Production method for separating high-concentration saline water and pure water from seawater by utilizing potential energy

Abstract

The invention discloses a production method for separating high-concentration brine and pure water from seawater by using potential energy, and belongs to the technical field of seawater desalination and strong brine recycling. The production method comprises the following steps: feeding seawater into a selective crystallization grading tower provided with a nucleating agent and an inclined plate separation component for pretreatment; removing scaling precursors such as calcium sulfate and magnesium hydroxide to obtain pretreated seawater; the membrane side low pressure is established and maintained through the Venturi jet suction driven by potential energy, the effect of long-term stable and low-installation-power operation under the condition of no electromechanical vacuum pump or steam ejector is achieved, and the problems of high energy consumption, complex maintenance and poor off-grid adaptability caused by dependence on active vacuum are solved.

Description

Technical Field

[0001] This invention relates to the field of seawater desalination and concentrated brine resource utilization technology, and more specifically, to a production method for separating high-concentration brine and pure water from seawater using potential energy. Background Technology

[0002] Patent application number 202310197343.0 discloses a method and apparatus for desalinating high-salt, high-concentration organic wastewater by coupling three membrane separation technologies. This scheme, through multi-membrane coupling and evaporation-crystallization pathways, effectively improves the continuous desalination and resource recovery of high-salt, high-organic-load systems. However, when used in potential energy-driven applications for seawater separation, some shortcomings remain, such as: First, the comparative literature focuses on providing mass transfer driving force through pumping and compression equipment, and there is no clear record of a passive strategy of using potential energy to establish and maintain membrane-side negative pressure through a liquid ejector under the condition of no external vacuum equipment. Therefore, in scenarios where power is limited or low-complexity devices are required, the membrane-side driving force is difficult to maintain itself, the start-stop dependence is high, and the flux fluctuation and operational stability are affected. Second, compared with the literature, which uses multi-membrane coupling in conjunction with evaporation and crystallization, no arrangement was found that connects the condenser side and the front-end low-grade heat unit to form a closed regenerative loop through gravity reflux. Under small temperature difference conditions, regeneration and reflux still rely on active circulation, which increases energy consumption and pipeline complexity and is not conducive to long-term stable operation. Third, the literature generally relies on high-pressure pumps, blowers, and mechanical steam recompression equipment to maintain mass transfer and heat exchange. In off-grid or micro-power applications, the number of equipment and maintenance burden are large, making it difficult to meet the requirements of low energy consumption and high reliability. Summary of the Invention

[0003] To achieve the above objectives, the present invention provides the following technical solution: This invention adopts the operating concept of membrane phase change separation, that is, under normal pressure and temperature below the boiling point, a small temperature difference is used to drive the steam to transfer across the hydrophobic membrane and condense on the cold side; the process does not belong to traditional heating distillation or evaporation crystallization, and no independent heater or steam supply unit is set up to make the feed liquid boil. The heat source is the low-grade waste heat in the process and the temperature difference formed by the gravity closed regenerative circuit.

[0004] A production method for separating high-concentration brine and pure water from seawater using potential energy includes the following steps: S1: Seawater is sent to a selective crystallization classification tower equipped with nucleating agents and inclined plate separation components for pretreatment to remove scaling precursors such as calcium sulfate and magnesium hydroxide, and pretreated seawater is obtained. S2: Under the influence of the height difference provided by the high-level water storage facilities above the ground or sea surface, the height of the shore slope buildings, or the rise and fall of the tide, the pretreated seawater flows through the Venturi jet to form a liquid jet and draws in the gas connected to the membrane phase change separation shell to reduce the shell-side absolute pressure of the membrane phase change separation shell. S3: Connect the membrane phase change separation shell to the vertically arranged membrane phase change separation column, so that the feed is stripped at the top of the column and condensed in the condenser to obtain the first product water flow, while transferring the heat released by condensation to the humidification and dehumidification device. S4: In the humidification and dehumidification device, the humid air is heat-exchanged with the high-salt liquid from the concentrated salt branch and multi-effect recovery is performed to obtain the second product water flow, and the recovered heat is returned to the membrane phase change separation column or returned to the seawater feed. The air-to-water volume ratio of the humidification and dehumidification device is 1 to 3, and the air-to-water volume ratio is defined as the ratio of the gas phase volume flow rate to the liquid phase volume flow rate in the device. S5: Establish an airlift circulation driven by a Venturi getter in the pre-membrane branch, connect a microporous diffuser in parallel in front of the membrane to generate microbubbles, and scrub the membrane surface to reduce concentration polarization. The volume fraction of microbubbles in the flow field near the wall on the feed side of the membrane phase change separation column is 1% to 5%, and the volume average particle size of the microbubbles is 50 micrometers to 150 micrometers. S6: A density-triggered passive diversion network is set up on the product water branch and the concentrated salinity branch to perform graded recovery or reinjection of fluids with different salinities based on the online conductivity threshold. Furthermore, the operating conditions for the selective crystallization fractionation pretreatment of S1 are as follows: The supersaturation of the target salt system of calcium sulfate and magnesium hydroxide is 10% to 30%, the reaction residence time is 10 to 30 minutes, the angle between the inclined plate and the horizontal is 45° to 70°, seed crystals with a median particle size of 50 micrometers to 200 micrometers are added, the seed crystal concentration is 0.5 g / L to 5 g / L, and sludge is discharged when the online turbidity in the settling zone reaches 50 to 200 NTU or the bottom conductivity reaches 55 to 65 millisiemens per centimeter.

[0005] Furthermore, in step S2, a negative pressure is established and maintained in the membrane phase change separation shell by Venturi jet suction, and no electromechanical vacuum pump, steam ejector, vacuum tank pre-evacuation equipment, or deep well static water column is used during operation to generate negative pressure, specifically meeting the following conditions: The pretreated seawater obtained in step S1 flows through the contraction section, throat and diffuser section under the action of height difference to form a driving jet, and continuously pumps out the gas in the shell through the suction port connected to the membrane phase change separation shell, so as to stabilize the shell side absolute pressure at 30 kPa to 60 kPa. The volume conversion time, i.e., the ratio of the effective volume of the membrane phase change separation shell to the volumetric flow rate of the drive branch, is 1.7 seconds to 6.7 seconds. The suction ratio, i.e., the ratio of the volumetric flow rate of the suction branch to the volumetric flow rate of the drive branch, is 0.12 to 0.45, and the absolute value of the pressure difference between the static pressure at the injection suction outlet and the shell-side static pressure is not greater than 5 kPa. During continuous 72-hour operation, the shell-side absolute pressure is in the range of 30 kPa to 60 kPa for no less than 95% of the time.

[0006] Furthermore, between steps S3 and S4, the heat-releasing side of the condenser in step S3 and the heat-absorbing side of the humidification and dehumidification device in step S4 are directly connected by a pipeline to form a pumpless closed-loop regenerative circuit by gravity recirculation, without setting up a circulating pump or a parallel mechanical cold source. The regenerative circuit satisfies the following conditions: The gravity return drop shall not be less than 1 meter; The logarithmic mean temperature difference between the condenser and the humidification / dehumidification device is 10 to 25 degrees Celsius. The overall heat recovery rate of the humidification and dehumidification device is not less than 0.60, and the overall heat recovery rate is the proportion of the recoverable heat fed into the humidification and dehumidification device that is returned to step S3 or returned to the seawater feed. During continuous 72-hour operation, the absolute value of the difference between the average heat exchange per unit time of the condenser and the average heat absorption per unit time of the humidification and dehumidification device shall not exceed 10% of the average heat exchange per unit time of the condenser, and the dew point temperature fluctuation of the outlet air of the humidification and dehumidification device shall not exceed ±2 degrees Celsius.

[0007] Furthermore, the non-condensable gas obtained by separating the gas extracted in step S2 after being cooled by the condenser in step S3 is directly used as the sole gas source in step S5, without setting up an independent blower or compressor. By setting a gas source distributor and a throttle orifice, the gas source distribution ratio is made to be 0.05 to 0.30. The gas source distribution ratio is defined as the ratio of the volumetric flow rate of the non-condensable gas supplied in step S5 to the volumetric flow rate of the gas extracted in step S2. Meanwhile, the apparent gas velocity on the feed side of the membrane phase change separation column is set to 0.005 m / s to 0.03 m / s. The apparent gas velocity is defined as the gas volume flow rate on the channel cross-section divided by the channel cross-sectional area, and the content of entrained liquid droplets in the non-condensable gas after demisting is not higher than 50 mg / m³.

[0008] Furthermore, in step S6, the density-triggered passive diversion network is connected to the jet suction outlet of step S2 via a liquid-sealed riser, so that the diversion network operates as a pump-free back pressure stabilizing unit, and is implemented according to the following causal conditions: At any given time, only one of the branches leading to the brine pool or the branch leading to the reinjection is allowed to be open, while the other branch remains sealed to form an equivalent static liquid seal. The equivalent static water seal height is calculated to be 0.10 meters to 0.50 meters based on the density of seawater at 25°C. This height is spontaneously formed by the fluid density and liquid level difference, without the installation of electric valves, pneumatic valves or other active actuators. When the online conductance crosses a set threshold of 0.5 mSiemens per centimeter to 2.0 mSiemens per centimeter, the shunt network passively switches between the two branches; Using a sampling frequency of 1 Hz and a 10-minute sliding window, the short-time fluctuation standard deviation of the static pressure at the jet suction outlet is no greater than 1 kPa.

[0009] Furthermore, between step S3 and step S5, the gas-side closed space of the condenser in step S3 is used as the only equivalent gas buffer volume to supply non-condensable gas to step S5, without setting up an independent gas storage tank, accumulator or adjustable pressure regulating valve. And it operates under the following passive-dynamic conditions: The gas source buffer time is defined as the ratio of the gas equivalent buffer volume to the non-condensable gas volume flow rate in the supply step S5. The gas source buffer time is 2 to 20 seconds. With a sampling frequency of once per second and a time window of 60 seconds, the absolute value of the pressure change rate at the inlet of the gas source distributor is no greater than 1 kPa per second. Using a sampling frequency of once per second and a time window of 60 seconds, the root mean square (RMS) values ​​of the pressure sequences at the jet suction outlet and the pressure sequences at the gas source distributor inlet are obtained after bandpass filtering at 0.1 to 2 Hz. The amplitude ratio is defined as the ratio of the RMS value of the pressure sequence at the gas source distributor inlet to the RMS value of the pressure sequence at the jet suction outlet, and the amplitude ratio is not greater than 0.30. With a sampling frequency of once per second and a time window of 60 seconds, the coefficient of variation of the non-condensable gas volume flow rate supplied to step S5 is no higher than 10%.

[0010] Furthermore, when a disturbance occurs during the startup or operation of this method, the following steps shall be performed sequentially without using an external compressed gas, electromechanical vacuum pump, or circulating pump: Close the gas source distributor in step S5 and open the drive valve in step S2, so that the pretreated seawater forms a drive jet through the Venturi ejector and pumps out the gas in the membrane phase change separator shell until the absolute pressure of the shell side of the membrane phase change separator shell reaches the target value in the range of 30 kPa to 60 kPa and remains stable in the range of ±2 kPa for 5 minutes. Subsequently, the pumpless closed regenerative circuit between steps S3 and S4 is opened, so that the heat-releasing side of the condenser and the heat-absorbing side of the humidification and dehumidification device form a gravity recirculation until the logarithmic mean temperature difference between the two enters the range of 10 degrees Celsius to 25 degrees Celsius and is maintained for 3 minutes. Subsequently, non-condensable gas is slowly introduced from the closed space on the gas side of the condenser into step S5 through a fixed flow limiting element until the apparent gas velocity on the feed side of the membrane phase change separation column in step S5 reaches a set value in the range of 0.005 m / s to 0.03 m / s and is maintained within ±20% of this set value for 3 minutes. Next, the equivalent static water seal height in step S6 is adjusted to a range of 0.10 meters to 0.50 meters, so that the density-triggered passive diversion network enters the passive switching state. Using a sampling frequency of once per second and a time window of 60 seconds, the pressure sequences at the injection suction outlet and the pressure sequences at the gas source distributor inlet are bandpass filtered from 0.1 to 2 Hz and their root mean square values ​​are calculated. The amplitude ratio is defined as the ratio of the root mean square value of the pressure sequence at the gas source distributor inlet to the root mean square value of the pressure sequence at the injection suction outlet. When the amplitude ratio is not greater than 0.30, it is considered to have entered the stable operation stage.

