Page 18 - Process Equipment and Plant Design Principles and Practices by Subhabrata Ray Gargi Das

12 Chapter 1 General aspects of process design

All details/features of a plant need not be present in a PFD. Specific facilities and streams for start-
up, shut down or emergency may not be shown. A PFD does not include the minor components, piping
systems, piping ratings and other details. These are found in the P&ID. An example PFD is shown in
Fig. 1.2.
A Piping and Instrumentation Diagram (P&ID) is a schematic illustration of the functional
relationship of piping, instrumentation, and system equipment com-
ponents. This shows all of the piping, including the physical sequence
of branches, reducers, valves, and the equipment. This also shows the
P&ID instrumentation and control, as well as the control interlocks. P&IDs are
usually drawn using ISO standard symbols. However, slight variations
can be found in P&IDs from some established engineering companies.
A typical P&ID should include:

• Instrumentation and designations
• Process equipment with names and numbers
• All valves and their identifications
• Process piping, sizes and identification
• Miscellaneousdvents, drains, special fittings, sampling lines, etc.
• Permanent start-up and flushing lines
• Flow directions
• Interconnections’ references
• Control inputs and outputs, interlocks
• Interfaces for class changes
• Annunciation inputs
• Vendor and contractor interfaces
• Intended physical sequence of the equipment

P&IDs use a numbering/coding system to uniquely identify the equipment, piping and instruments.
Such codes may vary from plant to plant as this is usually decided by the technology vendor and the
detailed engineering contractor. As an example, the equipment code in a plant can have a format
xx-EQ-NNN. A specific code of 13-P-011 shall be denoting a pump numbered 11 in a processing unit
having code 13 and a control valve in the same process unit can be uniquely identified as 13-CV-006.
The line numbering normally contains the following information: service fluid code, line size, pipe
material of construction (MOC), line pressure and temperature rating and unique line identification.
Thus a line in the same process unit with identification 13-CA-100-CS-PN16-013 would be interpreted
as CAecompressed air service, 100eDN100 (nominal pipe size), CSecarbon steel, PN-16 line
pressure and temperature rating and 013eLine no.
Two simple P&IDs are shown in Fig. 1.3.
The plant (and/or equipment) layout in the Plot Plan is decided by referring to the PFD. The designer
knows the equipment required from the PFD and decides the plant layout, usually placing the equipment
in a natural sequence of flow of material. However, there are other
considerations like terrain elevations, wind direction, ease of movement
for operation/maintenance and emergency actions and evacuation plans,
Plot plan
the proximity of another existing plant/equipment/locality, location of
facilities like drainage, access for maintenance, transport and fire safety,