Chemical Engineering August 2012 - 9

Edited by Gerald Ondrey
August 2012
Coke oven offgases may help
to increase steel production
T
wo dissimilar iron-making methods - a
conventional blast furnace using coke from
coal, and gas-based direct reduction of iron ore
- are combined in a process being developed
by Midrex Technologies, Inc. (Charlotte, N.C.;
www.midrex.com) and Praxair Inc. (Danbury,
Conn.; www.praxair.com). Designed to
use offgases from the coke-making operation
in integrated steel mills, the process offers
three advantages: it uses the unwanted offgases
from the coke ovens to produce direct
reduced iron (DRI); it provides an alternate
process gas for DRI, and it can increase the
efficiency of blast furnaces by adding DRI to
the conventional iron-ore feed.
Midrex, the world's leading supplier of
DRI plants, is providing the direct reduction
technology. In the standard Midrex process,
natural gas (methane) is reformed to produce
hydrogen and carbon monoxide (typically
about 2:1 H2:CO), then these gases
are reacted with the Fe2O3 in iron pellets at
800-1,000°C, leaving metallic sponge iron.
In the new arrangement, offgases from
coke ovens will be reformed to obtain H2 and
CO, which will be fed into a Midrex shaft
furnace to react with iron ore pellets. Unlike
methane, coke oven gases are a complex
mixture comprised of approximately 50% H2
and 30% methane, plus small amounts of CO,
CO2, O2 and volatile hydrocarbons, says Robert
Hunter, a Midrex marketing manager. In
contrast with conventional steam reforming,
which takes place at around 2,000°F
over a catalyst, the Midrex-Praxair process
ifferential pressure can be a tough
problem for butterfly valves, in that it
Thermal
reactor
O2
Air
separation
plant
Syngas
Reducing
gas
COG
Integrated mill
Coke
DRI/HBI/HDRI
Gas
heater
Thermal reactor system
Clean
coke oven gas
(COG)
COG
pre-heater
CO2
removal
Shaft
furnace
Scrubber
Plant
Recycle gas
Iron oxide
Iron oxide
HBI
DRI/HBI/HDRI
Hot metal
Coke oven
Blast furnace
uses a thermal reformer, which operates at a
" higher " temperature, but without a catalyst,
says Hunter. The thermal reactor is heated by
part of the coke oven gases. Praxair is providing
the O2 for the process and has designed
special burners to handle the gases.
Part of the resultant DRI can be fed to a
blast furnace and/or to a steel furnace. Adding
10 wt.% metallic iron to a blast furnace
increases the production rate by 8% and
achieves fuel savings of 7%, says Hunter.
Midrex is pilot-testing the thermal reactor.
This valve tolerates up to 80% differential pressure
D
can cause damaging cavitation. As a rule
of thumb, for instance, a typical butterfly
valve can only handle a maximum of 30%
differential pressure (DP), explains René
van der Gaag, global product manager
lined-valves process for Tyco Flow Control
(Breda, The Netherlands; www.tyco.com/
flowcontrol). Tyco's new Monovar control
valve, however, can take up to 80% DP. This
is a benefit for many applications, such as
water-treatment systems where high DP
is common in both effluent streams and
streams into treatment steps.
Monovar's operating principle is very
simple, van der Gaag says. " There are two
Note: For more information, circle the 3-digit number
on p. 60, or use the website designation.
plates, each with the same number of holes, "
he explains. One plate is fixed, while the
other can move. As the plate moves, the
individual hole openings can be decreased,
thereby reducing the flow of fluid and the
DP. Cavitation might occur with the Monovar,
van der Gaag says, but with effects that
are far-less severe. Unlike what happens in
other butterfly valves, cavitation does not
occur near the pipe walls, and therefore is
not of a damaging type.
Turbulence downstream of the valve is very
short, so elbows and other fittings can be installed
at closer lengths downstream. Meanwhile,
there are limited moving parts, so the
maintenance burden is low and reduces total
cost of ownership, van der Gaag says.
Basic oxygen furnace
A new electrolysis cell
At Achema 2012, ThyssenKrupp
Uhde GmbH (Dortmund,
Germany; www.uhde.
eu) introduced a new generation
of its single-element
electrolysis cell, Generation
6, which offers improved
energy consumption and
increased active-membrane
area. These improvements
are due to an elastic element
that enables the entire active
area of the membrane to
be positioned between the
electrodes without any gaps.
This development ensures
that a uniform pressure is
transferred across the entire
area of the membrane. Zero
gap is achieved across every
square inch, without compromising
the advantages of
the single-element design,
says Uhde.
Fine-tuning biomass
A team of researchers at
the Joint BioEnergy Institute
(JBEI; Emeryville,
Calif; www.jbei.org; part of
(Continues on p. 10)
CHEMICAL ENGINEERING WWW.CHE.COM AUGUST 2012 9
http://www.midrex.com http://www.praxair.com http://www.uhde http://www.tyco.com/ http://www.jbei.org http://WWW.CHE.COM
Chemical Engineering August 2012

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