JP6592406B2 - Crystallizer, methane fermentation facility, and scale prevention method in methane fermentation facility - Google Patents

Description

  The present invention relates to an apparatus for crystallizing magnesium ammonium phosphate (MAP). The present invention also relates to a methane fermentation facility for decomposing organic matter (typically organic waste) by the action of anaerobic microorganisms. Furthermore, this invention relates to the scale prevention method in a methane fermentation installation.

  The method of methane fermentation treatment of organic waste is that the operation cost is low, that the digested liquid after methane fermentation treatment is biologically stable, and the digestion gas (methane gas) obtained by methane fermentation treatment is used as energy There are many advantages such as being available. Therefore, in recent years, there is an increasing demand for methane fermentation facilities for organic waste such as rice cake, leftover food, food and beverage manufacturing residues, sewage sludge, organic wastewater treatment sludge, and livestock manure.

In the methane fermentation facility, the inside of the methane fermenter is in a reducing atmosphere and is in an environment where ammonium ions (NH ₄ ⁺ ) and phosphate ions (PO ₄ ³⁻ ) are likely to elute into the solution. For this reason, when the concentration of magnesium ions (Mg ²⁺ ) in the methane fermentation tank is high, crystals of magnesium ammonium phosphate (hereinafter referred to as MAP) are precipitated by the following chemical equilibrium reaction.
Mg ²⁺ + NH ₄ ⁺ + HPO ₄ ²⁻ + 5H ₂ O + OH ⁻ ⇔Mg (NH ₄ ) (PO ₄ ) · 6H ₂ O
From the above reaction formula, when ^ions of Mg ²⁺ , NH ⁴⁺ and PO ₄ ³⁻ (HPO ₄ ² + OH ⁻ ⇔PO ₄ ³ + H ₂ O) are present and alkalinity is supplied, the equilibrium is It can be seen that MAP crystals are formed.

  In methane fermentation facilities, in addition to methane fermentation tanks, there are often cases where scales derived from MAP are generated in systems in which digested liquid in methane fermentation tanks stays or circulates. Since the scale leads to the blockage of the digestion liquid extraction pump and the failure of the methane fermenter agitator, it was necessary to periodically remove the operation and remove the scale. When the scale is remarkable, it may be necessary to discharge the entire digestive liquid in the methane fermentation tank and clean the inside of the tank. In that case, the disposal cost of a huge digestive juice is required. Furthermore, it is necessary to stop the operation of the equipment for a long time until the digestive juice is discharged, cleaned, and restarted. Furthermore, since it is necessary to outsource the disposal of waste while the operation of the methane fermentation facility is stopped, the burden on the cost was also large.

  Several techniques have been proposed in the past for scaling against MAP. For example, in Japanese Patent Laid-Open No. 2000-271595, sludge is produced for the purpose of preventing obstruction in a pipeline due to MAP particles adhering to a pipeline that transports sludge generated in a sewage treatment facility to a sludge treatment facility or the like. An aeration device or a MAP reactor is provided upstream of the pipeline for transporting the slag, and sludge is aerated in the aeration device or the MAP reactor in advance to form MAP particles in the sludge, so that the MAP particle formation factor component A method is described in which the sludge is removed from the pore water and the sludge is sent into the pipe. In the embodiment shown in FIG. 4 of the publication, the alkalinity in the sludge is increased by anaerobically treating the sludge before introduction into the aeration apparatus or the MAP reactor with anaerobic microorganisms in the anaerobic digestion tank. Is described as being useful.

  Japanese Patent Application Laid-Open No. 2003-117306 describes that a crystallization method has been used as one method for removing specific ions from a liquid. And in the waste water which contains phosphate ion and ammonium ion in liquids, such as a dehydrated filtrate of anaerobic digested sludge, adding magnesium and precipitating MAP crystals is described. In the examples of the publication, it is described that the treated water of methane fermentation contains phosphorus and ammonia, and magnesium ammonium phosphate (MAP) is crystallized by supplying magnesium and alkali, and dephosphorized. Has been.

In Japanese Patent Laid-Open No. 2001-252689, digested sludge discharged from an anaerobic fermenter is decompressed with a decompression device, then sent to the MAP first tank, and MgCl ₂ as an Mg source is added to generate MAP particles. Is described. After separating the MAP particles, the digested sludge is returned to the anaerobic fermenter. According to the technique described in the publication, the sludge can increase the decomposition rate by fermentation by circulating the anaerobic fermentation tank, the decompression device, and the MAP first tank, and the decomposed carbon content is converted into methane gas. It is described in MAP that nitrogen and phosphorus are recovered in useful forms.

  In International Publication No. 2006/078012, a magnesium compound is added to the digested sludge in a method for preventing scale in the piping when the digested sludge generated by anaerobic digestion of organic waste is transported by piping. Fine particles containing MAP from the digested sludge treated by the crystallization step of crystallizing MAP and the residue removal step of removing the residue from the digested sludge and the residue removal step as the crystallization step A method for preventing scale in a pipe is described in which digested sludge from which fine particles have been removed is transported by pipe. At this time, it is described that when aeration treatment, decompression treatment, or the like is used in combination, decarboxylation increases the pH, and MAP can be precipitated more efficiently.

