JP2010012386A - Wastewater treatment method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable carrying out flotation treatment without using a pressure apparatus and an air nozzle. <P>SOLUTION: A nozzle 22 is formed which has a passage 25 between a cylindrical outer peripheral electrode 5a and a center electrode 5b disposed in the axial position. The nozzle 22 is installed at the treating water inlet 4a of a flotation tank 4, and is connected to a sedimention separation-treated water collecting line 17 for introducing sedimention separation-treated water 3a after previously sedimenting and separating a washing wastewater 3 produced by washing a combuntion exhaust gas 2 of a boiler 1 with water in a sedimentation tank 12. A power source 6 is connected to the outer peripheral electrode 5a and the center electrode 5b. When the sedimention separation-treated water 3a is made to flow into the flotation tank 4 through the passage 25 of the nozzle 22, fast pulse discharge is caused between both electrodes 5a, 5b to which fast high-voltage pulse is applied from the power source 6 to generate fine air bubbles 7 in the sedimention separation-treated water 3a flowing into the flotation tank 4, and the fine air bubbles 7 float and separate suspended material in the sedimentation separation-treated water 3a stored in the flotation tank 4. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a wastewater treatment method and apparatus for removing suspended matter contained in wastewater, and is particularly suitable for treating wastewater containing tar and the like generated in various plants as a suspended matter. The present invention relates to a wastewater treatment method and apparatus.

  In plant chemical processes, tar-containing waste water (waste liquid) may be generated. Also, in coal-fired and oil-fired boilers and exhaust gas treatment plants, the combustion exhaust gas is washed with water using a spray tower or the like to remove tar contained in the combustion exhaust gas. The cleaning waste water after being used for cleaning the combustion exhaust gas in the spray tower or the like contains tar.

  The wastewater containing tar as described above needs to be subjected to a removal treatment of the tar contained in the wastewater until it reaches a level satisfying the emission standard. In the wastewater containing tar, the tar is usually in a suspended state.

  By the way, a pressurized flotation separation process is known as one of the solid-liquid separation techniques for removing suspended matters in water such as fats and oils floating in water and suspended organic substances.

  This is because the water to be treated is mixed with pressurized air dissolved water produced by dissolving under pressure the compressed air compressed by the compressor into the water previously pressurized by the pressure pump. Utilizing the fact that the dissolved air is vaporized into fine bubbles when the dissolved water is returned to normal pressure, the fine bubbles are generated in the treated water and suspended in the treated water. It is designed to allow the floating separation of objects.

  Moreover, by adding a flocculant that adsorbs the separation target in advance to the water to be treated, and then subjecting the water to be treated to which the flocculant has been added, the same pressure levitation separation treatment as described above, There is also known an agglomeration pressure flotation separation process in which a separation object is floated and separated together with an aggregating agent that adsorbs the separation object and agglomerated (see, for example, Patent Document 1).

  In addition, a simple type of floating separation treatment is generally known in which bubbles are blown directly into the water to be treated stored in the separation tank to float and separate the suspension in the water to be treated. Yes.

Japanese Patent Laid-Open No. 10-211499

However, in order to carry out the pressurized flotation separation process and the agglomerated pressure flotation separation process, it is necessary to produce pressurized air-dissolved water obtained by dissolving air in water under pressure. There is a need for a pressurized tank that is a container for producing dissolved air, a pressurized pump for supplying water to the pressurized tank, a compressor for compressing and supplying air to the pressurized container, and , Supply water to the water to be treated with water pressurized by the pressure pump and air compressed by a compressor to the pressurized container, and pressurized air dissolved water produced by the pressurized container As piping for mixing, pressure piping is also required. Therefore, there is a problem that the number of devices constituting the apparatus is increased, the structure of the apparatus is complicated, the size is increased, and the cost is increased. Further, the compressor is operated with electric power to pressurize the air, and this pressure is increased. The air is dissolved in water under pressure, and then returned to atmospheric pressure to vaporize the air dissolved in the pressurized water and generate minute bubbles. In addition to the problem that the efficiency of generating simple bubbles is low, there is also the problem that the controllability of the amount of minute bubbles generated in the water to be treated is low.

