JP3629988B2 - Electric power control method for ash melting furnace - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power control method for an electric resistance ash melting furnace using three-phase alternating current.
[0002]
[Prior art]
Large amounts of ash are emitted from incinerators such as municipal waste or industrial waste. In the past, these ashes were simply used for landfill, but in recent years, ash melting treatment has been developed in the face of difficulties in the location of landfills.
[0003]
For example, JP-A-8-8060 proposes a power control method for a three-phase arc ash melting furnace. In this technique, the calorific value is distributed to each electrode as required, and therefore, a target impedance is determined for each electrode, and the electrode is moved up and down.
[0004]
Japanese Laid-Open Patent Publication No. 9-105507 proposes an ash melting furnace operating method that detects the molten slag level in an electric resistance ash melting furnace and provides an optimal and stable operating method. This method detects the slag level in the furnace with a molten slag level detector installed in the vertical direction on the furnace lid of the ash melting furnace, thereby controlling the ash supply amount and the power input amount to achieve optimum and stable. It is to drive.
[0005]
[Problems to be solved by the invention]
However, the prior art has the following problems.
[0006]
First, in the technique described in JP-A-8-8060, a target impedance is determined for each electrode, so that the current of each electrode is not necessarily constant. In general, when using a three-phase alternating current, it is desirable to keep the current of each phase constant so that the three phases do not become unbalanced.
[0007]
In this prior art, the current of each phase of the three-phase alternating current is unbalanced, an excessive current flows through some cables, and the heating efficiency of input power is reduced. In addition, when the neutral point of the three-phase alternating current deviates from the core and approaches the furnace wall, there is a problem that the furnace wall in that part is in contact with the hot molten slag and is easily damaged.
[0008]
In addition, when the arc heating method is used as in this prior art, the current concentrates on the surface of the object to be heated (molten slag), which makes it difficult to make the temperature distribution in the furnace uniform. In addition, the generation of harmonics is a problem peculiar to arc-type heating furnaces, which may cause adverse effects on control devices and computers, noise, or radio wave interference in the vicinity.
[0009]
The technique described in Japanese Patent Laid-Open No. 9-105507 is based on a DC electric resistance ash melting furnace, and cannot be easily applied to a three-phase electric resistance ash melting furnace using three-phase AC. In particular, although it is described that the input power amount is controlled by the power supply facility, in the case of three-phase alternating current, it is difficult to control the input power amount individually for each phase by the power supply facility.
[0010]
In general, in the case of the electric resistance heating method, there is a limit to the controllable range for power control by adjusting the electrode position. In order to increase the power from the value when the electrode is at the reference position, it is necessary to insert the electrode deeper. However, the electrode in the electric resistance heating method is inserted deeply into the object to be heated (molten ash), and there is little margin for movement from the reference position to the furnace bottom.
[0011]
As described above, in the electric resistance heating method, since the optimum position of the electrode is limited to a narrow range, the electric power cannot be changed greatly depending on the electrode position as in the arc heating. Thus, in the electrical resistance heating method, there is a limit to controlling the power by adjusting the electrode position.
[0012]
Furthermore, when the impedance is changed for power control, impedance matching between the power source and the load cannot be achieved, and the power that can be supplied to the electrode is reduced. There is also a problem that the impedance of the electrode cannot be set to an optimum value for operation.
[0013]
The present invention has been made to solve the above-described problems, and can control the amount of power input while maintaining the balance of the current of each phase, and the electrode impedance can be optimized. An object of the present invention is to provide a power control method for an electric resistance type ash melting furnace using a three-phase alternating current that can be operated in the same manner.
[0014]
[Means for Solving the Problems]
The above problems are solved by the following invention.
[0015]
