JP2008183494A - Wastewater treatment system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wastewater treatment system which can efficiently dissolve combustion exhaust gas from a power generation facility etc. in a gas-liquid mixing tank, and efficiently discharge the dissolved combustion exhaust gas as bubbles in a pressure floatation tank. <P>SOLUTION: The wastewater treatment system comprises the gas-liquid mixing tank 2 that mixes wastewater to be treated and gas under pressure to dissolve the gas in the wastewater, and the pressure floatation tank 4 that floats sludge contained in the wastewater by bubbles generated when pressure is released. As the gas, a combustion exhaust gas from a combustion facility or a power generation facility 14 is used. The combustion exhaust gas is mixed with the wastewater in the gas-liquid mixing tank 2, and the pressure floatation tank 4 is warmed by utilizing the heat of the combustion exhaust gas supplied from the combustion facility 14 or the power generation facility to the gas-liquid mixing tank 2. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a treatment system for treating wastewater such as sewage and industrial wastewater.

  For example, as a treatment system for treating sewage or the like, a system using a gas-liquid mixing tank and a pressure levitation tank (so-called pressure levitation separation method) is known (see, for example, Patent Document 1). In the gas-liquid mixing tank, wastewater to be treated and gas, for example, carbon dioxide gas, are mixed in a pressurized state, and in the pressurized levitation tank, the pressurized state is released and the pressure is reduced. The sludge contained in the wastewater is floated by the air bubbles, and is thus separated into the floating sludge and the separated water in the pressurized flotation tank.

JP 2002-28700 A

  In such a pressurized flotation separation system, it is preferable to dissolve a large amount of gas (for example, air) in the wastewater to be treated in the gas-liquid mixing tank as one way to increase the separation efficiency. If it is going to make it, pressurization pressure must be raised and the problem that the pressurization power for maintaining a pressurization state will increase will arise.

  In addition, since carbon dioxide has higher solubility in water than air, the solubility can be increased by using carbon dioxide as the gas to be mixed. However, as disclosed in Patent Document 1, When digestion gas generated from an anaerobic digestion process (this digestion gas component is 80% methane, 20% carbon dioxide, for example) is used, the digestion gas generated in the anaerobic digestion process is not stable. In addition, the liquefied gas cannot be dissolved in the wastewater as required in the gas-liquid mixing tank, and as a result, bubbles generated during decompression in the pressurized flotation tank are not constant, and the sludge contained in the wastewater There is a problem that the separation efficiency is deteriorated.

  The object of the present invention is to efficiently dissolve the combustion exhaust gas from the combustion facility or power generation facility in the waste water in the gas-liquid mixing tank and to efficiently dissolve the dissolved combustion exhaust gas in the pressurized levitation tank. It is to provide a wastewater treatment system that can be discharged as.

In the wastewater treatment system according to claim 1 of the present invention, when the wastewater to be treated and the gas are mixed in a pressurized state and the gas-liquid mixing tank for dissolving the gas in the wastewater is released, the pressurized state is released. A sludge treatment system comprising a pressurized flotation tank that floats sludge contained in drainage by bubbles generated in
Combustion exhaust gas of combustion equipment or power generation equipment is used as gas mixed in the gas-liquid mixing tank, and this combustion exhaust gas is mixed with waste water in the gas-liquid mixing tank, and from the combustion equipment or power generation equipment. The pressurized levitation tank is heated using heat of combustion exhaust gas supplied to the gas-liquid mixing tank.

  Moreover, in the wastewater treatment system according to claim 2 of the present invention, a first supply line for supplying a part of the wastewater to the gas-liquid mixing tank and a remaining part of the wastewater are supplied to the pressurized floating tank. And a second supply line for exchanging heat between the waste water supplied to the pressurized flotation tank and the combustion exhaust gas supplied to the gas-liquid mixing tank. An exchanger is provided.

  Furthermore, in the wastewater treatment system according to claim 3 of the present invention, the pressurized floating tank is provided with a part of a warming circulation line through which a warming fluid is circulated, and the warming circulation line includes A heat exchanger for exchanging heat between the heated fluid flowing in the heating circulation line and the combustion exhaust gas supplied to the gas-liquid mixing tank is provided.

