JP3755018B2 - Sand-capping material and water-capping method - Google Patents

Description

  The present invention covers the surface of sludge (bottom mud) accumulated on the bottom of the lake and the sea, suppresses the elution of nutrient salts such as phosphorus and nitrogen from the bottom mud, and provides eutrophication to closed waters such as lakes and inland seas. The present invention relates to a sand-capping material for purifying bottom sediment and a sand-capping method.

  In closed water areas such as lakes and inner bays, eutrophication is caused by nutrient salts such as phosphorus and nitrogen flowing in from the outside, or contaminated pollutants accumulate on the lake and sea bottom of closed water areas, and harmful substances are eluted from these. As a result, red tides and blue tides were caused, causing serious damage to marine resources and the waterfront environment.

  Therefore, reducing the inflow load from the outside by improving the sewer network and river water treatment technology, aeration to the anoxic layer of the bottom water area in the closed water area, forcing the surface water and bottom water In addition to measures to prevent water stagnation by mixing, the surface of sludge (bottom mud) accumulated on the bottom of the lake and the sea is covered with sand, etc., and elution of nutrients such as phosphorus and nitrogen from the bottom mud Suppressing sand covering has been done.

  Further, the following invention is known as a method for purifying sediment using coal ash generated from a thermal power plant instead of sand.

  (1) Artificial zeolite obtained by hydrothermal chemical treatment of coal ash is laid on the upper surface of the sedimentary mud layer in the sea area and adsorbs nutrient salts to the artificial zeolite to prevent the elution of nutrient salts into water invention. (For example, refer to Patent Document 1).

  (2) Cover the bottom surface of the sediment containing the eutrophication component with sand, and further cover the sand with at least one adsorbable inorganic substance selected from zeolite, granulated slag, and cristobalite. An invention that suppresses the release of nutrient components into water and adsorbs these eutrophication components with zeolite or the like. (For example, refer to Patent Document 2).

  On the other hand, coal-fired fluidized bed thermal power generation using limestone having a desulfurization effect as a fluid medium is a power generation method that can remove sulfur oxides simultaneously with combustion, generates less nitrogen oxides, and has a low environmental load. There is known an invention in which artificial aggregate is manufactured by adding water or seawater to kneaded fluidized bed ash generated by such fluidized bed type thermal power generation and kneading it into a granule with a roll press or the like. (For example, refer to Patent Document 3).

Japanese Patent Laid-Open No. 2001-29951.

Japanese Patent No. 2716271.

JP 2000-169204 A.

  Conventionally, natural sand such as sea sand and mountain sand has been used as the covering sand, but in recent years, high-quality covering sand has been depleted and it has become difficult to obtain. In addition, problems such as the erosion of sand covered by the ocean current, etc., resulting in thinning of the layer thickness, deterioration of the function of inhibiting the dissolution of nutrients in the sand, and the re-elution of nutrients such as phosphorus and nitrogen from the bottom mud are apparent. Turned into.

  Moreover, the sand-capping material using natural sand maintains an 80-90% reduction effect immediately after sand-covering for nitrogen and COD even after 5 to 6 years of construction, but phosphorus is eluted immediately after sand-covering. It has been reported that the removal function is not sufficient.

  In addition, the invention described in Japanese Patent Application Laid-Open No. 2001-29951 requires labor and cost to obtain an artificial zeolite, and the coal ash itself does not have self-hardness, so that it is placed in a bag having water permeability when laying. It had to be stored, laminated with soil, mixed with a binder, and processed into a plate shape.

  The invention described in Japanese Patent No. 2716271 has a problem of high cost because it uses a large amount of zeolite and cristobalite.

  An object of this invention is to provide the sand-capping material which can suppress the elution of phosphorus from bottom mud effectively, and is low-cost and high in durability, and its sand-capping method.

  Accordingly, the inventors of the present invention have combusted ash (hereinafter referred to as fluidized bed ash) in a coal-fired fluidized bed furnace using limestone as a fluid medium, which contains a large amount of calcium, and is pressurized by adding an appropriate amount of water. Focusing on the fact that this coal-fired fluidized bed thermal power plant will have a small environmental impact and will increase in the future and a large amount of fluidized bed ash will be generated. The fluidized bed ash granule was used as a sand covering material instead of natural sand.

  As a method for producing a high-strength fluidized bed ash granule, there is, for example, “a method for producing an artificial aggregate using fluidized bed ash as a raw material” described in Japanese Patent Application No. 2002-249515. And kneaded, and then pressed by a roll press to form a granule.

