Water treatment device

Abstract

This water treatment device comprises: an adsorption element; and a supply line that supplies, to the adsorption element, water to be treated containing a substance to be treated. The water treatment device repeats an adsorption treatment, in which the water to be treated is brought into contact with the adsorption element so that the substance to be treated is adsorbed and treated water is discharged, and a desorption treatment, in which steam is brought into contact with the adsorption element so that the substance to be treated is desorbed and desorbed gas is discharged. In the desorption treatment, the following are performed in the given order: an early-period treatment, in which the steam is introduced at a first temperature that is an initial temperature; a high-temperature treatment, in which the steam is introduced at a second temperature higher than the first temperature; and a late treatment, in which the steam is introduced at a third temperature lower than the second temperature.

Description

Water treatment equipment

[0001] The present invention relates to a water treatment device that removes a substance to be treated from water to be treated that contains the substance to be treated, thereby purifying the water.

[0002] Conventionally, continuous adsorption / desorption water treatment devices have been known that purify water by removing target substances from it. These devices alternate between an adsorption step in which the target substances are adsorbed and removed by contacting the water with an adsorption element, and a desorption step in which heated gas is brought into contact with the adsorption element to desorb the target substances from the adsorption element (see, for example, Patent Document 1). From the standpoint of economy and heat resistance, heated air or steam at around 140°C is used as the heating gas. This water treatment device essentially does not require replacement of the adsorbent, and can stably remove adsorbed substances with high efficiency.

[0003] However, in cases where the water to be treated contains substances that are difficult to desorb, if the substances are adsorbed and attached to the adsorption element, they are difficult to desorb with heated gas at the above temperature and remain in the adsorption element, reducing the adsorption performance, which may require replacement of the adsorption element. Therefore, water treatment devices have been studied that use steam at 300°C, which is higher in temperature than the above steam, to improve desorption performance and reduce the frequency of replacement of the adsorption element (for example, Patent Document 2).

[0004] Examples of difficult-to-desorb substances described herein include inorganic substances such as sulfates, sulfides, and iron rust, organic polymers, organic oligomers, proteins, sugars, fatty acids, fatty acid esters, amines, amide compounds, oils and fats, resins, surfactants, and organic substances with a boiling point of 140°C or higher, such as high-boiling-point solvents, such as triethylene glycol, and chemicals classified as perfluoroalkyl and polyfluoroalkyl compounds (PFAS) (perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), perfluorobutanesulfonic acid (PFBS), perfluorononanoic acid (PFNA), perfluorohexanesulfonic acid (PFHxS), perfluorocarboxylic acids (PFCAs), and fluorothermal alcohols (FTOHs)). Difficult-to-desorb substances also include organic substances that undergo polymerization during desorption and become resins on the surface of the adsorbent. Examples include cyclohexanone, acrylic acid esters, epichlorohydrin, and adipic acid.

[0005] JP 2006-55712 A JP 2017-77522 A JP 9-94422 A

[0006] As described above, conventional water treatment devices require high-temperature steam when the water contains substances that are difficult to desorb. In this case, the pipes and adsorption tanks that come into contact with the high-temperature steam may deform or crack due to thermal expansion or contraction caused by sudden temperature changes. This can result in a decrease in the performance of the adsorption and desorption processes.

[0007] In view of the above problems, an object of the present invention is to provide a water treatment device that can perform continuous treatment stably with high efficiency and with improved safety.

[0008] As a result of extensive research, the present inventors have finally completed the present invention, which is as follows.

[0009] 1. A water treatment device comprising an adsorption element and a supply line for supplying water to be treated containing a substance to be treated to the adsorption element, the water treatment device repeating an adsorption treatment in which the water to be treated is brought into contact with the adsorption element to adsorb the substance to be treated and then discharge the treated water, and a desorption treatment in which steam is brought into contact with the adsorption element to desorb the substance to be treated and then discharge a desorbed gas, the water treatment device being characterized in that the desorption treatment sequentially includes an early treatment in which the steam is introduced at a first temperature that is an initial temperature, a high-temperature treatment in which the steam is introduced at a second temperature that is higher than the first temperature, and a later treatment in which the steam is introduced at a third temperature that is lower than the second temperature.

