H2Tech - Q3 2021 - 32

SPECIAL FOCUS HYDROGEN INFRASTRUCTURE DEVELOPMENT
system and a lower cost module than both PEM and AEL. The
AEM stack creates a physical barrier between H2
and O2
so that
they never mix in an explosive ratio.
The significant advantage of AEM technology is that it works
very well with intermittent power sources like solar and wind.
AEM electrolyzers can work with filtered tap water and rainwater.
Total annual maintenance costs are much less than for
other technologies. AEM is an emerging technology; as such,
few companies are developing AEM electrolyzers, and limited
commercial products are available.
Balance of plant (BOP) for all types of electrolyzers includes
the transformer, rectifier, control system, water purification, H2
dryer and H2
electrolysis technologies is offered in TABLE 2.
The quality of product H2
purification. A comparison of PEM and alkaline
, the plant's scale, available utilities
and heat input methods decide the electrolyzer selection
and configuration. Major utilities required for an electrolyzer
are power, demineralized water and cooling water. The major
gaseous effluent is O2
.
Comparison of major H2
eters for all three major H2
production routes. Key paramproduction
routes are shown in
TABLE 3 for an H2 production capacity < 1,000 Nm3/hr and
India as the geographical location. The cost of natural gas used
for this case study is assumed at $9/MMBtu-$10/MMBtu,
TABLE 2. Comparison of PEM and alkaline electrolyzers7,8
Electrolyzer type
PEM
Investment, $MM/MW*
Product purity, mol%
Stack life expectancy, hr
Pressure, barg
Demineralized water, µS/cm
Turndown, %
Maintenance
System size range, kW
1.6-2.7
> 99.995
60,000
0-40
< 0.1
10
Less
0.2-1,150
Alkaline
1.2-1.5
> 99.5
90,000
0-3
0.5
40-50
More
1.8-5,300
* Investment varies with the size of the unit; the comparison basis is literature survey
and in-house data
TABLE 3. Key parameters for different low-carbon
H2
production routesa
SMR plus
Parameter
CAPEX, $1,000/tpy H2
Cost of production, $/kg
Specific energy,
Gcal/1,000 Nm3
H2
Carbon footprint, kg CO2/kg H2
Water footprint, l/Nm3
of H2
Power consumption,
kW/Nm3
of H2
Land use, m2/tpy H2
a
0.15-0.2
0.5-3.4
1-3c
Values presented in the table are typical and depend on many factors including
geographical location, size of the unit, feedstock price, utility cost, etc.
b Carbon footprint when the source of electricity is renewable only
c Land use is for the electrolyzer without accounting for the renewable source footprint
32 Q3 2021 | H2-Tech.com
0.2-4
0.9-1.7
0.01-0.04
Neutral
0.5-1.1
0.4-0.45
0.3-0.9b
5.6-6
5.5-6
carbon capture Biomass Electrolysis
10-16
2-2.5
8-10
3.5-4.2
3.4-3.9
5-5.5
10-50
3.5-6
4.9-5
biomass feedstock prices are $27/t-$70/t, and electricity prices
are $25/MWh-$107/MWh.
Electricity cost is assumed at $50/MWh for renewable electricity.
In the case of the SMR and biomass routes, the grid electricity
cost is assumed at $100/MWh for the cost of production. As evident
from TABLE 3, the overall CAPEX of electrolysis is more than
40%-50% compared to SMR, and the overall cost of production
is lowest in the case of SMR plus carbon capture. Furthermore,
the CAPEX of the SMR plus carbon capture route decreases drastically
as the scale of production increases-e.g., for capacity >
50,000 Nm3
/hr, the CAPEX is $1,000/tpy H2
-$2,000/tpy H2
.
At present, SMR is the most efficient process, while biomass
is the least efficient. However, the biomass route has the highest
net energy ratio as the only inputs are power and steam, and feedstock
biomass does not account for energy input since it is waste.
Conversely, electrolysis requires a considerable amount of
water for operation, and it will increase further if the water requirement
for cleaning solar photovoltaic (PV) is considered.
However, recycling of cleaning water will optimize the water
uses for solar PV. The SMR and biomass routes are in the same
range of water consumption. In reality, the biomass route is a net
water production process, as it captures water from organic matter.
Biomass gasification requires a good amount of utility water
to clean syngas, which can be further optimized.
The least amount of power is required in SMR, while electrolysis
requires much more power than the SMR and biomass routes.
Land use has a broad range in the biomass route due to
the large footprint required for conveyor and biomass storage,
which can be further optimized. The lowest land use is for SMR
because of the compactness of layout, which has improved over
the years. Land use by the electrolysis route increases greatly (>
100-fold) when accounting for the solar PV footprint.
CO2
emissions are lowest in the electrolysis route since a
renewable source of electricity is used. However, the biomass
route is actually carbon negative, considering that some carbon
is inevitably fixed in the char extracted during the process.
In electrolysis, two main options exist for estimation. One
is to select a large-capacity electrolyzer and a large-capacity H2
storage to maintain continuous H2
production. The second is to
consider renewable energy with battery storage. In the second
option, the electricity cost will be 2-3 times greater than the
first option, but a smaller electrolyzer and storage would be required.
A third, less desirable option is mixed-origin power (renewable
energy with fossil-fuel grid electricity), but this results
in some CO2
emissions and is not considered a " green " process
Part 2. To be published in the Q4 issue, Part 2 will present a
sensitivity analysis of H2
production cost and a case study for
FCEVs.
LITERATURE CITED
Complete literature cited available online at www.H2-Tech.com.
KALPANA GUPTA is Deputy Chief Engineer at Technip India Ltd. She has more
than 20 yr of experience in the downstream industry. She holds an MS degree
from IIT Delhi and a diploma in renewable energy from TERI Delhi.
MARUTHI ETHAKOTA is Head of the process and technology department of
Technip India Ltd. He has executed several H2
He holds an MS degree from IIT Kanpur.
and syngas projects worldwide.
PALLAVI KUHIKAR is a Principal Process Engineer at Technip India Ltd. She has
more than 13 yr of experience in the downstream industry. She holds a BTech
degree from PIET Nagpur.
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