WO2007012755A1 - Method and installation for unsupported lean fuel gas combustion, using a burner and related burner - Google Patents

Abstract

The invention concerns a method for a lean gas combustion using at least one burner comprising a combustion nozzle on a central axis (x), said method consisting in: creating a mixture of fuel gas and combustion air rotating about the central axis. The method is characterized in that it includes the following steps which consist in: ejecting in front of the combustion nozzle a flow of non-flammable premix containing a mixture of premix air and fuel gas, a complementary flow so as to achieve 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

 Process and installation of combustion of lean fuel gas, without support, using a burner and associated burner.

The invention relates to a method for producing the combustion of a lean fuel gas without auxiliary support flame, by means of a burner comprising a combustion nose on a central axis, in which a mixture of combustible gas is created and of combustion air rotating around the central axis, in front of the combustion nose.

It also relates to a burner structure, in particular of high power, for the implementation of the method and any gas combustion installation using this burner.

The invention finds application, in particular, in the following different installations:

- Gas boilers with very low calorific values, recovery gas (blast furnace gas, etc.), bio-gas and landfill gas, gases from various processes;

- Burning towers and flares of poor, residual gas and bio-gas; - Ovens and drying ovens for heating and drying of various materials and products;

- Ovens and dryers and residual sludge treatments of various processes;

- Burning plant for volatile organic compounds "VOC". These compounds are derived from drying or cooking in different processes; they are often vapors of solvents or oils and are found in very low concentrations (a few% to a few ppm or traces) in neutral carrier gases or in air. They can be blocked by dedicated filters or destroyed by thermal pathways. The low concentration does not allow to burn them directly and the large volume of air that contains them greatly disrupts the combustion of "conventional" burners.

By means of all lean gas low calorific gas (PCI) of less than 3000 Kcal per m ³ and in particular any very lean gas that has a PCI less than 1000 Kcal and which relates more particularly to the subject of the present invention.

The burner according to the invention can nevertheless be used for richer gases or with support gases.

The poor or residual gas burners generally comprise different fuel fluid supply ducts at the nose of the burner, the ducts being configured, in particular in coaxial form, so as to produce one or more fuel rings centered on the axis of the burner.

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

The above provisions are intended to achieve a sufficient air / fuel mixture for localized and stabilized combustion at the nose of the burner.

On boilers with large capacities (> 100 MW) which have several burners (> 4 burners), the combustion air is generally distributed from a box common to the different burners and rotated by adjustable shutters of the outside by means of return organs and connecting rods.

This combustion air is generally brought to the nose of the burner (so-called combustion thereafter) in one flow, or two.

These burners generally comprise gas distribution pipes rich in peripheral ring and accessory tubes (ignition burner, flame control tube, ...) which disturb the rotation of the air flow.

The majority of the poor or residual gas burners are complex designs and require random adjustments and adjustments and very rigid operating conditions with a significant amount of incidents due to the instability of combustion, the attachment of the flame generating untimely stops of the installation.

These burners require reheating of the fuel and especially combustion air at high temperatures (250 to 350 ° C) to improve combustion, which assumes more suitable equipment and additional costs.

Poor fuels are generally very difficult to fuel because they consist mostly of neutral gases, and are distributed in large volumes and at low pressures.

Their mixtures with the combustion air are very difficult to obtain in adequate proportions taking into account the volumes involved, which considerably hampers combustion and does not promote the stability and structure of the flames obtained.

The instability of the flames produced causes significant pressure variations in the furnace, which generates vibrations of the structure of the boilers or installations concerned.

Therefore, the burners always require a support flame, representing 10 to 20% of the total power of the burner, to ensure the stability of the main flame and ensure the safety of the installation. EN 746-2 operating standards require supporting flame systems in the burners.

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

This obligation aggravates the complexity of the burner and inevitably leads to very high operating costs, given the price of rich gas.

These burners often require operation with a large excess of air so that all combustible fractions can meet oxygen to burn all and ensure the quality of the products of combustion, which greatly reduces the yield, increases the specific consumption of rich gas and therefore the cost of operation and inevitably increases the level of polluting emissions.

The object of the invention is to solve the above disadvantages.

It aims in particular a burner design that allows:

- as much as possible, the removal of rich gas support;

- the suppression of the reheating of the gas or the combustion air; - the reduction of the oxygen content of the fumes;

- the suppression of vibrations;

- the reduction of the electrical consumption of the fans of air and smoke.

A preferred basic principle of the process is to fragment as much as possible the amount of air required for combustion and to incorporate it as soon as possible and as closely as possible into the combustible gas stream (or vice versa), improving the mixing by jets impacts at high speed, creating turbulence and setting the mixture in maximum rotation to reduce the axial speed of the mixture and ensure the compactness and continuity of combustion.

