Pellet storage method and pellet storage equipment

Abstract

Provided is a pellet storage method, said method comprising: a pile formation step for piling up pellets (10) derived from biomass to form a pellet pile (100e); and a suppression means placement step for, partway through the pile formation step, placing a steam migration suppression means (for example, a sheet member (20)) on at least part of the pile (100a), (100c) being piled up, wherein: after the suppression means placement step, pellets (10) are further piled up on the placed steam migration suppression means to form the pellet pile (100e); and the steam migration suppression means suppresses the migration of steam from the inside of the pellet pile (100e) to the outer surface side thereof.

Description

Method for storing pellets and pellet storage equipment

[0001] The present invention relates to a method for storing pellets and pellet storage equipment.

[0002] In recent years, biomass fuels have been considered in order to reduce the emissions of CO ２ which is regarded as a cause of global warming. When biomass is burned, CO ２ is generated, but since plants absorb CO ２ and grow, the use of biomass fuels manufactured from materials such as wood, etc. does not change the amount of CO ２ in the atmosphere as a whole (carbon neutral). If this biomass fuel is used as fuel for a power plant, it is expected to significantly reduce CO ２ emissions compared to a power plant that conventionally uses fossil fuels such as coal. In addition, although the spread of renewable energies such as solar power generation and wind power generation is also progressing, compared to those that depend on natural conditions (sunlight, weather, etc.), biomass fuel can be stored in a silo, etc., so flexible power generation according to the demand for electricity is also possible (supply-demand adjustment function). Therefore, it is a renewable energy that is excellent in that it can be operated in the same way as a conventional thermal power plant using fossil fuels.

[0003] On the other hand, since biomass has the property of being prone to spontaneous heating, technologies for enhancing the safety of biomass are being considered. For example, Patent Document 1 discloses a biomass storage device. This biomass storage device includes a storage container that stores either one or both of herbaceous biomass and woody biomass, and a reduction environment formation prevention means that suppresses the growth of microorganisms in the storage container. As the reduction environment formation prevention means, means for blowing a gas (for example, an oxidizing gas and an inert gas, etc.) at a temperature above the growth limit temperature of microorganisms adhering to the biomass from vertically below the upper surface of the biomass stored in the storage container is described. In addition, Non-Patent Document 1 describes the results of studies on the spontaneous ignition mechanism when storing wood pellets and an evaluation method for spontaneous ignitability. Non-Patent Document 2 describes an evaluation method for spontaneous heat generation when storing coal.

[0004] Japanese Patent Publication No. 2014-118187

[0005] "Investigation on the spontaneous combustion properties of wood pellets during storage," Masayoshi Kimoto, Masami Tozawa, Research Report: M08022, Central Research Report of Electric Power Industry, May 2009. "Examination of evaluation methods for spontaneous heating properties in coal storage management," Masaharu Matsumoto, 55th Coal Science Conference (Kitakyushu City), October 29, 2018.

[0006] Biomass is used as fuel and as an energy source for biomass power generation. Biomass pellets used as fuel may be stored on the ground, in silos, warehouses, or containers until they are used, and during storage, spontaneous heat generation by the biomass itself can occur, leading to ignition. Non-patent document 1 describes a mechanism by which spontaneous combustion of wood pellets occurs due to microbial fermentation and spontaneous oxidation, but there are no actual cases of reproducing and verifying the phenomenon from microbial fermentation to ignition, including this document (details will be discussed later). The technology in patent document 1 focuses on suppressing the growth of microorganisms attached to the biomass and does not take into account the phenomenon of spontaneous oxidation. Furthermore, the technology in patent document 1 requires means to suppress the growth of microorganisms in the container containing the biomass (means to prevent the formation of a reducing environment), which makes the equipment complicated. In recent years, fires caused by spontaneous heat generation of wood pellets have been reported at biomass power plants. There is a strong need for the development of safer methods and equipment for storing biomass pellets.

[0007] The object of the present invention is to provide a method for storing biomass-derived pellets and a pellet storage facility that can suppress spontaneous combustion when storing biomass-derived pellets.

