JP2011148681A - Method and apparatus for treating dust in bleed gas of cement kiln combustion gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance purity of recovered heavy metals and gypsum at low equipment and operation costs in recovering the heavy metals from dust in a bleed gas of a cement kiln combustion gas. <P>SOLUTION: An apparatus 1 and the like for treating the dust in a bleed gas of a cement kiln combustion gas includes a bleeder 6 to cool and bleed part of the combustion gas from a kiln exhaust gas duct between the outlet port 5a of a cement kiln 5 and a lowermost cyclone; a wet dust collector 11 to perform wet collection of the dust D2 contained in the bleed gas G1 bled by the bleeder, removing sulfur oxides contained in the bleed gas, and to adjust the pH of a slurry S1 formed in the wet dust collection and desulfurization so that the heavy metals contained in the slurry dissolve in the liquid phase of the slurry; a first solid/liquid separator 21 to perform solid/liquid separation of the slurry of which the pH is adjusted by the wet dust collector; and a second solid/liquid separator 23 to separate and recover the heavy metals from a filtrate W1 separated by the first solid/liquid separator. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method and an apparatus for treating cement kiln combustion gas bleed dust, and in particular, extracting a portion of combustion gas from a kiln exhaust gas passage from the kiln bottom of the cement kiln to the lowest cyclone to remove chlorine. The present invention relates to a method for removing heavy metals such as lead from dust contained in the extracted combustion gas.

  Focusing on chlorine, sulfur, alkali, etc., which causes problems such as blockage of preheaters in cement manufacturing facilities, from the bottom of the kiln of the cement kiln to the bottom cyclone A chlorine bypass system for extracting a part of combustion gas and removing chlorine from the kiln exhaust gas flow path is used.

  In this chlorine bypass system, for example, as described in Patent Document 1, after cooling the extracted combustion gas, dust in the extracted gas is separated into coarse powder and fine powder by a classifier, and the separated chlorine content ( This system recovers fine powder (chlorine bypass dust) containing a large amount of potassium chloride / KCl).

  However, in recent years, as the amount of lead brought into the cement kiln increases as the amount of waste processed increases, the recycling of waste from cement raw materials or fuel is promoted, and the amount of lead brought into the cement kiln increases. There is also a risk of exceeding.

  Therefore, Patent Document 2 proposes a cement kiln combustion gas extraction dust treatment system as shown in FIG. 2 in order to keep the lead concentration in the cement below the control reference value.

In this processing system 41, the extraction gas from the bottom of the kiln 42 of the cement kiln 42 is cooled by the cold air from the cooling fan 44 in the probe 43, and then introduced into the cyclone 45, and the separated fine powder and gas having a high chlorine content are wetted. In the scrubber 46, the slurry supplied from the circulating liquid tank 47 is cooled by moisture or the like to collect fine powder. At this time, SO ₂ in the extraction gas reacts with Ca (OH) ₂ in the slurry to be desulfurized, and gypsum is generated.

Further, sodium hydrosulfide (NaSH) is added to the wet scrubber 46 from the storage tank 52, and fine powders such as lead chloride and lead oxide contained in the extraction gas are sulfided and precipitated as sulfides, and discharged from the circulating liquid tank 47. The slurry is supplied to the flotation machine 57. Next, a flotation agent such as xanthate group (R—O—Ca ₂ Na) is supplied from the storage tank 54 to the flotation machine 57, a foaming agent is further supplied from the storage tank 58, and air is supplied. The slurry is separated into a floss containing lead and a tail side slurry containing gypsum.

  Next, the floss containing lead is supplied to the filter press 61, separated into a cake containing lead oxide and water, and the cake containing lead oxide is reused by reducing it to the mountain. On the other hand, the tail side slurry containing gypsum from the flotation machine 57 is solid-liquid separated in the solid-liquid separator 62 to collect the gypsum, and the separated salt water is added to the cement grinding step.

  On the other hand, Patent Document 3 discloses an extraction gas extracted from the kiln bottom of a cement kiln when processing dust contained in the kiln combustion gas while suppressing discharge of harmful heavy metals such as cadmium and lead out of the system. After cooling, dry dust is collected, water is added to the collected dust to form a slurry, and a pH adjuster is added so that the solubility of cadmium and lead contained in the slurry is minimized, and the pH of the slurry is adjusted to 2 degrees. In addition to recovering the precipitated cadmium and lead and reusing them as cement raw materials, etc., the water from which cadmium and lead have been removed is used as it is as sewage or ocean. Or recycled to the above processing system.

