fuel systems_PPT_NPTI(3).pptx

Bharat Heavy Electricals Limited, Tiruchirappalli
Theory of ignition –Igniters – Fuel
oil firing system for boilers

FUNDAMENTAL CONCEPTS OF IGNITION ENERGY
• Ignition takes place when the flammable furnace input is heated above the ignition
temperature.
• The degree of flammability depends on how easy it is to turn into a gas, because nothing
truly burns until it is a gas. This in turn depends on the nature and quantity of the
substance, compared with amount of heat available to start combustion
• The functional requirement of the fuel firing system is to supply a controllable and
uninterrupted flammable furnace input of fuel and air and to continuously ignite and burn
the fuel as rapidly as it is introduced into the furnace.
• No flammable mixture should be allowed to accumulate in the furnace.

FACTORS DECIDING THE IGNITION ENERGY REQUIREMENT
• Fuel Quality
• Fuel Preparation
• Air Preparation
• Burner Product distribution
• Total Air fuel ratio
• Main burner flow rate

Supply of Ignition Energy
• In a pulverized fuel fired boilers, auxiliary ignition energy is provided by oil guns and by
igniters. Since the cost of these fuels are large, the system designs are made so as to
provide adequate energy with minimum use of premium fuel and for short duration of
operation.

Ignition system- Oil
• High Energy Arc Ignitor
• No.2 to No.6 oil

High Energy Arc Ignitor
• The High Energy Arc Ignitor can ignite warm up fuel oils distillate
to heavy oils and crude oils. The ignitor is a self contained
electrical discharge device for producing a high intensity spark.
• Use of high resistance transformer to produce a full wave
charging circuit and to control spark rate, enables the sealed
power supply to store maximum energy and to deliver a greater
percentage of this energy through insulated cables to the ignitor
tip in a very short time, in terms of micro seconds.

HIGH ENERGY ARC IGNITER (HEAI) – SPARK RODEA
Spark Rod Tip
The ignitor is designed to produce rapid pulses (arcs) across its
outer surface. In producing these arcs metal is eroded which
requires periodic replacement of the spark rod tip.

RETRACTOR ASSEMBLY

Igniter Disposition in a TT Firing Assembly

Purpose of Fuel oil system
• Light up / Start up fuel
• Stabilizing fuel
• Load carrying fuel

Types of fuel oil
• Light fuel oil
• Heavy fuel oil
No.6 Fuel
oil
No.2 Fuel
oil

Combustion of Fuel oil
• Atomization
Atomization is the process of spraying the fuel oil into fine mist, for
better mixing of the fuel with the combustion air. While passing
through the spray nozzles of the oil gun, the pressure energy of the oil
converts into velocity energy, which breaks up the oil stream into fine
particles.
• Types of atomizers
– Mechanical atomizer/Pressure Jet atomizers
– Steam or compressed air atomizers
– Rotary cup atomizers

Maintaining the HFO temperature constant, corresponding to the
atomising viscosity of 15 to 20 centistokes, is essential for better
fuel oil atomisation.
A lower temperature of fuel oil impairs the burner performance and a
higher temperature causes oil cracking.
Temperature Control

Fuel Oil Atomisation
Atomisation is the process of spraying the fuel oil into fine mist, for better
mixing of the fuel with the combustion air. While passing through the spray
nozzles of the oil gun, the pressure energy of the steam converts into velocity
energy, which breaks up the oil stream into fine particles.
Poorly atomised fuel oil would mean bigger spray particles, which takes longer
burning time, results in carryovers and makes the flame unstable due to low
rate of heat liberation and incomplete combustion.
Other than pressure, viscosity of the oil is the major parameter which
decides upon the atomisation level. For satisfactory atomisation the
viscosity shall be 15 to 20 centistokes.

Oil Recirculation
Before putting in the first burner into service, it is necessary to warm up the long
oil supply lines to the burners, so that the oil does not get cooled in the colder
pipings and that the oil at correct atomising temperature becomes available at
the burners. To achieve this the heated oil is circulated up to the burners and
back to the oil tank through oil return lines till adequate oil temperature is
reached near the burners.
System Vents
Fuel oil heaters, strainers and lines are provided with vent cocks or
valves on oil and steam sides to get rid of air locks while charging system.

