Thermal power generation method

Abstract

Provided is a thermal power generation method in which emission of carbon dioxide during power generation is suppressed by using techniques gained in coal-fired power generation. The present disclosure relates to a resource circulation-type thermal power generation method comprising: a power generation step for generating power by combusting fuel in a combustion chamber of a boiler device; and a resource regeneration step for generating a raw material for fuel from combustion ash generated in said combustion. The fuel is magnesium or calcium, or magnesium hydride or calcium hydride having a layer hydrogenated on at least the surface thereof. The combustion ash contains magnesium oxide, magnesium hydroxide, or a mixture thereof, or calcium oxide, calcium hydroxide, or a mixture thereof. The resource regeneration step serves to generate, from the combustion ash, magnesium or calcium, or magnesium hydride or calcium hydride having a layer hydrogenated on at least the surface.

Description

Thermal power generation method

[0001] The present disclosure relates to a thermal power generation method.

[0002] Coal-fired power generation systems equipped with power-generating 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 coal emitting carbon dioxide when burned.

[0003] One technology that may provide a solution to 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 CCS efforts in Tomakomai City, Hokkaido, specifically explaining that carbon dioxide is separated and captured from exhaust gases from thermal power plants, and then the captured carbon dioxide is injected and stored deep underground beneath the seabed about 3 to 4 km from the coast. Carbon dioxide injected deep underground in this way is thought to be stored stably for a long period of time, and to dissolve in 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.

[0006] “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>, “CCS: Capture and Bury CO2: After Demonstration Tests, Realization is Near (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>

[0007] The present disclosure has been made in consideration of the above circumstances, and aims to provide a thermal power generation method that utilizes technology cultivated in coal-fired power generation and reduces carbon dioxide emissions during power generation.

[0008] To achieve the above object, the present disclosure is grasped by the following configuration: (1) A resource recycling thermal power generation method according to an embodiment of the present disclosure includes a power generation step of burning fuel in a combustion chamber of a boiler apparatus to generate power, and a resource recycling step of producing raw material for fuel from combustion ash generated by the combustion, wherein the fuel is magnesium or calcium, or magnesium hydride or calcium hydride having at least a hydrogenated layer on its surface, and the combustion ash contains magnesium oxide, magnesium hydroxide, or a mixture thereof, or calcium oxide, calcium hydroxide, or a mixture thereof, and the resource recycling step produces magnesium or calcium, or magnesium hydride or calcium hydride having at least a hydrogenated layer on its surface, from the combustion ash.

[0009] (2) In the above configuration (1), the resource recycling step may include a microparticulation step of microparticulating the produced magnesium or calcium.

[0010] (3) In the configuration of (2) above, the combustion may be performed using a powder combustion burner.

[0011] (4) In the configuration of (2) above, the atomization process may include a coarse grinding process for coarsely grinding the produced magnesium or calcium, and a fine grinding process for further grinding the magnesium or calcium ground in the coarse grinding process.

[0012] (5) In the above configuration (4), the fine pulverization step may be carried out by adding powder of an inorganic compound as a pulverization aid.

[0013] (6) In the above configuration (5), the inorganic compound may be magnesium oxide or calcium oxide.

[0014] (7) In the configurations (2) to (6) above, the resource recycling process may further include a hydrogenation process in which the surface of the magnesium or calcium atomized in the atomization process is hydrogenated to produce magnesium hydride or calcium hydride having a hydrogenation rate of 30 mass% or less.

[0015] (8) In the above configuration (7), after the atomization step, the atomized magnesium or calcium may be handled so as not to come into contact with oxygen until the hydrogenation step is completed.

[0016] (9) In the configurations (1) to (8) above, moisture may be supplied into the combustion chamber as a combustion promoter.

[0017] (10) In the configurations of (1) to (9) above, the fuel may be magnesium or the magnesium hydride, and the resource recycling process may include a chlorination process for producing magnesium chloride using the combustion ash, and a molten salt electrolysis process for producing magnesium by performing molten salt electrolysis using the magnesium chloride produced in the chlorination process.

[0018] According to the present disclosure, it is possible to provide a thermal power generation method that utilizes technology cultivated in coal-fired power generation and reduces carbon dioxide emissions during power generation.

[0019] 1 is a diagram for explaining the configuration of a power generation system for performing a power generation step according to an embodiment of the present invention; 2 is a diagram for explaining an apparatus for performing a hydrogen chloride gas method according to an embodiment of the present invention; 3 is a diagram for explaining the configuration of an apparatus for performing a hydrogenation step according to an embodiment of the present invention;

[0020] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a detailed description of the present invention will be given with reference to the accompanying drawings. The same elements are designated by the same reference numerals throughout the description of the embodiments.

[0021] (Embodiment) FIG. 1 is a diagram illustrating the schematic configuration of a power generation system (hereinafter, sometimes referred to as a "power plant," and in this specification, "power plant" can be replaced with "power generation system") according to this embodiment. The power generation system includes a power generator 1 and a boiler unit 2 (hereinafter, sometimes referred to as a "power generation boiler 2," and in this specification, "power generation boiler" can be replaced with "boiler unit") having a combustion chamber B1. In the power generation system of this embodiment, the power generator 1 generates power using steam generated by the boiler unit 2. The resource recycling thermal power generation method of this embodiment includes a power generation process in which fuel is combusted in the combustion chamber B1 of the boiler unit 2 to generate power, and a resource recycling process in which raw materials for fuel are generated from combustion ash generated by the combustion. Therefore, the power generation process and the resource recycling process will be described below in that order.

[0022] (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.

[0023] In the embodiment shown in FIG. 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 denitration 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 denitration device 5, and a combustion ash storage tank 7 that stores the combustion ash.

[0024] The power generation boiler 2 may include a combustion chamber B1, a steam turbine B2 whose rotating shaft is connected to the generator 1 and 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.

[0025] A water supply pump P is provided in the middle of the pipe B3 connecting the condenser FU and the combustion chamber B1, and supplies water to the combustion chamber B1.

