Page 45 - Analysis, Synthesis and Design of Chemical Processes, Third Edition

Up to this point, we have kept the amount of process information displayed on the PFD to a minimum. A
more representative example of a PFD for the benzene process is shown in Figure 1.5. This diagram
includes all of the elements found in Figure 1.3, some of the information found in Table 1.5, plus
additional information on the major control loops used in the process.

Figure 1.5 Benzene Process Flow Diagram (PFD) for the Production of Benzene via the
Hydrodealkylation of Toluene

Stream information is added to the diagram by attaching “information flags.” The shape of the flags
indicates the specific information provided on the flag. Figure 1.6 illustrates all the flags used in this text.
These information flags play a dual role. They provide information needed in the plant design leading to
plant construction and in the analysis of operating problems during the life of the plant. Flags are mounted
on a staff connected to the appropriate process stream. More than one flag may be mounted on a staff.
Example 1.4 illustrates the different information displayed on the PFD.

Figure 1.6 Symbols for Stream Identification