Chemical Looping Combustion System

Abstract

To improve an energy efficiency of an entire chemical looping combustion system.SOLUTION: A chemical looping combustion system includes an oxidation tower which oxidizes metal particles, and a fuel tower to which hydrogen and a chemical compound containing carbon are supplied as a fuel and the oxidized metal particles are supplied from the oxidation tower, and which reduces the metal particle by means of the fuel and discharges gas containing carbon dioxide.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a chemical looping combustion system. [Background technology]

[0002] Chemical looping combustion systems capable of essentially separating carbon dioxide are known (see, for example, Patent Document 1 and Non-Patent Document 1). In the system described in Patent Document 1, a metal as a solid oxygen carrier is oxidized by reacting with oxygen in the air in an air reactor, and the oxidized metal is reduced by fuel in a fuel reactor and then oxidized again in the air reactor. An oxidation catalyst installed downstream of the fuel reactor burns unburned carbon monoxide discharged from the fuel reactor and converts it into carbon dioxide.

[0003] In the technology described in Non-Patent Document 1, the metal reduction reaction that occurs in the fuel tower is an endothermic reaction, and the heat lost by the endothermic reaction is compensated for by an external heater on the fuel tower. Loop seals are also installed between the oxidation tower, which oxidizes the metal, and the fuel tower, and between the fuel tower and the oxidation tower. Steam is supplied into the loop seal to fluidize the metal particles. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2013-522149 [Non-patent literature]

[0005] [Non-Patent Document 1] Carl Linderholm, et al. "160h of chemical-looping combustion in a 10kW reactor system with a NiO-based oxygen carrier." International Journal of Greenhouse Gas Control Volume 2, issue 4, October 2008, Pages 520-530 Summary of the Invention [Problem to be solved by the invention]

[0006] In the technology described in Non-Patent Document 1, the heat lost in the endothermic reaction in the fuel tower is compensated for by heating with an external heater, resulting in a large heat loss. Also, energy is required to generate the steam supplied to the loop seal. Therefore, there has been a demand for further improvement in the overall energy efficiency of chemical looping combustion systems. Patent Document 1 does not mention compensation for the heat lost in the fuel reactor or the loop seal.

[0007] The present invention has been made to solve at least part of the above-mentioned problems, and has an object to improve the energy efficiency of the entire chemical looping combustion system. [Means for solving the problem]

[0008] The present invention has been made to solve at least part of the above-mentioned problems, and can be realized in the following forms. A chemical looping combustion system comprising: an oxidation tower that oxidizes metal particles, a fuel tower that is supplied with hydrogen and a carbon-containing compound as fuel and that receives the oxidized metal particles from the oxidation tower and reduces the metal particles using the fuel, and a water electrolysis unit that electrolyzes water to produce hydrogen and oxygen, and the water electrolysis unit supplies the produced hydrogen and oxygen to the fuel tower. The present invention can also be realized in the following forms.

[0009] (1) According to one aspect of the present invention, there is provided a chemical looping combustion system comprising: an oxidation tower for oxidizing metal particles; and a fuel tower, to which hydrogen and a carbon-containing compound are supplied as fuel and which receives the oxidized metal particles from the oxidation tower and which reduces the metal particles using the fuel.

[0010] According to this configuration, an endothermic reaction occurs in the fuel tower when oxidized metal particles are reduced by a carbon-containing compound serving as fuel. Meanwhile, hydrogen, which is supplied to the fuel tower in addition to the carbon-containing compound, reduces the oxidized metal particles, causing a weakly exothermic reaction. Therefore, all or part of the heat lost in the endothermic reaction caused by the carbon-containing compound reducing the metal particles can be compensated for by the heat generated by the weakly exothermic reaction caused by hydrogen reducing the metal particles. In this configuration, because the fuel tower is directly heated by a weakly exothermic reaction, heat loss is less than when the fuel tower is heated, for example, by an external heater. As a result, the energy efficiency of the entire system is improved compared to when only a carbon-containing compound is supplied to the fuel tower as fuel.

[0011] (2) The chemical looping combustion system of the above aspect may further include a temperature acquisition unit that acquires a temperature inside the fuel tower, and a control unit that determines a flow rate of a compound containing hydrogen and carbon to be supplied to the fuel tower using a difference between the temperature acquired by the temperature acquisition unit and a predetermined temperature. According to this configuration, the temperature inside the fuel tower is acquired. The flow rate ratio of fuel hydrogen and carbon-containing compounds is controlled according to the difference between the temperature inside the fuel tower and a predetermined temperature. This controls the heating inside the fuel tower using a weakly exothermic reaction in which metal particles are reduced to hydrogen according to the temperature inside the fuel tower, and also controls the amount of metal particles reduced. As a result, the temperature inside the fuel tower can be controlled to a desired temperature, and the oxidized metal particles can be reduced.

[0012] (3) The chemical looping combustion system of the above aspect may further include a water electrolysis unit that electrolyzes water to generate hydrogen and oxygen, and the water electrolysis unit may supply the generated hydrogen and oxygen to the fuel tower. According to this configuration, hydrogen and oxygen generated by the water electrolysis unit are supplied to the fuel tower. The oxygen that flows into the fuel tower reoxidizes metal particles that have been reduced by the fuel inside the fuel tower. The fuel tower is heated by an exothermic reaction caused by the oxygen oxidizing the metal particles. Unlike oxygen in the air, the oxygen generated by water electrolysis does not contain impurities such as nitrogen, making it possible to recover high-purity carbon dioxide from the fuel tower. Furthermore, because oxygen is a by-product of the hydrogen generated by water electrolysis, the energy efficiency of the entire system is improved.

