JP2009045521A - Exhaust gas treating method and treatment apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas treating method and a treatment apparatus with which mercury can be highly efficiently removed regardless of the kinds of coal or properties of exhaust gas discharged from a combustion apparatus when burning the coal in the combustion apparatus like a boiler, and a further reduced cost can be achieved. <P>SOLUTION: In the exhaust gas treating method for removing mercury contained in exhaust gas discharged from a coal-burning boiler B when burning fossil fuel like coal in the coal-burning boiler B, the fossil fuel carried from a coal storage yard 20 is fed to the combustion apparatus for combustion, and absorbing liquid is brought into contact with the exhaust gas discharged from the coal-burning boiler B to perform removal process like desulfurization, in a wet desulfurization part 7 disposed in a flue R from the coal-burning boiler B. The chlorine-containing absorbing liquid being the used absorbing liquid from the wet desulfurization part 7, is fed to at least one of the coal storage yard 20, coal-burning boiler B, and the flue R from the coal-burning boiler B to the wet desulfurization part 7. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust gas treatment method and an exhaust gas treatment device that are used to remove mercury contained in exhaust gas discharged from a combustion device when fossil fuel such as coal is burned by a combustion device such as a boiler. It is about.

Mercury resulting from coal is contained in the above-described fossil fuel combustion apparatus, for example, coal combustion exhaust gas discharged from a coal-fired boiler. This mercury is present in the exhaust gas in three forms: hardly soluble metallic mercury Hg ⁰ , water-soluble divalent mercury Hg ²⁺ (HgCl ₂ ), and particulate mercury Hg ^P adhering to combustion ash. .
As an exhaust gas treatment apparatus for removing mercury from exhaust gas, for example, there is an apparatus in which a denitration part, a dust removal part, and a wet desulfurization part are sequentially arranged in a flue from a coal-fired boiler to a chimney.

Of the mercury contained in the exhaust gas, most of the particulate mercury Hg ^P is removed by a dust removal part such as an electric dust collector or a bag filter of this exhaust gas treatment device, and the divalent mercury Hg ²⁺ is wet desulfurization. However, most of the metallic mercury Hg ⁰ contained in the exhaust gas is released to the atmosphere without being almost removed by the dedusting part or the desulfurization part.
Metallic mercury Hg ⁰ released into the atmosphere is converted into more harmful organic mercury (methylmercury) in the environment, and this organic mercury is accumulated in edible organisms such as fish and shellfish, which passes through the food chain. There is concern about entering the human body.

In light of this situation, the US Environmental Protection Agency has decided to regulate mercury emissions from coal-fired thermal power plants, reducing mercury emissions by 30% by 2010, and 2018 In the same way, Canada has decided to regulate mercury emissions from coal-fired thermal power plants.
Metallic mercury Hg ⁰ contained in the exhaust gas is converted into denitration catalyst, coal ash, and unburned carbon as shown in the reaction formula (1) by hydrogen chloride (HCl) caused by chlorine contained in coal as well as mercury. Oxidized on the surface.

Hg ⁰ + 2HCl + 1 / 2O ₂ → HgCl ₂ + H ₂ O Reaction formula (1)
However, divalent mercury Hg ²⁺ is HgCl ₂ .
The mercury oxidation efficiency on the denitration catalyst increases as the HCl concentration increases. That is, the higher the hydrogen chloride concentration, the higher the generation ratio of HgCl ₂ , and as a result, the ratio of mercury collected in the dedusting section and desulfurization section also increases.

Conventionally, as a technology for removing mercury in exhaust gas discharged from combustion equipment, mercury adsorbents such as activated carbon are blown upstream of dust removal parts such as electric dust collectors and bag filters that remove dust. There has been proposed a method for removing mercury by adsorbing mercury on the surface of the agent (see, for example, Patent Document 1).
However, this removal technique using an adsorbent has the disadvantages that the adsorbent needs to be constantly blown, so that the running cost is high and the efficiency varies depending on the gas properties such as HCl concentration in the exhaust gas.

  In terms of the concentration of HCl in the exhaust gas, the amount of chlorine contained in the coal is originally small, from several ppm to several hundred ppm, and the content varies greatly depending on the type of coal. When converted to the HCl concentration in the exhaust gas, the concentration is less than 1 ppm to several tens of ppm. If the HCl concentration in the exhaust gas is low, the denitration catalyst, unburned carbon and ash, depending on the properties of the exhaust gas. The mercury oxidation efficiency in the above is lowered, and accordingly, the mercury collection efficiency in the dedusting part and the desulfurization part is also lowered.

