COMBUSTION DEVICE AND METHOD FOR OPERATING A COMBUSTION DEVICE FOR LOW-NOX AND LOW-CO COMBUSTION

Abstract

There exists a tendency in the construction of combustion devices to employ a multi-level, spatially distributed feed of the combustion air in order to be able to better influence the stoichiometric ratios during the combustion. These solutions are little suited for the compact construction and, in addition, the flame temperature is too high in the region of the air feed relative to a low NOx combustion if one does not employ expensive constructions with additional cooling bodies.

Description

[0001] The invention relates to a combustion device as well as a corresponding method for a low NOx and low CO combustion with largely separate feeds of fuel and combustion air to the combustion chamber, wherein the entire or the major part of the combustion air is fed to the combustion chamber in continuous gradation over several points in the chamber.

[0002] The term fuel includes substances which react exothermally with oxygen and which are present in a gaseous or vapor state at ambient temperature and/or upon feeding into the combustion chamber. The term fuel further includes also liquid or dustlike substances with air, vapor and/or waste gas as carrier gas. In this case, the term combustion air also includes gases and/or vapors having an oxygen content which assures a stable combustion in regard to the selected fuel. It is permissible in this connection that the combustion air also contains waste gases. The term combustion zone includes in this case also the spatial area in which the combustion takes place.

[0003] The feed-in of the combustion air occurs normally coaxially relative to the feed-in of the fuel in case of the combustion devices known from the German printed patent documents DE OS 4,419,345 and DE OS 4,231,788 with largely separate feeds of fuel and combustion air to the combustion chamber. For this purpose, a fuel jet flow is generated in the region of the entrance of the combustion device. The combustion air is fed on the outer side of the fuel jet flow and outside of the flame region through a substantially annular distributor, wherein the distributor is placed in the proximity of the fuel nozzle and mostly coaxially to the fuel nozzle. Because of the substantial spatial distance of the combustion air distributor from the flame region, in particular from the flame core, a uniform mixture of the fuel with the combustion air or, respectively, a defined or certain level mixture resulting from predetermined parts, is not achieved during practical operation in case of this type of combustion devices. In order to diminish this disadvantage, the combustion air is subdivided into primary air and secondary air, whereby locally limited peak values of the oxygen concentration are decreased and the stoichiometrical ratios during the combustion are somewhat better automatically controllable. The principle disadvantage of this type of combustion device, namely the unsatisfactory automatic control of the stoichiometric ratios of fuel and combustion air, which are decisive for the formation of harmful and noxious substances of contaminants and pollution, such as nitrogen oxide and carbon monoxide, can however only be reduced at a relatively high expense. As cause for this disadvantage can be cited that the feed of the combustion air extends only over a relatively small spatial area of the combustion zone such that the stoichiometric ratios during the combustion are essentially determined only by the relatively difficultly controllable convection behavior in the combustion zone. It is attempted to reduce this disadvantage by means of special installations which provide for a more intensive turbulence of fuel and combustion air, which is however connected with a larger energy expenditure based on the increased pressure losses.

[0004] Another method to lower the NOx formation in the combustion space of combustion devices without a partial premixture comprises to inject the combustion air and the fuel at a high speed into the combustion zone preheated to about 950° C. This is however an energetically and constructively very expensive solution and pyrotechnically of little interest since it leads to long flames and does not result in an optimum mixture.

[0005] Frequently, also a multi-stage feed of the combustion air is realized for the improvement of the combustion and for the lowering of the emission of harmful substance, such as pollutants and contaminants, in combustion devices without premixing. Such a solutions is for example employed in the combustion devices according to the German printed patent document DE OS 4,041,360. This combustion device has a horizontal burner pipe, which exhibits a plurality of gas exit openings at its upper side, comprises additional openings above the primary-air feed for the feed of secondary air within the so-called jet-flow rods or radiation rods, which serve for the cooling of the flames. The thermal load and stress of such jet-flow rods is however very high such that only high-temperature-resistant material can be employed for these jet-flow rods. Moreover, an optimum automatic control of the combustion device, relative to the harmful substances is rendered substantially more difficult in case of differing thermal load levels because the ratio of primary air amounts and secondary air amounts can be changed only within narrow limits. In particular, the feed of secondary air into the upper frame zone is insufficient in the region of the full thermal load.

[0006] It is attempted to diminish these advantages by means of separately automatically controllable secondary air feed or, respectively, by means of a partial premixing, wherein the two-step air feed is possible increased to a three-step or four-step air feed. A combustion device, operated according to such a method, is for example described in the German printed patent document DE OS 4,142,401. The combustion device, operating in this case with premixing, is operated substantially below stoichiometric levels of oxygen. The oxygen, missing for the combustion, is fed only at a marked distance from the combustion mouth at one or several places, wherein the injection direction of the oxygen cannot be in the same direction parallel to the main flow direction of the combustion gases. This method undoubtedly provides an improvement for the operation of large-size industrial furnaces, such as cylindrical rotary kilns, drum-type furnaces and the like, even though this method is relatively complicated to control based on the complicated flow control and flow guiding of the combustion air, which flow guiding is to be coordinated and adapted to the geometry of the furnace walls. This method is however too expensive for the operation of compact combustion devices with lower heating output powers. Moreover, this method has the general disadvantage that the combustion air is fed essentially from point sources into the region of the combustion zone with a relatively high flame temperature.

