I don't really know how you are calculating the airflow, but it sounds like you are using a pitot tube. Without getting into the theory, your calculations of 37000 ACFM are probably correct, as the velocity of the 42" duct is around 3800 fpm, which is normal for your application where you have to keep the cement dust in suspension until the dust collector.

Beware of the velocity pressure you read at the round to square transition as it is very difficult to get a good average reading in these areas.

I am a bit baffled as to how you get the 15000 (S?)CFM value for the exhaust. Doing a rough calculation for 5300 feet elevation and 37000 ACFM using air only (assuming that the hot gases are coming from the clinker cooler and at a temperature of 400 deg F), I get approximately 18000 SCFM and change.

Please let me know if I can be of further help.

Joe ■

Hi LB,

I did understand that you had a cement mill, I was speaking of the source of the gases used for grinding the clinker and additives into cement. I just assumed that the gases would come from the clinker cooler vent, and used this to estimate a temperature into the mill.

Yes, you are right, the goesinta should always equal the goesouta. It would help me greatly if you could explain the entire circuit or send me a flowsheet with all pertinent information, including temperature and negative pressure in each location. Usually the outlet gas volume is actually higher than the inlet due to all of the false air infiltration, so I am with you, your measurements or calculations don't make a whole lot of sense. I would also be interested in knowing what you have been using for measurement, what is the physical location (proximity to elbows, etc.) and how many points you have measured to determine the averages.

If you like, you could send the information to jriley@boldeco.com, and I can help you much more effectively.

Joe ■