A Process Flow Diagram (PFD) is a type of flowchart that illustrates the relationships between major components of an industrial plant. It is a diagrammatic representation of the process, which is normally drawn in a stylized pictorial form using international standards symbols. PFDs use a series of symbols and notations to depict a process. The symbols vary in different places, and the diagrams may range from simple, hand-drawn diagrams to professional-looking diagrams with expandable detail, produced with software. A process flow diagram (PFD) illustrates the arrangement of the equipment and accessories required to carry out the specific process; the stream connections; stream flow rates and compositions; and the operating conditions.
Purpose of Process Flow Diagrams
A Process Flow Diagram has multiple purposes:
- To model a better process or create a brand-new process.
- To document a process for better understanding, quality control and training of employees.
- To standardize a process for optimal efficiency and repeatability.
- To study a process for efficiency and improvement. It helps to show unnecessary steps, bottlenecks, and other inefficiencies.
Elements of a Process Flow Diagram
A typical PFD for a single unit process will include these elements:
- Major equipment including names and ID numbers. Examples include compressors, mixers, vessels, pumps, boilers, and coolers.
- Process piping which moves the product, usually fluids, between equipment pieces.
- Process flow direction.
- Control valves and process-critical valves.
- Major bypass and recirculation systems.
- Operational data such as pressure, temperature, density, mass flow rate and mass-energy balance. Values often will include minimum, normal and maximum.
- Composition of fluids.
- Process stream names.
- Connections with other systems.
The most common PFD symbols in use today come from agencies such 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 symbols, which are often similar but vary as they become more detailed.
