Ultrapure water production system

Abstract

This system provides an ultrapure water production system that can reduce power costs in secondary pure water systems and decrease energy consumption associated with heating / cooling the water to be treated. [Solution] Subsystem 1 comprises a sub-tank 2, a supply pipe 3, a pump 4, a membrane degasser 5 located downstream of the supply pipe 3, and an ultraviolet oxidation device 6. Downstream of the ultraviolet oxidation device 6, the supply pipe 3 branches in two directions. One branch supplies room temperature ultrapure water W1 to the use point 10 via a cooling heat exchanger 7, a non-regenerative ion exchanger 8, and an ultrafiltration membrane 9, and the unused ultrapure water W1 is returned to the sub-tank 2. The other branch is capable of supplying warm ultrapure water W2 to the use point 16 via a non-regenerative ion exchanger 12, a preheat recovery heat exchanger 13, a heating heat exchanger 14, and an ultrafiltration membrane 15, and the unused warm ultrapure water W2 is returned to the sub-tank 2 via a return pipe 17 and the preheat recovery heat exchanger 13.

Description

Technical Field

[0001] The present invention relates to an ultrapure water production system capable of reducing the power and heating / cooling costs in the ultrapure water production process.

Background Art

[0002] Ultrapure water used as semiconductor cleaning water in a semiconductor factory is produced by treating raw water (industrial water, municipal water, well water, etc.) with an ultrapure water production system having a pretreatment system, a primary pure water production device, and a subsystem (secondary pure water production device).

[0003] In this semiconductor factory, there are multiple heat sources and drain waters that can be expected for waste heat recovery. On the other hand, there is often excess heat in the entire factory, and effective utilization of the waste heat is required to reduce the environmental load.

[0004] For example, Patent Document 1 discloses that in a secondary pure water production device that produces and supplies both ultrapure water and warm ultrapure water, the heat of the return water when returning unused warm ultrapure water to a sub-tank at the use point is recovered to preheat the warm ultrapure water. However, in principle, there is heat that cannot be completely recovered in the heat exchanger, and unused warm ultrapure water with latent heat energy that cannot be recovered returns to the sub-tank.

[0005] Furthermore, an ultrapure water production system that supplies both room temperature ultrapure water and warm ultrapure water, as shown in Figure 2, is commonly used. In Figure 2, the subsystem (secondary pure water unit) 21 of the ultrapure water production system includes a sub-tank 22 that stores primary pure water W produced in the primary pure water unit as raw water for treatment, a supply pipe 23 and a pump 24, a heat exchanger 25 for cooling to which the supply pipe 23 is provided, a membrane degasser 26, an ultraviolet oxidation unit 27, and a non-regenerative ion exchange unit 28. Downstream of the non-regenerative ion exchange unit 28, the supply pipe 23 branches in two directions. One branch supplies room temperature ultrapure water W1 to the use point 30 via an ultrafiltration membrane (UF membrane) 29, and the unused ultrapure water W1 is returned to the sub-tank 22. On the other hand, the system is configured to supply warm ultrapure water W2 from the warm ultrapure water piping 31 to the use point 35 via a preheat recovery heat exchanger 32, a heating heat exchanger 33, and an ultrafiltration membrane (UF membrane) 34. Unused warm ultrapure water W2 at the use point 35 is returned to the sub-tank 22 via the return piping 36 and the preheat recovery heat exchanger 32. Therefore, in the subsystem 21 described above, the primary pure water W, the ultrapure water W1 unused at the use point 30, and the warm ultrapure water W2 unused at the use point 35 become the raw water W0 to be treated.

