JP3648039B2 - Plasma arc melting furnace and method for melting a material to be melted using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a melting treatment technology such as industrial waste and combustion residue from waste incinerators, fly ash, etc., and the slag temperature in the plasma melting furnace is the lowest temperature at which slag overflows from the slag outlet. , Refractory material damage in the melting furnace is suppressed, and there is no unmelted or incomplete melt in the molten slag overflowing from the main body of the plasma melting furnace, and the temperature of the molten slag is raised to whiten the granulated slag The present invention relates to a plasma arc melting furnace in which a high-quality granulated slag having a wide range of use can be obtained, and a method for melting a material to be melted using the same.
[0002]
[Prior art]
In recent years, in order to reduce the volume and detoxify combustion residues and fly ash discharged from incinerators such as municipal waste, methods for melting and solidifying combustion residues have been put into practical use. Combustion residues, etc. are reduced in volume to 1/2 to 1/3 by melting and solidifying, and it becomes possible to prevent the elution of hazardous substances such as heavy metals, reuse molten slag, and extend the life of the final landfill site. Because.
[0003]
Thus, in the method of melting and solidifying the combustion residue, fly ash, etc., using a plasma arc furnace, an arc furnace, an electric resistance furnace, etc., a method of melting and solidifying the melted object by electric energy, a surface melting furnace, A swirling melting furnace, a coke bed furnace, etc., and the method of melting and solidifying the material to be melted by the combustion energy of fuel are often used, and when the power generation equipment is juxtaposed with the municipal waste incineration equipment, the former The method using electric energy and the method using combustion energy of the latter are often adopted when the power generation equipment is not juxtaposed.
[0004]
FIG. 2 shows an example of a graphite electrode type plasma arc melting furnace that is installed in a conventional waste incineration facility. In the figure, 1 is an ash hopper that is a melted material, and 2 is a melted material. 3 is a plasma melting furnace body, 4 is a graphite main electrode, 5 is a graphite start electrode, 6 is a furnace bottom electrode, 7 is a furnace bottom cooling fan, 8 is a DC power supply, 9 is inert such as nitrogen gas, etc. Gas supply device, 10 is a molten slag outlet, 11 is a tap hole, 12 is a combustion chamber, 13 is a combustion air fan, 14 is an exhaust gas cooling fan, 15 is a bag filter, 16 is an induction fan, 17 is a chimney, 18 is A molten fly ash conveyor, 19 is a fly ash reservoir, 20 is a slag water cooling tank, 21 is a slag carry-out conveyor, 22 is a slag reservoir, and 23 is a slag cooling water cooling device.
[0005]
A material to be melted A such as combustion residue or fly ash is stored in the ash hopper 1 and continuously supplied into the plasma melting furnace main body 3 by the supply device 2. The plasma melting furnace main body 3 is provided with a graphite main electrode 4 (-electrode) inserted perpendicularly from the top of the furnace and a furnace bottom electrode 6 (+ electrode) installed at the furnace bottom. , 6 is applied with a DC voltage (200 to 350 V) of a DC power supply 8 (capacity of about 600 to 1000 kW / T / melted material), an electric current flows to generate an arc as a plasma generation source. . The material A to be melted is heated to 1300 ° C. to 1500 ° C. by the plasma arc, and becomes a molten slag B sequentially.
Since the melted material A before melting has no electrical conductivity, when starting the melting furnace, the start electrode 5 is inserted into the melting furnace body 3 to make it a positive electrode, and a current is passed between this and the main electrode 4. To wait for the material A to melt. And since a to-be-melted material will have electroconductivity, it will switch the start electrode 5 to the furnace bottom electrode 6 side.
[0006]
The inside of the plasma melting furnace main body 3 is maintained in a reducing atmosphere in order to prevent oxidation of the molten slag B, the main electrode 4 and the like, and for that purpose, from an inert gas supply device 9 such as a PSA nitrogen production device. An inert gas (nitrogen gas) C is continuously supplied into the melting furnace main body 3 through the hollow holes of the main electrode 4 and the start electrode 5.
