JP2010051869A - Method and system for washing incineration ash and dust extracted from cement kiln combustion gas with water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress equipment cost and operating cost including chemical cost to a low level when washing incineration ash and dust extracted from cement kiln combustion gas with water. <P>SOLUTION: When incineration ash A and dust D contained in combustion gas extracted from a kiln exhaust gas passage from a cement kiln end to the lowest cyclone are washed with water, filtrate L3 of slurry S2 containing the incineration ash A and obtained by filtration carried out after dissolving the incineration ash A in water and filtrate L1 of slurry S1 containing the dust D and obtained by filtration carried out after dissolving the dust D in water are subjected to water treatment separately, and filtrates L4 and L2 obtained by the water treatment are joined. The filtrate L2 containing the dust D after the water treatment can be discharged while being diluted with the filtrate L4 containing the incineration ash A after the water treatment. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method and a system for flushing dust contained in combustion gas extracted from a kiln exhaust gas flow path from a kiln bottom of a cement kiln to a lowermost cyclone when incineration ash generated from incineration of municipal waste or the like About.

  Incineration ash generated when municipal waste is incinerated has recently been recycled as a cement raw material in view of the danger of depleting the final disposal site. Of municipal incineration ash, fly ash that is carried with gas and collected by the dust collector contains 10 to 20% chlorine, so it is necessary to remove the chlorine before recycling as cement raw material. . Therefore, water-washing desalination equipment such as a belt filter is used to wash away water-soluble chlorine compounds contained in the incineration fly ash and use them as cement raw materials.

  On the other hand, from chlorine, sulfur, alkali, etc. that cause problems such as blockage of preheaters in cement manufacturing facilities, paying attention to the problem of chlorine, from the kiln bottom of the cement kiln to the bottom cyclone A chlorine bypass facility is used for extracting chlorine from a part of the kiln exhaust gas flow path to remove chlorine.

  In this chlorine bypass facility, for example, as described in Patent Document 1, since chlorine is unevenly distributed on the fine powder side of the dust generated by cooling the extracted exhaust gas, the dust is divided into coarse powder and fine powder by a classifier. Separated, the coarse powder was returned to the cement kiln system, and the fine powder (chlorine bypass dust) containing potassium chloride and the like was collected and added to the cement grinding mill system.

  However, in recent years, the recycling of waste containing incineration ash as cement raw material or fuel has been promoted, and as the amount of waste processed increases, the amount of volatile components such as chlorine brought into the cement kiln also increases. The amount of chlorine bypass dust is increasing. Therefore, all the chlorine bypass dust cannot be used in the cement crushing process, and the chlorine bypass dust is also washed with water.

  In addition, with the increase in the amount of waste processed in cement manufacturing facilities, the amount of heavy metals brought into the cement kiln also increases, and it is predicted that heavy metals will exceed the allowable cement concentration. Therefore, for example, in the waste cement raw material processing method described in Patent Document 2, chlorine bypass dust or the like that has been conventionally washed with water is desalted, and water is added to the waste containing chlorine to add to the waste. Chlorine Bypass Dust without causing environmental pollution by purifying and filtering the chlorine and using the resulting desalted cake as a raw material for cement as well as purifying waste water to remove heavy metals such as copper and lead. Is being used effectively.

  On the other hand, in the cement manufacturing process, selenium (Se) and thallium (Tl) are provided in addition to copper and lead. For example, pulverized coal supplied to kilns and calcining furnaces contains about 1 ppm of thallium and waste tires contain about 8 ppm of thallium. This thallium has a low boiling point, volatilizes between the kiln and the preheater of the cement baking apparatus, and most of the thallium is concentrated in the preheater, so that it is contained in the waste water treated with chlorine bypass dust.

  As mentioned above, conventionally, when recycling municipal waste incineration ash etc. as cement raw material, it is necessary to remove chlorine from fly ash and chlorine bypass dust, and heavy metals such as thallium, lead, selenium etc. from chlorine bypass dust Since there are cases where it is necessary to remove water, a plurality of processing facilities are required, and there is a problem that facility costs and operation costs increase, such as the need to be assigned to each processing facility.

