JP2005262004A - Gas washing water treatment device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas washing water treatment device requiring no expensive acid-proof materials, capable of recovering ammonia or salt in a reusable form, with superior economic performance and causing little waste. <P>SOLUTION: Heavy metals in washing waste water from a gas washing apparatus 1 recovering harmful components in exhaust gas into washing water are separated and recovered by a heavy metal separation device 4. The waste water with the heavy metals separated therefrom is separated into ammonia water and saline by an evaporation concentration device 6 to separate and recover ammonia independently for easy reuse. Separation of ammonia with alkali requires no expensive acid-proof material to compose the device at a low cost. Further, as ammonia can be separated from cyan, the separation efficiency of cyan can be enhanced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a recovery type gas cleaning water treatment apparatus for treating cleaning waste liquid from a gas cleaning apparatus that recovers harmful components in exhaust gas into cleaning water.

  Conventionally, exhaust gas generated when a waste is burned or the like has an environmental problem if it is released into the atmosphere as it is, and is usually cleaned by an exhaust gas cleaning device. That is, cleaning water is sprayed on exhaust gas, harmful components in the exhaust gas are recovered in the cleaning water, and harmful substances are removed and then released into the atmosphere. Naturally, a large amount of cleaning waste liquid is discharged from such an exhaust gas cleaning apparatus. This washing waste liquid contains harmful components separated and recovered from the exhaust gas, and it is environmentally problematic to discharge it to a river or the like as it is.

  Therefore, various methods for detoxifying the cleaning waste liquid have been proposed. One of them uses ozone (for example, see Patent Document 1). Ozone is effective in decomposing and detoxifying harmful components, but enormous amounts of power are required to generate a large amount of ozone, which increases both equipment costs and maintenance costs. It was difficult to apply.

As water treatment other than ozone, the removal of harmful components is conventionally performed by coagulation sedimentation or evaporation concentration. In this case, solid components and heavy metal components are removed from the washing waste liquid by coagulation precipitation, and further, impurities, ammonia, Cl ⁻ , SO ₄ ²⁻ , and CN ⁻ are separated. Separation into salt water is carried out.

In this case, sulfuric acid (H ₂ SO ₄ ) is added to the solution to be concentrated to make it acidic so that ammonia does not evaporate in the distilled water, and then the distillation process is performed by a salt concentrator. However, since the separation efficiency of ammonium salt is unstable, the quality of distilled water was poor. Concentrated salt water contains ammonia as ammonium chloride and ammonium sulfate, and cyanide is also contained in the presence of ammonia. In general, ammonium chloride and ammonium sulfate are not reused as they are, but are actually discarded and a lot of waste is generated. Also, cyan is difficult to handle due to poor separation and decomposition characteristics in the presence of ammonia.

In addition, since the salt concentrator handles a liquid acidified by sulfuric acid, an acid-resistant expensive metal material must be used as a constituent material, and both initial cost and running cost are expensive, which is economical. The improvement was desired.
JP 2001-41437 A

  In this way, conventional detoxification technology using ozone is difficult to apply in terms of cost, and when coagulation precipitation or evaporation concentration technology is used, it becomes acidic when salt concentration is finally performed, so it is expensive. There is a problem that there is room for improvement in cost and waste such as ammonium chloride and ammonium sulfate is generated.

  An object of the present invention is to provide a gas cleaning water treatment apparatus which is cost-effective and can be recovered in a reusable form, which does not require an expensive acid-resistant material, is excellent in economy, and has little waste.

  The gas cleaning water treatment apparatus of the present invention is a gas cleaning water treatment apparatus for treating cleaning waste liquid from a gas cleaning apparatus for recovering harmful components in exhaust gas into cleaning water, and separates and recovers heavy metals in the waste liquid. It is characterized by comprising a separation device and an evaporation concentration device for separating treated water from which heavy metals have been separated by this heavy metal separation device into ammonia water and salt water.

