FIELD OF THE INVENTION
The present invention relates to a low capacity mixed gas burner for long flame generation.
More particularly, the present invention is directed to providing a low capacity mixed gas
burner adapted for controlled mixing of gas and combustion air with minimum excess air to
generate long flame suitable for application in flame heating furnace and the like for
preheating of steel strips. Importantly, the low capacity mixed gas burner according to the
present invention comprises concentric gas and air pipes of suitable dimensions to obtain
desired mixing of gas and air streams at the burner nozzle involving specially configured air
nozzle for sending combustion air surrounding the gas stream and a gas nozzle with suitable
flame stabilizer to generate stable and long flame inside the furnace with mixed gas.
BACKGROUND OF THE INVENTION
It is well known that Coke Oven (CO), Blast Furnace (BF) and L D gases are generated as
byproduct fuels in Integrated Iron and Steel industries. BF gas is a low Calorific Value (CV)
combustible gas having CV of about 780 kcal/Nm3 and LD gas has a CV of about 1800
kcal/Nm3. CO gas is a richer gas, having CV of about 4250 kcal/Nm3. Mixed gas is prepared
by mixing BF and/or LD gas(es) with CO gas in desired proportion depending on the desired
CV of mixed gas.
In applicants steel plant, mixed gas is prepared by mixing BF and CO gases in the ratio of
1:10 to 2:10 to prepare mixed gas of CV 3600-3900 kcal/Nm3 and supply it to different
shops of integrated steel mills.
Cold Rolling Mill (CRM) of applicants steel plant is equipped with two continuous galvanising
lines for coating of steel strip with zinc. The Flame Heating Furnace (FHF) serves as strip
cleaning section by oxidising oils and it also preheats the strip. The original arched
refractory roof of the FHF was provided with 35 small capacity gaseous burners, distributed
along the length and width of the roof for burning mixed gas of CV 3700kcal/Nm3. The
purpose of these roof top burners is to supply required heat flux to the top surface of the
sheet travelling through the furnace. The furnace is also provided with additional 10 bottom
side burners ( 5 each on the two side walls) to supply required heat flux to the bottom
surface of the moving sheet.

Due to deposition of hydro-carbons, all the 35 small roof burners were getting choked
frequently. It was very difficult to clean and maintain these burners, especially during
running condition of the furnace since these burners are located on the arched refractory
roof of the FHF.
The process decides the type of flame configuration and temperature required in the furnace
and burners are designed accordingly. The chemical composition and caloric value of the
gas are important factors while designing any burner. In general, rapid mixing between gas
and combustion air issuing from burner is required for lean gases to generate stable and
medium size flame. Conversely, delayed or slow mixing is required for rich gases having
moderate / high calorific value.
In the existing technology, mixing of gas and combustion air is controlled by tangential
entry of air or/and gas streams to the burner. In some cases, swirlers are used in air or/and
gas passages to facilitate mixing. In both the cases air and /or gas flow is churned / mixed
in the burner nozzle by imparting rotating motion to gas or air stream. In some cases gas
and air are sent through separate concentric tubes having single or multiple holes at their
tips. Apart from this, air stream is sent to the burner in separate streams like primary air,
secondary air, tertiary air etc. for required interfacial contact area between gas and air
streams to control mixing and generate desired flame length and configuration. It is very
difficult to generate long flame in low capacity burner. It requires desired mixing rate
between gas and combustion air to generate long and stable flame.
There has been thus a need in the art to developing a suitable low capacity burner to
generate long flame with mixed gases for application in flame heating furnace and the like.
To generate long flame from a low capacity mixed gas burner controlled mixing of gas and
combustion air is required with minimum excess air. Very high rate of inter mixing between
gas and combustion air generates short flame and very slow mixing causes flame lift up and
sometime incomplete combustion. There was thus a need for advancement in burner and
air/gas nozzle configuration which would take care of the known limitations of existing low
capacity burners and generate stable and long flame with mixed gas of moderate calorific
value.

OBJECTS OF THE INVENTION
The basic object of the present invention is directed to providing a low capacity mixed gas
burner for long flame generation.
A further aspect of the present invention is directed to providing a low capacity mixed gas
burner wherein concentric gas and air pipes of suitable dimensions are introduced to obtain
desired mixing of gas and air streams at the burner nozzle to generate stable flame with
mixed gas.
A still further object of the present invention is directed to providing a low capacity mixed
gas burner wherein a suitable air nozzle is provided for sending combustion air surrounding
the gas stream.
A still further object of the present invention is directed to providing a low capacity mixed
gas burner wherein a selectively configured gas nozzle with suitable flame stabilizer is
provided to generate stable and long flame inside the furnace.
A still further object of the present invention is directed to providing a low capacity mixed
gas burner wherein back end of the gas pipe is closed with flange connection so that burner
gas nozzle can be easily cleaned in case of deposition or choking.
A still further object of the present invention is directed to providing a low capacity mixed
gas burner wherein the dimensions of gas nozzle and air nozzle are worked out in such a
way that desired mixing of gas and air streams is achieved to generate required long flame.
A still further object of the present invention is directed to providing a low capacity mixed
gas burner wherein the mixed gas stream issuing through the gas nozzle, is completely
surrounded by combustion air stream at the air nozzle.
A still further object of the present invention is directed to providing a low capacity mixed
gas burner wherein the gas nozzle with a flame stabilizer is fixed inside the combustion
air nozzle at a certain distance inside the air nozzle tip to obtain desired gas /air mixing and
long flame even at low heat load.

