Abstract
The PosHYdon project (PosHYdon website) is an innovative energy transition pilot project in the Dutch North Sea. The project is the first of its kind in the world and will produce green hydrogen using offshore wind power on an operational platform. Electricity from offshore wind will be used to electrolyze filtered sea water, producing hydrogen for transportation to shore using existing North Sea gas infrastructure. This has the potential to vastly reduce complexity and cost. However, using the existing gas infrastructure means the newly produced hydrogen will pass through other existing operational platforms which can impact the safety risk profile of the existing assets.
This paper presents recent modelling work carried out by Kent to help a Dutch North Sea operator understand the change in risk on their production platform due to the presence of this hydrogen passing through the facility. Advanced Computational Fluid Dynamics (CFD) modelling techniques have been applied to quantify the consequences of accidental releases of gas mixtures containing hydrogen. This modelling work includes simulating the dispersion of releases and subsequent build-up of flammable gas, as well as the overpressures generated by vapour cloud explosions caused by the ignition of flammable clouds.
These consequences have been combined with historical leak frequency data and ignition probabilities to calculate probabilistic explosion loads for critical locations on the platform, allowing the operator to understand and manage any change in risks due to this novel project.
The following conclusions have been drawn from the study:
The ignition probabilities for hydrogen releases are higher than for conventional hydrocarbons. It is difficult to quantify the extent to which ignition probabilities will be increased for releases which are a mixture of hydrogen and conventional hydrocarbons, so there is an opportunity for further work in this area. For the purposes of this study, ignition probabilities have been taken from UK Offshore Operators Association (UKOOA) curve 21 (International Association of Oil & Gas Producers, 2010) and doubled, following the Energy Institute guidance (Energy Institute, 2006).
The wider flammable range of hydrogen resulted in increased flammable cloud volumes for large hydrogen containing releases, compared to conventional hydrocarbons. The flammable volumes for smaller releases were similar between the hydrogen containing releases and the conventional hydrocarbon releases.
The higher reactivity of hydrogen resulted in an increase in overpressure on a key target of between 25% and 90% depending on the hydrogen content.
The combination of these factors resulted in an increase in overpressure loads at critical frequencies of up to 40% for a key target on the platform.
