Liquid purification or separation – With gas-liquid surface contact means
Reexamination Certificate
1998-10-06
2001-01-23
Simmons, David A. (Department: 1724)
Liquid purification or separation
With gas-liquid surface contact means
C210S151000, C210S195100, C210S205000, C210S260000, C210S264000, C210S274000, C210S290000, C210S900000, C210S605000, C210S614000, C210S617000, C210S618000, C210S629000, C210S681000
Reexamination Certificate
active
06177005
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an ultrapure water producing system, and in particular, to an ultrapure water producing method and ultrapure water producing system capable of producing ultrapure water having a reduced amount of TOC (Total Organic Carbon) and a low electrical conductivity.
The water quality required for ultrapure water in a semiconductor manufacturing factory has become more and more strict in accordance with the microstructural progress of semiconductor devices. Particularly in a factory for manufacturing semiconductor devices of a degree of integration higher than that of 64 Mbit-DRAM (Dynamic Random-Access Memory), the TOC is reduced to a density of not higher than 1 ppb (Parts Per Billion) in the ultrapure water.
In general, an ultrapure water producing system is constructed of a pretreatment unit, a primary pure water producing unit and a secondary pure water producing unit. Then, the pretreatment unit adopts physicochemical methods such as coagulative sedimentation, coagulative filtration and coagulative pressurized floatation. Concrete examples of such pretreatment units are shown in
FIGS. 16A and 16B
. The pretreatment units shown in FIG.
16
A and
FIG. 16B
adopt the methods of sedimentation and filtration that are both physicochemical treatments and are pretreatment units intended mainly for the removal of sludge in the water to be treated. Therefore, the pretreatment units shown in
FIGS. 16A and 16B
cannot be regarded as a treatment system for effectively treating organic nitrogen compounds that cause an increase in TOC density.
As the above primary pure water producing unit, there is a system of a combination of a reverse osmosis unit, an ion exchange resin unit and an infrared sterilization unit. As the above secondary pure water producing unit, there is one constructed of an ultraviolet oxidation unit, an ion exchange resin unit, an ultrafiltration membrane unit and so on.
According to the recent research, it has been discovered that the remaining TOC in the ultrapure water is caused by the organic nitrogen compounds coming from raw water. In this case, “raw water” means industrial water, underground water and the like. In contrast to this, drinking water and tap water are called “city water”.
In general, for the method of treating the carbon compounds and organic nitrogen compounds and the like that cause an increase in TOC density in the water to be treated, a reverse osmosis unit, a special ion exchange resin unit or an ultraviolet oxidation unit, as described above, are used. However, according to the recent demand for a water quality of a TOC density of not higher than 1 ppb in ultrapure water, a pretreatment unit has also been developed that adopts a biotic treatment method utilizing an aerobic microbe in addition to the aforementioned generic organic matter treatment system (prior art reference of Japanese Patent Laid-Open Publication No. HEI 6-63592).
In accordance with the growing consciousness of the water resources, many ultrapure water producing systems have been proposed that collect waste water and reuse the same instead of limitlessly using the city water, industrial water, underground water and the like as raw water. A method has been proposed for producing ultrapure water by mixing raw water with waste water containing several parts per million of IPA (isopropyl alcohol) and acetone that serve as organic solvents and biologically treating the organic nitrogen compounds (prior art reference of Japanese Patent Laid-Open Publication No. HEI 6-233997). According to this ultrapure water producing method, the organic nitrogen compounds in the water to be treated are treated through a biotic treatment by the pretreatment unit and thereafter treated successively by a primary pure water producing unit and a secondary pure water producing unit, finally obtaining ultrapure water having a TOC density of not higher than 1 ppb. It is to be noted that an aerobic microbe is utilized and activated carbon is used as filler for the biotic treatment in the pretreatment unit, thereby treating the organic nitrogen compounds represented by urea.
An ultrapure water producing system that performs pretreatment by means of a microbe, is shown in FIG.
17
. In this ultrapure water producing system, industrial water and collected water are introduced as raw water into a water receiving tank
1
. Then, after a lapse of a retention time of at least three hours, the water is introduced into an upward flow type biotic decomposition unit
3
by a conveying pump
2
. This upward flow type biotic decomposition unit
3
is stowed with activated carbon or the like, where an aerobic microbe is propagating. The water to be treated from the upward flow type biotic decomposition unit
3
is introduced into an aeration tank
4
. Then, the water is aerated by aeration air discharged from an air diffusion pipe
5
. A part of the water to be treated inside the aeration tank
4
circulates while being conveyed back to the upward flow type biotic decomposition unit
3
by an aeration tank pump
6
. Another part of the water to be treated inside the aeration tank
4
is introduced into a pump pit
7
and conveyed successively to a filter unit
9
and a primary pure water producing unit
10
by a water conveyance pump
8
.
Ultrapure water producing systems utilizing a biotic treatment with an anaerobic microbe and an aerobic microbe for the pretreatment unit, are shown in FIG.
18
and FIG.
19
. In these ultrapure water producing systems, aerobic organic matter treatment sections
12
and
22
are arranged in upper portions of anaerobic organic matter treatment sections
11
and
21
. Charcoal pieces
13
and
23
are stowed as filler, where an anaerobic microbe and an aerobic microbe are propagating. It is to be noted that the reference numerals
14
and
24
denote plastic fillers, the reference numerals
15
and
25
denote vinylidene chloride and the reference numerals
16
and
28
denote membrane filter tanks. The reference numeral
26
denotes a hydrogen peroxide oxidation tank, while the reference numeral
27
denotes a hydrogen peroxide decomposition tank.
As described above, the ultrapure water producing system is constructed of the pretreatment unit, the primary pure water producing unit and the secondary pure water producing unit. In general, the above primary pure water producing system is constructed by combining a reverse osmosis (RO) unit, an ion exchange resin unit, an ultraviolet sterilization unit and so on. The above secondary pure water producing unit is constructed of an ultraviolet oxidation unit, an ion exchange resin unit, an ultrafiltration membrane unit and so on.
The ion exchange resin unit of the above primary pure water producing unit exchanges ions in the water to be treated by the ion exchange resin. Then, after a lapse of a specified time, the ion exchange function is restored through regeneration by hydrochloric acid and sodium hydroxide. In the regeneration stage, mineral acid (hydrochloric acid or sulfuric acid) or sodium hydroxide are needed as a chemical, and regenerated waste water results having ion concentration. In regard to this regenerated waste water, acid waste water is generated when the ion exchange resin is regenerated by the mineral acid or generated alkaline waste water is generated when the ion exchange resin is regenerated by sodium hydroxide. Either type of waste water necessitates waste water treatment of neutralization or the like as well as waste water equipment for that purpose. A tank for reserving the mineral acid or sodium hydroxide, a pump and piping for conveying the chemical are also needed.
Accordingly, from the viewpoint of reducing the space and cost, an electric deionizing system, which obviates the need for the chemicals such as ion exchange resin regenerating chemicals and the installation of regenerating equipment having no direct relation to ultrapure water production, has started to attract attention.
However, the above prior art ultrapure water producing method and ultrapu
Miyamoto Takahide
Nasu Toyoichi
Okamoto Seiji
Sakata Kazuyuki
Sera Masami
Nixon & Vanderhye PC
Prince Fred
Sharp Kabushiki Kaisha
Simmons David A.
LandOfFree
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