KR20230113005A - System for reducing the concentration of effluent salts in wastewater containing high concentrations of sodium sulfate - Google Patents

Abstract

The present invention includes an evaporator for concentrating wastewater containing sodium sulfate (Na2SO4) by evaporation; a supply pump controlled to supply wastewater to the evaporator and to adjust the amount of wastewater supplied to the evaporator; a condensate heat exchanger for increasing the temperature of the wastewater supplied to the evaporator by using the condensation heat of the steam generated in the evaporator; And a sedimentation tank into which the concentrated water generated in the evaporator is introduced and cooled to precipitate and precipitate sodium sulfate salt by cooling the concentrated water, solving the operation problem due to the scale of the evaporator and lowering the concentration of the discharged salt Disclosed is an effluent salt concentration reduction system for wastewater containing high sodium sulfate.

Description

System for reducing the concentration of effluent salts in wastewater containing high concentrations of sodium sulfate}

The present invention relates to a system for reducing environmental pollution caused by salts discharged by reducing the concentration of salts discharged when wastewater containing high concentration sodium sulfate (Na2SO4) is discharged.

In general, in order to recover nickel, cobalt, manganese, lithium, etc. contained in the cathode material of a waste battery, sulfuric acid is used to melt the waste cathode material, and sodium hydroxide (NaOH) is used to convert it into hydroxide, or sodium carbonate It is recovered by making it into carbonate using (Na2CO3).

Metals in the waste cathode material are recovered using this chemical reaction, and sodium sulfate (Na2SO4) and other salts generated by the chemical reaction are present in high concentration in the remaining wastewater. In addition, these wastewaters also contain unrecovered metals and lithium. When such wastewater is discharged into the sea as it is, high concentrations of salt and lithium contained in the wastewater adversely affect the ecosystem. For this reason, according to the enforcement regulations of the Water Environment Conservation Act of Korea, the allowable discharge standard of water pollutants is limited to less than 2TU (Toxic Unit). In order to meet these ecotoxic emission standards, the concentration of lithium discharged should be about 10 mg/L or less.

On the other hand, according to the Water Environment Conservation Act, if the cause of ecotoxicity is found to be 'salt', there is a regulation that it is regarded as not exceeding the ecotoxic effluent water quality standard because it does not cause a major problem to the marine ecosystem. However, when high concentrations of salt are discharged, they can adversely affect the marine ecosystem, and many developed countries are regulating or legislating in the direction of limiting the discharge concentration of salt. So far, Korea has discharged high-concentration salt-containing wastewater as it is without reducing the salt concentration, and in particular, high-concentration salt wastewater generated by secondary battery cathode material recycling companies is discharged to the coast as it is, becoming a social problem.

In order to lower the concentration of salt in high-concentration salt wastewater, the wastewater is treated through several pretreatment steps, and a certain amount of the treated wastewater is put into an evaporation concentration device to evaporate water to make condensate and reuse or discharge it. In addition, the salt concentrated in the evaporation concentration unit is dried and processed into a solid. However, there is a problem that such an evaporation and concentration device is expensive, and the operation cost of the evaporation and concentration device is also high.

In order to solve this problem, it is necessary to minimize the amount of wastewater treated by the evaporator. For this reason, a method of treating a part of the wastewater with an evaporation concentration device and mixing and discharging the condensate water generated in the evaporation concentration device and the remaining wastewater is used to reduce the concentration of salt and reduce the device and operating cost.

However, in order to concentrate the salt at a high concentration in the evaporative concentrating device, since the device is operated at a concentration rate of 90% or more, a lot of scale is formed during operation, and difficulties arise in operation due to the scale adhered to the device.

In addition, a method of applying a reverse osmosis membrane system may be considered to reduce the throughput of the evaporation concentrating device, but the salinity concentration is too high to treat high-concentration salt wastewater with the reverse osmosis membrane device, so it is difficult to apply.

On the other hand, referring to FIG. 1, the conventional sodium sulfate-containing wastewater discharge salt concentration reduction system is a system for concentrating a certain amount of wastewater with an evaporator 20, and the wastewater in the wastewater storage tank 10 is pumped 11 and a filter ( 12) is supplied to the evaporator 20, the evaporator 20 is operated at a concentration rate of 90% or more, the concentrated water is crystallized by applying heat through the crystallization device 30, and the crystallized salt is dried in a dryer ( In 40), heat is applied to make the salt into a solid and discarded, and the treated water having the reduced concentration of the discharged salt is discharged to the outside 50. In this conventional system, since the concentration rate of the evaporator 20 is 90% or more, a lot of scale is formed due to salt during operation of the evaporator 20. Accordingly, the operating efficiency of the evaporator 20 is reduced, increasing energy costs, and since the operation of the evaporator 20 must be frequently stopped to remove scale, the operation maintenance cost increases and there are many difficulties in operation. In addition, since the crystallization device 30 and the dryer 40 apply heat, energy costs are high and the cost of the entire device increases.

