JP2020125236A - Method of producing methane gas and compost using biomass resource - Google Patents

Abstract

To provide a method of performing methane fermentation in a method efficient and inflicting little burden to an external environment in an external circulation type methane fermentation reaction facility filled with biomass.SOLUTION: This invention relates to a batch type methane fermentation facility that produces methane gas and fermented compost using airtight methane fermentation tanks 11 and 12 by: filling the tanks with coarsely crushed biomass being a raw material; externally circulating reaction water including methanogen and flowing the reaction water, spraying from above the filling material; and repeating the above steps to perform methane fermentation. The method of producing the methane gas and compost includes: using a pair of methane fermentation tanks of the same shape and the same volume; at the time when starting spraying of the reaction water to start the methane fermentation in one of the methane tanks (11), starting injecting inert gas for reaction termination to finish the methane reaction in the other of the methane tanks (12); and making adjustment so that an injection amount of the inert gas in the fermentation tank 12 becomes substantially equal to an amount of generation of biogas including the methane gas in the fermentation tank 11.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to a method for producing methane gas and compost using unused biomass resources such as rice straw and straw. More specifically, by using a methane fermentation facility filled with an external circulation type biomass resource, by devising the operating method and operating method of the fermentation facility, it is possible to ferment simultaneously with methane gas with less environmental impact and more efficiently. The present invention relates to a method for producing methane gas and compost using biomass resources capable of producing compost.

In agriculture, a large amount of various unused agricultural organic substances such as rice straw, straw, corn stalks, vegetable stalks and leaves are generated. Also, in the forest industry, a large amount of unused forest-derived organic substances is generated due to defoliation and undergrowth work. Conventionally, these various unused resources have been treated by leaving them as they are, incinerating them, or burying them. Furthermore, in the food industry, livestock industry, etc., various organic wastes such as processing wastewater, livestock wastewater, viscous excrement such as livestock faeces are generated, and these wastes are chemically treated or activated sludge is generated. It was necessary to remove the organic waste by treating it with a treatment or the like.

On the other hand, as various environmental problems have been highlighted in recent years, there has been a strong demand for industrial activities that have the least impact on the environment. In particular, in order to prevent global warming, greenhouse gases such as carbon dioxide are used. There is a strong demand for reduction of effect gas. In such a situation, it is not preferable to simply incinerate various kinds of wastes generated in agriculture and forestry as described above into carbon dioxide gas by natural decomposition. If these wastes can be effectively reused and utilized as biomass resources, it will be a win and profit, as well as the effective use of resources and the purpose of preventing global warming. In addition, organic waste such as livestock viscous excrement is desired to be used more effectively and rationally and economically than ever before.

It is estimated that the amount of carbon dioxide gas mainly derived from various biomass resources in the natural world reaches about 2.8 times that of the greenhouse effect gas generated by various industrial activities. Therefore, if various unused organic substances, which are such biomass resources, can be effectively used without spontaneous decomposition or incineration treatment, it is extremely significant in reducing greenhouse gases.

In order to deal with such problems, it has been considered to effectively utilize various biomass resources that have not yet been used, and in particular, the phenomenon of methane fermentation is used to convert to methane gas or compost. It has been noticed to do. For example, there are those for high-concentration organic wastewater discharged from animal excrements such as livestock and food factories, etc., but mainly those that undergo methane fermentation treatment of liquid or slurry state, As a method for treating a solid organic substance, a method using a large-scale fermenter made of steel or concrete has been proposed (see Patent Document 1).

Under such circumstances, the present inventor has proposed a method of utilizing this methane fermentation technique to carry out a methane fermentation reaction of such a solid biomass resource at a simpler and lower cost. That is, as a methane fermentation tank, a framework made of iron or wood is used, and the framework is covered with a flexible gas impermeable sheet material to form an airtight space inside, and biomass resources are used in this. A methane fermentation reaction facility for filling and circulating the reaction water externally to perform a fermentation reaction has been proposed, and a patent has already been obtained (see Patent Documents 2 and 3).

JP, 2007-90340, A Japanese Patent No. 4615052 Japanese Patent No. 5555395

Yi Yutomo: JEFMA No. 53 [2005.8], Special contribution, Outline of methane fermentation technology and its application prospects Civil Engineering Research Institute, National University Corporation Tohoku University, Takuma Co., Ltd.: Joint Research Report on Development of Highly Efficient Fermentation System for Sewage Sludge (October 2010) Kitama Yu, Osamu Mizuno, Keisuke Funaishi, Koji Yamashita: Fast Methane Fermentation System for Garbage, ECO INDUSTRY, 8(6) PP. 5-19 (2003) Tomio Nagai; Papers and posters presented at the 5th Biomass Science Conference of the Japan Institute of Energy (2011.01.20-21). Tomio Nagai; Proceedings of the 26th Japan Society for Energy and Resources Research Conference, Conference Presentations and Oral Presentations, (2010.01.26.-27.)

The present invention, in an external circulation type methane fermentation reaction equipment filled with biomass resources, by utilizing such equipment, by performing a methane fermentation more efficiently and by a method with less load on the external environment It is an object of the present invention to provide a method for producing methane gas and fermented compost.

The present inventor has examined a method of utilizing various solid biomass resources that have been left unused or incinerated in large amounts, and in an external circulation type methane fermentation reaction facility filled with such solid biomass resources. The inventors have found a method of performing methane fermentation more efficiently and with a method having a smaller load on the environment without discharging wastewater to the outside by devising a method of operating the equipment, and completed the present invention.

That is, the present invention is an invention having the following contents.
(1) The inside is filled with the coarsely crushed material of the biomass resource as the raw material, and the reaction water containing the methane bacteria is externally circulated and sprayed from the upper part of the filling, and this is repeated to perform the methane fermentation reaction. In a batch-type methane fermentation facility that produces methane gas and fermented compost using an airtight methane fermenter, the amount of water contained in the obtained fermented compost is determined by the amount of water contained in the biomass resource crushed product and the fermentation reaction. A method for producing methane gas and compost using biomass resources, characterized in that the water content of the fermented compost is set to a maximum of 75% by weight or more, which is not less than the amount of water consumed.

(2) A method for producing methane gas and compost using the biomass resource according to (1) above, characterized in that a fully dried biomass resource having a fully dried water content of 35% by weight or less is used. ..

(3) The method for producing methane gas and compost using the biomass resource according to (1) or (2) above, wherein the water content of the obtained fermented compost is 50 to 75% by weight.

(4) As a raw material to be filled in a methane fermentation tank, a mixture of coarsely crushed biomass resources, sticky extruded livestock extruded into a rod, and dried is mixed. A method for producing methane gas and compost using the biomass resource according to any one of 1.

(5) The method for producing methane gas and compost using biomass resources according to (4) above, wherein the viscous excrement of livestock is extruded into a rod shape having a diameter of 10 to 20 mm by a screw feeder and a snake pump.

(6) Place the viscous excrement of livestock on a flatly spread coarsely crushed biomass resource, and place an extruded product of the viscous excrement of livestock so that the water content is 35% by weight or less. A method for producing methane gas and compost using the biomass resource according to (4) or (5) above, which is dried by sunlight ventilation.

(7) The inside is filled with the coarsely crushed material of the biomass resource as the raw material, and the reaction water containing the methane bacteria is externally circulated and sprayed from the upper part of the filling, and this is repeated to carry out the methane fermentation reaction. In a batch type methane fermentation facility that produces methane gas and fermented compost using an airtight methane fermentation tank, a pair of methane fermentation tanks of the same shape and the same volume are used, and one methane fermentation tank (fermenter A) Starts spraying the reaction water and starts the methane fermentation reaction, the other methane fermentation tank (fermentation tank B) finishes the methane fermentation reaction at the same time and injects an inert gas to stop the reaction. The operation of starting and adjusting the injection amount (flow rate) of the inert gas in the fermenter B to be approximately the same as the generation amount (flow rate) of the biogas containing methane gas in the fermenter A is performed. A characteristic method for producing methane gas and compost using biomass resources.

(8) Injection of biogas generated from the start of the reaction of one methane fermenter (fermentor A) to the stage before the stage of the steady fermentation reaction and the inert gas of the other methane fermenter (fermentor B) The method for producing methane gas and compost using biomass resources according to (7) above, characterized in that biogas generated from the start to the end operation is collected in the same methane gas storage tank.

