Note: Descriptions are shown in the official language in which they were submitted.
SPECIFICATION
TITLE OF THE INVENTION:
RO~ARY KILN FOR USE IN REDUCTION-~MELTING ORES
OF OXIDES OF IRON GROUP ELEMENTS AND 5MELTING
METHOD THEREOF
BACKGROUND OF THE INVENTION:
Field of the Invention:
This in~ention relates to a rotary kiln for use
in subjecting an ore o~ an oxide of at least one kind
of element selected ~rom the eleme~s in the Iron
Group to semi-molten reduction-smelting, and a smelt-
ing method uslng s~ch a kiln, and more particularly
to a rotary kiln ~or use in sub~ecting an ore contain-
ing at least one kind o~ oxide of an element selected
from the elements in the Iron Group, in particular9
iron, nickel and cobalt, to semi-molten reduction-
smelting, and a ~melting method using such a kiln.
Description o~ the Prior Art:
Methods of reduction-smelting ores of oxides of
elements in the Iron Group to obtain elements i~ the
Iron Group have been known. These reduction-smelting
methods can be divided into the following three
groups.
(1) Completely-molte~ reductlon-smelting method:
In this method of reduction-smelting, an oxide
z~
ore, a flux and a reducing agent are placed in a
rotary kiln and completely melted therein to reduce
the oxide ore and form a molten metal and slag, which
are then discharged from the kiln. The Basset process
for smelting pulverized iron ore by using a rotary
kiln for cement is typical of this sort of reduction-
smelting method. However, the Basset process is not
used in practice at present since it causes the lining
of a kiln to be damaged greatly.
(2) Non-molten solid reduction-smelting method:
In this method, pulverized oxide ore is mixed
with a pulverized reducing agent, and the mixture is
pelletized. The pellets thus obtained are heated in
a kiln to reduce the oxide ore maintaining solid state,
and the reduced pellets are discharged from the kiln.
These reduced pellets are usually melted in an electric
furnace to be separated into metal and slag~ This method
is often used for the preliminary reduction-smelting
of an ore of an oxide of iron, nickel, or chromium.
(3) Semi-molten reduction-smelting method:
This method is generally called the ~rupp-
Rennanlage method and is known as a suitable method
for the reduction smelting of a pulverized oxide ore
having a high water content. In this method, an oxide
ore, a reducing agent and flux are heated in a kiln
, .,
_ 3- 7 0 7 ~i6 _D~
-to carry out the reduction O:e a me-tal with these materials when
semi-molten. This method is applied at present to the reduction-
smelting of nickel oxide ores.
The above are known methods oE reduction smelting ores
of oxides of elements in the Iron Group. All of these methods
are known as methods generally suited to reduction-smelt a low-
~uality pulverized oxide ore.
The part, improvement or combination claimed as invent-
ion herein is a rotary kiln having a product-reserving dam ring,
heating burners, and a combustion chamber in which the burner~
are ignited. The kiln is used to subject therein an ore of an
oxide of at least one element selected from the elements in the
Iron Group to a semi-molten reduction-smelting operation while
heating the ore with the burners~ The invention is characterized
in that the product-reserving dam ring consists of a refractory
material projecting Erom the portion of refractory lining on the
inner surface of the kiln, which corresponds to the product dis-
charge end of the kiln. The ratio of the height of the projecting
dam ring to the diameter of the cross section of the cylindrical
space defined by the refractory lining in the kiln is within the
range of 0.15 to 0.25.
Other embodiments of the invention as claimed are
defined in the claims attached hereto, which set forth the precise
subject matter in which an exclusive property or privilege is
claimed.
-3a- 70756-4
IN THE ACCOMPANYING DRAWINGS
Figure 1 is a longitudinal section in schematic repre-
sentation of a conventional rotary kiln for use in subjecting
oxide ores to semi-molten reduction s:melting.
Figure 2 is a longitudinal section in schematic repre-
s:entation of a product-retaining dam ring provided at the dis-
charge end of the rotary kiln shown in Figure l;
Figure 3 is a graph showing the relationship between
the H/D ratio (which will be hereinafter called the dam height
ratio), wherein D is the inner diameter of the circular cross
section of the space surrounded by the lining on the inner sur-
face of the rotary kiln according to the present invention, and
H is. the height of the dam ring projecting from the lining, and
the yield of metal;
Figure 4 is a longitudinal section of half of the body
of the rotary kiln according to the present invention which is at
the discharge end thereof, and a combustion chamber;
Fiq. 5 is a front elevation o-f the rotary kiln ac-
cording to the present inyention, in which the kiln body is
at the front and the combustlon chamber at the rear;
Fig. 6A is a graph showing the rela-tionship between
the distance between -the Eree end of the main burner and
various positions in the interior of the kiln, and the -tem~
peratures at these positions;
Fig. 6B is a longitudinal view of the shapes of
combustion flames which extend along the interior of the kiln
body from the main and auxiliary burners;
Fig. 7 is a longitudinal section of the discharge end
of a rotary kiln for use in subjecting oxide ores to semi-
mo]ten reduction-smelting, and a graph showing the relationship
between the positions of burners and the temperatures of the
flames therefrom; and
Fig. 8 is a diagram showing the relationship between
the distances between the free end of the burner and various
axial portions of the flame therefrom and the temperatures in
the central portions of the flame which are in ver-tical planes
including these various axial portions of the flame.
