Fixed bar of a stepped grate and stepped grate

Abstract

One aspect of the invention relates to a fixed bar (2) of a stepped grid (11) having a flat upper surface (23) and a cooling circuit with a coolant inlet (20) and outlet (21) located on a lower face, characterized in that the lower face has at least one flat surface (200, 210) into which the coolant inlet (20) and outlet (21) open, and that the coolant inlet and outlet are each bordered by two diametrically opposed holes (201, 202; 211, 212). Thus, the coolant inlet and outlet can be connected to the cooling circuit by flanges through the two holes.

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The technical field of the invention is that of stepped grates used in combustion furnaces or incinerators of solid materials such as, for example, waste, biomass or solid recovered fuels.

[0002] The invention relates in particular to the bars equipping these stepped grids. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0003] Solid matter incinerators include grates onto which this fuel is introduced from the top and descends as the combustion process progresses, to exit in the form of ash / clinker at the bottom of the grate, and as fumes in the boiler.

[0004] The combustion grate mechanism moves the fuel from the entry point to the exit point. Combustion air is injected under the grate, ensuring the fire is stoked and controlled.

[0005] The grate consists of rows of bars arranged in steps, a fixed part alternating with a movable part. In the rest position (most of the time), the movable bars are under the fixed bars. They slide on these fixed bars, pushing the fuel to move it forward. When they return to the rest position, the fuel falls into the free space created by the advance of the bars. This operation allows the fuel to move forward.

[0006] The bars are counter-inclined to the inclination of the grate, which allows the maintenance of a sufficient fuel layer height to protect the bars from the radiation of the fire.

[0007] The search for increasing the lower calorific value (LCV) of fuels using appropriate technologies (for example, for household waste, sorting to separate the components and extract a non-recyclable combustible fraction with high added value in terms of energy capacity) leads to the need to move from an air-cooling system for the bars to a water-cooling system, which is a much better heat transfer agent than air. However, the use of water requires the installation of a cooling circuit.

[0008] Stepped grate type bar grates are widely used for this type of combustion.

[0009] In this technology, these water-cooled bar grates mostly have rows of both fixed bars and water-cooled movable bars. The movable bars are supplied with water by flexible connection hoses, the connection being made by threaded fittings.

[0010] In addition to the friction problems that can occur with hoses, which are a weak point in the water circuit, threaded connections are also sensitive points because they can loosen and leak, or be poorly tightened because they are difficult to access, or difficult to loosen after a certain period of operation, leading to breakages.

[0011] The movable bars, moving back and forth on the fixed bars (on some grids all the rows of bars are movable, and these play alternately the role of fixed row and the role of movable row), cause, in the event of roughness on the bars by molten metal for example ("scraping"), slight lifting of the fixed and movable bars. Anti-lifting devices are provided, but the connections at the connection must also be designed to absorb the potential movements of the bars.

[0012] Furthermore, the alternation of starts and stops linked to the alternating movement of the bars entering and leaving causes vibrations and shocks to which the connection points are sensitive. SUMMARY OF THE INVENTION

[0013] The invention provides a solution to the problems mentioned above, by preventing leaks from the cooling circuit.

[0014] A first subject of the invention relates to a fixed bar of a stepped grid comprising a flat upper surface and a cooling circuit with an inlet and an outlet for a cooling liquid located on a lower face, it is characterized in that the lower face has a flat surface where the inlet and outlet of the cooling liquid open and that the inlet and outlet of the cooling liquid are each bordered by two diametrically opposite holes.

[0015] Thus, the coolant inlet and outlet can be connected to the cooling circuit by flanges thanks to the two holes which can be threaded or not.

[0016] Advantageously, the flat surface is parallel to the upper surface and the tapped holes are through. In this way, the connection is easier, as the screwing into the holes can be done from above.

[0017] A second object of the invention relates to a stepped grid comprising fixed bars with at least one of the preceding characteristics and it is characterized in that the cooling circuits of two adjacent fixed bars are connected to each other by a rigid connecting tube fixed by flanges on one side to the inlet of the cooling circuit of a first fixed bar and on the other side to the outlet of the cooling circuit of a second fixed bar.

[0018] The connection by a rigid connecting tube between two adjacent bars makes it possible to constitute part of the cooling circuit and the rigid nature of the tube prevents any damage by friction. The flanges connecting the bars to the rigid connecting tubes make it possible to eliminate threaded connections which are often a source of leaks and assembly difficulties. The connecting tubes of the bars between them are calculated to absorb thermal expansion. The bars are connected together rigidly, for example by screw / nut or rod type screwing.

[0019] Advantageously, the connecting tube is U-shaped. The U-shape allows for some flexibility that can accommodate assembly and expansion tolerances. These tolerances are minimal since the bars are all clamped together on machined surfaces during manufacturing.

[0020] Advantageously, the flanges are fixed with a gasket. This gasket allows for a watertight assembly on all joint faces the first time and without retightening as must be done on assemblies with only screwed connections.

