Page 195 - Chemical engineering design

172
CHEMICAL ENGINEERING
Purge
Compressor
Decanter
Condenser

Hydrogen Decanter
Nitrobenzene

Vaporiser Reactor
Crude
aniline
Distillation
column
(a)
Purge
Splitting
tee
2

Hydrogen
1 3 4 5 6 7 8 9

Mixing Reactor Condenser Decanter Mixing Decanter
tee tee
Crude
Nitrobenzene
Vaporiser aniline
(b)
Note: (1) Modules have been added to represent mixing and separation tees.
(2) The compressor is omitted.
(3) The distillation module includes the condenser and reboiler.
Figure 4.5. (a) Process flow diagram: hydrogenation of nitrobenzene to aniline (b) Information flow diagram
hydrogenation of nitrobenzene to aniline (Figure 4.5a)

4.6. MANUAL CALCULATIONS WITH RECYCLE STREAMS

If a proprietary simulation program is not available, problems involving recycle streams
can be solved on a spreadsheet using the procedure described below.
The procedure is based on the theory of recycle processes published by Nagiev (1964).
The concept of split-fractions is used to set up the set of simultaneous equations that
define the material balance for the process. This method has also been used by Rosen
(1962) and is described in detail in the book by Henley and Rosen (1969).

4.6.1. The split-fraction concept

In an information flow diagram, such as that shown in Figure 4.5b, each block repre-
sents a calculation module; that is, the set of equations that relate the outlet stream
component flows to the inlet flows. The basic function of most chemical processing units
(unit operations) is to divide the inlet flow of a component between two or more outlet