JP2010195615A - System and method for treating cement kiln extraction gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently remove organic contaminants such as dioxins included in a cement kiln extraction gas. <P>SOLUTION: The system 1 for treating a cement kiln extraction gas includes: a probe 5 extracting a part of a combustion gas from a kiln exhaust gas channel from an inlet of a cement kiln 4 to the lowermost stage cyclone of a preheater; a wet dust collector 10 subjecting dust included in the extracted gas G1 extracted by the probe 5 to wet dust collection; a solid-liquid separator 17 subjecting slurry generated in the wet dust collector 10 to solid-liquid separation; a first removing means 18 removing organic contaminants from a cake C separated by the solid-liquid separator 17; and a second removing means 19 removing organic contaminants from a filtrate W of the solid-liquid separator 17. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a processing system and a processing method for a cement kiln extraction gas, and in particular, organic pollutants contained in the extraction gas extracted from the kiln exhaust gas passage from the bottom of the cement kiln to the bottom cyclone of the preheater. The present invention relates to a processing system for removal.

  Focusing on chlorine, sulfur, alkali, etc., which causes problems such as clogging of preheaters in cement manufacturing facilities, focusing on the problem of chlorine, from the kiln bottom of the cement kiln to the bottom cyclone of the preheater Chlorine bypass systems are used to extract chlorine from a part of the kiln exhaust gas flow path and remove chlorine.

  In this chlorine bypass system, 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 combustion gas, the dust is separated into coarse powder and fine powder by a classifier. In addition to returning the coarse powder to the cement kiln system, fine powder (chlorine bypass dust) containing the separated potassium chloride and the like is recovered.

  As described above, in the chlorine bypass system, dust containing chlorine is separated and recovered from the extracted combustion gas, but dioxins (PCDD, PCDF, co-PCB) are used as the extracted gas after separating the dust. Persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs) and volatile organic pollutants (VOC) may be included, and these need to be treated appropriately.

International Publication No. 97/21638 Pamphlet

  As one of the methods for removing organic pollutants such as POPs and VOCs, a method of decomposing using a catalyst is known. Even in a chlorine bypass system, by providing a catalyst device on the exhaust path, chlorine bypass exhaust is provided. It is conceivable to remove organic pollutants from water.

  However, a large amount of acidic gas derived from sulfur oxide (SOx) is present in the chlorine bypass exhaust, which poisons the catalyst and lowers the catalytic activity. Therefore, the catalyst device is simply installed on the exhaust passage. Therefore, practical application is difficult. In addition, if the recycling of wastes into cement raw materials or fuels continues to increase in the future, there is a concern that the content of POPs and VOC components in the chlorine bypass exhaust will increase, so organic pollutants can be removed more efficiently Is expected.

  Accordingly, the present invention has been made in view of the above-described problems in the prior art, and is a cement kiln extraction gas processing system capable of efficiently removing organic pollutants contained in the cement kiln extraction gas. The purpose is to provide.

  As a result of intensive research to achieve the above object, the present inventor has found that most of the organic pollutants contained in the extraction gas are wet when the dust contained in the cement kiln extraction gas is wet-collected by a wet dust collector. It was found that it is unevenly distributed on the slurry side produced by the dust collector.

  The present invention has been made based on such knowledge, and is a cement kiln extraction gas processing system, in which a combustion gas is supplied from a kiln exhaust gas passage from a kiln bottom of a cement kiln to a lowermost cyclone of a preheater. An extraction means for extracting a part, a wet dust collector for wet collecting dust contained in the extraction gas extracted by the extraction means, and a removal means for removing organic pollutants from the slurry generated by the wet dust collector Features.

  Here, organic pollutants refer to residual organic pollutants (POPs) such as dioxins (PCDD, PCDF, co-PCB), polychlorinated biphenyls (PCBs), and volatile organic pollutants (VOC).

  According to the present invention, after the dust contained in the extraction gas extracted from the kiln exhaust gas passage is wet-collected, the organic pollutant removal process is performed on the slurry discharged from the wet dust collector. It becomes possible to efficiently remove organic pollutants in the gas.