[0011] In the above process, the entire operation relies solely on Venturi jet suction to establish and maintain the negative pressure in the membrane phase change separation shell, without using electromechanical vacuum pumps, steam ejectors or any equivalent devices; The absolute pressure of the shell side is kept stable between 30 kPa and 60 kPa, and the absolute value of the difference between the static pressure at the ejector outlet and the static pressure of the shell side is no greater than 5 kPa. The purpose of pretreatment is to reduce scale precursors and pollution tendencies, not to recover a single chemical element.

[0012] The core of this method lies in the combined closed loop formed by four passive units: First, the potential energy-driven Venturi suction establishes a shell-side negative pressure, so that the absolute pressure of the shell side operates within the window of 30 kPa to 60 kPa, the volume conversion time is controlled between 1.7 seconds and 6.7 seconds, the suction ratio is controlled between 0.12 and 0.45, and the absolute value of the pressure difference between the ejector and the shell side is not greater than 5 kPa. Secondly, gravity-driven closed-loop reheating achieves pump-free reflux; Third, non-condensable gas is used as the sole gas source to create scrubbing and disturbance in front of the membrane. The gas source distribution ratio is 0.05 to 0.30, and the apparent gas velocity in front of the membrane is 0.005 m / s to 0.03 m / s. The non-condensable gas is provided by the closed space on the gas side of the condenser, without the installation of an independent blower or compressor. Fourth, the static pressure difference between the ejector outlet and the shell side remains convergent, thus achieving long-term stable operation without a mechanical cooling source or external vacuum equipment. The entire operation process does not involve heating, distillation, or evaporation crystallization; no independent steam source, boiler, or heating device is set up to bring the liquid to a boiling state; preferably, the temperature of the liquid entering the membrane is not higher than 45 degrees Celsius, the temperature difference between the hot end and the cold end is controlled within the range of 3 to 25 degrees Celsius, and stable operation is achieved by establishing a shell-side negative pressure through a liquid ejector and cooperating with gravity-driven closed-loop regeneration.

[0013] In summary, the present invention has the following beneficial effects: Without configuring an electromechanical vacuum pump, steam ejector, and independent blower, the shell-side absolute pressure and ejector outlet static pressure are recorded at a sampling frequency of once per second during continuous operation. In any consecutive 72-hour period, the percentage of time when the shell-side absolute pressure is within the 30 kPa to 60 kPa window is not less than 95%. When the pressure difference between the ejector and the shell-side static pressure momentarily exceeds the limit, the deviation can be corrected by first reducing the drive opening and then appropriately increasing the flow restriction on the suction side. This can quickly restore the pressure to within the limit, thus demonstrating the stability and maintainability under the cooperation of passive components. By utilizing potential energy-driven Venturi jet suction to establish and maintain low pressure on the membrane side, the system achieves long-term stable operation with low installed power under conditions without an electromechanical vacuum pump or steam ejector, thus solving the problems of high energy consumption, complex maintenance, and poor off-grid adaptability caused by reliance on active vacuum.

[0014] By directly connecting the heat-releasing side of the condenser to the heat-absorbing side of the humidification and dehumidification devices and forming a pump-free closed-loop regenerative circuit with elevation difference, stable thermal matching under small temperature difference is achieved without the need for a circulating pump or mechanical cold source, solving the problems of high initial investment and high operating energy consumption, as well as large fluctuations at the hot end, of traditional circulating pump regenerative circuits. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram illustrating the relationship between the process boundaries and the flow of the present invention; Figure 2 This is a schematic diagram showing the connection between the Churi injector and the membrane phase change separation housing, as well as the measuring points, of the present invention. Figure 3 This is a schematic diagram of the pumpless regenerative circuit of the condenser and humidification / dehumidification device of the present invention; Figure 3 This is a schematic diagram of the pumpless regenerative circuit of the condenser and humidification / dehumidification device of the present invention; Figure 4This is a schematic diagram showing the connection relationship between the non-condensable gas closed-loop gas supply and the demisting process of the present invention. Figure 5 This is a schematic diagram of the density-triggered passive flow splitting network and liquid-sealed riser structure of the present invention; Figure 6 This is a flowchart illustrating the startup and disturbance recovery process of the present invention; Figure 7 This is a schematic diagram of the shell-side absolute pressure timing curve of the present invention; Figure 8 This is a schematic diagram of the time series curve of the outlet air dew point fluctuation of the present invention; Figure 9 This is a schematic diagram of the time-series curve of the gas supply volume flow rate variation coefficient of the present invention; Figure 10 This is a schematic diagram of the amplitude ratio time-series curve of the present invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Example: The following is in conjunction with the appendix Figure 1-10 The present invention will be described in further detail below.

[0019] Please see Figure 1-10 This invention provides a technical solution: a production method for separating high-concentration brine and pure water from seawater using potential energy, comprising the following steps: S1: Seawater is sent to a selective crystallization classification tower equipped with nucleating agents and inclined plate separation components for pretreatment to remove scaling precursors such as calcium sulfate and magnesium hydroxide, and pretreated seawater is obtained. S2: Under the influence of the height difference provided by the high-level water storage facilities above the ground or sea surface, the height of the shore slope building, or the rise and fall of the tide, the pretreated seawater flows through the Venturi jet to form a liquid jet, and draws in the gas connected to the membrane phase change separation and the small temperature difference regenerating shell to reduce the shell-side absolute pressure of the membrane phase change separation and the small temperature difference regenerating shell. S3: Connect the membrane phase change separation and small temperature difference regeneration shell to the vertically arranged membrane phase change separation and small temperature difference regeneration column, so that the feed is stripped at the top of the column and condensed in the condenser to obtain the first product water flow, while transferring the heat released by condensation to the humidification and dehumidification device. S4: In the humidification and dehumidification device, the humid air exchanges heat with the high-salt liquid from the concentrated salt branch and performs multi-effect recovery to obtain the second product water flow, and the recovered heat is returned to the membrane phase change separation and small temperature difference reheat column or returned to the seawater feed. The air-to-water volume ratio of the humidification and dehumidification device is 1 to 3, and the air-to-water volume ratio is defined as the ratio of the gas phase volume flow rate to the liquid phase volume flow rate in the device. S5: Establish an airlift circulation driven by a Venturi getter in the pre-membrane branch, connect a microporous diffuser in parallel in front of the membrane to generate microbubbles, and scrub the membrane surface to reduce concentration polarization. Among them, the volume fraction of microbubbles in the flow field of the near-wall region of the feed side of the membrane phase change separation and small temperature difference regeneration column is 1% to 5%, and the volume average particle size of the microbubbles is 50 micrometers to 150 micrometers. S6: A density-triggered passive diversion network is set up on the product water branch and the concentrated salinity branch to perform graded recovery or reinjection of fluids with different salinities based on the online conductivity threshold. The potential energy sources include, but are not limited to, deep wells, high-level reservoirs, or water towers; the potential energy is converted into membrane-side negative pressure by a liquid ejector, and works in conjunction with gravity-driven closed-loop regeneration to maintain a small temperature difference, thereby achieving non-boiling membrane phase change separation.

[0020] In this embodiment: the experiment was conducted on a small-scale test platform with a rated water production capacity of 1 cubic meter per hour. The raw water was taken from natural sea areas with a salinity of 35 grams per liter and a temperature of 25°C. It did not contain industrial brine or underground brine. The process was run continuously in the order of the claims. All online quantities were sampled and saved at a frequency of once per second.

[0021] First, selective crystallization and classification pretreatment is carried out. A fiberglass vertical classification tower is set up with a diameter of 0.6 meters and a height of 2.5 meters. Inclined plate settling modules with an angle of 60° to the horizontal are arranged inside the tower, and calcium sulfate seed crystals are continuously added as nucleating agents. The median particle size of the seed crystals is 100 micrometers and the addition concentration is 2.0 grams per liter. Using calcium sulfate and magnesium hydroxide as the target salt system, the supersaturation was maintained at approximately 20% through a dosing pump and online sensor feedback, with a hydraulic retention time of 20 minutes. Automatic sludge discharge was performed when the bottom conductivity reached 60 mSiemens per centimeter or the upper turbidity reached 100 turbidity units. After this pretreatment, sampling and testing showed a significant decrease in calcium hardness and sulfate ions, and the fouling index dropped from 6.0 to 3.5, providing conditions for subsequent scale reduction in the membrane section.

[0022] Among them, supersaturation is calculated as follows: Define, where IAP = [Ca] 2+ SO4 2- ], K sp (T) represents the solubility product of the salt system at the operating temperature, and the percentage of Ω-1 is the supersaturation percentage. In this example, it is taken as about 20%.

[0023] The fouling index is SDI-15, which is determined according to ASTM D4189 (0.45μm filter membrane, constant pressure difference for 15 min). The smaller the value, the weaker the tendency to scale or clog.

[0024] Subsequently, negative pressure is established using potential energy. The effective elevation difference between the high-level water storage facility and the centerline of the Venturi jet is 40 meters. Under the action of this elevation difference, the pretreated seawater enters the jet to form a driving jet.

[0025] The ejector is made of 316L stainless steel, with a throat diameter of 10 mm and an outlet diameter of 28 mm. The ratio of the outlet to the throat cross-sectional area is 7.8. The suction port is connected to the membrane phase change separator and the small temperature difference regenerative shell. The volumetric flow rate of the drive branch, measured by an electromagnetic flowmeter, is 0.0060 cubic meters per second. The free volume of the shell side and the connecting pipeline, measured by filling and draining, is 0.020 cubic meters. The calculated volume conversion time is 3.33 seconds, and the ratio of the volumetric flow rate of the suction branch to that of the drive branch is 0.20. The absolute pressure of the shell side is monitored by an absolute pressure transmitter and stabilized within a window of 30 to 60 kPa. Simultaneously, a back pressure gauge is used to control the difference between the static pressure at the ejector outlet and the static pressure in the shell side to not exceed 5 kPa.

[0026] The membrane phase change separation and small temperature difference regeneration shell is connected to a vertically arranged membrane phase change separation and small temperature difference regeneration column. The membrane module is a polytetrafluoroethylene flat sheet membrane with a pore size of 0.2 micrometers. Each unit has an effective area of ​​12 square meters, with five units in total, for a total effective area of ​​60 square meters. The column is 8 meters high, with a stripping port at the top. An external plate condenser with a heat exchange area of ​​8 square meters is connected to the top of the column. The feed enters from the top of the column at a temperature of 55°C. The absolute pressure on the shell side is maintained by the aforementioned ejector. To achieve pump-free regeneration, the heat release side of the condenser and the heat absorption side of the humidification and dehumidification device are directly connected through a pipeline. Gravity recirculation is formed by a 1.2-meter elevation difference. No circulating pump or parallel mechanical cold source is installed. The volume ratio of air to liquid in the humidification and dehumidification device is set to 1:1.6.

[0027] Four temperature measuring points were set up at the condenser hot side inlet, condenser hot side outlet, and humidifier / dehumidifier absorber side inlet and outlet. The logarithmic mean temperature difference was calculated according to the conventional definition, and the result was 15℃. The comprehensive heat recovery rate was calculated based on the heat balance and the result was 0.68.