International Publication No. 97/21638 Pamphlet International Publication No. 06/035631 Pamphlet Japanese Patent No. 2764508

  However, in the processing system described in Patent Document 2, in order to recover heavy metals using a flotation machine, it is necessary to add a hydrophobizing agent or the like as a scavenger in addition to equipment costs. There was a problem of soaring.

  Moreover, in the processing system described in Patent Document 3, gypsum can be recovered together with cadmium and lead. However, since the recovered gypsum is accompanied by cadmium and lead, when added as it is to cement clinker, the lead of cement There was a risk of exceeding control standard values such as concentration. Also, heavy metals such as cadmium and lead could not be obtained with high purity and could not be reduced to Yamamoto.

  Therefore, the present invention has been made in view of the above problems in the prior art, and in processing cement kiln combustion gas extraction dust, recovered heavy metals and gypsum while keeping equipment costs and operation costs low. The purpose is to increase the purity of.

  In order to achieve the above object, the present invention provides a method for treating cement kiln combustion gas bleed dust, wherein a part of the combustion gas is cooled from the kiln exhaust gas flow path from the bottom of the cement kiln to the bottom cyclone. During the extraction, the dust contained in the extraction gas is wet-collected, and at the same time, sulfur oxides contained in the extraction gas are removed, and the heavy metal contained in the slurry generated by the wet dust collection and desulfurization is removed from the slurry. The pH of the slurry is adjusted so as to be dissolved in the liquid phase, the pH-adjusted slurry is subjected to solid-liquid separation, and heavy metals in the filtrate obtained by the solid-liquid separation are recovered.

  And according to the present invention, since heavy metals are dissolved in the liquid phase of the slurry produced by wet dust collection, gypsum and heavy metals contained in the solid phase of the slurry can be separated by solid-liquid separation, The purity of each can be increased. In addition, since heavy metals can be recovered without using a flotation process, it is not necessary to add a hydrophobizing agent or the like, and apparatus costs and drug costs can be greatly reduced.

  In the cement kiln combustion gas extraction dust treatment method, the pH of the slurry generated by the wet dust collection can be adjusted to 1 or more and 6 or less, thereby further reducing the heavy metal contained in the slurry after the wet dust collection. A large amount can be dissolved in the slurry, and the recovery rate of heavy metals can be increased.

  In the method for treating cement kiln combustion gas bleed dust, the heavy metal in the filtrate can be recovered by a sulfurization reaction or pH adjustment, or a combination of a sulfurization reaction and pH adjustment.

  In the cement kiln combustion gas extraction dust processing method, gypsum can be recovered from the slurry generated by the wet dust collection and desulfurization and added to the cement clinker. Since this gypsum has high purity, it can be used without worrying about an increase in the concentration of heavy metals in the cement.

  Furthermore, a salt can be recovered from the filtrate obtained by recovering the heavy metal and used as an industrial salt having a high potassium chloride purity.

  Moreover, in the processing method of the said cement kiln combustion gas extraction dust, chlorine removal efficiency can be improved by removing the coarse powder in the extraction gas before performing the said wet dust collection.

  Further, the present invention is a cement kiln combustion gas extraction dust processing apparatus for extracting air while cooling a part of the combustion gas from a kiln exhaust gas flow path from the bottom of the cement kiln to the bottom cyclone. And the dust contained in the bleed gas extracted by the bleeder is wet-collected, and at the same time, the sulfur oxide contained in the bleed gas is removed and contained in the slurry generated by the wet dust collection and desulfurization. A wet dust collector that adjusts the pH of the slurry so that heavy metal dissolves in the liquid phase of the slurry, a first solid-liquid separator that separates the slurry adjusted in pH by the wet dust collector, and the first Characterized in that it comprises: an adjustment tank for precipitating heavy metals in the filtrate separated by the solid-liquid separator; and a second solid-liquid separator for solid-liquid separation of the slurry supplied from the adjustment tank.

  According to the present invention, as described above, heavy metals contained in the slurry after wet dust collection can be separated on the liquid phase side, and gypsum can be separated on the solid phase side, and high-purity heavy metals and gypsum can be recovered. can do. Further, since heavy metals can be recovered without using a flotation machine, it is not necessary to add a hydrophobizing agent, and it is possible to significantly reduce apparatus costs and drug costs.

