Biogas Engine System

Abstract

To provide a biogas engine system which can easily suppress inhibition of fermentation of organic waste cause by ammonia.SOLUTION: A biogas engine system 1 comprises a biogas generation section 2 for generating a biogas, a biogas engine 3 for combusting the biogas, a combustion gas discharge line 4 for discharging combustion gas of the biogas to the outside, a combustion gas supply line 5 for supplying the combustion gas to the biogas generation section 2, a switching unit 6 for switching between the combustion gas discharge line 4 and the combustion gas supply line 5, a pH sensor 7 for measuring a pH value in the biogas generation section 2, and a control unit 8 for controlling drive of the switching unit 6 and the biogas engine 3. When the pH value measured by the pH sensor 7 exceeds a first threshold, the control unit 8 controls the drive of the biogas engine 3 so that an air mixing ratio is higher than a theoretical air-fuel ratio, and controls the switching unit 6 so as to open the combustion gas supply line 5.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, biogas engines have been attracting attention. Biogas engines are engines that use biogas, which is produced by fermenting organic waste (e.g., food waste, sewage, livestock excrement, and food waste), as fuel.

[0003] On the other hand, when organic waste is fermented, the organic waste is decomposed and biogas is produced, but ammonia may also be generated as a by-product. This ammonia reduces the activity of the microorganisms that decompose the organic waste, slowing the fermentation rate of the organic waste. For this reason, systems to remove ammonia are being considered.

[0004] As such a system, for example, a waste treatment device has been proposed that includes an ammonia removal means that brings the product gas produced by methane fermentation of solid organic waste into contact with an acid (e.g., sulfuric acid) to decompose and remove ammonia (see, for example, Patent Document 1 below). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-276880 Summary of the Invention [Problem to be solved by the invention]

[0006] On the other hand, the waste treatment device of Patent Document 1 requires the addition of acid to decompose and remove ammonia, which increases the amount of wastewater, resulting in higher treatment costs.

[0007] The present invention provides a biogas engine system that can easily suppress the inhibition of fermentation of organic waste by ammonia. [Means for solving the problem]

[0008] The present invention [1] is a biogas engine system comprising: a biogas generation unit that ferments organic waste to generate biogas; a biogas engine that combusts the biogas; a combustion gas exhaust line for exhausting combustion gas from the biogas generated by the biogas engine to the outside; a combustion gas supply line for supplying the combustion gas to the biogas generation unit; a switching unit that switches between the combustion gas exhaust line and the combustion gas supply line; a pH sensor that measures the pH value in the biogas generation unit; and a control unit that controls the operation of the switching unit and the biogas engine based on the pH value measured by the pH sensor, wherein the control unit controls the operation of the biogas engine so that the air mixture ratio is higher than the stoichiometric air-fuel ratio when the pH value measured by the pH sensor exceeds a first threshold value, and controls the switching unit to open the combustion gas supply line.

[0009] According to this configuration, when the pH value measured by the pH sensor exceeds the first threshold value, the control unit controls the operation of the biogas engine so that the air mixture ratio is higher than the theoretical air-fuel ratio, and controls the switching unit to open the combustion gas supply line.

[0010] When the biogas engine is controlled so that the air mixture ratio is higher than the theoretical air-fuel ratio, the nitrogen oxides (NO ) in the combustion gas of the biogas generated by the biogas engine are reduced. X ) and sulfur oxides (SO X ) increases.

[0011] Then, such combustion gas is supplied to the biogas generating section via a combustion gas supply line.

[0012] The combustion gas transported to the biogas generating section is X ) and sulfur oxides (SO X ), and the hydrogen ions generated from these neutralize the ammonia in the biogas generation unit. This makes it possible to suppress the inhibition of fermentation of organic waste by ammonia. As a result, it is possible to suppress the inhibition of fermentation of organic waste by ammonia without increasing the amount of wastewater from the biogas generation unit.

[0013] The present invention [2] includes the biogas engine system described in [1] above, wherein the control unit controls the operation of the biogas engine to achieve a theoretical air-fuel ratio when the pH value measured by the pH sensor falls below a second threshold value that is lower than the first threshold value, and controls the switching unit to close the combustion gas supply line.

[0014] According to this configuration, when the pH value measured by the pH sensor falls below the second threshold, the operation of the biogas engine is controlled to achieve the theoretical air-fuel ratio, and the switching unit is controlled to close the combustion gas supply line.