[0026] The combustion chamber B1 is equipped with a burner 31 that burns fuel supplied from the fuel storage 3. The burner 31 may be, for example, a powder combustion burner 31 that burns powder fuel. Although an embodiment in which the burner 31 is a powder combustion burner will be described below, it is not intended that the fuel be limited to powder.

[0027] The combustion chamber B1 may further include an auxiliary combustion burner 41 that burns liquid fuel (for example, heavy oil, light oil, etc.) supplied from the auxiliary fuel storage 4.

[0028] The burner 31 or powder combustion burner 31 may be the same as a 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 the same as that used in coal-fired power generation.

[0029] In addition, the auxiliary combustion burner 41 is a burner for generating auxiliary heat 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.

[0030] The auxiliary combustion burner 41 may be stopped after the combustion in the powder combustion burner 31 has stabilized. Note that, since thermal power plants often operate without being shut down, the amount of carbon dioxide generated by the auxiliary combustion burner 41, which is mainly used at the start of operation, is extremely small.

[0031] The fuel storage 3 stores a fuel that does not emit carbon dioxide when burned, preferably a powder fuel such as magnesium or calcium, or magnesium hydride or calcium hydride having at least a hydrogenated layer on its surface. In this embodiment, the fuel is preferably adjusted to an appropriate particle size.

[0032] However, since magnesium or calcium, or magnesium hydride or calcium hydride having at least a hydrogenated layer on its surface, is not perfectly spherical, the particle size referred to here can be considered to be a size that allows the particle to pass through a sieve with a specified mesh opening.

[0033] In the powder combustion burner 31, the fuel mixed with air is burned, but since the fuel is magnesium or calcium, or a substance consisting of magnesium or calcium and hydrogen, no carbon dioxide is generated during the combustion. Note that the combustion ash may contain hydroxides due to the reaction between water generated by the combustion of the hydride and some of the oxides.

[0034] The magnesium hydride and calcium hydride used in the fuel may have particle sizes of, for example, 150 μm or less. Furthermore, the magnesium hydride and calcium hydride are not 100% pure, but are preferably low-purity hydrides with a hydrogenation rate of 30 mass% or less, at least on the surface side.

[0035] In other words, it is preferable that the magnesium or calcium is not hydrided to the core, but that the surface of the magnesium or calcium is covered with a layer of magnesium hydride or calcium hydride.

[0036] In the case of such low-purity hydrides, when air is used as a combustion supporting gas, two reactions must be considered: the combustion reaction of the magnesium hydride portion or calcium hydride portion, and the combustion reaction of the magnesium portion or calcium portion.

[0037] However, the combustion reaction between the magnesium hydride portion or calcium hydride portion and oxygen is as shown in the following formulas (1) and (1'), and the combustion reaction between the magnesium portion or calcium portion and oxygen is as shown in the following formulas (2) and (2'). Therefore, even if a low-purity hydride is used as the fuel, no carbon dioxide is generated during combustion. ２ + O ２ → MgO + H ２ O・・・・・・・・・・・・(1) 2Mg + O ２ → 2MgO・・・・・・・・・・・・・・・(2) CaH ２ + O ２ → CaO + H ２ O・・・・・・・・・・・・(1') 2Ca + O ２ → 2CaO・・・・・・・・・・・・・・・(2')

[0038] On the other hand, when hydrides mixed with air are burned in the powder combustion burner 31, nitrogen and a small amount of carbon dioxide are present along with oxygen. In particular, magnesium and calcium may also react with nitrogen at high temperatures and in an oxygen-deficient atmosphere, producing magnesium nitride and calcium nitride as shown in the following formulas (3) and (3'). Furthermore, the reactions of magnesium and calcium, as well as magnesium hydride and calcium hydride, with carbon dioxide are shown in the following formulas (11) to (14). 3Mg + N ２ → Mg ３ N ２ ・・・・・・・・・・・・・・・・・・(3) 3Ca + N ２ → Ca ３ N ２ ・・・・・・・・・・・・・・・・・・(3') 2Mg + CO2 → 2MgO + C・・・・・・・・・・・・・・・(11) 2MgH2 + CO2 → 2MgO + 2H2 + C・・・・・・・・・(12) 2Ca + CO2 → 2CaO + C・・・・・・・・・・・・・・・(13) 2CaH2 + CO2 → 2CaO + 2H2 + C・・・・・・・・・(14)

[0039] Therefore, when fuel is incompletely burned, nitrides may be formed and mixed into the combustion ash. Note that, since high temperature and oxygen-deficient conditions are favorable for nitride formation, it is thought that the nitride formation reaction occurs in or near the combustion flame.

[0040] The nitride quickly decomposes in reaction with water, and changes into magnesium hydroxide or calcium hydroxide and ammonia, as shown in the following formulas (4) and (4'). ３ N ２ + 6H ２ O → 3Mg(OH) ２ + 2NH ３ ... (4) Ca ３ N ２ + 6H ２ O → 3Ca(OH) ２ + 2NH ３ ... (4')

[0041] Therefore, when nitrides are produced, there is a possibility that ammonia gas may be generated from the combustion ash after the combustion ash is collected.

[0042] For this reason, it is preferable to increase the humidity in the combustion chamber B1 so that even if nitrides are generated, they can be decomposed quickly. In this way, even if nitrides are generated, they will be decomposed immediately, and the ammonia generated by the decomposition can also contribute to combustion as combustion gas. Therefore, moisture may be supplied into the combustion chamber B1 as a combustion promoter. By doing so, it is possible to suppress incomplete combustion that generates nitrides.

[0043] 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 fuel to form a burner flame.

[0044] Furthermore, considering that moist air has a higher thermal conductivity than dry air, this embodiment tends to increase the heat exchange efficiency in the pipe B3 passing through the combustion chamber B1.

[0045] When air is used as a combustion supporting gas, nitrogen gas is contained therein, and therefore nitrogen oxides (NOx) may be generated during combustion. Therefore, in the embodiment shown in FIG. 1 , the power generation system is provided with a denitration device 5 in the exhaust pipe 8 that sends the exhaust gas from the combustion chamber B1 to the dust collector 6 in order to neutralize the nitrogen oxides (NOx) in the exhaust gas. Instead of or in addition to providing the denitration device 5, 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, in order to suppress the generation of nitrogen oxides (NOx). 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 denitration device 5 may be omitted.

