JP2009285550A - Exhaust gas treating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas treating method highly efficiently removing hydrogen sulfide in a bioreactor, causing no volatilization of hydrogen sulfide into exhaust air from the bioreactor. <P>SOLUTION: In the exhaust gas treating method, exhaust gas containing malodor components is introduced into an absorbing tower 13; the exhaust gas is brought into contact with absorption liquid in an absorbing layer 34 of the absorbing tower 13 to absorb the malodor components into the absorbing liquid; the exhaust gas after cleaning is discharged from the absorbing tower 13; the absorbing liquid having absorbed the malodor components in the absorbing tower 13 is introduced into the bioreactor 12; gas containing oxygen is injected into the bioreactor 12 to oxidizing and decomposing the malodor components in the liquid by microorganisms; and the gas after the reaction is discharged from the bioreactor 12 and the liquid 1 in the bioreactor 12 is circulated to the absorbing tower 13 as the absorbing liquid. The inside of the bioreactor 12 is agitated with an agitation device 17 other than aeration, and the gas containing oxygen is injected to make the dissolved oxygen concentration in the liquid of the bioreactor 12 to be 0.1-1.0 mg/L. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for purifying exhaust gas containing odor components such as biosulfide such as biogas from a methane fermentation tank, and more particularly to an exhaust gas treatment method capable of removing odor components in exhaust gas with microorganisms with high efficiency. .

  As a purification method of exhaust gas containing odorous components such as biogas and hydrogen sulfide from methane fermentation tanks, a method of absorbing by chemicals such as alkali, a method of adsorbing to activated carbon, etc., and a method of purifying by microorganisms in recent years have been used. It has been. For example, hydrogen sulfide is toxic to the human body, has a strong odor, and is corrosive. Therefore, when exhaust gas is diffused into the atmosphere or when biogas is effectively used in a boiler or the like, it must be removed in advance. Biological deodorization (Non-Patent Document 1), biological desulfurization (Non-Patent Document 2), and the like are used as techniques for removing hydrogen sulfide with microorganisms.

  In general, since microorganisms work efficiently in water, the main mechanisms of hydrogen sulfide removal are (1) dissolution of hydrogen sulfide in water, and (2) decomposition of hydrogen sulfide or dissolved sulfide dissolved in water by microorganisms. There are two steps. For this reason, a method (Non-patent Document 3, Patent Document 1) for improving efficiency by dividing the processes (1) and (2) has been proposed.

Japanese Patent No. 3890804 Japanese National Patent Publication No. 8-506271 Supervision of Sewerage Department, City Bureau, Ministry of Construction, “Sewerage Facility Planning and Design Guidelines and Explanation (Part 2)”, 1994 edition, Japan Sewerage Association, November 25, 1994, P718 Environmental purification technology, Vol. 11. Let's stop together, global warming, Toshihisa Masuda and one other, "Biodesulfurization equipment" 2007, 11, p52-53 Cameron Cline et al.

  Although these conventional techniques are certainly expected to reduce the maintenance cost, in Non-Patent Document 2, the removal rate of hydrogen sulfide remains around 90%. This is due to the conflicting requirement that as much oxygen as possible be supplied in order to reduce the amount of oxygen remaining in the purified gas as much as possible in order to cause the oxidation of hydrogen sulfide by microorganisms in the desulfurization tower. (See FIG. 1 of non-patent literature).

  In addition, this technology blows air into the exhaust gas (raw material biogas) (see FIG. 1 of the non-patent document), so if air is blown in under the condition that the supply of exhaust gas has stopped due to some trouble, The risk of explosion hazards arises due to the balance of oxygen in the air.

  On the other hand, in Non-Patent Document 3, since the absorption tower and the biological reaction tank are separated, it is not necessary to obtain the above-mentioned conflicting conditions, and the hydrogen sulfide removal rate is reported to be 99% or more.