Note that the inert gas C is supplied into the furnace body through the hollow holes of the main electrode 4 and the start electrode 5 because (1) the plasma discharge region is filled with the rich inert gas C. This is because the so-called plasma discharge properties such as the generation and stability of the plasma arc are considered to be favorable, and (2) the consumption of the graphite main electrode 4 and the graphite start electrode 5 is considered to be less. is there.
[0007]
The furnace bottom of the plasma melting furnace main body 3 is air-cooled by the cold air from the furnace bottom cooling fan 7, thereby preventing an excessive temperature rise in the vicinity of the furnace bottom electrode 6. The plasma melting furnace main body 3 itself is composed of a refractory material that can withstand a high temperature of about 1700 ° C. and an insulating material that covers the refractory material. A water cooling jacket (not shown) is provided outside the insulating material as necessary. Yes.
[0008]
When the melted material A is melted, volatile components present inside it, carbon monoxide, etc. generated by the oxidation of carbon become gas bodies D, and non-combustible components such as metals such as iron, glass, sand, etc. Becomes a molten state, and the molten slag B is sequentially formed.
The gas body D enters the combustion chamber 12 from the upper part of the molten slag outlet 10 or from the top of the furnace, and the combustion air fed by the combustion air fan 13 is added here, so that the unburned portion inside is completely removed. Burned. Further, the completely burned gas body D is cooled by the cold air from the exhaust gas cooling fan 14, passes through the bag filter 15, and is discharged to the chimney 17 by the induction fan 16. The molten fly ash E captured by the hugging filter 15 is sent to the fly ash reservoir 19 by the molten fly ash conveyor 18.
[0009]
On the other hand, the molten slag B formed in the plasma melting furnace body 3 continuously overflows from the molten slag outlet 10 and falls into a slag water cooling tank 20 filled with water to become a granulated slag, and a slag carry-out conveyor 21 is discharged to the slag reservoir 22.
Further, when the plasma arc melting furnace is stopped, hot water is removed from the tap hole 11 attached to the bottom level of the molten slag B, and the plasma melting furnace main body 3 is emptied.
[0010]
Thus, the melt A supplied into the plasma melting furnace main body 3 is heated to about 1300 to 1500 ° C., which exceeds its melting point (1200 to 1300 ° C.) by being supplied with the heat of the plasma arc. The liquid molten slag B is heated to a temperature and has fluidity.
By the way, in order to melt the melt A in the melting furnace body 3 efficiently and uniformly without leaving unmelted or incomplete melt, (1) the temperature distribution in the plasma melting furnace body 3 is almost equal. It is uniform and the melted material A is heated and melted almost evenly. (2) There is sufficient residence time until the melted material is continuously supplied in a certain amount and discharged from the molten slag outlet 10. And (3) the outer dimensions, composition, porosity, etc. of the material A to be melted are almost uniform and can be convected even in the vertical direction together with the molten slag B. It becomes a requirement.
[0011]
However, in this type of plasma arc melting furnace, as shown in FIG. 2, the main electrode 4 is disposed in the direction of 竪 on the central axis of the plasma melting furnace body 3 having a substantially circular cross section as shown in FIG. Since the main electrode 4 and the furnace bottom electrode 6 are energized, the central axis of the plasma melting furnace body 3 inevitably reaches the maximum temperature range, and the peripheral wall of the plasma melting furnace body 3 radiates heat to the outside. Therefore, the low temperature range and (2) the low temperature melted material A is intensively supplied to a specific part of the peripheral part away from the center point of the plasma melting furnace body 3, and before melting. Since the material A to be melted is low temperature and lacks thermal conductivity, the temperature distribution in the plasma melting furnace main body 3 is extremely non-uniform because the supply region of the material A to be melted is a low temperature region. It will be something.
As a result, the temperature distribution of the molten slag B itself is inevitably nonuniform, and is far from an ideal state for completely melting the material A to be melted with high efficiency.
[0012]
The melted material A such as ash is usually a fine powder or fine particle having an outer diameter of 5 to 70 μm (in the case of fly ash) or 30 to 50 mm (in the case of incineration residue), and the plasma melting furnace main body. Although there are variations in the size, composition, porosity, etc. of individual fine powders / fine granules, the heat slag is good and bad, or has a sedimentation property. Some are floating.
