JP2024148424A - Chemical Looping Combustion System - Google Patents

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

The present invention relates to a chemical looping combustion system.

A chemical looping combustion system capable of essentially separating carbon dioxide is 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 to carbon dioxide.

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 in the fuel tower. In addition, loop seals are placed 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.

Special Publication No. 2013-522149

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

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 radiation loss. In addition, energy is required to generate the steam to be supplied into the loop seal. For this reason, there has been a demand to further improve the overall energy efficiency of the chemical looping combustion system. However, Patent Document 1 does not mention compensation for the heat lost in the fuel reactor or loop seals.

The present invention has been made to solve at least some of the above problems, and aims to improve the energy efficiency of the entire chemical looping combustion system.

The present invention has been made to solve at least some of the above problems, and can be realized in the following form.

(1) According to one aspect of the present invention, a chemical looping combustion system is provided. The chemical looping combustion system includes an oxidation tower that oxidizes metal particles, and a fuel tower that is supplied with hydrogen and a compound containing carbon as fuel, and that receives the oxidized metal particles from the oxidation tower and reduces the metal particles using the fuel.

According to this configuration, an endothermic reaction occurs in the fuel tower as the oxidized metal particles are reduced by the carbon-containing compound as fuel. Meanwhile, a weakly exothermic reaction occurs as the hydrogen supplied to the fuel tower in addition to the carbon-containing compound reduces the oxidized metal particles. 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 of the weakly exothermic reaction caused by hydrogen reducing the metal particles. In this configuration, the inside of the fuel tower is directly heated by the weakly exothermic reaction, so there is less heat loss compared to, for example, heating the inside of the fuel tower from the outside with a heater or the like. As a result, the energy efficiency of the entire system is improved compared to when only the carbon-containing compound is supplied to the fuel tower as fuel.

(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 weak exothermic reaction in which metal particles are reduced to hydrogen according to the temperature inside the fuel tower, and controls the amount of metal particles to be 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.

(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 in the fuel tower. The fuel tower is heated by an exothermic reaction caused by the oxygen oxidizing the metal particles. Unlike the oxygen in the air, the oxygen generated by water electrolysis does not contain impurities such as nitrogen, so high-purity carbon dioxide can be recovered 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.

(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 suppressing inflow of gas from the oxidation tower to 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. It is preferable that a gas is supplied into the loop seal to promote the flow of metal particles and prevent condensation and adhesion between the metal particles. Furthermore, it is preferable that the gas supplied into the loop seal does not contain impurities such as nitrogen, since it may flow into the fuel tower. The oxygen supplied into the loop seal suppresses the inflow of impurities such as nitrogen that flow from the oxidation tower into the loop seal. Furthermore, by supplying oxygen into the loop seal, it is not necessary to supply other gases (e.g., water vapor) 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 metal particles in the fuel tower to heat the fuel tower, thereby improving the energy efficiency of the entire system of this configuration.

(5) The chemical looping combustion system of the above aspect may further include a hydrogen tank for storing 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 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 to oxidize metal particles and cause an exothermic reaction. As a result, the amount of heat lost due to the reduction reaction of the carbon-containing compound in the fuel tower is compensated for by the exothermic reaction. When power is not supplied and the water electrolysis unit does not perform water electrolysis, the hydrogen stored in the hydrogen tank is supplied to the fuel tower, and the amount of heat lost due to the reduction reaction of the carbon-containing compound is compensated for by the weak exothermic reaction. That is, according to this configuration, oxygen, a by-product of water electrolysis, is effectively used according to the amount of power supplied to the water electrolysis unit, and when power is not supplied, the hydrogen stored in the hydrogen tank is used to heat the inside of the fuel tower. As a result, the energy efficiency of the entire system is improved.

The present invention can be realized in various forms, for example, in the form of 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, a non-transitory storage medium that stores the computer program, etc.

