JP5329369B2 - Sludge solubilizer and sludge solubilization method - Google Patents

Description

  The present invention relates to a sludge solubilizer and a sludge solubilization method that are preferably used to form a solubilized sludge used for digestion of sludge generated from wastewater treatment facilities such as sewage.

  Surplus sludge generated from wastewater treatment facilities using activated sludge from organic wastewater such as sewage has been disposed of in landfills after dehydration and incineration and after reduction. However, with the increase in sludge volume, it has become difficult year by year to secure a landfill site for disposal of ash after incineration. Although excess sludge has been reused for construction materials, it has not spread to society as a whole due to problems such as economic efficiency and distribution systems.

  On the other hand, in recent years, with the growing awareness of global environmental protection, there is a need for a shift to a resource recycling social system that promotes recycling of waste and energy recovery. Therefore, anaerobic digestion treatment such as methane fermentation has been used as a basic technology for recovering energy (electricity, heat, fuel) from surplus sludge generated from wastewater treatment facilities using activated sludge such as sewage and industrial wastewater. Is being reviewed again. In addition, an increasing number of local governments are proceeding with energy recovery and power generation through anaerobic digestion in the form of PFI projects using private life. By using such a digestion process, it is possible to generate electricity by collecting and burning methane generated from methane fermentation. In addition, solid matter can be reduced by decomposing and digesting excess sludge.

  FIG. 4 shows a general process flow of a conventionally used sludge digestion facility. The sludge digestion facility of FIG. 4 includes a concentrator 50, a digester tank 51, a heating boiler 52, a dehydrator 53, and a generator 54. A part of the activated sludge precipitated in the final settling basin in the wastewater treatment facility using activated sludge is returned to the biological treatment layer as return sludge, and the remainder as surplus sludge is used as a concentrator 50 such as a centrifugal concentrator or a flotation concentrator. To concentrate to a solids concentration of about 2-5%. The raw sludge precipitated in the first settling tank in the wastewater treatment facility is also concentrated in the same manner as described above. These concentrated sludge is stored in the digestion tank 51 where it is heated to an appropriate temperature (usually 54 to 57 ° C.) by a heating boiler 52 to perform acid fermentation by acid-producing bacteria and methane fermentation by methanogenic bacteria. It is used for the anaerobic digestion process that contains it, generating digestive gas containing methane as the main component.

  Digested sludge (digested liquid) produced by this anaerobic digestion process is dehydrated by a dehydrator 53 comprising, for example, a belt press dehydrator. The dewatered sludge is transported by truck to a treatment plant outside the sewage treatment facility, and the other dewatered separation liquid is first returned to the inlet side of the settling basin as return water. On the other hand, digestion gas from the digestion tank 51 is stored in a gas holder after hydrogen sulfide is removed by a desulfurization tower, and is supplied as fuel to a gas engine for driving the generator 54 as necessary. The electric power obtained from the generator 54 is transmitted outside the facility for use as general electric power, or is used as electric power for driving the heating boiler 52. That is, such excess sludge digestion equipment can reduce the amount of solid matter from excess sludge and simultaneously use digestion gas as an energy source.

  However, the digestibility of organic waste such as food waste and livestock manure by digestion with methane fermentation (decomposition rate of organic matter) is about 90-95%, while sludge methane fermentation in the above sludge digestion equipment. The digestibility by is only about 50%. This is thought to be due to the low solubilization rate of surplus sludge obtained from wastewater treatment equipment using activated sludge by acid fermentation, which is the previous stage of methane fermentation. Therefore, before the concentrated excess sludge is supplied to the digester, the solubilization of the excess sludge is promoted to further reduce the solids from the excess sludge and further increase the digestion gas (improve the digestibility). ) Is required to develop technology. “Solubilization” of surplus sludge here means that water and organic components inside the sludge cell group are dissolved in water.

