JP2007050334A - Exhaust gas purification method and facility - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas purification facility reducing a replenishment amount of liquid for capturing mercury. <P>SOLUTION: This exhaust gas purification facility is equipped with an absorbing column 1 through which a gas G to be purified containing sulfur dioxide and metal mercury is passed from a lower part toward an upper part, a first nozzle 9 for spraying desulfurization liquid 3 to an intermediate portion in the vertical direction of the absorbing column 1, and a second nozzle 10 which is located at the upper side of the first nozzle 9 and sprays the liquid for capturing mercury 4 into the absorbing column 1. After bringing the gas G to be purified into contact with the desulfurization liquid 3 for desulfurization, the gas G to be purified is brought into contact with the liquid for capturing mercury 4 at the upper part so as to separate metal mercury, to avoid contact of sulfur oxides with the liquid for capturing mercury 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification method and equipment mainly for gas generated by coal combustion.

  The combustion exhaust gas of coal contains metallic mercury although it is a minute amount (about 10 μg / cubic meter).

  Therefore, in recent years, it has been proposed to remove metallic mercury from exhaust gas from a plant using coal as a heat energy source to further purify the exhaust gas.

  FIG. 3 shows an example of a conventional exhaust gas purification facility. An absorption tower 1 through which a gas to be purified G containing sulfur oxides and metallic mercury passes from below to above and an intermediate in the vertical direction in the absorption tower 1 A nozzle 2 arranged in a plurality of stages in the part, and a first desulfurization treatment liquid 3 and a mercury capture liquid 4 are sent to the nozzle 2 and liquids 3 and 4 accumulated in the bottom of the absorption tower 1 are sent to the nozzle 2 again. A pump 5 and a second pump 7 for sending unused mercury-capturing liquid 4 stored in the liquid tank 6 to a liquid flow path from the outlet of the first pump 5 to the nozzle 2 (for example, , See Patent Document 1).

  A valve 8 is interposed between the liquid flow path from the outlet of the first pump 5 to the nozzle 2 and the outlet of the second pump 7.

  The purification target gas G is subjected to dust removal and cooling in the cooling tower, separated into droplets by the upstream mist eliminator, and then sent to the lower end of the absorption tower 1.

  The desulfurization treatment liquid 3 is a calcium carbonate slurry using limestone as a raw material, and a predetermined amount is charged in the absorption tower 1 in advance.

  When the first pump 5 is operated when the gas to be purified G is passed through the absorption tower 1 and the liquid 3 for desulfurization treatment stored in the bottom of the absorption tower 1 is sprayed from the nozzle 2, calcium carbonate is obtained using water as a medium. It reacts with sulfur oxides such as sulfur dioxide (sulfurous acid gas) contained in the gas G to be purified to produce calcium sulfate (gypsum), which is a stable substance.

  The mercury-capturing liquid 4 is an aqueous sodium hypochlorite solution, and when the gas to be purified G is passed through the absorption tower 1, the second pump 7 is appropriately operated (the valve 8 is opened as a matter of course. ), When a predetermined amount is mixed in the desulfurization treatment liquid 3 and sprayed from the nozzle 2 together with the desulfurization treatment liquid 3, gaseous metal mercury containing sodium hypochlorite contained in the purification target gas G using water as a medium And then reacts with chlorine ions in the desulfurization treatment liquid 3 to produce mercuric chloride (sublimation), which is a water-soluble substance.

  In other words, the purification step for desulfurizing the purification target gas G and the purification step for separating the metal mercury from the purification target gas G proceed in parallel, and calcium sulfate is precipitated in the liquids 3 and 4 at the bottom of the absorption tower 1 and the chloride chloride Dimercury is dissolved in the liquids 3 and 4.

