Biogas reforming system

Abstract

To provide a biogas reforming system that efficiently removes carbon dioxide from methane fermentation-type biogas.SOLUTION: A biogas reforming system comprises a biogas reforming apparatus having a filter layer containing an adsorbent, and a fluidized bed incinerator connected to the biogas reforming apparatus via a first transfer path and a second transfer path, wherein the first transfer path transfers the adsorbent from the biogas reforming apparatus to the fluidized bed incinerator, and the second transfer path transfers the adsorbent from the fluidized bed incinerator to the biogas reforming apparatus.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] One embodiment of the present invention relates to a biogas reforming system. [Background technology]

[0002] Conventionally, power plants that recover energy from methane fermentation biogas (hereinafter simply referred to as "biogas") have been known. Biogas is composed primarily of approximately 60% methane and 40% carbon dioxide, and can be produced by fermenting organic waste such as food waste. The power plants described above generate electricity using the calorific value of biogas, but the calorific value of biogas is lower than that of city gas, resulting in poor energy recovery efficiency. In light of this problem, a technique is known for removing carbon dioxide contained in biogas and increasing the methane concentration in order to increase the calorific value of biogas. For example, Patent Document 1 discloses a method for concentrating methane from biogas, which uses a separation membrane process to concentrate and recover methane from biogas. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-095727 Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned conventional methane concentration methods use multi-stage separation membranes to remove carbon dioxide, but separation membranes are essentially consumables, and deteriorated membranes must be replaced each time they deteriorate. Therefore, devices using conventional methane concentration methods have the problem of high operating costs. Furthermore, conventional methane concentration methods using separation membranes require a high-pressure compressor to pressurize and supply biogas to the separation membrane, and the need for such equipment also hinders efforts to reduce the cost and size of the device.

[0005] One object of the present invention is to provide a biogas reforming system that efficiently removes carbon dioxide from methane fermentation biogas. Another object of the present invention is to provide a biogas reforming system that efficiently removes nitrogen oxides from methane fermentation biogas. [Means for solving the problem]

[0006] In one embodiment of the present invention, a biogas reforming system includes a biogas reformer having a filter layer containing an adsorbent, and a fluidized bed incinerator connected to the biogas reformer via a first transfer path and a second transfer path, wherein the first transfer path transfers the adsorbent from the biogas reformer to the fluidized bed incinerator, and the second transfer path transfers the adsorbent from the fluidized bed incinerator to the biogas reformer.

[0007] In the biogas reforming system, the adsorbent transferred to the fluidized bed incinerator by the first transfer path may be mixed into a fluidized medium filled inside the fluidized bed incinerator.

[0008] In the biogas reforming system, the adsorbent transferred from the fluidized bed incinerator by the second transfer path may be mixed into the filter layer of the biogas reforming system.

[0009] In the biogas reforming system, the second transfer path may be provided at a position higher than the filter layer.

[0010] In the biogas reforming system, the fluidized bed incinerator may be provided with a shielding plate at a position higher than the second transfer path, for changing the movement path of the combustion gas.

[0011] In the biogas reforming system, the biogas reformer may further include a vibrating plate disposed below the filter layer, and the vibrating plate may be inclined such that the closer it is to the first flow path, the lower it is positioned.

[0012] In the biogas reforming system, the biogas reformer may include a reaction liquid injection unit that injects an alkaline reaction liquid into the inside of the device body.

[0013] In the biogas reforming system, the first transfer path and the second transfer path may each have a double flap damper.

[0014] The biogas reforming system may further include an exhaust fan connected to the second transfer path and configured to exhaust the combustion gas generated inside the fluidized bed incinerator to the outside. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic diagram showing the configuration of a biogas reforming system according to a first embodiment. [Figure 2] 1 is a schematic diagram showing the configuration of a biogas reforming device according to a first embodiment. [Figure 3] 1 is a schematic diagram showing the configuration of a fluidized bed incinerator according to a first embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention can be embodied in various forms without departing from the spirit of the present invention, and should not be construed as being limited to the description of the embodiments exemplified below. To clarify the explanation, the drawings may show the size, width, thickness, shape, etc. of each part schematically compared to the actual form, but these are merely examples and do not limit the interpretation of the present invention. In this specification and each drawing, elements having the same functions as those described with reference to the previous drawings may be assigned the same reference numerals, and redundant explanations may be omitted.

[0017] In this specification and drawings, "up" refers to the direction opposite to the direction of gravity, and "down" refers to the direction of gravity. Also, "left" and "right" refer to directions perpendicular to "up" and "down." For convenience of explanation, the "up-down direction" of a biogas reformer or a fluidized-bed incinerator may be expressed as the "height direction," and the "left-right direction" may be expressed as the "width direction."

[0018] Furthermore, in this specification and drawings, when multiple identical elements (components) are provided, they may be distinguished by adding alphabetical letters such as "a" or "b" to the same reference numeral (number). However, for the sake of convenience of explanation, when there is no need to distinguish between individual elements, they may be collectively referred to by the reference numeral alone, omitting the alphabetical letters.

