JP2006095512A - Biogas refining method and biogas refining equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biogas refining method which dispenses with the installation of a large-sized low pressure gas holder, can achieve the space saving and cost reduction of biogas refining equipment as a whole and can stably take a biogas out of an anaerobic fermentation tank. <P>SOLUTION: In the biogas refining method, the biogas is generated by anaerobically fermenting organic waste in the anaerobic fermentation tank, the biogas from the anaerobic fermentation tank is raised in pressure by a gas compressor 402 to be sent to an absorbing column, the biogas is brought into contact with water in the absorbing column in a high pressure state, carbon dioxide and sulferous impurities contained in the biogas are dissolved in high pressure water to be separated from the biogas to obtain a refined gas with highly concentrated methane, the gas pressure in the anaerobic fermentation tank is measured at this time and the number of rotations of the gas compressor is controlled from the measuring result to be increased and decreased so that the gas pressure in the anaerobic fermentation tank becomes a predetermined almost constant set value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention generates biogas by anaerobic fermentation of organic waste such as sewage sludge generated in a sewage treatment plant, purifies the biogas to remove carbon dioxide, sulfur impurities, etc. The present invention relates to a biogas purification method and a biogas purification facility for obtaining highly concentrated purified gas.

Biomass resources are expected to be used to prevent global warming and build a recycling-oriented society (sustainable society). Food waste such as garbage, livestock manure, organic wastewater, and sewage generated at sewage treatment plants Development of a technology for generating biogas by subjecting organic waste such as sludge to anaerobic fermentation and using this biogas as energy has been underway. In particular, according to the comprehensive biomass strategy decided by the Cabinet in Japan in December 2002, biogas (digestion gas) produced by anaerobic fermentation of sewage sludge generated in the first sedimentation basin and final sedimentation basin at a sewage treatment plant. ) Is expected. This digestion gas (sewage sludge digestion gas) is mainly composed of methane (CH ₄ ) and carbon dioxide (CO ₂ ) (methane: about 60% by volume, carbon dioxide: about 40% by volume), and as a trace amount of impurities. It is a gas containing sulfur-based impurities (H ₂ S and the like). It is known that shampoo-derived siloxane compounds are contained in digestion gas of sewage sludge in urban areas.

  FIG. 3 is a diagram for explaining the prior art (Patent Document 1), and is a flow diagram showing the configuration of a digestion gas purification facility (biogas purification facility) that purifies digestion gas to obtain purified methane gas.

  As shown in FIG. 3, a conventional digestion gas purification facility includes a digestion tank as an anaerobic fermentation tank (not shown), a desulfurization tower 51, a gas holder 52, and a digestion gas purification device as a biogas purification device. ing. The digestion gas purification apparatus includes a compressor 53, an absorption tower 54, a diffusion tower 56, a pump 55, and a dehumidifier 57.

In FIG. 3, digestion gas (sewage sludge digestion gas) from a digestion tank in a sewage treatment plant is supplied to a desulfurization tower 51, and H ₂ S and the like are removed by water absorption. The digested gas subjected to the desulfurization treatment is temporarily stored in the low-pressure gas holder 52, and a part thereof is supplied to the boiler from here. The remaining digestion gas after the desulfurization treatment is purified and used for city gas. It is sent to the absorption tower 54 for use as a raw material. A compressor 53 is installed in front of the absorption tower 54, and is pressurized into the absorption tower 54 from the bottom of the absorption tower 54 using a packed tower having a plurality of packed beds partitioned by gas backflow prevention plates.・ Sent in. On the other hand, the absorption water is supplied into the absorption tower 54 from the top of the absorption tower 54. The desulfurized digestion gas is repeatedly brought into gas-liquid contact with the absorption water and the plurality of packed beds in the absorption tower 54, and carbon dioxide and the like are absorbed and removed, from the top of the absorption tower 54 via the dehumidifier 57. Then, it is taken out as purified methane gas.