The purification target gas G after the desulfurization and separation of the metal mercury is separated into droplets by a post-stage mist eliminator, discharged through the chimney to the atmosphere, and the liquids 3 and 4 accumulated in the bottom of the absorption tower 1 are the first It is sucked up by the pump 5 and sprayed from the nozzle 2 again.
JP-A-10-216476

  However, it has been clarified by tests that the mercury trapping power of sodium hypochlorite is greatly influenced by the concentration of sulfur oxide in the purification target gas G.

  That is, in the space below the lowermost nozzle 2 in the absorption tower 1 shown in FIG. 3, the untreated purification target gas G containing sulfur oxide and the mercury capturing liquid 4 are in gas-liquid contact. Therefore, the mercury capturing ability of sodium hypochlorite tends to be impaired, and the mercury capturing liquid 4 has to be replenished one after another, resulting in a high running cost.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide an exhaust gas purification method and equipment that can reduce the replenishment amount of the mercury capturing liquid.

  In order to achieve the above object, the present invention desulfurizes the gas to be purified by spraying a liquid for desulfurization treatment at a predetermined portion of the exhaust path through which the gas to be purified containing sulfur oxide and metal mercury passes from below to above. The first purification step to be performed and the second purification step to separate the metallic mercury from the gas to be purified by spraying the mercury-capturing liquid at a site above the desulfurization treatment liquid spray position in the exhaust path are sequentially performed. .

  As an example of a specific facility, a desulfurization treatment liquid is sprayed on an absorption tower through which a gas to be purified containing sulfur oxides and metal mercury passes from below to above, and an intermediate portion in the vertical direction in the absorption tower; A liquid circulating means for spraying again the liquid accumulated in the bottom of the absorption tower to the intermediate portion in the vertical direction in the absorption tower, and a liquid feeding means for spraying a liquid for trapping mercury above the desulfurization liquid spray position in the absorption tower; The structure with is adopted.

  In addition to this, the liquid circulating means sends the first nozzle disposed in the absorption tower and the desulfurization liquid to the first nozzle, and again sends the liquid accumulated at the bottom of the absorption tower to the first nozzle. A second pump disposed in the absorption tower so as to be positioned above the first nozzle, and a liquid for capturing mercury to the second nozzle. The structure which has a 2nd pump is taken.

  Furthermore, a configuration is adopted in which a liquid flow path connected to the first nozzle from the outlet of the first pump is connected to the liquid flow path leading to the second nozzle via a valve.

  That is, in the exhaust gas purification method of the present invention, after performing the first purification step of bringing the purification target gas into contact with the desulfurization treatment liquid and performing desulfurization, the purification target gas is brought into contact with the mercury capturing liquid at an upper portion thereof. A second purification step for separating metallic mercury is performed to avoid contact between the sulfur oxide and the mercury capturing liquid in the exhaust path.

  Further, in the exhaust gas purification facility of the present invention, after purifying the gas to be purified with the desulfurization treatment liquid sprayed by the liquid circulation means, the gas to be purified is converted into a mercury capturing liquid sprayed by the liquid supply means on the upper side thereof. Contact to separate metallic mercury and avoid contact of sulfur oxides with mercury capture liquid in the absorption tower.

  According to the exhaust gas purification method and facility of the present invention, the following excellent effects can be obtained.

  (1) In the exhaust gas purification method of the present invention, the first purification step of spraying the desulfurization treatment liquid onto the purification target gas, and the second purification of spraying the mercury trapping liquid onto the purification target gas at the upper portion thereof In order to prevent contact between the sulfur oxide and the mercury capturing liquid, the capacity of the mercury capturing liquid is not reduced due to the sulfur oxide, and the replenishment amount of the mercury capturing liquid is reduced. The running cost of gas purification can be kept low.

  (2) In the exhaust gas purification facility of the present invention, a liquid supply means for spraying a mercury capturing liquid to the purification target gas is provided on the upper side of the liquid circulation means for spraying the desulfurization treatment liquid to the purification target gas. Prevents the mercury capture liquid from coming into contact with the product, so that the capacity of the mercury capture liquid is not reduced due to sulfur oxides, the replenishment amount of the capture liquid is reduced, and the running cost of gas purification is kept low. Can do.

