WATER-COOLED GRATE FOR A COMBUSTION FURNACE

Abstract: A grate device (1) for a combustion furnace comprises a grate element (2) and a turnable shaft assembly (3) connected thereto. The grate element (2) has a first system of ducts (17.1) for circulating coolant through the grate element (2). The shaft assembly (3) has a second system of ducts (17.2), which communicates with the first system of ducts and forms a coolant inlet and outlet (14, 16). The grate element (2) comprises a girder means (6) which is non-rotatably connected with the shaft assembly (3) and which contains a part of the first system of ducts (17.1), which part communicates with the second system of ducts (17.2). The grate element (2) comprises a plate means (5) which is mounted on the girder means (6) and forms a grate area and through which the remaining part (7) of the first system of ducts extends for cooling the grate area.

Description: ater-Cooled Grate for a Combustion Furnace. The present invention relates to a grate device for a combustion furnace, said device comprising a grate element and a turnable shaft assembly connected thereto. Such devices are already known, for instance, from US-A-4 , 981, 090. In these devices, use is made of slots between the individual grate elements, on which material intended for combustion is placed, for supplying primary air for the combustion. To make the supply of primary air as uniform as possible, it is important for said slots not to change size when the grate elements pivot in relation to each other or due to wear. Wear is caused by abrasive wear by the material which is burnt, this wear being further increased if the surface temperature of a grate element is approaching the point of softening of the grate material because of the combustion heat. In view of this, it would be desirable to provide a grate device, in which the temperature of the grate elements is always kept at such a low level that the risk of excessive abrasive wear is eliminated. One way of achieving this is to provide the grate elements with coolant ducts, through which water, for instance, is passed for cooling of the elements to an acceptable temperature level. The problem of such cooling is the actual supply of coolant, which is rendered more difficult by the fact that the grate elements have to be pivotable for construction reasons. An obvious solution could be to supply the coolant by means of flexible tubes, which are directly connected to the grate elements and follow their movement. Because of the above-mentioned slots between the individual grate elements, it is not, however, possible to eliminate the risk of heated combustion material and especially melted metal or glass passing such a slot when refuse is being burnt and damaging a coolant tube connected under a grate element. Thus it will be understood that a solution involving flexible tubes, which are arranged in a combustion chamber, is not satisfactory. A grate device without such flexible tubes under the grate element is disclosed in US-A-4 , 596 , 233. However, in this device, which is considered to be the closest prior art, parts of the grate element, that is a great number of grate bars, on which the actual combustion takes place, are not included in a coolant coil. This is a dis- advantage to the service life of the grate element, since a high grate temperature causes great erosion of the grate bars. In addition, a high grate temperature, naturally, also implies that the material selected for the grate element should satisfy strict requirements. For this reason, cast grate bars made of high-grade steel are predominant today. In view of this, an object of the present invention is to provide a new solution for the supply of coolant to grate elements which are cooled by a coolant and which are of the type mentioned by way of introduction, said solution being distinguished by being very reliable and contributing to an increased service life of the grate elements. Moreover, the solution according to the invention should be easy to implement and require less in terms of material selection than the above-mentioned grate bars. This object is achieved by means of a grate device for a combustion furnace, said device comprising a grate element and a turnable shaft assembly connected thereto, the grate element having a first system of ducts for circulating coolant through the grate element, the shaft assembly having a second system of ducts, which communicates with the first system of ducts and forms a coolant inlet and outlet, and the grate element comprising a girder means which is non-rotatably connected with the shaft assembly, said device being characterised in that the girder means contains a part of the first system of