knowledge-based system for conceptual design 3. Aspen Process Economic Analyzer: economic evaluation of process alternatives, sensitivity analysis, optimization. 4. Aspen Batch: batch process design and scheduling. 5. Aspen Custom Modeler: object-oriented environment for rigorous modeling of non-standard unit operations. 6. Aspen Process Optimization: steady state optimization and dynamic optimization of processes. 7. Aspen PIMS: plant information management system. 8. Aspen Petroleum Supply Chain: supply chain modeling. 9. Aspen One: plant-wide real-time optimization. 10. Aspen InfoPlus.21: plant information management.

1. CHEG 5161 –Computer Aided
Process Design And
Simulation
Adane $ Addis
Department of Chemical Engineering
BiT-BDU
Lecture No. 1 – Introduction to simulation in Chemical
Processes
October , 2012 ET

2. Class Overview (cont…)
• Lecture Assistants
– Mr. Addis Lemessa Mr. Adane Adugna
• Office hours: Friday 2:30-6:00LT
• Location: BiT Block 031, office No. 01
• Reality: Any time the door is open
• Course Materials
– Textbook
• Alexandre C. Dimian, integrated design & simulation chemical
process.
• Lecture notes of the instructor

3. Class Overview (cont…)
• Grading
– Simulation Project (25%)
– Assignment I (11%)
– Assignment II (12%)
– Lab Activity I (4)
– Lab Activity II (4)
– Lab Activity III (4)
– Final exam (40%)
Will be
given any
time

4. Tentative Class Schedule
Week Course Contents Teaching Methodology Reference
Week 1-4 Chapter 1:Introduction simulation in
Chemical Processes.
1.1. Computer aided process engineering
1.2. Approaches of simulation problems
1.3. Architecture of flow sheeting software
1.4. Selection of simulation software
1.5. Application of computer simulation
 Lecture Text Book No.1
(pp: )33-55
Instructors Note
Week 5-7 Chapter 2: Fundamentals of Steady state
flow sheeting.
2.1. Fundamental issues in flow sheeting.
2.2. unit operations
2.3. Thermodynamic issues
2.4. Simulation procedures
o Lecture Text book No.1.
(pp:) 59-81
Week 8-11 Chapter 3: Basics of computer aided
Process modeling and simulation.
3.1. Reactors simulation
3.2. Separator simulation
Separation Processes- binary, multi-
component
3.3. Process synthesis by Hierarchical
Approach,
3.4. Reactor-separators synthesis
3.5. Reactor – separator –recycle
3.7. Mass transfer equipment
3.8. Solid processing
o Lecture
o group discussion
o Laboratory activity
Text book 1:pp.229-294
Week 12-15 Chapter 4. Computer aided project
evaluation of process with aspen plus and
aspen hysis.
4.1. chemical process modeling and
simulation of whole plant
4.2 Economic analysis, sensitivity and
optimization of chemical plant.
4.3. 3.6. Heat exchangers network
o Lecture
o Group discussion
o Laboratory activity
Lecture note

5. Tentative Lab Schedule
Time (in week) Laboratory Topic
Week 8
-Introducing inside ASPEN software.( Brief introduction , setting up)
-Principle of flow sheet simulation (Getting started in ASPEN , convergence)
-Lab recitation lecture #1 (Heuristic for process synthesis )
-Pump , compressor and expanders (overview, pump, compressor and expanders)
-Heat exchangers (Introduction , heat requirement models , Shell and tube , Multiple stream Heat
exchangers )
Week 9
-Reactor simulation
-stoichiometric reactor, equilibrium reactor , PFR, CSTR
Week 10
-Separators simulating ( phase equilibrium and flash )
-Physical property estimation (property estimation ( phase equilibrium, equilibrium diagram ,
property data regression))
- Lab recitation lecture #2 (separation train )
- separator (introduction, split fraction model , phase equilibra and flash, distillation )
-Lab recitation lecture (azeotropic distillation, choosing property Model)
-Physical property estimation ( property package selection )
Week 11
- Reactor-separator simulation
- Reactor –separaetor – recycle simulation
Week 12
- Simulating entire plant
-Material and energy balance.
- Feasibility of plant,
-Sensitivity analysis
Week 13
- Lab recitation lecture # 3 (heat integration )
Introducing aspen heat exchanger network (Pinch analysis, Design of heat exchanger network/heat
integration.) Simulation assisted with
software
Recitation lecture