In order to cope with this, a method of injecting a halogen-containing substance into a flue from a coal-fired boiler (see, for example, Patent Document 2), or supplying a chlorine compound together with coal to a combustion apparatus and burning it, A method has been proposed in which the exhaust gas temperature is cooled to 150 ° C. or lower in front of a dust removing part such as a duster and mercury is removed in the dust removing part (see, for example, Patent Document 3).
U.S. Patent No. 6521021 Japanese Patent Laid-Open No. 10-230137 JP 2000-325747 A

However, in the method of removing mercury by injecting a halogen-containing substance into the flue as described above, or the method of supplying chlorine to a combustion device together with coal and burning it to remove mercury in the dedusting part, a denitration catalyst In order to increase mercury oxidation efficiency on unburned carbon and ash, it is necessary to increase the hydrogen chloride concentration in the exhaust gas.
In other words, chemicals such as chlorine compounds need to be newly added, and when burning coal, a huge amount of fuel is burned, so a large amount of chlorine is needed to meet that, and only that much. There is a problem of increasing the cost, and it has been a conventional problem to solve this problem.

  The present invention has been made to solve the above-described problems, and relates to the type of coal and the properties of exhaust gas discharged from the combustion device when fossil fuel, for example, coal, is burned by a combustion device such as a boiler. In addition, an object of the present invention is to provide an exhaust gas treatment method and an exhaust gas treatment apparatus that can remove mercury with high efficiency and can realize further cost reduction.

  The invention according to claim 1 of the present invention is an exhaust gas treatment method for removing mercury contained in exhaust gas discharged from a combustion device when fossil fuel such as coal is burned in a combustion device such as a boiler, The fossil fuel transported from the storage is supplied to the combustion device and combusted, and in the wet removal section disposed in the flue from the combustion device, the absorbent is brought into contact with the exhaust gas discharged from the combustion device and desulfurized. The chlorine-containing absorption liquid, which is a used absorption liquid, is supplied from the wet removal section to at least one of the storage, the combustion apparatus, and the flue leading from the combustion apparatus to the wet removal section. In order to solve the conventional problems described above, the configuration of the exhaust gas treatment method is characterized in that the concentration of hydrogen chloride contained in the exhaust gas discharged from the combustion device is increased. It is a means.

In the invention according to claim 2 of the present invention, after reducing the moisture of the chlorine-containing absorbent and increasing the chlorine concentration, the storage area, the combustion device, and the flue from the combustion device to the wet removal section It is configured to supply to at least one location.
In the invention which concerns on Claim 3 of this invention, it is set as the structure which supplies the said chlorine containing absorption liquid to the said combustion apparatus side flue of the denitration part located between the said combustion apparatus and the said wet removal part.

In the invention which concerns on Claim 4 of this invention, it is set as the structure which sprays and supplies the said chlorine containing absorption liquid to the coal storage place which is a coal storage place as a fossil fuel.
In the invention according to claim 5 of the present invention, the chlorine-containing absorbent is mixed with the secondary combustion air used in the combustion device and supplied to the combustion device.
In this case, the amount of the chlorine-containing absorbent to be supplied is determined based on the amount of chlorine necessary for the oxidation / removal of mercury.

  On the other hand, the invention according to claim 6 of the present invention is an exhaust gas treatment device that removes mercury contained in exhaust gas discharged from a combustion device when fossil fuel such as coal is burned by a combustion device such as a boiler. A wet removal unit that is disposed in the flue from the combustion device and contacts the exhaust gas discharged from the combustion device to remove the desulfurization, etc. by contacting the absorption liquid, and is included in the exhaust gas discharged from the combustion device In order to increase the concentration of hydrogen chloride, at least one of the fossil fuel storage site, the combustion device, and the flue leading from the combustion device to the wet removal unit is used as a used absorbent from the wet removal unit. It is set as the structure provided with the chlorine containing absorption liquid supply part supplied to one place.

In the invention according to claim 7 of the present invention, the chlorine-containing absorbent supplied to at least one of the storage, the combustion device, and the flue leading from the combustion device to the wet removal section is reduced in water The absorption liquid concentrating part for increasing the concentration is provided.
In the invention according to claim 8 of the present invention, the chlorine-containing absorbent supply section supplies the chlorine-containing absorbent to the combustion apparatus side flue of the denitration section located between the combustion apparatus and the wet removal section. It is configured to have a flue delivery pipe to be supplied.

