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Journal of Applied and Industrial Sciences, 2014, 2 (4): 188-200, ISSN: 2328-4595 (PRINT),ISSN: 2328-4609(ONLINE)
Research Article 188
Advanced Control of the Delayed Coking Unit in
Khartoum Refinery
Tomadir A. I. Hamed*1, Gurashi A. Gasmelseed2, Ibrahim H. Elamin3.
1Department of Chemical Engineering, University of Science and Technology, Khartoum- Sudan
Department of Chemical Engineering, University of Science and Technology, Khartoum- Sudan
Email:[email protected]
Department of Chemical Engineering, University of Science and Technology, Khartoum- Sudan
E-mail:[email protected]
(Received: April 04, 2014; Accepted: July 31, 2014)
Abstract :Delayed coking units convert heavy
crude oil or topping refinery residue to more
light valuable products including diesel,
gasoline and naphtha by thermal catalytic
treatment. The residue from the fractionation
column is to 500oC in the furnace. The
thermally treated residue enters the delayed
coking tower where cracking and
condensation reactions occur to produce oil
gas and coke.
A cascade control strategy was developed to
control the pressure of the coking drum using
the flow of the heater fuel as manipulated
variable. The block diagrams of the systems
were constructed and the process transfer
functions were identified using MATLAB
Black Box model. Then the overall transfer
functions, the open and closed-loops, and the
characteristic equations were determined, and
the control systems were tuned to obtain the
adjustable parameters using Routh-Hurwitz,
Direct Substitution, Root locus, Nyquist, and
Bode methods. The adjustable parameters
were appropriately inserted into the
characteristic equation for the offset
investigation, stability analysis and response
simulation. It is found that using of PID
controller for the Primary loop provides the
highest gain than P and PI controllers and
also it eliminates the Offset.
Indexterms: Delayed coking, Thermal
cracking, Advance control.
1. INTRODUCTION
Delayed coking is a thermal cracking process
used in petroleum refineries to upgrade and
convert petroleum residuum (bottoms from
atmospheric and vacuum distillation of crude
oil) into liquid and gas product streams leaving
behind a solid concentrated carbon material,
petroleum coke.
The delayed coker is the only main process in
a modern petroleum refinery that is a batch-
continuous process. The flow through the tube
furnace is continuous. The feed stream is
switched between two drums. One drum is on-
line filling with coke while the other drum is
being steam-stripped, cooled, decoked,
pressure checked, and warmed up. The
overhead vapors from the coke drums flow to a
fractionator, usually called a combination
tower. This fractionator tower has a reservoir
in the bottom where the fresh feed is combined with condensed product vapors (recycle) to make up
the feed to the coker heater [1].
A fired heater with horizontal tubes is used in the
process to reach thermal cracking temperatures of
485 to 505oC (905 to 941oF). With short residence
time in the furnace tubes, coking of the feed
material is thereby “delayed” until it reaches large
coking drums downstream of the heater. Three
physical structures of petroleum coke: shot, sponge,
or needle coke can be produced by delayed coking.
These physical structures and chemical properties of
the petroleum coke determine the end use of the
material which can be burned as fuel, calcined for
use in the aluminum, chemical, or steel industries,
or gasified to produce steam, electricity, or gas
feedstocks for the petrochemicals industry [2].
In Khartoum refinery a delayed coking unit with
a capacity of 1 Mt/year was constructed in Phase
I and a second delayed coking unit with a
capacity of 1 Mt/year was constructed in Phase II
where the overall delayed coking capacity
reached 2 Mt/year. A set of delayed coking unit
with annual capacity of 1Mt was constructed in
Phase I, which is composed of 8 sections, these
are electrostatic desalting; coking tower; heating
furnace; fractionation column; steaming out and
venting; rich gas compression; rich gas
desulfurization, coke storage, basin-settling, base
coking, and cold coking water circulation. The
second set of delayed coking unit consists of 6
sections, these are coking tower, heating furnace,
fractionation column, rich gas compression,
absorption and stabilization, LPG desulfurization
and dethioalcoholization. The 3 sections coking
tower, heating furnace and fractionation column
are matched with the annual capacity of 1Mt;
while the electrostatic desalting, rich gas
desulfurization, steaming out venting, coke
storage basin- settling, basin cutting coking,
water circulation and cold coking water
circulation match with the annual capacity of
2Mt.
