AU2002238385B2 - Burner for the combustion of particulate fuel - Google Patents

Abstract

The burner has a secondary air tube (3) placed around the longitudinal axis (27) of the burner and closed by an end wall (38) at the end away from the burner mouth (2). The secondary air tube is enclosed by a primary mixer pipe (4) which introduces primary air or a mixture of gas and fuel and which has a flow stabilising area (49) placed upstream in the flow direction of the primary mixture. Secondary air (19) is brought in through an inlet housing (28) which encloses part of the primary mixer pipe and forms a radial channel (40) which is connected to the internal cross section of the secondary air tube through ducts (35) which cross the ring shaped cross section and feed secondary air from the channel into the secondary air pipe.

Description

Translation from German of PCT Application PCT/DE02/O0116 Burner for the Combustion of Particulate Fuel This invention pertains to a burner and a process to combust particulate fuel, specifically particulate and inert-rich coal.

There are known burners to combust particulate fuel, in particular coal dust, for example from the document "Entwicklung von schadstoffarmen Staubfeuerungssystemen" [Development of Low-Contaminant Dust-Fired Systems] from VGB Kraftwerkstechnik 76 (1996), Volume 5. There are essentially two different types of burners for the combustion of particulate fuel, the usual rectangular radiant burners and the round burner, which in general is designed as a vortex burner. Radiant burners usually consist of a dust nozzle through which the particulate fuel is fed via a carrier gas, which can be primary air or primary gas, to the furnace for combustion, and an upper and a lower air nozzle that sit adjacent to the dust nozzle above and below it through which the secondary air is fed to the furnace. These nozzles are designed with rectangular cross-sections. Frequently, radiant burners have a number of dust nozzles, two to four dust nozzles in fact. In this case, the upper and the lower air nozzles lying between two dust nozzles in the vertical direction can be combined to form an intermediate air nozzle.

When using these types of radiant burners for the combustion of lignite, the lignite is usually ground in hammer mills, dried using hot flue gases that are drawn from the furnace or combustion chamber, and fed to the dust nozzles of the burner via the ventilation effect of the hammer mill. This results in a mixture of fuel dust, flue gas, water vapour and primary air exiting the dust nozzle into the furnace. This mixture is called primary mixture below. The secondary air exits the upper, lower and if present intermediate air nozzles. There are in general also core air tubes integrated inside of the rectangular dust nozzle through which a small part of the combustion air exits.

The ignition zone of a radiant burner of this type generally sits at a specific distance from the burner outlet, in fact at the point where contact takes place between the secondary air streams and the dust stream. In the process, the dust stream is first heated to the ignition temperature and pyrolised by the hot flue gas that is drawn from the furnace. Due to the geometric arrangement of the dust and air nozzles, the recirculated hot flue gas is drawn by the dust stream mainly at the side surfaces of the rectangular dust nozzle. It is not possible for heating and pyrolization of the dust stream to occur at the upper and lower surfaces of the stream since these surfaces are jacketed by the secondary air streams.

The rectangular radiant burner described above works well as a design for the majority of existing lignite types where ignition stability is concerned, and is the optimum with regard to NOx emission levels and the slagging behaviour of the furnaces. For lignites that have an extremely high inert content due to a very high water and/or ash content, it is desirable to further increase the ignition stability as an alternative or in addition to the vapour separation usually implemented for these fuels by making design modifications to the burner. A disadvantage of the radiant burners described above is that due to the geometric arrangement, the entire circumference of the dust stream of the dust nozzle cannot be used in the intake of hot flue gases and thus there can be no total-perimeter heating of the dust stream. Likewise, a priority of furnace operation can be, depending on the specific limiting parameters, to increase the reaction density at the burner to ensure that sufficient combustion occurs in small furnaces, for example. However, radiant burners have lower reaction densities than vortex or round burners due to their flow characteristics.

In addition to radiant burners, round burners are known that contain a central, round dust mixture or primary mixture tube and secondary air tube concentric to it that surrounds the central dust tube and forms an annular cross-section between the two tubes. The fuel dust is introduced to the furnace together with primary air or primary gas via the dust or primary mixture tube, and secondary air is introduced via the annular cross-section of the secondary air tube. In these round burners, in most cases both the secondary air as well as the dust stream is vortexed. To accomplish this, vortex blades are installed, for example in the dust tube, as well as a spiral secondary air inlet housing on the secondary air side with tangential secondary air feed. As in radiant burners, core air tubes can be integrated into round burners as, well inside the circular dust tube. A small portion of the combustion air can exit through these core air tubes into the furnace.

A disadvantage of the known round burners with vortexed dust streams, however, is that a pressure loss is produced by the vortexing of the dust stream that must be made up for, in general by the upstream hammer mill. This usually requires that the RPM of the impeller be increased or that other measures be performed on the mill that increase the energy requirements and the wear in the mill in general and at the impact plates in particular.