JP 2000-271595 A JP 2003-117306 A Japanese Patent Laid-Open No. 2001-252689 International Publication No. 2006/0778012

  The technique described in Japanese Patent Application Laid-Open No. 2000-271595 is a technique for forming MAP particles on the upstream side of a pipeline for transporting sludge to a sludge treatment facility. Further, MAP is added to an anaerobic digester on the upstream side. It cannot be prevented that the scale of origin originates. In addition, if the aeration apparatus or MAP reactor described in the publication is intended to form MAP particles on the upstream side of the anaerobic digester, it is sufficient to aerate sludge if the fermentation raw material has a low pH. Can not be raised, a huge amount of alkali is required.

  The technology described in Japanese Patent Application Laid-Open No. 2003-117306 is merely adding magnesium to precipitate the MAP crystals to dephosphorize the treated water discharged from the methane fermentation tank. It is not a technique for preventing the occurrence of MAP-derived scale.

  Japanese Patent Application Laid-Open No. 2001-252689 describes that digested sludge discharged from an anaerobic fermentation tank is subjected to a decompression process with a decompression device and then sent to the MAP first tank to generate MAP particles. The scale derived from MAP grows in the pipe between the MAP and the first MAP tank, resulting in a pipe clogging risk. In addition, it is described that after adding Mg source to the digested sludge discharged from the anaerobic fermenter to generate MAP particles, the MAP particles are separated and the digested sludge is returned to the anaerobic fermenter. Since the MAP is generated by adding the source, the unreacted magnesium component is fed into the anaerobic fermenter even if the digested sludge after the generation and separation of MAP is returned to the anaerobic fermenter. Therefore, there is a risk that the scale generation risk derived from MAP in the anaerobic fermenter is increased.

  The purpose of International Publication No. 2006/0778012 is to prevent the scale in the piping when the digested sludge is transported by piping, and cannot prevent the scale in the anaerobic digester. Moreover, since MAP is crystallized by adding a magnesium compound, there is a possibility that the magnesium concentration in the digested sludge after MAP separation may be increased. Therefore, it is preferable to return this to an anaerobic digester from the viewpoint of scale prevention. Absent.

  The present invention was created in view of the above circumstances, and an object of the present invention is to provide a MAP crystallizer useful for scale prevention of methane fermentation equipment. Another object of the present invention is to provide a methane fermentation facility equipped with a MAP crystallizer. Another object of the present invention is to provide a scale prevention method in a methane fermentation facility.

  The present inventor has intensively studied to solve the above-mentioned problems. As a result, the MAP crystallizer holds the seed crystal by extracting the digested liquid from the system in which the digested liquid in the methane fermenter, which is typified by the methane fermenter, stays or circulates. After MAP is crystallized and removed, the digestive liquid is returned to the system in which the digestive liquid in the methane fermentation tank stays or circulates, thereby generating scale derived from MAP in the system in which the digestive liquid in the methane fermentation tank stays or circulates. It was found that risk can be effectively reduced.

  At this time, instead of installing a device for increasing the pH between the methane fermenter and the MAP crystallizer, it is possible to increase the pH by decarboxylation in the crystallization reactor in the MAP crystallizer. It is effective from the viewpoint of suppressing the risk of scale generation in the circulation path between the MAP crystallizer and the MAP crystallizer.

  Moreover, when the Mg source is added in the MAP crystallizer, the Mg source flows into the methane fermentation tank together with the returned digestive liquid, and the scale generation risk in the methane fermentation tank is increased. For this reason, the Mg source should not be added in the MAP crystallizer, and further, the Mg source should not be added in the circulation path between the methane fermenter and the MAP crystallizer. By not adding the Mg source, compared to the Mg concentration in the digested liquid discharged from the methane fermentation tank, the Mg concentration in the digested liquid returned to the methane fermenter through the MAP crystallizer can be lowered. .

  Furthermore, since the pH of the digested liquid returned from the MAP crystallizer is higher than that in the methane fermenter, the pH of the digested liquid being returned from the MAP crystallizer to the methane fermenter should be lowered. The scale generation risk in the methane fermentation tank and return route can be further reduced.

In one aspect, the present invention completed based on the above findings,
An inlet for introducing a digestion liquid containing ammonium ions, magnesium ions, and phosphate ions extracted from the system in which the digestive liquid in the methane fermentation tank stays or circulates;
A reactor for containing a seed crystal and a digestive juice introduced from an inlet, and for crystallization of MAP by reacting ammonium ions, magnesium ions and phosphate ions contained in the digestive fluid;
One or more decarboxylation mechanisms selected from the group consisting of an aeration mechanism, a decompression mechanism and an agitation mechanism for decarboxylating the digestion fluid in the reactor;
A separation mechanism for separating the crystallized MAP from the digestive juice;
An outlet for returning the digested liquid after separation of MAP to a system in which the digested liquid in the methane fermentation tank stays or circulates the digested liquid in which the magnesium ion concentration is reduced compared to the digested liquid in the methane fermenter;
Is a crystallizing apparatus.

  In one embodiment, the crystallizer according to the present invention further includes a mechanism for adding an organic acid to the digested liquid after separating MAP and before discharging from the outlet.

