CN114715976B - Direct contact type membrane distillation device suitable for pure water preparation and pure water preparation method - Google Patents

Abstract

The invention provides a direct contact type membrane distillation device suitable for pure water preparation and a pure water preparation method, wherein the device comprises a raw water side component, a membrane component, a water production side component and a controller; the raw water side assembly comprises a raw water pool and a raw water heating pool which are communicated through a pump, water in the raw water heating pool is heated only during working, a stirring device such as a propeller is installed in the heating pool, and the controller is optimized through computational fluid mechanics analysis, so that water temperature can be rapidly and uniformly, and energy consumption is reduced. The water producing pool of the water producing side component is divided into two stages. The constant temperature refrigeration component only cools a small amount of distilled water participating in membrane distillation circulation in the first stage, and redundant produced water flows into the second stage water producing pool to be naturally cooled, so that the water cooling energy consumption is greatly reduced. The invention realizes automatic monitoring in the whole process, and the system is closed in time when the water level at the feeding and heating side is lower than the safe water level and can not be added, and flux concentration reduction, membrane breakdown and the like caused by membrane pollution occur.

Description

Direct contact membrane distillation device and pure water preparation method suitable for pure water preparation

technical field

The invention belongs to the field of membrane distillation, and the technology relates to a direct-contact membrane distillation device suitable for pure water preparation and a pure water preparation method.

Background technique

Membrane distillation is a new membrane separation process that has emerged in recent years. It is a membrane technology that uses hydrophobic microporous membranes to separate aqueous solutions containing non-volatile solutes. Due to the surface tension of water, liquid water cannot pass through the micropores of the membrane under normal pressure, but water vapor can. When there is a certain temperature difference on both sides of the membrane, due to the difference in vapor pressure, water vapor molecules pass through the micropores and condense on the other side, making the solution gradually concentrated. This process can make full use of cheap energy such as factory heat or solar energy, plus the process is easy to automate and the equipment is simple, and it is becoming a separation process with practical significance. Since the technology was launched in 1963, according to the different condensation methods of volatile components on the permeation side of the membrane, it can be divided into four structures: direct contact membrane distillation, air gap membrane distillation, scavenging membrane distillation, and vacuum membrane distillation. Among them, direct contact membrane distillation is the most widely studied.

Direct contact membrane distillation is relatively simple to implement, mainly including three parts: feed side, membrane module, and product water side.

On the feed side, it mainly includes the solution to be separated (aqueous solution of non-volatile solutes, such as seawater, brackish water, sewage, etc.), heating equipment, pumps, etc. This part is mainly to heat the solution to be separated to the preset temperature, and transport it to the membrane module through the pump.

The membrane module is the central unit of the membrane distillation system, the place where the membrane separation process is carried out, and the carrier of the membrane distillation process. The advantages and disadvantages of membrane module structure will directly affect the separation efficiency and economic performance of membrane distillation. Membrane modules commonly used in industry include plate and frame membrane modules, circular tube membrane modules, hollow fiber membrane modules, spiral wound membrane modules, etc. Among them, the most important thing in the membrane module is the porous hydrophobic membrane placed therein. Porous hydrophobic membranes commonly used in industry include polytetrafluoroethylene (PTFE), polypropylene (PP), polyethylene (PE), polyvinylidene fluoride (PVDF), etc., among which PTFE is widely used.

On the product water side, it mainly includes product water pipes, pumps, condensing equipment, etc. This part is mainly to condense the steam passing through the hydrophobic porous membrane and collect the liquefied distilled water.

The ubiquitous shortcoming of prior art mainly comprises:

(1) High energy consumption and low membrane distillation flux lead to high cost of water production. Relevant literature shows that increasing the temperature of the feed side is an effective way to increase the membrane flux. However, increasing the temperature on the feed side means increasing the processing cost. On the product water side, refrigeration equipment is required to condense water vapor. Currently, direct contact membrane distillation equipment cools down the water body on the product water side as a whole. As the water volume on the product water side increases, the energy consumption increases and the The cooling effect is reduced, and even the temperature control requirements on the product water side cannot be realized.