The rotary kiln used in the conventional Krupp-
Rennanlage method is the rotary kiln schematically shown in
Fig. 1, it has in most cases a total length of 60-120 m,
an outer diameter of 3.6-5.2 m, an inner diameter of 2.5-4.8 m,
and an angle of inclination of the axis thereof with respect to
the horizontal plane of 1-4%. The kiln has at its upper end
portion, i.e. its material-insertion portion 2 a preheating
zone A in which the materials introduced into the kiln are
reheated to increase the tempera-ture thereof; on the clown-
stream side of the preheating zone A there is a reduction
zone B, in which an oxide ore-reducimg reaction occurs
with the materials in a solid or semi-molten state; and at its
lower end portion a granulation zone C, in which the granules
of reduced sponge metal formed by the reduction reaction grow
into granular iron. The granular iron and slag formed there-
with are discharged from a dam ring 3 provided at a lower end,
i.e. the discharge end of the kiln. Namely, the drying and
preheating of materials is mainly carried out in a preheating
zone A in the kiln, the reduction of the oxide ore in the
reduction zone B, and the growing of granules of the reduced
metal and the formation of slay in the granulation zone C.
The rotary kiln referred to above consists of ~n iron
shell and chamotte bricks with which the iron shell is lined.
The portions of the kiln which correspond to the reduction
zone ~ and granulation zone C have temperatures higher than
that of the portion of the kiln which corresponds to the
preheating zone A, and , therefore, the first two portions
2~ of the kiln are further lined with chrome-magnesia bricks,
fused alumina bricks, or fused silica bricks~
An example in which a lean silicic iron ore (having
a Fe content of around 30%) is smelted in the above kiln
will now be described. Pulverized lean iron ore and a reducing
agent are introduced into the kiln from the upper end thereof to
be burnt with pulverized coal by a burner 5 inserted into the
kiln from the lower end thereof. As a result, the ore is pre-
heated and then reduced to become sponge iron.
;~ -5-
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When the sponge iron is heated further to 1200-1300C,
it absorbs about 1 % carbon to become granular iron
as the sponge iron is kneaded in slag having a basi-
city of about 0.3 and a high acidity. The granular
iron thus formed over~lows the dam ring 3 to be dis-
charged from the kiln~ The granular iron i~ then
sieved by a powdering machine and subjected to magnetic
separation. About 1-2 ~ slag is left in the granular
iron, and about 1-2 % metal in the slag. This method
is characterized i~ that lean silicic iron ores,
nickel ores and cobalt ores, which cannot be used
directly in a blast furnace, can be treated with a
low-quality pulveriæed reducing agent or a fuel.
In order to reduce as far as possible the ratio
of the quantity of granular iron lost in the slag
in the kiln to the total ~uantity of granular iron
formed, it is advantageous that the rate of formation
of fine granular ir3n, for example, granular iron
having a particle size of not ~ore than 0.5 mm, is
minimized.
m e yield of granular iron formed by using a
rotary kiln is 90-97 ~ The rate of formation of slag
increases generally in inverse proportion to the quality
of -the metal in the oxide ore used, the lower the
quality of the metal in the oxide ore used, the
.,, ~
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lower the yield of granular me-tal. The characteristics
of the reduction-smel-ting of an oxide ore in a kiln
reside in that low-quality pulverized coal can be
used as the reducing agent, and in that, especially,
low-quali-ty ore having a high silicic acid conten-t
can be suitably used. In recent years, low-quality
nickel containing ores, especially garnierite and
laterite, which have a Ni content of about 0.2~
have been treated in a ro-tary kiln. However7 when
a particularly low quality nickel-containing oxide
ore is subjected to semi-molten reduction-smelting
in a rotary kiln, slag is formed at an extremely
high rate. In addition, the rate of formation o~
fine particles of granular nickel among all the
particles of granular nickel ~ormed is comparatively-
high. Such fine p~icles of granular nickel mix into
and are lost in the slag.
A conventio~al rotary kiln Por use in subjecting
oxide ores to semi-molten reduction-smelting is
provided with a ~urner by which a heavy oil or
pulverized coal is burnt to heat the interior of
the kiln. The temperature in the kiln is thus
increa~ed to carry out the semi-molten reduction-
smelting of the oxide ore In such a rotary kiln~
the temperature of the product remaining in the dam
!J ~
ring provided at the discharged end -thereof cannot
be maintained at a predetermined level, and a slag
ring in the vicinity of the bo~dary between the
reduction zone B and the granulation zone C cannot
be fixed in position closer to the discharge end of
the kiln. Furthermore, when the slag ring grows to
an excessively great extent, the size thereof cannot
be reduced easily. Consequently, the reduction-
smelting operation cannot be carried out continuously
o~er a long period of time.
SUMMARY OF THE INVENTICN:
An object of the present invention is to provide
a rotary kiln used to subject an ore of an ox~de of
at least one kind of element selected from the
elements in the Iron Group to the semi molten reduction
smelting, and which has an improved dam ring capable
of increasing -the yield of metal i~ the smelting
operation.
Another object of the present invention is to
provide a rotary kiln which is capable of maintaining
at a predetermined level the temperature of the
product remaining in the dam ring provided at the
discharge end thereof, fixing in the closest possible
position with respect to the discharge end of the
rotary kiln the slag ring occurring in the vicinity
$~ 3~
of the boundary be-tween the reduction zone and the yranulation
zone, and easily reducing the size Oe the slay riny when the
slag ring has grown to an excessively great extent, and whlch
has a main burner and an auxiliary burner; and a smelting
method using this rotary kiln.
Still another object of the present invention is to
provide a rotary kiln having a combustion chamber formed so
as to surround the discharge end portion thereof, the length
of which combustion chamber in the axial direction of the
rotary kiln is set as appropriate r and a burner disposed in
an appropriate position in such a manner that, in particular,
the dis-tance between the free end of the burner and the sur-
face of the dam ring facing it is at an appropriate level;
and a reduction-smelting method using this rotary kiln.
These and other features and advantages of the present
invention will become apparent from the following description
in connection with the accompanying drawings.
