CN113149158B - System for desalinating brackish water by using pure capacitance deionization technology and method for desalinating brackish water by using system - Google Patents

Abstract

The invention discloses a system for desalting brackish water by using a pure capacitance deionization technology and a method for desalting the brackish water by using the system. The system comprises a sedimentation tank, a filter tank, a first desalination module, a second desalination module, an alternating current and direct current power supply and a waste liquid tank. The method for desalinating the brackish water by using the system comprises the following steps: the brackish water stock solution is precipitated and filtered and then is introduced into a first desalination module to prepare fresh water, when the electrode adsorption capacity of the first desalination module is close to saturation, the electrodes of the first desalination module are subjected to desorption regeneration, and meanwhile, a second desalination module starts to perform adsorption desalination according to the mode of the first desalination module. The AC/DC power supply supplies DC power during adsorption and AC power during desorption. The system only uses a capacitive deionization technology, does not need to be combined with other fresh water preparation technologies, the two modules work simultaneously to alternately perform adsorption and desorption, a reverse power supply is not needed during desorption, and continuous and efficient fresh water production can be realized.

Description

A system for desalinating brackish water using pure capacitive deionization technology and method for desalinating brackish water

technical field

The invention belongs to the field of water treatment, and in particular relates to the utilization of unconventional water resources, in particular to a system for desalinating brackish water using capacitive deionization technology and a method for using the system to desalinate brackish water.

Background technique

At present, about one tenth of the world's population has no access to clean drinking water, and since the beginning of the new century, the problem of water resources has become more and more serious. It is urgent to comprehensively change the way of water resources utilization and actively develop and utilize unconventional water sources such as reclaimed water, mine water and seawater. Traditional saltwater desalination technologies, such as reverse osmosis, electrodialysis and ion exchange, have been difficult to achieve due to the problems of high energy consumption, high cost and secondary pollution that cannot be ignored. Capacitive desalination technology, namely capacitive deionization technology (CDI), also known as electrosorption, it removes ions in solution by electrosorption by forming an electric field between porous electrode materials. It has the advantages of high desalination efficiency, low energy consumption, and environmental friendliness. It is a new type of salt water desalination technology that has received increasing attention with the development of carbon material science in recent decades. The emergence of capacitive desalination technology makes up for the shortcomings of traditional seawater desalination technology, and makes low-energy consumption, high-efficiency desalination technology a realistic possibility.

CN111875007A discloses a scale-resistant electro-adsorption system suitable for high-hardness wastewater. The system includes a first adsorption module, a second adsorption module, a raw water tank, a first regeneration water tank, a second regeneration water tank, a fresh water tank, a water pump, valve. The original water tank is used to store the original wastewater, the first adsorption module and the second adsorption module are used to adsorb the original wastewater to obtain the initial treated water; the first regeneration water tank and the second regeneration water tank are used for the circulating desorption regeneration of the adsorption module and the concentrated solution of discharge. Compared with other membrane concentration reduction technologies, the system has better tolerance to the water hardness index. There is no need to soften the actual wastewater before treatment, only simple clarification can be performed, which can avoid problems such as hardness scaling on the electrode surface and fouling of the flow channel. However, the adsorption and desorption of the system cannot be carried out at the same time, the fresh water cannot be continuously produced during the desorption, and the working efficiency of the system is not high enough.

CN111718052A discloses a method for desalination of brackish water, which includes the following steps: introducing brackish water into a water collecting well; introducing the brackish water in the collecting well into a filter tank through a water pump for filtering; the filtered brackish water enters a first Capacitive deionization device is connected to the power supply of the first capacitive deionization device, and the positive and negative ions in the bitter and salty aqueous solution are adsorbed on the electrodes of the first capacitive deionization device to achieve desalination and reduce the ion concentration in the bitter and salty aqueous solution; desalination The resulting brackish water passes through the reverse osmosis device under the action of the high-pressure pump to obtain fresh water; the first capacitive deionization device and the second capacitive deionization device are used in parallel, when the first capacitive deionization device is reversely connected to desorb ions , the second capacitor deionization device continues to perform the desalination work to improve the desalination efficiency. Although this method can continue the desalination treatment while the electrode is regenerated, it needs to combine the capacitive deionization technology with the reverse osmosis technology to prepare qualified fresh water. The inorganic fouling on the permeable membrane surface is fast, requiring frequent cleaning and replacement of membrane elements; and the use of solar collectors to evaporate the recovered brackish water is greatly affected by the climate, and the conversion efficiency is low; there are too many devices, and the The equipment required in industrial continuous production occupies a large area.

