CA1224920A - Rotary kiln for use in reduction-smelting ores of oxides of iron group elements and smelting method thereof - Google Patents
Rotary kiln for use in reduction-smelting ores of oxides of iron group elements and smelting method thereofInfo
- Publication number
- CA1224920A CA1224920A CA000430061A CA430061A CA1224920A CA 1224920 A CA1224920 A CA 1224920A CA 000430061 A CA000430061 A CA 000430061A CA 430061 A CA430061 A CA 430061A CA 1224920 A CA1224920 A CA 1224920A
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- CA
- Canada
- Prior art keywords
- kiln
- burner
- reduction
- ore
- burners
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F27—FURNACES; KILNS; OVENS; RETORTS
- F27B—FURNACES, KILNS, OVENS, OR RETORTS IN GENERAL; OPEN SINTERING OR LIKE APPARATUS
- F27B7/00—Rotary-drum furnaces, i.e. horizontal or slightly inclined
- F27B7/20—Details, accessories, or equipment peculiar to rotary-drum furnaces
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21B—MANUFACTURE OF IRON OR STEEL
- C21B13/00—Making spongy iron or liquid steel, by direct processes
- C21B13/08—Making spongy iron or liquid steel, by direct processes in rotary furnaces
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B23/00—Obtaining nickel or cobalt
- C22B23/02—Obtaining nickel or cobalt by dry processes
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/10—Reduction of greenhouse gas [GHG] emissions
- Y02P10/134—Reduction of greenhouse gas [GHG] emissions by avoiding CO2, e.g. using hydrogen
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- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Mechanical Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- General Engineering & Computer Science (AREA)
- Manufacture And Refinement Of Metals (AREA)
- Muffle Furnaces And Rotary Kilns (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE:
The invention relates to a rotary kiln for use in the subjecting of 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, the rotary kiln having a dam ring of an improved construction provided so as to project from the portion of the lining of said kiln which is at the product-discharging end thereof. A main burner as well as an auxiliary burner provided at the discharge end of the kiln is used to heat the kiln, and a combustion chamber having a high heat insulating capability is connected to the kiln. In the combustion chamber, the distance between the free ends of the burners and the discharge end of the kiln is set at a suitable level. The invention also relates to a method of semi-molten reduction-smelting such an ore in the above rotary kiln, this method enables an improvement in the yield of valuable metals, and the carrying out of such a reduction-smelting operation in the kiln over a long period of time.
The invention relates to a rotary kiln for use in the subjecting of 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, the rotary kiln having a dam ring of an improved construction provided so as to project from the portion of the lining of said kiln which is at the product-discharging end thereof. A main burner as well as an auxiliary burner provided at the discharge end of the kiln is used to heat the kiln, and a combustion chamber having a high heat insulating capability is connected to the kiln. In the combustion chamber, the distance between the free ends of the burners and the discharge end of the kiln is set at a suitable level. The invention also relates to a method of semi-molten reduction-smelting such an ore in the above rotary kiln, this method enables an improvement in the yield of valuable metals, and the carrying out of such a reduction-smelting operation in the kiln over a long period of time.
Description
SPECIFICATION
TITLE OF THE INVENTION:
RO~ARY KILN FOR USE IN REDUCTION-~MELTING ORES
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.
TITLE OF THE INVENTION:
RO~ARY KILN FOR USE IN REDUCTION-~MELTING ORES
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.
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-~L~
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 .,, ~
~}~
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 ~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 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 . ~., ., ,~_ ~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 ,JJ,,~
~z~
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 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.
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-~L~
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 .,, ~
~}~
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 ~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 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 . ~., ., ,~_ ~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 ,JJ,,~
~z~
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 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.
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A rotary kiln having a product-reserving dam ring, heating burners, and a combustion chamber in which said burners are ignited, 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 said ore with said burners, characterized in that: the ratio of the height of said product-reserving dam ring to the diameter of the cross section of the cylindrical space defined by said refractory lining in said kiln is within the range of 0.15-0.25; said heat-ing burners consist of a main burner and an auxiliary burner;
the length of said combustion chamber in the axial direction of said kiln is 80-130% of the inner diameter of an iron shell of said kiln; and the distance between the free end of said main burner provided in said combustion chamber and the discharge end of said kiln is within the range of 70-90% of the inner diameter of said iron shell of said kiln.
the length of said combustion chamber in the axial direction of said kiln is 80-130% of the inner diameter of an iron shell of said kiln; and the distance between the free end of said main burner provided in said combustion chamber and the discharge end of said kiln is within the range of 70-90% of the inner diameter of said iron shell of said kiln.