[0013] (4) The chemical looping combustion system of the above aspect may further include a loop seal disposed downstream of the oxidation tower and upstream of the fuel tower, the loop seal preventing gas from flowing from the oxidation tower into the fuel tower, and the water electrolysis unit may supply generated hydrogen to the fuel tower and supply generated oxygen to the loop seal instead of the fuel tower. According to this configuration, oxygen generated as a by-product of hydrogen by the water electrolysis unit is supplied into the loop seal. A gas is preferably supplied into the loop seal to promote the flow of metal particles and prevent condensation and adhesion between the metal particles. Furthermore, since the gas supplied into the loop seal may flow into the fuel tower, it is preferable that the gas does not contain impurities such as nitrogen. The oxygen supplied into the loop seal prevents impurities such as nitrogen from flowing into the loop seal from the oxidation tower. Furthermore, supplying oxygen into the loop seal eliminates the need to supply other gases (e.g., steam) to prevent the inflow of impurities. In other words, the oxygen supplied into the loop seal is a by-product of hydrogen generated by water electrolysis and reoxidizes the metal particles in the fuel tower, heating the fuel tower, thereby improving the energy efficiency of the entire system.

[0014] (5) The chemical looping combustion system of the above aspect may further include a hydrogen tank that stores hydrogen generated by the water electrolysis unit, and the control unit may supply the generated oxygen to the fuel tower when hydrogen and oxygen are generated by the water electrolysis unit and store at least a portion of the generated hydrogen in the hydrogen tank, and may supply the hydrogen stored in the hydrogen tank to the fuel tower when hydrogen and oxygen are not generated by the water electrolysis unit. According to this configuration, when the power supply from the power supply source that supplies power for water electrolysis to the water electrolysis unit fluctuates, the supply of hydrogen and oxygen from the water electrolysis unit is controlled according to the amount of power supply. When power is supplied and the water electrolysis unit generates hydrogen and oxygen, the generated hydrogen is stored in the hydrogen tank. Meanwhile, the generated oxygen is supplied to the fuel tower and oxidizes metal particles, causing an exothermic reaction. As a result, the heat lost due to the reduction reaction of carbon-containing compounds in the fuel tower is compensated for by the exothermic reaction. When power is not supplied and the water electrolysis unit is not performing water electrolysis, hydrogen stored in the hydrogen tank is supplied to the fuel tower, and the heat lost due to the reduction reaction of carbon-containing compounds is compensated for by the weakly exothermic reaction. In other words, according to this configuration, oxygen, a by-product of water electrolysis, is effectively utilized according to the amount of power supplied to the water electrolysis unit, and when power is not supplied, hydrogen stored in the hydrogen tank is used to heat the fuel tower. As a result, the energy efficiency of the entire system is improved.

[0015] The present invention can be realized in various forms, such as a chemical looping combustion system, a chemical looping combustion device, a chemical looping combustion method, a system including these devices, a computer program for executing these devices, a server device for distributing this computer program, and a non-transitory storage medium on which the computer program is stored. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic block diagram of a chemical looping combustion system according to one embodiment of the present invention. [Figure 2] FIG. 1 is an explanatory diagram of the principle of chemical looping combustion. [Figure 3] FIG. 1 is a schematic block diagram of a chemical looping combustion system according to a comparative example. [Figure 4] FIG. 1 is a schematic block diagram of a chemical looping combustion system according to a second embodiment. [Figure 5] FIG. 10 is a schematic block diagram of a chemical looping combustion system according to a third embodiment. [Figure 6] FIG. 10 is a schematic block diagram of a chemical looping combustion system according to a fourth embodiment. [Figure 7] 10 is a flowchart of a fuel flow rate control method according to a fourth embodiment. [Figure 8] FIG. 10 is a schematic block diagram of a chemical looping combustion system according to a fifth embodiment. [Figure 9] 10 is a flowchart of a fuel flow rate control method according to a fifth embodiment. [Figure 10] FIG. 10 is a schematic block diagram of a chemical looping combustion system according to a sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] First Embodiment FIG. 1 is a schematic block diagram of a chemical looping combustion system (hereinafter, simply referred to as the "combustion system") 100 according to one embodiment of the present invention. In the combustion system 100, an air tower-side loop seal (loop seal) 60 is disposed between an oxidation tower 10, which oxidizes metal particles (mg), and a fuel tower 20, which reduces the metal particles (mg). This prevents nitrogen from flowing from the oxidation tower 10 into the fuel tower 20, allowing high-purity carbon dioxide (CO2) to be recovered from the fuel tower 20. In conventional chemical looping combustion systems, the temperature inside the fuel tower 20 drops due to an endothermic reduction reaction between the metal particles (mg) and hydrocarbons (carbon-containing compounds) in the fuel tower 20. Therefore, an external heater is used to heat the fuel tower 20. In contrast, in this embodiment, hydrogen (H2) is supplied to the fuel tower 20 as fuel in addition to hydrocarbons. The reduction reaction between H2 and the metal particles (mg) is a weakly exothermic reaction, which prevents a temperature drop inside the fuel tower 20. The weakly exothermic reaction using H2 directly heats the fuel tower 20, resulting in less heat loss than an external heater. As a result, the energy efficiency of the entire combustion system 100 of this embodiment can be improved.

[0018] Within the combustion system 100, metal particles (mg) circulate, repeatedly undergoing oxidation in the oxidation tower 10 and reduction in the fuel tower 20 to transport oxygen (O2) from the air from the oxidation tower 10 to the fuel tower 20. In this embodiment, an example will be described in which the oxidation reaction of Fe3O4 is used as the metal particles (mg). The particle size of the metal particles (mg) is 50 mm or more and 250 mm or less. As shown in FIG. 1, the combustion system 100 of the first embodiment includes the oxidation tower 10, the fuel tower 20, the air tower side loop seal unit 60, the fuel tower side loop seal unit 70, a cyclone 15, and a dehydrator 40.

[0019] The oxidation tower 10 uses air containing O2 to oxidize Fe3O4 through the reaction shown in the following formula (1). The oxidation reaction of formula (1) is an exothermic reaction. Therefore, the reaction of formula (1) generates heat, which warms the gas in the oxidation tower 10, heating the interior of the oxidation tower 10 to approximately 1000 degrees Celsius (°C).

