Lecture 2 - BFD and PFDs

By the end of this lesson, students will be able to:
- Distinguish between block flow diagrams (BFD) and process flow diagrams (PFD).
- Understand the uses and key elements of BFDs and PFDs.
- Identify key information needed for PFDs, including heat and material balance tables.
- Understand common conventions for equipment names and numbers.

Definition: A diagram consisting of a series of blocks representing different equipment or unit operations connected by input and output streams.
Applications:
- Can represent a single process (block flow process diagram) or an entire chemical complex (block flow plant diagram).
- Note that the definition of BFD can be somewhat vague.

Example Reaction: 78 + 2 → 66 + 4
- Figure 1.1 shows a Block Flow Process Diagram for the Production of Benzene.

Operations are shown by blocks.
Major flow lines are illustrated with arrows to indicate the direction of flow.
Flow typically goes from left to right; recycles are shown going from right to left.
Light streams (gases) are depicted toward the top; heavy streams (liquids and solids) are toward the bottom.
Critical information unique to the process is included.
When lines cross, the horizontal line is continuous while the vertical line is broken.
A simplified material balance is provided.

BFDs are effective for:
- Explaining the overall operation of a chemical plant.
- Developing an understanding of a process.
- Communicating at a high level.
- Outlining and screening potential process alternatives for early comparisons.

A PFD contains a much more detailed and comprehensive body of data compared to a BFD.
It includes essential chemical engineering information for designing a chemical process.
Though varied, PFDs typically contain four specific categories of information:
- Equipment descriptions and identification.
- Process flow streams and their conditions.
- Utility streams supplied to major equipment.
- Basic control loops illustrating operational control strategies.

The information on PFDs is categorized into three groups:
- Process Topology: Location and connections of equipment in the process.
- Stream Information: Details about the streams connected between equipment.
- Equipment Information: Specifics related to the equipment involved in the process.

Equipment is typically identified by:
- Equipment classification letters and numbers (e.g., C for Compressor, E for Heat Exchanger, R for Reactor, etc.).
Equipment names describe their functions but should be clear and concise, ensuring identification within the process context.
Common conventions dictate that both equipment numbers and names are displayed in a standard format on the PFD for easy reference.

Each stream is designated with a diamond labeled with a number, which corresponds to a stream table.
Essential information in the stream table includes:
- Stream numbers, temperatures, pressures, vapor fractions, mass flow rates, and chemical component breakdowns.

Essential information captured in the utility heat balance table includes:
- Equipment number, type of utility, heat duty, and utility inlet/outlet temperatures and flowrates.

Notations for various utilities include:
- lps: Low-pressure steam
- hps: High-pressure steam
- cw: Cooling (Tower) Water
- ng: Natural Gas
Complexity and variations term specified utilities are detailed to ensure clarity in the process diagrams.