(2) The process control of membrane distillation is lacking. At present, the related equipment of the existing technology needs human monitoring and control. When the liquid level on the feed side drops, in order to prevent the heating equipment from drying out, it is necessary to add raw materials in time; When the rate is too high, it will pollute the water body on the current production side, and the equipment needs to be stopped immediately and repaired; when the membrane flux is low, continuing to produce water will increase the cost of water production and increase the risk of pollution to the water side of the production side. Stop the machine in time and replace the diaphragm with a new one.

Contents of the invention

In order to overcome the deficiencies of the prior art, the invention provides a direct contact membrane distillation device and a pure water preparation method suitable for pure water preparation.

Technical scheme of the present invention is as follows:

The present invention firstly provides a direct contact membrane distillation device suitable for pure water preparation, which includes a raw water side component, a membrane component, a product water side component and a controller;

The raw water side components include a raw water pool, a raw water side pump, a raw water heating pool, and a raw water circulation pump; the raw water pool is connected to the raw water heating pool through a pipeline and a raw water side pump, and the raw water can only be pumped from the raw water pool to the raw water heating pool in one direction. send; the raw water heating pool is provided with a heating assembly; and a stirring device;

The raw water heating pool is connected to the raw water inlet of the membrane module through the pipeline and the raw water circulating pump, the raw water outlet of the membrane module is connected to the raw water heating pool through the pipeline, and the raw water heating pool, the raw water circulating pump and the membrane module are formed by the pipeline Raw water side circulation;

The permeated water side assembly includes a permeated water pump, a first-stage permeated water tank, a second-stage permeated water tank, and an electronic scale; The water outlets are connected to form a water production side circulation, and a water production pump is arranged on the circulation pipeline;

The water outlet of the first-stage water-producing pool is located at the set height of the first-stage water-producing pool, and the first-stage water-producing pool is connected to the water inlet of the second-stage water-producing pool through the water outlet, and the water level in the first-stage water-producing pool is high At the height of the water outlet, water flows into the second-stage water-producing pool in one direction from the first-stage water-producing pool, and the second-stage water-producing pool is set on an electronic scale; the first-stage water-producing pool is provided with a constant temperature refrigeration assembly;

The controller is connected to the raw water side pump, raw water circulation pump, heating assembly, stirring device, product water pump, and constant temperature refrigeration assembly for control, and the controller is connected to the electronic scale to obtain the weighing signal; the controller is also equipped with a buzzer.

Further, the membrane assembly includes a raw water side membrane tank, a water production membrane tank, and a hydrophobic porous membrane and a support grid arranged between the raw water side membrane tank and the water production measurement membrane tank; wherein the hydrophobic porous membrane is arranged on the support On the grid, a raw water inlet and a raw water outlet are provided on the raw water side membrane tank; a water production measurement inlet and a production water measurement outlet are provided on the production water measurement membrane tank.

Further, the membrane module also includes an upper cover plate of the membrane module and a lower cover plate of the membrane module, and the upper cover plate of the membrane module and the lower cover plate of the membrane module are respectively fixed on the upper and lower surfaces of the membrane module by bolts, and the membrane module is encapsulation.

Further, the material of the hydrophobic porous membrane is PTFE, PP, PE or PVDF.

Further, the raw water heating pool is also provided with a liquid level gauge, which is connected to the controller, and the liquid level gauge is used to obtain the liquid level height in the raw water heating pool and transmit it to the controller; when the raw water side pump is working When the liquid level of the raw water heating pool still cannot reach the working safe water level, the controller controls the heating components to stop heating, turns off the raw water circulation pump and the produced water pump, and the buzzer alarms.

Further, a conductivity sensor is installed at the entrance of the first-stage water production tank, and when the conductivity detected by the conductivity sensor is higher than the preset value or the detected conductivity suddenly rises, the raw water circulation pump and the produced water pump are turned off And the buzzer alarm.

