Method for controlling reverse osmosis membrane device in pure water production device

Abstract

In this method for controlling a reverse osmosis membrane device in a pure water production device, when the amount of ultrapure water used at a water consumption point is reduced and the value measured by a water level gauge (63) is increased, a narrowing control valve (62) reduces the amount of primary pure water (W2) supplied to a sub-tank (41). Therefore, according to the measurement value of the pressure gauge (61), the control mechanism reduces the output of the high-pressure pump (32A) so that the measurement value of the pressure gauge (61) is substantially constant at the predetermined pressure. On the other hand, when the amount of ultrapure water used at the water use point increases and the measured value of the water level of the sub-tank (41) decreases, the control valve (62) is opened and the amount of water supplied to the sub-tank (41) is increased. Therefore, according to the measurement value of the pressure gauge (61), the control mechanism increases the output of the high-pressure pump (32A) so that the measurement value of the pressure gauge (61) is substantially constant at the predetermined pressure. Thus, even if the flow rate varies with the amount of water used, stable water delivery is achieved.

Description

Technical Field

[0001] The present invention relates to a control method for a reverse osmosis membrane device constituting a pure water production device, and in particular to a control method for a reverse osmosis membrane device in a pure water production device capable of controlling the delivery rate of pure water according to the amount of water used when producing ultrapure water used in the electronic industry fields such as semiconductors and liquid crystals. Background Art

[0002] In the past, ultrapure water used in the semiconductor and other electronic industries, e.g. Figure 1 As shown, ultrapure water is produced by treating raw water W using an ultrapure water production apparatus 1 comprising a three-stage apparatus consisting of a pretreatment apparatus 2, a primary pure water apparatus (pure water production apparatus) 3, and a secondary pure water apparatus (subsystem) 4. Specifically, in the pretreatment apparatus 2, the raw water W is pretreated by filtration, coagulation and sedimentation, and microfiltration membranes, thereby primarily removing suspended matter.

[0003] The primary pure water device 3 includes a treated water tank 31 for storing pretreated water (treated water) W1, a high-pressure pump 32 for delivering the pretreated water W1, a reverse osmosis membrane device 33, a first degassing membrane device 34A for removing dissolved gases using air, a second degassing membrane device 34B for further degassing dissolved gases using nitrogen, an ultraviolet oxidation device 35, an electrodeionization device 36, and a water supply pump 37 for supplying water to the electrodeionization device 36. The primary pure water device 3 removes most of the electrolytes, particulates, and live bacteria in the pretreated water W1, and decomposes organic matter.

[0004] Subsystem 4 is a facility for using pure water produced using the primary pure water unit 3. It comprises a subtank 41, located downstream of the electrodeionization unit 36 ​​storing primary pure water (pure water) W2; an ultraviolet oxidation unit 42, which processes the primary pure water W2 supplied from subtank 41 via a pump (not shown); a non-regenerative mixed-bed ion exchange unit 43; and an ultrafiltration (UF) membrane 44, serving as a membrane filtration device. Furthermore, an RO (reverse osmosis) membrane separation unit may be provided as needed. In subsystem 4, trace organic matter (TOC (total organic carbon)) contained in the primary pure water W2 is oxidized and decomposed by the ultraviolet oxidation unit 42. The water is then treated in the non-regenerative mixed-bed ion exchange unit 43, thereby removing residual carbonate ions, organic acids, and anionic substances through ion exchange, and further removing metal ions and cationic substances. Then, the ultrapure water W3 is obtained by removing fine particles using an ultrafiltration (UF) membrane 44 and supplied to the water consumption point 5 . Unused ultrapure water flows back to the sub-tank 41 .

[0005] In order to stably supply primary pure water of a predetermined quality, the ultrapure water production apparatus 1 produces an excess amount of primary pure water W2 in advance, supplies only a necessary amount to the sub-tank 41 , and circulates the excess.

[0006] As a control method of the reverse osmosis membrane device 33 in the ultrapure water production device 1 as described above, Figure 8 As shown, a water level gauge 51 is used to measure the water level in the sub-tank 41, and the high-pressure pump 32 is controlled to be on / off to maintain the water level in the sub-tank 41 within a specified range. This is accompanied by repeated operation and shutdown of the reverse osmosis membrane device 33. During operation, the reverse osmosis membrane device 33 operates at a specified concentration ratio. Note that reference numeral 52 denotes a pressure gauge measuring the feed pressure of the permeate water passing through the reverse osmosis membrane 33, reference numeral 53 denotes the concentrated water recovery line from the reverse osmosis membrane device 33, and reference numeral 54 denotes a flowmeter.

