Green Hydrogen: The Challenge of Safety Engineering
In the course of the energy transition, hydrogen will become increasingly important – especially the ‘green’ hydrogen produced by electrolysis with renewable electricity. At present, the global share of electrolysis hydrogen is still very low at less than five per cent, which is due in particular to the high production costs. However, these will drop significantly in the future.
The entry into a ‘hydrogen economy’ is in full swing. Although the chemical industry is well-practised in handling hydrogen, new challenges arise, especially in the field of safety technology. From a safety point of view, the exceptionally low minimum ignition energy is an important factor. Also, because of the extremely high flame speed, which is about eight times higher than that of a methane flame, a hydrogen-air mixture is exceptionally challenging.
In addition to the danger of explosion, there is the fact that hydrogen molecules are very small and have a high diffusibility, even through solid metallic materials. Therefore, there are special challenges to the tightness of hydrogen equipment, which, however, can be mastered technically.
Safety Standards for Hydrogen
Internationally, there are several standards covering the safety-relevant aspects of the most important elements in the hydrogen value chain, including electrolysis.
Measures of primary explosion protection are intended in particular to prevent the release of hydrogen through sufficiently sealed plant components. This is ensured by monitoring the immediate environment with gas-measuring devices. Tightness is a determining aspect of most safety concepts for hydrogen plants.
In Germany, the two categories “technically tight” and “permanently technically tight” have been well-proven for many years. At the European level, this necessity has been taken into account in the latest edition EN 1127-1. However, the EN differs significantly from the German standards with regard to the concepts and some technical details.
Transport and Storage
The requirements for safety technology are also high for the storage, transport and re-conversion of hydrogen. As in the case of production, however, there are still no really adequate norms and standards internationally for all processes. The safety requirements for the operation of a comprehensive hydrogen infrastructure are not higher than those for fossil fuels, but neither are they lower – at least in terms of explosion hazards. Properties that are favourable in terms of safety, such as the high volatility due to the low density, are countered by less favourable properties such as the extremely low minimum ignition energy and the high diffusion coefficient.
In the future, hydrogen will not only be handled in plants well isolated from the public and operated by trained personnel, but many new applications will be decentralised. For instance, electrolysis plants will be built near wind farms, and extensive hydrogen supply and refuelling networks be established.
It is therefore very commendable that ISO and IEC address many important aspects of safety engineering along the hydrogen chains in international standards, writes Prof Dr Thorsten Arnold in the trade journal “Chemie Technik”.
Photo: Negro Elkha