accoustic pyrometry is the · 2020. 5. 6. · pyrometer develops a temperature array of the furnace...
TRANSCRIPT
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Page 1
Gas temperature measurement in the fireside of process heaters-using
Acoustic Pyrometry
"Presented at the 2003 NPRA Maintenance Conference in Salt Lake City, Utah"
Speaker: Mr. Roberto Roubicek, SEI, Inc. President
Introduction
The SEI Acoustic Pyrometer provides gas temperature measurement in real time thus
permitting adjustments to optimize combustion and provide a monitoring process for
furnace fault conditions. SEI utilizes the fundamental principal that the speed of sound in
a gas changes as a function of temperature. From the ideal gas law and precise
measurements of the process heater’s dimensions, accurate two-dimensional isothermal
temperatures and tendencies can be obtained in real time by measuring the speed of
sound.
Using acoustic pyrometry for furnace combustion control will reduce operating costs by
minimizing thermal stress due to flame impingement and increase furnace availability by
minimizing coke lay down. The real time measurement of gas temperature also plays a
very important role in the ever-tightening emissions standards being regulated into US
and worldwide refineries.
Discussion
From observed deviations of optimal temperature profiles, which are dictated by burner
manufacturers and heater designers, corrections in combustion parameters can be made
by precise adjustment of air registers, fuel flow and stack damper positions. In some
heaters with forced draft, the same precise controls can be achieved using acoustic
pyrometers. Optimized combustion can be implemented automatically by using the
acoustic pyrometer when connected to the refinery’s DCS. Operator intervention can
now be directed to maintain other key operational objectives.
The ideal gas law predicts temperatures in gases by simply knowing the molecular weight
of the gas being measured and the speed of sound as it propagates thru the medium.
Relative accuracies of 2% are possible using this technique. From the well understood
behavior of sound transmissions through gaseous media, the desired spectrum is a sound
source that generates a noise between 500hz and 3000hz. The spherical sound wave
projects in ALL directions - around bends, up, down and between process tubes -
permitting placement of transmitters and receivers in different planes so that two
dimensional temperature profiles can be depicted.
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The most important acoustic measurement is NOT sound intensity, BUT a unique
random sound that with today’s signal processing techniques yields accurate and fast
temperature readings. Using the SEI patented air driven sound generator which utilizes
plant air, our lightweight non-intrusive sensors can be either mounted directly to the
furnace wall or onto the observation door. By mounting on the observation door, visual
inspection of the furnace interior is still maintained.
Since 1986, SEI has developed and patented various technologies to measure gas
temperature. From the original chirp technology which used an electrodynamic speaker,
to the present and patented pneumatic impulse response technique, Acoustic Pyrometry
has become a mature technology for reliable continuous furnace gas temperature
measurement in real time. Our stand alone, low maintenance Acoustic Pyrometer has
been successfully tested in hydrogen reformers, delayed coker units, platformers, crude
distillation units, and recently a high vacuum furnace.
Since 2001, SEI, Inc. has introduced and installed acoustic pyrometers in various
refineries. Currently there are two permanent installations, in Complejo Refinador de
Paraguana, a 980,000 b/d refinery owned by Petroleos de Venezuela S.A.and Refineria
Isla N.V. in Curacao, Netherlands Antilles a 320,000 b/d., refinery leased by Petroleos de
Venezuela S.A. To assist in the control of fireside combustion, the SEI Acoustic
Pyrometer develops a temperature array of the furnace and continuously performs two
major functions. The first is to send temperature data (via serial and/or 4-20 mA outputs)
to the plant’s DCS for monitoring and /or control purposes. The second is the creation of
an isothermal map for the operator to visualize furnace combustion operation.
The following figures show excerpts from SEI, Inc. reports that and are available at our
web site, www.sciengr.com. These figures show innovative concepts for installations
and various test results of the acoustic pyrometer being used in the fireside of process
heaters.
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Furnace F-1202 at PDVSA-Refineria Isla N.V. in Curacao, Netherlands Antilles
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Typical Control Room Display
This graph is displayed in the operators control room and is used ONLY for monitoring
the status of the crude distillation unit. In this case we are observing furnace F-1202.
