Method and Installation for Unsupported Lean Fuel Gas Combustion, Using a Burner and Related Burner

Abstract

The invention concerns a method for a lean gas combustion using at least one burner including a combustion nozzle on a central axis (x). The method includes creating a mixture of fuel gas and combustion air rotating about the central axis, and ejecting a flow of non-flammable premix containing a mixture of premix air and fuel gas in front of the combustion nozzle. A complementary flow achieves a non-flammability threshold of the mixture in front of the combustion nozzle, the flow being ejected at the center of the premix flow via a central complementary flow and/or about the premix flow via a peripheral complementary flow. The invention also concerns a burner configured to implement the method and a combustion installation using same.

Description

CROSS-REFERENCE TO RELATED U.S. APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

REFERENCE TO AN APPENDIX SUBMITTED ON COMPACT DISC

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention concerns a method for achieving combustion of an unsupported lean fuel gas, using a burner including a gas port nose on a central axis, creating, inside the burner, a mixture of fuel gas and combustion air, rotating around the central axis and in front of the gas port nose.

It also concerns a burner structure, particularly of great strength, for the application of the method and any gas combustion installation using this burner.

The invention is applied particularly in the various following installations:

• • Heating boilers, using gas of very low calorific value, waste gas (blast furnace gas . . . ), biogas and relief gas and gas originating from various processes;
  • Burn-off towers and flares of lean, residual gases and biogas;
  • Furnaces and drying ovens for various materials and products;
  • Furnaces and devices for drying and treatment of residual sludge generated by various processes; and
  • Installations for burning volatile organic compounds “VOCs”. These VOC compounds originate from drying or baking in different processes. Often these are fumes of solvents or oils and are found in very weak concentration (a few % at a few ppm or traces) in neutral carrier gases or in air. They may be blocked by dedicated filters or destroyed by thermal means. The low concentration does not allow burning them off directly and the large volume of air containing them significantly disturbs the combustion of the “classic” burners.

By lean gas, it is meant any gas of low calorific value, i.e. less than 3000 Kcal/m³ and in particular any very lean gas with a net calorific value (NCV) below 1000 Kcal and which concerns more specifically the subject of this invention.

The burner in accordance with the invention may nevertheless be used with richer gases or with support gases.

2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98

The burners of lean or residual gases include generally various infeed pipes of combustible fluids to the burner nozzle, the pipes being configured, especially in a coaxial shape, so as to create one or more rings of combustibles centered on the axis of the burner.

These combustible fluids are generally distributed in a flux of combustion air or on the periphery of the latter.

The above dispositions have the ultimate goal of creating an adequate air/fuel mix for achieving localized and stabilized combustion at the nose of the burner.

On high capacity boilers (>100 MW) which include several burners (>4 burners), the combustion air is usually distributed from a common air box to all burners and put into rotation by flaps that are adjustable from the outside by gear mechanisms and link rods.

This combustion air is generally fed to the nose of the burner (hereafter called combustion burner) in one flux or even in two.

These burners usually include rich gas distribution tubes in a peripheral ring and accessory tubes (ignition burner, flame presence control tube, . . . ) which upset the rotation of the air flux.

The majority of lean or residual gas burners is of a complex design and require unplanned settings and adjustments as well as very rigid operating conditions with a considerable number of incidents due to the instability of the combustion, of the flame catching on, leading to ill-timed shut-down events of the installation.

These burners require reheating of the fuel and especially of the combustion air at high temperatures (250 to 350° C.) [480 to 660° F.] in order to improve combustion which involves more items of appropriate equipment and additional costs.

Lean combustibles are generally very difficult to burn because they consist primarily of neutral gases and present themselves distributed in large volumes and under low pressure.

Mixing them with combustion air in adequate proportions is a very difficult undertaking, considering the volumes involved which is seriously hindering combustion and does not favor the stability and structure of the flames obtained.

The instability of the flames produced causes major variations of pressure in the combustion chamber, thereby generating vibrations of the structure of the boilers or installations concerned.

For this reason the burners always require a support flame, representing 10 to 20% of the total capacity of the burner, to ensure stability of the main flame and to guarantee the safety of the installation. Operating norms EN 746-2 make support flame systems mandatory in the burners.

These support flames are obtained with rich gases (natural gas, Liquefied Petroleum Gas (LPG)): Butane and Propane.

This requirement increases the complexity of the burner and inevitably causes very substantial extra expenditures, considering the price of rich gases.

The burners often require to be operated with a substantial amount of excess air to make sure that all combustible fractions are exposed to oxygen for a complete burn and in order to ensure the quality of the combustion products, which causes profits to shrink considerably, increases the specific consumption of rich gas and hence the operating costs and inevitably raises the level of polluting emissions.

The invention aims to remedy the above drawbacks.

It offers in particular a burner design which allows:

• • as much as possible to do without a rich gas support;
  • to do without reheating of the gas or the combustion air;
  • to reduce the oxygen content of smoke;
  • to eliminate vibrations; and
  • to reduce the consumption of electric power of air and smoke ventilators.

