JP3849287B2 - Exhaust gas treatment method for ash melting furnace - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas treatment apparatus for an ash melting furnace, and more particularly to a dry exhaust gas treatment apparatus for a DC resistance ash melting furnace.
[0002]
[Prior art]
Various types of waste such as municipal waste and sewage sludge were incinerated at incineration facilities, and the resulting incinerated ash and dust were conventionally disposed of in landfills. However, there is a problem of depletion of landfill sites and groundwater contamination due to the elution of toxic heavy metals, so the need for weight reduction / volume reduction and detoxification by melting is increasing.
[0003]
Against this background, a melting treatment method using residual carbon in ash, coke, kerosene, and electric power as heat sources has been proposed, and some actual treatments have been performed. Among these, there are a plasma arc heating method and a resistance heating method as a melting furnace using electric power as a heat source.
[0004]
The resistance heating type ash melting furnace has a counter electrode in the molten slag and heats and melts the ash by electric resistance heat (Joule heat) by direct current or alternating current. 1) High thermal efficiency 2) Generation There is a feature that there is less gas, 3) no flicker is generated because no arc is generated, and 4) divided slag can be separated from molten slag and molten metal.
[0005]
As such a resistance heating type ash melting method, there is one disclosed in JP-A-7-77318. FIG. 2 shows the cross section of the ash melting furnace and the flow sheet of the front and rear equipment disclosed in the above publication. In the figure, a is an ash melting furnace, b is an upper electrode, c is a furnace bottom electrode, d is a power supply device, e is a molten metal layer, f is a molten slag layer, g is a molten salt layer, h is a CO gas combustion furnace, i is a dust collector, j is a dust collecting fan, k is a chimney, and m is an electrode buried position adjuster.
[0006]
A feature of the invention is a method of melting waste made of incineration ash, dust (fly ash) or a mixture of the two from a waste incineration facility using electrical resistance heat as a heat source, the tip position of the upper electrode b Is placed in the molten slag layer f between the molten salt layer g and the molten metal layer e, and the molten salt is electrolyzed by energizing the furnace bottom electrode c in the vertical direction by DC current or AC two-phase current. Without melting, the molten salt layer g is stably formed above the molten slag layer f to prevent generation of harmful chlorine gas, hydrogen chloride gas and the like.
[0007]
However, when the operation is performed to form the molten salt layer g in the ash melting furnace a as described above, the molten salt has a very strong property of invading the furnace wall material. It is necessary to use it. In addition, since a molten salt having good electrical conductivity penetrates into the furnace wall, a short circuit accident is likely to occur. Therefore, as a result of earnest research, the applicant of the present application conducted an energization between the cathode at the bottom of the furnace and the anode inserted from the furnace lid to melt the ash by electric resistance heat, and thus an alkaline salt such as sodium chloride (NaCl). We decided to adopt an operation method that positively electrolyzes. According to this operating method, for example, salt is electrolyzed into chlorine gas and metallic sodium. Chlorine gas reacts with water vapor to form hydrogen chloride and hypochlorous acid, while hypochlorous acid releases oxygen to form hydrogen chloride. Metal sodium evaporates and becomes sodium oxide in an oxidizing atmosphere. These substances are contained in the exhaust gas and released to the outside. Note that part of the metal sodium remains in the molten metal layer e.
[0008]
However, when exhaust gas containing these substances is dry-treated as shown in FIG. 2, these substances are highly hygroscopic, and when they absorb moisture, they adhere to dust collectors i such as bag filters and electric dust collectors or pipes and ducts along the way. , It is difficult to pay off, and easily clogs and deteriorates performance.
[0009]
Accordingly, the applicant of the present application has developed a wet exhaust gas treatment apparatus and filed a patent application. For example, Japanese Patent Application No. Hei 8-142631 “Exhaust gas treatment apparatus for ash melting furnace” introduces an exhaust gas generated from an ash melting furnace as shown in FIG. 3 and absorbs dust and soluble components in an absorption liquid. And a CO combustor that guides the exhaust gas from the gas absorption tower through a mist separator and burns the CO gas in the exhaust gas.