DESCRIPTION OF THE PREFERRED EMBODIMENTS:
The inventors of the present invention have hit upon
an idea that, in order to preheat in a preheating zone A
an oxide ore which has been introduced into the kiln shown
schematically in Figs. 1 and 2, form fine particles of a
reduced metal in a reduction zone B, and then melt these
fine particles together to grow larger particles in a granu-
lation zone C, the fine particles of reduced metal may be
retained for a longer period of time in the kiln, especially
_g_
in the granulation zone C. One of the objects of the present
invention can be achieved by setting to 0.15-0.25 a ratio
H/D, i.e. the dam height ratio H/D, obtained by dividing the
height ~ of a product-retaining dam ring provided at the lower
end of a conventional rotary kiln 60 as to project from the
lining on the inner surface thereof, by the diameter D of the
cross section of the circular space in the kiln surrounded by
the lining in the part of the inner surface of the kiln which
corresponds to the granulation zone (the diameter D of the
cross section of this circular section will be hereinaf-ter
called the inner diameter).
For example, paragraph 3 on page 324 of the thesis
entitle~ "Bau und Betrieb der Krupp-Rennanlage in Watenstedt"
included in "Stahl und Eisen", pages 319-325, published on
May 12, 1943, refers to techniques for optimally filling with
materials a rotary kiln used to practice the Krupp-Rennanlage
method. This paragraph of the thesis says "When the inner
diameter of kiln in Watenstedt is 3600 mm, the diameter of
the dam ring is 1600 mm. Accordingly, the height of the dam
ring is substantially 1000 mm, and the thickness of the
materials placed in the kiln decreases gradually from the dam
ring to a material introduction port at the upper end of the
kiln. .... It has been ascertained experimentally that the
--10--
~f~
optimum diameter of the dam ring for such a type
of kiln as is used in Watenstedt is 1600 mm.
There~ore, it can safely be said that the above values
are perfectly recommendable .. "r The ratio H/D,
i.e. the ratio of the height H (1000 mm) of the dam
ring -to the inner diame-ter D (3600 mm) of the kiln~
in this case is 0.278.
On the other hani~ the ratio of the height of
the dam ring to the inner diameter of the kiln body
in a rotary kiln for use in manufacturing cement, or
an Elkem type of rotary kiln for use in reducing
garnierite in a solid phase, is 0-0.05.
The in~entors of the present invention have newly
discovered that, when the ratio H/D, wherein H is the
height of ~he dam ring; and D the inner diameter of
the kiln body, iOe. the dam height ratio in a rotary
kiln used for subJecti~g an ore of an oxide of an
element in the Iron Group to semi-molten reduction-
smelting, and which has an inclinat~on oP 1-4 %, is
set in the range of 0.15 0.25, metal can be obtained
at the highest yield.
In a conventional rotary kiln having one burner,
the tempera ~re in the granulation zone therein can
be kept at a high level by the main burner, but the
temperature o~ the clinker, which consists of semi-
molten reduction products and ~lag at the dischargeend of the lower section of the kiln, cannot be kept
at a suitable level.
Therefore, in order to carry out a reduction~
smelting operation with an eye to maintaining the
te~perature of the clinker at the discharge end of
the kiln at a suitable level 9 it naturally becomes
necess~ry to increase the temperature in the granula-
tion zone. However7 when the te~perature in the
granulation zone is increased, the metal and slag
are melted, so that the lining in that zone is worn.
This makes it impossible to carry ~ut a reduction-
smelting operation stably over a long period of timeO
When an oxide ore is subjected to semi-mol-ten
reduction smelting in a rotary kiln having main and
auxiliary burners according to the present invention,
the temperature in the granulation zone can be kept
at a suitable laYel by the main burner~ and the tem-
perature of the clinke~ at the discharge end of the
kil~ by the auxiliary burner. This consti~utes the
novel characteristics of the present invention in
which,unlike the above conventional rotary kiln, the
rotary kiln according to the present i~vention permits
a~ impr~vement in the yield of metal 9 an extensior~
o~ the life of the lining on the kiln~ and the
,
_~ .
~2~ Z~D
carrying out of the reduction-smel-ting operation
stably over a long peri.od of time.
A rotary kiln according to the present invention
having main and auxiliary burners and used to subject
oxide ores to semirmolten reduction smel-ting will now
be described with reference to the drawings.
Figo 4 is a longitudinal section taken by verti-
cally cutting the discharge end portion of a rotary
kiln 1 according to the present in~ention and a com-
bustion chamber 6 therefor, along the axi.s of the kiln.
A dam ring 3 is provided at the discharge end of the
kiln 1. A main burner 9 and an auxiliary burner 11
are provided i~ -the upper half portion of a front
wall 7, which extends substantially at right angles
to the axis of the kiln, of the combustion chamber 6
in such a manner that the main and auxiliary burners
9, 11 extend side by side substantially parallel to
the axis of the kiln. The distance between the end
of the main b~rner 9 and the front wall 7 is slightly
longer than ~hat between the end of the auxiliary
burner 11 and the front wall 7. Namely, the end of
the main burner 9 is closer to the discharge end of
the kiln 1 than that of the auxlliary burner 11.
Fig. 5 is a ~ront elevation in which the inner surface
of the front wall 7 of the combustion chamber 6 is
3l~
shown from the outside of the discharge end o~ the
kiln of Fig. 4.
Referring to Fig. 5, reference numeral 9 denotes
the main burner, and 11 the auxiliary burner. Viewing
holes 13 are provided in the portions of the front
wall 7 of the combustion chamber 6 which are opposite
to an imaginary line Y-Y crossing the axis of the kiln
horizontally at right angles thereto. m e interior
o~ the kiln can be observed through -these viewing
holes~
The fol~owing are the reasons why main and auxi-
liary burners are provided in the kiln according to
the present invention.
