Clean hydrogen pathways

Hydrogen is an energy currency that is manufactured and, as such, its own production needs to be clean in order to affect positive greenhouse gas (GHG) emission impact. Today, the two predominant pathways for clean hydrogen production are:

Blue Hydrogen: Steam Methane Reforming (SMR) is the industry-standard in North America for its low production cost (~$1.20/kg-H2). However, the SMR process emits substantial GHGs (~10 kgCO2e/kgH2) that are costly and challenging to mitigate. Conventional approaches for decarbonising the SMR process, such as CO2 capture and sequestration (CCS), add cost (~$80/t-CO2) and are restricted to specific regions where CO2 infrastructure and storage can be deployed.
Green Hydrogen: Green hydrogen combines electrolysis with renewable electricity to produce hydrogen from feedstock water. This emerging pathway is attractive for its ultra-low GHG emissions. Moreover, electrolysis is commercial and scalable technology solution that can be readily deployed for distributed hydrogen production. Electrolysis, however, is an electricity-intensive process (50-60 kWhe/kg-H2) and as a result, electrolytic hydrogen production is often expensive, unless very low-cost and highly dispatchable electricity is available. Furthermore, electrolysis requires low carbon-intensity electricity generation in order to produce clean hydrogen, which is not presently the case in most regional electricity grids. Finally, electrolysis requires substantial feedstock water supply for hydrogen production, which adds environmental impacts and siting constraints.

Problem Statement: New clean hydrogen solutions are needed that can be flexibly deployed at large industrial scale … without adding cost.

Methane Pyrolysis Development

Methane Pyrolysis is an emerging alternative for clean hydrogen production. In a pyrolysis reactor, feedstock methane is heated in the absence of oxygen to pyrolysis conditions (1,000 – 1,500°C), at which point the methane molecules dissociate into solid carbon and hydrogen. Since solid carbon is the principle by-product, GHG emissions are significantly reduced when compared with a conventional SMR process.  Moreover, since methane pyrolysis does not require CO2 sequestration or water feedstock, it can be flexibly sited wherever natural gas infrastructure exists.

Numerous methane pyrolysis platforms are under development, each taking a different approach to energy delivery, feedstock heating and process integration. These approaches are summarised in the table below, which was previously published by H2 View and repeated here for convenience. The author has added an additional column to the table, which summarises Ekona’s pulsed methane pyrolysis (PMP) platform for completeness.

Challenges

Methane pyrolysis has been used commercially for decades to produce carbon black for tires and plastics but has seen only limited application to date for hydrogen production. Challenges with commercialising methane pyrolysis for hydrogen production include:

Materials: Methane pyrolysis is an endothermic reaction that occurs at high temperature (1,000 – 1,500C). Steady-state reactor designs can require specialised materials of construction to meet high temperature heat transfer requirements.
Catalysts: Catalysts can be employed in reactor designs to reduce the pyrolysis temperature, alleviating material challenges. However, these catalysts are often sensitive to poisoning and de-activation, which must be addressed through reactor and process design.
Carbon Fouling: Solid carbon produced by the pyrolysis reaction can foul reactor internals, as well as catalysts used to promote the reaction. Carbon fouling adds additional system complexity and cost for its remediation.
Electricity Cost: Platforms that use micro-wave or plasma for directly heating the pyrolysis reactor are electricity-intensive, which can add cost for plant operations and impose further constrains for clean electricity availability.
Solid Carbon Disposal: Industry has limited experience sequestering solid carbon, rather than CO2. New approaches for handing and storing solid carbon are needed that can demonstrate the viability of methane pyrolysis at scale.
Carbon Markets: Traditional carbon black markets for rubbers, tires and specialty plastics are significantly smaller than hydrogen markets and extremely demanding in terms of grade and morphology for carbon delivery. These considerations present a challenge to methane pyrolysis companies that are seeking to sell carbon as a means for offsetting production cost in their operations.  The availability of low-cost by-product carbon from hydrogen production presents new opportunities for large-scale, bulk carbon utilisation in ubiquitous markets such biochar replacement for agriculture and application in construction materials, such as asphalt and concrete. Developing these markets is a key step to maximising economic value for methane pyrolysis.

Techno-economic Analysis

A generic techno-economic analysis was conducted to explore the relative economics and greenhouse gas emissions intensity of competing clean hydrogen pathways.  A list of input assumptions is provided in the table below.  Inputs for the methane pyrolysis pathway capture a range of values that represent the diverse technology platforms under development.

Grey
Blue
Green
Turquoise
 
 
Technology

Process Inputs

Unit

(/kg-H2)

SMR
SMR

+CCS

PEM

Electrolysis

Methane Pyrolysis

Baseline Economic

Assumptions

Capacity (TPD-H2)

300
300
300
300

NG Feedstock Cost: 3/GJ
Installed CAPEX ($US)

$340M
$815M
$860M
+/-20% SMR

Industrial Electricity: $70/MWh
NG Input
kg-NG
3.7
3.7
–
4.8 – 5.3

Renewable Electricity: $30/MWh
Water Input
kg-H2O
6.0
6.0
9.0
–

Steam Sales Price: $3/GJ
Electricity Input
kWh
2.0
2.8
55.0
2.4 – 10

Carbon Sales Price: $0/t-C
Steam Production
MJ/kg
–
–
–
0 – 2.4

Cost of Water: $0.001/litre
Carbon Production
kg-Carbon
–
–
–
3.2 – 3.8

Cost of CO2: $0/t-CO2
CO2 Production
kg-CO2
10
1.0
–
0.6 – 1.0

Cost of CCS: $80/t-CO2
Water Production
kg-H2O
–
–
–
0 – 2.8

Electrolyser CAPEX: $1,000/kW

Electrolyser Efficiency: 55 kWh/kgH2
Upstream GHG Emissions Factors

(Canadian average)

Upstream NG Emissions (kg-CO2/GJ)
9.5

Cost of Capital: 10%
GHG Intensity Electricity Grid (kg-CO2/kWh)
0.129

Amortisation Period: 20 years
GHG Intensity Renewable Electricity (kg-CO2/kWh)
0.010

Fixed O&M: 5% CAPEX/year

 

Results of the analysis are illustrated in the figure below. Cost of hydrogen production includes all CAPEX and OPEX considerations for a 300 TPD plant capacity.  GHG emissions intensity is calculated to include process emissions, as well as all upstream emissions for natural gas and electricity needs.

Hydrogen produced from electrolysis can achieve very low GHG emissions intensity when renewable electricity is used as the feedstock.  However, when conventional electricity grids are used for driving the electrolysis process, GHG emissions are high and unattractive.  Moreover, the cost of electrolytic hydrogen is heavily dependent on the price of electricity, which adds further deployment and scaling constraints for this solution.

By contrast, methane pyrolysis platforms produce industrial-scale hydrogen with GHG emissions comparable to fully deployed SMR+CCS solutions.  More significant GHG emissions mitigation may be achieved by methane pyrolysis when renewable electricity and/or renewable natural gas are used for parasitic loads and heating, but these are not considered in the analysis. Moreover, with optimised architectures, methane pyrolysis solutions can achieve very compelling economics that competes closely with incumbent SMRs.

Conclusion: Methane pyrolysis provides a compelling pathway for low-cost and clean hydrogen production that can be flexibly deployed across global natural gas networks and deliver significant GHG emissions reductions … without adding cost.