[0010]
Further, Japanese Patent Application No. 8-146124 “Exhaust Gas Absorbing Device for Ash Melting Furnace” contains a bubbling tank that accommodates the absorbing liquid and causes the exhaust gas to submerge inside the absorbing liquid to cause foaming, and a cylindrical or inverted conical shape. The circulatory absorption liquid flows in the tangential direction through the pump from the bubbling tank to the upper end of the barrel portion, while the exhaust gas from the ash melting furnace flows in from the top portion. Has disclosed a flue gas absorbing device having a buffer tank in which the inner wall of the body is washed and whose lower end is immersed in the absorbing liquid in the bubbling tank.
[0011]
Furthermore, the 7th Waste Society Research Presentation Annual Proceedings 1996 discloses a flow sheet of a pilot plant of an ash melting furnace and an exhaust gas treatment apparatus including the above-described invention. FIG. 4 is the flow sheet. Since graphite is used for the upper electrode of the ash melting furnace and CO gas is generated, a CO combustion chamber is provided as shown in the figure. The bubbling tank is provided in order to seal the outside air and keep the inside of the ash melting furnace at a pressure higher than the atmospheric pressure so that the outside air does not flow back into the ash melting furnace.
[0012]
[Problems to be solved by the invention]
However, since the above-mentioned wet exhaust gas treatment device requires a waste water treatment device, and the initial cost and running cost are required, some users may dislike the wet exhaust gas treatment device.
[0013]
The present invention has been devised in view of such problems of the prior art, and is intended to diversify the technology of an exhaust gas treatment apparatus for an ash melting furnace, and to contain exhaust gas containing substances generated by electrolysis of alkali salts during ash melting An object of the present invention is to provide an exhaust gas treatment apparatus for an ash melting furnace that treats lime in a dry manner.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, an exhaust gas treatment apparatus for an ash melting furnace according to the present invention is an exhaust gas treatment apparatus for a direct current electric resistance type ash melting furnace, which burns CO gas in the exhaust gas discharged from the ash melting furnace. CO gas combustor, gas cooler that sprays water into the exhaust gas discharged from the CO gas combustor and cools it, introduces the exhaust gas discharged from the gas cooler, and drops slaked lime or slaked lime slurry from above The HCl gas in the exhaust gas is neutralized and removed, and the dust in the exhaust gas is removed by adhering to the slaked lime, and the exhaust gas discharged from the HCl removal reactor is introduced to remove the dust. A bug filter.
[0015]
According to a preferred embodiment of the present invention, a steam jacket for controlling the temperature of the pipe wall to 150 to 450 ° C. is provided in the pipe connecting the CO gas combustor and the gas cooler, and dust attached to the pipe wall is removed. A dust removal device should be provided.
[0016]
Next, the operation of the present invention will be described.
The exhaust gas from the direct current electric resistance type ash melting furnace contains 150 to 200 g / m ³ of dust, 2 to 3% of CO gas, HCl and heavy metal gas. Further, since the temperature of the exhaust gas from the direct current electric resistance type ash melting furnace is as low as 400 to 600 ° C., the dioxin contained in the ash moves into the exhaust gas and is discharged as it is without being decomposed. As for the exhaust gas from the ash melting furnace, CO gas is combusted by the air blown in the CO gas combustor. At this time, if the CO gas does not self-combust at a low concentration, the fuel is blown in with the air and burned. In the CO gas combustor, the dioxin contained in the exhaust gas is completely decomposed by maintaining the residence time at 2 to 4 seconds at a temperature of 900 to 1000 ° C.
[0017]
In the gas cooler, water is sprayed to cool the exhaust gas temperature to about 200 ° C. The exhaust gas discharged from the gas cooler is introduced into the HCl removal reactor. In the reactor, slaked lime or slaked lime slurry is dropped from above to neutralize and remove HCl in the exhaust gas, and dust is adhered to the slaked lime or slaked lime slurry and removed. Since a large amount of dust is removed by this reactor, the load on the downstream bag filter is reduced. The exhaust gas is exhausted to the outside through the chimney after the dust is completely removed by the bag filter.
