A combined device for acid and alkali preparation based on pulsed energy recovery and ultra-efficient concentration of acid and alkali wastewater recycling.

Abstract

This invention discloses a combined device for the recycling of acid and alkali wastewater for acid and alkali production based on pulsed energy recovery and ultra-efficient concentration. The device includes a nanofiltration desalination unit, a pre-concentrator unit, a bipolar membrane / electrodialysis unit, a post-concentrator unit, a high-pressure reverse osmosis membrane unit, and an electrical control system. Each of the nanofiltration desalination unit, concentrator unit, and high-pressure reverse osmosis membrane unit comprises a feed water pump, a security filter, a high-pressure pump, a reverse osmosis membrane or nanofiltration membrane module, a circulation pump, an energy storage tank assembly, a pulse generation unit, a flow sensor, and a pressure sensor. This device is applied in the field of wastewater treatment. The working medium is pre-treated acid and alkali wastewater. Membrane filtration is used for material desalination and concentration, while the bipolar membrane / electrodialysis unit generates the acid and alkali. The combination of the energy storage tank and pulse generation enables pressure energy recovery on the high-pressure side of the membrane unit. The membrane unit employs periodic pulsed traveling wave filtration to reduce deposits on the membrane surface, improve device operating efficiency, reduce operating costs, and turn waste into treasure.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment application technology, specifically a combined device for the recycling of acid and alkali wastewater based on pulsed energy recovery and ultra-efficient concentration to prepare acid and alkali. Background Technology

[0002] Wastewater treatment has become a bottleneck restricting industrial development. Membrane-based water treatment technologies, with reverse osmosis or nanofiltration membranes at their core, offer superior treatment effects, good system stability, and lower investment and operating costs, making them important water treatment and reuse technologies. However, they suffer from high system operating pressure and high energy consumption. In 2018, thermal power plants consumed nearly 6 billion tons of water and discharged approximately 270 million tons of wastewater. The treatment and recycling of various types of wastewater from power plants has become urgent, and technologies for treating acid and alkali wastewater discharge are receiving increasing attention. Membrane-based water treatment technologies, with reverse osmosis or nanofiltration membranes at their core, are a crucial technological means for zero-discharge wastewater systems.

[0003] Bipolar membranes are a novel type of composite membrane composed of a cation exchange layer and an anion exchange layer. Under the drive of a DC electric field, they can undergo water dissociation, producing corresponding H+. + and OH - When used in conjunction with cation and anion exchange membranes, the brine obtained after purifying acidic and alkaline wastewater under the influence of an electric field is regenerated into acids and alkalis. The existing process route for preparing acids and alkalis from wastewater using bipolar membrane electrodialysis technology is: pretreatment, nanofiltration desalination, reverse osmosis concentration, secondary pretreatment, electrodialysis concentration, and bipolar membrane electrodialysis regeneration of acids and alkalis. This process lacks energy recovery during reverse osmosis concentration, and the electrodialysis concentration technology consumes a large amount of electricity. Existing membrane systems employ a staged treatment approach to improve the quality of the permeate effluent and reduce the salinity of the permeate; a segmented treatment approach to improve the recovery rate of the membrane system and increase the concentration of the working medium on the concentrate side. Multi-stage, multi-segment membrane treatment is a classic process for reverse osmosis or nanofiltration. The system flow and configuration principles of existing concentration technologies suitable for reverse osmosis or nanofiltration membrane filtration systems are consistent with the above, but the specific combination of stages and segments used in practice needs to be determined based on the specific conditions of the working medium and concentration requirements. Furthermore, existing membrane concentration devices rarely have energy recovery capabilities, and the specific operating processes of membrane concentration filtration systems also differ. Therefore, existing acid-base preparation systems based on membrane systems suffer from problems such as low working medium concentration, high operating pressure, and lack of energy recovery technology, resulting in high energy consumption and low system efficiency. Ultra-concentration, energy recovery, and high-efficiency membrane filtration technologies are needed to improve system operating efficiency.

