JP3317792B2 - Method for detecting boundary between molten slag layer and molten salt layer in electric resistance melting furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric resistance type melting furnace for melting and processing materials to be melted such as fly ash and incinerated ash generated when incineration of municipal waste and industrial waste is performed. The present invention relates to a method for detecting a boundary between a molten slag layer and a molten salt layer.

[0002]

2. Description of the Related Art Generally, most of molten materials such as fly ash generated when incinerating municipal waste and industrial waste are landfilled. However, it is becoming increasingly difficult to secure landfill sites every year, and there is a demand for effective use and volume reduction of the material to be melted. Fly ash has been designated as a specially managed waste and must be rendered harmless by intermediate treatment for final disposal.

Therefore, in recent years, as a method for solving these problems, a melting process of a material to be melted such as fly ash using an electric resistance melting furnace or the like has been performed. When slag is formed by melting the material to be melted by an electric resistance melting furnace, the volume is greatly reduced, and it becomes a physically and chemically stable material, and is effectively used for aggregates and roadbed materials. It becomes possible.
Further, the electric resistance type melting furnace is often used because the molten material can be separated into slag and molten salt, which is extremely advantageous for effective use of slag.

FIG. 3 is a schematic longitudinal sectional view of an electric resistance type melting furnace used for melting a material to be melted such as fly ash. The melting furnace includes a supply port 10a, an exhaust gas outlet 10b, and a tap hole (shown in FIG. 1). (Omitted), respectively, and the furnace body 10
And a plurality of electrodes 11 and the like suspended vertically from the ceiling wall into the furnace.

[0005] The molten material 12 such as fly ash that has been introduced into the furnace from the supply port 10 a is applied by applying a voltage to the electrodes 11 to flow a current through the molten material 12 between the electrodes 11. The melt 12 is heated by the Joule heat of the melt 12 itself, and is sequentially melted. Also, when the material to be melted 12 such as fly ash is melted,
Since this is composed of various kinds of components, a molten slag layer 13 and a molten salt layer 14 are respectively formed from the furnace bottom due to a difference in specific gravity in the furnace. The molten slag and the molten salt are extracted from a molten slag outlet (not shown) and a molten salt outlet (not shown) formed on the peripheral wall of the furnace body in a state where both are separated.

Table 1 below shows an example of the composition of the molten slag and the molten salt.

[0007]

[Table 1]

As shown in Table 1, the main components of the molten slag and the main components of the molten salt are clearly different, and both have greatly different physical properties depending on their compositions. For example, the electric resistance of the molten slag is 2 to 10 Ω · cm, and the electric resistance of the molten salt is 0.2 to 0.6 Ω · cm. or,
The true specific gravity of the molten slag is 2.7 to 2.9, and the true specific gravity of the molten salt is 2.2 to 2.3. Further, the melting point and boiling point of the molten slag are higher than that of the molten salt.

As described above, the molten salt has a lower electric resistance than that of the molten slag, and the current easily flows. or,
The molten salt has a lower melting point and boiling point than molten slag. Therefore, in the electric resistance melting furnace, the heat used to heat the molten salt promotes the volatilization of the salt as a result. As a result, the electric input is consumed for volatilization of the molten salt to reduce the processing amount, and there arises a problem that the volatilized matter discharged from the exhaust gas outlet needs to be collected and processed.

As a means for solving these problems, it is necessary to extract the molten salt in a timely manner so that the molten salt does not form a layer in the furnace. For that purpose, it is necessary to know the boundary between the molten slag layer and the molten salt layer in the furnace.

Heretofore, the following methods have been known as methods for detecting the boundary between a molten slag layer and a molten salt layer in an electric resistance type melting furnace. A method of measuring the amount of contents by measuring the weight of the entire melting furnace. A method in which an electrode for detection is provided separately from an electrode for melting in a furnace, and the electrode is inserted into the melt to measure an electric resistance value. A method of measuring with a radiation level meter.

[0012]

However, in the above-mentioned method, if the difference in specific gravity between the separated molten slag layer and the molten salt layer is small, an error becomes large and accurate measurement cannot be performed.
Moreover, the exhaust gas duct, the supply chute, etc., and the furnace body must be connected by a flexible joint, which complicates the equipment. In the method (1), the life of the electrode is short (duration of about 10 hours in continuous use), and it takes time and cost to replace the electrode. In addition, since the electrodes are consumed over time, the electrode length at the time of measurement is uncertain, and accurate measurement cannot be performed. In the method of (1), there are various problems, such as the need for notification to the government office and the chief of handling in order to handle radiation, and poor handling.

