JPH0519277B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for melting and processing incinerated ash generated by incinerating municipal waste, sewage sludge, or other waste in an incinerator, for example. Regarding a plasma generator for a furnace.

[Conventional technology]

Generally, incineration ash generated by incinerating municipal waste, sewage sludge, or other waste in a waste incinerator is currently disposed of in a landfill in many cases. However, as it is becoming more and more difficult to secure landfill sites year by year, there is a need for a method of reducing the volume of incinerated ash to be landfilled, that is, a volume reduction process. In addition, if the incinerated ash is disposed of in a landfill without being treated, the incinerated ash itself contains harmful substances such as various heavy metals, so the harmful substances from the incinerated ash are released into rainwater, Unburnt organic substances are leached into groundwater or the like, or unburned organic substances in incinerated ash rot, and these phenomena cause secondary pollution. Therefore, there is a demand for pollution-free treatment of incineration ash discharged from incinerators.

For this reason, various incineration ash processing devices have been developed. For example, a treatment method that mixes incinerated ash with cement and solidifies the incinerated ash with cement, a treatment method that solidifies incinerated ash by mixing it with asphalt, or a treatment method that sinters and solidifies incinerated ash by mixing it with clay etc. is disclosed. However, these processing methods have problems in that the processing cost is high and the processing conditions of the incinerated ash lack technical reliability.

Further, as another method for treating incinerated ash, there is a method in which incinerated ash is put into a burner furnace or an electric furnace, that is, an open arc furnace, and the incinerated ash is melted.
The burner furnace method uses the combustion heat of oil.
The maximum temperature is around 1400℃, and it is necessary to remove high melting point iron and ceramics in the preliminary stage. Alternatively, the arc furnace method is a steelmaking arc furnace converted to melting, and utilizes arc heat between graphite electrodes.

For example, as a treatment method using an open arc furnace for steel manufacturing, there is a method disclosed in JP-A-52-86976. The method of burning and melting the sludge is as follows:
Sludge is charged into a closed arc furnace in which an arc is constantly generated between an electrode and molten metal, and the organic matter in this sludge is decomposed by the heat of the arc and taken out of the furnace as a gas. The inorganic material is melted by the arc heat of the arc and melted into the molten metal, or taken out of the furnace as molten slag.

Alternatively, JP-A-55-114383 discloses a method for melting incinerated ash. The method for melting incinerated ash involves sequentially introducing incinerated ash onto molten slag in a submerged arc furnace to form an incinerated ash layer;
The incineration ash in this layer is sequentially melted by the electrical resistance heat of the molten slag. In this case, the incinerated ash used is a mixed ash of ash incinerated in an incinerator and collected ash collected in a dust collector.

[Problem to be solved by the invention]

However, most of the above-mentioned burner furnace systems use a water crushing method to extract the slag because a high temperature cannot be obtained. The water crushing method is a method in which a water tank is installed at the bottom of the slag discharge port, the slag is continuously dropped from the discharge port into the water tank, and the slag cooled in the water tank is taken out of the melting furnace using a conveyor, etc. Although there is an advantage that the cold air leaking into the slag outlet will not be cooled by sealing the outside air, the granulated slag becomes glassy and brittle. There's a problem. Furthermore, the granulation method has the problem of a risk of steam explosion when a large amount of high-temperature slag falls into the water tank.

In addition, the sludge combustion melting method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 52-86976 uses an open arc furnace with graphite electrodes, so it is not possible to obtain a sufficiently high temperature. In particular, there is a problem in the case of municipal waste incineration ash that it is impossible to completely melt high melting point substances such as earth and sand, ceramics, metals, etc. Therefore, only the substances that can be melted in the open arc furnace are In order to feed into the arc furnace, high melting point substances are sorted out from the incinerator in advance and then put into the furnace, or lime,
It was necessary to add a melting point depressant such as fluorspar to the incineration ash for melting.

In addition, in an open arc furnace, an arc is generated between the electrode and the molten metal, so in order to treat waste mainly composed of oxides contained as slag components, such as incineration ash, it is necessary to It is necessary to melt metal such as iron in a furnace in advance to create a so-called base metal. Furthermore, when incineration ash with a non-uniform composition such as oxides was placed on the base metal, the arc power fluctuated greatly and the arc disappeared. Moreover, when the arc is extinguished, the base metal is covered with non-conductive incinerated ash, which often causes the problem that the incinerated ash cannot be re-ignited because it has to be disposed of again. occured.