[0010] According to the above-described configuration of the present invention, the desorption process is divided into an early process at a first temperature, a high-temperature process at a second temperature higher than the first temperature, and a late process at a third temperature lower than the second temperature, and the supply temperature of the steam is raised and lowered in stages. This reduces the rate of change in thermal expansion and contraction of components that come into contact with the steam, such as pipes and adsorption tanks, and suppresses cracks, deformation, etc. As a result, deterioration in the performance of the adsorption process and desorption process can be prevented, enabling highly efficient and stable continuous processing.

[0011] 2. The water treatment device according to claim 1, further comprising: a concentrated water line for discharging the desorption gas to the outside of the system as concentrated water; and a desorption water line for introducing the desorption gas to the supply line as desorbed water, wherein the concentrated water line and the desorption water line are switchably provided.

[0012] The amount of steam used for desorption varies depending on the target components in the water being treated. When difficult-to-desorb substances are present, a larger amount of steam is required, and the amount of concentrated water obtained by cooling and condensing the desorbed gas is correspondingly larger. The discharged concentrated water must be reprocessed in a secondary treatment facility or disposed of as industrial waste, increasing the cost of treating the concentrated water. However, with the above-described configuration of the present invention, at least a portion of the condensed water cooled and condensed in the condenser, which has a low concentration of the target substances, is returned as desorption water to the water treatment device, and at least a portion of the condensed water is discharged as concentrated water, thereby enabling a small amount of concentrated water to be discharged. This has the advantage of enabling the size of secondary treatment facilities for concentrated water to be reduced, and the disposal costs of disposing of concentrated water as industrial waste to be reduced.

[0013] 3. The water treatment device according to claim 1 or 2, wherein the first temperature is 100°C or higher and lower than 140°C, the second temperature is 140°C or higher and 450°C or lower, and the third temperature is 100°C or higher and lower than 140°C.

[0014] 4. The water treatment device according to any one of 1 to 3 above, further comprising a removal process between the adsorption process and the desorption process, in which adhering water on the adsorption element is removed and discharged as removed water, and a removed water line for supplying the removed water to the supply line.

[0015] By removing the adhering water, the subsequent desorption process can be carried out efficiently.

[0016] 5. The water treatment device according to any one of the above items 1 to 4, wherein the adsorption element contains at least one selected from the group consisting of granular activated carbon, activated carbon fiber, and zeolite.

[0017] In particular, when the adsorption element contains activated carbon fiber, the adsorption rate is faster, so that the target substance can be removed with high efficiency using a small amount, and a more economical water treatment device can be provided.

[0018] In the water treatment device of the present invention, the desorption treatment is divided into an early treatment at a first temperature, a high-temperature treatment at a second temperature higher than the first temperature, and a later treatment at a third temperature lower than the second temperature, and the supply temperature of the steam is raised and lowered in stages. This reduces the rate of change in thermal expansion and contraction of the piping and adsorption tank that come into contact with the steam, thereby suppressing cracks, deformation, etc. As a result, deterioration in the performance of the adsorption treatment and desorption treatment can be prevented, enabling highly efficient and stable continuous treatment.

[0019] The present invention relates to a water treatment device, and a method for treating water vapor in a water treatment system, and a method for treating water vapor in a water treatment system.

[0020] A water treatment device according to an embodiment of the present invention will be described below with reference to the drawings. In the following description, when reference is made to the number, amount, etc., the scope of the present invention is not necessarily limited to the number, amount, etc., unless otherwise specified. The same reference numerals are used for the same or equivalent parts, and redundant descriptions may not be repeated. It is intended from the outset that the configurations in the embodiments may be used in appropriate combinations.

