Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - HySEA (Improving Hydrogen Safety for Energy Applications (HySEA) through pre-normative research on vented deflagrations)

Teaser

It is common practice in the industry to install equipment for hydrogen energy applications in containers or smaller enclosures. Explosion venting is a frequently used measure for reducing the consequences of accidental hydrogen deflagrations in confined systems. International...

Summary

It is common practice in the industry to install equipment for hydrogen energy applications in containers or smaller enclosures. Explosion venting is a frequently used measure for reducing the consequences of accidental hydrogen deflagrations in confined systems. International standards provide guidance in the form of empirical or semi-empirical correlations for the design of venting devices. The fact that such correlations typically are derived from, and validated against, experiments performed with empty explosion vessels, and often at significantly smaller spatial scale than the actual industrial applications, represents a challenge for safe implementation of hydrogen systems in society. This situation motivated the Fuel Cells and Hydrogen Joint Undertaking (FCH JU) call for proposal FCH-04.3-2014. This resulted in the project “Improving Hydrogen Safety for Energy Applications through pre-normative research on vented deflagrations”, or HySEA (www.hysea.eu).

The HySEA project started on 1 September 2015 and ended on 30 November 2018. The members of the HySEA consortium were Gexcon (GEXCON, coordinator), University of Warwick (UWAR), University of Pisa (UNIPI), Fike Europe (FIKE), Impetus Afea (IMPETUS) and Hefei University of Technology (HFUT).

The overall goal of the HySEA project was to conduct pre-normative research on vented hydrogen deflagrations, with an aim to provide recommendations for European and international standards on hydrogen explosion venting mitigation systems, and to develop models based on empirical or semi-empirical correlations, computational fluid dynamics (CFD) and finite element (FE) methods that can be verified and validated against data from experiments performed in containers and smaller enclosures with industry-representative obstacles.

The objectives of the HySEA project included:
• To perform experiments in real-life enclosures and containers with industry-representative obstacles.
• To characterise different venting systems and include measurements of structural response in these tests.
• To broaden the participation in the project by inviting the broader scientific and industrial community to participate in blind-prediction benchmark studies.
• To develop, verify and validate empirical models and CFD-based tools for reliable predictions of the reduced over-pressure in vented explosions.
• To develop and validate models for predicting the over-pressure and impulse of vented explosions.
• To use the validated CFD models to explore vented hydrogen deflagrations in larger enclosures, such as warehouses.
• To formulate recommendations for a harmonised international standard on hydrogen explosion venting mitigation systems.

Work performed

The research activities in WP1 focused on engineering models and standards. UWAR reviewed empirical and semi-empirical models for predicting the overpressures generated in vented hydrogen deflagrations and developed a new model inspired by the modelling approach of FM Global. Members of the HySEA consortium communicated relevant results and recommendations to the European Committee for Standardization (CEN), Technical Committee 305 (TC305), Working Group 3 (WG3), the ad-hoc group on gas explosions.

In WP2, UNIPI, GEXCON and HFUT completed experimental campaigns with vented deflagrations in homogeneous and inhomogeneous hydrogen-air mixtures. UNIPI designed a generic small-scale enclosure (SSE), suitable for investigating vented hydrogen explosions in installations such as gas cabinets, cylinder enclosures, dispensers and backup power systems. UNIPI performed 76 experiments with homogeneous mixtures and 82 tests with inhomogeneous mixtures in the SSE facility.

HFUT performed 124 vented deflagration experiments in a mini cylindrical vessel (MCV), investigated the effect of the opening pressure of the venting device on hydrogen deflagrations in a 1-m3 vessel, and performed 40 vented hydrogen deflagration tests with inhomogeneous mixtures in a cubic box. HFUT has also constructed an enclosure with the same dimensions as a 40-foot ISO container and completed more than 40 vented deflagration tests in this facility.

GEXCON designed a test rig for 20-foot ISO containers and completed 42 tests with initially homogeneous and quiescent mixtures and 24 tests with inhomogeneous mixtures. The experiments included measurements of the structural response of the container walls to internal pressure loads.

The research activities in WP3 focus on development and validation of advanced model systems. UWAR, in cooperation with HFUT, developed and validated the in-house computational fluid dynamics (CFD) solver HyFOAM, based on the open-source solver OpenFOAM. GEXCON developed the CFD solver FLACS-Hydrogen for simulating dispersion and explosion phenomena with hydrogen. GEXCON and IMPETUS developed a methodology for one-way coupling between the CFD tool FLACS-Hydrogen and the IMPETUS Afea finite element (FE) solver.

The project website (www.hysea.eu) describes most of the dissemination activities in WP4, including an updated list of publications, workshops, popular science events, newsletters, demonstrations, and two blind-prediction benchmark studies.

Final results

The new semi-empirical model developed by UWAR for estimating the maximum reduced explosion pressures in vented hydrogen deflagrations will be a valuable addition to the European standard for gas explosion venting protective systems, and thereby contribute significantly to the safe implementation of hydrogen as an energy carrier in society.

The experimental study of vented hydrogen deflagrations in containers produced valuable validation data for modellers. The results demonstrate the strong effect of congestion on vented deflagrations and a rapid increase in explosion violence for more reactive mixtures and higher levels of congestion. The results also highlight the importance of considering projectiles, including the container doors, in risk assessments and design.

The results from the vented deflagration tests demonstrate that explosion protection by venting can be effective for 20-foot ISO containers under near worst-case conditions, as long as severe structural damage of the enclosure can be tolerated, and provided deflagration-to-detonation-transition (DDT) does not occur.

Future verification and validation of CFD and FE models should entail direct comparison between experimental results and model predictions, and it is foreseen that this process will result in improved understanding of the physical and chemical phenomena involved in vented hydrogen deflagrations.

Loss of containment of gaseous hydrogen in confined spaces will typically result in buoyant releases and stratified fuel-air clouds. The significantly higher overpressures obtained for stratified mixtures, compared to lean homogeneous mixtures with the same total mass of fuel, imply that models for vented hydrogen deflagrations need to account for the effect of inhomogeneous fuel-air clouds.

The second blind-prediction benchmark exercise in the HySEA project explored the predictive capabilities of consequence models with respect to simulating vented deflagrations resulting from stratified hydrogen-air mixtures ignited to deflagration in 20-foot ISO containers. There is significant room for improving the predictive capabilities of both the model systems and the modellers.

Website & more info

More info: http://www.hysea.eu.