JP2862945B2 - Membrane separation method and apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method and an apparatus for membrane separation. More specifically, a method and an apparatus for obtaining clear treated water by removing impurities by so-called circulation through water having relatively low membrane fouling having a water temperature fluctuation over time, and The present invention relates to a device capable of obtaining a stable permeated water amount at low cost.

2. Description of the Related Art A method of removing impurities in water using a membrane is widely known. If a membrane to be used is appropriately selected, a relatively large size of impurities such as removal of suspended particles can be removed to remove dissolved salts. It is also known that it can be applied to the removal of a wide range of impurities, up to the removal of impurities of very small size such as removal.

There are two types of membrane separation: the so-called excess system and the circulation system.The former is a system in which the entire amount of water to be treated is removed through a membrane to remove impurities as slag. Through a membrane to separate treated water and impurity-enriched water. In general, the latter has the advantage that the flow velocity parallel to the membrane surface due to the circulating flow prevents the accumulation of impurities near or on the membrane surface, and the over-resistance is less increased with time than the former. Is widely used.

When performing circulation excess, in addition to positive pressure (operating pressure) as excess driving force,
It is necessary to give a flow velocity parallel to the film surface (film surface flow speed). In order to apply operating pressure, the water to be treated is fed into the membrane device using a supply pump, but the temperature of the water inside the pump is prevented from rising due to water remaining in the pump, or the number of revolutions of the supply pump is kept constant. In some cases, the water to be treated is partially returned from the supply pump outlet side to the supply pump inlet side so that the operating pressure can be appropriately adjusted while maintaining the same. Further, in order to provide a membrane surface flow rate, a circulation system including a circulation pump and a membrane device is formed, and the membrane surface flow rate is controlled by adjusting the rotation speed of the circulation pump or a circulation valve provided in the circulation system. Although a single pump can be used for both the supply pump and the circulation pump, it is difficult to independently control the operating pressure and the membrane surface flow rate.

In the case of carrying out a membrane filtration of a circulation type on an industrial scale, a membrane module incorporating a membrane as an element is used. In general, the processing capacity of an apparatus is determined by the amount of permeated water per membrane module and the number of membrane modules. However, the permeated water amount per membrane module varies depending on the properties of the water to be treated and operating conditions. It is necessary to calculate the number of membrane modules based on the minimum permeated water volume, or to temporarily receive unprocessed water in an auxiliary tank to absorb fluctuations in permeated water volume, or to process with a separately provided membrane module auxiliary machine There is a need. For this reason, the cost of the apparatus is increased, and when the apparatus must be installed in a limited space, it may be extremely inconvenient in design.

Therefore, it is extremely advantageous if the amount of permeated water can be controlled to be constant, and in that case, conventionally,
By continuously measuring the amount of permeated water and controlling operating conditions such as operating pressure, membrane surface flow velocity, and water temperature in accordance with the fluctuation, the amount of permeated water has been maintained to be constant.

As described above, the conventional method directly measures the permeated water amount to be controlled and adjusts the water temperature and the circulation flow rate in accordance with the fluctuation, thereby performing feedback control of the permeated water amount. However, when the fluctuation of the permeated water amount is fed back to the temperature of the water to be treated and the operating conditions, there is a disadvantage that the control is likely to be unstable due to amplification of measurement noise and delay of response.

In addition, a device that outputs a water amount fluctuation as a signal has conventionally lacked compactness, and was not preferable from a space-saving viewpoint.

Further, in the past, steam injection was used as a means for raising the water temperature when the temperature of the water dropped, but this has the disadvantage that the equipment becomes large-scale.

Means for Solving the Problems In the present invention, instead of using the variation of the permeated water amount as an input parameter, the stability of the permeated water amount control is improved by measuring the temperature of the circulating water and using the variation as an input parameter. In addition, since the device for outputting the water temperature fluctuation as a signal is relatively compact, the space of the entire device can be saved.

In one preferred aspect of the present invention, there is provided an apparatus for adjusting a membrane surface flow velocity according to a water temperature fluctuation, thereby controlling the amount of permeated water to be constant.

In another preferred aspect of the present invention, there is provided an apparatus for adjusting a membrane surface flow rate and an operating pressure in accordance with a water temperature fluctuation, thereby controlling the amount of permeated water to be constant.

In still another preferred aspect of the present invention, there is provided an apparatus for performing heat exchange between treated water and treated water in order to increase the temperature of the treated water having a low temperature.

Action Since water temperature affects the viscosity of water, it is generally one of the factors that determine overresistance. In addition, the amount of impurities accumulated near or on the film surface is generally one of the factors that determine the overresistance. And when the present inventors circulate through the water to be treated that does not cause large membrane contamination, the overresistance is basically determined by the water temperature and the membrane surface flow rate, and keeps the permeated water amount constant under a constant operating pressure. It has been found that the relationship between the water temperature and the membrane surface flow rate is kept almost constant for a considerable period of time.

