Gas generator

Abstract

The present invention aims to provide a gas generator that can produce highly concentrated generated gases while suppressing energy consumption. [Solution] A gas generating apparatus having a plurality of membrane separation mechanisms and a circulation mechanism 1 arranged in series, characterized in that the circulation mechanism 1 circulates the permeate gas from the downstream membrane separation mechanism downstream of the reaction mechanism.

Description

Technical Field

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[0001] The present invention relates to a gas generation device, a gas generation plant, and a generated gas.

Background Art

[0002] As a method for selectively separating and purifying a specific gas component from a mixture containing a plurality of gas components, a membrane separation method is known. Since the membrane separation method utilizes a pressure difference, it has the advantage of low energy consumption compared to other separation and purification methods.

[0003] The gas separation membrane used in the membrane separation method is a separation membrane in which the gas permeability of a specific gas component (permeate gas) is high with respect to the gas permeability of other gas components (non-permeate gas), and the permeate gas and the non-permeate gas are separated by a difference in size or a difference in interaction with the separation membrane. As the gas separation membrane, a polymer membrane and an inorganic membrane are known, and an inorganic membrane is preferably used in applications where heat resistance and chemical resistance are required.

[0004] Biogas to be separated by the membrane separation method is a mixed gas mainly composed of methane and CO2 obtained by microbial fermentation of biomass. By removing CO2 by the membrane separation method, the methane concentration in biogas can be increased. Furthermore, as a method capable of achieving both an increase in the concentration of methane and an improvement in the reaction conversion rate, a method is known in which CO2 in biogas is removed by a gas separation membrane and the removed CO2 and the like are circulated to a biogas fermentation tank (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Patent Document 1 discloses a methane gas generator that includes carbon dioxide removal, which supplies hydrogen-containing gas and CO2-containing gas to an anaerobic biological reactor that performs microbial treatment, and discharges a treated gas containing methane gas, characterized in that it has a circulating gas line that circulates at least a portion of the treated gas back to the reactor. However, in the method of Patent Document 1, since the circulating gas is circulated back to the reactor, there is a problem that the energy required for circulation becomes large, especially when concentrating methane to a high concentration.

[0007] Therefore, the present invention aims to provide a gas generator that can produce highly concentrated generated gases while suppressing energy consumption. [Means for solving the problem]

[0008] To solve the above problems, the gas generating apparatus of the present invention is a gas generating apparatus having a plurality of membrane separation mechanisms and a circulation mechanism 1 arranged in series, characterized in that the circulation mechanism 1 circulates the permeate gas from the downstream membrane separation mechanism downstream of the reaction mechanism. [Effects of the Invention]

[0009] The gas separation apparatus of the present invention can improve the reaction conversion rate while suppressing the energy required for the circulation of permeate gas by circulating the permeate gas from the downstream membrane separation mechanism to a reaction mechanism that requires less energy for circulation. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing one embodiment of the gas generating apparatus of the present invention. [Figure 2] This is a schematic diagram showing another embodiment of the gas generating apparatus of the present invention. [Modes for carrying out the invention]

[0011] The present invention will be described below with reference to the drawings, but the present invention is not limited to these examples.

[0012] The gas separation apparatus of the present invention is a gas generation apparatus having a plurality of membrane separation mechanisms and a circulation mechanism 1 arranged in series, characterized in that the circulation mechanism 1 circulates the permeate gas from the downstream membrane separation mechanism downstream of the reaction mechanism.

[0013] As mentioned above, in conventional technology, the permeate gas from the membrane separation mechanism is circulated upstream of the reaction mechanism. This leads to problems such as a large pressurization load on the circulating gas in reaction mechanisms where the reaction proceeds in the liquid phase, such as biogas fermentation, and a large heating load on the circulating gas in reaction mechanisms where the reaction proceeds in the gas phase and at high temperatures, such as methanation. The gas generation apparatus of the present invention circulates the permeate gas from the downstream membrane separation mechanism downstream of the reaction mechanism, thereby improving the reaction conversion rate while suppressing the power required for circulation and the energy required for heating the circulated gas.