[0019] (First embodiment) [Configuration of biogas reforming system 500] 1 is a schematic diagram showing the configuration of a biogas reforming system 500 according to the first embodiment. The biogas reforming system 500 is a composite system including a biogas reformer 100 capable of reforming methane fermentation-type biogas, and a fluidized-bed incinerator 200 installed next to the biogas reformer 100.

[0020] The primary purpose of the biogas reformer 100 is to increase the methane concentration of biogas. However, as will be described later, the biogas reformer 100 can also secondarily reduce SOx (sulfur oxides) and NOx (nitrogen oxides) in the biogas. The primary purpose of the fluidized bed incinerator 200 is to incinerate the residue and sludge generated after methane fermentation to reduce their volume or render them harmless, or to use the combustion gas generated during incineration as a biogas boiler. However, as will be described later, the fluidized bed incinerator 200 can also be used as a regeneration means for activating the adsorbent used in the biogas reformer 100.

[0021] Next, we will explain the biogas reformer 100 and the fluidized bed incinerator 200. However, this explanation will be limited to an outline, and details will be described later using Figure 2 (biogas reformer 100) and Figure 3 (fluidized bed incinerator 200).

[0022] In the biogas reforming apparatus 100 shown in Figure 1, biogas supplied to the inside of the apparatus body 10 reacts with the alkaline reaction liquid 15 circulating inside the apparatus body 10 to remove carbon dioxide. The alkaline reaction liquid 15 is sent from the bottom of the apparatus body 10 via the reaction liquid return unit 40 to the reaction liquid injection unit 30 and injected into the inside of the apparatus body 10. At this time, the biogas rising from below comes into contact with the alkaline reaction liquid injected from above, removing carbon dioxide from the biogas and relatively increasing the methane concentration.

[0023] The biogas from which carbon dioxide has been removed by reaction with the alkaline reaction liquid 15 continues to rise inside the device main body 10, where moisture and NOx are removed in the gas-liquid separation section 60. Specifically, moisture contained in the biogas is removed in the first filter layer 61 containing a demister, and NOx contained in the biogas is removed in the second filter layer 62 containing an adsorbent (activated carbon in this embodiment). The biogas (reformed biogas) from which moisture and NOx have been removed is sent to an external gas holder (biogas storage tank).

[0024] Next, in the fluidized bed incinerator 200, a fluidized medium (for example, sand such as silica sand) that has been heated to a high temperature in advance is agitated by air (fluidizing air) inside the furnace body 110 to form a fluidized bed 130. In the example shown in Fig. 1, air supplied from the outside is sprayed from an air diffuser 132 inserted inside the fluidized bed 130, causing the sand filled inside the furnace body 110 to be blown upward and agitated.

[0025] Waste (e.g., residues generated by methane fermentation) fed through the waste inlet 120 is incinerated while flowing together with sand inside the fluidized bed 130, generating combustion gas (hereinafter referred to as "primary combustion gas"). The primary combustion gas rises inside the furnace body 110, passes through dust collectors such as a bag filter and an electrostatic precipitator, and is then discharged to the outside and sent to an external secondary combustion chamber or the like. Waste residues remaining after incineration (e.g., incombustible materials such as metals) are sent together with some of the sand to the incombustible material separator 140. In this embodiment, when incinerating the waste, biogas reformed in the biogas reformer 100 described above is supplied as auxiliary fuel.

[0026] A plurality of shielding plates 150a-150c are disposed at the upper interior of the furnace body 110, protruding from the side walls toward the interior. The shielding plates 150a-150c are attached alternately to the left and right side walls as they move upward. The primary combustion gas generated by the incineration of waste rises inside the furnace body 110, but since the plurality of shielding plates 150a-150c are provided along the way, the gas hits each of the shielding plates 150a-150c as it rises. For example, as shown in FIG. 1, the path that the primary combustion gas travels may be a zigzag path.

[0027] The biogas reformer 100 and fluidized bed incinerator 200 described above are connected to each other via a first transfer path 310 and a second transfer path 320. The first transfer path 310 transfers the adsorbent (activated carbon) used in the second filter layer 62 from the biogas reformer 100 to the fluidized bed incinerator 200. The adsorbent transferred into the furnace body 110 of the fluidized bed incinerator 200 via the first transfer path 310 is mixed into the fluidized bed 130. Therefore, the mixed adsorbent is heated at a high temperature inside the fluidized bed 130 and activated, thereby restoring its performance.

[0028] As described above, the adsorbent fluidizes together with the sand in the fluidized bed 130 while being activated. However, because the specific gravity of the adsorbent is very light, some of the adsorbent rises inside the furnace body 110 together with the primary combustion gas. At this time, the primary combustion gas collides with the multiple shielding plates 150a-150c to form a swirl (a swirling flow), causing some of the rising adsorbent to fall downward. For example, in this embodiment, most of the adsorbent falls downward due to the shielding plate 150a or 150b. In other words, some of the adsorbent that rose with the primary combustion gas returns to the fluidized bed 130, and most of the remaining material falls onto the shielding plate 150a. The adsorbent that fell onto the shielding plate 150a is deposited and transferred to the biogas reformer 100 via the second transfer path 320.

