Combustion system for alkaline metal containing fuel and combustion method for alkaline metal containing fuel

Abstract

To suppress poor fluidization due to agglomeration in a fluid medium that forms a fluidized bed within a combustion furnace.SOLUTION: A combustion system that uses a combustion furnace forming a fluidized bed by using a fluid medium and burning fuel containing alkaline metal in the fluidized bed includes: a sieve device that separates a fluid medium discharged from the combustion furnace into a fluid medium of which particle size is equal to or lower than a predetermined particle size value and a fluid medium of which particle size exceeds the predetermined particle size value; a measurement device that measures a γ-ray spectrum emitted from the fluid medium separated by the sieve device and having the particle size equal to or lower than the predetermined particle size value and estimates a concentration of radioactive potassium included in the fluid medium from a measurement result of the spectrum; and a control device that controls an amount of the fluid medium to be discharged from the combustion furnace and an amount of the fluid medium to be supplied to the combustion furnace in accordance with the concentration.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a combustion system for an alkali metal-containing fuel and a method for burning an alkali metal-containing fuel.

Background Art

[0002] There is a method using a fluidized bed furnace as a method for generating electricity using biomass as fuel. A fluidized bed furnace forms a fluidized bed in which a high-temperature fluid medium is fluidized by upwardly blowing fluidizing air, and burns the fuel supplied into the furnace in the fluidized bed. As biomass serving as fuel, for example, biomass derived from plants and inexpensive like palm empty fruit bunches (EFB) has attracted attention. However, when generating electricity by burning palm empty fruit bunches in a fluidized bed furnace, the following problems occur.

[0003] Palm empty fruit bunches contain a large amount of potassium, which is an alkali metal. Silica sand is used as the fluid medium in the fluidized bed furnace. However, gaseous potassium released from palm empty fruit bunches in the fluidized bed furnace reacts with silicon oxide of silica sand particles, and an SiO2-K2O compound is formed on the surface of the silica sand particles. Since the melting temperature of this SiO2-K2O compound is lower than the temperature in the fluidized bed furnace, it melts and an adhesive layer is formed on the surface of the silica sand particles. When this adhesive layer is formed, several silica sand particles fuse together, causing aggregation and agglomeration of silica sand, and the silica sand no longer flows, preventing the normal operation of the fluidized bed furnace. Therefore, as inventions for solving such problems, for example, there are inventions disclosed in Patent Documents 1 and 2.

[0004] The invention disclosed in Patent Document 1 is such that the fluid medium consists of particulate minerals and / or particulate slag, and the quartz content is 14% by mass or less. Since the amount of quartz contained in the fluid medium is 14% by mass or less, even if the quartz in the fluid medium reacts with the alkali metal component in the fuel to form an adhesive layer on the particle surface, aggregation or agglomeration of the fluid medium does not occur or occurs only slightly, and the fluidized bed can maintain good fluidity.

[0005] The invention disclosed in Patent Document 2 detects the blowing-up situation of the fluidized medium near the outlet of the fluidized bed furnace with a laser monitoring device while controlling the fluidization gas velocity inside the fluidized bed furnace to be near 4 m / s, and feeds back the amount of incineration air according to the blowing-up state to the supply side of the combustion air. By increasing the fluidization gas velocity in the fluidized bed furnace to about 4 m / s, the limit salt accumulation amount in the fluidized medium can be increased, thereby increasing the amount of waste that can be processed without causing poor fluidization in the fluidized bed.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the invention disclosed in Patent Document 1, examples of the fluidized medium include garnet, ilmenite, kanran stone, ferronickel slag, etc. However, as described in Table 2 of Patent Document 1, these are more expensive than inexpensive and general-purpose silica sand, and it costs to replace the fluidized medium. In the invention of Patent Document 2, although the limit salt accumulation amount in the fluidized medium can be increased, since agglomeration occurs due to a slight change in the alkali metal, there is a risk that agglomeration will occur suddenly and lead to poor fluidization when the limit salt accumulation amount is exceeded.

[0008] The present invention has been made in view of the above, and an object thereof is to suppress poor fluidization due to agglomeration in a fluidized medium that forms a fluidized bed in a combustion furnace.

