Heavy and dual reflux stripping pressure swing adsorption cycles: Carbon dioxide capture and concentration from flue gas at high temperature using a potassium-promoted hydrotalcite

In this dissertation, a series of theoretical studies were performed on twelve stripping pressure swing adsorption (PSA) cycle configurations that looked to increase the purity of the heavy component in the heavy product. What was found is that a heavy reflux (HR) step was needed to bring the heavy component purity close to 100%. The HR concept is not new to PSA cycles as it was first patented in the 1970's. This high pressure rinse or HR step involves delivering a purge, consisting of pure or highly enriched heavy product, to the feed (or heavy) end of the column at high pressure, usually, but not necessarily, at the feed pressure. It is carried out in series following the feed step and used to increase the loading of the heavy component in the column, which, in turn, increases its concentration during the countercurrent depressurization and/or low-pressure purge steps.; However, there are many ways to run the HR step in a PSA cycle that depend on the other steps in the cycle. Two fundamental questions arise in the design of a HR step: First, which cycle step should be used to produce the HR gas? In some cases there are two choices and in other cases there is only one choice. The HR gas can be obtained from the countercurrent depressurization step and/or the low-pressure light reflux purge step, depending on whether this latter step is included in the PSA cycle. If the light reflux purge step is included, then the PSA cycle is actually a dual reflux cycle with both light and heavy reflux steps.; Second, what should be done with the light gas effluent coming from the column undergoing the HR step? In most cases there are three choices. It can be taken as part of the light product. But, operating the cycle in this manner necessarily limits the recovery of the heavy component, as some of it is lost in this light product. Instead, it can also be recycled back into the process for subsequent recovery as heavy product. There are two ways to recycle this light gas effluent back into the process. The first way is to simply blend this light gas effluent with the feed gas during the feed step. This approach does not add another step to the cycle and is referred to here as the feed plus recycle (F+R) step. The second way is to feed this light gas effluent to the heavy end of another column in between the feed and heavy reflux steps. This approach adds another step to the cycle and is referred to here as the recovery (REC) step. The specific application that was addressed is the concentration and recovery of carbon dioxide from flue gas at high temperature using a K-promoted hydrotalcite-like adsorbent (HTlc).