JP2006136856A - Mercury removing device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To separate and remove zero valent mercury gas from treating object gas with a sufficient removal ratio, while suppressing a using amount of a mercury oxidizer. <P>SOLUTION: In this separation and removal method, a mercury oxidizer having tri-valent ferric ions Fe<SP>3+</SP>as a component is contained, an aqueous solution with pH about less than 1 is brought into contact with the treating object gas to convert zero valent mercury gas into bi-valent mercury gas and to dissolve it into the aqueous solution, to thereby separate and remove zero valent mercury gas from the treating object gas. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a mercury removal apparatus and method.

For example, Japanese Patent Laid-Open No. 10-216476 discloses several exhaust gas treatment apparatuses that remove zero-valent mercury Hg ⁰ in exhaust gas that is a processing target. Among the exhaust gas treatment apparatuses described in JP-A-10-216476, the exhaust gas treatment apparatus shown in FIG. 3 is an exhaust gas treatment apparatus provided with a two-column wet desulfurization apparatus comprising a cooling tower and an absorption tower. In the exhaust gas by adding mercury-removing agents such as sodium hypochlorite, copper chloride, manganese chloride, iron chloride, chelating agent, coal ash, etc. to the circulating water of the cooling tower placed in the previous stage Hg ⁰ is converted to water-soluble divalent mercury Hg ²⁺ and removed.
Japanese Patent Laid-Open No. 10-216476

By the way, the exhaust gas treatment apparatus of Patent Document 1 has the following problems.
(1) When the mercury removing agent is added to circulating water having a low pH, the mercury removing agent is decomposed at a considerable rate, so that a large amount of the mercury removing agent needs to be added.
(2) When the sulfur dioxide SO ₂ is contained in the exhaust gas to be treated, the mercury remover reacts with the sulfur dioxide SO ₂ and is consumed, so it is necessary to add a large amount of mercury remover. There is.

  The present invention has been made in view of the above-described circumstances, and aims to suppress the amount of mercury oxidant used and to separate and remove zero-valent mercury gas from the gas to be treated at a sufficient removal rate. It is.

In order to achieve the above object, in the present invention, as a first solution for a mercury removing apparatus, an apparatus for converting zero-valent mercury gas into water-soluble divalent mercury gas and separating and removing it from the gas to be treated. A solution means is provided which comprises a reaction separation means for bringing an aqueous solution containing a mercury oxidizing agent containing trivalent iron Fe ³⁺ as a component and having a pH of about 1 or less into contact with the gas to be treated.
According to this invention, the zero-valent mercury gas is converted into the divalent mercury gas by bringing the aqueous solution of the mercury oxidant containing trivalent iron Fe ³⁺ into pH 1 or lower and bringing it into gas-liquid contact with the gas to be treated. Since it dissolves in an aqueous solution and is separated from the processing target gas, the zero-valent mercury gas can be separated from the processing target gas with a sufficient removal rate while suppressing the amount of mercury oxidant used.

  As a second solving means relating to the mercury removing apparatus, in the first means, the reaction separation means recovers the aqueous solution after the aqueous solution is sprayed onto the gas to be processed and the nozzle contacts the gas to be processed by the nozzle. A recovery container, a circulation pump that supplies the aqueous solution recovered in the recovery container to the nozzle, a mercury oxidant addition device that adds a mercury oxidant to the aqueous solution, and a pH of the aqueous solution recovered in the recovery container A solution comprising a pH meter and a pH adjuster addition unit for adding a pH adjuster to the aqueous solution so that the pH of the aqueous solution sprayed from the nozzle is maintained at 1 or less based on the measurement result of the pH meter. Adopt means.

  As a third solution for the mercury removal apparatus, in the second means, the nozzle, the recovery container, and the circulation pump constitute a cooling tower arranged in the preceding stage in the two-column wet desulfurization apparatus, and the reaction The separation means employs a solution means in which a pH meter, a pH adjuster addition unit, and a mercury oxidizing agent addition device are added to the cooling tower.

As a fourth solving means relating to the mercury removing apparatus, a solving means is adopted in which the mercury oxidizing agent is iron chloride FeCl ₃ containing iron Fe ³⁺ as a component in any of the first to third means.