[0018]
In the pipe connecting the CO gas combustor and the gas cooler, dust tends to adhere to the tube wall, but it is easy to remove by keeping the temperature of the tube wall at 150 to 450 ° C, especially around 250 ° C. Since it adheres, this pipe is provided with a steam jacket and a dust removing device such as a brush is attached. In addition, it is preferable to provide the same apparatus also about piping between an ash melting furnace and a CO gas combustor.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a flow sheet of an exhaust gas treatment apparatus for an ash melting furnace according to the present invention. In the figure, 1 is a DC electric resistance ash melting furnace. Incinerated ash and fly ash 11 are introduced, and ash melting is performed by Joule heat by applying direct current between the main electrode 1a and the furnace low electrode 1b. In the ash melting furnace 1, a metal layer 1d such as iron is formed at the bottom, and a sludge layer 1c is formed thereon, and a solid ash layer 1e in which ash is floated is formed on the sludge layer 1c. The sludge 1c is discharged from the outlet 1f, and the exhaust gas 12 is discharged from the gas outlet 1g. The exhaust gas contains high-concentration dust, and since the main electrode is made of carbon, it is oxidized and thus CO gas is generated. Further, alkali salts such as salt are electrolyzed in an ash melting furnace to generate HCl gas, which is contained in the exhaust gas. Further, dioxins contained in the ash are volatilized in the ash solid layer 1e, and are not decomposed and discharged in the exhaust gas 12 because the temperature of the exhaust gas 12 is as low as 400 to 600 ° C.
[0020]
2 is a CO gas combustor. The CO gas combustor 2 is provided with a burner 2a at the top and a powder discharger 10 at the bottom. There are various types of the powder discharging apparatus 10, but here, two butterfly valves are illustrated. The valve is always closed by the weight 10a and is sealed from the outside air. When the powder accumulates on the valve body, it opens against the weight 10a by its weight and discharges the powder.
[0021]
3 is a gas cooler and 3a is an atomizing nozzle. The atomizing nozzle is connected to a water pipe (not shown) and a compressed air pipe, and ejects water in a thin mist. A powder discharge device 10 is also provided below the gas cooler 3. The ash melting furnace 1 and the CO gas combustor 2 are connected by a pipe 8, and the CO gas combustor 2 and the gas cooler 3 are connected by a pipe 9. The inside of the pipe 9 is particularly susceptible to dust, but it can be easily cleaned if the pipe temperature is kept around 250 ° C. Therefore, the temperature of the pipe wall is controlled by adjusting the steam flow rate by surrounding the steam jacket 9b. Control. 9a is a dust removing device of various types, but here a brush type is shown. The brush is retracted to the front side during normal operation, and when cleaning the pipe wall, it is moved in the pipe with a wire or the like.
[0022]
4 is an HCL removal reactor. A slaked lime slag spray nozzle 4 a is provided at the top of the reactor 4. A slaked lime slurry pipe and a compressed air pipe (not shown) are connected to the spray nozzle 4a, and the slaked lime slurry is sprayed in a spray form. A powder discharge device 10 is provided below the HCl removal reactor 4. 5 is a bag filter, 6 is an induction fan, and 7 is a chimney.
[0023]
Next, the operation of this embodiment will be described.
The exhaust gas 12 of the DC electric resistance ash melting furnace 1 contains high-concentration dust, CO gas, HCl gas, heavy metal gas, and the like. As for the exhaust gas 12, the CO gas contained in the exhaust gas is combusted by the air blown in the CO gas combustor 2. At this time, if the CO gas is low in concentration and does not self-combust, fuel is blown from the burner 2a and burned together with air. The temperature in the CO gas combustor 2 is set to 900 ° C. or higher, and the operation is performed so that the residence time of the exhaust gas is 2 to 4 seconds to completely decompose dioxins.
