Immersed membrane separation system and immersed membrane separation method

Abstract

Provided are an immersed membrane separation system and a separation method. The separation system includes a membrane pool, a membrane assembly, and a water outlet trough, wherein the upper edge of the water outlet trough is on the same horizontal plane as the upper edge of the membrane pool. The membrane assembly is installed inside the membrane pool and immersed in the water to be filtered in the membrane pool. The water collection pipe of the membrane assembly is connected to the water outlet trough and its port is located below the minimum allowable water level of the water outlet trough. The membrane assembly is not directly connected to the water pump. Under normal working conditions, the system maintains a constant external water supply to the water outlet trough and is lower than the injection flow rate of the water inlet pipe (101) of the membrane pool (1), so that the water level of the membrane pool is constant, while the water level of the water outlet trough changes in real time with the filtration process and is self-regulated.

Description

Technical Field

[0001] The present invention generally relates to an immersed membrane separation system and an immersed membrane separation method, which belong to the field of membrane separation and can be used for purification of various waters as well as other liquids (such as wine, beverages, etc.). Background Art

[0002] In water treatment and other fields, filtration is often required to remove suspended solid impurities from liquids. Membrane separation is a highly efficient and precise method that has gained widespread application in recent years. After membrane separation, suspended impurities in the liquid are removed, resulting in a clear and transparent liquid. The membrane separation process applies a pressure differential across a porous membrane, pushing the liquid through the membrane from one side to the other, while the suspended impurities are retained.

[0003] Membrane separation processes are categorized into two types based on their operation: immersed membrane separation and pressure membrane separation. In the immersed membrane separation process, the membrane assembly is submerged in the liquid to be purified. The suction of a suction pump creates negative pressure on one side of the membrane, thereby achieving membrane separation. In the pressure membrane separation process, the liquid to be purified is first pressurized by a pump, and the pressurized liquid flows through the membrane, thereby achieving membrane separation.

[0004] The immersed membrane separation process is gaining increasing popularity due to its simple structure and ease of large-scale expansion. During the membrane separation process, trapped impurities accumulate on the feed-side surface (or upstream surface) of the membrane, creating resistance to the membrane separation process. This makes the membrane separation process complex and variable: as the amount of liquid passing through the membrane increases, more and more impurities accumulate on the membrane surface, the membrane resistance also increases, and the membrane separation process becomes increasingly difficult. This creates a problem in the membrane separation process: in the early stages of the membrane separation process, the outflow rate of the membrane is very high, but then the outflow rate gradually decreases, resulting in a rapid decline in the efficiency of the membrane.

[0005] In order to maximize the efficiency of the filter membrane and maximize its output within a cycle (the time period available for production between two adjacent cleaning operations), it is usually necessary to control the outflow rate of the filter membrane to maintain it at a roughly constant level (the so-called constant-rate filtration). This requires real-time adjustment of the pressure difference applied to both sides of the filter membrane according to the resistance of the filter membrane, so that the pressure difference on both sides of the filter membrane and the resistance of the filter membrane are always kept in balance.

[0006] To achieve this goal, the current market often uses variable frequency speed control on the filtrate suction pump. Automated instrumentation monitors the filtrate flow rate and pressure upstream and downstream of the membrane in real time. These signals are input into a programmable controller (PLC). Using a specific algorithm, the inverter's output frequency is altered, thereby changing the speed of the suction pump's drive motor. While this automated control method can generally achieve the desired control objectives of membrane separation processes, it suffers from drawbacks such as the large amount of equipment required, high investment, complex management and maintenance, and low reliability. Furthermore, due to the limitations of the inverter and algorithm, it is impossible to truly balance the pressure differential across the membrane with the membrane's resistance in real time. Summary of the Invention

[0007] The present invention has been made in view of the above circumstances.

[0008] According to one aspect of the present invention, an immersed membrane separation system is provided, comprising a membrane pool, a membrane assembly and a water outlet trough, wherein the upper edge of the water outlet trough is on the same horizontal plane as the upper edge of the membrane pool, the membrane assembly is installed inside the membrane pool and immersed in the water to be filtered in the membrane pool, the water collection pipe of the membrane assembly leads to the water outlet trough and its port is located below the minimum allowable water level of the water outlet trough, and the membrane assembly is not directly connected to the water pump.

