JP2017029935A - Membrane separation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a membrane separation apparatus equipped with an air diffuser capable of uniformly cleaning a membrane element.SOLUTION: A membrane separation apparatus 100 for filtering a liquid to be treated to obtain a treated liquid comprises: a membrane element 4 for filtering the liquid to be treated with film-like filtration membranes for filtering the liquid to be treated to obtain the treated liquid, which is provided with the filtration membranes in a state forming a pair of extending surfaces facing each other to form an outline; a membrane module 5 which is provided with the plurality of membrane elements 4 arranged horizontally with a space of an intermembrane passage in a state where the extending surfaces of the membrane element 4 are along the vertical direction; a membrane separation tank 3 provided with the membrane module 5 therein; and air diffusing pipes 1, 2, 3 having aeration holes for aerating the liquid to be treated in the intermembrane passage. The axes of the diffusing pipes 1, 2, 3 intersect the extending direction of the membrane element 4 in a top view, and the diffusing pipes 1, 2, 3 are configured in a loop shape.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a membrane separation apparatus.

  Patent Document 1 discloses a membrane separation apparatus for obtaining a treatment liquid by subjecting a treatment liquid to a filtration process, in which a pair of flat membrane-like filtration membranes that filter the treatment liquid form an outer shell facing each other. A membrane element for obtaining the treatment liquid by filtering the liquid to be treated with the filtration membrane, and an extension surface of the membrane element along the vertical direction. A membrane module in which a plurality of the membrane elements are provided in a horizontal direction with a gap between the membrane channels, a membrane separation tank in which the membrane module is disposed, and the treatment of the membrane channels A membrane separation device is described in which an air diffuser tube in which air diffused holes are formed and the axis of the air diffuser tube is arranged to intersect the extending direction of the membrane element in a top view. .

JP 2013-158664 A

  With respect to the technique described in Patent Document 1, it is desired that air diffusion be performed sufficiently uniformly. The present invention has been made in view of such problems, and the problem to be solved by the present invention is to provide a membrane separation apparatus including a diffuser capable of uniformly cleaning a membrane element. That is.

  As a result of intensive studies to solve the above problems, the present inventors have arranged a diffuser tube in a direction crossing the extending direction of the membrane element, and forming the arranged diffuser tube in a loop shape. It has been found that the above problems can be solved.

  ADVANTAGE OF THE INVENTION According to this invention, a membrane separator provided with the diffuser which can perform the washing | cleaning of a membrane element uniformly can be provided.

It is a perspective view of a membrane separation unit. It is a perspective view of the membrane module which comprises a membrane separation unit. It is a perspective view of the membrane module which attaches a membrane element. It is a top view of an air diffusion pipe provided with an air supply pipe and a moisture pipe which constitutes an air diffusion apparatus attached to the lower part of a membrane separation unit, (a) and (b) are an example, (c) and (d ) Is a comparative example. It is a conceptual diagram which shows the flow of water and a bubble in the membrane separator provided with the membrane separation unit. It is a figure which shows the form of the aeration apparatus used by simulation. It is a figure explaining the simulation model of the membrane separator used by simulation. It is a figure explaining the diffuser tube used for simulation. It is a graph explaining the flow rate required for the film | membrane surface washing | cleaning obtained by simulation. It is a graph explaining the dispersion | variation in the flow velocity obtained by simulation. It is a graph explaining the shear force required for the membrane surface washing | cleaning obtained by the measurement (experimental value) in an actual membrane separator. It is a graph explaining the dispersion | variation in the shear force obtained by the measurement (experimental value) in an actual membrane separator. It is a figure explaining the flow rate required for the film | membrane surface washing | cleaning obtained by experiment. It is a figure explaining the flow velocity distribution of the diffuser used for simulation. It is a graph which compares the discharge pressure of the bubble generate | occur | produced from the diffuser hole of the diffuser tube obtained by simulation. It is a figure explaining the structure of the experimental apparatus which measures the discharge pressure of a diffuser. It is a figure explaining the position of the diffused hole which measured the discharge pressure. It is a figure explaining the nozzle part flow rate ratio of the diffused hole in a gaseous phase in each diffused hole. It is a figure explaining the nozzle part flow rate ratio of the diffused hole in a liquid phase in each diffused hole. It is a graph which compares the flow velocity of a gaseous phase and a liquid phase obtained by experiment using the experimental apparatus shown in FIG.

