JP5953726B2 - Ultrapure water production method and apparatus - Google Patents

Description

  The present invention relates to an ultrapure water production method and apparatus, and more particularly to an ultrapure water production method and apparatus improved in a control method for a heat exchanger of a primary pure water production apparatus.

  As shown in FIG. 2, the ultrapure water used as semiconductor cleaning water is a pretreatment system 1, a primary pure water production apparatus 10, and a secondary pure water production apparatus (often referred to as a subsystem) 20. It is manufactured by treating raw water (industrial water, city water, well water, etc.) with an ultrapure water manufacturing apparatus composed of (Patent Document 1). In FIG. 2, the role of each system is as follows.

  In the pretreatment system 1 comprising agglomeration, pressurized flotation (precipitation), filtration (membrane filtration) apparatus and the like (in this conventional example, agglomeration filtration apparatus), suspended substances and colloidal substances in raw water are removed. In this process, it is also possible to remove high molecular organic substances, hydrophobic organic substances, and the like.

  Primary pure tank comprising pretreated water tank 11, heat exchanger 15, reverse osmosis membrane treatment device (RO device) 12, ion exchange device (such as mixed bed type or 4 bed 5 tower type) 13 and deaeration device 14. The water production apparatus 10 removes ions and organic components from the raw water. In addition, as the temperature of water increases, the viscosity decreases and the permeability of the RO membrane improves. For this reason, as shown in FIG. 2, the heat exchanger 15 is installed in the front | former stage of the reverse osmosis membrane processing apparatus 12, and water is heated so that the temperature of the supply water to the reverse osmosis membrane processing apparatus 12 may become more than predetermined temperature. Steam is supplied to the primary side of the heat exchanger 15 as a heat source fluid. The reverse osmosis membrane treatment apparatus 12 removes salts and ionic and colloidal TOC. The ion exchange device 13 removes TOC components adsorbed or ion exchanged by an ion exchange resin while removing salts. In the deaeration device 14, inorganic carbon (IC) and dissolved oxygen are removed.

The primary pure water produced by the primary pure water production apparatus is sent to the secondary pure water production apparatus 20 via the pipe 19. The secondary pure water production apparatus 20 includes a pure water tank 21, a pump 22, a heat exchanger 23, a low-pressure ultraviolet oxidation apparatus (UV apparatus) 24, an ion exchange apparatus 25, and an ultrafiltration membrane (UF membrane) separation apparatus 26. I have. In the low-pressure ultraviolet oxidizer 24, TOC is decomposed into an organic acid and further to CO ₂ by 185 nm ultraviolet rays emitted from a low-pressure ultraviolet lamp. Organic substances and CO ₂ produced by the decomposition are removed by the ion exchange device 25 at the subsequent stage. In the ultrafiltration membrane separation device 26, the fine particles are removed, and the outflow particles from the ion exchange resin are also removed.

  The ultrapure water produced by the secondary pure water production apparatus 20 is sent to the use point 40 via the pipe 30, and the unused ultrapure water is returned to the tank 21 via the pipe 50. When the pressure of the pump 22 is insufficient, a booster pump may be installed upstream of the ion exchange device 25 (for example, between the UV oxidation device 24 and the ion exchange device 25).

  The heat exchanger 23 is for making the temperature of the ultrapure water sent from the secondary pure water production apparatus 20 to the use point 40 a predetermined temperature (for example, about 25 ° C.).

  In general, the ultrapure water produced by the secondary pure water production apparatus 20 is supplied to the use point, and surplus ultrapure water (unused) is returned from the use point 40 to the secondary pure water production apparatus 20 and again It is processed by the secondary pure water production apparatus 20 and circulates while maintaining a certain ultrapure water quality. And since it does not stagnate by always circulating, the reproduction of microorganisms is suppressed. During the circulation, the heat of the circulating ultrapure water is increased by the heat of the pump 22 and the ultraviolet irradiation lamp of the low-pressure ultraviolet oxidizer 24, and the temperature of the circulating ultrapure water is set to a predetermined value. Maintain temperature.

