JP2005098693A - Method for melting waste - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for melting wastes by gasification capable of reducing furnace inner pressure and preventing discharge of molten slag. <P>SOLUTION: According to the method for melting wastes, a waste layer is formed by loading wastes in a furnace body. The wastes are gasified by a high-temperature gas from a furnace bottom. The residue is melted and discharged as slag. When a height from the furnace bottom to the upper surface of the accumulated waste layer is H and a diameter of the furnace body facing the upper surface of the waste layer is D, H/D is set to two or less, and the pressure at the furnace bottom facing a molten slag discharge opening is set to a positive pressure equal to or less than 5 kPa. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for gasifying and melting dust which gasifies and melts the dust.

In the field of incineration of dust, in recent years, gasification melting furnaces that gasify dust from the viewpoint of dioxin generation suppression and ease of ash treatment, and discharge the residue as molten slag have been used.
One of these gasification melting furnaces is a shaft furnace type gasification melting furnace, which is described in JP-B-53-16633 and JP-B-60-22244. A coke bed is provided at the lower part of the furnace body, dust is deposited on the upper part, and the dust is gasified and partially burned in an oxygen-deficient state by the heat of the coke bed, and the residue is melted in the coke bed and slag is formed. The slag residue is discharged out of the furnace and rapidly cooled, and the ceramic state is disposed of in a landfill as appropriate.

In the gasification melting furnace described above, the contact height between the hot gas and the dust can be increased by increasing the height of the dust deposit, so that the heat exchange between the hot gas and the dust can be sufficiently performed. As a result, the temperature of the hot gas discharged from the furnace top is assumed to be 200 to 300 ° C.
Japanese Patent Publication No.53-16633 Japanese Patent Publication No. 60-22244

However, since the gasification and melting furnace described above has a higher deposition height of the dust than the inner diameter of the furnace body, the ventilation resistance is increased, and the furnace pressure at the furnace bottom is increased to about 1500 mmAq at a positive pressure. . As a result, there is a problem that when the molten slag is discharged, the molten slag is blown out, which is dangerous.
An object of the present invention is to solve the above-described problems and to provide a method for gasifying and melting refuse that can reduce the pressure in the furnace at the bottom of the furnace and prevent blowout of molten slag.

  In the method for melting dust according to the present invention, the dust is thrown into the furnace body to form a dust layer, the dust is gasified by the high temperature gas from the furnace bottom, the residue is melted into slag, and the molten slag discharge port provided at the furnace bottom In the melting method of dust discharged from the furnace, H / D is 2 or less, where H is the height from the bottom of the furnace to the upper surface of the deposited dust layer, and D is the inner diameter of the furnace body facing the upper surface of the dust layer. The discharge port is opened to the atmosphere, and the pressure at the bottom of the furnace facing the molten slag discharge port is set to a positive pressure of 5 kPa or less. In the present invention, H / D is preferably 1.5 or less. In addition, it is preferable that the distance from the coke layer to the upper surface of the dust layer is reduced by keeping the deposition height H of the dust relatively low so that the temperature of the gas passing through the dust layer is 500 to 1000 ° C.

Since the present invention has the above-described configuration, it is possible to provide a refuse gasification melting furnace capable of suppressing the occurrence of a shelf hanging phenomenon and reducing the pressure in the furnace at the bottom of the furnace and preventing the hot air and molten slag from being blown out violently. it can.
In the embodiment of the invention, a shaft furnace type garbage gasification melting furnace in which coke and a plasma torch are used together as a heating source has been described, but the effect of the present invention can be achieved even in a furnace using either a coke or a plasma torch. There is no change.

