EP1045203B1 - Multifuel burner - Google Patents

Abstract

Burner has, next to front nose (22), wings (20) to deviate internal flux of poor fuel coming from conduit (15). Wings form, combustion chamber, whirling jets around air jets form conduits (9, 11). Burner also comprises wings (21) for axial guiding of external flux of poor fuel coming from conduit (17). Nose has hoop (23) supporting wings (20) and inclined to rotate flux from conduit (15). An Independent claim is also included for the heating method of rotating furnace.

Description

The present invention relates to a burner with several fuels.

The technical sector of the invention is the field of manufacturing industrial burners for rotary kilns.

The present invention relates more particularly to a burner supplied with at least two different fuels: a first ordinary fuel known as rich, that is to say of PCI generally at least equal to 8000 kcal / Nm ³ , in solid form (pulverulent ), liquid or gaseous, and a second so-called lean fuel, that is to say with a PCI of less than 8000 kcal / Nm ³ , in particular whose PCI is located in a range from 0 to 3000 kcal / Nm ³ .

The second fuel (lean) is for example constituted by a gas resulting from the pyrolysis of metallurgical sludge, by a gas resulting from the fermentation of organic waste of animal or vegetable origin (“biogas”), by residual gases originating from installations for the production of chemicals, in particular petrochemical installations, by gases resulting from the distillation of alcohol in particular, or from a mixture of these poor gases; these poor gases have a relatively low PCI and also variable depending on the operating conditions of the installation from which they come; these gases may contain tars, acids and / or dust. Document GB 2 123 945 describes a lean gas burner.

• un conduit central de transport d'air primaire, à l'intérieur duquel s'étend une canne équipée d'une buse de pulvérisation d'un combustible liquide (huile) ;
• un deuxième conduit annulaire entourant le premier conduit, de transport d'un combustible solide pulvérisé ou gazeux ;
• un troisième conduit annulaire entourant le deuxième conduit, de transport de comburant (air primaire), muni à son extrémité d'ailettes de mise en rotation du flux d'air ;
• un quatrième conduit annulaire entourant le troisième conduit, de transport de comburant (air primaire), muni à son extrémité d'ailettes de guidage axial (c'est-à-dire de guidage selon une direction parallèle à l'axe longitudinal du premier conduit) du flux de comburant.

Patent EP 421903 (Entreprise Générale de Chauffage Industriel Pillard) describes a burner which comprises:

• a central duct for transporting primary air, inside which extends a rod fitted with a nozzle for spraying a liquid fuel (oil);
• a second annular duct surrounding the first duct, for transporting a pulverized or gaseous solid fuel;
• a third annular duct surrounding the second duct, for transporting oxidant (primary air), provided at its end with fins for rotating the air flow;
• a fourth annular duct surrounding the third duct, for transporting oxidant (primary air), provided at its end with fins for axial guide (that is to say guide in a direction parallel to the longitudinal axis of the first duct ) of the oxidizer flow.

The burner described in this document further comprises a flame stabilizer disposed at the end of the central duct, which comprises a hub in the form of a flange and a central orifice disposed in the extension of the oil spray nozzle; the hub has small openings and fins which guide the primary air exiting from these openings; the distance (measured radially) of the outlet openings of the third and fourth annular duct relative to the axis of the burner is at least equal to twice the radius of the central opening of the flame stabilizer; this configuration allows, by circulating in the central duct a small proportion (2 to 10%) of the primary air flow (the majority of this current being delivered by the third and fourth "axial" and "radial" air ducts ), the creation of an enlarged “dead” central zone (without notable combustion) and the appearance of combustion at a greater distance in front of the nozzle.

The object of the present invention is to adapt such burners designed for heating rotary kilns such as cement kilns, in order to make them compatible with such lean fuels.

The object of the present invention is to provide a burner allowing reliable and rational use of these essentially gaseous poor fuels.

To this end, the invention consists in proposing a burner which comprises two separate circuits for introducing (injecting) lean fuel into the combustion chamber: a first circuit includes means for rotating lean fuel, and a second circuit surrounds the first circuit and is substantially devoid of means for rotating the lean fuel; these two circuits are arranged outside the annular transport conduits "axial and" radial "air, which are themselves arranged outside a central air transport duct terminated by a flame stabilizer, and outside a fuel transport duct rich.

