Patent Application
20150233641
The invention relates to a machine for the thermal treatment of bulk material, in particular a sintering or pelletizing machine, comprising a traveling grate with a plurality of pallet cars, that are conveyed through at least one treatment station for effecting the thermal treatment of the bulk material, and a sealing structure sealing the pallet cars against the machine, wherein the sealing structure comprises a spring-loaded sealing strip contacting a planar sealing surface.
In pelletizing or sintering plants the bulk material to be treated, for example iron ore or zinc ore, is charged onto pallet cars forming an endless chain also referred to as “traveling grate”. The pallet cars are filled with the bulk material and pass through various treatment stations of a furnace, in which the material is thermally treatment, e.g., heated, dried, fired and cooled. Usually, wind boxes are provided below the traveling grate sucking hot air through the bulk material located on top of the pallet cars.
A standard problem of known sintering or pelletizing machines is so-called false air which is not sucked through the material to be treated, but for example through the space between the wind boxes and the support means for the traveling grates. Further, it should be avoided that gases escape from the furnace through gaps provided between the furnace hood and the traveling grate.
Various measures have been proposed to reduce the quantity of false air. As described in documents AT 290858 or EP 0 463 666 A1 a sintering machine may be provided with one or more bars under each pallet car, which bars are urged in the direction of a guide way connected to the fixed structure by spring force. Guide way and bar together provide a gastight seal. The sealing force is provided by gravity due to the weight of the loaded pallet car and the pressure spring. Still, however, there is a certain leakage between the sealing body and the fixed structure.
A lot of effort has to be taken to minimize the gaps necessary for the movement of the sealing bodies within the housing. If a simple slide seal without additional pressure force is used, the sealing effect results from the surface contact between the sealing strip and the sealing surface. Efficiency of this sealing structure, however, is reduced over time as the sealing means were down and sufficient contact cannot be secured. Further, the sealing strips have to be provided on each pallet car increasing the equipment costs. Actually, however, the sealing effect has to be provided only when the pallet cars pass the furnace, while the sealing strips are without any function over at least half their travel path when they are returned upside down along a bottom strand to the lifting wheel.
It is, therefore, the object of the present invention to provide for a reliable seal between the traveling grate and the fixed structure of a sintering or pelletizing machine. Further, the equipment costs should be reduced.
According to the present invention there is provided a machine comprising the features of claim 1. In particular, the sealing strip is held by at leaf-spring element biasing the sealing strip against the sealing surface.
The leaf-spring element combines the previously separated functions of providing the sealing force and guiding and holding the sealing strip. This integral structure reduces leakages necessarily related to previous solutions using gravity. It is necessary to seal against the primary sealing gap only that is formed between the moving pallet cars and the fixed structure of the sintering or pelletizing machine.
Another advantage of using leaf-springs is that they provide a torsional and lateral flexibility to the sealing system so that it is possible to absorb the constantly present lateral movement of the pallet cars without damage to the sealing system.
According to a preferred embodiment of the present invention the leaf-spring elements are mounted to the fixed structure of the machine, in particular a frame provided below the traveling grate and/or a hood provided above the traveling grate, while in both cases the sealing surface is provided on the pallet cars. As a result the sealing structure can be provided below the traveling grate to seal against the wind boxes, but also above the traveling grate if a hood is provided. Wind boxes are present in sintering and pelletizing plants while hoods are presently primarily used in pelletizing plants only. There is, however, a trend to use hoods in sintering plants as well. As the leaf-spring elements are provided on a stationary sections of the plant only it is possible to provide the sealing systems within the processing zones only and to thereby reduce the number of sealing systems by more than 50% as compared with the prior art providing a sealing systems on each pallet car.
Preferably leaf-springs are formed in a U-shape representing the simplest design, which can be manufactured easily and allows simple installation. Other forms, such as e.g. double U-shapes, V-, W-, or L-profiles would be possible as well. While the used profile can be adapted to the specific requirements in the sintering or pelletizing machines, the production of the above mentioned alternative profiles is more complex and they require a larger installation space.
