JP2014057912A - Mercury processing system in exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mercury processing system in exhaust gas capable of removing HIC and dust in the exhaust gas of becoming the cause of performance reduction in a process of installing a desulfurizer, by simultaneously removing bivalent mercury in the exhaust gas.SOLUTION: A mercury processing system in an exhaust gas removes the mercury included in the exhaust gas 12 from a boiler 11, and comprises a denitrator 17 for denitrating nitrogen oxide (NOx) in the exhaust gas 12 from the boiler 11 burnt by the boiler by supplying fuel F, an air heater (AH) 18 provided on a wake flow side of the denitrator 17 and adjusting the exhaust gas temperature, a dust collector 19 provided on the wake flow side of the air heater 18 and removing soot dust in the exhaust gas and mercury absorbing tower 50 provided on the wake flow side of the dust collector 19 and removing mercury oxide Hgin the exhaust gas 12 by a mercury absorbing liquid 51.

Description

  The present invention relates to a mercury treatment system in exhaust gas capable of removing mercury in exhaust gas to an extremely low concentration.

The exhaust gas generated when burning coal-fired exhaust gas or heavy oil may contain metal mercury (Hg ⁰ ) in addition to soot, sulfur oxide (SOx), and nitrogen oxide (NOx). In recent years, various devices and methods for treating metallic mercury (Hg ⁰ ) have been devised in combination with a denitration device that reduces NOx and a wet desulfurization device that uses an alkaline absorbent as an SOx absorbent.

As a method for treating metallic mercury (Hg ⁰ ) in exhaust gas, a method has been proposed in which an NH ₄ Cl solution is sprayed in the form of a liquid in the flue before the denitration device and supplied into the flue (for example, a patent) References 1 and 2). When the NH ₄ Cl solution is sprayed in a liquid state in the flue, NH ₄ Cl is dissociated to generate ammonium (NH ₃ ) gas and hydrogen chloride (HCl) gas. NH ₃ gas acts as a reducing agent, and HCl gas acts as a mercury chlorinating agent. That is, on the denitration catalyst filled in the denitration apparatus, NH ₃ undergoes a reduction reaction with NOx in the exhaust gas as represented by the following formula (1), and HCl represents Hg in the exhaust gas as represented by the following formula (2). ⁰ and the oxidation reaction proceed. NH ₃ is reduced and denitrated on the denitration catalyst, and metal mercury (Hg ⁰ ) is oxidized to form water-soluble mercury chloride (HgCl ₂ ), and then HgCl is used in a desulfurization apparatus using a wet lime gypsum method installed on the downstream side. ₂ is dissolved in the gypsum slurry solution to remove mercury contained in the exhaust gas.
4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O (1)
Hg ⁰ + 1 / 2O ₂ + 2HCl → HgCl ₂ + H ₂ O (2)

JP 2008-142602 A JP 2009-202107 A

By the way, in the conventional proposal for removing mercury in the exhaust gas, a part of the absorbed and removed mercury oxide (Hg ²⁺ ) is again converted to metallic mercury (Hg ⁰ ) when the absorbing liquid of the wet desulfurization apparatus becomes a reducing atmosphere. It may be reduced and released from the chimney as well.

Moreover, there exists a problem that the performance of a desulfurization apparatus falls on the conditions with high HCl concentration and dust concentration in waste gas. When performing NH4Cl spray for mercury oxidation, since the HCl concentration in the gas compared with the case without NH ₄ Cl spray becomes higher than conventional, it may lead to the desulfurization performance degradation.

  The present invention has been made in view of the above, and at the same time, removes divalent mercury in exhaust gas, and at the same time removes HCl and dust in exhaust gas that cause performance degradation in the process where a desulfurization apparatus is installed. An object of the present invention is to provide a mercury treatment system in exhaust gas that can be used.

  A first invention of the present invention for solving the above-mentioned problem is a mercury removal system for removing mercury contained in exhaust gas from a boiler, wherein the heat exchange is performed for heat exchange of the exhaust gas from the boiler. And a mercury absorption tower provided on the downstream side of the dust collector for removing mercury oxide in the exhaust gas with a mercury absorbing liquid. Located in mercury processing system.

