Welcome to Welcome to Fired Heater Training!Fired Heater Training!

The course is designed to give The course is designed to give you some background you some background information needed to operate a information needed to operate a fired heaterfired heater

AgendaAgenda

1.1. IntroductionIntroduction

2.2. Air/Fuel RatiosAir/Fuel Ratios

3.3. Fundamentals of BurnersFundamentals of Burners

4.4. Fundamentals of FurnacesFundamentals of Furnaces

5.5. Furnace Tuning and Use of AnalyzerFurnace Tuning and Use of Analyzer

6.6. NOx and Advanced Burner DesignNOx and Advanced Burner Design

7.7. Field Tuning of HeatersField Tuning of Heaters

8.8. Q & A and Wrap-upQ & A and Wrap-up

Heater and Burner OperationHeater and Burner Operation

Course ObjectiveCourse Objective

• To ensure that everyone fully To ensure that everyone fully understands how burners and understands how burners and heaters work.heaters work.

Course TopicsCourse Topics

• Combustion EssentialsCombustion Essentials

• Basic Burner DesignsBasic Burner Designs

• Furnace TypesFurnace Types

• DraughtDraught

• Heater TuningHeater Tuning

• Low NOx Burner DesignsLow NOx Burner Designs

Combustion EssentialsCombustion Essentials

What is Combustion?What is Combustion?

• A chemical reaction between fuel A chemical reaction between fuel and oxygen producing heat.and oxygen producing heat.

• Air is usually the source of oxygen.Air is usually the source of oxygen.

• The chemical reaction produces “flue The chemical reaction produces “flue gases” gases”

What Is Required For What Is Required For Combustion?Combustion?

Three Elements:Three Elements:

FuelFuel

AirAir

Source of IgnitionSource of Ignition

Fuel ComponentsFuel Components

• Gas, Oil and Coal are all basically a Gas, Oil and Coal are all basically a mix of Hydrocarbons.mix of Hydrocarbons.

• During combustion these break down During combustion these break down progressively as some parts burn progressively as some parts burn more easily.more easily.

• The most important components are The most important components are Carbon and Hydrogen compounds.Carbon and Hydrogen compounds.

Other ComponentsOther Components

• In addition to the Carbon and In addition to the Carbon and Hydrogen many fuels contain Sulphur.Hydrogen many fuels contain Sulphur.

• Sulphur also burns but produces Sulphur also burns but produces hazardous products.hazardous products.

• Liquid and solid fuels can contain Liquid and solid fuels can contain other non-combustibles which form other non-combustibles which form ash.ash.

• Nitrogen may be present as a gas or in Nitrogen may be present as a gas or in compound form in liquid/solid fuels.compound form in liquid/solid fuels.

Chemical FormulasChemical Formulas

• In formulas we will use the following basic In formulas we will use the following basic componentscomponents

• Carbon = CCarbon = C• Hydrogen = HHydrogen = H22

• Oxygen = OOxygen = O22

• Nitrogen = NNitrogen = N22

• Water = HWater = H22OO• Carbon Dioxide = COCarbon Dioxide = CO22

• Methane = CHMethane = CH44

Note on CalculationsNote on Calculations

• Each component in a formula is a Molecule Each component in a formula is a Molecule (of gas)(of gas)

• A Molecule of any gas occupies the same A Molecule of any gas occupies the same VolumeVolume

• The number of Molecules is therefore the The number of Molecules is therefore the same as the number of Volumessame as the number of Volumes

• All calculations are therefore Volumetric, All calculations are therefore Volumetric, including measured Gas Analysesincluding measured Gas Analyses

• e.g. 2 CO = 2 volumes of COe.g. 2 CO = 2 volumes of CO

Examples Of Combustion For Examples Of Combustion For Typical Fuel ComponentsTypical Fuel Componentswith Oxygenwith Oxygen

C + OC + O22 CO CO22

2H2H22 + O + O22 2H 2H22OO

S + OS + O22 SO SO22

HeatHeat

• Where does the heat come from?Where does the heat come from?

HeatHeat

++

C + OC + O22 CO CO22

Oxygen in Air(by volume)

Air ≈ 21% O2 + 79% N2

Ratio1 O2 : 3.75 N2

But we don’t have Pure Oxygen available

The other main component in air is Water Vapour. In humid conditions this can be 5% or

more and affects efficiency

Examples Of Combustion Examples Of Combustion For Basic Fuel Components For Basic Fuel Components

with Airwith Air

C + OC + O22 + 3.75N + 3.75N22 CO CO22 + 3.75N + 3.75N22

2H2H22 + O + O22 + 3.75N + 3.75N22 2H 2H22O + 3.75NO + 3.75N22

S + OS + O22 + 3.75N + 3.75N22 SO SO22 + 3.75N + 3.75N22

Example - Combustion Of Example - Combustion Of MethaneMethane

CHCH44 + 2O2 + 7.5N + 2O2 + 7.5N22 CO CO22 + 2H + 2H22O + O + 7.5N7.5N22

+ Heat+ Heat

StoichiometryStoichiometry

• The technical term used to define the The technical term used to define the theoretical amount of air or oxygen theoretical amount of air or oxygen required for complete combustion of required for complete combustion of a fuel is the a fuel is the StoichiometricStoichiometric ratio. ratio.

• e.g. - for a typical Natural Gas the e.g. - for a typical Natural Gas the Stoichiometric Ratio is approximately Stoichiometric Ratio is approximately 10 volumes of Air to one of Gas.10 volumes of Air to one of Gas.

