JP2010022977A - Biological desulfurization method and biological desulfurization apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biological desulfurization technique which reduces cost required for pH adjusting of water to be used and can efficiently desulfurize a gas with a small-sized facility. <P>SOLUTION: The biological desulfurization apparatus 1 includes a pH adjustment means 17, 19 for adjusting pH of an absorbing liquid mainly containing water to a pH value lower than 7, a gas-liquid contact means 5, 7, F which gas-liquid contacts the absorbing liquid with a H<SB>2</SB>S containing gas to absorb H2S in the absorbing liquid, and acidophilic sulfur-oxidizing bacteria for oxidizing H<SB>2</SB>S to be absorbed in the absorbing liquid. The pH of the absorbing liquid is adjusted to a pH value lower 7, the absorbing liquid is gas-liquid contacted with the H<SB>2</SB>S containing gas to absorb H<SB>2</SB>S in the absorbing liquid and H<SB>2</SB>S to be absorbed in the absorbing liquid is oxidized by the acidophilic sulfur-oxidizing bacteria. The acidophilic sulfur-oxidizing bacteria are set on the gas-liquid contact means and oxidizing by the bacteria is progressed in the substantially same site as gas-liquid contacting. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention is applied to a gasification fuel or synthesis gas made from coal, low-grade coal or biomass, biogas produced by methane fermentation of sewage sludge, and hydrogen sulfide contained in the energy gas. Contributing to the practical application of the purification of energy gas by biodesulfurization by improving the desulfurization efficiency of removing hydrogen sulfide by utilizing the oxidizing action of hydrogen sulfide by sulfur-oxidizing bacteria The present invention relates to a biodesulfurization method and a biodesulfurization apparatus.

  In recent years, global warming and resource depletion due to mass consumption of petroleum resources have become problems, and attention has been paid to effective use of resources that have not been used in the past. As such resources, hydrogen gas that is gasified from low-grade coal such as lignite that has not been used before, gasified fuel containing carbon monoxide, etc., and methane gas obtained by fermenting livestock manure, etc. are mainly used. There are biogas as a component. Since these energy gases contain poisonous hydrogen sulfide that causes catalyst poisoning and corrosion of the apparatus, it is necessary to desulfurize the gasified fuel in practical use.

  Conventional desulfurization treatment uses chemical desulfurization that uses chemical agents to desulfurize by chemical adsorption or reaction. For example, dry desulfurization that oxidizes and desulfurizes hydrogen sulfide using iron oxide, or contact with an amine-based absorbent. Wet desulfurization, in which hydrogen sulfide is removed by chemical absorption, is known.

  On the other hand, the use of biodesulfurization that uses the action of microorganisms has attracted attention from the viewpoints of cost and labor required for equipment maintenance, waste disposal, environmental considerations, and the like. In biodesulfurization, hydrogen sulfide is converted into sulfur or sulfate ions using sulfur-oxidizing bacteria, which are autotrophic aerobic bacteria using sulfide as a nutrient source.

  For example, Patent Documents 1 and 2 below disclose a biodesulfurization method that oxidizes hydrogen sulfide dissolved in water in a liquid phase in which microorganisms such as activated sludge are dispersed. Such a method has an extremely large liquid phase volume for biological desulfurization, and is not suitable for practical use in high-load processing such as an energy gas purification plant.

  On the other hand, in Patent Document 3 below, a carrier carrying microorganisms is used, and an absorption liquid in which hydrogen sulfide is absorbed by gas-liquid contact is introduced into the water to be treated into which the microorganism carrier is introduced, and sulfurized by the microorganisms. It is disclosed to oxidize hydrogen to sulfate ions.

Moreover, in the following Patent Document 4, a circulating liquid and a biogas containing a nutrient substance and an alkali are supplied to a biological desulfurization tower using a resin base material having a biofilm by a microorganism having a desulfurization action as a packing. And a method for desulfurizing hydrogen sulfide absorbed by gas-liquid contact between a biogas and a circulating fluid by a microorganism on a substrate. Furthermore, Patent Document 5 below describes a desulfurization method in which a hydrogen-sulfide-containing gas and a cleaning solution are brought into gas-liquid contact with a gas-liquid contact tower in which a filler carrying sulfur-oxidizing bacteria is laminated, and biological desulfurization is performed. The ratio between the flow rate of the contained gas and the flow rate of the cleaning solution and the time during which the hydrogen sulfide-containing gas stays in the filler laminate portion are defined.
JP 2003-62421 A JP 2004-135579 A JP 2002-79294 A JP 2006-36961 A JP 2008-12489 A

  Compared with the method using microorganisms dispersed in a liquid phase as in Patent Documents 1 and 2, the method using a carrier supporting microorganisms as in Patent Documents 3 and 4 reduces the volume required for biological reaction. This is considered advantageous.