The normal flow imbalance can be as high as 300 tn/day and when the Flow Imbalance
exceeds 500 tn/day, the operator is requested to:
1) Review historical trend for the affected process tubes.
2) Field intervention is requested to detect burner problems.
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Sketch of furnace F-1202
This is an 8 pass, dual furnace, box style, single convective zone. The temperature
controllers maintain the set points, 245 ºC at inlet and 345 ºC at outlet. The furnace has
4 burners per cell and one fan and one fuel valve.
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Schematic layout of furnace F-1202 at PDVSA-Refineria Isla N.V.
For automated combustion control, an air register and stack damper control
loop would be added
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SEI Multi Point Acoustic Pyrometer-Boilerwatch MMP
SEI Acoustic Transceiver with Pre-Amplifier Box
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Installation of SEI receiver on an existing furnace access port
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Installation of an SEI standard waveguide on an existing observation door. The only
moving part is the ASCO air valve. The piezo electric microphone is rated up to 500 ºF.
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Example furnace modifications for a permanent installation
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Examples of acoustic pyrometer path configuration options.
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SEI generated isothermal map of unbalanced furnace detected by SEI equipment. Note
path lines in white used to generate map.
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The same furnace after the balance was improved.
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The following six illustrations compare several furnace parameters when the stack
damper and air registers were adjusted. The furnace fuel and air were held constant
throughout the test.
Po
sit
ion
sta
ck
dam
pe
r
Tim
e
ch
an
ge
Se
ttin
g
reg
iste
rs
Tim
e
ch
an
ge
1 friday 1 friday
2 8:48 2 10:37
3 11:30 3 12:58
4 14:03 4 14:58
5 15:47
Table 1 - Time when variable were changed
Position air registers
Air r
egis
ters
@
burn
er
se
ttin
g 1
se
ttin
g 2
se
ttin
g 3
se
ttin
g 4
Ra
dia
nt
ce
ll N
ort
h
F-1
202
13 *7 *7 *7 *7
14 7 7 9 6
19 7 2 2 2
20 7 2 2 6
Ra
dia
nt
ce
ll S
outh
F-1
202
15 7 7 9 9
16 7 7 9 6
17 7 2 2 2
18 7 2 2 6
* Indicates that register of burner 13 was stuck at position 7
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Table 2 - Settings of registers
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1. Combustion
0,00
200,00
400,00
600,00
800,00
1000,00
1200,00
1400,00
1600,00
7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00
Time
Co
mb
usti
on
air
(T
/D)
0,00
10,00
20,00
30,00
40,00
50,00
60,00
Fu
el fl
ow
(T
/D)
comb.air flow asph.
time when stack damper was movedtime when air register was moved
This graph depicts the fuel flow and air flow. Parameters were held constant during the test. A slight drop occurred after 14:30 hrs.
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2. B.W.T & O2
400
500
600
700
800
900
1000
1100
1200
1300
7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00
Time
Tem
pera
ture
(K
)
0,00
2,00
4,00
6,00
8,00
10,00
12,00
14,00
16,00
18,00
O2 (
%-v
ol.)
bwt O2
time when stack damper was movedtime when air register was moved
This graph illustrates the direct correlation between stack damper position and excess air/O2. Note that the air register position does
not influence O2. Also the BWT, an important control parameter, is non-reacting indicator of the combustion change.
(ºC
)
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3. A.P. Temperature north cell
400
500
600
700
800
900
1000
1100
1200
1300
7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00
Time
A.P
. te
mp
era
ture
(K
)
AN1 AN2 AN3 AN4
time when stack damper was movedtime when air register was moved
This graph illustrates the instantaneous change in SEI measured temperature in the north cell when the air register and or stack damper
are manipulated. After the first air register change, the furnace becomes balanced. After the second stack damper change, the furnace
becomes unbalanced. This furnace has two stack dampers and the coordination of the two will tune the combustion.
A.P
. t
em
pera
ture
(ºC
)
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4. A.P. Temperature south cell
400
500
600
700
800
900
1000
1100
1200
1300
7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00
Time
A.P
. te
mp
era
ture
(K
)
AS1 AS2 AS3 AS4
time when stack damper was movedtime when air register was moved
This graph illustrates the same instantaneous change in SEI measured temperature in the south cell as shown in graph three for the
north cell. Note the tremendous change in temperatures when the stack dampers and air register are moved. This might be an
indication of HI emission production.