SUMMARY OF THE INVENTION

In order to overcome the above problems in the prior art, the present invention provides a system for desalinating brackish water using pure capacitive deionization technology and a method for desalinating brackish water.

The system includes a sedimentation tank, a filter tank, a first desalination module, a second desalination module, an AC and DC power supply, and a waste liquid pool;

The first desalination module includes a first coarse desalination device and a first fine desalination device; the sedimentation tank, the filter tank, the first coarse desalination device, and the first fine desalination device are sequentially connected through a first pipeline; the filter tank, A first valve is arranged between the first coarse desalination device; a first water pump is arranged between the first coarse desalination device and the first fine desalination device; the water outlet of the first fine desalination device is sequentially arranged with a second valve , the first conductivity meter and the third valve;

The second desalination module includes a second coarse desalination device and a second fine desalination device; the sedimentation tank, the filter tank, the second coarse desalination device, and the second fine desalination device are sequentially connected through a second pipeline; the filter tank, A sixth valve is arranged between the second coarse desalination device; a second water pump is arranged between the second coarse desalination device and the second fine desalination device; the water outlet of the second fine desalination device is sequentially arranged with a seventh valve , the second conductivity meter and the eighth valve;

A third pipeline and a fourth pipeline are additionally provided, one end of the third pipeline is connected between the first valve and the first rough desalination device, and a fifth valve is arranged on the third pipeline; the One end of the fourth pipeline is connected between the sixth valve and the second rough desalination device, and the fourth pipeline is provided with a tenth valve;

A fifth pipeline and a sixth pipeline are additionally provided. One end of the fifth pipeline is connected between the first conductivity meter and the third valve, and the other end is connected to the waste liquid pool. The pipeline is provided with a fourth valve; one end of the sixth pipeline is connected between the second conductivity meter and the eighth valve, and the other end is connected with the waste liquid pool, and the sixth pipeline is provided with a fourth valve. There is a ninth valve;

The AC/DC power supply is provided with a first interface, a second interface, a third interface and a fourth interface; the first coarse desalination device, the first fine desalination device, the second coarse desalination device, and the second fine desalination device are all set There are two electrode plates; the first coarse desalination device is connected to the first interface, the first fine desalination device is connected to the second interface, and the second coarse desalination device is connected to the third interface , the second fine desalination device is connected to the fourth interface.

Preferably, the electrode plates of the first rough desalination device and the electrode plates of the second rough desalination device are made of carbon nanotubes, activated carbon or graphene.

Preferably, the electrode plates of the first fine desalination device and the electrode plates of the second fine desalination device are made of metal-organic framework carbon nanotube hybrid materials or metal-organic framework polypyrrole hybrid materials.

Preferably, in step S1, the sedimentation tank is a horizontal flow or radial flow or vertical flow sedimentation tank; the filter tank is a flat filter tank or a filter tank or a filter bag.

Preferably, the first valve, the second valve, the third valve, the fourth valve, the fifth valve, the sixth valve, the seventh valve, the eighth valve, the ninth valve and the tenth valve are all check valves. Use a check valve to prevent backflow of liquid in the line.

