WO2011016505A1

WO2011016505A1 - System for eliminating mercury from exhaust gas and method for eliminating mercury

Info

Publication number: WO2011016505A1
Application number: PCT/JP2010/063248
Authority: WO
Inventors: 展行鵜飼; 盛紀村上; 進沖野; 晴治香川; 立人長安
Original assignee: 三菱重工業株式会社
Priority date: 2009-08-05
Filing date: 2010-08-05
Publication date: 2011-02-10
Also published as: JP2011031212A

Abstract

Disclosed are a method for eliminating mercury and a system for eliminating mercury from exhaust gas, said system having long-term reliability and having a high mercury elimination efficacy, as well as being able to decrease the degradation of an exhaust gas treatment facility. The system for eliminating mercury from exhaust gas is provided with an ammonium chloride pre-treatment means (2) that performs pre-treatment of ammonium chloride, an ammonium chloride supply means (16) that supplies the pre-treated ammonium chloride to the exhaust gas, a reductive denitrification means (3) that performs chlorination of mercury and reduction of nitrogen oxides in the aforementioned exhaust gas, and a wet desulfurization means (6) that eliminates the aforementioned chlorinated mercury and sulfur oxides in the aforementioned exhaust gas by means of an alkali absorption fluid; and the aforementioned ammonium chloride pre-treatment means (2) is provided with a coarse material elimination means (21) that eliminates coarse material from the aforementioned ammonium chloride.

Description

Exhaust gas mercury removal system and mercury removal method

The present invention relates to treatment of combustion exhaust gas, and more particularly to a system and method for removing mercury in combustion exhaust gas.

There is a trace amount of mercury in the exhaust gas generated by the combustion of fossil fuels such as coal and heavy oil, and it has been necessary to develop a method for reducing the release to the environment. Various methods have been tried so far for the purpose of removing mercury from combustion exhaust gas.

It has been proposed that mercury contained in combustion exhaust gas is converted to mercury oxide such as mercury chloride, which is easily adsorbed on activated carbon, etc. by an additive containing halogen, and adsorbed on activated carbon in fly ash to be removed ( For example, see Patent Document 1). However, a mercury removal method using an adsorbent such as activated carbon or a selenium filter has already been put into practical use for waste incineration exhaust gas, but requires a special adsorption removal apparatus.

On the other hand, in exhaust gas, mercury exists mainly in the form of metallic mercury and mercury chloride, and mercury oxide such as mercury chloride is known to have higher solubility in water than metallic mercury. . From this, by adding a chlorinating agent to the exhaust gas and changing the mercury into a water-soluble form, NO _x , SO can be obtained without changing the exhaust gas treatment facility having the conventional reductive denitration device and the wet desulfurization device. A method of removing mercury simultaneously with the treatment of _x has been proposed (see, for example, Patent Document 2). In this method, after the mercury chlorinating agent is added to the combustion exhaust gas, the water-insoluble metal mercury is converted to water-soluble mercury chloride on the denitration catalyst, and is absorbed and removed by the subsequent wet desulfurization apparatus. However, the chlorinating agent added to the flue is often highly corrosive, and the chlorinating agent exceeding the required amount causes corrosion of the flue and the downstream equipment, resulting in a problem of shortening the plant life. .

Therefore, it has been proposed to adjust the supply amount of the chlorinating agent to the exhaust gas based on the measured values of the chlorinating agent concentration and mercury concentration in the flue (for example, Patent Document 3). According to this method, it is possible to prevent corrosion of an apparatus or the like due to an excessive amount of chlorinating agent. However, further improvements are desired, such as improved system reliability and improved mercury removal efficiency.

JP 2005-230810 A Japanese Patent Laid-Open No. 10-230137 JP 2007-167743 A

An object of the present invention is to provide an exhaust gas mercury removal system and a mercury removal method that can reduce deterioration of an exhaust gas treatment facility, have long-term reliability, and have high mercury removal efficiency.

The present invention has been made to solve the above problems. That is, according to one embodiment of the present invention, an ammonium chloride pretreatment means for pretreatment of ammonium chloride, an ammonium chloride supply means for supplying pretreated ammonium chloride to exhaust gas, and nitrogen oxidation in the exhaust gas are performed. Reduction denitration means for reducing substances and chlorination of mercury, and wet desulfurization means for removing sulfur oxides and chlorinated mercury in the exhaust gas with an alkali absorbing solution. The processing means includes a coarse substance removing means for removing the coarse substance from the ammonium chloride.

In another form of the exhaust gas mercury removal system according to the above embodiment, the ammonium chloride pretreatment means further includes a separate sublimation means for sublimating solid ammonium chloride, and the coarse substance removal means is a dust collector. is there. It is preferable that the supply unit further includes a dilution unit for diluting the sublimation gas of ammonium chloride. In the mercury removal system of this embodiment, since the denitration catalyst inhibitor is removed from ammonium chloride, mercury can be chlorinated efficiently.

In another form of the exhaust gas mercury removal system according to the above embodiment, the ammonium chloride supply means supplies the ammonium chloride aqueous solution so as not to adhere to the inner wall of the flue through which the exhaust gas circulates. The substance removal means includes at least one selected from the group consisting of a gravity precipitation tank, a hydrocyclone, a membrane separator, and a screen, and agitates the exhaust gas supplied with ammonium chloride before the reductive denitration means. Means are further provided. The structure for supplying ammonium chloride aqueous solution so that it does not adhere to the inner wall of the flue through which exhaust gas flows is that the spraying means provided in the ammonium chloride supply means is arranged at a certain distance from the inner wall of the flue in the flue. It is preferable that it is a structure. The distance above a certain distance is a distance sufficient for vaporizing the sprayed droplets before they reach the flue wall from the spraying means. Alternatively, the structure in which the ammonium chloride aqueous solution is supplied so as not to adhere to the inner wall of the flue through which the exhaust gas circulates means that the inner wall and the double tube are formed inside the inner wall of the flue where the droplets to be sprayed can reach. The structure provided with the partition provided in may be sufficient.

In the exhaust gas mercury removing system according to the above embodiment, the coarse substance removing means is one selected from the group consisting of a gravity precipitation tank, a liquid cyclone provided in a subsequent stage of the gravity precipitation tank, a membrane separation device, and a screen. It is preferable to provide the above.

Another aspect of the present invention is a method for removing mercury from exhaust gas, the step of removing coarse substances from ammonium chloride, the step of supplying ammonium chloride from which coarse substances have been removed to the exhaust gas, and the supply of ammonium chloride. A step of bringing the exhaust gas contacted with the denitration catalyst, and a step of bringing the exhaust gas brought into contact with the denitration catalyst into contact with an alkali absorbing solution. By bringing the exhaust gas into contact with the alkali absorbing liquid, sulfur oxides and mercury in the exhaust gas can be removed.

In another embodiment of the method for removing mercury from exhaust gas according to the above embodiment, the ammonium chloride is solid ammonium chloride, and the step of sublimating the solid ammonium chloride with a separate vaporizer is performed by adding a coarse substance. The ammonium chloride that is further included before the removing step and is supplied to the exhaust gas is a sublimation gas of ammonium chloride. The mercury removing method according to the above embodiment preferably further includes a step of supplying a dilution gas to the sublimation gas after the step of sublimating ammonium chloride.

In another form of the method for removing mercury from exhaust gas according to the above embodiment, the step of supplying the ammonium chloride to the exhaust gas in which the ammonium chloride is an ammonium chloride aqueous solution is a smoke in which the exhaust gas circulates through the ammonium chloride aqueous solution. It is a step of spraying so as not to adhere to the inner wall of the road, and further includes a step of stirring the vaporized gas of the aqueous ammonium chloride solution and the exhaust gas in the flue after the step of supplying the ammonium chloride to the exhaust gas. The supply of the ammonium chloride to the exhaust gas is preferably performed by an ammonium chloride supply means having a structure capable of supplying so that droplets of the ammonium chloride aqueous solution do not adhere to the inner wall of the flue.

According to the present invention, it is possible to provide an exhaust gas mercury removal system and a removal method that can reduce deterioration of an exhaust gas treatment facility, have long-term reliability, and have excellent removal efficiency. Further, according to the present invention, since coarse substances are removed from ammonium chloride, which is a mercury chlorinating agent, it is possible to prevent clogging / wearing of nozzles and the like in the mercury removal system.

