Block and Process Flow Diagrams

Block flow diagrams and process flow diagrams are familiar tools to engineers. They are important in digitizing industrial process plants. Process engineers learn about the block flow diagram early in their engineering education. The block flow diagram is a series of blocks connected with input and output flow streams (Turton et al. 1998, 2018; Woods 2005). The block flow diagram includes operating conditions (e.g., flow, temperature, and pressure) and other important information, such as conversion and recovery. It does not provide details regarding what is involved with the blocks, but concentrates on the main flow of the process.

Block Flow Diagrams

According to Turton et al. (2018), the block flow diagram can take one of two forms: a single process or a complete plant complex involving many different processes. The block flow diagram, as described in Table 3.1 and illustrated in Figure 3.9, represents a single process.

Figure 3.9 shows a simplified block flow diagram for the Proclndustries South Texas oil refinery. Each block in this diagram represents a complete chemical process. If further detail is needed, a block diagram can be drawn for each of the chemical process blocks.

Peter explained, "The advantage of such a diagram is that we get a complete picture of what the South Texas refinery does. And we can see the major


Block Flow Diagram Conventions and Format

Block Flow Diagram Construction

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


South Texas refinery process block diagram.

areas that need to be digitized, including all the important flows of material and information. The diagram includes associated sensors to incorporate into the EIDI context object model."

The block diagram also provides information on how all the different process units interact. This information is vital for analyzing interactions among the process units and to identify the response times to flow, temperature, and composition changes. To keep the diagram relatively uncluttered, only limited information is available about each process unit.

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