A preferred basic principle of the method is to partition as much as possible the quantity of air needed for combustion and to incorporate it as soon and as intimately as possible into the combustible gaseous flux (or the inverse), by improving the mixture through high-speed jet impacts by creating incidents of turbulence and by putting the mixture into maximum rotation in order to reduce the axial velocity of the mixture and to ensure the consistency and continuity of the combustion.

To reduce the axial velocity and to increase the flame surface, the lean gas is put into rotation by blades and the specific flow of the fraction of combustion air brought in at the periphery at the exit of the burner.

Since lean gases do not have a large volume, it is difficult to intimately mix the combustible elements of this gas with the oxygen of the combustion air. To lessen this less difficulty the invention consists of fragmenting the combustion air and of progressively incorporating chosen quantities of it into the lean gas flux.

The method consists therefore of creating a pre-mix of air and fuel (outside the flammability limit) preferably inside the body of the burner and to bring to the nose of the burner only the air complement on both sides of this mixture through the expedient of jets at very high speed (above 80 m/s) [above 262.5 ft/sec] by making the gas “in a sandwich”.

The combustion air directed to the nose of the burner has specific flows at high speed:

• • the central air is ejected in rotation and in divergent flow in order to penetrate the lean gas; and
  • the peripheral air is convergent and in strong rotation.

These two air flows also both have the function to form a barrier to potential “flashbacks” at a low intensity or during a shutdown of the installation.

BRIEF SUMMARY OF THE INVENTION

To that effect, the subject of the invention is a method to obtain the combustion of a lean fuel gas using at least one burner including a gas port nose or head on a central axis, a process in which a mixture of fuel gas and combustion air is created in rotation around a central axis.

The method distinguishes itself by consisting of the following stages in which the following are ejected in front of the combustion head:

• • a flux of nonflammable pre-mix containing a mixture of pre-mix air and of fuel gas; and
  • a complementary flux so as to reach an ignitibility threshold of the mixture in front of the gas port nose, the flux being ejected in the middle of the pre-mix flux by way of a complementary central flux and/or around the pre-mix flux by way of a complementary peripheral flux.

According to particular application modes of the method:

• • the complementary flux is an air flux;
  • the pre-mix flux is obtained through incorporation of pre-mix air into fuel gas;
  • the incorporation is achieved in a mixing chamber connected to the burner;
  • the incorporation is made, at an entry of the fuel gas into the burner by injection of pre-mix air into the fuel gas in a manner such as to draw the fuel gas in a pre-mix space, to obtain the pre-mix through incidents of turbulence resulting from the injection and to direct the pre-mix towards the gas port nose by initiating a rotation around the central axis; and
  • the mixture of fuel gas and combustion air is obtained by incorporating a necessary partitioned quantity of one in the other by numerous directed jets.

According to another mode of applying the method:

• • a) the flux of central complementary air is ejected in rotation in front of the gas port nose and in divergent discharge to penetrate the pre-mix flux; and
  • b) the flux of peripheral complementary air is ejected in convergent discharge and in a strong spiral rotation.

The invention is also concerned with a burner for lean fuel gas of the type that includes a gas port nose on a central axis and means to feed a mixture of fuel gas and combustion air in rotation around the central axis, the burner being especially noteworthy because it includes neither a mixing chamber nor a combustion chamber.

The burner distinguishes itself primarily by being configured so as to eject in front of the gas port nose:

• • a nonflammable pre-mix flux containing a mixture of pre-mix air and fuel gas, and
  • a complementary flux so as to reach an ignitibility threshold of the mixture in front of the gas port nose, said flux being ejected to the center of the pre-mix flux by way of a flux of central complementary air and/or around the pre-mix flux by way of a flux of peripheral complementary air.

According to a particular way of carrying out the invention, the burner is configured so as to divide a flux of air into at least one flux of pre-mix air and a flux of complementary air, comprising at least one flux of central complementary air and/or one flux of peripheral complementary air.

The invention is also concerned with an installation for the combustion of fuel gas applying the method or comprising at least one burner in conformance with the invention.

According to an advantageous characteristic, the installation uses or includes at least two burners that are configured so as to gear in a common direction the overall rotary motion resulting from their mixture flux in front of the gas port nose.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other particularities and numerous advantages of the invention will appear in the description below, given as an illustrative and non-limiting example, and made with reference to the attached figures.

FIG. 1 shows a schematic view of an installation for lean gas combustion, equipped with a burner in accordance with one way of carrying out the invention.

FIG. 2 shows a partial sectional view along axis AA of FIG. 1.

FIG. 3 shows a back view of the burner as per the right side view of FIG. 1.

FIG. 4 shows a partial sectional view of a beam as per section CC of FIG. 2.

FIG. 5 shows a partial bottom view as per D-D of FIG. 4.

FIG. 6 shows a detailed schematic view of the chamber 7 of the burner in FIG. 1.

FIGS. 7, 8, and 9 show different sectional and partial section views, respectively, of FIG. 6: a sectional view along E-E, a right side view along F, and a left side view along G.

