Methane gas generation apparatus and method

Abstract

Provided are a methane gas generation apparatus and a methane gas generation method with which it is possible to generate methane gas at a high concentration with higher efficiency than conventional means even when microorganisms are used.　This methane gas generation apparatus is for generating methane gas by supplying a hydrogen-containing gas A and a CO2-containing gas B to an anaerobic biological reaction tank T for carrying out microorganism treatment, and is characterized in that: a plurality of fixed beds (FB1, FB2) filled with a carrier to which microorganisms are adhered are arranged in the reaction tank T; the plurality of fixed beds are arranged in series with respect to the flow of a treatment gas in the reaction tank; a CO2 concentration measuring means S for measuring the concentration of CO2 contained in the treatment gas is provided between adjacent two of the fixed beds; and a hydrogen gas regulating means FC for regulating, on the basis of a measurement result of the CO2 concentration measuring means, the supply amount of a hydrogen-containing gas a to be supplied between said two fixed beds is included.

Description

Methane gas generation apparatus and method

[0001] The present invention relates to a methane gas generation apparatus and method, and more particularly to a hydrogen-containing gas and CO2 generation apparatus. ２ This invention relates to a methane gas production apparatus and method for producing methane gas by microbial treatment of contained gases.

[0002] In recent years, reducing and removing carbon dioxide, a major cause of global warming, has become a significant challenge. Since carbon dioxide is generated by the combustion of fossil fuels, its reduction, recovery, and reuse are required. Furthermore, biogas obtained through methane fermentation of organic wastewater, sewage sludge, organic waste, and food residues also contains carbon dioxide, making its removal necessary.

[0003] As a carbon dioxide removal and utilization technology, methanation technology, as shown in the following reaction equation (1), is already known. 4H ２ +CO ２ →CH ４ +2H ２ O・・・・・・・・・(1)

[0004] As shown in Patent Documents 1 and 2, a method for removing carbon dioxide and generating methane gas has already been disclosed that uses a catalyst and can achieve high methane production capacity under high pressure and high temperature conditions. However, such methods consume a large amount of energy, have high operating costs for the production system and equipment, and have poor durability.

[0005] In contrast, as shown in Patent Document 3, the above reaction (1) can also be carried out by the action of microorganisms. As shown in Figure 1, a liquid culture medium 10 containing microorganisms is placed inside the reaction vessel 1, and carbon dioxide and hydrogen gas are supplied as indicated by symbol C, and the liquid culture medium is supplied with air through the aeration means 2 inside the reaction vessel. In addition, a stirring blade MB is driven by a motor M to stir the suspended microorganisms and the liquid culture medium.

[0006] However, its methane production capacity is low and limited. For example, as shown in Patent Document 3, the maximum amount of methane gas generated per reactor is only about 10.8 L / L-Reactor / d (unit: amount of methane gas generated per liter in the reaction vessel per day), and the methane gas concentration in the processed gas discharged from the reaction vessel is also low, at about 55%. Microbial methanation reactions are greatly influenced by the microbial concentration, treatment conditions, especially the solubility and solubility rate of carbon dioxide and hydrogen gas in the reaction solution, and the diffusion rate to the microorganisms. For this reason, a stable and high methane production rate and the generation of high-concentration methane gas are major challenges in microbial methanation.

[0007] Patent Document 3 also proposes a method for producing methane gas using methane-producing bacteria immobilized on a carrier. For example, as shown in Figure 2, a fixed bed FB filled with a carrier to which microorganisms adhere is held in a reaction vessel T using a support net SN or the like. A discharge pipe ST is placed above the fixed bed, and a liquid containing nutrients for the microorganisms is supplied to the fixed bed. The liquid that falls from the fixed bed is stored in a liquid storage section LR located below the fixed bed. The symbol LQ indicates the liquid stored in the storage section LR. The liquid is circulated by a pump P in a circulating liquid line GL and supplied again to the fixed bed FB from the discharge pipe ST.

[0008] Carbon dioxide and hydrogen gas are supplied between the fixed bed FB and the liquid LQ stored in the liquid storage section LR, as indicated by symbol C. They are treated by microorganisms as they pass through the fixed bed FB, converted into a process gas containing methane, and discharged from the reaction vessel T as indicated by symbol E. Even in a methane gas generator using such a fixed bed, as in the case of Figure 1, the process gas contains a large amount of untreated carbon dioxide and hydrogen gas, making it a major challenge to achieve a stable, high methane production rate and the generation of high-concentration methane gas.

