EP0421903B2 - Process for operating a burner and burners for rotary drum furnace - Google Patents

Abstract

In a corresponding process, fuels and primary combustion air are introduced concentrically and the burner comprises a burner nozzle (1) which comprises concentric supply pipes for the fuel (10') and for the primary combustion air in the form of axial air (5') and swirling air (4'). In order to provide a process and a burner which can function with a lower proportion of primary air and a wider adjustment range, a dead zone is provided at the centre of the flame directly around a central fuel pipe and inside an annular fuel supply pipe, into which a very low proportion of fuel is sent. <IMAGE>

Description

The subject of the present invention is a method operating a burner for a rotary tube oven, in which fuel and primary air are brought concentrically.

The present invention also relates to a burner for a rotary tube furnace equipped a burner nozzle fitted with flues fuel and primary air, which are arranged substantially concentric with each other, which primary air has air rotated and axially flowing air.

A burner of this type is known from the DE patent. PS 2,905,746.

This known burner comprises, in addition to an inlet central fuel for oil, another concentrically arranged fuel supply to this one for pulverized coal or any other analogous fuel.

In order to obtain a good mixture, this solid fuel inlet is between two primary air streams, one of which is current central, is rotated or swirled, that is, it has a direction component tangential or peripheral and of which the other, which is external, has a flow velocity essentially axial in order to stabilize the flame penetrating far into the rotary kiln.

In other known burners, it is also expected primary air flow to expand relatively far inside.

The known burner has in its center, a arrival of liquid fuel, usually oil. Liquid fuel is sprayed into fines droplets by means of a nozzle and mixes after it leaves the central opening of the nozzle at primary air, which comes out of the outlet opening of swirling air, which opening is located radially around the central opening.

Known burners are usually operated with a proportion of primary air included between 8% and 25% of the total amount of air from combustion.

We adjust the burner output, that is to say walking pace by decreasing or increasing respective fuel and arrival of air in a specific setting range, in which the minimum adjustable gait to obtain a stable flame equals about 20 to 25% of the maximum possible pace.

When starting the burner, you must as a rule general, inject oil through the central opening of the nozzle and ignite it to preheat the oven, since the combustion of solid fuel, which is brought concentrically, is only possible in a sufficiently preheated oven.

In relation to this state of the art, the present invention aims to provide a operating method of a tube furnace burner rotary and also a burner for setting using this process, which can work with a lower proportion of primary air and have a larger adjustment range of the operating speed.

• on dispose lesdits conduits (4', 5') de courants d'air primaires, présentant respectivement des composantes périphériques et axiales, radialement à l'extérieur de tout conduit du combustible;
• on dispose un stabilisateur de flammme (3) dans la zone centrale (20), lequel stabilisateur déborde nettement en direction radiale par rapport à l'ouverture d'un conduit central (2) d'alimentation en combustible;
• on envoie dans la zone centrale (20) soit directement tout autour du conduit central (2) et/ou radialement à l'intérieur d'un conduit annulaire (15, 19) d'alimentation en combustible, tout au plus une petite quantité d'air primaire de 2% à 10% de la totalité de l'air primaire, de telle façon que dans ladite zone centrale ne se produise aucune combustion notable du combustible, qualifiant ladite zone centrale (2) de morte.

As regards the method, this objective is achieved for rotary tube ovens according to the first claim, in which fuels and primary combustion air are supplied concentrically in at least two ducts, said primary air itself being introduced. by at least two annular ducts (4 ′, 5 ′) respectively, by one in the form of a swirling air stream comprising peripheral flow components, and by the other in the form of an axial air stream having substantially axial flow components, such as:

• said conduits (4 ′, 5 ′) are disposed with primary air streams, having peripheral and axial components respectively, radially outside any fuel conduit;
• there is a flame stabilizer (3) in the central area (20), which stabilizer clearly protrudes in the radial direction relative to the opening of a central fuel supply duct (2);
• the fuel is sent to the central area (20) either directly around the central duct (2) and / or radially inside an annular fuel supply duct (15, 19), at most a small amount of primary air from 2% to 10% of the total primary air, so that in said central zone no significant combustion of the fuel occurs, qualifying said central zone (2) as dead.

