JP4840974B2 - Reverse osmosis concentration method - Google Patents

Description

  The present invention relates to a reverse osmosis concentration method. A method is known in which reverse osmosis concentration is performed by supplying a concentrated product such as vegetable juice or fruit juice to a concentration unit in which a plurality of tubular membrane modules are connected in series, and allowing the concentrated product to flow through under high pressure. . The present invention relates to an improvement of such a reverse osmosis concentration method.

  Conventionally, as a reverse osmosis concentration method as described above, a supply pump is attached to the flow path of the concentrate on the inlet side of the concentration unit, and a pressure control valve is attached to the flow path of the concentrate on the outlet side of the concentration unit. Usually, the pressure applied to the concentrating unit is controlled by adjusting the opening degree of the pressure control valve, and the condensate is supplied into the tubular membrane module of the concentrating unit with a supply pump and allowed to flow down under high pressure. However, the conventional reverse osmosis concentration method has a problem that the available membrane pressure is narrow. Although the membrane pressure applied to the tubular membrane module of the concentration unit is normally controlled to be about 6.5 MPa or less, it is necessary to allow for pressure loss due to the flow path of the concentrate downstream from the pressure control valve. For example, if the pressure loss is about 2.0 MPa, the available membrane pressure width is about 4.5 MPa. The membrane pressure applied to the tubular membrane module of the concentration unit increases over time due to the increase in the concentration of the concentrate and the contamination of the membrane surface as reverse osmosis concentration progresses. When the width is narrow, it is difficult to perform reverse osmosis concentration stably for a long time.

In order to improve the above problems, a supply pump (pressure booster pump) is attached to the flow path of the concentrate on the inlet side of the concentration unit, and a discharge pump (pressure increase) is connected to the flow path of the concentrate on the outlet side of the concentration unit. A method is also known in which a concentrate is discharged into a tubular membrane module of a concentration unit with a supply pump, and the concentrate is discharged with a discharge pump while being concentrated by reverse osmosis (for example, Patent Document 2). reference). However, the conventional reverse osmosis concentration method has a problem that the membrane pressure applied to the tubular membrane type module of the concentration unit is likely to fluctuate and is difficult to control in practice. If the membrane pressure is likely to fluctuate, reverse osmosis concentration becomes unstable accordingly, and for example, it becomes difficult to obtain a concentrate having a predetermined concentration by reverse osmosis concentration of vegetable juice or fruit juice.
JP 2001-78732 A JP 2001-347141 A

  The problem to be solved by the present invention is to widen the usable range while controlling the membrane pressure applied to a plurality of tubular membrane type modules connected in series in a concentration unit, and thus to stably perform reverse osmosis concentration for a long time. It is in place to provide a reverse osmosis concentration method that can be performed to obtain a concentrated concentrate as desired.

  The present invention that solves the above-mentioned problems is a method of concentrating in a reverse osmosis concentration method by supplying an object to be concentrated to a concentration unit in which a plurality of tubular membrane modules are connected in series and flowing down temporarily under high pressure. A pressure control valve is installed in the concentrate flow path on the outlet side of the unit, and a boost pump is attached to the concentrate flow path downstream of the pressure control valve, and the concentration is performed between the pressure control valve and the boost pump. A pressure gauge is connected to the flow path of the object, and the pressure gauge and the boost pump are connected via an inverter so that the pressure measured by the pressure gauge is maintained in a lifted state of 1.1 MPa or less. According to the reverse osmosis concentration method, the operation of the boost pump is controlled via the inverter.

  In the reverse osmosis concentration method according to the present invention, a supply pump is attached to the flow path of the concentrate on the inlet side of the concentration unit, and a pressure control valve is attached to the flow path of the concentrate on the outlet side of the concentration unit. While controlling the pressure applied to the tubular membrane type module of the concentration unit, the concentrate is supplied into a plurality of tubular membrane type modules connected in series with the concentration unit by a supply pump, and allowed to flow down temporarily under high pressure. Concentrate by reverse osmosis.

