EP1760400B1 - Water cooled grate element - Google Patents

Abstract

The unit (1) has oxidizing structures, which are divided into two parallel cooling channels within a burnout surface. The channels are formed as meander shaped water guiding channels by corresponding arrangement of deflecting units (8). The transition from one channel to another channel occurs over an overflowing section, which is free from the deflecting units and runs transverse to a middle axis of both water guiding channels. An independent claim is also included for a method for forming an oxidizing unit.

Description

The invention relates to a water-cooled grate element according to the preamble of independent patent claim 1 and to a production method according to the preamble of claim 11.

The large incinerators, which are used for example for thermal energy generation or waste incineration, have for receiving and combustion of the solids to be recycled so-called feed grids on which the combustion material is moved through the combustion chamber. This feed grates are made up of a variety behind and next to each other arranged grate elements, also called grate bars or grate plates together, which are firmly connected. The thermal expansion is absorbed by arranged at the ends of the rows of grate expansion boxes. In the bars are openings for the supply of combustion air. The adjacent grate elements are combined into rows and every other such grate element row is in view of the feed of the combustion material -. the periodic execution of Schürhüben - movably mounted and connected to an oscillating drive.

Since these grate elements are mostly used in large combustion plants with constantly changing composition of the combustion material, eg in waste incineration plants, the demands on their performance are very high. For example, consider that these incinerators are constantly charged with goods that differ by their specific gravity, their calorific value, their air permeability, the moisture content, etc., so it is easy to see that such gratings are often exposed to very high temperatures and require unusual technical effort, if you want to achieve the desired service life with optimal combustion process. Due to the heat released during the combustion process, the grate elements are constantly exposed to both chemical corrosion and mechanical wear and must be constantly cooled to achieve an acceptable life, the cooling should if possible ensure optimum heat distribution in the grate element, so that local overheating be avoided in the grate element.

With regard to the effective cooling of the highly stressed grate bars, numerous solutions have already been proposed, of which some will be discussed below that are of particular interest in the present context.

The European patent application published on July 3, 2002 EP 1 219 898 A1 shows a grate block, which is part of a grate within a plant for thermal treatment of waste. The flowed through by the cooling water pipe is in this case arranged between the created as a cast grate block and a separate holding part. The block body and the cooling channel formed in the form of a pipe are thus here two separate parts, which are subjected to different expansion. Due to the arrangement of the Cooling channel between the block body and a holding part arranged below the same, the heat transfer is limited from the outset, so that the pipe must be embedded in this intermediate layer in a thermally conductive material, which involves an additional manufacturing effort and hinders the heat transfer between the pipe and the grate block. In addition, the complete ventilation is in question.

Also the European patent application EP 0 921 354 A1 describes a liquid-cooled grate plate with an attached coolant channel. An essential feature is emphasized that the coolant connection is arranged approximately centrally between the edges of the grate plate. Although it is incidentally mentioned, by the way, that the coolant channel can be formed by a mold core during casting of the grate body in this. However, the entire description gives the expert no clues as to how this could be realized in practice, especially since the separate attachment of a cooling tube is shown as a particularly cost-effective and safe production. Again, in view of the unfavorable water flow at extremely low flow cross-section with poor ventilation and thus air bag formation in the rectangular, angular deflection zones must be expected. This type of multi-part structures made of cast steel and sheet also brings increased stress, which can be downright catastrophic especially in emergency situations, especially since the different materials show different coefficients of expansion and also in terms of are difficult to connect to an optimal heat transfer. - Due to the central arrangement of the water supply also the freedom of movement of the grate element is disturbed during periodic stoking.

The German Utility Model G 94 16 320.0 shows a grate bar, in which various parallel sections of a coolant channel are integrated, wherein the sections are interconnected by deflections. This embodiment of the coolant guide has the particular disadvantage that only very small flow cross-sections can be realized and the problem of venting is not solvable.

The European patent application EP 0 757 206 A2 describes for cooling the grate bars mounted on the underside, coolant-flow-through hollow profiles, which should be designed as half-tubes or with an oval cross-section. Again, due to the numerous, for example, from Fig. 10 apparent rectangular and sharp-edged deflection zones in addition to the difficult venting possibility, the formation of air bags in the deflection can not be avoided.