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[0020] As shown in FIG. 1, the oxidation tower 10 has a cylindrical shape extending vertically. A seal 10S is provided vertically below the oxidation tower 10. The seal 10S is a member with a number of small holes. The seal 10S allows air supplied from vertically below the oxidation tower 10 to flow into the oxidation tower 10 and carry the metal particles mg vertically upward. However, the size of the holes provided in the seal 10S is smaller than the metal particles mg, preventing the metal particles mg from passing through the seal 10S and escaping from the oxidation tower 10. The gas flow velocity moving vertically upward within the oxidation tower 10 is set to a terminal velocity at which gravity and the drag force due to the gas flow are balanced, or to a velocity greater than the terminal velocity.

[0021] The metal particles (mg) oxidized in the oxidation tower 10 flow into the cyclone 15 connected via a pipe. The cyclone 15 separates the metal particles (mg) from the heated gas using centrifugal force. As shown in FIG. 1, the gas heated in the oxidation tower 10 flows out from the vertically upper part of the cyclone 15 and is supplied to the heat utilization destination. The composition of the gas supplied to the heat utilization destination is mostly N2, because O2 has been reduced by the oxidation of the metal particles (mg) in the oxidation tower 10. The metal particles (mg) separated from the gas in the cyclone 15 move to the air tower side loop seal unit 60 through a pipe extending vertically downward in the center of the cyclone 15, as shown in FIG. 1.

[0022] As shown in FIG. 1, the air tower side loop seal unit 60 is located downstream of the oxidation tower 10 and upstream of the fuel tower 20. A seal 60S is provided vertically below the air tower side loop seal unit 60. The seal 60S is a member with multiple fine holes. The fine holes formed in the seal 60S are smaller than the particle size of the metal particles mg. Therefore, as shown in FIG. 1, a particle layer (the hatched area) made of multiple metal particles mg is formed on the upper surface of the seal 60S. Water vapor is used here because even if water vapor flows into the fuel tower 20, it can be removed by the dehydrator 40.

[0023] In the air tower side loop seal unit 60, water vapor is supplied from vertically below the seal 60S. The supplied water vapor passes through the seal 60S and flows into the fuel tower 20, which is connected downstream of the air tower side loop seal unit 60. Because water vapor is supplied into the air tower side loop seal unit 60 from below the seal 60S, the gas mainly composed of N2 is prevented from passing through the particle layer and flowing from the cyclone 15 into the fuel tower 20.

[0024] A fluidized bed that flows from the air tower side loop seal unit 60 to the fuel tower 20 is arranged in the piping that connects the air tower side loop seal unit 60 and the fuel tower 20. Due to the flow of the fluidized bed, the metal particles mg discharged from the cylindrical air tower side loop seal unit 60 move to the fuel tower 20.

[0025] In this embodiment, the fuel tower 20 is supplied with hydrogen (H2) and methane (CH4) as fuel, as well as with a gas containing oxidized metal particles mg from the oxidation tower 10 and water vapor supplied to the air tower-side loop seal unit 60. The fuel tower 20 reduces the metal particles mg using H2 and CH4. A mixed gas containing CO2 generated by the reduction reaction between CH4 and the metal particles mg is discharged.

[0026] As shown in FIG. 1, the fuel tower 20 has a cylindrical shape extending in the vertical direction. A seal 20S is provided vertically below the fuel tower 20. The seal 20S is a member with a number of small holes. In the fuel tower 20, gaseous fuel is supplied from below the seal 20S. The gas flow rate within the fuel tower 20 is set to a rate slower than the terminal velocity and is controlled based on the information of the fuel tower 20 to prevent metal particles (mg) from flying out.

[0027] In the fuel tower 20, to which CH4 is supplied as fuel, Fe2O3, which is the metal particles mg oxidized in the oxidation tower 10 shown in the above formula (1), is reduced by CH4 to Fe3O4 as shown in the following formula (2), generating CO2. The reduction reaction shown in the following formula (3) is an endothermic reaction.

[0028]

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[0029] Furthermore, in the fuel tower 20, to which H2 is supplied as fuel together with CH4, the oxidized metal particles (mg) of Fe2O3 are reduced by H2 and converted to Fe3O4 as shown in the following formula (3). The reduction reaction represented by the following formula (3) is a weakly exothermic reaction. Therefore, when the weakly exothermic reaction of the following formula (3) occurs, the inside of the fuel tower 20 is heated.

[0030]

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[0031] When the oxidation reaction in oxidation tower 10 represented by the above formula (1) and the reduction reaction of CH4 in fuel tower 20 represented by the above formula (2) are taken together, the reactions in oxidation tower 10 and fuel tower 20, including the reduction reaction by CH4 in fuel tower 20, are the same as the combustion of CH4 represented by the following formula (4). In other words, the total amount of heat obtained by the oxidation of metal particles mg and the reduction of metal particles mg by CH4 (the sum of the heat generated by oxidation tower 10 and the heat absorbed by fuel tower 20) is the same as that obtained by the combustion of CH4.

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[0032] As shown in Fig. 1, the mixed gas containing CO2 produced by the reduction reaction in the fuel tower 20 flows out from the vertically upper part of the fuel tower 20 and is sent to the dehydrator 40. The high-purity CO2 from which water vapor has been removed by the dehydrator 40 is sent to a destination where the CO2 will be used. For example, a destination where the CO2 will be used is a storage tank where the CO2 is liquefied or pressurized and stored.

[0033] The metal particles mg reduced by the reduction reaction in the fuel tower 20 move to the fuel tower side loop seal section 70 through a pipe extending vertically downward in the center of the fuel tower 20, as shown in Figure 1.

[0034] The fuel tower side loop seal unit 70, to which metal particles (mg) are supplied from inside the fuel tower 20, is located downstream of the fuel tower 20 and upstream of the oxidation tower 10. The fuel tower side loop seal unit 70 has the same configuration as the air tower side loop seal unit 60. A seal 70S is provided vertically below the fuel tower side loop seal unit 70. The seal 70S is a member with multiple small holes. Steam is supplied to the fuel tower side loop seal unit 70 from vertically below the seal 70S. The supplied steam passes through the seal 70S and flows into the oxidation tower 10, which is connected downstream of the fuel tower side loop seal unit 70. A fluidized bed is provided in the piping connecting the fuel tower side loop seal unit 70 and the oxidation tower 10, allowing the fuel tower side loop seal unit 70 to flow from the fuel tower side loop seal unit 70 to the oxidation tower 10. The fluidized bed moves the metal particles (mg) inside the cylindrical fuel tower side loop seal unit 70 to the oxidation tower 10. As described above, the metal particles mg are oxidized in the oxidation tower 10, reduced in the fuel tower 20, and circulated between the oxidation tower 10 and the fuel tower 20.