  In the cement kiln combustion gas extraction dust processing apparatus, a classification device for removing coarse powder in the extraction gas is provided between the extraction device and the wet dust collector, and fine powder and extraction gas separated by the classification device. Can be introduced into the wet dust collector. The coarse powder can be removed by the classifier, and the chlorine removal efficiency can be increased, and by preventing the coarse powder from being introduced into the wet dust collector, the equipment scale can be reduced, the life of the wet dust collector can be extended, and the pH can be increased. It is possible to reduce the amount of the regulator used.

  As described above, according to the present invention, it is possible to increase the purity of heavy metals and gypsum to be recovered while suppressing the facility cost and the operation cost when processing the cement kiln combustion gas extraction dust.

It is a flowchart which shows one Embodiment of the processing apparatus of the cement kiln combustion gas extraction dust concerning this invention. It is a flowchart which shows an example of the processing apparatus of the conventional cement kiln combustion gas extraction dust.

  Next, modes for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 shows an embodiment of a cement kiln combustion gas extraction dust processing apparatus according to the present invention. This processing apparatus 1 is roughly divided into a gas extraction unit 2, a gas processing unit 3, and a separation processing unit 4. It consists of.

  The gas extraction unit 2 is provided to extract a part of the combustion gas from the kiln exhaust gas passage from the kiln bottom 5a of the cement kiln 5 to the lowermost cyclone (not shown). The gas extraction unit 2 includes a probe 6 for extracting combustion gas, a cooling fan (not shown) for rapidly cooling the extracted combustion gas by supplying cold air into the probe 6, and an extraction gas G 1 discharged from the probe 6. A cyclone 7 as a classifier for separating the coarse powder D1 in the contained dust, and a fan 8 for supplying the gas G2 containing the fine powder D2 separated by the cyclone 7 to the scrubber 13 are configured.

  The gas processing unit 3 is provided to collect fine powder D2, sulfur oxides, and trace components such as heavy metals and organic components contained in the exhaust gas G2 discharged from the fan 8. The gas processing unit 3 is configured to remove the fine powder D2, the sulfur oxide, and the trace components such as heavy metals and organic components contained in the exhaust gas G2 by wet dust collection and removal, and the exhaust gas G3 of the wet dust collector 11 from the system. It consists of an exhaust fan 12 for discharging.

The wet dust collector 11 collects the fine powder D2 in the exhaust gas G2 and removes chlorine from the exhaust gas G2, and the sulfur content (SO ₂ ) in the exhaust gas G2 and quick lime (CaO) contained in the fine powder D2 react with water. The slaked lime (Ca (OH) ₂ ) generated in this manner and the slaked lime supplied to make up for the shortage of slaked lime generated from the fine powder D2 are reacted to produce gypsum (CaSO ₄ .2H ₂ O). The wet dust collector 11 includes a scrubber 13, a circulating liquid tank 14, and a cleaning tower 15, and a pump 14 a for circulating the slurry is provided between the scrubber 13 and the circulating liquid tank 14. The circulating liquid tank 14 is supplied with sulfuric acid to adjust the pH value of the circulating slurry to 1 to 6, the sulfuric acid storage tank 16 and the pump 16a, and lime milk for supplying lime milk to make up for the lack of slaked lime. A storage tank 17 and a pump 17a are provided.

  The separation processing unit 4 is provided to separate the liquid phase in the slurry S1 from the wet dust collector 11 into salt water and heavy metal such as lead and collect gypsum in the slurry S1. The separation processing unit 4 is a first tank that temporarily stores the slurry S1 from the wet dust collector 11, and the slurry S2 from the adjustment tank 20 is solid-liquid separated to recover the gypsum in the slurry S2 as the cake C1. Adjusting tank in which a solid-liquid separator 21 and a sulfur adjusting agent such as sodium hydrosulfide (NaSH) and / or a pH adjusting agent such as sodium hydroxide (NaOH) are added to the filtrate W1 from the first solid-liquid separator 21 22 and a second solid-liquid separator 23 that solid-liquid separates the slurry S3 after the addition of the sulfurizing agent, etc., and recovers cake C2 containing heavy metal and filtrate W2 as salt water. . For the first solid-liquid separator 21 and the second solid-liquid separator 23, any of the conventional existing technologies such as a filter press, a belt filter, a lamella separator, a microfilter, and a thickener can be used. These can be used in combination.

  Next, the operation of the processing apparatus 1 will be described with reference to FIG.

  A part of the combustion gas is extracted by the probe 6 from the kiln exhaust gas flow path from the kiln bottom 5a of the cement kiln 5 to the lowermost cyclone, and at the same time, the extracted combustion gas is cooled by the cold air from a cooling fan (not shown). Rapid cooling to 700 ° C. or lower, which is the melting point of the chlorine compound. Next, the extraction gas G1 from the probe 6 is separated into the coarse powder D1 and the exhaust gas G2 containing the fine powder D2 by the cyclone 7, and the coarse powder D1 is returned to the cement kiln system.

