Ultrapure water production method and ultrapure water production apparatus

Abstract

This method and apparatus for producing ultrapure water suppress a temporal increase of iron (Fe), calcium (Ca), fine particles, and the like in water. The method for producing ultrapure water treats water to be treated with one or more water treatment devices and involves a step for adjusting the temperature of the water to be treated, wherein the water treatment device includes a plate heat exchanger that adjusts the temperature of the water to be treated; the plate heat exchanger includes a first frame, a second frame, and a plurality of heat transfer plates between the first frame and the second frame; in the step for adjusting the temperature, a heat medium is supplied to the plate heat exchanger, the water to be treated is introduced from the first frame side, and the water to be treated is derived from the second frame to perform heat exchange with the heat medium; and the differential pressure between an introduction pressure and a derivation pressure of the water to be treated in the plate heat exchanger is 0.05-0.3 MPa.

Description

Method for producing ultrapure water and ultrapure water production apparatus 【0001】 The present invention relates to a method for producing ultrapure water and an ultrapure water production apparatus. 【0002】 Ultrapure water used in semiconductor manufacturing processes and the like is produced by an ultrapure water production system including a primary pure water apparatus and a secondary pure water apparatus in this order. The primary pure water apparatus has a reverse osmosis membrane apparatus and an ion exchange apparatus, and these remove total organic carbon (TOC) components and ion components in raw water or pretreated water to produce primary pure water. The secondary pure water apparatus has a membrane degassing apparatus, an ultraviolet irradiation apparatus, a non-regenerative ion exchange apparatus, an ultrafiltration apparatus, etc., and these remove extremely minute amounts of impurities in the primary pure water to produce ultrapure water. The produced ultrapure water is sent to the place of use (POU) of the ultrapure water and used here. The secondary pure water apparatus may include a heat exchanger for adjusting the temperature of the primary pure water supplied to the secondary pure water apparatus and a heat exchanger for adjusting the temperature of the ultrapure water produced by the secondary pure water apparatus to the use temperature at the place of use. As this heat exchanger, a plate-type heat exchanger provided with air outflow means for suppressing the remaining of air inside is known (for example, refer to Patent Document 1). 【0003】 JP 2017-172932 A 【0004】 By the way, in recent years, with the remarkable progress of miniaturization and high integration of semiconductor circuits, the required water quality for ultrapure water used in semiconductor manufacturing processes has become increasingly strict. For example, according to the International Technology Roadmap for Semiconductors (ITRS), as fine particles contained in ultrapure water, it is required to manage fine particles having a particle size of 10 nm or more to 1 particle / ml or less. However, as a result of the study by the present inventors, when the secondary pure water apparatus is provided with a heat exchanger, there is a problem that a temporary increase in iron (Fe), calcium (Ca), fine particles, etc. in the water passing through the heat exchanger is likely to occur. That is, immediately after the installation of the secondary pure water apparatus, ultrapure water with a constantly stable water quality can always be obtained, but it has been found that when the operation is continued for more than half a year, temporary deterioration of the water quality gradually occurs frequently. 【0005】This temporary deterioration in water quality is generally called a "spike." Figure 8 is a graph showing the concentration of iron and particulate matter in the water before and after a spike occurs in a comparative example described later. A "spike," as shown in Figure 8, is a phenomenon in which the iron and particulate matter concentrations rise sharply, causing water quality to deteriorate, and then gradually decrease, returning to the original water quality. It often occurs when there are changes in the amount of water used in the POU or changes in the operating conditions of the secondary pure water system. Impurities can accumulate in various parts of the secondary pure water system, such as the equipment, piping, valves, branching points, and stagnant areas. It is thought that spikes occur when the water flow rate and pressure in the secondary pure water system fluctuate due to changes in the amount of water used in the POU or changes in the operating conditions of the secondary pure water system, causing the accumulated impurities to flow out. Although spikes are temporary, it goes without saying that they adversely affect products such as semiconductors manufactured during the spike period, so it is important to reduce spikes as much as possible. While it is practically difficult to reduce these temporary spikes, the inventors identified that one of the factors causing these temporary spikes is the heat exchanger installed in the secondary pure water system, and thus completed the apparatus and method of this embodiment. 【0006】 This embodiment was made to solve the above-mentioned problems, and aims to provide a method and apparatus for producing ultrapure water that suppresses the temporary increase of iron (Fe), calcium (Ca), fine particles, etc. in water. 【0007】The apparatus or method of the embodiment has the following configuration: [1] A method for producing ultrapure water, comprising a step of treating water to be treated with one or more water treatment devices and adjusting the temperature of the water to be treated, wherein the water treatment device includes a plate-type heat exchanger for adjusting the temperature of the water to be treated, the plate-type heat exchanger has a first frame and a second frame and a plurality of heat transfer plates between the first frame and the second frame, in the step of adjusting the temperature, a heat transfer medium is supplied to the plate-type heat exchanger, water to be treated is introduced from the first frame side and water to be treated is discharged from the second frame side to perform heat exchange with the heat transfer medium, and the differential pressure between the introduction pressure and discharge pressure of the water to be treated in the plate-type heat exchanger is 0.05 MPa or more and 0.3 MPa or less. [2] The method for producing ultrapure water according to [1], wherein a heat transfer medium is introduced into the plate-type heat exchanger from the second frame side and the heat transfer medium is discharged from the first frame side. [3] The method for producing ultrapure water according to [1] or [2], wherein the flow direction of the water to be treated and the flow direction of the heat transfer medium in the plate-type heat exchanger are opposite flows. [4] The method for producing ultrapure water according to [1] or [2], wherein the calcium concentration in the water to be treated discharged from the plate-type heat exchanger is 2 ng / L or less, or the iron concentration is 2 ng / L or less. [5] The method for producing ultrapure water according to [1] or [2], wherein the water treatment equipment is a pump, the plate-type heat exchanger, a non-regenerative ion exchange device, and an ultrafiltration membrane device, in this order. [6] The method for producing ultrapure water according to [1] or [2], wherein the water treatment equipment is a pump, the plate-type heat exchanger, and an ultrafiltration membrane device, and the water to be treated is heated in the plate-type heat exchanger to produce warm ultrapure water.[7] An ultrapure water production apparatus having one or more water treatment devices for treating water to be treated, wherein the water treatment device includes a plate heat exchanger, the plate heat exchanger having a first frame and a second frame, a plurality of heat transfer plates between the first frame and the second frame, an inlet for introducing a heat transfer medium into the plate heat exchanger, an outlet for discharging a heat transfer medium from the plate heat exchanger, an inlet for water to be treated provided on the first frame, and an outlet for water to be treated provided on the second frame, wherein the differential pressure between the introduction pressure and the discharge pressure of water to be treated in the plate heat exchanger is 0.05 MPa or more and 0.3 MPa or less. [8] The ultrapure water production apparatus according to [7], wherein the plate heat exchanger has an inlet for a heat transfer medium in the second frame and an outlet for a heat transfer medium in the first frame. [9] The ultrapure water production apparatus according to [7], wherein the calcium concentration or iron concentration in the water to be treated, discharged from the plate-type heat exchanger, is 2 ng / L or less.