On the other hand, the absorption water after the absorption treatment discharged from the bottom of the absorption tower 54 is sent to the top of the stripping tower 6. In this case, since there is a pressure difference between the absorption tower 54 and the diffusion tower 56, the absorption water after the absorption treatment can be transferred without using a pump. Since the inside of the stripping tower 56 is at atmospheric pressure, unnecessary gas components such as carbon dioxide dissolved in the absorbed water after the absorption treatment are flushed by the pressure difference and removed from the water. Absorbed water that has been flashed descends to the packed portion at the bottom of the stripping tower 56 and comes into gas-liquid contact with a carrier gas such as air or methane gas supplied from the bottom of the stripping tower 56 to further dissolve. Gas is removed. The carrier gas containing the dissolved gas is sent to the boiler. When the carrier gas is air, it is used as combustion air, and when it is methane gas, it is used as part of the fuel. And the absorption water after the discharge process discharged | emitted from the tower bottom of the diffusion tower 56 pressurizes with the pump 55, returns to the absorption tower 54, and is reused as absorption water.
Japanese Patent Laying-Open No. 2004-83542 (FIG. 1)

  However, in the conventional digestion gas purification equipment described above, the digestion gas from the digestion tank is temporarily stored in a large low-pressure gas holder (pressure of the gas holder: 0.002 MPaG, for example) and then supplied to the biogas purification device. Therefore, in order to use more digestion gas (biogas) as an energy resource, it is necessary to install a larger low-pressure gas holder. For this reason, the installation of a large-sized low-pressure gas holder requires a large installation space, and the initial cost and the maintenance cost are high, and the investment becomes a heavy burden, which is a negative factor for promoting the effective use of biogas. .

  Accordingly, an object of the present invention is to generate biogas by subjecting organic waste such as food waste and sewage sludge to anaerobic fermentation, and purify the biogas to obtain a purified gas having a high concentration of methane. This eliminates the need to install a large-sized low-pressure gas holder that requires a large installation space and high initial costs and maintenance costs, and can save space and reduce costs for the entire biogas purification facility. An object of the present invention is to provide a biogas purification method and a biogas purification facility that can stably extract biogas from an anaerobic fermenter against fluctuations in the amount.

  In order to solve the above problems, the present invention takes the following technical means.

  In the invention of claim 1, biogas is generated by anaerobic fermentation of organic waste in an anaerobic fermentation tank, and the biogas from the anaerobic fermentation tank is boosted by a gas compressor to an absorption tower. The biogas and water are brought into contact with each other at a high pressure in the absorption tower, so that carbon dioxide and sulfur-based impurities contained in the biogas are dissolved in the high-pressure water and separated from the biogas. Obtaining a concentrated purified gas, measuring the gas pressure of the anaerobic fermenter at that time, so that the gas pressure of the anaerobic fermenter becomes a substantially constant set value determined in advance based on the measurement result A method for purifying biogas, characterized in that the number of rotations of the gas compressor is increased or decreased.

  The invention of claim 2 is the biogas purification method according to claim 1, wherein the biogas and water are brought into contact with each other in a high pressure state satisfying a range of 0.55 to 2.0 MPaG in the absorption tower. The carbon dioxide and the sulfur-based impurities are separated and removed, and the siloxane compound contained in the biogas is condensed and separated from the biogas to obtain a purified gas having a high concentration of methane. is there.

  The invention according to claim 3 is the biogas purification method according to claim 2, wherein the biogas and water are contacted in the absorption tower in a high pressure state satisfying a range of 0.7 MPaG or more and less than 1.0 MPaG. It is what.

  The invention of claim 4 is an anaerobic fermenter that generates biogas by anaerobic fermentation of organic waste, and the biogas from the anaerobic fermenter is boosted by a gas compressor and sent to an absorption tower. The biogas and water are brought into contact with each other at a high pressure in the absorption tower, so that carbon dioxide and sulfur impurities contained in the biogas are dissolved in the high pressure water and separated from the biogas. The gas pressure of the anaerobic fermenter is measured, and the gas pressure of the anaerobic fermenter is set to a substantially constant preset value based on the measurement result. And a control means for controlling the increase / decrease of the rotational speed of the gas compressor.

