TIER 2 STEADY STATE SIMULATION
PIECE
Tier
2
Use of computer as a
simulation tool
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Statement of intent
Use of computer as simulation tool
It contain a series of closed problems with their
solution. It is explained the assumption made, and
the methods apply to solve them.
 To review the process to create a simulation
flowsheet.
 To give the student some tips to simulate.
 To run some simulations in a computer.
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Contents
Table of content
 Solving closed problem.
 Resolution of problems with a spreadsheet
(excel).
 Using advance mathematic software (matlab).
 Separation NH4 – H20 using specialize software
(aspen tech).
 Using tools
optimization.
PAPRICAN
as
sensitivity
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and
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Solving
Closed problem
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Closed problems
Closed Problems
Closed problems are the
type with only one right
answer. These are the
same types of problems
that are usually found at
the end of chapters in text
books, and they reinforce
concepts learned in the
corresponding chapters.
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Closed problems
Algorithm
1.
Write out the problem statement.
2.
Draw and label a sketch.
3.
List assumptions and approximations involved
in solving the problem.
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Closed problems
PIECE
Algorithm
4.
Check to see if the problem is
either under – specified or over –
specified.
5.
Relate problem to a
problem or experience.
6.
Develop, derive, integrate or
manipulate an equation from
which the desired variable can be
determined.
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Closed problems
Algorithm
7.
Substitute numerical values
and calculate the desired
variable.
8.
Examine and evaluate the
answer to see it makes sense.
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Closed problems
Some advice when running a simulation
1.
Are you designing trays? Pressure drop is
important and surface tension plays a key role
in pressure drop calculation.
2.
Do you have azeotropes? Do you suspect they
may exist? Check them out before proposing a
modification that will violate the second law of
thermodynamics.
3.
Trace components should not be brushed
aside.
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Closed problems
Some advice when running a simulation
4.
Check your pure component and mixture
densities.
5.
Check your pure-component and mixture
enthalpies and heat capacities if you are going
to do any calculations related to energy
balance.
6.
Are you going to design heat exchangers? It is
good idea to check your transport properties.
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Closed problems
Some Advice when running a simulation
7. Talk with people. (chemist, vendor, other
engineers doing the same).
8. Beware of using estimated parameters and
interaction
parameters
when
screening
process alternatives.
9. Go see the plant. Plant personnel are usually
helpful. Their insight and your knowledge of
modeling can form a strong bond for problem
solving.
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Closed problems
Some Advice when running a simulation
Simulation is a means, not an end, no matter how
much effort you put into the model. Once, after
finishing a large simulation model with several
hundreds of unit operations, one of us had to
spend many hours fixing the model, because air
leakage into equipment was not taken into
account .
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Closed problems
Commercial Simulation Software Packages
There are many of them, some of them are:








