Title of Invention	"METHOD FOR COMBUSTION OF A LIQUID FUEL WITH STAGED ATOMIZATION"
Abstract	The present invention relates, on the one hand, to a method for combustion of a liquid fuel comprisisng the steps for producing a spray (10) of the liquid fuel by injecting a main stream (3) of an atomizing gas is contact with the liquid fuel (4), the said method being characterized an that at least one secondary stream (11) of atomizing gas is injected close to the spray (10) is order to produce a secondary atomization of the said spray (10) prior to its contact with a jet of cjxidizer in order to carry out the combustion of the spray, and, on the other, to a burner implementing such a combustion method.

Title of Invention

"METHOD FOR COMBUSTION OF A LIQUID FUEL WITH STAGED ATOMIZATION"

Abstract

The present invention relates, on the one hand, to a method for combustion of a liquid fuel comprisisng the steps for producing a spray (10) of the liquid fuel by injecting a main stream (3) of an atomizing gas is contact with the liquid fuel (4), the said method being characterized an that at least one secondary stream (11) of atomizing gas is injected close to the spray (10) is order to produce a secondary atomization of the said spray (10) prior to its contact with a jet of cjxidizer in order to carry out the combustion of the spray, and, on the other, to a burner implementing such a combustion method.

Full Text	The present invention relates to a method fo combustion of a liquid fuel, and to a burne. implementing the same. During the installation of a combustion system for an industrial furnace, for example, one of the major concerns is to optimize the combustiom efficiency optimally controlling the flame properties, while meeting the needs of the heated method in terms of heat transfers and minimizing air pollutant releases. The two-phase combustion of a liquid fuel by ar oxidizing gas comprises two main stcps before the actual combustion takes place. In the first step, it is necessary to atomize the liquid ; fuel using ai ) atomizing gas injected so as to destabilize the liqui fuel stream and to form a fuel spray with a higher contact surface area with the oxidizer in order to promote the combustion. The atomizing gas used may be air, oxygen, steam or even natural gas, for example ' i It is then necessary for the liquid fuel drops thus formed to evaporate before the fuel :burns with tbe oxidizer. Since the fuel drop vaporization time it longer than the reaction time, the 'mixture of th drops formed. The spray characteristics depend on the type of injector used. Most injectors use a high speecd differential between the atomizing gas and the liquid fuel to destabilize the fuel and form the spray. Two types of injector are available according to whether high speed flow is imposed on the fuel or the atomizinc gas, that is, mechanical injectors in which the fuel is subjected to high pressure and flows at high speed through a small-diameter orifice, and injectora called i r "dual fluid" injectors in which a fuel jet flows at a relatively low speed and is destabilized by a high speed flow of atomizing gas. However, mechanical injectors are little used because, on the one hand they incur higher risks of blocking , of the fue infection orifice by deposits, and 0n the other, limited flow range due to the high cost of the compressors needed to reach high liquid pressures. Dual fluid injectors can allow for very ihigh atomizing gae flow speeds. In this category, a distinction in made between air-assiated atomizers, Qpieriating with low flow rates of gas ejected at very high ;sp(«ed, and spray atomizers characterized by lower atomizing gas flow speeds but higher flow rates. Two fluids can be mix in a confined environment (internal mixiing injector) outside the injection system {external mixing injector). Furthermore, the liquid fuel flow may optionally be oriented to form a film on an appropriate surface before its contact with the atomizing, gas flow. In this case, the injector is called a prefilmins atomizer, with prior formation of a liquijd film, and i the opposite case, a plain jet atomizer, with full liquid flow. The most commonly used injectors in oxy-combustion are injectors of the dual flow type with spraying with an atomizing gas speed lower than 200 m.s-1, with external mixing, and plain jet injectors. The combustion properties of a spray produced by such injectors are mainly controlled by changing relative atomizing gag and liquid fuel speeds. Is doing so, the mean drop size of the fuel spray is modified, and consequently, the vaporization time compared with the combustion reaction I time is also changed. The drop size and vaporization time control the mixing of the evaporated fuel with \| the oxidizer and are hence very important combustion parameters, determining particularly whether the combustion is complete or not. However, although controlling the injection speeds serves to adjust the properties of the spray and of the two-phase combustion to adapt them to the heated process, such injectors still have a lack of flexibility. For example, it is difficult to effectively control the cooling of the injector. In fact, an increase in the atomizing gas flow rate results in a reduction in the mean drop size, and consequently, a closer