  Invention of Claim 5 is equipped with the refined gas tank for storing the refined gas from the said biogas refiner | purifier temporarily, and supplying to refined gas consumption equipment in the biogas refinement | purification equipment of Claim 4 It is characterized by.

  According to a sixth aspect of the present invention, in the biogas purification facility according to the fifth aspect, when the biogas purification apparatus is started, the pressure in the absorption tower reaches a predetermined set value and the gas compressor Until the biogas from the anaerobic fermenter is supplied to the gas compressor, the gas compressor is provided with a purified gas circulation line for supplying purified gas from the purified gas tank.

  The invention according to claim 7 is the biogas purification facility according to any one of claims 4 to 6, wherein the biogas purification device supplies 0.55 to 2 of biogas and water in the absorption tower. The carbon dioxide and the sulfur-based impurities are separated and removed by contacting in a high pressure state satisfying a range of 0.0 MPaG, and the siloxane compound contained in the biogas is condensed and separated from the biogas, thereby increasing the methane content. It is configured to obtain a concentrated purified gas.

  The invention according to claim 8 is the biogas purification facility according to claim 7, wherein the biogas purification apparatus satisfies a range of 0.7 MPaG or more and less than 1.0 MPaG of biogas and water in the absorption tower. It is comprised so that it may contact with.

  The biogas purification method or biogas purification facility of the present invention generates biogas in an anaerobic fermentation tank, and passes the biogas from the anaerobic fermentation tank through a desulfurization tower and a large-sized low-pressure gas holder. Carbon dioxide and sulfur impurities by introducing into a gas compressor of a biogas refining device, increasing the pressure by the gas compressor, sending the gas to the absorption tower, and bringing the biogas and water into contact with each other at a high pressure in the absorption tower Is dissolved in high-pressure water and separated from the biogas to obtain a purified gas. At that time, the gas pressure of the anaerobic fermenter is measured, and the gas pressure of the anaerobic fermenter is predetermined based on the measurement result. The number of revolutions of the gas compressor is controlled to increase or decrease so as to obtain a substantially constant set value. Therefore, it is not necessary to install a large-sized low-pressure gas holder that requires a large installation space and high initial costs and maintenance costs, and it is possible to save space and reduce costs as a whole biogas refining equipment. The biogas can be stably taken out from the anaerobic fermenter with respect to the fluctuation of the generated amount.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a flowchart showing the overall configuration of a digestion gas utilization system to which a digestion gas purification facility according to an embodiment of the present invention is applied, and FIG. 2 is a flowchart showing the configuration of the digestion gas purification apparatus in FIG.

  In this embodiment, a digestion gas purification facility as a biogas purification facility is provided in a sewage treatment plant, and as shown in FIG. 1, digestion tanks (digestion tanks) 1A to 1C as anaerobic fermentation tanks, Digestion gas purification apparatuses 4A and 4B as biogas purification apparatuses, medium pressure (for example, 0.8 MPaG) purification gas tanks 5A and 5B, and control means described later are provided. The digestion gas refining equipment and the refined gas consuming equipment constitute a digestion gas utilization system, and in this embodiment, the refined gas consuming equipment is a surplus gas combustion device 21, hot water boilers 22A and 22B, and an on-site air conditioning equipment 23. A gas engine (cogeneration system) 24 and a gas filling facility (natural gas stand) 25 are provided.

  A line L2 having a three-way valve 3A communicates with the digestion gas purification apparatus 4A from the digestion tanks 1A to 1C via a line L1 having a gas pressure gauge 2 for measuring the gas pressure in the digestion tanks A to C. A line L3 having a three-way valve 3B communicates from the tanks 1A to 1C to the digestion gas purifier 4B via the line L1.

