Bed material regeneration device, combustion system, and combustion method for fluidized bed combustion furnace

Abstract

This fluid medium regeneration device of a fluidized bed is provided with a cooling unit in which, at least, a fluid medium recovered from the fluidized bed of a fluidized bed combustion furnace is supplied, the fluid medium is cooled through contact with a liquid medium that has a boiling point of less than or equal to -20°C at 1 atm, and a coating layer is separated from the fluid medium.

Description

[Technical Field]

[0001] The present invention relates to a fluidized bed regeneration device for regenerating a fluidized bed material that forms a fluidized bed in a fluidized bed combustion furnace, a combustion system, and a combustion method for a fluidized bed combustion furnace. [Background technology]

[0002] In recent years, in order to secure fuel, there has been an increasing demand for power generation using biomass fuels other than wood-based materials and waste fuels such as waste tires and waste plastics. One example of such a power generation mechanism is a technology that uses a circulating fluidized bed boiler (hereinafter sometimes referred to as a "CFB boiler") that includes a combustion furnace (e.g., a fluidized bed combustion furnace) that burns a combustion target and generates saturated steam, and a superheater that is connected to the combustion furnace and uses the combustion gas generated in the combustion furnace to superheat the saturated steam generated in the combustion furnace and use it for power generation.

[0003] On the other hand, due to the future depletion of petroleum resources and biomass fuels themselves, it is predicted that low-grade biomass fuels such as rice husks and EFB (Empty Fruit Bunches) will be widely used. However, low-grade biomass fuels and waste-derived fuels contain large amounts of impurities, such as alkaline components such as Na and K. The use of such low-grade fuels containing impurities such as alkaline components can produce low-melting-point compounds (hereinafter referred to as "low-melting-point compounds"), which can cause poor fluidity in the fluidized bed. For this reason, it is urgent and essential to expand the range of biomass fuels that can be used in CFB boilers and to prevent poor fluidity in such boilers.

[0004] For example, the following techniques have been developed as techniques for low-grade fuels containing impurities such as alkaline components (see, for example, Patent Documents 1 and 2 below). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2005-226930 [Patent Document 2] Patent Publication No. 2011-106701 Summary of the Invention [Problem to be solved by the invention]

[0006] The technology described in Patent Document 1 addresses the generation of low-melting-point compounds during the combustion of high-alkali biomass fuel by setting the air ratio in the fluidized bed within a specific range, recirculating exhaust gas to set the ratio of the recirculated exhaust gas flow rate to the total air flow rate within a specific range, and maintaining a ratio of the superficial velocity to the fluidization initiation velocity within the fluidized bed of 2 to 6 while controlling the fluidized bed temperature to 600 to 750°C. This suppresses aggregation of the fluidized material (e.g., bottom ash) due to low-melting-point compounds, prevents poor fluidization, and enables smooth and stable operation. However, consistently maintaining the fluidized bed temperature at 600 to 750°C is not easy. Furthermore, even with this technology, the fluidized material still tends to become large, requiring a considerable supply of new fluidized material such as sand. Therefore, there is still room for improvement in terms of the fluidized material and cost.

[0007] The technology of Patent Document 2 is equipped with a cooling water tank that separates deposits from a fluidized medium such as bottom ash extracted from a fluidized bed of a combustion furnace by pouring the fluidized medium, such as bottom ash, into water to cool it. This technology also makes it possible to efficiently separate deposits from the fluidized medium, but there is still room for improvement in terms of efficiently suppressing poor fluidity of high-alkali-content biomass fuel.

[0008] In order to solve the above-mentioned problems, an object of the present invention is to provide a fluidized bed regeneration device, a combustion system, and a combustion method for a fluidized bed combustion furnace that can efficiently separate a coating layer from a fluidized bed. [Means for solving the problem]

[0009] That is, the present invention is as follows.