[10] The ultrapure water production apparatus according to [7], wherein the water treatment equipment comprises a pump, the plate-type heat exchanger, a non-regenerative ion exchanger, and an ultrafiltration membrane device in that order.

[11] The ultrapure water production apparatus according to [7], wherein the water treatment equipment comprises a pump, the plate-type heat exchanger, and an ultrafiltration membrane device in that order, and the water to be treated is heated in the plate-type heat exchanger to produce warm ultrapure water. The symbol "~" indicates a numerical range including the numbers before and after it. 【0008】 According to the ultrapure water production method and apparatus of the embodiment, ultrapure water can be produced while suppressing the temporary increase of iron (Fe), calcium (Ca), fine particles, etc. in the water. 【0009】This is a schematic diagram of a plate-type heat exchanger. This is a schematic diagram of the heat transfer plate of this embodiment. This is a schematic diagram of another heat transfer plate of this embodiment. This is a schematic elevation view of the plate-type heat exchanger of this embodiment. This is a schematic elevation view of a conventional plate-type heat exchanger. This is a schematic diagram of a secondary pure water system having the plate-type heat exchanger of this embodiment. This is a schematic diagram of a hot ultrapure water system having the plate-type heat exchanger of this embodiment. This is a graph showing the changes in water quality before and after a rapid increase in iron (Fe) concentration and particulate matter concentration in the comparative example. 【0010】 The method for producing ultrapure water according to this embodiment will be described below with reference to the drawings. The method for producing ultrapure water according to this embodiment includes a step of treating the water to be treated with one or more water treatment devices and adjusting the temperature of the water to be treated. The water treatment device includes a plate-type heat exchanger, and in the step of adjusting the temperature of the water to be treated, the water to be treated is passed through the plate-type heat exchanger in a specific direction. The plate-type heat exchanger has a first frame, a second frame, and a plurality of heat transfer plates between the first frame and the second frame, and in the step of adjusting the temperature, the water to be treated is introduced from the first frame side and discharged from the second frame side. The differential pressure between the introduction pressure and the discharge pressure of the water to be treated in the plate-type heat exchanger is 0.05 MPa or more and 0.3 MPa or less. Preferably, the differential pressure between the introduction pressure and the discharge pressure of the water to be treated is 0.1 MPa or more and 0.25 MPa or less, and more preferably 0.15 MPa or more and 0.23 MPa or less. 【0011】Figure 1 is a schematic diagram of a plate-type heat exchanger 1 used in the ultrapure water production method of this embodiment, and is a side view when the plate-type heat exchanger 1 is placed on the ground or the like, with the surface of the first frame facing forward. The plate-type heat exchanger 1 has a first frame 11 and a second frame 12. The first frame 11 and the second frame 12 are spaced apart, and a plurality of heat transfer plates 4 are arranged between the first frame 11 and the second frame 12. The first frame 11 is provided with an inlet 2a for the water to be treated, and the second frame 12 is provided with an outlet 2b for the water to be treated. The heat transfer plates 4 of the plate-type heat exchanger 1 of this embodiment are substantially rectangular, and their surfaces are made up of irregularities that serve as fluid passages. The heat transfer plates 4 have passage holes 5a, 5b, 13a, and 13b at the four corners of their irregular heat transfer surface, which serve as fluid inlets and outlets (see Figure 2). Gaskets 3 are provided between the outer peripheries of the multiple heat transfer plates 4, and the first frame 11 and the second frame 12 are fixed from both sides with tightening bolts (not shown). Note that fixing is not limited to bolting; for example, welding may be used. Between the multiple heat transfer plates 4, alternating passages for water to be treated 21a, 22a, 23a, 24a, 25a, 26a and passages for heat transfer medium 21b, 22b, 23b, 24b, 25b, 26b, 27b are formed. The water to be treated passages 21a to 26a are connected to an inlet 2a and an outlet 2b provided on the first frame 11. Heat from the heat transfer medium flowing through the heat transfer medium passages 21b to 27b is transferred to the water to be treated flowing through the water to be treated passages 21a to 26a via the heat transfer plates 4, and the water to be treated is heated or cooled. 