JP7686482B2 - Waste incineration ash processing method and processing system - Google Patents

Description

This invention relates to the treatment of bottom ash from waste incineration ash.

It is known that metal and solid foreign matter are separated from the bottom ash in waste incineration ash, and the remaining ash is used as a cement raw material, etc. For example, in Patent Document 1 (Patent 4979164), the bottom ash is processed through a sieve with 20 mm openings and a magnetic separator to separate large foreign matter and metals from the ash. The ash is then crushed in a crusher to an average particle size of 1 mm or less, and then processed through a sieve with 5 mm openings to separate small solid foreign matter. The under-sieve components are then washed with water, the solids are separated, and the effluent is treated as wastewater.

Patent 4979164

By the way, bottom ash can contain wire-like foreign objects. When wire-like foreign objects are put through a vibrating sieve, a typical type of sieve, the vibrations cause the wire-like foreign objects to stand up and pass through the sieve openings in a dancing manner. Furthermore, since a large amount of incineration ash adheres to the wire-like foreign objects that pass through the sieve, they may not be adsorbed by a magnetic separator. It is difficult to completely remove wire-like foreign objects using either a vibrating sieve or a magnetic separator, so there is a possibility that the wire-like foreign objects may become mixed into cement raw materials, etc.

The objective of this invention is to more reliably separate wire-like foreign matter from ash.

In the method for treating waste incineration ash of this invention, the main ash from a waste incinerator is treated with a roll screen to separate it into an under-screen component that falls below the roll screen and an above-screen component that passes above the roll screen (a roll screen step), the under-screen component and the above-screen component are treated separately with magnetic force to separate the magnetic materials (a first magnetic separation step), and after separating the magnetic materials, the under-screen component and the above-screen component are sifted into non-magnetic foreign matter and ash (a sieving step). Note that magnetic separation refers to separating magnetic materials from non-magnetic materials by magnetic force.

The waste incineration ash treatment system of this invention is configured to separate the waste incineration ash into magnetic materials, non-magnetic foreign matter, and ash by using a magnetic separator that uses magnetic force to separately treat the under-screen components that have fallen to the bottom of the roll screen and the above-screen components and separate the magnetic materials from the under-screen components and the above-screen components after separating the magnetic materials from the above-screen components.

A roll screen is a device equipped with rotating rolls that allows small objects to fall through the openings between the rolls and allows larger objects to climb over the openings and be carried away. Because roll screens do not apply vibrations, wire-like foreign objects rarely rise up due to vibrations and fall vertically through the openings, but rather climb over the openings and are carried away. With roll screens, wire-like foreign objects and other foreign objects are primarily sorted by their long diameter and become the above-screen components. Foreign objects with smaller long diameters, such as screws, gravel, and pottery fragments, fall through the openings of the roll screen along with the ash and become the below-screen components.

The components above the screen are treated with magnetic force to separate wire-like foreign matter. The components below the screen are treated with magnetic force separately from the components above the screen to separate small metal screws and other objects from the ash. After removing the magnetic objects, the components above the screen and below the screen are sieved to separate non-magnetic foreign matter.

In this way, wire-like foreign objects are removed from the bottom ash, as well as other magnetic and non-magnetic objects. Because the foreign objects can be sufficiently removed from the bottom ash, the bottom ash after the foreign object separation is suitable for use as a cement raw material. Wire-like foreign objects can also be recovered from the bottom ash.

Preferably, a crushing step in which the components on the screen are crushed by an impact crusher is performed between the roll screen step and the first magnetic separation step. Crushing makes it easier for ash that has gotten inside large foreign objects such as empty cans to fall off, and some of the ash attached to foreign objects such as wires also peels off and falls off. When the ash falls off, the foreign objects become smaller in size and lighter. With the ash removed and the foreign objects lighter, it becomes easier to separate foreign objects such as wires and large foreign objects by magnetic force.

Preferably, when the amount of foreign matter in the bottom ash is large, the roll screen step is performed, and when the amount of foreign matter in the bottom ash is small, the roll screen step is omitted and a second magnetic separation step is performed in which the bottom ash is processed by magnetic force and magnetic substances are separated. Since the roll screen step is omitted for bottom ash containing little foreign matter, the processing of the garbage incineration ash is simplified. The amount of foreign matter may be determined each time the incineration ash is received, or may be determined in advance for each source of the incineration ash. The amount of foreign matter is determined, for example, by passing the incineration ash through a sieve with the same mesh size as the sieve used in the screening step, and a large amount of foreign matter is determined when the weight ratio of the sieved components to the incineration ash is 10% or more.

