Glass manufacturing – Processes – Slag – utilization
Reexamination Certificate
1999-09-02
2001-06-26
Derrington, James (Department: 1731)
Glass manufacturing
Processes
Slag, utilization
C065S029180, C065S137000, C065S163000, C065S327000, C065S356000
Reexamination Certificate
active
06250109
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a process for continuously producing a glassy or vitrified blast furnace slag, in which the slag is applied onto a cooling roll or onto articulately interlinked cooling plates conducted as an endless conveyor belt over deflection pulleys and wherein cooling of the slag is effected dry, as well as an arrangement for carrying out the process.
The invention, in particular, aims at providing an efficient process by which the subsequent dry granulation of blast furnace slag is feasible at operating costs as low as possible while saving the environment to the largest extent possible.
2. Prior Art
Usual processes for granulating blast furnace slag, for instance in view of further processing in the cement industry, at present are devised as wet processes. The liquid blast furnace slag is united with large amounts of water, thereby solidifying to glassy granulates. In doing so, the total heat content is destroyed and SO
2
and H
2
S are usually formed, wherein, to make things worse, sulphur-containing waste waters are formed, the disposal of which involves additional expenditures.
From DE 29 50 974 A, an arrangement for the production of a glassy or vitrified blast furnace slag is known, in which an endless conveyor belt is provided with cooling grooves extending on the external surface and narrowing towards the groove roots. Via a slag melt vessel, slag melt is filled into the cooling grooves and, after cooling and solidification, is ejected from the cooling grooves on a predetermined site by means of a scraper provided on the internal surface of the conveyor belt.
From AT B 380 490 an arrangement for recovering the sensible heat of dumpable hot material may be taken, such an arrangement being intended for cooling, in particular, liquid blast furnace slag while recovering the sensible heat.
The known arrangement comprises an endless conveyor belt conducted over at least two deflection pulleys and formed of articulately interlinked plates, on the upper half of which conveyor belt the hot material is applied, the empty lower half of the conveyor belt being conducted through a cooling zone. With such a dry cooling, the high cooling speed required for vitrification without involving the risk of subsequent crystallization or recrystallization usually cannot be readily realized. For that reason, such known arrangements are frequently operated primarily with a view to as complete a recovery of energy as possible during cooling, thus accepting subsequent crystallization or recrystallization.
The known arrangement is applicable, in particular, also for hot material that must be cooled while avoiding the access of air such as, for instance, in the dry quenching of coke.
The known arrangement comprises a plurality of cooling plates, the cooling plates in the upper half being appropriately heated and in the lower half cooperating with cooling devices, which may be formed, for instance, by cooling plates through which a coolant flows. Heat transfer in that arrangement is effected by radiation or by the immediate contact of the counter cooling plates of the conveyor belt with the cooling plates for the purpose of cooling the cooling plates of the conveyor belt. The cooling device may also be formed by consecutively arranged holler counter cooling plates, wherein the upper sides of such counter cooling plates may be designed as smooth sliding surfaces getting into contact with the cooling plates of the conveyor belt.
SUMMARY OF THE INVENTION
The invention especially aims at providing a process of the initially defined kind, in which an arrangement as basically represented in AT B 380 490 may be successfully employed for the rapid solidification of slags at high flow rates. It is to be feasible, in particular, to immediately form a cooled vitrified blast furnace slag suitable for subsequent further comminution or granulation in a dry manner and capable of being thrown off the cooling belt by simple means completely and without residues.
To solve this object, the process according to the invention essentially consists in that the liquid slag is supplied to an intermediate storage and from that intermediate storage is continuously applied onto the cooling plate belt via a distributing channel in parallel strands at temperatures of above 1350° C., whereupon the cooled slag is thrown off and comminuted or granulated dry in a crusher.
Due to the fact that the liquid slag is supplied to an intermediate storage and continuously charged onto the cooling plate belt from that intermediate storage via a distributing channel at temperatures of above 1350° C., continuous operation is rendered feasible, on the one hand, and the rheologic conditions required for attaining, by dry cooling, the cooling speeds necessary for the formation of a glassy or vitrified state of the material to be cooled are safeguarded, on the other hand. The application of slag onto the cooling roll, or the cooling plate belt, in parallel strands ensures a uniform, thin slag layer on the cooling roll or cooling plate belt, respectively. The numerous individual streams converge into a single broad thin strip. In this manner, it is ensured that extremely thin coatings of the cooling roll, or the cooling plates, are obtained over a large width, thereby safeguarding the high cooling speed required for the formation of a glassy state without any risk of recrystallization. By applying the liquid slag at temperatures of above 1350° C., uniform distribution without lump formation on the cooling plates is ensured. By realizing the process according to the invention on a cooling roll, or on an endless conveyor belt formed of articulately interlinked cooling plates, the simple control of the material properties and of the state of vitrification of the material to be cooled is feasible.
The cooled vitrified slag immediately after this may be crushed or granulated dry in a crusher in a simple manner such that, on the whole, there is the opportunity to granulate blast furnace slag dry at the lowest operating costs and with the slightest environmental impacts. Since no water is used in the granulation of slag, no formation of hydrogen sulphide and no relevant formation of sulphur dioxide will occur, either. Also the conventional problems involved in treating waste water are obviated. The extremely slight layer thickness causes the slag to rapidly solidify at least surfacially. Since solidified slag exhibits a substantially better thermal conductivity than liquid slag, rapid and efficient cooling may be obtained at only a slight layer thickness and by doing with short-structure apparatus.
Advantageously, the process according to the invention is carried out in that the layer thickness on the cooling roll, or the cooling plate belt, is adjusted to 1 to 15 mm and, preferably, 2 to 10 mm, that the liquid slag on the cooling plate belt is cooled by at least 300° C. at a cooling speed of above 10° C./s and that the cooled slag is thrown off at temperatures of above 600° C. By adjusting the layer thickness on the cooling plates to 1 to 15 mm and, preferably, 2 to 10 mm, it has become feasible to attain the necessary cooling speed with structurally simple means. By cooling the liquid slag on the cooling plate belt by at least 300° C. at a cooling speed of above 10° C./s, vitrification is safeguarded, on the one hand, and cooling to a temperature at which the speed of crystal growth starts to decrease substantially so as to avoid recrystallization is effected, on the other hand, wherein, by the cooled slag being thrown off at temperatures of above 600° C., it is ensured that a coherent slag strip can be thrown off and hence a complete and simple separation of the cooled material from the cooling plates is achieved. Additional cooling may cause a spontaneous disintegration of the cooled material due to internal stresses, which can be avoided by the throw-off temperature, i.e., at temperatures of above 600° C.
The process according to the invention advantageously is carried out in a mann
Hulek Anton
Ritzberger Franz
Wawrina Rainer
Derrington James
Pillsbury & Winthrop LLP
Voest-Alpine Industrial Services GmbH
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