WO2010076368A1

WO2010076368A1 - Method for producing a cooling element for pyrometallurgical reactor and the cooling element

Info

Publication number: WO2010076368A1
Application number: PCT/FI2008/050791
Authority: WO
Inventors: Pasi Rinne; Tuomas Renfors
Original assignee: Luvata Espoo Oy
Priority date: 2008-12-29
Filing date: 2008-12-29
Publication date: 2010-07-08
Also published as: RU2487946C2; EP2370603A4; EP2370603A1; RU2011124544A; ZA201104065B

Abstract

Cooling element (2) for pyrometallurgical reactors and method of manufacturing the element, the element comprising a body (4) having at least one cooling channel (5) within, the direction of the cooling channel determining the lengthwise direction of the element (2). In the element there is at least one attachment groove (6) on one surface of the element (2) for attaching refractory tiles to the element and a passage (7) for cooling fluid into at least one cooling channel (5). At least one attachment groove (6) runs parallel to at least one cooling channel (5)and at least the surface opposite to the surface wherein the attachment groove (6) is made is continuously and evenly curved in direction crosswise to the cooling channels.

Description

Method for producing a cooling element for pyrometallurgical reactor and the cooling element

This invention relates to cooling elements of pyrometallurgical reactors such as blast furnaces and similar used for producing and refining metals or metal alloys. The largest field of use of such reactors is manufacture of steel.

Pyrometallurgical reactors comprise a reactor vessel, usually made of steel, cooling elements arranged inside the reactor vessel and against its wall and a refractory layer forming the inside surface of the reactor. The refractory layer is made of bricks or flowing refractory material that is spread on the surface of the cooling elements. The cooling elements have crosswise grooves for attaching the bricks to the elements. When the cooling elements are attached to the reactor vessel, the grooves run horizontally as well as the brick layers. In addition of above mentioned elements, the reactor vessel includes passages and means for introducing metal materials, fuel, air, oxygen or shield gases and additives to the reactor, all according to the process for which the reactor is used.

The refractory layer of reactors in pyrometallurgical processes is protected by water- cooled cooling elements so that, as a result of cooling, the heat coming to the refractory surface is transferred via the cooling element to water, whereby the wear of the lining is significantly reduced compared with a reactor which is not cooled. Reduced wear is caused by the effect of cooling, which brings about forming of so called autogenic lining, which fixes to the surface of a heat resistant lining. This lining is formed from slag and other substances precipitated from the molten phases.

Conventionally cooling elements are manufactured in two ways: primarily, elements can be manufactured by sand casting, where cooling pipes made of a highly thermally conductive material such as copper are set in a sand-formed mould, and are cooled with air or water during the casting around the pipes. The element cast around the pipes is also of highly thermally conductive material, preferably copper. This kind of manufacturing method is described in e. g. GB patent no. 1386645. One problem with this method is the uneven attachment of the piping acting as cooling channel to the cast material surrounding it. Because of this some of the pipes may be completely free of the element cast around it and part of the pipe may be completely melted and thus damaged. If no metallic bond is formed between the cooling pipe and the rest of the cast element around it, heat transfer will not be efficient. Again, if the piping melts completely, that will prevent the flow of cooling water. The casting properties of the cast material can be improved, for example, by mixing phosphorus with the copper to improve the metallic bond formed between the piping and the cast material, but in that case, the heat transfer properties (thermal conductivity) of the copper are significantly weakened by even a small addition. One advantage of this method worth mentioning is the comparatively low manufacturing cost and independence from dimensions.

Another method of manufacture is used, whereby glass tubing in the shape of a channel is set into the cooling element mould. The glass is broken after casting to form a channel inside the element.

US patent 4,382,585 describes another, much used method of manufacturing cooling elements, according to which the element is manufactured for example from rolled copper plate by machining the necessary channels into it. The advantage of an element manufactured this way, is its dense, strong structure and good heat transfer from the element to a cooling medium such as water. Disadvantages are limited size because of dimensional limitations and high cost.

A well-known method in the prior art has been to manufacture a cooling element for a pyrometallurgical reactor by casting a hollow profile as continuous casting i. e. slip casting through a die. Lengthwise holes can be made to the element by mandrels. The element is manufactured of a highly thermally conductive metal such as copper. The advantage of this method is a dense cast structure, good surface quality and the cast cooling channel gives good heat transfer from the element to the cooling medium, so that no effects impeding heat transfer occur, rather the heat coming from the reactor to the cooling element is transferred without any excess heat transfer resistance directly to the surface of the channel and onwards to the cooling water. The cross-section of the cooling channel is generally round or oval and the mandrel has a smooth surface. This type of cooling channel is mentioned in US patent 5,772,955. The main disadvantage of this kind of cooling element is that the grooves for refractory tiles or bricks are arranged vertically in order to make mounting of the tiles possible. Because of this, the element has to be straight in crosswise direction so that the tiles can be slid in the grooves. Since the inner surface of the reactor vessel is circular, only the edges of the cooling elements are supported by the wall of the vessel and empty space is left between the back of the cooling element and vessel.

