JP5702560B2 - Waste water treatment method and waste water treatment equipment - Google Patents

Description

  The present invention relates to a wastewater treatment method and wastewater treatment equipment including at least a water-based paint.

  In recent years, from the viewpoint of reducing volatile organic compounds (VOC), there is an increasing trend of switching from a solvent paint using a volatile organic solvent as a solvent to an aqueous paint using water as a solvent. Water-based paints are generally water, resin (which is the main component of the coating film and becomes the coating film), organic solvents (those that dissolve and disperse the resin), pigments (those that color), surfactants, antifoaming agents, and freezing. Consists of an inhibitor, sagging inhibitor, rust inhibitor and the like. The organic solvent is generally composed of alcohols, esters, ketones, ether alcohols, aliphatic hydrocarbons, aromatic hydrocarbons, and the like. Of these, generally, alcohols, esters, ketones, and ether alcohols are hydrophilic, and aliphatic hydrocarbons and aromatic hydrocarbons are hydrophobic.

  In the painting process using paint, various paints are applied to the object by spray painting or the like. However, the coating efficiency of the water-based paint sprayed on the object to be coated is not always perfect. For example, since the painting efficiency on the body of an automobile is about 60%, the remaining 40% is not used effectively. Therefore, in order to collect excess paint that has not been painted in a painting booth or the like, it is usually collected and removed with washing water. The washing water is recycled.

Since water-based paints are not easily separated from water due to their properties, they are accumulated in a state of being dissolved in flush water used for circulation, resulting in the following problems.
(A) Wastewater overflow from the aquarium due to foaming, environmental deterioration (b) BOD (Biochemical Oxygen Demand) component decays and a decaying odor occurs (c) Paint component to aquarium, piping, etc. (D) High concentration COD (Chemical Oxygen Demand) and high concentration BOD make it difficult to discharge.

  In order to solve these problems, chemical treatment and treatment by evaporation to dryness are conventionally performed (see, for example, Patent Documents 1 and 2).

Japanese Patent Laid-Open No. 11-672 JP 2009-220047 A

  By the way, the present inventors examined a method for separating each of the waste water containing water-based paint by heating the waste water to evaporate the low boiling point components of the waste water and concentrating the high boiling point components. . In this treatment method, water containing evaporated low boiling point components is recovered and used again for wastewater treatment to prevent adhesion / sedimentation, foaming, decay, and the like of paint components on pipes and the like. I found out that I can do it. However, if the wastewater treatment is continuously performed, the paint scale adheres to the indirect heating part for heating the wastewater, and the heat transfer efficiency of the indirect heating part is reduced. There is a risk that it cannot be done.

  Then, the objective of this invention is providing the washing | cleaning method of the evaporative concentrator which can suppress the fall of the heat transfer efficiency of an indirect heating part, the washing | cleaning apparatus of an evaporative concentrator, the waste water treatment method, and a waste water treatment apparatus.

The present invention is a wastewater treatment method for wastewater containing at least a water-based paint, wherein an evaporative concentrator provided with an indirect heating unit for heating the wastewater discharged from a storage tank in which the wastewater is stored is used to reduce the amount of wastewater. Evaporating and concentrating the water containing the boiling point component to concentrate the high boiling point component and recovering at least a part of the water containing the evaporated low boiling point component and including the low boiling point component after the evaporating and concentrating step A cleaning step of cleaning the indirect heating portion with a part of water, and a return step of returning the remaining portion of the water containing the recovered low-boiling components to the storage tank.

In the wastewater treatment method, an organic solvent that dissolves the paint scale is preferably added to the water containing the recovered low-boiling component.

Moreover, in the said waste water treatment method, it is preferable to make the temperature of the water containing the said low boiling point component at the time of wash | cleaning the said indirect heating part into the range of 60-100 degreeC.

