A high pressure air driven negative pressure separation forward osmosis membrane separation apparatus and method

Abstract

This invention relates to the field of water separation technology, and provides a high-pressure gas-driven negative pressure separation forward osmosis membrane separation device and method. The forward osmosis membrane separation device includes a forward osmosis membrane system, a concentrate storage tank, a high-pressure tank, a negative pressure tank, a water source heat pump unit, an air pump, and a water pump. The forward osmosis membrane system includes a wastewater inlet, a concentrate outlet, a dilute draw solution outlet, a draw solution inlet, and a wastewater circulation pump. The concentrate outlet of the forward osmosis membrane system connects to the concentrate storage tank, the dilute draw solution outlet connects to the negative pressure tank, and the draw solution inlet is connected to the high-pressure tank. The water source heat pump unit is connected to both the high-pressure tank and the negative pressure tank. The negative pressure tank has a gas outlet and a liquid outlet. The gas outlet of the negative pressure tank is connected to the air pump, which connects to the high-pressure tank. The liquid outlet of the negative pressure tank is connected to the water pump. This invention enables the solution of draw solution regeneration and water molecule separation under extremely low energy consumption conditions.

Description

Technical Field

[0001] This invention belongs to the field of regeneration of draw solution and separation of pure water from draw solution in forward osmosis membrane separation technology, and in particular relates to a device and method for high-pressure regeneration of draw solution and negative-pressure separation of pure water from forward osmosis membrane. Background Technology

[0002] Leachate membrane filtration concentrate treatment mainly includes technologies such as evaporation, advanced oxidation, and recirculating incinerators. Recirculating incinerators require the landfill to be adjacent to the incineration plant and are therefore less commonly used. Most treatments employ evaporation or advanced oxidation technologies, but these methods are costly. Reducing the volume of concentrate before treatment can lower costs. Forward osmosis (FO) uses the osmotic pressure difference between low-salt wastewater and high-salt draw solution (DS) across a semi-permeable membrane as the driving force, causing H2O in the high-potential wastewater to spontaneously diffuse into the low-potential DS. This process requires no external pressure or energy. Then, combined with reverse osmosis or other technologies, salts are separated from pure water, achieving the extraction of pure water from wastewater. FO relies on the osmotic pressure difference across the membrane for mass transfer, eliminating the need for external pressure. Therefore, its energy consumption and membrane fouling are lower than pressure-driven membrane processes. Membrane fouling is reversible, and the density of the fouled layer is lower than in pressure-driven processes.

[0003] The "Water Treatment Device and Method Coupled with Bioelectrochemistry and Forward Osmosis Membrane Bioreactor" (patent number CN109704452B) applies an electric potential to the membrane to enrich salt ions on the surface of the forward osmosis membrane, thereby increasing the salt concentration on the membrane surface and thus increasing the osmotic pressure difference across the membrane. However, this solution cannot precisely control the electrochemical process, which may lead to the generation of strong oxidizing chemicals such as hydroxyl radicals or hypochlorous acid, damaging the forward osmosis membrane and harming the survival of microorganisms. In addition, the presence of the electric potential makes it easier for calcium and magnesium ions to accumulate and precipitate on the membrane surface, leading to membrane blockage. The "Landfill Leachate Concentrate Reduction System" (patent number CN214270480U) utilizes a high-concentration sodium chloride solution as the absorbent. Sodium chloride and the feed solution to be treated are passed through opposite sides of a forward osmosis membrane. The chemical potential difference between the two solutions draws water molecules from the feed solution into the high-concentration sodium chloride solution. The sodium chloride solution from the forward osmosis membrane unit is then treated by a nanofiltration system. Since nanofiltration has a low salt rejection rate, the osmotic pressure difference between the nanofiltration concentrate side and the permeate side is small. This allows for the treatment of the dilute absorbent at a lower feed water pressure. The permeate from the nanofiltration system enters a high-salt reverse osmosis system. Since the salt concentration of the permeate from nanofiltration has already been reduced, high-salt reverse osmosis can recover the sodium chloride regeneration absorbent and further improve the quality of the permeate with lower energy consumption. This patent first utilizes a multi-stage forward osmosis unit to concentrate the feed solution step by step. Water molecules in the feed solution enter a high-concentration sodium chloride draw solution, which then requires nanofiltration and reverse osmosis to concentrate the draw solution and separate the water molecules. Although the method described in this patent can reduce some energy consumption, nanofiltration and reverse osmosis still need to overcome the osmotic pressure of the high-concentration sodium chloride solution to separate water molecules, thus the energy consumption remains high, and the process chain is long and complex. The patent titled "A Method for Separation Using Forward Osmosis Coupled with Photothermal Evaporation Technology" (patent number CN112919564A) introduces a photothermal film at the interface between the draw solution and air during the forward osmosis separation process. A light source is used to irradiate the film, converting light energy into heat energy on the surface of the photothermal film, which concentrates the draw solution through photothermal evaporation. This maintains a stable osmotic pressure difference between the feed solution and the draw solution during the forward osmosis process, continuously achieving efficient separation of the feed solution. This method converts light into heat to evaporate and concentrate the water in the dilute draw solution, but the water evaporation is extremely slow, making it difficult to apply in practical engineering.The patent CN113651420A, entitled "An Anaerobic Self-Driven Membrane Reactor Applicable to the Treatment and Regeneration of High COD Wastewater," discloses an anaerobic self-driven membrane reactor applicable to the treatment and regeneration of high COD wastewater. This invention incorporates a forward osmosis membrane within the anaerobic tank. After anaerobic treatment, the wastewater quality is improved, and methane is generated. Water molecules in the anaerobic system enter the draw solution through the forward osmosis membrane. The methane generated by the anaerobic process is then used as an energy source to pass the draw solution into a membrane distillation unit for methane heating and distillation, thereby separating the water molecules from the system. This design makes full use of the methane gas generated by the anaerobic process, resulting in lower overall energy consumption. However, since the forward osmosis membrane is built into the anaerobic tank, it is not conducive to membrane maintenance and cleaning. The patent, CN114853284A, describes a near-zero wastewater discharge device and process based on anaerobic MBR and forward osmosis. The anaerobic unit degrades most of the COD, and then the water molecules in the anaerobic unit are extracted through forward osmosis. The concentrated water discharged from the forward osmosis unit is evaporated using methane, a byproduct of the anaerobic unit. However, this method does not mention how to treat the water molecules extracted from the anaerobic unit by forward osmosis to meet the standards. In reality, the permeate (i.e., the dilute extract) after forward osmosis treatment still contains a large amount of salt, making it difficult for the permeate to meet the standards. The patent titled "A Forward Osmosis Zero-Discharge System Using Ammonium Bicarbonate as Draw Liquid and Its Operating Process" (patent number CN114605012A) uses an ammonia stripping process to produce ammonia water, which is then reacted with carbon dioxide to produce ammonium bicarbonate. Ammonium bicarbonate is used as the draw liquid to extract water molecules from the wastewater. The diluted draw liquid is then concentrated and water molecules are separated using reverse osmosis or electrodialysis. This method effectively utilizes the ammonia gas generated in the wastewater, achieving the goal of "treating waste with waste." However, the salt concentration of the diluted draw liquid is still relatively high for reverse osmosis, inevitably leading to high energy consumption when using reverse osmosis to concentrate the draw liquid. The patent titled "A Membrane Treatment System for Landfill Leachate Treatment" (patent number CN217051834U) uses a forward osmosis membrane to highly concentrate wastewater. The concentrated wastewater enters an evaporation treatment system, while the diluted draw liquid of the forward osmosis system is separated into water molecules and regenerated through membrane distillation. Both "An FO Device for Treating Leachate from Transfer Stations" (Patent No. CN216303525U) and "A Milk Concentrator Using Forward and Reverse Osmosis and Its Treatment Method" (Patent No. CN113457452A) utilize a forward and reverse osmosis coupling method. First, water molecules from wastewater are drawn into the draw solution through forward osmosis. Then, water molecules in the diluted draw solution are separated through reverse osmosis, thereby achieving the purpose of draw solution regeneration and discharge of compliant water.

