H2Tech - Q3 2021 - 19

HYDROGEN INFRASTRUCTURE DEVELOPMENT
collection of the bottom sludge, which is continuously removed
from the system, and clarified water is reused as cooling water in
the quench. The sedimentation works under a low-pH condition
(1.5-3) to promote the migration of volatile metals in the liquid
phase. The syngas exiting the sedimentation tank is routed to an
acidic column that further promotes metals removal.
Syngas exiting from the acidic columns of each gasification
line is collected and sent to a common section based on an alkaline
scrubbing column, wet electrostatic precipitators (WESP)
and a subcooling column. The water stream collected from the
bottom of the washing columns are routed to the wastewater
treatment unit, due to the potential presence of pollutants.
The gasifier works under atmospheric pressure and achieves
pressure on the order of a few mbar at the end of the cleaning
section. In this scheme, a compression section is needed before
routing the syngas to the downstream section. To ensure stable
conditions in terms of syngas pressure and flowrate at the suction
of the compressors, a gas holder is installed between the
gasification and compression sections.
The cleaned syngas still contains sulfur compounds, mainly
in the form of H2
S and COS, together with residual chlorine,
HCN and traces of Hg. Once compressed, the syngas
is routed to the purification section involving the following
steps: removal of residual dust and metals, removal of HCl,
hydrolysis of the COS and HCN, H2
S removal through an
oxy-reduction system and a final polishing step based on zinc
oxide absorbents. These steps help reduce sulfur content to
SPECIAL FOCUS
ppb, as required by catalyst used in downstream synthesis.
The high temperature regime and the use of waste as feedstock
requires dedicated maintenance work around the gasifier
to prevent damages to refractory materials and avoid excessive
fouling along the quench wall and sedimentation. A plant architecture
based on multiple gasification lines working in parallel is
recommended to ensure plant availability during maintenance.
When a gasification line is shut down for maintenance, the other
lines are operated at maximum capacity to ensure continuous
syngas production with minimum reduction in productivity.
The described purification procedure delivers a syngas suitable
for feeding to catalyst-based synthesis. Depending on the
desired end product, a conditioning step to adjust H2
content may be required.7,8,9
and CO
When applied for H2
production,
the conditioning section consists of a shift section and an H2
purification section with pressure swing adsorption (PSA).
Waste to H2 production. The proposed waste-to-H2
case
study is developed around a waste feedstock having an average
composition describing a mixture of 50% RDF and 50% PW.
The resulting mixture composition is detailed in TABLE 2.
By applying the process scheme depicted in FIG. 2, the resulting
syngas composition at the end of the purification section
has a composition as shown in TABLE 3. The process architecture
for H2
production from waste is depicted in FIG. 3.
To increase H2 content, a shift reaction (Eq. 1) is carried
out in two intercooling steps. To promote the shift reaction,
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Thursday, September 23, 2021 | 10 a.m. CDT / 3 p.m. UTC
Speaker:
Anatomy of a Hydrogen Fitting
Hydrogen must be stored at high pressures to achieve the energy density
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H2Tech | Q3 2021 19
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H2Tech - Q3 2021

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