Numerical Modeling of Bayonet-Type Heat Exchanger and Decomposer for the Decomposition of Sulfuric Acid to Sulfur Dioxide

Abstract

The growth of global energy demand during the 21st century, combined with the necessity to master greenhouse gas emissions, has led to the introduction of a new and universal energy carrier: hydrogen. The Department of Energy (DOE) proposed using a bayonet-type heat exchanger as a silicon carbide integrated decomposer (SID) to produce the sulfuric acid decomposition product sulfur dioxide, which can be used for hydrogen production within a sulfur–iodine thermochemical cycle. A two-dimensional computational model of SID having a boiler, superheater and decomposer was developed using GAMBIT and fluid. The thermal and chemical reaction analyses were carried out in FLUENT. The main purpose of this study is to obtain the decomposition percentage of sulfur trioxide for the integrated unit. Sulfuric acid (H2SO4), sulfur trioxide (SO3), sulfur dioxide (SO2), oxygen (O2), and water vapor (H2O) are the working fluids used in the model. Concentrated sulfuric acid liquid of 40 mol% was pumped into the inlet of the boiler and the mass fraction of concentrated sulfuric acid vapor obtained was then fed into the superheater to obtain sulfur trioxide. The decomposer region, which houses the pellets, placed on the top of the bayonet heat exchanger acts as the porous medium. As the decomposition takes place, the mass fraction of SO3 is reduced and mass fractions of SO2 and O2 are increased. The percentage of SO3 obtained from the integrated decomposer was compared with the experimental results obtained from Sandia National Laboratories (SNL). Further, effects of various pressures, flow rates, and acid concentrations on the decomposition percentage of sulfur trioxide were studied.