[0021] First, referring to FIG. 1 , a water treatment device 100 according to the present embodiment will be described. The water treatment device 100 includes a first treatment tank 110 and a second treatment tank 120, each containing an adsorbent 111, 121 as an adsorption element. The adsorbents 111, 121 adsorb substances contained in the water to be treated by contacting the water. Therefore, in the water treatment device 100, the water to be treated is supplied to the adsorbents 111, 121, whereby the substances are adsorbed by the adsorbents 111, 121. The water to be treated is purified and discharged as treated water. Furthermore, the adsorbents 111, 121 desorb the adsorbed substances by contacting the water with steam. The water vapor and the desorbed adsorbed substances discharged from the first treatment tank 110 and the second treatment tank 120 are cooled and condensed by a condenser 130 and discharged as condensed water. The discharged condensed water is discharged outside the system as concentrated water, but a portion of the condensed water can be returned to the water to be treated as desorbed water.

[0022] Next, the connecting lines will be described. The first treatment tank 110 and the second treatment tank 120 are connected to a supply line for supplying the water to be treated (raw water), a discharge line for discharging the treated water, a steam line for supplying steam, a high-temperature steam line for supplying high-temperature steam, and a desorption gas line for discharging the desorption gas. The desorption gas line is also connected to a removed water line, a desorbed water line, and a concentrated water line, and each line is equipped with a valve, which is a flow path switching means for switching between connection and disconnection.

[0023] Next, flow path switching will be described. The water treatment device 100 includes a detector 140 and a control unit 150. The detector 140 is connected to one or more of the treatment tanks 110, 120, the adsorbents 111, 121, and the desorption gas line, and detects one or more of the temperature, humidity, pressure, flow rate, and concentration, and transmits the detected values ​​as physical property values ​​to the control unit 150. The control unit 150 issues a command to switch the water path by opening and closing a valve based on the physical property values. The control unit 150 may be provided with a timer and execute control based on the timer.

[0024] Next, the adsorption / desorption process will be described. The first treatment tank 110 and the second treatment tank 120 alternately function as an adsorption tank and a desorption tank by opening and closing the valves of the connected lines. While the first treatment tank 110 functions as an adsorption tank, the second treatment tank 120 functions as a desorption tank. Specifically, when a flow path is established so that the water to be treated (raw water) is supplied to the first treatment tank 110 and the treated water is discharged from the first treatment tank 110, the flow path is configured so that water vapor is supplied to the second treatment tank 120 and desorbed gas is discharged from the second treatment tank 120. The water treatment device 100 of this embodiment is configured so that adsorption and desorption processes alternate over time in each tank.

[0025] Next, the desorption process will be specifically described using the first treatment tank 110 as an example. As shown in FIG. 2 , the desorption process is performed in the following order: an initial process in which steam is supplied to the first treatment tank 110 at a first temperature, which is an initial temperature, to promote desorption of the target substance adsorbed on the adsorbent 111; a high-temperature process in which steam (high-temperature steam) at a second temperature higher than the first temperature is supplied to the first treatment tank 110 to desorb the target substance adsorbed on the adsorbent 111; and a later process in which steam at a third temperature lower than the second temperature is supplied to the first treatment tank 110 to cool the adsorbent 111. The desorbed gas discharged from the first treatment tank 110 during the desorption process is sent to the condenser 130. In FIG. 1 , steam at the first temperature and steam at the second temperature are introduced from the steam line, and high-temperature steam, which is steam at the second temperature, is introduced from the high-temperature steam line. These steam introduction lines may be a common line.

[0026] Although not shown, when the water treatment device 100 switches from the adsorption tank to the desorption tank, it is preferable to remove (dehydrate) the moisture adhering to the adsorbents 111, 121 and discharge it as removed water before starting desorption. This is because desorption efficiency can be improved by removing the adhering water from the adsorbents 111, 121 before desorption. Means for removing the adhering water include gravity removal, high-speed purging with high-pressure gas such as compressed air, nitrogen, or steam, and suction using a vacuum pump, but high-speed purging with steam is preferred. This is because no purge gas is generated by the purging process, so a separate gas treatment device is not required and desorption efficiency can be improved.

