Operation method for boiler device, boiler device, and power generation system

Abstract

Provided is an operation method for a boiler device with which a carbon dioxide discharge amount during operation is limited. This operation method for a boiler device includes: burning an organic fuel in a first combustion chamber; burning an inorganic fuel in a second combustion chamber connected to the first combustion chamber; and supplying a carbon oxide gas generated by burning the organic fuel to the second combustion chamber. The inorganic fuel is an inorganic substance that can be burned in the presence of a combustion-assisting gas containing a carbon oxide gas, a hydrogenated inorganic substance resulting from hydrogenation of at least a part of the inorganic substance, or a mixture of the two.

Description

Boiler device operating method, boiler device, and power generation system

[0001] The present disclosure relates to a method for operating a boiler apparatus, a boiler apparatus, and a power generation system.

[0002] Thermal power generation systems equipped with power generation boilers are generally known (see, for example, Non-Patent Document 1). However, thermal power generation systems that use so-called fossil fuels have a problem in that they emit carbon dioxide, which is believed to be a cause of global warming.

[0003] Therefore, efforts are being made to reduce the atmospheric release of carbon dioxide even in thermal power generation systems that use fossil fuels.

[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.

[0005] 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.

[0006] However, there are many constraints to achieving this type of storage, such as the need for a geological layer with gaps that allow carbon dioxide to be stored, and for the layer to be covered with a layer that does not allow carbon dioxide to pass through.

[0007] “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>

[0008] The present disclosure has been made in consideration of the above circumstances, and aims to provide a boiler apparatus operating method, a boiler apparatus, and a power generation system that reduce carbon dioxide emissions during operation.

[0009] To achieve the above object, the present disclosure is grasped by the following configuration: (1) A method of operating a boiler apparatus according to an embodiment of the present disclosure includes: burning an organic fuel in a first combustion chamber, burning an inorganic fuel in a second combustion chamber connected to the first combustion chamber, and supplying carbon oxide gas generated by the combustion of the organic fuel to the second combustion chamber as a combustion supporting gas, wherein the inorganic fuel is an inorganic substance combustible in the presence of a combustion supporting gas containing carbon oxide gas, a hydrogenated inorganic substance in which at least a portion of the inorganic substance is hydrogenated, or a mixture thereof.

[0010] (2) In the above configuration (1), the inorganic substance is at least one of lithium, magnesium, calcium, and aluminum.

[0011] (3) In the above configurations (1) and (2), the combustion supporting gas contains carbon oxide gas and oxygen gas.

[0012] (4) A boiler apparatus according to an embodiment of the present disclosure includes a first combustion chamber for burning organic fuel and a second combustion chamber connected to the first combustion chamber for burning inorganic fuel, and the pressure of the second combustion chamber can be adjusted so that carbon dioxide gas generated in the first combustion chamber is supplied to the second combustion chamber.

[0013] (5) A power generation system according to an embodiment of the present disclosure includes the boiler device of (4) above, and a generator that generates electricity using steam generated by the boiler device.

[0014] According to the present disclosure, it is possible to provide a boiler apparatus operating method, a boiler apparatus, and a power generation system that reduce carbon dioxide emissions during operation.

[0015] Fig. 1 is a diagram for explaining a thermal power plant that implements a thermal power generation method of a first embodiment according to the present invention. Fig. 2 is a diagram for explaining a thermal power plant that implements a thermal power generation method of a second embodiment according to the present invention. Fig. 3 is a diagram for explaining a thermal power plant that implements a thermal power generation method of a fourth embodiment according to the present invention.

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the same elements are designated by the same reference numerals throughout the description of the embodiments.

[0017] (First embodiment) A thermal power generation method according to a first embodiment of the present invention can be implemented in a thermal power plant. However, since many of the components are similar to those of current thermal power plants, a description of the similarities may be omitted.

[0018] (Power Generation System and Power Generation Method) Fig. 1 is a diagram for explaining the schematic configuration of a power generation system (hereinafter sometimes referred to as a "thermal power plant", and in this specification, "thermal power plant" can be replaced with "power generation system") according to this embodiment. The power generation system includes a generator 1 and a boiler device 2 (hereinafter sometimes referred to as a "power generation boiler 2", and in this specification, "power generation boiler" can be replaced with "boiler device") that has a first combustion chamber A and a second combustion chamber B. In the power generation system, the generator 1 generates electricity using steam generated by the boiler device 2.

[0019] In the embodiment shown in FIG. 1 , the power generation system includes, in addition to the generator 1 and the boiler device 2, an organic fuel storage tank 3 that stores organic fuel to be supplied to the boiler device 2, and an inorganic fuel storage tank 4 that stores inorganic fuel to be supplied to the boiler device 2.

[0020] In the embodiment shown in Figure 1, the boiler device 2 includes a first combustion chamber A and a second combustion chamber B (which may be collectively referred to as combustion chambers 21), a steam turbine 22 whose rotating shaft is connected to the generator 1 and which is driven by steam produced in the combustion chambers 21, and piping 23 for supplying the steam to the steam turbine 22 and for supplying water that has been returned to a liquid state in a condenser (not shown) back to the combustion chambers 21.