  The type or form of the pressure control valve attached to the concentrate flow path on the outlet side of the concentration unit is not particularly limited, but it is preferable to use a pressure control valve that is open under no control. Here, under no control means a state in which control is not performed as a result, and typical situations in which the pressure control valve is under no control are at the time of failure or power failure. In addition, the open state here means that the primary side of the pressure control valve, that is, the supply side (inlet side) and the secondary side, that is, the discharge side (exit side) are in communication with each other. The case where the open state is maintained even under no control and the case where the open state is maintained under no control are included. A typical example of a pressure control valve that maintains an open state even under non-control is a lift valve having a screw spindle. Further, the pressure control valve that is opened under no control is a normally open type pressure control valve, and is distinguished from the normally closed type pressure control valve that is closed under no control. As the pressure control valve of the former type, for example, a needle valve manufactured by Swagelok Corporation in the United States and trade names SS-18RM8 and SS-16DKF4, and a diaphragm valve made by Swagelok Corporation in the United States and trade name SS-DLS8MM are used. As the control valve, for example, a commercially available product under the trade name SR100 manufactured by Fujikin Co., Ltd. can be used. A needle valve for pressure control is preferable, and in particular, the needle as a valve element is advanced and retracted due to expansion and contraction of the diaphragm due to pressure change. Are particularly preferred.

  In the reverse osmosis concentration method according to the present invention, a boost pump is attached to the concentrate flow path downstream of the pressure control valve as described above. The boost pump reduces the load on the supply pump for the upstream side, and at the same time functions as a transport pump or a new supply pump for the downstream side. The same applies to the supply pump on the inlet side of the concentrating unit. As such a boost pump, a reciprocating pump, a rotary pump, a snake pump, etc., which can be of various types known per se, can be used. A pump or snake pump is preferred.

  In the reverse osmosis concentration method according to the present invention, a pressure gauge is connected to the flow path of the concentrate between the pressure control valve and the boost pump as described above, and the pressure gauge and the boost pump are connected via an inverter. Then, the operation of the boost pump is controlled via the inverter so that the measured value by the pressure gauge becomes a set value, that is, a lifting pressure of 1.1 MPa or less, preferably a lifting pressure of 0.2 to 0.5 MPa. The operation control of the boost pump is performed by controlling the rotation speed of the motor for driving the boost pump via the inverter. In the reverse osmosis concentration method according to the present invention, the operation control of the boost pump via the inverter The flow path of the concentrate between the pressure control valve located on the upstream side and the boost pump is maintained in a lifted state of 1.1 MPa or less, preferably in a lifted state of 0.2 to 0.5 MPa. . When the flow path of the concentrate between the pressure control valve and the boost pump is maintained in a lifted state of 1.1 MPa or less, the lifted state of 1.1 MPa or less corresponds to a pressure loss downstream of the pressure control valve. Therefore, when the membrane pressure applied to the tubular membrane module of the concentration unit is about 6.5 MPa or less as described above, the available membrane pressure range is about 6.4 MPa at the maximum and about 5.4 MPa at the minimum. Therefore, reverse osmosis concentration can be performed stably for a long time. In the present invention, the MPa indicating the pressure means not the gauge pressure but the absolute pressure, and the lifted state means a state equal to or higher than the atmospheric pressure.

  In the reverse osmosis concentration method according to the present invention, a first branch path is provided in the flow path of the concentrate between the pressure control valve and the boost pump as described above, and an intake valve is attached to the first branch path, It is preferable to maintain the flow path of the concentrate between the pressure control valve and the first branch path in a lifted state of 1.1 MPa or less in the same manner as described above. The intake valve opens the valve when the pressure on the primary side, that is, the first branch passage becomes a negative pressure lower than a certain value, and sucks air. Such an intake valve prevents the negative pressure from being sucked into the atmosphere by opening the valve when the inside of the tubular membrane module of the concentration unit is going to become an abnormal negative pressure for some reason, and thus the reverse osmosis membrane Prevents deformation, cracks and cracks that cause performance degradation. The intake valve can be provided with a first branch path in the concentrate flow path upstream of the pressure control valve, and can be attached to the first branch path. Therefore, it is preferable to provide a first branch path in the concentrate flow path downstream from the pressure control valve and upstream from the boost pump, and to be attached to the first branch path.

