GB1572566A - Creación de Inventos y Patentes con Inteligencia Artificial

GB1572566A – Process for producing reduced iron pellets from iron-containing dust
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GB1572566A – Process for producing reduced iron pellets from iron-containing dust
– Google Patents
Process for producing reduced iron pellets from iron-containing dust

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Publication number
GB1572566A

GB1572566A
GB2997677A
GB2997677A
GB1572566A
GB 1572566 A
GB1572566 A
GB 1572566A
GB 2997677 A
GB2997677 A
GB 2997677A
GB 2997677 A
GB2997677 A
GB 2997677A
GB 1572566 A
GB1572566 A
GB 1572566A
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United Kingdom
Prior art keywords
pellets
percent
dust
mixture
iron
Prior art date
1977-07-16
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GB2997677A
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Nippon Steel Corp

Sumitomo Heavy Industries Ltd

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Sumitomo Heavy Industries Ltd
Sumitomo Metal Industries Ltd
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1977-07-16
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1977-07-16
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1980-07-30

1977-07-16
Application filed by Sumitomo Heavy Industries Ltd, Sumitomo Metal Industries Ltd
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Sumitomo Heavy Industries Ltd

1977-07-16
Priority to GB2997677A
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patent/GB1572566A/en

1980-07-30
Publication of GB1572566A
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patent/GB1572566A/en

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Classifications

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

C21—METALLURGY OF IRON

C21B—MANUFACTURE OF IRON OR STEEL

C21B13/00—Making spongy iron or liquid steel, by direct processes

C21B13/0046—Making spongy iron or liquid steel, by direct processes making metallised agglomerates or iron oxide