[0046] The denitration device 5 may be similar to the denitration devices generally used in coal-fired power plants, and may have a configuration in which, for example, ammonia is added to the exhaust gas and the exhaust gas is passed through a catalyst layer to decompose nitrogen oxides (NOx) into harmless nitrogen and water.

[0047] The exhaust gas that has passed through the denitration device 5 may contain combustion ash that has an extremely small particle size, which is generated during combustion. Therefore, in the embodiment shown in Fig. 1, the exhaust pipe 8 is 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.

[0048] This dust collector 6 may be the same as that used in coal-fired power plants, specifically, an electrostatic precipitator. As shown in Figure 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 released into the atmosphere via the denitration device 5 and the dust collector 6.

[0049] On the other hand, in coal-fired power generation, coal is used as fuel, and therefore the sulfur components contained in the coal are contained in the exhaust gas. For this reason, in coal-fired power generation, a desulfurization device is further installed before the exhaust gas is released into the atmosphere. In contrast, in this embodiment, the fuel does not contain sulfur components, so there is an advantage that a desulfurization device is not required.

[0050] Furthermore, in coal-fired power generation, carbon dioxide is contained in the exhaust gas, so when the exhaust gas is released into the atmosphere, it is necessary to release it from a tall chimney. However, in this embodiment, the generation of carbon dioxide during power generation is suppressed, so such a tall chimney is not necessary.

[0051] The combustion ash that accumulates 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, they undergo the resource recycling process described below and are recycled into fuel that can be used again in the power generation process.

[0052] 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 the mechanism for collecting the combustion ash generated in this embodiment can be a similar mechanism.

[0053] However, in this embodiment, since the amount of combustion ash generated is greater than when coal is burned, it is preferable to improve the capacity of the recovery mechanism compared to the recovery mechanism used in coal-fired power generation.

[0054] As can be seen from the above explanation, if magnesium or calcium, or magnesium hydride or calcium hydride having at least a hydrogenated layer on its surface, is used as fuel, it is possible to carry out a power generation process that is extremely compatible with the coal-fired power generation technology that has been cultivated up to now and that reduces carbon dioxide emissions.

[0055] Furthermore, the combustion ash generated when the fuel is burned is magnesium oxide or calcium oxide. Magnesium oxide and calcium oxide have high melting points (for example, the melting point of magnesium oxide is approximately 2850°C), so they are prevented from melting even in high-temperature locations such as the inside of the combustion chamber B1.

[0056] On the other hand, since coal contains silicon as an ingredient, some of its combustion ash melts at 1000°C to 1300°C, which can cause molten deposits to form in various places such as the inside of the combustion chamber and the chimney.

[0057] Therefore, in this embodiment, it is possible to suppress the occurrence of molten deposits, and it is also possible to reduce the effort required for cleaning, etc.

[0058] (Resource Recycling Step) The power generation method of this embodiment includes a resource recycling step of generating raw materials for fuel from combustion ash generated in combustion. The resource recycling step of this embodiment is a step of generating magnesium or calcium, or magnesium hydride or calcium hydride having at least a hydrogenated layer on its surface, from the combustion ash. Hereinafter, a resource recovery step will be described, in which magnesium or calcium, or magnesium hydride or calcium hydride having at least a hydrogenated layer on its surface is generated again using combustion ash (including magnesium oxide, magnesium hydroxide, calcium oxide, and / or calcium hydroxide) generated in the power generation step as a starting material.

[0059] In addition, hydroxides undergo a dehydration reaction when heated to become oxides, so the starting material for the resource recovery process can be considered to be oxides. For example, magnesium hydroxide contained in combustion ash undergoes a dehydration reaction when heated to become magnesium oxide, as shown in the following formula (5): Mg(OH) ２ → MgO + H ２ O・・・・・・・・・・・・・・・(5)

[0060] In addition, when the combustion ash contains calcium hydroxide (Ca(OH)2), a dehydration reaction occurs by heating, as shown in the following reaction formula (5'), to produce calcium oxide (CaO). Ca(OH) ２ → CaO + H ２ O・・・・・・・・・・・・・・・(5')

[0061] The resource recycling step preferably produces a fuel (magnesium or calcium) from an oxide (magnesium oxide or calcium oxide) contained in the combustion ash of the fuel. The resource recycling step may produce the fuel by directly reducing the oxide by a known method, or may produce an intermediate from the oxide and reduce the intermediate to produce the fuel. Such an intermediate may be a chloride.

[0062] Therefore, the resource regeneration process may include a chlorination process for producing chlorides using oxides contained in the fuel combustion ash as a material, and a molten salt electrolysis process for producing fuel using the chlorides produced in the chlorination process as a material. Alternatively, the resource regeneration process may include a direct reduction process for producing fuel by directly reducing oxides contained in the fuel combustion ash.

[0063] When the fuel is magnesium or magnesium hydride, a chlorination process is first carried out to produce magnesium chloride from magnesium oxide as a starting material, and then the magnesium chloride produced in the chlorination process is used as a material to carry out molten salt electrolysis to produce magnesium.

[0064] When the fuel is calcium or calcium hydride, the resource recovery process may include a chlorination process in which calcium chloride is produced using calcium oxide in the combustion ash as a material, and a molten salt electrolysis process in which calcium is produced using the calcium chloride produced in the chlorination process as a material, or may include a direct reduction process in which calcium oxide in the combustion ash is directly reduced to produce calcium.

[0065] The magnesium or calcium thus obtained may be further pulverized in an atomization step and may be subjected to a hydrogenation step to produce a hydride having at least a hydrogenated layer on the surface.

[0066] (Chlorination process) The chlorination process is a process for producing chlorides using oxides contained in the combustion ash of the fuel as a material. Hereinafter, an example of producing magnesium chloride using magnesium oxide, which is the combustion ash, as a material will be described. The magnesium chloride can be used in the subsequent molten salt electrolysis process.