To reduce the axial speed and increase the surface of the flame, the lean gas is rotated by fins and the particular flow of the combustion air fraction brought to the periphery at the outlet of the burner.

The poor gases having a large volume, it is difficult to intimately mix the fuel elements of this gas with the oxygen of the combustion air. To overcome this difficulty, the invention consists in breaking up the combustion air and gradually incorporating selected quantities into the lean gas stream.

The method therefore consists in producing an air-fuel premix (outside the flammability limit), preferably in the burner body and supplying the burner nozzle with only the additional air on either side of the burner. this mixture by the very high velocity jets (greater than 80 m / s) by taking the sandwich gas.

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

the central air is ejected in rotation and in divergent flow to penetrate the poor gas;

- the peripheral air is convergent and in strong rotation.

These two air flows each also have the function of providing a barrier to possible "low flameback" at low speed or during a shutdown of the installation.

For this purpose, the subject of the invention is a method for producing a combustion of a lean fuel gas using at least one burner comprising a nose or combustion head on a central axis, in which method a mixture of combustible gas and combustion air rotating around the central axis.

The method is distinguished in that it comprises the following steps according to which ejection in front of the combustion head:

a flow of non-flammable premix containing a mixture of premix air and combustible gas,

a complementary flow so as to reach a flammability threshold of the mixture in front of the combustion nose, the flow being ejected at the center of the premix flow through a central complementary flow and / or around the premix flow by the through a peripheral complementary stream.

According to particular embodiments of the method:

the complementary flow is an air flow;

The premix flow is obtained by incorporating premix air into combustible gas; the incorporation is obtained in a box connected to the burner;

the incorporation is carried out at an inlet of the fuel gas into the burner by injecting premix air into the fuel gas so as to entrain the fuel gas in a pre-mixing space, carry out the premixing by turbulence resulting from the injection and direct the premix in the direction of the combustion nose while initiating a rotation around the central axis;

- The mixture of fuel gas and combustion air is achieved by incorporating a necessary amount parceled from one into the other by many oriented jets.

According to another embodiment of the method: a) the central complementary air stream is ejected in rotation in front of the combustion nose and in divergent flow to penetrate the premix flow, b) the complementary air flow peripheral is ejected in convergent flow and in strong spiral rotation.

The subject of the invention is also a burner for a lean fuel gas of the type comprising a combustion nose on a central axis and means for feeding a mixture of combustible gas and combustion air in rotation about the axis. Central burner, particularly notable in that it has no mixing chamber and no combustion chamber.

The burner is distinguished mainly in that it is configured to eject in front of the combustion nose:

a flow of non-flammable premix containing a mixture of premix air and combustible gas,

a complementary flow so as to reach a flammability threshold of the mixture in front of the combustion nose, said flow being ejected at the center of the premix flow through a central complementary air flow and / or around the flow of premix through a peripheral airflow.

According to a particular embodiment, the burner is configured to split a flow of air into at least one pre-mix air flow, and a complementary air flow comprising at least one central complementary air flow. and / or a peripheral complementary air flow. The invention also relates to a combustion plant of a fuel gas implementing the method or comprising at least one burner according to the invention.

According to an advantageous characteristic, the installation uses or comprises at least two burners configured so as to mesh in a common sense with the overall rotational movement resulting from their mixing flow in front of the combustion nose.

Other features and numerous advantages of the invention will appear on reading the description which follows, given by way of illustrative and nonlimiting example, and with reference to the appended figures for which:

- Figure 1 illustrates a lean gas combustion plant provided with a burner according to one embodiment of the invention; Figure 2 illustrates a sectional view along the axis AA of Figure 1; Figure 3 illustrates the rear of the burner in a right view B of Figure 1; Figure 4 illustrates a partial sectional view of a beam according to section CC of Figure 2; Figure 5 illustrates a partial bottom view along D-D of Figure 4;

FIG. 6 illustrates an isolated main view of the box 7 of the burner of FIG. 1;

- Figures 7, 8, 9 respectively show different views of Figure 6: a sectional view along E-E, a right view along F, and a left view along G; Figures 10, 11 and 11A respectively illustrate an insulated main view of the central tube 13 of the burner of Figure 1, a left view along H and a right view; - Figure 12 illustrates an isolated main view of the central pole 50 according to Figure 1;

FIG. 13 illustrates a view of an alternative embodiment of a burning cone of the central pole;

- Figure 14 illustrates a detail I of Figure 9; FIGS. 15 and 16 respectively show the sections along LL and KK of FIG. 14;

In FIG. 1 is shown a plant 1 for the combustion of lean fuel gas using a burner 2 arranged between four main parts ZA, ZB, ZC, ZD separated by three walls 3, 4, 5.

