A production method for separating high-concentration brine and pure water from seawater by using potential energy

Abstract

The application 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 concentrated brine resource utilization, and comprises the following steps: seawater is sent into a selective crystallization grading tower provided with nucleating agents and inclined plate separation components for pretreatment, so that scale precursors such as calcium sulfate and magnesium hydroxide are removed, and pretreated seawater is obtained; a membrane side low pressure is established and maintained by using a potential energy driven Venturi jet suction, so that the effect of long-term stability and low installed power operation under the condition of inorganic electric vacuum pumps or steam ejectors 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] The present application relates to the technical field of seawater desalination and concentrated brine resource utilization, more specifically, it relates to a production method for separating high-concentration brine and pure water from seawater by using potential energy. BACKGROUND

[0002] Patent application No. 202310197343.0 discloses a method and device for desalination of high-salt and high-concentration organic wastewater by coupling three membrane separation technologies. The scheme indeed improves the continuous desalination and resource recovery of high-salt and high-organic load systems through multi-membrane coupling and evaporation crystallization paths. However, in the application scenario relying on potential energy driving and facing seawater separation, there are still some deficiencies in use, such as:

[0003] Firstly, the comparative literature focuses on providing mass transfer driving force through pumping and compression equipment, and there is no explicit record of establishing and maintaining membrane-side negative pressure by using potential energy through liquid ejector without external vacuum equipment. Therefore, in the scene 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 operation stability are affected.

[0004] Secondly, the comparative literature adopts multi-membrane coupling and cooperates with evaporation crystallization, and there is no arrangement of a closed heat recovery loop formed by the condensation side and the front low-grade heat unit through gravity reflux. In the condition of small temperature difference, heat recovery and reflux still rely on active circulation, which increases energy consumption and pipeline complexity, and is not conducive to long-term stable operation.

[0005] Thirdly, the comparative literature relies on high-pressure pumps, air blowers, and mechanical vapor recompression equipment to maintain mass transfer and heat exchange. In off-grid or micro-power supply applications, the number of equipment and maintenance burden is large, which is difficult to meet the requirements of low energy consumption and high reliability. SUMMARY

[0006] To achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0007] The present application adopts the operation idea of membrane phase change separation, that is, under the condition of normal pressure and below the boiling point, small temperature difference is used to drive the vapor 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 for boiling the feed liquid. The heat source is the temperature difference formed by the low-grade waste heat in the process and the gravity closed heat recovery loop.

[0008] A production method for separating high-concentration brine and pure water from seawater by using potential energy, comprising the following steps:

[0009] S1: The seawater is sent into a selective crystallization grading tower provided with nucleating agent and inclined plate separation components for pretreatment to remove scale precursors such as calcium sulfate and magnesium hydroxide, and pretreated seawater is obtained.

[0010] S2: under the action of the height difference provided by the height of the high water storage facility above the ground or sea surface, the height of the bank slope building or the tidal range, the pretreated seawater flows through the venturi injector to form a liquid jet, and the gas in communication with the membrane phase separation shell is sucked to reduce the shell absolute pressure of the membrane phase separation shell;

[0011] S3: the membrane phase separation shell is communicated with the vertically arranged membrane phase separation column, the feed is stripped at the top of the column and condensed in the condenser to obtain a first water production flow, and the condensation heat is transferred to the humidification and dehumidification device;

[0012] S4: in the humidification and dehumidification device, the wet air exchanges heat with the high salt liquid from the concentrated salt branch and carries out multi-effect recovery to obtain a second water production flow, and the recovered heat is returned to the membrane phase separation column or returned to the seawater feed;

[0013] Wherein, the gas-water volume ratio of the humidification and dehumidification device is 1 to 3, and the gas-water volume ratio is defined as the ratio of the volume flow rate of the gas phase to the volume flow rate of the liquid phase in the device;

[0014] S5: in the pre-membrane branch, an air-lift circulation driven by a venturi aspirator is established, a microporous diffusion plate is connected in parallel in front of the membrane to produce micro-bubbles, and the membrane surface is scrubbed to reduce the concentration polarization;

[0015] Wherein, the volume fraction of micro-bubbles in the flow field of the near-wall region of the membrane phase separation column feed side is 1% to 5%, and the volume average particle size of the micro-bubbles is 50 microns to 150 microns;

[0016] S6: a density-triggered passive shunt network is provided on the water production branch and the concentrated salt branch, and different salinity fluids are recovered or recharged according to the online conductivity threshold;

[0017] Further, the operation conditions of the selective crystallization grading pretreatment of S1 are:

[0018] The supersaturation of calcium sulfate and magnesium hydroxide as the target salt system is 10% to 30%, the reaction residence time is 10 minutes to 30 minutes, the angle between the inclined plate and the horizontal is 45° to 70°, the median particle size of the seed crystal is 50 microns to 200 microns, the seed crystal concentration is 0.5 grams per liter to 5 grams per liter, and the sludge is discharged when the online turbidity in the sedimentation zone reaches 50 to 200 NTU or the bottom conductivity reaches 55 millisiemens per centimeter to 65 millisiemens per centimeter.

[0019] Further, in step S2, the negative pressure of the membrane phase separation shell is established and maintained by the venturi suction, and during the operation, no mechanical vacuum pump, steam ejector, vacuum tank pre-extraction equipment is used, and no negative pressure is generated by relying on the deep well static water column, which specifically meets the following conditions:

[0020] The pretreated seawater obtained in step S1 flows through the contraction section, the throat and the diffuser section under the action of the height difference to form a driving jet, and the gas in the shell is continuously pumped out through the suction port connected with the membrane phase separation shell to stabilize the absolute pressure in the shell side at 30-60 kPa;

[0021] The volume conversion time, i.e. the ratio of the effective volume of the membrane phase separation shell to the volume flow rate of the driving branch, is 1.7-6.7 seconds;

[0022] The suction ratio, i.e. the ratio of the volume flow rate of the suction branch to the volume flow rate of the driving branch, is 0.12-0.45, and the absolute value of the pressure difference between the static pressure at the jet suction outlet and the static pressure in the shell side is not greater than 5 kPa;

[0023] During the continuous 72-hour operation, the proportion of time during which the absolute pressure in the shell side is in the range of 30-60 kPa is not less than 95%.

[0024] Further, the heat release side of the condenser in step S3 and the heat absorption side of the humidifying and dehumidifying device in step S4 are directly connected through a pipeline to form a pump-free closed heat recovery circuit by gravity return, and no circulating pump or parallel mechanical cold source is arranged;

[0025] The heat recovery circuit satisfies the following conditions:

[0026] The gravity return drop is not less than 1 meter;

[0027] The logarithmic mean temperature difference between the condenser and the humidifying and dehumidifying device is 10-25°C;

[0028] The comprehensive heat recovery rate of the humidifying and dehumidifying device is not less than 0.60, and the comprehensive heat recovery rate is the proportion of the heat returned to step S3 or returned to the seawater feed among the recoverable heat entering the humidifying and dehumidifying device;

[0029] During the continuous 72-hour operation, the absolute value of the difference between the average heat exchange amount per unit time of the condenser and the average heat absorption amount per unit time of the humidifying and dehumidifying device accounts for not more than 10% of the average heat exchange amount per unit time of the condenser, and the fluctuation amplitude of the dew point temperature of the outlet air of the humidifying and dehumidifying device is not more than ±2°C.

[0030] Further, the non-condensable gas separated from the gas pumped out in step S2 after being cooled by the condenser in step S3 is directly used as the only gas source for step S5, and no independent air blower or compressor is arranged;

[0031] And by arranging a gas source distributor and a throttling orifice, the gas source distribution ratio is 0.05-0.30, and the gas source distribution ratio is defined as the ratio of the volume flow rate of the non-condensable gas supplied to step S5 to the volume flow rate of the gas pumped out in step S2.

[0032] Simultaneously, the apparent gas velocity of the membrane phase separation column feed side is 0.005 m / s to 0.03 m / s, which is defined as the value of the gas volume flow on the cross section of the side passage divided by the cross-sectional area of the passage, and the entrainment of the non-condensable gas after demisting is not higher than 50 mg / m3.

[0033] Further, the density-triggered passive shunt network in step S6 is communicated with the jet suction outlet in step S2 through a liquid seal standpipe, so that the shunt network operates as a pump-free back pressure stabilizing unit, and the following causal conditions are implemented:

[0034] Only one of the branch leading to the salt pool or the branch leading to the recharge is allowed to be in an open state at any time, and the other branch is kept liquid sealed to form an equivalent hydrostatic liquid seal;

[0035] The equivalent hydrostatic liquid seal height is 0.10 m to 0.50 m calculated at the seawater density of 25°C, and the height is spontaneously formed by the fluid density and the liquid level difference, without electrically driven valves, pneumatically driven valves or other active actuators;

[0036] When the online conductivity crosses the set threshold of 0.5 mS / cm to 2.0 mS / cm, the shunt network passively switches between the two branches;

[0037] The short-term fluctuation standard deviation of the static pressure at the jet suction outlet is not greater than 1 kPa, calculated at a sampling frequency of 1 Hz and with a 10-minute sliding window.

[0038] Further, only the gas side closed space of the condenser in step S3 is used as the only gas equivalent buffer volume to provide non-condensable gas to step S5 between step S3 and step S5, without independent gas storage tanks, accumulators or adjustable pressure regulating valves;

[0039] and the following passive dynamic conditions are implemented:

[0040] The ratio of the gas equivalent buffer volume to the non-condensable gas volume flow supplied to step S5 is defined as the gas source buffer time, and the gas source buffer time is 2 s to 20 s;

[0041] The absolute value of the pressure change rate at the gas source distributor inlet is not greater than 1 kPa / s, calculated at a sampling frequency of once per second and with a 60-second time window;

[0042] The pressure sequences at the jet suction outlet and the gas source distributor inlet are respectively band-pass filtered at 0.1 to 2 Hz after being filtered at a sampling frequency of once per second and with a 60-second time window, and the root mean square values are calculated, and 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 jet suction outlet, and the amplitude ratio is not greater than 0.30.

[0043] The coefficient of variation of the non-condensable gas volume flow rate supplied to step S5 is not higher than 10% at a sampling frequency of once per second and using a 60-second time window calculation.