  According to the wastewater treatment system of the first aspect of the present invention, the combustion exhaust gas discharged from the combustion facility or the power generation facility is used as the gas dissolved in the wastewater. No special equipment is required, and the entire system configuration can be simplified. Such a combustion facility (for example, a boiler) or a power generation facility (for example, a gas engine) is often installed in a sewage sludge treatment plant, an industrial wastewater sludge treatment plant, etc., and is discharged from the combustion facility or the power generation facility. Combustion exhaust gas is stably discharged and can be effectively used as a gas for floating sludge. In addition, since the pressurized levitation tank is heated using the heat of the combustion exhaust gas supplied to the gas-liquid mixing tank, the temperature of the combustion exhaust gas supplied to the gas-liquid mixing tank is lowered and the temperature is increased. The temperature of the drainage of the pressure levitation tank is raised. In general, the solubility of combustion exhaust gas containing carbon dioxide gas in water increases as the temperature decreases, and decreases as the temperature increases. As a result of the heat exchange as described above, the gas temperature of the combustion exhaust gas decreases. In the gas-liquid mixing tank, the solubility of the combustion exhaust gas containing carbon dioxide in the waste water is increased, and more combustion exhaust gas containing carbon dioxide gas can be dissolved in the waste water. In the pressurized flotation tank, Since the temperature of the waste water becomes high, the solubility of the combustion exhaust gas containing carbon dioxide gas is reduced, and more combustion exhaust gas containing dissolved carbon dioxide gas can be released as bubbles, resulting in sludge contained in the waste water. Can be efficiently levitated and separated.

  Moreover, according to the wastewater treatment system according to claim 2 of the present invention, the heat exchanger disposed in the second supply line is supplied to the wastewater and gas-liquid mixing tank supplied to the pressurized levitation tank. Therefore, the temperature of the combustion exhaust gas supplied to the gas-liquid mixing tank is lowered, while the waste water supplied to the pressurized flotation tank is heated. Therefore, in the gas-liquid mixing tank, the solubility of the combustion exhaust gas in the waste water is increased, and in the pressurized flotation tank, the solubility of the combustion exhaust gas is low, and the sludge contained in the waste water can be efficiently levitated and separated. it can.

  Furthermore, according to the wastewater treatment system according to claim 3 of the present invention, the heat exchanger disposed in the heating circulation line is supplied to the heating fluid and gas-liquid mixing tank flowing through the heating circulation line. Therefore, the temperature of the combustion exhaust gas supplied to the gas-liquid mixing tank is lowered, while the waste water is heated in the pressurized levitation tank. Therefore, in the gas-liquid mixing tank, the solubility of the combustion exhaust gas in the waste water is increased, and in the pressurized flotation tank, the solubility of the combustion exhaust gas is low, and the sludge contained in the waste water can be efficiently levitated and separated. it can.

Hereinafter, an embodiment of a wastewater treatment system according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a simplified diagram schematically illustrating the wastewater treatment system according to the first embodiment.
In FIG. 1, the illustrated wastewater treatment system includes a gas-liquid mixing tank 2 for mixing gas with the wastewater, and a pressurized floating tank 4 for levitating and separating sludge contained in the wastewater. In this embodiment, a part of the waste water is supplied to the gas-liquid mixing tank 2, and the remainder is supplied to the pressurized levitation tank 4. That is, waste water to be treated is supplied through a waste water supply line 6, and a waste water supply pump 8 for supplying waste water to the waste water supply line 6 is provided. Further, the downstream side of the drainage supply flow path 6 is branched into a first supply line 10 and a second supply line 12, the first supply line 10 is connected to the gas-liquid mixing tank 2, and the second supply line 12 is pressurized and floated It is connected to the tank 4.

  Moreover, it is comprised so that combustion exhaust gas may be utilized as gas melt | dissolved in waste_water | drain. For example, when a cogeneration system is used as the power generation facility 14, combustion exhaust gas from an engine (for example, a gas engine) of the cogeneration system is used. In other words, the exhaust system of the power generation facility 14 (for example, a gas engine) is connected to the gas-liquid mixing tank 2 via the exhaust gas supply line 16, and the exhaust for supplying pressurized combustion exhaust gas to the exhaust gas supply line 16. A gas supply pump 18 (so-called pressurizing pump) is provided.

