JPH09324910A - Exhaust gas treatment apparatus for ash fusion furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effect treatment of an exhaust gas without generation of plugging and take out heavy metals in an easily disposable configuration by causing an absorption liquid in a gas absorption tower to absorb dust and soluble components from the exhaust gas from an ash fusion furnace and burning CO gas in the exhaust gas from the gas absorption tower in a CO combustor. SOLUTION: Electric current is passed between an anode 1b on a furnace cover 1i and a cathode 1a on a furnace bottom in a direct current type ash fusion furnace 1 to melt ash 1j with electric resistance heat. The ash 1j molten is separated into an upper molten slug layer 1d and a lower molten metal layer 1c owing to a difference in their specific gravities, and an ash cover layer 1e with the non-molten ash 1j floating is generated above the molten slug layer 1d. Exhaust gas 2 is introduced into a gas absorption tower 3 and an absorption liquid is jetted from a nozzle 3c to absorb thereinto dust and soluble components. Then the exhaust gas 2 is conducted to a mist separator 4 from the gas absorption tower 3 for separation of water droplets, and CO gas in the exhaust gas is made to burn in a CO combustor 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention makes harmless the exhaust gas generated when melting ash discharged from various incinerators including municipal waste incinerators and makes it easy to reuse the components contained in the exhaust gas. The present invention relates to an exhaust gas treatment device for an ash melting furnace.

[0002]

2. Description of the Related Art Various wastes such as municipal solid waste and sewage sludge have been incinerated in an incineration facility, and the resulting incinerated ash and dust have conventionally been disposed of in landfills. 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.

[0003] Under such a background, a melting treatment method using a residual carbon in ash, coke, kerosene, and electric power as a heat source has been proposed.
Actual processing is performed in part. Among them, there are a plasma arc heating method and a resistance heating method as a melting furnace using electric power as a heat source. The melting furnace of the plasma arc heating system is provided with a hollow graphite electrode penetrating the upper furnace lid, the tip of which is located near the upper surface of the molten slag, and Ar gas or N ₂ gas is caused to flow from above into the hollow portion of the electrode. A direct current is applied between the electrode and the bottom electrode of the furnace, and the arc is continued by the flow of the plasmaizing gas to heat and melt the ash. Although the electrodes have a long life and a high melting rate and can make the furnace compact, on the other hand, there is a problem that the incinerated ash and dust are scattered by the gas flow before the melting and the dust collector is heavily burdened.

In the resistance heating type ash melting furnace, a counter electrode is arranged in the molten slag and the ash is heated and melted by electric resistance heat (juule heat) due to direct current or alternating current.
1) High thermal efficiency, 2) Small amount of generated gas, 3) Flicker does not occur because arc is not generated, and 4) Molten slag and molten metal can be separated and separated separately.

As such a resistance heating type ash melting treatment method, there is one disclosed in JP-A-7-77318. FIG. 2 discloses the cross section of the ash melting furnace and the flow sheet of the front and rear equipment as disclosed in the above publication. In the figure, a is an ash melting furnace, b is an upper electrode, c is a 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 fuel furnace, and i is Is a dust collector, j is a dust collecting fan, k is a chimney, and m is an electrode burial position adjuster. A feature of the above invention is a method of melting incineration ash generated from a refuse incineration facility, waste consisting of dust or a mixture of the two by using electric resistance heat as a heat source, and melting the tip position of the upper electrode with a molten salt layer. It is positioned in the molten slag layer between the metal layer and the furnace bottom electrode, and direct current or alternating current 2
The molten salt layer g is stably formed above the molten slag layer f without electrolyzing the molten salt by energizing in the vertical direction by the phase energization to prevent generation of harmful chlorine gas, hydrogen chloride gas, etc Is what you are trying to do.

[0006]

However, when the operation for forming the molten salt layer g in the ash melting furnace a is carried out as described above, the molten salt has a very strong property of corroding the furnace wall material, so To prevent this, it is necessary to use expensive furnace wall material.
In addition, the molten salt, which has a good electric conductivity, penetrates into the furnace wall, which is likely to cause a short circuit accident. Therefore, the applicant of the present application, as a result of diligent research, energized between the cathode of the furnace bottom and the anode inserted from the furnace lid, when melting the ash by electric resistance heat,
We decided to adopt an operating method that positively electrolyzes alkaline salts such as sodium chloride (NaCl). According to this operating method, for example, salt is electrolyzed into chlorine gas and metallic sodium. Chlorine gas reacts with water vapor to become hydrogen chloride and hypochlorous acid, but hypochlorous acid releases oxygen to hydrogen chloride. Further, metallic sodium is evaporated and becomes sodium oxide in the oxidizing atmosphere. And all of these substances are contained in the exhaust gas and released to the outside. In addition, a part of sodium remains in the molten metal layer e.

However, the exhaust gas containing these substances is shown in FIG.
When the dry treatment is performed as shown in Fig. 2, these substances have strong hygroscopicity, and when they absorb moisture, they adhere to dust collectors i such as bag filters and electric dust collectors, or pipes and ducts in the middle, together with dust,
It is difficult to wipe off and it is easy to cause clogging and performance deterioration. Further, hydrogen chloride is difficult to dry process.

