Page 155 - Chemical process engineering design and economics

138 Chapter 3

Table 3.5.6 Revised Degrees of Freedom Calculation—Methanol-
Synthesis Process

Process Unit Unit Unit
Vari- Equations
ables VD Ru

Mixer 12 7
Converter 14 9
Condenser- 15 10
Separator
Splitter 18 11
Total 59 37

Line Re- Repeated
Number peated Equations
Vari- RR
ables V R

2 6 0
3 5 1
4 7 1
7 6 0
Total 24 2

Process Degrees of Freedom

F P = (Vu - V R) - (Ru - RR) = (59 - 24) - (37 - 2) = 35 - 35 = 0

Now that the problem is formulated we turn our attention to solving the
equations. One solution method that we could use is the sequential modular
method. For this method, select one of the process units as the starting point for
the calculation. Then, assume values for some of variables to reduce the degrees of
freedom to zero for that unit. Next, precede unit-by-unit through the flow sheet

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