JP4936002B2 - Exhaust gas treatment method and exhaust gas treatment apparatus - Google Patents

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, it becomes less than 1 ppm to several tens of ppm. If the HCl concentration in the exhaust gas is low as described above, it depends on the denitration catalyst and unburned carbon depending on the properties of the exhaust gas. As a result, the mercury oxidation efficiency decreases, and the mercury collection efficiency in the dedusting section and desulfurization section also decreases.

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 for combustion, A method has been proposed in which the exhaust gas temperature is cooled to 150 ° C. or lower in front of a dust removing unit such as a duster and mercury is removed in the dust removing unit (see, for example, Patent Document 3).
However, in the above-described method for removing mercury by injecting a halogen-containing substance into the flue, or the method for removing mercury in a dedusting section by supplying a chlorine compound together with coal to a combustion device and burning it, a denitration catalyst In order to increase the mercury oxidation efficiency on unburned carbon, it is necessary to increase the concentration of hydrogen chloride in the exhaust gas by newly adding chemicals such as chlorine compounds. Since a huge amount of fuel is burned, a large amount of chlorine corresponding to that amount is required, resulting in an increase in cost.

In addition, an oxidizing agent such as NaClO or iodine is mixed in the absorbing solution in the wet desulfurization section, and the absorbing solution containing the oxidizing agent is brought into contact with the metallic mercury in the gas, thereby converting the metallic mercury into water-soluble mercury oxide. A mercury absorption and removal method using an oxidizing agent that converts and removes mercury in the absorbing solution has also been proposed, but this also requires an oxidizing agent such as NaClO or iodine in the absorbing solution. This causes an increase in cost (see, for example, Patent Documents 4 and 5).
U.S. Patent No. 6521021 Japanese Patent Laid-Open No. 10-230137 JP 2000-325747 A Japanese Unexamined Patent Publication No. 2000-325746 JP 2001-038147

However, in the mercury absorption and removal method using the oxidizing agent described above, for the convenience of always blowing the oxidizing agent into the absorbing solution, the running cost is increased and the concentration of SO _{2 in} the exhaust gas increases. There is a problem that the amount of oxidant necessary for removal increases, and it has been a conventional problem to solve this problem.
The present invention has been made to solve the above-described problems. When fossil fuel, for example, coal, is burned by a combustion apparatus such as a boiler, the mercury removal cost is reduced, and mercury is highly efficient. It is an object to provide an exhaust gas treatment method and an exhaust gas treatment device that can be removed by the above method.

The invention according to claim 1 of the present invention, there is provided a gas processing method for removing mercury contained in exhaust gas discharged from the combustion apparatus when burning a fossil fuel combustion equipment, said fossil fuel the supplied to the combustion apparatus is combusted, the wet desulfurization unit was disposed in the flue from the combustion device, it said perform desulfurization by blowing by spraying the absorption liquid into the exhaust gas discharged from the combustion apparatus, the wet desulfurization unit After adjusting to reduce the pH of the absorption drainage obtained by draining the used absorption liquid from 5 to about 1, the flue immediately before the wet desulfurization section is adjusted to reduce the pH of the absorption drainage, Supplying to any one of the spray in the wet desulfurization section and the flue immediately after the wet desulfurization section, it is configured to be used as an oxidizing agent that converts metallic mercury into water-soluble mercury oxide And this And a means for solving the conventional problems described above the construction of gas treatment method.

The invention according to claim 2 of the present invention, there is provided a gas processing method for removing mercury contained in exhaust gas discharged from the combustion apparatus when burning a fossil fuel combustion equipment, said fossil fuel the supplied to the combustion apparatus is combusted, the wet desulfurization unit was disposed in the flue from the combustion device, it said perform desulfurization by blowing by spraying the absorption liquid into the exhaust gas discharged from the combustion apparatus, the wet desulfurization unit After adjusting to reduce the pH of the absorption drainage obtained by draining the used absorption liquid from 5 to about 1, the flue immediately before the wet desulfurization section is adjusted to reduce the pH of the absorption drainage, Supplying to any two places of the spray in the wet desulfurization section and the flue immediately after the wet desulfurization section, it is configured to be used as an oxidizing agent that converts metallic mercury into water-soluble mercury oxide And this And a means for solving the conventional problems described above the construction of gas treatment method.

