module 7 - flame safeguard principles

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Module 7. Flame SafeguardPrinciples

Prepared and Presented By :

Youdhiyan [email protected]

+62-811886021

POWER PLANT WORKSHOP PLN PuslitbangBogor, 5-8 May 2014

5/5/2014 Flame Safeguard - Principles 2

Flame Safeguard ?

Consists of a Flame scanning device and Amplifiersystem to monitor the Burner flame in acombustion chamber to assure safe and reliableoperation

FLAME

SCANNER

BMS

SCANNER

CABLE

FLAME

AMPLIFIER

CUSTOMER

INTERFACE

POWER
mailto:[email protected]:[email protected]


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What is a Burner ?A device to convert fossil fuel into usableheat energy


What is combustion ?Combustion, or burning, is the combinationof Oxygen with Fuel, resulting in the releaseof Heat


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What is a Flame ?

Flame FrontCombustion reaction occurs at a ratethe produces visible radiation, fuel-air

mixture and combustion process.

Flame EnvelopeContour along which the combustionstarts, dividing line between the fuel-air mixture and the combustionprocess.


Principles used for Flame Detection

Temperature of gases in the flame

Visible Light radiation

Infrared Light radiation

Ultra-violet Light radiation

Ionized gas molecules in the flame

= Ability to conduct current

Flame Flicker frequency


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Flame Radiation

Detection of flame radiation is the mostwidely used method for flame detection

Flames emit radiation along a wide bandof the electromagnetic spectrum, calledthe Flame Spectrum

The Flame Spectrum is made up of ultra-violet, visible, and infra-red radiation


What is Flame Safeguarding System ????

A single input for a BMS!

Fireye Flame Detector

Detector Signal

Output to BMS

Flame Radiation


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Flame Safeguarding Definition

A system which is detects thepresence or absence of a flame in

burner in order to preventuncontrolled combustion .

Every Burner

Needs A Detector!!!


What is the Characteristics ofa Flame ??

Its HOT

It expands the gases

It makes By-Products There is Ionization in

and around it

It emits radiation Visible light

Infrared

Ultraviolet

D.Shunn


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Types of Radiation in Combustion

UV = least available(1%) 1st third of flame:Blue for gas

Visible = 10% of flameBlue /orange /yellow for gas

Bright yellow for oil.

Infrared = 90% of flame2/3 of flame = Red


What is UV and IR signal ?

A bundle of energy focused at a specific wavelength


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Relation between Fuels and Radiant Energy

Fuel Infrared Visible UV

Oil (Pressure) High High Medium

Oil (Steam) High High Low

Gas (Air Premix) Low Low High

Gas (No Premix) Medium Medium Medium

Pulverized Coal High Medium Low


Methods of FlameDetection

Visible Light. . . . . . . . . . . .Photocells

Infrared (IR) . . . . . . . . . . . LeadSulfide (typically) (InGa As)

Ultraviolet (UV) . . . . . . . . . UVTube (gas filled) UV Cell (solidstate: Super Blue Silicon)

Flame Rod . . . . . . . . . . . . .KANTHAL Rod


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What is Flame Amplifiers ??

Scanner outputElectrical pulses

Fireye Scanner

Output to System

400 Threshold on

Operating Range300 Pre-Alarm250 Threshold off

-----


Conventional Ultraviolet Flame Detectors:

UV Tube ( Optical ) Vacuum Tube Method

Two tungsten ormolybdenumelectrodes in a gas-

backfilled quartzvacuum tube

850 to 950 volts ACapplied from step-uptransformer in thescanner

Gas Discharge DeviceConducts in presenceof UV radiation


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Ultraviolet Flame Detection- UV Tube

Vacuum Tube Method (continued) UV radiation passes through the quartz and

strikes the electrodes

A small current flows between electrodes,ionizing the gas, resulting in characteristic blue

glow

The current flow (or avalanche) will be in smallbursts at a rate from 0 to 2,000 pulses persecond


UV Tube Operation


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Why you need a Self Checking Scanner ?

An Electro-mechanical shutter means ofblocking the flames radiation to thedetectorssensor.

This blocking action detects and alarms afaulty sensor.

Undetected faulty sensors can inadvertentlyhold in a fuel valve, although a flame is notpresent.


Disadvantages of UV Tube Detectors

Requires high AC Voltage

Limited Life Time

Signal Deteriorates with time

Can fire continuously

Electro-Mechanical Shutter Failures leading to spurious shutdown of Boilers

UV Radiation absorbed by moisture (steam)

Low Discrimination capabilities in a Multi Burner Environment.

Respond to non-flame sources

Spark Ignition

Welding Arcs

Halogen light

X-Ray exposure


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UV Tube Flame Scanner

Disadvantages

Low DiscriminationCapabilities

Precautions / UV Blockers Water vapor (FGR)

Atomizing steam Unburned fuel

Some process gases (H2S, NH3)


Today's conditions present a challenge , a good scanner mustnot only able to detect the absence or presence of targeted

flame BUT also Flame DISCRIMINATION .

Whatis Flame Discrimination ???

4


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Flame Discrimination Defined

Detector

DISCRIMINATION :

The ability to distinguish the target flame from allother flames in the furnace and the Background

Background Flame

Target Flame

Field ofView


Conventional DiscriminationMethods

1. Scanner mounting and aiming

2. Controlling the optical field of view 3. Adjustments within the scanner

4. Adjustments within the amplifier


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Discrimination Methods

1. Scanner mounting and aiming


Discrimination MethodsScanner Mounting and Aiming

Flame must be in front of the Scanner


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Scanner Mounting and Aiming

Target flame must fill the scanners field ofview



2. Controlling the optical field of view

Installing orifices (field stops) or extendingscanner sight pipe


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3. Adjustments within the scanner UV tube position

Scanner GAIN

Flame flicker target frequency



4. Adjustments within the amplifier

Adjustable sensitivity (fixed flame relay threshold)

Adjustable flame relay threshold (fixed sensitivity)


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Optical Flame Scanners -

Discrimination capabilities -Flicker Flame


What is Flame Flicker ?

A Flame is a combination of small controlled explosionswhen Fuel and Air Mixes.

The PULSATING behaviour of the explosions is FlameFlicker

Each Fuel, in combination with a Burner design has itsown Bandwidth of Flicker Frequency

The Flicker Frequencies in Flames can be found from

5 Hz to well over 200 Hz

The heavier the fuel, the lower the Flicker Frequency


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Flame Flicker Frequency :

Characteristics

The Flicker Frequency varies with differentregions of the Flame .

Theoretically, the first 1/3 of the Flameproduces the highest Flicker Frequencies (atlikely the lowest Amplitude)

The final 2/3 of the Flame produces theLowest Flicker Frequencies (and the highestAmplitude)


Flicker Frequency

Line of Sight

40 Hz

120 Hz40 Hz

Background

TargetFlame

FlickeringFlame

Flame Signal FlickerFrequency

High Amplitude-Low Frequency

Low Amplitude-High Frequency


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Bandpass Filters

Allows you to tune into the frequency of the flame

FFT

Background Signal

Target Flame Signal

Bandpass Filter


module 7 - flame safeguard principles

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