The parts represent, respectively, a combustion zone ZA where combustion is carried out, a zone ZB containing or in communication with the combustible lean gas, a zone ZC containing or in communication with combustion air, a zone ZD external to the combustion zone. installation accessible to people.

The installation is for example a superheated steam production facility of 40 T / hour in which blast furnace gas must be burnt at ambient temperature (humidity = 2.5% H ₂ O by volume) fed low pressure (<300 mm CE in relative pressure) and an average composition on dry gas: N ₂ = 58%, H ₂ = I, 7%, CO ₂ = 20.3%, CO = 20% (PCI = 660 Kcal / m3n). Combustion products that must contain less than 50 ppm CO with less than 1% oxygen in these fumes. The flammability of this gas occurs when there is 35% to 73% of gas in the mixture.

The burner comprises a combustion nose 6 opening into zone A of the hearth; the nose is centered on a central axis X which is in this case, the main axis of the burner to the extent that it has a general shape of revolution around this axis.

The burner also comprises supply means for this nose, which are able to eject a flow of air and fuel gas in rotation about a central axis centered on the combustion nose.

This nose, constituting the front end of the burner, is intended to receive in front of or on it, on the left of the figure, a flow of combustible gas and air combustion which is rotated about the central axis, with supply means of this nose provided for this purpose, which is described later.

The burner also comprises a central box 7 connected to the nose and upstream of it (with respect to the direction of flow flow), arranged in the zone ZB between the walls 3 and 4, and having at least one opening 8 opening in this zone ZB.

In the zone ZC is a rear end 7B of the burner connected to the box 7, upstream thereof, and having at least one access for at least one combustion air inlet of the zone ZC.

The air supply in the preferred example is carried out completely by the rear face of the burner for several advantages:

- guarantee the tightness of the assembly, - facilitate access to the pre-mix air controls,

- to be able to install the burner in box of air,

- Power, according to the application, realize separate power supplies of different combustion airs.

In the zone ZD, open various pipes which extend between the hearth and the outside, while passing through the burner and among which one finds, if necessary, a pipe of supply of rich gas, a tube of control of the flames, an ignition pipe or other pipes or equipment known to those skilled in the art (not shown).

According to one embodiment of the invention, the method may comprise a first step in which a flow of air for combustion is split into at least one pre-mix air stream and an air stream. complementary. The complementary air consists of at least one central air flow and / or a peripheral air flow.

In the illustrated example, both the central and peripheral air flow are used for greater efficiency and flexibility of use and the split is effected by different air inlets at the rear of the burner or flow path. the air in the burner. For this purpose, in the exemplary embodiment illustrated, the burner is configured to divide the air coming from the space ZC into several streams. It comprises several arrivals or access on its rear end: a central access 9 to receive a central air flow inlet, a peripheral access 10 to receive a peripheral air inlet, and at least a main access 10A to receive an arrival premix air. Other accesses can be added as indicated later.

In an alternative embodiment, this division step could be done differently, for example by external pipes outside the burner, and each of the air flows could be brought by these independent and external pipes.

In a second step of this embodiment, a premix flow is introduced in front of the combustion nose, containing a mixture of premix air and combustible gas, rotating about the central axis, the flow premixing being non-flammable to the extent that it is mixed at a rate remote from the flammability ranges, for example greater than a flammability threshold. In fact, in the example described, a 100% lean gas rate is increased to a rate of 80-85% of gas (in the gas + air mixture) while the flammability limits are 30 to 73%. % of gas in the mixture.

This assumes that premixing and spinning of the latter is done beforehand, as explained below.

To improve the combustion and ensure a good flame retention, it is interesting and important to carry out a pre-mix as much as possible and as soon as possible.

For this second step, the burner, in the example described, is configured to carry out premixing beforehand inside itself, in this case in a space 16 called pre-mixing of the box 7. It is also configured to rotate the premix. This rotation, in the illustrated example, is preferably also carried out in the box upstream of the combustion nose.

For this purpose, the pre-mixing air accesses 10A mentioned above open into the caisson as well as the access ports 8 of fuel gas so that a premix can be carried out with the aid of mixing means 11 described later.

However, in one variant, the pre-mixing could be carried out beforehand outside the burner, for example in a chamber provided for this purpose in which a higher rate than the flammability rate is respected.

For the gas concerned of the example, the mixture is carried out at a level 5 to 20% higher than the flammability threshold with an insufficient air ratio (proportions ranging from 78 to 95% of gas in the mixture) .