reaction zone and hence overheating of the injecttor. Moreover, for an excessively high atpmiiing gas flow rate, the atomization mode may go from a fibre mode, that is, with a fully developed liquid cone, to a superpulse mode, that is, with a short ;and truncated liquid con«. In this case, the reaction zone is liable to stabilize in the immediate neighbourhood of the burnei and cause its destruction. , Moreover, an excessively high atomizing gas speed can also cause instability of the flame. In fact, it has been demonstrated that the stability of the flame could be related to the ratio of the mixiing .time to th« characteristic time of the combustion, chemistry, the flame being stable when this ratio is above 1- In the case of an excessive increase in the .atomizing gas speed, the mixing time becomes shorter than the characteristic time of the combustion chemistry, and the stability condition is no longer satisfied. Another drawback is that the spray characteristics affect several parameters which are therefore not possible to control independently of one another Thus, it is not possible to control the spray drop siz and spray angle independently, charactieristics both dependent on the ratio of the momentum of atomizing gas to that of the fuel. More particularly, if this momentum ratio is lower than 5, an. , increase in the atomizing gas flow rate simultaneously, results in a decrease in the drop size and a widening of the spray angle, the flame being liable to inte^cti with those of adjacent burners. Another drawback appears in the cases tin which a hig i viscosity fuel is used. In this case, a simple atomizing gas stream injected in a ring around th liquid fuel stream does not permit uniform atomization producing a spray with uniform drop sizes. This causes irregular combustion and problems of flatw stabilization. : i ' i , ; ; it ie the object of the present invention to overconv i the abovementioned drawbacks and therefore consists o a method for combustion of a liquid fueil comprising th steps for producing a spray of the; liquid fuel b; : injecting a main stream of an atomizinjg gas in contac' ; with the liquid fuel, the said method being characterized in that at least one secondary stream of atomizing gas is injected close to the spray in order to produce a secondary atomization of the said spray prior to its contact with a jet of oxidizer in order to carry out the combustion of the fuel. ' ' i Thus, for the same total atomizing gas flow rate, the flow rate of the first atomizing stream is decreased, causing the formation of a spray with a higher size of th* drops formed in the neighbourhood, of the injector The fuel drops of the first spray then undergo a second atomization, leading to a modified spray with smaller drops. A first spray having already been formed, the secondary atomization is more effective; particularly in the case of a high viscosity fuel, land entrains the drops of the modified spray further from the injector. Due to this staged atomization of thet liquid fuel, the combustion reaction takes place further from the iniector, thereby decreasing the risks of burner overheating and destruction. It is important to observe that in the case in which the burner has a retractable injection head, the secondary atomization allows it to operate with a higher retraction.; Moreover, the atomizing gas flows thereby multiplied permit more effective cooling of the burner. The injector service life is thereby increased and its maintenance reduced. This improvement in cooling the injector is , , ' ! particularly advantageous in the case in which the atomizing gas used is oxygen, a gas for which the risks of overheating are high. Furthermore, the presence of a secondary atomization stream reduces the dependence between the drop size, (flame length) and the spray angle (flame width) by: limiting the increase of the latter. The flame length can therefore be controlled more easily); while limiting the risks of interaction with adjacent turner flames. A further advantage of the invention is the reduction of emissions of NOx compounds. In faet, the flame temperature obtained is more uniform, so that NOx; formation is reduced. This process is accentuated by a better dilution of the reagents and combustion products thanks to the secondary atomizing gas stream According to a first exemplary embodiment of the, method, the secondary stream of atomizing gas is injected in a direction parallel to the injectior; direction of the liquid fuel. . According to a second exemplary embodiment of the method, the secondary stream of atomizing gas is injected in an oblique direction convening towards the injection direction of the liquid fuel. This makes it possible to control the spray angle more accurately the modified spray angle being equal to twice the angle between the secondary atomizing gas stream injection direction and the fuel flow direction. Advantageously, the secondary atomizing gas stream is injected at an angle of between 0 and 60°, praferably at an angle of between 0 and 30°. Optionally, adjusting means can be provided for orienting the secondary atomizing gas stream injection direction as regards the liquid fuel injection direction in order to increase the flame width, and consequently, the heat transfer to the heated process, if