[0010] <1> A fluidized bed fluidized medium regeneration device equipped with a cooling section, which is supplied with at least a fluidized medium recovered from the fluidized bed of a fluidized bed combustion furnace, cools the fluidized medium by bringing it into contact with a liquid medium having a boiling point of -20°C or less at 1 atmosphere, and separates a coating layer from the fluidized medium. <2> The liquid medium is at least one of liquid air, liquid nitrogen, and liquid oxygen. <1> The fluidized bed regenerating device according to claim 1. <3> a sorting means for sorting the fluidized medium and the coating layer discharged from the cooling section, <1> or the above <2> The fluidized bed regenerating device according to claim 1. <4> the temperature of the fluidized medium recovered from the fluidized bed of the fluidized bed combustion furnace is equal to or lower than the melting point of the coating layer; <1> ~The above <3> 10. The fluidized bed regenerating device according to claim 9, wherein the fluidized bed regenerating device is a fluidized bed regenerating device. <5> The cooling unit further includes an intermediate cooling unit that cools the fluid medium, and the fluid medium cooled by the intermediate cooling unit is brought into contact with the liquid medium. <1> ~The above <4> 10. The fluidized bed regenerating device according to claim 9, wherein the fluidized bed regenerating device is a fluidized bed regenerating device. <6> The fluidized bed further includes a return unit that recovers the fluidized medium from which the coating layer has been separated, and returns the fluidized medium, the particle size of which has been adjusted to 50 to 1000 μm, to the fluidized bed. <1> ~The above <5> 10. The fluidized bed regenerating device according to claim 9, wherein the fluidized bed regenerating device is a fluidized bed regenerating device. <7> a fluidized bed combustion furnace; <1> ~The above <6> A combustion system comprising: a fluidized bed bed material regeneration device according to any one of the above items. <8> A combustion method for a fluidized bed combustion furnace using an alkaline component-containing fuel, comprising: recovering a fluidized medium from the fluidized bed of the fluidized bed combustion furnace, bringing the fluidized medium recovered from the fluidized bed into contact with a liquid medium having a boiling point of −20° C. or less at 1 atmosphere to cool the fluidized medium, and separating the coating layer from the fluidized medium; Combustion method for fluidized bed combustion furnace. <9> The liquid medium is at least one of liquid air and liquid nitrogen. <8> The combustion method for a fluidized bed combustion furnace according to claim 1. <10> separating the fluid medium and the coating layer; <8> or the above <9> The combustion method for a fluidized bed combustion furnace according to claim 1. <11> the temperature of the fluidized medium recovered from the fluidized bed of the fluidized bed combustion furnace is equal to or lower than the melting point of the coating layer; <8> ~The above <10> 1. The combustion method for a fluidized bed combustion furnace according to claim 1, <12> The fluid medium is cooled by an intermediate cooling section before being brought into contact with the liquid medium. <8> ~The above <11> 1. The combustion method for a fluidized bed combustion furnace according to claim 1, <13> The fluidized medium from which the coating layer has been separated is recovered, and the fluidized medium whose particle size has been adjusted to 50 to 1000 μm is returned to the fluidized bed. <8> ~The above <12> 1. The combustion method for a fluidized bed combustion furnace according to claim 1, [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a fluidized bed regeneration device, a combustion system, and a combustion method for a fluidized bed combustion furnace, which are capable of efficiently separating a coating layer from a fluidized bed. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram showing a combustion system equipped with a fluidized bed bed material regeneration device according to a first embodiment of the present invention. [Figure 2] 1A and 1B are schematic diagrams for explaining the mechanism of agglomerate formation, in which (a) is a schematic diagram showing the mechanism of agglomerate coating induction, and (b) is a schematic diagram showing the mechanism of agglomerate melting induction. [Figure 3] K2O-SiO2 phase diagram. [Figure 4] FIG. 4 is a schematic diagram showing a combustion system equipped with a fluidized bed bed material regenerator according to a second embodiment of the present invention. [Figure 5] 2 is a flow chart for explaining a combustion method applicable to the combustion system and the bed material regeneration device in the present embodiment. [Figure 6]FIG. 1 is a schematic diagram showing a combustion system including a fluidized bed bed material regenerator according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail with reference to the drawings. However, the following embodiment is an example for explaining the present invention, and is not intended to limit the present invention to the following content. The present invention can be implemented by modifying it as appropriate within the scope of its gist. Note that the same elements are given the same reference numerals, and redundant explanations will be omitted. Furthermore, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings unless otherwise specified. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0014] [First embodiment] A combustion system equipped with a bed material regeneration device according to a first embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing a combustion system equipped with a bed material regeneration device for a fluidized bed according to the first embodiment of the present invention.

[0015] As shown in Fig. 1, the combustion system 1 includes a fluidized bed combustion furnace 2, which receives a material to be burned and burns the material therein, and a bed material regeneration device 3. The bed material regeneration device 3 is supplied with a bed material Fa recovered from the fluidized bed F of the combustion furnace 2, and includes a screw conveyor 11 that functions as a cooling unit, which cools the bed material Fa by bringing the bed material Fa into contact with a liquid medium LM having a boiling point of -20°C or less at 1 atmosphere, and separates a coating layer from the bed material Fa. The bed material regeneration device 3 in the first embodiment is configured to separate a coating layer from bed material Fa, such as sand, recovered from the fluidized bed F of the combustion furnace 2, thereby regenerating the bed material Fa.

[0016] The combustion system 1 can use, as the combustion target, alkali-containing fuels such as high-alkali biomass fuels such as rice husks and EFB (Empty Fruit Bunches). Hereinafter, the high-alkali biomass fuels may be simply referred to as "biomass fuel." The combustion system 1 includes a combustion furnace 2 that burns biomass fuel and heats water in a sealed container to generate steam. The combustion furnace 2 is an external circulation fluidized bed combustion furnace, a so-called CFB (Circulating Fluidized Bed) boiler. A fuel inlet for charging fuel is provided in the middle of the combustion furnace 2, and the biomass fuel is charged through this fuel inlet. However, the combustion target used in the combustion system 1 is not limited to biomass fuel; any alkaline-containing fuel can be used without any particular limitation.