  In this embodiment, the heat exchanger 20 is disposed in the second supply line 12. As understood from FIG. 1, the combustion exhaust gas supplied through the exhaust gas supply line 16 flows through the heat exchanger 20, and the waste water supplied through the second supply line 12 and the exhaust gas supply line 16 flow through the heat exchanger 20. Heat exchange is performed with the combustion exhaust gas, the waste water heated by this heat exchange is supplied to the pressurized levitation tank 4, and the cooled combustion exhaust gas is supplied to the gas-liquid mixing tank 2.

  The gas-liquid mixing tank 2 and the pressurized levitation tank 4 are connected via a drainage supply line 22, and the wastewater in which the combustion exhaust gas is dissolved in the gas-liquid mixing tank 2 passes through the drainage supply line 22 to the pressurized levitation tank 4. Supplied. The drainage supply line 22 is provided with a pressure reducing valve 24 for depressurizing supplied wastewater.

  A discharge part 26 for discharging waste water is provided at the bottom of the pressurized levitation tank 4, and the waste water supplied through the waste water supply line 22 is discharged from the discharge part 26 into the pressurized levitation tank 4. In the upper part of the pressurized levitation tank 4, a scraping and collecting machine 28 for scraping and collecting the sludge that has floated and separated is disposed. The illustrated scraping and collecting machine 28 includes a belt 30 that is rotated in the direction of an arrow, and a scraping member 32 is provided on the surface of the belt 30 with an interval therebetween, and is floated and separated by the scraping member 32. Sludge is scraped to the predetermined side and collected. The scraping and collecting machine 28 may be of any appropriate form known per se.

  Next, processing by the above-described wastewater processing system will be described. The waste water to be treated is supplied through the waste water supply line 6 by the action of the waste water supply pump 8, and the supplied waste water is supplied to the gas-liquid mixing tank 2 through the first supply line 10 and through the second supply line 12. It is supplied to the pressure levitation tank 4. Further, combustion exhaust gas from the power generation facility 14 (for example, a gas engine of a cogeneration system) is supplied to the gas-liquid mixing tank 2 through the exhaust gas supply line 16 at a predetermined pressure by the action of the exhaust gas supply pump 18. At this time, in the heat exchanger 20, heat exchange is performed between the waste water flowing through the second supply line 12 and the combustion exhaust gas flowing through the exhaust gas supply line 16, and the combustion exhaust gas (for example, the temperature is lowered by the heat exchange (for example, , About 50 ° C.) is supplied to the gas-liquid mixing tank 2, and waste water (for example, about 40 ° C.) whose temperature has been raised by heat exchange is supplied to the pressure levitation tank 4.

  In the gas-liquid mixing tank 2, the combustion exhaust gas is mixed with the waste water, and the combustion exhaust gas containing carbon dioxide gas is dissolved in the waste water by mixing in this way. The combustion exhaust gas supplied to the gas-liquid mixing tank 2 is cooled by heat exchange, and therefore, the temperature of the waste water in the gas-liquid mixing tank 2 does not rise greatly, and thereby combustion in a predetermined pressure state The solubility of the exhaust gas can be increased, and more combustion exhaust gas can be dissolved without increasing the pressure state.

  The waste water in which the combustion exhaust gas is dissolved in the gas-liquid mixing tank 2 passes through the waste water supply line 22, is decompressed by the pressure reducing valve 24, and is supplied to the pressurized floating tank 4. Are released into the pressure levitation tank 4. Since the pressurized state is released when the wastewater is discharged from the discharge part 26, the combustion exhaust gas dissolved in the wastewater is discharged as bubbles, and the generated bubbles adhere to the sludge contained in the wastewater. Then this sludge is floated and separated. In this embodiment, since the pressure state in the gas-liquid mixing tank 2 can be kept low, when the pressure state is released in the pressurized levitation tank 4, the generated bubbles become fine, and thus the pressure of the sludge is increased. The flying characteristics can be improved. In addition, the wastewater supplied to the pressurized levitation tank 4 through the second supply line 12 is heated by heat exchange. Therefore, the wastewater in the pressurized levitation tank 4 is heated (for example, about 40 ° C.). As a result, the solubility of the combustion exhaust gas is reduced, and the dissolved combustion exhaust gas is released as bubbles, which can improve the pressurized levitation performance.

