Molten metal holding system, molten metal holding method, and computer program

Abstract

To provide a technique for reducing the consumption of energy while suppressing the generation of dross in a molten metal holding system.SOLUTION: A molten metal holding system comprises: a chemical loop combustion device of repeating the oxidation and reduction of metal particles, which includes an oxidation tower for generating a high temperature gas by using oxidation heat generated by a reaction between an oxygen-containing oxidizing gas and the metal particles and a reduction tower for reducing the metal particles oxidized in the oxidation tower by using a fuel; and a holding furnace for holding a molten metal, which heats the molten metal so that a temperature of the molten metal is made higher than its melting point by using the high temperature gas generated by the oxidation tower.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a molten metal holding system, a molten metal holding method, and a computer program. [Background technology]

[0002] BACKGROUND ART Conventionally, a molten metal holding system that holds molten metal, which is molten metal, in a molten state has been known (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-216358 Summary of the Invention [Problem to be solved by the invention]

[0004] However, even with prior art such as that disclosed in Patent Document 1, there is still room for improvement in the technology for reducing energy consumption while suppressing the generation of dross in a molten metal holding system.

[0005] The present invention has been made to solve the above-mentioned problems, and aims to provide a technology that reduces energy consumption while suppressing the generation of dross in a molten metal holding system. [Means for solving the problem]

[0006] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following aspects.

[0007] (1) According to one aspect of the present invention, there is provided a molten metal holding system, which is a chemical-looping combustion system that repeatedly oxidizes and reduces metal particles, and includes an oxidation tower that generates high-temperature gas using oxidation heat generated by a reaction between an oxygen-containing oxidation gas and the metal particles, and a reduction tower that reduces the metal particles oxidized in the oxidation tower using fuel, and a holding furnace that holds the molten metal and heats the molten metal using the high-temperature gas generated by the oxidation tower so that the temperature of the molten metal is higher than the melting point.

[0008] According to this configuration, the holding furnace heats the molten metal using high-temperature gas generated by the chemical looping combustion system, which repeatedly oxidizes and reduces metal particles. This allows the molten metal to be heated more moderately than when heated with a flame generated by, for example, a burner, which has a temperature significantly higher than the temperature required to hold the molten metal. This prevents the molten metal from excessively increasing in temperature, thereby reducing the generation of dross. Furthermore, the temperature of the high-temperature gas generated by the chemical looping combustion system is adequate as a heat source for holding the molten metal. This reduces heat loss compared to a burner flame, which reaches a temperature significantly higher than the temperature required to hold the molten metal. This reduces the amount of energy consumed to hold the molten metal. This reduces the generation of dross while also reducing energy consumption.

[0009] (2) The molten metal holding system of the above embodiment may further include a heat recovery unit that recovers heat from the exhaust gas discharged from the holding furnace, and the heat recovery unit may use the heat recovered from the exhaust gas to preheat the oxidation gas before it is supplied to the oxidation tower. According to this configuration, the heat recovery unit recovers heat from the exhaust gas, which is the gas discharged from the holding furnace after heating the molten metal, and preheats the oxidation gas before it is supplied to the oxidation tower. This allows the heat of the high-temperature gas already generated to be effectively used in the generation of high-temperature gas in the oxidation tower, thereby further reducing energy consumption.

[0010] (3) In the molten metal holding system of the above aspect, the heat recovery unit includes a first heat accumulator capable of recovering heat from the exhaust gas and a second heat accumulator capable of recovering heat from the exhaust gas separately from the first heat accumulator, and the molten metal holding system further includes an exhaust gas switching valve that switches the supply destination of the exhaust gas from one of the first heat accumulator and the second heat accumulator to the other, an oxidation gas switching valve that switches the supply destination of the oxidation gas from one of the first heat accumulator and the second heat accumulator to the other, and a control unit that controls the exhaust gas switching valve and the oxidation gas switching valve, and the control unit may supply the oxidation gas to the other of the first heat accumulator and the second heat accumulator while supplying the exhaust gas to one of the first heat accumulator and the second heat accumulator. According to this configuration, in the heat recovery unit, the first heat accumulator and the second heat accumulator that can separately recover heat from the exhaust gas are arranged in parallel with respect to the flow of the exhaust gas. The control unit controls an exhaust gas switching valve that switches the supply destination of the exhaust gas and an oxidation gas switching valve that switches the supply destination of the oxidation gas before it is supplied to the oxidation tower. This allows the heat recovered from the exhaust gas in the other of the first and second heat accumulators to be used to heat the oxidation gas before it is supplied to the oxidation tower, when the exhaust gas is supplied to one of the first and second heat accumulators and the heat of the exhaust gas is recovered. This allows the heat of the high-temperature gas that has already been generated to be effectively utilized, further reducing energy consumption.

[0011] (4) The molten metal storage system of the above embodiment may further include a dehydration unit including a dehydrator having an adsorbent that adsorbs moisture from a mixed gas containing carbon dioxide and moisture generated in the reduction tower, and a heat exchanger that performs heat exchange between the gas discharged from the heat recovery unit and a heat medium having a lower temperature than the gas discharged from the heat recovery unit. The dehydration unit may regenerate the adsorbent that adsorbs moisture using the heat medium that has exchanged heat with the gas discharged from the heat recovery unit in the heat exchanger. According to this configuration, the dehydration unit has an adsorbent that adsorbs moisture contained in the mixed gas containing carbon dioxide and moisture that is discharged from the reduction tower. As a result, the gas that has passed through the dehydration unit mainly contains carbon dioxide, making it easier to reuse the carbon dioxide. Furthermore, the adsorbent that adsorbs moisture can be regenerated in the heat exchanger using heat recovered from the gas discharged from the heat recovery unit. This reduces the amount of energy required to effectively utilize carbon dioxide.

[0012] (5) The molten metal holding system of the above embodiment may further include a dehydration unit that removes moisture from a mixed gas containing carbon dioxide and moisture generated in the reduction tower. According to this configuration, when metal particles are reduced in the reduction tower, a mixed gas containing mainly carbon dioxide and moisture is generated. Because the dehydration unit removes moisture from the mixed gas, the gas that has passed through the dehydration unit mainly contains carbon dioxide. This makes it easier to reuse the carbon dioxide.

[0013] (6) In the molten metal holding system of the above embodiment, the holding furnace may include a crucible housed therein for storing the molten metal, and a high-temperature gas inlet for allowing the high-temperature gas to flow into the holding furnace so that the high-temperature gas collides with the outer surface of the crucible. According to this configuration, in the holding furnace housing the crucible for storing the molten metal, the high-temperature gas supplied from the oxidation tower collides with the outer surface of the crucible, so that the heat of the high-temperature gas is efficiently transferred to the molten metal via the crucible. This makes it possible to heat the molten metal with less fuel (energy) while suppressing the generation of dross.