[0009] Optionally, in the immersed membrane separation system, under normal working conditions, the external water supply of the water outlet tank is kept constant and less than or equal to the injection flow of the water inlet pipe (101) of the membrane pool (1), so that the water level of the membrane pool remains constant, while the water level of the water outlet tank changes in real time with the filtration process.

[0010] Optionally, in the immersed membrane separation system, when the water level in the outlet tank (3) drops to a preset minimum level, the water inlet pipe of the membrane pool is closed, the current filtration cycle is ended, and the cleaning process of the filter membrane is started.

[0011] Optionally, in the submerged membrane separation system, the submerged membrane separation system performs the following membrane separation method:

[0012] (1) Preparatory stage: First, the water inlet pipe (101) of the membrane pool (1) is opened to inject water into the membrane pool at a certain flow rate. The water level in the membrane pool (1) rises and submerges the highest point of the water collection pipe (201) of the membrane assembly (2). Water begins to pass through the filter membrane of the membrane assembly (2) and flows to the water outlet trough (3) through the water collection pipe (201), thereby causing the water level in the water outlet trough (3) to rise. At this time, the water outlet of the water outlet trough (3) is closed. The water level in the water outlet trough (3) will continue to rise until it reaches the same height as the water level in the membrane pool (1). The pressure difference between the upstream and downstream sides of the filter membrane of the membrane assembly (2) disappears, and the filtration process is temporarily terminated.

[0013] (2) Open the outlet of the water outlet trough (3) to maintain a constant external water supply flow rate and equal to or lower than the injection flow rate of the water inlet pipe (101) of the membrane pool (1); thereby keeping the water level in the membrane pool (1) constant. The highest water level of the membrane pool is determined by the overflow port height of the overflow pipe (102) of the membrane pool (1) and always submerges the membrane assembly (2); the water level of the water outlet trough (3) slowly decreases as the water continues to flow, thereby forming a static pressure difference on the water level of the membrane pool (1);

[0014] (3) When the water level in the outlet tank 3 drops to the minimum level allowed, close the water inlet pipe of the membrane pool and the water outlet pipe of the outlet tank, ending the current filtration cycle.

[0015] Optionally, the immersed membrane separation system starts a membrane cleaning process after step (3), and after the cleaning process, returns to step (1) and circulates the above process.

[0016] Optionally, under normal working conditions, the water level of the membrane pool (1) remains constant and always submerges the membrane assembly (2).

[0017] Optionally, in the immersed membrane separation system, the water level in the outlet tank changes in real time with the filtration process and self-regulates as follows:

[0018] As the outlet trough (3) starts to supply water, the water level in the outlet trough (3) drops; as the water level in the outlet trough (3) drops, the pressure difference between the upstream and downstream sides of the filter membrane also increases, and the water flow rate passing through the membrane assembly (2) also increases accordingly, until the flow rate is the same as the flow rate of the outlet pipe (301) of the membrane pool (3), and the water level in the outlet trough (3) stops dropping; then the filtration process continues, the outlet pipe (301) of the outlet trough (3) and the outlet pump (301a) maintain a constant water flow rate, and the cumulative amount of water passing through the filter membrane of the membrane assembly (2) also increases accordingly. The suspended impurities trapped on the upstream surface of the filter membrane accumulate, and the resistance of the filter membrane to the water flow continues to increase, which has a tendency to cause the water flow rate passing through the filter membrane to decrease; when the filtration flow rate of the filter membrane decreases, the water level in the outlet trough (3) decreases, thereby correspondingly increasing the pressure difference between the upstream and downstream sides of the filter membrane, and the increase in the pressure difference compensates for the increase in the resistance of the filter membrane. Therefore, at every moment, the increase in the resistance of the filter membrane caused by the accumulation of impurities on the filter membrane surface is just compensated by the increase in the water level difference between the upstream and downstream sides of the filter membrane caused by the drop in the water level in the outlet trough (3).

[0019] According to another aspect of the present invention, an immersion membrane separation method using the above-mentioned immersion membrane separation system comprises:

[0020] (1) Preparatory stage: Open the water inlet pipe (101) of the membrane pool (1) to inject water into the membrane pool at a certain flow rate. The water level in the membrane pool (1) rises and submerges the highest point of the water collection pipe (201) of the membrane assembly (2). Water begins to pass through the filter membrane of the membrane assembly (2) and flows to the water outlet tank through the water collection pipe (201).

