Biogas generation system

Abstract

To provide a biogas generation system capable of efficiently generating biogas with an ammonia concentration below the level that inhibits biogas generation.SOLUTION: A system 1 includes a generator 3, a recovery unit 4, a reflux line 5, and a control unit 6. The generator 3 generates biogas. The recovery unit 4 separates the water-containing material into solid-liquid and collects the liquid. The reflux line 5 returns a part of the liquid to the generator 3. In the generator 3, a part of the liquid returned from the reflux line 5 is mixed with the new water-containing raw material to again produce biogas. The control unit 6 includes steps (1) through (3) in an executable manner. In the step (1), the ammonia concentration C1 in the new water-containing raw material is predicted. In the step (2), the ammonia concentration C2 in the liquid in the reflux line 5 is predicted. In the step (3), based on the concentrations C1 and C2, the mixing ratio of the liquid and the new biomass raw material is determined. In such a mixing ratio, the ammonia concentration C3 in the mixed liquid at the generator is less than the fermentation inhibition concentration.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a biogas production system. [Background technology]

[0002] There is known a biogas system that performs a methane fermentation process, an ammonia stripping process, and a deoxygenation process (see, for example, Patent Document 1 below). In the methane fermentation process, biomass is introduced into a methane fermentation tank and fermented into methane.

[0003] In the ammonia stripping process, the digested liquid extracted from the methane fermentation tank is introduced into an ammonia stripping device to dissipate ammonia, and in the deoxygenation process, oxygen dissolved in the digested liquid from which ammonia has been dissipated is removed.

[0004] In the biogas system described in Patent Document 1, the digestive liquid is deoxygenated in a deoxygenation step and a part of the digestive liquid is returned to a methane fermentation tank. In addition, in an ammonia stripping device, the digestive liquid is brought into contact with air to extract ammonia as a gas. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2009-66558 A Summary of the Invention [Problem to be solved by the invention]

[0006] In the biomass system described in Patent Document 1, the methane fermentation tank contains a mixture of a portion of the deoxygenated digestive liquid and biomass, and there is a problem in that if the ammonia concentration in the mixture is high, the production of methane gas is inhibited.

[0007] The present invention provides a biogas production system that can efficiently produce biogas while keeping the ammonia concentration in the production device below the level that inhibits biogas production. [Means for solving the problem]

[0008] The present invention [1] is a biogas generation system including a generator that generates biogas from a moist feedstock containing biomaterials and water, a recovery device that performs solid-liquid separation of the moist feedstock after the biogas is generated and recovers the liquid, a reflux line that refluxes at least a portion of the liquid to the generator, and a control device, in which the generator mixes at least a portion of the liquid refluxed from the reflux line with new moist feedstock to prepare a mixed liquid, and generates biogas again from the mixed liquid, and the control device is capable of performing the steps of: predicting an ammonia concentration C1 in the new moist feedstock to be supplied to the generator; predicting an ammonia concentration C2 in the liquid in the reflux line; and determining a mixing ratio of the liquid and the new biomaterial based on the ammonia concentrations C1 and C2, such that the ammonia concentration C3 in the mixed liquid in the generator is less than a concentration that inhibits the generation of biogas in the generator.

[0009] In this biogas generation system, in step (3), the mixing ratio of the liquid recovered in the recovery device to the new biomaterial to be supplied to the generation device is determined so as to be less than the inhibitory concentration of biogas in the generation device, so that biogas can be efficiently generated in the generation device.

[0010] The present invention [2] includes the biogas generation system described in [1], wherein the generation device includes a screw conveyor that transports the water-containing raw material and a tank that stores the water-containing raw material transported by the screw conveyor, and the control device is capable of executing step (4) of setting the transport time and / or the transport temperature of the screw conveyor so that the ammonia concentration C3 is less than the concentration.

[0011] In this biogas generation system, the calculation processing unit of the control device sets the transport time and / or transport temperature of the screw conveyor so that the ammonia concentration C3 is below the concentration that inhibits biogas generation in the generation device, thereby enabling more efficient generation of biogas.

[0012] The present invention [3] includes the biogas production system described in [2], wherein the screw conveyor has blades and protrusions arranged on the surface of the blades.

[0013] In this biogas production system, the screw conveyor is provided with protrusions, which enables efficient removal of ammonia from the moist raw material inside the screw conveyor and efficient production of biogas.