In another aspect of the present invention,
A system in which digested liquid in the methane fermentation tank stays or circulates;
A crystallizer according to the present invention;
A first piping system for withdrawing digestive juice from the system and sending it to the crystallizer;
A second piping system for returning the digested liquid discharged from the outlet of the crystallizer to the system;
Is a methane fermentation facility equipped with

  In one embodiment, the methane fermentation facility according to the present invention is connected to a second piping system, and further includes a mechanism for adding an organic acid to the second piping system.

  In another embodiment of the methane fermentation facility according to the present invention, the system in which the digested liquid in the methane fermentation tank stays or circulates includes the methane fermentation tank.

In another aspect of the present invention,
One or more selected from the group consisting of aeration, reduced pressure and agitation, the pH of the digestive fluid containing ammonium ions, magnesium ions and phosphate ions extracted from the system in which the digestive fluid in the methane fermentation tank stays or circulates And a step of crystallizing MAP by reacting ammonium ions, magnesium ions and phosphate ions contained in the digested liquid in the presence of seed crystals.
Separating the crystallized MAP from the digestive juice;
A step of returning the digested liquid after separation of MAP to the system, the digested liquid having a reduced magnesium ion concentration compared to the digested liquid in the methane fermentation tank;
It is the scale prevention method in the methane fermentation installation containing this.

  In one embodiment, the scale prevention method according to the present invention includes a step of lowering the pH of the digestive liquid by adding an organic acid to the digestive liquid while returning the digested liquid after separating MAP to the system. Including.

In another aspect of the present invention,
An inlet for introducing a digestion liquid containing ammonium ions, magnesium ions, and phosphate ions extracted from the system in which the digestive liquid in the methane fermentation tank stays or circulates;
A reactor for containing a seed crystal and a digested liquid introduced from an inlet, and reacting ammonium ions, magnesium ions and phosphate ions contained in the digested liquid to crystallize MAP;
A mechanism for raising the pH of the digestive fluid in the reactor;
A separation mechanism for separating the crystallized MAP from the digestive juice;
A mechanism for adding organic acid to the digestive juice after separating MAP and before being discharged from the outlet;
An outlet for returning the digested liquid after separation of MAP to a system in which the digested liquid in the methane fermentation tank stays or circulates the digested liquid in which the magnesium ion concentration is reduced compared to the digested liquid in the methane fermenter;
Is a crystallizing apparatus.

In another aspect of the present invention,
・ A system in which digested liquid in the methane fermentation tank stays or circulates,
A crystallizer comprising the following (a) to (e):
(A) an inlet for introducing a digestion liquid containing ammonium ions, magnesium ions, and phosphate ions extracted from a system in which the digestion liquid in the methane fermentation tank stays or circulates;
(B) A reactor for containing the seed crystal and the digestive juice introduced from the inlet and reacting ammonium ions, magnesium ions and phosphate ions contained in the digestive fluid to crystallize MAP;
(C) a mechanism for raising the pH of the digestive fluid in the reactor;
(D) Separation mechanism for separating crystallized MAP from the digestive juice; and (e) Digested liquid after separation of MAP, in which the magnesium ion concentration is reduced compared to the digestive fluid in the methane fermentation tank Outlet for returning the liquid to the system in which the digestion liquid in the methane fermenter stays or circulates;
A first piping system for withdrawing digestive juice from the system and sending it to the crystallizer;
A second piping system for returning the digested liquid discharged from the outlet of the crystallizer to the system;
A mechanism connected to the second piping system for adding organic acid to the second piping system;
Is a methane fermentation facility equipped with

In another aspect of the present invention,
Increases the pH of digestive fluid containing ammonium ions, magnesium ions, and phosphate ions extracted from the system in which digestive fluid in the methane fermentation tank stays or circulates, and is contained in the digestive fluid in the presence of seed crystals Crystallization of MAP by reacting ammonium ions, magnesium ions and phosphate ions,
Separating the crystallized MAP from the digestive juice;
A step of returning the digested liquid after separation of MAP to the system, the digested liquid having a reduced magnesium ion concentration compared to the digested liquid in the methane fermentation tank;
A step of reducing the pH of the digestive liquid by adding an organic acid to the digestive liquid in the course of returning the digested liquid after separation of MAP to the system;
It is the scale prevention method in the methane fermentation installation containing this.

  According to the present invention, scale generation in a methane fermentation facility can be effectively prevented. According to a preferred embodiment of the present invention, it is possible to smoothly operate the methane fermentation facility over a long period of time at a low running cost without performing a periodic descaling operation.

It is a figure which shows the specific aspect of a decarboxylation mechanism. It is a figure which shows the structural example of the MAP crystallizer which concerns on this invention. It is a figure which shows the structural example of the methane fermentation equipment which concerns on this invention, and is equivalent to the structure employ | adopted in the Example. It is a structure of the methane fermentation installation in a comparative example.