The present invention has been made in view of such problems, and can perform relatively high-accuracy measurement without the need for a special detection device, and is excellent in handleability and safety. An object of the present invention is to provide a method for detecting a boundary between a molten slag layer and a molten salt layer in an electric resistance type melting furnace.

[0014]

In order to achieve the above-mentioned object, a method for detecting a boundary between a molten slag layer and a molten salt layer according to the present invention comprises the steps of: In the electric resistance type melting furnace, the electrodes are melted by applying a voltage to a plurality of electrodes suspended vertically from the ceiling wall of the furnace to form a molten slag layer and a molten salt layer from the bottom of the furnace. Then, at least one electrode outer peripheral surface is slidably covered with a vertically movable electrode cover made of an insulating material, and the electrode is immersed for a certain length in the molten slag layer and the molten salt layer. Move the electrode cover up and down while applying voltage,
The boundary between the molten slag layer and the molten salt layer is detected by measuring the length of insertion of the electrode cover into the furnace and the change in the current flowing through the electrode.

[0015]

When detecting the boundary between the molten slag layer and the molten salt layer in the electric resistance melting furnace, the electrode is immersed in the molten slag layer and the molten salt layer for a certain length, and the electrode cover is applied while applying a voltage to the electrode. The electrode is gradually lowered from the ascending position, and the insertion length of the electrode cover into the furnace and the value of the current flowing through the electrode are continuously measured. As the electrode cover is lowered, the electric resistance increases and the value of the current flowing through the electrode gradually decreases. When the lower end of the electrode cover falls from the molten salt layer to the molten slag layer, the rate of increase in the electric resistance value suddenly becomes gentle. Therefore, the boundary between the molten slag layer and the molten salt layer can be detected by calculating the continuously detected insertion length of the electrode cover and the change in the value of the current flowing through the electrode.

According to this method, the boundary between the molten slag layer and the molten salt layer can be detected relatively accurately regardless of the difference in specific gravity between the molten slag layer and the molten salt layer and the consumption of the electrodes.
Further, since the electrode for melting shares the electrode for boundary detection, it is only necessary to add an electrode cover and an elevating device to the melting furnace, and the maintenance and management are simple and easy.
Furthermore, it does not use radiation or the like, and is extremely excellent in handleability and safety.

[0017]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an electric resistance type melting furnace for carrying out the method of the present invention, 1 is a furnace body, 2 is an electrode, 3 is a lifting device for an electrode, 4 is a power supply, 5 is an electrode cover, and 6 is a lifting and lowering for an electrode cover. Apparatus, 7 is a molten layer, 7a is a molten slag layer, 7b
Is a molten salt layer, and 8 is a material to be melted.

The furnace body 1 includes a peripheral wall 1a, a ceiling wall 1b, and a bottom wall 1c formed of a steel plate and a refractory material such as a refractory brick.
Is formed in a cylindrical box shape, and a supply port 1 for introducing molten material 8 such as fly ash into the furnace is provided in a peripheral portion of the ceiling wall 1b.
d and an exhaust gas outlet 1e for discharging the exhaust gas in the furnace are formed respectively. Although not shown, the peripheral wall 1a
Are provided with a molten slag outlet (not shown) for extracting molten slag and a molten salt outlet (not shown) for extracting molten salt, respectively. An opening / closing device (not shown) for opening and closing is provided.

A plurality of carbon electrodes are used for the electrodes 2, and each of the electrodes 2 is inserted in the center of the ceiling wall 1 b of the furnace main body 1 so as to be vertically movable and connected to a power supply 4. ing. Each electrode 2 is held by a support arm 3a of an independent electrode lifting / lowering device 3 so as to be able to move up and down, and a melt layer 7 (a molten slag layer) is provided in accordance with the amount of melting of the material 8 to be melted or the amount of current. 7a and a molten salt layer 7b). The value of the current flowing through the electrode 2 is continuously measured by an ammeter or the like.

Each of the electrode lifting devices 3 includes a support arm 3a for holding the electrode 2, a guide column (not shown) for guiding the support arm 3a so as to be able to move up and down, and moving the support arm 3a up and down along the guide column. And a driving mechanism (not shown). Although the drive mechanism is not shown,
It is composed of a wire for suspending the support arm 3a, a winding drum for winding the wire, a motor for rotating the winding drum, and the like, and is supported by winding the wire on the winding drum and feeding the wire from the winding drum. The arm 3a can be moved up and down along the guide column. Note that a hydraulic cylinder or the like may be used for the drive mechanism.

