EP1801499B1

EP1801499B1 - Combustion grate for solid fuels

Info

Publication number: EP1801499B1
Application number: EP05425910A
Authority: EP
Inventors: Daniele De Lodovici
Original assignee: Wte Waste To Energy Srl
Current assignee: Wte Waste To Energy Srl
Priority date: 2005-12-23
Filing date: 2005-12-23
Publication date: 2009-04-29
Anticipated expiration: 2025-12-23
Also published as: ATE430288T1; DK1801499T3; EP1801499A1; DE602005014256D1

Abstract

The present invention relates to a combustion grate (1) for solid combustible materials, comprising fixed supporting elements (2b) and movable supporting elements (2a). According to the present invention, the supporting elements (2a, 2b) are each constituted by a beam-shaped element. Each beam-shaped element (2a, 2b) supports a plurality of fire bars (3) arranged side-by-side along its length, and can be crossed by a system for cooling the fire bars.

Description

The present invention relates to a combustion grate for solid fuels, particularly suitable for the combustion of municipal solid waste, refuse-derived fuel, biomasses, fossil fuels in general, and the like.
The type of combustion grate according to the present invention is particularly suitable in incineration ovens and particularly in the field of the waste-to-energy conversion of the solid fuels cited above.
Every incineration plant has a region where combustion occurs. The combustible material is usually introduced in the combustion chamber of the plant by gravity from above. The combustion material then falls onto the combustion grate, where a "mat" of combustible material forms. In order to produce a uniform layer of combustible material along the grate, such grate can be inclined with respect to the horizontal direction with a certain inclination, so as to prevent the combustion material from piling up proximate to the region where it is introduced by gravity, producing the gravity descent of the combustion material, which is thus distributed more evenly along the entire length of the combustion grate.
In the chamber, the combustion of the solid combustible material occurs continuously by spontaneous combustion. Part of the comburent (usually air) is sent to the region below the combustion grate and, by passing through it, feeds the combustion of the overlying material.
The combustion grates suitable for this purpose comprise a series of fire bars, elements which are suitable to withstand the high temperatures reached on the surface of the combustion grate. Such fire bars cover the structure of the grate and constitute the supporting surface of the combustion material. Said supporting surface is provided by arranging a plurality of elements side by side. In this manner it is also possible to replace elements compromised by the thermal stress. The more superficial portion of material of the bed, by being more exposed to the flame, bums at higher temperatures, while the underlying layers remain at lower temperatures, making the combustion process uneven. In order to homogenize the layer of material, improve its distribution and make it advance, the grates are generally constituted by rows of alternately fixed and movable fire bars, so that it is possible to optimize the combustion process of the material.
Therefore, combustion grates are complex systems, which must meet several requirements, including the need to allow the flow of comburent through the bed of combustible material and to remix and redistribute continuously the material that undergoes the combustion process.
The combustion grate reaches very high operating temperatures, and therefore it is necessary to provide a system for cooling the elements that compose it, especially the fire bars, which are the parts subjected to the most intense thermal stresses.
The combustion grates are in fact subject to corrosion caused by high temperatures. In order to solve these problems, air- and water-based cooling systems have been devised. In practice, it has been found that traditional air cooling achieves inferior results with respect to water cooling.
The limitation of water-cooled grates is the considerable plant complexity of the cooling systems and the fact that since there are no alternative cooling systems, a failure of the liquid cooling system compromises the operation of the entire grate. As regards the complexity of liquid cooling systems, it has to be considered that the heat conveying liquid must flow through each individual fire bar and that the entire system must therefore have appropriate connectors which are adapted to avoid hindering the relative motion of the rows of movable fire bars with respect to the rows of fixed fire bars. Feeding the coolant to the fire bars, when working in a particularly hostile environment, is particularly delicate.
A combination of features as set forth in the pre-characterizing portion of the appended claim 1 is disclosed for example in BE 420 333 .
The aim of the present invention is to provide a new type of combustion grate which solves or at least reduces the drawbacks that affect the background art.
Within this aim, an object of the present invention is to provide a new type of combustion grate, which while allowing to stir effectively the combustible material deposited thereon uses a particularly simple cooling system.
Another object of the present invention is to optimize the cooling of the elements that compose the grate, particularly the fire bars.
Another object of the present invention is to provide a new type of combustion grate which can be liquid- and air-cooled effectively, i.e., so that the two cooling systems are independent from each other, so as to allow operation even without one of the two cooling fluids.
Another object of the present invention is to provide a combustion grate which is capable of optimizing the uniformity of the combustion along the grate.
In accordance with the invention, there is provided a combustion grate for solid combustible materials, as defined in the appended claims.
Further characteristics and advantages of the present invention will become better apparent from the following detailed description, given by way of nonlimiting example and illustrated in the accompanying figures, which exemplify a possible embodiment, wherein:

Figure 1 is a schematic sectional side view of the combustion grate, illustrating the supporting structure and the corresponding fire bars, the movable fire bars being in a retracted position;
Figure 2 is the same sectional side view as Figure 1, wherein the movable fire bars of the combustion grate are in a forward position;
Figure 3 is the same side view as in Figures 1 and 2, wherein the movable fire bars are in a full-forward position, which allows to disassemble said fire bars from the combustion grate;
Figure 4 is a transverse sectional side view of a fire bar with which the combustion grate according to the present invention is provided;
Figure 5 is a sectional view, taken along the horizontal plane E-E, of the fire bar of Figure 4;
Figure 6 is a sectional view, taken along the vertical plane A-A, of the fire bar of Figure 4;
Figure 7 is a sectional view, taken along the horizontal plane H-H, of the fire bar of Figure 4.

With reference to the figures, a possible embodiment of the combustion grate 1 according to the present invention comprises a supporting structure, generally designated by the reference numeral 2, which comprises a plurality of movable and fixed supporting elements 2a and 2b.
The movable supporting elements 2a can perform a translational motion because they are mounted on a structure, for example of the carriage type, which is provided with suitable movement means.
Each movable supporting element 2a is arranged laterally adjacent at least to a fixed supporting element 2b and is restrained by the presence of the fixed supporting element 2b so as to perform a translational motion parallel thereto.
With reference to the structure shown in Figure 1, for example, it can be seen that the repetitiveness of the modular structure of the grate entails that each movable element 2a is flanked by two fixed elements 2b, so that the movable elements 2a are restrained so as to perform a translational motion parallel to the two adjacent fixed elements 2b.
According to the present invention, the supporting elements 2a and 2b are constituted by beams. Said beams 2a, 2b may have any cross-section and can for example have a rectangular cross-section, according to what is shown in the accompanying figures.
Again with reference to Figures 1 to 3, a fire bar, designated by the reference numeral 3, is mounted on each supporting element 2a, 2b. The fire bars 3 arranged so as to cover the supporting elements 2a, 2b are, as mentioned, in contact with the combustible material, by generically constituting the supporting surface of said material.
The fire bars 3 can be of the same type, both when they are mounted on the movable supporting elements 2a and when they are mounted on the fixed supporting elements 2b. For the sake of convenience in description, the fire bars also have been designated as movable fire bars 3a and fixed fire bars 3b, depending on whether they are fitted respectively on a movable supporting element 2a or a fixed supporting element 2b.
Each supporting element 2a, 2b supports a plurality of fire bars arranged side-by-side, so that the fire bars are substantially mutually parallel along a same beam.
In the combustion grate 1 according to the present invention, said supporting beams are crossed by a fluid-based cooling system. In particular, the structure might provide that only the fixed supporting beams 2b be crossed by the liquid cooling system.
The cooling system allows to cool the fixed fire bars 3b which are in contact with the fixed beam 2b, since said beam is crossed by the cooling fluid, which can be constituted for example simply by water or by other liquids. The cooling system that passes through the beams 2b can be constituted for example simply by pipes capable of allowing heat exchange. The cooling of the movable fire bars 3a, if only the fixed beams 2b are cooled, occurs indirectly due to the proximity of the movable fire bars with respect to the fixed supporting beams 2b crossed by the liquid cooling system.
According to another aspect of the present invention, the fire bars, which may for example have the configuration shown in Figure 4, are constituted by a main body 4, having a lower surface 6 which is shaped conveniently for the contact of said fire bar against the supporting beam 2. In particular, in the embodiment described by way of example in the accompanying figures, the lower supporting surface 6 of the fire bar has a profile which is adapted to rest against the supporting beam 2 having a rectangular cross-section. Such lower supporting surface 6 therefore has a substantially rectilinear portion 6c, which is adapted to rest against the upper surface 21 of the supporting bar 2.
Two portions 6a and 6b, which are substantially perpendicular to the supporting surface 6c, by abutting against the lateral surfaces respectively 22 and 23 of said beam 2, allow to stabilize the contact of the fire bar 3 against the beam 2. Of course, different configurations of the cross-section of the beam 2 might be matched by different configurations of the lower supporting surface 6 of the fire bar 3.
The external surfaces of the fire bar 3 might be substantially flat, like the upper surface 7 and the lower end surface 8, so as to facilitate the relative translational motion of the movable fire bars 3 with respect to the fixed fire bars that are adjacent thereto.
The fire bars 3 can be crossed advantageously by one or more means adapted to convey the combustion air that arrives from the region below the grate. In particular, said air conveyance means can be constituted, for example, by one or more grooves or guides which cross the fire bars, as shown in Figures 4 to 7. In particular, Figures 6 and 7 show that said grooves or guides 5 run across the entire length of the fire bar 3.
With reference to Figure 4, the fire bar 3 has a rear region 10 and a front region 11, where the front part of the fire bar is defined as the part that faces toward the outside of the combustion grate, i.e., toward the combustible material. The front part 11 of the fire bar 3 is conveniently spoon-shaped so as to contain the combustion ash.
Moreover, the fire bars 3 can be provided with protrusions 12, 13, which are arranged at the upper surface 7, are variously shaped and are adapted to engage corresponding recesses 14, 15 provided at the lower end surface 8 of the adjacent fire bar. These coupling means allow to engage each fire bar with the fire bars that are adjacent thereto in order to vary, with their relative position, the load loss of the air that flows through them.
