Low-energy-consumption differential pressure reverse osmosis wastewater concentration system and process thereof

Abstract

The invention relates to the technical field of wastewater concentration treatment, and discloses a low-energy-consumption differential pressure reverse osmosis wastewater concentration system which comprises a first reverse osmosis section and a second differential pressure reverse osmosis section, the first reverse osmosis section comprises first reverse osmosis equipment and is provided with an inlet and two outlets, and the two outlets are a fresh water outlet and a concentrated solution outlet respectively; the second differential pressure reverse osmosis section comprises differential pressure reverse osmosis equipment with multiple layers of permeable membrane elements, a permeable membrane unit comprises a sheet permeable membrane and a filter plate, flow channels are formed between the two sides of the sheet permeable membrane and the filter plate, and a water inlet and a water outlet are formed in the filter plate; the water inlet, the water outlet and the flow channel which are positioned on the same side of the sheet permeable membrane are communicated and form a first channel and a second channel which are independent; a first-section concentrated solution outlet is divided into two parts which are respectively conveyed to a first channel and a second channel in a pressurized and normal-pressure manner; the solution at the outlet of the second channel is conveyed to the inlet of the first reverse osmosis equipment. The solution is subjected to secondary concentration through the differential pressure reverse osmosis equipment, so that the energy consumption of the system is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater concentration treatment, and particularly relates to a low-energy consumption differential pressure reverse osmosis wastewater concentration system and its process. Background Art

[0002] Concentration is a commonly used step in the wastewater treatment process. By reducing the volume of wastewater, the wastewater discharge can be effectively reduced, the pressure on the environment can be alleviated, and at the same time, it is convenient to recycle valuable metals, chemicals or other substances contained in the wastewater after concentration.

[0003] The reverse osmosis system is a commonly used system in wastewater treatment projects. Its main principle is that under the action of pressure, pure water passes through the permeable membrane into the other side to obtain clean pure water, thereby increasing the concentration of the solution on the pressure side. For this kind of reverse osmosis system based on spiral wound membranes, the problems are that the osmotic pressure difference between the two sides of the membrane is high, the operating pressure is large, the energy consumption is high, and at the same time, due to the large pressure, it exceeds the bearing capacity of the equipment and the membrane material itself, resulting in significant technical bottlenecks, that is, the concentration that the reverse osmosis membrane concentration system can reach is limited. Practical application data shows that using the seawater desalination membrane system with the highest applicable concentration can only reach 7%-8% at most.

[0004] To realize the resource utilization of concentrated water, it is usually necessary to further adopt an evaporation concentration process for deep concentration after reverse osmosis concentration. However, the evaporation concentration process consumes a large amount of heat energy, resulting in high energy consumption in the whole wastewater concentration process; at the same time, the evaporation concentration process has extremely high requirements for the high-temperature resistance and corrosion resistance of the equipment, and the equipment selection and maintenance costs are high; in addition, the evaporation concentration operation under high-concentration conditions is difficult, and various process parameters need to be strictly controlled, and the operation process is complex, which not only increases the labor cost, but also increases the risk of safety accidents caused by improper operation. Finally, the cost investment of the whole wastewater treatment project increases significantly, seriously restricting the sustainable development and economic benefit improvement of the wastewater treatment industry. Summary of the Invention

[0005] The present invention aims to provide a low-energy consumption differential pressure reverse osmosis wastewater concentration system and its process to solve the problems of high energy consumption and high investment cost in the wastewater concentration treatment by traditional reverse osmosis membrane technology.