[0004] Existing energy recovery devices, due to their high cost, are mainly used in large-scale seawater desalination. These include centrifugal turbine energy recovery devices, isobaric or positive displacement energy recovery devices, and energy cycle or triple-unit bundled energy recovery devices. The system configuration of a centrifugal turbine energy recovery device is as follows:Figure 6 As shown, energy recovery is achieved by converting pressure energy into mechanical energy using a hydraulic turbine, and then converting the mechanical energy into seawater pressure energy. Pressure energy is lost in both conversion steps, resulting in an overall energy recovery efficiency below 90%. Low-pressure seawater is pressurized by a high-pressure pump and enters the membrane module. The high-pressure brine discharged from the membrane module is converted into rotational mechanical energy within the turbine. The centrifugal turbine and the high-pressure pump motor are coaxial, jointly driving the high-pressure pump. The energy recovery device achieves energy saving and consumption reduction by inputting shaft work to the high-pressure pump motor. Compared with the method of pressurizing with a separate high-pressure pump, the fluid output flow rate and boost pressure remain unchanged. Another option for the centrifugal turbine energy recovery device is to directly connect the hydraulic turbine coaxially with the high-pressure pump, with the centrifugal turbine directly driving the high-pressure pump. Essentially, this is a hydraulically driven pump or turbocharger. The high-pressure brine in a centrifugal turbine energy recovery device undergoes a two-step conversion process of "pressure energy - mechanical energy - pressure energy," with an energy conversion efficiency generally around 50-70%. Furthermore, it requires coaxial connection with a high-pressure pump to achieve energy recovery and utilization. Therefore, this device suffers from disadvantages such as low energy conversion efficiency, large equipment size, and stringent installation and positioning requirements. An isobaric energy recovery device, also known as a positive displacement energy recovery device, has the following system configuration: Figure 7 As shown, isobaric energy recovery devices are the most widely used in existing energy recovery systems. Based on their principle, isobaric energy recovery devices can be divided into two main categories: valve-regulated and rotor-regulated. The low-pressure working medium is divided into two streams by a low-pressure pump and delivered to the high-pressure pump and the isobaric energy recovery module respectively. One stream of low-pressure working medium is directly pressurized by the high-pressure pump and then delivered to the reverse osmosis membrane module. The other stream of low-pressure working medium first enters the isobaric energy recovery module (such as a rotor-type isobaric energy recovery module or a valve-regulated energy recovery module) and exchanges pressure with the high-pressure working medium discharged from the membrane module. Then, it is boosted to high pressure by a booster pump before entering the membrane module, significantly reducing the system's water production energy consumption. The valve-regulated energy recovery module consists of three parts: an active switching valve, a pressure exchange chamber, and a check valve assembly. The active switching valve and the check valve assembly work together to achieve orderly switching between pressurization and depressurization processes, with pressure energy exchange taking place within the pressure exchange chamber. The most significant feature of the rotor-type energy recovery module is that it achieves rapid switching between pressurization and depressurization processes through the high-speed rotation of the rotor. Pressure exchange is achieved within multiple axial channels on the rotor. In isobaric energy recovery units, the flow rate of the high-pressure pump is basically consistent with the processing capacity of the membrane module, and the energy conversion efficiency is slightly higher than that of centrifugal turbine energy recovery units. However, fine particulate matter can easily cause the rotary valve core to jam or scratch the sealing surface. Other issues include low energy conversion efficiency, internal leakage, and salinity mixing between the working medium (food solution) and the concentrated fluid on the high-pressure side of the membrane module. There are no products for this type of energy recovery unit designed for small-flow or small-scale systems; large-scale systems require multiple units connected in parallel. The system configuration of an energy cycle or triple-unit bundled energy recovery unit is as follows... Figure 8As shown, it is basically similar to the isobaric energy recovery device. The flow rate of its high-pressure pump is basically consistent with the processing capacity of the membrane module. The high-pressure working medium of this type of energy recovery device can be circulated and cross-flowed, which has strong adaptability to the processing capacity of the membrane system. The energy circulation system is the core component of this type of energy recovery device, which has the problems of a large number of valves and complex pipelines. When the fluid is in a high-concentration state, it is easy to generate deposits to contaminate the membrane surface and easily generate concentration polarization, which leads to uneven flux when the membrane element is working. Therefore, the energy recovery efficiency of the device is reduced and the separation performance of the membrane filtration system is reduced. Summary of the Invention

[0005] To address the issues of low concentration efficiency and high energy consumption in existing bipolar membrane electrodialysis technologies for acid and alkali preparation, this invention discloses a combined device for the recycling of acid and alkali wastewater based on pulsed energy recovery and ultra-efficient concentration. Compared with existing acid and alkali wastewater treatment devices, the hardware configuration and system operation mode are different. This invention combines nanofiltration and reverse osmosis membrane technologies with bipolar membrane and electrodialysis technologies. The membrane unit uses a pulse generation unit combined with an energy storage tank assembly. According to the periodic pulsed traveling wave filtration, the acid and alkali wastewater is regenerated into recyclable acid and alkali solutions, realizing energy recovery and ultra-efficient concentration of the working medium, turning wastewater into regenerated acid and alkali, reducing system operating energy consumption and improving system operating efficiency.

[0006] To achieve the above objectives, the technical solution of the present invention is: a combined device for preparing acid and alkali from acid and alkali wastewater based on pulsed energy recovery and ultra-efficient concentration, comprising a nanofiltration desalination unit, a pre-concentrator unit, a post-concentrator unit, a bipolar membrane / electrodialysis unit, a second-stage high-pressure reverse osmosis membrane unit, a water tank, an acid tank, an alkali tank, and an electrical control system; the working medium of the system is acid and alkali wastewater that has undergone coagulation sedimentation and ultrafiltration pretreatment.

[0007] In this device, the acid and alkali wastewater input pipeline is connected to the inlet of the nanofiltration desalination unit, and the concentrated wastewater output interface of the nanofiltration desalination unit is connected to the concentrated wastewater output interface. Its product water side is connected in series with the concentrated water side of the pre-concentrator unit via a water tank, pipeline, and valves. After concentration, the permeate from the nanofiltration desalination unit is connected to the concentrated brine tank. The product water outlet of the pre-concentrator unit is connected in series with the concentrated water inlet of the second-stage high-pressure reverse osmosis membrane unit via a pipeline, valve, and pump. The concentrated water outlet of the second-stage high-pressure reverse osmosis membrane unit and the product water outlet of the post-concentrator unit are connected to the working medium inlet pipeline of the pre-concentrator unit via pipelines and valves. The permeate from the second-stage high-pressure reverse osmosis membrane unit is connected to the desalination water reuse outlet. The concentrated brine from the concentrated brine tank and the medium from the electrode water tank are pumped to the bipolar membrane / electrodialysis unit. The acid and alkali solution pipelines of the bipolar membrane electrodialysis unit are connected to the acid tank and alkali tank, respectively.

[0008] This device includes a nanofiltration desalination unit, a pre-concentrator unit, a post-concentrator unit, and a second-stage high-pressure reverse osmosis membrane unit. Each individual membrane filtration unit comprises a feed water pump, a security filter, a high-pressure pump, an energy storage tank assembly, a circulation pump, a reverse osmosis or nanofiltration membrane assembly, a pressure relief valve, an exhaust valve, a pulse generator unit, a flow sensor, and a pressure sensor. The feed water pump and the security filter are connected in series via pipelines. The outlet of the security filter is connected to the high-pressure pump via a branch pipe. The outlet pipeline of the reverse osmosis or nanofiltration membrane assembly on the high-pressure concentrate side is connected to the inlet pipeline of the circulation pump. The outlet pipeline of the high-pressure pump is connected to the outlet pipeline of the circulation pump via a tee connector. The device also includes an energy storage tank assembly, a pressure relief valve, and a pulse generator unit component. The outlet of the security filter is connected to the inlet of the energy storage tank assembly and the pulse generator unit via branch pipes. The outlet pipe of the circulation pump is connected to the inlet pipe of the energy storage tank assembly, and the outlet pipe of the energy storage tank assembly is connected to the high-pressure concentrate side inlet of the reverse osmosis or nanofiltration membrane assembly. A circulation pipeline is formed between the concentrate side of the reverse osmosis or nanofiltration membrane assembly, the circulation pump, and the energy storage tank assembly to realize the filtration and concentration functions of the membrane system. The outlet pipe of the pulse generator unit is connected to the outlet main pipe of the energy storage tank assembly via a tee connector. The high-pressure concentrate inlet side pipe of the reverse osmosis or nanofiltration membrane assembly is connected to a pressure safety valve. Valves are provided at the inlet and outlet of the feed water pump, security filter, high-pressure pump, energy storage tank assembly, circulation pump, reverse osmosis or nanofiltration membrane assembly, and pulse generator unit.

