JP3350169B2 - Waste melting method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for melting waste such as incineration ash, dust, or a mixture of the two in a waste incinerator using electric power as a heat source.

[0002]

2. Description of the Related Art Various wastes such as municipal waste and sewage sludge are
The incineration ash and soot that are incinerated at the incineration facility
Previously, it was landfilled. However, due to the problem of depletion of landfill sites and the problem of groundwater contamination due to elution of harmful heavy metals, the necessity for weight reduction, volume reduction, and detoxification by melting is increasing. In addition, a part of the system was revised in 1992, and soots generated from the incineration of municipal solid waste were required to undergo intermediate treatment such as melting. Against this background, a melting process using coke, kerosene, and electric power as heat sources has been proposed, and some of the processes are actually performed.

[0003] The current state of the technology of the melting treatment system is disclosed in Ichiro Kojima, "Current State and Issues of Melting Technology of Incineration Residue", City and Waste, VOL.23, No.5, pp.92-107 (1993). Have been.
Among these, the plasma arc heating method and the resistance heating method have recently been promising as melting furnaces using electric power as a heat source, and the plasma arc heating method is "Development of refuse incineration ash melting plasma arc furnace". , VOL.29, No.4, 3
46-351 (1992-7), and the resistance heating method
"Municipal waste incineration ash melting technology using an electric resistance melting furnace" N
KK Technical Report, No. 143, pp. 9-16 (1993).

FIG. 4 shows an outline of the above-mentioned plasma arc heating equipment. In this method, one hollow graphite electrode 33 is provided in the upper furnace lid of the furnace 48, the tip of the graphite electrode is positioned near the upper surface of the molten slag 37 of the furnace, and Ar is placed in the hollow part of the electrode.
A gas or N ₂ gas is flowed from above, and direct current is applied between the upper hollow graphite electrode 33 and the furnace bottom electrode 34 to maintain an arc with a plasma gasified gas flow, thereby heating and melting the ash. In addition to prolonging the life, reducing the electrode cost and stabilizing the arc, it has the characteristic that the melting rate is large and the furnace can be made compact.

FIG. 5 shows an outline of the equipment of the resistance heating system. In this method, for example, a melting furnace technique conventionally used for making rock wool from blast furnace slag is applied to ash, and each technique is an AC resistance heating method using AC current. That is, two or three graphite electrodes 54 are provided on the upper furnace lid of the furnace 51, and the tips of the graphite electrodes 54 are buried in the molten slag 37 of the furnace. An AC current is applied, and the ash itself in the molten state is used as a resistor to generate electric resistance heat, and the heat maintains the molten state of the slag, and the ash is heated and melted by the heat transfer from the molten slag 37. is there. This system has a longer electrode life and lowers electrode cost, as well as high thermal efficiency, low gas generation, no flicker because no arc is generated, and separation of molten slag and molten metal to separate slag. There is a feature that can be.

[0006]

However, if a plasma arc heating method involving the generation of a gas flow is applied to the melting of incinerated ash or dust having a small particle size, the incinerated ash or dust before melting can be reduced by the gas flow. It has a problem that it is physically scattered and increases secondary fly ash generated in the dust collector 27. Further, since the high-temperature gas and the molten slag 37 come into contact with each other while being stirred, volatilization of heavy metals and alkali salts is promoted. There is also a problem that the secondary fly ash is further increased, and as a result, the effect of confining heavy metals in the slag is reduced.