  As a fifth solving means relating to the mercury removing apparatus, a solving means is adopted in which the pH adjuster is hydrochloric acid HCl in any one of the first to fourth means.

  As a sixth solving means relating to the mercury removing apparatus, a solving means in any one of the above first to fifth means that the processing object gas is combustion exhaust gas of a combustion furnace is adopted.

On the other hand, in the present invention, as a first solution for the mercury removal method, in the method of converting zero-valent mercury gas into water-soluble divalent mercury gas and separating and removing it from the gas to be treated, trivalent iron Fe ^The zero-valent mercury gas is converted into a divalent mercury gas by contacting an aqueous solution containing a mercury oxidant containing ³⁺ as a component and having a pH of about 1 or less with the gas to be treated, and dissolved in the aqueous solution for treatment. The solution of separating and removing from the target gas is adopted.

  As a second solution for the mercury removal method, in the first means, a pH adjusting agent and a mercury oxidizing agent for reducing the pH to about 1 or less are arranged in a two-stage wet desulfurization apparatus in the previous stage. The solution is to separate and remove the zero-valent mercury gas from the gas to be treated by adding it to the washing water or circulating water of the cooling tower.

As a third solving means relating to the mercury removing method, a solving means is adopted in which the mercury oxidizing agent is iron chloride FeCl ₃ containing trivalent iron Fe ³⁺ as a component in the first or second means.

  As a fourth solving means relating to the mercury removing method, a solving means is adopted in which the pH adjuster is hydrochloric acid HCl in any one of the first to third means.

  As a fifth solving means related to the mercury removing method, a solving means is adopted in which the processing target gas is combustion exhaust gas of a combustion furnace in any of the first to fourth means.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a system diagram of an exhaust gas treatment apparatus to which a mercury removal apparatus according to this embodiment is applied. As shown in this figure, this exhaust gas treatment device is composed of a boiler 1, a denitration device 2, an electric dust collector 3, a two-column desulfurization device 4 and a chimney 5. The boiler 1 is, for example, for generating steam for power generation in a thermal power plant, and generates steam using petroleum, natural gas, coal, or the like as fuel. Exhaust gas generated by burning such fuel in the boiler 1 is supplied from the boiler 1 to the denitration device 2.

The denitration device 2 is for removing nitrogen oxides NOx contained in the exhaust gas. The denitration device 2 decomposes nitrogen oxides NOx into nitrogen N ₂ and water H ₂ O, for example, by causing ammonia to act on exhaust gas in the presence of a catalyst. The electric dust collector 3 adsorbs and removes dust contained in the exhaust gas by the electric field between the counter electrodes. The double tower type desulfurization apparatus 4 is a double tower type wet desulfurization apparatus that wet-removes sulfur oxide SOx contained in the exhaust gas, and as shown in the drawing, the cooling tower 4A arranged in the front stage and the absorption arranged in the rear stage. It consists of tower 4B.

The cooling tower 4A has both the function of cooling the exhaust gas using circulating water and the function of the mercury removing apparatus according to this embodiment. Here, since the cooling tower in the general two-column desulfurization apparatus aims at cooling and dust removal of the exhaust gas, the circulating water is general water, but the circulating water W in the present embodiment has a function of cooling and removing the exhaust gas. In addition, since it is necessary to have a function of oxidizing the zero-valent mercury (Hg ⁰ ) gas contained in the exhaust gas into a water-soluble divalent mercury (Hg ²⁺ ) gas, trivalent iron Fe ³⁺ is used as a component. It is an aqueous solution containing mercury oxidant.

The use of such an aqueous solution as the circulating water W is one of the features of this embodiment. The mercury oxidizing agent is preferably iron chloride FeCl ₃ , but is not limited thereto as long as it contains trivalent iron Fe ³⁺ as a component. Instead of the circulating water W, the cleaning water for the cooling tower 4A may be an aqueous solution containing a mercury oxidizing agent.