[0007] In addition, if Figure 9 As shown, although the reverse osmosis membrane device is often arranged in parallel as a plurality of series (in Figure 8 In this case, the reverse osmosis membrane devices 33A and 33B are operated under specified conditions (specified flow rate / specified water supply pressure), and the start and stop of both reverse osmosis membrane devices 33A and 33B are controlled based on the water usage or the water level of the sub-tank 41 of the downstream equipment. Alternatively, the water production amount is controlled by increasing or decreasing the operation series (by successively stopping one or more of the reverse osmosis membrane devices 33A and 33B) in conjunction with the long-term adjustment of the water usage. Summary of the Invention

[0008] Problems to be solved by the invention

[0009] However, in Figure 8 and Figure 9 The control method for the reverse osmosis membrane device 33 shown above not only faces the risk of a decrease in the permeate flow through the RO membrane due to scaling caused by organic matter and the accumulation of inorganic scale due to high concentration over years of use, but also poses the risk of physical damage to the membrane surface within the reverse osmosis membrane element and a decrease in ion removal efficiency due to water hammer caused by the frequent startup and shutdown of the reverse osmosis membrane device 33 (33A, 33B). Furthermore, the passage of time while the reverse osmosis membrane device 33 is stopped can degrade the permeate quality due to ion diffusion from the concentration side, leading to deterioration in the water quality immediately after resuming operation. Therefore, cleaning is typically performed before resuming operation, resulting in a wasteful start-up time and water usage.

[0010] The present invention has been completed in view of the above-mentioned problems, and its purpose is to provide a control method for a reverse osmosis membrane device in a pure water production device, which can stably deliver water even if the flow rate follows changes in the amount of water used, avoid membrane degradation and water quality degradation associated with start-up and shutdown, and eliminate the need for membrane washing during restart.

[0011] Means for solving problems

[0012] In view of the above-mentioned purpose, the present invention provides a control method for a reverse osmosis membrane device in a pure water manufacturing device, which is a control method for a reverse osmosis membrane device in a pure water manufacturing device having a water supply mechanism for treated water, a reverse osmosis membrane device and a pressure gauge for measuring the water supply pressure on the permeate water side of the reverse osmosis membrane device, wherein a pure water using device is provided at the rear section of the pure water manufacturing device, and a flow regulating mechanism for pure water supplied to the pure water using device is provided between the pure water manufacturing device and the pure water using device, the supply amount of pure water is regulated by the flow regulating mechanism according to the required water amount of pure water of the pure water using device, and the water supply output of the water supply mechanism is controlled so that the measured value of the pressure gauge becomes approximately constant at a predetermined water supply pressure (Invention 1).

[0013] According to the aforementioned invention (Invention 1), the flow rate regulating mechanism is controlled to increase or decrease the supply of pure water produced by the pure water production device in response to increases or decreases in the required pure water volume of the pure water-using equipment. As the supply volume increases or decreases, the water supply pressure decreases or increases, provided it remains constant. Therefore, by controlling the water supply output of the water supply mechanism to maintain a substantially constant supply pressure at a predetermined pressure, the reverse osmosis membrane can be supplied with a stable supply of permeated water. This eliminates the membrane degradation and water quality degradation associated with startup and shutdown, and significantly reduces the frequency of membrane cleaning during restart.

[0014] In the above invention (Invention 1), the reverse osmosis membrane devices are arranged in parallel in a plurality of series (Invention 2). In particular, in the above invention (Invention 2), it is preferred that all of the reverse osmosis membrane devices arranged in parallel in a plurality of series are operated (Invention 3).

[0015] According to the above inventions (Inventions 2 and 3), even when multiple series of reverse osmosis membrane devices are arranged in parallel, the water supply output of the water supply mechanism is controlled so that the total water supply pressure becomes approximately constant at a predetermined pressure, and the permeate water volume of each reverse osmosis membrane device is reduced for operation, thereby eliminating the need to stop the reverse osmosis membrane device.

