JP2006224090A - Methane fermentation system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a methane fermentation system which can downsize a fermentor, can prevent the deposition of foreign matters, can reduce agitation power and the amount of digestive sludge, and can increase biogas. <P>SOLUTION: A hardly degradable organic waste, which, when fed, together with an easily degradable organic waste, into a methane fermentor designed for methane fermentation of an easily degradable organic waste in priority to the hardly degradable organic waste, leads to an increase in size of the methane fermentor, the deposition of foreign matters, and an increase in agitation power and the amount of digestive sludge, is separated from the easily degradable organic waste. The easily degradable organic waste is subjected to methane fermentation in a first methane fermentor 5, while the hardly degradable organic waste is subjected to methane fermentation in a second methane fermentor 8. In this case, each of the first and second methane fermentors can be optimally designed for methane fermentation. At the same time, the solid concentration of the easily degradable organic waste introduced into the first methane fermentor is brought to 5 to 15%, and the solid concentration of the hardly degradable organic waste introduced into the second methane fermentor is brought to 20 to 50% to optimize the solid concentrations of the organic wastes introduced into the respective methane fermentors. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a methane fermentation system that obtains biogas by treating organic waste with methane fermentation.

In this type of methane fermentation system, combustible waste, which is an organic waste, is sorted into garbage and foreign substances by a sorting device, and the garbage sorted by this sorting device is solubilized in a solubilization tank. A methane fermentation system is known in which raw garbage solubilized in a tank is subjected to a methane fermentation process involving agitation in a methane fermentation tank to obtain biogas mainly composed of methane and carbon dioxide (for example, Patent Document 1). reference).
JP 2003-275686 A

However, in the methane fermentation system, foreign matter is mixed into the garbage even if the sorting device performs sorting. Examples of the foreign matter include lightweight items such as fibers such as grass and trees, papers (paper waste), plastic films, and heavy items such as earth and sand and metal pieces. And since this foreign material is introduced into a methane fermentation tank with garbage, it is necessary to enlarge a methane fermentation tank. The capacity of this methane fermenter varies depending on the process and the presence or absence of addition of trace salts, but it requires about 7 to 30 days for the amount of input. For example, the amount of methane fermenter input (sorted garbage) is In the case of 100 t / day, the foreign matter contamination rate is 30%, and the methane fermentation tank stays for 20 days, the capacity of the methane fermentation tank is required to be 2000 m ³ , but if no foreign matter is mixed, 1400 m ³ is sufficient. is there. Thus, since the enlargement of a methane fermentation tank is required, a construction cost will increase and the heating calorie | heat amount of a methane fermentation tank will increase.

Moreover, large stirring power is required to prevent foreign matter from staying in the methane fermentation tank. Incidentally, if the foreign material is not mixed, the stirring power per methane fermentation tank capacity 1 m ³ may be about 8W, but the foreign material is mixed about 30%, the methane fermentation tank capacity 1 m ³ stirring power per Requires about 100W.

  In addition, the above heavy foreign matter can be deposited at the bottom in the methane fermentation tank and pulled out together with the digested sludge. It floats and accumulates on the surface to form scum (sediment), and when the stirring force is weak, it is pushed up by the generated biogas and the entire amount floats on the liquid surface to form hard scum. In any case, a scum is formed, and once this scum is formed, it is difficult to remove. And this scum may make it difficult for the biogas to escape to the gas phase and bumping may occur. When this bumping occurs, the pressure in the methane fermentation tank rises rapidly, and the safety valve installed in the methane fermentation tank opens, and biogas leaks to the outside. Here, the formation of this scum is also closely related to the sludge concentration in the methane fermentation tank, and the higher the sludge concentration in the methane fermentation tank, the higher the viscosity of the liquid. It becomes difficult to occur. Therefore, if the sludge concentration is, for example, 8% or more and an appropriate stirring force is applied, the generation of scum will be almost eliminated, but in reality, the stirring force needs to be increased as the sludge concentration increases, On the other hand, if stirring is stopped, scum is easily generated.

  In addition, when the digested sludge from the methane fermentation tank is extracted and dehydrated by a dehydrator, a dehydrated digested sludge having a water content of about 70% is obtained. This dehydrated digested sludge may be recycled as a composting or carbonizing treatment. In some cases, the incineration equipment is incinerated together with the sorted foreign matter, and therefore, the amount of digested sludge generated is required to be reduced.