On the other hand, in the AC resistance heating method, an incineration ash or a soot and dust ash cover layer 35 is formed on a molten slag layer 37 which maintains a molten state by electric resistance heat, and is slowly heated by radiant heat and heat conduction from the molten slag layer. Although the above-described problems of the plasma arc heating method can be avoided by melting at a predetermined speed, there is a problem that the electric resistance value is not stable. That is, in the AC resistance heating method, since the slag is slowly stirred only by convection, NaCl, K contained in incinerated ash and dust and soot is not used.
Alkaline salt such as Cl is separated from the molten slag layer by specific gravity, and the molten salt layer 36 is formed separately on the molten slag layer 37. As a result, two or three graphite electrodes 54 penetrate the molten salt layer 36. Will do. At this time, since the specific resistance of the molten salt is very small, about 1/200 of the specific resistance of the molten slag, an AC voltage is applied between two or three electrodes in this method, as shown in FIG. 2 different resistance values between the electrodes
The presence of a molten salt having a small specific resistance value is equivalent to a circuit in which R _EE-SALT is connected in parallel to two resistance loads R _EE-SLAG , and lowers the resistance value R _EE between the electrodes. Causes a decrease in As a result, there has been a problem that the energization is not stable, the power consumption is deteriorated, and in severe cases, a sufficient voltage is not generated under the rated current and resistance heating cannot be performed.

Further, in the method of applying a voltage to the molten salt layer, there is a possibility of electrolysis of the molten salt as shown in the following formula. 2Na ⁺ + 2Cl ⁻ → 2Na + Cl ₂ ↑ 2K ⁺ + 2Cl ⁻ → 2K + Cl ₂ ↑ If the molten salt is decomposed, chlorine gas is generated and peripheral equipment is corroded, so that it becomes difficult to treat the exhaust gas.

As a method for solving the above-mentioned disadvantages such as a decrease in the resistance value R of current flow and electrolysis of a molten salt, for example, as shown in FIG. 7 disclosed in Japanese Patent Publication No. 2-10342, FIG.
There is a means in which the direction of the electrode is horizontal and the position is inserted into the molten slag layer 37 below the molten salt layer 36. However, in this method, additional electrodes need to be inserted into the furnace while successively adding consumable electrodes, and the electrodes must be provided horizontally freely through the side wall of the furnace body where the molten slag exists. Another problem is that the sealing structure is complicated, and it is difficult to insert the electrodes in the horizontal direction.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and melts waste produced from incineration ash, dust, or a mixture of two generated from a refuse incineration facility using electric resistance heat as a heat source. In the method, the tip position of the upper electrode is located in the molten slag layer between the molten salt layer and the molten metal layer, and the current is vertically applied between the furnace bottom electrode by direct current or two-phase alternating current. It is characterized by the following.

As a specific apparatus configuration for realizing the above method, a DC power source or an AC two-phase power source is connected between the upper electrode and the lower electrode, and the molten material is located between the upper electrode and the lower electrode. The lower electrode is fixed to the furnace bottom so that the current flows in the vertical direction, and the upper electrode composed of one or more electrodes of the same potential can be vertically moved vertically through the furnace lid. And an adjustment mechanism for adjusting the buried position of the electrode tip in the melt is disposed on the upper electrode.

[0012]

According to the present invention, the position of the tip of the upper electrode is located in the molten slag layer between the molten salt layer and the molten metal layer, and is vertically applied between the furnace bottom electrode by direct current or alternating current two-phase current. Even if molten slag and molten salt with different resistance values are stacked because they are energized in the same direction, they do not lead to a decrease in the resistance value of current flow as occurs with conventional AC resistance heating, and even when a large amount of alkali salt is contained, the molten slag layer A molten salt layer can be stably separated and grown on the molten salt layer, and the molten salt can be discharged while being separated from the slag. Further, since heat is concentrated on the furnace bottom below the tip of the upper electrode, the convection of the molten slag is increased and uniform slag can be generated.

Further, since the molten salt layer and the molten metal layer, which are good conductors, have a structure sandwiching the molten slag layer, apparently, the upper electrode and the furnace bottom electrode have the effect of spreading over the entire horizontal section of the furnace, Unidirectional heating and stabilization of the resistance value are realized by the energization in the direction occurring over the entire horizontal section of the furnace.
In addition, when the upper electrode is composed of a plurality of electrodes having the same potential, a voltage gradient does not occur in the molten salt layer and no current flows through the molten salt layer, so that electrolysis of the molten salt or resistance heating of the molten salt is performed. And volatilization as a result thereof is suppressed, so that there is no loss of current flowing through the molten salt layer, and the power consumption can be reduced. Hereinafter, the present invention will be described in detail based on an embodiment shown in the drawings.

