C + 2

There are no restricting relationships when the stream is considered only at a point. Henley and Seader (Equilibrium-Stage Separation Operations in Chemical Engineering, Wiley, New York, 1981) count all C concentrations as variables, but then have to include

i t as a restriction.

A stream divider simply splits a stream into two or more streams of the same composition. Consider Fig. 13-21, which pictures the division of the condensed overhead liquid Lc into distillate D and

FIG. 13-21 Stream divider.

reflux Ln+x. The divider is permitted to operate nonadiabatically if desired. Three mass streams and one possible "energy stream" are involved; so

Each mass stream contributes C + 2 variables, but an energy stream has only its rate q as a variable. The independent restrictions are as follows:

Inherent

T and P identities between LN +1 and D 2

Concentration identities between LN +1 and D C - 1

Mass balances C

Energy balance 1

The number of design variables for the element is given by

Specification of the feed stream Lc(C + 2 variables), the ratio LN+i/D, the "heat leak" q, and the pressure of either stream leaving the divider utilizes these design variables and defines one unique operation of the divider.

A simple equilibrium stage (no feed or sidestreams) is depicted in Fig. 13-22. Four mass streams and a heat-leak (or heat-addition) stream provide the following number of variables:

Vapor and liquid streams Vn and Ln respectively are in equilibrium with each other by definition and therefore are at the same T and P. These two inherent identities when added to C-component balances, one energy balance, and the C phase-distribution relationships give

Specifications |
Nie |

Specification of Ln +1 stream |
C + 2 |

Specification of Vn -1 stream |
C+2 |

Pressure of either leaving stream |
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