4. FLAME
A flame (from Latin flamma) is
the visible, gaseous part of a fire. It is
caused by a highly exothermic reaction
taking place in a thin zone. Very hot
flames are hot enough to have ionized
gaseous components of sufficient density
to be considered plasma.
5. MECHANISM
Colour and temperature of a flame are dependent on
the type of fuel involved in the combustion, as, for
example, when a is held to a candle The applied heat
causes the fuel molecules in the candle
wax to vaporize. In this state they can then readily
react with oxygen in the air, which gives off
enough heat in the subsequent exothermic reaction to
vaporize yet more fuel, thus sustaining a consistent
flame. The high temperature of the flame causes the
vaporized fuel molecules to decompose, forming
various incomplete combustion products and free
radicals and these products then react with each
other and with the oxidizer involved in the reaction.
6. Sufficient energy in the flame
will excite the electrons in some of the transient
reaction intermediates such as the Methylidyne
radical (CH) and Diatomic carbon(C2), which
results in the emission of visible light as these
substances release their excess energy (see
spectrum below for an explanation of which
specific radical species produce which specific
colours.. As the combustion temperature of a
flame increases (if the flame contains small
particles of un burnt carbon or other material), so
does the average energy of the electromagnetic
radiation given off by the flame (see Black body).
7. FLAME COLOUR
Flame colour depends on several factors, the
most important typically being black-body
radiation and spectral band emission, with both
spectral line emission and spectral line
absorption playing smaller roles. In the most
common type of flame, hydrocarbon flames,
the most important factor determining colour is
oxygen supply and the extent of fuel-oxygen
pre-mixing, which determines the rate of
combustion and thus the temperature and
reaction paths, thereby producing different
colour hues.
8. FLAME
TEMPERATURE
When looking at a flame's temperature there
are many factors which can change or apply.
An important one is that a flame's colour does
not necessarily determine a temperature
comparison because black-body radiation is
not the only thing that produces or determines
the color seen; therefore it is only an estimation
of temperature. Here are other factors that
determine its temperature:
9. >Adiabatic flame; i.e., no loss of heat to the
atmosphere (may differ in certain parts).
>Atmospheric pressure
>Percentage oxygen content of the atmosphere.
>The fuel being burned (i.e) depends on how
quickly the process occurs.
10. FLAME
STABILITY
One of the major challenges facing designers of low NOx
combustion systems (like lean premixed combustion and
flue gas recirculation) is flame stability; as the weaker
combustion process is more vulnerable to small
perturbations in combustor operating conditions. Since
further reduction of NOx will likely require even leaner (or
more diluted) mixtures, schemes for lean stability
extension must be considered. Stability of the combustor
is linked to the type of combustion process that occurs
within it. If the burning occurs in a thin flame zone that is
mixing limited, combustor stability can be dependent on
the balance between flow and flame propagation
velocities. In combustors where combustion is limited by
reaction rates, for example a stirred reactor, the stability at
a given stoichiometry is primarily limited by the residence
time.
11. However, practical combustors do not operate in
either limit The relative importance of 8 reaction to
the mixing timescales in a combustor is usually
expressed in terms of the Dahmkohler number
(Da). Knowledge of this quantity can helps us
conceptualize, model and identify the parameters
that control static stability of a given combustor.
Due to engine flow rate requirements, the injection
velocities in a typical combustor are usually a few
orders of magnitude higher than laminar flame
propagation velocities. Therefore, to stabilize a
flame in the desired region of interest, various
stabilization methodologies are adopted that either
enhance the flame propagation speeds or create
zones with low velocities where a flame can be
sustained, or do both.
12. Many designs are used by combustion researchers
to create low velocity zones, including bluff body
and swirl arrangements, where a flame can be
sustained in the recirculation zone, and turbulent
jets, where the flame is stabilized in the low
velocity shear layer. On the other hand, various
schemes for enhancement of reaction rates,
including reactant preheating, exhaust gas
recirculation or the use of an ignition source like a
pilot flame to make the flame more stable, have
been explored. Stability can also enhanced by
Exhaust Gas Recirculation (EGR), which involves
mixing reactants with hot combustion products
laden with radicals prior to combustion.
13. Flame Stability in (SPRF)
STAGNATION POINT REVERSE FLOW
COMBUSTOR
The results of an investigation to determine the
reasons for the ability of the SPRF combustor to
burn fuel stably very close to its lean
flammability limit. For this purpose we begin be
examining the velocity field in the combustor in
order to identify features that would influence
flame stability. The various flame stabilization
mechanisms exhibited in the combustor are
explored.