Description

(54) PROCESS FOR PRODUCING REDUCED IRON PELLETS FROM
IRON-CONTAINING DUST
(71) We SUMITOMO METAL
INDUSTRIES, LTD., and SUMITOMO HEAVY
INDUSTRIES LTD., both Japanese body cor prorates, of No. 15, 5-chome, Kitahama,
Higashi-ku, Osaka, Japan and 2-1, Ohtemachi 2-chome, Chiyoda-ku, Tokyo 100, Japan respectively, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:
The present application relates to a process for preparing metallic iron containing pellets suitable for use as the burden for a blast furnace.
A large amount of iron containing dust is exhausted from iron and steel making works, e.g., from a sintering shop, iron making shop, steel making shop, rolling mill shop, etc. The dusts cause environmental pollution and thus it has long been a matter of great concern in the iron and steel making industries to recover and utilize the dusts for the purpose of preventing pollution and of conserving natural resources. As a solution to this, it has been proposed to produce reduced iron pellets from the dusts for reuse as a charge material to a blast furnace.
For the production of high quality pellets from the dust, it is necessary to chemically reduce the oxides of iron, zinc and lead contained in the dust. Two methods have been proposed for reducing the dust. In one method, carbonaceous material is charged into the reduction zone of a rotary kiln to supplement the necessary carbon to complete the reducing reaction of the oxides. However, the large difference in specific gravity and the angle of repose between the added carbonaceous material and the pellets causes segregation and, makes the reducing reaction ineffective. Therefore, the operation of this method requires reducing carbon in a considerably larger amount than the theoretically required amount.Because of expensiveness of the reducing carbon, it is preferable to incorporate carbon in the pellets in advance of charging to the kiln, thereby making it possible to control the external charging of carbon to the kiln to a small amount.
In the other method, green pellets are prepared to contain a sufficient amount of carbon for the reducing reaction of the oxides, and therefore, there is almost no charging of carbon to the kiln. Accordingly, it is important to ensure a sufficient carbon content in the green pellets in both methods.
A second problem encountered in the art is pulverization of pellets during the reducing in the rotary kiln. A kiln of the class of 10,000 or more metric tons per month production is about 4.5m or more in diameter, about 70m or more in length and operates at a velocity of about 0.7 rpm. The reaction zone in the kiln is also maintained at high temperatures. Accordingly, it is required that the pellets have a sufficient resistance to pulverization under such severe conditions. In this connection, it had been proposed to preheat or dry the green pellets prior to charging them to the kiln.
Another way to prevent the pulverization is to strengthen the pellets. Azami (U.S. Patent
No. 3,652,260) discloses the use of 70 to 30 percent of blast furnace dust and 30 to 70 percent of basic oxygen furnace dust as the materials for pellets, Bentonite is also disclosed as useful to improve the strength of the pellets.
However, the process according to Azami’s teaching also results in pulverization of pellets to a large extent as explained in detail hereinafter.
A third problem is that the iron containing dust exhausted from an ordinary modern iron and steel making works is deficient in carbon content for complete reduction of the oxides contained therein without externally supplementing carbon thereto. Blast furnace dust contains about 30 percent of carbon, but steel making furnace dust is substantially free of carbon. The ordinary modern iron and steel making works equipped with blast furnaces and basic oxygen furnaces and/or electric furnaces, however, exhaust steel making furnace dust in an amount about twice as great as that of blast furnace dust. The terms «steel making furnace dust» herein used mean the dusts exhausted from the steel making furnaces including basic oxygen furnace, electric furnace and open hearth furnace.Examples of the amounts of the iron-containing dusts exhausted from ordinary iron and steel making works or plants are shown in Table 1.
It is apparent from Table 1 that if substantially all of the iron-containing dust in the works is used for preparing reduced iron pellets, it is necessary to add a considerable amount of carbon to the dust in order to accomplish the complete reduction of oxides thereof.
We have also found that when the ratio of amount of blast furnace dust to that of steel making furnace dust is less than 45 : 55, it is necessary to add carbon to the dust. Azami mentions that a mixture of 70 to 30 percent of blast furnace dust and 30 to 70 percent of basic oxygen furnace dust always affords an amount of carbon required to complete the reduction of the oxides contained therein; however, we have found that the amount of carbon in a mixture of 30 percent of blast furnace dust and 70 percent of basic oxygen furnace dust does not effect the reduction without adding carbon.
Accordingly, it is an object of the present invention to provide a process for preparing high quality reduced iron pellets suitable for use as charging material for a blast furnace.
In accordance with the present invention there is provided a process for preparing reduced iron pellets containing a high quantity of metallic iron. The process comprises the steps of:
(1) forming a mixture of iron-containing dust and carbonaceous material substantially free from volatile matter, the ratio of the number of free carbon atoms to that of oxygen atoms bonded to iron, zinc or lead in the mixture being adjusted to a range of from 0.75 to 1.25;
(2) adding to said mixture from 0.5 to 7 percent of bentonite by weight on the basis of said mixture;
(3) pelletizing the resulting mixture while adding water thereto so that the resulting green pellets contain from 9.5 to 15.6 percent of water on the basis of the obtained green pellets;;
(4) preheating the green pellets at such a temperature that carbon does not burn while water contained in the green pellets is removed therefrom, thereby providing dried pellets having a porosity of from 27.5 to 40.0 percent; and
(5) chemically reducing the dried pellets in a rotary kiln. The resulting pellets can easily be handled and utilized in an iron-and-steel making plant.
The iron-containing dust can be a mixture of blast furnace dust and steel making dust in a ratio of less than 45/55, and the carbonaceous material can be a coke.
Figure 1 is a graph showing the effectiveness of bentonite to increase the compression strength of dried pellets;
Figure 2 is a graph showing the relationship between compression strength of dried pellets and water content of the pellets before drying; and
Figure 3 is a graph showing the relationship between thermal shock resistance and water content of green pellets.
As mentioned in the foregoing, it is necessary to reduce the oxides of iron, zinc and lead in the pellets in order to supply reduced iron pellets suitable for the burden for a blast furnace. We have found that the reduction of the oxides in the pellets proceeds at a rate expressed by the following equation: -d(At.O)=k exp (- E At.O At.C dt.
wherein At.O: number of oxygen atoms bonded
to Fe, Zn or Pb
At.C: number of free carbon atoms
k : constant
T : reaction temperature in absolute
degree
R : gas constant
E : activation energy
T : duration time of reaction.
The terms «free carbon atoms» designates carbon atoms which are effective in reducing oxides, and therefore they do not include carbon atoms of carbonate.
From analysis of this equation, it is deduced that the reduction in the kiln is not effected by gaseous carbon monoxide but by solid carbon, and thus, it is considered that the reduction occurs according to the following equations:
Fe2O3 + 3C = 2Fe + 3CO FeO+C =Fe+CO ZnO+C=Zn+CO
PbO+C=Pb+CO
Accordingly, it is necessary to supply a considerable amount of carbon in intimate contact with the oxides in the pellets. Based on the foregoing, we have conducted experimental operation of a reducing rotary kiln and have found that the carbon content in the green pellets should be such an amount that the ratio of number of free carbon atoms to that of oxygen atoms bonded to iron, zinc or lead falls within a range of from 0.75 to 1.25.The lower
TABLE 1
Amount Composition (wt%)
MT/month Fe
Plant Variety of Dust (dry base) (total) Zn C Pb
A blast furnace dust 2,342 34.0 0.70 33.4 0.24
BOF dust 6,932 67.0 0.20 0 0.04
electric furnace dust 200 35.63 0.26 0.15 0.21
other iron dust 2,242 47.8 0.06 8.3 0.38
B blast furnace dust 2,036 24.24 3.74 43.15 1.28
BOF dust 5,294 69.23 0.55 1.41 0.06
electric furnace dust none – – –
other iron dust 6,772 41.45 0.02 1.0 0.036
C blast furnace dust 5,000 23.5 10.1 24.0 6.8
BOF dust 23,000 58.7 3.2 0 0.9
electric furnace dust none – – –
other iron dust 7,500 43.0 1.6 – 5.3 limit of the range is determined, since a considerable amount of carbon should be charged to the kiln with a low carbon content, as when the ratio is below 0.75. As mentioned hereinbefore, the operation of the kiln with such low carbon pellets is uneconomical.On the other hand, a ratio exceeding 1.25 is undesirable because an excessive amount of carbon results in a decrease in pellet strength. Pellets with such a high carbon content tend to break into particles in the kiln and the resulting particles deposit in the form of a scaffold onto the inside wall of the kiln, thereby requiring labor to remove them.
An iron-containing dust exhausted in an ordinary modern iron and steel making works is too deficient in carbon content to satisfy the above-mentioned requirement of the ratio
At.C/At.O. For the beneficiation of substantially all of the iron-containing dust in the iron and steel making works to reduced iron pellets, we have developed a process for adding carbon to the dust.
In accordance with an embodiment of the present invention, substantially all of the ironcontaining dust in the works is utilized for the production of reduced iron pellets. For this purpose, carbon should be added to the dust in intimate contact thereto. In this embodiment coke particles, at least 50 percent of which pass through a 125 micron mesh, are mixed with the dust composed of blast furnace dust, steel making furnace dust (the weight ratio of the amount of blast furnace dust to that of steel making furnace dust is less than about 45 : 55) and other iron-containing dust exhausted in the works. Such coke particles are easily obtained as the sludge from a quenching tower of a coke even in the iron and steel making works.Mixing is effected by adding coke particles to a water slurry containing at least 30 percent by weight of solid dust and coke, and then the resulting mixture slurry is subjected to filtration to obtain a cake of the mixture. With a water slurry containing less than 30 percent solids, intimate mixing is difficult to obtain because of the difference in specific gravity between the iron oxides and coke particles.