<1. Crystallizer>
In one embodiment, a MAP crystallizer according to the present invention includes:
A digestion solution containing ammonium ions (NH ₄ ⁺ ), magnesium ions (Mg ²⁺ ), and phosphate ions (PO ₄ ³⁻ ) extracted from the system in which the digestive fluid in the methane fermentation tank stays or circulates An entrance to introduce,
A reactor for containing a seed crystal and a digested liquid introduced from an inlet, and reacting ammonium ions, magnesium ions and phosphate ions contained in the digested liquid to crystallize MAP;
A mechanism for raising the pH of the digestive fluid in the reactor;
A separation mechanism for separating the crystallized MAP from the digestive juice;
An outlet for returning the digested liquid after separation of MAP to a system in which the digested liquid in the methane fermentation tank stays or circulates the digested liquid in which the magnesium ion concentration is reduced compared to the digested liquid in the methane fermenter;
Is provided.

  Examples of the system in which the digestive liquid in the methane fermentation tank stays or circulates include a digestion liquid heating apparatus, a sampling apparatus, a solid-liquid separation apparatus, and a digestive liquid circulation pipe connected to these in addition to the methane fermentation tank. . The digested liquid in the methane fermentation tank to be treated by the present invention contains ammonium ions, magnesium ions, and phosphate ions. The source of these ions is not particularly limited, but is included in, for example, organic waste such as straw, leftover food, food and beverage manufacturing residues, sewage sludge, organic wastewater treatment sludge, and livestock manure. Can be. Since the pH of the digestive fluid is generally 7.0 to 8.0, it has a potential for precipitation of MAP according to the above-described reaction formula. It is possible to reduce the MAP precipitation potential of the digested liquid by continuously or intermittently drawing the digested liquid from the system in which the digested liquid in the methane fermentation tank stays or circulates and crystallizing MAP with a crystallizer. . In particular, in this embodiment, there is no magnesium ion supply source other than the magnesium ion source contained in the digestive juice. For this reason, the magnesium ion concentration in the digestive fluid after separating MAP is reduced compared to the magnesium ion concentration in the digestive fluid in the methane fermentation tank extracted from the system. For example, the magnesium ion concentration in the digestive juice after separation of MAP can be preferably 50% or less, more preferably 40% with respect to the magnesium ion concentration in the digestive fluid in the methane fermentation tank extracted from the strain. Or less, more preferably 30% or less, even more preferably 20% or less, for example, 10 to 50%. Therefore, the scale generation prevention effect in the system is high when the digestive juice having a lowered MAP precipitation potential is returned to the system.

  The MAP crystallization reaction proceeds by raising the pH of the digested liquid introduced from the inlet of the MAP crystallizer. Examples of the means for raising the pH include one or more decarboxylation methods selected from the group consisting of aeration and reduced pressure, and these can be carried out by a known aeration mechanism, reduced pressure mechanism and stirring mechanism. Originally, the pH of the digested liquid in the methane fermenter is about 7 to 8, and the preferable pH for advancing the MAP crystallization reaction is 8 or more, for example, 8 to 9, so the pH is 0.5 to 1. It is sufficient to raise it by about 0.0. In addition, although a method of adding an alkali is also mentioned, since carbonic acid is dissolved in a saturated or near-saturated state in the digestion liquid in the methane fermentation tank, it is a kind selected from aeration, decompression operation and stirring mechanism Alternatively, by carrying out a combination of two or more, decarboxylation is easily performed according to Henry's law, and the pH of the digestive juice easily rises. For this reason, it is preferable to employ one or more decarboxylation methods selected from aeration, decompression and stirring in view of economy. An alkali such as sodium hydroxide may be supplementarily added, but in that case, an acid equivalent to the alkali added before returning the digested liquid to the methane fermentation tank is added to suppress the influence on the methane fermentation. It is preferable.

  Examples of a specific decarboxylation mechanism for carrying out the decarboxylation method are shown in FIGS. 1 (a), (b) and (c). In any mechanism, external air is not actively introduced, but by not having a completely sealed structure, it is possible to take in air corresponding to the amount of air supplied to the outside of the reactor from the surrounding environment. (A) and (b) are circulation aeration mechanisms that draw gas from the gas phase portion in the reactor 10 and send it to the digestive fluid in the reactor 10 via the circulation blower 11. Among these, (b) is a draft tube type aeration mechanism, and the whole reactor can be aerated with a small aeration amount. (C) is a surface aeration type aeration mechanism, and the surface of the digestive liquid is aerated by stirring the surface of the digestive liquid with the agitator 12. Since this method does not use a circulating blower, it is characterized by low cost in terms of power and maintenance. By aeration, methane gas and carbon dioxide dissolved in the digestion liquid are removed and enter the gas phase portion in the reactor 10. A part is circulated in the reactor 10 by the circulation blower 11, while the rest is discharged by the exhaust blower 13. The digestion liquid in the reactor 10 is gradually decarboxylated by the decarboxylation mechanism.

  For the decompression process, it is desirable to use a deaeration device as disclosed in JP-A-7-136406. By using the deaeration device, the digestion liquid is accelerated by the centrifugal force of the bottomed sieve rotating in the vacuum container, and the digestion liquid collides with the wall surface in the vacuum container, so that the carbon dioxide in the digestion liquid is removed. Can be removed.