[0008] [1] A method for storing pellets, comprising: a deposit formation step of stacking biomass-derived pellets to form a pellet deposit; and a suppression means placement step of placing a water vapor movement suppression means on at least a portion of the deposit being stacked during the deposit formation step, wherein after the suppression means placement step, pellets are further stacked on the placed water vapor movement suppression means to form the pellet deposit, and the water vapor movement suppression means is a means for suppressing the movement of water vapor from the back to the surface of the pellet deposit. [2] The pellet storage method according to [1], wherein the pellet deposit is at least one of a pellet deposit piled up on the ground, a pellet deposit piled up in a silo and in a warehouse, and a pellet deposit piled up in a container. [3] The pellet storage method according to [1] or [2], wherein the suppression means placement step is a step of placing the water vapor movement suppression means so as to cover at least a portion of the deposit being stacked. [4] The pellet storage method according to any one of [1] to [3], wherein the suppression means placement step is performed two or more times during the stacking of the pellets. [5] The pellet storage method according to [3] or [4], wherein the suppression means placement step is a step of arranging the water vapor transfer suppression means along the contour of the stacked material. [6] After the deposition formation step is carried out, the pellet deposition has a pellet dry region mainly composed of pellets with a moisture content of less than 6% by mass, and a pellet wet region mainly composed of pellets with a moisture content of 6% by mass or more, wherein the pellet dry region is a region that occurs on the surface side of the pellet deposition as the moisture content of the pellets present on the surface of the pellet deposition becomes lower than the moisture content of the pellets immediately after the formation of the pellet deposition, the pellet wet region is a region that occurs on the inner side of the pellet deposition, and the water vapor transfer suppression means is arranged to cover at least a part of the region that may become the pellet wet region, the pellet storage method according to any one of [1] to [5].[7] The pellet storage method according to [6], wherein the area that may become a pellet wet area is 30% to 90% of the total volume of the pellet deposit. [8] The pellet storage method according to [6] or [7], wherein the water vapor transfer suppression means is arranged between the area that may become a pellet wet area and the area that may become a pellet dry area. [9] The pellet storage method according to any one of [1] to [7], wherein the water vapor transfer suppression means is arranged horizontally with respect to the bottom surface of the pellet deposit.

[10] The pellet storage method according to [9], wherein the water vapor transfer suppression means is arranged at intervals of 0.5 m to 5.0 m from the top of the pellet deposit towards the bottom surface.

[11] The pellet storage method according to any one of [1] to

[10] , wherein the water vapor transfer suppression means is at least one selected from the group consisting of sheet members and plate members.

[12] The pellet storage method according to any one of the items [1] to

[11] , wherein the pellet is at least one selected from the group consisting of woody biomass pellets, herbaceous biomass pellets, crop residue biomass pellets, and palm oil biomass pellets.

[13] The pellet storage method according to any one of the items [1] to

[12] , wherein the pellet is a woody biomass pellet.

[14] A pellet storage facility comprising: means for stacking biomass-derived pellets in a storage place to form a pellet deposit; and means for arranging a water vapor movement suppression means in at least a part of the storage place to suppress the movement of water vapor from the back to the surface of the pellet deposit, wherein the storage place is at least one of the ground, a silo, a warehouse, and a container; and the water vapor movement suppression means is at least one selected from the group consisting of sheet members and plate members.

[0009] According to one aspect of the present invention, it is possible to provide a method for storing biomass-derived pellets and a pellet storage facility that can suppress spontaneous combustion when storing the pellets.

[0010] A diagram illustrating the mechanism by which pellets piled up in a pellet deposit spontaneously ignite. A schematic diagram of the spontaneous heating test apparatus. A graph showing the results of the spontaneous heating test for samples 1 and 2. A graph showing the results of the spontaneous heating test for test examples 1 to 4. A diagram illustrating the first example of the storage method according to this embodiment. A diagram illustrating the second example of the storage method according to this embodiment.

[0011] In this specification, numerical ranges expressed using "~" mean a range that includes the number before "~" as the lower limit and the number after "~" as the upper limit. In this specification, mass percentage concentration (unit: mass%) and weight percentage concentration (unit: weight%) are the same value.

[0012] [First Embodiment] [Pellet Storage Method] The pellet storage method according to this embodiment (hereinafter also referred to as "storage method according to this embodiment") comprises a deposit formation step of stacking biomass-derived pellets to form a pellet deposit, and a suppression means placement step of placing a water vapor movement suppression means on at least a part of the deposit being stacked during the deposit formation step. After the suppression means placement step, pellets are further stacked on the placed water vapor movement suppression means to form the pellet deposit. The water vapor movement suppression means is a means of suppressing the movement of water vapor from the back to the surface of the pellet deposit.

[0013] According to the storage method of this embodiment, a water vapor movement suppression means is placed in at least a portion of the pile during stacking. This suppresses the movement of water vapor from the back of the pellet pile to the surface. The movement of water vapor from the back of the pellet pile to the surface is considered to be a factor that causes spontaneous combustion of pellets, as will be described later. Therefore, according to the storage method of this embodiment, spontaneous combustion can be suppressed when pellets are stored.

[0014] The water vapor transfer suppression means is preferably at least one selected from the group consisting of sheet members and plate members, and more preferably a sheet member. Examples of materials for the sheet member include plastics, polymers, metals, ceramics, cloth, straw, and grasses. When the material of the sheet member is straw and grasses, the sheet member may be a sheet woven from straw and grasses (e.g., straw). Examples of materials for the plate member include plastics, polymers, metals, and ceramics. It is preferable that the water vapor transfer suppression means is removed from the pellet deposit when the pellets in the pellet deposit are used as fuel. When the water vapor transfer suppression means is a sheet member, it is preferable that the sheet member is not removed from the pellet deposit and is used for combustion together with the pellets.

