JP4952935B2 - 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 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.

The above-mentioned fossil fuel combustion apparatus, for example, coal combustion exhaust gas discharged from a coal-fired boiler contains a trace amount of mercury due to coal. 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 that removes mercury from exhaust gas, for example, there is an apparatus in which a denitration unit, a dedusting unit, and a desulfurization unit 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 concentration of hydrogen chloride increases. That is, the higher the concentration of hydrogen chloride, the higher the generation ratio of divalent mercury Hg ²⁺ (HgCl ₂ ). As a result, the ratio of mercury collected in the dedusting section and desulfurization section also increases.

Since divalent mercury Hg ²⁺ (HgCl ₂ ) is more adsorbable than metallic mercury Hg ⁰ , it is adsorbed on the ash surface and collected as particulate mercury Hg ^{P in the} dust removal part. At this time, since the proportion of mercury collected in the dust removal part depends on the amount of unburned carbon in the ash, if there is little unburned carbon, the percentage collected by the ash in the dust removal part Will be less.
Thus, if the ratio collected as particulate mercury Hg ^P in the dedusting part is not so high, it is equivalent to metal mercury Hg ⁰ oxidized on the denitration catalyst and divalent mercury Hg ²⁺ (HgCl ₂ ). The amount passes through the dedusting part and is collected in the drainage of the desulfurization part.

Here, the ash collected in the dust removal part is effectively used as a cement or concrete material. However, since it contains more mercury than in the past, further consideration must be given to measures such as mercury elution.
On the other hand, mercury that has reached the desulfurization section is collected as part of the sludge in the drainage of the desulfurization section, and can be treated in a state managed as industrial waste.
Therefore, it is considered that mercury oxidized on the denitration catalyst is more preferably collected in the desulfurization part than in the dust removal part.

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 the concentration of hydrogen chloride in the exhaust gas.

  In terms of the concentration of hydrogen chloride 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. Converted to the concentration of hydrogen chloride in the combustion exhaust gas, it becomes less than 1 ppm to several tens of ppm. If the concentration of hydrogen chloride in the exhaust gas is thus low, depending on the properties of the exhaust gas, Mercury oxidation efficiency on unburned carbon is reduced, and accordingly, mercury collection efficiency in the dedusting section and desulfurization section is also decreased.

In order to cope with this, a method of injecting a halogen-containing substance into the flue from the coal-fired boiler to the chimney (see, for example, Patent Document 2), or a chlorine compound is supplied to the combustion device together with the coal and burned. Thereafter, a method (for example, see Patent Document 3) in which the exhaust gas temperature is cooled to 150 ° C. or lower in front of a dust removing part such as an electric dust collector and mercury is removed in the dust removing part has been proposed. Thus, if the concentration of hydrogen chloride in the exhaust gas is increased by adding a chlorine compound, the conversion of metallic mercury Hg ⁰ to divalent mercury Hg ²⁺ (HgCl ₂ ) can be promoted.

Here, molecular chlorine (Cl ₂ ) is known to have higher oxidation activity of metallic mercury Hg ⁰ than hydrogen chloride (HCl) (see, for example, Non-Patent Document 1), and reaction formula (2 ), This molecular chlorine can also convert metallic mercury Hg ⁰ to divalent mercury Hg ²⁺ (HgCl ₂ ).
Hg ⁰ + Cl ₂ → HgCl ₂ reaction formula (2)
U.S. Patent No. 6521021 Japanese Patent Laid-Open No. 10-230137 JP 2000-325747 A Study of Mercury Speciation from Simulated Coal Gasification Dennis Y. Lu, David L. Granatstein, and Donald J. Rose CANMET Energy Technology Center, Natural Resources Canada, Building # 1, 1Haanel Drive, Ottawa, ON K1A 1M1 Canada, and Electricity and Industrial Combustion Branch, Environment Canada, 351 St. Joseph Boulevard, 10th Floor, Gatineau, Quebec, QC K1A 0H3 Canada Ind. Eng. Chem. Res. 2004, 43, 5400-5404

