Actual Trays for Steam Stripping

The rich benzolized wash oil is stripped of its light oil content by fractional distillation—most commonly in a tray column operated at substantially atmospheric pressure with direct-steam addition to the bottom. The number of theoretical trays required for the separation can be calculated by conventional techniques and the actual requirement estimated on the basis of an assumed tray-efficiency. Overall efficiencies of 45 to 70% have been reported as typical for light oil stripper stills (Silver and Hopton, 1942 Glawacki, 1945), and 10 to 15 actual trays are commonly employed below the feed. 

Lj = Liquid flowrate down stripping section of distillation tow er, lb mols/hr Light key component in volatile mixture Internal reflux ratio Actual external reflux ratio Minimum external reflux ratio Molecular weight of compound Total mols steam required Number of sidestreams above feed, n Number of theoretical trays in distiUation tower (not including reboiler) at operating finite reflux. For partial condenser system N includes condenser or number theoretical trays or transfer units for a packed tower (VOC calculations) Nb = Number of trays from tray, m, to bottom tray, but not including still or reboiler Nmin = Minimum number of theoretical trays in distillation tower (not including reboiler) at total or infinite reflux. For partial condenser system,... 

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