accoustic pyrometry is the · 2020. 5. 6. · pyrometer develops a temperature array of the furnace...

MC-03 –

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.

MC-03 –

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.

http://www.sciengr.com/

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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.

MC-03 –

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.

MC-03 –

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

MC-03 –

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.

MC-03 –

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


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


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


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


This graph indicates how the DCS controls the outlet temperature with NO consideration for gas temperature swings that induce

coking and high emissions

(ºC

)

MC-03 –

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

MC-03 –

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)

accoustic pyrometry is the · 2020. 5. 6. · pyrometer develops a temperature array of the furnace...

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