[0009] In a single-unit membrane filtration unit, the circulating pump pressurizes the high-pressure working medium at the concentrate outlet of the reverse osmosis or nanofiltration membrane module and mixes it with the high-pressure working medium from the high-pressure pump. The mixed working medium flows through the energy storage tank module and then through the concentrate side of the reverse osmosis or nanofiltration membrane module. Part of the working medium permeates through the membrane surface to become permeate, while the remaining high-pressure, high-concentration working medium flows out of the membrane module and into the inlet of the circulating pump. The working medium forms a high-pressure, high-flow, circulating cross-flow operation mode.

[0010] Before operation, the single-unit membrane filtration unit is filled with working medium by the feed water pump. After the unit is completely filled with the working medium, the high-pressure pump and the circulating pump are started, and the unit is put into operation. The initial pressure is set by the control system, which adjusts the operating frequency of the feed water pump motor to achieve the specific set value. As the working medium operates in a high-pressure, high-flow, and cross-flow mode, the concentration of the working medium increases, and the osmotic pressure gradually rises. The electrical control system increases the operating frequency of the high-pressure pump unit, increases the output power of the high-pressure pump, and increases the operating pressure of the working medium while maintaining the output of the membrane filtration system. When the operating pressure of the working medium rises to the maximum set value, the unit completes one working cycle. The maximum set value is determined according to the specific conditions of the working medium, generally 5.0 to 8.0 MPa. The energy storage tank assembly is divided into two parts: the energy storage working group and the energy storage standby group. The two groups alternately participate in the cyclic operation of the energy recovery unit. When the operating pressure of the unit reaches the maximum set value, the energy storage working group participating in the cyclic operation in the energy storage tank assembly exits operation and switches to the energy storage standby group; the energy storage standby group in the energy storage tank assembly participates in the cyclic operation and switches to the energy storage working group. After being drained and replenished, the out-of-operation energy storage tank becomes a standby energy storage unit, awaiting commissioning in the next cycle. Its cycle time is determined by the effective residence time or effective storage volume of the working medium in the energy storage tank components, and the maximum operating pressure factor of the unit's design. The unit operates in a high-pressure, high-flow-rate, cross-current cycle mode.

[0011] During each working cycle of the single-unit membrane filtration unit, the pulse generation unit receives makeup liquid from the security filter and rapidly injects it into the connecting pipe at the concentrate inlet of the reverse osmosis or nanofiltration membrane module under hydraulic or electric drive. This inlet pipe also serves as the outlet header of the energy storage tank module. The liquid output from the pulse generation unit alters the operating pressure of the reverse osmosis or nanofiltration membrane module, resulting in high-pressure pulsations in the concentrate pressure. The system achieves periodic pulsating traveling wave filtration. The number, duration, and pressure of the high-pressure pulses are preset by the system. The electrical control system also compares the pressure sensor readings with the set values, and triggers the pulses only when the preset conditions are met.

[0012] In this unit, pretreated acidic and alkaline wastewater is fed into the nanofiltration desalination unit. The nanofiltration membrane traps large molecular organic impurities and high-valence ions in the wastewater on the concentrate side. The nanofiltration desalination unit discharges concentrated wastewater from its concentrate side during each working cycle. The remaining acidic and alkaline wastewater, as permeate from the nanofiltration desalination unit, flows through the concentrate side of the pre-concentrator. After being concentrated by the nanofiltration membrane to a preset concentration, the concentrated brine is connected to the concentrated brine tank. The product water outlet of the pre-concentrator is connected to the concentrate inlet of the second-stage high-pressure reverse osmosis membrane unit. The post-concentrator concentrates the brine discharged from the bipolar membrane / electrodialysis unit, and its concentrate outlet is connected to the concentrated brine tank. The concentrate from the second-stage high-pressure reverse osmosis membrane unit and the product water from the post-concentrator are piped back to the working medium inlet of the pre-concentrator unit. The permeate from the second-stage high-pressure reverse osmosis membrane unit is reused as freshwater. The concentrated brine from the concentrated brine tank and the medium from the electrodialysis tank are pumped to the bipolar membrane / electrodialysis unit. The acid and alkali solutions generated under the action of the bipolar membrane / electric field are pumped to the acid tank and alkali tank, respectively.

[0013] In this device, the aforementioned single-unit membrane filtration unit achieves concentration and energy recovery of the working medium through periodic pulsating traveling wave filtration. The high-pressure pulses of the working medium increase the turbulence on the concentrate side of the membrane, preventing impurities in the high-concentration brine from depositing on the membrane surface, reducing concentration polarization, and improving the flux balance of membrane filtration. This, in turn, improves the operating efficiency of the membrane system and the energy recovery efficiency of the high-pressure side pressure energy of the device.

[0014] This invention features a simple and compact system configuration, capable of concentrating and recovering energy for acid and alkali wastewater treatment systems of varying scales. It boasts high energy recovery efficiency and strong adaptability, with the maximum concentration of the concentrated working medium approaching its saturation concentration at that temperature. This device reduces the high energy consumption problem in bipolar membrane acid and alkali preparation processes, improving system operating efficiency. This invention transforms waste into valuable resources, recycling acid and alkali wastewater to produce acids and alkalis, promoting industrial upgrading and achieving energy-saving, low-carbon, and sustainable development. Attached Figure Description

[0015] Figure 1 This is a system flow diagram of the combined device for preparing acid and alkali from acid and alkali wastewater based on pulsed energy recovery and ultra-efficient concentration according to the present invention.

