Water jacket of arc furnace

Details Water jacket of arc furnace Water jacket of arc furnace

2002-06-03

2003-05-13

Hoang, Tu Ba (Department: 3742)

Industrial electric heating furnaces

Arc furnace device

Furnace body detail

C373S071000, C373S073000

Reexamination Certificate

active

06563855

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to novel water-cooling jackets that are chiefly used in electric arc furnaces for steelmaking.
BACKGROUND ART
The internal sections of electric arc furnaces for steelmaking, such as inner walls, ceilings and dust collection port other than those ones that are made with refractories and that come direct contact with molten steel, for example, bottom linings, lower side walls, tapping trough and slag-off holes, are cooled by water so that they can withstand high temperatures. Water-cooling devices for use in electric arc furnaces are called “water-cooling jackets”, “water-cooling panels”, “water-cooling boxes”, “water-cooling pipes” or the like, depending upon the structure and shape. In this specification, the term “water-cooling jacket” is used to describe the present invention.
Water-cooling jackets in various shapes are illustrated in the accompanying drawings. FIGS.
1
(
a
) and
1
(
b
) show a water-cooling jacket for inner walls, which is a welded structure
1
made by the use of carbon steel plates. A cooling water channel having a water inlet
3
and a drain port
4
is provided in the inside of this jacket so that cooling water at a temperature of 40 to 70° C. can flow evenly throughout the jacket. Further, a large number of steel-plate-made slag catchers
2
, each having a thickness of 25 mm, a width of 50 mm and a length of 130 mm are welded to the outer surface of the jacket. These slag catchers
2
are provided in order to positively catch, at the surface of the water-cooling jacket, the slag scattered in the furnace; they can also serve as studs, which are often provided in the case where the slag catchers are covered with a refractory material.
FIG. 2
shows a water-cooling jacket for ceilings. This jacket comprises concentrically arranged many water-cooling pipes
5
made of carbon steel, covered with a castable refractory
6
. Cooling water at the above-described temperature is fed to the water-cooling pipes
5
from a water inlet
3
, and discharged from a drain port
4
.
FIG. 3
shows a water-cooling jacket for dust collection port. This jacket comprises a water-cooling pipe
7
made of carbon steel, coiled into a nearly cylindrical configuration, and studs
8
welded to the surface of the water-cooling pipe
7
, the pipe
7
and the studs
8
being covered with a castable refractory
6
. FIGS.
4
(
a
) and
4
(
b
) show a water-cooling jacket for ceilings. The basic structure and the plate thickness of this jacket are the same as those of the water-cooling jacket for inner walls shown in FIG.
1
. However, since the slag deposited on the slag catchers made with steel plates easily comes off and falls, a deformed bar is used, instead of steel plates, to provide slag catchers
10
on the outside of the body
9
of the jacket shown in FIG.
4
. Specifically, a deformed bar having a diameter of 25 mm is cut into small pieces of 30 mm in length, and these pieces are welded to the body with the space of approximately 75 mm. Reference numeral
3
denotes a water inlet, and reference numeral
4
denotes a drain port.
Owing to arc heat in the process of melting and refining scrap steel, combustion heat of fuel generated by a stabilizing burner, combustion heat of carbon powder, aluminum ashes, etc. generated when they are added to a furnace or to molten steel, and gasses emitted when vinyl chloride, etc. contained in scrap steel are burned, the surfaces of the aforementioned water-cooling jackets are exposed to high-temperature (more than 1300° C.) oxidizing and corrosive atmospheres for a long period of time. At the same time, splashes of the molten steel and slag at temperatures of more than 1500° C. repeatedly deposit on and come off the surfaces of the water-cooling jackets, so that the surfaces of the jackets are rapidly heated by the molten steel and slag, and then rapidly cooled by cooling water. Further, in the case of the water-cooling jacket incorporated into the inner wall of a furnace, the jacket directly receives mechanical shock when scrap steel is charged, so that the falling of the slag catchers, the deterioration of the welded joints, the abrasion of the steel plate surfaces, and the deformation of the water-cooling jacket are extremely accelerated.
The water-cooling jacket for dust collection port is constantly exposed to a high-temperature oxidizing, corrosive and abrasive atmosphere. This is because, unlike the inner wall and ceiling of a furnace, a large amount of exhaust gas at a high temperature of more than 1000° C., containing dusts is constantly passing through the dust passage at a high speed.
Thus, water-cooling jackets for electric arc furnaces are used, regardless of parts of furnaces for which the jackets are used, under such extremely aggressive conditions that oxidation, corrosion, thermal shock, mechanical shock and abrasion are brought about at high temperatures.
On the other hand, water-cooling jackets that are fixed to the inside of arc furnaces are large-sized structures, so that they are divided into 20-40 parts and then incorporated. The production of such large-sized water-cooling jackets requires great cost. Moreover, the replacement of the jackets requires much labor and a long time, so that it inevitably requires heavy expenditure, increasing the steelmaking cost. It is thus desirable that the life of water-cooling jackets be as long as possible.
In the extremely aggressive environments as mentioned above, it is unavoidable that the slag catchers and the refractories with which the slag catchers are covered fall with the passage of time, and the surfaces of the jacket bodies are eventually bared. The decisive causes of the falling of the slag catchers are cracks formed in welded joints due to repetitive heating and cooling, and, in the case of the water-cooling jacket for inner walls, mechanical shock given to the slag catchers in high-temperature environments when scrap steel is charged. The causes of the falling of the refractories are as follows: the slag deposited on the refractories comes off together with the refractories; and the studs that serve to prevent the falling of the refractories are oxidized and abraded at high temperatures, and become impossible to hold the refractories any more. If the surfaces of the jacket bodies are bared in this manner, they are exposed to high temperatures, and the strain energy that developed in steel plates when they were weld-bonded to make the water-cooling jackets is partially released. As a result, the jackets begin to entirely undergo deformation, and the welded joints are cracked due to repetitive abrasion, thermal shock and mechanical shock, especially mechanical shock. Cracking then spreads even to the steel plates themselves, inducing water leakage.
Water leakage disturbs the flow of water in the jackets, and some parts of the jackets are insufficiently cooled and become very hot, inducing further cracking. Moreover, water that leaks into the furnaces can cause steam explosion. It is therefore very important to repair water leakage earlier. To repair leakage, it is firstly needed to suspend operation after the steel produced is tapped, and to cool down the inside of the furnace; the leaks are then weld-repaired. The suspension of operation directly raises the steelmaking cost, so that it is necessary to complete the repair in a period of time as short as possible. To attain this, it is inevitable to conduct operations at high temperatures; however, this is unfavorable from the viewpoints of safety and hygiene.
The thus cracked parts are weld-repaired from the surface side; however, welding can reach only to a depth equal to about ⅓ of the thickness of the steel plate, and the other portion (about ⅔ of the thickness) remains cracked. The weld-repaired parts therefore become weaker than non-repaired parts, and those parts that have been once cracked tend to be cracked again even after they are repaired. The once repaired parts and newly cracked parts are repeatedly repaired so as to use the jackets until th

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