A PFD is a schematic
representation of the sequence of all relevant operations occurring during a
process and includes information considered desirable for analysis.
The Purpose of a PFD:
Process Flow Diagrams
are required for the following reasons:
Plant Design Basis:
A PFD shows the plant
design basis indicating feedstock, product and main streams flow rates and
operating conditions.
Scope of Process:
A PFD serves to identify the scope of the process.
Equipment Configuration:
A PFD shows graphically the arrangement of major
equipment, process lines and main control loops.
Required Utilities:
A PFD shows utilities which are used continuously
in the process
A PFD typically contains the following information:
This list is by no means exhaustive.
1. All
process lines, utilities and operating conditions essential for material balance
and heat
2. Type and utility flow lines which are used
continuously within the battery limits
3. Equipment diagrams to be arranged according to
process flow, designation,
and
equipment number
4. Simplified control instrumentation pertaining
to control valves and the likes to
be
involved in process flows.
5. Major process analyzers
6. Operating conditions around major equipment
7. Heat duty for all heat transfer equipment
8. Changing process conditions along individual
process flow lines, such as flow rates,
operating
pressure & temperature, etc
9. All
alternate operating conditions
10. Material balance table
There are also items that are not part of a PFD
except in special cases or circumstances. These items include:
1. Minor process lines which are not usually used
in normal operation and minor
equipment,
such as block valves, safety/relief valves, etc.
2. Elevation of equipment.
3. All spare equipment.
4. Heat transfer equipment, pumps, compressor,
etc., to be operated in parallel
or in
series shall be shown as one unit.
5. Piping information such as size, orifice plates,
strainers, and classification into
hot or
cold insulated of jacket piping.
6. Instrumentation not related to automatic
control.
7. Instrumentation of trip system, (because it
cannot be decided at the PFD
preparation
stage).
8. Drivers of rotating machinery except where they
are important for control line
of the
process conditions.
9. Any dimensional information on equipment, such
as internal diameter, height,
length,
and volume. Internals of equipment shall be shown only if required for
a clear
understanding of the working of the equipment.
This is essentially the basics of what a process flow diagram is and how they are used in the process and other industries depict a process.