  FIG. 2 is a block diagram showing a detailed configuration of the cooling tower 4A, that is, the mercury removing apparatus according to this embodiment. As shown in FIG. 2, the mercury removing apparatus includes a tower body 6 (collection container), a spray nozzle 7, a circulation pump 8, a pH measuring device 9, a pH adjusting agent adding device 10, a mercury oxidizing agent adding device 11, and the like. It is configured. The tower body 6 is, for example, a hollow cylindrical container. The spray nozzle 7 that injects the circulating water downward is formed in the upper part of the inside of the tower body 6. ing. This mercury removing apparatus is an essential constituent element as a cooling tower, that is, a constituent element for adding a function as a mercury removing apparatus to the tower body 6, spray nozzle 7 and circulation pump 8, that is, a pH measuring device 9 and a pH adjusting agent. An addition device 10 and a mercury oxidant addition device 11 are added.

  Further, an exhaust gas inlet 6a is provided at the side of the tower body 6, and a treated gas outlet 6b is provided at the upper part. The exhaust gas taken into the tower main body 6 from the inlet 6a moves upward while making gas-liquid contact with the circulating water sprayed from the spray nozzle 7, and is discharged to the outside of the tower main body 6 as a processed gas. The spray nozzle 7 is disposed so as to expand in the upper part of the tower body 6 so that the circulating water is in uniform gas-liquid contact with the exhaust gas in a wide area in the tower body 6.

  The circulation pump 8 pumps the circulating water accumulated in the lower part of the tower body 6 and supplies it to the spray nozzle 7. When the circulating pump 8 is continuously operated with respect to the exhaust gas continuously supplied into the tower body 6 by continuously operating the thermal power plant, the circulating water is sequentially injected from the spray nozzle 7 into the exhaust gas. Thus, the gas-liquid contact between the exhaust gas and the circulating water is continuously performed.

The pH measuring device 9 is provided between the circulation pump 8 and the spray nozzle 7. The pH measuring device 9 measures the pH value of the circulating water supplied from the circulation pump 8 to the spray nozzle 7, that is, the circulating water injected into the exhaust gas, and outputs the pH value to the pH adjuster adding device 10 as pH information. The pH adjusting agent adding device 10 supplies the pH adjusting agent to the circulating water so that the pH value of the circulating water measured by the pH measuring device 9 is maintained at about 1 or less. This pH adjuster is preferably hydrochloric acid HCl. For example, sulfuric acid H ₂ SO ₄ is not preferable because it reduces the zero-valent mercury gas removal performance. The mercury oxidant addition device 11 supplies, for example, iron chloride FeCl ₃ to the circulating water as a mercury oxidant.

On the other hand, the absorption tower 4B is for removing sulfur oxide SOx from the treated gas discharged from the cooling tower 4A (that is, the mercury removing device). The absorption tower 4B separates sulfur oxide SOx into the absorption liquid as gypsum CaSO ₄ by reacting the exhaust gas with an absorption liquid containing, for example, lime slurry. The chimney 5 discharges the exhaust gas discharged from the absorption tower 4B, that is, the two-column desulfurization apparatus 4, to the outside air at a high place.

  Next, the operation and effect of the mercury removing apparatus configured as described above will be described with reference to experimental data shown in FIGS.

FIG. 3 shows experimental results showing the effectiveness of using a trivalent iron Fe ³⁺ component as a mercury oxidant. More specifically, iron chloride FeCl ₃ containing trivalent iron Fe ³⁺ as a component, iron chloride FeCl ₂ containing divalent iron Fe ²⁺ as a component, and tetravalent titanium Ti ⁴⁺ used in this embodiment are used. Titanium chloride TiCl ₄ as a component, Titanium chloride TiCl ₃ as a component of trivalent titanium Ti ³⁺ , Aluminum chloride AlCl ₃ as a component of trivalent aluminum Al ³⁺ , and Phosphorus as a component of pentavalent phosphorus P ⁵⁺ An aqueous solution containing acid H ₂ PO ₄ was prepared, and the capture rate of zero-valent mercury Hg ⁰ when a mixed gas of zero-valent mercury (Hg ⁰ ) gas and nitrogen (N ₂ ) gas was brought into gas-liquid contact is shown. Yes. In this experiment, the concentration of the target component (Fe ³⁺ , Fe ²⁺ , Ti ⁴⁺ , Ti ³⁺ , Al ³⁺ , phosphorus P ⁵⁺ ) was adjusted to 100 ppm, and the pH of each aqueous solution was adjusted to about 1 by adding HCl HCl. .

