The UK Government’s Energy White Paper (2020) has identified hydrogen as a potential source of decarbonised heat in buildings. In order to prove the viability of hydrogen the UK Government requires a strong evidence base before deciding whether to promote hydrogen distributed in the existing gas network infrastructure (at all current pressures) to decarbonise heat.
Benefits
This Project focusses on a feasibility study to investigate the requirements of a hydrogen gas distribution network, focusing on the storage and gas pressures gas networks would be required to provide in order to meet the demands of the grid. The National Composites Centre (NCC) will investigate the feasibility of the existing methane gas storage architecture to transition to support hydrogen distribution and also investigate conceptual designs for storage solutions.
Learnings
Outcomes
Current Vessels
Due to the difference in storable energy between CNG and hydrogen, the existing vessels would need to be cycled at a higher rate than they are currently if hydrogen were used. This has implications on the fatigue life of the vessels.
HE is a cause for concern when repurposing metallic vessels for hydrogen storage. HE is a process that results in the reduced fracture toughness or ductility of metallics due to the effect of atomic hydrogen on the molecular structure and is the most probable cause of failure for metallic structures storing/distributing hydrogen. The current steel was assessed for its susceptibility to HE.
HE poses a potential threat to vessel structural integrity and containment capabilities. To alleviate this issue, hydrogen barrier materials were investigated. A low permeability barrier coating on the inside of the vessels will limit the amount of hydrogen contacting the tank steel, mitigating the risk of HE damage. There was no commercially available barrier material available at the scale required that has been proven compatible with and effective in preventing hydrogen permeation.
Future Storage Solutions
Numerous storage technologies show promise for hydrogen storage, including large-scale capacity in existing geological formations. Physical storage, in the form of compressed gas, remains the most feasible option for storage capacity requirements for the WSM site in terms of cost and manufacturability.
Assessment against requirements defined for conversion of the WSM storage facility deduced that metallic large-scale vessels, but in a revised steel that is minimally prone to HE, may provide a potential solution at high TRL, immediate supply chain, and cost. Vessels including composite materials can provide benefit where site logistics present challenges through the associated advantages in high pressure vessels, increased capacity, and modularity. However, these solutions will require additional development in manufacturing route, supply chain, and inspection strategy to demonstrate large-scale feasibility.
Lessons Learnt
Given the conflicting evidence around HE, testing of the current vessel steels is recommended, with a particular focus on comparison of the effects of hydrogen exposure on the fracture toughness and crack propagation resistance of pristine and weld area specimens.
Commercially available hydrogen barriers must be tested to prove adherent to BS EN ISO 11114-2:2020 and other appropriate certification standards, with cost approximation requiring a site visit. Testing on appropriate hydrogen barriers includes permeability testing (to accurately calculate barrier thicknesses required to reduce hydrogen pressure), testing against HE and permeability standards, and non-steady state modelling (long-term effects of hydrogen permeation through liners).
Viability of the vessel conversion will be determined by the requirements of route to certification by the approving body, including consultation with a PED approved ‘notified body’. Definition of this trajectory is essential to conversion.
Cost modelling on future solutions, both CapEx and OpEx, for any likely future duty cycles, compatibility with network and delivery, and storage longevity.
In future phases of work, WWU are encouraged to evaluate the future of hydrogen storage within the context of full network overhaul. Evaluation of requirements within the concept design work showed a bias towards an existing solution; realignment of robust requirements that describe the future (projected) energy network is needed.
Given requirement bias, detailed design is required for an informed decision into selection of a tangible storage solution. Further investigation into appropriate materials (both metallic and composite architectures), manufacturability, and design configuration will be necessary. Relevant standards around design (e.g. BS EN 17533:2020 Gaseous Hydrogen – Cylinders and tubes), transportation, inspection, maintenance, and environmental protection, will need to be identified and adhered to.