[0015] Biomass-derived pellets are not particularly limited as long as they contain biomass. The biomass content in the pellets is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, and even more preferably 90% by mass or more. The upper limit for the biomass content in the pellets is 100% by mass. Hereinafter, biomass-derived pellets may be simply referred to as pellets or biomass pellets. When pellets are used as fuel, it is preferable that the biomass in the pellets is semi-carbonized. "Semi-carbonization" is a process also known as "torrefaction," which is a technique to increase the carbon ratio by heating biomass at 200°C to 350°C to decompose volatile components (low boiling point components). When biomass is gradually heated, carbonization progresses above 200°C while generating pyrolysis gases. Although the weight of the biomass decreases, the calorific value increases due to carbonization, thus improving the energy density per unit weight.

[0016] The pellet piles are preferably at least one of the following: pellet piles piled up on the ground, pellet piles piled up in silos and warehouses, and pellet piles piled up in containers. It is preferable that the pellet piles are at least one of the following: pellet piles piled up on the ground and pellet piles piled up in warehouses. The pellet piles may be formed outdoors or indoors (e.g., dome-type and warehouse-type structures).

[0017] Spontaneous combustion of biomass often occurs through a pathway where the biomass itself generates heat, causing its temperature to rise and eventually leading to ignition. Possible causes of biomass self-heating include oxidation, microbial fermentation, water adsorption, and water vapor adsorption. While oxidation is ultimately the primary cause of biomass ignition, oxidation reactions are slow at room temperature. Therefore, it is thought that some other factor must be involved to accelerate the oxidation process to a sufficient rate before spontaneous combustion occurs.

[0018] For example, Non-Patent Literature 1 proposes a mechanism of spontaneous combustion in which, at around room temperature, the heat generated by fermentation by microorganisms attached to the biomass raises the temperature of the biomass (fermentation heat), and from that temperature, the temperature of the biomass continues to rise until oxidation proceeds at a sufficient rate (oxidation heat) (see Figure 2.5 in Non-Patent Literature 1).

[0019] However, the inventors have observed that heat-treated semi-carbonized pellets generate heat even when they are not exposed to the external environment and have low moisture content after production. Believing that this cannot be explained solely by microbial fermentation, they investigated the effect of water vapor.

[0020] The inventors of the present invention, using the spontaneous heating test apparatus shown in Figure 2 (with a configuration similar to the adiabatic heating test apparatus described in Non-Patent Literature 2), found that when water vapor was added to dry pellets at around room temperature, the temperature of the pellets rose by more than 10°C in about 8 hours (see Figure 3). As a result, they hypothesized that the oxidation rate was greatly increased by the rise in pellet temperature due to the water vapor, and that this could serve as a model for spontaneous combustion from room temperature.

[0021] In actual biomass storage sites, it is assumed that both high-moisture areas (wet areas) and relatively dry areas (dry areas) exist, and that the movement and adsorption of water vapor between these areas causes a temperature increase from room temperature (see Figure 1).

[0022] Therefore, we believe that if the movement of water vapor can be suppressed, the onset of spontaneous heating can be suppressed, which will lead to a reduction in the rate at which oxidation becomes the dominant process, and ultimately to the suppression of spontaneous combustion. This led to the completion of the present invention.

[0023] Based on the analysis results described below, the inventors inferred that the movement of water vapor from the inner to the surface of the pellet deposit is a factor that causes the pellets to spontaneously combust. Specifically, they inferred the following events (1) to (5). Figure 1 is a diagram illustrating the mechanism by which pellets piled up in a pellet deposit spontaneously combust (the following events (1) to (5)). Figure 1 shows a state in which pellets are piled up on the ground to form a pellet deposit.

[0024] Event (1): After a pellet deposit is formed and a certain period of time has passed, the surface of the pellet deposit is exposed to sunlight and wind, so the moisture content of the pellets deposited on the surface side decreases. In Figure 1, this surface area is labeled as the "pellet dry area DR1". On the other hand, the inner part of the pellet deposit is not exposed to air, so the moisture content of the pellets deposited on the inner part tends to be maintained (less likely to change). In Figure 1, this inner area is labeled as the "pellet wet area WR1". Event (2): Moisture (water vapor) moves from the inner part of the pellet deposit (pellet wet area WR1) to the surface of the pellet deposit (pellet dry area DR1). Event (3): Pellets in the pellet dry area DR1 (hereinafter also referred to as dry pellets) adsorb water vapor and generate heat of adsorption (see Figures 3 to 4 below). Event (4): The generated heat is transferred to other dry pellets in the pellet dry area DR1. Event (5): The heated dry pellets oxidize and spontaneously ignite.

[0025] <Analysis Results on the Mechanism of Spontaneous Combustion> First, the spontaneous combustion test apparatus will be described. Figure 2 is a schematic diagram of the spontaneous combustion test apparatus (adiabatic combustion test apparatus). The spontaneous combustion test apparatus 300 comprises a constant temperature bath 50, a gas supply unit 80, a gas preheating unit 44, and a reactor 70A. The gas supply unit 80 comprises a first flow path 91 through which oxygen gas flows, a second flow path 92 through which nitrogen gas flows, a third flow path 93, a fourth flow path 94, and a plurality of switching valves BV. A mass flow controller (MFC1) and a gate valve SV1 are arranged in the first flow path 91. A gas flow meter 82 and a gate valve SV2 are arranged in the second flow path 92. A humidifier 84 (for example, a water bubbling device) and a hygrometer 86 downstream of the humidifier 84 are arranged in the third flow path 93. The gas preheating unit 44 is made of copper pipes. The gas preheating unit 44 receives heat from the constant temperature bath 50 as the test gas (nitrogen gas or oxygen gas containing water vapor) supplied from the gas supply unit 80 passes through the copper pipe, preheating the test gas to the same temperature as the constant temperature bath 50.

