CN113149158B

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

Info

Publication number: CN113149158B
Application number: CN202110335416.9A
Authority: CN
Inventors: 李承龙; 杨侃
Original assignee: Hohai University HHU
Current assignee: Hohai University HHU
Priority date: 2021-03-29
Filing date: 2021-03-29
Publication date: 2022-08-05
Anticipated expiration: 2041-03-29
Also published as: CN113149158A

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

System for desalinating brackish water by using pure capacitance deionization technology and method for desalinating brackish water by using system

Technical Field

The invention belongs to the field of water treatment, particularly relates to utilization of unconventional water resources, and particularly relates to a system for desalting brackish water by using a capacitive deionization technology and a method for desalting brackish water by using the system.

Background

At present, about one-tenth of the world's population cannot obtain clean drinking water, and water resource problems have become more severe since the new century. The utilization mode of water resources is comprehensively changed, and the active development and utilization of unconventional water sources such as reclaimed water, mine water, seawater and the like are urgently needed. The traditional salt water desalination technologies, such as reverse osmosis, electrodialysis, ion exchange and the like, have the problems of high energy consumption, high cost, secondary pollution and the like which are not negligible, so that the salt water desalination and utilization are difficult to realize all the time. The capacitive desalination technology, namely Capacitive Deionization (CDI), also known as electroadsorption, removes ions in a solution by electroadsorption in a manner of forming an electric field between porous electrode materials, has the advantages of high desalination efficiency, low energy consumption, environmental friendliness and the like, and is a novel salt water desalination technology which is increasingly and widely valued along with the development of carbon material science in recent decades. The appearance of the capacitive desalination technology makes up the defects of the traditional seawater desalination technology, so that the desalination technology with low energy consumption and high efficiency has practical possibility.

CN111875007A discloses a resistant electric adsorption system that scales suitable for high rigidity waste water, this system include first adsorption module, second adsorption module, former water tank, first regeneration water tank, second regeneration water tank, fresh water tank, water pump, valve. The raw water tank is used for storing raw wastewater, and the first adsorption module and the second adsorption module are used for adsorbing the raw wastewater to obtain initial treated water; the first regeneration water tank and the second regeneration water tank are used for cyclic desorption regeneration of the adsorption module and discharge of concentrated solution. Compared with other membrane concentration and reduction technologies, the system has better tolerance of the hardness index of the inlet water. The method does not need to be softened before actual wastewater is treated, and only simple clarification is carried out, so that the problems of hardness scaling, channel fouling and the like on the surface of the electrode can be avoided. However, the adsorption and desorption of the system can not be carried out simultaneously, fresh water can not be continuously produced during desorption, and the working efficiency of the system is not high enough.

CN111718052A discloses a method for desalinating brackish water, which comprises the following steps: introducing brackish water into the sump; the brackish water in the water collecting well is introduced into a filtering tank through a water pump for filtering; enabling the filtered bitter water to enter a first capacitive deionization device, switching on a power supply of the first capacitive deionization device, and adsorbing positive and negative ions in the bitter water solution onto an electrode of the first capacitive deionization device to realize desalination and reduce the ion concentration in the bitter water solution; the desalted brackish water passes through a reverse osmosis device under the action of a high-pressure pump to obtain fresh water; the first capacitive deionization device and the second capacitive deionization device are connected in parallel, and when the first capacitive deionization device is reversely connected to desorb ions, the second capacitive deionization device continues to desalt, so that the desalinization efficiency is improved. Although the method can continue desalination treatment while the electrodes are regenerated, qualified fresh water can be prepared only by combining a capacitance deionization technology with a reverse osmosis technology, and the desalination of brackish water requires higher operating pressure, so that the reverse osmosis membrane surface is quick in inorganic scaling and needs to be cleaned and replaced frequently; the solar heat collection device is used for evaporating the recovered brackish water, so that the influence of weather is great, and the conversion efficiency is low; the device is too many, and the occupied area of equipment required in the industrial continuous production is large.