[0006] To achieve the above object, the present invention adopts the following technical solution: A low-energy consumption differential pressure reverse osmosis wastewater concentration system, comprising a first reverse osmosis section and a second differential pressure reverse osmosis section. The first reverse osmosis section is used for the primary osmotic concentration of wastewater and includes a first reverse osmosis device containing a spiral wound osmotic membrane. The first reverse osmosis device has one inlet and two outlets, namely a fresh water outlet and a concentrated solution outlet. The second differential pressure reverse osmosis section includes a differential pressure reverse osmosis device for the secondary osmotic concentration of wastewater. The differential pressure reverse osmosis device includes multiple osmotic membrane units and a clamping assembly for clamping the osmotic membrane units. The osmotic membrane unit includes a sheet-shaped osmotic membrane and filter plates. The filter plates are located on both sides of the sheet-shaped osmotic membrane and are provided with water inlets and water outlets. Flow channels are provided between the sheet-shaped osmotic membrane and the filter plates on both sides, through which a first solution and a second solution flow respectively. The water inlets, water outlets and flow channels on the same side of the sheet-shaped osmotic membrane in each osmotic membrane unit are connected to form independent first channels and second channels. The solution at the concentrated solution outlet of the first reverse osmosis section is divided into two parts. One part is pressurized and transported to the first channel of the second differential pressure reverse osmosis section, and the other part is transported to the second channel at normal pressure. The solution at the outlet of the second channel is circulated and transported to the inlet of the first reverse osmosis device.

[0007] The principle and advantages of this solution are as follows:

[0008] The concentration system of this solution includes a first reverse osmosis section and a second differential pressure reverse osmosis section. The first reverse osmosis section is used for the primary osmotic concentration of wastewater, and the second differential pressure reverse osmosis section is used for the secondary osmotic concentration of wastewater. Compared with traditional wastewater concentration, differential pressure reverse osmosis is used instead of evaporation concentration. Specifically, the principle of the differential pressure reverse osmosis technology is to place solutions with the same solute but different concentrations on both sides of the osmotic membrane. Due to the concentration difference between the two solutions, different osmotic pressures exist on both sides of the osmotic membrane. At this time, if the solvent in the concentrated solution is to permeate through the osmotic membrane into the dilute solution, the pressure required to overcome is exactly equal to the osmotic pressure difference between the concentrated solution and the dilute solution, that is, an additional corresponding pressure needs to be applied to the concentrated solution. In this way, the concentrated solution obtained after the primary concentration is subjected to secondary differential pressure reverse osmosis to achieve deep concentration. The present invention has the following technical effects:

[0009] 1. Reduce the overall concentration energy consumption: In the existing wastewater concentration technologies, traditional spiral wound reverse osmosis membrane concentration has a low concentration upper limit and requires deep treatment by relying on evaporation concentration. Evaporation concentration needs continuous supply of high-grade heat energy and also needs to maintain a high-temperature environment to ensure evaporation efficiency, resulting in extremely high energy consumption costs. In contrast, this wastewater concentration system replaces evaporation concentration with the differential pressure reverse osmosis technology. After preliminary concentration in the first reverse osmosis stage, the concentrated solution enters the second differential pressure reverse osmosis stage. Utilizing the pressure difference between the two sides of the solution, the solvent can permeate through the sheet-like permeation membrane without heating. The main energy consumption in this process is the mechanical energy to maintain the pressure difference. Compared with the heat energy consumption of evaporation concentration, its energy utilization efficiency is higher, thus fundamentally reducing the system energy consumption. Moreover, after the concentration treatment in the second reverse osmosis stage, the concentration of the concentrated liquid increases significantly, meeting the requirements of most wastewater deep treatment, greatly reducing the treatment volume of the evaporation concentration link, and even eliminating the need for evaporation concentration. From the perspective of the overall system, it not only avoids the large amount of heat energy consumption in the evaporation concentration link but also reduces the energy consumption during the operation and maintenance of the equipment due to the reduced use of high-temperature and corrosion-resistant equipment.

[0010] 2. Segment-by-segment concentration improves concentration efficiency and concentration: The second differential pressure reverse osmosis stage of the present invention is a key link for deep concentration. Its differential pressure reverse osmosis equipment adopts a multi-layer permeation membrane unit design. The permeation membrane unit consists of a sheet-like permeation membrane and filter plates on both sides of it. With this structure, after preliminary concentration in the first reverse osmosis stage, the wastewater enters the first channel of the second differential pressure reverse osmosis stage. Since the two sides of the sheet-like permeation membrane are the same solute solution, and one side is the high-pressure side connected to the first channel, and the other side is the low-pressure side connected to the second channel, under the drive of the pressure difference, the solvent can permeate from the high-pressure side to the low-pressure side, thereby further concentrating the wastewater. Compared with the traditional single spiral wound reverse osmosis membrane concentration method, the segment-by-segment concentration method can gradually increase the concentration of the concentrated liquid, break through the limitation that the concentration of the wastewater concentrated liquid in the existing technology can only reach 7%-8%, be closer to the requirements of wastewater deep treatment, reduce the necessity of subsequent evaporation concentration, and fundamentally solve the problem of insufficient concentration in the existing technology.