  However, a post-treatment of the air discharged from the bioreactor is necessary. This is because a method of stirring by aeration is adopted in order to efficiently perform a microbial reaction in a biological reaction tank (Patent Document 2), and it may be necessary to supply more oxygen than necessary to maintain stirring. is there. By supplying more oxygen than necessary, hydrogen sulfide dissolved in the liquid from the absorption tower is not oxidized by microorganisms, but the amount volatilized in the air increases. It is discharged as exhaust air from the biological reaction tank and requires post-treatment.

  Accordingly, an object of the present invention is to provide an exhaust gas treatment method that solves the above-described problems, can perform hydrogen sulfide removal in a biological reaction tank with high efficiency, and does not volatilize hydrogen sulfide in exhaust air from the biological reaction tank. There is to do.

  In order to achieve the above object, the invention of claim 1 introduces exhaust gas containing an odor component into an absorption tower, and makes the absorption liquid absorb the odor component by bringing the exhaust gas into contact with the absorption liquid in the absorption layer of the absorption tower. The exhaust gas after the purification is exhausted from the absorption tower, the absorption liquid in which the odor component is absorbed by the absorption tower is introduced into the biological reaction tank, and a gas containing oxygen is blown into the biological reaction tank, so that the odor component in the liquid In the exhaust gas treatment method in which the gas after the reaction is oxidatively decomposed by microorganisms, the gas after the reaction is exhausted from the biological reaction tank, and the liquid in the biological reaction tank is circulated to the absorption tower as an absorption liquid, stirring means other than aeration in the biological reaction tank And a gas containing oxygen is blown so that the dissolved oxygen concentration of the liquid in the biological reaction tank is 0.1 to 1.0 mg / L.

  The invention of claim 2 introduces exhaust gas containing an odor component into an absorption tower, contacts the exhaust gas with an absorption liquid in an absorption layer of the absorption tower to absorb the odor component into the absorption liquid, and then converts the purified exhaust gas into The absorption liquid exhausted from the absorption tower and absorbing the odor component in the absorption tower is introduced into the biological reaction tank, and a gas containing oxygen is blown in the biological reaction tank, and the odor component in the liquid is oxidatively decomposed by microorganisms, In the exhaust gas treatment method in which the gas after the reaction is exhausted from the biological reaction tank and the liquid in the biological reaction tank is circulated to the absorption tower as an absorption liquid, the inside of the biological reaction tank is stirred by a stirring means other than aeration, The exhaust gas treatment method is characterized in that a gas containing oxygen is blown so that the oxygen concentration of exhausted exhaust air is 0.5% to 18%.

  The invention of claim 3 is the exhaust gas treatment method according to claim 1 or 2, wherein the odor component in the exhaust gas is a sulfur compound such as hydrogen sulfide, and the microorganism working in the biological reaction tank is a sulfur-oxidizing bacterium.

  The invention of claim 4 is the exhaust gas treatment method according to claim 1 or 2, wherein the stirring means comprises a mechanical stirring device.

  The invention according to claim 5 is the exhaust gas treatment method according to claim 1 or 2, wherein the stirring means is configured to stir with an aqueous flow when the absorbing solution having absorbed the odor component in the absorption tower is introduced into the biological reaction tank. is there.

  According to the present invention, since a stirrer other than aeration is provided in the biological reaction tank, the amount of aeration can be suppressed without worrying about poor stirring, and as a result, the amount of hydrogen sulfide and the like volatilized from the biological reaction tank by aeration is minimized. Can be controlled. Moreover, the optimal aeration amount can be determined by monitoring dissolved oxygen in the biological reaction tank or oxygen in the exhaust air from the biological reaction tank.

  A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 shows an apparatus for carrying out the exhaust gas treatment method of the present invention.

  In FIG. 1, a central portion of a vertical cylindrical main body 10 having a circular or quadrangular cross section is partitioned by a partition plate 11, a biological reaction tank 12 is formed at the lower portion, and an absorption tower 13 is formed at the upper portion.