  In addition, in power generation facilities using anaerobic digestion treatment such as methane fermentation, unmanned operation equipment for 24 hours by heating with a simple boiler that does not require operation qualification is widespread from the viewpoint of cost reduction such as labor costs. . However, as described above, the digestibility (gasification rate) by methane fermentation in the sludge digestion facility is only about 50% because the sludge solubilization rate is small. As a result, power generation facilities using such anaerobic digestion treatment have low power generation efficiency, making it difficult to make a profit. Therefore, from the viewpoint of profitability of such business, simple and inexpensive sludge heating that does not require operating qualification (sludge heating by unmanned operation using inexpensive equipment) and digestibility by promoting sludge solubilization Development of a device for solubilization of sludge that can simultaneously achieve improvement (improvement of gasification rate by promoting solubilization of sludge) is strongly demanded.

  JP 2007-117801 A discloses a methane fermentation treatment method capable of stably performing methane fermentation at a substantially constant temperature setting value when organic waste is subjected to high temperature methane fermentation treatment. Has been. The methane fermentation treatment method of this document includes a step of high-temperature solubilization treatment of organic waste, and a step of cooling the solubilization treatment product by heat exchange between the solubilization treatment product and a cooling medium. This methane fermentation treatment method relates to a technology that enables stable methane fermentation by minimizing the fluctuation of the fermentation temperature, but as a high-temperature solubilizer for sludge, sludge can be used under high-temperature and high-pressure conditions. Only a complex apparatus having a reactor that is a tank for solubilization and a flash tank that is a tank for storing solubilized sludge as a solubilized product and continuously charging it into a digester is illustrated. Japanese Patent No. 3808475 discloses a heating tower provided with a concentrator for concentrating digested sludge, a digestion gas combustion furnace generated in a digestion tank, and heat for generating high-temperature and high-pressure steam by the combustion heat. An anaerobic digestion system comprising an exchanger and heating digested sludge concentrated in a heating tower by direct contact with high-temperature and high-pressure steam is disclosed. The anaerobic digestion system of the said literature is related with the technique which aims at the improvement of a digestibility by concentrating the digested sludge obtained from the digester, heating with high temperature / high pressure steam, and circulating to a digester. However, this document does not specifically explain the heating and solubilization treatment of sludge before it is sent to a digestion tank such as excess sludge recovered from a wastewater treatment apparatus.

JP 2007-117801 A Japanese Patent No. 3808475

  The present invention has been made in view of these disadvantages, and promotes solubilization of surplus sludge in the previous stage of supplying concentrated surplus sludge to the digestion tank, thereby further solidifying the surplus sludge. An object of the present invention is to provide a sludge solubilization device and a sludge solubilization method that can further reduce the weight loss and digestibility, and can heat and solubilize sludge by unmanned operation using an inexpensive device. To do.

The first aspect of the present invention made to solve the above problems is as follows.
A sludge solubilizer for forming solubilized sludge for methane fermentation from concentrated sludge,
A heat exchanger for heating the concentrated sludge and cooling the solubilized sludge by heat exchange between the flow of the concentrated sludge and the flow of the solubilized sludge;
Solubilizing means for forming solubilized sludge heated to 100 ° C. or higher by jetting high-temperature and high-pressure steam into the heated concentrated sludge flow so as to face the flow. The sludge solubilizing device.

  According to the sludge solubilization apparatus, heat exchange is performed between the flow of concentrated sludge and the flow of solubilized sludge using a heat exchanger. The concentrated sludge can be heated to a temperature suitable for the feedstock (for example, around 60 ° C), and at the same time, the solubilized sludge heated to 100 ° C or higher is a temperature suitable for methane fermentation of 50 ° C or higher and 60 ° C or lower. It is possible to cool down to a certain level. In addition, according to the sludge solubilizer, 100 ° C. is obtained by ejecting high-temperature high-pressure steam from the opposite direction into the flow of concentrated sludge heated to a temperature suitable for the feedstock to the solubilization means. Since the above-described solubilization means for forming the solubilized sludge heated is provided, such a solubilization means is not a pressure vessel (sealed vessel) but an open air vessel, and therefore does not require an operating qualification, is inexpensive and Heated and solubilized sludge can be formed by safe continuous unattended operation. In the sludge solubilizer, the formation of the solubilized sludge heated to 100 ° C. or higher generates a dynamic pressure of atmospheric pressure or higher in a part of the concentrated sludge by jetting the high-temperature high-pressure steam, and at the same time, It is possible to improve the digestibility of the solubilized sludge formed by accelerating the heating using the sensible heat and latent heat of condensation and promoting the decomposition of the concentrated sludge by the condensation impact of water vapor. In addition, it is possible to drastically reduce the amount of solid matter generated from sludge.