  Therefore, Patent Document 3 discloses that incineration ash and chlorine bypass dust are washed with water at the same time, and at least one substance selected from thallium, lead, and selenium eluted in the filtrate obtained after washing with a sulfiding agent and / or A method has been proposed for reducing the facility cost and the operating cost when recycling municipal waste incineration ash or the like as a cement raw material by removing it by adding a reducing agent.

International Publication No. 97/21638 Pamphlet JP 2000-281398 A JP 2007-268398 A

  However, if the incineration ash and the chlorine bypass dust are washed simultaneously with the incineration ash treatment method described in Patent Document 3, the water washing equipment can be shared, so that the equipment cost can be kept low. In addition, substances contained only in either incineration ash or chlorine bypass dust, or substances contained in a large amount only in either one, are dispersed throughout the filtrate after washing with water. As a result, the cost of drugs has increased.

  Therefore, the present invention has been made in view of the above-described problems in the prior art, and in the incineration ash and cement kiln combustion gas extraction dust, the operation cost including the chemical cost and the equipment cost are kept low. For the purpose.

  In order to achieve the above-mentioned object, the present invention provides an incineration ash and the incineration ash for washing the dust contained in the combustion gas extracted from the kiln exhaust gas flow path from the bottom of the cement kiln to the bottom cyclone. The slurry filtrate containing the incinerated ash obtained by filtering in water and the slurry filtrate containing the dust obtained by filtering the dust after dissolving the dust in water. After each water treatment separately, each filtrate after water treatment is made to join.

  And according to the present invention, since the slurry filtrate containing incinerated ash and the slurry filtrate containing chlorine bypass dust and the like are separately water-treated, it corresponds to the target component of the water treatment of each slurry filtrate. Since the water treatment can be performed using the chemicals to be treated and a small amount of components can be treated with a small amount of the chemicals, the operation cost including the chemical costs can be kept low. Moreover, since each filtrate is merged, the density | concentration of a specific component can also be made low. Furthermore, since the facilities after joining the respective filtrates are shared, the facility cost can be reduced.

  Moreover, the filtrate of the slurry containing the dust after the water treatment can be discharged while being diluted with the filtrate of the slurry containing the incinerated ash after the water treatment. By diluting chlorine bypass dust containing heavy metals such as selenium and thallium with a filtrate of slurry containing incinerated ash not containing these heavy metals, the concentration of selenium and thallium in the wastewater can be kept low.

  The target component of water treatment of the incinerated ash washing filtrate may be one or more selected from the group consisting of lead, zinc, and copper, and in the water treatment of the incinerated ash washing filtrate, One or more selected from the group consisting of soda, sodium sulfide, liquid chelate, ferrous chloride, ferric chloride, a polymer flocculant, and caustic soda can be used.

  Moreover, the target component of the water treatment of the dust washing filtrate can be one or more selected from the group consisting of selenium, thallium, lead, zinc, and copper, and the water treatment of the dust washing filtrate. , One or more selected from the group consisting of hydrochloric acid, ferrous chloride, ferrous sulfate, sodium hydrosulfide, sodium sulfide, caustic soda, and lime milk can be used.

  As described above, according to the present invention, when the incineration ash and the cement kiln combustion gas extraction dust are subjected to the water washing treatment, the operation cost including the chemical cost and the equipment cost can be kept low.

  Next, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an embodiment of a flushing system for incinerated ash and cement kiln combustion gas extraction dust (hereinafter referred to as “water washing system”) according to the present invention. The flushing system 1 is roughly divided into cement kiln kilns. A dust washing system 2 for washing the dust (hereinafter referred to as “dust”) D contained in the combustion gas extracted from the kiln exhaust gas flow path from the bottom to the bottom cyclone, and municipal waste incineration ash Among them, the ash washing system 3 for washing the fly ash (hereinafter simply referred to as “fly ash”) A, which is carried with the gas and collected by the dust collector, and the vertical used in common to both systems. A mold filter press 11, a mixing tank 12, and a common system for the drum filter 13 are provided.