[0044] Further, when the method is started or a disturbance occurs during operation, the following steps are sequentially performed without using external compressed gas, electromechanical vacuum pumps or circulation pumps:

[0045] The gas source distributor of step S5 is closed and the drive valve of step S2 is opened, so that the pretreated seawater forms a driving jet through the Venturi ejector and exhausts the gas in the membrane phase separation shell, until the shell side absolute pressure of the membrane phase separation shell reaches a target value in the range of 30 kPa to 60 kPa and remains stable within ±2 kPa for 5 minutes;

[0046] Subsequently, the pumpless closed heat recovery circuit between step S3 and step S4 is opened, so that the condenser heat release side and the heat absorption side of the humidification and dehumidification device form a gravity reflux, until the logarithmic mean temperature difference between the two enters the interval of 10°C to 25°C and remains for 3 minutes;

[0047] Then, the non-condensable gas is slowly introduced from the condenser gas side closed space to step S5 through a fixed flow limiting element, until the superficial gas velocity of the feed side of the membrane phase separation column of step S5 reaches a set value in the range of 0.005 m / s to 0.03 m / s and remains within the range of ±20% of the set value for 3 minutes;

[0048] Next, the equivalent hydrostatic liquid seal height of step S6 is adjusted to the range of 0.10 m to 0.50 m, so that the density triggered passive flow splitting network enters the passive switching state;

[0049] At a sampling frequency of once per second and using a 60-second time window, the pressure sequence at the jet suction outlet and the pressure sequence at the gas source distributor inlet are respectively band-pass filtered at 0.1 to 2 Hz and the 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 jet suction outlet. When the amplitude ratio is not greater than 0.30, it is considered to enter the stable operation stage.

[0050] In the above, the whole process relies only on the Venturi jet suction to establish and maintain the negative pressure of the membrane phase separation shell, without using electromechanical vacuum pumps, steam ejectors or any equivalent devices;

[0051] The shell side absolute pressure is stably maintained at 30 kPa to 60 kPa, and the absolute value of the difference between the static pressure at the outlet of the ejector and the static pressure in the shell is not greater than 5 kPa;

[0052] The purpose of pretreatment is to reduce the scaling precursors and contamination tendency, and not to recover single chemical elements.

[0053] The core of the method is the combined closed loop formed by four passive units:

[0054] First, the potential energy driven Venturi suction establishes a shell negative pressure, so that the absolute pressure of the shell runs within the window of thirty to sixty kilopascals, the volume conversion time is controlled within 1.7 to 6.7 seconds, the suction ratio is controlled within 0.12 to 0.45, and the absolute value of the static pressure difference between the injection port and the shell is not greater than five thousand pascals;

[0055] Second, gravity closed heat recovery realizes pump-free backflow;

[0056] Third, non-condensable gas as the only gas source forms scrubbing and disturbance in front of the membrane, the gas source distribution ratio is 0.05 to 0.30, the superficial gas velocity in front of the membrane is 0.005 meters per second to 0.03 meters per second, the non-condensable gas is provided by the closed space on the gas side of the condenser, and no independent air blower or compressor is set;

[0057] Fourth, the static pressure difference between the ejector outlet and the shell is kept convergent, so that long-term stable operation is realized without mechanical cold source and external vacuum equipment;

[0058] The whole process does not carry out heating distillation or evaporation crystallization process; no independent steam source, boiler or heating device for bringing the liquid to boiling state is set; preferably, the temperature of the liquid into 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, the shell side negative pressure is established by the liquid ejector, and stable operation is realized by the gravity closed heat recovery.

[0059] In summary, the present application has the following beneficial effects:

[0060] Without configuring mechanical and electrical vacuum pumps, steam ejectors and independent air blowers, the absolute pressure of the shell and the static pressure of the ejector outlet are recorded at a sampling frequency of one second during continuous operation, and within any continuous seventy-two hours, the time ratio of the absolute pressure of the shell within the window of thirty to sixty kilopascals is not less than ninety-five percent; when the static pressure difference between the injection port and the shell appears transient over-limit, the correction is carried out in the order of first reducing the driving opening and then moderately increasing the suction side flow restriction, so as to quickly recover to within the limit, thereby reflecting the stability and maintainability under the cooperation of passive parts;

[0061] By using the potential energy driven Venturi injection suction to establish and maintain the low pressure of the membrane side, the effect of long-term stable and low installed power operation without mechanical and electrical vacuum pumps or steam ejectors is achieved, and the problems of high energy consumption, complex maintenance and poor off-grid adaptability caused by dependence on active vacuum are solved.

[0062] By directly connecting the condenser heat release side and the humidification and dehumidification device heat absorption side and forming a pump-free closed heat recovery circuit with a height difference, stable heat matching at a small temperature difference is achieved without the need for a circulating pump or mechanical cold source, solving the problems of high initial investment and operating energy consumption of traditional circulating pumps and large fluctuations in the heat end. BRIEF DESCRIPTION OF DRAWINGS

[0063] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0064] Figure 1 The process boundary and flow relationship diagram of the present application;

[0065] Figure 2 The connection of the Churi ejector and the membrane phase change separation shell and the measurement point diagram of the present application;

[0066] Figure 3 The pump-free heat recovery circuit schematic diagram of the condenser and the humidification and dehumidification device of the present application;

[0067] Figure 3 The pump-free heat recovery circuit schematic diagram of the condenser and the humidification and dehumidification device of the present application;

[0068] Figure 4 The connection relationship schematic diagram of the non-condensing gas closed loop gas supply and the demisting of the present application;

[0069] Figure 5 The density trigger passive shunt network and the liquid seal riser structure schematic diagram of the present application;

[0070] Figure 6 The start-up and disturbance recovery flowchart of the present application;

[0071] Figure 7 The absolute pressure time sequence curve schematic diagram of the shell side of the present application;

[0072] Figure 8 The outlet air dew point fluctuation time sequence curve schematic diagram of the present application;

[0073] Figure 9 The gas volume flow variation coefficient time sequence curve schematic diagram of the present application;

[0074] Figure 10 The amplitude ratio time sequence curve schematic diagram of the present application. DETAILED DESCRIPTION

[0075] With reference to the drawings of the embodiments of the present application, the technical solutions in the embodiments of the present application will be described clearly and completely. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the scope of the present application.

[0076] Embodiments:

[0077] The following will be described in detail with reference to the accompanying drawings. Figures 1-10 The present application will be further described in detail.

[0078] Please refer to Figures 1-10 The present application provides a technical solution: a production method for separating high-concentration brine and pure water from seawater by potential energy, comprising the following steps:

[0079] S1: send seawater into a selective crystallization grading tower provided with nucleating agents and inclined plate separation components for pretreatment to remove scale precursors such as calcium sulfate and magnesium hydroxide, to obtain pretreated seawater;

[0080] S2: under the action 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 tidal range, make the pretreated seawater flow through the Venturi ejector to form a liquid jet, and suck the gas connected with the membrane phase separation and small temperature difference heat recovery shell to reduce the shell side absolute pressure of the membrane phase separation and small temperature difference heat recovery shell;

[0081] S3: connect the membrane phase separation and small temperature difference heat recovery shell with the vertically arranged membrane phase separation and small temperature difference heat recovery column, so that the feed is stripped at the top of the column and condensed in the condenser to obtain a first water stream, and the condensation heat is transferred to the humidification and dehumidification device;

[0082] S4: in the humidification and dehumidification device, heat the wet air with the high-salt liquid from the concentrated salt branch and carry out multi-effect recovery to obtain a second water stream, and return the recovered heat to the membrane phase separation and small temperature difference heat recovery column or return to the seawater feed;

[0083] Wherein, the gas-water volume ratio of the humidification and dehumidification device is 1 to 3, and the gas-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;

[0084] S5: establish a gas-lift circulation driven by a Venturi air aspirator in the pre-membrane branch, and connect a microporous diffusion plate in parallel in front of the membrane to generate microbubbles, and scrub the membrane surface to reduce the concentration polarization;

[0085] Wherein, the volume fraction of microbubbles in the flow field of the membrane phase separation and small temperature difference heat recovery column near the wall region of the feed side is 1% to 5%, and the volume average particle size of the microbubbles is 50 microns to 150 microns;

[0086] S6: setting a density-triggered passive diversion network on the water production branch and the concentrated salt branch, and grading recovery or reinjection of fluids with different salinities according to an online conductivity threshold;

[0087] Wherein, the potential energy sources include but are not limited to deep wells, high-level reservoirs or water towers; the potential energy is converted into negative pressure on the membrane side by liquid ejectors, and cooperates with gravity closed heat recovery to maintain a small temperature difference, so as to realize non-boiling membrane phase separation.

[0088] In this embodiment: the test is completed on a small test platform with a rated water production of 1 cubic meter per hour, the raw water is taken from natural sea areas, the salinity is 35 grams per liter, the temperature is 25°C, and it does not contain industrial brine and underground brine, the process is continuously operated in the order of the claims, and all online quantities are sampled and saved at a frequency of one second.

[0089] First, selective crystallization grading pretreatment is carried out, a glass steel vertical grading tower is set, the tower body is 0.6 meters in diameter and 2.5 meters in height, a inclined plate sedimentation module with a horizontal angle of 60° is arranged in the tower, and calcium sulfate seeds are continuously added as nucleating agents, the median particle size of the seeds is 100 microns, and the addition concentration is 2.0 grams per liter;

[0090] Taking calcium sulfate and magnesium hydroxide as the target salt system, the supersaturation degree is maintained at about 20% by adding a dosing pump and online sensor feedback, and the hydraulic retention time is 20 min; the sludge is automatically discharged when the bottom conductivity reaches 60 millisiemens per centimeter or the upper turbidity reaches one hundred turbidity units. After the pretreatment, the sampling detection shows that the calcium hardness and sulfate are significantly reduced, and the fouling index is reduced from 6.0 to 3.5, which provides conditions for the subsequent membrane section.

[0091] Wherein, the supersaturation degree is defined, wherein, IAP = [Ca 2+ ] [SO4 2- ], K sp (T) is the solubility product of the salt system at the operating temperature, and the percentage of Ω-1 is the percentage of supersaturation, which is about 20% in this embodiment.

