JP2006305491A - Fermentation system and biogas generating system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fermentation system which can more stably obtain biogas when excreta and the like are fermented to output the biogas. <P>SOLUTION: The fermentation system 10 has a fermentation tank 11 for receiving material 12 to be treated, such as excreta, and outputting the biogas 19 obtained by its fermentation, an agitation device 20 for driving impellers 21, 22 in the material 12 to be treated to agitate it, and a bubble supply system 30 for emitting a part of the biogas 19 output from the fermentation tank 11 into the material 12 to be treated through bubble discharge pipes 31, 32 moving synchronously with the impellers 21, 22. By driving the impellers 21, 22 and the bubble discharge pipes 31, 32 synchronously with each other, bubbles 39 can be caught in whirlpools 25, 26 formed by the impellers 21, 22 without being atomized, and the bubbles 39 collect minute gas bubbles in the material to be treated to improve recovery efficiency. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a system that uses manure or the like as an object to be processed, ferments it, and outputs biogas.

  Research has been conducted on a system for generating electricity or heating / cooling using biogas generated in the process of collecting and processing livestock manure. Various systems have been studied, such as thermal power generation by burning biogas, or reforming biogas and using it as fuel for fuel cells.

  In the process of treating manure, manure is received as an object to be treated in a container or tank called a digester or fermenter, and methane fermentation is performed by retaining the manure in an anaerobic state for a certain period of time to extract biogas. At that time, for the purpose of promoting the methane fermentation by mixing the processed material containing methane bacteria and the processed material immediately after receiving it, or preventing the accumulation of scum on the surface of the processed material The material to be treated in the fermenter is agitated by an appropriate method.

Japanese Patent Laid-Open No. 5-269494 describes blowing in digestion gas (biogas) generated in a digester (fermenter) as one method of stirring. Further, as another method of stirring, it is also described that mechanical stirring is performed by inserting a stirring shaft having a stirring blade vertically and rotating the stirring shaft.
Japanese Patent Laid-Open No. 5-269494

  When methane fermentation is performed in a fermenter, it is important to increase fermentation output and increase gas output. For that purpose, it is desirable to sufficiently agitate the object to be treated in the fermenter to promote contact between the new object to be treated and the object to be treated in which methane bacteria have been propagated. On the other hand, when examining a system for producing biogas, it is preferable that the amount of biogas produced is large, but it is desirable that the variation in production amount with time is small.

  The object to be treated for methane fermentation may be organic sludge collected by sewage. However, since sewage mixed with miscellaneous wastewater contains a lot of waste other than organic sludge, fermentation efficiency is poor, residence time is too long, separation or treatment of waste becomes too complicated, and equipment becomes large. The economic efficiency is bad. On the other hand, in farms that raise a certain number of livestock, it is possible to obtain a large amount of processed materials with stable components as livestock manure. Suitable as

  However, the timing of collecting manure on the farm is limited, for example, once a day. Therefore, the work of adding manure to the fermenter is a batch process, and in the fermenter, fermentation proceeds rapidly and a large amount of biogas is output for a short period after a new workpiece is introduced. As time passes, the fermentation rate decreases and the biogas output decreases. Therefore, a biogas generation system is required to be capable of processing a large amount of biogas generated in a short period of time, and has an amount of biogas sufficient to fill the gap between upstream supply and downstream consumption. A tank or receiver is needed.

  It is also possible to adopt a method of generating electricity only when a large amount of biogas is generated in the fermenter. However, this method is also economical because a very large power generation device is required for the average power demand, and a charging device and a large-capacity battery for storing the generated power are also required. Absent.

  Then, in this invention, it aims at providing the fermentation system which can maintain the output of biogas over a long time in a fermenter. To provide a fermentation system that can reduce the gap with the demand on the consumer side by minimizing temporal fluctuations in the amount of biogas produced, even when receiving workpieces in batch processing. It is an object. It is another object of the present invention to provide a biogas generation system that can perform power generation or the like for a long time.