[0011] 3. The differential pressure reverse osmosis equipment has a simple structure and reduces investment costs: The independent first channel and second channel in the differential pressure reverse osmosis equipment not only make the flow path of the wastewater in the system clear, but also facilitate control and management. Each filter plate is provided with an inlet and an outlet. The inlet, outlet and flow channel on the same side of the sheet-shaped permeable membrane in each permeable membrane unit are connected to form an independent first channel and a second channel. This standardized and modular design not only facilitates the installation and maintenance of the equipment, reduces the equipment selection and maintenance costs, but also makes the operation process simpler and more intuitive. Compared with the evaporation concentration process, which requires strict control of various complex process parameters and is difficult to operate, the operation process of this solution is more stable and controllable, reduces the dependence on the professional skills of the operator, reduces labor costs, and also reduces the risk of safety accidents caused by improper operation. It reduces the cost investment of the entire wastewater treatment project from multiple dimensions and improves the economic benefits and sustainability of the project.

[0012] 4. This solution circulates the outlet solution obtained from the second channel of the differential pressure reverse osmosis device to the first reverse osmosis device for primary concentration, which not only further recovers valuable substances in the wastewater, but also avoids the additional energy consumption required for its separate treatment.

[0013] Furthermore, folded channels are engraved on both sides of the filter plate, and the depth of the folded channels is 3-5 mm. The folded channel design makes the solution distribution on both sides of the sheet-like permeable membrane more uniform, and can fully carry out differential pressure reverse osmosis, avoid too fast flow to achieve osmotic concentration, and ensure the efficiency and quality of wastewater concentration. In addition, the channel depth is limited to this range to ensure that the solution on both sides of the sheet-like permeable membrane can fully penetrate. If the channel is too deep, part of the solution in the channel away from the sheet-like permeable membrane cannot participate in the osmotic concentration, reducing the concentration efficiency. If the channel is too shallow, the solution will flow too fast and will not have time to participate in the concentrated osmosis, affecting the concentration effect.

[0014] Furthermore, the solutions on both sides of the sheet-like permeable membrane flow in the same direction. The same flow direction of the two solutions on both sides of the sheet-like permeable membrane can maintain a relatively stable concentration difference on both sides of the membrane, reduce the fluctuation of the membrane's permeability performance caused by the unstable concentration difference, and ensure the wastewater concentration efficiency and quality; at the same time, it can also reduce the damage to the sheet-like permeable membrane and the equipment as a whole, and improve the reliability and stability of the equipment.

[0015] Furthermore, the initial concentration difference between the solution in the first channel and the second channel is no more than 0.1 mol / L. The differential pressure reverse osmosis process relies on reducing the concentration difference between the solutions on both sides of the sheet-like permeable membrane, thereby reducing the osmotic pressure difference, and promoting the migration of the solvent from the high concentration (high pressure) side to the low concentration (low pressure) side under a low external pressure. Setting the initial concentration difference to no more than 0.1 mol / L can ensure that the system osmotic pressure difference is small and reduce system energy consumption.

[0016] Further, a grid for supporting the folded flow channel is provided between the filter plate and the sheet-like permeable membrane, and a pressing bolt is installed at the water outlet of the filter plate. The matching pressing nut fixes the sheet-like permeable membrane and the grid to isolate the first and second channels from each other.

[0017] Further, the clamping assembly includes plate frames located on both sides of the permeable membrane unit, and avoidance grooves for avoiding the pressing bolts are formed on the plate frames.