necessary. ' Advantageously, the secondary stream of atomizing gas is injected so as to produce a turbulent flow. . Thus, the turbulent flow improves the dilution of the' reagents and combustion products andj further reduces the emissions of NOx compounds. Preferably, the secondary atomizing gas floW rate. represents between 20% and 70% of the total flow rate of atomizing gas. - .' Advantageously, the secondary stream of atomizing gas is divided into a plurality of streams injected in a uniformly distributed manner and equidistant arownd the liquid fuel stream. The injection can be carried out inter alia, by a concentric flow around the fuel injection or by a plurality of openings terminating in the burner head and uniformly distributed around the fuel injection. More precisely, the main atomizing gas stream is injected coaxially around the liquid fuel while the secondary stream is injected via the ! plurality of openings. The method according to the invention is ideal for the staged combustion process in which the oxidizer ill injected and divided into several streams introduced at various distances from the fuel spray, as described is particular in WO 2004/094902. Thus, the oxidizer jet can be divided into a primary oxidizer jet and a secondary oxidizer jet, the primary oxidizer jet being injected close to the fuel spray in order to cause i first, incomplete combustion, the gases issuing from this first combustion still comprising at least part of the fuel, while the secondary oxidizer j«t is injected at a distance I2 from the fuel spray; which is higher than the distance between the fuel Spray and the primary oxidizer jet closest to the fuel spray, in order to enter into combustion with the part of the fuel present in the gases issuing from the first combustion. The invention also covers, the case is which a third oxidizer jet is injectecd at a distance I2 from the fuel spray which is longer than the distance I1 The method according to the invention IS ideal for two phase burners an which the atomizing Gas ie injected, on the one hand, at a speed at least, 10 times higher than the fuel injection speed, and on the other, with an atomizing gas mass flow rate higher than 10% of the fuel mass flow rate. The present invention further relates to a burner implementing the preceding two-phase combustion method the said burner comprising at least one fuel injection means combined with at least one atomizing gas injection means in order to produce a fuel spray, and at least one oxidizer injection means characterized in that it comprises at least one secondary atomizing gas injection means arranged close to the fuel injection means. It should be observed that in the case of a burner with highly separated jets. such a burner comprises a primary oxidizer injection means, * secondary oxidizer injection means arranged at a distance from the fuel injection means that is; longer than that of the primary injection means, and optionally, a tertiary oxidizer injections means arranged at the edge of the burner. Advantageously, the secondary atomizing gas injection means is obtained by bypassing a common atomizing gas feed. The choice of the bypass diameter serves to define a ratio between the primary atomizing gas stream and the main stream. Further advantageously, the secondary injection means is oriented parallel to or, obliquely to the fuel injection means. The implementation of the invention will be better understood from the detailed description given below with reference to the drawing appended here to in which: Figure 1 is an enlarged partial schematic representation of a longitudinal cross section of an atomization head of a burner acjcbrding to the invention; Figure 2 is a front view of the atomization head in Figure 1; and Figure 3 is an enlarged partial schematic: representation of a longitudinal cross section of another atomization head of a burner according to the invention. A combustion method according to the invention is; implemented by a burner comprising a spray-guidef atamization head 6 with external mining as shown in Figures 1 and 2. This atomization head 6 comprises: an ejection line 7 for a liquid fuel stream 4; delivered by a fuel feed 2; and an atomizing gas ejection If line 8 concentric; with the fuel ejection line 7 and connected to an atomizing gas feed 9 and terminating) in contact with the fuel stream 4 in order to produce la liquid fuel spray 10 under the action of a main atomizing gas stream 3, Furthermore, the atomization head 6 has six secondary ejection channels ll oriented parallel to the fuel ejection line 7 and to the atomizing gas ejection line 8. These six secondary ejection channels 11 are uniformly distributed around the ejection lines 7, 8 and are designed to create secondary atomizing gas, streams 1 tapped off from the atomizing gas feed 9 by bypass channels 12. Under the effect of these secondary atomizing gas streams 1, the. liquid fuel spray 10 thereby undergoes a second atomization producing a modified spray 13. Thia modified spray 13 is then contacted with an oxidizer stream (not shown), optionally divided into a primary stream and a secondary stream, to carry out the combustion of the fuel. A tertiary oxidizer feed may alao be located at a relatively long distance from the atomization head 6 