Prior Art Document 1: Registered Patent Publication No. 10-1137251 (Announced on April 20, 2012)

Prior Art Document 2: Patent Publication No. 10-2018-0021277 (published on March 2, 2018)

The present invention was invented to solve the above problems, and an object of the present invention is to solve the operation problem caused by the scale of the evaporator and to provide a system for reducing the concentration of discharged salt of wastewater containing high concentration sodium sulfate, which can lower the concentration of discharged salt. ,

In addition, an object of the present invention is to provide a system for reducing the discharge salt concentration of wastewater containing high concentration sodium sulfate, which can reduce equipment and operating costs by minimizing the throughput of the evaporator.

In order to achieve the above object, the present invention is an evaporation concentrator for evaporating and concentrating wastewater containing sodium sulfate (Na2SO4); a supply pump controlled to supply wastewater to the evaporator and to adjust the amount of wastewater supplied to the evaporator; a condensate heat exchanger for increasing the temperature of the wastewater supplied to the evaporator by using the condensation heat of the steam generated in the evaporator; and a precipitation tank into which concentrated water generated in the evaporation concentrator is introduced and cooled to precipitate and precipitate sodium sulfate salt.

Preferably, the evaporator concentrates wastewater having a total dissolved solids (TDS) of 60,000 mg/L or more and a concentration of sodium sulfate (Na2SO4) of 50% or more, and the evaporator concentrates the wastewater at a concentration rate in the range of 40 to 70%. It is operated, and the supply pump is characterized in that it is controlled to adjust the amount of wastewater supplied to the evaporator in the range of 50 to 80% of the total capacity of the evaporator.

Additionally, the present invention further includes a cooler for cooling the concentrated water introduced into the precipitation tank, and the cooler cools the temperature of the concentrated water in the precipitation tank in the range of 0 to 10 °C.

Preferably, it further comprises a reverse osmosis membrane device for treating the supernatant of the precipitation tank, discharging the treated water to the outside, and introducing untreated concentrated water into the evaporator to reduce the TDS concentration of the supernatant of the precipitation tank. do.

More preferably, a dehydrator is installed at the bottom of the settling tank to dehydrate sodium sulfate precipitated in the settling tank and discharge it as a solid, and the water generated in the dehydrator is introduced back into the settling tank.

Preferably, a supernatant pump for supplying the supernatant of the sedimentation tank to the reverse osmosis membrane device and a supernatant filter for filtering the supernatant water supplied to the reverse osmosis membrane device through the supernatant pump are installed between the precipitation tank and the reverse osmosis membrane device. .

Here, it characterized in that it further comprises a concentrated water heat exchanger for cooling the concentrated water flowing into the precipitation tank from the evaporation concentrator using the supernatant water that has passed through the supernatant water filter.

Preferably, when the TDS concentration of the supernatant of the settling tank is equal to or greater than a preset value, the condensed water generated in the evaporation concentrator is supplied to the reverse osmosis membrane device to reduce the TDS concentration of the supernatant of the settling tank.

The system for reducing the discharge salt concentration of wastewater containing high-concentration sodium sulfate according to the present invention solves the operation problem caused by scale by lowering the concentration rate of the evaporator and lowers the temperature of the concentrated water using the solubility difference according to the temperature to precipitate and precipitate sodium sulfate. It can reduce the ecotoxicity of the ecosystem by lowering the concentration of discharged salt.

In addition, the system for reducing the discharge salt concentration of wastewater containing high concentration sodium sulfate according to the present invention treats the salt contained in the supernatant of the precipitation tank with a reverse osmosis membrane device and circulates the concentrated water of the reverse osmosis membrane device to the evaporator to minimize the throughput of the evaporator. and can reduce operating costs;

1 is a view schematically showing the configuration of a conventional evaporation concentration system;
Figure 2 is a view schematically showing the configuration of the discharge salt concentration reduction system of high-concentration sodium sulfate-containing wastewater according to the present invention.