The electrode cover 5 is formed in a cylindrical shape with an insulating material (for example, zirconia ceramic) and slidably covers one electrode 2. That is, the electrode cover 5 is vertically slidably fitted to the outer peripheral surface of one electrode 2, penetrates through the ceiling wall 1 b of the furnace body 1, and projects upward from the ceiling wall 1 b. Also, the electrode cover 5
Is held by the support arm 6a of the lifting device 6 for the electrode cover so as to be able to move up and down, gradually changing the contact area between the electrode 2 and the melt layer 7 and changing the amount of current flowing from the electrode 2 to the melt layer 7. It is to let. The lifting stroke of the electrode cover 5 is set so that the lower end of the electrode cover 5 can be set at the highest position where the lower end of the electrode cover 5 is located near the ceiling wall 1b (the solid line position in FIG. 1) and the position where it is immersed in the molten slag layer 7a. Have been. The length of the electrode cover 5 is set such that the upper end protrudes upward from the ceiling wall 1b even if the lower end is immersed in the molten slag layer 7a.

The elevating device 6 for the electrode cover has the same structure as the elevating device 3 for the electrode, and includes a support arm 6a for holding the electrode cover 5 and a guide column (shown in the figure) for guiding the support arm 6a up and down. And a drive mechanism (not shown) for moving the support arm 6a up and down along the guide column.

The length of the electrode cover 5 inserted into the furnace is continuously measured. That is,
The insertion length of the electrode cover 5 into the furnace is determined by detecting the amount of protrusion of the electrode cover 5 projecting upward from the ceiling wall 1b, or detecting the position of the support arm 6a, the position of the upper end of the electrode cover 5, and the like. Or by measuring. For this measurement, a visual method (for example, a method in which a scale is erected on the ceiling wall 1b and the protruding amount of the electrode cover 5 and the position of the support arm 6a and the like are visually read) or a stroke of a hydraulic cylinder for lifting and lowering is used. A method of electrically detecting (for example, a potentiometer, a rotary encoder) or the like is used. The length of insertion of the electrode cover 5 into the furnace is measured with reference to the highest position (solid line position in FIG. 1) where the lower end of the electrode cover 5 is located near the ceiling wall 1b.

Next, a description will be given of a case where the material to be melted 8 such as fly ash is melted using an electric resistance melting furnace.

An object 8 to be melted such as fly ash is introduced into the furnace from the supply port 1d of the furnace body 1 in an appropriate amount, and the material 8 to be melted between the electrodes 2 is supplied.
Is melted by being heated to about 1400 ° C. by the Joule heat of the melt 8 itself. At this time, the electrode cover 5 is at the highest position (solid line position in FIG. 1).

When the material to be melted 8 is melted, a molten slag layer 7a and a molten salt layer 7b are respectively formed in the furnace from the bottom due to a difference in specific gravity.

A constant amount of a new material 8 to be melted is continuously supplied from the supply port 1d into the furnace, and is sequentially melted.

When a certain amount of molten slag and molten salt accumulate in the furnace, they are separated from a molten slag outlet (not shown) and a molten salt outlet (not shown) formed on the peripheral wall 1a of the furnace body 1. And extracted.

In order to extract the molten salt, it is necessary to detect the boundary between the molten slag layer 7a and the molten salt layer 7b.

That is, at the time of detecting the boundary between the molten slag layer 7a and the molten salt layer 7b, the electrode 2 is immersed in the molten slag layer 7a and the molten salt layer 7b by a certain length, The electrode cover 5 is gradually lowered from the highest position (solid line position in FIG. 1) by the electrode cover lifting device 6, and the length of the electrode cover 5 inserted into the furnace and the value of the current flowing through the electrode 2 are continuously measured.

As the electrode cover 5 is lowered, the electrode 2
Is gradually covered from the part immersed in the molten salt layer 7b, and the electric resistance becomes large, so that the current hardly flows. As a result, the value of the current flowing through the electrode 2 decreases.

When the lower end of the electrode cover 5 falls from the molten salt layer 7b to the molten slag layer 7a, the electric resistance of the molten slag is extremely large compared to the electric resistance of the molten salt. The rate of increase in the resistance value suddenly decreases. Therefore, the boundary between the molten slag layer 7a and the molten salt layer 7b can be detected by continuously detecting the insertion length of the electrode cover 5 into the furnace and the change in the value of the current flowing through the electrode 2. .

