JP7055916B1 - Organic waste treatment system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic waste treatment system capable of efficiently producing not only biogas but also compost raw materials from organic waste such as food residue. SOLUTION: The digestive juice is sent to the reaction tank 4 of the high temperature and high pressure hydrolyzing device 1 again to perform the high temperature and high pressure hydrolyzing treatment. Further, after the organic waste is reduced in molecular weight and sterilized in the reaction tank 4 of the high-temperature and high-pressure hydrolyzing device 1, the inside of the reaction tank 4 is emptied, and the digestive juice from the fermentation tank 12 is sent into the reaction tank 4. The digested juice sent in is hydrolyzed at high temperature and high pressure to decompose or inactivate compounds, bacteria and organic poisons that are the basis of bad odors, and the advanced water treatment device is located on the downstream side of the solid-liquid separation device 17 as before. It is possible to discharge the water separated by the solid-liquid separator 17 into the river without arranging the water. [Selection diagram] Fig. 1

Description

The present invention decomposes organic waste such as food residues using a hydrolyzed region and a sub-critical water treatment region (hereinafter referred to as "high temperature and high pressure water solution"), generates biogas, and uses it as a power generation and heat source. Regarding the system.

There are many power generation systems in Japan that are based on the generation of methane gas, but the amount of power generated is often too low to be profitable. These causes are when the amount of methane gas generated is small and it is not profitable, and because a solubilization (slurry) tank seen in the conventional type is required, methane gas is used as a heat source to heat it, so it is used for power generation. In many cases, the amount of methane gas is reduced, and as a result, the amount of power generation is significantly reduced.
In addition, the digestive juice discharged from the fermenter emits a strong foul odor and bacteria, and therefore, although it has a sufficient effect as liquid fertilizer, most of it is treated as waste.

If the organic waste is directly put into the solubilization tank to form a slurry and then put into the fermenter, the initial cost and running cost are greatly increased due to the processing time and heating of the solubilization tank.
However, treating organic waste with high-temperature and high-pressure water solution eliminates the need for a solubilization tank, significantly shortens the time required to generate biogas, and increases the amount of biogas generated.

Patent Document 1 describes a boiler that generates saturated steam as a high-temperature and high-pressure hydrolyzing device for treating organic waste, and heated steam generation that converts saturated steam from this boiler into superheated steam in a high-temperature and high-pressure hydrolyzed state. The device, the heated steam supply path for supplying the heated steam from the heated steam generator from the ceiling of the reaction tank, and the superheated steam from the superheated steam generator arranged along the outside of the housing of the reaction tank. A device consisting of a circulation path to return to the boiler has been proposed.

Patent Documents 2 and 3 describe, as an organic waste treatment system, a high-temperature and high-pressure water solution treatment device for reducing the molecular weight of organic waste, and biogas generated from the reduced molecular weight organic waste by methanogenic bacteria. A methane fermentation device that removes carbon dioxide from the biogas produced by methane fermentation, and a solid-liquid separation device that pressurizes and separates harmful substances from the digestive juice produced by methane fermentation. Have been described.

Patent Document 4 describes a step of crushing food waste into a slurry and separating it into a squeezed liquid and a cake, a first gas recovery step of recovering the gas produced by methane fermentation of the squeezed liquid, and water in the cake. A step of mixing, a step of hot and high pressure hydrolyzing a mixture of the cake and water in the first tank reactor, a step of storing the contents of the first tank reactor in a buffer tank, and a step of methane fermentation of the contents. A biogas recovery method comprising a second gas recovery step of recovering the produced gas and a step of purifying the gas produced in the step to recover the methane gas is described.

Patent Document 5 describes organic waste as a methane fermentation treatment in which organic waste is solubilized and then decomposed by anaerobic bacteria to obtain biogas, and the organic waste is treated by high-temperature and high-pressure water solution in a closed treatment container. After that, it is described that the high-temperature and high-pressure hydrolyzed product in a pressurized state is dehydrated by reducing the pressure to obtain a dehydrated product, and the dehydrated product is put into a methane fermentation treatment tank for methane fermentation.

Further, in Non-Patent Document 1, when sub-critical water treatment technology is introduced in the process of methane fermentation from food waste, it is expected that the decomposition of plastic will reduce the labor for sorting on the inlet side (raw material). On the outlet side (manufacturing), it is stated that the improvement of nutritional value by treatment and the bactericidal effect by treatment at high temperature are expected.

