JP4781005B2 - Wet dust collector wastewater treatment method - Google Patents

Description

The present invention relates to a method of treating a liquid to be discharged from the wet dust collector for use in a combustion exhaust gas treatment instrumentation 置等 for processing municipal waste incinerators, the flue gas, such as cement burning facility.

  In addition to SOx, NOx, etc., trace amounts of highly toxic residual organic pollutants are contained in the combustion exhaust gas from incinerators that incinerate municipal waste. Various techniques have been proposed to remove this residual organic pollutant. However, if an adsorbent such as activated carbon is used to remove the residual organic pollutant, the activated carbon adsorbing the residual organic pollutant is discharged as waste, so that it is necessary to dispose of the used activated carbon. Also, municipal waste incinerators and the like use a denitration agent in order to reduce NOx, but there is a problem that the operation cost increases when the amount of the denitration agent is large.

  In recent years, in response to requests for the utilization of recycled resources, various recycling resources have been put into raw materials and firing systems in cement firing facilities. Like waste incinerators, etc., there are concerns about increased emissions of hazardous substances and increased operating costs. In particular, the amount of combustion exhaust gas generated in the cement firing equipment is large, so even if the amount of harmful substances contained in the combustion exhaust gas is very small, the equipment for removing harmful substances becomes large-scale, and the equipment costs and operating costs May increase.

  Therefore, in the patent document 1, the present applicant can apply to municipal waste incinerators, cement kilns, etc., and does not need to dispose of used activated carbon, and can reduce the equipment cost and operation cost. An exhaust gas treatment device and a treatment method were proposed.

  As shown in FIG. 2, the combustion exhaust gas treatment device 31 includes an electrostatic precipitator 32 disposed in a subsequent stage of the cement burning facility 51, a wet dust collector 33 that collects water-soluble components and dust in the combustion exhaust gas, A heater 37, a catalyst tower 38 that decomposes and removes NOx and the like, a heat recovery device 39, a solid-liquid separator 42 that solid-liquid separates the slurry discharged from the wet dust collector 33, and a solid-liquid separator 42 It comprises a mercury adsorption tower 43 that adsorbs mercury in the separated liquid, a wastewater treatment facility 44 that treats the liquid from which mercury has been removed, and the like.

  In the combustion exhaust gas treatment device 31, the combustion exhaust gas G from the cement kiln 52 is brought to the electric dust collector 32, and most of the dust in the combustion exhaust gas G is collected and then introduced into the wet dust collector 33. Here, water-soluble components and residual dust in the combustion exhaust gas G are collected, and dust, mercury (Hg), and the like that greatly affect the life of the subsequent catalyst tower are removed.

  The slurry generated in the wet dust collector 33 circulates through the circulating liquid tank 35 and the pump 36, and the combustion exhaust gas G and the liquid are sufficiently brought into contact with each other, and sodium hypochlorite supplied from the oxidizer addition device 45. Oxidation of mercury, etc., and water-soluble components and dust are recovered.

The combustion exhaust gas G from which water-soluble components, dust and the like are removed is introduced from the mist separator 34 into the reheater 37 and heated, and then introduced into the catalyst tower 38. Ammonia (NH ₃ ) as a denitration agent used in the catalyst tower 38 is injected into the inlet side of the reheater 37. In the combustion exhaust gas G, NOx and residual organic pollutants are decomposed in the catalyst tower 38. The combustion exhaust gas G from the catalyst tower 38 is released to the atmosphere through the heat recovery device 39, the fan 40 and the chimney 41.

On the other hand, the slurry S discharged from the circulating liquid tank 35 is subjected to solid-liquid separation by the solid-liquid separator 42, and mercury in the separated liquid is dissolved in water as chloro complex ions (HgCl ₄ ²⁻ ). Is adsorbed by the mercury adsorption tower 43 and then processed outside the system. The liquid from which mercury has been removed is processed by the wastewater treatment equipment 44 and can be reused by the wet dust collector 33 or can be used for cooling the combustion exhaust gas G of the cement kiln 52.