[0067] Examples of methods for the chlorination step include a method using hydrogen chloride water (hydrochloric acid) (hereinafter referred to as the "hydrogen chloride water method"), a method using hydrogen chloride gas (hereinafter referred to as the "hydrogen chloride gas method"), a method using chlorine gas (hereinafter referred to as the "chlorine gas method"), and a method using ammonium chloride (hereinafter referred to as the "ammonium chloride method"). Among these, the chlorine gas method is preferred in this embodiment. By using the chlorine gas method, the chlorination step and the molten salt electrolysis step can be easily carried out continuously. In particular, the chlorine gas method is preferred in that the chlorination step can be carried out using the chlorine gas generated in the molten salt electrolysis step described below as it is.

[0068] (Hydrogen chloride gas method) The hydrogen chloride gas method is a method for producing magnesium chloride by causing the reaction of magnesium oxide and hydrogen chloride gas at a temperature of about 300 to 600°C according to the following formula (6). This will be explained with reference to Figure 2, which is a diagram illustrating the apparatus for carrying out the hydrogen chloride gas method. Note that Figure 2 shows only the main parts. MgO + 2HCl → MgCl ２ + H ２ O・・・・・・・・・(6)

[0069] 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.

[0070] The reaction vessel 9 includes a cylindrical body 91 that opens at the top and bottom, an upper lid 92 that closes the upper opening of the body 91 , and a lower lid 93 that closes the lower opening of the body 91 .

[0071] 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.

[0072] 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.

[0073] Specifically, the process may be performed by first placing magnesium oxide in the reaction vessel section 9, heating the reaction vessel section 9 with the heater H so that 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. Note that a process performed while both supplying and discharging gas is performed is sometimes called a streamer process.

[0074] As a result, moisture adhering to the magnesium oxide can be removed. After the magnesium oxide has been dried as described above, the gas supplied from the gas supply port IN may be changed to hydrogen chloride gas, and a chlorination treatment may be carried out in which the magnesium oxide and the hydrogen chloride gas are reacted to produce magnesium chloride.

[0075] As can be seen from the formula (6) shown above, water is also generated in the reaction, but by carrying out this chlorination treatment using the streamer treatment, magnesium chloride does not become a hydrate, and anhydrous magnesium chloride can be produced.

[0076] 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.

[0077] As described above, the produced anhydrous magnesium chloride is removed from the reaction vessel part 9 by opening the bottom lid 93 and used as a material in the next step, which is the molten salt electrolysis step. Before opening the bottom lid 93, the supplied gas may be switched to, for example, dry nitrogen, to replace the hydrogen chloride gas in the reaction vessel part 9.

[0078] Alternatively, a chloride of an alkali metal or alkaline earth metal may be introduced into the reaction vessel section 9 together with magnesium oxide. Examples of the chloride of an alkali metal or alkaline earth metal include sodium chloride, potassium chloride, and calcium chloride.

[0079] In this way, by adding an alkali metal or alkaline earth metal chloride, the alkali metal or alkaline earth metal chloride can be melted at a temperature lower than the melting point of magnesium oxide, and magnesium oxide can be chlorinated in the molten salt. Therefore, it is preferable that the alkali metal or alkaline earth metal chloride has a melting point lower than that of magnesium oxide.

[0080] In this method, the reaction vessel section 9 contains a molten salt of an alkali metal or alkaline earth metal chloride and magnesium oxide, and hydrogen chloride gas is supplied from a gas supply port IN. This method may include a step of drying the magnesium oxide before introducing the magnesium oxide into the reaction vessel section 9. The drying step may be, for example, a step of blowing the magnesium oxide with a dry gas (e.g., dry air or dry nitrogen) before supplying the magnesium oxide to the reaction vessel section 9.

[0081] The magnesium chloride produced by the reaction dissolves because it is a substance with high solubility in the molten salt of an alkali metal or alkaline earth metal chloride. On the other hand, magnesium oxide exists as a solid in the molten salt until it reacts according to the above reaction formula (6). Therefore, the progress of the reaction in the chlorination step can be estimated by monitoring the amount of solid in the reaction vessel section 9. For example, the completion of the chlorination step can be determined when the rate of decrease in the amount of solid in the reaction vessel section 9 becomes equal to or less than a certain value.

[0082] In this method, the chlorination treatment is carried out by the windsock treatment, so that the magnesium chloride does not become a hydrate, and anhydrous magnesium chloride can be produced. In this case, the hydrogen chloride gas that did not contribute to the reaction and is exhausted from the gas exhaust port OUT may be dehydrated and supplied again from the gas supply port IN.

[0083] When the chlorination reaction has progressed completely, a molten salt of alkali metal or alkaline earth metal chlorides including magnesium chloride is obtained as a liquid phase. This liquid phase may be used in the next step, the molten salt electrolysis step. Before discharging the liquid phase, the hydrogen chloride gas in the reaction vessel section 9 may be replaced with, for example, dry nitrogen.

[0084] (Chlorine gas method) The chlorine gas method is a method in which, for example, magnesium oxide, optionally together with an alkali metal or alkaline earth metal chloride, is charged into a chlorination furnace and the magnesium oxide is brought into contact with chlorine gas to produce magnesium chloride. The chlorine gas method can be carried out in the same manner as the hydrogen chloride gas method, except for the following points, and the configuration of the apparatus used may be the same as that explained in FIG. 2.

[0085] In the chlorine gas method, magnesium oxide and chlorine gas react with each other to produce magnesium chloride according to the following reaction formula (16). The reaction temperature may be 300 to 800°C. Examples of chlorides of alkali metals or alkaline earth metals include sodium chloride, potassium chloride, and calcium chloride. 2MgO + 2Cl → 2MgCl + O (16)

[0086] In the chlorine gas method, chlorine gas is supplied from a gas supply port IN. In the chlorination of magnesium oxide by the chlorine gas method, oxygen is generated as shown in the above formula (16). Therefore, by monitoring the oxygen concentration in the reaction vessel section 9, the reaction progress of the chlorination step can be estimated. For example, when the oxygen concentration in the reaction vessel section 9 becomes equal to or greater than a pre-calculated value, it may be determined that the chlorination step is complete.