[0035] Figure 2 is an explanatory diagram of the principle of chemical looping combustion. Figure 2 shows a schematic block diagram of a combustion system 100. In Figure 2, the metal atoms (or molecules) used as the metal particles mg are represented as Me.

[0036] In the oxidation tower 10, air is supplied as an oxidizing gas, and the reaction heat from the oxidation reaction of the metal particles (mg) is supplied to the heat utilization destination as high-temperature N2 containing no CO2. In the fuel tower 20, the oxidized metal particles (mg) are reduced to fuels such as H2 and CH4, and the mixed gas containing CO2 produced by the reduction reaction is supplied to the dehydrator 40. Note that no CO2 is generated when the metal particles (mg) are reduced by H2. The dehydrator 40 removes H2O from the mixed gas, and the mixed gas containing high-purity CO2 is supplied to the CO2 utilization destination.

[0037] <Comparative Example> 3 is a schematic block diagram of a chemical looping combustion system (combustion system) 100x of a comparative example. In the combustion system 100x of the comparative example shown in FIG. 3, CH4 is supplied as fuel to the fuel tower 20x, but H2 is not supplied. Therefore, in the fuel tower 20x of the comparative example, a reduction reaction of metal particles mg by H2 does not occur, that is, a weakly exothermic reaction between H2 and metal particles mg does not occur. In the comparative example, the inside of the fuel tower 20 is not heated by a weakly exothermic reaction, so the combustion system 100x is provided with a heater 25 that heats the inside of the fuel tower 20.

[0038] In contrast, in the combustion system 100 of this embodiment, hydrogen (H2) and methane (CH4) are supplied to the fuel tower 20 as fuel. In the fuel tower 20, the H2 and CH4 as fuels reduce the oxidized metal particles mg from the oxidation tower 10. In this embodiment, an endothermic reaction occurs in the fuel tower 20 as CH4 reduces the oxidized metal particles mg. Meanwhile, H2, which is supplied to the fuel tower 20 in addition to CH4, reduces the oxidized metal particles mg, causing a weakly exothermic reaction. Therefore, all or part of the heat lost in the endothermic reaction caused by CH4 reducing the metal particles mg can be compensated for by the heat of the weakly exothermic reaction caused by H2 reducing the metal particles mg. Because the interior of the fuel tower 20 is directly heated by the weakly exothermic reaction, this embodiment has less heat radiation loss than heating using an external heater 25 as in the comparative example. As a result, the energy efficiency of the entire combustion system 100 is improved compared to when only CH4 is supplied to the fuel tower 20 as fuel.

[0039] Second Embodiment Fig. 4 is a schematic block diagram of a chemical looping combustion system (combustion system) 100a of the second embodiment. As shown in Fig. 4, the combustion system 100a of the second embodiment further includes a water electrolysis device (water electrolysis unit) 30 that electrolyzes water to produce H2 and O2. The combustion system 100a of the second embodiment differs from the combustion system 100 of the first embodiment in that the H2 supplied to the fuel tower 20 is H2 produced by water electrolysis in the water electrolysis device 30, and O2 produced by water electrolysis is supplied to the fuel tower 20. In the second embodiment, only the configurations that are different from those of the first embodiment will be described, and a description of the same configurations will be omitted.

[0040] In the second embodiment, O2 is supplied into the fuel tower 20, which causes an exothermic reaction of reoxidation of the metal particles mg reduced in the fuel tower 20, as represented by the above formula (1). The inside of the fuel tower 20 is heated by the exothermic reaction caused by oxidation. When O2 generated by water electrolysis is supplied to the fuel tower, it is possible to save on the supply of H2 for heating the inside of the fuel tower 20. Unlike air, O2 supplied into the fuel tower 20 does not contain N2. Therefore, even if O2 generated by water electrolysis is supplied to the fuel tower 20, a decrease in the CO2 concentration in the mixed gas discharged from the fuel tower 20 can be suppressed.

[0041] As described above, the water electrolysis apparatus 30 of the second embodiment electrolyzes water to generate H2 and O2. The generated H2 and O2 are supplied to the fuel tower 20. In the second embodiment, the O2 that flows into the fuel tower 20 reoxidizes the metal particles mg that have been reduced by CH4 or H2 within the fuel tower 20. The inside of the fuel tower 20 is heated by an exothermic reaction caused by the oxidation of the metal particles mg by O2. Unlike O2 in the air, O2 generated by water electrolysis does not contain impurities such as N2, and therefore high-purity CO2 can be recovered from the fuel tower 20. Furthermore, because O2 is a by-product of H2 generated by water electrolysis, the energy efficiency of the entire combustion system 100a is improved.

[0042] <Third embodiment> 5 is a schematic block diagram of a chemical looping combustion system (combustion system) 100b of the third embodiment. The combustion system 100b of the third embodiment differs from the combustion system 100a of the second embodiment in that O2 generated in the water electrolysis device 30b is supplied to the air tower side loop seal unit 60 instead of the fuel tower 20. In the third embodiment, only the configurations different from those of the second embodiment will be described, and a description of the same configurations will be omitted.

[0043] In the third embodiment, O2 generated in the water electrolysis device 30b is supplied together with water vapor from below the seal 60S of the air tower side loop seal unit 60. When O2 is supplied to the air tower side loop seal unit 60, some of the O2 flows into the fuel tower 20, and the remaining O2 flows into the cyclone 15. The O2 flowing into the fuel tower 20 reacts with the reduced metal particles mg in the fuel tower 20, similar to the O2 supplied to the fuel tower 20 in the second embodiment. The inside of the fuel tower 20 is heated by the heat generated by the oxidation reaction between O2 and the metal particles mg.