[0027] Furthermore, it is preferable that the removed water be returned to the water to be treated and treated again, since this eliminates the need to treat the removed water separately in a water treatment device.

[0028] Although two treatment tanks have been described in this embodiment, the number of treatment tanks is not particularly limited. For example, a single treatment tank may be used, and the water to be treated may be stored in a tank or the like during desorption and regeneration, and then adsorbed after desorption and regeneration. Alternatively, three treatment tanks may be used, and, for example, two treatment tanks may perform adsorption treatment while the remaining treatment tank performs desorption treatment, and these processes may be performed in sequence.

[0029] In this embodiment, the first temperature and the third temperature of the water vapor are preferably 100°C or higher and lower than 140°C. If the temperature is 100°C or higher, the water vapor does not condense and the amount of heat required to promote desorption can be obtained. If the temperature is lower than 140°C, there is no need to secondarily heat the water vapor, which is economically advantageous. The pressure of the water vapor is not particularly limited.

[0030] In this embodiment, the third temperature of the steam, i.e., the temperature of the high-temperature steam, is preferably 140°C or higher and 450°C or lower. At 140°C or higher, desorption of difficult-to-desorb substances can be easily performed, and at 450°C or lower, risks such as adsorbent embrittlement can be suppressed. Methods for supplying high-temperature steam include supplying high-pressure steam or secondarily heating low-pressure steam to produce superheated steam. Although not particularly limited, superheated steam is preferred from the viewpoint of avoiding the pressure-resistant structure of the treatment tank. Alternatively, a supply method in which the supply temperature is adjusted and gradually increased or decreased in temperature may also be used. This is because the thermal expansion and thermal contraction change rates of the piping and adsorption tank that come into contact with the steam can be mitigated.

[0031] In an embodiment of the present invention, difficult-to-desorb substances include inorganic substances such as sulfates, sulfides, and iron rust, organic polymers, organic oligomers, proteins, sugars, fatty acids, fatty acid esters, amines, amide compounds, oils and fats, resins, surfactants, and organic substances with a boiling point of 140°C or higher, such as high-boiling-point solvents. Examples include triethylene glycol and chemicals classified as perfluoroalkyl and polyfluoroalkyl compounds (PFAS) (PFOA, PFOS, PFBS, PFNA, PFHxS, PFCAs, FTOHs, etc.). Difficult-to-desorb substances also include organic substances that undergo polymerization during desorption and become resins on the surface of the adsorbent. Examples include cyclohexanone, acrylic esters, epichlorohydrin, and adipic acid.

[0032] By using the water treatment device described above, there is basically no need to replace the adsorbent, the cost of treating concentrated water can be reduced, the substances to be treated in the water to be treated can be continuously removed with high efficiency, and cracks and deformations in the adsorption tank can be suppressed, allowing for more stable continuous treatment.

[0033] The above-described embodiments disclosed herein are illustrative in all respects and are not limiting. The technical scope of the present invention is defined by the claims, and includes all modifications within the meaning and scope of the claims.

[0034] EXAMPLES The present invention will be described in detail below using examples, but the present invention is not limited to these examples. The methods for measuring various properties of the adsorption element in the examples are as follows.

[0035] The adsorbent was placed in a U-shaped tube for adsorption testing of the adsorption test apparatus shown in Figure 1 of Patent Document 3, the temperature was adjusted to 30°C, and nitrogen containing 3,000 ppm of toluene was flowed for 60 minutes, and the weight increase of the adsorption element was measured. The toluene adsorption rate q was calculated using the following formula.

[0036] q (weight %) = w1 / w2 × 100 where w1 is the weight increase (g) of the adsorption element and w2 is the mass (g) of the adsorption element.

[0037] The calculation method for thermal expansion and thermal contraction changes when the material that water vapor may come into contact with is SUS304 is as follows: Change rate (%) = (thermal expansion coefficient x 10^-6 x temperature change (°C)) x 100 The thermal expansion coefficient of SUS304 was calculated as 17.3.

[0038] The water to be treated in the examples and comparative examples contained triethylene glycol as the substance to be treated, and the concentration was determined by gas chromatography.

