Ladle, a ladle heating system and methods of heating the ladle

Details Ladle, a ladle heating system and methods of heating the ladle Ladle, a ladle heating system and methods of heating the ladle

2000-08-23

2003-04-01

Kastler, Scott (Department: 1742)

Metallurgical apparatus

Process

C266S901000, C432S009000, C432S037000

Reexamination Certificate

active

06540957

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ladle which is used in a converter process to convey molten steel received from a converter and, more particularly, to a method of heating a ladle.
2. Description of the Related Art
A description will be given first of a conventional art.
1) Referring to
FIG. 3
, a ladle
1
used in a converter process is used to supply molten steel to a continuous casting process and is thereafter moved to a slag discharge station B
1
by means of a crane
2
or the like. At the slag discharge station B
1
, the ladle
1
is tilted so that slag remaining in the ladle is discharged. The ladle is then moved to an inspection/maintenance station (not shown) where a sliding nozzle is scrubbed or replaced with a new sliding nozzle. The ladle is then moved to a pre-heating station C
1
where the ladle
1
is pre-heated by means of, for example, a burner (not shown) to dehydrate the ladle
1
and make up for any reduction of the temperature of molten steel which is to be received from a converter
3
.
The ladle
1
is then moved by, for example, the crane
2
mounted on a steel carrier ladle truck
5
which transports the ladle
1
to a tapping station D
1
. The ladle
1
which has been moved to the tapping station D
1
is stationed for a predetermined period of time and, thereafter; receives molten steel directly from converter
3
. After receiving the molten steel, the ladle
1
is again moved by the ladle truck
5
to a secondary refining station (not shown) where the molten steel in the ladle
1
is subjected to a secondary: refining performed by, for example, an RF method.
Subsequently, the ladle
1
on the ladle truck
5
is conveyed by, for example, the crane
2
to a continuous casting station A
1
. The ladle
1
conveyed to this station A
1
is mounted on a continuous casting machine, and a sliding nozzle provided on the bottom of the ladle
1
is opened and closed, whereby the molten steel is continuously teemed into a tundish at an appropriate rate, so as to be cast continuously. The ladle
1
is then subjected again to the described process.
The tapping temperature at which the molten steel is discharged from the converter
3
is so determined and controlled that the molten steel is maintained high enough to enable the casting until the end of the continuous casting. As a consequence, the tapping temperature is largely ruled by the reduction in the temperature which the molten steel
1
sustains while the molten steel is held in the ladle
1
.
In the conventional converter process, however, a considerably long time is involved from the pre-heating of the ladle
1
in the pre-heating station C
1
until the ladle
1
receives the molten steel at the tapping station D
1
. In particular, the temperature of the ladle refractory is lowered due to natural heat dissipation while the ladle
1
is stationed for receiving the molten steel at the tapping station. This causes a large temperature drop of the molten steel received in the ladle
1
. This requires the tapping temperature at which the molten steel is discharged from the converter to be set at a high level so that the molten steel temperature is high enough for casting even at the end of continuous casting. As a result, a greater amount of carbonaceous material such as coke, which is supplied into the molten steel to act as a temperature-raising material during blowing in the converter process, is consumed.
In addition, a greater degree of thermal attack is caused on the ladle refractory lining, due to the large difference between the temperature of the ladle refractory lining and the tapping temperature at which the molten steel is discharged from the converter, with the result that the refractory lining cannot be sustained for extended use. Further, the molten steel in the ladle
1
exhibits large local variations in temperature.
Furthermore, pre-heating the ladle at the pre-heating station requires a long time and, hence, consumes a large quantity of combustion gas (C gas) for pre-heating.
The present invention is aimed at overcoming these problems of the known art. Thus, it is an object of the present invention to provide a method of heating a ladle which permits the tapping temperature at which the molten steel is discharged from a converter to be set to a low level to permit reduction in the consumption of carbonaceous material, while suppressing thermal attack on the ladle refractory material to improve the unit ratio of the refractories, and which reduces consumption of the combustion gas used for heating the ladle by burners, thus contributing to saving energy.
2) A heating method has been known for heating a ladle by means of regenerative-type burners while closing the top opening of the ladle by means of a ladle lid on which the burners are mounted. This type of heating method is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 7-112269.
This heating method employs a pair of burner units which alternately supply fresh air and discharges combustion exhaust gas,.while recovering heat through a heat regenerator disposed therebetween. These burner units are mounted on the ladle lid which closes the top opening of the ladle. The pair of burner units alternately perform combustion. While one of the burner units is operating to heat the ladle, the combustion gas after the heating is exhausted and recovered through an exhaust gas pipe which runs through a heat regenerator which is associated with the other burner unit.
In a steady operation of this type of regenerative-type burner equipment, the rate of recovery of the exhaust gas is set to be almost equal to the rate of supply of the combustion air, for the reason stated below. Recovery of the exhaust gas at a rate in excess of the rate of supply of the combustion air causes the exhaust gas temperature at the heat-accumulator outlet to rise to an extraordinarily high level, beyond temperatures which can be sustained by structural members supporting the heat regenerator and devices arranged in the exhaust gas pipe such as a change-over valve and an exhaust fan. This makes the whole heating system inoperative and impractical. For this reason, the rate of recovery of the combustion exhaust gas is controlled to be almost equal to the rate of supply of the combustion air, from the beginning to the end of combustion.
This controlling method, however, suffers from the following disadvantage. Namely, at the beginning of combustion, most of the exhaust gas recovered through the exhaust gas pipe is used for heating the heat regenerator. In this state, the temperature of the combustion air after the heat exchange across the heat regenerator is considerably lower than the temperature of the exhaust gas collected from the ladle, so that the heat recovery ratio is undesirably low. With this controlling method, it is impossible to rapidly heat the ladle in a short time, because the combustion temperature and, hence, the combustion gas temperature cannot be raised in the beginning period of the combustion.
In view of this problem, another object of the present invention is to provide a quick heating method for rapidly heating a ladle by means of a regenerative-type burner system, wherein the high temperature of the atmosphere in the ladle is maintained without allowing the combustion gas at the heat-accumulator outlet to exceed the temperature tolerable by the heat regenerator supporting structure and the devices in the exhaust gas pipe such as a change-over valve, thus achieving high heating efficiency for heating the ladle.
3) In the known art for heating the ladle, the ladle is transported to a predetermined station by means of a truck, where the top opening of the ladle is closed by the ladle lid on which burners are mounted. Heating the ladle is conducted by combustion of a fuel by means of the burner system on the ladle lid closing the top opening of the ladle, while the combustion gas is exhausted therefrom. Movement of the ladle lid carrying the burner system is performed b

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