Vacuum Column Overhead Design
Vacuum Column Overhead Design
(OP)
We have a vacuum column designed with a three stage overhead (ejector/condenser) system. From inception the pressure obtained in the column was above design (40 mmHgabs compared to design 20 mmHgabs). This was so whether the first stage ejectors were on or not. We had three first stage ejectors with three first stage condensers of equal capacity in paralell. So the first stage ejectors were decommisioned and remained that way for many years. We have been told that the original design first stage condenser pressure of 64 mmHgabs was too low for 86 degF cooling water (seawater). Uncondensed steam would load up the second stage condensers. Does this claim seem reasonable. For a three stage system, what would people normally design for the first condenser pressure to ensure adequate steam condensation.





RE: Vacuum Column Overhead Design
Steam, 0.932; air equivalents, 0.062; light hydrocarbons, 0.006.
If the total pressure was 64 mm Hg and the partial pressure (ie, mol fraction) of steam corresponds to 59.6 mm Hg, a shell-side condensing temperature of 107 deg F could be comfortably attained with cooling water at 86 deg F.
The general assumption is that the first condensers would be capable of condensing about 90% of the steam coming from the first-stage ejectors ("dry vacuum tower").
RE: Vacuum Column Overhead Design
RE: Vacuum Column Overhead Design