Degree Type

Thesis

Date of Award

2009

Degree Name

Master of Science

Department

Mechanical Engineering

First Advisor

Robert C. Brown

Abstract

Two sets of gasification experiments were performed in an effort to understand the fate of biomass nutrients and the effects of feedstock potassium on carbon conversion during gasification. The purpose of this research was to develop a comprehensive understanding of the issues of sustainability and efficiency facing biomass gasification. The results of these studies are described in detail within this thesis. The first study evaluated the fate of biomass nutrients in an integrated system of biomass production and gasification. Eight plots of switchgrass were grown and harvested for use in this study. Four plots were fertilized with 65 kg ha-1 of nitrogen (N) and four plots were not fertilized. Three essential biomass nutrients N, phosphorus (P), and potassium (K) as well as carbon (C) were individually tracked through a fluidized bed gasifier and subsequent gas clean up equipment. Mass balances were performed on each element to determine the percentage of that element that was able to be accounted for and the percentage that was able to be recovered in a form suitable for use as a soil amendment. The percentage of C recovered in a form suitable for field sequestration was independent of fertilizer N input and represented 13y1% (meanySD) of switchgrass C. Recovery of N in a form suitable for soil amendment was 55y7% of switchgrass N and was also independent of fertilizer N. The percentages of P and K recovered in forms suitable for soil amendment were both higher for the fertilized treatment of switchgrass than the unfertilized treatment. Recovery of P in a form suitable for soil amendment was 73y21% for the unfertilized treatment and 104y24% for the fertilized treatment. Likewise for K, recovery percentages for unfertilized and fertilized treatments were 61y9% and 71y9% respectively. The second study investigated the role of potassium and reaction temperature on carbon conversion during air blown fluidized bed gasification. To accomplish this, corn fiber, a low potassium biomass, was doped with varying amounts of potassium chloride and gasified at different temperatures. A statistical design of experiments consisting of 12 experiments was completed. Mass balances were performed and carbon conversion was determined. The results were used to generate a statistical model that was subsequently analyzed. The model predicted maximum carbon conversion for a feedstock potassium content of 1.85 wt% K and a bed temperature of 817 yC. The model also showed that carbon conversion was affected more by changes in bed temperature than changes in feedstock potassium content over the range of operating conditions used in this study. The observation that carbon conversion decreased above 817 yC was surprising but may be the result of increased volatilization of K, which would decrease the amount of K in contact with gasifying biomass. The apparently negligible effect of feedstock K on carbon conversion could be due to the potency of K as a gasification catalyst at concentrations as low as 0.3 wt%.

DOI

https://doi.org/10.31274/etd-180810-994

Copyright Owner

Patrick Marshall Meehan

Language

en

Date Available

2012-04-30

File Format

application/pdf

File Size

91 pages

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