[0006] The subsystem 21 described above is controlled, for example, as follows: Primary pure water W at 25°C produced by the primary pure water system, return ultrapure water W1 at 23°C, and return warm ultrapure water W2 at 32°C after heat recovery are stored in the sub-tank 22. As a result, the raw water W0 is approximately 30°C. This raw water W0 is cooled to 23°C in a cooling heat exchanger 25 and treated in a membrane degasser 26, an ultraviolet oxidation unit 27, and a non-regenerative ion exchange unit 28. The treated water is then divided into 70% for room temperature (COLD) and 30% for hot water (HOT). The room temperature (23°C) treated water passes through an ultrafiltration membrane 29 to supply room temperature ultrapure water W1 to the use point 30, and the unused ultrapure water W1 is returned to the sub-tank 22. Furthermore, if the treated water for hot water is to recover Δ40°C of energy through heat exchange with the 75°C return ultrapure water W2 in the preheat recovery heat exchanger 32, the temperature will rise to 63°C, and then be heated to 75°C in the heating heat exchanger 33, before being supplied to the use point 35 as 75°C ultrapure water W2 via the ultrafiltration membrane 34. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2013-202581 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, due to the nature of heat exchangers, there is heat that cannot be fully recovered, and the 32°C ultrapure water W2 from which the thermal energy could not be recovered returns to the sub-tank 22. Therefore, when room temperature ultrapure water W1 and warm ultrapure water W2 are shared in the sub-tank 22, as shown in subsystem 21 in Figure 2, the water is cooled once to a predetermined temperature, prioritizing the performance of the components used in ultrapure water production. In other words, there is waste in cooling the raw water W0 with cold water and then reheating it using steam or hot water. Furthermore, in production equipment such as wafer washing machines, there are cases where ultrapure water supplied at around 25°C is heated to nearly 40°C near the production equipment, resulting in heat waste when viewed from the perspective of the entire production line.

[0009] In this conventional subsystem, the heat from the primary pure water production unit and the heat from the return water at the point of use are cooled before being processed by the units that make up subsystem 21. This has the problem of excessive energy costs due to the constant exchange of cooling (chilled water) and heating (steam / hot water).

[0010] This invention has been made in view of the above problems, and aims to provide an ultrapure water production system that can reduce the costs of power and heating / cooling in the ultrapure water production process. [Means for solving the problem]

[0011] In view of the above objectives, the present invention provides an ultrapure water production system comprising a primary pure water production apparatus and a secondary pure water apparatus, wherein the secondary pure water apparatus uses primary pure water produced by the primary pure water apparatus stored in a sub-tank and return water of room temperature ultrapure water and / or warm ultrapure water supplied to the point of use as raw water for treatment, and has one or more water treatment units downstream of the sub-tank, and is equipped with heat exchange means for adjusting the treated water treated by the water treatment units to a required temperature (Invention 1). In the above invention (Invention 1), it is preferable that there is no heat exchanger for cooling upstream of the heat exchange means (Invention 2).

[0012] According to this invention (Invention 1), by not cooling the water temperature at which it is processed in the water treatment unit, the energy required to heat the treated water after treatment in the water treatment unit and the energy required to cool the raw water can be reduced. Furthermore, the size of heat exchangers and other components for cooling / heating can be reduced. In addition, it becomes easier to remove components that are easily removed at high water temperatures, such as gaseous components.

[0013] In the above invention (Invention 2), it is preferable that the outlet temperature of the treated water from the heat exchange means is 20 to 80°C (Invention 3). In the above invention (Invention 3), it is preferable that the secondary pure water production apparatus produces either room temperature ultrapure water or warm ultrapure water, or both (Invention 4).

[0014] According to these inventions (inventions 3 and 4), since either room temperature ultrapure water or hot ultrapure water, or both, the energy required for cooling and / or heating the treated water can be reduced.

[0015] In the above inventions (Inventions 1 to 4), it is preferable that one or more water treatment units downstream of the sub-tank have had their eluted substances reduced in advance (Invention 5).

[0016] According to this invention (Invention 5), since highly purified treated water can be obtained, the purity of the room-temperature ultrapure water or warm ultrapure water produced can be improved. [Effects of the Invention]

[0017] The present invention provides a thermal ultrapure water production system that uses primary pure water produced by a primary pure water device stored in a sub-tank and return water of ultrapure water supplied to a point of use as raw water for treatment. The system has one or more water treatment units downstream of the sub-tank and is equipped with a heat exchange means for adjusting the treated water treated by the water treatment units to the required temperature. Since there is no heat exchanger for cooling upstream of the heat exchange means, the energy required to heat the treated water after treatment by the water treatment units and the energy required to cool the raw water for treatment can be reduced by increasing the temperature of the water passed through the water treatment units.

Brief Description of the Drawings

[0018] [Figure 1] It is a flowchart showing a subsystem of an ultra - ultra pure water production system according to an embodiment of the present invention. [Figure 2] It is a flowchart showing a subsystem of a conventional ultra - ultra pure water production system.

Embodiments for Carrying Out the Invention

[0019] Hereinafter, the ultra - pure water production system of the present invention will be described with reference to the accompanying drawings.

