2006 Volume 114 Issue 1333 Pages 739-742
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.