In the other embodiment of the present invention, mixing is effected by stirring the coke particles with the dust in dried state.
The carbonaceous material added to the dust should be substantially free of volatile matter since it tends to break the pellets upon heating.
In accordance with the present invention, bentonite is added to the mixture in an amount of from about 0.5 to about 7 percent by weight.
In order to examine the effectiveness of bentonite in enhancing the crushing strength or compression strength of pellets, we have carried out compression tests on pellets containing variable amounts of bentonfte. A mixture of 32.6 parts by weight of blast furnace dust, 60.4 parts by weight of basic oxygen furnace dust, 7.0 parts by weight of coke fines and bentonite was prepared. Then tne mixture was pelletized in the form of balls to provide sample green pellets containing variable amounts of bentonite. Each sample was dried at 2000C. to a porosity of 35.1 percent. The compression strength of the dried pellets was determined and the result is shown in Figure 1, wherein the amount of bentonite is represented in the abscissa and the compression strength in the ordinate. The effect of bentonite is readily appreciated from Figure 1.Bentonite of less than 0.5 percent is ineffective, and on the other hand, amounts exceeding 7 percent are uneconomical because of expense.
A mixture of iron-containing dust, carbonaceous material and bentonite can be pelletized in well-known methods, e.g., by disc type pelletizer. In the pelletizer, an amount of water is added to the mixture so that the green pellets contain from 9.5 to 15.6 percent of water on the basis of the weight of the green pellets, which range corresponds to a range of porosity of from about 27.5 to about 40.0 percent of the dried pellets. The green pellets preferably contain from 9.5 to 13.0 percent of water.
The green pellets obtained are dried and preheated at such a temperature that carbon and/ or wustite (FeO) contained therein do not burn, and water is removed therefrom to below 0.7 percent. The preheating temperature is preferably lower than 51 70C. If the pellets contain a substantial amount of wustite, the temperature is preferably lower than 230″C. The preheated pellets are then charged to the rotary kiln and chemically reduced therein according to wellknown methods.
As may be readily understood from the above, a main characteristic of the present invention resides in adjusting the water content within the above-mentioned range. This is explained in detail with reference to Figures 2 and 3.
In preparing green pellets, water addition is made to control the size of green pellets and the porosity of the dried pellets. The spaces occupied by water in green pellets are converted to void upon drying the pellets. Therefore, the water content of green pellets is nearly proportional to the porosity of the dried pellets, which in turn, has a great influence on the compression strength of the dried pellets.In order to ascertain the effect of the water content on the compression strength of the dried pellets, we have carried out compression tests on dried pellets obtained from green pellets containing variable amounts of water. (The compression test was carried out according the Japanese
Industrial Standards M871 8 and the porosity of dried pellets was determined according to the
Japanese Industrial Standards M8716.) A mixture was prepared of the following composition:
Blast furnace dust 32.6 weight percent
Basic oxygen furnace 60.4 weight percent
dust
Coke fines 7.0 weight percent.
The mixture was mixed with about 1 percent of bentonite and variable amounts of water, and then it was pelletized to provide samples of green pellets. Each of the green pellets was dried at 2000C. and the dried pellets were subjected to the compression test. The results are shown in Figure 2, wherein the content of water is represented in the abscissa and the compression strength is in the ordinate. The results of 3 percent and 5 percent bentonitecontaining pellets are also exhibited in Figure 2. As seen from Figure 2, the compression strength is inversely proportional to the water content of the green pellets. Thus, dried pellets were not obtained with porosities of less than 27.0 per cent by such a steep heating as that when charged into a practical preheater.
The mark «X» shows the result obtained with pellets dried by mild heating of green pellets. The result of these experiments shows that green pellets containing water of more than 9.3 percent are usable for operation of the drying kiln. However, green pellets should contain water of more than about 9.5 percent in order to conduct stably commercial operation of the drying kiln. On the other hand, the green pellets preferably contain water of less than about 13.0 percent, because the compression strength of green pellets decreases with higher water content.
In the above connection, we have carried out a thermal shock test of the above-mentioned green pellets containing variable amounts of water. In the test, the thermal shock was made by putting the green pellets into an oven at 400″C. and maintaining them therein for 15 minutes. Unbroken pellets after the test were weighed and the percent thereof to the charged pellets was estimated as the thermal shock resistance. The results are shown in Figure 3, wherein the water content of green pellets is represented in the abscissa and the thermal resistance is in the ordinate.