[0004] A summary of existing technologies reveals that the core processes of forward osmosis membrane filtration are essentially the same within the forward osmosis filtration unit. This involves using a concentrated draw solution as an intermediate, drawing water molecules from the feed solution into the concentrated draw solution, thus transforming the concentrated draw solution into a dilute draw solution. The differences between various patented technologies lie in the different methods employed for draw solution regeneration, which can be broadly categorized into heating evaporation for concentrated draw solution, membrane distillation for concentrated draw solution, and reverse osmosis for concentrated draw solution. Evaporation methods for concentrating the absorbent include: using solar energy to convert it into thermal energy for concentration; however, this method is generally difficult to apply in engineering due to its low photothermal conversion efficiency and susceptibility to weather conditions; using methane gas from landfills or anaerobic digestion as a heat source to evaporate the dilute absorbent for regeneration; however, the amount of methane gas cannot guarantee that the absorbent will be evaporated to the required concentration, and the energy consumption of MVR evaporation method for concentrating the absorbent is relatively high; high-pressure reverse osmosis method for concentrating dilute absorbent requires overcoming the high osmotic pressure of the dilute absorbent itself, so this method requires multi-stage reverse osmosis for gradual concentration, and the required pressure is high, resulting in high energy consumption; and electrodialysis method for concentrating the absorbent has low desalination efficiency, leading to serious salt loss and requiring frequent replenishment of industrial salt or other absorbent solutes. Summary of the Invention

[0005] The purpose of this invention is to provide a high-pressure gas-driven negative pressure separation forward osmosis membrane separation device and method to solve the problems of draw solution regeneration and water molecule separation under extremely low energy consumption conditions. The high-pressure gas-driven negative pressure separation forward osmosis membrane separation device provided by this invention includes a forward osmosis membrane system, a concentrate storage tank, a high-pressure tank, a negative pressure tank, a water source heat pump unit, a gas pump, and a water pump. The forward osmosis membrane system includes a wastewater inlet, a concentrate outlet, a dilute draw solution outlet, a draw solution inlet, and a wastewater circulation pump. The concentrate outlet of the forward osmosis membrane system connects to the concentrate storage tank, the dilute draw solution outlet of the forward osmosis membrane system connects to the negative pressure tank, and the draw solution inlet of the forward osmosis membrane system is connected to the high-pressure tank. The water source heat pump unit is connected to both the high-pressure tank and the negative pressure tank. The negative pressure tank is provided with a gas outlet and a liquid outlet. The gas outlet of the negative pressure tank is connected to the gas pump leading to the high-pressure tank. The liquid outlet of the negative pressure tank is connected to the water pump.

[0006] Furthermore, the high-pressure gas-driven negative pressure separation forward osmosis membrane separation device created by this invention also includes a reverse osmosis system and a standard water tank. The liquid outlet of the negative pressure tank is connected to a water pump and then to the reverse osmosis system and the standard water tank, respectively. The reverse osmosis system includes a product water outlet and a retentate outlet. The product water outlet of the reverse osmosis system leads to the standard water tank, and the outlet of the standard water tank is connected to the water pump. The retentate outlet of the reverse osmosis system is controlled by a valve to lead to the negative pressure tank or the high-pressure tank.

[0007] Furthermore, the high-pressure gas-driven negative pressure separation forward osmosis membrane separation device created by the present invention also includes a cooling water tank, which is connected to the negative pressure tank and the reverse osmosis system respectively. A water pump is installed between the cooling water tank and the reverse osmosis system, and the water source heat pump unit is connected to the high-pressure tank, the negative pressure tank and the reverse osmosis system respectively.

[0008] Specifically, the negative pressure tank is equipped with a packing layer and a sprayer inside, and a circulation pump is installed outside the negative pressure tank. The packing layer is used to increase the surface area inside the tower, and the circulation pump is used to continuously pump the dilute extractant from the bottom of the negative pressure tank to the top of the tower and spray it down through the sprayer. Under negative pressure conditions, the gas-liquid contact area of ​​the dilute extractant is increased, accelerating the gas evaporation rate.

[0009] Specifically, the gas pumps connected to the gas outlet of the negative pressure tank are, in sequence, a vacuum pump and a high-pressure pump.

[0010] The high-pressure gas-driven negative pressure separation method for forward osmosis membrane separation provided by the present invention is characterized by comprising the following steps:

[0011] (1) The soluble pressure-sensitive gas is dissolved in water to prepare the draw solution. The gas that is easily soluble in water is dissolved in water to form a salt solution, which is then placed in a high-pressure tank. The high pressure drives the draw solution into the forward osmosis membrane system to draw water molecules from the feed solution to be treated.

[0012] (2) When the feed solution to be treated passes through the forward osmosis membrane system, water molecules diffuse into the draw solution with a lower water chemical potential;

[0013] (3) After water molecules enter the draw liquid, the draw liquid is diluted into a dilute draw liquid. The dilute draw liquid enters the negative pressure tank. In the negative pressure tank, the heat energy of the draw liquid in the high pressure tank is transferred to the draw liquid in the negative pressure tank through the water source heat pump, which raises the temperature of the draw liquid in the negative pressure tank and lowers the temperature of the draw liquid in the high pressure tank. At the same time, the air pump draws gas from the negative pressure tank and fills the high pressure tank with gas, which results in a decrease in pressure and an increase in temperature in the negative pressure tank. A large amount of dissolved gas in the dilute draw liquid is released and is pumped into the high pressure tank by the air pump to dissolve again. Thus, the separation of solute and product water in the negative pressure tank and the regeneration of draw liquid in the high pressure tank are achieved at the same time.

[0014] (4) Drain the water from the negative pressure tank.

[0015] For situations where the water to be treated is more severely polluted, we provide a high-pressure gas-driven negative pressure separation forward osmosis membrane separation method, characterized by the following steps:

[0016] (1) Dissolve the water-soluble gas in water to form an extractant, which is then placed in a high-pressure tank. The high pressure drives the extractant into the forward osmosis membrane system to extract water molecules from the feed solution to be treated.

