“My UV flame detector worked last week, and now it keeps shutting down the system, even though the flame is there. I ran diagnostics, and it’s not the detector. Can you help?”
When an instrument or technology works, it’s frustrating when all of a sudden, it stops… especially when it causes your burner or boiler process to stop unexpectedly and without reason. What’s the cause? Is it the flame detector? The control? Wiring? A valve or switch in the fuel train? Or might it be caused by the flame?
More and more chemical plants are mixing hydrogen into their natural gas fuels in incinerator and super-heater applications, either for burn-off or to cut costs. Studies have shown that adding even 5% hydrogen can descrease NOx and CO emissions by up to 50%. And, hydrogen is considerably less expensive than natural gas for an equivalent BTU output.
It’s a great plan: The plant saves fuel costs and reduces greenhouse gas emissions, reducing their potential for costly EPA violations. But, unfortunately, sometimes the last people to know about the fuel mixture change are the instrumentation engineer and the operator.
Here’s the catch: As the fuel mixture changes, so does the flame it produces. So, if you’re using a UV scanner that’s tuned specifically for a natural gas flame, it may not properly detect the flame from a natural gas/hydrogen mixture. When that happens, your combustion system shuts down unnecessarily, wasting time and money. 
Last week, Lalit Mehta from Honeywell talked about this and a bunch of other flame detection applications in a free webinar to Lesman customers. It’s available to watch or download from our website. If the topic interests you, check it out.
Beside this application, he also talks about flare stack monitoring and greenhouse emissions, detecting flame on low NOx burners, flame discrimination issues with recovery boilers, sulfur recovery units, and cement, lime, and material processing kilns. Finally, he’ll introduce you to Honeywell’s Iris Systems line of combustion control and flame safety instruments.
There’s a lot more flame safety information available on my company’s website: http://www.lesman.com/unleashd/combustion.htm
Lesman Tech Tips 
#1 by Andrew Nelson on November 23, 2018 - 11:52 am
Does anyone no why my flame scanner or 7800 faults every two weeks. Exactly 336 hours to the second.
#2 by nandeep on February 11, 2016 - 12:43 pm
Sir i want to know y flame detector failure while burner getting on…in sone times..
#3 by danstips on February 11, 2016 - 4:46 pm
There’s a number of reasons why a scanner would shut a system down even though the burner is still on. If the flame front moves away from view of the scanner or the scanner lens is blocked, this would of course explain why it no longer detected a flame since it can’t see the flame. There’s also internal issues with the scanner itself and the associated components that could also fail, causing a shutdown as well. Keep in mind that a scanner is not looking for visible light, but for UV or IR energy generated by the flame. Although we can “see” the visible light that the flame generates, if the flame has weak UV or IR energy the scanner will shut the burner down.