  In the reverse osmosis concentration method according to the present invention, a pressure buffer member, and further a safety valve is connected to the flow path of the concentrate between the pressure control valve and the first branch path as described above, and the pressure buffer member It is preferable that the flow path of the concentrate between the first branch path is maintained in a lifted state of 1.1 MPa or less in the same manner as described above. The pressure buffering member reduces pressure fluctuations in the flow path of the concentrate, and a manifold, bellows, or the like can be used as the pressure buffering member. Depending on what type of supply pump or pressure control valve is used, there is a difference in degree, but in any case, pulsation is unavoidable, and this causes pressure fluctuations in the flow path of the concentrate. When the pressure fluctuation is reduced by the pressure buffering member, the flow path of the concentrate on the downstream side of the pressure control valve can be stably held in the desired lifted state. Further, when connecting a safety valve, it is preferable to provide a second branch path in the flow path of the concentrate between the pressure control valve and the pressure buffer member as described above, and attach the safety valve to the second branch path. Such a safety valve opens the valve when the pressure on the primary side, that is, the second branch passage exceeds a certain value, and allows the concentrate to escape. For some reason, the inside of the tubular membrane module of the concentration unit is abnormal. To prevent high pressure.

  Although the reverse osmosis concentration method according to the present invention has been described above, the flow path of the concentrate, specifically, the flow path of the concentrate between the pressure control valve and the boost pump, and the first branch path in this flow path When the intake valve is attached and the flow path of the concentrate between the pressure control valve and the first branch path, and when the pressure buffer member is connected to the flow path, the pressure buffer member and the first flow path are connected. In order to hold the flow path of the concentrate between one branch path more stably and surely at a pressure of 1.1 MPa or less, a pressure gauge is connected to the flow path of the concentrate as described above. The pressure gauge and boost pump are connected via an inverter, and the measured value by the pressure gauge is a set value, that is, a lifting pressure of 1.1 MPa or less, preferably a lifting pressure of 0.2 to 0.5 MPa. Operation of the boost pump via an inverter It is Gosuru of.

  According to the reverse osmosis concentration method according to the present invention described above, the usable range is widened while controlling the membrane pressure applied to a plurality of tubular membrane type modules connected in series in the concentration unit. There is an effect that it is possible to obtain a concentrate which is carried out stably over time and concentrated as desired.

  FIG. 1 is a system diagram schematically showing one embodiment of the reverse osmosis concentration method according to the present invention. As a reverse osmosis membrane module, a concentration unit 11 in which a plurality of tubular membrane type modules (not shown, the same applies hereinafter) are connected in series is installed in one stage, and the concentration of an object to be concentrated on the inlet side (upstream side) of the concentration unit 11 is installed. A supply pump 31 is attached to the flow path 21. A normally open type pressure control valve 41 is attached to the concentrate flow path 22 on the outlet side (downstream side) of the concentration unit 11, and the concentrate flow path on the downstream side of the normal open type pressure control valve 41. A boost pump 32 is attached to 22. The concentrate flow path 22 between the normally open type pressure control valve 41 and the boost pump 32 is provided with a first branch path 51 on the downstream side and a second branch path 52 on the upstream side. The intake valve 61 is attached to the first branch passage 51, and the safety valve 62 is attached to the second branch passage 52. Further, a manifold 63 is connected to the concentrate flow path 22 between the first branch path 51 and the second branch path 52. The functions of the intake valve 61, the safety valve 62, and the manifold 63 are as described above. A pressure gauge 71 is connected to the concentrate flow path 22 between the first branch 51 and the manifold 63. The pressure gauge 71 is connected to the inverter 72. The inverter 72 drives the boost pump 32. Connected to a motor (not shown, the same applies hereinafter).

  In the case of FIG. 1, during the reverse osmosis concentration of the concentrate, while controlling the membrane pressure applied to the tubular membrane module of the concentration unit 11 by adjusting the opening of the normally open type pressure control valve 41, The rotational speed of the drive motor of the boost pump 32 is controlled via the inverter 72 so that the measured value of the pressure gauge 71 is a set value, that is, a boosted state of 1.1 MPa or less, specifically 0.35 MPa, for example. Yes.

