Microwave Swing Adsorption for post-combustion CO2 capture from flue gases using solid sorbents
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In recent years, there has been an increasing global interest in carbon dioxide capture and storage (CCS) as an important technology for climate change mitigation. However, improved technologies for the CO2 capture process that could possibly lead CCS to be highly competitive against the renewable energy market, are necessary. The evaluation of a CO2 capture system is often driven by energy demands and in adsorption technology this energy is particularly required for the desorption step. As a result, efficient regeneration systems ensuring multiple re-use of adsorbent materials, while minimizing energy use, are required, in an attempt to replace the conventional PSA (Pressure Swing Adsorption) and TSA (Temperature Swing Adsorption) technologies. This study presents and analyses a relatively new approach for CO2 sorbent regeneration, namely Microwave Swing Adsorption (MSA). The aim of this research is to intensify the CO2 desorption process from solid materials, focusing on improving the regeneration efficiency and kinetics as well as the energy spent during this step. The hypothesis that the direct absorption of energy during microwave heating by the solid adsorbent may enable a fast process with a low purge gas flow rate low desorption temperature resulting in low energy demands, is examined. However, MSA depends on numerous parameters, divided in two main categories, namely process parameters (flue gas composition, desorption temperature, moisture presence, gas flow rate) and material parameters (adsorbent shape and size, porosity, surface modifications, dielectric properties). To this regard, an extensive investigation of the above criteria and their connection with the performance of the MSA system is studied. In terms of the adsorption step, it was found that a switch to higher total flow rates results in an increase in the CO2 adsorption capacity of the GAC. Moreover, moisture presence also enhances the CO2 adsorption, as a result of an increase in the total flow rate and in the adsorption temperature. With regards to the desorption step, it was shown that MSA technology leads to enhanced performance efficiency of the sorbent by ~10%, while preserving its porous structure. Moreover, the regeneration time and the energy consumption were also considerably reduced (30% and 40%, respectively), for MSA compared to TSA.