through flame thermal cameras

7/27/2019 Through Flame Thermal Cameras

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Temperature Sensors Temperature Sensors

When it comes to the

industrial furnaces,

heaters and boilers

used in the chemical,

petrochemical and utility industries, the

actual operational designs are as varied

as the many applications. Some plants

have only two or three heaters while

larger plants may have more than 50.

Some heaters simply deliver the feed at

a predetermined temperature to the next

stage of the reaction process while oth-

ers perform reactions on the feed while

it travels through the tubes.

Whatever the applicat ion, accurate,cost-effective inspection of these pro-

cess heaters, furnaces or fired heaters in

action presents unique challenges. Ever

more, industrial predictive maintenance

(PdM) programs and external inspec-

tion companies turn to thermal cameras

fitted with a spectral waveband filter

designed specifically to see through

flame, at temperatures from -40 to

1500°F (-40 to 816°C) and more.

Infrared Locates Coking,Provides TemperatureValidation

Tube metal temperatures are particula r-

ly critical to distillation furnace opera-

tions. When operating a furnace close

to the maximum allowable tube metal

temperature, changes of less than 200°F

(111°C) can dramatically reduce tube

life on tubes rated for 100,000 hours to

only a few hundred hours.

In distillation furnaces, a primary ser-

vice consideration is the determination of

carbon scale buildup, or coke formation.

Areas with coke buildup preclude the

product from uniformly absorbing the

tube’s heat and can result in higher fur-

nace firing rates. In some cases, overfir-

ing can cause temperatures that exceed

the tube metal design criteria, and this,

coupled with pressure inside a plugged

tube, may cause a rupture and leak.

Unfortunately, viewing buildup on

the inside of a tube (coking) from a set

number of access ports can only supply

a limited amount of information that is

somewhat compromised by an oblique

viewing angle. A through-f lame ther-

mal camera, however, fitted with an

Through-FlameThermal CamerasCan Take the HeatDoes your process heating operation need a fast, noncontact, nondestructive way to

gather both qualitative and quantitative information to prevent or minimize downtime? Of

course it does, and that is why you should consider a through-flame thermal camera.

By Paul Czerepuszko,FLIR Systems, Inc.

Thermal imaging combined with visual images allows you to see conditions

invisible to the naked eye yet place them in context in a visible world. A visual

image of a ruptured tube (left); a visual image of tube through a viewing port

(middle); and a hydrogen fire from a leaking tube that cannot be seen visually,

causing impingement overheating on adjacent tubes (right) provides insights

into the process equipment. The thermal image was taken with a long-wave

thermal camera so the flame would be obvious.

As seen in Process Heating Magazine

Reprinted with permission from the October 2013 issue of Process Heating magazine



Temperature Sensors

extender, at that same port, can provide

an improved angle of vision that safely

allows for a far more comprehensive

scan. Thermal data and imagery can

clearly reveal areas of coking, usually

due to excessive temperatures, as well aslocations where there are tube restric-

tions or outright plugging.

An expert examination of furnaces

with a through-f lame thermal camera

can reveal whether refractory is dam-

aged, if flames have the right shape

and even dust deposits on the tubes,

which cause poor heat transfer and

typically lower the product tempera-

ture. Unlit burners are revealed as are

burners causing flame impingement on

the tubes. Oxidation development also

shows up on the thermal image — valu-

able knowledge as this area will eventu-

ally become a weak spot.

Infrared cameras also can provide

insight into process equipment by

valid at ing trad it ional temperature-

measurement devices. In furnaces,

thermocouples are installed at sev-

eral points to provide accurate tube

temperature readings. However, when

coking occurs around a thermocouple,

the sensor is liable to detach or pro-

vide inaccurate data. An inf rared scan

can quickly validate the accuracy of

a furnace tube temperature reading

provided by a thermocouple. Withthermal imaging cameras to validate

the thermocouple readings, refineries

can safely increase production with-

out safety concerns.

The data provided by thermocouples

is limited, however. Typically, only one

to three thermocouples per pass are

installed that supply data for a specific

point on the tube.

Thermal imaging cameras al low tem-

peratures to be read from every pixel

in the radiometric thermal image or

video taken during internal and external

furnace and maintenance inspections.

Coking can be detected over the extent

of the tube with suitable high-tempera-

ture infrared equipment because areas

with coke buildup show up as warmer

than other areas of the tube surface.

Potentially catastrophic problems that

could be easily missed when relying

solely on thermocouple data or visual

inspection are caught in the early stag-

es, preventing unscheduled shutdowns

and creating safer working conditions.

With the implementation of an ongoing

infrared inspection program, compara-

tive and trending analysis is possible,permitting changes in firing conditions

so that run times can be extended. As

an added benefit, the cameras can do

double duty in thermal inspections of

mechanical or electrical components.

How Through-FlameImaging WorksDesigned specifically to monitor all

types of furnaces, the flame filter on

cooled mid-wave thermal cameras

allows only thermal radiation with cer-

tain wavelength — 3.8 to 4.05 µm — to

pass through to the detector. Flames

emit much more thermal radiation at

some wavelengths than others, and at

certain points in the spectrum. A flame

emits hardly any thermal radiation at

all. Because everything but that spe-

cific range of the spectrum is filtered

out, the thermal imaging camera can

see through the flame and make tem-

Through-flame thermal imaging cameras can detect many equipment problems during operation.



Temperature Sensors

perature measurements even through

exceptionally hot flames.

Thermodynamically and hydraul i-

cally complex, process heaters incor-

porate turbulent convective gas flow in

addition to radiant heat from the flame,

refractory and other tubes, with tem-peratures fluctuating widely over time.

