Degree Name

Master of Science (MS)

Semester of Degree Completion

2014

Thesis Director

Jonathan P. Blitz

Abstract

In this study gasification of three different biomasses were performed to study the impact of process conditions and different feed stocks on final syngas composition. Final composition of the syngas determines the energy value of the resulting syngas and the suitability of syngas in chemical synthesis applications. Three kinds of feedstocks studied include switch grass pellets:wood chips 50:50 mixture, wood pellets:wood chips 50:50 mixture and wood pellets.

The effect of process conditions including temperature and feed stock composition on syngas composition were studied. Gas chromatography was used to analyze the final gas composition of syngas samples collected at five different temperature between 650 and 850 °C, in 50 °C intervals. A significant increase in CO and H2 was observed with increasing temperature which results in increasing energy values of syngas ranging from 4.60 to 6.30 MJ/Kg for wood pellets, and from 4.79 to 6.06 MJ/Kg for the grass pellets:wood chip mixture. Increasing temperature also has a significant influence in CO/H2 and CO2/(CO2 +CO) ratios which influences product selectivity in chemical synthesis. Different types of biomass also showed significant differences in gas composition. Differences in elemental composition, for example grass pellets contain high Na, K and Mg, and wood chips containing high Ca and Fe, can explain the increased H2 and CO2 content in the gasification of grass pellets:wood chips 50: 50 mixture. These metal elements may also enhance the water gas shift reaction which produces H2 and CO2 from H2O and CO. High moisture content found in grass pellets and the presence of relatively high amounts of metal elements may enhance the water gas shift reaction in the grass pellets:wood chips 50: 50 mixture. However high alkaline content along with high Si content forms clinkers which cause problems in gasifier operation.

Three kinds of thermal efficiency methods were used to evaluate the thermal efficiency of gasification of different types of biomasses: equivalence ratio method, elemental balance method and stoichiometric ratio method. From the results obtained, equivalence ratio method was predicted to be most suitable for the gasification system used in this study.

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