The present invention has been devised in view of the above-mentioned problems, and it is possible to stably treat exhaust gas containing a decomposed substance of a molten salt without causing clogging and to easily treat harmful heavy metals. An object is to provide an exhaust gas treatment device for an ash melting furnace that can be taken out.

[0009]

In order to achieve the above object, an exhaust gas treating apparatus for an ash melting furnace according to the present invention is energized between a cathode provided on a furnace bottom and an anode inserted through a furnace lid, Guide the exhaust gas generated from the ash melting furnace that melts ash by electric resistance heat, and the gas absorption tower that absorbs dust and soluble components in the absorbing liquid, and guide the exhaust gas from the gas absorption tower through the mist separator C that burns CO gas
O combustor.

Next, the operation of the present invention will be described. The ash melting furnace is a direct current melting furnace that applies a direct current, and the bottom side of the furnace is a cathode, and the electrode inserted through the furnace lid is an anode. The ash is melted by Joule heat generated when electricity is applied between the anode and the cathode. Since ash is a poor conductor of electricity when it is in a solid state, metal powder such as iron is mixed in the ash, and initial electricity is applied. When the ash is melted by the initial energization and becomes a molten slag layer, it becomes a good conductor of electricity and continuous melting becomes possible. In the ash melting furnace, due to the difference in specific gravity, the molten metal layer such as iron at the bottom,
Separated into the upper molten slag layer and discharged separately. Salts such as salt contained in the ash are electrolyzed during melting to generate chlorine gas on the anode side and metallic sodium on the cathode side. Chlorine gas reacts with water vapor in the freeboard in the upper part of the furnace to form hydrogen chloride and hypochlorous acid, but hypochlorous acid releases oxygen to hydrogen chloride.

Since metallic sodium has a low boiling point, a portion thereof is immediately evaporated and oxidized in the freeboard in the upper part of the furnace to become sodium oxide gas. Hydrogen chloride and sodium oxide are soluble components that are soluble in water. Exhaust gas containing these soluble components and dust is discharged from the ash melting furnace and introduced into the gas absorption tower. The gas absorption tower may be of a spray type in which the absorbing liquid is sprinkled from the upper portion, or may be of a bubble type in which the exhaust gas is dipped in the absorbing liquid. There is carbon in the ash and carbon contained as a carbonate, and the graphite used as the anode is also carbon. These carbons are burned to carbon monoxide (CO) because oxygen is insufficient in the freeboard of the ash melting furnace. Therefore, this gas cannot be discharged to the outside as it is, so that the gas discharged from the gas absorption tower is subjected to a mist separator to remove water droplets and then burned by a CO combustor to form carbon dioxide gas, and then discharged to the outside.

Since the exhaust gas is wet-processed as described above, even if the exhaust gas contains a soluble component obtained by electrolyzing an alkali salt, the exhaust gas processing device is not clogged and is stable. Various operations are possible.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a flow sheet of an exhaust gas treating apparatus for an ash melting furnace of the present invention. In the figure, 1 is a direct current type ash melting furnace, a cathode 1a and a furnace lid 1i on the furnace bottom.
Anodes 1b are respectively provided so as to penetrate through. In addition,
The cathode 1a is made of a conductive brick, and the anode 1b is made of graphite. 1f is a DC power supply device. The ash 1j is thrown in through the furnace lid 1i. In the ash melting furnace 1, the anode 1b
When electricity is applied between the cathode 1a and the cathode 1a, electric resistance heat (Joule heat) is generated and the ash 1j is melted. The molten ash 1j is separated into an upper molten slag layer 1d and a lower molten metal layer 1c due to a difference in specific gravity, and an ash cover layer 1e in which unmelted ash 1j is suspended is formed on the molten slag layer 1d.

The voltage applied between the anode 1b and the cathode 1a is 70 to 80V, and the temperature in the molten slag layer 1d is controlled to 1100 to 1200 ° C. The resistivity ρ (Ω · cm) of the molten slag layer 1d is ρ = 0.1 to 0.5
On the other hand, the resistivity of the molten metal layer 1c is ρ = 10
^{Since it is -6} to 10 ^-8, almost all Joule heat is generated in the molten slag layer 1d. Therefore, in the molten metal layer 1c, only the upper surface is molten, the inside is solid, and the whole functions as a cathode. Alkaline salt such as salt contained in the ash 1j is electrolyzed in the molten slag layer, and becomes chlorine gas and metallic sodium when the alkali salt is salt. Chlorine gas is generated on the anode 1b side,
Reacts with water vapor in the freeboard 1k to form hydrogen chloride and hypochlorous acid. Hypochlorous acid releases oxygen to hydrogen chloride. Metallic sodium is generated on the cathode side, but since the cathode has a temperature above the boiling point (880 ° C.), part of it is immediately evaporated. The evaporated metallic sodium gas reacts with oxygen in the freeboard 1k to become sodium oxide.

