JP2004148317A - Method for treating waste gas from melting furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the equipment cost by simplifying the structure of a wastewater treatment equipment for treating wastewater withdrawn from the wet smoke washing equipment and to prevent the bag filter from generating a low-temperature corrosion in a system for treating a waste gas from an ash melting furnace. <P>SOLUTION: The cleaning of the waste gas from the melting furnace by successively passing it through a temperature-lowering apparatus that lowers the temperature of the waste gas with a temperature-lowering water fed from a water supply tank, a bag filter, and a wet smoke washing equipment, is characterized in that water withdrawn from the wet smoke-washing equipment is introduced into the water supply tank, fed therefrom into the temperature-lowering equipment, and sprayed as the temperature-lowering water. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a method for treating a molten exhaust gas in which exhaust gas from an ash melting furnace such as a plasma melting furnace is subjected to a purification treatment while sequentially passing the exhaust gas through a temperature reducing device, a bag filter, and a wet smoke washing facility.

FIG. 3 is a system diagram showing an example of a technique for studying an exhaust gas treatment system of a plasma melting furnace attached to a waste incinerator.
In FIG. 3, reference numeral 1 denotes a plasma melting furnace, 8 denotes a hopper for charging combustion products such as industrial wastes into the melting furnace 1, 10 denotes an exhaust gas pipe from the plasma melting furnace 1, and 17 denotes a residue discharge pipe. .
Reference numeral 2 denotes a temperature reducing device for lowering the exhaust gas temperature, which is connected to the plasma melting furnace 1 via the exhaust gas pipe 10. Reference numeral 3 denotes a bag filter for removing fly ash and the like from the melting furnace in the gas, which is provided with a heater 31 and a fly ash transport conveyor 32, and transports the removed fly ash to a fly ash processing facility (not shown). Reference numeral 19 denotes an exhaust gas pipe connecting the temperature reducing device 2 and the bag filter 3.

Reference numeral 4 denotes a wet smoke washing tower for removing high-concentration acidic gas components in the exhaust gas, which is brought into wet contact with the high-concentration acidic gas components by alkaline water added from the NaOH tank 41 to precipitate salts. Reference numeral 11 denotes an exhaust gas pipe for connecting the bag filter 3 and the wet-type smoke washing tower 4, and the exhaust gas pipe 11 is provided with an exhaust gas fan 7 for feeding exhaust gas under pressure.
Reference numeral 18 denotes an exhaust gas pipe connected to the outlet of the wet smoke washing tower 4.
Reference numeral 6 denotes a wastewater treatment device for removing heavy metals and the like in the wastewater drawn out from the wet-type smoke washing tower 4.
Reference numeral 5 denotes a water supply tank in which the temperature-reducing water to be supplied to the temperature-reducing device 2 is stored.

During the operation of the exhaust gas treatment system of the melting furnace, the exhaust gas discharged from the plasma melting furnace 1 is introduced into the temperature reducing device 2 through the exhaust gas pipe 10.
In the temperature reducing device 2, the temperature-reduced water introduced from the water supply tank 5 via the temperature-reducing water pipe 9 is sprayed into the exhaust gas to adjust the exhaust gas temperature to the required inlet temperature of the bag filter 3 (preferably about 150 ° C. to 160 ° C.). Cool down to
Exhaust gas that has passed through the temperature reducing device 2 is introduced into the bag filter 3 through an exhaust gas pipe 19 to remove fly ash and the like in the melting furnace, and the fly ash is supplied to a fly ash treatment facility (not shown) via a fly ash conveyor 32. Transport to

The exhaust gas that has passed through the bag filter 3 is sent by an exhaust gas fan 7 through an exhaust gas pipe 11 to a wet-type smoke washing tower 4, where high-concentration acidic gas is removed. (Shown) or is discharged to the outside.
After the heavy metals are removed in the wastewater treatment device 6, the wastewater drawn out from the wet smoke washing tower 4 is discharged or sent to an incinerator-side wastewater treatment device (not shown).

Patent Document 1 discloses a technique in which a bag filter and a washing tower are attached to a melting and solidifying apparatus for melting and solidifying fly ash of a garbage incinerator.
JP-A-9-276651

  In the exhaust gas treatment system for a plasma melting furnace shown in FIG. 3, when a large wet-type smoke washing tower is installed on the side of a waste incinerator (not shown) provided in parallel with the plasma melting furnace, the bag filter 3 is used. After mixing the flue gas of the melting furnace after the dust reduction with the flue gas of the incinerator, batch treatment is performed in the wet-type smoke washing tower 4.

