METHOD FOR PRODUCING METAL FROM METAL OXIDE BY CARBOTHERMIC REDUCTION AND HOLED CAKE USED THEREFOR

Info

Publication number: 20190055616
Type: Application
Filed: Dec 21, 2017
Publication Date: Feb 21, 2019
Inventors: TSUNG-YEN HUANG (KAOHSIUNG), FENG-YI LIN (KAOHSIUNG), SHIH-HSIEN LIU (KAOHSIUNG), WEI-KAO LU (KAOHSIUNG)
Application Number: 15/851,394

Abstract

A high-efficiency method for producing metal from metal oxide by carbothermic reduction includes step in which a holed cake is provided, which has a composition comprising a metal oxide, a carbonaceous reducing agent, and a binder, and the holed cake has a plurality of holes. The method continues with step in which the holed cake is placed in a high-temperature furnace for carbothermic reduction, to reduce the metal oxide in the holed cake into a metal.

Description

Description

FIELD

The disclosure relates to a method for producing metal, more particular to a high-efficiency method for producing metal from metal oxide by carbothermic reduction and a holed cake used therefor.

BACKGROUND

Nowadays, blast furnace (BF) is the most popular commercial ironmaking process, in which the raw materials are mainly including sinter, pellet, lump ore and coke, and the product is hot metal which is the source to the following steelmaking process. However, the BF process requires high quality of the raw materials and the raw materials requires to be pretreated to qualified properties. Coke is made from coking coal by coking process; fine ore needs to be sintered into agglomeration. Therefore, the ironmaking process via BF is relatively long. In addition, coking and sintering process consumes a lot of energy and cause severe pollution. The capital using in the prevention of pollution is particularly high. Furthermore, the most important thing is that it is very difficult to further reduce the emission of carbon dioxide (CO₂).

Rotary hearth furnace (RHF) process is one of commercial ironmaking process by the means of carbothermic reduction. In generally, the metal oxide mixing with carbonaceous material is pelletized into pellets. 1 or 2 layers of pellets are charged on the hearth of RHF for reduction. After the pellets are heated, the pellets are induced to the reduction reaction. Finally, the direct reduced iron (DRI) will be obtained. However, the metal iron conversion rate and yield of metal iron of DRI is not high enough. It is because the combustion gas content high CO₂and H₂O which is easy to re-oxidize the reduced iron.

FIG. 1 illustrates the radiation heat receiving behavior of the conventional multi-layer pellet bed in (a) the initial stage of the reduction reaction and (b) under the stage of the reduction reaction. In order to improve the shortcomings of the RHF process, increasing the layers of pellet bed and increasing furnace temperature at the same time is helpful to prevent the re-oxidization of iron and to increase the yield of metal iron. This is well known and is disclosed. However, the packing in multi-layer pellet bed is not the perfect method. It is because that some of pellets in the middle and bottom layers of bed cannot directly receive the heat radiation. Even through the top layer pellet would be shrinking after reduction, the pellets on the top layers still shelter the path of radiation transferring into the middle and bottom layer pellets. As shown in FIG. 1, the pellets of the first and second layers can receive the radiation heat directly, but the pellets of the n^thlayer are shielded by the upper pellets and cannot receive the radiation heat directly, resulting in a slow reaction rate. Therefore, the pellets of the n^thlayer cannot receive the radiation, until the upper pellets are heated, reduced, and sintered to shrink. The path of radiation is locally opened, and the radiation is gradually transferred from the upper layer to the next layer of pellets. As the pellets receive the heat, the pellets start reducing, sintering and shrinking.

However, the reduction behaviors of the pellets of different raw materials or at different operation temperatures in the furnace are various. As shown in FIG. 1(b), the pellets of the n^thlayer may swell up or may collapse into powdering. On the other hand, as the reducing conditions are not well controlled, the pellets may even get into softening and melting during the reduction reaction. Once the above phenomena occur at the upper pellets, the radiation path leading to the bottom layer will be blocked, causing the radiation fail to be passed to the next layer of pellets, so the reduction reaction cannot be induced, and a high metal reduction rate cannot be achieved.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present disclosure, a high-efficiency method for producing metal from metal oxide by carbothermic reduction includes step in which a holed cake is provided, which has a composition comprising a metal oxide, a carbonaceous reducing agent, and a binder, and the holed cake has a plurality of holes. The method continues with step in which the holed cake is placed in a high-temperature furnace for carbothermic reduction, to reduce the metal oxide in the holed cake into a metal.

