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
operating under twin fuel supply regime with low pollutant emissions, high burning
efficiency and high flame stability.
BACKGROUND OF THE INVENTION
The present rate of depletion of fossil fuel reserves and increase in global
temperature lead us to search for an alternative sustainable energy resources as
well as adoption 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 low calorific
value gaseous fuel called producer gas (PG) or syngas, which is then used in
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 has lower calorific value, which is approximately l/4th 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 high calorific value fuel 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. Therefore, many aspects must be considered such as
velocities of the fuel and air, volumetric flow rate of flue gas, peak flame
temperature of the flame, stoichiometric ratio, air flow staging, swirling ratio, etc. In
present days of higher fuel price, fuel scarcity, fuel supply fluctuations and
emergency situation like transportation delays or pipe line ruptures, consideration of
dual burner offers many advantages over single fuel fired burners in terms of
operation flexibility and uninterrupted operation of heat treatment process. It also
offers an additional advantage of establishing required furnace temperature in
shortest time during start-up and in urgent situations. Installation of dual fuel
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. Dual fuel burner designs are most
popular in industrial applications for example in US Patent No. 7,901,204 B2, they
have designed for gas/non-gaseous fuel burner in steam cracking applications,
where as in US Patent No. 5,351,477, they have described gas and/or liquid fuel
mixing burner design for turbine engine. In US Patent No. 6,422,858 Bl, they have
also designed a low NOx burner with liquid and gaseous fuels in industrial
applications. In US Patent No. 0,315,586 Al, they have developed a low NOx dual
fuel burner where, pressurized, preheated liquid fuel atomized and flash vaporized
and mixed with primary oxidizer. This mixture has partially burnt and producing
secondary gaseous fuel mixture. This is subsequently burnt completely with help
second stage oxidizer.

Since both liquid and fuel mixture is burnt in the same burner they have termed it as
dual-fuel burner. Whereas, in US Patent No. 0143295 Al, they have 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. Very
few innovative designs of burner are found in the literature firing two or more
gaseous fuels. In Australian Patent No. 2008212067, they have described dual gas
burner design 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. In Chinese Patent No. CN 201706505 U, they have designed a tri-fuel
burner for high calorific, low calorific and a liquid fuel fired burner. Which is simple
design with one air supply for all fuels but for the applications where only gaseous
fuels are preferred, it may not be useful. A component of swirl is missing in their
design, which provides better mixing between fuel and oxidizer and gives higher
flame stability. In recently filed Indian Patent (1070/KOL/2012), they have proposed
a dual fuel burner of two different calorific value fuels with each fuel having a
separate air entry, this may not be suitable for space constrained furnace
applications and when a series of burners are connected for heat treatment process.
In addition, in many industrial applications like glass plants liquid fuels are not
preferred due to their higher burning time, presence of sulphur components and
soot formation. Therefore, only gas fired burners are the obvious choice for these
industrial applications. However, prior art does not appear to use firing two distinct
calorific value fuels in the same burner in a simple burner.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a dual fuel burner operating
under twin fuel supply regime with low pollutant emissions, high burning efficiency
and high flame stability.

A further object of the invention is to propose a dual fuel burner operating under
twin fuel supply regime with low pollutant emissions, high burning efficiency and
high flame stability, in which a single air entry is provided to burn two different fuels
with dissimilar calorific values.
SUMMARY OF THE INVENTION
According to the invention, there is provided a dual fuel burner with common air
entry for two fuels which is useful in heat treatment furnaces and pipe bending
furnaces where series of burners are installed to heat an object along its length.
However, the same burner concept can also be applied to power plants and steel
plants, with suitable modifications.
The dual fuel burner for gaseous fuels according to the invention offers advantages
of low pollutant emissions, high burning efficiency, fuel flexibility for the operators,
same thermal capacity and high flame stability for both fuels. In the present
invention of dual fuel burner, either of the fuels is fired in non-premixed condition.
The dual fuel burner can be used in a pipe bending furnace where a number of
burners are connected in parallel to operate simultaneously. These burners are fired
either with liquefied petroleum gas (LPG), natural gas, or with a PG, syngas, or in
combination of the first and second fuel such as natural gas/producer gas or
LPG/syngas. But, when both fuels are fired, the total burner capacity must be less
than 1.5 times of full load of any of the fuels. Basically, the dual fuel burner consists
of two fuel inlets and one air inlets, wherein air is supplied commonly for either of
the fuels based on their stoichiometric proportion for a given burner rating. To
accommodate these fuels and air flows, one inner pipe and two annular spaces
between three pipes are provided. If the higher calorific value fuel is to be fired in
the furnace, the fuel is sent through the innermost pipe and the corresponding air is