  In addition to the above documents, Patent Document 2 discloses that water to be treated after being treated by an electrochemical method is treated with hypochlorous acid, in order to efficiently treat nitrogen compounds and to reduce the size of the apparatus. Alternatively, a nitrogen treatment apparatus including post-treatment means for performing denitrification treatment by a chemical method using ozone or active oxygen is described.

  Also in Patent Document 3, in order to efficiently treat nitrogen compounds, water to be treated that has been treated in the ammonia removal treatment is denitrified by a chemical method using hypochlorous acid, ozone, or active oxygen. A method is disclosed.

WO2005 / 005025 Publication JP 2003-190958 A JP 2003-164877 A

  In the combustion exhaust gas treatment apparatus and treatment method described in Patent Document 1, the wet dust collector 33 also has an action of condensing and collecting moisture in the combustion exhaust gas G. For this reason, it has been found that the wastewater from the wastewater treatment facility 44 after removing mercury exceeds the amount of water that can be used for reducing the temperature and humidity of the cement kiln exhaust gas, for example. Therefore, a method for treating this surplus water has been demanded.

In addition to the above, after oxidizing mercury or the like, the oxidized mercury or the like is absorbed by the wet dust collector. Therefore, when ozone is added to the circulating water of the wet dust collector 33, NO in the exhaust gas is oxidized and NO. _2, and there is also a problem that causes rather increase the odor.

  Therefore, the present invention has been made in view of the above-described problems in the prior art, and an object of the present invention is to minimize drainage outside the system when processing combustion exhaust gas. Another object of the present invention is to efficiently reduce NOx and the like in exhaust gas.

In order to achieve the above-mentioned object, the present invention is a wet dust collector wastewater treatment method, in which a slurry discharged from a wet dust collector that collects water-soluble components and dust in combustion exhaust gas is solid-liquid separated, and the separated liquid While adsorbing mercury in the solution, the trace dissolved component in the separated liquid is decomposed by an ozone catalyst tower, and at least a part of the liquid after adsorption of the mercury and after decomposition of the trace dissolved component is drained out of the system. The sodium chloride produced from the liquid after the mercury adsorption and the decomposition of the trace dissolved component is used for the production of sodium hypochlorite added to the circulating water of the wet dust collector .

And according to this invention, sodium chloride in waste_water | drain can be used effectively, releasing the liquid after adsorption | suction of mercury and the decomposition | disassembly of the said trace dissolved component out of the system as waste_water | drain. In particular, by using manganese dioxide as a catalyst to decompose the trace dissolved components in an ozone catalyst tower, residual organic pollutants (POPs) such as NOx, dioxins (DXNs) and polychlorinated biphenyls (PCB) are used. , Volatile organic compounds (VOC), odorous substances and the like can be decomposed into N ₂ , CO ₂ , water and the like.

  Moreover, calcium hydroxide or calcium oxide can be supplied to the slurry circulated by the wet dust collector to convert the sulfuric acid mist into gypsum.

  As described above, according to the present invention, when processing combustion exhaust gas, waste water to the outside of the system can be minimized, and NOx and the like in the exhaust gas can be efficiently reduced.

