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1.0 INTRODUCTION
1.1 Literature Review
An industrial furnace or direct fired heater is equipment used to provide heat
for a process or can serve as reactor which provides heats of reaction. Furnace designs
vary as to its function, heating duty, type of fuel and method of introducing
combustion air. However, most process furnaces have some common features.
Fuel flows into the burner and is burnt with air provided from an air blower.
There can be more than one burner in a particular furnace which can be arranged in
cells which heat a particular set of tubes. Burners can also be floor mounted, wall
mounted or roof mounted depending on design. The flames heat up the tubes, which
in turn heat the fluid inside in the first part of the furnace known as the radiant section
or firebox. In this chamber where combustion takes place, the heat is transferred
mainly by radiation to tubes around the fire in the chamber. The heating fluid passes
through the tubes and is thus heated to the desired temperature. The gases from the
combustion are known as flue gas. After the flue gas leaves the firebox, most furnace
designs include a convection section where more heat is recovered before venting to
the atmosphere through the flue gas stack. (HTF=Heat Transfer Fluid. Industries
commonly use their furnaces to heat a secondary fluid with special additives like anti-
rust and high heat transfer efficiency. This heated fluid is then circulated round the
whole plant to heat exchangers to be used wherever heat is needed instead of directly
heating the product line as the product or material may be volatile or prone to
cracking at the furnace temperature.)
There are two major objectives for operation of the furnace. First, in order to
minimize fuel costs, the furnace must be operated with proper oxygen composition to
ensure complete combustion of the fuel (carbon monoxide is an undesired product).
Second, the hydrocarbon feed stream must be delivered to the cracking unit at the
desired temperature.
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1.2 Theory
The manipulated variables for the furnace are the Air Flow Rate and Fuel Gas
Flow Rate. The controlled variables are the Hydrocarbon Outlet Temperature and
Oxygen Exit Concentration. The system also has the disturbance variables that are
Hydrocarbon Flow Rate and Fuel Gas Purity. This furnace is the first order system, so
the system has system gain and time constant.
This experiment represents a furnace fuelled by natural gas which is used to
preheat a high molecular weight hydrocarbon feed (C16 – C26) to a cracking unit at a
petroleum refinery. The combustion of fuel is assumed to occur according to the
following reaction equation:
CH4 + 3/2 O2 → CO + 2H2O
CO + 1/2 O2 → CO2
1.3 Objectives
The purpose of this module is to demonstrate the properties of a first order
system for various values of the system gain and time constant. This modules also
illustrates the dynamic response of a first order to a different input signals.
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2.0 METHODOLOGY
2.1 Material
MATLAB 7.0 software
2.2 Procedure
1) Started by selecting the Furnace from the Main Menu. This is done by clicking
the left mouse button once on the Furnace button. This opens the menu window
for the furnace modules. Clicked the left mouse button on the Furnace button.
Two additional windows should open, one for the input and output graphs and
one for the furnace process flow sheet.
2) Under the Simulation menu, selected Start. This command should be executed
once during a lab session. It is a simulated equivalent to a perfect process start-up.
The process output graphs are located on the window labelled Furnace Process
Monitor. Notice how the outputs remain unchanged with time.
3) Next, try decreasing the fuel gas purity. This will act as a disturbance to the
system. By double clicking on the Fuel Gas Purity Box, the value is changed
from 1.0 to 0.95 by clicking on the value box and using the backspace key to
erase the old value. When you have entered a new value, the Close button is
clicked. Again, notice how the outputs on the process monitor are changing with
time. Now return the Fuel Gas Purity to 1.0 by double clicking on the Fuel Gas
Purity box and adjusting the value as done before.
4) The furnace is started. The initial steady state values for each of the inputs and
outputs of the furnace are recorded.
5) The following sequence of increases in the air flow rate is made by double
clicking the left mouse button on the Air Flow Rate box. The remaining inputs
(the six other inputs) should be kept at their initial steady state values. After each
change in the air flow rate, the system is allowed to reach a new steady state
(approximately 40 simulation minutes) and then the values of the output variables
obtained is recorded using the pointers on the output graphs. The steady state
values are recorded. The Air Flow Rate is returned to its initial value and allows
the furnace to reach steady state.
6) The following sequence of increases in the fuel gas flow rate by is made by
clicking the left mouse button on the Fuel Gas Flow Rate box. The remaining
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inputs (the six other inputs) should be kept at their initial steady state values.