In a method of subjecting an oxide ore to semi-
molten reduction-smelting using a rotary kiln, it is
necessary that the temperat~re required to grow the
reduced metal particles into a spherical form is
maintained in the granulation zone over a considerably
long period of time. In order to maintain such a
temperature for a long period time in a conventional
semi-molten reduction-smelti~g method, it is neces-
sary that the ler~th of the flame from the burner is
increased to a higher level, and that the brightness
of the flame is maintained at a sufficiently high
level. Although it is easy to increase the length of
2~
the flame, lt is difficult to maintain the brightness
thereof at a sufficiently high level.
The reactions occurring in a kiln cc~n be roughly
divided into three kinds of reactions, i.e. the
preheating reaction, the reduction reaction and the
granular iron-forming reaction A preheating zone,
a reduction zone and a granulation zone are formed in
that order from ~he upper end of the kiln to the lower
end thereof. The lengths of these three zones in the
axial direction of the kiln each vary a little,
depending upon the reduction-smelting method used.
These lengths are each usually about 1/~ of the
total length o~ a kiln body.
As pre~iously described, the fine metal Parti-
cles formed due to the reduction reaction in the
reduction zone are joined and combined with one another
to grow into granular iron in the granulation zone.
Deposited matter; i.e. a slag ring, necessarily
occurs on the portion of the i~ner surface o~ the
kiln which corresponds to the boun~ary region between
the reduction zone and the granulation zone. In the
Krupp-Rennanlage method, it is desirable that the
displacement of the slag ring toward the upper end,
i.e. toward the center, of the kiln is prevented
so as to increase the length of the granulation zone
~"~
~L~ ~A~
to a sufficiently high level to grow the fine metal
particles into gra~ular iron, and carry out the
reduction-smelting operation smoothly. On the other
hand, when the slag ring is displaced -toward the lower
end of the kiln, the length of the granulation zone
becomes too short, so that the size of the granular
iron and -the yield of the metal both decrease.
A slag ring serves as a kind of a material~
reservi~g dam. When a slag ring is formed in a sui-
table position and has a suitable height, the reduc-
tion reaction and the granular iron-growing reaction
progress excelle~tly~
A slag ring is advantageously formed in a posi-
tion which i5 separated inward from the discharge end
of the kiln by a distance 5-6 times as great as the
inner diameter of the lining ~hereof. The inventors
of the present invention have discovered by experience
that an advantageous pro~ection of a slag ring from
the ir~ner sur~ace of the lining is a distance about
10 % of the inner diameter of the li~ing.
I~ a normal reduction-smelting operation, the
slag ring tends to be displaced with the elapse of
time toward the central portion of the kiln. The
more a slag ring is displaced toward the central
portion of the kiln, the more difficult it becomes
16
to stop the displacement thereof. WhEn the distance
between the position at which a slag ring is formed in
the kiln and ~he discharge end -thereof is at least
about 10 times the inner diameter of the lining, it
becomes very difficult to prevent the slag ring from
bei~g displaced further toward the central portion of
the kiln.
When the granular iron formed in the granulation
zone touches the lining and it deposited thereon, it
grows on the lining to form a metal ring. The forma-
tion of such a metal ring causes the inner diameter
of the kiln to decrease, and hampers the reduction-
smelting operation. Consequently, it becomes neces-
sary to remove the metal ring periodically. In order
to remove such a metal ring, coal is mixed at an
increased ratio with the materials placed in the kiln,
and the amount of oil for ~he main and auxiliary
burners, or the amount of pulverized coal, is increased.
In addition? the number of revolutions per minute of
a blower for waste gas in the kiln is decreased.
Thus the metal ring is melted a~d removed. It has been
newly discovered by the inventors that a combustion
flame from an auxiliary burner has a great effect for
efficiently increasing the temperature in the vicinity
of the dam ring during a metal ring~removing operation
17
. ~., ., ,~_
~2~ 2(~
carried out in the above manner.
There alrea~y is a conventional ~o-tary kiln
provided with a pilot burner in addition to a main
burner~ me pilot burner is used to stabilize the
flame of the main burner9 and it is impossible to
operate a pilot burner instead of the auxiliary
burner used in ~he present invention.
~ hen the main and auxiliary burners are operated
simultaneously as mentioned above~ the combination
and growth of reduction products, i,e. the metal
particles in the reduc-tion zone are promoted, and
a temperature of 1250-1300 C, the upper limit of the
temperature up to which gangue is not melted, can be
maintained until the reaction products have reached
the dam ring provided at the discharge end of the kiln.
Also, the formation of the slag ring can be limited
to an approPriate position in the kilnt and the forma-
tion of a metal ring can be prevented.
The relation between the various portions o~ the
combustion flames from the main and auxiliary burners
and the relative portions of the interior of the
kiln, and the temperatures at these portions of the
interior of the kiln will now be described.
Fig. 6A shows the distribution of temperatures
of flames LF, SF from main aQd auxiliary burners,
g
~,2~
respectively~ in the in-terior of a kiln in the axial
direction thereof with the main and auxiliary burners
operating at hea~y oil consumption rates of 1000 ~/h
and 300 ~/h, respectively. As can be understood from
the graph, the temperature of the portion of the flame
LF which is about 4 m away from the free end of the
main burner reaches substantially 2000C, and that
temperature is maintained up to the portion o~ -the
flame which is about 10 m away from the free end of
-the main burner, this temperature gradually decreases
in the portion of the flame which is more than 10 m
away from -~e free end of the burnerO Fig. 6B is a
longitudinal section of the combustion chamber 6 and
a lower half section of the kiln including the lower
end portion thereo~, cut along the axis o~ the kiln.
