JP2001336721A - Method for melting refuse - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a furnace for melting refuse directly in which consumption of auxiliary fuel, e.g. coke, and oxygen for enriching air being supplied from a tuyere is reduced or eliminated utilizing electricity generated from thermal energy of the refuse. SOLUTION: In the furnace for melting refuse directly, incombustible matters in refuse is melted by blowing oxygen containing gas from a lower section of the furnace body such that an air column gas in the furnace has a velocity of 0.3 m/sec-Vt, and conducting an AC current to a heating coil arranged on the outer circumference at the core floor section of the furnace body thereby induction heating a molten deposited on the core floor section or a conductive heater.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing slag by directly melting municipal solid waste, industrial waste, sludge, waste buried in landfill waste, and the like.

[0002]

2. Description of the Related Art At present, most waste is treated by an incineration method, but the incineration method has a drawback that a disposal site for incinerated ash is required. Particularly in metropolitan areas, it is difficult to secure a disposal site for incinerated ash.
There is an increasing need to dissolve incinerated ash from waste in a manner that allows volume reduction and further recycling.

[0003] As a method of melting incinerated ash of waste, Japanese Patent Publication No. 4-81084 discloses a method of melting in an arc furnace, and a method of melting by induction heating is disclosed in Japanese Patent Application Laid-Open No. 5-237468.
And Japanese Patent Application Laid-Open No. Hei 11-211032.

[0004] Japanese Patent Publication No. 60-11766 discloses a method of directly melting waste in a shaft furnace without incineration.
It is disclosed in JP-A-5-346218.

[0005] The arc furnace method and the induction heating method for melting incineration ash require two-stage treatment because the waste is once incinerated and then melted. Therefore, cooling equipment for the incineration ash discharged from the incinerator, a melting furnace, In addition, the arc furnace has problems such as the fact that expensive graphite electrode rods are often worn and noise due to generation of arc discharge noise.

[0006] Further, the shaft furnace or the method of fluidizing waste directly to melt it has a problem that an auxiliary fuel such as coke is required.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention is directed to a method of melting waste which directly melts waste without incineration and reduces the consumption of auxiliary materials such as coke. It is intended to provide a furnace.

[0008]

Means for Solving the Problems The means for solving the above-mentioned problems according to the present invention has the following features.
Assuming that the waste is charged from the upper part of the furnace body and the terminal velocity at the time of charging the waste is Vt, the superficial gas flow velocity in the furnace is 0.3 m /
Air or oxygen-enriched air is blown from the lower part of the furnace main body so as to be in a range of seconds to Vt to thermally decompose and partially burn flammable substances in waste, and to supply an alternating current to a coil installed in the lower part of the furnace main body. This is a method for melting waste, comprising inductively heating the melted incombustible material and melting the pyrolysis residue in the waste that has fallen to the hearth.

According to a second aspect of the present invention, air or oxygen-enriched air is blown so as to attain the gas flow rate in the furnace, and a conductive heating element such as coke or graphite is supplied. This is a waste melting method characterized by melting the dry distillation residue in the waste that has fallen to the hearth by inductively heating the conductive heating element.

The method according to claim 3 is a method according to claims 1 and 2, wherein a basicity adjusting agent such as limestone is charged.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A melting furnace has a preheating, drying, pyrolysis and melting zone formed from the upper part of the furnace toward the lower part of the furnace, and the waste supplied from the upper part of the melting furnace descends in the furnace. Then, it is sequentially preheated, dried and thermally decomposed, and melted at the furnace bottom. As a heating source for preheating, drying and pyrolysis, combustible substances in coke and waste are partially burned by air blown from the lower part of the furnace body or air added with oxygen to generate hot gas. Then, the high-temperature hot gas rises inside the furnace, preheating, drying,
Decomposes thermally.

Since the preheating, drying and pyrolysis zones are formed in the melting furnace, the heat gas and the waste exchange heat in countercurrent, so that the heat efficiency is high. Since the low-temperature waste containing water does not come into contact with the high-temperature portion, stable melting can be performed.