  The dust washing treatment system 2 is provided for purifying the filtrate L1 by removing heavy metals from the filtrate L1 generated after washing the dust D with water and removing chlorine, and a dust tank 21 for storing the dust D. And a dissolution tank 22 for adding water to dust D to generate slurry S1, a filtrate tank 23 for storing filtrate L1 generated by solid-liquid separation of slurry S1 by vertical filter press 11, and filtrate L1. It is comprised with the chemical | medical solution reaction tank 24 (24A-24C) for removing heavy metals, the slurry tank 25, the filter press 26, and the filtrate tank 27. FIG.

The chemical reaction tank 24A is provided to add sodium hydrosulfide (NaSH) as a sulfiding agent to the filtrate L1 and sulfidize lead and thallium in the filtrate L1 to generate lead sulfide (PbS) and thallium sulfide. In the chemical reaction tank 24B, a ferrous compound that functions as a flocculant and a selenium reducing agent (in the example shown, ferrous chloride (FeCl ₂ )) is added to the filtrate L1 to which a sulfurizing agent has been added, and then sulfided. It is provided for aggregating lead and thallium sulfide and reducing hexavalent or tetravalent selenium in the filtrate L1 to zero-valent selenium. The chemical reaction tank 24B also has a role of discharging carbonate radical, which is an interference element for removing selenium, as a gas by adding hydrochloric acid to a pH of 4 or less. In the chemical reaction tank 24C, lime milk is added as an alkaline agent to the filtrate L1 to which the pH is adjusted to 4 or less by adding a sulfurizing agent and a ferrous compound, and the pH is adjusted to 7.5 or more and 11 or less. , To provide an optimum pH for the reduction of selenium.

  The filter press 26 is provided for solid-liquid separation of the slurry from the slurry tank 25 and for separating thallium sulfide, lead sulfide and selenium from the slurry.

  On the other hand, the ash / water washing treatment system 3 is provided to remove the heavy metals from the generated filtrate L3 after washing the fly ash A with water and removing chlorine, and to store the fly ash A in order to purify the filtrate L3. Fly ash tank 31, dissolving tank 32 for adding water to fly ash A to generate slurry S 2, and filtrate tank 33 for storing filtrate L 3 produced by solid-liquid separation of slurry S 2 by vertical filter press 11. And a chemical reaction tank 34 (34A to 34C) and a sedimentation separator 35 for removing heavy metals from the filtrate L2.

  The chemical reaction tank 34A is provided for adding sodium hydrosulfide as a sulfiding agent to the filtrate L3 to sulfidize lead in the filtrate L1 to generate lead sulfide. The chemical reaction tank 34B is agglomerated. It is provided for adding heavy metals such as lead by adding ferrous chloride as a reducing agent and reducing agent. The chemical reaction tank 34C is provided for adding a polymer flocculant for the purpose of increasing the cohesiveness of heavy metals or the like and facilitating sedimentation.

  The sedimentation separator 35 is provided for sedimenting and collecting heavy metals and the like. The sedimentation separator 35 is an inclined plate sedimentation separator having a plurality of separation plates inclined at a predetermined angle.

  The vertical filter press 11, the mixing tank 12, and the drum filter 13 are facilities commonly used in the dust water washing treatment system 2 and the ash water washing treatment system 3.

  The vertical filter press 11 is provided for solid-liquid separation of the slurry S1 supplied from the dissolution tank 22 and the slurry S2 supplied from the dissolution tank 32, respectively. The vertical filter press 11 includes a plurality of filter plates that are horizontally arranged and stacked in a vertical direction, a jack (not shown) that raises and lowers each filter plate, and a plurality of guide rollers that are arranged laterally. A batch-type filtration device comprising an endless filter cloth wound around the plurality of guide rollers, and configured to run on the upper surface of each filter plate.

  The mixing tank 12 and the drum filter 13 are provided for collecting suspended substances such as heavy metals remaining in the filtrate from the sedimentation separator 35 and the filtrate tank 27 and purifying the waste water.

  Next, a water washing method according to the present invention using the water washing system 1 will be described with reference to FIG. In the water washing method according to the present invention, the filtration and water treatment of the slurry containing dust D are performed using the dust water washing treatment system 2 and the common system, and the filtration and water treatment of the slurry containing fly ash A are carried out by the ash water washing treatment system. 3 and common system. First, the operation of the dust washing system 2 using the common system will be described.