For reasons of safety and efficiency, it is preferred to adopt a lower rate of 10 to 20% of the total air to be supplied.

Alternatively, for certain applications, the process could be implemented by performing a premix with an insufficient fuel gas content in the same proportions of 5 to 20% or with different proportions for particular applications of bio gas or VOC burns.

In a third implementation step, the complementary flow is ejected at the center of the premix flow through the central complementary air flow and / or around the pre-mix flow via the air flow. additional peripheral, so as to reach the flammability threshold at the combustion nose.

In the example described, the ejection of the complementary flow takes place both at the center and at the periphery so as to achieve a better final mixture. For this purpose, the burner is configured to open the crown-shaped premix flow 12 located between a central pipe 13 and the periphery 14 of the front end of the box.

According to one embodiment of the method, the pre-mix flow is obtained by incorporating premix air into combustible gas.

Indeed, poor fuels, generally residual, are distributed under very low pressures and given the large volumes often involved, it is important to facilitate the flow of these gases through the effects of mechanical drives.

For this implementation, the burner comprises the incorporation means 11 mentioned above which inject air into the fuel gas.

The incorporation is carried out directly in an enclosure of the box having a premix space 16 (Figure 2) delimited between a central pipe 13 and an inner wall 31 of the box.

According to one embodiment, the incorporation is carried out by injecting premix air at an inlet of the fuel gas into the burner so as to:

- driving the fuel gas in a premix space 16,

- Make the premix by turbulence resulting from the injection,

and directing the premix in the direction of the combustion nose while initiating a rotation around the central axis.

For this purpose, the burner comprises injection means comprising nozzles 17 or high-flow directional calibrated orifices arranged in the profiled means of incorporation 11 and oriented towards the premix space 16 at the level of the openings 8.

The gas located near and around the lights 8 is driven by the depression generated by the air jets at the outlet of the nozzles directed by the orientation of the jets and mixed by the turbulence of the jets. A rotation of the mixing is also initiated at this level in the premix space by the orientation of the air jets.

These injection means preferably have a steady state.

The incorporation means may also preferably comprise second premix air injection means. These injection means are arranged so as to achieve an incorporation of air parallel to the central axis and directing the flow of premix in the direction of the combustion nose.

These injection means preferably have a progressive regime according to the power level used.

These second injection means may be formed, as in the illustrated example, of tubes 21 around orifices 22 in the wall 23 of the rear end of the burner (FIGS 3, 10, 11). These tubes preferably have different lengths and are five in the example. They extend inside the premix space from air inlets or orifices 22 disposed on the wall 23 or rear face of the burner.

The orifices 22 are preferably closed by valves (not shown) operable by calibrated springs or electrical controls.

The valves can be arranged on the orifices with or without tubes. The tubes make it possible, on the one hand, to prevent the respective flows from being disturbed and, on the other hand, to bring air to different points with a guarantee of its distribution.

The orifices have a size determined so as to avoid being too massively within the flammability limits, and that there are locally favorable conditions for combustion that would deteriorate the burner.

Alternatively, one could realize the incorporation of gas in the air, for example by permuting the different arrivals and by adjusting the respective flow rates. This variant is possible in particular for heating large volumes of air (drying applications) or burn VOCs. In this case, the premix gas would replace the premix air and the flows, the premix could be unchanged and the central and peripheral flows could concern for example combustible gas instead of combustion air.

According to one embodiment, the central complementary air flow is ejected in rotation in front of the combustion nose and in divergent flow to penetrate the premix flow and the peripheral complementary air flow is ejected in convergent flow and in strong spiral rotation.

For this purpose, the burner is configured in the example with a conical deflector 18 at the outlet of the central pipe 13 and fins 19 in the pipe which put the central air flow in rotation. Other equivalent means may also be suitable, for example, calibrated directional or oriented openings in a partition wall.

Preferably, the central air is divergent with an apex angle of 60 to 180 ° or 30 to 90 ° with respect to the burner axis.

This ejection thus produced makes it possible to obtain good penetration of the air into the premix so as to best complete the missing air ratio.

The central air flow of the example has previously penetrated the inlet 9 in the inner pipe of the pipe 13, in the annular space around the central pole 51.

If necessary, this central air can have another function explained later, which is to come to feed at its ejection base a rich gas which would be distributed in a ring around the central air, during its use especially at startups or poor gas deficiency.

As for the additional peripheral air, the burner is configured with injection nozzles 20a, 20b disposed on a ring 14 of the end or front face of the box 26a. The nozzles are oriented both tangentially to a circle centered on the central axis and facing forward. The spiral rotation is obtained by this double inclination of the nozzles.