As is apparent from the experimental results, an aqueous solution of iron chloride FeCl ₃ containing trivalent iron Fe ³⁺ as a component exhibits a high Hg ⁰ capture rate, but iron chloride FeCl ₂ containing divalent iron Fe ²⁺ as a component is used. Other aqueous solutions, including the first, show very low Hg ⁰ capture rates. It can be seen that trivalent iron Fe ³⁺ has an oxidizing power with respect to zero-valent mercury Hg ⁰ , that is, an ability to accept electrons from zero-valent mercury Hg ⁰ to form divalent mercury Hg ²⁺ is extremely higher than other target components.

Next, FIG. 4 is an experimental result showing the influence of pH on the Hg ⁰ capture rate when using iron chloride FeCl ₃ having excellent oxidation performance against zero-valent mercury Hg ⁰ as described above. In this experiment, the concentration of trivalent iron Fe ³⁺ in an aqueous solution of iron chloride FeCl ₃ was kept constant at 100 ppm, and the pH was adjusted by adding HCl HCl.

As a result of this experiment, when the pH of the aqueous solution of iron chloride FeCl ₃ decreases to near 1, the Hg ⁰ capture rate increases rapidly, and in the region below pH 1, the chlorine Cl ⁻ concentration, that is, the amount of hydrochloric acid HCl added is increased. This also shows that the Hg ⁰ capture rate hardly increases. Therefore, in order to suppress the amount of iron chloride FeCl ₃ used as a mercury oxidizing agent as much as possible and to obtain a high Hg ⁰ capture rate, it is preferable to set the pH to about 1 or less, preferably 1 or less. I understand.

Next, FIG. 5 is an experimental result showing the dependence of the Hg ⁰ capture rate on the concentration of trivalent iron Fe ³⁺ . In this experiment, the concentration of trivalent iron Fe ³⁺ (Fe ³⁺ concentration) in the case where the pH is set to 1 or less by adding hydrochloric acid and the case where the pH is set to about 2.5 without adding hydrochloric acid. A mixed gas of about 5 μg / m ³ N zero-valent mercury (Hg ⁰ ) gas and nitrogen (N ₂ ) gas was circulated through the different aqueous solutions, and the Hg ⁰ capture rate was measured.

As can be seen from the experimental result, in the case of pH1 below, trivalent iron ^{Fe 3+} concentration Hg ⁰ capture rate is rapidly increased with increasing trivalent iron ^{Fe 3+} concentration is in the relatively low area (approximately 50ppm neighboring region) In the region where the trivalent iron Fe ³⁺ concentration is about 100 ppm or more, the Hg ⁰ trapping rate increases relatively slowly. On the other hand, when the pH is about 2.5, the Hg ⁰ capture rate increases with a substantially constant slope with respect to the increase of the trivalent iron Fe ³⁺ concentration, but the pH is 1 or less. The value of the Hg ⁰ capture rate is low compared to Therefore, in order to obtain a high Hg ⁰ capture rate in a region where the trivalent iron Fe ³⁺ concentration is relatively low, that is, in a state where the amount of iron chloride FeCl ₃ used as a mercury oxidizing agent is suppressed as much as possible, the pH is also reduced to about It can be seen that it is preferable to set it to 1 or less.

The experimental results shown in FIGS. 3 to 5 are different from the exhaust gas discharged from the boiler 1 of the actual thermal power plant, that is, a mixed gas of zero-valent mercury (Hg ⁰ ) gas and nitrogen (N ₂ ) gas. Is about. On the other hand, the experimental results shown in FIGS. 6 and 7 show the Hg ⁰ removal rate for the simulated combustion exhaust gas having substantially the same composition as the exhaust gas of the boiler 1 containing nitrogen oxide NOx, sulfur oxide SOx, and the like. Show.