However, in the mercury removal method described above, in the method described in Patent Document 2 in which a substance containing halogen is injected into the flue, assuming a chlorine compound, compounds such as CaCl ₂ , NaCl, and NH ₄ Cl are exemplified. These compounds can be decomposed into hydrogen chloride by heating to oxidize metallic mercury Hg ⁰ , but it is sufficient when a halogen compound is injected except when hydrogen chloride is directly injected into the flue. It is necessary to heat at a temperature and take sufficient residence time to allow the decomposition to proceed.

On the other hand, the method described in Patent Document 3 in which mercury is removed in the dust removing section has a problem that only a part of mercury can be removed.
In addition, in any method, ammonia (NH ₃ ) is preferentially adsorbed on the active metal (V) on the surface of the denitration catalyst, and divalent mercury of metallic mercury Hg ⁰ on the denitration catalyst. It is known that the conversion reaction to Hg ²⁺ (HgCl ₂ ) is hindered, and in order to improve the conversion efficiency of metallic mercury Hg ⁰ while maintaining the denitration performance of the denitration catalyst, the hydrogen chloride in the exhaust gas The concentration must be increased.

At this time, if the concentration of hydrogen chloride in the exhaust gas is increased, there is a problem that the flue and the heat exchanger are corroded, and if an excessive amount of hydrogen chloride is dissolved in the absorbent of the wet desulfurization section, the desulfurization performance is reduced. The problem of degradation occurs.
Although molecular mercury (Cl ₂ ) can also oxidize metallic mercury Hg ⁰ , almost all of the chlorine present in the exhaust gas exists as hydrogen chloride, and molecular chlorine is present in the exhaust gas. Hardly exist.

  The present invention has been made in order to solve the above-described problems.When fossil fuel, for example, coal, is burned by a combustion apparatus such as a boiler, mercury is not affected regardless of the properties of exhaust gas discharged from the combustion apparatus. An object of the present invention is to provide an exhaust gas treatment method and an exhaust gas treatment apparatus that can be removed with high efficiency and low cost.

  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 is supplied to the combustion device for combustion, and a part of the hydrogen chloride contained in the exhaust gas discharged from the combustion device is converted to chlorine by a hydrogen chloride conversion catalyst disposed in the flue from the combustion device. The exhaust gas treatment method is configured to promote the oxidation reaction of metallic mercury contained in the exhaust gas with a denitration catalyst disposed downstream of the hydrogen chloride conversion catalyst in the flue. Is a means for solving the above-described conventional problems.

In the exhaust gas treatment method according to claim 2 of the present invention, hydrogen chloride is supplied to the upstream side of the hydrogen chloride conversion catalyst in the combustion device or the flue, and a part of the hydrogen chloride is converted to chlorine by the hydrogen chloride conversion catalyst. It is configured to convert and flow downstream.
The invention according to claim 3 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, After the fossil fuel is supplied to the combustion device and burned, hydrogen chloride is added to the hydrogen chloride conversion catalyst disposed in the vicinity of the flue from the combustion device, and a part of this hydrogen chloride is converted into chlorine, This chlorine is supplied to the upstream side of the denitration catalyst disposed in the flue to promote the oxidation reaction of metallic mercury contained in the exhaust gas at the denitration catalyst.

  On the other hand, the invention according to claim 4 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 such as coal is burned by a combustion device such as a boiler. A denitration catalyst that oxidizes metallic mercury contained in the exhaust gas discharged from the combustion device located in the flue from the combustion device, and an upstream side of the denitration catalyst in the flue in the exhaust gas The structure of this exhaust gas treatment apparatus solves the above-mentioned conventional problems, characterized by comprising a hydrogen chloride conversion catalyst that converts part of the hydrogen chloride contained in the gas into chlorine and flows it downstream. As a means for.