The present invention also provides a pure water preparation method based on the above-mentioned device. A liquid level gauge is also provided in the raw water heating tank, and a conductivity sensor is provided at the entrance of the first-stage water production tank; the method includes the following steps:

1) Fill the raw water pool and the raw water heating pool with raw water, and the amount of water should be greater than or equal to the safe water level of the raw water heating pool;

2) Add pure water to the first-stage water production tank to achieve the necessary water volume required for the water production cycle;

3) Turn on the controller, set the temperature of the raw water heating pool at 60-80°C and the temperature of the first-stage water production pool at 20-40°C;

4) The raw water heating pool starts the heating component and the stirring device, and the controller provides the optimal heating components and stirring device working parameters in the heating process of the raw water heating pool through computational fluid dynamics analysis, reduces heating energy consumption, and monitors the overall water temperature ;The constant temperature refrigeration component cools down the pure water in the first-stage water production tank; when the temperature of the raw water in the raw water heating tank and the temperature in the first-stage water production tank on the production water side reach the preset range, the controller turns on the raw water circulation pump, and the water production pump , start pure water preparation work;

5) The water in the first water production tank participates in the water production cycle. When the water volume in the first water production tank is higher than the outlet height of the first water production tank, the water enters the second water production tank, and the water in the second water production tank Does not participate in the water production cycle;

6) During the working process, the liquid level gauge monitors the water level of the raw water heating pool in real time. When the water level is lower than the first set threshold, the water pump on the raw water side starts to work and automatically fills the raw water into the raw water heating pool; when the water level is lower than the safe water level, The liquid level gauge feeds back the signal to the controller, the controller controls the heating component to stop heating, turns off the raw water circulation pump and the produced water pump and the buzzer alarms; wherein, the first set threshold is higher than the safe water level; the conductivity sensor monitors in real time The conductivity of the product water entering the first-stage water production tank. When the conductivity is higher than the preset value or a sudden increase in the conductivity is detected, the raw water circulation pump and the product water pump will be turned off and the buzzer will alarm; at the same time, the controller will The weight change of the scale detects the membrane flux of the product water side in real time. When it is less than the system preset or user setting value, the raw water circulation pump and the product water pump are turned off and stop working.

Compared with the prior art, the present invention has at least the following beneficial effects:

(1) Because the present invention has carried out two-stage treatment on the raw material side and the produced water side, added functions such as liquid level detection and automatic water renewal, optimized the heating and cooling process, and avoided possible problems caused by liquid in existing equipment. If the position is too low, it will cause dry burning or even equipment damage, and the cooling energy consumption of the product water side will be high, and the cooling effect will not meet the control requirements.

(2) Because the present invention realizes automatic monitoring throughout the whole process, the system will shut down in time when the water level on the heating side of the feed material is lower than the safe water level and cannot be added, the flux accumulation decreases due to membrane fouling, and membrane breakdown occurs. . Therefore, the problems in the prior art such as the pollution of the water body on the production water side caused by untimely detection and untimely monitoring, and the increase in water production cost caused by the decrease of membrane flux have been overcome.

Description of drawings

Fig. 1 is the structural representation of direct contact membrane distillation device of the present invention;

Fig. 2 is a schematic structural view of the membrane module of the present invention.

In the figure, 1. Controller; 2. Raw water tank; 3. Raw water side pump; 4. Raw water heating tank; 5. Heating component; 6. Propeller; 7. Raw water circulation pump; 8. Membrane module; ;10. Constant temperature refrigeration assembly; 11. First-level water production tank; 12. Second-level water production tank; 13. Electronic scale; 14. Upper cover plate of membrane module; 15. Raw water inlet; 16. Raw water outlet; 17. Hydrophobic porous membrane; 18. Supporting grid; 19. Produced water measuring membrane tank; 20. Raw water side membrane tank; 21. Lower cover plate of membrane module; 22. Produced water side inlet; 23. Produced water side outlet; . Fixing bolts; 25. Bolt holes on the raw water side; 26. Bolt holes on the produced water side.

Detailed ways

The present invention will be further elaborated and described below in combination with specific embodiments. The embodiments are merely exemplary of the disclosure and do not delineate the scope of limitation. The technical features of the various implementations in the present invention can be combined accordingly on the premise that there is no conflict with each other.

