JPH10317050A - Method for injecting powdery material into molten metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for injecting powdery material into molten metal which can easily execute the protection of a nozzle hole and the restraint of slopping of molten metal at the initial stage of injecting the powdery material into the molten metal. SOLUTION: At the time of refining the molten metal by injecting the powdery refining agent into the molten metal with carrier gas through an immersion lance, gas pressure in a pressure vessel is adjusted as in the following steps in order. The first step: Firstly, an immersion lance is lowered and the gas pressure in the pressure vessel is set to the lower limit value, in which the molten metal is not invaded into the lance hole at the depth of the lance hole into the molten metal in a refining period, until the lance hole arranged at the tip part of the lance reaches the molten metal surface. The second step: Further, the immersion lance is lowered, and the gas pressure in the pressure vessel is set to the value realizing the discharging speed of the powdery material in the refining period until the lance hole reaches the dipping depth in the molten metal during the refining period and after reaching.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of blowing powder into molten metal, and more specifically, to a powder blowing lance (hereinafter simply referred to as a lance) protected by a refractory in hot metal held in a hot metal pot, for example. This is a technique in which a smelting material is immersed from above and blown into the hot metal to pulverize the refining material, and at the initial stage of the blowing, the lance hole is prevented from being worn and the hot metal is prevented from dropping.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 2, an apparatus for injecting powder into a molten metal contains a powder 1 as a refining agent such as a flux and pressurizes and fluidizes it with a carrier gas. And a lance 5 at the end of a pipe 9 connected to the pressure vessel 4. Then, the relationship between the gas pressure in the pressure vessel 4 and the powder blowing speed is known in advance, and the gas pressure that achieves the target blowing speed during refining is determined from the relationship, and the blowing amount of the powder 1 is determined. ing.

However, since the above relationship is determined when the lance 5 is immersed in the molten metal 7 at a certain depth, during the lowering of the lance 5 at the beginning of blowing (initial control), The immersion depth is shallow, and the powder 1 is blown at a speed higher than the target blowing speed, often resulting in an excessive blowing amount. The outlet of the powder 1 provided at the tip of the lance (hereinafter referred to as the lance hole 8)
In many cases, the molten metal or slag is inserted and closed during immersion in the molten metal 7, and for protection thereof, blowing of the powder 1 is started before the lance hole 8 is immersed in the molten metal 7. It is desirable. For this reason, in the descent period of the lance 5 at the beginning of the blowing, the carrier gas 2 and the powder 1 having an excessive flow rate exceeding the target value are blown into a shallow portion of the molten metal 7, and the molten metal 7 is ejected from the refining vessel 6. This causes a so-called slopping phenomenon (hereinafter simply referred to as slopping).

In order to solve these problems, it is necessary to know the above relationship depending on the immersion depth of the lance 5, and to control the blowing with a gas pressure suitable for the immersing depth at the start of the blowing. It is. However, there is another problem that the control time constant of the blowing gas pressure is long and it is difficult to perform the optimum control, and the blowing control software becomes more complicated than necessary.

[0005]

SUMMARY OF THE INVENTION In view of the foregoing, the present invention has been made in consideration of the above circumstances, and has been made in consideration of the above circumstances. It is intended to provide a body blowing method.

[0006]

Means for Solving the Problems In order to achieve the above object, the inventor of the present invention has conducted intensive studies, focusing on the amount of blowing of the lance until the lance reaches the immersion depth during the refining period. Was completed. That is, in the present invention, a powdery refining agent is blown into a molten metal with a carrier gas through an immersion lance, and in refining the molten metal, the gas pressure in the powder supply pressure vessel is adjusted through the following steps in order. This is a method of blowing powder into a molten metal.

First step: First, lower the immersion lance,
Until the lance hole provided at the lance tip reaches the surface of the molten metal bath, the gas pressure in the powder supply pressure vessel is
Setting a lower limit value at which the molten metal is not inserted into the lance hole at a depth of the molten metal in the lance hole during a refining period. Second stage: Further, the immersion lance is lowered, and the gas pressure in the powder supply pressure vessel is increased until the lance hole reaches the immersion depth during the refining period in the molten metal. Setting the value to realize the powder cutting speed in the above.

The present invention is also a method for blowing powder into a molten metal, wherein the lower limit of the gas pressure is determined in advance according to the position of a lance hole. In the present invention,
At the position where the immersion depth is small when the lance descends, the pressure of the blown gas is set to a value necessary only for protection of the lance hole, and then, after reaching the lance position in the refining period, the pressure required for refining is set. , So that excessive blowing can be prevented. As a result, it is possible to suppress the slopping of the hot metal at the initial stage of blowing while preventing the lance hole from being worn.

[0009]

Embodiments of the present invention will be described below in detail with reference to FIG. The arithmetic and control unit (not shown) used in the embodiment of the present invention has a lower limit value of the gas pressure before the lance hole reaches the position of the refining period measured in advance,
And the relationship between the gas pressure after the arrival and the blowing speed (see FIG. 3). Then, the present invention is implemented by using the control of the lance height and the control of the gas pressure in combination as shown in FIG.