In order to improve the heat transfer capability of a cooling element it is however preferable to increase the heat transfer surface area of the element. This can be done by increasing the wall surface area of the flow channel without enlarging the diameter or adding length. The wall surface area of the cooling element flow channel is increased by forming grooves in the channel wall during casting or by machining grooves or threads in the channel after casting so that the cross-section of the channel remains essentially round or oval. As a result, with the same amount of heat, a smaller difference in temperature is needed between the water and the flow channel wall and an even lower cooling element temperature. This method is described in WO/2000/037870.

The purpose of this invention is to produce a new method for making cooling elements for pyrometallurgical reactors and new cooling element made according to the method.

Further, the purpose of the invention is to create a cooling element that is more cost effective to produce.

Further, purpose of one embodiment of the invention is to produce a cooling element that uses less space within a reactor that has a circular inner wall.

Purpose of one embodiment of the invention is to diminish machining required for producing the cooling element. The invention is based in that the grooves for refractory tiles run parallel to cooling channels and the element has at least one continuous curvature that is greater in crosswise direction to the cooling channels than in the direction of the cooling channels.

According to one preferred embodiment of the invention the element is straight in direction of cooling channels.

According to one preferred embodiment of the invention the cooling channels and grooves for tiles are both made by continuous casting process.

According to one preferred embodiment of the invention at least one of the cooling channels or grooves for tiles are made by machining.

More specifically, the cooling element and method for its manufacture according to the invention is characterized by what is presented in the independent claims.

The embodiments of the invention provide essential benefits.

One very clear benefit is the saving of material and machining time. Compared to conventional continuously cast element the savings in material can be about 20% and machining time is reduced to machining the through- holes for cooling liquid. Since the curved back surface of the element can be dimensioned to fit against the surface of the reactor vessel, the volume of the vessel is increased giving more manufacturing capacity. The length of the element is not limited by the manufacturing process, since cooling channels and tile grooves can be made by casting as long as desired, contrary to drilled channels. Since the elements are curved, the central part of the element is not stressed more than edge parts, which leads to more even wear of the element and longer lifetime.

Because of savings in the material and manufacturing costs, it can be contemplated that cast iron cooling elements used in upper regions of the reactors are replaced with elements according to the invention. This would be beneficial since service life of copper elements is greater than that of the iron elements whereby need of maintenance and downtime could be decreased.

The invention is now described in more detail on basis of following examples and appended drawings.

Fig. 1 shows cooling elements according to prior art arranged in a reactor vessel.

Fig. 2 shows a cooling element according to the invention on the side facing the reactor space.

Figs 3 and 4 show a cooling element according to the invention on the side facing the wall of a reactor vessel.

Fig. 5 shows cooling elements according to the invention arranged in a reactor vessel.

Fig. 6 is a schematic drawing of the continuous casting process for making a cooling element according to the invention.

In the figure 1 , the wall of the reactor vessel described conceptually by a circle 1. The cooling elements 2 are placed inside wall 1 and the pipes 3 for cooling water run through the wall 1. Typical dimensions of a reactor, for example a blast furnace are 12 m in diameter and tens of meters in height, as an example about 30m. The length of cooling elements 3 in upward direction is typically 2 m and the width 1 m. When the element is placed in the reactor vessel, its straight back surface faces the inside wall of the reactor and only the edges of the cooling element touch the wall. Thus, empty space is created between the back surface of the element 2 and the wall 1 and the volume of the reactor vessel is unnecessarily diminished. Also, the inside surface formed by the cooling elements becomes multifaceted, which increases the stress of the central parts of the cooling elements and leads to shortened lifetime. Figures 2 - 4 show one embodiment of the invention. The cooling element 2 comprises a body 4 made of thermally conductive material, such as copper, aluminum or steel or their alloys. Since the thermal conductivity of copper is superior to that of the aluminum or steel, it is the preferred material in highly demanding uses as in pyrotechnical reactors. On the other hand materials like titanium and its alloys may provide excellent properties in some uses but their high price limits the use. In the body there are lengthwise cooling channels 5, having an oval cross section in this embodiment. Dimensioning and design of cooling channels is described in more detail in WO/2000/037870, which is included herein by reference. The surface facing the interior of the reactor vessel the element 2 has grooves 6 for attaching refractory tiles. The grooves 6 can have a form of a dovetail or any cross section that corresponds with the attaching elements of the tiles. The important thing is that the grooves 6 run parallel to the cooling channels in order to make it possible to manufacture the element by continuous casting. The curvature of the element should also be preferably straight in length direction of the grooves 6 so that the tiles can be slid easily on the grooves 6. The surface of the element facing the wall of the reactor vessel is smooth and the curvature of this surface and the whole element in above defined direction is continuous, even and most preferably follows a curve of a circle having same diameter as the inside wall of the reactor vessel. Continuous and even curvature is considered to be defined by arc that has constant radius of curvature over a surface in question.

