JPH10230239A - Slag recovering device of waste and slagging method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a slag recovering device for waste and slagging method which are easy to handle and are capable of maintaining the reducing atmosphere of a fluidized bed and directly yielding slag recoverable as useful resources. SOLUTION: This slag recovering device for waste consists of a fluidized bed gasifying furnace 1 which gasifies the waste 11 at a low temp. and a melting furnace which further burns the gaseous materials and char discharged from this fluidized bed gasifying furnace at a high temp. and slags the incombustibles or nongasified matter. The device has the melting furnaces in two stages in series so that the molten slag generated in the melting furnace 5 of the fore stage is cooled to solidify by bringing the slag into contact with the fluid medium of the fluidized bed gasifying furnace 1. The device has a curing device 7 having a heating mechanism which is communicated with the melting furnace 6 of the post stage and executes the heating and heat insulating of the molten slag generated by this melting furnace and a separating mechanism for separating the slag and the metal. This curing device is an external heating type melting furnace 6. The fluidized bed gasifying furnace is a swivel type fluidized bed gasifying furnace and the melting furnaces are preferably selfcombustion type swivel melting furnaces.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the conversion of waste into slag, and more particularly, to a waste slag recovery apparatus for melting waste by gasifying or gasifying and burning non-combustible waste and converting the waste into slag. It relates to a slag conversion method.

[0002]

2. Description of the Related Art Conventionally, in waste treatment, incineration as intermediate treatment and landfill as final disposal have been performed.
However, due to the ever-increasing amount of waste, there is a concern that the final disposal site will be drained, and during the incineration stage, substances such as dioxin, SOx, and NOx are generated, which is seriously affecting the environment. In such a situation, a gasification or gasification combustion-melting system has been proposed for performing a safe intermediate treatment and finally reducing the volume of waste. The system utilizes the energy of the gas produced,
The product gas can be used as a raw material for chemical synthesis without providing a complete combustion process. In addition, the generated slag can be reduced in volume to about 1/3 of ash, and has an excellent property that heavy metals and the like can be sealed in the slag to prevent elution into the soil. Since it passes through a high temperature of 〜1500 ° C., complete decomposition of dioxin and the like is possible. Further, thermal NOx derived from the introduced air can be minimized. Furthermore, double and triple measures are taken in terms of environmental protection through a waste gas treatment process and the like.

[0003] On the other hand, the safety of slag has been confirmed, and its use has been studied mainly for construction materials such as concrete aggregates, roadbed materials and others. However, slag is usually required due to transport requirements after discharge.
Generally, it is granulated and collected as granules of about several mm. For this reason, the particle size varies, needle-like projections are formed, and it is difficult to say that the material is easily handled.Moreover, depending on the melting method, slag and heavy metal are mixed and discharged, so that the slag There was a problem that the recycling could not be carried out effectively, and a separate slag regeneration step had to be provided for use.

[0004]

DISCLOSURE OF THE INVENTION In view of the above prior art, the present invention is directed to a slag which is easy to handle, can maintain a reducing atmosphere of a gasification fluidized bed at a high temperature, and is directly useful as a waste resource in a waste plant. It is an object of the present invention to provide a waste slag recovery apparatus and a slag conversion method capable of obtaining wastewater.

[0005]

According to the present invention, there is provided a fluidized-bed gasifier for gasifying waste, preferably at a low temperature, and a fluidized-bed gasifier connected to the fluidized-bed gasifier. In a waste slag recovery apparatus comprising a gaseous substance discharged from a fluidized bed gasifier and a char, and more preferably, a melting furnace which burns or gasifies at a high temperature and slags an incombustible substance or a non-gasified substance, The melting furnace is provided in two stages in series, and the molten slag generated in the preceding melting furnace is brought into contact with the fluidized medium of the fluidized-bed gasification furnace to be cooled and solidified. The apparatus is provided with a curing mechanism having a heating mechanism for heating and keeping the molten slag generated from the furnace, and a separation mechanism for separating the slag and the metal. In the slag recovery device, it is preferable to use an externally heated melting furnace as a curing device, use a swirling type fluidized bed gasification furnace as a fluidized bed gasification furnace, and use a self-combustion type swirling melting furnace as a melting furnace. is there.

