Allothermally Heated Reactors for Solar-Powered Implementation of Sulphur-Based Thermochemical Cycles

Abstract

Catalytic sulphur trioxide splitting is the highest-temperature (650-950oC), endothermic step of several sulphur-based thermochemical cycles targeted to production of hydrogen or solid sulphur. Concentrated solar power tower plants are an attractive renewable energy source to provide the necessary heat. Furthermore, the development of solar receivers capable of delivering solid or gaseous heat transfer fluids at these temperature ranges enable the implementation of such endothermic reactions in allothermally-heated reactors/heat exchangers placed away from the solar receiver. In this context, a 2-kW laboratory-scale shelland-tube reactor/heat exchanger to perform thermal sulphuric acid decomposition and catalytic sulphur trioxide splitting was in-house designed, built and tested with electrically heated bauxite particles, in the perspective of eventually coupling such a reactor with a centrifugal particle solar receiver. Thermal test runs demonstrated the in-principle feasibility of the concept. The temperatures reached were sufficient to ensure complete sulphuric acid evaporation. However, the ones in the SO3 splitting zone were of the order of 750°C, high enough to demonstrate SO3 splitting but not reaching the levels required for close-toequilibrium conversion of the Fe2O3 catalyst system used (~ 850oC). An improved version of the reactor is under construction incorporating design modifications based on lessons learned from the test campaigns, in the perspective of scaling up the process.