  As the heat exchanger provided in the sludge solubilizer, a double-pipe heat exchanger can be used. By using such a double-pipe heat exchanger, heat exchange between the concentrated sludge flow and the solubilized sludge flow enables efficient heat transfer and can be heated to 100 ° C or higher. The solubilized sludge can be reliably cooled to 50 ° C. or higher and 60 ° C. or lower, and at the same time, the concentrated sludge can be sufficiently heated to a temperature suitable for the feedstock to the solubilizing means.

  The sludge solubilization apparatus is configured to use a multi-tube heat exchanger as a heat exchanger, and high-temperature high-pressure steam is ejected to each of a plurality of tubes of the multi-tube heat exchanger by the solubilizing means. It may be. If there is a flow of concentrated sludge heated to a temperature suitable for the feedstock to the solubilization means in multiple tubes of the multi-tube heat exchanger, each of these tubes is heated to high temperature and pressure by the solubilization means. By ejecting water vapor from the opposite direction, sludge sufficiently heated and solubilized can be efficiently formed.

  The ejection speed of the high-temperature and high-pressure steam from the solubilizing means in the sludge solubilizer is preferably 5 to 100 times the flow rate of the concentrated sludge facing this. By jetting high-temperature and high-pressure steam from the opposite direction to the flow of concentrated sludge at such a large relative speed, it is possible to further promote the solubilization of sludge by the dynamic pressure effect of steam and the condensation impact of steam. It becomes possible.

  The concentrated sludge supplied to the sludge solubilizer typically includes a concentrated sludge recovered from a wastewater treatment apparatus using activated sludge. For example, by condensing excess sludge from wastewater treatment equipment using activated sludge such as sewage and industrial wastewater with the sludge solubilizer, the digestibility of the heated and solubilized sludge can be increased, It is possible to effectively reduce the amount of material, and it is possible to achieve improvement in energy efficiency and reduction in environmental load.

  Concentrated sludge supplied to the sludge solubilizer is not only concentrated concentrated sludge recovered from wastewater treatment equipment using activated sludge, but also reconcentrated sludge partially digested after methane fermentation. May be included. In this way, by re-concentrating sludge partially digested after methane fermentation and reusing it as concentrated sludge for supply to the sludge solubilizer, the amount of solids finally disposed of is further reduced. Thereby, the utilization efficiency of sludge can be further improved.

  Digestion including methane fermentation for the sludge solubilization apparatus, the concentration apparatus for forming the concentrated sludge to be supplied to the sludge solubilization apparatus by dehydrating the sludge, and the solubilized sludge formed by the sludge solubilization apparatus A sludge treatment system can be constructed by combining with a digester that performs treatment. Since such a sludge treatment system is equipped with the sludge solubilization device described above, solubilization of excess sludge is performed in a stage prior to supplying the excess sludge concentrated by the concentration device to the digestion tank for digestion treatment. This makes it possible to simultaneously reduce the amount of solids from the excess sludge and improve the digestibility, and to efficiently heat and solubilize the sludge by unmanned operation using an inexpensive device.

The second aspect of the present invention made to solve the above problems is as follows.
A sludge solubilization method for forming a solubilized sludge for methane fermentation,
A step of heating the concentrated sludge by performing heat exchange between the flow of the concentrated sludge including the concentrated excess sludge collected from the wastewater treatment apparatus using activated sludge and the flow of the solubilized sludge;
Forming a solubilized sludge heated to 100 ° C. or higher by spraying high-temperature high-pressure steam in the heated concentrated sludge flow so as to face the flow;
A step of cooling the solubilized sludge to 50 ° C. or higher and 60 ° C. or lower by performing heat exchange between the flow of the solubilized sludge heated to 100 ° C. or higher and the flow of the concentrated sludge. This is a sludge solubilization method.