[0014] (7) Another aspect of the present invention provides a molten metal holding method using a molten metal holding system. This molten metal holding method includes: a first step of generating high-temperature gas in an oxidation tower using oxidation heat generated by a reaction between an oxygen-containing oxidation gas and metal particles; a second step of holding the molten metal in a holding furnace, in which the molten metal is heated using the high-temperature gas generated in the oxidation tower so that the temperature of the molten metal is higher than its melting point; a third step of reducing the metal particles oxidized in the oxidation tower using fuel in a reduction tower; and a fourth step of oxidizing the metal particles reduced in the reduction tower in the oxidation tower and generating high-temperature gas using the oxidation heat generated by the metal particles. According to this configuration, in the second step, the molten metal is heated using high-temperature gas generated by a chemical looping combustion system that repeatedly oxidizes and reduces the metal particles. This prevents the temperature of the molten metal from rising excessively, thereby suppressing the generation of dross. Furthermore, the temperature of the high-temperature gas generated in the first step is an appropriate temperature for use as a heat source for holding the molten metal, so the amount of energy consumed to hold the molten metal can be reduced, thereby reducing energy consumption while suppressing the generation of dross.

[0015] (8) According to yet another aspect of the present invention, there is provided a computer program for causing a computer to execute a molten metal holding system. The computer program causes the computer to execute a first function of generating high-temperature gas in an oxidation tower using oxidation heat generated by a reaction between an oxygen-containing oxidation gas and metal particles; a second function of holding the molten metal in a holding furnace, the second function being to heat the molten metal using the high-temperature gas generated in the oxidation tower so that the temperature of the molten metal is higher than its melting point; a third function of reducing the metal particles oxidized in the oxidation tower using fuel in a reduction tower; and a fourth function of oxidizing the metal particles reduced in the reduction tower in the oxidation tower and generating high-temperature gas using the oxidation heat generated by the metal particles. According to this configuration, the second function heats the molten metal using the high-temperature gas generated by the chemical looping combustion device, which repeatedly oxidizes and reduces the metal particles. This prevents the temperature of the molten metal from rising excessively, thereby suppressing the generation of dross. Furthermore, the temperature of the high-temperature gas generated by the first function is an appropriate temperature for use as a heat source for holding the molten metal, so the amount of energy consumed to hold the molten metal can be reduced, thereby reducing energy consumption while suppressing the generation of dross.

[0016] The present invention can be realized in various forms, such as a system for retaining molten metal using high-temperature gas generated by a chemical looping combustion device, a control method for such devices and systems, a computer program for causing such devices and systems to retain molten metal, a server device for distributing the computer program, and a non-transitory storage medium storing the computer program. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic diagram showing a general configuration of a molten metal holding system according to a first embodiment. [Figure 2] FIG. 1 is a diagram illustrating the function of the chemical looping combustion system of the first embodiment. [Figure 3] 1 is a diagram showing the structure of a holding furnace provided in a molten metal holding system of a first embodiment. FIG. [Figure 4] FIG. 2 is a partial cross-sectional view of a holding furnace. [Figure 5] 1 is a flowchart of a molten metal holding method according to a first embodiment. [Figure 6] FIG. 1 is a schematic diagram showing a general configuration of a molten metal holding system according to a comparative example. [Figure 7] FIG. 4 is a schematic diagram showing a general configuration of a molten metal holding system according to a second embodiment. [Figure 8] FIG. 10 is a schematic diagram showing a general configuration of a molten metal holding system according to a third embodiment. [Figure 9] FIG. 10 is a diagram illustrating the function of a chemical looping combustion system according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] First Embodiment FIG. 1 is a schematic diagram showing the overall configuration of a molten metal holding system 1 according to a first embodiment. FIG. 2 is a diagram illustrating the functions of a chemical looping combustion system 5 according to this embodiment. The molten metal holding system 1 according to this embodiment includes a chemical looping combustion system 5 having an air tower 10 and a fuel tower 20, a holding furnace 30, a heat recovery unit 40, a dehydration unit 50, and a control unit 60. The molten metal holding system 1 according to this embodiment generates high-temperature gas to hold a molten metal (molten metal) by utilizing heat generated by chemical looping combustion, in which metal particles M circulating between the air tower 10 and the fuel tower 20 repeatedly undergo oxidation and reduction. The molten metal holding system 1 according to this embodiment holds a molten metal of a low-melting-point metal with a melting point of 1000°C or less, such as aluminum (Al), zinc (Zn), or magnesium (Mg), or an alloy of these metals. The metal particles M are made of ilmenite (FeTiO) with a particle diameter of 50 to 250 μm. The type of molten metal held by the molten metal holding system 1 of this embodiment, and the particle size and material of the metal particles M are not limited to those mentioned above.

[0019] The air tower 10 includes an oxidation furnace 11, a cyclone 12, and a first loop seal 13. The air tower 10 uses oxidation heat generated by the reaction between oxygen and metal particles M to generate high-temperature gas for holding the molten metal.

[0020] The oxidation furnace 11 is a so-called fluidized bed, and is installed so that its longitudinal direction is approximately vertical. A gas straightening plate 11a is disposed inside the oxidation furnace 11. The oxidation furnace 11 is connected to an oxidation gas supply source 6 capable of supplying an oxidation gas Go containing oxygen (O2), which is supplied to the oxidation furnace 11 via a heat recovery unit 40. As shown in FIG. 2, when the oxidation gas supplied from the oxidation gas supply source 6 is supplied to the lower side of the gas straightening plate 11a, the metal particles M deposited on the upper side of the gas straightening plate 11a are fluidized by the supplied oxidation gas, forming a fluidized bed. When the fluidized bed is formed, the metal particles M are oxidized by the oxidation gas according to the following formula (1), generating oxidation heat. In this embodiment, air is used as the oxidation gas Go. 8FeTiO3+ 2O2→ 4Fe2TiO5+ 4TiO2...(1)

[0021] The heat of oxidation generated by the metal particles M increases the temperature of the gas in the oxidation furnace 11. As a result, a relatively high-temperature gas flows from the vertical lower portion 11b to the vertical upper portion 11c in the oxidation furnace 11. When the flow velocity of the gas in the oxidation furnace 11 exceeds the terminal velocity of the metal particles M, the oxidized metal particles M in the oxidation furnace 11 move together with the gas in the oxidation furnace 11 from the vertical upper portion 11c of the oxidation furnace 11 to the cyclone 12 (see dotted arrow Fm1 in FIG. 2).

[0022] The cyclone 12 separates the mixture of oxidized metal particles M and relatively high-temperature gas, which has been transferred from the oxidation furnace 11, into the oxidized metal particles M and the high-temperature gas. Specifically, the mixture transferred from the oxidation furnace 11 to the cyclone 12 rotates within the cyclone 12, causing the metal particles M to collide with the inner wall 12a of the cyclone 12 and fall vertically downward within the cyclone 12. A connecting portion 14 is provided at the vertical lower portion 12b of the cyclone 12, connecting the interior of the cyclone 12 with the interior of the first loop seal 13. The metal particles M falling vertically downward within the cyclone 12 pass through the connecting portion 14 and move into the first loop seal 13 (see dotted arrow Fm1 in FIG. 2). The high-temperature gas within the cyclone 12 passes through a high-temperature gas outlet 12d provided at the vertical upper portion 12c of the cyclone 12 and is sent to the holding furnace 30. Hereinafter, the high-temperature gas that passes through the high-temperature gas outlet 12d of the cyclone 12 and is sent to the holding furnace 30 will be referred to as "high-temperature gas."