In the exhaust gas treatment apparatus according to claim 5 of the present invention, a hydrogen chloride supply section for supplying hydrogen chloride to the upstream side of the hydrogen chloride conversion catalyst in the combustion device or the flue is provided.
The invention according to claim 6 of the present invention is an exhaust gas treatment apparatus that removes mercury contained in exhaust gas discharged from a combustion apparatus when fossil fuel such as coal is burned in a combustion apparatus such as a boiler, A denitration catalyst that oxidizes metallic mercury contained in the exhaust gas discharged from the combustion device located in the flue from the combustion device, a hydrogen chloride conversion catalyst disposed near the flue from the combustion device, and A hydrogen chloride supply unit for supplying hydrogen chloride to the hydrogen chloride conversion catalyst, wherein the hydrogen chloride conversion catalyst converts a part of the hydrogen chloride supplied from the hydrogen chloride supply unit to chlorine, and a denitration catalyst in the flue The configuration is such that it is supplied to the upstream side.

In the exhaust gas treatment method and exhaust gas treatment apparatus of the present invention, conversion from hydrogen chloride (HCl) to more active chlorine (Cl ₂ ) is performed on the hydrogen chloride conversion catalyst as shown in the reaction formula (3). It has become so.
HCl + 1 / 4O ₂ → 1 / 2H ₂ O + 1 / 2Cl ₂ reaction formula (3)
As the hydrogen chloride conversion catalyst, for example, iron chloride (FeCl ₃ ) or copper chloride (CuCl ₂ ) is used, or these are used as aluminum oxide (Al ₂ O ₃ ), titanium oxide (TiO ₂ ), or silicon oxide (SiO ₂ ). ₂ ) or the like supported on a carrier can be used.

Here, some fossil fuels such as coal, for example, coal, contain a lot of chlorine and some contain little.
The exhaust gas treatment method according to claim 1 of the present invention and the exhaust gas treatment device according to claim 4 are suitable for use in the case of burning coal containing a large amount of chlorine. In this exhaust gas treatment method and exhaust gas treatment device, If a part of hydrogen chloride generated in large quantities due to combustion of coal containing a large amount of hydrogen is converted to chlorine by a hydrogen chloride conversion catalyst, the chlorine concentration in the exhaust gas will increase, and the downstream side of this hydrogen chloride conversion catalyst The oxidation reaction of metallic mercury in the denitration catalyst located in the center is promoted without being hindered by ammonia, and mercury is efficiently captured in the dedusting section and wet desulfurization section located downstream of the flue. Become.

  On the other hand, the exhaust gas treatment method according to claims 2 and 3 and the exhaust gas treatment apparatus according to claims 5 and 6 of the present invention are suitable for use when burning coal containing almost no chlorine. And in the exhaust gas treatment device, hydrogen chloride is supplied to the upstream side of the hydrogen chloride conversion catalyst in the combustion device or flue to compensate for the small amount of hydrogen chloride generated by coal combustion. If a part is converted into chlorine with a hydrogen chloride conversion catalyst, the chlorine concentration in the exhaust gas becomes high as in the exhaust gas treatment method according to claim 1 and the exhaust gas treatment device according to claim 4, and hydrogen chloride is produced. The oxidation reaction of metallic mercury at the denitration catalyst located downstream of the conversion catalyst is promoted without being inhibited by ammonia.

  In particular, in the exhaust gas treatment method according to claim 3 of the present invention and the exhaust gas treatment apparatus according to claim 6, easy-to-handle hydrogen chloride is directly supplied to the hydrogen chloride conversion catalyst disposed in the vicinity of the flue and is corrosive on the spot. Since it is converted to chlorine which is high and is not easy to handle and flows into the flue, conversion to chlorine in the hydrogen chloride conversion catalyst is efficiently performed and workability is improved.

  In order to prevent mercury from being adsorbed by the ash in the dedusting part arranged on the downstream side of the denitration catalyst in the flue, there is no particular limitation, but the dedusting part is at a relatively high temperature of 150 ° C. or higher. It is desirable to operate.