【0012】Figure 2 is a schematic diagram of the heat transfer plate 4 of this embodiment. The heat transfer plate 4 has irregularities (not shown) formed on its surface that serve as fluid passages, and is usually made of a metal material such as stainless steel or titanium. The heat transfer plate 4 has fluid passage holes 5a, 13a, 5b, and 13b around its outer circumference. The passage holes 5a and 5b are a pair of fluid inlets 5a and outlets 5b. The passage holes 13a and 13b are a pair of fluid inlets 13a and outlets 13b. The heat transfer plate 4 has two pairs of inlets and outlets: inlet 5a and outlet 5b and inlet 13a and outlet 13b. Preferably, the pairs of inlets and outlets are spaced apart so that the passage for the water to be treated or heat transfer medium flowing through the heat transfer plate is as long as possible. If the heat transfer plate 4 is substantially rectangular, the inlets and outlets are provided at two diagonal corners of the four corners of the rectangle. Specifically, the inlet 5a and outlet 5b are located at two diagonal corners, and the inlet 13a and outlet 13b are located at two diagonal corners. The heat transfer plate 4 has gaskets 3 near its outer circumference and near the outer circumferences of the passage holes 5a, 13a, 5b, and 13b. The heat transfer plate 4 shown in Figure 2 allows the water to be treated to flow through the flow path formed by the gaskets 3 and the heat transfer plate 4. The water to be treated flows in from the passage hole (inlet) 5a, flows in the direction of the dotted line in the figure, and flows out from the passage hole (outlet) 5b. Note that Figure 2 shows an configuration in which the inlet 5a and outlet 5b are located at two diagonal corners, but for the sake of explanation, Figure 1 shows an configuration in which the inlet 5a and outlet 5b are located at adjacent corners. 【0013】 Figure 3 is a schematic diagram showing one of the multiple heat transfer plates 4 of the plate-type heat exchanger 1 of this embodiment. The heat transfer plate 4 shown in Figure 3 allows a heat transfer medium to flow through the flow path formed by the gasket 3 and the heat transfer plate 4. The heat transfer medium flows in from the passage hole (inlet) 13a, flows in the direction of the dotted line in the figure, and flows out from the passage hole (outlet) 13b. 【0014】In Figures 1 to 3, the gasket 3 is positioned at the outer edge of the heat transfer plate 4. The gasket 3 is made of an elastic material having a predetermined width and thickness, and has a sealing function to prevent fluid leakage by liquid-tightly sealing the outer edge of the heat transfer plate 4. Preferably, the gasket 3 is sandwiched between the heat transfer plate 4 and in surface contact with the heat transfer plate 4. Furthermore, it is preferable that the shape of the gasket 3 is such that its cross-section, at least the cross-section perpendicular to the longitudinal direction, is rectangular, and the outer edge of the gasket 3 facing the outside and inside of the plate-type heat exchanger 1 is a flat surface without curves. The rectangular cross-section minimizes the gap between the gasket 3 and the heat transfer plate 4, thereby suppressing water accumulation in the plate-type heat exchanger 1. Similarly, the flat outer edge minimizes the gap between the gasket 3 and the heat transfer plate 4, thereby suppressing water accumulation in the plate-type heat exchanger 1. Furthermore, in this embodiment, since the plate-type heat exchanger 1 introduces the water to be treated from the first frame side and discharges the water to be treated from the second frame side, air is less likely to accumulate inside. Also, since an air outlet means can cause the accumulation of impurities, it is preferable not to have an air outlet means. In addition, by installing the inlet for the water to be treated at the bottom of the heat exchanger and the outlet at the top of the heat exchanger, and by having the water to be treated flow upward along the heat transfer plate 4 within the heat exchanger, the accumulation of air can be easily prevented. 【0015】 Furthermore, in Figures 1 to 3, it is preferable that the inner diameter of the inlet 2a and the inner diameter of the passage hole 5a be approximately the same as the inner diameter of the gasket 3 surrounding the inlet 2a and the passage hole 5a, thereby creating a shape that does not produce irregularities in the inflow path of the water to be treated flowing into the plate-type heat exchanger 1 that could cause the accumulation of impurities. Similarly, it is preferable that the inner diameter of the outlet 2b and the inner diameter of the passage hole 5b be approximately the same as the inner diameter of the gasket 3 surrounding them. In addition, it is preferable that the inner diameter of the passage hole 13b be approximately the same as the inner diameter of the gasket 3 surrounding them to suppress the accumulation of the water to be treated. The shape of the gasket 3 is preferably such that no accumulation areas such as irregularities are created between it and the passage hole provided on the heat transfer plate 4. The gasket 3 sandwiched between the two heat transfer plates 4 may be integrally molded, or multiple gaskets may be used. 【0016】 In the ultrapure water production method of this embodiment, the water to be treated is introduced into the plate-type heat exchanger 1 from the inlet 2a of the first frame 11, flows through the flow path on the surface of the heat transfer plate 4, and is discharged from the outlet 2b of the second frame 12. 【0017】 The material of the plate-type heat exchanger 1 in the embodiment is stainless steel, titanium, iron, etc., and in order to avoid deterioration of the water quality of the ultrapure water produced, it is preferable that it be titanium, and at least the wetted surfaces of the heat transfer plates and the first and second frames are made of titanium. 