The_Catalyst_Review_August_2023 - 7

SPECIAL FEATURE
However, the additional equipment required in SEG to supply pure O2 for the calcination process and the compression of captured
CO2 results in an additional electricity requirement.
Consequently, the net electric efficiency, and thus the amount of electricity exported to the grid, tends to be lower for SEG than for
conventional gasification (Figure 5). Therefore, it is expected that SEG would result in an overall energy penalty of about 4% points.15
The Role of Catalysis in Biomass Gasification
Research demonstrates that catalysts can play a prominent role in the gasification equation. Biomass gasification results in the
production of tars, chars and syngas. Syngas composition typically includes 30-50%vol
of H2
6-15%vol of CH4
. The H2 yield and the composition are influenced by the use of catalysts,
as well as biomass characteristics, gasification operating conditions and reactor design
configurations.15
It needs to be emphasised that the key drawback of biomass gasification is the formation
of undesired by-products, for example, tars and inorganic impurities (H2
S, NH3
and HCL).
However, the content of tars, which increase the risk of fouling and blockage in the
pipelines and equipment, can be reduced by introducing a catalyst such as Ni nanoparticles
embedded carbon nanofiber/porous carbon, perovskite or CaO. Zhang et al. (2021) found
that the use of Ni nanoparticles embedded carbon nanofiber/porous carbon (synthesized
by the method of hydrothermal treatment combined with carbothermal reduction)
outperformed other catalysts, enhancing the tar conversion efficiency to 94.78% at 700 °C.15
In addition, Umar et al. (2021) demonstrated that perovskite dopped with nanoparticles
alkaline metals can be an effective catalyst on steam reforming of glycerol for H2
concentration increased from 12.1%vol
production;
furthermore, this catalyst has proven to contribute to the fouling reduction. In another
context, Jordan and Akay (2021) compared the syngas composition for the process with
and without CaO. Their team concluded that H2
16.5%vvol
to
without and with 6%wt CaO, respectively. Furthermore, the carbon nanotubes
supported Pt-bimetallic catalysts with CaO have proven to be an effective catalyst for H2
production from sorption-enhanced aqueous phase reforming of glycerol. Since the WGS
reaction is favoured in detriment to methanation reaction, the H2
yield reduces.15
Waste Marble
Powder as
a Catalyst
Irfan et al. (2019) studied the
potential of using waste marble
powder, whose main component
is CaCO3
, as a catalyst, as well
as a CO2 capture sorbent, in the
process of MSW gasification. The
effect of temperature, steam/
MSW and sorbent/MSW on the
gas composition, dry gas yield, tar
content and carbon conversion
yield increases and the CH4
Regardless of marginally lower energy efficiency, the key advantage of SEG over
conventional gasification is a reduction in the carbon intensity associated with hydrogen
production. The conversion of MSW using conventional technology would result in specific
CO2
emissions of about 181 gCO2
/MJH2
supply heat for the gasification process and produce electricity for the auxiliary equipment.
The carbon intensity would drop by more than 90% (11.67 gCO2
enhanced process.15
. This is due to the char and tail gas combustion to
) for the sorption/MJH2
efficiency
were investigated in a
laboratory-scale batch-type fixed
bed reactor. The researchers found
the rise of the four variables analysed
have a positive effect on the
production of H2
an increase in the H2
-rich gas resulting in
mole fraction,
the dry gas yield and the carbon
conversion efficiency. Furthermore,
the tar content was reduced.15
SEG achieves such a reduction in the carbon intensity because the char and tail gas combustion takes place in the oxy-fired calciner (as
per Figure 2 in Part One of this article). A small fraction of tail gas is used in the gas turbine to supply electricity to drive the auxiliary
equipment, hence the carbon intensity is still positive.15
that hydrogen can be considered low-carbon when the specific CO2
MSW will produce low carbon hydrogen (LCH) that meets this standard.23
/MJH2
, the SEG of
Therefore, such processes can substantially contribute to improving waste management and reduce our reliance on fossil fuels to
increase the LCH supply.
Economic Viability
Based on 20 years of past research and development activities, we know that carbon capture is expected to increase the cost of
hydrogen production compared with conventional production technologies due to increased capital and operational expenditures.24
This also applies to SEG processes, although the cost estimations for this technology are scarce due to its low technology maturity.
The Catalyst Review
August 2023
7
, 25-40%vol of CO, 8-20%vol
of CO2
and
However, considering the UK's Low-Carbon Hydrogen Standard, which specified
emissions of its production is less than 20 gCO2
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