FIELD OF THE INVENTION
The present invention generally relates to combustion of gaseous fuels in
industrial burners. More particularly, the present invention relates to a dual fuel
burner for gaseous fuels with low pollutant emissions, high burning efficiency
and high flame stability for twin fuels.
BACKGROUND OF THE INVENTION
Depletion of fossil fuel reserves and increase in global temperature leading to
search of alternative sustainable energy resources as well as design of clean
combustion technologies (CCT) with high efficiency. As a step towards achieving
CCT, gasification of solid fuels has attracted many industrialist,
environmentalists, policy makers and scientists. It has many advantages when
compare with existing combustion technologies with solid fuels such as lower
fuel cost, competitive capital cost, high thermal efficiency and reduction in the
dangerous pollutant emissions such as nitrogen oxides (NOx), sulphur dioxide
(SO2), particulates, etc. Recently, to make effective use of resources, solid waste
(sewage sludge/industrial), petroleum coke, coal, biomass or other solid fuels are
gasified in presence of insufficient air to generate gaseous fuel called producer
gas (PG) or syngas, which is then used different industrial/utility applications. In
general composition of PG includes carbon monoxide (CO), hydrogen (H2),
Methane (CH4), other higher hydrocarbon and inert gases such as CO2, N2 etc.
The composition of PG may vary depending upon the source of solid fuel but the
constituents are same. The resulting producer gas usually have lower calorific
value, which is approximately 1/4th to 1/5th of the calorific value natural gas or
liquefied petroleum gas (LPG). Therefore, it needs a special burner design
(higher quantity of fuel need to be fired for the same thermal

output) to replace existing LPG/natural gas fired burners to meet heat flux
requirement in industrial applications.
Burner design is one of the crucial aspect in determining the combustion
efficiency, flame stability, turndown, pollutant formation and uniform heat
distribution in industrial applications. Enough care must be taken while designing
a low calorific value fuel burners. In present days of fuel scarcity, fuel price
fluctuations and emergency situation like transportation delays, having dual
burner offers many advantages over single fuel fired burners in terms of
operation flexibility and uninterrupted operation of heat treatment process.
Installation of these kind of burners provide great advantages in small and
moderate operational units such as heat treatment furnaces, furnaces for pipe
bending and pipe cutting and in glass industries, boilers, power plants and steel
plants.
In dual fuel burners, design of innovative liquid and gas fired dual burners are
commonly observed in industrial application for example in US Pat. No.7,901,204
B2, for gas/non-gaseous fuel burner in steam cracking applications. US Pat.
No.5,351,477, described gas and/or liquid fuel mixing burner design for turbine
engine. US Pat. No. 6,422,858 Bl, teaches a low NOx burner with liquid and
gaseous fuels in industrial applications. US Pat. No. 0143295A1 described a
burner for multiple fuel inlets with wide range of heating value but this is for
cooking applications the same design cannot be used in heat treatment
applications. Australian patent No.2008212067, described a dual gas burner with
gaseous fuels but, both gaseous fuels must have the same calorific value.
Therefore, it is not suitable for fuels of substantially different calorific value fuels.
Chinese Pat. No. CN 201706505 U, designed a tri-fuel burner for high calorific,
low calorific and a liquid fuel fired burner, with one air supply for all fuels but for

the applications where oniy gaseous fuels are preferred, it may not be useful. A
component of swirl is missing in this prior art, which provides better mixing
between fuel and oxidizer and gives higher flame stability. In addition, in many
industrial applications like glass and steel plants liquid fuels are not preferred due
to their higher burning time, presence sulphur components and soot formation.
Therefore, only gas fired burners are obvious choice for these industrial
applications. However, prior art does not appear to teach firing two distinct
calorific value fuels in the same burner.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a dual fuel burner for
gaseous fuels with low pollutant emissions, high burning efficiency and high
flame stability for twin fuels, which eliminates the disadvantages of prior art.
Another object of the invention is to propose a dual fuel burner for gaseous fuels
with low pollutant emissions, high burning efficiency and high flame stability for
twin fuels, which can fire either low calorific value fuel or high calorific value fuel
or in combination without reducing the thermal power output of the burner.
A further object of the invention is to propose a dual fuel burner for gaseous
fuels with low pollutant emissions, high burning efficiency and high flame
stability for twin fuels, which provides higher stability to the flame, lower NOx
production and operational flexibility in industrial heat treatment applications.