  In the pressurized levitation tank 4, the sludge that has floated upward due to the generated bubbles is scraped and collected by the scraping and collecting machine 28, and the collected floating sludge is dehydrated and dried as required, and added. The separated water discharged from the pressure levitation tank 4 is drained as required, and the wastewater is thus treated as required.

  In this embodiment, the combustion exhaust gas is dissolved in the waste water. However, the following advantages are obtained by dissolving the combustion exhaust gas. When the sludge is separated by pressurized flotation, a flocculant is added to the pressurized flotation tank 4 as necessary to promote solid-liquid separation. When this flocculant is used, the charge of the sludge particles in the charged waste water is neutralized, flocs are formed, solid-liquid separation is promoted, and sludge can be separated and recovered efficiently. A zeta potential is used as an indicator of this charge, but it is generally known that the pH is slightly lower than “7” in a state where the charge is neutralized, that is, in a state where the zeta potential is closest to zero. When treating alkaline wastewater by pressurized flotation, the carbon dioxide gas in the combustion exhaust gas is dissolved in the wastewater, so that the property of the wastewater changes from alkaline to neutral or slightly acidic. It is possible to reduce the amount of flocculant input for promoting liquid separation.

  Next, another embodiment of the wastewater treatment system according to the present invention will be described with reference to FIG. FIG. 2 is a simplified diagram schematically illustrating the wastewater treatment system according to the second embodiment. In this embodiment, components that are substantially the same as those in the embodiment shown in FIG. 1 are given the same reference numerals, and descriptions thereof are omitted.

  In FIG. 2, in the second embodiment, the waste water supply line 6 </ b> A is connected to the gas-liquid mixing tank 2, and all the waste water is supplied to the gas-liquid mixing tank 2. Further, a heating circulation line 42 is provided through the inside of the pressurized levitation tank 4, and a heat exchanger 44 is disposed in the heating circulation line 42. Etc. are circulated. As understood from FIG. 2, the combustion exhaust gas supplied through the exhaust gas supply line 16 flows through the heat exchanger 44, and flows through the fluid circulated through the heating circulation line 42 and the exhaust gas supply line 16. Heat exchange is performed with the combustion exhaust gas. The other configuration of this embodiment is substantially the same as that of the above-described embodiment.

  In this embodiment, the combustion exhaust gas whose temperature has been reduced by heat exchange in the heat exchanger 44 is supplied to the gas-liquid mixing tank 2 through the exhaust gas supply line 16, and in the gas-liquid mixing tank 2, the exhaust gas supply line 6A is used. Combustion exhaust gas containing carbon dioxide gas supplied through the exhaust gas supply line 16 is dissolved in the supplied waste water, and as described above, more combustion exhaust gas is dissolved without increasing the pressure state of the combustion exhaust gas. Can be made.

  Further, the fluid whose temperature has been raised by heat exchange in the heat exchanger 44 flows to the heat exchange portion 48 disposed in the pressurized floating tank 4 through the forward line 46 of the heating circulation line 42, and this heat exchange portion 48. The heat exchange is performed between the fluid and the wastewater in the pressurized levitation tank 4, and the wastewater in the pressurized levitation tank 4 is heated by this heat exchange. Therefore, as in the above-described embodiment, the waste water in the pressurized levitation tank 4 is heated, and thereby, more dissolved combustion exhaust gas is released as bubbles, and also in this embodiment, the pressurized levitation performance is improved. Can be made.

  As mentioned above, although embodiment of the sludge processing system according to this invention was described, this invention is not limited to this embodiment, A various deformation | transformation thru | or correction | amendment are possible without deviating from the scope of this invention.

  For example, in the above-described embodiment, the combustion exhaust gas discharged from the power generation facility is used as the gas dissolved in the waste water, but the combustion exhaust gas discharged from the combustion facility (for example, a boiler) is used. May be.

