EP3967926B1 - Grate block with rising lug - Google Patents

Description

The present invention generally relates to a combustion grate intended for use in a waste incineration plant. Combustion grates for the large-scale incineration of waste have been known to those skilled in the art for a long time. They are usually constructed from a large number of individual grate bars that are joined together to form a corresponding combustion grate. This construction allows individual grate bars to be easily replaced if individual areas of the grate are damaged.

In such waste incineration plants, the fuel is normally conveyed from the inlet end of the combustion grate to the outlet end (ie in the conveying direction) and burned during this process. To supply combustion air, also called primary air, to the fuel, the grate bars or grates are exposed to an air stream from the bottom and have outlet openings through which the flow of combustion air can reach the fuel. Such grates or grate bars are made, for example, from the DE 20111804 U1 known.

A frequently used combustion grate is the so-called stepped grate. This comprises grate blocks arranged next to each other, each forming a row of grate blocks. The rows of grate blocks are arranged one above the other in a stepped manner, whereby in the case of so-called pusher grates, the grate blocks in the push direction (or conveying direction) of the combustion material), the front end of a first grate block rests on a support surface of a second grate block arranged offset in the thrust direction below the first grate block and is moved on this support surface with a corresponding thrust movement.

Due to the fuel being transported over the grate blocks, the former are generally exposed to relatively high levels of abrasive wear. In the front area (also known as the nose) of each grate block, the fuel is thrown from the support surface over a corresponding discharge edge onto the support surface of the following grate block. The abrasion or wear is therefore particularly high in this front end area of the support surface, also known as the feed section.

Due to the high temperatures during combustion and in the combustion chamber, the grate blocks are also exposed to very high thermal loads. During normal operation of the combustion grate, this thermal load is particularly high in the area of the support surface, although the combustion material lying on the grate block has a certain insulating effect. However, peak loads occur particularly when the combustion material is unevenly distributed on the combustion grate and only forms a thin insulating layer in places, or when this insulating layer is completely missing. The thermal load promotes erosion through abrasion and chemical reactions taking place on the support surface, which further damage the support surface. These processes lead to ultimately leading to a shortening of the service life of the grate block.

The US 4,515,560 A discloses a fixed or movable grate element for a heat exchanger between a particulate solid at a very high temperature and a fluid at a lower temperature. The grate element is connected to a carrier via a connecting piece, said connecting piece having a foot and a head. The grate element consists of a fireproof cast steel plate, on the upper side of which the solid particles are moved and which has several holes in a rising area through which the fluid flows from bottom to top. In said rising area, the cast steel plate also has a recess with a bottom hole into which the foot of the connecting piece engages. In this way, the connecting piece can be protected from excessive heat.

In order to reduce the thermal load, the grate blocks are normally cooled with a coolant from below, i.e. on the side of the combustion grate opposite the combustion. Air or water are usually used as coolants. As mentioned above, the thermal load can also be reduced by evenly distributing the combustion material on the grate.

In the EP 1 321 711 A1 a grate bar for a moving grate furnace is disclosed, said grate bar being provided with a cooling system through which air flows on its underside. The cooling system consists of a cooling gap that runs in the longitudinal direction of the grate bar and extends over the entire width of the grate bar between the side flanks.

In order to shred and/or stir the waste more or less strongly during transport from one grate block to the next (underneath) grate block, grate blocks with special nose shapes have been proposed in the prior art.

The German patent application No. 568 164 discloses a feed grate with movable and fixed grate elements (movable rams and fixed plates). The fixed grate elements have a bead at the front end, whereby the inner edge of the bead is designed to be either flat or steep depending on the composition of the waste to be burned. A rather flat inner edge is chosen to convey the waste more efficiently, - 7A - a steep inner edge is chosen to stir up the waste more intensively.

A disadvantage of this grate design is that it is unsuitable for widely varying waste compositions, since the slope of the inner edge of the bead cannot be changed during operation. Furthermore, two different types of grate bodies are used (tappets and plates), which makes the construction of the grate and the replacement of the grate bodies more complex.

The German patent specification No. 1 301 421 and 969 643 reveal grate bars that are provided with sharp-edged, pyramid-shaped projections in the respective feed section. These projections are used to shred the waste to be burned by means of stoking movements.