  In addition, as described above, combustible waste is mixed with organic hard-to-decompose waste (hereinafter referred to as “hard-to-decompose”) such as paper and pruning waste such as grass and trees. ing. Biogas is also obtained from refractory organic waste such as pruned waste, such as fibers and paper, by methane fermentation. The methane fermentation rate is significantly slower than that of organic wastes. Here, since methane fermentation tanks are designed with priority given to methane fermentation of food waste, even if the above-mentioned pruning garbage, fibers, paper, and other persistent organic wastes are put into the methane fermentation tank A sufficient amount of biogas generated cannot be obtained, and the hardly decomposable organic waste that could not be decomposed floats in the methane fermentation tank, so that a large stirring power is required. On the other hand, when a methane fermentation tank is designed by giving priority to the methane fermentation rate of difficult-to-decompose organic waste such as pruning waste, fibers and paper, an extremely large methane fermentation tank is required, which is not economical.

  The present invention has been made to solve such problems, and it is possible to reduce the size of a methane fermentation tank, prevent foreign matter accumulation, reduce stirring power, increase the amount of biogas generated, and reduce the amount of digested sludge. The object is to provide an illustrated methane fermentation system.

  A methane fermentation system according to the present invention includes a first methane fermenter for methane fermentation of easily decomposable organic waste, and a second methane fermenter for methane fermentation of hardly decomposable organic waste. The easily degradable organic waste is put into the first methane fermenter with a solid concentration in the range of 5 to 15%, and the hardly degradable organic waste has a solid concentration of 20 to 50%. It is characterized by being put into the second methane fermenter in the range of.

  According to such a methane fermentation system, when the methane fermentation tank is designed with priority given to methane fermentation of readily decomposable organic waste, when the methane fermentation system is supplied together with easily decomposable organic waste, Refractory organic waste that leads to an increase in tank size, foreign matter accumulation, stirring power and digested sludge volume is separated from readily decomposable organic waste. While the methane fermentation is performed in the first methane fermenter, the hardly decomposable organic waste is methane fermented in the second methane fermenter. For this reason, the first methane fermenter is designed with priority given to methane fermentation of readily degradable organic waste, and the second methane fermenter gives priority to methane fermentation of persistent organic waste. Each methane fermenter is designed to be optimal for methane fermentation. Here, the readily degradable organic waste is adjusted to a solid concentration of 5 to 15% at the time when it is put into the first methane fermentation tank, and the hardly decomposable organic waste is the second The solid matter concentration is adjusted to 20 to 50% at the time when it is put into the methane fermenter, and the solid matter concentration of the organic waste put into each methane fermenter is optimized. As a result, it is possible to reduce the size of the methane fermentation tank, prevent foreign matter accumulation, reduce the stirring power and the amount of digested sludge, and increase the total amount of biogas generated.

  Here, as a structure of the 2nd methane fermentation tank which show | plays the said effect | action effectively, maintaining the methane fermentation temperature in the said 2nd methane fermentation tank in the range of 55 +/- 2 degreeC is mentioned. This means that when methane fermentation is performed on persistent organic waste, the fermentation rate is higher than that of medium temperature fermentation at around 38 ° C when the methane fermentation temperature is maintained in the range of 55 ± 2 ° C. This is because the organic matter decomposition rate is high and the amount of biogas generated is large. Moreover, in a 1st methane fermenter, either middle temperature fermentation around 38 degreeC or high temperature fermentation around 55 degreeC may be sufficient. The specific composition of readily degradable and hardly decomposable organic waste is as follows: easily degradable organic waste mainly includes garbage, and hardly degradable organic waste is pruning waste and Examples include a configuration including at least one of paper waste.

  In addition, the second methane fermenter mixes the digested sludge generated in the first methane fermenter with the hard-to-decompose organic waste. Therefore, the solid concentration is easily adjusted to 20 to 50%.

  In addition, as a specific configuration that effectively exhibits the above-described action, an organic waste in which easily decomposable organic waste and hardly decomposable organic waste are mixed is used as easily decomposable organic waste. The first methane fermenter methane-ferments easily degradable organic waste separated by the separator, and separates it into second methane. The fermenter has a configuration in which refractory organic waste separated by a separation device is subjected to methane fermentation.

  Here, if a solubilization tank for solubilizing organic waste in which easily decomposable organic waste and difficult-to-decompose organic waste are mixed is provided on the front side of the separation device, this is possible. The solubilization tank solubilizes easily degradable organic waste so that it can be rapidly methane-fermented in the first methane fermentation tank on the rear stage side.

  Furthermore, it is preferable to add digested sludge after methane fermentation to the solubilization tank. This is because the acid fermentation rate of organic waste decreases with decreasing pH, but digested sludge has a high alkalinity, so it is effective in buffering the pH and adding bacteria necessary for solubilization. Because there is. By adding digested sludge to the organic waste in this way, the easily degradable organic waste that should be methane-fermented in the first methane fermenter is added to the hardly-decomposable organic waste separated by the separator. The proportion of organic waste mixed in decreases, the second methane fermentation tank can be reduced, and the amount of biogas generated from the first methane fermentation tank increases. Therefore, a sludge supply line that supplies a part of the digested sludge generated in the first methane fermentation tank to organic waste that is a mixture of easily decomposable organic waste and difficult-to-decompose organic waste. It is suitable to have.