  The gas generated by fermentation of the object to be processed becomes fine bubbles. When fermentation is performed rapidly, the density of fine bubbles is high, the fine bubbles gather and become coarse, reach the surface of the workpiece by buoyancy, and are released from the workpiece as biogas. On the other hand, when the fermentation rate is low, fine bubbles are present in the object to be processed, but there are few opportunities to collect and coarsen, and as a result, the amount of biogas released is small. For this reason, in this invention, in addition to the stirring apparatus which stirs a to-be-processed object mechanically in a fermenter, the means to blow in biogas to a to-be-processed object is provided. If biogas is introduced into the object to be processed in the form of bubbles with a certain size and buoyancy, the biogas present in the object to be processed is collected and released from the object to be processed as the bubbles rise. The Therefore, even when the fermentation rate is reduced, a rapid decrease in biogas output can be suppressed.

  In the present invention, the bubbles of biogas introduced into the object to be processed may exhibit the effect of stirring the object to be processed as a result, but the fine bubbles in the object to be processed are collected from the object to be processed. The purpose is to escape. Therefore, it is not preferable that the introduced biogas bubbles are crushed or finely divided. In addition, if the introduced biogas bubbles rise through the same path in the object to be processed, the fine bubbles in the object to be processed cannot be collected efficiently, and the amount of biogas released can be improved. Not much contribution. Furthermore, when the fermentation rate after introducing the material to be processed is large and the amount of biogas produced is large, there is no positive meaning of introducing biogas bubbles, and when the amount of biogas produced has decreased, It is desirable to actively introduce biogas bubbles. Since the residence time of the biogas in the fermenter is short, the influence on the consumption side is small even if the biogas is recycled, but it is not preferable that the biogas output fluctuates greatly even temporarily. Therefore, it is necessary to efficiently collect fine biogas bubbles in the object to be processed with few biogas bubbles.

  For this reason, the fermentation system of the present invention accepts an object to be processed and outputs a biogas obtained by fermentation of the object to be processed, and a stirrer that moves and moves the impeller inside the object to be processed. And a bubble supply means for discharging a part of the biogas output from the fermenter to the inside of the object to be processed through a bubble discharge tube that moves in synchronization with the impeller. By discharging the bubbles of biogas into the object to be processed through the bubble discharge pipe that moves in synchronization with the impeller, the vortex of the object to be processed formed by the movement of the impeller and the bubble discharge pipe are released. The relative speed difference with the bubble can be almost eliminated. Therefore, the bubbles of the biogas are not easily crushed from the injected state, and are caught in the vortex of the object to be processed in a state having a unique and sufficient buoyancy without being miniaturized. For this reason, the injected bubbles are collected by collecting the fine bubbles in the object to be processed around them, and then floated. In addition, by introducing biogas bubbles in synchronization with the movement of the impeller, the bubbles can be dispersed and introduced into the object to be processed, and the small amount of air bubbles dispersed in the object to be processed can be introduced. Bubbles can be collected and released from the object to be processed, and a reduction in the recovery rate of biogas can be suppressed.

  The bubble supply means may be an independent mechanism that rotates the bubble discharge tube in synchronization with the impeller by a drive device independent of the impeller. Further, the bubbles of the biogas can be discharged from the impeller, and the bubble supply means can be completely integrated with the stirring device. However, providing the impeller with a plurality of functions makes the impeller expensive and also causes a reduction in the ability to stir. Therefore, it is desirable that the bubble supply means includes a bubble discharge tube driven by a shaft that drives the impeller. Since the drive mechanism of the bubble supply means can be shared with a mechanical stirring device, it is economical and the impeller and the bubble discharge tube can be separated, so that each can be designed in an optimum shape. By providing a pipe for guiding the biogas to the bubble discharge pipe along the shaft, the biogas can be easily supplied to the rotating bubble discharge pipe.