[0029] The second transfer path 320 transfers the activated adsorbent from the fluidized bed incinerator 200 to the biogas reformer 100. The second transfer path 320 is provided at an angle downward from a position higher than the second filter layer 62 of the furnace body 110. Therefore, the adsorbent transferred to the inside of the biogas reformer 100 via the second transfer path 320 is mixed again into the second filter layer 62. The adsorbent returned to the second filter layer 62 is reused as an adsorbent for removing NOx from the reformed biogas again.

[0030] In this embodiment, in order to physically isolate the biogas reformer 100 from the fluidized bed incinerator 200, double flap dampers 312 and 322 are provided for the first transfer path 310 and the second transfer path 320, respectively. The adsorbent transferred via the first transfer path 310 and the second transfer path 320 is transferred in fixed amounts by the double flap dampers.

[0031] In addition, in this embodiment, in order to prevent high-temperature primary combustion gas from flowing into the biogas reforming device 100 through the second transfer path 320, the primary combustion gas is discharged to the outside through an exhaust fan 324.

[0032] The biogas reforming system 500 described above can efficiently produce reformed biogas by connecting and installing the biogas reformer 100 and the fluidized bed incinerator 200 side by side. Specifically, carbon dioxide is efficiently removed from the biogas produced by methane fermentation in the biogas reformer 100, significantly increasing the methane concentration. Furthermore, waste generated by methane fermentation (fermentation residue) can be incinerated in the fluidized bed incinerator 200 installed side by side.

[0033] In addition, the adsorbent used in the biogas reformer 100 can be activated in the fluidized bed incinerator 200 and then returned to the biogas reformer 100, allowing the adsorbent to be reused in a cyclical manner.

[0034] Furthermore, it is possible to supply the biogas reformed by the biogas reforming device 100 (biogas with an increased methane concentration) to the fluidized bed incinerator 200 as auxiliary fuel, thereby improving the combustion efficiency of the fluidized bed incinerator 200.

[0035] The outline of the biogas reforming system 500 has been explained above. Next, the configurations of the biogas reformer 100 and the fluidized bed incinerator 200 will be explained with reference to FIGS. 2 and 3, respectively.

[0036] [Configuration of biogas reformer 100] 2 is a schematic diagram showing the configuration of a biogas reformer 100 according to the first embodiment. The biogas reformer 100 is a device equipped with a function for reforming methane fermentation-type biogas. The primary purpose of the biogas reformer 100 is to increase the methane concentration of biogas. However, as will be described later, the biogas reformer 100 can also secondarily reduce SOx and NOx in the biogas.

[0037] The biogas reformer 100 includes an apparatus main body 10, a biogas supply unit 20, a reaction liquid injection unit 30, a reaction liquid return unit 40, a concentration adjustment unit 50, and a gas-liquid separation unit 60. However, the configuration of the biogas reformer 100 is not limited to the configuration shown in the figure, and some of the components may be omitted or other components may be added. For example, in Figure 1, the reaction liquid return unit 40, the concentration adjustment unit 50, and the gas-liquid separation unit 60 are not essential components and may be omitted.

[0038] The device main body 10 is a part corresponding to the housing of the biogas reforming device 100, and corresponds to a reaction vessel in which the biogas reforming process is carried out. The biogas reforming process (processing to increase the methane concentration in the biogas) is carried out inside the device main body 10.

[0039] A gas exhaust pipe 91 is connected to the top of the device main body 10. The gas exhaust pipe 91 is a pipe that exhausts the biogas reformed by the biogas reforming device 100, i.e., biogas with an increased methane concentration. The reformed biogas is sent via the gas exhaust pipe 91 to downstream facilities (for example, a gas holder that stores methane gas).

[0040] A reactant discharge pipe 92 is connected to the lower part (bottom) of the apparatus main body 10. As will be described in detail later, when the biogas reforming apparatus 100 is operated, reactants mainly composed of calcium carbonate and sodium carbonate precipitate over time at the bottom of the apparatus main body 10. For this reason, in this embodiment, the valve 81 is opened periodically to discharge the precipitated reactants to the outside. The reactants discharged through the reactant discharge pipe 92 are sent to a downstream sludge treatment device (not shown).

[0041] The biogas supply unit 20 is a section that supplies biogas to the inside of the apparatus main body 10. The biogas supply unit 20 in this embodiment includes a gas supply port 21 and a gas distribution pipe 22. The gas supply port 21 corresponds to an introduction section (opening) for supplying biogas to the inside of the apparatus main body 10. A gas supply pipe 93 is connected to the gas supply port 21 via a valve 82. Biogas generated in an upstream facility (for example, a fermentation treatment device such as a bioreactor that generates methane gas) is supplied to the gas supply port 21 via the gas supply pipe 93.