FIG. 1 is a diagram illustrating an embodiment of the mercury removal system of the present invention. FIG. 2 is a diagram illustrating a second embodiment of the mercury removal system of the present invention. FIG. 3 is a graph showing the gas-solid equilibrium of NH ₃ and HCl. FIG. 4 is a diagram for explaining the ammonium chloride pretreatment means 2 constituting a part of the mercury removal system of the present invention. FIG. 5 is a diagram for explaining a hot cyclone which is an embodiment of the coarse substance removing means of the present invention. FIG. 6 is a diagram illustrating a third embodiment of the mercury removal system of the present invention. FIG. 7 is an enlarged view illustrating the configuration of an embodiment of the ammonium chloride supply unit 16 of the present invention. FIG. 8 is a graph in which the time taken for the droplets of the aqueous ammonium chloride solution to evaporate in the flue is predicted in relation to the droplet diameter. FIG. 9 is a view for explaining an embodiment of the ammonium chloride supply means 16 of the present invention. FIG. 10 is a diagram for explaining a fourth embodiment of the mercury removal system of the present invention.

Hereinafter, the mercury removal system for exhaust gas and the mercury removal method according to the present invention will be described in more detail with reference to embodiments thereof. The present invention is not limited to the following embodiments.

FIG. 1 shows an exhaust gas treatment system including a first embodiment of a mercury removal system 100 of the present invention.
A mercury removal system 100 shown in FIG. 1 includes an ammonium chloride pretreatment unit 2, an ammonium chloride supply unit 16, a reduction denitration unit 3, an air heater 4, an electrostatic precipitator 5, a wet desulfurization unit 6, and a chimney 7 as main components. Yes.

The mercury removal system 100 according to the present embodiment includes reductive denitration means 3 connected to the downstream of the boiler 1 by a flue 26. Ammonium chloride supply means 16 is installed in the flue 26 connecting the boiler 1 and the reductive denitration means 3. The ammonium chloride supply means 16 is connected to the ammonium chloride pretreatment means 2 via a pipe line. An air heater 4 connected by a flue is provided downstream of the reducing denitration means 3. An electric dust collector 5 is provided downstream of the air heater 4, and the electric dust collector 5 is connected to the air heater 4 by a flue. The wet desulfurization means 6 is provided in the downstream of the electric dust collector 5, and the wet desulfurization means 6 is connected to the electric dust collector 5 by a flue. A chimney 7 connected by a flue is installed downstream of the wet desulfurization means 6. A belt filter 8 is further installed downstream of the wet desulfurization means 6.

The boiler 1 is provided in the upstream of the mercury removal system 100, burns fossil fuels such as heavy oil and coal, and discharges exhaust gas. The exhaust gas contains harmful substances such as nitrogen oxides, sulfur oxides, and mercury.

The ammonium chloride pretreatment means 2 of this embodiment pretreats ammonium chloride before being supplied into the flue gas in the flue. The ammonium chloride pretreatment means 2 includes a coarse substance removal means 21. The coarse substance removing means 21 separates and removes the coarse substance from ammonium chloride. As the coarse substance removing means 21, a cyclone, an electrostatic precipitator, a gravity sedimentation tank, a film, or the like can be used. A coarse substance means an impurity mixed in ammonium chloride as a raw material. Impurities include coarse dust, insects, minerals, earth and sand, vegetation, glass, metal scraps, and the like.

The ammonium chloride supply means 16 supplies ammonium chloride after removing coarse substances to the exhaust gas in the flue 26. The ammonium chloride supply means 16 is provided downstream of the coarse substance removing means 21 and is connected to the coarse substance removing means 21 by a pipe line. As the ammonium chloride supply means 16, for example, a spray grid having a plurality of spray nozzles and a spray grid having a plurality of spray nozzles can be used.

The reductive denitration means 3 is an apparatus that reduces nitrogen oxides in exhaust gas with a denitration catalyst and generates mercury chloride by HCl and metal mercury generated by decomposition of ammonium chloride. As the reductive denitration means 3, a general one having a reductive denitration catalyst can be used. The denitration catalyst provided in the reduction denitration means 3 is not particularly limited, but, for example, a metal oxide such as W, Sn, In, Co, Ni, Fe, Ni, Ag, or Cu supported on a support such as zeolite. Can be used. The amount of the reductive denitration catalyst provided in the reductive denitration means 3 can be increased from the usual amount in order to increase the mercury oxidation efficiency.

The wet desulfurization means 6 is an apparatus that absorbs and removes sulfur oxides present in exhaust gas and mercury oxides such as mercury chloride. As the wet desulfurization means 6, a conventional one having an alkali absorbing liquid can be used. Examples of the alkali absorbing liquid include, but are not limited to, aqueous solutions of calcium carbonate, calcium hydroxide, sodium hydroxide, sodium sulfite, ammonia, magnesium hydroxide, and the like. It is preferable that the wet desulfurization means 6 further includes a mercury re-scattering prevention device (not shown). The mercury re-scattering prevention device is a device that keeps the oxidation-reduction potential of the alkaline absorbent in a certain range by supplying an oxidizing agent or air to the alkaline absorbent. The mercury re-scattering prevention device prevents the mercury oxide (Hg ²⁺ ) in the absorption liquid from being reduced to metallic mercury (Hg ⁰ ) by SO ₂ or the like, as shown in the following formula (1). To prevent it.
Hg ²⁺ + 2e ⁻ ⇔ Hg ⁰ (1)
The mercury re-scattering prevention device is preferably a device capable of adjusting the redox potential of the absorbing solution to 150 to 600 mV. A belt filter 8 is installed downstream of the wet desulfurization means 6. The belt filter 8 is a device that dehydrates and collects the gypsum slurry generated in the absorption tower of the wet desulfurization means 6, and discharges the gypsum 9.

The air heater 4 is a device that adjusts the exhaust gas temperature. The electric dust collector 5 removes soot in the exhaust gas. The chimney 7 discharges the exhaust gas out of the system. The air heater 4, the electrostatic precipitator 5, the chimney 7 and the like can be general ones.

Next, an embodiment of a method for removing mercury from exhaust gas using the mercury removal system according to this embodiment will be described. The mercury removal method of the present embodiment includes a step of removing coarse substances from ammonium chloride, a step of supplying ammonium chloride from which coarse substances have been removed to exhaust gas, and a step of contacting exhaust gas supplied with ammonium chloride with a denitration catalyst. And a step of bringing the exhaust gas brought into contact with the denitration catalyst into contact with the alkali absorbing solution.

In the mercury removal method according to the present embodiment, ammonium chloride is used to oxidize metallic mercury in the exhaust gas. Ammonium chloride having a purity that is usually used for fertilizers can be used. The ammonium chloride may be a solid or an aqueous solution. A coarse substance is mixed in the ammonium chloride as a raw material.

Exhaust gas generated by combustion of coal and heavy oil usually contains mercury in addition to harmful substances such as nitrogen oxides and sulfur oxides. The exhaust gas flows out of the boiler 1 and flows in the flue 26.

In the step of removing coarse substances from ammonium chloride, the coarse substance removing means 21 separates and removes coarse substances mixed in ammonium chloride. By this step, even when ammonium chloride having a purity that is low enough to be used for fertilizer is used as a raw material, it can be provided to the ammonium chloride supply means 16 in a state in which coarse substances are removed.

Following the step of removing coarse material, a step of supplying ammonium chloride from which the coarse material has been removed to the exhaust gas is performed. The step of supplying ammonium chloride is performed in the flue 26 connecting the boiler 1 and the reducing denitration means 3. The ammonium chloride supplied into the exhaust gas is in the form of an aqueous solution or a gas. The ammonium chloride is preferably sprayed as droplets in the exhaust gas or introduced as a sublimated gas. It is preferable to supply ammonium chloride so that the concentration in the exhaust gas is in the range of 10 to 200 ppm.

Most of the ammonium chloride supplied into the exhaust gas exists in a state dissociated into NH ₃ and HCl as shown in the formula (2). This is because the exhaust gas in the flue 26 is usually at a high temperature of 350 to 380 ° C.
NH ₄ Cl ⇒ NH ₃ + HCl (2)

The method according to the present embodiment may further include a step of adding HCl to the exhaust gas. This is because HCl alone generated by dissociation of ammonium chloride may be insufficient to oxidize metallic mercury. The addition of HCl is preferably performed after the step of supplying ammonium chloride in the flue connecting the ammonium chloride supply unit 16 and the reductive denitration unit 3.

In the step of bringing the exhaust gas supplied with ammonium chloride into contact with the denitration catalyst, the mixture of the exhaust gas and ammonium chloride is caused to flow into the reducing denitration means 3 through the flue 26 and is brought into contact with the denitration catalyst provided in the reduction denitration means 3. Under the denitration catalyst, NH ₃ produced by decomposition of ammonium chloride reacts with nitrogen oxides in the exhaust gas, and nitrogen oxides are reduced to nitrogen as shown in formula (3).
4NO + 4NH ₃ + O ₂ ⇒ 4N ₂ + 6H ₂ O (3)
At the same time, under the denitration catalyst, metal mercury in the exhaust gas is oxidized to mercury chloride by HCl generated by the decomposition of ammonium chloride, as shown in formula (4).
Hg ⁰ + 2HCl + 1 / 2O ₂ ⇒ HgCl ₂ + H ₂ O (4)
As a result, the exhaust gas that has undergone the step of contacting with the denitration catalyst mainly contains SO _x , CO, CO ₂ , HgCl ₂ , N ₂ , O ₂ , and water vapor, and unreacted NH ₃ , HCl, and NO also remain. .