However, the absorption of hydrogen sulfide in water by gas-liquid contact is very difficult to absorb at pH 7 or lower because the dissociation equilibrium to HS ^- ions is rate-limiting. For this reason, in order to promote absorption of hydrogen sulfide, it is necessary to adjust the basicity using an alkali agent. In the biological desulfurization of Patent Documents 3 and 4, the pH of the liquid that absorbs hydrogen sulfide is made basic. An alkaline agent is used for holding. Therefore, the operating cost increases depending on the alkaline agent used.

  On the other hand, the biological desulfurization method of Patent Document 5 is intended for absorption and reaction at a pH of about 7.5, and can reduce the amount of alkaline agent used compared to Patent Documents 3 and 4, but it is still effective for neutralization. The amount of alkaline agent used is considerable and significantly exceeds the theoretical amount required to neutralize the sulfuric acid produced by the bacteria.

  In view of the above problems, it is an object of the present invention to provide a biological desulfurization method that has low operating costs, enables downsizing of equipment to be used, and has high desulfurization efficiency.

  Another object of the present invention is to provide a biological desulfurization apparatus that can efficiently perform desulfurization, reduce the volume to be used, and can operate with low cost for pH adjustment and other treatments.

  In order to solve the above problems, the present inventors have conducted extensive research and found a structure capable of promoting absorption of hydrogen sulfide by gas-liquid contact using the high oxidizing action of acidophilic sulfur-oxidizing bacteria. Based on this, the present invention that can effectively perform biodesulfurization can be achieved by significantly reducing the cost required for adjusting the pH of water that absorbs hydrogen sulfide by realizing acidic hydrogen sulfide absorption and oxidation. It came to. Therefore, it is very effective in terms of operating cost and resource saving, and is advantageous in reducing the size of the processing equipment.

  According to one aspect of the present invention, a biological desulfurization apparatus includes a pH adjusting unit that adjusts the pH of an absorption liquid mainly composed of water to less than 7, and hydrogen absorption by bringing the absorption liquid into gas-liquid contact with a hydrogen sulfide-containing gas. The gist of the present invention is to have a gas-liquid contact means for absorbing water into the absorption liquid and an acidophilic sulfur-oxidizing bacterium for oxidizing hydrogen sulfide absorbed in the absorption liquid.

  Further, according to one aspect of the present invention, the biological desulfurization method adjusts the pH of an absorption liquid mainly composed of water to less than 7, and causes the absorption liquid to come into gas-liquid contact with a hydrogen sulfide-containing gas so that the hydrogen sulfide is mixed with the hydrogen sulfide. The gist is to oxidize hydrogen sulfide absorbed in the absorbing solution and absorbed into the absorbing solution by acidophilic sulfur-oxidizing bacteria.

  In the above, the sulfur-oxidizing bacteria are disposed on the gas-liquid contact means, and oxidation by the sulfur-oxidizing bacteria proceeds in substantially the same field as the gas-liquid contact.

  According to the present invention, by efficiently proceeding a biological reaction in an acidic state using an acidophilic sulfur-oxidizing bacterium, hydrogen sulfide ions in water are consumed and the concentration is reduced, and dissociation equilibrium and gas-liquid equilibrium are achieved. Since the shift is always in the direction of dissolving hydrogen sulfide, absorption of hydrogen sulfide gas proceeds even in an acidic state. Therefore, the alkali agent necessary for adjusting the water of the biodesulfurization system to basic can be omitted, and the concentration of carbon dioxide dissolved in water is lowered in an acidic state, so that the alkali agent required for neutralization of carbon dioxide is required. Can be omitted, and the amount of the alkaline agent used as a whole is remarkably reduced, which is advantageous in reducing the operating cost.

  Sulfur-oxidizing bacteria are autotrophic aerobic bacteria that use sulfide as a nutrient source, and oxidize hydrogen sulfide to sulfur or sulfuric acid. In conventional biological desulfurization, when hydrogen sulfide gas is absorbed in water and supplied to sulfur-oxidizing bacteria, the water adjusted to basic is brought into contact with hydrogen sulfide to enhance the absorption of hydrogen sulfide gas. This is because the degree of dissociation of hydrogen sulfide is low and the contact absorption of hydrogen sulfide gas into water becomes the rate-determining step. Therefore, it is necessary to increase the absorbency with basic water in order to increase the reaction efficiency. . Therefore, sulfur-oxidizing bacteria utilize species that can react in the basic region (referred to as neutral bacteria). However, the cost required for the alkaline agent for adjusting the water to basicity is a non-negligible amount, particularly in the treatment of biogas. This is because carbon dioxide contained in air or the like can be absorbed when basic, and sulfur dioxide containing carbon dioxide at a ratio of 30 to 40% with respect to 0.5 to 2% of hydrogen sulfide like biogas. In the desulfurization of a hydrogen-containing gas, the main part of the alkaline agent consumed during neutralization is rather attributed to carbon dioxide.

