JP2002069521A - Method of steelmaking using plural refining furnaces - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower steel tapping temperature and to extend the service life of a refractory by performing an operation based on an operational schedule by which heat loss and time loss can be restrained to the absolute minimum without lowering productivity by following the schedule of continuous casting. SOLUTION: When three or more heats of the sequentially continuous castings are cast into one or more sets of the continuous casters by casting molten steels tapped in order from plural refining furnaces having not lower than the number of the continuous casters, plural refining furnaces are alternately used so as to satisfy formulas (1) and (2). 0.8<=Ttap(N)/Tcast(N)<=1.2...(1), 0.6<=Tkill(N)/Tkill(F)<=1.2...(2). Wherein, Ttap(N): the time interval between the Nth heat steel tapping and (N+1)th heat tapping in the refining furnace, Tcast(N): the interval in the starting time between the Nth heat casting and (N+1)th heat casting, Tkill(N): the killing time between the tapping completion time and the casting start after tapping of the Nth heat and (F): the killing time between the tapping completion and the casting start in the last heat steel tapping from the refining furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a steel making method using a plurality of smelting furnaces.

[0002]

2. Description of the Related Art As is well known, in a steelmaking process including a plurality of converters, secondary refining equipment, and a continuous casting machine, molten steel is stored in a ladle and transported from the converter to the continuous casting machine by, for example, a crane. Then, casting into the continuous casting mold is performed. In such a steelmaking process, it is desirable to prevent a delay in continuous casting in a continuous casting machine (so-called continuous casting breakage) in order to improve the production efficiency of the entire process. Therefore, usually, a plurality of ladles are used, molten steel is stored in each of the ladles, and casting is sequentially performed in a continuous casting machine, thereby preventing continuous casting breakage.

There are various combinations of the number of refining furnaces and continuous casting machines in the steelmaking process. However, at the beginning of the development of a steelmaking process using a continuous casting machine, the number of refining furnaces and continuous casting machines are the same. In some cases it was mainstream. That is, at the beginning of the development, the time interval between the N-th tapping and the (N + 1) -th tapping in the refining furnace is Ttap (N), and the N-th casting and the (N + 1) -th tapping in the continuous casting machine. The start time interval of each casting is Tca
Assuming that st (N), by operating under the condition of Ttap (N) / Tcast (N) = 1, it was possible to suppress both heat loss and time loss. But,
In recent years, the process has been diversified due to improvements in required steel material quality and high efficiency by continuous continuous casting, and accordingly, Ttap (N)> Tcast (N)
Operation under such conditions, and both thermal loss and time loss have been increasing.

[0004] Therefore, in order to compensate for the extension of the tapping time interval without reducing the production capacity, excessive tapping, that is, tapping is preferentially performed and the casting must be started. Was. Therefore, the killing time Tkill, which is the time from the completion of tapping after the Nth tapping to the start of casting.
In order to increase (N), it has become necessary to raise the tapping temperature. At this time, Tkill (N)
> Tkill (N + 1)>...> Tkill (F).

[0005] Naturally, an increase in the tapping temperature greatly affects the life of the refractory in the smelting furnace. In other words, the life of the refractory decreases significantly with increasing tapping temperature. In this case, life extension by repair is important, but when supplying molten steel using a smaller number of refining furnaces than a continuous casting machine, a sufficient repair time cannot be secured. Conventionally, there are refractory repairing means such as slag coating, baking, spraying, and brick coating. However, in order to perform refractory repairing by these means, (working time + curing time) is usually about 7 to 30 minutes. Work time is indispensable. On the other hand, if the supply of molten steel is continued without lowering production capacity, repair time and curing time cannot be secured, and not only the repair effect cannot be fully exerted, but also refractory costs will deteriorate due to the increase in repair frequency. Resulting in.

Therefore, there has been proposed an invention for easily creating an operation schedule with high accuracy while observing a continuous casting schedule. For example,
Japanese Patent Application Laid-Open No. 9-235610 discloses a method of tentatively determining an operation schedule based on a casting schedule of a continuous casting machine while considering a logistics interference while going back a time axis and a process from a casting process to an upstream process. One step,
Based on the blowing schedule obtained from the first step, the operation schedule is re-executed while verifying the effect of the operation schedule of the ladle post-treatment process while moving down the process and time axis from the converter to the downstream process. It is disclosed that process management is performed using a schedule creation system that combines the second step of calculation.

Further, Japanese Patent Application Laid-Open Nos. 10-245614 and 11-193414 disclose a first converter for dephosphorizing and refining hot metal, and a method for receiving the hot metal and removing the hot metal within a dephosphorizing refining time. A steelmaking method using a second converter for performing charcoal refining is disclosed.

[0008]

SUMMARY OF THE INVENTION However, Japanese Patent Application Laid-Open No. Hei 9-2
The invention disclosed in Japanese Patent No. 35610 discloses a method for preheating a molten iron, a time for a steelmaking process in a refining furnace, a time for a secondary refining, and a time for pouring to be constant according to the type of steel. It is difficult to adjust the time based on the result of adjustment. Also, considering the results of changes in the hot metal composition and the temperature adjustment after refining on the system, it is not possible to cope with the reprocessing of hot metal pretreatment and the readjustment of temperature (heating, cooling), etc. Both thermal and time losses increase.