(9) The biomass according to (7) or (8), characterized in that a combustion exhaust gas obtained by completely burning biogas with an air excess coefficient of 1.08 to 1.10 is used as the inert gas. A method for producing methane gas and compost using resources.

(10) One of the above (7) to (9), characterized in that the inert gas is injected through the perforated pipe provided at the bottom of the fermenter so that it is substantially even over the entire bottom surface of the fermenter. A method for producing methane gas and compost using the biomass resource described in.

As the biomass resource used according to the present invention, a sufficiently dried product is used, and the water content contained in the obtained fermented compost is set to be equal to or more than the water content of the biomass resource minus the water content consumed in the fermentation reaction. This allows for long-term methane fermentation reaction using only the reaction water stored in the fermentation equipment, without discharging excess water to the outside, and methane fermentation with zero process wastewater. Can proceed. Therefore, in the production of methane gas and compost using biomass resources by methane fermentation over a long period of time, no process wastewater is emitted outside the system of the production facility, and the environmental load is very low and environmentally friendly. It is a manufacturing method.

Further, in the method of the present invention, a sticky extrudate of livestock which has been difficult to use as a raw material, which has been difficult to use until now, is extruded into a rod shape and dried, and is used together with a coarsely crushed material of a biomass resource. Further, by adjusting the water content as described above, methane gas and compost can be produced without producing process wastewater outside the production equipment. Therefore, viscous excretions of livestock, which are difficult to perform methane fermentation and have a large load on the environment when discharged, can be used for methane fermentation by the method of the present invention.

Furthermore, by using two or more pairs of batch-type methane fermentation tanks, the timing of the methane fermentation reaction start time and the timing of the methane fermentation reaction end time are aligned, and the inert gas injection rate at the methane fermentation reaction end time is adjusted. By the method of the present invention for controlling the above, not only a high concentration of methane gas of about 56% by volume can be obtained in the stationary fermentation reaction period, but also in a non-steady operating state such as a methane fermentation reaction start period or a methane fermentation reaction end period. The advantage is that methane gas having a low concentration of about 28% by volume and a constant concentration can be obtained. In this case, even at the end of the reaction, a constant concentration of methane gas of about 28% by volume can be obtained by mixing different concentrations of methane gas from the two fermentors forming a pair. This is a concentration much higher than the explosion limit of methane gas, and the operation of the device can be performed without fear of gas explosion.

It is an explanatory view showing an example of the whole methane fermentation equipment of the present invention when there is one fermenter. It is explanatory drawing which shows an example of the whole methane fermentation equipment of this invention at the time of using two fermenters. It is a graph which shows the operation cycle of each methane fermentation tank by the method of this invention, when using two fermenters, and the methane gas concentration in the biogas which generate|occur|produces.

When methane fermentation is carried out in a reaction facility that carries out methane fermentation reaction on biomass resources such as rice straw and straw, the methane fermentation proceeds in the medium to high temperature range of about 20 to 60°C over a period of about two months. In this case, a decomposition rate of about 70% of the biomass resources used can be achieved.
This is because the decomposition rate of raw garbage is generally about 80% according to "report on high-speed methane fermentation of raw garbage" by Li Yu-Tama et al. (see Non-Patent Documents 1 and 3) and sewage. An example in which a reaction rate of 73% was obtained in a continuous experiment with a multistage digestion tank for sludge (see Non-Patent Document 2), the fermentation conditions differ, but rice straw and straw that were plowed into the soil of paddy fields in the summer were one It is also estimated from the phenomenon of almost 100% decomposition during the summer.

In addition, in the case of non-edible agricultural biomass raw materials, there are few ammonia-causing substances such as proteins in the raw materials, and reaction water is contact-flowed by the external circulation spray method, so volatile reaction-inhibiting substances such as ammonia are present. It is considered that the influence of the reaction-inhibiting substance is also reduced since it is easily removed by diffusion. As a result of methane fermentation, about 80 to 90% of the biodegradable polymer organic matter COD contained in the biomass raw material is converted to biogas, and the remaining 10 to 20% becomes proliferating bacterial cells, which are non-degradable solids. It is said that it becomes a digestion residue (compost) along with food.

In the present invention, a coarsely crushed material of a biomass resource as a raw material is filled inside, and reaction water containing methane bacteria is circulated by an external circulation pump, and sprayed from above the coarsely crushed material of a biomass resource. This allows a specific operation using a batch-type methane fermentation facility that uses a so-called fixed-bed type solid-liquid contact reaction tank, which causes the methane fermentation reaction to be performed with the surface of the raw material biomass resource crushed material being sufficiently wet. This is a method for producing methane gas and compost using biomass raw materials, in which this methane fermentation equipment is operated under operating conditions to carry out a methane fermentation reaction.

First, the invention that is the first characteristic technique of the present invention will be described.
The present invention is a fermented compost obtained when producing methane gas and compost by performing a methane fermentation reaction using an external circulation type methane fermenter that is a fixed-bed type solid-liquid contact reaction tank filled with biomass raw materials as described above. The amount of water contained in is not less than the difference between the amount of water contained in the biomass resource crushed product and the amount of water consumed in the fermentation reaction, and the water content of the fermented compost is up to 75% by weight, preferably up to The methane fermentation reaction is carried out under the condition of up to 60% by weight.

The water content of the fermented compost obtained here is up to 75% by weight, preferably up to 60% by weight. The compost, which is the residue obtained after the reaction of methane fermentation, has a water content of about 70 to 85% as it is, but it is squeezed and dehydrated to a water content of up to 75% by weight, preferably up to 60% by weight. Up to When the water content of the fermented compost becomes high, the liquid may be exuded by the pressure of the upper part in the lower part when stacking the compost bags. Also, referring to the fact that the maximum water content is about 60 to 75% in various examples of water-based organic matter filter cakes and water-based activated carbon filter cakes, the practical water content of pressed dehydrated compost is 75%. Hereafter, it is necessary to set it to preferably 60% or less.

The coarsely crushed biomass resources used as raw materials here are roughly crushed from agricultural biomass resources such as rice straw and wheat straw, and forest biomass resources generated by defoliation and pruning of trees and undergrowth work. It is dried and used by filling it into a fermentation reaction tank.

In the present invention, it is preferable to use a coarsely crushed material of such a biomass resource having a water content of 35% by weight or less. It is a value that is sufficiently realizable. A dry product of agricultural biomass, such as rice straw, having a water content of 35% by weight or less can be easily obtained by sun-drying and if left unfolded, and the quality deterioration due to leaving is not a problem. If the water content is 50% by weight, a soft material having a little moisture can be used, and if used, it can be roughly judged by touching with a hand. The biomass raw material having a water content of about 50% by weight can be easily realized by putting it in a net bag or the like and covering it with a waterproof sheet and leaving it at 35% by weight or less.

In such a coarsely crushed material of the biomass material, the surface of the biomass material is almost dry, and thus it is difficult to proceed with fermentation as it is. In order for the methane-fermenting fungi to act, it is desirable that fluid mixing be sufficient and that the biomass resources of the raw materials and the cells be sufficiently contacted with water. Therefore, in order to facilitate the reaction, reaction water is mixed down the surface of the raw material to promote the reaction due to mass transfer between the bacterial cells and the raw material. It is desirable to start the fermentation reaction by ensuring a necessary and sufficient minimum amount of the circulating reaction water to wet and circulate the raw material.

The amount of water contained in the fermented compost is compressed and dehydrated by compressing and dehydrating the compost after the reaction so that the amount of water contained in the raw material biomass resource crushed product and the amount of water consumed in the fermentation reaction become larger than the subtracted amount. The water content in the fermentation system decreases. When the methane fermentation is promoted by such a method, the amount of water remaining in the system continues to decrease for each fermentation batch, and it is necessary to supplement the decreased amount. The amount of water in the system before and after the start of fermentation can be measured and checked, and the amount of water can be replenished so that it is almost constant every time. At that time, it is convenient to supplement with excess digested sludge water containing fermented bacterial cells procured from the outside, which is economically advantageous. By continuing such operation, production can be continued without taking the process wastewater out of the system of the fermentation plant.

This can be analyzed by approximating with a simplified reaction formula as shown below. That is, assuming that the system does not contain other substances in and out, the whole methane fermentation is approximated as shown in the following formula (I), the substance balance is calculated, and it can be confirmed by the approximate analysis.
Agricultural or forest biomass is a polymer whose main component is cellulose produced by the polymerization of (C ₆ H ₁₀ O ₅ ). In nature, many microorganisms and methane-fermenting bacteria cause a decomposition reaction similar to the following. It is thought to be done.

