Ventilation flowrate for concentration limits

[vinhermes]

Good morning to all,

I have a question about ventilation flowrate definition in order to stay below a concentration threshold during a leakage scenario. In concrete words, we have a room of 24 m3 that contains hydrogen fuel cells. The gaseous hydrogen maximum flow rate in the pipe is 4370 m3/h. In case of a pipe failure, the rules require that we stay below 1% concentration (meaning there can't be more than 0.24 m3 of H² in the room at any time).

This means that without ventilation, the 0.24m3 will be filled with hydrogen in 0.2 seconds approximately (0.24m3 / 4370m3/h * 3600).

The approach from there is that the volume needs thus to be renewed every 0.2 seconds -> 300 times per minutes -> 18 000 times per hour -> 18 000 * 24 m3 = 432 000 m3/h ventilation requirements.

Is this correct? This seems unmanageable to integrate... Thanks for your feedback. Vincent

 

[GT-EGR]

In short when you are pushing to stay below 1% then yes you need 99x that much to counter act.

I’d take another look at using the full pipe flowrate, leakage into the space and full pipe failure are two different things. In the end it’s up to whatever hazard you find possible that you want to protect, but in the past I’ve simulate leakage points in the pressurized pipes, not a full pipe break.

 

[nuuvox000]

What rules are you referring to? Do you have a code section for this requirement? What is the occupancy classification of this area? My guess is there is another way to skin the cat (who ever skinned cats anyway? What a strange phrase).

 

[BenMacier]

Firstly the H2(g) in pipe will expand further in the room on pipe rupture or leak, because of the pressure differential between the pipe and the room.

Secondly your approach is to supply fresh air to dilute the H2 in the air and stay under the maximum recommended concentration. Note this 1% is a rule of thumb and may not be safe for the equipment or utilisation of this room. However the approach of full extraction could also be considered where a hood may be placed directly on the pipe.

* Finding a solution is great * Knowing how to implement it is fantastic * Believing it is the only one and best is naive ?

 

[Sean Lim]

The first consideration is the fan’s airflow or its volumetric flow rate, usually measured in CFM or cubic feet per minute. Airflow requirements vary on the specific setup but are usually dependent on the volume of space that requires air to move through. This is particularly important in industrial areas where a steady airflow is required to remove generated fumes. This keeps the air clean, so you need a fan system that can move up to 300 to 600 CFM for 2000 ft3 space. Airflow is measured from the operating static pressure relative to the fan speed (or RPMs).

you may find more here

 

[MedicineEng]

Is it possible to consider a pipe in pipe configuration where a potential H2 pipe leak would be contained within another pipe and directed to a place where could be easily vented out?

 

[BronYrAur]

I can't think metric..... converting units, you have 2,570 CFM in the pipe. The room volume is roughly 850 cubic feet. So I am getting that the room would fill up in roughly 20 seconds. Considering that, I don't think the volume of the room needs to be considered. The room fills up almost immediately. So, you really need to ventilate the entire amount. You didn't mention how high the room is, but let's say 10', so you have an area of 85 square feet.

Ventilating with this much air would be 30 CFM per square foot. That is 180 air changes per hour. This is clean room territory.

The chances of a complete pipe failure are small. As GT-EGR said, a small leak is more realistic. Once released, it will not immediately be uniform within the room, so local exhaust options may be better (i.e. containment).

Also, how quickly will your exhaust/makeup system be able to react?

 

[vinhermes]

Cheers guys. Good material to think of! My issue is that the marine regulation refers to the concerntration only.most gas codes require 30 air changes. I'll go with that and ensure local extraction with this flow rate. Many thanks!!!

 

[MintJulep]

You might want to read NFPA 2.
Available on line for the price of making an account.

https://www.nfpa.org/codes-and-stan...rds/list-of-codes-and-standards/detail?code=2