  The ultrapure water from the secondary pure water production apparatus may be further processed by the tertiary pure water production apparatus to further reduce the impurity concentration. As the tertiary pure water production apparatus, one having the same configuration as the secondary pure water production apparatus is used.

JP2010-214300

  Conventionally, the amount of steam supplied to the heat exchanger 15 is controlled so that the outlet water temperature of the heat exchanger 15 becomes a predetermined temperature. However, when the temperature fluctuates depending on the season, secondary pure water is produced from the pipe 19. The temperature of the water sent to the tank 21 (hereinafter also referred to as the sub tank 21) of the device 20 (sub system) changes. In summer and the like, the temperature of the water flowing into the sub tank 21 may become unnecessarily high.

  The present invention prevents ultrapure water that prevents the temperature of primary pure water supplied to a secondary pure water production apparatus from being unnecessarily high and reduces the heating cost of a heat exchanger of the primary pure water production apparatus. An object is to provide a manufacturing method and apparatus.

  Although not shown in FIG. 2, a relay tank is installed between the reverse osmosis membrane treatment device 12 and the ion exchange device 13 of the primary pure water production apparatus 10, and the collected water from the semiconductor production process is relayed to the relay tank. It may be introduced into a tank, and RO treated water and recovered water may be mixed and supplied to the ion exchange device 13. Since the temperature of the recovered water is usually as high as 25 to 30 ° C., the temperature of the water flowing into the sub tank 21 may fluctuate due to fluctuations in the flow rate of the recovered water.

  In one aspect of the present invention, an object of the present invention is to provide a method and an apparatus for producing ultrapure water that can reduce the temperature fluctuation of subtank inflow water even when the flow rate of recovered water varies.

The ultrapure water production apparatus according to the first aspect of the present invention supplies a heat exchanger, reverse osmosis membrane separation means provided at the rear stage of the heat exchanger, and recovered water from the semiconductor production process to the rear stage side of the reverse osmosis membrane separation means. Ultra pure water is produced by passing raw water through a primary pure water production apparatus equipped with recovered water supply means to produce primary pure water, and passing this primary pure water through a secondary pure water production apparatus. In the pure water production apparatus, the temperature detection means of the primary pure water supplied to the secondary pure water production apparatus, the detection means of the supply amount of the recovered water, and the detection temperature of the temperature detection means of the primary pure water The means for setting the target temperature of the effluent water of the heat exchanger based on the detection flow rate of the means for detecting the supply amount of the recovered water, and the supply amount of the heat source fluid to the heat exchanger so as to be the target temperature And a means for controlling.

The ultrapure water production method of the second invention is a heat exchanger, a reverse osmosis membrane separation means provided at the rear stage of the heat exchanger, and a supply of recovered water from the semiconductor production process to the rear stage side of the reverse osmosis membrane separation means Ultra pure water is produced by passing raw water through a primary pure water production apparatus equipped with recovered water supply means to produce primary pure water, and passing this primary pure water through a secondary pure water production apparatus. in pure water production process, and the primary pure water temperature supplied to the secondary pure water producing device, detects the supply amount of the recovered water, the heat exchanger on the basis of the recovered water supply amount and the detected temperature A target temperature of the effluent water is set, and the supply amount of the heat source fluid to the heat exchanger is controlled so as to be the target temperature.

First, according to the ultrapure water production apparatus and method of the second invention, based on the temperature of the primary pure water supplied to the secondary pure water production system, and the flow rate of the recovered water is introduced into the primary pure water production system The target temperature of the effluent of the heat exchanger of the primary pure water production equipment is set, and the supply amount of the heat source fluid to the heat exchanger is controlled so that this target temperature is reached, so it is supplied to the secondary pure water production equipment It is prevented that the temperature of the primary pure water is unnecessarily increased or excessively decreased.

It is a systematic diagram of the ultrapure water manufacturing apparatus concerning an embodiment. It is a systematic diagram of the ultrapure water manufacturing apparatus which concerns on a prior art example.

  The ultrapure water production apparatus of the present invention comprises a primary pure water production apparatus and a secondary pure water production apparatus or further a tertiary pure water production apparatus, and is based on the inflow water temperature of the sub tank of the secondary pure water production apparatus. Control the set temperature of the heat exchanger of the pure water production equipment.