First, before the lance is lowered (standby position), the set gas pressure SP in the pressure vessel 4 is increased until the initial pressure, that is, the pressure P _S at which the molten metal 7 is not inserted into the lance hole 8. You. When a command to lower the lance 5 is issued, the lowering of the lance 5 is started, but the powder has not yet been blown. Then, when it is detected that the position of the lance 5 has reached the melt surface of the molten metal 7, open the on-off valve 3 which is attached to the pressure vessel 4, the locking hole 8, the carrier corresponding to the gas pressure P _S at that time The blowing of the gas 2 and the powder 1 is started. However, the lance 5 continues to descend until the lance hole 8 is buried in the molten metal 7 and reaches the immersion depth during the refining period. At the same time, the set pressure SP in the pressure vessel 4
And it is set to be the gas pressure P _F at the time of refining determined by the relationship of FIG. 3 with respect to the powder blowing speed of a target. However, even if the SP value from P _S to P _F, the actual gas pressure PV is, gradually increase does not become at once P _F. By the time the lance reaches the immersion depth during refining, the PV is set to approximately P _F and the amount of the powder 1 to be blown is set to an amount necessary for refining. After locking hole 8 has reached the immersion depth during refining is to maintain the gas pressure P _F to refining ends.

According to the present invention, the blowing pressure when the lance 5 is lowered is set to a low pressure necessary for protecting the lance hole 6 at a shallow place in the molten metal 7 bath. , The blowing pressure gradually increases,
High pressure required during refining. Therefore, the sloping of the lance hole 8 which is prevented from occurring at the beginning of the blowing, which has conventionally occurred, is prevented.
It is also possible to achieve the prevention of wear.

[0012]

EXAMPLE A powder injection method for molten metal according to the present invention was carried out at a steelmaking plant having two 235-ton scale bottom-blowing converters. The molten metal 7 was hot metal, which was accommodated in a hot metal pot 6 shown in FIG. 2 and subjected to so-called hot metal pretreatment for desulfurization. 2 is a pressure vessel 4 having a capacity of 1 m ^3.
And a lance 5 and its turning / elevating means 10 and 11. The lance 5 is formed by lining the outside of a steel pipe with a refractory, and the lance hole 8 is of a horizontal two-hole type.
The powdered refining agent blown is 80% CaCO ₃ , metal M
g was 20%. The blowing capacity of this device is 30 to 70 kg per minute.

As a result, the slopping at the initial stage of blowing can be completely prevented, and the pre-treatment time caused by the slopping is not extended, so that the throughput is greatly improved as compared with the conventional case.
Specifically, in the case of the above-mentioned bottom-blowing converter, the loss of refining time decreased by 0.5% on an annual average compared with the conventional case. Lance 5
The service life was 30 times on average, and the service life of the conventional level could be maintained. Further, since the present invention can be implemented with simple control software and hardware, it was possible to achieve the object only at a low construction cost without requiring a large-scale device modification. By the way, of the construction costs, software production costs decreased by 10%.

[0014]

As described above, according to the present invention, it is possible to prevent the initial slopping when the powder is blown into the molten metal, and to prevent the refining time from being delayed due to the slopping. . As a result, productivity of molten steel has been greatly improved. In addition, the life of the lance used can be maintained at the conventional level, and an increase in operating costs has been suppressed.

[Brief description of the drawings]

FIG. 1 is a flowchart of a method for blowing powder into a molten metal according to the present invention.

FIG. 2 is a diagram showing an example of a general apparatus for blowing powder into a molten metal.

FIG. 3 is a diagram showing a relationship between a gas pressure in a pressure vessel and a powder blowing speed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Powder (blown material) 2 Carrier gas 3 On-off valve 4 Pressure vessel 5 Lance 6 Refining vessel (hot metal pot) 7 Molten metal (hot metal) 8 Lance hole 9 Pipe 10 Lance lifting arm 11 Lifting arm support column

Claims (2)

[Claims] Claims: 1. A carrier and a molten metal are immersed in a molten metal through an lance.
A method for blowing powder into a molten metal, comprising: blowing a powdery refining agent with a gas to adjust the gas pressure in a powder supply pressure vessel through the following steps in refining the molten metal. First stage: First, the immersion lance is lowered, and the gas pressure in the powder supply pressure vessel is reduced until the lance hole provided at the tip of the lance reaches the surface of the molten metal bath. Setting the lower limit of the depth of the hole in the molten metal such that the molten metal does not enter the lance hole. Second stage: Further, the immersion lance is lowered, and the gas pressure in the powder supply pressure vessel is increased until the lance hole reaches the immersion depth during the refining period in the molten metal. Setting the value to realize the powder cutting speed in the above. 2. The method according to claim 1, wherein the lower limit of the gas pressure is determined in advance according to the position of the lance hole.