  For this reason, the present inventors examined the relationship between the biodesulfurization reaction and pH, and the oxidation rate of the acidophilic sulfur-oxidizing bacteria decreases as the pH increases. Since it is much larger than the sex bacteria, we investigated the utilization of the oxidation rate of bacteria, and found a method that can promote the absorption of hydrogen sulfide gas into water using this oxidation rate. In the biological desulfurization method and biological desulfurization apparatus of the present invention, the hydrogen sulfide absorbed in the absorption liquid by the gas-liquid contact between the absorption liquid mainly composed of water and the hydrogen sulfide-containing gas is oxidized using an acidophilic sulfur-oxidizing bacterium. To do. Hereinafter, the biodesulfurization method of the present invention and the biodesulfurization apparatus used therefor will be described in detail.

Sulfur-oxidizing bacteria generally have acid resistance, and in acidophilic bacteria (growth pH: about 0.5 to 6) and neutral bacteria (growth pH: about 5 to 9), reaction of sulfur oxidation reaction by environmental pH. The speed is different. Specifically, the biological oxidation rate V [× 10 ⁻¹³ ( ^gS / h / cell)] per cell is V = about 0 (pH 3) and V = about 0.2 (neutral for neutral bacteria. pH = 7.5), whereas in acidophilic bacteria, V = about 3.5 (pH 2), V = about 3.0 (pH 3), and V = about 1.6 (pH 7.5). That is, the biooxidation rate of acidophilic bacteria decreases with an increase in pH, but even in neutrality, it maintains an oxidizing ability of about half of the acidic range, and is about 7 times that of neutral bacteria. Therefore, if the reactivity of acidophilic bacteria can be suitably used at pH 7 or lower, biological desulfurization with a high hydrogen sulfide gas treatment capacity can be realized. In this case, the problem is the low absorbability of hydrogen sulfide gas into water. In the present invention, the high reactivity of acidophilic bacteria is used as a means for enhancing the absorption of hydrogen sulfide gas. That is, absorption of hydrogen sulfide by gas-liquid contact and oxidation reaction of sulfur-oxidizing bacteria proceed in substantially the same field, and sulfurization by sulfur-oxidizing bacteria's hydrogen sulfide consumption (HS ⁻ → S ⁰ → SO ₄ ²⁻ ). The decrease in the hydrogen ion concentration is linked to the vapor-liquid equilibrium balance of hydrogen sulfide (H ₂ Sgas⇔H ₂ Saq⇔HS ⁻ + H ⁺ ) to promote the transition from the gas state to the absorption / dissociation state.

In the acidic region, the dissociation degree of carbon dioxide gas (CO ₂ + H ₂ O → HCO ₃ ⁻ + H ⁺ ) is lowered, and particularly at pH 5 or lower, the carbon dioxide gas is hardly dissociated and the solubility of carbon dioxide gas becomes extremely low. The amount of alkaline agent consumed for neutralization is reduced. Therefore, by adjusting the absorption liquid to an acidic range below pH 7, particularly pH 5 or less, it is only sulfuric acid produced by oxidation of hydrogen sulfide that is neutralized during pH adjustment. The consumption can be brought close to the theoretical neutralization amount based on the amount of hydrogen sulfide to be treated.

  Specifically, such biological desulfurization can be carried out in the following forms.

  FIG. 1 shows an embodiment of a biodesulfurization apparatus for performing biodesulfurization of the present invention. In FIG. 1, the biological desulfurization apparatus 1 has a biological reaction tank 3 that holds a packing F that supports sulfur-oxidizing bacteria on its surface, and makes the absorption liquid and the hydrogen sulfide-containing gas in gas-liquid contact on the packing F. Therefore, as supply means for supplying the absorption liquid and the hydrogen sulfide-containing gas to the biological reaction tank 3, a liquid supply pipe 5 connected to the upper part of the biological reaction tank 3 and an air supply pipe connected to the lower part of the biological reaction tank 3 7 The filling F is a member through which liquid and gas can pass while being filled and held in the tank. Specifically, the filling F is a member made of a granular, net-like or porous material, Raschig ring or lessing. It can be configured using a member that can obtain a high specific surface area in a form generally used for increasing the gas-liquid contact area such as a ring.

