Gas compression is a key process for transporting, distributing, storing and dispensing hydrogen. It accounts for a relevant share of costs and energy consumption in most hydrogen supply chains from initial hydrogen sourcing to final hydrogen use. Today, various compression technologies are applied, depending on use cases, flow rates, and input and output pressure levels.
Hydrogen refueling stations (HRS) are a specially challenging application for compressors. The input pressure levels are often in the range of atmospheric pressure up to about 5 MPa, depending on the gas supply concept of the station. The output pressures of the compressors need to be as high as 90 to 100 MPa i case of passenger car refueling (nominal vehicle tank pressure at 70 MPa) or at about 50 MPa in case of heavy-duty vehicle refueling of e.g., buses, trains or trucks (nominal vehicle tank pressure at 35 MPa). This results in large compression ratios that need to be covered within the HRS. Multiple serial compressor stages are usually applied to do the job.
Industry is permanently working on the optimization of existing compressor technologies to reduce compressor’s energy consumption, wear and tear, costs and footprint and also to increase reliability and operation dynamics. Novel compression concepts are also developed and tested such as ionic liquid pistons, bladder accumulator-based compression, electrochemical compression or compression based on the use of metal hydrides.
The Fuel Cell and Hydrogen Joint Undertaking (FCH JU) has supported the development of metal hydride-based compression since 2017 under the Horizon 2020 program. In an initial project called “COSMHYC” (COmbined Solution of Metal HYdride and mechanical Compressors) a prototypical hybrid compressor combining metal-hydride and diaphragm compression for 70 MPa refueling was developed and tested between 2017 and 2021. Based on positive results from this project, a second project called “COSMHYC XL” was started in 2019 (ongoing) to also address 35 MPa heavy-duty refueling of buses and trucks. In 2021, a third project “COSMHYC DEMO” started to support the demonstration of the technology at a real HRS, in France. Within this project series, the metal-hydride compression technology is to be increased from initially TRL 3 to a targeted TRL 7 at the end of the demo project. Further, the diaphragm compressor is adapted and optimized for the use in the hybrid concept. The project consortium consists of the following partners: EIFER (project coordination and hydride compressor development), Mahytec (hydride and reactor development), NEL (adaption of mechanical booster compressor), Steinbeis 2i (communication and innovation management), LBST (techno-economic evaluation).
How metal-hydride compression works
Hydrogen compression with metal hydrides works completely differently compared to conventional mechanical compression technologies. The key component of a hydride compressor is the reactor which is made out of a pressure vessel containing a heat exchanger and a special metal alloy – the hydride. Compression itself is a four-phase process.
First, hydrogen is fed into the reactor chamber at source pressure and ambient temperature. The metal hydride absorbs the hydrogen into its matrix while emitting heat. This heat is permanently taken from the reactor. The amount of hydrogen absorbed increases, the pressure in the reactor remains constant. […]
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Author: Jan Zerhusen – Ludwig-Bölkow Systemtechnik GmbH, Ottobrunn, Germany