JP2000167567A - Ultrapure water making apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably produce ultrapure water satisfying desired required quality over a long period of time by providing a trihalomethane removing device removing the greater part of trihalomethane in water to be treated at the arbitrary position of a pretreatment device and a primary pure water making device in an ultrapure water making apparatus. SOLUTION: An ultrapure water making apparatus is constituted of a pretreatment device, a primary pure water making device and a secondary pure water making device, and a trihalomethane removing device is arranged at the arbitrary position of the pretreatment device and the primary pure water making device to remove the greater part of trihalomethane to produce ultrapure water of high water quality. As the trihalomethane removing device, for example, a volatilizing tower subjecting trihalomethane to volatilizing treatment to remove the same is used. That is, the volatilizing tower is constituted of a sprinkling pipe 1 for sprinkling water into the tower from above to from a water membrane and an equipment 3 blowing air into the tower from below, and trihalomethane in water is removed by forming the water membrane to be expelled into the atmosphere by the force of air or inert gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrapure water producing apparatus capable of stably producing ultrapure water having higher purity, that is, ultrapure water having a TOC of 2 ppb or less.

[0002]

2. Description of the Related Art Conventionally, pure water has been used for cleaning water for semiconductors, lenses, liquid crystals, etc., medical water, etc. In recent semiconductor manufacturing, ultrapure water having a higher purity than before has been used. In particular, TOC is 2 ppb (μg /
L) There is a need for an ultrapure water production apparatus capable of stably producing the following high-purity ultrapure water.

[0003]

However, conventionally, TOC, that is, removal of total organic carbon, is considered to be sufficient for the relationship between TOC and individual substances constituting TOC, apart from typical organic substances. No consideration was given.

[0004] On the other hand, surface water, well water, and clean water using peatlands as water sources contain a large amount of corrosive substances such as humic acid and fulvic acid. Since city water and industrial water often contain corrosive substances, when such corrosive substances are chlorinated for sterilization at water purification plants, etc., trihalomethane is generated, and the amount becomes extremely large. I have. This trihalomethane can be partially removed by an activated carbon (AC) tower, a reverse osmosis membrane (RO) apparatus, a UV oxidizing apparatus, etc., which are usually constituent units of an ultrapure water production apparatus. Removal capacity is not continuous.

[0005]

In view of the above, the present inventor has considered,
Investigations on substances that could not be completely removed by a conventional ultrapure water production system revealed that trihalomethane had a considerable effect on the strict TOC requirement (2 ppb or less). Therefore, in an ultrapure water system consisting of a pretreatment device, a primary pure water production device, and a subsystem (secondary pure water device), a large amount of trihalomethane in the water to be treated can be placed at any position of the pretreatment device and the primary pure water production device. The present invention proposes an ultrapure water production apparatus, which is provided with a trihalomethane removal apparatus for removing a part, preferably 90% or more.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of a conventional ultrapure water producing apparatus. In this conventional ultrapure water production apparatus, trihalomethane can be removed by an activated carbon (AC) tower, a reverse osmosis membrane (RO) apparatus, a UV oxidation apparatus, and the like. However, each of these apparatuses has the following problems. However, it has not been possible to stably produce ultrapure water satisfying the required quality of TOC of 2 ppb or less over a long period of time.

[0007] In the AC tower, it is possible to remove nearly 100% of trihalomethane at first, but it reaches the saturated adsorption amount and leaks in only 1 to 2 months. Moreover, when the leakage starts, the trihalomethane concentration at the outlet from the AC inlet is 2 to
5x, and the condition continues unless AC is replaced. This phenomenon is because the trihalomethane precursor is converted into trihalomethane, particularly chloroform, using AC as a catalyst in the AC tower. When a large amount of chloroform is generated in the AC tower in this way, the TOC removal becomes overloaded and cannot be handled. Therefore, although it can be dealt with by replacing the AC once every 1 to 3 months, the running cost becomes large.

Further, in the RO apparatus, regardless of the concentration,
Although the removal of about 0% of trihalomethane can be maintained, TOTO
At the required quality of C 2 ppb or less, the removal ability is insufficient.