[0014] Figure 1 shows a schematic diagram of one embodiment of the gas generation apparatus of the present invention. Figure 1 is a schematic diagram representing a gas generation apparatus having a reaction mechanism, two membrane separation mechanisms arranged in series, and two circulation mechanisms.

[0015] The gas generator 1 has a reaction mechanism 2 and a preceding membrane separation mechanism 3 connected by a circuit. The reaction mechanism 2 is a liquid-phase reaction mechanism and consists of a liquid phase (fermentation liquid) 16 and a gas phase 17. Between the reaction mechanism 2 and the preceding membrane separation mechanism 3, there may be a compressor for pressurizing the gas generated in the reaction mechanism and a buffer tank for holding the pressurized gas. The preceding membrane separation mechanism 3 has its non-permeable side connected by a circuit to the subsequent gas separation mechanism 4, and its permeable side connected by a circuit (circulation mechanism 2) 13 to circulation mechanisms 2 and 6. Circulation mechanisms 2 and 6 include the circuit (circulation mechanism 2) 13 and compressor (circulation mechanism 2) 9, and have the function of circulating the permeate gas from the preceding membrane separation mechanism 3 upstream of the reaction mechanism 2, i.e., to the liquid phase (fermentation liquid) 16. On the other hand, the subsequent membrane separation mechanism 4 has its non-permeable side connected to a circuit (generated gas), and its permeable side connected by a circuit (circulation mechanism 1) 12 to circulation mechanisms 1 and 5. The circulation mechanism 1;5 includes the circuit (circulation mechanism 1) 12 and the compressor (circulation mechanism 1) 8, and has the function of circulating the permeate gas from the downstream membrane separation mechanism 4 to the downstream of the reaction mechanism 2, i.e., the gas phase 17. The permeate side of the upstream and downstream membrane separation mechanisms may be provided with a depressurizing pump or the like to ensure a differential pressure with the non-permeate side. In other words, in the gas generator 1, raw material gas is supplied from the circuit (raw material gas) 10 to the reaction mechanism 2, and the gas generated in the reaction mechanism 2 is recovered as product gas from the circuit (product gas) 11 after passing through two membrane separation mechanisms. The gas that has permeated through the membrane separation mechanisms is circulated upstream or downstream of the reaction mechanism 2 via the two circulation mechanisms.

[0016] A reaction mechanism is a mechanism for obtaining reactants from raw materials. For example, reaction mechanisms for obtaining methane include biogas fermentation, which obtains biogas from biomass; methanation, which obtains methane from CO2 and hydrogen; and biomethanation, which combines both.

[0017] The gas generation apparatus of the present invention has multiple membrane separation mechanisms arranged in series. A membrane separation mechanism is a mechanism that concentrates another gas component by removing a specific gas component from a mixed gas to be separated using a gas separation membrane. The configuration in which the membrane separation mechanisms are arranged in "series" refers to a configuration in which the non-permeable gas from the preceding membrane separation mechanism is supplied to the subsequent membrane separation mechanism. By arranging multiple membrane separation mechanisms in series, a higher concentration of generated gas can be obtained.

[0018] Furthermore, if the gas generator has three or more membrane separation mechanisms arranged in series, one or more from the upstream end will be designated as the pre-stage, and one or more from the downstream end as the post-stage. The number of pre-stage or post-stage membrane separation mechanisms can be set according to the performance of the gas separation membrane and the separation conditions.

[0019] The circulation mechanism of the present invention is a mechanism for circulating the permeate gas from a membrane separation mechanism to the upstream or downstream of a reaction mechanism. The circulation mechanism consists of a gas supply mechanism and a circuit. Examples of gas supply mechanisms include pumps, blowers, and compressors. The circuit refers to the piping through which the gas flows. It is more preferable that the circulation mechanism includes a mechanism for measuring the composition, flow rate, pressure, etc., of the gas passing through it.