The US Pat. No. 2001/0003266 A1 shows a grate element consisting of two chambers, wherein the cooling chamber - delimitation on the underside of the grate element is performed by a corrugated sheet, which must be subsequently inserted into the prefabricated cast body, which greatly affects the uniformity of the heat-related expansion over the entire grate element. To compensate for this disadvantage, curvatures in the cooling chamber boundary are described on the underside of the grate element (paragraph 0039), through which the occurring Thermal stresses are to be reduced. Also, the opening connecting the cooling passages is obviously much smaller than each of the individual cooling passages, which causes the flow velocity to increase in this region, thereby restricting the heat transfer from the vulnerable end region of the grate element and preventing complete venting. From the figures of this patent it can be clearly seen that the cooling channel partition wall is pulled into the radius or even beyond, so that complete ventilation and flow around is impossible. The one in there Fig. 5 with the position 43 marked cooling channel is limited to a minimum passage in the lower region of the end face. The heat that is introduced in the front section of the surface, in the radius and in the upper region of the frontal surface, can not be optimally transported here due to the large accumulation of material here. Due to the different temperatures in the structure of the entire casting, thermal stresses can occur, which can lead to cracking and thus leaks.

The Patent Abstracts of Japan show in Volume 1997, No. 06 , A method for cooling of grate elements by means of saturated steam and such methods are therefore already for this reason entirely different criteria than water-flowed grate elements, especially since the saturated steam is fed to the flow of the grate element to another superheater and then directed into the turbine. It was asked whether such a steam guide would be considered in principle by a power plant operator - it is certainly true that the flowing saturated steam basically behave differently than cooling water. In the Fig. 4 At right angles to the flow of the vaporous medium arranged vortex elements are the medium only to be whirled, but not able to perform. In addition, the respect of the US Patent 2001/0003266 A1 in view of the cooling effect situation here exacerbated because the front is completely separated by a bridge, so that the existing air can not escape at all. - Incidentally, it should also be noted that this grate element is operated anyway with saturated steam, which virtually makes a comparison with a water-cooled grate element impossible. Again, the effect of material accumulation plays a role, especially as the saturated steam is known to have far worse heat conduction properties than water, which additionally hampers the cooling effect.

Furthermore, in the two last-mentioned embodiments, production in a casting method is completely precluded due to the shape of the internals or the cooling channels. The production of a dense hollow body can be achieved there only with two or more steps in which each has to be welded. Welding can also lead to manufacturing errors due to the local structural change and the combination of different materials.

The European patent application EP 0 811 804 A2 Techform Engineering GmbH shows a grate element for incineration plants, according to which at least one Räumvorsprung for the air outlet of the assembled in the assembled state above the grate element is fixed on the top of the grate element. These Execution of a free-breaker, according to which the cross-sectional shape of the space projection is adapted to the required movement of the cross-sectional shape of the air outlet opening (column 5, lines 54 to 57), based on the prejudice, a satisfactory evacuation of the air outlet opening and a free blowing of the same could only be done when the Räumvorsprung fills the quasi-complete cross-section of the air inlet opening. Practice shows, however, that eviction, in contrast to this view, is far more successful if the cross section of the clearing protrusions is considerably lower than the total cross section of the air outlet. - The mentioned in this patent application air pressure surges (Section 45 and 50) in addition to the effect described there to a vacuum fluctuation in the furnace, which affects the fire control in a negative respect massive.

According to the DE 196 07 007 C1 For example, mechanical grate devices that are adapted to the shape of the air inlet openings and that can make a relative movement to the openings are proposed for a grate that can be used for waste incineration. These mechanical devices are free space lobes, which obviously - except for the required clearance - fill the entire cross section of the air inlet opening and thus, according to a prejudice, can not achieve a perfect cleaning, as for the EP 0 811 804 A2 already described.

In the prior art describes US 2001/003266 A1 a water-cooled grate element made of cast steel for equipped with combustion grates solid combustion systems, which have a plurality of behind and juxtaposed grate elements, each grate element with respect to the required Kühlng directly below the Verbrutz carrying Ausbrandfläche in two practically parallel to each water inlet or Water outlet connected cooling channels is divided, which are flowed through in opposite directions from the cooling water.

