Thermal power generation method

Abstract

To provide a thermal power generation method that leverages the technology developed in coal thermal power generation to reduce carbon dioxide emissions.SOLUTION: A resource-recirculating thermal power generation method according to the present invention includes a power generation step for burning fuel in a combustion chamber of a power generation boiler to generate power, and a resource regeneration step for producing raw materials for fuel from combustion ash. The fuel is magnesium, or magnesium hydride having a hydrogenated layer at least on its surface. The combustion ash is magnesium oxide, magnesium hydroxide, or a mixture thereof. The resource regeneration step further includes a chlorination step for producing magnesium chloride from the combustion ash, and a molten salt electrolysis step for producing magnesium from the magnesium chloride.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a thermal power generation method. [Background technology]

[0002] 2. Description of the Related Art Coal-fired power generation systems equipped with power generation boilers are generally known (see, for example, Non-Patent Document 1). And although Japan possesses some of the world's leading coal-fired power generation technology, opportunities for utilizing this technology are disappearing due to the problem of coal emitting carbon dioxide when burned.

[0003] One technology that could provide a solution to these problems is the so-called CCS initiative, which involves separating and capturing carbon dioxide from exhaust gases from thermal power plants and storing the captured carbon dioxide.

[0004] For example, Non-Patent Document 2 introduces the CCS efforts being undertaken in Tomakomai City, Hokkaido, and specifically explains that carbon dioxide is separated and captured from exhaust gases from thermal power plants, and that the captured carbon dioxide is injected deep underground beneath the seabed, approximately 3 to 4 km from the coast, and stored there. It is believed that the carbon dioxide injected deep underground in this way will be stored stably for a long period of time and will dissolve into salt water over a long period of time and become minerals in the gaps between rocks.

[0005] However, there are many constraints to this type of storage, such as the layer having gaps large enough to store carbon dioxide, and being covered by a layer that is impermeable to carbon dioxide. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] “Promoting regional environmental conservation: The structure of coal-fired power plants and various environmental conservation measures”, [online], Okinawa Electric Power Co., Inc., [Retrieved June 30, 2022], Internet<URL:https: / / www.okiden.co.jp / environment / report2017 / sec6 / sec63.html> [Non-Patent Document 2] “CCS: capturing and burying CO2: After demonstration tests, it is finally nearing realization (Part 1)”, [online], November 27, 2020, Agency for Natural Resources and Energy, Ministry of Economy, Trade and Industry, [Retrieved June 16, 2022], Internet<URL:https: / / www.enecho.meti.go.jp / about / special / johoteikyo / ccs_tomakomai.html> Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention has been made in view of the above circumstances, and has an object to provide a thermal power generation method that utilizes technology cultivated in coal-fired power generation and suppresses carbon dioxide emissions. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention is realized by the following configuration. (1) The resource recycling type thermal power generation method of the present invention comprises: a power generation process for generating power by burning fuel in a combustion chamber of a power generation boiler; and a resource regeneration process for generating raw materials for fuel from combustion ash generated by the combustion, wherein the fuel is magnesium or magnesium hydride having at least a hydrogenated layer on its surface, and the combustion ash is magnesium oxide, magnesium hydroxide, or a mixture thereof, and the resource regeneration process comprises a chlorination process for generating magnesium chloride from the combustion ash, and a molten salt electrolysis process for performing molten salt electrolysis on the magnesium chloride generated in the chlorination process to generate magnesium.

[0009] (2) In the configuration of (1) above, the fuel is the magnesium hydride having a hydrogenation rate of 30 mass% or less, the resource recycling process includes an atomization process for atomizing the magnesium produced in the molten salt electrolysis process to particles of 150 μm or less, and a hydrogenation process for hydrogenating the surface of the magnesium atomized in the atomization process to produce magnesium hydride having a hydrogenation rate of 30 mass% or less, and the combustion is performed using a powder combustion burner.

[0010] (3) In the configuration of (2) above, the atomization process includes a coarse crushing process for coarsely crushing the magnesium produced in the molten salt electrolysis process, and a fine crushing process for crushing the magnesium crushed in the coarse crushing process to 150 μm or less, and the magnesium crushed in the fine crushing process is handled so as not to come into contact with oxygen until the hydrogenation process is completed.

[0011] (4) In the above configuration (3), the fine pulverization step is carried out by adding powder of an inorganic compound as a pulverization aid.

[0012] (5) In the above configuration (4), the inorganic compound is magnesium oxide.

