JP3759200B2 - Thermal decomposition / melting method and apparatus for waste - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a method for thermally decomposing and melting waste that simultaneously decomposes and melts industrial waste such as shredder dust, waste plastic, wood waste, paper waste, sludge, waste oil, and waste liquid from municipal waste, waste automobiles and waste home appliances, and It relates to the device.
[0002]
[Prior art]
The amount of waste generated has been increasing year by year, causing problems such as tight final disposal capacity and secondary pollution (groundwater contamination). Conventionally, wastes have been landfilled as they are or incinerated. However, due to the strengthening of laws and regulations, melting and volume reduction and fixation are proceeding.
[0003]
As a melting method of the waste, there are a direct melting method using a shaft furnace and a method in which the waste is incinerated by a rotary kiln or a fluidized bed furnace and the incinerated ash is melted by a plasma melting furnace or a swirl flow melting furnace. The direct melting method is considered optimal in order to simplify the process and reduce the equipment cost and operation cost when the melting process becomes full-scale. As a technique for directly melting waste, there is a conventional technique in which waste and coke are alternately charged into a shaft furnace and melted.
[0004]
The conventional coke bed melting furnace is configured as shown in FIG. That is, the melting furnace 1a is formed in a vertical cylindrical shape, and an exhaust gas extraction port 11a is provided at the top, a processed material supply port 12a that opens obliquely downward is connected near the lower part of the main body, and a slag is further formed at the bottom. A discharge port 13a is formed. Waste such as sludge and coke are supplied by natural fall from the treated product supply port 12a and are stored at the bottom of the melting furnace 1a to form a coke bed 3a, from which primary air and two are supplied from the side of the melting furnace 1a. Combustion is performed by supplying secondary air. That is, organic combustibles are gasified in the upper part of the coke bed 3a (upper part of the melting zone), and secondary air is supplied to the gas from the side part of the melting furnace 1a in the free board part 2a on the upper side of the coke bed 3a. Combustion is promoted, and the exhaust gas is discharged from the exhaust gas outlet 11a. In addition, the inorganic component is melted by this combustion, flows down between the coke grains, and is discharged from the slag discharge port 13a.
[0005]
[Problems to be solved by the invention]
In the above configuration, coke is used in order to ensure the gas and air permeability in the waste layer, and this coke is consumed in large quantities by combustion, so the fuel cost becomes high. In particular, industrial waste has various shapes and properties, so when processing various industrial waste, coke alone cannot ensure sufficient air permeability, so-called shelves and shelves in the waste layer. There was a problem that a drop or the like was likely to occur and a smooth melting operation could not be performed.
[0006]
Also, for example, automobile shredder dust (mixed waste mainly composed of plastics generated when shredded cars are crushed with shredders and recovered valuables) is as small as 0.1 to 0.3 g / cm ³ and floats. When a waste with a characteristic is introduced, the waste rides on the rising gas flow in the furnace and scatters. In this case, the scattered waste has a shorter residence time in the furnace, so it will be scattered unburned and a large amount of dioxin will be generated due to incomplete combustion. However, there has been a problem that a large dust collection process is required.
[0007]
The present invention has been made in order to eliminate such conventional drawbacks, and performs smooth melting operation by ensuring the air permeability of the waste packed bed without using a large amount of expensive coke. , A method for thermal decomposition and melting of waste that has a small specific gravity and is completely gasified and melted in a furnace with sufficient residence time without being scattered, and hardly generates dioxins. The object is to provide an apparatus.
[0008]
[Means for Solving the Problems]
The method of the present invention is a method in which waste is thermally decomposed and melted by a vertical shaft furnace, in which a waste molten slag discharge part is formed at the bottom of the furnace, a waste layer is formed above, and a waste layer is further formed above it. By forming a coke layer and supplying hot gas and oxygen-containing gas (oxygen, air and mixtures thereof) to the lower part of the waste layer, the waste is pyrolyzed and melted while the hot gas rises in the furnace. The waste slag is discharged from the bottom of the furnace, and the scattered dust in the rising high-temperature gas is collected by the coke layer and then discharged as exhaust gas from the top of the furnace. is there.
[0009]
Further, the apparatus of the present invention is a vertical shaft furnace, in which a waste melting slag discharge portion is formed at the bottom of the furnace, and on the upper side, a thermal decomposition / melting zone filled with waste supported by a rooster, Furthermore, a dust collection zone filled with coke supported by a rooster is formed on the upper side, an exhaust gas discharge part is formed on the top of the furnace on the upper side, and a high-temperature gas is placed below the pyrolysis / melting zone. High temperature gas supply means for supplying the waste layer is provided.
