Patent Publication Number: US-2006000396-A1

Title: Grate panel, as well as corresponding incineration grate and waste incineration plant

Description:
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 refuse) 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 EP 0 391 146 A1.  
      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. 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.  
      The invention is based on the objective of disclosing an option for also incinerating materials (waste material) with higher calorific values, particularly calorific values&gt;10 MJ/kg, by means of an air-cooling system.  
      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 the bottom, 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.  
      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 from below in a targeted fashion against the upper side and the adjacent front long side.  
      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 below” with a correspondingly high flow speed.  
      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 targeted 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.  
      The conventional cooling system used so far serves for cooling the “rear” section of the grate panel.  
      According to its most general embodiment, the invention pertains to a grate panel for an incineration grate with the following characteristics: 
          the grate panel has an upper side, a lower side, two long sides and two broadsides;     the grate panel comprises at least one device for connecting a support element adjacent to a first long side, and     at least one flow channel is arranged underneath the upper side and adjacent to the second long side, wherein air is conveyed along said flow channel from a region that is situated underneath the grate panel to an opening in the section of the second long side that is situated adjacent to the lower side.        

      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 realize the upper side (upper face area of the grate panel) with a relatively small thickness, for example, of 10-15 mm.  
      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.  
      As mentioned above, this “front” section of the grate panels is particularly at risk. In this respect, 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% usually suffices. This is in particular the panel section that is not passed (covered) by an adjacent panel in a reciprocating incineration grate.  
      The periphery of a grate panel (also called grate plate) 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&lt;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 (following) 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 according to the invention 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.  
      Grate panels of the aforementioned type have a width (broad side), 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 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 5-25 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 bars with the aid of connecting rods. The thusly formed panels of grate bars can then be interconnected analogously.  
      According to one embodiment, the grate panels are realized 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.  
      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 respective 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:  
       FIG. 1 , the front sections of two grate panels of a conveyor grate that lie on top of one another, namely in the form of a vertical section, and  
       FIG. 2 , a section along the line A-A in  FIG. 1 . 
    
    
      The basic design of a grate panel is described with reference to the lower grate panel in  FIG. 1 : the grate panel has an upper side  10 , a lower side  12 , a rear long side  14 , a front long side  16  and two broadsides that are not visible due to the chosen line of section. The upper face area  10   o  of the upper side  10  is realized in a plane fashion. The second, front long side  16  is angled relative to the upper surface  10   o  by an angle α (approximately 45°) and subsequently angled at  16   w.    
      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 round rod  20  lies in said recess and supports the grate panel. The upper grate panel shown in  FIG. 1  can be moved in the direction of the arrow P with the aid of this round rod  20 .  
      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  14   a  of the first long side, wherein the recess is limited by the front (second) long side  16  on the front end (that points into an incineration chamber  26 ). Several cooling ribs  28  protrude from the wall  24  into the recess  22 .  
      A wall  30  that essentially has the shape of an arc in said sectional view transforms into a thickened section  30   v  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  16   u  of the second, front long side  16  and forms a support surface  30   u  for the grate panels.  
      This wall  30  forms a lower (inner) wall of a flow channel  32  that extends from the lower end  16   u  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  10   u  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 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 upper grate panel shown in  FIG. 1 , the part of the cooling air conveyed through the flow channel  32  is symbolized by the arrow K. This means that the cooling air enters the flow channel  32  on the funnel-shaped end  32   k  and is then initially conveyed along the inner surface  10   u  of the upper side  10  and then along the inner surface  16   i  of the long side  16  before the cooling air is discharged in the region of the opening  32   o  and blown onto the upper side  10  of the adjacent grate panel.  
      The supply of additional cooling air is symbolized by arrows L in the lower portion of  FIG. 1 .  
      The air flowing against the upper side  10  of the 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  FIG. 1  can be prevented in this fashion.  
      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 12 mm in the rear section  10   r  and a thickness of only 6 or 8 mm in the front section (that is situated adjacent to the flow channel  32 ). This applies analogously to the wall thickness of the second long side  16 .  
      In the embodiment shown, the grate panel is composed of a plurality of adjacently arranged segments that directly adjoin and are connected to one another. These segments are also referred to as grate bars.  
       FIG. 2  shows that each grate bar T 1 , T 2  forms a wall  24  approximately in its center such that a recess  22  is respectively limited by two adjacent grate bars T 1 , T 2 . This also applies to the flow channel  32  that has an approximately oval cross section in this view.  
      Bores  36  illustrated in  FIG. 1  serve for receiving rods that are used for interconnecting adjacent segments T 1 , T 2 . A grate panel is composed of a plurality of such segments T 1 , T 2 , for example, 50-   60   segments.  
      The grate panel shown may be realized in the form of a cast iron part, wherein each grate bar T 1 , T 2  is realized integrally, i.e., the ribs  28  and the wall  30 , for example, are realized in one piece together with the wall  24 .