Effects of feed composition and gasification parameters on product gas from a pilot scale fluidized bed gasifier
Abstract
Scope and Method of Study: Biomass gasification is an integral part of a holistic project where low-value feedstocks are converted into ethanol via a gasification fermentation process. Because microbial catalysts are used in the fermentation process, it is vital to know the product gas characteristics. In addition to carbon monoxide, hydrogen, and carbon dioxide utilized in the bioconversion process, potentially toxic tar compounds are present and must also be evaluated. In this study, a 10-inch diameter, fluidized bed gasifier was operated in three gasification modes: air, flaming pyrolitic and steam. Switchgrass, bermudagrass, and corn gluten have been gasified at equivalence ratios from 0.0 to 0.35 and steam-tobiomass ratios of 0.4 to 1.25. At each operating condition, synthesis gas and tar compositions were measured. A Gibbs reactor equilibrium model of gas, tar and char compounds was developed for each gasification mode. Findings and Conclusions: As expected, steam gasification generated significantly higher levels of carbon monoxide and hydrogen compared to the air gasification modes. At steam-to-biomass ratio of 1.0, product gas measured over 30 mol% carbon monoxide and 35 mol% hydrogen. Results also showed quantitative and qualitative variations in tars, consisting of over 210 compounds, depending on the feedstock and reactor operating conditions. Of all three biomasses, switchgrass exhibited the highest gas compositions and lowest tar concentrations. High ash content in bermudagrass and corn gluten induced bed agglomeration at reactor temperatures above about 800°C. Steam gasification of corn gluten showed gas results equivalent to those of switchgrass. Tar atomic composition was constant at C7.55H8.62O0.37N0.20 over the range of 700 to 800°C reactor bed temperatures. Gibbs reactor equilibrium modeling showed tar levels were mostly influenced by unreacted carbon.
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- OSU Dissertations [11222]