Method for discharging solidified pellets and silo system

Abstract

To provide a method for discharging consolidated pellets, which can efficiently remove and discharge consolidated pellets produced in a silo, and a silo system, which can efficiently discharge consolidated pellets produced in a silo. [Solution] A method for discharging consolidated pellets 50, which are wood-based pellets that remain after being extinguished after ignition, from a silo 1 having consolidated pellets 50 inside, in which the consolidated pellets 50 are discharged from a discharge outlet 2D formed at the bottom of a housing 2 that forms the silo 1, and a softening heat medium, which is at least one of a gas and a liquid at 60°C or higher and 150°C or lower, is supplied from the outside to the inside of the housing 2 through a supply port 2E formed in the housing 2.

Description

[Technical Field]

[0001] The present invention relates to a method for discharging consolidated pellets produced in a silo, and a silo system capable of efficiently discharging consolidated pellets produced in a silo. [Background technology]

[0002] At businesses that require large amounts of wood pellets, such as biomass power plants, the wood pellets used in operations are stored in silos. However, due to the powdering of the wood pellets and pressure caused by their own weight, the wood pellets can adhere or accumulate on the inner walls of the silo, resulting in deposits. For this reason, Patent Document 1 discloses a deposit removal device that can mechanize the work of removing deposits such as grains that have adhered to or accumulated inside a silo.The method involves injecting grains, which are sprayed as granules, together with compressed gas, causing them to collide with the deposits on the inner wall of the silo, and removing the deposits such as grains that have adhered to or accumulated on the inner wall of the silo due to the impact of the sprayed granules colliding. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-253493 Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, since wood pellets are mostly made of wood, they can catch fire inside the silo, and to extinguish the fire, water may be sprayed from the top of the silo or nitrogen gas may be injected from the bottom. In this way, the wood pellets that remain after the fire has been extinguished have been denatured by the effects of pressure, heat, moisture, etc., and compared to the wood pellets before ignition, they may become stronger solidified pellets (pellet masses) due to the strengthened bonding force caused by the compaction of the components that make up the wood pellets themselves and the strengthened bonding force caused by the adhesive components of the wood pellets. Furthermore, because such consolidated pellets are very hard and tough, it can be difficult to remove them from inside the silo using physical cutting equipment such as the deposit removal device described in Patent Document 1, silo cleaners used in silo cleaning, boring machines, and chippers.

[0005] The present invention has been made in consideration of the above-mentioned problems, and its purpose is to provide a method for discharging consolidated pellets that can efficiently remove and discharge consolidated pellets produced in a silo, and a silo system that can efficiently discharge consolidated pellets produced in a silo. [Means for solving the problem]

[0006] To achieve the above-mentioned object, the method for dispensing consolidated pellets according to the present invention is a method for dispensing consolidated pellets, which are wood-based pellets that remain after being extinguished after ignition, from a discharge outlet formed at the bottom of a housing that forms a silo having consolidated pellets inside, and is characterized by the fact that a softening heat medium, which is at least one of a gas and a liquid at a temperature of 60°C or higher and 150°C or lower, is supplied from the outside of the housing to the inside through a supply port formed in the housing.

[0007] The silo system of the present invention, which is intended to achieve the above-mentioned objective, is characterized by the configuration thereof, in that it comprises a silo having inside a housing consolidated pellets, which are wood-based pellets that remain after being extinguished after ignition, and a supply mechanism that supplies a softening heat medium, which is at least one of a gas and a liquid at 60°C or higher and 150°C or lower, from the outside to the inside of the housing through a supply port formed in the housing.

[0008] As mentioned above, wood pellets remaining after ignition and extinguishing are denatured by the effects of pressure, heat, moisture, etc., and may become stronger agglomerated pellets (pellet clumps) compared to the wood pellets before ignition due to the strengthened bonding forces of the components that make up the wood pellets themselves due to compaction and the strengthened bonding forces of the adhesive components of the wood pellets. These agglomerated pellets are thought to be formed after the combustion of wood pellets containing cellulose as the main component and lignin as the secondary component, when adhesive components such as lignin softened by the heat of ignition cool in the presence of moisture under pressure due to the swelling of cellulose and the weight of the wood pellets. It is thought that the strengthened bonding forces of adhesive components such as lignin at the time of formation result in stronger agglomerated pellets.