Methods other than the water crushing method include the wind crushing method and the slow cooling method, but the slag produced by these methods is crystalline and hard, so it can be effectively used as construction aggregate, road base material, etc. A common slag discharge method such as this slow cooling method is the tap method used in steel manufacturing such as blast furnaces. The tap method is to store slag in the melting furnace by filling the slag discharge port with clay to prevent the slag from flowing out, and when a predetermined amount of slag has accumulated, the clay at the slag discharge port is broken down and the slag is released. This method involves letting the slag flow out from the discharge port, and then filling the discharge port with clay again after the slag has finished flowing out.As the slag remains in the furnace, the slag discharge operation is intermittent, and the volume of the furnace increases. , there is a problem with work safety.

In general, plasma is a state in which electrons are ejected from atoms and ionized. The high energy generated when electrons eject from atoms creates a high-temperature atmosphere around the plasma. Plasma arc furnaces are provided to generate this plasma. This plasma arc furnace is equipped with a plasma torch. In addition, the incinerated ash and combustion exhaust gas generated from the incinerator are cleaned and dust-collected using a dust collector such as an electrostatic precipitator, and the incinerated ash is melted in a melting furnace. It is discharged from the chimney through a fan.

The purpose of this invention is to solve the various problems mentioned above, and to provide a melting furnace that melts incinerated ash from municipal waste incinerators in order to reduce the volume, make it harmless, and effectively utilize it. Melting incinerated ash without separating the types requires a high temperature of 1,500°C or higher, but focusing on the fact that high temperatures of 1,500 to 2,000°C can be easily obtained with plasma arc, we have developed a method for melting incinerated ash regardless of its type and composition. For example, even if the incinerated ash contains high-melting point substances such as metal pottery or earth and sand, the incinerated ash is directly put into the melting furnace without first sorting and removing these high-melting point substances from the incinerated ash. , a plasma arc is generated using a plasma torch, which is a plasma generator installed in the melting furnace, and the incinerated ash is melted by the high energy of the plasma arc, thereby always stably melting the incinerated ash. An object of the present invention is to provide a furnace plasma generator.

[Means to solve the problem]

In order to achieve the above object, the present invention is configured as follows. That is, the present invention provides an incinerated ash supply device for feeding incinerated ash into a melting furnace, a plasma torch disposed in the melting furnace for generating plasma, and means for switching alternating current to direct current to supply direct current to the plasma torch. a cooling water supply device that supplies cooling water to cool the plasma torch; an air supply device that includes an air compressor to supply air as a plasma forming gas to the plasma torch; The present invention relates to a plasma generation device for a melting furnace, which includes a control device that applies voltage to the plasma torch to generate a plasma arc.

[Effect]

The plasma generator for a melting furnace according to the present invention includes:
It is configured as described above and has the following effects. That is, the plasma generator of this melting furnace is
Direct current is supplied through a power supply device to a plasma torch that generates plasma placed in a melting furnace.
The plasma torch is cooled by cooling water supplied from a cooling water supply device, air as a plasma forming gas is supplied to the plasma torch by an air supply device equipped with an air compressor, and the plasma torch is further cooled by cooling water supplied from a cooling water supply device. Since the voltage applied to the melting furnace is controlled by the control device, a high temperature plasma arc is continuously and stably generated in the plasma torch provided in the melting furnace. Therefore, even if the incinerated ash containing high-melting-point substances discharged from the incinerator is directly fed into the melting furnace as it is, the thermal energy of the high-temperature plasma arc can be applied to the incinerated ash by radiation or conduction. Incineration ash can be melted quickly.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a plasma generator for a melting furnace according to the present invention will be described below with reference to the drawings. The plasma generator for a melting furnace according to the present invention can generate incinerated ash generated by incinerating waste etc. from an incinerator, and in some cases dust collected by the dust collector in the incinerator system. This is to generate a plasma arc for melting the incinerated ash in the plasma arc furnace. An example is shown.

In FIG. 1, the plasma generator for this melting furnace is mainly composed of a plasma arc furnace 5, a plasma torch 8 provided in the plasma arc furnace 5, and a plasma system 1 that causes the plasma torch 8 to generate plasma. There is.