Example According to the state of implementation described above with reference to FIG. 1, reverse osmosis concentration of Brix 5% tomato juice at 20 ° C. was continued for 18 hours as follows. Three tubular membrane modules (membrane area 2.6 m ² ) each equipped with a reverse osmosis membrane having a salt rejection rate of 99% were connected in series. Tomato juice was supplied to the concentrating unit 11 with an inlet flow rate of 250 L / hour and an inlet pressure of 5 to 6 MPa by a supply pump 31, and allowed to flow down in a transient manner. At the same time, the set value of the pressure gauge 71 was set to 0.35 MPa, and the rotation speed of the drive motor of the boost pump 32 was controlled via the inverter 72 so that the measured value of the pressure gauge 71 became the set value. The pressure (MPa) of the flow channel 21 of the concentrate (tomato juice) on the inlet side of the concentration unit 11 with respect to the passage of the operation time (hours), the measurement pressure (MPa) of the pressure gauge 71, and the concentration of the obtained concentrate ( (Brix.% At 20 ° C.) is shown by white circles and solid lines connecting them in FIGS.

Comparative Example Tomato juice was concentrated by reverse osmosis in the same manner as in the Example except that the boost pump 32 was omitted and therefore the rotation speed was not controlled. As in the example, the pressure (MPa) of the flow channel 21 of the concentrate (tomato juice) on the inlet side of the concentration unit 11 over the operation time (hours) and the concentration of the concentrate (at 20 ° C.) Brix.%) Is shown in FIG. 2 and FIG. 4 by a black circle and a broken line connecting it.

  As apparent from the results of FIGS. 2 to 4, according to the reverse osmosis concentration method according to the present invention, while controlling the membrane pressure applied to the reverse osmosis membrane module of the concentration unit, that is, a plurality of tubular membrane type modules connected in series. There is an effect that the usable range is widened, and therefore, reverse osmosis concentration can be stably performed for a long time, and a concentrate concentrated as desired can be obtained.

1 is a system diagram schematically showing one implementation state of a reverse osmosis concentration method according to the present invention. The graph which shows the change of the pressure (MPa) of the inlet side of a concentration unit with respect to operation time (hour) in the one implementation state etc. of FIG. The graph which shows the change of the measured pressure (MPa) of a pressure gauge with respect to operation time (hour) in the one implementation state of FIG. The graph which shows the change of the density | concentration of the obtained concentrate (Brix.% At 20 degreeC) with respect to operation time (hour) in the one implementation state etc. of FIG.

DESCRIPTION OF SYMBOLS 11 Concentration unit 21 Condensate flow path 22 Concentrate flow path 31 Supply pump 32 Boost pump 41 Normally open type pressure control valve 51 First branch path 52 Second branch path 61 Intake valve 62 Safety valve 63 Manifold 71 Pressure Total 72 Inverters 81-83 Polygonal lines showing the results of the examples 91, 92 Polygonal lines showing the results of the comparative examples

Claims (6)

A method of reverse osmosis concentrated by Do flow in once-through under high pressure is supplied to the concentration unit where the object to be concentrate by connecting a plurality of tubular membrane modules in series, of the concentrate at the outlet side of the concentration unit A pressure control valve is installed in the flow path, a boost pump is attached to the flow path of the concentrate downstream of the pressure control valve, and a pressure gauge is installed in the flow path of the concentrate between the pressure control valve and the boost pump. And connecting the pressure gauge and the boost pump via an inverter, and the boost pump via the inverter so that the pressure measured by the pressure gauge is maintained in a lifted state of 1.1 MPa or less. The reverse osmosis concentration method characterized by controlling the action | operation of .   Further, a first branch path is provided in the flow path of the concentrate between the pressure control valve and the boost pump, an intake valve is attached to the first branch path, and the pressure control valve and the first branch path are disposed between the pressure control valve and the boost pump. The reverse osmosis concentration method according to claim 1, wherein the flow path of the concentrate is maintained in a lifted state of 1.1 MPa or less by controlling the operation of the boost pump.   Further, a pressure buffer member is connected to the flow path of the concentrate between the pressure control valve and the first branch path, and the flow path of the concentrate between the pressure buffer member and the first branch path is connected to the boost pump. The reverse osmosis concentration method according to claim 2, wherein the operation is controlled so as to maintain a lifted state of 1.1 MPa or less.   The reverse osmosis concentration method according to any one of claims 1 to 3, wherein the pressure control valve is a pressure control valve that is open under no control.   5. The reverse osmosis concentration method according to claim 4, wherein the pressure control valve that is open under no control is a normally open type pressure control valve. The reverse osmosis concentration method according to any one of claims 1 to 5 , wherein the pressure of the flow path of the concentrate is maintained within a range of 0.2 to 0.5 MPa.

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