  However, when only a dry-type exhaust gas treatment facility is installed on the incinerator side, it is necessary to provide the wet-type smoke washing tower 4 alone in the exhaust gas treatment system on the plasma melting furnace 1 side as shown in FIG. It costs.

  For this reason, in the system in which the wet smoke washing tower 4 is provided in the exhaust gas treatment system on the side of the plasma melting furnace 1 as described above, when the smoke washing tower 4 is withdrawn and the wastewater can be discharged to the sewer as it is, It is only necessary to remove heavy metals in the wastewater by a simple wastewater treatment device. However, when the discharge is not possible, complicated maintenance is required for the drainage drainage channel of the wet-type smoke cleaning tower 4, and a wide range of substances must be removed. It is necessary to provide the wastewater treatment device 6 having a removing function, and the structure of the wastewater treatment device 6 is complicated and large, and the cost is high.

  In such an exhaust gas treatment system for a melting furnace, water is sprayed in the temperature reducing device 2 to lower (reduce) the temperature of the exhaust gas to the required exhaust gas temperature at the inlet of the bag filter 3. There is a problem that low-temperature corrosion occurs due to the acid gas component.

  In view of the foregoing, the present invention provides an exhaust gas treatment system for treating exhaust gas from an ash melting furnace through a temperature reducing device, a bag filter, and a wet smoke cleaning facility. It is an object of the present invention to simplify the structure of a processing device, reduce the cost of the device, and prevent low-temperature corrosion in the bag filter.

  In order to solve such problems, the present invention provides, as a first invention, a temperature-reducing device for lowering the temperature of exhaust gas from an ash melting furnace by using temperature-reducing water supplied from a water supply tank, a bag filter, and a wet-type smoke cleaning facility. When purifying while sequentially passing through, the drawn wastewater of the wet-type smoke washing facility is introduced into the water supply tank, and supplied to the temperature reducing device from the water supply tank and sprayed as temperature-reduced water. An exhaust gas treatment method is proposed.

  The wet smoke cleaning equipment is preferably installed in the exhaust gas pipe on the ash melting furnace side, but may be used also as the wet smoke cleaning equipment on the combustion furnace side. Therefore, the second invention is characterized in that the exhaust gas from the ash melting furnace is mixed with the exhaust gas on the combustion furnace side and introduced into the wet smoke washing tower.

Further, a third invention relates to an exhaust gas treatment method using the exhaust gas treatment apparatus according to the first invention, wherein alkali water is reduced by adding a base component such as NaOH or NaHCO ₃ to the temperature-reduced water, specifically, a water supply tank. It is characterized in that it is supplied as hot water to the temperature reducing device.

According to the first and second aspects of the present invention, the drainage drained from the wet-type smoke washing facility is introduced into the water tank after the heavy metal removal treatment is performed by the wastewater treatment apparatus or as it is, and reduced in the water tank. Mix with hot water. (If a closed circuit is configured, the heavy metal removal processing need not be performed.)
Then, the mixed desuperheated water is sent to the desuperheater and sprayed into the exhaust gas to lower the temperature of the exhaust gas to a required inlet temperature of the bag filter.

  The mixed temperature-reduced water sprayed by the temperature-reducing device has been subjected to alkali treatment in the wet-type smoke-cleaning facility, so that salts in the drawn wastewater are mixed therein. The spray of hot water is sent to the bag filter together with the mixed exhaust gas, and is removed together with the fly ash by the bag filter. Thus, the wastewater treatment device only needs to remove heavy metals.

  Therefore, according to this invention, the (precipitated) salts in the extracted wastewater are reduced by mixing the extracted wastewater of the wet-type smoke cleaning equipment into the deheated water and sending it to the temperature reducing device, and spraying the mixed deheated water into the exhaust gas. The mixed desuperheated water is sprayed by the warming device, mixed into the exhaust gas, sent to the bag filter, and reliably removed together with the melting furnace fly ash by the bag filter.