and is used to inject oxygen at high spiced in order to obtain a sufficient dilution of the reagents before the main combustion zone and thereby to prevent an excessive formation of thermal NOx compounds. Experiments hav« demonstrated that such a burner, in which 50% of the total oxygen was injected at the tertiary feed level, served, all other things remaining. equal, to obtain a flame stabilization, distance equal to about four times the flame stabilization distance of a conventional injector without secondary atomizing gas stream. This longer stabilization distance serves to reduce the overheating of the atomization head 6. Furthermore, it has also been demonstrated that the flame obtained was more uniform and longer due to the delayed atomization, the spray 10 having a larger drop size than a spray issuing from a conventional burner while the modified spray 13 has a smaller drop size and; better diluted and hence more uniformly distributed drops. The more uniform flame thus obtained, conseiquently reduces the temperature difference between the hot; spots and the cold spots. A significant reduction of NOx compound emissions by a burner equipped with an atomization head 6 according to the invention has also been demonstrated. A reduction by a factor of between 1.2 and 1.5, depending on the oxidizer distribution selected, can be obtained for the same total atomizing gas flow rate. This reduction can ibe explained by the lag of the reaction zone obtained thanks to the invention. As a variant, an atomization head 1, as shown in, Figure 3, differs from the atomization head 6 only in the fact that it comprises secondary ejection lines 14 obliquely oriented by an angle a to the fuel flew direction. The angle a is advantageously between 0 and 60°, preferably between 0 and 30°. These secondary injection lines 14 deliver secondary atomizing gas streams 5 which, with the spray 10, form a modified spray 13 having a spray angle of 2a. Such an atomization head 1 is suitable for more accurate adjustment of the flame width. Although the invention has only been described in connection with particular embodimentis, it is quite obvious that it is not limited thereby and that it comprises all the technical equivalents of the means described and of their combinations if these fall within the scope of the invention. CLAIMS 1. Method for combustion of a liquid fuel comprising the steps for producing a spray (10) of the liquid fuel by injecting a main stream (3) of ar atomizing gas in contact with the liquid;fuel (4), the said method being characterized in that; at least one secondary stream (1,5) of atomizing) gas is injectecd close to the spray (10) in order to produce a secondary atomization of the said spray (10) prior to its contact, with a jet of oxidiser in order to carry out th«, combustion of the fuel.; 2. Combustion method according to Claim 1, characterized in that the secondary stream (1) of atomizing gas is injected in a direction parallel to the injection direction of the liquid fuel. 3. Combustion method according , to Claim 1, characterized in that the secondary stream (5) of atomizing gas is injected in an oblique direction converging towards the injection direction of the liquid fuel 4. Combustion method according to any one or Claims 1 to 3, characterized in that the secondary stream (l, 5) of atomizing gas is injected so as to produce a turbulent flow. 5. Combustion method according to, any one of Claims 1 to 4, characterized in that the atomizing gas flow rate in the secondary stream (1,5)of atomizing gas represents between 20% and 70% of the total flow rate of atomizing gas. 6. Combustion method according to any one of Claims 1 to 5, characterized in that the secondary stream (1, 5) of atomizing gas is "divided into a plurality of streams injected in a uniformly distributed manner and equidistant around the liquid fuel stream (4) 7. Combustion method according to i any one of Claims 1 to 6, characterized in that the oxidizer jet is divided into a primary oxidizer jet and a secondary oxidizer jet, the primary oxidizer jet being injected close to the liquid fuel spray in order to cause a first incomplete combustion, the gases issuing from this first combustion still comprising at least part of the fuel, while the secondary oxidizer jet is injected at a distance I3 from the fuel spray which is higher than the distance between the liquid fuel jet and the primary oxidizer jet closest to the liquid fuel spray, in order to enter into combustion witt the part of the fuel present in the gases issuing from the first combustion. : 8. Burner comprising at least one liquid fuel injection means (7) combined with at least one; atomizing gas injection means (8) in order to produce a fuel spray (10) , and at least one oxidizer injection; means/ characterized in that it comprises at least one secondary atomizing gas injection means (11, 12, 14). arranged close to the fuel injection means. 9. Burner according to Claim 8, Characterized in. that the secondary atomizing gas injection means (11, 12, 14) is obtained by bypassing a common; atomizing gas feed (9) . 10. Burner according to either of claims 8 and 9,- characterized in that the secondary injection means (11, 12, 14) is oriented parallel to or obliquely to the fuel injection means (7) .