• The purpose of Air Cooled Oil Guns is to eleminate the more expensive and
cumbersome retract mechanism prone to increased maintenance with retract
cylinders, solenoid valves, limit switches and electrical connections.
• The Air Cooled Oil gun is cooled by a low pressure stream of air passing
through a specially designed gun cap with finned surfaces. The low Pressure
air passing around the atomiser shields and reduce the furnace radiation
falling on the atomiser parts by extracting heat through the finned surfaces.
• It is more economical than steam or compressed air cooling as the power
requirements for low pressure cooling air is minimum. No reduction in the life
of tip due to erosion or high temperature exposure.
Air Cooled Oil Gun

Air Cooled Oil Gun - Complete
• The Complete oil gun assembly consists of two major sub-assemblies.
• Stationary Part
• Removable Part.

Air Cooled Oil Gun – Stationary Part
• The Stationary part is bolted on to the wind box by means of mounting
plate or flange. The entire assembly can be removed from the wind box
compartment after the removal of the mounting plate bolts.

Air Cooled Oil Gun – Removable Part
• The removable part of oil gun consists of the removable union, two
parallel oil gun pipes with flexible portions and nozzle assembly.

Air Cooled Oil Gun Assembly

• The atomiser having provision for mixing of oil and air/steam at the nozzle tip
after issuing out into the furnace is called external mixing gun.
• The Air or steam pressure is always maintained constant and oil pressure is
varied according to the requirements for firing operations.
External Mix Atomiser

Atomiser & Spray Plate
• Oil is admitted to outer holes in the spary plate through the outer row of the holes in
the nozzle body. The atomising agent(Air.Steam) passes through the inner hole of the
nozzle body. Oil passes through the outer holes of the spray plate and mixes with the
atomising agent which passes through the inner radial holes of spray plate.
• In the process oil gets atomised. Atomised oil is discharged into the furnace in the
form of fine spray. Sparay angles can be changed by using different spray plate.

External Mix Atomisers (J Type)

Systems of Fuel oil system
• Unloading system
• Fuel oil tank
• Fuel oil Pressurizing and Heating systems
• Main lines & Pipe racks
• Boiler Fuel oil control systems (Operating Floor)
• Atomizing media control systems (Operating Floor)
• Burner station
• Ignition system
• Oil gun
• Safety interlocks

Critical parameters in design of fuel oil
system
• Selection of atomizer
• Turn down of oil burner
• Estimation of pressure drop
• Fuel oil pump selection
• Sizing of HFO heaters
• Control valve selection
• Trip valves / Nozzle valves
• Special valves like Plug valves, Ball
valves

Fuel Oil System Scheme - Pump House

Fuel Oil System Scheme – Boiler Front

Fuel oil Pressuring Units
• Pumping system – Triple
screw pumps
• NPSH requirements
• Re-circulation control
station
• Fuel oil strainers

Fuel oil Heating units
• Viscosity of oil
• U-tube heat exchangers /Tube side steam& Shell
side Oil
• Temperature control station
• Pressure control station

FUEL OIL HEATERS (U-TUBE ASSEMBLY

HEAT EXCHANGER ASSEMBLY

Boiler front stations
• HFO Operating Floor Piping
• LFO Operating Floor Piping
• Atomizing steam Operating Floor Piping
• Atomizing air Operating Floor Piping
• Burner station

BURNER SKID ASSEMBLY

TILTING TANGENTIAL BURNER ASSEMBLY
1. Seperated By pass Over Fire Nozzles
(BOFA) along with Close Coupled Over
Fire Air Nozzles for maximum Nox
reduction.
2. High Performance Flame attachment
Coal Nozzles & Tips.
3. Air Cooled Oil gun arrangement which
avoids complicated retractor assembly.
4. Secondary Damper Drives for
proportioning the Secondary Air into the
furnace.
5. Burner Tilt Drives, which operates in
unison for SH/RH temperature Control.
For smooth functioning, two drives per
corner are envisaged based on the
height of burner assembly.