FIGS. 10, 11, and 11A show, respectively, a detailed schematic view of the central tube 13 of the burner of FIG. 1, a left side view along H and a right side view.

FIG. 12 shows a detailed sectional view of the central pole 50 as per FIG. 1.

FIG. 13 shows a partial sectional and schematic view of a construction variant of a flaring cone of the central pole.

FIG. 14 shows a detailed sectional view of FIG. 9.

FIGS. 15 and 16 show, respectively, the sectional views along L-L and K-K of FIG. 14, respectively.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an installation 1 for the combustion of lean fuel gas, using a burner 2 mounted between 4 main parts ZA, Zb, ZC, ZD that are separated by three partitions 3,4,5.

The parts represent, respectively, a zone ZA firebox where combustion takes place, a zone ZB containing or in communication with the lean fuel gas, a zone ZC containing or in communication with combustion air, a zone ZD that is exterior to the installation and accessible to personnel.

The installation is, for example, a production facility for superheated steam at a rate of 40 T/hour in which blast furnace gas is to be burnt, at ambient temperature, (humidity=2.5% of H₂O by volume), low-pressure fed (<300 mm CE relative pressure) and an average composition on dry gas: N2=58%, H₂=1.7%, CO₂=20.3%, CO=20% (PCI=660 Kcal/m³n). The products of combustion must contain less than 50 ppm of CO with less than 1% of oxygen in these fumes. Ignitibility of this gas occurs when there is 35% to 73% of gas in the mixture.

The burner includes a gas port nose 6 ending in Zone A of the chamber. The nose is centered on a central axis X which happens to be, under the circumstances, the main axis of the burner to the extent that the latter has a general circular shape around this axis.

The burner also includes means to feed this nose which are capable of ejecting a flux of air and fuel gas in rotation around a central axis centered on the gas port nose.

This nose which constitutes the front end of the burner is intended to receive, in front of or on it, to the left of the figure, a flux of fuel gas and combustion air which is put into rotation around the central axis, with means to feed this nose provided for this purpose and which are described subsequently.

The burner also comprises a central chamber 7 connected to the nose and upstream of the burner (relative to the direction of the flux discharge) and mounted in zone ZB between partitions 3 and 4, with at least one opening 8 ending in this zone ZB.

In zone ZC, there is a back end 7B of the burner linked to chamber 7, upstream of the latter, and presenting at least one access for at least one inflow of combustion air of zone ZC.

The air supply in the preferred example is done entirely by the rear face of the burner for several advantages:

• • guarantee the tightness of the assembly;
  • facilitate access to the pre-mix air controls;
  • be able to install the burner in the air chamber; and
  • be able, depending on the application, to realize separate supplies of different types of combustion air.

In zone ZD, various pipes discharge which extend between the chamber and the exterior, while crossing the burner and among which pipes one finds, if applicable, a rich gas supply pipe, a flame control pipe, an ignition pipe or other pipes or equipment known to the experts (not shown).

According to a way of carrying out the invention, the method may include a first stage in which a flux of air intended for combustion is divided into at least one flux of ore-mix air and a flux of complementary air. The complementary air is constituted of at least one central flux of air and/or one flux of peripheral air.

In the example shown, one uses both the central and the peripheral flux of air for improved efficiency and versatility in usage and the division is made by different air inlets at the back of the burner or routing of the air in the burner.

To this effect, in the example of execution shown, the burner is configured to divide the air coming from the space ZC into several flux (flows). It comprises a number of intakes or access on its back end: a central access 9 to receive an intake of a flux of central air, a peripheral access 10 to receive an intake of peripheral air, and at least one main access 10A to receive an intake of pre-mix air. More access points can be added as indicated later on.

In a variant execution, this dividing step could be done differently, for example by external pipes outside the burner, and each flux of air could be supplied by independent and external pipes.

In a second step of this type of execution, in front of the gas port nose, a pre-mix flux is ejected containing a mixture of pre-mix air and of fuel gas, in rotation around the central axis. The pre-mix flux is nonflammable to the extent that it is mixed at a rate far from the ignitibility ranges, for example above an ignitibility threshold. In effect, in the example described here, one goes from a lean gas rate of 100% to a rate of 80-85% (in the gas+air mixture) whereas the limits of ignitibility are between 30 and 73% in the mixture.

This assumes that the pre-mixture and its rotation are carried out beforehand, as described below.

In order to improve combustion and to ensure good flame retention, it is of interest and importance to achieve the most thorough pre-mixture and at the earliest moment possible.

For this second step, the burner, in the example described, is configured to achieve the preceding pre-mix inside itself, in this particular case in a so-called pre-mix space 16 of the chamber 7.

It is also configured to place the pre-mix into rotation. This rotation, in the example described, is also preferably achieved in the chamber upstream of the gas port nose.

To this effect, the pre-mix air access points 10A mentioned above lead to the chamber for the same reason as the fuel gas access ports 8 for the purpose of obtaining a pre-mixture using the mixing devices 11 described later on.

