JP2945615B2 - Reignition method for plasma 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 a re-ignition method for a plasma melting furnace, and more particularly to a re-ignition method for a plasma melting furnace suitable for stably and continuously operating the plasma melting furnace.

[0002]

2. Description of the Related Art Municipal waste, sewage sludge, industrial waste, etc.
Most of them are now incinerated, reduced in volume, and landfilled. However, in recent years the amount of emissions has been increasing, and it is difficult to secure a new final disposal site. There is a demand for landfills with even smaller volumes instead of landfills.

[0003] Under such circumstances, a technique has been proposed in which incinerated ash is melted and then cooled and solidified to form slag. For example, a melting technique based on a combustion method using a fossil fuel has been already proposed, but in recent years, from a viewpoint of effectively utilizing unused energy such as surplus power by so-called garbage power generation, an electric melting technique has attracted attention. . In particular, the plasma melting technique is gaining importance because it has the advantages of easily generating an extremely high temperature which cannot be realized by the combustion method, having a small amount of exhaust gas, and capable of reducing the size of exhaust gas treatment equipment.

[0004] The operation of a plasma melting furnace is generally performed in a transition type. That is, the operation is performed with the plasma torch side as the anode and the counter electrode provided on the furnace body as the cathode. During normal operation, the incineration ash is completely melted in the melting furnace in a liquid molten slag state, and electricity flows from the torch to the furnace body electrode.

[0005] In some cases, the plasma must be stopped during operation for various reasons. However, once the plasma is stopped, it is very difficult to reignite stably. That is, once the plasma is stopped, the molten slag in the furnace solidifies over time and changes into an insulator, and when this state is reached, conduction is no longer possible.

The following can be considered as causes for stopping the plasma. First, the incinerator may supply too much incineration ash to cover the surface of the slag bath, causing no electricity to flow and suddenly extinguishing the plasma arc. Next, when the plasma is stopped at the end of the normal operation, the molten slag naturally cools and solidifies. Further, the plasma arc may be extinguished due to an unstable factor such as an abnormal furnace pressure in the furnace.

As means for reigniting plasma,
Some have been proposed so far. For example, the first
As a conventional example, the plasma torch has a structure that allows combustion fuel and air to flow from the periphery as an auxiliary heating source,
If the plasma arc is suddenly extinguished due to the instability of the furnace, fuel and air flow immediately from around the torch, and a combustion flame is formed near the tip of the torch. There is one that facilitates ignition (Japanese Patent Laid-Open No. 3-17412).

[0008] As a second conventional example, reignition means is usually used only when the operation of the plasma melting furnace is restarted. However, a graphite start electrode as a substitute for the bottom electrode of the furnace is provided with a graphite start electrode. From the other side into the furnace, to form an arc between the plasma torch (main electrode) and the start electrode,
After melting the solidified slag with the ultra-high temperature gas injected downward, there is also a means for retracting the start electrode outside the furnace and restarting the steady operation (Mitsubishi Heavy Industries Technical Report Vol. 29N).
o. 4P346-351).

The above two examples are means aimed at melting the solidified slag, but as a third conventional example, at the stage when the plasma is stopped, the liquid molten slag before the solidification is once melted in the furnace. Take out the furnace and set the inside of the furnace to the exposed or empty state of the metal layer settled in the lower part of the slag bath during operation, re-ignite through the cooled solidified metal layer or re-ignite directly to the bottom electrode There is also a means for performing this (Japanese Patent Laid-Open No. 3-55412).

[0010]

However, in the case of the first conventional example, it is effective as an emergency re-ignition when the arc is extinguished due to an abnormal cause. Since the slag is already solidified and it is difficult to melt the solidified slag only by the heat of combustion, it is very difficult to smoothly resume the operation.

In the case of the second conventional example, since graphite is used for the start electrode, not only the arc generating part but also all parts existing in the furnace are oxidized and consumed by the furnace atmosphere. Therefore, it is necessary to replace the start electrode with a new one every time re-ignition occurs, which causes a problem of increasing the operating cost. In addition, not only is it necessary to use an electric circuit for switching the start electrode to the furnace bottom electrode and use the start electrode, but also to support the start electrode,
Since a device for inserting and extracting a furnace is also required, the structure becomes complicated. Another problem is that it is not possible to quickly respond to an emergency stop of the plasma.