[0016] Figure 2 This is a system configuration diagram of the single-unit membrane filtration unit of the combined device for acid and alkali wastewater recycling based on pulsed energy recovery and ultra-efficient concentration, which is the present invention.

[0017] Figure 3 This is a schematic diagram of the operating pressure of the single-unit membrane filtration unit of the combined device for acid and alkali wastewater recycling based on pulsed energy recovery and ultra-efficient concentration, which is a combination device of the present invention.

[0018] Figure 4This is a structural diagram of the energy storage tank of the combined device for preparing acid and alkali from acid and alkali wastewater based on pulsed energy recovery and ultra-efficient concentration according to the present invention.

[0019] Figure 5 This is a structural diagram of the pulse generation unit of the combined device for preparing acid and alkali from recycled acid and alkali wastewater based on pulsed energy recovery and ultra-efficient concentration, as described in this invention.

[0020] Figure 6 A system configuration diagram for an existing centrifugal turbine energy recovery device.

[0021] Figure 7 Configuration diagram of existing isobaric or positive displacement energy recovery device systems;

[0022] Figure 8 Configuration diagram of existing technology energy cycle or triple-bundle energy recovery device system;

[0023] Figure 9 This is a flow chart of the bipolar membrane / electrodialysis unit of the combined device for acid and alkali wastewater recycling and preparation of acid and alkali based on pulsed energy recovery and ultra-efficient concentration, which is the basis of this invention.

[0024] Reference numerals: 1: Feed pump; 2: Security filter; 3: High-pressure pump; 4: Energy storage tank assembly; 5: Circulation pump; 6: Reverse osmosis membrane or nanofiltration membrane assembly; 7: Pressure safety valve; 8: Pulse generating unit; 9: End cap; 10: Fixed orifice plate; 11: Housing; 12: Thin-walled energy storage tube; 13: Floating orifice plate; 14: Actuator; 15: Piston rod; 16: Cylinder; 17: Piston; 18: Centrifugal turbine; 19: Booster pump; 20: Isobaric energy recovery assembly; 21: Energy circulation system; 22: Exhaust valve; 23: Pressure sensor; 24: Flow sensor; 25: Pressure sensor; 26: Flow sensor; 27: Pressure sensor; 28: Flow sensor; 29: Flow sensor; 30: Positive electrode; 31: Anion membrane; 32: Anode membrane; 33: Bipolar membrane; 34: Negative electrode. Detailed Implementation

[0025] The combined device for recycling acid and alkali wastewater based on pulsed energy recovery and ultra-efficient concentration treats acid and alkali wastewater after coagulation sedimentation, filtration, and ultrafiltration pretreatment. It employs a comprehensive technology combining nanofiltration, reverse osmosis, bipolar membranes, and electrodialysis to further purify and concentrate the wastewater, regenerating it into recyclable acid and alkali solutions, turning waste into treasure. Each individual membrane filter unit in the device operates in a periodic pulsed traveling wave mode to minimize energy consumption during system operation. Combined with high-pressure pulsed technology, it improves system efficiency, recovers the pressure energy of the high-pressure working medium on the concentrate side of the reverse osmosis or nanofiltration membrane filtration system, increases the working medium concentration, and reduces operating energy consumption and costs. The system flow of this invention is as follows: Figure 1As shown, the system consists of a nanofiltration desalination unit, a pre-concentrator unit, a post-concentrator unit, a bipolar membrane / electrodialysis unit, a second-stage high-pressure reverse osmosis membrane unit, a water tank, an acid tank, an alkali tank, and an electrical control system. The working medium of the system is acid and alkali wastewater that has undergone coagulation sedimentation, filtration, and ultrafiltration pretreatment.

[0026] This device first performs salt separation and purification treatment on the pretreated acidic and alkaline wastewater. The input pipeline of the acidic and alkaline wastewater is connected to the inlet of the nanofiltration salt separator. After being pumped by the water supply pump 1 and pressurized by the high-pressure pump 3, the high-pressure acidic and alkaline wastewater flows into the concentrate side of the nanofiltration membrane. The nanofiltration membrane traps large molecular organic impurities and high-valence ions in the acidic and alkaline wastewater on the concentrate side. Part of the acidic and alkaline wastewater flows through the surface of the nanofiltration membrane to the water tank for concentration. The remaining working medium flows out of the concentrate side of the nanofiltration membrane and enters the circulation pump 5 of the nanofiltration salt separator. Under the action of the circulation pump 5, the working medium mixes with the acidic and alkaline wastewater from the high-pressure pump 3 in the pipeline. The mixed working medium undergoes periodic circulation and salt separation purification on the concentrate side of the nanofiltration membrane. In each working cycle, the nanofiltration salt separator periodically discharges the concentrated waste liquid on the concentrate side.

[0027] In the pre-concentration stage of this unit, feedwater pump 1 delivers the permeate from the nanofiltration desalination unit to the high-pressure pump 3 of the pre-concentrator unit for pressurization. The high-pressure pump 3 pressurizes and pumps the working medium to the concentrate side of the nanofiltration / reverse osmosis membrane in the pre-concentrator unit for concentration. Part of the working medium permeates through the membrane surface, and the remaining working medium flows out of the concentrate side of the nanofiltration / reverse osmosis membrane and enters the circulation pump 5 of the pre-concentrator unit. Under the action of the circulation pump 5, the working medium mixes with the acid and alkaline wastewater from the high-pressure pump 3 of the concentrator unit in the pipeline. The mixed working medium undergoes periodic circulation and concentration in the pre-concentrator unit. In each working cycle, the concentrated brine is periodically discharged to the concentrated brine tank. The product water outlet of the pre-concentrator unit is connected in series with the concentrate side inlet of the second-stage high-pressure reverse osmosis membrane unit via pipelines and valves. The permeate from the membrane of the second-stage high-pressure reverse osmosis membrane unit is connected to the freshwater reuse outlet.

