JP5495010B2 - Magnesium oxide reduction method and reaction apparatus - Google Patents

Description

  The present invention relates to a magnesium oxide reduction method for reducing magnesium oxide powder to magnesium powder or magnesium hydride powder, and a reactor for carrying out the magnesium oxide reduction method.

Fuel cells are attracting attention as a means of solving environmental energy problems. Fuel cells use hydrogen H ₂ as an energy source and do not release greenhouse gases, environmental pollutants, etc. generated by burning fossil fuels, thus solving problems such as global warming, environmental pollution, and fossil fuel depletion Expected as a means.

As a method of storing hydrogen H ₂ is the energy source for fuel cells, high pressure cylinder system for storing hydrogen H ₂ into the cylinder at a high pressure of for example 350 atmospheres, with hydrogen H ₂ liquefied at -253 ° C. or less of cryogenic Examples thereof include a liquid hydrogen method for storing, a storage alloy method for storing hydrogen H ₂ in a hydrogen storage alloy, and the like. In particular, the storage alloy method does not need to store hydrogen H _{2 in} special conditions such as ultra-high pressure and cryogenic temperature, so it is easy to handle and highly safe, and has an excellent hydrogen storage capacity per unit volume. have.

Patent Document 1 discloses that a reaction vessel containing magnesium hydride MgH ₂ powder having an average particle size of less than 45 μm, a water storage vessel for supplying water to the reaction vessel, and ultrasonicating magnesium hydride MgH ₂ in the reaction vessel. And a sonic wave generating unit for generating power, and a power generation device that generates power using hydrogen H ₂ generated by hydrolysis of magnesium hydride MgH ₂ is disclosed.

Magnesium hydride MgH ₂ can be produced by holding magnesium Mg in a hydrogen H ₂ gas atmosphere and increasing or decreasing the temperature and pressure in the hydrogen H ₂ gas atmosphere (for example, Patent Document 2). However, since magnesium Mg has a very high reactivity, it becomes difficult to handle it safely if the average particle size is less than 45 μm. Further, since magnesium Mg has high ductility and malleability, it is difficult to grind itself to an average particle size of less than 45 μm. Therefore, first, magnesium hydride MgH ₂ coarse particles are produced using magnesium Mg raw material particles having an average particle diameter of 45 μm or more, and the produced magnesium hydride MgH ₂ coarse particles are reduced to less than 45 μm by an interparticle collision type jet pulverizer. By pulverizing, magnesium hydride MgH ₂ powder is produced.

On the other hand, when hydrogen H ₂ which is an energy source of the fuel cell is generated by hydrolysis of magnesium hydride, magnesium hydroxide Mg (OH) ₂ powder is generated as a residue, but magnesium hydroxide Mg (OH) An effective recycling method from ₂ powder to magnesium hydride MgH ₂ powder has not been proposed yet.

JP 2009-99534 A JP 2008-44832 A

  The present invention has been made in view of such circumstances. Magnesium oxide powder and methane obtained by heating and dehydration of magnesium hydroxide are supplied to a plasma furnace, and the magnesium oxide powder is reduced by plasma to obtain magnesium powder or An object of the present invention is to provide a magnesium oxide reduction method capable of producing magnesium hydride powder and enabling recycling from magnesium hydroxide powder to magnesium hydride powder, and a reaction apparatus for carrying out the magnesium oxide reduction method. And

The magnesium oxide reduction method according to the present invention supplies magnesium oxide powder and methane and / or hydrogen to a plasma reactor that generates thermal plasma of an inert gas, and generates the inert gas, methane and / or hydrogen. reducing the magnesium oxide magnesium powder in thermal plasma of the reducing atmosphere is, by condensing the magnesium reduced gas to form magnesium powder, after formation of the magnesium powder, the hydrogen to the plasma reactor The magnesium hydride powder is produced by supplying and bringing the magnesium powder in the plasma reactor into contact with hydrogen.

  The magnesium oxide reduction method according to the present invention is characterized in that the thermal plasma is generated using power from a power plant.