[0087] Even in the chlorine gas method, by performing the chlorination treatment by the wind-sink treatment, magnesium chloride does not become a hydrate, and anhydrous magnesium chloride can be produced. In this case, the chlorine gas that did not contribute to the reaction and is exhausted from the gas exhaust port OUT may be optionally subjected to oxygen removal treatment and supplied again from the gas supply port IN.

[0088] In order to improve the reaction efficiency, the chlorination step by the chlorine gas method may be carried out followed by the chlorination step by the hydrogen chloride gas method. In this case, after supplying chlorine gas, the oxygen concentration and the amount of solids in the molten salt may be monitored to confirm that the chlorination has progressed to a certain extent, and then the supply gas may be switched from chlorine gas to hydrogen chloride gas, thereby carrying out chlorination by hydrogen chloride gas.

[0089] (Ammonium chloride method) The ammonium chloride method is a method of reacting magnesium oxide with ammonium chloride, and there are two possible procedures for this method. In either procedure, the apparatus configuration may be the same as that described with reference to Fig. 2, and therefore the following description will also refer to Fig. 2.

[0090] 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 shown in formula (7) below: MgO + 2NH ４ Cl → MgCl ２ + H ２ O + 2NH ３ ... (7)

[0091] For example, a mixture 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 .

[0092] As shown in formula (7), in terms of the chemical formula, the molar ratio of magnesium oxide to ammonium chloride should be 1:2. However, in actual treatment, taking into consideration 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 about 1:3 to 1:5.

[0093] Then, while blowing dry nitrogen, heating is performed with heater H so that the temperature inside reaction vessel section 9 reaches around 400° C. By this heating, ammonium chloride, which is solid at room temperature, begins to sublimate at a temperature of around 300° C. and decomposes into ammonia gas and hydrogen chloride gas, and the hydrogen chloride gas generated by this decomposition reacts with magnesium oxide, progressing the generation of magnesium chloride. After the heating treatment has been performed for a predetermined time, heating with heater H is stopped, the system is cooled, and the generated magnesium chloride is then recovered.

[0094] The reason for blowing dry nitrogen is that, as can be seen from formula (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. 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 midway.

[0095] 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.

[0096] Specifically, a mixture of magnesium oxide and ammonium chloride in a molar ratio of 1:3 is introduced into the reaction vessel 9. After that, dry nitrogen is blown in for a while to replace the inside of the reaction vessel 9 with a dry nitrogen atmosphere.

[0097] Then, when the inside of the reaction vessel part 9 becomes a dry nitrogen atmosphere, the gas supply port IN and the gas exhaust port OUT are closed to seal the reaction vessel part 9, and heating with the heater H is started so that the inside of the reaction vessel part 9 becomes around 400°C.

[0098] This causes the reaction shown in formula (8) below to produce ammonium carbohydrate: MgO + 3NH ４ Cl → MgCl ２ ・NH ４ Cl-H ２ O + 2NH ３...(8)

[0099] As can be seen from equation (8), in this reaction, the solid magnesium oxide reacts with ammonium chloride, generating ammonia as gas, which causes an increase in internal pressure.

[0100] For this reason, it is preferable that the reaction vessel section 9 be 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 suppress the pressure increase, and it is not necessary to use a pressure-resistant vessel.

[0101] After the heating process has been carried out 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 (a temperature about 5 to 20° C. lower than the sublimation temperature).

[0102] When the temperature inside the reaction vessel part 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.

[0103] In this way, when the ammonium carbohydrate hydrate is heat-treated under an ammonia gas atmosphere, the water content of the hydrate inhibits the hydrolysis reaction of the ammonium carbohydrate, and the dehydration reaction shown in the following formula (9) proceeds. ２ ・NH ４ Cl-H ２ O → MgCl ２ ・NH ４ Cl+H ２ O... (9)

[0104] In addition, since the ammonia gas is blown away, the water generated by dehydration is quickly discharged outside the reaction vessel section 9, thereby suppressing the formation of hydrates again.

[0105] 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.).

[0106] 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.

[0107] As a result, as shown in the following formula (10), the ammonium carbohydrate decomposes into magnesium chloride, ammonia gas, and hydrogen chloride gas, and the ammonium chloride moiety is removed from the ammonium carbohydrate (hereinafter also referred to as "ammonium dechlorination treatment"), producing anhydrous magnesium chloride. ２ ・NH ４ Cl → MgCl ２ +NH ３ +HCl・・・・・・(10)

[0108] The ammonia gas and hydrogen chloride gas are exhausted together with the blown-away dry nitrogen to the outside of the reaction vessel section 9. After the ammonium chloride removal treatment is completed, the heater H is turned off to cool the system, and the anhydrous magnesium chloride produced is recovered.

[0109] (Hydrogen chloride water method) The hydrogen chloride water method is a method in which combustion ash and hydrogen chloride (HCl) water are dropped into a chlorination tank to chlorinate magnesium oxide. Magnesium oxide undergoes the reaction shown in the following reaction formula (15) in hydrogen chloride water to become magnesium chloride (MgCl2). MgO + 2HCl → MgCl2 + HO (15)

[0110] Since magnesium chloride produced by the reaction has a high solubility in water, it will dissolve in the hydrogen chloride solution if the hydrogen chloride solution contains a sufficient amount of water. On the other hand, magnesium oxide exists as a solid in the hydrogen chloride solution until it reacts according to the above reaction formula (15). Therefore, the progress of the reaction in the chlorination step can be estimated by monitoring the amount of solids in the chlorination tank. For example, the completion of the chlorination step can be determined when the rate of decrease in the amount of solids in the chlorination tank falls below a certain level.

