H2 N2 dilution

[ashishmali28]

Hi, In hydrogenator we vent hydrogen gas to knockdown drum and want to mix with nitrogen gas 20 time of hydrogen gas which vent for safe disposal. So whether it should mix on 20 Times of volume or weight basis.? How to calculate?

 

[EdStainless]

What concentration are you aiming for?
Is the 5% target weight or volume based?
My guess is vol based since this is the more common measure.

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P.E. Metallurgy, Plymouth Tube

 

[rotw]

Found in the literature a quote:
Usually the LFL and UFL of a combustible material are expressed in volume percentage (vol%) in the literature; however, as the hydrocarbon gas could be taken as an ideal gas at atmospheric pressure, the LFL and UFL could also be explained as the molar fraction.

So volume based is in line with what EdStainless indicated.

As for the conversion weight% <-> volume%, this link appears helpful:

https://sciencing.com/convert-volume-percent-weight-percent-8740558.html

 

[MortenA]

LEL for H2 is 4% vol, so i would say that its vol based!

You sure could save some N2 of it was weight based

Near atm vol is just vol.

Best regards, Morten

 

[ashishmali28]

Hi morten, instead of inert gas, can i use steam for dilution. But there is little chance of steam or water get back into the reactor through vent line. Because present line is not aufficient for nitrogen flow rate. Or we have to keep control valve for release of hydrogen.

 

[MortenA]

I have discussed this wit a colleague for cost reason. The big issue with steam is that it can/will condense. Then you risk vacuum etc and also dilution is gone…

 

[EdStainless]

As Morten said, with steam you have to have flow controls on the outlet of the system to assure that you always have enough flow.
And steam demand can change a lot based on weather conditions (temp, RH, pressure).
Look at your nitrogen system again.

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P.E. Metallurgy, Plymouth Tube

 

[georgeverghese]

Also there would be corrosion concerns with flooding the vent header ( and vent stack ) with steam.
Other suggestions for disposing this H2 stream: Install a dedicated H2 burner in one of the fired heaters in your plant (or replace an existing fuel gas burner with a special H2 burner).

 

[ashishmali28]

Thank you for your responses , just want to check for calculation part for batch process I have to check the volume of hydrogenator in which hydrogen is present (remaining part is liquid catalyst suspension in that hydrogenator) .IF That V volume will be released in (suppose) 180 second , will need 20 times nitrogen and on that particular flow rate of nitrogen , I have to design diameter of pipe, am I correct?

 

[georgeverghese]

That would be approximately correct provided the release flowrate of H2 is constant throughout the 180sec.