[0016] Furthermore, in the above invention (Invention 2), the operation of a portion of the reverse osmosis membrane devices installed in a plurality of series in parallel may be stopped (Invention 4).

[0017] According to the above invention (Invention 4), when the required amount of pure water in the pure water using equipment drops below the flow rate of the water supply output that can be adjusted using the water supply mechanism, the operation can be further efficiently performed by appropriately combining operations to reduce the number of operating series.

[0018] Effects of the Invention

[0019] According to the control method for a reverse osmosis membrane device in a pure water production apparatus of the present invention, the pure water supply rate is adjusted by a flow control mechanism based on the pure water demand of the pure water-consuming equipment, and the water supply output of the water supply mechanism is controlled so that the measured value of the pressure gauge remains substantially constant at a predetermined water supply pressure. This method enables a stable supply of the required amount of permeated water to the reverse osmosis membrane without stopping the reverse osmosis membrane. This significantly reduces membrane degradation and water quality degradation associated with startup and shutdown, and significantly reduces the frequency of membrane cleaning during restart of the reverse osmosis membrane device. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram showing an ultrapure water production apparatus to which the control method of the reverse osmosis membrane apparatus in the pure water apparatus of the present invention can be applied.

[0021] Figure 2 This is a schematic diagram showing a method for controlling a reverse osmosis membrane device in a pure water production apparatus according to the first embodiment of the present invention.

[0022] Figure 3 This is a schematic diagram schematically showing a method for controlling a reverse osmosis membrane device in a pure water production apparatus according to a second embodiment of the present invention.

[0023] Figure 4 Schematic diagram showing the reverse osmosis membrane device in the pure water production apparatus in Example 1 and Comparative Example 1.

[0024] Figure 5 Graph showing the relationship between the feed water pressure and the permeated water pressure in Example 1.

[0025] Figure 6 Graph showing the water quality (electrical conductivity) of the permeated water in Example 1.

[0026] Figure 7 Graph showing the water quality (electrical conductivity) of permeated water in Comparative Example 1.

[0027] Figure 8 This is a schematic diagram showing a control method of a reverse osmosis membrane device in a conventional pure water production device.

[0028] Figure 9This is a schematic diagram showing a control method of a reverse osmosis membrane device in another conventional pure water production device. DETAILED DESCRIPTION

[0029] Hereinafter, a method for controlling a reverse osmosis membrane device in a pure water device according to the present invention will be described with reference to the accompanying drawings.

[0030] [First embodiment]

[0031] (Pure water production equipment)

[0032] The present invention is a pure water manufacturing device having the characteristics of controlling the reverse osmosis membrane in a pure water manufacturing device (primary pure water device) such as an ultrapure water manufacturing device. Here, as a pure water manufacturing device (primary pure water device), there is no particular limitation, and it has: a water supply pump as a water supply mechanism for supplying treated water; a reverse osmosis membrane device, which is arranged at the rear section of the water supply pump; and a pressure gauge, which measures the water supply pressure on the permeate water side of the reverse osmosis membrane device. One or more water treatment equipment is arranged between the water supply pump and the pressure gauge as needed. As long as it is the above-mentioned pure water manufacturing device, various pure water manufacturing devices can be applied. For example, it can be appropriately applied to Figure 1 The primary pure water device 3 in the ultrapure water production device 1 shown.

[0033] In such Figure 1 In the water production process in the primary pure water device 3 shown in FIG. Figure 2 The control system shown controls the reverse osmosis membrane device 33. Figure 2In the embodiment, the primary pure water device 3 is configured as follows: a high-pressure pump 32A serving as a water supply mechanism is provided at the rear section of the treated water tank 31, and the high-pressure pump 32A can adjust the output through inverter control, and can supply pre-treated water (treated water) W1 to the reverse osmosis membrane device 33. After treatment using the reverse osmosis membrane device 33, the water treatment equipment is used for treatment to produce primary pure water W2, and the primary pure water (pure water) W2 produced by the primary pure water device 3 is stored in the sub-tank 41. In the primary pure water device 3, the following sections are provided at the rear section of the reverse osmosis membrane device 33: a pressure gauge 61 for measuring the water supply pressure on the permeate side of the reverse osmosis membrane device 33; and a control valve 62 as a flow regulating mechanism, and a water level gauge 63 is provided in the auxiliary tank 41. These pressure gauges 61 and water level gauges 63 are provided so as to be able to transmit information to a control mechanism not shown in the figure. The control mechanism is provided so as to be able to perform inverter control on the high-pressure pump 32A so that the measured value of the pressure gauge 61 becomes approximately constant (for example, ±5%) at a predetermined pressure, and is provided so as to be able to control the opening of the control valve 62 according to the measured value of the water level gauge 63. 71 is a recovery line for concentrated water of the reverse osmosis membrane device 33, and a flow control valve 72 and a flow meter 73 are provided in the recovery line 71 respectively. The concentrated water is processed using a recovery reverse osmosis membrane and is returned to the tank 31 for the treated water. It should be noted that in Figure 2 Although water treatment units other than the reverse osmosis membrane device 33 are omitted, other water treatment units may be provided between the reverse osmosis membrane device 33 and the pressure gauge 61. Specifically, one or more selected from an ultraviolet oxidation device, a degassing membrane, an electrodeionization device, a regenerative ion exchange device, and a non-regenerative ion exchange device may be provided.

