DESCRIPTION
STAVE COOLER FOR BLAST FURNACE
FIELD OF THE INVENTION
This invention relates to stave cooler for a blast furnace made capable of withstanding prolonged use by a structure that can absorb stress produced by thermal expansion of a stave body and a shell, particularly of minimizing stress acting on a weld between a supply/drainage pipe and the stave body. DESCRIPTION OF THE RELATED ART
The stave cooler (sometimes called simply "stave" hereinafter) is currently in wide use as a means for cooling the wall of a blast furnace during operation.
In recent years, measures taken to increase pig iron output and improve pig iron production efficiency in blast furnace operation have increased the thermal load on the furnace stack higher than heretofore, so that a need has come to be felt for a stave cooler capable of cooling the furnace stack more efficiently. This situation has recently led to the development and application of copper and copper-alloy stave coolers having better thermal conductivity than the conventional cast iron staves.
However, when copper or copper-alloy stave coolers are utilized in a blast furnace, another issue not experienced with conventional cast iron staves arises. The conventional cast iron stave is fabricated by first placing a cooling pipe inside the stave body mold and conducting casting to join the cooling pipe and stave body into an integrated structure. This results in a structure having no joint between the inlets/outlets and the supply/drain pipes to as far as the outside the shell.
In contrast, with the copper or copper-alloy stave cooler, it is necessary to first form the cooling pipe
inside the stave body and then to join the inlets/outlets of the stave body and the supply /drain pipes by welding. Welds are therefore present in the vicinity of the stave body.
During blast furnace operation, the welds near the stave body of the copper or copper-alloy stave cooler become stress concentration zones when stress is produced owing to displacement caused by difference in thermal expansion and difference in thermal contraction between the furnace interior side of the stave body exposed to high temperature and the shell side of the stave body subjected to cooling and heat dissipation. As a result, fatigue cracking occurs at these locations to shorten the service life of the stave cooler.
As shown in FIG. 6, the stave is ordinarily installed by fixing the stave body 1 to the shell 6 with fastening bolts 8 and shell nuts 9, thereby distributing the weight load of the stave body 1 so that it does not act directly on the supply/drainage pipe 2.
As shown in FIG. 3, the supply/drainage pipe 2 of a copper or copper-alloy stave cooler is welded to an inlet/outlet of the stave body 1. The opening in the shell 6 for passing the supply/drainage pipe 2 is sealed to prevent leakage of furnace gas from inside the blast furnace to outside the shell by welding the supply/drainage pipe 2 and the shell 6 together via a seal plate 5.
In the conventional staves shown in FIGs. 3 and 6, stress fluctuation occurs during blast furnace operation owing to displacement caused by difference in thermal expansion between the furnace interior side and shell side of the stave body and further by difference in thermal expansion between the shell side of the stave body and the shell. Although the fastening bolts 8 can distribute the weight load of the stave body, they cannot absorb the stress fluctuation caused by the thermal expansion differences.
Therefore, during operation of a blast furnace equipped with the copper or copper-alloy stave cooler, the supply/drainage pipe welds near the stave body, which become stress concentration zones, are especially apt to sustain fatigue cracking caused by the stress fluctuation produced by the thermal expansion differences.
The seal plate 5 connecting the supply/drainage pipe 2 and the shell 6 is readily deformed when displacement is caused by a difference in thermal expansion between the stave body and the shell. Although the seal plate 5 therefore works to reduce the stress at the weld of the supply/drainage pipe near the stave body, the seal plate 5 itself is likely to be broken by the deformation caused by repeated application of stress, thus posing of risk of furnace gas leakage.
A conventional method of dealing with the aforesaid technical problems is to connect the supply/drainage pipe and the shell through an expansion pipe capable of expanding and contracting (see, for example, Japanese Patent Publication (A) No. S52-8553). In this method, as shown in FIG. 4, an expansion pipe 7 is installed to enclose the supply/drainage pipe 2 and the supply/drainage pipe 2 is welded to the shell 6 through the expansion pipe 7.
In this case, the seal plate 5 is welded between the distal end of the expansion pipe 7 and the periphery of the supply/drainage pipe 2 to establish a seal that prevents furnace gas in the blast furnace from leaking to outside the shell.
With this method, when displacement occurs because of a difference in thermal expansion between the stave body and the shell, the displacement is absorbed by deformation of the expansion pipe 7 in the direction of the thermal expansion or thermal contraction, thereby absorbing the stress. The method therefore effectively inhibits fatigue fracture of the seal plate 5 and the supply/drainage pipes welds near the stave body owing to
stress caused by difference in thermal expansion.