A method for desalinating brackish water by a system for desalinating brackish water using pure capacitive deionization technology described in any of the above, comprising the following steps:

S1, introduce the brackish water stock solution into the sedimentation tank for precipitation; then introduce the supernatant into the filter tank for filtration to obtain impurity-free brackish water;

S2, open the first valve, the second valve and the third valve, introduce the impurity-free brackish water obtained in step S1 into the first rough desalination device at a flow rate of 0.5～2cm/s, and simultaneously make the first rough desalination device and the first rough desalination device. The fine desalination device is respectively connected with the first interface and the second interface of the AC and DC power supply, and the AC and DC power supply is fed with DC power; the first water pump is started once every minute, and the liquid flow rate is maintained at 0.5 ~ 2cm/s; The brackish water after the adsorption and desalination of the coarse desalination device is input into the first fine desalination device by the first water pump to continue the adsorption and desalination; the water flowing out of the first fine desalination device is detected by the first conductivity meter, and if the conductivity is less than the preset threshold value A, Then the water flows out through the third valve to get fresh water;

S3. If the conductivity is greater than or equal to A in step S2, close the third valve and open the fourth valve at the same time to discharge the water with conductivity greater than or equal to A into the waste pool; close the first valve, open the fifth valve, and set the flow rate to 6 -12cm/s pulse inflow to the first rough desalination device to introduce flushing liquid; switch the output current of the AC and DC power supply to alternating current; the starting frequency of the first water pump is consistent with the frequency of the flushing liquid pulse inflow, and increase the first water pump When the flow rate reaches 6-12cm/s, the waste liquid in the first desalination module is discharged to the waste liquid pool; when the conductivity detected by the first conductivity meter is less than the preset threshold B, the fifth valve is closed, and the first desalination module In a standby state; while closing the first valve and opening the fifth valve, open the sixth valve, the seventh valve and the eighth valve, and introduce the impurity-free brackish water obtained in step S1 into the second valve at a flow rate of 0.5～2cm/s Coarse desalination device, connect the second coarse desalination device and the second fine desalination device with the third interface and the fourth interface of the AC/DC power supply respectively, and supply the DC power to the AC/DC power supply; the second water pump is started once every minute, and the Keep the liquid flow rate at 0.5-2cm/s; the brackish water after adsorption and desalination by the second coarse desalination device is fed into the second fine desalination device by the second water pump to continue the adsorption and desalination; the water flowing out of the second fine desalination device passes through the second electrical conductivity. If the conductivity is less than A, the water flows out through the eighth valve to obtain fresh water;

S4. If the conductivity of the water flowing out of the second fine desalination device in step S3 is greater than or equal to A, then close the eighth valve, open the ninth valve, and discharge the water with conductivity greater than or equal to A into the waste liquid pool, and make the first desalination module Repeat step S2; at the same time close the sixth valve, open the tenth valve, and introduce the flushing liquid to the second coarse desalination device with a pulse inflow with a flow rate of 6-12 cm/s; switch the output current of the AC-DC power supply to 0.1-1.0 Hz AC ; The starting frequency of the second water pump is consistent with the pulse inflow frequency of the flushing liquid, and the flow rate of the second water pump is increased to 6-12cm/s, and the waste liquid in the second desalination module is discharged to the waste liquid pool; when the second conductivity When the conductivity detected by the rate meter is less than B, the tenth valve is closed, and the second desalination module is in a standby state.

The technical scheme of the present invention only uses the capacitive deionization technology to desalinate the brackish water, without using other desalination technologies such as reverse osmosis technology, electrodialysis technology, multi-effect evaporation or ion exchange technology, etc., it can achieve the purpose of treating brackish water. Its conductivity complies with the regulations. After the water flowing out of the first fine desalination device is detected by the first conductivity meter, if the conductivity is less than the preset threshold value A, it is considered that the fresh water prepared by the first desalination module meets the requirements; according to the required fresh water quality, the threshold value A It can be set to different values, A≤2000μS/cm; if the conductivity ≥A, it means that the adsorption of the electrode plate in the first desalination module is saturated, and the electrode needs to be desorbed and regenerated. At this time, close the third valve and open the fourth valve , so that the water with unqualified conductivity is discharged into the waste liquid pool; then open the fifth valve, so that the flushing liquid enters the first desalination module, and the AC and DC power supply outputs ultra-low frequency AC to the first coarse desalination device and the first fine desalination device. , so that the ions on the electrode plate are desorbed; the power supply does not need to be reversed during the process from adsorption to desorption. The conductivity of the wastewater generated after desorption by the first desalination module is detected by the first conductivity meter. If the conductivity is less than the preset threshold B, it means that the electrode plate desorption meets the requirements and can be used for subsequent adsorption and desalination. Threshold B is much smaller than threshold A. When the first desalination module performs desorption, the second desalination module starts adsorption work at the same time, and the work flow is the same as that of the first desalination module. Similarly, it is judged whether the electrode plate in the second desalination module needs to be desorbed according to the detection result of the second conductivity meter. The desalination module performs adsorption work; the two modules are used alternately, which can continuously produce fresh water and improve work efficiency. The desorption process in the first desalination module and the second desalination module uses ultra-low frequency alternating current to repeatedly change the direction of the electric field between the electrode plates to prevent the desorbed ions from attaching to the electrode plates again, and to increase the pumping speed of the water pump. The timely flushing out prevents the desorbed ions from being re-adsorbed to the other plate. When the liquid in the waste liquid pool is close to full capacity, the waste liquid is discharged and handed over to a professional department for processing.