[0021] The combustion chamber 21 comprises a first combustion chamber A which receives organic fuel from the organic fuel storage 3 and burns the organic fuel, and a second combustion chamber B which receives inorganic fuel from the inorganic fuel storage 4 and burns the inorganic fuel.

[0022] The boiler apparatus 2 of this embodiment is a commonly known stoker-type boiler, and differs mainly in that its combustion chamber 21 is separated by a wall as shown by the dotted line into a first combustion chamber A and a second combustion chamber B.

[0023] The fuel supply mechanism that supplies fuel to the first combustion chamber A and the second combustion chamber B may be similar to that provided in a stoker-type boiler, and although not shown, in this embodiment, such a fuel supply mechanism may be provided in the first combustion chamber A and the second combustion chamber B, respectively.

[0024] That is, in the embodiment shown in FIG. 1, a fuel supply mechanism may be provided that supplies organic fuel from the organic fuel storage tank 3 to the first combustion chamber A, and a fuel supply mechanism that supplies inorganic fuel from the inorganic fuel storage tank 4 to the second combustion chamber B.

[0025] The piping 23 passes through the first combustion chamber A and the second combustion chamber B, and the heat of combustion of the organic fuel in the first combustion chamber A and the heat of combustion of the inorganic fuel in the second combustion chamber B are used to generate steam that drives the steam turbine 22.

[0026] Air is supplied to the first combustion chamber A, and the oxygen in the air combusts with the organic fuel, generating carbon dioxide gas. For example, coal can be used as the organic fuel, and carbon dioxide gas (CO2) is generated as a carbon oxide gas upon combustion. Note that air also contains nitrogen gas, which may also generate nitrogen oxides (NOx), and if the organic fuel is coal, it may also generate sulfur dioxide gas because it contains sulfur components.

[0027] In the boiler apparatus of this embodiment, carbon oxide gas generated in the first combustion chamber is supplied to the second combustion chamber, and the embodiment shown in Figure 1 shows a mechanism for removing impurities such as nitrogen oxides (NOx) and sulfur dioxide gas. Therefore, in the boiler apparatus of this embodiment, exhaust gas containing carbon oxides gas, nitrogen oxides (NOx), and sulfur dioxide gas is sent from the first combustion chamber A through an exhaust pipe (not shown) as shown by the solid arrow to a denitration device 5, where the nitrogen oxides (NOx) are detoxified. The denitration device 5 may be the same as that generally used in coal-fired power plants, etc.

[0028] The exhaust gas that has passed through the denitration device 5 is sent to the dust collector 6 through an exhaust pipe (not shown) as indicated by the solid arrow, where soot and other particles contained in the exhaust gas are removed. The dust collector 6 may be the same as those generally used in coal-fired power plants and the like.

[0029] Furthermore, the exhaust gas that has passed through the dust collector 6 is sent to a desulfurization device 7 through an exhaust pipe (not shown) as indicated by the solid arrow, where sulfur dioxide gas contained in the exhaust gas is removed. The desulfurization device 7 may be the same as that generally used in coal-fired power plants, etc.

[0030] The exhaust gas that has passed through the desulfurization device 7 is then sent through an exhaust pipe (not shown) to a separation and recovery device 8 that separates and recovers carbon oxide gas, as indicated by the solid arrow, and the carbon oxide gas contained in the exhaust gas is recovered.

[0031] The carbon oxide gas thus recovered by the separation and recovery device 8 is supplied to a storage tank 81 for storing carbon oxide gas through a gas pipe (not shown), as indicated by the dotted arrow. A booster (not shown) is provided at the inlet of the storage tank 81 so that the carbon oxide is supplied to the storage tank 81 in a pressurized state, and the carbon oxide may be stored in the storage tank 81 in a partly liquefied state.

[0032] On the other hand, the exhaust gas from which carbon oxide gas has been removed in the separation and recovery device 8 is sent to an exhaust fan 9 through an exhaust pipe (not shown) as indicated by the solid arrow, and then released into the atmosphere. This exhaust fan 9 also has a configuration that is generally provided in coal-fired power plants, and may be similar to that.

[0033] The storage tank 81 is connected to the second combustion chamber B through a gas pipe (not shown), as indicated by the dashed arrow, so that the carbon dioxide gas stored in the storage tank 81 can be supplied to the second combustion chamber B.

[0034] Specifically, for example, carbon oxide gas is supplied from the storage tank 81 so that the pressure in the second combustion chamber B becomes positive according to the value of a pressure measuring instrument (not shown) connected to the second combustion chamber B. To control this pressure, a flow control valve for controlling the flow rate of the carbon oxide gas is provided in the gas piping (not shown) from the storage tank 81 to the second combustion chamber B.