Journal of Applied and Industrial Sciences, 2014, 2 (4): 188-200, ISSN: 2328-4595 (PRINT),ISSN: 2328-4609(ONLINE)
Fig. 1: Delayed Coking Unit flow sheet
The farction heavier than coker gas oil (CGO) in
the feedstock oil flows to the column bottom
together with the condensated fraction (called
circulation oil) of overhead oil gas from the
coking tower. At a temperature of 366ºC, the
mixture is pumped to the radiation section of the
furnace by heating furnace radiation section
feeding pump to be promptly heated up to 500ºC.
Then it enters the coking tower via four way
valve, where cracking and condensation reactions
occurred to produce oil gas and coke. The
mixture at high temperature oil gas transferred
from coking tower top to the duckbilled type tray
in the lower section at the bottom of the
fractionation column. Circulation oil fraction is
condensated, the rest large amount of oil gas
passes through washing plate to enter the
vaporization stage where it rises to the
distillation stage above the CGO collection pot to
separate the cuts such as coking rich gas,
gasoline, diesel oil and CGO [3].
One of the most useful concepts in advanced control
is cascade control. It is one of the most successful
schemes for enhancing the performance of single-
loop control [4], A cascade control structure has two
feedback controllers with the output of the primary
(or master) controller changing the set point of the
secondary (or slave) controller. The output of the
secondary goes to the valve, as shown in fig. 2.
There are two purposes for cascade control:
1. To eliminate the effects of some disturbances
2. To improve the dynamic performance of the control
loop
Fig. 2: Cascade Control Loop
There are many reasons for installing advanced process control
(APC) in a delayed coking unit, in order to maximize the
throughput in compliance with all given product qualities and
security limits. Unit security as well as product yields would be
improved. APC monitors all the process variables of the unit and
reacts on changes instantly inside the pre-specified limits [5].
The objectives of this study are to: develop a cascade control
strategy for the Coking Drum of the Delay Coking Unit, Identify
the Transfer Functions of control loops, Stability analysis of the
control loops, Controllers tuning, Offset investigation, and
response simulation.
II. METHODLOGY
Standards tests for raw material and products were carried out by
ASTM D, the raw material standard tests are shown in table 1 as
example.
Journal of Applied and Industrial Sciences, 2014, 2 (4): 188-200, ISSN: 2328-4595 (PRINT),ISSN: 2328-4609(ONLINE)
Table 1: Raw material, parameters and methods of determination [3]
190
System Control, Tuning, and Stability analysis
A control strategy was developed as shown in figure
3, the block diagrams were constructed, the transfer
functions were identified using System
Identification Toolbox in MATLAB and the
characteristic equations were obtained. These
characteristic equations are used for tuning, stability
analysis and simulation responses. A system is
considered unstable if, after been disturbed by an
input change, its output takes off and does not return
to the initial state of rest.
The stability analysis of a system can be treated in a
unified way independently if it is closed or open.
The location of the poles of a transfer function gives
the first criterion for checking the stability of a
system: If the transfer function of a dynamic system
has even one pole with positive real part, the system
is unstable
The criterion of stability for closed loop systems
does not require calculation of the actual value of
the roots of the characteristic polynomial. It only
requires that if any root is to the right of the
imaginary axis [6].The Routh-Hurwitz test is a
numerical procedure to determine how many roots
of a polynomial are in the Right Hand Plane and
how many are on the imaginary axis. It doesn't give
specific root locations but performing the test is
generally far easier than factoring [7]. As we change
gain, we notice that the system poles and zeros
actually move around in the S-plane. This fact can
make life particularly difficult, when we need to
solve higher-order equations repeatedly, for each
new gain value. The solution to this problem is a
technique known as Root-Locus graphs.
The root locus analysis is another criterion of
stability. The root loci are merely the plots, in the
complex plane, of the roots of the characteristic
equation as the controller gain is varied from zero to
infinity. Bode and Nyquist diagrams of the open-
loop transfer functions are used to study the stability
characteristics of a closed-loop system. A feedback
control system is unstable if the amplitude ratio of
the corresponding open-loop transfer function is
larger than 1 at the crossover frequency, this is
known as the Bode stability criterion. The Nyquist
stability criterion states that: if the open-loop
Nyquist plot of a feedback system encircles the
point (-1, 0) as the frequency takes any value from -
∞ to +∞, the closed-loop response is unstable [6].
