nozzles and other internal considerations must be addressedto eliminate problems. Kister21 presented a series of articleswhich discussed these areas in detail.

Top Feed Nozzles Fig. 19-32 illustrates various ar-rangements used for top-tray feed and reflux nozzles. Fig.19-33 lists factors and restrictions in each design. For costreasons, arrangements of Fig. 19-32a, b, c, e, and f are pre-ferred. However, for a two-phase stream only b, d, e, and h aresuitable. Most installations use arrangement a or c for all-liq-uid feed while b and e are popular for a two-phase feed.

Tray sections and baffles that are contacted by an enteringfeed should be strengthened and feed nozzles should be an-chored to the tower shell. Feed lines containing two phase flowshould be designed to minimize slugging which causes columninstability and possible tray damage. For liquid feeds, the noz-zle velocity should not exceed 0.9 m/s.

Intermediate Feed Nozzles Fig. 19-34 shows vari-ous methods for introducing intermediate column feeds.Fig. 19-35 summarizes the application area for each design.Fig. 19-34a is only suitable for subcooled liquids. Vapor con-taining or hot feeds would cause flashing in the downcomerand loss of capacity. Fig. 19-34b is only suitable for low-veloc-ity liquid feeds and is seldom recommended. Fig. 19-34c andd show a similar nozzle location with a baffle to direct the feedstream. These are both designed for two-phase streams withd being the preferred arrangement. Fig. 19-34c can be used for

FIG. 19-36Bottom Vapor Inlet22

Operating conditionMinimumresidencetime, min

Liquid is withdrawn by level control andfeeds another column directly by pres-sure

2

Liquid is withdrawn by level control andpumped away. Spare pump starts manu-ally.

3

Liquid is withdrawn by level control andpumped away. Spare pump starts auto-matically.

1

Liquid is withdrawn by level control anffeeds a unit that is some distance awayor that has its instruments on a differ-ent control board.

5-7

Liquid is withdrawn by flow control. 3-5

Liquid flows through a thermosyphon re-boiler without a level controller, to main-tain a level in the sump.

1

FIG. 19-37Residence Time for Liquid in the Sump21

ReboilerReturn

BottomProduct

ToReboiler

BottomProduct

ToReboiler

BottomProduct

ToReboiler

BottomProduct

ToReboiler

a. b. c. d.

ReboilerReturn

ReboilerReturn

AuxiliaryBaffle

PreferentialBaffle

ReboilerReturn

FIG. 19-38Example Baffle Arrangements for Bottom Sumps for Recirculating Reboilers21

19-25