Further, the present invention is a wastewater treatment apparatus for wastewater containing at least an aqueous paint, comprising a storage tank for storing the wastewater, and an indirect heating unit for heating the wastewater discharged from the storage tank, Evaporating and concentrating means for evaporating the water containing the low-boiling component and concentrating the high-boiling component, collecting at least a part of the water containing the evaporated low-boiling component, and part of the water containing the low-boiling component Is supplied to the indirect heating unit, and cleaning means for cleaning the indirect heating unit, and return means for returning the remaining water containing the recovered low-boiling components to the storage tank.

Moreover, the waste water treatment apparatus preferably includes an adding means for adding an organic solvent that dissolves the paint scale to the water containing the recovered low-boiling component.

Moreover, it is preferable that the said waste water treatment apparatus is equipped with the auxiliary | assistant heat source which makes the temperature of the water containing the said low boiling point component at the time of washing | cleaning the said indirect heating part the range of 60-100 degreeC.

  ADVANTAGE OF THE INVENTION According to this invention, the paint scale adhering to the indirect heating part installed in an evaporative concentrator can be washed away, and the heat transfer efficiency of the reduced indirect heating part can be recovered.

It is a schematic diagram which shows an example of a structure of the waste water treatment equipment which concerns on embodiment of this invention. It is a schematic diagram which shows an example of a structure of the waste water treatment equipment which concerns on other embodiment of this invention.

  Embodiments of the present invention will be described below. This embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment.

  Drawing 1 is a mimetic diagram showing an example of the composition of the waste water treatment equipment concerning the embodiment of the present invention. A wastewater treatment apparatus 1 shown in FIG. 1 includes an aqueous paint drainage tank 10, an evaporative concentrator 12 (heating separation means), a concentrated water tank 14, a compressor 16, an evaporating water supply line 32 (heat recovery utilization means), and a heat exchanger 18. , Washing water tank 19, drainage pump 20, concentrated water pump 22, vacuum pump 24, drainage inflow line 26, concentrated water circulation line 28, concentrated water discharge line 30, evaporated water return line 34 (return means), wash water introduction line 35, An exhaust line 36, an auxiliary steam line 37, and an organic solvent addition line 39 are provided.

  The evaporation concentrator 12 used in the present embodiment is particularly limited as long as it has a structure capable of concentrating the high boiling point component by evaporating water containing the low boiling point component in the waste water by indirect heating. Although not intended, indirect heat exchange is performed indirectly between the evaporation section, where the evaporation takes place, and a heat source such as a heat transfer plate or heat transfer tube, between the heat source and the object to be heated. A heating unit. The evaporation concentrator 12 shown in FIG. 1 includes an evaporator 12a (evaporating unit), an indirect heating unit 38, an auxiliary steam line 37, and an auxiliary steam supply source. The indirect heating unit 38 installed in the evaporator 12a of the evaporation concentrator 12 is composed of a large number of heat transfer tubes, as described in, for example, JP-A-2004-237136 and JP-A-2008-188514, Each of the heat transfer tubes is provided so as to be horizontally oriented. In addition, an inlet header is provided at one end of each heat transfer tube, and an outlet header is provided at the other end, and the liquid to be heated outside the heat transfer tube is heated by heating steam passing through the inside of the heat transfer tube. Further, the evaporation concentrator 12 of the present embodiment is not necessarily limited to the above. For example, as described in JP 2009-090228 A, an evaporator and heat installed outside the evaporator You may provide the indirect heating part which is an exchanger. This heat exchanger has a steam inlet, a condensed water outlet, and a large number of horizontal and horizontal heat transfer tubes. And while the to-be-heated liquid passes the inside of a heat exchanger tube, the steam introduce | transduced from the steam inlet heats a to-be-heated liquid from the exterior of a heat exchanger tube. Moreover, as described in JP-A-5-84401, the indirect heating unit may have a hollow structure constituted by a hollow plate-like heating element or the like instead of the heat transfer tube. The shape of the indirect heating portion having such a hollow structure is not particularly limited as long as heat exchange is possible between the inside and the outside of the hollow structure.