[0017] The combustion furnace 2 is further charged with a bed material Fa, such as sand primarily composed of quartz particles. Air is supplied to the bed material Fa from the lower portion (bottom) of the furnace, causing the bed material Fa to flow and form a fluidized bed F. The formation of the fluidized bed F promotes the combustion of the biomass fuel. Furthermore, combustion gases resulting from the combustion of the biomass fuel ascend within the combustion furnace 2, carrying some of the bed material Fa with them. Here, the term "bed material" as used herein also includes bottom ash resulting from the combustion of the biomass fuel. Furthermore, "bottom ash" refers to bed material Fa primarily composed of bed material such as sand, including combustion ash resulting from the combustion of the biomass fuel and bed material Fa that has been coated and agglomerated with components in the biomass fuel. According to the combustion system equipped with the bed material regeneration device of this embodiment, the bed material Fa can be regenerated for reuse by separating the "coating layer" (including deposits) formed by the components in the biomass fuel from the bed material Fa (agglomerates) that have been coated and agglomerated with the components in the biomass fuel. Hereinafter, when simply referred to as a "coating layer," it also includes a simple deposit formed by components in the biomass fuel.

[0018] A gas outlet 2A is provided at the top of the combustion furnace 2 for discharging combustion gas. A cyclone separator 4, which functions as a solid-gas separator, is connected to the gas outlet 2A. The combustion gas generated in the combustion furnace 2 is introduced into the cyclone separator 4, entraining solid particles. The cyclone separator 4 separates the collected solid particles from the combustion gas by centrifugal separation. The collected solid particles separated from the combustion gas are returned to the combustion furnace 2 through a return line 5. The collected solid particles include bed materials such as bottom ash and sand. Meanwhile, the combustion gas from which the collected solid particles have been removed is sent to a heat recovery device 6 through an outlet 4A.

[0019] The return line 5 is composed of a pipe connected to the bottom of the combustion furnace 2, with a loop seal 5A installed midway along the line. The loop seal 5A is equipment that prevents combustion gas from flowing back into the combustion furnace 2. The bed material Fa sent from the cyclone separator 4 accumulates inside the loop seal 5A. The bed material Fa inside the loop seal 5A is then introduced into the combustion furnace 2 through a return chute 5B, which serves as the outlet of the loop seal 5A.

[0020] The heat recovery device 6 has boiler tubes (not shown) that form a flow path for the combustion gas and allow water to flow as a heat medium. The boiler tubes are installed so as to cross the flow path of the combustion gas within the heat recovery device 6, and recover the heat of the combustion gas sent from the cyclone separator 4 by heat exchange with the water inside the tubes. Inside the boiler tubes, high-temperature steam is generated by the recovered heat, and this steam is sent through the boiler tubes to a power generation turbine (not shown) or the like. The heat recovery device 6 also sends the combustion gas after heat recovery to a bag filter 7 through an outlet 6A.

[0021] The bag filter 7 is a filtering device that removes fine particles such as fly ash that are still entrained in the combustion gas. The combustion gas filtered by the bag filter 7 is sucked into a suction pump 8 and discharged to the outside of the combustion system 1 through a chimney 9.

[0022] Meanwhile, in the combustion furnace 2, during the combustion of biomass fuel, some of the combustion ash and fuel produced by the combustion melt with the surrounding bed material Fa to form clumps. These clumps are sometimes called "agglomerates," and if they accumulate at the bottom of the combustion furnace 2, they can cause poor fluidity in the fluidized bed F. For this reason, the clumps must be periodically removed from the combustion furnace 2 along with the bed material Fa. In this embodiment, in order to remove the coating layer (deposits), the bed material Fa containing the agglomerates is removed from the discharge port of the combustion furnace 2 and transported to the bed material regeneration device 3.

[0023] The mechanism of formation of agglomerates in the combustion furnace 2 will be described with reference to Fig. 2. Fig. 2 is a schematic diagram for explaining the mechanism of formation of agglomerates.

[0024] First, the formation of agglomerates, which is the main cause of poor fluidity in the fluidized bed F, is mostly caused by the adhesion of a melt of a low-melting-point compound, i.e., a melt of a substance (e.g., KCl (solid)) formed due to the alkaline components in the biomass fuel, to the surface of the bed material Fa, or by the chemical reaction of components in the biomass fuel on the surface of the bed material Fa, resulting in the formation of a eutectic of the alkaline components on the surface of the bed material Fa. Thus, there are two main known mechanisms for the formation of agglomerates: coating induction and melting induction.

[0025] (Coating induction mechanism) Figure 2(a) shows the mechanism of coating-induced agglomerate X formation. Figure 2(a) is a schematic diagram illustrating the coating-induced mechanism of agglomerate formation. As shown in Figure 2(a), the formation of agglomerate X due to coating is caused by a chemical reaction between vapor (e.g., KCl, K2SO4, etc.) ("N" in Figure 2(a)) of alkaline components (e.g., potassium and sodium) in biomass fuel and quartz particles (sand), the main component of bed material Fa. KCl, in particular, tends to vaporize easily at temperatures above 700 °C. This chemical reaction forms an adhesive eutectic coating C (e.g., K2O-SiO2: alkali silicate phase) on the surface of bed material Fa. Subsequently, the bed material Fa with the eutectic coating C repeatedly bonds and separates within the fluidized bed F. As a result, particle aggregation begins, gradually forming agglomerates X, which impede fluidization.