[0026] Reactor 70A is designed to be filled with sample 52. A lid 72A is placed on top of reactor 70A, and a gas supply pipe 64, a gas discharge pipe 66, and a thermocouple 53 are arranged through this lid 72A toward the inside of reactor 70A. The gas supply pipe 64 extends to position E. Inside reactor 70A, sample 52 is placed between quartz wool 74 and 75 to ensure that the flow of the test gas is as uniform as possible. A heater (not shown) is provided in the constant temperature bath 50. The heater temperature is controlled by a temperature controller 46 so that it is equal to the temperature of the thermocouple 53 (temperature of sample 52). In other words, the temperature of the constant temperature bath 50 is controlled to be the same as the temperature of the thermocouple 53.

[0027] The spontaneous heating test is conducted while maintaining a pseudo-insulated state inside the reactor 70A. During the spontaneous heating test, the test gas supplied from the gas supply unit 80 has its humidity measured by a hygrometer 86, is preheated to the same temperature as the constant temperature bath 50 in the gas preheating unit 44, then flows through the gas supply pipe 64 and is introduced into the reactor 70A, and is released at position E (bottom of reactor 70A). The released test gas comes into contact with the lower quartz wool 75, then rises and flows through the sample 52 filled inside the reactor 70A, passes through the upper quartz wool 74 and is discharged from the gas discharge pipe 66. The nitrogen gas used in the test is introduced into the reactor 70A by flowing through the second channel 92, the fourth channel 94, and the gas supply pipe 64 in that order. Oxygen gas with saturated water vapor added is introduced into the reactor 70A by flowing through the first channel 91, the third channel 93, and the gas supply pipe 64 in that order.

[0028] (Enhanced exothermic reaction by water vapor) The spontaneous exothermic reaction of samples 1 and 2 was tested using the following method. The results are shown in Figure 3. Sample 1 was semi-carbonized biomass powder (particle size 200 μm or less), and Sample 2 was semi-carbonized biomass pellets (cylindrical shape, diameter 8 mm, length 10 mm to 30 mm). The type of biomass was acacia.

[0029] (Sample 1) Sample 1 was dried in advance at 70°C under vacuum for 3 days to adjust the moisture content of the biomass powder to 0%. 200 g of Sample 1 was packed into reactor 70A, and nitrogen gas was flowed into reactor 70A from the gas supply unit 80 (50 mL / min). When the sample temperature reached 34°C, measurement of the sample temperature was started.

[0030] (Sample 2) Sample 2 was dried in advance at 70°C under vacuum for 3 days to adjust the moisture content of the biomass pellet to 0%. 200 g of Sample 2 was packed into reactor 70A, and nitrogen gas was flowed from gas supply unit 80 into reactor 70A (50 mL / min). When the sample temperature reached 40°C, the nitrogen gas was switched to "oxygen gas with saturated water vapor added (50 mL / min)," and the measurement of the sample temperature was started. The measurement was stopped when the sample temperature reached 150°C.

[0031] (Results) As shown in Figure 3, the time required to heat up to 150°C was significantly shorter for the biomass pellets to which water vapor was introduced (Sample 2) compared to the biomass powder to which water vapor was not introduced (Sample 1). In the case of Sample 2, it is thought that adsorption heat (coagulation heat) was generated when water vapor was adsorbed (or coagulated) onto the pellet surface at temperatures below 60°C. Furthermore, in Sample 2, it is thought that the initial temperature rose by more than 10°C in a short time (about 8 hours), which accelerated subsequent oxidation.

[0032] (Effect of Pellet Moisture Content and Water Vapor) Biomass pellets were used to conduct spontaneous exothermic tests according to Test Examples 1 to 4 below. The results are shown in Figure 4. The biomass pellets were dried in advance at 70°C under vacuum for 3 days to adjust the moisture content of the biomass pellets to 0%. This was used as Sample 3. Sample 3 was prepared under the same conditions as Sample 2 above to adjust the moisture content of the biomass pellets to 0%. The biomass pellets were dried in advance in the sun (indoors) to adjust the moisture content of the biomass pellets to 2%. This was used as Sample 4.

[0033] (Test Example 1) 200 g of sample 3 was packed into reactor 70A, and nitrogen gas was supplied to reactor 70A from gas supply unit 80 (50 mL / min). When the sample temperature reached 52°C, measurement of the sample temperature was started. When the sample temperature reached 150°C, the measurement was stopped.