[0015] This makes it possible to prevent the pH value in the biogas generating section from continuing to decrease. [Effects of the Invention]

[0016] According to the biogas engine system of the present invention, it is possible to suppress the inhibition of fermentation of organic waste by ammonia without increasing the amount of wastewater from the biogas generation section. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a block diagram showing one embodiment of a biogas engine system of the present invention. [Figure 2] FIG. 2 shows a flowchart of the operation of the biogas engine system shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0018] 1. Biogas engine system configuration Referring to FIG. 1, one embodiment of the biogas engine system of the present invention will be described in detail.

[0019] The biogas engine system 1 is a power source connected to, for example, a power generation device 100 (see dashed line in FIG. 1). The biogas engine system 1 includes a biogas generation unit 2 that ferments organic waste to generate biogas, a biogas engine 3 that combusts the biogas, a combustion gas discharge line 4 that discharges combustion gas of the biogas generated by the biogas engine 3 to the outside, a combustion gas supply line 5 that supplies the combustion gas to the biogas generation unit 2, a switching unit 6 that switches between the combustion gas discharge line 4 and the combustion gas supply line 5, a pH sensor 7 that measures the pH value in the biogas generation unit 2, and a control unit 8 that controls the operation of the switching unit 6 and the biogas engine 3 based on the pH value measured by the pH sensor 7.

[0020] In detail, the biogas engine system 1 includes a biogas generating unit 2 having a pH sensor 7, a biogas engine 3 having a combustion gas exhaust line 4 and a switching unit 6, It includes a combustion gas supply line 5 and a control unit 8.

[0021] <Biogas generation section> The biogas generating section 2 is provided to ferment (methane ferment) organic waste (for example, food waste, sewage, livestock excrement, and food waste) to generate biogas.

[0022] The biogas generation unit 2 includes a fermenter 10, a biogas transport line 11, a biogas storage tank 12, and a pH sensor 7.

[0023] The fermenter 10 is a tank for fermenting organic waste. The fermenter 10 is a heat-resistant and pressure-resistant container. Microorganisms capable of fermenting organic waste are placed in the fermenter 10.

[0024] The fermenter 10 is equipped with a biogas transport port 13 capable of transporting biogas, a combustion gas supply port 14 capable of supplying a combustion gas described later, and a combustion gas discharge port 15 capable of discharging the combustion gas described later that has been supplied to the fermenter 10.

[0025] The biogas transport line 11 is a pipe for transporting biogas from the fermenter 10 to the biogas storage tank 12. The upstream end of the biogas transport line 11 in the biogas transport direction is connected to a biogas transport port 13 of the fermenter 10. The downstream end of the biogas transport line 11 in the biogas transport direction is connected to a biogas supply port 16 (described below) of the biogas storage tank 12. Although not shown, a pump and a valve are interposed midway along the flow direction of the biogas transport line 11. By driving the pump and opening and closing the valve, the biogas can be transported from the fermenter 10 to the biogas storage tank 12.

[0026] Although not shown, a treatment device for pretreating the biogas by any method is interposed midway in the flow direction of the biogas transport line 11. Examples of treatment devices include a desulfurization device and a desiloxane device.

[0027] The biogas storage tank 12 is a storage tank that temporarily stores biogas. The biogas storage tank 12 is made of a heat-resistant and pressure-resistant container.

[0028] The biogas storage tank 12 includes a biogas supply port 16 through which biogas can be supplied, and a biogas discharge port 17 through which biogas can be discharged.

[0029] The downstream end of the biogas transport line 11 in the biogas transport direction is connected to the biogas supply port 16 of the biogas storage tank 12. As a result, the biogas produced in the fermenter 10 is transported to the biogas storage tank 12 and temporarily stored therein. Furthermore, the upstream end of a biogas supply line 21 (described below) in the biogas supply direction is connected to the biogas discharge port 17 of the biogas storage tank 12. As a result, the biogas in the biogas storage tank 12 can be supplied to the biogas engine 3 at any time.

[0030] The pH sensor 7 is a known pH sensor that is provided in the fermenter 10 and measures the pH value in the fermenter 10 .

[0031] <Biogas engine> The biogas engine 3 includes an engine 20 , a biogas supply line 21 , an air supply line 22 , a combustion gas discharge line 4 , a catalyst unit 23 , and a switching unit 6 .

[0032] A known reciprocating engine may be used as the engine 20. The engine 20 is driven by the supply of biogas.

