JP2004177080A - Dc electric resistance type melting furnace and its operation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DC electric resistance type melting furnace and its operation method for realizing stable operation. <P>SOLUTION: A position of a central electrode 2 is controlled by an electrode lifting device 3 so that electric power supplied by a DC power source 1 becomes constant. A temperature under a furnace cover of the melting furnace and in the vicinity of an exhaust gas outlet of the furnace is measured by thermocouples 40 and 41, and an input quantity of incineration ash is controlled by estimating the thickness of an ash layer 11 by this measured value. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a DC electric resistance melting furnace for melting and processing inorganic wastes such as refuse incineration ash using a DC electric resistance method, and a method for controlling the operation thereof.
[0002]
[Prior art]
In recent years, as the location of landfills has become more difficult, incineration ash that has come out of incinerators due to garbage incineration has been melted in an ash melting furnace, and a process to detoxify harmful substances contained in the ash has been implemented. Is being done.
[0003]
In a DC electric resistance type melting furnace, a current is passed from a DC power source between an electrode installed at the bottom of the furnace and a movable central electrode made of carbon material so that a large current can be passed, and the Joule heat is generated. The incineration ash is heated and melted, and the powdered or solid incineration ash is integrated to contain harmful substances and reduce the volume. Since the center electrode is made of carbon material, a combustion reaction with oxygen in the furnace, a sublimation reaction, or a reduction reaction with metal oxides in ash due to an increase in the furnace temperature causes carbon dioxide or carbon monoxide. Gasification. Therefore, the center electrode is consumed with operation.
[0004]
[Patent Document 1]
Japanese Patent Application Laid-Open No. Hei 9-112449 (FIG. 1)
In the above patent document, for the control of the melting furnace, a plurality of temperature detectors are provided on the furnace wall, the temperature distribution of the furnace wall is examined, and the melting slag level and the furnace temperature are detected from this temperature distribution, A melting furnace for controlling the input amount of ash and the input amount of electric power is disclosed.
[0005]
When treated in a melting furnace, the incinerated ash melts into slag, which has a correlation between melting temperature and resistivity. The slag has a resistivity of, for example, 4 Ωcm when the melting temperature is 1500 ° C., and has a high resistance but is electrically conductive. Then, a direct current flows between both electrodes through the molten slag, and the slag is heated by resistance loss generated in the molten slag.
[0006]
In addition, the incinerated ash to be treated is cut out quantitatively from the upper side or upper side of the melting furnace and charged on the slag, but it is necessary to melt a certain amount of the ash in a certain time in order to perform a stable operation. . When the melting rate of the ash is unstable or the height of the ash layer on the slag is not kept constant, the volatile substances such as NaCl, KCl, ZnCl ₂ , PbCl _{2 and the} like, which are present in the ash, are present. Irregularities occur in the generation of gas, hindering the stable operation of the exhaust gas device, or the low-boiling substances solidify in the ash, causing the gas to pass through the ash, causing bumping of the gas and the liquid level of the slag Problems such as fluctuations occur.
[0007]
Therefore, in order to perform stable operation in the melting furnace, it is necessary to operate the slag temperature and the convection flow velocity constant in order to keep the ash melting rate constant, and to keep the ash layer height constant Control operation is required.
[0008]
[Problems to be solved by the invention]
However, the temperature of molten slag is about 1500 ° C., and there is no method for continuously measuring the temperature of such a high-temperature liquid. In addition, the radiation thermometer cannot measure because ash covers the slag.
[0009]
In addition, a measuring instrument for measuring ash height is required to have heat resistance, and must withstand chemical reactions at a high temperature, for example, a chlorine gas atmosphere. difficult.
[0010]
Further, as a driving method for maintaining the temperature of the slag constant, a control method for controlling the operation so that the output power of the DC power supply is constant, since the heat source is resistance loss due to the slag, to thereby stabilize the heating value is considered. Can be However, the center electrode wears and becomes shorter or thinner with operation, and the current distribution changes due to the wear of the center electrode, and the position of a heat generating point (hot point) formed in the slag changes. Therefore, the temperature of the slag surface in contact with the ash and the convective flow velocity of the slag, which greatly affect the melting of the ash, are not constant but change.
