FID shut-off frequently during operation. what need to be check for that?

Question

Equipment used 7890A natural Gas GC with extended analysis. During operation, FID is frequently shut-off. Try to ignite manually and temporarily solve the problem. But what need to check for identifying the problem?

Admin · Accepted Answer

This question has been marked as assumed answered.

apcharles · Answer

Hello mdabdullahalmamun, I attached a document that lists several things you can check on the FID when there are problems with the flame. A plugged jet could potentially be the problem, but it could also be a low detector temp or H2 or air flow. You can check for a plugged jet in the following way: Jet Restriction Diagnostic Test – Turn off Air and Makeup Gas and set the H2 flow to 75 (you may have to increase the H2 supply pressure). Monitor the Makeup Gas flow reading while turning the H2 flow off and on – it should remain very close to zero ml/min – if pressure builds up due to a plugged jet, the Makeup Gas flow reading will increase by >1 ml/minute.

james_jenkins · Answer

The signal value when lit was 10.7. I wouldn't recommend lowering lit offset to 0.1 as you could possibly have a flame out situation and the detector fuel gas would not turn off (Hydrogen). A lit offset of 2.0 is sufficient in most cases. If the signal is quiet you can go lower, but caution should be used.

caduceon · Answer

It's possible the signal drops lower during a run, or lower than what was shown at that time. I regularly have had several FID's with base signals below 2. In fact the 2 FID's right in front of me both have a signal value of 1.6. I've also never seen a positive signal value for an unlit FID, so 0.1 should still be safe, though if you know your normal baseline, then for sure it can stay elevated.

james_jenkins · Answer

Hi mdabdullahalmamu, I went ahead and flagged this post as “Assumed Answered”. If you still need help though, please let us know and we would be happy to continue working with you. James

james_jenkins · Answer

I have updated the tags for better visibility of your post. Could you reply with the FID parameters that you are using? Temperature, flows etc? If there hasn't been any problems in the past, the most likely cause is that the jet needs to be changed. James

mdabdullahalmamun · Answer

mdabdullahalmamun · Answer

Please see the attached problem statement and method parameters for better understanding. Let me know if additional data you need.

james_jenkins · Answer

I would still focus on the FID, the PCM shut down and other shut downs could be related to hydrogen safety shut downs. Simple and quick would be to change the jet or in the very least run the test that apcharles suggested.

caduceon · Answer

Have you tried lowering the LIT offset? Perhaps it's set a little high, and that would account for the FID shutting itself off repeatedly. You can access the LIT offset by pressing the config button on the front of the GC, and selecting your FID detector. Scroll through the options and you should see LIT offset. Try lowering it down to 0.1 or something like that.

FID shut-off frequently during operation. what need to be check for that?

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