In the pyrolysis zone, a part of the waste is burned (reduced combustion), which is different from oxidative combustion such as a waste incinerator. That is, since the temperature inside the melting furnace is high and the amount of combustible substances such as carbon is large relative to oxygen supplied from the tuyere, the following reaction occurs.

C + O ₂ = CO ₂ C + CO ₂ = 2CO As described above, high-temperature hot gas contains carbon monoxide C
Highly combustible gas such as O remains. The waste is thermally decomposed by the heat generated by the reduction combustion. The pyrolysis gas includes combustible gases such as carbon monoxide, hydrogen, and methane. These gases are discharged from the furnace top of the melting furnace and are completely burned (oxidized combustion) in the combustion furnace. If the waste is incinerated without thermal decomposition, the waste will contain various things such as high-moisture and low-moisture materials. Since wastes such as incinerators burn incompletely while smoking, harmful substances such as dioxin are likely to be generated. On the other hand, as in the present invention, once the waste is once reduced and thermally decomposed to gasify and then burned, gas combustion is easier to completely burn than solid combustion, and harmful substances such as dioxin are reduced. It is possible to prevent occurrence.

In the melting zone at the bottom of the furnace, the pyrolysis residue of the waste is melted by induction heating a melt or a conductive heating element. That is, electricity generated by recovering heat from the heat generated by the waste as a heat source for melting the waste is used as an induction heating source.

The conductive heating element serves as a heating medium by electromagnetic induction heating and has conductivity and heat resistance.
Practically, carbon materials such as coke and graphite, conductive ceramics, and the like are used.

The melting zone will be described in detail below. The carbonized residue in the waste is preheated and falls to the lower part of the furnace.
When an alternating current is applied to a coil installed at the lower part of the furnace body, the incombustible material melted is induction-heated, and a pool of hot molten material is formed. The non-combustible substances in the waste fall into the hot water pool and melt one after another. Non-combustible substances in waste are substances containing SiO ₂ , Al ₂ O ₃ , and CaO as main components, and do not conduct electricity in a solid state, but in a molten state at a high temperature, the electric resistance is small, and electric current can be passed. Heating is possible.

In the initial stage of starting the melting furnace, a conductive heating element such as coke or graphite is charged to first heat the conductive heating element to a high temperature state. Melts incombustible substances in waste. Alternatively, auxiliary fuel is blown into the furnace, and the heat of combustion melts the incombustible substances of the waste, thereby forming a pool of molten material on the hearth.

Assuming that the terminal velocity of the gas containing oxygen from the lower part of the furnace body at the time of charging the waste is Vt, the gas flow rate from the lower part of the furnace body is from 0.3 m / sec to Vt. It is necessary to inject a gas containing oxygen.

The lower limit of the superficial gas velocity in the furnace is that the gas containing oxygen blown from the lower part of the furnace needs to reach the center of the furnace, and for that purpose, 0.3 m / sec or more is required. Was found as a result of the verification test. If the superficial gas velocity is less than 0.3 m / sec, the injected gas flows around the furnace, and it is impossible to thermally decompose and burn the waste in the center of the furnace.

The upper limit of the operable superficial gas velocity is as follows:
It was similarly confirmed that the flow velocity was such that the waste charged from the upper part of the furnace did not blow away, that is, the terminal velocity Vt. The calorific value is 2
As a result of melting treatment of municipal solid waste of 500 kcal / kg, it was possible to operate in the range of 0.3 m / sec to Vt, but the superficial gas velocity was set to V = 0. The furnace condition was more stable in the flow rate range where the waste fluidized as 5 to 2.0 Vmf.

In the technique of the present invention, since a high-temperature pool that is induction-heated is formed in the hearth, it can be operated in a wider flow rate range than a conventional coke-bed melting furnace. That is, in the conventional technology, a high-temperature coke bed is formed by the combustion of coke and combustible substances, and stable combustion is maintained with the coke bed as a fire point, but the combustion temperature is easily influenced by the properties of the waste and the furnace condition. For example, if the temperature decreases for some reason, an unstable phenomenon such as a decrease in the combustion speed and a further decrease in the temperature tends to occur. On the other hand, in the present invention, since the high-temperature pool in the hearth is heated by induction heating, it is not affected by the properties of the waste, etc. maintain.