• un premier conduit, dit central, de préférence cylindrique de section circulaire, de transport d'air primaire, à l'intérieur duquel peuvent le cas échéant s'étendre un ou plusieurs conduits de transport de produits à incinérer, et qui comporte un stabilisateur de flamme ;
• au moins un deuxième conduit de transport d'un combustible riche sous forme solide pulvérisée, liquide ou gazeuse ;
• un troisième conduit de section annulaire, entourant lesdits premier et deuxième conduit, de transport de comburant (air), muni à son extrémité de premiers moyens (ailettes) de mise en rotation du flux de comburant ;
• un quatrième conduit de section annulaire, entourant ledit troisième conduit, de transport dudit comburant (air), muni à son extrémité de premiers moyens (ailettes) de guidage axial (c'est-à-dire de guidage selon une direction parallèle à l'axe longitudinal du premier conduit) du flux de comburant ;
• un cinquième conduit de section annulaire, entourant ledit quatrième conduit, de transport dudit combustible pauvre, qui est muni à son extrémité de deuxièmes moyens (ailettes) de mise en rotation du flux de combustible (gazeux) pauvre ;
• un sixième conduit de section annulaire, entourant ledit cinquième conduit, de transport dudit combustible pauvre, qui est muni à son extrémité de deuxièmes moyens (ailettes) de guidage axial du flux de combustible pauvre.

According to a preferred embodiment, the burner comprises:

• a first duct, said to be central, preferably cylindrical with a circular section, for transporting primary air, inside which may, if necessary, extend one or more conduits for transporting products to be incinerated, and which comprises a stabilizer for flame ;
• at least one second conduit for transporting a rich fuel in pulverized solid, liquid or gaseous form;
• a third duct of annular section, surrounding said first and second duct, for transporting oxidant (air), provided at its end with first means (fins) for rotating the flow of oxidant;
• a fourth duct of annular section, surrounding said third duct, for transporting said oxidant (air), provided at its end with first means (fins) for axial guidance (that is to say guidance in a direction parallel to the longitudinal axis of the first duct) of the oxidant flow;
• a fifth duct of annular section, surrounding said fourth duct, for transporting said lean fuel, which is provided at its end with second means (fins) for rotating the flow of lean (gaseous) fuel;
• a sixth duct of annular section, surrounding said fifth duct, for transporting said lean fuel, which is provided at its end with second means (fins) for axial guidance of the lean fuel flow.

Each of the two lean fuel (fuel) transport conduits is preferably supplied by a manifold provided with a member (such as a movable shutter valve) for adjusting the lean fuel flow rate delivered to each conduit; this makes it possible to adjust the speed of ejection of the swirling jet (or jets) leaving the fifth duct and the axial jet (or jets) leaving the sixth duct; the adjusting these speeds - and the flow rates - makes it possible to adjust the flow rate of lean fuel injected into the combustion chamber of the furnace as a function of its pressure, its nature, its temperature and its PCI, and makes it possible to avoid disturbance of the combustion of the rich fuel by the jets of lean fuel; the output speed of the lean fuel into the combustion chamber can be lower than that of the rich fuel as well as that of the oxidizer injected between the transport lines of the rich fuel and the transport lines of the lean fuel; in particular, the lean fuel circulation speed is of the order of 20 to 70 meters per second when the lean fuel is hot, that is to say at a temperature of the order of at least 300 ° C. ( in particular of the order of 300 ° C. to 500 ° C.), and is of the order of 20 to 30 meters per second when the lean fuel is cold, that is to say at a temperature of range from 0 ° to 100 ° C; a minimum speed of approximately 20 meters per second is used so as to cause entrainment of particles (dust) or droplets possibly present in the lean fuel.

In fact, the kinetic energy (and / or the momentum) of the gas with low PCI must be as low as possible so as not to disturb the combustion of the rich fuel, and therefore not to modify the shape of the flame too much; however, the speed of the lean fuel must be sufficient to avoid the deposit of dust (in the case of a dusty gas), therefore generally greater than 20 meters per second, and / or to avoid condensations of heavy tars (in the case of 'a pyrolysis gas). The two lean fuel transport circuits are designed to receive gas at a fairly high temperature (above 300 ° C). The temperature is chosen and maintained above that of the deposition of the heaviest compounds. The nozzle can be preheated by passing hot (clean) gases before the introduction of the pyrolysis gas; preferably the internal (radial) lean fuel transport circuit is thermally isolated from the central part of the nozzle, in particular by means of a double wall (filled stainless steel tube insulation). The outer tube of the oxidizer transport duct (axial), is also thus protected from heat by the insulation.