[0013] (6) In any one of the above configurations (1) to (5), moisture is supplied into the combustion chamber as a combustion promoter. Effect of the Invention

[0014] According to the present invention, it is possible to provide a thermal power generation method that utilizes technology cultivated in coal-fired power generation and suppresses carbon dioxide emissions. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram for explaining the configuration of a power plant for carrying out a power generation process according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a diagram for explaining an apparatus for performing a hydrogen chloride gas method according to an embodiment of the present invention. [Diagram 3]FIG. 2 is a diagram illustrating the configuration of an apparatus for carrying out a hydrogenation step according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, modes for carrying out the present invention (hereinafter, referred to as embodiments) will be described in detail with reference to the accompanying drawings. In addition, the same elements are denoted by the same reference numerals throughout the description of the embodiments.

[0017] (Embodiment) A resource-circulating thermal power generation method according to an embodiment of the present invention includes a power generation process in which fuel is combusted in a combustion chamber B1 of a power generation boiler 2 to generate power, and a resource regeneration process in which raw material for fuel is generated from combustion ash generated by the combustion. Therefore, in the following, the power generation process will be explained first, followed by the resource recycling process.

[0018] (Power generation process) The power generation process is a process carried out at a power plant. The technology used there utilizes technology that has been developed for coal-fired power generation, so explanations of points that are similar to conventional technology may be omitted. FIG. 1 is a diagram for explaining the configuration of a power plant for carrying out a power generation process.

[0019] As shown in Figure 1, the power plant includes a generator 1, a power generation boiler 2 that drives the generator 1, a fuel storage tank 3 that stores fuel to be supplied to the power generation boiler 2, an auxiliary fuel storage tank 4 that stores auxiliary fuel to be supplied to the power generation boiler 2, a denitrification device 5 that neutralizes nitrogen oxides (NOx) contained in the exhaust gas from the power generation boiler 2, a dust collector 6 that recovers combustion ash contained in the exhaust gas that has passed through the denitrification device 5, and a combustion ash storage tank 7 that stores the combustion ash.

[0020] The power generation boiler 2 is equipped with a combustion chamber B1, a steam turbine B2 whose rotating shaft is connected to the generator 1 and is driven by steam produced in the combustion chamber B1, and piping B3 for supplying the steam to the steam turbine B2 and for supplying water that has been returned to a liquid state in the condenser FU back to the combustion chamber B1.

[0021] A water supply pump P is provided in the middle of the pipe B3 connecting the condenser FU and the combustion chamber B1, so as to send water to the combustion chamber B1.

[0022] The combustion chamber B1 is equipped with a powder combustion burner 31 that burns powdered fuel supplied from the fuel storage tank 3, and an auxiliary combustion burner 41 that burns liquid fuel (e.g., heavy oil, light oil, etc.) supplied from the auxiliary fuel storage tank 4.

[0023] The powder combustion burner 31 is similar to the pulverized coal burner used in coal-fired power generation, and a supply system (not shown) that supplies powdered fuel to the powder combustion burner 31 may also be similar to that used in coal-fired power generation.

[0024] In addition, the auxiliary combustion burner 41 is a burner for obtaining auxiliary heat until the temperature in the combustion chamber B1 rises and the combustion in the powder combustion burner 31 becomes stable, and this may be similar to the one used in coal-fired power generation.

[0025] Once the combustion in the powder combustion burner 31 becomes stable, this auxiliary heating power is no longer necessary. And because thermal power plants are basically operated without being shut down, the amount of carbon dioxide emitted by auxiliary thermal power plants, which are only used at the start of operations, is negligible.

[0026] In the fuel storage 3, magnesium hydride having a particle diameter of 150 μm or less and at least a hydrogenated layer on its surface is stored as a powder fuel that does not emit carbon dioxide when burned.

[0027] However, since magnesium hydride is not perfectly spherical, a particle size of 150 μm or less here can be considered to be a size that can pass through a sieve with a mesh opening of about 0.16 mm.

[0028] In addition, the pulverized coal used in pulverized coal burners used in coal-fired power generation is generally 150 μm or less, and by making the particle size of the magnesium hydride 150 μm or less, there is an advantage that a burner with a similar structure to the pulverized coal burner can be used as the powder combustion burner 31.

[0029] In the powder combustion burner 31, magnesium hydride mixed with air is burned. Since magnesium hydride is a substance composed of magnesium and hydrogen, the only substances produced during combustion are magnesium oxide and water, and no carbon dioxide is produced. However, some of the generated water may react with magnesium oxide, resulting in magnesium hydroxide being contained in the combustion ash.

[0030] By the way, the reason for this will be explained later in the section on the resource recycling process, but the magnesium hydride with a particle size of 150 μm or less used as fuel is not 100% pure, but rather low-purity magnesium hydride with a hydrogenation rate of 30 mass% or less, where at least the surface side is hydrogenated.