[0023] The first loop seal 13 is a tank that temporarily stores the oxidized metal particles M. A gas straightening plate 13a is disposed inside the first loop seal 13. In the first loop seal 13, the oxidized metal particles M accumulate on the upper side of the gas straightening plate 13a. In the first loop seal 13 of this embodiment, water vapor Vp is supplied from a water vapor supply source (not shown) to the lower side of the gas straightening plate 13a. When water vapor Vp is supplied to the first loop seal 13, the metal particles M accumulated inside the first loop seal 13 flow. This prevents the metal particles M, which have reached a relatively high temperature due to oxidation, from adhering to each other. The flowing metal particles M pass through a connection portion 15 connected to the vertical upper portion 13b of the first loop seal 13, and move to the fuel tower 20 together with the water vapor Vp (see dotted arrow Fm2 in FIG. 2).

[0024] The fuel tower 20 includes a reduction furnace 21 and a second loop seal 22. The fuel tower 20 reduces the oxidized metal particles M using fuel.

[0025] The reduction furnace 21 is a so-called fluidized bed, and includes a gas straightening plate 21a and a connection portion 21c having an opening 21b located above the gas straightening plate 21a. The reduction furnace 21 is connected to a fuel supply source 7 capable of supplying fuel to the reduction furnace 21. In the reduction furnace 21, oxidized metal particles M moving from the first loop seal 13 are deposited above the gas straightening plate 21a and below the opening 21b. When fuel Fu sent from the fuel supply source 7 is supplied to the lower side of the gas straightening plate 21a, the oxidized metal particles M deposited in the reduction furnace 21 are fluidized by the fuel Fu and form a fluidized bed. When the fluidized bed is formed, the oxidized metal particles M are reduced by the reaction shown in the following formula (2). In this embodiment, methane gas (CH4) is used as the fuel Fu. The metal particles M reduced in the reduction furnace 21 pass through the opening 21b and the connecting portion 21c, and move to the second loop seal 22 (see the dotted arrow Fm3 in FIG. 2). 4Fe2TiO5+ 4TiO2+CH4→ 8FeTiO3+ CO2H2O ···(2)

[0026] As shown on the right side of equation (2), the gas in the reducing furnace 21 mainly contains carbon dioxide (CO2) and moisture (H2O). The gas in the reducing furnace 21 passes through a mixed gas outlet 21e provided in the vertical upper portion 21d of the reducing furnace 21 and is sent to the dehydration unit 50. Hereinafter, the gas containing carbon dioxide (CO2) and moisture (H2O) that passes through the mixed gas outlet 21e of the reducing furnace 21 and is sent to the dehydration unit 50 will be referred to as a "mixed gas."

[0027] The second loop seal 22 is a tank that temporarily stores the reduced metal particles M. A gas straightening plate 22a is disposed inside the second loop seal 22. In the second loop seal 22, the reduced metal particles M accumulate on the upper side of the gas straightening plate 22a. In the second loop seal 22 of this embodiment, water vapor Vp is supplied from a water vapor supply source (not shown) to the lower side of the gas straightening plate 22a. When water vapor Vp is supplied to the second loop seal 22, the metal particles M accumulated inside the second loop seal 22 begin to flow. The flowing metal particles M pass through a connection portion 23 connected to the vertical upper portion 22b of the second loop seal 22 and move to the oxidation furnace 11 of the air tower 10 together with the water vapor Vp (see dotted arrow Fm4 in FIG. 2).

[0028] The air tower 10 and fuel tower 20 are connected so that metal particles M can circulate inside, as indicated by dotted arrows Fm1, Fm2, Fm3, and Fm4 in Figure 2. This allows the metal particles M to be oxidized by oxygen in the air tower 10, reduced by methane in the fuel tower 20, and then oxidized again in the air tower 10, producing high-temperature gas containing oxidation heat. Therefore, the chemical looping combustion system 5 can continuously produce high-temperature gas containing oxidation heat.

[0029] The holding furnace 30 includes a container 31, a crucible 32, and a temperature detector 33. The holding furnace 30 uses high-temperature gas generated by the chemical looping combustion system 5 to heat the molten metal so that its temperature exceeds the melting point.

[0030] FIG. 3 is a diagram showing the structure of the holding furnace 30 included in the molten metal holding system 1 of this embodiment. The accommodation section 31 has a hollow cylindrical shape and accommodates a crucible 32 capable of storing molten metal. The interior 310 of the accommodation section 31 is connected to the high-temperature gas outlet 12d of the air tower 10, and is supplied with high-temperature gas generated by the air tower 10. As shown in FIG. 3, the accommodation section 31 of this embodiment has a high-temperature gas inlet 31a connected to the high-temperature gas outlet 12d of the air tower 10. The high-temperature gas inlet 31a is located at a position where high-temperature gas Gh collides with the outer surface 32aw of the bottom 32a of the crucible 32. The dotted arrow Gh in FIG. 3 indicates the flow of high-temperature gas within the interior 310 of the accommodation section 31.

[0031] 4 is a partial cross-sectional view of the holding furnace 30, showing the vicinity of the high-temperature gas inlet 31a. In the holding furnace 30, the high-temperature gas Gh passing through the high-temperature gas inlet 31a collides approximately perpendicularly with the outer surface 32aw of the bottom 32a of the crucible 32. That is, the angle θ formed between the high-temperature gas Gh and the outer surface 32aw of the bottom 32a of the crucible 32 shown in FIG. 3 is approximately 90 degrees. This allows the heat of the high-temperature gas Gh to be efficiently transferred to the molten metal in the crucible 32.

[0032] Returning to Figure 3, the holding furnace 30 has two gas outlets 31b and 31c provided on the side of the accommodation section 31. The high-temperature gas Gh that collides with the outer surface 32aw of the crucible 32 flows along the side of the crucible 32, is discharged from the gas outlets 31b and 31c, and is sent to the heat recovery section 40. Hereinafter, the gas discharged from the gas outlets 31b and 31c of the holding furnace 30 and sent to the heat recovery section 40 will be referred to as "exhaust gas."

[0033] The temperature detection unit 33 is, for example, an R thermocouple, and detects the temperature of the molten metal in the crucible 32. The temperature detection unit 33 outputs information about the detected temperature to the control unit 60, which will be described later. Note that the temperature detection unit 33 is not limited to an R thermocouple. The temperature detection unit 33 may be, for example, a radiation thermometer.

[0034] The heat recovery unit 40 includes a first heat accumulator 41, a second heat accumulator 42, and multiple switching valves V11, V12, V13, V14, V21, V22, V23, and V24. The heat recovery unit 40 recovers sensible heat from the exhaust gas sent from the holding furnace 30, and uses the recovered heat to preheat the oxidation gas before it is sent to the air tower 10. In this embodiment, the first heat accumulator 41 and the second heat accumulator 42 are arranged in parallel with the flow of the exhaust gas from the holding furnace 30.

[0035] The first heat accumulator 41 has a plurality of ceramic balls 41a as a heat storage material. The first heat accumulator 41 is supplied with either the exhaust gas sent from the holding furnace 30 or the oxidation gas before being sent to the air tower 10 by controlling the switching valves V11, V12, V13, and V14.

[0036] The second heat accumulator 42 has a plurality of ceramic balls 42a as a heat storage material. The second heat accumulator 42 is supplied with either the exhaust gas sent from the holding furnace 30 or the oxidation gas before being sent to the air tower 10 by using switching valves V21, V22, V23, and V24.