[0039] [Example] The following test was carried out as an example based on the water treatment device 100 shown in Figure 1. 200 g of activated carbon fiber with a toluene adsorption rate of 52% was placed in an adsorption tank as an adsorbent, and 200 L of water to be treated containing 300 mg / L of triethylene glycol was brought into contact with the adsorbent at a water temperature of 30°C to obtain an adsorbent that had adsorbed triethylene glycol.

[0040] Next, 115°C steam was supplied to the adsorption vessel to remove adhering water, and 115°C steam was supplied as the initial temperature steam for 1.3 minutes to perform desorption, after which the adsorbent was sampled and the toluene adsorption rate was measured. It was confirmed that the toluene adsorption rate had decreased to 45%. Next, 300°C steam was supplied as the high-temperature steam for 13 minutes to perform desorption, and the adsorbent was periodically sampled and the toluene adsorption rate was similarly measured. It was confirmed that the toluene adsorption rate had recovered to 51% after 13 minutes. The toluene adsorption rate measurement results are shown in Table 1.

[0041]

[0042] Next, steam at 300°C was supplied for 13 minutes to the adsorbent obtained in the same manner after desorption for 1.3 minutes with steam at 115°C, and the desorbed gas discharged from the adsorption tank was cooled and condensed in a condenser. The condensed water was periodically sampled and the triethylene glycol concentration was measured. During this period, the inlet and outlet temperatures of the adsorption tank were also measured.

[0043] From the results obtained above, the relationship between the 300°C steam supply time, the inlet temperature of the adsorption tank, the outlet temperature, the triethylene glycol concentration in the condensed water, and the toluene adsorption rate of the adsorbent was analyzed. This relationship is shown in Figure 2. During the 4 min period from 0 min after the start of high-temperature steam supply and the 1 min period from 12 min to 13 min, a total of 5 min, i.e., approximately 38% of the desorption time with high-temperature steam, no significant triethylene glycol concentration was detected, and the concentration was below 100 mg / L, lower than the concentration in the water being treated. Furthermore, during the 4 min period from 0 min after the start of 300°C steam supply, the outlet temperature of the adsorption tank remained around 106°C due to the influence of moisture adsorbed on the adsorbent and heat loss by the adsorption tank.

[0044] For example, if the triethylene glycol concentration in the condensed water obtained in the test is lower than that in the raw water, returning this water to the raw water as desorbed water will not increase the concentration in the raw water after the two flows, and since there is no effect on the adsorption performance of the water treatment device in terms of concentration, it is considered acceptable to return it.Here, as shown in Table 2, it was estimated that by returning 38% of the condensed water to the raw water as desorbed water and discharging the remaining 62% to the system as concentrated water, it would be possible to reduce the amount of concentrated water by 38%.

[0045] 2, the temperature at the outlet of the adsorption tank was maintained at 106°C, which is close to the boiling point of water, 100°C, from 0 min to 4 min after the start of the supply of high-temperature steam at 300°C. This result suggests that the removal of moisture contained in the adsorption tank and adsorbent was insufficient, and that if the purpose is to remove moisture, the steam supplied does not need to be high in temperature.

[0046] The results showed that the toluene adsorption rate recovered to 50% 9 minutes after the start of high-temperature steam supply, and to 51% after 13 minutes. The recovery trend of the toluene adsorption rate suggests that desorption was sufficient after 9 minutes. The results also showed that the triethylene glycol concentration between 12 and 13 minutes dropped to 100 mg / L or less, which was lower than the concentration in the water being treated. These results suggest that the steam supplied after 12 minutes does not need to be high-temperature steam. In other words, it is believed that steam with a temperature lower than that of high-temperature steam can be used in the later stages of the desorption process.

[0047] Here, if 115°C steam is used for a total of 5 minutes (4 minutes from 0 to 4 minutes and 1 minute from 12 to 13 minutes) out of the 13 minutes in which 300°C steam is used, it is estimated that the energy consumed by high-temperature steam can be reduced by 38%. In other words, it can be seen that energy can be reduced by using steam at a lower temperature than high-temperature steam in the early and late stages of the desorption process.