Excess AirExcess Air

• Because of many factors, including Because of many factors, including imperfect mixing, extra air is always imperfect mixing, extra air is always needed to ensure complete needed to ensure complete combustion.combustion.

• The extra air above the The extra air above the Stoichiometric amount required is Stoichiometric amount required is known as the excess air.known as the excess air.

Stoichiometric Air Stoichiometric Air ExampleExample

CHCH44 + + 22OO22 + + 7.57.5NN22

COCO22 + + 22HH22O +O + 7.57.5NN22 + Heat+ Heat

Note – no Excess Oxygen in Flue GasNote – no Excess Oxygen in Flue Gas

Excess Air ExampleExcess Air Example

CHCH44 + (2 + + (2 + 0.40.4)O)O22 + (7.5 + + (7.5 +1.51.5)N)N22 CO CO22 + 2H+ 2H22O + 9N2 + O + 9N2 + 0.40.4OO22 + Heat+ Heat

0.40.4/2.0 = 0.2 or 20% excess air/2.0 = 0.2 or 20% excess air

0.4/(1+2+9+0.4/(1+2+9+0.40.4)=0.032 or 3.2%O)=0.032 or 3.2%O22 in in flue gases (wet)flue gases (wet)

0.4/(1+9+0.4/(1+9+0.40.4)=0.038 or 3.8%O)=0.038 or 3.8%O22 (dry) (dry)

Fuel Rich ExamplesFuel Rich Examples(Sub-stoichiometric)(Sub-stoichiometric)

3C + O3C + O22 2 CO + C 2 CO + C + heat+ heat

4H4H22 + O + O22 2 H 2 H22O + 2HO + 2H22 + heat + heat

Products include Combustible Gases Products include Combustible Gases and free Carbon (soot)and free Carbon (soot)

Some Dangers of operatingSome Dangers of operatingbelow Stoichiometricbelow Stoichiometric

• Flue gases contain combustibles.Flue gases contain combustibles.• When these gases find a supply of air When these gases find a supply of air

they will burn.they will burn.• If this happens in the convection tubes If this happens in the convection tubes

it can damage the tubes.it can damage the tubes.• Pockets of gas can build up in ducting Pockets of gas can build up in ducting

and cause explosions.and cause explosions.• Flames eventually back out of burners.Flames eventually back out of burners.

Heater Control Problems with Heater Control Problems with Sub-Stoichiometric CombustionSub-Stoichiometric Combustion

• Increasing fuel flow will reduce heat Increasing fuel flow will reduce heat to the process as more combustibles to the process as more combustibles are generated.are generated.

• This can lead to total loss of control This can lead to total loss of control and very high levels of unburned and very high levels of unburned gases in the heater.gases in the heater.

How do you get out of this How do you get out of this situation?situation?

• Do not open up air suddenly, as this Do not open up air suddenly, as this will cause unburned gas to burn will cause unburned gas to burn rapidly and possibly explosively.rapidly and possibly explosively.

• Reduce the gas flow slowly until Reduce the gas flow slowly until temperature starts to recover. This temperature starts to recover. This allows unburned gases to disperse allows unburned gases to disperse safely.safely.

Flue Gas AnalysisFlue Gas Analysis

• We control the excess air by measuring We control the excess air by measuring the excess Oxygen in the Flue Gasthe excess Oxygen in the Flue Gas

• The amount of excess air we need to The amount of excess air we need to know is what goes through the burners.know is what goes through the burners.

• The ideal sample point is at the exit of The ideal sample point is at the exit of the firebox, as there should be little or the firebox, as there should be little or no air leaks in this box.no air leaks in this box.

Sample Points

On-Line AnalysisOn-Line Analysis

• The oxygen analyser is located in the The oxygen analyser is located in the stack.stack.

• This analyser measures in the gas This analyser measures in the gas stream, so it indicates what we call a stream, so it indicates what we call a “WET” analysis since water vapour is “WET” analysis since water vapour is present.present.

• Air leaks between the firebox and Air leaks between the firebox and stack affect the readings.stack affect the readings.

Portable (off-line) AnalysisPortable (off-line) Analysis

• Portable analysers can be used to check Portable analysers can be used to check gases wherever a test point is available.gases wherever a test point is available.

• They draw a sample through a cold line so They draw a sample through a cold line so water condenses out. The analysis is water condenses out. The analysis is therefore known as “DRY”. This gives higher therefore known as “DRY”. This gives higher OO22 readings but standard compensations can readings but standard compensations can be made.be made.

• Analysers can also measure CO and NOx for Analysers can also measure CO and NOx for combustion efficiency and emissions checks.combustion efficiency and emissions checks.

Flue Gas LossesFlue Gas Losses

• The gases passing out of the stack The gases passing out of the stack are above the ambient are above the ambient temperature, so they carry unused temperature, so they carry unused heat into the atmosphere.heat into the atmosphere.

• Increasing Flue gas temperature Increasing Flue gas temperature increases these losses.increases these losses.

• Increasing Excess air increases the Increasing Excess air increases the amount of flue gases, giving even amount of flue gases, giving even more loss. more loss.

