Page 145 - Pressure Swing Adsorption

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120 PRESSURE SWING ADSORPTION EQUILIBRIUM THEORY 121

0.16
100
0.8
c 100
• c 0.12
•
C
0 0.6 C
0. 0
E 0.
0 E
u 0
u
0.08
0.4 CONVENTIONAL PSA
I
0.2 0.04 10

CONVENTIONAL
0.00 1 oo
1 0 2 1 0 2
I

!
0.30 Figure 4.10 (Commued).
/,J = I
F
~
<D 0.25
c YF = 0.9, resoect1vely. It can be seen that recovery always increases by
• l combining feed and partial cocurrcnt hlowdown: the increase can he dra~
C
0 0.20
0. matte for a large value of PF and a low or moderate value of PH· Conversely,
E 50
0 recovery always declines when oressurization and feed are combined (i.e.,
u
0.15 i PF < PH). The first plot shows the case of excellent select1v1ty, but the feed is
~ very contammatect with the heavy component; the resuits suggest that. for
10
,__ this system, combined feed and cocurrent blowdown will yield only a small
"' 0.10 CONVENTIONAL PSA improvement over conventwnal PSA. The second plot. m which the seleCt1v-
w
>
0 1ty 1s poor and the feed 1s prectommateiy the light -comoonent, shows that
u
w very large improvements in recovery are possible for combined feed and
"' 0.05
cocurrent blowdown. For examoie, the maximum recovery via conventional
PSA IS 10% (at a very high pressure ratto). Combinmg feed and cocurrent
0.00 1 oo blowdown can match that recovery at a pressure ratio of only 6, or vastly
1 0 2 exceed it (e.g., reaching 25% recovery at a pressure ratto of 50). The third
example shows a system havmg ooor adsorbent selectivity and heavily con-
tammated feed. Recovery ,s improved for this case, too, by, for example,
{b) initially pressurizing to a pressure ratio of 50 then feeding while blowing
down cocurrently to a pressure ratio of 15. The resuit exceeds the maximum
Figure 4.10 Recovery as affected by oressure ratios, for a four-step cycle tn which
the feed step pressure rises or falls. (al /3 - 0.1, YF ~ 0.9; (bl /3 ~ 0.9, y, ~ 0.1; recovery of the convent1onal cycle (at very high pre'Ssure ratios.). lncreasing
(c) /3 ~ 0,9, YF ~ 0.9, the initial oressure ratio to 100 yields a 50% increase in recovery. The
advantages of mcreased recovery must, of course, be weighed against the