Energy transition and hydrogen
At the United Nations climate change conference in Paris, COP 21, governments agreed that mobilizing stronger and more ambitious climate action was urgently required to achieve the goals of the Paris Agreement. The goal of this agreement was to limit global warming to well below 2°C, preferably to 1.5°C, compared to pre-industrial levels.
Its entry into force has already sparked low-carbon solutions and new markets. More and more countries, regions, cities, and companies are establishing carbon neutrality. But at the same time, the demand for energy is continuously increasing. Petroleum and natural gas are currently the main sources of energy worldwide, but their combustion contributes to greenhouse gases and air pollutant emissions. Therefore, the search for an alternative fuel that provides as much energy and is environmentally friendly is of utmost importance.
Hydrogen is considered one of the most promising fuels for generalized use in the future, mainly because it is a versatile, energy-efficient, low-polluting, and renewable fuel. Hydrogen is a high-quality energy carrier, which can be used with high efficiency and zero or near-zero emissions at the point of use (carbon dioxide is still released during the production of grey or blue hydrogen). Nevertheless, to ensure the safe handling, production and storage of hydrogen, its chemical and physical properties need to be studied.
Incidents involving hydrogen
Hydrogen has been produced and used for years with a high safety record for commercial and industrial purposes such as refinery, chemical processes, and rocket propulsion. However, when introducing this material in other environments, we will have to consider the fact that hydrogen is a substance that needs to be handled with care.
Recent accidents like the explosion at the Uno-X hydrogen refuelling station in Kjørbo (June 2019), the gas explosion at the Airgas facility in Wisconsin (December 2019), the explosion at the One H2 Hydrogen Fuel plant in North Carolina (2020), or the explosion at Medupi Power Station in South Africa (August 2021), help us realise the dangers of using hydrogen and learn from the past.
Safety aspects of hydrogen
We can ensure the safe production, transportation, and usage of hydrogen by carefully considering its typical properties and associated safety aspects.
Some of the hydrogen’s properties are as follows:
- It is an extremely buoyant gas. It has a density 14 times lighter than the density of the air. That means that the buoyant forces of hydrogen are 6 times the ones of natural gas.
- It diffuses faster than any other gas.
- It has a very wide flammability range, specifically 4-75%.
- When directly burned (in a furnace, for example), NOx emissions are higher than for other hydrocarbons due to hydrogen’s wide flammability range. Thus, not only water is released, but NOx is also produced.
- Its laminar burning velocity is about 3 m/s, which is 6 times faster than hydrocarbon gases.
- It has a very low ignition energy of 0.02 mJ, which is about 10% of the ignition energy for petrol fumes.
- It exposes a Negative Joule-Thompson effect, implying it might heat up during expansion.
- It has a tendency for auto-ignition when leaked at high pressures.
- A hydrogen flame is almost invisible as the heat radiation from the flame surface is very low.
- The solubility of hydrogen is very pronounced in metals.
- The adsorption of hydrogen in steel may cause embrittlement which may lead to failure of equipment.
- Because it can only be liquefied at temperatures below -240°C, the use of liquefied hydrogen presents some additional hazards such as possible frostbite burns, hypothermia, accumulation of ice formed from moisture in the air in vents and valves, and storage vessels must be under pressure to prevent air from entering and producing flammable mixtures.
Chemical properties
At current ambient temperature, hydrogen is non-reactive. At higher temperatures, the hydrogen atom is chemically very reactive, so it is not found chemically free in nature. Most of the hydrogen is bound to either oxygen or carbon atoms in nature. Hence, to obtain hydrogen from natural compounds, energy expenditure is needed. That is why hydrogen must be considered an energy carrier; a means to store and transmit energy derived from a primary energy source.
Hydrogen hazards
Hydrogen hazards can be classified under three categories: physical hazards, chemical hazards, and explosion phenomena [1].
Physical hazards
Embrittlement causes the mechanical properties of metals to degrade and, hence, to fail, resulting in leaks. Embrittlement can be controlled by oxide coatings, stress concentration elimination, alloy selection, etc. Low-temperature behaviour shows the transition from ductile to brittle, plus elastic and plastic changes due to phase transformation in the crystalline structure. Thermal contraction coefficients should be considered to avoid leaks due to thermal contraction and expansion at cryogenic temperatures.
Chemical hazards
LH2 and liquid or solid O2 can detonate when initiated by a shock wave. Ignition energy is minimal (0.02 mJ); hence, open flames, electrical and heating equipment should be safely isolated in buildings containing liquid hydrogen systems.
Explosion phenomena
Hydrogen systems should be carefully evaluated on potential vapour cloud explosion risks. Although the light gas might quickly rise, it can be captured under roofs or ceilings. The high laminar burning velocity can lead to an explosion strength reaching detonation levels. The stoichiometric mixture of H2 – air produces 2/3 of the explosion energy of TNT. However, explosive combustion will only occur at concentrations above 10 vol%. Therefore, leak detection and avoiding a build-up of concentration are of extreme importance in the application’s design.
Research and development
Gexcon has been and is still actively involved in multiple hydrogen safety research projects and offers a complete solution to support their clients in understanding and mitigating the consequences of hydrogen hazards. As research results become available, Gexcon continuously works to improve the models in their software tools and uses the experimental data available to validate the software.
In the videos below, you can see some tests that have been conducted by or in collaboration with Gexcon.
The experiment in the video below involved the release of 700g of hydrogen. For comparison purposes, the explosion that took place at the hydrogen filling station in Sanfvika (2019) involved the release of approximately 1.5 and 3 kg of hydrogen.
The experiment in the video below involved the release of 21% hydrogen stored in a 20ft container, and it was one of the test cases used to validate Gexcon’s CFD software FLACS.
The two videos below show the significant difference in the release of 12%vol hydrogen and 15%vol hydrogen.
By understanding all of the hydrogen’s properties, we can improve Gexcon’s consequence models, such as those implemented in the software tools EFFECTS and RISKCURVES. These software tools have undergone and still undergo significant improvements, emphasising hydrogen releases, jet fires, fireballs, and lighter-than-air dispersion clouds.
This way, we can accurately simulate the consequences of the accidental release of hydrogen and thus, ensure the implementation of the relevant prevention and mitigation measures.
References:
[1] Yousef S.H. Najjar. Hydrogen safety: the road toward green technology. Mechanical Engineering Department, Jordan University of Science and Technology. 2013
Free viewing demo version of EFFECTS available for download
Access EFFECTS free viewing demo and view the results of already calculated projects.
Do you like what you read?
Get the latest trends in the field of process safety management straight to your inbox, and enhance your skills through knowledge sharing from industry experts.