So, thanks to the presence of a dead zone central, combustion starts at a higher long distance in front of the center of the nozzle burner in comparison with processes and burners known.

So we send in the central area either directly around the central supply duct in fuel and / or radially inside the annular fuel supply duct, qualifying said central area as dead.

So, thanks to the presence of a dead zone central, combustion starts at a higher long distance in front of the center of the nozzle burner in comparison with processes and burners known.

Thus, seen in longitudinal section, starting from center of the front end of the nozzle, the flame resulting has a central area that extends forward and radially, in which it does not produces virtually no noticeable combustion fuel with oxygen from the air.

Such a central flame core is certainly also present in principle in burners known, however according to the present invention, this central dead zone is brought about consciously and enlarged and this more particularly by the fact that we bring in the least primary air possible in this area.

However, even if it is not provided for in first place for combustion, a small proportion primary air is brought into this central zone, and this low proportion of primary air primarily serves to stabilize the flame and to prevent gas from going back of combustion, coal ash and coke, which would otherwise lead to fouling of the central part of the nozzle.

A small primary air flow in this area central, which is between 2 and 10% of the air total primary, avoid such a backtrack of products of combustion, without providing a lot of oxygen which would decrease the central area rich in fuel.

Surprisingly, it turned out that, thanks to the presence of such a central dead zone enlarged, the burner setting range can be significantly increased and this to less 10% of the maximum speed, for which the burner is designed.

Insofar as such a burner must operate especially with solid and powdery fuels, this means that after a brief warm-up with oil, it can already work with the solid fuel.

At the same time, it turned out that in such a process and in a burner designed for this process, the proportion of primary air to be used to stabilize the flame, can be reduced preferably below 6% per relative to the overall amount of combustion air. This facilitates the manufacture of the feeding devices in primary air which can be designed respectively weaker.

A particular advantage of consumption reduced primary air lies in the economy of energy attached to it for a performance equal in addition and also in the reduction the proportion of nitrogen oxides in the gases of combustion.

In accordance with the invention, it is intended that, separately from the introduction of a small proportion primary air in the central area, at least two other separate primary air streams are brought in, one of which is essentially axial and the other has a large part of the flow components in the peripheral direction.

Regarding the device mentioned above, the object of the invention is achieved in that the swirling air inlets and axial air are located outside the holes for the fuel supply and that the radial distance minimum with respect to the center of the nozzle of the vortex air outlet burner and axial air is at least twice the radius of a central orifice of the flame stabilizer.

Flame stabilizer has a flange which surrounds a central opening, and which is located in the center of the burner nozzle and preferably at the end of an oil nozzle holder. he helps to form and stabilize the flame. The flame stabilizer which overflows in the direction radial with respect to the central nozzle holder for oil, thus provides sufficient radial distance from other annular openings for primary air and / or other fuels which are located radially outside the flame stabilizer.

The spokes of the central opening of the stabilizer flame and the annular orifice for the primary primary air stream closest to the interior are chosen, so that the current of interior primary air is at a distance from center of the nozzle which corresponds to at least the double the central opening of the stabilizer flame. So the central opening of the stabilizer of flame corresponds substantially to the orifice of the central fuel line nozzle.

In this way, we prevent the fuel coming out centrally don't come in contact too soon with oxygen from the main primary air streams.

Furthermore, in the preferred embodiment of the invention, there is further provided, a conduit annular for solid and / or gaseous fuel, arranged radially inside the air duct primary and radially outside the stabilizer of flame.

The expression "primary air duct" refers to in general to most of the primary air which is brought axially or in swirling form and should not include the small proportion of air primary (central air) which is brought into the area central flame to avoid the return in rear of combustion products.

For bringing this last small proportion primary air, according to the invention, openings are provided in the stabilizer flame, outside the central opening.

The circulation of this small part of primary air takes place in an annular conduit between the central support of the oil nozzle and the internal wall next in radial direction for another fuel supply or for one of the streams primary air.