Disclosure of Invention

In order to overcome the problems in the prior art, the invention provides a system for desalinating brackish water by using a pure capacitance deionization technology and a method for desalinating 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 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 connected in sequence 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.

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

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

Preferably, the sedimentation tank in the step S1 is a horizontal flow type or radial flow type or vertical flow type sedimentation tank; the filtering tank is a flat filtering tank or a filtering 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. The use of the check valve prevents the reverse flow of the liquid in the pipe.

A method for desalinating brackish water using a system for desalinating brackish water using a pure capacitive deionization technique according to any one of the preceding claims, comprising the 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 the first valve, the second valve and the 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, simultaneously opening the fourth valve, and discharging 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 enabling the first desalination module to repeat the step S2; simultaneously closing the sixth valve, opening the tenth valve, and introducing flushing liquid into the second coarse desalting device by pulse inflow with the flow speed of 6-12 cm/s; switching the output current of the alternating current and direct current power supply into 0.1-1.0 Hz alternating current; the starting frequency of the second water pump is kept consistent with the frequency of flushing liquid pulse inflow, the flow velocity of the second water pump is increased to 6-12cm/s, and the waste liquid in the second desalting module is discharged to a waste liquid pool; and when the conductivity detected by the second conductivity 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 invention only uses the capacitive deionization technology to desalinate the brackish water, and can achieve the purpose of treating the brackish water to ensure that the conductivity of the brackish water meets the specification without being combined with other desalination technologies such as reverse osmosis technology, electrodialysis technology, multi-effect evaporation or ion exchange technology and the like. After the water flowing out of the first fine desalination device is detected by a first conductivity meter, if the conductivity is smaller than a preset threshold value A, the fresh water prepared by the first desalination module is considered to meet the requirement; the threshold A can be set to different values according to different required fresh water qualities, and A is less than or equal to 2000 mu S/cm; if the conductivity is larger than or equal to A, the electrode plate in the first desalting module is saturated in adsorption, the electrode needs to be desorbed and regenerated, at the moment, the third valve is closed, and the fourth valve is opened, so that the wastewater with unqualified conductivity is discharged into a waste liquid pool; then opening a fifth valve to enable flushing fluid to enter the first desalting module, and enabling an alternating current/direct current power supply to output ultralow-frequency alternating current to the first coarse desalting device and the first fine desalting device to enable ions on the electrode plate to be desorbed; the reverse connection of the power supply is not needed from the adsorption to the desorption process. And detecting the conductivity of the wastewater generated after the desorption of the first desalination module by using a first conductivity meter, and if the conductivity is smaller than a preset threshold value B, indicating that the desorption of the electrode plate meets the requirement and can be used for subsequent adsorption desalination. Threshold B is much smaller than threshold a. When the first desalination module is used for desorption, the second desalination module starts to perform adsorption work at the same time, and the work flow is the same as that of the first desalination module. Judging whether the electrode plates in the second desalination module need to be desorbed or not according to the detection result of the second conductivity meter, and performing desorption according to the desorption mode of the first desalination module when the second desalination module needs to be desorbed, and enabling the first desalination module to perform adsorption work; the two modules are used alternately, so that fresh water can be continuously and uninterruptedly produced, and the working efficiency is improved. The desorption process in first desalination module and the second desalination module prevents through using ultralow frequency alternating current to change the ion that prevents the desorption again that the electric field direction between the polar plate from attaching to the polar plate, improves the pumping speed of water pump, prevents when in time rushing out the ion of desorption that the ion of desorption from being adsorbed to another polar plate once more. When the liquid in the waste liquid pool is close to the full-capacity state, the waste liquid is discharged and handed to a professional department for treatment.

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

Preferably, the output current of the ac/dc power supply is 0.1Hz alternating current when the first desalination module is performing desorption and when the second desalination module is performing desorption.

Preferably, when the first desalination module performs adsorption in step S2, the flow rate of the impurity-free brackish water is 1cm/S, and the pumping speed of the first water pump is 1 cm/S; 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.

