Page 95 - Pressure Swing Adsorption

70
PRESSURE SWING ADSORPTION PSA CYCLES: BASIC PRINCIPLES 71

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E D~mens1onless bed length
m O. 66 Figure 3.2 Expenmental concentration profiles for air pressunzation m a bed of SA
0 SYMBOL STEP
::;; zeolite. The lines represent the best curves through the exoenmental data. (From
; HIGH PRESSURE FEED Ref. 1; reprmted with permiss10n.)
0.58 2 SLOWDOWN
3 PURGE
4 PAESSURIZATION
1
agreement with the profiles measured by Fernandez and Kenney for air
0.50
0.0 0,2 0,4 0.6 0,8 .i .0 oressunzation in a bed of 5A zeolite {Figure 3.2). In the high-pressure reed
step the concentratton wave front travels down the coiumn, and a raffinate
Dimensionless bed length
product, enriched in the iess strongly adsorbed species, is withdrawn at the
lbl product end. In the blowctown and ourge steos the concentration wavefront 1s
pushed back and a relat1veiy clean initial bed condition is estahlished for the
Figure_ 3.1 Comouted steady-stale gas-phase concentration profiles at the end of
four elementary steps 111 (a) equilibnum-controlled PSA scparatmn of air on 5A next cycle. The more 1moortant features of these steps and tllc1r,vanants will
zeolite and (b) kinet1cally controlled separation of air on a modified 4A zcolitc. The be discussed in relation to various different t..ycles.
arrows indicate the directmn of flow, the sequence of operat10n 1s 4,1,2,3; the
s11nulatmn models are described in Section 5.2.
3.2 Equilibrmm-Controlled Separations for the Production
of Pure Raffinate Product
The_ early PSA cycles were developed for equilibrium separations, onmarily
for the recovery of the less strongly adsorbed raffinate product at high ounty.