Since the exhaust gas treatment method according to claim 1 and the exhaust gas treatment apparatus according to claim 4 of the present invention are configured as described above, when the fossil fuel, for example, coal, is burned by a combustion device such as a boiler, Regardless of the nature of the exhaust gas discharged, it is possible to obtain a very excellent effect that mercury can be removed with high efficiency and low cost.
In addition, since the exhaust gas treatment method according to claim 2 and the exhaust gas treatment apparatus according to claim 5 of the present invention are configured as described above, when the fossil fuel, for example, coal is burned by a combustion device such as a boiler, Even if it contains almost no chlorine, it is possible to remove mercury with high efficiency and low cost regardless of the properties of the exhaust gas.

  Furthermore, since the exhaust gas treatment method according to claim 3 of the present invention and the exhaust gas treatment device according to claim 6 are configured as described above, they are the same as the exhaust gas treatment method according to claim 2 and the exhaust gas treatment device according to claim 5. In addition to obtaining the effect, it is possible to improve the efficiency of conversion to chlorine in the hydrogen chloride conversion catalyst, and it is possible to achieve an excellent effect that it is possible to improve workability.

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 a case where it is applied and the coal containing a lot of chlorine is burned will be described as an example.

As shown in FIG. 1, the exhaust gas treatment apparatus 1 includes a hydrogen chloride conversion catalyst 3, a denitration catalyst 4, an air heater 5, a dust removal unit 6, which are sequentially arranged in a flue R from a coal burning boiler B to a chimney 2. A heat exchanger 7, a desulfurization section 8, and a heat exchanger 9 are provided. On the upstream side of the denitration catalyst 4 in the flue R, although not shown, NO _X contained in the exhaust gas is reduced and converted into nitrogen and water. Therefore, ammonia is added.

The hydrogen chloride conversion catalyst 3 converts a part of hydrogen chloride contained in the exhaust gas discharged from the coal-fired boiler B into chlorine and flows it downstream, while the hydrogen chloride conversion catalyst 3 denitration catalyst 4 located downstream of, along with reducing the NO _X converted to nitrogen and water, which is intended to oxidize metallic mercury contained in the exhaust gas.
That is, a part of hydrogen chloride generated in large quantities due to combustion of coal containing a large amount of chlorine is converted into chlorine by the hydrogen chloride conversion catalyst 3 and flows downstream to increase the chlorine concentration in the exhaust gas. The oxidation reaction of metallic mercury Hg ⁰ in the denitration catalyst 4 located on the downstream side of the conversion catalyst 3 is promoted without being inhibited by ammonia.

At this time, water-soluble divalent mercury Hg ²⁺ (HgCl ₂ ) produced by the oxidation reaction of metallic mercury Hg ⁰ and chlorine Cl ₂ in the denitration catalyst 4 is adsorbed by the ash in the dedusting unit 6. In order to suppress this, the air heater 5 is adjusted to operate the dust removing unit 6 at a temperature of 150 ° C. or higher.
Then, in the wet desulfurization unit 8, divalent mercury Hg 2+ which has passed through the dedusted section 6 ^(HgCl ₂₎ and a liquid phase absorption, so that collecting incorporate in the sludge.

  In the exhaust gas treatment apparatus 1, coal containing a large amount of chlorine is supplied to the coal-fired boiler B to start combustion. And when processing the exhaust gas discharged | emitted from the coal burning boiler B, first, in the hydrogen chloride conversion catalyst 3 in the flue R, a part of hydrogen chloride contained in the exhaust gas discharged | emitted from the coal burning boiler B Is converted to chlorine and flows downstream, whereby the concentration of chlorine in the exhaust gas increases on the downstream side of the hydrogen chloride conversion catalyst 3.