[0018] The present invention also provides a technical solution: a low-energy differential pressure reverse osmosis wastewater concentration process, which realizes wastewater concentration based on the above concentration system, and includes the following steps:

[0019] Step 1: The pre-softened wastewater is transported to the first reverse osmosis section through a high-pressure pump for primary osmotic concentration to obtain fresh water and concentrated solution.

[0020] Step 2: The concentrated solution is divided into two parts. One part is pressurized by a high-pressure pump to form a high-pressure concentrated solution and transported to the first channel, and the other part is an atmospheric pressure concentrated solution directly transported to the second channel.

[0021] Step 3: The high-pressure concentrated solution and the atmospheric pressure concentrated solution perform differential pressure osmosis in the differential pressure reverse osmosis device to respectively obtain concentrated liquid and dilute solution, and the concentrated liquid is the final concentrated product.

[0022] Step 4: The dilute solution and the untreated wastewater are converged and jointly transported to the first reverse osmosis device for primary concentration.

[0023] Further, in the Step 2, the volumes of the high-pressure concentrated solution and the atmospheric pressure concentrated solution are the same.

[0024] The beneficial effects of this solution are as follows:

[0025] 1. Segment concentration and differential pressure drive cooperate to achieve deep concentration:

[0026] Through the primary osmotic concentration in Step 1 of this concentration process, the traditional spiral wound permeable membrane is used to achieve preliminary solvent separation and solute enrichment, providing a basis for subsequent deep concentration. In Steps 2-3, the concentrated solution is divided into a high-pressure concentrated solution and an atmospheric pressure concentrated solution, which are respectively transported to the first channel and the second channel of the differential pressure reverse osmosis device, and secondary osmotic concentration is carried out by using the pressure difference on both sides of the sheet-like permeable membrane. This way of combining segment concentration and differential pressure drive can achieve a higher degree of concentration effect compared with single reverse osmosis concentration.

[0027] The concentration of the concentrated solution after concentration by the traditional spiral wound reverse osmosis membrane can only reach 7%-8% at most. However, through staged treatment in this process, the differential pressure reverse osmosis equipment can further separate the solvent under the drive of the pressure difference, and the concentration of the concentrated solution can be increased to a higher level, effectively breaking through the concentration bottleneck of traditional technologies, meeting the requirements of advanced wastewater treatment, reducing the use of high-energy-consuming evaporation concentration processes that may be required subsequently, and reducing the overall system energy consumption.

[0028] 2. Material recycling improves resource utilization efficiency and reduces energy consumption:

[0029] In step 4, the dilute solution generated by the differential pressure reverse osmosis equipment is converged with the untreated wastewater and jointly transported into the first reverse osmosis equipment for primary concentration. This design of material recycling has multiple advantages. On the one hand, the dilute solution still contains a certain amount of recoverable resources. By mixing with the wastewater and reprocessing, the maximum recovery and utilization of resources are achieved, and the extraction efficiency of valuable substances in the wastewater by the entire system is improved.

[0030] On the other hand, from the perspective of energy consumption, reusing the dilute solution avoids the additional energy consumption required for its separate treatment. If the dilute solution is treated separately, whether it is further concentrated or made to meet the standards before discharge, energy is required; while mixing it with the wastewater for treatment, through the treatment process of the first reverse osmosis stage, the reprocessing of the dilute solution is achieved without adding excessive energy consumption, reducing the overall energy consumption of the system and improving the energy utilization efficiency.

[0031] 3. Parameter optimization ensures the stable and efficient operation of the process:

[0032] The limitation of the volume ratio of the high-pressure and atmospheric-pressure concentrated solutions in the process makes the volumes of the high-pressure concentrated solution and the atmospheric-pressure concentrated solution the same. In this way, the pressure difference on both sides of the sheet-shaped osmotic membrane in the differential pressure reverse osmosis equipment can be accurately regulated, which is the key to ensuring the stable and efficient operation of the process. A stable and appropriate pressure difference is the basis for the efficient progress of the differential pressure osmosis process. This setting ensures that the osmosis rate of the solvent on both sides of the membrane is stable, making the concentration process more uniform and efficient, reducing the energy consumption waste and unstable treatment effects caused by pressure fluctuations, further improving the stability and reliability of the entire process, and reducing the operation and management costs. Description of the Drawings

[0033] Figure 1 is a schematic diagram of the overall structure of the system according to an embodiment of the present invention Figure One 。

[0034] Figure 2 is a schematic diagram of the overall structure of the system according to an embodiment of the present invention Figure Two 。

[0035] Figure 3 is a schematic structural diagram of the differential pressure reverse osmosis equipment according to an embodiment of the present invention.

