Sediment classification system and classification method

Abstract

To provide a sediment classification system and classification method that can classify dredged sediment with high accuracy into materials of desired particle sizes using an inexpensive apparatus, and can effectively utilize the classified materials as construction materials such as downstream return materials and aggregates.SOLUTION: The sediment classification system includes mud-loosening means 2 that loosens sediment 1, and a classification unit 3 that classifies the sediment 1 loosened by the mud-loosening means 2 into desired particle sizes, where the classification unit 3 is configured so as to be constituted by a combination of arbitrary classification means.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a classification system and method for classifying soil and sand, such as dredged soil, into desired particle sizes for reuse. [Background technology]

[0002] Mud, sediment, etc. (hereinafter referred to as sediment, etc.) flow into dams from upstream rivers, and since there is a risk that this sediment, etc. will accumulate at the bottom and impair the dam's function, dredging of the accumulated sediment is carried out regularly.

[0003] In addition, in recent years, climate change has led to more severe rainfall, resulting in increased river flooding and flood damage. In order to respond to these issues, ensuring dam functions is becoming increasingly important, and it is expected that the frequency of dredging accumulated sediment will increase.

[0004] The soil and sand produced by dredging this dam (hereinafter referred to as dredged soil and sand) has traditionally been disposed of by being buried in soil disposal sites, but in recent years it has become difficult to secure soil and sand disposal sites, and there is a need to reduce the volume of soil and sand that is buried in soil and sand disposal sites.

[0005] Therefore, conventionally, dredged soil is classified into sand and silt / clay materials, allowing part of the soil to be reused and reducing the volume of soil disposal sites.

[0006] A known method for classifying this dredged soil involves removing impurities such as garbage using a vibrating screen, separating the dredged soil into sand and gravel and silt / clay using a trommel, and then classifying the sand and gravel and silt / clay using a vibrating screen, cyclone classifier, etc. (See, for example, Patent Document 1).

[0007] On the other hand, in rivers downstream of dams, the amount of sediment that flows downstream is reduced when sediment is blocked by the dam, causing problems such as the riverbed becoming coarse-grained, with coarse gravel covering the riverbed, and the bedrock becoming exposed.As a countermeasure, downstream return is being implemented, in which sand and other materials obtained from dredged sediment are returned to the river downstream of the dam. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-89016 Summary of the Invention [Problem to be solved by the invention]

[0009] Construction materials such as downstream reduction materials, beach nourishment materials, and aggregates each have their own set of standards, and in order to reuse dredged soil as a material, the dredged soil must be classified into particle sizes that meet the standards. For example, downstream reduction materials and beach nourishment materials are required to have a fine particle content Fc of 10% or less.

[0010] However, with the conventional technology described above, there was a problem in that the materials of each particle size contained in the dredged soil adhered firmly to each other, making it difficult to easily classify the materials into the desired particle sizes.

[0011] Therefore, in order to reuse the waste as downstream reducing material or construction materials such as aggregate, it is necessary to carry out multiple classification processes so that the waste can be classified into desired particle sizes, which poses a problem of increased costs.

[0012] In view of the above-mentioned conventional problems, the present invention has been made with the aim of providing a soil classification system and method that can accurately classify dredged soil into materials of desired particle sizes using inexpensive equipment, and can be effectively used as construction materials such as downstream reduction materials and aggregates. [Means for solving the problem]

[0013] The feature of the invention described in claim 1 for solving the above-mentioned conventional problems is a classification system for classifying soil and sand into desired particle sizes, A means for dissolving the materials of each particle size contained in the slurry into a state in which the adhesion between them is weakened. and a classification unit for classifying the soil and sand dissolved by the mud-dissolving means into desired particle sizes, and the classification unit can be configured by any combination of classification means.

[0014] The feature of the invention described in claim 2 is that, in addition to the configuration of claim 1, the mud-removing means comprises a horizontally placed drum with scraping blades protruding from its inner surface, and a driving means for rotating the drum.

[0015] The invention described in claim 3 is characterized in that, in a method for classifying soil and sand into desired particle sizes, Desilting means By the sediment The materials of each particle size contained in the After the thawing step, the soil and sand thawed in the thawing step is classified into desired particle sizes by a classification unit constituted by any classification means.

