WO2014008575A1

WO2014008575A1 - Furnace air cooling system

Info

Publication number: WO2014008575A1
Application number: PCT/CA2012/050467
Authority: WO
Inventors: Bert O. Wasmund; Kerry MCKENNA
Original assignee: Hatch Ltd.
Priority date: 2012-07-10
Filing date: 2012-07-10
Publication date: 2014-01-16
Also published as: AU2012244251A1

Abstract

A cooling system for a furnace comprises a cover member covering at least a portion of the outer surface of the furnace side wall and spaced therefrom to form an air circulation space, the cover member having at least one inlet and at least one outlet through which air enters and leaves the air circulation space. The cooling system also comprises a plurality of cooling fin members provided within the air circulation space and extending between the outer surface of the furnace side wall and the cover member, each of said cooling fin members being in thermal contact with the furnace side wall. The cooling fins may be corrugated and may extend horizontally along the outer surface of the furnace side wall.

Description

FURNACE AIR COOLING SYSTEM

FI ELD OF THE INVENTION

[0001 ] The present invention relates to cooling systems for furnaces, and particularly to cooling systems in which the cooling fluid is air. BACKGROUND OF THE I NVENTION

[0002] Metallurgical process vessels typically have a hearth and side walls formed of refractory brick, with an outer metal plate which may be provided with a system to cool the outer shell. Herein these process vessels, which generally hold a bath of both molten metal and overlying slag, are referred to as furnaces. [0003] Due to the aggressive nature of many slags produced in metallurgical processes, cooling is required to freeze a layer of slag on the inner surface of the vessel to maintain a stable side wall. As discussed in Voermann et al. , Furnace Cooling Design for Modern High Intensity Pyrometallurgical Processes (Proceedings at the Copper 99 - Cobre 99 International Conference, Phoenix, AZ, U.S.A.), the cooling required is dictated by the process conditions in the vessel. To keep the crucible lining in equilibrium, the process heat flux imposed by the process must be matched by the cooling system's heat removal capacity.

[0004] In practice a wide range of heat fluxes are encountered in various metallurgical furnaces. Heat fluxes are dependent on the intensity of the process and whether the containment is for slag or metal. Heat fluxes can typically range from a low value of about 5 kW/m², which can be removed by natural air cooling, to over 2,500 kW/m², which requires intense forced water cooling. Generally, for heat fluxes in the lower range, about 15 kW/m² or less, forced air cooling of the furnace shell plate can be used. For heat fluxes above about 15 kW/m², some type of water cooling is generally adopted to avoid overheating of the furnace shell plate and structural members. Due to the potential risk of an explosion in the event that molten material from inside the furnace contacts water in the cooling system, it is desirable to avoid using water as the cooling medium wherever possible. [0005] Considerable progress has been made in improving the capacity and safety of furnace water cooling systems, such as the use of solid copper blocks installed in the furnace wall and cooled on the exterior portion, as described in U.S. patent No. 3,849,587 (Hatch et al.). However, such systems require openings in the shell plate, either for inserting the cooling blocks or for accommodating the cooling water pipes if the blocks are installed entirely inside the shell plate. These openings are undesirable in that they provide areas for ingress of furnace molten products through the wall, and also encumber shell design thereby adding cost.

[0006] Moreover, while many furnaces can be improved through increased side wall cooling, certain processes are adversely affected by over cooling, and for such processes the need exists for a system with variable heat removal. One such process is that using Hall-Heroult reduction cells for primary aluminum production. Aggressive cooling of the shell of a furnace used in this process can cause excessive buildup on the inside of the vessel, reducing the production capacity of the cell. Too little cooling and the cell integrity may be compromised over time. Thus it is advantageous to use a cooling system which can be controlled to suit cell conditions.

[0007] Furnace bottom plates also benefit from variable cooling in order to control the thickness of frozen accretion forming in the hearth / crucible and wall area around tapholes where cooling generally improves the life of the refractories but extensive cooling can create serious difficulties in opening the tapholes.