  According to a second aspect of the present invention, there is provided a wet desulfurization apparatus provided in a rear stage side of the mercury absorption tower in the first aspect of the invention, wherein the wet desulfurization apparatus desulfurizes sulfur oxides in the exhaust gas after removing mercury. Located in mercury processing system.

A third invention is the denitration means according to the first or second invention, comprising a denitration catalyst which is provided on the upstream side of the heat exchanger and denitrates NOx in the exhaust gas and oxidizes metallic mercury (Hg ⁰ ). It is in the mercury processing system in waste gas characterized by comprising.

  A fourth invention is the mercury treatment system in exhaust gas according to any one of the first to third inventions, wherein the oxidation-reduction state in the mercury absorption tower is judged by oxidation-reduction potential measurement control means. .

  A fifth invention is the mercury treatment system in exhaust gas according to any one of the first to fourth inventions, wherein the mercury absorption liquid is extracted from the mercury absorption tower, and the extracted mercury absorption liquid is drained. It is in.

  According to a sixth aspect of the present invention, in any one of the first to fourth aspects, the mercury absorption liquid is extracted from the mercury absorption tower, the solid content in the extracted mercury absorption liquid is separated, and the mercury absorption after the solid content separation is performed. The present invention is in a mercury treatment system in exhaust gas, wherein the liquid is reused in the mercury absorption tower.

  A seventh aspect of the present invention is the process according to any one of the first to fourth aspects, wherein the mercury absorption liquid is extracted from the mercury absorption tower, the solid content in the extracted mercury absorption liquid is separated, and the treated water after the solid content separation is separated. In a mercury treatment system in exhaust gas, characterized by evaporating the gas.

  According to an eighth invention, in any one of the first to fourth inventions, a mercury absorption liquid is extracted from the mercury absorption tower, a solid content in the extracted mercury absorption liquid is separated, and treated water after the solid content separation is separated. It is in a mercury treatment system in exhaust gas characterized by treating waste water.

  According to a ninth invention, in any one of the first to fourth inventions, the mercury absorbing liquid is extracted from the mercury absorption tower, the solid content in the extracted mercury absorbing liquid is aggregated, and treated water containing aggregates is obtained. It is in a mercury treatment system in exhaust gas characterized by evaporating treatment.

  According to the present invention, mercury oxide in the boiler exhaust gas is efficiently removed before being introduced into the desulfurization apparatus, so that divalent mercury in the exhaust gas can be removed. Moreover, in the process in which the desulfurization apparatus is installed, HCl and dust in the exhaust gas that cause the performance degradation can be removed.

FIG. 1 is a schematic diagram showing a mercury treatment system in exhaust gas according to Embodiment 1 of the present invention. FIG. 2 is a schematic view showing a mercury treatment system in exhaust gas according to Embodiment 2 of the present invention. FIG. 3 is a schematic view showing a mercury treatment system in exhaust gas according to Embodiment 3 of the present invention. FIG. 4 is a schematic view showing a mercury treatment system in exhaust gas according to Embodiment 4 of the present invention. FIG. 5 is a schematic view showing a mercury treatment system in exhaust gas according to Embodiment 5 of the present invention. FIG. 6 is a relationship diagram between the ORP value in the mercury absorbing solution and the mercury re-scattering rate. FIG. 7 shows the potential-pH value (Pourbaille diagram) of mercury.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by this Example, Moreover, when there exists multiple Example, what comprises combining each Example is also included.

FIG. 1 is a schematic view of a mercury treatment system in exhaust gas according to Embodiment 1 of the present invention.
As shown in FIG. 1, the mercury treatment system 10A in the exhaust gas according to the present embodiment is a mercury treatment system in the exhaust gas that removes mercury contained in the exhaust gas 12 from the boiler 11, and is supplied with fuel F. A denitration device 17 for denitrating nitrogen oxides (NOx) in the exhaust gas 12 from the boiler 11 that is burned, and an air heater (AH) 18 provided on the downstream side of the denitration device 17 for adjusting the exhaust gas temperature; The dust collector 19 provided on the downstream side of the air heater 18 for removing the dust in the exhaust gas, and the mercury oxide Hg ²⁺ in the exhaust gas 12 provided on the downstream side of the dust collector 19 are removed by the mercury absorbing liquid 51. The mercury absorption tower 50 is provided.
In FIG. 1, reference numeral 13 denotes a flue from which exhaust gas is discharged, 25 denotes a chimney for discharging the purified exhaust gas to the outside, and V ₀ , V ₁ , V ₂ denote valves.

