Technical Description In general most of the burners which fi nd

their application in the sulphur recovery unit

(SRU), are furnished with two fl ame detec-

tors. � e goal of these detectors is to monitor

continuously whether there is a fl ame pres-

ent inside the burner. In the event that the

fl ame would go off , the fl ame detectors will

immediately lose their signal so that the acid

gas and air valves in the supply lines can be

automatically shut off by the emergency shut-

down system (ESD). � e system is designed

to ensure that an essential part of the safety

aspect of the SRU plant is met and that risk of

explosions is reduced.

We see many diff erent detectors which are

applied in the SRU: ultra violet detectors (UV),

infrared detectors (IR) and detectors with

a combination of UV and IR receivers. � e

design philosophy of all these detectors is that

the radiation receivers measure absolute radi-

ation signals. For many combustion processes

these detectors provide suffi cient accuracy to

distinguish if the fl ame is on or off , e.g. oil and

gas fi ring furnace burners. However fl ames

in acid gas burners are not easy to detect in

a reliable way with these detectors since the

combustion of acid gas does not provide

enough UV radiation to detect the fl ame with

a UV detector. Although acid gas fl ames can

be perfectly detected with an IR detector,

this does not result in a reliable safeguarding

method as the hot refractory lining around

the fl ame also emits suffi cient IR radiation to

keep the detector on!

� erefore the main question is, is there a

detector available which can detect the acid

gas fl ame properly without having problems

discriminating between IR from the fl ame

and the refractory? Luckily yes there is, the

answer is the DFD fl ame detector! DFD is an

abbreviation of Duiker Flame Detector and

this detector has been specifi cally designed to

deal with the above diffi culties.

Before we explain how the system inter-

nally works we would like to give you as the

reader a somewhat better understanding of

what happens inside the fl ame. � e goal of

the burner is to create an intense mixture

between the acid gas and the combustion

air, so that the Claus reactions can optimally

take place inside the fl ame zone of the burner

and the main combustion chamber. In this

mixture the oxygen reacts with the acid gas to

form sulphur dioxide, during which electro-

magnetic radiation is emitted with a specifi c

wavelength. One of the characteristics of this

DUIKER FLAME DETECTOR (DFD)

Improved safety realized with the DFD fl ame detector

Duiker Combustion Engineers

Duiker Combustion Engineers b.v.

Turfschipper 91

2292 JK Wateringen

� e Netherlands

Postal Address:

P.O. Box 114

2290 AC Wateringen

� e Netherlands

Phone: +31 (0)174 282 700

Fax: +31 (0)174 298 220

E-mail: sales@duiker.com

Website: www.duiker.com

electromagnetic radiation is that the intensity

modulates continuously. As soon as a reaction

takes place, the radiation intensity suddenly

increases to a maximum level and decreases

directly afterwards. � is happens on a large

scale in the fl ame zone where millions of

reactions take place. � is radiation intensity

is thus a measure of the temperature and the

most reliable method to guarantee that the

fl ame is present.

� is brings us back to the essence of how the

fl ame will be detected with the DFD detector.

� e DFD detector makes use of two elements

behind a lens system, which each monitor the

fl ame at a specifi c spot. � e radiation intensity

of these two spots inside the fl ame vary con-

tinuously, as the fl ame is a turbulent area in

which the reaction intensity pulsates. � e re-

sult is that the measured signals fl uctuate with

respect to each other. � rough monitoring

the diff erence between these two signals, we

in the most reliable method available, verify

the presence of the fl ame. � rough using the

diff erential of two signals, we eliminate the

problem of the radiation component emitted

by the hot refractory. In other words: if there

is no fl ame, there is no diff erential in radiation

between the two measurements, with the

result that the detector signal will be zero.

Swivel mount� e swivel mount can be found between the

fl ame detector and the ball valve. � e function

of this device is to aim the view opening of the

detector exactly at the centre of the opening

to the combustion area. Small misalignments

of the detector lead to a weaker detector out-

put signal, since the detector will now observe

the inner surface of the nozzle or refractory

lining, rather than the combustion area.

In the swivel mount a special barrier glass is

incorporated to separate the detector from

the combustion process. � e barrier glass is

continuously purged with a small fl ow of ni-

trogen to avoid sulphur from freezing on the

barrier glass and to keep the nozzle free from

sulphur build up. � e eff ective design of the

small purge fl ow channels inside the swivel

ensure improved visibility through the barrier

glass over long periods of time.

Sun screenMany failures of electrical equipment, such as

fl ame detectors, are due to overheating of the

internal electrical components. � e maximum

temperature of the fl ame detector at which

safe operation is guaranteed is limited to 70°C.

Although the ambient temperatures will be

lower, direct sun radiation can easily lead to

higher temperatures inside the explosion

proof housing. � is is the reason that the

fl ame detector will be supplied with its own

sun screen to avoid direct exposure to sun ra-

diation. � e sun screen can be easily removed

from the assembly allowing the operators to

carry out maintenance.

SoftwareWith the supplied software, the detector

parameters can be changed and made more

selective for various types of fuels, such as

refi nery fuel gas, acid gas, natural gas and

syngas. � is feature enables interchangeability

and thus to keep just one detector in stock as

a spare part, for replacing any fl ame detector

in your plant. As a standard, the fl ame scan-

ner comes pre-programmed, specifi cally for

the gas composition which the burner has

been designed for.

Compact detector

Technical DataType of detector DFD fl ame detector with built in amplifi er

Power supply 24 V DC / 6 W

Current consumption approx. 300 mA

Safety level SIL 3

Current output 0(4)...20 mA (Ra < 250 Ohm)

Nozzle size on burner 2’’

Dimension (Length x Diameter) 223 x 120 mm

Class of protection IP 65 ATEX Zone 1 - II2G EEx d IIC T6

Weight of total assembly 25 kg (detector+swivel+ball valve+sun screen)

Nozzle Ball valve Swivel mount Detector

Sun screen