JP2002159934A - Process and equipment for treating incineration ash with fuel firing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an incineration ash treatment process using fuel firing, by which sticky dust can be inhibited from being caused and the heat energy efficiency can be improved, and also to provide a treatment equipment for the process. SOLUTION: The process for treating incineration ash of combustible solid waste by fusing the incineration ash through fuel firing and solidifying the fused ash, involves performing the heat recovery of a high-temperature off-gas containing low-boiling substances volatilized from the incineration ash when fused, and the preheating of combustion air to a temperature in the region of 1,450-790 deg.C, and instantly cooling the off-gas after the heat recovery to 180 deg.C so as to pass the off-gas through the solidification temperature region in which stickiness of each of the low-boiling substances is caused, as rapidly as possible by injecting water into the off-gas under such conditions as to completely evaporate the injected water. The equipment comprises, as its constituent devices, an ash fusion furnace (A) provided with an incineration ash charge port 1 and a slag withdrawal port 5, an off-gas combustor (B) provided with a discharge port 11 for the combusted off-gas of a lowered temperature, and a gas cooling column (C) wherein these devices (A), (B) and (C) are arranged in series.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating exhaust gas generated from an ash melting furnace when incinerated ash generated by incinerating general household garbage or industrial waste is fuel-fired and solidified. The present invention relates to an apparatus used for the above.

[0002]

2. Description of the Related Art In recent years, in Japan, the amount of general household garbage and waste has been increasing year by year, and the disposal thereof has become a social problem. In 1993, major municipalities were required by law to provide municipalities with incineration facilities. As a result, large cities and municipalities began to have more than one incineration facility. Various problems, such as securing a final disposal site to fill the waste and secondary pollution from the buried incineration ash, have come to the fore.

[0003] Recently, household waste is also designated as specially managed municipal waste, and fly ash is separated from main ash (incinerated ash), so that it cannot be buried at the final disposal site without intermediate treatment. For this reason, attention has been focused on incineration ash fusion and solidification technology that can prevent the elution of harmful substances such as heavy metals contained in incineration ash, and the Ministry of Health and Welfare has set up a construction plan for incineration ash melting and treatment facilities targeting metropolises and cities. It has been promoted since 1994.

At present, garbage discharged from ordinary households is collected by type and processed according to the quality of the garbage.
For example, combustible garbage is partially used as a raw material for compost fertilizer, but is mostly incinerated at an incinerator in an incinerator. In this incineration process, incineration ash discharged from the incinerator and fine fly ash collected by a dust collector or the like are generated. The latter fly ash is light and easy to fly,
Since it contains a lot of heavy metals, it is usually solidified with concrete or neutralized with carbon dioxide in exhaust gas to stabilize it as carbonate and then buried. on the other hand,
The incinerated ash is melted and solidified at a temperature of about 1400 to 1500 ° C., and is effectively used for burying or covering material.

[0005] As the incineration ash melting furnace, electric melting furnaces (arc heating method, plasma heating method, resistance heating method), coke bed melting furnace (coke heating method), surface melting furnace (heavy oil burner heating method) and the like have hitherto been used. Are known.

[0006] Most of the incineration ash melting furnaces currently in operation are electric melting furnaces, for example, plasma heating melting furnaces, which consume 800 to 100 tons of incinerated ash.
Since it is as high as 0 kW, in order to perform economical operation, it is necessary to provide a power generation facility for recovering heat from exhaust gas from an incinerator, and to use the generated power as a heat source of the melting furnace. However, the limit of the incineration scale of this power generation facility is as large as 200 tons of garbage per day, and because it is a continuous furnace, it is unsuitable for a small incineration facility with a processing capacity of less than that. Since it is difficult to cope with the rapid fluctuation of the ash, when the ash having a high water content or the ash containing the unburned organic matter is to be treated, it is complicated to perform a drying treatment in advance.

Further, the coke bed melting furnace uses solid fossil fuel which is difficult to obtain at present, so that it is inevitable that the cost will increase, and 0.3 tons of coke and lime per ton of incinerated ash, respectively. There is a drawback that the volume reduction rate is low due to the required degree. Therefore, household waste has recently been designated as a specially managed municipal waste, and incinerated fly ash has been separated from main ashes, and burial at the final disposal site has become impossible without intermediate treatment. Attention has been focused on surface melting furnaces for burning fuel.