  Further, in the present invention, a solid content separation device is provided in front of the heavy metal separation device, and this solid content separation device has a pH adjustment device that adjusts the pH of the washing waste liquid to almost neutral, and separates the solid content. You may have a pump which sends a part of treated water to the gas cleaning device as cleaning water.

  Further, in the present invention, the heavy metal separation device has a pH adjusting device that adjusts the pH of the heavy metal separation target treated water to an arbitrary pH that meets the heavy metal separation conditions, and separates heavy metals from the heavy metal separation target treated water. It is preferable to have a flocculant charging device for charging the flocculant into

  In the present invention, the evaporative concentration apparatus evaporates and concentrates the water to be concentrated and separates it into distilled water containing ammonia and concentrated water containing salt, and purifies the distilled water to remove ammonia water and ammonia. It is connected to an ammonia recovery device that obtains recovered water that does not contain it.

  Moreover, in this invention, you may have a crystallizer which concentrates the concentrated water containing the salt content isolate | separated with the evaporation concentration apparatus, and collect | recovers solid salts.

  Further, in the present invention, the crystallizer includes a heat evaporation concentrator that heats and evaporates concentrated water containing salt and precipitates the salt by overconcentration, and takes out the concentrated solution from which the salt has been precipitated, and is solidified by centrifugal force or a membrane. It is good to comprise with the salt separation apparatus which collect | recovers salt.

  Further, in the present invention, it is preferable to provide a cyan separation device that obtains reusable recovered water by decomposing cyanide in the recovered water not containing ammonia from the ammonia recovery device, or by separating it with an ion exchange resin.

  Moreover, in this invention, it is good to provide the pH adjustment apparatus which adjusts the pH of the process liquid of the evaporation concentration object thrown into an evaporation concentration apparatus to 9 or more.

  Further, in the present invention, the agglomerates separated by the heavy metal separator are dried and recovered as sludge having a low water content, and the recovered sludge is heated and dried by vacuum to reduce the moisture content of the sludge. It is good to provide.

  In the present invention, a membrane separation device is used as the cyan separation device, and a hydrogen peroxide input device for supplying hydrogen peroxide to the cyan separation target treated water is provided on the upstream side, and cyanide ions are converted into cyanic acid by its oxidizing power. It is preferable to change to ions and separate and collect them by the membrane separator.

  According to the present invention, ammonia can be separated and recovered alone, so that it can be easily reused as an industrial raw material or as a denitration agent, a neutralizing agent, etc. in a plant.

  Moreover, since ammonia is separated by alkali, it is not necessary to use an expensive acid-resistant material for the evaporation concentrating device, and the device can be configured at low cost.

  Furthermore, since ammonia and cyan can be separated, the separation efficiency of cyan can be increased, and equipment for cyan decomposition can be simplified.

  Hereinafter, an embodiment of a gas cleaning water treatment apparatus according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a basic system configuration showing this embodiment. Reference numeral 1 denotes a gas absorption tower constituting an exhaust gas cleaning device, in which exhaust gas from a waste combustion device (not shown) is introduced, and harmful components in the exhaust gas are recovered in the cleaning water by spraying the cleaning water, and harmful substances are removed from the exhaust gas. To do. Reference numeral 2 denotes a solid content separation device which is constituted by a precipitation tank (hereinafter described as a precipitation tank), and separates and recovers solid content in the waste liquid from the gas absorption tower 1. The sedimentation tank 2 is provided with a pH adjusting device 27, and a neutralizing agent is added to adjust the pH of the washing waste liquid to be almost neutral.

  The settling tank 2 is supplied with the cleaning waste liquid from which the exhaust gas has been washed as described above, and precipitates and separates coarse particles (solid content) recovered from the exhaust gas or precipitated by the neutralization operation. A pump 3 is provided on the outlet side of the settling tank 2, and a part of the treated water from which the solid content has been separated is returned to the gas absorption tower 1 of the gas cleaning device as cleaning water.

  In addition, although the processing liquid with a reduced solid content is sent again to the gas absorption tower 1 as exhaust gas cleaning water by the cleaning pump 3, since the concentration of dissolved matter in the cleaning water increases as it is, only a part as described above Is returned to the absorption tower 2 together with clean water gas to be newly replenished, and the rest is extracted to the subsequent stage.

