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Title:
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The Effect of Equivalence Ratio on the Gasification of Torrefied and Un-Torrefied Biomass – Miscanthus x giganteus
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Author(s):
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Published by:
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Publication date:
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ECN
Biomass & Energy Efficiency
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27-2-2015
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ECN report number:
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Document type:
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ECN-W--15-007
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Article (scientific)
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Number of pages:
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8
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Abstract:
Torrefaction is a thermal pre-treatment process to improve the properties of biomass prior to gasification. It involves heating the biomass between 200°C and 300°C under an inert atmosphere. Water and some light volatiles are released during this process; the hygroscopic biomass is rendered hydrophobic which makes it more convenient for long distance transport and long-term storage. The process also reduces the quantity of chemically bound oxygen in the biomass and so is suggested to improve the performance of the product material when gasified.
In order to investigate this proposition, torrefied and un-torrefied Miscanthus x giganteus (MxG) was gasified in a pilot scale electrically heated air-blown bubbling fluidized bed gasifier using olivine ((Mg, Fe)2SiO4) as the bed material. The influence of a series of initial conditions on the gas composition were parameterised by measurement of biomass (93-153.5 kg/m2/hour) and air flow rates (110.3-234.9 kg/m2/hour) corresponding to equivalence ratios of 0.18–0.32 (0.5 equates to 50% of stoichiometric oxygen) at a bed temperature of 800°C. At steady state operation, the flow rate of product gas obtained, and its fraction compositions of N2, CO, CO2, CH4, H2 ethylene, ethane and acetylene was determined by gas chromatographic. From this data, the corresponding higher heating value of the produced gas was calculated. In addition, from compositional information of the Miscanthus starting material, carbon and hydrogen conversion efficiencies were determined.
In order to understand any advantage arising from the torrefaction process, the experimental data set was further compared to the equivalent data we had previously reported in Xue et al. [1] for torrefied Miscanthus. This comparison shows that for fluidized bed gasification the yield of gas produced and hydrogen conversion are slightly higher for torrefied MxG, but the heating value and carbon conversion efficiency is higher for un-torrefied Miscanthus.
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