As can be understood from the dra~ing, the flame LF
from the main burner is long and increases the tem~
perature mainly in the i~terior of the kiln~ the
flame SF from the auxiliary burner is short and serves
to maintain the temperature mainly in the lower end
portion of the kiln at a suitable level, i.e. the
portion of the kiln which is in the vicinity of the
dam ring at the discharge end thereof
When the main and auxiliary burners are thu3
operated relative to each other, the temperature at
the discharge end of the kiln can be maintained at a
high level. Consequently, the yield of Ni from
garnierite nickel ore or the yield of Fe from
laterite iron ore can be improved to a grea-t extent
when compared with those in a conventional rotary
kiln.
According to the pre~ent invention, the ratio of
the calorific power of the auxiliary burner to that
of the main burner is ad~antageously in the range of
between 1/10 to less than 1.
A further object of the present i~ention is to
provide a rotary kiln including a combustion chamber
which is an improvement over the combustlon chamber
in a rotary`kiln ufied for the conventional Krupp-
Rennanlage method, and which has a high heat retain-
ability.
In the kiln used ~or the Krupp-Rennanlage method,
it is advantageous to minimize the ra-te of formation
of fine particles of granular iron, for example
granular iron having a particle size o~ less ^than
0.5 mm9 for the purpose of reducing as far as possible
the amount of granular iron lost in the slag. However,
when a low~quali~y nickel-con-taining ore, such as
garnierite or laterite having a Ni content of 0.2-
~% is subjected to semi-molten reduction-smelting in
~.Z2'~
such a rotary kiln, slag is formed at an extremely
high rate, and the rate of formation of fine particles
Of granular nickel among all the particles of granular
nickel formed is comparat.ively high. Such fine
particles of granular nickel mix into and are lost
in the slag.
According to the present invention, a reduction
temperature in the range of 900-1400C is suitably
used9 which is highly by 300-400C than the reduction
temperature of 600-1000 C used in a direct iron
manufacturing method, which is known as a solid-phase
reduction method carried out in a conventional rotary
kiln for use in sub~ecting oxide ores to semi-molten
reduction-smelting. When the slag ring, which is
inevitably ~ormed in the vicinity of -the boundary
between the reductio~ zone and ~he granulation zone
in a kiln due to the materials placed therein and
deposited on the inner surface thereof~ has gro~n to
an excessively large size, it hampers the movement
of the materials placed in the kiln, air and combustion
gases and pre~ents the reduction~smelting operation
from being carried out smoothly. However~ when the
slag ri~g occurs in a proper position and has a
reasonable size, it does not give rise to problems
in the reduction-smelting operation, rather i-t has
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the favourable effect that the material in the kiln
can be retained therein for a suitable period o~ time.
When ~he slag rlng occurs in a portion of the
interior of a kiln wbich is comparatively close to
the discharge end thereof9 it is comparatively easy
to red~ce the size thereof even if the slag ring
grows large. When the slag ring grows in a central
or upstream portion of the interior of a kiln, it is
difficult to reduce the size thereof, and it becomes
necessary in some cas~s to interrupt the reduction
smelting operation. Therefore7 it is one of the im-
~portant condition~ for carr~ing out a reduction-
smelting operation in a rotary kiln, to maintain at
a suitable level the temperature of the product
remaining in the dam ring at the discharge end o~ the
kiln and control the position at which the slag ring
is formed~
Fig. 7 shows the relationship with respect to
various positions along the interior of the combu-
stion chamber and rotary kiln, between various
portions corresponding to these various positions 9
and which are vario~s distances away ~rom the ~lames
from the free ends of burners 5a or 5b, and the tem-
peratures of these various portions of the flames,
when the burners 5a, 5b are operated to heat the
v
interior of the kiln with their flames extending
from the discharge end of the kiln toward the upper
end thereof, to carry out the semi-molten reduction
operation in practice. According to the graph, the
distance between the free end of the burner 5a and the
inner end (which will be hereinafter called the
dam end) of the ridge portion of the dam ring at the
discharge end of the kiln is 3.5 m. When the burner
5a positioned relative to the dam end in this way
is ignited, the flame starts at a position about 80
cm away from the free end thereof toward the discharge
end of the kiln as shown by the curve a, and the
temperature of the flame increases suddenly to reach
about 1900C at the dam end~ m e temperature then
gradually increases to exoeed 2000C in the inner
portion of the kiln. Accordingly, the temperature of
the products in the vicinity of the dam ring can be
maintained at a required le~el easily.
On the other hand, when the burner 5b is ignited,
the flame starts at a position about 80 cm away from
the free end thereof toward the inner side of the
kiln as shown by the curve b, and the temperature of
the flame increases suddenly. Since the relative
positions of the free end of the burner 5b and the
dam end of the kiln substantially agree with each
~,. ~
other, ~he dam end is not heated by the flame; the
flame from the burner 5b starts at a position about
80 cm away from -the dam end tow~rd the i~ner side of
the kiln, and the temperature of the flame increases
in the in~er side of the kilnO m erefore, the burner
5b is not capable of maintaining the temperature of
the products remaining in the vicinity of the dam ring
at the required temperature of 1000-1200C.
In the conventional Krupp-Rennanlage kiln des-
X cribed in the thesis "~rupp-Rennanlage Method" in Stahl
und Eisen 20, September 1934 Heft 38, the distance
between th~ free end o~ the burner and the dam end
of the kiln is in the range of 25-30 % of the inner
diameter of the iron shell of the kiln, and the
distance between the outer surface of the front wall
of the combustion chamber and the dam end is in the
range of 70-75 % -~lereof. The i.nventors of the present
invention, who h~ve continued to carry out reduction-
smelting operations for many years using such a con-
ventional Krupp-Rennanlage kiln, have noticel that,
when such a kiln is used to carry out a reduction-
smelting operation, an excessively large slag ring
occurs at an inner portion of the kiln, and that
this makes it impossible to continue the reduction-
smelting operation over a long period of time and
- .! ~
obtain a sufficiently high yield of useful metal.