In such a fuel-fired surface melting furnace, there is no problem if the exhaust gas heat is recovered after rapidly cooling the molten exhaust gas to around 350 ° C. once in a gas cooling tower. Normally, the temperature of the exhaust gas at the outlet of the gas cooling tower is set at 550 to 650 ° C., and this temperature coincides with the temperature at which metals volatilized from the furnace precipitate as chlorides, oxides, and silicates. And sticky dust adheres to the inside of the pipe and the pipeline, and the device is blocked.

Further, in a fuel-fired surface melting furnace, 1
Since a high temperature of 350 ° C. or more is required, the exhaust gas heat must be recovered as much as possible and used effectively, and maintaining an economical heat energy balance is a prior problem, but this point cannot be solved until now. Therefore, it has not been put to practical use.

[0010]

SUMMARY OF THE INVENTION Under such circumstances, the present invention suppresses the generation of sticky dust in the fuel-fired incineration ash treatment, and reduces the efficiency of the operation by periodically stopping the operation for cleaning. It is an object of the present invention to provide a method for economically improving the balance of heat energy by preventing the decrease and using the exhaust gas heat as effectively as possible, and an apparatus used for the method.

[0011]

The present inventors have conducted various studies on the treatment of fuel-fired incinerated ash. As a result, the exhaust gas from the ash melting furnace was first heat-exchanged with normal-temperature air for fuel combustion. If it is preheated and then cooled under a condition that can completely evaporate the molten exhaust gas that has cooled down to some extent, the low-melting substance gasified in the melting furnace becomes a viscous solid, and thus the exhaust gas is recovered. The present inventors have found that it is possible to efficiently recover thermal energy by appropriately selecting a temperature range and a temperature range to be quenched, and have made the present invention based on this finding.

That is, the present invention relates to a method of burning and melting and solidifying incinerated ash of combustible refuse by burning fuel, wherein heat recovery of high-temperature exhaust gas containing a low-melting substance volatilized at the time of melting from the incinerated ash and generation of combustion air are performed. Preheat from 1450 ° C to 790 ° C
Temperature, and by passing water through the solidified temperature range as quickly as possible to 180 ° C by injecting water under conditions that can completely evaporate the exhaust gas after heat recovery and causing stickiness of low melting point substances. And (A) an incineration ash inlet 1, a burner 2,
An ash melting furnace having an air inlet 3, 3 'for supplying combustion air via 2', a flue gas outlet 4, and a slag outlet 5 for removing slag to be produced;
(B) A heat exchange section 6 for heating the combustion air, a main body 8 provided with a heat receiving surface 7, an inlet 9 for a combustion exhaust gas generated in a melting furnace, and unburned combustible contained in the combustion exhaust gas. Air blowing nozzle 10 for mixing and burning the reactive gas, an exhaust gas combustor provided with an outlet 11 for the cooled combustion exhaust gas, and an inlet 12 for the cooled combustion exhaust gas described above, and free sedimentation inside. The ash melting furnace, the exhaust gas combustor and the gas cooling tower are provided in series with a gas cooling tower provided with a dust outlet 13 for taking out dust and an exhaust gas outlet 14 and having a cooling water spray mechanism 15 disposed therein. A pipe 18 for supplying the combustion air from the heat exchange section 6 of the exhaust gas combustor to the ash melting furnace via the burners 2, 2 'is provided. Characteristic fuel burning There is provided an ash treatment apparatus.

[0013]

Next, the present invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is an explanatory view showing an example of the method of the present invention and an apparatus for carrying out the method. This apparatus includes an ash melting furnace A, an exhaust gas combustor B, and a gas cooling tower C. According to the method of the present invention, the incinerated ash of combustible waste to be treated is supplied to the ash melting furnace A from the incinerated ash inlet 1. The incineration ash includes a main ash that accumulates under the incinerator and a fly ash that is collected by a dust collector, and has different compositions. Table 1 shows their compositions.