The peripheral air envelops the flow of lean gas and accentuates the rotation. It is distributed at high speed and optimizes the mixture.

The nozzles 20a, 20b are fed by the peripheral pre-ejection space 30 located in a double wall of the box at the front of the box, itself fed by the arrival means 10A formed near the rear end 26b of the box.

Sub-parts of the burner will be described below with reference to the corresponding figures, namely, the box, the central tube and the central pole.

The burner box:

With reference to FIGS. 6 to 9, the box 7 has a general shape of revolution and comprises:

a double peripheral wall formed of an external and internal wall 25, an end or front face 26a, formed of a ring 14 comprising the peripheral injection means 20a, 20b;

one end or rear face 7B comprising different feeds or feeds 10, 10A at least in peripheral air flow and premix,

a space 27 of air circulation delimited by the double wall making it possible to put the two ends 26a and 26b in communication,

- Admission ports 8 on the double wall device, these lights being intended to interface between an internal space 16 in the box said premix space and the outside.

pipes, in the form of hollow beams 11, located in the thickness of the double wall. These lines extend between the lights 8, between an airflow reception space 10A or arrival disposed at the rear end 7B and a pre-ejection space 30 of the peripheral air located at the front end.

- Premix air injection nozzles 17 arranged under the pipes. These nozzles are configured to perform said first permanent injection of premix air; these pipes and the nozzles are part of the incorporation means mentioned above.

These nozzles are in fact exit holes formed in the ring, one of whose functions is to close the front end of the double wall of the box; the other rear end of the double wall being closed by a wall 23B.

These holes communicate with the pre-ejection space 30 of the double wall and open out through an inner wall of the box; the nozzles are disposed on the ring being offset with respect to the radial axis R of the box and inclined forwardly relative to a plane perpendicular to the box.

The nozzles are offset and inclined in different ways alternately. The proposed angles are specific to this burner power, but would inevitably be modified for another size of burner. These angles are determined so that the jets of the consecutive orifices do not disturb, and they do not come to strike the end of the tube 13 nor hinder the flow of fluids leaving the gas ring contained between 13 and 56, nor the complementary central air diverges. This diverging cone must almost "mesh" with the convergent peripheral complementary jet whose angle is the most closed (here 15 °).

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

A first series of nozzles (20a) can be inclined from 5 ° to 45 ° forwards, (15 ° preferred in the embodiment) and from 30 to 65 ° with respect to the radial axis (R), (44 ° preferred in the example) and a second series of nozzles (20b) inclined 25 to 65 ° forward (45 ° preferred in the example), and 30 to 70 ° relative to the axis radial (53 ° preferred in the example).

The box may also include orifices 55 disposed on the inner wall 25 at the pre-ejection chamber 30. These orifices make it possible to feed the fin device 37 from the chamber 30 to improve the poor air / gas mixture. between the fins. The central tube:

Referring to Figures 10 and 11, a central tube 13, intended to be mounted centered on the central axis, is sized to extend longitudinally between the two ends of the box and put in communication.

This tube comprises:

an outer surface 35 intended to delimit the premixing space with the inner wall 25 or inner face 31 of the double wall of the box, and an inner surface 52;

means for fastening to the box and receiving an air or gas box 36 disposed at the rear of the tube;

a first fin device 37, disposed at the front of the tube; said fins 37 extending in the flow space of the premix between the outer wall 35 of the tube and the inner wall of the box 25 or inner face 31; they are profiled so as to create a rotation of the premix flow as it flows towards the outlet of the box; a space between the box and the tube forms a ring-shaped conduit 38 (FIG 1) for conveying the premix air flow; - A wall 23 forming a radial shoulder of the central tube, said wall separating the premix space with the rear of the central tube itself in communication with the air box.

The central pole: With reference to FIG. 12, the central pole 51 is intended to be disposed in the central tube 13 and centered on the central axis.

The burner also has a second fin device 19 disposed within and adjacent the front of the central tube.

The fins are fixed in the example on the central pole 51 which passes through the central tube; they are intended to extend from the surface of the pole 50 to the inner wall 52 of the central tube.

The burner may also comprise a "burning cone" 18 forming a deflector located downstream of the central tube and spaced from it so as to effect a exhaust diverging from the central air flow. In the illustrated example, the burning cone is disposed at the front end of the axial pole 51.

The gas is ejected at the end of the pole, at a divergent angle defined by a series of calibrated orifices 54 arranged in a ring around the conical baffle 18 which allows ejection of this gas on a maximum circumference, so that the possible jets Rich gas originates as close to the central combustion air, and have a maximum pulse by striking the poor gas flow.

