Page 158 - Analysis, Synthesis and Design of Chemical Processes, Third Edition

of which, Stream 12, is returned to the column to provide reflux. The other portion of the condensed
liquid is cooled to 38°C in E-105, prior to being sent to storage as benzene product, Stream 15. The
bottoms product from T-101, Stream 11, contains virtually all of the toluene fed to the column and is
recycled back to V-101 for further processing.

The vapor stream leaving V-102 contains most of the methane and hydrogen in the reactor effluent stream
plus small quantities of benzene and toluene. This stream is split into two, with one portion being fed to
the recycle gas compressor, C-101. The stream leaving C-101 is again split into two. The major portion
is contained in Stream 5, which is recycled back to the front end of the process, where it is combined
with fresh hydrogen feed, Stream 3, prior to being mixed with the toluene feed upstream of E-101. The
remaining gas leaving C-101, Stream 7, is used for temperature control in the reactor, R-101. The second
portion of the vapor leaving V-102 constitutes the major portion of the fuel gas stream. This stream is
first reduced in pressure and then combined with the flashed vapor from V-103, Stream 17, and with the
noncondensables from the overhead reflux drum, Stream 19. The combination of these three streams is

the total fuel gas product from the process, Stream 16.

The process description should capture all the knowledge that you have developed in the last two
chapters and represents a culmination of our understanding of the process up to this point.

5.7 Summary

This chapter showed how to trace many of the chemical species through a PFD, based solely upon the
information shown on the skeleton PFD. It introduced operations involving splitting and mixing, not
explicitly shown on the PFD, which were helpful in tracing these streams.

For situations where there was no single input or output stream, systems containing multiple unit
operations were created. The tracing techniques for these compound systems did not provide the
information needed to determine the internal flows for these systems. In order to determine reflux ratios
for columns, for example, the process flow table must be consulted.

With the information provided, an authoritative description of the process can be prepared.

Problems

Identify the main reactant and product process streams for the following:

1. The ethylbenzene process shown in Figure B.2.1, Appendix B.

2. The styrene production facility shown in Figure B.3.1, Appendix B.

3. The drying oil production facility shown in Figure B.4.1, Appendix B.

4. The maleic anhydride production process shown in Figure B.5.1, Appendix B.