In accordance with another aspect of the present disclosure, a holed cake has a composition comprising a metal oxide, a carbonaceous reducing agent, and a binder, and the holed cake has a plurality of holes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are understood from the following detailed description when reading with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 illustrates the radiation heat receiving behavior of the conventional multi-layer pellet bed in (a) the initial stage of the reduction reaction and (b) under the stage of the reduction reaction.

FIG. 2 shows a flow diagram of a high-efficiency method for producing a metal from a metal oxide by carbothermic reduction according to the present disclosure.

FIG. 3 shows a schematic structural view of a holed cake according to the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

It is to be understood that the following disclosure provides many different embodiments or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the present disclosure. The present disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided so that this description will be thorough and complete, and will fully convey the present disclosure to those of ordinary skill in the art. It will be apparent, however, that one or more embodiments may be practiced without these specific details.

In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

It will be understood that when an element is referred to as being “on” another element, it can be directly on the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present.

It will be understood that singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms; such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

FIG. 2 shows a flow diagram of a high-efficiency method for producing a metal from a metal oxide by carbothermic reduction according to the present disclosure. FIG. 3 shows a schematic structural view of a holed cake according to the present disclosure. Referring to Step S21 shown in FIG. 2, and FIG. 3, a holed cake 30 is provided, which has a composition comprising a metal oxide, a carbonaceous reducing agent, and a binder.

The content of the metal oxide is 70 to 90 wt % inclusive, and preferably the metal oxide is iron oxide, nickel oxide, copper oxide, lead oxide, manganese oxide, tin oxide, potassium oxide, sodium oxide, zinc oxide, or a combination of at least two of the foregoing. In the present embodiment, the metal oxide is powdered to improve the metal conversion rate.

In one or more embodiments, the metal oxide is a mineral containing the metal oxide.

The content of the carbonaceous reducing agent is 10 to 30 wt % inclusive, and preferably the carbonaceous reducing agent is carbon black, activated carbon, coal, coke, graphite, charcoal, or a combination of at least two of the foregoing. In the present embodiment, the carbonaceous reducing agent is powdered to improve the utilization rate of reducing agent.

The binder is added in an amount of 0.1 to 6% based on the total weight of the metal oxide and the carbonaceous reducing agent.

In the present embodiment, the holed cake 30 is prepared by the following steps: the metal oxide, the carbonaceous reducing agent and the binder are uniformly mixed to form a mixture; and then the mixture is disposed in a mold to form the holed cake 30. Preferably, the holed cake 30 has a thickness T ranging from 30 to 150 mm.

The holed cake 30 has a first surface 30A, a second surface 30B, and a plurality of holes 30H. The second surface 30B is opposite to the first surface 30A. The holes 30H can or cannot in communication with the first surface 30A and the second surface 30B. In the present embodiment, the cross section of the holes 30H is circular. Or, in another embodiment, the cross section of the holes 30H is polygonal.

In the present embodiment, each of the holes 30H has a diameter d, and a to-be-reduced material portion 30M is present between two adjacent holes 30H, wherein the to-be-reduced material portion 30M has a thickness t.

Moreover, each of the holes 30H has a center C, and a distance G exists between the centers C of two adjacent holes 30H. Preferably, the thickness t of the to-be-reduced material portion 30M is less than the distance G, such that the to-be-reduced material portion 30M can be heated evenly.

Referring to Step S22 shown in FIG. 2, and FIG. 3, the holed cake 30 is placed in a high-temperature furnace for carbothermic reduction, whereby the metal oxide in the holed cake 30 is reduced into a metal. In this step, the holes 30H of the holed cake 30 face a heat source of the high temperature furnace (not shown), to allow the radiation heat to be uniformly transmitted to the holes 30H.

In the present embodiment, a reaction temperature of the carbothermic reduction is 900 to 1600° C. inclusive; and for the purpose of improving the metal conversion rate and the metal yield, the reaction temperature of the carbothermic reduction is preferably 1000 to 1550° C. inclusive. A reaction time of the carbothermic reduction is 30 to 80 min inclusive, and preferably 35 to 45 min inclusive.