Another disadvantage is the wear that takes place at the vortex blades on the dust side. It has also been shown to be disadvantageous that, due to the geometric arrangement with the central dust tube and the concentric secondary air tube, the dust stream only contacts the hot flue gas of the furnace through internal recirculation of the flue gas in the flame root of the burner flame, but that the entire external perimeter of the dust stream has no direct contact with the hot flue gas of the furnace. The result of this is that at the entire circumference hot flue gas from the furnace can only be mixed using relatively cold secondary air. This keeps the dust stream from being heated and pyrolized ahead of time.

A coal dust burner has been disclosed in the document "Patent Abstracts of Japan, Publication Number 58011308 A" that provides an air feed in a central air feed tube and that provides the coal dust feed in an annular channel that is formed from the inner air feed tubes and an outer coal dust feed tube that surrounds it. By O introducing the abrasive coal dust stream, which is at an CI angle to and offset with respect to the burner's o longitudinal axis, into the coal dust feed channel, very Z costly and maintenance-intensive ceramic linings must be 'q 5 placed on the inner wall of the coal dust feed tube and on the outer wall of the air feed tube in order to maintain the 0Olifespan of the coal dust burner within reasonable ranges.

OO The objective of this invention is thus to provide a M- more efficient and cost-effective burner than the prior art that is suitable for the combustion of particulate and c- inert-rich coals in particular, as well as to provide a process to operate a burner of this type.

With this in mind, the present invention provides in one aspect a burner to combust particulate fuel, in particular inert-rich coal dust, involving a secondary air tube located about a burner longitudinal axis and closed off at the end facing away from the burner opening with an end wall, to introduce the entirety of the secondary air, a primary mixture tube that surrounds the secondary air tube, forming an annular cross-section, to introduce primary air or primary gas and fuel, wherein the primary mixture tube has a flow stabilization zone placed upstream of the secondary air tube as seen in the flow direction of the primary mixture, an inlet housing that surrounds at least a portion of the primary mixture tube as seen along the perimeter and that forms a radial channel to feed the secondary air, and at least two penetration channels that connect the channel to the inner cross-section of the secondary air tube and that pass across the annular crosssection to introduce the secondary air stream from the channel into the secondary air tube.

CI According to another aspect of the present invention, o there is provided a process to combust particulate fuel, in Z particular inert-rich coal dust, by means of a burner that c- 5 involves a central secondary air tube and a primary mixture tube that surrounds the secondary air tube concentrically and that forms an annular cross-section, wherein all

OO

M secondary air fed to the burner, or air not included in the 00 M primary air, is fed to the burner via the secondary air tube, and wherein a primary mixture consisting of primary c-i air or gas and fuel is fed through the primary mixture tube, and wherein the secondary air is fed to the secondary air tube through at least two penetration channels that penetrate the annular cross-section between the secondary air tube and the primary mixture tube.

The solution according to the invention offers a burner and a process to operate a burner that has the following advantages: By constructing the burner according to the invention with a central secondary air tube and a primary mixture tube concentrically surrounding it, forming an annular cross-section between the two tubes, the primary mixture or dust stream that exits the primary mixture or dust tube into the furnace has direct contact along its entire circumference with the hot flue gases of the furnace that can be drawn unimpeded and that can heat up the dust stream. In comparison to round burners in which the primary mixture stream is usually jacketed by the secondary air stream, which means there are no surfaces of contact between the primary mixture or dust stream and the hot flue gas of the furnaces, these contact surfaces are now created to their full extent. Also, in comparison to the known radiant burners with rectangular primary mixture und secondary air nozzles, the contact surfaces between primary mixture or dust stream and hot flue gases have been made much larger. This results in a significant improvement in heating the fuel particles of the primary mixture or dust stream to the ignition temperature ahead of time in the burner according to the invention, as well as the pyrolysis of the same, thus increasing the ignition stability considerably.

The primary mixture stream is introduced axially to the burner through the flow stabilization zone that is upstream of the secondary air tube from the point of view of the primary mixture stream, thus effecting an even distribution of the solids across the cross-section and effecting a lower pressure loss in the system. By introducing the primary mixture stream to the burner axially, erosion of the primary mixture and secondary air lines can be prevented for the most part in an especially advantageous manner so that the use of costintensive wear parts and maintenance thereof can be prevented. The axial introduction of the primary mixture stream to the burner is lastly also facilitated by the introduction of the secondary air by means of a secondary air inlet housing placed according to the invention on the perimeter of the primary mixture tube and by means of the penetration channels that originate from it and that feed into the secondary air line.

The lower pressure loss in the system mentioned above also takes a load off of the upstream hammer mill, that is, it requires less power.

In an advantageous embodiment of the invention, the penetration channel is designed such that the secondary air stream can be introduced tangentially, radially and at an angle in between into the secondary air tube. These design features make it possible to feed the secondary air stream to the secondary air tube using an auxiliary aid, for example a vortex control device, with a strong vortex, a weak vortex or with no vortex at all.