[0044] As described above, in the third embodiment, O2 generated in the water electrolysis device 30b is supplied to the air tower side loop seal unit 60 instead of the fuel tower 20. A gas such as water vapor is preferably supplied to the air tower side loop seal unit 60 to promote the flow of metal particles (mg) and prevent condensation and adhesion of the metal particles (mg). Furthermore, the gas supplied to the air tower side loop seal unit 60 preferably does not contain impurities such as N2 because it may flow into the fuel tower 20. The O2 supplied to the air tower side loop seal unit 60 suppresses the inflow of impurities such as N2 that would flow from the oxidation tower 10 into the air tower side loop seal unit 60. Furthermore, supplying O2 to the air tower side loop seal unit 60 reduces the flow rate of water vapor required to prevent the inflow of impurities. Specifically, the O2 supplied to the air tower side loop seal unit 60 is a by-product of H2 generated by water electrolysis. It reoxidizes the metal particles (mg) in the fuel tower 20 and heats the fuel tower 20, thereby improving the energy efficiency of the entire combustion system 100b.

[0045] <Fourth embodiment> 6 is a schematic block diagram of a chemical looping combustion system (combustion system) 100c of the fourth embodiment. The combustion system 100c of the fourth embodiment is significantly different from the combustion system 100 of the first embodiment in that the flow rates of CH4 and H2 as fuels supplied to the fuel tower 20 are controlled. In the fourth embodiment, only the configuration and control different from those of the first embodiment will be described, and a description of the same configuration, etc. will be omitted.

[0046] As shown in FIG. 6, the combustion system 100c of the fourth embodiment further includes a temperature T FR and a temperature sensor (temperature acquisition unit) 26 that detects the temperature T FR The control unit 50 controls the flow rates of CH4 and H2 supplied to the fuel tower 20 using the above. The temperature sensor 26 in this embodiment is a thermocouple inserted in the fuel tower 20.

[0047] Although not shown in Fig. 6, the combustion system 100c includes valves for controlling the flow rates of CH4 and H2 supplied to the fuel tower 20. The control unit 50 controls the temperature T FR and a predetermined target temperature T FR_tar The flow rate Q of H2 supplied to the fuel tower 20 is determined according to the difference between FR_H2 and CH4 flow rate Q FR_HC Determine.

[0048] The control unit 50 of this embodiment calculates the temperature T in the fuel tower 20 detected by the temperature sensor 25 in the following equation (5). FR By substituting the above, the flow rate Q of H2 supplied to the fuel tower 20 after Δt seconds from the current time t is FR_H2 In addition, k1 in the formula (5) is a positive constant, which can be set arbitrarily by the user.

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[0049] Here, both CH4 and H2 as fuels react with the oxidized metal particles mg. Therefore, the control unit 50 of this embodiment controls the flow rate Q of H2. FR_H2 When the flow rate of the other CH4, Q FR_HC On the other hand, the control unit 50 reduces the flow rate Q of H2. FR_H2 When the flow rate of the other CH4, Q FR_HC Here, the flow rate Q of CH4 after Δt seconds from time t is increased. FR_HC (t+Δt) is expressed as in the following equation (6).

[0050]

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[0051] 7 is a flowchart of a fuel flow rate control method according to the fourth embodiment. In the flow rate control flow shown in FIG. 7, first, control of the combustion system 100c is started (step S1). The control unit 50 detects the temperature T FR (Step S2). The control unit 50 calculates the temperature T FR By substituting the above, the flow rate Q of H2 supplied to the fuel tower 20 is FR_H2 (Step S3). The determined flow rate Q FR_H2 of H2 is fed to the fuel tower 20.

[0052] The control unit 50 determines the flow rate Q of H2. FR_H2 The flow rate Q of CH4 to be supplied to the fuel tower 20 is determined by substituting Q into the above equation (6) (step S4). FR_HC The flow rate Q of CH4 is supplied to the fuel tower 20. FR_HCIt is determined whether a predetermined time Δt has elapsed since the determination of (Step S5). If it is determined that the predetermined time Δt has not elapsed (Step S5: NO), the control unit 50 waits until the predetermined time Δt has elapsed.

[0053] If it is determined that the predetermined time Δt has elapsed (step S5: YES), the control unit 50 determines whether or not to terminate the flow rate control flow (step S6). The control unit 50 determines whether or not to terminate the flow rate control flow, for example, by determining whether or not an end operation has been received from the user. If it is determined that the flow rate control flow should not be terminated (step S6: NO), the processing from step S2 onwards is repeated. If it is determined that the flow rate control flow should be terminated (step S6: YES), the flow rate control flow is terminated. Note that the determination of whether or not to terminate the flow rate control flow may be made by interrupting another process being performed.

[0054] As described above, the control unit 50 of this embodiment controls the temperature T FR and the target temperature T FR_tar The CH4 flow rate Q supplied to the fuel tower 20 is calculated using the difference between FR_HC and H2 flow rate Q FR_H2 The temperature T in the fuel tower 20 is determined. FR The flow rate ratio of the fuel H2 and CH4 is controlled according to the temperature T FR The heating in the fuel tower 20 is controlled by the weak exothermic reaction in which the metal particles mg are reduced to H2 according to the temperature T2, and the amount of the reduced metal particles mg is controlled. As a result, the temperature in the fuel tower 20 is controlled to the target temperature T2. FR_tar The oxidized metal particles mg can be reduced by controlling the temperature to approach .

[0055] <Modification of the Fourth Embodiment> In the fourth embodiment, the flow rate Q of H2 supplied to the fuel tower 20 FR_H2 and CH4 flow rate Q FR_HCThe method of determining the flow rate Q of H2 is an example and can be modified. For example, the control unit 50 determines the flow rate Q of H2 by the following equations (7) and (8): FR_H2 and the flow rate of CH4 Q FR_HC and may be supplied to the fuel tower 20. Note that k2 and b2 in equation (7) and Q in equation (8) FR_HC_0 is an arbitrarily set constant.