[0034] (Test Example 2) 200 g of sample 3 was packed into reactor 70A, and nitrogen gas was supplied to reactor 70A from the gas supply unit 80 (50 mL / min). When the sample temperature reached 40°C, the nitrogen gas was switched to "oxygen gas with saturated water vapor added (50 mL / min)," and the measurement of the sample temperature was started. The measurement was stopped when the sample temperature reached 150°C.

[0035] (Test Example 3) 200 g of sample 4 was packed into reactor 70A, and nitrogen gas was supplied to reactor 70A from the gas supply unit 80 (50 mL / min). When the sample temperature reached 45°C, the nitrogen gas was switched to "oxygen gas with saturated water vapor added (50 mL / min)," and the measurement of the sample temperature was started. The measurement was stopped when the sample temperature reached 150°C.

[0036] (Test Example 4) 200 g of sample 4 was packed into reactor 70A, and nitrogen gas was supplied to reactor 70A from the gas supply unit 80 (50 mL / min). When the sample temperature reached 45°C, measurement of the sample temperature was started. However, in the case of Test Example 4, the sample temperature did not rise, so the measurement was stopped after 7 days.

[0037] (Results) As shown in Figure 4, in a comparison between Test Example 1 and Test Example 2, which used biomass pellets with a moisture content of 0%, Test Example 2, in which water vapor was introduced, showed a significantly shorter heating time to 150°C compared to Test Example 1, in which water vapor was not introduced. In Test Example 3, which used biomass pellets with a moisture content of 2%, when water vapor was introduced, the temperature initially rose by nearly 10°C due to the heat of adsorption, and then gradually increased for about 25 days, finally reaching 150°C after 30 days. In Test Example 3, it is thought that the biomass pellets transitioned to autonomous oxidation during the period when the temperature was gradually rising for about 25 days. In Test Example 4, which used biomass pellets with a moisture content of 2% and did not introduce water vapor, the sample temperature actually decreased. It is thought that the water in the pellets evaporated, and the temperature decreased due to the heat of vaporization.

[0038] The relationship between the events (1) to (5) inferred by the inventors and the aforementioned analysis results will be explained. • Regarding events (1) to (3): The biomass pellets in the pellet wet region WR1 in Figure 1 correspond to the biomass pellets of Test Example 3, and the biomass pellets in the pellet dry region DR1 in Figure 1 correspond to the biomass pellets of Test Example 1. From Figure 4, when moisture (water vapor) moves from the pellet wet region WR1 to the pellet dry region DR1 (Test Example 3 → Test Example 1), the dry pellets in the pellet dry region DR1 (Test Example 1) adsorb the water vapor, generating heat of adsorption. As a result, the temperature of the pellets rises rapidly (Test Example 1 → Test Example 2). • Regarding events (4) to (5): The heat generated by the heat of adsorption is transferred to the surrounding dry pellets. The heated dry pellets are oxidized, leading to spontaneous combustion.

[0039] Each step of the storage method according to this embodiment will be described.

[0040] <Deposit Formation Process> In the storage method according to this embodiment, the deposit formation process is a process of stacking biomass-derived pellets to form a pellet deposit. Known means can be used to form the pellet deposit. Examples of means for forming the pellet deposit include stackers, excavators, cranes, conveyors, and wheel loaders (so-called bulldozers). If the storage location for the pellets is a silo, warehouse, or container, known transport equipment (e.g., a belt conveyor) may be used to drop the pellets into the silo, warehouse, or container.

[0041] <Suppression Means Placement Step> In the storage method according to this embodiment, the suppression means placement step is a step of placing water vapor movement suppression means on at least a portion of the piles being piled up during the pile formation step. Examples of means for placing water vapor movement suppression means include cranes, stacker cranes, and wheel loaders. When using a crane as a means for placing water vapor movement suppression means, for example, one method is to use the crane's hook to hold the water vapor movement suppression means with the hook, lower a wire rope suspension to place it in a predetermined location, and then remove the hook.

[0042] The water vapor movement suppression means is preferably at least one selected from the group consisting of a sheet member and a plate member. When the water vapor movement suppression means is a sheet member, after arranging the sheet member, for example, the end portion of the sheet member may be folded into the deposit during stacking or fixed using a fixture. When the water vapor movement suppression means is a plate member, after arranging the plate member, for example, the end portion of the plate member may be fixed using a fixture. In the storage method according to the present embodiment, the suppression means arranging step is preferably a step of arranging the water vapor movement suppression means so as to cover at least a part of the deposit during stacking. In the storage method according to the present embodiment, the suppression means arranging step is preferably carried out two or more times during the stacking of the pellets. That is, it is preferable to arrange two or more water vapor movement suppression means on the deposit during stacking. The materials of the two or more water vapor movement suppression means may be the same as or different from each other. In the storage method according to the present embodiment, the suppression means arranging step is preferably a step of arranging the water vapor movement suppression means along the contour of the deposit during stacking. In this case, the water vapor movement suppression means is preferably arranged at an area ratio of 70% or more and 100% or less with respect to the entire exposed area of the deposit during stacking. The area ratio is more preferably 80% or more and 100% or less, and even more preferably 90% or more and 100% or less. In the storage method according to the present embodiment, the water vapor movement suppression means is preferably arranged horizontally with respect to the bottom surface of the pellet deposit during stacking. In this case, the water vapor movement suppression means is preferably arranged at an area ratio of 70% or more and 100% or less with respect to the entire horizontal exposed area of the deposit during stacking. The area ratio is more preferably 80% or more and 100% or less, and even more preferably 90% or more and 100% or less. In the storage method according to the present embodiment, when the water vapor movement suppression means is arranged horizontally with respect to the bottom surface of the pellet deposit during stacking, the water vapor movement suppression means is preferably arranged at an interval of 0.5 m or more and 5.0 m or less in the direction from the top to the bottom of the pellet deposit, and more preferably at an interval of 1.0 m or more and 5.0 m or less.