The dust melting furnace according to the present invention forms a coke layer at the bottom of the shaft furnace, heats the coke layer with hot air blown from a plasma torch, and burns a part of the coke layer, and this heat causes the coke layer to burn. The dust layered on the top is burned and gasified in an atmosphere below the stoichiometric air amount, and the resulting ash is melted into slag in the coke layer and discharged out of the furnace.
Since ash and char are melted into slag, when it is cooled, the molten slag becomes a glassy material, the volume of ash and char is reduced to about 1/5, and heavy metals are confined in the glassy material. Does not elute.
In the melting furnace according to the present invention, hot air of the plasma torch is blown toward the coke layer, and the temperature of the hot air from the plasma torch becomes 1000 to 2500 ° C., thereby heating the coke layer and in the hot air. Since part of the coke layer burns with this oxygen, the temperature in the coke layer can be stably maintained at about 1500 ° C.

In the melting furnace of the present invention, the ratio (H / D) of the deposition height H of the dust to the furnace body inner diameter D is set to 2 or less. Therefore, in the dust melting method of the present invention, the air flow resistance is reduced, and the pressure in the furnace at the bottom of the furnace is reduced as compared with the conventional one. That is, the blowout pressure of plasma air and shroud air of the plasma torch is 14.7 kPa, but the furnace bottom with the coke layer has a positive pressure not exceeding 5 kPa.
When the furnace pressure at the bottom of the furnace exceeds 5 kPa, when the molten slag discharge port communicates with the inside of the furnace, hot air of about 1500 ° C. in the furnace is strongly blown out. There is a disadvantage of taking it out and there is a risk of burns to people working around the furnace.

  The distance from the coke layer to the upper surface of the dust layer can be reduced by keeping the dust accumulation height H relatively low, and the temperature of the gas passing through the dust layer can be set to 500 to 1000 ° C., so that the resin melts. It does not form a bridge. Further, even when the resin is fused to form a large lump, it is difficult to form a bridge by increasing the furnace body inner diameter D.

  However, when the value of H / D is too small, that is, when the height H of the dust is too small, the temperature of the gas passing through the dust layer becomes too high and the gasification reaction of the dust becomes unstable, Inconveniences such as an increase in the fluctuation range of the deposition height H occur. In addition, when the furnace body inner diameter D is too large, it is easy to cause variation in dust accumulation height due to the dust quality in the radial direction and the angle of repose of the dust, so it is difficult to maintain the gasification and melting reaction in the radial direction uniformly. Become. Therefore, the value of H / D is preferably 0.8 or more, and more preferably 1.0 or more.

Next, an embodiment of the refuse melting furnace of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing a gasification melting furnace of the present invention, a schematic view showing a dust melting furnace system, and FIG. 2 is a schematic view showing a gasification melting furnace system according to the present invention.
1 and 2, reference numeral 2 denotes a furnace body, and a plasma torch 1 and a first tuyere 3 and a second tuyere 4 are provided above the plasma torch 1 near the bottom of the furnace. In this embodiment, the plasma torch 1 is provided at two places on the circumference of the same height of the furnace body, and the direction of the hot air blown out from the plasma torch is flat in the diameter direction of the furnace body and in the elevational direction at the bottom of the furnace body. The direction of the intersection of the bottom and the vertical part. Similarly, the first tuyere 3 and the second tuyere 4 were 6 places on the circumference. The air blown from the first tuyere 3 and the second tuyere is heated to a high temperature by exchanging heat with a high-temperature gas in the secondary combustion furnace, which will be described later, with a heat exchanger.
The furnace body 2 is formed by attaching a refractory material 202 inside the outer shell 201.

A supply port 5 is provided in a substantially intermediate portion of the furnace body 2, and a pusher 6 is provided in connection with the supply port 5, and a dust supply device 7 and a coke supply device 8 are connected to the pusher 6. It is set up. Although not shown, the dust supply device 7 and the coke supply device 8 are provided with a double butterfly valve so as to block the intrusion of outside air as much as possible.
An exhaust gas port 9 is provided near the upper portion of the furnace body 2, and a secondary combustion furnace 10, a primary cooling tower 11, a heat exchanger 12, a secondary cooling tower 13, and a dust collector 14 are connected to the exhaust gas port 9. An attracting fan and an exhaust tower (not shown) are connected after the dust collector 14.
A molten slag discharge port 22 communicating with the inside of the furnace body 2 is provided at the furnace bottom portion 21 of the furnace body 2, and a slag tank 15 and a slag cooling water tank 16 are provided in connection therewith.