A rust block with pyramid-shaped projections in the area of the nose is also in the US 2013/0167762 A1 Specifically, a grate bar is disclosed with a replaceable head which is provided with a transport nose. The latter has a triangular cross-section and is mounted on an inclined surface of the replaceable head. In addition, the replaceable head comprises a scraper nose which is mounted on a horizontal surface of the head and also has a pyramid shape. The transport nose supports the backward movement and the circulation of the waste on the grate, while the scraper nose supports the forward and downward movement of the waste on the grate.

The previously known grate blocks in pusher grates have the disadvantage that the waste to be treated falls in batches or in batches onto the grate block below during the usual pushing movements. The transfer of the waste from a first grate block to a second grate block below can take place in two ways: On the one hand, by the first grate block carrying out a pushing movement in the conveying direction and thus pushing the waste onto the grate block below. the first grate block. On the other hand, the waste can also fall onto the second grate block arranged underneath when the first grate block is pulled back. When the grate block is pulled back (opposite to the transport or conveying direction), the waste lying on top of it is only set in motion with a delay due to its inertia. Since the waste lies as a layer on the grate block, its backward movement is additionally prevented, causing the grate block to move backwards more than the layer of waste lying on top of it. This means that with each withdrawal of the grate block, the front part of the layer of waste, seen in the transport direction, falls onto the grate block arranged underneath.

As described above, the waste layer has an insulating effect and protects the grate block from excessive thermal stress. In this respect, a regular distribution of the waste is desirable. However, the "falling down" of the waste in batches described above often leads to an irregularly thick waste layer on the "receiving" grate block, which encourages the formation of temperature peaks. Furthermore, the "falling down" of the waste creates air holes in the waste layer formed on the lower grate block, which also leads to increased flame formation in certain areas and a consequent increased thermal stress on the grate block.

Rust blocks with pyramid-shaped projections, such as those found in the EN 1 301 421 and DE 969 643 to be discribed, Although they cause the waste to move when the grate block is moved, the waste is still transferred to the grate block below in batches, which leads to an irregular distribution or thickness of the waste layer.

Due to the different positions of the grate blocks in the grate, their wear also varies. In general, the higher the thermal load, the greater the abrasion of the support surface. Measured in longitudinal section, the abrasion of a grate block after one year is on average 5 mm. In a zone with high thermal load, the abrasion can be up to 10 mm after one year, which corresponds to a service life of 2 - 3 years for the grate block.

The US 4,078,883 A discloses a grate block with a horizontal grate plate or one that rises slightly in the conveying direction and is equipped with wear elements in the area of a material support surface. Said elements can be attached to the grate plate without screws or other separate fastening devices and thus allow for quick and easy replacement.

It is therefore the object of the invention to eliminate the disadvantages of the prior art and to provide a combustion grate which allows the fuel conveyed over the grate blocks to be evenly distributed over the support surface of the grate blocks in order to avoid temperature peaks and the associated thermal load peaks.

The object is achieved according to the invention with a grate block according to claim 1 and a combustion grate according to claim 14. Preferred embodiments of the invention are given in the dependent claims.

The grate block according to the invention is part of a combustion grate, which consists of several such grate blocks and in which the grate blocks are arranged one above the other in a stepped manner. The The combustion grate is intended for use in a plant for the thermal treatment of waste, in which the grate blocks are designed in such a way that the combustible material is rearranged during combustion and conveyed in a conveying direction by means of thrust movements carried out relative to one another.

The grate block according to the invention comprises a block body designed as a cast part with a rear end and a front end opposite the rear end in the conveying direction. The block body further comprises an upper wall which forms an outer, rear support surface for the waste to be treated, which extends at least partially parallel to a longitudinal axis L of the block body. The rear support surface defines a substantially horizontal plane. The grate block according to the invention also comprises a nose arranged in the region of the front end which is raised relative to the horizontal plane. The raised nose comprises a front support surface which rises in the conveying direction up to a culmination point, as well as a sloping end section which adjoins the front support surface after the culmination point. The sloping end section comprises a discharge surface which slopes down in a substantially arcuate manner in the conveying direction. Seen in longitudinal section along the conveying direction F, the front support surface is S-shaped.

For the purposes of the present invention, grate blocks arranged one above the other in a staircase-like manner are defined as grate blocks on a grate which are arranged like the steps of an ascending or descending staircase.

The term "pushing movements that can be carried out relative to one another" refers to pushing movements that are carried out in or against the conveying direction of the combustion material. In a stepped grate, the conveying direction of the combustion material therefore runs parallel to the incline or slope of the grate.