The inventors of the present invention have
conducted a several experiments with a view to elimi-
nating the drawbacks encountered in the conven-tional
Krupp-Rennanlage kiln, and have finally obtained a
novel discovery regarding the distance between the
free end of the burner and the dam end in a kiln,
the length of the combustion chamher in the axial
direction of the kiln, and the distance between the
free end of the burner and the dam end, and have com-
pleted the present invention.
The inventors of the present invention studied
the relationship between the distances between a free
end of a burner and various portions of the flame
therefrom and the temperatures in the axial portions
of the flame which correspond to those various portions
of the flame, with 9600 Kcal/~(25C) of heavy oil burnt
at an air ratio of m=l and at 1000 ~/h. The results are
shown in Fig. 8. The air ratio _ is a value which can
be calculated using the equation m = A/Ao, wherein Ao
is the amount of air required to completely the carbon,
hydrogen and sulphur in 1 ~ of fuel; and A is
the amount of air used in practice. Accord-
ing to the graph, the temperature of the axial
portions of the flame which are 3.5-10 m away from
the free end of a burner is about 2000C. It ha~ been
newly ascertained that9 in order to control the tempe-
rature of the dam ring (in the posi-tion corresponding
to that of the dam end mentioned previously), provided
in the vicinity of the discharge end of a kiln, at
between 1000C to 1200C, the distance between the
free end of the burner and the discharge end of the
kiln may be controlled correspondingly to the inner
diameter~ which in~luences the temperature of the
dam ring, of the iron shell of the kiln~
The flame of the burner, which serves to control
the temperature of the dam ring in ~he vicinity of
the discharge end of a kiln at a suitable level, and
which ignites the fuel at a positionJ for example,
about 80 cm away from the free end of the burner,
spreads parabolically to a diameter substa~tially
equal to the inner diameter o~ the dam ring to heat
it. m e products in the dam ring and granulation
zone are heated by the conduction of heat from the
flame to a small extent, and by radiation heat
therefrom to a larger extent. When the flame passing
through the granulation zone has reached the reduction
zone, i.e. when the combustion gases have advanced by
a distance equal to 1/~ of the total length of the
kiln from the discharge end of the kiln toward the
~,.'
3~
upper end thereof, the gases come into contact with
the material or the lining of -the kiln to transfer
the heat ~hereto. Accordingly, in the Krupp-Rennanlage
method 9 it is disadvantageous to use a fuel ha~ing a
low heat radiation, such as a natural gas or producer
gas; heavy oil or coal, which have a high heat radia-
tion, can be advantageously used to improve the thermal
efficiency. When heavy oil is used as the fuel, the
portion of the flame which displays the hgihest heat
radiation effec-t is the portion thereof around 10 m
away from the free end of the burner, and the transfer
of heat of at leas-t 1200C due to heat radia-tion from
the flame terminates at a position 15 m away from the
free end o~ the burner~
When the-burner 5a is in ~he position shown in
Fig. 7, a slag ring starts to occur at an inner posi-
tion in the kiln about 15 m away from the discharge
end thereof. When the burner 5a is at the position of
the burner 5b shown in -the same drawing, the slag ring
starts to occur at an inner position in the kiln
which is about 18.5 m away from the discharge end
~hereof. ~hen the slag ring occurs in such a position9
i t moves toward the inner portion of the kiln with the
elapse of timeO There~ore, the more a slag ring moves
toward the inner portion o~ the kiln, the longer the
time required for reducing the size ~hereof becomes.
Namely, when the posi-tion at which the slag ring starts
to occur varies greatly, the feed rate of materials
varies greatly~ I~ other words, the more the position
at which the dam ring starts to occur is separated
from the discharge end of a kiln, the more the ~eed
rate of materials decreases, so ~hat the production
e~ficiency of metal is reduced.
The reasons why the distance between the free
end of the burner and the discharge end o~ the kiln
is limited in the present invention will now be
explained.
Whe~ the distance re~erred to above is less than
70 % o~ the inner diameter of the iron shell o~ the
kiln, the temperature of the products remaining in
the dam ring cannot be m intained at a suitable le~el,
i.e. in the range of 1000-1200C~ On the other ha~d9
when this distance is more than 90 % of the inner
diameter of the iron shell o~ the kiln9 the slag ring
occurs at an inner portion of the kiln, and the mate-
rials placed therein stagnate. mis causes a
decrease not only in the productivity of the kiln but
also in the life thereof. Therefore, it is necessary
that this distance is set io be within the range of
70-90 % of the inner diameter o~ the iron shell of
~ 2
the kiln.
When the distance between the free end of the
burner and the discharge end of the kiln is set to
be within the range of 70-90 % of the inner diameter
of ~he iron shell of the kiln, the length of the
combustion chamber in the axial direction of the kiln
is inevitably restricted. In order to maintain the
temperature of the re~ractory materials on the por-
tion of the inner surface of the combustion chamber
which is around the discharge end of the kiln within
the range o~ 1000-1200C9 it is necessary that the
length o~ the combustion Ghamber is within the range
of 80-1~0 % of the inner diameter of the iro~ shell
of the kiln. When this length is less than 80 % of
the inner diameter of the iron shell of the kiln,
heat is absorbed by the outer cylinder of the burner,
the blast pipe and viewing windows, so that the tem-
perature o~ the refractory materials on the inner
surface of the combustion chamber becomes less than
1000C. In such a case9 the position at which the
burner ignites becomes excessively far from the free
end thereof, and tha temperature of the products in
the discharge end of the ki~n cannot be maintained
at an approprlate levelO On the o~her hand, when the
length of the combustion chamber is larger than 130 %
~f ~ 7
of the inner diameter of the iron shell of the kiln,
the amount of heat escaping from the combustion chamber
to the outside becomes excessively large.