Preferably, for best results, the conical baffle may be a deflector 18b having a peripheral serration 52, and having central orifices 53 opening into the conduit of the central pole.

In general, the burner is sized to receive, in normal operation, a complementary flow ejection at a very high speed greater than 100 m / s while the premix flow is ejected at a speed of 40 to 80 m / s.

If appropriate as an alternative embodiment, the burner may comprise a rich gas supply. In the example, the rich gas is pressurized at the periphery of the central tube directly into the premix space.

Preferably, for burners of very high power (greater than 20 megawatts), the rich gas is distributed around the central tube so as to mix intimately with the premix.

For this purpose, the central tube may comprise:

an annular casing 36 for receiving and distributing the gas around a plurality of orifices passing through the rear wall 23 in the form of an annular shoulder of the central tube;

a portion of tube 56 arranged in partial double wall around the central tube so as to convey the flow entering the premix chamber to substantially a half distance from the chamber; and a connecting cone 57 of the double wall to the box via the shoulder so as to collect the rich gas;

- incidentally, an annular baffle 58 placed at a distance from the end of the double wall so as to diverge the rich gas and promote mixing with the air;

alternatively or in addition to the deflector above, a series of orifices, calibrated and arranged through the central tube, is arranged in a ring just upstream of the deflector 58 so as to allow the central complementary air to be ejected into the rich gas stream and thus help to make it diverge.

According to an alternative embodiment, the box 36 may be connected to a rich gas supply tube (the orifices 10A2 being closed) or another box 36B (not shown) enveloping the box 36 and being connected to the feed tube. Calibrated orifices arranged at a divergent angle may be formed in a ring connecting the two tubes 13 and 56B to the front end.

Optionally, the tube portion 56 (double wall) 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 combustion nose around the central air.

On the other hand for less powerful burners (for example less than 20 Mega Watt), the rich gas is always brought under pressure but in 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 serrations 52) which makes it possible to eject this gas on a maximum circumference, so that the jets Rich gas originates as close to the combustion air, and have a maximum pulse by striking the poor gas flow.

These configurations allow to obtain a consistent flame and continuous structure and maximum surface (optimization of heat transfer in the home). 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 mixtures. The burner is designed in mechanically welded modules allowing maximum flexibility and ease of design, adaptation, construction, installation and maintenance, knowing that: - the combustion air can be more or less hot ,

- for multiple burner installations arranged side by side, the directions of rotation of the fluids must mesh so as not to disturb the combustion and the flows in the hearth,

it makes it possible to replace existing burners easily, the rich fuels can be of different qualities.

The possible flows of the different flows will now be described according to a mode of operation of the burner.

An ignition flame is provided in front of the nose of the burner via a guide tube of the ignition burner 60 (FIG 1). The permanent air circuit is then activated by a pump (not shown) which blows combustion air at the rear of the burner by putting the air supply box ZC under pressure.

A fraction of the combustion air enters the double wall 27 of the box (FIG 6) through the inlet orifices 10 for example rectangular and formed in the annular wall 23B closing the double wall on the back; while another fraction directly enters the double box to the nozzles 20a, 20b.

Part of this fraction enters the beams 11 (FIG 8) while the other portion directly feeds a peripheral air pre-ejection chamber 30 via a partial double wall of the box (FIG. which is free of light and extends at an angle of approximately 90 ° between radial walls 32 and 33.

The beams are pressurized and combustion air escapes from the nozzles tangentially (Fig. 7) to a circle centered on the central axis and towards the fins of the first rotating device. The flue gas which may be under slight pressure (generally less than 200 mm CE) enters transversely into the box under a driving effect of the air jets at the openings 8 between the beams 11; the turbulences carry out a premixing or stirring in the premixing space 16 of the box at the inlet of the fin device (FIG.7) notably by inflection against the inflection wall 31.

As the beams also open into the pre-ejection chamber 30 of peripheral air, they contribute to conduct air in addition to that conveyed by the interior of the double wall inflection or guide 24, 25.

Combustion air also enters through the inlet 9 of the central tube 13

(Fig. 10, 11) and opens directly at the nose 6 after passing into the space between the fins of the second fin device 19 (Figure 2) where it takes a rotational movement. This air spring in front of the nose divergently through the conical deflector 18 placed in front.

During this time, the peripheral air is ejected from the chamber 30 (FIG. 9, 14-16) in the form of two vortices via the peripheral nozzles 20 a, 20 b in front of the combustion nose.

When the premix arrives at the front exit of the burner where it is ejected in an annular whirlpool, it is caught and handled by the two central and peripheral air flows which penetrate it intimately.