FIG. 2 is a graph showing changes in the electric resistance value, the current value, and the like in the melt layer 7. As is clear from this graph, when the lower end of the electrode cover 5 extends from the molten salt layer 7b to the molten slag layer 7a, the rate of increase in the electrical resistance suddenly decreases, and the rate of decrease in the current value also decreases gradually. It turns out to be. Therefore, the boundary between the molten slag layer 7a and the molten salt layer 7b can be easily and easily detected by measuring the change in the length of the electrode cover 5 inserted into the furnace and the value of the current flowing through the electrode 2.

The electrode cover 5 is raised to the highest position except when the boundary between the molten slag layer 7a and the molten salt layer 7b is detected, and is taken out of the molten material layer 7. Thereby, the consumption of the electrode cover 5 is reduced.

In the above embodiment, the electrode cover 5 is gradually lowered from the highest position while applying a voltage to the electrode 2,
The length of insertion of the electrode cover 5 and the value of the current flowing through the electrode 2 are continuously measured to detect the boundary between the molten slag layer 7a and the molten salt layer 7b.
The electrode cover 5 is gradually raised from the lowest position (not shown) while applying a voltage to the molten slag layer 7 by continuously measuring the insertion length of the electrode cover 5 and the current value flowing through the electrode 2.
Alternatively, the boundary between a and the molten salt layer 7b may be detected.
In this case, the length of insertion of the electrode cover 5 into the furnace is measured with reference to when the electrode cover 5 is at the lowest position.

In the above embodiment, one of the electrodes 2 is covered by the electrode cover 5, but in another embodiment, a plurality of electrodes 2 are covered by the electrode cover 5, By moving the cover 5 up and down, the insertion length of the electrode cover 5 into the furnace and the value of the current flowing through the electrode 2 are continuously measured in the same manner as described above, and the boundary between the molten slag layer 7a and the molten salt layer 7b is detected. You may do it.

[0037]

As described above, according to the present invention, at least one outer peripheral surface of the electrode is slidably covered with an electrode cover made of an insulating material, and the electrode is inserted into the molten slag layer and the molten salt layer by a predetermined length. After immersion, the electrode cover is moved up and down while applying voltage to the electrode, and the length of the electrode cover inserted into the furnace and the change in the value of the current flowing through the electrode are measured. The boundary of the salt layer is detected.
As a result, since the specific gravity difference between the molten slag layer and the molten salt layer is small as in the conventional method, the error increases and accurate measurement cannot be performed, or the electrode for level detection is exhausted and accurate measurement is performed. The boundary between the molten slag layer and the molten salt layer can be detected relatively accurately without saying that it cannot be performed. Further, since the electrode for melting shares the electrode for boundary detection, it is only necessary to add an electrode cover and an elevating device to the melting furnace, and the maintenance and management are simple and easy. Furthermore, it does not use radiation and the like, and is extremely excellent in handleability and safety.

[Brief description of the drawings]

FIG. 1 is a schematic longitudinal sectional view of an electric resistance type melting furnace for carrying out a method of the present invention.

FIG. 2 is a graph showing changes in an electric resistance value, a current value, and the like in a melt layer of an electric resistance melting furnace.

FIG. 3 is a schematic longitudinal sectional view of a conventional electric resistance melting furnace.

[Explanation of symbols]

1 is a furnace body, 1b is a ceiling wall, 2 is an electrode, 5 is an electrode cover, 7a is a molten slag layer, and 7b is a molten salt layer.

Continuation of the front page (56) References JP-A-6-194210 (JP, A) JP-A-59-132931 (JP, A) JP-A-58-37479 (JP, A) JP-A-2-54125 (JP) , A) JP-A-6-176866 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F23J 1/00 F23G 5/00 F23G 5/50

Claims (1)

(57) [Claims] 1. A plurality of electrodes (2) suspended from a ceiling wall (1b) of a furnace body (1) so that a melted material (8) such as fly ash introduced into the furnace body (1) is vertically movable. ) Is melted by applying a voltage to the molten slag layer (7) from the furnace bottom in the furnace.
a) and at least one electrode (2) in an electric resistance melting furnace in which a molten salt layer (7b) is formed, respectively.
The outer peripheral surface was slidably covered with an electrode cover (5) made of an insulating material capable of ascending and descending, and the electrode (2) was immersed in the molten slag layer (7a) and the molten salt layer (7b) by a certain length. Thereafter, while applying a voltage to the electrode (2), the electrode cover (5) is moved up and down to measure the length of insertion of the electrode cover (5) into the furnace and the change in the value of the current flowing through the electrode (2). A boundary between the molten slag layer and the molten salt layer in the electric resistance type melting furnace, wherein the boundary between the molten slag layer and the molten salt layer is detected.