~ he pre~en~ invention will now be described with
reference to experimental data.
Experiment 1:
me inventors of the present invention determined
the filling rates of a rotary kiln having a length
of 70 m, an inner diame-ter of the iro~ shell thereof
of 3600 mm, a thickness of 200 mm and an inner diameter
of 3200 mm, A was ~he cross-sectional area of the
cylindrical space in the granulation zone in the
kiln, and S the cro~s-sectional area o~ the hollow bcw-shaped
space within the dam ring. m e filling rates (S/A)
x 100 % ca~ be determined by calculations based on
dam height ratios (H/D) x lOOo The results are shown
in Table 1.
Tab
Dam height 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Filling rates
(%) 1.8 5.2 9.4 14.2 lg.5 25.~ 31.3
(S/A) x 100
According to the present in~ention, when the dam
height ratlo was between 0.15-0,25, the filling rate,
(S/A) x 100 (%), which can be determined by calculations;
was in the range of 904-19.5 %.
2(J~
The inventors of the present in~ention checked
the influence of the height of the product-reserving
dam ring upon the yield of nickel by using garnierite
ores ha~ing the compositions shown in Table 2, with
the dam height varying within the range of 300-900 mm.
Table 2
Si2 Fe2~ A~z03 NiO Cr23 CaO MgO
__ _ . _ _ _ _ _
3~.61 17.03 1.02 3.28 0.09 1.0~ 0 12 24.78
Fe ~ ~Ni ~ ~Co
~13. loJ ~2.581 ~-7~
In this test, 200 kg of anthracite ha~ing the
compositlon shown in Table 3 and 70 kg of limestone~
were used as reducing agent and flux, respectively,
for 1000 kg o~ garnierite ~L.O.I.: 10.91 %). The ore
wa~ fed at 12.5 t/hr to carry out the semi~moltsn
reduction-smelting thereof.
~3~
FC(~
74.9 6~ 0.008 0.37 16.9 6970
The clinker obtalned by carrying out the reduc-
tion-smelting operation in the above manner, and
which consisted of granular iron and slag, was crushed
and subjected to ore dressing. The ratio of the amount
of nickel contained in the granules thus obtained to
'~ ~1
,--
that of the nickel con-tained in -~e ore placed in
the kiln, i.e. -~he yield of nickel9 was determined.
The result~ are shown in Table 4.
Table 4
__
Dam Dam Fllli Flow rate Yield of nickel
hei~ht height
ratio x
100
3009.4 5 1 86.3, 87~0
40012.5 7 0.71 89.0, 91.5
60018 .8 1~. 5 0 .37 9208, 93 .7,
9~.0, 94.~i
80025.0 19.5 0026 91.1~ 93.0,
94.0
9ûO28.1 22.5 0.22 87.09 88.0
Experime~t 2:
A semi-molten reductian smelting test was
conducted using the same rotary kiln as was used in
Experiment 1, with the lat~rite iron ore having the
composition shawn in Table 5. In this experiment,
260 kg of anthracite was used for 1000 kg of ore, and
the height o~ the product re~ervi~g dam was varied
in the same manner as in Experiment 1. Thus, the
influence of the height of -the dam upon the yield
of nickel was checked. The resul-ts are shown in
Table 6.
Table 5
.
L.O.I. SiO2 Fe203 ~ NiO Cr203 CaO MgO
11.51 11~71 61.06 6.g 0.2 3.9 0.22 1.0
(45e.7) (Ni,16)
Table 6
Dam Dam Fillin~ Flow rate Yield o~ iron
hei~ht height
ratio
x 100
300 9.4 5
40012.5 7 0.71 87.0, a8.5
60018.8 13.5 0.37 90.5, 9108
800Z5~0 19.5 0,26 90.4, 92.0
90028,1 22~5 0.22 ~5.3, 86.2
The relationship between the dam height ratio
and the yield of metal 3 i.e. Ni (when garnierite was
used) and Fe (when laterite was used), which was
determined on the basis of the results of Experi-
ments 1 and 2, is sh~wn in the graph of Fig. 3.
Referring to the graph, the solid curve represents the
yield of Ni, and the broken curve the yield of Fe.
It can be understood from the graph that the yields
of Ni and Fe were at least 90 % when the dam height
ratio H/D was 0.15-0.25.
~ 33
When an ore of an oxid~ of an element in the
Iron Group is subjected to semi-molten reduction-
smelting using a rotary kiln according to the present
invention, which has a produc-t-reserving dam ring,
the element o~ the Iron Group can be obtained a-t a
high yield.
Examples oX the present invention will now be
described in contrast with Comparative Examples.
Example 1:
Semi=-molten reduction~smelting operations were
carried out in a rotary kiln according to the present
invention using both a nickel aQd a laterite iron
ore, the composition of which were as shown in Table 7.
Table 7 (%)
L-O I- Si2 Fe ~23 NiO CaO MgO
ore 10.91 39.61 17.03 1.02 3.28 0.09 24.78
LrOtnroree 11.51 11.17 61.06 6.90 0.20 0.06 1.01
Anthracite was used as a reducing agent. 200 kg
and 260 kg of anthracite were used ~or 1000 kg of
nickel ore and laterite iron ore, respectively~ The
composi-~on and calori~ic value of the anthraci~e used
were as shown in Table 8.