  According to the sludge solubilization method, the concentrated sludge is heated by exchanging heat between the flow of the concentrated sludge containing the concentrated excess sludge recovered from the wastewater treatment apparatus using activated sludge and the flow of the solubilized sludge. Therefore, the concentrated sludge can be efficiently heated to a temperature suitable for the feedstock to the solubilized sludge forming step (for example, around 60 ° C.) without applying energy from the outside. Moreover, the said sludge solubilization method is the process of forming the solubilized sludge heated at 100 degreeC or more in the flow of this heated concentrated sludge by spouting high temperature / high pressure steam so as to oppose this flow. Therefore, the high-temperature and high-pressure steam jetting means may be an open-air container rather than a pressure vessel (sealed vessel). Solubilized sludge can be formed. Moreover, according to the said sludge solubilization apparatus, by performing heat exchange with the flow of this solubilized sludge heated to 100 degreeC or more, and the flow of concentrated sludge, solubilized sludge is 50 degreeC or more and 60 degrees C or less. Since it has the process to cool, the solubilized sludge heated at 100 degreeC or more can be reliably cooled to the temperature suitable for methane fermentation. In the sludge solubilization method, when the solubilized sludge heated to 100 ° C. or more in the solubilized sludge forming step generates a dynamic pressure of atmospheric pressure or higher in a part of the concentrated sludge by high-temperature high-pressure steam jetting. At the same time, the digestion rate of the solubilized sludge formed is achieved by accelerating the heating using the sensible heat and latent heat of condensation of the high-temperature and high-pressure steam, and by promoting the decomposition of the concentrated sludge by the condensation impact of the steam. Can be improved, and the amount of solid matter produced from sludge can be significantly reduced.

  As described above, according to the sludge solubilization apparatus and the sludge solubilization method of the present invention, the dynamic pressure effect and steam condensation impact due to high-temperature and high-pressure steam jetting in the previous stage of supplying concentrated excess sludge to the digestion tank By promoting the solubilization of sludge due to the above, it becomes possible to further reduce the amount of solids from the excess sludge, further improve the digestibility, and heat and solubilize the sludge by cheap and simple continuous unattended operation. .

FIG. 1 is a schematic cross-sectional view showing a sludge solubilizer according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a sludge solubilizer according to an embodiment different from FIG. 1 of the present invention. FIG. 3 is a process flow diagram of the sludge treatment system using the sludge solubilizer according to the present invention. FIG. 4 is a process flow diagram of a conventional sludge digestion facility.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.
The sludge solubilizer 1 according to the first embodiment shown in FIG. 1 mainly has a double-pipe heat exchanger 2 and a solubilizing means 3.

  The double-pipe heat exchanger 2 includes an outer tube 5 having a circular cross section and an inner tube 4 having a circular cross section that is inserted concentrically inside the outer tube 5 at intervals. Although the material of the inner tube 4 and the outer tube 5 is not particularly limited, for example, an aluminum extruded profile is used. Both end portions of the inner tube 4 protrude outward from both end portions of the outer tube 5. The sizes of the inner tube 4 and the outer tube 5 can be designed without limitation depending on the processing capacity of the process, but it is preferable to select from the sizes set as standard specifications because they are inexpensive.

  The surplus sludge obtained from the final sedimentation basin in the wastewater treatment facility using activated sludge is concentrated by a known concentrating device until the solid content concentration is usually about 2 to 5% to form concentrated sludge. This concentrated sludge is fed from one end of the inner pipe 4 of the double pipe heat exchanger 2 as a feed of the sludge solubilizer 1 (A in the figure). The concentrated sludge A generally has a temperature of about 15 ° C. to 30 ° C. and a pressure of about 250 kPa to 350 kPa at one end of the inner pipe 4. As the concentrated sludge A flows through the inner pipe 4, it is gradually heated by exchanging heat with the flow of solubilized sludge sent from the solubilizing means 3 described later (B in the figure). The concentrated sludge A thus heated has a temperature of, for example, about 50 ° C. or more and 70 ° C. or less when reaching the other end of the inner tube 4 (when provided as feed to the solubilizing means 3). .