  Furthermore, the shaft can be hollow, and the bubble discharge tube can be configured to output biogas supplied via the flow path inside the shaft, which can simplify the fermentation system of the present invention, Economical. In addition, it is desirable that the bubble discharge tube outputs the biogas bubbles dispersed in the longitudinal direction of the bubble discharge tube so that the biogas bubbles can be further dispersed and introduced into the workpiece.

  The bubble discharge tube can be installed either before or after the impeller (downstream or upstream). In terms of increasing the contact distance between the bubbles and the object to be processed, it is desirable that the bubble discharge tube is attached upstream of the impeller. If the impeller creates a swirl that extends from the impeller downstream of the impeller, it is possible to disperse and introduce the bubbles over a wide range by introducing a bubble from the upstream side of the impeller with a short and low resistance bubble discharge tube. .

  A first impeller in which a stirrer stirs a region near the bottom of the workpiece to form an upward flow, and a second impeller that stirs a region near the surface to form a downward flow The bubble supply means includes a first bubble discharge tube disposed below the first impeller, and a second bubble discharge tube disposed below the second impeller. It is desirable to have. By providing a bubble discharge tube corresponding to each impeller, it becomes possible to introduce bubbles at a speed synchronized with the vortex formed by each impeller, and more efficiently collect fine bubbles of the object to be processed. be able to. Further, although the upper side is upstream with respect to the second impeller, considering that the bubbles rise due to buoyancy, it is better to dispose the bubble discharge tube on the lower side with respect to the second impeller. The contact distance with the object can be increased, which is effective.

  As described above, in the present invention, when the amount of biogas produced (production amount) is reduced, the introduction of bubbles is suppressed to reduce the production amount of biogas. Therefore, in the biogas production method of the present invention in which the biogas is obtained by fermenting the material to be processed in the fermenter, the first step of stirring the material by moving the impeller inside the material to be processed; The second step of stirring the workpiece by moving the impeller and discharging a part of the biogas output from the fermenter to the inside of the workpiece through a bubble discharge tube that moves in synchronization with the impeller It is desirable to have When the amount of biogas produced is sufficient, the first step outputs the biogas by mechanically stirring the object without introducing bubbles, and the amount of biogas produced is reduced. In the second step, it is possible to suppress the decrease in the amount of biogas produced by introducing bubbles.

  Therefore, in the biogas production system using the fermentation system of the present invention, it is desirable that the biogas for the fermenter can be turned on and off. That is, the biogas generation system of the present invention includes a processing object supply system that supplies a processing object to a fermenter, a receiver that temporarily stores biogas output from the fermentation system, a receiver, or a fermentation system. A biogas return system that supplies the biogas to the bubble supply means discontinuously from a pipe route leading to the receiver. In this biogas generation system, a stable amount of biogas can be supplied over a long period of time even when the object supply system supplies the object to be fermented by batch processing. Therefore, the receiver or tank of the biogas serving as a buffer with the consumer can be reduced, and an economical biogas generation system can be provided.

  FIG. 1 shows a schematic configuration of a biogas generation plant that supplies a power plant on the consumption side as an example of a biogas generation system that generates biogas from livestock manure. The biogas generation plant 1 includes a raw material receiving tank 3 for receiving primitive manure 2a. In the raw material receiving tank 3, the manure 2a is mixed with clean water 2b and the like by a stirrer 3a and diluted to an appropriate viscosity. The processed object 12 is obtained. The biogas generation plant 1 includes a fermentation system 10 that outputs a biogas mainly composed of methane by subjecting the workpiece 12 to methane fermentation. The fermentation system 10 is attached to the fermenter 11 that receives and fermented the workpiece 12, the stirring device 20 that stirs the workpiece 12 inside the fermenter 11, and the stirring device 20. And a bubble supply system 30 for introducing the bubbles as bubbles.