  Hereinafter, a form for carrying out the present invention (this embodiment) will be described with reference to the drawings as appropriate.

  FIG. 1 is a perspective view of the membrane separation unit 10. In this embodiment, the membrane separation unit 10 is used in a membrane separation activated sludge method (MBR) for solid-liquid separation. And the membrane separation apparatus 100 (refer FIG. 5) provided with the membrane separation unit 10 filters the to-be-processed water (to-be-processed liquid), and obtains a process liquid. The membrane separation unit 10 includes a membrane module 5 that separates clarified water by filtering water to be treated, and an air diffuser 8 that is provided below the module and discharges bubbles. Although not shown in FIG. 1, the membrane separation unit 10 is provided with a filtration pump 12 and a pipe 2 (both see FIG. 5) for filtering and sucking water to be treated.

  FIG. 2 is a perspective view of the membrane module 5 constituting the membrane separation unit 10. The membrane module 5 is configured by arranging a plurality of membrane elements 4 vertically. The membrane element 4 is provided so as to form a pair of extending surfaces that form an outer shell with a membrane-like filtration membrane that filters the water to be treated (treatment liquid) facing each other. It is for obtaining filtration treated water (treatment liquid) by filtration with the filtration membrane. Therefore, the membrane module 5 is configured such that a plurality of membrane elements 4 are arranged in the horizontal direction with a gap between the membrane channels so that the extending surface of the membrane element 4 is along the vertical direction. The

  FIG. 3 is a perspective view of the membrane module 5 to which the membrane element 4 is attached. The membrane module 5 is formed by mounting an assembly of a plurality of membrane elements 4 on a casing 7.

  FIG. 4 is a top view of the air diffuser 8 including an air supply pipe and a moisture pipe (both not shown in FIG. 4) that constitute the air diffuser 8 attached to the lower part of the membrane separation unit 10. (A) and (b) are examples, and (c) and (d) are comparative examples. In FIG. 4, the membrane element 4 arranged so as to intersect (perpendicular in the present embodiment) with respect to the axial direction of the diffuser tubes 1, 2, and 3 constituting the diffuser device 8 as viewed from above It is indicated by a virtual line.

  As shown in FIG. 4A, the air diffuser 8 has a header pipe 15 (upstream header pipe) connected to an air supply pipe 14 (gas supply port) not shown in FIG. Header pipes 17 (connected to three diffuser pipes 1, 2, 3 (connecting pipes) connected in parallel and the diffuser pipes 1, 2, 3 connected to a normally-closed moisture pipe 16 ( Downstream header pipe). In other words, the header pipe 15 and the header pipe 16 are communicated with each other by the diffuser pipes 1, 2 and 3 laid in parallel. In the air diffuser 8, a loop is formed by the header pipe 15, the air diffusers 1, 2, 3 and the header pipe 17. In other words, the air diffuser 8 includes a loop of the air diffuser 1, the header pipe 17, the air diffuser 3 and the header pipe 15, and the air diffuser 2 which bypasses the loop.

  Here, conventionally, as shown in FIG. 4 (c) and FIG. 4 (d), no loop is formed, and the air supplied from the air supply pipe 14 branches once and flows through the connection pipe. Then they will not merge. Therefore, after air is introduced into the diffuser tubes 1, 2, 3 through the header tube 15, among the diffuser holes formed in the diffuser tubes 1, 2, 3, a large amount of air is diffused from the diffuser holes on the front side. On the other hand, there is little air diffused from the back side air holes. For this reason, uneven air diffusion occurs, and the membrane element cannot be uniformly cleaned.

