Method for burning alkali metal-containing fuel and system for burning alkali metal-containing fuel

Abstract

To suppress defective flow due to agglomeration on a fluid medium that forms a fluidized bed in a combustion furnace.SOLUTION: A method for burning that forms a fluidized bed with a fluid medium in a furnace and uses a combustion furnace that burns a fuel containing an alkaline metal with the fluidized bed includes the steps of: measuring density of alkaline metal adhering to the fluid medium discharged from the combustion furnace with a measuring apparatus by fluorescent X-ray analysis; and controlling an amount of the fluid medium to be discharged from the combustion furnace and an amount of the fluid medium to be supplied into the combustion furnace with a control device in accordance with the density.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] One method for generating electricity using biomass as fuel is to use a fluidized bed furnace. A fluidized bed furnace uses upward-flowing fluidizing air to create a fluidized bed of high-temperature fluidizing material, and the fuel supplied to the furnace is combusted within the fluidized bed. Low-cost plant-derived biomass, such as palm empty fruit bunches (EFBs), has been attracting attention as a fuel. However, the following problems arise when burning palm empty fruit bunches in a fluidized bed furnace to generate electricity:

[0003] Palm empty fruit bunches contain a large amount of potassium, an alkali metal. Silica sand is used as the fluidizing medium in a fluidized bed furnace. The gaseous potassium released from the palm empty fruit bunches reacts with the silicon oxide in the silica sand particles inside the furnace, producing the SiO2-K2O compound on the surface of the silica sand particles. Because the melting temperature of this SiO2-K2O compound is lower than the temperature inside the fluidized bed furnace, it melts and forms an adhesive layer on the surface of the silica sand particles. When this adhesive layer forms, several silica sand particles fuse together, causing the silica sand to aggregate and agglomerate, preventing the silica sand from flowing and hindering normal operation of the fluidized bed furnace. Patent documents 1 and 2, for example, disclose inventions that address these issues.

[0004] In the invention disclosed in Patent Document 1, the bed material is made of particulate minerals and / or particulate slag, and the quartz content is 14 mass% or less. Because the amount of quartz contained in the bed material is 14 mass% or less, even if the quartz in the bed material reacts with the alkali metal components in the fuel to form an adhesive layer on the particle surface, aggregation or clumping of the bed material does not occur, or if it does occur, it occurs only to a small extent, and the fluidized bed can maintain good fluidity.

[0005] The invention disclosed in Patent Document 2 uses a laser monitoring device to detect the upward flow of the bed material near the outlet of the fluidized-bed furnace while controlling the fluidizing gas velocity inside the furnace to approximately 4 m / s, and feeds back the amount of incineration air corresponding to the upward flow state to the combustion air supply side. By increasing the fluidizing gas velocity inside the fluidized-bed furnace to approximately 4 m / s, it is possible to increase the limit of salt accumulation in the bed material, thereby increasing the amount of waste that can be treated without causing poor fluidization in the fluidized bed. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-106244 [Patent Document 2] Patent No. 3294172 Summary of the Invention [Problem to be solved by the invention]

[0007] The invention disclosed in Patent Document 1 lists garnet, ilmenite, olivine, ferronickel slag, and the like as bed materials. However, as shown in Table 2 of Patent Document 1, these are more expensive than inexpensive, general-purpose silica sand, and replacing the bed material is costly. The invention of Patent Document 2 can increase the critical salt accumulation amount in the bed material, but because agglomeration occurs with even a slight change in alkali metal, there is a risk that agglomeration will occur suddenly if the critical salt accumulation amount is exceeded, resulting in poor flow.

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

[0009] A method for burning an alkali metal-containing fuel according to one aspect of the present invention uses a combustion furnace to form a fluidized bed using a fluidized medium within the furnace and burn a fuel containing alkali metal in the fluidized bed, wherein a measuring device measures the concentration of alkali metal adhering to the fluidized medium discharged from the combustion furnace by X-ray fluorescence analysis, and a control device controls the amount of the fluidized medium discharged from the combustion furnace and the amount of the fluidized medium supplied to the combustion furnace in accordance with the concentration.