[0035] Note that a combustion supporting gas other than the carbon oxide gas from the storage tank 81 may be supplied to the second combustion chamber B. Examples of such a combustion supporting gas include carbon oxide gas, oxygen, air, etc. For example, the second combustion chamber B may be provided with an intake port that can take in atmospheric air (air) depending on the amount of carbon oxide gas in the storage tank 81 and the pressure of the second combustion chamber B.

[0036] Then, inorganic fuel that can be combusted in the presence of a combustion-supporting gas containing carbon oxide gas (e.g., carbon dioxide gas) is supplied to the second combustion chamber B from the inorganic fuel storage tank 4, and combustion occurs using the supplied carbon oxide gas as the combustion-supporting gas.

[0037] The inorganic fuel is an inorganic substance that can be burned using a carbon oxide gas such as carbon dioxide gas (CO) or carbon monoxide gas (CO) as a combustion supporting gas, a hydrogenated inorganic substance in which at least a part of the inorganic substance is hydrogenated, or a mixture thereof. Such inorganic substances include lithium (Li), magnesium (Mg), calcium (Ca), and aluminum (Al).

[0038] When non-hydrogenated inorganic materials are used as inorganic fuel, they may become flammable when in a fine powder form.

[0039] For this reason, when a non-hydrogenated inorganic substance is used as the inorganic fuel, it is desirable that the inorganic substance have a particle size that allows safe handling in terms of transportation, storage, and the like.

[0040] For example, in the case of magnesium, it is preferable that the particle size is 400 μm or more or 500 μm or more.

[0041] As the inorganic substance used for the inorganic fuel, magnesium or calcium is preferred from the viewpoint of good combustibility in the second combustion chamber B. For example, when carbon dioxide is supplied as a combustion supporting gas and the inorganic fuel is magnesium, the combustion reaction shown in the following formula (1) occurs, and when the inorganic fuel is calcium, the combustion reaction shown in the following formula (1') occurs: 2Mg + CO2 → 2MgO + C (1) 2Ca + CO2 → 2CaO + C (1')

[0042] In the combustion reactions shown in equations (1) and (1'), solid inorganic fuel and carbon dioxide gas (CO2) undergo a combustion reaction, producing oxides of the inorganic fuel and solid carbon (C). This reaction consumes gas components, i.e., it is a decompression reaction, and the gas concentration decreases as the reaction progresses. Note that if moisture is present in the second combustion chamber B, some hydroxide may be formed in addition to the oxides of the inorganic fuel.

[0043] Since the combustion reaction cannot be continued if the combustion supporting gas is consumed in this way, as explained above, the second combustion chamber B is configured so that carbon dioxide gas is supplied while measuring the pressure so as to maintain a positive pressure. Note that even when carbon monoxide gas or oxygen is included as the combustion supporting gas, the reaction with the inorganic fuel is a reduced pressure reaction.

[0044] As mentioned above, the combustion reaction in the second combustion chamber B is a reduced pressure reaction, and a positive pressure environment is maintained by supplying a combustion-supporting gas. Therefore, it is preferable that the inner diameter of the exhaust pipe (not shown) that exhausts the exhaust gas from the second combustion chamber B be relatively small.

[0045] For example, by keeping the inner diameter at about 100 to 300 mmφ, it becomes easier to control the positive pressure inside the second combustion chamber B.

[0046] However, since the specific inner diameter of the exhaust pipe (not shown) needs to be matched to the internal volume of the second combustion chamber B, an inner diameter of 100 to 300 mmφ is not necessarily optimal.

[0047] For example, in a clean room or the like, a positive pressure of 5 Pa or more is maintained to prevent outside air from entering the room, and similarly maintaining a positive pressure of 5 Pa or more tends to prevent backflow of exhaust gas through an exhaust pipe (not shown) into the second combustion chamber B. Therefore, it is preferable that the pressure in the second combustion chamber B be adjusted to 5 Pa or more, a pressure more positive than atmospheric pressure.

[0048] The second combustion chamber B is provided with an exhaust pipe (not shown) connected to an exhaust pipe (not shown) that runs from the first combustion chamber A to the denitration device 5, as shown by the solid arrow, so that exhaust air is removed to prevent the internal pressure from becoming too high.

[0049] However, even if the second combustion chamber B is at a slightly negative pressure compared to atmospheric pressure, it does not lead to a shortage of combustion supporting gas, so for example, the exhaust pressure immediately after leaving the first combustion chamber A (in the exhaust pipe (not shown) near the first combustion chamber A before the exhaust pipe (not shown) from the second combustion chamber B joins) may be measured, and the pressure in the second combustion chamber B may be kept slightly higher than the measured pressure (for example, 5 Pa or more higher). Even in this way, the pressure is controlled to be higher than the main exhaust, so it is possible to suppress backflow of exhaust into the second combustion chamber B.

[0050] The exhaust gas discharged from the second combustion chamber B in this manner reaches the separation and recovery device 8 in the flow described above, and if it contains carbon oxide gas, it is stored again in the storage tank 81.

