JP2013202588A - Concentration method for waste liquid - Google Patents

Abstract

Disclosed is a method for concentrating waste liquid, which can reduce the amount of scale generated when an evaporator concentrates brine waste liquid that has been biologically treated and treated with a reverse osmosis membrane in an electronic component manufacturing process, and can prevent corrosion of the evaporator. .
In a method of biologically treating waste water from an electronic component manufacturing process and concentrating a brine waste liquid obtained by treating the biological treated water with a reverse osmosis membrane using an evaporator having at least an inner surface made of stainless steel, the pH of the waste liquid supplied to the evaporator Is 5 to 5.7, the pH of the concentrate is 8 to 9, and after the scale is deposited, the evaporator is washed with caustic soda and sulfamic acid.
[Selection] Figure 1

Description

  The present invention relates to a method of biologically treating waste water from an electronic component manufacturing process and concentrating a brine waste liquid obtained by treating the biologically treated water with a reverse osmosis membrane using an evaporator.

  Cleaning waste liquids such as boilers, heat exchangers, and chemical plants contain a large amount of scale components such as iron oxide, cleaning components such as acids and alkalis used for cleaning, and salts generated by the reaction during cleaning. Yes. An evaporator may be used to reduce the volume of this cleaning waste liquid. When the operation of concentrating the cleaning waste liquid by the evaporator is continued, the scale gradually adheres to the inner surface, particularly the heating tube. Therefore, the evaporator is cleaned using a cleaning chemical periodically or according to the amount of attached scale.

  Patent Document 1 exemplifies citric acid, formic acid, EDTA, and the like as cleaning agents for removing the heat transfer tube scale.

JP2002-205056

  The present invention can biologically treat waste water from the manufacturing process of electronic components, reduce the amount of scale generated when the waste water obtained by treating the biologically treated water with a reverse osmosis membrane is concentrated with an evaporator, and prevent corrosion of the evaporator. It aims at providing the concentration method of a waste liquid.

  The waste liquid concentration method of the present invention is a method of biologically treating electronic component manufacturing process wastewater and supplying the wastewater obtained by reverse osmosis membrane treatment of the biologically treated water with an evaporator having at least an inner surface made of stainless steel. The pH of the brine waste liquid is 5 to 5.7, the pH of the evaporator concentrate is 8 to 9, and the evaporator is washed with caustic soda and sulfamic acid after the scale is attached.

  In this invention, it is preferable to concentrate so that pH of an evaporator concentrate may be set to 8.5-9.

  When the wastewater from the electronic component manufacturing process is biologically treated, and the brine waste liquid obtained by treating the biologically treated water with a reverse osmosis membrane is concentrated with an evaporator, the carbonic acid component is volatilized as carbon dioxide gas when the water evaporates, increasing the pH of the concentrated liquid. Calcium scales such as calcium and calcium sulfate are easily generated.

  In the present invention, by setting the pH of the brine waste solution supplied to the evaporator to 5 to 5.7, the pH of the evaporator concentrate does not rise to more than 9 even when carbon dioxide gas evaporates from the solution, and the calcium scale Generation is suppressed. In the present invention, corrosion of the inner surface of the stainless steel evaporator can be prevented by setting the pH of the evaporator concentrate to 8 or more.

  When the scale adheres to the inner surface of the evaporator, it can be removed including the Fe scale and Mn scale by washing with sulfamic acid and caustic soda. Note that sulfamic acid is suitable because it has low corrosiveness to stainless steel.

It is sectional drawing of the heating pipe | tube type evaporator used for the concentration method of the waste liquid which concerns on embodiment. It is sectional drawing of the flash type evaporator used for the concentration method of the waste liquid which concerns on embodiment.

  Hereinafter, the present invention will be described in more detail.

As the liquid concentrated in the evaporator, the RO concentrated liquid (brine waste liquid) is produced when the wastewater from the electronic component manufacturing process such as liquid crystal is biologically treated, agglomerated and pressurized and floated, and then subjected to the reverse osmosis membrane (RO) treatment. Is preferred. This brine waste liquid contains a carbonic acid component generated during biological treatment. Usually, the TOC of this RO concentrate is 100 to 300 mg / L, the soluble salt concentration is 5000 to 15000 mg / L, the CaCO ₃ concentration is 10 to 50 mg / L, and the pH is about 6.5 to 7.5.