[0043] In the storage method according to this embodiment, after the step of arranging the suppression means, pellets are further stacked on the arranged water vapor movement suppression means to form a pellet deposit. As the "means for further stacking pellets on the arranged water vapor movement suppression means", the same means as the aforementioned "means for forming a pellet deposit" can be used. In the storage method according to this embodiment, in view of the fact that the size of the water vapor movement suppression means increases and the arrangement work becomes difficult, it is preferable not to arrange the water vapor movement suppression means in the formed pellet deposit.

[0044] <After the implementation of the deposit formation step> In one aspect of the storage method according to this embodiment, after the implementation of the deposit formation step, the pellet deposit has a pellet dry region containing "pellets with a water content of less than 6% by mass" as the main component and a pellet wet region containing "pellets with a water content of 6% by mass or more" as the main component. In this specification, the main component means that the ratio in the total mass of the target region is 50% by mass or more. The water content of the pellets can be measured by a known method. In one aspect of the storage method according to this embodiment, the pellet dry region is a region that occurs on the surface layer side of the pellet deposit because the water content of the pellets in the surface layer portion of the pellet deposit is lower than the water content of the pellets immediately after the formation of the pellet deposit. The pellet wet region is a region where the water content of the pellets hardly changes from immediately after the formation of the pellet deposit, and specifically, it is a region that occurs on the inner side of the pellet deposit. In the storage method according to this embodiment, it is preferable that the water vapor movement suppression means is arranged so as to cover at least a part of the region that can become the pellet wet region.

[0045] In the storage method according to this embodiment, the region that can become the pellet wet region is preferably 30% to 90% by volume with respect to the total volume of the pellet deposit. In the storage method according to this embodiment, it is preferable that the water vapor movement suppression means is arranged between the region that can become the pellet wet region and the region that can become the pellet dry region.

[0046] Figure 5 is a diagram illustrating a first example of a storage method according to this embodiment. Figure 5 shows a pellet storage facility 1. The storage facility 1 includes a stacker 60A and a crane 70. The stacker 60A is an example of a means for forming a pellet pile. The crane 70 is an example of a means for arranging a water vapor transfer suppression means. In the case of Figure 5, the pellets are piled up on the ground. The water vapor transfer suppression means is a sheet member 20. The stacker 60A includes a first main body 61A and a supply unit 62A for supplying pellets 10. The crane 70 includes a second main body 71 and an arrangement unit 72 for arranging the sheet member 20. The arrangement unit 72 includes a holding unit 721 that holds the sheet member 20 with four hooks (not shown) and a wire rope 722 for raising and lowering the holding unit 721. In the storage facility 1, the pellets 10 are stored, for example, as follows. First, the stacker 60A supplies pellets 10 from the supply unit 62A toward the ground, thereby forming a first pile 100a in the process of being stacked. Next, the crane 70 suspends the wire rope 722 and places the sheet member 20 on the outer surface (exposed surface) of the first pile 100a so as to follow the contour of the first pile 100a. After that, the hooks that were holding the sheet member 20 are released. This forms the second pile 100b. After this, the pellets 10, sheet member 20, and pellets 10 are stacked or placed in the same manner to form the third pile 100c and the fourth pile 100d, and finally the fifth pile 100e as a pellet pile is obtained. The height of the fifth pile 100e is, for example, 1 m or more and 30 m or less.

[0047] In Figure 5, the pellet deposit 100 schematically shows the state after a certain period of time has elapsed since the pellet deposit was formed using the method of the first example. Due to the aforementioned event (1), the pellet deposit 100 has a pellet-drying region DR2 on the surface side and a pellet-wetting region WR2 on the inner side. According to the storage method of the first example, two sheet members 20 are placed on the deposit in the process of being stacked, and these two sheet members 20 cover the pellet-wetting region WR2. This suppresses the movement of water vapor from the inner side (pellet-wetting region WR2) to the surface side (pellet-drying region DR2) of the pellet deposit 100, and as a result, spontaneous combustion can be suppressed when storing pellets. According to the storage method of the first example, the effect can also be achieved when storing large quantities of pellets.