The method according to the present embodiment may further include a step of adding activated carbon to the exhaust gas. The step of adding the activated carbon is preferably performed after the step of bringing the exhaust gas into contact with the denitration catalyst. By this step, mercury chloride in the exhaust gas can be adsorbed on the activated carbon, and there is an advantageous effect of reducing the amount of mercury flowing into the wet desulfurization means 6.

The temperature of the exhaust gas flowing out from the reducing denitration means 3 is adjusted by the air heater 4. Next, the dust is removed from the exhaust gas in the electric dust collector 5. Next, the exhaust gas from which the dust and the like are removed is caused to flow into the wet desulfurization means 6. In the step of bringing the exhaust gas into contact with the alkali absorbing liquid, the exhaust gas after being brought into contact with the denitration catalyst is brought into contact with the alkali absorbing liquid. In this step, SO _x in the exhaust gas is absorbed into the alkali absorbing solution and removed as a precipitate of gypsum 9, and water-soluble mercury chloride is also absorbed into the alkali absorbing solution and removed. The gypsum slurry precipitated in the alkali absorbing liquid is dehydrated by the belt filter 8 and collected as gypsum 9. The exhaust gas flowing out from the wet desulfurization means 6 is discharged from the chimney 7. In the illustrated embodiment, the step of bringing the exhaust gas into contact with the alkali absorbing liquid supplies air to the alkali absorbing liquid. This is to keep the oxidation-reduction potential within a stable range where HgCl ₂ in the alkali absorbing solution is not reduced to metallic mercury Hg ⁰ and to prevent re-scattering of mercury. In addition to air, an oxidizing agent may be added to the alkali absorbing liquid.

The mercury removal method according to the present embodiment can remove mercury in the exhaust gas, preferably with a mercury removal rate of 90% or more. The mercury removal rate is more preferably 95% or more.

According to the mercury removal system and the mercury removal method of the first embodiment, ammonium chloride is supplied into the exhaust gas after removing the coarse substance, so that the coarse substance is supplied to the ammonium chloride supply means 16 ahead of the coarse substance removal means 21. And does not enter the flue 26. Therefore, it is possible to prevent the ammonium chloride supply means 16 such as a spray nozzle from being clogged with a coarse material, and it is possible to improve the life of the exhaust gas treatment facility.

FIG. 2 is a diagram showing a main part of a second embodiment of the mercury removal system of the present invention. The system according to the second embodiment of the present invention includes an economizer 10, a raw material supply means 23, a sublimation means 22, a coarse substance removal means 21, an ammonium chloride supply means 16, an NH ₃ supply means 11, a reductive denitration means 3, an air heater 4, A wet desulfurization means 6 and a chimney 7 are provided. In FIG. 2, the wet desulfurization means 6 and the chimney 7 on the downstream side of the air heater 4 are omitted. In addition, the component which attached | subjected the same number has the same structure and effect | action. In the present embodiment, the ammonium chloride pretreatment unit 2 includes a raw material supply unit 23 and a sublimation unit 22 in addition to the coarse substance removing unit 21.

The raw material supply means 23 is an apparatus for supplying ammonium chloride 101 as a raw material to the sublimation means 22. The raw material supply means 23 is installed upstream of the sublimation means 22 so that ammonium chloride can be supplied to the sublimation means 22. As the raw material supply means 23, a combination of a silo and a screw feeder can be used, but is not limited to these.

The sublimation means 22 is a device for heating and sublimating solid ammonium chloride. The sublimation means 22 is installed in the front stage of the coarse substance removal means 21 connected by a pipe line. The sublimation means 22 is installed outside the flue 26 as an independent apparatus used for sublimation, not as an apparatus shared with other devices such as the raw material supply means 23 and the flue 26 in the mercury removal system. In the sublimation means 22, the heat necessary for sublimation is supplied from the outside and does not depend only on the heat of the exhaust gas flowing in the flue. In the system according to the present embodiment, by providing the sublimation means 22 independently, it becomes possible to heat ammonium chloride to a high temperature that is impossible with only flue gas, for example, 400 ° C. or higher, or 500 ° C. or higher. Can be heated. Thus, by making it high temperature, ammonium chloride can be sublimated almost completely and can be supplied in exhaust gas as gas. According to the system according to the present embodiment, ammonium chloride can be supplied into the flue as a gas. Therefore, unlike the method of sublimating ammonium chloride with the heat of exhaust gas flowing through the flue, the spray means such as a spray nozzle is blocked.・ Abrasion can be prevented.

In the sublimation means 22, ammonium chloride is preferably sublimated by heating to 400 ° C. or higher. When ammonium chloride sublimes, it decomposes to produce NH ₃ and HCl. Therefore, the sublimation gas of ammonium chloride is a gas containing equimolar NH ₃ and HCl.

As the sublimation means 22, a vaporizer capable of sublimating solid ammonium chloride with a large capacity can be used. Preferably, a vaporizer such as a kiln furnace or a fluidized bed furnace is used. When a kiln furnace is used as the sublimation means 22, L (cylinder length) / F (cylinder diameter) is preferably 3 or more. The solid ammonium chloride supplied to the kiln furnace preferably has a volume ratio of 15% or less in the cylinder of the kiln furnace. Most of the non-volatile material remaining without sublimation remains in the sublimation means 22 as a coarse material 102. Accordingly, the sublimation means 22 of the present embodiment has a function of removing coarse substances 102 such as nonvolatile substances from the exhaust gas in addition to the function of sublimating ammonium chloride.

The coarse substance removing means 21 is an apparatus that can remove coarse substances contained in the sublimation gas of ammonium chloride. The coarse material removed by the coarse material removing means 21 of the present embodiment is a nonvolatile substance. Here, the non-volatile substance mainly refers to a substance that does not gasify even when heated by the sublimation means 22. Nonvolatile substances mixed in ammonium chloride include coarse dust, insects, minerals, earth and sand, vegetation, glass, metal scraps, and denitration catalyst inhibitors such as sodium compounds, phosphate compounds, and calcium compounds. It is done. Specific examples of the denitration catalyst inhibitor include NaCl, PbSO ₄ , and Ca ₃ (PO ₄ ) ₂ . The coarse substance removing means 21 can also remove fine ammonium chloride particles having a particle diameter of 10 μm or more that have flowed out of the sublimation means 22 without being completely sublimated. The coarse substance removing means 21 is installed at the subsequent stage of the sublimation means 22 connected by a pipe line. Ammonium chloride supply means 16 connected by a pipe line is provided downstream of the coarse substance removing means 21. The coarse material removing means 21 is preferably a dust collector such as a cyclone, an electric dust collector, and a bag filter. The coarse substance removing means 21 can remove fine coarse substances having a particle size of preferably 20 μm or more, more preferably a particle size of 10 μm or more. As a whole, the ammonium chloride pretreatment means 2 sublimates ammonium chloride to remove coarse substances.

The ammonium chloride supply means 16 is an apparatus for supplying the sublimation gas of ammonium chloride sublimated by the sublimation means 22 into the exhaust gas flowing in the flue 26. The ammonium chloride supply means 16 is installed in a flue 26 connecting the economizer 10 and the reductive denitration means 3. The ammonium chloride supply means 16 is preferably installed in a straight region of the flue 26 through which exhaust gas flows linearly. The ammonium chloride supply means 16 is not particularly limited as long as the sublimation gas can be mixed with the exhaust gas. The ammonium chloride supply means 16 can preferably use a spray grid or the like having a plurality of nozzles. The pipe line connecting the sublimation means 22 and the ammonium chloride supply means 16 and the inside of the nozzle and the like provided in the ammonium chloride supply means 16 are periodically washed with water and passed through a sublimation gas of ammonium chloride sublimated after drying. Is preferred.

The economizer 10 is a device that recovers thermal energy from the exhaust gas and preheats the water supplied to the boiler 1. The economizer 10 is provided downstream of the boiler 1, and ammonium chloride supply means 16 connected by a flue 26 is installed on the downstream side of the economizer 10.

The NH ₃ supply means 11 injects NH ₃ from the NH ₃ tank into the exhaust gas. The NH ₃ supply means 11 is connected to the flue. As the NH ₃ supply means 11, an ammonia injection grid can be used. The NH ₃ supply means 11 preferably sprays NH ₃ gas into the flue. The NH ₃ supply unit 11 is connected to a flue connecting the ammonium chloride supply unit 16 and the reductive denitration unit 3. The NH ₃ supply unit 11 may be connected to a flue that connects the economizer 10 and the ammonium chloride supply unit 16.