Further, in the case of the third conventional example, re-ignition itself when restarting after the end of normal operation can be carried out smoothly. However, similarly to the second conventional example, not only the device becomes complicated and large, but also the size becomes large. When the molten slag is taken out, the furnace body (pot part) is temporarily moved from the place where it was operated, the furnace body is tilted and the molten slag is taken out and returned to its original position, so the plasma is suddenly stopped suddenly There is a problem that you can not respond quickly when you do.

Therefore, the present invention according to claim 1 of the present invention can provide an electric circuit or a device without making it particularly large.
It is another object of the present invention to provide a method for reigniting a plasma melting furnace that can reliably obtain stable reignition regardless of whether the plasma is stopped in an emergency, abnormal, or normal operation. It was done. Another object of the present invention is to provide a re-ignition method for a plasma melting furnace in which rapid re-ignition can be obtained in addition to the object of the first aspect.

[0014]

According to one aspect of the present invention, there is provided a method for re-igniting a plasma melting furnace operated in a transitional operation mode. At the same time as stopping the plasma, a conductor is driven into the slag bath from the top of the melting furnace, and further, after confirming the conduction between the conductor and the electrode of the furnace body, the ignition operation is started again. . According to a second aspect of the present invention, in addition to the configuration of the first aspect, a means for cooling the periphery of the conductor driven into the slag bath is added.

Here, the "transitional operation mode" refers to a system in which the plasma torch is used as an anode and a counter electrode provided on a furnace body is used as a cathode. Further, as the “conductor”, for example, an iron bar or the like can be generally used, but there is no particular limitation. Furthermore, as long as it can be driven just below the torch as a driving position into the slag bath, it may be driven from anywhere above the melting furnace. The term “implant” means that part of the conductor is rushed into the slag bath and the remaining part is retracted outside the furnace.

[0016] The "means for cooling the periphery of the conductor" employs means for introducing a gas which does not adversely affect the atmosphere in the furnace from outside the furnace and blowing the gas toward the conductor. I do. Therefore, as a gas, an inert gas,
Air and the like are preferred.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention; FIG.
FIG. 3 is a schematic explanatory view showing a state during operation of the plasma melting furnace. That is, during operation of the melting furnace, the incinerated ash 5 which is the material to be melted is continuously charged into the furnace 8. The incinerated ash 5 is heated and melted in the furnace 8 by the high-temperature plasma arc 4 at 5000 to 10000 ° C., overflows from the slag port 7 and is discharged as molten slag 6. 1 is a plasma torch, 2 is an electrode provided on the furnace bottom, and a power supply 3
And a plasma torch 1 as an anode and a furnace bottom electrode 2 as a cathode
Are connected to form a DC circuit.

Although the incineration ash 5 is a liquid slag in the furnace 8, as the operation time elapses, the components of the incineration ash having a high specific gravity gradually settle down, and the slag bath is separated from the upper slag layer 9 by the slag bath. The lower metal layer 10 is separated into two layers. Therefore, the metal layer 10 is in contact with the bottom electrode 2, and during the melting operation, electricity flows from the plasma torch 1 to the slag layer 9, the metal layer 10, and the bottom electrode 2. Then, when the plasma is stopped due to the end of the normal operation or due to the occurrence of an emergency or abnormal situation, the slag layer 9 and the metal layer 10 start to cool and solidify. Once solidified, the slag layer 9 becomes an insulator, so that it is not possible to reignite the plasma in this state.

Therefore, according to the method of the present invention, re-ignition can be performed easily, quickly and reliably, and will be described below with reference to FIGS. Immediately after stopping the plasma, both the slag layer 9 and the metal layer 10 of the slag bath are in a liquid state. At this point, the iron lance 11 is moved from the upper part of the furnace 8 to the plasma torch 1.
Into the slag bath just below.

The lance tip 12 has a detachable structure, and a short time after the driving, the lance tip 1
2, leaving the lance 11 out of the furnace. Even if the cooling progresses and the slag layer 9 solidifies to become an insulator, the lance tip 12, which is the implanted conductor, penetrates the slag layer 9 and comes into contact with the metal layer 10 under the slag bath. is there. As a result, the lance tip 12
Thus, a circuit through which electricity flows to the metal layer 10 and the furnace bottom electrode 2 through the metal layer 10 is secured.

