JP2006289309A - Membrane breakage diagnostic method of membrane filter and its apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane breakage diagnostic method and apparatus of a membrane filter, in which the diagnostic of the membrane broken condition is easy to use and exact, and high in applicability even in case a shape of a hollow fiber membrane and a sealing volume sealing a pressurized gas are different without acquiring reference data in various conditions to judge the membrane breakage. <P>SOLUTION: In a method of diagnosing the membrane broken condition from the change with time of the pressure in a high-pressure space after sealing by introducing a pressurization gas inside the hollow fiber membrane, and stopping the introduction of the pressurization gas when the previously set pressure is attained to seal the pressurized side, the change with time in the pressure of the high-pressure space in case of assuming the broken condition of the hollow fiber membrane on trial is asked by a calculation, and the comparison of an actual measurement of the change with time in the pressure with the operational value produces the diagnosis of the broken condition of the hollow fiber membrane. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a membrane filtration device for treating surface water such as river water and lake water and groundwater with a microfiltration membrane or an ultrafiltration membrane using a hollow fiber membrane, and a membrane for diagnosing breakage of the hollow fiber membrane. The present invention relates to a damage diagnosis method and apparatus.

  The danger of Cryptosporidium, which is a chlorine-resistant protozoa, mixed in environmental water, which is raw water for tap water, has become a concern. Since the size of Cryptosporidium is about 3 to 5 μm, in order to remove Cryptosporidium of raw water, it is sufficient to completely remove larger fine particle components. Is shown to be less than 0.1. As a countermeasure against Cryptosporidium, an effective method compared with the conventional sand filtration method is a water purification method using a microfiltration membrane or an ultrafiltration membrane. In this method, the component larger than the membrane pore diameter is theoretically removed almost completely.

  However, when a part of the film is broken for some reason, leakage proceeds from that part, and fine particles (such as Cryptosporidium) may be mixed in the treated water. For this reason, in membrane processing, it is important to quickly detect and deal with membrane breakage. Currently, a method using air pressure is widely used as a method for detecting film breakage (see, for example, Patent Document 1).

  Patent Document 1 refers to the description of claim 1, “It is a membrane damage detection method for a hollow fiber membrane filtration device, in which water is applied to the outside of the hollow fiber membrane and pressurized air is introduced from the inside. Then, a fixed pressure injection time obtained from the relationship between the pressure injection time by pressurized air and the pressure change rate is set, and the inside is maintained in a pressurized state from the set time, and the pressure holding rate of the hollow fiber membrane is determined. Membrane damage detection of a hollow fiber membrane filtration device characterized by detecting the membrane damage of the hollow fiber membrane by determining the change over time and comparing the pressure retention rate of the normal state with the pressure retention rate of the state due to membrane damage Method. "

  That is, the method described in Patent Document 1 is a “method for obtaining the time-dependent change in the pressure retention rate of the hollow fiber membrane and detecting the presence or absence of membrane damage of the hollow fiber membrane from the comparison with the normal pressure retention rate”. is there.

  However, the method of Patent Document 1 has the following problems. That is, in the case of the method of Patent Document 1, in order to detect the presence or absence of film damage by comparing the pressure holding ratio in a state where the film is normal and the pressure holding ratio in a state where the film is damaged, It is necessary to acquire both data. In addition, in order to respond to a request for diagnosing a membrane breakage state such as the number of broken hollow fiber membranes and the diameter of a breakage hole, hollow fiber membranes having various breakage states with different membrane breakage states are prepared and used as a reference. You have to get a lot of data. Furthermore, when the shape of the hollow fiber membrane or the sealed volume filled with pressurized gas is different, it is necessary to acquire the reference data each time.

