JP3700163B2 - Operation method of ash melting furnace - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas absorbing device for an ash melting furnace that treats dust and soluble components in exhaust gas discharged from an ash melting furnace by absorbing them in water.
[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 ash by electric resistance heat (juule heat) by direct current or alternating current. 1) High thermal efficiency 2) Generated gas 3) Since no arc is generated, flicker does not occur, and 4) it is possible to divide molten slag and molten metal separately.
[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 burning furnace, i is a dust collector, j is a dust collecting fan, k is a chimney, and m is an electrode buried position adjuster. A feature of the above invention is a method for melting waste generated from incineration ash, dust, or a mixture of the two using an electrical resistance heat as a heat source, wherein the tip position of the upper electrode b is the molten salt layer g Molten slag without electrolyzing the molten salt by passing current in the vertical direction by direct current or two-phase current between the furnace bottom electrode c positioned in the molten slag layer f between the molten metal layer e and the molten metal layer e The molten salt layer g is stably formed above the layer f to prevent generation of harmful chlorine gas, hydrogen chloride gas, and the like.
[0006]
[Problems to be solved by the invention]
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. Moreover, since a molten salt with 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.
[0007]
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.
[0008]
The present invention has been devised in view of the above-described problems, and it is possible to stably treat exhaust gas containing a molten salt decomposition substance without causing clogging and to remove harmful heavy metals in an easy-to-treat form. An object of the present invention is to provide an exhaust gas treatment apparatus for an ash melting furnace.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an exhaust gas absorption apparatus for an ash melting furnace according to the present invention includes a bubbling tank that accommodates an absorption liquid and causes the exhaust gas to dive inside the absorption liquid to cause foaming, and a cylindrical or inverted conical body. The inside wall of the body is washed by the circulating absorption liquid flowing in the tangential direction from the bubbling tank through the pump to the upper end of the body and the exhaust gas from the ash melting furnace from the top. And a buffer tank whose lower end is immersed in the absorbing liquid in the bubbling tank.
[0010]
According to a preferred embodiment of the present invention, the liquid level of the bubbling tank is kept constant by taking an overflow.
[0011]
According to another preferred embodiment, the exhaust gas discharged through the bubbling tank is absorbed and washed by a jet scrubber provided on the downstream side.
[0012]
According to another preferred embodiment, the connecting pipe connecting the bubbling tank and the jet scrubber is washed in the direction opposite to the flow of the exhaust gas by the circulating absorption liquid flowing from the bubbling tank through the pump.
[0013]
According to another preferred embodiment, the volume of the buffer tank is sufficiently larger than the volume of the portion of the bubbling tank corresponding to the depth of immersion in the absorbing liquid at the lower end of the buffer tank.
[0014]
Next, the operation of the present invention will be described. The exhaust gas discharged from the ash melting furnace is guided to the bubbling tank through the buffer tank. And it is immersed in the inside of the absorption liquid accommodated in the bubbling tank, floats as a bubble, and flows out to the next process. Dust contained in the exhaust gas and soluble components such as hydrogen chloride and sodium oxide are absorbed in the absorbent in the bubbling tank. Since the wall surface of the buffer tank is washed with the absorbing liquid flowing in the tangential direction, dust and soluble components do not adhere to the wall surface.
[0015]
If the liquid level in the bubbling tank is kept constant, pressure fluctuations in the ash melting furnace can be prevented.
[0016]
If the exhaust gas discharged from the bubbling tank is further absorbed and washed by the jet scrubber, all the dust and soluble components that have not been absorbed by the bubbling tank are absorbed by the absorbent.
[0017]
If the absorbing liquid is injected from the absorbing liquid inlet provided near the jet scrubber inlet of the connecting pipe between the bubbling tank and the jet scrubber and then returned to the bubbling tank to wash the inside of the connecting pipe, the connecting pipe will be clogged. Can be prevented.
[0018]
The volume of the buffer tank is the volume of the portion of the bubbling tank corresponding to the immersion depth of the lower end of the buffer tank into the absorbing liquid (that is, the bubbling tank corresponding if the charging depth is H and the area of the bubbling tank is S) If the volume in this part is HS), even if the pressure in the ash melting furnace becomes negative, the absorbent in the bubbling tank will not flow back into the ash melting furnace. There is no danger of a steam explosion.
[0019]
Note that halogen elements such as chlorine (hydrogen chloride) and alkali metals such as sodium (sodium oxide) generated by electrolysis in the ash melting furnace and discharged into the exhaust gas are almost completely released into the exhaust gas. In contrast, a part of the alkali metal remains in the molten slag layer or the molten metal layer, so that the absorbing solution becomes acidic. Accordingly, heavy metals contained in dust and exhaust gas are effectively dissolved and absorbed in the absorbing solution.