The inventions disclosed in JP-A-10-245614 and JP-A-11-193414,
Since the scheduling of the hot metal pretreatment and the steelmaking refining is performed and is not aimed at minimizing the treatment cycle time, neither the thermal loss nor the time loss can be reduced.

[0010] The object of the present invention is based on an operation schedule capable of minimizing thermal loss and time loss without reducing production capacity while observing the schedule of continuous casting. The operation is to reduce the tapping temperature and extend the life of the refractory.

[0011]

SUMMARY OF THE INVENTION The present invention provides one or two units.
When performing three or more continuous castings by supplying molten steel sequentially discharged from a plurality of refining furnaces equal to or more than the number of the continuous casting machines to at least two or more continuous casting machines, the above formula (1) and A steelmaking method using a plurality of refining furnaces, wherein a plurality of refining furnaces are alternately used so as to satisfy the expression (2).

In the equations (1) and (2), Ttap (N) is the time interval between the N-th tapping and the (N + 1) -th tapping in the smelting furnace.
(N) is the interval between the start time of each of the Nth casting and the (N + 1) th casting in the continuous casting machine, and Tkill (N) is the casting time from the completion of tapping after the Nth tapping. Is the time until the start of refining, and F indicates the final tapping from the refining furnace.

Further, in the steel making method using a plurality of refining furnaces according to the present invention, the refining furnace is used after the final tapping from the refining furnace is completed and before the next tapping is started. It is desirable to repair refractories.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a steel making method according to the present invention will be described in detail. In the present embodiment, multiple steel castings are performed by supplying molten steel that has been sequentially discharged from two refining furnaces to one continuous casting machine.

Here, the time interval between the N-th tapping and the (N + 1) -th tapping in the refining furnace is Ttap (N), and the N-th casting in the continuous casting machine and (N +
1) Tcast the start time interval of each casting
Assuming that (N), the time from the completion of tapping after the Nth tapping to the start of casting is Tkill (N), and the final tapping from the smelting furnace is F, then in this embodiment, 1)
A plurality of smelting furnaces are used alternately so as to satisfy the expression and the expression (2).

0.8 ≦ Ttap (N) / Tcast (N) ≦ 1.2 (1) 0.6 ≦ Tkill (N) / Tkill (F) ≦ 1.2 (2) If Ttap (N) / Tcast (N) is less than 0.8, tapping is performed preferentially (early tapping), so that the heat loss increases, and the tapping of hot steel more than necessary is required. On the other hand, when Ttap (N) / Tcast (N) is more than 1.2, the time loss becomes large, so that it is impossible to cope with the time loss in the refining process, and the production capacity is reduced. Therefore, in the present embodiment, Ttap (N) / Tcast (N) is 0.8 or more.
Limited to 2 or less. From the same viewpoint, Ttap (N) / Tcast
(N) is desirably 0.9 or more and 1.1 or less.

Further, if Tkill (N) / Tkill (F) is less than 0.6, the thermal loss increases in the charge in the latter half of the continuous casting. On the other hand, when Tkill (N) / Tkill (F) is more than 1.2, the thermal loss increases in the charge in the first half of the continuous casting. Therefore, in the present embodiment, Tkill (N) / Tkill
(F) is limited to 0.6 or more and 1.2 or less. From the same viewpoint, Tkill (N) / Tkill (F) is desirably 0.8 or more and 1.1 or less.

By performing steelmaking using a plurality of refining furnaces according to the present embodiment, the following effects 1 to 3 can be obtained. Since the relation of tapping pitch ability> casting pitch ability can be secured, the tapping interval can be shortened without reducing the production capacity. For this reason, both thermal loss and time loss can be suppressed.

By synchronizing tapping and pouring, the tapping temperature can be reduced because the operation can be performed while minimizing the heat loss. Therefore, it is possible to reduce heat loss and extend the life of the refractory. As a result, the influence of the reduction of the production efficiency due to the inevitable replacement of the refractory of the smelting furnace is reduced, and the production efficiency can be greatly improved.

Since the tapping pitch can be freely changed, a repair time and a repair curing time can be secured. For this reason, it is possible to extend the life of the refractory and reduce the repair cost.

In the present embodiment, tapping is performed retroactively from the casting start time. At this time, a schedule is created so as to conform to the above equations (1) and (2). Conventionally, the tapping pitch, that is, tapping capacity is a bottleneck, and it has not been possible to create a schedule that satisfies the equations (1) and (2). On the other hand, according to the present embodiment, the above-described schedule can be created because the tapping capacity is enhanced.

In the present embodiment, the refractory of the refining furnace is repaired after the final tapping from the refining furnace is completed and before the next tapping is started. In other words, by changing the tapping pitch according to the repair method to be implemented,
Since a repair time can be secured, the refractory of the smelting furnace can be reliably repaired within this time.