  Line L7 communicates from the digestion gas purification device 4A to the purification gas tank 5A via lines L4 and L6, and line L8 communicates from the digestion gas purification device 4B to the purification gas tank 5B via lines L5 and L6. Yes. Further, a line L9 communicates from the purified gas tank 5A to the purified gas supply line L11, and a line L10 communicates from the purified gas tank 5B to the purified gas supply line L11. Further, a purified gas circulation line L12 is provided that branches from the purified gas supply line L11 and communicates with the second inlets β of the three-way valves 3A and 3B.

  A line L15 having an excess purified gas control valve V1 and an excess gas pressure reducing valve V2 communicates with the excess gas combustion device 21 from the purified gas supply line L11. A line L20 is branched from the downstream side of the gas pressure gauge 2 in the line L1 and has an excess digestion gas control valve V7. The surplus gas combustion device 21 is a combustion gas that can be discharged into the atmosphere by completely combusting surplus sewage sludge digestion gas or surplus refined gas in a surplus gas combustion furnace.

  A line L16 having a hot water boiler pressure reducing valve V3 communicates from the purified gas supply line L11 to the hot water boilers 22A and 22B, and the air conditioning pressure reducing valve 23 is connected from the purified gas supply line L11 to the on-site air conditioning equipment 23. Line L17 with V4 is in communication. The hot water boilers 22A and 22B produce hot water using purified gas as fuel, and supply the hot water to the heat exchangers 1Aa to 1Ca using hot water as a heating medium for heating the digestion tanks 1A to 1C.

  A line L18 having a gas engine pressure reducing valve V5 communicates from the purified gas supply line L11 to the gas engine (cogeneration system) 24, and a gas filling facility (natural gas station) is connected to the purified gas supply line L11. ) 25 communicates with a line L19 having a gas filling pressure reducing valve V6 and a mixing device 26.

  The gas engine (cogeneration system) 24 generates electric power by the power of the engine using purified gas as fuel, and produces hot water by cooling the engine body (jacket), heat recovery from the hot water boiler from the intercooler, and exhaust gas. The hot water is supplied to the heat exchangers 1Aa to 1Ca as a heating medium. Further, the gas filling facility (natural gas stand) 25 mixes an odorous gas (for example, city gas) with a mixing device 26 to add odor to the purified gas, and pressurizes the odorized purified gas with a gas compressor. The gas storage device is filled and stored, and a natural gas vehicle is provided with a dispenser for filling the odor-purified gas (odorous natural gas) from the gas storage device.

  Next, the digestion gas purification apparatus 4A will be described with reference to FIG. The other digestion gas purification apparatus 4B has the same configuration as this, and a description thereof will be omitted.

  As shown in FIG. 2, the digestion gas purification apparatus 4A includes a mist separator 401, gas compressors 402a and 402b, an absorption tower (scrubber) 404, a dehumidifier 405, a water supply tank 406, a water supply pump 407, and a water circulation pump 408. , A heat exchanger 409, a chiller 410, a decompression tank (flushing tank) 411, a stripping tower (stripping tower) 412, and an exhaust blower 413. The gas compressors 402a and 402b have a rotational speed controller 403 that performs rotational speed control by variable voltage variable frequency (VVVF) control.

  In this digestion gas purification apparatus 4A, the sewage sludge digestion gas guided from the digestion tanks 1A to 1C via the lines L1 and L2 is removed from the mist (water) and dust in the gas by the mist separator 401. The pressure is increased to a predetermined pressure higher than the atmospheric pressure by the gas compressors 402a and 402b connected in series. Sewage sludge digestion gas pressurized by the gas compressors 402 a and 402 b is introduced into the lower part of the absorption tower 404. On the other hand, the absorption tower 404 is supplied with water from the top thereof in a state of being pressurized by a water circulation pump 408.