[0007] The advantages of a multi-step air feed are employed without premixing also in a special variant of the combustion devices or burners, wherein the burners exhibit a combustion chamber which expands conically in the direction of the flame, and wherein the combustion chamber forms a diffuser and provides for a more intensive mixing of the fuel and the combustion air. Fuel and primary combustion air are fed into the combustion devices or burners of this type (compare German printed patent document DE OS 3 600 784) by means of the diffuser and are burned in said combustion devices. Secondary combustion air is fed in addition through wall openings in the diffuser in radial direction into the flame. However, the length of the diffuser cannot be enlarged as desired because otherwise the diffuser shields the flame too strongly, which impairs the transmission of heat to the kiln wall or, respectively, the heating furnace wall. Since the length of the flames can substantially surpass the length of the diffuser in case of higher heating output powers, this means that insufficient secondary combustion air is fed to the region of the tip of the flames particularly in case of higher heating output powers. This has an unfavorable effect on the emission of pollutants of the combustion device or burner.

[0008] The hottest flame zones are always in the interior of the diffuser in combustion processes according to this method and lead to the annealing of the walls of the diffuser. This is disadvantageous for two reasons, first, the annealing leads to an increased formation of environmentally hazardous nitrogen oxide due to the increased temperature and, second, special temperature-resistant materials are required for the walls of the diffuser. Overall, the feed of combustion air is limited to relatively small spatial areas of the combustion zone also in these types of combustion devices, wherein the relatively small spatial areas exhibit in addition a very high flame temperature.

[0009] Another kind of air distribution according to the U.S. Pat. No. 1,247,740 is employed in order to improve the mixing of combustion air and fuel. The combustion air is led through a plurality of openings at an elongated rounded wall, positioned within the furnace chamber, into the mixing chamber. This mixing chamber is limited by a second elongated rounded wall, surrounding the first wall, and is closed by a sealed connection of the two walls at the top part. The thereby resulting hollow, double-walled, cylindrical chamber remains open in the bottom portion region and is connected in this region to an annular opening for the feed of fuel. The second (outer) wall of this double-walled cylinder ring also exhibits openings, where the air-gas mixture is ignited. The combustion occurs directly at these openings as well as at the surface of the outer wall, and there are formed a plurality of individual flames. A substantial disadvantage of such combustion processes is the therefore especially required expensive materials, which have to withstand the high temperatures and thermal stresses and are nevertheless limited in their service life.

[0010] Even though the multi-level spatial air leveling delivers a below stoichiometric mixing zone in the bottom region, which mixing zone gradually passes into an above stoichiometric level with an increasing air ratio, a control of the mixing ratios cannot be guaranteed in case of the double-walled structure of the burner of this state of the art, since a complete mixing of fuel and combustion air is induced quickly in the double-walled enclosed, limited space of the cylinder ring before the ignition occurs at the openings of the outer wall. The combustion also exhibits the disadvantages of premixing flames. The important reduction effect is therefore not given for the lowering of the nitrogen oxide emission.

[0011] In addition, the method and manner of the exhaust gas discharge from the furnace space does not allow an application of such combustion technologies in heating furnaces and industrial furnaces since an effective transmission of heat to the material to be heated is not assured.

[0012] Further disadvantages of this double-walled burner structure brings also its positioning within the furnace space in addition to its complicated construction.

[0013] Another way for improving the mixture state comprises a series-connection of an additional mixing chamber in front of the combustion chamber, whereby there results a combustion device or burner with enlarged dimensions, which now as a combustion device or burner also exhibits the disadvantages of this type of combustion device or burner. Such a combustion device with a very intensive premixing is described for example in the German printed patent document DE OS 3,915,704, which combustion device however is of an extremely expensive construction. The multimember mixing channels cause a high energy demand in order to compensate for the pressure loss caused by them. Furthermore, the mixing channels are difficult to access and are therefore difficult to clean.

[0014] In summary, the following is to be noted in regard to the state of the art:

[0015] There exists a tendency in the combustion device construction to employ a multi-stage feed of the combustion air into the combustion chamber in order to be able to better influence the stoichiometric ratios during the combustion and to meet thereby the presently high requirements by the lawmakers for an economical and ecological combustion. The consistent continuation of such solution arrangements would however lead to relatively complicated burner constructions with a plurality of combustion air distribution lines, penetrating the furnace walls or, respectively, the boiler shell disposed in the combustion zone, as well as additional jet-flow rods for the cooling of the flames. Such solutions are neither safe for operation nor suited for a compact construction.

[0016] Another development tendency uses the principle of the surface combustion in order to achieve a good mixture, a full combustion, and a low emission of harmful or noxious substances. In this principle, the air-gas mixture is distributed over the entire surface of the burner body, protruding into the furnace chamber, by means of a plurality of openings and is ignited there. The combustion occurs directly at the surface and leads to the glowing and annealing of the surface. The combustion air is either completely mixed with the fuel before entering the burner body, or the combustion air is lead by means of a plurality of openings at the inner wall of a double-wall cylindrical combustion device structure into the cylindrical annular space, enclosed between the inner wall and the outer wall, and the combustion air is mixed there with the fuel. Subsequently, the mixture is ignited at the surface of the outer burner wall. All surface burner, operating according to this principle, require the use of expensive materials and have particular difficulties during the set-up of the burner in the furnace chamber. In addition, their service life and their area of application are limited to small power capacity ranges and to gaseous fuels.