• Die bekannten, im Strömungsmedium angeordneten Umlenkorgane können die Strömung lediglich durchwirbeln, aber nicht gezielt führen. Die rechtwinkligen und scharfkantigen Umlenkzonen führen, insofern Wasser als Kühlmedium eingesetzt wird, zu enormer Luftsackbildung und entsprechender Reduzierung der Kühlwirkung. Die Luft würde in den Umlenkabschnitten hängen bleiben und würde von der Wasserströmung nicht mitgerissen,
• die mehrteiligen, aus Guss und Blech zusammengesetzten Konstruktionen weisen unvermeidbare Schweissnähte an schlecht zugänglichen Stellen mit schwieriger Schweissnahtvorbereitung auf;
• in Anbetracht der Verwendung unterschiedlicher Werkstoffe mit voneinander abweichenden Ausdehnungseigenschaften ergibt sich bei Beanspruchung der Notlaufeigenschaft eine erhöhte Spannungsbeanspruchung innerhalb des Elementes,
• die bei Verwendung separat erstellter und dann mit dem Gussblock verbundener Rohrleitungen unvermeidlichen engen Querschnitte im Wasserkanal und bei den Anschlussstellen führen zu hohen Druckverlusten, die durch die erforderlichen Verschraubungen noch vergrössert werden,
• ferner lassen sich bei all diesen bekannten Rostelementen nur relativ kleine Durchflussquer - schnitte mit begrenzter Kühlwirkung erzielen und
• schliesslich gehen die dem Stande der Technik entnehmbaren Vorschläge zur Verbesserung der Verbrennungsluftzufuhr von der falschen, auf einem Vorurteil beruhenden Vorstellung aus, der Querschnitt des Freiräumers müsse zwecks gründlicher Freiräumung der Luftdurchlassöffnung den gesamten Querschnitt dieser Öffnung ausfüllen.

In conclusion, these suggestions of grate cooling can be summarized as follows:

• The known deflecting members arranged in the flow medium can only stir through the flow, but not targeted. The rectangular and sharp-edged deflecting lead, inasmuch as water is used as a cooling medium, to enormous airbag formation and corresponding reduction of the cooling effect. The air would get stuck in the turnaround sections and would not be carried along by the water flow,
• the multi-part, composed of cast iron and sheet metal structures have unavoidable welds in hard to reach places with difficult weld preparation;
• in view of the use of different materials with differing expansion properties, when the emergency running property is stressed, there is an increased stress load within the element,
• the unavoidable narrow cross-sections in the water channel and at the connection points when using separately created and then connected to the cast block pipes lead to high pressure losses, which are further increased by the necessary fittings,
• Furthermore, only relatively small flow cross sections with limited cooling effect can be achieved with all these known grate elements, and
• Finally, the removable from the prior art go Suggestions to improve the supply of combustion air from the wrong, based on a prejudice idea, the cross section of the freedreamer must for the purpose of thorough clearance of the air passage opening fill the entire cross section of this opening.

It is therefore an object of the present invention to provide a grate element advantageously usable in large incinerators, which is characterized on the one hand by an uncomplicated, economical production and also ensures a uniform cooling water flow in a one-piece cast element uniform thermal stress on the grate element and thus its life significantly extended. The inventive solution now provides, in contrast to the prior art, a real - meandering - cooling water guide in which the cooling water is not vortexed in the first place, but is deliberately guided. In addition to be avoided by this special shape of the cooling water channel, the formation of air sacs in the deflection and corner areas and along the channel edges.

The erfindungemässe solution to this problem arises from the characterizing part of the independent claims. Preferred embodiments are defined in the dependent claims.

Thanks to the manufacture of the grate element according to the invention in one piece, it is ensured that virtually all of them are made

Make the grate element results in a practically constant coefficient of thermal expansion. In a preferred embodiment, the two are parallel, in In the opposite direction flowed through cooling water ducts by a front in the direction of material flow, ie frontal transition section larger flow cross-section; in this most exposed to the heat exposed front grate element section results in a maximum cooling effect and better ventilation.