Given the rotation imparted to the lean fuel leaving the fifth conduit by the rotation means, the "internal flow of lean fuel tends to diverge in the combustion chamber, that is to say tends to diverge of the longitudinal axis after its exit from the fifth conduit; the "external" flow of lean fuel leaving the sixth conduit axially (longitudinally) opposes the divergence of this flow by enveloping it; adjusting the speeds and flow rates of these two lean fuel flows surrounding the fuel flow (rich) and oxidant (causing the main flame) avoids disturbing the main combustion by the supply of lean fuel.

In addition, the rotation imparted to the “internal” swirling flow of lean fuel ejected near the axial flow of oxidant which it surrounds promotes the gradual and intimate mixing of the fuel and the oxidant, which promotes good combustion of the lean fuel.

According to a preferred characteristic, the annular duct (the fifth duct) for transporting the lean fuel surrounding the annular duct (the fourth duct) for transporting the oxidant, is separated from the latter (fourth) duct by a layer of thermal insulator on a substantial part of its length; this makes it possible to avoid cooling (and / or limiting cooling) of the lean fuel by the oxidizer (air), which could lead to the condensation of condensable compounds and the deposit of condensates on the walls of the fifth fuel transport duct poor; since these deposits (acids, tars, dust) are likely to disturb the operation of the burner, and / or to cause corrosion, this thermal insulation may be made necessary.

The advantages provided by the invention will be better understood through the following description which refers to the appended drawings, which illustrate without any limiting character the preferred embodiments of the invention.

In the drawings, identical or similar elements bear the same references from one figure to another, unless otherwise indicated.

Figure 1 illustrates in front view the end 22 of the burner nozzle.

Figure 2 is a half-view in section along the broken line A-A of Figure 1, on an enlarged scale.

FIG. 3 schematically illustrates a fin for rotating the “internal” flow of lean fuel and is a view along III-III of FIG. 2.

Figure 4 illustrates in the same way as Figure 2 a cement kiln burner, according to an alternative embodiment.

The nozzle 31 and the main conduits 5, 7, 9, 11, 15, 17 of the burner extend along a longitudinal axis 1; in the case of a tubular cement kiln, the axis 1 can be substantially coaxial with the axis of the kiln, in a horizontal position or slightly inclined relative to the horizontal.

The central part of the nozzle has a central air transport duct 5 delimited by a tube 6 of axis 1 inside the duct 5 extend four ducts (Figure 2) parallel to the axis 1 a duct 3 solvent injection, which is delimited by a tubular wall 4 of axis 2, as well as a conduit for transporting animal meal; the products transported in these two conduits are intended to be incinerated in the combustion chamber of the oven; two other conduits are used to transport combustible gas and waste water to be incinerated (and / or to contain an ignition rod); In the variant illustrated in Figure 4, a single conduit 3 for transporting fuel is shown; the conduit 3 is terminated by a fuel spray nozzle 3a.

In the two variants illustrated in FIGS. 2 and 4, the central duct 5 for transporting part of the primary air ends in a flame stabilizing device 5a, which is pierced with a plurality of small orifices 5b for passage of air; in the variant of Figure 4, the stabilizer is pierced with a central opening 5e extending in the extension of the nozzle 3a in the variant illustrated in Figure 2, the stabilizer 5a through which extends the end 3a of the conduit 3, comprises on the one hand small orifices 5b distributed over its surface, and on the other hand a peripheral annular opening 5c; the orifices 5b, 5c and the pressure of the air entering the duct 5 are provided so that the air flow rate passing through the stabilizer is low.

