No abstract

Carbon dioxide removal from flue gas with a two-stage vacuum pressure swing adsorption (VPSA) process, which uses activated carbon (AC) beads as the adsorbent, was investigated both theoretically and experimentally. First, single-column VPSA experiments were studied for CO 2 /N 2 separation with high CO 2 feed concentration. Then, a two-stage VPSA process composed two columns for each stage was designed, and the effects of different parameters were investigated. The first-stage VPSA unit operates with a four-step Skarstrom cycle, which includes feed pressurization, adsorption, blowdown, and countercurrent purge with N 2 . For the second-stage VPSA process, a cycle with feed pressurization, adsorption, pressure equalization, blowdown and pressure equalization was employed. With the proposed two-stage VPSA process, a CO 2 purity of 95.3% was obtained with 74.4% recovery. The total specific power consumption of the two-stage VPSA process is 723.6 kJ/kg-CO 2, while the unit productivity is 0.85 mol-CO 2 /kg•h.

Vacuum pressure swing adsorption (VPSA) for CO 2 capture has attracted much research effort with the development of the novel CO 2 adsorbent materials. In this work, a new adsorbent, that is, pitch-based activated carbon bead (AC bead), was used to capture CO 2 by VPSA process from flue gas. Adsorption equilibrium and kinetics data had been reported in a previous work. Fixed-bed breakthrough experiments were carried out in order to evaluate the effect of feed flowrate, composition as well as the operating pressure and temperature in the adsorption process. A fourstep Skarstrom-type cycle, including co-current pressurization with feed stream, feed, counter-current blowdown, and counter-current purge with N 2 was employed for CO 2 capture to evaluate the performance of AC beads for CO 2 capture with the feed compositions from 15-50% CO 2 balanced with N 2 . Various operating conditions such as total feed flowrate, feed composition, feed pressure, temperature and vacuum pressure were studied experimentally. The simulation of the VPSA unit taking into account mass balance, Ergun relation for pressure drop and energy balance was performed in the gPROMS using a bi-LDF approximation for mass transfer and Virial equation for equilibrium. The simulation and experimental results were in good agreement. Furthermore, two-stage VPSA process was adopted and high CO 2 purity and recovery were obtained for post-combustion CO 2 capture using AC beads.