Hereinafter, a preferred embodiment of a system for reducing the discharge salt concentration of wastewater containing high concentration sodium sulfate according to the present invention will be described with reference to the accompanying drawings. For reference, in describing the present invention below, the terms referring to the components of the present invention are named in consideration of the functions of each component, so they should not be understood as limiting the technical components of the present invention. It will be.

Referring to FIG. 2, the system for reducing the salt concentration of wastewater containing high-concentration sodium sulfate according to the present invention reduces the salt concentration of wastewater supplied from the wastewater storage tank 10 and discharges it to the outside 20, such as the sea. It includes a concentrator 100, a supply pump 200 for supplying wastewater to the evaporation concentrator 100, a condensate heat exchanger 300 for increasing the temperature of the wastewater, and a precipitation tank 400 for precipitating and precipitating sodium sulfate.

The evaporator 100 serves to concentrate by evaporating wastewater containing sodium sulfate (Na2SO4). The evaporator 100 is a device configured to discharge water vapor by applying heat and increase the solids content in the solution, and is composed of at least one of known evaporation devices such as a rotary evaporator, a centrifugal evaporator, and a film evaporator. can

The supply pump 200 is installed between the wastewater storage tank 10 and the evaporator 100 and operates to supply wastewater from the wastewater storage tank 10 to the evaporator 100 . The supply pump 200 is controlled to adjust the amount of wastewater supplied to the evaporator 100. In addition, a supply filter 210 for removing floating substances in wastewater may be installed between the supply pump 200 and the evaporator 100 .

The condensate heat exchanger 300 is installed on the bypassed flow path A between the upstream flow path and the downstream flow path of the evaporator concentrator 100. The temperature of wastewater supplied to the evaporative condenser 100 is increased by using condensation heat generated while steam is condensed. The increase in the temperature of the wastewater reduces the energy consumption of the evaporator 100, thereby reducing operating costs.

The precipitation tank 400 is installed downstream of the evaporator 100, and the concentrated water generated in the evaporator 100 flows into the precipitation tank 400. The precipitation tank 400 cools the introduced concentrated water to precipitate and precipitate the sodium sulfate salt.

Here, the evaporator 100 is configured to evaporate and concentrate wastewater having a total dissolved solids (TDS) of 60,000 m/L or more and a sodium sulfate concentration of 50% or more. In addition, the supply pump 200 is controlled to adjust the amount of wastewater supplied to the evaporator 100 in the range of 50 to 80% of the total capacity of the evaporator 100 . And, the evaporation concentrator 100 is controlled to operate at a concentration rate in the range of 40 to 70%, preferably in the range of 50 to 60%.

By controlling the amount of wastewater treatment and operating conditions of the evaporator 100, the energy consumed for operation of the evaporator 100 can be reduced, and the amount of scale generated in the evaporator 100 can be reduced. In addition, it is possible to increase the temperature of the wastewater supplied to the evaporator 100 through the condensate heat exchanger 300, thereby increasing the evaporation efficiency of the evaporator 100 compared to the same operating conditions.

Additionally, the system for reducing the discharge salt concentration of wastewater containing high-concentration sodium sulfate according to the present invention further includes a cooler 500 for cooling the concentrated water introduced into the precipitation tank 400. The cooler 500 is installed on one side of the settling tank 400 and operates to cool the temperature of concentrated water in the settling tank 400 to a range of 0 to 10°C. Sodium sulfate salt in the concentrated water is precipitated and precipitated by this cooler 500.

Here, the solubility of sodium sulfate (Na2SO4) is 47.6 g/L at 0°C, 100 g/L at 10°C, and 427 g/L at 25°C. For example, if 60,000 mg/L (60 g/L) of sodium sulfate (Na2SO4) is contained in wastewater with a TDS of 70,000 mg/L, the solubility of sodium sulfate at 10°C is about 100 g/L, so at 10°C or less Sodium sulfate does not precipitate. However, in the case of concentrated water concentrated to 50%, 120 g/L (60 g/L × 100/50 = 120) is dissolved, and sodium sulfate is precipitated even at 10 ° C or lower, and about 20 g / L is precipitated. The concentration of excreted salts is reduced. Condensate that is evaporated and condensed has a very low TDS, so ignoring this, the TDS estimate at 50% concentration is approximately 140,000 mg/L (140 g/L), and excluding the previously precipitated 20 g/L, the TDS is 120,000 mg /L (120 g/L). In addition, since the solubility of sodium sulfate at 0 ° C is 47.6 g / L, when the temperature of the concentrated water in the precipitation tank 400 is lowered to near 0 ° C, 72.4 g / L minus 47.6 g / L from 120 g / L is obtained in the precipitation tank 400. precipitate and precipitate Then, the TDS of the supernatant water (clear water at the top of the precipitation tank) discharged from the settling tank 400 is lowered to 67.6 g/L by subtracting 72.4 g/L from 140 g/L.

