198. SOLAR THERMOCHEMICAL HYDROGEN PRODUCTION PLANT DESIGN
Name: Jesse Littlefield
Grad Year: 2012
A plant was designed that uses a solar thermochemical water-splitting cycle for the production of hydrogen. Hydrogen is useful as a fuel for stationary and mobile fuel cells. The chemical process simulator Aspen Plus was used to model the plant and conduct simulations. The process utilizes the electrolytic oxidation of aqueous ammonium sulfite in the hydrogen production half cycle, and the thermal decomposition of molten potassium pyrosulfate and gaseous sulfur trioxide in the oxygen production half cycle. The reactions are driven using solar thermal energy captured from a heliostat mirror array focused on a receiver. The reactions for the cycle are listed below: Hydrogen Production Half Cycle: SO2(g) + 2 NH3(g) + H2O(l) → (NH4)2SO3(aq) (NH4)2SO3(aq) + H2O(l) → (NH4)2SO4(aq) + H2(g) Oxygen Production Half Cycle: (NH4)2SO4(aq) + K2SO4(l) → 2 NH3(g) + K2S2O7(l) + H2O(g) K2S2O7(l) → SO3(g) + K2SO4(l) SO3(g) → SO2(g) + 0.5 O2(g) The plant's feed stream is water and the two product streams are hydrogen and oxygen; all other materials are contained within the plant. The model is for full-scale operation that would generate 133,333 kg of hydrogen per day, which is equivalent to 185 MW on a lower heating value basis. Thermodynamic properties of chemical species obtained from literature, and from laboratory experiments conducted in another part of this project, were entered into the model to improve its accuracy. Design specifications were placed in strategic areas of the model to aid in the convergence of the model. Model convergence is challenging to obtain because of the many material and energy recycle loops within the plant. Calculator blocks were utilized to obtain power requirements for the electrolyzer and efficiencies of the entire plant based on definitions from the Department of Energy, which funds this project. Results from this work will aid in the design of a large-scale hydrogen production plant.