[0048] (Second Example of Storage Method) Figure 6 is a diagram illustrating a second example of the storage method according to this embodiment. Figure 6 shows a pellet storage facility 1A. Storage facility 1A has the same configuration as storage facility 1 in the first example. The storage method according to the second example using storage facility 1A is the same as the storage method according to the first example, except that the sheet members 20 are placed horizontally on the ground, three sheet members 20 are placed, and the pellets 10 are stacked in a frustoconical shape until the third sheet member 20 is placed. As shown in Figure 6, in the storage method according to the second example, a first deposit 101a, a second deposit 101b, a third deposit 101c, a fourth deposit 101d, a fifth deposit 101e, and a sixth deposit 101f are formed in order, and finally a seventh deposit 101g as a pellet deposit is obtained. The three sheet members 20 are positioned on their respective horizontally exposed surfaces with respect to the bottom surface (ground) of the first deposit 101a, the third deposit 101c, and the fifth deposit 101e.

[0049] In Figure 6, the pellet deposit 101 schematically shows the state after a certain period of time has elapsed since the pellet deposit was formed using the method of the second example. Due to the aforementioned event (1), the pellet deposit 101 has a pellet-drying region DR3 on the surface side and a pellet-wetting region WR3 on the inner side. In the pellet deposit 101, the three sheet members 20 are arranged at intervals D1 from the top T1 of the pellet deposit 101 to the bottom B1. The interval D1 is preferably 0.5 m or more and 5.0 m or less. According to the storage method of the second example, for the same reasons as in the first example, the movement of water vapor from the inner side (pellet-wetting region WR3) to the surface side (pellet-drying region DR3) of the pellet deposit 101 can be suppressed. As a result, spontaneous combustion can be suppressed when pellets are stored. According to the storage method of the second example, the effect can also be achieved when a large amount of pellets are stored.

[0050] The storage method according to this embodiment is not limited to the first and second examples.

[0051] [Second Embodiment] [Pellet Storage Facility] The pellet storage facility according to the second embodiment comprises means for stacking biomass-derived pellets in a storage area to form a pellet deposit, and means for arranging a water vapor movement suppression means in at least a part of the storage area to suppress the movement of water vapor from the back to the surface of the pellet deposit, wherein the storage area is at least one of the ground, a silo, a warehouse, and a container, and the water vapor movement suppression means is at least one selected from the group consisting of sheet members and plate members. The storage facility according to the second embodiment is, for example, the storage facilities 1 and 1A shown in Figures 5 and 6.

[0052] According to the storage equipment of the second embodiment, by providing means for arranging water vapor transfer suppression means, the movement of water vapor from the back of the pellet deposit to the surface can be suppressed. As a result, spontaneous combustion can be suppressed when pellets are stored. The storage equipment of the second embodiment can be used, for example, when implementing the storage method of the first embodiment described above. Therefore, the water vapor transfer suppression means, means for arranging the water vapor transfer suppression means, etc., used in the storage equipment of the second embodiment can be the same as those of the first embodiment.

[0053] The configurations common to the embodiments described above will now be explained.

[0054] <Biomass> In the storage method according to this embodiment, the pellet is preferably at least one selected from the group consisting of woody biomass pellets, herbaceous biomass pellets, crop residue biomass pellets, and palm oil biomass pellets, and more preferably woody biomass pellets. In addition to woody biomass, herbaceous biomass, crop residue biomass, and palm oil biomass, the pellet may also contain cellulose products and pulp products, etc.

[0055] In this specification, agricultural residue biomass means everything except the edible portion. In this specification, palm biomass means agricultural waste from palm trees.

[0056] Examples of woody biomass include coniferous trees (e.g., Japanese cedar, pine, cypress, and fir) and broad-leaved trees (e.g., acacia, eucalyptus, birch, black locust, beech, zelkova, katsura, paulownia, rubber tree, and camphor tree). Woody biomass may also include construction waste (e.g., cut scraps, wood chips and sawdust generated at processing plants), forest residues, thinned timber, and bamboo. Examples of herbaceous biomass include grass, naturally growing plants, and artificially planted plants. Herbaceous biomass may also include hemp, cotton, rice straw, rice husks, wheat straw, bamboo grass, Napier grass, sorghum, and Japanese pampas grass.

[0057] Examples of agricultural crop residue biomass include leaves, fruit clusters, stems, roots, and other non-edible parts of crops. Examples of such crops include wheat, corn, potatoes, sugarcane (including bagasse), and bananas.

[0058] Examples of palm kernel biomass include palm kernel shells (PKS), empty fruit bunches (EFB), and palm trunks. The biomass described above may be used individually or in combination of two or more.

[0059] In this embodiment, semi-carbonized pellets are obtained, for example, by (i) heating biomass pellets at 220°C to 320°C, or (ii) molding semi-carbonized biomass powder into pellets. The semi-carbonized biomass powder in (ii) is obtained by known methods (such as steam explosion of biomass). For molding into pellets, known pelletizers can be used. Semi-carbonized pellets have a high proportion of fixed carbon. The proportion of fixed carbon is the value of fixed carbon determined by industrial analysis. The industrial analysis value is measured in accordance with JIS M8812 (2004). The proportion of fixed carbon (by mass) of semi-carbonized pellets is preferably 20% or more, more preferably 20% to 40%, and even more preferably 20% to 35%.