[0008] Many furnace cooling systems use water as a cooling medium. Water has the ability to remove significant amounts of heat; however, it has a narrow range of operating temperatures. Due to the potential risk of an explosion in the event that molten material from inside the furnace contacts water in the cooling system, it is desirable to use a furnace cooling system which does not use water as a cooling fluid. Although typical air-cooling systems cannot match the heat removal capacity of water cooling systems, they have a wider operating temperature range and hence offer significant advantages in cooling applications where adjustable heat removal rates are required. [0009] A number of furnace cooling systems are known in which air is used as the cooling fluid. For example, U.S. Patent No. 5,230617 (Klein et al.) discloses a cooling arrangement in which a number of metal shrouds encircle a cylindrical furnace. Each shroud forms a hollow cooling chamber through which air is circulated, and into which water is atomized to enhance the cooling effect. However, the introduction of water vapour into the system will complicate the cooling air supply system, and create corrosion problems that will impact material selection. Both of these issues will increase complexity and cost.

[00010] U.S. Patent No. 1 ,674,422 to Allen, Jr. et al. discloses an air-cooled furnace wall in which cast hangers support refractory walls separated by air circulation spaces. U.S. Patent No. 3,315,950 to Potocnik et al. discloses a heating chamber wall for a furnace, in which the wall has an interior space through which air is allowed to circulate. U.S. Patent No. 3,777,043 (O'Neill) discloses an annular air circulation channel formed within the refractory furnace wall. U.S. Patent No. 4, 199,652 (Longenecker) discloses J-shaped channels formed between the refractory side wall and the metal outer shell of a furnace. U.S. Patent No. 6,251 ,237 (Bos) discloses localized jets blowing directly onto the shell with variable flow for Hall-Heroult aluminum electrolytic pots.

[00011] In the above-mentioned patent to O'Neill, and in U.S. Patent No. 1 ,751 ,008 (La France), the structure of the refractory furnace side wall is modified to provide increased surface area for enhanced cooling. In La France, this is accomplished by forming ribs and channels in the outer surfaces of the blocks making up the refractory walls. In O'Neill, the annular cooling channels can be made in the form of "tortuous paths" by using bricks of varying lengths. While these techniques can help to enable increased heat removal capacity, it is extremely difficult to distribute the air evenly over the wall, a problem which worsens as the furnace ages due to shifting and movement of the brickwork. Also, the addition of air into the brickwork behind the shell plate would not be feasible in many furnaces since air would react with the furnace products, e.g. CO gas, metals, etc.

[00012] Thus, known air-cooling arrangements for metallurgical furnaces generally provide insufficient cooling and/or are unduly complex, requiring specially constructed furnace side walls. Such systems are also relatively expensive and cannot be practically adapted to existing furnace installations.

SUMMARY OF THE I NVENTION

[00013] The cooling system according to the present invention comprises a series of corrugated high thermal conductivity fins attached to at least a portion of a furnace outer shell, where the outer shell is in thermal contact with the inner refractory lining of the furnace. The fins are positioned within at least one air circulation space defined by the outer surface of the shell and a cover member. The fins are closely arranged in spaced relationship to define a plurality of air circulation paths. Air is forced through the circulation space between the fins to remove heat from the furnace.

[00014] The cooling system according to the present invention may in addition include means to control the flow of air into the plurality of air circulation paths so as to vary the rate of heat removal of the cooling system. The fins preferably include corrugated cooling plates.

[00015] The cooling system according to the present invention is particularly adapted for installation on new or existing furnaces having an inner refractory layer and an outer metal shell. In such furnaces, the cooling fin members are preferably secured to the outer metal shell, and are covered by the cover member, which may preferably comprise a plurality of metal sheets supported by a number of support members attached to the outer metal shell of the furnace. The flow rate of cooling air may be controlled with feed back from shell temperatures to vary heat removal.

[00016] The furnace air cooling system of the present invention achieves a number of important advances over the existing cooling technologies. First, it can extend the cooling range of existing forced air technology from about 10 kW/m² to over 40 kW/m², which enables effective adoption of safe air cooling to many new applications currently limited to water cooling, such as the portion of furnace walls around tapholes. Secondly, it provides the ability to adjust the cooling rate in a reliable, controllable manner to suit the needs of the process, a feature which is not possible with water cooling and which is an important requirement in numerous applications, such as aluminum production with Hall-Heroult cells.