[0028] In the acid and alkali production stages of this unit, the concentrated brine from the concentrated brine tank and the medium from the electrode water tank are pumped to the bipolar membrane / electrodialysis unit. The acid and alkali solutions generated under the action of the bipolar membrane / electric field are connected to the acid tank and alkali tank, respectively. The brine outlet of the bipolar membrane / electrodialysis unit is connected to the inlet pipeline of the post-concentrator unit. The post-concentrator unit concentrates the brine discharged from the bipolar membrane / electrodialysis unit, and the concentrated solution flows into the concentrated brine tank. The product water outlet of the post-concentrator unit and the concentrate outlet of the second-stage high-pressure reverse osmosis membrane unit are connected to the inlet of the pre-concentrator unit via pipelines and valves. These two working media are mixed with the permeate from the salt separator unit and then enter the pre-concentration process.

[0029] This invention is based on energy recovery technology to achieve low-energy consumption and highly efficient concentration of the working medium. Existing energy recovery devices mainly include centrifugal turbine energy recovery devices, isobaric energy recovery devices, and energy circulation energy recovery devices. The system configuration of a centrifugal turbine energy recovery device is as follows: Figure 6 As shown, the device consists of a feed water pump 1, a security filter 2, a high-pressure pump 3, a centrifugal turbine 18, a reverse osmosis membrane or nanofiltration membrane module 6, instruments, valves, and an electrical control system. Low-pressure seawater is pressurized by the high-pressure pump 3 and enters the reverse osmosis membrane or nanofiltration membrane module 6. The high-pressure brine discharged from the reverse osmosis membrane or nanofiltration membrane module 6 is converted into rotational mechanical energy within the centrifugal turbine 18. The centrifugal turbine 18 is coaxial with the motor of the high-pressure pump 3, jointly driving the high-pressure pump 3. Another option for the centrifugal turbine energy recovery device is to directly connect the centrifugal turbine 18 coaxially with the high-pressure pump 3, directly driving the high-pressure pump 3. Essentially, this is a hydraulically driven pump or turbocharger. The high-pressure brine in the centrifugal turbine energy recovery device undergoes a two-step conversion process of "pressure energy - mechanical energy - pressure energy," with an energy conversion efficiency generally around 50-70%. Furthermore, it requires coaxial connection with the high-pressure pump 3 to achieve energy recovery and utilization. Therefore, this device suffers from disadvantages such as low energy conversion efficiency, large equipment size, and high requirements for installation and positioning. The isobaric energy recovery device, also known as the positive displacement energy recovery device, has the following system configuration: Figure 7 As shown, the system consists of a feed water pump 1, a security filter 2, a high-pressure pump 3, a booster pump 19, an isobaric energy recovery module 20, a reverse osmosis membrane or nanofiltration membrane module 6, instruments, valves, and an electrical control system. This device is the most widely used among existing energy recovery devices. Isobaric energy recovery devices can be broadly classified into two categories based on their principle: valve-controlled and rotor-controlled. The low-pressure working medium is split into two streams by the feed water pump 1 and delivered to the high-pressure pump 3 and the isobaric energy recovery module 20 respectively. One stream of low-pressure working medium is directly boosted to high pressure by the high-pressure pump 3 and then delivered to the reverse osmosis membrane or nanofiltration membrane module 6. The other stream of low-pressure working medium first enters the isobaric energy recovery module 20 (such as a rotor-type isobaric energy recovery module or a valve-controlled energy recovery module) to exchange pressure with the high-pressure working medium discharged from the reverse osmosis membrane or nanofiltration membrane module 6, and then is boosted to high pressure by the booster pump 19 before entering the reverse osmosis membrane or nanofiltration membrane module 6. This significantly reduces the system's water production energy consumption. The device has internal leakage and mixing issues between the working medium (stock solution) and the concentrate on the concentrate side of the reverse osmosis or nanofiltration membrane module 6. The system configuration of the energy cycle or triple-cluster energy recovery unit is as follows: Figure 8 As shown, it consists of a feed water pump 1, a security filter 2, a high-pressure pump 3, an energy circulation system 21, a reverse osmosis membrane or nanofiltration membrane module 6, instruments, valves, and an electrical control system. The high-pressure working medium of this type of energy recovery device can circulate cross-flow, consistent with the working mode of existing closed-loop reverse osmosis membrane filtration systems, and has strong adaptability to the processing capacity of the membrane system. However, its core component, the energy circulation system, suffers from a large number of valves and complex piping. Furthermore, the fluid is prone to deposits that contaminate the membrane surface under high-concentration circulating flow conditions, easily leading to concentration polarization and uneven flux distribution during membrane element operation. This affects the energy recovery efficiency of the device and reduces the separation performance of the membrane filtration system.

[0030] Existing membrane system technologies typically employ staged treatment to improve the quality of the permeate, reducing the salinity of the permeate. This staged treatment also increases the recovery rate of the membrane system and the concentration of the working medium on the concentrate side. Multi-stage, multi-fraction membrane treatment processes are classic forms of reverse osmosis or nanofiltration. While the principles of existing membrane concentration technologies are consistent with these classic processes, the specific combination of stages and fractions used in practice depends on the specific working medium and concentration requirements. Existing membrane concentration devices rarely utilize energy recovery methods, and the specific operating processes of membrane concentration and filtration systems also differ. This invention, as... Figure 3 As shown, the system adopts a periodic pulsating traveling wave operation mode, combined with the energy storage tank component 4, to achieve the concentration of the working medium, recover the pressure energy of the high-pressure working medium on the concentrate side of the reverse osmosis or nanofiltration membrane concentration system, and improve the concentration effect.