FIG. 1 is a schematic block diagram of a chemical looping combustion system according to one embodiment of the present invention. FIG. 1 is an explanatory diagram of the principle of chemical looping combustion. FIG. 2 is a schematic block diagram of a chemical looping combustion system of a comparative example. FIG. 5 is a schematic block diagram of a chemical looping combustion system according to a second embodiment. FIG. 11 is a schematic block diagram of a chemical looping combustion system according to a third embodiment. FIG. 13 is a schematic block diagram of a chemical looping combustion system according to a fourth embodiment. 13 is a flowchart of a fuel flow rate control method according to a fourth embodiment. FIG. 13 is a schematic block diagram of a chemical looping combustion system according to a fifth embodiment. 13 is a flowchart of a fuel flow rate control method according to a fifth embodiment. FIG. 13 is a schematic block diagram of a chemical looping combustion system according to a sixth embodiment.

First Embodiment
FIG. 1 is a schematic block diagram of a chemical looping combustion system (hereinafter, simply referred to as a "combustion system") 100 according to an embodiment of the present invention. In the combustion system 100, an air tower side loop seal (loop seal) 60 arranged between an oxidation tower 10 for oxidizing metal particles mg and a fuel tower 20 for reducing metal particles mg suppresses nitrogen flowing from the oxidation tower 10 to the fuel tower 20, and high-purity carbon dioxide (CO ₂ ) is recovered from the fuel tower 20. In a conventional chemical looping combustion system, the temperature in the fuel tower 20 is lowered by an endothermic reaction caused by the reduction of metal particles mg and hydrocarbons (compounds containing carbon) in the fuel tower 20, so the inside of the fuel tower 20 is heated by an external heater. In contrast, in this embodiment, hydrogen (H ₂ ) is supplied as fuel to the fuel tower 20 in addition to hydrocarbons. Since the reduction reaction between H ₂ and metal particles mg is a weakly exothermic reaction, the reaction suppresses the temperature drop in the fuel tower 20. The weakly exothermic reaction using _H2 directly heats the inside of the fuel tower 20, and therefore the heat loss is smaller than that of an external heater. As a result, the energy efficiency of the entire combustion system 100 of this embodiment can be improved.

In the combustion system 100, metal particles (mg) are circulated to carry oxygen ( _O2 ) in the air from the oxidation tower 10 to the fuel tower 20 by repeating oxidation in the oxidation tower 10 and reduction in the fuel tower 20. In this embodiment, an example in which an oxidation reaction of _Fe3O4 is used as the metal particles (mg ₎ is described. 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 an oxidation tower 10, a fuel tower 20, an air tower side loop seal unit 60, a fuel tower side loop seal unit 70, a cyclone 15, and a dehydrator 40.

The oxidation tower 10 uses air containing _O2 to oxidize _Fe3O4 by causing 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, and the inside of the oxidation tower 10 is heated to approximately 1000 degrees Celsius (°C).

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 multiple 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. On the other hand, the size of the holes provided in the seal 10S is smaller than the metal particles mg, so that the metal particles mg are prevented from passing through the seal 10S and leaking out of the oxidation tower 10. The gas flow velocity moving vertically upward in the oxidation tower 10 is set to a terminal velocity at which the resistance of gravity and the gas flow are balanced, or a velocity greater than the terminal velocity.

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 by 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 composed of N ₂ because O ₂ has been reduced due to 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 section 60 through a pipe extending vertically downward provided in the center part of the cyclone 15 as shown in FIG. 1.

As shown in FIG. 1, the air tower side loop seal section 60 is disposed 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 section 60. The seal 60S is a member with multiple small holes. The small 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 (hatched portion) formed of multiple metal particles mg is formed on the upper surface of the seal 60S. The reason for using water vapor here is that even if water vapor flows into the fuel tower 20, it can be removed by the dehydrator 40.

In the air tower side loop seal section 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 connected to the downstream side of the air tower side loop seal section 60. Since water vapor is supplied into the air tower side loop seal section 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.

A fluidized bed that flows from the air tower side loop seal part 60 to the fuel tower 20 is arranged in the piping that connects the air tower side loop seal part 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 part 60 move to the fuel tower 20.

In this embodiment, the fuel tower 20 is supplied with hydrogen ( _H2 ) and methane ( _CH4 ) as fuel, as well as with a gas containing the 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.

As shown in FIG. 1, the fuel tower 20 has a cylindrical shape that extends vertically. A seal 20S is provided vertically below the fuel tower 20. The seal 20S is a member with multiple 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 information from the fuel tower 20 so that metal particles mg do not fly out.