[0051] As can be seen from the above explanation, the operating method of the boiler apparatus of this embodiment can consume carbon oxide gas generated by the combustion of organic fuel through the combustion of inorganic fuel, thereby suppressing the emission of carbon oxide gas such as carbon dioxide gas during operation.

[0052] On the other hand, in this embodiment, combustion ash is generated in the second combustion chamber B. Therefore, it is preferable that the second combustion chamber B is provided with a recovery mechanism for recovering the generated combustion ash. Similarly, it is preferable that the first combustion chamber A is provided with a recovery mechanism for recovering the generated combustion ash. The combustion ash recovered from the first combustion chamber A may be stored in the first combustion ash storage unit, and the combustion ash recovered from the second combustion chamber B may be stored in the second combustion ash storage unit.

[0053] The soot and the like collected by the dust collector 6 may be sent to the first combustion ash storage section that stores the combustion ash collected from the first combustion chamber A.

[0054] The combustion ash stored in the first combustion ash storage unit is almost the same as the combustion ash produced in general coal-fired power plants, and can therefore be used as an admixture for concrete, etc.

[0055] On the other hand, the combustion ash stored in the second combustion ash storage section, i.e., the combustion ash containing solidified carbon together with oxides of inorganic fuel, consists of oxides of inorganic fuel and carbon, and in principle contains almost no other impurities.

[0056] Therefore, the carbon obtained by separating the solidified carbon from the combustion ash can be used as a raw material for carbon materials that require high purity.

[0057] Furthermore, inorganic fuel can be regenerated by extracting the oxides of the inorganic fuel from the combustion ash and reducing them.

[0058] (Resource Regeneration Step) The power generation method of this embodiment may include a resource regeneration step of regenerating inorganic fuel from the combustion ash produced in the second combustion chamber B in the power generation step and recovered in the second combustion ash storage section, and recovering carbon. For example, when the inorganic fuel is magnesium, the resource regeneration step is a resource recovery step of regenerating magnesium using, as a starting material, an oxide of magnesium (specifically, magnesium oxide) contained in the combustion ash as a combustion product generated in the power generation step.

[0059] In addition, the hydroxides contained in the combustion ash 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, when magnesium hydroxide (Mg(OH)2) is heated, a dehydration reaction occurs to turn it into magnesium oxide (MgO) as shown in the following reaction formula (3): Mg(OH)2 → MgO + HO (3)

[0060] Furthermore, when the combustion ash contains calcium hydroxide (Ca(OH)), a dehydration reaction occurs upon heating, producing calcium oxide (CaO), as shown in the following reaction formula (3'): Ca(OH) → CaO + HO (3')

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

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

[0063] For example, taking the procedure of producing magnesium from magnesium oxide as a starting material as an example, the resource regeneration process may include a chlorination process in which magnesium chloride is produced using magnesium oxide in the combustion ash as a material, and a molten salt electrolysis process in which magnesium is produced using the magnesium chloride produced in the chlorination process as a material.

[0064] Furthermore, taking the procedure of producing calcium from calcium oxide as a starting material as an example, the resource recycling 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] 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"). In this embodiment, the hydrogen chloride water method is preferred. In this embodiment, the combustion ash contains not only oxides of the inorganic fuel but also carbon (C) generated by the reduction of carbon oxide gas. By using the hydrogen chloride water method, it is likely possible to efficiently chlorinate magnesium oxide while removing carbon from the combustion ash. In the chlorination step, in addition to the hydrogen chloride water method, the hydrogen chloride gas method, the chlorine gas method, and / or the ammonium chloride method may be combined.

[0066] For example, if the oxide of inorganic fuel is magnesium oxide, when combustion ash consisting of magnesium oxide and carbon is placed in a hydrogen chloride solution (hydrochloric acid), the magnesium oxide reacts with the hydrochloric acid to become magnesium chloride, which dissolves in the solution. On the other hand, carbon does not react with hydrochloric acid, so it does not dissolve in the solution and remains solid.

[0067] Therefore, carbon powder can be recovered by filtering this aqueous solution through a filter. In order to achieve high purity, the recovered carbon powder should be further washed with pure water or the like.

[0068] In the above step, 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).

[0069] Prior to the chlorination step using the hydrogen chloride water method, it is preferable to carry out a step of pretreating inorganic oxides in the combustion ash. Because inorganic oxide particles in the combustion ash may be coated with carbon, carrying out such a pretreatment step tends to increase the efficiency of the chlorination reaction in the chlorination step. Furthermore, from the viewpoint of further increasing the efficiency of the chlorination reaction, 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, the chlorination step may be not only a chlorination step using the hydrogen chloride water method, but also a chlorination step using the hydrogen chloride gas method, the chlorine gas method, or the ammonium chloride method. When multiple chlorination steps are carried out, it is preferable to first carry out a chlorination step using the hydrogen chloride water method, and then carry out a chlorination step using any of the hydrogen chloride water method, the hydrogen chloride gas method, the chlorine gas method, and the ammonium chloride method. A pretreatment step may be carried out before each chlorination step.