[0092] Wherein, the fouling index is SDI-15, which is measured according to the method of ASTM D4189 (0.45 μm filter membrane, 15 min constant pressure difference condition), and the smaller the value, the weaker the tendency of scaling or plugging.

[0093] Then, negative pressure is established by using potential energy, the effective elevation difference between the high-level water storage facility and the center line of the Venturi ejector is 40 meters, and the pretreated seawater enters the ejector to form a driving jet under the action of the elevation difference.

[0094] The ejector is made of 316L stainless steel, with a throat diameter of 10 mm, an outlet diameter of 28 mm, an outlet-to-throat cross-sectional area ratio of 7.8, and a suction port connected to the membrane phase separation and small temperature difference heat recovery shell. The volume flow rate of the driving branch is measured by an electromagnetic flowmeter to be 0.0060 cubic meters per second, the free volume of the shell side and the connecting pipeline is determined by water filling and draining to be 0.020 cubic meters, the volume conversion time is calculated to be 3.33 seconds, and the volume flow rate ratio of the suction branch to the driving branch is 0.20. The absolute pressure in the shell is monitored by an absolute pressure transmitter and stabilized in the window of 30 to 60 kPa, and at the same time, the difference between the static pressure at the outlet of the ejector and the static pressure in the shell is controlled by a back pressure gauge to be not more than 5 kPa.

[0095] The membrane phase separation and small temperature difference heat recovery shell is connected to a vertically arranged membrane phase separation and small temperature difference heat recovery column, the membrane assembly is a polytetrafluoroethylene flat membrane with a pore size of 0.2 microns and an effective area of 12 square meters per unit, a total of five groups, and a total effective area of 60 square meters. The column body is 8 meters high, with a stripping port at the top, and the top is connected to a plate condenser with a heat exchange area of 8 square meters. The feed enters from the top of the column, with a temperature of 55℃, and the shell side absolute pressure is maintained by the aforementioned ejector. In order to achieve pumpless heat recovery, the heat release side of the condenser is directly connected to the heat absorption side of the humidification and dehumidification device through a pipeline, relying on a one-meter-two elevation difference to form a gravity return, without a circulating pump and a parallel mechanical cold source. The volume ratio of air to liquid in the humidification and dehumidification device is set to 1 to 1.6.

[0096] Four temperature measuring points are arranged at the inlet of the condenser hot side, the outlet of the condenser hot side, the inlet of the humidification and dehumidification device heat absorption side, and the outlet of the humidification and dehumidification device heat absorption side. The logarithmic mean temperature difference is calculated according to the conventional definition, and the result is 15℃; the comprehensive heat recovery rate is calculated based on heat balance, and the result is 0.68.

[0097] Among them, the logarithmic mean temperature difference is calculated according to , 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 ; the four-point temperature is collected by PT100.

[0098] The dew point of the air at the outlet of the humidification and dehumidification device is configured with a dew point instrument, and the fluctuation amplitude of the dew point temperature is recorded, which is maintained at ±1.3 degrees Celsius during stable operation.

[0099] Air-lift and micro-bubble scrubbing are arranged in the channel before the membrane.

[0100] The gas is only taken from the non-condensable gas obtained by ejecting and separating after condensation, and is used as the only gas source before the membrane. No air blower or compressor is arranged, and the non-condensable gas is sent into the channel before the membrane after being limited by four one-millimeter pore size fixed orifice plates in parallel.

[0101] Parallel sintered ceramic microporous diffusion plate with average pore size of 40 microns and total layout area of 0.20 square meters, 30 millimeters from the membrane surface. The apparent gas velocity of the pre-membrane channel under this configuration is 0.012 meters per second; the microbubble volume fraction is 2.2% measured at a distance of 30 millimeters from the membrane surface by means of differential pressure and phase fraction calibration, and the volume average particle size is about 80 microns obtained by high-speed imaging and image processing statistics, with a sample size of not less than five thousand.

[0102] A passive shunt network is provided on the water production and concentrated salt side, and a float valve and specific gravity valve are used to realize pump-free back pressure stabilization. Only one branch leading to the salt pool or recharging is allowed to open at any time, and the other branch remains liquid sealed to form an equivalent static water liquid seal. The liquid seal height is set to 0.25 meters according to the seawater density at 25 degrees Celsius; the online conductivity threshold is set to 1.5 millisiemens per centimeter, and when the threshold is crossed, passive switching between the two branches is realized.

[0103] To quantify the dynamic stability of the gas supply and negative pressure, a pressure transmitter is provided at the outlet of the ejector and the inlet of the gas source distributor, with a sampling frequency of one second and a band-pass filtering of 0.1 to 2 hertz, and then the root mean square is calculated. The amplitude ratio is defined as the ratio of the root mean square of the pressure sequence at the inlet of the gas source distributor to the root mean square of the pressure sequence at the outlet of the ejector. The ratio is 0.24 during stable operation, indicating that passive buffering and passive shunting have a significant damping effect on pressure disturbance.

[0104] The whole process is continuously operated for 72 hours without using mechanical and electrical vacuum pumps, circulating pumps and air blowers. The record shows that the time ratio of the shell side absolute pressure in the 30 to 60 kilopascal window is 97.2%; the water production flux is 16.2 liters per square meter per hour, and the flux variation coefficient is 3.8%; the integrated water production conductivity is 480 microsiemens per centimeter; and the transmembrane pressure difference before the membrane increases by 2.0 kilopascals within 72 hours.

[0105] The unit water production power consumption is 0.06 kilowatt-hours per cubic meter, the installed electrical power is 0.05 kilowatts, and there is no unplanned downtime within 72 hours. All instruments are completed according to the calibration record table and two-point comparison on site, and the pressure comparison deviation at two points of 40 and 60 kilopascals is not more than 0.2 kilopascals, and the dew point comparison deviation is not more than 0.1℃, to ensure the calculation of derived quantities such as logarithmic mean temperature difference, amplitude ratio and flux variation coefficient has traceable accuracy.

[0106] The specific experimental data are as follows:

[0107] Experimental data table (Table #1)

[0108] Parameter / Unit Invention - Pumpless Unified Path Control A - Venturi + Blower Control B - Vacuum Pump + Blower Control C - Vacuum Pump + Mechanical Recuperation Inlet water 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 Mean shell side absolute pressure (kPa) 40 42 48 50 Time fraction of 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-water volume ratio (-) 1.6 1.6 1.8 1.7 Log mean temperature difference (°C) 15 15 28 20 Overall heat recovery (-) 0.68 0.61 0.35 0.50 Superficial gas 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 (pm) 80 120 110 100 Overall product water conductivity (pS / cm) 480 520 540 550 Product water flux (L / m²·h) 16.2 15.0 14.3 14.6 Product water flux coefficient of variation 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 Transmembrane pressure difference increase before membrane DP (kPa / 72 h) 2.0 5.5 7.8 8.4 Specific product water electricity consumption (kWh / m³) 0.06 0.15 0.32 0.38 Unplanned shutdown times (times / 72 h) 0 1 2 2 Installed electrical power (kW) 0.05 0.20 0.45 0.55 Rated product water production (m³ / h) 1.0 1.0 1.0 1.0

[0109] Instrument calibration record table (Table #2)

[0110] Calibration parameters / items Pressure transmitter P1 (shell side absolute pressure) Pressure transmitter P2 (injector outlet pressure) Electromagnetic flowmeter F1 (Qd) Mass flowmeter 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 (membrane front phase holdup) Power meter PW1 (installed power) Instrument model Rosemount 3051S ABB 266 Endress Promag 10W Brooks SLA58 PT100 Class A four branches Vaisala DMT143 Hach sc200+ four ring probe Emerson 3051DP Fluke 1730 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 0-3 kW ± 1% reading Date of last calibration 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 bench flowmeter three points Standard gas flowmeter three points Thermostatic bath three points (0 / 25 / 60 °C) Salt water saturation point comparison - U-tube calibration curve Standard source comparison Zero error 0.05 kPa 0.06 kPa 0.00 m³ / h 0.00 Nm³ / h ≤0.05°C ≤0.05°C 0.00 mS / cm 0.00 kPa 0.00 kW Range error ± 0.18 kPa ± 0.20 kPa ± 0.11 m³ / h ± 0.35 Nm³ / h ±0.12°C ±0.08°C ± 0.3 mS / cm ± 0.02 kPa ± 0.01 kW Field two-point comparison results (point 1 / point 2) 40 / 60 kPa difference ≤ 0.2 kPa 40 / 60 kPa difference ≤ 0.2 kPa 10 / 20 m3 / h difference < 0.1 10 / 30 Nm3 / h difference < 0.3 0 / 25 °C difference < 0.1 °C 10 / 20 °C dew point difference < 0.1 °C 5 / 50 mS / cm difference < 1% 1 / 5 kPa difference < 0.05 kPa 0.5 / 1.0 kW difference < 1% Pass / Fail Pass Pass Pass Pass Pass Pass Pass Pass Figure 1-10

[0111] The data show that this embodiment has substantial improvements in energy consumption, stability and anti-fouling compared with the three controls, and has a clear causal relationship with the key technology path in the claims. First, looking at the energy consumption index, the unit water production power consumption is 0.06 kWh / m³, which is lower than 0.15 kWh / m³ of control A, 0.32 kWh / m³ of control B and 0.38 kWh / m³ of control C. The difference comes from two core designs: one is to establish the shell side negative pressure directly through the potential energy through the texturized jet, which saves the continuous power consumption of the mechanical vacuum pump; the second is that the condenser and the humidifying and dehumidifying device form a pump-free closed heat recovery loop, which realizes gravity backflow through a 1.2 m elevation difference and achieves a comprehensive heat recovery rate of 0.68 at a logarithmic mean temperature difference of 15°C, greatly reducing the external heating demand. After control B cancels the closed heat recovery, the logarithmic mean temperature difference expands to 28°C and the comprehensive heat recovery rate decreases to 0.35, and the unit energy consumption increases significantly, verifying the decisive role of pump-free heat recovery closed loop in energy efficiency.

