CO₂ capture at ambient temperature in a fixed bed with CaO-based sorbents

This work investigates post-combustion CO₂ capture at ambient temperature in a fixed bed by means of CaO-based sorbents. Two sorbents were used: limestone and pellets prepared from powdered limestone using calcium aluminate cement as a binder. The results showed that pre-hydration had a significant effect on CO₂ capture performance of the two sorbents. For instance, after 8h pre-hydration, the breakthrough time increased from 21min to 660min for lime, and from 19min to 750min for pellets. The performance of pellets was more sensitive to hydration conditions than for the lime. At breakthrough, full carbonation conversion over half of the reactor was achieved in a pre-hydrated bed of pellets exposed to a feed with 0.5% CO₂, resulting in an average specific capture of 0.51gCO₂/gbed material. This was considered a sufficient capture performance, with a distinct mass transfer zone (MTZ) located in the upper half of the reactor. However, increasing CO₂ inlet concentration to 2% shortened the breakthrough time and shifted the MTZ toward the entrance zone of the reactor. It was concluded that capturing CO₂ from low-CO₂ flue gases at ambient temperature using a fixed bed of pre-hydrated CaO-based pellets is a promising approach that has the potential to achieve reasonable capture performance at relatively low cost. The proposed process can be used for CO₂ capture from CO₂-depleted flue gases (residual CO₂) from processes such as amine scrubbing and calcium looping. And it would allow for the possibility that capture could be increased to any given level required by new legislation for plant with carbon capture.