EP0741267B1 - Method and furnace for incinerating waste - Google Patents

Abstract

The method involves delivering waste onto a grid, moving it forward and burning it with the exhaust gas deflected through an opening into an exhaust channel. Near the opening, secondary air jets are blown into the two channel halves which are separated by the central plane of the exhaust channel. The jets have a torsion impulse relative to the centre axis of the channel cross-section. The sense of rotation of all the secondary air jets blown into one channel half is the same but the sense of rotation in one half is opposite that in the other half. The jets can be blown mirror-symmetrically relative to the central plane. For each channel half, one secondary air jet has a higher impulse and one jet a lower impulse.

Description

The invention relates to a method according to the preamble of claim 1 and a Furnace according to the preamble of claim 10.

In the DE-Z "Die Industriefeerung", Vulkan-Verlag Dr. W. Classen, Essen 1986, pages 23 to 32, are featured in an article by D. O. Reimann under the heading "Process engineering of waste incineration" shown different furnace designs and discussed: co-current, counter-current and medium-current firing. Two different DC furnaces are shown schematically by drawings. The firebox ceiling is roof-like in both cases. Over the burnout area of the grate and the subsequent chute connects the combustion chamber to the flue gas duct. The lower part, the afterburning zone, is used as a direct current firing Inclined pull, the failure-side roof surface of the firebox ceiling the lower Boundary wall forms. At the top of the diagonal pull is a vertical pull. The In this arrangement, the flue gas flow is particularly on the lower edge of the failure side Roof surface strongly deflected. The flue gas flue is in the second DC combustion continuously vertical. At the transition between the combustion chamber and the flue gas flue an equally pronounced, if somewhat less, redirection can be seen.

In the article, special attention is paid to the cold flue gas flow, that starts from the front grate area adjacent to the loading chute. Out Drawings in which the different firings are compared, it can be clearly seen that with the direct current firing the cold partial flow on one comparatively long way through the hottest combustion zone (see also document DE-A-3 125 429).

In the case of waste incineration in a grate furnace, this is done via a loading shaft supplied waste in the front area of the grate is first dried and preheated. In addition to the evaporation of the water, this also results in outgassing flammable Ingredients of the waste. Furthermore, they run from lower temperatures to about 500 ° C marked zone also pyrolytic processes. For a low overall The pollutant content of the exhaust gases from such grate combustion is therefore of decisive importance Meaning that the gaseous and particulate substances in the drying and Ignition area of the grate pass into the flue gas due to an energetic turbulent Mixing with the high temperature exhaust gas streams from the actual combustion area of the grate are brought into intimate contact. With sufficient oxygen content is the temperature and turbulence of the flow field Dwell time in areas of high temperature and high turbulence for the degree of destruction organic ingredients vital.

A rotary tube furnace is known from EP 0 579 987 A1, in which at least two primary air nozzles are so directed towards each other and towards the fuel bed that two opposing Vortexes are generated in the rotary tube whose axes of rotation are essentially parallel to the axis of the rotary tube and which rotate about these axes of rotation so that the thermally induced Support the movement of the fuel gases. There are additional burners in an afterburner or mixed air nozzles arranged and aligned so that the from the rotary tube outgoing two opposing vertebrae are strengthened.

The invention has for its object a method according to the preamble of the claim 1 and to improve a furnace according to the preamble of claim 10, that each sub-volume of the flue gas changes during a prescribed dwell time is at a sufficiently high temperature level.

This object is solved by the characterizing features of claims 1 and 10, respectively.

Further advantageous features of the invention are the subject of the dependent claims.

Figur 1 zeigt eine Gleichstromfeuerung im Längsschnitt

Figur 2 zeigt einen Querschnitt durch den Rauchgaskanal etwa in Höhe der Mündungsöffnung

Figur 3 verdeutlicht in perspektivischer Darstellung die Anordnung einer Düse

Figur 4 zeigt eine andere Gleichstromfeuerung im Längsschnitt

Figur 5 zeigt für die Feuerung gemäß Figur 4 einen Querschnitt durch den Rauchgaskanal etwa in Höhe der Mündungsöffnung.