[0010] In addition, in the method for burning an alkali metal-containing fuel according to the present invention, the lumps of the bed material discharged from the combustion furnace are crushed, and the concentration of the alkali metal components attached to the crushed bed material is measured by X-ray fluorescence analysis.

[0011] In the method for burning an alkali metal-containing fuel according to the present invention, the amount of the fuel supplied to the combustion furnace is controlled in accordance with the amount of the bed material supplied to the combustion furnace.

[0012] In the method for burning an alkali metal-containing fuel according to the present invention, an auxiliary fuel is supplied to the combustion furnace in accordance with the amount of the bed material supplied to the combustion furnace.

[0013] A combustion system for an alkali metal-containing fuel according to one aspect of the present invention is a combustion system that uses a combustion furnace in which a fluidized bed is formed using a fluidized medium within the furnace and a fuel containing alkali metal is burned in the fluidized bed, and includes a measuring device that measures the concentration of alkali metal attached to the fluidized medium discharged from the combustion furnace by fluorescent X-ray analysis, and a control device that controls the amount of the fluidized medium discharged from the combustion furnace and the amount of the fluidized medium supplied to the combustion furnace in accordance with the concentration. [Effects of the Invention]

[0014] According to the present invention, it is possible to suppress poor flow due to agglomeration in a fluidized medium that forms a fluidized bed in a combustion furnace. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing the configuration of a combustion system 1000 according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the present invention is not limited to the embodiments described below. It should be noted that the drawings are schematic and that the dimensional relationships between elements may differ 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 fluidizes a bed material 81 inside to form a fluidized bed, and combusts fuel 73 supplied into the combustion furnace 1 in the fluidized bed. The combustion furnace 1 is mainly composed of a riser 10 as the furnace body, and a downcomer 20 that collects a portion of the bed material 81 and returns it to the riser 10.

[0018] The riser 10 is provided at its lower part with an air diffuser 11 for blowing the primary air supplied from the air blower 91 upward. In addition, on the side wall at the lower part of the riser 10, there are provided, in order from the bottom, a bed material supply port 12 for supplying the bed material 81 into the riser 10 above the air diffuser 11, a fuel supply port 13 for supplying the fuel 73 into the riser 10, and a secondary air blowing port 14 for blowing the secondary air supplied from the air blower 92 into the riser 10. In addition, a discharge part 15 for discharging the bed material 81 inside the riser 10 is provided at the bottom part of the riser 10.

[0019] The downcomer 20 is connected to the upper part of the riser 10 by a pipe 30. The downcomer 20 has a collection section 21 that collects the bed material 81 sent from the riser 10 together with the exhaust gas, a return pipe 22 for returning the bed material 81 collected in the collection section 21 to the lower part of the riser 10, and a seal section 23 that prevents the gas from the riser 10 from ascending inside the collection section 21.

[0020] A circulation line 40 is provided near the combustion furnace 1 for returning the bed material 81 discharged from the discharge section 15 and regenerated to the combustion furnace 1. In the circulation line 40, a sieving device 41, a polishing device 42, a sorting device 43, and a bed material supplying device 44 are arranged in this order from the discharge section 15.

[0021] The sieving device 41 receives the bed material 81 discharged from the discharge section 15 and separates the bed material 81 into bed material 81 having a predetermined particle size or less, lumps of the bed material 81 that have become larger than the predetermined particle size due to agglomeration, and incombustible matter generated after the combustion of the fuel 73. The sieving device 41 sends the separated bed material 81 having a predetermined particle size or less to the grinding device 42, and sends the separated lumps of the bed material 81 to the crusher 53.

[0022] The polishing device 42 polishes the bed material 81 supplied from the sieving device 41 to remove alkali metal components adhering to the bed material 81. There is no limitation on the polishing method used in the polishing device 42, and for example, an autogenous crushing method, a shear grinding method, a blasting method, etc. can be applied. The bed material 81 from which the alkali metal components have been removed by the polishing device 42 and the alkali metal components removed from the bed material 81 are sent to the sorting device 43.

[0023] The sorting device 43 sorts the bed material 81 from the mixture of the alkali metal component and the bed material 81 sent from the polishing device 42. There is no limitation on the sorting method used in the sorting device 43, and for example, a wind sorting method, a gravity sorting method, etc. can be applied. The bed material 81 sorted by the sorting device 43 is sent to the bed material supply machine 44.