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.

In the fuel tower 20 to which _H2 as fuel is supplied together with _CH4 , _{Fe2O3 ,} which is oxidized metal particles mg, is reduced to _Fe3O4 by _H2 as shown in the following formula (3 ₎ . The reduction reaction shown in 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.

When the oxidation reaction in the oxidation tower 10 represented by the above formula (1) and the reduction reaction of _CH4 in the fuel tower 20 represented by the above formula (2) are taken as the sum, the reactions in the oxidation tower 10 and the fuel tower 20, including the reduction reaction by _CH4 in the 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 the metal particles mg and the reduction of the metal particles mg by _CH4 (the sum of the heat generated by the oxidation tower 10 and the heat absorbed by the fuel tower 20) is the same as the combustion of _CH4 .

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, the destination where _{the CO2} will be used is a storage tank where the _CO2 is liquefied or pressurized and stored.

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 FIG. 1.

The fuel tower side loop seal section 70, to which the metal particles mg are supplied from the fuel tower 20, is arranged downstream of the fuel tower 20 and upstream of the oxidation tower 10. The fuel tower side loop seal section 70 has the same configuration as the air tower side loop seal section 60. A seal 70S is provided vertically below the fuel tower side loop seal section 70. The seal 70S is a member with multiple fine holes. In the fuel tower side loop seal section 70, water vapor is supplied from vertically below the seal 70S. The supplied water vapor passes through the seal 70S and flows into the oxidation tower 10 connected to the downstream side of the fuel tower side loop seal section 70. A fluidized bed that flows from the fuel tower side loop seal section 70 to the oxidation tower 10 is arranged in the piping connecting the fuel tower side loop seal section 70 and the oxidation tower 10. Due to the flow of the fluidized bed, the metal particles mg in the cylindrical fuel tower side loop seal section 70 move 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.

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.

In the oxidation tower 10, air is supplied as an oxidation 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 generated by the reduction reaction is supplied to the dehydrator 40. Note that when the metal particles mg are reduced by H2, no _CO2 is generated. The dehydrator 40 removes _H2O from the mixed gas, and the mixed gas containing high-purity _CO2 is supplied to the _CO2 utilization destination.

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, CH ₄ is supplied as fuel into the fuel tower 20x, and H ₂ is not supplied, as compared with the combustion system 100 shown in FIG. 1. Therefore, in the fuel tower 20x of the comparative example, a reduction reaction of metal particles mg by H ₂ does not occur, that is, a weak exothermic reaction between H ₂ and metal particles mg does not occur. In the comparative example, since the inside of the fuel tower 20 is not heated by the weak exothermic reaction, the combustion system 100x is provided with a heater 25 that heats the inside of the fuel tower 20.

In contrast, in the combustion system 100 of this embodiment, hydrogen (H ₂ ) and methane (CH ₄ ) are supplied to the fuel tower 20 as fuel. In the fuel tower 20, H ₂ and CH ₄ 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 CH ₄ reduces the oxidized metal particles mg. Meanwhile, H ₂ supplied to the fuel tower 20 in addition to CH ₄ reduces the oxidized metal particles mg, causing a weakly exothermic reaction. Therefore, all or part of the heat lost by the endothermic reaction caused by CH ₄ reducing the metal particles mg can be compensated for by the heat of the weakly exothermic reaction caused by H ₂ reducing the metal particles mg. Since the inside of the fuel tower 20 is directly heated by the weakly exothermic reaction, in this embodiment, the heat loss is smaller than that of heating using the heater 25 from the outside as in the comparative example. As a result, the energy efficiency of the entire combustion system 100 is improved compared to the case where only CH ₄ is supplied to the fuel tower 20 as fuel.

Second Embodiment
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 generate H ₂ and O _2. The combustion system 100a of the second embodiment is different from the combustion system 100 of the first embodiment in that the H ₂ supplied to the fuel tower 20 is H ₂ generated by water electrolysis in the water electrolysis device 30, and O ₂ generated by water electrolysis is supplied to the fuel tower 20. In the second embodiment, the configurations different from those of the first embodiment will be described, and the description of the same configurations will be omitted.