  Furthermore, the fluidized bed ash granule is appropriately cured by, for example, curing in a constant temperature curing room having a room temperature of 20 ° C. or higher and a humidity of 95% or higher for a predetermined period of time to increase the strength, the water absorption expansion and the substance in the seawater. It can prevent destruction and mudification by reaction. In addition, the manufacturing method of a fluidized bed ash granular material is not restricted to the said method.

  According to the sand-capping material and the method for sand-covering the bottom of the water, the following effects can be obtained.

  (1) Since calcium contained in fluidized bed ash particulates reacts with phosphorus to produce hydroxide apatite, phosphorus from the bottom mud can be fixed to prevent elution into water.

(2) Since CaCO ₃ is generated by the formation of hydroxide apatite or the reaction between carbon dioxide in water and calcium contained in the fluidized bed ash particulates, fluidized bed ash particulates are connected to each other, and the sand is covered by water flow. It can prevent the movement and loss of materials.

(3) Since the fluidized bed ash particulate matter becomes neutral by being covered with CaCO ₃ generated on the surface by the carbonation action in seawater, it becomes a bedrock base for seaweed.

  (4) Since the particle size of the fluidized bed ash granule is 3 mm or more and 30 mm or less, good handleability and sufficient shielding effect can be obtained, and a state with a high oxidation-reduction potential equivalent to that of the conventional sand-capping material is obtained. It can be formed in the sand-capping layer, preventing the elution of nutrient salts such as phosphorus and nitrogen, and water pollution caused by hydrogen sulfide and methane.

  (5) Since the particle size of the fluidized bed ash granule was adjusted to 2 mm or more and 20 mm or less after crushing the fluidized bed ash granule, an oxygen-rich state equivalent to the conventional natural sand was used in the covered sand layer. It can be formed, and good handleability and sufficient bottom mud blockage can be obtained.

  (6) Fluidized bed ash discharged from a fluidized bed thermal power plant can be used as an effective resource, and waste can be reduced.

  According to the sand-capping material and the method for sand-covering a water bottom according to the present invention, the following effects can be obtained.

According to the first aspect of the present invention, the granular material formed into granules by adding water or seawater to the combustion ash of the coal-fired fluidized bed furnace using limestone as a fluid medium and kneading, and applying pressure to the kneaded combustion ash. Since it is made of sand-capping material, it can cover the bottom mud as normal sand-capping material, and the calcium contained in a large amount reacts with phosphorus to produce hydroxide apatite, so that the phosphorus can be effectively eluted from the bottom mud. Can be suppressed. Since CaCO ₃ is generated and the fluidized bed ash particulates are connected to each other, it is possible to prevent movement and outflow of the sand-capping material itself due to a sea current or the like, which is a problem with conventional sand-capping. When CaCO ₃ is generated on the surface, it is neutralized, so that a seabed on which seaweed grows can be formed.

  According to invention of Claim 2, since the particle size of the sand covering material of Claim 1 was 3-30 mm, formation of a fluid bed ash granular material is easy by setting it as this particle size, Effective sand covering can be realized. In addition, when the particle size is 3 mm or less, it is difficult to produce, and when it is 30 mm or more, the handleability of the fluidized bed ash particulate matter and the blockage when sanding is not sufficiently obtained.

  According to the invention described in claim 3, the sand-carrying material described in claim 1 is crushed, and the particle size of the fluidized bed ash granule is set to 2 to 20 mm. An oxygen state can be formed in the sand cover layer, and the elution of nutrient salts such as phosphorus and nitrogen can be prevented, water pollution by hydrogen sulfide, methane, etc. can be prevented, and good handleability and sufficient blockage can be obtained.

  According to the invention described in claim 4, since the sand covering material according to any one of claims 1 to 3 is deposited on the bottom mud upper layer, sand is covered with a sand covering material containing a large amount of calcium. Therefore, the dissolution of phosphorus from the bottom mud is suppressed, and the fluidized bed ash particulates are not easily washed away and can provide an effective sand covering method for a long period of time. Moreover, according to this method, since the surface of the sand-capping layer is neutralized, it is possible to form a seabed on which seaweeds land.

  DESCRIPTION OF EMBODIMENTS An embodiment of a sand covering material and sand covering method according to the present invention will be described with reference to the drawings.