In the present disclosure, the holed cake 30 having a plurality of holes 30H is used as a raw material for carbothermic reduction, through which the problem that the bottom layer of the conventional multi-layer pellets cannot receive the radiation heat can be effectively solved, and the heat transfer rate inside the material can be increased, thereby enhancing the carbothermic reduction rate at the bottom of the hearth.

The present disclosure is illustrated in detail with the following embodiments, but it does not mean that the present disclosure is only limited to the content disclosed by these embodiments.

Referring to Table 1, which shows the source and chemical composition of the metal oxide minerals in the comparative example, and Embodiments 1 and 2 of the present disclosure. Referring to Table 2, which shows the source and chemical composition of the carbonaceous reducing agent in the comparative example, and Embodiments 1 and 2 of the present disclosure.

TABLE 1 Source and chemical composition of the metal oxide minerals in the comparative example, and Embodiments 1 and 2 of the present disclosure. Chemical composition of the minerals (wt %) Total Ferrous Ferric Magnetic Unburned Mineral No. Source Iron oxide oxide iron Carbon carbon Silica Alumina Waste oxide Solid mixed 71.62 56.80 39.18 0.19 2.26 Not 0.24 Not #01 material from detected detected steel mill Mineral #01 Brazil 63.14 0.12 90.16 Not 0.06 1.50 5.48 0.72 detected Mineral #02 Australia 56.69 0.11 80.86 Not Not 10.37 4.95 2.80 detected detected Chemical composition of the minerals (wt %) Magnesium Calcium Potassium Sodium Mineral No. oxide oxide Manganese Phosphorus Sulfur Titania oxide oxide Waste oxide 0.04 0.28 Not 0.07 0.11 0.010 0.005 0.009 #01 detected Mineral #01 0.04 0.02 0.18 0.048 0.006 0.056 0.008 0.013 Mineral #02 0.03 0.11 0.05 0.031 0.022 0.133 0.011 0.014

TABLE 2 Source and chemical composition of the carbonaceous reducing agent in the comparative example, and Embodiments 1 and 2 of the present disclosure. Industrial analysis (ad) Total Elemental analysis (ad) Reducing moisture Volatile Ash Fixed Total agent Source content matter content carbon carbon Hydrogen Sulfur Nitrogen Oxygen Coal #1 Australia 2.02 34.66 8.44 54.88 75.84 4.92 0.48 1.8 10.16 Coal #2 China 2.42 5.21 13.92 78.45 80.66 0.87 0.22 0.08 Not detected

Comparative Example

In the comparative example, the reduction reaction was carried out with a multi-layer stacked spherical material. Table 3 shows the reduction reaction conditions and the characteristics of the reduced iron produced in the comparative example.

TABLE 3 Reduction reaction conditions and characteristics of the reduced iron produced in the comparative example. Metal iron Sample Metal oxide conversion rate Yield of metal iron No. mineral No. Reduction reaction conditions (%) Kg-M · Fe/(h * m²) P-1 Waste oxide Carbon/oxygen ratio (C/O) = 1.1 91.4 65.2 #01 Reaction temperature: 1500° C. Reaction time: 65 min P-2 Mineral #01 Carbon/oxygen ratio (C/O) = 1.0 84.2 43.6 Reaction temperature: 1500° C. Reaction time: 60 min P-3 Mineral #02 Carbon/oxygen ratio (C/O) = 1.1 89.8 48.6 Reaction temperature: 1500° C. Reaction time: 65 min

The content ratio of the metal oxide to the carbonaceous reducing agent in the raw material depends on the carbon/oxygen ratio (C/O). C in the carbon/oxygen ratio (C/O) is calculated based on the total carbon in the reducing agent, and O in the carbon/oxygen ratio (C/O) is the total number of O atoms in the metal oxide that can be reduced by carbon. The carbon/oxygen ratio (C/O) is the atomic ratio of C to O contained in the material.

After the metal oxide was mixed with the carbonaceous reducing agent according to the carbon/oxygen ratio (C/O), a suitable amount of a binder was added. In the comparative example, the binder was added in an amount of 2% of the total amount of the metal oxide and the carbonaceous reducing agent.