[0017] (2) When the feed solution to be treated passes through the forward osmosis membrane system, water molecules diffuse into the draw solution with a lower water chemical potential;

[0018] (3) After water molecules enter the draw liquid, the draw liquid is diluted into a dilute draw liquid. The dilute draw liquid enters the negative pressure tank. In the negative pressure tank, the heat energy of the draw liquid in the high pressure tank is transferred to the draw liquid in the negative pressure tank through the water source heat pump, which raises the temperature of the draw liquid in the negative pressure tank and lowers the temperature of the draw liquid in the high pressure tank. At the same time, the air pump draws gas from the negative pressure tank and fills the high pressure tank with gas, which results in a decrease in pressure and an increase in temperature in the negative pressure tank. A large amount of dissolved gas in the dilute draw liquid is released and is pumped into the high pressure tank by the air pump to dissolve again. Thus, the separation of solute and product water in the negative pressure tank and the regeneration of draw liquid in the high pressure tank are achieved at the same time.

[0019] (4) Test the water in the negative pressure tank. If it meets the standard, it will be discharged directly. If it does not meet the standard, the water outlet of the negative pressure tank will be connected to the cooling water pool for cooling. The cooling method is to use a water source heat pump group to transfer the heat of the water in the cooling water pool to the negative pressure tank. After passing through the cooling water pool, the liquid is treated by the reverse osmosis system and the produced water meets the standard before being discharged. Part of the concentrated water in the reverse osmosis system is returned to the negative pressure tank and part is returned to the high pressure tank.

[0020] The purpose of returning the concentrate to the high-pressure tank in the reverse osmosis system is to replenish the water flowing out of the draw solution, and the purpose of returning it to the negative pressure tank is to further process it in the negative pressure tank so that the gas is released again.

[0021] Preferably, in the above method, the dilute extractant at the bottom of the negative pressure tank is continuously drawn to the top of the negative pressure tank by a circulation pump and sprayed down by a sprayer.

[0022] The forward osmosis membrane system of this invention includes a feed water pump, a circulation pump, a forward osmosis membrane, a draw solution, a pressure gauge, and an online conductivity meter. This system primarily extracts water molecules from the feed solution into the draw solution. The high-pressure tank is mainly used for draw solution regeneration or concentration and to provide water driving force to the draw solution side of the forward osmosis membrane module. The draw solution described in this invention is mainly prepared by dissolving a soluble pressure-sensitive gas in water. The gas, which is easily soluble in water, dissolves in water to form a salt solution. Increasing the pressure inside the high-pressure tank increases the solubility of the gas, thereby increasing the salt solution concentration. Simultaneously, the increased pressure inside the tank provides driving force for the salt solution (also known as the concentrated draw solution), driving the draw solution into the forward osmosis membrane to extract water molecules from the feed solution. After the water molecules enter the draw solution, it is diluted. The diluted draw solution then enters a negative pressure tank. Because the solubility of the gas increases with increasing pressure and decreases with decreasing pressure, and also decreases with increasing temperature, the draw solution... Inside the pressure tank, a water source heat pump transfers the heat energy of the absorbent liquid in the high-pressure tank to the absorbent liquid in the negative-pressure tank, causing the temperature of the absorbent liquid in the negative-pressure tank to rise and the temperature of the absorbent liquid in the high-pressure tank to drop. Simultaneously, an air pump draws gas from the negative-pressure tank and fills the high-pressure tank. This results in a decrease in pressure and an increase in temperature in the negative-pressure tank, causing a large amount of dissolved gas in the dilute absorbent liquid to precipitate out and be pumped into the high-pressure tank. If the water in the negative-pressure tank meets the standards at this point, it can be discharged; otherwise, the water from the negative-pressure tank can be reconnected to the intermediate pressure tank. The intermediate water tank is cooled down (depending on the actual water temperature; if the water temperature does not exceed 40 degrees Celsius, cooling is not necessary). Cooling is also achieved using a water source heat pump, transferring the heat from the water in the intermediate tank to the negative pressure tank. The downstream end of the intermediate water tank is connected to a low-pressure reverse osmosis system for appropriate treatment, after which the permeate is discharged in compliance with standards. Part of the concentrate is returned to the negative pressure tank, and part is returned to the high-pressure tank. The purpose of returning to the high-pressure tank is to replenish the water flowing out of the draw solution, and the purpose of returning to the negative pressure tank is for further treatment, allowing gases to be released again. It is important to note that the moment the dilute draw solution from the forward osmosis membrane enters the negative pressure tank, the external environment of the draw solution suddenly changes from positive pressure to negative pressure, causing flash evaporation. That is, due to the sudden pressure drop, the draw solution suddenly becomes a portion of saturated vapor and saturated liquid under container pressure, which is more conducive to the release of dissolved gases. In this way, the re-concentration of the feed solution is achieved through the above process.

[0023] In the above process, the combined use of the high-pressure tank and negative-pressure tank described in this invention solves the problems of extractant regeneration and water molecule separation under extremely low energy consumption conditions. The water source heat pump simultaneously addresses the temperature control requirements of each process unit. Furthermore, since the working principle of the water source heat pump is not to directly generate heat using electrical energy, but rather to transfer heat from the water in the high-pressure tank (or intermediate water tank) that needs cooling to the negative-pressure tank that needs heating, it achieves the purpose of "one machine for two uses," saving energy. Because the water in the intermediate water tank has already had dissolved gases extracted, this portion of water may actually meet the standards. However, to be on the safe side, if this portion of water does not meet the standards, the dissolved gas content in the water will also be extremely low. Therefore, it can be connected to a low-pressure reverse osmosis system for further deep treatment, safeguarding the water quality of the effluent from this invention. Since it is low-pressure reverse osmosis and may not be used, the overall energy consumption of the solution described in this invention is relatively low.

[0024] The terms used in this invention are explained as follows:

[0025] High-pressure gas drive: This refers to a process where gas is continuously injected into a sealed pressure tank from the top, increasing the internal pressure. Liquid flows through the lower part of the tank, which has a liquid outlet at the bottom. When the outlet valve is opened, the high internal gas pressure forces the liquid out of the sealed tank. In short, high-pressure gas drive utilizes high-pressure gas to drive liquid flow.

[0026] Negative pressure separation refers to the process of separating a gas from a solution by heating and suction within a closed container after the gas has dissolved in the liquid. This process causes the temperature inside the closed container to rise and the pressure to drop, resulting in a rapid decrease in the solubility of the gas in the solution. This includes the flash evaporation process that occurs when the solution suddenly enters a high-temperature negative pressure tank.

[0027] Forward osmosis: Forward osmosis is the process by which water flows from the region with higher hydrochemical potential (or lower osmotic pressure) to the region with lower hydrochemical potential (or higher osmotic pressure) through a selectively permeable membrane. Two solutions with different osmotic pressures are placed on either side of a selectively permeable membrane: a feed solution with lower osmotic pressure and a drive solution with higher osmotic pressure. Forward osmosis utilizes the osmotic pressure difference between the solutions on both sides of the membrane as the driving force, allowing water to spontaneously pass from the feed solution side through the selectively permeable membrane to the drive solution side. When an external pressure less than the osmotic pressure difference is applied to the solution on the side with higher osmotic pressure, water will still flow from the feed solution side to the drive solution side; this process is called pressure-damped osmosis. The driving force of pressure-damped osmosis is still osmotic pressure, therefore it is also a type of forward osmosis.