[0016] The invention as set forth in claim 4 is characterized in that, in addition to the configuration of claim 3, the mud thawing step repeats the work of thawing the soil and sand by the mud thawing means a plurality of times. [Effects of the Invention]

[0017] The soil classification system of the present invention, equipped with the configuration described in claim 1, allows dredged soil to be accurately classified into materials of desired particle size using an inexpensive device, enabling effective use as construction materials such as downstream reduction materials and aggregates. Furthermore, organic matter such as wood chips and leaves can be efficiently removed from the sand, and the sand from which the organic matter has been removed can be used as high-quality aggregate because it does not inhibit the strength development of cement. Furthermore, nutrients such as nitrogen and phosphorus adhering to fine particles can be separated from the sand and concentrated in the fine particles for removal, thereby separating and concentrating the nutrients. Furthermore, the fine particles with concentrated nutrients can be used for farmland improvement and environmental restoration of nutrient-poor beaches.

[0018] Furthermore, in the present invention, by providing the configuration described in claim 2, it is possible to efficiently break down soil and sand, and to facilitate the separation of materials classified by particle size, i.e., sand, gravel, silt, fine particles, etc., from one another.

[0019] Furthermore, by incorporating the configuration described in claim 3, the method for classifying soil and sand according to the present invention allows dredged soil and sand to be accurately classified into materials of desired particle sizes, which can be effectively used as downstream reduction materials, aggregates, and other construction materials. Organic matter such as wood chips and leaves can also be efficiently removed. Furthermore, nutrients such as nitrogen and phosphorus adhering to fine particles can be separated from the sand and concentrated in the fine particles for removal, thereby separating and concentrating the nutrients.

[0020] Furthermore, in the present invention, by providing the configuration described in claim 4, it is possible to improve the mud-resolving effect. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a block diagram schematically illustrating an example of a soil classification system according to the present invention. [Figure 2] FIG. 2 is a vertical cross-sectional view showing an example of the mud-resolving means of the same. [Figure 3] 4(a) to 4(c) are cross-sectional views for explaining the operation of the mud-resolving means of the same. DETAILED DESCRIPTION OF THE INVENTION

[0022] Next, an embodiment of the soil classification system according to the present invention will be described based on the examples shown in FIGS.

[0023] This soil classification system (hereinafter referred to as the classification system) comprises a thawing means 2 that thaws the soil 1, and a classification unit 3 arranged downstream of the thawing means 2. The input soil 1 is thawed by the thawing means 2, reducing adhesion between materials of each particle size, so that the soil 1 can be classified into desired particle sizes by the classification unit 3, which is composed of a combination of any classification means.

[0024] In the figure, reference numeral 4 denotes a quantitative feeder, and reference numeral 5 denotes a belt conveyor for transporting the material from the quantitative feeder 4 to the sludge dissolving means 2.

[0025] As shown in Figures 2 and 3, the mud deflocculating means 2 comprises a horizontally placed drum 7 with a number of scraping blades 6, 6... protruding from its inner peripheral surface, and a driving means 8 for rotating the drum 7. The soil 1 put into the drum 7 is scraped up from the bottom side along the inner peripheral surface of the drum 7 by the scraping blades 6, 6..., and then falls down by its own weight at the top, repeating this process.

[0026] The drum 7 is formed in a cylindrical shape with end plates 7a, 7a arranged on both ends, and is installed horizontally with the cylindrical axis direction horizontal or inclined at a predetermined angle, and is rotated around the cylindrical axis by a driving means 8.

[0027] Each of the end plates 7a, 7a has an opening in the center, and soil 1 is poured in from a hopper 7b through the opening in one of the end plates 7a, while the thawed soil 1 is discharged from a discharge pipe 7c through the opening in the other end plate 7a.

[0028] Additionally, annular partition plates 7d, 7d are fixed to the inner periphery of the drum 7 at an interval in the axial direction.

[0029] The scraper blades 6, 6 . . . are each formed in a thin plate shape and are provided radially protruding from the inner peripheral surface of the drum 7 at intervals in the circumferential direction, with their short sides directed inward in the radial direction.