[0070] Examples of the pretreatment step include a step of pulverizing inorganic oxides in the combustion ash and a step of heating inorganic oxides in the combustion ash.

[0071] The step of pulverizing the inorganic oxides 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. By pulverizing the inorganic oxides, the carbon coating layer can be removed from the inorganic oxide particles, and the chlorination step can be enhanced.

[0072] For example, the pulverization using a ball mill may be carried out at 50 to 1000 rpm, preferably 100 to 600 rpm, for example, for 1 minute to 30 hours, preferably 10 minutes to 20 hours, and more preferably 1 to 10 hours.The pulverization using a bead mill may be carried out at 50 to 5000 rpm, preferably 100 to 1000 rpm, for example, for 15 seconds to 10 hours, preferably 1 minute to 3 hours.

[0073] The step of heating the inorganic oxides in the combustion ash is a step of heating the combustion ash in a heating furnace. By heating the inorganic oxide, the carbon coating the inorganic oxide particles can be converted into carbon dioxide gas and 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.

[0074] The pretreatment step may be a combination of a step of pulverizing the inorganic oxides in the combustion ash and a step of heating the inorganic oxides in the combustion ash, for example, a step of pulverizing the inorganic oxides in the combustion ash and then further heating the inorganic oxides in the combustion ash.

[0075] The chlorination step using the chlorine gas method may be, for example, a step of charging combustion ash, optionally together with an alkali metal or alkaline earth metal chloride, into a chlorination furnace, and bringing the inorganic oxides in the combustion ash into contact with chlorine gas to chlorinate the inorganic oxides. In this case, for magnesium oxide, the magnesium oxide and chlorine gas react with each other as shown in the following reaction formula (4) to produce magnesium chloride. The reaction temperature may be 300 to 800°C. Examples of alkali metal or alkaline earth metal chlorides include sodium chloride, potassium chloride, and calcium chloride. To improve the reaction efficiency, the chlorination step using the chlorine gas method may be followed by the chlorination step using the hydrogen chloride gas method described below. 2MgO + 2Cl → 2MgCl + O (4)

[0076] The chlorination process using the hydrogen chloride gas method may be, for example, a process in which combustion ash, optionally together with an alkali metal or alkaline earth metal chloride, is introduced into a chlorination furnace, and inorganic oxides in the combustion ash are brought into contact with hydrogen chloride gas to chlorinate the inorganic oxides. In this case, for magnesium oxide, the magnesium oxide and hydrogen chloride gas react with each other as shown in the following reaction formula (5) to produce magnesium chloride. The reaction temperature may be 300 to 800°C. Examples of alkali metal or alkaline earth metal chlorides include sodium chloride, potassium chloride, and calcium chloride. MgO + 2HCl → MgCl + HO (5)

[0077] The chlorination process using the ammonium chloride method may be, for example, a process of chlorinating inorganic oxides by dropping combustion ash and ammonium chloride (NH4Cl) into a chlorination tower and heating them. In the above case, for magnesium oxide, the reaction between magnesium oxide and ammonium chloride (NH4Cl) occurs according to the following reaction formula (6) to produce magnesium chloride. The reaction temperature may be 300 to 600°C: MgO + 2NH4Cl → MgCl2 + HO + 2NH3 (6)

[0078] The chlorination step using the ammonium chloride method may be, for example, a step in which inorganic oxides in the combustion ash and ammonium chloride (NH4Cl) are reacted at an appropriate equivalent ratio to produce ammonium carnallite hydrate, and then the ammonium carnallite hydrate is heated in a state where ammonia gas is blown over it to a temperature slightly lower than the sublimation temperature of ammonium chloride (for example, a temperature about 5 to 20°C lower than the sublimation temperature) to cause a dehydration reaction and remove moisture, and further heated in a state where dry nitrogen is blown over it to a temperature higher than the sublimation temperature of ammonium chloride (for example, around 400°C) to remove the ammonium chloride moiety and obtain anhydrous chloride. In the above case, for magnesium oxide, the molar ratio of magnesium oxide to ammonium chloride is 1:3 and the reaction shown in the following reaction formula (7) is carried out at a temperature of about 400°C to produce ammonium carnallite hydrate. The ammonium carnallite hydrate is then heated in a stream of ammonia gas to a temperature slightly lower than the sublimation temperature of ammonium chloride to cause the dehydration reaction shown in the following reaction formula (8) to remove moisture. The ammonium chloride portion is then removed by heating in a stream of dry nitrogen to a temperature higher than the sublimation temperature of ammonium chloride to cause the reaction shown in the following reaction formula (9) to produce anhydrous magnesium chloride: MgO + 3NHCl → MgCl.NHCl.H0 + 2NH (7) MgCl.NHCl.H0 → MgCl.NHCl + H0 (8) MgCl.NHCl → MgCl + NH + HCl (9)

[0079] Since magnesium chloride is dissolved in the hydrogen chloride water after filtering the carbon, magnesium can be produced by recovering the magnesium chloride and performing molten salt electrolysis. One method for recovering anhydrous magnesium chloride from hydrogen chloride water is to heat the hydrogen chloride water while blowing hydrogen chloride gas into it. This method is well known, so a detailed explanation will be omitted.