Next, the operation and operating conditions of the melting furnace of the present invention will be described.
First, when starting to raise the temperature of the furnace body 2 in the normal temperature state, the coke is filled in the furnace bottom portion 21 to form the coke layer 25, and then the plasma torch 1 is ignited and hot air of about 1800 ° C. is applied to the coke layer 25. Blow toward. The furnace bottom portion 21 and the coke layer 25 are heated to about 1500 ° C. after about 3 hours by the hot air of the plasma torch 1 and the combustion heat that the coke burns. The dust is supplied from the dust supply device 7 to the furnace body 2 by the pusher 6 and the mixture of coke and limestone is supplied from the coke supply device 8 by the pusher 6. In this example, the weight ratio of coke to dust was 2%.
When dust and coke are supplied, a dust layer 26 in which dust and coke are alternately formed into a substantially layer shape is formed on the coke layer 25.

The initial charging amount is adjusted so that the height H of the dust layer 26 is approximately 2000 mm, and thereafter, the supplying amount and the consumption amount are balanced by quantitatively charging to maintain the above-described H level. Can do. As a result, the ratio H / D between the dust deposition height H and the furnace body inner diameter D is kept at 2 or less. By doing so, the dust shelving phenomenon can be suppressed as described above, and the furnace pressure at the furnace bottom can be reduced to 5 KPa or less.
In the present embodiment, the air supplied into the furnace body 2 is supplied from the plasma torch 1 and the first and second tuyere 3 and 4, and the total amount of air is combustible materials such as coke and dust in the furnace body 2. The stoichiometric air amount is less than the stoichiometric air amount, and the ratio of the stoichiometric air amount to the total air amount is set to 1: 0.2 to 0.5 in practice.

The dust layer 26 deposited on the heated coke layer 25 is dried and partly combusted by the combustion air, and the other part is gasified because the combustion air is consumed by the combustion. The ash generated by the combustion of the dust and the char generated by the gasification are melted by hot air from the coke layer 25 heated to about 1500 ° C. to form molten slag and flow down through the coke layer 26 and accumulate in the furnace bottom 21. The molten slag accumulated in the furnace bottom 21 is discharged out of the furnace through a molten slag discharge port 22 provided in the furnace bottom.
As described above, the supply of dust and coke is performed at a ratio of 3: 1, so it is considered that dust and coke are almost alternately layered, and the quantitative ratio is about 2%. Since combustion is much quicker than coke, most of the combustion air described above is consumed in the combustion of dust, making it difficult for the coke to burn, and therefore, the consumption of coke is low. As a result, the upper part of the dust layer 26 becomes a zone 261 rich in dust, the middle part of the dust layer 26 where the combustion and gasification of dust progresses, and the zone 262 in which dust and coke are mixed, and most of the lower part of the dust layer 26 is coke. Becomes a zone 263. As a result, the coke layer 25 is continuously formed at a predetermined height in the furnace bottom 21, and the level of the coke layer 25 is maintained in a state where the consumption amount of coke and the supply amount are balanced. is there.

Next, an embodiment in which dust is gasified and melted using the melting furnace of the present invention shown in FIG. 1 will be described.
The properties of the dust used in this example are shown below.
Waste type: General waste (mainly household waste)
Moisture content: 55w%
Resin content: 12w%
Lower heating value: 358 kJ / kg
The dust having the above properties was gasified and melted under the following conditions.
Waste supply rate: 1000 kg / h
Coke supply amount: 20kg / h
Total air volume: 700 Nm ³ / h
Air volume from plasma torch: 150 Nm ³ / h
Air pressure from plasma torch: 14.7 MPa
H / D: 2.0
Although it was carried out under the above-mentioned conditions, there was no shelf hanging phenomenon of the thrown dust. The pressure at the furnace bottom 21 was 5 kPa as a positive pressure on average.