However, in a variant, the pre-mixing could be done beforehand outside the burner, for example, in an enclosure provided for this purpose in which a rate above the ignitibility rate is maintained.

For the gas concerned of the example, the mixing occurs at a rate between 5 and 20% above the ignitibility threshold with an insufficient air percentage (proportions going between 78 and 95% gas in the mixture),

For reasons of safety and efficiency, one prefers to adopt a rate that is 10 to 20% below the total air to be supplied.

As a variant, one could, for certain applications, implement the method by obtaining a pre-mixture with an insufficient rate of fuel gas in the same proportions between 5 and 20% or with different proportions for particular applications of biogas or VOC (volatile organic compounds) burns.

In a third step of execution, the complementary flux is ejected a the center of the pre-mix flux by way of the flux of central complementary air and/or around the pre-mix flux by way of the flux of peripheral complementary air, in a manner so as it reaches the threshold of ignitibility at the gas port nose.

In the example described, ejection of the complementary flux occurs simultaneously at the center and in the periphery in order to achieve a better final mix.

For this purpose, the burner is configured so as to deliver the pre-mixture flux in the form of ring 12 located between a central pipe 13 and the periphery 14 of the front end of the chamber.

According to a mode of execution of the method, the pre-mixture flux is obtained by incorporating pre-mixture gas in fuel gas.

In effect the lean, and generally residual, combustibles are distributed under very low pressure and in consideration of the large volumes involved, it is important to facilitate the flow of these gases by the effects of mechanical drives.

For this application, the burner includes the incorporating devices 11 mentioned earlier which inject air into the fuel gas.

Incorporation is done directly in an enclosure of the chamber having a pre-mixture space 16 (FIG. 2) located between a central pipe 13 and an internal partition 31 of the chamber.

According to a mode of execution, incorporation is achieved by injection of pre-mix air at an entry point of the fuel gas into the burner so as to:

• • drive the fuel gas into a pre-mix space 16,
  • obtain the pre-mixture by turbulence resulting from the injection, and
  • direct the pre-mixture towards the gas port nose while initiating a rotation around the central axis.

For this purpose, the burner includes injection devices including nozzles 17 or calibrated directional high-output orifices located in the incorporation devices 11 that are profiled and directed towards the pre-mixture space 16 at the ports 8.

The gas located near and around the ports 8 is driven by the partial vacuum generated by the air jets at the exits of the nozzles which are directed by the orientation of the jets and [the gas] is mixed by the turbulence created by the jets. A rotational movement of the mixture is also initiated in the pre-mixing space by the orientation of the air jets.

These injection devices are preferably for constant duty.

The incorporating devices may also preferably comprise second means of pre-mix air injection. These means of injection are placed so as to obtain an incorporation of air parallel to the central axis and by directing the pre-mix flux towards the gas port nose.

These means of injection have preferably a progressive state condition depending on the level of power used.

These second means of injection may be formed, as in the example described, by tubes 21 around orifices 22 in the partition 23 of the back end of the burner (FIGS. 3, 10, 11). These tubes are preferably of different lengths and are five in number in the example. They extend to the interior of the pre-mixing space from air intakes or orifices 22 located on the partition 23 or back face of the burner.

The orifices 22 are preferably capped by flaps (not shown) that can be operated by scaled springs or electric controls.

The flaps may be located on the orifices with or without tubes. The tubes allow, on the one hand, to avoid the respective flows upsetting each other and, on the other hand, to supply air at different points with a guarantee of its distribution.

The orifices have a determined size so as to avoid finding themselves too massively inside the limits of ignitibility and that there may locally be conditions that are favorable to a combustion that would deteriorate the burner.

Alternatively, one could obtain the incorporation of gas in the air, for example by interchanging the different inflows and regulating the respective outflows. This variant may be considered in particular for heating large volumes of air (drying applications) or for burning VOCs.

In this case, the pre-mixture gas would replace the pre-mixture air and the flows, the pre-mixture could be unchanged and the central and peripheral flows could involve for instance fuel gas instead of combustion air.

According to one way of carrying out the invention, the flux of central complementary air is ejected in rotation in front of the gas port nose and in divergent flow to penetrate the pre-mix flux and the flux of peripheral complementary air is ejected in a convergent flow and in strong spiral rotation.

To this effect the burner is configured in the example with a cone-shaped deflector 18 at the exit of the central pipe 13 and blades 19 in the pipe which put the central flux of air into rotation. Other equivalent means may also be suitable, as for example calibrated directional orifices or oriented ports in a separating partition.

Preferably the central air is divergent with an angle at the top of 60 to 180° or of 30 to 90° in relation to the axis of the burner.

This ejection produced in this way allows achieving good penetration of the air in the pre-mixture so as to best complete the rate of missing air.

The flux of central air of the example has previously penetrated the intake 9 in the internal conduit of pipe 13, in the ring space around the central pole 51.