At this time, ammonia is added to the upstream side of the denitration catalyst 4, and NO _X contained in the exhaust gas is reduced and converted into nitrogen and water.
In this denitration catalyst 4, in an atmosphere with a high chlorine concentration, metallic mercury Hg ^{0 in} mercury contained in exhaust gas undergoes an oxidation reaction with chlorine Cl ₂ to convert it into water-soluble divalent mercury Hg ²⁺ (HgCl ₂ ). To flow downstream.

At this time, the dedusting part 6 located downstream of the denitration catalyst 4 is operated at a temperature of 150 ° C. or more by adjusting the air heater 5, so that divalent mercury Hg ²⁺ (HgCl ₂ ) Adsorption to ash is avoided.
In the wet desulfurization section 8, the divalent mercury Hg ²⁺ (HgCl ₂ ) that has passed through the dedusting section 6 is absorbed in the liquid phase, taken into the sludge and collected, and then the mercury-containing sludge is collected. The collection process is made.

As described above, in the exhaust gas treatment method and the exhaust gas treatment apparatus 1 of this embodiment, when coal containing a large amount of chlorine is burned by the coal-fired boiler B, the adsorbent is not used for removing mercury. The running cost can be reduced, and in addition, the oxidation reaction of the metallic mercury Hg ⁰ in the denitration catalyst 4 can be promoted without being inhibited by ammonia, so the dedusting part 6 disposed on the downstream side of the flue R In the wet desulfurization section 8, mercury can be removed with high efficiency and low cost regardless of the properties of the exhaust gas.

FIG. 2 shows an exhaust gas treatment apparatus according to another embodiment of the present invention. The difference between the exhaust gas treatment apparatus 1 of this embodiment and the previous exhaust gas treatment apparatus 1 is that of the hydrogen chloride conversion catalyst 3 in the flue R. The other structure is the same as that of the exhaust gas treatment apparatus 1 except that the hydrogen chloride supply unit 10 for supplying hydrogen chloride is provided upstream.
The exhaust gas treatment apparatus 1 of this embodiment is suitable for use when burning coal containing almost no chlorine. In this exhaust gas treatment apparatus 1, the amount of hydrogen chloride generated along with the combustion of coal is small. In order to compensate for this, hydrogen chloride is supplied from the hydrogen chloride supply unit 10 to the upstream side of the hydrogen chloride conversion catalyst 3 in the flue R, and a part of this hydrogen chloride is converted into chlorine by the hydrogen chloride conversion catalyst 3 and flowed. For example, the chlorine concentration in the exhaust gas becomes high, and the oxidation reaction of metallic mercury Hg ⁰ in the denitration catalyst 4 located downstream of the hydrogen chloride conversion catalyst 3 is promoted without being inhibited by ammonia.

Therefore, even in the exhaust gas treatment apparatus 1 of this embodiment, mercury is highly efficient and low cost regardless of the properties of the exhaust gas in the dedusting unit 6 and the wet desulfurization unit 8 disposed on the downstream side of the flue R. It can be removed.
The supply of hydrogen chloride from the hydrogen chloride supply unit 10 may be performed directly to the coal fired boiler B.

  FIG. 3 shows an exhaust gas treatment apparatus according to still another embodiment of the present invention. The exhaust gas treatment apparatus 1 of this embodiment is different from the previous exhaust gas treatment apparatus 1 in that a hydrogen chloride conversion catalyst 3 and this hydrogen chloride are used. A hydrogen chloride supply unit 10 for supplying hydrogen chloride to the conversion catalyst 3 is arranged in the vicinity of the flue R. In the hydrogen chloride conversion catalyst 3, a part of the hydrogen chloride supplied from the hydrogen chloride supply unit 10 is converted to chlorine. The other configuration is the same as that of the previous exhaust gas treatment apparatus 1 in that it is supplied to the upstream side of the denitration catalyst 4 in the flue R.