In the normal stage of the primary pure water production apparatus, a pretreatment apparatus is usually provided. In the pretreatment device, pretreatment by raw water filtration, coagulation sedimentation, microfiltration membrane or the like is performed, and suspended substances are mainly removed. By this pretreatment, the number of fine particles in water is usually 10 ³ / mL or less.

  Primary pure water production equipment includes reverse osmosis (RO) membrane separators, deaerators, regenerative ion exchangers (such as mixed bed or 4 bed 5 tower type), electrodeionizers, ultraviolet (UV) irradiation oxidizers Etc., and removes most of the electrolytes, fine particles, viable bacteria, etc. in the pretreated water. The primary pure water production apparatus is composed of, for example, a heat exchanger, two or more RO membrane separation apparatuses, a mixed bed ion exchange apparatus, and a deaeration apparatus.

  Secondary pure water production equipment includes feed water pumps, heat exchangers, UV irradiation equipment such as low pressure UV oxidation equipment or sterilization equipment, non-regenerative mixed bed ion exchange equipment or electrodeionization equipment, ultrafiltration (UF) membrane separation The apparatus is constituted by a membrane filtration device such as a device or a microfiltration (MF) membrane separation device, and may further be provided with a demineralization device such as a membrane deaeration device, an RO membrane separation device, or an electrodeionization device. In the secondary pure water production apparatus, a low-pressure ultraviolet oxidation apparatus is applied, and a mixed bed type ion exchange apparatus is provided at the subsequent stage, whereby TOC in water is oxidized and decomposed by ultraviolet rays, and oxidation decomposition products are removed by ion exchange. .

  The tertiary pure water production apparatus has the same configuration as the secondary pure water production apparatus as a device configuration, and thereby purifies the secondary pure water to produce high purity ultrapure water. .

  Hereinafter, an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a flowchart showing an ultrapure water production method and apparatus according to an embodiment, and the same members as those in FIG. 2 are denoted by the same reference numerals.

  In this embodiment, a temperature sensor 16 that detects the temperature of water heated by the heat exchanger 15 of the primary pure water production apparatus and supplied to the RO apparatus 12 is provided. Steam is supplied to the heat exchanger 15 as a heat source fluid through a steam line 15a. A steam flow control valve 15b is provided in the steam line 15a. In addition, a relay tank 17 is provided between the RO device 12 and the ion exchange device 13, and recovered water from the semiconductor manufacturing process flows in via the line 18. The recovered water line 18 is provided with a flow meter 18a.

  In this embodiment, a temperature sensor 21 a is provided so as to detect the temperature of primary pure water flowing into the sub tank 21 of the secondary pure water production apparatus 20 through the pipe 19.

  Detection data of the temperature sensors 16 and 21a and the flow meter 18a is input to the control device 60. The control device 60 is configured to send a control signal to the steam flow control valve 15b based on these input data.

[First control example]
In the first control example, the control device 60 sets a target temperature of the temperature detected by the temperature sensor 16 based on the temperature detected by the temperature sensor 21a, so that the temperature detected by the temperature sensor 16 becomes this target temperature. The steam flow control valve 15b is controlled.

  In general, since the time from flowing into the heat exchanger 15 to reaching the sub tank 21 is as long as about 2 to 3 hours, for example, about 3 hours, the heat exchange simply follows the fluctuation of the inflow water temperature into the sub tank 21. Even if the steam flow rate to the vessel 15 is controlled, accurate control is not performed.

  Therefore, in this first control example, the target temperature of the temperature detected by the temperature sensor 16 is set based on the temperature detected by the temperature sensor 21a, and the steam flow rate is set so that the temperature detected by the temperature sensor 16 becomes this target temperature. The control valve 15b is controlled.

Specifically, previously set the lower limit value T ₂₀ and the upper limit value T ₂₁ tolerance of the inlet water temperature to the sub tank 21. Further, based on the operation record data, the inflow water temperature of the sub-tank 21 is set to the temperature of the outlet water of the heat exchanger 15 serving as a temperature between the lower and upper limits as the target temperature T _1. Then, the temperature detected by the temperature sensor 16 to control the steam flow rate control valve 15b so that the target temperature T _1.