[0031] In other words, it is preferable that the magnesium is not hydrogenated to the center, but that the surface of the magnesium is covered with a layer of magnesium hydride.

[0032] In the case of such low-purity magnesium hydride, when air is used as the combustion supporting gas, two reactions must be considered: the combustion reaction of the magnesium hydride portion and the combustion reaction of the magnesium portion.

[0033] However, the combustion reaction between the magnesium hydride portion and oxygen is as shown in the following formula (1), and the combustion reaction between the magnesium portion and oxygen is as shown in the following formula (2). Therefore, even if the magnesium hydride is low-purity, no carbon dioxide is generated during combustion. MgH2+ O2→ MgO +H2O (1) 2Mg + O2→ 2MgO (2)

[0034] On the other hand, in the powder combustion burner 31, magnesium hydride mixed with air is burned, so more precisely, it is necessary to take into consideration the presence of nitrogen together with oxygen. In particular, magnesium also reacts with nitrogen at high temperatures and in an oxygen-deficient atmosphere to produce magnesium nitride, as shown in formula (3) below. 3Mg + N2→ Mg3N2 (3)

[0035] Therefore, if any of the magnesium hydride fuel is incompletely burned, it may turn into magnesium nitride and mix with the combustion ash. Considering that magnesium nitride formation requires high temperature and oxygen-deficient conditions, it is believed that magnesium nitride formation itself occurs in the combustion flame or in the vicinity of the flame.

[0036] When magnesium nitride is exposed to moisture, it quickly decomposes and turns into magnesium hydroxide and ammonia, as shown in formula (4) below. Mg3N2+ 6H2O → 3Mg(OH)2+ 2NH3... (4)

[0037] If magnesium nitride is mixed in the combustion ash, there is a possibility that ammonia gas will be generated from the combustion ash after the combustion ash is collected.

[0038] For this reason, it is preferable to increase the humidity in the combustion chamber B1 so that even if magnesium nitride is produced, it can be decomposed quickly. In this way, even if magnesium nitride is produced, it is quickly decomposed, and the ammonia generated by the decomposition can also contribute to combustion as a combustion gas. That is, moisture may be supplied into the combustion chamber B1 as a combustion promoter that suppresses incomplete combustion that produces magnesium nitride.

[0039] As a method for increasing the humidity inside the combustion chamber B1, an intake port may be provided to send humid air (for example, air with a humidity of 50% or more, desirably 70% or more, and more preferably 80% or more) into the combustion chamber B1, or air with increased humidity may be sent to the powder combustion burner 31 in advance, and the humid air may be mixed with magnesium hydride to form a burner flame.

[0040] Furthermore, considering that moist air has a higher thermal conductivity than dry air, this is also expected to have the effect of increasing the heat exchange efficiency in the pipe B3 passing through the combustion chamber B1.

[0041] On the other hand, as mentioned above, if magnesium hydride is used as the fuel, no carbon dioxide is produced during combustion to generate electricity; however, the combustion supporting gas used is air, which contains nitrogen gas. Therefore, nitrogen oxides (NOx) may be generated during combustion, and in order to render the nitrogen oxides (NOx) in the exhaust gas harmless, a denitrification device 5 is provided in the exhaust pipe 8 that sends the exhaust gas from the combustion chamber B1 to a dust collector 6. In order to suppress the generation of nitrogen oxides (NOx), air with an increased oxygen concentration may be used as the combustion supporting gas, or oxygen itself may be used as the combustion supporting gas. If the oxygen concentration of the combustion supporting gas can be increased and the amount of nitrogen oxides (NOx) generated can be suppressed to a level that satisfies environmental standards, the denitrification device 5 may be omitted.

[0042] Specifically, the denitration device 5 may be similar to a denitration device generally used in coal-fired power plants, which adds ammonia to the exhaust gas and passes it through a catalyst layer to break down nitrogen oxides (NOx) into harmless nitrogen and water.

[0043] The exhaust gas after passing through the denitrification device 5 does not contain any harmful gases, but it does contain combustion ash generated during combustion, which has an extremely small particle size. Therefore, the exhaust pipe 8 is further connected to a dust collector 6, and after the combustion ash is collected by the dust collector 6, the exhaust gas is released into the atmosphere.

[0044] This dust collector 6 may be the same as that used in coal-fired power plants, and specifically, an electric dust collector may be used. As shown in FIG. 1, an exhaust device 81 is provided downstream of the dust collector 6, so that the exhaust gas from the combustion chamber B1 can be discharged into the atmosphere via the denitration device 5 and the dust collector 6.