The exhaust gas treatment device 1 of this embodiment is also suitable for use when burning coal containing almost no chlorine. In this exhaust gas treatment device 1, the amount of hydrogen chloride generated with the combustion of coal is small. In order to compensate for this, hydrogen chloride is supplied from the hydrogen chloride supply unit 10 to the hydrogen chloride conversion catalyst 3 in the vicinity of the flue R, and a part of this hydrogen chloride is converted to chlorine by the hydrogen chloride conversion catalyst 3 to thereby form the flue R It is allowed to flow to the upstream side of the denitration catalyst 4 in the, higher the chlorine concentration in the exhaust gas, so that the oxidation reaction of metallic mercury Hg ⁰ in the denitration catalyst 4 is promoted without being hindered by the ammonia.

Therefore, even in the exhaust gas treatment apparatus 1 of this embodiment, mercury is highly efficient and low cost regardless of the properties of the exhaust gas in the dedusting unit 6 and the wet desulfurization unit 8 disposed on the downstream side of the flue R. It can be removed.
Further, in the exhaust gas treatment apparatus 1 of this embodiment, hydrogen chloride that is easy to handle is directly supplied to the hydrogen chloride conversion catalyst 3 disposed in the vicinity of the flue R, and the chlorine that is highly corrosive and not easy to handle on the spot. Since the gas is converted to flow into the flue R, the hydrogen chloride conversion catalyst 3 is efficiently converted to chlorine, and the workability is improved.

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 the exhaust gas processing apparatus by other embodiment of this invention. It is schematic structure explanatory drawing which shows the exhaust gas processing apparatus by further another embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust gas treatment device 3 Hydrogen chloride conversion catalyst 4 Denitration catalyst 10 Hydrogen chloride supply part B Coal-fired boiler (combustion device)
R Flue

Claims (6)

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,
Supplying and burning the fossil fuel to the combustion device;
A portion of hydrogen chloride contained in the exhaust gas discharged from the combustion device is converted into chlorine and flowed with a hydrogen chloride conversion catalyst disposed in the flue from the combustion device,
An exhaust gas treatment method characterized in that an oxidation reaction of metallic mercury contained in the exhaust gas is promoted by a denitration catalyst disposed downstream of a hydrogen chloride conversion catalyst in the flue.   The hydrogen chloride is supplied to the upstream side of the hydrogen chloride conversion catalyst in the combustion device or the flue, and a part of the hydrogen chloride is converted into chlorine by the hydrogen chloride conversion catalyst and flows downstream. Exhaust gas treatment method. 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,
Supplying and burning the fossil fuel to the combustion device;
After adding hydrogen chloride to the hydrogen chloride conversion catalyst placed in the vicinity of the flue from the combustion device and converting a part of this hydrogen chloride to chlorine,
An exhaust gas treatment method, wherein the chlorine is supplied to an upstream side of a denitration catalyst arranged in the flue to promote an oxidation reaction of metallic mercury contained in the exhaust gas at the denitration catalyst. 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 denitration catalyst that oxidizes metallic mercury contained in the exhaust gas discharged from the combustion device located in the flue from the combustion device;
An exhaust gas treatment apparatus comprising a hydrogen chloride conversion catalyst located upstream of a denitration catalyst in the flue and converting a part of hydrogen chloride contained in the exhaust gas into chlorine and flowing it downstream. .   The exhaust gas treatment apparatus according to claim 4, further comprising a hydrogen chloride supply unit that supplies hydrogen chloride to an upstream side of the hydrogen chloride conversion catalyst in the combustion device or the flue. 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 denitration catalyst that oxidizes metallic mercury contained in the exhaust gas discharged from the combustion device located in the flue from the combustion device;
A hydrogen chloride conversion catalyst disposed near the flue from the combustion device;
A hydrogen chloride supply unit for supplying hydrogen chloride to the hydrogen chloride conversion catalyst is provided,
The exhaust gas treatment apparatus characterized in that the hydrogen chloride conversion catalyst converts a part of hydrogen chloride supplied from the hydrogen chloride supply unit into chlorine and supplies it to the upstream side of the denitration catalyst in the flue. .

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