[0026] The main controlling factors of the coating-induced agglomerate X formation mechanism are the eutectic coating thickness (ease of bonding separation), the eutectic coating composition (bonding strength), and the local temperature. In addition to alkali components, phosphorus has also been confirmed to be an important factor in the formation of agglomerate X in biomass fuels.

[0027] The eutectic coating C begins to melt at approximately 700°C, as shown in the K2O-SiO2 phase diagram in Figure 3. Therefore, in the high-temperature region (high-temperature combustion region) (approximately 700°C to 900°C) in the combustion furnace 2, the eutectic coating C becomes molten, and the fluidized medium Fa easily aggregates together.

[0028] (Mechanism of melting induction) Next, the mechanism of melt-induced agglomerate X formation will be explained. FIG. 2(b) is a schematic diagram showing the melt-induced mechanism. Melt-induced agglomerate X is caused by the adhesion of molten material M, a low-melting-point compound (alkali silicate) formed by the alkaline components in the biomass fuel, to the surface of the bed material Fa. The bed material Fa with the molten material M attached to it gradually agglomerates within the fluidized bed F, forming agglomerate X. The controlling factors of the melt-induced agglomerate X formation mechanism are the local temperature and the fuel ash composition, and agglomerate X tends to form through the melt-induced mechanism in combustion ash that contains high concentrations of alkaline components and chlorine.

[0029] (Fluid medium regenerator 3) A fluidized medium regeneration device 3 that separates a coating layer such as an alkali silicate phase from a fluidized medium Fa and regenerates (reuses) the fluidized medium Fa will be described. As shown in FIG. 1 , the fluidized medium regeneration device 3 includes a supply unit 10 to which the fluidized medium Fa recovered from the fluidized bed F of the combustion furnace 2 is supplied, and a screw conveyor 11 that conveys the fluidized medium Fa supplied from the supply unit 10 and brings it into contact with a liquid medium LM supplied from a supply pipe 11A to cool the fluidized medium Fa. As described above, the screw conveyor 11 serves as a cooling unit for the fluidized medium Fa. The fluidized medium regeneration device 3 also includes a sorting device 12 that separates the fluidized medium Fa discharged from the screw conveyor 11 from the coating layer, and a return mechanism 13 that collects the fluidized medium from which the coating layer has been separated and returns it to the fluidized bed F of the combustion furnace 2.

[0030] The supply unit 10 is connected to an outlet provided at the bottom of the combustion furnace 2, and is supplied with the bed material Fa recovered from the fluidized bed F of the combustion furnace 2. The bed material recovered from the combustion furnace 2 is at a high temperature (for example, 700°C), and is supplied into the screw conveyor 11 via the supply unit 10.

[0031] The temperature of the fluidized material Fa recovered from the fluidized bed F of the combustion furnace 2 and supplied to the supply section 10 is not particularly limited, but is preferably, for example, at room temperature (e.g., 25°C) or higher and below the melting point of the coating layer (deposit) of the fluidized material Fa (e.g., 700°C or lower when a coating layer of SiO-KO is formed on the fluidized material Fa).

[0032] There is no particular limitation on the location from which the bed material Fa is recovered from the combustion furnace 2, but from the viewpoint of efficiently recovering the high-temperature bed material Fa, it is preferable to recover the bed material Fa of the fluidized bed F that has accumulated from the bottom of the combustion furnace 2.

[0033] The screw conveyor 11 is connected to a supply unit 10 connected to the exhaust port of the combustion furnace 2, and is supplied with the high-temperature fluidized medium Fa extracted from the bottom of the combustion furnace 2. The screw conveyor 11 is configured so that the screw rotates when driven by a motor indicated by "M" in the figure, thereby conveying the fluid within the device. The screw conveyor 11 is pre-cooled, and cooling means other than the liquid medium L, such as water, can be used to pre-cool the screw conveyor 11. A supply pipe 11A is connected to the screw conveyor 11, and the liquid medium LM is supplied into the conveying path of the screw conveyor 11 by a pump or the like (not shown). The position at which the liquid medium LM is supplied to the screw conveyor 11 is not particularly limited, and the supply position of the liquid medium LM can be set so that the liquid medium LM contacts the fluidized medium Fa at an optimal location within the screw conveyor 11. For example, as shown in FIG. 1, the liquid medium LM may be supplied from the downstream side of the screw conveyor 11, from the upstream side of the screw conveyor 11, or throughout the entire screw conveyor 11.

[0034] In this embodiment, the liquid medium LM is a liquid having a boiling point of −20°C or lower at 1 atmosphere pressure and capable of maintaining a low temperature below 0°C. Throughout this specification, the term “liquid medium” also includes a gaseous medium formed by evaporation of a liquid medium. Examples of the liquid medium LM include liquid air (boiling point at 1 atmosphere pressure: approximately −190°C), liquid nitrogen (boiling point at 1 atmosphere pressure: approximately −196°C), liquid oxygen (boiling point at 1 atmosphere pressure: approximately −183°C), and liquid hydrogen (boiling point at 1 atmosphere pressure: approximately −252.6°C). The liquid medium LM can be appropriately selected depending on, for example, the fuel conditions in the combustion furnace 2 (the amount of alkaline components (e.g., potassium) brought into the furnace). However, from the viewpoints of ease of handling, availability, safety, and the like, at least one of liquid air, liquid nitrogen, and liquid oxygen is preferred.