Further, a UV oxidizer can decompose trihalomethane, mainly chloroform, but it is very difficult to decompose in a UV oxidizer, and even if it decomposes, halogen ions are generated, and its removal is a new burden. Further, since it cannot cope with about 0.3 kW / m ^3, it is necessary to increase the size of the equipment, and the running cost (power consumption, annual lamp replacement cost) and the burden on the factory side become large. It should be noted that trihalomethane cannot be expected to be removed at all by an organic scavenger resin or an ion exchange resin pure water apparatus. That is, the organic scavenger resin is used to remove humic acid and fulvic acid in the water to be treated,
Although trihalomethane is non-ionic and uncharged, it cannot be removed with this organic scavenger resin.

Therefore, by providing a trihalomethane removing device in the ultrapure water producing apparatus, most of the trihalomethane, preferably 90% or more, is removed, and the remaining trihalomethane is partially removed in another structural unit of the ultrapure water producing apparatus. When the residual concentration of trihalomethane is finally reduced to 1 ppb or less, high-purity ultrapure water having a TOC of 2 ppb or less can be stably produced.

As described above, the ultrapure water production apparatus of the present invention
As in the conventional case, it is composed of a pretreatment device, a primary pure water production device and a subsystem (secondary pure water device). The pretreatment device is
Coagulation, solid-liquid separation (filtration, pressure flotation, membrane separation), activated carbon,
Each unit technique of ion exchange is appropriately selected according to the quality of raw water, and is formed by arranging in any order. Primary pure water production equipment
Unit technologies such as ion exchange and reverse osmosis membrane (RO), as well as electric regeneration type desalination equipment, evaporator, decarbonation tower, deaerator,
It is formed by appropriately combining a UV oxidation device and the like. The subsystem is formed by appropriately combining UV oxidation (UV sterilization), a mixed-bed desalination apparatus, and membrane separation.

As described above, the pretreatment device of the ultrapure water production device and the trihalomethane removal device provided at an arbitrary position of the primary pure water production device are mostly, preferably 90%, as described above.
The configuration is not particularly limited as long as the above trihalomethane can be removed. Specifically, a volatilization tower for stripping and removing trihalomethane is used. In this stripping tower, a hydrophobic and volatile trihalomethane contained in water is formed into a thin film of water and is forcibly expelled into the atmosphere by the power of air or an inert gas.

As shown in FIG. 2, the volatilization tower includes a spray tube 1 for spraying water into the tower from above to form a thin film of water, a packed bed 2 and a bottom for air (or nitrogen gas or the like) from below. And a facility 3 for blowing an inert gas. In FIG. 2, reference numeral 4 denotes water to be treated, 5 denotes a support plate, 6 denotes treated water, and 7 denotes exhaust gas. Trihalomethane is mixed into the exhaust gas 7 and discharged.

As the filler, a synthetic polymer compound or a stainless steel (SUS) having an increased surface area, for example, a polypropylene (PP) net ring (diameter 25 mm) is used.
φ, length 25mm) or unbaked Raschig ring tube, SUS
Pipes or projections may be used, or any other shape having voids or projections.
Those having a size of about 30 mm are used. In particular, a net ring made of PP is preferably used in consideration of the weight and generation of crushed pieces. The use of this net ring is also preferable in that the wall flow can be reduced. The filling height of such a filling is between 1500 and 1800 mm.

The spraying tube 3 is not particularly limited, but it is desirable to use a seven-head conical nozzle because uniformity of spraying is important. As the support plate 5, a net-shaped sheet is placed on a punching metal or a grating, and the grating may be made of plastic.

The flow velocity of water to the stripping tower is LV = 20-50 m /
H, air flow rate is 10 Nm ³ / min / m ² or more, preferably 1
0 to 16 Nm ³ / min / m ² . An appropriate water temperature is 20 to 70 ° C. Since peat areas are often cold, it is necessary to keep the water temperature at 20 ° C. or higher so as not to lower the volatilization efficiency. In addition, the water temperature may be set to 40 ° C. or higher for the purpose of further improving the volatilization efficiency. However, in this case, a heat insulation facility is required. Become.

