1) A step test was performed on a simulated gas processing plant to generate data for building a dynamic model predictive controller (DMC). 2) An economic model was generated using the steady state gains from the plant test data to calculate the linear programming (LP) costs associated with changes in economic variables like duty rates. 3) Equal concern errors were calculated for controlled variables (CVs) like sales gas dew point and propane composition based on their relative importance, with a higher weight given to maintaining propane composition given its greater economic impact.

1. Project Report
Industrial Process Control
Fall-2014
LAMAR UNIVERSITY
Dan F. Smith
Department of Chemical Engineering
Submitted To
Dr. Payton Richmond
Submitted By
Ratul Das ( L20315495)
Asad Vora ( L20357679)
Jayur Mistry ( L20350957)
Sakshi Yadav ( L20349879)

2. Problem Statement
Design, build, and tune a controller for the HYSYS gas processing tutorial flowsheet.

3. Solution
Project Steps
1) Pretest- Approximation of time to steady state and Estimation of step testing time
2) Step Testing
3) Model Identification
4) Model Building
5) LP Cost Calculation
6) Equal Concern Error
MV, DV, CV, and Economic Variables data
Tag name Description Type
Cold-TC Cold gas temperature MV
STG9-TC Tray 9 temperature MV
F1-FL Feed 1 Flow DV
F2-FL Feed 2 Flow DV
DEW PT Sales gas temperature CV
COMP Composition of Liquid Product CV
Economic Variables
Sr. No Economic Variables
1 Chiller Duty
2 Heater Duty
3 Reboiler Duty
4 Condenser Duty
5 Sales Gas Production
6 Liquid Product Flow
7 Overhead Product Flow

4. 1. Pretest
The TTSS is determined by giving a step change in feed flowrate and looking for maximum
time required by CV’s to reach steady state. Total time required for step testing is
calculated below.
Step Test Time = TTSS * (No. of Independent Variables) * 8 = 100*4*8 = 3200 minutes
2. Step Testing
Allowable Step Changes
Independent Variables Maximum Allowable Step Change
Feed 1 Flow 2 MMSCFD
Feed 2 Flow 2 MMSCFD
Cold TC SP 3 F
Stage 9 TEMP SP 17 F
According to the step-test plan, a plant test schedule was made by HYSYS event scheduler. And this
plant test plan satisfies the following requirements in order to help us generated the plant test data
for further usage.
 Step each MV multiple times at several times during the test
 One minute data for all variables related to unit being tested
 Data for cost factors are included

5. Step Test Plan
Step No. Variable Time (min) Previous Value New Value Step Size
1 53 5 5.5 0.5
2 76 5.5 6 0.5
3 101 6 5 -1
4 127 5 4.5 -0.5
5 152 4.5 4 -0.5
6 176 4 3.5 -0.5
7 202 3.5 5 1.5
8 229 5 5.5 0.5
9 253 5.5 6 0.5
10 280 6 4 -2
11 305 4 5 1
12 331 5 6 1
13 357 6 3.5 -2.5
14 383 3.5 4.5 1
15 409 4.5 6 1.5
16 436 6 6.5 0.5
17 461 6.5 4.5 -2
18 487 4.5 3.5 -1
19 512 3.5 5 1.5
20 537 5 5.5 0.5
21 565 5.5 6 0.5
22 590 6 4 -2
23 615 4 4.5 0.5
24 640 4.5 5.5 1
25 665 5.5 6 0.5
26 690 6 4 -2
27 716 4 3.5 -0.5
28 742 3.5 3 -0.5
29 766 3 5 2
30 781 5 5.5 0.5
31 806 5.5 5 -0.5
COLD TC
(F)
32 852 190 195 5
33 877 195 185 -10
34 903 185 180 -5
35 928 180 190 10
36 952 190 183 -7
37 978 183 192 9
38 1003 192 187 -5
39 1027 187 180 -7
40 1053 180 186 6
41 1079 186 194 8
42 1104 194 190 -4
43 1129 190 183 -7
44 1154 183 188 5
45 1179 188 196 8
46 1205 196 180 -16
47 1231 180 175 -5
48 1256 175 170 -5
49 1281 170 179 9
50 1306 179 184 5
51 1332 184 190 6
52 1357 190 195 5
53 1383 195 178 -17
54 1409 178 185 7
55 1435 185 180 -5
56 1462 180 170 -10
57 1488 170 180 10
58 1513 180 185 5
59 1536 185 190 5
60 1562 190 180 -10
61 1586 180 185 5
62 1612 185 190 5
STG 9 TC
(F)
1650 6 6.5 0.5
1675 6.5 5 -1.5
1700 5 5.5 0.5
1725 5.5 6 0.5
1750 6 6.5 0.5
1779 6.5 7 0.5
1804 7 7.5 0.5
1830 7.5 7 -0.5
1855 7 6 -1
1880 6 5 -1
1905 5 4 -1
1930 4 3 -1
1955 3 4.5 1.5
1980 4.5 5 0.5
2006 5 5.5 0.5
2029 5.5 6 0.5
2054 6 6.5 0.5
2079 6.5 7 0.5
2105 7 7.5 0.5
2130 7.5 7 -0.5
2156 7 6 -1
2182 6 5 -1
2207 5 4 -1
2233 4 3 -1
2258 3 3.5 0.5
2283 3.5 4 0.5
2308 4 4.5 0.5
2333 4.5 5 0.5
2358 5 5.5 0.5
2383 5.5 6.5 1
2410 6.5 6 -0.5
F FLOW1
(MMSCFD)
2450 4 4.5 0.5
2476 4.5 5 0.5
2501 5 6 1
2526 6 6.5 0.5
2553 6.5 5 -1.5
2578 5 4 -1
2604 4 3.5 -0.5
2630 3.5 4.5 1
2656 4.5 5 0.5
2682 5 5.5 0.5
2707 5.5 6.5 1
2733 6.5 3 -3.5
2758 3 7 4
2783 7 4 -3
2808 4 5 1
2833 5 6 1
2859 6 5.5 -0.5
2885 5.5 5 -0.5
2910 5 4 -1
2935 4 6 2
2960 6 6.5 0.5
2985 6.5 5 -1.5
3011 5 3.5 -1.5
3036 3.5 4 0.5
3062 4 4.5 0.5
3088 4.5 5 0.5
3114 5 5.5 0.5
3139 5.5 6 0.5
3164 6 6.5 0.5
3189 6.5 6 -0.5
3214 6 4 -2
F FLOW2
(MMSCFD)

