JP7812845B2 - Bed material regeneration device, combustion system, and combustion method for fluidized bed combustion furnace - Google Patents

Description

The present invention relates to a fluidized bed bed material regeneration device for regenerating the fluidized bed material that forms the fluidized bed of a fluidized bed combustion furnace, a combustion system, and a combustion method for a fluidized bed combustion furnace.

In recent years, in order to secure fuel, there has been an increasing demand for power generation using biomass fuels such as construction waste wood materials and other wood-based materials, as well as waste fuels such as scrap tires and 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"), which includes a combustion furnace (e.g., a fluidized bed combustion furnace) that burns the material to be combusted and generates saturated steam, and a superheater connected to the combustion furnace that superheats the saturated steam generated in the combustion furnace using the combustion gas generated in the combustion furnace and uses it to generate power.

Meanwhile, 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 Empty Fruit Bunches (EFB) will be used in many cases. However, low-grade biomass fuels and waste-derived fuels contain large amounts of impurities, such as alkaline components such as Na and K. Using 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 prevent poor fluidity in such boilers.

For example, the following technologies have been developed for low-quality fuels containing impurities such as alkaline components (see, for example, Patent Documents 1 and 2 below):

JP 2005-226930 A JP 2011-106701 A

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 within a specific range in the fluidized bed, 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 the aggregation of the fluidizing medium (e.g., bottom ash) due to low-melting-point compounds, prevents poor fluidization, and enables smooth and stable operation. However, consistently controlling the fluidized bed temperature to 600 to 750°C is not easy. Furthermore, even with this technology, the fluidizing medium still tends to become larger, requiring a significant supply of new fluidizing medium such as sand. Therefore, there is still room for improvement in terms of the fluidizing medium and cost.

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

In order to solve the above-mentioned problems, the present invention aims 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.

In other words, the present invention is as follows.

<1> A fluidized bed fluidized medium regeneration device including a cooling section that receives 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 fluidized bed fluidized medium regeneration apparatus according to <1>, wherein the liquid medium is at least one of liquid air, liquid nitrogen, and liquid oxygen.
<3> The fluidized bed regenerating device according to <1> or <2>, further comprising a sorting unit for sorting the fluidized bed material and the coating layer discharged from the cooling unit.
<4> The fluidized bed fluidized bed material regeneration device according to any one of <1> to <3>, wherein the temperature of the fluidized bed material 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 fluidized medium regeneration device according to any one of <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 fluidized medium regeneration device according to any one of <1> to <5>, further comprising 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.
<7> A combustion system comprising a fluidized bed combustion furnace and the fluidized bed bed material regeneration device according to any one of <1> to <6>.
<8> A combustion method for a fluidized bed combustion furnace using an alkaline component-containing fuel,
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 combustion method for a fluidized bed combustion furnace according to <8>, wherein the liquid medium is at least one of liquid air and liquid nitrogen.
<10> The combustion method for a fluidized bed combustion furnace according to <8> or <9>, wherein the fluidized medium and the coating layer are separated.
<11> The combustion method for a fluidized bed combustion furnace according to any one of <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 <8> to <11>, wherein the fluidized medium is cooled by an intermediate cooling section before being brought into contact with the liquid medium.
<13> The combustion method for a fluidized bed combustion furnace according to any one of <8> to <12>, wherein 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.

The present invention provides 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.

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. 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. K ₂ O—SiO ₂ phase diagram. FIG. 10 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. 2 is a flow chart for explaining a combustion method applicable to the combustion system and the bed material regeneration device according to the present embodiment. 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.

Hereinafter, a form for implementing 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 identical elements will be 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 the ratios shown.

[First embodiment]
A combustion system equipped with a bed material regeneration device according to a first embodiment of the present invention 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.

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 it within the furnace, 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 section, which cools the bed material Fa by bringing it 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 used to separate the coating layer from bed material Fa, such as sand, recovered from the fluidized bed F of the combustion furnace 2, and regenerate the bed material Fa.