  Here, the low boiling point component in the present embodiment is a component that evaporates with water under the pressure and temperature conditions for evaporation, and the high boiling point component does not evaporate with water under the pressure and temperature conditions for evaporation. Ingredients. For example, ethylene glycol monobutyl ether (commonly called butyl cellosolve), which is an aqueous coating solvent having a boiling point of 171 to 172 ° C. at atmospheric pressure, is a low-boiling component because it evaporates with water at 90 ° C. and 0.07 MPa.

  In the water-based paint drain tank 10, waste water containing at least the water-based paint is stored. One end of a drainage inflow line 26 is connected to the water-based paint drainage tank 10, and the other end is connected to the evaporator 12 a via a drainage pump 20 and a heat exchanger 18. One end of the concentrated water circulation line 28 is connected to the lower side of the evaporator 12 a, and the other end is connected to the upper side of the evaporator 12 a through the concentrated water pump 22. Further, one end of a concentrated water discharge line 30 is connected to the concentrated water circulation line 28, and the other end is connected to the concentrated water tank 14. Moreover, one end of the evaporating water supply line 32 is connected above the evaporator 12a, and the other end is connected to the indirect heating part 38 (inlet side: inlet header, for example) via the compressor 16. Further, one end of the evaporative water return line 34 is connected to an indirect heating unit 38 (exit side: for example, an outlet header), and the other end is connected to the washing water tank 19 or the aqueous paint drain tank 10 via the heat exchanger 18. . An organic solvent addition line 39 is connected to the washing water tank 19. One end of the cleaning water introduction line 35 is connected to the cleaning water tank 19, and the other end is connected to the drainage inflow line 26. Further, one end of the exhaust line 36 is connected to the evaporated water return line 34 between the heat exchanger 18 and the evaporator 12 a, and the other end is opened to the atmosphere via the vacuum pump 24. One end of the auxiliary steam line 37 is connected to the evaporating water supply line 32, and the other end is connected to an auxiliary steam supply source (not shown).

  Next, the operation of the waste water treatment apparatus 1 according to this embodiment will be described.

  The waste water containing the aqueous paint is stored in the aqueous paint drain tank 10. Water-based paints are generally water, resin (which is the main component of the coating film and becomes the coating film), organic solvents (those that dissolve and disperse the resin), pigments (those that color), surfactants, antifoaming agents, and freezing. Consists of an inhibitor, sagging inhibitor, rust inhibitor and the like. The organic solvent is generally composed of alcohols, esters, ketones, ether alcohols, aliphatic hydrocarbons, aromatic hydrocarbons, and the like. An organic solvent etc. are mainly mentioned as a low boiling-point component of an aqueous coating material. Of these, generally, alcohols, esters, ketones, and ether alcohols are hydrophilic, and aliphatic hydrocarbons and aromatic hydrocarbons are hydrophobic. In addition, examples of the high-boiling component of the water-based paint include mainly resins, pigments, surfactants and antifoaming agents. In addition, the waste water containing the water-based paint may contain a solvent paint, a cleaning liquid, and the like.

  Wastewater containing the aqueous paint stored in the aqueous paint drainage tank 10 (hereinafter sometimes simply referred to as “drainage”) is introduced into the heat exchanger 18 through the drainage inflow line 26 by the drainage pump 20. Then, the heat exchanger 18 exchanges heat between the waste water and steam discharged from the evaporator 12a (evaporated water containing low-boiling components). Here, since the evaporated water has a higher temperature than the waste water, the waste water is preheated. The preheated waste water is supplied to the evaporator 12 a through the waste water inflow line 26. As in the present embodiment, the waste water introduced into the evaporator 12a of the evaporator concentrator 12 can be preheated, and the waste water before being introduced into the evaporator 12a of the evaporator concentrator 12 and the evaporated water return line. It is preferable to install a heat exchanger 18 for exchanging heat with the evaporated water before being returned to the waste water by 34.

