Metallurgical apparatus – Means for treating ores or for extracting metals – By means applying heat to work – e.g. – furnace
Reexamination Certificate
2000-07-07
2002-07-02
Kastler, Scott (Department: 1742)
Metallurgical apparatus
Means for treating ores or for extracting metals
By means applying heat to work, e.g., furnace
C432S138000
Reexamination Certificate
active
06413471
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for producing reduced iron by mixing an iron material and a reducing agent to form a mixed powder, agglomerating the mixed powder to form compacts like pellets, or briquettes and reducing the compacts in a high temperature atmosphere.
2. Description of the Related Art
To produce reduced iron, the first step is to mix an iron ore powder, a coal powder, a fluxstone (limestone) powder, and a binder, and humidify and agglomerate the mixture to form wet compacts called green compacts. Then, the wet compacts are dried to some degree. The dried compacts are heated to a high temperature in a reducing furnace (a rotary hearth furnace, RHF), where iron oxide in the iron ore is reduced with the coal to form reduced iron compacts.
FIG. 13
shows a vertical section of a conventional RHF.
FIG. 14
shows a section of a compact supply portion in the conventional RHF.
As shown in
FIGS. 13 and 14
, a conventional RHF
001
has a pair of parallel rails
003
mounted in an annular formon a circular base
002
installed on a floor surface. To a lower surface of an annular hearth
004
, a plurality of pairs of (right and left) wheels
005
are attached along a peripheral direction. The wheels
005
can roll on the rails
003
. On the base
002
, vertical frames
006
are erected inwardly and outwardly of the rails
003
. On an upper portion of the inner and outer vertical frames
006
, furnace walls
007
are fixed on both sides of the hearth
004
. On top of the furnace walls
007
, a ceiling
008
is fixed to cover an area above the hearth
004
.
Inside the RHF
001
, a space portion S for forming a high temperature atmosphere is defined by the hearth
004
, the right and left furnace walls
007
, and the ceiling
008
. On the furnace walls
007
, a multiplicity of burners
009
are provided for heating the space portion S. To the right and left vertical frames
006
, water sealing portions
010
by water seal are attached. A lower end portion of a skirt
011
fixed to the furnace wall
007
, and a lower end portion of a skirt
012
fixed to the hearth
004
are submerged in the water sealing portion
010
.
At a predetermined position of the RHF
001
, a compact supply portion
013
for supplying green compacts (raw compacts) onto the hearth
004
, and a compact discharge portion
014
for discharging reduced compacts (reduced iron) reduced on the hearth
004
to the outside are provided adjacently. That is, a low ceiling portion
015
is provided detachably in correspondence with the compact supply portion
013
. In the ceiling portion
015
, a compact acceptance opening
015
a
is formed. Above the ceiling portion
015
, a compact supply hopper
016
and a vibrating feeder
017
having a compact supply port
017
a
are provided. A low ceiling portion
018
is provided detachably in correspondence with the compact discharge portion
014
. In the ceiling portion
018
, a compact discharging screw
019
is provided.
Thus, dried green compacts are heaped in the compact supply hopper
016
in the compact supply portion
013
, and supplied onto the hearth
004
by the vibrating feeder
017
through the compact acceptance opening
015
a
via the compact supply port
017
a.
The hearth
004
rotates at a predetermined speed in the direction of an arrow T in
FIG. 14
, and forms a high temperature atmosphere upon heating of the space portion S by the burners
009
. Hence, while the green compacts on the hearth
004
are moving in the high temperature atmosphere, iron oxide in the iron ore is reduced with the coal to become reduced iron. In the compact discharge portion
014
, the reduced green compacts are discharged out of the furnace by the compact discharging screw
019
, and packed into a container (not shown).
To produce direct-reduced iron having a high degree of metallization in a reduced iron production process in the RHF
001
, it is important to prevent direct-reduced iron after reduction from becoming reoxidized. Thus, a task for discharge from the compact discharge portion
014
is performed such that direct-reduced iron is carried under airtight conditions into the container, and passed on to a subsequent step.
With the conventional RHF
001
, the green compacts supplied from the compact supply portion
013
onto the hearth
004
are immediately heated with a high temperature gas inside the furnace. To avoid the situation that the high temperature gas flows reversely and gushes from the compact supply portion
013
(compact supply port
017
a,
compact acceptance opening
015
a
), the high temperature gas inside the furnace is discharged through an off-gas duct (not shown) to keep the interior of the furnace at a negative pressure. Hence, when the green compacts are supplied from the compact supply portion
013
onto the hearth
004
, outside air F enters the furnace together with the green compacts, and divides into air F
1
directed forward in the direction of rotation of the hearth
004
, and air F
2
directed rearward in the direction of rotation of the hearth
004
, i.e., toward the compact discharge portion
014
, as shown in FIG.
14
. The air F
2
directed toward the compact discharge portion
014
contacts the direct-reduced iron to be discharged from the compact discharge portion
014
, reoxidizing the direct-reduced iron and lowering the degree of metallization.
As shown in
FIG. 13
, both sides of the hearth
004
are sealed by the submersion of the skirts
011
,
012
in the water sealing portion
010
to prevent the outflow of the high temperature gas inside the furnace, and the inflow of the outside air. As stated earlier, however, air enters the furnace from the compact supply portion
013
, because the interior of the furnace is maintained at a negative pressure. This air flows in the entire periphery of the RHF
001
through a space portion Q above the water sealing portion
010
, adversely affecting the high temperature atmosphere and the regulation of the pressure inside the furnace.
SUMMARY OF THE INVENTION
The present invention has been accomplished to solve the above-mentioned problems. It is an object of this invention to provide an apparatus for producing reduced iron, which can produce reduced iron at a high degree of metallization by preventing entry of the outside air into an RHF, and which can increase the operating efficiency of the RHF.
An apparatus for producing reduced iron according to the invention, designed to attain the above object, is an apparatus for producing reduced iron by agglomerating a mixed powder of an iron material and a reducing agent to form compacts like pellets, or briquettes and reducing the compacts in a high temperature atmosphere, comprising:
a rotary hearth in an annular form and rotatably supported;
a frame for covering an area above the rotary hearth to form a high temperature atmosphere space portion;
a compact supply portion for supplying the compacts onto the rotary hearth;
a compact discharge portion for outwardly discharging reduced iron reduced on the rotary hearth; and
supply portion partitioning means as a partition between the compact supply portion and the high temperature atmosphere space portion.
Thus, even if the outside air enters the furnace from the compact supply portion, the partitioning means suppresses air flow to the high temperature atmosphere space portion and the compact discharge portion, and prevents reoxidation of direct-reduced iron. This makes it possible to produce direct-reduced iron having a high degree of metallization. Also by diminishing the influence on the high temperature atmosphere or the regulation of pressure inside the furnace, the operating efficiency can be increased.
In the apparatus for producing reduced iron according to the invention, discharge portion partitioning means may be provided as a partition between the compact discharge portion and the high temperature atmosphere space portion. Thus, air flow from the compact discharge portion to the high temperature atmosphere space porti
Fujioka Hironori
Hirata Kouichi
Kamikawa Susumu
Mizuki Hideaki
Santo Akihiro
Kastler Scott
Mitsubishi Heavy Industries Ltd.
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