By designing the penetration channel with a vortex control device or vane, the introduction or direction of flow of the secondary air stream into the secondary air tube can be controlled in an advantageous manner. In this way, the secondary air stream can be introduced radially, that is, with no vortex, or tangentially, that is, with a vortex, into the secondary air tube without having to provide special equipment inside the secondary air tube for this purpose. It is also possible to introduce the air with a weak vortex if the direction of introduction produced by the vortex control vane is between a radial and a tangential introduction. By imparting a vortex to the secondary air stream, a low-pressure zone is produced at the burner outlet in the vicinity of the burner axis that transports additional hot flue gases from the flame back to the flame root and thus raises the ignition stability and the reaction density in the flame. In the ignition zone defined in the vicinity of the burner outlet, an area is created in which both an ignitable dust/air concentration is reached by means of the mixing of the dust stream and the secondary air and the ignition temperature is reached due to the mixing of hot flue gases from the furnace and hot flue gases from the flame itself. If no vortexed secondary air is necessary in the furnace, or if the fuel does not require it, it can be introduced radially into the secondary air tube.

In an advantageous embodiment of the invention, the channel of the inlet housing has smaller depth along the perimeter with increased angle in order to attain an even flow velocity inside the inlet housing and in the penetration channels branching off from it. This can be accomplished most effectively using a spiral inlet housing.

To be able to optimise the position of the ignition zone at the burner, the secondary air tube, or at least a section of the secondary air tube on the exhaust side, can be shifted axially inside the primary mixture tube in an advantageous manner.

It is advantageous for the plane of the secondary air tube outlet to lie downstream or upstream of the primary mixture tube outlet as seen along the longitudinal axis of the secondary air and primary mixture tubes, or in the same plane as the primary mixture tube outlet. This arrangement enables an optimum alignment of the two air tubes with respect to one another in reference to the ignition zone and the ignition stability.

It is advantageous to design the end wall of the secondary air tube and the penetration channel on the upstream side of the primary mixture facing away from the burner opening with a wear-resistant and flow deflecting means in order to prevent turbulence and wear at the end wall.

In an advantageous embodiment of the invention, the end wall of the penetration channel at the downstream side of the primary gas mixture facing toward the burner opening is designed with a deviation element in order to likewise prevent turbulence and deposits.

In an advantageous embodiment of the invention, the secondary air tube is designed with a baffle ring on its outer circumference at the outlet end, or it is widened conically as it discharges into the furnace. Both of these measures can also increase the ignition stability.

In an advantageous manner, the contact surface between primary mixture and hot flue gases is further increased and an improved mixing of primary mixture, secondary air and flue gases is accomplished by placing multiple baffle segments at the burner outlet, wherein each baffle segment extends radially between the secondary air tube and the primary mixture tube and angularly covers a portion of the burner outlet perimeter, that is, covers a portion of the annular outlet between the secondary air tube and the primary mixture tube, and wherein the baffle segments are at an even angular distance from one another. The result is increased ignition stability.

It is advantageous to place a vortex device inside the primary mixture tube and/or a spiral primary mixture housing directly in front of the primary mixture tube, that is, upstream of it in the flow stream. Either of these measures can produce a vortexed dust stream and additional ignition stability of the mixture stream.

In an effective embodiment of the invention, the distance L between the burner opening and the end wall of the secondary air inlet housing facing away from the burner opening is 1.0 to 10 times the diameter dsL of the secondary air tube in order to have a sufficient and effective rotational vortex of the secondary air at the burner opening.

In another advantageous embodiment of the invention, the primary mixture tube has at its outlet end a conical widening in order to influence the ignition stability.

An effective embodiment of the invention has at least one smoothing element placed downstream of the primary mixture tube inlet at the side of the inner surface of the primary mixture tube opposite the primary mixture tube inlet to smooth out the primary mixture stream. In this way, mixture hang-ups in the primary mixture tube that form mainly on the opposite side of the mixture inlet can be dislodged and the mixture stream can be smoothed out.

It is furthermore advantageous to design the longitudinal axis of the secondary air tube and the primary mixture tube to be tilted by 0 to 200 to horizontal in the outlet direction in order to push the combustion zone deeper into the combustion chamber and thus to achieve a longer combustion path for the fuel.

In another advantageous embodiment of the invention, an annular guide is placed on the inner circumference or inner surface of the primary mixture tube near the secondary air tube or in the area of the secondary air tube outlet, said annular guide taking up a portion of the annular cross-section between the primary mixture tube and the secondary air tube. This allows a local accumulation of the primary mixture at the inner periphery of the annular cross-section, and as a result a more efficient mixing of the primary mixture with the secondary air.

It is also advantageous to place the penetration channels at the same angular offset from one another as well as to design them with the same width, so that they each take up the same size partial section of the annular crosssection in order to achieve the same size of passage cross-section for the primary mixture stream.

The burner according to the invention is intentionally operated sub-stoichiometrically, or under oxygen deprivation, in order to attain an as low-NOx a combustion as possible of the fuel and to produce as environmentally safe a furnace as possible.

Below, exemplary embodiments of the invention are explained in more detail with the help of illustrations and a description.