[0014] The present invention [4] includes the biogas generation system described in [2] or [3], wherein the screw conveyor includes blades and a casing that houses the blades, and the screw conveyor has a gap between the blades and the casing through which air can flow in the conveying direction.

[0015] In this biogas generator, the screw conveyor has gaps through which air can flow in the conveying direction, so that ammonia in the moist raw material inside the screw conveyor can be efficiently removed and biogas can be efficiently generated in the generator.

[0016] The present invention [5] includes a biogas production system described in any one of [2] to [4], wherein the screw conveyor has a heating device capable of heating the inside.

[0017] In this biogas generator, the screw conveyor is equipped with a heating device, so that ammonia in the moist raw material inside the screw conveyor can be efficiently removed and biogas can be efficiently generated. Effect of the Invention

[0018] The biogas production system of the present invention can efficiently produce biogas by keeping the ammonia concentration in the production device below the level that inhibits biogas production. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram of one embodiment of a biogas production apparatus of the present invention. [Diagram 2] FIG. 2 is a cross-sectional view of a screw conveyor in the biogas generator shown in FIG. 1. [Diagram 3] 2 is a first table stored in a control device in the biogas production apparatus shown in FIG. 1. [Figure 4] 2 is a second table stored in a control device in the biogas production apparatus shown in FIG. 1. [Diagram 5] FIG. 2 is a flow diagram of steps (1) to (4) that can be executed by a control device in the biogas production apparatus shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] 1. Biogas Generation System An embodiment of the biogas production system of the present invention will be described with reference to FIGS.

[0021] The biogas production system 1 transports a water-containing raw material (described later) while producing biogas from the water-containing raw material. The biogas production system 1 includes a mixer 2, a generator 3, a supply line 35, a collector 4, a reflux line 5, and a controller 6.

[0022] 1.1 Mixing device 2 The mixing device 2 includes a mixing tank 21, an agitation unit 22, and a moisture meter 23.

[0023] The mixing tank 21 contains a water-containing raw material. The water-containing raw material contains a bio-raw material and water.

[0024] The biological raw material may be, for example, animal feces, preferably livestock feces, more preferably cow feces. The cow may be, for example, beef cattle and dairy cattle, preferably beef cattle. The proportion of the biological raw material in the water-containing raw material M is, for example, 1% by mass to 60% by mass, preferably 40% by mass to 30% by mass or more.

[0025] The proportion of water (moisture content) R in the water-containing raw material is, for example, 40 mass % to 99 mass % or less, or preferably 60 mass % to 70 mass % or less.

[0026] The mixing vessel 21 may be, for example, a sealed vessel.

[0027] The stirring unit 22 is disposed in the mixing tank 21. The stirring unit 22 is rotatable in the mixing tank 21. The stirring unit 22 includes, for example, a rotating rod 221.

[0028] The moisture meter 23 is disposed in the lower part of the mixing tank 21. The moisture meter 23 measures the proportion of water (moisture content) in the above-mentioned water-containing raw material.

[0029] 1.2 Generator 3 The formation device 3 is disposed downstream in the conveying direction of the water-containing raw material with respect to the mixer 2. The formation device 3 includes a screw conveyor 31 and a tank 32.

[0030] As shown in FIGS. 1 and 2, the screw conveyor 31 has a casing 311, blades 312, protrusions 313 (see FIG. 2), a gap 314 (see FIG. 2), and a heating device 315.

[0031] The casing 311 extends in the conveying direction. One end of the casing 311 is connected to the mixing tank 21. In other words, the screw conveyor 31 is connected to the mixer 2. As shown in FIG. 2, the casing 311 includes a casing body 3111 and a lid 3112.

[0032] The casing body 3111 has a lower part 3113 and an upper part 3114. The lower part 3113 has a semicircular arc shape in a cross-sectional view. The upper part 3114 extends upward from an upper end part of the lower part 3113. The upper part 3114 has two parallel walls. The two walls are spaced apart in the width direction. The width direction is perpendicular to the conveying direction and the vertical direction.

[0033] The lid 3112 extends in the width direction. The lid 3112 has a flat plate shape. The lid 3112 closes the upper end of the casing body 3111. The lid 3112 is continuous with the upper end of the upper portion 3114.

[0034] The blade 312 is housed in the casing 311. Specifically, the blade 312 is fitted into a lower portion 3113 of the casing body 3111. The blade 312 is a screw blade. The axis of the blade 312 extends in the conveying direction. The blade 312 is rotatable about the axis. The blade 312 has a helical shape.

