25-02-2011
teste 1
Programa doutoral em Engenharia da Refinação, Petroquímica e Química
Engenharia de Processos e Sistemas
Process Simulators
Fernando G. Martins
Departamento de Engenharia Química
Faculdade de Engenharia da Universidade de Porto
Programa EngIQ - EPS
FGM (FEUP) - February 2011 Slide #1
Module objective and module contents
Module contents
• Overview of process simulation;
• Comparison between hand and computer calculation;
• Types of chemical process problems;
• Solution of problems in steady-state mode;
• Systematic methodology in process simulation;
• Process simulators – examples.
Module objective
To present the potentialities of software tools to solve problems related with design and
revamping of chemical processes.
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #2
25-02-2011
teste 2
Process simulation - I
• Simulation is the tool that chemical engineers use:
– To analyse process flowsheets;
– To locate process malfunctions;
– To predict the performance of the processes.
• Mathematical models are the basis for simulation which correspond a collection
of equations that relate the process variables, such as stream temperature,
pressure, flow rate, and composition, to surface area, valve settings geometrical
configuration , and so on.
FGM (FEUP) – February 2011 Slide #3
Programa EngIQ - EPS
Process simulation - II
• Simulation models can be composed by different levels of complexity involving
material balances, material and energy balances, equipment sizing and
profitability analysis;
• Additional equations are added at each level. New variables are introduced and
the equation-solving algorithms become more complicated;
• Most chemical process involve conventional process equipment:
– Heat exchangers;
– Pumps;
– Distillation columns;
– and so on.
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #4
25-02-2011
teste 3
Process simulation - III
• For the process units referred in the previous slide:
– The equations do not differ among chemical processes;
– The physical and thermodynamic properties and chemical kinetic constants
differ, but not the equations.
• It is possible to develop one or more equation-solving algorithms for each
process unit to solve the material and energy balances and to compute
equipment sizes and costs. These algorithms are the heart of process simulators.
These algorithms are often referred as procedures, modules or blocks.
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #5
The importance of the process simulation
•• Conception/DesignConception/Design: Analysis of different process conditions and calculation of
operational variables;
•• StartStart--upup: Prediction of operational conditions through the plants start-up;
•• OperationOperation: Studies of the limit operation conditions and changes in project
specifications;
•• OptimizationOptimization: : Changing of the operation parameters to process optimization
attending to economic, energy, time and environment objectives.
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #6
25-02-2011
teste 4
Main steps in process simulation
Analysis of
the results
Problem Problem
definitiondefinition
Process model
development
Additional data
collection
Solving model
equations
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #7
Problem definition – which can be selected from simulator?
• Components;
• Unit operations;
• Process flowsheet;
• Libraries
– Unit operation models;
– Models to estimate termophysical properties;
– Equation solving methods.
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #8
25-02-2011
teste 5
Problem definition – required information
• Components;
• Unit operations;
• Process flowsheet;
• Thermophysical properties estimation;
• Data that must be knowing:
– Data for input streams;
– Equipment data;
– Operation data.
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #9
Types of process simulation problems
• Flowsheeting;
• Specification;
• Optimization;
• Synthesis.
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #10
25-02-2011
teste 6
Flowsheeting problem
FlowsheetFlowsheet
Inputs Outputs
Operational conditions
Equipment
parameters
Calculation of all output information and some internal variables using all
information from the inputs.
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #11
Specification problem - performance
Flowsheet
Inputs Outputs
Operational conditions Equipment
parameters
Some data from the outputs are specified. The other variables are predicted from models.
Some data from inputs needn't be specified.
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #12
25-02-2011
teste 7
Optimization problem
Data::
- Feed composition
- Feed flowrate
Select::
-Target product composition
-Column trays, feed composition
Minimize
Objective=f(yield, energy, capital costs, ...)
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #13
Synthesis problem
?
Inputs Outputs
Inputs and outputs are known but the flowsheet, the equipment
parameters and the operational conditions are unknown.
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #14
25-02-2011
teste 8
Example of a synthesis problem
Technology ?
Design ?
Inputs Outputs
Separation technology – distillation, flash, extraction, separation
based on membranes.
How many unit operations are needed?
How is the equipment design performed?
Ethanol
WaterEthanol
Water
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #15
Solution of problems in steady-state mode - summary
Sequential-modular approximation Equation-oriented approximation
Each unit operation is simulated at once All unit operations are simulated at once
The flowsheet is decomposed The equations are sorted
Iterative procedures using tear-streams All variables are updated at once
Less flexible but more robust More flexible but less robust
The initialization is important The initialization is much important
Memory requirements not very high Memory requirements may be very high
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #16
25-02-2011
teste 9
Systematic methodology in process simulation
• Data collection and reconciliation;
• Perform additional measures if necessary;
• Creation/adaptation of models of the equipments involved;
• Model validation;
• Model optimization.
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #17
Modular process simulator - I
Databases (Termophysical properties, model parameters, etc)
Interfaces to introduce information and to see results
Simulator
core
Numerical
methods
Model
libraries
Cost models
Properties
estimation
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #18
25-02-2011
teste 10
Modular process simulators - II
• Computer-aided process design programs, often referred as process or simulators,
flowsheet simulators or flowsheeting packages, are widely used in process design;
• These packages are comprised of the data banks, physical properties models, and
equipment operation and sizing models;
• The extensive data banks contain data on the thermophysical and transport property
constants for hundreds of chemicals, equipment sizing, capital and operating costs and
profitability measures;
• The simulators contain many models of the reactors and unit operation, so-called
simulation models that can be used to calculate material and energy balances.
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #19
Modular process simulators - III
• Simulators sometimes give wrong results, even though no error messages appear. Therefore,
simulation results need to be checked carefully before being used as a basis for process and
equipment design;
• It is particularly important to verify the heat and mass balances for any simulation.
Otherwise, you might develop an incorrect design;
• The checks that must be done:
– Input data – are units and numerical values correct;
– Model scope – Is the simulator model scope sufficient to define the problem and thus
obtain meaningful results;
– Thermophysical property models – Is the vapor/liquid equilibrium model used
appropriate for the mixture being modelled and for the range of temperatures,
pressures and compositions simulated;
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #20
25-02-2011
teste 11
Modular process simulators - IV
• The checks that must be done (cont.):
– Thermophysical properties computed – Are calculated values of operating conditions
and stream properties reasonable for all streams;
– Specifications – Did the simulator converge on all specifications;
– Process equipment – Are the parameters and variables used for sizing and specifying
such equipment reasonable? Are the equipment sizes reasonable?
• In conclusion – If a process simulator is used properly and well, the results can be very
beneficial; if not use careful and wisely, the consequences may be dire.
Programa EngIQ - EPS
FGM (FEUP) – February 2011 Slide #21