  However, since the loop is formed as shown in FIG. 4A, in the air diffuser 8, each air diffuser 1, 1 in the header pipe 17 on the back side as viewed from the air supply pipe 14 to which air is supplied. The air that is not diffused in 2 and 3 is merged, and an appropriate air pressure is maintained as a whole. Therefore, uniform aeration is possible in the entire diffusion tubes 1, 2, and 3. In addition, since uniform air diffusion is possible, in the past, air was allowed to flow more than the calculation amount in order to perform reliable air diffusion throughout the entire area. Even in the whole area, uniform aeration is possible.

  Further, although the end 15a of the header pipe 15 and the end 17a of the header pipe 17 are both sealed, both of them are designed to protrude slightly outside the diffuser pipes 1 and 3. Is formed. Therefore, the air flowing through the header pipe 15 flows through the diffuser pipes 1, 2, 3 through the inside of the end portion 15 a of the header pipe 15. For this reason, the air flowing through the header pipe 15 causes an appropriate pressure loss due to the end portion 15a, thereby preventing the air from flowing through the diffuser pipe 2 at a stretch. , 3 can be supplied with sufficient air. As a result, uniform air diffusion over the entire area of the air diffusion tubes 1, 2, 3 can be achieved more reliably.

  Further, among the tubes constituting the air diffuser 8, air diffusers 1 x, 2 x, 3 x are formed in the air diffusers 1, 2, 3 arranged below the membrane element 4. On the other hand, no air diffusion holes are formed in the header pipes 15 and 17 arranged in a direction parallel to the extending direction of the membrane element 4. That is, in the present embodiment, the air holes are formed only in the air pipes 1, 2, 3, and are not formed in the header pipes 15, 17. And the diffuser hole formed in the diffuser tubes 1, 2, 3 is formed at equal intervals in each of the diffuser tubes 1, 2, 3. For these reasons, a uniform amount of air is uniformly diffused to the membrane element 4 from the air holes 1x, 2x, 3x formed in the air diffusers 1, 2, 3 respectively.

  In addition, as shown in FIG.4 (b), the said loop may be comprised including the diffuser tube in which the diffuser hole is not formed in the outer shell.

  FIG. 5 is a conceptual diagram showing the flow of water and bubbles in the membrane separation apparatus 100 including the membrane separation unit 10. In FIG. 5, each member is shown in a simplified manner for simplification of illustration. In FIG. 5, the membrane separation apparatus 100 is configured by stacking the three-stage membrane modules 5. The membrane separation device 100 is a membrane separation activated sludge device, and the membrane separation unit 10 is immersed in a tank 3 (membrane separation tank) into which raw water (treated liquid) such as sludge flows. Then, solid-liquid separation is performed by filtration operation, and water to be treated is taken out from the membrane separation device 100.

  The air bubbles 11 are generated from the air diffuser 8 and the air bubbles 11 stay and float in the inter-membrane water channel formed between the membrane elements 4 and 4 (not shown in FIG. 5), thereby being in a gas-liquid mixed phase state. Due to the density difference between the inside of the water channel and the outside in a single phase state, as shown in FIG. 5, the gas-liquid mixed phase fluid in the water channel rises and the liquid phase circulates. This is a phenomenon generally called an air lift. On the other hand, the filtered water to be treated which has been absorbed by the membrane element 4 rises inside the membrane element 4 by the suction force used as a drive source for the treated water suction device (pump) 12 and is discharged to the outside.

  Here, the non-uniformity of air diffusion, which is a problem of the conventional membrane separation apparatus (see Patent Document 1), will be described.

  As shown in FIG. 5, after the air is diffused from the air diffuser 8, the bubbles 11 are ejected all at once to the upper region of the air diffuser 8 and rise. At this time, the liquid phase is also sucked in here. For this reason, the gas-liquid two-phase flow rises in the intermembrane flow path and reaches the upper part of the membrane separation unit 10, and then the bubbles 11 are released from the free surface (that is, the water surface) of the upper region to the atmosphere. .

  On the other hand, the liquid (liquid to be treated) descends in the region between the membrane module 5 and the inner wall of the tank 3 due to the gravitational energy and the suction effect in the vicinity of the air diffuser 8. Then, the air is sucked in again from the vicinity of the air diffuser 8 and rises again in the intermembrane flow path to form a circulation flow. The driving force that forms this circulating flow is approximately the density of the fluid in the region where the gas-liquid two-phase flow rises, and the fluid density (liquid density) of the single-phase flow region such as the downflow portion. The difference.