As a result, the melted material A having poor heat receiving property and floatability does not convect in the vertical direction together with the molten slag B on the flow of heat, and floats on or in the surface layer portion of the molten slag B. It will flow to the slag outlet 10 side in the state of cocoon, and unmelted material (incomplete melt) will exist in the molten slag B.
In order to avoid this, if the temperature of the plasma melting furnace body 3 is raised and the temperature of the molten slag B is increased, it is possible to avoid mixing of unmelted material and incompletely melted material. This causes a problem that the life of the refractory material is shortened.
[0013]
As described above, the conventional DC arc discharge graphite electrode type plasma arc melting furnace can melt the material to be melted relatively stably, but still has problems to be solved. The problem is the expansion of the use range of molten slag and the erosion of refractory materials.
That is, as described above, in this conventional plasma arc melting furnace, erosion of the refractory material is suppressed due to the complicated flow of the molten slag B and the heat conduction caused by the structure of the plasma melting furnace body 3. At a melting temperature of 1500 ° C. or less, it is inevitable that a part of the melted material A overflows from the molten slag discharge port 10 together with the molten slag B in an incomplete molten state. In addition, in the molten slag B overflowing from the slag outlet 10, a considerable amount of unmelted material exists depending on the properties of the ash.
As a result, the quality of the molten slag B will be inhomogeneous, and the quality of the granulated slag will inevitably deteriorate so that it will be difficult to effectively use it.
In addition, the granulated slag obtained by water-cooling the relatively low-temperature (1500 ° C. or less) molten slag B discharged in this manner is black, which is an obstacle when used as a cement raw material or an aggregate. Therefore, its effective use is restricted.
[0014]
[Problems to be solved by the invention]
The present invention has the above-mentioned problems in the conventional DC arc discharge type graphite electrode type plasma arc melting furnace, that is, (1) the structure of the plasma melting furnace main body is not suitable for the molten slag overflowing from the slag outlet. It is easy to mix the complete melt, and the quality of the granulated slag deteriorates, making it difficult to effectively use it. (2) To be melted in the main body of the plasma melting furnace to reduce the incomplete melt. If the residence time of the product is extended, the melting capacity of the plasma arc melting furnace will be greatly reduced. (3) If the temperature of the plasma arc melting furnace is raised to raise the temperature of the molten slag, Mixing of materials can be avoided, however, it becomes disadvantageous in terms of thermoeconomics and the life of the furnace refractory is shortened. (4) Granulated slag rapidly quenched with molten slag discharged at 1300-1500 ° C is black. Present, Overflow from the slag outlet without reducing the melting capacity of the plasma arc melting furnace or increasing the running cost. A plasma arc melting furnace in which incomplete molten material is not mixed into the molten slag and the temperature of the molten slag itself is increased so that high-quality white granulated slag can be stably obtained. The present invention provides a melt processing method for a material to be melted.
[0015]
[Means for Solving the Problems]
The invention of claim 1 includes a plasma melting furnace body having a molten slag outlet and a melt supply port on the side wall, a melt supply apparatus for supplying the melt into the plasma melting furnace body, and a DC power supply. The main electrode and the furnace bottom electrode that generate a plasma arc by the electric power of, the inert gas supply device that supplies the inert gas into the plasma melting furnace body, and the molten slag overflowing from the molten slag outlet through the slag chute In a plasma arc melting furnace provided with a slag water cooling tank to be received, the melting temperature of the melted material of the plasma arc melting furnace is set to 1400 ° C. or less, and in the slag chute outside the molten slag outlet, and Okoshisei the plasma arc by the power from the DC power supply device provided with a reheating electrodes for heating the molten slag overflow from the molten slag outlet, of the reheating electrode The non-melt in the molten slag from the molten slag outlet causes completely melted by Razumaaku, in which the basic configuration of the invention that was configured to reheat the slag to 1600 ° C. to 1800 ° C..