[0111] In the above method, it is preferable to proceed with the chlorination reaction while heating the chlorination tank. The temperature of the chlorination tank may be, for example, room temperature to 400°C, or 80 to 300°C. It is also preferable to proceed with the chlorination reaction while stirring the hydrogen chloride water. When the temperature of the chlorination tank exceeds the boiling point of the hydrogen chloride water at atmospheric pressure, the chlorination step may be carried out under pressure-resistant conditions (sealed conditions).

[0112] (Pretreatment step) Note that, prior to the chlorination step by any of the above methods, a step of pretreating the combustion ash may be carried out. Also, the pretreatment step and the chlorination step may be repeated as a set. The number of repetitions is not particularly limited, but may be, for example, 2 to 10 times. In this case, any of the above methods may be used for the chlorination step.

[0113] The pretreatment step includes a step of pulverizing the magnesium oxide in the combustion ash and a step of heating the magnesium oxide in the combustion ash.

[0114] The step of pulverizing the magnesium oxide in the combustion ash is a step of pulverizing the combustion ash using a pulverizer such as a ball mill, bead mill, hammer mill, pin mill, roller mill, or jet mill, or a combination of these pulverizers. For example, pulverization using a ball mill may be carried out under conditions of, for example, 50 to 1000 rpm, preferably 100 to 600 rpm, for example, 1 minute to 30 hours, preferably 10 minutes to 20 hours, and more preferably 1 to 10 hours. Pulverization using a bead mill may be carried out under conditions of, for example, 50 to 5000 rpm, preferably 100 to 1000 rpm, for example, 15 seconds to 10 hours, preferably 1 minute to 3 hours.

[0115] The step of heating the magnesium oxide in the combustion ash is a step of heating the combustion ash in a heating furnace. By heating the magnesium oxide, impurities coated on the magnesium oxide particles can be removed. The heating conditions may be, for example, 100 to 1000°C, preferably 200 to 900°C, and preferably 400 to 600°C, for example, 5 minutes to 40 hours, preferably 10 minutes to 30 hours, and more preferably 1 to 20 hours.

[0116] The pretreatment step may be a combination of a step of pulverizing the magnesium oxide in the combustion ash and a step of heating the magnesium oxide in the combustion ash, for example, a step of pulverizing the magnesium oxide in the combustion ash and then further heating the magnesium oxide in the combustion ash.

[0117] (Molten Salt Electrolysis Process) The molten salt electrolysis process is a process for producing fuel using the chloride produced in the chlorination process as a material. Hereinafter, an example will be described in which magnesium is produced by electrolysis using anhydrous magnesium chloride produced in the chlorination process as a material. The molten salt electrolysis process may be, for example, a method used to produce magnesium.

[0118] Therefore, briefly explained, in the molten salt electrolysis process, for example, magnesium chloride is heated to a temperature of about 700° C. in a molten salt electrolysis bath (for example, a brick furnace) to melt the magnesium chloride.

[0119] At least one pair of electrodes is provided in the molten salt electrolytic cell. 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.

[0120] The chlorine gas generated in the molten salt electrolysis step may be used in the chlorination step by a chlorine gas method. Also, since hydrogen chloride gas is produced by reacting hydrogen gas with chlorine gas, hydrogen chloride gas may be produced from the chlorine gas generated in the molten salt electrolysis step and used in the chlorination step by a hydrogen chloride gas method, a hydrogen chloride water method, or an ammonium chloride method.

[0121] (Direct Reduction Step) The direct reduction step is a step of producing fuel by directly reducing oxides contained in the combustion ash of a fuel. When the combustion ash contains calcium oxide, calcium may be produced by directly reducing the oxides contained in the combustion ash without going through the chlorination step.

[0122] The direct reduction process can be carried out with reference to the molten salt electrolysis process, except that the starting material is an oxide.

[0123] Unlike the molten salt electrolysis process using inorganic chlorides, the direct reduction process may generate oxygen at the anode. Therefore, the anode material may be different from that used in the molten salt electrolysis process. Examples of such anodes include solid oxide electrodes made of oxides such as zirconia and carbon electrodes. Solid oxide electrodes are stable against oxygen, so oxygen is generated at the anode. On the other hand, when a carbon electrode is used, carbon dioxide may be generated at the anode.

[0124] (Regeneration System) The resource recycling process has been described above, but the resource recycling process may be performed by a regeneration system that integrates a reaction vessel section (hereinafter referred to as a chlorination furnace) for performing the chlorination process and a molten salt electrolysis cell for performing the molten salt electrolysis process. By using such a regeneration system, for example, chlorine generated at the anode in the molten salt electrolysis process can be utilized in the chlorination process. Since chlorine gas is highly corrosive, it is preferable to be able to utilize the chlorine generated in the molten salt electrolysis process in the chlorination process, as this shortens the storage time of the chlorine gas. Since the chlorine generated in the molten salt electrolysis process can be utilized directly in the chlorination process, a regeneration system for performing the chlorination process using a chlorine gas method will be described below.

[0125] In the regeneration system, the chlorination furnace and the molten salt electrolysis furnace are preferably connected by at least a supply path for supplying the inorganic chloride produced in the chlorination step from the chlorination furnace to the molten salt electrolysis furnace, and a supply path for supplying the chlorine gas produced in the molten salt electrolysis step from the molten salt electrolysis cell to the chlorination furnace. From the viewpoint of shortening the storage time of the chlorine gas, the chlorine gas storage chamber may be omitted from the supply path for the chlorine gas.

[0126] The chlorination furnace may be a batch type or a flow type. In the batch type reaction, after detecting the completion of the chlorination reaction in the chlorination furnace, the inorganic chloride is transferred from the chlorination furnace to the molten salt electrolytic cell. In the flow type reaction, the inorganic chloride is continuously transferred from the chlorination furnace to the molten salt electrolytic cell.

[0127] Hereinafter, an example will be described in which magnesium oxide and chlorine gas are added in a chlorination furnace to produce magnesium chloride, and chlorine and magnesium are produced from the magnesium chloride in a molten salt electrolytic cell.

