Chemical Engineering August 2012 - 10

CHEMENTATOR
A more-efficient Fischer-Tropsch reactor
T
he production rate (per
amount of catalyst) for
generating liquid hydrocarbons
from syngas by
the Fischer-Tropsch (F-T)
process, using a slurry reactor
or tubular reactor, is
generally limited to about
30% of the maximum rate. The restraining
factor is heat removal from the highly exothermic
reaction, says Steven Vallee, chemical
applications engineer for Chart Energy
& Chemicals Inc. (La Crosse, Wisc.; (www.
chartindustries.com). Chart is developing a
new reactor, called a compact heat exchange
reactor (CHER), that is said to solve this
problem and could theoretically achieve
close to 100% conversion.
A conventional fixed-bed F-T reactor is typ4.5
mm
1 mm
Heat path
ically a shell-and-tube vessel in which the gas
flows through the catalyst-laden tubes, while
coolant flows outside. When a cobalt catalyst
is used, the temperature must be limited to
about 200-240°C (higher for an iron-based
catalyst), explains Vallee. This is achieved by
diluting the syngas with nitrogen or diluting
the catalyst, in addition to cooling.
In contrast, CHER is a plate-and-fin
structure (diagram) comprised of process
layers of narrow channels (under 10 mm),
sandwiched between coolant layers. Syngas
flows over a cobalt catalyst in the channels
and a conventional hot-oil-based coolant
passes through the coolant layers. In this arrangement
" heat exchange is intensified, so
we don't have to dilute the gas or the catalyst, "
says Vallee. Consequently, he adds, a
commercial unit would be about one-tenth
the size of a commercial F-T reactor.
Chart has done pilot tests and is working
up to a 100-bbl/d unit. Because of the smaller
size, the company expects the capital and
operating costs would be roughly 50% below
those of conventional plants.
(Continued from p. 9)
Lawrence Berkeley National
Laboratory; Berkeley, Calif.;
www.lbl.gov) has demonstrated
a technology that
allows temporal and spatial
control of gene expression in
biomass plants. The scientists,
led by Dominique Loqué and
Henrik Scheller, introduced
gene transcription promoters
to various biomass plants
that induce increased gene
expression of the same gene
in a positive feedback loop.
The team was able to improve
desirable properties of bio(Continues
on p. 13)
5 mm
2 mm
Simultaneous heat transfer
and mass transfer model
in column.
Good thinking.
Feedback from our users is what inspires us to keep making
CHEMCAD better. Many features, like this one, were added to
the software as a direct response to user need. That's why we
consider every CHEMCAD user part of our development team.
Get the whole story behind this user-inspired feature and
learn more about how CHEMCAD advances engineering
at chemstations.com/transfer.
C
Engineering advanced
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Chemical Engineering August 2012

Table of Contents for the Digital Edition of Chemical Engineering August 2012