ducts, which part communicates with the second system of ducts, and that the grate element comprises a plate means, which is mounted on the girder means and forms a grate area and through which the remaining part of the first system of ducts extends for cooling the grate area. By means of the inventive cooling by the coolant in the entire grate element, it is possible to increase the service life of the element and avoid the conventional structure of grate elements comprising a plurality of re- placeable grate bars. At the same time, the use of the inventive plate means, which covers a larger surface than an ordinary grate bar, results in only a few connections being needed for the first system of ducts between the girder means and the plate means. It will be understood that all this taken together makes it possible to produce an inventive grate device which is both cheaper and better than the prior-art solutions. In the device according to the invention, the second system of ducts is preferably a feeding and a return con- duit, of which at least one is formed of an inner pipe which is concentric with the axis of the shaft assembly. The advantage of this solution is that it is very easy to implement. In this solution, the other of the feeding and the return conduit is suitably formed of an outer pipe on the outside of the inner pipe. Preferably, the outer pipe comprises an end portion which is non-rotatably connected with the grate element and through which lateral ducts extend, which communicate with the feeding and the return conduit and which form the connection of the second system of ducts with the first system of ducts. It will be understood that an end portion formed in this manner considerably facilitates the interconnection of the different systems of ducts as well as the non-rotary connection of the shaft assembly with the grate element. The part of the girder means in the first system of ducts can be formed of two separate chambers in the gir- der means, or pipes which are laid in or cast into the girder means. Whatever solution may be selected, this part of the system of ducts is well protected and allows a simple connection to the shaft assembly. According to one embodiment, the inlet and/or outlet of the shaft assembly can be connected to an outer cooling coil by means of a rotary connection. However, the inlet and/or outlet of the shaft assembly is/are preferably connected to the outer cooling coil by means of a flexible tube. Since the rotary connection or the tube does not, thanks to the invention, need to be arranged directly under the combustion chamber, thus avoiding the high temperatures present in the same, it will be understood that also such simple construction elements as flexible tubes very well can be used when the shaft assembly only needs to perform a limited turning movement to pivot the associated grate element. Below, preferred embodiments of the invention will be described in more detail with reference to the accom- panying drawings, in which: Fig. 1 is a longitudinal cross-sectional view showing a part of an inventive grate device from the side; Fig. 2 is a longitudinal cross-sectional view showing an alternative connection means from the side; Fig. 3 is an end view along the line A-A in Fig. 1 indicating some details by dashed lines; Fig. 4 is a cross-sectional view, along the line E-E in Fig. 1, of the girder means in section; Fig. 5 is a cross-sectional view of the girder means along the line B-B, schematically showing a grate plate element arranged on the same; Fig. 6 is a view corresponding to Fig. 1 and showing an alternative embodiment; Fig. 7 is an end view along the line A-A in Fig. 6, indicating some details by dashed lines; Fig. 8 is a view corresponding to Fig. 5 along the line B-B in Fig. 6; Fig. 9 is a view corresponding to Fig. 1 and showing a third embodiment of the invention; Fig. 10 is an end view along the line A-A in Fig. 9 indicating some concealed details by dashed lines; Fig. 11 is a view corresponding to Fig. 5 along the line B-B in Fig. 9 ; Fig. 12 is a cross-sectional view of several co- acting grate elements according to Fig. 11; and Fig. 13 is an end view illustrating how an outer cooling coil can be connected to the inventive grate device . The grate device 1 in Fig. 1 comprises a grate element 2 and a turnable shaft assembly 3 connected thereto and constitutes a part of a combustion furnace having a combustion chamber 4. In this chamber 4, refuse, for instance, can be burnt by supplying combustion air both from the underside (primary air) and from above (secondary air) . To produce better conditions for the grate element 2 during combustion, it comprises according to the invention at least one plate element 5, which