[0014]

[Table 1]

Thus, the main component of the main ash is SiO ₂ ,
Al ₂ O ₃ , CaO and Fe ₂ O ₃ , and the main component of fly ash is CaO. These incinerated ash are supplied from the air inlets 3, 3 'in the ash melting furnace A,
1350 to 1 due to the combustion air heated by 2 '
It is heated to 500 ° C., usually about 1400 ° C., and melted and solidified. At this time, volatilization of the metal occurs, and the metal is mixed in the gas discharged from the discharge port 4. The volatilization amount of this metal depends on the basicity of the ash. In other words, all heavy metal components are weakly basic, and alkali metals and alkaline earth metals are strong bases. Therefore, in places with high basicity, that is, in places with a large amount of CaO, basic oxides repel each other. It is easy to volatilize, and conversely, where the basicity is low, that is, where there is a large amount of SiO ₂ , it is difficult to volatilize and remains as slag, and this slag is taken out from the slag outlet 5. Line 20 indicates a fuel supply pipe. Table 2 shows the volatility of each metal at a melting temperature of 1400 ° C.

[0016]

[Table 2]

These metals which are volatilized and contained in the exhaust gas form chlorides, oxides and silicates as the temperature of the exhaust gas decreases. That is, the low-melting substance evaporates during melting, and solidifies with a temperature drop. This adheres as viscous deposits to the walls of the exhaust gas combustor and the heat exchanger.

In the method of the present invention, the temperature 1350 to 1500 discharged from the exhaust gas discharge port 4 of the ash melting furnace A is used.
° C high temperature gas is introduced into an exhaust gas combustor B provided with a heat exchange section 6 from an exhaust gas inlet 9 and exchanged heat with combustion air to produce a temperature at which a low-melting substance is gasified without solidification. That is, the temperature is lowered from 1500 to 1100 ° C, preferably from 1500 ° C to 790 ° C. Therefore, this heat exchange section 6
There is a limit to the temperature of the preheated air that can be recovered by the method described above, and generally it is 450 ° C. at the maximum, depending on the conditions of the inlet air temperature. Due to this heat exchange, the combustion air becomes 100 to 450
C., and is sent through line 18 to burners 2, 2 'from air inlets 3, 3' of ash melting furnace A. If desired, part of the combustion air can be used as secondary combustion air of the combustion exhaust gas sent to the exhaust gas combustor B through the branch pipe line 19.

The exhaust gas combustor B injects combustion air in the vicinity of the flue gas inlet or near the introduced gas rising portion, and recovers the radiant heat of the flue gas rising in the combustor by the heat exchange unit 6. It has the function of one possible radiant heat exchanger. This can be achieved by covering the outside of the combustor B with an outer cylinder and forming an outer wall of the combustor B, that is, a gap between the heat receiving surface 7 and the inner wall of the outer cylinder, in the air flow path. It is preferable that the outer wall of the combustor B, that is, the heat receiving surface 7 and the inner wall of the outer cylinder be lined with a refractory. This refractory has a thickness of 70 to 150 mm and a thermal conductivity of 3-1.
The temperature is preferably set to 0 kcal / mh ° C. If a refractory with a lower thermal conductivity is used, heat will not be transferred sufficiently, so that it will not serve as a heat exchanger.If a refractory with a higher thermal conductivity is used, the heat transfer cannot be sufficiently suppressed, and Cannot protect hot surface.

In this way, the combustion exhaust gas whose temperature has dropped to 790 to 1100 ° C. is introduced into the gas cooling tower C from the introduction port 12 through the introduction pipe 17. Inside the gas cooling tower C, a cooling water spraying mechanism, for example, a water spray pipe 15 for cold water is disposed, and cold water is injected into the above-mentioned combustion exhaust gas, and this is sprayed 180 times.
Rapidly cool to ~ 300 ° C. As a result, the temperature of the low-melting substance in the exhaust gas instantaneously drops, resulting in a powder having no viscosity.
It is taken out from the dust outlet 13 and can be easily collected by a subsequent dust collector. On the other hand, the exhaust gas is discharged from the exhaust gas outlet 14 to the outside of the system.

[0021]

Next, the present invention will be described in more detail by way of examples.