Means for Solving the Problems

[0009] A combustion system for an alkali metal-containing fuel according to one aspect of the present invention is a combustion system using a combustion furnace that forms a fluidized bed with a fluid medium and burns a fuel containing an alkali metal in the fluidized bed. The combustion system includes a sieve device that separates the fluid medium discharged from the combustion furnace into a fluid medium having a particle size equal to or less than a predetermined particle size value and a fluid medium having a particle size exceeding the predetermined particle size value, a measuring device that measures the spectrum of gamma rays emitted from the fluid medium having a particle size equal to or less than the predetermined particle size value separated by the sieve device and estimates the concentration of radioactive potassium contained in the fluid medium from the measurement result of the spectrum, and a control device that controls the amount of the fluid medium discharged from the combustion furnace and the amount of the fluid medium supplied to the combustion furnace according to the concentration.

[0010] Further, the combustion system for an alkali metal-containing fuel according to the present invention may include a polishing device that polishes the fluid medium and a sorting device that sorts the fluid medium polished by the polishing device. When the concentration is equal to or less than a predetermined threshold value, the fluid medium in which the concentration is estimated by the measuring device may be sent to the polishing device, and the fluid medium sorted by the sorting device may be sent to the combustion furnace.

[0011] Further, in the combustion system for an alkali metal-containing fuel according to the present invention, when the concentration exceeds a predetermined threshold value, the fluid medium in which the concentration is estimated by the measuring device may be discarded.

[0012] Further, in the combustion system for an alkali metal-containing fuel according to the present invention, the control device may control the amount of the fuel supplied to the combustion furnace according to the concentration.

[0013] A method for burning an alkali metal-containing fuel according to one aspect of the present invention is a combustion method using a combustion furnace that forms a fluidized bed with a fluid medium in the furnace and burns a fuel containing an alkali metal in the fluidized bed. The method includes a separation step of separating the fluid medium discharged from the combustion furnace into a fluid medium having a particle size equal to or less than a predetermined particle size value and a fluid medium having a particle size exceeding the predetermined particle size value, a measurement step of measuring a spectrum of gamma rays emitted from the fluid medium having a particle size equal to or less than the predetermined particle size value separated in the separation step and estimating the concentration of radioactive potassium contained in the fluid medium from the measurement result of the spectrum, and a control step of controlling the amount of the fluid medium discharged from the combustion furnace and the amount of the fluid medium supplied to the combustion furnace according to the concentration.

Advantages of the Invention

[0014] According to the present invention, there is an effect that it is possible to suppress poor fluidization due to agglomeration in the fluid medium that forms a fluidized bed in the combustion furnace.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the present invention is not limited by the embodiments described below. Also, the drawings are schematic, and it is necessary to note that the dimensional relationships of each element may be different from the actual ones.

[0017] [Embodiment] FIG. 1 is a diagram showing the configuration of a combustion system 1000 according to an embodiment of the present invention. The combustion furnace 1 is a circulating fluidized bed (CFB) furnace. The combustion furnace 1 is a furnace that forms a fluidized bed by flowing a fluid medium 81 inside and burns the fuel 73 supplied into the combustion furnace 1 in the fluidized bed. The combustion furnace 1 mainly includes a riser 10 as a furnace body and a downcomer 20 that collects a part of the fluid medium 81 and returns it to the riser 10.

[0018] The riser 10 is provided with a diffuser pipe 11 at the lower part for blowing the primary air supplied from the blower 91 upward. Also, on the side wall of the lower part of the riser 10, a fluid medium supply port 12 for supplying the fluid medium 81 into the riser 10 above the diffuser pipe 11, a fuel supply port 13 for supplying the fuel 73 into the riser 10, and a secondary air injection port 14 for blowing the secondary air supplied from the blower 92 into the riser 10 are provided in order from below. Further, at the bottom of the riser 10, a discharge part 15 for discharging the fluid medium 81 and furnace bottom ash inside the riser 10 is provided.

[0019] The downcomer 20 is connected to the upper part of the riser 10 by a pipe 30. The downcomer 20 has a collection part 21 for collecting the fluid medium 81 sent together with the exhaust gas from the riser 10, a return pipe 22 for returning the fluid medium 81 collected by the collection part 21 to the lower part of the riser 10, and a seal part 23 for preventing the gas from the riser 10 from rising inside the collection part 21.