The "longitudinal axis of the block body or the grate block" refers to an axis which extends parallel to the overall inclination of the stepped grate and thus runs parallel to the conveying direction of the waste to be treated.

For the purposes of the present application, a "supporting surface" is understood to mean a surface that is arranged on the outer top of the grate block and on which the waste intended for thermal treatment rests. As mentioned at the beginning, this supporting surface is known to be exposed to increased mechanical and thermal stress in incineration plants and is susceptible to caking of combustion products.

The "nose" is generally the frontmost part of the block body in the conveying direction. For the purposes of the present application, a "raised nose" is understood to mean a nose whose highest point is located vertically above the rear support surface.

The "culmination point" is generally defined as a highest point and in this application as the highest point of the raised nose. The culmination point can be a singular point, for example as the tip of a pyramid or as the highest point of a curve or a arch. The culmination point can also be a horizontal plane. In this case, the entire plane would be defined as a culmination point in the sense of a culmination plane.

The term "descending end section" refers to a surface which is located at the front end of the block body in the conveying direction and which descends from the culmination point. According to the invention, the descending end section descends in a vertical direction. This means that the descending end section has a negative gradient.

The term "essentially arcuate" defines that the sloping discharge surface is arcuate or preferably circular. Such an arcuate surface can also be formed by arranging a large number of short, straight surface segments in a row, which overall have an arcuate shape.

The grate block according to the invention has the advantage over the prior art that, thanks to the raised nose, the waste is discharged successively and regularly, so to speak in a flowing manner, from a first grate block to a second grate block below it, thus counteracting the waste being discharged in batches or in increments. The raised nose acts as an obstacle that prevents the waste from falling down in batches when it is pulled back. In an analogous manner, waste that has been discharged from the first to the second grate block is conveyed from the second to the third grate block when the first grate block is advanced. This controlled The feed movement prevents the waste from "falling down" in batches and enables the waste to be conveyed in a continuous flow movement, which ultimately leads to the formation of a more regular layer of waste on the support surface of the grate blocks. This regular layer of waste has a uniform insulating effect and thus prevents thermal load peaks on the grate block.

In a preferred embodiment of the grate block, the culmination point is spaced from the horizontal plane in the vertical direction by 10 - 35 mm, preferably 15 - 30 mm and particularly preferably 18 - 25 mm and most preferably 20 - 21 mm.

It has been shown that a grate block with the above-mentioned values for the distance in the horizontal plane (also referred to as clear width or clear distance) is particularly suitable for producing a regular layer of waste on the grate block below.

Preferably, the rising front support surface is ramp-shaped and has an average positive gradient of 10 - 35%, preferably 15 - 32% and particularly preferably 20 - 30% and most preferably 26 - 28% in a central part.

In the context of the present invention, a "ramp" or "ramp-shaped" refers to a surface that adjoins the horizontal plane and has a positive gradient, i.e. leads to a point that is higher than the horizontal plane. The ramp can can have any shape (e.g. convex or S-shaped).

It has been shown that a ramp-shaped support surface with an average gradient according to the above values is particularly suitable for producing a regular layer of waste on the grate block below.

According to the invention, the front support surface of the grate block is S-shaped when viewed in longitudinal section along the conveying direction.

For the purposes of the present invention, an "S-shaped" front support surface (viewed in longitudinal section) is understood to mean that the support surface has a continuously increasing positive slope in a first region, which adjoins the horizontal plane, and a continuously decreasing positive slope in a second region, which adjoins the first region directly or indirectly in the conveying direction. Preferably, the positive slope can be constant in a third region, which is arranged between the first and second regions. Other names for an "S-shaped" curve are sigmoid function, swan neck function or Fermi function. An equation for an example S-shaped curve is: $$\mathrm{sig}\left(\mathrm{t}\right)=0.5*\left(1+\tanh \left(\mathrm{t}/2\right)\right)$$

It has been shown that a grate block with an S-shaped front support surface viewed in longitudinal section allows a very regular transfer of the fuel to be burned. waste and thereby creates a regular layer of waste on the grate blocks below.

Preferably, the arcuately sloping discharge surface comprises a preferably rounded discharge edge at a point lying at the front in the conveying direction.