• une paroi 8 cylindrique séparant le conduit 7 d'un conduit 9 annulaire de transport d'air primaire radial ;
• une paroi 10 cylindrique séparant le conduit d'un conduit 11 annulaire de transport d'air primaire axial ;
• une paroi 12 cylindrique séparant le conduit 11 d'un isolant thermique 13 ;
• une paroi 14 cylindrique séparant l'isolant 13 d'un conduit 15 annulaire de transport de gaz de pyrolyse à écoulement radial et/ou tourbillonnant ;
• une paroi 16 cylindrique séparant le conduit 15 d'un conduit 17 annulaire de transport de gaz de pyrolyse à écoulement axial ;
• une paroi 18 cylindrique séparant le conduit 17 d'un revêtement 19 cylindrique externe en béton réfractaire.

Around the cylindrical wall 6 separating the duct 5 from an annular duct 7 for transporting pulverized coal, extend six walls 8, 10, 12, 14, 16, 18 metal tubulars, of increasing diameter, of axis 1:

• a cylindrical wall 8 separating the duct 7 from an annular radial primary air duct 9;
• a cylindrical wall 10 separating the duct from an annular axial primary air transport duct 11;
• a cylindrical wall 12 separating the conduit 11 from a thermal insulator 13;
• a cylindrical wall 14 separating the insulator 13 from an annular conduit 15 for transporting pyrolysis gas with radial and / or swirling flow;
• a cylindrical wall 16 separating the conduit 15 from an annular conduit 17 for transporting axial flow pyrolysis gas;
• a cylindrical wall 18 separating the conduit 17 from an external cylindrical covering 19 made of refractory concrete.

As illustrated in FIG. 2, the tubes 6, 8, 10, 12, 16, 18 are respectively terminated at their free end by a sleeve 6a, 8a, 10a, 12a, 16a, 18a; these sleeves have a shape having a symmetry of revolution along axis 1; the thickness of the sleeves can be variable along the axis 1, to delimit annular (and / or flared) conduits for ejecting the products respectively transported into the combustion chamber, which provide each with gas flows and / or pulverulent ejected into the chamber, a predetermined speed and direction; for this purpose, in addition, fins 9a inclined relative to the axis 1 provide radial guidance of the air delivered by the conduit 9, for the formation in the room of a whirlpool; fins 11a parallel to the axis 1 provide axial guidance of the air delivered by the duct 11.

According to one aspect of the invention, the burner, in the vicinity of its nose or front end 22 (of ejection into the combustion chamber), comprises fins 20 for deflecting the internal flow of lean fuel leaving the duct 15, to the formation in the chamber of swirling jets around the air jets from the ducts 9 and 11, and comprises fins 21 for axial guidance of the external flow of lean fuel leaving the duct 17.

In fact, the nose comprises a ferrule 23 supporting the fins 20 which extend along a longitudinal axis 24, which is inclined to cause the flow leaving the duct 15 to rotate.

The angle 25 of inclination of the axis 24 relative to the axis 1 is generally located in a range from 10 ° to 50 °.

The pyrolysis gas is supplied to the conduits 15 and 17 of the nozzle by pyrolysis gas supply conduits, which are preferably respectively equipped with a valve 30 for adjusting the pyrolysis gas flow rate introduced into each of the conduits 15 , 17.

The burner has an annular outlet opening 7b for solid and / or gaseous fuel, which is situated radially inside the outlet openings 9b, 11b of the primary air rotated and of the axial air, and at the exterior of the flame stabilizer 5a; the stabilizer (Figure 4) is disposed at the front end of a central oil nozzle holder; the minimum radial distance of the openings 9b, 11b for the outlet of most of the primary air from the center of the burner nozzle is at least twice the radius of the central opening of the flame stabilizer ( Figure 4); said stabilizer clearly protrudes in the radial direction relative to the opening of a central duct which corresponds substantially to the orifice of the nozzle 3a of the central fuel duct 3 (FIG. 4) and has openings (5b) for the passage of 'a small part of the primary combustion air, located outside this central opening; the axial air outlet opening 11b is located (radially) outside the opening 9b and comprises an outer edge (end of the sleeve 12a) which projects axially forwards (on the left in Figures 2 and 4); the annular supply conduits may have, upstream of their outlet opening, portions of conical walls (such as 7c, 7d, 11c, 11d) axially movable relative to each other; some of the annular supply conduits may comprise an axial cylindrical end portion extending a portion of conical wall giving the end of the conduit an “S” shape (in longitudinal view). The annular channel 11 for the axial air comprises partitions 11a for the supply and the axial orientation of the primary air in separate channels, arranged on a ring and extending axially the annular passage section for the air. axial or the corresponding channels arranged in a crown may be partly at least closed and closable; the sum of the free passage sections of the axial channels is appreciably smaller than the section of the annular duct for the primary air flowing in the axial direction the stabilizer 5a is offset axially backwards with respect to the outlet openings 9b, 11b of l rotating air and axial air, and relative to the outlets 7b, 15b, 17b of solid or gaseous fuels, rich and lean.

