Strategies for CO2 capture from different CO2 emission sources by vacuum swing adsorption technology☆

Different VSA (Vacuum Swing Adsorption) cycles and process schemes have been evaluated to find suitable process configurations for effectively separating CO₂ from flue gases from different industrial sectors. The cycles were studied using an adsorption simulator developed in our research group, which has been successfully used to predict experimental results over several years. Commercial zeolite APGIII and granular activated carbon were used as the adsorbents. Three-bed VSA cycles with- and without-product purge and 2-stage VSA systems have been investigated. It was found that for a feed gas containing 15% CO₂ (representing flue gas from power plants), high CO₂ purities and recoveries could be obtained using a three-bed zeolite APGIII VSA unit for one stage capture, but with more stringent conditions such as deeper vacuum pressures of 1-3 kPa. 2-stage VSA process operated in series allowed us to use simple process steps and operate at more realistic vacuum pressures. With a vacuum pressure of 10 kPa, final CO₂ purity of 95.3% with a recovery of 98.2% were obtained at specific power consumption of 0.55 MJ·(kg CO₂)^-1 from feed gas containing 15% CO₂. These numbers compare very well with those obtained from a single stage process operating at 1 kPa vacuum pressure. The feed CO₂ concentration was very influential in determining the desorption pressure necessary to achieve high separation efficiency. For feed gases containing >30% CO₂, a singlestage VSA capture process operating at moderate vacuum pressure and without a product purge, can achieve very high product purities and recoveries.