CO2 capture from dry flue gas by vacuum swing adsorption: A pilot plant study

The capture and concentration of CO2 from a dry flue gas by vacuum swing adsorption (VSA) has been experimentally demonstrated in a pilot plant. The pilot plant has the provision for using two coupled columns that are each packed with approximately 41 kg of Zeochem zeolite 13X. Breakthrough experiments were first carried out by perturbing a N-2 saturated bed with 15% CO2 and 85% N-2 feed, which is representative of a dry flue gas from coal-fired power plants. The breakthrough results showed long plateaus in temperature profiles confirming a near adiabatic behavior. In the process study, a basic four-step vacuum swing adsorption (VSA) cycle comprising the following steps: pressurization with feed, adsorption, forward blowdown, and reverse evacuation was investigated first. In the absence of any coupling among the steps, a single bed was used. With this cycle configuration, CO2 was concentrated to 95.9 +/- 1% with a recovery of 86.4 +/- 5.6%. To improve the process performance, a four-step cycle with light product pressurization (LPP) using two beds was investigated. This cycle was able to achieve 94.8 +/- 1% purity and 89.7 +/- 5.6% recovery. The Department of Energy requirements are 95% purity and 90% recovery. The proposed underlying physics of performance improvement of the four-step cycle with LPP has also been experimentally validated. The pilot plant results were then used for detailed validation of a one-dimensional, nonisothermal, and nonisobaric model. Both transient profiles of various measured variables and cyclic steady state performance results were compared with the model predictions, and they were in good agreement. The energy consumptions in the pilot plant experiments were 339-583 +/- 36.7 kWh tonne(-1) CO2 captured and they were significantly different from the theoretical power consumptions obtained from isentropic compression calculations. The productivities were 0.87-1.4 +/- 0.07 tonne CO2 m(-3) adsorbent day(-1). The results from our pilot plant were also compared with available results from other pilot plant studies on CO2 capture from flue gas. (c) 2014 American Institute of Chemical Engineers AIChE J, 60: 1830-1842, 2014