[0020]
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 absorbing device for an ash melting furnace according to the present invention. In the figure, reference numeral 1 denotes a direct current ash melting furnace, in which a cathode 1a and an anode 1b are provided at the bottom of the furnace through a furnace lid 1i. The cathode 1a is made of conductive brick, and the anode 1b is made of graphite. If is a DC power supply. Ashes 1j are charged through the furnace lid. In the ash melting furnace 1, electric resistance heat (Joule heat) is generated by energizing between the anode 1b and the cathode 1a, 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 floated is formed above the molten slag layer 1d.
[0021]
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 1200 ° C to 1300 ° C. The resistivity ρ (Ω · cm) of the molten slag layer 1d is ρ = 0.1 to 0.5, whereas the resistivity of the molten metal layer 1c is ρ = 10 ⁻⁶ to 10 ^−8. Almost all occurs in the molten slag layer 1d. Therefore, the molten metal layer 1c is in a state where only the upper surface is melted, the inside is solid, and the whole serves as a cathode. Alkali salts such as salt contained in the ash 1j are electrolyzed in the molten slag layer, and when the alkali salt is salt, it becomes chlorine gas and metallic sodium. Chlorine gas is generated on the anode 1b side, but reacts with water vapor in the free board 1k to become hydrogen chloride and hypochlorous acid. Hypochlorous acid releases oxygen to hydrogen chloride. Although metallic sodium is generated on the cathode side, the cathode evaporates because it has a temperature higher than the boiling point (880 ° C.). The evaporated metallic sodium gas reacts with oxygen in the free board 1k to become sodium oxide. A part of the metallic sodium remains in the molten slag layer 1d or the molten metal layer 1c.
[0022]
An exhaust gas 2 is discharged outside the furnace through a connecting pipe 13 connected to an outlet 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 carbonate in the ash 1j, etc. become CO gas because the oxygen is insufficient in the furnace. 1 g is molten slag, and 1 h is molten metal. The main components of the molten slag 1g are silica sand and calcium oxide, and the main component of the molten metal 1h is iron. 1 g of molten slag is discharged intermittently or continuously. The molten metal 1h generates an arc discharge between the anode 1b and the molten metal layer 1c, and melts and discharges the metal.
[0023]
Reference numeral 3 denotes a bubbling tank that stores the absorbing liquid 20. The bubbling tank 3 absorbs dust and soluble components in the exhaust gas 2 by removing the exhaust gas 2 from the ash melting furnace 1 in the absorption liquid 20 and removes it. 4 is a buffer tank. The upper part is a cylindrical body part 4a, and the lower part is a cylindrical reduced diameter part 4b having a smaller diameter than the body part 4a. The exhaust gas 2 flows into the buffer tank 4 from the inlet provided in the center of the lid portion 4c through the connecting pipe 13, and flows out from the lower end of the reduced diameter portion 4b. Although the communication pipe 13 is not shown, it is cleaned by an appropriate means such as a rotating brush. The lower end of the buffer tank 4 is immersed in the absorbing liquid 20 of the bubbling tank 3 by about 100 mm.
[0024]
The volume of the buffering tank 4 is the volume of the portion of the bubbling tank 3 corresponding to the immersion depth (H) at the lower end of the reduced diameter portion 4b of the buffering tank 4 (ie, the liquid level 3a of the bubbling tank). If the area of S is S, the volume is sufficiently larger than HS).
[0025]
Reference numeral 5 denotes a buffer tank cleaning pump, which allows the absorbing liquid 20 in the bubbling tank 3 to flow tangentially into the upper end of the body of the buffer tank 4 so as to wash the inner wall of the buffer tank 4 with a swirling flow. Reference numeral 6 denotes a jet scrubber that sucks the exhaust gas 2 from the bubbling tank 3 through the connecting pipe 14 by the jet jet of the absorbing liquid 20 and cleans it by the jet jet. The communication pipe 14 is backwashed with the absorbent 20.
[0026]
A scrubber tank 7 is provided below the jet scrubber 6, and the exhaust gas 2 and the absorbing liquid 20 flow from the jet scrubber 6. 8 is a scrubber pump, which sucks the absorbent 20 from the scrubber tank 7 and sends it to the jet scrubber 6. 9 is an overflow tank, and the absorbing liquid 20 flows from the bubbling tank 3 and the scrubber tank 7 through the overflow pipes 3b and 7a, respectively. The liquid levels of the bubbling tank 3 and the scrubber tank 7 are kept constant by the overflow pipes 3b and 7a.
[0027]
The exhaust gas 2 discharged from the scrubber tank 7 flows into the exhaust gas treatment device 12 through the connection pipe 15. The exhaust gas treatment device includes a CO gas combustor, an exhaust gas cooler, an induction blower, a chimney, and the like. The CO gas contained in the exhaust gas is burned to form carbon dioxide and then released into the atmosphere.