If applicable, this central air can have another function that is explained later on, which is to feed at its ejection base a rich gas which would be distributed in ring shape around the central air, during its use, in particular during startups or shortages of lean gas.

As to the peripheral complementary air, the burner is configured with injection nozzles 20a, 20b located on a ring 14 on the front end or face of chamber 26a. The nozzles are oriented both tangentially to a circle centered on the central axis and oriented towards the front. Spiral rotation is obtained by this dual slant of the nozzles.

The peripheral air wraps around the flux of lean gas and enhances its rotation. It is distributed at high speed and optimizes the mixing.

Nozzles 20a, 20b are fed by the space of peripheral pre-ejection 30 located in a double partition of the chamber at the front of the chamber which is itself fed by the intake devices 10A that have been provided in the vicinity of the back end 26b of the chamber.

The sub-components of the burner are now described below, with reference to the corresponding figures, namely, the chamber, the central tube and the central pole.

The chamber of the burner:

In reference to FIGS. 6 to 9, the chamber 7 has a general rotational shape and consists of:

• • a dual peripheral wall formed by an external wall 24 and an internal one 25,
  • a front end or face 26a, formed by a ring 14 including the means for peripheral injection 20a, 20b;
  • a back end or face 7B including different intakes or feeds 10, 10A at least for a flux of peripheral air and of pre-mixture,
  • a space 27 for air circulation divided by the double wall allowing to let the two ends 26a and 26b be in communication with each other,
  • intake ports 8 on the double peripheral wall, these ports being intended to interface each other between an internal space 16 in the so-called pre-mix space chamber and the outside,
  • conduits, in the form of hollow girders 11, located in the thickness of the double wall, these conduits extending between the ports 8, between a receiving space for air flux 10A or intake located at the back end 7B and a pre-ejection space 30 of the peripheral air located at the front end, and
  • pre-mix air injection nozzles 17 located under the conduits, these nozzles being configured so as to perform said first permanent injection of pre-mix air, these conduits and the nozzles being part of the means of incorporation mentioned previously.

The nozzles are in fact exit perforations made in the ring one of the functions of which is to close off the front end of the double wall of the chamber. The other back end of the double wall is closed off by a wall 23B.

These perforations communicate with the pre-ejection space 30 of the double wall and lead to the outside through an internal wall of the chamber. The nozzles are arranged on the ring, being offset relative to the radial axis R of the chamber and slanted towards the front relative to a plane perpendicular to the chamber.

The nozzles are offset and slanted in different ways according to an alternation. The angles proposed are specific to this power of the burner, but would be inevitably modified for another size burner. These angles have been determined so that the jets of consecutive orifices do not interfere with each other and do not collide with the end of tube 13 nor impede the flow of fluids coming out of the gas ring contained between 13 and 56, nor the divergent complementary central air. This divergent cone must practically “mesh” with the convergent complementary peripheral jet with the most acute angle (here 15°).

The angle of the next orifice is more open in order to continue further along in the rotation the work of the preceding orifice.

A first series of nozzles (20a) maybe slanted from 5° to 45° to the front, (15° preferred in the example of execution) and from 30 to 65° relative to the radial axis (R), (44° preferred in the example) and a second series of nozzles (20b) slanted from 25 to 65° to the front (45° preferred in the example), and from 30 to 70° relative to the radial axis (53° preferred in the example).

The chamber may also include orifices 55 arranged on the internal wall 25 at the height of the pre-ejection chamber 30. These orifices permit feeding the blade device 37 from the chamber 30 in order to improve the air/lean gas mixture between the blades.

The central tube:

In reference to FIGS. 10 and 11, a central tube 13, meant to be installed centered on the central axis, is dimensioned to extend longitudinally between the two ends of the chamber and to put in communication with each other.

This tube includes:

• • an outside surface 35 for the purpose of delimiting the pre-mix space with the inside wall 25 or the inside face 31 of the double wall of the chamber, and an inside surface 52;
  • fasteners at the chamber and reception devices of an air or gas chamber located at the end of the tube; and
  • a first set of blades 37, located at the front of the tube, said blades 37 extending into the pre-mix flow space between the outside wall 35 of the tube and the inside wall of vessel 25 or inside face 31.

The blades are profiled so as to create a rotation of the pre-mix flux during its flow towards the exit of the vessel. A space between the vessel and the tube forms a ring-shaped conduit 38 (FIG. 1) intended to convey the flux of pre-mix air. A wall 23 forms a radial collar of the central tube, said wall separating the pre-mix space with the back end of the central tube which is itself in communication with the air chamber.

The central pole:

In reference to FIG. 12, the central pole 51 is intended to be located in the central tube 13 and centered on the central axis.

The burner also includes a second set of blades 19 located inside and in proximity to the front end of the central tube.

In the example, the blades are attached to the central pole 51 which crosses the central tube. They are meant to extend from the surface of the pole 50 to the inside wall 52 of the central tube.

The burner may also include a “burn cone” 18 as a deflector located downstream of the central tube and spaced from it so as to provide a divergent outflow of the central flux of air. In the example shown, the burn cone is placed at the front end of the axial pole 51.

