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] BACKGROUND ART Coal-fired power generation systems equipped with power generation boilers are generally known (see, for example, Non-Patent Document 1). Although Japan possesses some of the world's leading coal-fired power generation technologies, opportunities for utilizing this technology are being lost due to the problem of carbon dioxide emissions when coal is burned.

[0003] One technology that could solve these problems is the so-called CCS initiative, which involves separating and capturing carbon dioxide from the exhaust gases of 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 the exhaust gases of thermal power plants, and that the captured carbon dioxide is then injected and stored deep underground beneath the seabed, approximately 3 to 4 km from the coast. It is believed that 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 achieving this type of storage, such as the layer having gaps that allow carbon dioxide to be stored, and the layer being covered with a layer that does not allow carbon dioxide to pass through. [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: CO2 Capture and Burial, Demonstration Tests Now Close to 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 aims 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 thermal power generation method of the present invention comprises a power generation process in which fuel is combusted in a combustion chamber of a power generation boiler to generate power, and a resource recycling process in which raw materials for fuel are produced 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 recycling process comprises a chlorination process in which magnesium chloride is produced from the combustion ash, and a molten salt electrolysis process in which molten salt electrolysis is performed on the magnesium chloride produced in the chlorination process to produce magnesium.

[0009] (2) In the configuration of (1) above, the fuel is the magnesium hydride having a hydrogenation rate of 30% by 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% by mass or less, and the combustion is carried out using a powder combustion burner.

[0010] (3) In the configuration of (2) above, the atomization process comprises 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 accelerator. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a thermal power generation method that reduces carbon dioxide emissions by utilizing technology developed in coal-fired power generation. [Brief explanation 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. [Figure 2] FIG. 1 is a diagram illustrating an apparatus for performing a hydrogen chloride gas method according to an embodiment of the present invention. [Figure 3]FIG. 1 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 INVENTION

[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. It should be noted that 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 electricity, and a resource regeneration process in which raw materials for fuel are produced from combustion ash generated by the combustion. Therefore, the following description will be given in the order of the power generation process and the resource recycling process.

[0018] (Power generation process) The power generation process is a process carried out at a power plant, but 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 illustrating 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 collects 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 comprises 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 a pipe 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, and sends 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 the 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 heating power until the temperature in the combustion chamber B1 rises and the combustion of the powder combustion burner 31 stabilizes, and this may also be similar to that used in coal-fired power generation.

[0025] Once the combustion in the powder combustion burner 31 is stabilized, this auxiliary heating power is no longer necessary. Furthermore, since thermal power plants are generally operated without being shut down, the amount of carbon dioxide generated by auxiliary thermal power plants, which are only used at the start of operation, is negligible.

[0026] The fuel storage 3 stores magnesium hydride, which has a particle diameter of 150 μm or less and at least a hydrogenated layer on its surface, 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 can be considered to be a size that can pass through a sieve with a mesh opening of approximately 0.16 mm.

[0028] 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, but since magnesium hydride is a substance made of magnesium and hydrogen, only magnesium oxide and water are produced during the combustion, 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] Incidentally, the reason for this will be explained later in the section on resource recycling processes, 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 core, 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 the following formula (3). 3Mg + N2→ Mg3N2 (3)

[0035] Therefore, if any of the magnesium hydride fuel is incompletely burned, it may be converted into magnesium nitride and mixed into 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 in the presence of moisture, it quickly decomposes in reaction with the moisture, and changes into magnesium hydroxide and ammonia, as shown in the following formula (4). Mg3N2+ 6H2O → 3Mg(OH)2+ 2NH3... (4)

[0037] If magnesium nitride is mixed in the combustion ash, there is a possibility that ammonia gas may 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 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, preferably 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 the thermal conductivity of moist air is higher than that of dry air, it is expected that the heat exchange efficiency in the pipe B3 passing through the combustion chamber B1 will also be improved.

[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, but the combustion supporting gas used for combustion is air, which contains nitrogen gas. Therefore, nitrogen oxides (NOx) may be generated during combustion, and in order to neutralize the nitrogen oxides (NOx) in the exhaust gas, 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 meets 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 decompose 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, some of which has 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, which allows the exhaust gas from the combustion chamber B1 to be released 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 sulfur components contained in coal are contained in the exhaust gas. For this reason, coal-fired power plants are equipped with a desulfurization unit before releasing exhaust gas into the atmosphere, but magnesium hydride has the advantage of not requiring a desulfurization unit because it does not contain sulfur components.

