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actuality it is necessary merely to provide 560
◦
C as the set point to heaters B and D.
This is implemented at Example Twelve-4b.
12.9 MISCELLANEOUS CONSIDERATIONS
Pumps are not used at this level of development. It is understood that the use of a mostly
constant 14.7 psi pressure in this flowsheet is technically incorrect but introduces only a
small error. The feed to the distillation column was changed to 18 psi to accommodate
the column's internal pressure. The actual size and location of the equipment has not
been defined since the physical layout there has not yet been developed; therefore,
pump selection cannot proceed since the actual service is unknown. For example, the
distillation column has 60 theoretical stages, and if the efficiency is 100% and the tray
spacing is 2 ft, the column is at least 120 ft tall (a 12-story building). If the site is in
a windy area, this column may be built as two 60-ft columns with pumps in between.
Similarly, the type of equipment used for heating some streams to high temperatures
and cooling off others is unknown; thus, detailed design will be carried out by others.
The amount of water used to control the formation of by-products is unknown. The
reaction kinetics is unknown, and therefore at this point in the flowsheet development,
a reaction conversion of 35% is used. Scale-up would be from laboratory data.
12.10 WORKSHOPS
Workshop 12.1
Figure 12.11 shows a section of a process for converting toluene
to benzene in a hydroalkylation reactor. The main reaction is
C
7
H
8
+
H
2
→
C
6
H
6
+
CH
4
FEED
MIX1
RECYCLE
1
GAS-RECY
VAP
6
6H
FLSH
MIX2
HX
HEATER
2
4
LIQ
3
FURNACE
REACTOR
QUENCH
PUMPED
PROD
PUMP
SPLIT
SPLIT
Figure 12.11
Process for production of benzene.