  The magnesium oxide reduction method according to the present invention provides a cylindrical torch electrode provided at an upper part of the plasma reactor, a torch nozzle surrounding the torch electrode, and a lower electrode facing the torch electrode, Magnesium oxide powder (or methane and / or hydrogen) is supplied through a torch electrode, and methane and / or hydrogen (or magnesium oxide powder) is supplied through the torch nozzle.

The reaction apparatus according to the present invention includes a plasma reactor, a cylindrical torch electrode provided at an upper portion of the plasma reactor, a torch nozzle surrounding the torch electrode, and the plasma so as to face the torch electrode. A lower electrode provided in a lower part of the reaction furnace, a power source for supplying electric power to the torch electrode and the lower electrode, and a first supply path for supplying magnesium oxide powder (or methane and / or hydrogen) through the torch electrode A second supply path for supplying methane and / or hydrogen (or magnesium oxide powder) through the torch nozzle, and magnesium oxide powder and methane and / or hydrogen through the first and second supply paths. A raw material supply unit for supplying to the plasma reactor, magnesium oxide powder, and methane and / or hydrogen are supplied to the plasma reactor. And then, as hydrogen is supplied to the plasma reactor, characterized in that it comprises a control unit for controlling the operation of the material supply unit.

In the present invention, thermal plasma in a reducing atmosphere is generated by the inert gas supplied to the plasma reactor and methane. Moreover, you may produce | generate the thermal plasma of a reducing atmosphere with an inert gas, methane, and hydrogen. Furthermore, thermal plasma in a reducing atmosphere may be generated by an inert gas and hydrogen.
Then, the magnesium oxide powder supplied to the thermal plasma is reduced to magnesium. When methane is supplied, when the temperature of the thermal plasma is about 2000 degrees, a plasma mainly composed of magnesium, carbon monoxide and hydrogen gas is obtained, and when magnesium is further cooled, gaseous magnesium is condensed, Magnesium powder and / or magnesium hydride powder is produced. Note that when methane is supplied, water is not contained in the main component of the plasma, so there is no possibility that magnesium will be oxidized again. Magnesium powder and / or magnesium hydride powder means magnesium powder, magnesium hydride powder, or magnesium powder and magnesium hydride powder.
Further, when methane and hydrogen are supplied or when hydrogen is supplied, magnesium powder and / or magnesium hydride powder is produced.

  In the present invention, when magnesium powder is produced by plasma reduction, the magnesium powder is hydrogenated by supplying hydrogen to the plasma reactor. Accordingly, magnesium hydride powder is produced.

  In the present invention, thermal plasma is generated using the power of the power plant. Therefore, for example, surplus power energy such as nuclear power plants and hydroelectric power plants, particularly nighttime power can be stored as magnesium powder or magnesium hydride powder.

In the present invention, magnesium oxide powder is supplied through a cylindrical torch electrode provided in the upper part of the plasma reactor, and methane and / or hydrogen is supplied through a torch nozzle surrounding the torch electrode. Therefore, the magnesium oxide powder and methane and / or hydrogen are supplied to the plasma reactor from approximately the same location and are plasma reduced. Magnesium powder obtained by plasma reduction accumulates in the lower electrode facing the torch electrode.
Similarly, methane and / or hydrogen may be supplied through a torch electrode, and magnesium oxide powder may be supplied through a torch nozzle.

  According to the present invention, magnesium powder or magnesium hydride powder can be produced by plasma reduction of magnesium oxide powder, and recycling from magnesium hydroxide powder to magnesium hydride powder becomes possible.

It is explanatory drawing which shows notionally the reduction method of a magnesium hydroxide powder and a magnesium oxide powder. It is a graph which shows the plasma composition of the mixed gas of magnesium oxide powder and methane. It is explanatory drawing which shows notionally the plasma reaction apparatus for enforcing the magnesium oxide reduction method. It is a flowchart which shows the reduction | restoration procedure of magnesium oxide powder.

The magnesium oxide reduction method according to the present embodiment enables magnesium hydride MgH ₂ particles having excellent hydrogen storage and release properties to function as a safe and economical clean energy carrier. . That is, the present invention is a technology that enables recycling of magnesium hydroxide Mg (OH) ₂ powder from which energy has been released to magnesium hydride MgH ₂ powder that has accumulated energy.

Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof.
FIG. 1 is an explanatory view conceptually showing a method for reducing magnesium hydroxide powder and magnesium oxide powder. First, magnesium hydroxide Mg (OH) ₂ powder to be reduced, methane CH _{4 as} a reducing agent, and argon Ar, and a plasma reactor (see, for example, FIG. 3) are prepared. Magnesium hydroxide Mg (OH) ₂ powder is recovered from a power generator using magnesium hydride MgH ₂ powder as a hydrogen source. The recovered magnesium hydroxide Mg (OH) ₂ powder is heated and dehydrated to produce a magnesium oxide MgO powder.

Next, a mixed gas of methane CH ₄ and argon Ar as a reducing agent is supplied to the plasma reactor 1, and power obtained by nuclear power generation or hydroelectric power generation is supplied to the plasma reactor 1, thereby reducing the heat of the reducing atmosphere. Generate plasma. Further, the magnesium oxide MgO powder is plasma-reduced to magnesium Mg by supplying the magnesium oxide MgO powder to the thermal plasma in the reducing atmosphere in the plasma reactor with argon Ar gas. The plasma reduction reaction of magnesium oxide MgO powder using methane CH ₄ gas as a reducing agent is represented by the following chemical formula (1).
MgO + CH ₄ = Mg (g) + 2H ₂ + CO (1)

FIG. 2 is a chart showing the plasma composition of a mixed gas of magnesium oxide MgO powder and methane CH ₄ . The chart shows the results of numerical calculations showing the composition of plasma and the amount of substance when a mixed gas of magnesium oxide 1 (mol) and methane 1 (mol) is turned into plasma at 1 (atm) and about 2000 (K). . As can be seen from the chart, the main components of the plasma are hydrogen H ₂ , carbon monoxide CO, and magnesium Mg. Moreover, only 0.55899 × 10 ⁻⁴ (mol) of water causing oxidation of magnesium exists, and it is considered that oxidation of magnesium Mg hardly proceeds.

Although it is conceivable to directly reduce the magnesium hydroxide Mg (OH) ₂ powder by plasma using hydrogen H ₂ as a reducing agent, as shown in the following formula (2), water is generated and thermal plasma is generated. When the temperature decreases, magnesium Mg is reoxidized.
Mg (OH) ₂ + H ₂ = Mg + 2H ₂ O (2)

In addition, it is conceivable to reduce the magnesium oxide MgO powder by plasma using hydrogen H ₂ as a reducing agent. However, as shown in the following formula (3), water is generated and the temperature of the thermal plasma is lowered. In this case, magnesium Mg is reoxidized.
MgO + H ₂ = Mg + H ₂ O (3)

Next, as shown in FIG. 1, by reducing the temperature of the plasma gas generated by the plasma reduction, solid magnesium Mg powder that has undergone nuclear condensation is obtained. After the solid magnesium Mg powder is produced, hydrogen H ₂ is supplied to the plasma reactor to bring the magnesium Mg powder into contact with the hydrogen H ₂ to produce magnesium hydride MgH ₂ powder. Since magnesium Mg is in a powder form, magnesium Mg is immediately hydrogenated under a predetermined temperature condition. Hydrogenation of magnesium Mg powder is represented by the following formula (4).
Mg + H ₂ = MgH ₂ (4)

  FIG. 3 is an explanatory view conceptually showing a plasma reactor for carrying out the magnesium oxide reduction method.

  The plasma reactor includes a hollow cylindrical plasma reactor 1, a plasma torch 2 composed of a torch electrode 21 and a torch nozzle 22 provided at the upper part of the plasma reactor 1, and a lower part of the plasma reactor 1. The lower electrode 3, the power source 4 that supplies power between the torch electrode 21 and the lower electrode 3, the raw material supply unit 5 that supplies various raw materials to the plasma reactor 1, and the control unit that controls the operation of the raw material supply unit 5 6 and an operation unit 7.