It is apparent from Figure 3 that almost all of the green pellets of water contents below 9.3 percent were broken in the test and that, in contrast thereto, green pellets containing water of more than about 9.5 percent had sufficient resistance to the thermal shock. The dotted line indicates that with a water content of less than 9.3 percent, the green pellets were broken to particles by thermal shock on drying.
Since an ordinary practical preheater is operated at temperatures of from about 200 to 300″C., green pellets of water content of less than about 9.5 percent are believed to be unsuitable for commercial production of reduced iron pellets.
The mark «X» in Figure 3 exhibits the result of the thermal shock test on green pellets having a composition similar to that of the above-mentioned green pellets but not containing bentonite. The result indicates that green pellets not containing bentonite are much inferior to those of the present invention.
The following Examples are included merely to aid in the understanding of the invention, and variations may be made by those skilled in the art without departing from the scope of the invention.
EXAMPLES 60 Parts of thickener dust exhausted from a blast furnace were mixed with 40 parts of dust exhausted from a converter furnace. 1 Part of bentonite was added to the mixture. Green pellets having an average diameter of 14 mm were prepared from the mixture. Water content of the green pellets was 13 percent. The ratio of free carbon atoms contained in the pellets to oxygen atoms bonded to iron, zinc and lead contained in the pellets was 0.91. The proportion of each component in the pellets was as shown in Table 2.
The preheated pellets were reduced in a rotary kiln of 0.46m inner diameter and 6.57m in length. The metallization ratio (the ratio of metallic iron to total iron contained in the metallized pellets) of the resulting metallized pellets was 92 percent, the average compression strength was 264 kg/pellet and the percent of powder that passed through mesh of 6 mm size was 1.6 percent.
TABLE 2
Component Part
C 12.33
FeO 18.93 Fez03 44.93
Metallic Fe 1.05
Zn 0.52
Pb 0.10
The compression strength of the preheated pellets was 12 kg/pellet.
EXAMPLE 2
A mixture having components as shown in
Table 3 was prepared:
TABLE 3
Percent
Thickener dust from blast furnace 23
Dust from converter furnace of
gas recovery type 20
Dust from LD converter of gas non
recovery type 24
Dust from dust collector 24
Coke powder 9
One part of bentonite was added to 100 parts of the mixture. The mixture was pelletized.
The proportions of components in the pellets are shown in Table 4.
TABLE 4
Component Part
C 18.1
FeO 14.4 Fe2 O3 54.3
Zn 00.34
Pb 0.15
«At.C/At.O» of the pellets was 1.23, water content of the green pellets was 10.5 percent and the compression strength of the preheated pellets was 17.5 kg/pellet. The resulting pellets were reduced in the same rotary kiln as used in
Example 1. The resulting metallized pellets had a metallization ratio of iron of 96 percent and an average compression strength of 140 kg/ pellet; the percent of fines that passed through mesh of 6 mm size was 6 percent.
EXAMPLE 3
One part of thickener dust from a blast furnace was mixed with 2 parts of dust from a converter furnace of gas recovery type. 1 Part of bentonite was added to 100 parts of the resulting mixture. The mixture was pelletized.
The proportions of components in the raw pellets are shown in Table 5.
TABLE 5
Component Part
C 10.0
FeO 9.3
Fe203 51.1
Zn 0.33
Pb 0.11
«At.C/At.O» of the pellets was 0.755, water content of the green pellets was 12.0 percent and the compression strength of the preheated pellets was 15 kg/pellet. The resulting pellets were reduced in the same kiln as used in
Example 1. The resulting metallized pellets had a metallization ratio of iron of 89.7 percent and an average compression strength of 160 kg/ pellet; the percent of fines that passed through mesh 6 mm size was 1.5 percent.
EXAMPLE4 Green pellets prepared in Example 2 were placed in a preheater having a movable lattice of 0.6m width x 4m length of 100 mm thickness. They were dried and preheated by hot air of various temperatures. The results are shown in Table 6.
It was apparent from the above experiment that when the pellets were dried and preheated at a temperature above 230″C., loss of carbon in the pellets occurs because of combustion of carbon at the temperature employed. Therefore, when the pellets were heated at such temperatures, At.C/At.O was decreased.
TABLE 6
Percent
Carbon of
Water content pellets
Temp. of Temp. of content Strength in pellets broken
heated dried in dried of after after
air pellets pellets pellets drying drying ( C.) ( C.) (%) kg/p (%) (%) At.C/At.O
150 142 0.9 12 18.0 0 1.23
200 205 0.4 17 17.9 0 1.21
230 240 0.05 19 16.8 4 1.05
250 530 0 – 12.5 36 0.73
300 785 0 – 10.4 59 0.60
Note: Speed of heated air before being passed through pellets layer was 0.72 m/sec.
Residence time of pellets in the preheater was 35 minutes.
EXAMPLE 5
The mixture shown in Table 7 was prepared.
One part of bentonite was added to 100 parts of the mixture. The mixture was pelletized. The green pellets were dried in the same way as in
Example 4.
TABLE7 Percent
Thickener dust from a blast furnace 29.5
Dust from a LD converter of boiler
type 30.8
Dust from a dust collector 30.7
Coke powder 9.0
The proportions of components in the pellets are shown in Table 8. FeO content was much lower than in Example 4.
TABLE 8
Component Part
C 17.9
FeO 3.4
Fe203 65.7
Zn 0.42
Pb 0.14
