EP0462538B1

EP0462538B1 - Vacuum-suction continuous degassing apparatus

Info

Publication number: EP0462538B1
Application number: EP91109889A
Authority: EP
Inventors: Masamichi Sano; Nobuo Miyagawa; Kunji Yamamoto
Original assignee: TYK Corp
Current assignee: TYK Corp
Priority date: 1990-06-16
Filing date: 1991-06-17
Publication date: 1996-10-16
Anticipated expiration: 2011-06-17
Also published as: EP0462538A1; DE69122667T2; ATE144293T1; ES2096602T3; DE69122667D1; JPH0448026A; JPH0753894B2; CA2044722A1

Abstract

A melt flow pipe (15) is arranged penetrating a vacuum container (14). The melt flow pipe is made of a porous material having pores which allow premeation of gases but does not allow permeation of melts (2) such as molten metal, molten slag, and molten matte. And, in the wall of this melt flow pipe are buried a pipe-like member (16) wherein a cooling medium flows in a form of coil. As the melt contact the external surface of the flow pipe and this section is exposed to a vacuum state, gases in the melt or gases generated through reactions between the melt and the porous member pass through the porous flow pipe to the internal surface side and removed. When the melts flows therein, the flow pipe is cooled by a cooling medium, so that degasification of the melt can be made continuously. <IMAGE>

Description

The present invention relates to a vacuum-suction continuous degassing apparatus, in which gas-forming solute ingredients are removed or recovered from a metallurgical melt, such as a molten metal, matte, or slag, through a porous member.
Conventionally, the RH method, DH method, and other degassing methods are used to remove gas-forming solute ingredients from a molten metal. According to the RH or DH method, a large quantity of argon gas is blown into the melt, the surface of which is kept at a vacuum or at reduced pressure so that the partial pressure of the gas-forming ingredients is lowered, thereby removing these ingredients.
Requiring the use of argon gas in large quantity, however, the conventional RH or DH degassing method entails high running cost. Since much argon gas is blown into the melt, moreover, the melt is liable to splash so that many metal drops adhere to the wall surface or some other parts of the apparatus, which requires troublesome removal work. To cope with this splashing of the melt, furthermore, the apparatus is inevitably increased in size, resulting in higher equipment cost.
From GB-A-829 777 a vacuum-suction degassing apparatus is known. Said GB-A-829 777 discloses a device for degassing liquid melts, wherein two chambers are separated from one another by a preferably metallic wall having a portion which is gas-permeable but which portion is not permeable to the liquid melt. The melt is introduced into the one chamber while in the other chamber there is maintained low pressure so as to have a refining effect.
From US-A-2 809 107 a method of degassing molten metals is known wherein a tube of preferably steel is immersed into liquid metal. The tube is closed at its bottom portion. The other end of the tube is connected to a vacuum source.
It is the object of the present invention to provide a vacuum-suction degassing apparatus having improved durability of the porous member. This object is solved by a vacuum-suction degassing apparatus comprising the features of claim 1 or claim 5.
Preferred developments of the invention are given in the subclaims.
According to the present invention, a first surface of a porous member which is made of a porous materials permeable to gas and impermeable to melts, contact the melt, and a second surface is kept in vacuum or under reduced pressure, so that gases in the melt or gases produced by reactions between the melt and components of the porous member permeate through said porous member from the first surface side to the second surface side, and are released on the second surface into vacuum or depressurized atmosphere.
Also, a pipe member is buried in said porous member and a cooling medium flows in the pipe member, so that said porous member is cooled together with said pipe member, thus softening and melting thereof being prevented. Thefore, degasfication of the melt can be performed continuously. Also, if the melt penetrates into pinholes of the porous member. the melt is cooled by the pipe members and solidified so that the intrusion of melt into the vacuum atmosphere side can be prevented.
Different from the conventional method where a large volume of argon gas is blown, in this invention, argon gas is not blown, or a small volume of argon gas only enough to stir the molten metal is blown, so that an amount of argon gas can remarkably be reduced. Also, as the amount of argon gas is extremely low, generation of splashes is suppressed, and deposition of base metal on a wall surface of the apparatus can be reduced. Thus, according to this invention, reduction of equipment cost by minimizing the apparatus and remarkable reduction of running cost can be realized.

Fig 1 is a diagram for illustrating the principle of the present invention,
Fig. 2 is a schematic cross-sectional view showing a vacuum-suction continuous degassing apparatus according to a first embodiment of the invention,
Fig. 3 is a schematic cross-sectional view showing a vacuum-suction continuous degassing apparatus according to a second embodiment of the invention,
Fig. 4 is a schematic cross-sectional view showing a vacuum-suction continuous degassing apparatus according to a third embodiment of the invention.