[0045] On the other hand, in coal-fired power generation, coal is used as fuel, so the sulfur components contained in the coal are contained in the exhaust gas. For this reason, in coal-fired power plants, a desulfurization unit is installed before the exhaust gas is released into the atmosphere. However, magnesium hydride has the advantage that a desulfurization unit is not required because it does not contain any sulfur components.

[0046] In addition, in coal-fired power plants, carbon dioxide is contained in the exhaust gas, which requires that the exhaust gas be released into the atmosphere through a tall chimney; however, such a tall chimney is not necessary.

[0047] The combustion ash deposited at the bottom of the combustion chamber B1 and the combustion ash collected by the dust collector 6 are collected in the combustion ash storage 7 and, for resource circulation, are regenerated into magnesium hydride again through the resource regeneration process described below.

[0048] In addition, in coal-fired power generation, coal residue accumulates at the bottom of the combustion chamber and is also contained in the exhaust gas, so a dust collector is used, and a similar mechanism can be used to recover the combustion ash of magnesium hydride.

[0049] However, since the amount of combustion ash generated is greater than when burning coal, the capacity of the recovery mechanism needs to be increased.

[0050] As can be seen from the above explanation, if magnesium hydride with particles of 150 μm or less is used as fuel, it is extremely compatible with the coal-fired power generation technology that has been developed so far, in which pulverized coal is burned in a pulverized coal burner to generate electricity, and a power generation process with reduced carbon dioxide emissions can be carried out.

[0051] Furthermore, as explained above, the combustion ash generated when magnesium hydride or magnesium is burned is magnesium oxide.

[0052] In addition, magnesium oxide has a high melting point of approximately 2850° C., so it will not melt even in high-temperature locations such as the inside of the combustion chamber B1.

[0053] On the other hand, since coal contains silicon as an ingredient, a part of the combustion ash melts at 1000°C to 1300°C, and molten deposits are generated in various places, such as inside the combustion chamber B1 and the chimney.

[0054] Therefore, in this embodiment, which can suppress the occurrence of molten deposits, there is an advantage in that the effort required for cleaning and the like can be reduced.

[0055] (Resource recycling process) Next, a resource recovery process in which magnesium hydride is produced again using the combustion ash (magnesium oxide, magnesium hydroxide) generated in the power generation process as a starting material will be described.

[0056] Regarding the magnesium hydroxide contained in the combustion ash, when heated, a dehydration reaction occurs and it becomes magnesium oxide, as shown in the following formula (5). Therefore, the starting material for the resource recovery process can be considered to be magnesium oxide. Mg(OH)2→ MgO + H2O (5)

[0057] To briefly explain the procedure, first, magnesium is produced from magnesium oxide, which is the starting material. Specifically, a chlorination process is carried out to produce magnesium chloride using magnesium oxide, which is combustion ash, and then the magnesium chloride produced in the chlorination process is used to perform molten salt electrolysis to produce magnesium.

[0058] The magnesium obtained in this manner is further pulverized to 150 μm or less in an atomization process, after which a hydrogenation process is carried out to produce magnesium hydride having at least a hydrogenated layer on its surface, and the magnesium hydride is then recycled again into fuel for use in the power generation process.

[0059] (Chlorination process) As described above, the chlorination process is a process in which magnesium chloride is produced from magnesium oxide, which is combustion ash, as a material for use in the subsequent molten salt electrolysis process. There are several methods for doing this, including a method of producing magnesium chloride using magnesium oxide and hydrogen chloride gas (hereinafter also referred to as the "hydrogen chloride gas method"), and a method of producing magnesium chloride using magnesium oxide and ammonium chloride (hereinafter also referred to as the "ammonium chloride method"), and any of these methods may be used.

[0060] (Hydrogen chloride gas method) The hydrogen chloride gas method is a method for producing magnesium chloride by reacting magnesium oxide with hydrogen chloride gas at a temperature of about 300 to 600°C according to the following formula (6). The method will be described with reference to FIG. 2, which is a diagram illustrating an apparatus for carrying out the hydrogen chloride gas method. Note that FIG. 2 shows only the main parts. MgO + 2HCl → MgCl2+ H2O (6)

[0061] As shown in FIG. 2, the apparatus for carrying out the hydrogen chloride gas method includes a reaction vessel portion 9 for reacting magnesium oxide with hydrogen chloride gas, and a heater H for heating the reaction vessel portion 9.

[0062] The reaction vessel section 9 comprises a cylindrical body section 91 that opens at the top and bottom, an upper lid 92 that closes the upper opening of the body section 91, and a lower lid 93 that closes the lower opening of the body section 91.

[0063] A gas supply port IN is provided on the lower side surface of the body 91, and a gas exhaust port OUT is provided on the upper side surface of the body 91.