The gas is ejected at the end of the pole, at a divergent angle that is defined by a series of calibrated orifices 54 placed in a ring form around the cone shaped deflector 18 which allows to eject this gas over a maximum circumference so that any rich gas jets that may be present and originate as close as possible to the central combustion air and have maximum momentum when colliding with the flow of lean gas.

Preferably, for best results, the cone shaped deflector maybe a deflector 18b with a peripheral serration 52 and have central orifices 53 leading to the inside of the conduit of the central pole.

In general, the burner is designed to receive, under normal operating conditions, an ejection of complementary flux at a very high speed above 100 m/second whereas the pre-mix flux is ejected at a speed between 40 and 80 m/sec.

If applicable in a variant of execution, the burner may include a rich gas supply. In the example, the rich gas is brought in under pressure to the periphery of the central tube directly to the pre-mix space.

Preferably, for very high capacity burners (over 20 Megawatt), the rich gas is distributed around the central tube so as to mix thoroughly with the pre-mixture.

To that effect the central tube may contain:

• • a ring-shaped vessel 36 for receiving and distributing gas around several orifices crossing the rear wall 23 in the shape of a radial collar of the central tube;
  • a portion of tube 56 arranged in double wall around the central tube so as to convey the flux entering the pre-mix chamber to essentially half way into the chamber; and
  • a connection cone 57 from the double wall to the vessel through the intermediary of the collar so as to collect the rich gas;
  • as an accessory, a ring-shaped deflector 58 placed at a distance from the end of the double wall so as to diverge the rich gas and promote a good stirring with the air; and
  • alternatively or as a complement to the deflector above, a series of orifices 59 that are calibrated and placed across the central tube is arranged in form of a ring just upstream of the deflector 58 so as to let the complementary central air be ejected into the flux of rich gas and to contribute in this way to make it diverge.

According to a variant of execution, the vessel 36 maybe connected to a rich gas supply tube (the orifices 10A2 being blanked off) or another vessel 36B (not shown) wrapped around vessel 36 and connected to the supply tube. Calibrated orifices arranged with a divergent angle may be made in a ring connecting the two tubes 13 and 56B at the front end.

Possibly, the double wall 56 tube portion may extend to the end of the central tube 13, forming a central double wall 56B so as to eject the rich gas directly to the gas port nose around the central air.

On the other hand, for burners of lower capacity (for instance less than 20 MW), the rich gas is, still under pressure, brought into the central pole. It is ejected at a defined divergent angle by a series of calibrated orifices 53 arranged in a ring around a particular device (deflector with peripheral serration 52) which allows to eject this gas on a maximum circumference so that the rich gas jets originate as close as possible to the combustion air and have maximum momentum when colliding with the flow of lean gas.

The above configurations make it possible to obtain a consistent flame of a continuous structure and maximum surface (optimization of thermal transfer in the burn chamber). The rich gas is thus supplied with combustion air at its base, whatever the composition/proportion of the fuels: single and pure gas or gas in mixtures.

The burner is designed in mechanic/welded modules which allow for a maximum of flexibility and ease of design, adaptation, construction, installation and maintenance, in the knowledge that:

• • the combustion air may be more or less hot,
  • for installations with multiple burners mounted next to each other, the directions of rotation of the fluids must be coordinated so they won't upset the combustion and the flows in the burn chamber,
  • it allows to easily replace existing burners, and
  • the rich fuels may be of different qualities.

The possible flows of the different flux are described in accordance with one operating mode of the burner.

An ignition flame is brought to the nose of the burner through the intermediary of a guide tube 60 (FIG. 1). The permanent air system is then activated by a pump (not shown) which blows combustion air into the back end of the burner by putting the air supply vessel ZC under pressure.

A fraction of the combustion air penetrates into the double wall 27 of the vessel (FIG. 6) across the inlet orifices 10 that are for example rectangular and made in the ring-shaped wall 23B closing the double wall at the rear. Whereas another fraction penetrates directly into the double vessel towards the nozzles 20a, 20b.

A portion of this fraction penetrates into the girders 11 (FIG. 8), whereas the other portion feeds directly into a pre-ejection chamber of peripheral air 30 by way of a partial, so-called deflection double wall of the vessel (FIG. 7) which features no ports and which extends at an angle of approximately 90° between the radial walls 32 and 33.

The girders are put under pressure and combustion air escapes from the nozzles in a tangential direction (FIG. 7) to a circle centered on the central axis and towards the blades of the first rotation device.

The combustion gas which may be under light pressure (generally less than 200 CE) enters crosswise into the vessel under an effect of entrainment of the air jets at the level of the ports 8 between the girders 11. The turbulence results in a pre-mixing or stirring inside the pre-mix space 16 of the vessel at the entry of the blade device (FIG. 7), especially by deflection against the deflection wall 31.

Since the girders also open into the pre-ejection chamber 30 of peripheral air, they contribute to the air supply there in addition to the air conveyed by the inside of the deflection or guide double wall 24, 25.