  The shear stress acting on the membrane surface, which is generated by the gas-liquid two-phase flow in the intermembrane channel formed in this way, continuously peels off the contaminants attached to the membrane surface by filtration and recovers it by washing. Efficient membrane filtration operation becomes possible. The enhancement of the membrane surface cleaning effect can be achieved by increasing the shear stress by generating a high-speed two-phase flow by increasing the amount of air diffused.

  However, simply increasing the amount of diffused air increases the diffused power and is costly. Further, while the void ratio represents a dimensionless driving force, if it becomes too high, speed slip occurs and a high flow rate cannot be given. In addition, increasing the amount of air diffusion causes the compressibility of the gas-liquid two-phase flow in the intermembrane flow path, causing vibrations and stresses in the membrane element, and adverse effects such as deformation and destruction of the element. Such a phenomenon is more likely to occur due to the difference in compressibility between the flow paths, particularly when the bubbles entering the intermembrane flow path are uneven.

  In the diffuser pipes 1, 2, and 3 (see FIG. 4 (d)) arranged in parallel to the membrane element 4 (crossed over the header pipes 15 and 17), bubbles discharged from the diffuser holes are formed on the upper part of the diffuser pipe. In order to concentrate, it is designed with an excessive amount of air diffused to distribute the bubbles to the membrane element 4 away from the air diffuser. Furthermore, depending on the type of MBR, there are cases where the membrane module 5 is installed in multiple stages for the purpose of improving the efficiency of air diffusion, and the membrane module 5 installed in the upper stage is subject to a greater air gap than the lower stage. Further stress concentration is added. For this reason, the bubbles concentrate on the intermembrane flow path in the upper part of the air diffuser 8, whereby stress concentrates on the membrane element 4, leading to non-uniform cleaning of the membrane element 4.

Therefore, in this embodiment, the air diffuser has an efficient air diffuser structure in which the air diffuser can be reduced more than before by reducing the air diffuser in excess and deficiency. A diffuser 8 that does not occur is being considered.
Hereinafter, the structure of the air diffuser 8 was examined in more detail by performing simulations and experiments.

  FIG. 6 is a diagram showing a configuration of the air diffuser 8 used in the simulation. FIGS. 6A to 6D are diagrams showing the relationship of arrangement of the diffuser tubes 1a, 1b, 1c, and 1d and the membrane element 4 in the diffuser 8 respectively. This simulation was based on computational fluid dynamics (CFD). In the simulation, a diffuser structure in which one diffuser tube (diffuser tube 1a) is arranged in parallel to the membrane element 4 (Case 1 in FIG. 6A) and a plurality of diffuser tubes are arranged orthogonally (FIG. 6B). ) To (d) Cases 2 to 4). As the Case number increases, the number of diffusers also increases. Specifically, the diffuser tubes 1b, 1c are used in Case 2, the diffuser tubes 1b, 1c, 1d are used in Case 3, and the diffuser tubes 1b, 1c, 1d, 1e are used in Case 4. On the other hand, if the number of diffuser tubes increases, the amount of ventilation per one decreases, so the diffuser pitch is also shortened. The width in the longitudinal direction of the membrane element 4 is 484 mm, and the thickness when the membrane elements 4 are arranged to face each other is 165 mm.

  Among these, particularly as shown in FIG. 6 (d), the diffused holes are widely and two-dimensionally distributed with respect to the entire intermembrane flow path projection plane region (projection plane of the membrane element 4), thereby It is possible to evenly distribute bubbles to a specific flow path that enters and rises into the intermembrane flow path. Therefore, based on the result of FIG. 6, it is considered that the number of diffuser tubes is preferably about 3 or more.

  FIG. 7 is a diagram illustrating a simulation model of the membrane separation apparatus 100 used in the simulation. That is, FIG. 7 shows the examination conditions for the diffuse structure by CFD. In this CFD study, commercially available calculation software ANSYS FULL is used, a discrete particle model (hereinafter referred to as “DPM”) is used as a multiphase flow model, and a standard k-ε model is used as a turbulent flow model.