[0021] Advantageously, the coolant is water. Water is a much better heat transfer fluid than air and is easily accessible.

[0022] Advantageously, the stepped grate includes movable bars of a shorter length than the fixed bars. Instead of having movable and fixed bars of the same length, the movable bars are shorter and are therefore more protected from the heat by the fixed bars when they are moved back.

[0023] Advantageously, the movable bars and the fixed bars have a length difference greater than the width of the flange.

[0024] Advantageously, the stepped grate comprises air-cooled movable bars. The movable bars can be cooled only by air because they are protected by the water-cooled fixed bars.

[0025] A third object of the invention relates to an oven comprising a stepped grid with at least one of the preceding characteristics. BRIEF DESCRIPTION OF THE FIGURES

[0026] The figures are presented for information purposes only and in no way limit the invention. [ Fig. 1 ] represents a diagram of a combustion furnace for high calorific fuels; [ Fig. 2 ] is a top view of a rack in the oven of the figure 1 ; [ Fig. 3 ] is a sectional view of the grid of the figure 2 showing the movable bars in the retracted and extended positions, [ Fig. 4 ] is a bottom view of a fixed bar according to the invention; [ Fig. 5] is a rear view of fixed bars connected together by tubes according to the invention; [ Fig. 6 ] is a perspective view of the connecting tubes; [ Fig. 7 ] is a top view of fixed bars according to the invention [ Fig. 8 ] is a bottom view of the figure 7 ; [ Fig. 9 ] is a sectional view of a grid according to the invention, [ Fig. 10 ] shows fixed and movable bars of an oven grid according to the invention. DETAILED DESCRIPTION

[0027] The figures are presented for information purposes only and in no way limit the invention.

[0028] Unless otherwise specified, the same element appearing in different figures has a single reference.

[0029] Throughout the description we will call "top", "above" or "upper" the upper part of the figures 1 to 3 And 5 has 7 and “bottom”, “below” or “lower”, the bottom of said figures.

[0030] There figure 1 shows a combustion furnace 1 for high calorific fuels which comprises: a fuel supply system 10 consisting of solid materials with high calorific value 14, a hearth with walls made of refractory materials 12 and a stepped grate 11, a boiler 13 an outlet 15 for the ashes a convective part 16.

[0031] The solid materials 14 (fuel) arrive at the top via the feed system 10 to the stepped grate 11 which is inclined so as to allow the fuel to spread in the hearth 12, this inclination is slight, for example between 0° and 20°. The fuel emits smoke which passes through the boiler 13 then into the smoke treatment system (not shown). The rest of the burnt fuel is in the form of ash which is discharged to an outlet 15.

[0032] The stepped grid 11 comprises stepped bars with alternating rows 110 of fixed bars 2 and rows 111 of movable bars 3 offset vertically.

[0033] As visible figure 3 : on the R side, the movable bars are retracted and on the S side, the movable bars are extended. The movable bars 3 slide back and forth between two fixed bars 2a and 2b, between a retracted position where they are partially covered by an upper fixed bar 2a and an extended position where they are advanced onto a lower fixed bar 2b. The movement of the movable bars 3 combined with the stepped position of the bar grates 11 makes it possible to push the solid materials 14 downwards and facilitate their combustion.

[0034] The rungs of a step are placed side by side on a beam 4 and fixed together by a system of screws / nuts.

[0035] The combustion of solid materials 14 with high calorific value can raise the temperature in the hearth 12 to 1300°C and sometimes higher at peak, while the temperature of the bars must be kept as low as possible, ideally below 300°C, and in any case at a temperature below 500°C, the wear rate (abrasion-corrosion) being linked to the temperature.

[0036] The fixed bar 2 according to the invention, the underside of which can be seen at figure 4comprises an inlet 20 and an outlet 21 connected to each other by a U-shaped or serpentine loop 22 and covering the majority of the surface of the fixed bar 2. The shape of the loop 22 is adapted to the width of the fixed bar. The inlet 20 and the outlet 21 each open respectively onto a flat surface 200 and 210. These surfaces 200 and 210 are preferably parallel to each other and to the upper surface of the fixed bar. Each surface 200 and 210 comprises two holes 201, 202 and 211 and 212 intended to fix a flange. These holes can be tapped or through-holes. If they are tapped, the flange will be screwed from below, if they are through-holes, the screwing will be from above, the flange being ideally tapped in this case.

[0037] It is possible to provide a single surface covering the inlet and outlet without departing from the scope of the present invention.

[0038] The size of the surfaces 200 and 210 is linked to the flange fixing of the cooling circuit, in fact, this requires at least two fixing points around the opening, the space requirement is therefore greater than direct screwing of a tube into a tapped hole. Thus, the fixed bar 2 is longer and wider than a bar of the state of the art.

[0039] On the figure 4 , the holes 201, 202, 211 and 212 are through and aligned parallel to the width of the fixed bar 2, but they can be aligned symmetrically with an angle between 0 and 90° relative to the width of the fixed bar 2.