With particular reference to Figure 3, the stroke limit of the movement means that support the movable beams 2a may allow to move the movable fire bars 3a forward enough to disengage them from the adjacent fixed fire bars 3b. This allows, if necessary, to remove the fire bars, both the fixed ones and the movable ones, which need to be replaced. Likewise, they can be retracted in order to allow the disassembly of the fixed fire bars.
Operation of the combustion grate 1 according to the present invention can be illustrated as follows.
As described up to now with reference to a preferred embodiment of the combustion grate according to the present invention, said grate comprises rows of fire bars 3b and 3a, which are respectively fixed and movable, since they rest on beam-shaped supporting elements 2a and 2b, which are respectively movable and fixed. Each movable supporting element 2a is mounted on a carriage, which allows its advancement and retraction substantially along a straight line with respect to the fixed beam-shaped supporting element 2b, and fixed and movable beams are alternated.
The relative movement of the fire bars allows to stir the combustion material, achieving even distribution of said material in the various points of the grate as well as continuous recirculation of the material that lies at the top of the bed of material with the material that is in contact with the fire bars of the combustion grate.
The fixed supporting elements 2b are provided conveniently with a cooling system which is adapted to convey a heat conveying fluid. The passage of the cooling fluid within the fixed supporting elements 2b contributes to the cooling mainly by conduction of the fixed fire bars 3b and movable fire bars 3a which rest thereon. The movable supporting element 2a which supports the movable fire bars 3a might not be crossed by the cooling fluid, thus simplifying considerably the cooling system and eliminating any possible hindrance to the movement of the carriage which constitutes the movable part of the supporting structure. In this case, when the movable fire bars 3a are in the more retracted position shown in Figure 2, each movable fire bar 3a is substantially laterally adjacent to an adjacent fixed beam 2b. The proximity of the movable fire bar 3a with respect to the adjacent fixed supporting element 2b allows to also cool said movable fire bar 3a by convection/conduction, even if each movable supporting element 2a is not crossed by the cooling fluid.
According to what has been described earlier, the air conveyance or guiding means 5 provided inside each fire bar 3 contribute to the cooling of the fire bars. The combustion air in fact passes through the grate in order to reach the upper region of the grate, where the bed of combustion material is burning. The combustion air reaches the combustion area of the material by utilizing passages which are provided appropriately between one fire bar and the other, as shown for example in Figure 1. However, by also being conveyed into the grooves or guides 5 for the conveyance of the air which are provided inside each fire bar, such combustion air also performs a cooling function, helping to reduce the temperature of the fire bars.
The possibility to convey inside the fire bars part of the air designed to feed combustion allows to further cool the fire bars. If air cooling is associated with the water cooling described above, if water cooling is interrupted due to breakage or to a technical fault, the described air flow alone would still ensure a good cooling of the elements of the combustion grate that are most intensely subjected to thermal stresses.
The described configuration for the fire bars allows to meet a further requirement, which is constituted by control of load losses through the grate. The combustion material arranged on the grate in fact inevitably causes resistance to the flow of combustion air. By way of a higher load loss of the air that passes through the grate, it is possible to better control, and therefore optimize, the distribution of the combustion air. A high load loss of the grate when empty in fact allows to reduce the influence that the bed of combustible material, arranged above the grate and generally uneven, has on the distribution of the air.
The overlap of the fire bars which are mutually engaged by way of the coupling means constituted by the protrusions 12, 13 and by the recesses 14, 15 forms a hindrance to the flow of the air, which is consequently forced to pass through the grate only through the regions provided specifically for this purpose between the fire bars. The reduced cross-section provided for the flow of the combustion air entails a high value of the load losses through the grate when empty, i.e., without considering the load losses caused by the presence of the combustion material. Moreover, the passage section of the air can vary depending on the position of the movable fire bar with respect to the fixed adjacent ones. Accordingly, it is possible to change from the outside, by modifying the stroke limit positions of the movable fire bars 3a, the load loss imposed on the combustion air in passing through the grate. Therefore, by controlling and, if necessary, increasing the value of the load loss associated with the grate, it is possible to achieve a more even distribution of the combustion air and therefore, ultimately, a more even process of combustion of the material.
It has thus been shown that the present combustion grate achieves the intended aim and objects. In particular, a new type of combustion grate has been described which allows to optimize the cooling of the elements, i.e., of the fire bars, of the grate which constitute the supporting surface of the combustible material.
Moreover, the combustion grate according to the present invention achieves this aim by means of a cooling system which is considerably simplified with respect to those currently used in the field, leading to savings in execution, assembly and maintenance of said combustion grate.
Moreover, the present combustion grate allows to improve the uniformity of the combustion process along the entire grate thanks to the possibility to control load losses for the combustion air which passes through the grate.
Numerous modifications may be performed by the person skilled in the art without abandoning the scope of the protection of the present invention.
Therefore, the scope of the protection of the claims must not be construed as being limited by the illustrations or by the preferred embodiments shown by way of example in the description, but rather the claims must comprise all the characteristics of patentable novelty that can be deduced from the present invention, including all the characteristics that would be treated as equivalent by the person skilled in the art.
Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

