Simulation of decomposition of sulfur trioxide gas on a self-catalytic material

This thesis deals with the development of a two-dimensional numerical model to predict the wall-catalyzed homogeneous decomposition of sulfur trioxide gas in tubular component geometry for the production of hydrogen by the sulfur-iodine thermochemical water splitting cycle, a candidate cycle in the U.S. Department of Energy Nuclear Hydrogen Initiative. Cross flow type of heat exchanger concept is chosen for the analysis. The reacting fluid is a mixture of sulfur trioxide gas and water vapor inside the tubes of a heat exchanger. The heat exchanger tubes are made of Incoloy alloy 800H with ALFA-4 coated on the inner walls which acts as a catalyst for the chemical decomposition of sulfur trioxide into sulfur dioxide and oxygen. Decomposition of sulfur trioxide depends on many different parameters such as catalyst used, wall surface temperature, mole flow rate of the reacting mixture, diameter of the reactor tube, length of the reactor tube, operating pressure and inlet temperature of the reacting mixture. The effects of variation of wall surface temperature, diameter of the reactor tube, length of the tube and mole flow rate of the incoming mixture on the decomposition of sulfur trioxide were investigated using a two-dimensional numerical model using computational fluid dynamics (CFD) techniques. It is observed that smaller diameter reactor tubes, higher temperatures and lower flow rates allow having higher decomposition. Sulfur trioxide decomposition reaction in the presence of catalyst platinum is also analyzed using a three-dimensional numerical model where helium acts as a hot fluid that supplies thermal energy required for the endothermic sulfur trioxide decomposition reaction.