[0040] We can see Figure 5, a fixed bar 2n with two U-shaped connecting tubes 5n and 5n+1 which are each inserted respectively into an inlet 20n-1 of a first fixed bar 2n-1 and an outlet 21n of a second fixed bar 2n, and an inlet 20n of a first fixed bar 2n and an outlet 21n+1 of a second fixed bar 2n+1. Thus the loops 22 of each fixed bar 2 are connected in series to constitute the complete cooling circuit.

[0041] Each connecting tube 5 comprises two flanges 6a and 6b fixed to two adjacent fixed bars by compression screws 60 passing through the bars and screwed to the flange 6a or 6b. The screws 60 are therefore accessible from the upper surface 23 of the bar 2. A flat gasket 61 is arranged on the connecting tube 5 between the flange 5 and the inlet 20, and the flange and the outlet 21 of each fixed bar 5 and guarantees sealing.

[0042] The row 110 of fixed bars 2 is supplied with coolant by an inlet pipe 50 which brings the coolant to one side of the row 110 and an outlet pipe 51 which evacuates said liquid, the fixed bars 2 are in this way supplied in series.

[0043] Depending on the width of the grid 11 and the PCI, it is possible to split the cooling circuit in two along the X axis of the grid, in order to balance the coolant temperatures along this X axis and send the coldest coolant to the middle in said X axis.

[0044] The grate 11 may comprise fixed bars 2 cooled with the coolant and fixed bars 2A cooled with air. Indeed, the fixed bars 2 cooled with the coolant are located in first combustion zones where the temperature is higher, i.e. towards the top of the grate 11 while the fixed bars at the bottom are air cooled where the heat is lower.

[0045] The coolant can circulate with a variable flow rate in the fixed bars 2. This flow rate is then controlled according to the outlet temperature of the liquid which is fixed. The liquid heated by the passage in the bars 2 can be cooled by an exchanger placed on the combustion air, which allows the extracted calories to be reinjected into the hearth 12.

[0046] The fixed bars 2A at the bottom of the air-cooled grid 11 are designed on the same principle as the movable bars 3, but are longer because they have a sliding surface for the movable bars and can be narrower than the fixed bars 2 since it is not necessary to connect them to a cooling circuit. The bars 2A are the same width as the movable bars 3.

[0047] The air-cooled bars are half as wide as the liquid-cooled bars 2, so the fixed bars 2, 2A and the movable bars 3 can easily overlap.

[0048] As can be seen in the figure 9 , the movable bars 3 are air-cooled because they are mostly under the fixed bars 2 and 2A and are in particular protected from heat by the fixed bars 2 cooled with the cooling liquid in the hottest area at the top of the grid 11.

[0049] The fixed bars 2 according to the invention have the advantage of being easy to assemble and disassemble. Thus, to disassemble or reassemble them with their connecting tube 5, they must be loosened from below the grid 11. Then the operations are carried out from above the grid. The four clamping screws 60 are removed from the same bar 2. The bar can then be disassembled from above. Since the connecting tubes 5 are connected to two bars, they remain in place. The seals 61 do not fall out because they are held by flanges 6a and 6b. Either the bar 2, or the seals 61, or the connecting tube 5 can be replaced; in the latter case, the flange of the next bar must also be disassembled using the same principle.

Claims

1. Fixed bar (2) of a stepped grid (11) comprising a flat upper surface (23) and a cooling circuit with an inlet (20) and an outlet (21) for a cooling liquid located on a lower face, characterized in that the lower face has at least one flat surface (200, 210) where the inlet (20) and the outlet (21) of the coolant open and that the inlet and the outlet of the coolant are each bordered by two diametrically opposite holes (201, 202; 211, 212).

2. Fixed bar (2) according to claim 1 characterized in that the flat surface (200, 210) is parallel to the upper surface (23) and the holes (201, 202; 211, 212) are through holes.

3. Stepped grid (11) comprising fixed bars (2) according to one of the preceding claims, characterized in thatthe cooling circuits of two adjacent fixed bars (2) are connected to each other by a rigid connecting tube (5) fixed by flanges (6a, 6b) on one side to the inlet (20) of the cooling circuit of a first fixed bar and on the other side to the outlet (21) of the cooling circuit of a second fixed bar.

4. Stepped grid (11) according to the preceding claim characterized in that the connecting tube (5) is U-shaped.

5. Stepped grid (11) according to one of claims 3 or 4. characterized in that the flanges (6a, 6b) are fixed with a gasket (61).

6. Stepped grid (11) according to one of claims 3 or 5. characterized in that the coolant is water.

7. Stepped grid (11) according to one of claims 3 to 6 characterized in that it comprises movable bars (3) of a length less than that of the fixed bars (2).

8. Stepped grid (11) according to the preceding claim characterized in thatthe movable bars (3) and the fixed bars (2) have a length difference greater than the width of the flange (6a, 6b).

9. Stepped grid (11) according to one of claims 7 or 8 characterized in that It includes mobile bars (3) cooled by air.

10. Oven comprising a stepped grid (11) according to one of claims 3 to 7.

Images