  The reason why most of the organic pollutants in the extraction gas are unevenly distributed in the slurry generated by the wet dust collection is not necessarily clear, but in the wet dust collector, the temperature of the extraction gas when the extraction gas is brought into contact with moisture. As a result, the organic pollutant in the extracted gas becomes solid and is separated from the gas (gas), and as a result, it is presumed that it may be taken into the slurry.

  The cement kiln extraction gas processing system includes a solid-liquid separator for solid-liquid separation of the slurry, and the removing means can remove organic contaminants from the cake separated by the solid-liquid separator. According to this, organic pollutants contained in the slurry of the wet dust collector can be efficiently removed.

  The cement kiln bleed gas processing system may include a second removing means for removing organic contaminants from the filtrate of the solid-liquid separator. According to this, organic contaminants remaining in the filtrate can be removed, and further safety measures can be taken.

  In the cement kiln bleed gas processing system, a flotation machine that floats organic contaminants contained in the slurry and separates organic pollutants from the slurry is provided, and the removing means removes organic pollutants from the floss of the flotation machine. Contaminants can be removed. According to this, organic pollutants contained in the slurry of the wet dust collector can be efficiently removed.

  In the cement kiln extraction gas processing system, the wet dust collector can cool the extraction gas so that the temperature of the exhaust gas of the wet dust collector is 30 ° C. or more and less than 100 ° C. When the temperature of the exhaust gas is lower than 30 ° C., the condensed water increases. As a result, the amount of water taken out to the subsequent process increases, and devices such as ducts and fans in the subsequent process may be corroded. Furthermore, the amount of new water required for the system will be increased. On the other hand, when the temperature of the exhaust gas is 100 ° C. or higher, there is a possibility that organic pollutants cannot be properly collected.

  In the cement kiln extraction gas processing system, the removal means can remove the organic pollutant by a low-temperature reductive thermal decomposition method, an oxidizing atmosphere low-temperature heating method, a chemical decomposition method, or a solvent extraction method.

  Further, the present invention extracts a part of the combustion gas from the kiln exhaust gas passage from the bottom of the kiln of the cement kiln to the lowermost cyclone of the preheater, and wet-collects dust contained in the extracted extraction gas. The organic pollutants are removed from the slurry produced by the wet dust collection. According to the present invention, it is possible to efficiently remove organic pollutants contained in the extraction gas, as in the above-described invention.

  As described above, according to the present invention, it is possible to efficiently remove organic pollutants contained in a cement kiln extraction gas.

It is a block diagram which shows 1st Embodiment of the processing system of the cement kiln extraction gas concerning this invention. It is a block diagram which shows 2nd Embodiment of the processing system of the cement kiln extraction gas concerning this invention.

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

  FIG. 1 shows a first embodiment of a cement kiln extraction gas processing system according to the present invention. The processing system 1 is roughly composed of a gas extraction unit 2 and a gas processing unit 3.

  The gas extraction unit 2 is equipment for extracting a part of the combustion gas from the kiln exhaust gas flow path from the bottom of the cement kiln 4 to the lowermost cyclone (not shown) of the preheater. The gas extraction unit 2 separates a probe 5 for extracting combustion gas, a cooling fan 6 for supplying cold air into the probe 5 to rapidly cool the extraction gas G1, and coarse dust D1 contained in the extraction gas G1. It consists of cyclone 7 etc. as a classifier.

  The gas processing unit 3 uses the wet dust collector 10 that wet-collects the fine powder D2 contained in the exhaust gas G2 of the cyclone 7, the exhaust fan 16 that attracts the exhaust gas G3 of the wet dust collector 10, and the slurry S generated by the wet dust collector 10. The solid-liquid separator 17 for solid-liquid separation, the first removing means 18 for removing organic contaminants from the cake C separated by the solid-liquid separator 17, and the organic contaminants from the filtrate W of the solid-liquid separator 17 And a second removing means 19 for removing.