Its invention provides a power control method of the electric resistance type ash melting furnace according to the three-phase AC, the current and voltage for each electrode was measured, calculates the impedance and power for each electrode from the measured current and voltage, three-phase An electric resistance ash melting furnace characterized by controlling the impedance of each electrode by raising and lowering each electrode so that the current of each phase of power is balanced, and controlling the entire power by switching the tap of the furnace power transformer This is a power control method.
[0016]
Here, the impedance and power for each electrode can be easily obtained by measuring the voltage E and current I of each electrode. For example, the impedance Z is Z = E / I. These variables are represented by a vector display including the phase.
[0017]
The impedance magnitude Z ₀ becomes Z ₀ = E ₀ / I ₀ when the effective values of the voltage E and the current I are E ₀ and I ₀ , respectively. Here, the resistance R and the reactance X are expressed as follows, where δ is the phase difference between the voltage E and the current I:
Z = R + jX = Z ₀ (cos δ + jsin δ)
Because
R = Z ₀ cos δ
X = Z ₀ sin δ
It is expressed.
[0018]
When the effective value of power is P ₀ , the power is
P ₀ = E ₀ I ₀ cos δ
It becomes. Note that cos δ represents a power factor.
[0019]
In the present invention, the entire power is controlled by switching the tap of the furnace power transformer. Thereby, unlike the prior art, it is possible to control electric power that cannot be controlled only by raising and lowering the electrodes. Further, it is possible to control the electric power in a state where the impedance is maintained at an optimum value for operation.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing an embodiment of the present invention. Power is supplied from the power transformer 1 to the three electrodes 2. Each electrode 2 is supported by an electrode lifting / lowering device 21 (some of the electrodes 2 are not shown) and inserted into a molten ash (molten slag) 9 in the ash melting furnace 3.
[0021]
For each electrode 2, the current and voltage are measured by an ammeter 41 and a voltmeter 42 (not shown for some electrodes 2). Here, what is measured by the voltmeter 42 is a voltage between each electrode 2 and the ground. These measurement results are transmitted to the power adjustment device 5 for signal processing.
[0022]
In the power adjustment device 5, the impedance is calculated for each electrode 2 and compared with a set value given in advance. When the impedance of the electrode 2 is increased or decreased based on the comparison result, the electrode lifting / lowering command means 51 in the power adjustment device 5 transmits a lifting / lowering command signal to the electrode lifting / lowering device 21 that supports the electrode 2. The electrode lifting / lowering device 21 raises / lowers the electrode 2 based on the transmitted command, and adjusts the impedance of the electrode 2 to be a set value.
[0023]
In the power adjustment device 5, the power of each electrode is calculated from the current and voltage of each electrode 2. These values are summed to calculate the power of the ash melting furnace 3 as a whole, and is compared with a separately set power setting value. Here, the power set value is a value set from the operation cycle of the ash melting furnace 3, the amount of ash charged, etc., and may be set manually or automatically.
[0024]
When increasing or decreasing the electric power of the ash melting furnace 3 as a whole based on the comparison result, the tap switching command means 52 in the power adjustment device 5 transmits a tap switching command signal to the tap switching means 11 of the power transformer 1. The tap switching unit 11 switches the tap of the power transformer 1 based on the transmitted command, and increases or decreases the power supplied to each electrode 2.
[0025]
【The invention's effect】
According to the present invention, it is possible to greatly control the input power amount while maintaining the balance of the current of each phase of the three-phase power. Further, at that time, it is possible to operate while maintaining the impedance of the electrode at the optimum value.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of the invention.
[Explanation of symbols]
1 Power transformer 2 Electrode 3 Ash melting furnace 5 Power conditioner 9 Ash (molten slag)
DESCRIPTION OF SYMBOLS 11 Tap switching means 21 Electrode raising / lowering apparatus 41 Ammeter 42 Voltmeter 51 Electrode raising / lowering instruction means 52 Tap switching instruction means

Claims (1)

In the electric resistance type ash melting furnace power control method by three-phase alternating current,
The current and voltage for each electrode was measured, it calculates the impedance and power for each electrode from the measured current and voltage, the three-phase power as each phase current is balanced, of each electrode by the lifting of the electrodes A power control method for an electric resistance ash melting furnace characterized by controlling the impedance and controlling the entire power by tap switching of a furnace power transformer.

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