[0016]
The invention of claim 2 is the invention of claim 1, wherein the material to be melted is incineration residue and / or fly ash from a waste incinerator , and a slag reservoir is provided in the slag chute, and the slag reservoir is re-introduced. A heating electrode is provided.
[0017]
In the invention of claim 3, the melted material is melted by the plasma arc generated by the main electrode in the main body of the plasma melting furnace, and the melt containing unmelted or incomplete melt overflowed from the molten slag outlet The white slag is obtained by heating the slag with a plasma arc generated by the reheating electrode and supplying the molten high-temperature slag in which the unmelted or incomplete melt is melted into the slag water cooling tank. Is a basic configuration of the invention.
[0018]
The invention of claim 4 is the invention of claim 3, wherein the material to be melted is the combustion residue and fly ash from the waste incinerator, and the molten slag in the plasma melting furnace body is formed by the plasma arc of the main electrode. The molten slag overflowed from the molten slag outlet by the plasma arc of the reheating electrode is heated to a temperature of about 1600 ° C. to 1800 ° C.
[0019]
According to a fifth aspect of the present invention, in the third or fourth aspect of the present invention, the molten slag overflowing from the molten slag outlet is caused to flow into a molten slag reservoir provided downstream, and the molten slag in the molten slag reservoir is melted. The slag is heated by a plasma arc generated by a reheating electrode.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to FIG. In FIG. 1, the same reference numerals are used for the same parts and members as in FIG.
FIG. 1 is a longitudinal sectional view showing the main part of the plasma arc melting furnace according to the present invention, and the configuration of the other parts except for the reheating electrode 24 is almost the same as in FIG. For this reason, it is omitted here.
[0021]
In FIG. 1, 1 is the ash hopper of the melt A, 2 is the melt A feeding device, 3 is the melting furnace body, 3a is the melt feed port, 4 is the graphite main electrode, and 5 is the graphite start. Electrode, 6 is a furnace bottom electrode, 7 is a furnace bottom cooling fan, 8 is a DC power supply, 9 is an inert gas supply device, 10 is a molten slag outlet, 11 is a tap hole, 12 is a combustion chamber, 13 is combustion air A fan, 24 is a reheating electrode, and 25 is a DC power supply for the reheating electrode.
[0022]
The plasma melting furnace body 3 has a substantially circular cross section, and is formed of a cylindrical body and an inverted conical ceiling. A melt slag outlet 10 for the melt A is opened on one side of the cylindrical body, and a supply port 3a for the melt A is opened on the other side opposite to the melt slag outlet 10.
A main electrode 4 is inserted and supported in the furnace main body 3 so as to be movable up and down in a vertical posture in an electrode insertion hole provided in the center of the furnace ceiling wall. Similarly, the start electrode 5 is inserted and supported in the furnace main body 3 so as to be able to advance and retreat in an inclined posture in an electrode insertion hole provided in a side portion of the furnace ceiling wall.
[0023]
In this embodiment, the graphite main electrode 4 is a hollow cylindrical body, and the inert gas C necessary for maintaining the inside of the plasma melting furnace body 3 in a reducing atmosphere is passed through the hollow holes of the electrodes 4 and 5. Supply in.
Moreover, although argon and nitrogen are used as the inert gas C, nitrogen is usually used from the viewpoint of economy.
[0024]
The graphite reheating electrode 24 is a non-transfer type electrode or a twin torch type electrode that generates a plasma arc between two electrodes, and the molten slag B overflows into the combustion chamber 12 via the molten slag outlet 10. It is inserted and supported in the combustion chamber 12 so as to be able to move forward and backward in an inclined posture from the side of the combustion chamber 12 so that a plasma arc is generated at the falling point.
A DC voltage (about 100 to 200 V) is supplied to the reheating electrode 24 from the DC power supply device 25 for the reheating electrode, and a current of about 500 to 1000 A per ton of slag flows when a plasma arc is generated. .
In the embodiment of FIG. 1, a reheating power source DC power supply 25 is provided separately from the DC power supply device 8 for the main electrode 4. Of course, it is also good.
[0025]
Next, the melting process of the material A to be melted using the plasma arc melting furnace according to the present invention will be described.