[0028] Draw solution: A salt solution prepared in the forward osmosis membrane. The salt concentration of this solution is generally many times higher than that of the wastewater on the wastewater side, resulting in a higher chemical potential difference between the two sides of the forward osmosis membrane. Water molecules in the wastewater spontaneously cross the forward osmosis membrane and enter the draw solution. The draw solution after the water in the wastewater enters the draw solution is called dilute draw solution. The process of concentrating the dilute draw solution through other units is called draw solution regeneration.

[0029] Reverse osmosis: Also known as reverse osmosis, reverse osmosis is a membrane separation process that uses a pressure difference as the driving force to separate the solvent from the solution. Pressure is applied to the feed solution on one side of the membrane. When the pressure exceeds its osmotic pressure, the solvent will permeate in the opposite direction of natural osmosis. Thus, the permeated solvent, i.e., the permeate, is obtained on the low-pressure side of the membrane, while the concentrated solution, i.e., the concentrate, is obtained on the high-pressure side.

[0030] The inventive point of this invention:

[0031] 1. A draw solution is prepared by dissolving a temperature-sensitive or pressure-sensitive solute in water. When the temperature rises and the pressure drops, the solute in the draw solution decomposes and desorbs, thereby separating the water and solute in the dilute draw solution. The separated solute is then pumped back into a high-pressure tank to cool and pressurize, where it recombines and dissolves in the water, thus regenerating the draw solution in the high-pressure tank.

[0032] 2. The combined use of high-pressure tank and negative-pressure tank replaces the traditional feed water pump on the draw liquid side. Therefore, the process of draw liquid entering and exiting the forward osmosis membrane can be completed under extremely low energy consumption conditions. It provides two conditions for temperature-sensitive and pressure-sensitive solute separation and regeneration, and simultaneously completes the work of draw liquid regeneration and pure water separation.

[0033] 3. The water source heat pump simultaneously addresses the temperature control requirements of each process unit. Since its working principle does not directly generate heat using electricity, but rather transfers heat from the water in the high-pressure tank (or intermediate water tank) that needs cooling to the negative-pressure tank that needs heating, it achieves a "dual-purpose" function, saving energy. Because the water in the intermediate water tank has already had dissolved gases extracted, this water may already meet the standards. However, to be on the safe side, if this water does not meet the standards, the solute concentration in the water will be extremely low. Therefore, it can be connected to a low-pressure reverse osmosis system for further deep treatment, safeguarding the quality of the wastewater from this invention. Due to the low-pressure reverse osmosis, the overall energy consumption of the solution described in this invention is relatively low.

[0034] The beneficial effects of this invention are:

[0035] 1. Because a water source heat pump is used in the solute separation and concentration process, the heat energy in the draw liquid regeneration tank is directly transferred to the draw liquid solute separation tank. In this process, no electrical energy is directly converted into heat energy; only electrical energy is used for heat transfer. Compared with other technologies that use heating and evaporation to recover solute, this solution is more energy-efficient.

[0036] 2. A vacuum pump, air compressor, or similar air pump is used to create a vacuum in the dilute draw solution storage tank. The extracted gas is then pumped into the draw solution regeneration tank, simultaneously achieving the following three objectives: First, a large amount of ammonia, carbon dioxide, water vapor, and other gases enter the draw solution regeneration tank, increasing the pressure within the tank and promoting the formation and solubility of ammonium carbonate and ammonium bicarbonate, thus regenerating the draw solution. Second, the vacuum pump continuously creates a negative pressure in the dilute draw solution storage tank, drawing the diluted draw solution from the forward osmosis membrane into the tank. The sudden change in the environment of the draw solution upon its entry into the tank, resulting in a negative pressure, further contributes to the regeneration process. In a relatively hot environment, the dilute draw solution undergoes partial flash evaporation, achieving the separation of ammonia and carbon dioxide from the dilute draw solution. Furthermore, due to the negative pressure and high temperature environment of the tank, the solubility of various gases is extremely low, and ammonia and carbon dioxide automatically escape from the dilute draw solution, thereby achieving the separation of solute and purified water. Thirdly, under the combined effect of the negative pressure environment of the dilute draw solution storage tank and the positive pressure environment of the draw solution storage tank, the draw solution is forced into the membrane by positive pressure at the inlet of the forward osmosis membrane, and the draw solution is extracted by negative pressure at the outlet, thereby achieving extremely low pressure on the draw solution side of the forward osmosis membrane and minimizing the degree of reverse osmosis.

[0037] 3. The feed pump for the draw solution in forward osmosis is removed. Instead, a large amount of ammonia and carbon dioxide gas is introduced into the draw solution storage tank and dissolved in water to produce (regenerate) concentrated draw solution. At the same time, due to the large amount of gas introduced, the pressure in the sealed storage tank is high. The gas pressure is used to drive the draw solution into the forward osmosis membrane, thus saving energy again. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a schematic diagram of the structure and process of a high-pressure gas-driven negative pressure separation positive osmosis membrane separation device in a specific embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of the structure and process of a high-pressure gas-driven negative pressure separation forward osmosis membrane separation device (including a reverse osmosis system) in a specific embodiment of the present invention.

[0041] Figure 3 This is a schematic diagram of the structure and process of a high-pressure gas-driven negative pressure separation positive osmosis membrane separation device in a specific embodiment of the present invention (negative pressure tank includes a sprayer).

[0042] Figure 4 This is a schematic diagram of the structure and process of a high-pressure gas-driven negative pressure separation forward osmosis membrane separation device (including a reverse osmosis system and a negative pressure tank with a sprayer) in a specific embodiment of the present invention.

[0043] Figure 5 This is a graph showing the relationship between the temperature of the high-pressure tank's draw liquid and the temperature of the dilute draw liquid in the negative-pressure reaction tower. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] I. Specific Implementation Examples of High-Pressure Gas-Driven Negative-Pressure Separation Forward Osmosis Membrane Separation Equipment

[0046] In one embodiment of the present invention, such as Figure 1 As shown, the high-pressure gas-driven negative pressure separation forward osmosis membrane separation equipment includes a forward osmosis membrane system 1, a concentrate storage tank 7, a high-pressure tank 2, a negative pressure tank 3, a water source heat pump unit 4, air pumps (51, 52), and water pumps (61, 62, 63). The forward osmosis membrane system includes a wastewater inlet, a concentrate outlet, a dilute draw solution outlet, a draw solution inlet, and a wastewater circulation pump 62. The wastewater inlet is connected to the water pump 63. The concentrate outlet of the forward osmosis membrane system 1 leads to the concentrate storage tank 7, the dilute draw solution outlet of the forward osmosis membrane system 1 leads to the negative pressure tank 3, and the draw solution inlet of the forward osmosis membrane system 1 is connected to the high-pressure tank 2. The water source heat pump unit 4 is connected to the high-pressure tank 2 and the negative pressure tank 3 respectively. The negative pressure tank 3 is provided with a gas outlet and a liquid outlet. The gas outlet of the negative pressure tank 3 is connected to the air pumps (51, 52) leading to the high-pressure tank 2. The liquid outlet of the negative pressure tank 3 is connected to the water pump 61. The gas outlet of the negative pressure tank 3 is connected in sequence to a vacuum pump 51 and a high-pressure pump 52.