  On the other hand, the solubilized sludge B sent out from the solubilizing means 3 described later is sent from one end of the outer tube 5 of the double-tube heat exchanger 2 (the outlet side of the inner tube 4). The solubilized sludge B has, for example, a temperature of about 110 ° C. to 140 ° C. and a pressure of about 200 kPa to 300 kPa at one end of the outer tube 5. As the solubilized sludge B flows through the outer pipe 5, it is gradually cooled by exchanging heat with the flow of the concentrated sludge A. The solubilized sludge B cooled in this way has a temperature suitable for methane fermentation when it reaches the other end of the outer pipe 5 (before being provided as a feed to the downstream digester) 50. It has a temperature of not less than about 60 ° C. and not more than 60 ° C.

  The solubilizing means 3 includes an ejector (high temperature / high pressure steam jetting part) 6, a high temperature / high pressure steam supply part 7, and a solubilized sludge delivery part 8. In the solubilizing means 3, the flow of high-temperature and high-pressure steam (C in the figure) flows through the ejector 6 from the opposite direction to the concentrated sludge A supplied from the inner pipe 4 of the double-pipe heat exchanger 2. Spouted and blown. The high-temperature and high-pressure steam here has, for example, a temperature of 150 to 200 ° C. and a pressure of 600 to 900 kPa. Concentrated sludge A is heated at a high speed by high-temperature and high-pressure steam C at a high speed, and at the same time, dynamic pressure of atmospheric pressure or higher is generated. Thus, the flow of the solubilized sludge B is formed with a temperature of about 110 ° C. to 140 ° C. and a pressure of about 200 kPa to 300 kPa. The formed solubilized sludge B is delivered from the solubilized sludge delivery section 8 and supplied to the outer tube 5 of the double-tube heat exchanger 2. Further, by blowing high-temperature high-pressure steam C into the concentrated sludge A at a high speed, decomposition and solubilization of sludge cell groups is promoted by condensation impact of the steam. The jetting speed (blowing speed) of the high-temperature and high-pressure steam C is preferably 5 to 100 times the flow rate of the concentrated sludge A facing it. By jetting high-temperature and high-pressure steam C from the direction opposite to the flow of the concentrated sludge A at such a large relative speed, further solubilization of sludge due to the dynamic pressure effect of steam and condensation impact (cavitation) of steam is further achieved. As a result, it is possible to improve the digestibility in the downstream digester and to reduce the solids.

  According to the sludge solubilization apparatus of this embodiment, the concentrated sludge is efficiently heated to a temperature suitable for the feedstock to the solubilization means (for example, about 50 ° C. or more and about 70 ° C. or less) without applying energy from the outside. At the same time, the solubilized sludge heated to 100 ° C. or higher can be reliably cooled to 50 ° C. or higher and 60 ° C. or lower, which is a temperature suitable for methane fermentation. Further, in this sludge solubilizer, the solubilizing means is not a pressure vessel (sealed vessel) but an open-air vessel, so there is no need for operation qualification and it is heated and solubilized by safe unmanned operation for 24 hours. Sludge can be formed at low cost. In particular, since unmanned operation for 24 hours is possible, the boiler for heating the digester can be simplified and downsized, and the construction cost and operation cost of the digestion facility can be reduced. Furthermore, in this sludge solubilizer, heating and solubilization of sludge can be greatly promoted by high-speed blowing of high-temperature and high-pressure steam, so that the digestibility of the formed solubilized sludge is further improved and the sludge is generated It is possible to simultaneously achieve a dramatic reduction in the amount of solid matter.

  The sludge solubilizer 10 according to the second embodiment shown in FIG. 2 mainly includes a multi-tube heat exchanger 11 and a solubilizing means 12. In the present embodiment, a part of the structure of the multi-tubular heat exchanger 11 and the solubilizing means 12 (a part of the high-temperature and high-pressure steam jetting portion 17 described later) is formed in a single casing. Yes.