Preferably, in the magnetic separation step, the under-screen component and the above-screen component are processed by separate magnetic separation devices. That is, small magnetic objects in the under-screen component and large magnetic objects in the above-screen component are magnetically separated separately. The above-screen component has a lower ash content than the under-screen component, so it is easier to magnetically separate it if it is not mixed with the under-screen component. Also, the small magnetic objects in the below-screen component do not have a large amount of ash attached to them. At least, they do not have a thick layer of ash attached to them. This allows them to be easily separated by magnetic force.

Preferably, a wet step is further performed in which water is added to at least a part of the ash sieved in the sieving step, and a water washing step is further performed in which the magnetic material and the non-magnetic material are placed in separate water-permeable baskets and washed with water, and at least a part of the wastewater generated in the water washing step is used in the wet step, for example, in a state where it contains the ash. By using the water-permeable baskets, water washing can be easily performed. In addition, the wastewater generated in the water washing step can be used in the wet step and can be reused in the treatment system.

FIG. 1 is a diagram showing an overview of a first embodiment. FIG. 1 is a plan view of a main part of a roller screen used in a first embodiment; FIG. 1 is a vertical cross-sectional view of a roll in a roll screen used in a first embodiment. FIG. 2 is a diagram showing an overview of a second embodiment. Schematic cross-sectional view of a net cage and a water tank used in the second embodiment. FIG. 13 is a diagram showing an outline of a third embodiment. FIG. 13 is a diagram showing an outline of a fourth embodiment.

The following are examples of how to implement the present invention. The scope of the present invention should be determined based on the claims, taking into account the description in the specification and well-known techniques in this field, and in accordance with the understanding of those skilled in the art.

Example 1
Figures 1 to 7 show embodiments of a method and system for treating incineration ash, and Figures 1 to 3 show the first embodiment. As shown in Figure 1, a receiving hopper 1 receives bottom ash from a waste incineration plant and supplies it to a roll screen 2. Bottom ash is incineration ash discharged from the bottom of a stoker furnace or the like, and ash discharged together with exhaust gas is called fly ash.

The roll screen 2 is shown in Figures 2 and 3. The roll screen 2 has multiple rolls 20, and a pair of a small diameter flange 21 and a large diameter flange 22 protrudes radially from the roll shaft 24 of each roll 20. These flanges 21, 22 are sometimes called disks in industrial terms. The large diameter flange 22 and the small diameter flange 21 of adjacent rolls 20, 20 face each other, and the gap between the facing flanges 21, 22 is narrow. Each roll 20 is provided with multiple pairs of flanges 21, 22. Between the roll shafts 24, 24, there is an opening 25 sandwiched between the left and right flanges 21, 22. Ash and small foreign matter in the main ash fall from the opening 25, and large foreign matter is transported without passing through the opening 25.

As shown in Figure 3, the flanges 21 and 22 are triangular to pentagonal polygons with the center of the sides bulging outward. With flanges 21 and 22 of this shape, it is difficult for foreign matter to pass through the gap between the flanges 21 and 22. If the size of the opening 25 in the direction parallel to the roll axis 24 is a and the size in the direction perpendicular to it is b, then a:b is preferably, for example, about 1:1 to 1:2. Size a is preferably, for example, 5 mm or more and 50 mm or less, and size b is preferably, for example, 10 mm or more and 60 mm or less. The rolls 20 rotate in the same direction, and the main ash is transported by the rolls 20. The component that falls from the opening 25 is the under-screen component, and the component that does not fall is the above-screen component.

The adjacent openings 25, 25 are separated by flanges 21, 22, and wire-like foreign matter cannot pass through the gap between the flanges 21, 22. In order for wire-like foreign matter to pass through the opening 25, it must rise vertically due to vibration, but the roll 20 does not vibrate the main ash. As a result, the wire-like foreign matter does not pass through the opening 25 and is discharged as an on-screen component.

The number of rolls 20 can be any number, and the flanges 21, 22 can be circular instead of polygonal. Also, instead of a combination of large and small diameters, flanges of the same diameter can be arranged facing each other between adjacent rolls, or can be arranged alternately. However, in the roll screen 2 of Figures 2 and 3, it is difficult for wire-like foreign matter to pass between adjacent openings 25, 25, so wire-like foreign matter is unlikely to be mixed into the components below the screen.