[0014]

FIG. 1 shows an example of an entire facility for carrying out the present invention. FIG. 2 is an enlarged view of a DC electric resistance melting furnace in FIG. In FIG. 1 or FIG. 2, reference numeral 2 denotes an incinerator, reference numeral 42 denotes a generator, reference numeral 20 denotes a DC resistance heating type ash melting furnace, which together with its auxiliary equipment constitutes an incineration treatment facility, a power generation facility, and an ash melting facility. ing.

One of the incineration facilities is a garbage pit which stores the received garbage and sequentially puts it into an incinerator 2 for incineration. The generated exhaust gas is boiler 3,
Hazardous gas removal device 4, bag filter 5, induction blower 6
And discharged from the chimney 7. Soot and dust in the exhaust gas is removed by the bag filter 5 and the collected soot is collected by the soot transfer conveyor 16 to the soot storage tank 1.
It is stored at 7. The incineration ash, boiler ash, etc. generated in the incineration process are collected in a dry ash removal device 8 and guided to a magnetic separator 10 and a vibrating sieve 11 by an ash transfer conveyor 9 to remove iron 12 and bulky materials 13 and then transfer the ash. It is stored in the incineration ash storage tank 15 by the conveyor 14.

In the power generation facility, the heat generated by the incineration process is recovered by the boiler 3, and the boiler 3, turbine 39, condenser 4
0, power is converted into power in a cycle constituted by the condensate tank 41, and further converted into power by the generator 42. Generator 4
2 is operated in parallel with an external electric power system, and the electric power is supplied to an incinerator and a melting furnace.

In the ash melting facility, ash is cut out from the dust storage tank 17 and the incinerated ash storage tank 15 and an ash supply conveyor 18 is provided.
Is supplied to an ash melting furnace 20 through an ash hopper 19. The ash that has entered the ash melting furnace 20 spreads over the entire cross section of the furnace due to the convection of the melt to form an ash cover layer 35. The ash of the ash cover layer 35 is gradually melted by the heat transfer from the melt, melts into the melt, and the alkali salt component, the slag, and the metal component in the ash are converted into the molten salt layer 36, the molten slag layer 37, and the molten metal layer, respectively. Separated into 38.

The upper hollow graphite electrode 33 is provided so as to penetrate the furnace lid, and is supported vertically vertically by an electrode lifting / lowering device 32 so as to be buried in the molten slag layer 37. Is controlled by the heater 59. A DC voltage is applied between the upper hollow graphite electrode 33 and the furnace bottom electrode 34 in the vertical direction by applying a DC voltage from the DC power supply device 31 to generate electric resistance heat using the molten slag layer as a resistor to generate a molten slag 38. Is maintained in a molten state. In addition, a water cooling device is inserted into the hollow portion of the upper hollow graphite electrode 33 to cool the tip of the red-hot electrode from the inside,
It suppresses the oxidative wear of graphite.

Further, in this embodiment, in order to prevent the electrode from being oxidized and worn, the gas duct at the outlet of the melting furnace is branched to keep the atmosphere in the furnace oxygen-free, and a gas circulation fan 46 and an exhaust gas circulation duct 47 are provided to the ash chute. , High temperature combustible gas including CO gas is circulated. In this case, a small amount of air or moisture contained in the ash comes into contact with the high-temperature circulating gas in the ash chute, so that the air burns with the high-temperature flammable gas to make the furnace atmosphere oxygen-free, By drying in advance, contact with a high-temperature portion of the electrode can be suppressed, and oxidation damage of the electrode can be prevented.

