HyDelta 2: safe operations of the high-pressure transmission grid. D5.1 Venting and flaring

As part of the national research programme HyDelta, a study was carried out into the possibilities of depressurising high-pressure hydrogen transport pipelines by venting and flaring. The research as described in this report is part of work package 5 "Working safely on the high-pressure transport network". Gasunie was commissioned by the Dutch government to create a national hydrogen transport system. During the operation of this network sometimes modifications have to be made to this transport system. In some cases hydrogen needs to be extracted from the network in a controlled manner to be able to work safely. To decrease the amount of hydrogen that has to be extracted, this will be done by pressure equalisation and followed by recompression. The residual hydrogen in the transport network has to be removed via venting or flaring. To determine whether high-pressure hydrogen pipelines can be depressurised using venting and flaring, 13 more specific research questions were formulated. These were answered by conducting theoretical and practical research. The theoretical study considered the differences between venting and flaring in general and made a comparison between flaring of natural gas and hydrogen. In addition, market information was gathered by interviewing two large industrial users familiar with hydrogen flaring and two flare installation suppliers. In the practical investigation, a flare was assessed for: • Direct ignition behaviour, • The behaviour in delayed ignition, • The risk of flame impact. Various measurements were performed; flow rate, heat radiation, flame appearance, noise levels, wind speed and NOx emissions. The findings of the experiments were compared with theory and various mathematical models. In particular, the flow profile through the flame arrestor, flame height, heat radiation and noise production were compared. The overall conclusion is that flaring is preferable instead of venting. This is after pressure equalisation and recompression has taken place. With the utilized flare installation, flaring of flow rates of 500, 2500, 4000 and 6000 Nm3/h were possible. During the experiments, no excessive noise production or excesses in pressure waves were observed. It is recommended to validate to what extent the results can be extrapolated for the application of flaring of larger flow rates and at larger diameters. In any hydrogen combustion process, forming NOx can be an issue. It is recommended to carry out further research on NOx measurements and reducing measures. For the design of hydrogen flare plants, existing theoretical models can be used. The results obtained from the experiments appear to be in reasonable agreement with the theoretical findings.