As shown in Figure 1, the direct contact membrane distillation device suitable for pure water preparation illustrated in this embodiment includes a raw water side component, a membrane component 8, a product water side component and a controller 1;

The raw water side components include a raw water pool 2, a raw water side water pump 3, a raw water heating pool 4, and a raw water circulation pump 7; One-way pumping to the raw water heating pool; a heating assembly 5 is arranged in the raw water heating pool; and a stirring device; the raw water heating pool 4 is connected to the raw water inlet of the membrane module 8 through a pipeline and a raw water circulation pump 7, and the membrane The raw water outlet of module 8 is connected to the raw water heating tank through pipelines, and the raw water heating tank 4, the raw water circulation pump 7 and the membrane module 8 form the raw water side circulation through the pipelines;

The water production side assembly includes a water production pump 9, a first water production tank 11, a second water production tank 12 and an electronic scale 13; The water inlet and the water outlet on the water production side are connected to form a water production side circulation, and the water production pump 9 is arranged on the circulation pipeline; the water outlet of the first water production pool 11 is located at the set height of the first water production pool 11, The first-stage water-producing pool 11 is connected to the water inlet of the second-stage water-producing pool 12 through a water outlet. When the water level in the first-stage water-producing pool 11 is higher than the height of the water outlet, water flows into the second-stage water-producing pool 11 in one direction from the first-stage water-producing pool. A secondary water production pool 12, the second water production pool 12 is arranged on an electronic scale 13; a constant temperature refrigeration assembly 10 is arranged in the first water production pool 11;

The controller 1 is respectively connected to the raw water side pump 3, the raw water circulation pump 7, the heating assembly 5, the stirring device, the produced water pump 9, and the constant temperature refrigeration assembly 10 for control, and the controller 1 is connected to the electronic scale 13 to obtain a weighing signal; the controller 1 is also equipped with a buzzer.

Further, a liquid level gauge is also provided in the raw water heating pool 4, and the liquid level gauge is connected to the controller 1, and the liquid level gauge is used to obtain the liquid level height in the raw water heating pool 4 and transmit it to the controller 1; When the raw water side water pump 3 is working and the liquid level of the raw water heating pool 4 still cannot reach the working safety water level, the controller controls the heating assembly 5 to stop heating, and the buzzer gives an alarm.

Further, a conductivity sensor is installed at the entrance of the first-stage water production tank 11, and when the conductivity sensor detects a conductivity higher than a preset value or detects a sudden and rapid rise in conductivity, a buzzer will sound an alarm.

As shown in Figure 2, the membrane module 8 includes a raw water side membrane tank 20, a water production membrane tank 19, and a hydrophobic porous membrane 17 and a support grid 18 arranged between the raw water side membrane tank and the water production membrane tank Wherein the hydrophobic porous membrane 17 is arranged on the supporting grid 18, the raw water side membrane pool 20 is provided with a raw water inlet 15 and a raw water outlet 16; Measure water outlet 23. The membrane module 8 also includes a membrane module upper cover plate 14 and a membrane module lower cover plate 21, and the membrane module upper cover plate 14 and the membrane module lower cover plate 21 pass through the fixing bolts 24, the raw water side bolt holes 25, and the produced water side respectively. Bolt holes 26 are fixed on the upper and lower surfaces of the membrane module to package the membrane module. Wherein, the material of the hydrophobic porous membrane 17 is PTFE, PP, PE or PVDF. The total height of the membrane module is between 1 and 3mm. The bolt type, quantity, position, etc. can be adjusted according to the actual situation.

In the present invention, the controller provides the optimal heating rod and propeller working parameters in the heating process through computational fluid dynamics analysis (CFD), reduces system heating energy consumption, and realizes constant temperature control (±0.5-1°C).

The models of the above-mentioned controllers, host computers, pipelines and other components can be selected according to actual needs. Among them, the liquid level sensor on the heating side can be replaced by a scale. That is, the scale is placed under the raw water heating side water tank. When the overall weight is less than a certain set value, it is equivalent to the detection value of the liquid level sensor.