[0034] (Control Method of Reverse Osmosis Membrane Device)

[0035] Secondly, Figure 2 A control method for the reverse osmosis membrane device shown will be described.

[0036] exist Figure 2 In the process, the high-pressure pump 32A is started to supply pre-treated water (treated water) W1 from the treated water tank 31, and pure water (primary pure water) W2 produced by treatment using the reverse osmosis membrane device 33 and other water treatment units (not shown) appropriately provided as needed is stored in the sub-tank 41. Then, based on the amount of ultrapure water used at the water point (not shown), the primary pure water W2 stored in the sub-tank 41 is sent to the sub-system, where ultrapure water is prepared and supplied to the water point.

[0037] In the treatment process using the reverse osmosis membrane device 33 performed by the primary pure water device 3 as described above, the reverse osmosis membrane device 33 is controlled as follows by the pressure gauge 61 for measuring the water supply pressure, the control valve 62, the water level gauge 63, and the high-pressure pump 32A that can be controlled by the inverter.

[0038] First, a reference value (or a value within a specified range) for the water level of the sub-tank 41 is predetermined. Then, if the amount of ultrapure water used at the water point decreases and the measured value of the water level of the water level gauge 63 increases to exceed the reference value, the control mechanism (not shown) reduces the control valve 62 to reduce the amount of pure water W2 supplied to the sub-tank 41. As a result, the water supply pressure rises. Therefore, based on the measured value of the pressure gauge 61, the control mechanism reduces the output of the high-pressure pump 32A through inverter control so that the measured value of the pressure gauge 61 becomes approximately constant at a predetermined pressure. On the other hand, if the amount of ultrapure water used at the water point increases and the measured value of the water level of the sub-tank 41 decreases to less than the reference value, the control mechanism (not shown) opens the control valve 62 to increase the amount of water supplied to the sub-tank 41. As a result, the water supply pressure decreases. Therefore, based on the measurement value of the pressure gauge 61, the control means increases the output of the high-pressure pump 32A through inverter control so that the measurement value of the pressure gauge 61 becomes substantially constant (for example, ±5%) at a predetermined pressure.

[0039] In this manner, the supply of primary pure water W2 is adjusted by the control valve 62 according to the required level of the auxiliary system (the water level of the auxiliary tank 41) used as the pure water user. Furthermore, the water supply output of the high-pressure pump 32A, whose output can be adjusted by inverter control, is controlled so that the measured value of the pressure gauge 61 remains substantially constant at a predetermined water supply pressure. This allows for a stable supply of primary pure water W2 without stopping the reverse osmosis membrane device 33. This achieves the following effects (1) to (3).

[0040] (1) Conventionally, the reverse osmosis membrane device 33 is operated with the water supply and the concentration ratio set to be constant. For example, when the concentration ratio is 5 times, the operating conditions are set as shown in Table 1 below. In contrast, in this embodiment, the reverse osmosis membrane device 33 is operated with the concentrated water volume set to be approximately constant. Furthermore, the water volume of the reverse osmosis membrane device 33 is changed in accordance with the water consumption of the subsequent water use point. For example, when the concentrated water volume is set to be constant at 20m 3 / hour, the operating conditions shown in Table 2 below are set. As Tables 1 and 2 clearly show, in this embodiment, the amount of concentrated water is kept constant while the amount of supplied water is adjusted. Therefore, if the concentration ratio is varied and the maximum amount of supplied water is set to the same as the existing supply water amount, the average value becomes smaller than that of the existing operating method. This can be said to achieve a high water-saving effect. It should be noted that since the amount of concentrated water in the reverse osmosis membrane device 33 is kept constant, the effect of preventing the adhesion of fouling substances due to linear velocity remains the same.