  Since the seed crystal is accommodated in the reactor, MAP can be efficiently generated on the surface of the seed crystal. Moreover, by separating new MAP on the surface of the seed crystal, the separation of MAP in the subsequent separation step becomes good. As a seed crystal, MAP crystallized in a reactor or MAP crystallized in another reactor can be used. Furthermore, it naturally occurs in a system in which digested liquid in a methane fermentation tank such as a methane fermentation tank stays or circulates. Alternatively, MAP that has been deposited can be used. In addition, powders or granular materials such as phosphate ore, dolomite, bone charcoal, activated carbon, silica sand and calcium silicate can be used. The seed crystal can be of any particle size, but the larger the particle size, the better the solid-liquid separation, while the smaller one is excellent in fluidity in the reactor. The diameter is preferably 0.05 to 3.0 mm, more preferably 0.1 to 0.5 mm. The average particle diameter of the seed crystal is defined as a median diameter (d50) obtained by wet sieving in accordance with JIS Z8815-1994 and determined from a cumulative particle diameter distribution (mass basis). As the amount of MAP charged in the reactor increases, the MAP generation efficiency tends to increase, and the concentration of MAP charged in the reactor is preferably 10 g / L or more.

  The MAP crystallized in the reactor is separated from the digestive juice by the separation mechanism. Although there is no restriction | limiting in particular as a separation mechanism, Solid-liquid separation, such as filtration, centrifugation, and gravity precipitation, is mentioned. A filtration membrane may be used to carry out the solid-liquid separation, and a gravity precipitation part is formed in the upper part of the reaction tank as described in FIG. You may employ | adopt the solid-liquid separation structure provided with the inner cylinder for liquid separation. In this case, when the digestive liquid containing MAP crystals is flowed toward the upper enlarged portion together with the bubbles, the bubbles are discharged upward through the inner cylinder, and the rising speed of the remaining liquid is reduced at the enlarged portion. The crystals fall. For this reason, the MAP crystal is flowing in the lower part of the inner cylinder, and the MAP can be recovered therefrom. Further, for example, a liquid cyclone can be used as a device for centrifugal separation.

  A part of MAP crystals separated by solid-liquid separation may be returned to the reactor. Since the MAP crystals returned to the reactor can be used as seed crystals, it is not necessary to repeatedly add seed crystals from the outside.

  In the MAP crystallizer, a mechanism for adding the organic acid to the digested liquid after separating MAP and before discharging from the outlet may be provided. Since the pH of the digested liquid returned from the MAP crystallizer is higher than the pH of the digested liquid in the system in which the digested liquid in the methane fermenter stays or circulates, the MAP crystallizer is in the process of returning to the system. By reducing the pH of the digestive juice, the risk of scale generation in the system and the return route to the system can be further reduced. The mechanism for adding the organic acid to the digested liquid can be installed outside the MAP crystallizer, but in that case, in order to reduce the risk of scale generation in the return piping system, the MAP should be used as much as possible. It is preferable to install in the vicinity of the outlet of the crystallizer.

  The mechanism for adding the organic acid to the digested liquid after the MAP separation is not particularly limited, and the organic acid supply pipe may be directly connected to the pipe through which the digested liquid after the MAP separation flows, but in order to increase the mixing efficiency. It is preferable to connect via a mixing device such as an ejector or an in-line mixer. Furthermore, it is also preferable to install an organic acid mixing tank, connect an organic acid supply pipe and a pipe through which the digested liquid after MAP separation flows to the tank, and mix the organic acid and the digested liquid in the mixing tank. From the viewpoint of maintenance, an embodiment in which an organic acid mixing tank with a low risk of clogging is installed is preferable. The organic acid mixing tank can be installed either inside or outside the MAP crystallizer.

  An inorganic acid may be used instead of an organic acid if the pH is only lowered. However, when adding an inorganic acid, the digested liquid after separation of MAP is put in the system where the digested liquid in the methane fermentation tank stays or circulates. It is preferable to add an organic acid in order to affect the ion balance in the system when returned. In the case of an organic acid, since the organic acid itself is fermented and gasified in the methane fermenter, it is possible to prevent an unexpected adverse effect on the methane fermentation process. There are no particular restrictions on the organic acid, but it is not expected to add one or a combination of two or more of the substances contained in the raw material or generated in the decomposition process of the raw material in an acid fermentation tank. It is preferable in terms of prevention. Examples of the material contained in the raw material include acetic acid, lactic acid, and citric acid, and examples of the material generated in the decomposition process of the raw material include formic acid, acetic acid, propionic acid, and lactic acid.

  The addition amount of the organic acid is preferably an amount that can be lowered until the pH of the digested liquid after separation of MAP to be returned reaches a pH that is the same as or slightly lower than the digested liquid in the methane fermentation tank. Specifically, it is preferable to adjust to 8 or less, more preferably to 7.5 or less, for example, 6 to 8 can be adjusted.

  As an organic acid supply source, a dedicated organic acid supply line may be laid, but in an methane fermentation facility, an acid fermentation tank is often installed in front of the methane fermentation tank. It is convenient to withdraw a part of the liquid and use it as an organic acid source.

  In FIG. 2, the structural example of the crystallizer 20 which employ | adopted the liquid cyclone 26 as a separation mechanism is shown. The reactor 21 includes a supply pipe for digestion liquid 22 supplied from a methane fermentation tank, a return pipe 23 communicating with the reactor 21 and the lower part, a withdrawal pipe 24 for extracting the digestion liquid and MAP particles in the reactor 21, and a liquid. The particulate discharge pipe 25 of the cyclone 26 is connected. Although not shown, the reactor 21 is provided with the aeration mechanism described above. In the reactor 21, it is preferable to perform liquid stirring by the stirring device 31 in order to improve the mixing of the seed crystal and the liquid and to maintain a good flow state of the seed crystal. Stirring can also be performed by an aeration mechanism.

