Thermal design and management towards high capacity CO₂ adsorption systems

One of the most immediate technologies to mitigate the emission of carbon dioxide is carbon capture and storage. This study investigates different thermal design alternatives to increase the capacity of adsorption system given a desired cycle time. This is equivalent to investigating the reduction of the cooling and heating times during the adsorption and desorption processes, respectively. The thermal design investigation involves the variation of bed aspect ratio, the option of using water as a coolant, and augmenting the bed by fins with varying length and pitch. Mg-MOF-74 is used as adsorbent since it shows high CO₂ uptake at flue gas conditions. An experimentally validated CFD model is implemented by using user-defined-function (UDF) linked to the ANSYS Fluent program. Results show that rising the bed aspect ratio from 2.8 to 41.6 improves the CO₂ uptake by 13% and reduces the desorption period to the third. Additional improvement in the CO₂ uptake (10.9–13.6%) can be obtained by cooling and heating the bed by water as a function of the bed aspect ratio. The improvement jumps to 22.2% if fins are used to augment the heat transfer rates in the bed. The optimal CO₂ uptake enhancement (35.2%) is achieved by using finned annular-pipe (fin-pitch is 12.5 mm) as the adsorbent bed with water cooling. This design methodology can be adopted to other adsorption systems, including solar-driven adsorption chillers and solar-driven adsorption desalination systems.