Three molecules of methane gas and three molecules of carbon dioxide gas are generated by decomposition from one cellulose unit (C ₆ H ₁₀ O ₅ ). Theoretically, when 100% of solid cellulose is decomposed, 162 kg of cellulose and 18 kg of water generate 48 kg of methane gas and 132 kg of carbon dioxide gas. In this case, stoichiometrically, the water content of the raw material biomass resource is {18/(162+18)}×100, that is, 10% by weight.

In a realistic methane fermentation reaction, the average decomposition rate of the agricultural biomass raw material is considered to be about 2/3 (66.7%), so the decomposition rate of the agricultural biomass raw material was set to 2/3 and compressed and dehydrated. When the water content of the subsequent fermented compost is set to 60% by weight, the substances shown below are used, assuming that the biomass raw material before and after the methane fermentation reaction and a system other than the fermented compost do not enter and exit. When the water content of the biomass raw material is calculated from the balance calculation, the water content is 36.5% by weight.

This means that if "the total amount of water consumed in the reaction and the water content of the fermented compost (the amount of water output)" is covered only by the "moisture content of the biomass material (the input amount of water)," the water content of the biomass material It means that the rate needs to be 36.5% by weight. When using a biomass raw material with a low water content of less than 36.5% by weight, the amount of water in the reaction system will decrease by the subtracted amount, so supplement the decreased amount to circulate in the system. It is necessary to keep the amount of water necessary for the methane fermentation to be almost constant, and it is important to wet the surface of the coarsely crushed biomass raw material and to make good contact and mixing with the bacterial cells involved in the reaction in order to promote methane fermentation smoothly. Is. Therefore, the reaction water stored in the system is turbulently flowed down to the surface of the raw material by the external circulation spray method to promote solid-liquid mixing. In this way, the required amount of water is secured in the system to proceed the reaction.

Specifically, based on the above formula (I) and calculating the balance based on 162 kg of absolutely dried biomass raw material, the residual biomass in the compressed compost (the total amount of the incompletely decomposed product of cellulose and proliferating cells) Since the dry product) is 54 kg, which is 1/3 of the initial amount (162 kg), the relationship of {M/(54+M)}×100=60 is established if the water content in the compost is Mkg. From this relational expression, the water content (M) in the compost is 81 kg. Since the compressed compost is 54 kg of the total dry matter of biomass incomplete decomposition products and bacterial cells and 81 kg of water, the total amount is 135 kg.

On the other hand, if the moisture content of the biomass feedstock is Nkg, the decomposition rate is 2/3 and the moisture content in the compost is just 60% by weight in a system where other substances do not come and go before and after the methane fermentation reaction. The relationship of “weight of biomass raw material before reaction+content of water content=decomposition amount of biomass after reaction+weight of residual biomass of compost dried product+water content of compost” is established. When this is expressed by a mathematical formula based on the formula (I), it is as follows.

From this relational expression, the water content (N) of the biomass raw material is 93 kg. Therefore, the water content of the biomass raw material for making the water content in the compressed dehydrated compost 60% by weight is 93/(162+93)×100=36.5, and the water content of the biomass raw material is 36.5% by weight. ..

Similarly, when the decomposition rate of the biomass raw material in methane fermentation is set to 2/3 (66.7%) on average, and the moisture content of the compost after pressing and dehydrating the fermented compost is 55% by weight, A water content of 32% by weight is required, and if the water content of the compost after pressing and dehydration is 50% by weight, the water content of the biomass raw material is 29% by weight from the mass balance calculation under the same conditions. You will need one.

As a specific example, in the case of methane fermentation using 1,000 kg of a biomass raw material having a water content of 30% by weight, the substance balance is calculated as follows.
When the decomposition rate of the biomass material is 2/3 (66.7%) and the water content of the compost is 60% by weight, the absolute dry biomass content in the material is 700 kg and the water content in the material is 300 kg. The amount of biomass decomposed in 2/3 of 700 kg is 467 kg, and the weight of dried fermented compost is 1/3 of 700 kg, which is 233 kg.
According to the above formula (I),
Amount of methane gas generated = (467/162) x 48 = 138 kg,
If methane gas and carbon dioxide gas are equal,
The total biogas generation amount = 22.4 × (138/16) × 2 = 387m 3
Moisture content in fermented compost = 233 x (60/40) = 350 kg
Water consumption in methane fermentation reaction = 467 x (18/162) = 52 kg
Water content in biomass feedstock-Water content consumed in reaction = 300-52 = 248 kg
Moisture content taken out from the fermentation system = Moisture content in the fermented compost-(Water in raw material-Water consumed by reaction)
=350-(300-52)=102kg
Therefore, in this case, 102 kg of water is taken out from the reaction system per 1,000 kg of the biomass material each time methane fermentation is performed, so that the reaction water in the reaction circulation system decreases. This may be supplemented with this water before starting the next fermentation reaction.

The above examination results mean the following. That is, this was derived by a reaction system premised on a system in which other substances do not come and go before and after the methane fermentation reaction, and for example, the water content of the obtained compressed dehydrated compost is 60% by weight. In this case, if the water content of the biomass raw material is set to 36.5% by weight, the amount of water contained in the biomass raw material and the amount of water taken out by the obtained compost are balanced, and insufficient water is added or surplus is left over. It shows that the methane fermentation can be continued without draining water. Similarly, when the water content in the compressed dehydrated compost is 55% by weight, the water content of the biomass raw material is 32% by weight, and when the water content in the compost is 50% by weight, the water content of the biomass raw material is 29% by weight. This relationship is established if it is expressed as %.

In the methane fermentation reaction, the amount of water consumed in the reaction is about 10% by weight of the dried biomass raw material as shown in the above formula (I). In such a case, in order to obtain a compressed dehydrated compost having a water content of 60% by weight, use a biomass material having a water content of less than 36.5% by weight to discharge excess water to the outside. It is possible to proceed with methane fermentation without doing so. When a dried material having a water content of 35% by weight or less and a low water content is used as the biomass raw material, the water content in the reaction system gradually decreases, and thus the insufficient water content may be appropriately supplemented. In that case, it is economically advantageous to use fermented digestion sludge water containing bacterial cells generated in other factories or low-concentration wastewater of livestock as supplementary water.

It should be noted that many dry raw materials for agricultural biomass have a large water content of cell tissues in the growth stage, and have many fine spaces partitioned by cell membranes in a dry state. For example, it is considered to be a tissue state similar to a sponge. Therefore, the specific gravity of the dried product is small, and when it comes into contact with water, the water content gradually increases, and many have a water content of about 75 to 80% by weight. This contains about 3 to 4 times the weight of water as the dry raw material, and there is a very large difference in water content between the dry product and the fully wet product. According to the pilot experiment, the replenishment amount of circulating water increases with the increase of the raw material water content in the early stage of fermentation, and it stabilizes without replenishment in the middle stage of fermentation, and it is observed that the amount of water in the relay tank increases due to its release at the end of fermentation. Was given. Since changes in the water content of biomass raw materials and compost in commercial plants also change depending on the equipment and operating method, it is desirable to confirm it in a large-scale practical experiment plant.

Next, a method for producing methane gas and fermented compost by the method of the present invention as described above will be described with reference to FIG.
A methane fermentation tank 1 is filled with a coarsely crushed material 2 of a biomass resource as a raw material. The reaction water containing the methane-fermenting bacteria is stored in the relay tank 6, and the reaction water is supplied through the pipe 9 and the external circulation pipe 4, and the methane fermentation tank 1 is filled with the biomass crushed product 2 It is sprayed on the filling from the spray nozzle 3 provided at the upper part. After a certain amount of reaction water is introduced, thereafter, this reaction water is repeatedly circulated and sprayed from the external circulation pipe 4 through the spray nozzle 3, and the methane fermentation reaction is carried out by continuing this for a long time. The amount of the reaction water sprayed at this time is circulated so that the reaction water flows on the surface of the coarsely crushed material 3 of the biomass resource filled in the methane fermentation tank 1 and the surface is sufficiently wet.