[0046] Furthermore, in coal-fired power plants, carbon dioxide is contained in the exhaust gas, which must be released into the atmosphere through a tall chimney, but this technology eliminates the need for such a tall chimney.

[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 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 a particle size of 150 μm or less is used as fuel, it is highly 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] Furthermore, 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, part of the combustion ash melts at 1000°C to 1300°C, and molten deposits are formed 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 labor required for cleaning and the like can be reduced.

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

[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, as a material, and then the magnesium chloride produced in the chlorination process is used to carry out 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, and then subjected to a hydrogenation process to produce magnesium hydride having a hydrogenated layer at least on the surface, which is then recycled into fuel to be used in the power generation process.

[0059] (Chlorination process) As explained above, the chlorination step is a step in which magnesium chloride, which is used in the subsequent molten salt electrolysis step, is produced from magnesium oxide, which is combustion ash. 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 causing a reaction of magnesium oxide with hydrogen chloride gas at a temperature of about 300 to 600°C according to the following formula (6), and will be described with reference to FIG. 2, which is a diagram illustrating an apparatus for performing the hydrogen chloride gas method. Note that Figure 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 includes 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 section 9, the upper lid 92 is opened, and when magnesium chloride is removed after the reaction, the lower lid 93 is opened.

[0065] Specifically, the process involves first placing magnesium oxide in the reaction vessel section 9, heating it with a heater H until the temperature inside the reaction vessel section 9 reaches around 400°C, supplying a dry gas (e.g., dry air or 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 of performing both gas supply and exhaust is sometimes called windsock 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 changed to hydrogen chloride gas, and the magnesium oxide and hydrogen chloride gas are reacted to produce magnesium chloride, thereby carrying out a chlorination treatment.

[0067] As can be seen from equation (6) shown above, water is also produced in the reaction, but by carrying out this chlorination process using the streamer method, 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 section 9 by opening the lower 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 procedure involves treating magnesium oxide with ammonium chloride at a temperature of approximately 300 to 600°C to produce magnesium chloride. The reaction that occurs at this time is shown in formula (7) below. MgO + 2NH4Cl → MgCl2+ H2O+2NH3···(7)

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

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

[0074] Then, while blowing dry nitrogen, the reaction vessel section 9 is heated by the heater H so that the temperature inside the reaction vessel section 9 becomes about 400°C. As a result of this heating, ammonium chloride, which is 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, and the production of magnesium chloride progresses. After the heating process has been carried out for a specified time, the heater H is turned off and the material is cooled, after which the produced magnesium chloride is recovered.

[0075] The reason for blowing dry nitrogen is that, as can be seen from equation (7), moisture is generated simultaneously with the generation of magnesium chloride, and the generated moisture is quickly discharged outside the reaction vessel section 9, preventing the magnesium chloride from becoming a hydrate and generating anhydrous magnesium chloride. Furthermore, 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 procedure involves reacting magnesium oxide with ammonium chloride in a molar ratio of 1:3 to produce ammonium carbohydrate, and then removing the water and ammonium chloride to obtain anhydrous magnesium chloride.

[0077] More specifically, a mixture of magnesium oxide and ammonium chloride in a molar ratio of 1:3 is placed in the reaction vessel section 9 .

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

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

[0080] This causes the reaction shown in formula (8) below to produce an 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 preferable that the reaction vessel section 9 is a pressure-resistant vessel that can withstand the pressure increase. However, if the pressure exceeds atmospheric pressure slightly, the gas exhaust port OUT may be opened to prevent the pressure from increasing, 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 that the temperature inside the reaction vessel portion 9 is kept 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 drops 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 carried out for a predetermined time.

[0085] In this way, when a hydrate of ammonium carbohydrate is heat-treated in 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 to the outside of 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 that the temperature inside the reaction vessel section 9 is maintained 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 section 9, so the state is changed to a dry nitrogen stream when 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, 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 about 700°C in a brick furnace to melt the magnesium chloride.

[0094] At least one pair of electrodes is installed inside the brick furnace, and 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] Since hydrogen chloride gas is produced by reacting hydrogen gas with chlorine gas, hydrogen chloride gas may be produced 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 of converting the magnesium produced in the molten salt electrolysis step into powdered magnesium, and may be carried out using a general grinder or a fine powder production device called a gas atomizer.

[0097] When the atomization step is carried out using a pulverizer, it is advisable to carry out the pulverization step in two stages in consideration of pulverization efficiency. Specifically, the atomization process should preferably include a coarse crushing process in which the magnesium is coarsely crushed to a particle size of about 180 to 800 μm using a device that does not achieve atomization 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 size of the particles that can pass through a sieve with a mesh opening of about 0.8 mm in the coarse pulverization process.