FIG. 1 shows an example of a flue gas treatment apparatus for carrying out a wet dust collector wastewater treatment method according to the present invention. The flue gas treatment apparatus 1 is an electric dust collector disposed at a subsequent stage of a cement firing facility (not shown). The wet dust collector 2 that collects water-soluble components and dust in the combustion exhaust gas G discharged from the waste gas, the mist separator 3, the circulating liquid tank 4, the pump 5, and the slurry S discharged from the circulating liquid tank 4 The settling device 6 for settling and removing the contained sludge SL1, the filtration filter 7 for solid-liquid separation of the slurry S discharged from the settling device 6 to discharge the sludge SL2, and the liquid discharged from the filtration filter 7 A mercury adsorption tower 8 that adsorbs mercury, an ozone catalyst tower 9 that decomposes trace dissolved components in the liquid, an ozone generator 10 that generates ozone to be supplied to the ozone catalyst tower 9, A circulation route 11 for returning the waste water W of the Zon catalyst tower 9 to the wet dust collector 2 and a salt disposed in the circulation route 11 for concentrating the salt in the waste water W and supplying it to the electrolytic sodium hypochlorite generator 13 It is comprised with the salt concentration film | membrane 12 and the electrolytic-type sodium hypochlorite production | generation apparatus 13 which generate | occur | produces the sodium hypochlorite added to the combustion exhaust gas G introduce | transduced into the wet dust collector 2. FIG.

  The wet dust collector 2 is provided to collect water-soluble components and dust in the combustion exhaust gas G, and has a great influence on the life of a catalyst tower (not shown) in the subsequent stage, such as dust, sulfuric acid mist, hydrogen chloride (HCl), mercury ( Hg) and the like are removed. For this wet dust collector 2, for example, a mixing scrubber (such as a muscrubber manufactured by Mu Company Limited) can be used.

  A circulating liquid tank 4 is provided below the wet dust collector 2, and a pump 5 for returning a part of the dust collection dust slurry in the circulating liquid tank 4 to the wet dust collector 2 is disposed. A mist separator 3 is disposed on the downstream side of the circulating liquid tank 4.

  The settling device 6 is provided for settling and removing the sludge SL1 contained in the slurry S discharged from the circulating liquid tank 4 of the wet dust collector 2. Further, the filtration filter 7 solid-liquid separates the slurry S discharged from the settling device 6.

  The mercury adsorption tower 8 adsorbs mercury in the liquid introduced through the settling device 6 and the filtration filter 7.

The ozone generated in the ozone generator 10 is supplied to the ozone catalyst tower 9 and, under the manganese dioxide catalyst, residual organic pollutants (POPs) such as NOx, dioxins (DXNs) and polychlorinated biphenyls (PCB) are provided. ), Volatile organic compounds (VOC), odorous substances and the like are decomposed and removed into N ₂ , CO ₂ , water and the like.

  The circulation route 11 is provided for returning the waste water W from the ozone catalyst tower 9 to the wet dust collector 2 through the salt concentration film 12. Further, the circulation route 11 is provided with a route for discharging the waste water W outside the system. A salt concentration membrane 12 is provided on the circulation route 11, and sodium chloride (NaCl) in the waste water W can be concentrated and used in the electrolytic sodium hypochlorite generator 13. The salt concentration membrane 12 can also eliminate scale components (Ca, Mg, etc.) that affect the electrolytic sodium hypochlorite generator 13.

The electrolytic sodium hypochlorite generator 13 is provided for adding sodium hypochlorite (NaClO) as an oxidizing agent for oxidizing mercury or the like contained in the combustion exhaust gas G. This sodium hypochlorite is added to the circulating slurry of the wet dust collector 2. The electrolytic sodium hypochlorite generator 13 can not only generate sodium hypochlorite but also decompose nitrate nitrogen contained in the circulating slurry into N ₂ .

The catalyst tower (not shown) is configured in, for example, a honeycomb shape in order to decompose and remove NOx and residual organic pollutants in the combustion exhaust gas G using NH ₃ or the like.

  Next, the operation of the flue gas treatment apparatus 1 having the above configuration will be described with reference to FIG. In the following description, a case where a combustion exhaust gas from a cement kiln is treated will be described as an example.

  Combustion exhaust gas G from a cement kiln (not shown) is brought to an electric dust collector (not shown), and dust in the combustion exhaust gas G is collected and then introduced into the wet dust collector 2. The wet dust collector 2 collects water-soluble components and dust in the combustion exhaust gas G, and removes dust, mercury (Hg), and the like that have a great influence on the life of the subsequent catalyst tower.