  FIG. 8 is a diagram for explaining the diffusing tubes 1, 2, and 3 used in the simulation. As shown in FIG. 8, the air diffusion hole diameter in the structural schematic diagram used for the simulation is 4 mm, and the membrane module 5 is constituted by three air diffusion tubes 1, 2, and 3. Each diffusing tube was provided with 51 diffusing holes in a staggered pattern in two rows. Further, the pipe lengths of the header pipes 15 and 17 having no air diffusion holes are longer than the arrangement width of the three air diffusion pipes 1, 2, and 3, so that the end portions 15 a and 17 a are provided on the header pipes 15 and 17. Formed.

Hereinafter, a specific method of simulation will be described.
In the calculation of the discharge state of the diffuser tube by CFD, the discharge speed from all the diffuser holes was obtained, and the variation from the overall average value was evaluated. The variation was evaluated by the Cv value with respect to the overall average value obtained from the discharge speeds of all the air holes. The Cv value used for evaluation was determined by the following formula (1). Here, N is the number of diffused holes, V _i is the discharge speed of each diffused hole, and V _avg is the average value of the entire discharge speed. A commercially available general-purpose fluid calculation code ANSYS-FLUENT was used for the calculation.

  The standard k-ε model was adopted as the turbulent flow model in this calculation. Since the evaluation in the gas phase is a calculation of a single phase flow only in the gas phase, steady calculation was performed by a normal Euler method. Here, since there is no steady calculation solver in FLUENT, the time point at which the flow velocity has stopped changing at one point in the diffuser tube is considered to have reached the steady solution, and the profile of the time is adopted as the steady solution. In the evaluation in the liquid phase, the fluid phase outside the diffuser tube shown in FIG. 8 is defined as the liquid phase in the initial state, and the unsteady calculation of the gas-liquid two-phase flow for discharging the gas phase from the diffuser holes is performed. It was.

  In the calculation of gas-liquid two-phase flow, since the calculation load is very high, data at 2 seconds when the flow velocity and pressure in the diffuser tube are considered to have developed sufficiently was adopted as data for evaluation. In both the calculation of the gas phase and the gas-liquid two-phase flow, the supply surface of the diffuser pipe (the boundary between the air supply pipe 14 and the header pipe 15 in FIG. 8) is defined as the inlet boundary condition, and from this boundary surface The gas phase is supplied at a constant flow rate. Therefore, the gas phase inside the diffuser pipe is also calculated. In the evaluation in the gas phase, the gas phase inside and outside the diffuser pipe is calculated. In the liquid phase evaluation, the gas phase inside the diffuser pipe is calculated. Calculation of gas-liquid two-phase flow.

  In the liquid phase evaluation, a gas-liquid two-phase flow calculation method (multiphase flow calculation model) in the region outside the diffuser was used. The VOF method (Volume of Fluid method) was used for the gas-liquid two-phase flow calculation in this region. In this calculation, VOF was used as a method for visualizing the gas-liquid interface by resolving the bubbles with a mesh, in addition to evaluating the discharge speed from the air holes, and confirming the expansion of the bubbles after discharge by visualization. .

The VOF model is a surface tracking technique applied to a fixed Euler mesh. As a result, the calculation is performed for two or more types of non-mixed fluids whose boundary positions between the fluids are noted. In the VOF model, a set of equations of motion is shared by each fluid, and the volume fraction of each fluid in each computation cell is tracked over the entire region. Therefore, although it is a multiphase flow, it is a one-fluid model, so that the equation of motion as one kind of fluid phase is solved. This equation of motion is expressed by the following equation (2).

Further, the physical property values such as the density ρ and the viscosity coefficient μ are obtained by using the volume fraction α _q of each fluid phase in each calculation cell as shown in the following equations (3) and (4). Given by weighting.