1. 1. Der gegenüber den bekannten Rostausführungen extrem grosse Kühlwasser-Durchflussquerschnitt erlaubt höhere Durchflussmengen bei geringerem Druckverlust. Dies führt zu einem besseren Wärmeübergang und somit zu einer gleichmässigen Kühlung des gesamten Rostelementes. Lokale Überhitzungen werden dadurch vermieden.
2. 2. Die als Konsequenz der hohen Kühlleistung sich ergebende relativ niedrige Oberflächentemperatur des Rostelementes verhindert das unerwünschte Anbacken von Verbrennungsrückständen und bringt vor allem eine Verringerung des mechanischen Verschleisses mit sich. Von weiterem Vorteil ist ferner die wasserseitige Temperaturbelastbarkeit hinsichtlich einer Heisswasseranlage.
3. 3. Die spezielle Anordnung der von beiden Seiten in den Strömungsquerschnitt hineinragenden - bis über die Kanalachse hinausragenden und einen mäanderförmigen Strömungsweg bildenden - Umlenkorgane bringt es mit sich, dass die gesamte Kühlwasserströmung bereits nach wenigen Anlaufminuten absolut entlüftet ist und der Wärmeübergang gleichmässig auf der gesamten Innenwandung des Rostelementes erfolgt.
4. 4. Gemäss einer besonderen Ausführungsform der Erfindung sind die die Kühlwasserströmung umgrenzenden Wandungen überall praktisch gleich dick. Die hieraus resultierende gleichmässige Temperaturverteilung gewährleistet ein ausgezeichnetes Dehnungsverhalten in allen Temperaturbereichen, sowie eine gleichmässige Verteilung der auftretenden Wärmespannungen und übt gleichzeitig einen günstigen Einfluss auf die angestrebte Formstabilität des Rostelementes aus. Herstellungsbedingte Fehler werden dadurch in grösstmöglichem Masse ausgeschlossen.
5. 5. Bei der Ausbildung des Kühlkanals wurde ferner darauf geachtet, dass dieser bis auf die Übergangszone in allen Bereichen mindestens annähernd gleich hoch ist bzw. annähernd den gleichen Querschnitt aufweist. Dadurch können Strömungsverluste des Rostelementes verhältnismässig gering gehalten werden.

As a result of the inventive design of the grate element shows in the practical testing that the above-described aspects of the problem underlying the invention are optimally solved. In comparison to the known state of the art, the following improvements in the operating behavior of the grate elements are particularly significant:

1. 1. The compared to the known grate designs extremely large cooling water flow area allows higher flow rates with less pressure loss. This leads to a better heat transfer and thus to a uniform cooling of the entire grate element. Local overheating is avoided.
2. 2. The result of the high cooling capacity resulting relatively low surface temperature of the grate element prevents the unwanted caking of combustion residues and brings, above all, a reduction of mechanical wear with it. Another advantage is the water-side temperature capacity with respect to a hot water system.
3. 3. The special arrangement of the projecting from both sides in the flow cross-section - up beyond the channel axis and a meandering Flow path forming - Umlenkorgane entails that the entire cooling water flow is vented absolutely after a few minutes of startup and the heat transfer takes place uniformly on the entire inner wall of the grate element.
4. 4. According to a particular embodiment of the invention, the walls surrounding the cooling water flow are practically the same everywhere. The resulting uniform temperature distribution ensures excellent elongation behavior in all temperature ranges, as well as a uniform distribution of the thermal stresses occurring and at the same time exerts a favorable influence on the desired dimensional stability of the grate element. Manufacturing-related errors are thereby excluded to the greatest extent possible.
5. 5. In the formation of the cooling channel was also taken to ensure that this is at least approximately the same height or approximately the same cross-section in all areas except for the transition zone. As a result, flow losses of the grate element can be kept relatively low.

In this case, the two-part or multi-part design of the broaches, whereby the cross-sectional constriction is even more effectively counteracted during the clearing turns out to be particularly advantageous. Due to the only insignificantly reduced pressure loss during cleaning, the acceleration of the always approximately evenly exiting air is prevented. Furthermore, the reduction of the exit velocity reduces the entrainment of dust and unburned components into the flue gas stream, resulting in a reduction of unburned flue gas and fly ash.

• Fig. 1 eine Perspektivdarstellung einer Ausführungsform des erfindungsgemässen Rostelementes in einer Ansicht von unten, bei der die Kanalführung sichtbar gemacht wurde,
• Fig. 2 eine Ansicht des Rostelementes von oben,
• Fig.3 einen Horizontalschnitt des Rostelementes zur Veranschaulichung der Kühlwasserführung,
• Fig. 4 drei hintereinander angeordnete Rostelemente im Schnitt,
• Fig. 5 einen vereinfachten Seitenriss eines solchen Rostelementes.