Preferably, the AC and DC power supply can provide DC power with a voltage between 1.0-2.0V and AC power with a frequency of 0.1-1.0Hz.

Preferably, when the first desalination module performs desorption, and when the second desalination module performs desorption, the output currents of the AC and DC power sources are both 0.1 Hz AC.

Preferably, when the first desalination module performs adsorption in step S2, the flow rate of impurity-free brackish water is 1 cm/s, and the speed of water pumped by the first water pump is 1 cm/s; when the second desalination module performs adsorption in step S3, there is no The flow rate of impurity brackish water is 1cm/s, and the speed of the second water pump is 1cm/s.

Preferably, when the first desalination module is desorbing in step S3, the flow rate of the flushing liquid is 10 cm/s, and the speed of the first water pump is 10 cm/s; when the second desalting module is desorbed in step S4, the washing The flow rate of the liquid was 10 cm/s, and the speed of the second water pump was 10 cm/s.

Preferably, the flushing liquid used in the desorption of the first desalination module and the second desalination module is tap water, distilled water or purified water.

Compared with the prior art, the advantages of the present invention are:

(1) The brackish water desalination system of the present invention does not need to use other equipment such as reverse osmosis device, electrodialysis device, ion exchange device, etc. The entire desalination process is purely realized by capacitive deionization technology, using a low-voltage AC and DC power supply of 1.0-2.0V Power supply, extremely low energy consumption, high water utilization rate, and no secondary pollution; (2) The entire desorption process does not require reverse power supply; when desorbing ions, the electrode plate is repeatedly changed by using 0.1-1.0Hz ultra-low frequency alternating current. The direction of the electric field prevents the desorbed ions from attaching to the electrode plate again, increases the pumping speed of the water pump, and flushes out the desorbed ions in time while preventing the desorbed ions from being adsorbed to the other electrode plate again; (3) Two The alternate use of desalination modules improves the work efficiency; the device is simple, and does not require too many bulky and demanding equipment; the role of the salt electrode reduces the cost of the entire equipment at the same time.

Description of drawings

Fig. 1 is the system that the present invention uses pure capacitive deionization technology to desalinate brackish water;

FIG. 2 is a schematic diagram of adsorption of ions by electrode plates of the system for desalinating brackish water according to the present invention.

In the figure: 1, sedimentation tank; 2, filter tank; 3, the first desalination module; 31, the first coarse desalination device; 311, the first electrode plate; 312, the second electrode plate; 32, the first fine desalination device; 33, the first water pump; 4, the second desalination module; 41, the second coarse desalination device; 42, the second fine desalination device; 43, the second water pump; 5, the AC and DC power supply; 51, the first interface; Second port; 53, third port; 54, fourth port; 6, waste pool; 34, first valve; 35, second valve; 36, third valve; 37, fourth valve; 38, fifth valve ;44, the sixth valve; 45, the seventh valve; 46, the eighth valve; 47, the ninth valve; 48, the tenth valve; Y1, the first conductivity meter; Y2, the second conductivity meter; K1, the first conductivity meter A switch; K2, the second switch; K3, the third switch; K4, the fourth switch.

Detailed ways

The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention. Any equivalent transformation or substitution made by those skilled in the art according to the following embodiments falls within the protection scope of the present invention.

