Process flow diagram
diagram indicating general flow of plant processes and equipment; typically used to show major relationships in chemical and process engineering
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 process flowsheet. It is the key document in process design.
Typical content of a process flow diagram
Typically, process flow diagrams of a single unit process include the following:
Process piping
Major equipment items
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
Instrumentation details
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 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:
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:
Other items of interest
A PFD can be generated by process simulators (see List of Chemical Process Simulators), CAD packages, or flow chart software using a library of chemical engineering symbols. Rules and symbols are available from standardization organizations such as DIN, ISO or ANSI. Often PFDs are produced on large sheets of paper.
PFDs of many commercial processes can be found in the literature, specifically in encyclopedias of chemical technology, although some might be outdated. To find recent ones, patent databases such as those available from the United States Patent and Trademark Office can be useful.
Standards
ISO 15519-1:2010(en): Specification for diagrams for process industry — Part 1: General rules
ISO 15519-2:2015(en): Specifications for diagrams for process industry — Part 2: Measurement and control
ISO 10628-1:2014(en): Diagrams for the chemical and petrochemical industry — Part 1: Specification of diagrams
ISO 10628-2:2012(en): Diagrams for the chemical and petrochemical industry — Part 2: Graphical symbols
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)
Symbolic language (engineering)
Shit flow diagram
References
Further reading
Raymond E. Kirk & Donald F. Othmer (2001).
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