[00017] Thirdly, cooling can be achieved with moderate air velocities, which reduces the energy consumption for providing the air, and avoids excessive ambient noise levels in the furnace work place. In addition, the air cooling system of the present invention can be installed without cutting openings in the furnace shell plate, thereby protecting the cold-face integrity of the shell against run-outs of molten slag or metal and simplifying shell design.

BRIEF DESCRIPTION OF THE DRAWINGS [00018] The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[00019] Figure 1 is a cross-sectional side view of an air cooling system according to the invention applied to the outer shell of a furnace;

[00020] Figure 2 is a side cross-section of the furnace cooling system of Figure 1 , showing the outlet duct;

[00021] Figure 3 is an enlarged cross-section of the upper portion of the furnace cooling system shown in Figure 1 ;

[00022] Figure 4 is an enlarged cross-section of the bottom of the furnace cooling system shown in Figure 1 ; [00023] Figure 5 is a side elevation showing a preferred arrangement of cooling fin members according to the invention on the outer shell of a furnace;

[00024] Figure 6 is a side elevation showing a preferred arrangement of cooling fin members according to the invention on the outer shell of a furnace, in an area surrounding a tap hole; and [00025] Figure 7 is a schematic plan view of a circular furnace having a cooling system according to the invention.

DETAILED DESCRI PTION OF PREFERRED EMBODI MENTS

[00026] A preferred air cooling system 10 will now be described in connection with the drawings. The air cooling system 10 is described as being installed on a metallurgical furnace 12 which, unless otherwise indicated, can be circular or rectangular. Only a portion of furnace 12 is schematically shown in fig. 1 . It will be appreciated that the air cooling system according to the invention can be applied to furnaces of various shapes, including circular and rectangular furnaces. [00027] The furnace 12 has a side wall 14 extending between an upper portion (not shown) and a lower portion 16 of the furnace 12, the lower portion 16 comprising a hearth 18 and a base 20. Both the hearth 18 and side wall 14 are formed of a refractory material, preferably refractory bricks (not shown). Surrounding the refractory side wall, hearth and base of the furnace is a structural metal shell 22, which has an inner surface 24 in contact with the side wall 14, hearth 18 and base 20, and an opposed outer surface 26 which defines an outer surface of the furnace 12.

[00028] The cooling system 10 according to the invention is attached to the outer surface 26 of furnace 12. The cooling system 10 preferably comprises a cover member 28 covering at least a portion of the furnace outer surface 26 and being spaced therefrom such that an air circulation space 30 is formed between the furnace outer surface 26 and the cover member 28.

[00029] Preferably, the cover member 28 is comprised of one or more metal sheets which extend about substantially the entire outer perimeter or circumference of the furnace 12, preferably surrounding the lower portion 16 of the furnace 12 from a point below the hearth 18 to a point proximate the bottom of the side wall 14. It will also be appreciated that the air cooling system 10 may be extended further upward along the side wall 14. [00030] The cover member 28 may preferably be mounted as shown in figures 3 and 4 by attachment to a top plate 34 at the upper end of air cooling system 10 and a bottom plate 36 at the lower end of air cooling system 10. The top and bottom plates substantially close the top and bottom of the air circulation space 30 so as to prevent excessive flow of air out of the top and bottom of the cooling system 10.

[00031] The cover member may be secured to the top plate 34 through a support angle 38, as shown in figure 3. Alternatively, the support plates may be integrally formed with a support angle, as in the bottom plate 36 shown in figure 4. It will be appreciated that there are numerous means for closing the top and bottom of air space 30 and for securing the cover member 28 to the metal shell 22 of the furnace, and that the invention is not limited to the specific attachment means shown in the drawings.

[00032] The cooling system 10 further comprises at least one inlet 40 through which air enters the air circulation space 30 and at least one outlet 42 through which air is exhausted from the air circulation space 30. Figure 7 shows one example of a possible inlet/outlet configuration for a cooling system 10 applied to a circular furnace, having a pair of inlets 40 separated from one another by about 180 degrees and a pair of outlets 42 separated from each other by about 180 degrees. In the cooling system 10 of figure 7, each inlet 40 is spaced from the adjacent outlets 42 by about 90 degrees.

