Gas flow measurement in large stacks 1

[adeb]

Hi everybody,
have anybody any experience on combustion flue gas flow measurement in large stacks?
Large means 40m. with 5m. diameters + 50m. with 4m. diameter. Total 90 m.
Flow is about 100.000 SCFM at 700°F.

I'm oriented on S-type pitot tube as claimed by the EPA code (mot mandatory in my case).

But I'm not sure about the accuracy and repetability I can get.
Another problem is the location, in order to meet the 5 diam. straight run upstream and downstream the only suitable place is 64m. height (!!). Of course the maintenance dpt. is not happy.

Suggestion/Improvements?

Thanks.

 

[JimCasey]

The multihole pitot devices like the Annubar or the Meriam Accutube work well in this sort of application. They measure and average the velocity over 4 zones, so they tend to give you a more representative reading than a single-point aircraft-type pitot. These devices can even be installed in an elbow, if you follow the instructions.
Since your pipe diameter is so large, I would use one with both ends supported. Then gather the signal with a draft-range D/P transmitter.

 

[hacksaw]

Single point pitot is actually preferred for EPA measurements. Pull the code and you'll see why.