Units Of Heat FlowUnits Of Heat Flow

• British Thermal UnitBritish Thermal Unit BTU/hrBTU/hr

• KilocalorieKilocalorie 1 KCal/hr=3.938 BTU/hr1 KCal/hr=3.938 BTU/hr

• KiloJouleKiloJoule 1 KJ/hr = 0.9478 Btu/hr1 KJ/hr = 0.9478 Btu/hr

• KilowattKilowatt 1 KW = 3,413 BTU/hr1 KW = 3,413 BTU/hr(1W = 1J/s)(1W = 1J/s)

GrossGross and and NetNet Heating Heating ValueValue

• Higher (Gross) Heating Value (HHV):Higher (Gross) Heating Value (HHV):

The total heat theoretically available The total heat theoretically available from combustion of a fuel. from combustion of a fuel.

Lower (Net) Heating Value (LHV):Lower (Net) Heating Value (LHV): the the HHV less the latent heat used to HHV less the latent heat used to convert the produced water to convert the produced water to vapour.vapour.

Heating Values (Btu/FtHeating Values (Btu/Ft33))

LHVLHV HHVHHV----------------------------------------------------------------------------------------------------------------Methane (CHMethane (CH44)) 911911 10121012

Ethane (CEthane (C22HH66)) 16221622 17731773

Propane (CPropane (C33HH88)) 23222322 25242524

Butane (CButane (C44HH1010)) 30183018 32713271

Hydrogen (HHydrogen (H22)) 275275 325325

Carbon Monoxide (CO)Carbon Monoxide (CO) 321321 321321

Wobbe IndexWobbe Index

• This is a factor used in the design of This is a factor used in the design of Premix Burners only.Premix Burners only.

• It is based on Calorific Value and It is based on Calorific Value and Density.Density.

• If 2 gases have the same Wobbe If 2 gases have the same Wobbe index they should work equally well index they should work equally well in the same premix burner. in the same premix burner.

Products Of CombustionProducts Of Combustion

• Water Vapour - HWater Vapour - H22OO

• Carbon Dioxide - COCarbon Dioxide - CO22

• Sulphur Dioxide - SOSulphur Dioxide - SO22, SO, SO33

• Carbon Monoxide - COCarbon Monoxide - CO

• Unburned Hydrocarbons - UBCUnburned Hydrocarbons - UBC

• Nitrogen Oxides - NO, NONitrogen Oxides - NO, NO2 2

Flame SpeedFlame Speed

• Another important factor in Another important factor in Combustion is the Flame SpeedCombustion is the Flame Speed

• Each gas burns in air at a particular Each gas burns in air at a particular speed under reference conditionsspeed under reference conditions

• A stable flame is produced when the A stable flame is produced when the Flame Speed and gas/air mixture Flame Speed and gas/air mixture velocity correspondvelocity correspond

Typical Flame Speeds Typical Flame Speeds (ft/sec)(ft/sec)MethaneMethane 1.481.48

EthaneEthane 2.302.30

PropanePropane 2.782.78

ButaneButane 2.852.85

HydrogenHydrogen 9.309.30

Carbon MonoxideCarbon Monoxide 1.701.70

Other Gas CharacteristicsOther Gas Characteristics

• All fuel gases will burn within a mixture All fuel gases will burn within a mixture range both below Stoichiometric and range both below Stoichiometric and above Stoichiometric.above Stoichiometric.

• The “flammability range” varies between The “flammability range” varies between gases, and is another indicator of how gases, and is another indicator of how easily a gas will burn.easily a gas will burn.

• Gas density affects burner design as Gas density affects burner design as heavier gases have higher pressure drops heavier gases have higher pressure drops though gas jets.though gas jets.

Sowhyhave

burners?

Basic Objects of a BurnerBasic Objects of a Burner

• The burner must mix the fuel and the The burner must mix the fuel and the air effectively to ensure complete air effectively to ensure complete combustion.combustion.

• The flame must be stabilised in a The flame must be stabilised in a fixed position so that its heat can be fixed position so that its heat can be absorbed effectively.absorbed effectively.

• The flame shape must be controlled The flame shape must be controlled to suit its working environment.to suit its working environment.

Process Heater Process Heater BurnersBurners

Basic Burner TypesBasic Burner TypesNatural DraughtNatural Draught

• PremixPremix

• Raw Gas (Nozzle Mix)Raw Gas (Nozzle Mix)

• Combination Oil & GasCombination Oil & Gas

Natural DraughtNatural Draught

• Air is pulled through the burner by draft Air is pulled through the burner by draft created by the heat in the furnace and created by the heat in the furnace and stack (explained in a later section).stack (explained in a later section).

• Since air velocity is low we need to use Since air velocity is low we need to use the energy in the gas (typically at 1 the energy in the gas (typically at 1 barg) to improve the gas/air mixing.barg) to improve the gas/air mixing.

• We have 2 basic ways we do this.We have 2 basic ways we do this.

Premix BurnersPremix Burners

• Fuel pressure drop occurs in the gas jet.Fuel pressure drop occurs in the gas jet.• Gas velocity in venturi induces part of Gas velocity in venturi induces part of

the air so air flow adjusts with gas flow.the air so air flow adjusts with gas flow.• Fuel and primary air mix before the Fuel and primary air mix before the

nozzle.nozzle.• Secondary air mixes in burner throat.Secondary air mixes in burner throat.• All domestic gas burners are premix, All domestic gas burners are premix,

including cooking appliancesincluding cooking appliances..

Basic Burner TypesBasic Burner TypesPre-Mix Heater BurnerPre-Mix Heater Burner

GAS NOZZLE

Pre-Mix Burner AdvantagesPre-Mix Burner Advantages

• Large fuel gas discharge orifice.Large fuel gas discharge orifice.

• Large ports in firing nozzle.Large ports in firing nozzle.

• Small flame volume.Small flame volume.

