Date on Master's Thesis/Doctoral Dissertation

5-2015

Document Type

Master's Thesis

Degree Name

M. Eng.

Department

Mechanical Engineering

Committee Chair

Sharp, Michael Keith

Committee Co-Chair (if applicable)

Park, Sam

Committee Member

Berson, Robert E. (Eric)

Author's Keywords

Hydrogen-chlorine fuel cell; Solar energy conversion; Thermochemical energy storage; Renewable energy; Vanadium trichloride; Vanadium-chloride cycle

Subject

Solar energy; Energy storage; Fuel cells; Energy conversion

Abstract

As annual energy consumption grows, developing renewable solar energy conversion systems, storage systems, and high density electrical energy production systems is growing increasingly important. The proposed system utilizes vanadium trichloride thermal decomposition to produce chlorine gas and vanadium dichloride. A second reaction combines gaseous hydrogen chloride and the product vanadium dichloride to reform vanadium trichloride and produce hydrogen gas. Hydrogen gas and chlorine gas can be stored indefinitely and electrical energy is obtained from the chemicals by a non-humidified dry membrane hydrogen – chlorine fuel cell. The fuel cell produces the gaseous hydrogen chloride needed to reform vanadium trichloride. The cycle operates in a closed loop where vanadium trichloride is recycled. Chemical equations and reaction kinetics are discussed for vanadium trichloride decomposition and synthesis. TRNSYS 16 software was used to evaluate the efficiency of the solar collection cycle with an SES parabolic dish Stirling collector in Louisville, KY and Phoenix, AZ. Thermodynamic calculations for the chemical reactions were performed. A dry membrane hydrogen – chlorine fuel cell model was developed from both theoretical calculations and experimental data (Liu, Zhou et al. 2013). The system efficiency was evaluated for two fuel cell current densities of 0.039 A/cm2 and 0.085 A/cm2. The potential efficiency of the vanadium trichloride cycle was compared to efficiency values for thermal energy storage (TES), compressed air energy storage systems (CAES), vanadium flow battery (Battery), pumped hydro electrical storage (PHES), and thermochemical ammonia storage (NH3), evaluated by Shakeri, et al. (2014). All systems, with the exception of the vanadium trichloride system, used a Stirling engine for electric energy production. Short – term storage system efficiency, cumulative system efficiency, and long – term energy storage system efficiency were compared for each storage system. The analysis found that the vanadium trichloride cycle offers a significant advantage over other storage systems. The highest efficiency obtained was 39.3%, which was significantly higher than TES systems at 22.8% and the NH3 system at 19.3%. Despite the difference in climate, system efficiency was decreased by only 1.3% in Louisville, KY when compared to Phoenix, AZ. The efficiency difference was due to a lower collector and receiver efficiency in Louisville than in Phoenix. In addition, the vanadium trichloride system had a lower efficiency of energy to storage than both the TES and NH3 cycles. Energy production from the vanadium trichloride system remained more efficient due to the high efficiency of the hydrogen – chlorine fuel cell, giving the vanadium trichloride system the overall advantage. A comparison of the long – term energy storage efficiency of the systems showed that the vanadium trichloride system had a significant advantage over other storage and energy production systems. After seven months of continuous energy storage, the TES system efficiency reduced to 0.58%, the NH3 system efficiency reduced to 18.7%, and the vanadium trichloride system efficiency reduced to 38.1%. The ability to store energy for long periods of time with low losses gives the vanadium trichloride system a significant advantage.

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