Table 8
Ash VM FC P S Xcal/kg
16.9% 6.4% 74.9% 0.008% 0.37% 6970
The rotary kiln had a length of 70 m, an inner
diameter of the lining of 3600 mm, a thickness of the
lining of 200 mm, and a height of the dam ring provided
at the discharge end of the kiln of 700 mm. The kiln
was rotated at 0.7 r.p.m. to carry out a semi-molten
reduction smelting operation under the following
conditions.
Standard feed rate of ore: 12 t/h
Main burner (oil pressure return type):
Feed rate of oil:lO00 ~/h
Primary air ratio m: 0.2
Secondary air ratio _: 0.5
Air pressure: 500 aq
Auxiliary burner (hydraulic jet type):
Feed rate of oil: 300 Q/h
Primary air ratio _: 0.2
Secondary air ratio m: 0.7
Air pressure: 500 aq
The same quality of heavy oil was used for com-
bustion purposes for the main and auxiliary burners,
the heavy oil having a calorific value of 9600 Kcal/~
at 25C.
~ ~ ~6
The same semi molten reduction-smelting operation
was carried out by a conventional method without
using an auxiliary burner. During this reduction-
smelting operation, the feed rate of oil to the burner
was 1300 ~/h. Table 9 shows a comparison of the yields
of Ni from nickel ore and Fe from laterite iron ore
in the method according to the present invention
using both main and auxiliary burners, and a conven-
tional method using a single burner.
~.
Method according Con~entional
to the present method (using
invention (using s1n~ e
main and auxiliary
Yield of Ni 94 89
Yield of Fe 90 76
In Example 1 and the comparative example, the
te~perature of the top surface of the dam ring at
the lower end of the kiln was measured with an
optical thermometer to control the temperature
thereof. In the conventional method, the temperature
of the top surface of the dam ring was 900 C. The
method according to the present invention permitted
the stable maintenance of the temperature of the top
surface of the dam ring at 1100C using ~he same
amount of heavy oil as in the conventional method~
,.~,' ~ ,.
~,2~:t2C~
and obtaining such an extremely high yield of metals
as shown aboveO
When a rotary kiln according to the present
i~vention described above ls used, an extremely
high yield of metal can be obtained, and, moreover,
the reduction-smelting operation can be carried out
stably and continuously over a long period of -time
when compared with a reduction-smelting operation
carried out in a con~en-tional rotary kiln, which has
a comparatively short life.
E~ample 2:
Semi-molten reduction-smelting operations were
carried out in a Krupp-Rennanlage kiln using a nickel
ore and an iron ore, the compositions of which were
as shown in Table 10.
... . ...
bO I ~ ~
o ~l ~
~ ~ .
c~ o o
o o ~
~ ~ .
h r-l 1
O O
O
V O
O I CO O
,1
æ
~ o
r~ ~ o
o o
~i
o o o
~ O
~ r~
O ~D
.,,
~n a~ ~
H ~ ,_1
. a~
O
~i ~ ~
a~
~ a) o
.,~ h h
~Z; H O
Anthracite, the composition of which is shown
in Table 11 below, was used as the reducing agent in
amounts of 200 kg and 260 kg based on lOC0 kg of the
nickel ore and iron ore, respec-tively.
Table 11
Ash VM FC P S Kcal/k~
16.9 6.4 74.9 0.008 0037 6970
m e kiln used in Example 2 had a length of 70 m,
an inner diameter of the iron shell of 3600 mm, a
thickness of the lining of 200 mm9 a height of the dam
of 640 mm, and an inclinati.on of the kiln of 2 %.
Each of the ores was fed at 12.5 t/h into the kiln
rotating at 0.75 r.p.m. while 9600 Kcal/~ (25C) of
heavy oil was burnt at 1000 B/h. The above operations
were carried out with the dis^tance (which will be
hereinafter referred to as the burner position ratio
(%)) between the free end of the burner and the
discharge end of the kiln set to ~10 9'o to 110 yO of
the inner diameter ~f the iron shell of the kiln.
The yields of Ni and Fe with such various burner
position ratios are shown in Table 12.
~able 12
Rurner
position-10 50 60 70 80 86 90100 110
ratio(%)
Yield of86 88 90 92 94 94 9392 90
Yield ~ 70 86 89 90 90 91 9189 87
Only when the burner position ratio was -10 %, the
length of the combustion chamber ln the axial direc-
tion o~ the kiln was 28 % of the inner diameter of
the iron shell thereof, i.e. 1 m. When the burner
position ratio was higher than -10 ~, the length o~
the combustion chamber was 100 % o~ the inner diameter
of the iron shell o~ the kiln, i.e. 3.6 ml
Each o~ the yields re~erred to above is a value
obtained by dividing -~he weight o~ metal granules
recovered as products after the clinker discharged
i`rom the kiln has been crus~ed and then subjected to
ore dressing by gravity separation and magnetic
separation, by the weight o~ Ni or Fe contained ln
the ore used; it is not the so-called reduction
rate ~
The in~entors o~ the present inven-tion discovered
that, since the reduction rate does not vary substan~
tially to a great extent with the burner position
ratio, the yields shown above are in~luenced by the
U~
~z~
degree of growth of the metal particles formed due
to the reduction reaction into larger metal particles.
In the above examples 9 the feed rates of the
ores with respect to the burner position ratios were
as shown in Table 13.
Burner position ratio: -10 % 86 %
Feed rate o~ nickel ore~ 3 t/h 14.6 t~h
Feed rate of iron ore: 1208 t/h 16.2 t/h
~ hen a kiln according to the present invention
was used, the yields o~ valuable metals were improved~
and, moreover, the feed rates of ores increased from
280 t/day to 380 t/day. In addition, the production
rates of me~als also increased~ and the life of a
conventiQnal kiln of 90 days was prolonged to as
long as 150 days.