SUMMARY OF THE INVENTION
Accordingly, there is provided a dual fuel burner for gaseous fuels with low
pollutant emissions, high burning efficiency and high flame stability for twin
fuels, which can operate with either higher calorific value fuel or lower calorific
value fuel or both. High calorific value fuel is termed as a first fuel and low
calorific value fuel is termed as second fuel. This innovative configuration of the
burner also provides stable flame and lower NOx emissions with either of the
fuel. In the present dual fuel burner, fuel would be fired in non-premixed
condition with either fuel.
The operation of the present invention can be manifested in a process for pipe
bending furnace where a number of burners are connected in parallel to operate
simultaneously. These burners are fired either with the first fuel such as natural
gas, LPG, etc. or with a second fuel such as producer gas, syngas, etc. or in
combination of the first and second fuel such as natural gas/producer gas or
LPG/syngas, etc. Basically, the inventive dual fuel burner consists of two fuel
inlets and two air inlets, air is supplied for each fuel separately based on
stoichiometric proportion. To accommodate these fuels and air flows one inner
pipe and three annular spaces between four pipes are provided. If the first fuel is
to be fired in the furnace, the fuel is inputted through the inner pipe and the
corresponding air is supplied in the first annular space immediately after the
inner pipe. The total air needed for the fuel is split into three stages, first and
second staged air is supplied directly and third staged air is supplied with swirl
action to provide better mixing between the fuel and air. The staged supply of air
ensures staged fuel combustion hence, NOx formation reduces via thermal NOx
mechanism due to lower peak temperatures. When the second fuel is to be fired

in the furnace, it is passed through the second annular space and the
corresponding air is sent through the third annular space (outermost annular
space of the burner). Here, all the air is supplied in single stage. A swirler block
to act as a swirl mechanism is provided to enhance mixing between fuel and air.
The second fuel and corresponding air outlet pipes are configured to direct these
flows radially inwards towards the exit for better mixing between the fuel and
oxidant. The first fuel is provided with spark ignition to lit up the flame but the
same is not provided for the second fuel. Therefore, the second fuel is ignited
either by first establishing flames of the first fuel, or with help of a pilot flame
externally. The first Fuel is also provided with a flame scanner, where an
ultraviolet or infrared flame scanner monitors the existence of the flame for
safety purpose. If there is no flame in the burner, fuel supply is cut-off
immediately. The second fuel has no such provision, hence it must be installed
externally near the flame. For better mixing of the second fuel and air, a partial
air is sent to the first annular space even though the first fuel is completely
switched off.
Based on the requirement and availability of fuel, one can operate with both the
gaseous fuels with partial or full load conditions. The unique advantage of this
dual fuel burner is, it can operate with either fuel with the same thermal energy
output without decreasing the burner rating for any of the fuel.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrates the cross sectional view of dual fuel burner configuration, fuel
and air flow arrangements of the dual fuel burner along its principle axis X-X,
according to the invention.

Figure 2 illustrates the side view of the burner of Figure 1 with all piping
connections.
Figure 3 illustrates a swirl block arrangement for the burner of Figure 1 in case of
high calorific value fuel.
Figure 4 illustrates the swirl block arrangement for low calorific value fuel in the
outermost annular space.
Figure 5 illustrates a variant of low calorific value fuel nozzle exit in the dual fuel
burner.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE
INVENTION
The present invention provides a dual fuel burner for small to medium scale
operations in heat treatment furnaces and pipe bending furnace applications.
However, the same burner concept can also applied can be extended for large
scale industries such as in power plants and steel plants, etc with suitable
modifications.
Figures 1 to 5 show the detailed arrangements of a duel fuel burner (1), where
Figure 1 illustrates the longitudinal cross sectional view of the duel fuel burner
(1), whose principle axis is shown as X-X. Burner (1) consists of an inner most
tube (2) for high calorific value fuel i.e the first fuel and air is supplied through
an inner tube (3) to the first fuel by first staged air holes (4) and second staged
air holes (5) and third staged air holes (6) through a swirler block (18). Burnt

flue gas of the first fuel is exited through a radially inward nozzle (7). The low
calorific value fuel i,e the second fuel enters through a second inner tube (8) and
pass through a first annular space (9) and exit at an annular ring (10). The
required air for the second fuel enters through a third inner tube (11) then it
pass through a second annular space (12) and exited by (13) through a second
swirler block (19). The burner (1) also consists of an ignition (14) and a flame
scanner (15). An orifice (16) is fitted for the innermost tube (2) and similarly
another orifice (17) is fitted for the pipe (3) for flow measurement.
Figure 2 shows the side view of the burner (1), which highlights the flange
connections for the tubes (2), (3), (8) and (11).
Figures 3 and 4 illustrates the swirl arrangement in the first and second annular
space (6) and (12), where the air flow pass through the swirling blocks (18) and
(19) respectively. The number of swirl blades in the first swirler block (18) are
generally twelve and similarly in the second swirler block (19) comprises at least
eight blades. The swirler blades in the first block (18) are longer than the swirler
blades of the second block (19).
Figure 5 shows a variant of nozzle exit for the second fuel, where fuel exit
through the two series of holes (20) in the annular exit space instead of the
annular ring (10).

