Selective CO2 capture using solid sorbents: theoretical study

MARÍA LAURA RODRÍGUEZ; BORIO, DANIEL

Conferencia; World Online Conference on Sustainable Technologies; 2022

Carbon capture can be very important in the production of hydrogen fromfossil fuels and the generation of synthetic fuels starting from CO2 capturedand renewable hydrogen. CO2 capture systems in post-combustion processes,such as the treatment of exhaust gas from NGCC plants, are based onchemical absorption/desorption cycles. The most widely investigatedtechnologies correspond to absorption with liquid solvents (especially amine-based), solid absorbents and membranes, among others [1]. Processes basedon solid sorbents constitute an efficient separation technology for CO2 capture,especially for high-temperature applications [2], such as NGCC plants. Inparticular, lithium orthosilicate (Li4SiO4) is considered a promising material forhigh temperature capture applications, due to its good CO2 capture capacity(up to 36.7 wt%) and lower regeneration temperature (< 750 °C), in additionto its high cyclic and thermal stability [3]. When Li4SiO4 is exposed to a gasstream containing CO2 at suitable temperatures, the following exothermic andreversible gas-solid reaction takes place:Li4SiO4 (s) + CO2 (g)  Li2SiO3 (s) + Li2CO3 (s) Eqn.1The bed configuration for the absorbent system has a great influence on theefficiency of the process. The most studied configurations have been fixed bed,fluidized bed and moving bed [4]. Although fluidized beds offer some inherentadvantages of better gas-solid contact over fixed beds, vigorous agitation ofabsorbent particles could damage them. For absorbents that do not withstandfluidized bed conditions, fixed beds can be used. Efficient heat management inthe bed is a priority in these cases. Before the saturation of the column occurs,the operation must be interrupted to carry out the CO2 desorption, whichallows the regeneration of the solid. To achieve continuous operation, theprocess must be carried out cyclically, using several columns in parallel.In the present contribution, the CO2 capture process in a fixed-bed columnpacked with spherical particles of lithium orthosilicate is analysed. To simulatethe column behaviour, a one-dimensional, isothermal, non-steady state modelis used, coupled at particle level with the unreacted shrinking core model torepresent the gas-solid reaction.