[0030] Then, inside the tilted drum 7, as shown in Figures 3(a) to (b), the soil and sand 1 is repeatedly scraped upward along the inner surface of the drum 7 by the scraper blades 6, 6... and then reaches the top of the drum 7 as shown in Figures 3(b) to (c) and falls, causing the soil and sand 1 to break up and move toward the discharge pipe 7c, and finally fall toward the opening of the discharge pipe 7c.

[0031] The configuration of the scraper blades 6, 6... is not limited to the above-mentioned multiple thin plate-shaped scraper blades 6, 6... protruding from the inner peripheral surface of the drum 7, but may be formed in a spiral shape, for example.

[0032] The driving means 8 is composed of a driving wheel 8a that contacts the outer periphery of the drum 7, a motor 8b that rotates the driving wheel 8a, and the like, and is configured to rotate the drum 7 at a predetermined rotation speed.

[0033] The rotation speed of the drum is not particularly limited, but is set to a speed that efficiently dissolves the soil and sand 1 in accordance with the properties of the soil and sand 1. For example, it is preferable to set the speed so that the rotation of the drum 7 does not disturb the soil and sand 1 inside the drum 7, and the soil and sand 1 is scraped up along the inner surface of the drum 7 by the scraping blades 6, 6, etc. in predetermined amounts, and once it reaches the top, it falls gently toward the bottom of the drum 7.

[0034] In addition, loosening the soil and sand 1 (deflocculation) refers to a state in which the materials of each particle size contained in the soil and sand 1, which are in a state of adhering to each other, are physically kneaded, pushed, impacted, shaken, etc. using a machine, etc., so that the adhesion between the materials of each particle size is weakened, in particular, the adhesion between the fine particles 24 of less than 0.075 mm and materials of other particle sizes is weakened. The form of the de-mudding means 2 is not limited to the above-mentioned embodiment, and may be any form that is capable of de-mudding.

[0035] The classification unit 3 is composed of a three-stage vibrating screen with a cyclone showering mechanism, and is a composite combination of a liquid cyclone classifier 10, three stages of vibrating screens (top, middle and bottom), and a showering machine 14.

[0036] In addition, the classification unit 3 can improve the precision of removing fine particles by arranging a high-mesh separator 30 downstream of the three-stage vibrating screen with a cyclone showering mechanism, if necessary.

[0037] The vibrating screens 11 to 13 have meshes set so that the upper screen 11 can collect medium pebbles 20 of 15 mm or more, the middle screen 12 can collect small pebbles 22 of 2 mm to 15 mm, and the lower screen 13 can collect sand 25 of 0.075 mm to 2 mm.

[0038] The screens 11 to 13 are not limited to ordinary screens with lattice-like meshes. For example, the screen 13 may be a so-called wedge wire screen, which is made by arranging multiple wires with an inverted triangular cross section at equal intervals to form slit-like meshes, in order to prevent clogging with sand and promote solid-liquid separation.

[0039] In the liquid cyclone classifier 10, fine particles 24 of less than 0.075 mm in the residual sediment 23 are suspended in the treated water, while residual particles including sand 25 of 0.075 mm or larger are allowed to settle to the bottom as solids.

[0040] The classification unit 3 is not limited to a single composite classification means formed by combining classification means such as the above-mentioned three-stage vibrating screen with a cyclone showering mechanism, but may be formed by a combination of any classification means such as a vibrating screen, a cyclone classifier, a high-mesh separator, or a combination of multiple classification means of the same type such as a combination of multiple single-stage screens, or may be formed by a combination of a composite classification means and any single classification means.

[0041] Next, a method for classifying soil and sand using the above-described classification system will be described with reference to Figures 1 and 3. Note that the same components as those in the above-described embodiment will be given the same reference numerals and their description will be omitted.

[0042] In this embodiment, the dam sediment 1, which has a fine particle content Fc of 20% or more and is mainly generated by dredging sediment 1 deposited on the bottom of a dam lake, is classified into fine particles 24 (less than 0.075 mm), sand 25 (0.075 mm to 2.0 mm), small gravel 22 (2 mm to 15 mm), and medium gravel 20 (15 to 100 mm), and finally, sand 25 with a fine particle content Fc of 10% or less is extracted, which can be reused as downstream reduction material or beach nourishment material.

[0043] First, large gravels of 100 mm or more are removed from the soil 1 (dam deposit soil 1) using a fixed sieve (grizzly), and then the water content is adjusted in an adjustment tank (not shown) as necessary.