  In this way, the gas compressors 402a and 402b pressurize the sewage sludge digested gas and feed it into the absorption tower 404 from the lower part, and the water circulation pump 408 boosts the water and feeds it into the absorption tower 404 from the upper part. Thus, the inside of the absorption tower 404 is maintained in a high pressure state satisfying the range of 0.55 to 2.0 MPaG, and the sewage sludge digestion gas and water are brought into contact with each other in the high pressure state satisfying the pressure range in the absorption tower 404. Yes. The absorption tower 404 is filled with a packing such as Raschig ring in order to bring the sewage sludge digestion gas and water into sufficient contact.

The carbon dioxide and sulfur system contained in the gas state in the sewage sludge digestion gas by contacting the sewage sludge digestion gas and water in a high pressure state satisfying the range of 0.55 to 2.0 MPa in the absorption tower 404. Impurities (such as H ₂ S) are dissolved and absorbed in high-pressure water, while methane is taken out from the top of the absorption tower 404 with almost no dissolution in high-pressure water. At the same time, the siloxane compound contained in the sewage sludge digestion gas is condensed from the gas state into a droplet state due to the high pressure state, and collides with the high pressure water flowing down inside the absorption tower in this droplet state. Then, it collects at the bottom of the absorption tower 404 together with water.

Thus, when refine | purifying sewage sludge digestion gas, it is good to make sewage sludge digestion gas and water contact in the high pressure state which satisfy | fills the range of 0.55-2.0 MPaG. Carbon dioxide, sulfur-based impurities (H ₂ S, etc.) and siloxane compounds are not sufficiently separated and removed in a lower pressure atmosphere than this range, and carbon dioxide, sulfur-based impurities (H ₂ S, etc.), the removal rate of the siloxane compound is not improved so much, which is not preferable from the viewpoints of operation cost and increase in apparatus cost due to high pressure specifications. In addition, it is more preferable to contact a sewage sludge digestion gas and water in the high pressure state which satisfy | fills the range of 0.7 MPaG or more and less than 1.0 MPaG from the point of removal of a siloxane compound, an operating cost, and an apparatus cost.

The separated carbon dioxide and sulfur impurities (H ₂ S, etc.) are dissolved, and the water containing the separated siloxane compound is extracted from the bottom of the absorption tower 404 through the valve V10. And introduced into the decompression tank 411. The pressure in the decompression tank 411 is reduced compared to that in the absorption tower 404. For example, when the pressure in the absorption tower 404 is 0.9 MPaG, the pressure in the decompression tank 5 is 0.3 MPaG. For the purpose of increasing the methane recovery rate, the methane slightly dissolved in the water from the bottom of the absorption tower 404 is separated as a gas, and gas compressors 402a, It is returned to the intermediate stage of 402b and joined to the sewage sludge digestion gas from the gas compressor 402a. The water in which carbon dioxide and sulfur-based impurities (such as H ₂ S) are dissolved after the methane is separated and recovered is introduced from the bottom of the decompression tank 411 to the upper portion of the stripping tower 412 through the valve V12.

  In the stripping tower 412, water extracted from the decompression tank 411 is introduced from the top, while a stripping gas (for example, air) is introduced from the bottom by the exhaust blower 413, and both are in countercurrent contact at atmospheric pressure. To do. As a result, the carbon dioxide and sulfur impurities dissolved in the water extracted from the decompression tank 411 move to the emission gas side and are discharged from the top of the diffusion tower 412 together with the emission gas, and deodorized via the line L14. Guided to the facility. Then, the water regenerated by removing the dissolved gas is extracted from the bottom of the diffusion tower 412, boosted by the water circulation pump 408, and between the brine from the chiller 410 by the heat exchanger 409. After the heat is exchanged, the temperature is cooled to a predetermined temperature, and then supplied to the upper portion of the absorption tower 404. The diffusion tower 412 is filled with a packing such as a Raschig ring in order to sufficiently bring the diffusion gas into contact with water.