  First, the manufacturing method of a sand covering material is demonstrated. A suitable amount of water, seawater, or a mixture of water and seawater is added to and mixed with the combustion ash (fluidized bed ash) of a coal-fired fluidized bed furnace using limestone as a fluid medium without adjusting the particle size. The powder weight ratio of water or seawater to be added (as a powder, when cement is mixed with fluidized bed ash, the cement is included) is about 12 to 20% with respect to 100 parts by weight of fluidized bed ash. . If the weight ratio is less than this or more than this, the moldability is hindered.

  The fluidized bed ash and water are kneaded uniformly using a mixing device such as a mortar mixer. When the kneading is completed, the fluidized bed ash is pressed with a roll press to form a granular shape. The roll press machine has a pressing force of about 50 to 70 kN / cm as a linear load, and is performed by installing a predetermined form called a segment in the roll part. The fluidized bed ash is formed into granules having a diameter of 3 to 30 mm. If the particle size is 3 mm or less, it is difficult to produce, and if it is 30 mm or more, the handling of fluidized bed ash particulate matter becomes inconvenient, and there are problems that the gap in the sand-capping layer increases and the outflow of bottom mud cannot be sufficiently suppressed. The roll press machine can arbitrarily change the shape of the formed body by replacing the formwork, and the fluidized bed ash granule is not limited to a spherical shape.

  When the strength of the fluidized bed ash granule is not sufficient, curing is performed for about 4 days in a high temperature curing room (for example, 30 ° C. to 60 ° C., humidity of 95% or more) in order to increase the strength to a predetermined value. The curing is performed as necessary, and the curing period is not limited to 4 days.

  The formed fluidized bed ash granule is laid at a predetermined thickness on the bottom mud such as a lake or an inland sea. When laying fluidized bed ash particulates, it is more likely that the fluidized bed ash particulates will spread into the water during the fall or be settled down when it is laid on the bottom of the water via a guide pipe that is poured into the water rather than directly from the water surface. It is preferable in terms of preventing the bottom mud from rising. The thickness of the sand covering layer is about 30 to 100 cm. Note that the thickness of the layer is not limited to this, and is appropriately adjusted according to the depth of the bottom mud, the degree of dirt, the amount of running water, and the like.

  In addition, the fluidized bed ash granule may be crushed by a crusher or the like and sieved to adjust the particle size to 2 to 20 mm.

  FIG. 1 shows a state where fluidized bed ash particulates are laid on the bottom of the water as sand-capping material. As shown in FIG. 1, a fluidized bed ash granule 1 as a sand covering material is laid with a predetermined thickness on the surface of the bottom mud 4. Then, a part of the upper layer of the bottom mud 4 and the fluidized bed ash granule 1 are in an aerobic state containing more oxygen than the bottom mud 4 of the lower layer, and an oxide layer 5 is formed in the upper layer of the bottom mud 4. Is done. The fluidized bed ash granule 1 provides the following operational effects.

  The fluidized bed ash granule laid covers the upper surface of the bottom mud and prevents physical nutrients from eluting from the bottom mud in the same manner as conventional sand-covered sand.

  Calcium contained in the fluidized bed ash granule reacts with phosphorus in the bottom mud to produce hydroxide apatite, so that phosphorus in the bottom mud is insolubilized and prevented from dissolving in water. The reaction formula between calcium and phosphorus is shown below.

3HPO ₄ ²⁻ + 5Ca ²⁺ + 4OH ⁻ = Ca ₅ (OH) (PO ₄ ) ₃ + 3H ₂ O
Fluidized bed ash granules are chemically linked by the formation of hydroxide apatite shown in the above reaction formula or the reaction of carbon dioxide in water with calcium contained in the fluidized bed granules to generate CaCO _3. Therefore, movement and loss due to ocean currents can be prevented.

The fluidized bed ash granule can generate CaCO _{3 on the} surface by the carbonation action in seawater (CaO + CO ₂ → CaCO ₃ ), and thereby the surface becomes neutral and the seabed on which seaweed can be deposited can be obtained.

  A layer with a high oxidation-reduction potential can be formed in the sand-capping layer to prevent elution of nutrient salts such as phosphorus and nitrogen, and water pollution due to hydrogen sulfide, methane, etc. can be prevented.