A rectifier 12 is provided in the flue 26 connecting the economizer 10 and the ammonium chloride supply unit 16 and in the flue connecting the NH ₃ supply unit 11 and the reductive denitration unit 3. The rectifier 12 is an apparatus that rectifies the flow of exhaust gas and leveles the flow velocity distribution. When the rectifying device 12 is installed in a region where the flue is bent, the flow rate of the exhaust gas can be prevented from being damaged by the bending. As the rectifier 12, a guide vane, a tube group, or the like can be used. As a result, the flow velocity distribution of the exhaust gas is leveled and the dispersion of the concentration distribution can be eliminated, so that ammonium chloride and mercury can be reacted with higher efficiency, and ammonium chloride that is not used in the reaction is generated. Can be prevented.

In another example, the ammonium chloride pretreatment unit 2 according to the present embodiment may further include a dilution unit (not shown in FIG. 2). In order to dilute the ammonium chloride sublimation gas, the dilution means mixes a gas such as high-temperature air with the sublimation gas to reduce the concentration of the sublimation gas. The dilution means is preferably connected to the sublimation means 22 via a conduit. The dilution means sends the dilution gas to the sublimation means 22 and mixes it with the sublimation gas in the sublimation means 22. As a gas for dilution, in addition to air, water vapor can be used, or exhaust gas flowing in the flue may be reused. When the reused exhaust gas is used as a dilution gas, it is preferable to remove dust in the exhaust gas in advance by a hot cyclone or the like. The dilution means can preferably dilute the sublimation gas concentration to preferably 10,000 to 100,000 ppm. Here, the sublimation gas is a gas generated by sublimation of ammonium chloride, and is a gas containing equimolar NH ₃ and HCl generated by dissociation of NH ₄ Cl. Accordingly, the concentration of the sublimation gas is equal to the concentration of NH ₃ and HCl. As the diluting means, for example, a blower, an exhaust gas bypass pipe or the like can be used.

Next, an embodiment of a mercury removal method using the exhaust gas mercury removal system according to the present embodiment will be described. The method according to this embodiment includes a step of sublimating solid ammonium chloride with a separate vaporizer, a step of removing coarse substances from ammonium chloride, a step of supplying ammonium chloride to exhaust gas, and ammonium chloride is supplied. A step of bringing the exhaust gas contacted with the denitration catalyst and a step of bringing the exhaust gas contacted with the denitration catalyst into contact with the alkaline absorbent. According to the mercury removal system of the present embodiment, a sublimation gas of ammonium chloride is supplied to the exhaust gas in the flue.

In the present embodiment, the solid ammonium chloride 101 is supplied to the sublimation means 22 (vaporizer) by the raw material supply means 23. The solid ammonium chloride supplied to the sublimation means 22 (vaporizer) is preferably ammonium chloride particles. The size of the particles is not particularly limited, but preferably the particle size is 0.1 to 3 mm, more preferably 0.1 to 1 mm. The smaller the particle size, the shorter the time required for sublimation. In the step of sublimating solid ammonium chloride with a separate vaporizer, the solid ammonium chloride is heated and sublimated with an independent vaporizer. The heating temperature is preferably 400 ° C. or higher. By this process, ammonium chloride sublimes to generate sublimation gas.

Most of the non-volatile material remaining without sublimation remains as a coarse substance in the sublimation means 22. Examples of non-volatile substances mixed in ammonium chloride include compounds such as NaCl, PbSO ₄ , and Ca ₃ (PO ₄ ) ₂ in addition to coarse dust and earth and sand. Since these compounds have the property of inhibiting mercury oxidation in a denitration catalyst, it is preferable to remove them before supplying them into the flue. In the present embodiment, these compounds can also be removed by remaining inside the sublimation means 22 as a nonvolatile substance. The coarse substance 102 such as a non-volatile substance accumulated in the sublimation means 22 is periodically extracted from the sublimation means 22 and removed.

The method of the present embodiment may include a step of diluting a sublimation gas of ammonium chloride after the sublimation step or at the same time as the sublimation step and before the step of removing coarse substances. This is because reducing the concentration of the sublimation gas sublimated by the sublimation means 22 is advantageous in that precipitation of ammonium chloride accompanying a temperature drop can be prevented. In the step of diluting the sublimation gas, a dilution gas is mixed with the sublimation gas. The sublimation gas dilution is preferably performed when the concentration of the sublimation gas exceeds 10,000 ppm.

The dilution gas is preliminarily heated to 240 ° C. or higher, more preferably 365 ° C. or higher before mixing with the sublimation gas. This is to prevent ammonium chloride from precipitating due to a decrease in the temperature of the sublimation gas. FIG. 3 is a graph showing the gas-solid equilibrium of NH ₃ and HCl generated by decomposition of ammonium chloride. In the graph, the concentration of the sublimation gas when the sublimation gas is not diluted with the diluting gas is shown as 1,000,000 ppm. When the gas temperature falls below 365 ° C., solid ammonium chloride may precipitate. Recognize. When the sublimation gas is diluted with a diluting gas and the sublimation gas concentration is 20,000 ppm, ammonium chloride solids are deposited when the temperature of the mixed gas of the sublimation gas and the diluting gas falls below 240 ° C. Thus, when the gas temperature falls and solid ammonium chloride precipitates, it will cause clogging of the ammonium chloride supply means 16 such as a nozzle and cause ammonium chloride to remain without being used in the reaction.

The concentration of the sublimation gas after dilution is preferably 10,000 to 100,000 ppm. If the concentration of the sublimation gas supplied to the exhaust gas exceeds 100,000 ppm, precipitation of ammonium chloride due to high concentration and the amount of sublimation gas supplied to the flue will be small, and it may be difficult to level the concentration distribution. This is because if the amount is less than 000 ppm, the amount of sublimation gas supplied to the flue increases and the amount of exhaust gas may increase.

After the sublimation gas is diluted arbitrarily, it flows into the coarse substance removing means 21 through the pipeline. In the step of removing a coarse substance from ammonium chloride, the coarse substance mixed in the sublimation gas is removed by the coarse substance removing means 21. The coarse material to be removed is a non-volatile material that has not been removed in the sublimation process, and includes coarse dust, earth and sand, and compounds such as NaCl, PbSO ₄ , and Ca ₃ (PO ₄ ) ₂ . Preferably, a coarse material having a size of 20 μm or more, more preferably 10 μm or more can be removed. By this step, it is possible to prevent coarse substances mixed in the ammonium chloride from flowing into the ammonium chloride supply means 16, the flue 26, etc. on the downstream side of the coarse substance removing means 21. Wear can be prevented. Furthermore, mercury oxidation in the denitration catalyst can be efficiently performed by removing the inhibitory substance of the denitration catalyst.

In the step of supplying ammonium chloride to the exhaust gas, the sublimation gas after removal of coarse substances is supplied into the flue 26 by the ammonium chloride supply means 16 and mixed with the exhaust gas. The supply of ammonium chloride is preferably performed by injecting a sublimation gas into the flue 26. The concentration of the sublimation gas after supplying the sublimation gas is preferably 10 to 1000 ppm in the exhaust gas. More preferably, it is 10 to 200 ppm. If the concentration of sublimation gas in the exhaust gas is excessive, unreacted ammonium chloride may increase, and if it is insufficient, the oxidation of mercury and the reduction denitration of nitrogen oxides in the reduction denitration means 3 will decrease. Because there is.

The method according to the present embodiment may include a step of supplying NH ₃ into the exhaust gas by the NH ₃ supply means 11. By this step, NH ₃ can be replenished when only NH ₃ generated by decomposition of ammonium chloride is insufficient to reduce nitrogen oxides in the exhaust gas. Supply of NH ₃ is _{preferably NH} 3 / NO _x mole ratio in the flue takes place when less than 0.9. If the NH ₃ / NO _x molar ratio in the flue is lower than 0.9, nitrogen oxides are not sufficiently reduced, and the remaining nitrogen oxides may be discharged from the flue 7 without being reduced. It is. The supply of NH ₃ is performed in the flue 26 connecting the economizer 10 and the reducing denitration means 3. NH ₃ is preferably supplied after ammonium chloride is supplied into the exhaust gas. Alternatively, NH ₃ may be supplied before supplying ammonium chloride into the exhaust gas. In the exhaust gas in the flue 26 after supplying NH ₃ , the NH ₃ / NO _x molar ratio is preferably 0.9 to 1.0.

The subsequent step of bringing the exhaust gas into contact with the denitration catalyst and the step of bringing the exhaust gas brought into contact with the denitration catalyst into contact with the alkaline absorbent can be performed in the same manner as in the first embodiment.