Introduction and General overview
 The premise of a tangential firing
system is to provide a tiered
introduction of fuel and air
alternated through a confined
structure to ensure proper mixing
and staging of the fuel and air
mixture.
 Windbox to direct the fuel and air
to the furnace and to encompass
accessories of firing system.
 To be designed for contractual
firing capacity and emissions
requirements.
Fuel Systems / Product Engineering (FB)

Modern Burners are equipped with:
(a)Separate flame envelope ports for coal,oil and gas
(b)Secondary air control to adjust the flame envelops.
(c)Ignitors.
(d)Flame Scanners to detect the distinct flames in an
enclosure.
(e) Flame Stabilisers.
(f) Flame Analysers
TT FIRING SYSTEM

TANGENTIAL BURNERS

FURNACE FIRING ANGLES AND ELEVATIONS

TILTING DRIVE MECHANISM

COAL COMPARTMENT ASSEMBLY

OIL COMPARTMENT ASSEMBLY

NOx Formation
and
Control Strertegies

NOX FORMATION AND REDUCTION
THE FORMATION OF NITROGEN OXIDES WITH THE COMBUSTION OF FOSSIL FUELS MAY
RESULT FROM THREE DIFFERENT REACTION MECHANISMS
• THERMAL NOx FORMATION
• PROMPT NOx FORMATION
• Nox FORMATION FROM FUEL NITROGEN

Tangential Firing System and NOx
• The swirling motion, which
creates an aerodynamics in the
entire belt of the array of
burners enabling the
segregation of air and fuel
around the central vortex.
• This increase the residence
time and delay the combustion
process and hence the NOx
formation, which is the
inherent advantage of
tangential firing system

TYPES OF NOx

Nox FORMATION MECHANISMS

BASIC Nox REDUCTION STRATEGIES

AIR STAGING
• TO REDUCE NOX FORMATION DURING COMBUSTION, THE TWO MAJOR
NOX- GENERATION MECHANISMS - CONVERSION OF FUEL BOUND
NITROGEN AND HIGH-TEMPERATURE FORMATION OF THERMAL NOX-
MUST BE CURTAILED.
• ONE SUCSSESFUL TECHNIQUE INVOLVES WITHHOLDING SOME O2 FROM PRIMARY
FLAME ZONE AND INTRODUCING IT GRADUALLY THEREAFTER TO ENSURE SMOOTH,
COMPLETE COMBUSTION AT RELATIVELY LOW TEMPERATURES. THIS METHOD IS
KNOWN AS AIR STAGING, IS USED IN SOME FORM FOR VIRTUALLY ALL LOW –NOx
WALL AND TANGENTIALLY FIRED BURNERS.

Close Coupled Over Fire Air System
OVER FIRE AIR COMPARTMENTS
• OVERFIRE AIR IS INTRODUCED INTO THE
FURNACE TANGENTIALLY THROUGH
TWO ADDITIONAL AIR COMPARTMENTS,
TERMED AS OVERFIRE AIR PORTS,
DESIGNED AS VERTICAL EXTENSIONS
OF THE CORNER WINDBOXES.
• THE OVERFIRE AIR PORTS ARE SIZED TO
HANDLE 15 PERCENT OF TOTAL
WINDBOX AIR FLOW
• AT DESIGN LEVELS OF OVERFIRE, A 20
TO 30% REDUCTION IN NOX FORMATION
IS ACHIEVED

Separated Over Fire Air System (SOFA)
• In the current units CCOFA(close coupled overfire air) feature
is incorporated in the windbox itself.
• To meet the latest trends in the NOx control measures ,
provision of a separate over fire air( SOFA ) is being developed .
• The SOFA developed was tested at Suratgarh Site yielded
good results in reduction of Nox.

VERTICAL STAGED COMBUSTION FOR Nox REDUCTION
• Air staged Low Nox Firing
Approach.
• Utilizes a flexible, multipoint air
injection design.
• Controls build-up of lower furnace
stoichiometry.

Low Nox Firing System (with SOFA)
• Close Coupled Over Fire Air
(CCOFA)
• Single level Seperated Over Fire Air
(SOFA)

fuel systems_PPT_NPTI(3).pptx

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to fuel systems_PPT_NPTI(3).pptx

Similar to fuel systems_PPT_NPTI(3).pptx (20)

Recently uploaded

Recently uploaded (20)

fuel systems_PPT_NPTI(3).pptx