11.1 Introduction
Plot plans, process flow diagrams, piping and instrumentation diagrams, and electrical one-line diagrams are important ‘maps’ used by operators and maintenance personnel in their everyday production and maintenance work. Training in this subject is important because understanding the information contained in these drawings is necessary to conduct your daily activities.
11.2 Types of process drawings
The technical naming convention used to indicate the different types of process related drawings/documents are mentioned below:
- Block Flow Diagram (BFD)
- Process Flow Diagram (PFD)
- Piping and Instrument Diagram (P&ID)
- Utility Flow Diagram (UFD)
- Data Sheets
11.3 Block Flow Diagram (BFD)
Theses are the simplest drawings that are used in the Process Industry. They provide a very broad overview of the process and contain very few specific details. Block Flow diagrams represent sections of the process as blocks and they show the order and relationship between sections using flow arrows. Block Flow diagrams are useful in getting a high level initial understanding of a process.
Typical block flow diagram
11.4 Process Flow Diagram (PFD)
A process flow diagram is one in which all incoming and outgoing materials along with related utilities are indicated. It should be clearly understood that such a diagram is different from the P&ID.
11.4.1 Details in a process flow diagram
PFDs essentially illustrate the following:
- Indicates the critical equipments and instrumentation along with process conditions of pressure, flow, and temperature. May also include a material balance including compositions of the streams
- They are used to trace the process flow through a chemical plant or refinery
- Shows all the major equipments and piping, temperatures, and pressures at critical points, and the flow of the process
- Represents with symbols, a fluid system and the equipment associated with a fluid system
- Source of information to process technicians because they show how the process works and the steps associated with each unit operation
It also provides critical information about:
- The major instruments in each area of the plant and where they are located
- The kind of equipment and the type of piping used in each stage of the process
- The utilities consumed in a process
11.4.2 Generation of a Process Flow Diagram
To develop a process flow diagram a considerable amount of information needs to be gathered. The essential details that need to be reflected in a PFD are:
- Flow rate or quantity of each stream
- Operating conditions of each stream, such as pressure and temperature
- Heat added/removed in particular equipment
- Any other specific information, which is useful in understanding the process
From the above, it is clear that the PFD is a very useful diagram in the chemical process industry. It effectively communicates design information. It helps the operator in adjusting his parameters, the supervisor in checking/controlling the plant operation. If the basic process is simple and involves only a few steps, the P&ID and the PFD can be combined into one sheet.
11.4.3 Checklist for the preparation of process diagrams
- Identify an equipment arrangement diagram and describe the kinds of information available on it
- Identify an elevation plan diagram and describe the kinds of information available on it
- Identify a block diagram and describe the kinds of information available on it
- Identify a flow diagram and describe the kinds of information available on it
11.4.4 Typical Process Flow Diagrams
A typical process flow diagram for Lime-Sulphuric Acid recovery process is shown below:
Typical process flow diagram
To make it more complete, material and energy balance calculations are required to indicate the flow components into each unit operations.
11.5 Piping and Instrument Diagram (P&ID)
P&IDs are detailed drawings that reflect the piping, instrumentation and equipments (Appendix C&D) along with design information such as piping size and other specifications.
P&IDs include:
- All the equipments used
- Complete instrumentation methodology
- Size and type of pipe
- Design conditions of the equipment
It contains information about the ways in which piping sections are connected and the instruments associated with the system. P&IDs describe the way in which fluids are directed and controlled. The majority of information about the piping systems comes from instruments that help control and monitor the system. It is critical that process personnel know where in the system the instruments are located.
They illustrate the equipment in detail and give information on piping dimensions and types. They show all the instruments used and the operating conditions of all the steps in a stage. It also provides valuable information about maintenance and repair work on piping systems.
A typical P&ID is included in the Appendix- E for reference.
11.6 Utility Flow Diagram (UFD)
They primarily indicate the following details:
- Show the piping and major instrumentation used to operate the utilities in a process
- UFDs are basically P&ID drawings for utilities
- Show the way in which utilities are connected to the process equipment for service
Typical utilities include:
Steam Condensate, Fuel oil, Instrument air, Utility air, Cooling water Drains, Process and reclaim water.
Typical utility flow diagram
11.7 Data sheets
Data sheets are specific formats used to arrive at equipment and instrument specifications.
A typical data sheet is included in the Appendix-F for reference.
They may be classified into the following categories:
Process data sheets
They define the operating and design parameters for an equipment or a rotating machinery envisaged for a plant or unit operation. They form the basic document to consolidate on the basic engineering package for any project.
Instrument data sheets
These formats explain the instruments involved in a project and the control philosophy adopted for plant operation and safety.
Mechanical data sheets
It explains the mechanical aspects for all the stationary and moving machinery including heavy equipments like cranes, trucks etc.
Electrical data sheets
All the motors, switches, transformers and other circuits are indicated in these formats.
Civil data sheets
Plant layouts designs, foundations, structural details etc are mentioned in these formats.
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