In the second embodiment, by supplying _O2 into the fuel tower 20, an exothermic reaction of reoxidation of the metal particles mg reduced in the fuel tower 20 occurs as expressed by the above formula (1). The inside of the fuel tower 20 is heated by the exothermic reaction due to the 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.

As described above, the water electrolysis device 30 of the second embodiment electrolyzes water to generate H ₂ and O _2. The generated H ₂ and O ₂ are supplied to the fuel tower 20. In the second embodiment, the O ₂ that flows into the fuel tower 20 reoxidizes the metal particles mg that have been reduced by CH ₄ or H ₂ in 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 O ₂ . Unlike the O ₂ in the air, the O ₂ generated by water electrolysis does not contain impurities such as N ₂ , so that high-purity CO ₂ can be recovered from the fuel tower 20. Furthermore, since O ₂ is a by-product of the H ₂ generated by water electrolysis, the energy efficiency of the entire combustion system 100a is improved.

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 is different 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 part 60 instead of the fuel tower 20. In the third embodiment, the configurations different from the second embodiment will be described, and the description of the same configurations will be omitted.

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 section 60. When _O2 is supplied to the air tower side loop seal section 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 heat generated by the oxidation reaction between _O2 and the metal particles mg.

As described above, in the third embodiment, O ₂ generated in the water electrolysis device 30b is supplied to the air tower side loop seal part 60 instead of the fuel tower 20. In the air tower side loop seal part 60, it is preferable to supply a gas such as water vapor to promote the flow of the metal particles mg and prevent the metal particles mg from condensing and adhering to each other. Furthermore, since the gas supplied to the air tower side loop seal part 60 may flow into the fuel tower 20, it is preferable that it does not contain impurities such as N _2. The O ₂ supplied to the air tower side loop seal part 60 suppresses the inflow of impurities such as N ₂ that are trying to flow from the oxidation tower 10 into the air tower side loop seal part 60. In addition, by supplying O ₂ into the air tower side loop seal part 60, the flow rate of water vapor to prevent the inflow of impurities can be reduced. That is, the O ₂ supplied to the air tower side loop seal part 60 is a by-product of H ₂ generated by water electrolysis, and reoxidizes the metal particles mg in the fuel tower 20 to heat the inside of the fuel tower 20, thereby improving the energy efficiency of the entire combustion system 100b.

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, the configuration and control different from those of the first embodiment will be described, and the description of the same configuration and the like will be omitted.

6, the combustion system 100c of the fourth embodiment further includes a temperature sensor (temperature acquisition unit) 26 that detects the temperature _TFR in the fuel tower 20, and a control unit 50 that controls the flow rates of _CH4 and _H2 supplied to the fuel tower 20 using the detected temperature _TFR in the fuel tower 20. The temperature sensor 26 of this embodiment is a thermocouple inserted in the fuel tower 20.

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 determines the flow rate QFR_H2 of H2 and the flow rate _{QFR_HC} of _CH4 supplied to the fuel tower 20 according to the difference between the temperature _TFR in the fuel tower 20 and a target temperature _{TFR_tar , which} is a predetermined temperature.

The control unit 50 of this embodiment determines the flow rate QFR_H2 of H2 to be supplied to the fuel tower 20 Δt seconds after the current time t by substituting the temperature _TFR in the fuel tower 20 detected by the temperature _{sensor 25} into the following formula (5). Note that _k1 in formula (5) is a positive constant and can be set arbitrarily by the user.

Here, both _CH4 and _H2 as fuel react with the oxidized metal particles mg. Therefore, in this embodiment, when the flow rate _{QFR_H2} of _H2 is increased, the control unit 50 decreases the flow rate _{QFR_HC} of the other _CH4 . On the other hand, when the flow rate _{QFR_H2} of _H2 is decreased, the control unit 50 increases the flow rate _{QFR_HC} of the other _CH4 . Here, the flow rate _{QFR_HC} (t+Δt) of _CH4 Δt seconds after time t is expressed as in the following formula (6).