[0112] In terms of stability, the time ratio of shell-side absolute pressure in the 30-60 kPa window reaches 97.2%, which is significantly higher than 92.1% of control A, 88.5% of control B and 85.3% of control C; the amplitude ratio is 0.24, while control A, control B and control C are 0.62, 0.55 and 0.70 respectively. The amplitude ratio is calculated by taking the root mean square of the pressure sequence of the ejector outlet and the gas source distributor inlet after band-pass filtering at 0.1-2 Hz, and then taking the ratio, the smaller the value, the weaker the disturbance transmitted from the negative pressure side to the gas supply side. This embodiment uses the closed space on the gas side of the condenser as the only equivalent buffer volume of gas, and uses the liquid-sealed standpipe to form a pump-free back pressure stabilizing unit, which passively filters pressure disturbance, so that the gas supply pressure and superficial gas velocity remain at a stable level around the set value. This passive integration of "only one gas source with only one buffer" is different from the active shunt control of control A and control B using a blower and a pressure regulator, avoiding the residual vibration and random fluctuations introduced by additional moving parts.

[0113] In terms of anti-fouling and anti-scaling, the trans-membrane pressure difference of the membrane before 72h increased by only 2.0kPa, which was significantly lower than 5.5kPa of Control A, 7.8kPa of Control B and 8.4kPa of Control C. Although the superficial gas velocity was set at a relatively low level of 0.012m / s, the fine and dense scouring with a micro-bubble volume fraction of 2.3% and a volume average particle size of about 80μm effectively reduced the concentration polarization and initial deposition. The key point is that the gas supply comes from non-condensable gas after pumping and exhaust and is condensed to remove mist, so that the entrained liquid droplets are controlled at a low level, reducing secondary salt mist deposition; while the air supply of Control A and Control B can temporarily increase the shear, but the larger particle size and more severe fluctuations are easy to cause re-deposition and flux fluctuation. Correspondingly, the flux coefficient of variation under the working condition of the application is reduced to 3.8%, while that of Control A, Control B and Control C is 6.3%, 7.1% and 7.8% respectively. The comprehensive water production conductivity is maintained at 480μS / cm, which is better than each control, indicating that the pretreatment and passive shunt backfilling jointly reduce the penetration of high salt solutes and limit the cyclic accumulation.

[0114] The calibration records show that the key instruments such as pressure, flow, temperature, dew point, conductivity and power have completed standard calibration and on-site two-point comparison before the test. The two-point deviation of pressure is not more than 0.2kPa, and the dew point deviation is not more than 0.1°C, which ensures 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 realizes the synergy of no-pump negative pressure, no-pump heat recovery and passive pressure stabilization with unified potential energy and non-condensable gas path. Without introducing mechanical vacuum pumps, circulating pumps and independent air blowers, it realizes lower unit water production energy consumption, higher operation stability and slower pollution growth.

[0115] As shown in Parameter / Unit , the operating conditions of the selective crystallization fractional pretreatment of S1 are:

[0116] The supersaturation of calcium sulfate and magnesium hydroxide as the target salt system is 10% to 30%, the reaction residence time is 10 minutes to 30 minutes, the angle between the inclined plate and the horizontal is 45° to 70°, the median particle size of the seed crystal is 50 microns to 200 microns, the seed crystal concentration is 0.5 grams per liter to 5 grams per liter, and the sludge is discharged when the online turbidity in the sedimentation zone reaches 50 to 200 NTU or the bottom conductivity reaches 55 to 65 millisiemens per centimeter.

[0117] In this embodiment: the test is completed on a continuous flow pilot plant. The raw water is natural seawater with a salinity of 35g / L and a temperature of 25°C, and does not contain industrial brine and underground brine. The pretreatment unit is a vertical glass steel fractional crystallization tower with a tower body diameter of 0.6m and a height of 2.5m. The inside is provided with inclined plate sedimentation components with an angle of 60° to the horizontal, with a net distance of 50mm between the plates, and an effective sedimentation area of about 12m².

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] Sludge control is based on threshold comparison + minimum interval logic: sludge discharge is performed when upper turbidity ≥ set value or bottom conductivity ≥ set value and 10 min has elapsed since last sludge discharge, sludge discharge is stopped to set liquid level or for 30-45 s to prevent excessive sludge discharge causing backflow disturbance.

[0126] The sampling and measurement caliber is as follows: calcium, magnesium and sulfate are quantified by inductively coupled plasma emission spectroscopy after 0.45 μm filtration; SDI15 is determined by constant pressure method according to ASTM D4189; turbidity is measured by infrared turbidimeter; conductivity is measured by four-electrode conductivity probe; pH is measured by glass electrode. To verify the sufficiency of disclosure and stable reproducibility, three independent repetitions are performed for each of the three working conditions, each running for 4 to 6 h, and the key working conditions and effluent indicators are recorded and the mean and standard deviation are calculated. The three working conditions are defined as follows: the present application is selective crystallization grading, the process includes continuous seeding, mild alkalization and grading sedimentation; control A is lime softening, the pH is adjusted to 10.5 to 10.8 and no seed is added; control B is coagulation and clarification, 50 mg / L of polyaluminum chloride and 2 mg / L of cationic flocculant are added, the supersaturation is not controlled and no seed is added. The same tower body and inclined plate structure are used for the three working conditions, only the addition strategy and control target are changed to ensure the comparability of the comparison.

[0127] The running results show that under the working condition of the present application, the effluent calcium ion concentration is reduced from 410 mg / L to about 250 mg / L, the sulfate is reduced from 2700 mg / L to about 2100 mg / L, the supersaturation percentage of calcium sulfate is reduced from about 22% to about 3%, the supersaturation percentage of magnesium hydroxide is reduced from about 25% to about 8%; the effluent SDI15 is reduced from 6.0 to about 3.5, the overflow turbidity is maintained at 3 to 5 NTU, the unit sludge yield is about 0.13 kg dry solid / m³, and the alkali consumption is about 95 g NaOH / m³. In comparison, control A significantly reduces magnesium ions at a higher pH, but the supersaturation percentage of calcium sulfate is still about 10%, the effluent SDI15 is 4.6, the alkali consumption is about 210 g / m³, and the unit sludge yield is about 0.31 kg dry solid / m³; the effluent turbidity and SDI15 of control B are both high, the turbidity is 8 to 15 NTU and the SDI15 is 6.1, and the two types of supersaturation are maintained at a high level, which is not conducive to the subsequent membrane phase change separation and the scaling control of small temperature difference backheating.

[0128] The data are as follows:

[0129] Experimental data table (Table #3)

[0130] Invention - Selective Crystallization Fractionation (Mean) Invention - Selective Crystallization Fractionation (Standard Deviation) Control A - Lime Softening (Mean) Control A - Lime Softening (Standard Deviation) Control B - Coagulation Clarification (Mean) Control B - Coagulation Clarification (Standard Deviation) Operating Temperature (°C) Residence Time (min) 30.0 0.2 30.0 0.2 30.0 0.2 Inclination to Horizontal (°) 20 0 20 0 20 0 Seed Median Particle Size (pm) 60 0 60 0 60 0 NA 100 5 NA NA NA Seed Dosage Concentration (g / L) NA 1.5 0.1 NA NA NA pH (Mixing Zone) Target Supersaturation_CaS04 (%) 10.0 0.1 10.6 0.1 7.7 0.1 NA 20 1 NA NA Target Supersaturation_Mg(OH)2 (%) NA NA 25 1 >30 NA Effluent Ca2+ (mg / L) Effluent SO42- (mg / L) Effluent Mg2+ (mg / L) 250 8 320 10 395 12 Supersaturation_CaS04 Effluent (%) 2100 50 2450 60 2680 70 Supersaturation_Mg(OH)2 Effluent (%) 950 30 820 25 1240 35 Overflow Turbidity (NTU) 3 0.5 10 1.0 22 1.5 SDI-15 (-) 8 1.0 5 0.8 25 1.2 Unit Sludge Yield (kg dry solids / m3) 4 0.6 8 1.0 12 1.5 Alkalinity Consumption (g NaOH / m3) 3.5 0.2 4.6 0.3 6.1 0.4 PAC Consumption (mg / L) 0.13 0.02 0.31 0.03 0.09 0.02 Cationic Coagulant Consumption (mg / L) 95 5 210 10 0 0 CaS04 Scaling Risk Index (Relative) 0 0 0 0 50 5 72 h Effluent Conductivity Mean (mS / cm) 0 0 0 0 2 0.2 Calibration Items / Parameters 0.25 0.03 0.55 0.05 1.00 0.10 pH Meter PH1 52.0 0.6 53.5 0.7 54.1 0.8

[0131] Instrument calibration record table (Table #4)

[0132] Conductivity Meter EC2 Turbidity Meter NTU1 Thermometer T-PT100 In-line Flow Meter F-EMF ICP-OES Lab Model / Spec Mettler Seven2Go Hach sc200 Four Electrode Hach 2100Q PT100 Class A Endress Promag 10W Agilent 5110 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 Element Quantification RSD < 2% Most Recent Calibration Date Calibration Method NIST Buffer Three Points 4.01 / 7.00 / 10.01 2025-07-05 2025-07-06 2025-07-06 2025-07-05 2025-07-08 2025-07-02 Conductivity Standard 12.88 and 50.0 mS / cm Formazin Fractionation Standard Thermostat Two Points 0 and 25 °C Standard Bench Flow Meter Three Points Internal Standard Recovery 95 - 105% On-site Two-Point Comparison Results 6.50 and 10.00 pH difference < 0.02 12.88 and 50.0 mS / cm difference < 1% 10 and 100 NTU difference < 2% 0 and 25 °C difference < 0.1 °C 10 and 20 m3 / h difference < 0.1 Internal Standard Recovery 99% Pass / Fail Pass Pass Pass Pass Pass Pass Figure 1-10 Figure 1-10

[0133] The above data show that the selective crystallization fractionation has the comprehensive advantages of "reducing the risk of scaling, improving the treatability of effluent, and reducing the consumption of chemicals and sludge", and the mean value and standard deviation are given through 3 repeated tests to ensure the repeatability and detectability of the results.