[0009] In Patent Document 4, the applicant disclosed a methane gas generation apparatus and method, including carbon dioxide removal, that can generate high-concentration methane gas with high efficiency even when using microorganisms. Specifically, as shown in Figure 3, hydrogen-containing gas A and CO ２A methane gas production apparatus comprising carbon dioxide removal, in which a gas B containing carbon dioxide is supplied (indicated by reference sign C) to an anaerobic biological reaction tank T that performs microbial treatment, and a processing gas E containing methane gas is discharged, wherein the reaction tank T is provided with a fixed bed FB filled with a carrier to which microorganisms adhere, and has a circulating gas line that circulates (indicated by reference sign D) at least a part of the processing gas E to the reaction tank. Reference sign BL indicates a blower (gas blower), reference sign F indicates replenishment of a liquid containing nutrient sources for microorganisms, and reference sign G indicates a discharge route for a part of the liquid.

[0010] In the methane gas production apparatus using circulating gas, a methane conversion rate of 90% or higher has been achieved, but many users expect the provision of a methane gas production apparatus and method that can reduce the proportion of carbon dioxide remaining in the processed gas to, for example, 1% by volume or less, and achieve a higher methane conversion rate (for example, 95% or higher).

[0011] Japanese Patent No. 5562873, Japanese Patent No. 6956665, Japanese Patent Publication No. Sho 63-49999, International Publication WO2024 / 034541A1

[0012] The problem to be solved by the present invention is to solve the above-mentioned problems and provide a methane gas production apparatus and method capable of producing high-concentration methane gas with higher efficiency even when microorganisms are used.

[0013] In order to solve the above problems, the methane gas production apparatus and method of the present invention have the following features. (1) A methane gas production apparatus that produces methane gas by supplying a hydrogen-containing gas and a CO ２ 2-containing gas to an anaerobic biological reaction tank that performs microbial treatment, wherein a plurality of fixed beds filled with a carrier to which microorganisms adhere are arranged in the reaction tank, the plurality of fixed beds are arranged in series with respect to the flow of the processing gas in the reaction tank, and between two adjacent fixed beds, CO contained in the processing gas ２ 2 concentration is measured by a CO ２ 2 concentration measuring means is provided, and the CO ２ 2 concentration measuring means, characterized by comprising hydrogen gas adjusting means for adjusting the supply amount of the hydrogen-containing gas supplied between the two fixed beds based on the measurement result of the 2 concentration measuring means.

[0014] (2) The methane gas generating apparatus described in (1) above is provided with a gas flow rate measuring means for measuring the flow rate of the processed gas passing between the two adjacent fixed beds, and the gas flow rate measuring means and the CO ２ The hydrogen gas adjustment means is controlled based on the measurement results of the concentration measuring means.

[0015] (3) The methane gas generating apparatus described in (1) above is characterized in that a portion of the processed gas discharged from the reaction tank or a portion of the processed gas at an intermediate stage of processing in the reaction tank is extracted and circulated to the reaction tank located upstream of the flow of the processed gas from the extraction point.

[0016] (4) In the methane gas generating apparatus described in any of (1) to (3) above, the reaction vessel is made up of a single container, and the plurality of fixed beds are arranged vertically inside the container.

[0017] (5) The methane gas generating apparatus described in (4) above is characterized in that a pressure regulating device is provided in the piping that discharges the processed gas from the container to maintain the gas pressure inside the container within a predetermined range.

[0018] (6) In the methane gas generating apparatus described in any of (1) to (3) above, the reaction vessel is composed of a plurality of containers, the fixed bed is placed in each of the containers, and the plurality of containers are connected by gas flow paths so that the processed gas passes through them sequentially.

[0019] (7) A methane gas generating apparatus as described in (6) above, characterized in that at least one of the plurality of containers is equipped with a pressure regulating device in the piping that discharges the processed gas from the container, for maintaining the gas pressure inside the container within a predetermined range.

[0020] (8) Hydrogen-containing gas and CO ２ In a methane gas production method in which a contained gas is supplied to an anaerobic biological reactor for microbial treatment to produce methane gas, a plurality of fixed beds filled with carriers to which microorganisms adhere are arranged in the reactor, and CO2 contained in the treated gas is introduced into the treated gas as it passes through the plurality of fixed beds. ２ The concentration is measured, and the CO２ The method is characterized by adjusting the amount of hydrogen-containing gas supplied to the processed gas based on the concentration measurement results.

[0021] (9) In the methane gas production method described in (8) above, the flow rate of the processed gas is measured, and the flow rate of the processed gas and the CO ２ The method is characterized by controlling the supply amount of the hydrogen-containing gas based on the concentration measurement results.

[0022] (10) The methane gas production method described in (8) above, characterized in that a portion of the processed gas discharged from the reaction tank or a portion of the processed gas at an intermediate stage of the treatment in the reaction tank is extracted and circulated to the reaction tank located upstream of the flow of the processed gas from the extraction point.