In addition, it is advantageous that the opening of axial air flow outlet is most the outside possible in the radial direction and that it has, in addition, an external edge which overflows axially.

This outer crown contributes to better constancy of the axial direction of the air, so that combustion is improved and the flame is stabilized.

According to the invention, the annular conduits primary air and / or fuel supply solid or gaseous have conical walls and these walls as well as the connected concentric tubes to these are axially movable one by relation to each other, so that one can as well adjust the free cross section of the annular passage.

However, preferably, the ends of each conduit are cylindrical to avoid a divergent flow parallel to the direction conical walls.

According to the invention, in the part conical of the annular duct by axial air, are arranged radial partitions for orientation axial and primary air circulation in separate channels, which are arranged on a ring and which basically extend in the direction axial.

These partitions contribute to an axial orientation additional corresponding primary air and also increase the axial output speed, by the fact that they reduce the free section of the annular duct and they divide it into a plurality of individual channels arranged all around of a ring. In addition, in one embodiment preferential of the invention, some of these channels are at least partially closed or are adjustable. For this purpose, the partitions can by example be made wide enough towards peripheral so that they close a channel at least in part or that they correspond to a closed channel.

So it is possible to obtain that the sum free sections of the channels is less than the cross section of the annular air duct primary flowing in axial direction.

As already explained, the flow velocity axial air is thus increased, which further contributes to stabilizing the flame.

In addition, according to the invention, it is intended that the flame stabilizer is shifted backwards by axial direction relative to outlet openings of the main part of the primary air and solid or gaseous fuels. This can be made for example by fixing the stabilizer flame in the tube casing of the burner rod, which is axially movable, which tube is offset axially accordingly.

Other advantages, characteristics and possibilities of use of the present invention arise of the following description of embodiments preferential in relation to the drawings which represent :

Figure 1: an overview of a burner with part of the power installations.

Figure 2a: a longitudinal section of a first embodiment of a burner nozzle.

Figure 2b: a partial left view of the Figure 2a.

Figure 3: a longitudinal section of another embodiment of a burner nozzle with possibility of supplying solid fuels sprayed.

Figure 4: a longitudinal section of a nozzle burner with additional possibility supply of a gaseous fuel.

Figure 5: a longitudinal section of a nozzle burner with additional possibility supply of solid fuel and fuel gaseous.

Figure 1 shows a burner nozzle 1 placed at the end of an external burner tube 5 ", which is at the same time the outer wall of a 5 'primary air duct flowing towards axial.

At the other end of the 5 "external tube, different feeding devices are attached or connected by flanges.

The axial air is supplied by a tube 25, the arrival of the swirling air takes place via a tube 24, and these two parts of primary air are adjustable separately by respective valves 45 and 44 and are connected on the same main pipe primary air. At the rear end of the burner shown in FIG. 1, a pipe 22 derives from this primary air line and this bypass ends in a tube that concentrically surrounds the burner rod casing tube 10 '.

So a small part of the primary air coming of bypass 22 flows through a conduit annular 11 'and exits through openings 13 (see Fig. 2b) in the central flame area. A liquid fuel, such as oil is supplied centrally to the burner nozzle through the line 21.

A tube 23, which is intended for the supply of pulverized solid fuels, generally pulverized carbon, is connected to the annular duct 15 'visible in Figures 3 and 5.

Concentric tubes 10 ", 11", 4 ", 5", 15 "and 19 ", which are engaged with each other, have different lengths. The tubes placed more inside protrude axially towards the rear of the tubes located more outside, so that, as we see in Figure 1, we can set up adjustment devices 33, 34, 35 which allow a relative axial displacement of the tubes relative to one another to the other. For this purpose, the individual tubes are connected to each other by means of deformable bellows.

A control unit 30 is used for monitoring and the control of primary air currents.

Figure 2a shows a longitudinal section and Figure 2b a partial front view of a burner nozzle which is designed to operate exclusively with a fuel, for example oil, arriving in the center.