A gasification and melting treatment was carried out under the conditions shown below with the dust having the same properties as in Example 1.
Waste supply rate: 1000 kg / h
Coke supply amount: 20kg / h
Total air volume: 700 Nm ³ / h
Air volume from plasma torch: 150 Nm ³ / h
Air pressure from plasma torch: 14.7 MPa
H / D: 1.5
Although it was carried out under the above-mentioned conditions, there was no shelf hanging phenomenon of the thrown dust. The pressure at the furnace bottom 21 was 1.5 kPa as a positive pressure on average.

In Examples 1 and 2, the temperature of each part in the furnace body 2 was substantially constant at about 1500 ° C. in the coccus layer, and was 500 to 900 ° C. in the space above the dust layer 26.
About 60 minutes after starting to supply the dust, molten slag began to come out from the molten slag discharge port. The average amount of molten slag discharged was about 80 kg per hour.

  In this embodiment, the blowing pressure of shroud air blown from the plasma torch is 14.7 kPa, but the pressure in the vicinity of the furnace bottom 21 is about 5 kPa to 1.5 kPa due to the ventilation resistance of the coke layer 25 and the dust layer 26 described above. And acts as a differential pressure sufficient to extrude the molten slag from the molten slag discharge port 22. However, even if the liquid level of the molten slag falls and the hot air in the furnace blows out, the momentum is weak and does not cause the molten slag to be blown out vigorously.

(Comparative example)
A gasification and melting treatment was carried out under the conditions shown below with the dust having the same properties as in Example 1.
Dust supply amount: 1000 kg / hour Coke supply amount: 20 kg / hour Total air amount: 700 Nm ³ / hour Air amount from plasma torch: 150 Nm ³ / hour Air pressure from plasma torch: 14.7 MPa
H / D: 2.5
Although it implemented on above-mentioned conditions, the furnace pressure of the furnace bottom part 21 was 8 kPa by positive pressure on the average. In addition, a shelf hanging phenomenon occurred in the dust layer in the furnace. Since the height of the dust deposition layer is high, the temperature of the high temperature gas from the bottom of the furnace decreases when it rises in the furnace, and the temperature is about 200 to 350 ° C. above the dust layer. At this temperature, since the resins contained in the dust are in a semi-molten state, they are fused together to form a large lump, which is considered to facilitate the formation of a bridge.

  The present invention relates to a method for gasifying and melting dust that gasifies and melts dust, and can be used for a method for gasifying and melting dust that can reduce the pressure in the furnace at the bottom of the furnace and prevent blowing out molten slag.

It is sectional drawing which shows the gasification melting furnace of this invention. It is the schematic which shows the system of the gasification melting furnace concerning this invention.

Explanation of symbols

1 plasma torch, 2 furnace body, 3, 4 tuyere, 5 supply port,
7, dust supply device, 8 coke supply device, 9 exhaust port,
21 furnace bottom, 22 molten slag outlet, 25 coke layer,
26 Dust layer

Claims (3)

In the melting method of dust that is thrown into the furnace body to form a dust layer, the dust is gasified with high-temperature gas from the furnace bottom, the residue is made into molten slag, and discharged from the molten slag discharge port provided in the furnace bottom.
When the height from the bottom of the furnace to the upper surface of the deposited dust layer is H and the inner diameter of the furnace body facing the upper surface of the dust layer is D, H / D is set to 2 or less, the molten slag discharge port is opened to the atmosphere and the molten A method for melting dust, wherein the pressure at the bottom of the furnace facing the slag discharge port is a positive pressure of 5 kPa or less. The method for melting dust according to claim 1, wherein the temperature of the gas passing through the dust layer is 500 to 1000 ° C. The method for melting dust according to claim 1 or 2, wherein the molten slag is continuously discharged from the molten slag discharge port.

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