Further, in the present invention, a gasification step of gasifying waste at a low temperature in a fluidized-bed gasification furnace, and gaseous matter and char obtained in the gasification step are further burned at a high temperature.
In a method for slagging waste which is treated in a gasification and melting step for slagging incombustibles or non-gasified substances, a part of the molten slag generated in the gasification and melting step is introduced into a fluidized medium of the fluidized bed gasifier. In addition to cooling and solidifying, the remainder is introduced into a curing step having a heating function and a separating function, aged, and then discharged. In the above method, in the curing step, a substance containing a reducing agent, a magnesium compound and, if necessary, a basicity adjusting compound is preferably added to the molten slag. The substance containing the magnesium compound and the basicity adjusting compound as necessary is added to the gasification portion or the melting portion in the gasification and melting step, so that sufficient mixing can be obtained, so that more uniform slag can be generated. Become.

It is convenient to substitute the reducing agent with slag to which carbon and a fluidized medium accumulated during operation are attached to the bottom of a fluidized-bed gasifier used for gasification. Then, the fine slag generated when the slag generated from the curing device is recycled can be used for replenishment of a reduced amount of the fluidized medium of the fluidized bed gasifier used for gasification. In the above method, in the gasification melting step, a two-stage melting furnace is used,
A fluidized medium can be circulated between the former melting furnace and the fluidized bed gasifier used in the gasification step, and the fluidized bed gasifier used in the gasification step is replaced with a supply of combustion air. Alternatively, a part of the exhaust gas from the gasification melting step can be used.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In general, a fluidized bed gasifier used for gasification of wastes needs to perform sufficient gasification while maintaining a low temperature. If not more than (° C.), gasification itself may be insufficient. For this reason, gasification is promoted by increasing the amount of air to keep the temperature of the fluidized medium high, but there is a problem that it is difficult to maintain the reducing atmosphere of the fluidized bed gasifier. In the present invention, as the above solution, the melting furnace is divided into two stages of a former stage and a latter stage, and the slag of the former melting furnace is returned to a fluidized bed gasifier, and is brought into contact with a fluidized medium to be cooled and solidified. Used as heat source for gasifier. The invention for returning the molten slag from the melting furnace to the fluidized-bed gasification furnace has been previously filed as Japanese Patent Application No. 8-187033. As a result, the temperature of the fluidized bed gasifier is raised while maintaining the reducing property, and the gasification proceeds sufficiently. Further, if the fluidized medium is circulated between the former melting furnace and the fluidized bed gasifier, the temperature of the fluidized bed gasifier can be controlled by adjusting the flow. Furthermore, even if the air supplied to the fluidized-bed gasification furnace uses a part of the exhaust gas in the latter stage, the exhaust gas is insufficient in oxygen compared to the air, so that the reducing atmosphere is maintained in the fluidized-bed gasification furnace. be able to.

Next, the present invention will be described in detail. As the fluidized bed gasification furnace used in the present invention, it is particularly preferable to use a swirling type fluidized bed gasification furnace (also referred to as a swirling fluidized bed gasification furnace). A swirling flow of a fluid medium is formed in a fluidized bed in the same reaction vessel,
The swirling flow is generated by setting a part of the fluidized gas to be blown into the fluidized bed. Therefore, unlike a simple bubbling type fluidized bed, it has excellent waste dispersion and crushing functions, the raw material and char are uniformly dispersed in the bed, and the heat generated by partial combustion is quickly diffused, so that a high hearth load can be obtained. Can be In addition, by setting the fluidized bed temperature to a low temperature condition of 450 to 600 ° C., the gasification reaction is slowed, so that excellent operation operability and stability can be obtained. Furthermore, due to the swirling flow of sand, large-sized incombustibles can be easily discharged, and since the fluidized bed temperature is low and the reducing atmosphere is used, useful metals such as iron, copper, and aluminum can be recovered in an unoxidized state. .

Next, the gasification reaction product is introduced into a melting furnace. In the fluidized bed gasification furnace, gasification is incomplete due to low-temperature operation and char and tar are entrained. The melting furnace can realize high-temperature combustion of 1350 ° C. or more using only the generated gasification reaction products including char and tar. At this time, if the melting furnace is a swirling melting furnace, high load combustion can be performed, and the char contained in the gas is blown to the furnace wall due to the centrifugal force associated with the swirling flow and formed on the wall surface. It is burned over time in the slag phase. In this manner, since the char can be completely burned, a device or the like for reburning the char is not required. Dioxin can be completely decomposed by high-temperature combustion, and high-efficiency power generation can be achieved by high-temperature, high-pressure steam recovery. In the case of gasification combustion, gas combustion is mainly performed in the melting furnace, so that a low air ratio combustion of about 1.3 can be achieved.