  The multi-tube heat exchanger 11 mainly includes a plurality of tubes 13, a peripheral portion (gap) 14, and a plurality of baffles 15 in a cylindrical outer cylinder. The tubes 13 have a circular cross section, and a large number are arranged at substantially uniform intervals. Although the material of the pipe | tube 13 is not specifically limited, For example, the product made from an aluminum extrusion shape material is used. The size of the inner tube 13 can be designed without any limitation depending on the processing capacity of the process, but it is preferable to select from the size set as a standard because it is inexpensive.

  Concentrated sludge formed from excess sludge obtained in the wastewater treatment facility is fed from one end of each of the tubes 13 of the multi-tube heat exchanger 11 as a feed of the sludge solubilizer 10 (FIG. Middle A). The concentrated sludge A generally has a temperature of about 15 ° C. to 30 ° C. and a pressure of about 250 kPa to 350 kPa at one end of the tube 13. As the concentrated sludge A flows through the pipe 13, it is gradually heated by exchanging heat with the flow of solubilized sludge (B in the figure) treated with high-temperature and high-pressure steam in the solubilizing means 12 described later. The The concentrated sludge A thus heated has a temperature of, for example, about 50 ° C. or more and 70 ° C. or less immediately before receiving the high-speed high-pressure steam blown from the solubilizing means 12.

  On the other hand, the solubilized sludge B treated by the high-temperature and high-pressure steam in the solubilizing means 12 described later is sent from the other end of each of the tubes 13 and then forms a flow in the opposite direction. It is sent into the peripheral part 14 of. When the solubilized sludge B is heated and solubilized by receiving high-speed high-pressure steam blown from the solubilizing means 12, it has a temperature of about 110 ° C. to 140 ° C. and a pressure of about 200 kPa to 300 kPa, for example. The solubilized sludge B is gradually cooled by exchanging heat with the flow of the concentrated sludge A as it flows through the peripheral portion 14 while being rectified by the plurality of baffles 15. The solubilized sludge B cooled in this way has a temperature suitable for methane fermentation of 50 ° C. or higher when it reaches the discharge point of the surrounding portion 14 (before being provided as a feed to the downstream digester). It has a temperature of about 60 ° C. or less.

  The solubilizing means 12 has a high-temperature and high-pressure steam feed path 16 and a high-temperature and high-pressure steam jet part 17. The high-temperature and high-pressure steam spraying portion 17 is configured such that the high-temperature and high-pressure steam is ejected and blown into each of the plurality of tubes 13 of the multi-tube heat exchanger 11 through the high-temperature and high-pressure steam feed path 16. That is, in the solubilizing means 12, the high-temperature and high-pressure steam jetting portion 17 is inserted into each of the plurality of tubes 13 of the multitubular heat exchanger 11. The high-temperature and high-pressure steam flow (C in the figure) is supplied to the concentrated sludge A at a high speed from the direction in which the high-temperature and high-pressure steam passing through the high-temperature and high-pressure steam feed path 16 faces the concentrated sludge A through the high-temperature and high-pressure steam jet part 17. It is done by being blown. The high-temperature and high-pressure steam here has a temperature of, for example, 100 ° C. or more and 200 ° C. or less (corresponding pressure is a pressure of about 100 kPa or more and about 1600 kPa or less), as in the first embodiment. Concentrated sludge A is heated at a high speed by high-temperature and high-pressure steam C being blown at a high speed, and at the same time, a dynamic pressure higher than atmospheric pressure is generated. The flow of the solubilized sludge B is formed in a state of having a temperature of about 100 ° C. to 140 ° C. (corresponding pressure is about 100 kPa to about 400 kPa). The solubilized sludge B thus formed is fed from the end of the tube 13 and then fed into the peripheral portion 14 of the tube 13 to be used for heat exchange with the concentrated sludge A. Further, as described above, by blowing high-temperature high-pressure steam C into the concentrated sludge A at a high speed, decomposition and solubilization of sludge cell groups is promoted by the condensation impact of the steam. The ejection speed of the high-temperature and high-pressure steam C is preferably 5 to 100 times the flow rate of the concentrated sludge A facing it. By supplying the high-temperature and high-pressure steam C from the opposite direction to the flow of the concentrated sludge A at such a large relative speed, heating by the dynamic pressure effect of steam and the condensation impact of steam as in the first embodiment. The solubilization of sludge by (cavitation) can be further promoted, and as a result, the digestibility in the downstream digester can be improved and the solids can be reduced.