A combustion grate (1) for solid combustible materials, comprising a supporting structure (2) adapted to support a plurality of fire bars (3), which form a surface for supporting said combustible material, said supporting structure (2) comprising fixed supporting elements (2b) and movable supporting elements (2a) connected to movement means, said fixed supporting elements (2b) and said movable supporting elements (2a) being arranged so as to be mutually alternated, said movable and fixed supporting elements (2a, 2b) being each constituted by at least one beam-shaped element, each beam-shaped element (2a, 2b) being capable of supporting a plurality of fire bars (3) arranged side-by-side along its length, said combustion grate being characterized in that at least said fixed supporting element (2b) comprise fluid-based cooling means, and the cooling of said movable fire bars (3a) occuring by convection and conduction due to the vicinity of said movable fire bar (3a) to said fixed supporting element (2b) when said movable fire bar (3a) is in the retracted position.
The combustion grate (1) according to claim 1, characterized in that said pluralities of fire bars (3) arranged on each beam-shaped element (2) are also respectively fixed (3b) and movable (3a) with said supporting elements (2a, 2b), so that each fixed fire bar (3b) is adjacent to at least one movable fire bar (3a).
The combustion grate (1) according to claim 1, characterized in that the cooling of said fixed fire bars (3b) occurs substantially due to the contact of said fixed fire bar (3b) with said fixed supporting element (2b).
The combustion grate (1) according to any one of the preceding claims, characterized in that said movable supporting elements (2a) can move with respect to said fixed supporting elements (2b) with a substantially rectilinear alternating translational motion.
The combustion grate according to any one of the preceding claims, characterized in that said fire bars are air-cooled by the combustion air.
The combustion grate according to any one of the preceding claims, characterized in that said fire bars (3) comprise air conveyance means (5).
The combustion grate according to claim 6, characterized in that said air conveyance means (5) cross said fire bar (3) along its entire length.
The combustion grate according to claim 6 or 7, characterized in that said air conveyance means (5) are constituted by grooves formed within the body of said fire bar (3).
The combustion grate according to any one of the preceding claims, characterized in that said fire bars (3) further comprise coupling means which are adapted to engage each fire bar with the fire bars that are adjacent thereto.
The combustion grate according to claim 9, characterized in that said coupling means comprise protrusions (12, 13) which are arranged at the upper surface (7) of each one of said fire bars (3) and are adapted to engage corresponding recesses (14, 15) provided at the lower end surface (8) of said fire bars.
The combustion grate according to any one of the preceding claims, characterized in that passage ports for the combustion air which reaches said combustion material are provided between said fixed fire bars (3b) and said adjacent movable fire bars (3a).
The combustion grate according to claim 11, characterized in that the breadth of said passage ports for the combustion air can be adjusted by adjusting the stroke of said movable fire bars (3a), thus allowing to adjust the load loss of the air through the combustion grate.