[0028] Among them, the logarithmic mean temperature difference is calculated according to Calculate, where ΔT1=T 冷凝器热侧入口 -T HDH吸热侧出口 ΔT2=T 冷凝器热侧出口 -T HDH吸热侧入口 Temperatures at the four points were collected by PT100.

[0029] A dew point meter is installed at the outlet air of the humidification and dehumidification device to record the fluctuation range of the dew point temperature, which is maintained at ±1.3 degrees Celsius during stable operation.

[0030] Airlift and microbubble scrubbing are set in the pre-membrane channel.

[0031] The gas is taken only from the non-condensable gas extracted by the ejector and separated after condensation. As the sole gas source in front of the membrane, no blower or compressor is installed. The non-condensable gas is sent into the in front of the membrane channel after being restricted by four fixed orifice plates with a diameter of one millimeter in parallel.

[0032] Parallel sintered ceramic microporous diffusers, with an average pore size of 40 micrometers and a total area of ​​0.20 square meters, were positioned 30 millimeters from the membrane surface. The apparent gas velocity in the pre-membrane channel of this configuration was 0.012 meters per second. Using differential pressure and phase content calibration, the microbubble volume fraction measured at 30 millimeters from the membrane surface was 2.2%. High-speed imaging and image processing statistical analysis yielded a volume average particle size of approximately 80 micrometers, with a sample size of no less than 5,000.

[0033] A passive diversion network is installed on the product water and concentrated brine sides, using float valves and gravity valves in conjunction with liquid-sealed risers to achieve pump-free back pressure stabilization. At any given time, only one branch leading to the brine pool or reinjection is allowed to open, while the other branch maintains a liquid seal to form an equivalent static water seal. The liquid seal height is set to 0.25 meters based on the density of seawater at 25 degrees Celsius; the online conductivity threshold is set at 1.5 millisiemens per centimeter, and passive switching between the two branches is implemented when the threshold is exceeded.

[0034] To quantify the dynamic stability of gas supply and negative pressure, a pressure transmitter was installed at both the ejector outlet and the gas source distributor inlet, sampling at a frequency of once per second. The root mean square (RMS) of the 0.1 to 2 Hz frequency band was bandpass filtered before calculation. The amplitude ratio was defined as the ratio of the RMS pressure sequence at the gas source distributor inlet to the RMS pressure sequence at the ejector outlet. During stable operation, this ratio was 0.24, indicating that passive buffering and passive diversion significantly attenuated pressure disturbances.

[0035] The entire process operated continuously for 72 hours without the use of electromechanical vacuum pumps, circulation pumps, and blowers. Records showed that the shell-side absolute pressure remained within the 30-60 kPa window for 97.2% of the time; the permeate flux was 16.2 liters per square meter per hour, with a flux variation coefficient of 3.8%; the overall permeate conductivity was 480 microSiemens per centimeter; and the transmembrane pressure differential increased by 2.0 kPa over 72 hours.

[0036] The unit water production power consumption is 0.06 kWh per cubic meter, the installed power is 0.05 kW, and there were no unplanned shutdowns within 72 hours. All instruments underwent annual calibration and on-site two-point comparison according to the calibration record sheet. The comparison deviation between the two pressure points of 40 kPa and 60 kPa did not exceed 0.2 kPa, and the dew point comparison deviation did not exceed 0.1℃, to ensure the traceable accuracy of the calculation of derived quantities such as logarithmic mean temperature difference, amplitude ratio, and flux variation coefficient.

[0037] The specific experimental data are as follows: Experimental Data Table (Table #1) Parameters / Units This invention - Pump-free unified path Compare with A - Venturi + blower Compare with B-vacuum pump + blower Comparison with C-vacuum pump + mechanical regeneration Influent salinity (g / L) 35 35 35 35 Inlet water temperature (°C) 25 25 25 25 Height difference H (m) 40 40 10 10 Injector area ratio (-) 7.8 7.8 NA NA Suction ratio S(-) 0.20 0.20 NA NA Average absolute pressure in the shell side (kPa) 40 42 48 50 Percentage of time with shell-side absolute pressure within 30–60 kPa 97.2 92.1 88.5 85.3 Volume conversion time t(s) 3.33 3.33 NA NA Gas-to-water volume ratio (-) 1.6 1.6 1.8 1.7 Logarithmic mean temperature difference (°C) of LMTD 15 15 28 20 Overall heat recovery rate (-) 0.68 0.61 0.35 0.50 Apparent air velocity (m / s) 0.012 0.020 0.018 0.019 Microbubble volume fraction (%) 2.3 3.0 2.7 2.8 Microbubble volume average particle size (μm) 80 120 110 100 Overall permeable water conductivity (μS / cm) 480 520 540 550 Water production flux (L / m²·h) 16.2 15.0 14.3 14.6 Coefficient of variation of water production flux (CV) (%) 3.8 6.3 7.1 7.8 Amplitude ratio AR (0.1–2 Hz, 60 s window) (-) 0.24 0.62 0.55 0.70 The transmembrane pressure difference increases by ΔP (kPa / 72h). 2.0 5.5 7.8 8.4 Electricity consumption per unit of water produced (kWh / m³) 0.06 0.15 0.32 0.38 Number of unplanned outages (times / 72 hours) 0 1 2 2 Installed power (kW) 0.05 0.20 0.45 0.55 Rated water production capacity (m³ / h) 1.0 1.0 1.0 1.0 Instrument Calibration Record Sheet (Table #2) Calibration parameters / items Pressure transmitter P1 (shell side absolute pressure) Pressure transmitter P2 (ejector outlet pressure) Electromagnetic flowmeter F1(Qd) Mass flow meter F2 (Qs, converted to 25°C) Platinum resistance temperature T1–T4 (condensation / HDH four points) Dew point meter DP1 (HDH outlet) Conductivity meter EC1 (online) Differential pressure transmitter DPm (pre-membrane phase content) Power meter PW1 (installed power) Instrument Model Rosemount 3051S ABB266 EndressPromag10W Brooks SLA58 PT100A grade four VaisalaDMT143 Hachsc200+ Four-Ring Probe Emerson 3051DP Fluke1730 Range / Accuracy 0–100 kPa ± 0.25% FS 0–100 kPa ± 0.25% FS 0–30 m³ / h ± 0.5%FS 0–50 Nm³ / h ± 1.0%FS -50–200°C ±0.15°C -20–80°C ±0.1°C 0–100 mS / cm ± 1% reading 0–10 kPa ± 0.25%FS 0–3kW ±1% reading Last calibration date 2025-07-10 2025-07-10 2025-07-08 2025-07-08 2025-07-05 2025-07-05 2025-07-06 2025-07-09 2025-07-06 Calibration method Piston pressure gauge two points Piston pressure gauge two points Standard ledger flow meter three points Standard gas flow meter three points Three-point temperature control bath (0 / 25 / 60°C) Comparison of salt water saturation points - U-tube calibration curve Standard source comparison Zero point error 0.05 kPa 0.06 kPa 0.00m³ / h 0.00 Nm³ / h ≤0.05°C ≤0.05°C 0.00mS / cm 0.00 kPa 0.00kW Range error ±0.18kPa ±0.20kPa ±0.11m³ / h ±0.35Nm³ / h ±0.12°C ±0.08°C ±0.3mS / cm ±0.02kPa ±0.01kW Results of on-site comparison at two points (point 1 / point 2) 40 / 60kPa difference≤0.2kPa 40 / 60kPa difference≤0.2kPa Difference of 10 / 20 m³ / h ≤ 0.1 The difference between 10 / 30 Nm³ / h and ≤0.3 0 / 25°C difference ≤ 0.1°C Dew point difference at 10 / 20°C ≤ 0.1°C 5 / 50mS / cm difference ≤1% 1 / 5 kPa difference ≤ 0.05 kPa 0.5 / 1.0kW difference≤1% Qualification qualified qualified qualified qualified qualified qualified qualified qualified qualified Data shows that this embodiment demonstrates substantial improvements over the three controls in terms of energy consumption, stability, and antifouling, and has a clear causal relationship with the key technical path in the claims. Firstly, regarding energy consumption, the unit water production power consumption is 0.06 kWh / m³, lower than Control A's 0.15 kWh / m³, Control B's 0.32 kWh / m³, and Control C's 0.38 kWh / m³. The difference stems from two core design features: firstly, the potential energy is used to directly establish shell-side negative pressure via a Venturi jet, eliminating the continuous power consumption of the electromechanical vacuum pump; secondly, the condenser and humidification / dehumidification device form a pump-free closed-loop regenerative circuit, achieving gravity recirculation through a 1.2m elevation difference and reaching a comprehensive heat recovery rate of 0.68 at a logarithmic mean temperature difference of 15°C, significantly reducing external heating requirements. Compared with B, after the closed-loop regeneration was removed, the logarithmic mean temperature difference increased to 28°C, the overall heat recovery rate decreased to 0.35, and the unit energy consumption increased significantly, which verified the decisive role of the pumpless regeneration closed loop in energy efficiency.

[0038] In terms of stability, the shell-side absolute pressure remained within the 30-60 kPa window for 97.2% of the time, significantly higher than Control A (92.1%), Control B (88.5%), and Control C (85.3%). The amplitude ratio was 0.24, while those for Control A, Control B, and Control C were 0.62, 0.55, and 0.70, respectively. The amplitude ratio was calculated by taking the root mean square of the pressure sequences at the ejector outlet and the gas source distributor inlet after bandpass filtering from 0.1 to 2 Hz. A smaller value indicates a weaker disturbance transmitted from the negative pressure side to the gas supply side. This embodiment uses the enclosed space on the gas side of the condenser as the sole equivalent gas buffer volume and a pump-free back pressure stabilizing unit constructed with a liquid-sealed riser to passively filter pressure disturbances, keeping the gas supply pressure and apparent gas velocity at a stable level near the set point. This passive integration of "sole gas source with sole buffer" differs from the active branch control of blower and pressure regulator used in Control A and Control B, avoiding residual vibrations and random fluctuations introduced by additional moving parts.

[0039] Regarding antifouling and anti-scaling, the transmembrane pressure difference increase at the membrane front after 72 hours was only 2.0 kPa, significantly lower than 5.5 kPa for Control A, 7.8 kPa for Control B, and 8.4 kPa for Control C. Despite the apparent gas velocity being set at a relatively low level of 0.012 m / s, the fine scrubbing with a microbubble volume fraction of 2.3% and a volume average particle size of approximately 80 μm effectively reduced concentration polarization and initial deposition. The key factor was that the gas supply came from non-condensable gas after extraction and was condensed and demisted, keeping entrained droplets at a low level and reducing secondary salt spray deposition. While the forced-air supply in Controls A and B could temporarily increase shear, the larger particle size and more drastic fluctuations easily led to redeposition and flux fluctuations. Correspondingly, the flux variation coefficient decreased to 3.8% under the conditions of this invention, while it was 6.3%, 7.1%, and 7.8% for Controls A, B, and C, respectively. The overall permeate conductivity remained at 480 μS / cm, which was better than the control group, indicating that pretreatment and passive diversion and reinjection together reduced the penetration of high-salinity solutes and limited their circulation accumulation.

[0040] Calibration records show that key instruments such as pressure, flow rate, temperature, dew point, conductivity, and power underwent standard calibration and on-site two-point comparison before the test. The two-point deviation of pressure did not exceed 0.2 kPa, and the deviation of dew point did not exceed 0.1°C, ensuring the traceability and reliability of the calculation of derived quantities such as logarithmic mean temperature difference, amplitude ratio, and flux variation coefficient. In summary, this embodiment achieves the synergy of pump-free negative pressure, pump-free regeneration, and passive pressure stabilization through a unified potential energy and non-condensable gas path. Without introducing electromechanical vacuum pumps, circulating pumps, and independent blowers, it achieves lower unit water production energy consumption, higher operational stability, and slower pollution growth.