[0023] (11) In the methane gas production method described in any of (8) to (10) above, the amount of hydrogen contained in the hydrogen gas supplied to the first fixed bed among the plurality of fixed beds is the CO ２ CO2 contained in the gas ２ The molar ratio (A) of the supply amount is set to be greater than 4.

[0024] (12) In the methane gas production method described in (11) above, in the process of the process gas passing through the plurality of fixed beds, the amount of hydrogen supplied to the hydrogen-containing gas supplied to the process gas and the amount of CO contained in the process gas ２ The molar ratio (B) of the remaining amount is set to be greater than the molar ratio (A).

[0025] According to the present invention, hydrogen-containing gas and CO ２ In a methane gas generation apparatus and method for supplying a contained gas to an anaerobic biological reactor for microbial treatment and generating methane gas, a plurality of fixed beds filled with carriers to which microorganisms adhere are arranged in the reactor, and CO contained in the treatment gas is introduced into the treatment gas as it passes through the plurality of fixed beds. ２ The concentration is measured, and the CO ２ Based on the concentration measurement results, the amount of hydrogen-containing gas supplied to the treatment gas is adjusted, thereby reducing the amount of CO contained in the treatment gas discharged from the reaction vessel. ２It is possible to extremely reduce the concentration and further increase the methane conversion rate.

[0026] It is a diagram illustrating a conventional methane gas generator. It is a diagram illustrating an example of a methane gas generator using a fixed bed. It is a diagram illustrating an example of a methane gas generator according to Patent Document 3. It is a diagram showing a first embodiment of the methane gas generator according to the present invention. It is a diagram showing a second embodiment of the methane gas generator according to the present invention. It is a diagram showing a third embodiment of the methane gas generator according to the present invention. It is a diagram showing a fourth embodiment of the methane gas generator according to the present invention. It is a diagram showing a fifth embodiment of the methane gas generator according to the present invention. It is a diagram showing a sixth embodiment of the methane gas generator according to the present invention. It is a diagram showing a seventh embodiment of the methane gas generator according to the present invention.

[0027] Hereinafter, the methane gas generator and the method of the present invention will be described in detail with reference to FIGS. 4 to 10. To simplify the description, the following description will focus on the methane gas generator. As shown in FIG. 4, the present invention provides a hydrogen-containing gas A and CO ２ In a methane gas generator that supplies the contained gas B to an anaerobic biological reaction tank T for microbial treatment to generate methane gas, a plurality of fixed beds (FB1, FB2) filled with a carrier to which microorganisms adhere are arranged in the reaction tank T, the plurality of fixed beds are arranged in series with respect to the flow of the processing gas in the reaction tank, and between two adjacent fixed beds, CO contained in the processing gas ２ CO for measuring the concentration of ２ comprising a concentration measuring means S, the CO ２ It is characterized by comprising a hydrogen gas adjusting means FC that adjusts the supply amount of the hydrogen-containing gas a supplied between the two fixed beds based on the measurement result of the concentration measuring means.

[0028] As long as the gas B contains carbon dioxide gas, it can be supplied to the anaerobic biological reaction tank T for treatment. Biogas obtained by methane fermentation of organic wastewater, organic sludge or the like may be used as the gas B. Carbon dioxide (exhaust gas) generated by combustion from factories, thermal power plants and the like may also be used.

[0029] Gas A, as long as it contains hydrogen gas, can be supplied to and used in the anaerobic biological reactor T. Hydrogen gas obtained by electrolysis of water using renewable energy such as solar or wind power, or surplus nighttime electricity from power plants, may be used as Gas A. Alternatively, hydrogen gas generated as a by-product from factory production processes may also be used.

[0030] CO ２ Gas B, which contains gas A, and gas A, which contains hydrogen, are supplied to the anaerobic biological reactor T, and therefore preferably do not contain oxygen. Furthermore, as methods for supplying these gases to the reactor T, there are methods such as supplying a mixed gas C, which is a mixture of gas A and gas B, to the reactor, as shown in Figure 3, or supplying gas A and gas B separately, as shown in Figure 4.

[0031] When supplying gases A and B into the reaction vessel T, they can be supplied between the fixed bed FB1 and the liquid storage section LR, as shown in Figure 2, or, as shown in Patent Document 4, the fixed bed can be divided into multiple fixed beds (fixed bed units), and gas B, etc., can be supplied between adjacent fixed beds. Hereinafter, the entire fixed bed will be referred to as "fixed bed FB," and a specific fixed bed unit will be referred to as "fixed bed FB1," etc. Furthermore, as shown in Figures 3 and 4, it is also possible to place aeration means AD, such as a diffuser pipe, at the bottom of the reaction vessel T and aerate the liquid LQ containing the nutrient source stored in the liquid storage section LR. This makes it possible to mix and stir the liquid LQ, or to atomize a portion of the liquid LQ and supply nutrients to the microorganisms in the fixed bed FB together with gases A and B. Of course, aeration means corresponding to the mixed gas C may be provided, or aeration means corresponding to gas A or B, respectively.

