What are examples of process flow diagrams

What is a process flow diagram?

The most common PFD symbols currently in use come from agencies such as the International Organization for Standardization (ISO 10628 - Flow Diagrams for Process Plants, General Rules), the German Institute for Standardization (DIN) and the American National Standards Institute (ANSI). However, many companies use their own symbol systems, which are often similar to these common standards, but differ the more detailed they go.

A comprehensive list of PFD symbols can be found here.

A traditional PFD, which represents a process within a single work area, typically contains the following elements:

  • Most important systems or resources including names and ID numbers. These include, for example, compressors, agitators, containers, pumps, boilers and cooling devices.
  • Process piping: Conveys the product (mostly liquids) between the equipment components.
  • Process flow direction
  • Control valves and process-critical valves
  • Important bypass and return systems
  • Operating data such as pressure, temperature, density, mass flow rate and energy-to-mass ratio. In this context, minimum, normal and maximum values ​​are often given.
  • Liquid composition
  • Process stream names
  • Connections / connections to other systems

That doesn't belong in a PFD

As a rule, the following detailed information is omitted:

  • Pipe classes and pipe numbers
  • Process control instruments
  • Minor bypass values
  • Isolation and shut-off valves
  • Service valves and drains
  • Overpressure and safety valves
  • Code class information

Other types of PFDs

Shows a diagram Processes that take place across multiple business areas, it has more of an overview function and therefore contains fewer details. In this case one also speaks of Block flow diagrams or block flow diagrams as well as from schematic flow charts. Each block can represent a single item of equipment or a single phase within a process. Equipment is typically shown in the form of rectangles, while labels explain their function. The process flow usually runs from left to right, with arrows indicating the direction of flow.

A piping and instrument flow diagram (P&ID flow diagram), on the other hand, is a more technical diagram that provides mechanical details for pipeline planners, electrical engineers, equipment technicians and other technical experts who are more dependent on such information than process details. P&ID flow diagrams show the conceptual aspects of PFDs, but also have further details on equipment, process sequence, process and supply lines, bypass lines, devices, valves, vents, drains and other elements.