Chemical Engineering August 2014 - 11

Edited by Gerald Ondrey
August 2014
A sorbent that enhances the water-gas shift reaction
S
cientists at the National Energy Technology
Laboratory (NETL; Morgantown,
W. Va.; www.netl.doe.gov) have
demonstrated a process for enhancing
the efficiency of the water-gas shift
(WGS) reaction. The process revolves
around a magnesium hydroxide sorbent
material that can remove CO2 from coal
gasification products at elevated temperatures.
The industrially significant
WGS reaction, often used to increase H2
gas concentration following gasification,
is equilibrium-limited, and the carbon dioxide
removal helps drive the reaction in
the forward direction.
In a conventional WGS process using
pressure-swing absorption technology,
CO2 removal occurs at below 50°C, which
necessitates cooling and reheating steps
that reduce the overall efficiency of the
process. The NETL process (see flowsheet)
uses a patented Mg(OH)2 sorbent
material to remove CO2 at a temperature
between 200 and 300°C, which is
ideal for gas entering a WGS reactor.
The ability to remove CO2 at higher
temperatures retains most of the thermal
energy of the steam and improves
overall efficiency. The sorbent material
can be regenerated at temperatures of
400°C, significantly lower than other
sorbents reported in the scientific literature,
says the NETL research team,
led by Ranjani Siriwardane.
The Mg(OH)2 sorbent can react with
CO2 to form a carbonate and water, making
it a source of steam for the WGS reaction.
Its ability to generate water minWGS
reactor
MgO
Absorber
1
210 °C
280 psig
MgCO3
Regenerator 1
400 °C
280 psig
Hydroxylator 1
210 °C
280 psig
Capture
unit 2
Mg(OH)2
To power
island
Steam
injection
From
gasifier
sequestration
Condensed H2O
CO2 for
imizes the steam-injection requirements
for the WGS reaction, says Siriwardane.
Additional steam is required to maintain
the ideal water-to-CO ratio for the
WGS. But the additional steam requirement
saps the efficiency of the process.
The chemistry of the sorption process reduces
the amount of steam traditionally
required for the WGS reactor by 50%,
thus increasing the overall plant efficiency,
the NETL research team says.
The patented method was designed for
an integrated gasification combined cycle
(IGCC) plant, but can be used elsewhere.
It has been demonstrated in NETL laboratories
for over 100 cycles, and the technology
is available for licensing.
A heavy-metal recovery technique that produces
no waste streams or sludge
A
new remediation approach for industrial
heavy-metal waste has been developed
by Lewis Environmental Services, Inc.
(LES; Pittsburgh, Pa.; www.lesvc.com). The
patented Enviro-Clean process adsorbs
heavy metals from liquid waste streams
onto a bed of specially treated granular activated
carbon. Then, when the activated
carbon is spent and loaded with heavy
metals, the activated carbon is chemically
stripped to clean the carbon for reuse and
to concentrate the heavy metals in the
Note: For more information, circle the 3-digit number
on p. 68, or use the website designation.
stripping solution. The solution is then
processed in an electrolytic cell where the
metals are plated on a cathode. The metals
in the stripping solution can be selectively
recovered to produce a high-purity metal
for sale to third-party refiners.
Capable of treating single- or multicomponent
waste streams, this process
is applicable to a very broad range of
metals, including chromium, lead, zinc,
cadmium, copper, nickel, silver, iron, mer(Continues
on p. 12)
Advance in UF module
the latest offering of ultrafiltration
systems from
evoqua water technologies
(alpharetta, ga.; www.evoqua.com)
incorporates an
advanced polyvinylidene fluoride
(PVDF) membrane into a
hydraulically balanced, modular
filtration system. Known
as memcor CPii, the product
employs a PVDF membrane
with a uniform, but asymmetric
morphology that forms a
dense, permeable " skin " layer
over an open substructure.
the membrane allows
high permeability with good
abrasion resistance and can
achieve less than 5% flow variance
among the filtration units,
says russ swerdfeger, product
manager for memcor at
evoqua. the membranes are
used with optimized modules
that are assembled in up to 32unit
racks. the racks are very
compact and easily accessible
to minimize the footprint,
reduce installation costs and
simplify system operations.
the new CPii system is being
deployed as a pretreatment
strategy for reverse osmosis
units, and boiler feedwater.
ChemiCal engineering www.Che.Com august 2014 11
http://www.netl.doe.gov http://www.evo http://www.qua.com http://www.lesvc.com http://www.Che.Com
Chemical Engineering August 2014

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