In FIG. 6, a counter-current spray type wet scrubber having the same configuration as the cooling tower 4A described above is used, and the circulation rate of the aqueous solution of iron chloride FeCl _{3 as} the circulating water is switched to 2 l / min, 4 l / min, or 5 l / min. The Hg ⁰ removal rate of the simulated combustion exhaust gas in the case of According to this experimental result, it was confirmed that a simulated combustion exhaust gas having substantially the same component composition as the exhaust gas of the boiler 1 can obtain a Hg ⁰ removal rate of nearly 80% at any circulation amount.

FIG. 7 shows Experimental Examples 1 and 2 regarding the influence of gas-liquid contact on the simulated combustion exhaust gas. In this experiment, when 100 ml of absorption liquid (iron chloride FeCl ₃ aqueous solution) is filled in each, a plurality of containers (impinger) for bubbling simulated combustion exhaust gas are prepared, and simulated combustion exhaust gas is bubbled by one impinger Absorbed liquid amount when 100 ml of simulated combustion exhaust gas is bubbled with three impingers connected in series 300 ml Absorbed liquid amount when simulated combustion exhaust gas is bubbled with five impingers connected in series The Hg ⁰ removal rate was measured when the amount was 500 ml. Experimental Example 1 shows a case where the concentration of trivalent iron Fe ³⁺ is 100 ppm, and Experimental Example 2 shows a case where the concentration of trivalent iron Fe ³⁺ is 400 ppm.

That is, in this experiment, the amount of bubbling is 100 ml, the amount of bubbling is 100 ml, the amount of bubbling is 300 ml, and the amount of bubbling is 500 ml. According to this experimental result, it was confirmed that the Hg ⁰ removal rate increased as the number of bubbling, that is, the number of gas-liquid contact between the simulated combustion exhaust gas and the absorbing liquid (iron chloride FeCl ₃ aqueous solution) was increased. In this experiment, it was confirmed that the Hg ⁰ removal rate exceeding 80% was obtained by five bubbling.

Incidentally, the experimental results of FIG. 7, although the number of simulated flue gas and liquid contact have shown that a significant effect on Hg ⁰ removal rate, to the state of the gas-liquid contact better the It is also extremely important to increase the contact area and contact time. Therefore, by devising the shape of the spray nozzle 7 and the tower body 6 or the exhaust gas passage method in the tower body 6, the contact area and the contact time are increased, and the zero-valent mercury (Hg ⁰ ) gas removal rate is increased. It is important to improve.

According to the present embodiment, iron chloride FeCl ₃ containing trivalent iron Fe ³⁺ as a component is included as a mercury oxidizing agent, and the pH is about 1 or less by adding a pH adjuster such as hydrochloric acid HCl. The aqueous solution set to 1 is brought into gas-liquid contact with the gas to be processed such as the exhaust gas (combustion exhaust gas) of the boiler 1, and the zero value from the gas to be processed is reduced while suppressing the addition amount (usage amount) of the mercury oxidant as much as possible. Mercury (Hg ⁰ ) gas can be removed at a high removal rate.

  In addition, the present mercury removing device is an essential component for cooling tower, that is, a component for adding a function as a mercury removing device to the tower body 6, spray nozzle 7 and circulation pump 8, that is, pH measuring instrument 9, pH. A regulator addition device 10 and a mercury oxidant addition device 11 are added. Therefore, a zero-valent mercury gas removing function can be realized by adding the pH measuring device 9, the pH adjusting agent adding device 10 and the mercury oxidizing agent adding device 11 to the existing thermal power plant, so that the existing thermal power plant can be easily used. There is a merit that it can be introduced.

In addition, this invention is not limited to the said embodiment, For example, the following modifications can be considered.
(1) The mercury oxidizing agent is not limited to iron chloride FeCl ₃ , and may be any other compound as long as it is a compound containing trivalent iron Fe ³⁺ as a component.
(2) The pH adjuster is not limited to hydrochloric acid HCl, but may be other.
(3) The gas to be treated is not limited to the combustion exhaust gas of the combustion furnace of the boiler 1.
(4) Moreover, about the structure of a mercury removal apparatus, it is not limited to the said embodiment. Any other configuration may be used as long as it can achieve good gas-liquid contact between the gas to be processed and the aqueous solution of the mercury oxidizing agent.