SUMMARY OF THE INVENTION
The basic aspect of the present invention is directed to a Low capacity mixed gas burner for
long flame generation comprising:
concentric gas and air pipes
a gas nozzle with flame stabilizer ;and
an air nozzle for sending combustion air surrounding the gas stream;
said gas nozzle enclosed within said air nozzle for supplying combustion air
surrounding the gas stream and adapted to generate stable and long flame inside
the furnace.
A further aspect of the present invention is directed to said low capacity mixed gas burner
wherein the dimensions of said gas and air pipes are selectively provided such as to achieve
controlled mixing of gas and combustion air with minimum excess air.
A still further aspect of the present invention is directed to said low capacity mixed gas
burner wherein the dimensions of gas nozzle in combination with a rim type flame stabilizer
at the gas nozzle favour generation of stable and long flame inside the furnace.
A still further aspect of the present invention is directed to said low capacity mixed gas
burner wherein said gas nozzle comprises a disc/rim shaped flame stabilizer at its tip , the
gas nozzle having a converging part at its back with the back end of this converging part
operatively connected to a gas connecting pipe which is in communication with a gas pipe
for supply of mixed gas to the burner.
A further advantageous aspect of the present invention is directed to said Low capacity
mixed gas burner wherein the back end of the gas pipe is closed with flange connection
such that the gas nozzle can be viewed for any deposition and cleaning.
A still further aspect of the present invention is directed to said low capacity mixed gas
burner wherein said air nozzle comprises a converging part at its back with the back end of
said converging part operatively connected to a circular air connecting pipe for supply of
combustion air to the burner.

A still further aspect of the present invention is directed to said low capacity mixed gas
burner wherein said gas nozzle of suitable dimensions is provided to send the gas stream
along the burner axis and within the combustion air nozzle .
Yet another aspect of the present invention is directed to said low capacity mixed gas
burner which is having a low capacity of 20-25Nm3/n of mixed gas generates long, stable
and firmly anchored flame with mixed gas of CV 3600-3900 kcal/Nm3.
According to a further aspect said low capacity mixed gas burner is having a combustion air
pressure requirement 200 to 300 mmWG near the burner and mixed gas pressure
requirement 500 to 600mmWG near the burner.
Also said Low capacity mixed gas burner comprises flame igniter for initial light up.
The objects and advantages of the present invention are described hereunder in greater
details with reference to the following accompanying non limiting illustrative figure.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURE
Figure 1: is the schematic illustration of the longitudinal cross sectional view of the low
capacity burner for long flame generation according to the present invention showing its
different component parts/components and their locations.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING FIGURES
The present invention is thus directed to providing a low capacity mixed gas burner for long
flame generation. The long standing problem of uniform and controlled mixing of mixed gas
with combustion air as well as generating stable and firmly anchored yet long flame has
been solved by way of the present invention, particularly in case of a low capacity mixed
gas burner by selectively configuring the air and gas nozzle of the burner. Moreover, the
burner is provided with the advantageous features for easy cleaning/maintenance.

Accompanying Figure 1 schematically illustrates the longitudinal cross sectional view of an
embodiment of the low capacity burner for long flame generation according to the present
invention showing its different component parts/components and their locations.
It is apparent from Figure 1 that the burner according to the present invention is comprised
of a gas nozzle ( 1 ) having a disc/rim shaped flame stabilizer ( 2 ) at its tip. The gas nozzle
is having converging part ( 3 ) at its back. The back end of this converging part ( 3 ) is
welded to a circular pipe ( 4 ). A gas connecting pipe is welded perpendicularly to the gas
pipe ( 5 ) for supply of mixed gas to the burner. The back end of the gas pipe is closed with
flange connection ( 6 ) so that the gas nozzle can be viewed for any deposition. And in case
of deposition or choking of burner gas nozzle can be easily cleaned with the help of a
straight rod by opening the end blank flange (11).
The gas nozzle (1) is enclosed within a circular air nozzle (7) for supplying combustion air
surrounding the gas stream. The dimensions are worked out in such a way that desired
mixing of gas and air streams is achieved to generate required long flame. The air nozzle is
having converging part ( 8 ) at its back. The back end of this converging part (8) is welded
to a circular pipe (9). An air connecting pipe is welded perpendicularly to the air pipe (10)
for supply of combustion air to the burner. The blank flange (11) of gas pipe (4) and end
flange (6) are tightened together with nuts and bolts and gaskets.
In the new invention, the mixed gas stream, issuing through the gas nozzle (1), is
completely surrounded by combustion air stream at the air nozzle ( 7 ). The mixed gas
burner design is worked out for desired mixing rate of gas and combustion air.
The burner is provided with a gas nozzle (1) of suitable dimensions to send the gas stream
along the burner axis and within the combustion air nozzle (7). Also said gas nozzle (1) is
provided with a flame stabilizer (2) to attain flame stability. The gas nozzle ( 1 ) with a
flame stabilizer ( 2 ) is fixed inside the combustion air nozzle ( 7 ) at a certain distance
inside the air nozzle tip to obtain desired gas /air mixing and long flame even at low heat
load. The gas nozzle is place inside the burner tip to obtain certain amount of pre-mixing of
gas an air inside the air nozzle. This is done for high turn down ratio of 10:1 of the invented
burner at very low capacity. A flame igniter may be provided optionally for each burner for
initial light up.