The melt A supplied into the plasma melting furnace main body 3 is heated to a temperature of about 1300 ° C. to 1500 ° C. exceeding the melting point (1200 ° C. to 1300 ° C.) by the thermal energy by plasma arc discharge as described above. It becomes a high-temperature liquid molten slag B.
In the conventional plasma arc melting furnace, the temperature of the molten slag B is maintained at 1400 ° C. to 1600 ° C. in order to avoid the presence of unmelted or incomplete melt in the molten slag B. The plasma melting furnace body 3 is in operation. On the other hand, in the plasma arc melting furnace of the present invention, the temperature of the molten slag B is kept as low as possible so that it can be maintained at about 1400 ° C. As a result, the molten slag outlet 10 overflows. In the molten slag B, there is a possibility that some unmelted material or incomplete molten material is mixed.
[0026]
In this state, the molten slag B overflowing from the molten slag outlet 10 and falling is exposed to the plasma arc generated by the reheating electrode 24 and reheated to 1600 ° C. to 1800 ° C. By this reheating, the non-melted material and the incomplete molten material mixed in the molten slag B are completely melted.
[0027]
In the embodiment of FIG. 1, the molten slag B that overflows from the molten slag outlet and falls into the combustion chamber 12 as described above is directly heated by applying a plasma arc generated by the reheating electrode 24. However, a separate molten slag reservoir (not shown) may be provided in the slag chute 26, and the molten slag B received in the slag reservoir may be heated by a plasma arc generated by the reheating electrode 24. In this case, in addition to the twin torch and the non-transfer type electrode as the heating electrode, it is also possible to use one heating electrode as the negative electrode and the slag reservoir as the positive electrode.
[0028]
The high-temperature molten slag B, which is reheated by the plasma arc of the reheating electrode 24 and completely melts the unmelted or incomplete melt, falls into a slag water cooling tank filled with water, Become. Then, the slag is discharged into a slag reservoir by a slag carry-out conveyor (not shown).
[0029]
The material A to be melted is a mixture of combustion residue from the municipal waste incinerator and fly ash (fly ash / combustion residue = 1/10), and the material A to be melted is about 1300 ° C. in the plasma melting furnace body 3. According to the result of the melting test in which the molten slag B is reheated to a temperature of 1600 ° C. to 1800 ° C. in the combustion chamber 12 by the reheating electrode 24 while being heated to 1500 ° C. and melted. The granulated slag obtained from the water-cooled tank will exhibit a white color, and the granulated slag having a black color obtained using the conventional plasma arc melting furnace shown in FIG. It turns out to be different.
[0030]
In the case of the present invention, since the temperature of the molten slag B is about 1400 ° C. and relatively low, damage to the refractory material in the plasma melting furnace body 3 and in the vicinity of the molten slag outlet 10 is greatly reduced. It has been found that the service life can be extended.
[0031]
In the embodiment of FIG. 1, the case where the waste incineration residue or fly ash is used as the melted material A has been described, but the present invention is not limited to such combustion residue and fly ash, Needless to say, the present invention can also be applied to melting treatment of industrial waste and the like containing selenium.
[0032]
【The invention's effect】
In the present invention, a reheating electrode 24 is provided outside the molten slag outlet 10 of the plasma melting furnace body 3, and the molten slag B overflowing from the molten slag outlet 10 is plasma arc of the reheating electrode 24. By reheating with the above, the unmelted or incomplete melt in the molten slag B that has overflowed is completely melted.
As a result, the temperature of the molten slag B in the plasma melting furnace body 3 is set to a temperature (1250 ° C. to 1400 ° C.) lower than the temperature (about 1300 ° C. to 1500 ° C.) in the case of the conventional plasma arc melting furnace. The operation of the plasma arc melting furnace can be performed, and the damage to the refractory material inside the plasma melting furnace main body 3 and in the vicinity of the molten slag outlet 10 is significantly reduced.
Moreover, since the molten slag B overflowing from the molten slag outlet 10 is reheated to a high temperature of 1600 ° C. to 1800 ° C. by the plasma arc generated by the reheating electrode, the remaining unmelted or incomplete melt Will be completely melted, resulting in very high quality granulated slag.