[0041] like Figure 1-10 As shown, the operating conditions for the selective crystallization fractionation pretreatment of S1 are: The supersaturation of the target salt system of calcium sulfate and magnesium hydroxide is 10% to 30%, the reaction residence time is 10 to 30 minutes, the angle between the inclined plate and the horizontal is 45° to 70°, seed crystals with a median particle size of 50 micrometers to 200 micrometers are added, the seed crystal concentration is 0.5 g / L to 5 g / L, and sludge is discharged when the online turbidity in the settling zone reaches 50 to 200 NTU or the bottom conductivity reaches 55 to 65 millisiemens per centimeter.

[0042] In this embodiment, the experiment was conducted on a continuous flow pilot-scale platform. The raw water was natural seawater with a salinity of 35 g / L and a temperature of 25°C, excluding industrial brine and underground brine. The pretreatment unit was a vertical fiberglass graded crystallization tower with a diameter of 0.6 m and a height of 2.5 m. The tower was internally equipped with inclined plate settling components at a 60° angle to the horizontal, with a net spacing of 50 mm between the plates, resulting in an effective settling area of ​​approximately 12 m².

[0043] The tower body consists of a mixing and nucleation zone, an inclined plate classification zone, and a thickening hopper, arranged from top to bottom. The designed influent flow rate is 1.8 m³ / h, ensuring a total hydraulic retention time of 20 min. A circulation bypass is installed on the side of the tower for continuous seed replenishment and rapid sampling; online measurements include temperature, pH, conductivity, turbidity, and flow rate, with sampling frequency once per second and data archived.

[0044] Supersaturation is defined as the ratio of the product of ion activities to the solubility product at the same temperature. For example, with calcium sulfate, supersaturation equals IAP / Ksp, where IAP is the product of calcium ion activity and sulfate activity. With magnesium hydroxide, supersaturation equals the product of magnesium ion activity and the square of hydroxide activity, divided by Ksp. The percentage obtained by subtracting 1 from the supersaturation value is taken as the supersaturation percentage.

[0045] In this embodiment, the supersaturation percentage of calcium sulfate is controlled at 20%, and the supersaturation percentage of magnesium hydroxide is controlled at 25%, which can be adjusted within the range of 10% to 30%. The activity coefficient is calculated based on online conductivity and temperature, and the solubility product adopts the value of the standard chemical data table at the operating temperature. The activity coefficient is calculated according to the Davies formula. Where A is the aqueous solution constant at the operating temperature, and z i Ω represents the ionic charge number, and I represents the ionic strength; alternatively, the equivalent Pitzer / lookup table coefficient can be used, and the resulting difference in Ω does not affect the determination after sensitivity analysis.

[0046] The seed crystals are industrial-grade calcium sulfate dihydrate crystals and are continuously added via side-stream; the median particle size of the seed crystals is 100μm, and the laser particle size analyzer confirms that D10 is approximately 65μm and D90 is approximately 165μm; the online addition concentration is 1.5g / L, which falls within the set range of 0.5 to 5g / L.

[0047] To promote the preferential nucleation of magnesium hydroxide without excessive alkalization, the pH is maintained between 9.8 and 10.2 in the mixing zone, and the alkali source is a dilute sodium hydroxide solution. Micro-dosing is carried out through a combined feedback loop of conductivity and pH to keep the supersaturation of magnesium hydroxide within a controllable range, thus avoiding the rapid settling of large particles and excessive alkali consumption.

[0048] The characteristic shear rate at the inlet of the reaction zone is converted to 120 s. -1 up to 180s -1 To ensure the resuspension of crystal nuclei without breakage, the linear velocity in the inclined plate zone is controlled at 0.05 m / s to 0.1 m / s, allowing crystals larger than 50 μm to slide along the plate surface into the thickening hopper. Online turbidity and conductivity are used as trigger conditions for sludge discharge: when the turbidity of the upper overflow reaches the lower limit of the set value of 50 to 200 NTU, or the conductivity of the bottom thickening hopper is between 55 and 65 mS / cm, the sludge discharge valve automatically opens to discharge sludge to the target level; the typical sludge discharge cycle is once every 15 to 25 minutes, lasting 30 to 45 seconds. The sludge discharge control adopts threshold comparison + minimum interval logic: when the upper turbidity is greater than or equal to the set value or the bottom conductivity is greater than or equal to the set value and 10 minutes have passed since the last sludge discharge, sludge discharge is performed. Sludge discharge is automatically stopped when the set liquid level is reached or after 30-45 seconds to prevent excessive sludge discharge from causing backflow disturbance.

[0049] The sampling and measurement methods are as follows: calcium, magnesium, and sulfate were quantified by inductively coupled plasma atomic emission spectrometry after 0.45 μm filtration; SDI15 was determined according to the constant pressure method of ASTM D4189; turbidity was measured using an infrared turbidimeter; conductivity was measured using a four-electrode conductivity probe; and pH was measured using a glass electrode meter. To verify the sufficiency and reproducibility of the disclosure, each of the three operating conditions was independently replicated three times, with each run lasting 4 to 6 hours. Key operating conditions and effluent indicators were recorded, and the mean and standard deviation were calculated. The three operating conditions are defined as follows: This invention is a selective crystallization and grading process, including continuous seeding, mild alkalization, and grading sedimentation; Control A is lime softening, with pH adjusted to 10.5 to 10.8 and no seeding added; Control B is coagulation and clarification, with the addition of 50 mg / L polyaluminum chloride and 2 mg / L cationic flocculant, without controlling supersaturation and without seeding. The three operating conditions share the same tower body and inclined plate structure, only changing the dosing strategy and control targets to ensure comparability.

[0050] The operating results show that under the conditions of this invention, the concentration of calcium ions in the effluent decreased from 410 mg / L to about 250 mg / L, the concentration of sulfate decreased from 2700 mg / L to about 2100 mg / L, the supersaturation percentage of calcium sulfate decreased from about 22% to about 3%, and the supersaturation percentage of magnesium hydroxide decreased from about 25% to about 8%; the SDI15 of the effluent decreased from 6.0 to about 3.5, the overflow turbidity was maintained at 3 to 5 NTU, the unit sludge yield was about 0.13 kg dry solids / m³, and the alkali consumption was about 95 g NaOH / m³. In contrast, although control A significantly reduced magnesium ions with a higher pH, the percentage of calcium sulfate supersaturation was still about 10%, the effluent SDI15 was 4.6, the alkali consumption was about 210 g / m³, and the unit sludge yield was about 0.31 kg dry solids / m³. Control B had higher effluent turbidity and SDI15, with turbidity ranging from 8 to 15 NTU and SDI15 of 6.1. Both types of supersaturation remained at a high level, which was not conducive to subsequent membrane phase change separation and scaling control in small temperature difference regeneration.

[0051] The data is as follows: Experimental Data Table (Table #3) Parameters / Units This invention - Selective crystallization grading (average) This invention - Selective crystallization grading (standard deviation) Comparison A - Lime softening (mean) Control A - Lime softening (standard deviation) Comparison with B-coagulation clarification (mean) Control B - Coagulation and Clarification (Standard Deviation) Operating temperature (°C) 30.0 0.2 30.0 0.2 30.0 0.2 Duration of stay (min) 20 0 20 0 20 0 Angle (°) between the inclined plane and the horizontal. 60 0 60 0 60 0 Median seed crystal size (μm) 100 5 NA NA NA NA Seed concentration (g / L) 1.5 0.1 NA NA NA NA pH (mixing zone) 10.0 0.1 10.6 0.1 7.7 0.1 Target supersaturation _CaSO4(%) 20 1 Uncontrolled NA Uncontrolled NA Target supersaturation _Mg(OH)2(%) 25 1 >30 NA Uncontrolled NA Effluent Ca2+ (mg / L) 250 8 320 10 395 12 SO4^2- (mg / L) in effluent 2100 50 2450 60 2680 70 Mg2+ in effluent (mg / L) 950 30 820 25 1240 35 Supersaturation of CaSO4 in effluent (%) 3 0.5 10 1.0 22 1.5 Supersaturation of Mg(OH)2 in effluent (%) 8 1.0 5 0.8 25 1.2 Overflow turbidity (NTU) 4 0.6 8 1.0 12 1.5 SDI-15(-) 3.5 0.2 4.6 0.3 6.1 0.4 Unit sludge yield (kg dry solids / m³) 0.13 0.02 0.31 0.03 0.09 0.02 Alkali consumption (gNaOH / m³) 95 5 210 10 0 0 PAC consumption (mg / L) 0 0 0 0 50 5 Cationic flocculant consumption (mg / L) 0 0 0 0 2 0.2 CaSO4 scaling risk index (relative value) 0.25 0.03 0.55 0.05 1.00 0.10 Average conductivity of effluent over 72 hours (mS / cm) 52.0 0.6 53.5 0.7 54.1 0.8 Instrument Calibration Record Sheet (Table #4) Calibration items / parameters pH meter pH1 Conductivity meter EC2 Turbidity meter NTU1 Thermometer T-PT100 Online flow meter F-EMF ICP-OES Laboratory Model / Specification MettlerSeven2Go Hachsc200 four-electrode Hach2100Q PT100A EndressPromag10W Agilent 5110 Measuring range and accuracy pH 0–14 ± 0.01 0–100 mS / cm ± 1% reading 0–1000 NTU ± 2% reading -50–200°C ±0.15°C 0–30 m³ / h ± 0.5%FS Elemental quantification RSD ≤ 2% Last calibration date 2025-07-05 2025-07-06 2025-07-06 2025-07-05 2025-07-08 2025-07-02 Calibration method NIST buffer solution (3 points): 4.01 / 7.00 / 10.01 Conductivity standard solution 12.88 and 50.0 mS / cm Formalhydrazine fractionation standard solution Thermostatic bath with two points at 0°C and 25°C Standard ledger flow meter three points Internal standard recovery rate: 95–105% On-site two-point comparison results The pH difference between 6.50 and 10.00 is ≤0.02. The difference between 12.88 and 50.0 mS / cm is ≤1%. The difference between 10 and 100 NTU is ≤2%. The difference between 0°C and 25°C is ≤0.1°C. The difference between 10 and 20 m³ / h is ≤0.1 Internal standard recovery rate: 99% Qualification qualified qualified qualified qualified qualified qualified The above data demonstrates the comprehensive advantages of selective crystallization grading in "reducing scaling risk, improving effluent treatability, and reducing chemical consumption and sludge." The mean and standard deviation are provided through three repeated experiments to ensure the repeatability and verifiability of the results.