  The wet dust collector 10 collects water-soluble components and dust contained in the exhaust gas G2, and also includes residual organic pollutants (POPs) such as dioxins (PCDD, PCDF, co-PCB), polychlorinated biphenyls (PCBs), Provided to collect organic pollutants such as volatile organic pollutants (VOC).

  The wet dust collector 10 includes a mixing scrubber 11, a circulating liquid tank 12 and a cleaning tower 13, and a pump 12 a for circulating the slurry S is provided between the mixing scrubber 11 and the circulating liquid tank 12. Moreover, the slaked lime slurry storage tank 14 which supplies slaked lime slurry, and the pump 14a are connected to the slurry circulation path 12b for the purpose of supplementing slaked lime. Furthermore, the circulating liquid tank 12 is provided with a sulfuric acid storage tank 15 and a pump 15a for supplying sulfuric acid to adjust the pH value of the circulating slurry S to 4 to 8 in case slaked lime becomes excessive.

  The solid-liquid separator 17 is provided to take out organic contaminants in the slurry S by separating the solid phase (cake C) from the slurry S discharged from the wet dust collector 10.

  The first removing means 18 is provided for removing organic contaminants contained in the cake C separated by the solid-liquid separator 17. As a method for removing organic contaminants in the cake C, various treatment methods such as a low-temperature reductive thermal decomposition method, an oxidizing atmosphere low-temperature heating method, a chemical decomposition method, and a solvent extraction method can be used.

  The second removing means 19 is provided for removing organic contaminants remaining in the filtrate W of the solid-liquid separator 17. As a method for removing organic pollutants in the filtrate W, in addition to the above-mentioned low-temperature reductive pyrolysis method, oxidizing atmosphere low-temperature heating method, chemical decomposition method and solvent extraction method, accelerated oxidation treatment method (deodorization, COD treatment), Adsorption removal using an adsorbent and decomposition treatment with a catalyst can be used.

  If the filtration efficiency in the solid-liquid separator 17 is strictly controlled and the solid phase in the slurry S can be completely separated, organic contaminants will not remain in the filtrate W. The second removing means 19 can be omitted.

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

  From the kiln exhaust gas flow path from the kiln bottom of the cement kiln 4 to the lowermost cyclone, a part of the combustion gas is extracted by the probe 5 and at the same time, the melting point of the chlorine compound is 600 to 700 by the cold air from the cooling fan 6. Rapidly cool to below ℃. Next, in the cyclone 7, the extracted gas G1 exhausted from the probe 5 is separated into the coarse powder D1 and the exhaust gas G2 containing the fine powder D2, and the coarse powder D1 is returned to the cement kiln system while being 100 to 600 ° C. The exhaust gas G2 is introduced into the mixing scrubber 11 of the wet dust collector 10.

In the wet dust collector 10, the slurry S is circulated between the mixing scrubber 11 and the circulating liquid tank 12. In the slurry S produced by the wet dust collector 10, there is slaked lime (Ca (OH) ₂ ) generated by the reaction of quick lime (CaO) in the fine powder D2 with water, so that the sulfur content present in the exhaust gas G2 ( SO ₂ ) reacts 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 slaked lime is insufficient, slaked lime is appropriately added from the slaked lime slurry storage tank 14. Furthermore, when slaked lime becomes excessive and becomes higher than a predetermined pH, sulfuric acid from the sulfuric acid storage tank 15 is appropriately added.

  At the same time, organic pollutants such as POPs and VOC are collected from the exhaust gas G2 and moved to the slurry S side. The reason why most of the organic contaminants in the exhaust gas G2 move to the slurry S during the wet dust collection process is not necessarily clear, but when the exhaust gas G2 is brought into contact with moisture in the wet dust collector 10, the exhaust gas G2 As a result, the organic pollutant in the exhaust gas G2 becomes solid and separates from the gas (gas), and as a result, it is presumed that this is because it is taken into the slurry S.