【0018】 Figure 4 is a simplified schematic diagram showing the passage of water to be treated within the plate-type heat exchanger 1 shown in Figure 1. It is an elevation view when the plate-type heat exchanger 1 is placed on the ground or the like, with the surface of the first frame 11 facing forward. The plate-type heat exchanger 1 shown in Figure 4 has a first frame 11 and a second frame 12. Multiple heat transfer plates 4 are arranged between the first frame 11 and the second frame 12. The first frame 11 is provided with an inlet 2a, and the second frame 12 is provided with an outlet 2b. In Figure 4, the dotted line represents the flow path of the water to be treated. The diagonal lines represent the passage of the heat transfer medium. In the plate-type heat exchanger 1 shown in Figure 4, water to be treated is introduced from the inlet 2a on the first frame 11 side, and the water to be treated is discharged from the outlet 2b on the second frame 12 side. As a result, all of the multiple water passages to be treated, located between the heat transfer plates, have the same length. Therefore, the flow velocity in each of the multiple water passages to be treated does not differ, and a common flow velocity can be ensured across all of them. This makes it easier for the flow velocity of the water to be treated to be uniform within the plate-type heat exchanger 1, allowing for efficient heat exchange. Consequently, sufficient heat exchange can be achieved even if the number of heat transfer plates is reduced or the flow rate introduced from the inlet 2a is increased, making it possible to miniaturize the plate-type heat exchanger. In addition, because the flow velocity within the heat exchanger is increased, water stagnation inside is less likely to occur. Therefore, for example, impurity accumulation does not occur in areas where it is particularly likely to occur, such as the boundary between the heat transfer plates 4 and the gasket 3 within the heat exchanger, and stable water quality can be maintained. 【0019】 Figure 5 is a simplified schematic diagram showing the passage of water to be treated in a conventional plate-type heat exchanger 100. The conventional plate-type heat exchanger 100 has both the inlet and outlet of water to be treated on the first frame 11 side, and other components are the same as the plate-type heat exchanger 1 shown in Figures 1 and 4. Therefore, components that perform the same function are given the same reference numerals and detailed explanations are omitted. Figure 5 is an elevation view of the plate-type heat exchanger 100 when it is placed on the ground or the like, with the surface of the first frame 11 facing forward. In Figure 5, the dotted lines represent the flow path of water to be treated. 【0020】 In the plate-type heat exchanger 100 shown in Figure 5, the water to be treated is introduced from an inlet 80a located on the first frame 11 side, and the water to be treated is discharged from an outlet 80b located on the first frame 11 side. As a result, the multiple water-to-treat passages located between the heat transfer plates are shorter the closer they are to the first frame 11 and longer the further they are from the first frame 11. This difference in length affects the flow velocity of the water to be treated. That is, the flow velocity in the multiple water-to-treat passages is higher the closer they are to the first frame 11 and lower the further they are from the first frame 11. As a result, heat exchange within the plate-type heat exchanger 100 tends to be inefficient. Consequently, in order to perform sufficient heat exchange, it is necessary to reduce the flow rate introduced from the inlet 2a, and reducing the flow rate slows down the flow velocity within the plate-type heat exchanger 100. This makes it easier for water to accumulate in areas where impurities are particularly likely to accumulate, such as the boundary between the heat transfer plate 4 and the gasket 3. When water stagnates, impurities can accumulate inside the heat exchanger, and if the flow rate of the treated water fluctuates unexpectedly, these accumulated impurities may leak out, potentially degrading the water quality. 【0021】Figure 6 is a schematic diagram of the secondary pure water system 30 having the plate-type heat exchanger 1 described above. The secondary pure water system 30 shown in Figure 6 is equipped with a pure water tank (TK) 31, a pump (P) 32, a heat exchanger (HEX) 33, an ultraviolet oxidation device (UV) 34, a non-regenerative ion exchange device (Polisher) 35, and an ultrafiltration (UF) device 36 along the flow path L1 of the water to be treated, and processes the water to be treated to produce ultrapure water (secondary pure water). The ultrafiltration (UF) device 36 is connected to the place of use (POU) 40 of the ultrapure water, and the ultrapure water produced in the secondary pure water system 30 is used in the place of use (POU) 40. In addition, the secondary pure water system 30 has a circulation line L2, and the ultrapure water that is not used in the place of use (POU) 40 flows through the circulation line L2 and is circulated to the pure water tank 31. 