A.P
. t
em
pera
ture
(ºC
)
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5. T.C. Outlet
616
617
618
619
620
621
622
623
624
625
7:12 8:24 9:36 10:48 12:00 13:12 14:24 15:36 16:48 18:00
Time
Tem
pera
ture
(K
)
temp.outlet
N
time when stack damper was movedtime when air register was moved
This graph indicates how the DCS controls the outlet temperature with NO consideration for gas temperature swings that induce
coking and high emissions
(ºC
)
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Conclusion
As can be seen in the preceding pages, the acoustic pyrometer is a very dynamic indicator
of the combustion process. It is seen that in changes of stack damper and air register
position, the acoustic pyrometer is an indicator of combustion temperatures.
At the present time, many refineries worldwide have been purchasing furnace equipment
to further improve the efficiency of fired heaters. The advent of new legislation being
introduced in the US and world markets that measures ever tightening emissions is
directing R&D projects in burner technology to introduce new burners that will permit
refineries to meet the current and new standards. The acoustic pyrometer will effectively
detect any malfunctioning burner so that the refineries will be able to adhere to the
established standards very quickly without affecting the process outflow.
The current need is for real time temperature measurements and profiling for reduction of
thermal stress, coke formation, and emissions. The acoustic pyrometer is a tool that is
available for improved profitability of the refinery furnace.
References
[1] Roberto Roubicek –High Vacuum Report in Complejo Refinador
Paraguana, PDVSA, Dec. 2002
[2] Roberto Roubicek-Crude Distillation Report in Refineria Isla N.V.
PDVSA, June 2002
[3] Duarte Marquez-The Sound of Temperature-Thesis for: Fontys
Hogeschool. Applied Sciences, dept. of Engineering Physics with Commerce, Dec. 2002
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Addendum-
ACOUSTIC PYROMETER THEORY OF OPERATION
The BOILERWATCH SP and BOILERWATCH MMP gas pyrometer system is based
on the physical principal that the speed of sound traveling through a gas volume is
proportional to the temperature of that gas. The velocity at which acoustic waves propagate
through a gas mixture is a primary function of absolute temperature, and to a lesser extent,
a function of the gas composition. For most applications, the gas constituents and their
relative quantities are well known or fall within a small range of values. The average gas
temperature along a path volume between a sound source and a receiver can, therefore, be
determined by first measuring the 'flight-time' of the acoustic wave (that is the time taken
for the sound wave to travel from the acoustic source to the acoustic receiver), and by
knowing the distance between the source and receiver, the temperature can then be
computed.
A wide-band audio signal is launched from a pneumatically driven sound source placed on
one side of a furnace, and it's arrival is detected at the opposite side by a receiver
transducer. The time interval between launch and detection is the flight-time, which is then
used in the computation of average temperature of the gas in the volume between source
and destination transducers.
The fundamental principal of acoustic pyrometry is based on the fact that the speed of
sound in a gas changes as a function of temperature, and is further affected by the
composition of the gas along the acoustic path. These relationships are described by the
equation:
c = d
t =
rRT
M1 (1)
where:
c = speed of sound in a gas (meters/second)
d = distance over which sound wave travels, (meters)
t = flight time of sound wave, (seconds)
r = ratio of specific heats
R = universal gas constant, 8.314 J/mole -°K
T = temperature, °K
M = molecular weight (Kg/mole)
With a sound source (transmitter) installed on one side of the furnace and a microphone
(receiver) on the opposite side, a sound signal can be emitted from the transmitter and
detected by the receiver. Since the distance between the transmitters is known and fixed,
measurement of the flight-time of the sound signal allows computation of the average
temperature of the gas along that path.
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By applying a conversion from degrees K to degrees F, an expression is obtained that
relates gas temperature (in °F) to distance, flight-time, and gas composition:
F2 6T = (d / B ) x 10 - 460 2 (2)
where:
FT = gas temperature ( F) 3
d = distance, (ft) 4
B = acoustic constant = R / M 5
= flight - time, (milliseconds)6
Temperature can also be expressed in degrees C, using the following equation:
c2 6T = (d / B ) x 10 - 273.16 7 (3)
where:
d = distance, (meters)