The invention according to claim 3 of the present invention, there is provided a gas processing method for removing mercury contained in exhaust gas discharged from the combustion apparatus when burning a fossil fuel combustion equipment, said fossil fuel the supplied to the combustion apparatus is combusted, the wet desulfurization unit was disposed in the flue from the combustion device, it said perform desulfurization by blowing by spraying the absorption liquid into the exhaust gas discharged from the combustion apparatus, the wet desulfurization unit After adjusting to reduce the pH of the absorption drainage obtained by draining the used absorption liquid from 5 to about 1, the flue immediately before the wet desulfurization section is adjusted to reduce the pH of the absorption drainage, Supplying both the spray in the wet desulfurization part and the flue immediately after the wet desulfurization part, it is characterized in that it is configured to be used as an oxidizing agent that converts metallic mercury into water-soluble mercury oxide, This exhaust gas The structure of physical methods as a means for solving the conventional problems described above.

In the exhaust gas treatment method according to claim 4 of the present invention, the pH of the absorption waste water is adjusted by mixing an acid into the absorption waste water.
In the exhaust gas treatment method according to claim 5 of the present invention, the pH of the absorption waste water is adjusted by dissolving a part of the exhaust gas in the flue into the absorption waste water.
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 the combustion device when fossil fuel is combusted by the combustion device. A wet desulfurization section having a spray for desulfurization by spraying an absorption liquid on the exhaust gas discharged from the combustion device and disposed in the flue of the above, and a waste water for performing a waste water treatment of the used absorption liquid discharged from the wet desulfurization section A treatment part, a pH adjustment part for adjusting the pH of the absorption waste water obtained in the waste water treatment part, a flue immediately before the wet desulfurization part, the spray in the wet desulfurization part, and a flue immediately after the wet desulfurization part In any one place, the absorption waste water whose pH is adjusted to be low by the pH adjusting unit is supplied as an oxidizing agent, and a pipe for converting metallic mercury into water-soluble mercury oxide is provided.

The invention according to claim 7 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 is burned by the combustion device, the smoke from the combustion device A wet desulfurization section having a spray for desulfurization by spraying an absorption liquid on the exhaust gas discharged from the combustion device disposed on the road, and a waste water treatment section for performing a waste water treatment of the used absorption liquid discharged from the wet desulfurization section And a pH adjusting unit that adjusts the pH of the absorbed waste water obtained in the waste water treatment unit, a flue immediately before the wet desulfurization unit, the spray in the wet desulfurization unit, and a flue immediately after the wet desulfurization unit In two places, the absorption drainage whose pH has been adjusted to be low by the pH adjusting unit is supplied as an oxidizing agent, and piping for converting metallic mercury into water-soluble mercury oxide is provided.

The invention according to claim 8 of the present invention is an exhaust gas treatment device for removing mercury contained in exhaust gas discharged from a combustion device when fossil fuel is burned by the combustion device, and the smoke from the combustion device. A wet desulfurization section having a spray for desulfurization by spraying an absorption liquid on the exhaust gas discharged from the combustion device disposed on the road, and a waste water treatment section for performing a waste water treatment of the used absorption liquid discharged from the wet desulfurization section And a pH adjusting unit for adjusting the pH of the absorption waste water obtained in this waste water treatment unit, a flue immediately before the wet desulfurization unit, the spray in the wet desulfurization unit, and a flue immediately after the wet desulfurization unit For all, the absorption drainage whose pH is adjusted to be low by the pH adjusting unit is supplied as an oxidizing agent, and a pipe for converting metallic mercury into water-soluble mercury oxide is provided.

Air pollution control apparatus according to claim 9 of the present invention has a structure comprising an acid supply tube for supplying an acid to the pH adjustment unit.
In the exhaust gas treatment apparatus according to claim 10 of the present invention, the pH adjusting unit includes an exhaust gas supply pipe for introducing a part of the exhaust gas from the flue.
In the exhaust gas treatment method and the exhaust gas treatment apparatus according to the present invention, the absorption waste water whose pH is adjusted to be low is used as the mercury oxidant. As shown in the chemical formula (1), in the absorption waste water whose pH is adjusted to be low. It is considered that mercury is oxidized by the involvement of various metal species.

Hg ⁰ + Me (X) → Hg ²⁺ + Me (X-2) Chemical formula (1)
However, Me represents a metal species, and X represents a valence of the metal.
As described above, in the exhaust gas treatment method and the exhaust gas treatment apparatus according to the present invention, absorption and removal of mercury in the wet desulfurization section is performed by using the absorption waste water whose pH is adjusted to be low as the mercury oxidizing agent. In addition, since the oxidizing agent that is conventionally necessary for removing mercury in the wet desulfurization section is unnecessary, the running cost for removing mercury can be reduced.