【0022】 The pure water tank (TK) 31 stores the primary pure water, which is the water to be treated by the secondary pure water system 30. A pretreatment device 50 and a primary pure water system 60 are provided upstream of the secondary pure water system 30, and the raw water is treated sequentially in the pretreatment device 50 and the primary pure water system 60 to produce primary pure water. The raw water can be industrial water, tap water, groundwater, river water, etc. The pretreatment device 50 produces pretreated water by removing some suspended solids and organic matter from the raw water through turbidity removal treatment. Depending on the quality of the raw water, the pretreatment device 50 may be omitted. The primary pure water system 60 adsorbs particles remaining in the pretreated water using an adsorbent such as activated carbon, and removes inorganic ions, organic matter, fine particles, etc. contained in the pretreated water using a membrane filtration device such as a reverse osmosis membrane device. The primary pure water system 60 may also be equipped with an ion exchange device, an ultraviolet irradiation device, and a membrane degassing device. The ion exchange device can remove ionic components from the water using, for example, an ion exchange resin. The ultraviolet irradiation device can decompose and remove organic matter in the water by irradiating it with ultraviolet light. The membrane degassing device can remove dissolved gases such as dissolved oxygen from the pre-treated water. 【0023】Pump (P) 32 is, for example, a water supply pump that pressurizes the primary pure water in the pure water tank (TK) 31 and sends it to the next stage. The secondary pure water system 30 may also be equipped with a booster pump to increase the pressure of the water to be treated flowing through the piping, in addition to the water supply pump. In this case, it is preferable that the booster pump be installed between the non-regenerative ion exchange device (Polisher) 35 and the ultrafiltration (UF) device 36, or upstream of the non-regenerative ion exchange device (Polisher) 35. 【0024】 As the heat exchanger 33, the plate-type heat exchanger 1 (Figure 1) described above is used, with the water to be treated introduced from the inlet of the first frame 11 and the temperature-controlled water to be treated discharged from the outlet of the second frame 12. The heat transfer medium is, for example, steam or hot water when heating the water to be treated, and cold water when cooling it. In the heat exchanger 33, it is preferable to use cold water as the heat transfer medium. The heat transfer medium is introduced from the inlet of the second frame 12 and discharged from the outlet of the first frame 11. Inside the plate-type heat exchanger 1, heat is exchanged between the heat transfer medium and the water to be treated via the heat transfer plates 4, thereby adjusting the temperature of the water to be treated. At this time, the flow direction of the heat transfer medium and the water to be treated inside the plate-type heat exchanger 1 may be the same (parallel flow) or opposite, but it is preferable that they are opposite (counter-counter-counter flow) from the viewpoint of heat exchange efficiency. In addition, the differential pressure between the inlet and outlet of the water to be treated in the plate-type heat exchanger 1 is 0.05 MPa or more and 0.3 MPa or less. 【0025】 The material of the plate-type heat exchanger 1 in the embodiment is stainless steel, titanium, iron, Hastelloy®, copper, etc., and in order to avoid deterioration of the water quality of the ultrapure water produced, it is preferable that it be stainless steel or titanium, and at least the wetted surfaces of the heat transfer plates and the first and second frames are preferably made of stainless steel or titanium. 【0026】When the plate-type heat exchanger 1 has been installed for more than one year, the iron content of the treated water (inlet water) is, for example, 0.01 ng / L to 2 ng / L, and the calcium content is, for example, 0.01 ng / L to 2 ng / L. Furthermore, when the plate-type heat exchanger 1 has been installed for more than one year, the iron content of the treated water that has passed through the plate-type heat exchanger 1 is, for example, 0.01 ng / L to 2 ng / L, and the calcium content is, for example, 0.01 ng / L to 2 ng / L. In addition, when the plate-type heat exchanger 1 has passed through the non-regenerative ion exchange device 35 and the ultrafiltration device 36 described later, the iron content of the treated water is, for example, 0.01 ng / L to 1 ng / L, and the calcium content is, for example, 0.01 ng / L to 1 ng / L. 【0027】 The ultraviolet oxidation device 34 decomposes organic matter contained in the water to be treated by irradiating it with ultraviolet light. This reduces the amount of total organic carbon (TOC) in the water to be treated. When the ultraviolet oxidation device 34 irradiates the water to be treated with ultraviolet light, hydrogen peroxide may be generated in the water. Therefore, a hydrogen peroxide decomposition resin device, such as a catalyst resin device, may be installed downstream of the ultraviolet oxidation device 34 to decompose the hydrogen peroxide using a catalyst. In addition, a membrane degasser for removing gases present in the water to be treated may be installed downstream of the ultraviolet oxidation device 34. 【0028】 The non-regenerative ion exchange device 35 adsorbs trace amounts of ions in the water to be treated and removes them from the water. This non-regenerative ion exchange device 35 is a "non-regenerative" device that has a mixed-bed type ion exchange resin. In other words, it is a type that replaces the entire device without regenerating the ion exchange resin that has adsorbed ions, and can remove ions with a high removal rate. 