  An example of the configuration of a heated tube evaporator for concentrating this brine waste liquid is shown in FIG. In this heating tube type evaporator 1, the brine waste liquid is supplied into the can 3 from the stock solution supply pipe 2, and together with the concentrated liquid at the bottom of the can 3, the upper part of the can 3 is passed through the circulation pump 4, the pipe 5 and the nozzle 6. Sprayed into the can 3 as droplets. In the can 3, a lower stage heating pipe 7, a middle stage heating pipe 8, and an upper stage heating pipe 9 are provided substantially horizontally. The liquid droplet descending in the can 3 is heated by the heating tubes 9 to 7, and a part thereof is evaporated and concentrated. The concentrated droplet falls to the bottom of the can 3. The vapor generated by the evaporation is supplied to the lower heating pipe 7 through the duct 10, the compressor 11, the duct 12 and the chamber 13. Note that steam is supplied to the lower portion of the duct 12 through the steam supply pipe 14, mixed with the steam, and supplied to the lower stage heating pipe 7. The compressor 11 has a function of supplying steam and heating the steam by adiabatic compression.

  The steam exiting the lower stage heating pipe 7 is circulated to the middle stage heating pipe 8 via the chamber 16, further circulated to the upper stage heating pipe 9 via the chamber 17, and flows into the chamber 18. Vapor is taken out of the can 3 from the chamber 18 through the pipe 19 and the vacuum pump 20. The concentrated liquid is taken out of the can 3 by a concentrated liquid extracting pipe 21 branched from the pipe 5. The condensed water in the chamber 16 is taken out by the condensed water pump 22.

  The chambers 16 and 18 are partitioned by a plate 23 with a downcomer 24. The chambers 13 and 17 are partitioned by a plate 25 with a downcomer 26. The liquid on the plates 23 and 25 is sent to the lower chambers 16 and 13 by the downcomers 24 and 26.

  The inner surface of the evaporator 1 is entirely made of stainless steel (SUS304) including the heating tube. In addition, the structure of a heating pipe | tube type evaporator is not limited to this.

  In the present invention, a flash type evaporator may be used instead of the heating tube type evaporator.

  An example of the flash evaporator 30 is shown in FIG. The brine waste liquid is supplied to the bottom of the can 32 through the pipe 31, and is sent to the heat exchanger 40 from the can bottom through the circulation pump 33 and the pipe 34 together with the concentrated liquid in the can 32 to be heated. A concentrated liquid extraction pipe 35 is branched from the pipe 34. The concentrate from the pipe 34 passes through the heating pipe 42 from the inflow chamber 41 of the heat exchanger 40, is heated through the relay chamber 43, the heating pipe 44, and the outflow chamber 45, is sent from the pipe 50 to the nozzle 51, and can 32 Sprayed on top of inside. The sprayed droplets evaporate while falling in the can 32. The inside of the can 32 is decompressed by the vacuum pump 66 and the steam ejector 53.

  The top of the can 32 communicates with the suction part of the steam ejector 53 via the duct 52. Steam is supplied to the steam ejector 53 through the pipe 54 as a working fluid. The discharge flow of the steam ejector 53 is supplied to the heat source fluid chamber 46 of the heat exchanger 40 through the duct 55 to heat the liquid flowing in the heating pipes 42 and 44. The inside of the heat exchanger 40 is connected to a duct 59 by a pipe 47, and vapor and gas in the heat exchanger 40 are sucked into the condenser 60 by a vacuum pump 66. The condensate produced in the heat exchanger 40 is introduced into the bottom of the condenser 60 via the pipe 48.

  The capacitor 60 is connected to the duct 52 through a duct 59. Since the inside of the condenser 60 is depressurized by the vacuum pump 66, the steam in the can 32 and the heat exchanger 40 is sucked into the condenser 60. Cold water is circulated through the inflow chamber 61, the relay chamber 63, and the outflow chamber 65 to the cooling pipes 62 and 64 in the condenser 60. The condensed water generated in the condenser 60 and the condensed water sent from the heat exchanger 40 via the pipe 48 are taken out via the condensed water pump 68.

  The inner surface of the evaporator 30 is all made of stainless steel (SUS304). Since the flash type evaporator 30 has no heating tube in the can 32, the amount of scale attached is smaller than that of the heating tube type evaporator.

In the present invention, when the brine waste liquid is concentrated by the evaporator, the pH of the waste liquid supplied to the evaporator is set to 5 to 5.7 by adding an acid such as sulfuric acid or hydrochloric acid. As a result, even when carbon dioxide gas evaporates when it is concentrated in the can, the pH of the concentrated liquid does not become 9 or more, the generation of calcium carbonate scale and calcium sulfate scale is suppressed, and the washing frequency for removing the scale is reduced. Can be reduced. When the pH of the waste liquid is lower than 5, acid corrosion may occur in the equipment. On the other hand, when the pH of the waste liquid is higher than 5.7, the pH of the concentrated liquid is higher than 9, and the precipitation amount of CaCO ₃ and CaSO ₄ increases rapidly.

  In the present invention, the concentration is preferably performed so that the pH of the concentrated solution is 8 to 9, particularly 8.5 to 9. By setting the pH of the concentrate to 8 or more, particularly 8.5 or more, corrosion of the inner surface of the stainless steel evaporator is prevented.