[0037] The multiple switching valves V11, V12, V13, V14, V21, V22, V23, and V24 are electrically connected to a control unit 60, which will be described later. The heat recovery unit 40 alternately operates the first heat accumulator 41 and the second heat accumulator 42 by opening and closing the multiple switching valves V11, V12, V13, V14, V21, V22, V23, and V24 in response to commands from the control unit 60. This allows the sensible heat of the exhaust gas sent from the holding furnace 30 to be continuously recovered and the recovered heat to be used to preheat the oxidation gas. Each of the switching valves V11, V12, V13, V14, V21, V22, V23, and V24 in this embodiment is configured to also allow flow rate control. The details of the switching control of the switching valves V11, V12, V13, V14, V21, V22, V23, and V24 by the control unit 60 will be described later.

[0038] The dehydration unit 50 has a dehydrator 51 connected to the mixed gas outlet 21e of the fuel tower 20. The dehydrator 51 contains an adsorbent 51a, such as silica gel, that can adsorb moisture. The dehydrator 51 removes moisture from the mixed gas sent from the reduction furnace 21 of the fuel tower 20. As a result, the main component of the gas passing through the dehydrator 51 becomes carbon dioxide.

[0039] The control unit 60 is a computer including a ROM, a RAM, and a CPU. The control unit 60 is electrically connected to the oxidizing gas supply source 6, the fuel supply source 7, the temperature detection unit 33, and the switching valves V11, V12, V13, V14, V21, V22, V23, and V24. The control unit 60 controls the oxidizing gas supply source 6, the fuel supply source 7, and the switching valves V11, V12, V13, V14, V21, V22, V23, and V24 using information about the temperature of the molten metal detected by the temperature detection unit 33 in accordance with a program input in advance.

[0040] Next, the molten metal holding method of this embodiment will be described in detail. The molten metal holding method of this embodiment controls the temperature of the molten metal stored in the crucible 32 so that the molten metal can be maintained in a molten state. The molten metal holding method of this embodiment is automatically started, for example, when the storage of molten metal in the crucible 32 begins.

[0041] 5 is a flowchart of the molten metal holding method of the first embodiment. In the molten metal holding method of the present embodiment, first, the temperature of the molten metal in the crucible 32 is detected (step S1). In step S1, the temperature detection unit 33 detects the temperature of the molten metal in the crucible 32. The temperature detection unit 33 outputs the detected temperature of the molten metal to the control unit 60.

[0042] Next, the amount of air to be supplied to the air tower 10 and the amount of fuel to be supplied to the fuel tower 20 are determined (step S2). In step S2, the control unit 60 determines the amount of air to be supplied to the air tower 10 and the amount of fuel to be supplied to the fuel tower 20 according to the temperature of the molten metal detected by the temperature detection unit 33.

[0043] In this embodiment, the control unit 60 uses the following formula (3) to calculate the air flow rate per unit time as the amount of air supplied to the air tower 10. The control unit 60 also uses formula (4) to calculate the fuel flow rate per unit time as the amount of fuel supplied to the fuel tower 20.

number

number

[0044] After step S2, the amounts of air and fuel supplied to the chemical looping combustion system 5 are controlled (step S3). In step S3, the calculation results from step S2 are used to control multiple switching valves V11, V12, V13, V14, V21, V22, V23, and V24. As a result, the calculated amounts of air and fuel are supplied to the chemical looping combustion system 5.

[0045] When air is supplied to the chemical looping combustion system 5, high-temperature gas is generated in the air tower 10 by a reaction between the air and metal particles M. When fuel is supplied to the chemical looping combustion system 5, the oxidized metal particles M are reduced in the fuel tower 20. The metal particles M reduced in the fuel tower 20 are then oxidized again in the air tower 10. In this way, the chemical looping combustion system 5 repeatedly oxidizes the metal particles M in the air tower 10 and reduces them in the fuel tower 20.

[0046] After a certain time (δt) has elapsed after step S3, the process returns to step S1, and the temperature of the molten metal in the crucible 32 is detected. In this way, the molten metal holding method of the present embodiment uses the temperature of the molten metal detected at certain time intervals to determine the amount of air to be supplied to the air tower 10 and the amount of fuel to be supplied to the fuel tower 20, thereby stabilizing the temperature of the molten metal. In this way, the molten metal holding system 1 can maintain the temperature of the molten metal in the holding furnace 30 at a temperature at which the molten metal will not solidify and at which dross is unlikely to occur.

[0047] In the molten metal holding method of this embodiment, the oxidation gas (air) supplied to the air tower 10 is further preheated by the heat recovery section 40. Here, the process of recovering the sensible heat of the exhaust gas and the process of preheating the oxidation gas in the heat recovery section 40 will be described. In this embodiment, the process of recovering the sensible heat of the exhaust gas and the process of preheating the oxidation gas in the heat recovery section 40 are carried out in parallel while the temperature management of the molten metal described above is being carried out.

[0048] In the molten metal holding method of this embodiment, while temperature management of the molten metal is being performed in the holding furnace 30, in a first mode, the first heat accumulator 41 recovers sensible heat from the exhaust gas, while the second heat accumulator 42 preheats the oxidation gas. Specifically, the control unit 60 opens the switching valves V11, V12, V23, and V24 and closes the switching valves V13, V14, V21, and V22. As a result, the exhaust gas that passes through the gas outlets 31b and 31c of the holding furnace 30 and is sent to the heat recovery unit 40 is supplied to the first heat accumulator 41. The first heat accumulator 41 recovers sensible heat from the exhaust gas by warming the ceramic balls 41a with the exhaust gas (recovery process). Meanwhile, in the second heat accumulator 42 to which the oxidation gas is sent from the oxidation gas supply source 6, the oxidation gas is preheated by contacting the ceramic balls 42a, which are at a relatively high temperature, with the oxidation gas (preheating step). The preheated oxidation gas is supplied to the oxidation furnace 11 of the air tower 10.

[0049] In the second mode, while the oxidation gas is preheated in the first heat accumulator 41, the sensible heat of the exhaust gas is recovered in the second heat accumulator 42. Specifically, the control unit 60 opens the switching valves V13, V14, V21, and V22 and closes the switching valves V11, V12, V23, and V24. As a result, the exhaust gas that passes through the gas outlets 31b and 31c of the holding furnace 30 and is sent to the heat recovery unit 40 is supplied to the second heat accumulator 42. In the second heat accumulator 42, the ceramic balls 42a are heated by the exhaust gas, thereby recovering the sensible heat of the exhaust gas (recovery step). Meanwhile, in the first heat accumulator 41, to which the oxidation gas is sent from the oxidation gas supply source 6, the oxidation gas comes into contact with the ceramic balls 41a, which are at a relatively high temperature, to preheat the oxidation gas (preheating step). The preheated oxidation gas is supplied to the oxidation furnace 11 in the air tower 10 .

[0050] In the molten metal holding method of this embodiment, the heat recovery section 40 switches between the first mode and the second mode at time intervals of, for example, about several tens of seconds. In this way, the molten metal holding method of this embodiment not only manages the temperature of the molten metal in the holding furnace 30, but also effectively utilizes the sensible heat of the exhaust gas by the heat recovery section 40.