The flame stabilizer 3, which is located at the end of the tube 10 ', which wraps the rod oil burner nozzle holder which protrudes clearly in radial direction relative to the opening of the nozzle guarantees that the opening 4 of the duct annular feeder along 4 'leads to a significant radial distance from the central opening 2 of the flame stabilizer.

In the example shown, the radial distance D of the annular opening 4 relative to the axis of the burner is more than three times the radius d of the opening 2. The corresponding distances are indicated in Figure 4, in which the ratio D / d is even bigger.

The area essentially in front of the flame stabilizer constitutes a dead zone central 20, which is outside the current of central fuel and clearly inside of the main intake of primary air leaving the openings annulars 4 and 5.

This dead zone can extend towards axial up to a multiple of the stabilizer diameter of flame. A mixture of combustion air primary and sufficient fuel for training flame only occurs outside of this central dead zone. The stabilizer flame 3 has a hub in the form of flange surrounding a central hole 2. This hub has small openings 13. The outer face of the hub, i.e. the front face, carries fins 12 which guide the low proportion of air primary leaving openings 13.

The external supply conduit 5 'has at its end of the conical walls 6, which diverge outwards. In the area of these walls 6 there are juxtaposed partitions 6 ', which have a longitudinal section of triangular shape. These triangular walls are juxtaposed along a common side which is parallel to the axis of the burner and which is placed at the same radial distance from this axis as the outer wall of the conduit 5 '.

Thus, it is possible to axially move the 4 "tube compared to 5" tube without the function partitions 6 'is influenced.

We see in Figure 2b a front view of frontal edges of the partitions 6 '.

However, 6 'partitions can also have a sufficient width in the peripheral direction so that they correspond to the parts located between the channels 5 shown in Figure 2. These parties can also be considered closed channels 5.

The supply duct 4 'has in front from the conical end, a swirl device 14 air, i.e. rotating around the axis of the burner. This device is made up essentially air guide fins which are oriented obliquely to the axis of the burner.

Thanks to an axial displacement of the tube 11 'by compared to the 4 'tube, we can vary the distance between the conical walls 7 of the conduit 4 ', so that we can change the cross section of the 4 'duct. The terminal part of the 4 'conduit in the opening 4 area is however new cylindrical to prevent flow diverge from the swirling air coming out of this opening.

Likewise, edge 8, which projects forward in axial direction, provides exit direction axial of the axial air flow.

In connection with exit direction and acceleration axial air in the duct 5, this guarantees a stable, uniform and uniform axial air flow great range.

FIG. 3 represents an embodiment of the burner nozzle which differs from the mode embodiment shown in Figure 2 essentially by the presence of an additional conduit 15 ', for pulverulent solid fuels, which is located between the flame stabilizer 3 and the 4 'swirling primary air duct.

It is generally pulverized coal which is transported in the burner by a carrier gas, by example of air. Due to the abrasive properties of such solid fuel, the terminal area of the 15 'duct is only slightly conical to allow passage as easy as possible fuel.

FIG. 4 represents an embodiment comprising, in place of the conduit 15 'for a solid fuel, another 19 'duct for a gaseous fuel, the terminal section of which can be conical, as for the 4 'duct, and which may also include a device for swirl the gas coming out of this duct. In this case also, the terminal section of the conduit 19 'has a cylindrical shape in the area of the opening 19, in order to avoid a divergence of the gaseous fuel that comes out.

FIG. 5 represents an embodiment which includes both a 15 'supply duct for solid fuels and a 19 'duct for gaseous fuels.

4 'and 5' ducts for the main proportion primary air in the form of swirling air and air having an axial direction are arranged at the outside of these two fuel lines in radial direction. The internal edge of the opening 15, whereby a significant part of the combustion air primary can enter the burner under form of solid fuel transport gas is at a distance D 'from the axis of the burner, which is more than double the radius d of the opening 2 of the flame stabilizer, so that in all the cases, the existence in the center of the flame is guaranteed a sufficiently large dead zone, which provides the advantageous properties of this invention.