In the prior art, the auxiliary fuel is supplied and burned by air or the like blown from the lower part of the furnace, and the incombustible material is melted by the combustion heat. Can be eliminated or greatly reduced.

The power required for induction heating can be obtained from the thermal energy of the waste. That is, steam can be generated by recovering heat from a high-temperature exhaust gas obtained by burning waste by a boiler, and power can be generated by the steam. If the induction heating is performed by the electricity, the waste itself is melted by the calorific value of the waste, and as described above, the consumption of the auxiliary fuel can be reduced to none or significantly.

Depending on the nature of the waste, oxygen may be enriched in the air blown from the lower part of the furnace body in order to increase the combustion temperature. However, the induction heating according to the present invention reduces or reduces the oxygen. It can be unnecessary.

By using the conductive heating element during normal operation, a deposition layer of the conductive heating element is formed on the hearth, and the conductive heating element is induction-heated to form a coil for induction heating. The frequency of the alternating current to be supplied can be reduced. That is, since the non-combustible melt in the waste has a higher electric resistance than a conductive heating element such as coke or graphite, it is necessary to increase the frequency of the alternating current necessary for induction heating. Although a power supply with a high frequency is expensive in terms of equipment, it is possible to reduce the frequency of the power supply by using a conductive heating element to reduce equipment costs. Also, when a carbon material such as coke is used as the conductive heating element, it is known that the inside of the furnace can be set to a reducing atmosphere, and it is known that heavy metals such as lead in the slag are volatilized and reduced. There is no concern about the negative impact on the environment when using the system effectively.

As a heating method using electricity, there is a method such as energization heating. However, it is necessary to install electrodes through the furnace wall of the melting furnace, which complicates the structure and further replaces worn electrodes. However, in the case of induction heating, there is no such problem. Furthermore, in comparison with the case where incineration ash is melted in an arc furnace, in the present invention, since incineration and melting of waste are performed in one step, the equipment configuration is simple and the construction cost is low.

[0028]

EXAMPLE 1 FIG. 1 shows an example of melting waste.

In FIG. 1, limestone is charged from a charging device 2 at the upper part of the furnace body 1 as waste and auxiliary material.
Municipal waste was disposed of as waste. Table 1 shows the properties of the melted municipal solid waste.

[0030]

[Table 1] The furnace body 1 includes a furnace upper part 5, a furnace lower part 6, and a hearth part 7, and is supplied from an air supply pipe 3 provided around the furnace lower part. Further, waste oil is supplied from the auxiliary fuel supply device 4 as auxiliary fuel.

The amount of waste treated is 560 kg / h, limestone is 6% of the waste, and the air for flowing and combustion air is flowing and
600 Nm ³ / h was supplied from the combustion air supply pipe 3. The superficial gas velocity is 5 m / sec at the lower part of the furnace and 1 m / sec at the upper part of the furnace, and both ranges from 0.3 m / sec to Vt.

The waste charged in the melting furnace is fluidized in the furnace, and combustibles of the waste are burned by the blown air. The combustion gas preheats, dries, and thermally decomposes waste by sensible heat. Steam, pyrolysis gas and fine dust generated in the process of drying and pyrolysis of the waste are discharged from the gas discharge pipe 8.

The composition in the gas discharge pipe is CO ₂ = 9.4.
%, CO = 10%, H ₂ = 5, 6%, H ₂ O = 44.4
%, And the gas oxidation degree OD expressed by the following equation was 0.78. By changing the combustion air and the like, the operation was performed at a gas oxidation degree of OD = 0.1 to 0.9. OD = 0.1-0.6 when mainly gasification of waste
It is good to operate in.