The combustion system 1 can use alkali-containing fuels, such as rice husks and EFB (Empty Fruit Bunches) as high-alkali biomass fuels, as the combustion target. Hereinafter, the high-alkali biomass fuels will be referred to simply 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 is provided in the middle of the combustion furnace 2, through which the biomass fuel is introduced. However, the combustion target used in the combustion system 1 is not limited to biomass fuel; any alkaline-containing fuel can be used without particular limitations.

The combustion furnace 2 is further loaded with a bed material Fa, such as sand primarily composed of quartz particles. Air is supplied to the bed material Fa from the lower part (bottom) of the furnace, causing the bed material Fa to flow and form a fluidized bed F. The formation of this fluidized bed F promotes the combustion of biomass fuel. Furthermore, combustion gases resulting from the combustion of biomass fuel rise 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 biomass fuel. "Bottom ash" refers to bed material Fa primarily composed of bed material such as sand, including combustion ash resulting from the combustion of 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 components in the biomass fuel from the bed material Fa (agglomerates) that have been coated and agglomerated with 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.

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 via the 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 the heat recovery device 6 via the outlet 4A.

The return line 5 consists of a pipe connected to the bottom of the combustion furnace 2, with a loop seal 5A installed along the way. 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 within the loop seal 5A. The bed material Fa within the loop seal 5A is then introduced into the combustion furnace 2 through the return chute 5B, which serves as the outlet of the loop seal 5A.

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 within the heat recovery device 6 so as to cross the flow path of the combustion gas, 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 other device. The heat recovery device 6 also sends the combustion gas after heat recovery to a bag filter 7 through an outlet 6A.

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 the suction pump 8 and discharged outside the combustion system 1 through the chimney 9.

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, to remove the coating layer (deposits), the bed material Fa containing the agglomerates is removed from the discharge outlet of the combustion furnace 2 and transported to the bed material regeneration device 3.

The mechanism of agglomerate formation within the combustion furnace 2 will be explained using Figure 2. Figure 2 is a schematic diagram for explaining the mechanism of agglomerate formation.

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 formed due to alkaline components in the biomass fuel (e.g., KCl (solid)), to the surface of the bed material Fa, or by the formation of a eutectic of alkaline components on the surface of the bed material Fa due to a chemical reaction between components in the biomass fuel and the bed material Fa. Thus, there are two main known mechanisms for the formation of agglomerates: coating induction and melting induction.

(Coating induction mechanism)
FIG. 2( a) shows the mechanism of coating-induced agglomerate X formation. FIG. 2( a) is a schematic diagram illustrating the mechanism of coating-induced agglomerate formation. As shown in FIG. 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 FIG. 2( a)) of alkaline components (e.g., potassium and sodium) in biomass fuel and quartz particles (sand), which are the main component of the bed material Fa. KCl, in particular, tends to vaporize easily at temperatures above 700°C. This chemical reaction forms a sticky eutectic coating C (e.g., _K2O - _SiO2 : alkali silicate phase) on the surface of the bed material Fa. Subsequently, the bed material Fa with the eutectic coating C formed thereon repeatedly bonds and separates within the fluidized bed F. As a result, particle aggregation begins, gradually forming agglomerates X, which become a factor hindering fluidization.

The main controlling factors in the mechanism of coating-induced agglomerate X formation are the eutectic coating thickness (ease of bonding separation), the eutectic coating composition (bonding strength), and the local temperature. Furthermore, among the components contained in biomass fuels, it has been confirmed that in addition to alkali components, phosphorus is also an important factor in the formation of agglomerate X.

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 bed materials Fa easily aggregate together.

(Melt induction mechanism)
Next, the mechanism of the formation of agglomerates X due to melting induction will be explained. FIG. 2(b) is a schematic diagram showing the melting induction mechanism. The melting-induced agglomerates X are caused by the adhesion of a melt M of 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 materials Fa to which the melt M has adhered gradually agglomerate within the fluidized bed F, forming the agglomerates X. The controlling factors of the mechanism of the formation of agglomerates X due to melting induction are the local temperature and the fuel ash composition, and agglomerates X tend to form through the melting induction mechanism in combustion ash containing high concentrations of alkaline components and chlorine.