The highly sensitive cooled detectors

(NETD of less than 15 mK) utilized in

through-flame cameras permit these

heat transfer patterns to be visualized

— even minute temperature differences.

The real-time thermal video and still

image captures produced by these com-

pact, handheld infrared cameras can

reveal dangerous buildup on both the

interior (coking) and exterior (slag) of

furnace and boiler components that oth-

erwise would be obscured by flame, com-

bustion gases and dust. Images, generally

320 x 240 pixels in resolution, are viewed

through a high-resolution viewfinder and

on a color LCD display. Both radiometric

and nonradiometric infrared video can be

recorded directly to an internal memory

card along with visual digital camera

video and images. The traditional visual

images then can be associated with the

matching infrared footage. The stored

data can be transferred to a computer

via several output options and undergo

further processing in proprietary infrared

software programs to yield the most com-

plete picture of heat-related conditions

in the plant. Detachable heat-shields can

be added to reflect heat away from the

camera and camera operator, providing

increased protection.

3 Action Items for ReliableThrough-Flame ImagingNow that you understand how through-

flame imaging can help optimize plant

and process equipment operation, areview of the profiling process will help

you begin to plan your predictive main-

tenance plan.

1. Gather All the Necessary

Information

Before beginning any furnace inspection,

it is important to acquire as much pro-

cess information as possible, including:

Infrared energy is longer than visual light. For the purposes of furnace

inspection, there are two useable bands: mid-wave infrared and long-wave

infrared.

A quality, high-resolution camera with the proper flame filter will yield images

with the clarity to distinguish scale from coking. The visual image (left) shows

patchy external scale, not coking. The thermal image reveals that burner is

lit, but no flame is evident (middle). The thermal image reveals that several

burners are out (right).

A special notch filter narrows the spectral response of the detector so that it

nearly matches the peak transmission of the gas flame spectra, allowing the

user to see through flame.

Infrared Transmission Spectra – Gas Flame



Temperature Sensors

• Type of service (coking or fouling).

• Type of fuel (natural gas or

refinery fuel).

• Location of the heater unit in

the run.

• Inlet and outlet temperatures and

pressures.

• Whether the unit is prone to fouling.

Obtaining information on the target

to be imaged also is imperative. What is

its material composition? Tubing mate-

rial may vary from section to section,

and the acceptable temperature of coked

areas may vary accordingly. Ignorance of

that fact could result in a call for emer-

gency service when, in fact, the decoking

could have been performed in the regular

reduced production window.

2. Perform Baseline Scans

and Implement Continuous

Inspection Program

Thermal anomalies on furnace tubes

can be a function of actual hot tubes,

surface conditions such as scale and

oxidation, or a combination of several

factors. The thermographer must be

able to accurately evaluate the thermal

profile data and make a determination

on what is valid tube-metal tempera-ture data and what should be avoided.

A series of infrared scans over time can

help determine whether an anomalous

surface temperature is the result of

scaling or is actual coking on the tube

interior. Remember that consistency in

procedures always will facilitate com-

parative analysis and result in a better

understanding of the furnace.

Coked areas change in appearance

over time, usually increasing in tempera-

ture and size. If coke formation is sus-

pected in a furnace, it is much easier to

make a positive determination if previous

baseline data exists. A regular infrared

inspection program allows the extent of

the problem to be determined and pre-

emptive changes — firing configuration

changes or charge-rate reductions, for

example — to be made to mitigate the

issue. If decoking is necessary, post-infra-

red inspection can document effective-

ness. And if the decoking is a steam/air

process, infrared can be used to monitor

and control the actual procedure.

3. Understand Input Parameters,

Particularly Emissivity

Determining the actual tube-metal

temperature in some furnaces can be

extremely difficult. Be certain that the

area being measured is a valid target

— that is, tube metal and not scale or

other surface anomaly — and know the

emissivity of that target. Be certain of

background temperature based on field

measurement or furnace data. Correct

for interference from furnace atmo-

sphere. In very adverse atmospheres,

this is valid for a relatively limited area

and is based on a snapshot in time. Ifpossible, include a known valid ther-

mocouple or external reference ther-

mocouple in the image. Take multiple

images of the subject area and attempt

to minimize the interference. Minimize

the temperature span to determine the

extent of the flame interference. This

will be a factor of fuel type (natural gas

vs. ref inery gas), burner type, fir ing rate,draft, and infrared camera and filter.

To calculate temperatures correctly,

you need to know the emissiv ity of

both the material under regard and

the background. The emissivity of the

tube surface can be difficult to deter-

mine and typically is derived from two

sources correlated to thermocouple

measurements. To achieve the highest

degree of accuracy, some companies

have designed probes fitted with ther-

mocouples known to be accurate that

can be positioned in the furnace next to

the tube under regard.

In conclusion, furnace and boiler

equipment is prone to failure — cok-

ing that plugs the inside of tubes and

impedes product flow, slag buildup

on the outside of tubes, clinker dam-

age, under- and overheating, flame

impingement on tubes due to burner

misalignment, and product leaks that

ignite and cause serious damage to the

equipment. These failures cause more

than quality problems: They also can

shut down an entire process line.

Through-f lame thermal imag -

ing cameras can detect most of these

equipment problems during operation

— and at an early stage — so failures can

be prevented. This allows an orderly

shutdown and component replacement,

thereby reducing maintenance costs

and production losses.*

Paul Czerepuszko is a director of busi-

ness development at FLIR Systems,

Inc., a supplier of infrared technologyfor industrial applications. For more

information, call 603-324- 7778 or

visit www.flir.com.

The thermal image reveals that thermocouples may not be telling the

whole story (left). In another application, thermal overview reveals areas of

overheating (middle); the infrared image shows that one pass is much hotter

than the other (right).

through flame thermal cameras

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