Full Text

The present invention relates to a method fo
combustion of a liquid fuel, and to a burne.
implementing the same.

During the installation of a combustion system for an industrial furnace, for example, one of the major concerns is to optimize the combustiom efficiency optimally controlling the flame properties, while meeting the needs of the heated method in terms of heat

transfers and minimizing air pollutant releases.
The two-phase combustion of a liquid fuel by ar oxidizing gas comprises two main stcps before the actual combustion takes place. In the first step, it

is necessary to atomize the liquid ; fuel using ai ) atomizing gas injected so as to destabilize the liqui fuel stream and to form a fuel spray with a higher contact surface area with the oxidizer in order to promote the combustion. The atomizing gas used may be

air, oxygen, steam or even natural gas, for example
' i It is then necessary for the liquid fuel drops thus
formed to evaporate before the fuel :burns with tbe oxidizer. Since the fuel drop vaporization time it longer than the reaction time, the 'mixture of th drops formed.

The spray characteristics depend on the type of injector used. Most injectors use a high speecd differential between the atomizing gas and the liquid fuel to destabilize the fuel and form the spray. Two types of injector are available according to whether high speed flow is imposed on the fuel or the atomizinc gas, that is, mechanical injectors in which the fuel is subjected to high pressure and flows at high speed through a small-diameter orifice, and injectora called
i r
"dual fluid" injectors in which a fuel jet flows at a
relatively low speed and is destabilized by a high speed flow of atomizing gas. However, mechanical injectors are little used because, on the one hand they incur higher risks of blocking , of the fue infection orifice by deposits, and 0n the other, limited flow range due to the high cost of the compressors needed to reach high liquid pressures.
Dual fluid injectors can allow for very ihigh atomizing gae flow speeds. In this category, a distinction in made between air-assiated atomizers, Qpieriating with low flow rates of gas ejected at very high ;sp(«ed, and spray atomizers characterized by lower atomizing gas flow speeds but higher flow rates. Two fluids can be mix in a confined environment (internal mixiing injector) outside the injection system {external mixing injector).

Furthermore, the liquid fuel flow may optionally be oriented to form a film on an appropriate surface before its contact with the atomizing, gas flow. In this case, the injector is called a prefilmins atomizer, with prior formation of a liquijd film, and i the opposite case, a plain jet atomizer, with full liquid flow.
The most commonly used injectors in oxy-combustion are injectors of the dual flow type with spraying with an atomizing gas speed lower than 200 m.s-1, with external mixing, and plain jet injectors.
The combustion properties of a spray produced by such injectors are mainly controlled by changing relative atomizing gag and liquid fuel speeds. Is doing so, the mean drop size of the fuel spray is modified, and consequently, the vaporization time compared with the combustion reaction I time is also changed. The drop size and vaporization time control the mixing of the evaporated fuel with | the oxidizer
and are hence very important combustion parameters,
determining particularly whether the combustion is
complete or not. However, although controlling the
injection speeds serves to adjust the properties of the
spray and of the two-phase combustion to adapt them to
the heated process, such injectors still have a lack of
flexibility.
For example, it is difficult to effectively control the cooling of the injector. In fact, an increase in the atomizing gas flow rate results in a reduction in the mean drop size, and consequently, a closer reaction zone and hence overheating of the injecttor.
Moreover, for an excessively high atpmiiing gas flow rate, the atomization mode may go from a fibre mode, that is, with a fully developed liquid cone, to a superpulse mode, that is, with a short ;and truncated liquid con«. In this case, the reaction zone is liable to stabilize in the immediate neighbourhood of the burnei and cause its destruction. , Moreover, an excessively high atomizing gas speed can also cause instability of the flame. In fact, it has been demonstrated that the stability of the flame could be related to the ratio of the mixiing .time to th« characteristic time of the combustion, chemistry, the flame being stable when this ratio is above 1- In the case of an excessive increase in the .atomizing gas speed, the mixing time becomes shorter than the characteristic time of the combustion chemistry, and the stability condition is no longer satisfied.
Another drawback is that the spray characteristics affect several parameters which are therefore not possible to control independently of one another Thus, it is not possible to control the spray drop siz and spray angle independently, charactieristics both dependent on the ratio of the momentum of atomizing gas to that of the fuel. More particularly, if this
momentum ratio is lower than 5, an. , increase in the
atomizing gas flow rate simultaneously, results in a
decrease in the drop size and a widening of the spray
angle, the flame being liable to inte^cti with those of
adjacent burners.
Another drawback appears in the cases tin which a hig i
viscosity fuel is used. In this case, a simple
atomizing gas stream injected in a ring around th
liquid fuel stream does not permit uniform atomization
producing a spray with uniform drop sizes. This causes
irregular combustion and problems of flatw
stabilization. : i '
i , ; ;
it ie the object of the present invention to overconv i
the abovementioned drawbacks and therefore consists o
a method for combustion of a liquid fueil comprising th steps for producing a spray of the; liquid fuel b; :
injecting a main stream of an atomizinjg gas in contac' ;
with the liquid fuel, the said method being
characterized in that at least one secondary stream of
atomizing gas is injected close to the spray in order
to produce a secondary atomization of the said spray
prior to its contact with a jet of oxidizer in order to
carry out the combustion of the fuel.
' ' i
Thus, for the same total atomizing gas flow rate, the flow rate of the first atomizing stream is decreased,