【0029】 The ultrafiltration device 36 has an ultrafiltration membrane and removes fine particles from the water to be treated by cross-flow filtration using the ultrafiltration membrane. This produces ultrapure water. 【0030】In the secondary pure water system 30 of this embodiment, the water to be treated is introduced from the first frame side of the plate-type heat exchanger 1, and the water to be treated is discharged from the second frame side opposite to the first frame side, and the differential pressure between the introduction pressure and discharge pressure of the water to be treated is 0.05 MPa or more and 0.3 MPa or less. As a result, iron and calcium do not accumulate in the plate-type heat exchanger 1. As a result, even if water is passed through for a period of more than one year, the increase in iron by the plate-type heat exchanger 1 can be kept to 0.1% or less, and the increase in calcium can be kept to 0.1% or less. This suppression of the increase rate can be continued for, for example, two years. The increase rates of iron and calcium are calculated using the following formulas. 【0031】 Iron increase rate = [(Iron concentration of outlet water of plate heat exchanger 1 - Iron concentration of inlet water) / Iron concentration of inlet water of plate heat exchanger 1] × 100 (%) Calcium increase rate = [(Calcium concentration of outlet water of plate heat exchanger 1 - Iron concentration of inlet water) / Calcium concentration of inlet water of plate heat exchanger 1] × 100 (%) 【0032】 Figure 7 is a schematic diagram of a thermal ultrapure water production apparatus 70 having the plate-type heat exchanger 1 described above. The thermal ultrapure water production apparatus 70 shown in Figure 7 is installed downstream of the secondary pure water apparatus 30 shown in Figure 6. The thermal ultrapure water production apparatus 70 shown in Figure 7 has a preheater 71, a heater 72, and an ultrafiltration device 73. The thermal ultrapure water produced by the thermal ultrapure water production apparatus 70 is supplied to the use point 40 shown in Figure 6. 【0033】The preheater 71 is a heat exchanger that heats the ultrapure water (water temperature of about 23°C) sent from the secondary pure water system 30. The preheater 71 heats the ultrapure water to be treated through this heat exchange. For example, the preheater 71 can adjust the temperature of the ultrapure water to about 60°C to 70°C. The heater 72 further heats the ultrapure water heated by the preheater 71. By heating with the heater 72, the ultrapure water reaches the water temperature to be supplied to the use point 40, i.e., the supply water temperature. For example, if warm ultrapure water with a water temperature of 75°C is used at the use point 40, the heater 72 heats the ultrapure water to the supply water temperature of 75°C. The plate-type heat exchanger 1 of the above embodiment is used as the preheater 71 and heater 72. The preheater 71 and heater 72 may be integrated into a single plate-type heat exchanger 1, as long as it is possible to produce warm ultrapure water at the desired temperature. 【0034】 Inside the plate-type heat exchanger 1, which is used as a preheater 71 and heater 72, heat is exchanged between the heat transfer medium and the water to be treated via the heat transfer plate 4, thereby adjusting the temperature of the water to be treated. The flow direction of the heat transfer medium and the water to be treated inside the plate-type heat exchanger 1 at this time may be the same (parallel flow) or opposite, but it is preferable from the viewpoint of heat exchange efficiency for them to be opposite (counter-facing flow). In addition, the differential pressure between the inlet and outlet of the water to be treated in the plate-type heat exchanger 1 is 0.05 MPa or more and 0.3 MPa or less, preferably 0.1 MPa or more and 0.25 MPa or less, and more preferably 0.15 MPa or more and 0.23 MPa or less. 【0035】When the plate-type heat exchanger 1 has been installed for more than one year, the iron content of the treated water is, for example, 0.01 ng / L to 2 ng / L, and the calcium content is, for example, 0.01 ng / L to 2 ng / L. Furthermore, when the plate-type heat exchanger 1 has been installed for more than one year, the iron content of the treated water that has passed through it is, for example, 0.01 ng / L to 2 ng / L, and the calcium content is, for example, 0.01 ng / L to 2 ng / L. In addition, when the plate-type heat exchanger 1 and the ultrafiltration device 73 have passed through it, the iron content of the treated water is, for example, 0.01 ng / L to 1 ng / L, and the calcium content is, for example, 0.01 ng / L to 1 ng / L. 【0036】 In the ultrapure water production apparatus 70 of this embodiment, as described above, the water to be treated is introduced from the first frame side of the plate-type heat exchanger 1 and discharged from the second frame side opposite to the first frame side. The differential pressure between the introduction pressure and the discharge pressure of the water to be treated is 0.05 MPa or more and 0.3 MPa or less. As a result, impurities such as iron, calcium, and fine particles do not accumulate in the plate-type heat exchanger 1. As a result, even if water is passed through for a period of more than one year, the increase in iron by the plate-type heat exchanger 1 can be kept to 0.1% or less, and the increase in calcium can be kept to 0.1% or less. This suppression of the increase rate can be continued for, for example, about two years. The increase rates of iron and calcium are values ​​calculated by the above formula. 