[0020] The gas generation apparatus of the present invention is characterized by having a circulation mechanism 1 that circulates the permeate gas from the downstream membrane separation mechanism downstream of the reaction mechanism. In this way, in a liquid-phase reaction mechanism, the gas can be circulated to the gas phase, so the energy required for circulation can be reduced by an amount equivalent to the water pressure of the liquid phase. Furthermore, in a gas-phase, high-temperature reaction mechanism, circulation can be performed after a reaction that does not require high temperature, so the energy required to raise the temperature of the circulating gas can be reduced. In other words, the reaction conversion rate can be improved while suppressing the power required for circulation and the energy required for heating the circulated gas.

[0021] In one aspect of the present invention, it is preferable that the gas generation device has a circulation mechanism 2 that circulates the permeated gas of the front-stage membrane separation mechanism upstream of the reaction mechanism. By doing so, only the permeated gas containing a large amount of unreacted raw materials is supplied to the reaction mechanism again, so that the reaction conversion rate can be further improved while suppressing the energy required for the circulation of the permeated gas.

[0022] FIG. 2 shows a schematic diagram of another aspect of the gas generation device of the present invention. FIG. 2 is a schematic diagram showing a gas generation device obtained by adding a bypass circuit and a switching mechanism to the gas generation device of FIG. 1.

[0023] The gas generation device in FIG. 2 has a bypass circuit 14 from the circulation mechanism 1; 5 to the circulation mechanism 2; 6 and a switching mechanism 7. That is, the permeated gas of the subsequent-stage membrane separation mechanism 4 can circulate through the circulation mechanism 1; 5 to the gas phase 17 downstream of the reaction mechanism 2, or can circulate from the circulation mechanism 2; 6 to the liquid phase (fermentation broth) 16 upstream of the reaction mechanism 2 through the switching mechanism 7 and the bypass circuit 14.

[0024] In the aspect where the gas generation device has the circulation mechanism 2, it is more preferable to have a bypass circuit from the circulation mechanism 1 to the circulation mechanism 2. By doing so, the permeated gas of the subsequent-stage membrane separation mechanism can be circulated to the preferable circuit of the circulation circuit 1 and the circulation circuit 2 according to the composition of the permeated gas, so that the reaction conversion rate can be maintained even when the gas composition fluctuates greatly, such as at the initial stage of operation start or during the occurrence of troubles. It is more preferable that a switching mechanism is provided in the front stage of the bypass circuit.

[0025] Examples of the switching mechanism include manual or electric valves. From the viewpoint of enabling automatic control, an electric valve is more preferable. In an embodiment having a switching mechanism, it is preferable that the permeate gas from the downstream membrane separation mechanism is circulated to the circulation mechanism 2 via a bypass circuit when the specific gravity of the raw material gas contained in the gas is high, and circulated to the circulation mechanism 1 when the specific gravity of the raw material gas is low. That is, it is preferable to have a mechanism upstream of the switching mechanism for detecting the composition of the permeate gas from the downstream membrane separation mechanism, and it is more preferable that the switching mechanism is a mechanism that switches automatically according to the composition of the permeate gas.

[0026] The membrane separation mechanism of the present invention preferably has a gas separation membrane module (hereinafter also simply referred to as "module"). The gas separation membrane module is a module in which a gas separation membrane is housed in a vessel, and the permeable side and the non-permeable side of the gas separation membrane are partitioned. Examples of gas separation membrane shapes include hollow fiber membranes and flat membranes. From the viewpoint of improving the membrane area per unit volume, the gas separation membrane is preferably a hollow fiber membrane.

[0027] Examples of gas separation membranes used in gas separation membrane modules include zeolite membranes, metal-organic frame (MOF) membranes, inorganic membranes such as carbon membranes, and polymer membranes. When the temperature of the gas to be separated is high, an inorganic membrane with high heat resistance is preferable, and when the gas to be separated contains impurities such as water vapor or organic matter, a carbon membrane with low reactivity is more preferable.

[0028] Suitable zeolite membranes for gas separation include membranes made of aluminosilicates, such as NaX type (FAU), ZSM-5, MOR, silicalite, and type A. Two or more of these may be used. It is preferable to use zeolite species with a small Si / Al ratio because this reduces interaction with water vapor.