In particular, when the degree of contamination of raw water where there is a danger of Cryptosporidium or the like is high, diagnosis of the degree of membrane breakage is necessary even from a viewpoint of reducing the number concentration of Cryptosporidium, even when the pore diameter is small. Become. In response to such a request, it is extremely difficult to alarm the danger that the quality of the treated water by the membrane filtration apparatus will be abnormal depending on the method of Patent Document 1. To summarize the above problems, in the case of the conventional method,
1) It takes a lot of time and labor to acquire reference data for judging the film damage state.

2) There is no universality in the standard value for judging the film damage state.
JP 2000-342936 A

  The present invention has been made in view of the above-mentioned problems, and the object of the present invention is 1) without acquiring reference data under various conditions for judging film breakage, and 2) film breakage state. It is an object of the present invention to provide a membrane breakage diagnosis method and apparatus for a membrane filtration device that is simple, accurate and highly applicable even when the shape of the hollow fiber membrane and the sealed volume filled with pressurized gas are different.

  In order to solve the above-mentioned problems, the present invention introduces a pressurized gas into the inside of a hollow fiber membrane in a membrane filtration device having a hollow fiber membrane, and introduces the pressurized gas when a preset pressure is reached. In the method of diagnosing the membrane breakage state from the time-dependent change in pressure in the high-pressure space after stopping and sealing the pressure side, the time-dependent change in pressure in the high-pressure space when the breakage state of the hollow fiber membrane is assumed temporarily Is obtained by calculation, and the damage state of the hollow fiber membrane is diagnosed by comparing the measured value of the change with time of the pressure and the calculated value (invention of claim 1).

  As an embodiment of the invention of claim 1, the inventions of claims 2 to 4 below are preferable. That is, in the membrane breakage diagnosis method according to claim 1, it is assumed that the pressurized space including the inner space of the plurality of hollow fiber membranes is a high-pressure air reservoir, the hollow fiber membrane is assumed to be a circular tube, and Assuming that the membrane breakage hole is a nozzle provided in the high-pressure reservoir, and further assuming the hole diameter and number of the nozzle, and assuming the failure state of multiple types of hollow fiber membranes, the pressurized gas in the reservoir Based on the calculation model for the outflow from the nozzle, the time-dependent change in the enthalpy of the pressurized gas in the storage tank is calculated. On the other hand, the damage state of the hollow fiber membrane is diagnosed by calculating and comparing the calculated value and the actually measured value (invention of claim 2).

  Further, in the membrane breakage diagnosis method according to claim 2, the calculation of the change with time of the pressure P of the pressurized gas in the gas storage tank is performed based on the following formula (Equation 1) (Invention of claim 3). .

  In the equation (Equation 1), each symbol is as follows.

P: Pressure inside the storage tank at time [kg / m ² ]
P ₁ : External pressure at the nozzle outlet (hollow fiber membrane fracture) [kg / m ² ]
A ₁ : Nozzle cross-sectional area (hollow fiber membrane cross-sectional area) [m ² ]
V ₀ : Volume inside the storage tank [m ³ ], t: Time [sec]
d: Equivalent diameter of nozzle (hollow fiber membrane diameter) [m]
ι: Length of nozzle (length of hollow fiber membrane fracture) [m]
ζ ₁ : Loss coefficient at the nozzle inlet, ζ ₂ : Loss coefficient at the nozzle outlet
λ: Friction coefficient of nozzle flow path, κ: Specific heat ratio of gas (1.4 for air)
R: Gas constant of gas (in the case of air, 287 [m ² / s ² K]), T ₁ : Absolute temperature of gas
C: Constant determined when time t = 0 Further, in the method for diagnosing film breakage according to claim 3, the calculation model for the outflow of the pressurized gas in the storage tank from the nozzle is the compressed air in the storage tank. Two types of calculation models, the case where the air flows into the water environment outside the nozzle and the case where the pressurized air in the air storage tank flows out into the air environment outside the nozzle, and the inside of the air storage tank according to each model The time-dependent change of the pressure P of the pressurized air is calculated, and the actually measured value and the calculated value in any one of the environments are respectively compared (the invention of claim 4).