Reference numeral 2 denotes exhaust gas, which is discharged to the outside of the furnace through a connecting pipe 13 connected to a discharge port provided in the furnace lid 1i. The exhaust gas 2 contains dust and CO gas in addition to the above-described water-soluble components such as hydrogen chloride and sodium oxide. The unburned carbon contained in the ash, the graphite rod used as the anode 1b, the carbon present as the carbonate in the ash 1j, and the like become CO gas because oxygen is insufficient in the furnace. 1
g is molten slag, and 1h is molten metal. The main components of molten slag are silica sand and calcium oxide,
The main component of molten metal is iron. The molten slag is discharged intermittently or continuously. After the molten metal is discharged from the molten slag, arc discharge is generated between the anode 1b and the molten metal layer 1c to melt and discharge the metal.

Reference numeral 3 is a gas absorption tower. In this embodiment, the spray type is described, but a bubble type in which the exhaust gas is submerged in the absorbing liquid may be used. The exhaust gas 2 enters the tower through a gas inlet 3a provided below the gas absorption tower 3, and is discharged from a gas outlet 3b provided above. 3c is a nozzle for ejecting the absorbing liquid. The absorbing liquid becomes fine water droplets and descends in the tower, whereas the exhaust gas 2 rises in the tower and the soluble component is absorbed in the absorbing liquid together with dust. The exhaust gas 2 is guided from the gas absorption tower 3 to the mist separator 4 via the communication pipe 14. A baffle plate, a filler, and the like are provided in the mist separator 4, and the exhaust gas 2 is caused to collide with these to separate water droplets. The exhaust gas 2 exiting from the mist separator 4 flows into the CO combustor 5 via the connecting pipe 15. CO burners include those that carry an oxidation catalyst and those that have a pilot burner and burn directly. Reference numeral 6 denotes a suction fan, which is connected to the CO combustor via a communication pipe 16. 7 is a chimney.

Reference numeral 8 is an absorption liquid tank for receiving the absorption liquid from the gas absorption tower 3. A part of the absorption liquid from the absorption liquid tank 8 is circulated to the absorption tower via the circulation pump 9, and the rest is sent to the dissolution tank 10. In addition, 17 is water for make-up. The absorption liquid that has left the dissolution tank 10 is sent to the filtration tank 11, where it is separated, the sludge 18 is sent again to the ash melting furnace 1, and the filtrate 19 is sent to the water treatment device 12. The water treatment device has a reaction tank, a filtration tank, a precipitation tank, etc., and is used for neutralizing the absorption filtrate 19 discharged from the filtration tank 11 and immobilizing dissolved heavy metals (lead, zinc, mercury, chrome, etc.). To do.

Next, the operation of this embodiment will be described. As described above, the soluble components such as hydrogen chloride and sodium oxide generated by the electrolysis of the alkali salt are included in the exhaust gas 2 together with the dust and are discharged out of the furnace. Dust, soluble components, and evaporated heavy metals are all absorbed in the absorption liquid in the absorption tower. Therefore, the dust collector is not clogged and the performance is not deteriorated as in the dry treatment of exhaust gas, and stable operation is possible. Further, since the heavy metal is also dissolved in the absorbing solution, it is easy to handle even if it is insolubilized for landfill treatment or extracted for effective use.

The present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention.

[0020]

As described above, the present invention positively electrolyzes an alkali salt in an ash melting furnace so that the exhaust gas contains a soluble component generated by the electrolysis of the alkali salt, and the exhaust gas is wetted. Since (1) exhaust gas is processed dry, troubles such as clogging do not occur.

(2) Since the alkaline salt is positively electrolyzed, there is no molten salt layer in the furnace, and it is not necessary to use a special and expensive material for the brick of the furnace wall. It will be cheaper. (3) Since the heavy metal gas contained in the exhaust gas is dissolved in the treated water, it is easy to handle whether insolubilized and landfilled or extracted and recycled.

It has excellent effects such as

[Brief description of drawings]

FIG. 1 is an overall flow sheet of an exhaust gas treating apparatus for an ash melting furnace of this example.

FIG. 2 is a flow sheet of a conventional ash melting furnace and an exhaust gas treatment device.

[Explanation of symbols]

 1 Ash melting furnace 1a Cathode 1b Anode 2 Exhaust gas 3 Gas absorption tower 4 Mist separator 5 CO combustor

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuaki Matsuzawa 1 Shinshinarahara-cho, Isogo-ku, Yokohama-shi, Kanagawa Ishi Kawashima Harima Heavy Industries Co., Ltd. Technical Research Institute (72) Inventor Naoaki Yasuda 2-1-1 Toyosu, Koto-ku, Tokyo No. 1 Ishikawajima Harima Heavy Industries Ltd. Tokyo No. 1 factory

Claims (1)

[Claims] 1. An absorbing liquid is introduced by conducting an electric current between a cathode provided on the bottom of a furnace and an anode inserted through a furnace lid to guide exhaust gas generated from an ash melting furnace that melts ash by electric resistance heat. Gas absorption tower for absorbing dust and soluble components, and a CO combustor for guiding the exhaust gas from the gas absorption tower through a mist separator to burn the CO gas in the exhaust gas, the exhaust gas of an ash melting furnace Processing equipment.