On the other hand, the exhaust gas G2 containing fine powder D2 is supplied to the scrubber 13 of the wet dust collector 11 via the fan 8, and the slurry S1 is circulated between the scrubber 13 and the circulating liquid tank 14. In the slurry S1 produced by the wet dust collector 11, slaked lime (Ca (OH) ₂ ) generated by the reaction of CaO in the fine powder D2 with water is present, and the sulfur content (SO ₂ ) present in the exhaust gas G2 is It reacts with slaked lime as follows.
SO ₂ + Ca (OH) ₂ → CaSO ₃ .1 / 2H ₂ O + 1 / 2H ₂ O
CaSO ₃ · 1 / 2H ₂ O + 1 / 2O ₂ + 3 / 2H ₂ O → CaSO ₄ · 2H ₂ O
Thereby, the sulfur content in the exhaust gas G2 is decomposed and gypsum (CaSO ₄ .2H ₂ O) is generated. Further, when the slaked lime in the slurry S1 is insufficient, slaked lime is appropriately added from the lime milk storage tank 17, and when the pH of the slurry S1 is higher than a predetermined value, sulfuric acid is appropriately added from the sulfuric acid storage tank 16. .

Here, although the pH of the slurry S1 varies depending on the sulfur content (SO ₂ ) contained in the exhaust gas G2 and the calcium content (CaO) brought in, the amount of slaked lime from the lime milk storage tank 17 and the amount of sulfuric acid from the sulfuric acid storage tank 16 are changed. Adjust the pH of the slurry S1 to 1-6. Table 1 shows the weight ratio of fine powder (D2) 1 dissolved in water 4 and adjusted with sulfuric acid while stirring for 30 minutes to pH 7.3 and pH 4.4. Indicates. As shown in Table 1, by lowering the pH, more heavy metals such as lead contained in the slurry S1 can be dissolved in the liquid phase in the slurry S1.

  Next, the slurry S1 is temporarily stored in the adjustment tank 20, and then solid-liquid separated by the first solid-liquid separator 21, the filtrate W1 is separated from the slurry S1, and the cake C1 (gypsum) is recovered. By adjusting the pH in the wet dust collector 11, heavy metal in the slurry S1 is dissolved in the filtrate W1, so the cake C1 contains almost no heavy metal. Thereby, the purity of the gypsum collected as the cake C1 can be increased.

  Next, in the adjustment tank 22, sodium hydrosulfide as a sulfiding agent is added to the filtrate W1 from the first solid-liquid separator 21, and lead chloride, lead oxide, etc. in the filtrate W1 are sulfided to lead sulfide. To produce heavy metal sulfides. Also, instead of the sulfurizing agent, an alkali source such as sodium hydroxide, slaked lime, or coarse powder D1 is added to adjust the pH of the filtrate W1 to a pH that reduces the solubility of each heavy metal, and the concentration of each heavy metal in the solution is adjusted. It may be lowered. Furthermore, by combining sulfurization and pH adjustment, or by adding an auxiliary agent such as iron chloride, the recovery efficiency can be increased, and therefore the number of adjustment tanks 22 can be increased.

  Table 2 shows that, by weight, the fine powder (D2) 1 is dissolved in water 4 and the pH is adjusted to pH 4.5 with sulfuric acid while stirring for 30 minutes. An equivalent amount of sodium hydrosulfide was added, and each heavy metal concentration in the filtrate was dissolved in water 4 with respect to fine powder (D2) 1 in a weight ratio, and the pH was adjusted to pH 4.5 with sulfuric acid while stirring for 30 minutes. After the adjustment, the pH is adjusted to 10.5 with sodium hydroxide, and the concentration of each heavy metal in the filtrate is shown. From the table, it can be seen that the addition of these promotes precipitation of heavy metals such as lead contained in the filtrate W1, and can reduce the concentration of heavy metals in the filtrate W1.