  The biogas generation plant 1 further includes a transfer pump 4 that supplies the workpiece 12 from the raw material receiving tank 3 to the fermentation tank 11, and a gas bag 5 that temporarily stores the biogas 19 output from the fermentation tank 11. The gas return system 40 for supplying a part of the biogas 19 from the pipe 17 extending from the fermenter 11 to the gas bag 5 to the bubble supply system 30 and 35 to 42 ° C. suitable for fermentation of the workpiece 12 in the fermenter 11. Are provided with a hot water boiler system 6 that heats the digestion fluid, a digestion fluid transfer pump 7 that extracts the digestion fluid 18 from the fermenter 11, and a digestion fluid reservoir 8 that stores the extracted digestion fluid 18. The gas return system 40 includes an automatic valve 41 that can turn on and off the gas supply to the bubble supply system 30. A fuel cell plant 50 is connected to the gas bag 5 as a consumption plant, and the biogas supplied from the gas bag 5 is reformed and consumed as fuel for the fuel cell.

  FIG. 2 shows an example of the fermentation system 10. The fermentation system 10 includes a vertical fermenter 11, a stirring device 20 that stirs the workpiece 12 inside the fermenter 11, and a bubble supply system 30 attached to the stirring device 20. The stirrer 20 agitates a region near the bottom of the workpiece 12 to form an upward flow 25 and agitates a region near the surface to form a downward flow 26. A second impeller 22, a shaft 23 that drives these impellers 21 and 22, and a motor 24 that rotates the shaft 23.

  The bubble supply system 30 includes a first bubble discharge tube 31 disposed below the first impeller 21 and a second bubble discharge tube 32 disposed below the second impeller 22. Yes. The first bubble discharge tube 31 and the second bubble discharge tube 32 are attached to a shaft 23 that drives the impellers 21 and 22, and rotate in synchronization with the impellers 21 and 22. The bubble supply system 30 further includes a vertical pipe 33 that supplies the biogas 19 to the first and second bubble discharge pipes 31 and 32 along the shaft 23, and the biogas 19 from the gas return system 40 to the vertical pipe 33. And a swivel joint 34. The swivel joint 34 is a well-known joint having an appropriate seal structure for tightly connecting a rotating pipe and a fixed pipe.

  The system 40 that supplies the biogas 19 to the bubble supply system 30 includes an on / off valve 41, and can inject the biogas 19 into the workpiece 12 intermittently. Therefore, when biogas is generated using this fermentation system 10, immediately after receiving the workpiece 12 from the raw material tank 3, the impellers 21 and 22 of the stirring device 20 are driven to stir and the newly received coating is received. The processed object 12 and the existing processed object 12 containing a lot of methane bacteria are mixed. At this time, if there is a sufficient amount of biogas remaining in the gas bag 5, the bubbles 39 are discharged from the bubble supply system 30, so that stirring of the workpiece 12 can be assisted. Since the bubbles 39 move by buoyancy, if there is a region where the flow of the impellers 21 and 22 is not affected, stirring is promoted by the passage of the bubbles 39.

  When the newly received workpiece 12 and the existing workpiece 12 are mixed, the fermentation rate increases. Inside the fermenter 11, the organic sludge of the object to be treated 12 is decomposed by methane bacteria, the amount of biogas generated increases, and the bubbles 39 become coarse inside the object to be treated 12, so that the fermenter from the object to be treated 12 is fermented. 11 is released at the top. Then, the gas is collected in the gas bag 5 through the pipe 17. At this stage, the amount of methane gas generated inside the workpiece 12 is sufficiently large. Therefore, it is not necessary to promote fermentation more than necessary, and the valve 41 of the biogas supply system 40 is closed, and bubbles are not introduced, and stirring is performed with the impellers 21 and 22 so that the fermentation continues (first step). ).

  Although depending on the capacity of the fermentation system 10 and the like, when several hours have passed since the material 12 to be treated as a raw material was put into the fermenter 11, the fermentation rate decreased and the amount of biogas 19 produced also decreased. Therefore, the valve 41 of the biogas supply system 40 is opened to supply a part of the biogas 19 to the bubble supply system 30. As a result, the bubbles 39 are introduced into the workpiece 12 from the bubble supply pipes 31 and 32 rotating in synchronization with the impellers 21 and 22, and the bubbles 39 are processed in synchronization with the movement of the impellers 21 and 22. 12 (second step).