By this invention, a burner and a operating method of a burner intended to equip a rotary tube oven, which allow a reduced proportion of primary air and a more large burner adjustment range, which leads to lower energy consumption and reduced formation of harmful nitrogen oxides the environment.

Claims (13)

1. Process for operating a burner for rotary tube furnaces, in which fuels and primary combustion air are supplied concentrically, in at least two conduits, said primary air being itself introduced through at least two annular conduits (4', 5') respectively, through one in the form of a stream of eddying air comprising peripheral flow components, and through the other in the form of axial air current comprising substantially axial flow components, such that:

   said conduits (4', 5') of primary air streams respectively having peripheral and axial components, are disposed radially outside any conduit for the fuel;

   a flame stabilizer (3) is disposed in the central zone (20), which stabilizer projects substantially in a radial direction beyond the opening of a central fuel supply conduit (2); and

   only a small quantity of primary air from 2% to 10% of the totality of the primary air is sent into the central zone (20) either directly all around the central conduit (2) and/or radially inside an annular fuel supply conduit (15, 19), such that in said central zone there is no noticeable combustion of the fuel occurring, said central zone (2) being termed dead zone.
2. Process according to claim 1, characterized in that the percentage of primary combustion air sent into said central dead zone (20) is less than 10% of the total quantity of primary air including any vector gas for a solid fuel.
3. Process according to any one of claims 1 or 2, characterized in that the proportion of primary combustion air is less than 6%.
4. Burner for a rotary tube furnace, of the type comprising a burner nozzle, equipped with substantially concentric fuel supply conduits and primary combustion air conduits comprising axial air and eddying air, in which:

   the outlet orifices (4, 5) for the eddying air and for the axial air are disposed radially outside the outlet openings for the fuels (10, 15, 19);

   the minimum radial distance of said outlet openings (4, 5) for the major part of the primary air with respect to the center of the nozzle of the burner (1), is at least twice the radius of the central opening (2) of a flame stabilizer (3); and

      said stabilizer (3) projects substantially in a radial direction beyond the opening of a central conduit (2) which corresponds substantially to the orifice of the nozzle of a central fuel conduit, and comprises openings (13) for the passage of a small part of the primary combustion air, which openings are located outside said central opening (2).
5. Burner according to claim 4, characterized in that it comprises an annular outlet opening (15, 19) for solid and/or gaseous fuels, which is located radially inside the outlet openings (4, 5) for the eddying primary air and the axial air and outside the flame stabilizer (3).
6. Burner according to any one of claims 4 or 5, characterized in that the flame stabilizer (3) is disposed at the front end of a central oil nozzle-holder.
7. Burner according to any one of claims 4 to 6, characterized in that the outlet opening (5) for axial air is located radially as far to the outside as possible and comprises an outer edge (8) which projects axially towards the front.
8. Burner according to any one of claims 4 to 7, characterized in that the annular supply conduits present, upstream of their outlet opening (4, 5, 15, 19) conical wall portions (6, 7, 16, 17) which are axially displaceable with respect to one another.
9. Burner according to claim 8, characterized in that at least certain of the annular supply conduits comprise a cylindrical terminal portion (9) of at least one wall (6, 7, 16, 17) of each of said supply conduits, which is located between the conical wall portion and the annular outlet opening.
10. Burner according to any one of claims 8 to 9, characterized in that the annular channel (5') for the axial air comprises, in the conical zone (6), partitions (6') for the supply and axial orientation of the primary air in separate channels, disposed in a ring and extending axially.
11. Burner according to claim 10, characterized in that the section of the annular passage (5) for the axial air or the corresponding channels disposed in a ring are at least in part closed or adapted to be obturated.
12. Burner according to any one of claims 10 or 11, characterized in that the sum of the sections of free passage of the axial channels is substantially smaller than the section of the annular conduit (5') for the primary air flowing in axial direction.
13. Burner according to any one of claims 4 to 12, characterized in that the flame stabilizer (4) is offset axially to the rear with respect to the outlet openings (4, 5, 15, 19) for the eddying air, the axial air and/or for the solid or gaseous fuels.

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