Page 33 - Analysis, Synthesis and Design of Chemical Processes, Third Edition

This block flow diagram gives a clear overview of the production of benzene, unobstructed by the many
details related to the process. Each block in the diagram represents a process function and may, in reality,

consist of several pieces of equipment. The general format and conventions used in preparing block flow
process diagrams are presented in Table 1.1.

Table 1.1 Conventions and Format Recommended for Laying Out a Block Flow Process Diagram

1. Operations shown by blocks.
2. Major flow lines shown with arrows giving direction of flow.
3. Flow goes from left to right whenever possible.
4. Light stream (gases) toward top with heavy stream (liquids and solids) toward bottom.
5. Critical information unique to process supplied.
6. If lines cross, then the horizontal line is continuous and the vertical line is broken (hierarchy for
all drawings in this book).
7. Simplified material balance provided.

Although much information is missing from Figure 1.1, it is clear that such a diagram is very useful for
“getting a feel” for the process. Block flow process diagrams often form the starting point for developing
a PFD. They are also very helpful in conceptualizing new processes and explaining the main features of
the process without getting bogged down in the details.

1.1.2 Block Flow Plant Diagram

An example of a block flow plant diagram for a complete chemical complex is illustrated in Figure 1.2.
This block flow plant diagram is for a coal to higher alcohol fuels plant. Clearly, this is a complicated
process in which there are a number of alcohol fuel products produced from a feedstock of coal. Each
block in this diagram represents a complete chemical process (compressors and turbines are also shown
as trapezoids), and we could, if we wished, draw a block flow process diagram for each block in Figure

1.2. The advantage of a diagram such as Figure 1.2 is that it allows us to get a complete picture of what
this plant does and how all the different processes interact. On the other hand, in order to keep the
diagram relatively uncluttered, only limited information is available about each process unit. The
conventions for drawing block flow plant diagrams are similar to Table 1.1.

Figure 1.2 Block Flow Plant Diagram of a Coal to Higher Alcohol Fuels Process