  On the other hand, if it is a floating separation process in which fine bubbles are directly blown into the water to be treated stored in the separation tank, a pressurized tank, a pressurized pump, a compressor, and a pressurized pipe are not necessary. In general, however, bubbles generated using a nozzle are larger than bubbles generated by the above-described pressurized flotation separation process, so that there is a problem that the separation efficiency is low. In the case of a substance having such adhesive properties, there is a concern that the air nozzle may be clogged with the suspension. Further, since the air nozzle is also worn, there is a problem that frequent replacement of the air nozzle is required.

  Therefore, the present invention can eliminate the need for a pressurized tank and other pressurizing equipment required for the above-described pressurized floating separation, and can be used in the water to be treated without using an air nozzle for blowing air into the water to be treated. By generating fine bubbles and floating and separating the suspension, treated water with a reduced content of the suspension can be obtained, and dispersed in the water to be treated to perform the floating separation. It is an object of the present invention to provide a wastewater treatment method and apparatus capable of improving the generation efficiency of microbubbles to be generated and improving the controllability of the generation amount of the microbubbles.

  In order to solve the above-mentioned problem, the present invention, corresponding to claim 1, performs high-speed pulse discharge on the water to be treated stored in the floating separation tank or the water to be treated stored in the floating separation tank. By performing, it is set as the waste-water treatment method which produces | generates a micro bubble in this to-be-processed water, and makes the suspension in the said to-be-processed water float and separate by this micro bubble.

  Further, in accordance with claim 2, one or a plurality of electrode pairs that are submerged in the water to be treated stored in the levitation separation tank are provided at a required portion of the levitation separation tank, and the electrode pair has a required high speed. A power supply for applying a high-voltage pulse is provided, and a high-speed pulse discharge is performed between the electrode pair to which a required high-speed high-voltage pulse is applied from the power supply to generate microbubbles in the water to be treated. The wastewater treatment device has a configuration that can be used.

  Furthermore, in the above configuration, the position where the electrode pair is provided is set to a position where the flow path of the water to be treated at the inlet of the water to be treated in the floating separation tank is sandwiched.

According to the present invention, the following excellent effects are exhibited.
(1) Microbubbles are generated in the treated water by performing high-speed pulse discharge on the treated water stored in the floating separation tank or the treated water stored in the floating separation tank. The wastewater treatment method that floats and separates the suspension in the water to be treated, and a set or a plurality of sets that are submerged in the water to be treated stored in the floatation separation tank at a required portion of the floatation separation tank. An electrode pair is provided, and a power source that applies a required high-speed high-voltage pulse to the electrode pair is provided, and high-speed pulse discharge is performed between the electrode pair that applies the required high-speed high-voltage pulse from the power source. Since the wastewater treatment apparatus has a configuration that can generate microbubbles in the water to be treated, the microbubbles generated in the water to be treated by high-speed pulse discharge between the electrode pairs Suspension in treated water It is possible to perform the flotation, by separating and removing floated scum, it is possible to recover the suspension than the flotation tank has been cleaned is separated off water.
(2) Therefore, it is possible to eliminate the need for a pressurized tank or other pressurizing equipment, which was required when performing the pressure levitation separation process, and clogging due to the attachment of suspension during the levitation separation process. And an air nozzle that has been a concern for wear can be eliminated.
(3) Moreover, when high-speed pulse discharge is performed between the electrode pairs, the high-speed pulse discharge acts on OH in moisture, and a small amount of OH radicals or ozone microbubbles are formed on the surface of each electrode. Since it can be generated between the liquid surfaces in contact with each other, even if the suspension in the water to be treated has adhesive properties such as tar, each electrode forming the electrode pair is The possibility of being affected by the adhesion of the suspension can be suppressed.
(4) Furthermore, since the microbubbles are generated by an electric discharge called high-speed pulse discharge generated by applying a high-speed high-voltage pulse to the electrode pair, the electric control of the high-speed high-voltage pulse is performed. Thus, since the high-speed pulse discharge for generating the microbubbles can be directly controlled, the controllability of the amount of microbubbles generated can be made excellent.
(5) By setting the position where the electrode pair is provided as a position sandwiching the flow path of the treated water at the treated water inlet in the floating separation tank, the total amount of treated water supplied to the floating separation tank Thus, the microbubbles can be reliably dispersed, and the separation efficiency of the suspension in the water to be treated can be increased.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

