Vapor volume, reflux effect

The effect of increasing the reflux rate on a crude tower, even with a constant condenser duty, will be to increase the condenser pressure drop. This happens because the volume and the weight of the tower overhead vapors will increase as the tower-top temperature drops. At the Calumet Refinery in Shreveport, Louisiana, the crude tower reflux rate was increased by 25 percent and the tower-top temperature dropped by 50 F-60 F. The overhead condenser AP increased from about 12 to 24 psi. The tower pressure was kept constant, but the reflux drum pressure declined from 17 to 5 psig. 

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