Further, in the swirling melting furnace, the combustion load can be increased to the utmost due to the high-speed swirling flow, the slag can be efficiently separated by the centrifugal effect, and harmful substances such as heavy metals are converted into glassy solids. It is contained, and ash can be rendered harmless. However, while the swirling melting furnace exhibits excellent functions, it is impossible to set the residence time long enough, which is disadvantageous for operations such as sedimentation and separation of generated metal from slag with a specific gravity difference. There is. In the present invention, the slag once generated is further heated by a curing device in a reducing atmosphere, held for an appropriate residence time, and taken out from the curing device. At this time, since a sufficient residence time occurs, the heavy metal is accumulated as a simple substance at the bottom due to a difference in specific gravity, and can be taken out from the bottom.

As a suitable curing device, there is a noncombustion type melting furnace. In particular, an electric arc type melting furnace, an electric resistance furnace, an electric heating melting furnace and the like can be used. These melting furnaces are known furnaces as ash melting furnaces, and schematic explanatory diagrams of these furnaces are shown in FIGS. 2, 3, and 4. FIG. FIG. 2 shows an electric arc type melting furnace in which an arc is generated between a plurality of electrodes and a base metal at the bottom of the furnace, and ash and iron are melted by the heat. Base metal temperature is 1450-1500
℃, melt the incineration ash and soot and dust supplied on it, and take it out continuously or intermittently as slag,
Granulated slag or air-cooled slag is obtained. During this time, since the carbon electrodes are consumed, they are sequentially added. FIG. 3 shows an electric resistance furnace of a vertical electrode type, in which three electrodes are inserted from the furnace ceiling through the incineration ash layer, and the tip is immersed in the molten slag layer. The molten slag layer becomes an electric conductor and melts the ash by electric resistance heat (Joule heat). Slag is discharged from the furnace bottom.

FIG. 4 shows an electric heating type melting furnace in which an electric heater (Kanthal super) is suspended from a ceiling and dust is melted by radiant heat. The molten slag is continuously taken out of the furnace bottom and gradually cooled. The exhaust gas is quenched at the furnace exit by dilution air to prevent the volatiles from adhering to the flue due to reverse sublimation. Volatilized matter is collected by a bag filter, and it is considered that concentrated heavy metals are recovered. As shown in FIGS. 2 to 4, in these melting furnaces, the slag layer and the metal (metal) layer are superimposed by specific gravity and can be separated and recovered. Further, a plasma melting furnace or a low-frequency induction furnace can be applied. When slag is reused in the slag forming method, elution of harmful substances becomes a problem.

The Environment Agency Notification No. 13 test was conducted using hydrochloric acid to adjust pH.
Using distilled water adjusted to 5.8 to 6.3 as a solvent, a waste sample adjusted to a particle size of 0.5 to 5 mm and a liquid-solid ratio (liquid m
L / test weight g; hereinafter represented as L / S)
Shake time. The L / S is set to 10 in order to set a standard for the harmfulness when waste is eluted when it comes in contact with 10 times the amount of water. On the other hand, the Environment Agency Notification No. 46 test is a test method for measuring soil environmental standards. In recent years, when substances derived from waste are used for secondary products such as construction materials, their suitability is determined. Used as a method. The test method was the same solvent as in the Environment Agency Notification No. 13 test, using a sample adjusted to 2 mm or less using a sieve.
Shake parallel for 6 hours at L / S. After shaking, after standing still for 10 to 30 minutes, centrifuging at 3000 rpm for 20 minutes, the supernatant is filtered through a membrane filter having a pore size of 0.45 μm, and the filtrate is used as a test solution.

When slag is reused, it is often evaluated based on soil standards with severe conditions. However, lead may exceed the soil standard at high pH, and there is no guarantee that the soil standard can be completely cleared even in a low pH environment such as acid rain. Therefore, it was necessary to establish a slag production method with less elution of lead. In the present invention, by providing a slag curing device, a metal portion (Pb, Zn, Cr, F) containing heavy metals in the slag generated in the melting furnace is provided.
e) and the ceramic part (SiO ₂ , Al ₂ O _3, etc.)
Separation is performed under a sufficient residence time, the metal part is separately recovered, and the ceramic part is aged and homogeneously crystallized, and the harmful heavy metal remaining in the slag in a small amount is contained in the slag.