[0020] Near the combustion furnace 1, a circulation line 4 is provided for regenerating the fluid medium 81 discharged from the discharge part 15 and returning it to the combustion furnace 1. In the circulation line 4, a sieve device 41, a measuring device 52, a polishing device 42, a sorting device 43, and a fluid medium feeder 44 are arranged in order from the discharge part 15.

[0021] The screening device 41 receives the fluid medium 81 and the bottom ash discharged from the discharge unit 15, separates the fluid medium 81 with a particle size equal to or smaller than a predetermined particle size that has passed through the screen, and sends it to the measuring device 52. The particle size of the fluid medium 81 passing through the screen is, for example, 1 mm or less. Further, the screening device 41 sends out lumps of the fluid medium 81 that have become larger in diameter than the predetermined particle size due to agglomeration that does not pass through the screen, and incombustibles generated after the combustion of the fuel 73, to the disposal line 5 for disposing of the fluid medium 81. The incombustibles and lumps of the fluid medium 81 sent to the disposal line 5 are disposed of. The step of separating the fluid medium 81 with a particle size equal to or smaller than a predetermined particle size and the fluid medium with a particle size exceeding the predetermined particle size by the screening device 41 is an example of a separation step.

[0022] The measuring device 52 is a device that levels the fluid medium 81 to a predetermined width and height and estimates the concentration of radioactive substances in the fluid medium 81. By burning the fuel 73 containing potassium, which is an alkali metal, in the fluidized bed of the combustion furnace 1, a SiO2-K2O compound is formed on the surface of the fluid medium 81. Naturally occurring potassium contains a predetermined proportion of radioactive potassium, potassium 40. The measuring device 52 measures the γ-ray spectrum emitted from the fluid medium 81 sent to the circulation line 4 and estimates the concentration of potassium 40 contained in the fluid medium 81.

[0023] Figure 2 is a schematic diagram of the measuring device 52 viewed from above. The measuring device 52 includes a belt conveyor 521, a hopper 522, a width adjustment bar 523, a height adjustment bar 524, and a detector 525. The hopper 522 is charged with the fluid medium 81 having a particle size equal to or smaller than a predetermined particle size sent from the sieving device 41. The fluid medium 81 charged into the hopper 522 drops onto the belt conveyor 521. The belt conveyor 521 is a belt conveyor that conveys the fluid medium 81 dropped from the hopper 522 to the polishing device 42. The width adjustment bar 523 makes the width of the fluid medium 81 conveyed to the polishing device 42 by the belt conveyor 521 constant. The height adjustment bar 524 makes the height of the fluid medium 81, which has been made to have a constant width by the width adjustment bar 523 and is conveyed to the polishing device 42, constant. The detector 525 is, for example, a scintillation detector. The detector 525 measures the spectrum of the γ-rays emitted from the fluid medium 81 and estimates the concentration of potassium 40 contained in the fluid medium 81 from the measured spectrum of the γ-rays. The detector 525 transmits the estimation result of the concentration of radioactive potassium to the control device 51. The step of estimating the concentration of radioactive potassium contained in the fluid medium 81 with the measuring device 52 is an example of the measuring step.

[0024] The polishing device 42 polishes the fluid medium 81 sent from the sieving device 41 and removes the alkali metal component adhering to the fluid medium 81. There is no limitation on the polishing method used in the polishing device 42. For example, an autogenous crushing method, a shear milling method, a blasting method, etc. are applicable. The fluid medium 81 from which the alkali metal component has been removed by the polishing device 42 and the alkali metal component removed from the fluid medium 81 are sent to the sorting device 43.

[0025] The sorting device 43 sorts the fluid medium 81 from the mixture of the alkali metal component and the fluid medium 81 sent from the polishing device 42. There is no limitation on the sorting method used in the sorting device 43. For example, a pneumatic sorting method, a specific gravity sorting method, etc. are applicable. The fluid medium 81 sorted by the sorting device 43 is sent to the fluid medium feeder 44.