  The wastewater supplied to the evaporator 12a of the evaporator concentrator 12 is indirectly heated by the heat from the indirect heating unit 38 installed in the evaporator 12a of the evaporator concentrator 12. In the initial stage of operation, steam generated from the auxiliary steam supply source is supplied from the auxiliary steam line 37 to the indirect heating unit 38 (for example, inside each heat transfer tube), whereby the indirect heating unit 38 is heated and heated. The waste water is indirectly heated by the heat from the section 38. Here, since the inside of the evaporator 12a is depressurized by the vacuum pump 24, the water in the waste water and the low boiling point component (hereinafter may be referred to as water containing a low boiling point component) are at a saturated vapor pressure. Evaporates at an equal and relatively low temperature. On the other hand, the high boiling point component in the waste water is concentrated and stored as concentrated water containing the high boiling point component at the bottom. Concentrated water containing a high-boiling component is discharged from the evaporator 12a by the concentrated water pump 22, passes through the concentrated water circulation line 28, and is indirectly heated from the upper part of the evaporator 12a to the indirect heating unit 38 (for example, each heat transfer tube). Sprayed on the outer surface). Thereby, since the sprayed waste water (including concentrated water) becomes high temperature by the steam inside the indirect heating unit 38, low boiling point components in the waste water can be effectively evaporated on the surface of the indirect heating unit 38.

  The water (steam) containing the low boiling point component evaporated by the evaporation concentrator 12 is supplied to the compressor 16 through the evaporation water supply line 32. The compressor 16 and the evaporated water supply line 32 function as heat recovery and utilization means for supplying the thermal energy of the evaporated water to an indirect heating unit 38 (for example, inside each heat transfer tube) installed in the evaporator 12a. is there. Specifically, the water (steam) containing the evaporated low boiling point component is compressed and heated by the compressor 16, passes through the evaporated water supply line 32, and is supplied to the indirect heating unit 38 (for example, each heat transfer tube). Thus, the indirect heating unit 38 is heated, and the wastewater stored in the bottom of the evaporator 12a is indirectly heated by the heat from the heated indirect heating unit 38. The supply of auxiliary steam may be stopped if the drainage can be sufficiently heated by the evaporated water compressed and heated by the compressor 16.

  Thus, by recovering and utilizing the thermal energy of the evaporated water, the energy can be effectively used, and the energy efficiency required for the wastewater treatment can be improved. In this embodiment, if it has a function which supplies at least one part of the thermal energy of the evaporated water to the indirect heating part 38 installed in the evaporator 12a, it will not necessarily be the compressor 16 and the evaporative water supply line 32. For example, an ejector or the like may be used instead of the compressor 16. The configuration of the compressor 16 used in the present embodiment is not particularly limited as long as it has the above function.

  It should be noted that the heat recovery and utilization means is a system for heating wastewater by effectively utilizing energy, and thus is not necessarily installed. In the case where no heat recovery and utilization means is installed, the evaporated water (returned from water vapor to the liquid) may be supplied directly to the heat exchanger 18.

  Next, the water (gas to liquid) containing the low boiling point component that has passed through the indirect heating unit 38 is introduced into the heat exchanger 18 from the evaporated water return line 34. The water (liquid) containing the low boiling point component is heat-exchanged with the waste water containing the water-based paint by the heat exchanger 18. Here, since the wastewater containing the water-based paint is at a lower temperature than the water containing the low boiling point component, the water containing the low boiling point component is cooled. The cooled water containing the low boiling point component passes through the evaporating water return line 34 and is returned to the water-based paint drainage tank 10 through the washing water tank 19. Among the low-boiling components returned to the water-based paint drainage tank 10, there are those that have biological treatment inhibitory properties and contain components that dissolve the water-based paint. Is returned (supplied), so that bad odor due to decay, paint adhesion to the wall surface of the water-based paint drainage tank 10, each line, and the like can be suppressed. In this embodiment, the return means for collecting the evaporated water and returning it to the waste water is exemplified by the configuration of the evaporative water return line 34 alone, but is not limited to this. It is good also as a structure installed in the return line 34, etc. Moreover, in this embodiment, although the evaporative water return line 34 has taken the structure connected to the water-based paint drainage tank 10 as an example, the structure etc. which were connected to the waste_water | drain inflow line 26 may be sufficient.

