JPH0679273A - Ultra-pure water producing device - Google Patents

Abstract

PURPOSE:To provide an ultra-pure water producing device capable of being operated in accordance with the load, capable of reducing the pollution due to the device and having a durable polisher. CONSTITUTION:The returning water from the point 7 of use is returned to an ultra-pure water tank 1 and circulated in the ultra-pure water producing device. The returning water pipeline is branched into a returning water pipe 16 and a polisher bypass pipeline 17 through a control valve 8, and a controller 11 is provided to control the opening degree of the control valve 8 based on the input signals of the returning water quantity and resistivity of the returning water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing ultrapure water used in the semiconductor industry and the like.

[0002]

2. Description of the Related Art As shown in FIG. 3, a conventional ultrapure water producing apparatus mainly comprises an ultrapure water tank 1, a primary pure water inflow pipe 2, a heat exchanger 3, a UV oxidizer 4, a polisher (non-regeneration type ion exchange). A resin tower 5 and an ultrafiltration membrane device 6. The ultrapure water produced is sent from the ultrafiltration membrane device 6 to the use point 7, but for the purpose of preventing the retention of ultrapure water in the constituent units such as the pipe, the polisher 5, and the ultrafiltration membrane device 6. The return water from the use point 7 is returned to the ultrapure water tank for circulation operation. The quality and flow rate of this return water vary depending on the usage of ultrapure water at the point of use.

Usually, the quality of the return water is almost the same as that of the ultrapure water, and the purity of the return water is higher than that of the primary pure water (supply pure water). Therefore, when the ratio of the flow rate of the return water to the flow rate of the primary pure water increases, the load on the ultrapure water production system decreases, and conversely, when the ratio of the return water flow rate decreases, the ultrapure water production system operates. The load increases.

Recently, as the water quality of ultrapure water is increased, the elution of impurities from the unit constituting the apparatus cannot be ignored, and in particular, the elution of organic substances from the polisher becomes a problem. The ion removal performance of the polisher depends on the SV value (space velocity: flow rate / resin volume), and the smaller the SV value, that is, the longer the contact time between the ion exchange resin and the ultrapure water, the better the ion removal performance. Elution of organic substances from the ion exchange resin increases. FIG. 4 shows the relationship between the polisher SV value, the total organic carbon (TOC) of the treated water and the ion concentration of the treated water. In the conventional ultrapure water production system, the SV value is constant because the system is operated under the same operating conditions regardless of the load on the system. Therefore, when raw water having a small load is treated with a polisher, there is a problem that the effect of ultrapure water contamination due to elution of organic substances is greater than the effect of removing ions. Furthermore, because the ultrapure water passes through the polisher and wears the ion exchange resin,
There is a problem in that the life of the ion exchange resin is shortened by passing the raw water that does not require ion removal through the polisher.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, can automatically control the amount of water returned to the ultrapure water tank according to the flow rate and quality of the return water, and can prevent contamination by the device. It is an object of the present invention to provide an ultrapure water production apparatus capable of reducing the life of the polisher and extending the life of the polisher.

[0006]

The present invention pays attention to the fact that the quality of return water can be detected by the specific resistance of the return water, and the specific resistance value of the return water is constantly measured to determine the specific resistance value. The above problem is achieved by configuring the return water flow rate to be returned after the polisher.
That is, the apparatus for producing ultrapure water according to the present invention branches the return water pipe into the ultrapure water tank return water pipe and the polisher bypass pipe through the control valve, and based on the input signals of the return water amount and the specific resistance of the return water. A controller for controlling the opening of the control valve is provided.

In the apparatus for producing ultrapure water according to the present invention, when the specific resistance value of the return water is 18.0 MΩ · cm or more, it is not necessary to remove the ions with the polisher, but rather the pollution from the polisher is rather large. Most of the return water should bypass the polisher and return to the ultrapure water line because of the problem. On the other hand, the specific resistance value of the return water is 18.0.
If it is less than MΩ · cm, ion exchange removal with a polisher is necessary, and most return water is returned to the ultrapure water tank. In order to perform control by such a specific resistance value of return water, in the device of the present invention, a specific resistance meter is installed in the return water pipe and the measured value is input to the controller. In addition, a flow meter is installed to constantly measure the return water flow rate and send it to the controller as an input signal to calculate the specific resistance value of the return water and the opening degree of the control valve corresponding to the fluctuations of the return water flow rate. It is divided into the amount of water to be returned to and the flow rate to be divided into the polisher bypass pipe.