[0026] The fluid medium supply device 44 stores the fluid medium 81 sent from the sorting device 43 and supplies the fluid medium 81 into the riser 10. In the present embodiment, the fluid medium 81 is, for example, silica sand. A part of the fluid medium 81 stored in the fluid medium supply device 44 is discarded from the lower part of the fluid medium supply device 44. In the fluid medium supply device 44, since a part of the stored fluid medium 81 is discarded, new fluid medium 81 is replenished to compensate for the discarded portion. The fluid medium 81 stored in the fluid medium supply device 44 is sent to the fluid medium supply port 12 and supplied into the riser 10 from the fluid medium supply port 12. Note that a part of the fluid medium 81 may be discarded by the polishing device 42 or the sorting device 43.

[0027] The control device 51 is a device that controls the discharge unit 15 and the fluid medium supply device 44. The control device 51 controls the discharge unit 15 and the fluid medium supply device 44 based on the estimated result of the concentration of radioactive potassium transmitted from the measuring device 52. The step in which the control device 51 controls the discharge unit 15 and the fluid medium supply device 44 is an example of a control step.

[0028] The fuel supply device 61 is a device that sends the fuel 73 to be burned in the combustion furnace 1 to the fuel supply port 13. The fuel supply device 61 sends the fuel 73 obtained by mixing the first fuel 71 and the second fuel 72 to the fuel supply port 13. The first fuel 71 is a fuel with a high content of alkali metal components, for example, empty fruit bunches of palm coconuts. The second fuel 72 is a fuel with a lower content of alkali metal components compared to the first fuel 71, for example, wood chips.

[0029] Next, the operation of the combustion system 1000 will be described. By blowing the primary air sent from the blower 91 into the riser 10 from the air diffuser pipe 11 and blowing the secondary air sent from the blower 92 into the riser 10 from the secondary air injection port 14, a fluidized bed in which the fluid medium 81 is fluidized is formed in the riser 10.

[0030] Further, fuel 73 is supplied into the riser 10 from the fuel supply port 13. In the fuel 73 supplied from the fuel supply port 13, it is preferable that the proportion of the first fuel 71 is larger from the viewpoint of operation cost. The fuel 73 supplied into the riser 10 burns in a fluidized bed.

[0031] Specifically, the fluidizing medium 81 is brought into a fluidized state by the primary air blown from the air diffuser pipe 11, and a dense layer where the fluidizing medium 81 is dense is formed at the lower part inside the riser 10. In this dense layer, the drying of the fuel 73 and the release of volatile components are promoted by the high heat capacity and agitation effect. Further, at the upper part inside the riser 10, the fluidizing medium 81 is blown up by the blowing of the primary air and the secondary air, and a dilute layer where the fluidizing medium 81 is dilute is formed. In this dilute layer, the combustion of the fuel 73 is performed by the heat capacity and agitation effect possessed by the fluidizing medium 81. That is, the combustion furnace 1 forms a fluidized bed composed of a dense layer and a dilute layer inside the riser 10, thereby preventing the generation of char which is unburned carbon content, and efficiently burning the fuel 73 which is palm coconut empty fruit bunches. Note that the combustion region inside the riser 10 is maintained at about 850 to 900°C.

[0032] The exhaust gas generated by the combustion of the fuel 73 inside the riser 10 is supplied to the collection part 21 of the downcomer 20 through the pipe 30. Also, a part of the fluidizing medium 81 is also sent from the riser 10 to the collection part 21 together with the exhaust gas. In the collection part 21, the fluidizing medium 81, ash with a relatively large particle size, etc. are recovered and returned to the lower part of the riser 10 through the seal part 23 and the return pipe 22. Further, the exhaust gas, ash with a relatively small particle size, etc. are discharged from the top of the downcomer 20, sent to the exhaust gas treatment facility through a superheater (not shown), the steam is superheated by the superheater, and after dust removal in the exhaust gas treatment facility, it is discharged to the outside from a chimney (not shown).

[0033] In this embodiment, the first fuel 71 (palm empty fruit bunch) contained in the fuel 73 burned in the riser 10 releases gaseous potassium, which is an alkali metal component. This gaseous potassium reacts with silicon dioxide of the silica sand particles that are the fluid medium 81, and an SiO2-K2O compound is formed on the surface of the silica sand particles. This SiO2-K2O compound melts to form an adhesive layer on the surface of the silica sand particles. Due to this adhesive layer, several fluid media 81 adhere to each other and fall to the bottom of the riser 10. The fluid media 81 that have adhered and fallen further adhere to form a lump. The fluid media 81 containing this lump and the incombustibles remaining after the combustion of the fuel 73 are discharged from the discharge section 15 at a predetermined amount per unit time and sent to the screening device 41.