After each change in the fuel gas flow rate, the system is allowed to reach a new
steady state (approximately 40 simulation minutes) and then the values of the
output variables are recorded using the pointers on the output graphs. The steady
state values are recorded. The Fuel Gas Flow Rate is returned to its initial value
and the furnace is allowed to reach steady state.
7) The following sequence of increases in the hydrocarbon flow rate is made by
double clicking the left mouse button on the Hydrocarbon Flow Rate box. The
remaining inputs (the six other inputs) should be kept at their initial steady state
values. After each change in the hydrocarbon flow rate, the system is allowed to
reach a new steady state (approximately 40 simulation minutes) and then the
values of the output variables obtained is recorded using the pointers on the
output graphs. The steady state values are recorded.
8) The following sequence of increases in the fuel gas purity is made by double
clicking the left mouse button on the Fuel Gas Purity box. The remaining inputs
(the six other inputs) should be kept at their initial state values. After each change
in the fuel gas purity, the system is allowed to reach a new steady state
(approximately 40 simulation minutes) and then the values of the output variables
obtained are recorded using the pointers on the output graphs. The steady state
values are recorded. The Fuel Gas Purity is returned to its initial value and the
furnace is allowed to reach steady state.
9) The nominal Air Flow Rate is increased by 20% and Procedure 4-8 is repeated.
10) To end the session, the simulation is stopped by selecting Stop under the
Simulation menu, and then Yes is selected under the Quit menu from the main
menu window. This will return you to the MATLAB prompt. At this prompt, type
quit to exit MATLAB.
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3.0 RESULT & DISCUSSION
3.1 Result
Initial steady state values
a. t
e
b. F
u
e
l
g
a
s
p
u
r
i
t
y
Table 1: Initial steady state values
Inputs
Hydrocarbon Flow Rate 0.035 m3 /min
Hydrocarbon Inlet Temperature 310 K
Air Flow Rate 17.9 m3 /min
Air Temperature 310 K
Fuel Gas Flow Rate 1.21 m3 /min
Fuel Gas Temperature 310 K
Fuel Gas Purity 1 mol CH4 /mol total
Outputs
Hydrocarbon Outlet Temperature 609.8684 K
Furnace Temperature 1426.8144 K
Exhaust Gas Flow Rate 43.2896 m3 /min
Oxygen Exit Concentration 0.92171 mol O2 /min
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Air flow rate
i) ii)
Table 2: Air flow rate
Graph 1
1.056 1.057 1.058 1.059 1.06 1.061 1.062 1.063
x 104
590
600
610
620Hydrocarbon Outlet Temp.
Time (min)
T e m p .
( K )
1.056 1.057 1.058 1.059 1.06 1.061 1.062 1.063
x 104
1380
1400
1420
1440
1460
Furnace Temp.
Time (min)
T e m p .
( K )
1.056 1.057 1.058 1.059 1.06 1.061 1.062 1.063
x 104
40
45
50Exhaust Gas Flow Rate
Time (min)
F l o w
R a t e ( m 3 / m i n )
1.056 1.057 1.058 1.059 1.06 1.061 1.062 1.063
x 104
0.85
0.9
0.95
1O2 Concentration
Time (min)
C o n c .
( m o l / m 3 )
Pntr Val.=
at t =
608.0263
1726.0366
Pntr Val.=
at t =
1428.3682
4575.4268
Pntr Val.=
at t =
43.2018
4808.313
Pntr Val.=
at t =
0.92171
4961.7683
Air Flow Rate Hydrocarbon Outlet
Temperature
Oxygen Exit Concentration
17.9 (nominal) 609.8684 0.92069
18.1 606.9737 0.95066
18.3 604.6053 0.979697
18.5 602.5000 1.6088
18.7 599.0789 1.0343
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Fuel flow rate
Table 3: Fuel flow rate
Graph 2a
9810 9820 9830 9840 9850 9860 9870 9880
600
620
640Hydrocarbon Outlet Temp.
Time (min)
T e m p .
( K )
9810 9820 9830 9840 9850 9860 9870 9880
1400
1450
1500
Furnace Temp.
Time (min)
T e m p .
( K )
9810 9820 9830 9840 9850 9860 9870 988040
45
50Exhaust Gas Flow Rate
Time (min)
F l o w
R a t e ( m 3 / m i n )
9810 9820 9830 9840 9850 9860 9870 9880
0.7
0.8
0.9
1
1.1
O2 Concentration
Time (min)
C o
n c .
