Semester

Fall

Date of Graduation

2023

Document Type

Thesis

Degree Type

MS

College

Statler College of Engineering and Mineral Resources

Department

Mechanical and Aerospace Engineering

Committee Chair

Edward M. Sabolsky

Committee Member

Andrew C. Nix

Committee Member

Fernando V. Lima

Abstract

Due to the intermittent nature of renewable energy and the rigid operation of existing coal plants, the need for flexible power generation technology is eminent. Hybrid energy systems have shown potential for flexible, grid following dynamics while maintaining higher efficiencies. The work below focuses on the performance analysis of a proposed 100 kW pressurized Internal Combustion Engine (ICE) and Solid Oxide Fuel Cell (SOFC) hybrid system. The un-utilized fuel from the SOFC stack provided the chemical energy to operate the engine. A turbocharger was used to deliver the necessary air flow for both the stack and engine. An external reformer was utilized to provide fuel syngas to the fuel cell stack. Four alternative SOFC/ICE cycles were presented and analyzed. All components of the four cycles were numerically modeled using two different software. The SOFC and reformer were simulated using a 1-dimensional model written in MathWorks ® MATLAB/Simulink. The IC engine and balance of plant (BOP) model was developed using STEAG EBSILON® Professionals. These models were developed to evaluate several options for heat recovery and the anode exhaust cooling before feeding into the engine. The study was conducted by variating fuel utilization and anode methane content through reformer operating temperature, ranging from 70 to 90% and 600 to 1000 K, respectively. Additionally, a study on the effects of anode off-gas recirculation was conducted by variating the recirculation rate between 0, 25 and 70%. Furthermore, current density effects were analyzed when operating the stack at 0.2, 0.4, and 0.55 A/cm2 . At each design point, hardware was re-sized to 4 match the desired conditions. The cycle performance and fuel cell distributed profiles are discussed. Results indicated that both the stack and engine are thermally disconnected thus behaving as topping and bottoming cycles. The highest efficiency attained was 62% at a reformer operating temperature of 800 K and 90% fuel utilization. An optimal balance was found when the thermal load required for on-anode reformation is well matched with the heat generated from the electrochemical hydrogen oxidation reaction across the fuel cell.

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