Patent Application
20060011114
The invention pertains to a grate panel for an incineration grate, an incineration grate composed of such grate panels, as well as a waste (refuse) incineration plant with such an incineration grate.
The most important component of a waste incineration plant is the incineration grate that is arranged horizontally or in an inclined fashion and on which the material to be incinerated, for example, garbage, is conveyed from a first end to a second end that is usually referred to as the burnout grate. The required incineration air is forced through the incineration grate. Corresponding openings are provided in the incineration grate for this purpose. This means that the material being incinerated (waste material) is essentially processed in three steps, namely “dried,” then “incinerated” and ultimately converted into slag. These three steps may be individually controlled, if so required.
There exist various types of incineration grates including, among other things, the so-called reciprocating incineration grate. Such a grate comprises movable parts (grate panels) that are able to carry out stoking movements in order to convey the material being incinerated (the waste) along the incineration grate. The individual grate panels lie on top of one another such that they are offset in a stair-like fashion in the region of their long side that points to the incineration chamber. For example, if every second grate panel is realized in a movable fashion, the movement of such a grate panel causes the solid waste lying on the respectively ensuing grate panel referred to the transport direction to be additionally conveyed to the next grate panel.
Different types of waste can be incinerated in an incineration plant of the previously described type. Typical waste materials are household garbage, industrial garbage, wood sawdust, waste wood, used wood, processed fractions of various waste materials (RDF=refuse derived fuel), biomasses or the like, for example, sludge. The individual types of waste materials differ with respect to their calorific value. However, this also applies within the individual types of waste materials. For example, household garbage may have a calorific value between 5 and 20 MJ/kg. The thermal and mechanical stresses on the incineration grate or its grate panels, respectively, vary in dependence on this calorific value.
This wear phenomenon can be sufficiently counteracted by cooling the grate panels with air when incinerating waste with a calorific value up to approximately 10 MJ/kg. An air-cooled incineration grate is described in the EP 0 391 146 A1. If it is assumed that the temperature in the incineration chamber lies between 900° and 1250° C. and the temperature in the layer of material being incinerated that lies on the incineration grate is >800° C., the surface temperature of these air-cooled grate panels lies, for example, between 400° and 600° C.
When incinerating materials with a higher calorific value, it is frequently preferred to utilize incineration grates, the grate panels of which are cooled with a liquid, e.g., water (EP 954 722 B1). However, the expenditures for such a water-cooling system are significantly higher than those for an air-cooling system. The more effective water cooling also leads to a more intensive cooling of the grate panels that is undesirable in certain incineration processes, wherein the temperature on the surface of the grate panels may lie between 90° and 110° C. while the temperature in the layer of material being incinerated (on the incineration grate) lies, for example, between 700° and 800° C.
The described technologies and technical process parameters indicate that air-cooled and water-cooled grate panels/incineration grates represent two distinctly different systems. This also applies if both systems are connected in series in accordance with EP 954 722 B1.
The invention is based on the objective of disclosing an option for realizing known systems more variably with respect to their application.
This objective is attained based on the following notion: each grate panel is primarily subjected to particularly intense thermal stresses toward the incineration chamber, i.e., on its upper side and its front face. Primary air is conveyed against the lower side of the grate panels, i.e., it cools these grate panels from below, and forced into the layer of material being incinerated that lies on the grate panels through openings in the grate panels or between the grate panels. A certain cooling volume for carrying off the generated heat is available underneath the thermally stressed section of each grate panel. However, the cooling effect is insufficient, particularly in the edge region. This means that such regions, for example, the face (long side) of a grate panel that points to the incineration chamber, are at risk of corroding and eroding.
In this context, a first embodiment of the invention proposes to arrange at least one flow channel in the region underneath the upper side and adjacent to the front long side of the grate panel, wherein air is conveyed in a targeted fashion against the upper side and the adjacent front long side from below.
This design forms a structure similar to an air nozzle, wherein the air cools the critical front section of the respective grate panel (that points to the incineration chamber) “from the bottom” with a correspondingly high flow speed. This cooling effect is significantly higher than that of a conventional cooling system according to the state of the art, but lower than that of a water-cooling system.
This at least one flow channel is also realized with an air outlet opening in the section of the corresponding face (face area) that is situated adjacent to the lower side, namely such that the air flow is subsequently conveyed in a targeted fashion onto the surface of the ensuing grate panel--referred to the conveying direction of the material being incinerated--and also cools this surface. This directed air flow against the adjacent grate panel provides the additional advantage of largely preventing deposits observed in the state of the art at this location. Such deposits are also referred to as pick-ups and produced on incineration grates according to the state of the art, for example, by metals precipitating from the material being incinerated.
In the “rear” section of the grate panel, a channel extends in the first section of the upper side (i.e., between the first long side and the second section of the upper side). A cooling medium, for example, a liquid and/or a gas, can be conveyed through this channel.
The grate panel can be cooled by means of a liquid, particularly water, along this channel. In this embodiment, the “rear” section of the grate panel is intensively cooled by means of a liquid while the same panel (grate step) is cooled by means of air in the front section (adjacent to the material being incinerated and the incineration chamber), namely with a superior cooling effect than that of conventional air-cooling systems.