[0011]
In addition, in order to keep the height of the ash constant, a method is conceivable in which the charging amount of the ash is controlled in accordance with the slag slag discharging amount. However, ash contains metals such as iron and copper, which settle at the bottom of the furnace, so that the amount of ash and the amount of slag slag are not the same. The height of the ash cannot always be constant.
[0012]
It is an object of the present invention to provide a DC electric resistance melting furnace which realizes stable operation and an operation method thereof.
It is another object of the present invention to provide a DC electric resistance melting furnace and an operating method capable of maintaining the temperature and convective flow velocity of slag in contact with ash and keeping the amount of ash melted constant.
[0013]
It is another object of the present invention to provide a DC electric resistance melting furnace and an operating method that can control the height of the ash layer to be constant.
[0014]
[Means for Solving the Problems]
In order to solve the above problems, a first embodiment of a DC electric resistance type melting furnace according to the present invention has a first electrode and a second electrode that can move inside the melting furnace, and is characterized by a DC power supply and an electrode elevation control. Means.
[0015]
The DC power supply supplies power by flowing a current between the first electrode and the second electrode.
The electrode elevation control means controls the position of the first electrode so that the power supplied from the DC power supply is constant.
[0016]
In the DC electric resistance type melting furnace, for example, the DC power supply outputs a current of a designated value, and the electrode elevation control unit controls a resistance value between the first electrode and the second electrode to be constant. The position of the first electrode is controlled so that
[0017]
In the DC electric resistance melting furnace of the first embodiment, the position of the first electrode is controlled based on the power supplied by the DC power supply. Therefore, even if the first electrode is consumed, the temperature distribution and the flow velocity of the slag can be kept constant.
[0018]
A second embodiment of the DC electric resistance melting furnace according to the present invention includes a temperature measuring unit and a charging amount controlling unit.
The temperature measuring means measures the temperature in the melting furnace.
[0019]
The input amount control means estimates the thickness of the ash layer based on the measurement result of the temperature by the temperature measurement means, and controls the input amount of the incinerated ash to be input.
The temperature measuring means, for example, measures at least one of the temperature under the furnace lid of the melting furnace or the vicinity of an exhaust gas outlet of the furnace, and the charging control means measures the temperature near the furnace bottom or the exhaust gas outlet. The input amount is controlled using at least one of the temperatures in the vicinity.
[0020]
In the DC electric resistance melting furnace of the second embodiment, the thickness of the ash layer is estimated based on the temperature in the melting furnace, for example, the temperature near the bottom of the lid or the temperature near the exhaust gas outlet, and the amount of ash input , The thickness of the ash layer can be kept constant.
[0021]
The present invention also includes an operation method in an electric resistance melting furnace within the scope thereof.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
In order to solve the above problems, the present invention has focused on a slag heating mechanism in a melting furnace, and has realized a DC electric resistance melting furnace capable of performing control for keeping the temperature and flow rate of the slag constant. .
[0023]
In the vicinity of the tip of the center electrode, the electric field intensity is high, a large amount of current flows, and a hot point is formed at which heating is performed by resistance loss. The slag that has been heated and expanded at the hot point convects and floats upward, and then flows toward the side wall of the furnace. Therefore, even if the central electrode is consumed, by controlling the position of the central electrode up and down so that the hot spot is formed in the slag layer at substantially the same position, the output current of the DC power supply is kept constant. As a result, the heat quantity at the hot point can be kept constant, and as a result, the flow velocity can be kept constant.
[0024]
If the position of the tip of the center electrode changes, the resistance value changes. Therefore, if the resistance is constantly controlled, the position of the tip of the center electrode will be constant, and power = output current x output current X Since it is a resistance value, the electric power (the amount of heat applied) consumed to melt the ash is constant. Therefore, if control is performed to keep the value of the current flowing through the electrode constant, the temperature and flow rate of the slag that comes into contact with the ash can be kept constant.