1 is a system diagram of an exhaust gas treatment apparatus to which a mercury removal apparatus according to an embodiment of the present invention is applied. It is a block diagram which shows the detailed structure of the mercury removal apparatus concerning one Embodiment of this invention. It is an experimental result which shows the effectiveness of using what uses trivalent iron Fe3 ⁺ as a component as a mercury oxidizing agent in one Embodiment of this invention. In one embodiment of the present invention, the experimental results showing the effect of pH given to Hg ⁰ capture rate in the case of using a good iron chloride FeCl ₃ oxidation performance to zerovalent mercury Hg ^0. The experimental results showing the dependency on the trivalent iron concentration Fe ³⁺ of Hg ⁰ capture rate in an embodiment of the present invention. The experimental results shown Hg ⁰ removal rate of a simulated flue gas in accordance with the circulation rate of the aqueous solution of iron chloride FeCl ₃ and in an embodiment of the present invention. It is an experimental result which shows the influence of the gas-liquid contact regarding simulated combustion exhaust gas in one Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Boiler, 2 ... Denitration device, 3 ... Electric dust collector, 4 ... Two tower type desulfurization device, 5 ... Chimney, 6 ... Tower body (collection container), 7 ... Spray nozzle, 8 ... Circulation pump, 9 ... pH Measuring instrument, 10 ... pH adjuster adding device, 11 ... Mercury oxidizing agent adding device

Claims (11)

A device that converts zero-valent mercury gas into water-soluble divalent mercury gas to separate and remove it from the gas to be treated,
A mercury removing apparatus comprising a reaction separation means for bringing an aqueous solution containing a mercury oxidizing agent containing trivalent iron Fe ³⁺ as a component and having a pH of about 1 or less into contact with the gas to be treated. The reaction separation means is
A nozzle for spraying an aqueous solution onto the gas to be treated;
A collection container for collecting the aqueous solution after contact with the gas to be treated by the nozzle;
A circulation pump for supplying the aqueous solution recovered in the recovery container to the nozzle;
A mercury oxidizer addition device for adding a mercury oxidizer to an aqueous solution;
A pH meter for measuring the pH of the aqueous solution recovered in the recovery container;
2. A pH adjusting agent adding section for adding a pH adjusting agent to the aqueous solution so that the pH of the aqueous solution sprayed from the nozzle is maintained at 1 or less based on the measurement result of the pH measuring device. The mercury removal apparatus as described.   The nozzle, the recovery container, and the circulation pump constitute a cooling tower disposed in the preceding stage in the two-column type wet desulfurization apparatus, and the reaction separation means includes a pH meter, a pH adjuster addition unit, and mercury in the cooling tower. 3. The mercury removing apparatus according to claim 2, further comprising an oxidant adding device. The mercury removing apparatus according to any one of claims 1 to ₃ , wherein the mercury oxidizing agent is iron chloride FeCl ₃ containing trivalent iron Fe ³⁺ as a component.   The mercury removing apparatus according to any one of claims 2 to 4, wherein the pH adjuster is hydrochloric acid HCl.   The mercury removal apparatus according to any one of claims 1 to 5, wherein the gas to be treated is combustion exhaust gas from a combustion furnace. A method of converting zero-valent mercury gas into water-soluble divalent mercury gas and separating and removing it from the gas to be treated,
The zero-valent mercury gas is converted into a divalent mercury gas and an aqueous solution by contacting an aqueous solution containing a mercury oxidizing agent containing trivalent iron Fe ³⁺ and having a pH of about 1 or less with the gas to be treated. A method for removing mercury, which is characterized by being dissolved in and separated from the gas to be treated.   The zero-valent mercury gas is treated by adding a pH adjuster and mercury oxidizer to reduce the pH to about 1 or less to the washing water or circulating water of the cooling tower placed in the preceding stage in a two-column wet desulfurization system. The mercury removal method according to claim 7, wherein the mercury is separated and removed from the gas. The mercury removing method according to claim 7 or 8, wherein the mercury oxidizing agent is iron chloride FeCl ₃ containing trivalent iron Fe ³⁺ as a component.   The method for removing mercury according to claim 8 or 9, wherein the pH adjuster is hydrochloric acid HCl.   The mercury removal method according to claim 7, wherein the gas to be treated is a combustion exhaust gas from a combustion furnace.

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