[0031] The system configuration of any of the following membrane filtration units included in this device—nanofiltration desalination unit, pre-concentrator unit, post-concentrator unit, and second-stage high-pressure reverse osmosis membrane unit—is as follows: Figure 2 As shown, the system consists of a feed water pump 1, a security filter 2, a high-pressure pump 3, an energy storage tank assembly 4, a circulation pump 5, a reverse osmosis membrane or nanofiltration membrane assembly 6, flow sensors 24, 26, 28, and 29, and pressure sensors 23, 25, and 27. The system's working medium is seawater, reverse osmosis concentrate, or other high-concentration brine or solutions. Figure 2 As shown, PI represents a pressure gauge; PIT represents a pressure sensor; and FIT represents a flow sensor. The energy storage tank assembly 4 consists of multiple energy storage tanks connected in parallel. The structure of a single energy storage tank is as follows: Figure 4 As shown, it consists of an end cap 9, a fixed perforated plate 10, a housing 11, a thin-walled energy storage tube 12, and a floating perforated plate 13. One end of the thin-walled energy storage tube 12 is connected to the fixed perforated plate 10, and the other end is connected to the floating perforated plate 13 to form an assembly. This assembly is fixed to one end of the housing 11 by the fixed perforated plate 10 and the end cap 9, and is installed inside the housing 11 by the floating perforated plate 13; the other end of the housing 11 is fixed by the end cap 9; the thin-walled energy storage tube 12 is a thin-walled seamless straight tube, or a thin-walled corrugated steel tube, and the material is corrosion-resistant. The structure of the pulse generating unit 8 is as follows. Figure 5 As shown, it consists of an actuator 14, a piston rod 15, a cylinder 16, and a piston 17. The actuator 14 is a hydraulic cylinder or an electric push rod. In the pulse generating unit 8, one end of the piston rod 15 is connected to the actuator 14, and the other end is connected to the piston 17. The piston 17 is installed inside the cylinder 16. Under the drive of the electronic control system, the actuator 14 pushes the piston 17 to reciprocate within the cylinder 16 through the piston rod 15.

[0032] In any single membrane filtration unit of this invention, the inlet of the original working medium is connected to the inlet of the feed water pump 1 via a pipeline valve, and the outlet of the feed water pump 1 is connected to the inlet of the security filter 2 via a pipeline valve; the feed water pump 1 and the security filter 2 are connected in series via pipelines; the outlet of the security filter 2 is divided into three branch pipes, which are respectively connected to the inlets of the high-pressure pump 3, the energy storage tank assembly 4, and the pulse generator unit 8; the high-pressure concentrate side outlet pipeline of the reverse osmosis membrane or nanofiltration membrane assembly 6 is connected to the inlet pipeline of the circulation pump 5, the outlet pipeline of the circulation pump 5 is connected to the inlet main pipeline of the energy storage tank assembly 4, and the outlet main pipeline of the energy storage tank assembly 4 is connected to the high-pressure concentrate side inlet of the reverse osmosis membrane or nanofiltration membrane assembly 6; a circulation pipeline is formed between the reverse osmosis membrane or nanofiltration membrane assembly 6, the circulation pump 5, and the energy storage tank assembly 4; the outlet pipeline of the high-pressure pump 3 merges into the circulation pump 5 via a tee connector. The outlet pipeline of pulse generator unit 8 is connected to the outlet main pipe of energy storage tank assembly 4 via a tee connector; the high-pressure concentrate inlet side pipeline of reverse osmosis membrane or nanofiltration membrane assembly 6 is connected to pressure safety valve 7; the outlet pipeline of high-pressure pump 3 is equipped with flow sensor 26 and pressure sensor 25; the high-pressure concentrate inlet side main pipe of reverse osmosis membrane or nanofiltration membrane assembly 6 is equipped with flow sensor 24 and pressure sensor 23 respectively; the high-pressure concentrate outlet side main pipe of reverse osmosis membrane or nanofiltration membrane assembly 6 is equipped with flow sensor 28 and pressure sensor 27 respectively; the permeate outlet main pipe of reverse osmosis membrane or nanofiltration membrane assembly 6 is equipped with flow sensor 29; the feed water pump 1, security filter 2, high-pressure pump 3, energy storage tank assembly 4, circulation pump 5, reverse osmosis membrane or nanofiltration membrane assembly 6, and pulse generator unit 8 are all equipped with valves at their inlet and outlet. The highest point of the high-pressure circulation main pipe for the working medium is connected to exhaust valve 22 and pipeline. Energy storage tank assembly 4, reverse osmosis membrane or nanofiltration membrane assembly 6, and pulse generator unit 8 are respectively connected to vent valves and pipelines. Six reverse osmosis or nanofiltration membrane modules are skid-mounted together to form a membrane frame assembly.

[0033] In any single membrane filtration unit of the present invention, the circulating pump 5 pressurizes the high-pressure working medium at the concentrate outlet of the reverse osmosis membrane or nanofiltration membrane module 6 and mixes it with the high-pressure working medium stock solution from the high-pressure pump 3. The mixed working medium flows through the energy storage tank assembly 4 and then through the concentrate side of the reverse osmosis membrane or nanofiltration membrane module 6. Some pure water permeates through the membrane surface to become the product water effluent. The remaining high-pressure, high-concentration working medium flows out of the reverse osmosis membrane or nanofiltration membrane module 6 and enters the inlet of the circulating pump 5. The working medium operates in a high-pressure, high-flow, circulating cross-flow mode. The flow rate of the circulating pump 5 is about 1 to 5 times that of the high-pressure pump 3.