  In this case, in order to efficiently collect organic pollutants contained in the exhaust gas G2, the temperature of the exhaust gas G3 (gas discharged from the cleaning tower 13) of the wet dust collector 10 is 30 ° C. or more and less than 100 ° C. It is preferable to adjust the temperature. When the temperature of the exhaust gas G3 is less than 30 ° C., the condensed water increases. As a result, the water taken out to the subsequent process increases, and there is a possibility that the devices such as ducts and fans in the subsequent process are corroded. Furthermore, the amount of new water required for this system will be increased. On the other hand, when the temperature of the exhaust gas G3 is 100 ° C. or higher, there is a possibility that organic pollutants cannot be properly collected.

  The exhaust gas (clean gas) G3 after removing the dust is attracted by the exhaust fan 16 and released to the atmosphere, or used in other cement manufacturing processes. For further safety, the organic pollutant remaining in the exhaust gas G3 may be removed by performing an adsorption process or a decomposition process using a catalyst, or the exhaust gas G3 is returned to the cement kiln 4 or the like for organic contamination. The substance may be completely burned.

  On the other hand, the slurry S containing gypsum, dust and organic pollutants is introduced into the solid-liquid separator 17 and separated into a solid phase (cake C) and a liquid phase (filtrate W). Next, the cake C and the filtrate W are introduced into the first and second removing means 18 and 19, and the first removing means 18 removes organic contaminants contained in the cake C and the second removing means. At 19, the organic contaminants remaining in the filtrate W are removed.

  Cake C (gypsum) after removing organic pollutants can be added to a cement mill and pulverized with a clinker to be used as a part of cement. On the other hand, the filtrate W from which organic pollutants have been removed is separately subjected to advanced wastewater treatment to recover the salinity (KCl), which is then recycled in the present system 1 or discharged into sewage or the ocean.

  As described above, according to the present embodiment, after the exhaust gas G2 of the cyclone 7 is wet-collected by the wet dust collector 10, the organic contaminants in the extraction gas G1 are removed because the organic pollutant is removed from the slurry S. It becomes possible to remove pollutants efficiently.

  In the above embodiment, after the coarse powder D1 is classified by the cyclone 7, the exhaust gas G2 containing the fine powder D2 is introduced into the wet dust collector 10, but the extraction gas G1 extracted by the probe 5 without providing the cyclone 7 is used. May be introduced directly into the wet dust collector 10. Moreover, you may adjust the collection | recovery efficiency in a cyclone, and may change the quantity ratio of the coarse powder D1 collect | recovered and the fine powder D2 introduce | transduced into the wet dust collector 10. FIG.

  Next, a second embodiment of the cement kiln extraction gas processing system according to the present invention will be described with reference to FIG. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  The gas processing unit 21 includes a wet dust collector 10, an exhaust fan 16, a flotation machine 22 that attaches organic pollutants contained in the slurry S generated by the wet dust collector 10 to air bubbles, and floats and separates them. A first solid-liquid separator 23 for solid-liquid separation of the froth F from the machine 22; a first removal means 24 for removing organic contaminants from the cake C1 separated by the first solid-liquid separator 23; A second removal means 25 for removing organic pollutants from the filtrate W1 of the first solid-liquid separator 23, and a second solid-liquid separator 26 for solid-liquid separation of the tail T from the flotation machine 22. .

  Next, the operation of the processing system 20 will be described with reference to FIG.

  The slurry S containing the organic pollutant discharged from the wet dust collector 10 is supplied to the flotation machine 22, and in the flotation machine 22, a hydrophobic material as a scavenger is added to the slurry S and air is supplied. Generate bubbles. Since the organic pollutant has lipophilicity, it adheres to the air bubbles and floats, so that the organic pollutant can be taken out by collecting the floss F. At this time, gypsum contained in the slurry S is discharged from the flotation machine 22 as a tail T. In addition, after adding adsorbents, such as activated carbon, to the slurry S, you may perform the same operation (flotation process).

  Next, in the first solid-liquid separator 23, the floss F from the flotation machine 22 is subjected to solid-liquid separation, and separated into a solid phase (cake C1) and a liquid phase (filtrate W1). Next, as in the first embodiment, the cake C1 and the filtrate W1 are introduced into the first and second removing means 24 and 25, and the organic contaminants contained in the cake C1 are removed by the first removing means 24. At the same time, the second removing means 25 removes organic contaminants remaining in the filtrate W1.