[0010]
The pyrolysis / melting zone may have a refractory layer formed below the waste layer. The high-temperature gas supply means may be formed by a combustion chamber formed below the pyrolysis / melting zone. Further, a dust collecting means may be connected to the exhaust gas discharge section at the top of the furnace, and the dust collecting means may be provided with a collecting means for supplying the collected dust to the waste layer.
[0011]
[Action]
In the above configuration, each zone is supported by the rooster and the air permeability is maintained well.In the pyrolysis / melting zone, the waste is pyrolyzed and melted, and the elevated high temperature gas is scattered by coke in the collection zone. After being collected, it can be discharged out of the furnace as an almost completely gasified exhaust gas that does not contain dust. In the upper dust collection layer, the coke only collects scattered dust, and since the combustion is slight, the consumption of coke is small.
[0012]
In addition, when a refractory layer is formed below the waste in the pyrolysis / melting zone, the refractory can be used for a long period of time, so it is more economical than forming a coke layer. If a combustion chamber is formed as a high-temperature gas supply means below the pyrolysis / melting zone, a high-temperature gas having a uniform temperature can be uniformly fed into the pyrolysis / melting zone.
[0013]
In addition, if dust collecting means is connected to the exhaust gas discharge section, exhaust gas can be more completely purified, and the collected dust can be recovered and recovered in the furnace to reduce the waste slag conversion rate. Can be improved.
[0014]
【Example】
In FIG. 1, the melting furnace 1 is formed of a cylindrical vertical shaft furnace, and an exhaust gas extraction port 11 is provided at an upper end portion thereof, and a coke supply pipe 12 is inclined obliquely downward in an intermediate portion of the main body 10 of the melting furnace 1. The waste supply pipe 13 is opened obliquely downward and connected to the lower side, and an annular supply unit 3 is provided near the bottom of the main body 10. The annular supply portion 3 includes a portion formed in an annular shape so as to surround the outer periphery of the melting furnace 1, and a straight pipe portion extending obliquely downward from the portion in the circumferential direction and connected to the main body 10 as illustrated. The gas supplied from the supply source not supplied to the annular part is supplied to the bottom of the main body through the straight pipe part. The body 10 below the opening of the annular supply unit 3 is provided with auxiliary combustion means (burners) 70 at several locations in the circumferential direction, and a slag discharge port 14 and a molten metal take-out port 15 are provided at the bottom of the lower body. Is provided. The slag discharge pipe 14 is provided with auxiliary combustion means (auxiliary burner) 71 toward the inlet.
[0015]
Further, in the vicinity of the middle portion of the melting furnace 1, a water-cooled rooster 17 is provided immediately above the opening of the waste supply pipe 13, and a third zone (dust collecting zone) C is formed in the main body 10 on the upper side, A water-cooled rooster 18 is provided immediately below the opening of the annular supply unit 3, and a second zone (pyrolysis / melting zone) B is formed between the water-cooled rooster 17 in the main body 10 on the upper side thereof. A first zone (hot gas generation zone) A having a combustion chamber 72 is formed in the lower body 10. The first zone A serves to generate a high-temperature gas in the combustion chamber 72 and uniformly feed the high-temperature gas having a uniform temperature into the second zone B.
[0016]
In the melting furnace having the above-described configuration, first, a predetermined amount of refractory consisting of ceramic balls or other refractory pieces is supplied from the waste supply pipe to form the refractory layer 5 on the water-cooled rooster 18, and from the annular supply portion 3. Injects oxygen-containing gas and burns fuel in the first zone A by the auxiliary combustion means 70 to generate high-temperature gas. In this state, waste is supplied from the waste supply pipe 13 to form the waste layer 4 entirely in the second zone B on the refractory layer 5, and coke is supplied from the coke supply pipe 12 to be water-cooled. A coke layer 8 having a predetermined height is formed on the rooster 17. The high temperature gas generated in the first zone A rises and sequentially passes through the refractory layer 5, the waste layer 4 and the coke layer 8, thereby heating and igniting the waste and coke, and promoting the thermal decomposition of the waste. This heating is adjusted so that, for example, the first zone A is 1500 to 1600 ° C., the upper end portion of the waste layer 4 is 800 to 1200 ° C., and the upper end portion of the coke layer 8 is about 900 ° C.
[0017]
By the above operation, the waste in the waste layer 4 is dried by the rising high temperature gas and gradually descends while pyrolyzing. The pyrolyzed char, ash, and incombustibles descend to the lower part of the second zone B, where the oxygen-containing gas and char supplied from the annular supply unit 3 are combusted and the high temperature rising from the combustion chamber 72 is reached. The gas is heated to a high temperature of about 1400 to 1500 ° C., becomes molten slag, passes through the refractory layer 5, falls into the first zone A, and is discharged from the slag discharge pipe 14. At this time, combustion gas is blown to the inlet portion of the slag discharge pipe 14 by the auxiliary combustion means 71, thereby preventing the slag from being blocked at the inlet portion. Further, the molten metal and inorganic components of the incombustible component are collected at the bottom of the furnace and are sequentially discharged from the molten metal outlet 15.