[0025]
Further, when the height of the ash layer formed on the slag layer is reduced, the amount of heat absorbed by the ash layer from the radiant heat from the molten slag decreases, so that the temperature in the furnace naturally increases. Conversely, when the ash layer becomes thicker, the amount of heat absorbed by the ash layer increases, so that the temperature inside the furnace, for example, the temperature immediately below the exhaust gas outlet or immediately below the furnace lid decreases. Therefore, the thickness of the ash layer can be kept constant by controlling the charging amount of the incinerated ash based on the temperature in the furnace.
[0026]
The temperature immediately below the furnace lid is 900 to 1000 ° C, and the exhaust gas outlet temperature is 500 to 700 ° C, which is lower than the molten slag temperature. In the direct current resistance melting furnace in the present embodiment, the temperature in the exhaust gas outlet and the temperature immediately below the furnace lid can be continuously measured by using a thermocouple or the like as a means for measuring the temperature in the furnace. Then, the temperature of the exhaust gas outlet and the temperature immediately below the furnace lid are continuously measured, and the height of the ash layer can be kept constant by adjusting the amount of the incinerated ash to be charged based on the temperature.
[0027]
FIG. 1 is a diagram illustrating a configuration example of a DC electric resistance melting furnace according to the present embodiment.
In the figure, the furnace wall of the DC electric resistance melting furnace is composed of a double wall of a carbon wall 32 and a refractory wall 33, and a water-cooled steel shell. The DC electric resistance type melting furnace shown in the figure has a DC power supply 1, a central electrode 2, an electrode lifting device 3, a furnace bottom electrode 4, a control device 5, an exhaust gas outlet 20, a slag outlet 21, a metal tap 22, It has two ash storage bins 30a, 30b, their ash quantitative cutout devices 31a, 31b, a thermocouple under the furnace lid 40, and a thermocouple 41 for exhaust gas outlet.
[0028]
The cylindrical central electrode 2 made of carbon material and the bottom electrode 4 embedded in the bottom of the carbon wall 32 are connected to a DC power source 1, and the power supplied from the DC power source 1 is between them. Causes a current to flow. The DC power supply 1 supplies electric power between the center electrode 2 and the furnace bottom electrode 4 while maintaining an output current at a designated magnitude. The DC power supply 1 includes a measuring unit that measures the resistance value at both ends, and the measured value is notified to the control device 5. The center electrode 2 is moved up and down in the melting furnace by the electrode lifting device 3. The electrode lifting / lowering device 3 raises / lowers the center electrode 2 in the furnace based on an instruction from the control device 5 and moves the position of the tip thereof up and down.
[0029]
The exhaust gas outlet 20 is an outlet for discharging gas and the like generated when the incinerated ash is melted. The slag tap 21 is a tap for discharging slag from the molten slag layer 11, and the metal tap 22 is a tap for tapping the metal layer 12 that has accumulated more than a certain amount. The ash storage bins 30a and 30b store incinerated ash to be put into the melting furnace, and the stored ash is cut out by the ash fixed quantity cutting device 31 and charged into the melting furnace. The ash fixed amount cutout devices 31a and 31b cut out a fixed amount of ash from the ash storage bins 30a and 30b based on an instruction from the control device 5, and put the ash from the upper part of the melting furnace. The under-furnace thermocouple 40 measures the temperature under the furnace lid, and the exhaust gas outlet thermocouple 41 measures the temperature near the exhaust gas outlet 20. These measurement results are notified to the control device 5. .
[0030]
At the bottom of the furnace below the slag layer 11, there is a metal layer 12 made of metal that has settled due to a difference in specific gravity from slag. The incinerated ash is charged from the storage bins 30a, 30b into the quantitative furnace by the ash quantitative cut-out devices 31a, 31b. Therefore, the ash layer 10 made of the incinerated ash is formed above the slag layer 11. The ash layer 10 blocks the slag from reacting with the atmosphere in the furnace and prevents radiant heat from the slag layer.