[0080] As a method for recovering anhydrous magnesium chloride from hydrogen chloride water, the hydrogen chloride water may be heated in a nitrogen atmosphere to desorb water and obtain an anhydrous magnesium chloride, or the hydrogen chloride may be desorbed to obtain magnesium oxide, which may then be further processed.

[0081] When the water in the recovered filtrate is evaporated, magnesium chloride hexahydrate precipitates as crystals, and these crystals may be recovered.

[0082] Then, in order to remove moisture from the crystals, the magnesium chloride hexahydrate is heated to a temperature of about 300°C to 600°C while hydrogen chloride gas is blown over it. From the viewpoints of the reaction rate of the dehydration reaction and suppression of the production of magnesium oxide, it is preferable to set the temperature to 400°C to 550°C.

[0083] If you simply heat magnesium chloride hydrate to remove the water, it will turn into magnesium oxide. However, if you heat it while blowing hydrogen chloride gas through it, the reaction leading to magnesium oxide is inhibited, and the dehydration reaction proceeds, resulting in anhydrous magnesium chloride.

[0084] The anhydrous magnesium chloride thus produced is heated to around 700°C, molten, and electrolyzed to produce magnesium (hereinafter referred to as the molten salt electrolysis process).

[0085] Specifically, the molten salt electrolysis process produces an inorganic solid fuel using the inorganic 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, one method used to produce magnesium.

[0086] In the molten salt electrolysis step, 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.

[0087] At least one pair of electrodes is provided in the molten salt electrolysis cell, and when a power supply is connected between these electrodes and a voltage of 2.5 V or more is applied, chlorine (Cl2) gas is generated at the anode and magnesium is produced at the cathode.

[0088] The chlorine gas generated in the molten salt electrolysis step may be used in a chlorination step using a chlorine gas method. Also, since hydrogen chloride gas is produced by reacting hydrogen gas with chlorine gas, hydrogen chloride gas may be produced using the chlorine gas generated in the molten salt electrolysis step as a material and used in a chlorination step using a hydrogen chloride gas method, a hydrogen chloride water method, or an ammonium chloride method.

[0089] Therefore, it is possible to re-produce inorganic fuel using the oxides of inorganic fuel in the combustion ash as materials, and if the produced inorganic fuel is used in the thermal power generation described above, it becomes a resource-circulating thermal power generation method.

[0090] In terms of resource recycling, it is preferable that the oxides of inorganic fuel contained in the combustion ash are of a single type, since this saves the effort of separation.

[0091] Therefore, it is preferable that the inorganic fuel consists of only one inorganic substance, or is a mixture of inorganic hydrides.

[0092] For example, if the inorganic substance is magnesium, it is better to use magnesium hydride as the inorganic hydride to be mixed.

[0093] On the other hand, the molten salt electrolysis method described above uses only electricity as energy, and therefore can be carried out using the electricity of wind turbines and the like that cannot be connected to a grid, and can suppress the generation of carbon dioxide gases, which have an impact on global warming, including the overall resource circulation.

[0094] In the above, coal has been used as an example of an organic fuel, but similarly, any fuel that can be burned in a stoker-type boiler and generates carbon oxide gas (carbon monoxide gas, carbon dioxide gas, etc.) that acts as a combustion-supporting gas for inorganic fuels during combustion can be used.

[0095] Therefore, for example, wood chips may be used as organic fuel, and since wood chips are made from wood that is renewable in nature, they are positioned as a carbon-neutral, sustainable fuel.

[0096] Therefore, when wood chips are used as organic fuel, the carbon dioxide gas (carbon dioxide gas, etc.) generated by its combustion is decomposed by the combustion of inorganic fuel, resulting in a thermal power generation method that does not emit carbon dioxide gas, making this a carbon-negative power generation method.

[0097] (Second embodiment) Fig. 2 is a diagram for explaining a thermal power plant that implements a thermal power generation method according to a second embodiment of the present invention. The thermal power plant of this embodiment is also substantially similar to the thermal power plant of the first embodiment, so a description of the same parts may be omitted.

[0098] In the thermal power generation method of this embodiment, a hydrogenated inorganic material that is at least partially hydrogenated is used as the inorganic fuel. A specific example is low-purity magnesium hydride, at least the surface of which is hydrogenated and has a magnesium hydride layer.

[0099] The second embodiment differs from the first embodiment in that hydrogen is generated from an inorganic hydrogenated substance and hydrogen gas is recovered.