[0021] (3), thereby causing the water level in the outlet tank (3) to rise; closing the outlet pipe (301) and the outlet pump (301a) of the outlet tank (3) so that water is temporarily not supplied to the outside, when the water level in the outlet tank (3) continues to rise until it reaches the same level as the water level in the membrane pool (1), the pressure difference between the upstream and downstream sides of the filter membrane of the membrane assembly (2) disappears, and the filtration process is temporarily terminated;

[0022] (2) The outlet pipe (301) and the outlet pump (301a) of the outlet trough (3) are opened to maintain a constant external water supply flow rate and to be lower than the injection flow rate of the water inlet pipe (101) of the membrane pool (1), thereby keeping the water level in the membrane pool (1) constant. The highest point of the water level is determined by the overflow port height of the overflow pipe (102) of the membrane pool (1) and always submerges the membrane assembly (2); and the water level of the outlet trough changes in real time with the filtration process and is automatically adjusted.

[0023] Optionally, in the immersed membrane separation method, when the water level in the outlet tank (3) drops to a minimum threshold level, the water inlet pipe of the membrane pool and the water outlet pipe of the outlet tank are closed, the current filtration cycle is ended, and the cleaning process of the filter membrane is started.

[0024] Optionally, the submerged membrane separation method returns to step (1) after the cleaning process and circulates the above process.

[0025] The submerged membrane separation system and separation method according to embodiments of the present invention enable simple, reliable, efficient, and cost-effective submerged membrane separation. The pressure differential across the membrane is consistently balanced with the membrane resistance, optimizing the submerged membrane separation process and simplifying operational management. Furthermore, since the membrane assembly is no longer directly connected to the pump, the threat of water hammer to the membrane assembly caused by sudden pump startup and shutdown is avoided. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will be described below in conjunction with specific embodiments with reference to the accompanying drawings, in which:

[0027] Figure 1 Schematic diagram of the structure of an immersed membrane separation system according to an embodiment of the present invention.

[0028] Description of reference numerals:

[0029] 1 membrane pool, 101 membrane pool inlet pipe, 102 membrane pool overflow pipe, 103 membrane pool emptying pipe, 103a membrane pool emptying valve; 2 membrane assembly, 201 water collection pipe; 3 outlet tank, 301 outlet pipe, 301a outlet pump DETAILED DESCRIPTION

[0030] The present invention will be described below in conjunction with specific embodiments with reference to the accompanying drawings.

[0031] Figure 1 Schematic diagram of the structure of an immersed membrane separation system according to an embodiment of the present invention.

[0032] like Figure 1 As shown, the immersed membrane separation system according to an embodiment of the present invention includes a membrane pool 1, a membrane assembly 2 and a water outlet tank 3.

[0033] The top edge of the outlet trough 3 is on the same horizontal plane as the top edge of the membrane tank 1. The membrane assembly 2 is installed within the membrane tank 1 and submerged in the water to be filtered. The water collection pipe 201 of the membrane assembly 2 flows into the outlet trough 3, and its port is located below the minimum allowable water level of the outlet trough 3. Unlike traditional methods that use a filtrate suction pump to control the pressure differential across the membrane assembly, in this embodiment, the membrane assembly 2 is not directly connected to the water pump.

[0034] In the example shown in the figure, the membrane pool 1 also has an inlet pipe 101 for replenishing the water to be filtered, an overflow pipe 102 for preventing the overflow of the water to be filtered, and an emptying pipe 103, on which an emptying valve 103a is provided; the outlet tank 3 is equipped with an outlet pipe 301 and an outlet pump 301a for sending water outward.

[0035] The upper edges of the membrane pool 1 and the water outlet trough 3 are at the same horizontal plane in order to prevent overflow caused by rising water level in the water outlet trough 3 when the water outlet trough 3 stops supplying water to the outside.

[0036] In the immersed membrane separation system of this embodiment, under normal working conditions, the external water supply of the water outlet tank is controlled to be constant and lower than the injection flow of the water inlet pipe (101) of the membrane pool (1). By utilizing the siphon principle of hydraulics, the water level of the membrane pool is constant, while the water level of the water outlet tank changes in real time with the filtration process and is self-regulated.