Although, as can be seen from FIG. 4, the bellows or the like for enabling the expansion pipe 7 to extend and contract is of simple structure, it is likely in the course of prolonged use to collect dust that accelerates corrosion and makes fatigue fracture likely, thereby posing a durability problem.
Therefore, in order to ensure that leakage of furnace gas to the exterior does not occur because of holes or cracks occurring in the expansion pipe 7, it is necessary either to regularly replace the expansion pipe 7 or to carry out preventive repair of the regions of the expansion pipe 7 where holes or cracks have occurred. As a result, the considerable amount of labor required for these operations and the reduced productivity owing to blast furnace shutdown and the like become issues.
Moreover, if stave weight load comes to act on the weld between the stave body and the supply/drainage pipe owing to deformation or the like of the stave fastening bolts, the weld between the stave body and the supply/drainage pipe sustains fatigue fracture, so that there is a risk of cooling water leaking from the damaged regions and entering the ballast furnace to cause furnace flooding, which is a serious problem.
As shown in FIGs. 5 and 7, there is known another conventional method of attaching a cast iron stave to the shell which eliminates the bolts 8 and nuts 9 for fastening the stave body 1 and, for enabling rapid stave replacement, installs a protective pipe 3 on the cast iron stave body so as to enclose the supply/drainage pipe 2, installs a combing box 4 around the opening of the shell to surround the protective pipe 3, and fastens the supply/drainage pipe 2 to the protective pipe 3 by interposing a filler 10 and fastens the combing box 4 to the protective pipe 3 by interposing a fastening block 11 (see, for example, Japanese Patent Publication (A) No. H8-225813).
In this method, the rigidity of the supply/drainage pipe 2 is enhanced by fastening the supply/drainage pipe 2 and protective pipe 3 using the filler 10 etc. and the weight load of the stave body is supported by fastening the protective pipe 3 and the combing box 4 using the filler 10 etc., so that, as shown in FIG. 7, the fastening bolts 8 and the shell nuts 9 for the stave body 1 can be eliminated.
The method can also be applied to a copper or copper-alloy stave. However, the method combines the supply/drainage pipe 2, protective pipe 3 and combing box 4 into an integral structure. As a result, stress arising because of displacement caused by difference in thermal expansion between the stave body 1 and shell 6 cannot be absorbed, so that stress concentrates at the weld between the stave body 1 and the supply/drainage pipe 2, thereby increasing rather than decreasing the probability of fatigue fracture.
As explained in the foregoing, the increased thermal load on the blast furnace stack caused by the operation of blast furnaces at higher levels of pig iron output in recent years has increased the differences in thermal expansion between the furnace interior side and the shell side of the stave body and between the shell side of the stave body and the shell, thereby increasing the probability of fatigue fracture of the welds between the supply/drainage pipe and the shell. However, conventional staves have not been effective in extending stave service life.
SUMMARY OF THE INVENTION
In light of the state of the prior art explained in the forgoing, the object of the present invention is to provide a stave cooler for a blast furnace having a structure that enables absorption of stress caused by difference in thermal expansion occurring between the stave body and the shell owing to increased thermal load
on the blast furnace stack during high-output blast furnace operation, that inhibits occurrence of fatigue fracture at welds between the stave body and supply/drainage pipes and welds between the shell and the supply/drainage pipes, and that ensures highly reliable endurance over long periods of use.
The present invention, which overcomes the aforesaid technical problems, essentially provides a stave cooler for a blast furnace wherein a supply/drainage pipe is welded to a copper or copper-alloy stave body and the stave body is fastened to a blast furnace shell by multiple steel fastening bolts, which stave cooler comprises a protective tube welded to the stave body so as to enclose the supply/drainage pipe and a combing box provided on the shell surface at the periphery of an opening in the shell so as to enclose the protective tube, side panels of the combing box being welded at one end to the shell and welded at the other end to a peripheral surface of the protective tube through a seal plate.
The present invention provides a stave for cooling a blast furnace stack that, in the adoption of a copper or copper-alloy stave cooler offering excellent blast furnace stack and bosh cooling performance, has a structure that enables absorption of stress caused by difference in thermal expansion occurring between the stave body and the shell owing to increased thermal load on the blast furnace stack during high-output blast furnace operation, that inhibits occurrence of fatigue fracture at welds between the stave body and supply/drainage pipes and welds between the shell and the supply/drainage pipes, and that ensures highly reliable endurance over long periods of use.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram showing how the stave according to the present invention is installed on a blast furnace
wall.
FIG. 2 is a diagram showing how, in accordance with the present invention, the stave body and shell are connected through a protective tube of the stave supply/drainage pipe and a combing box.