Shown are in: Fig. 1 the front elevation of a radiant burner according to the prior art, shown schematically, Fig. 2a longitudinal section through the radiant burner according to section A-A of Figure i, Fig. 3 the front elevation of a round burner according to the prior art, shown schematically, Fig. 4a longitudinal section through the round burner according to section B-B of Figure 3, Fig. 5 the cross-section of a burner according to the invention at the tangential or radial feed section of the secondary air (Section E-E of Figure 6), shown schematically, Fig. 6a longitudinal section through the burner according to Section D-D in Figure Fig. 7a longitudinal section according to Section F-F in Figure 6, Fig. 8a partial longitudinal section through the burner according to Section D-D in Figure 5 between the tangential or radial secondary air feed and the burner opening, Fig. 9 the front elevation of a burner of alternative design according to the invention, shown schematically, Fig. 10 a partial longitudinal section through the burner according to Section D-D in Figure between the tangential or radial secondary air feed and the burner opening, in an alternative design, Fig. 11 a longitudinal section through the burner according to Section D-D in Figure 5, in an alternative design, Fig. 12 same as Figure 5, but an alternative design.

Figure 1 and 2 show a radiant burner according to one prior art. This burner consists of a dust nozzle 24, a lower air nozzle 25 and an upper air nozzle 26, the cross-sections of which being rectangular in design. The entire burner consists in most cases of numerous dust nozzles 24, usually 2 or 3 of them. In this case, the upper and lower air cross-sections that lie between two dust nozzles 24 in the vertical direction .can be combined into an intermediate cross-section.

Lignite is ground primarily in hammer mills, dried using hot flue gases drawn out of the combustion chamber or furnace 10 and fed to the dust nozzles 24 of the burner by way of the ventilating effect of the hammer mill, which is not shown. Thus, a mixture of powdered fuel, flue gas, water vapour and primary air exits the dust nozzle 24 into the furnace 10. This mixture is called primary mixture below. The secondary air exits the upper, lower and intermediate air nozzles 25, 26. Integrated within the rectangular dust nozzle 24 are in general core air tubes (not shown), through which a small portion of the combustion air exits.

Fig. 2 shows the longitudinal section of a radiant burner with the streams discharging into the furnace 10. The ignition zone 18 of a burner of this type generally lies at a certain distance from the burner outlet. This is the point where the secondary air streams 19 and the dust stream 20 come into contact with one another. In the process, the dust stream 20 is first heated to the ignition temperature and pyrolized by hot flue gas 21 that is drawn from the furnace 10. Due to the geometric arrangement of the dust 24 and air nozzles 25, 26, the re-circulated hot flue gas 21 is drawn by the dust stream 20 mainly at the side surfaces of the rectangular dust nozzle 24 (Fig. 1).

Figures 3 and 4 show a round vortex burner according to one prior art that has a central, round dust or primary mixture tube 4 and a secondary air tube 3 concentric to it. In these round burners, it is common for both the secondary air stream 19 as well as the dust stream 20 to be vortexed. To accomplish this, there are vortex blade 12 in the dust tube 4 and a spiral secondary air inlet housing 28 on the secondary air side with tangential secondary air feed.

Figures 5 through 12 show possible embodiments of a burner 1 according to the invention, with Figure 5 and 12 showing a cross-section at the point where the secondary air approaches and is introduced to the secondary air tube, and Figures 6, 8, 10, and 11 each showing a longitudinal section or partial longitudinal section of the burner 1, from which the design of this burner can be seen. According to Figures 5 and 6, the burner 1 is essentially made up of a central round secondary air tube 3, whose centreline is the longitudinal axis 27, and a round primary mixture tube or dust tube 4, that concentrically surrounds the secondary air tube 3 and forms an annular cross-section 9.The inlet end 6 of the primary mixture tube 4 is connected to a feed line 17 that is essentially perpendicular to the primary mixture tube 4. The inlet end 5 of the secondary air tube 3 is connected to a feed line 16 via penetration channels and via the channel 40 of the secondary air inlet housing 28. The outlet ends 7, 8 of the primary mixture tube 4 and secondary air tube 3 lead to the burner opening or burner opening 2 of the furnace wall 11. The secondary air tube outlet 7 covers the entire cross-section of the secondary air tube 3 and if necessary the conical widening 30, which in Figure 8 is depicted as a preferred embodiment of the invention. The primary mixture tube outlet 8 covers the entire cross-section of the annular section 9 between the two tubes 3 and 4 reduced by the bottleneck caused by the conical widening 30 of the secondary air tube 3 if present or expanded by the conical widening 48 of the primary mixture tube 4 if present.

All of the secondary air stream 19, or all air other than the primary air, that is fed to the burner 1 is fed in the direction of flow-through (shown using arrows in the Figures) via the feed line 16, which is preferably perpendicular to the burner longitudinal axis 27, the inlet housing 28 that forms a radial channel 40, the penetration channels 35 that penetrate the annular crosssection 9 and the secondary air tube inlet 5 to the secondary air tube 3. After the stream 19 is redirected in the secondary air tube 3 the back of the inlet end of the secondary air tube 3 is closed off by an end wall 38 according to the invention it flows parallel to the longitudinal axis 27 and exits the secondary air tube 3 into the furnace 10 at the open cross-section of the secondary air tube exit 7. In the process, the penetration channels 35 are designed such that the secondary air stream 19 can be introduced tangentially, radially and in any desired direction in between into the secondary air tube 3.