  4 is a heavy metal separator, which is installed in the latter stage and receives the wash water partially extracted from the wash water in which the solid matter is reduced by the settling tank 2. Then, by the neutralization operation by the pH adjusting device 11 and the flocculant charging device 12 by the flocculant charging device 12, the remaining solid content and the dissolved heavy metal content are separated, and the treatment liquid not containing harmful metals is recovered. The sludge containing the separated heavy metal is sent to the sludge dryer 5, where after removing the moisture in the sludge and reducing the volume, it is discharged out of the system as dry sludge.

  An evaporative concentration apparatus 6 evaporates and concentrates the water to be concentrated and separates it into distilled water containing ammonia and concentrated water containing salt. That is, the heavy metal is separated by the heavy metal separator 4 and the discharged processing liquid is sent to the evaporation concentrating apparatus 6 as processing water to be concentrated, and is separated into distilled water containing ammonia and a concentrated liquid containing dissolved salt by heating. The

  An ammonia recovery device 7 is connected to the distilled water discharge side of the evaporative concentration device 6, purifies the distilled water separated by the evaporative concentration device 6, and cleans the ammonia water not containing impurities and the ammonia free. Collect recovered water. The obtained ammonia is reused as an industrial raw material or a neutralizing agent in the plant.

  A cyan separator 9 is connected to the clean recovered water side of the ammonia recovery apparatus 7 that does not contain ammonia. That is, when cyanide is contained in the treated water (recovered water) in the ammonia recovery device 7, this treated water is sent to the cyan separation device 9, and after separation and decomposition of the cyan component, clean water is collected in the plant. Reuse or release outside the system.

  A crystallizer 8 is connected to the concentrated liquid side of the evaporative concentration apparatus 6 and concentrates the concentrated liquid separated by the evaporative concentration apparatus 6 again to separate and recover the dissolved salt as a dry salt. Since this dry salt contains almost no harmful substances, it can be reused as industrial raw materials or treated as general waste.

  Hereinafter, the details of the above-described parts will be described together with the operation.

  FIG. 2 shows the relationship between the gas cleaning device 1 and the solid content separation device 2 for processing the cleaning waste water. In this example, there are many harmful components in the exhaust gas. In order to improve the cleaning performance of the exhaust gas, a plurality of gas absorption towers 1 are installed in series (1A, 1B), and the cleaning water is sprayed on each. The washed waste liquid is sent to a precipitation tank (solid content separator) 2. In the sedimentation tank 2, the pH adjusting device 27 having a pH meter 27D is neutralized to maintain the cleaning performance of the exhaust gas, and should be controlled to an arbitrary pH of pH 6 to 8 (substantially neutral).

  In this sedimentation tank 2, solids are separated by natural sedimentation or floating separation using fine bubbles, and sludge (separated solids) is sent to a sludge dryer 5 by a sludge pump 28, and after drying and volume reduction, Is discharged. This reduces the solids concentration in the wash water and keeps it clean. The treated water cleaned in the settling tank 2 is sent to the gas absorption tower 1A and the second absorption tower 1B by the pump 3 and reused as washing water.

  Further, since the concentration of dissolved matter in the washing water increases by continuous operation, the exhaust gas washing performance of the gas absorption tower 1A and the second absorption tower 1B is maintained by extracting a part of the washing water and replenishing fresh water. be able to.

  As shown in FIG. 3, the heavy metal separation device 4 accepts a part of the wash water extracted as treated water for heavy metal separation. Then, the pH of the treated water (washing water) is adjusted to an arbitrary pH (weak alkali) that meets the heavy metal separation conditions by a pH adjusting device 11 having a pH meter 11D as necessary. Further, a flocculant is charged into the treated water by the flocculant charging device 12 so that heavy metals are flocculated and separated.