ａ₁：１ｍｏｌのＣＨ₄で還元できる金属粒子量（ｍｏｌ（金属）／ｍｏｌ（ＣＨ₄））
ｂ₁：１ｍｏｌのＨ₂で還元できる金属粒子量（ｍｏｌ（金属）／ｍｏｌ（Ｈ₂））
本実施形態では、上記式（２），（３）の還元反応が発生するため、上記式（５）において、ａ₁＝１２，ｂ₁＝３である。

_a1 : Amount of metal particles that can be reduced by 1 mol of _CH4 (mol (metal)/mol ( _CH4 ))
_b1 : Amount of metal particles that can be reduced by 1 mol of _H2 (mol (metal)/mol ( _H2 ))
In this embodiment, since the reduction reactions of the above formulas (2) and (3) occur, a ₁ =12 and b ₁ =3 in the above formula (5).

7 is a flowchart of the fuel flow rate control method of 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 acquires the temperature _TFR in the fuel tower 20 via the temperature sensor 26 (step S2). The control unit 50 determines the flow rate _{QFR_H2} of _H2 to be supplied to the fuel tower 20 by substituting the temperature _TFR into the above formula (5) (step S3). _H2 at the determined flow rate _{QFR_H2} is supplied to the fuel tower 20.

The control unit 50 determines the flow rate of _CH4 to be supplied to the fuel tower 20 by substituting the determined flow rate _{QFR_H2} of _H2 into the above formula (6) (step S4). _CH4 at the determined flow rate _{QFR_HC} is supplied to the fuel tower 20. The control unit 50 determines whether or not a predetermined time Δt has elapsed since the determination of the flow rate _{QFR_HC} of _CH4 (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.

When it is determined that a predetermined time Δt has elapsed (step S5: YES), the control unit 50 determines whether or not to end the flow control flow (step S6). The control unit 50 determines whether or not to end the flow control flow, for example, by determining whether or not an end operation has been received from the user. When it is determined that the flow control flow is not to be ended (step S6: NO), the processing from step S2 onwards is repeated. When it is determined that the flow control flow is to be ended (step S6: YES), the flow control flow is ended. Note that the determination of whether or not to end the flow control flow may be made by interrupting the processing while other processing is being performed.

As described above, the control unit 50 of this embodiment determines the CH4 flow rate _{QFR_HC} and the H2 flow rate _{QFR_H2} to be supplied to the fuel tower 20 using the difference between the temperature TFR in the fuel tower 20 detected by the temperature sensor 26 and the target temperature _{TFR_tar} . The flow rate ratio of the fuel _H2 and _CH4 is controlled according to the temperature _TFR in the fuel tower _20. This controls the heating in the fuel tower 20 using the _weak exothermic reaction caused by the reduction of the metal particles mg to _H2 according to the temperature _TFR in the fuel tower 20, and controls the amount of the reduced metal particles mg. As a result, the temperature in the fuel tower 20 can be controlled to approach the target temperature _{TFR_tar} , and the oxidized metal particles mg can be reduced.

<Modification of the Fourth Embodiment>
In the fourth embodiment, the method of determining the flow rate _{QFR_H2} of _H2 and the flow rate _{QFR_HC} of _CH4 supplied to the fuel tower 20 is one example and can be modified. For example, the control unit 50 may supply the flow rate _{QFR_H2} of _H2 and the flow rate _{QFR_HC} of _CH4 determined by the following equations (7) and (8) to the fuel tower 20. Note that _k2 and _b2 in equation (7) and _{QFR_HC_0} in equation (8) are constants that are set arbitrarily.

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 the control unit 50d controls the flow rate of the gas supplied to the fuel tower 20 in response to the fluctuating flow rates of _H2 and _O2 . In the fifth embodiment, the configuration and control different from those of the second embodiment will be described, and the description of the same configuration and the like will be omitted.

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, and does not supply power to the water electrolysis device 30d at night.

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 _{QFR_HC} of _CH4 supplied to the fuel tower 20, the flow rate _{QFR_O2} of _O2 , and the flow rate _{QFR_H2} of _{H2 supplied from the hydrogen tank 35 to the fuel tower 20 by controlling the opening and closing of various valves not shown in Fig. 8. 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 the _H2 stored in the hydrogen tank 35 together with _CH4 to the fuel tower 20. In addition, a part or all of the H ₂ produced during water electrolysis may be supplied to the fuel tower 20.

