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Fueling Stations, System Design

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Fueling Stations, System Design

There are no differences in the process design of the vent stack since the venting requirements will follow the same sizing and pressure rating requirements regardless of vent configuration. However, vent systems often create liquid air on their exterior due to the cold venting temperatures. Since this liquid air will drip off the stack, it should be diverted such that it does not directly…

Category: System Design

Flame arrestors can be installed on hydrogen gas vents. The purpose of a flame arrestor is to prevent the migration of flame backwards and upstream into the vent stack or system itself. Generally, flame arrestors are not needed since: 1) the vent stack should be designed to withstand fire or explosion within the stack, and 2) the process generally does not contain a flammable mixture within it…

Category: System Design
Keywords: Vent, Flame Arrestor

The main advantage of a “tee” style design is that the thrust loads at the vent exits are balanced. This means that an unequal force that might push the vent stack over is not present. Generally, the tee is also of the same size as the main vent line, thereby doubling the vent area for less pressure drop. The main disadvantage of a tee stack is that they generally vent with a horizontal…

Category: System Design

The most common modes of failure for vent lines is backpressure and thrust forces.
Backpressure failures can be from several causes:

  • Inadequate calculation of the backpressure caused by the high flow rates. Vent system design pressure is often only designed for the maximum 10% backpressure that is required by ASME Code. However, it should be noted that the large flowrates from…
Category: System Design

Vent systems are typically open to the atmosphere, so it’s easy to overlook that they must be designed to withstand significant internal pressure. The two primary sources of pressure within vent systems are: 1) backpressure from the flowing gas, and 2) internal deflagration/detonation.

The large flows of gas exiting relief devices and vents will create backpressure within the vent system…

Category: System Design

Yes, for all stacks. GH2 has a minimum prescriptive height of 10 ft. There is no minimum prescriptive height for LH2. However, 25 ft has been a best practice for the industry for years. Vent stack outlets that orient the release vertically help reduce the radiation exposure at ground level. Care must be taken to consider varying weather conditions, particularly wind, as well as surrounding…

Category: System Design
Keywords: LH2, GH2, Flare, Vent Stack

Generally flaring is not recommended. Normally GH2 is not flared for most hydrogen equipment as the piping diameters are smaller. The largest stacks are the LH2 vent stacks on trailers and on tanks for the main safety valves are 3”. For GH2 systems the flare stacks are generally smaller in diameter. 

Flaring is a deliberate ignition of a hydrogen stream. If the hydrogen stream is to…

Category: System Design

Fuels like gasoline are exempt from OSHA process safety management (PSM) requirements. When asked about the applicability for hydrogen storage larger than 10,000 lb (4500 kg) being used as a fuel, OSHA responded with an interpretation that can be found at https://www.osha.gov/laws-regs/standardinterpretations/…

NFPA 2 Annex G provides a summary of the conflicts with 29 CFR 1910.103. This is language that has been in NFPA 55 for several cycles as this conflict has existed for many years. The requirements in the Federal Regulations were established in the early 1970s. Since that time, OSHA has not had sufficient resources to update the applicable provisions.

The primary difference between OSHA…

Category: System Design

The recognized and generally accepted good engineering practices (RAGAGEP) for employing a nitrogen purge into a hydrogen vent stack is that inerting is not generally used for nitrogen purge in a hydrogen vent stack because most inert gases freeze at liquid hydrogen temperatures. The vent stack should be designed for a fire and the internal overpressure caused by a deflagration. If inerting is…

Category: System Design
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