[0064] When magnesium oxide is introduced into the reaction vessel portion 9, the upper lid 92 is opened, and when magnesium chloride after the reaction is removed, the lower lid 93 is opened.

[0065] The specific process involves first placing magnesium oxide in the reaction vessel section 9, heating it with heater H until the temperature inside the reaction vessel section 9 becomes around 400°C, while supplying a dry gas (e.g., dry air, dry nitrogen) from the gas supply port IN, and discharging the gas that has passed through the magnesium oxide from the gas exhaust port OUT. The process in which gas is both supplied and exhausted is sometimes called a blown-off process.

[0066] This removes moisture adhering to the magnesium oxide. As described above, after the magnesium oxide has been dried, the gas supplied from the gas supply port IN is replaced with hydrogen chloride gas, and a chlorination process is carried out in which the magnesium oxide and hydrogen chloride gas are reacted to produce magnesium chloride.

[0067] As can be seen from the formula (6) shown above, water is produced in the reaction. However, by carrying out this chlorination process using the blown-off process, the magnesium chloride does not become a hydrate, and anhydrous magnesium chloride can be produced.

[0068] Hydrogen chloride gas that has not contributed to the reaction is also exhausted from the gas exhaust port OUT, but this hydrogen chloride gas may be subjected to a dehydration treatment and then supplied again from the gas supply port IN.

[0069] Then, as described above, the produced anhydrous magnesium chloride is removed from the reaction vessel portion 9 by opening the bottom lid 93, and is used as a material in the next step, which is the molten salt electrolysis step. Before opening the lower lid 93, the gas being supplied is switched to, for example, dry nitrogen, etc., to replace the hydrogen chloride gas in the reaction vessel portion 9.

[0070] (Ammonium chloride method) The ammonium chloride method involves reacting magnesium oxide with ammonium chloride, and there are two possible procedures for this. In either case, the device configuration may be the same as that described with reference to FIG. 2, and therefore the following description will also refer to FIG.

[0071] The first step is to react magnesium oxide with ammonium chloride at a temperature of about 300 to 600°C to produce magnesium chloride. The reaction that occurs at this time is as shown in formula (7) below. MgO + 2NH4Cl → MgCl2+ H2O+2NH3···(7)

[0072] For example, a mixture of magnesium oxide and ammonium chloride, in which the molar ratio of ammonium chloride is at least twice as much as that of magnesium oxide, is charged into reaction vessel section 9.

[0073] As shown in formula (7), from a chemical standpoint, the molar ratio of magnesium oxide to ammonium chloride should be 1:2. However, when actually processing the material, taking into account that there may be ammonium chloride that cannot contribute to the reaction, it is better to make the molar ratio of magnesium oxide to ammonium chloride about 1:3 to 1:5.

[0074] Then, while blowing dry nitrogen, heating is performed with heater H so that the temperature inside reaction vessel portion 9 becomes about 400°C. As a result of this heating, ammonium chloride, which is a solid at room temperature, begins to sublime at a temperature of around 300°C and decomposes into ammonia gas and hydrogen chloride gas. The hydrogen chloride gas produced by this decomposition reacts with magnesium oxide, progressing the production of magnesium chloride. After the heating process has been carried out for a specified period of time, the heating by heater H is stopped, the material is cooled, and the magnesium chloride produced is collected.

[0075] The reason for blowing dry nitrogen is that, as can be seen from equation (7), moisture is generated at the same time as magnesium chloride is generated, and the generated moisture is quickly discharged outside the reaction vessel section 9, preventing the magnesium chloride from becoming a hydrate, and producing anhydrous magnesium chloride. In addition, an ammonium chloride supply port for supplying additional ammonium chloride may be provided in the reaction vessel section 9 so that ammonium chloride can be added during the reaction.

[0076] The second step is to react magnesium oxide with ammonium chloride in a molar ratio of 1:3 to produce ammonium carbohydrate hydrate, and then remove the water and ammonium chloride to obtain anhydrous magnesium chloride.

[0077] Specifically, a mixture of magnesium oxide and ammonium chloride in a molar ratio of 1:3 is charged into reaction vessel section 9 .

[0078] Thereafter, dry nitrogen is blown for a while to replace the atmosphere inside the reaction vessel portion 9 with a dry nitrogen atmosphere.

[0079] Then, when the inside of the reaction vessel portion 9 becomes a dry nitrogen atmosphere, the gas supply port IN and the gas exhaust port OUT are closed to seal the reaction vessel portion 9, and heating with the heater H is started so that the inside of the reaction vessel portion 9 becomes around 400°C.