Tuning cascade control systems is more complex
than tuning simple feedback systems, if only
because there is more than one controller to tune.
However, this does not mean it is difficult. Because
the inner loop by itself is a simple feedback loop,
this controller should be tuned as fast as possible-
avoiding instability, of course. The objective is to
make the inner loop fast and responsive in order to
minimize the effect of upsets on the primary
controlled variable. Tuning this system then comes
down to tuning the primary controller [7].
Item Analyzed Item Method
1 API degree N/A
2 Density (20ºC), g/cm3 ASTM D- 4052
3 Kinematic vis.
50/80ºC, mm2/s ASTM D- 445
4 Freezing point ºC ASTM D- 97
5 Flash point (open) ºC N/A
6 Conradson carbon residue, m% ASTM D- 189
7 Water content,m% ASTM D-4006
8 Salt content, mgNaCl/L ASTM D-6470
9 Acid value, mgKOH/g ASTM D-664
10 Sulfur content, m% ASTM D- 4294
11 Nitrogen content, m% ASTM D- 4175
12 Gum, m% ASTM D- 381
13 Asphaltene, m% ASTM D- 2006
14 Wax content, m% ASTM D- 9766
15 Fe/Ni/Cu/V/Pb/Ca/Mg/Na, ppm ASTM D- 5185
16 Characteritic factor N/A
17 Crude type N/A
18 BKP-distillate
at 240ºC, m% ASTM D- 1160
Journal of Applied and Industrial Sciences, 2014, 2 (4): 188-200, ISSN: 2328-4595 (PRINT),ISSN: 2328-4609(ONLINE)
Fig. 3: Control strategy physical diagram
Transfer function Identification:
The primary or Master loop:
The secondary or slave loop:
III. RESULTS AND DISCUSSION
The properties of mixed crude oil {light crude
(Fula-North-AG)/viscous crude (Fula-North-B)
=1:3} in the six districts of Sudan are shown in
Table 2. The basic characteristics of the crude oil
are high salt and calcium contents, high acidic
value, water content, high density, high viscosity
and high light component, and low sulfur content.
Tables 3.1 through 3.5 show the properties of the
oils.
Table 2: Properties of Mixed Crude Oil [3]
Item Analyzed Item Fula-North-B
(viscous crude)
Fula-North-AG
(light crude)
Mixed Crude*
1 API degree 18.07 33.1
2 Density (20ºC), g/cm3 0.9428 0.8596 0.936
3 Kinematic vis.
50/80ºC, mm2/s 1946.68/309.12 15.8/4.716 (50/100ºC) 267/117 (80/100ºC)
4 Freezing point ºC 2 13
5 Flash point (open) ºC 168 -
6 Conradson carbon residue,
m% 7.96 2.3
7 Water content,m% 1.12 6.40 2.35
8 Salt content, mgNaCl/L 683 1024
9 Acid value, mgKOH/g 13.82 0.09 10.455
10 Sulfur content, m% 0.15 589 ppm 0.1272
11 Nitrogen content, m% 0.29 1034 ppm
12 Gum, m% 13.69 -
13 Asphaltene, m% 0.18 -
14 Wax content, m% 13.50 -
15 Fe/Ni/Cu/V/Pb/Ca/Mg/Na,
ppm
97.9/18.3/1.2/0.9/0.1/1652.
0/8.5/264.0
16 Characteritic factor 12.0
17 Crude type Naphthenic- middle base Low sulfur middle base
18 BKP-distillate
at 240ºC, m% 8.3
* = Calculated data
The main products of the unit are purified dry gas, LPG, stabilized gasoline, coking diesel oil, coker gas oil and petroleum coke.