To facilitate the input of the secondary air stream 19 through the feed line 16, which is attached to the inlet housing 28, and into the central secondary air line 3, at least two penetration channels 35 in the example according to Figures 5 through 12 there are three penetration channels 35 are provided according to the invention that connect the channel 40 of the inlet housings 28 to the inner cross-section of the secondary air tube 3. At the penetration channels 35, both the primary mixture tube 4 and the secondary air tube 3 have openings 42, 43 for the secondary air stream 19 to pass through that are approximately as large as the crosssection of the penetration channel 35. Each penetration channel 35 thus takes up an angular portion of the annular cross-section 9 between primary mixture tube 4 and secondary air tube 3. In a preferred embodiment, each penetration channel 35 takes up the same angular portion of the annular cross-section 9.

The cross-section of the penetration channels 35 is in general of a rectangular design with a width b and a height h. In the flow direction, the penetration channel 35 is designed such that, as already explained above, the secondary air stream 19 can be introduced radially, tangentially or at an angle in between into the secondary air tube 3. This setting can be made by means of a penetration channel 35 according to Figure 12 in which the side walls 46, 47 are designed appropriate to this end. To control the direction of the incoming secondary air stream as desired, a vortex control device 34 can be provided, in particular a vortex control vane, which is located inside the penetration channel 35 or at the secondary air tube inlet 5 or at the opening 42. The penetration channel 35 is made up of end walls 39 and and sidewalls 46 and 47.

In a preferred mode of operation of the burner 1, the secondary air stream 19 is introduced tangentially into the secondary air tube 3 via the vortex control device 34, thus imparting to the stream 19 a rotational vortex that remains up until discharge to the furnace 10 and which is accomplished without special equipment in the secondary air tube 3. The vortex control device 34 is used to influence the vortex of the secondary air stream 19 or to weaken, even to the point of vortex-free feed at radial introduction of the secondary air stream 19 into the secondary air tube 3.

The vortex control device 34 of all penetration channels 35 can be operated from a central spindle adjustment mechanism, which is not shown, so that at each penetration channel 35 exactly the same control position exists, thus achieving the same secondary air amounts.

The penetration channels 35 are preferred to be at an even separation from one another inside the annular cross-section 9 so that the passages 44 for the primary mixture stream 20 also have the same cross-sections when the penetration channels 35 have the same cross-sectional dimensions, and so that an even distribution of the primary mixture stream 20 is attained.

The inlet housing 28, which is placed radially on the outside of the primary mixture tube 4 in the area of its penetration channels 35, covers at least a portion of the circumference of the tube 4 in such a way that all existing penetration channels 35 can be fed with secondary air. The inlet housing 28 can simply be a boxshaped housing that forms the channel 40, described above, between the tube 4 and the outer wall of the housing 28 (see Figure 12). In the process, the channel formed by the inlet housing 28 at the outer perimeter of the tube 4 is preferred to have an essentially smaller depth along the perimeter with increased angle in order to attain a fairly even velocity and distribution of the secondary air stream 19 along the circumference to each individual penetration channel 35 and further on into the secondary air tube 3. This specification can be achieved by means of a preferred spiral shaped design of the inlet housings 28, among other things.

Since the vortex produced by the tangential introduction into the secondary air tube 3 can decrease along the length of the tube 3, it makes sense to design the tangential introduction of the secondary air to be not too far from the burner opening 2. The distance L between the burner opening 2 and the end wall of the inlet housing 28 facing the burner opening 2 (which is essentially the same as the side of the inlet opening facing the burner opening 2) is preferred to be designed at 0.5 to 10 times the diameter dsL of the secondary air tube 3.

To be able to change or optimise the position of the ignition zone 18 at the burner outlet 2, the secondary air tube 3 or an outlet section 13 of the secondary air tube 3 is made to shift axially inside the primary mixture tube 4. This permits the outlet plane of the outlet end 7 of the secondary air tube 3 or of the outlet section 13 to be placed at various positions in relation to the outlet plane of the outlet end 8 of the primary mixture tube 4. In Figure 6, the outlet plane of the outlet end 7 of the secondary air tube 3 or of the outlet section 13 is upstream of the outlet plane of the outlet end 8 of the primary mixture tube 4 by the amount k as seen in the direction of flow. Depending on the fuel and the burner size, the dimension k can be up to 0.5 times the diameter dsL of the secondary air tube 3, and two outlet ends 7, 8 can also lie flush with one another. It is also possible to have the secondary air tube 3 protrude, that is, the outlet plane of the outlet end 7 of the secondary air tube 3 is downstream of the outlet plane of the outlet end 8 of the primary mixture tube 4 by the amount k. In this case as well, the dimension k can be up to 0.5 times the diameter dsL of the secondary air tube 3.

Where there exists an axially shifting outlet section 13, the secondary air tube 3 can consist of two parts, a stationary part and an axially shifting part 13, wherein both parts are overlapping (Figure The ignition stability can also be influenced by physical design measures at the outlet 7 of the secondary air tube 3 by having a conical widening 30 made on the end of the tube 3 as in Figure 6 or by providing a baffle ring 15 on the exterior circumference of the secondary air tube 3 that reduces the annular cross-section 9 at the primary mixture tube outlet 8.