In equations (3) and (4), the subscript _q of α _q represents the distinction of multiphase fluids. In the case of gas-liquid two-phase flow as in this calculation, the subscript order is 2. For example, the subscript 1 represents the liquid phase, and the subscript 2 represents the gas phase. In this case, when α ₁ is zero in a certain cell, it represents that all the cells are occupied by the gas phase. Similarly, with respect to the equation of conservation of mass, a set of the following equations (5) is solved in the same way as the equation of momentum, and at the same time, the sum of the volume fractions of all the fluid phases becomes 1. The transport equation (the following equation (6)) is solved.

  FIG. 9 is a graph for explaining a flow rate necessary for film surface cleaning obtained by simulation. In FIG. 9, the average value of the transmembrane average flow velocity obtained from the CFD result (hereinafter referred to as “average ascending flow velocity”) and the average value of the descending flow portion flow velocity (hereinafter simply referred to as “downflow portion flow velocity”). )It is shown. FIG. 10 is a graph for explaining the variation in the flow velocity obtained by the simulation. FIG. 10 shows the Cv value (variation).

  As shown in FIG. 9, the average flow velocity tended to increase as the number of air diffusers 1a, 1b, 1c, and 1d increased, with a slight increase and decrease. In addition, as shown in FIG. 10, when the diffusing tubes 1a, 1b, 1c, and 1d were one parallel (Case 1), the variation in the average flow velocity of the intermembrane flow path was large. The reason for this is that in Case 1, the void ratio, which is a dimensionless driving force, varies, so the average flow velocity is considered to be lower than when there are a plurality of diffuser tubes.

  FIG. 11 is a graph for explaining the shear force required for membrane surface cleaning obtained by measurement in an actual membrane separation apparatus. FIG. 12 is a graph for explaining the variation in shearing force obtained by measurement in an actual membrane separation apparatus. These graphs are different from the results of FIGS. 9 and 10 described above, and are the measurement results in the actual membrane separation apparatus 100.

  As shown in FIG. 11, in the case of one diffuser tube (Case 1), the shear stress of the central membrane surface (the membrane surfaces of No. 4 to No. 6 membrane elements 4 of the nine membrane elements 4) is Large and the shear stress of the film surface at both ends is small. In addition, as shown in FIG. 12, in the case of one diffuser tube (Case 1), the shear stress variation on each film surface is large (Cv value: 0.15 to 0.25), but perpendicular to the film surface. When a plurality of the diffuser tubes are arranged (Case 2 to 4), the variation is reduced as a whole (Cv value: about 0.05). There was no significant difference between three or more diffusers (Cases 3 to 4).

  FIG. 13 is a diagram for explaining the flow rate necessary for the membrane surface cleaning obtained by the experiment. FIG. 13 shows the variation among the 10 average ascending flow rates and the descending flow portion flow rates, and the 10 inter-membrane average flow velocities by the experiment. As with the CFD result (see FIG. 9), both the average ascending flow velocity and the descending flow velocity are the maximum in Case 3 (three orthogonal diffuser tubes), and are slightly higher than in Case 4 (four orthogonal diffuser tubes). The result is very high. The same applies to the downflow portion flow velocity, and a circulation flow rate in the tank equal to or higher than Case 1 is obtained.

  Regarding the average ascending flow velocity and descending flow velocity, the flow rate in the case of three diffuser tubes (Case 3) is slightly higher than that in the case of four diffuser tubes (Case 4), because the number of diffuser tubes is large. It is considered that the driving force decreases because the fluid resistance of the trachea installation part increases and a circulating flow is generated. Therefore, it can be seen that it is particularly preferable that the number of diffuser tubes in which diffused holes are formed be three.

  From the above, it can be seen that it is preferable to arrange the three air diffusing tubes so as to intersect the membrane element 4 and to form a loop. The reason is as follows. That is, when air is diffused from the air diffuser, variation occurs in ejection from the air diffuser. Therefore, suppressing such variations is preferable for uniform cleaning of the membrane element 4. Therefore, in the membrane separation apparatus 100, as described with reference to FIGS. 4A and 4B, the air diffuser is configured in a loop shape. In this way, a circulation flow is formed, and the pressure gradient in the loop-shaped air diffuser is reduced, so that air is evenly diffused from the air diffuser and air bubbles are evenly distributed to the intermembrane flow path. Can be given. According to this, an effective transmembrane cleaning is achieved by giving a transmembrane ascending flow velocity necessary for the membrane cleaning between the membranes, and evenly distributing the bubbles discharged from the air diffusing pipes to the channels between the membranes. I can expect.