As a result, the wastewater treatment device for treating the drainage water drawn from the wet-type smoke cleaning facility only needs to remove simple heavy metals. The structure of the wastewater treatment device is simple and small. When the drawn wastewater is circulated and used, a heavy metal treatment may be performed when discharging it to the outside.
Further, according to the present invention, it is possible to continuously discharge (precipitated) salts contained in the drainage drawn out from the smoke washing tower to the outside of the system by the above treatment, and to prevent the concentration of the salts in the exhaust gas treatment system. be able to.

According to the third aspect of the present invention, the temperature-reduced water is made alkaline by adding an appropriate amount of NaOH to the temperature-reduced water, and is sprayed into exhaust gas by the temperature-reducing device. In this way, salts are precipitated, and a high-concentration acidic gas component is weakly acidified.
Then, the weakly acidified melting furnace exhaust gas is sent to the bag filter together with the precipitated salts, and the bag filter removes the precipitated salts and suppresses low-temperature corrosion due to the exhaust gas.

  That is, according to this invention, an appropriate amount of NaOH is added to the desuperheated water to make the desuperheated water alkaline, and this is sprayed into the exhaust gas to weakly acidify the high-concentration acidic gas component and precipitate salts. By flowing the solution through the bag filter, it is possible to remove the salts from the bag filter and to prevent low-temperature corrosion of the bag filter due to acidic gas.

Further, instead of NaOH, NaHCO ₃ (baking soda) was added to the temperature-reduced water sprayed by the temperature-reducing device.
May be added, and this may be supplied to the temperature reducing device as alkaline temperature-reduced water.

Further, according to the invention, when the wet smoke cleaning equipment is installed on the incinerator side, an appropriate amount of NaHCO ₃ is added to the deheated water, and the deheated device is sprayed into the exhaust gas to make it alkaline, which is used for the bag filter. By sending, it is possible to prevent salt precipitation and low-temperature corrosion due to an acidic gas component such as a bag filter in the same manner as described above.
It is obvious that the same effect can be obtained by adding another basic component instead of NaOH or NaHCO ₃ .

  Hereinafter, preferred embodiments of the present invention will be illustratively described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, and are merely illustrative examples. Not just.

FIG. 1 is a system diagram of a molten exhaust gas treatment apparatus for a plasma melting furnace according to a first embodiment of the present invention.
In FIG. 1, reference numeral 1 denotes a plasma melting furnace, 8 denotes a hopper for charging combustion products such as industrial wastes into the melting furnace 1, 10 denotes an exhaust gas pipe from the plasma melting furnace 1, and 17 denotes a residue discharge pipe. . Reference numeral 2 denotes a temperature reducing device for lowering the exhaust gas temperature, which is connected to the plasma melting furnace 1 via the exhaust gas pipe 10.
Reference numeral 3 denotes a bag filter for removing fly ash and precipitated salts in the exhaust gas, which is provided with a heater 31 and a fly ash conveyor 32, and transports the fly ash after removal to a fly ash processing facility (not shown). Reference numeral 19 denotes an exhaust gas pipe connecting the temperature reducing device 2 and the bag filter 3.

Reference numeral 4 denotes a wet smoke washing tower for removing high-concentration acidic gas components in the exhaust gas, which is brought into wet contact with the high-concentration acidic gas components by alkaline water added from the NaOH tank 41 to precipitate salts. Reference numeral 11 denotes an exhaust gas pipe for connecting the bag filter 3 and the wet-type smoke washing tower 4, and the exhaust gas pipe 11 is provided with an exhaust gas fan 7 for feeding exhaust gas under pressure.
Reference numeral 18 denotes an exhaust gas pipe connected to the outlet of the wet-type smoke washing tower.
Reference numeral 5 denotes a water supply tank in which the temperature-reducing water to be supplied to the temperature-reducing device 2 is stored.
The above configuration is the same as that of the prior art shown in FIG.

In the first embodiment of the present invention, the system for treating the drainage of the wet smoke washing tower 4 is improved.
That is, in FIG. 1, reference numeral 6 denotes a wastewater treatment device, which draws wastewater from the wet-type smoke washing tower 4 and removes heavy metals in the wastewater as described above. The outlet of the treated wastewater of the device 6 is connected to the water supply tank 5 via a drainpipe 15.
Further, NaOH is added to the water supply tank 5 together with the drawn drainage so that the temperature-reduced water becomes alkaline temperature-reduced water.