[0035] The high-temperature differential cooling contraction transported through the screw conveyor 11 comes into contact with the liquid medium LM and is rapidly cooled. When the fluid medium Fa (agglomerate) with a eutectic coating C such as an alkali silicate phase formed by the coating induction mechanism described above or a coating layer such as a melt M of a low-melting-point compound (alkali silicate) formed on its surface by the melt induction mechanism comes into contact with the liquid medium LM, the fluid medium Fa and the coating layer are rapidly cooled from their high-temperature states, and the coating layer is separated from the fluid medium Fa due to the difference in thermal expansion (differential cooling contraction) between the fluid medium Fa and the coating layer. This separation utilizes the difference in cooling contraction due to the difference in material (i.e., the difference in physical properties) between the coating layer (e.g., alkali silicate) and the induction medium (sand, etc.).

[0036] Furthermore, although not particularly limited, from the viewpoint of effectively causing separation due to the difference in cooling contraction between the bed material Fa and the coating layer within the screw conveyor 11, it is preferable that the difference in temperature between the bed material Fa and the liquid medium LM is 120 to 410°C.

[0037] The bed material Fa and the coating layer cooled and separated in the screw conveyor 11 are discharged from the discharge port of the conveyor and supplied to the sorting device 12 located downstream. At this time, since the liquid medium LM volatilizes immediately after coming into contact with the bed material Fa, the separated bed material Fa and the coating layer are supplied to the sorting device 12 in a dry state.

[0038] The sorting device 12 is provided with a sieve as sorting means therein, and is further connected to a discharge pipe 12A and a supply pipe 12B. The mixture of bed material Fa and coating layer supplied from the screw conveyor 11 to the sorting device 12 via the supply pipe 12B is sorted into bed material Fa and unsuitable materials for combustion such as the coating layer in the sorting device 12. The sorting device 12 uses a sieve to separate the bed material Fa from materials other than the bed material Fa (i.e., unsuitable materials for combustion such as the coating layer) by utilizing the difference in particle size between the bed material Fa and the coating layer. The bed material Fa sorted out by the sorting device 12 is transported to a return mechanism 13. The unsuitable materials for combustion such as the coating layer sorted out by the sorting device 12 are discharged to the outside of the system via a discharge pipe 12A.

[0039] The mesh size of the sieve provided in the sorting device 12 is not particularly limited, but since the particle size of the coating layer to be removed is several μm or less, the bed material Fa and the coating layer can be separated by using a sieve with an opening size of, for example, 50 μm or less. Considering the particle size of the bed material Fa, for example, based on the mesh size specified by the ASTM (American Society for Testing and Materials) standard, the sieve provided in the sorting device 12 may have a mesh size of, for example, 270 to 325 mesh (opening size 45 to 53 μm). The sieve in the sorting device 12 may be configured as either a single-stage or multi-stage sieve.

[0040] The return mechanism 13 is a mechanism for recovering the bed material Fa from which the coating layer has been separated and returning it to the fluidized bed. The return mechanism 13 is also equipped with a particle size adjusting device 13A for adjusting the flow of the bed material Fa and a return line 13B.

[0041] The sorted bed material Fa transported from the sorting device 12 to the return mechanism 13 is first supplied to the particle size adjusting device 13A. The particle size adjusting device 13A is provided with a sieve as particle size adjusting means and adjusts the particle size of the bed material Fa. The particle size adjusting device 13A can adjust the particle size of the bed material Fa to, for example, 50 to 1000 μm in order to further remove foreign matter from the bed material Fa and increase the purity (quality) of the bed material Fa returned to the combustion furnace 2.

[0042] The mesh size of the sieve provided in the particle size adjusting device 13A is not particularly limited, but in order to remove foreign matter of 1000 μm or larger, the sieve may have an opening of 1000 μm or larger, for example. Based on the mesh size specified by the ASTM (American Society for Testing and Materials) standard, for example, from the viewpoint of the particle size of the bed material Fa, the sieve provided in the particle size adjusting device 13A may have a mesh size of 16 to 18 mesh (opening of 1000 to 1180 μm). The sieve in the particle size adjusting device 13A may have either a single stage or multiple stages.

[0043] A return line 13B is connected to the particle size adjustment device 13A, which returns the bed material Fa to the fluidized bed F of the combustion furnace 2. The bed material Fa, whose particle size has been adjusted in the particle size adjustment device 13A, is discharged through the return line 13B. In FIG. 1, the arrow "a" on the return line 13B communicates with the location marked "a" on the side of the combustion furnace 2, which means that the bed material Fa recovered by the return mechanism 13 is returned to the fluidized bed F from the fuel inlet of the combustion furnace 2.