Preferably, when the first desalination module is performing desorption in step S3, the flow rate of the rinse solution is 10cm/S, and the speed of the first water pump is 10 cm/S; 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.

Preferably, the flushing liquid used for 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 invention has the advantages that:

(1) the brackish water desalination system does not need other equipment such as a reverse osmosis device, an electrodialysis device and an ion exchange device, the whole desalination process is realized by using a capacitance deionization technology, a low-voltage alternating current and direct current power supply of 1.0-2.0V is used for supplying power, the energy consumption is extremely low, the water utilization rate is high, and no secondary pollution is caused; (2) the whole desorption process does not need to be reversely connected with a power supply; when ions are desorbed, the direction of an electric field between the electrode plates is repeatedly changed by using 0.1-1.0 Hz ultralow frequency alternating current to prevent the desorbed ions from being attached to the electrode plates again, the water pumping speed of the water pump is improved, the desorbed ions are flushed out in time, and the desorbed ions are prevented from being adsorbed to the other electrode plate again; (3) the two desalination modules are used alternately, so that the working efficiency is improved; the device is simple, and does not need too much equipment with large volume and high requirements on operation conditions; the salt electrode can reduce the cost of the whole equipment.

Drawings

FIG. 1 is a system for desalinating brackish water using pure capacitive deionization techniques according to the present invention;

FIG. 2 is a schematic diagram of the electrode plate of the brackish water desalination system according to the present invention for adsorbing ions.

In the figure: 1. a sedimentation tank; 2. a filtering tank; 3. a first desalination module; 31. a first coarse desalting device; 311. a first electrode plate; 312. a second electrode plate; 32. a first fine desalting device; 33. a first water pump; 4. a second desalination module; 41. a second coarse desalination device; 42. a second fine desalting device; 43. a second water pump; 5. an AC/DC power supply; 51. a first interface; 52. a second interface; 53. a third interface; 54. a fourth interface; 6. a waste liquid tank; 34. a first valve; 35. a second valve; 36. a third valve; 37. a fourth valve; 38. a fifth valve; 44. a sixth valve; 45. a seventh valve; 46. an eighth valve; 47. a ninth valve; 48. a tenth valve; y1, first conductivity meter; y2, second conductivity meter; k1, a first switch; k2, a second switch; k3, a third switch; k4, a fourth switch.

Detailed Description

The technical solution of the present invention is described in detail and fully with reference to the following examples, it is obvious that the described examples are only a part of the examples of the present invention, and not all of the examples. All other embodiments, which can be derived by a person skilled in the art from the embodiments of the present invention without any inventive step, are within the scope of the present invention. Any equivalent changes or substitutions by those skilled in the art according to the following embodiments are within the scope of the present invention.

Example 1

As shown in fig. 1, the system for desalinating brackish water by using pure capacitance deionization technology of the present embodiment includes a sedimentation tank 1, a filtration tank 2, a first desalination module 3, a second desalination module 4, an ac/dc power supply 5, and a waste liquid tank 6; the first desalination module 3 comprises a first coarse 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 valve 36, a fourth valve 37 and a fifth valve 38; the first valve 34 and the fifth valve 38 are disposed at the water inlet of the first coarse desalter 31, the second valve 35 is disposed at the water outlet of the first fine desalter 32, the first conductivity meter Y1 is disposed between the second valve 35 and the third valve 36, and the fourth valve 37 is disposed between the first conductivity meter Y1 and the waste liquid tank 6; the second desalination module 4 comprises a second coarse desalination device 41, a second fine desalination device 42, a second water pump 43, a second conductivity meter Y2, a sixth valve 44, a seventh valve 45, an eighth valve 46, a ninth valve 47 and a tenth valve 48; the sixth valve 44 and the tenth valve 48 are disposed at the water inlet of the second coarse desalting device 41, the seventh valve 45 is disposed at the water outlet of the second fine desalting device 42, the second conductivity meter Y2 is disposed between the seventh valve 45 and the eighth valve 46, and the ninth valve 47 is disposed between the second conductivity meter Y2 and the waste liquid tank 6; the alternating current and direct current power supply 5 is provided with a first interface 51, a second interface 52, a third interface 53 and a fourth interface 54; the first coarse desalting device 31, the first fine desalting device 32, the second coarse desalting device 41 and the second fine desalting device 42 are all provided with two electrode plates; the first coarse desalination device 31 is connected to the first port 51, the first fine desalination device 32 is connected to the second port 52, the second coarse desalination device 41 is connected to the third port 53, and the second fine desalination device 42 is connected to the fourth port 54; the first water pump 33 is disposed between the first coarse desalter 31 and the first fine desalter 32, and the second water pump 43 is disposed between the second coarse desalter 41 and the second fine desalter 42; the sedimentation tank 1 and the filtration tank 2 are both communicated with the water inlet of the first coarse desalting device 31, and the sedimentation tank 1 and the filtration tank 2 are both communicated with the water inlet of the second coarse desalting device 41.