The control unit 50d of this embodiment determines the flow rate _{QFR_O2} of _O2 to be supplied to the fuel tower 20 by the following formula (9). Note that _{QO2_WL} in formula (9) is the amount of _O2 produced by the water electrolysis device 30d at time t. Also, _k3 and _b3 are constants that may be arbitrarily set by the user.

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 supplies _H2 at a flow rate _{QFR_H2} determined by the following formula (10) as the additional fuel.

ｃ：１ｍｏｌのＨ₂の完全燃焼に必要なＯ₂のｍｏｌ量（ｍｏｌ（Ｏ₂）／ｍｏｌ（Ｈ₂））

c: The amount of moles of _O2 required for complete combustion of 1 mol of _H2 (mol( _O2 )/mol( _H2 ))

Since the chemical equation for _H2 combustion is expressed by the following equation (11), c in equation (10) is 0.5.

In the above formula (9), if the following relational expression (12) holds, the inside of the fuel tower 20 cannot be heated sufficiently just by supplying _O2 generated by water electrolysis at a flow rate _{QFR_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 determines the flow rate _{QFR_H2} of _H2 supplied to the fuel tower 20 by the following formula (13) instead of the above formula (10). Furthermore, the control unit 50d determines the flow rate _{QFR_HC} of _CH4 supplied to the fuel tower 20 by the following formula (14). _k4 and _b4 are constants that may be set arbitrarily by the user.

FIG. 9 is a flowchart of the fuel flow rate control method of 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 acquires the temperature _TFR in the fuel tower 20 via the temperature sensor 26 (step S12). The control unit 50d determines whether or not power is supplied from the power supply device PW to the water electrolysis device 30d (step S13). When it is determined that power is not supplied to the water electrolysis device 30d (step S13: NO), the control unit 50d determines the flow rate _{QFR_O2} of _O2 supplied to the fuel tower 20 to be zero (step S15A). In this case, the control unit 50d determines the flow rate _{QFR_H2} of _H2 supplied to the fuel tower 20 by substituting the temperature _TFR into the above formula (5) in the same manner as in the fourth embodiment (step S16A). _H2 at the determined flow rate _{QFR_H2} is supplied to the fuel tower 20. In addition, the control unit 50d determines the flow rate of _CH4 to be supplied to the fuel tower 20 by substituting the determined flow rate _{QFR_H2} of _H2 into the above formula (6) (step S17A). _CH4 at the determined flow rate _{QFR_HC} is supplied to the fuel tower 20.

When it is determined in the process of step S13 that power is being supplied to the water electrolysis device 30d (step S13: YES), the control unit 50d determines whether the inside of the fuel tower 20 can be sufficiently heated simply by supplying the flow rate _{QFR_O2} of _O2 generated by water electrolysis to the fuel tower 20 (step S14). In this embodiment, the control unit 50d determines whether the flow rate _{QO2_WL} of _O2 currently generated by water electrolysis, which is expressed on the left side of the above equation (12), is equal to or greater than the right side. In other words, it is determined whether sufficient _O2 is being generated by water electrolysis.

In the process of step S14, when it is determined that sufficient O ₂ is generated by water electrolysis and the inside of the fuel tower 20 can be sufficiently heated (step S14: YES), the control unit 50d determines the flow rate Q _{FR_HC} of CH ₄ to a constant flow rate Q _{FR_HC_0} (step S15B). CH ₄ at the determined flow rate Q _{FR_HC_0} is supplied to the fuel tower 20. The control unit 50d determines the flow rate Q FR_O2 of O ₂ supplied to the fuel tower 20 using the above formula (9) (step S16B). O ₂ at the determined flow rate Q _{FR_O2} is supplied to the fuel tower 20. The control unit 50d determines the flow rate Q _{FR_H2} of H ₂ supplied to the fuel tower 20 by substituting the flow rate Q _{FR_O2} determined by the above formula (9) into the above formula (10 ₎ (step S17B). H ₂ at the determined flow rate Q _{FR_H2} is supplied to the fuel tower.