[0060] In this embodiment, the pellets are typically cylindrical, preferably with a diameter of 5 mm to 10 mm and a length of 5 mm to 50 mm. In this embodiment, the pellets include briquettes. Briquettes are generally cylindrical, tablet-shaped, charcoal-shaped, cubic, or rectangular, and a volume of 1 mL to 1 L is convenient for use.

[0061] In this embodiment, the pellets may contain other components. Other components include emulsifiers, spreading agents, binders, and various additives. In this embodiment, the pellets may contain coal. When the pellets contain coal, the ratio of coal to biomass in the pellets (coal / biomass) is preferably 0 / 100 to 75 / 25 by mass ratio, and more preferably 0 / 100 to 50 / 50.

[0062] In this embodiment, the pellets can be widely used as fuel in power plants, steel mills, factories, and the like.

[0063] 1, 1A...Storage equipment, 10...Pellets, 20...Sheet material, 44...Gas preheating unit, 46...Temperature controller, 50...Constant temperature bath, 52...Sample, 53...Thermocouple, 60A...Stacker, 61A...First main body, 64...Gas supply pipe, 66...Gas discharge pipe, 62A...Supply unit, 70...Crane, 70A...Reactor, 71...Second main body, 72...Planting unit, 72A...Lid, 74, 75...Quartz wool, 80...Gas supply unit, 82...Gas flow meter, 84...Humidifier, 86...Hygrometer, 91-94...Flow path, 100, 101...Pellet deposits, 100a-100e, 101a-101g...Deposits, 300...Spontaneous heat generation test device, 721...Holding unit, 722...Wire rope.

Claims

1. A method for storing pellets, comprising: a deposit formation step of stacking biomass-derived pellets to form a pellet deposit; and a suppression means placement step of placing a water vapor movement suppression means on at least a portion of the deposit being stacked during the deposit formation step, wherein after the suppression means placement step, pellets are further stacked on the placed water vapor movement suppression means to form the pellet deposit, and the water vapor movement suppression means is a means for suppressing the movement of water vapor from the inner side to the surface side of the pellet deposit.

2. The pellet storage method according to claim 1, wherein the pellet pile is at least one of a pellet pile stacked on the ground, a pellet pile stacked in a silo and in a warehouse, and a pellet pile stacked in a container.

3. The method for storing pellets according to claim 1 or claim 2, wherein the step of arranging the suppression means is a step of arranging the water vapor transfer suppression means so as to cover at least a portion of the pile being stacked.

4. The pellet storage method according to any one of claims 1 to 3, wherein the step of arranging the suppression means is performed two or more times during the stacking of the pellets.

5. The method for storing pellets according to claim 3 or claim 4, wherein the step of arranging the suppression means is a step of arranging the water vapor transfer suppression means so as to follow the contour of the pile being stacked.

6. After the deposition formation step is carried out, the pellet deposition has a pellet-drying region mainly composed of pellets with a moisture content of less than 6% by mass, and a pellet-wetting region mainly composed of pellets with a moisture content of 6% by mass or more, wherein the pellet-drying region is a region that occurs on the surface side of the pellet deposition because the moisture content of the pellets present on the surface of the pellet deposition becomes lower than the moisture content of the pellets immediately after the formation of the pellet deposition, the pellet-wetting region is a region that occurs on the inner side of the pellet deposition, and the water vapor movement suppression means is arranged to cover at least a part of the region that may become the pellet-wetting region, the pellet storage method according to any one of claims 1 to 5.

7. The pellet storage method according to claim 6, wherein the area that may become a pellet-wet area is 30% by volume or more and 90% by volume or less of the total volume of the pellet deposit.

8. The method for storing pellets according to claim 6 or claim 7, wherein the water vapor transfer suppression means is arranged between the region that may become a pellet wet region and the region that may become a pellet dry region.

9. The method for storing pellets according to any one of claims 1 to 7, wherein the water vapor transfer suppression means is arranged horizontally with respect to the bottom surface of the pellet deposit.

10. The method for storing pellets according to claim 9, wherein the water vapor transfer suppression means are arranged at intervals of 0.5 m to 5.0 m from the top to the bottom of the pellet deposit.

11. The method for storing pellets according to any one of claims 1 to 10, wherein the water vapor transfer suppression means is at least one selected from the group consisting of sheet members and plate members.

12. The method for storing pellets according to any one of claims 1 to 11, wherein the pellet is at least one selected from the group consisting of woody biomass pellets, herbaceous biomass pellets, crop residue biomass pellets, and palm oil biomass pellets.

13. The method for storing pellets according to any one of claims 1 to 12, wherein the pellets are woody biomass pellets.

14. A pellet storage facility comprising: means for stacking biomass-derived pellets in a storage area to form a pellet deposit; and means for arranging a water vapor transfer suppression means in at least a part of the storage area to suppress the movement of water vapor from the back to the surface of the pellet deposit, wherein the storage area is at least one of the ground, a silo, a warehouse, and a container, and the water vapor transfer suppression means is at least one selected from the group consisting of sheet members and plate members.

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