is pivotably supported by a girder means 6. Naturally, a plurality of plate means 5 can be arranged on the girder means 6. In the plate element 5, there is a tubular coil 7, which is connected to a chamber 10 in the girder means 6 by means of connecting pipes, of which only the pipe 8 is shown in Fig. 1, and an aperture 9 communicating with the pipe 8. Finally, at the end facing the shaft assembly 3 the girder means 6 has an aperture 11, which communicates with the chamber 10. The shaft assembly 3 is arranged outside the combustion chamber 4 and thus not exposed to the high temperatures which may occur therein. The shaft assembly comprises a central inner pipe 12, which is enclosed by an outer pipe 13. At its end facing away from the girder means, the inner pipe 12 forms an inlet 14 for cooling water, and a space 15 between the inner pipe 12 and the outer pipe 13 forms an outlet 16 for cooling water. The inlet 14 and the outlet 16 are connected with the girder means 6 through separate lateral ducts 18, 19, which are indicated in Fig. 1 by dashed lines and which are formed in an end portion 20 of the shaft assembly 3. In Fig. 1, the shaft assembly 3 is connected with a rotary connection 21, which allows the coupling of the inlet 14 and the outlet 16 to an outer cooling coil which is generally designated 22. Alternatively, it is, how- ever, also possible to use a tube coupling 23, of the type shown in Fig. 2, instead of the rotary connection. Fig. 3 shows the end portion 20 of the shaft assembly 3 seen from the combustion chamber 4, some concealed details being indicated by dashed lines. In Fig. 3, it is possible to clearly distinguish the inner pipe 12, the outer pipe 13, the space 15 between the pipes and said lateral ducts 18, 19. Fig. 4 shows the girder means 6 with the duct 10 formed therein and the aperture 11 communicating with the lateral duct 18 of the shaft assembly 3. Moreover, this figure shows the second chamber 24 of the girder means 6 and its aperture 25 communicating with the lateral duct 19 of the shaft assembly 3. Fig. 5 illustrates the grate element 2, the girder means 6 being shown in cross-section and the plate element 5 supported by the same in a schematic view. It clearly appears from the figure that the chambers 10, 24 of the girder means 6 are connected to the tubular coil 7 in the plate element 5 by means of pipe bends 26, 27 and connecting pipes 8, 28. It is apparent from the above description that it is possible with the aid of the structure illustrated in the drawing to feed the tubular coil 7 included in the first system of ducts 17.1 with cooling water from an outer source, such as said outer cooling coil 22, by means of a second system of ducts 17.2, which is formed of the shaft assembly 3 and comprises a cooling water inlet 14 and a cooling water outlet 16, and a first system of ducts 17.1, which is formed of the grate element 2, thereby lowering the temperature of the grate element 2 to a level which is acceptable in long-time operation. Figs 6, 7, and 8 show a grate device 1 which to a great extent corresponds to the one shown in Figs 1, 3, 4 and 5. Therefore corresponding reference numerals are used and only the differences in relation to the above embodiment are described. In the grate device in Figs 6- 8, the girder means 6, instead of the chambers 10, 24, comprises pipes 29, 30 which are laid in borings 31, 32 in the upper portion 33 of the girder means 6 but which could also be cast into the same. The pipes 29, 30 are used directly for the transition to the lateral ducts 18, 19 of the shaft assembly 6, which according to Fig. 7 also end at a somewhat greater distance from each other than in Fig. 3, due to the fact that the pipes 29, 30 are placed at a greater distance from each other than the apertures 11, 25 of the chambers 10, 24. Figs 9, 10 and 11 show a further grate device 1, which to a great extent corresponds to the one shown in Figs 1, 3, 4 and 5. Therefore, also in this case, use is made of corresponding reference numerals and only the differences in relation to the embodiment which was first described are stated. In the grate device in Figs 9-11, the girder means 6, instead of the chambers 10, 24, comprises pipes 34, 35 which are laid in grooves 36, 37 in the upper portion 38 of the girder means 6. The pipes 34, 35 are used directly for the transition to the lateral ducts 18, 19 of the shaft assembly 3, which also, according to Fig. 10, end at a somewhat greater distance from each other than in Fig. 3, due to the fact that the pipes 34, 35 are placed at a greater distance from each other than the apertures 11, 25 of the chambers 10, 24. Fig. 12 illustrates, by means of a plurality of grate elements 2 according to Figs 