  In addition, there are various types of separation devices, but mainly a readily decomposable organic waste containing raw garbage and a hardly decomposable organic waste containing at least one of pruned waste and paper waste. It is preferable to employ a screw press having a high sorting and removing ability. By adopting this screw press, the solid concentration of the easily decomposable organic waste charged into the first methane fermenter is adjusted to 5 to 15%, and the solid of the hardly decomposable organic waste is The object concentration is adjusted to about 50%.

  In addition, when the screw press has a sorting particle size of 5 mm to 20 mm, it is difficult to decompose organic waste containing at least one of pruning waste and paper waste mainly from easily decomposable organic waste including raw waste. Waste is effectively removed.

  Thus, according to the methane fermentation system according to the present invention, the first methane fermenter is designed with priority given to methane fermentation of easily decomposable organic waste, and the second methane fermenter is difficult to decompose organic. It is designed with priority given to methane fermentation of organic waste, and each methane fermenter is designed to be optimal for methane fermentation, and the solids concentration of organic waste put into each methane fermenter is optimal Is done. As a result, it is possible to reduce the size of the methane fermentation tank, prevent foreign matter accumulation, reduce the stirring power and the amount of digested sludge, and increase the total amount of biogas generated.

  Hereinafter, a preferred embodiment of a methane fermentation system according to the present invention will be described with reference to FIGS. In the drawings, the same or corresponding elements are denoted by the same reference numerals, and redundant description is omitted. 1-3 is each figure which shows the methane fermentation system which concerns on 1st embodiment of this invention, Comprising: FIG. 1 is a block block diagram which shows a methane fermentation system, FIG. 2 is the separation apparatus in FIG. The side surface block diagram which shows the screw press as FIG. 3, FIG. 3 is a block diagram which shows the 2nd methane fermenter in FIG.

  As shown in FIG. 1, the methane fermentation system 1 includes a sorting device 2, a solubilization tank 3, a separation device 4, a first methane fermentation tank 5, a digested sludge storage tank 6, a mixing tank 7, and a second methane fermentation tank 8. The dehydrator 9 is connected in this order. The solubilization tank 3 and the digested sludge storage tank 6 are connected by a sludge supply line L1, and the separation device 4 and the mixing tank 7 are connected by a dehydrated foreign matter supply line L2.

  Moreover, this methane fermentation system 1 connects the gas holder 10 and the gas utilization equipment 11 in this order with respect to the 1st methane fermentation tank 5 and the 2nd methane fermentation tank 8, and with respect to the dehydrator 9 and the sorting apparatus 2. An incineration facility 12 is connected, and a wastewater treatment facility 13 is connected to the dehydrator 9.

  First, combustible waste as organic waste carried into the facility is crushed by a crushing device (not shown) in the preceding stage of the sorting device 2. As this crushing apparatus, a vertical or horizontal cutting machine, a vertical or horizontal swing hammer, a vertical or horizontal ring grinder, a single-axis or multi-axis low-speed rotary crusher, etc. are adopted. It is a vertical ring grinder or a low-speed rotary crusher that can be easily selected by the apparatus 2.

  The sorting device 2 at the latter stage of the crushing device sorts the combustible waste crushed by the crushing device into sorted garbage containing a lot of garbage and sorted foreign substances containing a lot of garbage other than this garbage. . Although this sorter 2 is roughly classified into a dry type and a wet type, in the case of a wet type, it is not necessary to provide a preceding crushing device. As this wet sorting apparatus, it is preferable to use an apparatus called a hydropulper which adds water, sludge or the like to combustible waste and crushes and sorts it with a strong stirring force.

  In addition, as a dry-type sorting device, a sieving type, a specific gravity difference type, an electromagnetic wave type, a magnetic type, an eddy current type, a combination method thereof, or the like is adopted. The sieving type is vibration type, rotary type, roller type, specific gravity type is wind type, mechanical type, composite type, electromagnetic type is X-ray type, near infrared type, visible light type, The magnetic type includes a suspension type, a drum type, and a pulley type, and the eddy current type includes a permanent magnet type and a linear motor type. Here, combining the specific gravity difference type by the wind type and the magnetic type with the sieving type is suitable for sorting garbage from combustible waste.

  In addition, a bag breaker and a bag removal machine may be provided in front of the crushing device in order to break a bag mixed with combustible waste, or a sorting device 2 may be provided between the bag breaking device and the crushing device. good. There are compression type, rotary type, and thermal cutting type as bag breakers, compression type includes pressure blade type and upright blade type, and rotary type includes drum type, rotary blade type, and shear type. However, the shearing type is preferable for the bag breaking of combustible waste.

  In addition, when the sorting device 2 is provided between the bag-breaking machine and the crushing device, any of the above sorting devices can be applied. However, since the sorting is performed on combustible waste that has not been crushed, It is preferable to adopt a roller type.

