Stack gas temperature

[vroma]

Hello everyone,

I am working on a project that would involve routing the exhaust of a number of combustion devices to an existing stack. In order to do some basic modeling, we need to know the stack gas temperature. We have the exhaust temperature from the devices and the existing stack height. Does anyone know of a method to estimate the stack gas temperature based on this information?

Many thanks,
Roma

 

[bimr]

It you can not get the information from the equipment supplier, it is relatively simple to measure the temperature.

 

[vroma]

Thanks. But the equipment (engines) have not been installed yet and I was looking for a way to predict the temperature at the top of the stack based on engine exhaust temperature, stack height, etc.

 

[mbeychok]

If you know the mass amount of each engine's exhaust gas and the corresponding temperature, simply calculate the average temperature (on a mass basis) and subtract about 15-20 degrees F for heat losses and you should be in the ball park then.

Average T = [T1(M1) + T2(M2) + T3 (M3) + ....] / [M1 + M2 + M3 + ....]

T is temperature and M is mass.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[vroma]

Thank you, Milton. Ball park is good and all I'm looking for at this point. The existing stack is about 80 feet high. Do you think that a 15 to 20 degree temperature decrease would still be reasonable for this height?

Roma

 

[bimr]

Ask the manufacturer for a reference installation close your office. Then you can get real world data instead of fudging some numbers.

 

[mbeychok]

vroma:

What is a reasonable estimate of heat loss for a calm summer night is entirely different than a reasonable heat loss for a cold wintry day when it is raining and there is a high wind. Unless you were to obtain the real world data (as suggested by bimr) for every hour of every day for a few years, it is eventually a judgement decision that will have to be made. I don't think of that as "fudging" numbers ... I think of that as facing up to reality.

I assume that you want that stack exit temperature to calculate the plume rise needed for your pollution dispersion modeling. Even with the best of data, the final dispersion calculations may vary from reality by a factor of about 2 if you believe the the U.S. EPA ... and I don't. I think the final dispersion calculations may vary from reality by a factor of as much as 10 or more.

Read the book "Fundamentals of Stack Gas Dispersion" (ISBN 0-9644588-0-2) which you might find in a good university library.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[Flareman]

vroma
Although the commonly used buoyancy characteristic for plume rise is temperature, the total heat flux is just as good a parameter. See my paper ".. model for Flare flames and Plumes" at

http://www.geocities.com/flareman_xs

for formulae which avoid temperature calculations.

David