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- Posts: 21
- Joined: Wed Jul 18, 2012 7:55 pm
I'm running ASTM D3612-02C (Dissolved Gasses in Electrical Insulating Oil by Gas Chromatography), specifically method C headspace analysis with a Agilent 7697A Headspace Sampler and 6890N with TCD & FID.
The instrument was running with the FID on but after changing the column, I can't get the FID to light. When checking flow rates at the FID I appear to get correct air flow rate but the hydrogen flow rate is too low to get the FID to light. It seems to start high and slowly decrease. Is this normal as the FID attempts to light, i.e. that the mixture is automatically adjusted lean during the ignition of the flame. It'll pop, but fail to light.
Without attempting to ignite the FID, I can adjust flow rates of the air but the hydrogen flow can't seem to get above about 25 ml/min.
This instrument runs a nickel catalyst methanizer where the sample and hydrogen flow is mixed and crossed through a tube heated with nickel powder catalyst. I was thinking that I had a restriction in the catalyst tube but on changing the catalyst powder, I still have the apparent hydrogen flow problem and a FID that will not light. It's possible that the restriction still exists in the catalyst tube as it contains a frit that may be plugged.
Questions....
If I have a leak in the column installation, how could this affect the hydrogen flow in the way I'm observing it?
I suspect the column installation because the instrument did in fact operate before I changed the column although with an odd ratio of 60 ml/min H2 and 400 ml/min air which is quite rich rather than the typical 1:10 ratio. I suspect that the instrument had been adjusted to that rich ratio to compensate for an existing problem. The instrument had problems with the FID going out, drift in retention time and response, and poor resolution of methane and CO. I suspect a more fundamental problem with the hydrogen flow, e.g. a restriction in the nickel catalyst tube, however, my attempts to correct this didn't solve the problem.
Can I simply remove the nickle catalyst tube and join the hydrogen and sample lines to a tee with the output to the FID to troubleshoot and eliminate the nickel catalyst tube as a source of the problem?
I think I need to redo the column installation and see if this solves the problem, but I have my doubts. Could I have a leak in the pneumatic control module or some other fitting on the H2 feed?
What would be a good way to proceed on troubleshooting this problem? I'm stumped.
The instrument was running with the FID on but after changing the column, I can't get the FID to light. When checking flow rates at the FID I appear to get correct air flow rate but the hydrogen flow rate is too low to get the FID to light. It seems to start high and slowly decrease. Is this normal as the FID attempts to light, i.e. that the mixture is automatically adjusted lean during the ignition of the flame. It'll pop, but fail to light.
Without attempting to ignite the FID, I can adjust flow rates of the air but the hydrogen flow can't seem to get above about 25 ml/min.
This instrument runs a nickel catalyst methanizer where the sample and hydrogen flow is mixed and crossed through a tube heated with nickel powder catalyst. I was thinking that I had a restriction in the catalyst tube but on changing the catalyst powder, I still have the apparent hydrogen flow problem and a FID that will not light. It's possible that the restriction still exists in the catalyst tube as it contains a frit that may be plugged.
Questions....
If I have a leak in the column installation, how could this affect the hydrogen flow in the way I'm observing it?
I suspect the column installation because the instrument did in fact operate before I changed the column although with an odd ratio of 60 ml/min H2 and 400 ml/min air which is quite rich rather than the typical 1:10 ratio. I suspect that the instrument had been adjusted to that rich ratio to compensate for an existing problem. The instrument had problems with the FID going out, drift in retention time and response, and poor resolution of methane and CO. I suspect a more fundamental problem with the hydrogen flow, e.g. a restriction in the nickel catalyst tube, however, my attempts to correct this didn't solve the problem.
Can I simply remove the nickle catalyst tube and join the hydrogen and sample lines to a tee with the output to the FID to troubleshoot and eliminate the nickel catalyst tube as a source of the problem?
I think I need to redo the column installation and see if this solves the problem, but I have my doubts. Could I have a leak in the pneumatic control module or some other fitting on the H2 feed?
What would be a good way to proceed on troubleshooting this problem? I'm stumped.
