Exp 5 Report

8/2/2019 Exp 5 Report

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1

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.

http://en.wikipedia.org/wiki/Chemical_reactor

http://en.wikipedia.org/wiki/Fuel

http://en.wikipedia.org/wiki/Burner

http://en.wikipedia.org/wiki/Firebox_%28steam_engine%29

http://en.wikipedia.org/wiki/Combustion

http://en.wikipedia.org/wiki/Radiant_energy

http://en.wikipedia.org/wiki/Fire

http://en.wikipedia.org/wiki/Flue_gas

http://en.wikipedia.org/wiki/Convection

http://en.wikipedia.org/wiki/Earth%27s_atmosphere

http://en.wikipedia.org/wiki/Flue_gas_stack

http://en.wikipedia.org/wiki/Rust

http://en.wikipedia.org/wiki/Cracking_%28chemistry%29

http://en.wikipedia.org/wiki/Cracking_%28chemistry%29

http://en.wikipedia.org/wiki/Rust

http://en.wikipedia.org/wiki/Flue_gas_stack

http://en.wikipedia.org/wiki/Earth%27s_atmosphere

http://en.wikipedia.org/wiki/Convection

http://en.wikipedia.org/wiki/Flue_gas

http://en.wikipedia.org/wiki/Fire

http://en.wikipedia.org/wiki/Radiant_energy

http://en.wikipedia.org/wiki/Combustion

http://en.wikipedia.org/wiki/Firebox_%28steam_engine%29

http://en.wikipedia.org/wiki/Burner

http://en.wikipedia.org/wiki/Fuel

http://en.wikipedia.org/wiki/Chemical_reactor



2

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.



3

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



4

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.



5

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



6

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



7

Fuel flow rate

Table 3: Fuel flow rate

Graph 2a

9810 9820 9830 9840 9850 9860 9870 9880

600

620


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


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



8

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



9

Graph 3a

Graph 3b: Increase 20% of air flow rate

9810 9820 9830 9840 9850 9860 9870 9880

600

620

640


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


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


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


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



10

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


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


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



11

Graph 4b

1.302 1.303 1.304 1.305 1.306 1.307 1.308 1.309

x 104

500

550

600


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


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



12

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



13

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



14

iii) Hydrocarbon Flow Rate

Graph 9: Hydrocarbon Outlet Temperature vs. Hydrocarbon Flow Rate

Graph 10: Oxygen Exit Temperature vs. Hydrocarbon Flow Rate



15

iv) Fuel Gas Purity

Graph 11: Hydrocarbon outlet temperature vs. fuel gas purity

Graph 12: Oxygen exit temperature vs. fuel gas purity

2)



16

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

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