  The biological reaction tank 12 is a sealed tank in which a liquid l containing microorganisms (such as sulfur-oxidizing bacteria) is stored. An air diffuser 14 is installed near the bottom of the biological reaction tank 12, and air (oxygen-containing gas) is supplied to the air diffuser 14 from a blower 15 outside the main body 10 through an air supply pipe 16.

  The biological reaction tank 12 is provided with a stirring device 17. The stirring device 17 is provided with a motor 18a on the outside of the inclined cylinder 19 formed in the biological reaction tank 12, and a stirring shaft 18b is inserted through a hole 19a formed in the inclined cylinder 19, and at the tip of the stirring shaft 18b. A blade 18c is provided and configured.

  In the biological reaction tank 12, a pH electrode 20 for detecting the pH of the liquid l and a DO electrode 23 for detecting the dissolved oxygen concentration of the liquid l are immersed in the liquid l through an inclined cylinder 21 formed in the biological reaction tank 12. It is provided as follows. The pH electrode 20 and the DO electrode 23 are installed via a hole in the inclined cylinder 21. The pH electrode 20 is connected to a pH meter 22, and the DO electrode 23 is connected to an oxygen concentration meter 25.

  A neutralizing agent inlet 26 is formed in the inclined cylinder 21 of the biological reaction tank 12, and a neutralizing agent pipe 29 is routed from the neutralizing agent tank 27 by a chemical injection pump 28 via the inlet 26. A neutralizer made of strong alkali such as caustic soda is injected into the liquid 1 in the biological reaction tank 12 from the neutralizer pipe 29.

  An exhaust air line 30 is connected to the upper water surface of the biological reaction tank 12, and an exhaust fan 42 is connected to the exhaust air line 30.

  A circulation line 31 is connected to the biological reaction tank 12, a circulation pump 32 is connected to the circulation line 31, and the liquid in the biological reaction tank 12 is sent to the absorption tower 13 and circulated.

  The absorption tower 13 is a closed tank, and a distributor 33 connected to the circulation line 31 is installed in the upper part, the liquid from the circulation line 31 is sprinkled, and a small amount of liquid is put on the partition plate 11 at the bottom of the absorption tower 13. A reservoir 36 for storing is formed. A support 35 such as a screen is provided above the liquid reservoir 36, and a filler having an appropriate porosity (50% or more) is provided on the support 35 to form the absorption layer 34.

  An exhaust gas line 37 is connected to the side surface of the absorption tower 13 between the absorption layer 34 and the liquid reservoir 36, and a purified gas line 39 is connected to the upper part of the absorption tower 13.

  An absorption liquid circulation line 40 for returning the liquid in the liquid storage section 36 to the biological reaction tank 12 is connected to the liquid storage section 36 of the absorption tower 13. The absorption liquid circulation line 40 is installed in such a manner that the tip penetrates the side wall of the absorption tower 13 from a water sealing part 40a opened below the water surface of the liquid storage part 36, passes through a siphon breaker 40b, and passes through the biological reaction tank 12. To the side wall. A drain line 41 is connected to the lower part of the biological reaction tank 12.

  Next, an exhaust gas treatment method in the exhaust gas treatment apparatus of FIG. 1 will be described.

  The exhaust gas to be treated enters the absorption tower 13 from the exhaust gas line 37, flows in an upflow through the absorption layer 34, and is discharged through the purified gas line 39. During this time, odor components such as hydrogen sulfide contained in the exhaust gas are absorbed by the liquid sprayed from the distributor 33 and flowing down the absorption layer 34 to become a purified gas.

  The liquid that has absorbed the odor component or the like collects in the liquid reservoir 36 and flows from the liquid reservoir 36 into the biological reaction tank 12 through the absorbent circulation line 40. The absorption liquid is introduced from the water sealing portion 40a of the absorption liquid circulation line 40 so as not to be mixed with the exhaust gas, and flows into the biological reaction tank 12 by gravity by the siphon breaker 40b.