(Fluid medium regeneration device 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 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. Furthermore, the fluidized medium regeneration device 3 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.

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 (e.g., 700°C) and is supplied into the screw conveyor 11 via the supply unit 10.

The temperature of the bed 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, above room temperature (e.g., 25°C) and below the melting point of the coating layer (deposit) of the bed material Fa (e.g., 700°C or below when a coating layer of SiO ₂ -K ₂ O is formed on the bed material Fa).

There are no particular limitations on the location from which the bed material Fa is recovered from the combustion furnace 2, but from the standpoint of efficiently recovering the high-temperature bed material Fa, it is preferable to recover the bed material Fa of the accumulated fluidized bed F from the bottom of the combustion furnace 2.

The screw conveyor 11 is connected to a supply section 10 connected to the exhaust port of the combustion furnace 2, and is supplied with 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, allowing the fluid within the device to be conveyed. The screw conveyor 11 is pre-cooled, and cooling means other than 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 other means (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 comes into contact with 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, or may be supplied from the upstream side of the screw conveyor 11, or may be configured to be supplied throughout the entire screw conveyor 11.

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 resulting from evaporation of the liquid medium. Examples of liquid medium LM include liquid air (boiling point at 1 atmosphere: approximately -190°C), liquid nitrogen (boiling point at 1 atmosphere: approximately -196°C), liquid oxygen (boiling point at 1 atmosphere: approximately -183°C), and liquid hydrogen (boiling point at 1 atmosphere: approximately -252.6°C). The liquid medium LM can be selected appropriately 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 standpoints of ease of handling, availability, safety, and the like, it is preferable to use at least one of liquid air, liquid nitrogen, and liquid oxygen.

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 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 takes advantage of the difference in cooling contraction due to the difference in material (i.e., physical properties) between the coating layer (e.g., alkali silicate) and the induction medium (sand, etc.).

In addition, 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 material LM is 120 to 410°C.

The fluid medium Fa and coating layer cooled and separated within the screw conveyor 11 are discharged from the conveyor's discharge port and supplied to the subsequent sorting device 12. At this time, the liquid medium LM volatilizes immediately after coming into contact with the fluid medium Fa, so the separated fluid medium Fa and coating layer are supplied to the sorting device 12 in a dry state.

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

The mesh size of the sieve installed in the sorting device 12 is not particularly limited, but since the particle size of the coating layer to be removed is several microns or less, it is possible to separate the bed material Fa and the coating layer by using a sieve with an opening size of 50 μm or less. Considering the particle size of the bed material Fa, for example, using mesh sizes based on the ASTM (American Society for Testing and Materials) standard, the sieve installed in the sorting device 12 can be, for example, 270 to 325 mesh (openings 45 to 53 μm). Furthermore, the sieve in the sorting device 12 may be configured as either a single stage or multiple stages.

The return mechanism 13 recovers the bed material Fa from which the coating layer has been separated and returns it to the fluidized bed. The return mechanism 13 also includes a particle size adjustment device 13A and a return line 13B that adjust the fluidity of the bed material Fa.

The sorted bed material Fa transported from the sorting device 12 to the return mechanism 13 is first supplied to the particle size adjustment device 13A. The particle size adjustment device 13A is equipped with a sieve as a particle size adjustment means, and adjusts the particle size of the bed material Fa. The particle size adjustment 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.

The mesh size of the sieve installed in the particle size adjustment device 13A is not particularly limited, but in order to remove foreign matter larger than 1000 μm, for example, the sieve's mesh size can be 1000 μm or larger. 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 installed in the particle size adjustment device 13A can be, for example, a 16-18 mesh (mesh size 1000-1180 μm). Furthermore, the sieve in the particle size adjustment device 13A may be configured as either a single stage or multiple stages.