When the methane fermentation tank 1 is hermetically closed and the spraying of the reaction water to the coarsely crushed biomass resource 2 filled therein is started, the oxygen present in the air inside the methane fermentation tank 1 is accompanied by heat generation. It is gradually consumed by the fermentation reaction of the air-fermenting bacteria, and finally the internal space is filled with only a mixed gas of nitrogen gas and carbon dioxide (inert gas). The process of consuming oxygen by the aerobic fermentation reaction is referred to as "aerobic fermentation period" in the present specification. During aerobic fermentation, the temperature of the raw material rises because of the exothermic reaction, but almost no volume change due to gas generation is observed.

When the oxygen in the methane fermentation tank 1 is completely consumed, and when the reaction water is further sprayed, the methane fermentation reaction by the anaerobic methane-fermenting bacteria proceeds and biogas containing methane gas is generated. start. In the present specification, a process in which the reaction by the anaerobic methane-fermenting bacterium starts, biogas starts to be generated, and the amount of biogas generated increases is referred to as a "methane fermentation reaction start period". The transition to methane fermentation can be confirmed by an increase in system pressure and an increase in gas volume, but almost no heat generation due to fermentation is observed. The generated biogas and the mixed gas such as nitrogen gas existing in the methane fermentation tank 1 are sent to the gas holder 7.

When the reaction water is further sprayed, the amount of biogas generated becomes stable, the methane fermentation reaction proceeds in a stable state for a certain period, and biogas is generated at a certain amount (flow rate). This state is referred to as "steady state fermentation reaction period" in the present specification. The biogas containing the generated methane gas is stored in the gas holder 7.

The reaction ends when about 2/3 of the roughly crushed biomass resource 2 is decomposed. The methane fermentation is stopped by injecting an inert gas such as nitrogen gas containing a small amount of oxygen gas from the inert gas injection pipe 10 at the bottom of the methane fermentation tank 1. When the injection of the inert gas is started, the methane fermentation reaction decreases, the amount of methane gas generated decreases, and finally it becomes zero, and the methane fermentation stops. In this specification, the process from the start of the injection of the inert gas to the stop of the injection of the inert gas is referred to as the "end stage of the methane fermentation reaction". Biogas containing the methane gas and the inert gas, which is expelled from the methane fermentation tank 1 by the injection of the inert gas, is sent to the gas holder 7.

In addition, in the injection of such an inert gas, a very small amount of oxygen contained therein acts on the methane-fermenting bacteria like the presence of a toxin, and the fermentation rate is rapidly reduced to stop the generation of methane gas. Along with the diffusive mixing of oxygen gas, the amount of methane gas generated becomes zero rapidly and in a short time, methane fermentation is stopped. Inside the fermenter, turbulent mixing inside the packed bed due to upward airflow due to injection of inert gas from the bottom of the packed bed and drop of reaction water from above and forced by spray droplets of reaction water in the space above the fermenter Due to the mixing, the gas is in a good mixed state.

Further, in this methane fermentation facility, almost the same amount of carbon dioxide gas is generated together with methane gas, and a small amount of nitrogen gas is also generated. In the present specification, as described above, a mixed gas containing these methane gas and carbon dioxide gas is referred to as “biogas”, and when only a methane gas component in this biogas is referred to, it is referred to as “methane gas”. I will.

After completion of the reaction, the reaction water initially introduced is returned to the relay tank 6, and the fermented compost is taken out from the obtained methane fermentation tank 1, and the water content is 75% by weight or less, preferably with a press. Depressurize to 60% by weight. Furthermore, if a high-performance compression dehydrator is used, it is possible to dehydrate up to about 50% by weight. The reaction water that came out by dehydration is also returned to the relay tank 6. After the treatment of the obtained fermented compost is completed, as a next batch, the crushed material 2 of the raw material biomass resource is charged into the methane fermentation tank 1 again, and the biogas and the water content of 75% by weight or less are obtained by the same operation. The fermented compost of can be obtained.

In this series of fermentation steps, for example, in the case of obtaining compressed dehydrated compost with a water content of 60% by weight, if the water content of the coarsely pulverized material 2 of the biomass resource is 36.5%, water as reaction water is especially replenished. It is possible to carry out a continuous fermentation reaction for a long period of time. Further, as the coarsely crushed biomass resource 2, for example, when a dried one having a water content of 35% or less is used, the circulating reaction water stored in the system decreases, so It is replenished from the relay tank 6 so that it does not fall below the value.

Next, regarding the operation of the methane fermentation reaction equipment, the invention of switching the generated biogas which is another characteristic technique of the present invention will be described.
As shown in FIG. 2, the present invention relates to handling of biogas generated from a pair of methane fermenters having the same capacity, such as a methane fermenter A and a methane fermenter B. Generally, in such a methane fermentation tank, a batch-type fermentation reaction is performed in each methane fermentation tank in the following operation cycle. First, after filling the roughly crushed material of the biomass resource as a raw material, the reaction water is circulated and sprayed from the top of the packed bed in a sealed state, and this is continued to start the operation for methane fermentation.

First, since oxygen remains inside the methane fermentation tank at the stage when the spraying of the reaction water is started, a fermentation reaction accompanied by heat generation by the aerobic fermenting bacterium occurs. At this stage, heat is generated due to aerobic fermentation, but no gas such as methane gas is generated (aerobic fermentation period). When the reaction water is continuously sprayed, oxygen in the system is exhausted and the anaerobic methane fermentation reaction starts, the generation of methane gas begins and the amount of the generated gas gradually increases (methane fermentation reaction start period). .. When the amount of biogas generated (flow rate) gradually increases, the amount of biogas generated becomes stable, and the methane fermentation reaction proceeds in a stable state for a certain period. Biogas is generated at a constant amount (flow rate) (steady fermentation reaction period). The amount of biogas generated (flow rate) gradually decreases as methane fermentation progresses and the amount of biomass raw materials inside decreases and the amount of raw materials involved in fermentation decreases. Period). At this time, an inert gas containing a trace amount of oxygen gas is injected from the bottom of the methane fermentation tank to expel the remaining biogas and completely stop the methane fermentation.

In the stationary fermentation reaction period, the gas generation amount changes due to changes in physical conditions such as temperature and chemical conditions such as PH, cell concentration, and raw material composition, but if those conditions are stable and almost constant, Biogas is generated at a substantially constant amount (flow rate).

In the present invention, in a methane fermentation facility having a pair of methane fermentation tanks having the same shape and the same capacity, one of the methane fermentation tanks 11 (methane fermentation tank A) starts the reaction of methane fermentation to generate biogas. In accordance with the timing of the started methane fermentation reaction start period, the operation start time is adjusted in advance so that the other fermentation tank 12 (methane fermentation tank B) is at the reaction end time of the methane fermentation that has already proceeded. Then, in synchronization with this timing, the other fermenter 12 (methane fermenter B) starts to inject the inert gas, and the biogas remaining therein is expelled and replaced. Further, in the purging by the inert gas, the injection amount (flow rate) of the inert gas to be injected becomes equal to the generation amount (flow rate) of the biogas generated in the methane fermentation tank 11 (methane fermentation tank A). It is necessary to supply it while adjusting.

The biogas generated in the methane fermentation tank A and the biogas generated in the methane fermentation tank B are introduced together into a biogas holder. As shown in FIG. 2, the high-concentration biogas generated in the stationary fermentation reaction period is stored in the biogas holder 26, and the low-concentration biogas generated in the methane fermentation reaction start period and the methane fermentation reaction end period is stored in the biogas holder 27, respectively. To collect.

The inert gas injected at the end of the methane fermentation reaction is to completely stop the methane fermentation and replace the biogas filled in the fermentor, and is generally nitrogen gas or carbon dioxide gas. Yes, it is desirable to contain a trace amount of oxygen. Since oxygen has the effect of stopping methane fermentation, it is convenient to include a trace amount of oxygen in the inert gas. Practically, it is convenient to use biogas combustion exhaust gas such as a heating utility boiler used in a methane fermentation plant for agricultural biomass or an accompanying plant factory heating boiler. This combustion exhaust gas may be sucked, cooled and washed by a jet scrubber. As a combustion condition of the boiler for that purpose, it is desirable that complete combustion with an excess air coefficient of 1.10, preferably 1.08 to 1.10.