The furnace wall of the ash melting furnace 20 has three slag outlets,
Each is disposed at the position of three slag layers, and each is separated and discharged. That is, with respect to the molten salt 36, a slag port A is provided on the furnace wall immediately above the liquid level of the molten salt, and the slag is intermittently discharged by tilting the furnace. About molten slag 37,
A slag port B is provided in the furnace wall near the upper part of the furnace bottom, and slag is continuously sunk by the head pressure of the molten slag, and the amount of the slag is adjusted by adjusting the head pressure by tilting the furnace. For the molten metal 38, a slag port C is provided on the furnace wall at the same level as the furnace bottom, and the slag is periodically or intermittently performed at a fixed amount of the molten metal. The mud is filled and the mud is drilled at the start of slagging, and the mud is filled again at the end of slagging. Further, the completion of the molten metal slag can be confirmed by visually confirming the difference in color between the molten metal and the molten slag.

The discharged slag is cooled by a slow cooling conveyor 21 and stored in a slag pit 22, and the discharged metal is cooled by a cooling conveyor 23 and stored in a metal pit 24. The molten salt is discharged into a molten salt ladle 25, cooled, and stored.

The combustible gas generated in the DC resistance type ash melting furnace 20 is burned in the combustion furnace 26 and then exhausted to the environmental dust collecting hood, where it is gradually cooled, the cooling conveyor 23, the cooling conveyor 23, and the ladle 25.
The secondary fly ash is collected by the dust collector 27 together with the gas generated in the above and sucked by the environmental dust collecting hood 61, and is exhausted to the chimney 7 via the dust collecting fan 28. The secondary fly ash collected by the dust collector 27 is sent to the secondary fly ash detoxifying device 30 via a conveyor, and is rendered harmless by ferrite treatment or the like.

In the above embodiment, the power supply device 31 is a DC power supply device. However, even when the power supply device 31 is an AC two-phase power supply device, the same effect and action can be obtained because the vertical energization occurs over the entire horizontal surface of the furnace. Needless to say.

FIG. 3 shows another embodiment in which the upper electrode is constituted by a plurality of hollow graphite electrodes 60 having the same potential. The structure other than the upper electrode is the same as that of FIG. 1 or FIG.
Although the number of upper electrodes is three, the center of heat generation can be tripled as compared with the case of one upper electrode, so that the furnace diameter can be increased. Unlike the case of the alternating current shown in FIG. 5, the number of upper electrodes can be arbitrarily set. Further, since the three upper electrodes are at the same potential, a voltage gradient hardly occurs in the molten salt layer 36 and no current flows through the molten salt layer. Since the volatilization of gas is suppressed, there is no current that flows through the molten salt layer and is lost, and the power consumption can be reduced.

[0025]

According to the above-described configuration, the present invention has the following effects. (1) Since the tip of the upper electrode is immersed in the melt and is vertically energized with the furnace bottom electrode, there is no adverse effect of a decrease in the resistance due to the molten salt. (2) Since the molten salt layer and the molten metal layer, which are good conductors, have a structure sandwiching the molten slag layer, the resistance value is stabilized, and uniform heating is possible. (3) Since no current flows through the molten salt layer, the power consumption can be reduced. In particular, when the upper electrode is a plurality of electrodes having the same potential, almost no voltage gradient occurs in the molten salt layer, and the power consumption can be effectively reduced. (4) Since the current flows through the molten salt layer and the molten salt is suppressed from being heated and volatilized, the molten salt layer can be separated and grown, and the slag can be removed while being separated from the slag. (5) In the vertical energization, heat is concentrated on the bottom of the furnace, so that the convection of the molten slag is increased and uniform heating is possible. (6) According to the resistance heating, it is possible to reduce the consumption of the electrode by wear. In particular, in the case of direct current, the effect is great. When the upper electrode is hollow and a water cooling device is provided in the hollow portion to cool the electrode, or when a gas circulating device is provided to circulate the gas, the consumption of the electrode can be further reduced. (7) When the upper electrode is a plurality of electrodes having the same potential, the number of the electrodes can be arbitrarily set, and the furnace diameter can be increased according to the number of the electrodes.

[Brief description of the drawings]

FIG. 1 shows the overall equipment for implementing the present invention.

FIG. 2 shows an enlarged view of a portion of the DC resistance furnace shown in FIG.