  According to the sludge solubilization apparatus of the present embodiment, the same effect as in the case of the first embodiment can be obtained. Further, in the sludge solubilization apparatus of the present embodiment, the high-temperature and high-pressure steam from the solubilizing means is ejected to each of the plurality of tubes of the multi-tube heat exchanger, so that sufficient heating and enabling are possible. It is possible to efficiently form solubilized sludge.

  The process flow of the sludge treatment system 20 in FIG. 3 includes a wastewater treatment facility comprising a first settling tank 21, a biological treatment tank 22 and a final settling tank 23, a concentrating device 24, a sludge solubilizing device 25, a digesting tank 26, and a dehydrating device 27. It is the flow of the process in the sludge processing system which has this.

  Wastewater such as sewage flows into the first sedimentation basin 21, and suspended solids that are likely to settle in the first sedimentation basin 21 are removed by sedimentation. Thereafter, activated sludge is precipitated in the final settling basin 23, and the purified supernatant water is discharged to the outside as treated water. The first settling basin 21, the biological treatment tank 22, and the final settling basin 23 constitute a wastewater treatment facility. The raw sludge (first sedimentation basin sludge) obtained by collecting the solid matter from the primary sedimentation basin 21 is directly supplied to the digester 26 without heating.

  A part of the activated sludge settled in the final sedimentation basin 23 is returned to the biological treatment tank 22 as a return sludge, while the remaining surplus sludge is reduced in volume, for example, a concentrator such as a centrifugal concentrator or a flotation concentrator. 24 and is concentrated until the solid concentration is about 2 to 5%. The concentrated sludge thus obtained is supplied to the sludge solubilizer 25 according to the present invention, and heated and solubilized sludge is generated. This solubilized sludge is supplied to the digestion tank 26 together with raw sludge (first sedimentation basin sludge), where it is subjected to high-temperature anaerobic digestion by the action of anaerobic bacteria such as acid-producing bacteria and methanogens. Digestion gas which is a mixed gas of about 60% and carbon dioxide about 40% is produced. This digested gas is desulfurized and then used as a fuel for power generation. The digester 26 is provided with a boiler in order to maintain a temperature suitable for methane fermentation. However, since this sludge treatment system is configured to include the sludge solubilizer 25 according to the present invention capable of continuous unmanned operation for 24 hours, the boiler for heating the digester can be simplified and miniaturized. Construction costs and labor costs related to digestion facilities can be reduced.

  The digested liquid (partially digested sludge) generated by the high-temperature anaerobic digestion process in the digestion tank 26 is dehydrated by a dehydrator 27 composed of, for example, a belt press dehydrator, thereby forming dehydrated sludge. While this dewatered sludge is discarded, the dehydrated separated liquid (dehydrated filtrate) separated from the digested liquid by dehydration is first returned to the inlet side of the settling basin 21 as return water. Further, a part of the digested liquid (partially digested sludge) obtained from the digestion tank 26 is returned to the concentrating device 24, concentrated again, and subjected to subsequent processing.

  According to the sludge treatment system of this embodiment, since the sludge solubilization apparatus according to the present invention is provided, the stage before supplying the concentrated excess sludge to the digestion tank for digestion treatment (anaerobic treatment) In addition, high-temperature and high-pressure steam is used to promote heating and solubilization of surplus sludge, thereby simultaneously reducing the amount of solids from surplus sludge and improving digestibility, and further, unattended operation using inexpensive equipment It is possible to efficiently heat and solubilize sludge. In addition, the sludge solubilizer included in this sludge treatment system can be operated unattended for 24 hours, so the boiler for heating the digester can be simplified and miniaturized, and the overhead for digestion equipment can be reduced. It can be greatly reduced.