• Automatic variation of air flow with Automatic variation of air flow with varying fuel rates.varying fuel rates.

Premix Burner Premix Burner DisadvantagesDisadvantages

• Can only accept small variations in Can only accept small variations in gas quality without adjustment (n.b. gas quality without adjustment (n.b. unless Wobbe Index is maintained)unless Wobbe Index is maintained)

• Limited turndown.Limited turndown.• Difficult to adapt for combination Difficult to adapt for combination

gas/oil firing (but not impossible)gas/oil firing (but not impossible)• Maintenance more difficult.Maintenance more difficult.• Hard to reduce NOx.Hard to reduce NOx.

Raw Gas BurnersRaw Gas Burners(Nozzle Mix)(Nozzle Mix)

• Gas and air are kept separate until Gas and air are kept separate until discharged into the combustion zone.discharged into the combustion zone.

• Fuel pressure drop occurs at the Fuel pressure drop occurs at the combustion zone.combustion zone.

• The energy in the gas helps mix fuel The energy in the gas helps mix fuel and air.and air.

Basic Burner TypesBasic Burner TypesNozzle Mixing Gas BurnerNozzle Mixing Gas Burner

GAS NOZZLE

FLAME HOLDER

BURNER THROAT

Basic Burner TypesBasic Burner TypesRaw GasRaw Gas

Zeeco Burner for UnitedZeeco Burner for United

Test Burner FlameTest Burner Flame

Nozzle Mixing Gas Burner Nozzle Mixing Gas Burner AdvantagesAdvantages

• A high turndown ratioA high turndown ratio

• No possibility of flashbackNo possibility of flashback

• The ability to burn a wide variety of fuels The ability to burn a wide variety of fuels with differing heating valueswith differing heating values

• Flame shape can be controlled as required Flame shape can be controlled as required by gas tip and tile design.by gas tip and tile design.

• Can be adapted many ways to reduce NOxCan be adapted many ways to reduce NOx

Nozzle Mixing Gas Burner Nozzle Mixing Gas Burner DisadvantagesDisadvantages

• Small fuel discharge portsSmall fuel discharge ports

• "Large" flame volume"Large" flame volume

• Fuel/air ratio is dependent on Fuel/air ratio is dependent on operatorsoperators

Raw Gas CombinationRaw Gas Combination

• Designed to burn gas and fuel oil either Designed to burn gas and fuel oil either separately or together.separately or together.

• Inner tile stabilizes oil flame with Inner tile stabilizes oil flame with controlled primary air.controlled primary air.

• Gas burners stabilize in secondary tile Gas burners stabilize in secondary tile throat.throat.

• Oil guns remove easily for cleaning while Oil guns remove easily for cleaning while gas burners are in service.gas burners are in service.

• Gas burners can also be maintained while Gas burners can also be maintained while oil burners are in service.oil burners are in service.

Combination Natural Draught Combination Natural Draught

Gas and Oil BurnerGas and Oil BurnerGAS TIPSPRIMARY

TILE

Combination Burner Combination Burner LimitationsLimitations

• Oil guns need frequent maintenance.Oil guns need frequent maintenance.

• Oil firing problems can cause fouling Oil firing problems can cause fouling of gas tips.of gas tips.

• Total capacity of burner is set by air Total capacity of burner is set by air flow available, so firing gas and oil at flow available, so firing gas and oil at the same time requires both fuels to the same time requires both fuels to be limited to give correct total Heat be limited to give correct total Heat Flow.Flow.

Forced Draught BurnersForced Draught Burners

• Basically similar to Natural Draught Raw Basically similar to Natural Draught Raw Gas Burners (including Combination Gas Burners (including Combination Oil/Gas Burners).Oil/Gas Burners).

• Higher air velocities give better mixing Higher air velocities give better mixing and smaller flames.and smaller flames.

• Air can be preheated, using various types Air can be preheated, using various types of heat exchanger.of heat exchanger.

• Flames are hotter, giving higher rates of Flames are hotter, giving higher rates of heat transfer.heat transfer.

Gas pilotsGas pilots

• Most process burners use a pilot to Most process burners use a pilot to provide the basic source of ignition.provide the basic source of ignition.

• Pilot is usually fully premixed.Pilot is usually fully premixed.

• Pilot can be ignited manually or have Pilot can be ignited manually or have a built-in spark ignition.a built-in spark ignition.

• Some pilots have flame rods to check Some pilots have flame rods to check flame is alight.flame is alight.

Pilot BurnerPilot Burner

Burners are only part of Burners are only part of the systemthe system

FurnacesFurnaces

• A furnace is basically an insulated box A furnace is basically an insulated box lined with tubes containing the process lined with tubes containing the process fluid.fluid.

• We fire burners inside the box to heat the We fire burners inside the box to heat the tubes by a mixture of radiation and tubes by a mixture of radiation and convection heat transfer.convection heat transfer.

• There are many different furnace designs There are many different furnace designs depending on the process application and depending on the process application and the companies involved.the companies involved.

• The next 2 slides show some basic types.The next 2 slides show some basic types.

Heater Types

Heater Types

Heater Parts

Burner LocationsBurner Locations

• Depending on the heater layout burners Depending on the heater layout burners may be installed up-fired, side-fired, end-may be installed up-fired, side-fired, end-fired and down-fired.fired and down-fired.

• Most heaters are up-fired, except for Most heaters are up-fired, except for special types such as Ethylene Crackers special types such as Ethylene Crackers and Reformers.and Reformers.