In this embodiment, ammonia (NH ₃ ) 14A as a denitration aid is added to ammonia (NH ₃ ) via an ammonia (NH ₃ ) supply line 15A in the exhaust gas flowing through the flue 13 on the upstream side of the denitration device 17. It is supplied from the supply means 16A, and reductive denitration with ammonia 14A is performed.
As the denitration device 17, a general device having a reduction denitration catalyst can be used. The reductive denitration catalyst is not particularly limited. For example, a catalyst in which a metal oxide such as W, Sn, In, Co, Ni, Fe, Ni, Ag, or Cu is supported on a support such as zeolite may be used. it can. The amount of the reducing denitration catalyst provided in the denitration device 17 may be increased from the normal amount in order to increase the mercury oxidation efficiency.

  The ammonia denitrated exhaust gas 12B has a gas temperature of, for example, about 330 ° C. The air (not shown) supplied from the outside to the boiler 11 by using the heat of the exhaust gas 12 is used by an air heater (AH) 18. Preheated.

In this embodiment, after removing the dust in the exhaust gas with the dust collector 19, the exhaust gas 12 is introduced into the mercury adsorption tower 50, and the mercury in the exhaust gas 12 is removed with the mercury absorbing liquid 51.
The top side of the mercury adsorption tower 50 is a nozzle 53 is provided, so that spraying the mercury absorbing liquid 51 to be circulated by a pump (not shown) circulation line L _11. The sprayed mercury absorption liquid 51 is brought into contact with the exhaust gas so that soluble mercury oxide (Hg ²⁺ ) moves to the mercury absorption liquid 51 side and is dissolved and removed.

Here, as the mercury absorbent solution 51, water or chelating solution is by using, if necessary, by opening the valve V ₁ interposed in introduction line L _12, be added to the oxidant 55 Good. Air may be introduced as the oxidant.
Here, as the oxidant, air is used in the present embodiment, but the present invention is not limited to this. For example, an oxygen-based oxidant such as O ₂ , O ₃ , H ₂ O ₂ , For example, oxygen acids such as permanganic acid, chromic acid, chloric acid, hypochlorous acid, perchloric acid, nitric acid, nitrous acid and their salts, and oxidizers such as chlorine (Cl ₂ ), HClO, NaClO, ClO Examples thereof include chlorine-based oxidizers, polyvalent metal salts such as Fe ³⁺ , Cu ²⁺ , and Sn ⁴⁺ .

This is because when the oxidation-reduction potential of the mercury absorbing solution 51 is kept within a certain range, the mercury oxide (Hg ²⁺ ) in the mercury absorbing solution 51 is converted into metallic mercury (SO ₂ ) as shown in the following formula (3). This is to prevent reduction to Hg ⁰ ) and to prevent mercury from re-scattering.
Hg ²⁺ + 2e ⁻ ⇔ Hg ⁰ (3)
As a means for keeping the oxidation-reduction potential of the mercury absorbing solution 51 constant, an ORP controller 56 for controlling the oxidation-reduction potential (ORP) of the mercury absorbing solution 51 is used. For example, the ORP value is +50 mV or more, preferably the ORP value. Is set to +80 mV or more, and more preferably, the supply amount of the oxidizing agent 55 is adjusted so that the ORP value is +100 mV.

FIG. 6 is a relationship diagram between the ORP value in the mercury absorbing solution and the mercury re-scattering rate.
FIG. 6 shows the relationship between the ratio of metallic mercury in the total mercury in the mercury absorbing solution at 48 ° C. and the ORP value. Here, the vertical axis represents the mercury re-scattering rate of “metal mercury (Hg ⁰ ) amount / total mercury (Hg _total ) amount”, and the horizontal axis represents the ORP value. At the value “1” on the vertical axis, the metal mercury is 100%, and at the value “0” on the vertical axis, the amount of metal mercury is 0%.
Here, the electrode is measured at a temperature of 48 ° C. using silver / silver chloride. Furthermore, Cl ^- concentration: Hg concentration = 13,000: 1.
As shown in FIG. 6, when the ORP value is 80 mV, it is almost zero. When the temperature is high, the value tends to be lower.