Next, FIG. 4 illustrates an ammonium chloride pretreatment means 2 when a kiln furnace 221 is used as the sublimation means 22 as a specific example of the second embodiment. The ammonium chloride pretreatment means 2 shown in FIG. 4 includes a silo 13, a screw feeder 14, a kiln furnace 221, a burner 222, a fuel tank 223, a blower 24, and a hot cyclone 211.

4, the silo 13 and the screw feeder 14 constitute a raw material supply means 16. The silo 13 accumulates ammonium chloride 101, and the screw feeder 14 supplies the ammonium chloride 101 from the silo 13 to the kiln furnace 221. A kiln furnace 221 is provided downstream of the raw material supply means 23. Inside the kiln furnace 221, a burner 222 connected to the fuel tank 223 by a pipe line is installed. The coarse material 102 is discharged from the kiln furnace 221. The kiln furnace 221 is heated and sublimated while stirring and transferring the ammonium chloride 101 in the furnace while rotating.

A blower 24 is further connected to the kiln furnace 221. The blower 24 constitutes a diluting means and dilutes the sublimation gas with air.

The hot cyclone 211 is provided in the rear stage of the kiln furnace 221 and is connected to the kiln furnace 221 by a pipe line. The hot cyclone 211 constitutes the coarse substance removing means 21 and removes the coarse substance from the mixture of the ammonium chloride sublimation gas and the air. Ammonium chloride supply means 16 (not shown) is connected to the subsequent stage of the hot cyclone 211.

The steps of pretreating ammonium chloride by the ammonium chloride pretreatment means 2 in FIG. 4 include a step of sublimating the solid ammonium chloride 101 in the kiln furnace 221, a step of diluting the sublimation gas of ammonium chloride with air, and ammonium chloride. And a step of removing coarse materials from the above.

Ammonium chloride 101 charged from the silo 13 is supplied to the kiln furnace 221 by the screw feeder 14. In the step of sublimating ammonium chloride in the kiln furnace 221, the solid ammonium chloride 101 is heated and sublimated inside the kiln furnace 221 by the heat released by the burner 222 supplied with fuel from the fuel tank 223. The inside of the kiln furnace 221 is preferably 400 ° C. or higher. In the step of diluting the sublimation gas of ammonium chloride with air, air 106 is supplied into the kiln furnace 221 by the blower 24 and mixed with the sublimation gas. Preferably, the air 106 is heated to 400 ° C. or higher by the burner 222 and supplied into the kiln furnace 221. In the step of removing the coarse substance, the coarse substance contained in the sublimation gas 104 diluted with air is separated and removed by the hot cyclone 211. Thereby, the non-volatile substance which was not gasified in the kiln furnace 221 can be removed as a coarse substance. Preferably, a coarse product having a size of up to 10 μm can be removed by the hot cyclone 211. After removing the coarse substance, the diluted sublimation gas 104 is sent to the ammonium chloride supply means 16 and supplied to the exhaust gas in the flue.

Next, FIG. 5 shows an enlarged view of the hot cyclone 211 as a specific example of the coarse substance removing means 21. FIG. 5 is a side view of a general hot cyclone 211. The hot cyclone 211 can separate and remove coarse substances from the sublimation gas 104 diluted by gravity and centrifugal force. When the diluted sublimation gas 104 containing a coarse substance flows into the hot cyclone 211, the diluted sublimation gas 104 descends as a swirl flow B inside the cyclone. At the same time, the coarse substance E mixed in the diluted sublimation gas 104 is directed to the outer wall by centrifugal force and is sent to the lower part of the cyclone by the downward flow C and discharged. The diluted sublimation gas 104 is inverted at the lower part of the cyclone 221 and rises as a cylindrical inverted flow D inside the cyclone 211. The diluted sublimation gas 104 rising inside the cyclone 211 is discharged from the upper part of the cyclone 211. In the upper part of the cyclone 211, a secondary flow vortex A is generated. The gas discharged from the cyclone 211 is, for example, a diluted sublimation gas 104 from which a fine coarse substance E having a particle size of 10 μm or more has been removed.

4 and FIG. 5, according to the ammonium chloride pretreatment means 2, coarse substances such as fine non-volatile substances having a particle size of 10 μm or more are removed from the sublimation gas of ammonium chloride. Further, since the sublimation gas is diluted with air, ammonium chloride is difficult to precipitate as a solid. Accordingly, since solid substances such as coarse substances and precipitated ammonium chloride do not flow out from the ammonium chloride pretreatment means 2, the nozzles provided in the ammonium chloride supply means 16 and the devices such as the flue 26 are prevented from being blocked or worn. can do.

According to the mercury removal system and the mercury removal method of the second embodiment, since coarse substances are previously removed from the ammonium chloride sublimation gas, there is a problem of clogging / wearing in the ammonium chloride supply means 16 provided with a nozzle or the like. Does not occur. In addition, since non-volatile substances such as NaCl that inhibit mercury oxidation are removed from the sublimation gas of ammonium chloride and are not supplied into the flue, mercury oxidation in the denitration catalyst can be performed more efficiently, and the mercury removal rate is increased. There is also an effect. Furthermore, when the ammonium chloride aqueous solution is evaporated and used as in the prior art, it is necessary to spend a large amount of energy for evaporation since the temperature rise and the latent heat of evaporation of the water occupying most of the aqueous solution are two-thirds of the required amount of heat. However, in the present embodiment, since solid ammonium chloride is sublimated and used, the required energy can be reduced. In addition, when ammonium chloride is supplied to the exhaust gas as a solid or an aqueous solution, there is a problem that the concentration distribution can be uneven in the flue, but in this embodiment, since it is supplied to the exhaust gas as a sublimation gas, Concentration distribution is easily uniformed, and there is an effect that mercury can be removed more efficiently.

FIG. 6 shows a main part of a third embodiment of the mercury removal system according to the present invention. The system according to the third embodiment of the present invention includes an economizer 10, a gravity precipitation tank 212, a water tank 27, an ammonium chloride supply means 16, an air compressor 25, a stirring means 15, an NH ₃ supply means 11, a reductive denitration means 3, An air heater 4, wet desulfurization means 6, and a chimney 7 are provided. In FIG. 6, the wet desulfurization means 6 and the chimney 7 provided on the downstream side of the air heater 4 are omitted. In addition, the component which attached | subjected the same number has the same structure and effect | action. In the present embodiment, a gravity sedimentation tank 212 is provided as a coarse material removing means. The ammonium chloride supply means 16 has a structure in which droplets of the ammonium chloride aqueous solution supplied into the flue 26 do not adhere to the inner wall of the flue. Furthermore, the mercury removal system of the present embodiment includes a stirring unit 15 that stirs the vaporized gas of the supplied ammonium chloride aqueous solution and the exhaust gas.

The gravity precipitation tank 212 is an apparatus capable of removing a water-insoluble coarse substance from the ammonium chloride aqueous solution 107 by solid-liquid separation by gravity sedimentation. The coarse substance 102 removed by the gravity sedimentation tank 212 which is the coarse substance removing means of the present embodiment is a water-insoluble substance such as coarse dust, insects, minerals, earth and sand, grass and trees, glass, and metal scraps. The gravity precipitation tank 212 can remove fine coarse particles having a size of preferably 100 μm or more, more preferably up to 10 μm. The gravity settling tank 212 is provided in front of the ammonium chloride supply means 16 connected by a pipe line. A dissolution tank or a dilution tank (not shown) connected by a pipe line may be provided in the front stage of the gravity precipitation tank 212. The dissolution tank is used to prepare solid ammonium chloride aqueous solution 107 by dissolving solid ammonium chloride in water, and the dilution tank is used to dilute ammonium chloride aqueous solution 107.

The mercury removal system of the present embodiment may include one or more selected from the group consisting of a hydrocyclone, a membrane separator, and a screen instead of or in addition to the gravity precipitation tank 212. . The hydrocyclone, the membrane separator, and the screen are generally known to be able to remove coarse substances having a size of 10 to 100 μm or more, and can be used in the same manner as the gravity precipitation tank 212. When the mercury removal system of this embodiment includes all of these apparatuses, the gravity precipitation tank 212 → the screen → the liquid cyclone → the membrane separation apparatus or the screen → the gravity precipitation tank 212 → the liquid cyclone → the membrane separation apparatus. It is preferable to install from the front side through a pipeline.