The drawing serves to explain the invention using schematically illustrated exemplary embodiments.

Figure 1 shows a direct current firing in longitudinal section

Figure 2 shows a cross section through the flue gas duct approximately at the level of the mouth opening

Figure 3 illustrates the arrangement of a nozzle in a perspective view

Figure 4 shows another direct current firing in longitudinal section

FIG. 5 shows a cross section through the flue gas duct approximately at the level of the mouth opening for the furnace according to FIG. 4.

The direct current firing shown in FIG. 1 has a firebox 1, a loading shaft 2, a chute 3 and a grate 4, which extends from the loading shaft 2 extends to the chute 3. It is designed as a roller grate and comprises a total six rollers 5, the axes of which are inclined in a direction towards the chute 3 inclined plane are arranged parallel to each other. The combustion chamber 1 is through at the top a roof-shaped firebox ceiling 6 completed. The failure-side roof edge 7 is located itself over the end region of the grate 4. Under the grate 4 are devices 8 for Primary air supply provided. Secondary air nozzles 9 penetrate several Place the combustion chamber ceiling 6. They are directed towards the main combustion zone, which is in one wide area is located in the middle of the grate 4. Through an opening 10 over the chute 3 and the adjacent end area of the grate 4 is the firebox 1 with a flue gas duct 11 in connection. The lower section of the flue gas duct 11 is designed as an inclined pull 12. It is towards the loading chute 2 inclined backwards. Its lower boundary wall is the roof surface on the dropout side the combustion chamber ceiling 6. At the top of the inclined cable 12 there is a vertical cable 13 on. In this respect, the firing corresponds to the state of the art.

Approximately at the height of the mouth opening 10 are in a cross-sectional plane, which is shown in FIG is symbolized by a broken line, 14 additional nozzles on the rear wall 15.1 to 15.6 attached. They are illustrated in Figure 2 by pulse vectors. The The direction of the pulse vector coincides with the blowing direction, the length is a measure of the size of the pulse with which the secondary air flow is injected. The length should also be a measure of the size of the nozzle. In the illustrated in Figures 1 and 2 In the exemplary embodiment, the pulse vectors are of equal length. This is meant to be symbolic are shown that all nozzles 15.1 to 15.6 are the same size. The nozzle arrangement is mirror-symmetrical with respect to the vertical center plane 16, which the flue gas duct in divided two channel halves, which in Figure 2, the two cross-sectional halves 10a and 10b correspond. The middle level 16 is an imaginary level, not a material level Partition wall.

Figure 2 shows the horizontal components of the individual pulse vectors. In each of the two cross-sectional halves 10a, 10b, the horizontal pulse components are aligned tangentially to circles 17.1 to 17.6 inscribed in the center of the cross-sectional halves. They therefore define a direction of rotation with respect to their center points Ma, Mb, symbolized by arrows 18a, 18b. Because of the mirror-symmetrical nozzle arrangement, the direction of rotation in cross-section half 10a is opposite to the direction of rotation in cross-section half 10b. In the exemplary embodiment illustrated in FIG. 2, the circles 17.1 to 17.3 or 17.4 to 17.6, which are assigned to the individual nozzles, have different diameters. However, it is also possible to align several nozzles of a cross-sectional half tangentially to a single circle. The diameters of the circles 17.1 to 17.6 are between approximately 0.15b and 0.4b. Here, b is the width of the flue gas duct 11. In the case of the nozzles 15.2 to 15.5, the distance from the central plane 16 of which is smaller or not much larger than b / 4, the horizontal component points away from the central plane 16. In the case of the nozzle 15.1, which is located at a distance a ₁ = 0.4b from the central plane 16, the associated horizontal component is oriented at right angles to the rear wall 14, ie parallel to the side wall 19a. The same naturally applies to the nozzle 15.6. In the case of the nozzle 15.2, which is arranged at a distance a ₂ = 0.25 b from the center line, the horizontal component forms an angle α ₂ = 70 ° with the rear wall 14. For the nozzle 15.3, the corresponding data are a ₃ = 0.08b and α ₃ = 50 °. The distances can deviate up to approximately ± 30%, the angles up to approximately ± 20% from the specified data.