  FIG. 14 is a diagram for explaining the flow velocity distribution of the air diffuser used in the simulation. The direction and length of the arrow shown in FIG. 14 indicate the air flow direction and the flow strength from that point. In the central air diffuser 2, the discharge amount from the air diffuser near the air supply pipe 14 tends to be slightly larger than the other air diffuser at any location. However, by providing the end portion 14a at the end of the header pipe 15 to which the air supply pipe 14 is connected, an increase in the discharge amount from the air diffusion holes close to the air supply pipe 14 is suppressed.

  FIG. 15 is a graph comparing the discharge speeds of bubbles generated from the diffuser holes of the diffuser tubes 1, 2, and 3 obtained by simulation. The horizontal axis is the position of the air diffuser hole, and the right end is the air diffuser hole disposed at the position closest to the air supply pipe 14. As shown in FIG. 15, the variation in the discharge speed due to the amount of air diffused is small. In particular, the diffusers 1 and 3 had almost no variation. Moreover, when Cv value was calculated by said Formula (1) and the dispersion | variation was evaluated, it was Cv = 0.0044 on the conditions of the rated amount of diffused air. It can be seen from the result of the equation (1) that the variation is sufficiently small, and the difference in the discharge amount is considered not to have a great influence on the performance.

  From these results, it can be expected that the bubbles are evenly distributed to the intermembrane flow path. Moreover, since a high flow rate can be obtained even if the amount of air diffused is lowered, operation is possible with the amount of air diffused lowered.

  Next, an actual experiment was performed to measure the discharge pressure of the diffuser.

  FIG. 16 is a diagram illustrating the configuration of an experimental apparatus that measures the discharge pressure of the air diffusing tube. In this experiment, the full-scale air diffuser 8 described in FIG. 8 was immersed in the experimental water tank 20, and air was supplied to the air diffuser 8 from the air cylinder 21. The flow rate of the supplied air was made constant by the flow meter 22. Furthermore, the compound pressure gauge 23 was connected to the air diffuser hole 8a (hole diameter 4 mm) of the air diffuser 8 with a tube (not shown). And when the air was diffused from the diffuser 8, the discharge pressure in the diffuser hole 8a was measured, and the discharge state from the diffuser hole 8a was evaluated.

  FIG. 17 is a diagram for explaining the positions of the air holes in which the discharge pressure is measured. In this measurement, the measurement was performed by selecting a specific air hole instead of measuring all the air holes shown in FIG. The three air diffusers are arranged in parallel with the header pipe 17 together with the header pipe 15 to which the air supply pipe 14 is connected, thereby forming a loop. Therefore, assuming that the air flow in the air diffuser is axisymmetric with respect to the air diffuser 2, the central air diffuser 2 of the three and one air diffuser 1 on one side are selected as measurement targets. . Then, the air diffuser holes 1x and 2A close to the air supply pipe 14, the furthest air diffuser holes 1C and 2C, and the air diffuser holes 1B and 2B at the center thereof were measured.

  FIG. 18 is a diagram for explaining the nozzle portion flow rate ratio of the diffused holes in the gas phase in the diffused holes 1A, 2A, 1B, 2B, 1C, and 2C. As shown in FIG. 18, if the positions of the diffuser holes (that is, the measurement points) are the same, the same nozzle part flow rate ratio is shown even if the discharge speed is different. For example, at the measurement point 1A, the nozzle part flow rate ratio tends to be small at any discharge speed, but at the measurement point 2C, the nozzle part flow rate ratio tends to be large at any discharge speed.

  FIG. 19 is a diagram for explaining the nozzle flow rate ratio of the diffused holes in the liquid phase in the diffused holes 1A, 2A, 1B, 2B, 1C, and 2C. As shown in FIG. 19, the discharge speed tends to be uniform under the condition that the liquid phase head is added to the diffuser hole as resistance, and the influence of the discharge state due to the position of the diffuser hole is small from the result in the liquid phase.