In view of the high temperatures present in sintering and pelletizing machines, the leaf-spring elements should be formed from a thermally resistant material, such as 1.4568, 1.4451, 1,4571, 1.45301, etc. with high stiffness properties at high temperature level according to standard EN 100088-2.
It is part of the present invention that the leaf-spring element is pre-stressed so that besides reacting to the weight of the pallet cars it provides an active pressure load to increase the sealing effect. This is in particular relevant with regard to the sealing against the hood provided above the traveling grate.
In order to facilitate maintenance work and reduce costs, several consecutive leaf-spring elements and or sealing strips are provided along the length of the treatment stations. In case of damage, only the relevant sections need to be exchanged. Further, the heat treatment sections in sintering and pelletizing plants often are very long so that it would be very difficult to provide integral leaf-spring elements or sealing strips extending along the total length of the heat treatment sections.
To avoid leakage between consecutive leaf-spring or sealing elements, the invention provides that adjacent leaf-spring elements and/or sealing strips overlap in the vertical and/or the horizontal direction. Thereby, gaps between adjacent sealing systems are closed or covered. Further, the overlap provides for a formfit connection between the sealing segments which enhances the stability and force bearing ability over the total length to be sealed.
In addition or as an alternative to an overlap of adjacent leaf-spring elements a connecting member may be provided between adjacent leaf-spring elements to seal the gaps therebetween and to provide for a stable connection.
If the spring force of the leaf-spring element is reduced due to the high temperature environment, it is possible to provide additional pressure springs within the leaf-spring elements to assist the biasing force thereof or to use leaf-spring elements having a higher modulus of resilience (spring constant) in specifically stressed regions.
The system according to the present invention provides for considerable . advantages in the reliability of the sealing system and reduces the equipment costs as the surfaces on the pallet cars that need to be processed are minimized and as the number of sealing system is decreased dramatically. The new system requires less than half the number of sealing systems that was considered necessary in the prior art as they now need to be provided in the process areas only and no longer on each pallet car.
The invention will now be described on the basis of preferred embodiments shown in the drawing. All features described and/or illustrated form the subject matter of the present invention per se or in any combination, independent of their inclusion in the claims or their back-reference.
In the drawing:
By way of example,
At a non-illustrated supply station under a hood 2, the bulk material is charged onto pallet cars 3 forming an endless pallet car chain referred to as “traveling grate” 4. Under the hood 2, the bulk material transported on the pallet cars 3 passes through a plurality of thermal treatment stations in which the bulk material is, e.g., dried, preheated, fired and finally cooled again. In particular, air is sucked through the bulk material carried on the pallet cars 3 by wind boxes not shown in
As shown in
As evident from
In order to compensate for a reduction of the biasing force of the leaf-spring elements 13 due to thermal stresses in the heat treatment process, additional pressure springs (not shown) may be provided between the upper and lower arms 13a, 13b of the leaf-spring element 13. Alternatively, leaf-spring elements having a higher spring constant may be provided in such regions.
In the drawing the leaf-spring elements 13 are shown to have a U-shape. This is the most preferred design of the elements 13. It is, however, also possible to use other shapes, in particular a double U-shape, a V-shape, a W-shape or an L-shape.
With the invention, it is possible to simplify the sealing structures provided in sintering or pelletizing machines wherein a continuous sealing force can be provided due to the resilient leaf-spring. As the functions of the force introduction and guidance of the sealing elements are combined, a closed structure is possible completely avoiding the sucking in of false air or leakage of air into the furnace. The torsional and bending properties of the leaf-spring elements absorb the lateral movement of the pallet cars by deformation without damage to the sealing system or the pallet cars.
Economically, there are considerable advantages in comparison to the known sealing systems as the number of sealing systems can be reduced by at least 50% since they have to be provided only in the processing region of the machine but not on every pallet car.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2012/069845 | 10/8/2012 | WO | 00 |