Heat TransferHeat Transfer(a) - Radiation(a) - Radiation

• In the firebox we get heat transferred In the firebox we get heat transferred initially by direct radiation from the initially by direct radiation from the flames to the tubes.flames to the tubes.

• Additional heat is radiated to the back Additional heat is radiated to the back of the tubes from the hot furnace walls.of the tubes from the hot furnace walls.

• Radiant efficiency depends on the Radiant efficiency depends on the emissivity of the flame and of the tube emissivity of the flame and of the tube surfaces, plus the temperatures of both.surfaces, plus the temperatures of both.

Heat TransferHeat Transfer(b) - Convection(b) - Convection

• Hot gases passing over tube surfaces Hot gases passing over tube surfaces heat the tubes mainly by Convection.heat the tubes mainly by Convection.

• Away from the Flames most heat is Away from the Flames most heat is transferred by Convection.transferred by Convection.

• A Convection Bank is a section of the A Convection Bank is a section of the Heater where Radiation is Heater where Radiation is insignificant, normally just below the insignificant, normally just below the Stack.Stack.

Process FlowProcess Flow

• In most heaters the coolest fluid is In most heaters the coolest fluid is exposed to the coolest heat source.exposed to the coolest heat source.

• Fluid passes first through the Fluid passes first through the Convection Tubes, where available.Convection Tubes, where available.

• Fluid exits near the burners.Fluid exits near the burners.

Furnace DraughtFurnace Draught

• Natural Draught burners depend on the air Natural Draught burners depend on the air flow being created by the difference in air flow being created by the difference in air pressure between the inside of the heater pressure between the inside of the heater and outside.and outside.

• The reason the pressure is different is that The reason the pressure is different is that the air inside the heater is hotter than the the air inside the heater is hotter than the air outside.air outside.

• Since hot air is lighter it rises and reduces Since hot air is lighter it rises and reduces the pressure inside the heater.the pressure inside the heater.

Furnace DraughtFurnace Draught

• Typically the temperature in a Typically the temperature in a firebox is 500 - 800firebox is 500 - 800°C.°C.

• At this temperature the draft At this temperature the draft increases by about 2.5 mm water increases by about 2.5 mm water for every 3 metres of firebox height.for every 3 metres of firebox height.

• If we have a convection section we If we have a convection section we need more draught above it to need more draught above it to overcome the pressure drop through overcome the pressure drop through the tube bank.the tube bank.

10ft column of cold air

=

0.15“w.g.

10ft column of

air at 1000degF

=

0.05”w.g.

DRAUGHT = 0.1” /2.5 m.m.

Where Draught comes from

Furnace DraughtFurnace Draught

• The temperature in the stack is The temperature in the stack is lower, so we need more stack height lower, so we need more stack height to give us the required draught.to give us the required draught.

• The next chart shows what happens The next chart shows what happens in our heater with a convection bank in our heater with a convection bank and a stack damperand a stack damper

More on DraughtMore on Draught

• We need just enough air to burn our We need just enough air to burn our fuel properly.fuel properly.

• We do not want any air to get in We do not want any air to get in except through the burners.except through the burners.

• Any air which does not pass through Any air which does not pass through the burners just absorbs some of the the burners just absorbs some of the heat available and throws it away up heat available and throws it away up the stack.the stack.

Even more on DraughtEven more on Draught

• We need to keep draught negative all the We need to keep draught negative all the way through the heater.way through the heater.

• If we get a positive draught then hot gases If we get a positive draught then hot gases will find small holes and make them will find small holes and make them bigger.bigger.

• The critical point is usually at the top of The critical point is usually at the top of the firebox – look at the chart again.the firebox – look at the chart again.

• Many heaters have alarms for positive Many heaters have alarms for positive pressure.pressure.

Smallest

Draught

Heater TuningHeater Tuning

Before TuningBefore Tuning

• Before tuning make a full check of Before tuning make a full check of the burner conditions.the burner conditions.

• Ensure air doors are open equally Ensure air doors are open equally and gas valves open completely.and gas valves open completely.

• Check flame appearance / stability. Check flame appearance / stability. Close all peep doors.Close all peep doors.

• Keep in Radio touch with panel Keep in Radio touch with panel operators.operators.

Heater TuningHeater TuningDraught Calculation / SettingDraught Calculation / Setting

• For a typical heater as in the sketch we should For a typical heater as in the sketch we should have about 2 mm draught at the arch.have about 2 mm draught at the arch.

• If the heater is 10 metres high we can expect an If the heater is 10 metres high we can expect an additional 8-9 mm at the flooradditional 8-9 mm at the floor

• This gives us 12 mm total.This gives us 12 mm total.• Burners should have been designed for slightly Burners should have been designed for slightly

less than this theoretical draught, so we close the less than this theoretical draught, so we close the air doors to control the excess air through the air doors to control the excess air through the burners.burners.

• After we close the air doors we may need to adjust After we close the air doors we may need to adjust the stack damper to maintain 2 mm at the arch.the stack damper to maintain 2 mm at the arch.

• We check OWe check O22 and draught and repeat adjustments and draught and repeat adjustments until we get both figures correct.until we get both figures correct.

