JP7779105B2 - Secondary pure water production equipment for ultrapure water production systems - Google Patents

Description

The present invention relates to a secondary pure water production device for ultrapure water production systems that produce ultrapure water for use in the electronics industry, such as semiconductors and liquid crystal displays, and in particular to a secondary pure water production device that allows for easy temperature control and reduces operating energy consumption.

Conventionally, ultrapure water used in the semiconductor and other electronics industries is produced by treating raw water (industrial water, city water, well water, etc.) W in an ultrapure water production system 1, which is composed of a pretreatment system 2, a primary pure water production system 3, and a secondary pure water production system (subsystem) 4 that treats the primary pure water, as shown in Figure 1.

The pretreatment system 2, which consists of coagulation, flotation (sedimentation), and filtration (membrane filtration) devices, removes suspended solids and colloidal matter from the raw water W to obtain pretreated water W0. This process also makes it possible to remove high-molecular-weight organic matter, hydrophobic organic matter, and other substances.

The primary pure water production system 3 includes a tank 11 for pretreated water W0, a preheater 15, a reverse osmosis (RO) membrane 12, a heat exchanger 16, an ion exchanger (mixed-bed or four-bed, five-tower type, etc.) 13, and a degasser 14. This primary pure water production system 3 removes ions and organic components from the pretreated water W0. Note that the higher the water temperature, the lower the viscosity and the higher the permeability of membrane devices. Therefore, as shown in FIG. 1 , a preheater 15 and a heat exchanger 16 are installed upstream of the reverse osmosis membrane 12. By controlling the outlet water of the heat exchanger 16 to a predetermined temperature, the viscosity of the water is reduced, and the water is heated so that the temperature of the water supplied to the reverse osmosis membrane 12, the ion exchanger 13, and the degasser 14 is above the predetermined temperature. The primary pure water W1, which is the water supplied to the secondary pure water production system 4, is also controlled to a predetermined temperature. Steam is supplied to the primary side of the heat exchanger 16 as a heat source fluid. The reverse osmosis membrane 12 processes the water to be treated at a predetermined recovery rate to remove salts, as well as ionic and colloidal TOC, and discharges concentrated water. The ion exchange unit 13 removes salts and TOC components that are adsorbed or ion-exchanged by ion exchange resin. The degassing unit 14 then removes inorganic carbon (IC) and dissolved oxygen.

The primary pure water W1 produced in the primary pure water production system 3 is delivered to the secondary pure water production system 4 via piping 17. This secondary pure water production system 4 includes a sub-tank 21, a pump 22, a heat exchanger 23, a temperature sensor 24 connected to a cooling means (not shown) for the heat exchanger, a low-pressure ultraviolet oxidation device (UV oxidation device) 25, a pressure gauge 26, a boost pump 27, a reverse osmosis (RO) membrane 28, and a non-regenerative ion exchanger 29. The low-pressure ultraviolet oxidation device 25 uses 185 nm ultraviolet light emitted from a low-pressure ultraviolet lamp to decompose TOC into organic acids and further to _CO2 levels. Next, the boost pump 27 boosts the primary pure water W1 to a predetermined pressure corresponding to the membrane surface pressure of the reverse osmosis (RO) membrane 28, and supplies the water to the reverse osmosis (RO) membrane 28, where particulates and ionic impurities are removed. The organic matter and _CO2 produced by decomposition in the low-pressure ultraviolet oxidation device 25 are removed in a non-regenerative ion exchange device 29 in the subsequent stage.

The ultrapure water W2 produced in this secondary pure water production system 4 is sent to the use point 5 via piping 30, and unused ultrapure water W2 is returned to the sub-tank 21 via return piping 31. If necessary, a particle removal means such as an ultrafiltration membrane may be provided downstream of the ion exchange system 29.

