Advantages: Implementing CCS to decarbonise the incumbent SMR process enables rapid impact to existing hydrogen production infrastructure. Disadvantages: Incorporating CCS adds substantial cost. Moreover, the CCS process cannot be ubiquitously deployed, as the permanent storage of CO 2 is not suitable to all locations. As such, the application of CCS as a decarbonisation pathway is limited in terms of its location and global impact. Green hydrogen Green hydrogen combines electrolysis with renewable electricity to produce hydrogen from feedstock water. This emerging pathway is attractive for its potentially low GHG emissions. Moreover, electrolysis is a commercial and scalable technology solution that can be readily deployed for distributed hydrogen production. Electrolysis, however, is an electricity-intensive process and, as a result, electrolytic hydrogen is often expensive unless very low-cost and highly dispatchable electricity is available. Furthermore, electrolysis requires low carbon- intensity electricity generation 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. Advantages: Potential for ultra-low GHG emissions when coupled with renewable electricity production. Disadvantages: Electrolysis is electricity- intensive and therefore often expensive to implement. Pink hydrogen Pink hydrogen combines water electrolysis with nuclear energy. The attributes of this pathway are largely aligned with those of nuclear power generation and its own regional considerations. Turquoise hydrogen Methane pyrolysis is an emerging alternative for clean hydrogen production. In a pyrolysis reactor, feedstock methane is heated to pyrolysis conditions (1,200-1,500°C) and dissociated into solid carbon and hydrogen. Since solid carbon is the principal byproduct,
process. These techniques are principally differentiated by the material feedstock and energy source used. Regardless of colour designation, the most important criteria that distinguish hydrogen production pathways are GHG emissions intensity (i.e., how much CO 2 is emitted during the hydrogen production process) and production cost. A brief description of each pathway is provided below, along with their unique attributes that describe cost and emissions: Black/brown hydrogen Black or brown hydrogen is produced from the gasification of coal. The colour refers to the type of coal used in the process, bituminous (black) and lignite (brown) coal. Gasification of coal is largely used in Asia, where coal is a lower cost and preferred feedstock to natural gas. Nevertheless, coal gasification is the most GHG- intensive of hydrogen production pathways and a technique not largely used in North America. Grey hydrogen Grey hydrogen is produced from natural gas. Steam methane reforming (SMR) produces hydrogen by passing natural gas and steam across a high-temperature catalyst bed. The reactor produces a hydrogen-rich stream that is subsequently purified for hydrogen delivery to the customer. SMR is the current industry standard process for large-scale hydrogen production. It accounts for roughly 90% of hydrogen production in North America and nearly 50% of global production. SMR is favoured for its low production cost, where low- cost natural gas feedstock exists. However, the SMR process emits substantial GHG emissions, which are costly to mitigate. Blue hydrogen Conventional SMRs can be equipped with carbon capture and sequestration (CCS) systems to reduce GHG emissions. CCS systems capture and purify the CO 2 from SMR emissions. The CO 2 is then compressed into a pipeline for delivery and permanent underground storage. Compared with a conventional SMR, the adoption of CCS can achieve GHG reductions in the range of 50- 90%, depending on the utilisation and location of the CO 2 capture process.
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