TABLE OF CONTENTS So far, construction of the mass exchange pinch diagram started by maximizing the use of process MSAs with the consequence of minimizing the external MSAs. Then, MSAs must be screened so as to determine which one(s) should be used and the task of each MSA. Two questions arise:
If the process has no process MSAs, how can the mass exchange pinch analysis be carried out? Since the flowrate of each external MSA is unknown, how can the lean composite stream be constructed?
If there are multiple external MSAs, how can they be screened?
In order to answer these questions, let us first consider the following motivating example. Suppose that it is desired to recover 10 kg/h of hydrogen from an industrial gas stream. Two candidate adsorbents are being screened: sand, whose cost is $0.01/kg of sand and activated carbon, whose cost is $1.00/kg of carbon. So, which adsorbent is cheaper? Is the cost per kilogram of the MSA an appropriate criterion to screen the candidate MSAs? The cost of the two adsorbents should be linked with the separation task. The following Table 4-4 summarizes the supply and target compositions for the two adsorbents.
| MSA | x s kg H 2 /kg MSA | x t kg H 2 /kg MSA |
|---|---|---|
| Sand | 0.0 | 10 ?9 |
| Activated carbon | 0.0 | 0.1 |
A material balance for the MSA...