2. A rotary kiln according to Claim 1, wherein said main and auxiliary burners are provided in said combustion chamber, which is formed to surround the product discharge end of said kiln, in such a manner that said main and auxiliary burners extend substantially parallel to the axial direction of said kiln, said main and auxiliary burners being fixed to portions of an end wall of said combustion chamber described below if said rotary kiln is adapted to be rotated clockwise when said rotary kiln is viewed from its material-introduction end toward its material-discharge end, each of said main and auxiliary burners being fixed to the portion of said end wall which is opposite to a position in one of four fan-shaped regions of a circular vertical cross section including the discharge end sur-face of said rotary kiln, said four fan-shaped regions being defined by vertical and horizontal center lines X-X, Y-Y in said circular vertical cross section, said main burner being opposite to the fan-shaped region which is on the right side of said vertical center line X-X and above said horizontal center line Y-Y, said auxiliary burner being opposite to the fan-shaped region which is on the left side of said vertical center line X-X and above said horizontal center line Y-Y, the distance between said main burner in the corresponding fan-shaped region and the corresponding point on said horizontal center line Y-Y
being longer than the distance between said auxiliary burner in the corresponding fan shaped region and the corresponding point on said horizontal center line Y-Y, the distance between said main burner in the corresponding fan-shaped region and the corresponding point on said vertical center line X-X being shorter than the distance between said auxiliary burner in the corres-ponding fan-shaped region and the corresponding point on said vertical center line X-X.
being longer than the distance between said auxiliary burner in the corresponding fan shaped region and the corresponding point on said horizontal center line Y-Y, the distance between said main burner in the corresponding fan-shaped region and the corresponding point on said vertical center line X-X being shorter than the distance between said auxiliary burner in the corres-ponding fan-shaped region and the corresponding point on said vertical center line X-X.
3. A rotary kiln according to claim 1 or 2, wherein the flame from said main burner is longer than that from said aux-iliary burner, said main burner being used to control the temperature in a granulation zone and a reduction zone in said kiln, the flame from said auxiliary burner being shorter than that from said main burner, said auxiliary burner being used to control the temperature in the vicinity of the dam ring provided at the discharge end of said kiln.
4. A method of subjecting 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 by using a rotary kiln, having the step of subjecting said ore to semi-molten reduction with a reducing agent while heating said ore with burners when said kiln is inclined at l-4% and rotated at 0.7-1.5 r.p.m., comprising the steps of: setting within the range of 0.15-0.25 the ratio of the height of a product-reserving dam ring provided at the product-discharging end of said rotary kiln, said ring consisting of a refractory material, to the diameter of the cross section of the cylindrical space defined by the refractory lining on the inner surface of said kiln;
setting the length in the axial direction of said kiln of the combustion chamber, which is formed so as to surround the dis-charge end of said kiln, to 80-130% of the inner diameter of an iron shell of said kiln; setting the distance between the free end of a main burner, which is one of main and auxiliary burners constituting said burners provided in said combustion chamber, and the discharge end of said kiln to 70-90% of the inner dia-meter of said iron shell; forming a longer flame from said main burner while forming a shorter flame from said auxiliary burner;
and controlling the temperatures in a preheating zone, a reduction, a granulation zone and a region in the vicinity of said dam ring in said kiln to 100°-600°C, 600°-1200°C, 1200°-1400°C and 1150°-1350°C, respectively.
setting the length in the axial direction of said kiln of the combustion chamber, which is formed so as to surround the dis-charge end of said kiln, to 80-130% of the inner diameter of an iron shell of said kiln; setting the distance between the free end of a main burner, which is one of main and auxiliary burners constituting said burners provided in said combustion chamber, and the discharge end of said kiln to 70-90% of the inner dia-meter of said iron shell; forming a longer flame from said main burner while forming a shorter flame from said auxiliary burner;
and controlling the temperatures in a preheating zone, a reduction, a granulation zone and a region in the vicinity of said dam ring in said kiln to 100°-600°C, 600°-1200°C, 1200°-1400°C and 1150°-1350°C, respectively.