  The reactor 21 preferably has a structure in which the area of the bottom flat cross section is smaller than the area of the top flat cross section. Further, it is preferable that the flat cross section from the upper end to the predetermined position below has the same shape and the same cross sectional area, and the lower portion from the predetermined position has a shape such that the cross section gradually decreases. For example, as shown in FIG. 2, it is preferable that the bottom has an inverted conical shape. The angle of the inverted cone is preferably 45 ° or more and more preferably 60 ° or more with respect to the horizontal. By providing such an angle, the MAP particles that have settled in the reactor 21 can be concentrated at one point on the bottom of the reactor. Furthermore, it is preferable that the particle extraction tube 24 is connected in the vicinity where the settled MAP particles are concentrated. Thereby, the blockage by a deposit can be prevented.

  The fine particle discharge pipe 25 of the hydrocyclone 26 discharges the MAP particles concentrated by the liquid cyclone 26 from the bottom of the liquid cyclone 26 and returns it to the reactor 21. By returning the MAP particles concentrated by the hydrocyclone 26 to the reactor 21, the concentration of MAP particles that become seed crystals in the reactor can be increased, and as a result, the MAP particle surface area can be maintained large. The crystallization reaction is composed of a nucleation phenomenon and a growth phenomenon of particles, and the larger the surface area of the seed crystal, the higher the growth phenomenon is prioritized over the nucleation phenomenon. Further, a recovery pipe 27 for recovering concentrated MAP particles can be connected to the bottom of the hydrocyclone 26 or the fine particle discharge pipe 25.

  A circulating water tank 28 is installed above the return pipe 23. The circulating water tank 28 is a tank for temporarily storing circulating water (the same property as the digested liquid after MAP separation), and can be of any size. Of course, you may mix so that it may become uniform by installing a stirring apparatus. The circulating water tank 28 is connected to the overflow rising pipe 33 of the hydrocyclone 26 and further communicates with the reactor 21 and the return pipe 23 at the bottom. The digested liquid from which the MAP particles have been separated in the hydrocyclone 26 is supplied to the circulating water tank 28 through the overflow riser 33. The circulating water tank 28 maintains the same water level as the water surface of the reactor 21, and a part of the returned digestive liquid is returned to the reactor 21, and a part of the digested liquid is discharged as a digested liquid 32 after MAP separation due to overflow. The liquid cyclone 26 is introduced into the liquid cyclone 26 through the liquid cyclone inflow pipe 29.

  It is preferable to lower the pH by adding an organic acid 34 to the digested liquid 32 after MAP separation before being discharged from the crystallizer 20. In the illustrated embodiment, the digested liquid 32 after the MAP separation is discharged from the crystallizer 20 after being mixed with the organic acid in the organic acid mixing tank 35 and the pH is lowered. In order to increase the mixing efficiency, it is preferable to stir the liquid in the organic acid mixing tank 35, and the organic acid mixing tank 35 is provided with a stirring mechanism 36. Examples of the stirring mechanism 36 include mechanical stirring and aeration.

  The MAP particles in the reactor 21 are extracted from the extraction tube 24 at a predetermined flow rate and are introduced into the hydrocyclone 26. At this time, it is preferable to connect the drawing tube 24 to the inflow tube 29 of the hydrocyclone. As a result, the MAP particle concentration in the extraction tube 24 can be introduced into the liquid cyclone 26 after being diluted with the circulating water (digestion fluid) from the circulating water tank 28. The concentration of MAP particles introduced into the hydrocyclone 26 is an important operating factor that affects the processing performance of the hydrocyclone 26, and prevents the decrease of the MAP particle concentration in the digested liquid after MAP separation and the blockage of the cyclone under (cyclone bottom). Therefore, it is preferable that the concentration of MAP particles is low.

  If the pH or water temperature in the reactor 21 fluctuates, install a pH meter 30 or a water temperature meter (not shown) to adjust the amount of aeration according to the measured value, add a pH adjuster, It is also possible to perform a temperature cooling operation.

  In addition, a residue removing device can be disposed in the supply pipe of the digestive fluid 22 and / or the drawing pipe 24 connected to the bottom of the reactor 21. By removing the residue, the stability of MAP particle separation using the liquid cyclone 26 can be dramatically improved. Examples of the method for separating the residue include a centrifugal sedimentator and a sedimentation tank using gravity separation.

<2. Methane fermentation equipment>
In one embodiment of the methane fermentation facility according to the present invention, the system in which the digested liquid in the methane fermentation tank stays or circulates, the crystallizer according to the present invention, and the digested liquid is drawn from the system to the crystallizer. A first piping system for sending and a second piping system for returning the digested liquid discharged from the outlet of the crystallizer to the system. In the case where the methane fermentation facility does not have an organic acid addition mechanism for the digested liquid after MAP separation in the crystallizer, a mechanism for adding an organic acid to the second piping system may be provided.

