(505f) CO2 Capture by Moving Bed Temperature Swing Adsorption

An “end-of-pipe” process has been developed to capture carbon dioxide (CO2) from flue gas from coal-burning power plants, cement plants, and the like. It will treat flue gas immediately after the fly ash is removed. The presence of minor amounts of fly ash, however, should not pose a serious problem. The process uses temperature swing adsorption (TSA), and it uses the heat contained in the flue gas to drive-off the enriched CO2 from the adsorbent. The keys to performance are: the flue gas temperature and the CO2 concentration, which are related to the available heat and the required heat, respectively. Together, they dictate whether the heat contained in the flue gas is sufficient to drive the separation. In contrast, scrubbing requires about 30% of the gross output of a power plant's steam in order to regenerate the absorbent; hence, the need for parasitic energy is enormous.

Our TSA process has been evaluated via experiments and computer simulations. They revealed important parameters, e.g, the amount of adsorbent required and the size of the equipment, which represent the majority of the capital cost. Adsorbent attrition is of minimal concern on account of features that allow less breakage and friction than for other moving bed designs, and a device by which adsorbent fines (if they occur) can be continuously removed. Our TSA process tests showed that both high CO2 purity (99%) and high recovery (89%) are possible. Additional tests with CO2, H2O, and SO2 showed no signs of adsorbent breakdown. The design is modular, i.e., the system will be comprised of dozens of identical parallel units, amenable to shut-down of portions for maintenance, without adversely affecting the processing capacity of the remainder. A patent application has been filed.