[0042] The gas distribution pipe 22 is a pipe-shaped component that extends toward the inside of the device body 10 and is connected to the gas supply port 21. The gas distribution pipe 22 has a longitudinal direction that corresponds to the width direction of the device body 10. The gas distribution pipe 22 is provided with a plurality of discharge holes 22a for discharging biogas at predetermined intervals. The biogas introduced from the gas supply port 21 travels through the inside of the device body 10 via the gas distribution pipe 22 and is discharged into the inside of the device body 10 from the plurality of discharge holes 22a. The discharge holes 22a may be simple through-holes or may be nozzles capable of spraying gas.

[0043] In this embodiment, an example has been shown in which the biogas supply unit 20 is configured with the gas supply port 21 and the gas distribution pipe 22, but this is not limited to this example, and only the gas supply port 21 may be provided, and the gas distribution pipe 22 may be omitted. Furthermore, in this embodiment, an example has been shown in which the biogas is diffused inside the device main body 10 using the gas distribution pipe 22, but this is not limited to this example, and the biogas may be released into the device main body 10 using another configuration (for example, a gas injector arranged on the side wall of the device main body 10).

[0044] The reaction liquid spraying unit 30 is a section that sprays a solution containing a component that reacts with carbon dioxide to immobilize (solidify) the carbon dioxide (hereinafter referred to as "alkaline reaction liquid") toward the inside of the device main body 10. In this embodiment, an example is shown in which milk of lime (for example, a solution containing slaked lime) is used as the alkaline reaction liquid 15, but the present invention is not limited to this example, and other solutions such as a sodium hydroxide solution (caustic soda solution) and a sodium carbonate solution (sodium carbonate solution) can also be used.

[0045] The reaction liquid jetting unit 30 of this embodiment includes a reaction liquid supply port 31 and a reaction liquid jetting pipe 32. The reaction liquid supply port 31 corresponds to an introduction part (opening) for supplying the alkaline reaction liquid 15 into the inside of the apparatus main body 10. A reaction liquid return pipe 41 of a reaction liquid return unit 40, which will be described later, is connected to the reaction liquid supply port 31. However, the present invention is not limited to this example, and a configuration may also be adopted in which another pipe is connected to the reaction liquid supply port 31 and the reaction liquid return unit 40 is connected to the other pipe.

[0046] The reaction liquid injection pipe 32 is a pipe-shaped component extending toward the inside of the apparatus body 10, and is connected to the reaction liquid supply port 31. Like the gas distribution pipe 22, the reaction liquid injection pipe 32 has a longitudinal direction in the width direction of the apparatus body 10. The reaction liquid injection pipe 32 is provided with a plurality of injection holes 32a for injecting the alkaline reaction liquid 15 at predetermined intervals. The plurality of injection holes 32a are provided facing downward toward the apparatus body 10. The alkaline reaction liquid 15 that flows in from the reaction liquid supply port 31 passes through the reaction liquid injection pipe 32 and advances inside the apparatus body 10, and is injected into the inside of the apparatus body 10 from the plurality of injection holes 32a. The injection holes 32a are preferably nozzles that have the function of injecting the alkaline reaction liquid 15 in the form of a mist.

[0047] In this embodiment, before the biogas reforming apparatus 100 is operated, the alkaline reaction liquid 15 is stored in advance at the bottom of the apparatus main body 10, and once the apparatus is started, the alkaline reaction liquid 15 is supplied to the reaction liquid spraying unit 30 using the reaction liquid return unit 40. However, the present invention is not limited to this example, and the alkaline reaction liquid 15 may be supplied from another reaction liquid storage tank (not shown).

[0048] The reaction liquid return section 40 is a section that returns the alkaline reaction liquid 15 stored at the bottom of the device body 10 to the reaction liquid injection section 30. The reaction liquid return section 40 includes a reaction liquid return pipe 41 and a pump 42. As described above, the reaction liquid return pipe 41 is connected to the reaction liquid supply port 31, and supplies the alkaline reaction liquid 15 pumped up by the action of the pump 42 to the reaction liquid supply port 31. In this way, the alkaline reaction liquid 15 stored at the bottom of the device body 10 is returned to the reaction liquid injection section 30 through the reaction liquid return pipe 41 by the action of the pump 42, and is injected again from the reaction liquid injection pipe 32. In other words, the biogas reformer 100 of this embodiment is configured so that the alkaline reaction liquid 15 circulates between the inside of the device body 10 and the outside of the device body 10 (the reaction liquid return section 40).

[0049] The concentration adjusting unit 50 is a component for adjusting the concentration of the alkaline reaction solution 15 supplied to the device body 10. As will be described in detail later, in this embodiment, the alkaline reaction solution 15 supplied to the device body 10 has a reduced slaked lime content as the biogas reforming process progresses. In other words, the hydroxide ion concentration contained in the alkaline reaction solution 15 decreases, causing the pH value to drop. Therefore, the concentration adjusting unit 50 has a function of increasing the slaked lime content that decreases as the reforming process progresses, and adjusting the concentration so as to maintain the hydroxide ion concentration contained in the alkaline reaction solution 15 at a predetermined concentration.