The heat exchanger 23 adjusts the temperature of the ultrapure water W2 delivered from the secondary pure water production system 4 to a predetermined temperature (e.g., approximately 25°C). Generally, the ultrapure water W2 produced by the secondary pure water production system 4 is supplied to the point of use 5, and the excess ultrapure water W2 (unused) is returned from the point of use 5 to the subtank 21, where it is treated again by the secondary pure water production system 4 and circulated while maintaining a constant ultrapure water quality. Repeated circulation prevents water from stagnating and inhibits the growth of microorganisms. During this circulation, the temperature of the circulating ultrapure water W2 increases due to heat from the pump 22 and the ultraviolet irradiation lamp of the low-pressure ultraviolet oxidation device 25. Heat is removed by the heat exchanger 23, and the temperature of the water delivered to the point of use 5 is adjusted to within ±1°C of the set temperature, for example.

However, if a reverse osmosis membrane (RO membrane) 28 is provided in the secondary pure water production system 4, high pressure must be applied to the water to be treated to force it through the reverse osmosis membrane (RO membrane) 28, which necessitates a booster pump 27 provided upstream. However, the drive energy of this booster pump 27 also contributes to an increase in water temperature, which may result in hunting in water temperature control. Furthermore, in recent years, there has been a demand for energy conservation in ultrapure water production systems, and it is desirable to be able to reduce the operating energy of the secondary pure water production system 4 itself.

The present invention was made in consideration of the above-mentioned problems, and aims to provide a secondary pure water production device in an ultrapure water production system that allows easier temperature control and reduces operating energy compared to conventional systems.

In view of the above object, the present invention provides a secondary pure water production apparatus for an ultrapure water production system comprising a primary pure water production apparatus equipped with at least an ion exchange device and a secondary pure water production apparatus for further treating the primary pure water treated in the primary pure water production apparatus, wherein the secondary pure water production apparatus is equipped with a reverse osmosis membrane having a permeation flux of 2.0 ^m3 /( ^m2 ·day) or more per membrane surface effective pressure of 1 MPa (water temperature 25°C, pure water (RO permeate)), and a booster pump for delivering the water to be treated to the reverse osmosis membrane.

According to this invention (Invention 1), by using a reverse osmosis membrane with a high permeation flux per 1 MPa of effective membrane surface pressure, the same amount of water can be supplied at a low operating pressure. This reduces the workload of the boost pump that pumps water to this reverse osmosis membrane, resulting in a significant reduction in operating energy compared to when a general-purpose reverse osmosis membrane with a lower permeation flux is used. Furthermore, by reducing operating energy, heat generation from the boost pump can be suppressed, thereby suppressing temperature increases in the secondary pure water, reducing energy required to cool the secondary pure water, and as a result, enabling stable control of the temperature of the secondary pure water.

In the above invention (Invention 1), it is preferable that the secondary pure water production system has a storage tank for the primary pure water, a heat exchanger, an ultraviolet oxidation device, a booster pump, the reverse osmosis membrane, and an ion exchange device installed in a water supply pipe that communicates with a use point connected to the storage tank, and a return pipe that returns water from the use point to the storage tank (Invention 2).

According to this invention (Invention 2), an ion exchange device is provided downstream of the reverse osmosis membrane, so even if ionic components leak from the reverse osmosis membrane, which has a high permeation flux per 1 MPa of effective membrane surface pressure, they can be removed. Furthermore, by providing a return pipe, secondary pure water can be used efficiently, while reducing operating energy consumption and efficiently adjusting temperature.

In the above inventions (Inventions 1 and 2), it is preferable that the reverse osmosis membrane has a permeation flux (flux) of 0.6 ^m3 /( ^m2 ·day) or more under the condition of an effective membrane surface pressure of 0.3 MPa (water temperature 25°C, pure water (RO permeate)), a salt rejection of 95% or more (effective membrane surface pressure 0.3 MPa (water temperature 25°C, feed water 500 mg/L at NaCl)), and an IPA rejection of 60% or more (effective membrane surface pressure 0.3 MPa (water temperature 25°C, feed water 500 mg/L at IPA)) (Invention 3).