  That is, a part of the wash water discharged from the gas cleaning device 1 is sent to the heavy metal separation device 4, and if necessary, adjusted to an arbitrary pH (weak alkali) that meets the heavy metal separation conditions by the pH adjustment device 11. . Further, an arbitrary amount of the flocculant is charged by the flocculant charging device 12, and the solid content in the waste liquid and the dissolved heavy metals are agglomerated and separated.

  As the heavy metal separation device 4, for example, a structure that separates into sludge containing harmful substances and treatment liquid not containing harmful heavy metals by sedimentation or floating separation using fine bubbles is adopted. The separated sludge is transferred to the sludge dryer 5 by the discharge pump 13, and the water in the sludge is removed and discarded as a dried sludge having a small volume. On the other hand, since the processing liquid does not contain harmful heavy metals, it can be discharged as factory wastewater as it is.

  The evaporative concentration device 6 and the ammonia recovery device 7 are configured as shown in FIG. That is, the heavy metal is separated by the heavy metal separation device 4 in the previous stage, and the discharged treatment liquid (concentration target treated water) is charged with NaOH by the pH adjusting device 16 if necessary, pH 9 or higher, pH 10 should be desired, That is, the alkali is adjusted. Thereafter, the evaporative concentration apparatus 6 evaporates and concentrates by heating with steam or the like. As a result, the ammonia contained in the treatment liquid moves to the vapor side and is separated and recovered together with distilled water.

  This distilled water is sent to the ammonia recovery device 7 and purified by heating again to purify ammonia. That is, the vapor containing ammonia as a main component is cooled by the condenser 14 and then recovered as ammonia water.

  Here, the evaporative concentration device 6 evaporates and concentrates the treatment liquid by making it alkaline and transferring ammonia to the vapor side. That is, in order not to transfer ammonia to the vapor side, it is based on a technical idea opposite to the conventional technique in which the treatment liquid is concentrated in an acidic state with sulfuric acid. For this reason, unlike the conventional evaporation concentrator, it does not have to be made of an expensive acid-resistant metal, and the evaporation concentrating device 6 can be configured using a normal metal material, so that the equipment cost can be greatly reduced.

  In this case, an ammonia recovery device 7 for taking out ammonia from distilled water is newly required, but compared with the case where a conventional evaporation concentrator is made of acid-resistant metal, even if the ammonia recovery device 7 is newly provided, The total equipment cost can be reduced as compared with the prior art.

  Further, since the recovered ammonia water contains almost no impurities, it can be easily reused as an industrial raw material or a neutralizing agent in a plant. In other words, since it is conventionally taken out as ammonium chloride or ammonium sulfide, it can be recovered as ammonia that contains almost no impurities as described above, so that it can be recovered as industrial material, neutralizing agent, denitration. It can be reused as it is.

  Further, since the treatment liquid containing no ammonia separated by the ammonia recovery device 7 contains almost no dissolved salt, it can be reused as out-of-system discharge or as water supply in the plant.

  On the other hand, the concentrate separated by the evaporative concentration apparatus 6 is salt water that does not contain harmful substances such as heavy metals and ammonia. For this reason, if necessary, it can be cooled by the cooler 15 and discharged as factory waste water, or it is sent as it is to the crystallizer 8 as shown in FIG.

  As shown in FIG. 5, the crystallizer 8 heats and concentrates again the concentrate discharged from the evaporative concentration device 6 and sent by the circulation pump 29. Thereby, the dissolved salt in the concentrate exceeds the solubility due to overconcentration and precipitates as a solid salt. The vapor evaporated here is returned to the evaporation concentrator 6 and concentrated again.

  The overconcentrated liquid on which the solid salt is precipitated is neutralized by the neutralization device 18 as necessary, and then sent to the solid-liquid separation device 17 to be separated into the solid salt and the treatment liquid. The recovered solid salt is used as a dry salt. It is discharged out of the system. This salt has a low content of impurities such as harmful substances and can be treated as a highly pure industrial raw material with a low water content or as a general waste. The overconcentrated liquid from which the solid salt has been separated is returned to the crystallizer 8 because the salt concentration is low, and is again overconcentrated. The overconcentrated liquid is always neutralized by the neutralizer 18.

