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.