The water tank 27 is an ammonium chloride supply means 16 and a water washing mechanism for washing the pipe line from the water tank 27 to the ammonium chloride supply means 16. The water tank 27 cleans spray means such as a spray nozzle provided in the ammonium chloride supply means 16 to prevent clogging. The water tank 27 is connected in the middle of a pipe line connecting the gravity precipitation tank 212 and the ammonium chloride supply means 16. The water tank 27 is provided with a dilution line 29 that connects the water tank 27 and the gravity sedimentation tank 212. The water tank 27 can also be used to supply water to the gravity settling tank 212 through the dilution line 29 to dilute the aqueous ammonium chloride solution. The dilution line 29 may not be provided as long as there is no problem in operation of the mercury removal system. Moreover, it is preferable to provide a concentration monitoring device or the like for monitoring the concentration of the ammonium chloride aqueous solution sent to the ammonium chloride supply means 16 in the dissolution tank or dilution tank.

The ammonium chloride supply means 16 is a device that supplies an aqueous ammonium chloride solution into the exhaust gas. The ammonium chloride supply unit 16 preferably includes a plurality of spraying units. The ammonium chloride supply means 16 is provided in the flue 26 on the downstream side of the economizer 10 and on the upstream side of the stirring means 15. The ammonium chloride supply means 16 is preferably installed in a straight region of the flue 26 through which exhaust gas flows linearly. This is because the flow rate distribution of the exhaust gas is not uniform at the bent portion of the flue, and if the ammonium chloride supply means 16 is installed in such a portion, the concentration distribution of ammonium chloride is not uniform. If the ammonium chloride concentration is uneven, the excess portion is not used for the mercury oxidation reaction at the high concentration portion, and the ammonium chloride is insufficient at the low concentration portion, and the mercury can be oxidized sufficiently. Can not. As the ammonium chloride supply means 16, for example, a spray grid provided with spray means such as a plurality of spray nozzles can be used. As the spray means provided in the ammonium chloride supply means 16, a two-fluid nozzle, a nebulizer or the like can be preferably used. The spraying means is preferably capable of setting the diameter of droplets to be sprayed to 80 μm or less, and more preferably capable of spraying with a droplet diameter of 40 μm or less. It is preferable that the end of the header pipe such as a spray nozzle has a structure that can be opened and closed by a valve and a gate. This is because it is possible to remove deposits accumulated in the header pipe and prevent clogging of the nozzle and the like.

An air compressor 25 is connected to the ammonium chloride supply means 16. The air compressor 25 is a device that compresses the air 108 and supplies the compressed air to the ammonium chloride supply means 16. The ammonium chloride supply means 16 sprays an aqueous ammonium chloride solution as droplets into the exhaust gas by the compressed air supplied from the air compressor 25.

The ammonium chloride supply means 16 according to this embodiment has a structure for supplying an aqueous ammonium chloride solution so as not to adhere to the inner wall of the flue through which exhaust gas flows. When the aqueous ammonium chloride solution is sprayed into the exhaust gas, it is evaporated by the heat of the exhaust gas to become a vaporized gas. The ammonium chloride aqueous solution further dissociates into NH ₃ and HCl after evaporation, and this HCl component causes corrosion when adhering to the inner wall of the flue together with moisture in the exhaust gas. The structure for supplying the ammonium chloride aqueous solution so that it does not adhere to the inner wall of the flue through which the exhaust gas flows is preferably a spray means such as a spray nozzle provided in the ammonium chloride supply means 16 in the flue 26, It is a structure arranged at a certain distance from The distance above a certain distance is a distance sufficient for vaporizing the sprayed droplets before they reach the flue wall from the spraying means. Alternatively, the structure for supplying the ammonium chloride aqueous solution so as not to adhere to the inner wall of the flue through which exhaust gas flows is provided so that the inner wall and a double pipe are formed inside the inner wall of the flue where the sprayed droplets can reach. The structure provided with the made partition may be sufficient. Below, the specific example of the structure of the ammonium chloride supply means 16 is demonstrated.

FIG. 7 shows an example of the configuration of the ammonium chloride supply means 16. Referring to FIG. 7, the ammonium chloride supply unit 16 includes an ammonium chloride solution introduction pipe 162 and a plurality of spraying units 161. The ammonium chloride solution introduction pipe 162 is a tubular device that supplies the ammonium chloride aqueous solution from the gravity precipitation tank 212 to the spraying means 161. The ammonium chloride solution introduction pipe 162 is installed so as to penetrate the flue wall 263 and is arranged so as to be substantially perpendicular to the direction of the exhaust gas flow 109. Further, the spraying means 161 is installed on the ammonium chloride solution introduction pipe 162 so that the spray outlet of the spraying means 161 faces the downstream side of the exhaust gas flow 109. A plurality of spraying means 161 are provided on the ammonium chloride introduction pipe 162. The ammonium chloride solution introduction pipe 162 preferably forms a lattice in the flue and forms a spray grid together with a plurality of spraying means 161 provided on the ammonium chloride solution introduction pipe 162.

The spray nozzle which is the spray means 161 is arranged at a certain distance or more from the flue inner wall surface 262. The droplets sprayed by the spraying means 161 spread in a solid conical shape with a spray angle α. The droplet moves to the wake side with the flow of the exhaust gas, and then evaporates. Some droplets, for example, droplets having a large spray angle and a large diameter, do not flow in the gas but collide with the flue inner wall surface 262. In order to prevent the spray droplets from adhering to the flue inner wall surface 262, the position of each spray means 161 is set so that the exhaust gas flow 109 from all the inner wall surfaces 262 in the flue when the exhaust gas flow velocity is about 15 m / s. The distance is preferably 0.5 to 2.0 m in the direction perpendicular to the distance. More preferably, the spraying means 161 is installed at a distance of 0.5 to 1.5 m in a direction perpendicular to the exhaust gas flow 109 from all the inner wall surfaces 262 in the flue. However, in consideration of variations in sprayed droplet diameter, exhaust gas flow velocity, vortex flow, spray angle, etc., the spraying means 161 is installed at a larger distance from the flue inner wall 262, for example, 1.0 to 1.5 m. It is preferable.

When the cross-sectional area of the flue is large and the distance between the spray means 161 and the flue inner wall surface 262 can be increased, a nozzle having a large spray angle α can be selected. When the cross-sectional area of the flue is small and the distance between the spraying means 161 and the flue inner wall surface 262 is short, it is preferable to select a nozzle having a small spray angle α. However, the spray angle α varies depending on the nozzle specifications and spray conditions, and varies depending on the pulsation, and is not limited to a specific spray angle α. If the spray angle α is too large, spray droplets having a large diameter do not get on the gas flow and may collide with the flue wall 262 before evaporating. However, if the spray angle α is small, the spray droplets become exhaust gas. And may not be mixed efficiently.

Here, FIG. 8 shows a graph in which the time required for the droplets of the aqueous ammonium chloride solution to evaporate in the flue is predicted in relation to the droplet diameter. The simulation of droplet evaporation was performed under the conditions of an exhaust gas temperature of 350 ° C. and an initial droplet temperature of 20 ° C. when ammonium chloride was introduced. Referring to FIG. 8, when the droplet diameter is 40 μm, it takes 0.032 seconds to evaporate in the flue. Therefore, it is necessary to arrange the spraying means 161 so that it takes at least 0.032 seconds to reach the flue wall 262 after the ammonium chloride droplets are sprayed from the spraying means such as a spray nozzle. . The spray droplets may come into contact with each other and actually take longer to evaporate. For this reason, it can be calculated that the spray means 161 is installed at a position where the spray droplet reaches the flue wall 262 over a time of at least 0.1 second as about three times 0.032 seconds. it can.

The installation position of the spray means 161 can be specifically determined as follows as an example. When the exhaust gas flow velocity in the flue is 15 m / s, the distance that the spray droplets fly during 0.1 seconds, which is the time required for evaporation from the spray, is 1. in the direction parallel to the exhaust gas flow 109 from the spray means 161. Calculated to be 5 m. When the spray angle α is 12.5 ° with respect to the direction of the exhaust gas stream 109, the spray droplets are 0.335 m at the maximum in the direction perpendicular to the exhaust gas stream 109 from the spray means 161 after 0.1 seconds of spraying. Reach far away. This value is calculated by a calculation formula of 1.5 × tan 12.5. Therefore, in this case, the spraying means 161 can be installed at a distance greater than 0.335 m in the direction perpendicular to the exhaust gas flow 109 from all the inner wall surfaces 262 of the flue. When the spray angle α is 27.5 ° with respect to the direction of the exhaust gas flow 109, the spray droplets are 0 in the direction perpendicular to the exhaust gas flow 109 from the spray means 161 after 0.1 second of spraying. Reach up to .78m away. This value is calculated by a calculation formula of 1.5 × tan 27.5. In such a case, the spraying means 161 can be installed at a distance greater than 0.78 m in the direction perpendicular to the exhaust gas flow 109 from all the inner wall surfaces 262 in the flue. Even if the exhaust gas flow velocity and temperature conditions may be different, the installation position of the spray means 161 can be determined as described above.