[0056]

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[0057] Fifth Embodiment 8 is a schematic block diagram of a chemical looping combustion system (combustion system) 100d of the fifth embodiment. The combustion system 100d of the fifth embodiment is significantly different from the combustion system 100a of the second embodiment in that the flow rates of H2 and O2 generated by the water electrolysis device 30d fluctuate, and a control unit 50d controls the flow rate of gas supplied to the fuel tower 20 in accordance with the fluctuating flow rates of H2 and O2. In the fifth embodiment, only the configuration and control different from those of the second embodiment will be described, and a description of the same configuration and the like will be omitted.

[0058] 8, the combustion system 100d further includes a control unit 50d, a hydrogen tank 35 capable of storing H2 generated by the water electrolysis device 30d, and a variable power supply device (power supply device) PW that supplies power for water electrolysis to the water electrolysis device 30d. The power supply device PW is a so-called solar cell. Therefore, the power supply device PW generates solar power during the day to supply power to the water electrolysis device 30d, but does not supply power to the water electrolysis device 30d at night.

[0059] The control unit 50d of this embodiment detects whether or not power is being supplied from the power supply device PW to the water electrolysis device 30d. The control unit 50d also controls the flow rate Q of CH4 supplied to the fuel tower 20 by controlling the opening and closing of various valves not shown in FIG. FR_HCand the O2 flow rate Q FR_O2 and the flow rate Q of H supplied from the hydrogen tank 35 to the fuel tower 20. FR_H2 When power is supplied from the power supply device PW and the water electrolysis device 30d performs water electrolysis to generate H2 and O2, the control unit 50d supplies the generated O2 together with CH4 to the fuel tower 20 and stores the generated H2 in the hydrogen tank 35. On the other hand, when power is not supplied from the power supply device PW and the water electrolysis device 30d does not perform water electrolysis, the control unit 50d supplies H2 stored in the hydrogen tank 35 together with CH4 to the fuel tower 20. Note that some or all of the H2 generated during water electrolysis may be supplied to the fuel tower 20.

[0060] The control unit 50d of this embodiment calculates the flow rate Q of O supplied to the fuel tower 20 by the following equation (9). FR_O2 In addition, Q in equation (9) is determined. O2_WL is the amount of O2 produced by the water electrolysis device 30d at time t. Furthermore, k3 and b3 are constants that may be set arbitrarily by the user.

[0061]

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[0062] The O2 supplied to the fuel tower 20 re-oxidizes the metal particles mg that have been reduced by the fuel. Therefore, additional fuel is required to reduce the re-oxidized metal particles mg. In this embodiment, the control unit 50d uses a flow rate Q determined by the following equation (10) as the additional fuel. FR_H2 supplies H2.

[0063]

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[0064] Since the chemical formula for H2 combustion is expressed by the following formula (11), c in formula (10) is 0.5.

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[0065] In the above formula (9), when the following relational expression (12) is satisfied, the flow rate Q generated by water electrolysis FR_O2 The inside of the fuel tower 20 cannot be heated sufficiently by only supplying O2 to the fuel tower 20. In this case, it is necessary to heat the inside of the fuel tower 20 with H2 generated by water electrolysis. In this case, the control unit 50d controls the flow rate Q of H2 supplied to the fuel tower 20. FR_H2 is determined by the following formula (13) instead of the above formula (10). Furthermore, the control unit 50d determines the flow rate Q of CH4 supplied to the fuel tower 20. FR_HC is determined by the following equation (14): k4 and b4 are constants that may be set arbitrarily by the user.

[0066]

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[0067] 9 is a flowchart of a fuel flow rate control method according to the fifth embodiment. In the flow rate control flow shown in FIG. 9, first, control of the combustion system 100d is started (step S11). The control unit 50d detects the temperature T FR (Step S12). The control unit 50d determines whether or not power is being supplied from the power supply device PW to the water electrolysis device 30d (Step S13). If it is determined that power is not being supplied to the water electrolysis device 30d (Step S13: NO), the control unit 50d acquires the flow rate Q of O2 supplied to the fuel tower 20. FR_O2 In this case, the control unit 50d determines that the temperature T FR By substituting the above, the flow rate Q of H2 supplied to the fuel tower 20 is FR_H2(Step S16A). The determined flow rate Q FR_H2 The control unit 50d controls the flow rate Q of the determined H2 to be supplied to the fuel tower 20. FR_H2 The flow rate Q of CH4 to be supplied to the fuel tower 20 is determined by substituting Q into the above equation (6) (step S17A). FR_HC of CH4 is supplied to the fuel tower 20.

[0068] In the process of step S13, when it is determined that power is being supplied to the water electrolysis device 30d (step S13: YES), the control unit 50d FR_O2 In this embodiment, the control unit 50d determines whether the flow rate Q of O2 currently produced by water electrolysis, which is expressed on the left side of the above equation (12), is sufficient to heat the inside of the fuel tower 20 (step S14). O2_WL is greater than or equal to the right-hand side of the formula. In other words, it is determined whether sufficient O2 is being produced by water electrolysis.

[0069] In the process of step S14, when it is determined that a sufficient amount of O2 has been generated by water electrolysis and that the inside of the fuel tower 20 can be sufficiently heated (step S14: YES), the control unit 50d FR_HC The constant flow rate Q FR_HC_0 (Step S15B). The determined flow rate Q FR_HC_0 The control unit 50d calculates the flow rate Q of O2 supplied to the fuel tower 20 using the above formula (9). FR_O2 (Step S16B). The determined flow rate Q FR_O2 The control unit 50d controls the flow rate Q FR_O2 By substituting into the above equation (10), the flow rate Q of H2 supplied to the fuel tower 20 is obtained. FR_H2 (Step S17B). The determined flow rate Q FR_H2 of H2 is fed to the fuel tower.