  When an absorption liquid mainly composed of water is stored in the water storage tank 17 and is supplied to the biological reaction tank 3 from the liquid feeding pipe 5 by driving the pump 9, it is submerged to the filling F from the submerged nozzle 11 attached to the tip. After passing while wetting F1, it falls to the bottom of the biological reaction part 3. On the other hand, a hydrogen sulfide-containing gas (energy gas containing hydrogen sulfide such as biogas or gasification resources) is supplied from the air supply pipe 7 below the filling F in the biological reaction tank 3 by a pump or the like (not shown). When passing through the filling F upward, the absorbing liquid and the hydrogen sulfide-containing gas come into gas-liquid contact on the surface of the filling F, and hydrogen sulfide is absorbed by the absorbing liquid. The absorbed hydrogen sulfide is oxidized into sulfur and sulfuric acid by the acidophilic sulfur-oxidizing bacteria carried on the filler F, and the sulfuric acid concentration of the absorbed water increases as it flows down the filler F. The absorbing liquid containing sulfuric acid that has passed through the packing F falls to the lower part of the biological reaction tank 3 and is stored at the bottom. The bottom of the biological reaction tank 3 is connected to a water storage tank 17 by a pipe 15, and the absorption liquid is configured to be able to return to the biological reaction tank 3 from the liquid feeding pipe 5 via the water storage tank 17. The gas from which hydrogen sulfide has been removed by the sulfur-oxidizing bacteria in the biological reaction tank 3 is discharged from the top of the biological reaction tank 3 through the air supply pipe 13, and is used as an energy gas after being appropriately treated as necessary. Is done.

  In the present invention, the biological desulfurization proceeds on the filling F of the biological reaction tank 3 in substantially the same field as the gas-liquid contact of hydrogen sulfide. Specifically, the hydrogen sulfide absorbed by the contact with the absorbing solution on the packing F is oxidized to sulfur and sulfuric acid by the acidophilic sulfur-oxidizing bacteria supported on the packing F, and thereby in the absorbing solution. Hydrogen sulfide decreases and sulfuric acid concentration increases. At this time, the gas-liquid equilibrium balance shifts due to a decrease in the hydrogen sulfide concentration of the absorption liquid, and further absorption of hydrogen sulfide from the gas into the liquid is promoted. In other words, the absorption of hydrogen sulfide by gas-liquid contact and the biological desulfurization by acidophilic sulfur-oxidizing bacteria proceed in substantially the same field (in the absorbent on the packing) and link each other, thereby reacting the biological desulfurization reaction. The speed acts to promote the absorption of hydrogen sulfide. As a result, the sulfuric acid concentration of absorbed water increases as it flows down through the filler F.

  The absorption liquid that has dropped to the lower part of the biological reaction tank 3 is supplied to the water storage tank 17 via the pipe 15, and the pH of the absorption liquid that has been lowered by sulfuric acid is the alkali supplied from the alkali tank 19 by the water supply pipe 21 and the pump 23. The liquid is appropriately adjusted to be maintained at a constant pH, and is refluxed to the biological reaction tank 3 through the liquid feeding pipe 5. The sulfuric acid produced by biodesulfurization is neutralized by this pH adjustment. In addition, the absorption liquid in the water tank 17 is prevented from rising in salt concentration by appropriately replacing a part of the liquid with external water, and the water discharged from the water tank 17 is appropriately diluted and discharged.

  The pH of the absorbent adjusted in the water storage tank 17 is less than 7, that is, adjusted to be acidic, and is preferably 6.0 or less, more preferably 5.0 or less in terms of suppressing dissolution of carbon dioxide. In the desulfurization of biogas containing carbon dioxide gas, it is very useful to adjust the pH of the absorbing solution to 5.0 or less. The lower the pH, the higher the rate of biooxidation of the acidophilic sulfur-oxidizing bacteria, but considering the absorbability of hydrogen sulfide in gas-liquid contact, it is practically adjusted to about pH 2-7, preferably pH 3-6. . A pH measuring device 25 for measuring the pH of the absorption liquid in the water storage tank 17 is attached, and it is accurately adjusted if the supply of the alkaline liquid from the alkaline tank 19 by the pump 23 is automatically controlled according to the measured value. It is advantageous to do. The sulfur-oxidizing bacterium is an aerobic bacterium, and oxygen supply is required to advance the oxidation reaction. For this purpose, for example, oxygen is supplied to the sulfur-oxidizing bacteria on the filler F together with the absorbing solution by adding an aeration device 27 to the water tank 17 and blowing oxygen into the absorbing solution to increase the dissolved oxygen concentration. Can do. In this case, since the absorption liquid is acidic with low solubility of carbon dioxide, even if air is used as an oxygen source supplied from the aeration device 27, an increase in the amount of alkaline agent required for neutralization is suppressed, and the pH is 5.0 or less. Is substantially the theoretical neutralization amount of sulfuric acid by desulfurization. When the hydrogen sulfide-containing gas to be treated is a gas that does not contain methane (for example, coal gasification fuel), the apparatus may be configured to supply oxygen gas directly to the biological reaction tank 3.

