Process Flow Diagram

Process Flow Diagram (PFD) is an engineering diagram to indicate the general flow of plant processes and equipment. The PFD shows the relationship between major equipment of a plant facility as per process requirement. Generally, a PFD shows only the major equipment and doesn't show details. The PFD is the most effective way of communicating information about a process. The PFD contains the bulks of the chemicals engineering data necessary for the design of a chemical process. The symbols used in PFD vary somewhat from company (plant) to company (plant). So you may see several different symbols that all represent a pump. PFD is used by process engineers for detail engineering purposes such as prepare P&ID. However, PFD can be used for “visitor” information, and employee/ operator training. On the other hand P&IDs are used by process technicians and instrument and electrical, mechanical, safety, and engineering personnel. PFD is used by process engineers to prepare DCS Graphi.


Typically, process flow diagrams (PFD) will include the following: Major equipment symbols, names and identification numbers, Process piping, major bypass and recirculation lines, Flow directions (indicated by arrows on the process streams), Control valves and major Control loops that affect operation of the system, Interconnection with other systems, In some cases, the PFD includes a material balance that lists the normal temperature, pressure, amount and composition of all the major process streams, Also included in some cases, are the amount of heat provided by any process furnaces and the amount of heat exchanged by any process heat exchangers. Process flow diagrams generally do not include: Pipe classes or piping line numbers, Process control instrumentation (sensors and final elements), Minor bypass lines, Isolation and shutoff valves, Maintenance vents and drains, Safety Valve, Flanges connection.

Following data are required by process engineers to prepare and design PFD such as Process description, Process diagram symbols/ legend, Material and heat balance, and Software AUTOCAD. The process unit should be broken down into sections such as: feed pretreatment, feed preheating, the main process, and the final product. The simple left-to-right approach allows a “reader” to identify where the process starts and where it will eventually end