Journal of Applied and Industrial Sciences, 2014, 2 (4): 188-200, ISSN: 2328-4595 (PRINT),ISSN: 2328-4609(ONLINE)
192
Table 3: The components of dry gas. [3]
Component Content (wt %) Component Content (wt %)
Hydrogen 1.22 Propene 1.86
Methane 51.92 Butane 0.06
Ethane 36.47 Butene 0.04
Ethene 5.98 Water 0.50
Propane 1.95 Sulfur 20mg/Nm3
Total 100.0
Table 4: Composition of LPG. [3]
Component Content (wt %) Component Content (wt %)
Hydrogen 0.0 Propene 17.99
Methane 0.0 Butane 26.50
Ethane 0.27 Butene 18.94
Ethene 0.0 C5+ 1.84
Propane 34.46 Thio-alcohol ≤10ppm
Total 100.0
Table 5: Main properties of stabilized gasoline, coker diesel oil and CGO (calculated data) [3]
Table 6: Properties of coke [3] (lab. data in Dec. 2001)
Table 7: Main properties of coker gasoline (stabilized gasoline), diesel oil and coker gas oil. [3]
Gasoline Diesel oil Coker gas oil
Density (20ºC) kg/m3 733.2 832.2 898.3
Distillate
ºC
Initial boiling
point 46 192 323
10% 76 215 351
30% 105 241 374
50% 126 264 384
70% 146 288 408
90% 169 318 440
Dry point 186 342
Acid value, mgKOH/100ml 18.0 13.8 5.56
Actual gum, mg/100ml ≯3 59 5.3(m%)
Induction period, min 669
Copper corrosion, (50ºC, 3h) Fail Fail
Sulfur content, mg/kg 244 600 0.16(m%)
Alkaline nitrogen content, mg/kg 55 414 1005
Stabilized gasoline Coker diesel oil Coker CGO
Density (20ºC) kg/m3 720 826 888
Distillate
ºC
Initial boiling point 48 131 320
5% 58 186 342
10% 63 212 358
30% 86 240 365
50% 110 264 373
70% 135 290 382
90% 160 324 396
95% 171 337 420
Dry point 183 350 430
property value
real density, g/cm3 2.101
Volatile, m% 8.8
sulfur content, m% 0.41
Ash, m% 3.33
metal content Ni/V/Na/Al/Fe/Cu/Ca
real density, g/cm3 2.101
Volatile, m% 8.8
Journal of Applied and Industrial Sciences, 2014, 2 (4): 188-200, ISSN: 2328-4595 (PRINT),ISSN: 2328-4609(ONLINE)
Bromine value, g Br/100ml 45.8 24.8
Conradson residual carbon, m% 0.27
Ni/V/Na/Al/Fe/Cu/Ca,μg/g 0.1/0.1/1.4/1.1/3.0/0.1/0.6
Cetane number 51.6
Freezing point, ºC -25 20
Flash point (close), ºC 80 195 (open)
Aniline point, ºC 61.8
Kinematic viscosity, 50ºC, mm2/s 2.135 3.595(100)
Aromatic hydrocarbon, m% 22.6 22.8
Asphaltene, m% 0.1
Saturated component, m% 71.8
Ash, m% 0.004
Table 8: Composition of acidic gas [3]
Component Content, wt %
H2O 4.09
H2S 94.42
Hydrocarbon 1.49
Stability, tuning, offset and simulation
Using MATLAB the transfer function for the process of the secondary loop is:
The open loop transfer function using P controller is:
i. Routh test:
For this test the Characteristic equation of the loop is:
ii. Direct substituting:
Putting in characteristic equation to get:
Journal of Applied and Industrial Sciences, 2014, 2 (4): 188-200, ISSN: 2328-4595 (PRINT),ISSN: 2328-4609(ONLINE)
Using Ziegler-Nichols table to calculate the controller parameter 194
Type of controller P 0.5 - -
PI 0.45 = 8 -
For the Primary loop:
When using P controller for the secondary loop:
Characteristic equation is:
iii. Routh test:
iv. Direct substituting:
s.
Using Ziegler-Nichols table to calculate the controller parameter
Type of controller P 0.5 - -
PI 0.45 =74 -
PID 0.6 = 44.45 =11.11
v. Root locus criterion:
Root locus plots for the Secondary loop and primary loop is shown in figure 4, and 5, respectively
root locus plot for the secondary loop
Real Axis
Imag
inary
Axis
-25 -20 -15 -10 -5 0 5 10 15 20-4
-3
-2
-1
0
1
2
3
40.9550.9780.989
0.995
0.998
1
0.70.890.9550.9780.989
0.995
0.998
1
510152025
System: T
Gain: 867
Pole: -0.00342 - 0.676i
Damping: 0.00505
Overshoot (%): 98.4
Frequency (rad/sec): 0.676
System: T
Gain: 867
Pole: -0.00342 + 0.676i
Damping: 0.00505
Overshoot (%): 98.4
Frequency (rad/sec): 0.676
0.70.89
Journal of Applied and Industrial Sciences, 2014, 2 (4): 188-200, ISSN: 2328-4595 (PRINT),ISSN: 2328-4609(ONLINE)
Fig. 4: Root locus for secondary loop 195
Fig. 5: Root locus for primary loop with P controller for secondary loop
vi. Bode and Nyquist plots:
Bode and Nyquist plots for the Secondary loop and primary loop are shown in figure 6 through 9.