[0037] The working principle and control process of the submerged membrane separation system of this embodiment are introduced below.

[0038] According to one embodiment of the present invention, the control process of the submerged membrane separation system is as follows:

[0039] (1) Preparatory stage: First, the water inlet pipe (101) of the membrane pool (1) is opened to inject water into the membrane pool at a certain flow rate. The water level in the membrane pool (1) rises and submerges the highest point of the water collection pipe (201) of the membrane assembly (2). Water begins to pass through the filter membrane of the membrane assembly (2) and flows to the water outlet trough (3) through the water collection pipe (201), thereby causing the water level in the water outlet trough (3) to rise. In the preparatory stage, the water outlet of the water outlet trough (3) is closed. The water level in the water outlet trough (3) will continue to rise until it reaches the same level as the water level in the membrane pool (1). The pressure difference between the upstream and downstream sides of the filter membrane of the membrane assembly (2) disappears, and the filtration process is temporarily terminated.

[0040] (2) opening the outlet of the water outlet trough (3) so as to maintain a constant external water supply flow rate and be equal to or lower than the injection flow rate of the water inlet pipe (101) of the membrane pool (1); thereby maintaining the water level in the membrane pool (1) constant, the highest value of which is determined by the overflow port height of the overflow pipe (102) of the membrane pool (1), and always submerging the membrane assembly (2); the water level of the water outlet trough (3) slowly decreases as the water continues to flow, thereby forming a static pressure difference on the water level of the membrane pool (1), wherein the water level of the water outlet trough changes in real time with the filtration process and is self-regulated;

[0041] (3) When the water level in the outlet tank 3 drops to the minimum level allowed, close the water inlet pipe of the membrane pool and the water outlet pipe of the outlet tank, ending the current filtration cycle.

[0042] Typically, during normal filtration of the system, after step (3), the membrane cleaning process is started, and after the cleaning process, the process returns to step (1) and the above process is cyclically executed.

[0043] The process in which the water level of the outlet tank in the above step (2) changes in real time with the filtration process and self-regulates is as follows:

[0044] As the water outlet trough (3) starts to supply water, the water level in the water outlet trough (3) drops; as the water level in the water outlet trough (3) drops, the pressure difference between the upstream and downstream sides of the filter membrane also increases, and the water flow rate through the membrane assembly (2) also increases accordingly, until its flow rate is the same as the flow rate of the water outlet pipe (301) of the membrane pool (3), and the water level in the water outlet trough (3) stops dropping; then the filtration process continues, the water outlet pipe (301) of the water outlet trough (3) and the water outlet pump (301a) maintain a constant water flow rate, and the cumulative amount of water passing through the filter membrane of the membrane assembly (2) also increases accordingly , the suspended impurities trapped on the upstream surface of the filter membrane accumulate, and the resistance of the filter membrane to the water flow continues to increase, which leads to a decrease in the water flow through the filter membrane; when the filtration flow of the filter membrane decreases, the water level in the outlet trough (3) decreases, thereby correspondingly increasing the pressure difference between the upstream and downstream sides of the filter membrane. The increase in the pressure difference compensates for the increase in the resistance of the filter membrane, so that at every moment, the increase in the resistance of the filter membrane caused by the accumulation of impurities on the filter membrane surface is just compensated by the increase in the water level difference between the upstream and downstream sides of the filter membrane caused by the drop in the water level in the outlet trough (3). Moreover, this adjustment process is real-time and continuous. In other words, at every moment, the increase in the resistance of the filter membrane caused by the accumulation of impurities on the filter membrane surface is just compensated by the increase in the water level difference between the upstream and downstream sides of the filter membrane caused by the drop in the water level in the outlet trough 3.

[0045] The above-described control of the immersed membrane filtration process can be achieved entirely through hydraulic principles, without the need for external forces or automated instrumentation. This also applies to the temporary termination of the filtration process. For example, if the outlet pipe 301 of the outlet tank 3 or the external water pump 301a suddenly stops operating due to a malfunction or power outage, the filtration process will also be stopped immediately without the need for external forces or manual intervention.

