Hydrogen Production Pathways

1. Hydrogen Production Pathways
Hydrogen production pathways can be broadly categorized into two groups:
Fossil fuel based production
Renewable based production
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2. Pathways
Figure: Classification of pathways
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3. Fossil Fuel Based Hydrogen Production
Steam methane reforming (SMR)
Coal gasification
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4. Steam Methane Reforming (SMR)
- SMR involves reacting methane (CH4) with steam (H2O) at high
temperatures (800-1000°C) and pressures (30-40 bar) in the presence
of a catalyst, usually nickel.
- The reaction produces hydrogen (H2) and carbon dioxide (CO2):
CH4 + H2O → CO2 + 3H2.
- SMR is the most widely used method for producing hydrogen,
accounting for over 90
- However, it is not considered a clean method due to the generation of
carbon dioxide as a byproduct.
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5. Coal Gasification
- Uses coal as the feedstock, which is heated in the absence of air to
produce a mixture of hydrogen, carbon monoxide, and carbon dioxide
known as synthesis gas or syngas.
- The hydrogen can be separated from the other gases and used as a
fuel.
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6. Renewable Based Hydrogen Production
Electrolysis of water
Biomass gasification
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7. Electrolysis of Water
Involves splitting water into hydrogen and oxygen using electricity. The
electrolysis process can be accomplished through two methods:
Alkaline electrolysis
Proton exchange membrane (PEM) electrolysis
- In both methods, an electrical current is passed through the water,
which splits the water into hydrogen and oxygen through a chemical
reaction.
- The hydrogen produced in this process is considered to be clean and
renewable, as the only byproduct is oxygen. However, the efficiency
and cost-effectiveness of the process depend on the source of
electricity used to power the electrolysis.
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8. Biomass Gasification
- Uses organic matter such as agricultural waste or forestry waste as
feedstock, which is heated in the absence of air to produce a mixture
of hydrogen and other gases. The hydrogen can be separated from
the other gases and used as a fuel.
- Biomass gasification is considered a clean and renewable method for
producing hydrogen, as the carbon dioxide produced during the
process is considered to be part of the carbon cycle, since the carbon
dioxide was originally taken up from the atmosphere by the organic
matter.
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9. Figure: Comparison of the pathways
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10. Steam Methane Reforming (SMR)
The main process for producing hydrogen, accounting for over 90% of
hydrogen production globally.
Involves reacting methane (CH4) with steam (H2O) in the presence
of a catalyst to produce hydrogen (H2) and carbon dioxide (CO2).
CH4 + H2O → CO2 + 3H2 (1)
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11. Steps involved in setting up a SMR plant
Procurement of feedstock: Natural gas must be obtained and
transported to the plant site.
Pre-treatment of feedstock: Impurities such as sulfur and moisture
may need to be removed from the natural gas.
Reactor design: Reactor must be designed to withstand high
temperatures/pressures and hold catalyst.
Catalyst selection: A suitable catalyst, such as platinum or
nickel-based, must be selected for the reaction.
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12. Continued...
Steam generation: A steam generation system must be designed and
installed to provide steam for the reaction.
Carbon dioxide removal: Remove CO2 from mixture via scrubbing,
cryogenic separation, or PSA.
Hydrogen purification: H2 must be purified from CO and N2 via PSA,
pressure filtration, or membrane separation.
Hydrogen storage and distribution: Store and distribute purified H2,
requiring designed and installed systems.
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13. Setting up a SMR Plant
Procurement of feedstock
Pre-treatment of feedstock
Reactor design
Catalyst selection
Steam generation
CO2 removal
Hydrogen purification
Hydrogen storage and distribution
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14. Steam Methane Reforming (SMR) Plant Operating
Parameters
Operating pressure: 500-1,000 kPa
Operating temperature: 800-1,200°C
Steam-to-carbon ratio: 2.5-3.5
Catalyst life: 5-10 years
Conversion rate: 80-85%
Purity of produced hydrogen: 95-99.999%
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15. The Economics of a Steam Methane Reforming (SMR)
Plant
Cost of natural gas: A significant factor in determining the economics
of a SMR plant
Capital costs: Costs of building the plant, including the reactor and
other systems
Operating costs: Labor, energy and maintenance costs can affect
profitability
Carbon capture and storage (CCS): Implementing and operating the
CCS system can impact the economics of the plant
Hydrogen demand and price: Higher demand and higher prices for
hydrogen can increase the profitability of the plant
Overall, SMR is considered to be relatively inexpensive compared to other
hydrogen production pathways when natural gas prices are low
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16. Natural Gas Pathways
SMR relies on natural gas as its main feedstock, and there are several
pathways to obtain it:
Conventional natural gas production, which involves drilling wells to
extract natural gas from underground reservoirs and is the most
common method globally.
Unconventional natural gas production, which involves extracting
natural gas from sources such as shale gas, coal bed methane, and
tight gas, and is typically more expensive and complex.
Importation of liquefied natural gas (LNG), which is natural gas that
has been cooled to a liquid state for transport by tanker, and is an
option for countries without access to domestic natural gas reserves.
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17. Continued...
Figure: Natural Gas Pathways
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18. Electrolysis of Water
Electrolysis of water is a process to produce hydrogen gas (H2) by
electrically splitting water molecules (H2O).
The process uses an electrical current to separate hydrogen and
oxygen atoms in water molecules.
The resulting hydrogen can be used as a fuel source or in various
industrial processes.
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19. The Chemical Reaction
2H2O + electrical energy → 2H2 + O2 (2)
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20. Components of an Electrolysis of Water Plant
Electrolyzer: The main component consisting of two electrodes and
an electrolyte membrane.
Electricity source: A necessary component that powers the
electrolyzer, either renewable or fossil fuel-powered.
Pumps: Required to circulate water through the electrolyzer.
Gas storage: The hydrogen produced must be stored until needed.
Safety equipment: Measures necessary to ensure safe plant operation,
including emergency shut-off valves, hydrogen detection systems, and
fire suppression systems.
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21. Setting up an Electrolysis of Water Plant
Determining production capacity and selecting an appropriate
electrolyzer.
Selecting an electricity source and determining required electrical
power.
Determining necessary pumps, gas storage, and safety equipment.
Installing the electrolyzer and other components.
Connecting the plant to the electricity source and monitoring its
operation.
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22. Cost of Setting Up an Electrolysis of Water Plant
The cost of setting up an electrolysis of water plant includes the cost
of equipment, such as the electrolyzer, pumps, gas storage, and safety
equipment.
The cost of electricity to power the electrolyzer is another significant
cost factor.
If the electricity source is a renewable energy source, such as wind or
solar, the cost of electricity is lower compared to if it is supplied by a
fossil fuel-powered generator.
The cost of hydrogen produced through electrolysis of water can be
higher compared to other hydrogen production pathways, especially if
the electricity source is not renewable.
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23. Economic analysis
NPV =
n
X
t=1
CFt
(1 + r)t
− I0
Where:
CFt = expected cash flow at time t
r = discount rate
t = time period (t = 1, 2, ...n)
I0 = initial investment (capital expenditure)
The formula calculates the present value of each future cash flow and
subtracts the initial investment to give the total NPV
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