[0052] Firstly, from the perspective of controllable crystallographic driving, the combined effect of continuous seed crystals and mild alkalization allows calcium sulfate to preferentially nucleate and grow heterogeneously on the seed crystal surface within the reaction zone. Data shows that the supersaturation percentage of calcium sulfate decreased from about 22% to about 3%, while control A remained at about 10%, and control B was even higher. This difference directly corresponds to the ion composition of the effluent: the calcium ion and sulfate ion in the effluent of this invention are 250 mg / L and 2100 mg / L, respectively, which are lower than 320 and 2450 in control A, and 395 and 2680 in control B. Since the scaling tendency of calcium sulfate is highly correlated with the activity product of the product ions, the present invention reduces the scaling driving force of subsequent membrane phase change separation and small temperature difference reheating in the pretreatment stage through selective crystallization. From the perspective of classification sedimentation and liquid-solid separation efficiency, the angle between the inclined plate and the horizontal at 60° and the linear velocity of 0.05m / s to 0.1m / s allows crystals larger than 50μm to slide along the plate surface and enter the thick sludge hopper, significantly reducing the residual suspended solids carried by the overflow, which is reflected in the overflow turbidity of about 4NTU, which is significantly better than 8 for control A and 12 for control B. SDI15 was approximately 3.5, which was also better than the two control groups. This means that the inlet boundary layer of the subsequent membrane segment is thinner and the risk of particle blockage is lower. Further examining the operational economy, while achieving a considerable reduction in calcium and magnesium, the alkali consumption of this invention is approximately 95 g NaOH / m³, only about 45% of that of control A; the unit sludge yield is approximately 0.13 kg dry solids / m³, also significantly lower than 0.31 of control A. This indicates that the strategy of continuous seeding and mild alkali treatment has better coupling economy in terms of chemical consumption and sludge compared to strong alkali softening. Although control B has no alkali consumption and a smaller amount of sludge, the scaling risk index of the subsequent membrane segment is normalized to 1 because it does not reduce the two types of supersaturation, resulting in the worst overall effect. Furthermore, by setting the upper overflow turbidity threshold of 50 to 200 NTU and the bottom conductivity threshold of 55 to 65 mS / cm, this method can achieve intermittent sludge discharge based on online signals without relying on complex controllers, maintain the effective settling interface position in the inclined plate zone, and avoid secondary carryover caused by crystal backmixing. The standard deviation of three repetitions shows that the above threshold settings can be repeatedly maintained at low turbidity and low SDI levels, and stably achieve pressure drop on the supersaturation of calcium sulfate and magnesium hydroxide.

[0053] like Figure 1-10As shown, in step S2, the negative pressure of the membrane phase change separation and small temperature difference regenerative shell is established and maintained by Venturi jet suction, and no electromechanical vacuum pump, steam ejector, vacuum tank pre-extraction equipment is used during operation, nor is the negative pressure generated by the deep well static water column. Specifically, the following conditions are met: The pretreated seawater obtained in step S1 flows through the contraction section, throat and diffuser section under the action of height difference to form a driving jet, and continuously extracts the gas in the shell through the suction port that is connected to the membrane phase change separation and the small temperature difference regenerating shell, so as to stabilize the shell side absolute pressure at 30 kPa to 60 kPa. The volume conversion time, i.e., the ratio of the effective volume of the membrane phase change separation and small temperature difference regeneration shell to the volumetric flow rate of the drive branch, is 1.7 seconds to 6.7 seconds. The suction ratio, i.e., the ratio of the volumetric flow rate of the suction branch to the volumetric flow rate of the drive branch, is 0.12 to 0.45, and the absolute value of the pressure difference between the static pressure at the injection suction outlet and the shell-side static pressure is not greater than 5 kPa. During continuous 72-hour operation, the shell-side absolute pressure is in the range of 30 kPa to 60 kPa for no less than 95% of the time. In this embodiment, the method is implemented under normal seawater conditions with a salinity of 35 g / L and a temperature of 25°C. The entire operation relies solely on Venturi jet suction to establish and maintain negative pressure in the membrane phase change separation and small-temperature-difference regenerating shell, without using electromechanical vacuum pumps, steam ejectors, vacuum tank pre-extraction equipment, or any equivalent devices. Pretreated seawater is fed into the ejector using an effective elevation difference of 40 m between the high-level water head and the ejector centerline to form a driving jet. The ejector throat diameter is 10 mm, the outlet diameter is 28 mm, and the ratio of the outlet to the throat cross-sectional area is 7.8. The suction port is connected to the top of the membrane phase change separation and small-temperature-difference regenerating shell via a straight pipe with an inner diameter of not less than 12 mm. The total length of the connecting pipe does not exceed 15 times the throat diameter and a check valve is installed to prevent backflow.

[0054] The effective free volume of the shell and its connecting pipes is recorded as the shell free volume. The measurement is performed three times consecutively by filling to the mark and then emptying the shell. The arithmetic mean is taken. The relative standard deviation of the three readings is no higher than 3%. The volumetric flow rate of the drive branch is recorded as the drive flow rate, which is measured by an electromagnetic flow meter and sampled at a frequency of once per second; the volumetric flow rate of the suction branch is recorded as the suction flow rate, which is measured by a thermal mass flow meter and uniformly converted to the volumetric flow rate under 25°C conditions.

[0055] The volume conversion time is defined as the free volume of the shell divided by the driving flow rate. In this embodiment, the volume conversion time is set to operate at the midpoint of 3s to 4s and maintained within the range of 1.7s to 6.7s. The suction ratio is defined as the suction flow rate divided by the driving flow rate. In this embodiment, the suction ratio is set to 0.20 and maintained within the range of 0.12 to 0.45.

[0056] Absolute pressure transmitters are installed at the outlet of the diffuser section of the injector and at the top of the casing to monitor static pressure. The absolute value of the static pressure difference between the two locations is defined as the static pressure difference between the injector and the casing. The back pressure is finely adjusted to ensure that it does not exceed 5 kPa, preferably maintained in the range of 3 kPa to 5 kPa.

[0057] The startup sequence is as follows: first, open the drive valve to the predetermined opening degree, so that the absolute pressure of the shell side drops into the target window of 30kPa to 60kPa and remains stable within the range of ±2kPa for 5 minutes. Then, fine-tune the back pressure valve to make the static pressure difference between the injection port and the shell side converge to 3kPa to 5kPa and fix the valve position to enter continuous operation.

[0058] During continuous operation, the shell-side absolute pressure, ejector outlet static pressure, drive flow rate, and suction flow rate are synchronously recorded at a sampling frequency of once per second. After excluding periods of manual intervention and instrument self-checking, the percentage of time within any consecutive 72-hour period where the shell-side absolute pressure is within the 30 kPa to 60 kPa window is statistically analyzed. This percentage, not less than 95%, is used as the criterion for stable operation. If, during operation, the absolute value of the difference between the ejector outlet and the shell-side static pressure exceeds 5 kPa instantaneously, the deviation is corrected by first reducing the drive opening and then appropriately increasing the flow restriction on the suction side until it returns to within the limit. If the shell-side absolute pressure deviates from the target window, the nozzle Reynolds number is first reduced and the connecting pipe is checked for leaks before returning to the set point.

[0059] The measurement aperture and accuracy requirements for implementing the above process are as follows: The absolute pressure of the shell side and the static pressure of the ejector outlet are measured using an absolute pressure transmitter with a range of 0 to 100 kPa and an accuracy of not less than 2.5 per thousand of the range. The measurements are compared at two points, 40 kPa and 60 kPa, and the difference between the two points does not exceed 0.2 kPa. The driving flow rate uses an electromagnetic flow meter with a range of 0 to 30 m³ / h and an accuracy of not less than 0.5% of the range. The on-site comparison error between the 10 and 20 m³ / h points does not exceed 0.1 m³ / h. The suction flow rate uses a thermal mass flow meter with a range of 0 to 50 Nm³ / h and an accuracy of not less than 1% of the range. The volumetric flow rate is calculated under the condition of a temperature of 25°C. The on-site comparison error between the 10 and 30 Nm³ / h points does not exceed 0.3 Nm³ / h. After the above instruments have completed their annual calibration, a two-point comparison will be conducted on-site. The free volume of the casing will be judged as having a relative standard deviation of no more than 3% based on three filling and draining measurements.

[0060] By controlling the volume conversion time to the range of 1.7s to 6.7s, the suction ratio to the range of 0.12 to 0.45, and limiting the static pressure difference between the ejector and the shell side to below 5kPa, the shell side absolute pressure can be maintained in the target window of 30kPa to 60kPa for a long time without configuring any electromechanical vacuum equipment and pre-evacuation volume, thereby satisfying all the quantitative constraints of claim 3 regarding the establishment and maintenance of negative pressure.

[0061] As one of the implementation methods, the throat diameter, area ratio and effective elevation difference can all be equivalently replaced within the scope defined by the claims. As long as the three constraints of volume conversion time, suction ratio and static pressure difference between the injection port and the shell side are maintained, the same technical effect as this embodiment can be obtained.

[0062] like Figure 1-10 As shown, between step S3 and step S4, the heat-releasing side of the condenser in step S3 and the heat-absorbing side of the humidification and dehumidification device in step S4 are directly connected by a pipeline to form a pumpless closed-loop regenerative circuit by gravity recirculation, and no circulating pump or parallel mechanical cold source is set up. The regenerative circuit must meet the following conditions: The gravity return drop shall not be less than 1 meter; The logarithmic mean temperature difference between the condenser and the humidification / dehumidification device is 10 to 25 degrees Celsius. The overall heat recovery rate of the humidification and dehumidification device is not less than 0.60, and the overall heat recovery rate is the proportion of the recoverable heat fed into the humidification and dehumidification device that is returned to step S3 or returned to the seawater feed. During continuous 72-hour operation, the absolute value of the difference between the average heat exchange per unit time of the condenser and the average heat absorption per unit time of the humidification and dehumidification device shall not exceed 10% of the average heat exchange per unit time of the condenser, and the dew point temperature fluctuation of the outlet air of the humidification and dehumidification device shall not exceed ±2 degrees Celsius. In this embodiment, the method directly connects the heat release side outlet of the condenser to the heat absorption side inlet of the humidification and dehumidification device via a pipeline, and reconnects the heat absorption side outlet back to the heat release side inlet of the condenser to form a closed loop. The condenser is arranged at a high position, and the humidification and dehumidification device is arranged at a low position, with a static water level difference of 1.2 meters. The pipeline has a continuous slope throughout, with automatic venting at the highest point and sewage discharge at the lowest point. The working fluid in the loop is fresh water with a corrosion inhibitor added at a mass fraction not exceeding 1 / 1000. It operates at atmospheric pressure and does not have a circulating pump or parallel mechanical cooling source. The logarithmic mean temperature difference is calculated as ΔT. lm =Calculated as (ΔT1-ΔT2) / ln(ΔT1 / ΔT2), where ΔT1 is the condenser hot-side inlet temperature minus the humidification / dehumidification device absorber-side outlet temperature, and ΔT2 is the condenser hot-side outlet temperature minus the humidification / dehumidification device absorber-side inlet temperature; during operation, ΔT... lm The temperature should be controlled within the range of 10 to 25 degrees Celsius.

[0063] Overall heat recovery rate as η hr =Q HDH吸热 / Q 冷凝放热 Calculate; where Q 冷凝放热 =V 热侧 ρc p (T) 入口 -T 出口 ), ; The moisture content is obtained by converting the outlet dew point and air temperature; four-point temperature, two-channel volumetric flow rate, and one-channel dew point are sampled once per second and statistically analyzed using a 60-second sliding time window, serving as the design threshold for feasible reflux. A head margin coefficient, Φ, is introduced. h =[(ρ 冷 -ρ 热 gΔz-Δp 沿+局 ] / Δp 沿+局 Φ is required h ≥0.2; In this embodiment, Φ is taken as Φ h =0.46, indicating that the density difference driving head is more than 40% higher than the total pressure drop in the loop, which can avoid vapor blockage and backflow interruption. Stability is judged according to the following specifications: Within any consecutive 72 hours, the absolute value of the difference between the average heat release per unit time of the condenser and the average heat absorption per unit time of the humidification and dehumidification device shall not exceed 10% of the former, and the dew point temperature fluctuation of the outlet air of the humidification and dehumidification device shall not exceed ±2 degrees Celsius. When calculating the percentage, timestamps for manual intervention and instrument self-tests were excluded, and the total duration of exclusions was no more than 5% of the total recorded duration. To demonstrate that it still possesses superior dynamic steady-state performance compared to pumped circuits under pump-free conditions, after 12 hours of stable operation, a positive step increase of 10% was applied to the vaporization load of the membrane phase change separation and small temperature difference regeneration column and maintained for 20 minutes. After 36 hours of operation, a negative step increase of 10% was applied and maintained for 20 minutes. The overshoot amplitude of the dew point trajectory and the settling time to recover to ±5% bandwidth were recorded and compared with two control systems: closed-loop pumped regeneration and non-regeneration (cooling tower heat dissipation and steam reheating).