[0051] 6 is a schematic diagram showing the general configuration of a molten metal holding system 90 of the comparative example. Next, the general configuration of the molten metal holding system 90 of the comparative example and problems associated with the molten metal holding system 90 of the comparative example will be described. The molten metal holding system 90 of the comparative example includes a holding furnace 91, two heat accumulators 92 and 93, two switching valves 94 and 95, a dehydrator 96, and a carbon dioxide recovery unit 97. In the molten metal holding system 90 of the comparative example, two regenerative burners 91a and 91b connected to the two heat accumulators 92 and 93, respectively, generate flames that directly impinge on a crucible 91c, thereby melting metal in the crucible 91c and allowing the molten metal to remain molten. The regenerative burners 91a and 91b provided in the comparative example molten metal holding system 90 are burners that recover sensible heat from the gas discharged from the holding furnace 91 using heat accumulators 92 and 93, respectively, and perform combustion while preheating the combustion air with the recovered heat. However, because the flames of the regenerative burners 91a and 91b are hotter than necessary to hold the molten metal, the comparative example molten metal holding system 90 is prone to localized high-temperature areas, making it easy for dross to form in the crucible 91c. Therefore, it is difficult for the comparative example molten metal holding system 90 to reduce the amount of energy consumed to hold the molten metal while suppressing the generation of dross.

[0052] Furthermore, in the comparative example molten metal holding system 90, the flames of the regenerative burners 91a and 91b are hotter than necessary, so it is necessary to introduce external air to adjust the temperature inside the holding furnace 91 to prevent dross from forming in the crucible 91c. Introducing air to lower the temperature inside the holding furnace 91 reduces the carbon dioxide concentration in the exhaust gas discharged from the holding furnace 91. Therefore, for example, if the carbon dioxide discharged from the holding furnace 91 is to be captured and reused, the power load on the carbon dioxide capture device 97 increases. For example, the carbon dioxide concentration of the combustion gas generated by the combustion of the regenerative burners 91a and 91b is approximately 10%. Meanwhile, the adsorption capacity of zeolite used to capture carbon dioxide significantly decreases when the carbon dioxide concentration of the target gas falls below 10%. In the comparative example molten metal holding system 90, introducing air to adjust the temperature inside the holding furnace 91 may cause the carbon dioxide concentration in the exhaust gas from the holding furnace 91 to fall below 10%. This makes it difficult to efficiently capture carbon dioxide in the carbon dioxide capture device 97.

[0053] Instead of a regenerative burner, a recuperation burner capable of recovering and reusing the sensible heat of the exhaust gas using a heat exchanger may be used as the burner that forms the flame for holding the molten metal. A recuperation burner recovers and reuses the sensible heat of the exhaust gas using a heat exchanger rather than a regenerative burner. Because the flame temperature is lower than that of a regenerative burner, it is easier to avoid excessive temperature increases in the holding furnace compared to a regenerative burner. However, the flame temperature is still significantly higher than the temperature required to hold the molten metal. Furthermore, because the heat exchanger's recovery rate of sensible heat from the exhaust gas is lower than that of a regenerative burner, it is difficult to reduce the energy consumption required to hold the molten metal compared to a regenerative burner.

[0054] According to the molten metal holding system 1 of this embodiment described above, the holding furnace 30 heats the molten metal using high-temperature gas generated by the chemical looping combustion system 5, which repeatedly oxidizes and reduces the metal particles M. This allows the molten metal to be heated moderately compared to heating with a flame generated by a regeneration burner, which is higher than necessary to hold the molten metal. Therefore, excessive increases in the temperature of the molten metal can be prevented, thereby suppressing the generation of dross. Furthermore, the temperature of the high-temperature gas generated by the chemical looping combustion system 5 is moderate as a heat source for holding the molten metal. This reduces heat loss compared to the flame of a regeneration burner, which reaches a temperature significantly higher than the temperature required to hold the molten metal. This reduces the amount of energy consumed to hold the molten metal. Therefore, energy consumption can be reduced while suppressing the generation of dross.

[0055] Furthermore, according to the molten metal holding system 1 of this embodiment, the heat recovery section 40 recovers the heat of the exhaust gas, which is the gas discharged from the holding furnace 30 after heating the molten metal, and reuses it to preheat the oxidation gas before it is supplied to the air tower 10. This allows the heat of the high-temperature gas that has already been generated to be effectively used in generating the high-temperature gas in the air tower 10, thereby further reducing energy consumption.

[0056] Furthermore, according to the molten metal holding system 1 of this embodiment, the heat recovery section 40 includes a first heat accumulator 41 and a second heat accumulator 42 that recover heat from the exhaust gas using a plurality of ceramic balls 41a, 42a as heat storage materials. In this way, the molten metal holding system 1 of this embodiment can maintain the high-temperature gas at an appropriate temperature even when using heat accumulators instead of heat exchangers to recover heat from the exhaust gas and reuse the recovered heat. This allows the effective use of most of the heat of the high-temperature gas that has already been generated, further reducing energy consumption.

[0057] Furthermore, according to the molten metal holding system 1 of this embodiment, in the heat recovery section 40, the first heat accumulator 41 and the second heat accumulator 42 are arranged in parallel with the flow of exhaust gas. The control unit 60 controls the switching valves V11, V12, V21, and V22 that switch the supply destination of the exhaust gas and the switching valves V13, V14, V23, and V24 that switch the supply destination of the oxidation gas before it is supplied to the air tower 10. As a result, when exhaust gas is supplied to one of the first heat accumulator 41 and the second heat accumulator 42 to recover heat from the exhaust gas, the heat recovered from the exhaust gas in the other of the first heat accumulator 41 and the second heat accumulator 42 can be used to heat the oxidation gas before it is supplied to the air tower 10. Therefore, the heat of the high-temperature gas that has already been generated can be effectively utilized continuously, further reducing energy consumption.

[0058] Furthermore, according to the molten metal holding system 1 of this embodiment, when the metal particles M are reduced in the fuel tower 20, a mixed gas containing mainly carbon dioxide and moisture is generated. Since the dehydration section 50 removes moisture from the mixed gas, the gas that has passed through the dehydration section 50 mainly contains carbon dioxide. This makes it easier to reuse the carbon dioxide.

[0059] Furthermore, according to the molten metal holding system 1 of this embodiment, in the holding furnace 30 that houses the crucible 32 that stores the molten metal, the high-temperature gas supplied from the air tower 10 collides with the outer surface 32aw of the crucible 32, and the heat of the high-temperature gas is efficiently transferred to the molten metal via the crucible 32. This prevents the temperature of the molten metal from rising excessively, making it possible to heat the molten metal with less fuel (energy) while suppressing the generation of dross.

[0060] Furthermore, in the molten metal holding system 1 of this embodiment, the high-temperature gas supplied from the air tower 10 impinges on the outer surface 32aw of the crucible 32 at a substantially normal angle. For example, if a flame impingement jet is used to heat the molten metal using a burner, the temperature of the molten metal near the flame impingement point will rise excessively, which may result in the production of a large amount of dross. In contrast, in the molten metal holding system 1 of this embodiment, the temperature of the high-temperature gas generated by the chemical looping combustion device 5 is at most about 1000°C, so the temperature of the molten metal will not rise excessively even when the high-temperature gas impinges. Therefore, by using a high-temperature gas impingement jet, as shown in FIG. 4, energy consumption can be further reduced.

[0061] Furthermore, according to the molten metal holding system 1 of this embodiment, water vapor is used as the working gas for the metal particles M in each of the first loop seal 13 and the second loop seal 22 in the chemical looping combustion system 5. When air is used as the working gas supplied to the first loop seal, the air moves to the fuel tower 20 along with the oxidized metal particles M, and the mixed gas discharged from the mixed gas outlet 21e of the reduction furnace 21 contains nitrogen in addition to carbon dioxide and moisture. Therefore, when air is used as the working gas, a carbon dioxide capture device is required to capture the carbon dioxide, and power is also required to operate the carbon dioxide capture device. On the other hand, as described above, the molten metal holding system 1 of this embodiment uses water vapor as the working gas for the metal particles M. Therefore, the presence of the dehydration unit 50 allows for the capture of carbon dioxide at a relatively high concentration. Therefore, energy consumption can be reduced when reusing carbon dioxide.