[0009] Here, the composition of wood pellets before ignition and combustion includes, for example, 40 to 50 mass % cellulose, 20 to 35 mass % lignin, 20 to 25 mass % hemicellulose, and a few mass % of trace components. It is known that the adhesive component lignin, when in a water-containing state (water content is about 20 to 40% of the wood pellets), softens at around 80°C. Therefore, it is presumed that the lignin melts due to the heat generated by the ignition (combustion) of the wood pellets and flows downward in the silo, and the composition of the wood pellets present below the silo after combustion contains a relatively high amount of lignin compared to the wood pellets before combustion. It is presumed that when wood pellets with a relatively high lignin content are cooled due to the effects of fire extinguishing or the like, the wood pellets are more firmly solidified to produce consolidated pellets. However, according to the above-mentioned characteristic configuration, the softening heat medium is at least one of a gas and a liquid at a temperature of 60°C or higher and 150°C or lower, so that lignin, which is the main adhesive component of the consolidated pellets, can be softened (melted) by heat (thermal energy), thereby reducing the bonding strength of the consolidated pellets. This makes it possible to break down the softened solidified pellets into smaller pieces using some kind of physical action, such as cutting with equipment, or to induce the solidified pellets to collapse under the influence of their own weight, making it possible to efficiently discharge the solidified pellets from the discharge outlet formed at the bottom of the housing.

[0010] Furthermore, in silos where wood pellets are stored, even if the fire is extinguished after the wood pellets have ignited, there is a risk of the pellets igniting again, so people cannot enter the silo to dispense the solidified pellets. However, according to the above-described characteristic configuration, the softening heat medium that softens the consolidated pellets is supplied from the outside to the inside of the housing through a supply port formed in the housing, thereby reducing the bonding strength of the consolidated pellets, so that the consolidated pellets can be dispensed without anyone having to enter the silo.

[0011] A further characteristic feature of the method for discharging consolidated pellets according to the present invention for achieving the above object is that the softening heat medium is steam.

[0012] A further characteristic feature of the silo system according to the present invention for achieving the above object is that the softening heat medium is steam.

[0013] According to the above characteristic configuration, since water vapor, which can retain a relatively large amount of heat (utilizing latent heat), is used as the softening heat medium, the amount of gas input is relatively small, and heat (thermal energy) can be supplied to the solidified pellets with high energy efficiency. In addition, the steam at 60°C or higher and 150°C or lower can soften the lignin, which is the main adhesive component of the consolidated pellets, by heat, thereby preventing the consolidated pellets from igniting and burning again.

[0014] A further characteristic feature of the method for discharging consolidated pellets according to the present invention for achieving the above object is that the softening heat medium is a non-flammable gas.

[0015] A further characteristic feature of the silo system according to the present invention for achieving the above object is that the softening heat medium is a non-flammable gas.

[0016] According to the above characteristic configuration, the non-flammable gas at 60°C or higher and 150°C or lower can soften the lignin, which is the main adhesive component of the consolidated pellets, by heat, thereby preventing the consolidated pellets from igniting and burning again. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic cross-sectional view of a silo system according to an embodiment of the present invention. [Figure 2] 1 is a schematic configuration diagram of a silo system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0018] A method for discharging consolidated pellets and a silo system according to an embodiment of the present invention will be described with reference to the drawings.

[0019] <Embodiment> As shown in Figures 1 and 2, the silo system S of this embodiment includes a silo 1 formed of a cylindrical housing 2 with a space 2a formed inside, a supply mechanism 10 that supplies a softening heat medium, which is at least one of a gas and a liquid at a temperature of 60°C or higher and 150°C or lower, from the outside to the inside of the housing 2 via a supply port 2E formed in the housing 2, and a control unit (not shown) that controls the various devices included in the silo system S.