In the present invention, the acidophilic sulfur-oxidizing bacteria are supported on the surface of the packing material F held in the biological reaction tank 3, and the biodesulfurization using the carrier supporting such microorganisms reduces the size of the equipment. Useful for. The material constituting the filler F may be any material capable of supporting microorganisms, such as a normal magnetic or resin filler for gas-liquid contact, a porous soft resin, a carbon material such as activated carbon, zeolite, ceramics, etc. The porous body etc. are mentioned, and forms, such as a fibrous form, a powder, or a particulate form, can be used suitably. For example, carbon fiber felt or charcoal can be used. As materials that easily carry microorganisms, there are materials whose critical surface tension is about 40 dyne / cm or less, and microorganisms are likely to adhere. Examples of materials having a low critical surface tension include various plastics. Examples of plastics having a critical surface tension of 40 dyne / cm or less include polyethylene, polypropylene, polyvinyl chloride, PVDC, PTFE, and the like. Although it can select and use suitably, it is not limited to these. In order to make gas-liquid contact efficiently, the filling F preferably has a specific surface area of about 10 cm ² / cm ³ or more (BET specific surface area). In consideration of preventing clogging, the packing F supports bacteria. Thus, it is preferable that the pressure is about 100 to 400 cm ² / cm ³ in the state of being held in the biological reaction tank 3.

  The packing F carried by the sulfur-oxidizing bacteria supplies the above-described packing F with water having a pH of 0.5 to 6 containing acidophilic sulfur-oxidizing bacteria and nutrient sources, and at a temperature suitable for bacterial propagation. It can be prepared by propagating bacteria on the surface of the packing while maintaining the contact. Examples of the acidophilic sulfur-oxidizing bacteria include Thiobacillus thioosidans, Acidithiobacillus thioosidans, T. ferrooxidans, Sulfolobus, and the like, but are not particularly limited and can be appropriately cultured from the bacterial group in the environment. The temperature suitable for breeding is generally about 28 to 35 ° C. The sulfur-oxidizing bacteria carried on the filler F need not be acidophilic sulfur-oxidizing bacteria alone, and neutral bacteria and other microorganisms may coexist as long as the action of the acidophilic sulfur-oxidizing bacteria is not inhibited. Therefore, for example, sulfur-oxidizing bacteria obtained by culturing appropriately using a microorganism group contained in activated sludge, mineral soil, or the like can be supported on the filler. The processing capacity per packing volume of the packing material F supporting bacteria varies depending on the amount of supporting bacteria, the effective contact area, and the pH of the absorbing solution, so that the supporting capacity and surface area that can exhibit the required processing capacity are obtained. What is necessary is just to change suitably the form of the member which comprises a filler, and the preparation conditions of a support | filler filler as needed.

  The biological desulfurization apparatus 1 of the present invention may be provided with means for heating, cooling or keeping the biological reaction tank 3 at an appropriate temperature as necessary in order to maintain a suitable progress of oxidation by sulfur-oxidizing bacteria. Thus, stable desulfurization treatment can be continued while eliminating the influence of fluctuations in the outside air temperature. In the biological desulfurization apparatus 1 of FIG. 1, a temperature adjusting device 29 for heating or cooling the absorbent supplied to the filler F is attached, and the temperature of the filler F is maintained at 25 to 35 ° C. by the absorbent. The operation of the temperature adjustment device 29 may be configured to be automatically controlled according to the temperature detected by the temperature sensor.