As such, the system for reducing the discharge salt concentration of wastewater containing high concentration sodium sulfate according to the present invention considers the TDS of the filtered water passing through the supply filter 210 and the TDS of the concentrated water discharged, and the amount of wastewater supplied to the evaporator 100 discharged from the settling tank 400 by adjusting the range of 50 to 80%, operating the concentration rate of the evaporator 100 in the range of 40 to 70%, and cooling the temperature of the concentrated water in the settling tank 400 to 10 ° C or less. By reducing the TDS of the supernatant to reduce the effluent salt concentration of the waste water.

Preferably, the system for reducing the discharge salt concentration of wastewater containing high concentration sodium sulfate according to the present invention may further include a reverse osmosis membrane device 600 for reducing the TDS concentration of the supernatant discharged from the precipitation tank 400. The reverse osmosis membrane device 600 treats the supernatant of the settling tank 400, discharges the treated water to the outside, and introduces the untreated concentrated water back into the evaporator 100 through the return passage B to return to the settling tank 400. It serves to reduce the TDS concentration of the supernatant of

In addition, a dehydrator 410 is installed at the bottom of the settling tank 400 to dehydrate sodium sulfate precipitated in the settling tank 400 and discharge it as a solid. Sodium sulfate discharged from the dehydrator 410 can be purified and reused. In addition, a circulation flow path C is formed so that water generated in the dehydrator 410 is re-introduced into the settling tank 400 .

Preferably, when it is difficult to treat the supernatant water using the reverse osmosis membrane device 600 because the TDS of the supernatant water in the settling tank 400 is high, the system may be configured to mix the condensed water generated in the evaporator 100 with the supernatant water. To this end, a bypass passage D connecting the evaporator 100 and the reverse osmosis membrane device 600 may be provided. And, when the TDS concentration of the supernatant in the settling tank 400 is equal to or higher than the predetermined value, the condensed water generated in the evaporation concentrator 100 is supplied to the reverse osmosis membrane device 600 side through the bypass passage D, so that the settling tank 400 The TDS concentration of the supernatant can be reduced.

For example, based on 50% of the supply flow rate to the evaporator 100 and 50% of the raw wastewater, the TDS of raw wastewater is 70,000 mg/L, the TDS of the condensate of the evaporator 100 with a concentration rate of 50% is 10 mg/L, When the TDS of the supernatant from which sodium sulfate is precipitated and removed is 67,600 mg/L, when the raw wastewater is mixed and discharged without being treated with the reverse osmosis membrane device 600, the TDS of the discharged water is calculated to be about 52,000 mg/L or less. That is, the TDS of discharged water compared to the TDS of raw wastewater can be lowered to at least 80% or less before being discharged.

Of course, when the supernatant water in the settling tank 400 is treated with the reverse osmosis membrane device 600 and discharged, the TDS of discharged water can be further lowered.

Additionally, between the settling tank 400 and the reverse osmosis membrane device 600, the supernatant pump 420 for supplying the supernatant of the settling tank 400 to the reverse osmosis membrane device 600 side, and the supernatant pump 420 to the reverse osmosis membrane device 600 side. A supernatant filter 430 for filtering the supplied supernatant water and a high pressure pump 440 for pressurizing and supplying the supernatant water supplied to the reverse osmosis membrane device 600 may be installed.

Here, a concentrated water heat exchanger 700 may be installed between the evaporator 100 and the precipitation tank 400 to lower the temperature of the concentrated water supplied from the evaporator 100 to the precipitation tank 400. The concentrated water heat exchanger 700 cools the concentrated water flowing into the precipitation tank 400 from the evaporative concentrator 100 using the supernatant water that has passed through the supernatant water filter 430 . Thus, the operating efficiency of the cooler 500 can be increased.

On the other hand, since the sensible heat to increase the temperature to 100℃ to evaporate 1 kg of 20℃ water is 80 Kcal, and the latent heat required for evaporation is very high at 540 Kcal, reducing the amount of evaporation in the evaporator reduces energy consumption. Best way. A simple cost comparison of the energy consumption of the conventional system and the system according to the present invention is as follows.