The volatilization tower having such a configuration can be provided at any position of the pretreatment device of the ultrapure water production device and the primary pure water production device as described above. First, it may be processed in a stripping tower. The inside of the subsystem should be avoided because of high purity water, water balance, etc. to maintain stable operation. More preferably, in the case of installing a multi-bed tower type pure water production apparatus, if it is installed also as a decarbonation tower, one unit is less. In addition, it is installed in front of the RO device to lower the pH and decarboxylate at the same time.
O may also serve to prevent calcium carbonate scale of O and to improve the quality of treated water. In order to further improve the volatilization effect, it is preferable to use a multi-stage system such as a high-efficiency nitrogen degassing tower.

As described above, most, preferably 90% or more, of the trihalomethane is removed in this stripping tower, and the remaining trihalomethane is partially removed by another constituent unit of the ultrapure water production apparatus. Other structural units include, for example, RO, UV
There are oxidizer, decarbonation tower and degassing tower.

The decarbonation tower is also a kind of volatilization tower,
What has been conventionally used as a decarbonation tower has a high flow rate of water, so that the effect of removing trihalomethane is about 50%, and even if it is well obtained, it is 70% or less, which is extremely insufficient. Therefore, in order to use this decarbonation tower as a stripping tower (trihalomethane removing device) for removing trihalomethane in the present invention, the effect of removing trihalomethane is 90%.
It is necessary to change the settings to special specifications so that
When water is sprinkled into the tower from the top, water is sprinkled as uniformly as possible with respect to the cross-sectional area of the tower, and the water flow velocity is adjusted to an appropriate range (LV = 20 to
50 m / H), and the air flow rate is also in an appropriate range (10 to 16
Nm ³ / min / m ² ), and a volatilization tower capable of heating water as needed.

The ultrapure water production apparatus of the present invention having such a configuration is not particularly limited to the water to be treated, and is also applicable to, for example, the treatment of surface water, well water, and tap water using a peat zone as a water source. can do. The residual concentration of trihalomethane is reduced to 1 ppb or less, and high-purity ultrapure water having a TOC of 2 ppb or less can be stably produced without increasing the load on running costs.

[0021]

[Example] [Chloroform removal test (preliminary experiment)] Test method The apparatus shown in FIG. 3 was used as a test apparatus. An aqueous solution of chloroform (CHCl ₃ ) dissolved in pure water was injected, and the TOC (chloroform) before and after the stripping tower was measured with a Sievers TOC meter to test and evaluate the removal performance. In addition, using a 7-head conical nozzle as a spray tube, a PP net ring (25 mm in diameter)
φ, length 25 mm) was used as the filler. The filling height of the filling was 1800 mm.

2. Test results The test results are shown in Table 1 and FIGS.

[Table 1]

The following is confirmed from Table 1. (1) Air flow rate 7.14 Nm ³ / min / m ² Constant conditions (= Run N
o.1-3), when the water flow velocity LV = 14.1m / H (= R
The removal rate of TOC (chloroform) in un No. 3) is 90.5.
%, But when LV = 38.2 m / H (= Run No.
The TOC (chloroform) removal rate in 2) was 83.2%, and it was confirmed that the water flow rate affected the volatilization ability of chloroform. (2) Flow rate LV = 20.1 m / H constant, air flow rate 6.7
8Nm ³ / min / m ^{2 Under} constant conditions (= Run Nos.5-8), the TO concentration in the feedwater chloroform concentration ranged from 10.04 to 92.95 ppb.
The C (chloroform) removal rate was not particularly affected, and was constant at about 80%. (3) Flow rate LV = 20.1m / H Constant conditions (= Run N
o. 9 to 11), it was confirmed that the higher the air flow rate, the higher the TOC (chloroform) removal rate, and that the air flow rate affected the volatilization ability of chloroform.

An additional experiment was performed as shown in FIG.
At an air flow rate of 15 Nm ³ / min / m ² , the water flow speed LV = 2
A chloroform removal rate of 90% or more was achieved at 0.1 m / H, and a chloroform removal rate of 80% or more was achieved at LV = 51.2 m / H.