[0018]
On the other hand, the high-temperature gas rising in the second zone B is discharged from the exhaust gas outlet 11 through the coke layer 8 from the upper part of the waste layer 4, and this gas contains waste dust. Waste dust is collected by the coke while the hot gas passes through the coke layer 8. The collected dust gradually accumulates as the coke burns slightly, falls as ash, and descends in the waste layer 4. In this way, coke is used to collect waste dust contained in the exhaust gas, and in order to minimize the consumption of coke, the coke combustion is suppressed by keeping the atmosphere reducible. To do. Therefore, it is preferable that the pyrolysis combustion of the waste in the second zone B is performed at a low air ratio of about 0.4 to 0.6. This can reduce the consumption of coke to about 2 to 3% of the waste to be treated. Further, when a reducing atmosphere is used, the metal content in the waste is hardly oxidized in the second zone B, which is preferable in terms of metal recycling. Further, due to the presence of the coke layer 8, the flow rate of the high temperature gas rising in the second zone B is maintained at an appropriate value, thereby suppressing the occurrence of shelves and shelves falling in the waste layer 4. It is.
[0019]
FIG. 3 shows an apparatus in which a means for treating the exhaust gas is attached to the melting furnace 1. A secondary combustion furnace 6 is connected to the exhaust gas outlet 11 via a cyclone 2, and further captured by the cyclone 2. A dust supply pipe 21 for supplying the collected dust into the annular supply portion 3 of the melting furnace 1 by pneumatic transportation is provided. The secondary combustion furnace 6 is provided with a waste heat boiler 61 and an air preheater 62 attached thereto, a generator 64 is connected to the waste heat boiler 61, and a combustion fan 63 is connected to the air preheater 62. In addition, the preheated air from the air preheater 62 is supplied to the annular supply unit 3 of the melting furnace. Further, a bag filter 9 is connected to the secondary combustion furnace 6 through a pipe 60, and an air discharge chimney 91 is connected to the bag filter 9 through an induction fan 90.
[0020]
1 and 2, an example in which automobile shredder dust, that is, waste car is pulverized with a shredder, and mixed waste mainly composed of plastic generated when recovering valuable materials is pyrolyzed and melted. explain. Shredder dust is supplied at 5000 kg / h as waste supplied from the waste supply pipe 13 of the melting furnace 1, hot air 12,000 Nm ³ / h preheated to 170 ° C. is supplied from the annular supply pipe 3, and the air ratio is 0 .4 gasified combustion. Oxygen 180 Nm ³ / h + combustion air 1430 nm ³ / h was supplied to the city gas 300 Nm ³ / h with burner air means 70 in the first zone A, is burned at an air ratio 0.8. Due to this combustion, the temperature in the combustion chamber 72 became a high temperature of 1500 to 1600 ° C. The air permeability when the high temperature gas rises is well maintained by the refractory layer 5 on the water-cooled rooster 18 in the second zone, and the waste layer 4 is thermally decomposed and melted while maintaining a fluid state. Yes. The temperature of the lower part in the second zone B is 1400 ° C. or higher due to the radiant heat from the first zone A or the high temperature gas, and the char in the shredder dust reacts with the high temperature gas in the waste layer 4 and burns. Further, the inorganic content and the metals in the waste became molten slag, dropped by its own weight, stored in the bottom of the furnace through the first zone A, and sequentially discharged from the molten metal outlet 15 to the outside of the furnace.
[0021]
In the upper part of the second zone B, the shredder dust is thermally decomposed by the exhaust gas rising from the lower part. At this time, the scattered dust containing unburned components rises in the furnace together with the pyrolyzed gas, and is collected by the coke layer 8. It is completely gasified here. The pyrolysis gas was sent from the exhaust gas outlet 11 through the cyclone 2 to the secondary combustion furnace 6 where secondary air 50,000 Nm ³ / h was blown in and completely combusted at an air ratio of 2.0. The complete combustion exhaust gas waste heat boiler 61, after performing the heat recovery in the air preheater 62, the addition of Ca (OH) ₂ and the activated carbon in the pipe 60 in order to remove HCl and SO _2, HCl and SO ₂ Was collected together with dust by the bag filter 9. Thereafter, the exhaust gas was sucked by the attracting fan 90 and released from the chimney 91 to the atmosphere.