FIG. 3 is a view showing another embodiment of the present invention, wherein the upper electrode of the DC electric resistance furnace shown in FIGS. 1 and 2 is constituted by a plurality of electrodes having the same potential; The part is shown in an enlarged view.

FIG. 4 shows an apparatus diagram of a plasma arc heating method among conventional melting processing apparatuses using electric power as a heat source.

FIG. 5 shows an apparatus diagram of a conventional melting processing apparatus using electric power as a heat source by a resistance heating method.

FIG. 6 is an equivalent electric circuit diagram when a molten salt layer is present in a conventional AC electric resistance heating furnace.

FIG. 7 is a diagram of a conventional melting treatment apparatus for solving the problem of lowering the resistance value R of energization and the inconvenience of electrolysis of a molten salt.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 garbage pit 2 incinerator 3 boiler 4 harmful gas removing device 5 bag filter 6 induction blower 7 chimney 8 dry ash removal device 9 ash transfer conveyor 10 magnetic separator 11 vibrating sieve 12 iron 13 bulk material 14 ash transfer conveyor 15 incinerated ash storage Vessel 16 Dust transfer conveyor 17 Dust storage tank 18 Ash supply conveyor 19 Ash hopper 20 DC resistance ash melting furnace 21 Slag slow cooling conveyer 22 Slag pit 23 Metal slow cooling conveyer 24 Metal pit 25 Molten salt collecting pot 26 Incinerator 27 Dust collector 28 Dust collection fan 29 Conveyor 30 Secondary fly ash detoxifying device 31 DC power supply device 32 Electrode lifting device 33 Hollow graphite electrode 34 Furnace bottom electrode 35 Ash cover layer 36 Molten salt layer 37 Molten slag layer 38 Molten metal layer 39 Turbine 40 Condensate Container 41 Condensate tank 42 Generator 3 Water Cooling Nozzle 44 Electrode Cooling Device 45 Air Fan 46 Gas Circulation Fan 47 Gas Circulation Duct 48 Plasma Arc Ash Melting Furnace 49 Quenching Tower 50 Slag Granulator 51 AC Electric Resistance Ash Melting Furnace 52 AC Power Supply 53 Sorting Conveyor 54 Graphite Electrode 55 Slag metal slow cooling conveyor 56 Slag metal pit 57 Molybdenum electrode 58 Tilting device 59 Electrode burial position adjuster 60 Hollow graphite electrode at the same potential 61 Environmental dust hood

Continued on the front page (72) Inventor Kazuhiro Kuribayashi 46-59 Ohara Nakahara, Tobata-ku, Kitakyushu-shi, Fukuoka Nippon Steel Corporation Machinery & Plant Business Department (56) References JP-A-2-97816 (JP, A) JP-A-2-97813 (JP, A) JP-A-6-42724 (JP, A) JP-A-55-67396 (JP, A) JP-A-4-251106 (JP, A) JP-A-55-114383 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F23G 5/00 115 F23G 5/10 H05B 3/00 350 F23J 1/00 B09B 3/00

Claims (2)

(57) [Claims] 1. A method for melting incineration ash, soot and dust generated from a refuse incineration facility using electric resistance heat as a heat source, wherein the tip of an upper electrode is melted with a molten salt layer. A method for melting waste according to claim 1, characterized in that a current is applied in a vertical direction by direct current or two-phase alternating current between a metal layer and a furnace bottom electrode positioned in a molten slag layer. 2. An apparatus for melting and processing incineration ash, soot and dust generated from a refuse incineration facility using electric resistance heat as a heat source, wherein a direct current power supply or an alternating current is applied between an upper electrode and a lower electrode. A two-phase power source is connected, and the lower electrode is fixed to the furnace bottom so that the current flowing through the melt located between the upper electrode and the lower electrode is vertical, and one or more An upper electrode composed of an electrode of a potential is disposed vertically vertically through the furnace lid, and furthermore, the upper electrode is provided with an adjustment mechanism for adjusting the burying position of the electrode tip in the melt. A waste melting apparatus characterized by the above-mentioned.