EXAMPLE An outer diameter of a stainless steel cylinder having an outer diameter of 1068 mm, an inner diameter of 850 mm (refractory castable inner diameter), and a length of 4000 mm (effective length) is 1104 mm in outer diameter, 1088 mm in inner diameter,
Ash with a water content of 1% by mass is melted at 1400 ° C in an exhaust gas combustor combined with an air preheater, which is covered with an outer cylinder having a length of 4000 mm (effective length) and a gap formed between them is formed in the air flow path. The combustion exhaust gas generated at the time of solidification was supplied, and heat exchange between the exhaust gas and air was performed at an excess air ratio of 10%. Table 3 shows the results.

[0023]

[Table 3]

In this case, the temperature of the combustion air preheated by the exhaust gas combustor also serving as an air preheater is 450 ° C. at the maximum.
Within ° C, that is, a temperature range in which the low-melting-point substance volatilized in the furnace maintained a gaseous state, and no adsorption of dust to the heat exchange heat transfer surface was observed. On the other hand, the air preheating temperature is set to 550, for example.
When the temperature was raised to ℃, the exhaust gas temperature of the ash melting furnace was lowered to about 700 ° C. in the exhaust gas combustor also serving as an air preheater, so that the formation of sticky deposits on the heat transfer surface was recognized.

[0025]

According to the present invention, it is possible to recover exhaust gas heat which can suppress the formation of sticky dust caused by fuel-fired incineration ash processing, and to efficiently perform incineration ash melting processing at a low fuel consumption rate. It can be carried out.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a method and an apparatus of the present invention.

[Explanation of symbols]

 A Ash melting furnace B Exhaust gas combustor C Gas cooling tower 1 Incineration ash inlet 2, 2 'burner 5 Slag outlet 6 Heat exchange unit 9 Exhaust gas inlet 13 Dust outlet 15 Cooling water spray mechanism

Continued on the front page F term (reference) 3K061 NB03 3K070 DA06 DA37 DA52 DA83 4D004 AA36 CA29 CA32 CA45 CB31 CC02 DA02 DA03 DA06

Claims (4)

[Claims] 1. A method of burning and melting and solidifying incinerated ash of combustible refuse by fuel burning, wherein heat recovery of high-temperature exhaust gas containing a low-melting substance which volatilizes during melting from the incinerated ash and preheating of combustion air are performed at 1450 ° C. To 790 ° C, and a solidification temperature range in which the temperature of the exhaust gas after heat recovery is reduced to 180 ° C at a stretch by pouring water under conditions that can completely evaporate to cause stickiness of the low-melting substance as much as possible. A fuel-fired incineration ash treatment method characterized by passing the ash quickly. (A) an incineration ash inlet (1), an air inlet (3, 3 ') for supplying combustion air via a burner (2, 2'), and an exhaust gas exhaust gas. Exit (4),
An ash melting furnace provided with a slag outlet (5) for removing slag to be generated, (B) a heat exchange section (6) for heating combustion air, and a main body (8) provided with a heat receiving surface (7) )
An inlet (9) for a combustion exhaust gas generated in the melting furnace, and an air injection nozzle (10) for burning the unburned combustible gas contained in the combustion exhaust gas while mixing and stirring the same.
An exhaust gas combustor provided with an outlet (11) for a cooled combustion exhaust gas, and (C) an inlet (1) for the cooled combustion exhaust gas described above.
2) a gas cooling tower provided with a dust outlet (13) for taking out dust that has settled freely therein and an exhaust gas outlet (14), and a cooling water spray mechanism (15) provided inside, and a gas cooling tower arranged in series. The combustion air heated from the pipes (16, 17) respectively connecting the ash melting furnace, the exhaust gas combustor and the gas cooling tower and the heat exchange section (6) of the exhaust gas combustor is burned into the burner (2, 2). ') A fuel-fired incineration ash treatment device, characterized in that a pipe line (18) for supplying to an ash melting furnace via ′) is provided. 3. The fuel-fired incineration ash treatment apparatus according to claim 2, wherein the heat exchange section of the exhaust gas combustor has a function of a radiation heat exchanger. 4. The heat receiving surface (7) has a thermal conductivity of 3 to 10 kca.
The fuel-fired incineration ash treatment device according to claim 2 or 3, wherein the refractory at 1 / mh ° C is lined with a layer having a thickness of 70 to 150 mm.