  Next, in the second solid-liquid separator 23, the slurry S3 from the adjustment tank 22 is subjected to solid-liquid separation, and the heavy metal precipitated in the slurry S3 is recovered as a cake C2. In addition, when solid-liquid-separating slurry S3, in order to improve filterability, you may add filter aids, such as a polymer flocculent, diatomaceous earth, and slaked lime. Table 3 shows the recovery rate of each heavy metal. That is, from the concentration of each heavy metal in the solution after filtration at pH 4.4 in Table 1 and the concentration in the solution after filtration when sodium hydrosulfide or sodium hydroxide in Table 2 was added, The recovery rate is calculated. According to the table, the recovery rate of each heavy metal is extremely high, and the filtrate W2 separated by the second solid-liquid separator 23 contains almost no heavy metal. After recovering the salt, it can be drained and discharged.

  As described above, according to the present embodiment, the purity of the recovered gypsum and heavy metal can be increased by solid-liquid separation after dissolving the heavy metal in the liquid phase of the slurry S1 generated by the wet dust collector 11. . In addition, since the flotation process is not used when recovering the heavy metal, it is not necessary to add a hydrophobizing agent as a collecting agent, and the equipment cost and the drug cost can be greatly reduced.

  In the above embodiment, after separating the coarse powder D1 with the cyclone 7, the exhaust gas G2 containing the fine powder D2 is introduced into the wet dust collector 11. However, the extraction gas G1 extracted by the probe 6 without providing the cyclone 7 is used. May be introduced directly into the wet dust collector 11.

DESCRIPTION OF SYMBOLS 1 Cement kiln combustion gas extraction dust processing device 2 Gas extraction unit 3 Gas processing unit 4 Separation processing unit 5 Cement kiln 5a Kiln bottom 6 Probe 7 Cyclone 8 Fan 11 Wet dust collector 12 Exhaust fan 13 Scrubber 14 Circulating fluid tank 14a Pump 15 Cleaning Tower 16 Sulfuric acid storage tank 16a Pump 17 Lime milk storage tank 17a Pump 20 Adjustment tank 21 First solid-liquid separator 22 Adjustment tank 23 Second solid-liquid separator G1 Extraction gas G2 Exhaust gas G3 Exhaust gas D1 Coarse powder D2 Fine powder S1 to S3 Slurry C1, C2 Cake W1, W2 Filtrate

Claims (8)

Extracting while cooling a part of the combustion gas from the kiln exhaust gas flow path from the bottom of the kiln of the cement kiln to the bottom cyclone,
Wet-collecting dust contained in the extraction gas, and at the same time, removing sulfur oxides contained in the extraction gas;
Adjusting the pH of the slurry so that heavy metals contained in the slurry produced by the wet dust collection and desulfurization are dissolved in the liquid phase of the slurry;
Solid-liquid separation of the pH adjusted slurry,
A method for treating cement kiln combustion gas bleed dust, comprising recovering heavy metals in the filtrate obtained by the solid-liquid separation.   The method for treating cement kiln combustion gas bleed dust according to claim 1, wherein the pH of the slurry produced by the wet dust collection is adjusted to 1 or more and 6 or less.   The method for treating cement kiln combustion gas bleed dust according to claim 1 or 2, wherein the recovery of heavy metals in the filtrate is performed through a sulfurization reaction or / and pH adjustment.   4. The method for treating cement kiln combustion gas extraction dust according to claim 1, 2 or 3, wherein gypsum is recovered from the slurry generated by the wet dust collection and desulfurization and added to the cement clinker.   The method for treating cement kiln combustion gas bleed dust according to any one of claims 1 to 4, wherein salt is recovered from the filtrate obtained by recovering the heavy metal.   4. The method for treating cement kiln combustion gas extraction dust according to claim 1, wherein coarse powder in the extraction gas is removed before the wet dust collection. 5. A bleeder that bleeds while cooling part of the combustion gas from the kiln exhaust gas flow path from the bottom of the kiln of the cement kiln to the bottom cyclone,
The dust contained in the bleed gas extracted by the bleeder is wet-collected, and at the same time, sulfur oxides contained in the bleed gas are removed, and the heavy metal contained in the slurry generated by the wet dust-collecting and desulfurization is A wet dust collector that adjusts the pH of the slurry to dissolve in the liquid phase of the slurry;
A first solid-liquid separator for solid-liquid separation of the slurry adjusted in pH by the wet dust collector;
An adjustment tank for precipitating heavy metals in the filtrate separated by the first solid-liquid separator;
A cement kiln combustion gas bleed dust treatment apparatus, comprising: a second solid-liquid separator that solid-liquid separates the slurry supplied from the adjustment tank.   A classification device for removing coarse powder in the extraction gas is provided between the extraction device and the wet dust collector, and fine powder and extraction gas separated by the classification device are introduced into the wet dust collector. The processing apparatus of the cement kiln combustion gas extraction dust of Claim 7.

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