[0128] In the chlorination furnace, magnesium oxide and chlorine gas are introduced into a molten salt of an alkali metal or alkaline earth metal chloride (e.g., sodium chloride, potassium chloride, calcium chloride, etc.). Since the solubility of magnesium oxide in the molten salt is low and the solubility of magnesium chloride is high, magnesium oxide exists as a solid, while magnesium chloride exists in the liquid phase. Furthermore, oxygen is generated during the chlorination reaction of magnesium oxide. Therefore, when the chlorination furnace is a batch type, the solid components in the liquid phase may be monitored, and the contents of the chlorination furnace may be transported to a molten salt electrolytic cell when the decrease in the solid components falls below a certain level. Alternatively, the oxygen concentration in the chlorination furnace may be measured, and the contents of the chlorination furnace may be transported to a molten salt electrolytic cell when the oxygen concentration reaches or exceeds a predetermined value.

[0129] Therefore, the chlorination furnace may be equipped with a measuring device for measuring the concentration of solid components in the liquid phase and / or a measuring device for measuring the oxygen concentration in the gas phase. Measuring devices for measuring the concentration of solid components in the liquid phase include absorption measuring devices for measuring the absorbance or light transmittance of the suspension. Measuring devices for measuring the oxygen concentration in the gas phase include known oxygen meters.

[0130] Furthermore, when the chlorination furnace is of a flow type, it is preferable to provide a filter at the outlet of the chlorination furnace to trap solid magnesium oxide so that unreacted magnesium oxide is not discharged from the chlorination furnace.

[0131] Incidentally, impurities may be removed from the liquid phase of the content of the chlorination furnace before being transported to the molten salt electrolytic cell. Furthermore, when a filter for trapping magnesium oxide is provided at the outlet of the chlorination furnace, the pore size of the filter may be set to a size that allows particulate impurities to pass through. Furthermore, particulate impurities may be separately recovered using a filter with an even smaller pore size.

[0132] The chlorides produced in the chlorination step are transferred from the chlorination furnace to the molten salt electrolytic cell via a supply path. The inorganic chlorides may be supplied to the molten salt electrolytic cell together with a molten salt of an alkali metal or alkaline earth metal chloride without being separated from each other along the supply path. For example, when a molten salt of sodium chloride is used as the molten salt of an alkali metal or alkaline earth metal, a molten salt of sodium chloride having magnesium chloride dissolved therein may be supplied to the molten salt electrolytic cell.

[0133] The inorganic chloride supplied from the chlorination furnace in this manner may differ from the operating temperature of the molten salt electrolytic cell. Therefore, the temperature of the liquid phase supplied to the molten salt electrolytic cell and the temperature of the molten salt electrolytic cell may be measured, and the temperature of the liquid phase supplied to the molten salt electrolytic cell may be adjusted depending on these temperatures. Therefore, the molten salt electrolytic cell may be equipped with a thermometer that measures the temperature of the molten salt, and the supply path from the chlorination furnace to the molten salt electrolytic cell may be equipped with a thermometer that measures the temperature of the supply (liquid phase), and a cooler and / or heater that controls the temperature of the supply.

[0134] As an example of temperature control, when the temperature of the molten salt electrolytic cell is higher than the desired reaction temperature, the temperature of the molten salt electrolytic cell may be lowered by supplying a liquid phase from a chlorination furnace that has a temperature lower than that of the molten salt in the molten salt electrolytic cell; when the temperature of the molten salt electrolytic cell is within the desired reaction temperature, the temperature change caused by supplying the liquid phase may be suppressed by adjusting the temperature of the liquid phase supplied from the chlorination furnace to the desired reaction temperature.

[0135] In a molten salt electrolytic cell, inorganic chlorides are electrolyzed in molten salt to produce chlorine and magnesium. The chlorine produced at the anode is recovered and supplied to a chlorination furnace for reuse in the chlorination process. Magnesium may liquefy in the molten salt and remain on the surface of the molten salt. In such cases, the liquefied magnesium can be recovered and cooled to obtain solid magnesium.

[0136] (Atomization step) The resource recycling step may further include an atomization step of powdering the fuel (magnesium or calcium) produced in the molten salt electrolysis step or the direct reduction step. The atomization step may be performed using a general pulverizer or a fine powder production device called a gas atomizer.

[0137] When the atomization step is carried out using a pulverizer, it is preferable to carry out the pulverization step in two stages in consideration of pulverization efficiency. Specifically, the atomization step may include a coarse pulverization step in which the fuel is coarsely pulverized to a primary particle size (for example, a particle size of about 180 to 800 μm) using a device with a high pulverization speed, and a fine pulverization step in which the fuel pulverized in the coarse pulverization step is further pulverized.

[0138] 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 step.

[0139] When the fuel is an inorganic solid fuel with low hardness, such as magnesium, it is preferable to add a grinding aid to the coarsely ground inorganic solid fuel in the fine grinding step, as this can prevent the fuel particles from sticking together during the grinding process.

[0140] For example, stearic acid or the like can be used as the grinding aid, but it is preferable to use an inorganic compound powder. Specifically, when magnesium or magnesium hydride is used as the fuel, it is preferable to use magnesium oxide, which is an inorganic compound powder, as the grinding aid, and when calcium or calcium hydride is used as the fuel, it is preferable to use calcium oxide, which is an inorganic compound powder, as the grinding aid. This makes it possible to reuse part of the combustion ash as the grinding aid.

[0141] (Hydrogenation Step) As described above, the inorganic solid fuel in this embodiment may be magnesium hydride or calcium hydride having a hydrogenated layer at least on its surface. Therefore, the resource recycling step may include a hydrogenation step of hydrogenating the magnesium or calcium atomized in the atomization step. Hereinafter, a step of producing magnesium hydride from magnesium will be described as an example.

[0142] In addition, when the inorganic solid fuel is a metal such as magnesium that is highly reactive with air, if the fuel comes into contact with oxygen after the atomization step, an oxide film may form on the surface, potentially reducing the reaction efficiency. If the resource recycling step includes a hydrogenation step, the formation of such an oxide film can be suppressed. Therefore, when the resource recycling step includes a hydrogenation step, it is preferable to handle the magnesium or calcium atomized in the atomization step so as not to come into contact with oxygen until the hydrogenation step is completed.

