Page 202 - Chemical engineering design
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so that the overheads from this unit approximate to the azeotropic composition, as a
first try put ˛ 154 D 0.05. FLOW-SHEETING 179
Estimation of fresh feeds
1. Isopropyl alcohol, take the basis of the flow sheet as 100 mol feed, g 101 D 100.
2. Acetone formed in the reaction. The overall yield to acetone is approximately 98
per cent, so acetone formed D 100 ð 98 D 980 mol, g 202 D 98 mol.
2
3. Hydrogen, it is formed in equimolar proportion to acetone, so g 203 D 98 mol.
4. Water, the feed of water to the scrubber will be dependent on the scrubber design. A
typical design value for mG m /L m for a scrubber is 0.7 (see Volume 2, Chapter 4). For
the acetone absorption this would require a value of L m of 200 mol, g 304 D 200 mol.
Matrices
Substituting the values for alcohol (k D 1) into the matrix (Figure 4.14) gives the following
set of equations for the flow of alcohol into each unit;
1 0 0 0 0.99 11 100
0.11 0 0 0 21 0
0 0.11 0 0
ð 31 D 0
0 0.9 0.99 1 0 41 0
0 0 0 0.99 1 51 0
Substitution of the values of the split-fraction coefficients for the other components will
give the sets of equations for the component flows to each unit. The values of the split-
fraction coefficients and fresh feeds are summarised in Table 4.2.
Table 4.2. Split-fraction coefficients and feeds
˛ k D 1 2 3 4
21k 0.1 1 1 1.0
32k 0.1 0.2 1 0.05
42k 0.9 0.8 0 0.95
43k 0.99 0.99 0 0.99
54k 0.99 0.01 1 0.99
15k 0.99 0.01 1 0.05
g 101 g 202 g 203 g 304
Mol 100 98 98 200
Solution of the equations
The most convenient way to set up and solve the equations is to use a spreadsheet; but any
of the standard procedures and programs available for the solution of linear simultaneous
equations can be used; Westlake (1968), Mason (1984).
Most proprietary spreadsheets include a routine for the inversion of matrices and the
solution of sets of linear simultaneous equations. By using cell references, with cell
copying and cell pointing, it is a simple procedure to set up the split fraction matrices
