Hydrogen Leakage: A Potential Risk for the Hydrogen Economy
Hydrogen has been identified as a potential safety issue based on the fact that it is the smallest molecule that exists and can easily pass through materials.
Hydrogen Leakage: Knowns and Unknowns
Hydrogen leakage risks have been identified along the entire value chain of hydrogen. In assessing these risks, this commentary divides the hydrogen value chain into three categories: production, delivery, and end use
The leakage rate stands between 2.9 percent (low-risk case) and 5.6 percent (high-risk case), and the total leakage volume stands between 15.3 Mt and 29.6 Mt. This can represent a non-negligible contribution to global warming and up to a $59 billion/yr value loss of hydrogen (assuming $2/kg-H2).
Detection, Monitoring, and Prevention Technologies
Hydrogen sensors, leak detection, and other safety infrastructure and techniques are still not at the scale of commercial production required to cover desired application scenarios. As the market has begun to adapt to meet new demands for hydrogen use, however, several technologies have been developed or are being refined to meet the challenge of fast, reliable hydrogen leakage detection across a range of production and fueling environments.
The highly flammable nature of hydrogen-air mixtures at concentrations above 4 percent and the conditions under which hydrogen is stored and transported require specific and concrete goals in the realm of hydrogen sensors. The DOE has set targets for hydrogen sensors using the parameters of accuracy, response recovery time, detection limit, ambient humidity, temperature, and pressure. After more than a decade of research, these targets have not yet been met (Granath 2015), but technology is improving, and several types of sensors are now available for production facilities, pipelines, and indoor and outdoor use.
Findings and Recommendations
Finding 1: There is almost no data on and regulation of present hydrogen leakage rates and risks beyond required safety management. Hydrogen leakage data is not available for many industrial production and application processes. Most sources are not cross-referenced for those processes where leakage data is available but are rather simulation based and sometimes extrapolated from similar studies. Moreover, the data does not include device-level analysis and therefore cannot support bottom-up analysis, which is the typical way of assessing economy-wide, aggregated leakage rates. The current literature does not provide a clear understanding of the actual status of hydrogen leakage today.
Finding 2: Few technologies are available for hydrogen leakage detection and monitoring. Few commercial products have been identified to support hydrogen leakage detection, a step that is essential to fully understanding the current and future situation. This market shortage is partially due to lack of regulation: many countries have not developed dedicated legislation and regulatory frameworks for hydrogen production, transportation, storage, and end use, including in regard to hydrogen leakage monitoring. The need for more commercial products may be exacerbated by the expansion of the hydrogen economy, especially distributed sources such as fueling stations, fuel-cell vehicles, and end-use appliances.
Finding 3: Hydrogen leakage seems to be concentrated in a few key processes. By 2050, green hydrogen production, transportation, and storage (both pipeline and trucks); road transport vehicles; electricity generation; and chemical synthetic fuel production are expected to become the major sources of leakage. Together, they would contribute 77 percent of economy-wide hydrogen leakage. The main reasons for this large contribution are their broad scale (chemical and synthetic fuels production), high leakage risks (road transport vehicles, truck transportation, and storage), or both (green hydrogen production and pipeline transportation and storage).
Finding 4: Initial analysis suggests an increased risk of higher economy-wide hydrogen leakage rates in the future chiefly from new production and delivery expansion. Many key leakage processes for 2050 scenarios do not exist in the current hydrogen system. With the expansion of the hydrogen economy, the scaling up of production/use and deployment of new processes will increase the chance of leakage and therefore risk levels. The 2050 high-risk scenario will lead to a 5.6 percent economy-wide leakage rate. In short, hydrogen leakage is expected to be a challenge for the hydrogen economy.
Recommendation 1: Develop research and data-gathering programs to better understand the existing hydrogen systems. A lack of understanding of the current hydrogen system and the significance of leakage prevents the development of realistic solutions and appropriate regulations. The current hydrogen system is mostly based on industrial production and applications, and the research and data gathering on leakage that is required will likely be impossible without support from industrial partners. In order to understand and rigorously estimate the scale of hydrogen leakage, new regulations and policies should emphasize hydrogen leakage detection.
Recommendation 2: Require monitoring programs for new hydrogen pilots and scale up programs to assess the leakage risk of new processes. In the future, the real leakage risk will likely be new processes such as green hydrogen production, fuel-cell vehicles, and dedicated hydrogen deliveries. If the goal is to address this potential leakage, monitoring programs will need to be implemented for all new processes at the production, delivery, and end-use stages. Active control of these processes through regulations and policies before they scale up can help reduce risks and potential economic losses associated with the future hydrogen economy.
Recommendation 3: Devote special attention to certain key processes that demonstrate potential to be scaled up or to address high leakage risks. Based on the available data at this stage, it is estimated that a handful of processes identified in Finding 3 would contribute to an estimated 77 percent of total hydrogen leakage in the 2050 scenarios. Significant resources have been dedicated to scaling up the production and use of hydrogen but not to controlling leakages in the process. To the extent that leakage estimates are confirmed and leakage is concentrated around key processes, research on leakage prevention and regulations for a few key processes will have greater impact than that for others if the goal is to effectively reduce overall hydrogen leakage.
Recommendation 4: Expand support for research and development programs on hydrogen leakage detection, prevention, and mitigation. There is insufficient research on how to prevent and mitigate hydrogen leakage. Moreover, the commercial products that currently exist for this purpose do not meet the requirements of device level, high sensitivity, and distributed small hydrogen leakage source detections. If the goal is to develop a thriving hydrogen economy without hydrogen leakage, research and development funding should be prioritized for hydrogen leakage detection, prevention, and mitigation, with special attention dedicated to bringing technologies currently at the research level to the commercial level.