[0024] The bed material supplier 44 stores the bed material 81 sent from the sorting device 43 and supplies the bed material 81 into the riser 10. In this embodiment, the bed material 81 is, for example, silica sand. A portion of the bed material 81 stored in the bed material supplier 44 is discarded from the bottom of the bed material supplier 44. In the bed material supplier 44, a portion of the stored bed material 81 is discarded, and new bed material 81 is replenished to make up for the discarded portion. The bed material 81 stored in the bed material supplier 44 is sent to the bed material supply port 12 and supplied from the bed material supply port 12 into the riser 10. Note that a portion of the bed material 81 may be discarded in the polishing device 42 or the sorting device 43.

[0025] The fuel supplier 61 is a device that sends fuel 73 to be burned in the combustion furnace 1 to the fuel supply port 13. The fuel supplier 61 sends fuel 73, which is a mixture of a first fuel 71 and a second fuel 72, to the fuel supply port 13. The first fuel 71 is a fuel with a high alkali metal content, such as palm empty fruit bunches. The second fuel 72 is a fuel with a lower alkali metal content than the first fuel 71, such as wood chips.

[0026] The crusher 53 crushes lumps of the bed material 81 sent from the sieving device 41, and breaks up the agglomerated bed material 81. The bed material 81 broken up by the crusher 53 is sent to the measuring device 52. The measuring device 52 is a device that analyzes the bed material 81 sent from the crusher 53 by X-ray fluorescence analysis and measures the concentration of alkali metal components. The measuring device 52 sends the measurement results of the measured concentration of alkali metal components to the control device 51. The control device 51 is a device that controls the discharge unit 15 and the bed material supply device 44. The control device 51 controls the discharge unit 15 and the bed material supply device 44 based on the measurement results of the concentration of alkali metal components sent from the measuring device 52.

[0027] Next, a description will be given of the operation of the combustion system 1000. Primary air sent from the blower 91 is blown into the riser 10 through the air diffuser 11, and secondary air sent from the blower 92 is blown into the riser 10 through the secondary air inlet 14, thereby fluidizing the bed material 81 and forming a fluidized bed in the riser 10.

[0028] Furthermore, fuel 73 is supplied into the riser 10 from the fuel supply port 13. From the viewpoint of operating costs, it is preferable that the proportion of the first fuel 71 is large in the fuel 73 supplied from the fuel supply port 13. The fuel 73 supplied into the riser 10 is combusted in the fluidized bed.

[0029] Specifically, the bed material 81 is fluidized by the primary air blown in from the air diffuser 11, forming a dense layer in the lower part of the riser 10. In this dense layer, the high heat capacity and stirring effect promote drying of the fuel 73 and release of volatile matter. In addition, in the upper part of the riser 10, the bed material 81 is blown up by the blowing of primary and secondary air, forming a thin layer in which the bed material 81 is thin. In this thin layer, the fuel 73 is burned by the heat capacity and stirring effect of the bed material 81. In other words, by forming a fluidized layer consisting of a dense layer and a thin layer in the riser 10, the combustion furnace 1 prevents the generation of char, which is unburned carbon, and efficiently combusts the palm empty fruit bunches, which are the fuel 73. The combustion region in the riser 10 is maintained at approximately 850 to 900°C.

[0030] The exhaust gas generated by the combustion of the fuel 73 in the riser 10 is supplied to the collection section 21 of the downcomer 20 via the pipe 30. A portion of the bed material 81 is also sent from the riser 10 to the collection section 21 together with the exhaust gas. In the collection section 21, the bed material 81 and ash with relatively large particle sizes are recovered and returned to the bottom of the riser 10 through the seal section 23 and the return pipe 22. The exhaust gas and ash with relatively small particle sizes are discharged from the top of the downcomer 20 and sent to an exhaust gas treatment facility via a superheater (not shown), where the steam is superheated, and after dust removal in the exhaust gas treatment facility, the steam is released to the outside from a chimney (not shown).

