Process Simulation
Ruel Peneyra
Simulation Concept
PM
CS
CaD
• Process
Modeling
• Computer
Simulator
• Computeraided Design
Process Design
design of process and methods,
including process flowsheet, design of
processing and control equipment and
economic evaluation of the process
Process Design Stages
Selection
of
flowsheet
to realize
the
required
production
Material
and
energy
balances,
process
req’mts of
the plant
Sizing and
rating of the
required
industrial
process
equipment
Cost
estimation
Financial
and
profitability
analysis
Parametric
optimization
Structural
optimization
of the
process.
Process Design Flowchart
Process Specifications
1. Process
Flowchart Synthesis
7. Structural
Optimization
2. Material and
Energy Balances
3. Equipment Sizing
and Rating
4. Equipment and
Utilities Costing
5. Financial and
Profitability Analysis
6. Parametric
Optimization
Basic Definition
Modeling
• procedure to translate the physical laws of a process to mathematical equations
Simulation
• appropriate software which guesses the real performance of a process
Design
• procedure to size and rate a process in order to obtain a specific goal
Sizing
• given the process specifications calculate the equipment size and characteristics
Rating
• given the process specifications and the equipment size and characteristics
calculate the operating conditions
Process Modeling
Process Model
Formulation
Degrees-ofFreedom
Analysis
Alternative
Problem
Formulation
Problem-Solution
Algorithm
Cost Estimation
and Project
Evaluation
Analysis
Process
Optimization
Process Simulation Procedure
Model Development
Implementation of
Alternative ProblemSolutions or
Optimization
Procedures
Development of
Graphic Interface
Degrees-of-Freedom
The degrees-of-freedom is characteristic of the process.
Given values corresponds to design specifications
The remaining values are considered the design variables
The number of design variable is a characteristic of the
problem.
The values of the design variables are decided by the design
engineer
Process design problem usually resulted to N x N set of
equations that is solved by mathematical techniques
Degrees-of-Freedom Analysis
Parameter
Symbol
Total Number of Variables
M
Total Number of Equations
N
Degrees-of-Freedom
F
Problem Specifications
K
Design Variables
D
Equation
Remarks
=M-N
DOF
Process Characteristics
=F-K
Problem Characteristics
Total Number of Variable (M)
Total Number of Equations (N)
Degrees-of-Freedom (F)
(Process Characteristics)
Problem Specification (K)
(Problem Characteristic)
Design Variables (D)
Typical Problems
Type
Given
Calculate
Direct
• the characteristics of input streams
• the equipment characteristics
• the operating conditions
• the characteristics of the
output streams
Design
• the characteristics of input streams
• the characteristics of output streams
• the equipment characteristics
• the operating conditions
Rating
• the characteristics of input streams
• the characteristics of output streams
• the equipment characteristics
• the operating conditions
Identification
• the characteristics of input streams
• the characteristics of output streams
• the operating conditions
• the equipment characteristics
 Note: The number of design variable is a characteristic of the problem.
Simulator Architecture on a Spreadsheet
Graphics UI
Worksheet
Problem
Solution
VB Module
Database
Worksheet
Process
Model
Worksheet
Model Implementation in Excel
Example 1. Shell and Tube Hx
In this example, the following Excel operations will
be introduced:
• Name variables (Ctrl + Shift + F3)
• Insert data
• Insert equations using names
Example 1. Shell and Tube Hx
A. Problem Formulation
Calculate the appropriate shell and tube
heat exchanger for a tomato paste heating
process using an available heating steam.
A.1. Design specifications
Variables
Values
Units
Remarks
F
1
kg/s
T1
50
◦C
Feed Temperature
T2
100
◦C
Target Temperature
T3
120
◦C
Steam Temperature
Feed flow rate
Example 1. Shell and Tube Hx
A. Problem Formulation
A.2. Required Data (Tomato Paste and Steam)
Variables
Values
Units

1130
kg/m3

0.55
Wm-1K-1

0.27
Pa s
Cp
3.50
kJkg-1K-1
Hs
2200
kJkg-1
Remarks
Fluid density
Fluid thermal conductivity
Fluid apparent viscosity
Specific heat
Latent heat of steam condensation
Example 1. Shell and Tube Hx
A. Problem Formulation
A.3. Assumed Design Variables
Variables
Values
Units
Remarks
u
1
ms-1
d
0.01
m
Tube diameter
dx
5
mm
Tube thickness
n
4
Fluid velocity in tubes
Number of passes in tubes
Example 1. Shell and Tube Hx
B. Problem Solution
b
c
B.1. Thermal Load Calculation
Q  FC p T 2 @T 1
B.2. Required Steam Flow
Q  F s H s
b
B.3. Mean Temperature DifferenceT m 
c
b
c
T
s @T 1 @ T s @T 1
ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
f
g
Tfffffffffffffffffffffffffffff
s @T 1
ln
T s @T 1
Example 1. Shell and Tube Hx
B. Problem Solution
B.4. Total Number of Tubes, N
B.5. Outside tube surface heat
transfer coefficient, ho
B.6. The Pr number
u
F
ffffffffffffffffffffffffffffffffffffffffffffffff
d
ef
2g

N
fffffffff
n

dffffffffff
4
1ffffff
G3
F Nd
fffffffffff
h o  2750
Fs
ffff
Pr  C p

Example 1. Shell and Tube Hx
B. Problem Solution
B.7. The Re number
Re  d
ufffff

f
B.8. The Nu number
1ffffff
g 3f
dffffff
Nu  1.86 RePr
L
B.9. The surface heat transfer
coefficient inside the tubes hi
Nu  h i
g 0.14

ffffffff
w
dffffff

f
with
g 0.14

ffffffff
w
 1.2
Example 1. Shell and Tube Hx
B. Problem Solution
B.10. The overall heat transfer
coefficient U
1ffffff
U

1
ffffffff
hi
1
fffffffff

ho
B.11. The overall heat transfer area
Q  AUT m
A
f
B.12. The shell diameter D
B.13. The tube length L
N  0.319
A  N dL
g 2.142
Dffffff
d
Worksheet for the Example
Excel Implementation
1.
In the range A2:A29, type the names of the process variables with range A2:A14 used for the data
while the range A16:A29 is for the results.
2.
In the next column and in the range B2:B29, type the symbols for these variables
3.
In the range C2:C29, type the corresponding names in Excel. Use names similar to their symbols in
the text if possible.
4.
In the range E2:E29, type the corresponding units.
5.
By selecting the range C2:D29 and by simultaneously pressing the buttons Ctrl + Shift + F3, the
names in column C are assigned to the cells of column D.
6.
Enter the data for the given variables in the range D2:D14.
7.
Enter the equations according to the problem solution procedure into the range D16:D29.
8.
These equations are presented for information in the range F16:F29.
9.
The problem will then be solved. Any change of the data will change the result.
10. The problem is solved with just 13 equations in the range D16:D29 by using 13 data in the range
D2:D14. All other text in the spreadsheet is for information.