  In order to maintain the quality of the circulating water supplied to the absorption tower 404, it is desirable to periodically open the valve V13. Thereby, a part of the circulating water is extracted, and the extracted water is sent to the waste water treatment facility via the line L13. When the amount of circulating water becomes equal to or less than a predetermined amount due to this extraction, the water replenishing pump 407 opens the valve V14 and replenishes the insufficient amount of water from the water supply tank 406. Examples of water used at this time include tap water or well water, and it is also possible to use treated water obtained by treating wastewater such as sewage. In this embodiment, in the sewage treatment plant, Sand filtered water from the sand filtering facility for treated water provided downstream of the final sedimentation basin is used.

  On the other hand, the purified gas having a high concentration of methane taken out from the top of the absorption tower 404 is sent to the dehumidifier 405. In this embodiment, the dehumidifier 405 is a dehumidifier that adsorbs and removes moisture by a pressure swing adsorption method (PSA method), and uses synthetic zeolite as an adsorbent. The purpose of dehumidification by the dehumidifier 405 is to prevent condensation even at a pressure when the purified gas is used (utilized) as fuel. The pressure of the purified gas taken out from the absorption tower 404 is, for example, 0.9 MPaG (when the pressure in the absorption tower 404 is 0.9 MPaG), and the purified gas is used, for example, as fuel for a natural gas vehicle. The dew point is -60 ° C or less, more preferably -70 ° C or less, and particularly preferably -80 ° C or less in terms of the dew point at atmospheric pressure so that no dew condensation occurs even at a pressure of 19.6 MPaG. Dehumidification by the dehumidifier 405 is performed. As described above, the purified gas dehumidified by the dehumidifier 405 is sent to the purified gas tanks 5A and 5B through the line L4 and the line L6 so that no dew condensation occurs even at the pressure when used as fuel. It has become.

  Next, the operation | movement operation | movement in the digestion gas utilization system provided with the digestion gas refinement | purification equipment comprised in this way is demonstrated with reference to FIG.1 and FIG.2.

  First, when starting up, the control device 7 communicates the second inlet β and the outlet γ with the three-way valve 3A of the line L2 and the three-way valve 3B of the line L3 to close the first inlet α. S13 is given. Thereby, until the pressure in the absorption tower 404 of the digestion gas purification apparatuses 4A and 4B rises to the set value, the purified gas passes from the purified gas tanks 5A and 5B to the digestion gas purification apparatuses 4A and 4B via the purified gas circulation line L12. Supplied. By doing so, it is possible to prevent a pressure drop in the suction side piping of the gas compressors 402a and 402b immediately after the digestion gas purification apparatuses 4A and 4B are started.

When the pressure in the absorption tower 404 of the digestion gas purification apparatuses 4A and 4B reaches the set value, the control device 7 communicates the first inlet α and the outlet γ with the three-way valves 3A and 3B, and the second inlet. A flow path switching signal S13 for closing β is given. Thereby, the sewage sludge digestion gas from digestion tank 1A-1C is supplied to digestion gas refinement | purification apparatus 4A, 4B. An extremely small low-pressure gas holder (for example, a capacity) is provided between the digestion tanks 1A to 1C and the digestion gas refining apparatuses 4A and 4B in order to reliably prevent pressure fluctuations in the piping at the start of sewage sludge digestion gas supply. (About 30 m ³ ) may be provided.

  Next, the normal operation will be described. The control device 7 receives the gas pressure signal S1 from the gas pressure gauge 2 in the line L1, and the gas pressure in the digestion tanks 1A to 1C is set to a substantially constant set value. The rotation speed control signal S11 for increasing / decreasing the rotation speed is supplied to the rotation speed controller 403 of the gas compressors 402a and 402b. That is, when the gas pressure in the digestion tanks 1A to 1C becomes higher than the set value, the number of revolutions of the gas compressors 402a and 402b is increased to increase the supply amount of the purified gas to the purified gas tanks 5A and 5B. When it is lower, the rotational speed of the gas compressors 402a and 402b is decreased to reduce the amount of purified gas supplied to the purified gas tanks 5A and 5B. Further, in this case, the control device 7 adjusts the pressure at the outlet of the dehumidifier 405 (not shown) so that the pressure in the absorption tower 404 becomes a predetermined substantially constant value based on the pressure measurement result in the absorption tower 404. The opening of the valve is adjusted. Here, the gas pressure gauge 2, the rotation speed controller 403, and the control device 7 measure the gas pressures of the digestion tanks 1A to 1C, and the gas pressures of the digestion tanks 1A to 1C are determined in advance based on the measurement results. Control means for increasing / decreasing the rotational speeds of the gas compressors 402a, 402b of the digestion gas purification apparatuses 4A, 4B so as to obtain the substantially constant set value.