Gas oxidation degree OD = ｛(CO₂) + (H
₂O)｝ / ｛(CO₂) + (CO) + (H ₂) + (H₂
O)｝ On the other hand, incombustible waste and limestone are heated to high temperature and
Go down to 7. Heating coil installed around the hearth
An alternating current is passed through 10 from a high frequency power supply 11 to
Induction heating of the incombustible material accumulated in
The incombustible material contacts and melts at a high temperature. Incombustibility
The material is heated from 1300 ° C to 1550 ° C and becomes molten.
Thus, the slag is discharged from the slag discharge port 9 to the outside of the furnace. Alternating current
Was 300 kHz. The temperature of the molten slag is
It is possible by adjusting the input power of induction heating.
You.

The limestone to lime CaO and the ratio of the silicic acid content of SiO ₂ basicity namely slag slag is 0.7 or more, was added to adjust the fluidity of the slag in the molten state. By maintaining the fluidity by raising the melting temperature,
It is also possible to omit the addition of limestone.

As the electric power for the induction heating, the gas discharged from the gas discharge pipe is burned in the secondary combustion chamber 14 as shown in the exhaust gas treatment system in FIG. 2, and the heat is used to generate steam in the boiler 15. The power generated by the generator 20 was used. Since the secondary combustion furnace burns combustible gas obtained by gasifying waste, generation of harmful substances such as dioxin can be prevented. The combustion exhaust gas is cooled by an exhaust gas cooler 16, dust is removed by a dust collector 17, and discharged from a chimney 18 to the atmosphere.

The molten slag discharged from the slag discharge port 9 is water-cooled to be fine sand-like particles. Also,
Slag in the molten state contains molten metal,
Similar to slag, fine slag of metal is used as aggregate or civil engineering material for secondary concrete products such as interlocking blocks.

Embodiment 2 FIG. 3 shows an embodiment using coke as a conductive heating element.
Shown in

The properties of the waste and the amount of fluidized / combusted air were the same as in Example 1, and coke was charged at 1% of the waste.

The coke is preheated in the furnace and descends, forming a layer of coke 12 on the hearth. An alternating current is applied from a high-frequency electric source 11 to the heating coil 10 installed on the outer periphery of the hearth to inductively heat the coke 12 deposited on the hearth, and the incombustible material that has fallen with the coke 12 in a high temperature state. Melts on contact. Incombustibles from 1300 ° C to 1550 ° C
And is discharged out of the furnace from the slag discharge port 9. The frequency of the alternating current was 50 kHz.

FIG. 4 shows a prior art direct melting furnace. When the same waste is treated by the conventional method, coke is required to be 6% of the waste and oxygen is supplied to the flow / combustion air. It was necessary to blow 45 Nm ³ enriched inside. Compared with the conventional method, the method of the present invention can reduce coke consumption and oxygen as shown in Examples 1 and 2.

[0042]

According to the present invention, the following effects can be realized.

1) Compared with the method in which the waste is incinerated and then melted in an arc furnace, the method of the present invention allows the waste to be directly melted in a single melting furnace in a single step, and the equipment configuration is simple and economical It is a target. Further, not only is it unnecessary to handle the incineration ash of the arc furnace type, but also the thermal efficiency is higher than the method of once cooling the incineration ash and melting it in an arc furnace.

2) When the waste is directly melted by the method of the present invention without incineration, the melt is induction-heated to melt the incombustible material, thereby eliminating the need for an auxiliary fuel such as coke, and flowing and burning. It is possible to reduce or eliminate the air-enriched oxygen. Further, the temperature of the molten slag can be easily adjusted by adjusting the power input amount of the induction heating.

3) The gas velocity in the furnace is 0.3 m / sec.
By blowing a gas containing oxygen from the lower part of the furnace main body to Vt, the combustible waste can be stably thermally decomposed and reduced and combusted. In the technology of the present invention, since a high-temperature pool that is induction-heated is formed in the hearth, compared to a conventional coke-bed melting furnace, the superficial gas flow rate in the furnace can be operated in a wide flow rate range. is there. That is, in the conventional technology, a high-temperature coke bed is formed by combustion of coke and combustible materials, and stable combustion is maintained using the coke bed as a fire point, but the coke bed temperature is affected by the properties of waste and the furnace condition. Cheap. On the other hand, in the present invention, since the high-temperature pool in the hearth is heated by induction heating, it is not affected by the properties of the waste, etc. maintain.