Combustion air also penetrates by entry 9 of the central tube 13 (FIGS. 10, 11) and opens directly at the level of the nose 6, after having entered the space between the blades of the second blade device 19 (FIG. 2) where it assumes a rotational movement. This air re-exits in front of the nose in a deflecting manner by way of the cone shaped deflector 18 placed in front of it.

During this time the peripheral air is ejected from the chamber 30 (FIGS. 9, 14-16) in the form of two swirls by way off the peripheral nozzles 20a, 20b in front of the gas port nose.

When the pre-mixture arrives at the exit in front of the burner where it is ejected in a ring shaped swirl, it is squeezed and stirred between the central and peripheral flux of air which penetrate it thoroughly.

The rotational direction of the different flux of air may be opposite that of the pre-mix flux, but preferably they should be in the same direction.

If applicable, supplemental air may enter the pre-mixture chamber by tubes 21 or flaps (FIGS. 10, 11) arranged on a ring-shaped wall 23 coming from the collar of the central tube and helping to enrich the air mixture.

Air may also come from the back end of the vessel 36 through orifices 10A2 and enrich the pre-mixture.

If applicable (FIG. 6), air may escape from the vessel beginning from the pre-ejection chamber 30 through orifices 55 made in the inside wall of the vessel and it penetrates radially in the blade device 37 between the blades. This helps to improve the stirring of the gas mixture with air.

If several burners are used which are arranged near each other in a combustion chamber of an installation, care must be taken to ensure that the different swirls mesh. To this effect, the orientation of different nozzles and blades must be adapted. For example, the peripheral swirls should be working in opposite between two burners.

In this way the invention provides the following advantages:

• • the flame is stable and has caught on well, and one eliminates all the vibrations caused by unstable combustion;
  • no adjustment is required;
  • the combustion air can be divided into more than two, even more than three fractions;
  • there is no need for a support fuel to compensate for irregularities in the mixture or in the leanness of the fuel gas, nor for devices or associated equipment which allows you to save rich gas if there is a shortage of lean gas;
  • possibility to function normally with pure rich gas and rich gas only;
  • elimination of the need for heating gas or combustion air, as a result of the burner's capability to properly burn gases with very low NCV (<750 Kcal/m³) in cold gas and cold air; generally heating of combustion air of a 20 MW occurred at 200° C. [392° F.];
  • reduction in the oxygen content of fumes because of very good combustion due to an optimized air-fuel mixture. The oxygen content in fumes has been reduced to 0.6-1% instead of 2%;
  • there is a rise in the flame temperature from 60 to 80° C. [140 to 176° F.] bringing about a significant increase of thermal transfers in the combustion chambers (+15%), productivity of the boiler being thereby improved, if the re-superheating can follow;
  • there is a significant reduction of losses to fumes (at constant temperature) because the volume of fumes drops in the same proportion as the air factor, by 10 to 15%, thereby the boiler output being improved by at least 1 point, for a 100 MW boiler, representing more than 10 GWh/year of fuel; and
  • reduction of electric power consumption of ventilators for air and fumes to be stirred to the extent that the volumes of air and fumes to be stirred are smaller, this also resulting in smaller size (by 15 to 20%) blower and draught fans and a reduction in their power consumption of more than 10%.

Claims

1. Method to achieve combustion of lean fuel gas using at least one burner comprising a combustion nose on a central axis, said method comprising the steps of: creating a pre-mixture containing pre-mixture air and fuel gas, said pre-mixture being inflammable; andejecting, in front of said combustion nose, said pre-mixture in a flux of pre-mixture in rotation around said central axis and a complementary flux, an ignitibility threshold of the mixture in front of the gas port nose being reached, a flux being ejected in a center of the pre-mixture flux by way of a central complementary flux or around the pre-mixture flux by way of a peripheral complementary flux.

2. Method as per claim 1, wherein said complementary flux is comprised of a flux of air.

3. Method as per claim 1, wherein the pre-mixture flux is obtained by incorporation of pre-mixture air into fuel gas.

4. Method as per claim 3, wherein said incorporation is carried out in a vessel connected to the burner.

5. Method as per claim 3, wherein said incorporation is performed, at an entry of the fuel gas in the burner, by an injection of pre-mix air so that this injection of pre-mix air drives that fuel gas into a pre-mixture space and achieves the pre-mixture by turbulence resulting from the injection and directs the pre-mixture towards the combustion nose while initiating a rotation around the central axis.

6. Method as per claim 1, wherein the complementary flux is ejected in rotation in the same sense of rotation as the pre-mixture flux.

7. Method as per claim 1, wherein the flux of central complementary air is ejected in rotation in front of the gas port nose or head and in divergent flow in order to penetrate the flux of pre-mixture, and wherein the flux of peripheral complementary air is ejected in convergent flow and in strong spiraled rotation.

8. Method as per claim 1, wherein the mixture of fuel gas and combustion air is achieved by incorporating a necessary partitioned quantity of one in the other by numerous oriented jets.