In the process of step S14, when it is determined that sufficient O ₂ is not generated by water electrolysis and the inside of the fuel tower 20 cannot be sufficiently heated (step S14: NO), the control unit 50d determines the flow rate Q _{FR_O2} of O ₂ to be supplied to the fuel tower 20 using the above formula (9) (step S15C). O ₂ at the supplied flow rate Q _{FR_O2} is supplied to the fuel tower 20. The control unit 50d determines the flow rate Q _{FR_H2} of H ₂ to be supplied to the fuel tower 20 by substituting the flow rate Q _{FR_O2} of O ₂ determined by the above formula (9) into the above formula (13) (step S16C). Hydrogen at the determined flow rate Q _{FR_H2} is supplied to the fuel tower 20. The control unit 50d determines the flow rate Q _{FR_HC} of CH ₄ to be supplied to the fuel tower 20 using the above formula (14) (step S17C). CH ₄ at the determined flow rate Q _{FR_HC} is supplied to the fuel tower 20.

When any of steps S17A to S17C has been performed, the control unit 50d determines whether or not to end the flow control flow (step S18). If it is determined that the flow control flow should not be ended (step S18: NO), the processes from step S12 onwards are repeated. If it is determined that the flow control flow should be ended (step S18: YES), the flow control flow ends. Note that the determination of whether or not to end the flow control flow may be made by interrupting the execution of other processing.

As described above, when the water electrolysis device 30d performs water electrolysis to generate H ₂ and O ₂ , the control unit 50d of this embodiment supplies the generated O ₂ together with CH ₄ to the fuel tower 20 and stores the generated H ₂ in the hydrogen tank 35. On the other hand, when the water electrolysis device 30d does not perform water electrolysis, the control unit 50d supplies the H ₂ stored in the hydrogen tank 35 together with CH ₄ 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 H ₂ and O ₂ from the water electrolysis device 30d is controlled according to the amount of power supply. When power is supplied and the water electrolysis device 30d generates H ₂ and O ₂ , the generated H ₂ is stored in the hydrogen tank 35. On the other hand, the generated O ₂ is supplied to the fuel tower 20 and oxidizes the metal particles mg to cause an exothermic reaction. As a result, the amount of heat lost by the reduction reaction of CH ₄ 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 a weak exothermic reaction. That is, according to this embodiment, oxygen, a by-product of water electrolysis, is effectively utilized according to the amount of power supplied to the water electrolysis device 30d, and when there is no power supply, _H2 stored in the hydrogen tank 35 is used to heat the inside of the fuel tower 20. As a result, the energy efficiency of the entire combustion system 100d is improved.

<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.

In the fifth embodiment, the generated O ₂ is supplied to the fuel tower 20 during the same period during which the water electrolysis device 30d generates O ₂ , but there may be a period during which the generated O ₂ is not supplied to the fuel tower 20. For example, when the amount of H ₂ stored in the hydrogen tank 35 is equal to or less than a predetermined value, the control unit 50d may release the O ₂ generated by water electrolysis to the atmosphere and store the generated H ₂ 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 for heating 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 H ₂ to the hydrogen tank 35. Furthermore, when the amount of storage in the hydrogen tank 35 exceeds a set upper limit value, the control unit 50d may supply only H ₂ to the fuel tower 20 without supplying CH ₄ to promote consumption of H ₂ .

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 is different 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 part 60 instead of the fuel tower 20. In the sixth embodiment, the configurations different from those of the fifth embodiment will be described, and the description of the same configurations will be omitted.

When the water electrolysis device 30e generates _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. If the flow rate of _O2 supplied to the air tower side loop seal unit 60 is defined as _{QULS_O2} , the flow rate _{QULS_O2} is expressed as shown in the following formula (15) using a constant _k5 and the flow rate _{QFR_O2} of _O2 flowing into the fuel tower 20. Note that the constant _k5 is 1 or more.

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 uses the _O2 flow rate _{QFR_O2} determined from formula (15) to control various flow rates supplied to the fuel tower 20, as in the flow rate control flow shown in Figure 9 of the fifth embodiment.

<Modifications of the 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 present invention, for example, the following modifications are possible: In the above-described embodiment, a part of the configuration realized by hardware may be replaced by software, and conversely, a part of the configuration realized by software may be replaced by hardware.