  (3) The liquid supply means composed of the second nozzle, the second pump, etc. is installed in the existing absorption tower where only the desulfurization of the exhaust gas has been performed. If it is incorporated so that the capture liquid can be sprayed, the metallic mercury contained in the gas to be purified can be separated without installing a separate absorption tower.

  (4) If the liquid flow path leading to the second nozzle is connected to the liquid flow path connected to the first nozzle from the outlet of the first pump via the valve, the valve is opened, Instead of the mercury trapping liquid used, the desulfurization liquid and the mercury trapping liquid collected at the bottom of the absorption tower can be sprayed from the second nozzle.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an example of an exhaust gas purification facility of the present invention. An absorption tower 1 through which a purification target gas G containing sulfur dioxide and metallic mercury passes from below to above and an intermediate in the vertical direction in the absorption tower 1 are shown. The first nozzle 9 disposed in a plurality of stages in the site, and the liquids 3 and 4 that send the desulfurization treatment liquid 3 and the mercury capturing liquid 4 to the first nozzle 9 and accumulate at the bottom of the absorption tower 1 are the first. The first pump 5 sent again to the nozzle 9, the second nozzle 10 disposed in the absorption tower 1 so as to be positioned above the first nozzle 9, and the unreserved liquid tank 6. And a second pump 7 for feeding the used mercury-capturing liquid 4 to the second nozzle 10.

  A valve 11 is incorporated in the liquid flow path that continues from the outlet of the second pump 7 to the second nozzle 10.

  Further, a liquid flow path connected from the outlet of the first pump 5 to the first nozzle 9 is connected via a valve 12 to a liquid flow path connected from the outlet of the valve 11 to the second nozzle 10.

  The purification target gas G is sent to the lower end of the absorption tower 1 after dust removal, cooling, and droplet separation by a dust collector, a cooling tower, a front mist eliminator, and the like.

  The desulfurization treatment liquid 3 is a calcium carbonate slurry using limestone as a raw material, and a predetermined amount is put in the absorption tower 1 in advance, and a sodium hypochlorite aqueous solution is used for the mercury capturing liquid 4.

  When passing the gas to be purified G through the absorption tower 1, the valve 11 is opened and the valve 12 is closed, and the first pump 5 and the second pump 7 are operated and stored in the bottom of the absorption tower 1. The desulfurization treatment liquid 3 is sprayed from the first nozzle 9 and the unused mercury-capturing liquid 4 stored in the liquid tank 6 is sprayed from the second nozzle 10.

  Thereby, in the space below the 1st nozzle 9 in the absorption tower 1, the calcium carbonate of the liquid 3 for desulfurization processes reacts with the sulfur oxide contained in purification object gas G, and is a stable substance. Produces calcium sulfate.

  Further, in the space above the first nozzle 9 in the absorption tower 1, sodium hypochlorite of the mercury capturing liquid 4 reacts with gaseous metallic mercury remaining in the desulfurized gas G to be purified. Then, mercuric chloride, which is a water-soluble substance, is generated by reacting with chlorine ions in the liquid 3 for desulfurization treatment.

  That is, the purification process for desulfurizing the purification target gas G and the purification process for separating the metal mercury from the purification target gas G are carried out in stages, and calcium sulfate is precipitated in the liquids 3 and 4 at the bottom of the absorption tower 1, Dimercury is dissolved in the liquids 3 and 4.

  The gas G to be purified after desulfurization and separation of metallic mercury is separated into droplets by a post-stage mist eliminator, discharged through the chimney to the atmosphere, and the liquids 3 and 4 accumulated at the bottom of the absorption tower 1 are the first pump 5 is sucked up and sprayed again from the first nozzle 9.