[00033] The cooling system 10 further comprises a plurality of cooling fin members 48 provided within the air circulation space 30 and extending between the outer surface 26 of furnace 12 and the cover member 28, each of the cooling fin members 48 being in thermal contact with the outer surface 26 of furnace 12. [00034] As shown in figures 3 and 4, each of the cooling fin members 48 comprises one or more cooling plates 50, each of which extends through the air circulation space 30 between the outer surface 26 of furnace 12 and the cover member 28. These cooling plates 50 are preferably corrugated so as to increase their surface area and thereby improve cooling efficiency. The cooling plates 50 shown in the drawings each include three corrugations. It will be appreciated that the cooling plates 50 may be provided with more or fewer corrugations.

[00035] In order to support the cooling fin members 48 and to provide thermal contact with the furnace 12, the cooling fin members 48 are preferably secured to the outer surface 26 of the furnace 12. In the preferred embodiment shown in the drawings, each of the cooling fin members 48 has a substantially U-shaped cross- section, comprising a bight portion 52 and a pair of legs extending from the bight portion 52, the legs comprising the cooling plates 50. The bight portion 52 is secured to the outer surface 26 of furnace 12, with the bight portion 52 preferably having one or more apertures through which it is secured to studs 54 projecting from the furnace outer shell 22 by nuts 56. In the drawings, the cooling plates 50 are shown as each having a distal end portion 58 which is substantially parallel to bight portion 52 and which is spaced from the cover member 28 by a small amount. The space between the distal end portions 58 and cover member 28 is preferably minimized in order to prevent substantial air flow between the distal end portions 58 and the cover member 28.

[00036] In the embodiment shown in figure 5, each of the cooling fin members 48 is elongate and is oriented substantially horizontally along the outer surface 26 of furnace 12. Furthermore, the cooling fin members 48 are arranged as a plurality of vertically spaced rows 60. The horizontal orientation and vertical spacing of the cooling fin members results in the formation of horizontally extending air circulation paths, some of which comprise air circulation paths 62 between the cooling fin members 48 of adjacent rows 60, and a plurality of which comprise air circulation paths 64 between the cooling plates 50 of each cooling fin member 48. Air circulation paths 62 and 64 are also shown in figure 3. Within each row 60, the cooling fin members 48 are arranged end to end, and the spacing between adjacent ends of cooling fin members 48 is preferably minimized in order to minimize vertical air flow through the cooling system 10.

[00037] Figure 6 illustrates a portion of furnace 12 in which the outer surface 26 is interrupted by a tap hole 68. In the vicinity of tap hole 68, a number of the horizontal rows 60 of cooling fin members 48 are interrupted, and the cover member 28 is provided with an aperture (not shown) through which molten metal or slag is permitted to flow. In order to divert the air flow around the tap hole 68, a number of the cooling fin members 48' are arranged vertically. This results in diversion of air flow from the interrupted rows 60 to the continuous rows 60 located above and below tap hole 68.

[00038] Figure 2 illustrates a preferred form of outlet duct 44. In order to ensure a substantially uniform airflow through each of the air circulation paths 62, 64, the outlet duct 44 has a manifold 66 which communicates with each of the air circulation paths 62, 64. Blower means (not shown), preferably comprising an exhaust fan associated with the outlet duct 44, is provided in order to ensure adequate air flow through the system 10.

[00039] When the cooling system according to the invention is applied to a rectangular furnace having a side wall 14 comprising four sides, a separate cover member 28 may be applied to each side being cooled, wherein at least one of the sides is cooled, and with each side being cooled preferably being provided with at least one inlet and at least one outlet. The arrangement of the cooling fin members 48 for a rectangular furnace is as shown in figures 1 to 6, with the rows 60 of cooling fin members 48 extending between along the sides thereof, and with the inlets and outlets preferably communicating with each of the air circulation paths 62 and 64. [00040] There are a number of possible inlet and outlet configurations which can be applied to an air cooling system in a circular or rectangular furnace. For example, one or more inlets may be provided at one end of the side wall 14 (or along each side being cooled in a rectangular furnace), and one or more outlets may be provided at the other end thereof, such that the air circulation paths 62, 64 extend horizontally between the inlet(s) and the outlet(s). Alternatively, each end of the side wall 14 (or along each side being cooled in a rectangular furnace) may be provided with one or more inlets, with the air flowing toward one or more outlets located centrally between the ends thereof. It will be appreciated that other inlet/outlet configurations are possible. [00041] Although the air circulation paths 62, 64 have been shown in the drawings as being horizontal, it will be appreciated that the cooling fin members 48 may be oriented so that the air circulation paths 62, 64 extend vertically or diagonally. Vertical or diagonal arrangement of the air circulation paths 62, 64 may require modification or elimination of the top and bottom plates 34, 36.