  In this case, the absorption waste water means the waste water obtained after processing the absorbent liquid of the wet desulfurization part to a state where it can be discharged out of the equipment facility, and since it is the water after treatment, it is dissolved in the absorption liquid. Mercury does not circulate in the plant.

Since the exhaust gas treatment method according to claims 1 to 3 of the present invention and the exhaust gas treatment apparatus according to claims 6 to 8 have the above-described configuration, an oxidant is not required for mercury removal. It is possible to remove mercury with high efficiency after realizing the reduction.
Further, in the exhaust gas treatment method according to claim 4 of the present invention and the exhaust gas treatment device according to claim 9, the pH can be easily adjusted, and further, the exhaust gas treatment method and claim according to claim 5 of the present invention. In the exhaust gas treatment apparatus according to item 10, it is possible to further reduce the running cost.

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 desulfurization unit 7 and a heat exchanger (not shown) are provided. Coal-fired boiler B is supplied with coal from coal storage 20 as a storage unit pulverized by mill 21.

The wet desulfurization section 7 sprays an absorbing liquid on the exhaust gas flowing from the dedusting section 5 side through a spray 7a to remove chlorine and SO _X in the exhaust gas. After being circulated and used by 7b, it is fed to the waste water treatment unit 9.
In this case, the waste water treatment unit 9 is connected to a pH adjustment unit 10 that adjusts the pH of the absorption waste water obtained in the waste water treatment unit 9 to a low level, and the pH adjustment unit 10 has a low pH value. A pipe 11 is connected so that the absorption waste water is supplied to the flue end Re immediately before the wet desulfurization section 7 through the pump 11a.

  The pH adjuster 10 is connected to an acid supply pipe 12 for supplying an acid such as hydrogen chloride or nitric acid to adjust the pH of the absorption wastewater to a low level, and similarly adjusts the pH of the absorption wastewater to a low level. Therefore, an exhaust gas supply pipe 13 for introducing a part of the exhaust gas from the flue is connected, and the acid supply pipe 12 and the exhaust gas supply pipe 13 are appropriately selected and at least one of them is used. Yes.

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.

Of the mercury contained in the exhaust gas discharged from the coal-fired boiler B, the metallic mercury Hg ⁰ is the surface of unburned carbon and ash present in the denitration part 3 and in the flue R, It is converted to water-soluble divalent mercury Hg ²⁺ (HgCl ₂ ) by reaction.
Subsequently, 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 a liquid phase.

In this wet desulfurization part 7, the absorbing liquid is sprayed to the exhaust gas flowing from the dedusting part 5 side through the spray 7a to remove chlorine and SO _X in the exhaust gas, and the used absorbing liquid is circulated by the pump 7b. After being used, it is fed to the waste water treatment unit 9.
At this time, in the pH adjustment unit 10 connected to the waste water treatment unit 9, the exhaust gas is discharged from an acid such as hydrogen chloride or nitric acid or the flue R through at least one of the acid supply pipe 12 and the exhaust gas supply pipe 13. Is adjusted to lower the pH of the absorption drainage, and the absorption drainage adjusted to a low pH is connected from the pH adjustment unit 10 to the flue end Re immediately before the wet desulfurization unit 7 through the pipe 11. Thus, it is used as an oxidizing agent that converts metallic mercury Hg ⁰ into water-soluble divalent mercury Hg ²⁺ (HgCl ₂ ).

As described above, in the exhaust gas treatment method and the exhaust gas treatment apparatus 1 of this embodiment, since the oxidizing agent is not used to remove mercury in the wet desulfurization unit 7, the running cost can be reduced to that extent. .
FIG. 2 shows an exhaust gas treatment apparatus according to another embodiment of the present invention. As shown partially in FIG. 2, the exhaust gas treatment apparatus of this embodiment is different from the exhaust gas treatment apparatus 1 of the previous embodiment. However, the absorption drainage water whose pH has been adjusted low is supplied from the pH adjusting unit 10 to the spray 7a in the wet desulfurization unit 7 via the pipe 15, and the other configuration is that of the previous embodiment. This is the same as the exhaust gas treatment device 1.