The low capacity mixed gas burner according to the present invention having the capacity of
20-25Nm3/h of mixed gas, generates long, stable and firmly anchored flame with mixed
gas of CV 3600-3900 kcal/Nm3. The burner requires a combustion air pressure of 200 to
300 mmWG near the burner and a mixed gas pressure requirement of 500 to 600mmWG
near the burner.
It is thus possible by way of the present invention to providing a low capacity mixed gas
burner for long and stable flame generation wherein gas coming at desired velocity through
gas nozzle surrounded by air streams has ensured desired mixing rate and thereby helped
in achieving long and stable flame for low capacity burner. Advantageously, the burner
according to the present invention has simplified the burner design and eased burner
cleaning and maintenance. Moreover, long flame generation has helped in achieving uniform
heat distribution along the flame length and thereby across the width of the steel strip
favouring wide scale application and use for a variety of purposes in industry.

We Claim:
1. Low capacity mixed gas burner for long flame generation comprising:
concentric gas and air pipes
a gas nozzle with flame stabilizer ;and
an air nozzle for sending combustion air surrounding the gas stream
said gas nozzle enclosed within said air nozzle for supplying combustion air
surrounding the gas stream and adapted to generate stable and long flame inside
the furnace.
2. Low capacity mixed gas burner as claimed in claim 1 wherein the dimensions of said
gas and air pipes are selectively provided such as to achieve controlled mixing of gas
and combustion air with minimum excess air.
3. Low capacity mixed gas burner as claimed in anyone of claims 1 or 2 wherein the
dimensions of gas nozzle in combination with a rim type flame stabilizer at the gas
nozzle favour generation of stable and long flame inside the furnace.
4. Low capacity mixed gas burner as claimed in anyone of claims 1 to 3 wherein said
gas nozzle comprises a disc/rim shaped flame stabilizer at its tip, the gas nozzle
having a converging part at its back with the back end of this converging part
operatively connected to a gas connecting pipe which is in communication with a
gas pipe for supply of mixed gas to the burner.
5. Low capacity mixed gas burner as claimed in claim 4 wherein the back end of the
gas pipe is closed with flange connection such that the gas nozzle can be viewed for
any deposition and cleaning.
6. Low capacity mixed gas burner as claimed in anyone of claims 1 to 5 wherein said
air nozzle comprises a converging part at its back with the back end of said
converging part operatively connected to a circular air connecting pipe for supply of
combustion air to the burner.

7. Low capacity mixed gas burner as claimed in anyone of claims 1 to 6 wherein said
gas nozzle of suitable dimensions is provided to send the gas stream along the
burner axis and within the combustion air nozzle.
8. Low capacity mixed gas burner as claimed in anyone of claims 1 to 7 which is having
a low capacity of 20-25Nm3/h of mixed gas generates long, stable and firmly
anchored flame with mixed gas of CV 3600-3900 kcal/Nm3.
9. Low capacity mixed gas burner as claimed in anyone of claims 1 to 8 which is having
a combustion air pressure requirement 200 to 300 mmWG near the burner and
mixed gas pressure requirement 500 to 600mmWG near the burner.
10. Low capacity mixed gas burner as claimed in anyone of claims 1 to 9 comprising
flame igniter for initial light up.

ABSTRACT

The present invention relates to a low capacity mixed gas burner for long flame generation.
The low capacity mixed gas burner is adapted for controlled mixing of gas and combustion
air with minimum excess air to generate long flame suitable for application in flame heating
furnace and the like. Importantly, the low capacity mixed gas burner according to the
present invention comprises concentric gas and air pipes of suitable dimensions to obtain
desired mixing of gas and air streams at the burner nozzle involving specially configured air
nozzle for sending combustion air surrounding the gas stream and a gas nozzle with suitable
flame stabilizer to generate stable and long flame inside the furnace with mixed gas. The
gas nozzle with said flame stabilizer is fixed inside the combustion air nozzle at a certain
distance inside the air nozzle tip to obtain desired gas /air mixing and long flame even at
low heat load.