[0017] A further development line in the construction of combustion devices or burners uses the underpressure, generated by the flow speed of the flame gas, in order to suction secondary, tertiary etc. combustion air. This principle requires however that the flame gases flow at a predetermined speed past a diffuser wall, provided with suction openings for the combustion air. Therefore, the combustion air volume, suctioned per time unit, cannot be changed independent of the flame parameters. Even though it is in the interest of a compact construction to limit the space available for the formation of flames, as this occurs through the diffuser wall, this construction is associated with the following substantial disadvantage:

[0018] The suction openings for the combustion air are disposed in a zone with a very high flame temperature, which leads to an increased formation of environmentally hazardous nitrogen oxides.

[0019] The purpose of the invention is therefore to provide for a constructively simple combustion device, suitable for a compact construction, with a substantially separate feed of fuel and combustion air to the combustion chamber having the result of a low NOx and low CO combustion as well as an intensification of the heat transfer between flame/exhaust gas and wall of the heat sink, wherein the feeding of the combustion air is performed with as many stages as possible into larger flame regions. In particular, the following partial objects result from this purpose:

[0020] Metering the amount of combustion air, fed per time unit, in such a way that lambda-number regions of the fuel-combustion air mixture, preset in the combustion chamber, are substantially realized.

[0021] Decrease of thermal loads of the component groups to the combustion air feed and flame cooling as well as assuring the use of economic materials for these component groups.

[0022] Elimination of impairments of the heat transfer between flame and wall of the heat sink due to diffusers and other means for mixing the fuel-combustion air streams.

[0023] Forming the combustion zone and the exhaust gas zone with a geometry, adapted to the walls of the heat sink.

[0024] According to the present invention, this object is solved with a combustion device according to the features of claims 1 and 13 as well as with a coordinated method to operate this combustion device according to the independent method claim 11.

[0025] The basic conception of the invention, which also concerns the claimed method for operating the combustion device, comprises the following: About 70 to 100 vol-% of the total of the supplied combustion air amount is fed by means of one or a plurality of combustion air distributor bodies or diffusers in a substantially radial direction into the chamber, filled by the flame and disposed between the outer wall of the fire box and the contour of the combustion-air distributor bodies along the entire or a large part of the flame length. Thereby a large-surface distribution of the combustion air occurs over the entire region of the flames or over a large part of the region of the flames. For this purpose, a plurality of openings for the combustion-air discharge are distributed over the contour of the combustion-air distributor bodies. The number per surface unit and the cross-section of the openings, distributed over the contour of the combustion-air distributor bodies, are selected such that a preset volume stream of combustion air enters into the combustion zone. In this way, the stoichiometric ratios in the fuel-combustion air mixture are easier to control. Furthermore, a predetermined course of the lambda-number region between the flame base and the flame tip can in this way be realized at the metering site.

[0026] In contrast to the feed of combustion air, the feed of fuel into the combustion zone occurs exclusively in the region of the flame base, disposed at the bottom part of the combustion-air distributor bodies, by means of one or a plurality of rows of nozzles disposed around the combustion-air distributor bodies.

[0027] In this case, the residual part of the combustion air, necessary for the combustion, i.e. 0 to about 30 vol-%, is admixed to the fuel before entry into the combustion zone in case of an air flow rate of less than 100%. The admixture of this part of the combustion air increases the impulse of the fuel, improves the mixing of the fuel and the combustion air, and leads to a faster attainment of the ignition limit. The NOx values thereby decrease drastically.

[0028] The advantages of this concept comprise that the combustion proceeds at first below stoichiometric oxygen values and passes to stoichiometric or, respectively, above stoichiometric oxygen values with a gradually increasing air feed only shortly before the flame tip, where the complete combustion is achieved. Temperature peaks are thereby suppressed in the entire flame region and the formation of harmful substances (NOx and CO) is drastically reduced. This type of feeding the combustion air also includes the advantageous effect that the flame is blown away from the combustion-air distributor body such that no direct combustion occurs at the surface of this combustion-air distributor body. This lowers the thermal load of the combustion-air distributor bodies, wherein the combustion-air distributor bodies are cooled in addition by the combustion air flowing-through.

[0029] A further advantageous effect of the combustion-air feed according to the invention includes, in particular in case of large-surface combustion-air distributor bodies, that these bodies lead at the same time to the cooling of the flame, whereby the formation of NOx is reduced. In addition, it can be achieved upon employment of large-surface combustion-air distributor bodies having a suitable structural shape that the geometry of the combustion box is decisively determined by the geometry of these combustion-air distributor bodies. An essential function according to the present invention of the combustion-air distributor bodies is seen in that the size of the fire box is influenced decisively by the selection of the dimensions of the combustion-air distributor bodies. Overall, a slight thermal load of the combustion-air distributor bodies results also in case of varying powers of the combustion device or burner, since the cooling effect increases with increasing output of the combustion device based on the then increasing throughput of combustion air.

[0030] Several advantageous embodiments of the invention combustion device result from the coordinated sub-claims.

[0031] There is a large variety of embodiments for the structure of the contour of the combustion-air distributor bodies. An optimization in regard to NOx and CO emissions and in regard to the thermal transfer can result from the selection of a suitable form of the combustion-air distributor bodies, depending on the geometry of the furnace space or of the boiler space.