Japanese Patent No. 6737561 Japanese Patent No. 6755057 Japanese Patent No. 6755058 Japanese Unexamined Patent Publication No. 2013-034988 Japanese Unexamined Patent Publication No. 2009-119378

https://www.maff.go.jp/j/shokusan/biomass/attach/pdf/arinkai-9.pdf (Consideration of introduction of sub-critical water treatment facility as methane fermentation pretreatment facility)

FIG. 4 is a schematic diagram of a conventional organic waste treatment system (biogas power generation system) to which the above-mentioned prior art is applied.
As shown in this figure, organic waste is hydrolyzed and reduced in molecular weight in sub-critical water treatment equipment, then slurried in a solubilization tank, and biogas is produced by methanogens in a fermenter. Since the generated biogas contains carbon dioxide and hydrogen sulfide in addition to methane gas, methane gas is supplied to the power generation device as fuel via the desulfurization device and the gas refining device.

Moisture needs to be adjusted depending on whether the fermenter is wet or dry.

The digestive juice remaining in the fermenter is drained through an advanced water treatment device using a filtration membrane after removing the solid content in the solid-liquid separation tank.

In the above-mentioned biogasification of conventional organic waste, the presence of the solubilization tank increases the initial cost and increases the energy loss for heating the solubilization tank. In addition, since the number of solubilization days is about 1 week to 10 days, running costs are also high. In addition, if the digestive juice remaining in the fermenter is directly put into the solid-liquid separation tank, bad odors, scattering of fermenting bacteria, and pests may occur. Further, an advanced water treatment device is required to remove solid content that cannot be separated in the solid-liquid separation tank.

In order to solve the above-mentioned problems, in the present invention, the organic waste is reduced in molecular weight and depolymerized by high-temperature and high-pressure water solution treatment, and the organic substance in a state where biogas is easily generated is not solubilized without going through a solubilization tank. In a treatment system for organic waste that is directly put into a fermenter and fermented with methane to generate biogas, a high-temperature and high-pressure water solution for treating digestive juice as a residue of biogas generated in the fermenter is provided.

In the above configuration, the treatment conditions for high-temperature and high-pressure hydrolyzing to reduce the molecular weight and depolymerize organic waste are 0.2 to 2 MPa, 100 to 300 ° C., about 5 minutes to 1 hour, and the treatment liquid from the fermenter is treated. The treatment conditions of the subcritical water treatment apparatus are preferably 0.2 to 2 MPa, 100 to 300 ° C., and 30 minutes or more.

In addition, in order to efficiently use one high-temperature and high-pressure hydrolyzing device, first, the high-temperature and high-pressure hydrolyzing device is used to reduce the molecular weight and depolymerize organic waste, and then the processing chamber of the high-temperature and high-pressure hydrolyzing device is emptied. It is also possible to supply the digested liquid after fermentation in the fermenter into this processing chamber for processing.

It is well known that when an organic substance is placed in a hydrolyzed state or a subcritical water-treated state (hereinafter referred to as "high-temperature and high-pressure hydrolyzed state"), it is reduced in molecular weight and depolymerized. Hydrolysis is defined as a reaction in which water is separated into hydroxy groups and hydrogen (protons) to give a decomposition product. On the other hand, sub-critical water treatment is defined as the reaction of steam under high temperature and high pressure to reduce the molecular weight, and it is clearly stated that there is a difference.

However, if an organic substance is placed in liquid water under high temperature and high pressure, the molecular weight will not be reduced even if it is subdivided. Therefore, according to the present invention, when an organic substance is exposed to steam under certain conditions of high temperature and high pressure hydrolyzing, a remarkable effect is observed in increasing the amount of biogas generated and shortening the time until it is generated. Therefore, the present invention is hydrolyzed. A heated steam generator and a housing heating device were attached to the device, etc., so that the degree of decomposition could be adjusted to increase the amount of biogas.

In addition, the methane gas fermentation tank is divided into medium temperature fermentation and high temperature fermentation, but by using organic matter heated to a certain temperature or higher, it is possible to prevent the temperature inside the fermentation tank from dropping when the raw materials are added, and fermentation is promoted. To.

In addition, the fermenter of methane gas can be seen as wet type or dry type, both of which require water adjustment, but since the device is provided with a housing heating device and a superheated steam generator, the water content In the case of a substance with a large amount of water, the heated steam generated from the housing heating device and the superheated steam generator can appropriately decompose the organic waste while reducing the water content.

Further, in the case of a substance having a low water content, by injecting saturated steam at a low temperature, the temperature in the reaction vessel can be lowered to produce condensed water while increasing the water content, and the water content can be increased.
From the above, regardless of the amount of water content, it is possible to shorten the time when biogas is generated and increase the amount of biogas generated.