In another example, the ammonium chloride supply unit 16 includes a spray unit 161, an ammonium chloride solution introduction pipe 162, and a partition wall 163. FIG. 9 shows an enlarged view of the ammonium chloride supply means 16 and the flue 26 in the vicinity thereof. The spraying means 161 and the ammonium chloride solution introduction pipe 162 are the same as those described with reference to FIG.

The partition wall 163 prevents ammonium chloride droplets from adhering to the flue wall 262. The partition wall 163 is installed so as to partially form a double pipe with the flue inner wall surface 262. The plurality of spraying means 161 are all located inside the double pipe portion. In the illustrated embodiment, the partition wall 163 is installed from the position of the ammonium chloride solution introduction pipe 162 to the droplet evaporation position 264. Here, a position where all the spray droplets are evaporated to become vaporized gas is set as a droplet evaporation position 264. In the flue from the ammonium chloride solution introduction pipe 162 to the droplet evaporating position 264, most of the droplets exist without evaporating, and almost all the droplets evaporate in the flue downstream from the droplet evaporating position 264. Exists as a gas. The droplet evaporation position 264 is calculated as a position of 1.5 m from the spray means 161 in a direction parallel to the exhaust gas flow 109 when the droplet diameter of the spray droplet is about 40 μm and the exhaust gas flow velocity is about 15 m / s. . However, considering that the droplet evaporation position 264 changes depending on the droplet diameter to be sprayed, the exhaust gas flow velocity, the vortex flow, the spray angle, and the like, the droplet evaporation position is, for example, 1.0 to 4.0 m. It is predicted. Therefore, specifically, the partition wall 163 is installed from the position of the ammonium chloride solution introduction pipe 162 to the position of 1.0 to 4.0 m, more preferably 2.0 to 2.5 m in the downstream. The partition wall 163 may be fixed to the ammonium chloride solution introduction tube 161. The partition wall 163 is preferably formed of a corrosion-resistant material. Examples of the corrosion-resistant material include stainless steel and nickel alloy.

The partition wall 163 may be deteriorated due to corrosion and can be periodically replaced. Since the ammonium chloride supply means 16 has the partition wall 163, it is possible to prevent low temperature droplets from adhering to the high temperature flue inner wall surface 262 of 320 to 380 ° C. Wall cracking and corrosion can be prevented.

Here, as an example, the embodiment in which the ammonium chloride supply unit 16 has a configuration in which the installation position of the spray unit 161 is set to a specific position and the configuration in which the partition wall 163 is provided has been described. However, the ammonium chloride supply unit 16 has both of these configurations. Also good.

Referring to FIG. 6, the stirring means 15 is a device for stirring the vaporized gas and the exhaust gas of the ammonium chloride aqueous solution. The stirring means 15 is provided in a flue connecting the ammonium chloride supply means 16 and the reductive denitration device 3. It is preferable that the stirring means 15 is installed in the straight part of a flue. This is because construction and maintenance are easier compared to the bent part. The installation position of the stirring means 15 is preferably on the downstream side of the position where the droplets of the ammonium chloride aqueous solution supplied by the ammonium chloride supply means 16 evaporate. This is because, by stirring the gas and the exhaust gas generated by evaporation of the spray droplets, the concentration distribution can be made more effective than when stirring the exhaust gas in the state of droplets. As the stirring means 15, a mixer is preferably used. The mixer may be one normally used for gas stirring. Moreover, the stirring means 15 may include a plurality of mixers. By the stirring means 15, the concentration distribution of the vaporized gas of the ammonium chloride aqueous solution in the exhaust gas can be made uniform, and the chlorination efficiency of mercury can be increased.

The boiler 1, economizer 10, rectifier 12, NH ₃ supply unit 11, reduction denitration unit 3, air heater 4, wet desulfurization unit 6, and chimney 7 are the same as those described in the second embodiment. Can do.

Next, an embodiment of a mercury removal method using the exhaust gas mercury removal system according to the present embodiment will be described. The method according to the present embodiment includes a step of removing coarse substances from the aqueous ammonium chloride solution by gravity sedimentation, and a step of supplying the aqueous ammonium chloride solution after removal of coarse substances to the exhaust gas in the flue so as not to adhere to the inner wall of the flue. After the step of supplying the ammonium chloride aqueous solution, the step of stirring the gas and the exhaust gas in which the ammonium chloride aqueous solution has evaporated in the flue, the step of bringing the exhaust gas supplied with ammonium chloride into contact with the denitration catalyst, And a step of bringing the contacted exhaust gas into contact with an alkali absorbing liquid.

The ammonium chloride aqueous solution 107 can be prepared by dissolving solid ammonium chloride in water. The ammonium chloride aqueous solution 107 may be supplied with a concentration adjusted in advance by a tank truck or the like and supplied to the gravity precipitation tank 212. Or after supplying ammonium chloride aqueous solution 107 to a dilution tank (illustration omitted), you may dilute as needed and send to gravity precipitation tank 212. In this case, the gravity precipitation tank 212 may be used also as a dilution tank. Alternatively, an ammonium chloride aqueous solution 107 prepared by supplying ammonium chloride powder to a dissolution tank and adding water to the dissolution tank may be sent to the gravity precipitation tank 212. In order to supply the ammonium chloride powder to the dissolution tank, the raw material supply means such as the silo and the supply feeder described in the second embodiment can be used. The concentration of the ammonium chloride aqueous solution 107 is preferably 0.01 to 45% by mass, and more preferably 0.01 to 23% by mass.

In the step of removing coarse substances from the aqueous ammonium chloride solution, coarse substances are removed from the aqueous ammonium chloride solution 107 by gravity precipitation in the gravity precipitation tank 212. Gravity sedimentation is preferably performed for 1 second to 24 hours. Examples of the coarse substance removed in the method of the present embodiment include water-insoluble impurities such as coarse dust, insects, minerals, earth and sand, vegetation, glass, and metal scraps. In the coarse substance removing step, it is preferable that even a coarse article as fine as possible can be removed, and it is preferable to remove a coarse article having a size of 100 μm or more. By this step, solid substances that do not dissolve in water can be removed, and blockage and wear of devices such as ammonium chloride supply means 16 and flue 26 can be prevented.

The method according to the present embodiment may optionally include a step of diluting the aqueous ammonium chloride solution before the step of removing coarse substances. In the step of diluting the ammonium chloride aqueous solution, the concentration of ammonium chloride is reduced by supplying water through the dilution line 29 from the water tank 27 to the ammonium chloride aqueous solution in the gravity precipitation tank 212. Preferably, water is supplied and diluted so that the concentration of the ammonium chloride aqueous solution sent to the ammonium chloride supply means 16 is 0.01 to 45% by mass. Thereby, the density | concentration of the ammonium chloride aqueous solution supplied in the flue 26 can be adjusted.

In the step of supplying the ammonium chloride aqueous solution after removal of coarse substances to the exhaust gas in the flue, the ammonium chloride aqueous solution from which coarse substances have been removed is sprayed into the exhaust gas in a mist form by the spraying means provided in the ammonium chloride supply means 16. Preferably, the aqueous ammonium chloride solution is sprayed into the exhaust gas together with the compressed air compressed by the air compressor 25. The preferable droplet diameter of the sprayed droplet is 100 μm or less, and more preferably 40 μm or less.

Each spraying means 161 sprays an ammonium chloride aqueous solution in the shape of a solid cone with the spraying means 161 at the top. At this time, the aqueous ammonium chloride solution is supplied so that the aqueous ammonium chloride solution does not adhere to the inner wall surface 262 of the flue. This is to prevent the flue from corroding. The supply of the ammonium chloride aqueous solution can be performed in the form described with reference to FIGS.

The aqueous ammonium chloride solution is preferably supplied into the exhaust gas so that the concentration of ammonium chloride in the flue 26 is 0.01 to 200 ppm with respect to the exhaust gas.

The droplets of the ammonium chloride aqueous solution are heated by the heat in the flue 26 and evaporated to generate gas. This gas is called vaporized gas. In the vaporized gas, NH ₃ and HCl exist as gases. In the step of stirring the vaporized gas and the exhaust gas of the ammonium chloride aqueous solution in the flue, the vaporized gas and the exhaust gas of the ammonium chloride aqueous solution supplied into the flue 26 are stirred by the stirring means 15. Preferably, NH ₃ , HCl, and exhaust gas generated by dissociation of evaporated ammonium chloride are stirred by the stirring means 15. By this step, the vaporization gas of the ammonium chloride aqueous solution in the flue and the concentration distribution of NH ₃ and HCl generated by further dissociation of ammonium chloride can be made uniform. The step of bringing the exhaust gas into contact with the denitration catalyst and the step of bringing the exhaust gas into contact with the alkali absorbing liquid can be the same as in the second embodiment.