  According to the first to fourth aspects of the present invention, the film breakage state is determined by comparing and collating the time-dependent change in pressure in the high-pressure space estimated from various calculation results with the time-measured change in pressure in the high-pressure space. Therefore, it is not necessary to acquire reference data under various conditions necessary for determining the film breakage. Moreover, even if the shape of the hollow fiber membrane and the sealed volume in which the pressurized gas is enclosed are different, it can be easily applied. Furthermore, if an alarm is issued before the permissible limit of the membrane breakage state according to the required quality level of the raw water or the treated water, the membrane filtration apparatus can be appropriately and reasonably operated. Details will be described later.

  The invention of the film breakage diagnosis apparatus for carrying out the film breakage diagnosis method of claim 1 is preferably the invention of claim 5 below. That is, a pressurized gas supply device and a pressure regulator for introducing a pressurized gas into the hollow fiber membrane to obtain a preset pressure, a hollow fiber membrane inner pressure gauge for measuring the pressure and temperature inside and outside the hollow fiber membrane, A pressure gauge inside and outside the hollow fiber membrane is stored and stored in advance as a result of calculation of a temporal change in pressure in the high-pressure space in the case of assuming a broken state of the hollow fiber membrane. And a memory determination means having a function of determining the breakage state of the hollow fiber membrane by comparing with the actual measurement value of the invention (invention of claim 5).

  According to this invention, without obtaining reference data under various conditions for judging membrane breakage, even when the diagnosis of the membrane breakage state is different in the shape of the hollow fiber membrane and the sealed volume filled with pressurized gas A membrane breakage diagnosis method and apparatus for a membrane filtration device that is simple, accurate, and highly applicable can be provided. Therefore, the membrane breakage diagnosis method and apparatus according to the present invention is used as a more suitable maintenance management means, particularly from the viewpoint of stable water supply, even in medium and large-scale water purification facilities where introduction of membrane filtration devices is expected. it can.

  An embodiment of the present invention will be described below with reference to FIGS.

  FIG. 1 is a schematic configuration diagram of a membrane breakage diagnosis apparatus installed in a membrane filtration apparatus to which the present invention is applied. In FIG. 1, 1 is a pressurized gas supply device, 2 is a pressure regulator, 3 is a pressurized gas inlet valve, 4 is an air release valve, 5 is a hollow fiber membrane inner pressure gauge, 6 is a thermometer, and 7 is a membrane unit. , 8 is a hollow fiber membrane outer pressure gauge, 9 is a drain valve a, 10 is a drain valve b, 11 is a membrane breakage diagnosis means, 12 is a memory / determination circuit unit, 51 is raw water, 52 is raw water supply pump, 53 is filtration An inlet valve, 54 is a filtration outlet valve, 55 is membrane filtrate, 56 is a backwash pump, and 57 is a backwash water inlet valve. Also, the broken lines in FIG. 1 are signal lines that connect various devices and indicate the flow of signals.

  First, the flow of the filtration process and backwashing process of the membrane filtration apparatus shown in FIG. 1 will be described. In the filtration step, the raw water 51 is pumped to the membrane unit 7 via the filtration inlet valve 53 by the raw water supply pump 52 to generate the membrane filtered water 55, and this filtered water is supplied to the membrane filtration device via the filtration outlet valve 54. Drained outside. At this time, the other valves are closed. Further, in the backwashing process performed by intermittently stopping the filtration process, the membrane filtrate 55 is pumped to the membrane unit 7 via the backwash water inlet valve 57 by the backwash pump 56, and the backwash after membrane washing is performed. The washing waste water is drained to the outside of the membrane filtration device through the drain valve a9. At this time, the other valves are closed.