The rounded discharge edge has the advantage of reducing material wear in this area of the nose. It also enables the waste to be transferred smoothly to the adjacent grate block below, which creates a regular layer of waste and prevents a local cutting torch effect.

In a preferred embodiment of the grate block, the sloping end section comprises a first arcuate segment in the region between the culmination point and a point lying foremost in the conveying direction.

Said first arcuate segment can be part of the arcuate discharge surface or form a connecting section between the culmination point and the arcuate discharge surface. The arcuate contour of the first arcuate segment enables a uniform flow of the waste to be burned on the front support surface, which reduces friction and thus wear on the grate block and creates a regular layer of waste on the grate blocks below.

Preferably, the first arcuate segment has a first radius of curvature R1 with a length of 60 - 120 mm, preferably from 70 - 110 mm, particularly preferably from 80 - 100 mm and most preferably from 90 mm.

The average radius of the first arcuate segment is defined as the "first radius of curvature R1". It is quite conceivable that the first arcuate segment is composed of smaller straight sections which as a whole form an arcuate segment. Preferably, the outer surface of the arcuate segment forms the arc line of a circular sector when viewed in longitudinal section. When viewed in longitudinal section, the area of the first arcuate segment is thus limited by the circular arc and two circular radii. With regard to uniform conveyance of the waste over the first arcuate segment, a radius of curvature with the previously defined values has proven to be particularly advantageous.

In a preferred embodiment of the grate block, the first arcuate segment in longitudinal section spans a sector surface with a central angle α between 60° and 72°, preferably of approximately 66°.

Preferably, the sloping end section comprises a second arcuate segment, which particularly preferably adjoins the first arcuate segment in the conveying direction and very particularly preferably adjoins the first arcuate segment directly.

The first and second arched segments can be connected directly to one another or via a middle piece. The middle piece can be designed as a straight surface or also as an arched segment.

In a preferred embodiment of the grate block, the second arcuate segment has a second radius of curvature R2 when viewed in longitudinal section, preferably with a length of 10 - 30 mm, preferably 15 - 25 mm, particularly preferably 18 - 22 mm and most preferably 20 mm.

The "second radius of curvature R2" is defined as the average radius of the second arcuate segment (seen in longitudinal section). It is quite conceivable that the second arcuate segment is composed of smaller straight sections, which as a whole form an arcuate segment.

Preferably, the first and second curvature radii are of different lengths. This also means that the first arcuate segment and the second arcuate segment preferably have a different arc curvature. Different arc curvatures, in particular with the above-mentioned preferred radii of curvature R1 and R2, have proven to be particularly effective with regard to successive waste disposal over the discharge edge.

Preferably, the second arcuate segment defines, when viewed in longitudinal section, a sector surface with a central angle β between 70° and 120°, preferably of approximately 90°.

In a preferred embodiment of the grate block, the block body has a front wall which is set back against the conveying direction relative to the foremost point of the sloping end section (seen in the conveying direction), so that an undercut is formed. In this preferred embodiment, the grate block thus has a protruding nose. The grate block particularly preferably comprises air openings in the front wall in the area of the undercut. This has the advantage that ventilation openings for supplying primary or secondary air can be arranged below the discharge edge and thus they are not blocked or clogged by falling waste. The preferably curved transition from the discharge edge to the undercut is advantageous with regard to a uniform waste discharge movement.

In a preferred embodiment, the distance measured in longitudinal section between the culmination point (23) and the discharge edge is 60 - 100 mm, preferably 70 - 90 mm and particularly preferably 80 - 82 mm.

Preferably, the nose has a length of 170 mm measured along the longitudinal axis. The length of the nose is defined as the clear distance between the starting point of the rising ramp-shaped front support surface and the discharge edge.

The above preferred dimensions with regard to distance between culmination point and discharge edge as well as length of the nose are particularly advantageous with regard to the use of the grate block in a waste incineration plant.

In a preferred embodiment, the grate block has a depression in the rear support surface, preferably adjacent to the front support surface. Ventilation openings are preferably arranged in the area of this depression. Said ventilation openings preferably define the Exit of an air duct that leads through a protrusion with a volcano-like outer contour. The air duct expands steadily, preferably from the ventilation opening towards the interior of the block body. This effectively counteracts clogging of the air supply openings by waste particles.

Furthermore, the invention relates to a grate comprising several grate blocks according to the invention.