[0143] 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.

[0144] 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.

[0145] The heating vessel HB has a valve HB4 at a conduit HB3 extending from the inlet HB1 to the heating section HB2, and when the valve HB4 is closed, the vessel becomes airtight. On the other hand, the piping 10 is connected to a hydrogen gas supply system, an argon gas supply system, and a vacuum pump, all of which are not shown.

[0146] The heating vessel HB also serves as a recovery vessel for recovering the pulverized magnesium in the pulverization process. Therefore, the pulverization process is carried out in an argon gas atmosphere, and before removing the heating vessel HB from the pulverization device performing the pulverization process, the valve HB4 is closed and the magnesium recovered in the heating vessel HB is connected to the device shown in Figure 3 while still filled with argon.

[0147] 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.

[0148] Thereafter, the heater H1 is driven to heat the temperature inside the heating section 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.

[0149] Magnesium is highly flammable when it is in a fine powder form, but magnesium hydride is less flammable due to its hydrogenation.

[0150] Furthermore, magnesium hydride with a hydrogenation rate of approximately 20% by mass has a calorific value almost equal to that of coal, and therefore 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 allows safe handling in terms of transportation, storage, etc.

[0151] 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.

[0152] After the short-term hydrogenation treatment, the heater H1 is stopped, and after cooling, the hydrogen gas in the heating vessel HB is replaced with argon gas, and the low-purity magnesium hydride is taken out. The low-purity magnesium hydride thus produced, with at least the surface side hydrogenated to a hydrogenation rate of 30 mass% or less, is reused as fuel in the power generation process.

[0153] As described above, the thermal power generation method of this embodiment does not produce carbon dioxide during power generation, and is a resource-circulating thermal power generation method in which fuel resources are recycled. Furthermore, since the resource recycling process described above is composed only of facilities that run on electricity, it is possible to regenerate and produce fuel using only surplus electricity that cannot be connected to a grid.

[0154] 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.

[0155] 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.

[0156] The above description has been given of a power generation boiler that uses a powder combustion burner 31. However, there are also coal-fired power plants that use what are called stoker boilers, in which the combustion chamber of the power generation boiler is simply configured like a combustion furnace without using pulverized coal burners, and coal is simply fed into the boiler so that combustion continues at all times, and the fuel described above may be used in such configurations.

[0157] Furthermore, in this case, the pulverization process that was necessary to sustain combustion as a burner flame is not required, and it is only necessary to supply fuel to maintain the heat, so relatively large fuel is sufficient.

[0158] Furthermore, even in the case of magnesium, ignition potential is reduced if the particle size is kept to about 500 μm and fine pulverization is avoided. Therefore, a thermal power generation method using magnesium as fuel may be adopted in which only appropriate coarse pulverization is performed to keep the size of the magnesium to 500 μm or more, and the hydrogenation step is omitted.

[0159] 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 can be limited to coarse pulverization, and the fine pulverization process and hydrogenation process described above can be omitted.

[0160] 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.

[0161] 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.

[0162] 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.

[0163] 1... Generator, 2... Boiler device (power generation boiler), B1... Combustion chamber, B2... Steam turbine, B3... Piping, 3... Fuel storage tank, 31... Powder combustion burner, 4... Auxiliary fuel storage tank, 41... Auxiliary combustion burner, 5... Denitrification device, 6... Dust collector, 7... Combustion ash storage tank, 8... Exhaust pipe, 81... Exhaust device, FU... Condenser, P... Feedwater pump, 9... Reaction vessel section, 91... Body section, 92... Top cover, 93... Bottom cover, IN... Supply port, OUT... Exhaust port, H... Heater, 10... Piping, HB... Heating vessel, HB1... Inlet, HB2... Heating section, HB3... Conduit section, HB4... Valve, H1... Heater

Claims

1. A resource - recycling type thermal power generation method, comprising: a power generation step of burning fuel in a combustion chamber of a boiler device to generate electricity; and a resource recycling step of generating raw materials of the fuel from combustion ash generated by the combustion, wherein the fuel is magnesium or calcium, or magnesium hydride or calcium hydride having at least a hydrogenated layer on the surface, the combustion ash contains magnesium oxide, magnesium hydroxide, or a mixture thereof, or calcium oxide, calcium hydroxide, or a mixture thereof, and the resource recycling step generates magnesium or calcium, or magnesium hydride or calcium hydride having at least a hydrogenated layer on the surface from the combustion ash.

2. The method according to claim 1, wherein the resource recycling step includes an atomization step of atomizing the generated magnesium or calcium.

3. The method according to claim 2, wherein the combustion is performed using a pulverized - fuel burner.

4. The method according to claim 2, wherein the atomization step includes a coarse - pulverization step of coarsely pulverizing the generated magnesium or calcium, and a fine - pulverization step of further pulverizing the magnesium or calcium pulverized in the coarse - pulverization step.

5. The method according to claim 4, wherein the fine - pulverization step is performed by adding a powder of an inorganic compound as a pulverization aid.

6. The method according to claim 5, wherein the inorganic compound is magnesium oxide or calcium oxide.

7. The method according to claim 2, wherein the resource recycling step further includes a hydrogenation step of hydrogenating the surface of the magnesium or calcium atomized in the atomization step to generate magnesium hydride or calcium hydride having a hydrogenation rate of 30% by mass or less.

8. The method according to claim 7, wherein the atomized magnesium or calcium is handled so as not to come into contact with oxygen until the hydrogenation step is completed after the atomization step.

9. The method according to any one of claims 1 to 8, wherein moisture is supplied into the combustion chamber as a combustion promoter.

10. The fuel is magnesium or magnesium hydride, and the resource recycling process includes a chlorination step of producing magnesium chloride using the combustion ash, and a molten salt electrolysis step of performing molten salt electrolysis using the magnesium chloride produced in the chlorination step to produce magnesium. The method according to any one of claims 1 to 8.

Images