Metallurgical apparatus – Means for treating ores or for extracting metals – By means applying heat to work – e.g. – furnace
Reexamination Certificate
2000-09-19
2002-07-09
Kastler, Scott (Department: 1742)
Metallurgical apparatus
Means for treating ores or for extracting metals
By means applying heat to work, e.g., furnace
C266S193000
Reexamination Certificate
active
06416708
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a blast furnace for iron making, which at least in the hearth portion, comprises a steel plate lining, inside which lining at least one layer of refractory brickwork is arranged, the steel plate lining being joined to the layer (layers) of brickwork by means of mortar joints and/or ramming compound joints to form a cohesive structure. The hearth portion of a blast furnace is often provided with an external cooling system.
BACKGROUND OF THE INVENTION
In modem large-scale blast faces, in which ever higher iron production levels at elevated gas pressure are reached, it is highly important for the period between two renovations of the brickwork to be as long as possible. This may lead to problems, in particular in the area of the hearth.
Especially in the hearth, the brickwork is exposed both to the action of the gas atmosphere in the furnace and to the action of liquid metal and/or liquid slag materials which are present in that area. The gas atmosphere may lead to a chemical attack on the brickwork, often an alkali attack, while the liquid iron may have a combined influence of high temperature, chemical attack and mechanical attack. This attack is partly caused by the fact that the liquid iron is often not saturated with carbon and therefore tends to dissolve carbon from bricks.
In terms of the structure of the hearth brickwork, it is important that the bricks should not crumble on the hot side at high temperature as a result of their tendency towards thermal expansion. It has been found that carbon-containing materials, such as graphite and semigraphite, are most resistant to crumbling under such circumstances, but the composition of these materials means that they are also susceptible to attack from the liquid iron which may or may not be saturated with carbon. This susceptibility manifests itself primarily by these carbon-containing materials being dissolved in the liquid iron.
It has been found that the bricks are not affected by the liquid iron if a solid layer based on a mixture, in various combinations, of solidified iron, slag and coke particles is able to form on the inside of the brickwork. This so-called “skull” forms on the brickwork at a temperature in the region of less than 1100 to 1150° C. In addition, the formation of this skull is also dependent on the speed at which the liquid iron is moving into the hearth. Since liquid iron flows out of the heart periodically only at the location of a few tapping points from the furnace, this liquid iron has not only a vertical flow component but also a flow component in the circumferential direction of the furnace, resulting in a higher speed of movement of iron along the brickwork. This iron flowing past has a tendency to redissolve the skull in this area. Only if the hot side of the brickwork can be kept sufficiently cool by means of sufficiently intensive heat dissipation through this brickwork will the skull formed on this brickwork always be sufficient to protect the brickwork from attack.
It should be noted that the “dead man” phenomenon often occurs in blast furnaces, i.e. a solid plug based predominantly on coke and iron forms inside the hearth. Especially if this “dead man” is extensive and has a low porosity, the circulation speed of liquid iron along the brickwork wall will increase and consequently the attack on the skull will be intensified. This phenomenon also requires an even more intensive dissipation of heat via the brickwork in order to keep the temperature on the hot side of the said brickwork sufficiently low for a skull to remain in place.
Heat dissipation from the hearth brickwork by means of cooling plates which extend deep into the brickwork and through which water flows or by means of so-called “stave coolers” arranged inside the steel plate lining is not preferred. Should the skull happen to fall or melt off and part of the brickwork be dissolved in that area, it is possible for liquid iron to come into contact with, for example, such a water-cooled copper cooling plate which extends deep into the brickwork. In such a situation, the copper of the cooling plate may melt through and then the water flowing into the furnace may lead to an explosion followed by rupture of the wall. For these reasons, it is often preferred to provide the steel plate lining of the wall structure with an external cooling feature for the purpose of cooling the hearth. As a rule, this cooling feature is a spray-cooling system with which the temperature of the steel plate lining can be kept at approximately 50° C. At a steel plate lining temperature of approximately 50° C., it will not always be possible to keep the hot side of the brickwork below a temperature of approx. 1100° C., even if bricks made from graphite and/or semigraphite, which have a good thermal conductivity, are used. In this case, it should be noted that the brickwork must have a sufficient thickness to keep the risk of occasional penetration sufficiently low.
It has been found that mortar joints and ramming compound joints form considerable obstacles to the heat dissipation through the brickwork. The outer layer of bricks is generally placed against the steel plate lining with a mortar or ramming compound between them, in which case the thickness of a mortar joint may, for example, be 3 to 5 mm and the thickness of a ramming compound joint may, for example, be 30 to 120 mm. This joint serves partly to compensate for the dimensional deviations of the steel plate lining and partly to bring about thermal contact between steel plate lining and outer brickwork layer. If a plurality of layers of bricks are employed in the radial direction in the wall structure, it will also be necessary to bridge a joint between these layers, and ramming compound is generally employed for this purpose. In any case, like the joint directly behind the steel plate lining, this joint may also serve as an expansion joint. For example, this joint may be 50 mm wide. It has been found that the mortar and/or ramming compound joints may be responsible for 50 to 80% of the total thermal resistance caused by the brickwork to the outer side of the steel plate lining, if the brickwork comprises bricks with a &lgr;>20
w
/m° C. This problem can become even greater if the structure “breathes”. For example, if there are considerable temperature differences in the steel plate lining, the mortar joint may open up, resulting in an insulating layer of gas. A similar phenomenon may occur if the thermal action of the various bricks causes the joint containing ramming compound to remain insufficiently tight.
SUMMARY OF THE INVENTION
The object of the invention is to provide a solution to these problems and, in particular, to improve the heat dissipation from the hot side of the brickwork in such a manner that a skull can continually be formed there. The invention consists in the fact that, in the hearth portion of blast furnace, metal bars which run in the circumferential direction inside the steel plate lining and project into the wall are present, which bars each are connected to the outer side of the steel plate lining by means of two horizontally spaced attachment means each separately running through the steel plate lining, the attachment means being provided with prestressing means for exerting a prestressing force to ensure that each bar always remains pressed against the bricks to maintain a surface-to-surface contact along horizontal and vertical surfaces between the metal bars and bricks during operation. The combination of improved thermal conductivity through the metal bars with a direct surface-to-surface contact between the metal bars and the bricks along horizontal and vertical surfaces, as a result of the attachment with the prestressing means of the metal bars, to a large extent minimizes the thermal resistance of part of the joints. It should be noted that the vertical attachment of the bars is required in order to ensure that, following assembly of the wall structure, the surface-to-surface contact between bars and bricks is maintain
Corus Staal BV
Kastler Scott
Stevens Davis Miller & Mosher LLP
LandOfFree
Wall structure for a metallurgical vessel and blast furnace... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Wall structure for a metallurgical vessel and blast furnace..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wall structure for a metallurgical vessel and blast furnace... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2903190