In the invention according to claim 9 of the present invention, the chlorine-containing absorbent supply unit includes a coal storage feed pipe that supplies the chlorine-containing absorbent by spraying the chlorine-containing absorbent to a coal storage that is a coal storage as fossil fuel. It has a configuration.
In the invention according to claim 10 of the present invention, the chlorine-containing absorbent supply unit includes a feed pipe communicating with a secondary combustion air introduction path for introducing secondary combustion air into the combustion device. It is configured.

In the exhaust gas treatment method and exhaust gas treatment apparatus of the present invention, in the denitration part disposed in the flue from the combustion device, Hg on the denitration catalyst inside the surface, the surface of unburned carbon and ash present in the flue, etc. ⁰ and allowed to react with HCl to oxidize to HgCl ₂ in.

  Since the exhaust gas treatment method according to claim 1 of the present invention and the exhaust gas treatment device according to claim 5 have the above-described configuration, the concentration of hydrogen chloride in the exhaust gas discharged from the combustion device increases, so that the combustion device From the flue from the air, for example, the mercury oxidation efficiency in the denitration part arranged in this flue is increased and the production rate of water-soluble divalent mercury is increased. Increases the amount of mercury collected in the dedusting section located in the flue.

Since no adsorbent is used for this mercury removal, the running cost can be reduced correspondingly, and the mercury collection efficiency does not decrease due to gas properties such as HCl concentration in the exhaust gas.
In other words, it is possible to remove mercury with high efficiency and low cost regardless of the type of coal and the nature of the exhaust gas discharged from the combustion device, and in addition, from the storage, the combustion device and the combustion device. The chlorine-containing absorbent supplied to at least one of the flues leading to the wet removal section is a used absorbent that has been removed by bringing the absorbent into contact with the exhaust gas in the wet removal section and removing it such as desulfurization. Therefore, it is possible to further reduce the cost because it is not necessary to separately prepare additives such as chlorine compounds.

In the exhaust gas treatment method according to claim 2 of the present invention and the exhaust gas treatment apparatus according to claim 7, the chlorine-containing absorbent having a high chlorine concentration reaches the wet removal section from the storage, the combustion device, and the combustion device. Since it can supply to at least one place of a flue, the calorie | heat amount loss for a vaporization latent heat can be suppressed small.
Further, in the exhaust gas treatment method according to claim 3 of the present invention and the exhaust gas treatment device according to claim 8, in particular, since the mercury oxidation efficiency in the denitration contact portion increases, the production ratio of water-soluble divalent mercury is further increased. It is possible to increase.

Furthermore, in the exhaust gas treatment method according to claim 4 of the present invention and the exhaust gas treatment apparatus according to claim 9, since the chlorine-containing absorbent is sprayed on the coal storage, which is a coal storage, Can be prevented.
Furthermore, in the exhaust gas treatment method according to claim 5 of the present invention and the exhaust gas treatment device according to claim 10, since the chlorine-containing absorbent is supplied to the combustion device together with the secondary combustion air, at a high temperature. It can be vaporized and decomposed at once, and as a result, gaseous hydrogen chloride can be efficiently generated.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an exhaust gas treatment apparatus according to an embodiment of the present invention. In this embodiment, the exhaust gas treatment method and the exhaust gas treatment apparatus of the present invention are used to treat exhaust gas discharged from a coal fired boiler (combustion device). The case where it is applied will be described as an example.
As shown in FIG. 1, the exhaust gas treatment apparatus 1 includes a denitration unit 3, an air heater 4, a dust removal unit 5, a heat exchanger 6, a wet type, which are sequentially arranged in a flue R from a coal burning boiler B to a chimney 2. A wet desulfurization unit 7 and a heat exchanger 8 as a removal unit are provided, and coal in the coal storage boiler 20 is supplied to the coal burning boiler B after being pulverized by a mill 21.

The wet desulfurization unit 7 sprays an absorbing liquid on the exhaust gas flowing from the dedusting unit 5 side through the spray 7a to remove chlorine compounds and SO _X in the exhaust gas. After being circulated and used by the pump 7b, it is fed to the waste water treatment section 9.
In addition, the exhaust gas treatment apparatus 1 is provided with a waste water treatment unit 9 for at least one of the coal storage 20, the coal fired boiler B, and the flue R extending from the coal fired boiler B to the wet desulfurization unit 7. A chlorine-containing absorbent supply unit 10 that supplies the used absorbent of the wet desulfurization unit 7 is provided, so that the concentration of hydrogen chloride contained in the exhaust gas discharged from the coal-fired boiler B is increased. Yes.