14. INDUSTRIAL GAS
BURNERS
A gas burner is a device to generate a flame
to heat up products using a gaseous fuel such
as acetylene, natural gas or propane. Some
burners have an air inlet to mix the fuel gas
with air to make a complete combustion.
Acetylene is commonly used in combination
with oxygen.
15. It has many applications such as soldering,
brazing and welding, the latter using oxygen
instead of air for getting a hotter flame which
is required for melting steel. For laboratory
uses a natural gas fired Bunsen burner is
used. For melting metals with melting points
of up to 1100 °C such as copper, silver and
gold a propane burner with natural drag of air
can be used.
16. INTRODUCTIO
N
Air for combustion can be supplied to the
burner in several ways. Primary air is a term
used to describe air supplied and mixed with
fuel prior to ignition. This is usually controlled
through orifices and valves where all
combustion air is mixed with the fuel and is
ready to ignite as soon as it reaches the
burner nozzle. The term “pre-mix” is used for
burners and combustion systems where the
air and gas are mixed prior to the burner
nozzle. When they are mixed at or within the
burner nozzle, it is called a “nozzle-mix”
system.
17. IMPORTANCE
The combustion gas analyzer is also known as
flue gas/stack gas analyzer. It is used to
measure the flue gases of boilers, burners, and
engines.
The equipment can simultaneously measure
oxygen (O2), Carbon monoxide (Co),carbon
dioxide (CO2), Nitrogen oxides (NOx), Sulpher
oxides (SO2) and flue gas temperature.
18. It calculates the Combustion efficiency, losses,
excess air, and carbon di oxide according to
ASME Parameters. This equipment is capable
to measure 7 different types of fuels having
integrated self check programs and
simultaneous display of eight parameters on
the illuminated display.
19. FEATURES
FULLY AUTOMATIC
ON/OFF OPERATION OPTIONAL
HI-LO OPERATION WITH 2 SET POINT TEMP.
CONTROLLER COMPACT DESIGN
HIGHLY EFFICIENT
EASY MAINTENANCE
RUGGED DESIGN
EASY ADAPTABILITY / INSTALLATION
20. CONTROLS AND SAFETY
Anyone who operates or maintains burners or
combustion systems must understand the basic function
of the various components that work together to make
their system work effectively and safely. Each component
has an important function. Some are for operation and
control, while others are strictly safety devices that
automatically shut the system down to prevent damage
and personal injury.
When looking at a combustion system for the first
time, people are often a bit overwhelmed with the
amount of valves, controls and other components. This
initial fear is normal because no one should operate a
combustion system without first understanding all of the
components involved, their function and their safe
operation. Having a healthy respect also provides good
motivation to learn what each device is doing and how
they are controlled for safe start-up, operation and
shutdown.
21. SYSTEM MONITORING
FOR SAFE OPERATION
Combustion systems have layers of safety
checks and devices designed to protect
operators and equipment from harm. In the event
that a safety device is not working properly, other
devices in the system are designed to back them
up. An example of this is the fact that two main
gas shutoff valves are used in series. If there is a
leak or failure of one, the other is there to shut off
the gas. Another example involves normally
closed valves (i.e. valves held open when power
is applied). These valves will automatically shut
in the event of an electric power outage.
22. TYPES OF
BURNERS
Gas Flat Burner: This burner
has been developed especially
for direct fresh-air heating.
Its special construction
allows operation without
an air ventilator.
The building-block,
design concept allows
for a variety of possible
uses.
23. Baffle Burner: Burners recirculate furnace gas
into the flame. Its appearance is deceptively
simple consisting of a body, gas nozzle, baffle
and port. Air enters the burner body directly and
the gas passes through the body separated from
the air with the fuel tube.
24. Air Staged Burners: In the first stage of an air
staged burner, all of the fuel is mixed with a portion
of the combustion air. The remaining combustion air
is then added in one or more additional stages until
the fuel is completely used. The first stage air is
introduced through the inner air jets and the second
stage air through the outer air jets. Fuel flows
through the centre.
25. Regenerative Burners: Regeneration uses a pair
of burners which cycle to alternately heat the
combustion air or recover and store the heat from
the furnace exhaust gases. When one
regenerative burner is firing, the other is
exhausting the furnace gases. Regenerative
burners have excellent thermal efficiency because
they achieve very high preheat temperatures
26. High Thermal Release (HTR) Burners: Bloom
HTR Burners are similar to the baffle burner. In the
small size range, the HTR burner uses a metallic
nozzle rather than a ceramic one. The air jets
have a high radial velocity component which
imparts a high spin to the air. The port block has a
dished area.