[0032] When injecting gas A and gas B separately into the reaction vessel, CO ２It is preferable that the injection point for gas B containing CO is in the gas phase section where the carrier is filled (particularly the space between the fixed bed T and the liquid storage section LR). It is preferable that the injection point for gas A containing hydrogen is in the liquid storage section LR of the circulating fluid. It is preferable that both gas A and gas B are supplied through diffusers (for example, AD, ADM1-2 in Figure 4). Supplying through diffusers results in a uniform gas flow in the reaction vessel, a uniform frequency of contact with the carrier, and high reaction efficiency. ２ Since CO2 is easily soluble in water, when supplying gas B to the gas phase, as shown in Figure 4, the gas diffuser ADM1 for gas B is positioned close to the lower surface of the fixed bed FB1 (the support net SN that supports the fixed bed). As will be described later, if a circulating gas line is provided in the methane gas generation apparatus or method, the circulating gas may be introduced into the reaction vessel T together with gas B containing CO2, or it may be introduced into the reaction vessel separately using a gas diffuser for the circulating gas.

[0033] As the aeration means AD, it is preferable to use a microbubble aeration device with high gas dissolution efficiency. A large number of microbubbles allows for the generation of more mist from the liquid LQ, which promotes the methane production reaction by microorganisms. Similar effects can be obtained using any of the microbubble aeration devices, such as membrane type, ceramic type diffuser, or ejector type. In the case of membrane or ceramic type devices, the smaller the surface pore size, the smaller the generated gas bubbles, making it possible to generate a fine mist that can easily diffuse into the interior of the fixed bed FB. Also, when the gas bubbles are small, the efficiency of dissolving a portion of the gas in the liquid LQ increases, and when the liquid LQ is circulated and supplied to the fixed bed FB, the dissolved gas can also be supplied to the microorganisms. A surface pore size of 30 μm or less is desirable.

[0034] In the case of ejectors and the like, since they generate microbubbles physically, it is preferable that the microbubble pore diameter is 30 μm or less. Furthermore, if the aeration means can produce microbubbles or nanobubbles, it is possible to generate fine mist and dissolve hydrogen, etc., with even greater efficiency, resulting in an improvement in methane production efficiency. These aeration means can also be applied to aeration means ADM1-2.

[0035] The fixed bed FB of the anaerobic biological reactor T contains microorganisms, mainly methane-producing bacteria, that react carbon dioxide gas and hydrogen gas to convert them into methane gas. As methane-producing bacteria, bacteria derived from digested sludge can be used, and it is desirable to use hydrogen-assimilating methane-producing bacteria that can produce methane from hydrogen and carbon dioxide. Specifically, *Methanobacterium thermoautotrophicum* and *Methanobacterium formicicum* of the genus *Methanobacterium*, *Methanococcus vanielii* of the genus *Methanococcus*, or *Methanosaricina barkerii* of the genus *Methanosaricina* are suitably usable.

[0036] A carrier is used to retain microorganisms. It is preferable to use a hydrophilic carrier that readily accommodates hydrogen-utilizing methane-producing bacteria. To ensure stable attachment of the methane-producing bacteria to the carrier surface, it is effective to pre-soak the carrier in anaerobic digested sludge. Furthermore, a polymer carrier that is not decomposed by microorganisms and is hydrophilic to which the hydrogen-utilizing methane-producing bacteria readily adhere is preferred. Examples of polymer carriers include rigid carriers made of polyethylene, polyurethane, polypropylene, etc., synthetic polymers such as polyethylene glycol (PEG), polyvinyl alcohol (PVA), polyacrylamide, polycarbonate, and photocurable resins, and gel carriers using polymers such as carrageenan and sodium alginate.

[0037] The carrier can be spherical, square, cylindrical, or tubular in shape. The effective diameter should be 5 to 20 mm, preferably 10 to 15 mm, to ensure stable separation from the support mesh. The specific surface area of ​​the carrier should be 100 to 5,000 m². ２ / m ３ It is preferable to do so.

[0038] Supports with a large number of micropores on their surface, those with a hollow interior, those with countless irregularities on their surface, and those impregnated with powdered activated carbon allow for rapid attachment and fixation of methanogenic bacteria, resulting in high concentrations of methanogenic bacteria attachment in a short period of acclimatization culture. Furthermore, because high concentrations of methanogenic bacteria can be attached and fixed to the support surface in the reaction vessel for extended periods, stable methane conversion performance can be obtained.

[0039] The specific gravity of the carrier is preferably around 0.9 to 1.0 so as not to cause overloading even when a large amount is packed into the biological reaction vessel. The height (thickness in the height direction) of the carrier layer (fixed bed) packed into the reaction vessel is 1 to 10 m, preferably 3 to 5 m.