While thus detected temperature of the temperature sensor 16 is operating ultrapure water production apparatus by controlling the steam flow control valve 15b such that the target temperature T _1, the temperature detected by the temperature sensor 21a is been reduced When the lower limit value T ₂₀ or less is reached, the target temperature is increased by a predetermined value ΔT ₁ , T ₁ + ΔT ₁ is set as a new target temperature, and steam is detected so that the detected temperature of the temperature sensor 16 becomes T ₁ + ΔT _1. The flow control valve 15b is controlled. If the temperature detected by the temperature sensor 21a is higher than T ₂₀ been restored (increased) to return the target temperature T _1.

On the other hand, while the temperature detected by the temperature sensor 16 is operating ultrapure water production apparatus by controlling the steam flow control valve 15b such that the target temperature T _1, the temperature detected by the temperature sensor 21a is been raised upper when a value _{T 21} or more, the lower the target temperature by ΔT _{2, T} 1 _{-ΔT 2} was a new target temperature, the steam flow rate so that the detection temperature of the temperature sensor 16 is _T 1 -.DELTA.T ₂ The control valve 15b is controlled. If the temperature detected by the temperature sensor 21a is lower than the T ₂₁ been lowered, returning the target temperature T _1.

ΔT ₁ and ΔT ₂ are preferably selected from 0.1 to 0.4 ° C., for example, ΔT ₁ = ΔT ₂ = 0.2 ° C. T ₂₁ -T _{20 is} also preferably selected from 0.1 to 0.4 ° C, and for example, T ₂₁ -T ₂₀ = 0.2 ° C. T ₂₀ and T ₂₁ are set according to the ultrapure water production apparatus. Usually, the temperature is selected from 20 to 25 ° C., for example, T ₂₀ = 23.1 ° C.

  Thus, the steam flow control valve 15b is changed so that the target temperature of the effluent of the heat exchanger 15 changes according to the temperature of the inflow water into the sub tank 21, and the detected temperature of the temperature sensor 16 becomes the target temperature after the change. By controlling, the inflow water temperature to the sub tank 21 is prevented from excessively decreasing or unnecessarily increasing.

In this first control example, the target temperature is changed from T ₁ + ΔT ₁ to a predetermined time (for example, from a range of 1.5 to 2 times the time Tr from leaving the heat exchanger 15 until reaching the sub tank 21). when the detected temperature of the selected time.) temperature even after the sensor 21a is not recovered (increased) to the lower limit value T ₂₀ may switch the target temperature T ₁ +2 · ΔT _1.

Further, the target temperature _{T 1 + k · ΔT 1 (} k = 2,3, .........) to recover after switching to the detected temperature is the lower limit value _{T 20} of the even predetermined time has elapsed temperature sensor 21a (rise If not, the target temperature may be switched to T ₁ + (k + 1) · ΔT ₁ .

In the first control example, when the target temperature the temperature detected by the temperature sensor 21a be the predetermined time has passed after switching to the T ₁ -.DELTA.T ₂ is not reduced to the upper limit value T ₂₁ is the target temperatures T ₁ It may be switched to -2 · ΔT ₂ .

Moreover, not lower the target temperature to _{T 1 -n · ΔT 2 (n} = 2,3, .........) detected temperature is an upper limit value _{T 21} of the temperature sensor 21a even after the predetermined time after switching on Sometimes, the target temperature may be switched to T ₁ − (n + 1) · ΔT ₂ .

In addition, in an ultrapure water production apparatus having an ultrapure water production capacity of 5,000 m ³ / day, T ₁ = 24.5 ° C., T ₂₀ = 23.1 ° C., T ₂₁ = 23.3 ° C., ΔT ₁ = ΔT ₂ When the operation was performed at = 0.2 ° C., the steam consumption of the heat exchanger 15 could be reduced by about 30% compared to the conventional example in which T ₁ was always 24.5 ° C.

[Second Control Example]
Next, a second control example considering the recovered water flow rate will be described.