[0044] According to the first embodiment of the bed material regeneration device 3 and the combustion system 1 incorporating the same, the high-temperature bed material Fa extracted from the bottom of the fluidized bed F of the combustion furnace 2 is rapidly cooled by contacting it with a liquid medium having a boiling point of −20°C or less at 1 atmosphere, thereby causing peeling of the coating layer due to the difference in shrinkage between the bed material Fa and the coating layer. This is because the physical properties of the alkali silicate phase such as K2O-SiO2 and the bed material Fa such as sand are different, and as a result, the difference in shrinkage occurs due to rapid cooling, resulting in separation of the bed material Fa and the coating layer.

[0045] In this way, the bed material regeneration device 3 and the combustion system 1 incorporating it utilize the difference in shrinkage based on the difference in physical properties between the bed material Fa and the coating layer, thereby separating the coating layer from the bed material Fa and regenerating the bed material Fa very efficiently compared to conventional devices that utilize physical collision, thereby ensuring the quality of the bed material Fa, which is a circulating material, and making effective use of it.

[0046] Furthermore, according to the fluidized medium recycling device 3, the fluidized medium Fa that has separated from the coating layer can be recovered by the return line 13B and returned to the fluidized bed F. This makes it possible to automatically replenish the fluidized medium Fa extracted from the fluidized bed F by returning it to the fluidized bed F, thereby reducing the labor required to replenish the fluidized medium Fa.

[0047] Furthermore, with the bed material regeneration device 3 and combustion system 1 of this embodiment, the bed material Fa particles can be handled in a dry state as in this embodiment. This allows smooth transport in the sorting device 12 and the return mechanism 13, facilitating recycling of the bed material Fa and reducing the amount of moisture carried over when the bed material Fa is returned to the fluidized bed F in the combustion furnace 2. Furthermore, with the bed material regeneration device 3 and combustion system 1 of this embodiment, the bed material Fa can be returned to the boiler without undergoing a drying process or the like. Therefore, the bed material regeneration device 3 and combustion system 1 of this embodiment can reuse the bed material advantageously in terms of efficiency and cost, and can also be suitably used in large-scale combustion furnaces 2 that use large amounts of bed material Fa (sand, etc.).

[0048] [Second embodiment] In the first embodiment, an embodiment has been described in which the high-temperature fluid medium recovered from the combustion furnace 2 is brought into contact with the liquid medium LM as is, but the present invention is not limited to such an embodiment. For example, in the first embodiment, a configuration may be adopted in which a conveying path of the cooling section (e.g., the screw conveyor 11) is secured to some extent so that the temperature of the fluid medium is lowered to some extent before it comes into contact with the liquid medium, or the cooling section may be provided with an intermediate cooling section that further cools the fluid medium, and the fluid medium cooled by the intermediate cooling section is brought into contact with the liquid medium.

[0049] An embodiment in which the screw conveyor 11 has a cooling medium flow path (intermediate cooling section) will be described below with reference to Fig. 4. Fig. 4 is a schematic diagram showing a combustion system equipped with a fluidized bed bed material regeneration device according to a second embodiment of the present invention.

[0050] 4, the bed material regeneration device 22 of the combustion system 21 in the second embodiment differs from the first embodiment only in that the bed material Fa is cooled when the bed material Fa is transported by the screw transport machine 11. Hereinafter, the same reference numerals will be used to designate the same components as those in the first embodiment, and their description will be omitted.

[0051] In the combustion system 21 of the second embodiment, the bed material regeneration device 22 has a cooling medium flow path 23 formed around the upstream portion of the screw conveyor 11, through which a cooling medium such as water flows. Both ends of the cooling medium flow path 23 are connected to a circulation pipe for circulating the cooling medium, and a cooling medium tank 24 for storing the cooling medium and a pump 26 for smoothly flowing the cooling medium are provided midway along this pipe. In addition, a cooler 25 for cooling the cooling medium in the cooling medium tank 24 is provided below the cooling medium tank 24.

[0052] In the bed material regeneration device 22, the high-temperature bed material Fa discharged from the outlet of the combustion furnace 2 is cooled by transferring heat to the cooling medium in the cooling medium flow path 23 as it is conveyed upstream of the screw conveyor 11. The bed material Fa is cooled until its temperature immediately before being fed into the screw conveyor 11 reaches a predetermined appropriate temperature. In this embodiment, the supply amount of the liquid medium LM is controlled so that the liquid medium LM is positioned near the downstream portion of the screw conveyor 11. By maintaining the temperature of the bed material Fa at an appropriate temperature upstream of the screw conveyor 11 when cooling the bed material Fa by contacting it with the liquid medium LM, peeling of the coating layer due to the difference in shrinkage between the bed material Fa and the coating layer downstream of the screw conveyor 11 can be appropriately caused, and cracks in the bed material Fa itself can be prevented from occurring due to excessively rapid cooling. The appropriate temperature is appropriately selected from room temperature (e.g., 25°C) or higher and below the melting point of the coating layer of the fluid medium (700°C or lower if the coating layer is a SiO2-K2O coating layer), depending on the temperature and supply amount of the liquid medium, and the amount of fluid medium Fa added.