[0064] The measuring points and accuracy are as follows: PT100A grade temperature element, basic error not exceeding 0.15 degrees Celsius from 0 to 200℃; electromagnetic flowmeter, basic error not exceeding 0.5% of the range from 0 to 30 cubic meters per hour; dew point meter accuracy not lower than 0.1 degrees Celsius; after annual calibration, on-site comparisons are performed at two points: 0 and 25℃, and 10 and 20 cubic meters per hour, with deviations not exceeding 0.1℃ and 0.1 cubic meters per hour, respectively; specific experimental data are shown in the table below: Performance Comparison and Disturbance Test Summary Table (Table #5) Parameters / Units This invention - Pump-free closed-loop regeneration (gravity reflux) Compare with A-Mechanical closed-loop regenerative system (with pump). Compare with B-type closed-loop regenerative cooling system (cooling tower + steam reheating). Elevation difference Δz (m) 1.2 0.0 0.0 The equivalent voltage drop Δp along the loop (Pa) 800 Overcome by pump Heat dissipation circuit Indentation head margin coefficient Φh(-) 0.46 NA NA Logarithmic mean temperature difference (°C) of LMTD 15 14 28 Overall heat recovery rate ηhr(-) 0.68 0.66 0.00 72h energy imbalance |Qcond-Qabs| / Qcond(%) 2.7 1.6 100 HDH outlet dew point fluctuation (±°C) ±1.3 ±1.0 ±3.8 Electricity consumption per unit of water produced (kWh / m³) 0.06 0.11 0.35 Additional mechanical power (regenerative circuit) (kW) 0.00 0.06 0.00 Coefficient of variation of water production flux (CV) (%) 3.8 4.2 7.5 Dew point overshoot (°C) at a step increase of +10%. 0.9 2.6 3.8 Step change +10% settling time (min, to ±5%) 7.5 24.0 35.0 Dew point drop (°C) at a step change of -10%. 0.8 2.1 3.1 Step change -10% settling time (min, to ±5%) 6.8 19.0 29.0 Qabs standard deviation / mean (%, 72h) 3.6 7.9 >50 From the table above, we can see that: Firstly, without the circulation pump, the overall heat recovery rate reaches 0.68 and the energy balance error is only 2.7%, which is comparable to 0.66 and 1.6% with the pump circuit. However, the unit water production power consumption is reduced to 0.06 kWh per cubic meter, showing the differentiated effect of equivalent heat recovery and non-equivalent energy consumption. Secondly, in the step disturbance test, which is most sensitive to wet end boundary conditions, the dew point overshoot of the pumpless closed-loop regeneration circuit is less than 1°C and the settling time is no more than eight minutes. However, due to the coupling oscillation caused by pump inertia and control delay, the overshoot and settling time of the pumped circuit are amplified to 2.6°C and 24 minutes, respectively, and the non-regeneration circuit is even worse. Two more sets of endpoint load case summaries are provided to demonstrate that the boundary conditions are feasible: When the elevation difference is one meter and the temperature is ten degrees Celsius, the calculated and measured energy imbalance is 4.5 percent and the dew point fluctuation is ±1.7 degrees Celsius. When the elevation difference is two meters, the temperature is 25 degrees Celsius, the energy imbalance is 2.1 percent, and the dew point fluctuation is ±1.1 degrees Celsius.

[0065] like Figure 1-10 As shown, the non-condensable gas obtained by separating the gas extracted in step S2 after being cooled by the condenser in step S3 is directly used as the sole gas source in step S5, without setting up an independent blower or compressor. By setting a gas source distributor and a throttle orifice, the gas source distribution ratio is made to be 0.05 to 0.30. The gas source distribution ratio is defined as the ratio of the volumetric flow rate of the non-condensable gas supplied in step S5 to the volumetric flow rate of the gas extracted in step S2. Meanwhile, the apparent gas velocity on the feed side of the membrane phase change separation and small temperature difference regenerating column is 0.005 m / s to 0.03 m / s. The apparent gas velocity is defined as the gas volume flow rate on the channel cross-section divided by the channel cross-sectional area, and the content of entrained liquid droplets in the non-condensable gas after demisting is not higher than 50 mg / m³. In this embodiment, the entire operation uses only the non-condensable gas obtained from the extraction in step S2 and the condensation separation in step S3 as the sole gas source for step S5, without setting up an independent blower or compressor. A composite demister is connected in series at the condenser gas phase outlet and then connected to a gas manifold. The gas manifold is equipped with two fixed orifice plates for flow limiting and one micro-bypass to form a gas source distributor. The first path supplies gas to step S5, and the second path is connected back to the low-pressure area of ​​the injection outlet to release pressure.

[0066] The gas supply distribution ratio is defined as the volumetric flow rate of the non-condensable gas supplied in step S5 divided by the volumetric flow rate of the gas extracted in step S2. The distribution ratio is stabilized around a central value of 0.18 by a combination of the orifice diameter and the throttling length, and can be adjusted within the range of 0.05 to 0.30. The apparent gas velocity is defined as the volumetric flow rate of the gas in the pre-membrane channel divided by the cross-sectional area of ​​that channel, with a set value of 0.012 m / s, and maintained within the range of 0.005 to 0.03 m / s.

[0067] The entrained droplet mass concentration is defined as the mass increment measured by dividing the sample volume by the mass increment of 1 m³ of gas extracted at constant velocity after the demister and retained by a 0.8 μm filter membrane. The acceptance limit is ≤50 mg / m³.

[0068] The volumetric flow rate of the pumping in step S2 is uniformly converted to 25°C conditions from the mass flow meter reading. The volumetric flow rate supplied to step S5 is calculated based on the pressure difference before and after the orifice plate and corrected by two-point on-site comparison using a portable mass flow meter. The cross-sectional area of ​​the membrane channel is a fixed value designed for the device.

[0069] The shell-side absolute pressure, gas manifold pressure, and volumetric flow rates of extraction and supply are sampled once per second and statistically analyzed using a 60-second sliding window. Within any consecutive 72 hours, the distribution ratio and apparent gas velocity are determined to be within the range of ±20% of the set value, and the entrained droplet mass concentration is ≤50mg / m³, which satisfies the requirements of this embodiment.

[0070] To ensure successful replication, the pressure transmitters must have a range of 0 to 100 kPa with a basic error of no more than 2.5 per thousand of the range, the mass flow meters must have a range of 0 to 50 Nm³ / h with a basic error of no more than 1% of the range, the sampling device must have a constant velocity deviation of ≤1%, and all instruments must have completed annual calibration and passed on-site two-point comparison.

[0071] like Figure 1-10 As shown, in step S6, the density-triggered passive diversion network is connected to the injection suction outlet of step S2 through a liquid-sealed riser, so that the diversion network operates as a pump-free back pressure stabilizing unit, and is implemented according to the following cause-and-effect conditions: At any given time, only one of the branches leading to the brine pool or the branch leading to the reinjection is allowed to be open, while the other branch remains sealed to form an equivalent static liquid seal. The equivalent static water seal height is calculated to be 0.10 meters to 0.50 meters based on the density of seawater at 25℃. The height is spontaneously formed by the fluid density and liquid level difference, and no electric valve, pneumatic valve or other active actuator is installed. When the online conductance crosses a set threshold of 0.5 mSiemens per centimeter to 2.0 mSiemens per centimeter, the shunt network passively switches between the two branches. Using a sampling frequency of 1 Hz and a 10-minute sliding window, the short-time fluctuation standard deviation of the static pressure at the jet suction outlet is no greater than 1 kPa. In this embodiment, the static pressure at the jet suction outlet is connected to two parallel liquid-sealed risers via a sealed gas cap. The gas cap inlet is connected to the jet suction outlet, and the two outlets lead to the brine pool branch and the reinjection branch, respectively. The risers have an inner diameter of not less than 20 mm, with the bottom opening located above the downstream liquid surface and the top connected to the gas cap. A one-way check valve is installed downstream of each riser to prevent backflow. To achieve passive interlocking and density triggering, the equivalent static water liquid seal heights of the brine pool branch and the reinjection branch are set to 0.25 meters and 0.35 meters, respectively, both calculated based on the density of seawater at 25 degrees Celsius and maintaining a non-overlapping gap. The equivalent static water liquid seal height is defined as... Where Δp is the pressure difference between the cap pressure and the downstream opening pressure. The density of seawater at 25 degrees Celsius This is the acceleration due to gravity.

[0072] The online conductivity probe is positioned on the liquid phase side of the mixing section downstream of the gas cap. The set threshold is located in the range of 0.5 mSiemens per centimeter to 2.0 mSiemens per centimeter. The conductivity crossing the threshold is only used for diagnostic timing. The actual switching is determined by the liquid seal height difference and density change. To prevent instantaneous concurrent surge, a small vent hole is set at the top of the two risers to form a hysteresis window of five to fifteen seconds.

[0073] Two absolute pressure transmitters, one with a range of 0 to 100 kPa and a basic error of no more than 2.5 per thousand of the range, are installed at the injection suction outlet and the gas cap, respectively, to record the pressure sequence at a frequency of once per second. The equivalent static water seal height is calibrated according to the pressure difference of the fixed gas cap. A stable pressure difference is applied using a standard pressure source, and liquid is slowly injected to the point where the seal breaks to read the liquid level and convert it to H. eq The two branches are calibrated to within ±5% of the target value.

[0074] The start-up and shutdown are performed in the following order: first, establish the jet suction and stabilize it to the target shell-side pressure window, then fill the pipes to establish a liquid seal, adjust the small hole at the top of the pipes until a noticeable hysteresis occurs but does not exceed fifteen seconds, and finally set the online conductivity threshold and start continuous recording.

[0075] The acceptance criteria for stable operation are as follows: with sampling once per second and a ten-minute sliding time window, the standard deviation of short-term pressure fluctuations at the jet suction outlet does not exceed one kPa within any consecutive 72 hours; at any given time, only one of the brine pool branch or the reinjection branch is allowed to conduct, while the other branch remains liquid-sealed; if simultaneous inrush of both branches is detected for more than two seconds, the equivalent static water liquid seal height of the higher threshold branch should be increased or its top orifice throttling should be tightened for correction; when the online conductivity crosses the set threshold, the two branches should complete a passive switching within no more than fifteen seconds; within the range of 0.10 meters to 0.50 meters, the equivalent static water liquid seal height remains effective and no steam plug failure occurs.

[0076] The above criteria were statistically excluded after removing timestamps for manual intervention and instrument self-testing, with the total excluded time not exceeding 5% of the total recording time. To ensure reproducibility, on-site two-point comparisons were performed using pressures of 40 and 60 kPa, with an allowable deviation of no more than 0.2 kPa; conductivity meter comparisons were performed using two points per centimeter of 12.88 and 50.0 millisieverts, with a reading deviation of no more than 1%; H eq The relative standard deviation of three replicates of calibration is no higher than three percent.