After being mixed uniformly, the raw materials were prepared into pellets of 14 to 17 mm in diameter. The pellets were laid on a hearth in a high-temperature furnace, and about 7 to 8 layers of the pellets were laid, as shown in FIG. 1. According to the reduction reaction conditions in Table 3, the maximum reduction reaction temperature in the high-temperature furnace was 1500° C. and the reduction reaction time was 60 min or 65 min.

As shown in Table 3, the metal iron conversion rates for the DRI obtained from the sample Nos. P-1, P-2 and P-3 (where the metal iron conversion rate is defined as the metal iron content of the DRI divided by the total iron content) are 91.4%, 84.2% and 89.8%, respectively. The yields of the metal iron (where the yield of metal iron is defined as the metal iron weight of the DRI divided by the hearth area and then by the total reduction time) are 65.2, 43.6 and 48.6 Kg-M.Fe/(h*m²) respectively.

Embodiment 1

In Embodiment 1 of the present disclosure, the reduction reaction was carried out with a holed cake. Table 4 shows the reduction reaction conditions and the characteristics of the reduced iron produced in Embodiment 1 of the present disclosure.

TABLE 4 Reduction reaction conditions and characteristics of the reduced iron produced in Embodiment 1 of the present disclosure. Metal iron Sample Metal oxide conversion rate Yield of metal iron No. mineral No. Reduction reaction condition (%) Kg-M · Fe/(h * m²) C-1 Waste oxide Carbon/oxygen ratio (C/O) = 1.0 90.5 90.2 #01 Reaction temperature: 1450° C. Reaction time: 35 min C-2 Mineral #01 Carbon/oxygen ratio (C/O) = 1.0 83.2 62.4 Reaction temperature: 1450° C. Reaction time: 35 min C-3 Mineral #02 Carbon/oxygen ratio (C/O) = 1.0 95.5 69.6 Reaction temperature: 1450° C. Reaction time: 35 min

The three metal oxide minerals used in Embodiment 1 are the same as those in the comparative example, and the mixing ratios of the carbonaceous reducing agents coal #1 and coal #2 are the same as that in the comparative example. The binder is also added in an amount of 2%.

After being mixed uniformly, the raw materials were prepared into a holed cake, as shown in FIG. 3. The holed cake has a parameter T of about 60 mm, a parameter d of about 16 mm, a parameter G of about 29 mm, and a parameter t of about 25 mm.

The holed cake was placed on a hearth in a high-temperature furnace. According to the reduction reaction conditions in Table 4, the maximum reduction reaction temperature in the high-temperature furnace was 1450° C. and the reduction reaction time was 35 min.

As shown in Table 4, the metal iron conversion rates obtained with the sample Nos. C-1, C-2 and C-3 are 90.5%, 83.2% and 95.5%, respectively. The yields of the metal iron are 90.2, 62.4, and 69.6 Kg-M.Fe/(h*m²) respectively.

It can be found through comparison of Embodiment 1 with the comparative example that when the reduction reaction is carried out with a holed cake, the reduced iron can be obtained with a comparable rate of conversion to metal iron at a low carbon/oxygen ratio (C/O), a low reduction reaction temperature, and with a short reduction reaction time, and the yield of metal iron is also increased considerably.

Embodiment 2

In Embodiment 2 of the present disclosure, the reduction reaction was carried out with a holed cake. Table 5 shows the reduction reaction conditions and the characteristics of the reduced iron produced in Embodiment 2 of the present disclosure.

TABLE 5 Reduction reaction conditions and characteristics of the reduced iron produced in Embodiment 2 of the present disclosure. Metal iron Sample Metal oxide conversion rate Yield of metal iron No. mineral No. Reduction reaction condition (%) Kg-M.Fe/(h * m²) C-4 Waste oxide Carbon/oxygen ratio (C/O) = 1.0 91.8 72.2 #01 Reaction temperature: 1350° C. Reaction time: 45 min C-5 Mineral #01 Carbon/oxygen ratio (C/O) = 1.0 81.1 52.0 Reaction temperature: 1350° C. Reaction time: 45 min C-6 Mineral #02 Carbon/oxygen ratio (C/O) = 1.0 88.6 57.3 Reaction temperature: 1350° C. Reaction time: 45 min

In Embodiment 2, the same raw materials are used, and the reduction reaction conditions are changed, in which the reduction reaction temperature drops from 1450° C. to 1350° C., and the reduction reaction time is prolonged from 35 min to 45 min, as compared with Embodiment 1 of the present disclosure.