[0036] Figure 4 Schematic diagram of the filter plate structure according to an embodiment of the present invention. Specific embodiments

[0037] The following is a further detailed description through specific embodiments:

[0038] The reference numerals in the accompanying drawings of the specification include: the first reverse osmosis section 1, the inlet 1-1, the fresh water outlet 1-2, the concentrated solution outlet 1-3, the second differential pressure reverse osmosis section 2, the differential pressure reverse osmosis device 3, the plate frame 4, the end plate 5, the osmotic membrane unit 6, the filter plate 7, the water inlet 8, the water outlet 9, the sheet-shaped osmotic membrane 10, the grid 11, the screw 12, the folded flow channel 13, the first solution inlet 14, the first solution concentrate outlet 15, the second solution inlet 16, the second solution diluent outlet 17, the first channel 18, the second channel 19, the compression bolt 20, the avoidance groove 21, and the high-pressure pump 22.

[0039] Embodiment 1

[0040] A low-energy consumption differential pressure reverse osmosis wastewater concentration system, as Figure 1 , Figure 2 shown, includes a first reverse osmosis section 1 and a second differential pressure reverse osmosis section 2. The first reverse osmosis section 1 is used for the primary osmotic concentration of wastewater and includes a first reverse osmosis device containing a spiral wound osmotic membrane. The first reverse osmosis device has an inlet 1-1 and two outlets, namely the fresh water outlet 1-2 and the concentrated solution outlet 1-3. The first reverse osmosis device is a traditional reverse osmosis device, which belongs to the prior art and will not be described in detail here.

[0041] The second differential pressure reverse osmosis section 2 includes a differential pressure reverse osmosis device 3, which is used for the secondary osmotic concentration of wastewater. As Figure 3 , Figure 4 shown, the differential pressure reverse osmosis device 3 includes a plurality of coaxially arranged osmotic membrane units 6, and a clamping assembly for clamping the osmotic membrane units 6, a sheet-shaped osmotic membrane 10 and filter plates 7 located on both sides of the sheet-shaped osmotic membrane 10. The clamping assembly includes plate frames 4 located on both sides of the osmotic membrane unit 6; corresponding mounting holes are provided on the filter plates 7 and the plate frames 4, and screws 12 are installed in the mounting holes. The screws 12 connect the filter plates 7 and the plate frames 4 into a whole to achieve axial through support.

[0042] A flow channel is formed between the sheet-like permeable membrane 10 and the filter plates 7 on both sides. Each filter plate 7 is provided with a water inlet 8 and a water outlet 9. The water inlets 8 and water outlets 9 of the two filter plates 7 in the permeation membrane unit 6 are arranged offset in the circumferential plane; the water inlets 8, water outlets 9 and the flow channels on the same side of the sheet-like permeable membrane 10 in each permeation membrane unit 6 are connected and form independent first channels 18 and second channels 19, in which a first solution and a second solution flow respectively. The pressure in the first channel 18 is greater than that in the second channel 19, and the concentration of the first solution is not less than that of the second solution.

[0043] The solution at the concentrated solution outlet 1-3 of the first reverse osmosis section 1 is divided into two parts. One part is pressurized by the high-pressure pump 22 and transported to the first channel 18 of the second differential pressure reverse osmosis section 2, and the other part is transported at normal pressure to the second channel 19; the outlet of the second channel 19 in the second differential pressure reverse osmosis section 2, that is, the second solution diluent outlet 17, is connected to the inlet 1-1 of the first reverse osmosis section 1 through a pipeline, so as to flow the obtained diluent into the untreated wastewater for concentration treatment and realize system circulation.