The combustion exhaust gas obtained by completely burning the high-concentration biogas of 56% by volume of methane gas under the above combustion conditions is used as an inert gas for expelling biogas in the fermenter at the end of the methane fermentation reaction. At this time, 28% by volume of low-concentration methane gas (concentration constant) obtained by joining two low-concentration biogas supplied from the bottom of the fermentation tank and flowing out from the top of the fermentation tank at the same volumetric flow rate as the low-concentration biogas at the beginning of fermentation Since the remaining volume% of O2 gas is maintained at less than 1.0% by volume, the gas of is far away from the explosion limit value of CH4 gas together with the O2 gas concentration and the CH4 gas concentration, and can be safely handled as a fuel gas. I have decided. Since aerobic fermentative fungi also exist in the biomass residue (compost) at the end of the fermentation reaction, a small amount of O2 gas present is further consumed by the action of these fungi, and residual O2 gas is further consumed. It is expected to decrease.

In addition, as a safety measure regarding equipment and operation, a gas leak detector is installed, static electricity is removed, daily gas concentration analysis is used for confirmation, and a fire is caused by attaching a 40-mesh wire mesh between packings on the flange of the pipe through which biogas passes. It is preferable to implement preventive measures.

By operating the methane fermentation equipment according to the method of the present invention as described above, in the theoretical calculation based on the above formula (I), the methane gas concentration in the biogas holder 26 is about 56% by volume during the steady fermentation reaction period. A high concentration of biogas can be obtained. Also, in the methane fermentation reaction start period and the methane fermentation reaction end period, the timing of switching between a pair of methane fermentation tanks should be aligned together, and the methane fermentation tank started at the same time as the methane fermentation tank A start period. By controlling the flow rate of the inert gas injection in B, the biogas holder 27 can obtain a low-concentration biogas having a methane gas concentration of about 28% by volume and a substantially constant concentration.

FIG. 3 shows changes in the concentration of methane gas generated over time in the above-described methane fermentation reaction process by the pair of methane fermentation tanks having the same capacity. The solid line graph shows the methane gas concentration change in the methane fermentation tank A, and the dashed-dotted line graph shows the methane gas concentration change in the methane fermentation tank B. Further, in the case of the methane fermentation tank A, I and V are the methane fermentation reaction start period, II is the steady fermentation reaction period, and III is the methane fermentation reaction end period. In the case of the methane fermentation tank B, I and V are the methane fermentation reaction end period. IV is a stationary fermentation reaction period, and III is a methane fermentation reaction start period. As for the two fermenters, as shown in FIG. 3, the operation timing of each fermenter is adjusted so that when one fermentor is in the methane fermentation reaction start period, the other fermenter is in the methane fermentation reaction end period. To do.

For example, at the start of the I-th cycle in FIG. 3, the methane fermentation reaction in the methane fermentation tank A starts and biogas generation starts. At this same timing, in the methane fermentation tank B, the steady-state reaction of methane fermentation ends, and the injection of an inert gas for ending the reaction starts. At the end of the 1st cycle, in the methane fermentation tank A, the reaction of methane fermentation becomes almost 100%, and in the methane fermentation tank B, the purging and replacement of the biogas inside is completed, and the inside of the tank is almost inert gas. It becomes 100%. In the second cycle II, the methane fermentation reaction proceeds in the methane fermentation tank A, and high concentration biogas of about 56% is obtained. On the other hand, in the methane fermentation tank B, the fermentation residue of the biomass resource, which is the fermentation product formed inside, is taken out, the post-treatment and the coarse crushed material of the biomass raw material for the next operation are charged, and then the methane fermentation tank A Start spraying the reaction water while observing the progress of the reaction, and proceed with the aerobic fermentation reaction (aerobic fermentation reaction period). In the third cycle, the methane fermentation tank A and the methane fermentation tank B are exchanged and the same operation is performed.

In the above-mentioned one methane fermentation tank (methane fermentation tank A), as a pre-stage of the I-th cycle in FIG. 3, the reaction water is sprinkled forward to start the sprinkling of the reaction water for a predetermined period to advance the reaction by the aerobic fermenting bacteria. The oxygen existing inside the methane fermentation tank is completely consumed (aerobic fermentation reaction period). By continuing to spray the reaction water in this state, the methane fermentation reaction by the anaerobic methane fermentation bacterium starts, and biogas gas containing methane gas starts to be generated (methane fermentation reaction start period).

On the other hand, the other methane fermenters (methane fermenter B) are set to end the methane fermentation reaction at this time, and at the start stage, the space inside the methane fermenter is 100% filled with biogas. Has been done. At this timing when the steady fermentation reaction ends, the inert gas (nitrogen gas and carbon dioxide gas are the main components and contains a small amount of oxygen) is started from the inert gas injection pipe 18 at the bottom of the fermentation tank to complete the methane fermentation reaction. To stop. At this time, it is important to adjust the injection rate of the inert gas in the methane fermentation tank B so that the injection rate (flow rate) is the same as the amount of methane gas generated in the methane fermentation tank A (flow rate). That is.

Bio generated from two methane fermentation tanks A and B by the operation operation of the above-mentioned methane fermentation reaction start period and methane fermentation reaction end period by the methane fermentation equipment comprising a pair of methane fermentation tanks of the same capacity according to the method of the present invention. By mixing the gases together, it is possible to obtain a low-concentration biogas having a substantially constant concentration with a methane gas concentration of about 28% by volume during all of the methane fermentation reaction initiation period and the methane fermentation reaction termination period. ..

According to this operating method of the present invention, the low-concentration biogas obtained by mixing the biogas discharged from the two fermenters always maintains a constant methane gas concentration, and the concentration is about 28 times that of the high-concentration methane gas. It becomes volume%. This gas contains less than 1.0% by volume of O2 gas, but the concentration is outside the range of explosion limit of methane gas (5.3 to 14% by volume), and stable and safe handling is possible. In addition, it is possible to theoretically accurately predict the displacement of biogas in the methane fermentation tank at the end of the methane fermentation reaction, and reduce the concentration of methane gas in the fermentation tank by increasing the degree of substitution to reduce the loss to the atmosphere. It is possible to bring them closer together. Also in that case, the mixed low-concentration biogas from the two tanks has a constant value of 28% by volume of methane gas. According to this method, it is possible to increase the recovery rate of methane gas and eliminate the need to install combustion equipment such as a flare stack.

The change in the concentration of biogas generated during the methane fermentation reaction initiation period and the methane fermentation reaction termination period by the method of the present invention as described above can also be confirmed by the following analysis.

First, the change in biogas concentration in the methane fermentation tank at the start of the methane fermentation reaction will be examined.
Here, the inside volume of the fermenter is V ₀ (m ³ ), the biogas concentration inside the fermenter is C ₁ (volume %), the generated biogas flow rate is v ₁ (m ³ /hr), and flows out of the system. The biogas flow rate is v ₁ (m ³ /hr), and the generated biogas concentration is C ₀ (volume %). The generated biogas concentration C ₀ is always constant at 100 (volume %).
From the material balance inside and outside the methane fermentation tank, the following relational expression is derived.

This formula (9) shows the relationship between the decreasing change in the inert gas concentration (100-C ₁ ) in the methane fermentation tank and the tank volume ratio of the biogas generation amount.

Next, the change in biogas concentration in the methane fermentation tank due to the injection of the inert gas at the end of the methane fermentation reaction will be examined.
At the start of the methane fermentation reaction where methane fermentation starts, the space inside the fermenter is filled with an inert gas (mainly nitrogen gas), and when the methane fermentation starts, the system is replaced with biogas generated in a completely mixed state. Although it was a phenomenon that is being carried out, at the end of the methane fermentation reaction, it becomes biogas instead of inert gas, and becomes only inert gas instead of methane gas. In both cases, the names of the gases are interchanged, but since the gas flow rates v ₁ and v ₂ are operated under exactly the same conditions, the values of equation (9) and the following equation (16) are used at all times. Are the same.

Again, the fermenter internal volume is V ₀ (m ³ ), the biogas concentration in the fermenter is C ₂ (volume %), and the low-concentration biogas flow rate flowing out of the system is v ₂ (m ³ /hr). , The concentration of the low-concentration biogas flowing out is C ₂ (volume %), the flow rate of the inert gas to be injected is v ₂ (m ³ /hr), the biogas concentration at the start of the inert gas injection is C ₀ (volume %). C ₀ is 100 (volume %).
In this case as well, the following relational expression is derived from the material balance inside and outside the methane fermentation tank.