  FIG. 3 schematically shows a device configuration example of the methane fermentation facility 40 using the MAP crystallizer according to the present invention. The methane fermentation facility 40 includes an acid fermentation tank 41, a methane fermentation tank 42, a MAP crystallizer 43, and an organic acid mixing tank 44. An organic matter (typically organic waste) 51 serving as a fermentation raw material is first put into an acid fermentation tank 41 and subjected to a solubilization / acid fermentation treatment. The acid fermentation broth after being subjected to the solubilization / acid fermentation treatment is put into a methane fermentation tank 42 where it is decomposed by the action of anaerobic microorganisms to generate methane and carbon dioxide, which are discharged as biogas 54. . From the viewpoint of promoting the decomposition of the acid fermentation broth by anaerobic microorganisms, it is preferable to stir the inside of the methane fermentation tank 42 by the stirrer 45.

  While the digested liquid 55 is discharged from the methane fermentation tank 42, a part of the digested liquid is transferred to the MAP crystallizer 43. In the MAP crystallizer 43, the MAP crystallization reaction described above is carried out using ions contained in the digestive juice as raw materials. The crystallized MAP 53 is discharged from the MAP crystallizer 43 after solid-liquid separation. Further, the MAP crystallizer 43 discharges exhaust gas 52 containing carbon dioxide gas and methane gas generated by decarboxylation. On the other hand, the digested liquid after MAP separation flows into the organic acid mixing tank 44 and is mixed with the organic acid-containing liquid extracted from the acid fermentation tank 41 to undergo a pH lowering process. In the acid fermenter 41, mixing of the organic acid-containing liquid and the digestive liquid is promoted by the stirrer 46. The digested liquid leaving the acid fermentation tank 41 is returned to the methane fermentation tank 42. By repeating the operation continuously or intermittently, it is possible to maintain a state in which the MAP generation potential in the methane fermentation tank 42 is lowered. According to one embodiment of the methane fermentation facility according to the present invention, it is possible to suppress the generation of scale over a long period of time, and it is not necessary to perform the scale removal operation and the operation stop of the methane fermentation facility associated therewith. The present invention can bring about a significant reduction in management costs associated with the operation of a methane fermentation facility, and its industrial utility value is extremely high.

  Examples of the present invention will be described below together with comparative examples, but these examples are provided for better understanding of the present invention and its advantages, and are not intended to limit the invention.

  An example of application of the present invention to a facility that treats waste generated in a food processing factory to methane fermentation is shown below.

(Comparative example)
In this factory, a maximum of 3.5 tons of garbage is generated per day, such as processing residues and returned products. The configuration of the methane fermentation facility conventionally employed in this factory is shown in FIG. The reference numerals in FIG. 4 are the same as those in FIG. Garbage as a raw material for fermentation is hydrated after removing foreign substances, and then passed through an acid fermentation tank with a capacity of 20 m ³ and put into a methane fermentation tank with a capacity of 200 m ³ . The fermentation raw material is adjusted to a liquid having a solid content of about 12% in an acid fermentation tank. At this time, the nitrogen partial average 4.5 kg / m ³ of acid fermentation tank, phosphorus 0.6 kg / m ^3, the magnesium is about 0.2 kg / m ^3. In an acid fermenter, hydrolysis of organic matter proceeds to produce an organic acid, and the pH drops to 4.0 or lower.

  The liquid that has passed through the acid fermentation tank is put into the methane fermentation tank. In the methane fermenter, organic matter is decomposed into methane and carbon dioxide by the action of methane fermentation bacteria. The pH in the methane fermenter rises to 7.0-8.0 because organic acids are converted into gas and removed by decomposition, and ammonia is generated by decomposition of proteins contained in organic matter. To do.

In general, food-based ingredients always contain nitrogen and phosphorus. In addition, in the case of this factory, a large amount of magnesium derived from salinity was contained, so the conditions for generating MAP inside the methane fermentation tank were in place. For this reason, scales occurred particularly near the liquid surface in the methane fermentation tank and around the digestion juice extraction tube. Since the scale leads to clogging of the digestion liquid drawing pump and failure of the methane fermenter agitator, it was necessary to stop the operation once every two to three years and remove the scale. In order to remove the scale, it is necessary to empty the methane fermentation tank with a capacity of 200 m ³ , remove the scale by chemical cleaning, and then start up the methane fermentation bacteria again. The facility had to be shut down. Moreover, since it was necessary to outsource the disposal of waste while the operation was stopped, the cost burden was large.

(Invention example)
On the other hand, in order to prevent generation | occurrence | production of a scale, the structure of the methane fermentation installation was improved into the structure shown in FIG. The digested liquid was extracted from the methane fermentation tank at 30 m ³ per day and introduced into a crystallizer using a liquid cyclone as a solid-liquid separation mechanism. In the crystallizer, carbon dioxide dissolved in the digestive fluid is discharged by circulating aeration from the gas phase inside the device and suction with an exhaust blower without adding chemicals from the outside, thereby raising the pH of the digestive fluid. It was. As a result, the pH of the digested liquid rose from 7.4 to 8.2. Note that caustic soda of about 15 kg / day is required in order to obtain a pH increase effect equivalent to the operation.