The nozzles 15.1 to 15.6 are inclined to the horizontal. According to FIG. 3, the angle of inclination β _{3 of} the nozzle 15.3 is the angle between the pulse vector and its projection into the horizontal cross-sectional plane of the orifice 10. The angle of inclination of the other nozzles, which are not shown in FIG. 3 for the sake of clarity, has to be imagined accordingly. In general, the angle of inclination β for all nozzles is between -20 ° and + 50 °. The negative sign indicates a downward slope. In the exemplary embodiment according to FIG. 2, the inclination angles for the individual nozzles are preferably selected as follows: β 1 = -10 ° ± 20 ° β 2 = + 10 ° ± 20 ° β 3rd = + 20 ° ± 30 °.

In operation, the waste is placed on the grate 4 in the usual way, by rotation the rollers 5 on the grate 4 moved forward and burned. At the end of the grate the combustion residues fail. Primary air is supplied to the grate from below. Secondary air is blown into combustion chamber 1 from above.

A flue gas flow occurs in the combustion chamber 1, which is shown in FIG. 1 by the streamlines 20, 21, 22 is illustrated. The partial stream symbolized by streamline 20 rises from the front area of the grate 4. It contains solid and gaseous flammable ones Components. This partial flow is the characteristic of direct current combustion Way through the main combustion zone. There are the flammable Components at high temperature already largely through targeted secondary air supply burned. The partial flow 21 escaping from the middle area has a very high high temperature, the partial flow 22 from the end region of the grate 4 still has a relative high oxygen content. The entire flue gas flow is reduced on the outlet side deflected at the top and passes through the opening 10 into the inclined pull 12 the flammable components that are still carried are completely burned out. This is in addition to an adequate supply of oxygen, intensive mixing of the strands required that form the flue gas flow.

According to the invention, in the region of the mouth opening 10, they are symmetrical to the central plane 16 secondary air jets blown in. The direction of the secondary air jets is like this chosen so that each beam has an angular momentum with respect to the central axis of the channel half. The direction of rotation is correct for all jets that are blown into one channel half. match. Because of the mirror symmetry, there is a sense of rotation in the cross-sectional half 10a, which is opposite to the direction of rotation in the cross-sectional half 10b. The secondary air is blown into the flue gas flow at a speed of 70 to 100 m / s. The Share of the secondary air blown in in the area of the mouth opening 10 of the total secondary air is around 25 to 35%.

The secondary air is blown into the flue gas duct 11 and in particular in the oblique draft 12 which forms the afterburning chamber, one to the central plane 16 symmetrical double vortex configuration created. That from the firebox 1 escaping flue gas is shaped by the arrangement and alignment of the nozzles two oppositely rotating vertebrae introduced obliquely upwards into the oblique pull 12. It has been shown that the separation vortex observed in the prior art is completely suppressed or at most on a harmless small detachment bubble directly on the Roof edge 7 is reduced. In the double vortex flow there is an extensive Homogenization in terms of temperature and material composition. Thereby the burnout of flammable components carried along is considerably improved and the Pollutant content in the exhaust gases significantly reduced.

Figure 4 shows a furnace, which is essentially compared to the furnace described so far has two differences: The one difference is that the flue gas duct 11 is designed as a continuous vertical train. The second difference is in the different configuration of the nozzles, which are at the level of the orifice 10 in the flue gas duct 11 are directed. This arrangement is shown symbolically in FIG.

According to Figure 5, the nozzles 24.1, 24.2 and 25.1 to 25.5 are not only attached to the rear wall 14, but also to the side walls 19a, 19b and the front wall 26 of the flue gas duct 11 over the edge 7. The nozzles 24.1, 24.2 are significantly larger than the nozzles 25.1 to 25.5. The nozzles 24.1, 24.2 are aligned tangentially to an inner circle 27, the smaller nozzles 25.1 to 25.5 tangentially to a larger circle 28. The angle of inclination β _24, which is not visible in FIG. 5, of the nozzles 24.1, 24.2 is different from the angle of inclination β _{25 of} the nozzles 25.1 to 25.5.