For a better understanding of the inventive concept, the invention will be explained below with reference to the accompanying drawings with reference to an embodiment. Show it:

• Fig. 1 1 is a perspective view of an embodiment of the grate element according to the invention in a view from below, in which the channel guide has been made visible,
• Fig. 2 a view of the grate element from above,
• Figure 3 a horizontal section of the grate element to illustrate the cooling water flow,
• Fig. 4 three consecutively arranged grate elements in section,
• Fig. 5 a simplified side elevation of such a grate element.

The perspective view after Fig. 1 shows the designated in its entirety by 1, created as a monoblock casting grate element in a view from below, in which the grate element on one side on a arranged in the axis AA support 9 (FIG. Fig. 4 ) rests. The opposite side of the grate element has a plurality of supports 2, with which the grate element 1 in a known manner loosely slidably rests on the underlying.

In operation, ie in the installation position, the in Fig. 1 represented grate element 1 thus turned by 180 ° to imagine. In this operating position of the grate element then shows the view from above Fig. 2 a cooling water inlet opening 3 and a cooling water outlet opening 4, through which the cooling water flowing through the grate elements enters the grate element, absorbs heat within it and leaves it again. In particular Fig. 3 shows, the cooling water entering through the opening 3 flows through the grate element in two practically parallel channels K1, K2 in opposite directions. By an end-side transition zone Ü the two channels are interconnected. Strictly speaking, the currents are in the two Channels K1, K2 but anything but parallel: how Fig. 3 shows, the interior of the grate element is divided by a central web 5 and from this web as well as the opposite walls 6 and 7 protrude into the interior of the channels K1, K2 guiding and deflecting 8. These are in principle of approximately triangular cross section with generous rounded corners E ( Fig. 2 ). In this case, the length of the deflecting members 8 projecting from the walls 6 and 7 or from the central web 5 into the flow is, according to one embodiment, dimensioned such that they preferably extend at least from one of the walls 6, 7 or from the center web 5 via the channel axis BB (FIG. Figure 3 ) protrude.

In the preferred embodiment, which is in Fig. 3 is shown, all deflecting members 8 project with their free end portions on the axis B - B addition. How further Fig. 3 can be seen, the adjacent deflecting members 8 are offset in the direction of the axis B - B against each other, that a turbulence generating, meandering flow guide is created, which generates a highly turbulent flow over the entire channel cross-section, in which no bubble can hold more. Due to the flow thus generated, the interior of the grate element 1 is thus constantly vented effectively. This applies in particular to the transition region Ü, which is known to be particularly prone to the formation of local and stationary air bubbles.

The deflecting members 8 may be formed by the skilled person with any, practice-oriented cross-sectional shapes. A preferred cross-section is that of the equilateral triangle, but for example semicircular, elliptical and quadrangular cross-sections are also possible. In contrast to the well-known, in the flow of the cooling channel projecting turbulence-generating elements here have the deflecting 8 the main task to form a targeted guided, preferably meandering cooling water channel in which the formation of unwanted air bubbles can be avoided with certainty.

Of particular importance is the efficient cooling of the grate element in the transition region Ü, since it is exposed to the greatest heat. With the front part of the grate element yes, the fuel is transported over the grate and pushed into the furnace. Due to the oscillating movement of the grate elements, the front surface, the frontal radius and more than 5% of the adjoining grate surface are temporarily and partially subject to a particularly high thermal load over the entire grate. The safe cooling of these surfaces is therefore of the utmost importance. Due to the design of the grate element according to the invention, this has been ensured by the fact that neither a web nor any other material accumulation is arranged in this particularly loaded zone and the risk of cracking is thus already greatly reduced. Rather, the connecting cooling channel Ü in the transition zone is constructed so that the frontal surface and the overlying radius on the one hand completely vented and also completely filled with water. The walls are all the same thickness in this area, so that the heat transfer into the cooling medium can take place completely and evenly. The same applies to the surface of the grate element adjoining the radius.

In order to achieve a particularly effective cooling effect on the frontal surface of the grate element, has the Transition region Ü an optimized cross-section on. According to a preferred embodiment, the cross section of this transitional region Ü is at least 1.5 times that of each individual cooling channel K1, K2.

As tests have shown, even after the initial filling of the water-flowed cooling channels K1, K2, complete deaeration results after a few minutes.

The triangular deflecting members 8 may have, for example, in their free end portion an angle of 20 to 40 °, preferably 30 °.