FIG. 20 is a graph comparing the flow rates of the gas phase and the liquid phase obtained by an experiment using the experimental apparatus shown in FIG. Here, it is assumed that the resistance coefficient related to the discharge from each of the diffuser holes is the same with respect to the discharge pressures of the six diffuser holes 1A, 2A, 1B, 2B, 1C, and 2C, and calculated from the Darcy-Weissbach relational expression. The nozzle flow rate ratio corresponding to the discharge speed is shown. Specifically, using each discharge pressure P obtained from the measurement and the average value P ₀ of the discharge pressure at the six air diffusers, the flow velocity ratio with respect to the average nozzle velocity and flow velocity is obtained from the following relational expression. It was.

  And about the calculated flow velocity ratio, the dispersion | variation (Cv value) of the nozzle flow velocity ratio was computed using said Formula (1). The result is shown in FIG. As shown in FIG. 20, in the gas phase, the smaller the amount of air diffused, the greater the variation. That is, if air is diffused into the air from the air diffuser holes, it can be seen that the variation increases depending on the amount of air diffused. On the other hand, it is understood that when performing aeration in the liquid phase that is an actual operation state, the variation becomes small regardless of the amount of the aeration air. This tendency is considered that the resistance at the outlet of the air diffuser becomes higher than that in the gas phase, so that the indentation pressure becomes higher and the inside of the air diffuser tube is relatively close to the pressure equalization state. Therefore, according to the air diffusing device 8, variations can be suppressed regardless of the amount of air diffused, and stable air can be diffused.

  In the above example, the field of solid-liquid separation in flat membrane filtration separation was mentioned, but the present invention relates to all solid-liquid separation using a flat membrane membrane element, and also serves as a biological treatment using activated sludge. The present invention can also be applied to the field of film processing.

  In the above example, the number of diffuser pipes (connection pipes) connecting the header pipe 15 (upstream header pipe) and the header pipe 17 (downstream header pipe) is two (FIG. 6B), There are three (Fig. 4 (a), Fig. 6 (c)), four (Fig. 6 (d)), and five (Fig. 4 (b)), but the number of diffusing tubes is six or more. Also good.

1, 2, 3, 1a, 1b, 1c, 1d Air diffusers 1A, 2A, 1B, 2B, 1C, 2C, 1x, 2x, 3x Air diffuser 3 Tank 4 Membrane element 5 Membrane module 8 Air diffuser 10 Membrane separation unit 14 Air supply pipe 15 Header pipe 17 Header pipe

Claims (3)

A membrane separation apparatus for obtaining a treatment liquid by subjecting a liquid to be treated to filtration,
A membrane-like filtration membrane for filtering the liquid to be treated is provided in a state of forming a pair of extended surfaces that form an outer shell facing each other, and the liquid to be treated is filtered by the filtration membrane and A membrane element for obtaining a treatment liquid;
A membrane module in which a plurality of the membrane elements are arranged in a horizontal direction with gaps between the membrane channels, in a state where the extending surface of the membrane element is along the vertical direction,
A membrane separation tank having the membrane module therein;
An air diffusion tube having air diffusion holes for air diffusion into the liquid to be treated in the intermembrane flow path;
The axis of the air diffuser has a state of crossing the extending direction of the membrane element in a top view,
The membrane separator is characterized in that the air diffuser is configured in a loop shape. The air diffuser is
A gas supply port for supplying a gas flowing through the inside of the air diffuser to the air diffuser;
An upstream header pipe in which the gas supply port is formed;
A connecting pipe in which the air diffusion holes are formed;
A downstream header pipe for joining the gas flowing through the connection pipe,
The membrane separator according to claim 1, wherein the upstream header pipe and the downstream header pipe are connected via at least two of the connection pipes and configured in a loop shape. In the air diffuser,
The upstream header pipe and the connection pipe are connected so that the end of the upstream header pipe protrudes outside the connection pipe connected to the upstream header pipe,
The gas flowing through the upstream header pipe flows through the connection pipe via the inside of the end portion of the upstream header pipe. Membrane separator.

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