[0020] The silo 1 is formed by a cylindrical housing 2 having a space 2a formed therein. In this embodiment, the housing 2 has a cylindrical side wall 2A that is open at the top and bottom, a ceiling 2B that closes the upper opening of the side wall 2A, and a hopper 2C that is integrated with the side wall 2A at the bottom of the space 2a formed inside the housing 2 (side wall 2A). The bottom of the side wall 2A is fixed to the ground. The silo 1 is formed to a size of, for example, approximately 25 m in diameter, approximately 45 m in height, and approximately 10,000 tons in capacity.

[0021] Hopper 2C is formed in a conical shape in side cross section, with the diameter decreasing downward, and has a discharge outlet 2D formed in the center in plan view, with a lid (not shown) that can open and close discharge outlet 2D. As a result, space 2a formed inside housing 2 (side wall 2A), i.e., space 2a formed by side wall 2A, hopper 2C, and ceiling 2B, functions as a storage section in which wood pellets are stored.

[0022] Hopper 2C is also provided with a nitrogen supply mechanism 20 that can supply nitrogen (gas) from the outside of hopper 2C to the inside of hopper 2C where wood pellets are present. By supplying nitrogen to the wood pellets present inside hopper 2C, it is possible to prevent the wood pellets from self-oxidizing and fermenting to accumulate heat, and to suppress the generation and combustion of carbon monoxide in the event of ignition, thereby preventing the spread of fire.

[0023] The nitrogen supply mechanism 20 includes a nitrogen supply source 21, a nitrogen pipe 22 that connects the nitrogen supply source 21 with the inside of the hopper 2C, and a pump 23 that sends nitrogen from the nitrogen supply source 21 to the inside of the housing 2 through the nitrogen pipe 22, and the nitrogen pipe 22 is arranged to connect with the inside of the hopper 2C through a nitrogen pipe through-hole 2F formed in the hopper 2C. The pump 23 is arranged on the nitrogen pipe 22 on the upstream side of the nitrogen supply source 21 (on the opposite side to the hopper 2C). A spray nozzle 24 for spraying nitrogen is connected to the tip of the nitrogen pipe 22, and the spray direction of the spray nozzle 24 can be set in any direction. For example, the spray direction of the spray nozzle 24 may be set in the vertical direction, in a direction perpendicular to the inner surface of the hopper 2C, or in a suitable direction inclined relative to the inner surface.

[0024] It is also preferable to provide a plurality of through-holes 2F for the nitrogen pipes. In this case, a plurality of nitrogen pipes 22 are also provided, and it is preferable to arrange the ends of the respective nitrogen pipes 22 so as to be located at dispersed positions within the casing 2 (including the hopper 2C).

[0025] Furthermore, when multiple through-holes 2F for the nitrogen pipe are arranged, it is preferable to arrange the multiple through-holes 2F at the same height in the vertical direction of the casing 2 (hopper 2C). Multiple groups of multiple through-holes 2F arranged at the same height may be arranged at different heights. In these cases, it is preferable to arrange the nitrogen pipe 22 in a substantially circular shape outside the casing 2 (including the hopper 2C) along the outer surface of the casing 2 (including the hopper 2C) so that it is at the same height as the multiple through-holes 2F arranged at the same height, and to arrange the nitrogen pipe 22 so that it branches out to communicate with each through-hole 2F. In addition, if necessary, it is preferable to arrange a nitrogen pipe seat (not shown) supporting the circular nitrogen pipe 22 in a substantially circular shape outside the hopper 2C along the outer surface of the hopper 2C.

[0026] A feeding mechanism (not shown) for feeding wood pellets into the housing 2 is disposed on the ceiling portion 2B, and a feeding opening (not shown) through which the wood pellets can be fed from the feeding mechanism is formed. Additionally, a fire extinguishing system (not shown) is disposed on the ceiling 2B to extinguish a fire when the wood pellets ignite. Specifically, the fire extinguishing system is configured to sprinkle or spray water (supplied via a pump or the like) onto the wood pellets stored inside the housing 2 from a pipe (not shown) formed on the ceiling 2B and communicating with the inside of the housing 2.

[0027] The wood pellets according to this embodiment are produced by pressurizing and drying crushed wood, and are formed into pellets (granules) that are, for example, cylindrical, have a diameter of about 6 to 8 mm, and a length of about 5 to 40 mm.