[0032] Additional advantageous embodiments of the invention relate to the structure of the nozzle rows for the fuel feed. For an optimum preservation of predetermined or preset value ranges of the air number lambda, it has been proven particularly effective when the jet flow direction of the fuel nozzles within the same nozzle row and/or the jet flow direction of the fuel nozzles of neighboring nozzle rows are directed to different longitudinal regions of the combustion-air distributor bodies. The recited jet flow directions are set at least in part at an angle relative to each other in order to impart the fuel flow with an additional rotary momentum or turbulence. Furthermore, the combustion-air distributor bodies and/or the fuel nozzles can be formed exchangeable in order to adapt their parameters optimally to the predetermined output powers of the combustion device.

[0033] The invention solution including its method of operation is described in the following in detail by way of exemplified embodiments. In the corresponding drawings there is shown in:

[0034] FIG. 1a a schematic representation of a first variant of a low CO and low NOx combustion device with conical combustion-air distributor bodies for heating purposes,

[0035] FIG. 1b a schematic representation of a second variant of a low CO and low NOx combustion device with conical combustion-air distributor bodies for industrial purposes,

[0036] FIG. 2a a schematic representation of a selection of various geometric variants of the combustion-air distributor bodies in a side view and a top view,

[0037] FIG. 2b a schematic representation of the exchangeability of the combustion-air distributor bodies,

[0038] FIG. 3a a schematic representation of variants of the jet flow direction of the fuel nozzles,

[0039] FIG. 3b a schematic representation of the exchangeability of the fuel nozzles,

[0040] FIG. 3c a schematic representation of the slanted fuel boreholes,

[0041] FIG. 3d a schematic representation of the fuel ring slot with an internal turbulence generator,

[0042] FIG. 4a a graphic representation of the dependency of the NOx emission values in the exhaust gas on the output power of the combustion device or burner for a selected variant of a combustion-air distributor body, wherein operation took place without premixing of the combustion air to the fuel,

[0043] FIG. 4b a graphic representation of the dependency of the NOx emission values in the exhaust gas on the output power of the combustion device or burner for a selected variant of a combustion-air distributor body, wherein operation took place with premixing of the combustion air to the fuel (increased fuel-nozzle impulse),

[0044] FIG. 5a a graphic representation of the dependency of the CO emission values in the exhaust gas on the output power of the combustion device or burner for a selected variant of a combustion-air distributor body, wherein operation took place without premixing of the combustion air to the fuel,

[0045] FIG. 5b a graphic representation of the dependency of the CO emission values in the exhaust gas on the output power of the combustion device or burner for a selected variant of a combustion-air distributor body, wherein operation took place with premixing of the combustion air to the fuel (increased fuel-nozzle impulse),

[0046] According to FIG. 1a, a cylindrical fire box or, respectively, burner chamber (2) with a longitudinal center axis (34) of a combustion device is limited by a conical combustion-air distributor body (7) and a surrounding outer wall (3) made of steel. The outer wall (3) includes a cylindrical jacket wall (3a), a cover wall (3b), and a floor wall (3c). Fire box details, such as view openings for the visual observation of the flame development in the fire box, openings for the ignition of the gas-air mixture and for the temperature measurement in the lower part of the fire box are not represented in the schematic drawing. A UV probe for the monitoring of the flame and a suction probe for the removal of exhaust gases for performing the concentration analysis of the exhaust gas, exiting at the exhaust gas exit (6), are also not illustrated. The exhaust gas exit (6) is disposed in the cover wall (3b) of the fire box. The fire box or burner chamber (2) can also be formed polygonally as a prism. The fire box or burner chamber (2) however always has a horizontally or vertically disposed longitudinal center axis (34).

[0047] An empty space (1) between the outer wall (3) and a combustion-air distributor body (7) are essentially available for the formation of flames. This empty space (1) is that part of the fire box (2) which is disposed below an imaginary level (10), wherein said level (10) sits on the end of the top part (9) of the truncated cone-shaped combustion-air distributor body (7), and wherein the base (15) of the combustion-air distributor body (7) is disposed at the lower floor wall (3c) of the fire box (2).

[0048] For heating purposes, the heat is led from the outer wall (3) over cooling water, which flows either in pipe coils (16) and/or in water chambers (17) around the outer wall (3).

[0049] The combustion-air distributor body (7) is made of simple steel sheet with a plurality of openings (11) for the exiting of the combustion air into the combustion zone. While the nearly horizontal top part (9) of the combustion-air distributor body is closed, the bottom part (8) of the combustion-air distributor body remains open and is screwed into the air-feed pipe (18). The entire combustion air or, respectively, the largest part of the combustion air (>70 vol-% of the combustion-air throughput of 100%, required in total for the combustion) is fed through the inner pipe (18) of a coaxial pipe into the interior of the combustion-air distributor body (7) by means of a blower (19), provided with a motor (20). The lower end of the inner pipe (18) of the coaxial pipe ends in the combustion-air feed (5).

[0050] The entire fuel is fed separately or, respectively, with the residual part of the combustion air (<30 vol-% of the entire combustion-air throughput of 100%) through a cylinder ring (21), disposed perpendicular to the longitudinal center axis (34), between the inner pipe (18) and the outer pipe (22) of the coaxial pipe to the combustion zone. The lower end of the outer pipe (22) of the coaxial pipe ends in the fuel feed (4).

[0051] The admixture of the combustion-air throughout to the fuel occurs in particular for the impulse increase of the fuel.