Secondary air with high momentum, i.e. great depth of penetration, blown in. The nozzles 25.1 to 25.5 generate secondary air with a significantly lower pulse blown in. The quantity of secondary air introduced through the nozzles 24.1, 24.2 is preferred greater than the amount of secondary air introduced through nozzles 25.1 to 25.5, at least the same size. The quantitative ratio is between 4: 1 and 1: 1. It is possible to replace all or part of the secondary air with recirculated flue gas.

In the nozzle arrangement according to FIG. 5, an inner vortex is formed in each channel half, which is fanned in particular by the nozzles 24.1, 24.2, and an outer vortex which is fanned by the nozzles 25.1 to 25.5. The vortices have different tangential speeds and, because of the different angles of inclination β ₂₄ , β _25, also different axial speeds. This creates a shear layer between the two vertebrae. This leads to the formation of medium and fine-scale turbulence, which contributes to homogenization and improves the reaction kinetics.

Claims (21)

1. Method of incineration of waste material in an combustion chamber (1), which is closed at the top by a roof-shaped combustion chamber ceiling, wherein a roof edge (7) at the outlet side is disposed above the end region of the grate, with the following features: the waste material is fed onto a grate (4), moved forwardly on the grate (4) and in that case combusted; combustion residues fall out at the end of the grate (4); primary air is fed from below through the grate (4); secondary air is blown into the combustion chamber (1); the flue gas is led to the end region of the combustion chamber (1) bounded by a rear wall (14), and is deflected and conducted through a communicating opening (10) from the combustion chamber (1) into a flue gas channel (11) which is vertical or inclined rearwardly and is bounded by the rear wall (14) and two side walls (19a, 19b); and solid and gaseous constituents are recombusted after the deflection; characterised in that in the vicinity of the communicating opening (10) at least one respective secondary air jet is injected through the rear wall (14) into the two channel halves (10a, 10b), which are separated by a centre plane (16) of the flue gas channel and are in mirror symmetry to the centre plane (16), the secondary air jet having a angular momentum which has a horizontal component oriented tangentially to a circle (17.1 to 17.6; 27, 28), which is inscribed centrally in the cross-section of the associated channel half (10a, 10b), and therefore defines a rotational sense with respect to the centre point (Ma, Mb) of that circle; that the secondary air jets are blown into the intermediate spaces between the centre points (Ma, Mb) and the associated side walls (19a, 19b) of the flue gas channel; that the rotational sense corresponds in the case of all secondary air jets blown into one channel half (10a, 10b); and that the rotational sense in one channel half (10a) is opposite to the rotational sense in the other channel half (10b), wherein separating eddies are suppressed at the roof edge (7).
2. Method according to claim 1, characterised in that a proportion of 25 to 35 % of the total secondary air is injected into the region of the communicating opening.
3. Method according to claim 1 or 2, characterised in that the secondary air jets are injected in a direction which includes an angle of inclination β between -20° and +50° with the horizontal.
4. Method according to one of claims 1 to 3, characterised in that several secondary air jets are injected in each channel half.
5. Method according to claim 4, characterised in that at least one secondary air jet with a higher momentum and one secondary air jet with a lower momentum are injected into each channel half.
6. Method according to claim 5, characterised in that at least one secondary air jet with a lower momentum is injected in between two secondary air jets which are injected in with higher momentum.
7. Method according to claim 5 or 6, characterised in that a secondary air jet injected in with a higher momentum is injected at a lower angle of inclination β than a secondary air jet injected in with a lower momentum.
8. Method according to one of claims 5 to 7, characterised in that the ratio between the secondary air quantity injected with higher momentum and the secondary air quantity injected with lower momentum lies between 4:1 and 1:1.
9. Method according to one of claims 1 to 8, characterised in that recirculated flue gas is admixed to secondary air or used as secondary air.