The magnetic separator separates the magnetic materials from the under-screen components that fall through the openings 25 in the roll screen 2 and the above-screen components. Because the sizes of the magnetic materials (mainly metals) differ between the under-screen components and the above-screen components, it is preferable to process them using different magnetic separators 4, 5. The magnetic separators 4, 5 may be electromagnetic, or may use a magnetic pulley with a permanent magnet attached to the end of a belt conveyor, so that magnetic materials and other materials fall at different positions.

The ash and solid foreign matter that pass through the magnetic separators 4 and 5 are passed through a sieve 6 to separate the solid foreign matter from the ash. The sieve 6 is, for example, a vibrating sieve, with a preferred mesh size of 8 mm to 25 mm, but the type and range of mesh size of the sieve are optional. The ash that passes through the sieve 6 is stored in a silo 7 or the like, a portion of it is shipped as unwashed ash, and the remainder is subjected to wet grinding, water washing, and other processes to be desalted before being shipped. In addition, the magnetic material from the magnetic separators 4 and 5 is collected as magnetic foreign matter, and the components that remain on the sieve from the sieve 6 are collected as non-magnetic foreign matter. In this way, wire-like foreign matter and the like are prevented from passing through the sieve 6 and being mixed into the ash to be shipped.

Example 2
A second embodiment is shown in Figs. 4 and 5, and is the same as the embodiment in Figs. 1 to 3 except for the points specifically mentioned. In the second embodiment, the on-screen components of the roll screen 2 are crushed by an impact crusher 3. The impact crusher 3 is, for example, a device in which a plurality of hammers are attached to a rotating shaft, and the rotating shaft is rotated to apply impacts from the hammers to the objects to be treated. In the impact crusher 3, the objects to be treated are sandwiched between a fixed gate and a rotating hammer, or between the hammer of one rotating shaft and another rotating shaft, and impacts are applied. Such impact crushers are put into practical use as crushers or shredders. Incidentally, a crusher using a toggle mechanism, which sandwiches the objects to be treated between a movable jaw and a fixed plate and gradually increases the pressure to crush them, is not suitable for separating ash from foreign matter.

A large amount of ash is attached to the foreign objects on the screen. If the ash is not peeled off from the foreign objects, the ash recovery rate will decrease, and the magnetic objects may not be able to be separated in the subsequent magnetic separator due to the attached ash. Therefore, by applying an impact with the impact crusher 3, the components on the screen (metallic and non-metallic foreign objects) are crushed and the ash attached to the foreign objects is peeled off. When an impact is applied, the ash attached to the foreign objects peels off. Ash may penetrate into the inside of containers such as empty cans and bottles, but by crushing the container, the ash inside can be separated from the container. In addition, some of the ash attached to the foreign objects peels off, making the foreign objects smaller and lighter. In addition, lumps of ash are also crushed, and the ash can be separated from the foreign objects. As a result, the magnetic foreign objects can be reliably separated in the next magnetic separator 5, and the ash recovery rate is also improved. Note that if the magnetic foreign objects do not pass through the impact crusher 3, they may not be magnetically selected in the magnetic separator 5.

The magnetized materials from the magnetic separators 4 and 5 are placed in a wire basket 8 in a water tank 10 and washed with water. Similarly, foreign materials remaining on the sieve 6 are placed in a wire basket 9 in a water tank 11 and washed with water. The wire baskets 8 and 9 and the water tanks 10 and 11 are shown in FIG. 4. Ash adhering to the magnetized materials (magnetic materials such as metals) and non-magnetic foreign materials can be removed by pouring water over the wire baskets 8 and 9 or vibrating the wire baskets 8 and 9 in the water tanks 10 and 11 using a device not shown. Removing the ash makes it easier to reuse the magnetized materials and non-magnetic foreign materials. The wire baskets 8 and 9 need only be permeable to water and not foreign materials, and any basket other than a wire basket can be used.