First, description is made for a principle of this invention with reference to Fig. 1. Partitioning member 1 is made of a porous material which is permeable to gas, but impermeable to melts, such as molten metal, molten matte, or molten slag. If melt 2 is brought into contact with one side of porous member 1, and if the other side of member 1 is kept at a vacuum ar at a reduced pressure 3, the pressure on the wall surface in contact with the melt drops without regard to the static pressure of the melt 2.
Accordingly, those impurities or valuables in melt 2 which produce gaseous substances easily nucleate on the wall surface of porous member 1 to form gas 4, and resulting gas 4 permeates through member 1 and sucked into space 3 at vacuum or reduced pressure atmosphere so that the impurities or valuables are removed from the melt and recovered into space 3 at vacuum or reduced pressure atmosphere.
The inventor hereof realized that gas-forming ingredients can be removed from the melt on the basis of the principle described above, and brought the present invention to completion.
The gas-forming ingredients dissolved in the melt are sucked and removed in the form of gases as follows:

N + N = N₂ (1)

H + H = H₂ (2)

C + O = CO (3)

S + 2O = SO₂ (4)
The impurities in the melt may react with the ingredients of the porous member, to form gases, and then they may be removed through the porous member.
If the porous member is an oxide (M_XO_Y), carbon in the melt is removed in the form of a gas as follows:

yC + M_XO_Y (solid) = xM + yCO (5)
If the porous member contains carbon, moreover, oxygen in the melt is sucked and removed according to the following reaction formula.

O + C (solid) = CO (6)
The separative recovery of a valuable component (M) which has high vapor pressure is achieved by gasifying the valuable component according to the following reaction formulas.

xM = M_X (gas) (7)

MO_Y = MO_Y (gas) (8)

MS_Y = MS_Y (gas) (9)
In this manner, the impurities, such as N, H, C, O, and S, and the valuable components are sucked and removed or recovered from the melt,
According to the present invention, by adjusting content of components of the partitioning member which react with the impurities or valuable components in a melt, it is possible to control a reaction rate between the impurities or valuable components in the melt and components of the partitioning member.
Various materials may be used for porous member, including metallic oxides or other metallic compounds (non-oxides), carbon and mixtures thereof and metal, such as Al₂O₃, MgO, CaO, SiO₂, Fe₂O₃, Fe₃O₄, Cr₂O₃, BN, Si₃N₄, SiC, C, etc. Preferably, the material used should not react with the principal ingredient of melt 2 so that porous member in contact with melt 2 can be prevented from erosion loss and melt 2 can be kept clean.
Also, a material which hardly gets wet with melts must be used for the partitioning member so that only gases can pass through the partitioning member but any melt can not pass through the partitioning member. Furthermore, it is preferable that a porosity of the partitioning member is not more than 40% and its diameter is about 200 µm or less.
According to the present invention, said pipe member buried in the porous member strengthens the porous member. In this case, when degasfication of melt is peformed continuously and for a long time, the pipe member is easy to be fused. However, according to the present invention, a cooling medium flows through the pipe member, softening and melting of the pipe member due to heat from melt can be prevented. For this reason, degasification can be made for a long time. Also, for instance, if the melt penetrates into pinholes of the porous member, the melt is cooled by the pipe members and solidified so that the intrusion of melt into the vacuum atmosphere side can be prevented.
Furthermore, in order to prevent a melt from entering the vacuum system even if a melt goes into the immersed porous tube, it is preferable to allocate a filter with small pressure loss in an upper section of the immersed porous tube to solidify the invading melt for trapping it.
The following is a description of a case in which the present invention is applied to the removal or recovery of gas-forming ingredients from a melt.

(1) First, the present invention can be applied to decarburization, denitrogenation, and dehydrogenation processes for removing carbon, nitrogen, or hydrogen from molten iron.
When this method is applied to remove carbon from molten iron, the main component of said partitioning member should be Al₂O₃ or MgO, and such a material as Fe₂O₃, Fe₃O₄, MnO, and SiO₂ etc. should be mixed in as main oxidizing agents for carbon in the molten iron. But if a compounding ratio of the main oxidizing agent is too high, a melting point of the partitioning member goes down, or the mechanical strength thereof becomes lower, and if carbon content in the molten iron is too low, oxygen content in the molten iron goes up, so that a compounding ratio of the main oxidizing agent must be decided according to the purpose and by referring to the phase diagram already established.
On the other hand, if this method is applied to removal of nitrogen in molten iron, a stable oxide such as CaO, Al₂O₃, or MgO should be used as said partitioning member.
Also, if this invention is applied to simultaneous removal of carbon and nitrogen in molten iron, the compounding ratio of the oxidizing agent should be changed according to target contents of carbon and nitrogen in the molten iron.
(2) The invention can be also applied to a deoxygenation process for removing oxygen from molten copper.
(3) Further, the invention can be applied to a dehydrogenation process for removing hydrogen from molten aluminum.
(4) Furthermore, the invention can be applied to decarburization, and dehydrogenation of molten silicon.
(5) According to the present invention, zinc can be recovered from molten lead.
(6) The invention can be also applied to a desulfurization/deoxygenation process for removing sulfur and oxygen from molten copper matte.
(7) Further, the invention can be applied to the recovery of valuable metals (As, Sb, Bi, Se, Te, Pb, Cd, etc.) from molten copper matte or nickel matte.
(8) Furthermore, the invention can be applied to the recovery of valuable metals (As, Sb, Bi, Se, Te, Pb, Cd, Zn, etc.) from slag.