Therefore, if the relationship between the water temperature and the membrane surface flow rate for obtaining a desired permeate flow rate at a predetermined operating pressure is first determined, then the water temperature fluctuation is measured by measuring the water temperature and adjusting the membrane surface flow rate. Therefore, the amount of permeated water can be kept constant even when the occurrence occurs. Of course, in the long term, the relationship between the water temperature and the membrane surface flow rate may change due to membrane contamination or the like. Therefore, it is preferable to examine this relationship at an appropriate time and correct it if necessary.

Instead of keeping the operating pressure constant, the flow rate of the permeated water can be controlled to be constant by simultaneously adjusting the membrane surface flow rate and the operating pressure. If the temperature of the water to be treated fluctuates greatly,
This method is effective.

Furthermore, when the temperature of the water to be treated fluctuates greatly, it is also effective to perform heat exchange between the water to be treated and the treated water.
Generally, the temperature of treated water is often higher than the temperature of the treated water. Therefore, heat exchange is performed to raise the temperature of the treated water, reduce the viscosity, and obtain the membrane flow rate and operating pressure required to obtain a predetermined amount of permeated water. Can also be reduced.

Alternatively, when the membrane surface flow rate is constant, the overresistance is determined substantially only by the water temperature, so that the permeation flow rate can be estimated from the measurement of the water temperature, and by increasing or decreasing the number of membrane modules to be used accordingly, the constant resistance is obtained. A throughput can also be obtained.

Example Hereinafter, a more specific description will be given with reference to the drawings.

 FIG. 1 shows one embodiment of the device of the present invention.

The water to be treated once flows into the adjusting tank 1 and is supplied to the membrane device 10 via the supply pump 2 and the circulation pump 5. Membrane device 10
When passing through the inside under pressure, some water permeates the membrane and is taken out as treated water. A part of the water to be treated that has passed through the membrane device without passing through the membrane is returned to the regulating tank through the return valve 14 for pressure adjustment, and most of the remaining water is passed through the circulation pipe to the inlet side of the circulation pump. Circulated to

The circulation pump 5 and the membrane device 10 constitute a pressurized circulation system together with the associated pipeline, and the inside of the pressurized circulation system is adjusted to a predetermined operating pressure by the supply pump 2 and the return valve 14. If the relatively small membrane permeation flow rate C is neglected, the membrane flow velocity in the membrane device is the sum of the circulation flow rate A and the return flow rate B. However, since the return flow rate is generally smaller than the circulation flow rate, the membrane flow rate is lower. It can be said that the flow velocity is largely determined by the circulation flow rate. In particular, when the operating pressure is kept constant, the return flow rate is substantially constant because the rotation speed of the supply pump and the opening of the return valve are constant, and the adjustment of the membrane surface flow rate is performed by the circulation flow rate (that is, the rotation speed of the circulation pump). Can be performed only by the adjustment. However, when adjusting the membrane surface flow rate and the operating pressure simultaneously,
Since the return flow fluctuates due to the adjustment of the operation pressure, it is necessary to adjust the circulation flow in consideration of the fluctuation of the return flow.

Means 8 for measuring the water temperature of the circulating water is provided in the pipeline constituting the pressurized circulation system, and the measured water temperature data is sent to the data processing device 7. The data processing device calculates a required membrane surface flow velocity from the water temperature data, and adjusts the rotation speed of the circulation pump 5 via the circulation pump control device 6 so that a predetermined membrane surface flow velocity can be obtained.

As the water temperature measuring means 8, various types of a type capable of converting a measured water temperature into an electric signal and inputting the electric signal to a data processing device are used.

As the data processing device 7, any device that can process input data such as water temperature according to predetermined conditions and send a control signal to a control device of the circulation pump as appropriate may be used, and a so-called personal computer can be used. .

Various devices are known as the control device 6 for the circulating pump, but a device for controlling the inverter of the induction motor is preferable from the viewpoint of energy saving.

FIG. 2 shows a flow sheet of the apparatus for performing heat exchange. In this case, the water to be treated flows into the regulating tank 1 after passing through the heat exchanger 13 provided in the middle of the treated water pipe.

The relationship between the permeated water amount and the water temperature and the membrane surface flow velocity or the operating pressure needs to be input in advance to the data processing device. For this purpose, the permeated water amount (processing amount) can be measured by the integrating flow meter 12. it can.

FIGS. 1 and 2 also show a flow meter 3 for feed water, a flow meter 11 for circulating water, and pressure gauges 4 and 9.

The following shows the results of membrane separation using the apparatus shown in FIG. 1 and treating wastewater discharged from a tunnel as water to be treated.

Table 1 shows the specifications of the main equipment of the device, and Table 2 shows the properties of the tunnel drainage.

