Skip to main content
Engineering LibreTexts

1.7: Process Flow Diagrams (PFDs)

  • Page ID
    101141

    \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

    \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)

    \( \newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\)

    ( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\)

    \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)

    \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\)

    \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)

    \( \newcommand{\Span}{\mathrm{span}}\)

    \( \newcommand{\id}{\mathrm{id}}\)

    \( \newcommand{\Span}{\mathrm{span}}\)

    \( \newcommand{\kernel}{\mathrm{null}\,}\)

    \( \newcommand{\range}{\mathrm{range}\,}\)

    \( \newcommand{\RealPart}{\mathrm{Re}}\)

    \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\)

    \( \newcommand{\Argument}{\mathrm{Arg}}\)

    \( \newcommand{\norm}[1]{\| #1 \|}\)

    \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\)

    \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\AA}{\unicode[.8,0]{x212B}}\)

    \( \newcommand{\vectorA}[1]{\vec{#1}}      % arrow\)

    \( \newcommand{\vectorAt}[1]{\vec{\text{#1}}}      % arrow\)

    \( \newcommand{\vectorB}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

    \( \newcommand{\vectorC}[1]{\textbf{#1}} \)

    \( \newcommand{\vectorD}[1]{\overrightarrow{#1}} \)

    \( \newcommand{\vectorDt}[1]{\overrightarrow{\text{#1}}} \)

    \( \newcommand{\vectE}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{\mathbf {#1}}}} \)

    \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \)

    \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)

    \(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)
    Learning Objectives

    By the end of this section, you should be able to:

    • Build process flow diagrams (PFDs)

    Process Flow Diagrams (PFDs)

    Process flow diagrams usually include:

    • Major pieces of equipment that are represented by a description and a unique equipment number and name
    PFD1-300x99.png
    • Process flow streams that are represented by a number and sometimes include process conditions and chemical composition of each stream. This information can be shown on the PFD itself or on an accompanying flow summary table
    PFD2-300x99.png
    • Utility streams for major equipment
    PFD3-300x208.png
    • Basic control loops that present the overarching control strategy used to operate the processes. These are generally optional, and not shown in the diagrams above.
    • An equipment summary table with key details (shown later in this chapter)
    PIDExp2-300x187.png

    PFD Equipment Numbering

    This is a typical way to label a piece of equipment using its position in the process. This is not the only way to label equipment, but a very common way. We will stick with this in this class and you will likely see it very commonly.

    P-101A

    • First letter: equipment (P = pump)
    • First number: plant section (1 = section 1 of plant)
    • Last numbers: equipment number (01 = pump 1 in this section)
    • Last letters: show duplicates/triplicates when two or more of the same equipment is used for the same stage of the process.
    Label Equipment Description
    C Compressor or Turbine
    E Heat Exchanger
    P Pump
    R Reactor
    T Tower
    TK Storage Tank
    V Vessel

    PFD Utility Naming

    Generally, rather than using numbers, utility streams will be labeled using a certain descriptor. These streams are labeled in this way as the same type of stream will generally have the same conditions, and so this saves repeatedly specifying these streams with numbers.

    Label Utility Description
    lps Low-Pressure Steam (3-5 bar)
    mps Medium-Pressure Steam (10-15 bar)
    hps High-Pressure Steam (40-50 bar)
    htm Heat Transfer Media (organic)
    cw Cooling Water
    rw Refrigerated Water
    rb Refrigerated Brine
    cs Chemical Waste Water
    ss Sanitary Waste Water
    el Electric Heat
    ng Natural Gas
    fg Fuel Gas
    fo Fuel Oil

    PFD Legend

    The legend should include everything to allow someone to read the PFD with no prior knowledge of the project.

    PFDLegend-300x193.png

    PFD Summary Tables

    Stream Summary Table

    Certain essential information must be included in stream summary tables, this may vary slightly depending on the industry, what we will stick within this class is the following:

    • Stream number
    • Temperature
    • Pressure
    • Vapour fraction
    • Total mass flowrate
    • Total mole flowrate
    • Individual component mole flowrates

    Other information may or may not be included as well:

    • Stream name
    • Component mole fractions
    • Component mass fractions
    • Individual component mass flowrates
    • Volumetric flowrates
    • Significant physical properties (density, viscosity, etc.)
    • Thermodynamic data (heat capacity, specific enthalpy)
    Stream Number 1 2 3 4 5 6
    Temperature (\(^{\circ}C\)) 25 25 90 90 95 250
    Pressure (atm) 1.5 1.5 1.5 1.5 30 20
    Vapor Fraction 1.0 1.0 0.3 0.6 0.5 1.0
    Mass Flow (kg/hr) 50,000 105,000 149,000 276,000 276,000 276,000
    Molar Flow (kmol/hr) 1,500 1,500 1,500 2,600 1,750 5,000
    Component Molar Flow (kmol/hr)
    Ethylene 1,500 0 0 0 0 0
    Chlorine 0 1,500 0 0 0 0
    1,2-dichloroethane 0 0 1,500 0 0 0
    Vinyl Chloride 0 0 0 2,600 0 2,500
    Hydrogen Chloride 0 0 0 0 1,750 2,500

    Equipment Summary Table

    The equipment summary table provides information on equipment specifications. These are essentially a short list of key details used for the designing or costing of equipment. Examples of what might be specified in this table for different types of equipment are shown below. As you can see, these can be quite detailed, and you’ll learn more about how to specify these parameters throughout your degree.

    Equipment Required Specification
    Vessels Height; diameter; pressure; temperature; materials of construction
    Pumps Flow; driver type; suction and discharge pressures; temperature; shaft power; materials of construction
    Towers Height; diameter; orientation; pressure; temperature; number and type of trays; height and type of packing; material of construction
    Compressors Inlet flow; driver type; suction and discharge pressures; temperature; shaft power; material of construction
    Heat Exchangers Type; area; duty; number of shell and tube passes; operating temperatures; pressures; pressure drops; material of construction
    Fired Heaters Type; tube pressure; tube temperature; duty; radiant heat transfer area; convective heat transfer area; material of construction

    Exercise

    PFD Components

    Consider the following diagram:

    Example1-300x212.png

    Image from CS Odessa / CC BY

    If we wanted to turn this into a PFD, what would need to be added or modified?

    Click here to see the solution!

    Solution

    • Add a legend
    • Label the streams in a logical manner
    • Name the equipment and utilities using the correct naming convention
    • Add unit operation labels and description to the top or bottom of the PFD
    • Also, consider adding stream and equipment summary tables

    This page titled 1.7: Process Flow Diagrams (PFDs) is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by .