[0047] In another embodiment of the invention, such as Figure 2 and 4As shown, the high-pressure gas-driven negative pressure separation forward osmosis membrane separation equipment also includes a reverse osmosis system 8 and a standard water tank 9. The liquid outlet of the negative pressure tank 3 is connected to the water pumps (64, 65) and then to the reverse osmosis system 8 and the standard water tank 9, respectively. The reverse osmosis system 8 includes a product water outlet and a retentate outlet. The product water outlet of the reverse osmosis system 8 leads to the standard water tank 9. The outlet of the standard water tank 9 is connected to the water pump 61. The retentate outlet of the reverse osmosis system 8 is controlled by a valve to lead to the negative pressure tank 3 or the high-pressure tank 2.

[0048] In another embodiment of the invention, such as Figure 2 , 4 As shown, the high-pressure gas-driven negative pressure separation forward osmosis membrane separation equipment also includes a cooling water tank 10, which is connected to the negative pressure tank 3 and the reverse osmosis system 8 respectively. A water pump 65 is installed between the cooling water tank 10 and the reverse osmosis system 8. The water source heat pump unit 4 is connected to the high-pressure tank 2, the negative pressure tank 3 and the reverse osmosis system 8 respectively.

[0049] In another embodiment of the invention, such as Figure 3 , 4 As shown, the negative pressure tank 3 is equipped with a packing layer 31 and a sprayer 32 inside, and a circulation pump 33 is installed outside the negative pressure tank 3. The packing layer 31 is used to increase the surface area inside the negative pressure tank, and the circulation pump 33 is used to continuously pump the dilute extractable liquid from the bottom of the negative pressure tank to the top and spray it down through the sprayer 32. Under negative pressure conditions, the gas-liquid contact area of ​​the dilute extractable liquid is increased, and the gas evaporation rate is accelerated.

[0050] In practice, the forward osmosis membrane system can be designed as a multi-stage forward osmosis membrane module according to the actual wastewater quality and needs.

[0051] II. Specific Implementation Examples of the High-Pressure Gas-Driven Negative-Pressure Separation Method for Forward Osmosis Membrane Separation

[0052] The high-pressure gas-driven negative pressure separation forward osmosis membrane separation method provided in a specific embodiment of the present invention includes the following steps:

[0053] (1) The soluble pressure-sensitive gas is dissolved in water to prepare the draw solution. The gas that is easily soluble in water is dissolved in water to form a salt solution, which is then placed in a high-pressure tank. The high pressure drives the draw solution into the forward osmosis membrane system to draw water molecules from the feed solution to be treated.

[0054] (2) When the feed solution to be treated passes through the forward osmosis membrane system, water molecules diffuse into the draw solution with a lower water chemical potential;

[0055] (3) After water molecules enter the draw liquid, the draw liquid is diluted into a dilute draw liquid. The dilute draw liquid enters the negative pressure tank. In the negative pressure tank, the heat energy of the draw liquid in the high pressure tank is transferred to the draw liquid in the negative pressure tank through the water source heat pump, which raises the temperature of the draw liquid in the negative pressure tank and lowers the temperature of the draw liquid in the high pressure tank. At the same time, the air pump draws gas from the negative pressure tank and fills the high pressure tank with gas, which results in a decrease in pressure and an increase in temperature in the negative pressure tank. A large amount of dissolved gas in the dilute draw liquid is released and is pumped into the high pressure tank by the air pump to dissolve again. Thus, the separation of solute and product water in the negative pressure tank and the regeneration of draw liquid in the high pressure tank are achieved at the same time.

[0056] (4) Drain the water from the negative pressure tank.

[0057] For situations where the water to be treated is more severely polluted, the high-pressure gas-driven negative pressure separation forward osmosis membrane separation method provided in the specific embodiment includes the following steps:

[0058] (1) Dissolve the water-soluble gas in water to form an extractant, which is then placed in a high-pressure tank. The high pressure drives the extractant into the forward osmosis membrane system to extract water molecules from the feed solution to be treated.

[0059] (2) When the feed solution to be treated passes through the forward osmosis membrane system, water molecules diffuse into the draw solution with a lower water chemical potential;

[0060] (3) After water molecules enter the draw liquid, the draw liquid is diluted into a dilute draw liquid. The dilute draw liquid enters the negative pressure tank. In the negative pressure tank, the heat energy of the draw liquid in the high pressure tank is transferred to the draw liquid in the negative pressure tank through the water source heat pump, which raises the temperature of the draw liquid in the negative pressure tank and lowers the temperature of the draw liquid in the high pressure tank. At the same time, the air pump draws gas from the negative pressure tank and fills the high pressure tank with gas, which results in a decrease in pressure and an increase in temperature in the negative pressure tank. A large amount of dissolved gas in the dilute draw liquid is released and is pumped into the high pressure tank by the air pump to dissolve again. Thus, the separation of solute and product water in the negative pressure tank and the regeneration of draw liquid in the high pressure tank are achieved at the same time.

[0061] (4) Test the water in the negative pressure tank. If it meets the standard, it will be discharged directly. If it does not meet the standard, the water outlet of the negative pressure tank will be connected to the cooling water pool for cooling. The cooling method is to use a water source heat pump group to transfer the heat of the water in the cooling water pool to the negative pressure tank. After passing through the cooling water pool, the liquid is treated by the reverse osmosis system and the produced water meets the standard before being discharged. Part of the concentrated water in the reverse osmosis system is returned to the negative pressure tank and part is returned to the high pressure tank.

[0062] In an optimized embodiment, the dilute extractant at the bottom of the negative pressure tank in the above method is continuously drawn to the top of the negative pressure tank by a circulation pump and sprayed down by a sprayer.

[0063] In practice, wastewater enters the forward osmosis membrane system via a wastewater feed pump. A wastewater circulation pump then circulates the wastewater at high speed on one side of the forward osmosis membrane unit, maintaining a flow velocity of approximately 4 m / s on the membrane surface. This high cross-flow velocity reduces concentration polarization and prevents contaminants from depositing on the membrane surface. The concentrated draw solution is pumped into the forward osmosis membrane system from a high-pressure tank (0.5-1 bar pressure). The draw solution outlet is connected to a negative pressure tank (or negative pressure reaction tower, -0.5-1 bar). The diluted draw solution is then drawn into the negative pressure reaction tower via negative pressure suction. The draw solution entering the negative pressure reaction tower can be sprayed into the negative pressure tank through spray nozzles, facilitating solute separation. Furthermore, packing material can be installed in the middle of the negative pressure reaction tower, and a circulation pump can be installed at the bottom to pump the liquid from the bottom to the top for spraying, increasing the specific surface area of ​​the liquid and accelerating the desorption rate of the draw solution. Simultaneously, a water source heat pump is connected between the high-pressure tank and the negative pressure tank (or negative pressure reaction tower). The heat pump transfers heat from the water in the high-pressure tank to the negative pressure tank (or negative pressure reaction tower), causing the high-pressure tank to cool down (to 10~30℃) and the negative pressure tank to heat up (to 40~70℃, and up to 100℃ under suitable conditions) simultaneously. This facilitates the decomposition and separation of the solute in the negative pressure tank and its regeneration and dissolution in the high-pressure tank. If the liquid in the negative pressure tank has reached the predetermined standard, it can be directly discharged. If it still does not meet the standard, the effluent from the negative pressure tank (or negative pressure reaction tower) is connected to a cooling water pool. The heat from the cooling water pool is transferred to the negative pressure tank (or negative pressure reaction tower) via the water source heat pump for cooling. Afterward, low-pressure reverse osmosis treatment is used to ensure the water meets the discharge standards.