  Next, following the backwash process, the flow of performing a film breakage diagnosis using pressurized gas will be described. The backwash pump 56 is stopped, the backwash water inlet valve 57 and the drain valve a9 are closed, and the backwash process is completed. After completion of the backwashing process, the air release valve 4 and the drain valve a9 are opened, and the water inside the hollow fiber membrane in the membrane unit 7 is drained by a water head difference. Next, the air release valve 4 and the drain valve a9 are closed, and the drain valve b10 and the pressurized gas inlet valve 3 are opened. Here, the outside of the hollow fiber membrane is opened to atmospheric pressure. In this state, the pressurized gas output from the pressurized gas supply device 1 and brought to a predetermined pressure by the pressure regulator 2 is introduced from the inside of the hollow fiber membrane in the membrane unit 7.

  After the introduction of the pressurized gas, the water remaining inside the hollow fiber membrane and in the pores is pushed out to the outer diameter side of the hollow fiber membrane by the pressurized gas and drained from the drain valve b10. After the outflow of water from the drain valve b10 has ceased, the introduction of the pressurized gas from the pressurized gas supply device 1 is stopped and the pressurized gas inlet valve 3 is closed. The pressure measured by the meter 5, the pressure measured by the hollow fiber membrane outer pressure meter 8, and the pressure gas temperature measured by the thermometer 6 are measured by the membrane breakage diagnosis means 11 in real time (for example, a cycle of 1 second). The data is input to the internal storage / determination circuit unit 12. In this case, if the pressurized gas is air, for example, both the inside and the outside of the hollow fiber membrane are air. However, as described in Patent Document 1, if necessary, the compressed air is stored only inside and the outside is watered. It can also be configured to be an environment (water filled state).

Here, the pressure is converted into the absolute pressure ratio of both, and the temperature is converted into the absolute temperature and stored. On the other hand, in the memory / determination circuit unit 12, a predetermined time t in which the ratio between the absolute pressure P inside the hollow fiber membrane and the absolute pressure P ₁ outside the hollow fiber membrane becomes a predetermined value is set in advance. The area A ₁ of the breakage hole in the thread membrane breakage part, the volume V _{1 of the} high-pressure space calculated from the design drawing of the membrane filtration device in FIG. 1, the loss factor of the flow flowing out from the breakage hole, and the pressurized gas The data under various conditions calculated by the mathematical formula (Equation 1) according to claim 3 is stored in advance based on a constant determined by the type of pressure, an absolute temperature T ₁ of the pressurized gas, a constant C determined as time t = 0, and the like.・ Store it.

  Here, the memory / determination circuit unit 12 collates the time change data of the actually measured absolute pressure ratio with the time change data of various absolute pressure ratios obtained by calculation, and obtains the calculation result obtained in advance by the equation (1). Based on this, the area of the broken hole in the film under the matched or approximate condition is estimated, and the damaged state of the film is determined. Further, if the membrane breakage diagnosis means 11 has an abnormality determination function based on the estimated area of the membrane breakage hole, an alarm or an operation signal can be output to a higher-level control device when the membrane breaks down. After the diagnosis, the air release valve 4 is opened to release the pressure, and if there is no abnormality in the membrane, the process proceeds to the filtration process.

  Next, based on FIG. 2 and FIG. 3, an outline of the calculation model of Equation 1 and the mathematical expression induction process will be described. FIG. 2 is a conceptual diagram of a calculation model of the outflow of pressurized gas in the storage tank from the nozzle, and FIG. 3 is an image diagram of the change over time of the pressurized gas in the storage tank. FIG. 2 assumes that the pressurized space including the inner space of a plurality of hollow fiber membranes is a high pressure reservoir, the hollow fiber membrane is assumed to be a circular tube, and a membrane breakage hole is provided in the high pressure reservoir. FIG. 2 shows a part of the model when it is assumed that the nozzle is assumed to be the same as that described in the third aspect of the invention. Symbols not described above are as follows.