The ultrapure water production system is designed to return approximately 20% of the produced ultrapure water flow rate to the ultrapure water tank as the minimum return water flow rate, and the return water flow rate is approximately 2 with respect to the produced ultrapure water.
It varies in the range of 0% to 120%.

In the apparatus of the present invention, a control valve is provided for controlling the flow rate of ultrapure water flowing into the polisher so that the polisher always operates at the optimum SV value, and a pipe for returning ultrapure water to the pump inlet is provided in this valve. Is preferably connected to a pipe for bypassing the polisher. The optimum SV value corresponding to the return water flow rate is peculiar to the ultrapure water production system, and the load on the ultrapure water production system is inversely proportional to the return water flow rate, but the degree of contamination of the return water from the use point. The relationship between the load and the return water flow rate varies depending on the ultrapure water production system. Therefore, it is necessary to formulate the relationship between the return water flow rate and the optimum SV value when starting up the ultrapure water production system. The controller that takes in the return water flow rate and the specific resistance value and the control valve that receives the output from the controller control the polisher inlet ultrapure water flow rate so that the polisher operates at the optimum SV value based on the above-mentioned mathematical formula. .

Further, the flow rate of ultrapure water at the outlet of the ultrapure water producing apparatus is preferably constant. Therefore, the flow rate at the outlet of the polisher can be constantly measured and taken into the controller, and the flow rate at the outlet of the ultrapure water production apparatus can be controlled to be constant by the control valve provided at the polisher outlet.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings, but the present invention is not limited thereto. FIG. 1 is a system diagram of an ultrapure water production apparatus showing an embodiment of the present invention. The apparatus for producing ultrapure water shown in FIG. 1 mainly comprises an ultrapure water tank 1, a primary pure water inflow pipe 2, a heat exchanger 3, a UV oxidizer 4, a polisher 5, an ultrafiltration membrane device 6,
It is composed of control valves 8, 9 and 10, controllers 11 and 12, a specific resistance meter 13, and flow meters 14 and 15. The amount of ultrapure water produced by this equipment is 30 m ³ / h
The minimum return water flow rate is 6 m ³ / h and the maximum return water flow rate is 36 m ³ / h. The volume of ion exchange resin in the polisher is 560 liters (70 liters x 8 liters).
Group).

When the specific resistance of the return water measured by the resistivity meter 13 is 18.0 MΩ · cm or more, 0.5 m is added to the ultrapure water tank return water pipe 16 in order to prevent stagnation in the pipe.
The return water of ³ / h is caused to flow, and the control valve 8 divides the remaining return water into the polisher bypass pipe 17. Conversely, the specific resistance of the return water is 18.0 MΩ · cm
If it is less than 0.5, 0.5% is added to the polisher bypass pipe 17 in order to prevent stagnation in the polisher bypass pipe 17.
The return water of m ³ / h is made to flow, and the remaining return water is made to flow to the ultrapure water tank return water pipe 16 by the control valve 8.

FIG. 2 shows the relationship between the return water flow rate and the optimum SV value of the ultrapure water production system of the present embodiment. When the specific resistance is 18.0 MΩ · cm or more and the return water flow rate is 5.5 m ³ / h (the amount of return water is minimum,
When the amount of primary pure water is large and the load is maximum: A in Fig. 2
Point), the optimum SV value is 65, so the flow rate of ultrapure water is 65
× 0.56 = 36.5 m ³ / h, and the specific resistance is 18.
It is less than 0 MΩ · cm, and the return water flow rate is 35.5 m ³
/ H (the amount of return water is maximum, the amount of primary pure water is small, and the load is minimum, point B in FIG. 2), the optimum SV value = 71, so the flow rate of ultrapure water is 71 × 0.56. = 4
It becomes 0.0 m ³ / h. Therefore, the controller 11 calculates the polisher inlet ultrapure water flow rate from the relationship between the return return water flow rate to the ultrapure water tank 1 and the optimum SV value, and the control valve 9 controls the amount of ultrapure water flowing into the polisher 5.

