Numerical modeling of a bayonet heat exchanger based reactor for sulfuric acid decomposition in thermochemical hydrogen production processes

Sulfur-based thermochemical hydrogen production cycles represent one of the most appealing options to produce hydrogen from water on a large scale. The Hybrid Sulfur is one of the most advanced thermochemical cycles. The high temperature section of the process, common to all sulfur-based cycles, operates the sulfuric acid thermal decomposition reaction at temperatures on the order of 800 degrees C. The paper shows and discusses the modeling results obtained for a bayonet heat exchanger based high temperature reactor that decomposes the sulfur compounds into sulfur dioxide and oxygen. A detailed transport phenomena model, including suitable decomposition kinetics, has been set up using a finite volume numerical approach. A preliminary configuration of the reactor, established based on process simulation results and on the initial reactor prototype developed at Sandia National Laboratory, has been examined and simulated. Results, obtained for a reactor driven by thermal power provided by helium flow, demonstrate the effective decomposition performance at maximum temperatures on the order of 800 degrees C and pressures of 14 bar. For a laminar flow configuration a sulfur dioxide production yield of about 28 wt% (with sulfur trioxide reduction from 69 wt% to approximately 33 wt%) has been achieved, representing decomposition rates practically equal to the corresponding equilibrium values. Limited pressure drops of approximately 2500 Pa have also been achieved in the sulfur mixture region. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.