With reference to FIG. 2, the opening 5c can, as a variant, be arranged at the periphery of the fuel spray nozzle 3a, or else at any other position situated between the nozzle 3a and the wall 6 delimiting the central duct 5 this opening 5c can be delimited by two concentric tubular walls delimiting a fourth primary air supply duct independently of the other three ducts; this opening can facilitate the control of the air-fuel mixture in the “dead” central zone, by reducing the reducing nature of the air / fuel mixture, and / or by improving this mixture; one or more deflecting wall (s) for guiding the primary air may be associated with this opening.

Claims (9)

1. Burner for a rotary tube furnace, comprising a nozzle (3a) and substantially concentric ducts (7, 9, 11) for supply of a first fuel and for axial and radial supply of primary air, in which the outlet orifices (9b, 11b) of the air ducts (9, 11) are placed to the outside of the outlet opening (7b) of a fuel duct (7), which burner includes a central primary air duct (5) fitted with a flame stabilizer (5a) having air flow openings (5b, 5c), characterized in that it includes two separate annular ducts for transporting a second fuel, called lean fuel, namely a duct (15) having means (20) for swirling the lean fuel and a duct (17) surrounding the internal duct (15).
2. Burner for a combustion apparatus which is supplied with a rich fuel and an essentially gaseous lean fuel, comprising:

   - a central primary air transport duct (5) equipped with a flame stabilizer (5a);

   - at least one annular second duct (7) surrounding the said central duct, for transporting a pulverized solid fuel;

   - an annular oxidizer transport third duct (9) surrounding the said second duct and fitted at its end with means (9a) for swirling the stream of oxidizer;

   - an annular fourth duct (11) for transporting the said oxidizer, which surrounds the said third duct and is fitted at its end with means (11a) for axially guiding the stream of oxidizer;

   - an annular fifth duct (15) for transporting the said lean fuel, which surrounds the said fourth duct and is fitted at its end with means (20) for swirling the stream of lean fuel; and

   - an annular sixth duct (17) for transporting the said lean fuel, which surrounds the said fifth duct and is fitted at its end with means (21) for axially guiding the stream of lean fuel.
3. Burner according to either of Claims 1 and 2, in which each of the two lean fuel transport ducts (15, 17) is fitted with a respective flow rate adjustment member (30), such as a swing valve.
4. Burner according to any one of Claims 1 to 3, which includes a thermal insulator (13) that separates the internal annular lean-fuel transport duct (15) from an annular air transport duct (11) placed inside the duct (15).
5. Burner according to any one of Claims 1 to 4, in which the means for swirling the internal stream of lean fuel comprise a plurality of stationary fins (20) placed at the end (22) of the nozzle (31) of the burner, which fins are placed in a regular fashion around the longitudinal axis (1) of the nozzle of the burner and are inclined relative to this axis at an angle (25), the value of which lies within a range from 10 to 50 degrees.
6. Method of heating a rotary furnace, characterized in that:

   - a burner according to any one of Claims 1 to 5 is used;

   - a rich fuel having an NCV of at least 8000 kcal/Sm³ is used and the rich fuel injected into the central part of the nose (22) of the nozzle is made to undergo combustion with an oxidizer injected around the rich fuel; and

   - a lean fuel having an NCV of at most 8000 kcal/Sm³ is also used and the lean fuel injected in the peripheral part of the nose, forming swirling internal jets and forming substantially axial external jets, is made to undergo combustion.
7. Method according to Claim 6, in which a mean velocity of the lean fuel in the nozzle is maintained within a range of values from 20 metres per second to 70 metres per second.
8. Method according to either of Claims 6 and 7, in which the rich fuel is in solid pulverulent form and in which the lean fuel is a pyrolysis gas.
9. Method according to Claim 8, in which the pyrolysis gas is introduced into the nozzle at a temperature of around 300°C to 500°C.