Patent Application
20130099430
1. Field of the Invention
The present invention relates to round-bottom pyrometallergical furnaces for the smelting, converting, or melting of concentrates, mattes, or metals; and more particularly to elastically interconnecting coolers arranged in ring segments and tiers to optimally compress the brick hearth and lower walls in a furnace refractory without resorting to a containment shell.
2. Description of the Prior Art
One type of smelting furnace for winning copper from ore is built with vertical, cylindrical, steel containment shells with layers of refractory bricks inside the walls and a downwardly dished bottom. A hearth brick sub-layer on the bottom is covered with a brick hearth working layer. The refractory brick layers inside the steel containment shells can withstand the very high operating temperatures usual to the smelting of copper concentrate, and the outer shell provides the necessary containment and support.
Hearth bricks swell up in size over their operational lives as the bricks slowly absorb molecules of metal. Many expensive and complex ways have been devised over the years to keep the refractory bricks tightly pressed together as they swell so that liquid metal, matte, or slag cannot leak through the gaps. For example, so-called “flexible shells” bind adjoining overlapping or segmented plates together using a combination of springs, tie rods, or levers and rods. The loose plate construction can allow for quite a lot of expansion and contraction. However, the cost of these kinds of containment shells is prohibitive.
Rigid hearth containment shells are much less expensive since they are constructed as a single rigid piece that does not require plate binding mechanisms. But conventional ways of keeping the hearth bricks together under the right pressures for these rigid shells accommodates only very limited growth in the hearth brick before shutdown and replacement with new brick is required.
Conventional systems are normally designed to accommodate the thermal expansion of the bricks, but do not maintain the pressure when the bricks cool down and shrink. This allows gaps to form which can invite molten materials to penetrate the brick joints. When the furnace finally reheats, the hearth is incrementally increased in diameter by the new material frozen in the joints. It therefore follows that extending the service life of the hearth bricks translates directly into substantial savings in the maintenance costs because shutdowns are fewer and less frequent, and not as many brick replacements are needed over the life of the furnace.
A basic problem with the design of circular furnaces has been the hearths tend to expand more than do the walls. This is especially pronounced if the walls are water cooled. What is needed are designs that can accommodate both hearth expansion and lesser expansions in the lower wall brick and any refractory.
Briefly, an elastically interconnected cooler compressed hearth embodiment of the present invention comprises a concave dished bottom lined with a sub-layer and a working layer of hearth bricks. Cylindrical walls rise up from the rim of the concave dished bottom. These are constructed with one or more tiers of coolers shaped in arc segments that are joined together into complete rings. The outer perimeter of the hearth brick within the ringed tiers is inwardly compressed toward the center to disallow any leaks from forming between the separate bricks. Flanges are provided on the outside peripheries of each cooler so the coolers themselves can be assembled into rings and elastically interconnected by fasteners and springs. Each spring can be individually adjusted to obtain optimal working pressures on the whole of the hearth bricks.
These and other objects and advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the various drawing figures.
While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Embodiments of the present invention do not rely on a full containment shell to provide the hoop strength and leverage necessary to compress the brick hearth in a furnace refractory. The coolers themselves are cast as segments of a ring that can be stacked in tiers, and then interconnected with springs and bolts through flanges on their outer perimeters to form an elastic hoop. The assembled coolers and adjustments provide the substantial inward compressive forces required to keep the gaps and joints closed in the brick hearth and walls that line the innards.
In
A concave bottom floor 140 comprises a refractory or a bottom lined with a hearth brick working layer 142 (
A notch 146 in the bottom inside edge of these cooling segments is used to nest a refractory or brick 148 which maintains a downward pressure on the top periphery of hearth brick working layer 142.
Tap holes 152 and 154 (best seen in
If the weight of the walls are not sufficient to balance the upward forces at the rim of the hearth, and enough to seal the spaces between the wall and hearth, then a clamping system will need to be included. The hold-down ring 108 is spring-clamped to bottom section 101 and capture a flange on each of the cooling segments in the first tier 102, e.g., 129-133. For example, a bolt 160 is passed through a hold-down ring 108 into a flange on base 104. Two springs 162 and 164 allow some give as the refractory and hearth brick swell during the hearth's campaign life. The bolt and springs are retained and rendered adjustable by a nut 166. Those skilled in the design of hearths will be familiar with many other ways to implement the required compression and adjustability.
Simpler arrangements can be used to interconnect the pieces together than is shown in
The shape of the wall cooler comes directly from the furnace geometry. The upper faces most often form a vertical cylinder that holds the feed and molten materials. A sloped face than bells out intersects with the hearth at the same angle as the outside, perimeter edges of the hearth brick. The bottom of the wall coolers are typically flat, e.g., to permit installation on the top of a brick or steel surface, or a lower water-cooled copper block.
The outside face of the wall coolers are relieved of as much as is possible by hollowing out to reduce weight and costs. The top, bottom, and side flanges, however, need to be kept quite robust to withstand the large forces involved in containing the furnace. These flanges are often tapered to simplify casting.
Similarly, the top and lower tiers 201 and 202 are fastened to a base 220 with a threaded rod 222 that passes through flange 204 and a base ring 224. A nut 226 is used to adjustably compress a spring down against flange 204, as is a nut 230 used to adjustably compress a spring 232 up against base ring 224. As before, the result is top and lower tiers 201 and 202 are able separate a little bit from base 220 and accommodate hearth growth by compressing springs 228 and 232.
