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