Patent Application
20190055616
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.
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 CO2 and H2O which is easy to re-oxidize the reduced iron.
However, the reduction behaviors of the pellets of different raw materials or at different operation temperatures in the furnace are various. As shown in
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.
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.
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.
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
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.
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.
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
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.
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.
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
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.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 106128019 | Aug 2017 | TW | national |