  By crushing the formed fluidized bed ash granule and adjusting the particle size to cover the sand, for example, by adjusting the particle size to 2 to 20 mm, it contains much oxygen equivalent to that of natural sand that has been used conventionally. The effect of sand covering similar to the case of using natural sand such as forming an aerobic layer or shielding the upper surface of the bottom mud can be obtained.

  Fluidized bed ash generated from the power plant can be used as an effective resource without being discarded. The pH value when fluidized bed ash particulates are used as sand-capping material satisfies the environmental standard value for water pollution of 5.0 or more and 9.0 or less (in the sea area), and covers standard sand. The turbidity is smaller than that used in the above, and it can be considered that there is almost no water pollution due to the laying of fluidized bed ash granules.

  Next, an experimental example of sand covering using fluidized bed ash particulates will be described.

In the experiment, 15% by weight of water was added to and mixed with combustion ash (fluidized bed ash) of a coal-fired fluidized bed furnace using limestone as a fluid medium, and after kneading, it was pressurized at a loading pressure of 50 N / mm ² with a roll press. The fluidized bed ash granule obtained by molding (hereinafter referred to as granule) was sieved with a 9.6 mm sieve, and a sand-clad material whose particle size was adjusted to a particle size of less than 9.6 mm was used. As a comparative example, Toyoura standard sand was used. For the bottom mud, seabed mud collected in Tokyo Bay was used, and commercially available artificial seawater was used for the seawater.

Experimental conditions are as shown in the following a to e.
a. No sand covering was performed, and only the bottom mud was 10 cm deep.
b. Toyoura standard sand was covered with 3 cm of sand at a depth of 10 cm.
c. Toyoura standard sand was covered with 6 cm of sand at a depth of 10 cm.
d. The granular material was covered with 3 cm of sand at a depth of 10 cm.
e. The granular material was covered with 6 cm of sand at a depth of 10 cm.

  In the experiment, as shown in FIG. 2, the bottom mud 4 is introduced from the bottom of the 2 liter measuring cylinder 2 to a height of 10 cm, and the sand covering material 6 is placed on the above-mentioned b to e so as not to be mixed with the bottom mud 4. The artificial seawater 8 was poured using a Komagome pipette to prevent the bottom mud 4 from being rolled up.

  After injecting the artificial seawater 8, it was allowed to stand for 6 hours, and 100 cc of seawater was collected at a position 5 cm from the surface of the sand-capping material 6 (the bottom mud surface in the case of a) (hereinafter referred to as sample water). About each sample water, the value of items, such as TP (phosphorus content), pH, and TOC (organic substance amount), was measured. Further, water was collected in the same manner on the 7th, 21st, 30th, and 70th days of the age, and each item was measured.

  The experimental results are shown in FIGS. From this result, the following can be understood.

  When fluidized bed ash particulates are used for the sand-capping material 6, it can be seen from the results shown in FIG. 3 that phosphorus elution (TP) is suppressed. Regarding pH, as shown in FIG. 4, the value does not increase to 9 or more, and it is considered that there is little influence on the organism. Regarding the TOC (amount of organic matter), it was confirmed that it was less than when standard sand was used as shown in FIG.

In addition, fluidized bed ash granules immersed in seawater for 91 days or more are observed to adhere to each other due to the formation of CaCO ₃ , and are not observed to be disintegrated or muddy, and the particle shape is maintained. It was. Further, whitening was observed on the entire surface, and it was confirmed by X-ray diffraction analysis that calcium carbonate was formed.

It is a figure which shows one Embodiment of the sand covering state concerning this invention.

It is a figure which shows an experimental apparatus.

It is a figure which shows an experimental result.

It is a figure which shows an experimental result.

It is a figure which shows an experimental result.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Fluidized bed ash granule 2; Measuring cylinder 4; Bottom mud 5; Oxidation layer 6; Sand-capping material 8;

Claims (4)

A sand-capping material that is laid on the upper surface of the bottom mud and covers the upper surface of the bottom mud, wherein the combustion is carried out by adding water or seawater to the combustion ash of a coal-fired fluidized bed furnace using limestone as a fluid medium, and kneading. A sand-capping material characterized in that it is formed into a granular shape by applying pressure to ash. The sand-capping material according to claim 1, wherein the particle size is 3 to 30 mm. The sand-capping material according to claim 1, wherein the combustion ash formed into a granular shape is crushed to a particle size of 2 to 20 mm. A sand-covering method for a water bottom, comprising depositing the sand-covering material according to any one of claims 1 to 3 on an upper layer of bottom mud and covering the sand.

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