Formula (16) shows the relationship between the decrease change in the biogas concentration C ₂ in the fermentor and the fermenter volume ratio of the inert gas supply amount, and v ₁ =v in the formulas (9) and (16). _When operating under the conditions of No. ₂ and when operating at the same time (t) and the same system internal volume V ₀ , the values are exactly the same.
That is, since the left sides of the equations (9) and (16) have exactly the same value, (100−C ₁ )=C ₂ holds, and therefore C ₁ +C ₂ =100. The meaning of this formula is that the flow rate of the inert gas injected at the end of the methane fermentation reaction is adjusted to match the flow rate of biogas generated at the start of the methane fermentation reaction in methane fermentation, and the biogas in the system is blown. The total of the values of the diluted mixed gas concentrations C ₁ and C ₂ flowing out from the respective fermenters to the outside of the system by carrying out the displacement purging is the value of the concentration of the generated biogas of 100% by volume. It shows that the values are equal.

That is, since the inside of both the methane fermentation tank A and the methane fermentation tank B can be regarded as a macroscopically completely mixed state, when the methane fermentation tank is operated under the conditions according to the method of the present invention described above, The total value of gas concentration C ₁ value and C ₂ value is always the same value as 100 volume% biogas concentration (almost 56 volume% methane gas and the rest are nitrogen gas, carbon dioxide gas and other inert gases). ..
Since the biogas having the concentration C _{1 and} the biogas having the concentration C ₂ are mixed by the same volume, the volume is doubled, and the concentration (C ₁ +C ₂ )/2 of the mixed gas is 100/2. It becomes 1/2 of the biogas generation concentration. This has a constant value of 56/2=28% by volume as the methane gas concentration, and the others are inert gases such as nitrogen gas and carbon dioxide gas.

During the methane fermentation reaction start period and the methane fermentation reaction end period, changes in the methane gas concentration in the fermenter greatly fluctuate due to gas replacement of newly generated biogas and injected inert gas. In the fermentation tank, the gas phase is judged to be in a completely mixed state both in the upper space of the packed bed and in the packed bed during the period from the start of the methane fermentation reaction of methane fermentation to the expelling of biogas from the end of the methane fermentation reaction. Since the whole of the above can be regarded as a macroscopically completely mixed state, the relational expression shown by the above-described mathematical expression is applied. Therefore, the formula (9) is the ratio of the generated gas volume (or the injected gas volume) to the fermenter volume v ₁ t/V ₀ , v ₂ t/ in the methane fermentation reaction start period and the formula (16) in the methane fermentation reaction end period. it is a relational expression showing the ratio of the residual gas to V _0. Using this formula, the residual rate (volume%) of the residual gas in the fermenter can be calculated from the amount of injected gas. On the contrary, the required amount of injected gas can be calculated from the residual rate of the residual gas in the fermenter. In addition, if the calculated value is written on a semi-logarithmic graph paper, it can be conveniently used for on-site operation management.

Further, regarding the operation operation of the methane fermentation reaction equipment, another characteristic technique of the present invention is that viscous excrement of livestock can be used together with various agricultural or forest biomass resources used as raw materials for the methane fermentation reaction. ..
Conventionally, a large amount of various unused agricultural biomasses such as rice straw, straw, corn stalk, soybean stalk, vegetable stalk and leaves have been generated in agriculture. Similarly, in forestry, a large amount of unused forest biomass is generated due to pruning and fallen leaves of trees, mowing work and the like. Also, in the livestock industry, a large amount of viscous excrement of livestock such as cattle and pigs is generated.

It is generally considered that such viscous excretions of livestock are difficult to undergo methane fermentation reaction in a solid state, and that methane fermentation cannot proceed without stirring and mixing in an aqueous solution system. In the present invention, such a viscous excrement of livestock is extruded into a noodle shape and dried as a rod-shaped solid material, and the methane fermentation equipment of the present invention is charged with the coarsely crushed material of the biomass resource to treat the methane fermentation reaction. Made possible.

Specifically, the viscous excrement of livestock is molded into noodles with a diameter of about 15 mm, and the amount of crude biomass resources in the range of 10 to 30% by weight based on the dry weight of the biomass resources is used. In addition to the raw material of the crushed product, the crushed product is dried by natural ventilation such that the average moisture content of the noodle molded product is reduced to 35% by weight or less. Even if the entire mixed raw material including other biomass raw materials is used, it is dried to an average water content of 35% by weight or less. By using a mixture of the coarsely pulverized material of the biomass resource and the dried product of the viscous excretion thus obtained, which is filled in the methane fermentation equipment of the present invention and used, methane gas and fermented compost are similarly produced by the methane fermentation reaction. Can be manufactured.

In particular, as with the coarsely crushed agricultural biomass resources having a water content of 35% by weight or less used as a raw material, the noodle moldings of viscous excrement of livestock dried to an average water content of 35% by weight or less and agricultural biomass resources Even when a methane fermentation reaction is performed using a mixture with a coarsely crushed material as the raw material, the amount of water contained in the obtained fermented compost is subtracted from the amount of water contained in the mixed biomass raw material and the amount of water consumed in the fermentation reaction. If the above operation is performed and the water content of the fermented compost is up to 75% by weight, preferably up to 60% by weight, the process wastewater is completely discharged as in the case of the biomass raw material crushed product alone. Can produce methane gas and compost without.

When viscous excrement of livestock is combined with agricultural biomass feedstock for methane fermentation, it is desirable to install equipment related to fermentation near the farm. As raw materials, in addition to livestock excrement, rod-shaped raw materials, rice straw, straw, livestock bedding and the like are used. When methane fermentation is performed by mixing livestock excrement with agricultural biomass raw material, paddle impeller agitator hopper, screw feeder, and mono pump are used in order to maintain the physical strength of stick-like dried livestock viscous excrement and dry it efficiently. It is sufficiently kneaded by, for example, extruding it from an extrusion nozzle to mold it into noodles.

Examples of the equipment for producing such a molded product include NES type feeders (a hopper with a paddle impeller agitator, a connecting device of a screw feeder and a Heishin Monono pump) manufactured by Hyōjin Kikai Co., Ltd. In addition, a viscous rod-shaped extrusion device is provided at the tip of which a hole is made in the bottom of the pipe in a diagonally downward direction, and nozzles having a diameter of about 15 mm are attached at equal intervals of about 10 cm.

The viscous excrement of livestock used is dried by the sunlight-ventilated natural drying method so that the average water content is 35% by weight or less. As an equipment for efficient drying, a light-permeable rainproof roof is installed on a paved surface that hardens the ground and has an inclination to allow water to flow, and prepares a space with good ventilation and natural drying. .. First, a rod-shaped raw material (soybean beans, pruned twigs, reeds, etc.) is dispersed on the floor surface in an amount of about 20% by weight. On top of that, rice straw, straw, bedding and the like are dispersed in an amount of about 60% by weight based on the dry product. Next, a noodle-shaped molded product having an outer diameter of about 15 mm manufactured as described above is dispersed on the uppermost surface. These are left as they are and dried by ventilation natural drying. After 3 to 5 days, it is confirmed that the water content of the viscous excretion is about 50% by weight and the hardness. After that, put it in a large net bag etc., cover the upper part with a waterproof sheet using a part of farmland and leave it for about 1 to 2 months, then perform the second stage natural drying, average water content It is about 25% by weight or less. The biomass resource obtained by mixing the viscous excrement of livestock thus obtained is used as a raw material of the methane fermentation equipment of the present invention.

If the viscous excrement of livestock is mixed with agricultural biomass such as rice straw and straw or stick-shaped solid matter, the undigested cellulose in the viscous excrement of livestock is entangled with each other, and the fermentation is carried out by external circulation. Since the inside is almost stationary, it is not considered that the shape collapses. Even if they are dispersed/dissolved in pieces, they intersect with the agricultural biomass and intersect to become trapped. It is preferable that the viscous excrement of livestock and the raw material of agricultural biomass are mixed and dried, because the odor of the excrement seems to be adsorbed to the surface of the agricultural biomass and the odor is hardly noticed. In addition, depending on the properties of livestock excrement, it is possible to add a small amount of natural cotton waste, lint, paper pulp waste, etc., to enhance the noodle excretion and prevent dissolution. is there.
Hereinafter, the present invention will be described with reference to examples.

