Block Flow Diagram

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Title: Block flow diagram

Authors: Nick Pinkerton, Karen Schmidt, and James Xamplas

Date Presented: January 15, 2013 /Date Revised: January 18, 2013



Block Flow Diagrams, BFDs, are process flow models used to simplify and understand the structure of a system. BFDs are the simplest form of the flow diagrams used where blocks can represent anything from a single piece of equipment to an entire plant. For a complex process, block flow diagrams can be used to break up a complicated system into more reasonable principle stages.

Block flow diagram

BFD's are a useful tool for reports, textbooks and presentations when a detailed process flow diagram is too cumbersome.


BFDs come in many forms and styles. They can be extremely simple or very detailed in their explanation of a process.

I/O Diagrams

The simplest form of BFD, the I/O (input/output) Diagram provides the material streams entering and exiting the process. The diagram is modeled using arrows entering and exiting a process box to represent the inputs and outputs respectively.


There are several conventions regarding the construction of BFDs that are used in the engineering community. These conventions are recommendations 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) towards the top of the block with heavy streams (liquids or solids) towards the bottom

5. Critical information unique to process supplied

6. Lines are straight turning at 90 degree angles.

7. If lines cross, the horizontal line is continuous and the vertical line is broken

8. Simplified material balance should be provided

Example 1: Acrylic Acid From Propylene by Catalytic Oxidation

Block Flow Diagram Example 1: Acrylic Acid From Propylene by Catalytic Oxidation

Example 2: Isopropyl Alcohol from Propylene by Direct Hydration

Block Flow Diagram Example 2: Isopropyl Alcohol from Propylene by Direct Hydration

Example 3: Caprolactam From Toluene

Block Flow Diagram Example 3: Caprolactam From Toluene


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