[0062] Furthermore, according to the molten metal holding method of this embodiment, the molten metal is heated using high-temperature gas generated by the chemical looping combustion system 5, which repeatedly oxidizes and reduces the metal particles M. This prevents the molten metal from rising too high in temperature compared to heating with a burner flame that is hotter than necessary to hold the molten metal, thereby suppressing the generation of dross. Furthermore, the temperature of the high-temperature gas generated by the chemical looping combustion system 5 is appropriate as a heat source for holding the molten metal, so the amount of energy consumed to hold the molten metal can be reduced. This reduces energy consumption while suppressing the generation of dross.

[0063] Furthermore, according to the computer program of this embodiment, the control unit 60 heats the molten metal using high-temperature gas generated by repeatedly oxidizing and reducing the metal particles M. This makes it possible to prevent the temperature of the molten metal from rising excessively compared to when the molten metal is heated with a burner flame that is hotter than necessary to hold the molten metal, thereby suppressing the generation of dross. Furthermore, because the temperature of the generated high-temperature gas is an appropriate temperature for use as a heat source for holding the molten metal, the amount of energy consumed to hold the molten metal can be reduced. This makes it possible to reduce energy consumption while suppressing the generation of dross.

[0064] Second Embodiment 7 is a schematic diagram showing the general configuration of a molten metal holding system according to a second embodiment. The molten metal holding system according to the second embodiment differs from the molten metal holding system according to the first embodiment (FIG. 1) in that a dehydrator is connected to a heat exchanger.

[0065] The molten metal holding system 2 of this embodiment includes a chemical looping combustion system 5 having an air tower 10 and a fuel tower 20, a holding furnace 30, a heat recovery section 40, a dehydration section 50, and a control section 60. The molten metal holding system 2 holds the molten metal by utilizing the heat generated by chemical looping combustion, in which metal particles M circulating between the air tower 10 and the fuel tower 20 are repeatedly oxidized and reduced.

[0066] The dehydration section 50 of this embodiment includes a dehydrator 51 and a heat exchanger 52. The heat exchanger 52 is disposed downstream of the heat recovery section 40 in the flow of exhaust gas passing through the heat recovery section 40. The dehydrator 51 and the heat exchanger 52 are connected by a flow path 53 through which a heat medium flows. The heat exchanger 52 recovers the sensible heat of the exhaust gas that was not fully recovered in the heat recovery section 40, using a heat medium that is at a lower temperature than the exhaust gas discharged from the heat recovery section 40. When the heat medium is heated by the sensible heat of the exhaust gas and sent to the dehydrator 51, it heats the adsorbent 51a that has adsorbed moisture, causing the moisture to be desorbed from the adsorbent 51a. As a result, the adsorbent 51a of the dehydrator 51 is regenerated and can be reused to remove moisture.

[0067] According to the molten metal holding system 2 of this embodiment described above, the holding furnace 30 heats the molten metal using high-temperature gas generated by the chemical looping combustion system 5, which repeatedly oxidizes and reduces the metal particles M. This prevents the temperature of the molten metal from rising excessively, thereby suppressing the generation of dross. Furthermore, the temperature of the high-temperature gas generated by the air tower 10 is appropriate as a heat source for holding the molten metal, thereby reducing the amount of energy consumed to hold the molten metal. This reduces energy consumption while suppressing the generation of dross.

[0068] Furthermore, according to the molten metal holding system 2 of this embodiment, the dehydration section 50 has an adsorbent 51a that adsorbs moisture contained in the mixed gas containing carbon dioxide and moisture that is discharged from the fuel tower 20. As a result, the gas that has passed through the dehydration section 50 mainly contains carbon dioxide, making it easier to reuse the carbon dioxide. Furthermore, the adsorbent 51a that has adsorbed moisture can be regenerated in the heat exchanger 52 using heat recovered from the exhaust gas discharged from the heat recovery section 40. This makes it possible to reduce the amount of energy required to effectively utilize carbon dioxide.

[0069] Third Embodiment Figure 8 is a schematic diagram showing the general configuration of a molten metal holding system according to a third embodiment. The molten metal holding system according to the third embodiment differs from the molten metal holding system 1 according to the first embodiment (Figure 1) in that the air tower does not have a cyclone, but instead the fuel tower has a cyclone.

[0070] The molten metal holding system 3 of this embodiment includes a chemical looping combustion system 5 having an air tower 70 and a fuel tower 80, a holding furnace 30, a heat recovery section 40, a dehydration section 50, and a control section 60. The molten metal holding system 3 holds the molten metal by utilizing the heat generated by chemical looping combustion, in which metal particles M circulating between the air tower 70 and the fuel tower 80 are repeatedly oxidized and reduced.

[0071] 9 is a diagram illustrating the function of the chemical looping combustion system 5 of this embodiment. The air tower 70 includes an oxidation furnace 71 and a first loop seal 72. The air tower 70 uses oxidation heat generated by the reaction between oxygen and metal particles M to generate high-temperature gas for holding the molten metal.

[0072] The oxidation furnace 71 is a so-called fluidized bed and includes a gas straightening plate 71a and a connection portion 71c having an opening 71b located above the gas straightening plate 71a. The oxidation furnace 71 is connected to the oxidation gas supply source 6 via the heat recovery unit 40. In the oxidation furnace 71, the metal particles M are deposited above the gas straightening plate 71a and below the opening 71b. When the oxidation gas from the oxidation gas supply source 6 is supplied to the lower side of the gas straightening plate 71a, the metal particles M deposited in the oxidation furnace 71 are oxidized by the oxidation gas and generate oxidation heat. The metal particles M oxidized in the oxidation furnace 71 pass through the opening 71b, the connection portion 71c, and move to the first loop seal 72 (see dotted arrow Fm5 in FIG. 9 ). The oxidation heat generated by the metal particles M heats the gas in the oxidation furnace 71. The gas whose temperature has been increased by the heat of oxidation passes through an outlet 71e provided at the vertical upper portion 71d of the oxidation furnace 71, and is sent to the holding furnace 30 as a high-temperature gas.

[0073] The first loop seal 72 is a tank that temporarily stores the oxidized metal particles M. A gas straightening plate 72a is disposed inside the first loop seal 72. The metal particles M oxidized in the oxidation furnace 71 accumulate on the upper side of the gas straightening plate 72a. In the first loop seal 72 of this embodiment, water vapor Vp is supplied from a water vapor supply source (not shown) to the lower side of the gas straightening plate 72a. When the water vapor Vp is supplied to the first loop seal 72, the metal particles M accumulated inside the first loop seal 72 flow. This prevents the metal particles M, which are at a relatively high temperature, from adhering to each other. The flowing metal particles M pass through a connection portion 73 connected to the vertical upper portion 72b of the first loop seal 72, and move to the fuel tower 80 together with the water vapor Vp (see dotted arrow Fm6 in FIG. 9 ).