  Generally, semiconductor manufacturing process wastewater is ozone oxidation → activated carbon tower → mixed bed ion exchange tower, activated carbon tower → UV oxidizer → mixed bed ion exchange tower, UV oxidizer → deoxygenator → activated carbon tower → mixed bed ion The exchange tower, activated carbon tower → ion exchange tower, etc. are processed to obtain recovered water, which is introduced into the relay tank 17.

The temperature of the recovered water is generally stable in the range of 25 to 30 ° C. Since the temperature of the recovered water is higher than the outlet water temperature of the heat exchanger 15, when the flow rate of the recovered water varies, the inflow water temperature of the sub tank 21 varies. Therefore, when the recovered water flow rate decreases below the reference flow rate, the target temperature of the outlet water temperature of the heat exchanger 15 is reset to a higher value correspondingly. For example, when the ratio of recovered water in the primary pure water from the primary pure water production apparatus 10 is about 30 to 50%, the target temperature is set when the recovered water flow rate is 20 to 40% or less of the reference flow rate. T _{1 is set} to T ₁ + ΔT _3, and the steam flow control valve 15b is controlled so that the temperature detected by the temperature sensor 16 becomes T ₁ + ΔT ₃ . Thereby, it is prevented that the subtank inflow water temperature falls excessively.

This ΔT ₃ is preferably selected from 1 to 2 ° C., for example, ΔT ₃ = 1.4 ° C.

In this second control example, the target temperature may be changed in multiple stages according to the reduction width of the recovered water flow rate. For example,
When the recovered water flow rate is 20 to 40% of the reference flow rate, the target temperature is T ₁ + ΔT ₄ ,
When the recovered water flow rate is 40% or less of the reference flow rate, the reference value may be switched to three levels so that the target temperature is T ₁ + 2 · ΔT ₄ , or may be switched to four or more levels. Further, the target temperature may be switched in proportion to the recovered water flow rate.

When the recovered water flow rate increases from the reference flow rate, the target temperature may be decreased by a predetermined value ΔT ₅ from T ₁ .

Also in this case, the temperature reference value may be changed in multiple stages according to the increase width of the recovered water flow rate. Note that even if the recovered water flow rate increases above the reference flow rate, the reference value may not be switched and T ₁ may be maintained.

DESCRIPTION OF SYMBOLS 10 Primary pure water manufacturing apparatus 15 Heat exchanger 20 Secondary pure water manufacturing apparatus 21 Sub tank 40 Use point 50 Ultrapure water return piping 60 Control apparatus

Claims (2)

Primary pure water provided with a heat exchanger, a reverse osmosis membrane separation means provided at the rear stage of the heat exchanger, and a recovered water supply means for supplying the recovered water from the semiconductor manufacturing process to the rear stage side of the reverse osmosis membrane separation means In the ultrapure water production apparatus for producing primary pure water by passing raw water through the production apparatus and producing ultrapure water by passing this primary pure water through the secondary pure water production apparatus,
Means for detecting the temperature of primary pure water supplied to the secondary pure water production apparatus;
Detection means the supply amount of the recovered water,
Means for setting a target temperature of effluent water of the heat exchanger based on a detection temperature of the primary pure water temperature detection means and a detection flow rate of the recovered water supply amount detection means;
An apparatus for producing ultrapure water, comprising: means for controlling a supply amount of the heat source fluid to the heat exchanger so as to achieve the target temperature. Primary pure water provided with a heat exchanger, a reverse osmosis membrane separation means provided at the rear stage of the heat exchanger, and a recovered water supply means for supplying the recovered water from the semiconductor manufacturing process to the rear stage side of the reverse osmosis membrane separation means In an ultrapure water production method for producing primary pure water by passing raw water through a production device and producing ultrapure water by passing this primary pure water through a secondary pure water production device,
And the temperature of the primary pure water supplied to the secondary pure water producing device, detects the supply amount of the recovered water,
Based on the detected temperature and the recovered water supply amount, set a target temperature of the effluent of the heat exchanger,
A method for producing ultrapure water, comprising: controlling a supply amount of a heat source fluid to a heat exchanger so as to achieve the target temperature.

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