In certain applications, it may suffice to cool the “front” section of the grate panels conventionally by means of air. This can be realized, for example, by simply conveying air against the grate panel from the bottom in this section instead of air-cooling the grate panel along the flow channel.
Alternatively, the rear section of the grate panel can also be cooled by forcing a gas, particularly air, through the channel. This embodiment with “double air-cooling” in the front and rear sections of the grate panel is chosen for applications, in which a less intensive cooling effect is required, in particular, in the rear section of the grate panel.
Depending on the material being incinerated and the process conditions during the incineration, it is also possible to switch over between air-cooling and water-cooling in the first section of the grate panel. When switching over from water-cooling to air-cooling, the channel (waterline) needs to be evacuated first.
According to its most general embodiment, the invention pertains to a grate panel for an incineration grate with the following characteristics:
In one embodiment, the grate panel is realized with a plurality of recesses underneath the upper side, wherein said recesses are respectively open toward the lower side and extend from a region that is situated adjacent to the first long side to a region that is situated adjacent to the second long side.
These recesses make it possible to air-cool the upper side additionally from the bottom such that the liquid/gas flowing through the channel can also be cooled.
In one embodiment, the flow channel or the flow channels extend(s) perpendicular to the long sides of the grate panel. In other words: the air flows along the flow channels in the direction toward the front face area of the grate panel.
The length of the flow channel can normally be limited to a length that corresponds to 10-50% of the grate panel width, wherein a length between 10 and 30% or 10 and 20% usually suffices. This is the section, in particular the panel section that is not passed by an adjacent panel in a reciprocating incineration grate. Accordingly, about 10-80% of the grate panel width is available for realizing the channel, wherein 40-70% appears to be a favorable range for most applications. It would also be conceivable, in principle, that the regions of the channel and the flow channel overlap one another.
In order to optimize the cooling effect, the channel may essentially extend over the entire length of the grate panel and be realized in a helical or meander-shaped fashion between the broadsides in order to extend the length of the cooling channel. The supply and discharge of the cooling medium are realized with the aid of corresponding connections, for example, as described in EP 954 722 B1, to which the invention hereby refers.
The periphery of a grate panel usually does not have an exactly cuboid shape. The front face area (second long side), in particular, does not extend perpendicular to the upper side of the grate panel. The second long side may extend at an angle α<90° relative to the upper side and, if so required, be additionally angled at least once.
With respect to the flow channel, this means that the flow channel also does not extend in a straight fashion, but rather follows the shape of the grate panel in this region. For example, the flow channel describes—if viewed in the form of a section—a semicircle or is angled several times. This simultaneously results in a longer flow channel. The cooling effect can be intensified if the flow channel extends relatively close to the respective surface areas of the grate panel. In other words: an upper (outer) wall of the flow channel is formed by an (inner) surface of the upper side and an (inner) surface of the second long side in this case.
A lower (inner) wall of the flow channel may be formed by a rib extending between walls or webs that form, for example, lateral limitations of the aforementioned recesses.
The support of adjacent grate panels and the transport of the material being incinerated along the incineration grate can be simplified if the lower side of the grate panel (also referred to as grate stage) is realized such that the upper side of the grate panel is inclined (for example, by 3-10°) from the first long side to the second long side (i.e., from the rear toward the front) when the grate panel is supported on a horizontal surface.
For this purpose, the lower side may be realized with a downwardly protruding projection adjacent to the second long side (front face) as discussed in the following description of the figures. In this case, the grate panel in question overlaps the following grate panel (grate stage) referred to the transport direction of the material being incinerated, with this projection.
However, its front long side preferably ends a certain distance from the upper side of the ensuing grate panel, and the outlet opening of the flow channel accordingly lies above the support surface of the ensuing grate panel. The targeted air flow against the upper surface of the adjacent grate panel is favorably influenced in this fashion. This is also discussed below in the description of the figures.
Alternatively, it would be possible to arrange the outlet opening of the flow channel in the lower section of the front long side. This would result in an air flow that essentially extends parallel to the upper side of the ensuing grate panel.
The additional cooling makes it possible to realize the sections of the grate panel that are situated adjacent to the flow channel thinner than the remaining sections of the grate panel. This not only lowers the material requirement, but also improves the cooling effect.
This “thinner” section is not limited to the front long side of the grate panel, but may also extend over adjacent sections of the upper side of the grate panel. However, the remaining (first) section of the upper side of the grate panel is realized thicker because the channel is arranged in this section.
Grate panels of the aforementioned type have a width, for example, of 40-60 cm and a length of several meters. In this respect, it is also known to realize a grate panel in the form of several adjacent, interconnected segments that are also referred to as grate bars. The individual segments may consist of cast parts, wherein the flow channel and the channel can be realized in situ. This means that each segment is realized integrally. The segments (grate bars) may also be composed of smaller segments, particularly if they are welded from sheet metal material. A grate bar may have a width, for example, of 30-100 cm or more (in the longitudinal direction of the entire grate panel).