[00042] Although the invention has been described in connection with certain preferred embodiments, it is not intended to be limited thereto. Rather, the invention is intended to include all embodiments which may fall within the scope of the following claims.

Claims

What is claimed is:

1 . A cooling system for a furnace having a furnace side wall with an inner surface facing an interior of the furnace and an opposed outer surface, the cooling system comprising:

(a) a cover member covering at least a portion of the outer surface and being spaced from the outer surface such that an air circulation space is formed between the outer surface and the cover member;

(b) at least one inlet through which air enters said air circulation space; (c) at least one outlet through which air is exhausted from said air circulation space;

(d) a plurality of cooling fin members provided within the air circulation space and extending between the outer surface of the furnace side wall and the cover member, each of said cooling fin members being in thermal contact with the furnace side wall.

2. The cooling system according to claim 1 , wherein each of said cooling fin members comprises one or more cooling plates.

3. The cooling system according to claim 1 or 2, wherein said cooling plates are corrugated.

4. The cooling system according to any one of claims 1 to 3, wherein said cooling fin members are secured to the outer surface of the furnace.

5. The cooling system according to any one of claims 1 to 4, wherein adjacent cooling fin members are spaced from one another such that air circulation paths are formed between said adjacent cooling fin members.

6. The cooling system according to any one of claims 1 to 5, wherein each of said cooling fin members has a substantially U-shaped cross-section, comprising a bight portion and a pair of legs extending from the bight portion, wherein the bight portion is secured to the outer surface of the furnace side wall and the legs comprise cooling plates extending between the outer surface of the furnace and the cover member.

7. The cooling system according to claim 6, wherein each of the cooling plates has one end in close proximity to the cover member.

8. The cooling system according to claim 6 or 7, wherein each of the cooling fin members is oriented substantially horizontally.

9. The cooling system according to claim 8, wherein the cooling fin members are arranged as a plurality of vertically spaced rows such that horizontally extending air circulation paths are formed between the cooling fin members of adjacent rows and between the cooling plates of each cooling fin member.

10. The cooling system according to claim 9, wherein the cooling fin members within each of said rows are arranged end to end.

1 1 . The cooling system according to claim 10, wherein each of said outlets communicates with each of the horizontally extending air circulation paths between adjacent rows of cooling fin members.

12. The cooling system according to any one of claims 1 to 1 1 , wherein the cooling fin members are formed from copper or a copper alloy.

13. The cooling system according to any one of claims 1 to 12, further comprising blower means for circulating air through said air circulation space.

14. The cooling system according to any one of claims 1 to 13, wherein the furnace is circular or rectangular.

15. The cooling system according to claim 14, wherein the furnace is circular and has a substantially cylindrical side wall, and wherein the cover member extends about substantially an entire circumference of the furnace.

16. The cooling system according to claim 15, wherein the furnace is rectangular the furnace side wall has four sides, and wherein the cover member is applied to at least one of the sides of the furnace side wall.

17. The cooling system according to any one of claims 1 to 16, wherein the furnace has a hearth in a lower portion thereof, and wherein the cover member surrounds the lower portion of the furnace.

18. The cooling system according to any one of claims 1 to 16, wherein the furnace has a base in a lower portion thereof, and wherein the cover member surrounds the lower portion of the furnace.

19. The cooling system according to any one of claims 1 to 18, wherein the furnace side wall comprises an inner refractory layer and an outer metal shell, the metal shell having an outer surface which defines the outer surface of the furnace.