An inside, hot face hearth wall 302 interfaces with castable, refractory, brick, or slag, and the wall itself may be patterned, ribbed, or otherwise textured. Outside, four flanges 304-307 with several bolt holes each facilitate interconnections with other cooling blocks and hearth bases. The top and lateral outside edges of cooling block 300 are provided with lap joints, with horizontal lap joint 308 and vertical lap joint 310 being visible in
It is critical that each of the cooler segments not be rigidly bolted together such that there is no flexibility or elasticity in the rings and tiers they form. In general, the hearth brick and/or refractory layered inside hearth 100 is kept in compression by providing bolt holes in the flanges so heavy compression type springs inserted under the bolt heads or nuts can maintain an even compression while also allowing some give during furnace thermal cycling. Other fastening and compression components can also be used. The use of compression springs drawn down by bolts and nuts allows the amount of compression and travel to be selectable and adjustable. The sizes and configurations of the springs, bolts, and nuts can be empirically selected and even refitted after furnace commissioning to optimize performance.
The interconnection of the cooling segments to one another to form a ring eliminates the need for an outer steel containment shell. In previous furnace designs, the outer containment shells provide the leverage and hoop strength needed by their compression systems to compress the hearth brick. Here, as seen in
In operation, adjustable spring assemblies are periodically set to a predetermined pressure value. The hearth brick working layer will inevitably grow in diameter as molecules of molten metal are absorbed into the refractory brick material and the infinitesimal spaces between them. Such growth necessitates routine readjustment of the adjustable spring assemblies, and so the conditions should be monitored.
The typical commercial furnace hearth size ranges from two to fifteen meters in diameter. The design configuration is used to impart initial compression of the hearth, which could result in an initial net shrinkage. The design must typically accommodate 20-150 mm of hearth expansion. On a percentage basis, this means up to a practical maximum of two percent of the hearth diameter.
The minimum compression forces on the hearth refractory brick should be sufficient to keep interfacial pressures between the bricks greater than the fluid pressures trying to come between them or the pressures to float the bricks. So an important design objective is to limit penetration of molten metal, matte or slag that gets into the joints. Too rapid a penetration can induce a quicker-than-normal rate of expansion of the hearth over the long term.
If too much molten metal penetrates under the bricks, individual bricks and sections of brick hearth can separate out and float to the top of the matte. Therefore, the hearth compression forces applied must be sufficient to maintain hearth stability, and overcome strong buoyancy pressures in spite of any molten metals getting beneath the hearth brick working layers.
Service life will be greatly increased at very modest cost when sufficient hearth compression pressures are applied. These help to maintain hearth stability by limiting melt penetration between the joints. The long-term hearth refractory rate-of-growth will not exceed that observed in conventional current hearth designs.
Corrosion can be an issue in those environments where corrosive gases are produced as part of the smelting process. Gases like SO2 and SO3 can readily form acids. Acid environments necessitate the use of stainless steel or nickel alloys to resist corrosion.
The parts that are exposed to high heat loads or molten materials will require cooling. If a component is to be cooled, it may be fabricated from a conductive alloy of copper or other metal, to minimize stresses and to reduce the potential for cracking. For example, the internal member used for distributing the compressive forces to the hearth may be cooled with air, water or other heat transfer fluid or gas. It may have internal cooling passages for conveying the heat transfer fluid or gas.
As the refractory core 414 swells during its campaign life due to metal absorption and joint penetration, the growth is taken up by springs 422 and 423. As it grows and the springs are compressed, small gaps will develop between the twelve cooler segments 401-412. However, the inward compressive pressure they cooperatively apply to the refractory core 414 will remain constant if nuts 421 and 424 on every spring-bolt assembly have been properly maintained.
In alternative designs where the coolers do not extend down as low as seen in
On circular furnaces, the normal practice is to brick the hearth right up against the lower tap hole. As the hearth brick expands, it compresses the expansion material behind the skews. Without any crush material to accommodate and absorb normal expansion and swelling at the lower tap holes, the tap hole brick, shell, and coolers would be over-stressed by the strong outward pressures that can develop. Excess pressures can lead to shell distortion, cracking, and a displacement of the tap hole cooler away from the shell plate. Such can force open gaps and permit molten materials to leak through.
Local expansion movements at the lower tap holes must be accommodated without having to compress the entire hearth. The embodiments described here could be adopted immediately in many conventional furnaces. The upper wall coolers can be like those described in connection with
For example,
An interconnecting plate with slots bolted onto the outside faces of the wall-cooling blocks with shoulder bolts may be necessary to prevent adjacent wall-cooling blocks from getting askew of one another. For example, between the vertical flanges of coolers 532 and 533, and all others in the same tier. No doubt other methods and devices could be adapted to prevent misalignments of the ship-lap joints between the coolers in order to control leakage.
A hearth floor 550 comprised of hearth brick 551 (
In some embodiments of the present invention, a notch 560 is milled into the bottom inside corner of the hot faces of the lower wall-cooling blocks to retain and compress a brick ring 562 down on to an annular hearth floor retaining ring 564. The notch 560 assists in retaining the refractory and brick at a point in the furnace where the forces are very great and where high metal/matte/alloy levels could otherwise damage the cooling-wall blocks.
In
Alternatively, the brick in front of the tap hole can be replaced by a separate cooler. The cavities inside conduits 572 and 573 can be filled with refractory material, and can be sized to permit proper installation.
Inside, the hot faces of hearth wall 602 can be horizontally ribbed, for example, to facilitate the attachment of refractory and hearth brick. Outside, four flanges 604-607 each facilitate interconnections with other cooling blocks and hearth bases. The top and side flanges are provided with bolt holes as well as lap joints. A horizontal lap joint 608 and vertical lap joint 610 are visible in
Embodiments of the present invention are used to best advantage as described herein for the lower walls and hearth, e.g., as in
The designs illustrated in
Although the present invention has been described in terms of the presently preferred embodiments, it is to be understood that the disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art after having read the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the “true” spirit and scope of the invention.