Next, the flow rate balance when the return water flow rate is controlled according to this embodiment will be described. The flow rate of ultrapure water flowing from the control valve 8 into the polisher bypass pipe 17 varies within the range of 0.5 to 35.5 m ³ / h.
The amount of ultrapure water in the pipe between the ultrapure water tank 1 and the control valve 9 is always 40.5 m ³ / h. Polisher 5
The flow rate is controlled by the control valve 9 so that the inlet flow rate of is the flow rate corresponding to the ultrapure water tank return return water flow rate calculated by the controller 11. The polisher inlet flow rate is controlled within the range of 36.5 to 40.0 m ³ / h, and the surplus ultrapure water is returned to the inlet of the pump 18. Polisher 5
Control valve 10 and controller 12 provided at the outlet
And the flow rate of the ultrapure water production device is set to 3 by the
It is controlled to be 6.0 m ³ / h. The surplus ultrapure water is returned to the inlet of the pump 18. In addition, in order to prevent the ultrapure water from staying in the pipes returning from the control valves 9 and 10 to the pump 18, at least 0.5 m ³ / h of ultrapure water flows.

In the above embodiment, the control valve for the flow rate of the polisher inlet is provided immediately before the polisher.
Between 8 and the polisher 5, the same effect can be obtained at any place, so that it can be appropriately changed according to the pipe arrangement of the ultrapure water producing apparatus.

[0016]

According to the apparatus for producing ultrapure water of the present invention, the apparatus can be operated under operating conditions according to the load, and the amount of water to be returned to the ultrapure water tank is automatically adjusted according to the flow rate and quality of return water. Of the ultrapure water in the pipes and equipment configuration unit, impurities elution from the equipment configuration unit, for example, contamination of ultrapure water by the equipment due to elution of organic substances from the polisher, etc. Can be reduced,
In addition, the life of the polisher can be extended.

[Brief description of drawings]

FIG. 1 is a system diagram of an ultrapure water production apparatus showing an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the return water flow rate and the optimum SV value in the device shown in FIG.

FIG. 3 is a system diagram of a conventional ultrapure water production apparatus.

FIG. 4 is a graph showing a relationship between a polisher SV value and a TOC concentration and an ion concentration of polisher-treated water in a conventional apparatus.

[Explanation of symbols]

 1 Ultrapure water tank 4 UV oxidizer 5 Polisher 6 Ultrafiltration membrane device 7 Use point 8 Control valve 9 Control valve 10 Control valve 11 Controller 12 Controller 13 Resistor meter 14 Flowmeter 15 Flowmeter 16 Ultrapure water tank Return water pipe 17 Polisher Bypass piping

Claims (4)

[Claims] 1. In an apparatus for producing ultrapure water in which return water from a point of use is returned to an ultrapure water tank to perform circulation operation, a return water pipe is connected to an ultrapure water tank return water pipe and a polisher bypass pipe through a control valve. An apparatus for producing ultrapure water, characterized in that a controller for controlling the opening of the control valve based on input signals of the amount of return water and the specific resistance of the return water is provided. 2. The specific resistance of the return water is 18.0 MΩ · c
The apparatus for producing ultrapure water according to claim 1, wherein the amount of water returned and returned to the ultrapure water tank is set to a minimum when m or more. 3. A polisher inlet flow rate control valve, the opening of which is controlled by the controller according to claim 1, wherein the SV value of the polisher is kept constant.
Alternatively, the apparatus for producing ultrapure water described in 2. 4. A control valve is provided in a pipe connecting the polisher and the ultrafiltration membrane device, and a controller is provided to control an opening of the control valve based on a flow rate to the ultrafiltration membrane device. 2. The apparatus for producing ultrapure water according to 2 or 3.