[0040] A fixed bed is constructed by filling and fixing a carrier. For example, a large number of carriers are placed inside a mesh-like frame and then placed on a support net SN provided at a predetermined position in the reaction vessel. As shown in Figure 4, it is also possible to construct the fixed bed by dividing it into multiple fixed bed units (FB1-FB2). The higher the carrier filling rate in the biological reaction vessel, the greater the amount of carrier per unit volume of the biological reaction vessel, and the greater the amount of microorganisms that can adhere to and be fixed to the carrier, resulting in high processing performance. On the other hand, considering the homogenization of gas flow within the biological reaction vessel and gas mixing in the gas layer, the carrier filling rate should be 60-80V%, preferably 50-70V%.

[0041] Anaerobic biological reactors can be rectangular or cylindrical in shape. A cylindrical shape is preferable considering the uniformity of the packing material and the flow of the supply gas. In the case of a cylindrical shape, the packing material can be packed almost uniformly, and the flow of the supply gas is uniform throughout.

[0042] A liquid containing nutrients for microorganisms is supplied to the fixed bed FB. The liquid can be continuously or intermittently supplied from the liquid storage section LR to the circulating liquid line GL by a circulating liquid pump P. Water is sprayed from the top of the fixed bed FB2 from a liquid supply means ST such as a spray pipe, and uniformly contacts the carrier layer packed in the fixed bed. As a result, nutrients in the liquid are supplied to the microorganisms on the carrier surface (the biofilm covering the carrier surface), allowing the activity of the microorganisms to be kept high and a stable methane production rate to be obtained. In the initial stages of the system's startup, when sufficient microorganisms have not yet adhered to the surface of the packed carrier, it is necessary to introduce seed sludge, such as sewage digested sludge containing methane-producing bacteria or digested sludge from organic waste treated with methane fermentation, into the liquid storage section LR in advance to allow methane-producing bacteria to adhere to the carrier surface.

[0043] The more seed sludge introduced into the LR liquid storage section during startup, the greater the amount of sludge adhering to the carrier surface, allowing for a shorter startup time. On the other hand, if the amount of seed sludge introduced is excessive, a large amount of sludge will accumulate not only on the carrier surface but also in the gaps between the packed carriers, causing localized blockages. This prevents the supplied hydrogen and carbon dioxide gases from flowing uniformly and making contact with the carrier surface, resulting in unstable treatment performance.

[0044] The amount of seed sludge to be added at startup needs to be determined considering the carrier packing amount, carrier shape, and packing rate, but generally, 0.5 to 5 g, preferably 0.5 to 2.5 g, of seed sludge is added per liter of carrier packing amount. The SS concentration of the liquid to which the seed sludge is added at startup should be 2,500 to 15,000 mg / L, preferably 2,500 to 10,000 mg / L. If the SS concentration (suspended solids concentration) is high, sludge may accumulate in the packed carrier layer, potentially leading to blockage of the liquid and supply gas flow paths. Therefore, if the SS concentration of the digested sludge used as seed sludge is high, it is preferable to dilute it with treated wastewater or the like.

[0045] The flow rate of the circulating liquid should preferably be set considering the volume of the packed carrier layer. Typically, the daily flow rate of the circulating liquid should be 2 to 20 times, preferably 5 to 10 times, the volume of the packed carrier. If the flow rate of the circulating liquid is too low, the contact between the microorganisms attached to the surface of the packed carrier and the liquid will not be uniform, making it impossible to stably supply the microorganisms with nutrients from the liquid. This reduces the activity of the microorganisms and prevents a stable methane production rate from being obtained. For this reason, it is important to maintain an appropriate flow rate of the circulating liquid.

[0046] This liquid contains nutrients for microorganisms (methane-producing bacteria) as shown in Table 1.

[0047]

[0048] The methane gas production apparatus and method according to the present invention are characterized in that, as shown in Figure 4, a plurality of fixed beds (FB1-FB2) filled with carriers to which microorganisms adhere are arranged in the reaction tank T, the plurality of fixed beds are arranged in series with respect to the flow of the treatment gas in the reaction tank, and CO2 contained in the treatment gas is placed between two adjacent fixed beds. ２ Measuring the concentration of CO２ The CO is equipped with a concentration measuring means (S), ２ The device has a hydrogen gas adjustment means (FC) that adjusts the amount of hydrogen-containing gas (a) supplied between the two fixed beds based on the measurement results of a concentration measuring means.