( m o l / m 3 )
Pntr Val.=
at t =
1426.81
1981.4837
Pntr Val.=
at t =
43.2895
2119.6951
Pntr Val.=
at t =
609.6454
9818.313
Pntr Val.=
at t =
0.92025
9829.6951
Fuel Gas
Flow Rate
Hydrocarbon
Outlet
Temperature
Increase 20%
of air flow rate
(21.48)
Oxygen Exit
Concentration
Increase 20%
of air flow rate
(21.48)
1.21
(nominal)
609.6454 544.2943 0.92025 1.6013
1.22 612.2368 545.7308 0.89983 1.5614
1.23 614.3421 547.1674 0.87897 1.5347
1.24 616.7196 548.6039 0.86043 1.5081
1.25 618.8903 550.0404 0.83858 1.4814
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Graph 2b: Increase 20% of air flow rate
Hydrocarbon Flow Rate
HydrocarbonFlow Rate
HydrocarbonOutlet
Temperature
Increase 20%of air flow rate
(21.48)
Oxygen ExitConcentration
Increase 20%of air flow rate
(21.48)
0.0350
(nominal)
609.5454 562.9691 0.92025 1.4814
0.0355 605.9474 560.096 0.92025 1.4947
0.0360 602.7117 577.223 0.92025 1.4947
0.0365 599.0138 552.9134 0.92025 1.4947
0.0370 595.7781 550.0404 0.92025 1.4947
Table 4: Hydrocarbon flow rate
1.257 1.258 1.259 1.26 1.261 1.262 1.263 1.264
x 104
500
550
600
Hydrocarbon Outlet Temp.
Time (min)
T e m p .
( K )
1.257 1.258 1.259 1.26 1.261 1.262 1.263 1.264
x 104
1100
1200
1300
1400
1500
Furnace Temp.
Time (min)
T e m p .
( K )
1.257 1.258 1.259 1.26 1.261 1.262 1.263 1.264
x 104
30
40
50
Exhaust Gas Flow Rate
Time (min)
F l o w
R a t e ( m 3 / m i n )
1.257 1.258 1.259 1.26 1.261 1.262 1.263 1.264
x 104
1
1.5
2
O2 Concentration
Time (min)
C o n c .
( m o l / m 3 )Pntr Val.=
at t =
43.2895
2119.6951
Pntr Val.=
at t =
71.1538
31.1881
Pntr Val.=
at t =
581.0167
11435.2642
Pntr Val.=
at t =
1.055
11423.0691
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Graph 3a
Graph 3b: Increase 20% of air flow rate
9810 9820 9830 9840 9850 9860 9870 9880
600
620
640
Hydrocarbon Outlet Temp.
Time (min)
T e m p .
( K )
9810 9820 9830 9840 9850 9860 9870 9880
1400
1450
1500
Furnace Temp.
Time (min)
T e m p .
( K )
9810 9820 9830 9840 9850 9860 9870 988040
45
50Exhaust Gas Flow Rate
Time (min)
F l o
w
R a t e ( m 3 / m i n )
9810 9820 9830 9840 9850 9860 9870 9880
0.7
0.8
0.9
1
1.1
O2 Concentration
Time (min)
C
o n c .
( m o l / m 3 )
Pntr Val.=at t =
1426.811981.4837
Pntr Val.=
at t =
43.2895
2119.6951
Pntr Val.=at t =
609.64549818.313
Pntr Val.=
at t =
0.92025
9829.6951
1.257 1.258 1.259 1.26 1.261 1.262 1.263 1.264
x 104
500
550
600
Hydrocarbon Outlet Temp.
Time (min)
T e m p .
( K )
1.257 1.258 1.259 1.26 1.261 1.262 1.263 1.264
x 104
1100
1200
1300
1400
1500
Furnace Temp.
Time (min)
T e m p .
( K )
1.257 1.258 1.259 1.26 1.261 1.262 1.263 1.264
x 104
30
40
50
Exhaust Gas Flow Rate
Time (min)
F l o w
R a t e
( m 3 / m i n )
1.257 1.258 1.259 1.26 1.261 1.262 1.263 1.264
x 104
1
1.5
2
O2 Concentration
Time (min)
C o n c .
( m
o l / m 3 )Pntr Val.=
at t =
43.2895
2119.6951
Pntr Val.=
at t =
71.1538
31.1881
Pntr Val.=
at t =
581.0167
11435.2642
Pntr Val.=
at t =
1.055
11423.0691
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Fuel Gas Purity
Fuel Gas
Purity
Hydrocarbon
Outlet
Temperature
Increase 20%
of air flow rate
(21.48)
Oxygen Exit
Concentration
Increase 20%
of air flow rate
(21.48)
1.00 (nominal) 595.7217 562.9691 0.92025 1.3349
0.99 592.4539 560.096 0.94475 1.3615
0.98 590.0031 558.6996 0.97334 1.3882
0.97 586.7353 555.7865 0.99784 1.4281
0.95 581.0167 550.0404 1.055 1.4814
Table 5: Fuel gas purity
Graph 4a
2.754 2.755 2.756 2.757 2.758 2.759 2.76 2.761
x 104
570
580
590
600
610
620Hydrocarbon Outlet Temp.