[0053] According to the fluidized medium regeneration device 22 of the second embodiment described above, it is possible to prevent excessive evaporation of the liquid medium LM and large temperature changes caused by the introduction of the fluidized medium Fa by cooling the high-temperature fluidized medium Fa to an appropriate temperature using the cooling medium flow path 23 before bringing the fluidized medium Fa into contact with the liquid medium LM. As a result, it is possible to avoid situations where a large amount of liquid medium LM needs to be supplied in order to prevent temperature changes in the liquid medium LM or where frequent temperature adjustments need to be made in the screw conveyor 11, which allows the screw conveyor 11 to be made more compact and its operating costs to be reduced.

[0054] In the combustion system 21 of the second embodiment, the bed material regeneration device 22 has the cooling medium flow path 23 installed around the upstream part of the screw conveyor 11, but the present invention is not limited to this configuration. For example, the bed material regeneration device 22 may be configured such that the cooling medium flow path 23 is installed around the downstream part of the screw conveyor 11 and the liquid medium LM is supplied from around the upstream part of the screw conveyor 11.

[0055] (Combustion method in a fluidized bed combustion furnace) Furthermore, the flow of a combustion method for a fluidized bed combustion furnace applicable to the above-mentioned combustion system and bed material regeneration device will be explained using the drawings. Figure 5 is a flow chart for explaining a combustion method applicable to the combustion system and bed material regeneration device of this embodiment.

[0056] The combustion method for a fluidized-bed combustion furnace in this embodiment is a combustion method for a fluidized-bed combustion furnace using an alkaline component-containing fuel such as biomass fuel, as described above. The combustion method in this embodiment includes first combusting an alkaline component-containing fuel such as biomass fuel in the fluidized-bed combustion furnace (combustion step in step S1), recovering a fluidized medium from the fluidized bed of the fluidized-bed combustion furnace (recovery step in step S2), contacting the recovered fluidized medium with a liquid medium having a boiling point of −20°C or lower at 1 atmosphere to cool it, and separating the coating layer from the fluidized medium (cooling and separation step in step S3). Specifically, this step involves contacting the fluidized medium Fa recovered from the combustion furnace 2 in FIG. 1 with the liquid medium LM in the screw conveyor 11. The liquid medium is not particularly limited, but may be at least one of liquid air and liquid nitrogen, as described above.

[0057] In the cooling and separating step, as described above, the temperature of the fluidized medium recovered from the fluidized bed of the fluidized bed combustion furnace is preferably equal to or lower than the melting point of the coating layer of the fluidized medium. Therefore, as will be described in the second embodiment, in the cooling and separating step, the fluidized medium may be brought into contact with a liquid medium after being cooled by an intermediate cooling section (for example, the cooling medium flow path 23 in FIG. 4).

[0058] Next, the bed material and the coating layer separated in the cooling and separating step can be sorted in a sorting step (sorting step in step S4). Specifically, the bed material Fa and the coating layer supplied to the sorting device 12 in Fig. 1 are sorted by a sieve in the device, and materials unsuitable for combustion, such as the coating layer, are discharged outside the system.

[0059] In this embodiment, a returning step can be included in which the fluidized medium from which the coating layer has been separated is recovered, the particle size of which is adjusted to 50 to 1000 μm, and the recovered fluidized medium is returned to the fluidized bed (step S6 in FIG. 5). In this embodiment, as shown in FIG. 5, a particle size adjusting step can be included prior to the returning step, in which the recovered fluidized medium is returned to the fluidized bed after the particle size has been adjusted to 50 to 1000 μm (step S5 in FIG. 5).

[0060] According to the combustion method of the present embodiment described above, similar to the combustion system and bed material regeneration device described above, the high-temperature bed material Fa extracted from the bottom of the fluidized bed F of the combustion furnace 2 is brought into contact with a liquid medium having a boiling point of −20° C. or less at 1 atmosphere to rapidly cool it, thereby realizing efficient separation of the bed material from the coating layer. This makes it possible to ensure the quality of the bed material, which is a circulating material, and to achieve effective utilization.

[0061] Furthermore, according to the combustion method of this embodiment, the fluidized medium separated from the coating layer can be recovered and returned to the fluidized bed by the return process, so that the fluidized medium extracted from the fluidized bed can be returned to the fluidized bed and automatically replenished, thereby reducing the labor required for replenishing the fluidized medium.

[0062] Furthermore, according to the combustion method of this embodiment, the particles of the bed material can be handled in a dry state, which makes it possible to smoothly transport the bed material in the sorting and return processes, facilitates recycling of the bed material, and reduces the amount of moisture carried over when the bed material is returned to the fluidized bed in the fluidized bed combustion furnace. Furthermore, according to the combustion method of this embodiment, the bed material can be returned to the fluidized bed combustion furnace without going through a drying process, etc., so it can be used effectively in large combustion furnaces that use large amounts of bed material (sand, etc.).

[0063] The bed material regenerating device, combustion system, and combustion method of the present invention are not limited to the above-described embodiments.

