JPS6094162A - Electrostatic purification device for pure water - Google Patents

Abstract

PURPOSE:To enable installation of an electrostatic purification device easily to an existing use point of superpure water and to perform secure removal of fine particles due to elution from an electrode plate and to prevent contamination due to eluted material by using a specified material for an electrode plate. CONSTITUTION:The whole body of an apparatus is formed to a tubular shape enclosed by an insulating body 10, and cylindrical positive electrode plates 18 and negative electrode plates 20 both having 500mm. length are arranged alternately in an expanded zone 16 with 4mm. distance along an axis of the tube, and the electrodes receive positive and negative charge respectively from terminals disposed to the inside of a supporting bar 22. By using stainless steel coated on its surface with a conductive ceramic or a material having low ionization tendency such as bismuth oxide, tungsten carbide, etc. for the electrode plates 18, 20, sure and quick removal of fine particles in water of superhigh purity is enabled for a long term.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an apparatus for electrostatically removing particulates from pure water, and more specifically to an electrostatic purification device for pure water that is optimal for the treatment of ultrapure water. Regarding equipment.

[Background technology]

Currently, the ultrapure water used for cleaning in the semiconductor production process has a specific resistance of 18 MΩ or more and a particle count of 50/- or less at the course point (the actual location where ultrapure water is used). is required as a condition. Ultrafiltration membranes, microfiltration membranes, etc. are generally used as particulate removal devices in ultrapure water production equipment, and are these membranes used at the equipment outlet? 1. Reduce the number of fine particles in pure water to 50 particles/me or less. However, while this ultrapure water passes through several six to several thousand meters of piping from the equipment outlet to the point of use, contaminants are introduced into the water in each 1% of the piping, and therefore, at the point of use, contaminants are introduced into the water. In this case, the number of particles in ultrapure water is even lower than the above condition value.Therefore, we are currently installing separate ultrafiltration membranes, microfiltration membranes, etc. at the point of use to remove particles in ultrapure water. However, these membranes have the disadvantage that a sufficient flow rate cannot be obtained unless the piping pressure is always maintained above a certain value, for example, above 3?/Cd.

As a method of solving the above problem, a method of using an electrostatic purifier in place of the above filtration membrane can be considered.

However, S! in insulating liquids such as oil! Conventional devices for electrostatically purifying nuclear particles do not have a structure in which fine particles are removed by passing a liquid between electrodes filled with fibers or porous materials; When a device with this type of structure is applied to remove fine particles from ultrapure water, the filling itself will shrink, the particles will flow out, and the specific resistance value of the ultrapure water will decrease due to the elution of dissolved substances from the filling and electrode plates. A problem arises in that the value decreases.

In addition, in the conventional Cottrell type electrostatic filtration device, the distance between llk is set at 3.0 mm in order to coalesce small water droplets in oil into large water droplets.
Despite applying a high voltage of 5 to 20 cfn and a high voltage of 3 to 30 KV, fine particles cannot be removed.

[The purpose of light]

The present invention has been made in view of such circumstances, and an object of the present invention is to provide an electrostatic purification device for pure water that can be installed at existing ultrapure water use points and that can reliably remove particulates. With the goal.

[Structure of the invention]

In order to achieve the above object, in the present invention, either conductive ceramics or stainless steel whose surface has been coated with a material having a low ionization tendency is used as the electrode plate of the electrostatic purification device.

With this configuration, it can be easily installed at existing ultrapure water use points, and O
The first step is to ensure the removal of particulates by preventing the emission of IL.

[Implementation 6 of U6S J] Figure 1 shows the surface dwell time of 1 second and the distance vl compared to the distance between the electrode plates.
It is a diagram (not shown in red) that shows the removal of fine particles in ultrapure water during the summer of 2015 when the field strength of 1L was limited. As shown in the figure, it can be seen that when the distance between the electrode plates is increased, the removal rate of particulates decreases due to the influence of turbulence.

The first table is a table showing the results of examining the relationship between the resistance of the electrode plate and the decrease in the specific resistance of ultrapure water.