9-11, how the grate elements 2 are intended to co-operate. It is apparent from the figure that the grate elements 2 are pivotable in a limited manner in opposite directions, thereby displacing the material (not shown) which is placed on the grate elements 2 and intended for combustion. It will be understood that such a limited pivoting does not require the use of a relatively expensive and sensitive rotary connection, a tube coupling 23 of the type shown in Fig. 2 therefore being perfectly usable. Fig. 13 shows a possible arrangement with a tube coupling 23 according to Fig. 2, seen from the inlet and outlet end of the shaft assembly 3. It clearly appears from this figure how tubes 39, which are connected to a plurality of inventive grate devices, take different positions according to the pivoting position of the associ- ated grate device (cf . Fig. 12) . It also clearly appears from the figure how the connection to the above-mentioned outer cooling coil 22 can be designed. It will be understood that the invention can be modified in various ways within the scope of the claims. Thus it is applicable also to grate elements of another type than the one illustrated herein, i.e. for example to different types of plate-shaped grate elements, such as cast or welded grate elements divided into several units and connected in series or in parallel. Furthermore, it will be understood that the inlet and the outlet of the shaft assembly can be arranged on each side of a grate element seen in the axial direction, the inlet suitably being formed of an inner pipe in the shaft assembly on one side of the grate element and the outlet suitably be- ing formed of an inner pipe in the shaft assembly on the other side of the grate element. Finally, it will be understood that normally a great number of inventive grate devices, which can co-operate, for instance, as the grate devices according to said US A-4,981,090, are mounted together in a combustion furnace.

Claims: CLAIMS 1. A grate device for a combustion furnace, said device comprising a grate element (2) and a turnable shaft assembly (3) connected thereto, the grate element (2) having a first system of ducts (17.1) for circulating coolant through the grate element (2), the shaft assembly (3) having a second system of ducts (17.2), which commu- nicates with the first system of ducts and forms a coolant inlet and outlet (14, 16), and the grate element (2) comprising a girder means (6) which is non-rotatably connected with the shaft assembly (3), c h a r a c t e r i s e d in that the girder means (6) contains a part of the first system of ducts (17.1), which part communicates with the second system of ducts (17.2) , and that the grate element (2) comprises a plate means (5) , which is mounted on the girder means (6) and forms a grate area and through which the remaining part (7) of the first system of ducts extends for cooling the grate area. 2. A device according to claim 1, c h a r a c t e r i s e d in that the second system of ducts (17.2) comprises a feeding and a return conduit, of which at least one is formed of an inner pipe (12) which is concentric with the axis of the shaft assembly. 3. A device according to claim 2, c h a r a c t e r i s e d in that the second return conduit is formed of an outer pipe (13) on the outside of the inner pipe (12) . 4. A device according to claim 3, c h a r a c t e r - i s e d in that the outer pipe (13) comprises an end portion (20) which is non-rotatably connected with the grate element (2) and through which lateral ducts (18, 19) extend, which are connected with the feeding and the return conduit and which form the connection of the sec- ond system of ducts (17.2) with the first system of ducts (17.1) . 5. A device according to any one of the preceding claims, c ha r a c t e r i s e d in that one part of the first system of ducts (17.1) is formed of two separate chambers (10, 24) in the girder means (6) . 6. A device according to claim 5, c h a r a c t e r i s e d in that said one part is formed of pipes (29, 30, 34, 35) which are laid in or cast into the girder means (6) . 7. A device according to any one of the preceding claims, c h a r a c t e r i s e d in that the inlet and/or outlet (14, 16) is/are connected to an outer cooling coil (22) by means of a rotary connection (21) . 8. A device according to any one of the preceding claims c h a r a c t e r i s e d in that the inlet and/or outlet (14, 16) is/are connected to an outer cooling coil (22) by means of a flexible tube (39) .

Inventors: ANDERSEN HANS BOEGH, ANDERSEN, HANS, BOEGH
Applicants: ANDERSEN HANS BOEGH, FLS MILJOE A S, ANDERSEN, HANS, BOEGH, FLS MILJOE A/S
Application year: 1999
Main classification: F23H3
IPC codes: F23H3, F23H7, F23H17