The absorption of hydrogen sulfide proceeds due to the concentration equilibrium of the gas-liquid contact portion, and the amount of hydrogen sulfide absorbed varies depending on the gas-liquid contact time (the time during which the hydrogen sulfide-containing gas stays in the filler F). In order to achieve a desired hydrogen sulfide removal rate, it is necessary to secure a gas-liquid contact time at which the absorbed amount of hydrogen sulfide can reach the amount to be removed, and the necessary gas-liquid contact time (gas residence time) is: It depends on the hydrogen sulfide gas concentration of the gas to be treated and the treatment capacity (reaction rate) of the biological reaction tank 3. Since the gas-liquid contact time is determined by the flow rate (supply speed) of the gas to be processed and the filling capacity (filling height) of the biological reaction tank 3, the supply speed of the gas to be processed (hydrogen sulfide-containing gas) and the biological reaction tank 3 The filling capacity (filling height) is set according to the hydrogen sulfide concentration of the gas to be treated and the treatment capacity of the filling F. In other words, when the sulfur load of the gas to be treated (the sulfur mass per day supplied volume [kgS / m ³ / d]) increases, the filling volume (packing height) of the biological reaction tank 3 is increased. Alternatively, it can be handled by reducing the gas supply rate. In addition, since the reaction rate of sulfur-oxidizing bacteria increases when the adjusted pH of the absorbing solution is lowered, it is possible to increase the treatment capacity of the biological reaction tank 3 and shorten the required gas-liquid contact time. . Such condition setting is performed by, for example, analyzing the contents of the gas discharged from the air supply pipe 13 by the gas meter 31 and appropriately changing the supply speed of the gas to be processed and the filling height of the biological reaction tank 3 based on the result. Is possible.

In the biodesulfurization of the present invention using acidophilic sulfur-oxidizing bacteria, the low hydrogen sulfide absorptivity of the acid absorbing solution can be compensated to the same level as that of the basic absorbing solution by the reaction rate more than 7 times that of neutral bacteria. It can be set to the same processing state as when a neutral or basic absorbent is used. For example, in the case of a desulfurization treatment of a hydrogen sulfide-containing gas containing about 0.1% hydrogen sulfide, the gas supply rate is set so that the gas-liquid contact time (gas residence time) is about 1 to 5 minutes. By adjusting according to the tower speed, it is possible to treat the sulfur load about 1 to 2 [kg S / m ³ / d]. At this time, in the case of desulfurization of biogas, by adjusting the pH of the absorbent in the water storage tank 17 to about 5.0, the amount of alkali agent used is substantially the theoretical neutralization amount of sulfuric acid by desulfurization.

  FIG. 2 shows an example of a biological desulfurization apparatus in which the biological reaction tank 3 and the water storage tank 17 are integrally formed. The biological reaction tank 43 of the biological desulfurization apparatus 41 has a capacity for storing water immediately below the packing F, and a pH measuring device 25 and an aeration device 27 are attached to this portion, and a water supply pipe connected to the alkaline tank 19 is provided. 21 is drawn. Therefore, the absorption liquid is circulated through the liquid feeding pipe 45 extending from the bottom of the biological reaction tank 43 to the top. 2 that are the same as those in FIG. 1 used in FIG. 2 are members having the same or the same functions as those in FIG. In the biological desulfurization apparatus 1 in FIG. 1, since the filler F is separated from the water tank 17, the supply of the hydrogen sulfide-containing gas is separated from the oxygen supply by the aeration apparatus 27. Since the oxygen supplied from the aeration device 27 can be brought into contact with and mixed with the hydrogen sulfide-containing gas supplied from the air supply pipe 7, there is a problem in terms of safety. Therefore, the use of the device in FIG. It is limited to the case where the mixing of is allowed. However, even in such an integrated configuration, treatment of methane-containing gas such as biogas is possible if the mixture of hydrogen sulfide-containing gas and oxygen is prevented by partition separation or oxygen supply restriction.

  Hereinafter, the biodesulfurization method and apparatus according to the present invention will be described in detail with reference to examples.

(Preparation of filler)
Acidithiobacillus thioosidans as an acidophilic sulfur-oxidizing bacterium was added to a culture solution (containing ammonium sulfate, potassium hydrogen phosphate, magnesium sulfate, potassium chloride, and sodium chloride) at pH 1.5 to 1.8, followed by immersing and culturing at room temperature. Using this, a dispersion of sulfur-oxidizing bacteria is prepared, soaked with a polypropylene mesh ring type filler (trical packing, manufactured by Takiron Co., Ltd.), and kept at 30 ° C. for several days to grow the bacteria. Bacteria were attached to the surface of the filler to obtain a filler carrying sulfur-oxidizing bacteria. This was held in the biological reaction tank 3 of the biological desulfurization apparatus of FIG. 1 to form a packing material F having a packing volume of 0.01 m ³ and a packing height of 0.8 m.

Example 1
50 L of water was stored in the water storage tank 17 of the biological desulfurization apparatus in FIG. 1, and the pH was adjusted to 5.0 using HCl to prepare an absorbing solution. The aeration apparatus 27 was operated, and air was blown into and supplied to the absorbing solution so that the air supply was 1 L / min.