[0029] Suitable MOF membranes for gas separation include, for example, membranes made of Cu-BTC, MOF-5, IRMOF-3, MIL-47, MIL-53, MIL-96, MMOF, SIM-1, ZIF-7, ZIF-8, ZIF-22, ZIF-69, ZIF-90, etc. Two or more of these may be used.

[0030] Suitable carbon membranes for gas separation include, for example, membranes made by carbonizing polyphenylene oxide, polyvinyl alcohol, polyacrylonitrile, phenolic resin, fully aromatic polyester, unsaturated polyester resin, alkyd resin, melamine resin, urea resin, polyimide resin, diallyl phthalate resin, lignin resin, urethane resin, etc. Two or more of these may be used.

[0031] In the gas separation membrane module used in the present invention, the cross-sectional shape of the vessel is preferably elliptical or circular, and more preferably circular, from the viewpoint of improving the pressure resistance of the vessel. Here, the cross-section of the vessel refers to the cross-section of the vessel perpendicular to the length direction of the gas separation membrane. Examples of materials for the vessel include metal, resin, fiber-reinforced plastic (FRP), etc., and can be appropriately selected depending on the environment of the installation site and the conditions in which it is used. In applications where pressure resistance and heat resistance are required, metal that combines strength and formability is preferred, and stainless steel is more preferred.

[0032] Methods for fixing the gas separation membrane to the vessel include directly fixing the gas separation membrane to the inner surface of the vessel with a potting material, or fixing a separation membrane element, in which multiple gas separation membranes are fixed with a potting material, inside the vessel via an adapter (for example, an O-ring) that can ensure liquid-tightness or airtightness. It is preferable to fix the separation membrane element inside the vessel via an adapter, etc., because when the performance of the separation membrane element deteriorates over time, only the separation membrane element can be replaced.

[0033] Potting materials include, for example, thermoplastic resins and thermosetting resins. Furthermore, other additives may also be included.

[0034] Examples of thermoplastic resins used as potting materials include polyethylene, polyethersulfone, polystyrene, polyphenylene sulfide, polyarylate, polyester, liquid crystal polyester, polyamide, and polymethyl methacrylate. Examples of thermosetting resins include epoxy resin, unsaturated polyester resin, urethane resin, urea resin, phenolic resin, melamine resin, and silicone resin. Two or more of these may be used. Among these, epoxy resin and urethane resin are preferred from the viewpoint of balancing moldability, curing time, adhesion, and hardness.

[0035] The gas generation plant of the present invention (hereinafter sometimes simply referred to as "plant") is a plant that includes the gas generation apparatus of the present invention. Preferably, the plant includes, in addition to the gas generation apparatus, pretreatment equipment, purified fluid recovery equipment, by-product fluid recovery equipment, etc. The pretreatment equipment is equipment for removing impurities from the gas to be separated before separation or for adjusting the composition of the gas to be separated before separation. The purified fluid recovery equipment is equipment for recovering the generated gas from which unwanted components have been removed from the gas to be separated before separation, and for further purification or supplying it to a pipeline, etc., as needed. The by-product fluid recovery equipment is equipment for recovering the by-product gas removed from the gas to be separated before separation, and for example, for detoxification after additional purification and discharge. Preferably, in the plant of the present invention, the gas generation apparatus, pretreatment equipment, purified fluid recovery equipment, and by-product fluid recovery equipment are connected by piping, etc., so that the gas to be separated before separation is continuously separated into generated gas and by-product gas.

[0036] The gas produced by the plant of the present invention is not particularly limited, but since the plant includes a reaction mechanism and a membrane separation mechanism, examples include biogas fermentation and methane production accompanied by methanation.

[0037] The generated gas of the present invention is a gas produced by the gas generating apparatus of the present invention. The generated gas may be produced by including additional steps before and after the production process in the gas generating apparatus of the present invention. Examples of additional steps include purification such as distillation, adsorption, and absorption, and component adjustment for mixing with another gas. [Examples]

[0038] The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to these. Evaluations in each example and comparative example were carried out by the following methods.