  The bubble 39 introduced in synchronism with the movement of the impellers 21 and 22 has a rotational speed comparable to the rotational speed of the vortices 25 and 26 of the workpiece 12 formed by the impellers 21 and 22. 26, the bubbles 39 are less likely to be crushed or divided. Therefore, the introduced bubble 39 rises along the movement of the vortex 25 or 26 by its own buoyancy, and in the process, takes in the bubbles of fine biogas 19 in the workpiece 12 and grows. Although the fermentation rate is reduced, in the state where the bubbles of the fine biogas 19 are still sufficiently generated inside the object 12 to be processed, in addition to the decrease in the fermentation rate, the probability that the bubbles will be combined is reduced. As a result, it is considered that the gas release rate rapidly decreases. On the other hand, by positively injecting the bubbles 39, it is possible to collect and actively release the fine bubbles inside the object 12 to be processed, and it is possible to suppress a decrease in the gas release rate. Furthermore, since the bubbles also have a function of stirring the object 12 to be processed, a decrease in fermentation rate can be suppressed, and a decrease in the release rate of the biogas 19 can be comprehensively suppressed.

  If bubbles are introduced from the same position, the bubbles have a high probability of rising inside the object to be processed 12 through the same path, so that biogas generated in other regions cannot be collected. Although it may be possible to improve the recovery efficiency of biogas by dispersing a huge amount of bubbles and introducing them into the object to be processed 12, this substantially reduces the amount of biogas generated even temporarily. So it makes no sense. In the bubble supply system 30 employed in the fermentation system 10 of this example, the bubble discharge pipes 31 and 32 that can be dispersed in the longitudinal direction to generate the bubbles 39 are rotated in synchronization with the impellers 21 and 22. For this reason, a small amount of bubbles 39 can be dispersed and introduced into the object 12 to be processed, and the biogas recovery efficiency can be increased by using a small amount of biogas.

  In this example, the bubble discharge pipe 31 that introduces the bubbles 39 from the bottom of the workpiece 12 is arranged upstream of the impeller 21, that is, below. The viscosity of the workpiece 12 in the fermenter 11 is quite high, and the impeller 21 cannot be rotated and stirred at such a speed that turbulence is generated around the impeller 21. Therefore, by introducing the bubble 39 at the same rotational speed as the impeller 21, the bubble 39 is not crushed and refined by the impeller 21, and is generated by the impeller 21 with a sufficient buoyancy size. The bubbles 39 are swallowed by the vortex 25. In many cases, the impeller 21 generates a vortex 25 that spreads radially outward. Therefore, rather than discharging the air bubbles 39 downstream of the impeller 21, the air bubbles 39 can be dispersed and discharged in a wider range, and the biogas recovery efficiency can be improved.

  On the other hand, the bubble discharge pipe 32 that introduces the bubbles 39 from the surface 12 of the workpiece 12 is disposed downstream of the impeller 22, that is, below. As described above, it is desirable to dispose the bubble discharge pipe 32 upstream of the impeller 22, that is, above the impeller 22 in that the bubbles 39 are dispersed on the vortex 26 formed by the impeller 22. However, the bubble 39 discharged from the bubble discharge tube 32 is desirably of a size having a buoyancy that can be raised by the discharged bubble itself in terms of collecting the biogas. When arranged above 22, the ratio of the bubbles 39 that are not caught in the vortex 26 and float on the surface as they are increases. Therefore, in terms of improving the recovery probability of biogas, it is desirable to dispose the bubble discharge pipe 32 below the impeller 22 that stirs the vicinity of the surface.