[0035] The protrusions 313 are disposed on the surface of the blade 312. Specifically, the protrusions 313 are disposed at intervals from one another on the surface of the blade 312. The protrusions 313 protrude from the surface of the blade 312.

[0036] The gap 314 extends along the conveying direction. The gap 314 allows air to flow in the conveying direction between the blade 312 and the casing 311. For example, the gap 314 is defined between the blade 312 and the lid 3112. In more detail, the gap 314 is defined by the upper part 3114, the lid 3112, and the blade 312.

[0037] The heating device 315 is capable of heating the inside of the casing 311. The heating device 315 is disposed on the outer surface of the casing 311.

[0038] 1, the tank 32 is, for example, a sealed container. The tank 32 is connected to the other end of the casing 311 of the screw conveyor 31. The generator 3 generates biogas from the water-containing raw material. The biomaterial in the water-containing raw material is hydrolyzed with time under specific conditions (for example, heating conditions) to generate biogas. An example of the biogas is methane. The tank 32 may be equipped with a heating device (not shown) as necessary.

[0039] 1.3 Supply Line 35 As shown in FIG. 1, a supply line 35 connects the production device 3 and the recovery device 4 .

[0040] 1.4 Recovery device 4 The recovery device 4 is disposed downstream of the generation device 3 in the conveying direction. Specifically, the recovery device 4 is connected to the downstream end of the supply line 35 in the conveying direction. The recovery device 4 performs solid-liquid separation of the water-containing raw material after biogas is generated in the generation device 3, and recovers the liquid. The method of solid-liquid separation is not limited. The recovery device 4 includes a pH meter 41 and an airborne ammonia meter 42.

[0041] The pH meter 41 measures the pH of the liquid.

[0042] The air ammonia meter 42 measures the air ammonia concentration C20 when the liquid is in a gas-liquid equilibrium state.

[0043] The solid separated from the water-containing raw material in the recovery device 4 is discarded.

[0044] 1.5 Reflux line 5 The reflux line 5 refluxes at least a portion of the liquid to the production apparatus 3. The reflux line 5 includes a pipe 51 and a valve 52. The pipe 51 is connected to the production apparatus 3 and the recovery apparatus 4. One end of the pipe 51 is connected to the tank 32.

[0045] The valve 52 is disposed at the downstream end of the pipe 51 in the conveying direction. The valve 52 adjusts the amount of liquid returned from the return line 5 to the tank 32. As a result, in the generator 3, at least a part of the liquid returned from the return line 5 is mixed with new water-containing raw material to prepare a mixed liquid, and biogas is generated again from the mixed liquid. Specifically, the opening of the valve 52 is adjusted to adjust the amount of liquid returned from the return line 5.

[0046] 1.6 Control device 6 The control device 6 is connected to the moisture meter 23, the pH meter 41, the air ammonia meter 42, and the valve 52. The control device 6 includes a storage unit 61 and a calculation processing unit 62.

[0047] The storage unit 61 stores a first table (see FIG. 3) and a second table (see FIG. 4).

[0048] 3, in the first table, the moisture percentage R in the new moisture-containing raw material supplied to the generator 3 is associated with the ammonia concentration C1 in the moisture-containing raw material. The new moisture-containing raw material supplied to the generator 3 is the moisture-containing raw material in the mixing tank 21. In the first table, for example, the moisture percentage R and the ammonia concentration C1 are associated with each other by a proportional equation.

[0049] As shown in Fig. 4, the second table correlates the ammonia concentration C2 in the liquid in the reflux line 5 with the ammonia concentration C20 in the air. In the second table, the ammonia concentration C2 in the liquid and the ammonia concentration C20 in the air are correlated by an inverse proportional equation. The second table also includes a number of inverse proportional equations with different slopes based on the pH.

[0050] As shown in FIG. 5, the control device 6 is capable of executing steps (1), (2), (3), and (4) in this order. 1.4.1 Step (1) In step (1), the calculation processing unit 62 predicts the ammonia concentration C1 in the new water-containing raw material to be supplied to the production device 3.

[0051] As shown in Fig. 3, in order to predict the ammonia concentration C1, first, the moisture content R of the wet raw material contained in the mixing tank 21 is obtained by the moisture meter 23. The wet raw material contained in the mixing tank 21 has a new moisture content to be supplied to the generator 3. When the moisture content R is substituted into the above-mentioned first table (see Fig. 3), the ammonia concentration C1 in the new wet raw material to be supplied to the generator 3 is obtained.

