(230b) Sulfuric Acid Decomposition with Heat and Mass Recovery Using a Direct Contact Exchanger

Catalytic sulfuric acid decomposition to produce sulfur dioxide, oxygen, and water is one of the essential reactions for both the Sulfur-Iodine (SI) and Hybrid-Sulfur (HyS) hydrogen production thermochemical cycles. The reaction occurs at the highest temperature of these cycles, on the order of 850 C, which is the temperature of the products and undecomposed acid. The high temperature heat from the products is useful for other parts of the cycle. Ozturk et al. (1995) have proposed an elegant approach for recovering this heat from the product vapors, and simultaneously separating undecomposed acid for recycling through the reactor. In this approach, the reactor vapor effluent flows in a countercurrent direction to the colder input liquid acid solution. Because the two streams maintain their respective phases, no intervening thermally conducting barrier is needed to transfer heat and separate the streams. Thus the two streams may make contact directly without a barrier, which greatly enhances heat transfer. Furthermore, by allowing direct contact, unreacted acid vapors condense into the liquid stream and some water from the liquid stream vaporizes into the vapor stream. Both of these mass transfer operations help by concentrating the liquid acid input to the reactor and recycling unreacted acid. To ensure that the phases can be readily separated after contact, the liquid stream is not heated above the acid boiling point. In this presentation we report on laboratory-scale experiments that are designed to demonstrate the viability of direct contact exchange as part of the sulfuric acid decomposition section of a thermochemical cycle. Initial performance data are also presented. *Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.