[0064] The selection and preparation of the three specific extraction solutions

[0065] The concentrated draw solution used in the example is the draw solution formed by ammonia gas dissolving in water. Under certain pressure conditions, the different solubilities of ammonia in water are used to achieve the purpose of preparing the draw solution, regenerating the draw solution, and separating the draw solution.

[0066] Data from existing technology shows that, under a pressure of 1.01 bar, the mass solubility of ammonia in water is 33.95% at 20°C, 23.3% at 40°C, 13.65% at 60°C, and 0% at 100°C. Converting this to volume concentration, then:

[0067] The concentration of ammonia at 100℃ is 0 mg / L;

[0068] The concentration of ammonia at 20℃ is 339.5 g / L, or 19.97 mol / L.

[0069] Assuming the system solution is an ideal solution, the osmotic pressure of the solution can be calculated using the van der Hoff formula, as shown below:

[0070] π=nCRT Equation (1)

[0071] In formula (1):

[0072] π represents the osmotic pressure of a dilute solution, measured in kPa.

[0073] n is the van der Hoff coefficient;

[0074] C represents the molar concentration of the solution, expressed in mol / L.

[0075] R is the gas constant, which is 8.31 kPa·L·K. -1 ·mol -1 ;

[0076] T represents absolute temperature.

[0077] Substituting the ammonia solution at 20℃ into the above formula to calculate the osmotic pressure of the solution, the osmotic pressure generated under various conditions is 97296.90 kPa (972.97 bar).

[0078] In the specific implementation method, ammonia solution is used as the draw solution. A water source heat pump raises the temperature of the negative pressure tank to 100℃, while the high-pressure tank temperature is lowered to 20℃. The draw solution then enters the forward osmosis membrane, generating a natural osmotic pressure of 927.97 bar. Water molecules in the wastewater pass through the forward osmosis membrane and enter the draw solution. The draw solution then enters the negative pressure reaction tower, where it is heated to 100℃. Ammonia is desorbed from the dilute draw solution and forced into the high-pressure tank by a high-pressure air pump for redissolving, thus regenerating the draw solution. The ammonia concentration in the water at the bottom of the negative pressure reaction tower is reduced to 0, allowing for direct discharge that meets standards.

[0079] In another specific implementation method, the concentrated draw liquid is the draw liquid formed by dissolving ammonium bicarbonate in water. Taking advantage of the characteristic that ammonium bicarbonate is easily decomposed by heating, the decomposition of ammonium bicarbonate is carried out in a high-temperature negative pressure reaction tower and the synthesis of ammonium bicarbonate is carried out in a low-temperature high-pressure tank, thereby realizing the regeneration of the draw liquid and the separation of pure water.

[0080] The drawing solution was prepared using ammonium bicarbonate (NH4HCO3). The properties of ammonium bicarbonate are as follows: it is stable at room temperature and pressure, but thermally unstable; the solid decomposes at 58℃ and the aqueous solution at 70℃. Its solubility in water is 14% (10℃), 17.4% (20℃), and 21.3% (30℃). Its aqueous solution is alkaline, with a concentration of 0.1 mol·L⁻¹ at 25℃. -1The solution has a pH of 7.8. Ammonium bicarbonate is chemically unstable and easily decomposes upon heating. When heated to approximately 60°C, it decomposes into a white fumes composed of 21.5% NH3, 55.7% CO2, and 22.8% H2O. It can be decomposed by hot water. Under normal pressure and in the presence of moisture, it begins to slowly decompose above 36°C, producing ammonia, carbon dioxide, and water.

[0081] Based on the above physicochemical properties of ammonium bicarbonate, a 2 mol / L ammonium bicarbonate solution is prepared as the draw solution at 30℃. According to formula (1), the osmotic pressure generated by the draw solution is 10081.56 kPa (100.82 bar), which is extremely strong. Wastewater is sent into the positive osmosis membrane by a low-pressure feed water pump. The draw solution enters the positive osmosis membrane system from the other side of the positive osmosis membrane under the dual action of the gas pressure in the high-pressure storage tank and the negative pressure extraction in the negative pressure storage tank. After the draw solution removes water molecules from the wastewater, it enters the negative pressure reaction tank. The water source heat pump extracts the heat from the high-pressure tank and transports it to the negative pressure reaction tank. This can cool down the high-pressure tank and raise the temperature of the negative pressure tank. The automatic control system of the water source heat pump keeps the temperature of the high-pressure tank at 30℃ and the negative pressure reaction tank at 60℃. At this point, the ammonium bicarbonate solution in the negative pressure reactor decomposes into ammonia, carbon dioxide, and water. The ammonia, carbon dioxide, and water vapor are drawn in by a vacuum pump and compressed into a high-pressure storage tank. In the high-pressure storage tank, after cooling and pressurization, they react and recombine to form ammonium bicarbonate, thus achieving the regeneration of the concentrated extract and the separation of solute and water in the dilute extract. Based on the concentration of the ammonium bicarbonate solution in the negative pressure reactor, it is determined whether a reverse osmosis system needs to be added at the downstream end. In this embodiment, since the ammonium bicarbonate decomposes sufficiently in the negative pressure reactor, it can be discharged directly without connecting to reverse osmosis. If the ammonium bicarbonate decomposes insufficiently in the negative pressure reactor, reverse osmosis can be connected for further filtration, and the concentrated liquid can be sent to the high-pressure storage tank for compliant water discharge. Even if the ammonium bicarbonate decomposes insufficiently, the concentration of residual ammonium bicarbonate in the water is low, resulting in low osmotic pressure. Therefore, ordinary low-pressure reverse osmosis can achieve solute-solvent separation at the downstream end, thus saving energy.

[0082] IV. Specific Implementation Results

[0083] Using 1.7 mol / L ammonium bicarbonate solution as the draw solution, the concentrated liquid produced after the landfill leachate has undergone "biochemical + ultrafiltration + nanofiltration + reverse osmosis" treatment is used as the feed liquid to be treated. The feed liquid to be treated is treated by high-pressure regeneration of the draw solution of the forward osmosis membrane and separation of pure water by negative pressure. The equipment used in the method is mainly composed of three parts: a forward osmosis membrane separation unit, a pure water and solute separation (desorption) unit in the dilute draw solution, and a draw solution concentration and regeneration unit.

