraft gasifiers based systems.
Highlights
Biomass gasification has attracted considerable attention as a tech nology to reduce environmental pollution and to face the steady increase in the world heat and power consumption
Olivine completely converted acetic acid, but a considerable amount of carbonaceous deposits was found on the catalyst and the catalytic activity decreased over time with 0.2 g/Nm3 hydroxyacetone measured in the last day of testing
The goal of this study was to evaluate in a labscale reactor the ability of olivine, dolomite and a metal-based catalysts to reform acetic acid and its thermal decomposition products using simulated biosyngas as gas carrier
Summary
Biomass gasification has attracted considerable attention as a tech nology to reduce environmental pollution and to face the steady increase in the world heat and power consumption. Biosyngas contains minor concentra tions of species that might damage downstream equipment. These contaminants include nitrogen compounds (NH3 and HCN), sulfur compounds (H2S), halides (HCl), particulate matter (carbon and solid metals), and tar (e.g., toluene and naphthalene). Milne et al defined tar as the organic compounds, largely aromatic, released during pyrolysis or gasification of any organic material [2]. The first step starts at 200–500 ◦C, with the conversion of cellulose, hemicellulose and lignin to oxygenated hydrocarbons called primary tar. When the temperature is increased above 800 ◦C, part of the secondary tar converts to polycyclic aromatic compounds, called tertiary [2]
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