[0050] The concentration adjusting unit 50 includes a tank body 51, an adjusting liquid supply pipe 52, a pump 53, a filter 54, and an adjusting liquid 55. The concentration adjusting unit 50 pumps up the adjusting liquid 55 stored inside the tank body 51 by the action of the pump 53, and supplies the adjusting liquid 55 to the reaction liquid spraying unit 30 via the adjusting liquid supply pipe 52. The adjusting liquid 55 is milk of lime that contains more slaked lime than the alkaline reaction liquid 15 supplied inside the apparatus body 10. The filter 54 is provided to filter out the slaked lime when the adjusting liquid 55 is pumped up by the adjusting liquid supply pipe 52.

[0051] In this embodiment, an example has been shown in which the adjustment liquid supply pipe 52 is connected to the reaction liquid return pipe 41 and the concentration is adjusted by mixing the adjustment liquid 55 into the alkaline reaction liquid 15 returned by the reaction liquid return unit 40, but the present invention is not limited to this example. Any other configuration may be adopted as long as it is possible to adjust the concentration by mixing the adjustment liquid 55 into the alkaline reaction liquid 15 supplied to the reaction liquid spray unit 30 at some timing.

[0052] The gas-liquid separation unit 60 is a section for removing moisture from the biogas that has been reformed. The gas-liquid separation unit 60 includes a first filter layer 61, a second filter layer 62, and a vibrating plate 63. Specifically, the gas-liquid separation unit 60 has a laminated filter structure in which the first filter layer 61 is disposed directly above the reaction liquid injection pipe 32, and the second filter layer 62 is disposed thereon. The vibrating plate 63 is disposed between the first filter layer 61 and the second filter layer 62, and applies vibrations to the adsorbent material (activated carbon in this embodiment) that constitutes the second filter layer 62, as will be described later.

[0053] The first filter layer 61 is a layer composed of a "filter material" generally called a demister. In this embodiment, a ball filter material is used as the demister, but this is not limited to this example, and other materials such as a composite corrugated sheet material can also be used. The ball filter material is a ball-shaped structure made of a plastic material or the like, and has the advantage of being less likely to clog due to its high porosity. Although not shown in the figures, the first filter layer 61 in this embodiment has a layered structure in which multiple ball filter materials are sandwiched between a net made of a material such as PVC. The first filter layer 61 mainly serves to separate the biogas that has been reformed inside the device main body 10 from the moisture contained in the biogas and return the separated moisture to the device main body 10.

[0054] The second filter layer 62 is a layer made of a filter material (for example, an adsorbent material such as activated carbon) having a lower porosity than the first filter layer 61. The second filter layer 62 mainly serves to separate NOx (nitrogen oxides) from the reformed biogas. Note that, although the present embodiment shows an example in which activated carbon is used as the second filter layer 62, the present invention is not limited to this example, and other adsorbents may also be used.

[0055] The vibrating plate 63 has the role of applying fine vibrations to the adsorbent that constitutes the second filter layer 62. The vibrating plate 63 is connected to a vibrating device 64. The vibrating device 64 has a drive source (not shown), such as a motor, and has the function of finely vibrating the entire vibrating plate 63. The vibrating plate 63 is also made of a fine mesh plate with openings of about 1 mm. In other words, the vibrating plate 63 also functions as a fall prevention means to prevent the adsorbent from falling downward.

[0056] As shown in Fig. 2, the vibrating plate 63 is attached at an angle. Specifically, the vibrating plate 63 is inclined so that the end of the vibrating plate 63 closer to the first transfer path 310 is positioned downward. Therefore, when the vibrating plate 63 vibrates, the adsorbent placed on the vibrating plate 63 gradually moves toward the first transfer path 310. In this way, the vibrating plate 63 functions as a transfer means for moving the adsorbent constituting the second filter layer 62 toward the first transfer path 310. The vibrating plate 63 also has the function of preventing the adsorbent constituting the second filter layer 62 from falling, and the function of passing the biogas that has passed through the first filter layer 61 to the second filter layer 62.

[0057] As described above, in this embodiment, the adsorbent activated in the fluidized bed incinerator 200 is transferred to the biogas reformer 100 via the second transfer path 320. As shown in Fig. 2, the adsorbent transferred via the second transfer path 320 is deposited on the second filter layer 62. That is, the second filter layer 62 in this embodiment is configured so that the more deteriorated adsorbent on the lower layer (adsorbent that is more likely to come into contact with biogas rising from below) is preferentially transferred to the fluidized bed incinerator 200 and activated, and the regenerated adsorbent is deposited on the upper layer.

[0058] In this case, the adsorbent in the lower layer comes into preferential contact with the biogas rising from below, so it is more likely to adsorb NOx but its adsorption capacity is also likely to decrease. However, because the NOx concentration in the biogas is high, the adsorption efficiency does not decrease significantly. On the other hand, the adsorbent in the upper layer comes into contact with biogas with a reduced NOx concentration, but because it is an activated adsorbent whose adsorption performance has been restored, it can efficiently adsorb even small amounts of NOx in the biogas. In this way, in this embodiment, nitrogen oxides such as NOx can be efficiently removed in the second filter layer 62.