[0028] The composition of wood pellets before ignition and combustion includes, for example, 40 to 50 mass % cellulose, 20 to 35 mass % lignin, 20 to 25 mass % hemicellulose, and a few mass % of trace components.

[0029] Cellulose is a polymer of β-glucose, which contains many hydroxyl groups within the molecule and is held together in a sheet by hydrogen bonding. Here, hydrogen bonding refers to the electrostatic force generated by weakly electropositive hydrogen atoms on electronegative atoms, which bind to surrounding electronegative atoms. Lignin is a biopolymer (crosslinkable polymer) with a three-dimensional network structure, and plays a role as an adhesive component in the molding of wood pellets. Hemicellulose is an insoluble, amorphous polysaccharide contained in plant cells, and acts as an adhesive component that binds cellulose and lignin.

[0030] When such wood pellets are ignited in a silo, the remaining wood pellets after the fire are extinguished are denatured by the effects of pressure, heat, moisture, etc., and may become stronger consolidated pellets 50 (pellet mass) compared to the wood pellets before ignition due to strengthened bonding forces caused by the compaction of the components that make up the wood pellets themselves and strengthened bonding forces caused by the adhesive components of the wood pellets. Such consolidated pellets 50 are thought to be formed after combustion of wood pellets containing cellulose as a main component and lignin as a secondary component, when adhesive components such as lignin softened by the heat of ignition cool in the presence of moisture under pressure caused by the swelling of cellulose and pressure due to the weight of the wood pellets. It is thought that the strengthened bonding forces caused by the adhesive components such as lignin at the time of generation result in stronger consolidated pellets 50.

[0031] In particular, the thermal softening properties of the adhesive component lignin when it is in a water-containing state (water content is about 20 to 40% of the wood pellets) are known to soften at around 80°C. Therefore, it is presumed that the lignin melts due to the heat accompanying the ignition (combustion) of the wood pellets and flows downward into the silo, and the composition of the wood pellets present below the silo after combustion contains a relatively high amount of lignin compared to the wood pellets before combustion. It is presumed that when wood pellets with a relatively high lignin content are cooled due to the effects of fire extinguishing or the like, the wood pellets are more firmly solidified to produce consolidated pellets 50. The solidified pellets 50 thus produced are very strong pellet lumps, and are difficult to remove using physical excavation equipment such as silo cleaners, boring machines, and chippers used in silo cleaning. The space 2a formed inside the housing 2 (side wall portion 2A) also functions as a storage portion in which consolidated pellets 50, which are wood pellets that remain after being extinguished after ignition, are stored (present).

[0032] As described above, the supply mechanism 10 supplies a softening heat medium, which is at least one of a gas and a liquid at 60°C or higher and 150°C or lower, from the outside to the inside of the housing 2 through the supply port 2E formed in the housing 2. The softening heat medium acts on the adhesive components of the consolidated pellets 50, such as lignin, thereby reducing the bonding strength of the adhesive components. Specifically, the supply mechanism 10 includes a softening heat medium source 11, a heating unit 14 that heats the softening heat medium from the softening heat medium source 11, a softening heat medium pipe 12 that connects the softening heat medium source 11 to the inside of the housing 2 via a supply port 2E of the housing 2, and a pump 13 that sends the softening heat medium from the softening heat medium source 11 through the softening heat medium pipe 12 to the inside of the housing 2. The pump 13 is disposed on the softening heat medium pipe 12 on the upstream side of the softening heat medium source 11 (the opposite side to the hopper 2C).