  Further, when the second pump 7 is stopped and the valve 11 is closed, the liquids 3 and 4 accumulated in the bottom of the absorption tower 1 can be sprayed from the second nozzle 10.

  In the exhaust gas purification equipment shown in FIG. 1, the second nozzle 10 for spraying the mercury capturing liquid 4 is provided on the upper side of the first nozzle 9 for spraying the desulfurization processing liquid 3, and sulfur oxide and Since contact with the mercury-capturing liquid 4 is prevented, a reduction in the capacity of the mercury-capturing liquid 4 due to sulfur oxides does not occur.

  In other words, the replenishment amount of the mercury capturing liquid 4 is reduced, and the running cost of gas purification can be kept low.

  FIG. 2 shows the mercury removal rate from the gas to be purified G in which 10 μg of metallic mercury per cubic meter exists in the initial state and the absorption liquid (substantially, calcium carbonate slurry and hypochlorous acid in the absorption tower 1. FIG. 5 is a diagram showing the relationship between the volume concentration of sodium hypochlorite in a liquid mixture of sodium aqueous solution), the absorption liquid volume (liter) / purified gas volume (cubic meter) being 20, and the gas composition concentration being oxygen. 5%, carbon dioxide 15%, sulfur dioxide 500ppm, all the rest is nitrogen.

  In addition to this, a liquid feeding means composed of the second nozzle 10 and the second pump 7 is installed on an existing absorption tower that has only performed desulfurization of exhaust gas, and is located above the liquid spraying position for desulfurization treatment. If incorporated so that the mercury-capturing liquid 4 can be sprayed at the site, metallic mercury contained in the exhaust gas can be separated.

  It should be noted that the exhaust gas purification method and equipment of the present invention are not limited to the above-described embodiments, and it goes without saying that changes can be made without departing from the scope of the present invention.

  The exhaust gas purification method and equipment of the present invention can be applied to various plants.

It is a conceptual diagram which shows an example of the exhaust gas purification equipment of this invention. It is a diagram which shows the relationship between the mercury removal rate from purification | cleaning object gas, and sodium hypochlorite volume concentration in absorption liquid. It is a conceptual diagram which shows an example of the conventional waste gas purification equipment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Absorption tower 3 Liquid for desulfurization processing 4 Liquid for mercury capture 5 1st pump 7 2nd pump 9 1st nozzle 10 2nd nozzle 12 Valve

Claims (4)

  A first purification step of desulfurizing the purification target gas by spraying a desulfurization treatment liquid at a predetermined portion of the exhaust path through which the purification target gas containing sulfur oxide and metal mercury passes from below to above; An exhaust gas purification method comprising sequentially performing a second purification step of spraying a mercury-capturing liquid and separating metallic mercury from a purification target gas at a position above the desulfurization treatment liquid spray position.   Absorption tower in which gas to be purified containing sulfur oxide and metallic mercury passes from below to above, and desulfurization treatment liquid is sprayed on the intermediate part in the vertical direction of the absorption tower, and the liquid accumulated at the bottom of the absorption tower is absorbed. A liquid circulation means for spraying again on the intermediate portion in the vertical direction in the tower, and a liquid feeding means for spraying a liquid for capturing mercury on the upper side of the liquid spray position for desulfurization treatment in the absorption tower are provided. Exhaust gas purification equipment.   A liquid circulation means, a first nozzle disposed in the absorption tower, and a first pump for sending the liquid for desulfurization treatment to the first nozzle and for sending again the liquid accumulated in the bottom of the absorption tower to the first nozzle; A second nozzle disposed in the absorption tower so that the liquid feeding means is located above the first nozzle, and a second pump for feeding the mercury-capturing liquid to the second nozzle The exhaust gas purification equipment according to claim 2, comprising:   The exhaust gas purification equipment according to claim 3, wherein a liquid flow path connected to the first nozzle from an outlet of the first pump is connected to a liquid flow path reaching the second nozzle through a valve.

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