  And when the garbage ratio of combustible waste is 30 to 50%, the sorting apparatus 2 makes the garbage ratio 70 to 80% and the garbage ratio other than the garbage is 20 to 20%. On the other hand, the sorted foreign matter has a garbage ratio of 5% or less and a garbage ratio other than the garbage of 95% or more.

  Here, the sorted garbage sorted by the sorting device 2 is specifically, garbage that is easily degradable organic waste, as well as fibers and paper including pruning garbage such as grass and trees. It contains hard-to-decompose organic waste such as paper (paper waste) and foreign materials such as metal pieces. In the following, fibers and papers including pruning garbage such as grass and trees are simply referred to as pruning garbage.

  The solubilization tank 3 at the rear stage of the sorting device 2 is solubilized so that the garbage, which is easily degradable organic waste in the sorted garbage, can be rapidly methane-fermented in the first methane fermentation tank 5 at the latter stage. To do. In this solubilization tank 3, temperature adjustment and concentration adjustment are performed so that methane fermentation of food waste is facilitated in the first methane fermentation tank 5, the food waste is acid-fermented, and the organic matter is low in lactic acid, acetic acid and the like. It is molecularized. The adjustment temperature of the sorted garbage in the solubilization tank 3 is 30 ° C to 60 ° C. Here, in the intermediate temperature fermentation in which the methane fermentation temperature in the first methane fermentation tank 5 is around 38 ° C., the temperature in the solubilization tank is 38 ° C. to 40 ° C., and the methane fermentation temperature in the first methane fermentation tank 5 is In high-temperature fermentation around 55 ° C, the temperature in the solubilization tank is set to 55 ° C to 60 ° C, respectively, but even in the methane fermentation of medium temperature fermentation, the temperature in the solubilization tank may be 55 ° C to 60 ° C. is there. Moreover, although the adjustment | control solid substance density | concentration of the sorting garbage in the solubilization tank 3 changes with systems of the methane fermentation tank 5, it is about 5%-25%.

  When using a dry sorting device in the previous stage, water and sludge are added to the sorted garbage in the solubilization tank 3 to adjust to a predetermined sludge concentration, but when using a wet sorting device, a hydropulper is used. Since water and sludge are added, it is not particularly necessary to adjust the concentration in the solubilization tank 3, and it is approximately 5% to 9%.

  Here, in this embodiment, the digested sludge storage tank 6 is connected to the solubilization tank 3 through the sludge supply line L1, and the digested sludge from the first methane fermentation tank 5 is connected through the sludge supply line L1. A part of it is supplied, and this digested sludge adjusts the garbage. Here, the acid fermentation rate of food waste decreases with decreasing pH, but digested sludge has high alkalinity, so it is effective in buffering pH lowering and has the effect of adding bacteria necessary for solubilization. .

  By supplying digested sludge to the sorted garbage in this way, the first methane fermenter is originally used for the hard-to-decompose organic waste such as pruned waste that is separated and discharged by the separation device 4 at the subsequent stage. 5, the rate of mixing garbage, which is an easily degradable organic waste to be methane-fermented, decreases, the amount of biogas generated in the first methane fermentation tank 5 increases, and the second methane fermentation tank 8 Can be reduced. Digested sludge may be added directly to the solubilization tank 3 or added to a line that connects the sorting apparatus 2 and the solubilization tank 3 and transfers the sorted garbage from the sorting apparatus 2 to the solubilization tank 3. In short, it is only necessary to add to the sorted garbage from the sorting device 2.

  By the way, if the addition rate of the digested sludge with respect to the sorting garbage from the sorting apparatus 2 is raised, it is necessary to enlarge the solubilization tank 3. Therefore, in order to reduce the size of the solubilization tank 3, a part of the digested sludge after methane fermentation is added to the sorted garbage from the sorting device 2 and the solubilized garbage from the solubilization tank 3. good. The digested sludge may be added to a line that connects the solubilization tank 3 and the separation apparatus 4 and transfers the solubilized garbage from the solubilization tank 3 to the separation apparatus 4. A mixing tank by mechanical stirring may be provided and added to the mixing tank, or may be added directly to the separation device 4. In short, it may be added to the solubilized garbage from the solubilizing tank 3. .

  Moreover, the solubilization tank 3 may be operated under anaerobic conditions while blocking oxygen, or may be operated under aerobic conditions in which air or oxygen is actively blown in contact with air. However, in any case, solubilization of garbage, which is an easily degradable organic waste, proceeds under appropriate operating conditions.

  The residence time in the solubilization tank 3 is preferably 1 to 48 hours. Here, the acid fermentation proceeds as the residence time becomes longer. However, since the pH in the solubilization tank is lowered and the acid fermentation rate is also lowered, the residence time is particularly preferably about 8 hours. Further, if the residence time is longer than this, it is necessary to increase the capacity of the solubilization tank 3 and the amount of heat to be heated is not economically preferable.