[0052] The above-mentioned ammonia concentration C1 is the total concentration of ammonia that can be removed by vaporization from the new water-containing raw material and ammonia that cannot be removed by vaporization from the new water-containing raw material.

[0053] The ammonia that can be removed from the water-containing raw material by vaporization is ammonia that is removed from the water-containing raw material by providing a relatively low energy to the water-containing raw material. It is assumed that such ammonia is bound to the components of the water-containing raw material by a relatively weak force. For example, providing a low energy to the water-containing raw material includes exposing the water-containing raw material to an air flow and heating at a relatively low temperature. The low temperature is, for example, 55°C or higher, or even 60°C or higher, 65°C or higher, 70°C or higher, or, for example, 100°C or lower.

[0054] Ammonia that cannot be removed from the water-containing raw material by vaporization is removed from the water-containing raw material only by providing a relatively high energy to the water-containing raw material. It is presumed that such ammonia is bound to the components of the water-containing raw material with a relatively strong force. For example, providing a high energy to the water-containing raw material includes heating at a relatively high temperature. The high temperature is, for example, above 100°C.

[0055] The above calculation (prediction) using the moisture content R determines both the ammonia that can be removed by vaporization from the new water-containing raw material and the ammonia that cannot be removed by vaporization from the new water-containing raw material.

[0056] 1.4.2 Step (2) Separately, the calculation processing unit 62 predicts the ammonia concentration C2 in the liquid in the reflux line 5.

[0057] To predict the ammonia concentration C2 in the liquid in the reflux line 5, first, the pH of the liquid is obtained using a pH meter 41 in the recovery device 4, as shown in Fig. 1. At the same time, the air ammonia concentration C20 in the recovery device 4 is obtained using an air ammonia meter 42 in the recovery device 4. The air ammonia concentration C20 in the recovery device 4 is equivalent to the air ammonia concentration C20 in the reflux line 5.

[0058] Next, when the above-mentioned pH and airborne ammonia concentration C20 are substituted into a second table (see FIG. 4) corresponding to pH, the ammonia concentration C2 in the liquid in the reflux line 5 is predicted. 1.4.3 Step (3) In step (3), the calculation processing unit 62 determines a blending ratio at which the ammonia concentration C3 in the mixed liquid in the generator 3 is less than the concentration that inhibits the production of biogas in the generator 3. The concentration that inhibits the production of biogas (inhibitory concentration) is, for example, 2300 ppm to 3000 ppm, specifically, 2700 ppm. The blending ratio is a blending ratio of the liquid and new biomaterial, and is determined based on the ammonia concentration C1 in the water-containing raw material newly supplied from the mixer 2 to the generator 3 and the ammonia concentration C2 in the liquid supplied from the reflux line 5 to the generator 3.

[0059] For example, the value obtained by subtracting the ammonia concentration C1 in the aqueous raw material from the inhibitory concentration C is set to the permissible concentration (C-C1), and the opening of the valve 52 in the reflux line 5 is adjusted so that the amount of liquid refluxed from the reflux line 5 to the generation system 1 is below the amount corresponding to the permissible concentration (C-C1).

[0060] Specifically, if the ammonia concentration C1 in the new water-containing raw material is close to the inhibitory concentration C (1500 ppm to 2000 ppm), the opening of valve 52 is adjusted to reduce the amount of liquid refluxed from reflux line 5 to the generator 3. On the other hand, if the ammonia concentration C1 in the new water-containing raw material is far from the inhibitory concentration (500 ppm to 1000 ppm), the opening of valve 52 is adjusted to increase the amount of liquid refluxed from reflux line 5 to the generator 3. If necessary, valve 52 may be fully opened to reflux all of the liquid from reflux line 5 to the generator 3.

[0061] 1.4.4 Step (4) In step (4), the calculation processing unit 62 of the control device 6 sets the transport time and / or the transport temperature of the screw conveyor 31 so that the ammonia concentration C3 is below a concentration that inhibits the production of biogas in the production device 3.

[0062] For example, by lengthening the transport time of the screw conveyor 31, the residence time of the water-containing raw material in the screw conveyor 31 is lengthened, and the ammonia concentration C3 in the mixed liquid in the generator 3 is reduced. Specifically, by lengthening the transport time of the screw conveyor 31, ammonia that can be removed by vaporization from new water-containing raw material is removed (or the amount is reduced). The transport time of the screw conveyor 31 is adjusted by the rotation speed of the blade 312 and / or the dimensions of the blade 312.