[0024]
In the gas cooler 3, water is sprayed in a fine mist from the atomizing nozzle 3a with compressed air, and the exhaust gas 12 is cooled to around 200 ° C. The cooled exhaust gas 12 flows into the HCl removal reactor 4. In the reactor 4, slaked lime slurry is sprayed together with compressed air from a spray nozzle 4 a provided at the top, and the atomized slurry descends in the reactor 4. The exhaust gas 12 and the mist-like slurry come into contact with each other in the reactor 4, and HCl in the exhaust gas 12 is neutralized, and dust adheres to the slurry and is removed. The slaked lime slurry evaporates into powder and is discharged from the bottom. In this way, a part of the dust in the exhaust gas 12 is removed in the HCl removal reactor 4, so that the load on the bag filter 5 is reduced.
[0025]
After the dust is removed by the bag filter 5, the exhaust gas 12 is discharged to the outside through the induction fan 6 and the chimney 7.
[0026]
The present invention is not limited to the embodiments described above, and various modifications can be made without departing from the scope of the invention.
[0027]
【The invention's effect】
As described above, the exhaust gas treatment apparatus of the ash melting furnace of the present invention is a dry exhaust gas treatment apparatus, but there is no problem of clogging of the bag filter as in the conventional dry exhaust gas treatment apparatus, and the conventional wet exhaust gas treatment apparatus. There is an excellent effect that a water treatment apparatus necessary for the apparatus is unnecessary.
[Brief description of the drawings]
FIG. 1 is a flow sheet of an exhaust gas treatment apparatus for an ash melting furnace according to the present invention.
FIG. 2 is a drawing including a cross-sectional view of a conventional ash melting furnace and a flow sheet of an exhaust gas treatment apparatus.
FIG. 3 is a flow sheet of a conventional wet exhaust gas treatment apparatus.
FIG. 4 is a flow sheet of a conventional wet exhaust gas treatment apparatus.
[Explanation of symbols]
1 DC electric resistance type ash melting furnace 2 CO gas combustor 3 Gas cooler 4 HCl removal reactor 5 Bag filter

Claims (3)

Included in ash when ash is melted in the furnace of an ash melting furnace that melts ash such as incineration ash and dust by direct current between the electrode provided through the furnace lid and the electrode provided at the furnace bottom Exhaust gas treatment for an ash melting furnace that actively electrolyzes alkali salt so that a molten salt layer is not formed on the molten slag layer and treats exhaust gas containing a large amount of dust that contains soluble components generated by electrolysis A method in which exhaust gas discharged from the ash melting furnace is introduced into a CO gas combustor to burn the CO gas in the exhaust gas, and exhaust gas discharged from the CO gas combustor is introduced into a gas cooler. The process of spraying water into the exhaust gas and cooling it , and introducing the exhaust gas discharged from the gas cooler into the HCl removal reactor, dropping slaked lime or slaked lime slurry from above to neutralize the HCl gas in the exhaust gas As well as removing Removing by attaching the dust in the gas to slaked lime, made and a step of removing the dust by introducing exhaust gas discharged from the HCl removal reactor bag filter, each of CO gas burner, An exhaust gas treatment method for an ash melting furnace, wherein the gas cooler, the HCl removal reactor, and the bag filter have a reduced diameter portion below, and a powder discharge device is provided at a lower end thereof. The powder discharge device is a double weighted butterfly valve connected up and down. The valve is always closed by the weight, and when the powder accumulates on the valve body, it opens against the weight by its weight. exhaust gas treatment method of the ash melting furnace according to claim 1, wherein the powder that has become to discharge. A pipe for connecting a CO gas combustor and a gas cooler is provided with a steam jacket for controlling the temperature of the pipe wall to 150 to 450 ° C and a dust removing device for removing dust adhering to the pipe wall. The exhaust gas treatment method for an ash melting furnace according to claim 1 or 2.

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