causing the formation of a spray with a higher size of th* drops formed in the neighbourhood, of the injector
The fuel drops of the first spray then undergo a second
atomization, leading to a modified spray with smaller
drops. A first spray having already been formed, the secondary atomization is more effective; particularly in the case of a high viscosity fuel, land entrains the drops of the modified spray further from the injector. Due to this staged atomization of thet liquid fuel, the combustion reaction takes place further from the iniector, thereby decreasing the risks of burner
overheating and destruction. It is important to observe that in the case in which the burner has a retractable injection head, the secondary atomization allows it to operate with a higher retraction.; Moreover, the atomizing gas flows thereby multiplied
permit more effective cooling of the burner. The injector service life is thereby increased and its
maintenance reduced.
This improvement in cooling the injector is
, , ' !
particularly advantageous in the case in which the
atomizing gas used is oxygen, a gas for which the risks
of overheating are high.
Furthermore, the presence of a secondary atomization
stream reduces the dependence between the drop size,
(flame length) and the spray angle (flame width) by: limiting the increase of the latter. The flame length can therefore be controlled more easily); while limiting the risks of interaction with adjacent turner flames.
A further advantage of the invention is the reduction of emissions of NOx compounds. In faet, the flame temperature obtained is more uniform, so that NOx; formation is reduced. This process is accentuated by a better dilution of the reagents and combustion products thanks to the secondary atomizing gas stream
According to a first exemplary embodiment of the, method, the secondary stream of atomizing gas is injected in a direction parallel to the injectior; direction of the liquid fuel.
.
According to a second exemplary embodiment of the
method, the secondary stream of atomizing gas is injected in an oblique direction convening towards the injection direction of the liquid fuel. This makes it possible to control the spray angle more accurately the modified spray angle being equal to twice the angle
between the secondary atomizing gas stream injection direction and the fuel flow direction. Advantageously, the secondary atomizing gas stream is injected at an angle of between 0 and 60°, praferably at an angle of
between 0 and 30°.
Optionally, adjusting means can be provided for orienting the secondary atomizing gas stream injection direction as regards the liquid fuel injection direction in order to increase the flame width, and
consequently, the heat transfer to the heated process,
if necessary. '
Advantageously, the secondary stream of atomizing gas
is injected so as to produce a turbulent flow. . Thus, the turbulent flow improves the dilution of the' reagents and combustion products andj further reduces the emissions of NOx compounds.
Preferably, the secondary atomizing gas floW rate.
represents between 20% and 70% of the total flow rate
of atomizing gas. - .'
Advantageously, the secondary stream of atomizing gas is divided into a plurality of streams injected in a uniformly distributed manner and equidistant arownd the liquid fuel stream. The injection can be carried out inter alia, by a concentric flow around the fuel injection or by a plurality of openings terminating in the burner head and uniformly distributed around the fuel injection. More precisely, the main atomizing gas stream is injected coaxially around the liquid fuel
while the secondary stream is injected via the
!
plurality of openings.
The method according to the invention is ideal for the staged combustion process in which the oxidizer ill injected and divided into several streams introduced at various distances from the fuel spray, as described is
particular in WO 2004/094902. Thus, the oxidizer jet
can be divided into a primary oxidizer jet and a
secondary oxidizer jet, the primary oxidizer jet being
injected close to the fuel spray in order to cause i first, incomplete combustion, the gases issuing from
this first combustion still comprising at least part of the fuel, while the secondary oxidizer j«t is injected at a distance I2 from the fuel spray; which is higher than the distance between the fuel Spray and the primary oxidizer jet closest to the fuel spray, in order to enter into combustion with the part of the fuel present in the gases issuing from the first combustion. The invention also covers, the case is which a third oxidizer jet is injectecd at a distance I2 from the fuel spray which is longer than the distance
I1
The method according to the invention IS ideal for two phase burners an which the atomizing Gas ie injected, on the one hand, at a speed at least, 10 times higher than the fuel injection speed, and on the other, with an atomizing gas mass flow rate higher than 10% of the
fuel mass flow rate.
The present invention further relates to a burner implementing the preceding two-phase combustion method the said burner comprising at least one fuel injection means combined with at least one atomizing gas injection means in order to produce a fuel spray, and at least one oxidizer injection means characterized in that it comprises at least one secondary atomizing gas injection means arranged close to the fuel injection means. It should be observed that in the case of a burner with highly separated jets. such a burner comprises a primary oxidizer injection means, * secondary oxidizer injection means arranged at a distance from the fuel injection means that is; longer than that of the primary injection means, and optionally, a tertiary oxidizer injections means
arranged at the edge of the burner.
Advantageously, the secondary atomizing gas injection means is obtained by bypassing a common atomizing gas feed. The choice of the bypass diameter serves to define a ratio between the primary atomizing gas stream and the main stream. Further advantageously, the secondary injection means is oriented parallel to or, obliquely to the fuel injection means.
The implementation of the invention will be better
understood from the detailed description given below with reference to the drawing appended here to in which:
Figure 1 is an enlarged partial schematic representation of a longitudinal cross section of an atomization head of a burner acjcbrding to the invention;
Figure 2 is a front view of the atomization head in Figure 1; and
Figure 3 is an enlarged partial schematic: representation of a longitudinal cross section of another atomization head of a burner according to the invention.
A combustion method according to the invention is; implemented by a burner comprising a spray-guidef atamization head 6 with external mining as shown in Figures 1 and 2. This atomization head 6 comprises:
an ejection line 7 for a liquid fuel stream 4; delivered by a fuel feed 2; and
an atomizing gas ejection If line 8 concentric; with the fuel ejection line 7 and connected to an atomizing gas feed 9 and terminating) in contact with the fuel stream 4 in order to produce la liquid fuel spray 10 under the action of a main atomizing gas stream 3,
Furthermore, the atomization head 6 has six secondary ejection channels ll oriented parallel to the fuel
ejection line 7 and to the atomizing gas ejection line 8. These six secondary ejection channels 11 are uniformly distributed around the ejection lines 7, 8 and are designed to create secondary atomizing gas, streams 1 tapped off from the atomizing gas feed 9 by bypass channels 12. Under the effect of these secondary atomizing gas streams 1, the. liquid fuel spray 10 thereby undergoes a second atomization producing a modified spray 13. Thia modified spray 13 is then contacted with an oxidizer stream (not shown), optionally divided into a primary stream and a secondary stream, to carry out the combustion of the fuel. A tertiary oxidizer feed may alao be located at a relatively long distance from the atomization head 6 and is used to inject oxygen at high spiced in order to obtain a sufficient dilution of the reagents before the main combustion zone and thereby to prevent an excessive formation of thermal NOx compounds. Experiments hav« demonstrated that such a burner, in which 50% of the total oxygen was injected at the tertiary feed level, served, all other things remaining. equal, to obtain a flame stabilization, distance equal to about four times the flame stabilization distance of a conventional injector without secondary atomizing gas stream. This longer stabilization distance serves to reduce the overheating of the atomization head 6. Furthermore, it has also been demonstrated that the flame obtained was more uniform and longer due to the delayed atomization, the spray 10 having a larger drop size than a spray issuing from a conventional burner while the modified spray 13 has a smaller drop size and; better diluted and hence more uniformly distributed
drops.
The more uniform flame thus obtained, conseiquently
reduces the temperature difference between the hot;
spots and the cold spots.
A significant reduction of NOx compound emissions by a
burner equipped with an atomization head 6 according to the invention has also been demonstrated. A reduction by a factor of between 1.2 and 1.5, depending on the oxidizer distribution selected, can be obtained for the
same total atomizing gas flow rate. This reduction can
ibe explained by the lag of the reaction zone obtained
thanks to the invention.
As a variant, an atomization head 1, as shown in, Figure 3, differs from the atomization head 6 only in the fact that it comprises secondary ejection lines 14 obliquely oriented by an angle a to the fuel flew direction. The angle a is advantageously between 0 and 60°, preferably between 0 and 30°. These secondary injection lines 14 deliver secondary atomizing gas streams 5 which, with the spray 10, form a modified spray 13 having a spray angle of 2a. Such an atomization head 1 is suitable for more accurate adjustment of the flame width.
Although the invention has only been described in connection with particular embodimentis, it is quite
obvious that it is not limited thereby and that it
comprises all the technical equivalents of the means
described and of their combinations if these fall within the scope of the invention.