[0052] The cylinder ring (21) is provided directly at the bottom part of the combustion-air distributor body (7) with a nozzle row (12). This nozzle row (12) has a plurality of fuel nozzles (13), disposed around the combustion-air distributor body (7), in jet flow directions (14), which can be set as desired into two planes disposed perpendicular to each other and intersecting the longitudinal center axis (34) (see FIGS. 3a- 3d), wherein the fuel nozzles (13) serve for the distribution of the fuel into the combustion zone .

[0053] Tests have been performed with natural gas H as a fuel. In this case, all forms of the combustion-air distributor bodies, illustrated in FIG. 2a, in each case in a side view and in a top view, have been employed, wherein the number of openings (11) for the combustion-air exit into the combustion zone or, respectively, their diameter along the contour of the combustion-air distributor bodies, were varied such that the mixing ratios can be changed in order to control the combustion course.

[0054] The output power of the combustion device was set in case of relatively small combustion-air distributor bodies (length 25-30 cm, width at the bottom part 2-3 cm, and at the top part 0-10 cm, in case of a length of the fire box or burner chamber of 80 cm) to values between 10 and 22 kW and the air number was varied between 1.1 and 1.5. This does however not represent a principle limitation. The distributor body, shown in FIG. 1a, to which the measurement values of FIGS. 4 and 5 refer, had a width of about 2.5 cm at the bottom part in case of a total length of about 30 cm. In all series of tests, a thin, slightly luminous (depending on the operation variant, also nearly invisible or, respectively, not visible) stable, turbulent flame placed itself around the combustion-air distributor body (7) and a complete combustion was recorded shortly above the top-part plane (10) of the combustion-air distributor body (7). The flame did not touch the surface of the combustion-air distributor body, the flame filled large areas in the empty space (1). The result was an intensive heat transfer to the outer wall (3) of the fire box. This necessarily leads to an improved and more intense heat exchange with the heat-transfer medium in the pipe coils (16) or, respectively, in the water chambers (17), disposed in the fire box walls (3a, 3b, 3c) or, respectively, around the fire box walls (3a, 3b, 3c).

[0055] The contour of the combustion-air distributor body did not glow and anneal and remained relatively cold in all construction embodiments according to FIG. 2a (below 300° C.). The exhaust gas analysis resulted, as the measurement data show in FIGS. 4a, 4b, 5a, and 5b, in particular in case of increased fuel nozzle impulse, in extremely low NOx and CO emission values, which are far below the legal limit values for industrial combustion devices and which even remain under the limit values for furnace heating planned in the novelization of the law.

[0056] A substantial advance of the invention resides therefore in the possibility to construct an energy-saving and environment-friendly combustion plant with compact combustion form and combustion chamber form, which is suitable for the heat generation for smaller output powers up to 100 kW (such as for example in household appliances, wall heaters, and furnaces), for medium output powers above 100 kW and up to 1 MW (such as for example in heating centers, heating and power stations, and biomass combustion), and also for larger output powers above 1 MW (such as for example in power station combustion and rotary revolving tubular kilns). The burner chamber of such plants is substantially reduced in comparison to the hitherto conventional burner chambers based on the better heat transfer ratio to the material to generate heat and the short combustion path. In summary, the new combustion device is preferred to the conventional combustion technique based on ecological and economic aspects.

[0057] FIG. 1b shows a schematical disposition of a plurality of combustion devices for industrial purposes in the power station technique. The fire box (2) has a square cross-section; the illustrated combustion devices have the same characteristics as in FIG. 1a and are installed at the lower wall (3c), as detailed above. The heat discharge occurs through the water pipes (23), built into the outer wall, as well as through the evaporator and overheater heating surfaces (24) and (25). A further heat output is achieved through an air preheater, which preheats the combustion air of the burner, in the exhaust gas channel, which is not illustrated in the schematic drawing.

[0058] FIG. 2a shows a schematic illustration of various geometrical variants of the combustion-air distributor bodies. These can have a rectangular parallelepipedal, cylindrical, conical, polygon prismatic or pyramidal structure or their contours can have a ellipsoidal and hyperbolical shape. Additional geometric construction forms are possible. In principle, all combustion-air distributor bodies exhibit an inner hollow space for the feed of combustion air, a thin, perforated or, respectively, porous wall surrounding the hollow space, a closed top part, and an open part. The dimensions of the combustion-air distributor bodies and the number and geometry of the openings on the circumference of the combustion-air distributor bodies are to be selected such that they assure a controlled combustion course around the combustion-air distributor body. This means that with the selection of these parameters the air delivery to the combustion region in dependence of the combustion device or burner output power according to the specific requirements of a combustion process is to be controlled such that a combustion with below stoichiometric oxygen occurs over a larger combustion region, that the complete combustion is concluded only close to the top part of the combustion-air distributor body. Measurements show that different dimensions of the combustion-air distributor body are required for different output powers of the combustion device or burner. For this reason, the combustion-air distributor bodies are to be manufactured separately and to be constructed exchangeable for a specific load region. This can be performed in the following way, as schematically illustrated in FIG. 2b: The bottom part (8) of the combustion-air distributor body (7) is provided with an outer thread (26) and the air feed pipe (18) is provided with an inner thread at the pipe exit. The combustion-air distributor body (7) is screwed into the air feed pipe (18). In principle, the measurements have confirmed that, in order to achieve a stable, low pollution, and complete combustion, the following parameter data are to be set at the combustion-air distributor body (see FIG. 1a):

[0059] The length (A) of the combustion-air distributor body (7) amounts to more than or equal to 40-85 percent of the fire-chamber length (B), the diameter (C) of the combustion-air distributor body (7) at the bottom part (8) amounts to more than or equal to 10 percent of the burner-chamber diameter (D), and the porosity of the combustion-air distributor body amounts to less than 20 percent.