[0034] In any single membrane filtration unit of this invention, the feed pump 1, high-pressure pump 3, and circulation pump 5 are connected to a variable frequency motor, and their operating frequencies are adjusted by the corresponding frequency converter of the electronic control system. Before operation, the feed pump 1 is used to fill the unit with working medium. After the unit is completely filled with working medium, the high-pressure pump 3 and circulation pump 5 are started, and the unit is put into operation. Only 1 to 4 membrane elements are installed in each reverse osmosis or nanofiltration membrane housing. In the initial stage of operation, the pressure of the working medium is set by the control system, which achieves the specific set value by changing the operating frequency of the feed pump 1 motor. As the working medium operates in a high-pressure, high-flow, and circulating cross-flow mode, the concentration of the working medium increases, the osmotic pressure gradually rises, the electronic control system increases the operating frequency of the high-pressure pump 3, the output power of the high-pressure pump 3 increases, and the operating pressure of the working medium rises, maintaining a constant output of the membrane filtration system under the control of the electronic control system. When the operating pressure of the working medium rises to the highest set value, the unit completes one working cycle. The highest set value is determined according to the specific conditions of the working medium, generally 5.0 to 8.0 MPa. The energy storage tank assembly 4 consists of multiple energy storage tanks connected in parallel. Each energy storage tank contains a thin-walled energy storage tube 12, installed between orifice plates at both ends. One orifice plate is a fixed orifice plate 10, and the other is a floating orifice plate 13. The working medium flows within the thin-walled energy storage tube 12. Higher working medium pressure results in greater free elastic deformation of the thin-walled energy storage tube 12 and the storage of pressure energy. The internal pressure of the thin-walled energy storage tube is consistent with the pressure of its internal working medium, while the pressure outside the tube is consistent with the atmospheric pressure. The energy storage tank assembly 4 is internally divided into two parts: an energy storage working group and an energy storage standby group. These two groups alternately participate in the circulation of the working medium according to the operating pressure of the device. During system operation, when the pressure value detected by the pressure sensor 23 reaches the system's set maximum operating pressure, the electrical control system changes the opening and closing status of the inlet and outlet valves of the energy storage tank. This switches the operating energy storage working group in the energy storage tank assembly 4 to the energy storage standby group, removing it from system operation, and switches the energy storage standby group back to the energy storage working group to participate in system operation. During the switching process, the two energy storage tanks are initially connected. Part of the elastic deformation energy of the thin-walled energy storage tubes in the working energy storage group is released and converted into pressure energy of the working medium in the standby energy storage group. The energy conversion is complete when the working medium pressures in both groups are equal. Then, the working states of the two energy storage tanks are switched via valve operation. The original energy storage group, after being decommissioned, undergoes drainage and replenishment to become the standby energy storage group, awaiting commissioning in the next cycle. Its cycle is determined by the effective residence time or effective energy storage volume of the working medium in the energy storage tank assembly 4, and the maximum working pressure factor designed for the device. The electrical control system detects the pressure values ​​of pressure sensors 23 and 27, as well as the pressure difference between them. When the pressure difference reaches a set value, the electrical control system drives actuator 14 to operate, and pulse generation unit 8 outputs the pulse flow rate of the working medium, enabling pulse filtration by the reverse osmosis or nanofiltration membrane filtration system.As described above, the membrane filtration unit operates cyclically in a high-pressure, high-flow, and cross-flow mode, with the flow rate of the circulating pump 5 being approximately 1 to 5 times that of the high-pressure pump 3.

[0035] In each filtration cycle of any membrane filtration unit in this invention, the branch pipe at the outlet of the security filter 2 replenishes the pulse generating unit 8 with liquid. The electronic control system detects the pressure values ​​of pressure sensors 23 and 27 and the pressure difference between them. When the pressure difference reaches a set value, or according to a preset time as a trigger condition, a control signal is issued. Under the drive of the hydraulic or electric actuator 14 of the pulse generating unit 8, the replenishing liquid in its cylinder 16 is rapidly forced into the concentrate side of the reverse osmosis membrane or nanofiltration membrane module 6, changing the operating pressure of the reverse osmosis membrane or nanofiltration membrane module 6. The concentrate pressure experiences high-pressure pulsation, and the system achieves periodic pulsating traveling wave filtration, specifically as follows: Figure 3 As shown; the number of high-pressure pulses per working cycle is 0-5, the pulse duration is 10-30 seconds, and the pulse pressure is 0.5-0.95 times the system's maximum working pressure. The membrane filtration system achieves the following: Figure 3 The high-pressure pulsating traveling wave operation shown reduces the accumulation of deposits on the membrane surface, reduces concentration polarization on the membrane surface, improves the flux equalization performance of the membrane element, and increases the system operating efficiency.

[0036] The bipolar membrane / electrodialysis unit consists of a positive electrode 30, an anion membrane 31, a cation membrane 32, a bipolar membrane 33, and a negative electrode 34. Its system flow is as follows: Figure 9 As shown, the bipolar membrane / electrodialysis unit contains, in sequence, an electrode water chamber, a brine chamber, an alkali chamber, an acid chamber, and another electrode water chamber. The brine, alkali, and acid chambers form a group, and this group is arranged in multiple sets between two electrode water chambers. The bipolar membrane 33 is a novel ion exchange resin composite membrane, composed of a cation exchange membrane, an intermediate hydrophilic interfacial layer, and an anion exchange membrane. Under the action of a DC electric field, water dissociates at the interface between the cation and anion membrane layers of the bipolar membrane, producing H₂. + OH - They migrate in reverse through the cation and anion membranes respectively. Along the migration path, H... + Ions in the acid chamber react with acid radicals from the brine chamber to form an acidic solution, OH- - In the alkali chamber, sodium ions from the brine chamber form an alkaline solution, while the hydrophilic interfacial layer sandwiched between the bipolar membranes 33 continuously absorbs water to replenish the consumed water. The bipolar membrane continuously absorbs water, causing the water to dissociate into H+. + OH -Ions combine with their corresponding cations and anions to ultimately produce acid and alkali solutions. These solutions circulate between the acid / alkali tanks and the acid and alkali chambers of the bipolar membrane / electrodialysis unit under the action of pumps. As the bipolar membrane / electrodialysis unit operates, the concentrations of the acid and alkali solutions continuously increase. During this process, electrode water circulates within the electrode water chamber under the action of pumps, while concentrated brine flows into the brine chamber of the bipolar membrane / electrodialysis unit under the action of pumps. Ions in the concentrated brine flow counter-currently to the acid and alkali chambers under the influence of the electric field, reducing the brine concentration. The outlet of the brine chamber of the bipolar membrane / electrodialysis unit is connected to a post-concentrator unit, where the concentrated brine is collected and flows into the concentrated brine tank for further circulation. When the concentration in the acid and alkali tanks reaches the preset value, one working cycle of the bipolar membrane / electrodialysis unit ends. The prepared acid and alkali solutions are discharged, and permeate from the secondary high-pressure reverse osmosis system is re-injected into the acid and alkali tanks, allowing the bipolar membrane / electrodialysis unit to begin the next working cycle. The working medium's temperature rises during the cycle, and a heat exchanger is used to cool it down.