P ₀ : Pressure in the storage tank when time = 0 [kg / m ² ]
P _a : Pressure outside the nozzle [kg / m ² ]
ρ ₀ : Mass density [kgs ² / m ⁴ ] when the pressure in the storage tank P ₀
ρ ₁ : Mass density [kgs ² / m ⁴ ] at the nozzle outlet (hollow fiber membrane fracture) pressure P ₁
Q: Outflow flow rate from nozzle [m ³ / s]
u ₁ : Flow velocity at the nozzle outlet [m / s]
In the calculation model of FIG. 2, the enthalpy (thermal energy) of the gas in the storage tank is reduced by the enthalpy flowing out of the nozzle. Using this, by calculating the time-dependent change in the enthalpy of the gas in the storage tank in the above model, the result of deriving an arithmetic expression for obtaining the time-dependent change in the gas pressure in the storage tank is Equation 1. FIG. 3 schematically shows the relationship between the pressure P [kg / m ² ] in the storage tank and the time t (sec) in Equation 1.

In Equation 1, as is well known, the friction coefficient of the nozzle channel is λ = 64 / Re (Re: Reynolds number) when the pipe is in a laminar flow region, and λ = 0.316 ^{Re −.25 in} a turbulent flow ^region. Ask for. The above Re varies depending on the equivalent diameter of the nozzle (hollow fiber membrane diameter), the gas flow velocity and the kinematic viscosity coefficient.

  By the way, Equation 1 has two types of calculations: the case where the pressurized gas in the storage tank flows out into the water environment outside the nozzle and the case where the pressurized gas in the storage tank flows out into the air environment outside the nozzle. This is a general formula common to the model, but the formula for determining the specifications such as the dimensions of the hollow fiber membrane and the constants such as the loss factor, and letting the pressurized gas flow into the water environment as air (temperature 10 ° C) An example of the derived result is shown in the following formula 2.

  Similarly, an example of a result of deriving an arithmetic expression when the pressurized gas is air (temperature: 10 ° C.) and flows out into the air environment is as shown in the following equation (3).

Next, an embodiment will be described with reference to FIG. FIG. 4 shows the result of comparative verification of the reliability of the result of calculation and estimation based on the present invention by attaching a broken membrane element obtained by cutting one hollow fiber membrane to a real scale membrane filtration device. For reference, the calculation results in the case of cutting two hollow fiber membranes and a broken hole diameter of 1.5 mm and the actual measurement values in a normal membrane are also shown. In FIG. 4, the change in pressure with time is shown by the pressure ratio inside and outside the hollow fiber membrane. Here, the membrane used is 6000 hollow fiber membranes having an inner diameter of 1.5 mm and a membrane area of 40 m ² . The pressurized gas and the external environment were air, and the initial pressure was 50 kPa. From FIG. 4, it can be seen that the calculated value (dotted line connecting ▲ in FIG. 4) and the measured value (solid line in FIG. 2) agree well. As a result, it was confirmed that the calculation result according to the present invention is highly reliable and practical.

The typical block diagram of the membrane breakage diagnosis apparatus installed in the membrane filtration apparatus which concerns on this invention. The conceptual diagram of the outflow calculation model from the nozzle of the pressurized gas in a storage tank concerning embodiment of this invention. The image figure of a time-dependent change of the pressurized gas in a storage tank concerning embodiment of this invention. The figure which shows the result of having compared the result of calculation estimation based on this invention, and the measured value.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pressurized gas supply apparatus 2 Pressure regulator 3 Pressurized gas inlet valve 4 Atmospheric release valve 5 Hollow fiber membrane inner pressure gauge 6 Thermometer 7 Membrane unit 8 Hollow fiber membrane outer pressure gauge 9 Drain valve a
10 Drain valve b
DESCRIPTION OF SYMBOLS 11 Membrane breakage diagnostic means 12 Memory | storage / judgment circuit part 51 Raw water 52 Raw water supply pump 53 Filtration inlet valve 54 Filtration outlet valve 55 Membrane filtration water 56 Backwash pump 57 Backwash water inlet valve

Claims (5)