PAPRICAN
Excel (spreadsheet)
Matlab (matrix laboratory)
Fortran (programming language)
Aspen tech
WinGEMS
CADSIM plus PAPDYN
G2 (Gensym)
IDEAS (Simons)
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Problem resolution
with spreadsheets
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Using spreadsheets
Excel spreadsheet
Used to calculate small mass or energy balances
from the conservation equations
Pinch Analysis
Add new streams
Add new streams
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Solving problems with
Advance mathematics software
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Advance mathematic software
Matlab
Is a mathematic specialized software,
which allows one to make use of
complicate equations, with rigorous
iterative convergence methods in an
easier way.
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Advance mathematic software
Reaction profile
of the pulp
digester
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Advance mathematic software
Mathematical Model
 The main equations in the model:
0
0
0
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Advance mathematic software
Source Code
is a series of instructions with a specific
sequence, to solve the mathematical equation.
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Advance mathematic software
Behavior Expected
Solving the model with the corresponding
assumptions, and the mathematics calculation,
the graphic output of the simulation is shown.
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Using specialized software
to simulate a process
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Using specialized software
What do more advanced simulation
package offer?
The use of specialized software, allows one to solve
complicated problems, using relationships such as
mass and energy balances, phase and chemical
equilibrium,
and
reaction
kinetics,
with
thermodynamic data, and rigorous equipment
models.
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Using specialized software
Advantage of specialized software
 Interactive interface.
 Different forms to enter data.
 Verification of incoming data against ranges.
 Check degrees of freedom.
 Sensitivity analysis.
 Optimization capabilities.
 Easy way to display results.
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Solution of some problems using specialized
software
 NH4 – H2O separation.
 Sensitivity analysis of C2H5Cl manufacture.
 Optimization of C2H5Cl manufacture.
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NH4 – H2O separation
Problem statement
Determine what will be the liquid composition and
the vapor composition after the separation.
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NH4 – H2O separation
Drawing the diagram
 Crating a process flowsheet.
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NH4 – H2O separation
Giving name, and selecting units to use
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NH4 – H2O separation
Components and Method
 Insert the components to use.
 Chose the base method to
solve the equations.
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NH4 – H2O separation
RK-Soave
Use this method for non-polar, mildly polar
mixtures. This property method is particularly
suitable in the high temperature and high
pressure regions. It is recommended for gas –
processing, refinery, and
petrochemical
applications.
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NH4 – H2O separation
Specify feed stream
 Specify the assumption made, and the
characteristics in the feed.
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NH4 – H2O separation
Specifying the process
 Give the specification to the condenser.
 Specify the valve assumptions.
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NH4 – H2O separation
Specifying the process
 Specify the separator conditions.
 Run the simulation.
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NH4 – H2O separation
Checking results
 The flow in “vap” stream is mainly ammonia,
so we can appreciate the separation.
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NH4 – H2O separation
What can be done with simulation
 Steady state simulation is useful to predict the
behave of a process in the plant.
 What if, situations can be check with simulation.
 Sensitivity analysis and optimization problems.
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Sensitivity analysis of
C2H5Cl manufacture
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Sensitivity analysis C2H5Cl
Sensitivity Analysis
Is a useful tool to know the respond of the output
variable when the input is varied in a range.
With this information one can appreciate which
variable cause the biggest change in the
process. Is easier to make a decision in the
parameter we obtain best results.
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Sensitivity analysis C2H5Cl
Ethyl chloride manufacture
One of the routes to produce ethyl chloride is by the
gas phase reaction of HCl with ethylene over a
copper chloride catalyst:
C2 H 4  HCl  C2 H 5Cl
Objective: Observe the effect in “recycle” stream,
“recycle” composition and “product” stream when
the flow in “w” stream vary from 5 to 13 kmol/h.
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Sensitivity analysis C2H5Cl
Diagram
P=1 Atm.
10 kmol/h
90% conversion
C2H4
DP=0
T=25 C
P=1 Atm.
P=1 Atm.
T=25 C
50% mol HCl
48% mol C2H4
2% mol N2
PAPRICAN
P=1 Atm.
C2H5Cl Pure
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Sensitivity analysis C2H5Cl
Input to run Simulation
 Give a name, and select
the specific units to the
process.
 Select the compounds
in the process.
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Sensitivity analysis C2H5Cl
Input to run Simulation
 Select the base method used to calculate the
thermodynamic and transport properties.
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Sensitivity analysis C2H5Cl
Peng – Robison Method
It
is recommended for hydrocarbon
processing application such as gas
processing, refinery, and petrochemical
process.
D.-Y. Peng and D. B. Robinson, "A New Two-Constant Equation-of-state," Ind. Eng. Chem. Fundam., Vol. 15, (1976), pp. 59–64.
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Sensitivity analysis C2H5Cl
Input to run simulation
 For feed stream, give the input data specified.
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Sensitivity analysis C2H5Cl
Input to run simulation
 For the mixer block give the next specifications.
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Sensitivity analysis C2H5Cl
Input to run simulation
 For the reaction block:
1. Specifications
2. Reaction
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Sensitivity analysis C2H5Cl
Input to run simulation
 For the “sep” block, enter the next input data
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Sensitivity analysis C2H5Cl
Input to run simulation
 For the “split” block, enter the next input data
Now, it is possible to run the simulation. In
order to create a sensitivity analysis, the
next steps need to be added.
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Sensitivity analysis C2H5Cl
Input to Sensitivity analysis
 Chose model analysis tools from data menu, and
then sensitivity.
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Sensitivity analysis C2H5Cl
Input to Sensitivity analysis
 Create a new sensitivity analysis case “weffect”
1. Create the next three variables in the case.
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Sensitivity analysis C2H5Cl
Input to Sensitivity analysis
2.
PAPRICAN
In the vary tab, input the next data which is the
variable range.
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Sensitivity analysis C2H5Cl
Input to Sensitivity analysis
3.
In the tabulate tab, select the way to tabulate
the results.