The curvature of the element in crosswise direction of the element, i.e. in perpendicular to cooling channels 5 is adapted to the curvature of the inner wall of the reactor vessel in which the elements are to be assembled. The curvature in this direction is easy to manufacture by continuous casting and can therefore be adjusted to any reactor vessel according to the customer's specifications. At the ends of the cooling channels 5 are pipes for feeding cooling liquid of other cooling fluid in to the element and removing the heated water. The pipes are mounted on holes made on that surface of the element that is facing the wall of the reactor vessel. The holes for the pipes can be made simply by drilling into the cooling liquid channel and the pies can be mounted by any suitable means such as welding or threading. The ends of the cooling channels on the end surfaces of the cooling elements are usually closed so that the cooling water fed in one cooling channel circulates only in one cooling element and channel independently. However, other arrangements can be used as needed, for example several cooling elements of channels can be joined in series if the temperature of the cooling liquid does not rise too much.

For the purposes of this document the end surfaces of the element are those on which the cooling channels terminate. The side surfaces are the surfaces running parallel to the cooling cannels. The side surfaces are angled to the surfaces facing the reactor wall and the inside of the reactor. The angle is determined so that it is directed along the radius r of the reactor vessel when the element is attached to the wall of the vessel. In other words, the element should be preferably dimensioned so that surface facing the wall of the reactor vessel has such a curvature and the side walls such an angle in relation to each other that the element forms a part of a sector of a circle that has same radius as the inside wall of the reactor vessel. This feature is illustrated in fig. 5. The end surfaces are usually straight and perpendicular to other surfaces.

From figure 5 it can be seen that the cooling elements fit perfectly to each other in sideways and also against the wall of the reactor vessel.

In continuous casting process the product is cast through a cooled die that forms the outer surface of the product. If holes or such are needed, they can be made using mandrels that are set within the cross section of the die. For example, in figure 1 the die 8 is formed so that it gives the outer form of the cooling element 2 and the mandrels 9 form the oval cooling channels. The continuous casting process is well known in the art whereby it is not discussed herein in more detail.

Instead of continuous casting the cooling element according to the invention can be made by machining. The one could start with a curved slab and bore the cooling channels in the slab and machine the grooves as required. However, this would be quite expensive but might be reasonable for making prototypes or a limited amount of tailored elements, for example. In any case the casting process gives already good flexibility in dimensioning and design of the product. For example the positioning of the cooling channels can be optimized as desired as well as outer dimensions and design of the element. Other casting methods may also be used. It is not necessary to form the element as whole curved, but the minimum is that the surface facing the inner wall of the reactor vessel is curved. However, keeping the surface facing the reactor space straight does not provide any benefits according to present knowledge.

Thus, while there have been shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the invention may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same results are within the scope of the invention. Substitutions of the elements from one described embodiment to another are also fully intended and contemplated. It is also to be understood that the drawings are not necessarily drawn to scale but they are merely conceptual in nature. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

Claims

Claims:

1. Method for manufacturing a cooling element (2) for pyrometallurgical reactors, the method comprising:

- forming a body (4) having at least one cooling channel (5), the direction of the cooling channel determining the lengthwise direction of the element (2),

- forming at least one attachment groove (6) on one surface of the element (2) for attaching refractory tiles to the element, and

- providing passage (7) for cooling fluid into at least one cooling channel (5),

characterized by

- forming at least one attachment groove (6) which runs parallel to at least one cooling channel (5), and

- forming at least the surface opposite to the surface wherein the attachment groove is made continuously and evenly curved in direction crosswise to the cooling channel.

2. Method according to claim 1 characterized in that the cooling element (2) comprising body (4), at least one cooling channel (5) and at least one attachment groove (6) is formed by continuous casting.

3. Method according to the claim 2, characterized in that the cooling element is cast straight in direction of coaling channels (5).

4. Method according to claim 1, characterized in that at least one attachment groove is made by machining.

5. Method according to any of the preceding claims, characterized in that the cooling element is made of copper or an alloy thereof.

6. Cooling element (2) for pyrometallurgical reactors, the element comprising:

- a body (4) having at least one cooling channel (5) within, the direction of the cooling channel determining the lengthwise direction of the element (2), - at least one attachment groove (6) on one surface of the element (2) for attaching refractory tiles to the element, and

- passage (7) for cooling fluid into at least one cooling channel (5),

characterized in that

- at least one attachment groove (6) runs parallel to at least one cooling channel

(5), and

- at least the surface opposite to the surface wherein the attachment groove (6) is made is continuously and evenly curved in direction crosswise to the cooling channels.

7. Cooling element according to claim 5, characterized in that the cooling element is made of copper or an alloy thereof.

8. Cooling element for a specific reactor and according to any of claims 6 or 7, characterized in that the element (2) is dimensioned so that surface facing the wall (1) of the reactor vessel has such a curvature and the side walls such an angle in relation to each other that the element (2) forms a part of a sector of a circle that has the same radius (r) as the inside wall of the reactor vessel.

9. Cooling element according to any of preceding claims 6 - 8, characterized in that the element is straight in direction of cooling channels (5).