A simple comparison of the conditions of evaporating and concentrating 4 tons of 10 tons of wastewater at 20 ° C and discharging 6 tons shows that the conventional system requires evaporation of 4 tons in the evaporator, crystallizer, and dryer, so that 4,000 kg × (80 Kcal + 540 Kcal) = 2,480,000 Kcal is consumed. In the case of the system of the present invention, when the evaporator 100 concentrates 50% of 4 tons, 2 tons are evaporated and concentrated, and the concentrated water is cooled to 20 ° C through the concentrated water heat exchanger 700 to the settling tank 400. Assuming that it is supplied, 20 kcal per 1 kg of water is consumed when 2 tons of concentrated water is cooled from 20 ° C to 0 ° C in the precipitation tank 400. If you simply calculate the energy consumption, 2,000kg × 80kcal + 2,000kg × (80kcal + 540kcal) + 2,000kg × (20kcal) = 1,440,000kcal. That is, the system according to the present invention can reduce energy consumption by 42% by using about 58% of energy compared to the conventional system. Even considering the electrical energy consumed by the reverse osmosis membrane device 600 and the electrical energy consumed by the dehydrator 410, it can be seen that the energy consumption of the system according to the present invention is significantly lower than that of the conventional system.

The embodiments of the present invention described above are only exemplarily showing the technical spirit of the present invention, and the protection scope of the present invention should be construed according to the following claims. In addition, those skilled in the art to which the present invention belongs will be able to make various modifications and variations without departing from the essential characteristics of the present invention, and all technical ideas within the equivalent scope of the present invention It should be interpreted as being included in the scope of rights.

100: evaporator 200: feed pump
210: supply filter 300: condensate heat exchanger
400: sedimentation tank 410: dehydrator
420: supernatant pump 430: supernatant filter
440: high pressure pump 500: cooler
600: reverse osmosis membrane device 700: concentrated water heat exchanger

Claims (8)

An evaporation concentrator for evaporating and concentrating wastewater containing sodium sulfate (Na2SO4);
a supply pump controlled to supply wastewater to the evaporator and to adjust the amount of wastewater supplied to the evaporator;
a condensate heat exchanger for increasing the temperature of the wastewater supplied to the evaporator by using the condensation heat of the steam generated in the evaporator; and
A system for reducing the discharge salt concentration of high-concentration sodium sulfate-containing wastewater, comprising a precipitation tank into which the concentrated water generated in the evaporator is introduced and cooled to precipitate and precipitate sodium sulfate salt.
According to claim 1,
The evaporative concentrator evaporates and concentrates wastewater having a total dissolved solids (TDS) of 60,000 mg/L or more and a sodium sulfate (Na2SO4) concentration of 50% or more,
The evaporator is operated at a concentration rate in the range of 40 to 70%,
The supply pump is controlled to adjust the amount of wastewater supplied to the evaporator in the range of 50 to 80% of the total capacity of the evaporator.
According to claim 1,
Further comprising a cooler for cooling the concentrated water flowing into the precipitation tank, wherein the cooler cools the temperature of the concentrated water in the precipitation tank to a range of 0 to 10 ° C. .
According to claim 3,
High-concentration sodium sulfate, characterized in that it further comprises a reverse osmosis membrane device for treating the supernatant of the precipitation tank, discharging the treated water to the outside, and introducing untreated concentrated water into the evaporator to reduce the TDS concentration of the supernatant of the precipitation tank. System for reducing the discharge salt concentration of containing wastewater.
According to claim 3 or 4,
At the lower part of the precipitation tank, a dehydrator is installed to dehydrate sodium sulfate precipitated in the precipitation tank and discharge it as a solid, and the water generated in the dehydrator is re-introduced into the precipitation tank. system.
According to claim 4,
Characterized in that, a supernatant pump for supplying the supernatant of the sedimentation tank to the reverse osmosis membrane device and a supernatant filter for filtering the supernatant water supplied to the reverse osmosis membrane device through the supernatant pump are installed between the precipitation tank and the reverse osmosis membrane device. Effluent salt concentration reduction system for wastewater.
According to claim 6,
The system for reducing the discharge salt concentration of wastewater containing high concentration sodium sulfate, characterized in that it further comprises a concentrated water heat exchanger for cooling the concentrated water flowing into the precipitation tank from the evaporation concentrator using the supernatant water that has passed through the supernatant water filter.
According to claim 4,
When the TDS concentration of the supernatant of the precipitation tank is greater than or equal to a predetermined value, the condensate generated in the evaporator is supplied to the reverse osmosis membrane device to reduce the TDS concentration of the supernatant of the precipitation tank. concentration reduction system.

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