START

LOWHIGH

CHECK O2 CHECK O2

TARGET

LOWHIGH

CLOSE STACK DAMPER

OPEN AIR REGISTERS

HIGH LOW

CLOSE AIR REGISTERS

OPEN STACK DAMPER

RETURN TO START RETURN TO START

CHECK O2

HIGH

CLOSE AIR REGISTERS

RETURN TO START

LOW

OPEN AIR REGISTERS

RETURN TO START

GOOD OPERATION

CHECK DRAFT

ON TARGET

TARGET DRAFT1 to 3 mm

water

TARGET OXYGEN

2 – 3 %

HEATER ADJUSTMENT FLOW CHART

START

TARGET

CHECK O2

HIGH

CLOSE AIR REGISTERS

RETURN TO START

LOW

OPEN AIR REGISTERS

RETURN TO START

GOOD OPERATION

CHECK DRAFT

ON TARGET

TARGET DRAFT1 to 3 mm

water

TARGET OXYGEN

2 – 3 %

HEATER ADJUSTMENT FLOW CHART

Heater TuningHeater TuningDraught Control – GeneralDraught Control – General

• There are differences in approach depending on There are differences in approach depending on the type of burner, if the heater has a convection the type of burner, if the heater has a convection bank, and if there is a stack damper.bank, and if there is a stack damper.

• If the burners are in a plenum and have their own If the burners are in a plenum and have their own air doors then we have an extra adjustment point. air doors then we have an extra adjustment point. In such cases the individual burner air doors In such cases the individual burner air doors should be fixed open unless a burner is stoppedshould be fixed open unless a burner is stopped, , when they should be shut.when they should be shut.

• Sinclair has almost every combination possible, Sinclair has almost every combination possible, so we have to look at all the possibilities. so we have to look at all the possibilities.

Heater TuningHeater TuningDraught Control – Raw Gas Draught Control – Raw Gas BurnersBurners• Basically the Flowchart given applies to Basically the Flowchart given applies to

this type of burner.this type of burner.• If there is no stack damper we need to If there is no stack damper we need to

monitor the arch Oxygen – assuming monitor the arch Oxygen – assuming that the furnace leaks have been fixed.that the furnace leaks have been fixed.

• We must still check that Draught is We must still check that Draught is negative as putting too much air negative as putting too much air through burners can cause draft to go through burners can cause draft to go positive at the arch.positive at the arch.

Heater Start-upHeater Start-up

• During start-up draught is low as During start-up draught is low as temperatures are low.temperatures are low.

• Pilots self-inspirate so should work normally.Pilots self-inspirate so should work normally.• High excess air is used to control furnace High excess air is used to control furnace

temperature rise.temperature rise.• Individual Burner light-off should be done Individual Burner light-off should be done

with air doors nearly closed, so gas lights with air doors nearly closed, so gas lights more smoothly.more smoothly.

• Increase air opening slowly so burner heats Increase air opening slowly so burner heats up quickly and flame can stabilize properly.up quickly and flame can stabilize properly.

Heater TuningHeater TuningFuel Gas ValvesFuel Gas Valves

• Valves fitted upstream of each burner are for isolation only.Valves fitted upstream of each burner are for isolation only.• The only time a valve should not be opened fully is during The only time a valve should not be opened fully is during

light-off.light-off.• If any valves are not completely open then the burners are If any valves are not completely open then the burners are

not all firing at the same rate.not all firing at the same rate.• Gas pressure trip settings are established on the basis that Gas pressure trip settings are established on the basis that

valves are fully open.valves are fully open.• If a trip setting interferes during normal operation it should If a trip setting interferes during normal operation it should

be checked and may be changed, provided that the burner be checked and may be changed, provided that the burner stability is checked at the revised setting.stability is checked at the revised setting.

• If an individual burner gives a problem with the valve open If an individual burner gives a problem with the valve open then the problem should be investigated. On many burners then the problem should be investigated. On many burners there are small gas jets which can plug easily and will there are small gas jets which can plug easily and will affect flame stability. affect flame stability.

What can go Wrong?What can go Wrong?

1.1. OO22 falls too low – Temperature control is falls too low – Temperature control is lost as fuel does not burn – flames search lost as fuel does not burn – flames search for air and blow back through registers – for air and blow back through registers – “Puffing” “Puffing” – – CUT BACK ON FUEL FIRSTCUT BACK ON FUEL FIRST

2.2. Draught goes positive – gas leaks out of Draught goes positive – gas leaks out of any gaps and causes damage, but Oany gaps and causes damage, but O22 still still looks OK. Heaters should have an alarm looks OK. Heaters should have an alarm for high pressure.for high pressure.

Heater TuningHeater TuningFlue Gas AnalysisFlue Gas Analysis• In general a good target for excess Oxygen is 3%In general a good target for excess Oxygen is 3%• We need this level in the firebox – that should We need this level in the firebox – that should

mean we are getting the right amount of air mean we are getting the right amount of air through the burners.through the burners.

• Gas samples taken above convection banks Gas samples taken above convection banks include any air which leaks in around the tubes.include any air which leaks in around the tubes.

• These leaks should always be minimised as they These leaks should always be minimised as they affect the convection bank efficiency.affect the convection bank efficiency.

• In serious cases the leaks can exceed our 3% In serious cases the leaks can exceed our 3% target, so we could actually be firing below target, so we could actually be firing below stoichiometric.stoichiometric.

Heater TuningHeater TuningFlue Gas AnalysisFlue Gas Analysis• One way to check what is really happening One way to check what is really happening

is to also measure CO levels.is to also measure CO levels.• Typically it is safe to run with a maximum Typically it is safe to run with a maximum

of 50 ppm of CO in flue gases.of 50 ppm of CO in flue gases.• Older burners will start producing CO at Older burners will start producing CO at

around 2% excess Oxygen, so we have a around 2% excess Oxygen, so we have a good indication of the actual excess air good indication of the actual excess air through the burners.through the burners.