  If the operation of concentrating the brine waste liquid by the evaporator is continued, the scale gradually adheres to the heating tube and the inner surface of the can. Therefore, the inside of the can 3 is cleaned periodically or according to the scale amount. NaOH and sulfamic acid are used for this washing.

  In addition, as above-mentioned, the pH of the concentrate is 9 or less because pH of the brine waste liquid supplied to an evaporator was 5.7 or less. In this region of pH 9 or less, a strong calcium-based scale is hardly generated.

  In order to clean the inside of the can, a method of spraying the cleaning liquid from the top of the can into the can and spraying the cleaning liquid falling on the bottom of the can again from the top can be employed. The inside of the can may be filled with a cleaning liquid, and this cleaning liquid may be circulated. The cleaning liquid may be heated to about 40 to 60 ° C.

  Washing is first performed for about 2 to 24 hours with a sulfamic acid solution having a concentration of about 2 to 10 wt. It is preferred to remove the silica-based scale and then flush. However, you may perform caustic soda washing | cleaning first.

  By this cleaning, almost all the scale on the inner surface of the can can be removed. Therefore, jet cleaning with high-pressure water, which has been conventionally required, becomes unnecessary.

[Example 1]
Liquid crystal production process wastewater was biologically treated, then coagulated and floated, and then RO treated. The brine waste liquid generated by this RO treatment was TOC 80 mg / L, soluble salts 7100 mg / L, CaCO ₃ 13 mg / L, pH 7.0. The pH was adjusted to 5.5 by adding sulfuric acid to this brine waste solution, and then concentrated 30 times with a heating tube evaporator (heating tube heat transfer area 1800 m ² ) shown in FIG. The pH of the concentrate was 8.5 to 9.0. Table 1 shows the average composition of the concentrate.

  When this operation was continued for 14 days, a large amount of scale adhered to the heating tube. (Operating continuation days = 14 days) Table 1 shows the results of collecting and analyzing the scale at this time.

The inside of the can 3 was cleaned for 12 hours by spraying and circulation using 4 m ³ of 5 wt% sulfamic acid aqueous solution. Thereafter, after flushing with water, 4 m ³ of 5 wt% aqueous solution of caustic soda was used and washed for 12 hours by spray and circulation. Thereafter, it was flushed with water. As a result, the scale was almost completely removed.

[Example 2]
Concentration was performed in the same manner as in Example 1 except that the pH of the RO concentrate was adjusted to 5.3. As a result, the pH of the concentrated solution became 8.0 to 8.5. A large amount of scale adhered to the heating tube 14 days after the start of operation. The number of days that can be continued was 14 days as in Example 1.

[Comparative Example 1]
In Example 1, the brine waste solution was concentrated in the same manner except that the pH of the brine waste solution was not adjusted to 5.5 and the raw solution was supplied to the evaporator with the pH of 7.0. As a result, the pH of the concentrated solution was 9.5 to 10, and a large amount of scale adhered to the heating tube 10 days after the start of operation. The number of days that can be continued was 10 days.

  The inside of the can was cleaned in the same manner as in Example 1, but the calcium scale partially remained in the heating tube, and the scale was not sufficiently removed.

[Comparative Example 2]
In Example 1, the brine waste liquid was concentrated in the same manner except that it was adjusted to pH 6.0 and supplied to the evaporator. As a result, the pH of the concentrated solution was 9.5 to 10, and a large amount of scale adhered to the heating tube 10 days after the start of operation. The number of days that can be continued was 10 days.

  The inside of the can was cleaned in the same manner as in Example 1, but the calcium scale partially remained in the heating tube, and the scale was not sufficiently removed.

  From Examples 1 and 2 and Comparative Examples 1 and 2, according to the present invention, it is recognized that brine waste liquid obtained by biologically treating electronic component manufacturing process wastewater and treating it with reverse osmosis membrane can be stably concentrated with an evaporator while suppressing scale failure. It was.

DESCRIPTION OF SYMBOLS 1 Heating tube type evaporator 3 Can 7, 8, 9 Heating tube 30 Flash type evaporator 32 Can 40 Heat exchanger 53 Ejector 60 Compressor

Claims (2)

In a method of biologically treating electronic component manufacturing process wastewater, and concentrating the brine waste liquid obtained by subjecting this biologically treated water to reverse osmosis membrane treatment using an evaporator having at least an inner surface made of stainless steel,
The pH of the brine waste solution supplied to the evaporator is 5 to 5.7, the pH of the evaporator concentrate is 8 to 9,
A method for concentrating waste liquid, wherein the evaporator is washed with caustic soda and sulfamic acid after the scale is deposited.   The method for concentrating waste liquid according to claim 1, wherein the pH of the concentrate is 8.5 to 9.

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