The plasma reactor 1 includes a disc-shaped bottom portion, a peripheral wall formed substantially perpendicularly from the periphery of the bottom portion, and a disc-shaped top plate portion formed on the upper end portion of the peripheral wall. A cylindrical torch electrode 21 having an open top and bottom is provided at an upper portion of the plasma reactor 1, that is, a substantially central portion of the top plate portion. The plasma reactor 1 is externally connected to the plasma reactor 1 through the torch electrode 21. 1 is communicated so that a mixed gas of methane CH ₄ and argon Ar can be supplied. A torch nozzle 22 is provided outside the torch electrode 21 so as to surround the torch electrode 21. The torch nozzle 22 has a cylindrical shape whose bottom is narrowed, and the plasma reaction furnace 1 communicates with the inside of the plasma reaction furnace 1 through the torch nozzle 22 so that magnesium oxide MgO powder, argon Ar, and hydrogen H ₂ can be supplied from the outside. Yes. In addition, an air supply hole for supplying a swirl gas for thermally insulating between the thermal plasma and the plasma reaction furnace 1 is provided at an appropriate location in the upper part of the plasma reaction furnace 1.

  At the lower part of the plasma reactor 1, that is, at the substantially central part of the bottom part, a lower electrode 3 having a bowl shape with the central part curved in a concave shape is provided so as to face the torch electrode 21. The lower electrode 3 is an electrode that generates thermal plasma with the torch electrode 21 and also functions as a container for depositing magnesium Mg powder by cooling the thermal plasma.

  A power supply 4 for generating thermal plasma is connected between the torch electrode 21 and the lower electrode 3. The power supply 4 is a DC power supply circuit that converts AC power obtained by nuclear power generation or hydropower generation into DC power and applies a DC voltage between the torch electrode 21 and the lower electrode 3. The polarity of the DC voltage is positive on the torch electrode 21 side and negative on the lower electrode 3 side. The torch electrode 21 side may be negative and the lower electrode 3 side may be positive. In this case, the secular change of the torch electrode 21 can be suppressed. Further, an AC voltage may be applied between the torch electrode 21 and the lower electrode 3.

The raw material supply unit 5 supplies methane CH ₄ from the methane gas cylinder 51 a to the plasma reactor 1 through the torch electrode 21, and argon Ar gas from the argon gas cylinder 51 b to the plasma reactor 1 through the torch electrode 21 and the torch nozzle 22. Argon supply pipes 54 b and 54 c to be supplied, and a hydrogen supply pipe 54 d for supplying hydrogen H ₂ gas from the hydrogen gas cylinder 51 c to the plasma reactor 1 through the torch nozzle 22. Gas flow control units 52a, 52b, 52c, 52d for controlling the gas supply amounts of methane CH ₄ , argon Ar, and hydrogen H ₂ , and on-off valves 53a, 53b are provided at appropriate locations of the supply pipes 54a, 54b, 54c, 54d. , 53c, 53d are provided.
Further, the raw material supply unit 5 includes a magnesium oxide MgO powder, and includes a magnesium oxide supply unit (MgO supply unit) 55 that supplies the magnesium oxide MgO powder through the magnesium oxide conveyance path 56 and the torch nozzle 22. The magnesium oxide conveyance path 56 is a screw conveyor, for example. The magnesium oxide supply unit 55 is a container that communicates with the magnesium oxide transport path 56, and has, for example, an inlet into which magnesium oxide MgO powder is charged. The charging port is provided with a door for closing the container in a sealed state. When the magnesium oxide transport path 56 is driven and the on / off valve 53c for supplying argon is opened, the magnesium oxide MgO powder is transported to the torch nozzle 22 and supplied to the plasma reactor 1 together with argon Ar.

  The control unit 6 is a microcomputer provided with a CPU (Central Processing Unit). A ROM (Read Only Memory), a RAM (Random Access Memory), and the like are connected to the CPU via a bus. The ROM is a non-volatile memory such as a mask ROM or EEPROM that stores a control program necessary for the operation of the CPU. The RAM is a volatile memory such as a DRAM or SRAM that temporarily stores various data generated when the arithmetic processing of the CPU is executed. The bus is connected to an operation unit 7 and a display unit (not shown) through an input / output port. The operation unit 7 includes an opening / closing operation of each on-off valve 53a, 53b, 53c, 53d, a flow control of the gas flow rate control units 52a, 52b, 52c, 52d, buttons for receiving various instructions, a dial, a touch panel, and the like. Yes. The display unit is a liquid crystal display, an organic EL display, a plasma display, a CRT display, or the like that displays the operating state of the plasma reactor. The CPU constantly monitors the operation state of the operation unit 7 and controls the opening / closing operations of the gas flow rate control units 52a, 52b, 52c, 52d and the on-off valves 53a, 53b, 53c, 53d according to the operation content of the operation unit 7. Is configured to do.