  In the biological reaction tank 12, air (oxygen-containing gas) is supplied from the lower part by the diffuser 14, and it is better to have microorganisms such as sulfur-oxidizing bacteria (initially seeded with activated sludge, etc. Hydrogen sulfide and the like are oxidatively decomposed by the action of (proliferating). The liquid l that has been treated with microorganisms is recirculated as a watering liquid in the absorption tower 13 via the circulation line 31 after removing hydrogen sulfide and the like.

  A pH electrode 20 is installed in the biological reaction tank 12, and a neutralizing agent is injected from the neutralizing agent storage tank 27 when the pH changes to an inappropriate range. The supplied air is exhausted from the exhaust air line 30, but if it contains volatilized hydrogen sulfide or the like, a deodorizing device (not shown) is provided downstream of the exhaust air line 30 for further purification. To do.

  Next, the operation of the present invention will be described.

  The biological reaction tank 12 is appropriately stirred by the stirring device 17 (stirring shaft 18b and blade 18a) so that sufficient stirring can be maintained even if the supply amount of air decreases.

A DO electrode 23 is installed in the biological reaction tank 12 to monitor dissolved oxygen. If the dissolved oxygen exceeds the set value, the supply of air is suppressed by the inverter control of the blower 15 or the control of an electromagnetic valve or motorized valve (not shown) provided in the middle of the air supply pipe 16, and the dissolved oxygen becomes below the set value. Increase the air supply. The control may be manual control or automatic control. The set value is determined in the range of 0.1 mg / L to 1.0 mg / L.
Further, the liquid l in the biological reaction tank 12 is detected by the pH electrode 20, and the chemical injection pump 28 is driven so that the pH of the liquid l becomes 7-9, thereby neutralizing the caustic soda (20-70% NaOH solution). It is supplied to the biological reaction tank 12 from the pipe 29 so that the oxidative decomposition reaction of the odor component by the microorganism is not inhibited.

  By installing equipment in the biological reaction tank 12, the gas phase part of the biological reaction tank 12 comes into contact with the outside air in the hole 19a for the stirring device, the hole 21a of the pH electrode 20, the hole 21b of the DO electrode 23, and the like. The possibility comes out. At that time, hydrogen sulfide volatilized in the gas phase portion of the biological reaction tank 12 may be diffused to the outside. Therefore, a deodorizing device (not shown) is provided at the rear stage of the exhaust air line 30, and the exhaust fan 42 performs suction more than the air supply amount to make the gas phase part negative pressure, and all hydrogen sulfide and the like are deodorized. It can be so.

  As described above, the present invention can suppress the aeration amount without worrying about poor stirring by providing the biological reaction tank 12 with the stirring device 17 other than aeration. That is, in the conventional stirring by aeration, the flow of bubbles and the flow of water are in the same direction, but by using the stirring method by the stirring device 17, the direction of the flow of bubbles and the flow of water is different, so It can be expected that the contact efficiency between the microorganism and the target substance is improved. As a result, the amount of hydrogen sulfide and the like volatilized from the biological reaction tank 12 by aeration can be controlled to a minimum. At this time, the optimum aeration amount can be determined by monitoring dissolved oxygen (or oxygen of exhaust air described later).

  In order to confirm this effect, a test was performed using an experimental apparatus simulating a biological reaction tank. That is, hydrogen sulfide was supplied while supplying a small amount of air to a reaction vessel provided with a stirring device (magnetic stirrer) having a capacity of 600 mL. Table 1 shows the results of monitoring the dissolved sulfide in the reaction tank and the hydrogen sulfide concentration in the exhaust air discharged from the reaction tank.

  As a result of Table 1, as long as proper agitation is maintained, suppressing the air supply amount and lowering dissolved oxygen not only has an adverse effect on hydrogen sulfide removal, but also causes a slight amount of hydrogen sulfide to be volatilized into the exhaust air. It turns out that there is an effect to prevent.