For the purpose of separating or containing the heavy metal, it is preferable to add a reducing agent such as coke, a magnesium compound and, if necessary, a basicity adjusting compound to the slag as an additive. Magnesium compounds are used as flux. Oxides are divided into two in terms of acids and bases. Alkali metal oxides, lime, manganese and the like are called basic oxides. Silica, alumina, and P ₂ O ₅ are called acidic oxides. When defining a scale indicating the strength of acidity and basicity, lime is a representative of a base and silica is a representative of an acid, and the ratio of CaO to silica is called basicity. All heavy metal components are weak bases, and alkalis are strong bases. Therefore, taking such a convenient basicity, a place with a high basicity, that is, Ca
In places with a large amount of O, the basic oxides repel each other, so that the basic oxides can easily fly out.

Conversely, when the amount of silica is large and the basicity is low, the slag is stable. That is, in general, when the basicity (CaO / SiO ₂ ) of the material to be melted increases, basic oxides (monovalent and divalent oxides, K ₂ O, Na ₂ O, CaO, Mg
Since the activity of O, ZnO, FeO, etc.) increases, the proportion of volatile components to fly ash relatively increases. Therefore, when a substance containing a calcium compound is added and the basicity is increased, the ratio of volatile compounds such as Zn and Pb transferred to fly ash increases. As described above, it is useful to add a substance containing a basicity adjusting compound as necessary. After leaving the curing device, the ceramic portion was gradually cooled, air-cooled, or water-cooled, so that it could be reused as a construction material without elution of heavy metals.

Next, the present invention will be specifically described with reference to the drawings. FIG. 1 shows an overall configuration diagram of a gasification and melting system including a slag recovery device of the present invention. 1, 1 is a fluidized bed gasifier, 2 is a screen, 3 and 4 are separators, 5
Is a front-stage rotary melting furnace, 6 is a rear-stage rotary melting furnace, 7 is a curing device, 8 is a boiler, 9 is a bag filter, and 10 is a resource recovery device. The waste 11 is charged into the fluidized bed gasification furnace 1 and gasified in a fluidized bed at 450 to 600 ° C. under a reducing atmosphere. The incombustibles contained in the waste are taken out of the furnace bottom together with the fluidized medium, separated from the fluidized medium and the like by the screen 2, and metals such as Cu, Al and Fe are separated by the separator 3. Further, the separator 4 separates the slag to which carbon or the fluid medium adheres from other substances (carbon or the fluid medium), and sends the slag to the curing device 7 described later.

On the other hand, a part of the gaseous product containing the char tar is melted in the pre-stage swirling melting furnace 5, and the molten slag falls into the fluidized bed gasification furnace 1 and is heated to fluidized bed gasification. The inside of the furnace 1 is heated. The remainder is introduced into the later-stage rotary melting furnace 6 and, together with the newly added fly ash 12 brought from another incineration plant, has an air ratio of about 1: 1 and a high temperature (about 14: 1).
(00 ° C.), and the fly ash melts. The generated molten slag 13 is supplied to a curing device (electric heating melting furnace) 7.
And aging and homogenization are performed under a sufficient residence time, and harmful heavy metals in the slag are settled and separated by a difference in specific gravity from the slag. Since carbon is attached to the slag 15 separated by the separator 4, the curing device 7
The carbon content acts as a reducing agent for the curing device 7,
There is no need to supply a new reducing agent to the curing device 7.

The molten fly ash generated in the curing device 7 is heated at about 1400 ° C. in a later-stage revolving melting furnace 6, and dioxin and the like adhere to carbon, a fluid medium, and slag supplied to the curing device 7. Even if it is harmless. The molten slag taken out of the curing device 7 is gradually cooled, air-crushed and processed in the resource recycling device 10 and is used for applications such as construction materials. As described above, the carbon and the fluidized medium adhere to the slag extracted by the separator 4 from the fluidized-bed gasifier 1, and the fluidized medium of the fluidized-bed gasifier 1 decreases. It can be supplemented by reusing the fine slag generated in the chemical conversion device 10. Exhaust gas from a swirling melting furnace (about 1400
(° C.), the mixture is sufficiently cooled by a waste heat boiler and an economizer (not shown), and an additive (MgO or the like) is blown into the bag filter 9 to collect dust. Table 1 shows the results of the dissolution test of the slowly cooled slag obtained when a curing device was provided (the present invention) and when no curing device was provided (comparative example) for the same waste.

[0021]

[Table 1] As shown in Table 1, the soil standard value was able to be cleared even in the comparative example. However, by using the system of the present invention, the elution amount of Pb could be further reduced. This can be said to be a numerical value that can sufficiently withstand changes in environmental conditions.