supplied through the air inlet. Here, the total air needed for the fuel to bum
completely is supplied in three stages, first and second stage of air is supplied
directly through the circumferential holes of the burner throat and the third stage air
is supplied through an annular space between the burner throat and an outermost
burner pipe. This air is supplied through a swirler block to provide better mixing
between the fuel and air. The split supply of air ensures staged fuel combustion of
fuel 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 passes through
the first annular space immediately after the innermost pipe and the corresponding
air is supplied in same way as supplied for first fuel. For the second fuel, a swirler
block is provided in the annular space to create a swirl mechanism, which allows
better mixing between the fuel and air for lower calorific value fuel. Both the fuels is
provided with a common spark ignition to lit up the flame near the flame injection
point and also a flame scanner is provided for safe operation of the burner. The
scanner can be an ultraviolet or infrared operated flame scanner to ensure
automatic operation of the burner, which means, if there is no flame in the burner,
fuel supply is cut-off immediately.
Based on the requirement and availability of fuel, one can operate with both the
gaseous fuels with partial load conditions. The unique advantage of the inventive
dual fuel burner is that the burner can operate with either fuel with the same
thermal energy output.
Some of the experimental data that has been observed during the test trails with
present invention is given in Table 1. Where producer gas (PG) is considered as
lower calorific value fuels and Liquefied Petroleum Gas (LPG) is considered as high
calorific value fuel. During the experiments stable flame was observed with either
fuel and switch over LPG to PG and vice-versa happened smoothly.

Table 1: Observed experimental data for present dual fuel burner

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 illustrates a 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 a side view of the burner of Figure 1 with all piping connections.
Figure 3 illustrates a swirl block arrangement for the burner for tertiary air entry of
Figure 1.
Figure 4 illustrates the swirl block arrangement for low calorific value fuel in the
annular space.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE
INVENTION
The present invention describes a dual fuel burner with single air entry for both fuels
for small to medium scale heat treatment operations. 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 4 show the detailed arrangements of a duel fuel burner with single air
entry, where Figure 1 illustrates the longitudinal cross sectional view of the duel fuel

burner, whose principle axis is shown as X-X. Burner consists of an inner most tube
(1) for high calorific value fuel i.e. the first fuel and first annular tube (2) for lower
calorific value fuel i.e., second fuel immediately after tube (1). This second fuel is
supplied through a swirler block (14) i.e., first swirler arrangement. For both
gaseous fuels, air is supplied through a pipe (3), where this air is supplied to the
fuel in different stages. First stage comes through the circumferential holes (4) very
near to the fuel inlet where ignition takes place and the second staged air comes
through circumferential holes (5). These holes are bore accurately on burner throat
pipe (6) circumferentially. After second stage, partially burnt fuel mixture comes out
through exit pipe (7) to contact the tertiary staged air through a radially inward pipe
(8). The tertiary stage air is supplied between burner throat pipe (6) and main
burner pipe (9) through a swirler block (15) i.e., second swirler. After complete
combustion of fuel in the burner, hot flue gases are exited through (11) a radially
inward nozzle (10). The dual fuel burner has provision for an ignition source (12)
and a flame scanner (13).
Figure 2 shows the side view of the dual fuel burner, which highlights the flange
connections for low calorific value fuel pipe (2) and air flow pipe (3).
Figure 3 illustrates the swirler block blades arrangement (14) of first swirler, through
which second fuel is supplied. The number of swirl blades and its arrangements are
detailed in the diagram.
Figure 4 shows the swirler block blades arrangement (15) of second swirler for
tertiary air supply. It also shows the circumferential holes (4) & (5) for primary air &
secondary air respectively and convergent section (7) of the burner exit.
Figure 5 shows the isometric view of dual fuel burner with high calorific value fuel
entry (1), lower calorific value fuel entry (2) and corresponding air entry (3).