【0037】 Next, examples will be described. The present invention is not limited to the following examples. 【0038】(Example) An apparatus similar to the secondary pure water apparatus 30 shown in Figure 6 was prepared, and the water to be treated (primary pure water) was supplied downstream from the pure water tank. The iron concentration, calcium concentration, and particulate matter concentration in the water were measured at the inlet side of the plate-type heat exchanger and at the outlet side of the ultrafiltration device (UF) (corresponding to the ultrafiltration device 36 in Figure 6). Table 1 shows the maximum values ​​of iron (Fe) concentration and calcium (Ca) concentration when water was continuously supplied to the secondary pure water apparatus for one year. In the plate-type heat exchanger of the example, the water to be treated was introduced from the first frame side of the plate-type heat exchanger and discharged from the second frame side opposite to the first frame side, and the differential pressure between the introduction pressure and discharge pressure of the water to be treated was 0.25 MPa. The iron concentration was measured by inductively coupled plasma mass spectrometry (ICP-MS) after evaporating and concentrating samples taken from each location. The particulate matter concentration was measured by an online particulate meter (UDI50). 【0039】 (Comparative Example) Instead of the plate-type heat exchanger in the example, a plate-type heat exchanger was used in which the water to be treated was introduced from the first frame side and discharged from the first frame side. The number of plates in the plate-type heat exchanger used in the comparative example was approximately 10 times that of the plate-type heat exchanger used in the example. In the comparative example, the differential pressure between the introduction pressure and discharge pressure of the water to be treated to the plate-type heat exchanger was set to 0.02 MPa. Otherwise, the water to be treated was supplied to the plate-type heat exchanger in the same manner as in the example, and the iron concentration, calcium concentration, and particulate matter concentration in the water at the inlet side of the plate-type heat exchanger and the outlet side of the ultrafiltration device were measured. Table 1 shows the maximum values ​​of iron (Fe) concentration and calcium (Ca) concentration at the time of installation, i.e., one week after the completion of startup (immediately after installation), and one week after one year of continuous water flow to the secondary pure water system (one year after installation). Furthermore, in the comparative example, the changes in water quality before and after a rapid increase in iron (Fe) concentration and particulate matter concentration are shown in the graph in Figure 8. 【0040】 【0041】Table 1 shows that in an example where water to be treated was introduced from the first frame side of the plate-type heat exchanger and discharged from the second frame side opposite the first frame side, and the differential pressure between the introduction and discharge pressures of the water to be treated was 0.25 MPa, no temporary deterioration in water quality was observed as a result of continuous measurement of particulate matter. Furthermore, it can be seen that there was no increase in iron and calcium for one year after the installation of the plate-type heat exchanger, and that ultrapure water with stable water quality can be obtained. 【0042】 In contrast, continuous measurement of particulate matter in the comparative example's plate-type heat exchanger confirmed that temporary water quality deterioration occurred approximately 15 times per month over a one-month period. This is because, in the comparative example's plate-type heat exchanger, the water to be treated is introduced from the first frame side and the water that has passed through the plate-type heat exchanger is similarly discharged from the first frame side, causing water to stagnate inside. It is thought that impurities such as iron, calcium, and particulate matter accumulated in this stagnation, and that these accumulated impurities contributed to the temporary deterioration of the end-user water quality. Furthermore, comparing the example and the comparative example, the number of plates in the example's plate-type heat exchanger is approximately 1 / 10 of that in the comparative example. Therefore, the example significantly reduces the possibility of water quality deterioration due to impurities originating from the heat exchanger. 【0043】 1: Plate-type heat exchanger, 2a: Inlet, 2b: Outlet, 3: Gasket, 4: Heat transfer plate, 11: First frame, 12: Second frame, 5a: Through hole (inlet), 5b: Through hole (outlet), 13a: Through hole (inlet), 13b: Through hole (outlet), 21a, 22a, 23a, 24a, 25a, 26a: Water to be treated passage, 21b, 22b, 23b, 24b, 25b, 26b, 27b: Heat transfer medium passage, 30: Secondary pure water system, 31: Pure water tank, 33: Heat exchanger, 34: Ultraviolet oxidation system, 35: Non-regenerative ion exchange system, 36: Ultrafiltration system, 40: Use point, 50: Pretreatment system, 60: Primary pure water system, 70: Hot ultrapure water production system, 71: Preheater, 72: Heater, 73: Ultrafiltration system, 80a: Inlet, 80b: Outlet, 100: Plate heat exchanger, L1: Flow path, L2: Circulation line