The method for desalinating the brackish water by the system comprises the following steps:

s1, as shown in figure 1, the salt lake water is led into a horizontal flow type sedimentation tank for sedimentation, so that the salt lake water is completely sedimentated; then introducing the supernatant into a filtering tank for filtering to obtain impurity-free brackish water;

s2, opening the first valve 34, the second valve 35 and the third valve 36, and keeping the other valves in a closed state; the first coarse desalting device 31 is connected with a first interface 51 of the alternating current-direct current power supply 5 through a first switch K1, and the first fine desalting device 32 is connected with a second interface 52 of the alternating current-direct current power supply 5 through a second switch K2; introducing 1.2V direct current into the first interface 51 and the second interface 52; the brackish water flows to the first desalination module 3 through the first valve 34 at a speed of 1cm/s, and is subjected to first ion adsorption through the first coarse desalination device 31, the adsorption principle is shown in fig. 2, wherein anions move to the first electrode plate 311, and cations move to the second electrode plate 312; the electrode plates of the first coarse desalting means 31 are made of carbon nanotubes; the water from the first crude desalting device 31 is accelerated by a first water pump 33 to keep the flow velocity of the water at 1cm/s, and then flows to a first fine desalting device 32 to further reduce the concentration of salt ions in the water; the electrode plate of the first fine desalting device 32 is made of metal-organic framework carbon nanotubes; detecting the water flowing out of the first fine desalination device 32 by a first conductivity meter Y1, and opening a third valve 36 to discharge the water to obtain fresh water when the detection result is smaller than a preset threshold value A; the electrical conductivity of water is specified to be less than 2000 mu S/cm in sanitary Standard for Drinking Water GB 5749-2006; the threshold A is set according to the requirement of the required fresh water quality, but cannot exceed 2000 muS/cm;

s3, if the detection result of the first conductivity meter Y1 is larger than or equal to A, closing the third valve 36, opening the fourth valve 37, and discharging the unqualified detected water into a waste liquid pool; at the same time, the first valve 34 is closed, the fifth valve 38 is opened, and tap water is introduced into the first coarse desalting device by pulse inflow at the speed of 10cm/s and the frequency of 10 seconds per time; adjusting the output currents of the first interface 51 and the second interface 52 of the alternating current and direct current power supply 5 to be ultralow-frequency alternating current with the frequency of 0.1Hz to desorb ions on the electrode plate; the water pumping speed of the first water pump 33 is increased to 10cm/s, the opening and closing interval time of the first water pump 33 is adjusted to 10 seconds, when the detection result of the first conductivity meter Y1 is smaller than the preset threshold value B, the regeneration of the electrodes is realized, the fifth valve 38 is closed, and the first desalination module 3 is in a standby state; closing the first valve 34 and opening the fifth valve 38, simultaneously opening the sixth valve 44, the seventh valve 45 and the eighth valve 46, introducing the impurity-free brackish water obtained in step S1 into the second coarse desalting device 41 at a flow rate of 1cm/S, and communicating the second coarse desalting device 41 and the second fine desalting device 42 with the third interface 53 and the fourth interface 54 of the ac/dc power supply 5, respectively, to supply dc power to the ac/dc power supply 5; the second water pump 43 was started once per minute and the liquid flow rate was kept at 1 cm/s; the brackish water after being adsorbed and desalted by the second coarse desalting device 41 is input into a second fine desalting device 42 by a second water pump 43 for continuous adsorption and desalting; the water flowing out of the second fine desalination device 42 is detected by a second conductivity meter Y2, and if the conductivity is less than A, the water flows out of the eighth valve 46 to obtain fresh water;