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 via the return line 13B. In Figure 1, the "a" mark indicated by the arrow on the return line 13B is connected to the location marked "a" on the side of the combustion furnace 2, meaning 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.

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 brought into contact with a liquid medium having a boiling point of -20°C or less at 1 atmosphere to rapidly cool the bed material Fa, 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.

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 achieving effective utilization.

Furthermore, with the fluidized medium recycling device 3, the fluidized medium Fa that has separated from the coating layer can be recovered via 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.

Furthermore, the bed material regeneration device 3 and combustion system 1 of this embodiment allow the bed material Fa particles to be handled in a dry state as in this embodiment. This allows smooth transport in the sorting device 12 and 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, the bed material regeneration device 3 and combustion system 1 of this embodiment allow the bed material Fa to 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 are advantageous in terms of efficiency and cost in terms of reusing bed material, and can also be used effectively in large-scale combustion furnaces 2 that use large amounts of bed material Fa (sand, etc.).

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 directly brought into contact with the liquid medium LM, but the present invention is not limited to this 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 may be brought into contact with the liquid medium.

Below, we will explain an embodiment in which the screw conveyor 11 has a cooling medium flow path (intermediate cooling section) using Figure 4. Figure 4 is a schematic diagram showing a combustion system equipped with a fluidized bed bed material regeneration device in a second embodiment of the present invention.

As shown in Figure 4, the bed material regeneration device 22 of the combustion system 21 in the second embodiment differs from the first embodiment only in that it cools the bed material Fa while it is being transported by the screw conveyor 11. Hereinafter, components having the same configuration as those in the first embodiment will be given the same reference numerals, and their description will be omitted.

In the combustion system 21 of the second embodiment, the fluidized medium 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.

In the bed material regeneration device 22, the high-temperature bed material Fa discharged from the discharge port of the combustion furnace 2 is cooled by transferring heat to the cooling medium in the cooling medium flow path 23 as it is transported upstream of the screw conveyor 11. The bed material Fa is cooled until the temperature immediately before being introduced 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 bed material Fa is located 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 it 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 above room temperature (e.g., 25°C) and below the melting point of the coating layer of the fluid medium (700°C or below 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.

In the fluid medium regeneration device 22 of the second embodiment described above, the high-temperature fluid medium Fa is cooled to an appropriate temperature using the cooling medium flow path 23 before being brought into contact with the liquid medium LM, thereby making it possible to suppress excessive evaporation of the liquid medium LM and significant changes in temperature caused by the introduction of the fluid medium Fa. As a result, it is possible to avoid situations where it is necessary to supply large amounts of liquid medium LM or frequently adjust the temperature inside the screw conveyor 11 in order to suppress temperature changes in the liquid medium LM, thereby enabling the screw conveyor 11 to be made more compact and reducing operating costs.

In the combustion system 21 of the second embodiment, the bed material regeneration device 22 has a cooling medium flow path 23 installed around the upstream portion 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 so that the cooling medium flow path 23 is installed around the downstream portion of the screw conveyor 11 and the liquid medium LM is supplied from around the upstream portion of the screw conveyor 11.

(Combustion method in a fluidized bed combustion furnace)
Furthermore, the flow of a combustion method for a fluidized bed combustion furnace that can be applied to the combustion system and bed material regeneration device described above will be explained using the diagram. Figure 5 is a flow chart for explaining a combustion method that can be applied to the combustion system and bed material regeneration device of this embodiment.

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 first includes 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), and cooling the recovered fluidized medium by contacting it with a liquid medium having a boiling point of -20°C or lower at 1 atmosphere, thereby 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 as described above, it can be at least one of liquid air and liquid nitrogen.