Fig. 6: Bode plot for secondary loop
root locus plot for the primary loop w ith(p secondary)
Real Axis
Imag
inary
Axis
-20 -15 -10 -5 0 5 10-150
-100
-50
0
50
100
150
0.5
0.0160.0360.0560.0850.115
0.17
0.26
0.5
20
40
60
80
100
120
140
20
40
60
80
100
120
140
System: T
Gain: 19.3
Pole: -0.0459 + 2.71i
Damping: 0.0169
Overshoot (%): 94.8
Frequency (rad/sec): 2.71
0.0160.0360.0560.0850.115
0.17
0.26
10-6
10-4
10-2
100
102
0
90
180
270
360
System: T
Frequency (rad/sec): 9.19
Phase (deg): 33.7
Phase (
deg)
bode plot for the secondary loop
Frequency (rad/sec)
-150
-100
-50
0
System: T
Frequency (rad/sec): 8.75
Magnitude (dB): -74.6
Magnitu
de (
dB
)
Journal of Applied and Industrial Sciences, 2014, 2 (4): 188-200, ISSN: 2328-4595 (PRINT),ISSN: 2328-4609(ONLINE)
Fig. 7: Nyquist plot for secondary loop
Fig. 8: Bode plot for primary loop with P controller for secondary loop
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0 dB
-20 dB
-10 dB-6 dB-4 dB-2 dB
20 dB
10 dB 6 dB 4 dB2 dB
Nyquist plot for the secondary loop
Real Axis
Imag
inar
y A
xis
bode plot for the primary loop w ith(p secondary)
Frequency (rad/sec)
10-3
10-2
10-1
100
101
102
103
-360
-180
0
180
360
System: T
Frequency (rad/sec): 2.72
Phase (deg): -176
Phase (
deg)
-200
-150
-100
-50
0
System: T
Frequency (rad/sec): 2.72
Magnitude (dB): -26.3
Magnitu
de (
dB
)
Journal of Applied and Industrial Sciences, 2014, 2 (4): 188-200, ISSN: 2328-4595 (PRINT),ISSN: 2328-4609(ONLINE)
Fig. 9: Nyquist plot for primary loop with P controller for secondary loop
vii. Offset investigation:
Secondary loop:
For P controller
For step change in input
For PI controller
For step change in input
Primary loop:
For P controller for primary and secondary loops:
For step change in input
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0 dB
-20 dB
-10 dB-6 dB-4 dB-2 dB
20 dB
10 dB 6 dB 4 dB 2 dB
Nyquist plot for the primary loop w ith(p secondary)
Real Axis
Imagin
ary
Axis
Journal of Applied and Industrial Sciences, 2014, 2 (4): 188-200, ISSN: 2328-4595 (PRINT),ISSN: 2328-4609(ONLINE)
198
For PI controller:
For step change in input
For PID controller:
For step change in input
viii. System response:
System response for secondary loop after
introducing unit step change in the input is shown in
figure 10, and for primary loop, system responses
are shown in figure 11 through 13.