[0034] The screening device 41 to which the fluid medium 81 is sent sends out the fluid medium 81 with a particle size below a predetermined size that has passed through the sieve to the measuring device 52. Further, the screening device 41 sends out the incombustibles after combustion and the lumps of the fluid medium 81 with a particle size exceeding the predetermined size to the waste line 5.

[0035] The measuring device 52 makes the width and height of the fluid medium 81 sent from the screening device 41 constant, measures the spectrum of the gamma rays emitted from the fluid medium 81 with a constant width and height using the detector 525, and estimates the concentration of potassium 40 in the fluid medium 81 from the measured gamma-ray spectrum. This estimated concentration is transmitted to the control device 51. The fluid medium 81 in which the concentration of potassium 40 in the fluid medium 81 has been estimated is sent to the polishing device 42.

[0036] In the polishing device 42, the fluid medium 81 is polished, and the alkali metal component adhering as an adhesive layer on the surface of the fluid medium 81 is removed from the surface of the fluid medium 81. The alkali metal component removed from the fluid medium 81 in the polishing device 42 and the fluid medium 81 from which the alkali metal component has been removed in the polishing device 42 are sent to the sorting device 43.

[0037] In the sorting device 43, the fluid medium 81 is sorted and the alkali metal component is separated, and the sorted fluid medium 81 is sent to the fluid medium feeder 44. In the fluid medium feeder 44, a part of the fluid medium 81 is discarded from the lower part of the fluid medium feeder 44, and new fluid medium 81 is replenished from the upper part.

[0038] The control device 51 controls the fluid medium feeder 44, and according to the amount of the fluid medium 81 discharged per unit time from the discharge part 15, sends the fluid medium 81 stored in the fluid medium feeder 44 to the fluid medium supply port 12, and supplies a predetermined amount of the fluid medium 81 into the riser 10.

[0039] Also, the control device 51 controls the discharge part 15 and the fluid medium feeder 44 based on the estimated result of the concentration of potassium 40 contained in the fluid medium 81 transmitted from the measuring device 52, thereby controlling the discharge amount of the fluid medium 81 from the riser 10 and the supply amount of the fluid medium 81 from the fluid medium feeder 44 to the riser 10.

[0040] For example, when the concentration transmitted from the measuring device 52 is equal to or higher than a predetermined threshold value, the control device 51 controls the discharge part 15 to increase the amount of the fluid medium 81 discharged per unit time from the discharge part 15 from a predetermined amount, and controls the fluid medium feeder 44 to increase the amount of the fluid medium 81 supplied into the riser 10 per unit time from a predetermined amount. Thereby, the mass of the fluid medium 81 can be discharged, and it is possible to suppress the fluid medium 81 from having poor fluidity.

[0041] Also, for example, when the concentration transmitted from the measuring device 52 is less than a predetermined threshold value, the control device 51 controls the discharge part 15 to return the amount of the fluid medium 81 discharged from the discharge part 15 to a predetermined amount, and controls the fluid medium feeder 44 to return the amount of the fluid medium 81 supplied from the fluid medium feeder 44 to the riser 10 to a predetermined amount.

[0042] Note that the control device 51 may control the supply amount of the first fuel 71 and the supply amount of the second fuel 72 based on the concentration transmitted from the measuring device 52. For example, when the concentration transmitted from the measuring device 52 is equal to or higher than a predetermined threshold value, the control device 51 may control the fuel supply device 61 so that the ratio of the first fuel 71 in the fuel 73 is decreased and the ratio of the second fuel 72 is increased. Further, when the concentration transmitted from the measuring device 52 is less than a predetermined threshold value, the control device 51 may control the fuel supply device 61 so that the ratio of the first fuel 71 in the fuel 73 is returned to a predetermined ratio. According to this control, when the alkali metal concentration increases, the ratio of the first fuel 71 containing the alkali metal decreases, so that the occurrence of agglomeration can be suppressed.