  When the operation is started, first, in the dissolution tank 22, the dust D from the dust tank 21 is mixed with water to produce a slurry S1, and the chlorine content contained in the dust D is dissolved in water. The slurry S1 is supplied from the dissolution tank 22 to the vertical filter press 11, and the slurry S1 is solid-liquid separated. The cake C1 produced by the vertical filter press 11 is charged into a cement kiln or the like as a cement raw material or the like, while the filtrate L1 containing chlorine is supplied to the filtrate tank 23 and temporarily stored.

Next, the filtrate L1 stored in the filtrate tank 23 is supplied to the chemical reaction tank 24A, and sodium hydrosulfide as a sulfiding agent is added to the filtrate L1 in the chemical reaction tank 24A. Thereby, lead and thallium in the filtrate L1 are sulfided to produce lead sulfide and thallium sulfide. In addition to sodium hydrosulfide, sodium sulfide (Na ₂ S) can be used as the sulfurizing agent.

Next, in the chemical reaction tank 24B, hydrochloric acid is added to the filtrate L1, the pH of the filtrate L1 is adjusted to 4 or less, the dissolved carbonate radical is discharged as a gas, and the pH of the filtrate L1 is adjusted. Ferrous chloride that functions as an aggregating agent and a selenium reducing agent is added to aggregate lead sulfide and thallium sulfide, and hexavalent or tetravalent selenium in the filtrate L1 is reduced to zero-valent selenium. In place of ferrous chloride, ferrous sulfate (FeSO ₄ ) can also be used.

  Next, in the chemical reaction tank 24C, an alkaline agent is added to the filtrate L1 having a pH of 4 or less due to the addition of the above-mentioned chemicals, and the pH is adjusted to 7.5 or more and 11 or less, which is optimal for reducing selenium.

  Next, the filtrate L1 from the chemical reaction tank 24C is solid-liquid separated by the filter press 26 through the slurry tank 25, and lead sulfide, thallium sulfide and selenium are recovered, and the secondary filtrate L2 is removed from the filtrate tank. 27 to supply to the mixing tank 12. The secondary cake C2 generated by the filter press 26 is reused as a cement raw material or the like.

  Next, operation | movement of the ash water washing processing system 3 using a common system is demonstrated.

  When the operation is started, first, in the dissolution tank 32, the fly ash A from the fly ash tank 31 is mixed with water to produce slurry S2, and the chlorine content contained in the fly ash A is dissolved in water. The slurry S2 is supplied from the dissolution tank 32 to the vertical filter press 11, and the slurry S2 is solid-liquid separated. The cake C3 produced by the vertical filter press 11 is put into a cement kiln or the like as a cement raw material or the like, while the filtrate L3 containing a chlorine content is supplied to the filtrate tank 33 and temporarily stored.

  The filtrate L3 from the filtrate tank 33 is supplied to the chemical reaction tank 34A, and lead in the filtrate L3 is sulfided to lead sulfide. Next, in the chemical reaction tank 34B, lead sulfide is precipitated by the aggregating action of ferrous chloride, and in the chemical liquid reaction tank 34C, the precipitate is aggregated into larger particles by the polymer flocculant.

  Next, the sediment is separated by sedimentation by the sedimentation separator 35. The sediment obtained by the sedimentation separator 35 is stored in a sludge pit (not shown), and then solid-liquid separated by a filter press or the like, and the cake can be reused as a cement raw material or the like.

  Next, the supernatant L4 from the sedimentation separator 35 is supplied to the mixing tank 12 and joined with the filtrate L2 from the filtrate tank 27 of the dust water washing treatment system 2.

  In the mixing tank 12, the heavy metal remaining in the supernatant L 4 from the sedimentation separator 35 and the filtrate L 2 from the filtrate tank 27 is collected, and remains in the filtrate from the mixing tank 12 by the drum filter 13. Remove heavy metals and suspended substances, add diluted water and discharge to sewers.