6. Software
Choice of Simulator Software
• Hysys
•Aspen Plus (optional )
• Matlab (optional)

7. Course objectives
Provide the student with a clear
understanding of what is process
simulation & process optimization and how
these can be employed to solve practical
problems commonly encountered in
process engineering.

8. Lesson objectives
At the end of the lesson you will be able to:
1. Have an appreciation of the process
simulation.
2. Be aware of and differentiate types of
simulation.
3. familiar with different strategies of solving
simulation problems.
4. Understand that chemical engineers use a
blend of hand calculations, spreadsheets,
computer packages, and process simulators
to design a process.

9. COMPUTER SIMULATION IN
PROCESS ENGINEERING
What is simulation?
 Process simulation is the act of representing some aspects of
the real world by numbers or symbols that may be easily
manipulated to facilitate their study.
 Simulation implies modelling, as well as tuning of models
on experimental data.
 Conducting 'virtual experiments'
 The important steps of process simulation are therefore,
description of the part of the “real world” that needs to be
simulated, representation of this part of the “real world” in
terms of a model (mathematical or symbolic), and finally,
solution of the mathematical model to obtain numbers or
symbols.
 Typically, process simulation is needed to solve problems
related to process design, process analysis, process control
and many more.

10. COMPUTER SIMULATION IN PROCESS
ENGINEERING (Cont…)
 Simulation is a process of designing an
operational model of a system and conducting
experiments with this model for the purpose
either of understanding the behaviour of the
system or of evaluating alternative strategies for
the development or operation of the system. It
has to be able to reproduce selected aspects of
the behaviour of the system modelled to an
accepted degree of accuracy.
(Thome, 1993)
 The scientific and engineering activity that makes
use of professional modelling and
simulation for Chemical Process Industries (GPI) is
designated by Computed Aided
Process Engineering (CAPE).

11. Competency
Simulation in Process Engineering requires
specific scientific knowledge among we
may cite
1. accurate description of physical
properties of pure components .
2. complex mixtures, models for a large
variety of reactors and unit operations.
3. Numerical techniques for solving large
systems of algebraic and differential
equations.

12. Types of simulation

13. Types of simulation (Cont…)
Process simulation (steady state)
• Flow sheeting problem
• Specification (design) problem
• Optimization problem
• Synthesis problem

14. Types of simulation (Cont…)
Flowsheeting problem
• Given:
– All of the input information
– All of the operating condition
– All of the equipment parameters
• To calculate:
– All of the outputs
FLOWSHEET
SCHEME
INPUT
OPERATING
CONDITIONS
EQUIPMENT
PARAMETERS
PRODUCTS

15. Types of simulation (Cont…)

16. Types of simulation (Cont…)
Specifying problem
• Given:
– Some input & some output information
– Some operating condition
– Some equipment parameters
• To calculate:
– Undefined inputs & outputs
– Undefined operating condition
– Undefined equipment parameters

17. Types of simulation (Cont…)
• The main simulation activity in process
engineering is flow sheeting.
• Flow sheeting is the use of computer
aids to perform steady state heat and
mass balancing, sizing and costing
calculation for a chemical process.