6. All the variables ( MV’s, DV’s, CV’s, Monitor, Economic) are included in the data logger so
that data for these variables will be recorded for full length of step testing. Logger size in
data logger is changed to the value so that it is large enough to record all data.
Total time interval of 800 minutes is given for each change in independent variable. For the
1st Cycle, 50(1/2 TTSS) minutes time interval is used and for all other cycles time interval
of 25 minutes (1/4th TTSS) is considered.
MPC Identification and Modeling
After the plant test plan carried out by the above step, we used the Step Model
Identification program to create a DMC model and obtain the coefficients for LPCost
calculation. The steps include:
 Collect data in the HYSYS DataBook
 Export data to Excel and calculate inferential variables
 Import data to the Step Model Identification program to create DMC model files and
to generate steady-state gains for computing LPCosts.
 Look for valve saturations. Times when valves are saturated should be marked as
bad data.

7. The faceplate of the step changes during 3200 min time interval
3. Model Identification
All the vector files are imported in step identification program. All the data is plotted to
check for any bad data. All the CV’s reach steady state for TTSS = 100. Thus it is selected as
a TTSS for given model.

8. Vector files are added in step model identification.
CLC plot representing all the variables considered

9. 4. Model Building
A model is built by using TTSS = 100 minutes.
The variables are distributed in MV, DV, and CV list.

10. A model is built considering all CV’s & Economic Varaibles.

11. 5. LP Cost Calculation
Raw gains obtained from the model identification program are corrected by using the mass balance. These corrected gains and
individual costs for items are used to calculate LP costs. (File Used: Original Model_economic.mdl)
Chiller Duty Condenser Duty Reboiler Duty Heater Duty Overhead Flow Sales Gas Flow Liquid Product Flow
0 0 -1.55E+05 1.19E+00 -4.65E+02 -7.92E-03 -3.54E+02
-4.88E+03 0 2.46E+03 -4.51E+03 -6.07E+00 7.71E+01 7.54E+00
Variables Price
Chiller Duty $1.5/Btu
Condensor Duty $1.5/Btu
Reboiler Duty $2.5/Btu
Heater Duty $2.5/Btu
Ovhd Prod (-)$1/lb
Sales Gas (-)$2/lb
Liq Prod (-)$3.5/lb
Chiller Duty Condenser Duty Reboiler Duty Heater Duty Overhead Flow Sales Gas Flow Liquid Product Flow LP Cost
0 0 -3.88E+05 2.98E+00 4.65E+02 1.58E-02 1.24E+03 -386197.876
-7.32E+03 0 6.15E+03 -1.13E+04 6.07E+00 -1.54E+02 -2.64E+01 -12611.5684
Economic Variables
MV'S
Stage 9 Temp
Cold TC SP
SS Gain of Economic Variables
Stage 9 Temp
Cold TC SP
Cost Assumptions
LP Cost Calculation
Economic Variables
MV'S

12. 6. Equal Concern Error :
Equal concern errors for CV’s are calculated depending on the relative weighting factor, wi.
Propane Composition in Liquid Product & Sales Gas Dew Point are considered as important
controlled variables for this particular system. Changes in these variables will ultimately
affect the economic output. For example small changes in Propane Composition will cause a
change in the price($/Lb) of the liquid product, even change in Dew Point would affect the
price of Sales gas but he market value of Liquid product is more than sales gas, therefore
weighting factor for the Propane Composition is selected higher than the weighting factor
for Sales Gas Dew Point. Weight of Dew Point is assumed to be half of Propane
Composition. Thus, assuming Wi = 20 for Propane Composition and Wi= 10 for Dew Point.
Equal Concern Error =
ECE values calculated are as below:
CV Wi ECE
Sales Gas Dew Point 10 0.1
Propane Composition in
Liquid Product
20 0.05
Conclusion
 The Step Test is performed on a simulated plant and the data is used to
configure a DMC.
 The LP Cost values are obtained from the Steady State Gains of Economically
Dependent Variables.
 The Equal Concern Error depends upon the control objective. The weightage
is given more to the liquid product (Propane Composition). So while
considering a constraint between the two CV’s the MPC will consider the
liquid product and will compromise the Sales Gas Flow.