Example 1 Production of methane gas and fermented compost with zero process wastewater .
Using a methane fermentation facility for a small pilot test as shown in FIG. 1 as an experimental apparatus, a methane fermentation reaction was performed under the following conditions.
As the methane fermentation tank 1, a cylindrical fermentation tank having a diameter of 600 mm, a height of 2300 mm and an internal volume of 650 liters was used. A spray nozzle 3 is provided on the upper part of the spray nozzle 3, which is connected to a circulation pump 5 and an external circulation pipe 4 to circulate the reaction water accumulated at the bottom of the methane fermentation tank 1 to spray a wide-angle full-face spray nozzle. I do. As the raw material biomass resource, rice straw and wheat straw collected from the field were mixed at a ratio of 1:1 and cut into a length of about 10 cm, and a roughly crushed biomass resource having an average water content of about 10% by weight was used. .. The coarsely crushed material of the biomass raw material was charged from the upper part of the methane fermentation tank 1 to fill the methane fermentation tank 1 with 450 liters to form a packed layer 2 of the coarsely crushed biomass resource. Digested sludge water of medium-temperature methane fermentation of pig excrement obtained from Meidensha Co., Ltd. commercialization plant was placed in the relay tank 6 as reaction water, and 50 liters of the reaction water from the relay tank 6 was supplied from the external circulation pipe 4. It sprayed on the upper part of the packed bed 2 through the spray nozzle 3, and was supplied into the methane fermentation tank 1.

Next, the methane fermentation tank 1 was sealed, and the reaction water introduced into the methane fermentation tank 1 was circulated through the circulation pump 5, the external circulation pipe 4 and the spray nozzle 3, and sprayed from the upper part of the packed bed. The circulating amount of the reaction water was 1.6 liters per minute so that the surface of the filled biomass raw material was wet, and the circulating and spraying of the reaction water was continuously performed. When the spray of reaction water was continued, an aerobic fermentation reaction occurred and the temperature in the methane fermentation tank 1 rose from room temperature to 48°C (aerobic fermentation period). Since the digested sludge water in the relay tank 6 was absorbed by the raw material biomass and decreased with the passage of time, the start of methane fermentation was waited for while supplementing the tap water from time to time to keep the tap water at an intermediate level in the relay tank 6 at a substantially constant level.

About 6 days after the start of circulation of the reaction water, it was confirmed from the level of the floating roof gas holder 7 that the methane fermentation reaction started and biogas was generated. Meanwhile, the amount of tap water replenished was about twice that of digested sludge water. Generation of biogas containing methane gas was confirmed 7 days after the start of circulation of the reaction water, so this biogas was introduced into the gas holder 7. In this state, circulation of reaction water and spraying were continuously repeated as it was, and production of methane gas was observed by methane fermentation of the biomass raw material. This was also confirmed in a combustion test of the generated gas.

When the circulating and spraying state of the reaction water to the packed bed was continued, the liquid volume in the relay tank gradually decreased with the passage of time. Replenished. About 60 days after starting the reaction, the amount of biogas generated decreased. It was at the end of September, and it was judged that the average temperature was below 22°C, the activity of methane-fermenting bacteria decreased, and the production activity stopped. Therefore, the circulation of the reaction water was stopped and the operation for ending the fermentation reaction was performed. After completion of the reaction, the top of the methane fermentation tank 1 was opened and the obtained fermented residue compost was taken out. The weight was about 63 kg and the water content was about 85% by weight. A wooden board was placed on the fermentation residue, which was pressed and dehydrated to obtain a pressed dehydrated compost. Its weight was about 40 kg and its water content was about 60% by weight. Further, 23 liters of reaction water was obtained by the squeezing treatment, and this was returned to the relay tank 6.

By one cycle of methane fermentation reaction using the pilot experimental apparatus shown in FIG. 1, good fermented compost having a water content of about 60% by weight was obtained. In the middle of this methane fermentation reaction, the amount of water in the relay tank decreased, so tap water was replenished in small increments, but the methane fermentation reaction could be completed without discharging excess water outside the reaction system, It was possible to produce methane gas and compost with zero process wastewater.

Example 2 Production of methane gas and fermented compost by switching operation cycles using a pair of fermenters .
A series of fermentation operations from raw material charging to compost removal using one fermenter were experienced in a small pilot experiment, but switching operation in the middle part of the operation cycle using a pair of fermenters was unexperienced. We conducted an experiment focusing on this part. Except for this part, the fermentation tanks A and B are reproduced in exactly the same manner, so it was performed to confirm the change in the methane gas concentration when the operation cycle was switched.

As an experimental apparatus, a methane fermentation facility for a small pilot test composed of two methane fermentation tanks, a methane fermentation tank 11 (methane fermentation tank A) and a methane fermentation tank 12 (methane fermentation tank B) as shown in FIG. Was used to carry out a methane fermentation reaction under the following conditions at an indoor temperature almost the same as the outdoor temperature in summer.
The methane fermentation tank 11 (methane fermentation tank A) and the methane fermentation tank 12 (methane fermentation tank B) have the same size and structure, and the size is the same as the methane fermentation tank used in Example 1. .. The methane fermentation tanks A and B are provided with spray nozzles 15 and 16 respectively at the upper part thereof, and inert gas injection pipes 17 and 18 are provided below the packed bed at the bottom thereof. In addition, the same coarsely crushed biomass resource as the raw material was used as in Example 1.

The coarsely crushed material of this biomass raw material was charged from the upper part of each of the methane fermentation tank 11 (methane fermentation tank A) and the methane fermentation tank 12 (methane fermentation tank B), and 450 liters were filled in each of the methane fermentation tanks. Packed layers 13 and 14 of the crushed material were formed. After that, the openings of both fermenters were closed to wait for the reaction to start by circulating the reaction water. In the relay tank 28, digested sludge water of medium temperature methane fermentation of pig excrement obtained from a commercial plant of Meidensha Co., Ltd. was placed as reaction water.

First, 50 liters of reaction water from the relay tank 28 to the methane fermentation tank A was sprayed from the external circulation pipe 21 through the spray nozzle 15 onto the top of the packed bed 13 and supplied into the methane fermentation tank A. The reaction water introduced into the methane fermentation tank A was circulated through the circulation pump 19, the external circulation pipe 21, and the spray nozzle 15. The circulation amount of the reaction water was 1.6 liters per minute so that the surface of the filled biomass raw material was wet, and the operation of circulating and spraying the reaction water was continuously performed.

Over time, aerobic fermentation reaction accompanied by heat generation by aerobic fermentation bacteria present in the raw material and subsequent reaction by facultative anaerobic fungi under both aerobic and anaerobic conditions occur, and inside the methane fermentation tank A. The oxygen gas in the air present was completely consumed. Due to this aerobic fermentation reaction, the temperature in the methane fermentation tank A rose from room temperature to 48°C. This period is the aerobic fermentation period.

Continuing the circulation and spraying of the reaction water, about 6 days after the start of circulation as the aerobic fermentation period, and when the absolute anaerobic conditions are met, the fermentation shifts in a chain to the absolute anaerobic methane fermentation reaction, Generation of biogas including methane gas was observed. With the passage of time, methane fermentation proceeded and the amount of biogas generated increased. The gas in the tank was sampled at the gas outlet of the methane fermentation tank A, and the methane gas concentration therein was measured. The concentration of methane gas was zero at the start of the reaction, but the concentration of methane gas increased with the passage of time. Eight days after starting the methane fermentation reaction, the concentration became about 56%. The generated biogas was introduced into the low concentration biogas holder 27 through the pipe 24. This period corresponds to the methane fermentation reaction start period of cycle I in the operation cycle of the methane fermentation tank A shown in FIG.

After this period, the amount of biogas generated in the methane fermentation tank A was stable and was generated at a substantially constant amount, but it was most affected by the temperature in the tank and was affected by the change in PH of the reaction circulating water. The operation was carried out with care so as not to change the temperature and PH abruptly. The concentration of methane gas generated during this period was almost constant at 56%. The generated biogas was introduced into the high-concentration biogas holder 26 through the pipe 23. This period corresponds to the stationary fermentation reaction period of cycle II in the operation cycle of the methane fermentation tank A shown in FIG.

8 days after the start of the methane fermentation reaction in the methane fermentation tank A, the methane gas concentration was 56% by volume, and it was confirmed that the stationary fermentation reaction period was reached. However, until the biogas generation from the fermentation tank B was confirmed, The operation of the fermenter A was continued as it was.
6 days after starting circulation/spraying of the reaction water in the methane fermentation tank B, a small amount of biogas was found in the fermentation tank B, so 2% from the inert gas injection pipe 17 at the bottom of the methane fermentation tank A. Fermentation of the methane fermentation tank A that had continued the steady fermentation reaction by supplying nitrogen gas containing oxygen was stopped, and the same amount of inert gas as the gas generation flow rate of the methane fermentation tank B was supplied to the bottom of the methane fermentation tank A. The gas was continuously injected while adjusting it from the gas injection pipe 17.