18. Types of simulation (Cont…)
Application of flowsheeting
Nowadays flow sheeting is involved not
only in the design of new processes, but
also in the continuous improvement of
existing technologies, by revamp and
debottlenecking, in managing process
operation and control, as well as in
research and development.
(Dimian, 1994)

19. Applications of computer
simulation
Simulation
Research and
development
Operation
Design

20. Process Simulation applications in Chemical Process Industries
Applications of computer
simulation (cont…)

21. Flow sheeting
The main simulation activity in process engineering is
flowsheeting.
Flow sheeting is the use of computer aids to perform
steady state heat and mass balancing, sizing and
costing calculation for a chemical process.
(Westerberg et al., 1979)
Flow sheeting: is a systematic description of material
and energy streams in a process plant by means of
computer simulation with the scope of designing a
new plant or improving the performance of an
existing plant. Flow sheeting can be used as aid to
implement a plant wide control strategy, as well as to
manage the plant operation.
Flow sheeting: is the use of computer aids to
perform steady state heat and mass balancing,
sizing and costing calculation for a chemical process.

22. Approach of a simulation
problem
1. Definition
2. Input
3. Execution
4. Results
5. Analysis

23. Approach of a simulation
problem(cont…)
Definition
- Convert PFD in PSD. Split the
flowsheet in several sub-
flowsheets, if necessary.
- Analyse the simulation model
for each flowsheeting unit.
- Define chemical components,
including user-defined.
- Analyse the thermodynamic
modelling issues regarding the
global flowsheet, sub-
flowsheets and key units.
- Analyse the specification
mode (degrees or freedom)
of complex units.

24. Approach of a simulation
problem (cont…)
Input
The steps are:
- Draw the flowsheet.
- Select the components, from
standard database or user
defined.
- Specify the input streams.
- Specify the units (degrees of
freedom analysis).
- Select the thermodynamic
models. Check model
parameters.
- Determine the computational
sequence.

25. Approach of a simulation
problem (cont…)
Execution
• The simulation is successful
when the convergence criteria
are fulfilled both at the
flowsheet and units' level.
Here the steps involved are:
- Check the convergence
algorithms and parameters,
and change them if necessary.
- Check the convergence errors
and the bounds of variables.
- Follow-up convergence history.

26. Approach of a simulation
problem (cont…)
Results
A simulation delivers a large
amount of results.
The most important are:
- Stream report (material and
heat balance), including
flowsheet convergence report.
- Unit report, including material
and heat balance, as well as
unit convergence report.
- Rating performances of units.
- Tables and graphs of physical
properties.

27. ARCHITECTURE OF FLOWSHEETING
SOFTWARE
1. Computation strategy
The architecture of a flow sheeting
software is determined by the
strategy of computation. Three basic
approaches have been developed
over the years:
• Sequential-Modular.
• Equation-Oriented.
• Simultaneous-Modular.

28. ARCHITECTURE OF FLOWSHEETING
SOFTWARE (cont…)
1. Sequential-Modular (SM):
 In Sequential-Modular (SM) architecture, the
computation takes place unit-by-unit following
a calculation sequence.
 A process with recycles must be decomposed
in one or several calculation sequences.
 incoming streams have to be known either as
inputs, or initialized as tear streams.
 The computation sequence of units involved in a
recycle defines a convergence loop.
 When tear streams are present, the final steady
state solution is obtained by iterative
calculations.

29. ARCHITECTURE OF FLOWSHEETING
SOFTWARE (cont…)
Calculation sequence and tear streams

30. ARCHITECTURE OF FLOWSHEETING
SOFTWARE (cont…)
 Sequential-Modular approach is
mostly used in steady state flow
sheeting.
 Some of the product which uses
these approach is:-
Aspen Plus, ChemCad, Hysys,
ProII, Prosim, and Winsim.
(Hysys)- dynamic simulators built on
this architecture.

31. ARCHITECTURE OF FLOWSHEETING
SOFTWARE (cont…)
A simulation model is obtained by means of
conservation equations for mass, energy and
momentum.
These lead finally to a system of non-linear
algebraic equations as:
f(u,x,d,p) = O
Where:
- u- connectivity variables formally classified in input
and output variables;
- x- internal (state) variables, as temperatures,
pressures, concentrations;
- d- variables defining the geometry, as volume, heat
exchange area, etc;
- p-variables defining physical properties, as specific
enthalpies, K-factors, etc.