  In the second embodiment, if necessary, a second heat exchanger (not shown) is provided in the return line 50 of the heating circulation line 42, and the fluid flowing through the return line 50 in the second heat exchanger. May be exchanged with the wastewater supplied through the wastewater supply line 6A.

  Next, the calculation of the pressurizing power when combustion exhaust gas and air are used as the levitation medium is as follows. For example, the composition of the combustion exhaust gas and air is as shown in Table 1, the pressure of the pressurizing pump (in the above-described embodiment, the exhaust gas supply pump) is 0.3 MPa, and floating sludge (concentrated sludge by pressurized flotation) When the solid matter concentration is 3% and the ratio of the floating medium and waste water is 0.08, the pressurizing power of the pressurizing pump at this time is as shown in Table 2.

この試算結果から、浮上媒体として空気を用いて１００ｍ^３／ｈの排水を加圧浮上により処理する場合、加圧ポンプの加圧動力は３０ｋＷとなるが、浮上媒体として燃焼排気ガスを用いて同様の溶解度を得ようとすると、加圧ポンプの加圧動力は１０ｋＷとなり、浮上媒体として燃焼排気ガスを用いることにより、加圧ポンプ（排気ガス供給ポンプ）の加圧動力を空気を用いた場合に比して大幅に削減することが判る。このように加圧圧力を低く抑えることで、加圧浮上槽において発生する気泡の径が大きくなるのを防ぐことができ、これによって、加圧浮上能力の向上が期待できる。

From this calculation result, when 100 m ³ / h wastewater is treated by pressure levitation using air as the levitation medium, the pressurization power of the pressure pump is 30 kW, but the same applies using combustion exhaust gas as the levitation medium When the pressure of the pressurizing pump (exhaust gas supply pump) is using air, the pressurizing power of the pressurizing pump is 10 kW, and combustion exhaust gas is used as the levitation medium. It can be seen that this is a significant reduction. By keeping the pressurization pressure low in this way, it is possible to prevent the bubble diameter generated in the pressurization levitation tank from becoming large, and thus the pressurization and floating ability can be expected to be improved.

BRIEF DESCRIPTION OF THE DRAWINGS The simplified diagram which shows simply the wastewater treatment system of the first embodiment. The simplification figure which shows simply the wastewater treatment system of 2nd Embodiment.

Explanation of symbols

2 Gas-Liquid Mixing Tank 4 Pressurized Flotation Tank 6,6A Drainage Supply Line 10 First Supply Line 12 Second Supply Line 14 Power Generation Equipment 20,44 Heat Exchanger 22 Drainage Supply Line 28 Scraping and Recovery Machine 42 Heating Circulation Line

Claims (3)

A gas-liquid mixing tank that mixes the wastewater to be treated and gas under pressure and dissolves this gas in the wastewater, and an addition that floats sludge contained in the wastewater by bubbles generated when the pressure is released. A wastewater treatment system comprising a pressure levitation tank,
Combustion exhaust gas of combustion equipment or power generation equipment is used as gas mixed in the gas-liquid mixing tank, and this combustion exhaust gas is mixed with waste water in the gas-liquid mixing tank, and from the combustion equipment or power generation equipment. The wastewater treatment system, wherein the pressurized levitation tank is heated using heat of combustion exhaust gas supplied to the gas-liquid mixing tank.   A first supply line for supplying a part of the wastewater to the gas-liquid mixing tank and a second supply line for supplying the remainder of the wastewater to the pressurized flotation tank are provided, and the second supply line The heat exchanger which performs heat exchange between the waste_water | drain supplied to the said pressurization levitation tank, and the combustion exhaust gas supplied to the said gas-liquid mixing tank is provided. Wastewater treatment system.   The pressurized levitation tank is provided with a part of a warming circulation line through which a warming fluid is circulated, and the warming fluid flowing through the warming circulation line and the gas-liquid mixing tank in the warming circulation line The waste water treatment system according to claim 1, further comprising a heat exchanger for exchanging heat with the combustion exhaust gas supplied to the exhaust gas.

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