CLAIMS
1. Method for combustion of a liquid fuel comprising the steps for producing a spray (10) of the liquid fuel by injecting a main stream (3) of ar atomizing gas in contact with the liquid;fuel (4), the
said method being characterized in that; at least one secondary stream (1,5) of atomizing) gas is injectecd close to the spray (10) in order to produce a secondary atomization of the said spray (10) prior to its contact, with a jet of oxidiser in order to carry out th«,
combustion of the fuel.;
2. Combustion method according to Claim 1, characterized in that the secondary stream (1) of atomizing gas is injected in a direction parallel to the injection direction of the liquid fuel.
3. Combustion method according , to Claim 1, characterized in that the secondary stream (5) of atomizing gas is injected in an oblique direction converging towards the injection direction of the
liquid fuel
4. Combustion method according to any one or
Claims 1 to 3, characterized in that the secondary stream (l, 5) of atomizing gas is injected so as to
produce a turbulent flow.
5. Combustion method according to, any one of Claims 1 to 4, characterized in that the atomizing gas flow rate in the secondary stream (1,5)of atomizing gas represents between 20% and 70% of the total flow rate of atomizing gas.
6. Combustion method according to any one of Claims 1 to 5, characterized in that the secondary stream (1, 5) of atomizing gas is "divided into a
plurality of streams injected in a uniformly distributed manner and equidistant around the liquid fuel stream (4)
7. Combustion method according to i any one of Claims 1 to 6, characterized in that the oxidizer jet is divided into a primary oxidizer jet and a secondary oxidizer jet, the primary oxidizer jet being injected close to the liquid fuel spray in order to cause a first incomplete combustion, the gases issuing from this first combustion still comprising at least part of the fuel, while the secondary oxidizer jet is injected at a distance I3 from the fuel spray which is higher than the distance between the liquid fuel jet and the primary oxidizer jet closest to the liquid fuel spray, in order to enter into combustion witt the part of the fuel present in the gases issuing from the first
combustion. :
8. Burner comprising at least one liquid fuel injection means (7) combined with at least one; atomizing gas injection means (8) in order to produce a
fuel spray (10) , and at least one oxidizer injection; means/ characterized in that it comprises at least one secondary atomizing gas injection means (11, 12, 14). arranged close to the fuel injection means.