[0031] In this embodiment, the first fuel 71 (palm empty fruit bunches) contained in the fuel 73 combusted in the riser 10 releases gaseous potassium, which is an alkali metal component. This gaseous potassium reacts with silicon oxide in the silica sand particles, which are the bed material 81, to produce SiO2-K2O compounds on the surfaces of the silica sand particles. This SiO2-K2O compound melts and forms an adhesive layer on the surfaces of the silica sand particles. This adhesive layer causes several grains of bed material 81 to fuse together and fall to the bottom of the riser 10. The fused and fallen bed material 81 further fuses to form clumps. A predetermined amount of the bed material 81 including the clumps and incombustible matter remaining after combustion of the fuel 73 is discharged per unit time from the discharge section 15 and sent to the sieve device 41.

[0032] The sieving device 41 to which the bed material 81 has been sent sends the separated bed material 81 having a particle size equal to or smaller than a predetermined size to the polishing device 42. The sieving device 41 also sends the separated lumps of bed material 81 to the crusher 53. In the polishing device 42, the bed material 81 is polished, and the alkali metal components adhering to the surface of the bed material 81 as an adhesive layer are removed from the surface of the bed material 81. The alkali metal components removed from the bed material 81 and the bed material 81 from which the alkali metal components have been removed are sent to the sorting device 43.

[0033] In the sorting device 43, the bed material 81 is sorted and the alkali metal components are separated, and the sorted bed material 81 is sent to the bed material supplier 44. In the bed material supplier 44, a portion of the bed material 81 is discarded from the bottom of the bed material supplier 44 and new bed material 81 is replenished from the top. The control device 51 controls the bed material supplier 44 to send the bed material 81 stored in the bed material supplier 44 to the bed material supply port 12 in accordance with the amount of bed material 81 discharged per unit time from the discharge section 15, and supply a predetermined amount of bed material 81 into the riser 10.

[0034] The crusher 53 crushes lumps of the bed material 81 sent from the sieving device 41, loosening the bonds between the bed material 81 and uniforming the diameter of the bed material 81 on which an adhesive layer has formed. The bed material 81 broken down by the crusher 53 is sent to the measuring device 52. The measuring device 52 analyzes the bed material 81 sent from the crusher 53 using X-ray fluorescence analysis at a predetermined interval to measure the concentration of alkali metal components. The measuring device 52 sends the measurement results of the concentration of alkali metal components to the control device 51. Here, because the diameter of the bed material 81 has been uniformed by the crusher 53, the concentration of alkali metal components on the surface of the silica sand particles can be accurately measured.

[0035] The control device 51 controls the discharge unit 15 and the bed material supplier 44 based on the measurement results sent from the measuring device 52, thereby controlling the amount of bed material 81 discharged from the riser 10 and the amount of bed material 81 supplied from the bed material supplier 44 to the riser 10. For example, when the measurement results are equal to or greater than a predetermined threshold, the control device 51 controls the discharge unit 15 to increase the amount of bed material 81 discharged from the discharge unit 15 per unit time from a predetermined amount, and controls the bed material supplier 44 to increase the amount of bed material 81 supplied from the bed material supplier 44 to the riser 10 per unit time from a predetermined amount. This allows lumps of bed material 81 to be discharged, thereby preventing poor flow of the bed material 81. In addition, if the measurement result is less than a predetermined threshold, the control device 51 controls the discharge section 15 to return the amount of bed material 81 discharged from the discharge section 15 to a predetermined amount, and controls the bed material supplier 44 to return the amount of bed material 81 supplied from the bed material supplier 44 to the riser 10 to a predetermined amount.

[0036] The control device 51 may control the amount of the bed material 81 discharged from the discharge section 15 and the amount of the bed material 81 supplied into the riser 10 according to the concentration of the alkali metal component indicated by the measurement result. For example, the control device 51 may control the discharge section 15 and the bed material supplier 44 so that the amount of the bed material 81 discharged from the discharge section 15 and the amount of the bed material 81 supplied into the riser 10 increases as the concentration of the alkali metal component indicated by the measurement result increases, and may control the discharge section 15 and the bed material supplier 44 so that the amount of the bed material 81 discharged from the discharge section 15 and the amount of the bed material 81 supplied into the riser 10 decreases as the concentration of the alkali metal component indicated by the measurement result decreases.