Example 1

As shown in FIG. 1 , the system for desalinating brackish water using pure capacitive deionization technology in this embodiment includes a sedimentation tank 1, a filter tank 2, a first desalination module 3, a second desalination module 4, an AC and DC power supply 5, a waste Liquid pool 6; the first desalination module 3 includes a first rough desalination device 31, a first fine desalination device 32, a first water pump 33, a first conductivity meter Y1, a first valve 34, a second valve 35, a third The valve 36, the fourth valve 37 and the fifth valve 38; the first valve 34 and the fifth valve 38 are arranged at the water inlet of the first crude desalination device 31, and the second valve 35 is arranged at the water inlet of the first crude desalination device 31. The water outlet of the first fine desalination device 32, the first conductivity meter Y1 is set between the second valve 35 and the third valve 36, and the fourth valve 37 is set at the first conductivity between the instrument Y1 and the waste liquid pool 6; the second desalination module 4 includes a second coarse desalination device 41, a second fine desalination device 42, a second water pump 43, a second conductivity meter Y2, and a sixth valve 44 , the seventh valve 45, the eighth valve 46, the ninth valve 47 and the tenth valve 48; the sixth valve 44 and the tenth valve 48 are arranged at the water inlet of the second rough desalination device 41, the The seventh valve 45 is arranged at the water outlet of the second fine desalination device 42, the second conductivity meter Y2 is arranged between the seventh valve 45 and the eighth valve 46, and the ninth valve 47 It is arranged between the second conductivity meter Y2 and the waste liquid pool 6; the AC/DC power supply 5 is provided with a first interface 51, a second interface 52, a third interface 53 and a fourth interface 54; the The first rough desalination device 31, the first fine desalination device 32, the second rough desalination device 41, and the second fine desalination device 42 are all provided with two electrode plates; The first interface 51 is connected, the first fine desalination device 32 is connected with the second interface 52, the second coarse desalination device 41 is connected with the third interface 53, and the second fine desalination device 32 is connected with the third interface 53. The desalination device 42 is connected with the fourth interface 54; the first water pump 33 is arranged between the first coarse desalination device 31 and the first fine desalination device 32, and the second water pump 43 is arranged at the between the second rough desalination device 41 and the second fine desalination device 42; the sedimentation tank 1 and the filter tank 2 are connected with the water inlet of the first rough desalination device 31, and the sedimentation tank Both the tank 1 and the filter tank 2 communicate with the water inlet of the second rough desalination device 41 .

The method for desalinating brackish water in the above-mentioned system comprises the following steps:

S1, as shown in Figure 1, the salt lake water is introduced into the advection sedimentation tank for precipitation to make it completely precipitate; then the supernatant is introduced into the filter tank for filtration to obtain impurity-free brackish water;

S2, open the first valve 34, the second valve 35, and the third valve 36, and the remaining valves are in a closed state; the first rough desalination device 31 is connected to the first interface 51 of the AC and DC power supply 5 through the first switch K1, and the first fine The desalination device 32 is connected with the second interface 52 of the AC/DC power supply 5 through the second switch K2; 1.2V direct current is fed into the first interface 51 and the second interface 52; the brackish water flows through the first valve 34 at a speed of 1cm/s. The first desalination module 3 performs the first ion adsorption through the first rough desalination device 31. The adsorption principle is shown in FIG. 2, the anions move to the first electrode plate 311, and the cations move to the second electrode plate 312; The electrode plate of the desalination device 31 is made of carbon nanotubes; the water from the first rough desalination device 31 is accelerated by the first water pump 33 to keep the water flow velocity at a speed of 1 cm/s and flows to the first fine desalination device 32 to further reduce the salt in the water. Ion concentration; the electrode plate of the first fine desalination device 32 is made of metal-organic framework carbon nanotubes; the water flowing out from the first fine desalination device 32 is detected by the first conductivity meter Y1, and the detection result is less than the preset threshold A When the third valve 36 is opened, the fresh water is discharged; the conductivity of the water is less than 2000μS/cm stipulated in the "Drinking Water Sanitation Standard GB5749-2006"; the threshold A is set according to the requirements of the required fresh water quality, but cannot exceed 2000μS/cm ;