  If the gas pressure gauge 2 detects that the gas pressure in the digestion tanks 1A to 1C has risen abnormally during the compressor rotation speed control during the normal operation, the control device 7 causes the gas pressure gauge 2 to In response to the gas pressure signal S1 indicating the abnormal rise from the above, the excess digestion gas control valve V7 of the line L20 is opened. In this way, the sewage sludge digestion gas from the digestion tanks 1A to 1C is supplied to the surplus gas combustion device 21 for combustion treatment, thereby eliminating an abnormal increase in gas pressure in the digestion tanks 1A to 1C.

  On the other hand, if the gas pressure gauge 2 detects that the gas pressure in the digestion tanks 1A to 1C has abnormally decreased during the compressor rotation speed control during the normal operation, the control device 7 In response to the gas pressure signal S1 indicating the abnormal decrease from the first, the three-way valves 3A and 3B are provided with a flow path switching signal S13 that connects the second inlet β and the outlet γ to close the first inlet α. As a result, the purified gas from the purified gas tanks 5A and 5B is supplied to the digestion gas purification devices 4A and 4B via the purified gas circulation line L12, and the sewage sludge digestion gas is supplied to the digestion gas purification devices 4A and 4B. By temporarily stopping, the abnormal drop in gas pressure in the digestion tanks 1A to 1C is resolved. In this case, the digestion gas purification apparatuses 4A and 4B are in an operation state similar to the unloaded state, and when the gas pressures in the digestion tanks 1A to 1C are recovered, the operation can be quickly started up.

  A gas pressure gauge 6 is provided in a purified gas supply line L11 for supplying purified gas from the purified gas tanks 5A and 5B to the purified gas consuming equipment. When the gas pressure gauge 6 detects that the purified gas consumption is reduced and the gas pressure in the purified gas tanks 5A and 5B exceeds the set value, the controller 7 gradually controls the excess purified gas control valve V1. By opening, the purified gas is burned by the surplus gas combustion device 21.

  As described above, according to the present embodiment, the sewage sludge digestion gas from the digestion tanks 1A to 1C is passed through the gas compressors 402a of the digestion gas purification apparatuses 4A and 4B without passing through the desulfurization tower and the large-sized low-pressure gas holder. The gas compressor 402a, 402b guides the gas to 402b and pumps it into the absorption tower. The sewage sludge digestion gas and water are brought into contact with each other at a high pressure in the absorption tower, so that carbon dioxide and sulfur-based impurities are converted into high-pressure water. It is dissolved and separated from the sewage sludge digestion gas to obtain purified gas. At that time, the gas pressures of the digestion tanks 1A to 1C are measured, and the gas pressures of the digestion tanks 1A to 1C are predetermined based on the measurement results. The number of revolutions of the gas compressors 402a and 402b is controlled to increase or decrease so as to obtain a substantially constant set value.

  Therefore, unlike conventional systems, it is not necessary to install a large-sized low-pressure gas holder that requires a large installation space and has high initial costs and maintenance costs. Thus, it is possible to contribute to the expansion of the use of sewage sludge digestion gas, and to stably take out the sewage sludge digestion gas from the digestion tanks 1A to 1C against fluctuations in the amount of sewage sludge digestion gas generated.