Use the apparatus shown in Figure 1 to carry out pure water preparation, can carry out as follows:

1) Fill the raw water pool and the raw water heating pool with raw water, and the amount of water should be greater than or equal to the safe water level of the raw water heating pool;

2) Add pure water to the first-stage water production tank to achieve the necessary water volume required for the water production cycle; (conductivity ≤ 10μs/cm is optimal);

3) Turn on the controller, set the temperature of the raw water heating pool at 60-80°C and the temperature of the first-stage water production pool at 20-40°C, and further preset the working flow rate of the peristaltic pump on the raw water side, the working flow rate of the peristaltic pump on the produced water side, and the production Estimated water level on the water side (by default, the production tank is full);

4) Start the heating components in the raw water heating pool, turn on the stirring device, and the controller provides the optimal heating components and stirring device working parameters in the heating process of the raw water heating pool through computational fluid dynamics analysis (CFD), reducing heating energy consumption and improving the overall The water temperature is monitored; the constant temperature refrigeration component cools down the pure water in the first-stage water production tank; when the temperature of the raw water in the raw water heating tank and the temperature in the first-stage water production tank on the production water side reach the preset range, the controller turns on the raw water circulation pump, Produced water pump, start pure water preparation;

5) The water in the first water production tank participates in the water production cycle. When the water volume in the first water production tank is higher than the outlet height of the first water production tank, the water enters the second water production tank, and the water in the second water production tank Does not participate in the water production cycle;

6) During the working process, the liquid level gauge monitors the water level of the raw water heating pool in real time. When the water level is lower than the first set threshold, the water pump on the raw water side starts to work and automatically fills the raw water into the raw water heating pool; when the water level is lower than the safe water level, The liquid level gauge feeds back the signal to the controller, the controller controls the heating assembly 5 to stop heating, turns off the raw water circulation pump and the produced water pump and the buzzer alarms; wherein, the first set threshold is higher than the safe water level;

The conductivity sensor monitors the conductivity of the product water entering the first-stage water production tank in real time. When the conductivity is higher than the preset value or detects a sudden increase in conductivity, the raw water circulation pump and the product water pump will be turned off and the buzzer will alarm;

At the same time, the controller detects the membrane flux of the product water side in real time through the weight change of the electronic scale. When it is less than the system preset or user setting value, the raw water circulation pump and the product water pump are turned off and stop working.

Among them, the membrane flux calculation formula is:

J＝M/(S T) (1)

Among them, J represents the membrane flux, the unit is kg/m ² ·h; M represents the weight of the total produced water, the unit is kg; S represents the effective area of the membrane in the membrane module, the unit is m ² ; T represents the distillation time, the unit is h.

The invention divides the raw material side into two parts, including a raw water pool and a raw water heating pool, and the two sets of equipment are connected through pumps. When the system works, it only heats the water in the raw water heating pool. In addition, a stirring device such as a propeller is installed in the heating pool, and the controller is optimized through computational fluid dynamics analysis, which can quickly equalize the water temperature and reduce energy consumption. Divide the product water side into two parts: the constant temperature refrigeration component and the product water tank. The production pool is divided into two levels. The constant temperature refrigeration component only cools a small amount of distilled water that participates in the membrane distillation cycle in the first stage, and the excess water flows into the second stage water tank for natural cooling, thus greatly reducing the energy consumption of water cooling, and thus suitable for the preparation of pure water in industry.

During the normal working process of the system of the present invention, the water level on the raw material side will continue to decrease due to reasons such as heating, distillation and water production. When it is lowered to a safe water level, it is easy to cause the heating equipment to dry out or even be damaged. To solve this problem, the raw material side is divided into two parts, including the raw water pool and the raw water heating pool, and the two sets of equipment are connected through pumps. A liquid level sensor is added to the raw water heating pool. When the water level is lower than the safe water level, the raw water side water pump 3 is started, and water is continued from the raw water pool to the raw water heating pool until reaching the first set threshold (the first set threshold can be selected as full water level); when the water level of the raw water heating pool cannot be raised above the safe water level after starting the raw water side water pump 3, the system automatically turns off the heating function. When the temperature of the heated raw water pool is lower than the preset minimum working temperature, the whole system will automatically stop working.