[0022]
The waste supplied into the melting furnace 1 was completely gasified in the furnace, and therefore it did not jump out of the furnace in an incomplete combustion state. As a result, the concentration of dioxins at the outlet of the secondary combustion furnace 6 is about 9 ngTEQ / Nm ³ , 98% of which is further removed by the bag filter 9, and the concentration of dioxins discharged from the chimney 11 is The value was 0.18 ng TEQ / Nm ³ , which was a value sufficiently lower than the guideline (standard determined by the Ministry of Health and Welfare: 0.5 ng TEQ / Nm ³ ). Further, the scattered dust collected by the cyclone 2 provided between the melting furnace 1 and the secondary combustion furnace 6 is supplied from the annular supply part 3 of the melting furnace 1 to the lower part of the second zone B by the dust supply pipe 21. Therefore, the slag conversion rate could be increased to 90%.
[0023]
In the above embodiment, an example of melting automobile shredder dust is shown. However, the waste to be input may be municipal waste, and industrial waste such as waste plastic, wood waste, paper waste, and sludge. The auxiliary combustion fuel used in the first zone A may be industrial waste such as waste oil, and industrial waste such as waste liquid may be supplied to the first zone A and processed at the same time. Further, by supplying lime or the like to the second zone B together with the waste, it is possible to perform de-HCl and de-SOx in the furnace.
[0024]
In the above-described embodiment, an example in which the high-temperature gas generation zone A composed of the combustion chamber 72 is separately formed below the pyrolysis / melting zone B has been shown. It is also possible to blow an oxygen-containing gas near the lower end of the melting zone B and blow a combustion flame by an auxiliary burner.
[0025]
【The invention's effect】
As described above, according to the present invention, each zone is supported by a rooster and has good air permeability, and waste is thermally decomposed and melted in the thermal decomposition and melting zone, and the elevated high temperature gas is trapped. After scattered dust is collected by coke in the collecting zone, it can be discharged out of the furnace as an almost completely gasified exhaust gas that does not contain dust. In the upper dust collection layer, the coke only collects scattered dust, and since the combustion is slight, the consumption of coke is small.
[0026]
Further, when a refractory layer is formed below the waste in the pyrolysis / melting zone, the refractory can be used for a long period of time, so it is more economical than forming a coke layer. If a combustion chamber is formed as a high-temperature gas supply means below the pyrolysis / melting zone, a high-temperature gas having a uniform temperature can be uniformly fed into the pyrolysis / melting zone.
[0027]
In addition, if dust collecting means is connected to the exhaust gas discharge section, exhaust gas can be more completely purified, and the collected dust can be recovered and recovered in the furnace to reduce the waste slag conversion rate. Can be improved.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view of a melting furnace showing an embodiment of the present invention.
FIG. 2 is an explanatory view of an apparatus in which an exhaust gas treatment means is attached to the melting furnace of FIG.
FIG. 3 is a schematic longitudinal sectional view of a conventional waste melting apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Molten hot water 2 Cyclone 3 Annular supply part 4 Waste layer 5 Refractory layer 6 Secondary combustion furnace 8 Coke layer 10 Main body surrounding wall 11 Exhaust gas outlet 12 Coke supply pipe 13 Waste supply pipe 14 Slag outlet 15 Molten metal outlet 17, 18 Water-cooled rooster 21 Dust supply pipes 70, 71 Auxiliary combustion means 72 Combustion chamber A Hot gas generation zone B Pyrolysis / melting zone C Dust collection zone

Claims (5)

  It is a method of pyrolyzing and melting waste by a vertical shaft furnace, forming a waste slag discharge part at the bottom of the furnace, forming a waste layer above it, and further forming a coke layer above it, By supplying hot gas and oxygen-containing gas to the lower part of the waste layer, the waste gas is pyrolyzed and melted and dropped to the furnace bottom while the hot gas rises in the furnace, and the waste is discharged from the furnace bottom. A waste pyrolysis / melting method characterized in that slag is discharged and scattered dust in the rising high-temperature gas is collected in a coke layer and then discharged as exhaust gas from the top of the furnace. This is a vertical shaft furnace, where a waste molten slag discharge part is formed at the bottom of the furnace, the pyrolysis / melting zone filled with waste supported by a rooster on the upper side, and coke on the upper side. A dust collection zone that is supported and filled is formed, an exhaust gas discharge part is formed at the top of the furnace, and a high temperature gas is supplied to the waste layer below the pyrolysis / melting zone. A waste pyrolysis / melting apparatus characterized in that a gas supply means is provided.   The waste pyrolysis / melting apparatus according to claim 2, wherein a refractory layer is formed below the waste layer in the pyrolysis / melting zone.   4. The waste pyrolysis / melting apparatus according to claim 2, wherein the high-temperature gas supply means is formed by a combustion chamber formed below the pyrolysis / melting zone.   The dust collecting means is connected to the exhaust gas discharge section at the top of the furnace, and the dust collecting means is provided with a collecting means for supplying the collected dust to the waste layer. The waste thermal decomposition / melting apparatus according to any one of 2 to 4.

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