[0100] In the following, an example will be described in which magnesium hydride is used as the inorganic fuel. In the second embodiment, the combustion reaction in the second combustion chamber B includes a combustion reaction of the magnesium hydride portion in addition to the combustion reaction of magnesium using carbon oxide gas (e.g., carbon dioxide gas) as the combustion supporting gas (see formula (1)) described in the first embodiment.

[0101] The combustion reaction of magnesium hydride (MgH2) begins with the reaction (endothermic reaction) shown in the following formula (2), in which magnesium hydride is decomposed by heat into magnesium and hydrogen gas (H2), and the magnesium produced thereby undergoes the combustion reaction previously shown in formula (1). MgH2 → Mg + H2 (2)

[0102] In the second embodiment, the boiler apparatus 2 is operated so that the hydrogen gas generated by the decomposition of magnesium hydride is not consumed in the second combustion chamber B, but is discharged to the outside of the second combustion chamber B together with the exhaust gas discharged from the second combustion chamber B. One method for achieving this is to adjust the amount of combustion supporting gas supplied to the second combustion chamber B and adjust the pressure in the second combustion chamber B.

[0103] Therefore, in this embodiment, as indicated by the solid arrow, the exhaust gas is first supplied through an exhaust pipe (not shown) to a hydrogen recovery device H that recovers hydrogen gas, where the hydrogen gas is recovered.

[0104] Then, for example, the recovered hydrogen gas can be supplied to a fuel cell F through a gas pipe (not shown) as indicated by the two-dot chain arrow, to generate electricity.

[0105] The recovered hydrogen gas may be temporarily stored in a hydrogen gas tank and then sent to the fuel cell F from the hydrogen gas tank.

[0106] For example, the electric power generated by the fuel cell F is used as the electric power required for the operation of a thermal power plant that implements this thermal power generation method. Therefore, all of the electric power generated by the generator 1 may be used for power transmission.

[0107] Although the above description has been given in the case where the inorganic fuel is at least partially hydrogenated magnesium, the same applies when a mixture of magnesium and at least partially hydrogenated magnesium, i.e., a mixture of an inorganic material and a hydrogenated inorganic material, is used as the inorganic fuel, or when a mixture of hydrides of other metals and / or a mixture of metals and metal hydrides is used.

[0108] (Third embodiment) In the first and second embodiments, the case of a stoker-type boiler has been described, but the present invention may also be applied to a thermal power generation method using a power generation boiler in the form of, for example, a pulverized coal combustion boiler.

[0109] In this case, a general pulverized coal burner for burning pulverized coal may be provided in the first combustion chamber A.

[0110] In addition, the second combustion chamber B may have a stoker-type structure, but it is also possible to provide a powder combustion burner with a structure similar to that of a pulverized coal burner, and use inorganic fuel that has been pulverized into a powder suitable for combustion in the powder combustion burner.

[0111] In this case, combustible inorganic materials tend to become flammable as they are further pulverized, so it is preferable to use hydrogenated inorganic materials having at least a hydrogenated layer on the surface.

[0112] In this way, the hydrogenated film suppresses the reaction between the inorganic substance and oxygen in the atmosphere and also protects it from ignition.

[0113] Since this hydrogenated film is for protection purposes, it does not need to be a highly pure inorganic hydrogenated material, but rather a low purity inorganic hydrogenated material of 30 mass % or less will suffice.

[0114] In this way, by limiting the hydrogenation rate to a low-purity hydrogenated inorganic material, the hydrogenation treatment time for treating the inorganic material in a hydrogen atmosphere can be significantly reduced, and production efficiency can be improved.

[0115] On the other hand, instead of the pulverized coal burner, the burner provided in the first combustion chamber A may be a burner for burning liquid fuel, and the organic fuel may be a petroleum-based liquid fuel (for example, heavy oil, light oil, etc.).

[0116] In this way, even if the organic fuel is a petroleum-based liquid fuel, it contains sulfur components and also generates soot, so the treatment of the exhaust gas discharged from the first combustion chamber A can be done in the same way as in the first embodiment.

[0117] That is, the carbon oxide gas may be recovered by a separation and recovery device that recovers the carbon oxide gas from the exhaust gas that has passed through a denitration device, a dust collector, and a desulfurization device.

[0118] (Fourth embodiment) The organic fuel is not limited to those described so far (that is, fossil fuels other than liquefied natural gas), but may also be liquefied natural gas.

[0119] In this case, a gas combustion burner may be provided in the first combustion chamber A, but in the case of thermal power generation that burns gas, it is better to use a gas turbine in consideration of power generation efficiency and the like.

[0120] Therefore, as a fourth embodiment, a case where the organic fuel is liquefied natural gas and a gas turbine is used will be described.

[0121] Furthermore, liquefied natural gas is produced through a process of refining natural gas obtained from oil and gas fields, and as such does not contain any sulfur components. Therefore, no sulfur dioxide gas is produced, and the production of sulfur dioxide gas is also suppressed when inorganic fuels are burned.

[0122] Therefore, when a gas combustion burner for burning liquefied natural gas is provided in the first combustion chamber A mentioned above, the desulfurization device described above may be omitted.

