A particle receiver-driven thermochemical cycle employing elemental sulphur for solar thermochemical energy storage: investigation of proppants as concentrated sunlight har-vesting media and sulphur trioxide splitting catalysts

Abstract

The present work is part of an approach targeted on demonstrating a concentrated solar energy-driven thermochemical cycle employing solid elemental sulphur as a chemical energy vector and a seasonal solar energy storage medium. In exploring the concept of coupling this cycle to a centrifugal particle solar receiver, bauxitebased particles, commercial and composition-modified, were tested and validated with respect to their suitability for simultaneous operation as solar energy harvesting media and sulphur trioxide splitting catalysts. Long-term catalytic activity tests exceeding 1000 h of operation at 850 ◦C, demonstrated that properly composition-modified bauxite particles were capable of achieving stable SO3 conversion exceeding 70% (about 80% of equilibrium value under conditions studied) and exhibiting no or negligible loss of catalytic performance after this extended operation. In addition, such composition modification enhanced the particles’ solar irradiation absorptance, which resulted in substantially higher than that of their commercial, non-modified bauxite counterparts. Commercial bauxite particles on the other hand, demonstrated much better mechanical strength, flowability, and attrition- and thermal shock resistance together with measurable, yet lower catalytic activity, which deteriorated with prolonged on-stream exposure. The combined results obtained advocate for the eventual selection of an “allothermal” cascaded sulphur trioxide splitting/sulphuric acid decomposition reactor, containing a non-moving catalytic bed that is heated indirectly by a moving bed of high-temperature (≥900 ◦C) nonmodified commercial bauxite particles irradiated in the centrifugal solar particle receiver