s4, if the detection result of the second conductivity meter Y2 is larger than or equal to A, closing the eighth valve 46, opening the ninth valve 47, discharging the unqualified detected water into a waste liquid pool, and enabling the first desalting module to repeat the step S2; meanwhile, the sixth valve 44 is closed, the tenth valve 48 is opened, tap water is introduced into the second coarse desalting device 41 at a speed of 10cm/s and a frequency pulse inflow of 10 seconds per time, and the output currents of the third interface 53 and the fourth interface 54 of the alternating current/direct current power supply 5 are adjusted to be ultra-low frequency alternating current with the frequency of 0.1Hz to desorb ions on the electrode plates; and the water pumping speed of the second water pump 43 is increased to 10cm/s, the opening and closing interval time 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 electrodes 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 realize continuous and uninterrupted fresh water production by alternately repeating adsorption and desorption.

Example 2

The system and steps for desalinating brackish water in this embodiment are substantially the same as those in embodiment 1, except that: in the step S2, the speed of the brackish water flowing into the first coarse desalting device 31 is 0.5cm/S, the speed of the first water pump 33 pumping water is 0.5cm/S, and 1.0V direct current is introduced into the first interface 51 and the second interface 52 of the alternating current/direct current power supply 5; in the step S3, the flow rate of the rinse liquid is 6cm/S when the first desalination module 3 desorbs, the current output by the ac/dc power supply 5 is 0.5Hz alternating current, and the speed of the first water pump 33 for pumping water is 6 cm/S; in the step S3, the speed of the brackish water flowing into the second coarse desalting device 41 is 0.5cm/S, the speed of the second water pump 43 pumping water is 0.5cm/S, and 1.0V direct current is introduced into the third interface 53 and the fourth interface 54 of the alternating current/direct current power supply 5; in step S4, the flow rate of the rinse solution during desorption by the second desalination module 4 is 6cm/S, the current output by the ac/dc power supply 5 is 0.5Hz ac, and the water pumping speed of the second water pump 43 is 6 cm/S.

Example 3

This example is the same as example 1 except that: in the step S2, the speed of the brackish water flowing into the first coarse desalting device 31 is 2cm/S, the speed of the first water pump 33 pumping water is 2cm/S, and 2.0V direct current is introduced into the first interface 51 and the second interface 52 of the alternating current/direct current power supply 5; in the step S3, the flow rate of the rinse solution during desorption of the first desalination module 3 is 12cm/S, the current output by the ac/dc power supply 5 is 1.0Hz alternating current, and the water pumping speed of the first water pump 33 is 12 cm/S; in the step S3, the speed of the brackish water flowing into the second coarse desalting device 41 is 2cm/S, the speed of the second water pump 43 pumping water is 2cm/S, and 2.0V direct current is introduced into the third interface 53 and the fourth interface 54 of the alternating current-direct current power supply 5; in step S4, the flow rate of the rinse solution during desorption by the second desalination module is 12cm/S, the current output by the ac/dc power supply 5 is 1.0Hz ac, and the water pumping speed of the second water pump 43 is 12 cm/S.

The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. The present invention may be subject to various modifications and changes by any person skilled in the art. Any simple equivalent changes and modifications made in accordance with the protection scope of the present application and the content of the specification are intended to be included within the protection scope of the present invention.

Claims

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 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;

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:

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.