Condensate receiver holdup

Level Control of Condensate Receiver and Required Holdup... 

Finally it should be noted from equation (18.30) that it is quite important to keep the dead time in the overhead system to a minimum. This means that transport times in the vapor and reflux lines should be as small as possible. The condensate receiver, if unagitated, should have as small a holdup as possible. See, however, the discussion in Chapter 3. 

It should also be noted that the open-loop transfer functions given in equations (18.43) and (18.44) are valid, strictly speaking, ftx onty one coinhiiiation of holdup volumes in the condensate receiver and the column base. Studies to date, however, suggest that if these holdups are no larger than the total holdup on the trays, then the open-loop transfer functions are relatively insensitive to variations in terminal volumes. This topic definitely needs more study. In the meantime we should determine terming volumes by material-balance and protective-control calculations before calculating column composition dynamics. 

Several final points remain to be considered, Fir, t, all of the discussions above ignored the effect of liquid holdup in the column and condenser, but because the combined volumes of these two are quite small as compared to the volumes in the still and receiver (particularly because so many batch stills include packed sections rather than trays), this assumption does not seem unwarranted, particularly for binary mixtures. 

We assume constant density, equimolal overflow, theoretical trays, total condenser, partial reboiler, and five-minute holdups in the column base and the overhead receiver. Tray holdups and the liquid hydraulic constants are calculated from the Francis weir formula using a one-inch weir height. 

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