5. A method according to Claim 4, wherein the ratio of the calorific value of said main burner to that of said aux-iliary burner is set to between 1/10 to less than 1.
6. A method according to Claim 4 or 5, wherein the size of the flame from said auxiliary burner is controlled to melt and remove a metal ring which is often formed on the portion of the lining of said kiln which corresponds to said granulation zone due to metal particles deposited thereon and growing inward.
Applications Claiming Priority (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP10310382A JPS58221375A (en) | 1982-06-17 | 1982-06-17 | Rotary kiln for reducing smelting |
| JP103103/82 | 1982-07-17 | ||
| JP12512582A JPS5916920A (en) | 1982-07-20 | 1982-07-20 | Rotary kiln for semifusion reduction smelting of iron group element oxide ore and smelting with this kiln |
| JP125125/82 | 1982-07-20 | ||
| JP13737182A JPS5927106A (en) | 1982-08-09 | 1982-08-09 | Rotary kiln with combustion chamber for semi-fused reduction smelting |
| JP137371/82 | 1982-08-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1224920A true CA1224920A (en) | 1987-08-04 |
Family
ID=27309890
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000430061A Expired CA1224920A (en) | 1982-06-17 | 1983-06-09 | Rotary kiln for use in reduction-smelting ores of oxides of iron group elements and smelting method thereof |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1224920A (en) |
| FR (1) | FR2528959B1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104212931A (en) * | 2014-08-21 | 2014-12-17 | 广西高澎矿业科技有限公司 | Method for producing metal iron powder by using deep reduction of rotary kiln |
Family Cites Families (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE493841C (en) * | 1930-03-14 | Arno Andreas | Rotary kiln for the production of molten cement with a retaining ring at the border between the de-acidification and melting zone | |
| DE508341C (en) * | 1927-03-24 | 1930-09-26 | Metallgesellschaft Ag | Rotary kiln for rusting sulfidic ores |
| US2026683A (en) * | 1934-05-22 | 1936-01-07 | Krupp Ag Grusonwerk | Treating ferriferous ores |
| US2047562A (en) * | 1934-08-25 | 1936-07-14 | Krupp Ag Grusonwerk | Process of producing wrought iron |
| US2228702A (en) * | 1938-06-01 | 1941-01-14 | Fried Krupp Grusonwerk Aktien | Production of lumped wrought iron |
| DE886872C (en) * | 1944-05-14 | 1953-10-19 | Smidth & Co As F L | Process for the combustion of fuel that is difficult to ignite and installation for carrying out the process |
| DE839207C (en) * | 1950-07-06 | 1952-05-19 | Eisen & Stahlind Ag | Rotary kiln with a retaining ring provided at the outlet end for processing metal sponge, in particular sponge iron, on lobes |
| US3272616A (en) * | 1963-12-30 | 1966-09-13 | Int Nickel Co | Method for recovering nickel from oxide ores |
| DE2243435C3 (en) * | 1972-09-04 | 1975-10-16 | Polysius Ag, 4723 Neubeckum | Rotary kiln |
-
1983
- 1983-06-09 CA CA000430061A patent/CA1224920A/en not_active Expired
- 1983-06-16 FR FR838309992A patent/FR2528959B1/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104212931A (en) * | 2014-08-21 | 2014-12-17 | 广西高澎矿业科技有限公司 | Method for producing metal iron powder by using deep reduction of rotary kiln |
| CN104212931B (en) * | 2014-08-21 | 2016-12-07 | 广西高澎矿业科技有限公司 | A kind of method utilizing rotary kiln drastic reduction to produce metal iron powder |
Also Published As
| Publication number | Publication date |
|---|---|
| FR2528959A1 (en) | 1983-12-23 |
| FR2528959B1 (en) | 1989-06-30 |
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