Commissariat à l’Énergie Atomique (CEA) and General Atomics (GA) have undertaken a study to compare flowsheets for the sulfuric acid decomposition and hydrogen iodide decomposition sections of the Sulfur-Iodine cycle for producing hydrogen on a large scale. CEA uses ProSimPlus software, with a thermodynamics package based on Neumann’s model. GA uses the thermodynamic model of Mathias with Aspen Plus software.
Both CEA and GA use flowsheets based on the method of Ozturk for simulation of the sulfuric acid decomposition section. The sulfuric acid feed stream is dewatered in a series of flashes before entering a high-temperature series of reactors. Recirculation rates within the decomposition loop, temperature, and heat exchanger network all factor into the efficiency achieved.
Each party uses a reactive distillation scheme for decomposing hydrogen iodide into the product hydrogen. The feed stream containing water, iodine, and hydrogen iodide is preheated before entering a distillation column. The column bottoms product containing largely iodine is recycled to the acid-forming section for reuse. Water, hydrogen, and unreacted hydrogen iodide form the product from the top of the column. Hydrogen is separated and water and hydrogen iodide are recycled to the acid-forming section for reuse. The same factors affect efficiency as in the sulfuric acid decomposition loop, with the addition of heat pumps to maximize heat exchange.
This paper examines how differences in flowsheet design assumptions, thermodynamic models, and software algorithms can affect the outcome of the simulations. Conclusions drawn from the work have resulted in optimized flowsheets for both parties.