PNNL-13501 - Pacific Northwest National Laboratory

Temperature ( o C)
50
45
40
35
30
25
20
15
Distance from condenser end (inches)
Heat Input
(Watts)
Figure 1. Temperature profiles at varying heat input for
starting composition of 5-mole percent acetone in a
2-component mixture of acetone and methanol
Acetone Conc in Liquid [mol fraction]
1.00
0.80
0.60
0.40
0.20
0.00
Distance from condenser end
428 FY 2000 Laboratory Directed Research and Development Annual Report
0.04
0.41
0.72
1.38
2.19
3.71
5.25
6.90
8.43
10.27
Heat Input
(Watts)
Figure 2. Composition profiles at varying heat input for
starting composition of 5-mole percent acetone in a
2-component mixture of acetone and methanol
HETP (inches)
20
16
12
8
4
0
0
0 2 4 6 8 10 12
Heat Input (Watts)
Figure 3. Height equivalence of a theoretical plate and
number of theoretical plates as a function of heat input in
the separation of acetone and methanol
5
4
3
2
1
0.04
0.41
0.72
1.38
2.19
3.71
5.25
6.90
8.43
10.27
Number of Theor. Plates
Table 1. Height equivalence of a theoretical plate for
advanced structure packings based on n-heptane/
cyclohexane separation
Packing HETP, in.
Flexipac 2 (Koch) 12-16
Gempak 2AT (Glitsch) 16-20
Gempak 2A (Glitsch) 12-16
Sulzer BX (Koch) 8-12
Flexeramic 48 (ceramic) (a) 10-15
(a) Based on chemical system of ammonia/air/water
The other measure of the potential for microchannel
concepts to reduce hardware size is comparisons of the
flow capacity per unit cross-sectional area. Because this
metric has not been fully explored, the interfacial surface
area to equipment volume, a related metric for capacity, is
used for comparison. Commercial advanced structured
packings achieve interfacial areas from 50 to 160 ft 2 /ft 3 .
Devices designed, built, and tested under this project also
ranged from 60 to 160 ft 2 /ft 3 . Designs for multi-channel
microchannel devices that employ the concepts developed
here are projected to achieve interfacial areas exceeding
500 ft 2 /ft 3 .
Summary and Conclusions
Concepts for microchannel distillation where mass
transfer occurs between counter-flowing gas and liquid
streams have been demonstrated. Height equivalence
values achieved were 4 to 6 times smaller than
commercial advanced structured packings with similar
interfacial contact area per unit hardware volume. This
was demonstrated in total reflux mode. Initial designs of
multi-channel microchannel devices are predicted to
achieve 3 to 10 times higher interfacial contact areas. The
combination of reduced height equivalence and increased
interfacial area per unit hardware volume is expected to
result in microchannel distillation technology that is at
least an order of magnitude more compact than existing
technologies.
Future directions include demonstration of the concepts
with flow through—adding a feed and producing
two product streams, detailed design and construction of a
multi-channel device, incorporation of integral heat
exchange for high energy efficiency, and reactive
distillation.
Reference
Humphrey JL and GE Keller II. 1997. Separation
Process Technology, McGraw-Hill, San Francisco.