In order to expose the grate element in view of the high demands on service life and optimal combustion of a uniform thermal load as possible, the walls delimiting the cooling channels, as already mentioned, of the same, or approximately the same, thickness. In addition, care was taken in the formation of the cooling channel that, with the exception of the transition zone in all areas at least approximately the same height, or has approximately the same cross-section. In this way, flow losses of the grate element can be kept relatively low.

In the production, the grate element described can advantageously be cast in one pass. This ensures that the coefficient of thermal expansion is the same throughout the element at all points. This feature now, in combination with the approximately constant wall thickness, that the heat-related expansion of the grate element is uniformly distributed over the entire grate element. Heat-induced stresses are thus practically excluded.

Fig. 4 shows three successively arranged grate elements 1a, 1b, 1c, which are respectively supported on rod-shaped support 9. The cooling water passes via supply lines 10 in the grate elements and is discharged on the opposite side again. Every second row of grate elements, in this case the row of grate elements 1b, is movably mounted and subjected to a periodical reciprocating motion by means of a drive, by means of which, on the one hand, a scouring effect and, on the other hand, a cleaning effect is achieved. The upper element glides with the in Fig. 1 with 2 designated supports on the underlying element.

In Fig. 5 such a locking element is shown in side elevation.

Thanks to the described construction of the grate element, the same is preferably poured as a single casting in a single pass.

Claims (11)

1. Water-cooled grate element made of cast steel for solids incineration plants which are equipped with combustion grates and have a large number of grate elements (1, 1a, 1b, 1c) disposed behind and beside one another, wherein, with a view to the necessary cooling, each grate element is subdivided, directly below the total-combustion surface carrying the material for combustion, into two cooling channels which are practically parallel and are connected to a water inlet (3) and a water outlet (4) respectively, and through which the cooling water flows in mutually opposed directions, characterised in that each of the two cooling channels is provided with deflecting components (8) which protrude into the cross-section of the channel from mutually opposed sides of the latter in an axially offset manner, and also that the cooling channels are constructed, by a suitable disposition of the deflecting components (8), as meander-shaped water-conducting channels (K1, K2) and transition from one water-conducting channel to the other takes place via an overflow section (Ü) which extends transversely to the central axis of the two water-conducting channels and is devoid of deflecting components and which extends over practically the entire end-face width of the grate element.
2. Grate element according to claim 1, characterised in that the end-face overflow section (Ü), which connects the two water-conducting channels (K1, K2) and lies at the front in the direction of the flow of material, has a larger cross-section of passage than each of the two water-conducting channels, in order to thereby also achieve the greatest possible cooling action in this zone which is exposed to the maximum effect of heat.
3. Grate element according to claim 2, characterised in that the overflow section (Ü) has at least one and a half times the cross-section of each of the two water-conducting channels (K1, K2).
4. Grate element according to one of claims 1 to 3, characterised in that the deflecting components (8) protrude, with their rounded-off, free end sections, beyond the central axes (B-B) of the water-conducting channels (K1, K2).
5. Grate element according to one of claims 1 to 4, characterised in that the cross-section of through-flow of the two water-conducting channels (K1, K2) is at least approximately constant, with a view to obtaining the most uniform possible thermal stressing, over their entire length, of the walls that delimit the channel.
6. Grate element according to one of claims 1 to 5, characterised in that the deflecting components (8) have, at least approximately, the cross-section of isosceles triangles, semicircles, ellipses or quadrangles.
7. Grate element according to claim 6, characterised in that those end sections of the triangular deflecting components (8) which protrude into the cooling channel have an angle of 20 to 40°, preferably 30°.
8. Grate element according to one of claims 1 to 7, characterised in that the plurality of walls that delimit the through-flow of cooling water have at least approximately the same wall thickness for the purpose of achieving a uniform thermal loading.
9. Grate element according to one of claims 1 to 8, characterised in that, with the exception of the overflow section (Ü), the water-conducting channels (K1, K2) are at least approximately the same height over their entire length in order to thereby keep the flow losses within the grate element small.
10. Grate element according to one of claims 1 to 9, characterised in that, for the purpose of avoiding the formation of air pockets and achieving optimum ventilation within the cross-section of through-flow, any rectangular or sharp-edged deflecting zones are made safe by large-scale rounding-off.
11. Process for manufacturing a grate element according to one or more of the preceding claims, characterised in that the entire grate element is cast in one pass.

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