Furthermore, when the molten slag B is reheated to a high temperature by the reheating electrode 24, the color of the granulated slag obtained from the molten slag B becomes white. As a result, the granulated slag obtained by the practice of the present invention can be used as a cement raw material or a cement aggregate, unlike the black granulated slag obtained from a conventional plasma arc melting furnace. The reuse range of crushed slag will be greatly expanded, and the reuse of waste resources will be further improved.
The present invention has excellent practical utility as described above.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a main part of a plasma arc melting furnace according to an embodiment of the present invention.
FIG. 2 is a longitudinal sectional view showing a DC arc discharge type graphite electrode type plasma arc melting furnace in which a conventional incineration residue, fly ash, or the like is melted.
[Explanation of symbols]
A is a material to be melted, B is a molten slag, C is an inert gas, D is a gas body, E is a molten fly ash, 1 is an ash hopper, 2 is a melt supply device, 3 is a plasma melting furnace body, 3a is Molten material supply port, 4 is a graphite main electrode, 5 is a graphite start electrode, 6 is a furnace bottom electrode, 7 is a furnace bottom cooling fan, 8 is a DC power supply, 9 is an inert gas supply device, and 10 is a molten slag flow Outlet, 11 is a tap hole, 12 is a combustion chamber, 13 is a combustion air fan, 14 is an exhaust gas cooling fan, 15 is a bag filter, 16 is an induction fan, 17 is a chimney, 18 is a molten fly ash conveyor, 19 is fly ash No. 20 is a slag water cooling tank, 21 is a slag carry-out conveyor, 22 is a slag reservoir, 23 is a slag cooling water cooling device, 24 is a graphite reheating electrode, 25 is a DC power supply device for reheating, 26 is a slag chute, and 27 is Gas cooling tower.

Claims (5)

A plasma melting furnace main body having a molten slag outlet and a melt supply port on the side wall, a melt supply apparatus for supplying the melt into the plasma melting furnace main body, and a plasma arc is generated by electric power from the DC power supply. A main electrode and a furnace bottom electrode, an inert gas supply device for supplying an inert gas into the plasma melting furnace body, and a slag water cooling tank for receiving the molten slag overflowing from the molten slag outlet through a slag chute. In the plasma arc melting furnace, the melting temperature of the melt in the plasma arc melting furnace is set to 1400 ° C. or less, and the slag chute outside the molten slag outlet is supplied with electric power from a DC power supply device. and Okoshisei the plasma arc is provided reheat electrodes for heating the molten slag overflow from the molten slag outlet, the plasma arc of the reheating electrode The non-melt molten slag from the molten slag outlet causes complete melting, plasma arc melting furnace, characterized in that the arrangement for re-heating the slag to 1600 ° C. to 1800 ° C.. The plasma according to claim 1 , wherein the material to be melted is incineration residue and / or fly ash from a waste incinerator , and further, a slag reservoir is provided in the slag chute and a reheating electrode is provided in the slag reservoir. Arc melting furnace.   In the main body of the plasma melting furnace, the melted material is melted by the plasma arc generated by the main electrode, and the molten slag overflowing from the molten slag outlet and the molten slag containing the incomplete melt is generated by the reheating electrode. Plasma arc melting characterized in that white granulated slag is obtained by supplying high-temperature molten slag that has been heated by the generated plasma arc and melted the unmelted or incomplete melt into the slag water cooling tank A method for melting a material to be melted using a furnace.   The material to be melted is incineration residue and / or fly ash from the waste incinerator, and the plasma slag in the main body of the plasma melting furnace is brought to a temperature of about 1400 ° C. or less by the plasma arc of the main electrode, and the plasma arc of the reheating electrode The molten slag overflowing from the molten slag outlet is heated to a temperature of about 1600 ° C. to 1800 ° C. according to claim 3.   The molten slag overflowing from the molten slag outlet is caused to flow into a molten slag reservoir provided downstream, and the molten slag in the molten slag reservoir is heated by a plasma arc generated by a reheating electrode. Or the melting processing method of the to-be-melted object using the plasma arc melting furnace of Claim 4.

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