[0060] FIG. 3a shows a schematic illustration of variants of the jet flow direction of the fuel nozzles (13), which are positioned in a nozzle row (12) or several nozzle rows at the bottom part of the combustion-air distributor body (7) and are disposed around the combustion-air distributor body (7). A nozzle row (12) includes a plurality of nozzles, wherein the jet flow direction (14) is changeable along the longitudinal center axis as well as diagonally. This allows on the one hand the distribution of the fuel onto different contour regions of the combustion-air distributor body, which contributes to the concerted control of the mixing behavior and favors the ignition. On the other hand, a fuel rotational turbulence can be generated by means of a suitable inclination of the jet flow direction which leads to a more intensive mixing of the fuel and the combustion air and to a longer dwelling time of the fuel particles in the flame region. Both fuel nozzle settings (axial and tangential inclination) assure together and in connection with the continuously flowing air from the openings of the combustion-air distributor bodies a low NOx and low CO combustion. It has been found during the investigations performed that the optimum range of the axial and tangential sloping angles of the fuel nozzles amounts from about −45° to +45° as referred to the longitudinal direction of the combustion zone. The angle setting depends on the form of the combustion-air distributor body and has a marked influence on the quality of the combustion. The admixture of low amount of air (less than 30 percent of the combustion-air volume jet flow) with the fuel leads to an improved mixing of fuel and combustion air and to the faster reaching of the ignition limit based on the increased impulse. The NOx values decrease drastically in this case.

[0061] The nozzle rows are to be manufactured for different load regions and should be exchangeable. This can occur for example as follows, as is shown if FIG. 3b: The coaxial ring 21 is closed directly before the entry of the fuel into the fire box and is provided with connection channels (32) for the fuel feed into the fire box. The channels (32) include inner threads (33) and the fuel nozzles (13) include outer threads (28). The fuel nozzles (13) are screwed into the connection channels (32). Inclined boreholes (29) or, respectively, an annular slot (30) with an inner turbulence generator (31) can be employed instead of the fuel nozzles (13) within one nozzle row (12), as this is illustrated in FIGS. 3c and 3d.

[0062] The application of liquid, gaseous, or dustlike fuels is possible based on the variety of construction possibilities.

[0063] The graphic illustrations in FIGS. 4a and 5a show die NOx and CO emission values, measured in the exhaust gas, in reference to the combustion device or burner output power at different air numbers for the variant illustrated in FIG. 1a with the conical combustion-air distributor body. Natural gas H was fed as fuel by means of a single nozzle row, wherein the nozzles were set such that each second nozzle was provided with a weak rotational vorticity or turbulence. While the output power of the combustion device or burner for the relatively small test plant was varied between 10 and 22 kW, air numbers have been set for the usual and interesting range for combustion plants of between 1.2 and 1.5. The illustrated NOx and CO emission values have been converted to 3 vol-% O2 in the exhaust gas such that a comparison with the limit values of the technical exhaust gas TA air becomes possible.

[0064] It can be clearly recognized from FIG. 4a that the NOx emission values in this variant of the combustion-air distributor bodies increase slightly with the burner load based on increased combustion temperatures. Since the flame temperature remains however below 1200° C. in case of all tested load regions, the NOx emission values tend to a constant course in case of higher output powers. An increase of the air number leads to a drastic reduction of the NOx emission values, for example, the maximum of the NOx emission values falls in case of the initial air number of 1.2 and the output power of 22 kW from 31 ppm to 19.5 ppm for an increased air number of 1.5 at the same starting load.

[0065] The influence of the impulse increase through the fuel nozzle is decisive for the further reduction of the NOx emission values; thus, a negligible addition of air to the fuel leads to a strong vorticity or turbulence and a better mixing between fuel and combustion air. The ignition limit is reached sooner. Furthermore, the flame becomes thinner and expanded over a large area, and burns in the present example already upon an admixture of about 20% combustion air to the fuel, and is hardly visible or, respectively, not visible. FIG. 4b shows extremely low NOx emission values for all air numbers and in all tested load regions in case of an admixture of about 20% combustion air to the fuel and in case of otherwise identical settings as in FIG. 4a.

[0066] If one looks at the corresponding CO emission values in FIG. 5a, one realizes that the CO emission values are in general very low and tend to disappear completely (zero values) in case of increasing burner output power and air number. The impulse increase of the fuel nozzles through the admixture of about 20% combustion air to the fuel leads, as shown in FIG. 5b, to a complete combustion. The exhaust gases are free of CO in case of air numbers larger than 1.05 and in all tested output powers. This behavior in regard to CO emission is also typical for all other forms and shapes of combustion-air distributor bodies. The experimental investigations show that the zero values of the CO emission can occur very fast based on a suitable setting of the fuel nozzles.

[0067] The axial and tangential setting of the fuel nozzles has a particular influence on the formation of NOx and CO, wherein however different optimum angle positions result depending on the employed combustion-air distributor body.

