Ultrapure water production system

Abstract

In an ultrapure water production system according to the present invention, a subsystem 1 has a sub-tank 2, a supply pipe 3, and a pump 4, and has a membrane-type deaeration device 5 and an ultraviolet oxidation device 6 which are provided at a downstream part of the supply pipe 3. The supply pipe 3 branches into two directions downstream of the ultraviolet oxidation device 6. In one of the directions, ultrapure water W1 at room temperature is supplied to a use point 10 via a heat exchanger 7 for cooling, a non-regenerative ion exchange device 8, and an ultrafiltration membrane 9, and the ultrapure water W1 that is unused recirculates to the sub-tank 2. In the other, heated ultrapure water W2 can be supplied to a use point 16 via a non-regenerative ion exchange device 12, a preheating-recovery heat exchanger 13, a heat exchanger 14 for heating, and an ultrafiltration membrane 15, and the heated ultrapure water W2 that is unused recirculates to the sub-tank 2 through a return pipe 17 via the preheating-recovery heat exchanger 13. Such an ultrapure water production system makes it possible to reduce power cost at a secondary pure water device and reduce energy consumption associated with heating / cooling of water being treated.

Description

Ultra-pure water production system

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

[0002] Ultra-pure 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 ultra-pure 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 wastewaters that can be expected to recover waste heat. 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 ultra-pure water and warm ultra-pure water, the heat of the return water when returning the unused warm ultra-pure water to the sub-tank at the use point is recovered to preheat the warm ultra-pure water. However, due to the principle of the heat exchanger, there is heat that cannot be completely recovered, and the unused warm ultra-pure water with potential heat energy that cannot be recovered will return 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 system) 21 of the ultrapure water production system includes a sub-tank 22 that stores primary pure water W produced in the primary pure water system 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 device 27, and a non-regenerative ion exchange device 28. Downstream of the non-regenerative ion exchange device 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 unused ultrapure water W1 at the use point 30, and the unused warm ultrapure water W2 at the use point 35 become the raw water W0 for treatment.

[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 device 27, and a non-regenerative ion exchange device 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 is supplied to the use point 30 as room temperature ultrapure water W1 via an ultrafiltration membrane 29, 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 return warm ultrapure water W2 at 75°C 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 warm ultrapure water W2 via the ultrafiltration membrane 34.

[0007] Japanese Patent Publication No. 2013-202581

[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 device and the heat from the return water at the use point 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 interplay between cooling (cold 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.

[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 treated 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.

[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.

[0018] This is a flowchart showing a subsystem of an ultrapure water production system according to one embodiment of the present invention. This is a flowchart showing a subsystem of a conventional ultrapure water production system.

[0019] The ultrapure water production system of the present invention will be described below with reference to the attached drawings.

[0020] (Urpure Water Production System) The ultrapure water production system of the present invention comprises an ultrapure water production unit equipped with a primary pure water production device and a secondary pure water production device, a hot ultrapure water supply pipe that supplies ultrapure water from the ultrapure water production unit to a point of use, and a water sampling line that branches off from the hot ultrapure water supply pipe and has heating means for heating the ultrapure water.

[0021] In this embodiment, the primary pure water production apparatus is not particularly limited, and any known primary pure water production apparatus can be applied with normal control, so this will be omitted.

[0022] The ultrapure water production system of this embodiment has a configuration as shown in Figure 1, for example. In Figure 1, the subsystem (secondary pure water system) 1 of the ultrapure water production system has a sub-tank 2 that stores primary pure water W produced by the primary pure water system as raw water for treatment, a supply pipe 3, a pump 4, and a membrane degasser 5 and an ultraviolet oxidation device 6 as water treatment units provided downstream of the supply pipe 3, and the supply pipe 3 branches in two directions downstream of the ultraviolet oxidation device 6. Here, it is preferable that the membrane degasser 5 and the ultraviolet oxidation device 6 have been treated in advance, such as by washing with ultrapure water to reduce eluted substances. One of the lines then supplies room temperature ultrapure water W1 to a use point 10 of room temperature ultrapure water via a heat exchanger 7 for cooling, a non-regenerative ion exchange device 8 and an ultrafiltration membrane (UF membrane) 9 as heat exchange means, and the unused ultrapure water W1 is returned to the sub-tank 2. On the other hand, the system is configured to supply warm ultrapure water W2 from the warm ultrapure water piping 11 to the use point 16 of the warm ultrapure water via a non-regenerative ion exchange device 12, a preheat recovery heat exchanger 13, a heating heat exchanger 14 as a heat exchange means, and an ultrafiltration membrane (UF membrane) 15. Unused warm ultrapure water W2 at the use point 16 is returned to the sub-tank 2 via the return piping 17 and the preheat recovery heat exchanger 13. Therefore, in the subsystem 1 described above, the primary pure water W, the ultrapure water W1 unused at the use point 10, and the warm ultrapure water W2 unused at the use point 16 become the raw water for treatment.

[0023] (Method for producing ultrapure water) Next, we will explain how to produce ultrapure water using such an ultrapure water production system.

[0024] In the pretreatment system, raw water is pretreated by filtration, coagulation and sedimentation, and microfiltration membranes, primarily to remove suspended solids.

[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 type), 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 raw water W0 at 30°C from the sub-tank 2 is treated directly in the membrane degasser 5 and the ultraviolet oxidation device 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 temperature of 30°C. 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] Although the present invention has been described above based on the above embodiments, 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 be varied in various ways, and in particular the return warm ultrapure water W2 may be 26 to 40°C. Furthermore, while it is preferable for the subsystem (secondary pure water production apparatus) 1 to produce both room temperature ultrapure water and warm ultrapure water, 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.

[0032] 1 Subsystem (Secondary Pure Water System) 2 Subtank 3 Supply Piping 4 Pump 5 Membrane Deaeration System (Water Treatment Unit) 6 Ultraviolet Oxidation System (Water Treatment Unit) 7 Heat Exchanger for Cooling 8 Non-Regenerative Ion Exchange System (Heat Exchange Means) 9 Ultrafiltration Membrane (UF Membrane) 10 Use Point 11 Hot Ultrapure Water Piping 12 Non-Regenerative Ion Exchange System 13 Preheat Recovery Heat Exchanger 14 Heat Exchanger for Heating (Heat Exchange Means) 15 Ultrafiltration Membrane (UF Membrane) 16 Use Point 17 Return Piping W Primary Pure Water W0 Raw Water W1 Ultrapure Water W2 Hot Ultrapure Water

Claims

1. 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 a point of use as raw water for treatment, has one or more water treatment units downstream of the sub-tank, and includes heat exchange means for adjusting the treated water treated by the water treatment units to a required temperature.

2. The ultrapure water production system according to claim 1, wherein the heat exchange means is not preceded by a cooling heat exchanger.

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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