  That is, the hydrogen sulfide load was set to 10.1 mg S / h, the air supply amount was increased from 1.1 L / h to 12.6 L / h, and the dissolved oxygen concentration (mg / L) during that time was measured. , The amount of air supply (1.1 L / h) is small, and even if the dissolved oxygen is 0.1 mg / L, the dissolved sulfide in the reaction tank is zero, and the amount of air supply is increased (12. 6 L / h) and hydrogen sulfide is volatilized in the exhaust air. Therefore, it was found that hydrogen sulfide does not volatilize in the exhaust air if the dissolved oxygen is in the range of 0.1 mg / L to 1.0 mg / L.

  In particular, even when the hydrogen sulfide load is increased to 33.2 mg / h, by supplying air so that the dissolved oxygen concentration becomes 0.1 to 0.3 mg / L of dissolved oxygen of 1.0 mg / L or less. The dissolved sulfide in the reaction tank is zero, and there is no volatilization of hydrogen sulfide into the exhaust air.

The result is
33.2 × 24/600 = 1.3 kgS / m ³ / d
This means that the removal rate of 100% was achieved with the hydrogen sulfide load, and high performance results are shown.

  FIG. 2 shows another embodiment of the present invention.

  In the embodiment of FIG. 1, the example has been described in which the dissolved oxygen concentration of the liquid 1 in the biological reaction tank 12 is measured by providing the DO electrode 23 positioned on the liquid surface so that the DO electrode 23 can detect the dissolved oxygen concentration. In the present embodiment, the oxygen electrode 13 a is installed in the middle of the exhaust air line 30.

  In this embodiment, the oxygen in the exhausted air exhausted from the biological reaction tank 12 to the exhausted air line 30 is monitored by the oxygen electrode 23a, so that if the oxygen exceeds a set value, the supply of air is performed by the blower 15 The oxygen supply is suppressed by the inverter control or the control of an electromagnetic valve or motor-operated valve (not shown) provided in the middle of the air supply pipe 16, and the supply of air is increased when the oxygen becomes a set value or less. The control may be manual control or automatic control.

  The set value of the oxygen concentration is in a range of 0.5% to 18%, and thereby the dissolved oxygen concentration of the liquid 1 in the biological reaction tank 12 is set to 0.1 to 1.0 mg / L. be able to.

  FIG. 3A and FIG. 3B show still another embodiment of the present invention.

  In the present embodiment, the liquid l in the biological reaction tank 12 is a liquid flow returned from the absorbent circulation line 40 to the biological reaction tank 12 without using the mechanical stirring device 17 described in the embodiment of FIG. Can be stirred.

  That is, as shown in FIG. 3 (b), the connecting portion 40 c of the absorption liquid circulation line 40 connected to the biological reaction tank 12 is connected so as to be tangential to the biological reaction tank 12, and the liquid reservoir 36 The liquid 1 in the biological reaction tank 12 is agitated by the principle of a cyclone by flowing the liquid in a tangential direction to the inner peripheral wall of the biological reaction tank 12 through the connecting portion 40c of the absorption liquid circulation line 40.

  4 (a) and 4 (b) show still another embodiment of the present invention.

  In this example, the stirring mechanism of the biological reaction tank 12 can be stirred by the water flow from the absorption liquid circulation line 40 as in FIG. 3, and the pH of the liquid l in the biological reaction tank 12 is detected by the pH electrode 20. Instead of injecting a neutralizing agent so that the pH becomes 7 to 9, a neutralizing agent container 43 containing pellets of weak alkali such as sodium bicarbonate or calcium carbonate is placed in the inclined cylinder 21 formed in the biological reaction tank 12. The neutralization agent container 43 is weakly alkaline and the pH of the liquid 1 in the biological reaction tank 12 is controlled to about 8 strong. The neutralizer container 43 has a mesh shape so that weak alkalis such as baking soda and calcium carbonate can be naturally dissolved in the liquid l as appropriate.