During operation of the exhaust gas treatment system of the plasma melting furnace having the above configuration,
The drainage drained from the wet smoke washing tower 4 is sent to a drainage treatment device 6, where heavy metals in the drainage are removed.
The drawn wastewater from which heavy metals have been removed by the wastewater treatment device 6 is sent to the water supply tank 5 through the drainage pipe 15 and mixed with the temperature-reduced water in the water supply tank 5.
Further, a small amount of NaOH (sodium hydroxide) is also mixed into the water supply tank 5 as described later, so that the temperature-reduced water becomes alkaline temperature-reduced water.

Then, the mixed temperature-reduced water in the water supply tank 5, that is, the temperature-reduced water mixed with the drawn drainage and NaOH is sent to the temperature-reducing device 2 through the temperature-reduced water pipe 9.
On the other hand, the exhaust gas discharged from the plasma melting furnace 1 is introduced into the temperature reducing device 2 through the exhaust gas pipe 10.

In the temperature reducing device 2, the mixed temperature-reduced water introduced from the water supply tank 5 through the temperature-reducing water pipe 9 is sprayed into the exhaust gas, and the temperature of the exhaust gas is adjusted to the required inlet temperature of the bag filter 3 (150 ° C. to 160 ° C.). And the temperature-reduced water becomes alkaline and is sprayed into the exhaust gas by the temperature-reducing device 2. Therefore, the alkaline temperature-reduced water is brought into wet contact with the exhaust gas to form a high-concentration acidic gas component in the exhaust gas. Is slightly acidified to precipitate salts.
The exhaust gas that has passed through the temperature reducing device 2 is introduced into the bag filter 3 via the exhaust gas pipe 19 together with the precipitated salts and fly ash, where the precipitated salts and fly ash are removed.

During the operation of the bag filter 3, the salts in the waste water extracted from the wet-type smoke-washing tower 4 are dissolved in the mixed de-heated water sprayed into the exhaust gas by the de-heater 2 with the alkali de-heated water and dissolved again. Deposited in the temperature reducing device 2 and sent to the bag filter 3.
Then, in the bag filter 3, solid components such as the salts and fly ash are removed, and these are transported to the fly ash processing equipment via the fly ash transport conveyor 32.

Therefore, the wastewater treatment device 6 for treating the wastewater extracted from the wet-type smoke washing tower 4 only needs to simply remove heavy metals, and the wastewater treatment device 6 has a simple structure and a small size.
Further, the salts contained in the drainage water drawn out from the smoke washing tower 4 and the salts precipitated by neutralizing the high-concentration acidic gas components in the exhaust gas are continuously discharged outside the system by the treatment as described above. In addition, concentration of salts in the exhaust gas treatment system can be prevented.

  After the above operation, the exhaust gas exiting the bag filter 3 is sent by the exhaust gas fan 7 through the exhaust gas pipe 11 to the wet-type smoke washing tower 4 where acid gas and the like are completely removed. , And is discharged to the outside or combined with exhaust gas from an incinerator (not shown).

  In addition, by adding an appropriate amount (a small amount) of NaOH to the temperature-reduced water in the water supply tank 5, the exhaust gas is brought into wet contact with the exhaust gas by the alkaline temperature-reduced water in the temperature-reducing device 2 so that the high-concentration acidic gas component in the exhaust gas becomes weakly acidic. And sent to the bag filter 3 to suppress low-temperature corrosion of the bag filter 3 due to acid gas.

  In the above embodiment, in order to avoid clogging of the spray nozzle of the temperature reducing device 2, the salt contained in the drainage water was once dissolved as an alkaline solution by adding NaOH supplied in the water supply tank 5 and then reduced. It is necessary to supply to the warming device 2 and neutralize the high-concentration acidic gas components in the exhaust gas to precipitate salts by the temperature reducing device 2. It is preferable to make the degree of weak alkaline, to keep the alkalinity of the temperature-reduced water in the water supply tank 5 as low as possible, and to prevent the generation of salts in the water supply tank 5.

FIG. 2 is a system diagram of an exhaust gas treatment system for a plasma melting furnace according to a second embodiment of the present invention.
In this embodiment, the wet-type smoke washing tower 4 of the first embodiment and the wastewater treatment device 6 attached thereto are installed on the incinerator (not shown) side.