[0041] [Table 1]

[0042] Water supply Concentrated water volume Permeate water volume Recovery rate Concentration ratio <![CDATA[100m 3 / hour]]> <![CDATA[20m 3 / hour]]> <![CDATA[80m 3 / hour]]> 80％ 5 times

[0043] [Table 2]

[0044] Water supply Concentrated water volume Permeate water volume Recovery rate Concentration ratio <![CDATA[100m 3 / hour]]> <![CDATA[20m 3 / hour]]> <![CDATA[80m 3 / hour]]> 80％ 5 times <![CDATA[80m 3 / hour]]> <![CDATA[20m 3 / hour]]> <![CDATA[60m 3 / hour]]> 75％ 4 times <![CDATA[60m 3 / hour]]> <![CDATA[20m 3 / hour]]> <![CDATA[40m 3 / hour]]> 67％ 3 times

[0045] (2) A typical reverse osmosis membrane device operates at a water supply pressure of 0.5 to 2.0 MPa. In the conventional operation control method of the reverse osmosis membrane device, in the reverse osmosis membrane device 33, a sudden pressure change occurs, in which the water supply pressure becomes 0 MPa, each time the reverse osmosis membrane device is started or stopped. As a result, there is a risk of physically damaging the reverse osmosis membrane surface of the reverse osmosis membrane device 33. In this regard, in the present embodiment, the water supply pressure of the reverse osmosis membrane device 33 is controlled by controlling the pump inverter control of the high-pressure pump 32A and the opening of the control valve 62 in accordance with the amount of water used. Therefore, the start-stop frequency of the reverse osmosis membrane device 33 becomes extremely low, the water supply pressure changes seamlessly, and the number of sudden pressure changes is greatly reduced. As a result, damage to the reverse osmosis membrane device 33 and the risk of physically damaging the reverse osmosis membrane surface are extremely low.

[0046] (3) If the reverse osmosis membrane device 33 is stopped and a certain period of time has passed, the ions and other components of the retained water diffuse back from the concentrated water side to the permeate water side, causing the water quality of the permeate water to deteriorate. Consequently, the quality of the permeate water immediately after operation is restarted deteriorates. Therefore, the reverse osmosis membrane needs to be washed before water flow is resumed. In this regard, the present embodiment not only suppresses temporary deterioration in water quality, but also minimizes the number of times the reverse osmosis membrane needs to be washed before operation is resumed, thereby reducing the amount of water required for washing.

[0047] [Second embodiment]

[0048] (Pure water production equipment)

[0049] exist Figure 2 In the first embodiment shown, due to Figure 3The second embodiment shown has the same structure except that the high-pressure pump 32A and the reverse osmosis membrane device 33, whose output can be adjusted by inverter control, are arranged in parallel in two series. Figure 3 In FIG. 3 , they are described as high-pressure pumps 32A, 32B, and reverse osmosis membrane devices 33A and 33B.

[0050] (Control Method of Reverse Osmosis Membrane Device)

[0051] Secondly, Figure 3 A control method for the reverse osmosis membrane device shown will be described.

[0052] exist Figure 3 In the process, the high-pressure pumps 32A and 32B are activated to supply pre-treated water (treated water) W1 from the treated water tank 31 to the reverse osmosis membrane devices 33A and 33B for treatment. The pure water (primary pure water) W2 produced by treatment in other water treatment units (not shown) appropriately provided as needed is stored in the sub-tank 41. Then, depending on the amount of ultrapure water used at the water point (not shown), the primary pure water W2 stored in the sub-tank 41 is sent to the sub-system, where ultrapure water is prepared and supplied to the water point.

[0053] In the treatment process using the reverse osmosis membrane devices 33A and 33B in this embodiment, the reverse osmosis membrane devices 33A and 33B are controlled as follows by a pressure gauge 61 for measuring the water supply pressure, a control valve 62, a water level gauge 63, and inverter-controllable high-pressure pumps 32A and 32B.