[0134] Firstly, from the controllable crystallographic driving, the continuous crystal seeds and the mild alkalization work together to make the calcium sulfate preferentially nucleate and grow on the surface of the crystal seeds in the reaction zone. The data show that the percentage of calcium sulfate supersaturation decreases from about 22% to about 3%, while the control A is still at about 10% level, and the control B is higher;

[0135] This difference directly corresponds to the ion composition of the effluent: the calcium ion and sulfate ion in the effluent of the present application are 250 mg / L and 2100 mg / L, respectively, which are lower than 320 and 2450 of the control A, and 395 and 2680 of the control B;

[0136] Since the scaling tendency of calcium sulfate is highly related to the activity product of product ions, the present application reduces the scaling driving force of subsequent membrane phase separation and small temperature difference heat recovery in the pretreatment stage through selective crystallization;

[0137] From the perspective of fractionation sedimentation and liquid-solid separation efficiency, the angle between the inclined plate and the horizontal 60° cooperates with the linear velocity of 0.05 m / s to 0.1 m / s, so that the crystals larger than 50 μm slip along the plate surface and enter the thick sludge hopper, and the residual suspended solids carried by the overflow are significantly reduced, which is reflected in the overflow turbidity of about 4 NTU, which is obviously superior to 8 of the control A and 12 of the control B;

[0138] The SDI15 is about 3.5, which is also better than the two groups of controls, which means that the inlet boundary layer of the subsequent membrane section is thinner and the particle plugging risk is lower;

[0139] Further looking at the operation economy, while achieving equivalent calcium and magnesium reduction, the alkali consumption of the present application is about 95 g NaOH / m³, which is only about 45% of the control A; the unit sludge yield is about 0.13 kg dry solid / m³, which is also significantly lower than the 0.31 of the control A, which indicates that the strategy of continuous crystal seeds and mild alkalization has a more optimal coupling economy of chemicals and sludge compared with strong alkali softening. Although the control B has no alkali consumption and the amount of sludge is small, since the two types of supersaturation are not reduced, the scaling risk index of the subsequent membrane section is normalized to 1, and the comprehensive effect is the worst;

[0140] 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.

[0141] like Parameter / Unit As 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:

[0142] 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.

[0143] 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.

[0144] 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.

[0145] 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.

[0146] 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.

[0147] The effective free volume of the shell and its connecting pipeline is recorded as the shell free volume, which is measured by filling to the scale and then emptying for three times in succession and taking the arithmetic mean value, and the relative standard deviation of the three readings is not higher than 3%;

[0148] The driving branch volume flow is recorded as the driving flow, which is measured by the electromagnetic flowmeter and sampled at a frequency of 1s; the suction branch volume flow is recorded as the suction flow, which is measured by the thermal mass flowmeter and converted to the volume flow under the condition of 25°C.

[0149] The volume conversion time is defined as the shell free volume divided by the driving flow, and in this embodiment, the volume conversion time works at the center point of 3s to 4s and is kept within the range of 1.7s to 6.7s; the suction ratio is defined as the suction flow divided by the driving flow, and in this embodiment, the suction ratio is set to 0.20 and kept within the range of 0.12 to 0.45.

[0150] Absolute pressure transmitters are arranged at the outlet of the ejector diffuser section and the top of the shell respectively for monitoring static pressure, and the absolute value of the difference between the two static pressures is defined as the static pressure difference between the injection port and the shell, and the back pressure is adjusted to make it not more than 5kPa, preferably maintained within the interval of 3kPa to 5kPa.

[0151] The starting sequence is to first open the driving valve to a predetermined opening degree, so that the absolute pressure of the shell is reduced to the target window of 30kPa to 60kPa and is continuously stable within the range of ±2kPa for 5min, then the back pressure valve is adjusted to make the static pressure difference between the injection port and the shell converge to 3kPa to 5kPa, and the valve position is fixed to enter continuous operation.

[0152] During continuous operation, the shell absolute pressure, the ejector outlet static pressure, the driving flow and the suction flow are recorded synchronously at a sampling frequency of 1s, after excluding the period of manual intervention and instrument self-checking, the proportion of the time within the window of 30kPa to 60kPa in any continuous 72h is calculated, and the proportion is not less than 95% as the criterion for stable operation. If the absolute value of the static pressure difference between the injection port and the shell exceeds 5kPa instantaneously during operation, the driving opening degree is first reduced and then the suction side flow is appropriately increased to correct the deviation until it is restored within the limit; if the absolute pressure of the shell deviates from the target window, the nozzle Reynolds number is first reduced and the communication pipeline is reviewed for air leakage, and then it is restored to the set point.

[0153] The measurement aperture and accuracy requirements for implementing the above process are as follows:

[0154] The shell absolute pressure and the ejector outlet static pressure use absolute pressure transmitters with a range of 0 to 100kPa, and the accuracy is not less than 1 / 250 of the range, and the comparison is made at two points of 40kPa and 60kPa in the field, and the difference between the two points is not more than 0.2kPa;

[0155] The driving flow rate adopts an electromagnetic flow meter with a range of 0-30 m3 / h and an accuracy of not less than 1 / 1000 of the range, and the on-site comparison error at two points of 10 and 20 m3 / h is not more than 0.1 m3 / h; the suction flow rate adopts a thermal mass flow meter with a range of 0-50 Nm3 / h and an accuracy of not less than 1% of the range, and the on-site comparison error at two points of 10 and 30 Nm3 / h is not more than 0.3 Nm3 / h;

[0156] After the above instrument completes annual calibration, then two-point comparison is carried out on site, and the relative standard deviation of the free volume of the shell determined by three times of filling and draining is not more than 3% as the pass criterion.

[0157] By controlling the volume conversion time in the range of 1.7 s to 6.7 s, controlling the suction ratio in the range of 0.12 to 0.45, and limiting the difference between the injection port and the shell static pressure to below 5 kPa, the absolute pressure in the shell can be maintained in the target window of 30 kPa to 60 kPa for a long time without configuring any electromechanical vacuum equipment and pre-extraction volume, thereby meeting all the quantitative constraints of claim 3 on establishing and maintaining negative pressure.

[0158] As one of the implementation manners, the throat diameter, the area ratio and the effective elevation difference can all be equivalently replaced within the range defined in the claims, as long as the three constraints of volume conversion time, suction ratio and the difference between the injection port and the shell static pressure are maintained, the same technical effect as the embodiment can be obtained.

[0159] As shown in Invention - Pumpless Closed Heat Recovery (Gravity Reflux) , the heat releasing side of the condenser in step S3 is directly connected with the heat absorbing side of the humidifying and dehumidifying device in step S4 through a pipeline between step S3 and step S4 to form a pump-free closed heat recovery loop by gravity backflow, and no circulating pump or parallel mechanical cold source is arranged;

[0160] The heat recovery loop meets the following conditions:

[0161] The gravity backflow drop is not less than 1 meter;

[0162] The logarithmic mean temperature difference between the condenser and the humidifying and dehumidifying device is 10-25 degrees Celsius;

[0163] The comprehensive heat recovery rate of the humidifying and dehumidifying device is not less than 0.60, and the comprehensive heat recovery rate is the proportion of the heat returned to step S3 or returned to the seawater feed among the recoverable heat entering the humidifying and dehumidifying device;

[0164] During the continuous 72-hour operation, the absolute value of the difference between the average heat exchange amount per unit time of the condenser and the average heat absorption amount per unit time of the humidifying and dehumidifying device accounts for not more than 10% of the average heat exchange amount per unit time of the condenser, and the dew point temperature fluctuation amplitude of the outlet air of the humidifying and dehumidifying device is not more than ±2 degrees Celsius;

[0165] In this embodiment, the method directly connects the outlet of the heat releasing side of the condenser to the inlet of the heat absorbing side of the humidifying and dehumidifying device through a pipeline, and connects the outlet of the heat absorbing side back to the inlet of the heat releasing side of the condenser to form a closed loop; the condenser is arranged at a high position, and the humidifying and dehumidifying device is arranged at a low position, and the difference in the static water level elevation between the two is one meter and two; the pipeline has a continuous slope throughout the whole pipeline, and an automatic exhaust is arranged at the highest point and a pollution discharge is arranged at the lowest point; the working medium of the loop is fresh water, and an inhibitor with a mass fraction of not more than one thousandth is added; the loop is operated at normal pressure and is not provided with a circulating pump and a parallel mechanical cold source. The logarithmic mean temperature difference is calculated according to ΔT lm = (ΔT1- ΔT2) / ln (ΔT1 / ΔT2), wherein ΔT1 is the temperature of the inlet of the heat side of the condenser minus the temperature of the outlet of the heat absorbing side of the humidifying and dehumidifying device, and ΔT2 is the temperature of the outlet of the heat side of the condenser minus the temperature of the inlet of the heat absorbing side of the humidifying and dehumidifying device; during operation, ΔT lm is controlled to be within the range of ten degrees Celsius to twenty-five degrees Celsius.

[0166] The comprehensive heat recovery rate is calculated according to η hr = Q HDH吸热 / Q 冷凝放热 ; wherein Q 冷凝放热 = V 热侧 ρc p (T 入口 -T 出口 ). ; The humidity content is obtained by converting the outlet dew point and the air temperature; the four temperature points, the two volume flow rates and the one dew point are sampled at one second, and are counted within a sliding time window of sixty seconds, as the design threshold value of the backflow, a pressure head margin coefficient Φ h = [ (ρ 冷 - ρ 热 ) g Δz - Δp 沿+局 ] / Δp 沿+局 is introduced, and Φ h ≥ 0.2 is required; in this embodiment, Φ h = 0.46, which indicates that the density difference driving pressure head is more than four tenths of the total pressure drop of the loop, and can avoid steam plugging and backflow interruption, and the stability is determined according to the following caliber:

[0167] In any continuous seventy-two hours, the absolute value of the difference between the average heat releasing amount of the condenser per unit time and the average heat absorbing amount of the humidifying and dehumidifying device per unit time accounts for not more than ten percent of the former, and the fluctuation range of the dew point temperature of the outlet air of the humidifying and dehumidifying device is not more than two degrees Celsius;

[0168] The statistical proportion is eliminated from the manual intervention and the instrument self-check timestamp, and the total time length is not more than 5% of the total record time length. To prove that it still has better dynamic and steady-state performance than the pump circuit under the condition of no pump, after twelve hours of stable operation, the vaporization load of the membrane phase separation and the small temperature difference regenerator is increased by 10% in a positive step and maintained for twenty minutes, and after thirty-six hours of operation, a negative step of 10% is implemented and maintained for twenty minutes. The overshoot amplitude of the dew point trajectory and the setting time to recover to a bandwidth of ±5% are recorded and compared with the closed pump regenerator and the non-regenerator (cooling tower cooling and steam heating).