According to this invention (Invention 3), by selecting a reverse osmosis membrane with such performance, which has a high permeation flux per 1 MPa of effective membrane surface pressure, it is possible to produce secondary pure water with stable water quality while reducing the operating energy of the secondary pure water production equipment and efficiently controlling the temperature.

In the secondary pure water production system of the present invention, by using a reverse osmosis membrane with a high permeation flux per 1 MPa of effective membrane surface pressure, the workload of the booster pump that delivers water to the reverse osmosis membrane is reduced, resulting in a significant reduction in operating energy compared to when a general-purpose reverse osmosis membrane with a lower permeation flux is used, thereby suppressing temperature increases in the secondary pure water. These combined effects make it possible to stably control the temperature of the secondary pure water.

1 is a flow diagram showing an ultrapure water producing system to which a secondary pure water producing apparatus according to a first embodiment of the present invention can be applied.

One embodiment of the secondary pure water production apparatus of the present invention will be described below with reference to the accompanying drawings.

(Ultra pure water production equipment)
The ultrapure water production system using the secondary pure water production apparatus of this embodiment has the same configuration as the ultrapure water production system shown in FIG. 1 described above, except that the reverse osmosis membrane (RO membrane) 28 of the secondary pure water production apparatus 4 has the following performance.

<Reverse osmosis membrane>
Permeation flux (flux) of 0.6 m ³ /(m ² ·day) or more under the condition of an effective membrane surface pressure of 0.3 MPa (water temperature 25°C, pure water (RO permeate)), permeation flux of 2.0 m ³ /(m ² ·day) or more per effective membrane surface pressure of 1 MPa (water temperature 25°C, pure water (RO permeate)) Salt rejection rate: 95% or more (effective membrane surface pressure 0.3 MPa (water temperature 25°C, feed water 500 mg/L at NaCl)
IPA removal rate: 60% or more (membrane surface effective pressure 0.3 MPa (water temperature 25°C, feed water 500 mg/L at IPA)

(Method of operating an ultrapure water production system)
The following describes the operation of the above-described ultrapure water production system 1. First, raw water W is supplied to the pretreatment system 2, where suspended solids and colloidal substances in the raw water W are removed by means of coagulation, pressure flotation (sedimentation), filtration (membrane filtration), etc., to obtain pretreated water W0. During this process, high-molecular-weight organic matter, hydrophobic organic matter, etc. are also removed to some extent.

This pretreated water W0 is supplied to the primary pure water production system 3 and temporarily stored in tank 11, after which it is supplied by a pump (not shown). It is preheated in a preheater 15 to reduce the viscosity of the pretreated water W0, and then supplied to the reverse osmosis membrane 12. The reverse osmosis membrane 12 processes the water to be treated at a predetermined recovery rate, removing salts as well as ionic and colloidal TOC. The ion exchanger 13 then removes salts and TOC components adsorbed or ion-exchanged by the ion exchange resin. Finally, the degassing unit 14 removes inorganic carbon (IC) and dissolved oxygen, producing primary pure water W1.

This primary pure water W1 is delivered to the secondary pure water production system 4 via piping 17. In the secondary pure water production system 4, the primary pure water W1 is delivered by a pump 22, and in a low-pressure ultraviolet oxidation system 25, TOC is decomposed to organic acids and further to ^CO2 levels using 185 nm ultraviolet light emitted from a low-pressure ultraviolet lamp. Next, the primary pure water W1 is boosted by a boost pump 27 to a predetermined pressure corresponding to the membrane surface pressure of the reverse osmosis membrane (RO membrane) 28, and then supplied. Particulates are removed by the reverse osmosis membrane (RO membrane) 28. The organic matter and _CO2 produced by decomposition in the low-pressure ultraviolet oxidation system 25 are then removed in a downstream non-regenerative ion exchanger 29, producing ultrapure water (secondary pure water) W2.