REFERENCES
1. Dual Fuel Gas-Liquid Burner, US 7,901,204 B2, Mar. 8, 2011, ExxonMobil
Chemical Patents Inc., Houston, TX (US)
2. Dual Fuel Mixer for Gas Turbine Combustor, US 5,351,477, 4 Oct., 1994, General
Electric Company, Cincinnati, Ohio
3. Low NOx Apparatus and Methods for Burning Liquid and Gaseous Fuels, US
6,422,858 Bl, 23 Jul., 2002, John Zink Company, LLC, Tulsa, OK (US)
4. Burner Designed for Wide Range of Input Rates, US 2011/0143295 Al, Pub.
Date: Jun. 16, 2011, Electrolux Home Products, INC., Cleveland, OH (US)
5. Dual Fuel Boiler, AU 2008212067, 9 Sept. 2008, Raheem Manufacturing
Company, 405 Lexington, Australia.
6. Method and System for Low-NOx Dual-Fuel Combustion of Liquid and/or Gaseous
Fuels, US Patent No. 0,315,586 Al, 13 Dec 2012, Gas Technology Institute, Des
Plaines, IL, US.
7. Tri-fuel burner, Chinese Patent No. CN 201706505 U 01 Jan 2011, Xun Jinghong.
8. A dual fuel burner for gaseous fuels with low pollutant emissions, high burning
efficiency and high flame stability for twin fuels, Indian Patent No.
1070/Kol/2012, BHEL Trichy, India. (Application filed on 18/09/2012).

WE CLAIM:
1. A dual fuel burner operating under twin fuel supply regime with low pollutant
emissions, high burning efficiency and high flame stability comprising:
- an innermost pipe (1) for supply of a higher calorific value fuel, a first
annular pipe (2) for supply of a lower calorific value fuel and a second
annular pipe (3) for supplying air corresponding to said fuels in three
stages through a plurality of holes (4,5) such that stage combustion of
each fuel takes place; and
- a first swirler block (14) acting as a first swirler for lower calorific value
fuel and a second swirler block (15) acting as a second swirler for the
tertiary staged air to generate a swirling action to the fuels and air flows
respectively;
wherein the length, angle and number of swirl blades in case of the first
swirler block (14) vary from 10 to 30 mm, 6 to 10 and 10 to 30° with axis
X-X respectively, and wherein the length, angle and number of swirl
blades of the second swirler block (15) of tertiary stage air vary from 30
to 60 mm, 5-150 with axis X-X and 8 to 16 respectively.
2. The dual fuel burner as claimed in claim 1, wherein identical thermal energy
output can be achieved with either of the fuel.
3. The dual fuel burner as claimed in claim 1, wherein either fuel can be fired at
partial or at full load.
4. The duel fuel burner as claimed in claim 1, wherein both the fuels can be
fired simultaneously at partial load but the combined load should not exceed

more than 50% of the rated capacity.
5. The dual fuel burner as claimed in claim 1, wherein the innermost pipe (1) is
for higher calorific value fuel can be used for lower calorific value fuel with
corresponding reduction in overall thermal energy rating.
6. The dual fuel burner as claimed in claim 1, wherein the second annular pipe
(2) for the lower calorific value fuel can be used to fire higher calorific value
fuel with same or reduced thermal energy rating.
7. The dual fuel burner as claimed in claim 1, wherein both the fuels can
interchange its firing location and fire simultaneously with a reduced or
determined thermal rating for both the fuels.
8. The dual fuel burner as claimed in claim 1, wherein number of circumferential
holes for primary stage air (4) and secondary stage air (5) on the burner
throat (6) is between 4 to 10 and 8 to 20 respectively,
9. The dual fuel burner as claimed in claim 1, wherein a convergent section (8)
of the partial burnt fuel exit angle varies between 20 and 40 degree in
respect of axis X-X.
10. The dual fuel burner as claimed in claim 1, wherein the convergent section of
the fuel gas exit angle (11) varies between 15 and 25 degree in respect of
axis X-X.
11. The dual fuel burner as claimed in claim 1, wherein the flue gas at the exit of
the burner for both the fuels is within a range of 20 to 50 m/s.

12.The dual fuel burner as claimed in claim 1, wherein the burner rating is
configurable for higher end application with selection of corresponding pipe
sizing.

ABSTRACT

The present invention relates to a dual fuel burner operating under twin fuel supply
regime with low pollutant emissions, high burning efficiency and high flame stability
comprising: an innermost pipe (1) for supply of a higher calorific value fuel, a first
annular pipe (2) for supply of a lower calorific value fuel and a second annular pipe
(3) for supplying air corresponding to said fuels in three stages through a plurality of
holes (4,5) such that stage combustion of each fuel takes place; and a first swirler
block (14) acting as a first swirler for lower calorific value fuel and a second swirler
block (15) acting as a second swirler for the tertiary staged air to generate a swirling
action to the fuels and air flows respectively; wherein the length, angle and number
of swirl blades in case of the first swirler block (14) vary from 10 to 30 mm, 6 to 10
and 10 to 30° with axis X-X respectively, and wherein the length, angle and number
of swirl blades of the second swirler block (15) of tertiary stage air vary from 30 to
60 mm, 5-15° with axis X-X and 8 to 16 respectively.