Preferably, the individual grate blocks move in the grate at a speed of 0 - 5 mm/s over a feed distance of 150 - 250 mm, particularly preferably around 200 mm. In comparable known systems, feed distances of up to 350 - 450 mm are common. Due to the comparatively short feed distances preferred according to the invention, the grate blocks are moved up to 45 times per hour from a starting position to an end position and back to the starting position. Shorter feed distances have proven to be advantageous with regard to the even transfer of the combustion material.

In the main combustion zone of the grate, the grate blocks preferably move at 2 - 3 mm/s and in the afterburning zone of the grate they preferably move at 1 mm/s. The speed of the individual block bodies is usually adjusted based on the composition of the waste to be burned.

Fig. 1

eine perspektivische Ansicht einer Ausführungsform eines erfindungsgemässen Rostblocks;

Fig. 2

ein Längsschnitt entlang der Längsachse L durch den Blockkörpers aus Fig. 1; und

Fig. 3

eine vergrösserte Ansicht eines Längsschnitts entlang der Längsachse L durch einen vorderen Bereich des Blockkörpers aus Fig. 1.

The invention is explained in more detail below using some embodiments shown in the figures. If alternative embodiments differ only in individual features, the same reference numerals have been used for the same features. They show purely schematically:

Fig.1

a perspective view of an embodiment of a grate block according to the invention;

Fig.2

a longitudinal section along the longitudinal axis L through the block body Fig.1 ; and

Fig.3

an enlarged view of a longitudinal section along the longitudinal axis L through a front region of the block body of Fig.1 .

The Fig.1 and 2 The grate block 1 shown comprises a block body 3 designed as a cast part with an upper wall 4, which extends in the conveying direction F from a rear end 5 to a front end 7. In the area of the rear end 7, the block body comprises a fastening device 9, with which the block body 3 is coupled to a drive system (not shown) in the grate and which initiates its movements in or against the conveying direction F. Furthermore, the block body 3 comprises in the area of the rear end 5 an outer, rear support surface 11 for the thermal treatment of the waste to be incinerated. In the area of the front end 7, the block body 3 comprises a raised nose 13. This comprises, viewed in the conveying direction F, an outer front support surface 15 rising up to a culmination point 17 and a sloping end section 19 adjoining the culmination point 17 with a substantially arcuately sloping discharge surface 21. The rear support surface 11 defines a substantially horizontal plane 23 which has a depression 25. The outer, front support surface 15 adjoins the horizontal plane 23 in the conveying direction F. The rising, outer front support surface 15 is ramp-shaped and, viewed in longitudinal section, is substantially S-shaped. In the embodiment shown, the slope of the front support surface 15 increases steadily following the horizontal plane 23 until it remains constant in a central part 27 and then decreases towards the culmination point 17, so that the slope approaches zero in the direction of the culmination point 17. The culmination point 17 is designed here as a singular point between the front support surface 15 and the sloping end section 19, but could alternatively also be designed as a "culmination plane". The sloping end section 19 of the raised nose 13 comprises a rounded discharge edge 31 at a point 29 that is the foremost point as seen in the conveying direction F.

The block body 3 further comprises a front wall 33 which is set back from the foremost point 29 of the sloping end section 19 in the opposite direction to the conveying direction F and which forms an undercut 35 with the sloping end section 19. The front wall 33 of the block body 33 is connected at the bottom by a sliding surface 37, with which the block body 3 slides on the outer rear support surface 11 of a second grate block located underneath (not shown). The front wall 33 comprises ventilation openings 39, which are protected from falling waste by their position in the area of the undercut 35, so that blockage of the ventilation openings 39 can be prevented. The upper wall 4 also comprises a further ventilation opening 41 in the area of the horizontal plane 23, which represents the outlet of an air duct through a pyramid-shaped or volcano-shaped elevation. The diameter of the air duct widens concentrically from the ventilation opening 41 towards the interior of the block body, so that waste which enters the air duct through the ventilation opening 41 falls downwards due to the widening diameter without blocking the ventilation opening 41. The ventilation openings 39 and 41 serve to supply primary or secondary air to enable efficient combustion.