In the previously described conventional ultrapure water production system 1, the reverse osmosis membrane (RO membrane) 28 was responsible for removing both ionic components and particulates. However, in this embodiment, the reverse osmosis membrane 28 with a predetermined effective membrane surface pressure is intended to remove particulates from the upstream boost pump 27 rather than ionic components. The reverse osmosis membrane 28 is generally capable of removing most components with a molecular weight of 200 or more, and particulates are subject to removal. In this embodiment, an ion exchange device 29 is used downstream of the reverse osmosis membrane (RO membrane) 28, which can remove ionic components. Therefore, even if a reverse osmosis membrane 28 with a high permeation flux per 1 MPa of effective membrane surface pressure is used, the quality of the ultrapure water W2 does not deteriorate.

The ultrapure water W2 produced in this secondary pure water production system 4 is then sent to the use point 5 via piping 30, and unused ultrapure water is returned to the sub-tank 21 via return piping 31 for circulating use. As a result of this circulating use, the temperature of the ultrapure water W2 rises due to the transfer of energy from the pump 22, low-pressure ultraviolet oxidation device 25, boost pump 27, etc., so the heat exchanger 23 cools the ultrapure water W2 sent from the secondary pure water production system 4 to the use point 5 to a predetermined temperature (e.g., 25±0.5°C).

In the process for producing ultrapure water W2 described above, in this embodiment, the reverse osmosis membrane used in the secondary pure water production system 4 has a permeation flux of 2.0 ^m3 /( ^m2 ·day) or more per effective membrane surface pressure of 1 MPa (water temperature 25°C, pure water (RO permeate)). This reduces the operating energy required for the boost pump 27. Furthermore, the boost pump 27 provides less heat to the ultrapure water W2, thereby suppressing a rise in the temperature of the secondary pure water W2. These combined effects enable stable control of the temperature of the secondary pure water W2.

The above has described the secondary pure water system 4 in the ultrapure water production system 1 of this embodiment, but the present invention is not limited to the above embodiment and can be applied to various types of primary pure water system 3. Furthermore, while a non-regenerative ion exchange device 29 is typically used as the ion exchange device in the secondary pure water system 4, an electrodeionization device may also be used.

The present invention will be explained in more detail below based on examples, but the present invention is not limited to the following examples.

Example 1
1 , the secondary pure water production system 4 was operated using a reverse osmosis membrane 28 having a flux (permeation flow rate) of 0.76 m ³ /(m ² ·day at 25°C) at an effective membrane surface pressure of 0.3 MPa. The circulating water volume was 100 m ³ /h (0.028 ^{m 3} /h), the water supply pressure of the boost pump 27 was 0.3 MPa (head: 30 m), and the pump efficiency η of the boost pump 27 was 0.7.

First, the hydraulic power (Pw) under these operating conditions can be calculated using the following formula (1).
Pw (kW) = ρgHQ/1000...(1)
(wherein ρ is the density of water (kg/m ³ ), g is the acceleration of gravity (9.8 m/S ² ), H is the total head (m), and Q is the discharge rate (m ³ /S)).

According to the above formula (1), the hydraulic power (Pw) is 1000 (kg/m ³ )×9.8 (m/S ² )×30 (m)×0.028 (m ³ /S)=8.2 kW.

Next, the shaft power (Pa) of the boost pump 27 can be calculated from the following equations (2) and (3).
η=Pw/Pa...(2)
Pa=Pw/0.7...(3)

According to the above equation (3), the shaft power (Pa) of the boost pump 27 is 8.2 (kW) / 0.7 = 11.7 kW.

Then, the loss energy (ΔP) can be calculated from the hydraulic power (Pw) and the shaft power (Pa) of the boost pump 27 using the following equation (4).
ΔP (kW) = Pa - Pw = 11.7 (kW) - 8.2 (kW) = 3.5 kW.

Comparative Example 1
1 , the secondary pure water production system 4 was operated using a general-purpose, high-flux reverse osmosis membrane 28 with a flux (permeation flow rate) of 1.00 m ³ /(m ² ·day at 25°C) at an effective membrane surface pressure of 0.75 MPa. The circulating water volume was 100 m ³ /h (0.028 m ³ /h), the water supply pressure of the boost pump 27 was 0.75 MPa (head: 75 m), and the pump efficiency η of the boost pump 27 was 0.7.

