Date of Award

8-19-2011

Document Type

Thesis

Degree Name

Master of Science in Mechanical Engineering (MSME)

Department

Mechanical Engineering

Abstract

This thesis introduces a thermodynamic model of an external reforming SOFC coupled with a biomass-to-syngas reactor in order to calculate energy and power that can be extracted from the fuel. Some of this energy will be used for electrical work and some of this energy will be used to provide heat to the reactor to drive the endothermic reactions occurring throughout the process. We analyzed four different feedstocks for their fuel cell heat dissipation and fuel cell power characteristic: pure syngas, pure carbon-derived syngas, coal-derived syngas, and biomass-derived syngas. Pure syngas consists of only CO and H2 while the other three cases of syngas consist of CO, H2, H2O, CO2, and CH4. Pure syngas did not take the reactor into account.

The results of the analysis had shown that the absolute value of the Gibbs free energy of the fuel cell for pure syngas increased as the hydrogen concentration increased for temperatures above 1100 K. Opposite behavior occured for temperatures below 1100 K due to entropy change being less significant at lower temperatures. The results had also shown pure carbon-derived syngas to have the highest hydrogen concentration coming out of the reactor, which led to a higher Gibbs free energy of the fuel cell. This consequently led to a much higher maximum power density for any given temperature, followed by coal-derived syngas and biomass-derived syngas. Pure carbon-derived syngas also allowed the fuel cell to dissipate more heat than coal-derived syngas and biomass-derived syngas. Pure carbon was oxygen-free before the reactor and hydrogenrich after the reactor, thus allowing for high overall performance. High oxygen content hindered the performance of biomass-derived syngas, thus requiring the incorporation of de-oxygenation in the reactor. Coal gives higher overall performance compared to biomass at the expense of excess burning of air in the reactor and excess ash emission.

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