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The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:
FIG. 1 shows in diagrammatic section an inventive firing grate , followed by a horizontal, air-cooled firing grate is provided;
FIG. 2 is a detail which illustrates the design of a block of grate bars; and
FIG. 3 is a perspective view which shows in detail the connection between the block of grate bars and the grate bar carrier.
The arrangement represented in FIG. 1 consists of an inventive firing grate 1 and downstream thereof, an air-cooled known firing grate 2. The firing grate 1 has an angle of inclination of 10° and in its front part is designed as counterflow grate and in its rear part is designed a feed grate, where these two constructions belong to the known prior art and employ movable grate bar blocks 3. Both parts of the firing grate 1 have a length of about 3.5 m and a width of 3 m. However, these dimensions may also be smaller or larger. The width may be varied corresponding to the mass flow rate of the fuel. The air-cooled firing grate 2 is disposed horizontally and has a length of about 3.4 m as well as a width of 3 m. The width of the air-cooled grate may also be varied corresponding to the mass flow rate of the fuel. The firing grate 1 is operated with an average thermal load of 0.94 MW/m 2 , whereas the air-cooled firing grate 2 operates with a thermal load of 0.64 MW/m 2 . The ash particles falling through the fire grate 1 and 2 are collected in the ash hoppers 4a, 4b and 4c, and this ash is delivered to the ash discharge 5, into which there is also dumped the ash from the end of the firing grate 2. As fuel, waste is supplied to the arrangement represented in FIG. 1 via the feeder 6. The combustion air is introduced into the fuel layer from the bottom via the ash hoppers 4a, 4b, 4c through the grates 1, 2. The firing grate 1 is operated with an average excess-air coefficient of about 1.1. In the front part of the firing grate 2 or at the transition between the firing grates 1 and 2, i.e. at the grate step 7, there are provided nozzles represented in the drawing by 7, through which the pulsed, hot combustion air can be introduced into the combustion space. In the combustion space, i.e. above the fuel layer, the temperature is 1100 to 950° C. In the fuel layer, the temperature is 700 to 800° C. At the surface of the grate bar blocks 3 of the firing grate the temperature is 90 to 110° C. due to the water cooling. At the surface of the grate bar blocks of the firing grate 2 the temperature is 400 to 600° C. It is quite obvious that the inventive firing grate cannot be designed as roller grate or as travelling grate , as in these constructions the cooling provided in accordance with the invention cannot be realized with a reasonable economic effort. It is possible to introduce combustion air into the combustion space above the firing grate 1. By introducing the combustion air into the combustion space, i.e. above the fuel layer, there is in particular achieved an optimum combustion of the gaseous constituents escaping from the fuel. The combustion air, which is introduced into the combustion space via the nozzles provided at the grate step 7, also promotes the combustion of the gaseous fuel constituents as well as the postcombustion of the fuel.
The grate bar block 3 schematically represented in FIG. 2 consists of several grate bars 8a, 8b, and 8c. The grate bars 8 have a length of 400 to 600 mm and a width of 400 to 700 mm. The grate bar blocks 3 are disposed inside the grate limits 9a, 9b. In the interior of each grate bar 8, a meandershaped channel 10 is provided, which for instance has a diameter of 20 mm, and in which flows the coolant water. The amount of cooling water is dimensioned such that after the passage through one or several grate bar blocks 3 it has a temperature of 60 to 95° C.; during the cooling process, no steam is formed. Into the grate bars 8, several grate slots 11 of equal length, width and shape have been milled, where the width of the grate slots 11 is 1 to 1.5 mm. Through the grate slots 11, combustion air is supplied to the fuel layer from the bottom. Each grate bar 8 has an inlet opening 12a and an outlet opening 12b for the cooling water. The cooling water is supplied to the grate bar block 3 from the outside via line 13 and is discharged to the outside via line 14.
Onto the grate bars 8a and 8c, which are positioned at the chain grate supplier boundary 9a, 9b, inlet and outlet pieces 15a and 15b are placed, which are screwed to the grate bars 8a and 8c. The lines 13 and 14 open into the inlet and outlet pieces 15a, 15b. The grate bars 8a and 8c are connected with the grate bar 8b by means of connecting pieces 16 placed onto the same and are firmly positioned. The connecting pieces 16 are screwed to the grate bars 8. All screws used 20 are guided at an angle of 90°, i.e. perpendiculary with respect to the supporting surfaces. In the interior of the connecting pieces 16 a connecting passage 17 extends, through which the cooling water flows from one grate bar into the other. The surfaces of the inlet and outlet pieces 15a, 15b and of the connecting pieces 16, which lie on the grate bars 8, as well as the corresponding opposite surfaces of the grate bars 8 are provided with a planar cut, so that in cooperation with the screw connection a high degree of tightness of the cooling system can already be achieved. In addition, the transition between the grate bars 8 and the connecting, inlet and outlet pieces is sealed by means of a graphite seal 21, so that finally a very reliable, durable and rugged seal of the cooling system is achieved. The individual grate bars 8 are positioned with respect to each other by means of the connecting pieces 16 such that between the same a grate slot 18 is formed, whose width likewise is 1 to 1.5 mm. The fixation of the grate bars 8 achieved by means of the connecting pieces 16 is so stable that the width of the grate slots 18 does not change during the operation. It was found out that merely the combination of the grate bars 8 by means of the connecting pieces 16 is not sufficient to ensure the dimensional accuracy of the grate bar blocks 3.
It is advantageous when the inlet and outlet pieces 15a, 15b as well as the connecting pieces 16 are fitted into corresponding recesses, formed in the fire grate bars 8. A corresponding representation is shown in FIG. 3.
The connection of the grate bar block 3 consisting-of several grate bars 8a, 8b, 8c with the drive members of the firing grate is produced by means of the grate bar carrier 19. The inlet and outlet pieces 15a, 15b as well as the connecting pieces 16 are firmly connected with the grate bar carrier 19. In accordance with FIG. 3, this can be achieved in that the inlet and outlet pieces 15a, 15b as well as the connecting pieces 16 are disposed flush around the grate bar carrier 19 and are screwed both to the grate bars 8 and to the grate bar carrier 19. The generally movable grate bar carrier 19 thus moves the grate bar block 3 both via the inlet and outlet pieces 15a, 15b acting as claws and via the connecting pieces 16 and drives said grate bar block. source:bloggumfire grate
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