First, when the hydraulic power (Pw) under these operating conditions is calculated in the same manner as in Example 1, the hydraulic power Pw is 1000 (kg/m ³ )×9.8 (m/S ² )×75 (m)×0.028 (m ³ /S)=20.6 kW.

Next, the shaft power (Pa) of the boost pump 27 is calculated in the same manner as in the first embodiment, and is found to be Pa=20.6 (kW)/0.7=29.4 kW.

Then, the lost energy (ΔP) can be calculated from the hydraulic power (Pw) and the shaft power (Pa) of the boost pump 27 as follows: ΔP (kW) = Pa - Pw = 29.4 (kW) - 20.6 (kW) = 8.8 kW.

As is clear from Example 1 and Comparative Example 1 above, in Example 1, which uses a reverse osmosis membrane 28 with a permeation flux of 2.0 ^m3 /( ^m2 ·day) or more per membrane surface effective pressure of 1 MPa (water temperature 25°C, pure water (RO permeate)) in the secondary pure water production apparatus 4, the shaft power and lost energy of the boost pump 27 are both 40% or less compared to Comparative Example 1, which uses a general-purpose reverse osmosis membrane with a high flux, and it is clear that operating energy can be reduced. Furthermore, it is clear that the lost energy of the boost pump 27 is converted into heat, etc., and affects the temperature rise of the ultrapure water W2, so that the effect on the temperature rise of the ultrapure water W2 is also small.

1 Ultrapure water production system 2 Pretreatment system 3 Primary pure water production equipment 4 Secondary pure water production equipment (subsystem)
5. Point of use 11. Tank 12. Reverse osmosis membrane (RO)
13 Ion exchange device 14 Degassing device 15 Preheater 16 Heat exchanger 17 Piping 21 Sub-tank 22 Pump 23 Heat exchanger 24 Temperature sensor 25 Low-pressure ultraviolet oxidation device (UV oxidation device)
26 Pressure gauge 27 Booster pump 28 Reverse osmosis membrane (RO membrane)
29 Non-regenerative ion exchange device 30 Pipe 31 Return pipe W Raw water W0 Pretreated water W1 Primary pure water W2 Ultrapure water (secondary pure water)

Claims (4)

A secondary pure water production system for an ultrapure water production system comprising a primary pure water production system equipped with at least an ion exchange device and a secondary pure water production system for further treating the primary pure water treated in the primary pure water production system,
The secondary pure water production apparatus comprises a reverse osmosis membrane having a permeation flux of 2.5 ^m3 /( ^m2 ·day) or more per membrane surface effective pressure of 1 MPa (water temperature 25°C, pure water (RO permeate)), and a booster pump for delivering the water to be treated to the reverse osmosis membrane. The secondary pure water production system of claim 1, comprising a storage tank for the primary pure water, a heat exchanger, an ultraviolet oxidation device, a booster pump, a reverse osmosis membrane, and an ion exchange device provided in a water supply pipe that communicates with a use point connected to the storage tank, and a return pipe that returns water from the use point to the storage tank. 3. The secondary pure water production system according to claim 1, wherein the reverse osmosis membrane has a permeation flux (flux) of 0.6 ^m3 /( ^m2 ·day) or more under conditions of an effective membrane surface pressure of 0.3 MPa (water temperature 25°C, pure water (RO permeate)), a salt rejection rate of 95% or more (effective membrane surface pressure of 0.3 MPa (water temperature 25°C, feed water 500 mg/L at NaCl)), and an IPA rejection rate of 60% or more (effective membrane surface pressure of 0.3 MPa (water temperature 25°C, feed water 500 mg/L at IPA). 3. The secondary pure water production system according to claim 2, wherein the heat exchanger cools the secondary pure water delivered from the secondary pure water production system to the point of use to a temperature of 25±0.5°C.