A pressurized gas is introduced into the inside of the hollow fiber membrane in the membrane filtration device having a hollow fiber membrane, and when the preset pressure is reached, the introduction of the pressurized gas is stopped and the pressurized side is sealed, In the method of diagnosing a membrane failure state from a change in pressure over time in a high-pressure space, when the failure state of the hollow fiber membrane is assumed, the change over time in the pressure in the high-pressure space is obtained by calculation, and the change over time in the pressure is measured. A membrane breakage diagnosis method for a membrane filtration device, wherein a breakage state of the hollow fiber membrane is diagnosed by comparing a value with the calculated value. 2. The membrane breakage diagnosis method according to claim 1, wherein a pressurized space including an inner space of a plurality of hollow fiber membranes is assumed to be a high-pressure air reservoir, a hollow fiber membrane is assumed to be a circular pipe, and a membrane breakage hole is assumed. Assuming that the nozzle is provided in the high-pressure reservoir, further assuming the hole diameter and number of the nozzle, and assuming the state of damage of a plurality of types of hollow fiber membranes, from the pressurized gas nozzle in the reservoir Based on the outflow calculation model, calculate the change in enthalpy of the pressurized gas in the storage tank over time, and calculate the change in the pressure of the pressurized gas in the storage tank over time for the multiple types of damage states. The membrane breakage diagnosis method for a membrane filtration device is characterized by diagnosing the breakage state of the hollow fiber membrane by comparing the calculated value and the actual measurement value. 3. The membrane failure diagnosis method according to claim 2, wherein the calculation of the change over time of the pressure P of the pressurized gas in the storage tank is performed based on the following mathematical formula (Equation 1). Damage diagnosis method.

In the above formula, each symbol is as follows.
P: Pressure inside the storage tank at time [kg / m ² ]
P ₁ : External pressure at the nozzle outlet (hollow fiber membrane fracture) [kg / m ² ]
A ₁ : Nozzle cross-sectional area (hollow fiber membrane cross-sectional area) [m ² ]
V ₀ : Volume inside the storage tank [m ³ ], t: Time [sec]
d: Equivalent diameter of nozzle (hollow fiber membrane diameter) [m]
ι: Length of nozzle (length of hollow fiber membrane fracture) [m]
ζ ₁ : Loss coefficient at the nozzle inlet, ζ ₂ : Loss coefficient at the nozzle outlet
λ: Friction coefficient of nozzle flow path, κ: Specific heat ratio of gas (1.4 for air)
R: Gas constant of gas (in the case of air, 287 [m ² / s ² K]), T ₁ : Absolute temperature of gas
C: Constant determined when time t = 0 4. The method for diagnosing a membrane failure according to claim 3, wherein the model for calculating the flow of pressurized gas in the storage tank from the nozzle includes a case where the pressurized air in the storage tank flows into the water environment outside the nozzle, Two types of calculation models for the case where the pressurized air in the air tank flows into the air environment outside the nozzle, and the time-dependent calculation of the pressure P of the pressurized air in the air storage tank is performed according to each model, A membrane breakage diagnosis method for a membrane filtration device, wherein the measured value and the calculated value in any one of the environments are respectively compared. A device for carrying out the membrane breakage diagnosis method for a membrane filtration device according to claim 1, wherein a pressurized gas supply device for introducing a pressurized gas inside the hollow fiber membrane to obtain a preset pressure and pressure adjustment A pressure gauge in the high-pressure space in the case of assuming a damaged state of the hollow fiber membrane, a hollow fiber membrane inner pressure gauge, a hollow fiber membrane outer pressure gauge and a thermometer for measuring pressure and temperature inside and outside the hollow fiber membrane. Storing and storing in advance the results obtained by calculating the change over time, and storing determination means having a function of determining the breakage state of the hollow fiber membrane by comparing the measured values of the pressure inside and outside the hollow fiber membrane A membrane breakage diagnosis device for membrane filtration devices.

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