The results are shown in Table 9. In this case with a higher temperature than that used in
Example 4, carbon does not decrease.
TABLE 9
Temperature of heated air ( C.) : 480
Temperature of dried pellets (‘C.) : 495
Water content of dried pellets (%) 0 Compression strength of dried
pellets (kg/p) : 27
Percent of carbon in pellets after drying : 17.6
EXAMPLE 6
The slurries shown in Table 10 were blended in a basin without coke fines.
TABLE 10
Ratio
Chemical Composition of
FeO Fe70s C Zn Pb dust Content
Blast furnace 14.58 32.41 33.0 0.70 0.24 35% 50%
LD converter 17.24 76.63 0 0.20 0.04 65% 30%
A blend of the slurries contains 37 percent of solids, and no deposition in the basin was observed. With a dehydrator and dryer, a dried dust mixture was obtained. Chemical composition of the mixture is shown in Table 11.
TABLE 11
Component Content (%)
C 11.55
FeO 16.31
Fe203 61.15
Zn 0.38
Pb 0.11
In this case, «At.C/At.O» of the dried dust mixture was 0.696.
After the addition of 1 percent bentonite, kneading and pelletizing, green pellets containing 12 percent of water were obtained. The preheated pellets have a compression strength of about 15.4 kg/pellet. The dried pellets are fed to the same rotary kiln as used in Example 1.
In order to obtain sufficient reduction and dezincification, a large amount of coal was necessary in the rotary kiln as shown in Table 12.
TABLE 12
Amount
Composition of coal (to) kg/ton
C(fixed) Volatile matter Size product
Coal A 76.4 14.7 -lOmm 160
(with pellets) Coal B 38.7 46.3 – 5mm 463
(blown from the
discharge end)
EXAMPLE 7
Coke fines were ground such that 80 percent of them were finer than 125,u in a wet-type ball mill. They were mixed with a blast furnace s’urry and a LD converter slurry as shown in
Table 13. The green pellets and preheated pellets obtained were almost the same as those obtained in Example 6. Chemical composition of the preheated pellets was as shown in Table 14.
TABLE 13
Chemical Compositions (%) Ratio of
FeO Fe203 C Zn Pb materials
Blast furnace 14.58 32.41 33.0 0.70 0.24 32.6%
LDconverter 17.24 76.63 0 0.20 0.04 60.4% Coke fines 0 0.21 88.2 0 0 7.0%
TABLE 14
Component Content (%) C 16.93
FeO 15.17 Fe2O3 56.86
Zn 0.35
Pb 0.10
In this case, «At.C/At.O» was 1.098. These pellets were reduced in the same rotary kiln as in Example 1. For stable operation, sufficient reduction of iron and elimination of zinc and lead, only 50 kg of coke (1(F20 mm)/ton of products was necessary to be fed into the rotary kiln with the preheated pellets.
EXAMPLE 8
A dried dust mixture obtained as in Example 6 was mixed in a ball mill with bentonite and ground coke fines in the dry stage in the ratio shown in Table 15.
TABLE 15
Material Ratio (parts)
Dust mixture 93
Fine coke 7
Bentonite 1
Chemical composition was the same as in
Table 14. However, the green pellets contain 10.7 percent of water and the compression strength of preheated pellets was 11.8 kg/ pellet.
In the rotary kiln, reduction of iron and elimination of zinc and lead was almost the same as in Example 7. However, the fines of the product were a little more than in Example 7 and, to maintain stable operation without the formation of a scaffold, temperature of the material in the kiln must be controlled carefully.
WHAT WE CLAIM IS:
1. A process for preparing reduced iron pellets containing a high quantity of metallic iron, which process comprises the steps of:
(1) forming a mixture of iron-containing dust and carbonaceous material substantially free from volatile matter, the ratio of the number of free carbon atoms to that of oxygen atoms bonded to iron, zinc or lead in the mixture being adjusted to a range of from 0.75 to 1.25;
(2) adding to said mixture from 0.5 to 7 percent of bentonite by weight on the basis of said mixture;
(3) pelletizing the resulting mixture while adding water thereto so that the resulting green pellets contain from 9.5 to 15.6 percent of water on the basis of the weight of the green pellets;;
(4) preheating the green pellets at such a temperature that carbon does not burn while water contained in the green pellets is removed therefrom, thereby providing dried pellets having a porosity of from 27.5 to 40.0 percent; and
(5) chemically reducing the dried pellets in a rotary kiln.
2. A process as claimed in claim 1, wherein the green pellets contain water of from 9.5 to 13.0 percent on the basis of the weight of the green pellets.
3. A process as claimed in claim 1 or claim 2, wherein bentonite is added in an amount of from 0.8 to 3 per cent on the basis of said mixture.
4. A process as claimed in any one of claims 1 to 3, wherein the green pellets are preheated at a temperature lower than 517″C.
5. A process as claimed in any one of claims 1 to 3, wherein the green pellets are preheated at a temperature lower than 230″C.
6. A process as claimed in claim 2, wherein bentonite is added in an amount of about 1 percent on the basis of said mixture.
7. A process for preparing reduced iron pellets from an iron-containing dust exhausted from an iron and steel making works equipped with at least one set of a blast furnace and a steel making furnace, which process comprises the steps of:
recovering an iron-containing dust in the iron and steel making works, the weight ratio of the amount of blast furnace dust to that of steel making furnace dust in the recovered dust being less than 45 : 55;
adding coke particles to the recovered dust in such an amount that the ratio of the number of free carbon atoms to that of oxygen atoms bonded to iron, zinc or lead is from 0.75 to 1.25; and carrying out the steps (2) to (5) of