[0123] Fig. 3 is a diagram for explaining a thermal power plant that implements the thermal power generation method of this embodiment. Note that the thermal power plant that implements the thermal power generation method of this embodiment is similar in many respects to the thermal power plant described with reference to Fig. 1, and therefore, a description of similar points may be omitted.

[0124] As shown in FIG. 3, in this embodiment, a gas turbine G that is powered by combustion of liquefied natural gas is added to drive the generator 1.

[0125] The liquefied natural gas, which is the organic fuel in this embodiment, is sent to the gas turbine G, rather than being sent from the organic fuel storage 3 to the combustion chamber 21 of the power generation boiler 2, in order to be burned in the gas turbine G.

[0126] The organic fuel storage 3 stores liquefied natural gas, and is therefore a tank for storing liquefied gas.

[0127] The exhaust gas containing carbon oxides gas remaining after the liquefied natural gas is burned in the gas turbine G is sent through an exhaust pipe (not shown) to a denitration device 5 as shown by the solid arrow, and then to a dust collector 6, where the carbon oxides gas is recovered in a separation and recovery device 8, and then released into the atmosphere via an exhaust fan 9.

[0128] On the other hand, the carbon dioxide gas recovered by the separation and recovery device 8 is supplied to the combustion chamber 21 of the power-generating boiler 2 via a storage tank 81 .

[0129] In this embodiment, the liquefied natural gas, which is an organic fuel, is combusted in the gas turbine G, and does not need to be combusted in the combustion chamber 21 of the power generation boiler 2.

[0130] Therefore, unlike the first embodiment, the combustion chamber 21 is not divided into a first combustion chamber and a second combustion chamber, and the combustion chamber 21 is used only for burning inorganic fuel.

[0131] The exhaust gas from the combustion chamber 21 flows through an exhaust pipe (not shown) as indicated by the solid arrow and merges with an exhaust pipe (not shown) between the gas turbine G and the denitration device 5.

[0132] In this embodiment, the exhaust gas containing fine powder that needs to be collected by the dust collector 6 is exhaust gas discharged from the combustion chamber 21, so the dust collector 6 is provided in the exhaust pipe (not shown) between the gas turbine G and the denitration device 5 before it joins the exhaust pipe (not shown), and the exhaust gas discharged from the gas turbine G may pass through the denitration device 5 without passing through the dust collector 6, and then be sent to the separation and recovery device 8 that separates and recovers carbon oxide gas.

[0133] Furthermore, some gas turbines that use liquefied natural gas as fuel can suppress the generation of nitrogen oxides (NOx) to levels below environmental standards if the combustion temperature can be maintained high, and some use a combustion-supporting gas with an increased oxygen concentration to suppress the generation of nitrogen oxides (NOx). In these cases, the denitration device 5 may be omitted.

[0134] Furthermore, when the inorganic fuel contains hydrogenated inorganic substances, a hydrogen recovery device H and a fuel cell F may be provided, as described with reference to FIG. 2, and when a large amount of hydrogen is recovered, the fuel cell F may be replaced with a hydrogen gas turbine for power generation.

[0135] The thermal power generation method of the present invention has been described above through specific embodiments, but the present invention is not limited to the specific embodiments, and appropriate modifications and improvements are also included in the technical scope of the present invention, which will be clear to those skilled in the art from the description of the claims.

[0136] 1...generator, 2...boiler device (power generation boiler), 21...combustion chamber, 22...steam turbine, 23...piping, 3...organic fuel storage tank, 4...inorganic fuel storage tank, 5...denitrification device, 6...dust collector, 7...desulfurization device, 8...separation and recovery device, 81...storage tank, 9...exhaust fan, A...first combustion chamber, B...second combustion chamber, F...fuel cell, H...hydrogen recovery device.

Claims

1. Burning an organic fuel in a first combustion chamber, burning an inorganic fuel in a second combustion chamber connected to the first combustion chamber, and supplying carbon dioxide gas generated by the combustion of the organic fuel to the second combustion chamber as a combustion-supporting gas, the method for operating a boiler device, wherein the inorganic fuel is an inorganic substance capable of burning in the presence of a combustion-supporting gas containing carbon dioxide gas, a hydrogenated inorganic substance in which at least a part of the inorganic substance is hydrogenated, or a mixture thereof.

2. The method according to claim 1, wherein the inorganic substance is at least one of lithium, magnesium, calcium, and aluminum.

3. The method according to claim 1 or 2, wherein the combustion-supporting gas contains carbon dioxide gas and oxygen gas.

4. A boiler device comprising a first combustion chamber for burning an organic fuel and a second combustion chamber connected to the first combustion chamber for burning an inorganic fuel, wherein the pressure of the second combustion chamber can be adjusted so that the carbon dioxide gas generated in the first combustion chamber is supplied to the second combustion chamber.

5. A power generation system comprising the boiler device according to claim 4 and a generator for generating power by steam generated by the boiler device.

Images