Multiple challenges needed to be overcome for opening the way to bladder accumulator based compression for hydrogen vehicle refuelling. These resided in
- The system design and specification
- The development of a 900 bar bladder accumulator in carbon composite material
- The identification of suitable bladder material for operation in hydrogen service
- The development of testing area, and specific test benches
- The development of novel hydraulic process functions
- A comprehensive component and system qualification testing
The following development activities were carried out:
Accumulator development:
- Development of an accumulator in carbon composite material suitable for hydrogen service, for two levels of operating pressure: 35 MPa and 90 MPa. One of the main challenges here was the development of a composite shell for this high level of pressure with the large diameter port required for bladder insertion and replacement.
- Identification of the right bladder material and operating conditions for resistance to rapid gas decompression and to the targeted volumetric ratios. In the foreseen pressure cycling conditions with hydrogen, most elastomers are likely to suffer critical damage due to the development of cavities from release of previously absorbed gas inside the material when the pressure is decreased. Furthermore, the allowable volumetric ratio (fully expanded volume / fully compressed volume) of the accumulator needed to be maximized as this determines the minimum admissible hydrogen supply pressure.
- Verification of fitness for service of the accumulator bladders. This was to be achieved through functional and endurance testing of the accumulator reproducing the foreseen operating conditions in hydrogen service.
- Accumulator endurance testing; endurance testing of accumulators to verify that the bladders withstand the repeated bending associated with the high volumetric ratio applied, in accordance with the target cycle life.
Compression and buffering module (CBM) process development
- Development of the CBM accumulator actuation process, optimizing performance and energy consumption, while ensuring bladder integrity. Both of these objectives are achieved through modelling and process simulation. CBM process design studies also need to cover physical integration optimization and projected costs.
- Definition of measures for process safety.
- CBM prototype engineering and construction: construction of a full-scale system designed to meet or exceed the performance requirements defined for an HRS
CBM system testing
- Development of a test area for full scale system testing with hydrogen in closed loop.
- Functional testing of CBM prototype, in order to demonstrate process performance, as well as system durability
- Evaluation of hydrogen purity, a critical point for dispensing to fuel cell electric vehicles.
Preparation of market introduction
- Techno-economic analysis of the CBM process based on project results
- Analysis of gaps in regulations, codes and standards (RCS) and development of recommendations for closing these with the objective of advancing the establishment of a globally harmonized standards framework for the CBM process.