  In the above embodiment, selenium, thallium and lead in the filtrate L1 are removed using the dust water washing treatment system 2 and the common system, but in addition to these, zinc, copper and the like can also be removed. Sodium sulfide can be used instead of soda, and caustic soda can be used instead of lime milk. These can be used simultaneously.

  In addition, even when the filtrate L3 is water-treated using the ash-water washing treatment system 3 and the common system, zinc, copper, etc. can be removed in addition to lead, and sodium sulfide, liquid chelate, and chloride can be used instead of sodium hydrosulfide. Ferric chloride can be used instead of ferrous iron, and these can be used simultaneously. Furthermore, caustic soda can be used for pH adjustment and the like.

  As described above, in the present invention, the filtration of the slurry containing the dust D and the filtration of the slurry containing the fly ash A are performed using the common vertical filter press 11, and the mixing tank 12 and the drum filter 13 are shared. Therefore, the facility cost and the operation cost can be kept low, and the water treatment of the slurry containing dust D and the water treatment of the slurry containing fly ash A are separately performed according to the characteristics of each slurry. Cost can be reduced. The effect of reducing the drug cost will be specifically described by the following test examples.

  Table 1 shows the concentrations of heavy metals contained in the fly ash A plain water washing filtrate. As shown in the table, this filtrate contains lead and zinc, but selenium and thallium are not present, and copper is slightly present.

  Table 2 shows the concentrations of heavy metals in the Dust D plain water wash filtrate. As shown in the table, since this filtrate contains selenium and thallium in addition to lead, it must be discharged after removing them by water treatment.

  Table 3 shows the concentration of heavy metals in the filtrate when the fly ash A and the dust D are mixed and washed with water. Here, the mixing ratio of the fly ash A and the dust D is adjusted to the ratio of each processing amount per day shown in FIG. That is, fly ash A: 85 t / d (processing amount per day (tons)) and dust D: processing amount of 20 t / d, the ratio of dust D to the whole is 20 / (85 + 20) × 100 = 19.1%.

  As shown in the first row of the table, the washing filtrate in the case of mixed water washing contains various heavy metals, so these are discharged as described in the third row of the table by water treatment. Must be below the reference value. In particular, in order to remove selenium, it is necessary to add a large amount of ferrous chloride, and “6000” in the second stage in the table shows that after adding 6000 mg / l of ferrous chloride as Fe. The content of each heavy metal is shown. By adding this amount of ferrous chloride, the selenium concentration almost reaches the discharge standard value, and the other heavy metals have concentrations below the discharge standard value.

  On the other hand, Table 4 shows the concentrations of heavy metals when 6000 mg / l of ferrous chloride is added as Fe to Dust D simple water-washed filtrate and then diluted with Flyash A plain water-washed filtrate. Indicates. “6000” in the second row of the table indicates the concentration of each heavy metal after adding 6000 mg / l ferrous chloride as Fe. “Dilution” in the third stage indicates the concentration of heavy metals after dilution with ferrous chloride and then with a fly ash A plain water washing filtrate. As described in the third column “Dilution”, all heavy metals including selenium have concentrations below the discharge standard value.

  Here, in the case of performing the mixed water washing of the fly ash A and the dust D (case A), and after adding ferrous chloride to the dust D plain water washing filtrate, the fly ash A simple water washing filtrate In the case of dilution (Case B), the amount of ferrous chloride (as Fe) used when the fly ash A filtrate: 340 t / d and the dust D filtrate: 80 t / d are compared. The specific gravity of the water washing filtrate is 1.09 kg / l.

In case A,
6000 mg / l ÷ 1.09 kg / l × (340 + 80) t / d = 2,311 kg / d
Thus, 2,311 kg / d of iron (Fe) is consumed.

On the other hand, in case B,
6000 mg / l ÷ 1.09 kg / l × 80 t / d = 440 kg / d
And 440 kg / d of iron (Fe) is consumed.

From the above, it can be seen that in case B, the amount of (FeCl ₂ ) used is one fifth that of case A.

