Process Flow Diagrams in Chemical Engineering

Process Flow Diagrams (P&IDs)

• PFDs are diagrams used in chemical and process engineering.
• They show the general flow of plant processes and equipment relationships.
• PFDs do not include minor details like piping or designations.
• Another term for PFD is flowsheet.

Process Flow Diagram Examples

• Single process unit: Depicts a single chemical engineering unit process (e.g., amine treating plant).
• Multiple process units: Depicts various unit processes within a typical oil refinery.

Schematic Flow Diagram of the Amine Gas Treating process

• Key equipment includes Absorber, Regenerator, Condenser, Reboiler, Pumps, Reflux drum, and more.
• Operating ranges: Absorber (35-50°C and 5-205 atm), Regenerator (115-126°C and 1.4-1.7 atm).
• Shows flow of materials (Sweet gas, Acid gas, Makeup water, Sour gas, Rich amine, Lean amine, etc.).
• Data includes pressure and temperature for each process unit.

Uses of Flow Diagrams/Flow Charts

• A flowchart is a diagram that represents workflow, showing steps as boxes connected by arrows.
• Flowcharts are used to analyze, design, document, and manage processes in various fields.

Equipment Symbols

• Diagrams show various equipment symbols (e.g. Compressor, Pump, Mixing Vessel, etc.)

Definitions

• Compressor: A mechanical device that takes in a medium and compresses it into a smaller volume.
• Pump: A mechanical apparatus used for raising or moving liquids, compressing gases, or forcing air into inflatable objects.
• Mixing: Combining materials to create a single substance or mass.
• Mixing Vessel: A container used to blend multiple components.
• Heat exchanger: Equipment to transfer heat energy between two processes or flows using conduction and convection.
• Cooling towers: Transfer heat energy to the outside air through evaporation.
• Cooler: Device or container that cools air by water evaporation or by other cooling means.
• Furnace: Tool used to heat air in a continuous current without mixing fresh air with combustion products.
• Boiler: Closed vessel used to heat water or other fluids.
• Tank: Used to store various types of process fluids.

Valve Symbols

• Different valve types have distinct symbols (e.g., Gate valve, Check valve, Globe valve, Ball valve, Butterfly valve, Angle valve).

Piping and Connection Shapes

• Diagrams use various shapes for piping, connections, and signals.

Process Flow Diagram Symbols - Instruments

• Process flow diagrams use special symbols and circles to represent instruments and how they are interconnected.

All Lines and Equipment Connections

• Piping lines are depicted in relation to other process lines.
• Major pipelines connect equipment in any position.
• Straight lines connect equipment in horizontal or vertical positions.
• Process connections are for flow between equipment.

Instruments

• Various instrument symbols are used to represent indicators, recorders, controllers, transmitters, and more.