In the above first to sixth embodiments, an example of a chemical looping combustion system has been described, but the chemical looping combustion system can be modified as long as it includes an oxidation tower 10 for oxidizing metal particles mg and a fuel tower 20 for reducing metal particles mg with a carbon-containing compound and H ₂ 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, H ₂ and O ₂ generated by the water electrolysis device 30 are supplied to the fuel tower 20, but the H ₂ and O ₂ supplied may not be generated by water electrolysis and may be supplied from other devices or tanks storing gas. The power supply device PW included in the combustion system 100d of the fifth embodiment is a solar cell, but a well-known device such as a power source using renewable energy can be adopted as a power source with a fluctuating power supply. The power supply device PW may be an external power source not included in the combustion system 100d.

The _O2- containing gas supplied to the oxidation tower 10 may be other than air. The oxidation tower 10 can also be described as an air tower to which air containing oxygen is supplied. The combustion system 100 may be equipped with a heater 25 (FIG. 3), and in addition to heating using the reduction reaction of metal particles mg by _H2 and the oxidation reaction of metal particles mg by _O2 in the fuel tower 20, the heating of the heater 25 may be utilized.

A known material other than _Fe3O4 may be used as the metal particles mg circulating through the combustion system 100. For example, Ni or _FeTiO3 shown in the following reaction formulas (16) and (17) as a reaction formula for reducing the oxidized metal particles mg with _H2 may be used as the metal particles mg.

The carbon-containing compound as fuel supplied to the _fuel tower 20 may be _C2H6 or _C3H8 other than _CH4, which is a hydrocarbon, or may be a compound other than a hydrocarbon, and known materials can be used. For example, when _C2H6 is used as the carbon- _containing compound, the reaction formula for reducing _Fe2O3 as the oxidized _metal particles _mg is expressed as the following formula (18).

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

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 compound containing carbon 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:
Equipped with a water electrolysis unit that electrolyzes water to produce hydrogen and oxygen,
The water electrolysis unit supplies generated hydrogen and oxygen to the fuel tower, thereby 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 an inflow of gas from the oxidation tower to the fuel tower;
The water electrolysis unit includes:
Supplying the produced hydrogen to the fuel tower;
A chemical looping combustion system that supplies generated oxygen to the loop seal instead of to 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 for storing hydrogen generated by the water electrolysis unit,
The control unit is
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 produced by the water electrolysis unit.

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 section)
35... Hydrogen tank 40... Dehydrator 50, 50d, 50e... Control unit 60... Air tower side loop seal unit (loop seal)
60S...Seal of air tower side loop seal section 70...Fuel tower side loop seal section 70S...Seal of fuel tower loop seal section 100, 100a, 100b, 100c, 100d, 100e...Combustion system 100x...Combustion system of comparative example PW...Variable power supply device Q _{FR_H2} ...Flow rate of hydrogen Q _{FR_O2} ...Flow rate of oxygen Q _{FR_HC} ...Flow rate of methane T _FR ...Temperature in fuel tower T _{FR_tar} ...Target temperature mg...Metal particles

Claims (5)

1. A chemical looping combustion system comprising:
an oxidation tower for oxidizing metal particles;
a fuel tower to which hydrogen and a compound containing carbon 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: 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: The chemical looping combustion system according to claim 1 or 2, further comprising:
Equipped with a water electrolysis unit that electrolyzes water to produce hydrogen and oxygen,
The water electrolysis unit supplies generated hydrogen and oxygen to the fuel tower, thereby forming a chemical looping combustion system. 4. The chemical looping combustion system of claim 3, further comprising:
a loop seal disposed downstream of the oxidation tower and upstream of the fuel tower, the loop seal suppressing an inflow of gas from the oxidation tower to the fuel tower;
The water electrolysis unit includes:
Supplying the produced hydrogen to the fuel tower;
A chemical looping combustion system that supplies generated oxygen to the loop seal instead of to the fuel tower. 5. The chemical looping combustion system of claim 4, further comprising:
A hydrogen tank for storing hydrogen generated by the water electrolysis unit,
The control unit is
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 produced by the water electrolysis unit.

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