KKA 3306 PROCESS AND PLANT DESIGN Lecture 6

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KKA 3306 - PROCESS AND PLANT DESIGN Lecture 6
By Robiah yunus Faculty of engineering Universiti
putra malaysia Serdang,43400 selangor.
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MASS AND ENERGY BALANCES

• Introduction
• Mass and energy balances are simple, fast and
  useful methods for evaluating the selected
  flowsheet
• consider only systematic and simplified methods
• detailed and time consuming
• precedes plant equipment sizing and costing

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MASS AND ENERGY BALANCES

• Introduction
• Typical flowsheet will have large set of
  equations non-linear and linear equations
  describing
• connectivity of units via process streams
• specific equation for units I.e. internal mass
  and energy balances and equilibrium relationships
• physical property relationships I.e.H, Keq,, m,
  etc

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MASS AND ENERGY BALANCES

• Introduction
• The equations are solved either by sequential
  modular or equation oriented approaches
• sequential modular
• equations for each unit written so that one
  calculates output stream values of a unit, given
  its input values and unit parameter values
• Use guess values for recycle s and iterate on
  these guesses

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MASS AND ENERGY BALANCES

• Introduction
• Equation oriented
• all equations are written in general form and
  stored as equation sets
• equations are solved simultaneously for unknown
  variables
• solution procedure is to solve a sparse matrix
  containing many thousand equations

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MASS AND ENERGY BALANCES

• Introduction
• Preliminary Design
• use approximations to solve non-linear equations
  
• ideal solutions/relations
• streams as saturated vapor or liquid only
• represent the flowsheet as linear system of
  equations
• Simulation strategies for more rigorous models
  will be covered later.

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MASS AND ENERGY BALANCES

• Developing Unit Models for Linear Mass Balances
• Given P,T of feed and output streams, develop
  linear equations for each unit based on this
  steps
• Fix T and Ps of all process streams
• approximate split fraction of outputs in relation
  to inputs of each unit
• combine linear equations and solve the overall
  mass balance
• Recalculate T and P based on equilibrium
  relationships
• If there is large difference, recalculate, if not
  proceeds with energy balance.

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MASS AND ENERGY BALANCES

• Flash Calculations
• most important and fundamental in flow sheeting
  calculations
• building blocks for deriving linear models in
  equilibrium staged calculations i.e.
  distillation, absorption, etc.

Typical Specifications 1. T P - Isothermal 2.
P Q 3. T V/F (or yi or di) 4. P V/F
(or yi or di) 5. V/F (or yi or si) Q