  A part of the concentrated water containing the high boiling point component passing through the concentrated water circulation line 28 passes through the concentrated water discharge line 30 and is stored in the concentrated water tank 14. The concentrated water (including the high boiling point component) stored in the concentrated water tank 14 is preferably evaporated to dryness by an evaporating and drying apparatus such as a drier in that the apparatus can be a non-drainage system.

  In this way, by collecting the water containing evaporated low-boiling components and using it again for wastewater treatment, it is possible to improve the energy efficiency required for the treatment, and the water tank by the adhesion, sedimentation and foaming of the paint components to the piping etc. The wastewater overflow from the water, the prevention of environmental deterioration, the increase in the salt concentration in the water due to the use of chemicals can be suppressed, and a low-cost treatment can be performed.

  In the present embodiment, the inside of the evaporator 12a is depressurized by the vacuum pump 24. However, the evaporator 12a only needs to be able to heat the waste water and evaporate the water containing the low-boiling components. It is not necessary to depressurize the interior of the interior of the interior by the vacuum pump 24. Furthermore, in this embodiment, it is preferable that the concentrated water is circulated by the concentrated water pump 22 in terms of efficiently evaporating the low boiling point component, but it is not always necessary to circulate the concentrated water.

  The heating temperature of the waste water inside the evaporator 12a is appropriately set according to the types of low boiling point components, high boiling point components, etc. in the waste water, but it is 60 to 100 ° C. in that it suppresses foaming that occurs during heating of the waste water. The range of 80-95 degreeC is more preferable.

  In the present embodiment, at the initial operation of the wastewater treatment apparatus 1 or when the capacity of the compressor 16 is low, the heat recovery and utilization by the compressor 16 is not sufficiently performed, and the wastewater is not sufficiently heated. Separation of the boiling point component and the high boiling point component may not be performed efficiently. Therefore, in the initial operation of the wastewater treatment apparatus 1 or when the capacity of the compressor 16 is low, the auxiliary steam generated by the auxiliary steam supply source is supplied from the auxiliary steam line 37 to the indirect heating unit 38 in the evaporator 12a, It is preferable to use for heating of waste water. For example, a small boiler or the like may be used as an auxiliary steam supply source, and the auxiliary steam generated in the small boiler may be used. If there is excess waste steam in the factory, the equipment that generates the waste steam is supported. As the steam supply source, steam generated in the facility may be used.

  The above is the process for separating the low-boiling component and the high-boiling component in the waste water in the present embodiment. If such a process is continued, the paint scale adheres to the indirect heating unit 38 in the evaporator 12a. For this reason, the heat transfer efficiency of the indirect heating unit 38 decreases, and the waste water cannot be heated sufficiently. As a result, the processing efficiency for separating the low-boiling component and the high-boiling component is reduced. Therefore, it is necessary to clean the paint scale attached to the indirect heating unit 38. The cleaning method (cleaning step) will be described below.