[0084] Forward osmosis membrane separation unit: The main components of the forward osmosis membrane separation unit include a forward osmosis membrane module, a feed pump, and a feed circulation pump. The forward osmosis membrane only allows water in the feed solution to pass through; other components cannot pass through. In this embodiment, the forward osmosis membrane consists of a membrane element and a membrane housing. The membrane element is a TFC membrane (channel thickness 85 mil, effective area of ​​one membrane element is 3 m², two elements are used), the active layer of the membrane is made of polyamide material, and the membrane housing is a 4-inch fiberglass membrane housing with a pressure rating of 20 bar.

[0085] Desorption unit for separating pure water and solute in dilute extract: Desorption separation is a process that uses heating, vacuuming, or other methods to separate dissolved gas (or solute) from pure water. Since ammonium bicarbonate extract is easily decomposed by heat, this embodiment uses vacuuming and heating (not direct electric heating) to separate ammonium bicarbonate from pure water. Its main equipment includes a negative pressure reaction tower (filled with packing material, specifically wire mesh corrugated plate packing, which is thin and has a large specific surface area, ensuring a stable thin liquid layer on the mesh, thorough mixing of the gas and liquid phases, and no dead zones), a water source heat pump (shared with the high-pressure tank and cooling water pool to transfer heat from the high-pressure tank and cooling water pool to the negative pressure reaction tower), a circulating pump, a sprayer, a vacuum pump, a drain pump, and related monitoring instruments.

[0086] The draw solution concentration and regeneration unit: The gases (NH3, CO2) generated by decomposition, separation, and desorption in the negative pressure reaction tower have high solubility in water. In order to enable NH3 and CO2 to dissolve quickly in water and be converted back into ammonium bicarbonate draw solution, and to generate a certain gas pressure in the regeneration unit to drive the draw solution into the forward osmosis membrane, this unit is designed in this embodiment as a high-pressure storage tank, a high-pressure air pump, a water source heat pump (shared with the negative pressure reaction tower, the purpose of which is to transfer the heat in the high-pressure tank to the negative pressure reaction tower, maintain the temperature in the high-pressure tank below 20°C, and ensure that the draw solution does not damage the forward osmosis membrane when it enters the forward osmosis membrane), and related detection instruments, etc.

[0087] The water quality of the liquid to be treated is as follows:

[0088] Table 1 Main physicochemical properties of the liquid to be treated

[0089] Testing items <![CDATA[COD(mg·L -1 )]]> <![CDATA[TN(mg·L -1 )]]> <![CDATA[Ammonia nitrogen (mg·L -1 )]]> <![CDATA[TDS(mg·L -1 )]]> <![CDATA[Conductivity (ms·cm -1 )]]> concentration 4042 2376 1890 14000 21.20

[0090] Example implementation process description: The above-mentioned feed solution to be treated enters the feed solution side of the forward osmosis membrane at a flow rate of 2.4 m³ / h. A circulation pump is set on the feed solution side to ensure that the flow rate at each point on the feed solution side of the forward osmosis membrane is 2.4 m³ / h. The draw solution enters the draw solution side of the forward osmosis membrane at a flow rate of 0.3 m³ / h.

[0091] After the feed solution undergoes forward osmosis treatment, the flow rate (concentrate flow rate) exiting the membrane is 2.33 m³ / h, and the flow rate of the dilute draw solution before entering the negative pressure reaction tower is 0.37 m³ / h. This means that approximately 0.07 m³ of water molecules in the feed solution cross the forward osmosis membrane per hour to enter the draw solution side. Calculations show that the ammonium bicarbonate in the draw solution is diluted to 1.378 mol / L, and the molar concentration of the draw solution after exiting the forward osmosis membrane is 1.378 mol / L.

[0092] Forward osmosis is the process by which the draw solution draws water molecules from the feed solution through a forward osmosis membrane. This process requires a high concentration of draw solution (which generates high osmotic pressure). Therefore, it is necessary to separate the water molecules from the ammonium bicarbonate in the dilute draw solution and discharge 0.07 m³ of pure water per hour. After separation, the ammonium bicarbonate is transferred to a high-pressure storage tank to dissolve and regenerate into a 1.7 mol / L draw solution for reuse.

[0093] Since the forward osmosis process is a convection process between wastewater and draw solution on both sides of the forward osmosis membrane, there is a heat exchange between the draw solution and wastewater, similar to the function of a heat exchanger. If there is a temperature difference between the draw solution and the feed liquid to be treated, heat exchange can spontaneously occur between the wastewater and the draw solution. The initial temperature of both the draw solution and the wastewater is 20℃. The draw solution volume is 1m³ (stored in a high-pressure storage tank). The negative pressure reaction tower also initially contains 1m³ of draw solution. After the equipment is running, the feed solution to be treated enters the feed solution side of the forward osmosis membrane at a flow rate of 2.4m³ / h. A circulation pump is installed on the feed solution side to ensure that the flow rate at each point on the feed solution side of the forward osmosis membrane is 2.4m³ / h. The draw solution enters the draw solution side of the forward osmosis membrane at a flow rate of 0.3m³ / h. After the feed solution to be treated undergoes forward osmosis treatment, the membrane outlet flow rate (concentrate flow rate) is 2.33m³ / h, the flow rate of the dilute draw solution before entering the negative pressure reaction tower is 0.37m³ / h, and the product water (pure water) outlet flow rate of the negative pressure reaction tower is 0.07m³ / h. In this process, the water source heat pump transfers heat energy from the high-pressure storage tank to the negative pressure reaction tower. The hot gas and water vapor extracted from the negative pressure reaction tower enter the high-pressure tank, release heat, and reform the absorbent. At the same time, the heat of the absorbent in the high-pressure storage tank is continuously transferred to the negative pressure reaction tower, causing its temperature to drop. After the absorbent enters the forward osmosis membrane, it exchanges heat with the liquid to be treated and its temperature rises. Therefore, the heat energy sources of the water source heat pump include the absorbent in the high-pressure storage tank, the liquid to be treated, the high-temperature gas extracted from the negative pressure reaction tower, and the water vapor (the heat transfer energy of the surrounding air is negligible).

[0094] During forward osmosis, heat exchange occurs between the draw solution and the feed solution through the forward osmosis membrane, while heat transfer occurs between the negative pressure reactor and the high-pressure tank via a water source heat pump with an efficiency ratio of 3. After system startup, the temperature of the dilute draw solution in the negative pressure reactor gradually increases, while the outlet temperatures of the draw solution and the feed solution in the high-pressure tank gradually decrease. However, because the feed solution continuously enters the forward osmosis system and exchanges heat with the draw solution, the heat exchange between the draw solution and the feed solution per unit time increases with the temperature difference between them, resulting in a slower rate of temperature decrease for the draw solution in the high-pressure tank. When the temperature of the negative pressure reactor rises to 95℃, the temperature of the draw solution in the high-pressure tank decreases to 3.12℃ (see [link to relevant documentation] for the relationship between the draw solution temperature in the high-pressure tank and the dilute draw solution temperature in the negative pressure reactor). Figure 5 At this time, the ammonia nitrogen concentration of the dilute extract in the negative pressure reaction tower was 23.2 mg / L, which is less than the standard limit (25 mg / L) in Table 2 of the "Standard for Pollution Control of Municipal Solid Waste Landfills" (GB16889-2008), and the ammonium bicarbonate desorption rate was 99.91%.