In the melting furnace of this plasma generator, the melting furnace, ie, the plasma arc furnace 5, is provided with a water-cooled fixed type furnace lid on the upper part of the furnace body. This furnace body is constructed of a refractory material such as carbon, magnesia, alumina, etc., and is equipped with a slag discharge port 25. In addition, the furnace lid includes a torch lifting device, an incineration ash input chute 9, and an exhaust gas duct 23 for exhaust gas.
is installed. The plasma torch 8 is installed on the furnace lid using a torch lifting device.

The plasma system 1 mainly includes a transfer type or non-transfer type plasma torch 8 arranged in a melting furnace to generate plasma, and a power supply device equipped with means for switching alternating current to direct current to supply direct current to the plasma torch 8. 4. Cooling water supply device 27 that supplies cooling water to cool the plasma torch 8;
An air supply device 28 equipped with an air compressor for supplying air as a plasma forming gas to the plasma torch 8, and in the case of a transfer type, an electrode built into the plasma torch 8 and a counter electrode embedded in the bottom of the melting furnace. 10 or, in the case of a non-transfer type, between the electrodes built into the plasma torch 8, and a control device 26 for controlling generation of a plasma arc.

In this melting furnace plasma generator, when the plasma arc furnace 5 is to generate an output of, for example, 150 KW, AC 400 V is applied to the power supply device 4 to convert the alternating current to direct current.

Furthermore, regarding the cooling water supply device 27, the cooling water pump 29 is operated to send the cooling water from the water tank 30 to the heat exchanger 33, and after exchanging heat in the heat exchanger 33, the cooling water is transferred from the heat exchanger 33 to the manifold. 34, the cooling water is then supplied to the plasma torch 8 through the cooling water pipes 19 and 20, and the cooling water is also supplied from the manifold 34 to the furnace lid provided with the plasma torch 8, thereby cooling the plasma torch 8 and the furnace lid. At this time, for example, increase the torch cooling water flow rate to 20~
40GPM and torch cooling water pressure 180~250PSIG
Set to .

Regarding the air supply device 28, the air compressor is operated to supply compressed air from the manifold 34 to the plasma torch 8 through the plasma forming air pipe 21, as shown by arrow A. FIG. 4 shows an example of a pressure change pattern of the air supply device 28 in the plasma generator of this melting furnace.

In addition, the electrode of the plasma torch 8 used in the plasma generator of this melting furnace has a transfer type as shown in Fig. 2 or a non-transfer type as shown in Fig. 3 as the type of arc discharge. can be used. The transfer type has a negative counter electrode 1 at the bottom of the melting furnace.
Since the non-transfer type uses the tip of the plasma torch 8 as the counter electrode, there is no need for a negative counter electrode at the bottom of the furnace other than the plasma torch. In addition, the thermal efficiency of the plasma torch 8 body is 92-94% for the transfer type and 85% for the non-transfer type.The transfer type is superior in terms of thermal efficiency, and requires a negative counter electrode at the bottom of the furnace for ease of handling. A non-transferable type is better. Molten slag is conductive, so when there is molten slag in the furnace,
The entire surface of the slag bath becomes the counter electrode.

First, when the plasma torch 8 is of a transfer type as shown in FIG. 2, a counter electrode 10 made of a graphite electrode of the plasma torch 8 is embedded in the bottom of the furnace body. In the plasma system 1, in order to generate plasma in the plasma torch 8, the + pole from the power supply device 4 is connected to the cable 17.
The negative electrode is connected to the plasma torch 8 through the cable 22, and the negative electrode is connected to the counter electrode 10, which is a graphite electrode, through the cable 22, and a voltage controlled by the controller 26 is applied between the plasma torch 8 and the counter electrode 10. In the case of the non-transfer type, the counter electrode of the graphite electrode is not required, and the - pole is connected to the electrode built in the plasma torch 8 through the cable 18, and the control device 26 connects the two electrodes built in the plasma torch 8. Then, a controlled voltage is applied. Further, in the case of a transfer type supply air pressure change pattern, the arc gas pressure is set to 18 PSIG and the arc gas flow rate is set to 7 SCFM, for example, at the time of startup to generate a pilot arc. Also, during operation to generate the main arc, for example, the low pressure arc gas pressure should be set to 20 PSIG, and the high pressure arc gas pressure should be set to 20 PSIG.
40PSIG, 3PSIG/sec moving gradient from startup to low arc gas pressure, 10sec low pressure setting time, 1PSIG/sec moving gradient from low arc gas pressure to high arc gas pressure, 10sec high pressure setting time, high pressure arc gas pressure to low pressure Set the transfer gradient to arc gas pressure to 1PSIG/sec. The distance between the tip of the plasma torch 8 and the counter electrode 10 is proportional to the voltage of the plasma torch 8, and as the distance increases, approximately
The voltage increases at a rate of 10.5V/cm. Since the current of the plasma torch 8 is controlled to be constant by the control device 26, the amount of electric power is proportional to the distance, and the longer the distance, the more power consumption increases, and the amount of heat given to the object to be melted increases. At this time, the current is controlled by the controller 26 using the PID
The voltage is controlled between the plasma torch 8 and the counter electrode 10.
is determined by the distance between the poles and the fluctuation cycle of the arc gas pressure.