[0080] This causes the reaction shown in formula (8) below to produce ammonium carbohydrate hydrate. MgO+3NH4Cl→MgCl2·NH4Cl·H2O+2NH3···(8)

[0081] As can be seen from equation (8), in this reaction, the solid magnesium oxide reacts with ammonium chloride, producing ammonia gas, which causes the internal pressure to increase.

[0082] For this reason, it is advisable that the reaction vessel section 9 is a pressure-resistant vessel capable of withstanding the pressure increase. However, if the pressure exceeds atmospheric pressure slightly, the gas exhaust port OUT may be opened to suppress the pressure increase, and it is not necessary to use a pressure-resistant container.

[0083] After the heat treatment is performed for a predetermined time, the set temperature of the heater H is changed so as to keep the temperature inside the reaction vessel portion 9 slightly lower than the sublimation temperature of ammonium chloride (about 5 to 20° C. lower than the sublimation temperature).

[0084] When the temperature inside the reaction vessel section 9 has dropped to the set temperature, ammonia gas is supplied from the gas supply port IN and exhausted from the gas exhaust port OUT so that the ammonia gas flows in a stream, and heating is performed for a predetermined period of time.

[0085] In this way, when a hydrate of ammonium carbohydrate is heat-treated under an ammonia gas atmosphere, the water content of the hydrate inhibits the hydrolysis reaction of the ammonium carbohydrate from proceeding, and the dehydration reaction shown in the following formula (9) proceeds. MgCl2·NH4Cl·H2O→MgCl2·NH4Cl+H2O···(9)

[0086] In addition, since the ammonia gas is blown away, the moisture generated by dehydration is quickly discharged outside the reaction vessel section 9, and the formation of hydrates again is suppressed.

[0087] After the dehydration process is completed, the set temperature of the heater H is changed so as to keep the temperature inside the reaction vessel portion 9 at a temperature higher than the sublimation temperature of ammonium chloride (for example, around 400° C.).

[0088] Furthermore, once the dehydration process is completed, there is no need to create an ammonia gas atmosphere inside the reaction vessel portion 9, so the atmosphere is changed to a dry nitrogen stream at the same time that the set temperature of the heater H is changed.

[0089] Then, as shown in the following formula (10), the ammonium carbohydrate decomposes into magnesium chloride, ammonia gas, and hydrogen chloride gas, and the ammonium chloride portion is removed from the ammonium carbohydrate (hereinafter, also referred to as "ammonium dechlorination treatment"), producing anhydrous magnesium chloride. MgCl2·NH4Cl→MgCl2+NH3+HCl·······(10)

[0090] The ammonia gas and hydrogen chloride gas are exhausted to the outside of the reaction vessel section 9 together with the blown dry nitrogen.

[0091] Once the ammonium chloride removal process is complete, the heater H is turned off to cool the system, and the anhydrous magnesium chloride that has been produced is then recovered.

[0092] (Molten salt electrolysis process) The molten salt electrolysis process is a process in which magnesium is produced by electrolysis using anhydrous magnesium chloride produced in the chlorination process as a material, and is a method commonly used to produce magnesium.

[0093] Therefore, to put it simply, for example, magnesium chloride is heated to a temperature of around 700°C in a brick furnace to melt the magnesium chloride.

[0094] At least a pair of electrodes is installed inside the brick furnace. When a power source is connected between the electrodes and a voltage of 2.5 V or more is applied, chlorine gas is generated at the anode and magnesium is produced at the cathode.

[0095] In addition, since hydrogen chloride gas is produced by reacting hydrogen gas with chlorine gas, hydrogen chloride gas may be generated using chlorine gas generated in the molten salt electrolysis process as a material and used in the chlorination process.

[0096] (Atomization process) The atomization step is a step in which the magnesium produced in the molten salt electrolysis step is converted into powdered magnesium, and may be carried out using a general grinding machine or a fine powder production device known as a gas atomizer.

[0097] When the atomization step is carried out using a pulverizing device, it is advisable to carry out the pulverization step in two stages in consideration of pulverization efficiency. Specifically, the micronization process should include a coarse crushing process in which the magnesium is roughly crushed to a particle size of about 180 to 800 μm using equipment that does not achieve micronization but has a high crushing speed, and a fine crushing process in which the magnesium crushed in the coarse crushing process is crushed to a particle size of 150 μm or less.

[0098] The particle size referred to here does not mean an exact sphere, but rather the particle size in the coarse crushing process may be considered to be the size that can pass through a sieve with a mesh opening of about 0.8 mm.

[0099] By the way, when magnesium is roughly crushed, the fact that it is a soft metal does not cause any problems. However, when it comes to the stage of fine crushing, the magnesium particles stick together during the crushing process, making it difficult to turn into a fine powder. For this reason, it is advisable to add a grinding aid to the coarsely ground magnesium in the fine grinding step.

