Hydrogen vent tubing size

[KM-USA]

I have a question about vent tubing size, to switch to hydrogen as carrier gas. I'll need to vent the hydrogen carrier gas split line (maybe up to say 150 ml/min) and the purge split (maybe 3 ml/min) to an exhaust hood for each GC.

So I have four GC units, and assuming all are operating at the same time and dumping into a single stainless steel exhaust tubing manifold to go into the exhaust hood, would 1/4 inch stainless steel tubing be large enough diameter? The GC systems would be about 25 to 30 feet away from the exhaust hood. Thanks.

[chromatographer1]

Do a quick check:

Attach hydrogen source regulated pressure to 30ft of 1/4 inch line and determine the pressure required to achieve 500mL/min. As long as the pressure required is low then there should be no problem. Make certain there is a positive rise from the GC to the hood.
I would be very surprised if there is a problem. But the old saying: measure twice, cut once.
In any case a plastic tube of 1 inch OD should be adequate. I guess there are no windows close to the GC benches.

good luck,

Rod

[KM-USA]

Your idea of measuring hydrogen flow/pressure through a similar length of 1/4 inch SS tubing is a good one.

My first idea was also to go with wider-bore polyethylene or polypropylene tubing, but supervisor seems to be set on SS. I will ask again about plastic tubing.

There are NO windows in the room at all. In our whole building, none of the windows open anyway.

[Peter Apps]

At 600 ml/min of hydrogen I expect the back pressure to be too small to measure. Nice to know that your lab has enough money to buy stainless for a job where garden hose would serve

Peter

[chromatographer1]

Well, Peter,

I tried to tell them.......

Glad we see alike.

Rod

[uzman]

May be the more important point is , you will need leak tight connections between the outlet of your GC ( 1/16'' or 1/8'' tubings ) to the vent tube , so connecting them to a ordinary water hose is not practical.

You will need swagelok adapters 1/16'' ( or 1/8'' ) to 1/4'' and a tee ( 1/4'' ) to make leak tight connections.

[Peter Apps]

It takes very little to make a leak tight seal when there is no pressure - in this case a rubber bung or a few steps up in hose size would be more than adequate.

Peter

[chromatographer1]

And with hydrogen there is hardly possible a leak tight seal, given that hydrogen will pass through the metal itself. It is a matter of amount and time. One does desire to limit the amount of leaking but to eliminate it is barely possible. In other words, always have good ventilation when working with hydrogen.

best wishes,

Rod

[uzman]

There are 4 GCs , so 8 outputs ( 4 split , 4 septum purge ) going to 1 vent line.
For a good connection , it needs 7 tee connections and 8 reducing adapters to connect the vent line.

You may use 8 separate plastic hoses to the vent line but it will be a mess , and final connection to the vent line will be problematic.

[chromatographer1]

All those connections can be a solution, but really, if you just have a wide diameter vertical tube to the roof,inserting the small diameter tubes into the bottom of the wide diameter tube an appropriate distance (perhaps 1-2 ft) then no nuts, ferrules, etc should be needed. Hydrogen RISES STRONGLY and FAST when released from a tube. There would have to be a resistance to flow for the H2 to 'back up' into the lab. Having a resistance to flow with a physical seal to the tubing would also cause problems, no?

Even better would be a crowned ceiling that had a vent to the roof. I had a full cylinder of H2 leak into a room with such a ceiling over a few hours time, a room full of electrical equipment, and no harm occurred. (engineers were involved prior to the use of the room)

The important factor is the unrestrained flow of the gases involved which implies a capable heat exchanger in the roof.

For best results a professional should be consulted rather than a DIF (do it yourself) solution.

best wishes,

Rod