Here is a step-by-step procedure for developing a process flow diagram (PFD) for a plant as per international standards:

Step 1 : Gather Information

Collect relevant data and information about the process, including:

• Process description
• Material balances
• Energy balances
• Equipment specifications
• Operating conditions (temperature, pressure, flow rates, etc.)
• Safety and environmental considerations
• Review existing documents, such as:
• Process design packages (PDPs)
• Piping and instrumentation diagrams (P&IDs)
• Hazard and operability studies (HAZOPs)
• Safety data sheets (SDSs)

Step 2 : Define the Process Boundaries

Identify the process boundaries, including:

• Feed stocks and raw materials
• Products and by-products
• Utilities (e.g., steam, water, electricity)
• Waste streams
• Determine the scope of the process, including:
• What is included in the process
• What is excluded from the process

Step 3 : Identify the Major Process Steps

Break down the process into major steps, including:

• Feed preparation
• Reaction or conversion
• Separation
• Purification
• Storage and handling
• Identify the key process variables, including :
• Temperature
• Pressure
• Flow rates
• Concentrations

Step 4 : Develop the PFD

Use a standardized symbol set, such as the International Organization for Standardization (ISO) 10628 or the American National Standards Institute (ANSI) Y32.11, to create the PFD.

Include the following elements on the PFD :

• Process vessels (e.g., tanks, reactors, columns)
• Process equipment (e.g., pumps, compressors, heat exchangers)
• Piping and connections
• Valves and fittings
• Instruments and controls
• Utilities and services
• Use a clear and consistent layout, including:
• A logical flow direction (e.g., from top to bottom or left to right)
• A consistent scale and orientation
• Clear and concise labeling

Step 5 : Add Process Information Add relevant process information to the PFD, including:

• Flow rates and velocities
• Temperatures and pressures
• Concentrations and compositions
• Energy inputs and outputs
• Material balances

Use standard notation and units, such as :

• SI units (e.g., kg/h, degree C, bar)
• Imperial units (e.g., lb/h, degree F, psi)

Step 6 : Review and Validate Review the PFD for accuracy and completeness, including:

• Checking for consistency with other process documents
• Verifying the accuracy of process information
• Ensuring that the PFD is easy to understand and interpret
• Validate the PFD through:
• Peer review
• Stakeholder feedback
• Comparison with industry benchmarks and standards

Step 7 : Finalize and Document Finalize the PFD, including :

• Adding a title block with relevant information (e.g., process name, date, revision number)
• Including a legend or key to explain symbols and abbreviations
• Providing a clear and concise description of the process
• Document the PFD, including:
• Storing the PFD in a secure and accessible location
• Maintaining a record of revisions and updates
• Sharing the PFD with relevant stakeholders and teams

International standards that may be relevant to PFD development include:

• ISO 10628:1997 - Flow diagrams for process plants
• ANSI Y32.11:2012 - Graphic symbols for process flow diagrams
• API RP 752:2019 - Management of hazards associated with location of process plant buildings
• OSHA 29 CFR 1910.119: Process safety management of highly hazardous chemicals

Note : The specific steps and standards may vary depending on the industry, location, and specific requirements of the project.