The directions of rotation of the different air flows may be contrary to that of the pre-mix flow but preferably in the same direction.

If necessary additional air can enter the premix chamber by the tubes 21 or valves (Fig.10, 11) disposed on an annular wall 23 in the shoulder of the central tube and enrich the mixture with air.

Air can also come from the back of the box 36 through orifices 10A2 and enrich the premix. If appropriate (FIG 6), air can escape from the box from the pre-ejection chamber 30 through orifices 55 formed in the bottom wall of the box and penetrates radially into the fin device 37 between the fins. This improves the mixing of the gas mixture with the air.

If several burners are used close to one another in a combustion chamber of an installation, make sure that the different vortices mesh. For this purpose, the orientation of different nozzles and fins must be adapted. For example, the peripheral vortices must be opposite between two burners.

Thus, the invention provides the following advantages:

The flame is stable and well hung, and all the vibrations due to the instabilities of combustion are eliminated; - No adjustment is required;

- A parcelization of the combustion air is possible in more than two or even more than three fractions;

- No need for fuel support to compensate for mixing irregularities or fuel gas poverty, or associated devices or equipment which allows a rich fuel economy in case of shortage of lean gas.

- Possibility of functioning normally in pure rich gas and alone;

- Suppression of gas heating or combustion air resulting from the burner's ability to properly burn very low LPG gases (<750 Kcal / m ³ ) in cold and cold air; Generally, the heating of the combustion air of a burner of 20 MW was carried out at 200 ⁰ C;

- Reduction of the oxygen content of the fumes due to a very good combustion thanks to an optimized air-fuel mixture. The oxygen content of the fumes was reduced to 0.6-1% instead of 2%; - There is an increase in the flame temperature of 60 to 80 ⁰ C, causing a sharp increase in heat transfers in households (+ 15%). The productivity of the boiler is actually improved if the reheating can follow; - There is a significant reduction in smoke losses (at constant temperature) because the volume of fumes decreases in the same proportion as the air factor, ie from 10 to 15%. The efficiency of the boiler is thereby improved by at least 1 point. For a 100 MW boiler, this represents more than 10 GWh / year of fuel;

- Reduction of the electrical consumption of the fans of air and fumes to be brewed to the extent that the volumes of air and fumes to be brewed being smaller, it also results in a decrease in the size of the blowers of blow and draw of the order of 15 to 20% and a reduction of their consumption by more than 10%.

Claims

A method for effecting the combustion of a lean fuel gas using at least one burner comprising a combustion head on a central axis (x), wherein a mixture of fuel gas and air is created of combustion in rotation about the central axis, said method being characterized in that it comprises the following steps according to which is ejected in front of the combustion head: - a flow of non-flammable premix containing a mixture of air of premix and combustible gas,

a complementary flow so as to reach a flammability threshold of the mixture in front of the combustion nose, the flow being ejected at the center of the premix flow through a central complementary flow and / or around the premix flow through a peripheral complementary stream.

2. Method according to claim 1, characterized in that the complementary flow is an air flow.

3. Method according to one of claims 1 or 2, characterized in that the premix flow is obtained by incorporating premix air into the fuel gas.

4. Method according to one of the preceding claims, characterized in that the incorporation is carried out in a box connected to the burner.

5. Method according to one of claims 3 or 4, characterized in that said incorporation is carried out at an inlet (8) of the fuel gas in the burner, by injecting premix air to drive the gas fuel in a pre-mixing space, perform the premixing by turbulence resulting from the injection and direct the premix in the direction of the combustion head while initiating a rotation about the central axis.

6. Method according to one of the preceding claims, characterized in that: a) the central complementary air stream is ejected in rotation in front of the nose or combustion head and in divergent flow to penetrate the flow of premix, b ) the peripheral complementary air flow is ejected converging flow and strong spiral rotation.

7. Method according to claim 1, characterized in that the mixture of combustible gas and combustion air is achieved by incorporating a necessary amount parceled from one into the other by many oriented jets.

8. Burner for lean fuel gas of the type comprising a nose or combustion head on a central axis (x) and means for feeding a mixture of combustible gas and combustion air in rotation around the central axis burner, characterized in that it is configured to eject in front of the combustion head (6):

a flow of non-flammable premix containing a mixture of premix air and combustible gas; a complementary flow so as to reach a flammability threshold of the mixture in front of the combustion head, said flow being ejected at the center of the pre-mixing flow through a central complementary air stream and / or around the premix flow through a peripheral complementary air flow.