[0039] (Energy-saving effect of permeate gas circulation) In the gas generation apparatus of the example and comparative example, the gas circulating upstream of the methane fermentation tank was circulated at approximately 3 atmospheres, and the gas circulating downstream of the methane fermentation tank was circulated at approximately 1 atmosphere, while biomethane was produced to a methane concentration of 95%. From the power required for the circulation of the permeate gas and the amount of methane produced, the energy required for circulation relative to the amount of methane produced was calculated, and the reduction compared to Comparative Example 1 was considered the energy-saving effect of the example.

[0040] (Manufacturing Example 1) Polymer membranes sampled from a polymer membrane module (manufactured by UBE Corporation, NM-B01) were bundled and placed inside an acrylic pipe having an inlet and outlet for the gas to be separated. Both ends of the acrylic pipe were then potted one at a time using epoxy resin. After the epoxy resin cured, the potted portion at one end was cut with a rotary saw to open the fluid separation membrane, obtaining the gas separation membrane module of Manufacturing Example 1.

[0041] (Example 1) In Example 1, a gas generator was manufactured in which a biogas fermentation tank, which is the reaction mechanism, and the gas separation membrane module of Manufacturing Example 1 were arranged in series. The permeate gas from the upstream gas separation membrane module (containing 1000 membranes) was circulated to the upstream (liquid phase) of the biogas fermentation tank, and the permeate gas from the downstream gas separation membrane module (containing 500 membranes) was circulated to the downstream (gas phase) of the biogas fermentation tank. As a result of evaluation using the method described above, the energy saving effect of the gas generator of Example 1 was 20%.

[0042] (Comparative Example 1) We manufactured a gas generation device for Comparative Example 1, which has a reaction mechanism consisting of a biogas fermenter and a gas separation membrane module (containing 1500 membranes) as in Manufacturing Example 1, and circulates the permeate gas from the gas separation membrane module upstream of the biogas fermenter. [Explanation of Symbols]

[0043] 1: Gas generator 2: Reaction mechanism 3: Pre-stage membrane separation mechanism 4: Subsequent membrane separation mechanism 5: Circulation mechanism 1 6: Circulation mechanism 2 7: Switching mechanism 8: Compressor (Circulation mechanism 1) 9: Compressor (Circulation mechanism 2) 10: Circuit (raw material gas) 11: Circuit (Evolved Gases) 12: Circuit (circulation mechanism 1) 13:Circuit (circulation mechanism 2) 14: Bypass Circuit 15: Gas separation membrane 16: Liquid phase (fermentation liquid) 17: Gas phase [Industrial applicability]

[0044] The gas generating apparatus and gas generating plant of the present invention can be suitably used for generating gases involving reaction mechanisms such as methane fermentation and methanation.

Claims

1. A gas generator having multiple membrane separation mechanisms and a circulation mechanism 1 arranged in series, A gas generating apparatus characterized in that the circulation mechanism 1 circulates the permeate gas from the subsequent membrane separation mechanism downstream of the reaction mechanism.

2. Furthermore, it has a circulation mechanism 2, The gas generating apparatus according to claim 1, characterized in that the circulation mechanism 2 circulates the permeate gas from the preceding membrane separation mechanism upstream of the reaction mechanism.

3. The gas generating apparatus according to claim 2, further characterized by having a bypass circuit from the circulation mechanism 1 to the circulation mechanism 2.

4. Furthermore, it has a switching mechanism, The gas generating apparatus according to claim 3, characterized in that the switching mechanism has the function of switching the flow path of the permeate gas of the subsequent membrane separation mechanism to circulation mechanism 1 or circulation mechanism 2.

5. The gas generating apparatus according to any one of claims 1 to 4, characterized in that the reaction mechanism generates methane.

6. A gas generation plant having the gas generation apparatus described in claims 1 to 4.

7. The generated gas produced by the gas generating apparatus described in claims 1 to 4.

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