[0031]
Since the molten slag has electric conductivity, an electric circuit including the center electrode 2, the slag layer 11, the metal layer 12, and the furnace bottom electrode 4 is formed at both ends of the DC power supply 1. Then, thermal energy is supplied to the slag due to the resistance loss generated in the slag layer 11, and the heat from the slag layer 11 causes the incinerated ash of the ash layer 12 that comes into contact with the slag to melt and become slag.
[0032]
FIG. 2 is a diagram showing a current distribution in the melting furnace, and current lines are indicated by broken lines 50.
The current flows from the center electrode 2 in the radial direction of the melting furnace to the furnace bottom electrode 4 through the carbon wall 32 and the route from the center electrode 2 to the furnace bottom electrode 4 almost straight. In the case of the electrode (2), since the electric field strength at the tip portion is high, the current flows intensively at the tip portion, and as a result, the current flows mainly from the tip portion of the central electrode 2 as shown by a broken line 50.
[0033]
Therefore, a hot point 60 is formed near the tip of the center electrode 2 as shown in FIG. The slag at the hot point 60 moves upward by convection, and a slag flow is formed along the arrow 61.
[0034]
Since the central electrode 2 is consumed with the operation of the melting furnace, if the central electrode 2 is fixed at the same position, the position where the hot point 60 is formed gradually moves upward with the consumption of the central electrode 2. go. Then, the flow 61 changes with the movement of the hot point 60, and the flow velocity of the slag in contact with the ash and the temperature distribution of the slag also change. As a result, the melting rate of the ash and the temperature of the furnace bottom also change, so that the melting state changes. Since the ash melt contains a volatile substance, it is required that the position of the tip of the center electrode 2 be always constant in order to stabilize the molten state and prevent bumping.
[0035]
In the DC electric resistance melting furnace according to this embodiment, the DC power supply 1 supplies a constant current value between the two electrodes 2 and 4, and the control device 5 monitors the resistance value between the electrodes. Then, the position of the center electrode 2 is controlled using the electrode lifting device 3 so that the resistance value becomes constant. Thereby, the position of the center electrode 2 can be lowered by an amount corresponding to the consumption amount, and the position of the hot point 60 generated in the slag layer 11 can be maintained at a substantially constant position. Since the electric resistance value of the metal layer 12 is much smaller than that of the slag layer 11, the effect can be neglected.
[0036]
Further, by keeping the output current of the DC power supply 1 constant and controlling the position of the center electrode 2 so that the resistance value is constant and operating the power consumption to be constant, the amount of heat added at the hot point 60 is increased. And the slag flow 61 can be kept constant. Therefore, it is possible to operate the slag in contact with the ash while keeping the temperature and the flow rate constant, and it is possible to keep the ash melting rate constant.
[0037]
The height of the ash layer 11 is adjusted so that the temperature of the thermocouple 40 provided under the furnace lid and the temperature of the thermocouple 41 provided near the exhaust gas outlet 20 of the furnace become constant. Control. When the incinerated ash melts to form slag and the ash layer 11 becomes thinner, the radiant heat from the slag absorbed by the ash layer 11 decreases, so that the temperature in the furnace increases. The control device 5 monitors the temperature inside the furnace with the thermocouples 40 and 41, estimates the thickness of the ash layer 11 from these temperatures, and controls the ash quantitative cut-out device 31 to determine the height of the ash layer 11. Keep constant.
[0038]
An example of the relationship between the thickness of the ash layer 11, the exhaust gas outlet temperature, and the temperature immediately below the furnace lid is shown below.
a) When the thickness of the ash layer 11 is 100 mm, the exhaust gas outlet temperature is 587 ° C., and the temperature immediately below the furnace lid is 900 ° C.
b) When the thickness of the ash layer 11 is 50 mm, the exhaust gas outlet temperature is 658 ° C., and the temperature immediately below the furnace lid is 990 ° C.
c) When the thickness of the ash layer 11 is 150 mm, the exhaust gas outlet temperature is 500 ° C., and the temperature just below the furnace lid is 820 ° C.