[0169] The measuring points and precision are as follows: PT100A level temperature element, basic error not greater than 0.15 degrees Celsius at 0 to 200 degrees Celsius; electromagnetic flowmeter, basic error not greater than 0.005% of the range at 0 to 30 cubic meters per hour; dew point instrument precision not less than 0.1 degrees Celsius; after annual calibration, on-site comparison is carried out at 0 and 25 degrees Celsius, 10 and 20 cubic meters per hour, with a deviation of not more than 0.1 degrees Celsius and 0.1 cubic meters per hour respectively; the specific experimental data are referred to the following table:

[0170] Performance comparison and disturbance test summary table (table #5)

[0171] Control A - Mechanical Circulation Closed Heat Recovery (With Pump) Control B - No Closed Heat Recovery (Cooling Tower + Steam Reheat) Elevation Difference Δz (m) ​ ​ 1.2 0.0 0.0 Loop equivalent pressure drop Δp along + (Pa) 800 Overcome by the pump Heat rejection circuit Head margin coefficient Φh (-) 0.46 NA NA LMTD Log mean temperature difference (°C) 15 14 28 Overall heat recovery ηhr (-) 0.68 0.66 0.00 72 h energy imbalance |Qcond - Qabs| / Qcond (%) 2.7 1.6 100 HDH outlet dew point fluctuation (± °C ±1.3 ±1.0 ±3.8 Specific electrical consumption for water production (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 at step +10% (°C) 0.9 2.6 3.8 Step +10% setting time (min, to ± 5%) 7.5 24.0 35.0 Dew point undershoot at step -10% (°C) 0.8 2.1 3.1 Step -10% setting time (min, to ± 5%) 6.8 19.0 29.0 Qabs standard deviation / mean (% 72 h) 3.6 7.9 >50

[0172] From the above table we can see:

[0173] First, under the condition of not setting a circulating pump, the comprehensive heat recovery rate reaches 0.68 and the energy balance error is only 2.7%, which is equivalent to the 0.66 and 1.6% of the pump circuit, but the unit water production power consumption is reduced to 0.06 kilowatt hours per cubic meter, showing the differentiated effect of equivalent regenerator and non-equivalent energy consumption;

[0174] Second, in the step disturbance test which is most sensitive to the boundary conditions of the wet end, the dew point overshoot of the pump-free closed regenerator is less than 1 degree Celsius, and the setting time is not more than eight minutes, while the coupled oscillation caused by pump inertia and control delay in the pump circuit amplifies the overshoot and setting time to 2.6 degrees Celsius and 24 minutes respectively, and the non-regenerator is worse;

[0175] Two sets of endpoint working condition summaries are given to prove that the boundary can be implemented:

[0176] When the elevation difference is one meter and ten degrees Celsius, the calculated and measured energy imbalance is 4.5%, and the dew point fluctuation is plus or minus 1.7 degrees Celsius;

[0177] When the elevation difference is two meters and twenty-five degrees Celsius, the energy imbalance is 2.1%, and the dew point fluctuation is plus or minus 1.1 degrees Celsius.

[0178] For example Figure 1-10The non-condensable gas separated from the gas extracted in step S2 is directly used as the only gas source for step S5 after being cooled by the condenser in step S3, without setting an independent air blower or compressor;

[0179] The gas source distribution ratio is defined as the ratio of the volume flow rate of the non-condensable gas supplied to step S5 to the volume flow rate of the gas extracted in step S2, and the gas source distribution ratio is set to be 0.05 to 0.30 by setting the orifice diameter and the throttling length.

[0180] The superficial gas velocity of the membrane phase transition separation and the small temperature difference heat recovery column feeding side is set to be 0.005 m / s to 0.03 m / s, the superficial gas velocity is defined as the value of the gas volume flow rate on the channel cross section divided by the channel cross-sectional area, and the entrained droplet content of the non-condensable gas after demisting is not higher than 50 mg / m³.

[0181] In this embodiment, only the non-condensable gas separated from the gas extracted in step S2 is used as the only gas source for step S5 during the whole operation process, without setting an independent air blower or compressor. The condenser gas phase outlet is connected in series with a composite demister and is connected with a gas collecting tank, the gas collecting tank is provided with two fixed orifice plate flow limiting and one trace bypass to form a gas source distributor, the first one supplies gas to step S5, and the second one is connected back to the low pressure area of the injection outlet to release pressure.

[0182] The gas source distribution ratio is defined as the ratio of the volume flow rate of the non-condensable gas supplied to step S5 to the volume flow rate of the gas extracted in step S2, and the gas source distribution ratio is set to be 0.05 to 0.30 by setting the orifice diameter and the throttling length.

[0183] The entrained droplet mass concentration is defined as the mass increment after sampling 1 m³ of gas after the demister and intercepting it with a filter membrane with a pore size of 0.8 μm, divided by the sampling volume, and the acceptance limit is ≤50 mg / m³.

[0184] The extraction volume flow rate of step S2 is uniformly converted to 25°C condition by mass flow meter reading, the volume flow rate supplied to step S5 is calculated by the pressure difference before and after the orifice plate and is corrected by two-point field comparison with a portable mass flow meter, and the cross-sectional area of the channel before the membrane is a fixed value designed by the device.

[0185] The shell side absolute pressure, the gas collecting tank pressure, the extraction and supply volume flow rate are sampled once every 1 s and are statistically analyzed by a 60 s sliding window, in any continuous 72 h, it is determined that the distribution ratio and the superficial gas velocity are both in the set value ± 20% interval and the entrained droplet mass concentration is ≤50 mg / m³, which is satisfied.

[0186] 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.

[0187] 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:

[0188] 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.

[0189] 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.

[0190] 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.

[0191] 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.

[0192] 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.

[0193] 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.

[0194] The jet suction outlet and the gas cap are respectively provided with a zero to one hundred kilopascal range absolute pressure transmitter with a basic error of not more than two and a half percent of the range, to record pressure sequence at a frequency of one second; the equivalent static water seal height is calibrated according to the fixed gas cap pressure difference, a stable pressure difference is applied by using a standard pressure source, and the liquid level is read at the position where the seal is just broken and converted into H eq The two branches are respectively calibrated to within five percent of the target value.

[0195] The start-stop is executed in the following order: first, establish jet suction and stabilize to the target shell course pressure window, then fill the liquid to establish the liquid seal of the two risers, adjust the small hole at the top of the riser to appear obvious but not more than fifteen seconds of delay, and finally set the online conductivity threshold and start continuous recording.

[0196] The acceptance criteria for stable operation are written as: sampling at one second and using a ten-minute sliding time window, within any continuous seventy-two hours, the standard deviation of the pressure fluctuation at the jet suction outlet is not more than one kilopascal; only one of the salt pool branch or the recharge branch is allowed to be on at any time, the other branch remains liquid sealed, if it is detected that both branches are on at the same time for more than two seconds, the equivalent static water seal height of the high threshold branch is increased or the small hole at the top of the branch is tightened to correct the deviation; when the online conductivity crosses the set threshold, the two branches complete passive switching within fifteen seconds; within the range of zero point one meter to zero point five meters, the equivalent static water seal height remains effective and there is no gas plug failure.

[0197] The above criteria are statistically excluded from manual intervention and instrument self-check timestamps, and the total time length is not more than five percent of the total recording time length. To ensure reproducibility, the two-point comparison on site is at forty and sixty kilopascals, with an allowed deviation of not more than zero point two kilopascals; the conductivity meter is compared at twelve point eight eight and fifty point zero millisiemens per centimeter, with a reading deviation of not more than one percent; H eq The relative standard deviation of three repeated calibrations is not higher than three percent.

[0198] As shown in Figure 1-10 , only the gas side closed space of the condenser in step S3 is used as the only gas equivalent buffer volume to provide non-condensable gas to step S5 between step S3 and step S5, without setting an independent gas tank, accumulator or adjustable pressure regulating valve;

[0199] and operates under the following passive dynamic conditions:

[0200] The ratio of the gas equivalent buffer volume to the volume flow of non-condensable gas supplied to step S5 is defined as the gas source buffer time, and the gas source buffer time is two to twenty seconds;

[0201] The absolute value of the rate of change of pressure at the inlet of the gas source distributor is not greater than 1 kPa / s, calculated at a sampling frequency of once per second and using a 60-second time window;

[0202] The amplitude ratio is defined as the ratio of the root mean square value of the pressure sequence at the inlet of the gas source distributor to the root mean square value of the pressure sequence at the outlet of the jet suction, and the amplitude ratio is not greater than 0.30, after the pressure sequences at the inlet of the gas source distributor and at the outlet of the jet suction are respectively band-pass filtered at 0.1 to 2 Hz and the root mean square values are calculated at a sampling frequency of once per second and using a 60-second time window;

[0203] The coefficient of variation of the volume flow rate of the non-condensable gas supplied in step S5 is not higher than 10%, calculated at a sampling frequency of once per second and using a 60-second time window;

[0204] In this embodiment, the gas-side closed space of the condenser in step S3 provides the non-condensable gas as the only gas equivalent buffer volume to step S5 throughout the entire operation, and no independent gas tank, pressure accumulator or adjustable pressure regulating valve is provided.

[0205] The closed space is communicated with the inlet of the gas source distributor in step S5 through a fixed orifice plate flow limiting pipeline, and the orifice diameter and the throttling length of the orifice plate are determined at the time of manufacture and are not adjusted during operation.

[0206] Before first commissioning, the isothermal perturbation volume calibration of the gas equivalent buffer volume is performed: under the condition that the ambient temperature is basically constant, a three-way valve is used to instantaneously connect a known volume of a calibration cavity with the gas-side space of the condenser, and the absolute pressures of the two cavities before connection and the common absolute pressure after connection are recorded respectively, and the gas equivalent buffer volume is obtained by solving the equation of state of the isothermal gas;

[0207] The ratio of the volume of the calibration cavity to the equivalent volume is controlled at 5% to 20% to reduce the uncertainty of the solution, and the "gas source buffer time" is defined as the ratio of the gas equivalent buffer volume to the volume flow rate of the non-condensable gas supplied in step S5;

[0208] The gas supply volume flow rate is measured by a mass flow meter and converted to 25°C, and by selecting the orifice diameter and the throttling length of the fixed orifice plate, the gas source buffer time is in the range of 2 seconds to 20 seconds (the center set value can be taken as 8 to 10 seconds), and accordingly the flow limiting member is locked.