  1 and 2 show an embodiment of the wastewater treatment method and apparatus according to the present invention, such as tar generated when the combustion exhaust gas 2 of a coal-fired or oil-fired boiler 1 is washed with water in an exhaust gas treatment facility. This shows a case where the suspended washing waste water 3 is treated as treated water, and at least a required portion of the floating separation tank 4 which accepts the washing waste water 3 as the treated water and can store it for a required period of time. Provided with a configuration in which a pair of electrodes (electrode pairs) 5a and 5b are provided and a power source 6 for applying a high-speed high-voltage pulse is connected to each of the electrodes 5a and 5b, In the washing waste water 3 stored in the tank 4, micro bubbles 7 are generated due to the high-speed pulse discharge between the electrodes 5 a and 5 b, and the micro bubbles 7 contain the above-mentioned washing waste water 3. Floating suspensions such as tar So as to separate.

  More specifically, the exhaust gas treatment facility of the boiler 1 is for cleaning the heat exchange part 9a of the waste heat recovery boiler 9 and the combustion exhaust gas 2 on the exhaust gas line 8 that guides the combustion exhaust gas 2 from the boiler 1, for example. The spray tower 10 and the gas cooler 11 for lowering the temperature of the combustion exhaust gas 2 are sequentially provided.

  The spray tower 10 is configured to wash the combustion exhaust gas 2 with water by using, as washing water, sedimentation-treated water 3a recovered as a supernatant after sedimentation-separation processing in a sedimentation tank 12 described later.

  The settling tank 12 is provided on the downstream side of the washing drainage line 13 for taking out the washing drainage 3 after being used for washing the combustion exhaust gas 2 from the spray tower 10, and the washing drainage 3 is separated from the floating separation tank. Before being sent to 4, in the sedimentation tank 12, particles having a large specific gravity such as heavy tar out of the suspension contained in the washing waste water 3 can be settled and separated in advance. Therefore, the sedimentation tank 12 contains particles such as light tar that cannot be separated by the sedimentation process, although the particles having a higher specific gravity than the washing wastewater 3 are separated and removed from the sedimentation tank 12. The separation treatment water 3a and the sedimentation tank sludge (sedimentation separation treatment sludge) 14 containing heavy tar or the like can be recovered.

  One end which is an upstream end of the washing water circulation line 16 is connected to the treated water collection section 12a for collecting the sedimentation treated water 3a in the settling tank 12 through the circulation pump 15, and the washing water circulation The other end portion which becomes the downstream end portion of the line 16 is connected to the spray tower 10, and a part of the settling separation treated water 3 a recovered in the settling tank 12 is washed by the operation of the circulation pump 15. Through the water circulation line 16, the spray tower 10 is circulated and supplied so that it can be used as washing water for washing the combustion exhaust gas 2.

  The treated water recovery section 12a in the settling tank 12 is connected to the treated water inlet 4a of the floating separation tank 4 via a settling separated treated water collection line 17, and is supplied to the spray tower 10 as washing water. Excess settling separation treated water 3a other than circulating supply can be made to flow into the floating separation tank 4 from the treated water inlet 4a through the settling separated treated water recovery line 17.

  Further, a centrifuge 19 is provided on the downstream side of the sludge recovery line 18 for recovering the sedimentation tank sludge 14 from the sedimentation tank 12, and the sedimentation tank sludge 14 is centrifuged by the centrifugal separator 19. Thus, the solid content 20 containing the heavy tar or the like and the centrifugally treated water 3b which is a liquid part can be separated into solid and liquid, and among these, the centrifugally treated water 3b is a centrifugal equipped with a pump (not shown). Through the separated treated water recovery line 21, the separated separated treated water 3 a led to the floating separation tank 4 through the settling separated treated water collecting line 17 is mixed.

