Chromatography Forum

Please help how can i measure my daily volume of air consumption by FID detector air flow is 400ml/min and hydrogen 40ml/min,i do use pressurised air cylinders,therefore would like to estimate my daily consumption.
Apprecaite your help.

Please help how can i measure my daily volume of air consumption by FID detector air flow is 400ml/min and hydrogen 40ml/min,i do use pressurised air cylinders,therefore would like to estimate my daily consumption.
Apprecaite your help.

Calculation is straightforward: just multiply air flow 400 mL/min by the time air flows through FID in minutes. You will get air consumption in mL (so called normal mL).

That will tell you the consumption but what you really want to know is how long will the tank last. For that, you need to determine how many mL of gas are present in the tank at atmospheric pressure (where the flow is measured). For a tank that is 2,500 psig:

P1 = 2,500 psig
V1 = 29.5 L (I just looked it up, these are the tanks that are approx. 5 ft tall)
P2 = 14.7 psig (pretty close to atmospheric pressure near sea level, good enough for these calculations)

Also:

P1xV1 = P2*V2

2,500 x 29.5/14.7 = 5,017 L

At 0.4 L/min

5,017/0.4 = 12,543 minutes (209 hours)

That's 26 days (8 hours per day).

In Europe* we usually have 50 L water capacity gas cylinders. And common gases are compressed to 200 bar.

This gives 10 000 N L of air.

Assuming 0.4 N L per minute consumption one gas cylinder would last 25 000 minutes of continuous work (ie. 17.36 days).

Assuming further 8 hours per day load that would give 52 working shafts.

Needless to mention that gas cylinders shouldn't be drained fully and at least 5% of gas should be left then 50 days is good estimation.


* - I dare to guess that "abdidhere" is not located in US or Canada

Mine last for 2 weeks when I keep the FID on constantly. I try to run samples during the day and shut it off at night and when I am not using it. I just leave the N2 makeup going if I expect to use it in the near future.

I am looking into buying an oiless compressor in the future and a refillable hydrocarbon trap. That is the alternative. We just had a thread on that.

No offense to the location of the original poster was intended. In this case, the pressure units used don't matter at all. Consistency is the key. Your tanks are about double so it took about 2X as long to get to the end of it.

No offense to the location of the original poster was intended.

I didn't even think of it.

In this case, the pressure units used don't matter at all. Consistency is the key. Your tanks are about double so it took about 2X as long to get to the end of it.

The most important information was not to empty gas cylinders completely (which was missing).
Having this knowledge the original poster will have practical ability to apply Boyle–Mariotte law when using gas cylinders

However he was only asking about estimation of daily air consumption by FID.

Thank you all for your help, i do appreciate your valuable time.