In Embodiment 2, the metal iron conversion rate is high for the sample No. C-1 and slightly low for sample Nos. C-5 and C-6; however, the reduced ion still has a high metal conversion rate, compared with Embodiment 1 of the present disclosure.

In Embodiment 2, the yield of the metal iron is low compared with Embodiment 1 of the present disclosure. The reason is that the reduction reaction time is prolonged, causing the yield of the metal iron to decrease. However, although the yield of the metal iron in Embodiment 2 of the present disclosure is lower than that in Embodiment 1 of the present disclosure, it is still higher than that in the comparative example.

In Embodiments 1 and 2, the reduction reaction is carried out with a holed cake, through which both a high metal iron conversion rate and a high yield of the metal iron are achieved. Moreover, the usage of the carbonaceous reducing agent is correspondingly reduced. Most importantly, the reduction reaction temperature is reduced from 1500 to 1350° C., which is an important breakthrough in the ironmaking technology.

Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, and composition of matter, means, methods and steps described in the specification. As those skilled in the art will readily appreciate form the present disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized in accordance with some embodiments of the present disclosure.

Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, and compositions of matter, means, methods or steps. In addition, each claim constitutes a separate embodiment, and the combination of various claims and embodiments are within the scope of the invention.

Claims

1. A method for producing metal from metal oxide by carbothermic reduction, comprising:

providing a holed cake having a composition comprising a metal oxide, a carbonaceous reducing agent, and a binder, and the holed cake having a plurality of holes; and

placing the holed cake in a high-temperature furnace for carbothermic reduction, to reduce the metal oxide in the holed cake into a metal.

2. The method of claim 1, wherein the holed cake is prepared by the following steps: the metal oxide, the carbonaceous reducing agent and the binder are uniformly mixed to form a mixture; and then the mixture is disposed in a mold to form the holed cake.

3. The method of claim 1, wherein the content of the metal oxide is 70 to 90 wt % inclusive.

4. The method of claim 1, wherein the content of the carbonaceous reducing agent is 10 to 30 wt % inclusive.

5. The method of claim 1, wherein the binder is added in an amount of 0.1 to 6% based on the total weight of the metal oxide and the carbonaceous reducing agent.

6. The method of claim 1, wherein the metal oxide is iron oxide, nickel oxide, copper oxide, lead oxide, manganese oxide, tin oxide, potassium oxide, sodium oxide, zinc oxide, or a combination of at least two of the foregoing.

7. The method of claim 1, wherein the carbonaceous reducing agent is carbon black, activated carbon, coal, coke, graphite, charcoal, or a combination of at least two of the foregoing.

8. The method of claim 1, wherein each of the holes has a center, and a distance exists between the centers of two adjacent holes.

9. The method of claim 8, wherein a to-be-reduced material portion is between two adjacent holes, the to-be-reduced material portion has a thickness, and the thickness of the to-be-reduced material portion is less than the distance.

10. The method of claim 1, wherein a reaction temperature of the carbothermic reduction is 900 to 1600° C. inclusive.

11. The method of claim 1, wherein a reaction time of the carbothermic reduction is 30 to 80 min inclusive.

12. A holed cake has a composition comprising a metal oxide, a carbonaceous reducing agent, and a binder, and the holed cake has a plurality of holes.

13. The holed cake of claim 12, wherein the content of the metal oxide is 70 to 90 wt % inclusive.

14. The holed cake of claim 12, wherein the content of the carbonaceous reducing agent is 10 to 30 wt % inclusive.

15. The holed cake of claim 12, wherein the binder is added in an amount of 0.1 to 6% based on the total weight of the metal oxide and the carbonaceous reducing agent.

16. The holed cake of claim 12, wherein the metal oxide is iron oxide, nickel oxide, copper oxide, lead oxide, manganese oxide, tin oxide, potassium oxide, sodium oxide, zinc oxide, or a combination of at least two of the foregoing.

17. The holed cake of claim 12, wherein the carbonaceous reducing agent is carbon black, activated carbon, coal, coke, graphite, charcoal, or a combination of at least two of the foregoing.