Therefore, in this embodiment, the wet-type smoke washing tower 4, the wastewater treatment device 6, and the drainage pipe 15 connecting the wastewater treatment device 6 and the water supply tank 5 are removed from the apparatus shown in FIG. The flue gas that has passed through is mixed with the flue gas on the combustion furnace side and introduced into the wet smoke washing tower 40.
Further, an appropriate amount (a small amount) of NaHCO ₃ (baking soda) is added to the temperature-reduced water in the water supply tank 5.
The configuration other than the above is the same as that of the first embodiment of FIG. 1, and the same members are denoted by the same reference numerals.

Also in this embodiment, a small amount of NaHCO ₃ is added to the temperature-reduced water to the temperature-reducing device 5 to make it alkaline, and this is sprayed into the exhaust gas by the temperature-reducing device 2, whereby the acid gas component of the bag filter 3 and the like is used. In addition to preventing low-temperature corrosion, the temperature-reduced water becomes alkaline and is sprayed into the exhaust gas by the temperature-reducing device 2, so that the alkaline temperature-reduced water makes wet contact with the exhaust gas to weaken the high-concentration acidic gas component in the exhaust gas. Acidify and precipitate the salts.
The exhaust gas that has passed through the temperature reducing device 2 is introduced into the bag filter 3 via the exhaust gas pipe 19 together with the precipitated salts and fly ash, where the precipitated salts and fly ash are removed.

  As described above, according to the first and second aspects of the present invention, the drainage of the wet-type smoke washing tower is mixed with the deheated water and sent to the deheater, and the mixed deheated water is sprayed into the exhaust gas. The salts in the drawn waste water are mixed into the exhaust gas by spraying the mixed de-heated water in the de-heater, sent to the bag filter and surely removed by the bag filter.

  As a result, in the wastewater treatment apparatus for treating the drainage water drawn from the wet-type smoke washing tower, it is only necessary to perform simple heavy metal removal, and the structure of the wastewater treatment apparatus is simplified, the size is reduced, and the apparatus cost is reduced.

  Further, it is possible to continuously discharge the salts contained in the drainage drawn out from the smoke washing tower to the outside of the system by the treatment with the temperature reducing device and the bag filter, thereby preventing the concentration of the salts in the exhaust gas treatment system. Can be.

According to the third and fourth aspects of the present invention, an appropriate amount of a base such as NaOH or NaHCO ₃ is added to the temperature-reduced water to make the temperature-reduced water alkaline, and this is sprayed into an exhaust gas to flow through a bag filter. As a result, the alkaline spray is sent to the bag filter, whereby the low temperature corrosion of the bag filter due to the acidic gas can be prevented.

  Furthermore, even when the wet smoke tower is installed on the incinerator side, low-temperature corrosion due to an acidic gas component such as a bag filter can be similarly prevented.

1 is a system diagram of an exhaust gas treatment system for a plasma melting furnace according to a first embodiment of the present invention. FIG. 6 is a view corresponding to FIG. 1 and illustrating a second embodiment of the present invention. FIG. 2 is a diagram corresponding to FIG. 1 showing a prior art studied by the present applicant.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 Plasma melting furnace 2 Temperature reducing device 3 Bag filter 4 Wet smoke washing tower 5 Water supply tank 6 Drainage treatment device 7 Exhaust gas fan 9 Temperature reducing water pipe 10, 11, 19 Exhaust gas pipe 15 Drain pipe 40 Wet smoke cleaning equipment (incinerator side)

Claims (4)

  At the time of purifying the exhaust gas from the ash melting furnace by sequentially passing it through a temperature reducing device for lowering the temperature with the temperature reducing water supplied from the water supply tank, a bag filter, and a wet smoke cleaning device, the wet smoke cleaning device is pulled out. A method for treating molten exhaust gas, comprising introducing wastewater into the water supply tank, supplying the wastewater from the water supply tank to the temperature reducing device, and spraying the same as reduced temperature water.   2. The method for treating a molten exhaust gas according to claim 1, wherein the exhaust gas from the ash melting furnace is mixed with the exhaust gas on the combustion furnace side and introduced into a wet smoke washing tower. The method for treating a molten exhaust gas according to claim 1, wherein a base component such as NaOH or NaHCO ₃ is added to the temperature-reduced water to make alkaline temperature-reduced water and supplied to the temperature-reducing device. _{3. The} method for treating molten exhaust gas according to claim 1, wherein a basic component such as NaOH or NaHCO3 is added to the water supply tank to form alkaline desuperheated water, and then supplied to the deheater as desuperheated water.

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