Claims (1)

claim 1.
8. A process as claimed in claim 7, wherein at least 50 percent of the carbon particles pass through 125 micron mesh.
9. A process as claimed in claim 7 or claim 8, wherein the recovered dust and the carbon particles are intimately mixed together by adding the coke particles to a water/recovered dust slurry containing at least 30 percent by weight of solids, and then the resulting mixture slurry is subjected to filtration to remove water therefrom, thereby providing a cake of the mixture of the dust and the coke particles.
10. A process as claimed in claim 9, wherein the green pellets contain water of from 9.5 to 13.0 percent on the basis of the weight of the green pellets.
11. A process as claimed in any one of claims 7 to 10, wherein bentonite is added to the mixture in an amount of from 0.8 to 3 percent by weight on the basis of the mixture.
12. A process as claimed in any one of claims 7 to 11, wherein the green pellets are preheated at a temperature lower than 517″C.
13. A process as claimed in any one of claims 7 to 11, wherein the green pellets are preheated at a temperature lower than 230″C.
14. A process as claimed in claim 10, whereing bentonite is added in an amount of about 1 percent on the basis of said mixture.
15. A process as claimed in claim 7 or claim 8, wherein the recovered dust and the carbon particles are mixed in the dry state.
16. A process as claimed in claim 15, whereing the green pellets contain water of from 9.5 to 13.0 percent on the basis of the weight of the green pellets.
17. A process as claimed in claim 16, wherein bentonite is added to the mixture in an amount of from 0.8 to 3 percent by weight on the basis of the mixture of the dust and coke.
18. A process as claimed in claim 16, wherein the green pellets are preheated at a temperature lower than 517″C.
19. A process as claimed in claim 16, wherein the green pellets are preheated at a temperature lower than 230″C.
20. A process as claimed in claim 16, wherein bentonite is added in an amount of about 1 percent on the basis of said mixture.
21. A process as claimed in claim 1 and substantially as hereinbefore described with reference to any one of the Examples.