  First, all the concentrated water is discharged from the concentrated water discharge line 30 by the concentrated water pump 22. Next, the valve 26a is closed, the waste water containing the aqueous paint is kept from flowing out of the aqueous paint drain tank 10 into the drain inflow line 26, the valve 35a is opened, and the low boiling point component stored in the washing water tank 19 is stored. The water containing water is introduced into the evaporator 12a by the drainage pump 20 through the drainage inflow line 26 from the washing water introduction line 35. And the water containing the low boiling-point component introduce | transduced into the evaporator 12a is sent to the concentrated water circulation line 28 with the concentrated water pump 22, and is supplied to the indirect heating part 38 in the evaporator 12a from the upper part of the evaporator 12a. This is repeated, and the indirect heating unit 38 is washed with water containing a low boiling point component. As described above, since the water containing the low-boiling component contains the component that dissolves the aqueous paint, the indirect heating unit 38 is washed by washing the indirect heating unit 38 with water containing the low-boiling component. The paint scale adhering to can be dissolved. Thus, after washing for a predetermined time, the washing waste water is discharged out of the waste water treatment apparatus 1 through the concentrated water discharge line 30 and the concentrated water tank 14.

  In this embodiment, the evaporative concentrator cleaning device for cleaning the indirect heating unit 38 with water containing a low boiling point component includes the evaporating water return line 34, the cleaning water tank 19, the cleaning water introduction line 35, the drainage inflow line 26, the drainage. The pump 20, the concentrated water pump 22, and the concentrated water circulation line 28 are configured. However, the evaporative concentrator cleaning device of the present embodiment recovers the water containing the evaporated low boiling point component, supplies the water containing the low boiling point component to the indirect heating unit 38, and cleans the indirect heating unit 38. If it is the structure which can do, it will not restrict | limit to the said structure. For example, since the drainage inflow line 26, the drainage pump 20, the concentrated water pump 22, and the concentrated water circulation line 28 among the configurations of the evaporative concentration machine cleaning apparatus are originally used in the process of evaporating and concentrating wastewater, As another example of the evaporation concentrator cleaning device, a line and a pump for supplying water containing a low boiling point component in the cleaning water tank 19 to the evaporator 12a (corresponding to the drainage inflow line 26 and the drainage pump 20), A line and a pump (corresponding to the concentrated water pump 22 and the concentrated water circulation line 28) for circulating and washing the water containing the low boiling point component supplied to the evaporator 12a may be separately provided. In addition, although the installation of the line and pump for circulating washing (equivalent to the concentrated water pump 22 and the concentrated water circulation line 28 etc.) is preferable at the point which wash | cleans a paint scale effectively, it is not necessarily required. As another example of the evaporative concentrator cleaning device, a high pressure injection nozzle is installed in the evaporator 12a at a position where it can be injected to the indirect heating unit 38, and the drainage inflow line 26 or concentrated water circulation is provided via the high pressure injection nozzle. The structure which sprays the water containing the low boiling point component supplied to the evaporator 12a from the line 28 to the indirect heating part 38 may be sufficient.

  Further, in the present embodiment, it is preferable to additionally add an organic solvent that dissolves the paint scale into the cleaning water tank 19 from the organic solvent addition line 39 (addition means). This is applied when the paint scale is firmly attached to the indirect heating unit 38 and the low boiling point component concentration in the washing water tank 19 is not sufficient. Since the organic solvent contained in the low-boiling component of the water-based paint can dissolve the paint scale, the concentration of the component capable of dissolving the paint scale can be increased in the washing water tank 19. is there. The organic solvent that dissolves the paint scale is preferably a highly polar solvent, for example. Specific examples include alcohol solvents such as methanol, ethanol, propanol, isopropanol, and butanol, butyl cellosolve, and the like. Also, a proton solvent such as N-methylpyrrolidone may be used.