[0068] It can be observed overall that the NOx and CO emission values of the novel combustion device are significantly below the limit values of the technical exhaust gas TA air (NO: 114 ppm, CO: 93 ppm) and of the new federal protective regulation BImSchV (NO: 45 ppm, CO: 55 ppm) and that even the generation of CO-free exhaust gas from combustion processes is possible.

[0069] The individual elements of the individual figures of the various embodiment variants can be combined with each other as desired without going beyond the character and the essence of the present invention and the scope of protection of the patent claims.

Claims

1. Combustion device for a low NOx and low CO combustion with largely separated feeds of fuel and combustion air to a combustion chamber, wherein the entire or the largest part of the combustion air is fed to the combustion chamber in continuous gradation over numerous points in the chamber, characterized in that

the combustion device comprises of a coaxial pipe, wherein the inner pipe (18) of the coaxial pipe joins in one or several feed lines (5) for the feed of combustion air in an area of an end of the coaxial pipe, and wherein the outer pipe (22) of the coaxial pipe joins at one or several feed lines (4) for the feed of fuel or, respectively, fuel-combustion air mixture in the area of said end of the coaxial pipe, and where a combustion-air distributor body (7) is sealingly connected with the inner pipe (18) of the coaxial pipe at the second end of the coaxial pipe, and wherein a nozzle row (12), including at least one or several fuel nozzles (13), sealingly closes the cylinder ring between the outer pipe and the inner pipe;

the combustion-air distributor body (7) is made of an elongated inner hollow space, wherein the hollow space is surrounded by a thin, perforated or, respectively, porous wall, and wherein the combustion-air distributor body (7) includes a closed top part (9), an open bottom part (8), and a plurality of distributedly disposed openings (11) for the exiting of combustion air into the combustion zone;

the combustion-air distributor body (7) is sealingly connected with its open bottom part (8) to the inner pipe (18) of the coaxial pipe;

the length ratio (A/B) of the longitudinal extension of the combustion-air distributor body (7) relative to the longitudinal extension of the fire box (2) and the diameter ratio (C/D) of the cross-section of the combustion-air distributor body (7) at the bottom part (8) to the equivalent cross-section of the fire box (2) are dimensioned such that there results an ignitable mixture and that there starts a stable combustion;

the fuel nozzles (13) are open on both sides and assure the feed of fuel or fuel-air mixture from the cylinder ring (21), enclosed between the inner pipe (18) and the outer pipe (22) of the coaxial pipe, into the combustion zone; the fuel nozzles (13) are disposed around the combustion-air distributor bodies in the region of the bottom parts (8) of the combustion-air distributor bodies (7);

the jet flow direction (14) of the fuel nozzles within one and the same nozzle row (12) and/or the jet flow direction (14) of the fuel nozzles of neighboring nozzle rows (12) are separately settable;

the combustion device is incorporated such into the fire box (2) that the end of the coaxial pipe with the feed lines for the combustion air and fuel feed (5) and (4) remains outside of the fire box (2), that the entire length of the combustion-air distributor body (7) is disposed in the fire box (2), and that the fuel nozzles (13) project into the fire box (2), however, do not surpass the distance of the bottom part (8) of the combustion-air distributor body (7) up to the start of the openings (11);

one or several combustion devices are incorporated such into the fire box (2) that the combustion devices penetrate the outer wall (3) surrounding the fire box (2), and that the combustion devices have a sealing connection to the outer wall (3);

the combustion zone in the fire box (2) is at the same time the zone for the complete mixing of the combustion air from the openings (11) with the fuel or, respectively, fuel-air mixture from the fuel nozzles (13);

the volume and the geometry of the combustion zone corresponds essentially to the volume and geometry of that empty space (1) which is delimited by an outer wall (3), surrounding a fire box (2), wherein the outer wall exhibits the openings, in particular the incorporation of the combustion device and the exhaust gas exit (6), and delimited by the outer contour of one or several combustion-air distributor bodies (7), of which each body is disposed completely within the fire box (2), and delimited by an imaginary plane (10), disposed within the fire box (2) and sitting on the end of the top part (9) of the combustion-air distributor body (7).

2. Combustion device according to

claim 1, characterized in that

exclusively the combustion air from the elongated combustion-air distributor body (7) is spatially distributed by means of the many openings (11) in the combustion zone (1) and mixes there with the fuel or, respectively, the fuel-air mixture from the fuel nozzles (13);

the mixture generated in the combustion zone (1) is ignited near the fuel nozzles (13) and burns in the same zone without a further subdivision;

the flame forms in the entire space of the combustion zone (1) and the combustion exhaust gases flow out through the imaginary plane (10) without hindrance and exit the fire box through the exhaust-gas opening (6);

the porosity of the combustion-air distributor body (7) is measured such that the predetermined value ranges of the air number lambda for the combustion zone occurs approximatingly for a below stoichiometric oxygen range in the neighborhood of the bottom part (8) up to an above stoichiometric oxygen range in the neighborhood of the top part (9);

the disposition and the number of openings (11) on the contour of the combustion-air distributor body (7) are selected such that the impulse of the combustion-air jet flows from the openings (11) blow the flame away from the combustion-air distributor body (7) such that no combustion occurs at the wall of the combustion-air distributor body (7) and that this wall exhibits no glowing or annealing.

3. Combustion device according to

claim 1 and

2, characterized in that the inner hollow space of the combustion-air distributor body (7) is enclosed by one single wall, wherein said wall has a rectangular parallelepipedal-shaped structure, a cylindrical structure, a conical structure, a polygon-prismatic-shaped structure or a pyramid-shaped structure or wherein said wall has an ellipsoidal or hyperbolic contour.