[0020] (Ultra - pure water production system) The ultra - pure water production system of the present invention includes an ultra - pure water production unit equipped with a primary pure water production device and a secondary pure water production device, a warm ultra - pure water supply pipe for supplying ultra - pure water from this ultra - pure water production unit to the use point, heating means for heating the ultra - pure water, and a water sampling line branched from the warm ultra - pure water supply pipe.

[0021] In this embodiment, the primary pure water production device is not particularly limited, and a known primary pure water production device can be applied under normal control, so this will be omitted here.

[0022] The warm ultrapure water production system of this embodiment has a configuration as shown in, for example, FIG. 1. In FIG. 1, a subsystem (secondary pure water device) 1 of the ultrapure water production system includes a sub-tank 2 that stores primary pure water W produced by a primary pure water device as raw water to be treated, a supply pipe 3, a pump 4, and a membrane degassing device 5 and an ultraviolet oxidation device 6 as water treatment units provided downstream of this supply pipe 3. The supply pipe 3 branches in two directions downstream of this ultraviolet oxidation device 6. Here, it is preferable that the membrane degassing device 5 and the ultraviolet oxidation device 6 have been subjected to treatments such as washing with ultrapure water in advance to reduce elution substances. And one side passes through a heat exchanger 7 for cooling as heat exchange means, a non-regenerative ion exchange device 8, and an ultrafiltration membrane (UF membrane) 9, and supplies ultrapure water W1 at normal temperature to the use point 10 of ultrapure water at normal temperature. The unused ultrapure water W1 flows back to the sub-tank 2. The other side can supply warm ultrapure water W2 to the use point 16 of warm ultrapure water through a non-regenerative ion exchange device 12, a preheating recovery heat exchanger 13, a heat exchanger 14 for heating as heat exchange means, and an ultrafiltration membrane (UF membrane) 15 from the warm ultrapure water pipe 11. At the use point 16, the unused warm ultrapure water W2 flows back to the sub-tank 2 through the preheating recovery heat exchanger 13 from the return pipe 17. Therefore, in the subsystem 1 as described above, the primary pure water W, the unused ultrapure water W1 at the use point 10, and the unused warm ultrapure water W2 at the use point 16 serve as raw water to be treated.

[0023] (Method for producing ultrapure water) Next, a method for producing ultrapure water using such an ultrapure water production system will be described.

[0024] In the pretreatment device, pretreatment such as filtration of raw water, coagulation sedimentation, and microfiltration membrane is performed, and mainly suspended substances are removed.

[0025] A primary pure water production system is equipped with a reverse osmosis (RO) membrane separator, a degasser, a regenerative ion exchange system (such as a mixed-bed or 4-bed 5-column system), an electrodeionizer, an ultraviolet (UV) irradiation oxidation system, and other oxidation devices to remove most of the electrolytes, particulate matter, and live bacteria from the pre-treated water. For example, a primary pure water production system consists of a heat exchanger, an RO membrane separator, a mixed-bed ion exchange system, and a degasser.

[0026] In this embodiment, the primary pure water W produced by this primary pure water production apparatus is processed in subsystem 1 as follows: The 25°C primary pure water W produced by the primary pure water apparatus is stored in sub-tank 2. The 23°C return ultrapure water W1 and the 32°C return warm ultrapure water W2 after heat recovery are also stored in sub-tank 2. As a result, the raw water W0 is approximately 30°C. This raw water W0 is treated in a membrane degasser 5 and an ultraviolet oxidation apparatus 6. The treated water is then divided into 70% for room temperature (COLD) and 30% for hot water (HOT). The 30°C treated water is cooled to 23°C in a cooling heat exchanger 7, treated in a non-regenerative ion exchange apparatus 8, and then supplied to the use point 10 as room temperature (23°C) ultrapure water W1 via an ultrafiltration membrane 9. The unused ultrapure water W1 is returned to sub-tank 2.

[0027] On the other hand, the treated water for hot water is treated in a non-regenerative ion exchange device 12 from the hot ultrapure water piping 11. Then, in a preheat recovery heat exchanger 13, if energy equivalent to Δ40°C is recovered through heat exchange with the 75°C return hot ultrapure water W2, the water is heated up to 70°C and then heated to 75°C in a heating heat exchanger 14. Finally, it is supplied to the use point 16 as 75°C hot ultrapure water W2 via an ultrafiltration membrane 15.