Example 1 An ultrapure water producing apparatus having the system configuration shown in FIG. 7A was constructed, and ultrapure water production was performed using city water as the water to be treated. The device for removing trihalomethane in FIG. 7 (a) is the stripping tower shown in FIG. 2, and has a water flow rate LV = 20 m / H, an air flow rate of 15 Nm ³ / min / m ² , and a PP net ring as a filler. (Diameter 25mmφ, length 2
5 mm) and the filling height was 1800 mm.
The water temperature was 30 ° C. The numerical values of the trihalomethane concentration and the TOC concentration described in FIG. 7A indicate the water quality at the place, and are values obtained by measuring the average water quality when the ultrapure water production apparatus is operated for two months. .

COMPARATIVE EXAMPLE 1 As shown in FIG. 7 (b), ultrapure water was prepared in the same manner as in the ultrapure water producing apparatus of Example 1 (FIG. 7 (a)) except that no trihalomethane removing apparatus was provided. A production apparatus was constructed, and ultrapure water was produced using city water as the water to be treated. Then, the concentration of trihalomethane and the concentration of TOC in the middle of the route were measured in the same manner as in Example 1, and FIG.
It was described in (b).

[Consideration] In the first embodiment of the present invention, 90% of the trihalomethane is removed by the trihalomethane removing device, and the finally obtained trihalomethane in the ultrapure water is 1%.
Removed to ppb. The TOC was also 1 ppb. Thus, it was confirmed that high-purity ultrapure water having a TOC of 2 ppb or less can be stably produced. As a result of continuous experiments, it was confirmed that the life of the conventional AC was 1 to 3 months, but could be extended to 6 to 1 year.
Further, according to another experiment which is not described in detail, in Example 1 of the present invention, the installation scale of the UV oxidizing apparatus can be reduced by about 30% as compared with Comparative Example 1 in which the trihalomethane removing apparatus is not installed, and the running cost is reduced. , The cost of replacing the lamp was reduced.

[0028]

As described above in detail, the ultrapure water producing apparatus of the present invention is provided with a trihalomethane removing apparatus for removing most of the trihalomethane which has not been conventionally sufficiently removed or has not been continuously removed. As a result, it is possible to stably produce ultrapure water satisfying the required quality of TOC 2 ppb or less for a long period of time. In addition, it can be applied to the treatment of surface water, well water, and tap water using peatland as a water source. The residual concentration of trihalomethane is 1 ppb.
In the following, high-purity ultrapure water having a TOC of 2 ppb or less can be stably manufactured without increasing the load of running cost.

[Brief description of the drawings]

FIG. 1 is a flow (flow system diagram) showing an example of a conventional ultrapure water production apparatus.

FIG. 2 is a flow (flow explanatory diagram) conceptually showing an example of a trihalomethane removing device.

FIG. 3 is a flow (flow explanatory diagram) conceptually showing a test apparatus used for a chloroform removal test in Examples.

FIG. 4 is a graph showing the results of a chloroform removal test in Examples and showing the effect of the water flow rate on the TOC removal rate.

FIG. 5 is a graph showing the results of a chloroform removal test in Examples and showing the effect of inlet concentration on the TOC removal rate.

FIG. 6 is a graph showing the results of a chloroform removal test in Examples and showing the effect of the air flow rate on the TOC removal rate.

FIG. 7 (a) shows a flow (flow diagram) showing an example of the ultrapure water production apparatus of the present invention in which the residual concentration of trihalomethane and the residual concentration of TOC in the process are added, and (b) residual trihalomethane in the process. It is a flow (flow system diagram) which shows an example of the conventional ultrapure water production apparatus which added the concentration and the residual concentration of TOC.

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Claims (1)

[Claims] An ultrapure water system comprising a pretreatment device, a primary pure water production device, and a subsystem removes most of the trihalomethane from the water to be treated at an arbitrary position of the pretreatment device and the primary pure water production device. An ultrapure water production device comprising a trihalomethane removal device.