[0044] A grid 11 for supporting the folded flow channel 13 is provided between the filter plate 7 and the sheet-like permeable membrane 10. A compression bolt 20 is installed at the water outlet 9 of the filter plate 7, and the matching compression nut fixes the sheet-like permeable membrane 10 and the grid 11 to separate the first and second channels 19. The plate frame 4 is provided with an avoidance groove 21 at the corresponding position of the compression bolt 20 to prevent the plate frame 4 from interfering with the compression bolt 20, and also ensure that the two plate frames 4 can compress and fix the intermediate permeation membrane unit 6 to ensure tightness.

[0045] The plate frames 4 at both ends are end plates 5, and interfaces are provided at both end plates 5. One of the interfaces is the first solution inlet 14 and the second solution diluent outlet 17, and the other interface is the first solution concentrate outlet 15 and the second solution inlet 16. The flow directions of the first solution and the second solution on both sides of the sheet-like permeable membrane 10 are the same, so as to maintain the relative stability of the concentration difference on both sides of the sheet-like permeable membrane 10, reduce the fluctuation of the permeation performance of the sheet-like permeable membrane 10 caused by the unstable concentration difference, and ensure the wastewater concentration efficiency and quality. As Figure 3 shown, it shows the flow paths of the first solution and the second solution in the device. The solid arrows represent the flow path of the first solution, and the hollow arrows represent the flow path of the second solution.

[0046] The filter plate 7 is engraved with a folded flow channel 13, which is a three-channel flow channel, and the depth of the folded flow channel 13 is 3-5mm. The design of the folded flow channel 13 makes the solution on both sides of the sheet-like permeable membrane 10 more evenly distributed, and can fully perform differential pressure reverse osmosis, avoid too fast flow to achieve osmotic concentration, and ensure the efficiency and quality of wastewater concentration. In addition, the flow channel depth is limited to this range to ensure that the solution on both sides of the sheet-like permeable membrane 10 can fully penetrate. If the flow channel is too deep, part of the solution in the flow channel away from the sheet-like permeable membrane 10 cannot participate in the osmotic concentration, reducing the concentration efficiency, and if the flow channel is too shallow, the solution will flow too fast and not have time to participate in the concentrated penetration, affecting the concentration effect.

[0047] The initial concentration difference between the solutions entering the first channel 18 and the second channel 19 is no more than 0.1 mol / L, which can effectively reduce the osmotic pressure difference caused by the concentration difference of the solutions on both sides of the sheet-like permeable membrane 10, and reduce the operating pressure acting on the concentration, so that under the same operating pressure conditions, water can pass through the sheet-like permeable membrane 10 more quickly and effectively, so that the solute content of the dilute solution in the second channel 19 is lower, and the solute concentration of the concentrated solution in the first channel 18 is higher, thereby reducing the overall system energy consumption.

[0048] Preferably, solutions of the same concentration enter the first channel 18 and the second channel 19. The smaller the difference in solution concentration on both sides of the sheet-like permeable membrane 10 is, the smaller the osmotic pressure difference between the two solutions is, the smaller the pressure that needs to be overcome to achieve differential pressure reverse osmosis is, the additional pressurization pressure is reduced, the concentration energy consumption is reduced, and it is more energy-saving and environmentally friendly.

[0049] This embodiment is specifically described by a wastewater concentration example:

[0050] The actual wastewater to be treated is 10m 3 / h, the design processing capacity of the first reverse osmosis section 1 is 16m 3 / h, the design processing capacity of the second differential pressure reverse osmosis section 2 is 4m 3 / h, according to the energy consumption of the first reverse osmosis stage 1 seawater desalination 3.53kwh / m 3 (With energy recovery, 2.5kwh / m 3 ) is estimated, when using the differential pressure reverse osmosis system to concentrate seawater to a concentration of 14%, the energy consumption required is 7.06 kwh / m 3 (5kwh / m with energy recovery 3 ).