[0059] The biogas reformer 100 having the structure described above can perform a reforming process in which carbon dioxide is removed from the biogas and the concentration of methane gas is increased by reacting the biogas supplied inside the device main body 10 with the alkaline reaction liquid 15. In controlling the biogas reformer 100, elements that require electronic control, such as valves (e.g., electromagnetic valves) and motors, can be controlled according to a predetermined sequence by a control unit (not shown).

[0060] Here, we will explain the reforming process by the biogas reformer 100. The biogas released into the inside of the device body 10 through the gas distribution pipe 22 rises inside the device body 10 as shown by the dashed arrow. At this time, the alkaline reaction liquid 15 sprayed downwards into the device body 10 through the reaction liquid spray pipe 32 turns into a mist and descends inside the device body 10. Therefore, inside the device body 10, the biogas containing carbon dioxide comes into contact with the alkaline reaction liquid 15 made of milk of lime (a solution containing calcium hydroxide), and calcium carbonate and water are produced by the following reaction: Ca(OH)2+CO2 → CaCO3+H2O

[0061] Since the calcium carbonate described above is a solid, most of it falls together with the alkaline reaction liquid 15 and is mixed into the alkaline reaction liquid 15 accumulated at the bottom of the device body 10. The mixed calcium carbonate (reactant) accumulates as a precipitate at the bottom of the device body 10. The reactant accumulated at the bottom of the device body 10 is periodically discharged via the reactant discharge pipe 92.

[0062] On the other hand, the biogas from which carbon dioxide has been removed by the above reaction rises as it is inside the device main body 10 as biogas with a high methane concentration. The rising biogas first comes into contact with the first filter layer 61 of the gas-liquid separation unit 60, where the moisture contained in the gas is separated. The moisture separated by the first filter layer 61 falls inside the device main body 10 and is returned to the alkaline reaction liquid 15 stored at the bottom of the device main body 10. The biogas from which moisture has been removed continues to rise and comes into contact with the second filter layer 62. In the second filter layer 62, the NOx components in the biogas are adsorbed and removed by the action of activated carbon. In this way, the biogas reformed by the above reaction formula passes through the gas-liquid separation unit 60, where moisture and NOx components are further removed, and the reformed biogas is sent to a downstream facility (such as a gas holder) via the gas exhaust pipe 91.

[0063] The alkaline reaction liquid 15 used in the above-described reforming process falls to the bottom of the apparatus main body 10 and is then returned to the reaction liquid injection unit 30 by the reaction liquid return unit 40 for reuse. Furthermore, as shown in the above reaction formula, the milk of lime contained in the alkaline reaction liquid 15 is consumed during the reforming process, and the slaked lime content of the alkaline reaction liquid 15 decreases over time. However, the biogas reforming apparatus 100 can replenish the lost slaked lime using the concentration adjustment unit 50, thereby appropriately maintaining the slaked lime content in the alkaline reaction liquid 15 (i.e., the concentration of hydroxide ions generated by dissolution of slaked lime). In this way, the biogas reforming apparatus 100 of this embodiment can be continuously operated while performing the biogas reforming process based on the above reaction formula.

[0064] As described above, the biogas reforming apparatus 100 of this embodiment can efficiently remove carbon dioxide from methane fermentation biogas containing methane gas and carbon dioxide, thereby producing biogas with an increased methane concentration. Such biogas with an increased methane concentration has a calorific value comparable to that of gas for 12A or 13A city gas standards, allowing for efficient energy recovery. Furthermore, this embodiment has the advantage that there is no need to prepare dedicated equipment to recover energy from biogas, and existing equipment for city gas applications (power generation equipment and gas appliances) can be used.

[0065] Furthermore, the biogas reforming apparatus 100 of this embodiment does not require a dedicated filter such as a decarbonation membrane used in membrane separation methods, or a high-pressure compressor, so there is also the advantage that the cost of the apparatus can be significantly reduced.

[0066] In addition, milk of lime also reacts with sulfur dioxide to produce calcium sulfite through the following reaction: Ca(OH)2+SO2 → CaSO3+H2O Calcium sulfite is easily removed because it becomes solid calcium sulfate through oxidation. In other words, inside the device body 10, it is possible to remove not only carbon dioxide but also SOx (sulfur oxides) contained in biogas.

[0067] [Configuration of fluidized bed incinerator 200] 3 is a schematic diagram showing the configuration of a fluidized bed incinerator 200 according to the first embodiment. The fluidized bed incinerator 200 is an apparatus equipped with a function of incinerating waste materials such as fermentation residues discharged from a bioreactor or the like that produces methane fermentation biogas. The main purpose of the fluidized bed incinerator 200 is to incinerate the waste materials to reduce their volume or render them harmless, or to use the combustion gas generated during incineration as a biogas boiler. However, in this embodiment, the fluidized bed incinerator 200 is also intended to be used as a regeneration means for activating the adsorbent used in the biogas reformer 100.

[0068] The fluidized bed incinerator 200 includes a furnace body 110, a waste inlet 120, a fluidized bed 130, an air diffuser 132, an incombustible material separator 140, an incombustible material discharge mechanism 141, a sand circulation mechanism 142, and a shielding plate 150. However, the configuration of the fluidized bed incinerator 200 is not limited to the configuration shown in the figure, and some of the components may be omitted or other components may be added. Furthermore, the mechanism for fluidizing the sand that constitutes the fluidized bed 130 is not limited to a configuration using an air diffuser 132, and other configurations may be used.