[0033] The biogas supply line 21 is a pipe for supplying biogas to the engine 20. The upstream end of the biogas supply line 21 in the biogas supply direction is connected to the biogas outlet 17 of the biogas storage tank 12. The downstream end of the biogas supply line 21 in the biogas supply direction is connected to the engine 20.

[0034] Although not shown, a pump and a valve are interposed in the flow direction of the biogas supply line 21. By driving the pump and opening and closing the valve, biogas can be supplied from the biogas storage tank 12 to the engine 20.

[0035] The air supply line 22 is a pipe for supplying air to the engine 20. An upstream end of the air supply line 22 in the air supply direction is open to the outside (outside air). A downstream end of the air supply line 22 in the air supply direction is connected to the engine 20.

[0036] Although not shown, a pump and a valve are interposed midway in the flow direction of the air supply line 22. By driving the pump and opening and closing the valve, air can be supplied from the atmosphere to the engine 20. In other words, a mixture of biogas and air can be supplied to the engine 20 via the biogas supply line 21 and the air supply line 22.

[0037] The combustion gas discharge line 4 is a pipe for discharging combustion gas of biogas generated from the biogas engine 3 to the outside. The upstream end of the combustion gas discharge line 4 in the combustion gas discharge direction is connected to the engine 20. The downstream end of the combustion gas discharge line 4 in the combustion gas discharge direction is open to the outside (open air).

[0038] The catalyst unit 23 is a storage tank that stores a known catalyst for purifying combustion gas.

[0039] The catalyst unit 23 is interposed midway in the combustion gas discharge direction in the combustion gas discharge line 4. The catalyst unit 23 is also provided downstream of the switching unit 6 in the combustion gas discharge direction.

[0040] The switching unit 6 is a solenoid valve that switches the flow path of the combustion gas generated from the biogas engine 3 between the combustion gas discharge line 4 and the combustion gas supply line 5 (described later).

[0041] The switching unit 6 is interposed midway in the combustion gas discharge line 4 in the combustion gas discharge direction.

[0042] <Combustion gas supply line> The combustion gas supply line 5 is a pipe for supplying the combustion gas generated from the biogas engine 3 to the biogas generation section 2 (specifically, the fermenter 10).

[0043] An upstream end of the combustion gas supply line 5 in the combustion gas supply direction is connected to the switching unit 6. A downstream end of the combustion gas discharge line 4 in the combustion gas supply direction is open to the outside (open air).

[0044] The combustion gas supply line 5 passes through the fermenter 10. Specifically, the combustion gas supply line 5 enters the interior of the fermenter 10 from a combustion gas supply port 14 in the fermenter 10 and is exposed to the outside of the fermenter 10 from a combustion gas discharge port 15 in the fermenter 10.

[0045] The combustion gas supply line 5 disposed inside the fermenter 10 is provided with a separation membrane 30. The separation membrane 30 separates nitrogen oxides (NO X ) and sulfur oxides (SO X This is a known separation membrane that can separate nitrogen oxides (NO X ) and sulfur oxides (SO X ) can be supplied to the biogas generating section 2 (specifically, the fermentation tank 10).

[0046] The control unit 8 is a unit (for example, an ECU: Electronic Control Unit) that executes electrical control in the biogas engine system 1, and is configured from a microcomputer that includes a processing unit, a memory, and the like.

[0047] 1, the control unit 8 is electrically connected to the pH sensor 7, and is also electrically connected to the biogas engine 3 (specifically, to a pump (not shown) and a valve (not shown) provided in the biogas supply line 21 and the air supply line 22) and the switching unit 6. This allows the biogas engine 3 and the switching unit 6 to operate based on the pH value measured by the pH sensor 7, as will be described in more detail below.

[0048] 2. Biogas engine system operation The operation of the biogas engine system 1 will be described in detail with reference to FIG.

[0049] The operation of the biogas engine system 1 is controlled by a control unit 8. The control unit 8, which will be described in detail later, has a program stored in its memory that switches between a normal operation mode and a pH reduction operation mode, and the program is executed by a processing unit to drive the biogas engine system 1 as follows.

[0050] That is, the biogas engine system 1 first executes the steady operation mode (S1). More specifically, the control unit 8 drives the biogas engine 3 so that the mixture of biogas supplied from the biogas supply line 21 and air supplied from the air supply line 22 has a stoichiometric air-fuel ratio, and controls the switching unit 6 to close the combustion gas supply line 5 and open the combustion gas discharge line 4. In this way, the steady operation mode is executed.