  Here, the solubilized garbage from the solubilization tank 3 is, in addition to the solubilized garbage which is an easily decomposable organic waste, and hardly decomposable organic matter such as pruned garbage. It contains foreign matter such as waste and metal pieces.

  The separation device 4 subsequent to the solubilization tank 3 separates the solubilized garbage from the solubilization tank 3 into garbage separation liquid and dehydrated foreign matter (separated sludge) that are easily decomposable organic waste. Is. The dehydrated foreign matter referred to here includes persistent organic waste such as pruning waste and foreign matters such as metal pieces.

  As the separation device 4, a screw press dehydrator, a centrifugal dehydrator, a filter press dehydrator, a belt press dehydrator, a multi-disc dehydrator, a drum screen, etc. are adopted, but easily decomposable mainly including garbage. It is preferable to employ a screw press dehydrator (hereinafter simply referred to as a screw press) that has a high ability to sort and remove organic wastes such as pruning waste and other hard-to-decompose organic wastes and foreign matters.

  As shown in FIG. 2, this screw press includes a rotating screw blade 4a inside, and a casing 4b that accommodates the screw blade 4a has a large number of sorting holes 4c having a predetermined diameter communicating inside and outside. The solubilized garbage thrown in from the mouth 4d is dehydrated by gravity in the first half, and dehydrated by the squeezing force by the extrusion of the screw blade 4a and the shearing force by the rotation in the second half, to separate the garbage separation liquid and dehydrated foreign matter. While separating and discharging the garbage separation liquid from the garbage separation liquid discharge port 4e, the dehydrated foreign matter is discharged from the dehydration foreign matter discharge port 4f provided at the end in the feed direction.

  Here, in order to effectively separate solubilized garbage into garbage separation liquid and dehydrated foreign matter, that is, to effectively remove hard-to-decompose organic waste and foreign matters such as pruning waste from raw garbage The selection particle size by the selection hole 4c of the screw press is preferably 5 mm to 20 mm.

  And when the solid substance concentration of the solubilized garbage introduced is 5 to 25% (the adjusted solid substance concentration of the selected garbage in the solubilization tank 3), The solid matter concentration is 5 to 15%, and 80% or more of the hardly decomposable organic waste and foreign matters such as pruning waste contained in the garbage are removed as dehydrated foreign matters. The dehydrated foreign matter has a solid concentration of about 50%. The sorting hole 4c may be a slit.

  The first methane fermentation tank 5 following the separation device 4 methane-ferments the garbage separation liquid from the garbage separation liquid discharge port 4e of the separation apparatus 4 to produce biogas mainly composed of methane and carbon dioxide. Is to be generated. Therefore, the first methane fermentation tank 5 is designed with priority on methane fermentation of readily decomposable organic waste including garbage separation liquid (according to methane fermentation).

  In this methane fermentation tank, stirring by a mechanical stirrer, liquid stirring by a pump, gas stirring by a gas blower or a gas compressor, and the like are performed, but stirring by a mechanical stirrer is preferable. Here, the methane fermentation temperature of the first methane fermenter 5 may be either medium temperature fermentation around 38 ° C or high temperature fermentation around 55 ° C. The fermentation temperature of methane fermentation is roughly divided into medium temperature fermentation and high temperature fermentation. Generally, high temperature fermentation is said to have a higher fermentation rate, higher organic matter decomposition rate, and more biogas generation than medium temperature fermentation. ing. On the other hand, compared with high temperature fermentation, medium temperature fermentation is less susceptible to inhibition by ammonia, and has the advantage of requiring less heating and cooling heat before and after methane fermentation. In methane fermentation of readily degradable organic waste, high-temperature fermentation has a higher fermentation rate in the initial stage of fermentation than intermediate-temperature fermentation, but the organic matter decomposition rate is small in the difference between intermediate-temperature fermentation and high-temperature fermentation, and the amount of biogas generated There is no big difference. Accordingly, the first methane fermenter 5 may be either medium temperature fermentation or high temperature fermentation. Moreover, in the 1st methane fermentation tank 5, the valve | bulb (not shown) for drawing out the digested sludge which is a residue after methane fermentation from a bottom part suitably is provided, and digested sludge is pulled out by opening this valve.

  The digested sludge storage tank 6 connected to the first methane fermentation tank 5 stores the digested sludge extracted from the methane fermentation tank 5, and the sludge supply line described above using a part of the digested sludge as a regulator. Supply to the solubilization tank 3 through L1.