  FIG. 6 shows a configuration example of the cyan separation device 9. In this example, the cyan separation device 9 includes a reaction tank 19 and a membrane ion separation device 20. When cyan is mixed in the ammonia recovery water described above, the recovery water is sent to the reaction tank 19 and cyan is changed to cyanate ions by adding an oxidizing agent. The treated water in which cyan is changed to cyanate ions is sent to the membrane ion separation device 20 to almost completely separate the cyan component. As a result, the recovered water can be reused as clean water or discharged out of the system. The concentrated waste liquid discharged from the membrane ion separator 20 is returned to the heavy metal separator 4 and processed again in the system.

  FIG. 7 shows another configuration example of the cyan separation device 9, which uses an ion exchange resin tower 21 instead of the membrane ion separation device 20 in FIG. 6. With this configuration, it is possible to separate cyanate ions by the ion exchange resin tower 21. The feature of this method is that the purity of recovered water is pure water, and water that can be reused in a wide range is obtained.

FIG. 8 shows still another configuration example of the cyan separation device. In this example, when cyanide is mixed in the ammonia recovery water, the recovered water is sent to the reaction tank 24, and hydrogen peroxide (H ₂ O ₂ ), which is one of the oxidizing agents, is input by the input device 25 to convert cyan to cyanic acid. Then, it is sent to the membrane ion separator 26 to almost completely separate the cyan component. As a result, the recovered water can be reused as clean water or discharged out of the system.

The concentrated waste liquid discharged from the membrane ion separator 20 is returned to the heavy metal separator 4 and processed again in the system. When H ₂ O ₂ is used as the oxidant, the oxidant undergoes a chemical reaction and then decomposes into oxygen and water, thereby reducing the processing load of the residual oxidant. For example, when sodium hypochlorite which has been conventionally used as an oxidizing agent is used, a large amount of sodium chloride is generated as a residue of the oxidizing agent and mixed into the processing liquid. This leads to an increase in the amount of waste generated, and increases the treatment capacity of the water device, which is inefficient. On the other hand, when H ₂ O ₂ is used as the oxidizing agent, as described above, it is decomposed into oxygen and water after the chemical reaction, so that the processing load of the residual oxidizing agent can be reduced.

  FIG. 9 shows a configuration example of the sludge dryer 5. A heater unit 22 is provided for the sludge dryer 5, and the sludge collected by the sludge dryer 5 is heated by hot water sent from the heater unit 22. Further, a vacuum pump 23 is connected to the sludge chamber of the sludge dryer 5, and the recovered sludge is vacuum dried by the vacuum pump 23. By this heating and vacuum drying, the recovered sludge can be kept to 30% or less in a short time even if the moisture content is at least, which can be useful for reducing the volume of waste.

  In the above embodiment, the solid content separation device 2 and the heavy metal separation device 4 have been described as separate devices. However, the solid content separation device may be used as a heavy metal separation device depending on the scale of the facility.

  In this way, the gas cleaning liquid can be treated water that does not contain harmful substances after the treatment by the apparatus of the present invention. In addition, ammonia and salt contained in the gas cleaning liquid can be taken out independently with almost no impurities, so that they can be reused and waste can be greatly reduced. In addition, since the treatment object is treated with alkali during evaporation and concentration, the equipment cost can be greatly reduced as compared with the case of using conventional acid-resistant metal. Furthermore, since cyan is separated from ammonia, the separation efficiency of cyan can be increased, and the facility for cyan decomposition can be simplified.