[0077] like Figure 1-10 As shown, between steps S3 and S5, the gas-side closed space of the condenser in step S3 is used as the only equivalent gas buffer volume to supply non-condensable gas to step S5, and no independent gas storage tank, accumulator or adjustable pressure regulating valve is provided. And it operates under the following passive-dynamic conditions: The gas source buffer time is defined as the ratio of the gas equivalent buffer volume to the non-condensable gas volume flow rate in the supply step S5. The gas source buffer time is 2 to 20 seconds. With a sampling frequency of once per second and a time window of 60 seconds, the absolute value of the pressure change rate at the inlet of the gas source distributor is no greater than 1 kPa per second. Using a sampling frequency of once per second and a time window of 60 seconds, the root mean square (RMS) values ​​of the pressure sequences at the jet suction outlet and the pressure sequences at the gas source distributor inlet are obtained after bandpass filtering from 0.1 to 2 Hz. The amplitude ratio is defined as the ratio of the RMS value of the pressure sequence at the gas source distributor inlet to the RMS value of the pressure sequence at the jet suction outlet, and the amplitude ratio is not greater than 0.30. With a sampling frequency of once per second and a time window of 60 seconds, the coefficient of variation of the non-condensable gas volumetric flow rate supplied to step S5 is no higher than 10%. In this embodiment, the entire operation process uses only the gas-side closed space of the condenser in step S3 to provide non-condensable gas to step S5 as the only equivalent gas buffer volume, without setting up an independent gas storage tank, accumulator or adjustable pressure regulating valve.

[0078] The enclosed space is connected to the gas source distributor inlet of step S5 through a fixed orifice plate flow-limiting pipeline. The orifice plate opening diameter and throttling length are determined during manufacturing and are not adjusted during operation.

[0079] Before the first operation, the gas equivalent buffer volume is calibrated by isothermal perturbation: under the condition that the ambient temperature is basically constant, a three-way valve is used to momentarily connect the calibration chamber of known volume with the gas side space of the condenser, and the absolute pressure of the two chambers before connection and the common absolute pressure after connection and rest are recorded respectively. The gas equivalent buffer volume is obtained by solving the isothermal gas state equation. The ratio of the calibration chamber volume to the equivalent volume is controlled within 5% to 20% to reduce the calculation uncertainty. The "gas source buffer time" is defined as the ratio of the gas equivalent buffer volume to the non-condensable gas volume flow rate supplied in step S5. The gas supply volume flow rate is measured by a mass flow meter and uniformly converted to 25℃ conditions. By selecting the orifice diameter and throttling length of the fixed orifice plate, the gas source buffer time is kept within the range of 2 to 20 seconds (the center setting value can be 8 to 10 seconds), and the flow limiting component is locked accordingly.

[0080] To ensure the detectability of dynamic quantitative indicators, absolute pressure transmitters with a range of 0–100 kPa (abs) and a basic error of no more than 0.25% of the range are installed at the gas source distributor inlet and the jet suction outlet, respectively, and the pressure sequences at the two locations are collected synchronously at a frequency of 1 Hz.

[0081] The absolute value of the pressure difference between adjacent sampling times divided by the sampling interval is defined as the "pressure change rate," and its maximum value is calculated using a 60-second sliding time window. The acceptance criterion is that it should not exceed 1 kPa / s. To evaluate the passive buffer's ability to attenuate upstream disturbances, the "pressure sequence at the injection suction outlet" and the "pressure sequence at the gas source distributor inlet" are subjected to zero-phase digital bandpass filtering (0.1–2 Hz) within the same time window. The root mean square (RMS) of the filtered sequences is calculated, and the "amplitude ratio" is defined as the ratio of the aforementioned inlet RMS to the injection suction outlet RMS. The acceptance criterion is that it should not exceed 0.30.

[0082] The non-condensable gas volumetric flow rate in step S5 is recorded at 1 Hz, and the average and standard deviation are calculated within a 60-second time window. The "coefficient of variation of the gas supply flow rate" is defined as the ratio of the standard deviation to the average, and the acceptance criterion is that it is not higher than 10%.

[0083] The above statistics were performed within any consecutive 72-hour period; timestamps for manual intervention and instrument self-testing were excluded during the statistical analysis, and the total duration of the excluded timestamps did not exceed 5% of the total recording time. To ensure traceability of measurement values, pressure transmitters were compared on-site at 40 kPa and 60 kPa, with the error between the two points not exceeding 0.2 kPa; mass flow rate measurements covered a range of 0–50 Nm³ / h, with a basic error not exceeding 1% of the range, and were compared on-site at 10 and 30 Nm³ / h, with a deviation not exceeding 0.3 Nm³ / h.

[0084] When it starts up or recovers from a disturbance, first close the downstream valve of the gas source distributor to complete the isothermal micro-perturbation calibration of the gas equivalent buffer volume and record the value. Then open the fixed orifice plate flow limiting channel and open the downstream of the gas source distributor to make the gas supply volume flow rate reach the set value and stabilize within ±20% of the set value for 3 minutes. Then start to continuously record and calculate the gas source buffer time, pressure change rate, amplitude ratio and gas supply flow variation coefficient according to the aforementioned caliber.

[0085] If the gas source buffer time is less than 2 seconds or greater than 20 seconds, reset it by changing the orifice diameter of the fixed orifice plate or adjusting the throttling length; if the pressure change rate exceeds 1 kPa / s or the amplitude ratio exceeds 0.30, prioritize increasing the flow limiting resistance and check whether there is bypass leakage in the gas-side closed space of the condenser and its connecting pipeline; if the coefficient of variation of the gas supply flow exceeds 10%, verify whether the converted diameter of the mass flow meter and the trace leakage before and after the gas source distributor are overly sensitive, and unify the time constant and statistical window of the mass flow meter to the above diameter to eliminate pseudo fluctuations introduced by the algorithm.

[0086] Based on the above connection method, calibration method, measurement and statistical caliber, and acceptance criteria, without setting up an independent gas storage tank, accumulator, or adjustable pressure regulating valve, the gas-side closed space of the condenser and fixed flow restriction can stably meet the requirements of a gas source buffer time of 2 to 20 seconds, a pressure change rate of no more than 1 kPa / s, an amplitude ratio of no more than 0.30, and a gas supply flow variation coefficient of no more than 10%.

[0087] like Figure 1-10 As shown, when this method is started or disturbed during operation, the following steps are performed sequentially without using an external compressed gas, electromechanical vacuum pump, or circulation pump: Close the gas source distributor in step S5 and open the drive valve in step S2, so that the pretreated seawater forms a drive jet through the Venturi ejector and pumps out the gas in the membrane phase change separation and small temperature difference regeneration shell until the absolute pressure of the shell side of the membrane phase change separation and small temperature difference regeneration shell reaches the target value in the range of 30 kPa to 60 kPa and remains stable in the range of ±2 kPa for 5 minutes. Subsequently, the pumpless closed regenerative circuit between steps S3 and S4 is opened, so that the heat-releasing side of the condenser and the heat-absorbing side of the humidification and dehumidification device form a gravity recirculation until the logarithmic mean temperature difference between the two enters the range of 10 degrees Celsius to 25 degrees Celsius and is maintained for 3 minutes. Then, non-condensable gas is slowly introduced from the closed space on the gas side of the condenser into step S5 through a fixed flow limiting element until the apparent gas velocity on the feed side of the membrane phase change separation and small temperature difference regenerating column in step S5 reaches a set value in the range of 0.005 m / s to 0.03 m / s and is maintained within ±20% of this set value for 3 minutes. Next, the equivalent static water seal height in step S6 is adjusted to a range of 0.10 meters to 0.50 meters, so that the density-triggered passive diversion network enters the passive switching state. Using a sampling frequency of once per second and a time window of 60 seconds, the root mean square (RMS) values ​​of the pressure sequences at the jet suction outlet and the gas source distributor inlet are obtained after bandpass filtering from 0.1 to 2 Hz. The amplitude ratio is defined as the ratio of the RMS value of the pressure sequence at the gas source distributor inlet to the RMS value of the pressure sequence at the jet suction outlet. When the amplitude ratio is not greater than 0.30, it is considered to have entered the stable operation stage. In this embodiment, the pretreatment and potential energy supply in steps S1 and S2 have been implemented according to the claims 1 and 3. The membrane phase change separation and small temperature difference regenerating shell, condenser, humidification and dehumidification device, venturi ejector, gas source distributor and density-triggered passive diversion network are connected according to claims 3 to 7.

[0088] To ensure verifiable measurement values, pressure transmitters with a range of 0–100 kPa (absolute pressure) and a basic error of no more than 0.25% of the range are installed at the jet suction outlet and the gas source distributor inlet, respectively. Four temperature measuring points are arranged at the condenser hot-side inlet, condenser hot-side outlet, humidification / dehumidification device absorber-side inlet and absorber-side outlet, using PT100A grade components with a basic error of no more than 0.15℃. The volumetric flow rate of the non-condensable gas supplied in step S5 is measured by a mass flow meter and uniformly converted to 25℃. The cross-sectional area of ​​the membrane pre-channel is a fixed value designed for the device and is used to calculate the apparent gas velocity. The above signals were sampled at 1Hz and statistically analyzed using a 60s sliding time window. During the statistical analysis, timestamps of manual intervention and instrument self-test were excluded, and the total duration of the excluded timestamps did not exceed 5% of the total recording time. The field comparison error between the pressure transmitter at 40kPa and 60kPa did not exceed 0.2kPa, the comparison error between the temperature at 0℃ and 25℃ did not exceed 0.1℃, and the comparison error between the mass flow meter at 10 and 30Nm³ / h did not exceed 0.3Nm³ / h.

[0089] During startup or disturbance recovery, first close the gas source distributor in step S5 to prevent air intake before the membrane. Then, open the drive valve in step S2. Utilize the effective elevation difference to allow pretreated seawater to flow through the Venturi ejector, forming a driving jet. This jet continuously extracts and discharges the gas inside the membrane phase change separation and small temperature difference regenerator shell through the suction port. Using the absolute pressure at the top of the shell as the benchmark, reduce the shell-side absolute pressure to the target window of 30–60 kPa and maintain it stable within ±2 kPa for 5 minutes. Stability is determined by sampling at 1 Hz and statistically analyzing over a 60-second window. Subsequently, without setting up a circulating pump or parallel mechanical cooling source, open the closed connection between the condenser's heat release side and the humidification / dehumidification device's heat absorption side, allowing them to form a gravity-driven reflux.

[0090] Let the first temperature difference be the condenser hot-side inlet temperature minus the humidification / dehumidification device absorber-side outlet temperature, and let the second temperature difference be the condenser hot-side outlet temperature minus the humidification / dehumidification device absorber-side inlet temperature. Then, calculate the logarithmic average temperature difference ΔT. lmCalculate the value of = (ΔT1-ΔT2) / ln(ΔT1 / ΔT2) by its definition, and then apply ΔT... lm Maintain the temperature within the range of 10–25℃ for 3 minutes.

[0091] After completing the regenerative closed loop, non-condensable gas is slowly introduced from the condenser gas-side closed space to the gas source distributor inlet through a fixed flow-limiting element. The apparent gas velocity is calculated as the non-condensable gas volume flow rate supplied in step S5 divided by the cross-sectional area of ​​the pre-membrane channel. This value is adjusted to a set value within the range of 0.005 to 0.03 m / s and maintained within ±20% of this set value for 3 minutes. If the apparent gas velocity is insufficient, the cleanliness of the flow-limiting element and whether the micro-venting of the gas manifold is abnormally activated are checked. If the apparent gas velocity exceeds the limit, the pre-flow-limiting element is appropriately increased or the venting orifice diameter is reduced until it returns to the set window.

[0092] Subsequently, the equivalent static water seal height in step S6 is adjusted to a range of 0.10 to 0.50 m and a non-overlapping high and low threshold relationship is formed to ensure that at any given time only one of the branches leading to the brine pool or the branch leading to the reinjection is open, while the other branch remains sealed.

[0093] When entering the stability determination stage, the pressure sequence at the injection suction outlet and the pressure sequence at the gas source distributor inlet are sampled at 1Hz and a time window of 60s. Zero-phase digital bandpass filtering (0.1~2Hz) is applied to them respectively. The root mean square of the two sequences is calculated and the amplitude ratio is defined as the ratio of the root mean square of the pressure sequence at the gas source distributor inlet to the root mean square of the pressure sequence at the injection suction outlet.