FIG. 3 is a diagram showing how a stave body and shell are conventionally connected without using a stave expansion pipe.
FIG. 4 is a diagram showing how a stave body and shell are conventionally connected through a stave expansion pipe.
FIG. 5 is a diagram showing how a stave body and shell are conventionally connected .through a protective tube of a stave supply/drainage pipe, a combing box and a filler.
FIG. 6 is a diagram showing how a stave is conventionally installed on a blast furnace wall through fastening bolts.
FIG. 7 is a diagram showing how a stave is conventionally installed on a blast furnace wall without using fastening bolts.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 schematically illustrates how the stave cooler for a blast furnace according to the present invention and the shell of the blast furnace are connected, and Figure 2 schematically illustrates how the stave body of the present invention, a supply/drainage pipe, a protective tube, a combing box, and the shell are respectively connected.
As shown in FIGs. 1 and 2, in the stave cooler for a blast furnace according to the present invention, supply/drainage pipes 2 are welded to a copper or copper-alloy stave body 1, and the stave body 1 and the blast furnace shell 6 are fastened together by multiple steel fastening bolts 8. The use of copper or copper-alloy as the material of the stave body makes the thermal
conductivity of the stave body higher than that of the conventional cast iron stave, so that heat can be efficiently removed from the furnace interior side of the stave body by cooling water circulating through the cooling water piping inside the stave body.
The weight load of the stave body 1 is supported by multiple steel fastening bolts 8. Although the steel fastening bolts 8 can share the weight load of the stave body 1, they cannot absorb the stress fluctuation caused by the difference in thermal expansion between the stave body 1 and the shell.
In the stave cooler for a blast furnace according to the present invention, therefore, as shown in FIGs. 1 and 2, a protective pipe 3 is welded to the stave body 1 so as to enclose the supply/drainage pipe 2 and a combing box 4 is provided on the shell surface at the periphery of an opening in the shell so as to enclose the protective tube, side panels of the combing box 4 being welded at one end to the shell 6 and at the other end to a peripheral surface of the protective pipe 3 through a seal plate 5.
In the aforesaid stave structure, the protective pipe 3 is welded to the stave body 1 so as to enclose the supply/drainage pipe 2. As a result, the sectional area of the region including the weld between the inlet/outlet of the stave body 1 and the supply/drainage pipe 2, which is a stress concentration zone, is enlarged. The load of this region is therefore shared by the protective tube, thereby making it possible to reduce the stress of the weld of the supply/drainage pipe 2 when displacement occurs owing to difference in thermal expansion.
When the thickness of the protective tube is less than 5 mm, sufficient strength cannot be achieved. When it is greater than 7 mm, the distance between it and the supply/drainage pipe becomes so small as to make welding difficult. Therefore, in the interest of achieving adequate strength and easy weldability, the thickness is
preferably 5 to 7 mm. As the protective tube is required to keep its strength under exposure to high temperatures and also needs to be easy to weld, it is preferably made of carbon steel for high pressure piping.
The combing box 4 is installed at an opening in the shell so as to enclose the protective pipe 3. Since the supply/drainage pipe 2 and the protective pipe 3 are installed so as not to be in direct contact with the shell, displacement owing to thermal expansion is possible. The supply/drainage pipe 2 and protective pipe 3 are welded to the shell through the combing box 4. With this arrangement, when displacement occurs owing to difference in thermal expansion, the combing box 4 is deformed in the direction of the displacement, thereby reducing the stress acting on the weld of the supply/drainage pipe 2.
The side panels of the combing box 4 are welded at one end to the shell surface at the periphery of the shell opening and at the other end to the peripheral surface of the protective tube 3 through the seal plate 5. The side panels of the combing box 4 and the seal plate 5 therefore establish a seal that prevents furnace gas in the blast furnace from leaking to the exterior of the shell.
The diameter of the opening of the shell 6 is preferably made larger than the diameter of the protective pipe 3 by an amount that enables the supply/drainage pipe 2 and protective pipe 3 to displace (shift) freely without touching the shell even if they are deformed to some degree owing to displacement caused by difference in thermal expansion during blast furnace operation.
The side panels and seal plate 5 constituting the combing box 4 are preferably made of thin steel or other metal plates capable of contracting in the direction of displacement when displacement occurs owing to difference in thermal expansion during blast furnace operation.
When the length of the side panels is less than 40 mm, they are too short to thoroughly absorb displacement caused by difference in thermal expansion. When they are longer than 120 mm, they interfere with surrounding equipment. The length of the side panels is therefore preferably 40 to 120 mm.