[0046] The immersed membrane filtration system of the embodiment of the present invention is a purely hydraulic immersed membrane filtration system, which has at least the following advantages:

[0047] (1) The control of the filtration process does not rely on mechanical or electronic devices, which significantly improves system reliability;

[0048] (2) Maintain the dynamic balance between the resistance of the filter membrane and the transmembrane pressure difference in real time to truly achieve ideal constant-speed filtration;

[0049] (3) The membrane assembly is not directly connected to the water pump, which completely avoids possible damage to the membrane assembly caused by water hammer or human operating errors.

[0050] While various embodiments of the present invention have been described above, the foregoing description is intended to be illustrative, non-exhaustive, and not limiting of the disclosed embodiments. Numerous modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. Therefore, the scope of the present invention shall be determined by the scope of the claims.

Claims

1. An immersed membrane separation method utilizing an immersed membrane separation system, the immersed membrane separation system comprising a membrane pool, a membrane assembly, and a water outlet trough, wherein the upper edge of the water outlet trough is coplanar with the upper edge of the membrane pool; the membrane assembly is mounted within the membrane pool and submerged in water to be filtered within the membrane pool; a water collection pipe of the membrane assembly leads to the water outlet trough, and its port is located below the minimum allowable water level of the water outlet trough; the membrane assembly is not directly connected to a water pump; and an overflow pipe is also provided on the membrane pool; The submerged membrane separation method comprises: (1) Preparatory stage: the water inlet pipe (101) of the membrane pool (1) is opened to inject water into the membrane pool at a certain flow rate, the water level in the membrane pool (1) rises and submerges the highest point of the water collection pipe (201) of the membrane assembly (2), water begins to pass through the filter membrane of the membrane assembly (2) and flows to the water outlet trough (3) through the water collection pipe (201), thereby causing the water level in the water outlet trough (3) to rise; the water outlet pipe (301) and the water outlet pump (301a) of the water outlet trough (3) are closed so that water is temporarily not supplied to the outside, the water level in the water outlet trough (3) will continue to rise until it reaches the same level as the water level in the membrane pool (1), the pressure difference between the upstream and downstream sides of the filter membrane of the membrane assembly (2) disappears, and the filtration process is temporarily terminated; (2) opening the outlet pipe (301) and the outlet pump (301a) of the outlet tank (3) to maintain a constant external water flow rate and to be lower than the injection flow rate of the water inlet pipe (101) of the membrane pool (1), thereby keeping the water level in the membrane pool (1) constant and always submerging the membrane assembly (2); and the water level of the outlet tank (3) changes in real time with the filtration process and is automatically adjusted; When the water level in the outlet tank (3) drops to a preset minimum level, the water inlet pipe of the membrane pool and the water outlet pipe of the outlet tank are closed, the current filtration cycle is ended, and the membrane cleaning process is started; After the cleaning process, return to step (1) and repeat the above process in a loop; The process in which the water level of the outlet tank (3) changes in real time with the filtration process and is automatically adjusted is as follows: As the outlet trough (3) starts to supply water, the water level in the outlet trough (3) drops; as the water level in the outlet trough (3) drops, the pressure difference between the upstream and downstream sides of the filter membrane also increases, and the water flow rate passing through the membrane assembly (2) also increases accordingly, until the flow rate is the same as the flow rate of the outlet pipe (301) of the outlet trough (3), and the water level in the outlet trough (3) stops dropping; then the filtration process continues, the outlet pipe (301) of the outlet trough (3) and the outlet pump (301a) maintain a constant water flow rate, and the cumulative amount of water passing through the filter membrane of the membrane assembly (2) also increases accordingly. The suspended impurities trapped on the upstream surface of the filter membrane accumulate, and the resistance of the filter membrane to the water flow continues to increase, which has a tendency to cause the water flow rate passing through the filter membrane to decrease; when the filtration flow rate of the filter membrane decreases, the water level in the outlet trough (3) decreases, thereby correspondingly increasing the pressure difference between the upstream and downstream sides of the filter membrane, and the increase in the pressure difference compensates for the increase in the resistance of the filter membrane. Therefore, at every moment, the increase in the resistance of the filter membrane caused by the accumulation of impurities on the filter membrane surface is just compensated by the increase in the water level difference between the upstream and downstream sides of the filter membrane caused by the drop in the water level in the outlet trough (3).

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