This study evaluated nine stripping PSA cycle configurations, all with a heavy reflux (HR) step, some with a light reflux (LR) step, and some with a recovery (REC) or feed plus recycle (F+R) step, for concentrating CO 2 from stack and flue gas at high temperature (575 K) using a K-promoted HTlc. Under the process conditions studied, the addition of the LR step always resulted in a better process performance; and in all cases, the addition of a REC or F+R step surprisingly did not affect the process performance except at low feed throughputs, where either cycle step resulted in a similar diminished performance. The best cycle based on overall performance was a 5-bed 5-step stripping PSA cycle with LR and HR from countercurrent depressurization (CnD) (98.7% CO 2 purity, 98.7% CO 2 recovery and 5.8 L STP/hr/kg feed throughput). The next best cycle was a 5-bed 5-step stripping PSA cycle with LR and HR from LR purge (96.5% CO 2 purity, 71.1% CO 2 recovery and 57.6 L STP/hr/kg feed throughput). These improved performances were caused mainly by the use of a very small purge to feed ratio (γ = 0.02) for the former cycle and a larger one (γ = 0.50) for the latter cycle. The former cycle was good for producing CO 2 at high purities and recoveries but at lower feed throughputs, and the latter cycle was useful for obtaining CO 2 at high purities and feed throughputs but at lower recoveries. The best performance of a 4-bed 4-step stripping PSA cycle with HR from CnD was disappointing because of low CO 2 recoveries (99.2% CO 2 purity, 15.2% CO 2 recovery and 72.0 L STP/hr/kg feed throughput). This last result revealed that the recoveries of this cycle

used as organic electrolytes in the study. Lithium Ion Conducting Glass Ceramic (LICGC), commercially acquired from Ohara Corporation (1 in. × 1 in., 150 μm thick) was used as the single ion conductor (SIC). A custom Li-Li symmetric diffusion cell was designed for this study. For a given electrolyte of known composition, constant current cycling experiments were first performed in the absence of the SIC. Thereafter, SIC was incorporated in the cell such that it was sandwiched between two electrolyte chambers. The polarization loss from the cell was then extracted from these two sets of experiments after accounting for the Ohmic drop in the SIC and concentration polarization effects in the liquid electrolyte for a given current density, using a mathematical model. Results suggest that liquid electrolyte/SIC junction polarization could be significant. Such polarization losses will lead to a decrease in the cell voltage at high currents in next generation Li-S and Li-O 2 cells.

An algebraic model was derived for obtaining complex pressure swing adsorption (PSA) cycle schedules. This new approach involves a priori specifying the cycle steps, their sequence and any constraints, and then solving a set of analytical equations. The solution identifies all the cycle schedules for a given number of beds, the minimum number of beds required to operate the specified cycle step sequence, the minimum number and location of idle steps to ensure alignment of coupled cycle steps, and a simple screening technique to aid in identifying the best performing cycles that deserve further examination. The methodology was tested successfully against 10, 12 and 16 bed PSA systems in the literature that all utilized the same 13 step cycle sequence that has four pressure equalization steps. It completely resolved all the corresponding cycle schedules for these 13 step multi-bed PSA systems with ease, and showed that the number of cycle schedules was hundreds to thousands of times greater than the few ever reported in the literature for each one. Overall, this new methodology for complex PSA cycle scheduling can be applied to any number of cycle steps, any corresponding cycle step sequence, and any number of constraints, with the outcome being the complete set of cycle schedules for any number of beds greater than or equal to the minimum number it determines.

A simple graphical approach for complex pressure swing adsorption (PSA) cycle scheduling has been developed. This new methodology involves a priori specifying the cycle steps, their sequence, and the number of beds, and then following a systematic procedure that requires filling in a 2-D grid based on a few simple rules, some heuristics and some experience. The outcome or solution is a grid comprised of columns that represent the total cycle time, rows that represent the total number of beds, and cells that represent the duration of each cycle step, i.e., the complete cycle schedule. This new approach has been tested successfully against several cycle schedules taken from the literature, including a two-bed four-step Skarstrom cycle, a four-bed nine-step process with two equalization steps, a nine-bed eleven-step process with three pressure equalization steps, and a six-bed thirteen-step process with four pressure equalization steps and four idle steps. This approach also revealed the existence of numerous cycle schedules for each bed and cycle step combination examined. Although it cannot identify the total number of permutations or which one is better, it does provide a very straightforward way to determine some of the possible cycle schedules of virtually any PSA process that can be conceived.

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