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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-421-2

International Heat Transfer Conference 15
August, 10-15, 2014, Kyoto, Japan

Effect of Temperature and Porosity Change on Numerical Analysis of CO2 Absorption Behavior in Porous Solid Sorbent Using the Unreacted-Core Model

Get access (open in a dialog) DOI: 10.1615/IHTC15.pmd.009347
pages 6761-6771

Résumé

Lithium ortho-silicate (Li4SiO4, LS) is one of the high-temperature solid sorbents for CO2 capture. The CO2 absorption capacity of the LS sorbent is equivalent to about 30wt% of the sorbent mass at temperatures around 600 oC and is accompanied by an exothermic reaction. At temperatures above 700 oC the sorbent is regenerated with the release of the captured CO2 in an endothermic reaction. CO2 absorption reactors packed with porous, spherical pellets of LS show unsteady temperature distribution and capture ratio behavior owing to the unsteady CO2 absorption rate and highly exothermic process. The CO2 absorption rate of this sorbent depends on temperature, CO2 concentration, and CO2 accumulation (expressed as the weight change of the sorbent). In previous studies the detailed mechanism of CO2 absorption by LS sorbents including the mass transport mechanism have been discussed. We proposed the modified unreacted core model to simulate the mechanism of CO2 absorption by a porous, spherical pellet. However, the model only simulated CO2 absorption behavior well for the initial absorption. The model was limited in its efficacy because the heat transfer of the particle was not considered in the CO2 absorption calculation, and because the porosity changes over time due to the formation of the product layer. In this study, we conducted numerical analyses combining unsteady mass and heat transfer equations applying the temperature-dependent parameters and proposed a modified model for porous sorbent to account for the decreasing porosity with CO2 absorption. The analytical result showed that the temperature distribution in a particle was nearly homogeneous under the conditions 10% CO2, 550oC and the porosity change was the dominant factor causing the decrease in the absorption rate for conditions below 20% CO2.