Chapter 1

Troubleshooting of Malfunctioned PLC Controlled Rectification Pilot Plant

Chapter 4Process Description

Chapter 4Process Description

Process Description:The column consists of a cylindrical structure divided into sections by a series of Bubble Cap trays which permit the upward flow of vapor. The liquid reflux flows across each tray, over a weir and down a down comer to the tray below. The vapor rising from the top tray passes to a condenser and then through a reflux divider, where part is withdrawn as the overhead product D, and the remainder is returned to the top tray as reflux R. The liquid in the base of the column is frequently heated by an electrically heated Circulatory evaporator and the vapor rises through the caps risers to the bottom tray.A more commonly used arrangement with an external reboiler is shown in Figure where the liquid from the still passes into the reboiler where it flows over the tubes and weir and leaves as the bottom product by way of a bottoms cooler, which preheats the incoming feed. The vapor generated in the reboiler is returned to the bottom of the column with composition ys, and enters the bottom tray where it is partially condensed and then revaporised to give vapour of composition y1. This operation of partial condensation of the rising vapor and partial vaporisation of the reflux liquid is repeated on each tray. Vapor of composition ytfrom the top tray is condensed to give the top product D and the reflux R, both of the same composition yt.

The feed stream is introduced on some intermediate tray where the liquid has approximately the same composition as the feed.

At the Plate where the feed is introduced, the liquid rate or the vapor rate may change, depending on the thermalcondition of the feed. Figure shows diagrammatically the liquid and vapor streams into and out of the feed platefor various feed conditions.All five of the feed types can be characterized by the useof a single factor denoted by q and defined as the molesof liquid flow in the stripping section that result from the introduction of each mole of feed. Then q has the followinglimits for the various conditions:

(a) Cold feed as liquor q >1 q line /(b) Feed at boiling point q = 1 q line |(c) Feed partly vapour 0 < q