Figure 4. Cost breakdown of PSA fiber module manufacturing for a MOF-μPCM-polymer fiber sorbent module with 75 wt. % solids loading and a 1:1.25 mass ratio of MOF:μPCM at varying cost of the sorbent.
Using the idealized cycle design (360 s cycle time) we estimated the cost of CO2 capture using a sub-ambient sorbent for a wide range of sorbent productivities and CO2 purities leaving the PSA unit. Figure 5 shows the effect of sorbent productivity and product CO2 purity on the overall cost of capture. The cost of capture is significantly less sensitive to sorbent productivity at productivities greater than 0.015 mol kg-1 s-1. Around this value the cost of the PSA unit is less than 25% of the total capital cost so the capital cost is dominated by the energy demand of the process and the other capital equipment.
An interesting implication of Figure 5 is that varying the rich product purity from the PSA unit leads to only minor variation in the total cost of CO2 capture. Reducing the CO2 rich product purity from the PSA unit to values from 85% to 75% CO2 showed a $1.00-$1.20/tonne CO2increase in total capture cost. This change stems from an increase in the size and energy requirement of the liquefaction system for the reduced purity case. Reducing the purity also leads to increased energy demand due to a reduction in the amount of expansion energy that can be recaptured. This analysis can offer some insights into the economic tradeoffs of slight improvements in productivity at the cost of purity. As an example for a situation where two theoretical adsorbents are considered, a PSA operating with one sorbent may give PSA purity of 95% and productivities of 6.66×10-3 mol kg-1 sec-1 with a resulting cost of capture of $88/tonne CO2. A second adsorbent, one which could only produce 75% purity would only achieve a similar cost of capture with productivities about 1.25 times higher (8.33×10-3 mol kg-1sec-1) to have a similar overall cost of capture.