GB2997677A
1977-07-16
1977-07-16
Process for producing reduced iron pellets from iron-containing dust

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(en)

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Process for producing reduced iron pellets from iron-containing dust

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GB1572566A
(en)

1977-07-16
1977-07-16
Process for producing reduced iron pellets from iron-containing dust

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GB1572566A
(en)

1980-07-30

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GB2997677A
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GB1572566A
(en)

1977-07-16
1977-07-16
Process for producing reduced iron pellets from iron-containing dust

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GB1572566A
(en)

Cited By (5)

* Cited by examiner, † Cited by third party

Publication number
Priority date
Publication date
Assignee
Title

DE3307175A1
(en)

1982-03-02
1983-09-08
Fundição Tupy S/A, Joinville

COMPACT NODULES FOR METAL PRODUCTION AND METHOD OF METAL PRODUCTION USING SUCH NODULES

WO2005084110A2
(en)

2004-02-27
2005-09-15
Rio Tinto Brasil
Pre-treatment process for feed material for direct reduction process

EP1740729A2
(en)

2004-02-27
2007-01-10
Rio Tinto Brasil
Combined pre-treatment process for enabling feed material to be charged in direct reduction processes

WO2011131433A1
(en)

2010-04-19
2011-10-27
Siemens Vai Metals Technologies Gmbh
Bentonite-bonded pressed articles from fine-grain oxidic iron carriers

EP2662457A1
(en)

2012-05-07
2013-11-13
Siemens VAI Metals Technologies GmbH
Method and apparatus for the production of agglomerates and using the agglomerates in a FINEX ® process

1977

1977-07-16
GB
GB2997677A
patent/GB1572566A/en
not_active
Expired

Cited By (10)

* Cited by examiner, † Cited by third party

Publication number
Priority date
Publication date
Assignee
Title

DE3307175A1
(en)

1982-03-02
1983-09-08
Fundição Tupy S/A, Joinville

COMPACT NODULES FOR METAL PRODUCTION AND METHOD OF METAL PRODUCTION USING SUCH NODULES

GB2118921A
(en)

1982-03-02
1983-11-09
Tupy Fundicao Sa
Method and apparatus for the production and use of compact nodules for metal production

WO2005084110A2
(en)

2004-02-27
2005-09-15
Rio Tinto Brasil
Pre-treatment process for feed material for direct reduction process

EP1718775A2
(en)

2004-02-27
2006-11-08
Rio Tinto Brasil
Pre-treatment process for feed material for direct reduction process

EP1740729A2
(en)

2004-02-27
2007-01-10
Rio Tinto Brasil
Combined pre-treatment process for enabling feed material to be charged in direct reduction processes

EP1718775A4
(en)

2004-02-27
2008-07-09
Rio Tinto Brasil
Pre-treatment process for feed material for direct reduction process

EP1740729A4
(en)

2004-02-27
2008-07-09
Rio Tinto Brasil
Combined pre-treatment process for enabling feed material to be charged in direct reduction processes

WO2011131433A1
(en)

2010-04-19
2011-10-27
Siemens Vai Metals Technologies Gmbh
Bentonite-bonded pressed articles from fine-grain oxidic iron carriers

CN102918169A
(en)

2010-04-19
2013-02-06
西门子Vai金属科技有限责任公司
Bentonite-bonded pressed articles from fine-grain oxidic iron carriers

EP2662457A1
(en)

2012-05-07
2013-11-13
Siemens VAI Metals Technologies GmbH
Method and apparatus for the production of agglomerates and using the agglomerates in a FINEX ® process

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