• On-line CO analysers allow burners to be On-line CO analysers allow burners to be run safely right down to their minimum run safely right down to their minimum achievable levels of excess air.achievable levels of excess air.

Heater TuningHeater TuningSummarySummary• We are aiming to have 3% excess oxygen We are aiming to have 3% excess oxygen in the in the

firebox.firebox.• We need all the burners in each heater to be We need all the burners in each heater to be

operating with the same amount of fuel and air.operating with the same amount of fuel and air.• This means air doors set equally, gas valves full This means air doors set equally, gas valves full

open, and clean gas tips.open, and clean gas tips.• If there is a stack damper, it should normally be If there is a stack damper, it should normally be

set to give a draft of 0.1” maximum at the heater set to give a draft of 0.1” maximum at the heater arch.arch.

• Some heaters may still need more draft to get Some heaters may still need more draft to get enough air through the burners.enough air through the burners.

Nitrogen Oxides (NOx) Nitrogen Oxides (NOx) FormationFormation

What is the Problem?What is the Problem?

• All combustion processes produce All combustion processes produce some Nitrogen Oxidessome Nitrogen Oxides

• In the atmosphere these oxides can In the atmosphere these oxides can form Nitric acid and fall as acid rainform Nitric acid and fall as acid rain

• They react with other gases and They react with other gases and sunlight, producing ozone and smogsunlight, producing ozone and smog

NONOxx Formation in Formation in CombustionCombustion

In ambient conditions In ambient conditions Nitrogen is an inert Nitrogen is an inert

gasgas

NONOxx Formation in Formation in CombustionCombustion

In hot flames we getIn hot flames we get

Thermal NOThermal NOxx

Fuel NOFuel NOxx

Thermal NOThermal NOxx

Created from atmospheric Nitrogen

Formation controlled by the breaking of N2 molecules to reactive nitrogen atoms by the supply of heat.

The N atoms then react with available Oxygen to form NO.

Thermal NOx formation rate is dependent on peak flame temperature and oxygen availability.

Controlling ReactionsControlling ReactionsThermal NOThermal NOxx

NOx definitionsNOx definitions

• The primary component formed in a flame is NO.The primary component formed in a flame is NO.• In the atmosphere this NO converts to NOIn the atmosphere this NO converts to NO22, which , which

is the harmful form.is the harmful form.• We define limits as NOx, where all measured We define limits as NOx, where all measured

levels are treated as having converted to NOlevels are treated as having converted to NO22..• Fired Heater limits are always expressed as the Fired Heater limits are always expressed as the

equivalent levels of NOx at 3% excess Oxygen.equivalent levels of NOx at 3% excess Oxygen.• EPA bases limits on lbs/million Btu rather than on EPA bases limits on lbs/million Btu rather than on

percentages.percentages.

Fuel NOxFuel NOx

• Some fuels contain ‘fixed’ Nitrogen as Some fuels contain ‘fixed’ Nitrogen as compounds. Liquids and Solids contain more of compounds. Liquids and Solids contain more of these than most gases.these than most gases.

• These compounds break down in the combustion These compounds break down in the combustion process and release the Nitrogen in a form which process and release the Nitrogen in a form which reacts easily to form NOx.reacts easily to form NOx.

• Nitrogen as a gas component is not significant.Nitrogen as a gas component is not significant.• NOx levels increase in direct proportion to the NOx levels increase in direct proportion to the

fixed Nitrogen in the fuel.fixed Nitrogen in the fuel.• NOx reduction techniques are also effective in NOx reduction techniques are also effective in

reducing Fuel NOx.reducing Fuel NOx.

How can we reduce NOx?How can we reduce NOx?

• Reduce the Flame TemperatureReduce the Flame Temperature

• Reduce the Oxygen availableReduce the Oxygen available

• Flue Gas TreatmentFlue Gas Treatment

Reducing Flame Reducing Flame TemperatureTemperature• Slow down fuel / air mixing Slow down fuel / air mixing • Inject cooler inert gases into the flame Inject cooler inert gases into the flame

(steam or recycled flue gas)(steam or recycled flue gas)• Increase the excess airIncrease the excess air• Reduce air below stoichiometricReduce air below stoichiometric

• Unfortunately all of these things conflict Unfortunately all of these things conflict with our requirement to get maximum with our requirement to get maximum heat from the flames to the processheat from the flames to the process

Reducing Available OxygenReducing Available Oxygen

• Reduce the excess airReduce the excess air

• Inject Inert gases into the flame to Inject Inert gases into the flame to reduce the oxygen concentration reduce the oxygen concentration available (recycled flue gas again)available (recycled flue gas again)