  The present invention is not limited to these embodiments. For example, a double-pipe heat exchanger may be used so that high-temperature and high-pressure steam from the solubilizing means is ejected to each of a plurality of tubes of the heat exchanger. Moreover, it is good also as a structure which the heat exchanger and the solubilization means isolate | separated using the multitubular heat exchanger which has a baffle.

  According to the sludge solubilization apparatus and method of the present invention, it is possible to further reduce the amount of solids from excess sludge and further improve the digestibility, and to heat and solubilize sludge by cheap and simple continuous unattended operation. Therefore, it can be suitably used in a power generation facility that uses digestion treatment provided in a wastewater treatment facility of a factory or a local government sewage treatment plant.

1 Sludge solubilizer 2 Heat exchanger 3 Solubilization means 4 Inner pipe 5 Outer pipe 6 Ejector (high-temperature high-pressure steam jet part)
7 High-temperature and high-pressure steam supply section 8 Solubilized sludge delivery section 10 Sludge solubilizer 11 Heat exchanger 12 Solubilization means 13 Pipe 14 Surrounding section 15 Baffle 16 High-temperature and high-pressure steam feed section 17 High-temperature and high-pressure steam ejection section 20 Sludge treatment system
21 First sedimentation tank 22 Biological treatment tank 23 Final sedimentation tank 24 Concentration device 25 Sludge solubilization device 26 Digestion tank 27 Dehydration apparatus 50 Concentration apparatus 51 Digestion tank 52 Heating boiler 53 Dehydration apparatus 54 Generator

Claims (8)

A sludge solubilizer for forming solubilized sludge for methane fermentation from concentrated sludge,
A heat exchanger for heating the concentrated sludge and cooling the solubilized sludge by heat exchange between the flow of the concentrated sludge and the flow of the solubilized sludge;
Solubilizing means for forming solubilized sludge heated to 100 ° C. or higher by jetting high-temperature and high-pressure steam into the heated concentrated sludge flow so as to face the flow. Sludge solubilizer.   The sludge solubilizer according to claim 1, wherein a double-pipe heat exchanger is used as the heat exchanger.   A multi-tube heat exchanger is used as the heat exchanger, and high-temperature high-pressure steam is jetted to each of a plurality of tubes of the multi-tube heat exchanger by the solubilizing means. The sludge solubilizer described in 1.   The sludge solubilizer according to claim 1, 2 or 3, wherein a jet speed of the high-temperature and high-pressure steam is 5 to 100 times the flow rate of the concentrated sludge facing the high-temperature and high-pressure steam.   The sludge solubilizer according to any one of claims 1 to 4, wherein the concentrated sludge includes a concentrate of excess sludge recovered from a wastewater treatment apparatus using activated sludge.   The sludge solubilizer according to any one of claims 1 to 5, wherein the concentrated sludge includes a product obtained by re-concentrating sludge partially digested after methane fermentation. The sludge solubilizer according to any one of claims 1 to 6,
Digestion which performs digestion processing including methane fermentation on the concentration device which forms concentrated sludge for supplying to the sludge solubilizer by dehydrating sludge, and the solubilized sludge formed by the sludge solubilizer Sludge treatment system with tank. A sludge solubilization method for forming a solubilized sludge for methane fermentation,
A step of heating the concentrated sludge by performing heat exchange between the flow of the concentrated sludge including the concentrated excess sludge collected from the wastewater treatment apparatus using activated sludge and the flow of the solubilized sludge;
Forming a solubilized sludge heated to 100 ° C. or higher by spraying high-temperature high-pressure steam in the heated concentrated sludge flow so as to face the flow;
A step of cooling the solubilized sludge to 50 ° C. or higher and 60 ° C. or lower by performing heat exchange between the flow of the solubilized sludge heated to 100 ° C. or higher and the flow of the concentrated sludge. Sludge solubilization method.

Images