[0028]
Reference numeral 10 denotes an absorption liquid transfer pump, which sends the absorption liquid 20 to the absorption liquid processing apparatus 11. The absorbent treatment apparatus 11 includes a neutralization tank, a dehydrator, and the like, and the acidic absorbent 20 is neutralized in the neutralization tank, and then solids are removed by a dehydrator such as a filter press and then discharged to the outside. The In addition, a reaction tank, a filtration tank, etc. are added as needed, and the dissolved heavy metal is fixed by ferritization, sulfide formation, chelate resin fixation, etc. Reference numeral 16 denotes a supply water pipe. 17 is a flow meter and 18 is a mixer.
[0029]
Next, the operation of this embodiment will be described. As described above, soluble components such as hydrogen chloride and sodium oxide generated by electrolysis of alkali salts are included in the exhaust gas 2 together with dust and discharged outside the furnace. Dust, soluble components, and evaporated heavy metal are absorbed by the absorbent 20 in the bubbling tank 3. Dust, soluble components, and heavy metals in the exhaust gas 2 that have not been absorbed in the bubbling tank 3 are further absorbed and removed by the jet scrubber 6. Alkaline salts contained in ash are neutral in nature, but when electrolysis occurs in the ash melting furnace 1, almost all acidic components such as chlorine are released into the exhaust, whereas alkali components such as sodium. Remains in the molten slag and molten metal, the exhaust gas 2 is rich in acidic components, and therefore the absorbent 20 is also acidic. Since the absorbing solution is acidic, the heavy metal dissolves well in the absorbing solution and is removed from the exhaust gas.
[0030]
A buffer tank 4 is provided above the bubbling tank 3 and the liquid level of the bubbling tank is kept constant, and the volume of the buffer tank corresponds to the depth of immersion in the absorbing liquid at the lower end of the buffer tank. Therefore, even if the pressure in the ash melting furnace 1 becomes negative, the absorbent 20 does not flow back into the furnace from the bubbling tank 3 and there is no danger of steam explosion.
[0031]
Since the inner wall of the buffer tank 4 is washed with the absorbing liquid 20, dust and soluble components do not adhere and cause clogging. In addition, the communication pipe 14 between the bubbling tank 3 and the jet scrubber 6 is backwashed by the absorbing liquid 20 so that it does not clog.
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.
[0033]
【The invention's effect】
As described above, the exhaust gas absorption apparatus for an ash melting furnace of the present invention is provided with a bubbling tank and an upper part thereof, which are exhausted from an ash melting furnace and containing high-concentration dust and soluble components. Since these components are absorbed through the buffer tank that has been washed, there is an excellent effect that stable operation is possible without causing clogging as seen in the dry treatment of exhaust gas. .
[Brief description of the drawings]
FIG. 1 is a flow sheet of an exhaust gas absorbing device for an ash melting furnace according to the present invention.
FIG. 2 is a cross section of a conventional ash melting furnace and a flow sheet of front and rear equipment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Ash melting furnace 2 Exhaust gas 3 Bubbling tank 4 Buffer tank 4a Buffer tank trunk | drum 4b Buffer tank diameter-reduction part 6 Jet scrubber

Claims (5)

A method of operating an ash melting furnace in which ash such as incineration ash and dust is melted by applying direct current between an electrode provided through the furnace lid and an electrode provided at the bottom of the furnace, in which the ash is melted in the furnace The alkaline salt contained in the ash is positively electrolyzed so that the molten salt layer is not formed on the molten slag layer, and the exhaust gas from the ash melting furnace containing soluble components generated by electrolysis is buffered. It is sent to the bubbling tank through the ring tank, and the inside of the absorbing liquid in the bubbling tank is submerged to cause foaming, and the buffering tank has a cylindrical or inverted conical body and has a reduced diameter downward. The exhaust gas from the ash melting furnace flows in from the top, and the inner wall of the body is washed by circulating absorption liquid flowing in the tangential direction from the bubbling tank through the pump to the upper end of the body, and The method of operation ash melting furnace, characterized in that the end is immersed in the absorbing liquid in the bubbling tank. 2. The method of operating an ash melting furnace according to claim 1, wherein the bubbling tank is kept constant by taking an overflow . The ash melting furnace operating method according to claim 1 or 2, wherein the exhaust gas discharged from the bubbling tank is suction-washed by a jet scrubber . The operation method of the ash melting furnace according to any one of claims 1 to 3, wherein the communication pipe between the bubbling tank and the jet scrubber is back-washed with a circulating absorbent . The ash according to any one of claims 1 to 4, wherein a volume of the buffering tank is larger than a volume of a portion of the bubbling tank corresponding to a depth of immersion in the absorbing liquid at a lower end of the buffering tank. How to operate the melting furnace .

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