Ganeshraj
Assume you mean Topsoe (as in Haldor Topsoe) SMR plant

10% sounds a lot, what unit load is this at?
A hydrogen unit should, when running above 75% be around 2.5 %. At turndown e.g. 40% you can reach higher numbers such as 6-8% O2.

There must be a sample position somewhere down towards the stack. Do you suspect the O2 probe to be faulty, why not replace the probe to check the result

What is the opinion of HTAS (the licensor)?

Hi Roger,
Even at 75% load, the O2 ex radiant section is approx 10%.
Recently we have made a provision at ID-Fan suction for portable O2 analyser. We are yet to check.
No reply from HTAS in this regard.

Ganeshraj
The last H2 units I run been KTI design but if I dont remember worng there should be a load controller incl. firing duty and oxygen/air control in HTAS units?

Is the air flow on minimum (like min stop ath the damper) or is the draft very low. Sometimes when adjusting the draft the air/flue gas dampers can get out of control

If you still have problems send me an email and I get you in touch with people that know a lot more than me in this area

RH

I think our problem is in burner design which was intended for Naphtha fuel. We are now firing Natural gas.
Thanks.