FIG. 7 shows the potential-pH value (Pourbaille diagram) of mercury.
As shown in FIG. 7, in the potential-pH value of mercury (Pourbé diagram), since there is a boundary between the oxidizing environment and the reducing environment when the ORP value is around 90 mV, it is preferably 90 mV or more, more preferably 100 mV or more. It is preferable to control the ORP value.

  As a result, by properly controlling the ORP, the mercury oxide dissolved in the mercury absorbing liquid 51 is prevented from being re-scattered as metallic mercury, and in the exhaust gas 12 introduced to the desulfurization apparatus 21 side. Mercury is prevented from being accompanied.

Mercury absorbing solution 51 obtained by dissolving the oxidized mercury at the mercury adsorption tower 50, every predetermined amount is discharged by opening the interposed a valve V ₂ to the collection tank 52 side to the discharge line L _13. Incidentally, the mercury absorbent solution 51 to be replenished separately from introduction line L _14, is introduced required amount of mercury absorption tower 50.

  In this way, the exhaust gas 12 from which the mercury in the exhaust gas 12 has been removed by the mercury absorption tower 50 is then discharged out of the system from the chimney 25 as the purified gas 24.

  Further, the mercury absorbing solution 51 in which the mercury oxide discharged to the collection tank 52 side is dissolved is sent to a known waste water treatment means for waste water treatment.

Next, a mercury treatment system in exhaust gas according to Embodiment 2 of the present invention will be described. In addition, the same code | symbol is attached | subjected to the same structural member as Example 1, and the overlapping description is abbreviate | omitted.
FIG. 2 is a schematic diagram of a mercury treatment system in exhaust gas according to Embodiment 2 of the present invention.
As shown in FIG. 2, the mercury treatment system 10B in the exhaust gas according to the present embodiment is the same as the mercury treatment system 10A in the exhaust gas according to the first embodiment.
A wet desulfurization device 21 that desulfurizes sulfur oxides contained in the exhaust gas 12 after mercury removal by the mercury absorption tower 50 is provided on the rear side of the mercury absorption tower 50.

The exhaust gas 12 from which mercury has been removed by the mercury adsorption tower 50 passes through the wet desulfurization device 21, thereby absorbing and removing sulfur oxides present in the gas.
When the sulfur oxide is less than the predetermined concentration, it may be discharged as it is as the purified gas 24 from the chimney as in the first embodiment, but the sulfur oxide exceeding the environmental standard at the place where the plant is installed is discharged. In such a case, a desulfurization means such as a wet or dry desulfurization apparatus is provided.

  Here, as the wet desulfurization apparatus 21, a conventional apparatus including an alkali absorbing liquid can be used. As the alkali absorbing liquid, for example, an aqueous solution of calcium carbonate, calcium hydroxide, sodium hydroxide, sodium sulfite, ammonia, magnesium hydroxide, or the like can be used, but it is not limited thereto.

In the wet desulfurization system 21, feeds feeding the flue gas 12 from the wall surface side of the bottom portion 21b of the apparatus main body 21a, lime gypsum slurry 20 to be used as an alkaline absorption liquid in the absorption liquid supply line L ₁ by the apparatus body 21a It is supplied and jetted from the nozzle 21c toward the tower top side. The exhaust gas 12 rising from the bottom side in the apparatus main body 21a and the lime-gypsum slurry 20 jetted from the nozzle 21c face each other in gas-liquid contact, and sulfur oxide (SOx) in the exhaust gas 12 is lime. It is absorbed in the gypsum slurry 20, separated and removed from the exhaust gas 12, and the exhaust gas 12 is purified.