According to the mercury removal system and mercury removal method of the present embodiment, coarse substances are previously removed from the ammonium chloride aqueous solution. For this reason, it can prevent that a spray nozzle etc. obstruct | occlude and wear. Since the aqueous ammonium chloride solution is vaporized by the exhaust gas in the flue, it is not necessary to supply heat from the outside, and the amount of energy required for the treatment of the exhaust gas can be reduced. Ammonium chloride and exhaust gas have an effect that mercury in the exhaust gas can be oxidized with high efficiency by stirring in the flue and making the concentration distribution uniform. Furthermore, since ammonium chloride droplets do not adhere to the inner wall of the flue, corrosion can be prevented, the durability of the exhaust gas treatment facility can be improved, and the life can be improved.

Next, FIG. 10 shows a main part of a fourth embodiment of the mercury removal system for exhaust gas according to the present invention. The mercury removal system according to the present embodiment includes an economizer 10, a gravity precipitation tank 212, a water tank 27, a separation unit 213, an ammonium chloride aqueous solution tank 28, an ammonium chloride supply unit 16, an air compressor 25, an agitation unit 15, and NH _3. A supply unit 11, a reduction denitration unit 3, an air heater 4, a wet desulfurization device 6, and a chimney 7 are provided. In FIG. 10, the wet desulfurization means 6 and the chimney 7 on the downstream side of the air heater 4 are omitted. Components with the same number have the same configuration / action. In addition to the system of the third embodiment, the mercury removal system of this embodiment further includes a separation unit 213 and an ammonium chloride aqueous solution tank 28.

Separation means 213 is a device for removing coarse substances that have not been removed in the gravity precipitation tank 212 from the aqueous ammonium chloride solution from which coarse substances have been removed in the gravity precipitation tank 212. The separation means 213 can separate and remove finer particles than the gravity sedimentation tank 212. The separation means 213 is installed in the middle of a pipe line connecting the gravity precipitation tank 212 and the ammonium chloride supply means 16. As the separation means 213, one or more combinations selected from a liquid cyclone, a membrane separator, a screen, and the like can be used. When a combination of all these devices is used as the separation means 213, it is preferable that the separation means 213 is installed via a pipe line from the preceding stage in the order of gravity precipitation tank 212 → screen → hydrocyclone → membrane separation device. It is preferable that the separating means 213 can remove coarse substances having a size of 100 to 1 μm.

The ammonium chloride aqueous solution tank 28 is a device for recovering and storing the ammonium chloride aqueous solution separated together with the coarse material by the separation means 213 and reflowing it into the separation means 213. The ammonium chloride aqueous solution tank 28 is connected to the separating means 213 by a pipe line. Furthermore, the ammonium chloride aqueous solution tank 28 is connected by a pipe line in the middle of a pipe line connecting the gravity precipitation tank 212 and the separating means 213.

Boiler 1, economizer 10, rectifier 12, NH ₃ supply means 11, gravity precipitation tank 212, water tank 27, air compressor 25, ammonium chloride supply means 16, stirring means 15, reductive denitration means 3, air heater 4, wet type The desulfurization means 6 and the chimney 7 can be the same as those described in the third embodiment.

An embodiment of a mercury removal method using the exhaust gas mercury removal system according to the present embodiment will be described. The method according to the present embodiment is different from the third embodiment in that after the step of removing coarse substances from the aqueous ammonium chloride solution 107 by gravity sedimentation, the step of removing coarse substances from the aqueous ammonium chloride solution by the separating means 213 is included.

In the step of removing coarse substances from ammonium chloride by the separating means 213, coarse substances are further separated and removed from ammonium chloride from which coarse substances have been removed by gravity sedimentation. One or more combinations selected from liquid cyclones, membrane separators, screens, and the like can be used to remove coarse substances. Thereby, finer particles than gravity sedimentation can also be removed. The ammonium chloride aqueous solution separated together with the coarse substance by the separation means 213 may be collected and stored in the ammonium chloride aqueous solution tank 28 and reflowed into the separation means 213. The step of supplying the ammonium chloride aqueous solution after removal of coarse substances to the flue gas in the flue, the step of bringing the exhaust gas into contact with the denitration catalyst, and the step of bringing the exhaust gas into contact with the alkali absorbing solution are the same as in the third embodiment. Can do.

In the exhaust gas mercury removal system and mercury removal method according to the present embodiment, the ammonium chloride aqueous solution is further removed by the separation means 213 after removing the coarse matter by the gravity precipitation tank 212. The gravitational precipitation tank 212 can remove most of the coarse substances, but it is effective when the time for gravity sedimentation is insufficient or when there are fine particles having a small particle size and low density that cannot be separated and removed by gravity sedimentation. According to the mercury removal system of the present embodiment, coarse particles such as coarse dust, insects, minerals, earth and sand, vegetation, glass, and metal scraps are removed from the aqueous ammonium chloride solution, so that the spray nozzle is difficult to block. Play.

The mercury removal system and mercury removal method of the present invention can be used for mercury removal treatment of exhaust gas generated by combustion of fossil fuels such as coal and heavy oil.

1 Boiler 2 ammonium chloride preprocessing means 3 reducing denitration unit 4 air heater 5 electric precipitator 6 wet desulfurization unit 7 chimney 8 belt filter 9 gypsum 10 economizer 11 NH ₃ supplying unit 12 rectifier 13 silo 14 screw feeder 15 agitation means 16 ammonium chloride Supply means 21 Coarse substance removal means 22 Sublimation means 23 Raw material supply means 24 Blower 25 Air compressor 26 Flue 27 Water tank 28 Ammonium chloride aqueous solution tank 29 Dilution line 100 Mercury removal system 101 Ammonium chloride 102 Coarse thing 103 Sublimation gas 104 Dilution sublimation Gas 105 Fuel 106 Air 107 Ammonium chloride aqueous solution 108 Air 109 Exhaust gas flow 110 Sodium chloride solution 161 Spraying means 162 Ammonium chloride solution introduction pipe 163 Partition wall DESCRIPTION OF SYMBOLS 11 Hot cyclone 212 Gravity sedimentation tank 213 Separation means 221 Kiln furnace 222 Burner 223 Fuel tank 262 Flue wall 263 Flue wall 264 Droplet evaporation position A Secondary flow vortex B Swirl C Downflow D Reverse flow E Coarse α Spray angle

Claims

Ammonium chloride pretreatment means for pretreatment of ammonium chloride;
Ammonium chloride supply means for supplying pretreated ammonium chloride to the exhaust gas;
Reductive denitration means for reducing nitrogen oxides in the exhaust gas and chlorinating mercury;
A wet desulfurization means for removing sulfur oxides in the exhaust gas and the chlorinated mercury with an alkali absorbing solution, and the ammonium chloride pretreatment means removes a coarse substance from the ammonium chloride. An exhaust gas mercury removal system.
The ammonium chloride pretreatment means further comprises a separate sublimation means for sublimating solid ammonium chloride,
The mercury removal system according to claim 1, wherein the coarse substance removing means is a dust collector.
The ammonium chloride supply means has a structure for supplying an aqueous ammonium chloride solution so as not to adhere to the inner wall of the flue through which exhaust gas flows,
The coarse substance removing means comprises one or more selected from the group consisting of a gravity sedimentation tank, a hydrocyclone, a membrane separator, and a screen,
The mercury removal system according to claim 1, further comprising a stirring unit that stirs the exhaust gas supplied with ammonium chloride before the reducing denitration unit.
The said coarse substance removal means is equipped with a gravity precipitation tank, and one or more selected from the group which consists of the liquid cyclone provided in the back | latter stage of the gravity precipitation tank, a membrane separator, and a screen. Mercury removal system.
Removing coarse material from ammonium chloride;
Supplying ammonium chloride from which coarse substances have been removed to the exhaust gas;
Contacting the exhaust gas supplied with the ammonium chloride with a denitration catalyst;
A method for removing mercury from exhaust gas, comprising the step of bringing the exhaust gas brought into contact with the denitration catalyst into contact with an alkali absorbing solution.
The ammonium chloride is solid ammonium chloride;
Sublimating the solid ammonium chloride in a separate vaporizer further before the step of removing coarse matter,
The mercury removal method according to claim 5, wherein the ammonium chloride supplied to the exhaust gas is a sublimation gas of ammonium chloride.
The ammonium chloride is an aqueous ammonium chloride solution;
The step of supplying the ammonium chloride to the exhaust gas is a step of spraying the ammonium chloride aqueous solution so as not to adhere to the inner wall of the flue through which the exhaust gas flows.
The mercury removal method according to claim 5, further comprising a step of stirring the vaporized gas of the ammonium chloride aqueous solution and the exhaust gas in a flue after the step of supplying the ammonium chloride to the exhaust gas.