[0051] Next, the control unit 8 determines whether the pH value measured by the pH sensor 7 exceeds a preset first threshold value (S2).

[0052] The first threshold is, for example, pH 7.4.

[0053] If the pH value measured by the pH sensor 7 does not exceed the first threshold value (No in S2), the control unit 8 returns to S1 and executes the steady operation mode.

[0054] On the other hand, if the steady-state operation mode continues, ammonia continues to be generated as a by-product in the biogas generation section 2 (specifically, in the fermentation tank 10), resulting in an increase in the pH value within the biogas generation section 2 (specifically, in the fermentation tank 10).

[0055] If the pH value measured by the pH sensor 7 exceeds the first threshold value (Yes in S2), the pH reduction operation mode is implemented (S3). More specifically, the control unit 8 drives the biogas engine 3 so that the air mixture ratio is higher than the stoichiometric air-fuel ratio in the mixture, and controls the switching unit 6 to close the combustion gas discharge line 4 and open the combustion gas supply line 5. This implements the pH reduction operation mode.

[0056] When the operation of the biogas engine 3 is controlled so that the air mixture ratio is higher than the theoretical air-fuel ratio, nitrogen oxides (NO X ) and sulfur oxides (SO X ) increases.

[0057] Then, such combustion gas is supplied via a combustion gas supply line 5 to the biogas generation section 2 (specifically, the fermentation tank 10).

[0058] The combustion gas transported to the biogas generating section 2 (specifically, the fermenter 10) contains nitrogen oxides (NO X ) and sulfur oxides (SO X ), and the hydrogen ions generated from these can neutralize the ammonia in the biogas generation unit 2 (specifically, the fermentation tank 10). As a result, the pH value in the biogas generation unit 2 (specifically, the fermentation tank 10) decreases.

[0059] Next, the control unit 8 determines whether the pH value measured by the pH sensor 7 is below a second preset threshold value (S4).

[0060] The second threshold is lower than the first threshold, and specifically, the second threshold is, for example, pH 6.8.

[0061] If the pH value measured by the pH sensor 7 does not fall below the second threshold value (No in S4), the control unit 8 returns to S3 and executes the pH reduction operation mode, which causes the pH value in the biogas generation unit 2 (specifically, the fermenter 10) to continue to decrease.

[0062] On the other hand, if the pH value measured by the pH sensor 7 falls below the second threshold value (Yes in S4), the steady operation mode is implemented (S5), causing the pH value in the biogas generation unit 2 (specifically, the fermenter 10) to start rising again.

[0063] Such a biogas engine system 1 repeats the above-described operations until a stop signal is input.

[0064] 3. Effects According to the biogas engine system 1, it is possible to suppress the inhibition of fermentation of organic waste by ammonia without increasing the amount of wastewater from the biogas generation section 2.

[0065] Specifically, when organic waste is fermented, the organic waste is decomposed and biogas is produced, but ammonia may also be generated as a by-product. This ammonia reduces the activity of the microorganisms that decompose the organic waste, slowing the fermentation rate of the organic waste. For this reason, systems to remove ammonia are being considered.

[0066] As a system for removing ammonia, for example, the waste treatment device of Patent Document 1 mentioned above, in which acid is introduced to decompose and remove ammonia, is being considered.

[0067] However, adding acid increases the amount of wastewater, which increases the cost of treatment.

[0068] On the other hand, in the biogas engine system 1, when ammonia is generated as a by-product in the biogas generation section 2 (specifically, the fermentation tank 10), the pH value inside the biogas generation section 2 (specifically, the fermentation tank 10) becomes high.

[0069] The pH value is measured by a pH sensor 7, and when the pH value exceeds a first threshold, the control unit 8 controls the operation of the biogas engine 3 so that the air mixture ratio is higher than the theoretical air-fuel ratio, and controls the switching unit 6 so that the combustion gas supply line 5 is opened (pH reduction operation mode).

[0070] When the operation of the biogas engine 3 is controlled so that the air mixture ratio is higher than the theoretical air-fuel ratio, nitrogen oxides (NO X ) and sulfur oxides (SO X ) increases.

[0071] Then, such combustion gas is supplied via a combustion gas supply line 5 to the biogas generation section 2 (specifically, the fermentation tank 10).

