CHAPTER 1 Chemical Process Diagrams

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CHAPTER 1 Chemical Process Diagrams
THE MOST EFFECTIVE WAY OF COMMUNICATING
INFORMATION ABOUT A PROCESS IS THROUGH THE USE
OF FLOW DIAGRAMS
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The Generic Block Flow Process Diagram

• There are features common to all chemical
  processes. Figure below provides a generic Block
  Flow Process Diagram that shows a chemical
  process broken down into six basic areas or
  blocks.

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The Generic Block Flow Process Diagram

• Each of these blocks may contain several unit
  operations. For example, A separation section
  might contain (four distillation columns, two
  flash units, and a liquid-liquid decanter)
• Reactor Feed preparation and Separator Feed
  Preparation sections mainly involve changing the
  conditions (temperature and pressure) of the
  process streams to the conditions required by the
  reactor or separator.

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CHAPTER 1 Chemical Process Diagrams

• Design is an evolutionary process
• Input/output is a crude block flow diagram in
  which only feed and product streams are
  identified.
• Generic Diagram Break the process into its basic
  elements such as reaction and separation , and
  recycle sections.
• BFD include the material balance calculations.
• PFD complete mass and energy balance and
  preliminary equipment specs.
• PID includes the mechanical and instrumentation
  details.

Input/output diagram Generic diagram
BFD PFD PID.
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Chemical Process Diagrams

• 3 Main Levels of Diagrams
• Block Flow Diagram (BFD)
• Process Flow Diagram (PFD)
• Piping and Instrumentation Diagram (PID) often
  referred to as Mechanical Flow Diagram

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Comparison

Level of Conceptual Understanding Increases
BFD
Level of Complexity Increases
PFD
PID
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The Block Flow Diagram (BFD)

• Shows overall processing picture of a chemical
  complex
• Useful as an orientation tool
• Used to sketch out and screen potential process
  alternatives.

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Definitions of BFD

• Block Flow Process Diagram (BFPD)
• BFPD forms the starting point for developing PFD
• BFPD is helpful in conceptualizing new processes
• See Fig 1.1
• Block Flow Plant Diagram
• Gives a general view of a large complex plant
• See Fig 1.2

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The Block Flow Process Diagram
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The Block Flow Plant Diagram
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Block Flow Diagrams

• Conventions and Formats for BFD
• Operations shown by blocks
• Major flow lines shown with arrows
• Flow goes from left to right whenever possible
• Light streams toward top with heavy stream toward
  bottom
• Critical information unique to process supplied
• If lines cross, then horizontal line is
  continuous
• Simplified material balance provided

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The Process Flow Diagrams (PFD)

• A PFD contains the bulk of the Chem Eng data
  necessary for the design of a chemical process.
• Basic information provided by a PFD
• Process Topology
• Stream Information
• Equipment Information

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The Process Flow Diagrams (PFD)

• A typical commercial PFD will contain the
  following information
• All major pieces of equipments in the process
  will be represented along with a descriptive name
  and number.
• All process flow streams will be shown and
  identified with a number. A description of the
  process conditions and chemical composition of
  each stream will be included.
• All utility streams supplied to major equipment
  that provides a process function will be shown.
• Basic control loops will be shown.

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The Process Flow Diagram (contd)

• The topology of the process showing the
  connectivity of all the streams and the
• equipment
• Example for toluene HDA figures 1.3 and 1.5
• Tables 1.2 lists information that should be on
  the PFD but cannot fit
• Use appropriate conventions consistency is
  important in communication of process information
  ex. Table 1.2

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The Process Flow Diagram (contd)
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Symbols for Drawing PFD
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The Process Flow Diagram (contd)
Table 1.2 Conventions Used for Identifying
Process Equipment  
 
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Equipment Numbering

• XX-YZZ A/B/
• XX represents a 1- or 2-letter designation for
  the equipment (P pump)
• Y is the 1 or 2 digit unit number (1-99)
• ZZ designates the equipment number for the unit
  (1-99)
• A/B/ represents the presence of spare equipment

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The Process Flow Diagram (contd)
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Equipment Numbering (contd)

• Thus, T-905 is the 5th tower in unit nine hundred
  P-301 A/B is the 1st Pump in unit three hundred
  plus a spare XX-YZZ A/B/
• Use unambiguous letters for new equipment
• Example Turbine use Tb or J not T (for tower)
• Replace old vessel V-302 with a new one of
  different design - use V-319 (say) not V-302
  since it may be confused with original V-302 the
  presence of spare equipment

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Stream Numbering and Drawing

• Number streams from left to right as much as
  possible
• Horizontal lines are dominant