Since the slurry generated in the wet dust collector 2 is circulated through the circulating liquid tank 4 and the pump 5, the combustion exhaust gas G and the liquid are sufficiently brought into contact with each other and supplied from the electrolytic sodium hypochlorite generator 13. Further, oxidation of mercury or the like with sodium hypochlorite or the like, and recovery of water-soluble components and dust can be efficiently performed. The sulfuric acid mist can be converted to gypsum by CaO contained in the dust introduced into the wet dust collector 2, but when the amount of CaO is insufficient, calcium hydroxide (Ca (OH ₂ ) or calcium oxide (CaO) is supplied. The combustion exhaust gas G from which water-soluble components, dust and the like have been removed is guided from a mist separator 3 to a catalyst tower (not shown), and NOx and residual organic pollutants are decomposed.

On the other hand, in the slurry S discharged from the circulating liquid tank 4, the sludge SL1 is removed by the settling device 6, and the sludge SL2 is removed by the filtration filter 7. Mercury contained in the liquid discharged from the filtration filter is adsorbed by the mercury adsorption tower 8, and further, the ozone catalyst tower 9 decomposes trace dissolved components in the liquid into N ₂ , CO ₂ , water and the like.

  Waste water W from the ozone catalyst tower 9 from which mercury, NOx and the like have been removed is returned to the wet dust collector 2 via the circulation route 11. The waste water W contains sodium chloride generated when mercury is oxidized using sodium hypochlorite. Therefore, the concentrated sodium chloride is obtained by supplying the waste water W to the salt concentration membrane 12 and concentrating with the salt concentration membrane 12, and the scale component (Ca, Mg, etc.) can be eliminated. This sodium chloride can be supplied to the electrolytic sodium hypochlorite generator 13 and used for the production of sodium hypochlorite. Thereby, the chemical cost can be reduced and the amount of chlorine in the cement when the waste water W is added to the cement can be reduced. The waste water W from the salt concentration membrane 12 is returned to the wet dust collector 2 and used for wet dust collection.

  It is also possible to directly introduce part of the waste water W from the circulation route 11 into the electrolytic sodium hypochlorite generator 13 without providing the salt concentration membrane 12. Further, a part of the circulation route 11 may be discharged out of the system.

  Moreover, in the said embodiment, although the electrolytic-type sodium hypochlorite production | generation apparatus 13 was provided independently from the wet dust collector 2, an electrode etc. were directly provided in the circulating liquid tank 4, and the wet dust collector 2 and an electrolytic-type hypochlorous acid generator were provided. It is also possible to integrate the sodium chlorate production device 13.

It is a flowchart which shows an example of the combustion exhaust gas processing apparatus for enforcing the wet dust collector waste_water | drain processing method concerning this invention. It is a flowchart which shows an example of the conventional combustion exhaust gas processing apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Combustion exhaust gas processing device 2 Wet dust collector 3 Mist separator 4 Circulating liquid tank 5 Pump 6 Sedimentation device 7 Filtration filter 8 Mercury adsorption tower 9 Ozone catalyst tower 10 Ozone generator 11 Circulation route 12 Salt concentration membrane 13 Electrolytic sodium hypochlorite Generator

Claims (2)

Solid-liquid separation of the slurry discharged from the wet dust collector that collects water-soluble components and dust in the combustion exhaust gas,
While adsorbing mercury in the separated liquid, it decomposes trace dissolved components in the separated liquid with an ozone catalyst tower,
At least a part of the liquid after the adsorption of the mercury and after the decomposition of the trace dissolved component is drained out of the system, sodium chloride produced from the liquid after the adsorption of the mercury and the decomposition of the trace dissolved component, A wet dust collector wastewater treatment method, which is used for producing sodium hypochlorite to be added to circulating water of the wet dust collector. The wet dust collector wastewater treatment method according to claim 1 , wherein calcium hydroxide or calcium oxide is supplied to the slurry circulating in the wet dust collector, and the sulfuric acid mist is converted into gypsum.

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