As shown in the same table, after long-term use, in the case of carbon steel and stainless steel, there is a tendency for the resistivity to decrease due to the effects of iron elution and corrosion, whereas conductive ceramics (oxidized In the case of stainless steel whose surface is coated with bismuth or tungsten carbide (preferably bismuth or tungsten carbide) or a material with low ionization ++S direction, there is hardly any decrease in specific resistance.

Particles attached to the electrode plate can be removed by applying a reverse charge to the electrode plate or using a device that promotes the peeling R function, such as ultrasonic irradiation.

FIGS. 2 and 3 are diagrams showing an embodiment of the pure water n-type purification apparatus according to the present invention, which was constructed based on the above study results. The entire device has a tubular shape surrounded by an insulator 10, with an ultrapure water inlet 12 formed on one side and an outflow 4 on the other side. In the illustrated embodiment, the diameters of the inlet 12 and the outlet 14 are each 25 m, and the diameter of the central enlarged diameter portion 16 is 50 m. The expanded diameter portion 16, that is, the inside of the device has a cylindrical shape with a length of 500 m.
A positive electrode plate 18 and a negative electrode plate 20 made of ceramic ceramics
are arranged alternately along the axial direction of the tube with a spacing of 4 mm. Each electrode plate 18, 20 is supported at both ends by a hollow insulating support rod 22, and receives positive and negative charges from terminals disposed inside the support rod 22. When the terminal is connected to a power source, an electric field force l is generated between the two electrode plates 18 and 20, and when ultrapure water is passed between them, the minute P particles in the water become negative particles and move to the positive electrode. Add a layer. In this way, fine particles in ultrapure water are continuously removed.

FIG. 4 shows the result of removing particulates from the 1001d continuous pile H by installing the above device at the end of the ultrapure water plant. The conditions are that the voltage between Kamesama is 450
(2) The electric field strength was 170 V/rn, and the electrode plate was subjected to ultrasonic irradiation 81 times to remove fine particles. As can be seen from the figure, the number of fine particles in ultrapure water can be maintained at 50 particles/d or less at the point of use over a long period of use.

In the above-mentioned embodiment, it is possible to obtain the same effect by using conductive ceramics as the electrode plate, or by using stainless steel with the above-mentioned surface coating treatment instead. it is obvious. In addition, the shape and arrangement of the electrode plates can be individually modified; for example, flat plate electrodes may be arranged in multiple layers, or linear electrodes and flat plate electrodes may be placed in parallel. [Effects of the Invention] As described above, the pure water electrostatic purification device according to the present invention has the following effects:
Since the structure is simple, it can be easily installed at existing ultrapure water use points, and it is possible to reliably remove particulates to prevent them from flowing out from the electrode plate.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the influence of the distance between the electrode plates on particulate removal, Fig. 2 is a sectional view showing an embodiment of the electrostatic purification device for pure water according to the present invention, and Fig. 3 is a diagram showing the effect of the distance between the electrode plates on particulate removal. FIG. 4 is a sectional view taken along the line A-A in the figure, and is a diagram showing the results of continuous operation of the same device. lO... Insulator, 12... Inlet, 14... Outlet, 16... Expanded diameter part, 18... Positive electrode plate, 20...
- Negative electrode plate, 22... support rod. Out 1 Jojin 11 Standing Bra, 1) I General 14 + J, 'v Company Figure 1 Figure 3 Figure 4 I History Condolences (B)

Claims (2)

[Claims] (1) In a device that passes a liquid between electrode plates to which a voltage is applied and electrostatically removes floating particles in the liquid, the electrode plate is surface coated with conductive ceramics or a material with a low ionization tendency. A patented electrostatic purification device for pure water that uses one of the stainless steels. (2) The electrostatic purification device for pure water according to Claim IJ, wherein the distance between the electrode plates is 1 crn or less. (3J) The stainless steel surface coating material is platinum, gold, silver, etc. The electrostatic purification device for pure water according to claim (1), which is any one of .