[0054] First, a reference value (or a value within a specified range) for the water level in the sub-tank 41 is predetermined. Then, if the amount of ultrapure water used at the water point decreases and the water level measured by the water level gauge 63 increases to exceed the reference value, the control mechanism (not shown) closes the control valve 62 to reduce the amount of primary pure water W2 supplied to the sub-tank 41. As a result, the water supply pressure increases. Therefore, based on the measured value of the pressure gauge 61, the control mechanism reduces the output of the high-pressure pumps 32A and 32B through inverter control so that the measured value of the pressure gauge 61 becomes approximately constant (for example, ±5%) at a predetermined pressure. On the other hand, if the amount of ultrapure water used at the water point increases and the water level measured by the sub-tank 41 decreases to less than the reference value, the control mechanism (not shown) opens the control valve 62 to increase the water supply to the sub-tank 41. As a result, the water supply pressure decreases. Therefore, based on the measurement value of the pressure gauge 61, the control means increases the output of the high-pressure pumps 32A, 32B through inverter control so that the measurement value of the pressure gauge 61 becomes substantially constant (for example, ±5%) at a predetermined pressure.

[0055] In this way, the supply amount of primary pure water W2 is regulated by the control valve 62 according to the required water volume of the subsystem as the pure water using equipment, and the water supply output of the high-pressure pumps 32A and 32B, which can be controlled by the inverter to adjust the output, is controlled so that the measurement value of the pressure gauge 61 becomes approximately constant at the predetermined water supply pressure, thereby eliminating the need to stop both the reverse osmosis membrane devices 33A and 33B, and thus enabling the primary pure water W2 to be stably supplied.

[0056] However, if the required amount of primary pure water W2 in the auxiliary system of the pure water user falls below the flow rate at which the water supply output of the high-pressure pumps 32A and 32B can be adjusted (for example, below the total value of the lowest output of each of the high-pressure pumps 32A and 32B), the treatment of the reverse osmosis membrane device 33A or 33B can be stopped by stopping either one, thereby enabling continued operation. It should be noted that although this second embodiment is a case of two trains, even in the case of three or more trains, when the flow rate falls below the flow rate at which the water supply output can be adjusted, although it is sufficient to stop the high-pressure pumps and reverse osmosis membrane devices to reduce the number of trains in operation, it is preferable to control the number of trains to be stopped to be as small as possible.

[0057] The present invention has been described above based on the above-mentioned embodiment, but the present invention is not limited to the above-mentioned embodiment and can be implemented in various modified forms. For example, as a water supply mechanism, not only a high-pressure pump 32A that can be controlled by an inverter can be provided, but also a high-pressure pump 32A can be provided at the rear section of the water supply pump, and these can be combined to serve as a water supply mechanism. Furthermore, unlike the auxiliary tank 41, in the process of a primary pure water device, for example, a water storage tank can be provided at the rear section of the electrodeionization device 36, and control can be performed based on the water level of the water storage tank. Regardless of the water level of the tank, as long as the required amount of pure water W2 in the pure water using equipment such as the auxiliary system 4 can be determined by other mechanisms such as a flow meter, it can also be applied to a system without a tank. Furthermore, the reverse osmosis membrane device can also be combined in parallel and in series. Furthermore, in addition, the pure water manufacturing device is not limited to a device used for an ultrapure water manufacturing device.

[0058] [Example]

[0059] Hereinafter, the present invention will be described in more detail based on specific examples, but the present invention is not limited to the following examples.

[0060] [Example 1 and Comparative Example 1]

[0061] (Reverse osmosis membrane number switching test)

[0062] like Figure 4As shown, a test apparatus is prepared having: a high-pressure pump 81 additionally provided with an inverter 81A; reverse osmosis membrane devices 82A and 82B arranged in parallel; and a reverse osmosis membrane device 83 for treating concentrated water from these reverse osmosis membrane devices 82A and 82B, and a sampling point 84 provided on the permeate water side of the reverse osmosis membrane 83.

[0063] In this test apparatus, the permeate water pressure and the concentrated water flow rate were controlled to be constant, and the number of water passes through the three reverse osmosis membrane devices was fixed to treat the water to be treated W1.