WE CLAIM :
1. A dual fuel burner for gaseous fuels with low pollutant emissions, high
burning efficiency and high flame stability for twin fuels, comprising :
(a) an innermost pipe (2) for a higher calorific value fuel and immediate
annular pipe (3) for supply of corresponding air, which air is supplied in
three stages through a plurality of holes (4,5,6);
(b) an outermost two annular pipes are used for low calorific value fuel and
its air, second fuel is supplied through second annular pipe (8) and
corresponding air send through outermost annular pipe (11);
(c) a first swirler block (18) provided for third staged air (6) to facilitate
swirling action; and
(d) a second swirling block (19) provided for low calorific value fuel to swirling
action for better mixing of fuel and air.

2. The dual fuel burner as claimed in claim 1, wherein either of the first or
second fuel can be fired at partial or at full load.
3. The dual fuel burner as claimed in claim 1, wherein a partial amount of air
can also be supplied from outermost annular pipe (11) when the higher
calorific value fuel is firing.
4. The dual fuel burner as claimed in claim 1, wherein at least 10 to 50% air
can be supplied through the second annular pipe (3), when the lower
calorific value fuel is firing to provide better mixing.

5. The duel fuel burner as claimed in claim 1, wherein both the fuels can be
fired simultaneously at partial or full load.
6. The dual fuel burner as claimed in claim 1, wherein the innermost pipe (2)
is for higher calorific value fuel can be replaced with lower calorific value
fuel with the reduction in thermal energy rating of the burner.
7. The dual fuel burner as claimed in claim 1, wherein the second annular
pipe (3) for the lower calorific value fuel can be used to fire higher
calorific value fuel with the reduction in thermal energy rating.
8. The dual fuel burner as claimed in claim 1, wherein both the fuels can
interchange its firing location and fire simultaneously with a decreased
burner rating for each fuels.
9. The dual fuel burner as claimed in claim 1, wherein identical thermal
energy output can be achieved with either of the fuel.
10. The dual fuel burner as claimed in claim 1, wherein a convergent section
for the lower calorific value fuel annular pipe (8) exit angle can vary
between 20 and 40° in respect of axis X-X.
11. The dual fuel burner as claimed in claim 1, the convergent section for
outermost annular pipe (11) exit angle can vary between 20 and 40°.
12. The dual fuel burner as claimed in claim 1, wherein the convergent
section for burnt high calorific value flue gas section (7) angle can vary
between 15 and 20° with axis X-X.

13. The dual fuel burner as claimed in claim 1, wherein the number of swirl
vane blades in the outermost swirler block (19) can be varied from 6 to
10.
14. The dual fuel burner as claimed in claim 1, wherein the angle of swirl vane
blades in the outermost swirler block (19) can be varied from 15 to 30°
with axis X-X.
15. The dual fuel burner as claimed in claim 1, wherein the length of the swirl
vane blades in the outermost swirler block can be varied from 70 to 100
mm.
16. The dual fuel burner as claimed in claim 1, wherein the length, angle and
number of swirl blades for the swirler block (18) in case of high calorific
value fuel vary from 30 to 50 mm, 5-15° with axis X-X and 8 to 16
respectively.
17. The dual fuel burner as claimed in claim 1, wherein the flue gas and fuel
velocity at the exit of the pipe in higher calorific fuel firing and lower
calorific fuel firing respectively is within a range of 24 to 48 m/s.
18. The dual fuel burner as claimed in claim 1, wherein the burner rating can
be increased for higher end application with selection of corresponding
pipe sizing.
19. The dual fuel burner as claimed in claim 1, wherein the lower calorific
value fuel exit (10), can be replaced with at least two annular rows of
holes (20), size of each hole varies from 4 mm to 8 mm.

20. The dual fuel burner as claimed in claim 19, wherein the number of holes
(20) can vary from 20 to 28 in each row.