[0099] By the way, when magnesium is roughly crushed, the fact that it is a soft metal does not cause any problems, but when it comes to the stage of fine crushing, the magnesium particles stick together during the crushing process, making it difficult to form 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, stearic acid or the like may be used as the grinding aid, but it is preferable to use powder of an inorganic compound. Specifically, if magnesium oxide, which is a powder of an inorganic compound, is used as the grinding aid, it has the same composition as combustion ash, so it becomes possible to use part of the combustion ash as the grinding aid.

[0101] (Hydrogenation process) The magnesium atomized in the atomization step is hydrogenated in the hydrogenation step, but 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 step must be handled so as not to come into contact with oxygen until the hydrogenation step is completed.

[0102] Specifically, a method for performing the hydrogenation step without exposing the material to the 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 Figure 3, the apparatus for carrying out the hydrogenation process includes a heating container HB that contains atomized magnesium and reacts it with hydrogen, a heater H1 that heats 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 that connects the inlet HB1 to the heating section HB2, and when the valve HB4 is closed, the vessel becomes airtight. 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 in the fine pulverization process. Therefore, the fine pulverization process is carried out in an argon gas atmosphere, and before removing the heating container HB from the pulverization device performing the fine pulverization 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 sealed in 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 temperature inside 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 treatment.

[0108] When magnesium is reduced to a fine powder, it becomes more flammable and is generally treated as a hazardous material under the Fire Service Act. On the other hand, magnesium hydride, even in its fine powder form, is not classified as a hazardous material under the Fire Service Act, and its hydrogenation makes it less flammable.

[0109] Furthermore, magnesium hydride with a hydrogenation rate of approximately 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 only needs to achieve a hydrogenation rate that does not make it 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 significantly as the purity increases. Therefore, as mentioned above, if low-purity magnesium hydride is produced in which at least the surface side is hydrogenated to a hydrogenation rate of 30 mass% or less, the time required for the hydrogenation process can be significantly reduced, and productivity can be significantly increased.

[0111] After the hydrogenation treatment is carried out for a short time in this manner, 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 this embodiment does not generate carbon dioxide during power generation, and is a resource-recycling thermal power generation method in which magnesium resources are recycled. Furthermore, since the resource recycling process described above is comprised entirely of facilities that run on electricity, fuel can be recycled and produced 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 for surplus electricity from renewable energy sources, etc., while the above-mentioned thermal power generation method is a power generation method 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 carried out using electricity without inertia, such as renewable energy, so that the thermal power generation method can convert 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 called stoker boilers, which do not use pulverized coal burners, but instead have a combustion chamber that is simply configured like a combustion furnace, with coal simply being fed into the boiler to keep it burning constantly.The fuel described above may also be used in such a configuration.

[0116] Furthermore, in this case, there is no need for the fine pulverization process to crush the material to 150 μm or less, which was necessary to sustain combustion as a burner flame, and since it is only necessary 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 hazardous material under the Fire Service Act. Therefore, it is also possible to use a thermal power generation method in which the magnesium is used as fuel by simply performing 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 it is possible to carry out a resource recycling process. 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 in the case where the fuel is not hydrogenated as described above but 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] Furthermore, 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 specific embodiments, and appropriate modifications and improvements are also included within the technical scope of the present invention, which will be clear 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 31 Powder combustion burner 4 Auxiliary Fuel Storage 41 Auxiliary combustion burner 5 Denitration equipment 6 Dust collector 7. Ash storage facility 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 step of burning fuel in a combustion chamber of the power boiler to generate power; a resource recycling process for generating raw materials for fuel from 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 composed only of magnesium oxide, magnesium hydroxide, or a mixture thereof; The resource recycling step a chlorination step of producing anhydrous magnesium chloride using the combustion ash as a material and hydrogen chloride gas; a molten salt electrolysis step of producing magnesium by performing molten salt electrolysis using the anhydrous magnesium chloride produced in the chlorination step as a material, The thermal power generation method, wherein anhydrous magnesium chloride is produced while both the supply and exhaust of the hydrogen chloride gas are carried out in the chlorination step.

2. the fuel is the magnesium hydride with a hydrogenation rate of 30 mass% or less, The resource recycling step an atomization step of atomizing the magnesium produced in the molten salt electrolysis step to particles having 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 pulverization step of coarsely pulverizing 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. The thermal power generation method according to any one of claims 1 to 5, further comprising a combustion chamber humidity increasing step of increasing 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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