The pump 9 was driven, and the absorbing liquid (temperature: 30 ° C.) of the water storage tank 17 was supplied to the biological reaction tank 3 at a rate of 3 L / min, and water pouring from the water pouring nozzle 11 to the filler F was started. After confirming that the entire filling F was sufficiently wetted with the absorbing solution, a hydrogen sulfide-containing gas (hydrogen sulfide concentration: 0.1% by mass, CO ₂ : 30% by mass, argon: 69.1 assuming biogas) Mass%) was supplied to the biological reaction tank 3 from the air supply pipe 7 at a rate of 6 L / min (sulfur load: 1 kgS / m ³ / d). The hydrogen sulfide-containing gas passed through the filler F upward, and in this case, the hydrogen sulfide-containing gas was in gas-liquid contact with the absorbing liquid on the surface of the filler F. The absorbing liquid falling from the filling F was refluxed to the water storage tank 17. In this state, the supply of the hydrogen sulfide-containing gas is continued for 8 hours to perform biological desulfurization. During this period, the hydrogen sulfide concentration of the gas discharged from the air supply pipe 13 is periodically measured by the gas detection pipe, The pH of the absorbing solution was measured, and when the pH decreased, an aqueous sodium hydroxide solution in the alkali bath 19 was added to adjust the absorbing solution to a constant pH of 5.0.

  The residual hydrogen sulfide concentration of the exhaust gas during the biological desulfurization was 60 ppm, and the hydrogen sulfide removal rate calculated from this was 94%. During this time, the amount of sodium hydroxide used to adjust the pH of the absorbent was 34 mmol / h. This amount corresponds to the theoretical neutralization amount of sulfuric acid by biological desulfurization calculated from the hydrogen sulfide removal rate.

(Example 2)
Biodesulfurization was performed in the same manner as in Example 1 except that the pH of the absorbent in the water storage tank 17 was constantly adjusted to 6.0. As a result, the residual hydrogen sulfide concentration of the gas discharged from the air pipe 13 was 50 ppm, and the hydrogen sulfide removal rate calculated from this was 95%. During this time, the amount of sodium hydroxide used for adjusting the pH of the absorbent was 70 mmol / h. This amount corresponds to twice the theoretical neutralization amount of sulfuric acid by biological desulfurization calculated from the hydrogen sulfide removal rate.

(Reference example)
Biodesulfurization was performed in the same manner as in Example 1 except that the pH of the absorbent in the water storage tank 17 was constantly adjusted to 7.0. As a result, the residual hydrogen sulfide concentration of the gas discharged from the air supply pipe 13 was 30 ppm, and the hydrogen sulfide removal rate calculated from this was 97%. During this period, the amount of sodium hydroxide used for adjusting the pH of the absorbent was 400 mmol / h. This amount corresponds to 12 times the theoretical neutralization amount of sulfuric acid by biological desulfurization calculated from the hydrogen sulfide removal rate.

(Comparative Example 1)
The sulfur-oxidizing bacterial dispersion used in the preparation of the above-mentioned filler is neutralized with Thiobacillus thioparus in a liquid medium (seawater supplemented with sodium thiosulfate, potassium hydrogen phosphate, magnesium oxalate, potassium hydrogen phosphate, ammonium chloride). A filler carrying sulfur-oxidizing bacteria was prepared in the same manner except that it was changed to a cultured one. This was held in the biological reaction tank 3 of the biological desulfurization apparatus of FIG.

  Biodesulfurization was performed in the same manner as in Example 1 except that the absorption liquid in the water storage tank 17 was constantly adjusted to pH 7.5. As a result, the residual hydrogen sulfide concentration of the gas discharged from the air supply pipe 13 was 30 ppm, and the hydrogen sulfide removal rate calculated from this was 97%. During this time, the amount of sodium hydroxide used to adjust the pH of the absorbent was 2000 mmol. This amount corresponds to 40 times the theoretical neutralization amount of sulfuric acid by biological desulfurization calculated from the hydrogen sulfide removal rate.

(Example 3)
The hydrogen sulfide-containing gas supplied to the bioreactor 3, the gas by coal gasification (water: 50 wt%, hydrogen sulfide concentration: 500 ppmv-dry, CO concentration: 20 wt% -dry, CO ₂ concentration: 25% -dry, Carbonyl sulfide: 10 ppmv, hydrogen: 50% -dry), and the same as Example 1 except that it was supplied from the air pipe 7 at a rate of 1 L / min (sulfur load: 0.1 kgS / m ³ / d) Biodesulfurization was performed. As a result, the hydrogen sulfide removal rate calculated from the residual hydrogen sulfide concentration of the gas discharged from the air supply pipe 13 was 99%. During this time, the amount of sodium hydroxide used to adjust the pH of the absorbent was 6 mmol / h. This amount corresponds to 2.3 times the theoretical neutralization amount of sulfuric acid by biological desulfurization calculated from the hydrogen sulfide removal rate.