When the thickness of the side panels is less than 8 mm, they are too thin for easy welding. When they are thicker than 10 mm, they cannot readily deform to absorb the difference in thermal expansion. Therefore, in the interest of maintaining adequate strength and realizing easy weldability, the thickness of the side panels is preferably 8 to 10 mm.
When the thickness of the seal plate 5 is less than 5 mm, it is too thin for easy welding. When it is thicker than 7 mm, it cannot readily deform to absorb the difference in thermal expansion. Therefore, in the interest of maintaining adequate strength and realizing easy weldability, the thickness of the seal plate 5 is preferably 5 to 7 mm.
The side panels and the seal plate are preferably made of ordinary carbon steel so as to have sufficient strength and good weldability.
In order to enable the combing box and seal plate to readily deform and absorb thermal expansion difference, it is preferable for the space inside the combing box and seal plate not to be charged with cast material, refractory or the like.
The method of fabricating the copper or copper-alloy stave of the present invention is not specially defined. But to give a general example, the following method is usable.
First, patterns having the same shape as the stave are fabricated one for the furnace interior side and one for the furnace exterior side. Second, the patterns are disposed on separate metal frames corresponding to the furnace interior side and furnace exterior sides of the
stave and then filled with sand. Third, the sand is compacted, whereafter the patterns are removed to make sand molds. Molds of compacted sand are separately made for the water channel and placed at the prescribed location in the aforesaid sand molds.
Fourth, the furnace interior side and furnace exterior side molds are placed one on top of the other and molten copper or copper-alloy is poured into the sprue. Fifth, after the melt has solidified, the sand mold is removed and a plug of the same material as the stave body is inserted and welded in the sand drain hole. The supply/drainage pipe is welded to the supply/drainage inlet/outlet and the protective tube is welded to enclose the supply/drainage pipe.
Another method of fabrication is to form a water channel in a rolled copper plate or rolled copper-alloy plate having the same shape as the stave, inserting and welding plugs of the same material as the stave body into unnecessary holes, welding the supply/drainage pipe to the supply/drainage pipe to the supply/drainage inlet/outlet, and welding the protective tube to enclose the supply/drainage pipe.
EXAMPLE
An embodiment of the present invention is explained with reference to the drawings in the following. As shown in FIGs. 1 and 2, a stave cooler according to the present invention was fabricated as a copper stave cooler having a protective pipe 3 and a combing box 4 installed to enclose a supply/drainage pipe 2 welded to a copper stave body 1. The stave body was fastened to the shell of a blast furnace stack at four locations using steel fastening bolts and nuts.
Simulation was carried out to ascertain the effect of the copper stave according to the present invention. Specifically, state of damage to the stave bodies, the welds of the supply/drainage pipes 2, and the seal plates
5 during blast furnace operation was simulated for the case of similarly attaching to the shell of the blast furnace stack the copper stave cooler according to the present invention and a conventional copper stave cooler having its supply/drainage pipe 2 welded to a conventional copper stave body 1 welded to the shell through a seal plate 5.
In the copper stave cooler according to the present invention, the combing box was made of 9-mm ordinary carbon steel and the seal plate was made of 6-mm ordinary carbon steel.
According to the simulation results, in the copper stave cooler according to the present invention no damage to the.weld between the stave body 1 and the supply/drainage pipe 2 or to the seal plate 5 was observed.
In contrast, it was found that in the conventional copper stave cooler, the thermal stress acting on the weld between the stave body 1 and the supply/drainage pipe 2 and on the weld between the seal plate 5 and the shell is about double the allowable stress, posing a possibility of supply/drainage pipe and seal plate breakage.
Industrial Applicability
As set out in the foregoing, the present invention provides a stave for cooling a blast furnace stack that, in the adoption of a copper or copper-alloy stave cooler offering excellent blast furnace stack and bosh cooling performance, has a structure that enables absorption of stress caused by difference in thermal expansion occurring between the stave body and the shell owing to increased thermal load on the blast furnace stack during high-output blast furnace operation, that inhibits occurrence of fatigue fracture at welds between the stave body and supply/drainage pipes and welds between the shell and the supply/drainage pipes, and that ensures
highly reliable endurance over long periods of use. The industrial applicability of the present invention is therefore considerable.

We Claim:-
1. A stave cooler for a blast furnace wherein a supply/drainage pipe is welded to a copper or copper-alloy stave body and the stave body is fastened to a blast furnace shell by multiple steel fastening bolts, which stave cooler comprises:
a protective tube welded to the stave body so as to enclose the supply/drainage pipe and
a combing box provided on the shell surface at the periphery of an opening in the shell so as to enclose the protective tube,
side panels of the combing box being welded at one end to the shell and welded at the other end to a peripheral surface of the protective tube through a seal plate.