S3. If the detection result of the first conductivity meter Y1 is greater than or equal to A, close the third valve 36, open the fourth valve 37, and discharge the unqualified water into the waste liquid pool; at the same time, close the first valve 34 and open the fifth valve 37. The valve 38 introduces tap water into the first rough desalination device at a speed of 10cm/s, a frequency pulse inflow of 10 seconds each time; and the output current of the first interface 51 and the second interface 52 of the AC and DC power supply 5 is adjusted to a frequency of The ultra-low frequency alternating current of 0.1Hz desorbs ions on the electrode plate; the pumping speed of the first water pump 33 is increased to 10cm/s, and the opening and closing interval of the first water pump 33 is adjusted to 10 seconds. When the detection result of the first conductivity meter Y1 When it is less than the preset threshold value B, the regeneration of the electrode is realized, the fifth valve 38 is closed, and the first desalination module 3 is in a standby state; while closing the first valve 34 and opening the fifth valve 38, open the sixth valve 44, the first Seven valves 45 and eighth valves 46, the impurity-free brackish water obtained in step S1 is introduced into the second rough desalination device 41 at a flow rate of 1cm/s, and the second rough desalination device 41 and the second fine desalination device 42 are respectively The third interface 53 of the AC/DC power supply 5 is connected with the fourth interface 54, and the AC/DC power supply 5 is fed with direct current; the second water pump 43 is started once per minute, and the liquid flow rate is maintained at 1cm/s; The brackish water after the adsorption and desalination of the device 41 is input into the second fine desalination device 42 by the second water pump 43 to continue the adsorption and desalination; the water flowing out of the second fine desalination device 42 is detected by the second conductivity meter Y2, if the conductivity <A, then The water flows out through the eighth valve 46 to obtain fresh water;

S4. If the detection result of the second conductivity meter Y2 is greater than or equal to A, close the eighth valve 46, open the ninth valve 47, discharge the unqualified water into the waste liquid pool, and repeat step S2 for the first desalination module; The sixth valve 44 is closed, the tenth valve 48 is opened, and tap water is introduced into the second rough desalination device 41 at a speed of 10cm/s and a frequency pulse of 10 seconds each time, and the third interface 53 of the AC and DC power supply 5 and The output current of the fourth interface 54 is adjusted to the ultra-low frequency alternating current with a frequency of 0.1Hz to desorb the ions on the electrode plate; the pumping speed of the second water pump 43 is increased to 10cm/s, and the opening and closing interval of the second water pump 43 is adjusted to 10 seconds, When the detection result of the second conductivity meter Y2 is less than B, the regeneration of the electrode is realized, the tenth valve 48 is closed, and the second desalination module is in a standby state.

The first desalination module 3 and the second desalination module 4 perform continuous and uninterrupted preparation of fresh water by alternately repeating adsorption and desorption.

Example 2

The system and steps for desalting brackish water in this embodiment are basically the same as those in Embodiment 1, except that: in step S2, the speed at which the brackish water flows into the first rough desalination device 31 is 0.5 cm/s, and the first water pump 33 pumps water. The speed of the first desalination module 3 is 0.5cm/s, and 1.0V direct current is fed into the first interface 51 and the second interface 52 of the AC and DC power supply 5; The current output by the power source 5 is 0.5Hz alternating current, and the speed of the first water pump 33 pumping water is 6cm/s; in step S3, the speed at which the brackish water flows into the second coarse desalination device 41 is 0.5cm/s, and the second water pump 43 pumps water. The speed of the second desalination module 4 is 0.5cm/s, and 1.0V direct current is passed to the third interface 53 and the fourth interface 54 of the AC and DC power supply 5; The current output by the power source 5 is 0.5 Hz alternating current, and the speed of the second water pump 43 is 6 cm/s.