  The separation tank 4 is also connected to the mixing tank 7 connected to the digested sludge storage tank 6 through a dehydrated foreign matter supply line L2, and from the dehydrated foreign matter discharge port 4f of the separation apparatus 4 through the dehydrated foreign substance supply line L2. The dehydrated foreign matter is supplied. The mixing tank 7 mixes the dehydrated foreign matter from the separation device 4 with the digested sludge supplied from the digested sludge storage tank 6 and supplied to the solubilization tank 3, and has a solids concentration of 20 Adjust to ˜50% and put into the second methane fermenter 8.

  The second methane fermentation tank 8 connected to the mixing tank 7 is a tank for producing biogas by methane fermentation of the mixture from the mixing tank 7, and is mainly used for organic waste that is difficult to decompose such as pruned waste. It is intended for the decomposition of things. Therefore, the second methane fermentation tank 8 is designed with priority given to methane fermentation of hardly decomposable organic waste such as pruned waste (according to methane fermentation). In the second methane fermentation tank 8, high-temperature fermentation is performed to maintain the methane fermentation temperature in the range of 55 ± 2 ° C. This means that when refractory organic waste is subjected to methane fermentation, the fermentation rate is higher than that of medium temperature fermentation around 38 ° C when the methane fermentation temperature is maintained in the range of 55 ± 2 ° C. This is because the organic matter decomposition rate is high and the amount of biogas generated is high. And when the digested sludge extracted from the 1st methane fermentation tank 5 is thrown into the 2nd methane fermentation tank 8 like this embodiment, the 1st methane fermentation tank 5 is also high-temperature fermentation. Is preferred. This is because the biota is different between high-temperature fermentation and medium-temperature fermentation. When the first methane fermentation tank 5 is subjected to methane fermentation by medium temperature fermentation, the digested sludge extracted from the first methane fermentation tank 5 is directly dehydrated without using the second methane fermentation tank 8. It is preferable to dehydrate.

  Here, in this embodiment, as shown in FIG. 3, a cylindrical horizontal methane fermenter capable of increasing the sludge concentration is employed as the second methane fermenter 8. Fig.3 (a) is a front cross-sectional block diagram which shows the 2nd methane fermenter in FIG. 1, FIG.3 (b) is a right view which shows a 2nd methane fermenter.

  The fermenter 8 has a cylindrical tank 8a whose both ends are closed, and a rotary shaft 8b which is disposed at the axial center of the tank 8a and passes through both ends of the tank 8a and is rotated by, for example, hydraulic pressure. And a partition plate 8c that is provided at a plurality of locations in the circumferential direction of the rotating shaft 8b (four equal positions in the present embodiment) and extends to the vicinity of the end of the tank 8a, and a peripheral wall that constitutes the tank 8a. An inlet 8d provided at the side of the end on one side, a digested sludge outlet 8e provided at the lower part of the other end of the peripheral wall, and a plurality provided at intervals along the axis at the upper part of the peripheral wall The biogas discharge port 8f is provided, and the mixture from the mixing tank 7 input from the input port 8d is stirred by the partition plate 8c and methane-fermented while being sent to the digested sludge discharge port 8e. At this time, the tank 8a Biogas generated from various locations inside the biogas outlet While collecting through f, discharging the digested sludge from the digested sludge outlet 8e.

  The gas holder 10 connected to the biogas discharge port 8f of the second methane fermentation tank 8 and the first methane fermentation tank 5 includes the biogas generated in the first methane fermentation tank 5 and the second methane fermentation tank. The biogas produced | generated by 8 is stored.

  The gas utilization facility 11 connected to the gas holder 10 uses biogas from the gas holder 10. The biogas is used as fuel for generators and boilers such as gas engines and fuel cells, or the methane concentration in biogas is concentrated by gas separation membrane method, PSA method or liquid absorption method, etc. as automobile fuel etc. Used.

  A dehydrator 9 is connected to the digested sludge outlet 8e of the second methane fermentation tank 8. The dehydrator 9 dehydrates the digested sludge extracted from the second methane fermentation tank 8. As the dehydrator 9, a screw press, a centrifugal dehydrator, a filter press dehydrator, a belt press dehydrator, a multiple disk dehydrator, or the like is employed.

  The incinerator 12 connected to the dehydrator 9 and the sorting device 2 incinerates the dehydrated digested sludge dehydrated by the dehydrator 9 and the sorted foreign matter sorted by the sorting device 2. As this incineration equipment 12, what has a fluid bed incinerator, what has a stoker incinerator, etc. are adopted.

  Moreover, the waste water treatment facility 13 connected to the dehydrator 9 is for treating the dehydrated separation liquid from the dehydrator 9 so as to have a prescribed water quality.

  According to the methane fermentation system 1 configured as described above, combustible waste brought into the facility is crushed by the crushing device, and the combustible waste from the crushing device is sorted by the sorting device 2 into sorted garbage and sorted foreign matter. The sorted garbage from the sorting device 2 is solubilized in the solubilizing tank 3 using the digested sludge from the digested sludge storage tank 6 as a regulator, and the solubilized garbage from the solubilized tank 3 is raw in the separating device 4. Separated into garbage separation liquid and dehydrated foreign matter.