[0049] The supply amounts of gases A and B to be introduced into reaction vessel T are determined by the amount of hydrogen gas contained in gas A and carbon dioxide (CO2) contained in gas B. ２ The gas is supplied such that the above-mentioned chemical formula (1) holds true. Ideally, the molar ratio of "hydrogen gas:carbon dioxide gas" is 4:1. However, the actual supply amount is determined by the amount of hydrogen supplied in hydrogen-containing gas A supplied to the first fixed bed (FB1) and the CO2. ２ CO2 contained in the gas ２ The molar ratio of hydrogen to the supply is set to be greater than 4. This is because, in addition to producing methane gas, microorganisms also produce hydrogen sulfide if sulfur "S" is present, as shown in Table 1, meaning that hydrogen gas is used for purposes other than methanation. For this reason, the supply of hydrogen gas needs to be more than four times that of carbon dioxide.

[0050] On the other hand, if the supply of hydrogen gas is too high, the volume fraction of carbon dioxide in the total gas decreases, and the frequency of carbon dioxide contact with microorganisms decreases. As a result, the efficiency of conversion to methane gas actually decreases. For this reason, the supply amount of hydrogen gas to carbon dioxide should be greater than four times in molar ratio, preferably four to six times, and more preferably 4.1 to 4.5 times.

[0051] However, actual experiments revealed that even when supplying more hydrogen gas than four times the amount of carbon dioxide (molar ratio), several percent of carbon dioxide remained in the processed gas, making it difficult to achieve a 100% methane conversion rate. On the other hand, the remaining amount of hydrogen gas in the processed gas was close to 0%. Therefore, when more hydrogen gas was supplied, not only did more hydrogen gas remain, but the amount of remaining carbon dioxide also increased. This is presumed to be because the increase in hydrogen gas reduced the frequency of contact between microorganisms and carbon dioxide, thereby decreasing the conversion efficiency to methane gas per unit volume of the fixed bed.

[0052] Therefore, the methane gas generation apparatus and method of the present invention are configured such that the process gas passes through a plurality of fixed beds, and at an intermediate stage, the carbon dioxide (CO2) contained in the process gas is removed. ２ The system measures the concentration of hydrogen gas and supplies additional hydrogen gas as needed.

[0053] The amount of additional hydrogen gas supplied is set to satisfy the following condition (2): FLH = SC × FLT × α .... (2) where FLH is the flow rate of the additional hydrogen gas (liters / minute, L / min), SC is the carbon dioxide concentration (volume %), FLT is the flow rate of the processed gas (L / min), and α is the coefficient.

[0054] The flow rate FLT of the process gas may be calculated by substituting a predetermined value, or, as shown in Figure 6 later, a means FM for measuring the flow rate of the process gas may be provided and its value may be used. The coefficient α is greater than 4, taking chemical formula (1) into consideration. The coefficient α varies depending on at which stage of the multiple fixed beds hydrogen gas is added. Generally, at stages close to the first fixed bed, it will be close to the molar ratio (A) of hydrogen gas to carbon dioxide gas introduced into the first fixed bed, but at stages close to the last fixed bed, in order to completely convert carbon dioxide gas to methane gas, it is set to a larger value, for example, 5 to 20 times, preferably in the range of 4.5 to 10 times. As a result, the coefficient α will be greater than the above molar ratio (A). Note that increasing the amount of hydrogen gas supplied will increase the amount of hydrogen gas contained in the process gas E, but even if the coefficient α is large, at stages close to the last fixed bed, the carbon dioxide concentration SC is also small, and the amount of hydrogen gas supplied is also relatively small. Therefore, the coefficient α is set within a range where the concentration of hydrogen gas contained in the processed gas E is 5 (volume) or less, preferably 4 or less, and more preferably 3 or less.

[0055] The above equation (2) can also be transformed into the following equation (3) if the hydrogen gas concentration in the process gas at the point where additional hydrogen gas is supplied can be measured: FLH = SC × FLT × α - SH × FLT ....(3) where SH is the hydrogen gas concentration in the process gas (volume %). Naturally, in the final stage near the fixed bed, the hydrogen gas concentration SH will be close to 0%.

[0056] A key feature of the methane gas generation apparatus of the present invention, as shown in Figure 4, is the placement of a pressure regulating device PR in the piping at the outlet of the vessel constituting the reaction tank (piping for discharging the processed gas from the vessel) to maintain the gas pressure inside the vessel within a predetermined range.

[0057] The methane production (methanation) reaction is a chemical reaction that involves a decrease in gas volume before and after the reaction, and therefore the gas flow rate in the reaction vessel tends to decrease as the reaction progresses. For this reason, if the pressure of the incoming gas or the pressure inside the reaction vessel is unstable, temporary backflow or localized flow velocity fluctuations may occur in the gas flow path. Therefore, by installing a pressure regulating device downstream of the reaction vessel, pressure fluctuations inside the reaction vessel can be mitigated, the occurrence of backflow and flow velocity fluctuations can be suppressed, and the methane production reaction can proceed stably and efficiently.