Time (min)
T e m p .
( K )
2.754 2.755 2.756 2.757 2.758 2.759 2.76 2.761
x 104
1350
1400
1450
Furnace Temp.
Time (min)
T e m p .
( K )
2.754 2.755 2.756 2.757 2.758 2.759 2.76 2.761
x 104
40
45
50Exhaust Gas Flow Rate
Time (min)
F l o w
R a t e ( m 3 / m i n )
2.754 2.755 2.756 2.757 2.758 2.759 2.76 2.761
x 104
0.9
1
1.1
O2 Concentration
Time (min)
C o n c .
( m o l / m 3 )
Pntr Val.=
at t =
1428.3682
4575.4268
Pntr Val.=
at t =
43.2018
4808.313
Pntr Val.=
at t =
595.5029
26844.0854
Pntr Val.=
at t =
1.0352
26976.0772
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Graph 4b
1.302 1.303 1.304 1.305 1.306 1.307 1.308 1.309
x 104
500
550
600
Hydrocarbon Outlet Temp.
Time (min)
T e m p .
( K )
1.302 1.303 1.304 1.305 1.306 1.307 1.308 1.309
x 104
1100
1200
1300
1400
1500
Furnace Temp.
Time (min)
T e m p .
( K )
1.302 1.303 1.304 1.305 1.306 1.307 1.308 1.309
x 104
30
40
50
Exhaust Gas Flow Rate
Time (min)
F l o w R a t e ( m 3 / m i n )
1.302 1.303 1.304 1.305 1.306 1.307 1.308 1.309
x 104
1
1.5
2
O2 Concentration
Time (min)
C o n c .
( m o l / m 3 )Pntr Val.=
at t =
43.2895
2119.6951
Pntr Val.=
at t =
71.1538
31.1881
Pntr Val.=
at t =
550.0404
13016.8089
Pntr Val.=
at t =
1.4814
13020.061
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3.2 Discussion (Question)
1) Calculate the steady state gain for each of the following input-output pairings.
i) Air Flow Rate
Graph 5: Hydrocarbon Outlet Temperature vs. air flow rate
Graph 6: Oxygen Exit Concentration vs. air flow rate
y = 0.1427x - 1.6322
0.9
0.92
0.94
0.96
0.98
1
1.02
1.04
1.06
17.8 18 18.2 18.4 18.6 18.8
oxygen exit
concentration
air flow
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ii) Fuel Gas Flow Rate
Graph 7: Hydrocarbon Outlet Temperature vs. fuel gas flow rate
Graph 8: Oxygen Exit Temperature vs. fuel gas flow rate
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iii) Hydrocarbon Flow Rate
Graph 9: Hydrocarbon Outlet Temperature vs. Hydrocarbon Flow Rate
Graph 10: Oxygen Exit Temperature vs. Hydrocarbon Flow Rate
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iv) Fuel Gas Purity
Graph 11: Hydrocarbon outlet temperature vs. fuel gas purity
Graph 12: Oxygen exit temperature vs. fuel gas purity
2)
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4.0 CONCLUSION & RECOMMENDATIONS
We have achieved our objectives in the experiment that is to demonstrate the
properties of a first order system for various values of the system gain and time
constant. We also have successfully illustrates the dynamic response of a first order to
different input signals.
From the experiment we also have learned that some of the factors that
influence to gain the value of steady state that are air flow rate, fuel gas flow rate,
hydrocarbon flow rate, and fuel gas purity.
5.0 REFERENCES
1) Norman A. Anderson (1980). Instrumentation for Process Measurement and
Control. 3th Edition. CRC Press.
2) Dale E. Seborg, Thomas F. Edgar, Duncan A. Mellichamp (2004). Process
dynamics and control. Second Edition.
3) Brian Roffel and Ben Betlem. Process dynamics and control: modeling for control
and prediction.
4)
Raymond Jay Emrich (1981). Fluid Dynamics: Fluid Dynamics. Academic Press.5) Marlin, T.E. Process Dynamic and Control Process Control: Designing Processes
and Control Systems for Dynamic Performance