Furthermore, as described above, in the cooling and separation process, it is preferable that the temperature of the fluidized medium recovered from the fluidized bed of the fluidized bed combustion furnace be equal to or lower than the melting point of the coating layer of the fluidized medium. Therefore, as described in the second embodiment, in the cooling and separation process, the fluidized medium may be cooled by an intermediate cooling section (e.g., cooling medium flow path 23 in Figure 4) before being brought into contact with a liquid medium.

Next, the bed material and coating layer separated in the cooling and separation process can be sorted in a sorting process (sorting process in step S4). Specifically, the bed material Fa and coating layer supplied to the sorting device 12 in Figure 1 are sorted using a sieve within the device, and materials unsuitable for combustion, such as the coating layer, are discharged outside the system.

In addition, this embodiment can include a return process in which the fluid medium from which the coating layer has been separated is recovered, the particle size of which has been adjusted to 50 to 1000 μm, and the resulting fluid medium is returned to the fluidized bed (step S6 in Figure 5). In addition, this embodiment can include a particle size adjustment process prior to the return process, as shown in Figure 5, in which the recovered fluid medium is adjusted to a particle size of 50 to 1000 μm and then returned to the fluidized bed (step S5 in Figure 5).

According to the combustion method of this 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 with a boiling point of -20°C or less at 1 atmosphere to rapidly cool it, thereby achieving 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.

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 through a return process, making it possible to automatically replenish the fluidized medium extracted from the fluidized bed by returning it to the fluidized bed, thereby reducing the labor required to replenish the fluidized medium.

In addition, according to the combustion method of this embodiment, the bed material particles can be handled in a dry state, which allows for smooth transport of the bed material in the sorting and return processes, facilitating recycling of the bed material, and reducing 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 undergoing a drying process, etc., making it suitable for use in large combustion furnaces that use large amounts of bed material (sand, etc.).

Note that the bed material regeneration device, combustion system, and combustion method of the present invention are not limited to the above-described embodiments.

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 high alkaline components.

Furthermore, the intermediate cooling means described above is not limited to the cooling medium flow path 23 described in the second embodiment, and may be, for example, a form in which the flow medium Fa is cooled by air cooling. It is also possible to configure the system so that the heat recovered by the cooling medium flow path 23 is utilized in other equipment. Furthermore, it is not necessarily required to provide a return line 13B.

Furthermore, in the combustion systems of the first and second embodiments, a configuration has been described in which 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, but 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 can be configured so that the bed material Fa transported from the screw conveyor 32 comes into contact with the liquid medium LM within the cooling section 33 and is cooled, and the coating layer is separated by this cooling. Note that in the bed material regeneration device 31, the screw conveyor 32 can serve as an intermediate cooling section.

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.

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 (13)

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. The fluidized bed fluidized medium regeneration apparatus according to claim 1, wherein the liquid medium is at least one of liquid air, liquid nitrogen, and liquid oxygen. The fluidized bed fluidized medium regeneration device according to claim 1 or 2, further comprising a sorting means for sorting the fluidized medium and the coating layer discharged from the cooling section. A fluidized bed fluidized material regeneration device according to any one of claims 1 to 3, wherein the temperature of the fluidized material recovered from the fluidized bed of the fluidized bed combustion furnace is below the melting point of the coating layer. A fluidized bed fluidized medium 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. A fluidized bed fluidized medium regeneration device according to any one of claims 1 to 5, further comprising a return unit that recovers the fluidized medium from which the coating layer has been separated, adjusts the particle size to 50 to 1000 μm, and returns the fluidized medium to the fluidized bed. A combustion system comprising a fluidized bed combustion furnace and a fluidized bed bed material regeneration device according to any one of claims 1 to 6. 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. 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. The combustion method for a fluidized bed combustion furnace according to claim 8 or claim 9, wherein the fluidized medium and the coating layer are separated. 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. A combustion method for a fluidized bed combustion furnace according to any one of claims 8 to 11, in which the fluidized medium is cooled by an intermediate cooling section before being brought into contact with the liquid medium. A 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 with a particle size adjusted to 50 to 1000 μm is returned to the fluidized bed.