As described above, also in the exhaust gas treatment method and the exhaust gas treatment apparatus 1 of this embodiment, since the oxidizing agent is not used for removing mercury in the wet desulfurization unit 7, the running cost can be reduced to that extent. Become.
FIG. 3 shows an exhaust gas treatment apparatus according to still another embodiment of the present invention. As shown in part in FIG. 3, the exhaust gas treatment apparatus of this embodiment is different from the exhaust gas treatment apparatus 1 of the previous embodiment. This is because the absorption drainage adjusted to a low pH is supplied from the pH adjustment unit 10 to the flue end Rf immediately after the wet desulfurization unit 7 via the pipe 17. It is the same as the exhaust gas treatment apparatus 1 of the embodiment.

As described above, also in the exhaust gas treatment method and the exhaust gas treatment apparatus 1 of this embodiment, since the oxidizing agent is not used for removing mercury in the wet desulfurization unit 7, the running cost can be reduced to that extent. Become.
Then, in order to investigate the relationship between the pH of the absorption waste water and the mercury removal rate, a test was performed under the following conditions, and the results shown in FIG. 4 were obtained.
[Test conditions]
Gas _{composition; O 2: 5vol%, CO} 2: 15vol%, N 2 balance Hg ⁰ inlet feed amount; 22.9~26.6μg / Nm ³
Absorption wastewater; 2 types of desulfurization wastewater (A, B)
From the results of FIG. 4, it was demonstrated that the mercury removal rate was significantly improved when the pH of the absorption wastewater was lowered to about 5 to 1.

  In the above-described embodiment, the absorption waste water adjusted to have a low pH is supplied to the flue end Re immediately before the wet desulfurization unit 7, supplied to the wet desulfurization unit 7 itself, or to the flue end Rf immediately after the wet desulfurization unit 7. Although it is made to supply, it is not limited to these, Both the flue end Re immediately before the wet desulfurization part 7 and the wet desulfurization part 7 itself, the wet desulfurization part, and the absorption waste water adjusted low in pH 7 may be supplied to both the flue end Re immediately before 7 and the flue end Rf immediately after the wet desulfurization unit 7, or both the wet desulfurization unit 7 itself and the flue end Rf immediately after the wet desulfurization unit 7.

  Moreover, you may make it supply the absorption waste water which adjusted pH low to any of flue edge part Re immediately before the wet desulfurization part 7, wet desulfurization part 7 itself, and flue end Rf just after the wet desulfurization part 7. FIG.

BRIEF DESCRIPTION OF THE DRAWINGS It is schematic structure explanatory drawing which shows the waste gas processing apparatus by one Embodiment of this invention. It is schematic structure explanatory drawing which shows partially the waste gas processing apparatus by other embodiment of this invention. It is a schematic structure explanatory view partially showing an exhaust gas treatment apparatus according to still another embodiment of the present invention. It is a graph which shows the relationship between the pH of the absorption waste_water | drain by the waste gas treatment method and waste gas treatment apparatus of this invention, and a mercury removal rate.

Explanation of symbols

1 Exhaust gas treatment device 7 Wet desulfurization section
7a Spray 9 Wastewater treatment unit 10 pH adjustment unit 11, 15, 17 Pipe 12 Acid supply pipe 13 Exhaust gas supply pipe B Coal-fired boiler (combustion device)
R Flue

Claims (10)