[0037] [Variations] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be implemented in various other forms. For example, the above-described embodiments may be modified as follows to implement the present invention. The above-described embodiments and the following modifications may be combined with each other. The present invention also includes configurations in which the components of the above-described embodiments and modifications are appropriately combined. Furthermore, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-described embodiments and modifications, and various modifications are possible.

[0038] In the above-described embodiment, the combustion furnace 1 is a circulating fluidized bed furnace, but it may also be a bubbling fluidized bed (BFB) furnace.

[0039] In the present invention, the bed material 81 sent from the crusher 53 may be polished, and the adhesive layer removed from the bed material 81 may be sent to the measuring device 52 .

[0040] In the present invention, in order to prevent a decrease in the temperature inside the riser 10 due to the supply of new bedrock material 81 into the riser 10, the amount of fuel 73 supplied into the riser 10 may be increased according to the amount of bedrock material 81 supplied. In this case, in order to prevent agglomeration from occurring, the proportion of the second fuel 72 may be increased. In addition, in order to prevent a decrease in the temperature inside the riser 10 due to an increase in the amount of bedrock material 81 supplied, kerosene or heavy oil may be supplied as an auxiliary fuel.

[0041] In the present invention, the fuel 73 may include palm kernel shells (PKS).

[0042] In the present invention, the temperature inside the riser 10 may be measured, and the amount of bed material 81 discharged from the discharge section 15 and the amount of bed material 81 supplied from the bed material supply device 44 to the riser 10 may be controlled according to the measured temperature. [Explanation of symbols]

[0043] 1. Combustion furnace 10 Liza 11 Air diffuser 12 Fluid medium supply port 13 Fuel supply port 14 Secondary air inlet 20 Downcomers 21 Collection section 22 Return pipe 23 Seal part 30 Piping 40 Circulation Line 41 Sieve device 42 Polishing equipment 43 Sorting equipment 44 Fluid medium feeder 51 Control device 52 Measuring equipment 53 Crusher 91, 92 Blower 1000 Combustion System

Claims

1. A combustion method using a combustion furnace in which a fluidized bed is formed with a fluidizing medium in the furnace and a fuel containing an alkali metal is burned in the fluidized bed, Disintegrating the lumps of bed material discharged from the combustion furnace that exceed a predetermined particle size using a disintegrator; a measuring device measuring the concentration of alkali metals attached to the fluidized medium disintegrated by the disintegrator by fluorescent X-ray analysis; removing the alkali metal from the bed material discharged from the combustion furnace and having a particle size equal to or smaller than a predetermined particle size using a polishing device; storing a new fluid medium and the fluid medium from which the alkali metal has been removed by the polishing device in a fluid medium supplier; A control device controls the amount of the bed material discharged from the combustion furnace and the amount of the bed material supplied from the bed material supply device to the combustion furnace in accordance with the concentration. A method for burning an alkali metal-containing fuel.

2. The amount of the fuel supplied to the combustion furnace is controlled in accordance with the amount of the bed material supplied to the combustion furnace.

2. A method for burning an alkali metal-containing fuel according to claim 1.

3. Auxiliary fuel is supplied to the combustion furnace in accordance with the amount of the bed material supplied to the combustion furnace.

2. A method for burning an alkali metal-containing fuel according to claim 1.

4. A combustion system using a combustion furnace in which a fluidized bed is formed by a fluidized medium in the furnace and a fuel containing an alkali metal is burned in the fluidized bed, a crusher for crushing lumps of bed material discharged from the combustion furnace that exceed a predetermined particle size; a measuring device that measures the concentration of alkali metals attached to the fluidized medium disintegrated by the disintegrator by fluorescent X-ray analysis; a polishing device for removing the alkali metal from the bed material discharged from the combustion furnace and having a particle size equal to or smaller than a predetermined particle size; a fluidized medium supplier for storing new fluidized medium and the fluidized medium from which the alkali metal has been removed by the polishing device; a control device that controls the amount of the bed material discharged from the combustion furnace and the amount of the bed material supplied from the bed material supplier to the combustion furnace in accordance with the concentration; A combustion system for an alkali metal-containing fuel comprising:

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