According to Figure 6, primary air or primary gas is fed to the burner 1, consisting essentially of primary air, flue gas and water vapour, together with particulate or powdered fuel through the feed line 17, which in most cases is placed perpendicular to the primary mixture tube 4. This mixture (primary mixture) passes through the primary mixture tube inlet 6 into the primary mixture tube 4. Downstream of the inlets 6 and upstream of the secondary air tube 3, the primary mixture tube 4 contains a flow stabilization zone 49 in which the redirected primary mixture stream 20 is stabilized, or redirected in the axial flow direction. The primary mixture tube 4 can be provided with a widening of the outer diameter downstream of the flow stabilization zone 49 and upstream of the secondary air tube 3 as seen in the direction of flow in order to essentially attain the same flow velocities in the annular cross-section 9 as in the flow stabilization zone 49. After flowing through the passages 44 present between the secondary air penetration channels and the primary mixture tube 4, occurring parallel to the longitudinal axis 27, the primary mixture stream discharges into the furnace 10 at outlet 8. There is a higher flow velocity in the passage 44 than in the free annular cross-section 9, and this has proven to be advantageous in preventing deposits at this narrowed cross-section.

At least one smoothing element 31 can be provided inside the primary mixture tube 4 to smooth out the primary mixture stream 20 inside the flow stabilization zone 49, since hang-ups, that is, accumulations of fuel dust, can form when the primary mixture stream 20 enters the primary mixture tube 4. This occurs in particular on the side of the primary mixture tube 4 that is directly opposite the primary mixture tube inlet 6. It is effective to place the smoothing element 31 or elements on this side on the inside surface of the primary mixture tube 4 and in fact downstream of the primary mixture tube inlet 6. The smoothing element 31 can be a sheet metal element, for example.

Figure 6 also contains an annular guide 32 that can be placed on the inner circumference or inner surface of the primary mixture tube 4 in the area of the secondary air tube 3, and preferably in the area of the secondary air tube outlet 7, that assumes a radial portion of the annular cross-section 9 between the primary mixture tube 4 and the secondary air tube 3. This produces a local accumulation of the primary mixture 20 at the interior periphery of the annular cross-section 9.

In feeding the primary mixture stream 20 into the burner 1 according to the invention, the pressure loss in this system is reduced in an advantageous manner. Furthermore, a more even distribution of the particulate fuel is achieved over the cross-section.

If the firing conditions require it, a vortex device can also be provided for the dust stream 20 inside the primary mixture tube 4 or immediately ahead of it in the direction of flow. This can be achieved in the form of a spiral shaped primary mixture inlet housing 29, which is not shown, that is placed on the outer circumference of the primary mixture tube 4 and that is connected to the feed line 17. By imparting a vortex to the dust stream the ignition stability is increased even more.

Instead of the spiral shaped primary mixture inlet housing 29, a vortex device 14 can be provided inside the primary mixture tube 4 or its annular cross-section 9 to impart a vortex to the dust stream 20 (Figure 8).

Furthermore, to increase the ignition stability, instead of a baffle ring 15 according to Figure 10, the outlet end 7 of the secondary air tube 3 can be alternatively designed with a conical widening To prevent the primary mixture stream 20, which is fed through the primary mixture tube 4 and distributed at the secondary air tube 3 to the annular cross-section 9, from impacting against the end wall 38 of the secondary air tube 3 and against the end wall 39 of the penetration channels 35, and in the process to prevent strong turbulence from forming for one thing and heavy erosion from occurring at the end walls for another, the end wall 38 and/or the end walls 39 are designed alike upstream with wear-resistant and flow deviating means 36 and 37 in an advantageous embodiment of the invention. These means 36, 37 can be solid or hollow element, can be made of known wear protection materials and can be designed in a known shape for deviation elements, for example flat, semicircular, streamlined, triangular, etc. (Figures 6 and 7).

After the primary mixture stream 20 has passed the passages 44 between the penetration channels turbulence and solids accumulation in the primary mixture stream 20 can occur downstream of the end wall 45 of each penetration channel 35 and thus to pressure losses and to an uneven feed of the fuel dust to the burner 1. In order to prevent this, the end wall 45 is preferably designed according to Figure 7 with a downstream deviation element or spoiler 41. This can also be designed like means 36 and 37.

In order to maintain an even velocity of the primary mixture stream 20 inside the cross-section 9, the outlet of the primary mixture tube 4 can also be provided with a conical widening 48 when the secondary air tube 3 is provided with conical widening 30 (Figure 8).

According to Figure 9, four baffle segments 33 can be arranged am burner outlet 2, with each baffle segments 33 extending radially between secondary air tube 3 and primary mixture tube 4 and covering an angular section of the annular outlet between the two tubes 3, 4 with the baffle segments 33 being evenly separated from one another. This further increases the contact surface between the exiting primary mixture stream 20 and the drawn hot flue gases and achieves an improved mixing of primary mixture 20, secondary air 19 and flue gases 21.