9. Burner according to Claim 8, Characterized in.
that the secondary atomizing gas injection means (11, 12, 14) is obtained by bypassing a common; atomizing gas
feed (9) .
10. Burner according to either of claims 8 and 9,-

characterized in that the secondary injection means (11, 12, 14) is oriented parallel to or obliquely to the fuel injection means (7) .

Documents:

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Patent Number

268482

Indian Patent Application Number

1668/DEL/2006

PG Journal Number

36/2015

Publication Date

04-Sep-2015

Grant Date

31-Aug-2015

Date of Filing

20-Jul-2006

Name of Patentee

L'AIR LIQUIDE SOCIETE ANONYME POUR L'ETUDE ET L'EXPLOITATION DES PROCEDES GEORGES CLAUDE

Applicant Address

75 QUAI D'ORSAY, 75007 PARIS, FRANCE

Inventors:

#	Inventor's Name	Inventor's Address
1	BERTRAND LEROUX	3 PASSAGE DE 1'INDUSTRIE, 92130 ISSY-LES-MOULINEAUX, FRANCE
2	MOHAND AMIRAT	9 RUE EUGENE BERTHOUD, 93400 SAINT-OUEN, FRANCE
3	GABRIEL CONSTANTIN	17, RUE ALEXIS CARREL, 78530 BUC, FRANCE
4	PATRICK JEAN-MARIE RECOURT	5 RUE TOULOUSE-LAUTREC, 91460 MARCOUSSIS, FRANCE
5	REMI PIERRE TSIAVA	71, RUE ANDRE BRETON, 91250 ST GERMAIN-LES-CORBEIL, FRANCE

PCT International Classification Number

C07C 51/02

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	05/52431	2005-08-04	France