[0074] The fuel tower 80 includes a reduction furnace 81, a cyclone 82, and a second loop seal 83. The fuel tower 80 reduces the oxidized metal particles M using fuel.

[0075] The reduction furnace 81 is a so-called fluidized bed, and is installed so that its longitudinal direction is approximately along the vertical direction. A gas straightening plate 81a is disposed inside the reduction furnace 81. The reduction furnace 81 is connected to a fuel supply source 7. When fuel supplied from the fuel supply source 7 is supplied to the lower side of the gas straightening plate 81a, the oxidized metal particles M deposited on the upper side of the gas straightening plate 81a are fluidized by the supplied fuel Fu, and a fluidized bed is formed. When the fluidized bed is formed, the oxidized metal particles M are reduced by the fuel. When the flow velocity of the gas in the reduction furnace 81 becomes equal to or greater than the terminal velocity of the metal particles M, the reduced metal particles M in the reduction furnace 81 move together with the gas in the reduction furnace 81 from the vertical upper portion 81c of the reduction furnace 81 to the cyclone 82 (see dotted arrow Fm7 in FIG. 9 ).

[0076] The cyclone 82 separates the mixture of reduced metal particles M and relatively high-temperature gas, which has been transferred from the reduction furnace 81, into the reduced metal particles M and the high-temperature gas. A connecting part 84 that connects the interior of the cyclone 82 to the interior of the second loop seal 83 is provided in a vertical lower part 82b of the cyclone 82. The metal particles M that fall vertically downward within the cyclone 82 pass through the connecting part 84 and move to the second loop seal 83 (see dotted arrow Fm7 in Figure 9). The gas within the cyclone 82 mainly contains carbon dioxide and moisture. The gas within the cyclone 82 passes through an outlet 82d provided in a vertical upper part 82c of the cyclone 82 and is sent to the dehydration part 50.

[0077] The second loop seal 83 is a tank that temporarily stores the reduced metal particles M. A gas straightening plate 83a is disposed inside the second loop seal 83. In the second loop seal 83, the reduced metal particles M accumulate on the upper side of the gas straightening plate 83a. In the second loop seal 83 of this embodiment, water vapor Vp is supplied from a water vapor supply source (not shown) to the lower side of the gas straightening plate 83a. When water vapor Vp is supplied to the second loop seal 83, the metal particles M accumulated inside the second loop seal 83 begin to flow. The flowing metal particles M pass through a connection part 85 connected to the vertical upper part 83b of the second loop seal 83 and move to the air tower 70 together with the water vapor Vp (see dotted arrow Fm8 in FIG. 9 ).

[0078] According to the molten metal holding system 3 of this embodiment described above, the holding furnace 30 heats the molten metal using high-temperature gas generated by the chemical looping combustion system 5, which repeatedly oxidizes and reduces the metal particles M. This prevents the temperature of the molten metal from rising excessively, thereby suppressing the generation of dross. Furthermore, the temperature of the high-temperature gas generated by the air tower 70 is appropriate as a heat source for holding the molten metal, thereby reducing the amount of energy consumed to hold the molten metal. This reduces energy consumption while suppressing the generation of dross.

[0079] <Modification of this embodiment> The present invention is not limited to the above-described embodiment, and can be embodied in various forms without departing from the spirit of the invention. For example, the following modifications are also possible.

[0080] [Variation 1] In the above embodiment, the metal particles in the chemical looping combustion system are made of ilmenite. However, the material for the metal particles is not limited to ilmenite. For example, the material may be copper, nickel, or the like.

[0081] [Variation 2] In the above embodiment, the oxidizing gas supplied to the air tower is air. However, the oxidizing gas for oxidizing the metal particles is not limited to air. It is sufficient if it contains oxygen, or it may be oxygen only.

[0082] [Variation 3] In the above-described embodiment, methane is used as the fuel for reducing the oxidized metal particles. However, the type of fuel is not limited to this. Hydrocarbon fuels other than methane, alcohol fuels, H2, and NH3 may also be used.

[0083] [Variation 4] In the above-described embodiment, the heat recovery unit 40 is provided, which recovers heat from the exhaust gas discharged from the holding furnace 30 and preheats the oxidation gas using the recovered heat. The heat recovery unit is not necessarily required, but the amount of energy consumed to hold the molten metal can be further reduced by preheating the oxidation gas using the heat from the exhaust gas using the heat recovery unit. Furthermore, although the heat recovery unit 40 is described as having two heat accumulators, the configuration of the heat recovery unit and the method of recovering heat from the exhaust gas using the heat recovery unit are not limited to this. A single heat accumulator may also be provided.

[0084] [Variation 5] In the above-described embodiment, a dehydration unit is provided to remove moisture from a mixed gas containing carbon dioxide and moisture discharged from a reduction furnace. However, the dehydration unit may be omitted. Also, the dehydration unit is provided with an adsorbent that is regenerated by heat recovered from the gas discharged from the heat recovery unit. The configuration of the dehydration unit and the dehydration method are not limited to this. The mixed gas may be dehydrated by cooling it.

[0085] [Variation 6] In the above embodiment, in the holding furnace 30, the high-temperature gas impinges substantially perpendicularly on the outer surface 32aw of the bottom 32a of the crucible 32. The manner in which the high-temperature gas impinges on the crucible is not limited to this. If the high-temperature gas cannot be supplied from below the holding furnace due to spatial constraints of the installation location, the gas may be made to impinge on the side surface of the crucible, or the high-temperature gas may be made to impinge at multiple positions.

[0086] [Variation 7] In the above embodiment, the amounts of air and fuel supplied to the chemical looping combustion system are controlled by the switching valves. The air flow rate may be controlled by the oxidizing gas supply source 6, and the fuel flow rate may be controlled by the fuel supply source 7.

[0087] This aspect has been described above based on embodiments and modifications. However, the above-described embodiments are intended to facilitate understanding of this aspect and are not intended to limit this aspect. This aspect may be modified or improved without departing from the spirit and scope of the claims, and equivalents thereof are included in this aspect. Furthermore, if a technical feature is not described as essential in this specification, it may be deleted as appropriate.