[0058] Known technologies can be used as pressure regulating devices, and for example, configurations such as water seal structures, overflow type water seal devices, hydraulic tanks, mechanical pressure regulators, and buffer tanks can be employed.

[0059] As shown in Figure 4, the reaction vessel may consist of a single container, or as shown in Figure 8, it may consist of multiple containers. The pressure regulating device can be installed in the piping that discharges the processed gas from each container. In particular, as in the present invention, in containers that supply additional hydrogen, pressure fluctuations are likely to occur in the reaction vessel, so it is preferable to install a pressure regulating device. Furthermore, when the reaction vessel consists of a combination of multiple containers, it is possible to install a pressure regulating device in each container or in the downstream container, but it is also possible to limit the number of containers to those where the methanation reaction proceeds most and install the pressure regulating device there.

[0060] Figure 5 shows an embodiment in which multiple steps are provided for adding hydrogen gas. At each step of adding hydrogen gas, the carbon dioxide concentration (S1, S2) is measured individually, and the hydrogen gas flow rate is adjusted using the above-described equation (2) or (3). The coefficients α that control each flow rate adjustment means (FC1, FC2) may be the same, but are usually different, and the relationship between the coefficient α1 of the flow rate adjustment means FC1 and the coefficient α2 of the flow rate adjustment means is α1 < α2.

[0061] Figure 6 shows an example in which a gas flow rate measuring means FM is provided to directly measure the flow rate of the processed gas during the hydrogen gas addition stage. The value of the gas flow rate measuring means FM is substituted into the flow rate of the processed gas FLT (L / min) in the above formula (2) or (3). In the methane gas generation apparatus of the present invention, the values ​​of various measuring means (sensors), such as the carbon dioxide concentration measuring means, are collected by a control device CU, which is composed of a computer or the like, as shown in Figure 6, to calculate the amount of hydrogen gas to be supplied and to control the hydrogen gas flow rate adjustment means FC. In addition to Figure 6, although not shown, it is also possible to control the hydrogen gas flow rate adjustment means using the control device in a similar manner.

[0062] Figure 7 shows an application of the circulating gas technology disclosed in Patent Document 4. In Figure 7, a portion D of the processed gas discharged from the reaction tank T is supplied to the upstream side of the initial fixed bed FB1. The methane gas generator of the present invention is not limited to this configuration, and various circulating gas line configurations, as disclosed in Patent Document 4, can be adopted. For example, a portion of the processed gas can be extracted from an intermediate stage of processing in the reaction tank T (between the fixed beds FB1 and FB2) and circulated to a reaction tank located upstream of the extraction point (upstream of the fixed bed FB1). For circulation, a blower (gas blower) BL can be used to forcibly circulate the gas.

[0063] The reaction vessel T may consist of a single container as shown in Figures 4 to 7, with multiple fixed beds (FB1, etc.) arranged vertically within it. Alternatively, as shown in Figures 8 to 10, the reaction vessel may consist of multiple containers (T1, etc.), with a fixed bed (FB1, etc.) placed in each of these containers, and the multiple containers may be connected by gas channels so that the processing gas (E1, etc.) passes through them sequentially.

[0064] Figure 8 shows a reaction vessel composed of two containers (T1, T2), with the processed gas E1 discharged from the first reaction vessel T1 being introduced into the aeration means ADM2 of the second reaction vessel T2. The carbon dioxide concentration measuring means may be provided on the upper side of the first reaction vessel T1, or it may be provided in the middle of the gas flow path of the processed gas E1 as indicated by symbol S'. In addition, the hydrogen gas a to be supplied can be supplied by joining the gas flow path of the processed gas E1, or it may be supplied through a separate aeration means provided in the liquid storage section LR2, such as the aeration means AD of the first reaction vessel T1.

[0065] The liquid LQ from liquid storage sections LR1 and LR2 may be returned to the liquid supply means ST provided in each reaction vessel, as shown in Figure 3, or, as shown in Figure 8, the liquid from each liquid storage section LR1 and LR2 may be collected in a single liquid storage tank and supplied to the liquid supply means ST of each reaction vessel with the same liquid in the same state using supply lines (L1, L2).

[0066] Figure 9 shows an example in which a reaction vessel is formed using three containers (T1-T3). Figure 10 shows an example in which each reaction vessel is provided with a circulating gas line (D1-D3). Various modifications can be made to the circulating gas line by referring to Patent Document 4, for example, it is possible to supply a portion of the processed gas (D3) discharged from the last reaction vessel T3 to the upstream side of the first reaction vessel T1.

[0067] The methane gas generator of the present invention includes NH as shown in Patent Document 4. ３ Needless to say, removal means (removal devices) and gas separation means (separation devices) can also be used in combination.