In addition, since the steam used in the housing heating device is kept at a high temperature, it is intended to recover heat and improve thermal efficiency by circulating it and returning it to the boiler again, so a condenser or heat exchanger is used. It doesn't matter, but water will be wasted.

Methane fermentation in the fermenter produces digestive juice along with biogas, but high-temperature and high-pressure hydrolyzing treatment reduces the amount of digestive juice. This digestive juice is sent to the reaction tank of the sub-critical water treatment device again to perform high-temperature and high-pressure hydrolyzing treatment. In addition, after the organic waste is reduced in molecular weight and sterilized in the reaction tank of the sub-critical water treatment device, the inside of the reaction tank is emptied, and the digestive juice from the fermenter is sent into this reaction tank. The digested liquid sent in is hydrolyzed at high temperature and high pressure to decompose or inactivate compounds, bacteria and organic poisons that are the basis of bad odors, and an advanced water treatment device is installed on the downstream side of the solid-liquid separation device as before. It is possible to discharge the water separated by the solid-liquid separator into the river without arranging it.

According to the present invention, biogas-producing bacteria decompose organic substances by high-temperature and high-pressure hydrolyzing treatment, and when the granulated state and water content that easily generate biogas are adjusted and the easily active substance is put into the fermenter, the fermenter is charged. Increases the amount of biogas generated in. Further, since the digested liquid after fermentation is subjected to high-temperature and high-pressure hydrolyzing treatment and then processed through a solid-liquid separator, no offensive odor is generated in the solid-liquid separator due to the scattering of bacteria or the like.

In addition, in the past, it was specified as sub-critical water treatment, but in the conventional sub-critical water treatment equipment, since the water content cannot be adjusted, there are many cases where decomposition has not progressed, and it ended up with only an image. However, when a hydrolyzer equipped with a housing heating device or a superheated steam generator was used, the effects of shortening the biogas generation time and increasing the amount of biogas generated were observed.

When the digestive juice was used as liquid fertilizer in an untreated state, it was treated as extremely difficult to use because of biogas-generating bacteria, foul odors, and solid matter inside, and most of it was discarded. In order to eliminate these problems, solid-liquid separation is performed, but pollution such as bad odors during solid-liquid separation, scattering of bacteria, and outbreak of pests is generated. Further, the water from which the solid content was removed by the apparatus was discarded via the advanced water treatment apparatus incorporating the filtration membrane, which increased the cost. However, according to the present invention, the advanced water treatment apparatus is used. It can be omitted, leading to pollution prevention and cost reduction.

By setting the treatment conditions for organic waste in high-temperature and high-pressure water solution to 0.2 MPa or more, 120 ° C or more, and 21 minutes or more, it is possible to sufficiently reduce the molecular weight, depolymerize, and sterilize, so the solubilization tank can be omitted. can. However, since it was sterilized, it is necessary to newly add methane gas-generating bacteria. Since this solubilization tank requires heating and stirring at low temperatures, it has a large energy loss, but the present invention makes it possible to eliminate it.

On the other hand, when the temperature changes from extremely hydrolyzed or high temperature and high pressure water solution treatment to high temperature and high pressure, the inside of the device becomes an acidic atmosphere, and oxidation of organic substances and corrosion of the device occur. By doing so, it is possible to suppress the oxidation of organic substances and the corrosion of equipment.

By using one device at different times, the high-temperature and high-pressure hydrolysis of organic waste and the high-temperature and high-pressure hydrolysis of digestive juice can be effectively used without letting the high-temperature and high-pressure hydrolysis treatment device itself play.

Schematic diagram of the organic waste treatment system according to the present invention Schematic diagram of high temperature and high pressure hydrolyzing treatment Cross section of reaction tank Schematic diagram of a conventional organic waste treatment system

Examples of the present invention will be described below with reference to the accompanying drawings.
In the organic waste treatment system, the organic waste is put into the high temperature and high pressure water hydrolyzing device 1 to reduce the molecular weight and depolymerize.

As shown in FIGS. 1 and 2, the high-temperature and high-pressure water solution treatment device 1 has a once-through and circulation type boiler 2 that generates steam in a high-temperature and high-pressure water solution state (1 to 3 MPa, 100 to 250 ° C.), and steam from the boiler 2. The heated steam generator 3 that further converts the above into high-temperature and high-pressure superheated steam, and the heated steam supply path 5 and the reaction tank 4 that supply the superheated steam from the heated steam generator 3 to the reaction tank 4 are used by heating the housing. It is provided with a recovery pipe 6 for recovering steam.