[0064] The flow rates of permeate water and concentrated water of the reverse osmosis membrane devices 82A and 82B in this test are shown in FIG. Figure 5 As the water quality of the permeated water measured at the sampling point 84, the electrical conductivity (EC) was measured and the results are shown in Figure 6 .

[0065] In addition, assuming that the required water volume at the water point changes, the water supply pressure of the high-pressure pump 81 and the flow rate of the permeated water (treated water) of the reverse osmosis membrane devices 82A and 82B are changed, and the water flow to the reverse osmosis membranes 82A, 82B and the reverse osmosis membrane 83 is controlled accordingly (Comparative Example 1). Specifically, in the order of the largest flow rate, the number of water flow sheets is changed in the order of reverse osmosis membranes 82A, 82B and reverse osmosis membrane 63 (three sheets), reverse osmosis membrane 82A and reverse osmosis membrane 83 (two sheets), and only reverse osmosis membrane 82A (one sheet), and a water flow test is similarly performed. As the water quality of the permeated water of the reverse osmosis membranes 82A and 82B at this time, the results of measuring the electrical conductivity (EC) and the change in the number of water flow sheets of the reverse osmosis membrane are shown together. Figure 7 .

[0066] like Figure 6 as well as Figure 7 As clearly shown, while the water quality (electrical conductivity (EC)) fluctuates slowly in Example 1, where reverse osmosis membranes 82A and 82B are controlled to operate constantly to maintain constant permeate pressure and concentrated water flow, water quality temporarily deteriorates as the number of reverse osmosis membranes in operation increases in Comparative Example 1, where the number of reverse osmosis membranes is increased or decreased. This is presumably because the quality of the water retained on the permeate side deteriorates when water flow through the reverse osmosis membranes is stopped. This deteriorated retained water is then released when water flow through the reverse osmosis membranes is resumed, indicating the need for cleaning before resuming operation.

[0067] Description of Reference Numerals

[0068] 1: Ultrapure water production device.

[0069] 2: Pre-processing device.

[0070] 3: Primary pure water device (pure water production device).

[0071] 31: Tank for treated water.

[0072] 32, 32A, 32B: High-pressure pump (water supply mechanism).

[0073] 33, 33A, 33B: Reverse osmosis membrane device.

[0074] 34A: First degassing membrane device.

[0075] 34B: Second degassing membrane device.

[0076] 35: Ultraviolet oxidation device.

[0077] 36: Electrodeionization device.

[0078] 37: Water supply pump.

[0079] 4: Secondary pure water production device (auxiliary system).

[0080] 41: Auxiliary tank.

[0081] 42: Ultraviolet oxidation device.

[0082] 43: Non-regenerative mixed bed ion exchange unit.

[0083] 44: Ultrafiltration (UF) membrane.

[0084] 5: Use water points.

[0085] 61: Pressure gauge.

[0086] 62: Control valve (flow regulating mechanism).

[0087] 63: Water level gauge.

[0088] 71: Recycling line.

[0089] 72: Flow control valve.

[0090] 73: Flow meter.

[0091] W: raw water.

[0092] W1: Pre-treated water (treated water). W2: Primary pure water (pure water). W3: Secondary pure water (ultrapure water).

Claims

1. A method for controlling a reverse osmosis membrane device in a pure water production device, the method comprising: providing a water supply mechanism for water to be treated, a reverse osmosis membrane device, and a pressure gauge for measuring a water supply pressure on a permeate side of the reverse osmosis membrane device; A pure water using device is provided at the rear section of the pure water manufacturing device, and a flow regulating mechanism for supplying pure water to the pure water using device is provided between the pure water manufacturing device and the pure water using device. The supply amount of pure water is regulated by the flow regulating mechanism according to the required amount of pure water of the pure water using device, and the water supply output of the water supply mechanism is controlled so that the measured value of the pressure gauge becomes approximately constant at a predetermined water supply pressure.

2. The method for controlling a reverse osmosis membrane device in a pure water production device according to claim 1, wherein: The reverse osmosis membrane devices are arranged in parallel in a plurality of series.

3. The method for controlling a reverse osmosis membrane device in a pure water production device according to claim 2, wherein: All of the reverse osmosis membrane devices arranged in a plurality of series in parallel are operated.

4. The method for controlling a reverse osmosis membrane device in a pure water production device according to claim 2, wherein: The operation of a part of the reverse osmosis membrane devices arranged in a plurality of series in parallel is stopped.

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