Publications

Underground hydrogen storage in salt caverns is a promising solution for short-term storage allowing multiple cycles per year. This study experimentally investigates the integrity of such caverns and their wellbores under operating conditions typical of German salt caverns. Specifically we measure the permeability of rock salt cement (API Class G and High Magnesium Resistant (HMR+)) rock salt-anhydrite composites cement-salt composites and casing-cement composites. Rock salt demonstrates extremely low permeability (10− 23 m2 ) while casing-cement composites (HMR+) exhibit permeabilities similar to pure cement (10− 20 m2 or lower). Both salt-cement (HMR+) and casing-cement (HMR+) composites meet the strict tightness requirements for hydrogen storage (10− 19 m2 or less). While thin anhydrite layers in rock salt can increase permeability compaction can reduce it to levels comparable to rock salt. This study’s novelty lies in evaluating the feasibility of a real German cavern for hydrogen storage using a custom-built transient permeability setup capable of testing casing-cement composites at a 1:1 wellbore scale.

Integration of hydrogen into the existing natural gas infrastructure is considered a potential pathway that can accelerate the incorporation of hydrogen into the energy sector. While blending renewable hydrogen with natural gas offers advantages such as reduced carbon intensity and the ability to utilize existing infrastructure for hydrogen storage and transportation there are several concerns including leakage and associated issues. Un derstanding the behavior of hydrogen blended with natural gas in the existing infrastructure is crucial to ensure safe and efficient integration. In this study the leakage rates of mixtures of hydrogen and methane at different molar concentrations (5% 10% 20% and 50% hydrogen) through both precision machined orifices and com mon pipe fitting threads were investigated. The experiments showed that the leakage rates of these mixtures increased as the hydrogen content increased; however gas chromatography (GC) analysis showed that hydrogen did not leak preferentially at a greater rate than methane. The results indicate that mixing hydrogen with methane can increase the volume of gas leakage under the same pressure conditions. These findings suggest that mixing hydrogen with natural gas may result in increased volumetric flow rate of gas leaks but hydrogen alone does not leak preferentially to methane.

Green hydrogen has the potential to decarbonize hard-to-abate sectors and processes and should therefore play an important role in the energy system in achieving climate goals. However the main hydrogen supply is still based on fossil fuels and only limited amounts of electrolyzers have been installed. Switching from fossil-based fuel sources to green hydrogen is highly dependent on when and at what price green hydrogen will become available which in turn is dependent on the technological development of electrolyzers. In this paper we apply the experience curve methodology to project the capital expenditure and electrical consumption developments of the three main electrolysis technologies: alkaline proton exchange membrane and solid oxide electrolysis. Based on our calculations we expect that both AEL and PEM will reach similar costs by 2030 of around 300 e per kW and SOEC will remain the most expensive technology with a considerable cost reduction down to 828 e per kW. The electrical consumptions will fall to 4.23 kWh per Nm3 for AEL 3.86 kWh per Nm3 for PEM and 3.05 kWh per Nm3 for SOEC. Based on this technological progress we calculate that the levelized cost of hydrogen will be reduced to 2.43–3.07 e per kg. To reach lower levelized cost of hydrogen notable reductions in electricity (purchase) cost are required.

The steel industry is one of the major sources of greenhouse gas emissions with significant energy demand. Currently 73% of the world’s steel is manufactured through the coal-coke-based blast furnace-basic oxygen furnace route (BF-BOF) emitting about two tonnes of CO2 per tonne of steel produced. This review reports the major technologies recent developments challenges and technoeconomic comparison of steelmaking technol ogies emphasising the integration of hydrogen in emerging and established ironmaking and steelmaking pro cesses. Significant trials are underway especially in Germany to replace coal injected in the tuyeres of the blast furnace with hydrogen. However it is not clear that this approach can be extended beyond 30% replacement of coke because of the associated technical challenges. Direct smelting and fluidised bed technologies can emit 20%–30% less CO2 without carbon capture and storage utilisation. The implications of hydrogen energy in these technologies as a substitute for natural gas and coal are yet to be fully explored. A hydrogen-based direct reduction of iron ore (DRI) and steel scrap melting in an electric arc furnace (EAF) appeared to be the most mature technological routes to date capable of reducing CO2 emission by 95% but rely on the availability of rich iron concentrates as feed materials. Shaft furnace technologies are the common DRI-making process with a share of over 72% of the total production. The technology has been developed with natural gas as the main fuel and reductant. However it is now being adapted to operate predominantly on hydrogen to produce a low-carbon DRI product. Plasma and electrolysis-based iron and steelmaking are some of the other potential technologies for the application of hydrogen with a CO2 reduction potential of over 95%. However these technologies are in the preliminary stage of development with a technology readiness level of below 6. There are many technological challenges for the application of hydrogen in steel manufacturing such as challenges in distributing heat due to the endothermic H2 reduction process balancing carbon content in the product steel (particularly using zerocarbon DRI) removal of gangue materials and sourcing of cost-competitive renewable hydrogen and highquality iron ore (65>Fe). As iron ore quality degrades worldwide several companies are considering melting DRI before steelmaking possibly using submerged arc technology to eliminate gangue materials. Hence sig nificant laboratory and pilot-scale demonstrations are required to test process parameters and product qualities. Our analysis anticipates that hydrogen will play an instrumental role in decarbonising steel industries by 2035.