Message Board Thread - "Oil Fired Refinery Heater Survey - Help! "

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Oil Fired Refinery Heater Survey - Help! AndyMellor 7/30/2003
I have recently conducted a refinery fired heater tube survey. I measured furnace ambient with both a thermocouple poked through an inspection hatch and by looking at the furnace wall and setting emissivity to 1. I got comparable results (c. 990 deg C. I then estimated tube emissivity by comparing tube surface temperature measured with a thermocouple with my IR camera reading. (I was able to see the wall side of a tube directly though a side inspection hatch). I recorded two values of 0.79 for an area with deposits and 0.86 for a clean area. I then started on my survey, the aim of which was to confirm tubeskin thermocouple readings. In all but one shot the IR temperatures were significantly (30-80 Deg C) higher than the tubeskin temperatures as recorded by the plant SCADA system. I had a second shot of the thermocouples that showed agreement - through an end, rather that a side door. This second shot showed a large discrepancy in temperatures, with the IR temperatures again being higher than the tubeskin thermocouples. I then looked at how the heater was fired - all burners had nominally the same amount of gas firing, but some burners were oil fired in addition.


Could I be picking up radiation direct from the flames, I thought? I went back to the two shots taken of the same thermocouples. I adjusted the transmissibility of the shot taken from the end door until the temperatures agreed with those taken through the side door. I then used this figure of transmissibility on all my other images. All but one set now agreed. Turning off the oil firing on the burner most affecting this shot brought much better agreement between the thermocouples and IR image. (I think this confirms my suspicion that the flames from an oil fired burner are affecting my apparent IR temperatures.)


I was using an AGEMA 550 camera on the 250 - 800 degree range with an HT3 filter. typical tubeskin temperatures were 500 to 550 deg C by thermocouple and 500 to 635 degrees with the camera. I arrived at a value of 0.94 for transmissibility.


Now for the questions
What was going on?

Can I ever correct for oil firing, or will I have to repeat the survey with the oil off?


Thank-you, gentle reader, for you time and patience.

 
Re:Oil Fired Refinery Heater Survey - Help! Gillian Aird 8/18/2008
AndyMellor wrote:
recently conducted a refinery fired heater tube survey. I measured furnace ambient with both a thermocouple poked through an inspection hatch and by looking at the furnace wall and setting emissivity to 1. I got comparable results (c. 990 deg C. I then estimated tube emissivity by comparing tube surface temperature measured with a thermocouple with my IR camera reading. (I was able to see the wall side of a tube directly though a side inspection hatch). I recorded two values of 0.79 for an area with deposits and 0.86 for a clean area. I then started on my survey, the aim of which was to confirm tubeskin thermocouple readings. In all but one shot the IR temperatures were significantly (30-80 Deg C) higher than the tubeskin temperatures as recorded by the plant SCADA system. I had a second shot of the thermocouples that showed agreement - through an end, rather that a side door. This second shot showed a large discrepancy in temperatures, with the IR temperatures again being higher than the tubeskin thermocouples. I then looked at how the heater was fired - all burners had nominally the same amount of gas firing, but some burners were oil fired in addition.


Could I be picking up radiation direct from the flames, I thought? I went back to the two shots taken of the same thermocouples. I adjusted the transmissibility of the shot taken from the end door until the temperatures agreed with those taken through the side door. I then used this figure of transmissibility on all my other images. All but one set now agreed. Turning off the oil firing on the burner most affecting this shot brought much better agreement between the thermocouples and IR image. (I think this confirms my suspicion that the flames from an oil fired burner are affecting my apparent IR temperatures.)


I was using an AGEMA 550 camera on the 250 - 800 degree range with an HT3 filter. typical tubeskin temperatures were 500 to 550 deg C by thermocouple and 500 to 635 degrees with the camera. I arrived at a value of 0.94 for transmissibility.


Now for the questions
What was going on?

Can I ever correct for oil firing, or will I have to repeat the survey with the oil off?


Thank-you, gentle reader, for you time and patience.

Dear Andy,

With regards to your quote for oil refinery fired heater survey, I was wondering if you have much more information or expertise in this area.

I work for a company who are involved in the removal of fouling from fired heater convection sections and we are looking into the possibility of assessing fouling characteristics to enhance cleaning and provide a more targetted approach.