Adjacent grate bars are interconnected by means of conventional connecting techniques, for example, with screws or by connecting several grate rods with the aid of connecting rods. The thusly formed panels of grate rods can then be interconnected analogously. The constructive options disclosed in EP 954 722 B1 also indicate how the fluidic connections between channel segments of the grate bars may be produced.
In this case, it is possible to realize the grate panels such that at least one recess is formed by two adjacent grate bars (segments), i.e., each grate bar forms part of the corresponding recess, for example, one half thereof. However, a flow channel could also be formed by two grate bars.
The invention also pertains to an incineration grate, particularly a reciprocating incineration grate, with a plurality of grate panels of the previously described type.
In this context, the term “reciprocating grate” includes all types of reciprocating grates, namely regardless of the fact if they extend horizontally or in an inclined fashion and if the material being incinerated is conveyed in one or the other direction. The term “reciprocating grate” also includes conveyor grates in which, for example, every second grate panel is realized in a movable fashion, as well as grates in which more than one stationary grate panel is positioned between two grate panels that carry out stoking movements.
The invention also pertains to a waste incineration plant, for example, a garbage incineration plant, with an incineration grate of the previously described type.
Other characteristics of the invention are disclosed in the dependent claims and the remaining application documents. The thus disclosed features may be essential to the invention in arbitrary combinations.
The invention is described in greater detail below with reference to one embodiment. The respective figures show—in the form of highly schematic representations:
The basic design of a grate panel is described below with reference to
Adjacent to the first (rear) long side 14, the lower side of the grate panel contains a recess 18 that extends in the longitudinal direction (into the plane of projection), wherein a connecting element 19 that contains another recess 19o is positioned in this recess, and wherein a round rod 20 lies in this additional recess and (indirectly) supports the grate panel. The grate panel shown in
The lower side 12 of each grate panel is provided with a plurality of adjacently arranged recesses 22. Each recess 22 is laterally limited (parallel to the broadsides) by walls, only one wall 24 of which is visible in the figure. On the rear end of the grate panel, the recess 22 is limited by a corresponding section 14a of the first long side, wherein the recess is limited by the front (second) long side 16 on the front end (that points into the incineration chamber 26).
A wall 30 that essentially has the shape of an arc in said sectional view transforms into a thickened section 30v at the front end adjacent to the second long side 16 and also extends between adjacent walls 24, which thickened section protrudes over a lower face edge 16u of the second, front long side 16 and forms a support surface 30u for the grate panels.
This wall 30 forms a lower (inner) wall of a flow channel 32 that extends from the lower end 16u of the second long side 16 parallel to the wall 30 (such that the inner surface of the long side 16 forms the other limitation of the flow channel 32) and is then limited by a lower surface 10u of the upper side 10 before it opens in the direction toward the lower side 12 of the grate panel. In the embodiment shown, the wall 30 ends on the lower end of the recess 22; however, it could also end before the lower end of the recess. In the embodiment shown, a funnel-shaped inflow opening 32k for the cooling air results underneath the grate panel, wherein the cooling air flows against the entire recess 22 including the section that is situated underneath the wall 30.
In the grate panel shown in
The supply of additional cooling air is symbolized by arrows L in the lower portion of
The air flowing against the upper side 10′ of the adjacent grate panel additionally cools the section situated adjacent to the flow channel 32 from outside. Deposits (so-called pick-ups) that are caused by precipitating materials, particularly metals precipitating from the material being incinerated, and indicated by the dotted region 34 in
The intensified cooling (additional cooling) in the particularly critical front section of the grate panel makes it possible to realize the wall thickness of the grate panel thinner in this section than in the rear section of the grate panel as shown in the figure.
For example, the upper side 10 has a thickness of 6 or 8 mm in the front section 10v (adjacent to the flow channel). This applies analogously to the wall thickness of the second long side 16.
In the embodiment shown (
The rear section 10r of the upper side 10 is realized much thicker, for example, with a thickness of 25-70 mm, in order to accommodate the channel 40 therein. The channel 40 essentially extends from one broadside of the grate panel to the opposite broadside, namely in an alternating fashion between the first long side 14 and the front section 10v of the upper side. In other words: the channel extends in the region 10r of the upper side 10 that lies behind the section 10v, in which the flow channel 32 is arranged. In the embodiment shown, the connections 40a for supplying and discharging a cooling medium are positioned on an inner surface of the recess 18. These connections are connected in a fluidic fashion to channel sections 40b in the above-mentioned connecting elements 19 that connect the channels 40 (segments of the channel) and simultaneously accommodate connecting lines for the cooling medium (arrow A)—in the region of the grate panel broadsides. The connecting elements 19 are fixed on the grate bars T1, T2 by means of screw connections 19v (
As mentioned above, the cooling of such a grate panel can be realized in different ways, for example:
It is also possible to change over between these cooling modes during operation. Naturally, the water needs to be removed from the channels 40 first, for example, sucked off.
The bores 36 illustrated in
The grate panel shown may be realized in the form of a cast iron part, wherein each grate bar T1, T2 is realized integrally, i.e., the wall 30 is realized, for example, in one piece together with the wall 24.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 034 322.5 | Jul 2004 | DE | national |