[0037] The feed water pump 1, security filter 2, high-pressure pump 3, energy storage tank assembly 4, circulation pump 5, reverse osmosis membrane or nanofiltration membrane assembly 6, and pulse generation unit 8 in the device can be constructed as a unit system, a main system system, or other combinations. The replenishment and drainage of the energy storage tank assembly 4 can be achieved by a separate water pump, and the replenishment of the pulse generation unit 8 can also be achieved by a separate water pump. Figure 1 , Figure 2 The system configuration described herein is merely a preferred embodiment of the present invention and is not intended to limit the implementation methods and scope of protection of the present invention. Those skilled in the art should recognize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the scope of protection of the present invention.

Claims

1. A combined device for preparing acid and alkali based on pulsating energy recovery and hyper-concentration of acid and alkali waste water, characterized in that This unit consists of a nanofiltration desalination unit, a pre-concentrator unit, a bipolar membrane / electrodialysis unit, a post-concentrator unit, a second-stage high-pressure reverse osmosis membrane unit, a water tank, an acid tank, an alkali tank, and an electrical control system. Acid and alkali wastewater input pipelines are connected to the inlet of the nanofiltration desalination unit. The product water side of the nanofiltration desalination unit is connected in series with the nanofiltration or reverse osmosis membrane concentrate side of the pre-concentrator unit, the concentrated brine tank, and the concentrated brine inlet of the bipolar membrane / electrodialysis unit. The brine outlet pipeline of the bipolar membrane / electrodialysis unit is connected to the post-concentrator unit, and the concentrated brine outlet pipeline of the post-concentrator unit flows into the concentrated brine tank at the inlet of the bipolar membrane / electrodialysis unit. The product water pipeline of the pre-concentrator unit is connected to the second-stage high-pressure reverse osmosis membrane unit, the concentrate pipeline of the second-stage high-pressure reverse osmosis membrane unit flows back into the inlet pipeline of the pre-concentrator unit, and the product water pipeline of the second-stage high-pressure reverse osmosis membrane unit is connected to the freshwater reuse outlet. This device includes a nanofiltration desalination unit, a pre-concentrator unit, a post-concentrator unit, and a second-stage high-pressure reverse osmosis membrane unit. Each membrane filtration unit comprises a feed water pump (1), a security filter (2), a high-pressure pump (3), a circulation pump (5), a reverse osmosis membrane or nanofiltration membrane module (6), flow sensors (24, 26, 28, 29), pressure sensors (23, 25, 27), an energy storage tank assembly (4), and a pulse generation unit (8). The feed water pump (1), security filter (2), and high-pressure pump (3) are connected in series via pipelines. The outlet of the high-pressure pump (3) merges into the inlet header of the membrane system. The inlet of the reverse osmosis membrane or nanofiltration membrane module (6) is located on the concentrate side. The concentrate outlet of the membrane module (6) and the circulating pump (5) are connected by a pipeline to form a high-pressure circulation loop; the electrical control system is electrically connected to the feed pump (1), high-pressure pump (3), circulating pump (5), flow sensors (24, 26, 28, 29), and pressure sensors (23, 25, 27); the unit realizes the mutual conversion between the pressure energy of the working medium and the mechanical energy of the energy storage tank assembly (4); the pulse generation unit (8) stimulates the pulsation of the flow and pressure of the working medium; the energy storage tank assembly (4), the pulse generation unit (8) and the electrical control system are electrically connected; the circulating pump (5), the reverse osmosis membrane or nanofiltration membrane assembly (6) and the energy storage tank assembly (4) are connected by a high-pressure circulation pipeline; In this device, the outlet of any membrane filtration unit is connected to the inlet main pipe of the energy storage tank assembly (4) via a branch pipe; the outlet main pipe of the energy storage tank assembly (4) is connected to the concentrate side inlet of the reverse osmosis membrane or nanofiltration membrane assembly (6); the energy storage tank assembly (4) is composed of multiple energy storage tanks and their valves at both ends connected in parallel via pipelines; the energy storage tank assembly (4) is divided into an energy storage working group and an energy storage standby group, and the electrical control system switches the energy storage tank assembly (4) to participate in the system operation by changing the opening and closing status of the inlet and outlet valves of the energy storage tank; The energy storage tank in the energy storage tank assembly (4) consists of an end cap (9), a fixed perforated plate (10), a shell (11), a thin-walled energy storage tube (12), and a floating perforated plate (13). One end of the thin-walled energy storage tube (12) is connected to the fixed perforated plate (10), and the other end is connected to the floating perforated plate (13) to form an assembly. The assembly is fixed to the end cap (9) at one end of the shell (11) by the fixed perforated plate (10), and installed inside the shell (11) by the floating perforated plate (13). The other end of the shell (11) is fixed by the end cap (9). The thin-walled energy storage tube (12) is made of thin-walled seamless straight pipe or thin-walled corrugated steel pipe, and the material is corrosion-resistant. In any membrane filter unit of this device, the outlet of the security filter (2) is connected to the inlet of the pulse generating unit (8) via a branch pipe; the outlet of the pulse generating unit (8) is fed into the outlet main pipe of the energy storage tank assembly (4); the pulse generating unit (8) consists of an actuator (14), a piston rod (15), a cylinder (16), and a piston (17); one end of the piston rod (15) is connected to the actuator (14), and the other end is connected to the piston (17); the piston (17) is installed inside the cylinder (16); the actuator (14) is driven by the electronic control system to push the piston (17) to reciprocate inside the cylinder (16) via the piston rod (15).

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