[0209] To ensure the detectability of the dynamic quantitative indicators, absolute pressure transmitters with a range of 0 to 100 kPa (abs) and a basic error not greater than 0.25% of the range are respectively arranged at the inlet of the gas source distributor and at the outlet of the jet suction, and the pressure sequences at the two places are synchronously collected at a frequency of 1 Hz.

[0210] The absolute value of the pressure difference between adjacent sampling instants divided by the sampling interval is defined as the "pressure rate of change", and the maximum value thereof is calculated in a 60-second sliding time window, with an acceptance criterion of not more than 1 kPa / s. To evaluate the ability of the passive buffer to attenuate upstream disturbances, the "pressure sequence at the outlet of the jet suction" and the "pressure sequence at the inlet of the gas source distributor" are zero-phase digitally band-pass filtered (0.1-2 Hz) in the same time window, and the root mean square of the filtered sequences is calculated, with the "amplitude ratio" defined as the ratio of the aforementioned inlet root mean square to the jet suction outlet root mean square, with an acceptance criterion of not more than 0.30.

[0211] The non-condensable gas volume flow rate of the supply step S5 is recorded at 1 Hz, and the average value and standard deviation are calculated in a 60-second time window, with the "coefficient of variation of the gas flow rate" defined as the ratio of the standard deviation to the average value, with an acceptance criterion of not more than 10%.

[0212] The above statistics are performed in any continuous 72 hours; timestamps of manual intervention and instrument self-checking are excluded, and the total time length is not more than 5% of the total recording time length. To ensure traceability of the quantity value, the pressure transmitter is compared in situ at two points of 40 kPa and 60 kPa, and the error at the two points is not more than 0.2 kPa; the mass flowmeter has a measurement range covering 0-50 Nm³ / h, with a basic error not more than 1% of the range, and is compared in situ at two points of 10 and 30 Nm³ / h, with a deviation not more than 0.3 Nm³ / h.

[0213] When it is started or disturbed, first close the valve downstream of the gas source distributor to complete the isothermal perturbation calibration of the equivalent buffer volume of the gas and record the value, then open the fixed orifice restrictor channel and open the downstream of the gas source distributor, so that the gas volume flow rate reaches the set value and stabilizes within the range of ±20% of the set value for 3 minutes; then start recording and calculating the gas source buffer time, pressure rate of change, amplitude ratio and gas flow rate variation coefficient according to the aforementioned caliber.

[0214] If the gas source buffer time is less than 2 seconds or more than 20 seconds, it is re-set by replacing the opening diameter of the fixed orifice or adjusting the throttling length; if the pressure rate of change exceeds 1 kPa / s or the amplitude ratio exceeds 0.30, the restrictor resistance is preferentially increased and the gas side closed space of the condenser and its connecting pipeline are checked for bypass leakage; if the variation coefficient of the gas flow rate exceeds 10%, the conversion caliber of the mass flowmeter and the sensitivity of the slight leakage before and after the gas source distributor are reviewed, and the time constant of the mass flowmeter and the statistical window are unified to the above caliber to exclude the pseudo fluctuations introduced by the algorithm.

[0215] Under the above communication mode, calibration method, measurement and statistical caliber, and acceptance criteria, without setting up an independent gas tank, pressure accumulator or adjustable pressure regulating valve, only relying on the condenser gas side closed space and fixed flow limiting, the requirements of gas source buffer time of 2 seconds to 20 seconds, pressure change rate not greater than 1 kPa / s, amplitude ratio not greater than 0.30, and gas flow variation coefficient not higher than 10% can be stably met.

[0216] As shown in Figure 1-10 When the method is started or a disturbance occurs during operation, the following steps are sequentially performed without using external compressed gas, electromechanical vacuum pump or circulating pump:

[0217] The gas source distributor of step S5 is closed and the drive valve of step S2 is opened, so that the pretreated seawater forms a driving jet through the Venturi ejector and exhausts the gas in the membrane phase separation and small temperature difference heat recovery shell, until the absolute pressure of the shell of the membrane phase separation and small temperature difference heat recovery shell reaches the target value in the range of 30 kPa to 60 kPa and remains stable within ±2 kPa for 5 minutes;

[0218] Subsequently, the pumpless closed heat recovery circuit between step S3 and step S4 is opened, so that the condenser heat release side and the heat absorption side of the humidification and dehumidification device form a gravity backflow, until the logarithmic mean temperature difference between them enters the interval of 10 degrees Celsius to 25 degrees Celsius and remains for 3 minutes;

[0219] Then, non-condensable gas is slowly introduced from the condenser gas side closed space to step S5 through the fixed flow limiting element, until the superficial gas velocity of the feed side of the membrane phase separation and small temperature difference heat recovery column of step S5 reaches the set value in the range of 0.005 m / s to 0.03 m / s and remains within the range of ±20% of the set value for 3 minutes;

[0220] Next, the equivalent hydrostatic liquid seal height of step S6 is adjusted to the range of 0.10 m to 0.50 m, so that the density triggered passive shunt network enters the passive switching state;

[0221] At a sampling frequency of once per second and using a 60-second time window, the pressure sequence at the jet suction outlet and the pressure sequence at the inlet of the gas source distributor are respectively band-pass filtered at 0.1 to 2 Hz and the 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 inlet of the gas source distributor to the root mean square value of the pressure sequence at the jet suction outlet. When the amplitude ratio is not greater than 0.30, it is considered to enter the stable operation stage;

[0222] In this embodiment, the pretreatment and potential energy supply of steps S1 and S2 have been realized according to the caliber of claim 1 and claim 3, and the membrane phase separation and small temperature difference heat recovery shell, the condenser, the humidification and dehumidification device, the Venturi ejector, the gas source distributor and the density triggered passive shunt network are connected according to claims 3 to 7.

[0223] To ensure the measurability, pressure transmitters with a range of 0-100 kPa (absolute pressure) and a basic error of not more than 0.25% of the range are arranged at the jet suction outlet and the gas source distributor inlet respectively. Four temperature measuring points are arranged at the hot side inlet of the condenser, the hot side outlet of the condenser, the heat absorption side inlet of the humidifying and dehumidifying device, and the heat absorption side outlet of the humidifying and dehumidifying device. PT100A level elements are used, and the basic error is not more than 0.15℃. The volume flow rate of the non-condensable gas supplied in step S5 is measured by a mass flow meter and converted to 25℃. The cross-sectional area of the channel before the membrane is a fixed value designed for the device, which is used to calculate the superficial gas velocity. The above signals are sampled at 1 Hz and statistically analyzed using a 60s sliding time window. During the statistical analysis, the time stamps of manual intervention and instrument self-checking are removed, and the total time length is not more than 5% of the total recording time length. The pressure transmitters have a field comparison error of not more than 0.2 kPa at two points of 40 kPa and 60 kPa, the temperature has a comparison error of not more than 0.1℃ at two points of 0℃ and 25℃, and the mass flow meter has a comparison error of not more than 0.3 Nm³ / h at two points of 10 and 30 Nm³ / h.

[0224] When starting or recovering from disturbance, first close the gas source distributor in step S5 to stop the gas before the membrane, open the drive valve in step S2, use the effective elevation difference to make the pretreated seawater flow through the Venturi ejector to form a driving jet, and continuously exhaust the gas in the membrane phase separation and small temperature difference reheating shell through the suction port. The absolute pressure at the top measuring point of the shell is used as the reference, and the shell absolute pressure is reduced to the target window of 30-60 kPa and continuously stabilized within ±2 kPa for 5 min. The stability judgment is completed by 1 Hz sampling and 60s window statistics. Subsequently, without setting a circulating pump or parallel mechanical cold source, open the closed communication between the heat releasing side of the condenser and the heat absorption side of the humidifying and dehumidifying device to form a gravity reflux between them.

[0225] Let the first temperature difference be the condenser hot side inlet temperature minus the humidifying and dehumidifying device heat absorption side outlet temperature, and the second temperature difference be the condenser hot side outlet temperature minus the humidifying and dehumidifying device heat absorption side inlet temperature. Calculate the logarithmic mean temperature difference ΔT lm = (ΔT1-ΔT2) / ln(ΔT1 / ΔT2) according to the definition, and control ΔT lm to be continuously maintained within 10-25℃ for 3 min.

[0226] After the completion of the heat recovery closed loop, the non-condensable gas is introduced slowly from the condenser gas side closed space to the gas source distributor inlet by fixing the 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, which is adjusted to a set value in the range of 0.005-0.03 m / s and maintained at the set value ±20% for 3 min; if the apparent gas velocity is insufficient, the cleanliness of the flow limiting element and whether the trace leakage of the gas collection bag is abnormally opened are checked; if the apparent gas velocity is over-limit, the pre-limiting flow is moderately increased or the leakage hole diameter is reduced until it returns to the set window.

[0227] Subsequently, the equivalent hydrostatic liquid seal height of step S6 is adjusted to the range of 0.10-0.50 m and a non-overlapping high-low threshold relationship is formed, ensuring that only one branch leading to the salt pool or one branch leading to the recharge is in an open state at any time, and the other branch remains liquid sealed.

[0228] When entering the stability judgment phase, the pressure sequence at the jet suction outlet and the pressure sequence at the gas source distributor inlet are respectively subjected to zero-phase digital band-pass filtering (0.1-2 Hz) with a sampling frequency of 1 Hz and a time window of 60 s, 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 jet suction outlet.

[0229] When the amplitude ratio is not greater than 0.30, it is determined that the start-up or disturbance recovery is completed and enters the stable operation phase. If the amplitude ratio is over-limit, the following sequence is used for correction: first, check whether there is a bypass leakage in the condenser gas side closed space and the connecting pipeline, recheck whether the fixed flow limiting element deviates from the manufacturing setting, moderately increase the flow limiting resistance, or increase the equivalent hydrostatic liquid seal height of the high threshold branch of the passive shunt network to enhance the delay and damping; the timestamp during the correction period is not included in the above determination window.

