Heat exchange – Conduit within – or conforming to – panel or wall structure – Wall forms enclosure
Reexamination Certificate
1998-11-12
2001-07-10
Atkinson, Christopher (Department: 3743)
Heat exchange
Conduit within, or conforming to, panel or wall structure
Wall forms enclosure
C165S162000, C165S168000, C165S171000
Reexamination Certificate
active
06257326
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a cooling element for shaft furnaces provided with a refractory lining, particularly blast furnaces. The cooling element is made of copper or a low copper alloy and is provided with coolant ducts arranged in the interior of the element.
2. Description of the Related Art
Cooling systems for the steel jackets of shaft furnaces, particularly blast furnaces, are extensively described in “Stahl und Eisen”, 106 (1986), No. 2, pages 205-210. In addition to cooling with so-called cooling boxes, in recent years cooling with cooling plates, so-called staves, of cast iron and copper has been used increasingly.
DE 39 25 280 discloses a cooling plate of grey cast iron in which the cooling ducts are formed by cooling tubes which are cast into the cast body. This cooling plate has the disadvantage that, for preventing carburization, a coating of the cooling tubes is required which impairs the thermal flux from the hot side of the cooling plate or stave through the stave body and the tube wall toward the cooling water. Accordingly, such staves frequently reached high temperatures in excess of 760° C. at which decomposition of the pearlite occurs; cracks formed in the cast body and the cast material in front of the cooling tubes wears off even after a relatively short period of operation.
It has been attempted to achieve a longer durability of these staves of cast iron by casting a plurality of cooling tubes in the staves and to arrange these cooling tubes partially also in different planes parallel to the hot side. This made the staves of grey cast iron much more complicated and expensive, but the durability of the staves did not increase to the same extent.
A significant improvement were the so-called copper staves which are disclosed in DE 29 07 511 and are manufactured from rolled copper material, wherein the cooling ducts are produced by deep hole drilling parallel to the hot side. This makes possible an unimpeded thermal flux which is not impaired by any coating of the tubes. Copper staves of this type are significantly cooler on their hot sides than staves of grey cast iron, so that, contrary to staves of grey cast iron, a stable crust of burden material acting as insulation is formed on the hot side. This is the reason why copper staves, even though the thermal conductivity of this material is high, discharge less heat from a blast furnace than staves of grey cast iron.
Another advantage of the copper staves is the fact that they can be constructed thinner at about 150 mm than staves of grey cast iron at about 250 mm. Consequently, at a given size of the blast furnace, the useful volume is increased significantly when copper staves are used.
However, the decisive advantage of the copper staves as compared to staves of cast iron is the fact that they do not exhibit the formation of cracks because of the material properties and their surface wear is extremely low. In a long term experiment extending over more than ten years, a material loss of only 3 to 4 mm was observed. In the case of a rib height of 50 mm, this results in a computed service life of about 150 years which substantially exceeds the service life of the remaining blast furnace.
A disadvantage of the conventional copper staves is the fact that they are still constructed of relatively substantial solid material and, therefore, are heavy and expensive. The staves must be processed to a significant extent because of the necessary mechanical working on all sides, the cutting of grooves, the deep hole drilling and the welding of the pipe connections. The material removed by chip-removing processes constitutes a substantial portion of the total weight and can be sold only at a significantly lower price. Another disadvantage is the fact that when deep hole drilling is carried out in excess of 2 to 3 m depth, the duct diameters may not be less than a certain dimension because otherwise there is the danger that the drill runs off center. The cooling ducts produced in this manner are larger than necessary; the same is true for the quantity of cooling water because a minimum speed of about 1.5 m/sec is necessary for separating steam bubbles which may form at the tube wall as a result of the high thermal load. Consequently, the cooling water heating rates are uneconomically low.
SUMMARY OF THE INVENTION
Therefore, it is the primary object of the present invention to provide a cooling element which, contrary to conventional copper staves, uses significantly less material and requires less processing, while still being stable and able to withstand the rough operating conditions of a blast furnace, wherein the cooling element can be mounted easily and has a service life which is at least in the same order of magnitude as a blast furnace plant.
Another object of the invention is to provide a suitable flow cross-section for the cooling water which has a shape deviating from the circular shape in order to achieve greater heating rates for the cooling water without dropping below the necessary minimum speed for the cooling water which is required for separating and conveying away the steam bubbles which form at the tube wall at high thermal loads.
Finally, the hot side is to be configured in such a way that a surface is produced in an uncomplicated manner to which crusts of burden material can adhere well.
In accordance with the present invention, the cooling element is composed of an extruded or rolled section which in the interior thereof has a plurality of cooling ducts which are round or have a shape which deviates from the circular shape. The cooling element is provided with lateral webs. The cooling element is equipped on the side facing away from the blast furnace wall in vertical direction with at least one continuous slag rib and the cooling element is equipped on the side facing the blast furnace wall with at least one fastening rib.
In accordance with another embodiment of the present invention, the cooling element is composed of an extruded rectangular section having a groove and an extruded rectangular section having a key. Cooling ducts are arranged in the sections. The sections can be closed with an upper cover and a lower cover, wherein in the upper cover and in the lower cover each is laterally placed a pipe piece which is connected to the cooling ducts of the cooling element.
While a conventional copper cooling element usually has four parallel cooling ducts which extend in a copper block parallel to the hot side, the cooling element according to the present invention is composed of an extruded or rolled copper section having an appropriately selected length, wherein the section has one or more cooling ducts which are round or have a shape deviating from the circular shape. By providing appropriate ribs which extend from the cooling duct or ducts, the extruded or rolled section has a sufficient stiffness necessary for withstanding the rough operating conditions of a blast furnace; this refers particularly to the fastening rib or ribs arranged on the cooling element on the side facing the steel jacket of the blast furnace. The ribs also serve for fastening the cooling element to the steel jacket of the blast furnace. The lateral webs of the copper elements extending parallel to the steel jacket of the blast furnace ensure that the complete surface area of the steel jacket of the blast furnace is protected. The width of the webs is selected in such a way that they overlap or extend flush with the corresponding web of the neighboring element. This makes it possible to also compensate for the diameter or circumference differences in the conical portions of the steel jacket of the blast furnace, i.e., at the bosh or the shaft. The slag ribs on the hot side facing the interior of the furnace are mechanically finished in such a way that they facilitate the formation and stable adherence of a layer of solid or pasty burden materials to the hot side of the copper cooling elements.
The copper cooling elements can be cut to the correct length and be
Atkinson Christopher
Friedrich Kueffner
SMS Schloemann--Siemag Aktiengesellschaft
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