[0069] The furnace body 110 is a part corresponding to the housing of the fluidized bed incinerator 200, and corresponds to a combustion tower that performs waste incineration. A biogas supply pipe 112 is connected to the furnace body 110. The biogas supply pipe 112 supplies biogas reformed in the biogas reformer 100 to the inside of the furnace body 110 as auxiliary fuel. The reformed biogas may be supplied directly from the biogas reformer 100, or may be supplied from a biogas storage tank such as a gas holder.

[0070] The waste inlet 120 is a portion for introducing waste (processing material) to be incinerated into the furnace body 110. Although not shown in the figures, an introduction hopper may be provided at the end of the waste inlet 120.

[0071] The fluidized bed 130 is a layer made of sand such as silica sand, and is also called a fluidized bed because the sand moves like a fluid. The part of the furnace body 110 where the fluidized bed 130 is formed is sometimes called a fluidized bed section. Air supplied from the outside (fluidizing air) travels inside via the air diffuser 132 and is sprayed from injection holes (not shown) provided in the air diffuser 132. The air sprayed from the air diffuser 132 stirs up and agitates the sand, forming the fluidized bed 130. The waste is incinerated while flowing together with the sand inside the fluidized bed 130.

[0072] As described above, in this embodiment, the adsorbent transferred from the biogas reformer 100 via the first transfer path 310 is also supplied to the fluidized bed 130. The adsorbent supplied to the fluidized bed 130 is heated by high-temperature sand to a temperature of 500 to 700°C and activated.

[0073] The incombustible material separator 140 is connected to the lower end of the furnace body 110 and separates the incombustible material that falls from the bottom of the furnace body 110 into incombustible material as garbage and sand. In the fluidized bed 130, the input waste is incinerated, but the remaining incombustible material, such as metal, gradually moves downward and falls from an opening provided in the bottom of the furnace body 110. In the incombustible material separator 140, of the incombustible material that has fallen, the incombustible material that should be discharged as garbage is transferred to an incombustible material discharge mechanism 141, and the sand is transferred to a sand circulation mechanism 142.

[0074] The non-combustible material discharge mechanism 141 transports the non-combustible material received from the non-combustible material separator 140 to a waste tank or the like using a conveyor or the like. The sand circulation mechanism 142 transports the sand received from the non-combustible material separator 140 upward using a transport mechanism called a sand elevator or the like, and returns it to the inside of the furnace body 110 again.

[0075] The shielding plates 150 are provided so as to protrude from the inner wall of the furnace body 110 toward the center of the furnace, and are components that change the movement path of the primary combustion gas rising inside the furnace body 110. In this embodiment, an example is shown in which three shielding plates 150a to 150c are arranged inside the furnace body 110, but this is not limited to this example, and the number of shielding plates 150 to be arranged is arbitrary depending on the scale of the incinerator.

[0076] The primary combustion gas generated by the incineration of waste rises inside the furnace body 110 while entraining the activated adsorbent, but because multiple shielding plates 150a-150c are provided along the way, the gas rises while hitting each of the shielding plates 150a-150c. At this time, the primary combustion gas that collides with the shielding plate 150 forms a swirl (a swirling flow) directly below the shielding plate 150. This swirl causes the adsorbent that has been entrained in the primary combustion gas to fall and accumulate on the shielding plate 150 located below. In this embodiment, most of the adsorbent that has been lifted up by the primary combustion gas falls onto the shielding plate 150a.

[0077] Since the shielding plate 150a is positioned higher than the second transfer path 320, the adsorbent that falls onto the shielding plate 150a gradually accumulates on the shielding plate 150a and is eventually returned to the second filter layer 62 of the biogas reformer 100 via the second transfer path 320.

[0078] On the other hand, the primary combustion gas that passes through the shielding plate 150 and rises further is discharged to the outside through an exhaust pipe 114 connected to the top of the furnace body 110. The primary combustion gas that has been discharged to the outside is sent to a secondary combustion chamber or the like through the exhaust pipe 114.

[0079] (Variation 1) The biogas reformer 100 of this embodiment may have a cleaning means disposed between the first filter layer 61 and the second filter layer 62 for cleaning both of them. For example, a cleaning pipe configured to be rotatable in the longitudinal direction may be disposed between the first filter layer 61 and the second filter layer 62. In this case, by rotating the cleaning pipe while supplying cleaning water into the inside of the cleaning pipe, it becomes possible to continuously clean the first filter layer 61 and the second filter layer 62.

[0080] To rotate the cleaning pipe, a general bearing unit may be used to rotate the cleaning pipe, while a cleaning water supply pipe fixed inside the cleaning pipe is inserted. However, this is not limited to this example, and any cleaning mechanism may be provided as long as it is capable of cleaning both or either of the first filter layer 61 and the second filter layer 62.

