Page 148 - Chemical process engineering design and economics

Process Circuit Analysis 131

We begin the analysis by collecting all the information that is known about
the process from the technical literature - journals, books, and patents. Also we
can obtain information from company brochures on plant operations, pilot plant
data, and laboratory data. Table 3.5.1 contains some of these data, operating con-
ditions, and specifications.
Utilizing Table 3.5.1 we generate initial specifications for the synthesis loop,
which are contained in Table 3.5.2. After completing the degrees of freedom analy-
sis, we may have to adjust the specifications to obtain zero degrees of freedom.
Market conditions determine the production rate of methanol, y^i trig, as given in
Table 3.5.2. The composition of the reformed gas in line 1, with a slight adjustment
to include nitrogen, is taken from Fulton and Fair's [32] case-study problem. The
methane and nitrogen, which are inerts, and excess hydrogen are maintained at ac-
ceptable concentrations by the purge stream. A small purge stream results in

Table 3.5.1 Process Conditions - Methanol-Synthesis Process

Reformer
Exit Temperature 3 - 850 °C
Exit Pressure 3 - 20 bar
Molar H 2O/CO Ratio 3 - 3.0
Equilibrium at Reformer Exit 3
Converter
Exit Temperature" - 270 °C
Inlet Pressure" -100 bar
Optimum Exit CH 3OH Concentration 15 - 5 %
Pressure Drop 0 - 5 to 6 bar

Separator
_____Crude Methanol Components_____________

Methanol 79 wt. %
11
Component Concentration , ppm
Dimethyl Either 20-150
Carbonyl Compounds 10-35
Higher Alcohols 100-2000
Methane None

a) Source: Reference 25
b) Source: Reference 28
c) Source: Reference 35
d) Source: Reference 32

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