The reaction tank 4 has a tubular shape with both ends closed, an organic waste or digestive juice charging section 7 described later is provided at the top, and a reaction-processed object extraction section 8 is provided at the bottom. Is provided, and a stirring device is arranged in the reaction tank 4. The stirring device has a structure in which support rods 10 are attached to a rotating shaft 9 inserted in the center of the reaction tank 4 at predetermined intervals, and a bending plate 11 is attached to the tip of the support rod 10 via a spring.

The treated organic matter taken out from the take-out section 8 is put into the fermenter 12. In the past, the object to be treated was sent to a solubilization tank, slurried, and then charged into the fermenter 12. However, by performing high-temperature and high-pressure hydrolyzing treatment under the conditions of the present invention, the molecular weight of organic waste can be reduced. Depolymerization and sterilization proceed, and biogas production can be increased in a short time without the solubilization tank.

Fermentation is carried out in the fermenter 12 by anaerobic methanogens. Since solids are mixed in the biogas produced by fermentation, the solids are removed by the solid / water separation device 13, and since the biogas contains sulfur and carbon dioxide, the desulfurization device 14 and Removed by the carbon dioxide gas removing device 15, only the methane gas is taken out, and this is used as fuel for, for example, the power generation device 16.

On the other hand, methane fermentation in the fermenter 12 produces digestive juice together with biogas. This digested liquid is sent to the reaction tank 4 of the high-temperature high-pressure hydrolyzing device 1 again to perform the high-temperature high-pressure hydrolyzing treatment. In this embodiment, an example in which one high-temperature and high-pressure water hydrolyzing device 1 is used is shown. In this case, the organic waste and the digestive juice cannot be treated in the same reaction tank 4.
Therefore, in the present invention, after depolymerizing the organic waste with low molecular weight in the reaction tank 4 of the batch type high temperature and high pressure water solution treatment apparatus 1, the inside of the reaction tank 4 is emptied, and the inside of the reaction tank 4 is filled with the fermentation tank 12. Send the digestive juice from.

The sent digestive juice is hydrolyzed at high temperature and high pressure to decompose or inactivate compounds, bacteria and organic poisons that are the basis of malodor, and an advanced water treatment device is installed on the downstream side of the solid-liquid separation device 17 as before. It is possible to discharge the water separated by the solid-liquid separator 17 into the river without arranging it. Further, the solid content recovered by the solid-liquid separation device 17 is used as a solid fertilizer.

In the examples, one high-temperature and high-pressure hydrolyzed device was used for low-molecular-weight treatment of organic waste and digestive juice treatment from a fermenter at different times, but organic waste was used. Individual high-temperature and high-pressure hydrolyzed devices may be used for treatment and digestive juice treatment, or the treatment space of one high-temperature and high-pressure hydrolyzed device may be divided into two, and organic waste and digestive juice may be placed in each space. It may be configured to be input.

1 ... High temperature and high pressure water solution treatment device, 2 ... Through-flow type and circulation type boiler, 3 ... Superheated steam generator, 4 ... Reaction tank (housing), 5 ... Superheated steam supply path, 7 ... Input section, 8 ... Extract section, 9 ... Rotating shaft, 10 ... Support rod, 11 ... Boiler plate, 12 ... Fermenter, 13 ... Solid / moisture separation device, 14 ... Desulfurization device, 15 ... Carbon dioxide gas removal device, 16 ... Power generation device, 17 ... Solid-liquid separation Device.

Claims (2)

The heated steam generator provided in the high-temperature and high-pressure hydrolyzing device converts steam at 1 to 3 Mpa and 100 to 250 ° C into further high-temperature and high-pressure superheated steam, and supplies this superheated steam to the reaction tank to reduce the amount of organic waste. When molecularization and depolymerization are performed, and at the same time, when the water content of the organic waste is so high that hydrolysis does not proceed , the water content of the organic waste is reduced by superheated steam, which is necessary for hydrolysis. When the water content is low enough to be insufficient, saturated steam is put into the reaction tank, and the reaction tank and organic waste are brought into contact with the saturated steam to generate condensed water, and this condensed water is generated. The water content was increased, and this water-adjusted, low-molecular-weight and hydrolyzed organic substance was methane-fermented in a methane fermentation tank without going through a solubilization tank to generate biogas, which was generated in the methane fermentation tank. An organic waste treatment system characterized by a high-temperature and high-pressure hydrolyzing device that facilitates removal of malodor, sterilization, decomposition of organic poisons, and solid-liquid separation of digested liquid as a residue after biogas generation. .. In the organic waste treatment system according to claim 1, the same device is used for the high temperature and high pressure hydrolyzing device for depolymerizing the organic waste and the high temperature and high pressure hydrolyzing device for treating the digestive juice. An organic waste treatment system characterized by staggered use.

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