[0064] For example, the present invention can be applied to fluidized bed combustion furnaces other than CFB boilers. Furthermore, the fuel used in the combustion furnace is not limited to biomass fuel. Any fuel that generates a sufficient difference in contraction between the coating layer and the bed material Fa can be used. The present invention is particularly suitable for use when using fuel containing a high alkaline component.

[0065] Furthermore, the intermediate cooling means is not limited to the cooling medium flow path 23 described in the second embodiment, and may be, for example, a mode in which the flow medium Fa is cooled by air cooling. Note that the heat recovered by the cooling medium flow path 23 may also be used in other equipment. Furthermore, the return line 13B is not necessarily provided.

[0066] Furthermore, in the combustion systems of the first and second embodiments, the liquid medium LM is supplied from the supply pipe 11A to the screw conveyor 11 and comes into contact with the bed material Fa within the screw conveyor 11; however, the present invention is not limited to this configuration. For example, as in the bed material regeneration device 31 of the combustion system 30 shown in FIG. 6, a cooling section 33 to which the liquid medium LM is separately supplied may be provided downstream of the screw conveyor 32. The bed material regeneration device 31 may be configured so that the bed material Fa transported from the screw conveyor 32 comes into contact with the liquid medium LM in the cooling section 33 and is cooled, and the coating layer is separated by this cooling. In the bed material regeneration device 31, the screw conveyor 32 may serve as an intermediate cooling section.

[0067] The disclosure of Japanese Patent Application No. 2021-055332, filed on March 29, 2021, is incorporated herein by reference in its entirety. In addition, all publications, patent applications, and technical standards mentioned in the specification are herein incorporated by reference to the same extent as if each individual publication, patent application, and technical standard was specifically and individually indicated to be incorporated by reference. [Explanation of symbols]

[0068] 1, 21, 30... Combustion system, 2... Combustion furnace (fluidized bed combustion furnace), 3, 22, 31... Bed material regeneration device, 11... Screw conveyor (cooling section), 33... Cooling section, 12... Sorting device (sorting section), 13... Return mechanism (return section), 23... Cooling medium flow path (intermediate cooling section), F... Fluidized bed

Claims

1. a cooling unit to which a fluidized medium recovered from the fluidized bed of a fluidized bed combustion furnace is supplied, the fluidized medium is brought into contact with a liquid medium having a boiling point of −20° C. or less under 1 atmosphere to cool the fluidized medium, and the coating layer is separated from the fluidized medium; The fluidized bed fluid medium regenerating device, wherein the cooling section includes a screw conveyor, and the liquid medium is supplied to the screw conveyor.

2. 2. The fluidized bed regenerating apparatus according to claim 1, wherein the liquid medium is at least one of liquid air, liquid nitrogen, and liquid oxygen.

3. 3. The fluidized bed regenerating device according to claim 1, further comprising a sorting means for sorting the fluidized bed material and the coating layer discharged from the cooling section.

4. 4. The fluidized bed regeneration device according to claim 1, wherein the temperature of the fluidized bed recovered from the fluidized bed of the fluidized bed combustion furnace is equal to or lower than the melting point of the coating layer.

5. The fluidized bed regeneration device according to any one of claims 1 to 4, wherein the cooling unit further includes an intermediate cooling unit that cools the fluidized medium, and the fluidized medium cooled by the intermediate cooling unit is brought into contact with the liquid medium.

6. The fluidized bed regeneration device according to any one of claims 1 to 5, further comprising a return section that recovers the fluidized medium from which the coating layer has been separated and returns the fluidized medium, the particle size of which has been adjusted to 50 to 1000 μm, to the fluidized bed.

7. A combustion system comprising a fluidized bed combustion furnace and the fluidized bed bed material regeneration device according to any one of claims 1 to 6.

8. A combustion method for a fluidized bed combustion furnace using an alkaline component-containing fuel, comprising: a fluidized medium is recovered from the fluidized bed of the fluidized bed combustion furnace, and the fluidized medium recovered from the fluidized bed is cooled by contacting it with a liquid medium having a boiling point of −20° C. or less under 1 atmosphere in a cooling section, and the coating layer is separated from the fluidized medium; The cooling section includes a screw conveyor, and the liquid medium is supplied to the screw conveyor. Combustion method for fluidized bed combustion furnace.

9. 9. The combustion method for a fluidized bed combustion furnace according to claim 8, wherein the liquid medium is at least one of liquid air and liquid nitrogen.

10. 10. The combustion method for a fluidized bed combustion furnace according to claim 8 or 9, further comprising the step of separating the fluidized medium and the coating layer.

11. The combustion method for a fluidized bed combustion furnace according to any one of claims 8 to 10, wherein the temperature of the fluidized medium recovered from the fluidized bed of the fluidized bed combustion furnace is equal to or lower than the melting point of the coating layer.

12. The combustion method for a fluidized bed combustion furnace according to any one of claims 8 to 11, wherein the fluidized medium is brought into contact with the liquid medium after being cooled by an intermediate cooling section.

13. The combustion method for a fluidized bed combustion furnace according to any one of claims 8 to 12, wherein the fluidized medium from which the coating layer has been separated is recovered, and the fluidized medium having a particle size adjusted to 50 to 1000 µm is returned to the fluidized bed.

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