4. Combustion device according to at least one of the preceding claims, characterized in that the wall of the combustion-air distributor body (7) is made of porous, ceramic materials or of metallic materials which are formed as sieve, perforated plate, wire mesh, grid or metal mesh, or that the combustion-air distributor body (7) is formed as a pressed wire body or as a sintered body.

5. Combustion device according to at least one of the preceding claims, characterized in that the combustion-air distributor body (7) has a guide device for the generation of a rotary turbulent stream of the combustion air.

6. Combustion device according to at least one of the preceding claims, characterized in that the combustion-air distributor body (7) is formed exchangeable.

7. Combustion device according to at least one of the preceding claims, characterized in that the nozzles (13) or, respectively, nozzle rows (12) are formed exchangeable.

8. Combustion device according to at least one of the preceding claims, characterized in that the jet flow direction (14) of the fuel nozzles (13) within the same nozzle row (12) and/or the jet flow direction of the fuel nozzles of neighboring nozzle rows (12) is aimed at different longitudinal regions of the combustion-air distributor body (7).

9. Combustion device according to at least one of the preceding claims, characterized in that the fuel nozzles (13) within the same nozzle row (12) and/or the fuel nozzles (13) of neighboring nozzle rows (12) are disposed inclined such that the fuel jet flow is imparted with a rotary turbulence.

10. Combustion device according to at least one of the preceding claims, characterized in that the fuel nozzles (13) within one nozzle row (12) are constructible as inclined boreholes (29) or, respectively, as annular slot (30) with an inner generator for rotary turbulence (31).

11. Method for operating a combustion device for a low NOx and low CO combustion with largely separate feed of fuel and combustion air to a combustion chamber, wherein the entire or the largest part of the combustion air is fed to the combustion chamber in continuous levels over numerous points in the chamber, characterized in that

about 70 to 100 vol-% of the altogether fed-in combustion-air throughput is fed by means of one or several elongated combustion-air distributor bodies (7), mainly in radial direction, into the combustion chamber, filled with the flame, along the entire flame length or a large part of the flame length;

the fuel is fed to the combustion zone exclusively by means of the fuel nozzles (13) of one or several nozzle rows (12), of the inclined bores (29) or of the annular slot (30) in the region of the base of the flame at the bottom part of the combustion-air distributor body (7) and around the combustion-air distributor body (7);

the residual volume portion of the combustion air, required for the combustion, is admixed to the fuel before the entry into the combustion zone;

a specific angle adjustment of the setting of the fuel nozzles (13), of the boreholes (29) or of the rotary turbulence generator (31) in combination with a specific mixing ratio of the combustion air in the fuel jet flow leads to a visible flame or to an invisible flame depending on the operation parameter and the fuel kind;

a specific angle adjustment of the setting of the fuel nozzles (13), of the boreholes (29) or of the rotary turbulence generator (31) in combination with a specific mixing ratio of the combustion air in the fuel jet flow leads to a minimum of the NOx and CO emission values in the exhaust gas depending on the operational parameter and the fuel kind.

12. Method for operating a combustion device according to

claim 1, characterized in that

the fuel or, respectively, the fuel-air mixture is fed essentially in direction of an angle range of about −45° to +45°, relative to the longitudinal direction of the combustion zone;

the portion of the combustion air in the fuel jet flow, exiting from the fuel nozzles (13), is in the value range of 0 to about 30 vol-% of the altogether fed-in combustion-air throughput.

13. Burner with a feed of fluid fuel and of an oxygen carrier, wherein the burner is disposed at a burner chamber, wherein the burner chamber exhibits a wall for the discharge of heat, characterized in that the feeds of the fuel are disposed on a ring (35), which ring (35) exhibits the outlets into the burner chamber, wherein a distributor body (7) for the oxygen carrier is disposed within the ring (35), wherein the distributor body extends in its longitudinal directions essentially in the predominant blowing-out direction of the fuel and exhibits blowing-out openings (11) for the oxygen-carrier, wherein the blowing-out direction of the blowing-out openings (11) for the oxygen-carrier crosses the blowing-out direction of the fuel outlets.

14. Burner according to

claim 13, characterized in that the burner chamber is formed cylindrical and that the fuel outlets are disposed at a front side of the cylinder.

15. Burner according to

claim 13, characterized in that the length of the distributor body (7) amounts to between 30% and 85% of the length of the burner chamber.

16. Burner according to

claim 13, characterized in that the diameter of the distributor body (17) in the region of the fuel outlets amounts to between 10% and 60% of the inner diameter of the burner chamber wall.

17. Burner according to one of the

claims 1 to

10 and

13 to 16, characterized in that an additional heat exchanger (24) is provided following to the distributor body (7) in the burner chamber.

18. Burner according to

claim 1 or

13, characterized in that the fuel nozzles (13) are disposed parallel to each other and inclined relative to the cylinder ring (21) such that there results a ring rotary turbulence.

19. Burner according to

claim 1 or

13, characterized in that the fuel nozzles (13) are disposed inclined divergingly or covergingly relative to the nozzle circle (35) at the cylinder ring (21) such that there results an expanding or contracting flow.

20. Burner according to

claim 18 and

19, characterized in that the fuel nozzles (13) are disposed at the cylinder ring (21) inclined in both directions.