Example 4
Coal gasification fuel was biodesulfurized in the same manner as in Example 3 except that the pH of the absorbent in the water storage tank 17 was constantly adjusted to 6.0. As a result, the hydrogen sulfide removal rate calculated from the residual hydrogen sulfide concentration of the gas discharged from the air supply pipe 13 was 99%. During this time, the amount of sodium hydroxide used to adjust the pH of the absorbent was 40 mmol / h. This amount corresponds to 15 times the theoretical neutralization amount of sulfuric acid by biological desulfurization calculated from the hydrogen sulfide removal rate.

It is a schematic block diagram which shows an example of the biodesulfurization apparatus which concerns on this invention. It is a schematic block diagram which shows the other example of the biological desulfurization apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,43 Biological desulfurization apparatus, 3 Biological reaction tank, F Filling 5 Liquid feeding pipe, 7 Air feeding pipe, 9, 23 Pump, 11 Flooding nozzle 17 Water storage tank, 19 Alkaline tank, 25 pH measuring device 27 Aeration apparatus, 29 Temperature Adjusting device

Claims (12)

PH adjusting means for adjusting the pH of the absorbent mainly composed of water to less than 7,
Gas-liquid contact means for bringing the absorption liquid into gas-liquid contact with the hydrogen sulfide-containing gas and absorbing the hydrogen sulfide into the absorption liquid;
A biological desulfurization apparatus comprising an acidophilic sulfur-oxidizing bacterium for oxidizing hydrogen sulfide absorbed by the absorption liquid.   The biodesulfurization apparatus according to claim 1, wherein the sulfur-oxidizing bacteria are disposed on the gas-liquid contact means.   The gas-liquid contact means includes a biological reaction section that holds a packing so that the absorption liquid and the hydrogen sulfide-containing gas can pass, and the absorption liquid and the hydrogen sulfide-containing gas are filled in the biological reaction section. The biological desulfurization apparatus according to claim 1, further comprising a supply unit configured to supply the product, wherein the sulfur-oxidizing bacteria are carried on the packing.   The biological desulfurization apparatus according to any one of claims 1 to 3, wherein the pH adjusting means adjusts the pH of the absorbent supplied to the biological reaction unit to 5 or less. The filling, the critical surface tension is composed of the following materials 40 dyne / cm, the liquid and gas can pass through the interior, a specific surface area according to any one of claims 3-4 is 10 cm 2 ^/ cm ³ or more Biological desulfurization equipment.   The biodesulfurization according to any one of claims 1 to 5, comprising means for supplying oxygen to the sulfur-oxidizing bacteria or the absorbing solution, and a heating device for maintaining the sulfur-oxidizing bacteria at a temperature of 25 to 35 ° C. apparatus.   Adjusting the pH of the absorption liquid mainly composed of water to less than 7, making the absorption liquid gas-liquid contact with a hydrogen sulfide-containing gas to absorb hydrogen sulfide in the absorption liquid, and absorbing hydrogen sulfide absorbed in the absorption liquid Biological desulfurization method that oxidizes by acidophilic sulfur-oxidizing bacteria.   The biodesulfurization method according to claim 7, wherein the oxidation by the sulfur-oxidizing bacteria proceeds in substantially the same field as the gas-liquid contact.   The sulfur-oxidizing bacteria are supported on a packing, and the absorption liquid and the hydrogen sulfide-containing gas are held so as to pass through the packing, and the absorption liquid and the hydrogen sulfide-containing gas are supplied to the packing. The biodesulfurization method according to claim 7 or 8, wherein the gas-liquid contact is performed on the filler.   The biological desulfurization method according to any one of claims 7 to 9, wherein the pH of the absorption liquid is adjusted to 5 or less. The sulfur-oxidizing bacteria are supported on the surface of a packing, and the packing is made of a material having a critical surface tension of 40 dyne / cm or less, allows liquid and gas to pass through the inside, and has a specific surface area of 10 cm ² / cm. ^The biodesulfurization method according to any one of claims 7 to 10, which is ³ or more.   The biodesulfurization method according to any one of claims 7 to 11, wherein oxygen is supplied to the sulfur-oxidizing bacterium or the absorbing solution, and the sulfur-oxidizing bacterium is maintained at a temperature of 25 to 35 ° C.

Images