[0100] For example, as the grinding aid, stearic acid or the like may be used, but it is preferable to use a powder of an inorganic compound. Specifically, if magnesium oxide, which is a powder of an inorganic compound, is used as the grinding aid, it becomes possible to use a portion of the combustion ash as the grinding aid, since it has the same composition as the combustion ash.

[0101] (Hydrogenation process) The magnesium atomized in the atomization step is hydrogenated in the hydrogenation step. However, if the magnesium comes into contact with oxygen after atomization, an oxide film is formed on the surface, significantly reducing the reaction efficiency. Therefore, the magnesium pulverized in the fine pulverization process must be handled in such a way that it does not come into contact with oxygen until the hydrogenation process is completed.

[0102] Specifically, a method for performing the hydrogenation step without exposing the mixture to outside air will be described with reference to FIG. 3 which is a diagram illustrating the configuration of an apparatus for performing the hydrogenation step.

[0103] As shown in FIG. 3, the apparatus for carrying out the hydrogenation process includes a heating container HB for containing atomized magnesium and reacting it with hydrogen, a heater H1 for heating the heating container HB, and a pipe 10 that is detachably connected to the inlet HB1 of the heating container HB.

[0104] The heating vessel HB is provided with a valve HB4 at a conduit section HB3 extending from an inlet HB1 to a heating section HB2, and when the valve HB4 is closed, the vessel is sealed. On the other hand, the pipe 10 is connected to a hydrogen gas supply system, an argon gas supply system, and a vacuum pump, although not shown.

[0105] The heating vessel HB also serves as a recovery vessel for recovering the pulverized magnesium from the fine pulverization process. Therefore, the fine grinding process is performed under an argon gas atmosphere, and before removing the heating container HB from the grinding device performing the fine grinding process, the valve HB4 is closed and removed, and the magnesium recovered in the heating container HB is connected to the device shown in Figure 3 while being sealed with argon.

[0106] Then, before opening the valve HB4, a vacuum is drawn to exhaust the air from the pipe 10 and above the valve HB4, and then the valve HB4 is opened to exhaust the argon gas from the heating part HB2.

[0107] Thereafter, the heater H1 is driven to heat the inside of the heating part HB2 to a temperature suitable for hydrogenation (specifically, 180° C. to 220° C.), and hydrogen gas is supplied to the heating vessel HB to perform the hydrogenation process.

[0108] When magnesium is turned into a fine powder, it becomes easily combustible and is generally treated as a hazardous material under the Fire Service Act. On the other hand, magnesium hydride is not classified as a hazardous material under the Fire Service Act even in fine powder form, and the fact that it has been hydrogenated makes it less flammable.

[0109] Magnesium hydride with a hydrogenation rate of about 20% by mass has almost the same calorific value as coal, so low-purity magnesium hydride can be used as a fuel to replace coal. Therefore, the hydrogenation carried out here needs to achieve a hydrogenation rate that does not qualify as a hazardous material in terms of transportation, storage, etc.

[0110] Here, the hydrogenation of magnesium is not proportional to time, but the hydrogenation rate slows down significantly as the purity increases. Therefore, as mentioned above, if the low-purity magnesium hydride has a hydrogenation rate of 30 mass% or less, at least on the surface side, the time required for the hydrogenation process can be significantly reduced, and productivity can be significantly increased.

[0111] After the short hydrogenation process is thus performed, the heater H1 is turned off, and after cooling, the hydrogen gas in the heating vessel HB is replaced with argon gas, and low-purity magnesium hydride is taken out. The low-purity magnesium hydride thus produced, in which at least the surface side has been hydrogenated to a hydrogenation rate of 30 mass % or less, is reused as fuel in the power generation process.

[0112] As described above, the thermal power generation method of the present embodiment does not generate carbon dioxide during power generation, and is a resource-circulating thermal power generation method in which magnesium resources are circulated. In addition, since the resource recycling process described above is composed only of equipment that runs on electricity, fuel recycling production can be carried out using only surplus electricity that cannot be connected to a grid.

[0113] Therefore, if the resource recycling process is carried out using surplus electricity, it functions as a receptacle of surplus electricity from renewable energy sources, etc., while the above-mentioned thermal power generation method is a type of power generation with inertia that can balance supply and demand in accordance with the demand and supply of electricity.

[0114] In other words, the resource regeneration process may be performed using electricity without inertia, such as renewable energy, so that the method may be a thermal power generation method capable of converting the electricity without inertia into electricity with inertia.