32. ARCHITECTURE OF FLOWSHEETING
SOFTWARE (cont…)
The SM architecture was the first used in flow sheeting, but
still dominates the technology of steady state simulation.
Advantage
Modular development of
capabilities.
 Easy programming and
maintenance.
Easy control of convergence,
both at the units and flow
sheet level.
Disadvantage
Need for topological analysis
and systematic initialization of
tear streams.
 Difficulty to treat more
complex computation sequences,
as nested loops or simultaneous
flow sheet and design specification
loops.
 Difficulty to treat specifications
regarding internal unit (block)
variables.
 Rigid direction of computation,
normally 'outputs from inputs'.
 Not well suited for dynamic
simulation of systems with recycles.

33. ARCHITECTURE OF FLOWSHEETING
SOFTWARE (cont…)
Equation-Oriented (EO)
approach all the modeling equations are
assembled in a large sparse system producing Non-
linear Algebraic Equations (NAE) in steady state
simulation, and stiff Differential Algebraic Equations
(DAE) in dynamic simulation.
Thus, the solution is obtained by solving
simultaneously all the modeling equations.

34. ARCHITECTURE OF FLOWSHEETING
SOFTWARE (cont…)
 In Equation-Oriented (EO) approach the software
architecture is close to a solver of equations.
 EO is more suited for dynamic simulation since this can
be modeled by a system of differential-algebraic equations
(DAE) of the form:
dx/dt = f (u,x,d,p)
 The steady state solution is obtained by setting the
derivatives to zero.
 The overall DAE system is sparse and stiff, its size varying
between 10^3 and 10^5 equations.
 In Aspen Dynamics, the problem definition starts at steady
state in Aspen Plus in an SM environment.
Adding accumulation terms to the equations of units
generates the DAE system.

35. ARCHITECTURE OF FLOWSHEETING
SOFTWARE (cont…)
Advantages
 Flexible environment
for specifications,
which may be inputs,
outputs, or internal
unit (block) variables.
 Better treatment of
recycles, and no need
for tear streams.
 Note that an object
oriented modeling
approach is well
suited for the EO
architecture.
Disadvantage
More programming
effort. Need of
substantial computing
resources, but this is
less and less a
problem.
 Difficulties in
handling large DAE
systems.
Difficult convergence
follow-up and
debugging.

36. ARCHITECTURE OF FLOWSHEETING
SOFTWARE (cont…)
Simultaneous-Modular
 Approach the solution strategy is a combination of
Sequential-Modular and Equation-Oriented approaches.
 Rigorous models are used at units' level, which are solved
sequentially, while linear models are used at flow sheet level,
solved globally.
 The linear models are updated based on results obtained with
rigorous models.
 It may be concluded that Sequential-Modular approach keeps a
dominant position in steady state simulation.
 The Equation-Oriented approach has proved its potential in
dynamic simulation, and real time optimization.
The solution for the future generations of flow sheeting
software seems to be a fusion of these strategies.

37. ARCHITECTURE OF FLOWSHEETING
SOFTWARE (cont…)
General layout of unit operation model

38. ARCHITECTURE OF FLOWSHEETING SOFTWARE
(cont…)
• In an EO simulator the algorithmic treatment includes not only the
mathematical solution, but also problem debugging,
compilation/linking, as well as correction and addition of equations.
Software architecture of an Equation-Oriented simulator

39. ARCHITECTURE OF FLOWSHEETING
SOFTWARE (cont…)
INTEGRATION OF SIMULATION TOOLS
The applications of process simulation are shared in
two categories, design and operation. These are
largely interdependent, but distinctive activities may be
identified inside each one.
 Computer Aided Design
- the key activity is Conceptual Design that includes
Process Synthesis (development of the process flowsheet
diagram) and Process Integration (optimal valorization
of material and energetic resources).
 Computer Aided Operation
- real time monitoring of material and energy balance.