[0048] Furthermore, as shown in Figure 2, the results show a correlation between the increase in temperature at the adsorption tank outlet and the tendency for the increase in the triethylene glycol concentration in the condensed water. For example, a method using temperature detection may be considered as a means for separating low-concentration and high-concentration condensed water. The detection method may be to install a thermometer on the surface of the adsorbent in the adsorption tank, at the bottom of the adsorption tank, or in the desorption gas line, etc.

[0049] The rate of change in thermal expansion and contraction was calculated for the following cases: the temperature of the water to be treated in the adsorption treatment was 30°C, the steam in the early stage of the desorption treatment was 115°C, the steam in the high-temperature treatment in the desorption treatment was 300°C, and the steam in the later stage of the desorption treatment was 115°C; and the material that the steam may come into contact with was SUS304. As a result, the maximum rate of change was 0.32. This is shown in Table 3. A small rate of change can suppress deformation and cracking of the adsorption tank, allowing for stable adsorption and desorption treatment.

[0050] [Comparative Example] In the Comparative Example, the same water treatment device as in the Example was used, but as shown in Figure 3, the desorption treatment was performed using steam at 300°C for the same period as the desorption treatment period in Example 1. In addition, in the Comparative Example, all of the condensed water obtained by cooling and condensing the desorbed gas was discharged outside the system as concentrated water. As shown in Table 2, the amount of concentrated water in the Comparative Example was 1.6 times greater than in the Example. Furthermore, it was estimated that the energy consumed for high-temperature steam in the Comparative Example was 1.6 times greater than in the Example.

[0051] In the comparative example, the water temperature in the adsorption treatment was 30°C, the water vapor temperature in the desorption treatment was always 300°C, and the material that could come into contact with water vapor was SUS304, and the rate of change in thermal expansion and contraction was calculated. As a result, the maximum rate of change was 0.47, which, as shown in Table 3, was higher than that of the examples.

[0052]

[0053]

[0054] The water treatment device of the present invention can be used as a device for removing substances to be treated from industrial wastewater discharged from various factories, research facilities, etc., leachate discharged from final disposal sites, groundwater, etc., and can make a great contribution to industry.

[0055] 100: Water treatment device, 110: First treatment tank, 111: Adsorbent, 120: Second treatment tank, 121: Adsorbent, 130: Condenser, 140: Detector, 150: Control unit.

Claims

1. A water treatment device comprising an adsorption element and a supply line for supplying water to be treated containing a substance to be treated to the adsorption element, and which repeats an adsorption process in which the water to be treated is brought into contact with the adsorption element to adsorb the substance to be treated and then discharge the treated water, and a desorption process in which steam is brought into contact with the adsorption element to desorb the substance to be treated and then discharge desorbed gas, characterized in that the desorption process sequentially involves an early process in which the steam is introduced at a first temperature, which is an initial temperature; a high-temperature process in which the steam is introduced at a second temperature higher than the first temperature; and a later process in which the steam is introduced at a third temperature lower than the second temperature.

2. The water treatment device according to claim 1, comprising: a concentrated water line for discharging the desorption gas as concentrated water to the outside of the system; and a desorption water line for introducing the desorption gas as desorption water into the supply line, wherein the concentrated water line and the desorption water line are switchable.

3. A water treatment device according to claim 1 or 2, wherein the first temperature is 100°C or higher and lower than 140°C, the second temperature is 140°C or higher and lower than 450°C, and the third temperature is 100°C or higher and lower than 140°C.

4. A water treatment device as described in claim 1 or 2, characterized in that a removal process is carried out between the adsorption process and the desorption process to remove water adhering to the adsorption element and discharge it as removed water, and that a removed water line is provided to supply the removed water to the supply line.

5. The water treatment device according to claim 1 or 2, wherein the adsorption element contains at least one selected from the group consisting of granular activated carbon, activated carbon fiber, and zeolite.

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