FIG. 4 is a flowchart showing a reduction procedure of the magnesium oxide powder. When the control unit 6 receives an instruction to reduce the magnesium oxide MgO powder through the operation unit 7, the control unit 6 turns on the power source 4 (step S11), and opens the on-off valves 53a and 53b, thereby allowing the plasma reactor 1 to have methane. A mixed gas of CH ₄ and argon Ar is supplied (step S12).
When methane CH ₄ and argon Ar are supplied to the plasma reactor 1 with the power supply 4 turned on, thermal plasma in a reducing atmosphere is generated.

Next, the controller 6 drives the magnesium oxide transport path 56 and controls the on-off valve 53c to open, thereby supplying magnesium oxide MgO powder together with argon Ar gas to the plasma reactor 1 (step S13).
When magnesium oxide MgO powder and argon Ar are supplied to the plasma reactor 1, the magnesium oxide MgO powder is plasma-reduced to magnesium Mg by thermal plasma as shown in the chemical formula (1). The thermal plasma that has reached the lower electrode 3 is cooled by the lower electrode 3, the gaseous magnesium Mg is condensed, and the solid magnesium Mg powder is deposited on the lower electrode 3.

  Then, the controller 6 stops supplying the magnesium oxide MgO powder by closing the on-off valve 53c and stopping the magnesium oxide conveyance path 56 when the set predetermined time has elapsed after the power source 4 is turned on (step). S14).

Next, the controller 6 stops the supply of methane CH ₄ and argon Ar by closing the on-off valves 53a and 53b (step S15), and turns off the power supply 4 (step S16).

Then, the controller 6 supplies hydrogen H ₂ to the plasma reactor 1 by opening the on-off valve 53d for a predetermined time (step S17). When hydrogen H ₂ is supplied to the plasma reactor 1, the magnesium Mg powder is hydrogenated as shown by the above chemical formula (4) to produce magnesium hydride MgH ₂ powder.

  Next, the control unit 6 supplies a gas purge, for example, a nitrogen gas (not shown) to the plasma reactor 1 (Step S18), and ends the process.

According to the present embodiment, magnesium Mg powder can be generated by plasma reduction of magnesium oxide MgO powder. At this time, it is also possible to obtain a mixture of magnesium Mg powder and magnesium hydride MgH ₂ powder by using a mixed gas of CH ₄ and H ₂ as the reducing gas. By adopting this process, it is possible to shorten the Mg hydrogenation step, which is the next step, and improve safety and economy. Further, only hydrogen H ₂ may be supplied to the plasma reactor 1 as a reducing gas. In this case, a part of magnesium Mg may be oxidized, but there is no problem even if a part of magnesium Mg is oxidized if an amount of magnesium hydride MgH ₂ having no problem in practical use can be obtained. On the other hand, after the production of magnesium Mg powder, magnesium hydride MgH ₂ powder can be produced by supplying hydrogen H ₂ to the plasma reactor 1. Therefore, recycling of the magnesium hydroxide Mg (OH) ₂ powder to magnesium hydride MgH ₂ powder becomes possible, and magnesium hydride MgH ₂ powder accumulated energy, magnesium hydroxide and releases energy Mg (OH) ₂ It becomes possible to circulate between powders.

The electric power obtained by nuclear power generation or hydroelectric power generation cannot be stored, and even if it is transported to the demand area, a large power transmission loss occurs. According to the present invention, surplus electric power energy is converted into hydrogen as a clean energy carrier. It can be stored as magnesium halide MgH ₂ , and the stored energy can be taken out as hydrogen H ₂ as required. According to the circulation system of magnesium hydride MgH ₂ , it is not always positive in terms of energy in the whole system, but it becomes possible to use surplus power effectively and suppress the generation of carbon dioxide CO _2. be able to.