It becomes.
[0039]
By examining such a relationship in advance and controlling the ash quantitative cut-out device 31 based on the temperature from the thermocouples 40 and 41 to control the amount of ash input, the thickness of the ash layer 11 can be controlled to a desired value. Thickness can be maintained. For example, in the above example, when it is desired to keep the thickness of the ash layer 11 at 100 mm, the exhaust gas outlet temperature is set to 590 ° C., and the temperature of 900 ° C. immediately below the furnace lid is set to a target value, for example, the ash input amount becomes 416 kg / h. Then, ash input control may be performed.
[0040]
In addition, as long as the thickness of the ash layer increases and the ash layer does not hinder the volatilization of volatiles, the ash is continuously charged at a constant speed for 1 minute, 1 minute pause, 5 minutes Intermittent charging such as charging 5 minutes pause may be used. In addition, thermocouples 40 and 41 are provided below the furnace lid and near the exhaust gas outlet to measure the temperature inside the furnace. However, if the temperature inside the furnace can be measured stably, the thermocouples may be placed at other positions. A pair may be provided, or measurement means other than a thermocouple may be used.
[0041]
Note that the above numerical examples are merely examples, and the detailed values vary depending on various conditions such as physical properties and furnace dimensions.
[0042]
【The invention's effect】
According to the present invention, a stable operation of a direct current resistance melting furnace can be realized.
[0043]
In addition, the temperature and convection flow velocity of the slag in contact with the ash can be maintained, and the amount of the ash melted can be kept constant.
Further, the height of the ash layer can be controlled to be constant.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration example of a direct current resistance melting furnace according to an embodiment.
FIG. 2 is a diagram showing a current distribution in a melting furnace.
FIG. 3 is a diagram showing hot points formed by a slag layer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 DC power supply 2 Central electrode 3 Electrode raising / lowering device 4 Furnace bottom electrode 5 Control device 10 Ash dust 11 Slag layer 12 Metal layer 20 Exhaust gas outlet 21 Slag tap hole 22 Metal tap hole 30 Ash storage bin 31 Ash quantitative cut-out device 32 Carbon Wall 33 Refractory wall 34 Iron shell 40 Thermocouple under furnace lid 41 Exhaust gas outlet thermocouple

Claims (6)

A DC power supply for supplying electric power by flowing a current between the first electrode and the second electrode in a DC electric resistance type melting furnace having a first electrode and a second electrode movable in the melting furnace;
Electrode elevation control means for controlling the position of the first electrode so that the power supplied by the DC power supply is constant;
A direct current resistance melting furnace comprising: The DC power supply outputs a current of a designated value, and the electrode elevation control means controls the first electrode so that a resistance value between the first electrode and the second electrode is constant. 2. The direct current resistance type melting furnace according to claim 1, wherein the position is controlled. Temperature measuring means for measuring the temperature in the melting furnace,
Estimating the thickness of the ash layer based on the measurement result of the temperature by the temperature measurement means, the input amount control means to control the input amount of incineration ash to be input,
A direct current resistance melting furnace comprising: The temperature measuring means measures at least one of the temperature under the furnace lid of the melting furnace or near the exhaust gas outlet of the furnace, and the charging control means measures the temperature near the furnace bottom or the vicinity of the exhaust gas outlet. 4. The DC electric resistance melting furnace according to claim 3, wherein the input amount is controlled using at least one of the temperatures. In an operation method in a direct current resistance type melting furnace having a first electrode and a second electrode movable in the melting furnace,
Supplying current by flowing a current between the first electrode and the second electrode;
An operation method, wherein the position of the first electrode is controlled so that the power supplied from the DC power supply is constant. Measure the temperature inside the melting furnace,
A method of operating a direct current resistance melting furnace, comprising controlling an amount of incinerated ash to be charged based on a result of temperature measurement by the temperature measuring means.

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