An increase in ignition stability is the result. The baffle segments 33 can be made of an appropriately prepared sheet metal segment, for example.

The feature wherein the primary mixture or dust stream 22 is not jacketed by an air jacket (secondary, tertiary air) at the outlet to the furnace 10, hot flue gases can be drawn directly from the outlet along the entire circumference of the dust stream outlet stream so that they act directly on the fuel particles and can heat them up. This heats the dust stream ahead of time to its ignition temperature, the particulate fuel pyrolizes much better, that is, it releases its gaseous components, and as a result the ignition stability is improved.

By introducing a central secondary air stream 19 with an imparted vortex into the furnace 10, a low pressure zone 23 arises at the burner outlet 2 in the direct vicinity of the longitudinal axis 27 that transports additional hot flue gases 22 from the flame back toward the root of the flame and thus increases the ignition stability and the reaction density in the flame. This results in a zone near the ignition zone 18 in the vicinity of the burner outlet in which, as a result of the mixing of dust stream and secondary air 19, an ignitable dust/air concentration is attained and the ignition temperature is reached due to the mixing of hot flue gases 21 from the furnace 10 ,and of hot flue gases 22 from the flame.

It is advantageous to combine two or more burners 1 according to Figure 11. Here, it is common for each of the secondary air and primary mixture tubes 3, 4 to be separated from one another vertically. This increases the reaction density in the ignition zone 18, and thus the ignition stability. The combination of a number of burners 1 can, however, also have physical design reasons, for example to size the furnace 10 no larger than necessary.

The longitudinal axis of the burner 1 can be designed to be horizontal or as in Figure 11, at an angle, which is preferably tilted by 0 to 200 from horizontal in the discharge direction, that is, in the direction toward the burner outlet 2. By slightly tilting the secondary air and primary mixture tubes 3, 4 in the downstream direction, the residence time of the fuel in the furnace can be increased and thus the combustion can be improved.

The burner 1 according to the invention can for example be implemented in direct-fired powdered lignite furnaces (that is, the fuel comes directly from the mill) with upstream coal mills, in particular hammer mills or bowl mills (not shown), and in indirect dry powdered lignite furnaces (not shown) (that is, the fuel is already ground and is fed from a fuel silo, for example, using pneumatic conveying equipment). The only differences are in the amount and in the composition of the gas mixture accompanying the fuel dust in the dust stream 26 The preferred mode of operation of the burner 1 according to the invention is sub-stoichiometric, that is, under oxygen deprivation, so as to attain an as low-NOx a combustion of the incoming fuel as possible and thus to create an as environmentally safe furnace as possible.

The air necessary to further combust the fuel is fed to the furnace, for example in the form of upper air as the combustion continues inside the furnace Reference List 1. Burner 2. Burner opening or outlet 3. Secondary air tube 4. Primary mixture tube Secondary air tube inlet 6. Primary mixture tube inlet 7. Secondary air tube outlet 8. Primary mixture tube outlet 9. Annular cross-section between secondary air tube and primary mixture tube Furnace 11. Furnace wall 12. Vortex device 13. Outlet section of the secondary air tube 14. Vortex device Baffle ring 16. Feed line for secondary air 17. Feed line for primary air or gas and fuel (primary mixture) 18. Ignition zone 19. Secondary air stream 20. Primary mixture or dust stream 21. Re-circulated hot flue gas stream 22. Re-circulated hot flue gas stream 23. Low pressure zone 24. Dust nozzle, or primary mixture nozzle 25. Lower air nozzle 26. Upper air nozzle 27. Longitudinal axis 28. Secondary air inlet housing 29. Spiral primary mixture inlet housing Conical widening of the secondary air tube 31. Smoothing element 32. Guide 33. Baffle segments 34. Vortex control vane Penetration channel 36. Flow deviating means or guide 37. Flow deviating means or guide 38. Secondary air tube end wall 39. Penetration channel end wall Channel 41. Flow deviation element or spoiler 42. Opening 43. Opening 44. Passage Penetration channel end wall 46. Penetration channel side wall 47. Penetration channel side wall 48. Conical widening of the primary mixture tube 49. Flow stabilization zone

Claims (19)

1. A burner to combust particulate fuel, in particular 0 Z inert-rich coal dust, involving a secondary air tube, located about a burner longitudinal axis and closed off at the end facing away from Sthe burner opening with an end wall, to introduce the OO M entirety of the secondary air, OO a primary mixture tube that surrounds the secondary air tube, forming an annular cross-section, to introduce primary air or primary gas and fuel, wherein the primary mixture tube has a flow stabilization zone placed upstream of the secondary air tube as seen in the flow direction of the primary mixture, an inlet housing that surrounds at least a portion of the primary mixture tube as seen along the perimeter and that forms a radial channel to feed the secondary air, and at least two penetration channels that connect the channel to the inner cross-section of the secondary air tube and that pass across the annular cross- section to introduce the secondary air stream from the channel into the secondary air tube.

2. A burner according to claim 1, wherein the penetration channel is designed such that the secondary air stream can be introduced to the secondary air tube tangentially, radially and at an angle in between.