Table 1 Table 1) Adjustment tank 1000 × 1800 × 1500 (mm) Effective volume 2.2m ³ 2) Membrane device Membrane type Internal pressure hollow fiber type organic ultra-super membrane Membrane material Polysulfone Nominal molecular weight cut-off 7000 Membrane area 5m ² / group Casing 100mmφ × 1000mm 3) Supply pump Maximum flow rate 10 liters / min Maximum head 30m Motor output 2.2kw 4) Circulation pump Maximum flow 50m ³ / hour Maximum head 30m Motor output 5.5kw Table 2 Tunnel drainage water quality BOD 5-20mg / 1 SS 5 to 40 mg / 1 [Relationship between flux and water temperature and membrane surface flow rate] The operating pressure is kept constant at 0.9 kg / cm ^2, and flux F [m ³ / m ² · day] and water temperature T [° C.] are set in advance. And the relationship with the membrane surface flow velocity V [m / sec] was determined and arranged by the following equation.

F = a.T + b.V + c (a, b, and c are constants) Under constant conditions of circulating water temperature T = 18 ° C., membrane flow rate V = 1 to 4 m
The flux F was measured in the range of / sec. Table 3 shows the results.

From the above results, the following relationship was obtained: F = 0.304V + 0.824 (T = 18 ° C.).

Next, the flux was measured while changing the circulating water temperature to 18 ° C., 20 ° C., and 22 ° C. under a constant condition of the membrane surface flow rate V = 1.0 m / sec. Table 4 shows the results.

From the above results, the following relationship was obtained: F = 0.0353T + 0.489 (V = 1.0 m / sec).

 By combining the above relations, a relational expression of F = 0.0353T + 0.304V + 0.191 was obtained.

 Therefore, the film surface velocity V is given by V = 3.33F-0.116T-0.628.

[Continuous Wastewater Treatment Test] The above wastewater was treated at a predetermined treatment amount of 0.27 m ³ / hour. The operating pressure of the membrane device was 0.9 kg / cm ² . The water temperature at the start of operation was 23 ° C. At this time, the required film surface flow rate for obtaining a predetermined treatment amount was 1.0 m / sec.

The temperature of the membrane circulating water dropped to 16 ° C. with the change of the drainage temperature. During this time, the membrane surface flow rate was adjusted while detecting the water temperature, and the predetermined treatment amount of 0.27 m ³ / hour was maintained. This point was confirmed with an integrating flow meter. The membrane surface flow rate of the membrane device at a water temperature of 16 ° C. was 1.8 m / sec.

Effects As described above, according to the present invention, the amount of permeated water can be kept constant, and therefore, membrane separation can be performed at low cost, in a small space, and in a small amount of energy without providing an excessive membrane module. In addition, the stability of the control of the amount of permeated water was very good.

[Brief description of the drawings]

FIG. 1 is a flow sheet showing one embodiment of the apparatus of the present invention. FIG. 2 is a flow sheet showing another embodiment of the apparatus of the present invention. [Explanation of Main Symbols] 1 ... Adjusting tank, 2 ... Supply pump, 5 ... Circulation pump,
6 circulating pump control means 7 data processing means 8
... water temperature measuring means, 10 ... membrane device, 13 ... heat exchanger.

Continuing from the front page (72) Inventor Daiki Toyohara 1-17-1-2, 107 Uesueyoshi, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture (72) Inventor Yoshinori Yushina 2-27-10 Konan-ku, Konan-ku, Yokohama-shi, Kanagawa Prefecture (56) Reference Reference JP-A-60-235604 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B01D 61/02-61/22 C02F 1/44

Claims (9)

(57) [Claims] 1. A membrane separation method for removing impurities from water to be treated whose temperature fluctuates over time by a circulation method, wherein the temperature of the water to be treated is detected, and the fluctuation of the temperature of the water is detected in accordance with the detected water temperature fluctuation. A method characterized by estimating a variation in the permeation flow rate, adjusting the membrane surface flow rate to compensate for the estimated variation in the permeation flow rate, and thus keeping the permeation flow rate constant, thereby controlling the permeate flow rate constant. . 2. The method according to claim 1, wherein said membrane surface flow rate is adjusted by inverter control of a circulation pump. 3. The method according to claim 1, wherein the operating pressure is adjusted together with the film surface flow rate. 4. The method according to claim 1, wherein heat exchange is performed between the water to be treated and the treated water after permeation through the membrane. 5. The method according to claim 1, wherein said water to be treated is a tunnel spring water. 6. A membrane separation apparatus for removing impurities from water to be treated whose temperature fluctuates with time by means of a circulation system, means for detecting the temperature fluctuation of the water to be treated, An apparatus comprising: means for estimating a change in the permeation flow rate caused by the above; and means for adjusting the membrane surface flow rate so as to compensate for the fluctuation in the estimated permeation flow rate. 7. The apparatus according to claim 6, wherein the means for estimating the fluctuation of the permeation flow velocity and adjusting the membrane surface flow velocity is an inverter control device of a circulation pump operated by a command from a personal computer. 8. An apparatus according to claim 6, further comprising means for adjusting the operating pressure together with the film surface flow rate. 9. The apparatus according to claim 6, further comprising means for performing heat exchange between the water to be treated and the treated water after permeation through a membrane.