Example 3

This embodiment is the same as that of Embodiment 1, except that: in step S2, the speed at which brackish water flows into the first rough desalination device 31 is 2 cm/s, the speed at which the first water pump 33 pumps water is 2 cm/s, and the speed at which the first water pump 33 pumps water is 2 cm/s. The first interface 51 and the second interface 52 of the DC power supply 5 are connected to 2.0V direct current; in step S3, the flow rate of the flushing liquid during the desorption of the first desalination module 3 is 12cm/s, and the current output by the AC and DC power supply 5 is 1.0Hz alternating current, The speed at which the first water pump 33 pumps water is 12cm/s; in step S3, the speed at which the brackish water flows into the second coarse desalination device 41 is 2cm/s, and the speed at which the second water pump 43 pumps water is 2cm/s, and the AC/DC power supply is supplied at a speed of 2cm/s. 5. The third interface 53 and the fourth interface 54 are connected to 2.0V direct current; in step S4, the flow rate of the flushing liquid during the desorption of the second desalination module is 12cm/s, the current output by the AC and DC power supply 5 is 1.0Hz alternating current, and the second water pump 43 The speed of pumping water is 12cm/s.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Various modifications and variations of the present invention are possible for anyone skilled in the art. Any simple equivalent changes and modifications made according to the protection scope of the application of the present invention and the contents of the description shall be included within the protection scope of the present invention.

Claims (8)

1. A system for desalting brackish water by using a pure capacitance deionization technology is characterized by comprising a sedimentation tank, a filter tank, a first desalting module, a second desalting module, an AC/DC power supply and a waste liquid tank;

the first desalination module comprises a first coarse desalination device and a first fine desalination device; the sedimentation tank, the filtering tank, the first coarse desalting device and the first fine desalting device are sequentially connected through a first pipeline; a first valve is arranged between the filter tank and the first coarse desalting device; a first water pump is arranged between the first coarse desalting device and the first fine desalting device; a water outlet of the first fine desalting device is sequentially provided with a second valve, a first conductivity meter and a third valve;

the second desalting module comprises a second coarse desalting device and a second fine desalting device; the sedimentation tank, the filtering tank, the second coarse desalting device and the second fine desalting device are sequentially connected through a second pipeline; a sixth valve is arranged between the filter tank and the second coarse desalting device; a second water pump is arranged between the second coarse desalting device and the second fine desalting device; a seventh valve, a second conductivity meter and an eighth valve are sequentially arranged at the water outlet of the second fine desalting device;

a third pipeline and a fourth pipeline are additionally arranged, one end of the third pipeline is connected between the first valve and the first coarse desalting device, and a fifth valve is arranged on the third pipeline; one end of the fourth pipeline is connected between the sixth valve and the second coarse desalting device, and a tenth valve is arranged on the fourth pipeline;

a fifth pipeline and a sixth pipeline are additionally arranged, one end of the fifth pipeline is connected between the first conductivity meter and the third valve, the other end of the fifth pipeline is connected with the waste liquid pool, and a fourth valve is arranged on the fifth pipeline; one end of the sixth pipeline is connected between the second conductivity meter and the eighth valve, the other end of the sixth pipeline is connected with the waste liquid pool, and a ninth valve is arranged on the sixth pipeline;

the alternating current and direct current power supply is provided with a first interface, a second interface, a third interface and a fourth interface; the first coarse desalting device, the first fine desalting device, the second coarse desalting device and the second fine desalting device are all provided with two electrode plates; the first coarse desalting device is connected with the first interface, the first fine desalting device is connected with the second interface, the second coarse desalting device is connected with the third interface, and the second fine desalting device is connected with the fourth interface;

the alternating current and direct current power supply can provide direct current with the voltage of 1.0-2.0V and alternating current with the frequency of 0.1-1.0 Hz;

the method for desalting the brackish water by using the system for desalting the brackish water by using the pure capacitance deionization technology comprises the following steps of:

s1, introducing the brackish water stock solution into a sedimentation tank for sedimentation; then introducing the supernatant into a filtering tank for filtering to obtain impurity-free brackish water;

s2, opening a first valve, a second valve and a third valve, introducing the impurity-free brackish water obtained in the step S1 into a first coarse desalting device at a flow rate of 0.5-2 cm/S, and simultaneously enabling the first coarse desalting device and a first fine desalting device to be respectively communicated with a first interface and a second interface of an alternating current/direct current power supply to supply direct current to the alternating current/direct current power supply; starting a first water pump once per minute, and keeping the flow rate of liquid at 0.5-2 cm/s; the brackish water after being adsorbed and desalted by the first coarse desalting device is input into the first fine desalting device by a first water pump for continuous adsorption and desalting; the water flowing out of the first fine desalting device is detected by a first conductivity meter, and if the conductivity is smaller than a preset threshold value A, the water flows out of a third valve to obtain fresh water;