  On the other hand, the solid content 20 of the sedimentation tank sludge 14 including the heavy tar recovered from the centrifugal separator 19 is sent to the boiler 1 so that it can be incinerated.

  The floating separation tank 4 is configured such that the water inlet 4a to be treated is provided at a lower required position, for example, a lower position of a side wall. Further, as shown in FIGS. 2 (a) and 2 (b), a cylindrical outer periphery provided with a through-hole 23 having a required diameter at the center as one of the electrodes 5a and 5b for forming the electrode pair. Inside the through hole 23 of the electrode 5a, a cylindrical center electrode 5b as the other electrode having an outer diameter smaller than the inner diameter of the through hole 23 is arranged along the axial direction, A required portion of the center electrode 5b is attached in an insulated state to a corresponding portion of the outer peripheral electrode 5a via, for example, a fixing member 24 extending in the radial direction, and a cylindrical shape is provided between the outer peripheral electrode 5a and the central electrode 5b. A nozzle 22 having a liquid flow path 25 is formed, and the nozzle 22 is installed at the treated water inlet 4 a in the floating separation tank 4, and the settling separated treated water recovery line is connected to the nozzle 22. 17 downstream end There as a connection configuration. As a result, the total amount of the settling separation treated water 3a supplied from the settling separation treated water recovery line 17 to the floating separation tank 4 is between the electrodes 5a and 5b of the nozzle 22 provided at the treated water inlet 4a. After passing through the flow path 25, it flows into the floating separation tank 4.

  Further, a power source 6 for applying a high-speed high-voltage pulse is connected to the outer peripheral electrode 5a and the center electrode 5b of the nozzle 22. Thereby, in the state in which the sedimentation separation treated water 3a flows from the sedimentation separation treated water recovery line 17 into the floating separation tank 4 through the flow path 25 between both electrodes 5a and 5b of the nozzle 22, By applying a high-speed and high-voltage pulse from the power source 6 to the electrodes 5a and 5b of the nozzle 22, it passes through the flow path 25 between the electrodes 5a and 5b of the nozzle 22 and flows into the floating separation tank 4. High-speed pulse discharge can be performed on the sedimentation-treated water 3a. Therefore, with the shock wave accompanying the high-speed pulse discharge, fine bubbles are generated by vaporizing or thermally expanding the dissolved gas dissolved in water, and also by the evaporation of water by the high-speed pulse discharge. Is generated so that the microbubbles 7 having a diameter of about several tens of μm to several hundreds of μm can be present in the water of the settling separation treated water 3a flowing into the floating separation tank 4 (note that In FIGS. 1 and 2, for convenience of illustration, the size of the microbubbles 7 is shown large).

  Further, drain water 26 generated when the combustion exhaust gas 2 of the boiler 1 is cooled by the gas cooler 11 is guided to the floating separation tank 4 through a drain line 27 and stored in the floating separation tank 4. It can be mixed in the sedimentation-treated water 3a.

  Therefore, in the floating separation tank 4, when passing through the flow path 25 of the nozzle 22 into the stored sedimentation-treated water 3 a (including the centrifugally-treated water 3 b and the drain water 26), The sedimentation treated water 3a containing the microbubbles 7 generated by the high-speed pulse discharge is sequentially introduced at a required flow rate from the treated water inlet 4a, whereby the treated water in the floating separation tank 4 is Since the fine bubbles 7 can be dispersed, the fine bubbles 7 dispersed in the flotation separation tank 4 can be used for the flotation separation treatment of the suspended matter such as the light tar contained in the settling separation treated water 3a. So that you can do it.

  A scum recovery device (not shown) is provided at the upper end of the levitation separation tank 4 for recovering the suspended scum (floating matter) 28 containing the modified tar that has been solid-liquid separated and floated by the levitation separation process. The scum 28 collected by the scum collecting device is sent to the boiler 1 so that it can be incinerated.

  Treated water provided with a pump 30 on the downstream side of the treated water take-out port for taking out the treated water 3c that has been purified after the suspension containing light tar is separated and removed by the floating separation treatment in the floating separation tank 4. An evaporator 31 is connected via a line 29.

