Process flow diagram

A process flow diagram (PFD) is a diagram commonly used in chemical and process engineering to indicate the general flow of plant processes and equipment. The PFD displays the relationship between major equipment of a plant facility and does not show minor details such as piping details and designations. Another commonly used term for a PFD is a flowsheet.

Typical content of a process flow diagram

Some typical elements from process flow diagrams, as provided by the open source program, Dia. Click for image legend.

Typically, process flow diagrams of a single unit process will include the following:

• Process piping
• Major equipment items
• Control valves and other major valves
• Connections with other systems
• Major bypass and recirculation (recycle) streams
• Operational data (temperature, pressure, mass flow rate, density, etc.), often by stream references to a mass balance.
• Process stream names

Process flow diagrams generally do not include:

• Pipe classes or piping line numbers
• Process control instrumentation (sensors and final elements)
• Minor bypass lines
• Isolation and shutoff valves
• Maintenance vents and drains
• Relief and safety valves
• Flanges

Process flow diagrams of multiple process units within a large industrial plant will usually contain less detail and may be called block flow diagrams or schematic flow diagrams.

Process flow diagram examples

The process flow diagram below depicts a single chemical engineering unit process known as an amine treating plant:

Flow diagram of a typical amine treating process used in industrial plants

Multiple process units within an industrial plant

The process flow diagram below is an example of a schematic or block flow diagram and depicts the various unit processes within a typical oil refinery:

A typical oil refinery-SL

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Standards

• ISO 10628: Flow Diagrams For Process Plants - General Rules
• ANSI Y32.11: Graphical Symbols For Process Flow Diagrams (withdrawn 2003)
• SAA AS 1109: Graphical Symbols For Process Flow Diagrams For The Food Industry

See also

• Hazop
• Piping and instrumentation diagram (P&ID)

Further reading

• Raymond E. Kirk; Donald F. Othmer (2001). Kirk-Othmer Encyclopedia of Chemical Technology (4th ed.). Wiley-Interscience. ISBN 0471419613. {{cite book}}: Unknown parameter |lastauthoramp= ignored (|name-list-style= suggested) (help)
• M.S. Ray; M.G. Sneesby (1998). Chemical Engineering Design Project: A Case Study Approach (2nd ed.). Gordan and Breach Science Publishers. ISBN 9056991361. {{cite book}}: Unknown parameter |lastauthoramp= ignored (|name-list-style= suggested) (help)
• R. Turton; R.C. Bailie; W.B. Whiting; J.S. Shaeiwitz (2002). Analysis, Synthesis, and Design of Chemical Processes (2nd ed.). Prentice Hall. ISBN 0-13-064792-6.
• Fritz Ullmann (2002). Ullman’s Encyclopedia of Industrial Chemistry (6th ed.). Wiley-VCH. ISBN 3-527-30385-5.
• Srikumar Koyikkal (2013). Chemical Process Technology and Simulation (1st ed.). Prentice Hall India. ISBN 978-81-203-4709-0.

External links

• Process Flow Sheet
• The PFD at The Engineering Tool Box
• Simplified process flowsheets and flow diagrams of process industries. Development of new integration methods and model flow diagrams.