[0033] In this embodiment, the supply mechanism 10 also uses the nitrogen pipe 22 of the nitrogen supply mechanism 20. Specifically, a flow path switching mechanism (not shown) is provided that can block communication between the nitrogen pipe 22 and the nitrogen supply source 21 and connect the softening heat medium pipe 12 of the supply mechanism 10 to the nitrogen pipe 22. The flow path switching mechanism can also connect the nitrogen pipe 22 to the nitrogen supply source 21 and block the connection between the softening heat medium pipe 12 and the nitrogen pipe 22. As a result, the pump 13, softening heat medium source 11, heating unit 14, and flow path switching mechanism are connected by the softening heat medium pipe 12, and the flow path switching mechanism and the ejection nozzle 24 are connected by the nitrogen pipe 22. In this case, the nitrogen pipe 22 also functions as the softening heat medium pipe 12, and the through hole 2F functions as the supply port 2E. Therefore, in this embodiment, the supply mechanism 10 and the nitrogen supply mechanism 20 operate selectively so that only one of them functions by switching the flow path switching mechanism.

[0034] The softening heat medium supplied by the supply mechanism 10 to the space 2a inside the housing 2 is at least one of a gas and a liquid heated to a temperature of 60° C. or higher and 150° C. or lower. The softening heat medium is heated by the heating unit 14 described above. When the softening heat medium is introduced into the consolidated pellets 50, the temperature of the softening heat medium is preferably 60°C or higher, more preferably 70°C or higher, and even more preferably 80°C or higher. This is because the thermal softening temperature of lignin is around 80°C, and therefore softening begins when the internal temperature of the consolidated pellets 50 reaches 60°C or higher. Furthermore, the raw material of the consolidated pellets 50 is wood, and excessive heating can cause fire. Therefore, when the softening heat medium is heated and introduced into the silo 1, the temperature should be 150°C or lower, more preferably 120°C or lower, and even more preferably 100°C or lower.

[0035] As a result, since the softening heat medium is at least one of a gas and a liquid heated to a temperature of 60°C or higher and 150°C or lower, the lignin, which is the main adhesive component of the consolidated pellets 50, can be softened (melted) by heat (thermal energy), thereby reducing the bonding strength of the consolidated pellets 50. This makes it possible to break down the softened solidified pellets 50 into smaller pieces using some kind of physical action, such as cutting with equipment, or to induce the solidified pellets 50 to collapse under the influence of their own weight, making it possible to efficiently discharge the solidified pellets 50 from the discharge outlet 2D formed at the bottom of the housing 2.

[0036] To simplify the process, the consolidated pellets 50 (which could not be broken down by hand or with a drill, had some loose sections, but the sap-like components were visible) were placed in a sealed container, and the sealed container was immersed in a hot water bath at 80°C for 20 minutes. After that, the state of the consolidated pellets 50 inside the sealed container was checked. The pellets 50 had broken down (fragmented), the sap components had lost viscosity and become sticky and stretchy, and the remaining moisture inside the pellets had eluted, giving off a sour, tar-like odor. Therefore, it has been confirmed that supplying a specified amount of heat (thermal energy) to the consolidated pellets 50 is effective in softening the consolidated pellets 50.

[0037] The softening heat medium is, for example, a non-flammable gas, such as nitrogen or argon, etc. This allows the non-flammable gas heated to 60°C or higher and 150°C or lower to thermally soften lignin, which is the main adhesive component of the consolidated pellets 50, and prevents the consolidated pellets 50 from igniting and burning again. When a non-flammable gas is used as the softening heat medium, the heating method in the heating section 14 may be a fuel combustion method or an electric heater heating method, and any heating method is acceptable.

[0038] Steam can also be used as the softening heat medium. By using steam, which can retain a relatively large amount of heat (utilizing latent heat), the amount of gas input is relatively small, allowing heat (thermal energy) to be supplied to the consolidated pellets with high energy efficiency. In addition, steam (mainly saturated steam) heated to a temperature of 60°C or higher and 150°C or lower can soften the lignin, which is the main adhesive component of the consolidated pellets 50, by heat, thereby preventing the consolidated pellets 50 from igniting and burning again. When steam is used as the softening heat medium, a boiler that generates steam from water by heating using heat generated when fuel is burned may be used as the heating unit 14. The heating method in the heating unit 14 may be a fuel combustion method or an electric heater heating method, and any heating method is acceptable.