[0044] Next, the soil 1 is fed into a quantitative feeder 4, and the soil 1 is discharged from the quantitative feeder 4 onto a belt conveyor 5 at regular intervals, and the soil 1 is sent by the belt conveyor 5 into a drum 7 of the mud deflocculating means 2.

[0045] The soil 1 put into the drum 7 repeats the process of being scooped up from the bottom of the drum 7 by the scooping blades 6, 6... along the inner surface of the drum 7 to the top as shown in Figures 3(a) to (b), and then falling down under its own weight after reaching the top as shown in Figures 3(b) to (c).

[0046] The operating conditions of the drum 7, such as the amount of water added, the rotation speed of the drum 7, and the residence time in the drum, are not particularly limited and can be adjusted as desired depending on the properties of the soil and sand 1. For example, in the case of a drum with a diameter of 500 mm, the standard is to add water in the drum 7 in an amount approximately four times the volume of the soil and sand, with a rotation speed of 32.5 rpm and a residence time in the drum of 2 minutes.

[0047] At this time, the materials of each particle size contained in the soil and sand 1 are shaken while adhering to each other, and are subjected to impact when dropped, causing the adhesion between the materials of each particle size to weaken (disintegration process).

[0048] Furthermore, the soil 1 in the deflocculating means 2 is transferred to the discharge port 7c side of the drum 7 while being deflocculated due to the tilt of the drum 7, and is discharged from the discharge port 7c in a deflocculated state.

[0049] In addition, the mud deflocculation step may be performed by feeding the soil deflocculated by the mud deflocculation means 2 back into the mud deflocculation means 2, and repeating the work of deflocculating the soil by the mud deflocculation means 2 multiple times.

[0050] The discharged deflocculated soil 1 is sent to the classification unit 3, where the soil 1 sent from the deflocculation means 2 is passed through an upper screen 11 to remove and recover medium gravel 20 of 15 mm or more, while the remaining soil 21 of less than 15 mm is sifted onto a middle screen 12, which in turn removes and recovers small gravel 22 of 2 mm to 15 mm, while the remaining soil 23 of less than 2 mm is sifted into a storage section (not shown).

[0051] Furthermore, the residual sediment 23 in a slurry state that has been sifted into the storage section is sent by a pump (not shown) to the liquid cyclone classifier 10, where fine particles 24 of less than 0.075 mm in the residual sediment 23 float in the treated water of the liquid cyclone classifier 10 and are discharged from the top of the liquid cyclone classifier 10, and residual sediment 26, including sand particles 25 of 0.075 mm or more, is discharged as solids from the bottom. The standard sludge pressure when sending the residual sediment 23 to the liquid cyclone classifier 10 is 0.15 MPa, but this sludge pressure can be adjusted as desired depending on the properties of the residual sediment 23.

[0052] In addition, the treated water containing the fine particles 24 is returned to the feed pump and sent to the thickener tank as the supernatant liquid of the feed pump, where the fine particles 24 are removed and the salts (nutritional salts such as nitrogen and phosphorus) dissolved in the treated water along with the fine particles 24 are also removed.

[0053] At this time, the adhesion between the fine particles 24 and the sand particles 25 is weakened by the sludge deflocculation process, so that the fine particles 24 are suitably separated from the sand particles 25, and salts can be efficiently removed together with the fine particles 24.

[0054] Furthermore, the treated water and the fine particles 24 are separated by coagulation and sedimentation in the thickener tank, so the separated treated water can be reused as the washing water required in the classification process, thereby reducing the amount of water used.

[0055] Meanwhile, the residual sediment 26, including sand 25 of 0.075 mm or larger, discharged from the bottom of the liquid cyclone classifier 10 is sent to the lower screen 13, which removes and recovers the sand 25 of 0.075 mm to 2.0 mm, while also shaking out and recovering the fine particles 24 of less than 0.075 mm that could not be completely separated by the liquid cyclone classifier 10.

[0056] The sand fraction 25 of 0.075 mm to 2.0 mm recovered by the lower screen 13 is sent to the showering machine 14, and after the remaining fine particles 24 are removed by washing with the showering machine 14, the sand fraction 25 with an Fc (fine particle content) of 10% or less is recovered.