  When this dehydrated foreign matter is supplied together with easily decomposable organic waste to a methane fermenter designed with priority given to methane fermentation of readily decomposable organic waste such as garbage, It contains hard-to-decompose organic waste such as pruning waste that leads to increased size, foreign matter accumulation, stirring power and increased amount of digested sludge.

  On the other hand, the garbage separation liquid separated from the dehydrated foreign matter by the separation device 4 is efficiently methane-fermented in the first methane fermentation tank 5 that is designed with priority given to methane fermentation of readily degradable organic waste. And biogas is efficiently generated.

  As described above, the first methane fermentation tank 5 is supplied with the easily decomposable organic waste by removing the hardly decomposable organic waste. Since it is only necessary to pay attention to the second methane fermentation tank 8 to which the product is supplied, the stirring power is reduced. In addition, easily degradable organic waste has a fast fermentation rate, and hardly any organic waste that is hardly degradable is supplied into the tank. Therefore, the methane fermentation tank is downsized compared to the conventional technology. Yes.

  In this way, dehydrated foreign substances are removed from the garbage separation liquid by the separation device 4, but some foreign substances are put into the methane fermentation tank 5 together with the garbage separation liquid. The foreign matter is appropriately extracted together with the digested sludge by opening the valve.

  The digested sludge is stored in the digested sludge storage tank 6, and the digested sludge from the digested sludge storage tank 6 is mixed with the dehydrated foreign matter separated by the separation device 4 in the mixing tank 7, and the mixture from the mixing tank 7 is Methane is efficiently fermented in the second methane fermenter 8 designed with priority given to methane fermentation of hard-to-decompose organic waste such as pruned waste, and biogas is efficiently generated.

  The biogas generated efficiently in each of the first methane fermentation tank 5 and the second methane fermentation tank 8 is mixed by the gas holder 10 and used in the gas utilization facility 11.

  On the other hand, the digested sludge (residue) from the second methane fermentation tank 8 is dehydrated by a dehydrator 9, and the dehydrated digested sludge dehydrated by this dehydrator 9 and the sorted foreign matter sorted by the sorting device 2 are incinerated as waste. 12, the dehydrated separation liquid from the dehydrator 7 is treated to a prescribed water quality by the wastewater treatment facility 13 and drained outside the system.

  Thus, in this embodiment, when it is supplied together with easily decomposable organic waste to a methane fermenter designed with priority given to methane fermentation of easily degradable organic waste (garbage). Refractory organic waste (pruning waste, etc.) that leads to an increase in the size of the methane fermentation tank, accumulation of foreign matter, stirring power, and digested sludge is separated from readily decomposable organic waste. The degradable organic waste is methane-fermented in the first methane fermenter 5, while the hardly decomposable organic waste is methane-fermented in the second methane fermenter 8. For this reason, the first methane fermenter 5 is designed with priority given to methane fermentation of easily decomposable organic waste, and the second methane fermenter 8 is methane of hardly decomposable organic waste. Designed with priority given to fermentation, each methane fermenter 5, 8 is designed to be optimal for methane fermentation. Moreover, the solid concentration of the easily decomposable organic waste put into the first methane fermenter 5 is 5 to 15%, and the hardly decomposable organic waste put into the second methane fermenter 8 The solids concentration of the organic waste to be introduced into each of the methane fermentation tanks 5 and 8 is optimal. As a result, the methane fermenter is miniaturized, foreign matter accumulation is prevented, stirring power and digested sludge amount are reduced, and in addition, the total biogas generation amount is increased.

  Note that the second methane fermenter 8 described in FIG. 3 is relatively expensive, and it is not economical to treat the entire amount of the selected garbage, but the raw material is separated by the separation device 4 as in this embodiment. It is effective when it can be separated into the waste separation liquid and the dehydrated foreign matter and the supply amount to the second methane fermentation tank 8 can be reduced.

  FIG. 4 is a block diagram showing a methane fermentation system according to the second embodiment of the present invention. The difference between the methane fermentation system 100 of the second embodiment and the methane fermentation system 1 of the first embodiment is that garbage that is easily decomposable organic waste and pruning garbage that is hardly decomposable organic waste. Is a point for combustible waste that has been separated in advance, and accordingly, a sorting device 2 that sorts sorted garbage and sorted foreign matter, and separation that separates solubilized garbage and dehydrated foreign matter. The apparatus 4 is eliminated, and raw garbage is directly supplied to the solubilization tank 3 and pruning waste is supplied directly to the mixing tank 7. It should be noted that the pruning waste does not change in properties even if it is solubilized in the solubilization tank 3 for several hours.