Is the exhaust gas treatment method for removing mercury contained in exhaust gas discharged the fossil fuel from the combustion apparatus when burned in combustion devices,
Supplying and burning the fossil fuel to the combustion device;
In wet desulfurization unit was disposed in the flue from the combustion device performs desulfurization by blowing by spraying the absorption liquid into the exhaust gas discharged from the combustion device,
After adjusting the pH of the absorption drainage obtained by draining the spent absorption liquid from this wet desulfurization part,
The absorption drainage adjusted to a low pH is supplied to any one of the flue immediately before the wet desulfurization section , the spray in the wet desulfurization section , and the flue immediately after the wet desulfurization section, so that metallic mercury is dissolved in water. An exhaust gas treatment method characterized by being used as an oxidant that converts to a functional mercury oxide. Is the exhaust gas treatment method for removing mercury contained in exhaust gas discharged the fossil fuel from the combustion apparatus when burned in combustion devices,
Supplying and burning the fossil fuel to the combustion device;
In wet desulfurization unit was disposed in the flue from the combustion device performs desulfurization by blowing by spraying the absorption liquid into the exhaust gas discharged from the combustion device,
After adjusting the pH of the absorption drainage obtained by draining the spent absorption liquid from this wet desulfurization part,
The absorption waste water adjusted to have a low pH is supplied to any one of the flue immediately before the wet desulfurization section , the spray in the wet desulfurization section , and the flue immediately after the wet desulfurization section, so that metallic mercury is dissolved in water. An exhaust gas treatment method characterized by being used as an oxidant that converts to a functional mercury oxide. Is the exhaust gas treatment method for removing mercury contained in exhaust gas discharged the fossil fuel from the combustion apparatus when burned in combustion devices,
Supplying and burning the fossil fuel to the combustion device;
In wet desulfurization unit was disposed in the flue from the combustion device performs desulfurization by blowing by spraying the absorption liquid into the exhaust gas discharged from the combustion device,
After adjusting the pH of the absorption drainage obtained by draining the spent absorption liquid from this wet desulfurization part,
The absorption waste water adjusted to a low pH is supplied to any of the flue immediately before the wet desulfurization section , the spray in the wet desulfurization section , and the flue immediately after the wet desulfurization section, so that the metal mercury is water-soluble. An exhaust gas treatment method characterized by being used as an oxidizing agent that converts to mercury oxide. The exhaust gas treatment method according to any one of claims 1 to 3, wherein the pH of the absorption waste water is adjusted by mixing an acid into the absorption waste water.   The exhaust gas treatment method according to any one of claims 1 to 3, wherein the adjustment of the pH of the absorption waste water is performed by dissolving a part of the exhaust gas in the flue into the absorption waste water. An exhaust gas treatment device for removing mercury contained in exhaust gas discharged from the combustion device when fossil fuel is burned by the combustion device,
A wet desulfurization section having a spray that is disposed in a flue from the combustion apparatus and sprays an absorbing liquid on the exhaust gas discharged from the combustion apparatus to perform desulfurization;
A waste water treatment part for performing waste water treatment of the used absorbent discharged from the wet desulfurization part;
A pH adjustment unit for adjusting the pH of the absorption wastewater obtained in this wastewater treatment unit,
The absorbing wastewater whose pH is adjusted to be low by the pH adjusting unit with respect to any one of the flue immediately before the wet desulfurization unit, the spray in the wet desulfurization unit, and the flue immediately after the wet desulfurization unit is an oxidizing agent. An exhaust gas treatment apparatus comprising a pipe for supplying metal mercury into water-soluble mercury oxide . An exhaust gas treatment device for removing mercury contained in exhaust gas discharged from the combustion device when fossil fuel is burned by the combustion device,
A wet desulfurization section having a spray that is disposed in a flue from the combustion apparatus and sprays an absorbing liquid on the exhaust gas discharged from the combustion apparatus to perform desulfurization;
A waste water treatment part for performing waste water treatment of the used absorbent discharged from the wet desulfurization part;
A pH adjustment unit for adjusting the pH of the absorption wastewater obtained in this wastewater treatment unit,
The wet desulfurization unit immediately before the flue, the to any two places of the spray and the wet desulfurization unit immediately after the flue in the wet desulfurization unit, oxidizing agent the absorption wastewater adjusted low pH in the pH adjustment unit An exhaust gas treatment apparatus comprising a pipe for supplying metal mercury into water-soluble mercury oxide . An exhaust gas treatment device for removing mercury contained in exhaust gas discharged from the combustion device when fossil fuel is burned by the combustion device,
A wet desulfurization section having a spray that is disposed in a flue from the combustion apparatus and sprays an absorbing liquid on the exhaust gas discharged from the combustion apparatus to perform desulfurization;
A waste water treatment part for performing waste water treatment of the used absorbent discharged from the wet desulfurization part;
A pH adjustment unit for adjusting the pH of the absorption wastewater obtained in this wastewater treatment unit,
For all three locations of the flue immediately before the wet desulfurization part, the spray in the wet desulfurization part and the flue immediately after the wet desulfurization part, the absorption wastewater whose pH is adjusted low by the pH adjustment part is used as an oxidizing agent. An exhaust gas treatment apparatus comprising a pipe for supplying and converting metal mercury into water-soluble mercury oxide . The exhaust gas treatment apparatus according to any one of claims 6 to 8, further comprising an acid supply pipe for supplying an acid to the pH adjusting unit.   The exhaust gas treatment apparatus according to any one of claims 6 to 8, further comprising an exhaust gas supply pipe that introduces a part of the exhaust gas from the flue to the pH adjusting unit.

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