Q & A > Question Details
In our vacuum column the column top pressure 75 mmHga and the flash zone pressure is showing 50 mmHga. The gauge near the ejector system is showing 40 mmHga. The PD of flash zone and the ejector system matches with the design value.
We have tried changing the gauge and the transmitter on overhead vapor also. The impulse line to the transmitter is clear.
what can be the reasons for this erratic reading in the vapor line.
 
Answers
09/06/2014 A: Bruce Carr, Suncor Inc, bcarr@suncor.com
Norm Leiberman discusses this phenomenon in one of his books....
09/06/2014 A: Bruce Carr, Suncor Inc, bcarr@suncor.com
pressure gauges in vapor lines are never accurate... the reduced diameter from tower shell head to vapor line causes an increase in vapor velocity resulting in an inaccurate pressure reading.
21/05/2014 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
The only way to have an accurate pressure survey in a vacuum column is with a manometer. Once, after a turnaround, I checked the flash zone and the 1st ejector inlet once a week for a year. Yes, I had to climb the ladder, even in cold, windy weather. We needed to determine the fouling rate within the column for future planning.