[0072] The combustion gas transported to the biogas generating section 2 (specifically, the fermenter 10) contains nitrogen oxides (NO X ) and sulfur oxides (SO X ) and, as shown in the following formula (1) and formula (2), nitrogen oxides (NO X ) and sulfur oxides (SO X The hydrogen ions generated from the ammonia neutralize the ammonia in the biogas generating section 2 (specifically, in the fermenter 10). NO X +H2O→HNO3=H + +NO3 - (1) SO X +H2O→H2SO4=2H ++SO4 2- (2)

[0073] This makes it possible to suppress the inhibition of fermentation of organic waste caused by ammonia, and as a result, it is possible to suppress the inhibition of fermentation of organic waste caused by ammonia without increasing the amount of wastewater from the biogas generator 2.

[0074] In addition, in the biogas engine system 1, when the pH value measured by the pH sensor 7 falls below the second threshold value, the operation of the biogas engine 3 is controlled to achieve the theoretical air-fuel ratio, and the switching unit 6 is controlled to close the combustion gas supply line 5 (steady-state operation mode).

[0075] This makes it possible to prevent a continuous decrease in the pH value inside the biogas generator 2. In other words, it is possible to switch between the normal operation mode and the pH reduction operation mode within the range set by the first threshold value and the second threshold value.

[0076] 4. Variations In the modified example, the same components and steps as those in the first embodiment are denoted by the same reference numerals, and detailed descriptions thereof will be omitted. Furthermore, the modified example can achieve the same effects as those in the first embodiment unless otherwise specified. Furthermore, the first embodiment and its modified example can be combined as appropriate.

[0077] In the above description, in the pH reduction operation mode, the switching unit 6 is controlled to open the combustion gas supply line 5, but at this time, the combustion gas discharge line 4 may be opened or closed. Preferably, from the viewpoint of efficiently supplying combustion gas to the biogas generation section 2, the combustion gas discharge line 4 is closed.

[0078] The switching unit 6 can also be controlled to adjust the opening degree of the combustion gas discharge line 4 and the opening degree of the combustion gas supply line 5.

[0079] In the above description, the separation membrane 30 is provided in the combustion gas supply line 5 inside the fermenter 10, but the nitrogen oxides (NO X ) and sulfur oxides (SO X ) can be separated by any means, but is not limited to this.

[0080] In the above description, the catalytic unit 23 is provided downstream of the switching unit 6 in the combustion gas discharge direction, but the catalytic unit 23 can also be provided upstream of the switching unit 6 in the combustion gas discharge direction. Preferably, from the viewpoint of efficiently supplying combustion gas to the biogas generation section 2, the catalytic unit 23 is provided downstream of the switching unit 6 in the combustion gas discharge direction.

[0081] Furthermore, in the above description, the steady operation mode and the pH reduction operation mode are switched using two thresholds (first threshold and second threshold), but it is also possible to switch between the steady operation mode and the pH reduction operation mode using a single threshold (first threshold).

[0082] Specifically, when the pH value measured by the pH sensor 7 exceeds the first threshold, the operation mode can be switched to the pH reduction operation mode, and when the pH value measured by the pH sensor 7 is equal to or less than the first threshold, the operation mode can be switched to the steady state operation mode.

[0083] Preferably, in order to prevent a decrease in operation efficiency due to frequent switching between the normal operation mode and the reduced pH operation mode, the normal operation mode and the reduced pH operation mode are switched using two thresholds (a first threshold and a second threshold). [Explanation of symbols]

[0084] 1 Biogas engine system 2 Biogas generation section 3 Biogas engine 4 Combustion gas exhaust line 5 Combustion gas supply line 6 Switching Unit 7 pH sensor 8. Control Unit

Claims

1. a biogas generation unit that ferments organic waste to generate biogas; a biogas engine that combusts the biogas; a combustion gas discharge line for discharging the combustion gas of the biogas generated from the biogas engine to the outside; A combustion gas supply line for supplying the combustion gas to the biogas generation unit; a switching unit for switching between the combustion gas exhaust line and the combustion gas supply line; a pH sensor for measuring a pH value in the biogas generating unit; a control unit that controls the switching unit and the biogas engine based on the pH value measured by the pH sensor; The control unit controls the operation of the biogas engine so that the air mixture ratio is higher than the theoretical air-fuel ratio when the pH value measured by the pH sensor exceeds a first threshold value, and controls the switching unit so that the combustion gas supply line is opened.

2. 2. The biogas engine system of claim 1, wherein the control unit controls the operation of the biogas engine so as to achieve a theoretical air-fuel ratio when the pH value measured by the pH sensor falls below a second threshold value that is lower than the first threshold value, and controls the switching unit to close the combustion gas supply line.

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