[0063] For example, by increasing the conveying temperature of the screw conveyor 31, the temperature of the water-containing raw material increases, and the ammonia concentration C3 in the mixed liquid in the generator 3 decreases. Specifically, by increasing the conveying temperature of the screw conveyor 31, ammonia that can be removed by vaporization from new water-containing raw material is removed (or the amount is reduced). The conveying temperature of the screw conveyor 31 is adjusted by the temperature of the heating device of the screw conveyor 31. For example, the temperature is set to, for example, 55°C or higher, further, 60°C or higher, 65°C or higher, 70°C or higher, or, for example, 100°C or lower.

[0064] 2. Effects of one embodiment In this biogas production system 1, in step (3), the mixing ratio of the liquid recovered in the recovery device 4 and the new biomaterial to be supplied to the production device 3 is determined so that the mixing ratio is less than the inhibitory concentration of biogas in the production device 3, so that biogas can be efficiently produced in the production device 3.

[0065] In this biogas generation system 1, the calculation processing unit 62 of the control device 6 sets the conveying time and / or conveying temperature of the screw conveyor 31 so that the ammonia concentration C3 is below a concentration that inhibits the generation of biogas in the generation device 3, thereby enabling even more efficient generation of biogas.

[0066] Furthermore, as shown in FIG. 3, the screw conveyor 31 is provided with the protrusions 313, so that ammonia in the wet raw material inside the screw conveyor 31 can be efficiently removed, and biogas can be efficiently generated in the generator 3.

[0067] Furthermore, since the screw conveyor 31 has the gap 314 through which air can flow in the conveying direction, ammonia in the wet raw material inside the screw conveyor 31 can be efficiently removed, and biogas can be efficiently generated in the generator 3.

[0068] Furthermore, since the screw conveyor 31 is equipped with the heating device 315, ammonia in the water-containing raw material inside the screw conveyor 31 can be efficiently removed, and biogas can be efficiently produced.

[0069] 3. Modifications The biogas generation system 1 may be a conveying line that does not include the screw conveyor 31 and does not have the blades 312 inside. Furthermore, the generation device 3 may be independent of the mixer 2. In this case, the water-containing raw material prepared in the mixer 2 is left for a long period of time, for example, outdoors in a well-ventilated place, and then the left water-containing raw material is supplied to the generation device 3. In this case, the control device 6 does not execute step (4).

[0070] The biogas production system 1 does not necessarily need to include the supply line 35. In this case, the water-containing raw material after the biogas is produced in the production device 3 is transported to the recovery device 4 using a separate transport device.

[0071] The reflux line 5 may be equipped with a pH meter 41 . [Explanation of symbols]

[0072] 1. Biogas generation system 2 Mixing device 3 Generator 31 Screw Conveyor 311 Casing 312 Feather 313 Protrusion 314 void 315 Heating device 32 tanks 4 Recovery device 5. Reflux Line 6. Control device

Claims

1. A generator for generating biogas from a biomaterial and a water-containing material containing water; A recovery device that performs solid-liquid separation of the water-containing raw material after generating the biogas and recovers the liquid; a return line for returning at least a portion of the liquid to the generator; A biogas production system comprising: In the generating device, at least a part of the liquid returned from the return line is mixed with new water-containing raw material to prepare a mixed liquid, and biogas is generated again from the mixed liquid; The control device includes: A step (1) of predicting an ammonia concentration C1 in a new aqueous feedstock to be supplied to the generator; A step (2) of predicting an ammonia concentration C2 in the liquid in the reflux line; and (3) determining a mixing ratio of the liquid and new bio-raw material based on the ammonia concentrations C1 and C2, such that an ammonia concentration C3 in the mixed liquid in the generation device is less than a concentration that inhibits generation of biogas in the generation device.

2. The generating device comprises: A screw conveyor that conveys the water-containing raw material; a tank for accommodating the water-containing raw material transported by the screw conveyor; The biogas generation system according to claim 1 , wherein the control device is operable to set a conveying time and / or a conveying temperature of the screw conveyor so that the ammonia concentration C3 is less than the concentration (4).

3. The biogas generation system according to claim 2 , wherein the screw conveyor has a heating device capable of heating the inside thereof.

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