The exhaust gas 12 purified by the lime gypsum slurry 20 is discharged from the tower top side, and then discharged from the chimney 25 as the purified gas 24 to the outside of the system.
The lime 26 replenished inside the apparatus main body 21a is supplied from a lime supply device 27.

The lime gypsum slurry 20 used for the desulfurization of the exhaust gas 12 includes a lime slurry (CaCO ₃ ) obtained by dissolving limestone powder in water, and a gypsum slurry (CaSO ₄ ) obtained by reacting and further oxidizing lime and SOx in the exhaust gas 12. It is produced by mixing with water. As the lime gypsum slurry 20, for example, a solution obtained by pumping liquid stored in the tower bottom 21b of the apparatus main body 21a of the wet desulfurization apparatus 21 with a pump (not shown) is used. Within the apparatus main body 21a, SOx in the exhaust gas 12 reacts with lime (CaCO ₃ ) in the lime-gypsum slurry 20 as shown in the following formula (4).
CaCO ₃ + SO ₂ + 0.5H ₂ O → CaSO ₃ .0.5H ₂ O + CO ₂ (4)

On the other hand, the lime-gypsum slurry 20 that has absorbed SOx in the exhaust gas 12 is mixed with the water 30 supplied into the apparatus main body 21a, and is oxidized by the air supplied to the tower bottom 21b of the apparatus main body 21a. At this time, the lime-gypsum slurry 20 flowing down in the apparatus main body 21a reacts with water 30 and air as shown in the following formula (5).
CaSO ₃ · 0.5H ₂ O + 0.5O ₂ + 1.5H ₂ O → CaSO ₄ · 2H ₂ O (5)
In this way, SO _x in the exhaust gas 12 is captured in the form of gypsum (CaSO ₄ .2H ₂ O) in the wet desulfurization apparatus 21.
At this time, mercury chloride (HgCl ₂ ) in the exhaust gas 12 is removed by the mercury adsorption tower 50 provided on the front stage side, so that it is prevented from being transferred to the lime gypsum slurry 20 side.

The lime gypsum slurry 20 used for desulfurization stored in the tower bottom 21b of the wet desulfurization apparatus 21 is oxidized and then extracted from the tower bottom 21b. The extracted lime gypsum slurry 20 is fed to the water separator 33 via the line L ₂ and then discharged out of the system as a dehydrated cake (gypsum) 28 containing mercury chloride (HgCl ₂ ).

As the water separator 33, for example, a belt filter or the like is used. Further, the dehydrated filtrate (dehydrated filtrate) 34 is fed to the waste water treatment device 35 via the line L ₃ . Then, for example, operations such as removal of suspensions in the dehydrated filtrate, heavy metal 36, and pH adjustment of the dehydrated filtrate are performed by the waste water treatment device 35. A part of the treated wastewater 37 subjected to the wastewater treatment is returned to the wet desulfurization apparatus 21, and the other part is treated as the wastewater 37.

  The supply method of the lime gypsum slurry 20 is not limited to the method of jetting from the nozzle 21c toward the tower top side. For example, the lime gypsum slurry 20 may flow down from the nozzle 21c so as to face the exhaust gas 12.

  According to the present embodiment, since the mercury absorption tower 50 is installed before being introduced into the desulfurization apparatus, mercury oxide in the boiler exhaust gas can be efficiently removed, and mercury is contained in the gypsum crystals generated by the desulfurization apparatus. It is possible to prevent mercury from being fixed in gypsum.

Next, a mercury treatment system in exhaust gas according to Embodiment 3 of the present invention will be described. In addition, the same code | symbol is attached | subjected to the same structural member as Example 1 and 2, and the overlapping description is abbreviate | omitted.
FIG. 3 is a schematic view of a mercury treatment system in exhaust gas according to Embodiment 3 of the present invention.
As shown in FIG. 3, the mercury treatment system 10C in the exhaust gas according to the present example supplies ammonium chloride instead of the ammonia used in the first example.
In this embodiment, an ammonium chloride (NH ₄ Cl) solution supply means 16B for spraying an NH ₄ Cl solution 14B containing ammonium chloride (NH ₄ Cl) as a reducing oxidation aid into the flue 13 downstream of the boiler 11; And a denitration device 17 having a denitration catalyst that reduces NOx in the exhaust gas 12 with NH ₃ gas and oxidizes metallic mercury (Hg ⁰ ) in the presence of HCl gas.