It is a whole lineblock diagram explaining one embodiment of the gas washing water treatment equipment by the present invention. It is a fragmentary figure which takes out the relationship between a gas washing | cleaning apparatus and solid content separation apparatus in one Embodiment same as the above, and explains it in detail. It is a fragmentary figure which takes out the heavy metal separation device part in one Embodiment same as the above, and explains it in detail. It is a partial figure which takes out the relationship between an evaporative concentration apparatus and an ammonia collection | recovery apparatus in one embodiment same as the above, and explains in detail. It is a partial figure which takes out the relationship between the evaporative concentration apparatus and the crystallizer connected with the concentrate side in one embodiment same as the above, and explains it in detail. It is a partial figure explaining the example of composition of a cyan separation device in one embodiment same as the above. It is a fragmentary figure explaining another example of composition of a cyan separation device in one embodiment same as the above. It is a fragmentary figure explaining another example of composition of a cyan separation device in one embodiment same as the above. It is a fragmentary figure which takes out the sludge dryer part in one embodiment same as the above, and explains it in detail.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas absorption tower of gas washing apparatus 2 Solid content separation apparatus 3 Pump 4 Heavy metal separation apparatus 5 Sludge dryer 6 Evaporation concentration apparatus 7 Ammonia collection apparatus 8 Crystallizer 9 Cyan separation apparatus 11, 16, 27 pH adjustment apparatus 12 Flocculant Input device

Claims (11)

A gas cleaning water treatment device for treating cleaning waste liquid from a gas cleaning device for recovering harmful components in exhaust gas into cleaning water,
A heavy metal separator for separating and recovering heavy metals in the waste liquid;
An evaporative concentration device for separating the treated water from which heavy metals have been separated by the heavy metal separation device into ammonia water and salt water;
A gas cleaning water treatment device comprising:   A solid content separation device is provided in front of the heavy metal separation device, this solid content separation device has a pH adjustment device for adjusting the pH of the washing waste liquid to almost neutral, and a part of the treated water from which the solid content has been separated The gas cleaning water treatment apparatus according to claim 1, further comprising a pump for supplying water as cleaning water to the gas cleaning apparatus.   The heavy metal separation device has a pH adjustment device that adjusts the pH of the heavy metal separation target treated water to an arbitrary pH that meets the heavy metal separation conditions, and inputs a flocculant to separate the heavy metal from the heavy metal separation target treated water. The gas cleaning water treatment device according to claim 1, further comprising a flocculant charging device.   The evaporative concentration apparatus evaporates and concentrates the water to be concentrated and separates it into distilled water containing ammonia and concentrated water containing salt, and purifies the distilled water to obtain ammonia water and recovered water not containing ammonia. The gas cleaning water treatment device according to claim 1, wherein the gas washing water treatment device is connected to an ammonia recovery device to be obtained.   The gas cleaning water treatment apparatus according to claim 1 or 4, further comprising a crystallization apparatus for concentrating concentrated water containing salt from the evaporative concentration apparatus to recover a solid salt.   The crystallizer consists of a heat-evaporating concentrator that heats and evaporates concentrated water containing salt and precipitates the salt by overconcentration, and salt separation that takes out the concentrated solution that precipitates the salt and collects the solid salt by centrifugal force or membrane. The gas cleaning water treatment apparatus according to claim 5, further comprising: an apparatus.   5. A cyan separator for obtaining reusable recovered water by decomposing cyanide in recovered water not containing ammonia from an ammonia recovery apparatus by oxidant decomposition or separation with an ion exchange resin. The gas washing water treatment apparatus as described.   The gas cleaning water treatment device according to claim 1 or 4, further comprising a pH adjustment device for adjusting a pH of a treatment liquid to be evaporated and concentrated to be 9 or more.   The agglomerates separated by the heavy metal separator are dried and collected as sludge with little moisture, and the collected sludge is heated and dried by vacuum to provide a sludge dryer that lowers the moisture content of the sludge. The gas cleaning water treatment apparatus according to claim 1 or 3.   A membrane separator is used as a cyan separator, and on the upstream side thereof, a hydrogen peroxide input device for supplying hydrogen peroxide to cyan separation target treated water is provided, and cyanide ions are changed to cyanate ions by its oxidizing power, The gas cleaning water treatment apparatus according to claim 7, wherein separation and recovery are performed by the membrane separation apparatus.   The gas cleaning water treatment apparatus according to claim 1 or 4, wherein the ammonia water recovered by the evaporative concentration apparatus is reused as a neutralizing agent for the gas cleaning apparatus or the heavy metal separation apparatus.

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