[0057] Furthermore, in cases where the fine particle content Fc is high, such as in dam sediment, and it is difficult to fully remove the fine particles using the hydrocyclone classifier 10, a high mesh separator 30 can be placed downstream of the lower screen 13 as the final step, thereby reducing the Fc of the sand content 25 recovered by the cleaning effect of the high mesh separator to 10% or less.

[0058] In the classification system for soil and sand 1 configured in this manner and the classification method using the same (hereinafter referred to as the present classification system, etc.), the soil and sand 1 is loosened by the sludge loosening means 2 before classification, making it possible to make the fine particles 24 of less than 0.075 mm easier to separate from the medium gravel particles 20, small gravel particles 22, sand particles 25, etc. of other particle sizes (hereinafter referred to as the sludge loosening effect).

[0059] With conventional technology, classification is carried out without going through the deflocculation process, which means that fine particles (in aggregate form) are discharged mixed with gravel and sand, resulting in poor classification quality and work efficiency. In order to improve classification quality, it was necessary to carry out multiple classification processes using multiple classification methods.

[0060] In contrast, in this classification system, by going through the sludge removal process, when the fine particles 24 are recovered by particle size in the classification unit 3, such as medium gravel 20, small gravel 22, and sand 25, the fine particles 24 become a homogeneous slurry state and can be removed efficiently. Therefore, the classification unit 3, which was previously composed of multiple classification means for removing the fine particles 24, can now be freely configured with any classification means selected according to the purpose.

[0061] In addition, in this classification system, the sludge-dissolving effect makes it easier to separate organic matter such as wood chips and leaves contained in the soil and sand 1 from the other fine particles 24, sand 25, small gravel 22, and medium gravel 20, allowing the organic matter to be removed efficiently.

[0062] Furthermore, salts (nutrients such as nitrogen and phosphorus) contained in the soil and sand 1 often adhere to the fine particles 24, and in this classification system, the sludge-dissolving effect makes it easy to separate the fine particles 24 from materials of other particle sizes, so by efficiently separating the fine particles 24 from materials of other particle sizes, the salts can also be efficiently removed from materials of other particle sizes.

[0063] Salts (nutrients) present in closed environments such as upstream reservoirs are feared to have an impact on the ecosystem when they are carried to downstream rivers or dams, causing eutrophication and disrupting the current nutrient balance. Therefore, if materials of other particle sizes (sand 25, small gravel 22, medium gravel 20) are used as downstream reducing materials, the salts can be efficiently separated from the materials of other particle sizes, making it possible to manage the impact of salts on downstream rivers, etc.

[0064] In the above-mentioned embodiment, the target sediment was explained as dam sediment created by dredging sediment accumulated in a dam lake, but the sediment is not limited to dam sediment and can be used for any type of sediment. [Explanation of symbols]

[0065] 1. Sediment (dam sediment) 2 Desilting means 3 Classification Units 4. Fixed quantity feeder 5. Conveyor belt 6 Swept-up Wings 7. Drums 8. Driving means 10. Liquid cyclone classifier 11 Upper Screen 12 Middle screen 13 Lower Screen 14 showering machine 20 medium gravel 21 Residual sediment 22 small pebbles 23 Residual sediment 24 Fine particles 25 sand 26 Residual soil and sand 30 High mesh separator

Claims

1. A soil classification system for classifying soil into desired particle sizes, The apparatus comprises a sludge thawing means for sludge thawing the soil and sand, and a classification unit for classifying the soil and sand sludge thawed by the sludge thawing means into desired particle sizes, A soil classification system characterized in that the classification unit can be configured by any combination of classification means.

2. 2. The soil classification system according to claim 1, wherein the mud deflocculating means comprises a horizontally placed drum having scraping blades protruding from its inner peripheral surface, and a driving means for rotating the drum.

3. A method for classifying soil and sand into desired particle sizes, comprising: After the mud deflocculation process in which the soil and sand are deflocculated by the mud deflocculation means, A method for classifying soil and sand, characterized in that the soil and sand dissolved in the sludge deflocculating step is classified into desired particle sizes using a classification unit constituted by any classification means.

4. 4. The method for classifying soil and sand according to claim 3, wherein the thawing step comprises repeating the thawing of the soil and sand by the thawing means a plurality of times.

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