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Purging is not recommended as a continuous part of vent stack operation. However, maintenance activity is a transient event and it’s prudent and recommended to purge a vent system prior to performing maintenance. It’s always possible that hydrogen could be leaking internally from a valve or other component and therefore create a hazard. Of particular note, care must be taken that proper…
There are many potential sources of delayed ignition. Hydrogen is easily ignited, and the larger the cloud, the more likely it is for it to find an ignition source. The cloud itself may serve as an ignition source as the force of the gas release may cause dust or other contaminants to mix in the air creating a static charge which ignites the hydrogen. Similarly, the force of the release can…
We are not aware of a study for blended NG/H2. However, for high concentrations of NG, the vent system should be similar to NG, which still recommends a vent system as NG is less dense than air. For nearly pure hydrogen the recommendations of this presentation are in effect.
We would not open the vent system to inspect the internal piping without a good reason.
It is recommended to check for water in the vent stack trap
Absolutely. Vent systems will experience a variety of transient conditions of pressure, temperature, and thrust load, so stress analysis to anticipate the strength and flexibility needed are important for safe design. These issues are often overlooked and only become an issue when they are called upon to operate in emergencies.
It is a best practice to include the vent system in…
Delayed ignition is a significant hazard for hydrogen releases, either intended or unintended. The primary concern is the overpressure and energy release created from a vapor cloud which could contain a significant quantity of hydrogen. The H2Tools Incidents database contains a number of examples of delayed ignition.
Recommended limits of heat flux for various exposures is provided in documents such as API Standard 521, the International Fire Code, the National Fire Protection Association and the Society of Fire Protection Engineers. Selection of a specific thermal radiation level is dependent upon a risk analysis. Some salient exposures are listed below.
Water icing at the exit of a stack is certainly an issue in cold climates. Significant effort has been put into vent stack outlet design to minimize the probability. Documents such as CGA G5.5 have topworks that are recommended. Stacks that face upward have a higher probability of having water, ice, or snow enter the stack and freeze.
The colors of hydrogen are not different hydrogen molecules. The colors represent the different methods to produce hydrogen. The colors are based on how much carbon is produced into the atmosphere during the manufacture of hydrogen.
That being said there is no difference in hydrogen vent systems design by color, only by the design parameters (i.e. temperature, pressure, flow rate,…
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