[0095] In the above process, because a water source heat pump with an energy efficiency ratio of 3 was used to heat the negative pressure reaction tower, it takes 3.15 × 10⁻⁶ m³ of dilute extract to raise the temperature from 20°C to 95°C. 8 J of energy, with a power consumption of 1.05 × 10 8 J (29.17 kWh); If a traditional electric boiler is used for direct heating, its heat conversion efficiency is 90%, and it takes 3.5 × 10⁻⁶ kWh of electricity to heat 1 m³ of dilute absorbent liquid from 20°C to 95°C. 8 The energy consumption is 97.22 kWh. This embodiment uses a water source heat pump, which saves approximately 70% energy compared to electric boiler heating.

[0096] The various embodiments in this specification are described in a related manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, the system embodiments are basically similar to the method embodiments, so the description is relatively simple; relevant parts can be referred to the descriptions of the method embodiments.

[0097] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A positive osmosis membrane separation method using high-pressure gas-driven negative pressure separation, characterized in that: The high-pressure gas-driven negative pressure separation forward osmosis membrane separation equipment includes a forward osmosis membrane system, a concentrate storage tank, a high-pressure tank, a negative pressure tank, a water source heat pump unit, an air pump, and a water pump. The forward osmosis membrane system includes a wastewater inlet, a concentrate outlet, a dilute draw solution outlet, a draw solution inlet, and a wastewater circulation pump. The concentrate outlet of the forward osmosis membrane system connects to the concentrate storage tank, the dilute draw solution outlet connects to the negative pressure tank, and the draw solution inlet is connected to the high-pressure tank. The water source heat pump unit is connected to both the high-pressure tank and the negative pressure tank. The negative pressure tank has a gas outlet and a liquid outlet. The gas outlet of the negative pressure tank is connected to the air pump, which connects to the high-pressure tank. The liquid outlet of the negative pressure tank is connected to the water pump. The method includes the following steps: (1) The soluble pressure-sensitive gas is dissolved in water to prepare the draw solution. The gas that is easily soluble in water is dissolved in water to form a salt solution, which is then placed in a high-pressure tank. The high pressure drives the draw solution into the forward osmosis membrane system to draw water molecules from the feed solution to be treated. (2) When the feed solution to be treated passes through the forward osmosis membrane system, water molecules diffuse into the draw solution with a lower water chemical potential; (3) After water molecules enter the draw liquid, the draw liquid is diluted into a dilute draw liquid. The dilute draw liquid enters the negative pressure tank. In the negative pressure tank, the heat energy of the draw liquid in the high pressure tank is transferred to the draw liquid in the negative pressure tank through the water source heat pump, which raises the temperature of the draw liquid in the negative pressure tank and lowers the temperature of the draw liquid in the high pressure tank. At the same time, the air pump draws gas from the negative pressure tank and fills the high pressure tank with gas, which results in a decrease in pressure and an increase in temperature in the negative pressure tank. A large amount of dissolved gas in the dilute draw liquid is released and is pumped into the high pressure tank by the air pump to dissolve again. Thus, the separation of solute and product water in the negative pressure tank and the regeneration of draw liquid in the high pressure tank are achieved at the same time. (4) Drain the water from the negative pressure tank.

2. The positive osmosis membrane separation method with high-pressure gas-driven negative pressure separation as described in claim 1, characterized in that: In the positive osmosis membrane separation equipment using high-pressure gas-driven negative pressure separation, the negative pressure tank is equipped with a packing layer and a sprayer, and a circulation pump is installed outside the negative pressure tank.

3. A positive osmosis membrane separation method using high-pressure gas-driven negative pressure separation, characterized in that: The high-pressure gas-driven negative pressure separation forward osmosis membrane separation equipment includes a forward osmosis membrane system, a concentrate storage tank, a high-pressure tank, a negative pressure tank, a water source heat pump unit, an air pump, and a water pump. The forward osmosis membrane system includes a wastewater inlet, a concentrate outlet, a dilute draw solution outlet, a draw solution inlet, and a wastewater circulation pump. The concentrate outlet of the forward osmosis membrane system connects to the concentrate storage tank, the dilute draw solution outlet connects to the negative pressure tank, and the draw solution inlet is connected to the high-pressure tank. The water source heat pump unit is connected to both the high-pressure tank and the negative pressure tank. The negative pressure tank has a gas outlet and a liquid outlet. The gas outlet of the negative pressure tank connects to the air pump, which leads to the high-pressure tank. The liquid outlet of the negative pressure tank connects to the water pump. The separation equipment further includes a reverse osmosis system and a compliant water tank. The liquid outlet of the negative pressure tank is connected to a water pump and then to the reverse osmosis system and the compliant water tank, respectively. The reverse osmosis system includes a product water outlet and a retentate outlet. The product water outlet of the reverse osmosis system leads to the compliant water tank, and the outlet of the compliant water tank is connected to a water pump. The retentate outlet of the reverse osmosis system is controlled by a valve to lead to the negative pressure tank or the high-pressure tank. The separation equipment also includes a cooling water tank, which is connected to the negative pressure tank and the reverse osmosis system. A water pump is installed between the cooling water tank and the reverse osmosis system. The water source heat pump unit is connected to the high-pressure tank, the negative pressure tank, and the reverse osmosis system, respectively. The method includes the following steps: (1) Dissolve the water-soluble gas in water to form an extractant, which is then placed in a high-pressure tank. The high pressure drives the extractant into the forward osmosis membrane system to extract water molecules from the feed solution to be treated. (2) When the feed solution to be treated passes through the forward osmosis membrane system, water molecules diffuse into the draw solution with a lower water chemical potential; (3) After water molecules enter the draw liquid, the draw liquid is diluted into a dilute draw liquid. The dilute draw liquid enters the negative pressure tank. In the negative pressure tank, the heat energy of the draw liquid in the high pressure tank is transferred to the draw liquid in the negative pressure tank through the water source heat pump, which raises the temperature of the draw liquid in the negative pressure tank and lowers the temperature of the draw liquid in the high pressure tank. At the same time, the air pump draws gas from the negative pressure tank and fills the high pressure tank with gas, which results in a decrease in pressure and an increase in temperature in the negative pressure tank. A large amount of dissolved gas in the dilute draw liquid is released and is pumped into the high pressure tank by the air pump to dissolve again. Thus, the separation of solute and product water in the negative pressure tank and the regeneration of draw liquid in the high pressure tank are achieved at the same time. (4) Test the water in the negative pressure tank. If it meets the standard, it will be discharged directly. If it does not meet the standard, the water outlet of the negative pressure tank will be connected to the cooling water pool for cooling. The cooling method is to use a water source heat pump group to transfer the heat of the water in the cooling water pool to the negative pressure tank. After passing through the cooling water pool, the liquid is treated by the reverse osmosis system and the produced water meets the standard before being discharged. Part of the concentrated water in the reverse osmosis system is returned to the negative pressure tank and part is returned to the high pressure tank.

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