  In the embodiment, the example in which the thermal plasma is generated using the arc discharge between the torch electrode and the lower electrode has been described. However, the thermal plasma is generated by inductively heating methane and argon in the high frequency electromagnetic field. Also good. Further, thermal plasma may be generated by supplying microwaves to the plasma reactor.

  Further, although an example in which the magnesium oxide MgO powder is directly supplied to the plasma reactor has been described, the magnesium oxide MgO powder may be suspended in a liquid and supplied to the plasma reactor.

  Furthermore, although the example which used argon Ar as an inert gas was demonstrated, it cannot be overemphasized that helium and other inert gas may be utilized.

Furthermore, methane CH ₄ and argon Ar are supplied from the torch electrode, and magnesium oxide MgO powder and argon Ar are supplied from the torch nozzle. Conversely, magnesium oxide MgO powder and argon Ar are supplied from the torch electrode, and from the torch nozzle. methane CH _4, and argon Ar may be configured to supply. It is also possible to constitute the hydrogen H ₂ so as to supply the torch electrode.

Furthermore, although the example in which hydrogen H ₂ is supplied to the plasma reactor to hydrogenate the magnesium Mg powder has been described, the magnesium Mg powder may be taken out of the plasma reactor and separately hydrogenated. good.

The example in which hydrogen H ₂ is supplied to the plasma reactor and magnesium Mg powder is hydrogenated has been described. As shown in the above formula (1), a sufficient amount of hydrogen is generated by the hydrogen H ₂ generated by the reduction reaction. When magnesium halide MgH ₂ is generated, hydrogen H ₂ may not be supplied separately.

  The embodiment disclosed this time is to be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Plasma reactor 2 Plasma torch 3 Lower electrode 4 Power supply 5 Raw material supply part 6 Control part 7 Operation part 21 Torch electrode 22 Torch nozzle 51a Methane gas cylinder 51b Argon gas cylinder 51c Hydrogen gas cylinder 54a Methane supply pipe 54b, 54c Argon supply pipe 54d Hydrogen supply pipe 55 Magnesium oxide supply section 56 Magnesium oxide conveyance path

Claims (4)

Supply magnesium oxide powder and methane and / or hydrogen to a plasma reactor that generates thermal plasma of inert gas,
The magnesium oxide powder is reduced to magnesium by a thermal plasma in a reducing atmosphere generated with an inert gas, methane and / or hydrogen,
By condensing the magnesium reduced gas to form magnesium Powder,
After the production of magnesium powder, magnesium is reduced by supplying hydrogen to the plasma reactor and bringing the magnesium powder in the plasma reactor into contact with hydrogen to produce magnesium hydride powder. Method. The magnesium oxide reduction method according to claim 1, wherein the thermal plasma is generated by using electric power of a power plant. A cylindrical torch electrode provided in the upper part of the plasma reactor, a torch nozzle surrounding the torch electrode, and a lower electrode facing the torch electrode are prepared, and magnesium oxide powder (or methane and / or hydrogen) is supplied to, magnesium oxide reduction method according to claim 1 or claim 2, wherein the supplying methane and / or hydrogen (or magnesium oxide powder) through the torch nozzle. A plasma reactor,
A cylindrical torch electrode provided at the top of the plasma reactor;
A torch nozzle surrounding the torch electrode;
A lower electrode provided at a lower portion of the plasma reactor so as to face the torch electrode;
A power source for supplying power to the torch electrode and the lower electrode;
A first supply path for supplying magnesium oxide powder (or methane and / or hydrogen) through the torch electrode;
A second supply path for supplying methane and / or hydrogen (or magnesium oxide powder) through the torch nozzle ;
A raw material supply unit for supplying magnesium oxide powder and methane and / or hydrogen to the plasma reactor through the first and second supply paths;
A control unit for controlling the operation of the raw material supply unit so that magnesium oxide powder and methane and / or hydrogen are supplied to the plasma reaction furnace, and then hydrogen is supplied to the plasma reaction furnace; A reactor characterized by.

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