  FIG. 3 shows a schematic configuration of a different fermentation system 10. The fermentation system 10 employs a hollow shaft 23 and supplies biogas to the upper and lower bubble discharge pipes 32 and 31 using the inside of the shaft 23 as a gas supply path. In FIG. 4, the connection state of the shaft 23 and the respective bubble discharge tubes 32 and 31 is enlarged and shown in cross section. Inside the hollow shaft 23 is a gas flow path 37, and a part of the biogas 19 is supplied from the gas supply system 40 via the swivel joint 34. Each bubble discharge tube 32 and 31 communicates with a gas flow path 37. Therefore, the biogas 19 is output to the workpiece 12 from the gas discharge holes 35 dispersed in the longitudinal direction of the bubble discharge pipes 32 and 31 as bubbles 39.

  As described above, in the fermentation system 10 of this example, a part of the biogas 19 output as a result of methane fermentation of the workpiece 12 containing organic sludge is returned to the workpiece 12 as bubbles 39. When the rate of methane fermentation is decreasing, the reduction in the recovery rate of biogas 19 is being suppressed. Therefore, when the workpiece 12 is supplied to the fermenter 11 by a batch job, the period during which the biogas 19 is output by a predetermined amount can be extended, and the output reduction of the biogas can be moderated. . Therefore, in the biogas generation plant 1, a certain biogas can be supplied to the power plant 50 on the consumption side for a long time. For this reason, the capacity | capacitance of the gas bag 5 used as a buffer can be made small, and an economical gas supply system can be provided. Furthermore, since the amount of biogas supplied is constant, the power plant 50 can be operated at a rated time for a long time, and facilities for accumulating power such as a battery can be eliminated or downsized. .

It is a figure which shows schematic structure of the biogas production plant which employ | adopted the fermentation system of this invention. It is sectional drawing which shows schematic structure of a fermentation system. It is sectional drawing which shows schematic structure of a different fermentation system. It is sectional drawing which expands and shows the connection part of the shaft and bubble supply pipe | tube of the fermentation system shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Biogas production plant, 10 Fermentation system 11 Fermenter, 12 To-be-processed object, 19 Biogas 20 Stirrer, 21, 22 Impeller, 23 Shaft 30 Bubble supply system, 31, 32 Bubble discharge pipe

Claims (8)

A fermentor that accepts a workpiece and outputs biogas obtained by fermentation of the workpiece;
An agitation device for agitating by moving an impeller inside the workpiece;
A fermentation system comprising bubble supply means for discharging a part of the biogas output from the fermenter to the inside of the object to be processed through a bubble discharge tube that moves in synchronization with the impeller. In Claim 1, the stirring device includes a shaft that drives the impeller,
The fermentation system, wherein the bubble discharge tube is driven by the shaft. In Claim 2, the shaft is hollow,
The said bubble discharge pipe is a fermentation system which outputs the said biogas supplied via the flow path inside the said shaft.   The fermentation system according to claim 1, wherein the bubble discharge tube outputs the biogas dispersed in the longitudinal direction of the bubble discharge tube.   The fermentation system according to claim 1, wherein the bubble discharge tube is attached upstream of the impeller. In Claim 1, the said stirring apparatus stirs the area | region near the bottom of the said to-be-processed object, and forms the flow toward the upper direction, and the flow which stirred the area | region near the surface and directed below And a second impeller for forming
The bubble supply means includes a first bubble discharge tube disposed below the first impeller and a second bubble discharge tube disposed below the second impeller. Fermentation system. A biogas production method for fermenting an object to be treated in a fermenter to obtain biogas,
A first step of stirring the workpiece by moving an impeller inside the workpiece;
The impeller is moved to agitate the object to be processed, and a part of the biogas output from the fermenter is discharged into the object to be processed through a bubble discharge pipe that moves in synchronization with the impeller. The biogas manufacturing method which has a 2nd process. A fermentation system according to any one of claims 1 to 6;
A processing object supply system for supplying the processing object to the fermenter;
A receiver that temporarily stores the biogas output from the fermentation system;
A biogas generation system comprising: a biogas return system that discontinuously supplies the biogas to the bubble supply means from the receiver or a piping path from the fermentation system to the receiver.

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