3. A burner according to claim 1 or 2, wherein the penetration channel is designed with a vortex control device to introduce the secondary air stream into the secondary air tube in a tangential or radial direction, or in a direction eccentric to the longitudinal axis of the secondary air tube. S 4. A burner according to one of claims 1 through 3, CI wherein the channel of the inlet housing has a depth that o essentially decreases along the perimeter with increased Z angle.

5. A burner according to claim 4, wherein the inlet Vhousing is spiral in design. OO 00 OO M 6. A burner according to one of claims 1 through (N (Ni wherein the secondary air tube or at least an outlet section Sof the secondary air tube can shift inside the primary mixture tube.

7. A burner according to one of claims 1 through 6, wherein the plane of the secondary air tube outlet lies upstream or downstream or in the same plane as the primary mixture tube outlet in the direction of flow and with respect to the longitudinal axis.

8. A burner according to one of claims 1 through 7, wherein the end wall of the secondary air tube upstream of the primary mixture and facing away from the burner opening is designed with a wear-resistant and flow deviating means.

9. A burner according to one of claims 1 through 8, wherein the end wall of the penetration channel upstream of the primary mixture facing away from the burner opening is designed with a wear-resistant and flow deviating means. A burner according to one of claims 1 through 9, wherein the end wall of the penetration channel on the downstream side of the primary mixture facing toward the burner opening is designed with a deviating element. I V)

11. A burner according to one of claims 1 through C wherein the secondary air tube is designed with a baffle O ring on the outer perimeter of the outlet end. z

12. A burner according to one of claims 1 through 11, wherein the secondary air tube is designed with a conical Swidening at its outlet end. 00 00 M13. A burner according to one of claims 1 through 12, (N wherein the burner outlet is designed with multiple baffle segments, wherein each baffle segment extends radially between the secondary air tube and the primary mixture tube and angularly across a portion of the annular outlet between the secondary air tube and the primary mixture tube and wherein the baffle segments are at an even angular distance from one another.

14. A burner according to one of claims 1 through 13, wherein there is a vortex device located inside the primary mixture tube or is attached directly upstream to it. A burner according to one of claims 1 through 14, wherein the distance L between the burner opening and the end wall of the inlet housing facing toward the burner opening is 0.5 to 10 times the diameter dsL of the secondary air tube.

16. A burner according to one of claims 1 through wherein the primary mixture tube is designed at its outlet end with a conical widening. C 17. A burner according to one of claims 1 through 16, Cl wherein at least one smoothing element is placed downstream o of the primary mixture tube inlet at the section of the Z inner surface of the primary mixture tube that sits opposite 5 the primary mixture tube inlet, said smoothing means intended to smooth out the primary mixture stream. VO 00

18. A burner according to one of claims 1 through 17, 00 Mwherein the longitudinal axis of the secondary air and primary mixture tubes is tilted by 0 to 200 to horizontal in c- 10 the discharge direction.

19. A burner according to one of claims 1 through 18, wherein an annular guide is placed at the inner circumference or the inner surface of the primary mixture tube in the area of the secondary air tube or in the area of the secondary air tube outlet that takes up a radial section of the annular cross-section. A burner according to one of claims 1 through 19, wherein the primary mixture feed line is designed as a spiral primary mixture housing directly upstream of the primary mixture tube inlet to produce a vortexed dust stream or primary mixture stream.

21. A burner according to one of claims 1 through wherein the penetration channels are placed at the same angular separation from one another.

22. A burner according to one of claims 1 through 21, wherein the penetration channels each take up the same size section of the annular cross-section. C 23. A process to combust particulate fuel, in particular CI inert-rich coal dust, by means of a burner that involves a o central secondary air tube and a primary mixture tube that Z surrounds the secondary air tube concentrically and that c- 5 forms an annular cross-section, wherein all secondary air fed to the burner, or air not included in the primary air, is fed to the burner via the secondary air tube, and wherein 00 M a primary mixture consisting of primary air or gas and fuel 0O Mis fed through the primary mixture tube, and wherein the secondary air is fed to the secondary air tube through at least two penetration channels that penetrate the annular cross-section between the secondary air tube and the primary mixture tube.

24. A process according to claim 23, wherein the secondary air stream is introduced into the secondary air tube by means of a vortex device placed in the penetration channel. A process according to claim 23, wherein the secondary air stream is introduced into the secondary air tube by means of a vortex device placed in the penetration channel, forming a rotating vortex flow tangentially or eccentric to the centre axis of the secondary air tube.

26. A process according to one of claims 23 through wherein a vortex is imparted to the primary mixture stream by a vortex device.

27. A process according to one of claims 23 through 26, wherein the ignition zone can be shifted within the burner opening by axially shifting the secondary air tube or an outlet section of the secondary air tube.

28. A process according to one of claims 23 through 27, O Z wherein the burner is operated sub-stoichiometrically. (N DATED this 28 th day of November 2005 in ALSTOM POWER BOILER GMBH 00 00 c WATERMARK PATENT TRADE MARK ATTORNEYS C 290 Burwood Road O Hawthorn Victoria 3122 SAustralia (Ni P23028AU00