4) As a heating method using electricity in the melting furnace, there is a method such as energization heating. However, it is necessary to dispose an electrode through a furnace wall applied to a shaft furnace and a furnace wall of the melting furnace. Although the structure is complicated and the replacement of the exhausted electrode is complicated, the induction heating according to the present invention does not have such a problem.

5) Compared to the case where incinerated ash is melted in an arc furnace, in a furnace body type melting furnace using coke as a conductive heating element, the inside of the furnace can be set to a reducing atmosphere, Since heavy metals such as lead in the subsequent slag can be volatilized and reduced, when using slag effectively,
There is no concern about adverse effects on the environment. Therefore, the present invention is a waste melting furnace having the advantages of using electricity while utilizing the advantages of the furnace body of reducing heavy metals in slag.

6) As the electric power for induction heating the coke, it is not necessary to purchase electric power from the outside by effectively generating and using the heat generated by the waste.

7) By recycling the slag after the melting treatment, not only is the slag disposal site unnecessary, but also natural destruction due to mining of natural sand can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an exhaust gas treatment system.

FIG. 3 is a diagram showing an embodiment using coke as a conductive heating element.

FIG. 4 shows a prior art direct melting furnace.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Furnace main body 2 Charging device 3 Air supply pipe
4 auxiliary fuel supply device 5 furnace upper part 6 furnace lower part 7 hearth part 8
Gas discharge pipe 9 Slag discharge port 10 Heating coil 11 High frequency power supply 12 Coke 14 Secondary combustion chamber 15 Boiler 16 Exhaust gas cooler 17 Dust collector 18 Chimney 20
Generator

Continued on front page F term (reference) 3K061 AA16 AB02 AB03 AC01 BA01 BA07 BA10 CA08 CA15 DA12 DA18 DA19 DB16 FA10 FA21 FA25 4D004 AA02 AA03 AA46 AB03 AC08 BA02 BA03 CA27 CA29 CB31 CB33 CC12 DA03 DA12 4D059 AA00 BB02 BB04 CA11 CC04 DA04 DA57 DA58 EB20

Claims (3)

[Claims] 1. A waste is charged from the upper part of a melting furnace, air or oxygen-enriched air is blown from a tuyere, the charged waste is reduced and burned, and the waste is preheated, dried and thermally decomposed. After that, in the method of melting and processing the thermal decomposition residue of the waste, when the terminal speed at the time of charging the waste is Vt,
Air or oxygen-enriched air is blown from the lower part of the furnace main body so that the superficial gas flow velocity in the furnace becomes 0.3 m / sec to Vt, and an alternating current is supplied to a coil installed in the lower part of the furnace main body, thereby preliminarily forming the furnace. A method for melting waste, comprising: inductively heating a melt stored in a lower portion to melt a pyrolysis residue in the waste that has fallen to a hearth. 2. Waste is charged from the upper part of the melting furnace, air or oxygen-enriched air is blown from the tuyere to reduce and burn the charged waste, and the waste is preheated, dried, pyrolyzed and gasified. After that, in the method of melting and processing the thermal decomposition residue of waste, assuming that the terminal velocity at the time of charging the waste is Vt, the furnace is set so that the superficial gas flow rate in the furnace becomes 0.3 m / sec to Vt. In addition to blowing air or oxygen-enriched air from the lower part of the main body, it supplies a conductive heating element, and applies alternating current to the coil installed at the lower part of the furnace body to induce the conductive heating element that descends and deposits at the lower part of the furnace. A method for melting waste, comprising heating to melt the pyrolysis residue in the waste. 3. A method for melting waste according to claim 1, wherein a basicity adjusting agent such as limestone is charged.