[0230] In summary, the present application does not configure an electromechanical vacuum pump, a steam jet and an independent blower, and records the shell absolute pressure and the jet outlet static pressure at a sampling frequency of one per second during continuous operation. Within any 72 consecutive hours, the time ratio of the shell absolute pressure in the window of 30 kPa to 60 kPa is not less than 95%; when the instantaneous over-limit of the static pressure difference between the jet port and the shell occurs, the correction is performed in the order of first reducing the driving opening and then moderately increasing the suction side flow limiting, which can quickly recover to within the limit, thereby reflecting the stability and maintainability under the cooperation of passive elements;

[0231] The total dissolved solids (TDS) of the concentrated brine produced by the method of the present application is greater than 80000 ppm, reaching the industrial brine standard; the TDS of fresh water is less than 500 ppm, meeting the drinking water standard.

[0232] By using potential energy driven Venturi jet suction to establish and maintain low pressure on the membrane side, the effect of long-term stable, low installed power operation under the condition of inorganic electric vacuum pump or steam ejector is achieved, and the problems of high energy consumption, complex maintenance and poor off-grid adaptability caused by relying on active vacuum are solved.

[0233] In the description of the present specification, the description referring to the terms "one embodiment", "an example", "a specific example" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0234] The basic principles, main features and advantages of the present application are shown and described above. It should be understood by those skilled in the art that the present application is not limited by the above embodiments, and the above embodiments and descriptions in the specification are only illustrative of the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application.

Claims

1. A production method for separating high-concentration brine and pure water from seawater using potential energy, characterized by, The method comprises the following steps: S1: sending seawater into a selective crystallization column provided with nucleating agents and inclined plate separation components for pretreatment to remove calcium sulfate and magnesium hydroxide fouling precursors, to obtain pretreated seawater; S2: under the action of a height difference provided by a high-level water storage facility above the ground or sea level, a shore slope building height, or a tidal range, the pretreated seawater flows through a Venturi ejector to form a liquid jet, and gas in communication with a membrane phase separation shell is sucked to reduce the shell-side absolute pressure of the membrane phase separation shell; S3: the membrane phase separation shell is communicated with a vertically arranged membrane phase separation column, the feed is stripped at the top of the column and condensed in a condenser to obtain a first water stream, and the condensation heat is transferred to a humidification and dehumidification device; S4: in the humidification and dehumidification device, wet air is heat-exchanged with high-salinity liquid from a concentrated salt branch and multi-effect recovery is performed to obtain a second water stream, and the recovered heat is returned to the membrane phase separation column or returned to the seawater feed; wherein the gas-water volume ratio of the humidification and dehumidification device is 1 to 3, and the gas-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: establishing a gas-lift circulation driven by a Venturi aspirator in the pre-membrane branch, and connecting a microporous diffusion plate in parallel to generate microbubbles and scrub the membrane surface to reduce concentration polarization; wherein the volume fraction of microbubbles in the flow field of the near-wall region of the membrane phase separation column on the feed side is 1% to 5%, and the volume average particle size of the microbubbles is 50 microns to 150 microns; S6: a density-triggered passive shunt network is arranged on the water production branch and the concentrated salt branch, and different salinity fluids are classified and recovered or recharged according to an online conductivity threshold; In step S2, the negative pressure of the membrane phase separation shell is established and maintained by suction through a Venturi ejector, and during operation, no electromechanical vacuum pump, steam ejector, vacuum tank pre-evacuation equipment is used, and no negative pressure is generated depending on a deep well static water column, which specifically meets the following conditions: The pretreated seawater obtained in step S1 flows through a contraction section, a throat, and an expansion section to form a driving jet under the action of the height difference, and continuously evacuates the gas in the shell through the suction port communicated with the membrane phase separation shell 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 separation shell to the volume flow rate of the driving branch, is 1.7 seconds to 6.7 seconds; The suction ratio, i.e., the ratio of the volume flow rate of the suction branch to the volume flow rate of the driving branch, is 0.12 to 0.45, and the absolute value of the pressure difference between the static pressure at the suction outlet and the shell-side static pressure is not greater than 5 kPa; During continuous 72-hour operation, the proportion of time that the shell-side absolute pressure is within the range of 30 kPa to 60 kPa is not less than 95%; In step S3 and step S4, the condenser heat release side of step S3 is directly communicated with the heat absorption side of the humidification and dehumidification device of step S4 through a pipeline to form a pump-free closed heat recovery circuit by gravity return, and no circulating pump or parallel mechanical cold source is arranged; The heat recovery circuit meets the following conditions: The gravity return drop is not less than 1 meter; The logarithmic mean temperature difference between the condenser and the humidification and dehumidification device is 10 degrees Celsius to 25 degrees Celsius; The comprehensive heat recovery rate of the humidification and dehumidification device is not less than 0.60, and the comprehensive heat recovery rate is the ratio of the heat returned to step S3 or returned to the seawater feed to the recoverable heat entering the humidification and dehumidification device; During the continuous 72-hour operation, the absolute value of the difference between the average heat exchange amount per unit time of the condenser and the average heat absorption amount per unit time of the humidification and dehumidification device accounts for not more than 10% of the average heat exchange amount per unit time of the condenser, and the fluctuation amplitude of the dew point temperature of the outlet air of the humidification and dehumidification device is not more than ±2 degrees Celsius.

2. The method for producing high-concentration brine and pure water from seawater using potential energy according to claim 1, characterized in that, The operation conditions of the selective crystallization fractional 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 minutes to 30 minutes, the angle between the inclined plate and the horizontal is 45° to 70°, the seed crystal with a median particle size of 50 microns to 200 microns is added, the seed crystal concentration is 0.5 grams per liter to 5 grams per liter, and the sludge is discharged when the online turbidity in the settling zone reaches 50 to 200 NTU or the bottom conductivity reaches 55 millisiemens per centimeter to 65 millisiemens per centimeter.

3. The method of claim 2, wherein the method is characterized by, 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 only gas source for step S5, and no independent air blower or compressor is provided; And by setting a gas source distributor and a throttle hole, the gas source distribution ratio is 0.05 to 0.30, and the gas source distribution ratio is defined as the ratio of the non-condensable gas volume flow rate supplied to step S5 to the step S2 gas extraction volume flow rate; At the same time, the superficial gas velocity on the feed side of the membrane phase transition separation column is 0.005 meters per second to 0.03 meters per second, and the superficial gas velocity is defined as the value of the gas volume flow rate on the channel cross section divided by the channel cross-sectional area, and the non-condensable gas after demisting has a droplet content of not more than 50 milligrams per cubic meter.

4. The method for producing high-concentration brine and pure water from seawater using potential energy according to claim 3, characterized in that, In step S6, the density-triggered passive shunt network is connected to the jet suction outlet of step S2 through a liquid-sealed standpipe, so that the shunt network operates as a pump-free back pressure stabilizing unit, and the following causal conditions are implemented: Only one of the branches leading to the salt pool or the branch leading to the recharge is allowed to be in an open state at any time, and the other branch is kept liquid-sealed to form an equivalent static water liquid seal; The equivalent static water liquid seal height is 0.10 meters to 0.50 meters calculated at a seawater density of 25°C, and the height is spontaneously formed by the fluid density and the liquid level difference, and no electric valve, pneumatic valve or other active actuator is provided; When the online conductivity crosses the set threshold of 0.5 millisiemens per centimeter to 2.0 millisiemens per centimeter, the shunt network passively switches between the two branches; With 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 not more than 1 kPa.

5. The method for producing high-concentration brine and pure water from seawater using potential energy according to claim 4, characterized in that, Only the gas side closed space of the condenser in step S3 is used as the only equivalent buffer volume of the non-condensable gas provided to step S5 between step S3 and step S5, and no independent gas tank, accumulator or adjustable pressure regulating valve is provided; And the following passive dynamic conditions are implemented: The ratio of the equivalent buffer volume of the gas to the volume flow rate of the non-condensable gas supplied in step S5 is defined as the gas source buffer time, and the gas source buffer time is 2-20 seconds; The absolute value of the rate of change of pressure at the gas source distributor inlet is not greater than 1 kPa / s, calculated at a sampling frequency of once per second and using a 60-second time window; 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 jet suction outlet, after 0.1-2 Hz band-pass filtering of the pressure sequences at the jet suction outlet and the gas source distributor inlet respectively, and the amplitude ratio is not greater than 0.30; The coefficient of variation of the volume flow rate of the non-condensable gas supplied in step S5 is not higher than 10%, calculated at a sampling frequency of once per second and using a 60-second time window.

6. The method of claim 5, wherein the method is characterized by, When the method is started or a disturbance occurs in the running, the following steps are sequentially performed without using external compressed gas, electromechanical vacuum pumps or circulating pumps: The gas source distributor in step S5 is closed and the drive valve in step S2 is opened, so that the pretreated seawater forms a driving jet through the Venturi ejector and exhausts the gas in the membrane phase separation shell, until the shell-side absolute pressure of the membrane phase separation shell reaches a target value in the range of 30-60 kPa and remains stable within ±2 kPa for 5 minutes; Subsequently, the pumpless closed heat recovery circuit between step S3 and step S4 is opened, so that the condenser heat release side and the heat absorption side of the humidification and dehumidification device form a gravity reflux, until the logarithmic mean temperature difference between them enters the interval of 10-25°C and remains for 3 minutes; Then, the non-condensable gas is slowly introduced from the condenser gas side closed space to step S5 through a fixed flow limiting element, until the superficial gas velocity of the membrane phase separation column feed side in step S5 reaches a set value in the range of 0.005-0.03 m / s and remains within ±20% of the set value for 3 minutes; Next, the equivalent hydrostatic liquid seal height in step S6 is adjusted to the range of 0.10-0.50 m, so that the density-triggered passive shunt network enters a passive switching state; 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 jet suction outlet, after 0.1-2 Hz band-pass filtering of the pressure sequences at the jet suction outlet and the gas source distributor inlet respectively, and the amplitude ratio is not greater than 0.30.

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