9. Burner according to the preceding claim, characterized in that it is configured to split an air flow into at least one premix air flow, and a complementary air flow comprising at least one flow of air. central complementary air and / or a peripheral complementary air flow.

10. Burner according to one of claims 8 or 9, characterized in that it is configured to eject: a) the complementary central air flow in rotation in front of the combustion nose and in divergent flow to penetrate the flow premix, b) the additional peripheral air flow convergent flow and strong spiral rotation.

11. Burner according to one of claims 8 to 10, characterized in that it comprises incorporation means (11, 17, 21) for incorporating premix air into combustible gas and to obtain the flow of pre -mixed.

12. Burner according to the preceding claim, characterized in that the incorporation means comprise injection means (17) for producing a first permanent injection of premix air in a premix space (16) upstream. of the combustion nose, said space being intended to be in communication with an enclosure (ZB) containing the fuel gas, said injection being carried out so as to entrain the fuel gas in the premix space (16), to make the mixing by turbulence resulting from the injection and direct the premix in the direction of the combustion nose (6) while initiating a rotation around the central axis (x).

13. Burner according to one of claims 11 or 12, characterized in that the incorporation means comprise second injection means (21) of premix air, said injection means being arranged so as to performing an air incorporation parallel to the central axis in a progressive manner, depending on the power level used, and so as to direct the flow of premix in the direction of the combustion nose.

Burner according to one of Claims 8 to 13, characterized in that it comprises a cylindrical box (7) having:

- a peripheral double wall (24, 25), a front end (26a) configured to output the peripheral air flow on the combustion nose and a rear end (26b) configured to receive at least air streams both ends communicating with each other at least through an air circulation space (27) delimited by the double wall,

- intake ports (8) on the double peripheral wall being intended to interface between an internal space in the box called premixing space (16) and the outside (ZB) in an enclosure containing the gas, pipes, in the form of hollow beams (11), located in the thickness of the double wall and extending between the openings (8), between an airflow receiving space (10) disposed at the rear end (26b) and a pre-ejection space (30) of the peripheral air at the front end, said ducts having pre-mixing air injection nozzles (17) configured to perform said first permanent injection of premix air.

15. Burner according to the preceding claim, characterized in that it comprises a central tube (13) centered on the central axis (x) inside the cylindrical box (7) and extending between the two ends of the box (26a, 26b), said tube comprising:

an outer surface (35) intended to delimit the premixing space (16) with the inner wall (31) of the double wall of the box,

means for fastening to the box and receiving an air or gas box (36) disposed at the rear of the tube,

a first finned device (37) disposed in front of the tube, said fins being profiled so as to create a rotation of the pre-mix flow as it flows towards the outlet of the box, said fins extending into the tube; flow space of the premix between the outer wall of the tube (35) and the inner wall (31) of the box.

16. Burner according to the preceding claim, characterized in that it comprises a second fin device (19) disposed inside and in the vicinity of the front of the central tube, said fins being fixed on a central pole (51). and extending between the surface (50) of the pole and the inner wall (52) of the central tube.

17. Burner according to claims 13 and 15, characterized in that the second air injection is effected through orifices (22) located on a wall (23) in the form of a shoulder of the central tube, said wall separating the premix space (16) with the rear of the central tube in communication with the air box (ZC), said orifices being closed by valves operable by calibrated springs or maneuverable controls.

18. Burner according to claim 14, characterized in that it comprises outlet bores in the form of nozzles (20a, 20b) communicating with the pre-ejection space (30) in the double wall and opening outwardly on an inner wall of the box or equivalent (25), said nozzles being arranged in a ring and offset with respect to the radial axis (R) of the box and directed towards the front.

19. Burner according to claim 18, characterized in that it comprises a first series of nozzles (20a) inclined from 5 ° to 45 ° forwards and 30 to 65 ° with respect to the radial axis (R). and a second series of nozzles (20b) inclined 25 to 65 ° forward and 30 to 70 ° to the radial axis.

20. Burner according to claim 16, characterized in that it comprises a "cone burning" conical baffle (18) located downstream of the central tube (13) and spaced from him so as to perform a divergent escape of the flow of central air.

21. Burner according to the preceding claim, characterized in that the conical baffle (18) is disposed at the end of the axial pole (51) passing through the central tube.

22. Burner according to the preceding claim, characterized in that the conical deflector (18) has a peripheral serration (52) and central orifices (43) opening into the conduit of the central pole.

23. A fuel gas combustion plant implementing the method according to claims 1 to 7 or comprising at least one burner according to claims 8 to 22.

24. Installation according to claim 23, characterized in that it implements or comprises at least two burners configured so as to mesh in a common sense global rotational movement resulting from their mixture flow in front of the combustion nose.