s3, if the conductivity is larger than or equal to A in the step S2, closing the third valve, and simultaneously opening the fourth valve to discharge the water with the conductivity larger than or equal to A into a waste liquid pool; closing the first valve, opening the fifth valve, and introducing washing liquid into the first coarse desalting device by pulse inflow with the flow speed of 6-12 cm/s; switching the output current of the AC/DC power supply into AC; the starting frequency of the first water pump is kept consistent with the frequency of flushing liquid pulse inflow, the flow speed of the first water pump is increased to 6-12cm/s, and the waste liquid in the first desalination module is discharged to a waste liquid pool; when the conductivity detected by the first conductivity meter is smaller than a preset threshold value B, the fifth valve is closed, and the first desalination module is in a standby state; opening a sixth valve, a seventh valve and an eighth valve while closing the first valve and opening the fifth valve, introducing the impurity-free brackish water obtained in the step S1 into a second coarse desalting device at a flow rate of 0.5-2 cm/S, and communicating the second coarse desalting device and a second fine desalting device with a third interface and a fourth interface of an alternating current/direct current power supply respectively to supply direct current to the alternating current/direct current power supply; the second water pump is started once per minute, and the flow speed of the liquid is kept at 0.5-2 cm/s; the brackish water after being adsorbed and desalted by the second coarse desalting device is input into the second fine desalting device by a second water pump for continuous adsorption and desalting; the water flowing out of the second fine desalting device is detected by a second conductivity meter, and if the conductivity is less than A, the water flows out of the eighth valve to obtain fresh water;

s4, if the conductivity of the water flowing out of the second fine desalination device in the step S3 is larger than or equal to A, closing the eighth valve, opening the ninth valve, discharging the water with the conductivity larger than or equal to A into a waste liquid pool, and desorbing the second desalination module according to the step of desorbing by the first desalination module in the step S3; simultaneously, the first desalination module repeats the adsorption step in the step S2 to prepare fresh water; the adsorption and desorption processes of the first and second desalination modules are then repeated according to steps S2-S3-S4-S2.

2. The system for desalinating brackish water according to claim 1, wherein the electrode plates of the first coarse desalination device and the electrode plates of the second coarse desalination device are made of carbon nanotubes, activated carbon or graphene.

3. The system for desalinating brackish water using pure capacitive deionization (CPDI) technology according to claim 1, wherein the electrode plates of the first and second fine desalination devices are made of metal-organic framework carbon nanotube hybrid material or metal-organic framework polypyrrole hybrid material.

4. The system for desalinating brackish water according to claim 1, wherein the sedimentation tank in step S1 is a horizontal flow type sedimentation tank, a radial flow type sedimentation tank, or a vertical flow type sedimentation tank; the filtering tank is a flat filtering tank or a filtering bag.

5. The system for desalinating brackish water according to claim 1, wherein the ac/dc power supply outputs a current of 0.1Hz ac when the first desalination module is performing desorption and a current of the second desalination module is performing desorption.

6. The system for desalinating brackish water according to claim 1, wherein the flow rate of the impurity-free brackish water is 1cm/S and the first water pump pumps water at 1cm/S during the adsorption of the first desalination module in step S2; when the second desalination module performs adsorption in step S3, the flow rate of the impurity-free brackish water is 1cm/S, and the pumping speed of the second water pump is 1 cm/S.

7. The system for desalinating brackish water according to claim 1, wherein the flow rate of the flushing liquid is 10cm/S and the speed of the first water pump for pumping water is 10cm/S during the desorption of the first desalination module in step S3; when the second desalination module is desorbed in step S4, the flow rate of the rinse solution is 10cm/S, and the water pumping speed of the second water pump is 10 cm/S.

8. The system for desalinating brackish water according to claim 1, wherein the rinse solution used for the desorption of the first desalination module and the second desalination module is tap water, distilled water or purified water.

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