  Since the gas discharged from the crystallizer contains hydrogen sulfide and ammonia gas in addition to carbon dioxide, it can be a source of odor if it is released into the atmosphere as it is, so it is blown into the activated sludge tank of the wastewater treatment facility in the factory. As a result, volatilization of hydrogen sulfide and ammonia was prevented.

  In the crystallizer, a MAP seed crystal having a particle size of 1.0 to 2.0 mm is held at a MAP concentration of 30 to 50 g / L. Since the digested liquid with an increased pH has conditions for MAP to crystallize, phosphate ions and magnesium ions in the digested liquid crystallize on the surface of the seed crystal and can be discharged out of the system as MAP. In the case of this factory, the pH was 7.4 at the inlet of the crystallizer, the phosphoric acid concentration was 72 mg-P / L, and the magnesium ion concentration was 26 mg / L, whereas the pH was 8.2 and phosphoric acid at the outlet of the crystallizer. The concentration was 49 mg-P / L, and the magnesium ion concentration was 4 mg / L. MAP crystals were recovered on average about 6 kg / day per day. MAP can be used as a fertilizer.

In order to prevent fine MAP crystals in the digested liquid after crystallization from recrystallizing in the methane fermentation tank and the return pipe to the methane fermentation tank, an organic acid addition facility is installed near the outlet of the crystallization apparatus. Provided. As the organic acid source, the liquid in the acid fermentation tank was used. The pH of the liquid was 3.8 on average. The pH could be lowered to 6.7 by adding 1.5 m ³ / day of acid fermentation broth. In order to obtain a pH lowering effect equivalent to that of the operation, about 50 kg / day of sulfuric acid is required.
Although the scale removal operation has not been carried out regularly for 5 years after the above improvements, clogging is also caused in the circulation path between the methane fermentation tank and the MAP crystallizer in addition to the methane fermentation tank. No equipment failure occurred. By introducing the crystallizer according to the present invention, the problem of MAP-derived scale generation in the methane fermentation treatment facility could be solved at low cost.

DESCRIPTION OF SYMBOLS 10 Reactor 11 Circulation blower 12 Stirrer 13 Exhaust blower 20 Crystallizer 21 Reactor 22 Digested liquid 23 before processing Return pipe 24 Extraction pipe 25 Fine particle discharge pipe 26 Hydrocyclone 27 Recovery pipe 28 Circulating water tank 29 Inflow pipe 30 pH meter 31 Stirrer 32 Digested liquid 33 after MAP separation Overflow riser 34 Organic acid 35 Organic acid mixing tank 40 Methane fermentation equipment 41 Acid fermentation tank 42 Methane fermentation tank 43 MAP crystallizer 44 Organic acid mixing tank 45 Stirrer 46 Stirrer 51 Fermentation raw material 52 MAP crystallizer exhaust gas 53 MAP
54 Biogas 55 Digestive fluid

Claims (7)

An inlet for introducing a digestion liquid containing ammonium ions, magnesium ions, and phosphate ions extracted from the system in which the digestive liquid in the methane fermentation tank stays or circulates;
A reactor for containing a seed crystal and a digested liquid introduced from an inlet, and reacting ammonium ions, magnesium ions and phosphate ions contained in the digested liquid to crystallize MAP;
One or more decarboxylation mechanisms selected from the group consisting of an aeration mechanism, a decompression mechanism and an agitation mechanism for decarboxylating the digestion fluid in the reactor;
A separation mechanism for separating the crystallized MAP from the digestive juice;
An outlet for returning the digested liquid after separation of MAP to a system in which the digested liquid in the methane fermentation tank stays or circulates the digested liquid in which the magnesium ion concentration is reduced compared to the digested liquid in the methane fermenter;
A crystallization apparatus comprising:   The crystallization apparatus according to claim 1, further comprising a mechanism for adding an organic acid to the digested liquid after separating MAP and before discharging from the outlet. A system in which digested liquid in the methane fermentation tank stays or circulates;
The crystallizer according to claim 1 or 2,
A first piping system for withdrawing digestive juice from the system and sending it to the crystallizer;
A second piping system for returning the digested liquid discharged from the outlet of the crystallizer to the system;
Methane fermentation equipment equipped with.   The methane fermentation facility according to claim 3, further comprising a mechanism connected to the second piping system and adding an organic acid to the second piping system.   The methane fermentation facility according to claim 3 or 4, wherein the system in which the digested liquid in the methane fermentation tank stays or circulates includes a methane fermentation tank. The pH of the digestive fluid containing ammonium ions, magnesium ions, and phosphate ions extracted from the system in which the digestive fluid in the methane fermenter stays or circulates is aerated, decompressed and stirred in the presence of seed crystals. is raised by one or more decarboxylation method selected from the group, comprising the steps of ammonium ions contained in the digestive juices by reacting magnesium ions and phosphate ions to crystallize MAP,
Separating the crystallized MAP from the digestive juice;
A step of returning the digested liquid after separation of MAP to the system, the digested liquid having a reduced magnesium ion concentration compared to the digested liquid in the methane fermentation tank;
A scale prevention method in a methane fermentation facility including   The scale prevention method according to claim 6, further comprising a step of lowering the pH of the digested liquid by adding an organic acid to the digested liquid in the course of returning the digested liquid after separating MAP to the system.