[0028] Thus, in the conventional system shown in Figure 2, the 30°C raw water W0 from the sub-tank 22 is cooled to 23°C, and then 30% of the non-regenerative ion exchange unit 28 is used for producing hot ultrapure water, and 70% is used for producing room-temperature ultrapure water. In this case, if energy equivalent to Δ40°C is recovered in the preheat recovery heat exchanger 32 when producing hot ultrapure water, then 12°C (63°C to 75°C) of heat is required in the heating heat exchanger 33.

[0029] In contrast, in the system of this embodiment shown in Figure 1, the 30°C raw water W0 from the sub-tank 2 is treated directly in the membrane degasser 5 and the ultraviolet oxidation unit 6, and similarly, 30% of it is used for the production of warm ultrapure water and 70% for the production of ultrapure water while maintaining the 30°C temperature. At this time, if energy equivalent to Δ40°C is recovered in the preheat recovery heat exchanger 13 when producing warm ultrapure water, then the heating heat exchanger 12 will require heat equivalent to 5°C (70°C to 75°C). In other words, in this embodiment compared to the conventional example, the heating heat exchanger 12 can be reduced by approximately (12-5) / 12×100 ≈ 58.3% of the heating energy by simple calculation. Also, on the ultrapure water production side, since cooling to 23°C is not performed, it only requires 70% compared to the conventional method (which is considered 100%), thus reducing the cooling energy by 30% by simple calculation.

[0030] Furthermore, this embodiment increases the water temperature of the water treatment unit constituting subsystem 1, which has the effect of making it easier to remove gaseous components and other substances that are easily removed at high water temperatures. In addition, it is possible to reduce the size of each heat exchanger and other component units.

[0031] The present invention has been described above based on the above embodiments, but the present invention is not limited to these embodiments and can be implemented in various modified forms. For example, in the above embodiments, the temperature of the primary pure water W is 25°C, the return ultrapure water W1 is 23°C, and the return warm ultrapure water W2 after heat recovery is 32°C, but each water temperature can vary in various ways, and in particular the return warm ultrapure water W2 can be 26 to 40°C. Furthermore, the subsystem (secondary pure water production apparatus) 1 is preferably designed to produce both room temperature ultrapure water and warm ultrapure water, but it may also produce only one of them, and is particularly suitable for producing warm ultrapure water. Therefore, the temperature control in the subsequent stages of the subsystem (secondary pure water production apparatus) 1 may be either cooling / heating or both. Moreover, the constituent elements of the subsystem (secondary pure water production apparatus) 1 may be appropriately selected and used from materials that can withstand the set water temperature range. [Explanation of Symbols]

[0032] 1. Subsystem (Secondary pure water system) 2 Sub-tanks 3. Supply piping 4 pumps 5. Membrane-type degassing device (water treatment unit) 6. Ultraviolet oxidation device (water treatment unit) 7. Heat exchanger for cooling 8 Non-regenerative ion exchange device (heat exchange means) 9 Ultrafiltration membrane (UF membrane) 10 Youth Points 11. Ultrapure water piping 12 Non-regenerative ion exchange devices 13. Preheat recovery heat exchanger 14 Heat exchanger for heating (heat exchange means) 15. Ultrafiltration membrane (UF membrane) 16 Youth Points 17. Return piping W Primary pure water W0 treated raw water W1 Ultrapure water W2 Warm Ultrapure Water

Claims

1. In an ultrapure water production system comprising a primary pure water production unit and a secondary pure water production unit, The secondary pure water system uses primary pure water produced by the primary pure water system stored in a sub-tank and return water of room temperature ultrapure water and / or warm ultrapure water supplied to the point of use as raw water for treatment. The sub-tank has one or more water treatment units downstream, An ultrapure water production system comprising a heat exchange means for adjusting the treated water treated by the aforementioned water treatment unit to a required temperature.

2. The ultrapure water production system according to claim 1, wherein the heat exchange means does not have a cooling heat exchanger in front of it.

3. The ultrapure water production system according to claim 2, wherein the outlet temperature of the treated water from the heat exchange means is 20 to 80°C.

4. The ultrapure water production system according to claim 3, wherein the secondary pure water production apparatus produces either or both of room temperature ultrapure water and warm ultrapure water.

5. The ultrapure water production system according to any one of claims 1 to 4, wherein one or more water treatment units downstream of the sub-tank have had eluted substances reduced in advance.

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