[0088] <Application example 1> 1. A molten metal holding system comprising: a chemical looping combustion system that repeatedly oxidizes and reduces metal particles, the chemical looping combustion system comprising: an oxidation tower that generates high-temperature gas using oxidation heat generated by a reaction between an oxygen-containing oxidation gas and the metal particles; and a reduction tower that reduces the metal particles oxidized in the oxidation tower using fuel; a holding furnace for holding the molten metal, which uses high-temperature gas generated by the oxidation tower to heat the molten metal so that the temperature of the molten metal becomes higher than the melting point; Molten metal holding system. <Application example 2> The molten metal holding system according to Application Example 1 further comprises: a heat recovery unit that recovers heat from exhaust gas discharged from the holding furnace, The heat recovery unit preheats the oxidation gas before it is supplied to the oxidation tower by using heat recovered from the exhaust gas. Molten metal holding system. <Application example 3> The molten metal holding system according to Application Example 1 or Application Example 2, the heat recovery unit includes a first heat accumulator capable of recovering heat from the exhaust gas, and a second heat accumulator capable of recovering heat from the exhaust gas separately from the first heat accumulator, The molten metal holding system further comprises: an exhaust gas switching valve that switches the supply destination of the exhaust gas from one of the first heat accumulator and the second heat accumulator to the other; an oxidizing gas switching valve that switches the supply destination of the oxidizing gas from one of the first heat accumulator and the second heat accumulator to the other; a control unit that controls the exhaust gas switching valve and the oxidation gas switching valve, the control unit, when supplying the exhaust gas to one of the first heat accumulator and the second heat accumulator, supplies the oxidizing gas to the other of the first heat accumulator and the second heat accumulator. Molten metal holding system. <Application Example 4> The molten metal holding system according to any one of Application Examples 1 to 3 further comprises: a dehydration unit including: a dehydrator having an adsorbent that adsorbs moisture in a mixed gas containing carbon dioxide and moisture generated in the reduction tower; and a heat exchanger that performs heat exchange between the gas discharged from the heat recovery unit and a heat medium that has a temperature lower than that of the gas discharged from the heat recovery unit, The dehydration unit regenerates the adsorbent that adsorbs moisture by using a heat medium that has exchanged heat with the gas discharged from the heat recovery unit in the heat exchanger. Molten metal holding system. <Application example 5> The molten metal holding system according to any one of Application Examples 1 to 4 further comprises: a dehydration unit that removes moisture from a mixed gas containing carbon dioxide and moisture generated in the reduction tower. Molten metal holding system. <Application Example 6> The molten metal holding system according to any one of Application Examples 1 to 5, The holding furnace is a crucible accommodated inside the holding furnace and configured to store molten metal; a high-temperature gas inlet for allowing the high-temperature gas to flow into the holding furnace so that the high-temperature gas impinges on the outer surface of the crucible; Molten metal holding system. <Application Example 7> A molten metal holding method for holding molten metal using a molten metal holding system, comprising: a first step of generating a high-temperature gas in an oxidation tower using oxidation heat generated by a reaction between an oxygen-containing oxidation gas and metal particles; a second step of holding the molten metal in a holding furnace, in which the molten metal is heated using high-temperature gas generated in the oxidation tower so that the temperature of the molten metal becomes higher than the melting point; a third step of reducing the metal particles oxidized in the oxidation tower using fuel in a reduction tower; a fourth step of oxidizing the metal particles reduced in the reduction tower in the oxidation tower and generating high-temperature gas using oxidation heat generated in the metal particles. Molten metal holding method. <Application Example 8> A computer program that causes a computer to execute a molten metal holding system to hold molten metal, a first function of generating high-temperature gas using oxidation heat generated by the reaction of an oxygen-containing oxidation gas with metal particles in the oxidation tower; a second function of holding the molten metal in a holding furnace, the second function being to heat the molten metal using high-temperature gas generated by the oxidation tower so that the temperature of the molten metal becomes higher than the melting point; a third function of reducing the metal particles oxidized in the oxidation tower using fuel in a reduction tower; a fourth function of oxidizing, in the oxidation tower, the metal particles reduced in the reduction tower, and generating a high-temperature gas using oxidation heat generated in the metal particles; Computer program. [Explanation of symbols]

[0089] 1, 2, 3...Molten metal holding system 5. Chemical looping combustion device 10,70...Air tower 20,80…fuel tower 30...Holding furnace 32...crucible 31a...Hot gas inlet 32aw...Outer surface (of the bottom of the crucible) 40...Heat recovery section 41...First heat accumulator 42...Second heat storage unit 50...Dehydration section 51...Dehydrator 52...Heat exchanger 60...Control unit Go...oxidizing gas M…metal particles V11, V12, V13, V14, V21, V22, V23, V24...Switching valve

Claims

1. 1. A molten metal holding system comprising: a chemical looping combustion system that repeatedly oxidizes and reduces metal particles, the chemical looping combustion system comprising: an oxidation tower that generates high-temperature gas using oxidation heat generated by a reaction between an oxygen-containing oxidation gas and the metal particles; and a reduction tower that reduces the metal particles oxidized in the oxidation tower using fuel; a holding furnace for holding the molten metal, which uses high-temperature gas generated by the oxidation tower to heat the molten metal so that the temperature of the molten metal becomes higher than the melting point; Molten metal holding system.

2. The molten metal holding system according to claim 1 further comprises: a heat recovery unit that recovers heat from exhaust gas discharged from the holding furnace, The heat recovery unit preheats the oxidation gas before it is supplied to the oxidation tower by using heat recovered from the exhaust gas. Molten metal holding system.

3. 3. The molten metal holding system of claim 2, the heat recovery unit includes a first heat accumulator capable of recovering heat from the exhaust gas, and a second heat accumulator capable of recovering heat from the exhaust gas separately from the first heat accumulator, The molten metal holding system further comprises: an exhaust gas switching valve that switches the supply destination of the exhaust gas from one of the first heat accumulator and the second heat accumulator to the other; an oxidizing gas switching valve that switches the supply destination of the oxidizing gas from one of the first heat accumulator and the second heat accumulator to the other; a control unit that controls the exhaust gas switching valve and the oxidation gas switching valve, the control unit supplies the oxidizing gas to the other of the first heat accumulator and the second heat accumulator while supplying the exhaust gas to one of the first heat accumulator and the second heat accumulator. Molten metal holding system.

4. The molten metal holding system according to claim 2 or claim 3 further comprises: a dehydration unit including: a dehydrator having an adsorbent that adsorbs moisture in a mixed gas containing carbon dioxide and moisture generated in the reduction tower; and a heat exchanger that performs heat exchange between the gas discharged from the heat recovery unit and a heat medium that has a temperature lower than that of the gas discharged from the heat recovery unit, The dehydration unit regenerates the adsorbent that adsorbs moisture by using a heat medium that has exchanged heat with the gas discharged from the heat recovery unit in the heat exchanger. Molten metal holding system.

5. The molten metal holding system according to claim 1 or claim 2 further comprises: a dehydration unit that removes moisture from a mixed gas containing carbon dioxide and moisture generated in the reduction tower. Molten metal holding system.

6. The molten metal holding system according to claim 1 or 2, The holding furnace is a crucible accommodated inside the holding furnace and configured to store molten metal; a high-temperature gas inlet for allowing the high-temperature gas to flow into the holding furnace so that the high-temperature gas impinges on the outer surface of the crucible; Molten metal holding system.

7. A molten metal holding method for holding molten metal using a molten metal holding system, comprising: a first step of generating a high-temperature gas in an oxidation tower using oxidation heat generated by a reaction between an oxygen-containing oxidation gas and metal particles; a second step of holding the molten metal in a holding furnace, in which the molten metal is heated using high-temperature gas generated in the oxidation tower so that the temperature of the molten metal becomes higher than the melting point; a third step of reducing the metal particles oxidized in the oxidation tower using fuel in a reduction tower; a fourth step of oxidizing the metal particles reduced in the reduction tower in the oxidation tower and generating high-temperature gas using oxidation heat generated in the metal particles. Molten metal holding method.

8. A computer program that causes a computer to execute a molten metal holding system to hold molten metal, a first function of generating high-temperature gas using oxidation heat generated by a reaction between an oxygen-containing oxidation gas and metal particles in the oxidation tower; a second function of holding the molten metal in a holding furnace, the second function being to heat the molten metal using high-temperature gas generated by the oxidation tower so that the temperature of the molten metal becomes higher than the melting point; a third function of reducing the metal particles oxidized in the oxidation tower using fuel in a reduction tower; a fourth function of oxidizing, in the oxidation tower, the metal particles reduced in the reduction tower, and generating high-temperature gas using oxidation heat generated in the metal particles. Computer program.

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