7 Process Flow Diagrams (PFDs)

Learning Objectives

By the end of this section, you should be able to:

Build process flow diagrams (PFDs)

Process Flow Diagrams (PFDs)

Process flow diagrams usually include:

  • Major pieces of equipment that are represented by a description and a unique equipment number and name

  • Process flow streams that are represented by a number and sometimes include process conditions and chemical composition of each stream. This information can be shown on the PFD itself or on an accompanying flow summary table

  • Utility streams for major equipment

  • Basic control loops that present the overarching control strategy used to operate the processes. These are generally optional, and not shown in the diagrams above.
  • An equipment summary table with key details (shown later in this chapter)

PFD Equipment Numbering

This is a typical way to label a piece of equipment using its position in the process. This is not the only way to label equipment, but a very common way. We will stick with this in this class and you will likely see it very commonly.


  • First letter: equipment (P = pump)
  • First number: plant section (1 = section 1 of plant)
  • Last numbers: equipment number (01 = pump 1 in this section)
  • Last letters: show duplicates/triplicates when two or more of the same equipment is used for the same stage of the process.
Label Equipment Description
C Compressor or Turbine
E Heat Exchanger
P Pump
R Reactor
T Tower
TK Storage Tank
V Vessel

PFD Utility Naming

Generally, rather than using numbers, utility streams will be labeled using a certain descriptor. These streams are labeled in this way as the same type of stream will generally have the same conditions, and so this saves repeatedly specifying these streams with numbers.

Label Utility Description
lps Low-Pressure Steam (3-5 bar)
mps Medium-Pressure Steam (10-15 bar)
hps High-Pressure Steam (40-50 bar)
htm Heat Transfer Media (organic)
cw Cooling Water
rw Refrigerated Water
rb Refrigerated Brine
cs Chemical Waste Water
ss Sanitary Waste Water
el Electric Heat
ng Natural Gas
fg Fuel Gas
fo Fuel Oil

PFD Legend

The legend should include everything to allow someone to read the PFD with no prior knowledge of the project.

PFD Summary Tables

Stream Summary Table

Certain essential information must be included in stream summary tables, this may vary slightly depending on the industry, what we will stick within this class is the following:

  • Stream number
  • Temperature
  • Pressure
  • Vapour fraction
  • Total mass flowrate
  • Total mole flowrate
  • Individual component mole flowrates

Other information may or may not be included as well:

  • Stream name
  • Component mole fractions
  • Component mass fractions
  • Individual component mass flowrates
  • Volumetric flowrates
  • Significant physical properties (density, viscosity, etc.)
  • Thermodynamic data (heat capacity, specific enthalpy)
Stream Number 1 2 3 4 5 6
Temperature ([latex]^{\circ}C[/latex]) 25 25 90 90 95 250
Pressure (atm) 1.5 1.5 1.5 1.5 30 20
Vapor Fraction 1.0 1.0 0.3 0.6 0.5 1.0
Mass Flow (kg/hr) 50,000 105,000 149,000 276,000 276,000 276,000
Molar Flow (kmol/hr) 1,500 1,500 1,500 2,600 1,750 5,000
Component Molar Flow (kmol/hr)
Ethylene 1,500 0 0 0 0 0
Chlorine 0 1,500 0 0 0 0
1,2-dichloroethane 0 0 1,500 0 0 0
Vinyl Chloride 0 0 0 2,600 0 2,500
Hydrogen Chloride 0 0 0 0 1,750 2,500

Equipment Summary Table

The equipment summary table provides information on equipment specifications. These are essentially a short list of key details used for the designing or costing of equipment. Examples of what might be specified in this table for different types of equipment are shown below. As you can see, these can be quite detailed, and you’ll learn more about how to specify these parameters throughout your degree.

Equipment Required Specification
Vessels Height; diameter; pressure; temperature; materials of construction
Pumps Flow; driver type; suction and discharge pressures; temperature; shaft power; materials of construction
Towers Height; diameter; orientation; pressure; temperature; number and type of trays; height and type of packing; material of construction
Compressors Inlet flow; driver type; suction and discharge pressures; temperature; shaft power; material of construction
Heat Exchangers Type; area; duty; number of shell and tube passes; operating temperatures; pressures; pressure drops; material of construction
Fired Heaters Type; tube pressure; tube temperature; duty; radiant heat transfer area; convective heat transfer area; material of construction

Exercise: PFD Components

Consider the following diagram:

Image from CS Odessa / CC BY

If we wanted to turn this into a PFD, what would need to be added or modified?


  • Add a legend
  • Label the streams in a logical manner
  • Name the equipment and utilities using the correct naming convention
  • Add unit operation labels and description to the top or bottom of the PFD
  • Also, consider adding stream and equipment summary tables



Icon for the Creative Commons Attribution-ShareAlike 4.0 International License

Foundations of Chemical and Biological Engineering I Copyright © 2020 by Jonathan Verrett is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted.

Share This Book


Comments are closed.