CO2 capture capacity of CaO in long series of pressure swing sorption cycles

One promising method for the capture of CO2 from point sources is through the usage of a lime-based sorbent. Lime (CaO) acts as a CO2 carrier, absorbing CO2 from the flue gas (carbonation) and releasing it in a separate reactor (calcination) to create a pure stream of CO2 suitable for sequestration. One of the challenges with this process is the decay in calcium utilization (CO2 capture capacity) during carbonation/calcination cycling. The reduction in calcium utilization of natural limestone over large numbers of cycles (>250) was studied. Cycling was accomplished using pressure swing CO2 adsorption in a pressurized thermogravimetric reactor (PTGA). The effect of carbonation pressure on calcium utilization was studied in CO2 with the reactor operated at 1000 degrees C. The pressure was cycled between atmospheric pressure for calcination, and 6, 11 or 21 bar for carbonation. Over the first 250 cycles, the calcium utilization reached a near-asymptotic value of 12.5-27.7%, depending on the cycling conditions. Pressure cycling resulted in improved long-term calcium utilization compared to temperature swing or CO2 partial pressure swing adsorption under similar conditions. An increased rate of de-pressurization caused an increase in calcium utilization, attributed to fracturing of the sorbent particle during the rapid calcination, as observed via SEM analysis. (C) 2010 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.