During the working process of the system, if the hydrophobic porous membrane in the membrane module is polluted by sewage, the membrane flux will continue to decrease. When the pollution is serious, even membrane breakdown will occur. That is, the two sides of the membrane are connected, and the conductivity of the produced water side will soar at this time, which will cause pollution to the water body on the produced water side. Therefore, in order to solve the above problems. The invention installs conductivity sensors, balances and other equipment on the water production side to monitor the membrane flux and conductivity changes during the working process of the system in real time. When the membrane flux decreases to the set value or the conductivity of the product water side suddenly increases (when the change rate of the conductivity is greater than the set threshold), the system will send out an alarm and stop working.

The above-mentioned embodiments only express several implementation modes of the present invention, and the description thereof is relatively specific and detailed, but should not be construed as limiting the patent scope of the present invention. For those skilled in the art, without departing from the concept of the present invention, several modifications and improvements can be made, and these all belong to the protection scope of the present invention.

Claims (8)

1. A direct contact type membrane distillation device suitable for pure water preparation is characterized by comprising a raw water side component, a membrane component (8), a water production side component and a controller (1);

the raw water side assembly comprises a raw water pool (2), a raw water side water pump (3), a raw water heating pool (4) and a raw water circulating pump (7); the raw water pool (2) is connected with the raw water heating pool through a pipeline and a raw water side water pump (3), and raw water can be pumped to the raw water heating Chi Shanxiang from the raw water pool (2); a heating component (5) and a stirring device are arranged in the raw water heating tank;

the raw water heating tank (4) is connected with a raw water inlet of the membrane component (8) through a pipeline and a raw water circulating pump (7), a raw water outlet of the membrane component (8) is connected with the raw water heating tank through a pipeline, and the raw water heating tank (4), the raw water circulating pump (7) and the membrane component (8) form raw water side circulation through pipelines;

the water producing side assembly comprises a water producing pump (9), a first-stage water producing tank (11), a second-stage water producing tank (12) and an electronic scale (13); the first-stage water producing tank (11) is connected with a water inlet at a water producing side and a water outlet at the water producing side of the membrane component (8) through a circulating pipeline to form water producing side circulation, and a water producing pump (9) is arranged on the circulating pipeline;

the water outlet of the first-stage water producing tank (11) is positioned at the set height of the first-stage water producing tank (11), the first-stage water producing tank (11) is connected with the water inlet of the second-stage water producing tank (12) through the water outlet, when the water level in the first-stage water producing tank (11) is higher than the height of the water outlet, water flows into the second-stage water producing tank (12) from the first-stage water producing tank (11) in a one-way mode, and the second-stage water producing tank (12) is arranged on the electronic scale (13); a constant-temperature refrigeration assembly (10) is arranged in the first-stage water producing tank (11);

the controller (1) is respectively connected with the raw water side water pump (3), the raw water circulating pump (7), the heating assembly (5), the stirring device, the water producing water pump (9) and the constant temperature refrigerating assembly (10) for control, and the controller (1) is connected with the electronic scale (13) to obtain a weighing signal; the controller (1) is also provided with a buzzer.

2. The direct contact membrane distillation apparatus suitable for pure water production according to claim 1, wherein the membrane module (8) comprises a raw water side membrane tank (20), a water production side membrane tank (19), and a hydrophobic porous membrane (17) and a support grid (18) arranged between the raw water side membrane tank and the water production side membrane tank; wherein the hydrophobic porous membrane (17) is arranged on the supporting grid (18), and the raw water inlet (15) and the raw water outlet (16) are arranged on the raw water side membrane pool (20); a water inlet (22) at the water producing side and a water outlet (23) at the water producing side are arranged on the water producing side membrane pool (19).