[0051] Traditional concentration technology often uses high pressure reverse osmosis + MVR (steam mechanical recompression technology). 3 / h wastewater calculation, calculated based on reverse osmosis concentration to 10%, the mass is reduced to 3.5 tons, and further concentrated to 14% by MVR, and 1 ton of water still needs to be evaporated. According to the energy consumption of MVR evaporation of 64 kwh / m 3 calculation, its comprehensive energy consumption is 9.93 kwh / m 3 (8.9 kwh / m in the case of having an energy recovery device 3 ). Therefore, compared with the traditional membrane concentration + MVR process, using the differential pressure reverse osmosis system for brine concentration can reduce the energy consumption by more than about 30%.

[0052] Example 2

[0053] Based on the above concentration system, this example provides a low-energy differential pressure reverse osmosis wastewater concentration process, including the following steps:

[0054] Step 1: The pre-softened wastewater is transported to the first reverse osmosis section 1 through the high-pressure pump 22 for primary osmotic concentration to obtain fresh water and concentrated solution. The pre-softening treatment can prevent scaling during the wastewater concentration process, which reduces the osmotic efficiency of the osmotic membrane and ensures the concentration efficiency and quality.

[0055] Step 2: The concentrated solution is divided into two parts. One part is pressurized by the high-pressure pump 22 to form a high-pressure concentrated solution and transported to the first channel 18, and the other part is an atmospheric-pressure concentrated solution directly transported to the second channel 19.

[0056] Step 3: The high-pressure concentrated solution and the atmospheric-pressure concentrated solution perform differential pressure osmosis in the differential pressure reverse osmosis device 3 to obtain concentrated liquid and dilute solution respectively, and the concentrated liquid is the final concentrated product.

[0057] Step 4: The dilute solution and the untreated wastewater are converged and jointly transported into the first reverse osmosis device for primary concentration, and the above steps are repeated. In this way, on the one hand, the dilute solution still contains a certain amount of recoverable resources. By mixing with the wastewater and reprocessing, the maximum recovery and utilization of resources are realized, and the extraction efficiency of valuable substances in the wastewater by the whole system is improved; on the other hand, from the perspective of energy consumption, reusing the dilute solution avoids the additional energy consumption required for its separate treatment, reduces the overall energy consumption of the system for concentration, and realizes energy conservation and environmental protection.

[0058] Through the above wastewater concentration process, first, through the primary osmotic concentration in Step 1, the traditional spiral-wound osmotic membrane is used to achieve preliminary solvent separation and solute enrichment, providing a basis for subsequent deep concentration. Then, in Steps 2-3, the concentrated solution is divided into a high-pressure concentrated solution and an atmospheric-pressure concentrated solution, which are respectively transported to the first channel 18 and the second channel 19 of the pressure-driven reverse osmosis device 3, and secondary osmotic concentration is carried out by using the pressure difference on both sides of the sheet-like osmotic membrane 10. This way of combining staged concentration with pressure difference driving can achieve a higher degree of concentration effect compared with single reverse osmosis concentration. Compared with the traditional spiral-wound reverse osmosis membrane, the highest concentration of the concentrated solution after concentration can only reach 7%-8%. However, through staged treatment in this process, under the drive of the pressure difference, the pressure-driven reverse osmosis device 3 further separates the solvent, and the concentration of the concentrated solution can be increased to a higher level, effectively breaking through the concentration bottleneck of traditional technologies. The highest concentration can reach 14%, meeting the requirements of deep wastewater treatment, reducing the use of high-energy-consuming evaporation concentration processes that may be required subsequently, and reducing the overall system energy consumption.

[0059] Example 3

[0060] The difference between this example and Example 1 is that in this example, the water inlet 8 and the water outlet 9 on the filter plate 7 are arranged radially instead of axially. By arranging connecting pipes outside the filter plate 7, the corresponding water inlets 8 / water outlets 9 in two adjacent osmotic membrane units 6 are connected, making the first channel 18 and the second channel 19 independent and unobstructed. Compared with Example 1, arranging the water inlets and outlets 9 radially on the filter plate 7 makes the sealing between the filter plate 7 and the sheet-like osmotic membrane 10 in the osmotic membrane unit 6 better. However, the thickness of the filter plate 7 will increase, and the connecting pipes outside will make the overall occupied space of the device larger. Therefore, in actual application, the setting method of the water inlets and outlets 9 in the filter plate 7 can be selected according to specific process requirements.