In order to implement the present embodiment most simply, it is sufficient to use a number of refining furnaces equal to or greater than the number of continuous casting machines.
However, increasing the number of smelting furnaces for this purpose requires a large amount of capital investment, and is hardly realizable in practice.
Therefore, in the present embodiment, it is conceivable to change the conventional furnace operation method of the smelting furnace, that is, to change the operation mode so as to improve the operation rate of the smelting furnace. For example, when two converters are installed, operating only one unit is referred to as 1/2 unit operation, and operating two units is referred to as 2/2.
When the term “basic operation” is used, 1/2 basic operation → 2/2 Changing the operation mode from basic operation to basic operation, or operating only one unit when three converters are installed, is one-third. When the operation of two units is described as 2/3 units operation and the operation of three units is described as 3/3 units operation, the operation is performed as 2/3 units operation → 3/3 unit operation. Changing the form is exemplified.

For this purpose, it is only necessary to deal with some equipment (modification of existing equipment). For example, it is desirable to make the dust collector of each refining furnace independent and to make the acid supply line independent and to take safety measures (corresponding to the increase of the linear flow rate). By remodeling these facilities, multiple refining furnaces can be used alternately,
A conventional tapping interval can be shortened, and both a drop in tapping temperature and a time required for refractory repair can be achieved.

As described above, according to the present embodiment, it is possible to easily and accurately prepare an operation schedule without reducing the production capacity while observing the continuous casting schedule. By performing the operation based on the schedule, it is possible to reduce the tapping temperature and extend the life of the refractory.

[0026]

EXAMPLES The present invention will be described more specifically with reference to examples. FIG. 1 is an explanatory view showing a conventional example in which molten steel is supplied from one refining furnace to one continuous casting machine.

In this conventional example, the tapping interval is 35 minutes and the casting interval is 25 minutes, so that tapping interval> casting interval. Even in such a case, in order to prevent the continuous casting from being interrupted, the first to fifth charges must be quickly discharged. Therefore, Ttap (N) / Tca
st (N) = 1.4> 1.2, and Tkill (N) /
Tkill (F) = 1.5> 1.2. For this reason, heat loss increases and leads to a rise in tapping temperature.

Also, the refractory repair time cannot be completely carried out between charges, and less than 10 minutes can be secured even between multiple castings. If a sufficient repair time is to be secured, the production capacity must be reduced. It turns out there is no.

FIG. 2 is an explanatory view showing an example of the present invention in which molten steel is supplied from two refining furnaces to one continuous casting machine. In this example of the present invention, the number of operating smelting furnaces was changed from the conventional one to two, and the equipment modification and the operation mode were changed so that these two refining furnaces were used alternately. The casting interval can be made equal, and Ttap (N)
/Tcast(N)=1.0, Tkill (N) / Tkill (F) = 1.0, and the heat loss can be minimized.

Also, the refractory repair time can be secured for 15 minutes between each charge and for 30 minutes or more between multiple castings, and the repair time can be sufficiently secured. further,
FIG. 3 shows an example of the present invention and a conventional example.
The tapping temperature and the converter life index are summarized in a graph.

From the graph shown in FIG. 3, according to the example of the present invention,
The tapping temperature could be reduced by 5 ° C compared to the conventional example, and the life of the smelting furnace could be extended to about 1.5 times. The significance of the present invention having such an effect is extremely remarkable.

[0032]

As described in detail above, according to the present invention, it is possible to easily and accurately prepare an operation schedule without reducing the production capacity while observing the continuous casting schedule. By performing the operation based on the obtained operation schedule, it was possible to lower the tapping temperature and extend the life of the refractory.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a conventional example in an embodiment.

FIG. 2 is an explanatory view showing an example of the present invention in an embodiment.

FIG. 3 is a graph showing the results of Examples.

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Claims (2)

[Claims] 1. A method for performing three or more continuous castings by supplying molten steel sequentially discharged from a plurality of refining furnaces equal to or more than the number of continuous casting machines to one or two or more continuous casting machines. A steelmaking method using a plurality of smelting furnaces, wherein the plurality of smelting furnaces are alternately used so as to satisfy the following equations (1) and (2). [Equation 1] 0.8 ≦ Ttap (N) / Tcast (N) ≦ 1.2 ・ ・ ・ ・ ・ ・ ・ (1) 0.6 ≦ Tkill (N) / Tkill (F) ≦ 1.2 ・ ・ ・ ・ ・ ・ ・ (2) However, in Equations (1) and (2), Ttap
(N) is the N-th tapping in the refining furnace and (N +
1) The time interval between the tapping and the Tcast (N)
N-th casting in the continuous casting machine, and (N +
1) The interval between the start times of each of the first castings, Tki
ll (N) is the time from the completion of tapping after the Nth tapping to the start of casting, and F indicates the final tapping from the refining furnace. 2. The refining furnace according to claim 1, wherein the refining furnace is repaired with refractories after the final tapping from the smelting furnace is completed and before the next tapping is started. Steelmaking method using multiple refining furnaces.