Alternatively, if the plasma torch 8 is of a non-transfer type as shown in FIG. 3, only the graphite electrode is unnecessary and the other configurations remain unchanged. In the case of a non-transfer type plasma torch 8, it is determined only by the variation cycle of the arc gas pressure.
Furthermore, a plasma arc is generated between the positive and negative electrodes built into the non-transfer type plasma torch 8, and the incinerated ash is melted by the arc heat, that is, the plasma energy. If the plasma torch 8 is a non-transfer type, for example, the arc gas pressure is adjusted at startup to generate a pilot arc.
Set the arc gas flow rate to 18PSIG and 7SCFM. Also, during operation that generates the main arc,
For example, the low pressure arc gas pressure is 20PSIG, the high pressure arc gas pressure is 35PSIG, the gradient of movement from startup to low pressure arc gas pressure is 1PSIG/sec, the low pressure setting time is 10sec, and the gradient of movement from low pressure arc gas pressure to high pressure arc gas pressure is 1PSIG/sec. , set the high pressure setting time to 10 sec, and set the movement gradient from high pressure arc gas pressure to low pressure arc gas pressure to 1 PSIG/sec.

The plasma arc furnace 5 in the plasma generator for a melting furnace according to the present invention is constructed as described above and operates as follows. In this plasma arc furnace 5, the drive device is operated to lower the plasma torch 8 into the plasma arc furnace 5, and the plasma torch 8 is set at a predetermined distance from the counter electrode 10. Next, metals generated from incinerators,
Incineration ash containing a high melting point substance such as ceramics or dust collected from a dust collector is put into an ash hopper 12. The incinerated ash charged into the ash hopper 12 is continuously or intermittently fed into the plasma arc furnace 5 through the chute 9. The conditions for discharging the plasma torch 8 to generate a plasma arc are set as described above, and under these set conditions,
The cooling water supply device 27 is activated, and the plasma torch 8
Cooling water is supplied to the plasma torch 8 under the above conditions, and then the air supply device 28 is operated to supply air to the plasma torch 8 under the above conditions. At this time, the arc gas pressure is
For example, the aforementioned setting conditions are 18PSIG, and the arc gas flow rate is 7SCFM. The initial DC voltage for generating the main arc is set to about 700 V, and this voltage is applied between the plasma torch 8 and the counter electrode 10 to give a high energy pulse to generate a pilot arc. Then, after the main arc occurs, a predetermined current (e.g. 200 ~
300A) and a given voltage (e.g. 400~500V)
By setting , the thermal energy of the plasma arc is given to the incinerated ash, which is the object to be heated, by radiation or conduction. In the case of the transfer type plasma torch 8, when igniting the plasma for the first time, the distance between the tip of the plasma torch 8 and the counter electrode 10, which is a graphite electrode, is set in the range of 25 to 75 mm. After ignition,
Since the tip of the plasma torch 8 and the counter electrode 10 of the graphite electrode are electrically connected by the plasma flow, the plasma will not be interrupted even if the distance between the electrodes is set to 75 mm or more by operating the drive device. Since the slag bath also serves as the counter electrode 10 of the plasma torch 8, it needs to have a certain depth. If the slag bath is too shallow, the incinerated ash will pile up and become non-conductive, causing plasma interruption. On the other hand, if the depth is too deep, the slag at the bottom of the slag bath will solidify. Therefore, the depth of the slag bath is 100
A range of ~400 mm is desirable. Therefore, a plasma arc is generated by the discharge of the plasma torch 8, and the incinerated ash containing oxides, highly molten substances, etc. becomes molten slag due to the thermal energy of the plasma arc. The metal contained in the incineration ash flows out as molten metal continuously or intermittently from the slag discharge port 25 of the furnace body, and is taken out as slag to the slag receiver 15 to the outside. In addition, the combustion gas generated by the melting of incineration ash is
The combustion gas is sent through an exhaust gas duct 23 from an exhaust gas outlet 16 formed below the slag discharge port 25 to, for example, an exhaust gas treatment device, where the combustion gas is treated and exhausted to the atmosphere from a chimney or the like.