[0115] In the above, a power generation boiler using the powder combustion burner 31 has been described. However, there are also coal-fired power plants that do not use pulverized coal burners, known as stoker boilers, and in which the combustion chamber of the power generation boiler is simply configured like a combustion furnace, with coal simply being fed into it so that combustion is constant. In such configurations, the fuel described above may be used.

[0116] Furthermore, in this case, there is no need for a fine pulverization process to crush the material into particles of 150 μm or less, which was previously necessary to maintain combustion as a burner flame. Since it is sufficient to supply fuel to maintain the heat, a relatively large fuel size is sufficient.

[0117] Furthermore, even if the magnesium has a particle size of about 500 μm, it does not fall under the category of a hazardous material under the Fire Service Act. Therefore, it is also possible to carry out a thermal power generation method in which the magnesium is used as fuel by only carrying out appropriate coarse crushing to limit the size of the magnesium to 500 μm or more, omitting the hydrogenation process.

[0118] Thus, even in a thermal power generation method using magnesium as fuel, carbon dioxide is not generated and the combustion ash becomes magnesium oxide, so that a resource recycling process can be carried out. In other words, the resource recycling process may be limited to coarse pulverization, and the fine pulverization process and hydrogenation process described above may be omitted.

[0119] Even if the fuel is not hydrogenated as described above and is instead magnesium itself, magnesium nitride will be produced if combustion occurs in an oxygen-deficient state. Therefore, as explained above, it is preferable to increase the humidity in the combustion chamber so that even if magnesium nitride is produced, it can be decomposed quickly.

[0120] In addition, a mixture of magnesium and magnesium hydride (i.e., a mixture of magnesium and magnesium hydride) may be used as fuel, and although production efficiency will be significantly reduced, using magnesium hydride with a high hydrogenation rate will not cause any problems as a thermal power generation method.

[0121] As such, the present invention is not limited to the specific embodiments, and appropriate modifications and improvements are also included within the technical scope of the present invention, which will be apparent to those skilled in the art from the description of the claims. [Explanation of symbols]

[0122] 1. Generator 2. Power generation boilers B1 Combustion chamber B2 Steam Turbine B3 Piping 3. Fuel storage facility 31 Powder combustion burner 4. Auxiliary Fuel Storage 41 Auxiliary combustion burner 5 Denitration equipment 6 Dust collector 7. Ash Storage 8. Exhaust pipe 81 Ventilation device FU Condenser P Water supply pump 9. Reaction vessel section 91 Torso 92 Top lid 93 Lower lid IN supply port OUT Exhaust port H Heater 10 Piping HB heating container HB1 entrance HB2 heating section HB3 Vessel section HB4 Valve H1 Heater

Claims

1. A resource recycling type thermal power generation method, A power generation process of burning fuel in a combustion chamber of a power generation boiler to generate power; A resource regeneration process for generating a raw material for fuel from the combustion ash generated by the combustion, the fuel is magnesium or magnesium hydride having at least a hydrogenated layer on its surface; The combustion ash is magnesium oxide, magnesium hydroxide, or a mixture thereof; The resource recycling step includes: a chlorination step of producing magnesium chloride from the combustion ash; and a molten salt electrolysis step of producing magnesium by performing molten salt electrolysis using the magnesium chloride produced in the chlorination step as a material.

2. the fuel is the magnesium hydride having a hydrogenation rate of 30 mass% or less, The resource recycling step includes: a microparticulation step of microparticulating the magnesium produced in the molten salt electrolysis step to a size of 150 μm or less; a hydrogenation step of hydrogenating the surface of the magnesium atomized in the atomization step to produce magnesium hydride with a hydrogenation rate of 30 mass% or less, The thermal power generation method according to claim 1 , wherein the combustion is carried out using a powder combustion burner.

3. The atomization step comprises: a coarse crushing step of coarsely crushing the magnesium produced in the molten salt electrolysis step; A fine pulverization step of pulverizing the magnesium pulverized in the coarse pulverization step to a size of 150 μm or less, 3. The thermal power generation method according to claim 2, wherein the magnesium pulverized in the fine pulverization step is handled so as not to come into contact with oxygen until the hydrogenation step is completed.

4. The thermal power generation method according to claim 3 , wherein the fine pulverization step is carried out by adding a powder of an inorganic compound as a pulverization aid.

5. The thermal power generation method according to claim 4 , wherein the inorganic compound is magnesium oxide.

6. A thermal power generation method as described in any one of claims 1 to 5, comprising a combustion chamber humidity increasing process for increasing the humidity in the combustion chamber.

7. The thermal power generation method according to claim 6 , wherein moisture is supplied into the combustion chamber as a combustion promoter.

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