Low NOLow NOxx Burners Burners

• Staged AirStaged Air

• Staged Fuel Low NOStaged Fuel Low NOxx

• Internal Flue Gas RecirculationInternal Flue Gas Recirculation

• Combination of FeaturesCombination of Features

Staged Air Burner FeaturesStaged Air Burner Features

• Sub-Stoichiometric Primary Sub-Stoichiometric Primary CombustionCombustion

• Presence of CO and HPresence of CO and H22

• Flame Cooling in Second StageFlame Cooling in Second Stage

• Works with Gas or OilWorks with Gas or Oil

Staged Air BurnerStaged Air Burner

Staged Air Burners Staged Air Burners DisadvantagesDisadvantages

• Long FlamesLong Flames

• Complicated Air AdjustmentComplicated Air Adjustment

• Fuel Composition affects Fuel Composition affects PerformancePerformance

• Higher Excess Air RequiredHigher Excess Air Required

• Limited NOLimited NOxx Reduction Reduction

Staged Fuel Low NOStaged Fuel Low NOxx BurnersBurners

• Features / AdvantagesFeatures / Advantages

• DisadvantagesDisadvantages

Staged Fuel Burner FeaturesStaged Fuel Burner Features

1.1. Two Stage Fuel InjectionTwo Stage Fuel Injection

2.2. Good Heat Transfer from Good Heat Transfer from Secondary FlameSecondary Flame

3.3. Combustion Product InjectionCombustion Product Injection

4.4. "Compact Flame“"Compact Flame“

5.5. Tolerates gas variationsTolerates gas variations

1. Two stage fuel injection1. Two stage fuel injection

• Primary gas burns with high excess Primary gas burns with high excess air, cooling the flameair, cooling the flame

• Secondary gas mixes into flame Secondary gas mixes into flame above the burner, where oxygen above the burner, where oxygen level is low, so burns at a lower level is low, so burns at a lower temperaturetemperature

2. Heat Transfer from Secondary 2. Heat Transfer from Secondary FlameFlame

• Secondary Flame burns slowly above Secondary Flame burns slowly above the burnerthe burner

• Maintains uniform radiant Heat Maintains uniform radiant Heat transfer further up the furnacetransfer further up the furnace

3. Combustion Product 3. Combustion Product InjectionInjection

• Secondary gas pokers are above the Secondary gas pokers are above the burner tileburner tile

• They induce furnace gases into the They induce furnace gases into the Secondary flameSecondary flame

• Oxygen is reduced but temperature Oxygen is reduced but temperature increases, maintaining flame increases, maintaining flame dimensions welldimensions well

4. Compact Flame4. Compact Flame

• High excess air primary flame gives High excess air primary flame gives strong core to flamestrong core to flame

• Controlled secondary mixing and Controlled secondary mixing and recirculation keeps flame relatively recirculation keeps flame relatively compactcompact

5. Tolerates Gas variations5. Tolerates Gas variations

• Balance of primary to secondary gas Balance of primary to secondary gas is fixed (typically 30-40% primary)is fixed (typically 30-40% primary)

• Stoichiometry is not affected by fuel Stoichiometry is not affected by fuel propertiesproperties

Staged Fuel BurnerStaged Fuel Burner

Staged Fuel Burner Staged Fuel Burner DisadvantagesDisadvantages

• Turndown is limitedTurndown is limited

• Stability sometimes a problemStability sometimes a problem

• Small Gas Port SizeSmall Gas Port Size

• Effectiveness of NOx reduction Effectiveness of NOx reduction depends on fuel propertiesdepends on fuel properties

Low Emission BurnersLow Emission Burners

Combination of Staged Fuel Combination of Staged Fuel and Internal Flue Gas and Internal Flue Gas

RecirculationRecirculation

Low Emission BurnerLow Emission Burner

• Based on Staged Fuel BurnerBased on Staged Fuel Burner

• Primary Gas induces furnace gases Primary Gas induces furnace gases

into Primary Flameinto Primary Flame

• ““Zoning” of air in burner throat Zoning” of air in burner throat

gives high stabilitygives high stability

• Self compensates for gas changesSelf compensates for gas changes

Internal Flue Gas RecirculationInternal Flue Gas Recirculation

Flue Gas

Recycle Gas

Recycle Gas

Furnace

Burner

Flue Gas RecirculationFlue Gas Recirculation

• Hot flue gases rise fast up the centre of Hot flue gases rise fast up the centre of the furnacethe furnace

• Cooler gases travel down wall around Cooler gases travel down wall around tubes to the floortubes to the floor

• Gases have only Excess Oxygen and Gases have only Excess Oxygen and relatively low temperaturerelatively low temperature

• Lighter fuel gases run at higher pressure / Lighter fuel gases run at higher pressure / velocity, maintaining recirculation levelsvelocity, maintaining recirculation levels

Flame RetentionFlame Retention

• Primary gas induces ‘inert’ gas into the Primary gas induces ‘inert’ gas into the burner throat.burner throat.

• Flame holder mixes limited air with fuel Flame holder mixes limited air with fuel and recirculated gases to give a fuel-rich and recirculated gases to give a fuel-rich zone around the outside of the flame zone around the outside of the flame holder for high stabilityholder for high stability

• Balance of air passes through centre of Balance of air passes through centre of flame holder to mix into the primary flameflame holder to mix into the primary flame

Staged FuelStaged Fuel

• Staged fuel induces more inert gases Staged fuel induces more inert gases into flameinto flame

• Mixing is delayed by the fuel-rich Mixing is delayed by the fuel-rich zone on the outside of the primary zone on the outside of the primary flameflame

Internal Flue Gas Recirculation BurnerInternal Flue Gas Recirculation Burner

Relative Process Heater Burner NORelative Process Heater Burner NOxx Levels for Levels for Conventional and Low NOConventional and Low NOxx Burners Burners

• Conventional - 0.12 # NOConventional - 0.12 # NOxx/MMBtu, 100 /MMBtu, 100 ppmvppmv

• Staged Fuel - 0.06 # NOStaged Fuel - 0.06 # NOxx/MMBtu, 50 ppmv/MMBtu, 50 ppmv

• Low Emission - 0.03 # NOLow Emission - 0.03 # NOxx/MMBtu, 25 ppmv/MMBtu, 25 ppmv

Boustead International Heaters.

END