At this time, the presence of oxygen gas in the inert gas had a function of dramatically acting on methane bacteria to stop the production of methane gas even in a trace amount. Since the biogas remaining in the methane fermentation tank A is expelled by this inert gas injection operation, this gas was introduced into the low-concentration biogas holder 27 via the pipe 24.

During this period, the concentration of methane gas was measured by sampling the gas emitted from the methane fermentation tank A. Although the methane gas concentration was about 56% immediately before the start of the termination operation, it gradually decreased to zero. The change in the concentration of the methane gas is shown in FIG. This period corresponds to the end period of the methane fermentation reaction of cycle III in the operation cycle of the methane fermentation tank A shown in FIG.

After confirming that the high-concentration biogas has reached a steady generation state after the methane fermentation tank A has entered the steady-state fermentation reaction period, the methane fermentation reaction can be performed by injecting a trace amount of oxygen-containing inert gas. Can be stopped at any time, and the generation of methane gas will not recover until some time has passed. Therefore, if the process enters the stationary fermentation reaction period, it is possible to shift to the end of fermentation period as an experiment. Here, by performing such an operation in which the operation cycle is different from the normal operation, the confirmation experiment of Example 2 was significantly shortened as compared with the normal operation.

On the other hand, since the aerobic fermentation period (the period of aerobic fermentation and facultative anaerobic fermentation) was required in the methane fermentation tank A for 6 days, the methane fermentation tank B started circulating and spraying the reaction water in anticipation of this period. .. That is, the methane fermentation tank B was filled with the biomass raw material and waited in a sealed state. However, the operation of starting the aerobic fermentation reaction was started at the timing 13 days after starting the methane fermentation reaction of the methane fermentation tank A. went. That is, 50 liters of reaction water from the relay tank 28 to the methane fermentation tank B was sprayed from the external circulation pipe 22 through the spray nozzle 16 onto the upper part of the packed bed 14 and supplied into the methane fermentation tank B. The reaction water introduced into the methane fermentation tank B was circulated through the circulation pump 20, the external circulation pipe 22, and the spray nozzle 16, and continuously sprayed on the top of the packed bed 14. All operating conditions such as the circulating amount of reaction water were the same as those for the methane fermentation tank A. The circulation rate of the reaction water was 1.6 liters per minute, and the circulation and spraying of the reaction water were continuously performed.

By continuing circulation of the reaction water and spraying, the reaction first occurred from the aerobic fermentation reaction accompanied by exotherm. With the progress of the aerobic fermentation reaction, oxygen remaining in the methane fermentation tank B was completely consumed. Furthermore, by continuing the circulation and spraying of the reaction water, the reaction proceeded to the methane fermentation reaction, and generation of biogas containing methane gas was observed. With the passage of time, methane fermentation proceeded, and the amount of biogas including methane gas increased. Similar to the methane fermentation tank A, the gas in the tank was sampled at the gas outlet of the methane fermentation tank B, and the methane gas concentration therein was measured. The concentration of methane gas was zero at the start of the reaction, but the concentration of methane gas increased with the passage of time. Eight days after starting the methane fermentation reaction, the concentration became almost 56% by volume. The generated biogas was introduced into the low concentration biogas holder 27 through the pipe 24. This period corresponds to the methane fermentation reaction start period of cycle III in the operation cycle of the methane fermentation tank B shown in FIG.

As described above, since the reaction start of the methane fermentation tank B is systematically matched with the end time of the fermentation reaction of the methane fermentation tank A, the methane fermentation reaction start cycle of the methane fermentation tank B is cycle III. It is the same time as the end of the methane fermentation reaction in tank A. In this cycle III, the concentration of methane gas in the gas expelled from the methane fermentation tank A rapidly decreased to zero at the end as shown in FIG. On the other hand, the concentration of methane gas in the biogas generated in the methane fermentation tank B rapidly increased as shown in FIG. 3, and finally reached about 56% by volume. The biogas from the methane fermentation tank A and the biogas from the methane fermentation tank B are united in the pipe 24 and introduced into the low concentration biogas holder 27. When the gas in the pipe 24 was sampled and the concentration of methane gas during the period of cycle III was examined, it was almost constant at around 28% by volume over the entire period of cycle III.

As shown in the above examples, when a pair of methane fermentation tanks having the same size and structure are used and the methane fermentation reaction of the biomass raw material is performed under the same operating conditions and reaction conditions, one methane fermentation tank is obtained. By shifting the reaction cycle of the (methane fermentation tank A) and the other methane fermentation tank (methane fermentation tank B) by half a cycle, high concentration methane gas of about 56% by volume in the steady fermentation reaction period and about 28 volumes of half thereof It was found that a low concentration of methane gas of about 10% was obtained. Moreover, both high-concentration methane gas and low-concentration methane gas can be constantly obtained at a constant concentration without interruption, and it has become possible to efficiently produce methane gas.

In addition, the concentration of low-concentration methane gas is always around 28% by volume, which is considerably larger than the explosive limit of methane gas of 5.3 to 14% by volume. It also has the advantage that it can be handled.

By using the method of the present invention, there is a possibility that the compost manufacturing method, which has been performed by the aerobic fermentation method until now, may be switched by the methane fermentation method described here. There is a high possibility of effective utilization of agricultural biomass resources such as rice straw and straw that were previously unused and plowed into plowed land. And the slopes of riverbeds and levees, weeds along roads and railways can be used effectively as biomass resources, and fermented compost and methane gas can be produced from these as raw materials for industrial production. Great availability. In addition, methane in biogas can be converted to hydrogen by a reformer and then supplied to a fuel cell to be converted into electricity or hot water for energy conversion, which can be used in industry or at home. Moreover, there is a possibility that it will be developed into an industry that helps prevent global warming by being used and developed in various places on the earth.

1. Methane fermentation tank 2. Packed bed of coarsely crushed biomass raw material 3. Spray nozzle 4. External circulation piping 5. Circulation pump 6. Reaction water relay tank 7. Biogas holder 8. Biogas piping 9. Reaction water supply pipe 10. Inert gas injection pipe 11. Methane fermenter A
12. Methane fermentation tank B
13. Packed bed of coarsely crushed biomass raw material 14. Packed bed of coarsely crushed biomass material 15. Spray nozzle 16. Spray nozzle 17. Inert gas injection pipe 18. Inert gas injection pipe 19. Circulation pump 20. Circulation pump 21. External circulation piping 22. External circulation piping 23. High concentration biogas pipe 24. Low concentration biogas pipe 25. Reaction water return pipe 26. High concentration biogas holder 27. Low concentration biogas holder 28. Reaction water relay tank

Claims (4)

Airtightness to fill the crushed material of the biomass resource as the raw material inside, to circulate the reaction water containing the methane bacteria externally and spray it from the top of the filling, and to carry out the methane fermentation reaction by repeating this. In a batch-type methane fermentation facility for producing methane gas and fermented compost using the methane fermentation tank of the above, a pair of methane fermentation tanks of the same shape and the same volume are used, and one methane fermentation tank (fermentation tank A) is the reaction water. When the methane fermentation reaction is started in the other methane fermentation tank (fermentation tank B) at the same time when the spraying of No. 1 is started and the methane fermentation reaction is started, the injection of the inert gas for stopping the reaction is started. Further, it is characterized by performing an operation of adjusting the injection amount (flow rate) of the inert gas in the fermenter B to be substantially the same as the generation amount (flow rate) of the biogas containing methane gas in the fermenter A. , A method for producing methane gas and compost using biomass resources. From the start of the injection of biogas generated from the start of the reaction in one methane fermenter (fermentor A) to the time before entering the stage of the steady fermentation reaction and the end of the injection of the inert gas in the other methane fermenter (fermentor B) The method for producing methane gas and compost using biomass resources according to claim 1, wherein biogas generated until the operation is completed is collected in the same methane gas storage tank. As the inert gas, combustion exhaust gas obtained by completely burning biogas with an air excess coefficient of 1.08 to 1.10 is used, and the biomass resource according to claim 1 or 2 is used. Methane gas and compost manufacturing method. The biomass according to any one of claims 1 to 3, wherein the inert gas is injected through the perforated pipe provided at the bottom of the fermenter so as to be substantially uniform over the entire bottom surface of the fermenter. A method for producing methane gas and compost using resources.

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