〔Effect of the invention〕

The plasma generator for a melting furnace according to the present invention includes:
It is configured as described above and has the following effects. That is, the plasma generation device of this melting furnace includes an incinerated ash supplying device for feeding incinerated ash into the melting furnace, a plasma torch disposed in the melting furnace for generating plasma, and an alternating current for supplying direct current to the plasma torch. a cooling water supply device for supplying cooling water to cool the plasma torch; and an air compressor for supplying air as a plasma forming gas to the plasma torch. Since it is composed of an air supply device and a control device that applies voltage to the plazzle torch to generate a plasma arc, the incinerated ash containing high melting point substances discharged from the incinerator is sequentially directly introduced into the melting furnace, A plasma arc is generated using air as a plasma forming gas in a plasma torch installed in the melting furnace, and a continuously stable high-temperature plasma can be obtained, and the thermal energy of the high-temperature plasma is transferred to the incinerated ash. The incineration ash can be melted quickly by giving
In addition, the heated area can be concentrated in a narrow area, the temperature rise of the entire furnace is small, heat loss from the surface of the furnace body is small, and there is almost no fluctuation in power, so there is little effect on the power supply. Moreover, since the molten slag can be continuously discharged from the plasma arc furnace, there is no need for the slag to remain in the furnace for a long time unlike in tap-type melting furnaces, so the volume of the furnace body can be configured to be small, making it economical. It is also possible to provide plasma arc furnaces at low cost. In addition, the plasma torch can be ignited and extinguished instantly, making operation and maintenance easy.

Furthermore, by using air as the plasma forming gas, the amount of air required is small and the amount of exhaust gas is small, making it possible to downsize the melting furnace. % of organic matter remaining) can be completely decomposed, and the exhaust gas does not contain harmful unburned gases such as CO, hydrocarbons, and dioxins, unlike open arc furnaces, making it safe. It is possible to provide a method for processing incineration ash that is highly versatile.

In particular, since the plasma generator for the melting furnace according to the present invention uses a plasma torch, it can obtain high thermal energy, and incineration ash containing high melting point substances such as earth and sand, ceramics, and metals can be directly fed into the melting furnace. It can be melted quickly in the same state as it is, and unlike conventional burner methods, electric furnace methods, etc.
There is no need to use a magnetic separator, a vibrating conveyor, or the like to separate and remove the high melting point substance from the incinerated ash, which not only reduces the number of work steps but also allows the equipment itself to be simplified and made more compact. Therefore,
During the melting process of incinerated ash, the heavy metals contained in incinerated ash are usually in the form of highly volatile chlorides, but due to the strong oxidizing effect of air, which is a plasma forming gas, they change to less volatile oxides. Therefore, most of the heavy metals are fused and fixed in the molten slag and do not volatilize into the exhaust gas, and no phenomenon in which these heavy metals are eluted from the generated slag occurs.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing one embodiment of a plasma generator for a melting furnace according to the present invention, FIG. 2 is an explanatory diagram illustrating a transfer type plasma torch used in the plasma arc furnace of FIG. 1, and FIG. FIG. 4 is an explanatory diagram illustrating a non-transfer type plasma torch used in the plasma arc furnace of FIG. 1, and FIG. 4 is an explanatory diagram illustrating an example of gas control in a plasma generator for a melting furnace according to the present invention. . DESCRIPTION OF SYMBOLS 1... Plasma system, 4... Power supply device, 5... Plasma arc furnace, 8... Plasma torch, 10... Counter electrode, 12... Ash hopper, 26...
...Control device, 27...Cooling water supply device, 28...
Air supply device.

Claims (1)

[Claims] 1. An incinerated ash supply device that inputs incinerated ash into the melting furnace, a plasma torch that generates plasma disposed in the melting furnace, and a power supply equipped with means for switching alternating current to direct current to supply direct current to the plasma torch. an air supply device comprising an air compressor for supplying air as a plasma forming gas to the plasma torch; and an air supply device comprising an air compressor for supplying air as a plasma forming gas to the plasma torch; A plasma generation device for a melting furnace, which consists of a control device that controls applying voltage to generate a plasma arc.