Environmental Engineering Reference
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2.1% CO
2
5 b
ar
1 bar
500 m
3
/sec
13% CO
2
2.1% CO
2
Blower
1.1 bar
1 bar
500 m
3
/sec
13% CO
2
0.22 bar
1 bar
28.9% CO
2
1 bar
28.9% CO
2
Vacuum pump
Compressor 151.3 MW
Turboexpander (-36.6 MW)
_________
Blower 7.2 MW
Vacuum pump 56.3 MW
_________
Total energy 63.5 MW
Membrane area 11
×
10
6
m
2
Total energy
114.7 MW
Membrane area
2.4
×
10
6
m
2
(a)
(b)
1 bar
500 m
3
/sec
13% CO
2
1 bar
500 m
3
/sec
13% CO
2
2.1% CO
2
2.1% CO
2
Blower
1.1 bar
Blower
1.1 bar
30 m
3
/sec
1 bar
40.6% CO
2
1 bar
40.6% CO
2
0.22 bar
0.22 bar
Vacuum pump
Vacuum pump
Blower 7.2 MW
Vacuum pump 38.8 MW
_________
Total energy 46.0 MW
Membrane area 6.8
×
10
6
m
2
Blower 7.2 MW
Vacuum pump 39.2 MW
_________
Total energy 46.4 MW
Membrane area 4.3
×
10
6
m
2
(c)
(d)
Figure 7.3.6
Different designs to separate fl ue gas
(a) In this design, the driving force for the separation is created by compressing the fl ue
gas. By using a turboexpander, we can recover part of the compression energy.
(b) In this design, a driving force for the separation is created by pulling vacuum on the
permeate side. We only have to pull vacuum for the gas that passes through the
membrane.
(c) We can make a more effi cient use of the membrane if we use a counterfl ow confi gu-
ration. These confi gurations are not very common commercially.
(d) Confi guration in which we use part of the product as a sweep fl ow. As the partial
pressure of CO
2
in the retentate is very low, this has a very small effect on the driving
force, but as not all the N
2
has to pass the membrane this signifi cantly reduces the
area of the membrane.
membranes in a countercurrent confi guration is more effi cient. Merkel
et al
. [7.1] have shown that indeed the total energy can be reduced to 46
MW for a countercurrent confi guration (see
Figure 7.3.6 (c) and (d)
).
Such membrane confi gurations are described in the patent literature, and
this application would benefi t from the further development of these
types of systems (see
Figure 7.3.5
).
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