3. The direct contact membrane distillation device suitable for pure water preparation according to claim 2, wherein the membrane module (8) further comprises a membrane module upper cover plate (14) and a membrane module lower cover plate (21), and the membrane module upper cover plate (14) and the membrane module lower cover plate (21) are respectively fixed on the upper surface and the lower surface of the membrane module through bolts to encapsulate the membrane module.

4. The direct contact membrane distillation apparatus for pure water production according to claim 2, wherein the hydrophobic porous membrane (17) is made of PTFE, PP, PE or PVDF.

5. The direct contact membrane distillation apparatus suitable for pure water preparation according to claim 1, wherein a liquid level meter is further disposed in the raw water heating tank (4), and the liquid level meter is connected to the controller (1) and is used for acquiring the liquid level height in the raw water heating tank (4) and transmitting the liquid level height to the controller (1); when the liquid level of the raw water heating pool (4) still cannot reach the working safety water level under the condition that the raw water side water pump (3) works, the controller controls the heating component (5) to stop heating, the raw water circulating pump and the water producing water pump are turned off, and the buzzer gives an alarm.

6. The direct contact membrane distillation apparatus for pure water production according to claim 1, wherein a conductivity sensor is provided at the inlet of the first stage water producing tank (11), and when the conductivity detected by the conductivity sensor is higher than a preset value or a sudden rise of the detected conductivity, the raw water circulating pump and the produced water pump are turned off and a buzzer alarms.

7. A pure water preparation method based on the device of claim 1, characterized in that a liquid level meter is arranged in the raw water heating pool (4), and a conductivity sensor is arranged at the inlet of the first-stage water producing pool (11); the method comprises the following steps:

1) Raw water is filled in the raw water pool and the raw water heating pool, and the water quantity is ensured to be more than or equal to the safe water level and water quantity of the raw water heating pool;

2) Adding purified water into the first-stage water producing pond to reach the necessary water amount required by water producing circulation;

3) Starting a controller, and setting the temperature of a raw water heating pool at 60-80 ℃ and the temperature of a first-stage water producing pool at 20-40 ℃;

4) Starting a heating assembly of the raw water heating pool, starting a stirring device, giving the optimal working parameters of the heating assembly and the stirring device in the heating process of the raw water heating pool by a controller through Computational Fluid Dynamics (CFD), reducing heating energy consumption and monitoring the whole water temperature; the constant-temperature refrigeration component cools the purified water in the first-stage water producing tank; when the temperature of raw water heating Chi Zhongyuan and the temperature in a first-stage water producing pool on a water producing side reach preset ranges, a controller starts a raw water circulating pump and a water producing pump to start pure water preparation;

5) The water in the first-stage water producing pond participates in water producing circulation, when the water amount in the first-stage water producing pond is higher than the outlet height of the first-stage water producing pond, the water enters the second-stage water producing pond, and the water in the second-stage water producing pond does not participate in the water producing circulation;

6) In the working process, the liquid level meter monitors the water level of the raw water heating pool in real time, and when the water level is lower than a first set threshold, the raw water side water pump starts to work and automatically fills raw water into the raw water heating pool; when the water level is lower than the safe water level, the liquid level meter feeds back a signal to the controller, the controller controls the heating component (5) to stop heating, the raw water circulating pump and the water producing pump are turned off, and the buzzer gives an alarm; wherein the first set threshold is higher than a safe water level; the conductivity sensor monitors the conductivity of the produced water entering the first-stage water producing pool in real time, and when the conductivity is higher than a preset value or the conductivity is detected to be suddenly increased, the raw water circulating pump and the produced water pump are closed, and a buzzer gives an alarm; meanwhile, the controller detects the membrane flux on the water production side in real time through the weight change of the electronic scale, and when the membrane flux is smaller than a system preset value or a user set value, the raw water circulating pump and the water production pump are closed, and the operation is stopped.

8. The pure water production method according to claim 7, wherein the membrane flux calculation formula is:

J＝M/(S·T) (1)

wherein J represents the membrane flux in kg/m ² H; m represents total produced water weight in kg; s represents the effective area of the membrane in the membrane module, unit m ² (ii) a T represents the distillation time in h.

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