(724c) Design of Pressure Swing Adsorption Cycles for Carbon Dioxide Capture From Flue Gas

The production and subsequent release of carbon dioxide into the atmosphere, no matter the source, is becoming an increasingly serious issue with respect to its affect on global warming. As one of the more familiar greenhouse gases, carbon dioxide has the ability to warm the planet by trapping energy radiated from the surface of the earth that would otherwise be released to space. A considerable effort is underway worldwide to curb CO2 emissions from coal fired and other fossil fuel based power plants, because these plants are responsible for over 40% of the carbon dioxide emissions in the USA alone. Among many viable CO2 capture options available, pressure swing adsorption (PSA) is gaining widespread industrial acceptance because of the economics involved. The goal is to capture CO2 from stack or flue gas, concentrate it to around 90 to 95 vol%, and sequester it somewhere in the Earth.

Studies show that a variety of PSA cycles and commercial adsorbents have been studied and even commercialized for concentrating CO2 from stack or flue gas. However, no consistent reasoning has ever been offered as to why a particular PSA cycle was selected. This work specifically focuses on the effect of cycle design on the overall process performance and how better design helps bring down the cost of CO2 capture from coal fired power plants. This PSA cycle schedule analysis has revealed that the design of a multi-bed PSA process for CO2 capture from flue gas is a non-trivial exercise. Since the PSA beds are always coupled together, usually contain more than one layer of adsorbent, and operate sequentially with each undergoing cycle steps such as pressurization, feed, heavy reflux, equalization, depressurization, light reflux, and repressurization, the number of possible cycles to explore becomes enormous, and unfortunately design strategies on how to best configure such a complex PSA cycle is more of an art than a science. To this end, this presentation will show how sensitive the performance of a PSA process is to slight changes in the PSA cycle schedule. It will also show that a PSA process can be easily designed to capture CO2 from flue gas with greater than 90% purity and 90% recovery, even in the presence of water vapor. This presentation will discuss the effect of various parameters like the total cycle time, feed temperature, pressure ratio, feed concentration, and purge to feed ratio on the overall process performance. Thus, this presentation will also highlight the power requirements and the cost of capturing and sequestering CO2.