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Stream Numbering and Drawing (contd)

• Add arrows for
• Change in direction
• Inlet of equipment
• Utility streams should use convention given in
  Table 1.3 (lps, cw, fg, etc)

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Stream Information

• Since diagrams are small not much stream
  information can be included
• Include important data around reactors and
  towers, etc.
• Flags are used see toluene HDA diagram
• Full stream data, as indicated in Table 1.4, are
  included in a separate flow summary table see
  Table 1.5

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Stream Information - Flags
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Stream Information
Table 1.4 Information in a Flow Summary

•  
• Essential Information
• Stream Number
• Temperature (C)
• Pressure (bar)
• Vapor Fraction
• Total Mass Flow Rate (kg/h)
• Total Mole Flow Rate (kmol/h)
• Individual Component Flow Rates (kmol/h)
• Optional Information
• Component Mole Fractions
• Component Mass Fractions
• Individual Component Flow Rates (kg/h)
• Volumetric Flow Rates (m3/h)
• Significant Physical Properties
• Density
• Viscosity
• Other
• Thermodynamic Data

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The Process Flow Diagram (contd)
   
A Portion of Table 1.5
   
 
 
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Equipment Information

• Equipment are identified by number and a label
  (name) positioned above the equipment on the PFD
• Basic data such as size and key data are included
  in a separate table (Equipment Summary Table)
  Table 1.7 (and Table 1.6) in TBWS

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Equipment Information
A Section of Table 1.7 Equipment Summary
Vessel V-101 V-102
Temperature (ºC) 55 38
Pressure (bar) 2.0 24
Orientation Horizontal Vertical
MOC CS CS
Size
Height/Length (m) 5.9 3.5
Diameter (m) 1.9 1.1
Internals s.p. (splash plate)
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PFD Summary

• PFD, Equipment Summary Table, and Flow Summary
  Table represent a true PFD
• This information is sufficient for a preliminary
  estimation of capital investment (Chapter 5) and
  cost of manufacture (Chapter 6) to be made

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The Piping and Instrument Diagram (PID)

• PID Construction Manual
• Contains plant construction information (piping,
  process, instrumentation, and other diagrams)
• PID construction convection is explained in
  Table1.9
• Conventions for instrumentation are shown in
  Table 1.10.

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PID
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Look at V-102 on PID

• V-102 contains an LE (Level Element)
• LE senses liquid level in separator and adjusts
  flow rate leaving
• LE opens and closes a valve depending on liquid
  level
• LE and valve represent a feedback control loop

The final control element in nearly all chemical
process control loops is a valve
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PID

• Based on the PID diagram
• Mech and Civil Engrs will design and install
  pieces of equipment.
• Instrument Engrs will specify, install and check
  control systems.
• Piping Engrs will develop plant layout and
  elevation drawings.
• Project Engrs will develop plant and construction
  schedules.

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Additional Diagrams

• UTILITY FLOWSHEET
• VESSEL SKETCHES
• WIRING DIAGRAMS
• SITE PLANS
• PLOT PLANS
• ELEVATION DIAGRAMS

DO NOT POSSESS ADDITIONAL PROCESS INORMATION
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Additional Diagrams

• Plot Plans plan or map drawn looking down on
  plant (drawn to scale with all major equipment
  identified)
• Elevation Diagrams show view from side and give
  information about equipments distance from ground
  

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Additional Diagrams
Section of Plot Plan
Section of Elevation Diagram
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Additional Diagrams (contd)

• Piping Isometrics show piping in 3-dimensions
• Vessel Sketches show key dimensions of
  equipment and locations of inlet and outlet
  nozzles etc.

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Scale Models and Virtual Plants

• 25 years ago physical models were used for review
  
• Now virtual or electronic models are generated
  using software (3-d plant diagrams)
• Purpose of Models catch errors such as
• Piping clashes
• Misaligned piping
• Equipment not easily accessed
• Sample points not easily reached by operators

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3-D Plant Diagrams
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Problem 1.9
Figure below is a portion of a PID. Find at
least six errors in it. All errors are actually
shown on the drawing.
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Solution

• Errors include
• 1. LI on pump discharge should be PI.
• 2. Direction of arrowheads should be reversed.
• 3. TCV on control valve should be labeled FCV.
• 4. LAH on control loop should be FAH (Since no
  level signal is shown)
• 5. Add isolation valve to the left of the
  control valve.
• 6. Add a bleed valve between control valve and
  isolation valve.
• 7. Suction piping should be larger than
  discharge piping,
• switch 4 with 8.
• 8. Label insulation.
• 9. Pumps should be labeled P-102 A and P-102B.

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Solution contd.
Corrected Diagram is