Detailed description is made below for embodiments of this invention.
Fig. 2 is a schematic cross-sectional view showing the vacuum suction-continuous degassing apparatus according to the first embodiment of this invention.
Cylindrical melt flow pipe 15 made of a porous material is arranged penetrating vacuum container 14. And, at both edges of melt flow pipe 15 are connected to melt flow pipe 15a.
Vacuum container 14 is connected to a vacuum pump in an appropriate manner, and inside of vacuum container 14 is kept in a vacuum state.
Melt flow pipe 15 is made of a porous material, and this melt flow pipe 15 has pores which allows permeation of gases but does not allows permeation of melts 2 such as molten metal, molten slag, and molten matte. Also, in the pipe wall of this melt flow pipe 15 is buried a pipe-formed center member 16 in the form of coil. And, a cooling medium such as gas or liquid flows in center member 16.
In the vacuum suction continuous degassing apparatus having the configuration as described above, when melt 2 flows in flow pipe 15 and passes through vacuum container 14, a portion of melt 2 contacting flow pipe 15 is exposed to vacuum through this flow pipe made of this porous material. With this, gases in melt 2 or gases generated through reactions between melt 2 and the porous member are removed, and a processing to remove gas generating components from melt 2 can be made continuously.
In this embodiment, as a cooling medium flows through center member 16 buried in flow pipe 15. softening and melting of center member 16 due to heat from melt 2 can be prevented. For this reason, degasification can be made for a long time. Also, for instance, if there is a pinhole on melt flow pipe 15 and molten 2 entered through this pinhole in an area around center member 16, intrusion of melt 2 into the vacuum atmosphere side can be prevented, because melt 2 is cooled by center member 16 and solidified.
Fig. 3 is a cross-sectional view showing a vacuum suction continuous degassing apparatus according to the second embodiment of this invention.
In box-type container 20, a plurality of plate-formed banks 21 (only 3 shown in Fig. 3) are arranged at an interval in parallel to each other. In each bank 21, plurality of melt pass-through holes 22 penetrating in the direction of width thereof are arranged at one edge in the direction of width thereof in the direction of height of bank 21. Also, in each bank 21, plurality of gas suction holes 23 penetrating in the direction of height thereof (5 holes shown in the figure) are formed and arranged in the direction of width of bank 21. Furthermore, pipe form of center member 24 is buried in bank 21. This bank 21 is made of a porous material having pores which allows permeation of gases but does not allow intrusion of melts such as molten metal, molten slag, and molten matte. Also, entrance 20a and exit 20b for melt 2 are arranged in container 20.
In the vacuum suction continuous degassing apparatus, melt 2 enters container 20 from entrance 20a, and a flow route thereof is restricted by bank 21. This melt 2 passes through melt pass-through hole 22 of bank 21 and flow in a zigzag form, when viewed from a top, in container 20 as shown by arrow marks in the figure. On the other hand, gas suction holes 23 arranged in bank 21 are kept in vacuum via piping (not shown), and melt is exposed to a vacuum state via bank 21 while flowing with a flow route restricted by bank 21. With this, gas generating components in melt 2 are removed. As center member wherein cooling liquid or cooling gas flows is buried in bank 21, softening or melting of center member 24 is prevented. For this reason, the apparatus can be run continuously. Also, if there is a pinhole in the porous material forming bank 21 and melt 2 enters through this pinhole into bank 21, melt 2 is cooled and solidified around center member 24, so that intrusion of melt into gas suction holes 23 can be prevented.
In this embodiment, degasification of a melt can be made continuously, and as an area where the melt contacts the porous member is large, gas-forming components in the melt can be removed at a high efficiency.
Fig. 4 is a cross-sectional view of a vacuum-suction continuous degassing apparatus according to the third embodiment of this invention.
Melt 2 flows through entrance for melt 33 into container 31 from near a wall surface of box-type container 31, and traverses container 31, and then flows out through exit for melt 34 from near another wall surface facing the aforementioned wall surface of container 31 to the outside.
Degassing member 32 comprises a plurality of partition members 32b having a form like a cylinder with the lower edge closed and non-porous member 32 linked to the upper edge of these partition members 32b. In degassing member 32 is buried a pipe-formed center member (not shown) with edges of the center edges leading to outside and connected to a cooler to feed a cooling gas or a cooling liquid into inside of the center member. And, degassing member 32 with partition member 32b immersed in melt 2 is allocated above container 31. Also, degassing member 32 is linked to an appropriate vacuum system, and inside of degassing member 32 is kept in a vacuum state being sucked by this vacuum system.
Partition block 32b is made or a porous material having pores which gases can permeate through and melts such as molten metal, molten slag, and molten matte can not permeate through. On the other hand, non-porous member 32a is made of a material which does not allow permeation of any gas, or a processing to inhibit permeation of gases is applied to non-porous member 32a.
Degassing member 32 can be made, for instance, by using pipe assembled into a specified form as a center member, allocating a porous material around the center member and forming it into a form of degassing member 32, and coating upper portion of degassing member 32 with a non-porous material which does not allows permeation of any gas to obtain a non-porous member 32a.
In the vacuum suction continuous degassing apparatus having the configuration as described above, melt 2 enters container 31 from entrance 33, traverses container 31, and flows out from exit 34. Inside of degassing member is kept in a vacuum, and melt 2 is exposed to a vacuum state through partition member 32b while flowing in container 31. And, gas-forming components in melt 2 moves through partition member 32b to inside of degassing member 32. As a cooling gas or a cooling liquid is flowing in the center member buried in degassing member 32, softening or melting of the center member due to heat of melt 2 can be prevented, and degasification of melt 2 can be made continuously. Also, melts going into degassing member 32, for instance, through a pinhole in the partition member 32 is cooled by a liquid or a gas flowing in the center member, so that intrusion of melt 2 into degassing member 32 can be prevented.
Note that, if any trouble occurs in degasification due to endothermic reactions of the melt with the melt flow pipe (in the first embodiment), banks ( in the second embodiment), or porous material components of the partition member ( in the third embodiment), an external heating apparatus can be arranged to heat the melt.
Also, in order to prevent a melt from coming into the vacuum system or other sections due to breakage of the aforementioned melt flow pipe, banks, or partition members, a filter with small pressure loss may be arranged between the degassing apparatus and the vacuum system to solidify and trap the melt.