[0061] The above are only examples of the present invention. Specific technical solutions and / or common knowledge such as characteristics well known in the art are not described in detail here. It should be noted that for those skilled in the art, without departing from the technical solution of the present invention, several deformations and improvements can still be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope required by this application should be based on the content of its claims, and the specific implementation manners described in the specification can be used to explain the content of the claims.

Claims

1. A low-energy differential pressure reverse osmosis wastewater concentration system, characterized in that: It includes a first reverse osmosis section and a second differential pressure reverse osmosis section. The first reverse osmosis section is used for the primary osmotic concentration of wastewater and includes a first reverse osmosis device with a spiral wound osmotic membrane. The first reverse osmosis device has one inlet and two outlets, namely a fresh water outlet and a concentrated solution outlet. The second differential pressure reverse osmosis section includes a differential pressure reverse osmosis device for the secondary osmotic concentration of wastewater. The differential pressure reverse osmosis device includes multiple osmotic membrane units and a clamping assembly for clamping the osmotic membrane units. The osmotic membrane unit includes a sheet-like osmotic membrane and filter plates. The filter plates are located on both sides of the sheet-like osmotic membrane and are provided with water inlets and outlets. Flow channels are provided between the sheet-like osmotic membrane and the filter plates on both sides, through which a first solution and a second solution flow respectively. The water inlets, outlets and flow channels on the same side of the sheet-like osmotic membrane in each osmotic membrane unit are connected to form independent first channels and second channels. The concentrated solution outlet of the first reverse osmosis section is divided into two parts. One part is pressurized and transported to the first channel of the second differential pressure reverse osmosis section, and the other part is transported to the second channel at normal pressure. The solution at the outlet of the second channel is circulated and transported to the inlet of the first reverse osmosis device.

2. The low-energy differential pressure reverse osmosis wastewater concentration system according to claim 1, wherein: The filter plate is engraved with a folded flow channel, and the depth of the folded flow channel is 3-5 mm.

3. A low-energy differential pressure reverse osmosis wastewater concentration system according to claim 2, characterized in that: The flow directions of the solutions on both sides of the sheet-like osmotic membrane are the same.

4. A low - energy differential pressure reverse osmosis wastewater concentration system according to any one of claims 1 - 3, characterized in that: The initial concentration difference of the solutions in the first channel and the second channel is not greater than 0.1 mol / L.

5. The low-energy differential-pressure reverse osmosis wastewater concentration system according to claim 4, characterized in that: A grid for supporting the folded flow channel is provided between the filter plate and the sheet-like osmotic membrane. A compression bolt is installed at the water outlet of the filter plate, and the matching compression nut fixes the sheet-like osmotic membrane and the grid to separate the first and second channels.

6. The low-energy differential-pressure reverse osmosis wastewater concentration system according to claim 5, characterized in that: The clamping assembly includes frame plates located on both sides of the osmotic membrane unit, and the frame plates are provided with avoidance grooves for avoiding the compression bolts.

7. A low-energy differential pressure reverse osmosis wastewater concentration process, which realizes wastewater concentration based on the concentration system described in claims 1-6, and is characterized in that: It includes the following steps: Step 1: The pre-softened wastewater is transported to the first reverse osmosis section through a high-pressure pump for primary osmotic concentration to obtain fresh water and a concentrated solution. Step 2: The concentrated solution is divided into two parts. One part is pressurized by a high-pressure pump to form a high-pressure concentrated solution and transported to the first channel, and the other part is an atmospheric pressure concentrated solution directly transported to the second channel. Step 3: The high-pressure concentrated solution and the atmospheric pressure concentrated solution perform differential pressure osmosis in the differential pressure reverse osmosis device to obtain a concentrated liquid and a dilute solution respectively, and the concentrated liquid is the final concentrated product. Step 4: The dilute solution and the untreated wastewater are converged and jointly transported into the first reverse osmosis device for primary concentration.

8. A low-energy differential pressure reverse osmosis wastewater concentration process according to claim 7, characterized in that: In Step 2, the volumes of the high-pressure concentrated solution and the atmospheric pressure concentrated solution are the same.

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