[0070] In the process of step S14, if it is determined that sufficient O2 is not produced by water electrolysis and the inside of the fuel tower 20 cannot be sufficiently heated (step S14: NO), the control unit 50d calculates the flow rate Q of O2 supplied to the fuel tower 20 using the above formula (9). FR_O2 (Step S15C). FR_O2 The control unit 50d controls the flow rate Q of O2 determined by the above formula (9) to be FR_O2 By substituting into the above equation (13), the flow rate Q of H supplied to the fuel tower 20 is obtained. FR_H2 (Step S16C). The determined flow rate Q FR_H2 The control unit 50d calculates the flow rate Q of CH4 to be supplied to the fuel tower 20 using the above equation (14). FR_HC (Step S17C). The determined flow rate Q FR_HC of CH4 is supplied to the fuel tower 20.

[0071] When any of the processes in steps S17A to S17C is performed, the control unit 50d determines whether or not to end the flow rate control flow (step S18). If it is determined not to end the flow rate control flow (step S18: NO), the processes from step S12 onward are repeated. If it is determined to end the flow rate control flow (step S18: YES), the flow rate control flow ends. Note that the determination of whether or not to end the flow rate control flow may be made by interrupting another process being performed.

[0072] As described above, in this embodiment, when the water electrolysis device 30d performs water electrolysis to generate H2 and O2, the control unit 50d supplies the generated O2 together with CH4 to the fuel tower 20 and stores the generated H2 in the hydrogen tank 35. On the other hand, when the water electrolysis device 30d is not performing water electrolysis, the control unit 50d supplies H2 stored in the hydrogen tank 35 together with CH4 to the fuel tower 20. That is, in this embodiment, when the power supply from the power supply device PW to the water electrolysis device 30d fluctuates, the supply of H2 and O2 from the water electrolysis device 30d is controlled in accordance with the amount of power supply. When power is supplied and the water electrolysis device 30d generates H2 and O2, the generated H2 is stored in the hydrogen tank 35. On the other hand, the generated O2 is supplied to the fuel tower 20 and oxidizes the metal particles mg, causing an exothermic reaction. As a result, the heat lost due to the reduction reaction of CH4 in the fuel tower 20 is compensated for by the exothermic reaction. When the water electrolysis device 30d is not performing water electrolysis, H2 stored in the hydrogen tank 35 is supplied to the fuel tower 20, and the heat lost due to the reduction reaction of CH4 is compensated for by the weakly exothermic reaction. That is, according to this embodiment, oxygen, a by-product of water electrolysis, is effectively utilized in accordance with the amount of power supplied to the water electrolysis device 30d, and when no power is supplied, H2 stored in the hydrogen tank 35 is used to heat the interior of the fuel tower 20. As a result, the energy efficiency of the entire combustion system 100d is improved.

[0073] <Modification of the Fifth Embodiment> In the fifth embodiment, power is supplied from the power supply device PW to the water electrolysis device 30d, and O2 generated by the water electrolysis device 30d is supplied to the fuel tower 20. At this time, as shown in the above formula (10), H2 is used as the fuel for reducing the metal particles mg reoxidized by O2 in the fuel tower 20, but the fuel used for reoxidation may be CH4, or both H2 and CH4 may be used.

[0074] In the fifth embodiment, the generated O2 is supplied to the fuel tower 20 during the same period during which the water electrolysis device 30d generates O2. However, there may be a period during which the generated O2 is not supplied to the fuel tower 20. For example, when the amount of H2 stored in the hydrogen tank 35 is equal to or less than a predetermined value, the control unit 50d may release the O2 generated by water electrolysis to the atmosphere and store the generated H2 in the hydrogen tank 35 or supply it to the fuel tower 20. In this case, the combustion system 100d may include a heater 25 that heats the fuel tower 20. When the water electrolysis device 30d is performing water electrolysis, the control unit 50d preferably supplies at least a portion of the generated H2 to the hydrogen tank 35. Furthermore, when the amount of hydrogen stored in the hydrogen tank 35 exceeds a set upper limit, the control unit 50d may supply only H2 to the fuel tower 20 without supplying CH4, in order to promote H2 consumption.

[0075] Sixth Embodiment 10 is a schematic block diagram of a chemical looping combustion system (combustion system) 100e of the sixth embodiment. The combustion system 100e of the sixth embodiment differs from the combustion system 100d of the fifth embodiment in that O2 generated in the water electrolysis device 30 is supplied to the air tower side loop seal unit 60 instead of the fuel tower 20. In the sixth embodiment, only the configurations different from those of the fifth embodiment will be described, and descriptions of the same configurations will be omitted.

[0076] When the water electrolysis device 30e is generating H2 and O2 by water electrolysis, the control unit 50e of the sixth embodiment stores the generated H2 in the hydrogen tank 35 and supplies the generated O2 to the air tower side loop seal unit 60. The flow rate of O2 supplied to the air tower side loop seal unit 60 is defined as Q ULS_O2 When the flow rate is defined as ULS_O2 is the constant k5 and the flow rate Q of O2 flowing into the fuel tower 20. FR_O2 Using the above, it is expressed as the following equation (15): where constant k5 is 1 or more.

[0077]

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[0078] In the above formula (15), when all of the O2 supplied to the air tower side loop seal unit 60 flows into the fuel tower 20, k5 is 1. On the other hand, when all of the O2 supplied to the air tower side loop seal unit 60 flows into the oxidation tower 10, k5 is infinity. Therefore, the control unit 50e determines the flow rate Q of O2 determined from formula (15) FR_O2 is used to control the various flow rates supplied to the fuel tower 20, as in the flow rate control flow shown in FIG. 9 of the fifth embodiment.

[0079] <Modifications of the embodiment> The present invention is not limited to the above-described embodiment, and can be implemented in various forms without departing from the spirit of the present invention, including, for example, the following modifications: In the above-described embodiment, part of the configuration realized by hardware may be replaced by software, and conversely, part of the configuration realized by software may be replaced by hardware.

[0080] Although the first to sixth embodiments described above are examples of chemical-looping combustion systems, the chemical-looping combustion system can be modified as long as it includes an oxidation tower 10 that oxidizes metal particles (mg) and a fuel tower 20 that reduces the metal particles (mg) using carbon-containing compounds and H2 supplied as fuel. For example, the combustion system 100 may not include the air tower-side loop seal unit 60 or the fuel tower-side loop seal unit 70. In the combustion system 100a of the second embodiment, H2 and O2 generated by the water electrolysis device 30 are supplied to the fuel tower 20. However, the supplied H2 and O2 may be supplied from other devices or gas storage tanks rather than being generated by water electrolysis. The power supply device PW included in the combustion system 100d of the fifth embodiment described above is a solar cell. However, known devices, such as power sources using renewable energy, can be used as power sources with variable power supply. The power supply device PW may also be an external power source not included in the combustion system 100d.