  On the other hand, the tail T discharged from the flotation machine 22 is solid-liquid separated by the second solid-liquid separator 26, and the gypsum content (C2) is recovered. The filtrate W2 discharged from the second solid-liquid separator 26 is treated with water and then recycled in the system 20 or discharged into sewage or the like.

  As described above, also in the present embodiment, since the organic contaminant removal process is performed on the slurry S of the wet dust collector 10, the organic contaminant contained in the extraction gas G1 can be efficiently removed. Become.

  In the present embodiment, since the first solid-liquid separator 23 separates the gypsum and the like in the slurry S by the flotation machine 22, the first and second removing means 24, 25, the cake C1 and the filtrate W1 can be introduced in a state where the content of substances other than organic pollutants is reduced. For this reason, it becomes easy to remove organic pollutants in the first and second removing means 24 and 25, and organic pollutants can be removed more efficiently.

  In the above-described embodiment, the flotation device 22 is provided immediately after the circulating liquid tank 12 of the wet dust collector 10, but in order to remove heavy metals such as a lead compound, a selenium compound, and a thallium compound contained in the extraction gas G1. In addition, between the circulating liquid tank 12 and the flotation machine 22, an adjustment tank for adding a sulfiding agent for sulfiding a lead compound or the like to the slurry S, or a pH adjustment of sulfuric acid or the like to the slurry S after adding the sulfiding agent You may make it provide the adjustment tank for adding an agent.

DESCRIPTION OF SYMBOLS 1 Cement kiln extraction gas processing system 2 Gas extraction part 3 Gas processing part 4 Cement kiln 5 Probe 6 Cooling fan 7 Cyclone 10 Wet dust collector 11 Mixing scrubber 12 Circulating liquid tank 12a Pump 12b Circulating path 13 Cleaning tower 14 Slaked lime slurry storage tank 14a Pump DESCRIPTION OF SYMBOLS 15 Sulfuric acid storage tank 15a Pump 16 Exhaust fan 17 Solid-liquid separator 18 1st removal means 19 2nd removal means 20 Cement kiln extraction gas processing system 21 Gas processing part 22 Flotation machine 23 1st solid-liquid separator 24 First removing means 25 Second removing means 26 Second solid-liquid separator

Claims (7)

An extraction means for extracting 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 lowermost cyclone of the preheater;
A wet dust collector that wet-collects dust contained in the extraction gas extracted by the extraction means;
A cement kiln bleed gas treatment system, comprising: removal means for removing organic contaminants from the slurry generated by the wet dust collector. Comprising a solid-liquid separator for solid-liquid separation of the slurry;
2. The cement kiln bleed gas processing system according to claim 1, wherein the removing means removes organic pollutants from the cake separated by the solid-liquid separator.   The cement kiln bleed gas treatment system according to claim 2, further comprising second removal means for removing organic contaminants from the filtrate of the solid-liquid separator. Comprising a flotation machine for levitating organic pollutants contained in the slurry and separating the organic pollutants from the slurry;
The cement kiln extraction gas processing system according to claim 1, wherein the removing means removes organic pollutants from the floss of the flotation machine.   The cement kiln extraction gas according to any one of claims 1 to 4, wherein the wet dust collector cools the extraction gas so that the temperature of exhaust gas from the wet dust collector is 30 ° C or higher and lower than 100 ° C. Processing system.   The cement according to any one of claims 1 to 5, wherein the removing means removes the organic pollutant by a low temperature reduction pyrolysis method, an oxidizing atmosphere low temperature heating method, a chemical decomposition method, or a solvent extraction method. Extraction gas processing system. Part of the combustion gas is extracted from the kiln exhaust gas passage from the kiln bottom of the cement kiln to the lowermost cyclone of the preheater,
Wet-collecting dust contained in the extracted gas,
A method for treating a cement kiln bleed gas, comprising removing organic pollutants from a slurry generated by the wet dust collection.

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