Fig. 10: system response for secondary closed loop
step change response for the primary loop w ith(p secondary)
Time (sec)
Amplit
ude
0 10 20 30 40 50 60 70 80 90 1000
0.5
1
1.5
System: T
Rise Time (sec): 0.544
System: T
Peak amplitude: 1.44
Overshoot (%): 45
At time (sec): 1.5
System: T
Settling Time (sec): 48
System: T
Final Value: 0.995
Journal of Applied and Industrial Sciences, 2014, 2 (4): 188-200, ISSN: 2328-4595
(PRINT),ISSN: 2328-4609(ONLINE)
Fig. 11: system response for primary closed loop with P controller
Fig. 12: system response for primary closed loop with PI controller
Fig. 13: system response for primary closed loop with PID controller
step change response for PI primary loop w ith(p secondary)
Time (sec)
Ampl
itude
0 200 400 600 800 1000 1200-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
System: k
Final Value: 1System: k
Settling Time (sec): 767System: k
Rise Time (sec): 419
step change response for PID primary loop w ith(p secondary)
Time (sec)
Ampli
tude
0 20 40 60 80 100 120 140 160 180-1.5
-1
-0.5
0
0.5
1
1.5
System: n
Settling Time (sec): 121System: n
Rise Time (sec): 102
System: n
Final Value: 1
step change response for P primary loop
Time (sec)
Am
plit
ude
0 50 100 150 200 250 300 350-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
System: v
Rise Time (sec): 61.5
System: v
Final Value: 0.34
System: v
Settling Time (sec): 171
Journal of Applied and Industrial Sciences, 2014, 2 (4): 188-200, ISSN: 2328-4595
(PRINT),ISSN: 2328-4609(ONLINE)
Delayed Coking Unit provides good processes to
upgrade the heavy crude, or to convert it to more
light valuable products.
Coke can be more utilized if it is gasified to Syngas
which is can be used to produce energy and also as a
feed for petrochemical industries.
Secondary loop gain using Routh test and Root
locus respectively, is 435, and 433.5 for P-
controller and 395.5, and 390.15 for PI-controller,
results of Routh test are identical to the results of
Direct Substitution method. Using Bode criterion
200
the value of the Gain Margin is 876, and the Phase
Margin is infinity, these results are identical to
Nyquist criterion. The offset is - 0.0038 for P-
controller and 0.0 for PI controller.
The primary loop with P- controller for the
secondary loop, the gain is 1.625, 1.463, and 1.95for
P, PI, and PID respectively using Routh test, and
9.6, 8.69, and 11.6 P, PI, and PID respectively using
Root locus criterion. The offset is - 0.64 for P-
controller and 0.0 for PI, and PID controller. A
summary for these results is shown in table 9.
Table 9: Summary for the Comparison between Stability and tuning method for Primary loop
Offset Pu Ku Method
P : - 0.612
- 3.73 Routh_Huwrtiz PI : 0
PID : 0
P : - 0.644
88.9 3.25 Direct Substitution PI : 0
PID : 0
P : - 0.2336
2.32 19.3 Root Locus PI : 0
PID : 0
IV. CONCLUSIONS
Delay Coking Unit is one of the most valuable units in the refinery
because it increases the economic benefits by converting low price
residue to valuable products with higher price.
Advance control has a great effect on the response of the chemical
plants. It increases stability and eliminate offset.
There are many methods that are used to get the adjustable
parameters such as Routh-Hurwitz, Direct substitution and there
are another three graphical method, Bode, Nyquist, and root locus.
Ziegler-Nicholas criterion is used to tune the adjustable parameters.
PID controller for the Primary loop provides the highest gain than
P, and PI controllers and also it eliminates the Offset.
ACKNOWLEDGEMENTS
The authors wish to thank the Faculty of Graduation Studies and
Scientistic Research of Karary University, and Khartoum
Refinery Company for their help and support, this Paper is
generated from a Thesis in partial fulfillment for Ph.D. in
Chemical Engineering.
REFERENCES
[1] Ellis, P. J., Paul, C. A., “Delayed Coking Fundamentals”,
Topical Conference on Refinery Processing, Paper 29, March 8-12,
1998.
[2] Meyers, R. A., “Hand Book of Petroleum Refining”, McGraw
Hill, third edition, 1986.
[3] Manual of Delayed Coking Unit at Khartoum Refinery, 2007.
[4] Jeng, J.-C., “Simultaneous closed-loop tuning of cascade
controllers based directly on set-point step-response data”, Journal
of Process Control, Elsevier, 2014.
[5] Haseloff, V., Friedman, Y. Z., et al., “Implementing coker
advanced process control”, Hydrocarbon Processing, Gulf
Publishing Company, p. 99 –103, June 2007.
[6] Stephanopolous, G., “Chemical Process Control”, Prentice-hall
of India, New Delhi, 2005.
[7] Tyner, M., May, F. P., “Process Engineering Control”, The
Ronald press company, New-York, 1968.
[8] P. C. Chau, “Chemical Process Control: A First Course with
MATLAB”, 2001.