The depth of the slag bath during operation varies depending on the output of the plasma torch 1 and the distance between the tip of the torch and the surface of the slag bath.
Must reach the metal layer 10 reliably, that is, whether conduction between the plasma torch 1 and the furnace bottom electrode 2 is ensured. Therefore, a circuit in which the lance 11 and the furnace bottom electrode 2 are connected via the sensor 15 is configured in advance.

After the above operation is completed, re-ignition operation is started.
This is performed after confirming a signal from the sensor 15 that the lance 11 and the furnace bottom electrode 2 are electrically connected. The ignition operation itself may be performed by an ordinary method.

Next, an embodiment of the present invention will be described. As described above, since the slag bath immediately after the plasma is stopped is in a liquid state, if the lance tip 12 is cut off immediately after driving the lance 11, the tip 12 sinks into the slag bath. In this,
Relighting becomes very difficult. Therefore, in the embodiment of the first aspect of the present invention, after a while, the slag bath starts to cool and the lance tip 12 starts to cool.
The lance tip 12 is cut off after the periphery of the lance is slightly solidified.

However, in order to ensure this operation and respond to the demand for quicker re-ignition, it is preferable to actively cool the periphery of the lance tip 12 to accelerate the solidification. Therefore, as a means, as shown in FIG. 4, an inert gas or air is injected into the furnace from the outer peripheral portion of the plasma torch 1. When air is used as the cooling gas, there is a method of using the working gas 13 at the time of generating a plasma arc. That is, since the working gas 13 is air,
When receiving a signal indicating that the lance 11 has been driven into the slag bath, the working gas 13 may be increased.

By such an operation, after stopping the plasma,
The lance tip 12 can be immediately fixed to the slag layer 9, and the lance tip 12 can be cut off very quickly.

[0026]

As described above, according to the first and second aspects of the present invention, both the electric circuit and the device need not be particularly large, and the emergency stop of the plasma can be achieved. It is possible to obtain a reliable and stable re-ignition in any stop state at the time of stop, abnormal stop, and at the end of normal operation. Further, according to the second aspect of the present invention, the re-ignition can be performed more quickly, so that it is possible to effectively cope particularly with an emergency stop or an abnormal stop of the plasma.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing a state during operation of a plasma melting furnace.

FIG. 2 is a schematic explanatory view showing a state where a lance is driven into the furnace after the operation of the plasma melting furnace is stopped.

FIG. 3 is a schematic explanatory view showing a state in which a lance is retracted from the inside of the furnace after the operation of the plasma melting furnace is stopped.

FIG. 4 is a schematic explanatory view showing an overall configuration of an embodiment according to the invention described in claim 2, and is a view corresponding to FIG. 2;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 lance 2 furnace bottom electrode 3 power supply device 4 plasma arc 5 incineration ash 6 molten slag 7 slag port 8 furnace 9 slag layer 10 metal layer 11 conductor 12 lance tip 13 plasma operating gas 14 inert gas 15 sensor

Continuing on the front page (72) Inventor Yoshiaki Shimizu 1-3-18 Wakihama-cho, Chuo-ku, Kobe City, Hyogo Prefecture Kobe Steel, Ltd. Kobe Head Office (72) Inventor Takahiro Kuno 1-chome Takatsukadai, Nishi-ku, Kobe City, Hyogo Prefecture No. 5-5 Kobe Steel, Ltd. Kobe Research Institute (56) References JP-A-56-133579 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F23G 5 / 00 115 F23G 5/00 ZAB F23J 1/00 H05H 1/32

Claims (2)

(57) [Claims] 1. A method for reigniting a plasma melting furnace operated in a transitional mode of operation, wherein a conductor is driven into the slag bath from the top of the melting furnace at the same time as the plasma is stopped.
A method for reigniting a plasma melting furnace, further comprising the step of confirming the continuity between the conductor and the electrode of the furnace body and then starting the ignition operation again. 2. The re-ignition method for a plasma melting furnace according to claim 1, wherein the periphery of the conductor is cooled after driving the conductor into a slag bath.