  Moreover, in this embodiment, the temperature of the water containing the low boiling point component at the time of washing | cleaning the indirect heating part 38 is set to the range of 60 to 100 degreeC at the point which improves the washing | cleaning effect of the paint scale adhering to the indirect heating part 38. It is preferable to do. Specifically, for example, auxiliary steam (auxiliary heat source) by a small boiler or waste steam (auxiliary heat source) in a factory is supplied into the evaporator 12a from the auxiliary steam line 37, and water or evaporator containing a low boiling point component is supplied. This is done by heating the inside of 12a. In addition, for example, as described later, the water containing the low boiling point component when the indirect heating unit 38 is cleaned is evaporated by installing the cleaning water tank 19 via the evaporated water return line 34 connected to the evaporator 12a. Since the remaining heat when evaporated by the can 12a can be used, the auxiliary heat source is not necessarily required.

  As described above, since the paint scale adhering to the indirect heating unit 38 can be washed away by washing the indirect heating unit 38 with water containing a low-boiling component, the reduction in the heat transfer efficiency of the indirect heating unit 38 is suppressed. It is possible to efficiently separate the low-boiling component and the high-boiling component by heating the waste water thereafter.

  FIG. 2 is a schematic diagram illustrating an example of a configuration of a wastewater treatment apparatus according to another embodiment of the present invention. In the waste water treatment apparatus 2 shown in FIG. 2, the same components as those in the waste water treatment apparatus 1 shown in FIG. The waste water treatment apparatus 2 shown in FIG. 2 includes an evaporating water discharge line 40.

  In the waste water treatment apparatus 2 shown in FIG. 2, the washing water tank 19 is connected to the evaporator 12 a by the evaporating water return line 34, and again through the washing water introduction line 35, the waste water inflow line 26 and the heat exchanger 18. It is installed so as to be connected to 12a. Thereby, the water containing the low boiling point component at the time of washing the indirect heating unit 38 can use the residual heat when evaporated by the evaporator 12a. As a result, the auxiliary heat source is not necessarily required when setting the temperature of the water containing the low boiling point component in the cleaning of the indirect heating unit 38 in the range of 60 ° C to 100 ° C.

  Further, in the waste water treatment apparatus 2 shown in FIG. 2, one end of the evaporated water discharge line 40 is connected to the evaporated water return line 34 and the other end is connected to the concentrated water discharge line 30. In this embodiment, in order to obtain a more stable non-drainage system, a part of the evaporated water is stored in the concentrated water tank 14 from the evaporated water discharge line 40 through the concentrated water discharge line 30, and then evaporated to dryness together with the concentrated water. It is preferable to make it. In the present embodiment, it is only necessary to evaporate and dry a part of the evaporating water. For example, the evaporating water discharge line 40 may be directly connected to an evaporating and drying apparatus such as a dehydrator or a dryer. Alternatively, it may be connected to the concentrated water tank 14 and evaporated to dryness with concentrated water by an evaporation / drying apparatus.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

  In the examples, the wastewater treatment apparatus shown in FIG. 1 was used to evaporate and concentrate the wastewater for one week, and then the indirect heating part was washed with water containing the evaporated low boiling point components for 1 hour. Water containing a low boiling point component at the time of washing was heated to 70 ° C., and the pressure in the evaporator was set to atmospheric pressure. Table 1 summarizes the test conditions for the evaporation and concentration of waste water.

  In Comparative Example 1, the waste water was evaporated and concentrated for one week, and then the indirectly heated portion was washed with 70 ° C. water (tap water) for 1 hour.

  In Comparative Example 2, the wastewater was evaporated and concentrated for 1 week, and then the indirectly heated portion was washed with a 70% sodium hydroxide 20% aqueous solution for 1 hour.

  In Comparative Example 3, the wastewater was evaporated and concentrated for 1 week, and then the indirectly heated portion was washed with a 20% household detergent 20% solution at 70 ° C. for 1 hour.

  In Comparative Example 4, the wastewater was evaporated and concentrated for one week, and then the indirectly heated portion was washed with a 20% aqueous sulfuric acid solution at 70 ° C. for 1 hour.