Please email me at gaird@clydebergemann.co.uk

Kind regards

Gillian Aird
 
Re:Oil Fired Refinery Heater Survey - Help! Bob Berry 8/18/2008
Andy,

This is a very difficult application, perhaps the most difficult in Infrared.
The tube skin thermocouple and your infrared camera are reading a different thing, and it is unlikely they will measure the same. The thermal camera is measuring emitted radiation and converting this to temperature mathematically. The thermocouple is not necessarily displaying the temperature of the tube skin, it will display its own temperature, and this may not be the same as the skin. Even if it is the same as the skin, it will only be valid in that spot and not necessarily some distance away. The infrared measurement is probably higher than the thermocouple anyway as the thermocouple is probably lower than the actual skin and the infrared measurement is more than likely taken from the skin. If you are measuring the thermocouple itself with infrared you could have issues with spot size. Yes you are getting some emitted energy from the flame too, and this will add to the difficulty, and the cleanness of the flame will affect this. Changing your viewing angle will change your reflected apparent temperature. If you are inspecting through a window material such as sapphire glass, the window transmission rates could be different for different windows as they could be a slightly different thickness, or a different temperature. The accuracy of the camera is +or-2% and this can mean an error of 10°C in your measurement, the thermocouple will have a simular accuracy level, and their errors could be in opposite directions. The 550 has a single setting for Tamb, this simultaneously sets reflected apparent temperature and atmospheric temperature, they might be different.

I think you did well to only have 30-80°C between your infrared measurement and the thermocouple on what seems to be one of your first efforts. Personally, I would not recommend trying to get the infrared and the thermocouple measurements to match. Finally, get yourself along to inframation, find someone that does this and speak to them.

www.thermalvision.ie
 
Re:Oil Fired Refinery Heater Survey - Help! ec 8/18/2008
Andy,
This is an extremely difficult situation to conduct an infrared inspection. In the first case, oil flames always interfere with your infrared signal due to its luminosity. Most of the time, flames are huge, bright and very yellow and pulsates. So, to get an accurate infrared picture, you definitely have to turn off the oil flames. In the second case, oil flames are known to foul the tube surfaces with combustion products. So, when you look at the tubes with the camera, you really don't know if the area is clean or coated with deposits. If the tubes and thermocouples are accessible, you could try scraping or cleaning a small area around the thermocouple with a steam cooled scraping tool.

I hope this helps.
 
Re:Oil Fired Refinery Heater Survey - Help! ec 8/18/2008
Andy,
This is an extremely difficult situation to conduct an infrared inspection. In the first case, oil flames always interfere with your infrared signal due to its luminosity. Most of the time, flames are huge, bright and very yellow and pulsates. So, to get an accurate infrared picture, you definitely have to turn off the oil flames. In the second case, oil flames are known to foul the tube surfaces with combustion products. So, when you look at the tubes with the camera, you really don't know if the area is clean or coated with deposits. If the tubes and thermocouples are accessible, you could try scraping or cleaning a small area around the thermocouple with a steam cooled scraping tool.

I hope this helps.
 
Re:Oil Fired Refinery Heater Survey - Help! ec 8/18/2008
Andy,
This is an extremely difficult situation to conduct an infrared inspection. In the first case, oil flames always interfere with your infrared signal due to its luminosity. Most of the time, flames are huge, bright and very yellow and pulsates. So, to get an accurate infrared picture, you definitely have to turn off the oil flames. In the second case, oil flames are known to foul the tube surfaces with combustion products. So, when you look at the tubes with the camera, you really don't know if the area is clean or coated with deposits. If the tubes and thermocouples are accessible, you could try scraping or cleaning a small area around the thermocouple with a steam cooled scraping tool.

I hope this helps.
 
Re:Oil Fired Refinery Heater Survey - Help! ec 8/18/2008
Andy,
This is an extremely difficult situation to conduct an infrared inspection. In the first case, oil flames always interfere with your infrared signal due to its luminosity. Most of the time, flames are huge, bright and very yellow and pulsates. So, to get an accurate infrared picture, you definitely have to turn off the oil flames. In the second case, oil flames are known to foul the tube surfaces with combustion products. So, when you look at the tubes with the camera, you really don't know if the area is clean or coated with deposits. If the tubes and thermocouples are accessible, you could try scraping or cleaning a small area around the thermocouple with a steam cooled scraping tool.

I hope this helps.
 


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