Run the simulation.
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Sensitivity analysis C2H5Cl
Results in sensitivity analysis
Flow rate of the “product” stream decreases
linearly as “W” is increase.
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Sensitivity analysis C2H5Cl
Results in sensitivity analysis
As a “W” flowrate increases, the recycle flow
decreases exponentially. When “W” is 13 Kmol/hr,
the flowrate at the recycle stream is less than 1.
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Sensitivity analysis C2H5Cl
“w” flow rate vs. N2 composition of the
recycle stream
The nitrogen fraction of the “recycle” stream is 40%
when the “W” is 5 kmol/h. As this is increased to 13
kmol/h the nitrogen mol percentage falls to less
than 10%.
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Sensitivity analysis C2H5Cl
Conclusion from the simulation
With this kind of analysis, one can appreciate how
sensitive is the process to the change in one
variable, in this case “W” flowrate.
In which cases the process behaves with a benefit
to the production.
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Optimization
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Optimization
Optimization
Is a way to simulate the process, making some
special consideration, just like, maximize or
minimize a stream or a composition, with the
corresponding constrains.
min f ( x )
f (x )
c( x)  0
g ( x)  0
PAPRICAN
s.t.
c( x)  0
g ( x)  0
x  Rn
objective function.
set of m equations in n variables x.
Constraints
set of r inequality constraints.
Bound the feasible region.
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Optimization
Problem statement
Maximize the venture profit of the ethyl chloride
process by adjusting the purge “W” flow rate.
Subject to: Recycle < 300 Kg/h
g(x)=0 (Mass balance)
100 kmol/hr
50% HCl
48% C2H4
2% N2
Pure C2H5Cl
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Optimization
Additional information supplied
Installed cost of equipment. 500 330  24 FR  $ / kg
 1000

FR reactor feed rate [Kg/h]
0.6
Cost of ethylene.
1.5 10 3 $ / kg
1103 $ / kg
Cost of HCl.
Revenue for ethyl chloride.
2.5 103 $ / kg
Assuming a 10% return on investment ROI.
330 operating day/year.
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Optimization
Objective Function
Maximize Venture Profit VP:
0.6


330

24


3
VP  330(24 10 )2.5P  1.5 xEt  xHCl  F   0.1500
S2  
 
  1000
P – product stream.
F – feed stream.
S2 – stream 2.
xEt – mass fraction of ethylene in feed stream.
xHCl – mass fraction of chloride acid in feed stream.
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Optimization
State an Optimization problem
Once the flowsheet is created, and the simulation
has been run, it is time to create an optimization
case.
1. Creating an
optimization case.
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Optimization
2.
Variable definition
All variables are
defined in a
similar way
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Optimization
3.
Defining the constrain
Recycle variable is
subject to:
R < 300 Kg/h
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Optimization
4.
Introducing
the objective
function as the
statement
maximize.
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Optimization
5.
Defining the
manipulate
variable and
the limits to
adjust, so we
can achieve the
specify
objective.
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Optimization
Check the results
We can now determine which recycle flow
maximize the venture profit.
As seen here: “W” 0.49 and Recycle 0.509, is
almost 50 – 50.
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Optimization
Mass flow rate
Temperature K
Pressure atm
Vapor Frac
Mole Flow kmol/hr
Mass Flow kg/hr
FEED
298.150
1.000
1.000
100.000
3225.639
PRODUCT RECYCLE
298.150
298.150
1.000
1.000
1.000
1.000
45.518
9.302
2936.567
299.978
W
298.150
1.000
1.000
8.965
289.094
1
298.148
1.000
1.000
109.303
3525.639
2
298.150
1.000
1.000
63.785
3525.639
3
298.150
1.000
1.000
18.267
589.072
The recycle stream mass flow rate has set 300 kg/h,
the upper limit of the specified stream.
We can also check the flow rate in the purge “W”
8.96 Kg/h calculated in the simulation.
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End of Tier 2
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