[0022]

As described above, according to the present invention, it is possible to maintain the reducing atmosphere of the gasification fluidized bed at a high temperature by using two melting furnaces. At the same time, detoxification of exhaust gas and effective utilization of carbon generated in a fluidized-bed gasification furnace and fine slag generated in a resource recycling device were enabled. In addition, by providing a curing device for molten slag, the amount of harmful substances eluted can be reduced to the reference value or less over the entire range, and in particular, the amount of Pb eluted can be reduced, and sufficient change in environmental conditions can be achieved. Therefore, applicability to construction materials and the like has been improved more than before.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a gasification and melting system including a slag recovery device of the present invention.

FIG. 2 is an explanatory view of an electric arc type melting furnace.

FIG. 3 is an explanatory view of a vertical electrode type electric resistance furnace.

FIG. 4 is an explanatory view of an electric heating type melting furnace.

[Explanation of symbols]

1: fluidized bed gasifier, 2: screen, 3, 4: separator, 5: former melting furnace, 6: latter melting furnace, 7: curing device,
8: Waste heat boiler, 9: Bag filter, 10: Recycling equipment, 11: Waste, 12: Fly ash, 13: Molten slag, 1
4: additive, 15: separated slag, 16: heavy metal, 17:
Steam, 18: salt + low-boiling heavy metal, 19: reuse

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FIF23J 1/00 B09B 3/00 ZAB 303K (72) Inventor Hiroaki Sato 11-1 Haneda Asahimachi, Ota-ku, Tokyo Ebara Corporation (72) Inventor Kazuo Takano 11-1 Haneda Asahi-cho, Ota-ku, Tokyo Inside Ebara Corporation

Claims (10)

[Claims] 1. A fluidized bed gasifier for gasifying waste,
Waste consisting of a gaseous substance connected to the fluidized-bed gasifier and discharged from the fluidized-bed gasifier, and a melting furnace for further burning or gasifying the char and slagging the incombustible or non-gasified matter In the slag recovery apparatus, the melting furnace is provided in two stages in series, and the molten slag generated in the preceding melting furnace is brought into contact with the fluidized medium of the fluidized bed gasification furnace to be cooled and solidified, and the latter melting furnace A slag recovery device having a heating mechanism for heating and keeping the molten slag generated from the melting furnace in communication with the slag and a separation mechanism for separating the slag and the metal. 2. The waste slag recovery device according to claim 1, wherein the curing device is an externally heated melting furnace. 3. The waste according to claim 1, wherein the fluidized bed gasifier is a swirling type fluidized bed gasifier, and the melting furnace is a self-combustion type swirling melting furnace. Slag recovery equipment. 4. A gasification step in which waste is gasified at a low temperature in a fluidized-bed gasifier, and a gaseous substance and char obtained in the gasification step are further burned at a high temperature, and a non-combustible or non-gasified substance is produced. In the method for slagging waste to be treated in the gasification and melting step of slagging, a part of the molten slag generated in the gasification and melting step is introduced into the fluidized medium of the fluidized bed gasifier, and cooled and solidified. A slag-making method for waste, which comprises introducing the remaining portion into a curing process having a heating function and a separating function, aging it, and discharging it. 5. The method according to claim 4, wherein in the curing step, a substance containing a reducing agent, a magnesium compound and, if necessary, a basicity adjusting compound is added to the molten slag. 6. A slag of waste according to claim 5, wherein the substance containing the magnesium compound and, if necessary, a basicity adjusting compound is added to a gasification portion or a melting portion in a gasification and melting step. Method. 7. The method according to claim 5, wherein the reducing agent is replaced by slag to which carbon and a fluidized medium accumulated during operation are attached to the bottom of the fluidized bed gasifier used in the gasification step. How to turn waste into slag. 8. The method according to claim 7, wherein the fine slag generated in the processing step of the molten slag is used for replenishment of a reduced amount of the fluidized medium of the fluidized-bed gasification furnace used in the gasification step.
A method for converting waste into slag. 9. The gasification and melting step, wherein a two-stage melting furnace is used, and a fluidized medium is circulated between the preceding-stage melting furnace and a fluidized-bed gasification furnace used in the gasification step. Item 4. The method for converting waste into slag according to Item 4. 10. The waste according to claim 4, wherein the fluidized bed gasifier used in the gasification step uses a part of the exhaust gas from the gasification melting step instead of supplying the combustion air. How to make things slag.