  The chlorine-containing absorbing liquid supply unit 10 sprays the used absorbing liquid to the coal storage 20 and the flue delivery pipe 11 that supplies the used absorbing liquid to the coal-fired boiler B side flue R of the denitration unit 3. The coal storage boiler feed pipe 12, the feed pipe 13 communicating with the secondary combustion air introduction passage Ba for introducing the secondary combustion air into the coal fired boiler B, and the absorption used in the coal fired boiler B A feed pipe 14 for directly supplying the liquid is provided, and these feed pipes 11 to 14 are appropriately selected and at least one is used.

The chlorine-containing absorbing liquid supply unit 10 includes feeding pipes 15 to 18 that supply used absorbing liquid to the flue R between the denitration unit 3 and the wet desulfurization unit 7 in addition to the feeding pipes 11 to 14. It has a structure that can be arranged as needed.
In this case, the absorption liquid concentration unit 19 is disposed in the vicinity of the waste water treatment unit 9, and the chlorine concentration is increased by reducing the water content of the used absorption liquid sent from the wet desulfurization unit 7 through the waste water treatment unit 9. I am doing so.

In this air pollution control apparatus 1, by adding ammonia to the upstream side of the denitration unit 3 in the flue R, so that converted by reducing NO _X contained in the exhaust gas to nitrogen and water.
Further, metal mercury Hg ⁰ reacts with HCl on the denitration catalyst in the denitration unit 3 or on the surface of the unburned carbon and ash present in the denitration unit 3 and in the flue R so that the water-soluble 2 Oxidized to valence mercury Hg ²⁺ (HgCl ₂ ).

Further, in the wet desulfurization section 7, the divalent mercury Hg ²⁺ (HgCl ₂ ) that has passed through the dedusting section 5 is liquid-phase absorbed, and taken into sludge and collected.
In this exhaust gas treatment device 1, the coal in the coal storage yard 20 is pulverized by the mill 21, and supplied to the coal-fired boiler B to start combustion. When performing the processing of the exhaust gas discharged from a coal-fired boiler B, first, by adding ammonia to the upstream side of the denitration unit 3 in the flue R, and nitrogen by reducing NO _X contained in the exhaust gas Convert to water.

Among the mercury contained in the exhaust gas discharged from the coal-fired boiler B, the metallic mercury Hg ⁰ is the unburned carbon content present on the denitration catalyst in the denitration unit 3 and in the denitration unit 3 and in the flue R. It reacts with HCl on the surface of ash or the like and is converted to water-soluble divalent mercury Hg ²⁺ (HgCl ₂ ).
Here, in order to increase the concentration of hydrogen chloride contained in the exhaust gas discharged from the coal-fired boiler B, the chlorine-containing absorbent supply unit 10 sends a chlorine-containing absorbent that is a used absorbent from the wet desulfurization unit 7. It supplies to the coal storage 20, the coal burning boiler B, and the denitration part 3 via at least one of the supply pipes 11-14 (the supply pipes 15-18 as needed).

Next, the dedusting unit 5 collects divalent mercury Hg ²⁺ together with soot dust, and the wet desulfurization unit 7 absorbs the divalent mercury Hg ²⁺ (HgCl ₂ ) that has passed through the dedusting unit 5 in the liquid phase. It is taken in and collected in sludge, and after that, the sludge containing mercury is disposed of as industrial waste.
As described above, in the exhaust gas treatment method and the exhaust gas treatment apparatus 1 of this embodiment, when coal is burned by the coal burning boiler B, the concentration of hydrogen chloride in the exhaust gas discharged from the coal burning boiler B is increased. Because the mercury oxidation efficiency in the denitration section 3 and the like arranged in the flue R from the coal-fired boiler B is increased and the production rate of water-soluble divalent mercury is increased, the flue from the coal-fired boiler B The amount of mercury collected in the dedusting unit 5 and the wet desulfurization unit 7 arranged in R increases.

Further, since no adsorbent is used for this mercury removal, the running cost can be reduced by that amount, and the mercury collection efficiency does not decrease due to gas properties such as HCl concentration in the exhaust gas.
That is, it is possible to remove mercury with high efficiency and low cost regardless of the type of coal and the nature of the exhaust gas discharged from the coal-fired boiler B. In addition, the coal storage 20, the coal-fired boiler B, and this The chlorine-containing absorbent supplied to at least one of the flues R from the coal-fired boiler B to the wet desulfurization section 7 is obtained by removing the desulfurization and the like by contacting the absorbent with the exhaust gas in the wet desulfurization section 7. Further, since it is a used absorbent, it is possible to realize further cost reduction because it is not necessary to separately prepare additives such as chlorine compounds.