First, the overall heat transfer coefficient of the indirect heating part before adhesion of the paint scale was 3000 kcal / m ² / ° C./h. Then, after one week of evaporation and concentration of the waste water, the overall heat transfer coefficient of the indirect heating portion after the paint scale adhered was 2000 kcal / m ² / ° C./h. And in Comparative Examples 1-4 which wash | cleaned the indirect heating part with water, sodium hydroxide, household detergent, and a sulfuric acid, the overall heat transfer coefficient of the indirect heating part after washing | cleaning is 2000 kcal / m < ² > / (degreeC) / h, respectively 2200 kcal. / ^{m 2} / ℃ / h, a ^{2000kcal / m 2 / ℃ / h} , 2200kcal / m 2 / ℃ / h, either could not be restored to the overall heat transfer coefficient of the indirect heating of the pre-coating scale deposition It was. On the other hand, in the Example which wash | cleaned the indirect heating part with the water containing a low boiling point component, the general heat transfer coefficient of the indirect heating part after washing | cleaning reaches 3040 kcal / m < ² > / degreeC / h, and it is indirect before paint scale adhesion. The overall heat transfer coefficient of the heating unit was recovered.

In addition, the general heat transfer coefficient of the Example and each Comparative Example was calculated from the concentrated water temperature, the indirectly heated portion temperature, the evaporation amount, and the heat transfer area by the following equation.
h = q / AΔT
h: Overall heat transfer coefficient q: Heat quantity A: Heat transfer area ΔT: Temperature difference of heating part (indirect heating part temperature-concentrated water temperature)

  1, 2 Wastewater treatment equipment, 10 Water-based paint drainage tank, 12 Evaporation concentrator, 12a Evaporator, 14 Concentrated water tank, 16 Compressor, 18 Heat exchanger, 19 Washing water tank, 20 Drain pump, 22 Concentrated water pump, 24 Vacuum Pump, 26 Wastewater inflow line, 28 Concentrated water circulation line, 30 Concentrated water discharge line, 32 Evaporated water supply line, 34 Evaporated water return line, 35 Wash water introduction line, 36 Exhaust line, 37 Auxiliary steam line, 38 Indirect heating section, 39 Organic solvent addition line, 40 Evaporative water discharge line.

Claims (6)

A wastewater treatment method for wastewater containing at least a water-based paint,
Evaporation and concentration step of evaporating water containing low-boiling components in the wastewater and concentrating high-boiling components by using an evaporative concentrator provided with an indirect heating unit that heats the wastewater discharged from the storage tank in which the wastewater is stored When,
A step of recovering at least a part of the water containing the low-boiling component evaporated and washing the indirect heating part with a part of the water containing the low-boiling component after the evaporation and concentration step;
A wastewater treatment method comprising: a returning step of returning the remaining water containing the recovered low-boiling components to the storage tank . The wastewater treatment method according to claim 1, wherein an organic solvent that dissolves the paint scale is added to the recovered water containing the low-boiling component. The wastewater treatment method according to claim 1 or 2, wherein the temperature of the water containing the low-boiling component when the indirect heating unit is washed is set to a range of 60 to 100 ° C. A wastewater treatment apparatus for wastewater containing at least a water-based paint,
A storage tank for storing the waste water;
An indirect heating unit for heating the wastewater discharged from the storage tank , evaporating water containing a low boiling point component in the wastewater, and concentrating the high boiling point component;
A means for recovering at least a part of the water containing the low-boiling point component evaporated, supplying a part of the water containing the low-boiling point component to the indirect heating unit, and cleaning the indirect heating unit;
Returning means for returning the remaining water containing the recovered low-boiling-point components to the storage tank . The wastewater treatment apparatus according to claim 4, further comprising an addition unit that adds an organic solvent that dissolves the paint scale to the water containing the recovered low-boiling component. The wastewater treatment apparatus according to claim 4 or 5 , further comprising an auxiliary heat source that sets the temperature of the water containing the low-boiling component when the indirect heating unit is washed to a range of 60 to 100 ° C.

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