[0043] [Modification Example] As described above, the embodiments of the present invention have been described. However, the present invention is not limited to the above-described embodiments and can be implemented in various other forms. For example, the present invention may be implemented by modifying the above-described embodiments as follows. Note that the above-described embodiments and the following modification examples may be combined with each other. The present invention also includes those configured by appropriately combining the components of the above-described embodiments and each modification example. Further, additional effects and modification examples can be easily derived by those skilled in the art. Therefore, a broader aspect of the present invention is not limited to the above-described embodiments and modification examples, and various changes are possible.

[0044] In the above-described embodiment, the combustion furnace 1 is a circulating fluidized bed type furnace, but may be a bubbling fluidized bed (BFB) type furnace.

[0045] In the present invention, in order to suppress the decrease in the temperature inside the riser 10 due to the supply of the new fluid medium 81 into the riser 10, the supply amount of the fuel 73 into the riser 10 may be increased according to the supply amount of the fluid medium 81. In this case, in order to suppress the occurrence of agglomeration, the ratio of the second fuel 72 may be increased. Further, in order to suppress the decrease in the temperature inside the riser 10 due to the increase in the supply amount of the fluid medium 81, kerosene or heavy oil may be supplied as auxiliary fuel.

[0046] In the present invention, the fuel 73 may include the shell of the seed of the oil palm (PKS: Palm Kernel Shell).

[0047] In the present invention, the temperature inside the riser 10 may be measured and controlled according to the measured temperature of the amount of the fluid medium 81 discharged from the discharge unit 15 and the amount of the fluid medium 81 supplied from the fluid medium supply machine 44 to the riser 10.

[0048] In the circulation line 4, when the concentration of potassium 40 in the fluid medium 81 measured by the measuring device 52 is equal to or higher than a predetermined threshold value, the fluid medium 81 may be discarded without being sent to the polishing device 42.

Explanation of reference numerals

[0049] 1 Combustion furnace 4 Circulation line 5 Waste line 15 Discharge unit 41 Screening device 42 Polishing device 43 Sorting device 44 Fluid medium supply machine 51 Control device 52 Measuring device 61 Fuel supply machine 71 First fuel 72 Second fuel 1000 Combustion system

Claims

1. In a combustion system using a combustion furnace that forms a fluidized bed with a fluid medium and burns a fuel containing an alkali metal in the fluidized bed, a sieve device that separates the fluid medium discharged from the combustion furnace into a fluid medium having a particle size equal to or less than a predetermined particle size value and a fluid medium having a particle size exceeding the predetermined particle size value; a measuring device that measures the spectrum of gamma rays emitted from the fluid medium having a particle size equal to or less than the predetermined particle size value separated by the sieve device, and estimates the concentration of radioactive potassium contained in the fluid medium from the measurement result of the spectrum; a control device that controls the amount of the fluid medium discharged from the combustion furnace and the amount of the fluid medium supplied to the combustion furnace according to the concentration; A combustion system for an alkali metal-containing fuel, comprising:

2. a polishing device that polishes the fluid medium; a sorting device that sorts the fluid medium polished by the polishing device; having when the concentration is equal to or less than a predetermined threshold value, the fluid medium in which the concentration is estimated by the measuring device is sent to the polishing device, and the fluid medium sorted by the sorting device is sent to the combustion furnace The combustion system for an alkali metal-containing fuel according to claim 1.

3. When the concentration exceeds a predetermined threshold value, the fluid medium in which the concentration is estimated by the measuring device is discarded The combustion system for an alkali metal-containing fuel according to claim 1.

4. The control device controls the amount of the fuel supplied to the combustion furnace according to the concentration The combustion system for an alkali metal-containing fuel according to any one of claims 1 to 3.

5. In a combustion method using a combustion furnace that forms a fluidized bed with a fluid medium in the furnace and burns a fuel containing an alkali metal in the fluidized bed, a separation step of separating the fluid medium discharged from the combustion furnace into a fluid medium having a particle size equal to or less than a predetermined particle size value and a fluid medium having a particle size exceeding the predetermined particle size value; a measurement step of measuring the spectrum of gamma rays emitted from the fluid medium having a particle size equal to or less than the predetermined particle size value separated in the separation step, and estimating the concentration of radioactive potassium contained in the fluid medium from the measurement result of the spectrum; a control step of controlling the amount of the fluid medium discharged from the combustion furnace and the amount of the fluid medium supplied to the combustion furnace according to the concentration; A combustion method for an alkali metal-containing fuel, comprising:

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