40. Aspen Technology
The integrated system includes both all-
purpose flow sheeting system, and
specialized packages.

41. Aspen Technology Hyprotech
1. Aspen Plus: steady state simulation environment with
comprehensive database and thermodynamic modeling;
feasibility studies of new designs, analysis of complex plants
with recycles, optimization.
1. Hysys.Concept: conceptual design package for
design and retrofit applications, with two components:
DISTIL: distillation column sequences, HX: heat
integration projects by Pinch analysis.
2. Aspen Dynamics: dynamic flow sheeting interfaced with
Aspen Plus.
2. Hysys.Process: steady state flowsheeting for
optimal new designs and modeling of existing plants,
evaluate retrofits and improve the process.
3. Aspen Custom Modeller: modeling environment for
user add-on units and programming in dynamic simulation.
3. Hysys.Plant: steady state and dynamic simulation
to evaluate designs of existing plants, and analyse
safety and control problems.
4. Aspen Pinch: Pinch analysis, optimal design of heat
exchanger networks.
4. Hysys.Operator Training: start-up, shutdown or
emergency conditions, consisting of an instructor
station with DCS interface, and combined with
Hysys.Plant as calculation engine.
5. Aspen Split: synthesis and design of non-ideal
separation systems.
5. Hysys.RTO+: real-time multivariable optimisation;
on-line models may be used off-
line to aid maintenance, scheduling and operations
decision-making.
6. Polymer Plus: simulation of polymerization processes. 6. Hysys.Refinery: rigorously modelling of complete
refining processes, integrating crude oil database and a
set of rigorous refinery reactor models.
7. Aspen Properties: physical property system including
regression capabilities and estimation methods. 7. Hysys.Ammonia: full plant modelling and
optimisation of ammonia plants.
8. Aspen OLI: simulation of aqueous electrolyte systems.
Aspen Technology (cont…)

42. Aspen Technology (cont…)
Simulation Sciences
Process Engineering: tools for process engineering design and operational
analysis.
 Pro/II” general-purpose process flowsheeting and optimisation.
 Hextran: Pinch analysis and design of heat-transfer equipment.
 Datacon: plant gross error detection and data reconciliation.
 Inplant: multiphase, fluid flow simulation for plant piping networks.
 Visual Flow: design and modelling of safety systems and pressure
relief networks.
Upstream Optimization: decision-support tools designed for oil and gas
production.
 Pipephase: multiphase fluid flow simulator for pipelines and networks.
 Tacite: multiphase simulator for complex transient flow phenomena.
 Netopt: optimization of oil and gas production operations.
On-line Performance: Advanced Process Control (APC) and on-line optimisation.
 ROMeo” on-line plant modelling and optimisation, off-line analysis tool.
 Connoisseur: APC multivariable controls several via the plant's DCS.

43. Aspen Technology (cont…)
SELECTION OF A SIMULATION
SOFTWARE
The selection of a simulation system is a
strategic decision for an organization. The
evaluation procedure takes the form of
questionnaire, as given hereafter.

44. Cont…

45. Summery
• Process Simulation is a key activity in Process Engineering
covering the whole life cycle of a process, from Research
& Development to Conceptual Design and Plant Operation.
• Flow sheeting is a systemic description of material and
energy streams in a process plant by means of computer
simulation with the scope of designing the plant or
understanding its operation.
• Steady state flow sheeting is an everyday tool of the
chemical engineer.
• The generalization of the dynamic simulation in the design
practice is the next challenge.
• Plant Simulation Model combine both steady state and
dynamic simulation.
• Flow sheeting is still dominated by the Sequential-Modular
architecture.
• A limited number of systems can offer both steady state
and dynamic flow sheeting simulators.