The ash stored in the silo 7 from which foreign matter has been removed is transported to, for example, a cement factory and used as part of the raw material for cement clinker. Cement clinker has an upper limit on the chlorine concentration. Therefore, part of the ash from which foreign matter has been removed is pulverized in a wet grinder 13 and immersed in water in a desalination tank 14 to dissolve the chlorine. Then, the ash and water are separated by a solid-liquid separator 15 such as a filter press. In this way, the average salinity of the treated ash is reduced to within an acceptable range. The wastewater separated by the solid-liquid separator 15 is treated in a wastewater treatment device 16, and part of the wastewater is made to comply with environmental standards before being discharged. When fly ash generated at a waste incineration plant is also treated, dioxins in the fly ash are removed by a dioxin removal device 12. The treated fly ash is then treated in a desalination tank 14.

The washing water used in the water tanks 10, 11 to separate foreign matter from ash contains ash. Even if the wastewater from the water tanks 10, 11 is used in the wet grinding machine 13 or the desalination tank 14 while still containing ash, it does not contaminate the object to be treated or the surrounding equipment. Therefore, the wastewater from the water tanks 10, 11 is reused in the wet step (wet grinding or desalination) in the treatment system. If the wastewater contains a high amount of ash, it may be treated in the solid-liquid separator 15. Alternatively, the ash may be allowed to settle from the wastewater, the supernatant may be used in the wet step, and the sediment may be treated in the solid-liquid separator 15. Furthermore, the wastewater may be used in the wet step without being treated to separate the ash from the wastewater.

Example 3
FIG. 6 shows a third embodiment, which is the same as the embodiment of FIG. 1 to FIG. 3 except for the points that are particularly pointed out. In the third embodiment, when the amount of foreign matter in the bottom ash is large, it is treated with a roll screen, and magnetic substances are separated by magnetic separators 4 and 5. When the amount of foreign matter in the bottom ash is small, the treatment with the roll screen is omitted, and the bottom ash is received and treated with the magnetic separator 4 via a hopper. The amount of foreign matter may be determined each time the incineration ash is received, or may be determined in advance for each source of incineration ash. The amount of foreign matter is determined, for example, by putting the incineration ash through a sieve with the same mesh size as the sieve used in the sieving step, and the weight ratio of the sieved component to the incineration ash is 10% or more, which indicates a large amount of foreign matter. The sieve 6 used in the sieving step has a mesh size of 8 mm or more and 25 mm or less, for example, so a sieve with a mesh size of 8 mm or more and 25 mm or less is used for determining the amount of foreign matter. In the third embodiment, the treatment of the roll screen 2 and the magnetic separator 5 is omitted for the bottom ash containing a small amount of foreign matter, so that the treatment of the refuse incineration ash is simplified.

Example 4
Fig. 7 shows the fourth embodiment, which is similar to the second embodiment shown in Fig. 4 and Fig. 5 except for the points specifically mentioned. In the fourth embodiment, the treatment of the roll screen 2, the crusher 3, and the magnetic separator 5 is omitted for the bottom ash containing a small amount of foreign matter, so that the treatment of the refuse incineration ash is simplified compared to the second embodiment.

Reference Signs List 1 Receiving hopper 2 Roll screen 3 Impact crusher 4, 5 Magnetic separator 6 Sieve 7 Silo 8, 9 Wire cage 10, 11 Water tank 12 Dioxin removal device 13 Wet grinder 14 Desalting tank 15 Solid-liquid separator 16 Wastewater treatment device 20 Rolls 21, 22 Flange 24 Roll shaft 25 Opening

Claims (2)

A roll screen step in which the bottom ash from the waste incinerator is treated with a roll screen and separated into an under-screen component that falls below the roll screen and an over-screen component that passes through the upper side of the roll screen;
a first magnetic separation step in which the under-screen component and the over-screen component are separately treated with a magnetic force to separate magnetic substances;
a sieving step for separating the under-screen component and the over-screen component after separating the magnetic material into non-magnetic foreign matter and ash ;
a wet step of adding water to at least a portion of the ash screened in the screening step and treating the ash;
a water washing step of accommodating the magnetized object and the foreign object in separate water-permeable baskets and washing them with water;
At least a portion of the wastewater generated in the water washing step is used in the wet step.
A method for treating garbage incineration ash, which separates the garbage incineration ash into magnetic materials, non-magnetic foreign materials, and ash. If the amount of foreign matter in the bottom ash is large, the roll screen step is carried out;
2. The method for treating refuse incineration ash according to claim 1 , characterized in that when the amount of foreign matter in the bottom ash is small, the roll screen step is omitted and a second magnetic separation step is carried out in which the bottom ash is treated by magnetic force to separate magnetically attached matter.

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