In this example, NH ₄ Cl is used as an example. However, this example is not limited to this example. The reduction oxidation aid is a halogen that generates an oxidation aid and a reduction aid when vaporized. Any compound can be used. Here, in this embodiment, the reduction oxidation aid is an oxidation aid used to oxidize metallic mercury (Hg ⁰ ) in the presence of the oxidation aid, and a reduction agent that reduces NOx with the reduction aid. As a function. In this embodiment, HCl gas is used as an oxidation aid, and NH ₃ gas is used as a reduction aid.
Note that an oxidation aid (for example, HCl gas) and a reduction aid (for example, NH ₃ gas) may be introduced separately.

The exhaust gas 12 discharged from the boiler 11 is supplied with an NH ₄ Cl solution 14B from an NH ₄ Cl solution supply means 16B via an ammonium chloride (NH ₄ Cl) supply line 15B.

The droplets of the NH ₄ Cl solution 14B sprayed into the flue 13 from the NH ₄ Cl solution supply means 16B are evaporated and vaporized by the high-temperature atmosphere temperature of the exhaust gas 12 to generate fine NH ₄ Cl solid particles. And decomposed into HCl and NH ₃ as shown in the following formula (6). Therefore, the NH ₄ Cl solution 14B sprayed from the spraying means is decomposed to generate HCl and NH ₃ , and NH ₃ gas and HCl gas are supplied into the flue 13.
NH ₄ Cl → NH ₃ + HCl (6)

  Although the temperature of the exhaust gas 12 in the flue 13 depends on the combustion conditions of the boiler 11, it is preferably 320 ° C. or higher and 420 ° C. or lower, and more preferably 320 ° C. or higher and 380 ° C. or lower. This is because the NOx denitration reaction and the Hg oxidation reaction can be efficiently generated on the denitration catalyst in this temperature range.

Further, the exhaust gas 12 contains HCl gas and NH ₃ gas generated from droplets of the NH ₄ Cl solution 14B sprayed into the flue 13 from the NH ₄ Cl solution supply means 16B, and then is sent to the denitration device 17. Is done. In the denitration device 17, NH ₃ gas generated by decomposition of NH ₄ Cl is used for NOx reduction denitration, HCl gas is used for Hg oxidation, and NOx and Hg are removed from the exhaust gas 12. The mercury removal rate is improved as compared with the case of using.

That is, NH ₃ gas reduces and denitrates NOx as shown in the following formula (7) on the denitration catalyst filled in the denitration device 17, and the following formula (8) is obtained using HCl gas. Thus, Hg is oxidized.
4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O (7)
Hg + 1 / 2O ₂ + 2HCl → HgCl ₂ + H ₂ O (8)

  After the NOx reduction in the exhaust gas 12 and the oxidation of Hg are performed in the denitration device 17, the exhaust gas 12 is lowered in temperature by the air heater 18.

  Next, after the dust is removed by the dust collector 19, the exhaust gas 12 is introduced into the mercury absorption tower 50, where the mercury oxide is absorbed and removed by the mercury absorption liquid 51, and then sent to the wet desulfurization apparatus 21 for desulfurization treatment.

  In this embodiment, mercury is oxidized in the exhaust gas by the denitration device 17, and this oxidized mercury is reliably treated with the mercury absorbing solution 51 in the mercury absorption tower 50, so that mercury is reliably removed. Will be able to.

Next, a mercury treatment system in exhaust gas according to Embodiment 4 of the present invention will be described. In addition, the same code | symbol is attached | subjected to the same structural member as Example 2 and 3, and the overlapping description is abbreviate | omitted.
FIG. 4 is a schematic diagram of a mercury treatment system in exhaust gas according to Embodiment 4 of the present invention.
As shown in FIG. 4, the mercury treatment system 10 </ b> D in the exhaust gas according to the present embodiment is provided with an aggregating device 71 that agglomerates the agglomerates in the mercury absorption liquid collected in the collection tank 52.
In the aggregating device 71, for example, an aggregating agent 72 such as an aggregating agent such as a heavy metal scavenger and a chelating agent is charged to agglomerate the agglomerates containing mercury in the mercury absorbing solution 51.