[0068] The above explanation mainly described an example in which the raw material gas is introduced from the bottom of the container and the processed gas is discharged from the top of the container, as is done when constructing a reaction vessel. However, it is not limited to this, and the raw material gas may be introduced from the top of the container and discharged from the bottom of the container. However, when injecting gas into the liquid storage section LR, it is necessary to supply the raw material gas from the bottom of the container.

[0069] As described above, the present invention provides a methane gas generation apparatus and method that can generate high-concentration methane gas with higher efficiency than conventional methods, even when using microorganisms.

[0070] T, T1-3 Anaerobic biological reactor AD, ADM1-3 Aeration means LR, LR1-3 Liquid storage section FB, FB1-3 Fixed bed PR Pressure regulator A, a Gas containing hydrogen B Gas containing carbon dioxide D, D1-3 Circulating gas E, E1-3 Processed gas

Claims

1. Hydrogen-containing gas and CO ２ In a methane gas generator that supplies a contained gas to an anaerobic biological reactor for microbial treatment and produces methane gas, a plurality of fixed beds filled with carriers to which microorganisms adhere are arranged in the reactor, the plurality of fixed beds are arranged in series with respect to the flow of the treatment gas in the reactor, and between two adjacent fixed beds, the CO contained in the treatment gas ２ Measuring the concentration of CO ２ Equipped with a means for measuring concentration, the CO ２ A methane gas generator characterized by having a hydrogen gas adjustment means that adjusts the amount of hydrogen-containing gas supplied between the two fixed beds based on the measurement results of a concentration measuring means.

2. The methane gas generating apparatus according to claim 1, comprising a gas flow rate measuring means for measuring the flow rate of the processed gas passing between the two adjacent fixed beds, the gas flow rate measuring means and the CO ２ A methane gas generating apparatus characterized by controlling the hydrogen gas adjustment means based on the measurement results of the concentration measuring means.

3. A methane gas generating apparatus according to claim 1, characterized in that a portion of the processed gas discharged from the reaction tank or a portion of the processed gas at an intermediate stage of processing in the reaction tank is extracted and circulated to the reaction tank located upstream of the flow of the processed gas from the extraction point.

4. A methane gas generating apparatus according to any one of claims 1 to 3, characterized in that the reaction vessel is composed of a single container, and the plurality of fixed beds are arranged vertically inside the container.

5. A methane gas generating apparatus according to claim 4, characterized in that a pressure regulating device for maintaining the gas pressure inside the container within a predetermined range is arranged in the piping that discharges the processed gas from the container.

6. A methane gas generating apparatus according to any one of claims 1 to 3, characterized in that the reaction tank is composed of a plurality of containers, the fixed bed is arranged in each of the containers, and the plurality of containers are connected by gas flow paths so that the processed gas passes through them sequentially.

7. A methane gas generating apparatus according to claim 6, characterized in that at least one of the plurality of containers is provided with a pressure regulating device in the piping for discharging the processed gas from the container, for maintaining the gas pressure inside the container within a predetermined range.

8. Hydrogen-containing gases and CO ２ In a methane gas production method in which a contained gas is supplied to an anaerobic biological reactor for microbial treatment to produce methane gas, a plurality of fixed beds filled with carriers to which microorganisms adhere are arranged in the reactor, and CO2 contained in the treated gas is introduced into the treated gas as it passes through the plurality of fixed beds. ２ The concentration is measured, and the CO ２ A method for producing methane gas, characterized by adjusting the amount of hydrogen-containing gas supplied to the processed gas based on the concentration measurement results.

9. The method for producing methane gas according to claim 8, wherein the flow rate of the process gas is measured, and the flow rate of the process gas and the CO ２ methane gas production method characterized by controlling the supply amount of the hydrogen-containing gas based on a concentration measurement result.

10. A method for producing methane gas according to claim 8, characterized in that a portion of the processed gas discharged from the reaction tank or a portion of the processed gas at an intermediate stage of processing in the reaction tank is extracted and circulated to the reaction tank located upstream of the flow of the processed gas from the extraction point.

11. In the methane gas production method according to any one of claims 8 to 10, the amount of hydrogen contained in the hydrogen-containing gas supplied to the first fixed bed among the plurality of fixed beds is the CO2 ２ CO2 contained in the gas ２ A method for producing methane gas, characterized in that the molar ratio (A) of the supply amount is set to be greater than 4.

12. In the methane gas production method according to claim 11, the amount of hydrogen supplied to the hydrogen-containing gas supplied to the treatment gas, and the amount of CO2 contained in the treatment gas, along the way the treatment gas passes through the plurality of fixed beds. ２ A method for producing methane gas, characterized in that the molar ratio (B) of the remaining amount is set to be greater than the molar ratio (A).

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