Page 260 - Pressure Swing Adsorption

236 PRESSURE SWING ADSORPTION PSA PROCESSES 237

I as reformer off gas. For most applications a high-pur:ity hydrogen product is
reamred (at least 99.99% and often 99.999%). Since hydrogen 1s adsorbed
much less strongly than almost any other species, a well-designed pressure
S1cp i swmg system can meet this challenge. Indeed this 1s one application for
~
• A B C D which PSA has a clear advantage over almost all other possible approaches,
'
a
C < for many of which these punty levels are unattamable.
0" A-I C I
u .":'.
_, , Commercial 1mpiementation of PSA processes for hydrogen recovery
E
0 C
u
~" 0 I dates from the late 1960s, but the earlier processes were small-scaie three- or
u,
C,
·" T Feed t Vac. .E four-bed umts with relatively modest perfonnance ( ~ 70% recovery) de-
"-
2-3 C
C
,
·2 "E.
08 Adsorbem SA zeolite
• ~ Table 6.2. Details of Test Conditions and Performance Data for a ·Four-Bed Hydrogen
<
0 C ~ PSA Purification System
A-2 A D
Size
i-4 mm (4-18 mesh)
Form spherical beads
I Vac. 1 Blow
Bulk density 0.74kg/l
Feed cone.
H, 69.2vol%
N, 26.8
co 2.2
" CH, 1.8
A C D
Pressure
Adsorption Pa 8.6 kg/cm 2
Vac. Purge PP I.5 kg/cm 2
First equilibration P 1 5.2 kg/cm 2
Second equilibration P,, 1.9 kg/cm 2
Al A2 Bl B2 Cl C2 DI D2
Run no. 2 3 4 5 6 7 8 9 IO 11
J
i
] . i Feed rate (Nljmin)a 14.9 14.6 14.6 21.0 20.9 20.9 8.3 8.3 14.6 14.6 14.5
8.0
Cyde Time {min)
12.0
6.0
47
48.0
24.0
,
~ 2 ---t-------r-- Column size 4.3 cm 1.d. x 200 cm L. 8.4 16.8 33.6 21.0 42.0 4.3 cm 1.d. x 100 cm L.
.!::<
Adsorbent (kg) 2.06 X 4 bed 1.0 x 4bed
• C
~ E Product cone.
iP ' ' H (vol%) 99.73 85.61 76.19 99.38 84.22 76.55, 99.93 83.48 99.87 97.93 88.41
" C
'
~v ' N, 2 0.27 13.41 21.15 0.62 14.52 20.86 0.07 15.19 0.13 2.06 10.9
'
' I ' I co 0.0 0.52 1.48 0.0 0.68 t.45 0.0 0.68 0.0 0.0 0.39
!
___ .J _______ J.._Q_ I ala
0.0 0.47 1.18 0.0 0.58 1.14 0.0 0.65 0.0 O.Ql 0.30
0 2 4 CH 4
H Recovery(%) 77.7 88.4 94.9 77.2 90.3 94.6 77.7 90.5 70.0 78.6 83.9
Time (mm.) 2
Adsorbent
Figure 6.12 Sequence of bed switching and pressure variation in a four-bed hydro- productivitv 21.7 42.7 84.9 21.4 42.6 85.2 21.3 42.5 17.0 21.8 29.0
gen PSA process. (From Suzuki, 29 with permission.) Q (NI/kg ads.,
cvcle)
Space veiocilV
0/mm) 0.66 0.63 0.62 0.90 0.87 0.84 0.37 0.37 1.30 1.29 i.26
NI = liters at 273 K I atm.
23
From Tomita et al., with perm1ss1on.