  In this embodiment, the agitation mechanism is agitated by the water flow from the absorption liquid circulation line 40, and neutralization is neutralized by the weak alkali contained in the neutralizer container 44, so that no pH electrode or chemical injection pump is required. Thus, the device cost can be reduced.

  As described above, in the present invention, hydrogen sulfide is removed if the oxygen-containing gas is blown into the biological reaction tank 12 as much as possible and the agitation is performed while the dissolved oxygen concentration is in the range of 0.1 to 1.0 mg / L. As well as not adversely affecting the air, it is possible to prevent volatilization of hydrogen sulfide into the exhaust air.

  The agitation of the liquid 1 in the biological reaction tank 12 has been described in the example of agitation with the water flow from the mechanical agitation device 17 shown in FIGS. 1 and 2 and the absorption liquid circulation line 40 shown in FIGS. As another stirring mechanism other than aeration, for example, a part of the liquid circulating the liquid 1 in the biological reaction tank 12 to the absorption tower 13 is returned to the biological reaction tank 12 by the circulation line 31 and stirred with the water flow. That is, the return line is connected to the circulation line 31 on the discharge side of the circulation pump 32, and the return line is connected to the biological reaction tank 12 in the tangential direction as described in FIG. It can also be stirred.

It is a figure which shows one embodiment of this invention. It is a figure which shows other embodiment of this invention. It is a figure which shows other embodiment of this invention. It is a figure which shows other embodiment of this invention.

Explanation of symbols

12 Bioreaction tank 13 Absorption tower 17 Stirrer 34 Absorption layer l Liquid

Claims (5)

  The exhaust gas containing odorous components is introduced into the absorption tower, and after the exhaust gas and the absorbing liquid are brought into contact with each other in the absorption layer of the absorption tower to absorb the odorous components into the absorbing liquid, the purified exhaust gas is exhausted from the absorption tower and absorbed. The absorption liquid that has absorbed odorous components in the tower is introduced into the biological reaction tank, and oxygen-containing gas is blown into the biological reaction tank, and the odorous components in the liquid are oxidatively decomposed by microorganisms. In the exhaust gas treatment method of exhausting from the biological reaction tank and circulating the liquid in the biological reaction tank to the absorption tower as an absorption liquid, the inside of the biological reaction tank is stirred with stirring means other than aeration, and the dissolved oxygen concentration in the liquid in the biological reaction tank However, an exhaust gas treatment method is characterized in that a gas containing oxygen is blown so as to be 0.1 to 1.0 mg / L.   After introducing exhaust gas containing odor components into the absorption tower, contacting the exhaust gas with the absorption liquid in the absorption layer of the absorption tower to absorb the odor components into the absorption liquid, exhausting the exhaust gas after purification from the absorption tower, The absorption liquid that has absorbed the odor component in the absorption tower is introduced into the biological reaction tank, and a gas containing oxygen is blown into the biological reaction tank. The odor component in the liquid is oxidatively decomposed by microorganisms, and the gas after the reaction is removed. In the exhaust gas treatment method of exhausting from the biological reaction tank and circulating the liquid in the biological reaction tank as an absorption liquid to the absorption tower, oxygen in the exhaust air that is stirred in the biological reaction tank by a stirring means other than aeration and exhausted from the biological reaction tank An exhaust gas treatment method, wherein a gas containing oxygen is blown so as to have a concentration of 0.5% to 18%.   The exhaust gas treatment method according to claim 1 or 2, wherein the odor component in the exhaust gas is a sulfur compound such as hydrogen sulfide, and the microorganism working in the biological reaction tank is a sulfur-oxidizing bacterium.   The exhaust gas treatment method according to claim 1 or 2, wherein the stirring means comprises a mechanical stirring device.   The exhaust gas treatment method according to claim 1 or 2, wherein the agitation means is configured to agitate with an aqueous flow when the absorption liquid having absorbed the odor component in the absorption tower is introduced into the biological reaction tank.

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