[0094] When the amplitude ratio is no greater than 0.30, the startup or disturbance recovery is considered complete and the system enters a stable operation phase. If the amplitude ratio exceeds the limit, the system will correct the deviation in the following order: first check whether there is bypass leakage in the condenser gas-side closed space and connecting pipelines; secondly verify whether the fixed flow limiting component deviates from the manufacturing setting; and thirdly, appropriately increase the flow limiting resistance or increase the equivalent static water seal height of the high-threshold branch of the passive diversion network to enhance hysteresis and damping. The timestamp during the correction period is not included in the above judgment window.

[0095] In summary, this invention, without configuring an electromechanical vacuum pump, steam ejector, and independent blower, records the shell-side absolute pressure and ejector outlet static pressure at a sampling frequency of once per second during continuous operation. Within any consecutive 72 hours, the shell-side absolute pressure is within the 30 kPa to 60 kPa window for at least 95% of the time. When the pressure difference between the ejector and the shell-side static pressure momentarily exceeds the limit, the deviation can be corrected by first reducing the drive opening and then appropriately increasing the flow restriction on the suction side, which can quickly restore the pressure to within the limit. This demonstrates the stability and maintainability under the cooperation of passive components. The total dissolved solids (TDS) of the concentrated brine produced by the method of this invention is greater than 80,000 ppm, which meets the industrial brine standard; the TDS of the freshwater is less than 500 ppm, which meets the drinking water standard.

[0096] By utilizing potential energy-driven Venturi jet suction to establish and maintain low pressure on the membrane side, the system achieves long-term stable operation with low installed power under conditions without an electromechanical vacuum pump or steam ejector, thus solving the problems of high energy consumption, complex maintenance, and poor off-grid adaptability caused by reliance on active vacuum.

[0097] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0098] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A production method for separating high-concentration brine and pure water from seawater using potential energy, characterized in that, Includes the following steps: S1: Seawater is sent to a selective crystallization classification tower equipped with nucleating agents and inclined plate separation components for pretreatment to remove scaling precursors such as calcium sulfate and magnesium hydroxide, and pretreated seawater is obtained. S2: Under the influence of the height difference provided by the high-level water storage facilities above the ground or sea surface, the height of the shore slope buildings, or the rise and fall of the tide, the pretreated seawater flows through the Venturi jet to form a liquid jet and draws in the gas connected to the membrane phase change separation shell to reduce the shell-side absolute pressure of the membrane phase change separation shell. S3: Connect the membrane phase change separation shell to the vertically arranged membrane phase change separation column, so that the feed is stripped at the top of the column and condensed in the condenser to obtain the first product water flow, while transferring the heat released by condensation to the humidification and dehumidification device. S4: In the humidification and dehumidification device, the humid air is heat-exchanged with the high-salt liquid from the concentrated salt branch and multi-effect recovery is performed to obtain the second product water flow, and the recovered heat is returned to the membrane phase change separation column or returned to the seawater feed. The air-to-water volume ratio of the humidification and dehumidification device is 1 to 3, and the air-to-water volume ratio is defined as the ratio of the gas phase volume flow rate to the liquid phase volume flow rate in the device. S5: Establish an airlift circulation driven by a Venturi getter in the pre-membrane branch, connect a microporous diffuser in parallel in front of the membrane to generate microbubbles, and scrub the membrane surface to reduce concentration polarization. The volume fraction of microbubbles in the flow field near the wall on the feed side of the membrane phase change separation column is 1% to 5%, and the volume average particle size of the microbubbles is 50 micrometers to 150 micrometers. S6: A density-triggered passive diversion network is set up on the product water branch and the concentrated salt branch to perform graded recovery or reinjection of fluids with different salinities based on the online conductivity threshold.

2. The production method for separating high-concentration brine and pure water from seawater using potential energy according to claim 1, characterized in that, The operating conditions for the selective crystallization fractionation pretreatment of S1 are as follows: The supersaturation of the target salt system of calcium sulfate and magnesium hydroxide is 10% to 30%, the reaction residence time is 10 to 30 minutes, the angle between the inclined plate and the horizontal is 45° to 70°, seed crystals with a median particle size of 50 micrometers to 200 micrometers are added, the seed crystal concentration is 0.5 g / L to 5 g / L, and sludge is discharged when the online turbidity in the settling zone reaches 50 to 200 NTU or the bottom conductivity reaches 55 to 65 millisiemens per centimeter.

3. The production method for separating high-concentration brine and pure water from seawater using potential energy according to claim 2, characterized in that, In step S2, a negative pressure is established and maintained in the membrane phase change separation shell by Venturi jet suction, and no electromechanical vacuum pump, steam ejector, vacuum tank pre-extraction equipment, or deep well static water column is used during operation to generate negative pressure. Specifically, the following conditions must be met: The pretreated seawater obtained in step S1 flows through the contraction section, throat and diffuser section under the action of height difference to form a driving jet, and continuously pumps out the gas in the shell through the suction port connected to the membrane phase change separation shell, so as to stabilize the shell side absolute pressure at 30 kPa to 60 kPa. The volume conversion time, i.e., the ratio of the effective volume of the membrane phase change separation shell to the volumetric flow rate of the drive branch, is 1.7 seconds to 6.7 seconds. The suction ratio, i.e., the ratio of the volumetric flow rate of the suction branch to the volumetric flow rate of the drive branch, is 0.12 to 0.45, and the absolute value of the pressure difference between the static pressure at the injection suction outlet and the shell-side static pressure is not greater than 5 kPa. During continuous 72-hour operation, the shell-side absolute pressure is in the range of 30 kPa to 60 kPa for no less than 95% of the time.

4. The production method for separating high-concentration brine and pure water from seawater using potential energy according to claim 3, characterized in that, Between step S3 and step S4, the heat-releasing side of the condenser in step S3 and the heat-absorbing side of the humidification and dehumidification device in step S4 are directly connected by a pipeline to form a pumpless closed-loop regenerative circuit by gravity backflow, without setting up a circulating pump or parallel mechanical cold source. The regenerative circuit satisfies the following conditions: The gravity return drop shall not be less than 1 meter; The logarithmic mean temperature difference between the condenser and the humidification / dehumidification device is 10 to 25 degrees Celsius. The overall heat recovery rate of the humidification and dehumidification device is not less than 0.60, and the overall heat recovery rate is the proportion of the recoverable heat fed into the humidification and dehumidification device that is returned to step S3 or returned to the seawater feed. During continuous 72-hour operation, the absolute value of the difference between the average heat exchange per unit time of the condenser and the average heat absorption per unit time of the humidification and dehumidification device shall not exceed 10% of the average heat exchange per unit time of the condenser, and the dew point temperature fluctuation of the outlet air of the humidification and dehumidification device shall not exceed ±2 degrees Celsius.

5. A production method for separating high-concentration brine and pure water from seawater using potential energy according to claim 4, characterized in that, The non-condensable gas obtained after the gas extracted in step S2 is cooled by the condenser in step S3 is directly used as the sole gas source in step S5, without setting up an independent blower or compressor. By setting a gas source distributor and a throttle orifice, the gas source distribution ratio is made to be 0.05 to 0.

30. The gas source distribution ratio is defined as the ratio of the volumetric flow rate of the non-condensable gas supplied in step S5 to the volumetric flow rate of the gas extracted in step S2. Meanwhile, the apparent gas velocity on the feed side of the membrane phase change separation column is set to 0.005 m / s to 0.03 m / s. The apparent gas velocity is defined as the gas volume flow rate on the channel cross-section divided by the channel cross-sectional area, and the content of entrained liquid droplets in the non-condensable gas after demisting is not higher than 50 mg / m³.

6. The production method for separating high-concentration brine and pure water from seawater using potential energy according to claim 5, characterized in that, In step S6, the density-triggered passive diversion network is connected to the jet suction outlet of step S2 via a liquid-sealed riser, so that the diversion network operates as a pump-free back pressure stabilizing unit, and is implemented according to the following causal conditions: At any given time, only one of the branches leading to the brine pool or the branch leading to the reinjection is allowed to be open, while the other branch remains sealed to form an equivalent static liquid seal. The equivalent static water seal height is calculated to be 0.10 meters to 0.50 meters based on the density of seawater at 25°C. This height is spontaneously formed by the fluid density and liquid level difference, without the installation of electric valves, pneumatic valves or other active actuators. When the online conductance crosses a set threshold of 0.5 mSiemens per centimeter to 2.0 mSiemens per centimeter, the shunt network passively switches between the two branches; Using a sampling frequency of 1 Hz and a 10-minute sliding window, the short-time fluctuation standard deviation of the static pressure at the jet suction outlet is no greater than 1 kPa.

7. A production method for separating high-concentration brine and pure water from seawater using potential energy according to claim 5, characterized in that, Between step S3 and step S5, the gas-side closed space of the condenser in step S3 is used as the only equivalent gas buffer volume to supply non-condensable gas to step S5, without setting up an independent gas storage tank, accumulator or adjustable pressure regulating valve. And it operates under the following passive-dynamic conditions: The gas source buffer time is defined as the ratio of the gas equivalent buffer volume to the non-condensable gas volume flow rate in the supply step S5. The gas source buffer time is 2 to 20 seconds. With a sampling frequency of once per second and a time window of 60 seconds, the absolute value of the pressure change rate at the inlet of the gas source distributor is no greater than 1 kPa per second. Using a sampling frequency of once per second and a time window of 60 seconds, the root mean square (RMS) values ​​of the pressure sequences at the jet suction outlet and the pressure sequences at the gas source distributor inlet are obtained after bandpass filtering at 0.1 to 2 Hz. The amplitude ratio is defined as the ratio of the RMS value of the pressure sequence at the gas source distributor inlet to the RMS value of the pressure sequence at the jet suction outlet, and the amplitude ratio is not greater than 0.

30. With a sampling frequency of once per second and a time window of 60 seconds, the coefficient of variation of the non-condensable gas volume flow rate supplied to step S5 is no higher than 10%.

8. A production method for separating high-concentration brine and pure water from seawater using potential energy according to claim 5, characterized in that, When this method is started or subjected to disturbances, the following steps shall be performed in sequence without using external compressed gas, electromechanical vacuum pump, or circulation pump: Close the gas source distributor in step S5 and open the drive valve in step S2, so that the pretreated seawater forms a drive jet through the Venturi ejector and pumps out the gas in the membrane phase change separator shell until the absolute pressure of the shell side of the membrane phase change separator shell reaches the target value in the range of 30 kPa to 60 kPa and remains stable in the range of ±2 kPa for 5 minutes. Subsequently, the pumpless closed regenerative circuit between steps S3 and S4 is opened, so that the heat-releasing side of the condenser and the heat-absorbing side of the humidification and dehumidification device form a gravity recirculation until the logarithmic mean temperature difference between the two enters the range of 10 degrees Celsius to 25 degrees Celsius and is maintained for 3 minutes. Subsequently, non-condensable gas is slowly introduced from the closed space on the gas side of the condenser into step S5 through a fixed flow limiting element until the apparent gas velocity on the feed side of the membrane phase change separation column in step S5 reaches a set value in the range of 0.005 m / s to 0.03 m / s and is maintained within ±20% of this set value for 3 minutes. Next, the equivalent static water seal height in step S6 is adjusted to a range of 0.10 meters to 0.50 meters, so that the density-triggered passive diversion network enters the passive switching state. Using a sampling frequency of once per second and a time window of 60 seconds, the pressure sequences at the injection suction outlet and the pressure sequences at the gas source distributor inlet are bandpass filtered from 0.1 to 2 Hz and their root mean square values ​​are calculated. The amplitude ratio is defined as the ratio of the root mean square value of the pressure sequence at the gas source distributor inlet to the root mean square value of the pressure sequence at the injection suction outlet. When the amplitude ratio is not greater than 0.30, it is considered to have entered the stable operation stage.

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