  The evaporator 31 includes the heat transfer pipe 32 for circulating the high-temperature steam 33 generated in the waste heat recovery boiler 9 that recovers waste heat from the combustion exhaust gas 2 of the boiler 1. 4, the treated water 3 c guided to the evaporator 31 through the treated water line 29 is indirectly heated through the wall of the heat transfer pipe 32 using the high-temperature steam 33 generated in the waste heat recovery boiler 9 as a heat source, and the treated water 3 c By evaporating the moisture and other evaporation components 34 therein, the non-evaporated components can be condensed and recovered as a concentrate 35. Note that the concentrated liquid 35 recovered from the evaporator 31 may be supplied to the boiler 1 for combustion treatment.

  On the other hand, moisture generated in the evaporator 31 and other evaporated components 34 are led to the exhaust gas line 8 between the boiler 1 and the spray tower 10 through the evaporated component line 36 and circulate through the exhaust gas line 8 of the portion. By mixing in the combustion exhaust gas 2, moisture is recovered by the spray tower 10 provided on the exhaust gas line 8 or the gas cooler 11 and can be recycled.

  37 is a steam supply line for supplying the high-temperature steam 33 from the waste heat recovery boiler 9 to the heat transfer pipe 32 of the evaporator 31, and 38 is a temperature drop after being supplied to the heat source for heating the treated water 3 c in the evaporator 31. This is a return line with a pump 39 for returning the steam and condensed water 33a to the waste heat recovery boiler 9.

  When the wastewater treatment apparatus having the above structure is used to treat the washing wastewater 3 in which tar generated by washing the combustion exhaust gas 2 of the boiler 1 with the spray tower 10 is suspended, When the waste water 3 is first supplied to the settling tank 12 and subjected to settling and separation, particles having a large specific gravity such as heavy tar are separated and removed as settling tank sludge 14.

  Next, the sedimentation-treated water 3a in which a suspension such as light tar recovered from the sedimentation tank 12 after the sedimentation-separation process is suspended is centrifuged from the water contained in the sedimentation tank sludge 14. The flow between the outer peripheral electrode 5a and the center electrode 5b of the nozzle 22 provided at the treated water inlet 4a to the floating separation tank 4 in a state where the centrifugally treated water 3b obtained by collecting with the machine 19 is mixed. When a high-speed high-voltage pulse is applied to the electrodes 5a and 5b from the power source 6 to generate a high-speed pulse discharge between the electrodes 5a and 5b when supplying through the path 25, the flow path 25 of the nozzle 22 is generated. Since the fine bubbles 7 generated by the high-speed pulse discharge are surely contained in the water of the sedimentation-treated water 3a flowing through the floating separation tank 4 and flowing into the floating separation tank 4, the floating separation tank 4 The stored sedimentation process It comes to be dispersed the microbubbles on the total amount of water 3a. Accordingly, in the water of the sedimentation-treated water 3a, the microbubbles 7 adhere to the suspension of light tar or the like suspended in the sedimentation-treated water 3a, or in the case of tar, the inside By adhering the microbubbles 7 so as to enter, the specific gravity of the suspension including the microbubbles 7 is reduced, so that the suspension is floated and separated.

  Therefore, the suspended scum 28 is recovered and separated and removed, so that the suspended water suspended in the settling separation treated water 3a is separated and removed from the floating separation tank 4 and purified. 3c can be recovered.

  Further, in the above embodiment, the recovered treated water 3c is supplied to the evaporator 31 and distilled using the high-temperature steam 33 generated in the waste heat recovery boiler 9 attached to the boiler 1 as a heat source. Thus, the concentrated liquid 35 formed by concentrating the non-evaporated component from the moisture and other evaporated components 34 is separated.

  Thus, according to the waste water treatment method and apparatus of the present invention, the light waste water 3 suspended in the sedimentation-treated water 3a formed by the sedimentation-separation process in advance is generated by the water washing of the combustion exhaust gas 2 of the boiler 1. When suspension of suspension such as tar is floated and separated, the suspension is floated and separated by causing high-speed pulse discharge to occur between the electrode pair consisting of the outer peripheral electrode 5a and the center electrode 5b provided in the nozzle 22. It is possible to generate the microbubbles 7 that are necessary for the operation.