  Needless to say, even in the methane fermentation system 100 configured as described above, it is possible to obtain substantially the same effect as in the first embodiment, and in addition, a sorting apparatus for sorting and separation. Since 2 and the separation device 4 are omitted, the equipment cost can be reduced.

  Hereinafter, Example 1 and Comparative Example 1 carried out by the present inventors to confirm the above effect will be described.

Example 1
The material balance using the methane fermentation system 1 of the first embodiment is shown in FIG. As shown in the figure, solubilized food waste is obtained by adding 150t of digested sludge generated in the first methane fermenter in a solubilization tank to 100t of selected food waste containing a large amount of food garbage sorted by the sorting device. Was separated by a separator. Here, a screw press having a sorting particle size of 10 mm was used as the separation device. As a result, 211.4t of garbage separation liquid and dehydrated foreign matter 38.6t containing persistent organic waste such as pruning waste and foreign matters were obtained. The garbage separation liquid was subjected to methane fermentation in the first methane fermenter, and 6755 m ³ of biogas was obtained. The digested sludge generated in the first methane fermentation tank is mixed with 53.2 t of the digested sludge other than that supplied to the solubilization tank with the dehydrated foreign matter separated by the separation device in the mixing tank, and a mixture of 91.8 t Got. The mixture was methane fermentation with second methane fermentation tank, a biogas is obtained of 10132M ^3, biogas 16887M ³ was obtained when combined with methane (6755m ³⁾ generated from the first methane fermentation tank. This is 168.87 m ³ when converted per 1 t of sorted garbage. The digested sludge generated in the second methane fermentation tank was dehydrated with a dehydrator to obtain 35.8 t of dehydrated digested sludge.

(Comparative Example 1)
Example 1 is the same as Example 1 except that the screw press, mixing tank, and second methane fermentation tank, which are the separators of Example 1, are eliminated and the solubilized garbage in the solubilization tank is directly introduced into the methane fermentation tank. It was. Further, 100 t of process water was added to the solubilization tank in order to adjust the selected garbage to a predetermined sludge concentration. The material balance is shown in FIG. As shown in the figure, the amount of biogas generated was 157.50 m ³ per ton of selected garbage, and 37.8 t of dehydrated digested sludge.

  As described above, in Example 1, the amount of biogas generated increased by 7%, and the dehydrated digested sludge decreased by 5%.

It is a block block diagram which shows the methane fermentation system which concerns on 1st embodiment of this invention. It is a side block diagram which shows the screw press as a separation apparatus in FIG. It is a block diagram which shows the 2nd methane fermenter in FIG. It is a block block diagram which shows the methane fermentation system which concerns on 2nd embodiment of this invention. 2 is a diagram showing a material balance of Example 1. FIG. It is a figure which shows the material balance of the comparative example 1.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,100 ... Methane fermentation system, 3 ... Solubilization tank, 4 ... Separation apparatus (screw press), 5 ... 1st methane fermentation tank, 8 ... 2nd methane fermentation tank, L1 ... Sludge supply line.

Claims (8)

A first methane fermenter for methane fermentation of readily degradable organic waste;
A second methane fermenter for methane fermentation of persistent organic waste,
The readily decomposable organic waste is charged into the first methane fermenter with a solid concentration in the range of 5 to 15%,
The said refractory organic waste is thrown into said 2nd methane fermentation tank in the range whose solid substance concentration is 20 to 50%, The methane fermentation system characterized by the above-mentioned.   2. The methane fermentation system according to claim 1, wherein a methane fermentation temperature in the second methane fermentation tank is maintained in a range of 55 ± 2 ° C. 3.   3. The methane according to claim 1, wherein the second methane fermentation tank mixes digested sludge generated in the first methane fermentation tank with the hardly decomposable organic waste and performs methane fermentation. Fermentation system. The organic waste in which the easily decomposable organic waste and the hardly decomposable organic waste are mixed into the easily decomposable organic waste and the hardly decomposable organic waste. A separation device for separating,
The first methane fermenter methane ferments easily degradable organic waste separated by the separation device,
The methane fermentation system according to any one of claims 1 to 3, wherein the second methane fermentation tank performs methane fermentation of the hardly decomposable organic waste separated by the separation device.   A solubilization tank for solubilizing organic waste in which the easily decomposable organic waste and the hardly decomposable organic waste are mixed is provided on the front side of the separation device. Item 5. The methane fermentation system according to item 4.   Sludge supply line for supplying a part of the digested sludge generated in the first methane fermentation tank to the organic waste in which the easily decomposable organic waste and the hardly decomposable organic waste are mixed The methane fermentation system according to claim 4 or 5, characterized by comprising:   The methane fermentation system according to any one of claims 4 to 6, wherein the separation device is a screw press.   The methane fermentation system according to claim 7, wherein the screw press has a selected particle size of 5 mm to 20 mm.

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