Claims

1. A method for producing ultrapure water, comprising the step of adjusting the temperature of water to be treated using a plate-type heat exchanger, wherein the plate-type heat exchanger has a first frame and a second frame and a plurality of heat transfer plates between the first frame and the second frame, and in the temperature adjustment step, a heat transfer medium is supplied to the plate-type heat exchanger, water to be treated is introduced from the first frame side and water to be treated is discharged from the second frame side to perform heat exchange with the heat transfer medium, and the differential pressure between the introduction pressure and discharge pressure of water to be treated in the plate-type heat exchanger is 0.05 MPa or more and 0.3 MPa or less.

2. The method for producing ultrapure water according to claim 1 or 2, wherein a heat transfer medium is introduced into the plate-type heat exchanger from the second frame side and the heat transfer medium is discharged from the first frame side.

3. The method for producing ultrapure water according to claim 1 or 2, wherein the flow direction of the water to be treated and the flow direction of the heat transfer medium in the plate-type heat exchanger are opposite flows.

4. The method for producing ultrapure water according to claim 1 or 2, wherein the calcium concentration or iron concentration in the treated water discharged from the plate-type heat exchanger is 2 ng / L or less.

5. A method for producing ultrapure water according to claim 1 or 2, wherein the water treatment equipment used is a pump, a plate-type heat exchanger, a non-regenerative ion exchange device, and an ultrafiltration membrane device in this order.

6. The method for producing ultrapure water according to claim 1 or 2, wherein the water treatment equipment includes a pump, the plate-type heat exchanger, and an ultrafiltration membrane device, and the water to be treated is heated in the plate-type heat exchanger to produce warm ultrapure water.

7. An ultrapure water production apparatus having a plate-type heat exchanger having a first frame and a second frame and a plurality of heat transfer plates between the first frame and the second frame, the plate-type heat exchanger having an inlet for introducing a heat transfer medium into the plate-type heat exchanger, an outlet for discharging a heat transfer medium from the plate-type heat exchanger, an inlet for water to be treated provided on the first frame and an outlet for water to be treated provided on the second frame, and the differential pressure between the introduction pressure and the discharge pressure of water to be treated in the plate-type heat exchanger being 0.05 MPa or more and 0.3 MPa or less.

8. The ultrapure water production apparatus according to claim 7, wherein the plate-type heat exchanger has an inlet for a heat transfer medium in the second frame and an outlet for a heat transfer medium in the first frame.

9. The ultrapure water production apparatus according to claim 7, wherein the calcium concentration or iron concentration in the water to be treated, discharged from the plate-type heat exchanger, is 2 ng / L or less.

10. The ultrapure water production apparatus according to claim 7, wherein the water treatment equipment comprises, in this order, a pump, the plate-type heat exchanger, a non-regenerative ion exchange device, and an ultrafiltration membrane device.

11. The ultrapure water production apparatus according to claim 7, wherein the water treatment equipment comprises a pump, the plate-type heat exchanger, and an ultrafiltration membrane device in that order, and the plate-type heat exchanger heats the water to be treated to produce warm ultrapure water.

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