[0081] (Variation 2) In the biogas reforming apparatus 100 of this embodiment, the biogas released from the gas distribution pipe 22 comes into contact with the alkaline reaction solution 15 falling from above as it rises, causing the alkaline reaction solution 15 containing calcium carbonate to rain down into the gas distribution pipe 22. In this case, there is a risk that the calcium carbonate adhering to the gas distribution pipe 22 will clog the discharge hole 22a. Therefore, the discharge hole 22a of the gas distribution pipe 22 may be arranged facing downward or to the side of the apparatus body 10. This configuration prevents the alkaline reaction solution 15 containing calcium carbonate falling from above from entering the inside of the gas distribution pipe 22 through the discharge hole 22a. In other words, calcium carbonate does not adhere to the inside of the gas distribution pipe 22, and clogging of the discharge hole 22a of the gas distribution pipe 22 can be prevented.

[0082] The biogas reformer 100 may further include a purge unit that performs air purging on the gas distribution pipe 22. Specifically, the purge unit may include a means for sending high-pressure air into the gas distribution pipe 22 and removing solid matter (calcium carbonate, etc.) adhering to the discharge hole 22a by air pressure.

[0083] As another means, it is also possible to provide a blade member such as a squeegee that moves on the surface of the gas distribution pipe 22. In this case, by periodically moving the blade member back and forth to remove solid matter adhering to the surface of the gas distribution pipe 22, it is possible to prevent the solid matter from becoming thicker near the discharge hole 22a and prevent the discharge hole 22a from becoming clogged.

[0084] The above-described embodiments (including modifications) of the present invention can be combined as appropriate as long as they are not mutually inconsistent. A person skilled in the art may add or delete components or modify designs, or add or omit processes or modify conditions based on the above-described embodiments, and these additions or deletions or modifications are included in the scope of the present invention as long as they include the gist of the present invention.

[0085] Furthermore, even if there are other effects and advantages different from those brought about by the above-described embodiments, if they are clear from the description in this specification or can be easily predicted by a person skilled in the art, they are naturally understood to be brought about by the present invention. [Explanation of symbols]

[0086] 10...Device body, 11...Side wall, 15...Alkaline reaction liquid, 20...Biogas supply section, 21...Gas supply port, 22...Gas distribution pipe, 22a...Discharge hole, 30...Reaction liquid injection section, 31...Reaction liquid supply port, 32...Reaction liquid injection pipe, 32a...Injection hole, 40...Reaction liquid return section, 41...Reaction liquid return pipe, 42...Pump, 50...Concentration adjustment section, 51...Tank body, 52...Adjusted liquid supply pipe, 53...Pump, 54...Filter, 55...Adjusted liquid, 60...Gas-liquid separation section, 61...First filter layer, 62...Second filter layer, 63...Vibration plate, 64...Vibration device, 81, 82...Valve, 91 ...Gas exhaust pipe, 92...Reactant exhaust pipe, 93...Gas supply pipe, 100...Biogas reforming device, 110...Furnace body, 112...Biogas supply pipe, 114...Exhaust pipe, 120...Waste inlet, 130...Fluidized bed, 132...Aeration pipe, 140...Non-combustible material separation device, 141...Non-combustible material discharge mechanism, 142...Sand circulation mechanism, 150, 150a to 150c...Shielding plate, 200...Fluidized bed incinerator, 310...First transfer path, 312...Double flap damper, 320...Second transfer path, 322...Double flap damper, 324...Exhaust fan, 500...Biogas reforming system

Claims

1. a biogas reformer having a filter layer containing an adsorbent; a fluidized bed incinerator connected to the biogas reforming apparatus via a first transfer path and a second transfer path; the first transfer path transfers the adsorbent from the biogas reformer to the fluidized bed incinerator; The second transfer path transfers the adsorbent from the fluidized bed incinerator to the biogas reformer.

2. The biogas reforming system according to claim 1, wherein the adsorbent transported to the fluidized bed incinerator by the first transport path is mixed into a bed material filled inside the fluidized bed incinerator.

3. The biogas reforming system according to claim 2 , wherein the adsorbent material transferred from the fluidized bed incinerator by the second transfer path is mixed into the filter layer of the biogas reforming system.

4. The biogas reforming system according to claim 1 , wherein the second flow path is provided at a position higher than the filter layer.

5. The biogas reforming system according to any one of claims 1 to 3, wherein the fluidized bed incinerator is provided with a shielding plate at a position higher than the second transfer path to change the movement path of the combustion gas.

6. The biogas reforming system according to claim 1 , wherein the biogas reformer further comprises a vibration plate disposed below the filter layer.

7. The biogas reforming system according to claim 6 , wherein the vibration plate is inclined downwards as it approaches the first transfer path.

8. The biogas reforming system according to claim 1 , wherein the biogas reforming device includes a reaction liquid injection unit that injects an alkaline reaction liquid into the inside of the device body.

9. The biogas reforming system according to claim 1 , wherein the first transfer path and the second transfer path have double flap dampers.

10. The biogas reforming system according to any one of claims 1 to 3, further comprising an exhaust fan connected to the second transfer path and configured to exhaust combustion gas generated inside the fluidized bed incinerator to the outside.

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