CO₂ Removal at High Temperature using Packed Bed of Lithium Silicate Pellets

Abstract

For the purpose of carbon dioxide (CO₂) capture at high temperatures, Toshiba developed a novel CO₂ absorbent, a lithium silicate (Li₄SiO₄). It shows an immediate CO₂ absorption and emission properties, which results in an obvious weight change of up to 36%. Since, in the case of Li₄SiO₄, CO₂ emission occurs at a considerably lower temperature than for a calcium oxide (CaO) absorbent, the reaction between Li₄SiO₄ and CO₂ is very reversible. The emission temperature in 101 kPa of pure CO₂ is ca. 800°C, whereas CaO absorbent requires a temperature of 950°C. Considering the practical use of this material as a CO₂ absorbent for power plants, a pellet-type absorbent is thought to be more realistic than a powder-type absorbent. Moreover, regarding the application to the system, the characterization of a reactor using Li₄SiO₄ pellets is required. This paper describes the removal efficiencies of a packed bed reactor using cylindrical pellets of Li₄SiO₄. In a gas flowing condition of 20 vol% CO₂, the reactor achieved 100% CO₂ removal at 500°C. Temperature dependence was also investigated. It is noteworthy that the reactor and gas stream were obviously heated during the CO₂ removal because of the exothermic reaction between the Li₄SiO₄ and CO₂. We believe that this phenomenon is one of the important findings to improve the energy penalty for CO₂ recovery.