Written by: A.J. Piskor
I was talking to a customer a few weeks ago, helping him with a Honeywell Flame Safeguard/scanner inquiry on a thermal oxidizer application. We started talking about the burner and he mentioned that he was tuning the burner based on the oxygen coming out of the stack.
This is a common practice for technicians working on boilers, radiant tubes, and immersion tube applications where 100% of the exhaust is coming from the burner and is not diluted by any process air. However, this is a bad practice to apply when working on an oxidizer, oven, dryer, or a multi-burner application.
Burner applications like this need to be tuned by measuring the air and fuel entering the burner, and not by just measuring the oxygen content in the exhaust stream.
The danger in setting up one of those applications (oxidizer, oven, dryer) by only using oxygen content in the exhaust stream is that other process air dilutes the products of combustion from the burner.
Boiler technicians typically set-up the air-fuel ratio to the burners so that they measure 3-5% oxygen in the stack (and there’s no dilution air in a boiler stack, it’s only the burner’s products of combustion). If a boiler technician did this for one of those applications, the danger is that they would add more and more fuel to the system (since the exhaust stack is being diluted, the oxygen being measured is higher than they would see in a boiler). Adding more fuel could cause the burner to overheat, or even worse, flood a chamber with fuel until it hit the lower explosive limit.
In the common practice scenario for boilers, radiant tubes, and immersion tube applications, the exhaust stack only contains products of combustion from the burner and no process air. When you have an application like this, you can accurately determine the optimal air-fuel ratio by simply measuring the oxygen level in the stack. It’s safer and more accurate. In all of the other applications, the optimal air-fuel ratio is determined by measuring the air and fuel flow entering the burner by means of a differential pressure measurement or flowmeter.
Have a question about burner tuning? I’m here to help.
Learn more about Honeywell Industrial and Commercial Combustion Products.
Lesman Instrument Company is the authorized Honeywell stocking distributor in Illinois, Indiana, Missouri, Paducah KY, Wisconsin, and Michigan’s Upper Peninsula. If you are located outside that area, you can find your local sales office or get technical assistance by visiting Honeywell’s contact page.
A.J. Piskor joined Lesman as the combustion and controls specialist in early 2014 after spending nearly 10 years with our manufacturer partner, Maxon, as a technical sales engineer. Prior to that, he served as a technical sales engineer for a specialty chemical company. He also holds a Bachelor’s degree in aerospace engineering and mechanics from the University of Minnesota.
Want to learn more about combustion control systems? Call Lesman at 800-953-7626 and ask to speak to A.J.