[0039] The method for discharging consolidated pellets 50 according to the embodiment is a method for discharging consolidated pellets 50 in a silo 1 having therein consolidated pellets 50, which are wood-based pellets that remain after being extinguished after ignition, and discharging the consolidated pellets 50 from a discharge outlet 2D formed at the bottom of a housing 2 that forms the silo 1, and a softening heat medium, which is at least one of a gas and a liquid at 60°C or higher and 150°C or lower, is supplied from the outside to the inside of the housing 2 via a supply port 2E formed in the housing 2. The method for discharging the consolidated pellets 50 can efficiently remove and discharge the consolidated pellets 50 produced in the silo 1 using the above-mentioned silo system S. On the other hand, the method for discharging the consolidated pellets 50 can efficiently remove and discharge the consolidated pellets 50 produced in the silo 1 even in a silo system S that is not configured to always include the supply mechanism 10 like the above-mentioned silo system S, but is configured to apply the supply mechanism 10 to the silo 1 and use it only when necessary.

[0040] [Another embodiment] (1) In the above embodiment, an example has been described in which one hopper 2C is provided in the lower part of the silo 1, but the number of hoppers 2C may be two or more.

[0041] (2) In the above embodiment, the supply mechanism 10 supplies the softening heat medium through the supply port 2E formed in the hopper 2C of the housing 2 of the silo 1. However, the supply mechanism 10 may supply the softening heat medium to the inside of the housing 2 in other ways. For example, the supply port 2E may be formed in the side wall 2A of the housing 2, and the softening heat medium may be supplied from the side of the space 2a inside the housing 2 through the supply port 2E.

[0042] (3) In the above embodiment, the supply mechanism 10 is described as also serving as the nitrogen supply mechanism 20. However, the supply mechanism 10 may not also serve as the nitrogen supply mechanism 20 and may be arranged separately as a different configuration. For example, a configuration is possible in which a spray nozzle for spraying the softening heat medium is connected to the tip of the softening heat medium pipe 12 of the supply mechanism 10, and the spray nozzle can spray the softening heat medium toward the consolidated pellets 50 in the space 2a through a supply port 2E formed in the housing 2 (side wall portion 2A, hopper 2C). In this case, the spray direction of the spray nozzle can be set in an appropriate direction. For example, the spray direction of the spray nozzle may be set in the vertical direction, a direction perpendicular to the inner surface of the housing 2, or an appropriate direction inclined relative to the inner surface.

[0043] (4) The configurations disclosed in the above embodiments (including other embodiments, the same applies below) can be applied in combination with configurations disclosed in other embodiments, as long as no contradiction arises. Furthermore, the embodiments disclosed in this specification are merely examples, and the embodiments of the present invention are not limited thereto. They can be modified as appropriate within the scope of the purpose of the present invention. [Explanation of symbols]

[0044] 1. Silo 2. Case 2a space 2A Side wall part 2B Ceiling section 2C Hopper 2D outlet 2E Supply port 2F penetration opening 10 Supply mechanism 11 Softening heat medium source 12 Heat medium piping for softening 13 Pump 14 Heating section 20 Nitrogen supply mechanism 21 Nitrogen Sources 22 Nitrogen piping 23 Pump 24 Spout nozzle 50 agglomerated pellets S Silo System

Claims

1. A method for discharging consolidated pellets, which are wood-based pellets that remain after ignition and are extinguished, from a discharge port formed in a lower part of a housing that forms a silo, the method comprising: A method for dispensing solidified pellets, comprising supplying a softening heat medium, which is at least one of a gas and a liquid at 60°C or higher and 150°C or lower, from the outside to the inside of the housing through a supply port formed in the housing.

2. 2. The method for discharging consolidated pellets according to claim 1, wherein the heat medium for softening is steam.

3. 2. The method for discharging consolidated pellets according to claim 1, wherein the softening heat medium is a non-flammable gas.

4. a silo having, inside a housing, consolidated pellets that are wood-based pellets that remain after being extinguished after ignition; a supply mechanism that supplies a softening heat medium, which is at least one of a gas and a liquid at 60°C or higher and 150°C or lower, from the outside of the housing to the inside of the housing through a supply port formed in the housing.

5. The silo system according to claim 4, wherein the softening heat medium is steam.

6. 5. The silo system according to claim 4, wherein the softening heat medium is a non-flammable gas.

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