Examples of the aggregating agent 72 include an Fe-based aggregating agent, an Al-based aggregating agent, and a polymer-based aggregating agent.
During this agglomeration treatment, the mercury oxide in the mercury absorbing solution 51 is agglomerated and solidified to be transferred from the liquid phase to the solid phase.

  The agglomerates 73 in the aggregating apparatus 71 are subjected to a non-draining process by separately evaporating by an evaporating process means.

Next, a mercury treatment system in exhaust gas according to Embodiment 5 of the present invention will be described. In addition, the same code | symbol is attached | subjected to the same structural member as Example 2 thru | or Example 4, and the overlapping description is abbreviate | omitted.
FIG. 5 is a schematic diagram of a mercury treatment system in exhaust gas according to Embodiment 5 of the present invention.
As shown in FIG. 5, the mercury treatment system 10E in the exhaust gas according to the present embodiment is provided with a dehydration processing device 74 that dehydrates the agglomerates 73 from the agglomeration device 71 of the third embodiment and separates them into solid and liquid. .
And since the dewatered sludge 75 contains mercury, it is processed separately.
Further, the treated water 76 which is a filtrate is reused as a part of the mercury absorbing solution 51.

  In addition to reuse, for example, it may be treated together with the drainage treatment for evaporating and the wastewater 37 of the wastewater treatment device 35.

10A-10E Mercury treatment system in exhaust gas 11 Boiler 12 Exhaust gas 17 Denitration equipment 18 Heat exchanger (AH)
50 Mercury absorption tower 51 Mercury absorption liquid

Claims (9)

A mercury removal system in exhaust gas for removing mercury contained in exhaust gas from a boiler,
A heat exchanger for exchanging heat from the exhaust gas from the boiler;
A dust collector to remove dust in the exhaust gas;
A mercury absorption tower that is provided on the downstream side of the dust collector and removes mercury oxide in the exhaust gas with a mercury absorbing solution;
A mercury treatment system in exhaust gas, comprising: a wet desulfurization device that desulfurizes sulfur oxides in exhaust gas after mercury removal by the mercury absorption tower. In claim 1,
A mercury treatment system in exhaust gas, comprising a wet desulfurization device that is provided on the rear stage side of the mercury absorption tower and desulfurizes sulfur oxides in the exhaust gas after mercury removal. In claim 1 or 2,
A mercury treatment system in exhaust gas, comprising a denitration means provided on the upstream side of the heat exchanger and denitrating NOx in exhaust gas and having a denitration catalyst that oxidizes metallic mercury (Hg ⁰ ) . In any one of Claims 1 thru | or 3,
A mercury treatment system in exhaust gas, wherein the oxidation-reduction state in the mercury absorption tower is judged by oxidation-reduction potential measurement control means. In any one of Claims 1 thru | or 4,
A mercury treatment system in exhaust gas, wherein a mercury absorption liquid is extracted from the mercury absorption tower, and the extracted mercury absorption liquid is drained. In any one of Claims 1 thru | or 4,
The mercury absorption liquid is extracted from the mercury absorption tower, the solid content in the extracted mercury absorption liquid is separated, and the mercury absorption liquid after the solid content separation is reused in the mercury absorption tower. Mercury treatment system. In any one of Claims 1 thru | or 4,
A mercury treatment system in exhaust gas, wherein a mercury absorption liquid is extracted from the mercury absorption tower, a solid content in the extracted mercury absorption liquid is separated, and treated water after the solid content separation is evaporated. In any one of Claims 1 thru | or 4,
A mercury treatment system in exhaust gas, wherein a mercury absorption liquid is extracted from the mercury absorption tower, a solid content in the extracted mercury absorption liquid is separated, and treated water after the solid content separation is drained. In any one of Claims 1 thru | or 4,
A mercury treatment system in exhaust gas, wherein a mercury absorption liquid is extracted from the mercury absorption tower, solids in the extracted mercury absorption liquid are aggregated, and treated water containing the aggregates is evaporated.

Images