FIG. 2 is a graph showing the relationship between the amount of ferrous chloride added and the selenium concentration of treated water when selenium (Se) is removed using ferrous chloride (FeCl ₂ ). As shown in the figure, the amount of ferrous chloride to be added increases as the selenium concentration decreases. In particular, in order to reduce the selenium concentration from 0.5 mg / l to 0.1 mg / l, it is necessary to add 6000 mg-Fe / l and a large amount of ferrous chloride. On the other hand, when the selenium concentration is lowered from 3.0 mg / l to 0.38 mg / l, it is necessary to add about 6000 mg-Fe / l of ferrous chloride. After that, by diluting with fly ash A washing filtrate that does not contain selenium, it becomes possible to achieve the discharge standard, and from the difference in the amount of filtrate to be processed, the amount of ferrous chloride added is greatly reduced. be able to.

  In the above embodiment, the case where the batch-type vertical filter press 11 is used as a filtration device for separately performing filtration of the slurry containing fly ash A and filtration of the slurry containing dust D has been described. A batch type horizontal filter press can also be used, and a continuous belt filter can also be used. Moreover, when the vertical filter press 11 is used in common for the dust water washing treatment system 2 and the ash water washing treatment system 3 as in the above embodiment, it is preferable because the equipment cost and the operation cost can be kept low. You may provide the vertical filter press 11 in the systems 2 and 3 separately.

  Moreover, in the said embodiment, although the case where the fly ash A was washed with water as an incineration ash was illustrated, this invention can be applied also when the main ash is washed with water instead of the fly ash A. The ash and main ash can be washed with water at the same time.

  Furthermore, each device, the type of chemical solution, the processing amount per day of the processing object, etc. shown in the above embodiment are merely examples, and can be appropriately changed without departing from the spirit of the present invention. Of course.

It is a flowchart which shows one Embodiment of the water washing system concerning this invention. It is a graph which shows the relationship between the addition amount of ferrous chloride at the time of removing selenium using ferrous chloride, and the selenium density | concentration of treated water.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Water washing system 2 Dust water washing processing system 3 Ash water washing processing system 11 Vertical filter press 12 Mixing tank 13 Drum filter 21 Dust tank 22 Dissolution tank 23 Filtrate tank 24 (24A-24C) Chemical reaction tank 25 Slurry tank 26 Filter press 27 Filtrate tank 31 Fly ash tank 32 Dissolution tank 33 Filtrate tank 34 (34A to 34C) Chemical reaction tank 35 Sediment separator A Fly ash C1 to C3 Cake D Dust

Claims (6)

In washing the incinerated ash and the dust contained in the combustion gas extracted from the kiln exhaust gas passage from the bottom of the kiln of the cement kiln to the bottom cyclone,
The slurry of the slurry containing the incinerated ash obtained by dissolving the incinerated ash in water and filtered, and the slurry containing the dust obtained by filtering after dissolving the dust in water. A method for rinsing incineration ash and cement kiln combustion gas bleed dust, wherein the filtrates are treated with water separately, and the filtrates after the water treatment are combined.   2. The incinerated ash and cement kiln according to claim 1, wherein the infiltrated ash and cement kiln are discharged while being diluted with the filtrate of the slurry containing the incinerated ash after the water treatment. A method for washing combustion gas bleed dust.   The incinerated ash and cement kiln according to claim 1 or 2, wherein the target component of water treatment of the incinerated ash washing filtrate is at least one selected from the group consisting of lead, zinc, and copper. A method for washing combustion gas bleed dust.   One or more selected from the group consisting of sodium hydrosulfide, sodium sulfide, liquid chelate, ferrous chloride, ferric chloride, polymer flocculant, and caustic soda is used in the water treatment of the incinerated ash washing filtrate. The method for washing incinerated ash and cement kiln combustion gas bleed dust according to claim 3.   The incinerated ash according to claim 1 or 2, wherein the target component of water treatment of the washing solution of dust is one or more selected from the group consisting of selenium, thallium, lead, zinc, and copper. And a method of washing cement kiln combustion gas bleed dust.   In the water treatment of the washing solution of the dust, at least one selected from the group consisting of hydrochloric acid, ferrous chloride, ferrous sulfate, sodium hydrosulfide, sodium sulfide, caustic soda, and lime milk is used. The method for washing water of incinerated ash and cement kiln combustion gas bleed dust according to claim 5.

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