  Therefore, it is possible to eliminate the need for a pressurized tank and other pressurizing equipment that are required when performing the conventional pressurized levitation separation process. Further, it is possible to eliminate the need for an air nozzle that has been concerned about clogging or wear due to adhesion of suspensions during the conventional floating separation process.

  In addition, when high-speed pulse discharge is performed between the electrodes 5a and 5b, the high-speed pulse discharge acts on OH in moisture, and a small amount of OH radicals or ozone microbubbles are generated on the surfaces of the electrodes 5a and 5b. And the liquid surface in contact therewith, the electrodes 5a and 5b are affected by the adhesion of the suspension even if the suspension has adhesive properties such as tar. The fear can be suppressed.

  Further, since the microbubbles 7 are generated by an electric discharge called high-speed pulse discharge generated by applying a high-speed high-voltage pulse from the power source 6 to the electrodes 5a and 5b, the electrodes 5a from the power source 6 are generated. , 5b can be controlled directly by the high-speed pulse discharge between the electrodes 5a, 5b for generating the microbubbles 7 by controlling the high-speed high-voltage pulse applied to the microbubbles 7. It can be.

  The generation of the microbubbles 7 by the high-speed pulse discharge between the electrodes 5a and 5b is mainly due to shock waves, thermal expansion, and water evaporation. Therefore, there is no possibility that a large amount of hydrogen or oxygen is generated.

  In addition, this invention is not limited only to the said embodiment, The nozzle 22 provided in the to-be-processed water inlet 4a of the floating separation tank 4 is equipped with the electrode 5b and 5a in the center part and its outer periphery. As shown, the electrode pair is provided so as to sandwich the flow path of the water to be treated flowing into the floating separation tank 4, and the electrode is provided for the liquid to be treated flowing through the flow path and flowing into the floating separation tank 4. As long as high-speed pulse discharge can be performed between the pair, for example, by providing a pair of parallel plate electrodes and forming a flat channel between the electrodes, the channel shape and the electrode shape are appropriately determined. It may be changed.

  Further, a pair of electrode pairs for performing the high-speed pulse discharge or a levitating separation in the vicinity of the water inlet 4a to be treated inside the levitating separation tank 4 or a lower required position inside the levitating separation tank 4 A plurality of sets may be provided according to the size of the tank 4.

  The wastewater treatment method and apparatus of the present invention can be applied to the case where any floating wastewater is treated as floating water in the floatation separation tank 4 as long as the wastewater is desired to be floated and separated. Of course, various modifications can be made without departing from the scope of the present invention.

It is a schematic diagram showing one embodiment of a wastewater treatment method and apparatus of the present invention. FIG. 2 is an enlarged view of the treated water inlet portion of the floating separation tank of the apparatus of FIG. 1, (A) is a cut side view, and (B) is a view taken in the direction of arrows A-A in (A).

Explanation of symbols

3 Washing wastewater (treated water)
3a Sedimentation separation treated water (treated water)
4 Floating separation tank 4a Water inlet 5a Peripheral electrode (electrode)
5b Center electrode (electrode)
6 Power supply 7 Microbubbles 25 Flow path

Claims (3)

  Microbubbles are generated in the treated water by performing high-speed pulse discharge on the treated water stored in the floating separation tank or the treated water stored in the floating separation tank. A method for treating waste water, characterized in that a suspension in treated water is floated and separated.   Provided with one or more electrode pairs submerged in the water to be treated stored in the levitation separation tank at a required location of the levitation separation tank, and provided with a power source for applying a required high-speed high-voltage pulse to the electrode pair And having a configuration in which microbubbles can be generated in the water to be treated by causing high-speed pulse discharge to be performed between the electrode pairs to which a required high-speed high-voltage pulse is applied from the power source. Characterized wastewater treatment equipment.   The wastewater treatment apparatus according to claim 2, wherein a position where the electrode pair is provided is a position sandwiching a flow path of the treated water at the treated water inlet in the floating separation tank.

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