The invention concerns a heating device for preheating a vessel, such as a transfer ladle, that is used for transferring liquid metal in melting operations and is lined with refractory material, where the vessel is heated in a heating stand that has a vessel cover.
In melting operations, e.g., in steel mills, the molten metal is conveyed in the liquid state by ladles from one stage of metal product production to the next. In this operation, the ladle must not be cold before it is filled with the liquid metal. On the one hand, this requirement is due essentially to the fact that the filled liquid metal may be allowed to lose only a minimal amount of energy due to heat losses to the ladle. On the other hand, the refractory lining is sensitive to a suddenly occurring heat load after the ladle has been filled with metal, and this leads to a high degree of wear and tear of the refractory material. Therefore, the goal must be to keep the temperature difference between the ladle lining and the liquid metal as small as possible.
For this reason, before they are to be used, the transfer ladles for the liquid metal are preheated or kept hot in heating stands by burners, as described, for example, by EP 1 078 704 B1. The air-natural gas burners used for this purpose have a capacity of up to 4 MW and produce a flame that causes the exhaust gas to move rapidly, shows a tendency to cause stratification, and has only a relatively small fraction of radiant energy.
Aside from the fact that the energy of the energy carrier is thus poorly utilized, this also results in unnecessarily high CO2 emissions. In addition, the stratification causes nonuniform heating of the ladle, which leads to thermal stresses and correspondingly high wear and tear of the lining material. Moreover, there is the problem that a residual amount of liquid metal left in the ladle reoxidizes.
Therefore, the objective of the invention is to create a heating device of this general type that does not have these disadvantages, so that better energy utilization is achieved, CO2 emissions are reduced, and wear and tear on refractory material or lining material is reduced.
In accordance with the invention, this objective is achieved by the use of porous burners for heating the vessel, especially a transfer ladle, and maintaining its temperature. By using, for example, porous burners disclosed by WO 2004/092646 A1 for preheating and maintaining the temperature of liquid metal transfer vessels, the more efficient combustion of the energy carrier in the porous burner is thus utilized for this heating task. This reduces the amount of exhaust gas and yet produces an exhaust gas of spatially uniform temperature and discharge velocity, so that stratification can be avoided. Furthermore, a relatively large fraction of the energy that is introduced is converted to radiant energy in the porous burner. All together, this makes it possible to achieve economical and effective utilization of the energy, reduced CO2 emissions, and more rapid heating of the vessel with uniform heating of the refractory material or the lining of the vessel.
In a preferred embodiment of the invention, the porous burners are constructed and arranged in the form of arrays. The construction of arrays of porous burners allows optimized use of the porous burners.
To this end, in accordance with an advantageous proposal of the invention, arrays of porous burners are provided, which are distributed with optimized utilization of space on the inner wall of the cover. In an advantageous alternative embodiment, a column is provided, which has arrays of porous burners that are distributed with optimized utilization of space and extends into the vessel through the cover.
In both cases, the hot exhaust gas enters the body of the furnace at a relatively low velocity in the cross-sectional outflow, and causes no stratification. At the same time, a high fraction of the energy is converted to radiation in the porous burner, and the radiation temperature is higher than the necessary temperature (1,100 to 1,200° C.) of the refractory material of the liquid metal transfer vessel.
In the embodiment of the device for heating and maintaining the temperature with a column that extends into the interior of the vessel to be heated, an advantageous design provides that the porous burners are arranged so as to be distributed over the entire circumference of the column. Even more effective action of the radiation can be realized by the column equipped with arrays of porous burners on the sides and optionally on the bottom.
If the column has the preferred polygonal construction, the construction of arrays of porous burners on the closed circumference of the column is simplified by virtue of the fact that the porous burners can be mounted in a simple way on the flat polygonal surfaces.
According to another proposal of the invention, a lifting device is assigned to the column. The raising and lowering of the column that this makes possible allows variable positioning of the heating column that can be adapted to the given heating task.
If, as is preferred, the column can also be rotated about its longitudinal axis, which can be accomplished in an advantageous way by the lifting device being designed for simultaneous rotation, even more uniform heating or heating up of the lining of the liquid metal transfer vessel can be achieved.
Additional features and details of the invention are revealed in the claims and in the following description of the specific embodiments illustrated in the drawings.
A liquid metal transfer vessel 3, which is to be preheated and/or kept hot, is realized here as a transfer ladle and is closed by a cover 2 or 20. This transfer vessel 3 is already positioned in a heating stand 1. The heating stand itself is of a standard design. It is equipped with a cover 2 or 20 that can be operated in the heating stand and is indicated in
In the embodiment illustrated in
In the embodiment according to
As is illustrated in a highly schematic way in
Number | Date | Country | Kind |
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10 2006 022 689.5 | May 2006 | DE | national |
10 2007 022 684.7 | May 2007 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2007/004195 | 5/11/2007 | WO | 00 | 8/31/2010 |