10. Furnace for incineration of waste materials in a combustion chamber in accordance with the method according to one of claims 1 to 9, with a feed shaft (2) for the waste material to be incinerated and an outlet shaft (3) for the combustion residues, with a grate (4) which extends from the feed shaft (2) to the outlet shaft (3) and is inclined in direction towards the outlet shaft (3), with a combustion chamber (1), which is disposed above the grate (4) and is bounded in the waste flow direction by a rear wall (14), and a roof-shaped combustion chamber ceiling (6), which extends into the vicinity of the outlet shaft (3), wherein a roof edge (7) at the outlet side is disposed above the end region of the grate (4), with devices for the feed of primary air through the grate (4), with nozzles (9) for the feed of secondary air through the combustion chamber ceiling (6) and with a flue gas channel (11), which is vertical or inclined rearwardly, is bounded by a rear wall (14) and two side walls (19a, 19b) and stands in communication with the combustion chamber (1) by way of a communicating opening (10) disposed above the outlet shaft (3) and the adjacent end region of the grate (4), characterised in that at least one respective nozzle (15.1 to 15.6) is arranged in the vicinity of the communicating opening (10) at the rear wall of the two channel halves separated by a centre plane (16) of the flue gas channel (11), that the nozzle arrangement of one channel half is in mirror symmetry to the nozzle arrangement of the other channel half with respect to the centre plane (16), that the vector momentum of each nozzle has a horizontal component which is oriented tangentially to a circle (17.1 to 17.6; 27, 28), which is inscribed centrally in the cross-section (10a, 10b) of the associated channel half and defines a rotational sense with respect to the centre point (Ma, Mb) of that circle, that the nozzles (15.1 to 15.6) are aimed into the intermediate spaces between the centre points (Ma, Mb) and the associated outer wall (19a, 19b), that the same rotational sense is associated with all nozzles of one channel half (arrow 18a, 18b), and that the rotational sense in one channel half is opposite to the rotational sense in the other channel half, wherein separating eddies are suppressed at the roof edge (7).
11. Furnace according to claim 10, characterised in that further nozzles (24.2, 25.3 to 25.5) are arranged at the side walls of the flue gas channel.
12. Furnace according to claim 10 or 11, characterised in that the nozzles (15.1 to 15.6; 24.1, 24.2, 25.1 to 25.5) include an angle of inclination β with the horizontal.
13. Furnace according to claim 12, characterised in that the angle of inclination β lies between -20° and +50°.
14. Furnace according to claim 12 or 13, characterised in that the angle of inclination β is of the same size for all nozzles (15.1 to 15.6).
15. Furnace according to claim 10 or 11, characterised in that the angle α for a nozzle arranged closer to the centre plane (16) is smaller than for a nozzle spaced further from the centre plane.
16. Furnace according to one of claims 16 to 18, characterised in that three nozzles (15.1 to 15.3; 15.4 to 15.6) are arranged in each of the two channel halves.
17. Furnace according to claim 16, characterised by the following specification of dimensions:

    a₁/b = 0.40 ± 30%

    a₂/b = 0.25 ± 30%

    a₃/b = 0.08 ± 30%

    α₁ = 90° ± 20°

    α₂ = 70° ± 15°

    α₃ = 50° ± 10°

    β₁ = -10° ± 20°

    β₂ = 10° ± 20°

    β₃ = 20° ± 30°

    wherein b is the width of the flue gas channel (11).
18. Furnace according to one of claims 10 to 17, characterised in that at least one larger nozzle (24.1, 24.2) and one smaller nozzle (25.1 to 25.5) is arranged in each channel half.
19. Furnace according to claim 18, characterised in that at least three nozzles are arranged in each channel half and that at least one smaller nozzle (25.1 to 25.4) is arranged between two larger nozzles (24.1, 24.2).
20. Furnace according to claim 18 or 19, characterised in that the larger nozzles (24.1, 24.2) are oriented tangentially to a smaller circle (27) and the smaller nozzles (25.1 to 25.5) are oriented tangentially to a larger circle (28).
21. Furnace according to claim 20, characterised in that the larger nozzles (24.1, 24.2) have a different angle of inclination β from the smaller nozzles (25.1 to 25.5).

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