Figure 3 shows an enlarged view of the raised nose 13 and the front area 7 of the grate block from Fig.1 . A vertical axis V, shown in dashed lines, runs through the culmination point 17. Starting from the culmination point 17, the outer contour of the falling end section 19 falls in the conveying direction F and forms a first arcuate segment 43. The first arcuate segment 43 has an average radius of curvature R1 and spans an angle α between the vertical axis V and a first segment axis A1. the first arcuate segment 43 adjoins a second arcuate segment 45. The second arcuate segment 45 has an average radius of curvature R2 and spans an angle β between the first segment axis A1 and a second segment axis A2. The first and second arcuate segments 43, 45 can be connected to one another directly or via a center piece (not shown). The center piece can be designed as a straight surface or also as an arcuate segment. Depending on the size of the angles α and β, the foremost point 29 with the rounded discharge edge 31 can be positioned in the first or second arcuate segment 43, 45.

Claims (14)

1. Grate block (1) as part of an incineration grate in a plant for the thermal treatment of waste, in which the grate blocks are arranged one above the other in a staircase-like manner and are designed in such a way that the material to be incinerated is rearranged during incineration by means of thrust movements carried out relative to one another and conveyed in a conveying direction F,
   wherein the grate block comprises a block body (3) designed as a casting with the following components:

   a rear end (5) and a front end (7) opposite the rear end (5) in the conveying direction F,

   an upper wall (4) extending substantially parallel to a longitudinal axis L of the block body (3) and forming a rear support surface (11) for the waste to be treated, wherein the rear support surface (11) defines a substantially horizontal plane (23),

   and a nose (13) arranged in the region of the front end (7) and raised relative to the horizontal plane (23),

   wherein the raised nose (13) has a front support surface (15) which rises in the conveying direction F up to a culmination point (17) and a descending end section (19) which adjoins the front support surface (15) after the culmination point (17), wherein the descending end section (19) comprises a discharge surface (21) which descends in a substantially arcuate manner in the conveying direction F,

   characterized in that, viewed in longitudinal section along the conveying direction F, the front support surface (15) is S-shaped.
2. Grate block according to claim 1, characterized in that the culmination point (17) is spaced from the horizontal plane (23) in the vertical direction by 10 - 35 mm, preferably 15 - 30 mm, particularly preferably 18 - 25 mm and most preferably 20 - 21 mm.
3. Grate block according to one of claims 1 to 2, characterized in that the rising front support surface (15) is ramp-shaped and has an average gradient of 10 - 35%, preferably 15 - 32%, particularly preferably 20 - 30% and most preferably 26 - 28%, in a central part (27).
4. Grate block according to one of the claims 1 to 3, characterized in that the arcuately sloping discharge surface (21) comprises a preferably rounded discharge edge (31) at a point (29) lying foremost in the conveying direction F.
5. Grate block according to one of claims 1 to 3, characterized in that the descending end section (19) comprises a first arcuate segment (43) in the region between the culmination point (17) and a point (29) lying uppermost in the conveying direction F.
6. Grate block according to claim 5, characterized in that the first arcuate segment (43) has a first radius of curvature R1 with a length of 60 - 120 mm, preferably of 70 - 110 mm, particularly preferably of 80 - 100 mm and most preferably of 90 mm.
7. Grate block according to claim 5 or 6, characterized in that the first arcuate segment (43), viewed in longitudinal section, spans a sector surface with a center point angle α of between 60° and 72°, preferably of about 66°.
8. Grate block according to one of claims 5 to 7, characterized in that the sloping end section (19) comprises a second arcuate segment (45), which preferably adjoins the first arcuate segment (43) in the conveying direction F and particularly preferably adjoins it directly.
9. Grate block according to claim 8, characterized in that the second arcuate segment (45) has a second radius of curvature R2, preferably with a length of 10 - 30 mm, preferably of 15 - 25 mm, particularly preferably of 18 - 22 mm and most preferably of 20 mm.
10. Grate block according to claim 9, characterized in that the second arcuate segment (45), viewed in longitudinal section, spans a sector surface with a center point angle β of between 70° and 120°, preferably of about 90°.
11. Grate block according to one of claims 4 to 10, characterized in that the block body (3) has a front wall (33) which is set back relative to the foremost point (29) of the descending end section (19) in the opposite direction to the conveying direction F, so that an undercut (35) is formed.
12. Grate block according to claim 11, characterized in that ventilation openings (41) are provided in the region of the front wall (33) of the undercut (35).
13. Grate block according to one of claims 1 to 12, characterized in that a depression (25) is formed in the rear support surface (11), preferably adjacent to the front support surface (15).
14. Grate comprising a plurality of grate blocks (1) according to one of claims 1 to 13.