9. Burner for lean fuel gas, the burner comprising: a gas port nose on a central axis; anda means for creating a non flammable pre-mixture containing a pre-mixture air and fuel gas the pre-mixture being ejected in front of the combustion nose, the non-flammable pre-mixture being in a flux of pre-mixture in rotation around the central axis, the pre-mixture in front of the combustion nose having a complementary flux so as to reach an ignitability threshold, a flux of the mixture being ejected at a center of the pre-mixture flux by way of a central complementary air flux or around the pre-mixture flux by way of a peripheral complementary air flux.

10. Burner as per claim 9, wherein an air flux is comprised of at least one flux of pre-mixture air; and one flux of complementary air, said one flux of complementary air being comprised at least one flux of central complementary air or one flux of peripheral complementary air.

11. Burner as per claim 9, wherein the complementary flux is ejected in rotation in the same sense of rotation as the pre-mixture flux.

12. Burner as per claim 9, wherein the flux of central complementary air in rotation in front of the combustion nose and in divergent flow to penetrate the pre-mixture flux, and the flux of peripheral complementary air in convergent flow and in strong spiraled rotation are ejected.

13. Burner as per claim 9, further comprising: means for incorporating pre-mixture air into fuel gas, obtaining the pre-mixture flux.

14. Burner as per claim 13, said means for incorporating comprising: means for injecting a first permanent injection of pre-mixture air into a pre-mixing upstream of the gas port nose, said space being intended to be in communication with an enclosure containing the fuel gas, said injection being performed so as to drive the fuel gas into the pre-mixture space, to achieve the pre-mixture by turbulence resulting from the injection and to direct the pre-mixture towards the gas port nose while initiating a rotation around the central axis.

15. Burner as per claim 14, said means for incorporating further comprising: a second means for injecting pre-mixture air, said second means for injecting being arranged so as to achieve an incorporation of air parallel to the central axis in a progressive manner, depending on the level of power used, and so as to direct the pre-mixture flow towards the gas port nose.

16. Burner as per claim 9, further comprising: a cylindrical vessel having a peripheral double wall, a front end configured to deliver the flux of peripheral air on the gas port nose, and a back end configured to receive at least air flows, the two ends communicating with each other by way of an air circulation space divided by the double wall, said cylindrical vessel having entrance ports on the peripheral double wall intended to interface each other between an internal, so-called pre-mix space space in the vessel and the outside in a gas-holding enclosure, and said cylindrical vessel having conduits, being comprised of hollow girders, located in the thickness of the double wall and extending between the ports between a receiving space of air flux situated at the back end and a pre-ejection space of peripheral air situated at the front end, said conduits comprising pre-mix air injection nozzles configured so as to achieve said first permanent injection of pre-mixture air.

17. Burner as claim 16, further comprising: a central tube centered on the central axis inside the cylindrical vessel and extending between the two ends of the vessel (26a, 26b) said tube being comprised of an outside surface intended to define the pre-mixture space with the internal wall of the double wall of the vessel, fasteners at the vessel and reception devices of an air or gas chamber (36) located at the end of the tube, and a first set of blades 37, located at the front of the tube said blades being profiled so as to create a rotation of the pre-mix flux during its flow towards the exit of the vessel and extending in the pre-mix flow space between the outside wall of the tube (35) and the inside wall (31) of the vessel.

18. Burner as per claim 17, said tube being further comprised of a second blade device located inside and in the vicinity of the front end of the central tube, said blades being attached to a central pole and extending between the surface of the pole and the inside wall of the central tube.

19. Burner as per claim 15, wherein the second air injection is performed through the intermediary of orifices located on a wall in the form of a collar of the central tube, said wall separating the pre-mixture space with the back of the central tube in communication with the air vessel, said orifices being closed off by flaps that can be operated by scaled springs or by switchable controls.

20. Burner as per claim 16, said cylindrical vessel further comprising exit perforations in the form of nozzles communicating with the pre-ejection space in the double wall and discharging to the outside on an internal wall of the vessel or equivalent, said nozzles being arranged in ring form and offset relative to the radial axis of the vessel and being directed towards the front.

21. Burner as per claim 20, further comprising: a first series of nozzles slanted forward between 5° and 45° and between 30 and 65° relative to the radial axis and a second series of nozzles slanted forward between 25° and 65° and between 30° and 70° relative to the radial axis.

22. Burner as per claim 18, further comprising: a burn cone forming a cone-shaped deflector located downstream of the central tube and spaced from the central tube so as to provide a divergent outflow of the central flux of air.

23. Burner as per claim 22, wherein the cone-shaped deflector is located at the end of the axial pole crossing the central tube.

24. Burner as per claim 22, wherein the cone-shaped deflector is comprised of a peripheral serration and central orifices leading to the inside of the conduit of the central pole.

25. Installation for the combustion of a fuel gas, implementing the method as per claim 1.

26. Installation as per claim 25, further comprising the step of using at least two burners so configured as to mesh in the same direction the overall rotational movement resulting from their mixture flow in front of the gas port nose.