  Further, in the above-described exhaust gas treatment device 1, the absorbent concentration unit 19 is disposed in the vicinity of the waste water treatment unit 9, so that the moisture of the used absorbent sent from the wet desulfurization unit 7 through the waste water treatment unit 9 can be reduced. Since the chlorine concentration is increased by reducing the heat loss, the heat loss due to the latent heat of vaporization can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS It is schematic structure explanatory drawing which shows the waste gas processing apparatus by one Embodiment of this invention.

Explanation of symbols

1 Exhaust gas treatment device 3 Denitration unit 7 Wet desulfurization unit (wet removal unit)
10 Chlorine-containing Absorbing Liquid Supply Units 11 to 18 Feeding Channel 19 Absorbing Liquid Concentrating Unit 20 Coal Storage (Storage)
B Coal-fired boiler (combustion device)
Ba Secondary combustion air introduction path R Flue

Claims (10)

An exhaust gas treatment method for removing mercury contained in exhaust gas discharged from a combustion device when fossil fuel such as coal is burned in a combustion device such as a boiler,
Supply fossil fuel carried from the storage to the combustion device and burn it,
In the wet removal unit disposed in the flue from the combustion device, the absorbent is brought into contact with the exhaust gas discharged from the combustion device to perform desulfurization and the like. Supply the absorbing liquid to at least one of the storage area, the combustion device, and the flue leading from the combustion device to the wet removal unit to increase the concentration of hydrogen chloride contained in the exhaust gas discharged from the combustion device. An exhaust gas treatment method characterized by:   The moisture content of the said chlorine containing absorption liquid is reduced, and after increasing a chlorine concentration, it supplies to at least one location of the said storage, the said combustion apparatus, and the flue from this combustion apparatus to a wet removal part. Exhaust gas treatment method.   The exhaust gas treatment method according to claim 1 or 2, wherein the chlorine-containing absorption liquid is supplied to the combustion device side flue of a denitration unit located between the combustion device and the wet removal unit.   The exhaust gas treatment method according to claim 1 or 2, wherein the chlorine-containing absorption liquid is supplied by spraying to a coal storage that is a storage for coal as fossil fuel.   The exhaust gas treatment method according to claim 1 or 2, wherein the chlorine-containing absorbing liquid is mixed with secondary combustion air used in the combustion apparatus and supplied to the combustion apparatus. An exhaust gas treatment device for removing mercury contained in exhaust gas discharged from a combustion device when fossil fuel such as coal is burned in a combustion device such as a boiler,
A wet removal unit that is disposed in a flue from the combustion device and that removes desulfurization and the like by contacting an absorption liquid with exhaust gas discharged from the combustion device;
In order to increase the concentration of hydrogen chloride contained in the exhaust gas discharged from the combustion apparatus, a chlorine-containing absorption liquid, which is a used absorption liquid, is removed from the wet removal unit from the fossil fuel storage, the combustion apparatus, and the combustion apparatus. An exhaust gas treatment apparatus comprising a chlorine-containing absorbent supply unit that supplies at least one of the flues leading to the wet removal unit.   Claims provided with an absorption liquid concentrating section that reduces the water content of the chlorine-containing absorption liquid supplied to at least one of the storage area, the combustion apparatus, and the flue leading from the combustion apparatus to the wet removal section to increase the chlorine concentration. Item 6. The exhaust gas treatment apparatus according to Item 6.   The chlorine-containing absorption liquid supply unit includes a flue feed pipe that supplies the chlorine-containing absorption liquid to the combustion device side flue of a denitration unit located between the combustion device and the wet removal unit. The exhaust gas treatment apparatus according to claim 6 or 7.   The said chlorine containing absorption liquid supply part is equipped with the coal storage feed pipe which sprays and supplies the said chlorine containing absorption liquid to the coal storage which is a storage of coal as a fossil fuel. Exhaust gas treatment equipment.   The exhaust gas treatment device according to claim 6 or 7, wherein the chlorine-containing absorbent supply unit includes a feed pipe communicating with a secondary combustion air introduction path for introducing secondary combustion air into the combustion device. .

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