[0081] The O2-containing gas supplied to the oxidation tower 10 may be other than air. In other words, the oxidation tower 10 is an air tower to which oxygen-containing air is supplied. The combustion system 100 may be equipped with a heater 25 (FIG. 3), and the heating of the heater 25 may be utilized in addition to the heating provided by the reduction reaction of the metal particles mg with H2 and the oxidation reaction of the metal particles mg with O2 within the fuel tower 20.

[0082] Well-known materials other than Fe3O4 may be used as the metal particles mg circulating through the combustion system 100. For example, as a reaction formula for reducing the oxidized metal particles mg with H2, Ni or FeTiO3 shown in the following reaction formulas (16) and (17) may be used as the metal particles mg.

[0083]

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[0084] Furthermore, the carbon-containing compound supplied as fuel to the fuel tower 20 may be C2H6 or C3H8 other than the hydrocarbon CH4, or may be a compound other than a hydrocarbon, and well-known materials can be used. For example, when C2H6 is used as the carbon-containing compound, the reaction formula for the reduction of Fe2O3 as the oxidized metal particles mg is expressed as the following formula (18).

[0085]

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[0086] 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.

[0087] The present invention can also be realized in the following forms. [Application example 1] 1. A chemical looping combustion system comprising: an oxidation tower for oxidizing metal particles; a fuel tower to which hydrogen and a carbon-containing compound are supplied as fuel, and to which the oxidized metal particles are supplied from the oxidation tower, and which reduces the metal particles using the fuel; A chemical looping combustion system comprising: [Application example 2] The chemical looping combustion system according to Application Example 1, further comprising: a temperature acquisition unit that acquires a temperature inside the fuel tower; a control unit that determines a flow rate of a compound containing hydrogen and carbon to be supplied to the fuel tower using a difference between the temperature acquired by the temperature acquisition unit and a predetermined temperature; A chemical looping combustion system comprising: [Application example 3] The chemical looping combustion system according to Application Example 1 or Application Example 2, further comprising: It has a water electrolysis unit that electrolyzes water to produce hydrogen and oxygen, The water electrolysis unit supplies the produced hydrogen and oxygen to the fuel tower, forming a chemical looping combustion system. [Application example 4] The chemical looping combustion system according to any one of Application Examples 1 to 3, further comprising: a loop seal disposed downstream of the oxidation tower and upstream of the fuel tower, the loop seal suppressing gas inflow from the oxidation tower to the fuel tower; The water electrolysis unit is supplying the produced hydrogen to the fuel tower; A chemical looping combustion system that supplies generated oxygen to the loop seal instead of the fuel tower. [Application example 5] The chemical looping combustion system according to any one of Application Examples 1 to 4, further comprising: a hydrogen tank that stores hydrogen generated by the water electrolysis unit; The control unit When hydrogen and oxygen are generated by the water electrolysis unit, the generated oxygen is supplied to the fuel tower, and at least a portion of the generated hydrogen is stored in the hydrogen tank; A chemical looping combustion system that supplies hydrogen stored in the hydrogen tank to the fuel tower when hydrogen and oxygen are not being produced by the water electrolysis unit. [Explanation of symbols]

[0088] 10...Oxidation tower 10S...Oxidation tower seal 15...Cyclone 20…Fuel tower 20S...Fuel tower seal 26...Temperature sensor 25...Heater 30,30d,30e...Water electrolysis device (water electrolysis part) 35...Hydrogen tank 40...Dehydrator 50, 50d, 50e...Control section 60...Air tower side loop seal (loop seal) 60S...Seal for air tower side loop seal 70...Fuel tower side loop seal 70S...Fuel tower loop seal 100, 100a, 100b, 100c, 100d, 100e...Combustion system 100x: Comparative example combustion system PW: Variable power supply equipment Q FR_H2 ...hydrogen flow rate Q FR_O2 …oxygen flow rate Q FR_HC …methane flow rate T FR ...Temperature inside the fuel tower T FR_tar …Target temperature mg…metal particles

Claims

1. 1. A chemical looping combustion system comprising: an oxidation tower for oxidizing metal particles; a fuel tower to which hydrogen and a carbon-containing compound are supplied as fuel, and to which the oxidized metal particles are supplied from the oxidation tower, and which reduces the metal particles using the fuel; a water electrolysis unit that electrolyzes water to generate hydrogen and oxygen; Equipped with The water electrolysis unit supplies the produced hydrogen and oxygen to the fuel tower, forming a chemical looping combustion system.

2. 10. The chemical looping combustion system of claim 1, further comprising: a temperature acquisition unit that acquires a temperature inside the fuel tower; a control unit that determines a flow rate of a compound containing hydrogen and carbon to be supplied to the fuel tower using a difference between the temperature acquired by the temperature acquisition unit and a predetermined temperature; A chemical looping combustion system comprising:

3. The chemical looping combustion system according to claim 1 or 2, further comprising: a loop seal disposed downstream of the oxidation tower and upstream of the fuel tower, the loop seal suppressing gas inflow from the oxidation tower to the fuel tower; The water electrolysis unit is supplying the produced hydrogen to the fuel tower; A chemical looping combustion system that supplies generated oxygen to the loop seal instead of the fuel tower.

4. 3. The chemical looping combustion system of claim 2, further comprising: a hydrogen tank that stores hydrogen generated by the water electrolysis unit; The control unit When hydrogen and oxygen are generated by the water electrolysis unit, the generated oxygen is supplied to the fuel tower, and at least a portion of the generated hydrogen is stored in the hydrogen tank; A chemical looping combustion system that supplies hydrogen stored in the hydrogen tank to the fuel tower when hydrogen and oxygen are not being produced by the water electrolysis unit.

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