Claims

A vacuum-suction continuous degassing apparatus for degassing a metallurgical melt (2), comprising:
a porous member (15, 21, 32b), made of a porous material which is permeable to gases and impermeable to metallurgical melts (2);

means (15a, 20, 20a, 20b, 31) for contacting a first surface of said porous member (15, 21, 32b) to said metallurgical melt (2);

means (14, 23, 32) for contacting a second surface of said porous member (15, 21, 32b) to vacuum or depressurized atmosphere and whereby gases in said metallurgical melt (2) or gases produced by reactions between said metallurgical melt (2) and components of said porous member (15, 21, 32b) are sucked to the side of the second surface through said porous member (15, 21, 32b);

a pipe member (16, 24) buried in said porous member (15, 21, 32b); and

cooling means for flowing a cooling media through said pipe member (16, 24).
The vacuum-suction continuous degassing apparatus according to claim 1, characterized by further comprising:
heating means for heating said melt (2).
The vacuum-suction continuous degassing apparatus according to claim 1, characterized in that
said porous member (15) has a cylindrical form and said first surface is formed by the internal surface thereof and said second surface is formed by the external surface.
The vacuum-suction continuous degassing apparatus according to claim 1, characterized in that
said porous member (21) has a plate-like form having front and back surfaces and gas pass-through holes (23) therein, said first surface is formed on the front and back surfaces, and said second surface is formed by said internal surface of said gas pass-through holes (23).
A vacuum-suction continuous degassing apparatus for degassing a metallurgical melt (2) comprising:
plurality of porous members (32b), each having a cylindrical form with a closed bottom;

a degassing member (32) commonly linked to the upper portions of said porous members (32b);

means for applying to the inside of said porous members (32b) vacuum or reduced pressure atmosphere through said degassing member (32), thereby sucking gases in said metallurgical melt (2) or gases produced by reactions between said metallurgical melt (2) and components of said porous members (32b);

a pipe member buried in said porous members (32b); and cooling means for flowing a cooling media through said pipe member.