It is a flow figure showing the whole digestion gas utilization system composition to which digestion gas refining equipment by one embodiment of the present invention is applied. It is a flowchart which shows the structure of the digestion gas refinement | purification apparatus in FIG. It is a figure for demonstrating a prior art (patent document 1), Comprising: It is a flowchart which shows the structure of the digestion gas refinement | purification equipment (biogas refinement | purification equipment) which refine | purifies digestion gas and obtains refinement | purification gas.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1A-1C ... Digestion tank 2,6 ... Gas pressure gauge 3A, 3B ... Three-way valve 4A, 4B ... Digestion gas refinement device 5A, 5B ... Refinement gas tank 7 ... Control device 21 ... Excess gas combustion device 22A, 22B ... Hot water boiler 23 Air conditioning equipment 24 Gas engine 25 Gas filling equipment 401 Mist separator 402a, 402b Gas compressor 403 Speed controller 404 Absorption tower 405 Dehumidifier 406 Water tank 407 Water supply pump 408 Water circulation Pump 409 ... heat exchanger 410 ... chiller 411 ... decompression tank 412 ... diffusion tower 413 ... exhaust blower

Claims (8)

  Biogas is generated by anaerobic fermentation of organic waste in an anaerobic fermentation tank, and the biogas from the anaerobic fermentation tank is pressurized by a gas compressor and sent to an absorption tower. By contacting biogas and water in a high-pressure state, carbon dioxide and sulfur impurities contained in the biogas are dissolved in the high-pressure water and separated from the biogas to obtain a purified gas having a high concentration of methane. In this case, the gas pressure of the anaerobic fermenter is measured, and the gas compressor is rotated so that the gas pressure of the anaerobic fermenter becomes a predetermined substantially constant set value based on the measurement result. A method for purifying biogas, wherein the number is controlled to increase or decrease.   In the absorption tower, the biogas and water are brought into contact with each other in a high pressure state satisfying a range of 0.55 to 2.0 MPaG to separate and remove the carbon dioxide and the sulfur-based impurities, and the biogas contains. The method for purifying a biogas according to claim 1, wherein a siloxane compound is condensed and separated from the biogas to obtain a purified gas having a high concentration of methane.   The biogas purification method according to claim 2, wherein the biogas and water are brought into contact with each other in a high pressure state satisfying a range of 0.7 MPaG or more and less than 1.0 MPaG in the absorption tower.   Anaerobic fermenter that generates biogas by anaerobic fermentation of organic waste, and biogas from the anaerobic fermenter is pressurized by a gas compressor and sent to an absorption tower. By contacting gas and water in a high-pressure state, the carbon dioxide and sulfur-based impurities contained in the biogas are dissolved in the high-pressure water and separated from the biogas to obtain a purified gas having a high concentration of methane The gas pressure of the gas compressor is measured so that the gas pressure of the anaerobic fermenter is measured with a gas refining device, and the gas pressure of the anaerobic fermenter is set to a predetermined constant value based on the measurement result. A biogas refining facility comprising: control means for increasing / decreasing the rotational speed.   5. The biogas purification facility according to claim 4, further comprising a purified gas tank for temporarily storing purified gas from the biogas purification device and supplying the purified gas to the purified gas consuming facility.   During the startup of the biogas purification device, until the pressure in the absorption tower reaches a predetermined set value and supplies the biogas from the anaerobic fermentation tank to the gas compressor, 6. The biogas purification facility according to claim 5, further comprising a purified gas circulation line for supplying purified gas from the purified gas tank to the gas compressor.   The biogas purification device separates and removes the carbon dioxide and the sulfur impurities by bringing biogas and water into contact with each other in a high pressure state satisfying a range of 0.55 to 2.0 MPaG in the absorption tower. The siloxane compound contained in the biogas is condensed and separated from the biogas to obtain a purified gas having a high concentration of methane. The biogas purification facility according to any one of the above.   The said biogas refiner | purifier is comprised so that biogas and water may be contacted in the high-pressure state which satisfy | fills the range of 0.7 MPaG or more and less than 1.0 MPaG in the said absorption tower. 7. The biogas purification facility according to 7.

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