Process Flow Diagram

Written by Jerry Ratzlaff. Posted in Designer

A Process Flow Diagram shows the relationships between the major components of a system or process plant. The PFD is more detailed than a Block Flow Diagram but does not contain as much detail as Piping and Instrumentation Diagram P&IDs.  A PFD indicates the general flow of plant processes and equipment and the relationship between major equipment of a plant facility.  A PFD does not show minor components, piping systems, piping ratings and designations.

A process flow diagram (PFD) is a diagram commonly used in chemical and process engineering to  and does not show minor details such as piping details and designations. Another commonly-used term for a PFD is a flowsheet.

Abbreviations

  • PFD - Process Flow Diagram

PFD Should Include

PFDs shouldPFDs should not
  • Process Piping - major process lines
  • Major equipment symbols, names and identification numbers
  • Flow directions
  • Major bypass and recirculation lines
  • Control valves and valves that affect operation of the system
  • Control loops that affect operation of the system
  • Interconnection with other systems
  • Major bypass and recirculation lines
  • System ratings and operational values as minimum, normal and maximum flow, temperature and pressure
  • Composition of Fluids
  • 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
  • Isolation and shutoff valves
  • Code class information
  • Seismic class information

Equipment Information

Columns & ScrubbersPressure Vessels & TanksHeat Exchangers
  • Equipment Number
  • Name
  • Internal Diameter & Height
  • Design Pressures and Temperatures
  • Number of Trays
  • Materials of Construction
  • Equipment Number
  • Name
  • Size
  • Capacity
  • Design Pressrures & Temperatures
  • Materials of Construction
  • Equipment Number
  • Name
  • Heat Transfer Area
  • Heat Duty at material balance conditions, Btu/hr
  • Design Pressures & Temperatures
  • Type
  • Materials of Construction
Compressors & BlowersPumps 
  • Equipment Number
  • Name
  • Design suction & discharge pressures
  • Design & estimated discharge temperatures
  • Design capacity, cfm at design suction conditions
  • Driver horsepower
  • Type
  • Equipment Number
  • Name
  • Design Capacity, GPM at flowing temperature
  • Suction & Discharge pressures
  • Drive Horsepower
  • Type
  • Materials
  • Pumping temperature (normal & maximum)
  • Specific Gravity of pumped fluids
 

 

notes

Since PFDs become permenant record, certain requirements should be considered when preparing the drawings. Specifically:

  • Requirements by Governmental Authorties or Agencies
  • Requirements by the client or the customer
  • Requirements of the equipment and process
  • The preparation of a tabulation of symbols, abbreviations and blocks used in the set of the drawings. It is very important to show any symbols, which are not recognized as industry standards, be shown and explained.