JPH0569773B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an ammonia water production apparatus for inexpensively producing ammonia water at a constant concentration with few impurities from liquefied ammonia.

[Conventional technology] For example, when forming integrated circuits on silicon wafers to make so-called IC chips in semiconductor factories, strict control measures are taken to prevent the contamination of impurities in order to maintain the quality of the chips. Of course, the cleaning agent for cleaning the wafer must be highly clean. In particular, since the presence of solid particles deteriorates the properties of semiconductors, their purity is checked by optical inspection using the Tyndall phenomenon.

Ammonia water is used as such a cleaning agent, but conventionally, ammonia water is commercially available sealed in cans, transported into the factory, filtered through a filter, and stored in a tank. was using something.

[Problems to be solved by the invention] However, the purity of commercially available ammonia water as described above is not high enough to meet the intended purpose, and furthermore, it is difficult to remove waste that remains in the container during transportation or tank transfer. The purity may further decrease due to absorption, or contact with air and absorbing the dust, and reacting with carbon dioxide in the air to produce ammonium carbonate.

Furthermore, it is not easy to filter ammonia water using a filter to remove fine particles of impurities, and it is difficult to obtain ammonia water with few impurities by such a method.

[Means for Solving the Problems] In order to solve the above problems, the present invention provides an evaporator that raises the temperature of liquefied ammonia to vaporize it, and a filter that filters the vaporized ammonia gas to remove impurities. A filter for removing the ammonia gas, an ammonia absorption tower for dissolving and absorbing the purified ammonia gas in ultrapure water, and a storage tank for storing the ammonia water discharged from the ammonia absorption tower,
The ammonia absorption tower is provided with a cooler for cooling ammonia water whose temperature has risen due to dissolution of ammonia gas.

[Function] According to such an ammonia water production apparatus, fine solid or liquid impurities contained in ammonia gas are filtered and removed by a fine-mesh filter. This purified ammonia gas is
It is dissolved and absorbed in ultrapure water in the ammonia absorption tower, but the heat of dissolution generated at this time is absorbed by the cooler, so the temperature inside the ammonia absorption tower does not rise and the efficiency of dissolution does not decrease. Moreover, the pressure inside the ammonia absorption tower will not be increased more than necessary, and accidents such as seal leakage will not occur.

[Example] Hereinafter, an example of the present invention will be described with reference to FIG.

Liquefied ammonia as a raw material is stored in a raw material tank 1 and guided to an evaporator 3 through a control valve 2.
This evaporator 3 has a meandering pipe 3b provided in a temperature raising tank 3a containing hot water or steam, and is designed to efficiently evaporate liquefied ammonia.

A well-known gas filter 4 having a cylindrical body filled with fine particles (particle size: 0.1 to 0.2 μm) of a tetrafluoroethylene polymer is attached to a pipe 3c on the discharge side of the evaporator 3.

Further, in the pipe 3c in front of the gas filter 4, there is provided a pressure regulator 5 that detects the pressure of the pipe 3c and opens and closes the control valve 2 based on the detected pressure.

A pipe 4a on the discharge side of the gas filter 4 is connected to an ammonia absorption tower 7 via a control valve 6. This ammonia absorption tower 7 has an upper small diameter section 7.
a and a lower large-diameter portion 7b, and this small-diameter portion 7
A gas-liquid contact layer 8 filled with a porous material (Raschig ring, telleret, etc.) is formed in a. A pressure regulator 9 is provided above the gas-liquid contact layer 8 to open and close the control valve 6 by detecting the pressure at the top of the column.

A circulation line 10 through which water is circulated by a pump P is provided between the bottom of the large diameter portion 7b and the top of the small diameter portion 7a. This circulation line 10 is provided with a cooler 11 after the pump P, which cools the ammonia water whose temperature has risen due to the heat of dissolution of ammonia to efficiently absorb ammonia. The cooler 11 is a conventional cooler consisting of a cooling water tank with internal piping, and the flow rate of the cooling water is set to a value that will prevent the temperature inside the ammonia absorption tower 7 from rising.

After this cooler 11, the circulation line 10 is
It is branched into a main line 10a connected to the top of the ammonia absorption tower 7 and a bypass line 10b directly introduced into the large diameter section 7b.

Further, this ammonia absorption tower 7 is provided with a supply line 12 for supplying new ultrapure water.

The circulation line 10 is branched after the pump P, and is provided with a discharge line 15 connected to a storage tank 14 via a filter 13. After this branch point, the circulation line 10 and the discharge line 15 are provided with solenoid valves 16 for opening and closing, respectively.
On the other hand, a conductivity meter (sensor) 18 is installed in front of the pump P in the circulation line 10 to detect the conductivity of the internal fluid.
When this detected value reaches a predetermined value (when the concentration of ammonia water reaches a required value), the automatic switching device 19 linked to the circulation line 1
The ammonia water is automatically discharged into the storage tank 14 by closing the solenoid valve 16 of the discharge line 15 and opening the solenoid valve 17 of the discharge line 15.

There is a relationship between the electrical conductivity of ammonia water and the ammonia concentration as shown in Figure 2, and when the concentration exceeds 5wt%, there is an almost linear one-to-one correlation, so this electrical conductivity is measured. This allows the ammonia concentration to be detected.

The filter 13 is provided to remove relatively large pieces of dirt that have suddenly been mixed in. Further, the storage tank 14 is hermetically sealed, and the inside thereof is filled with an inert gas such as high-purity nitrogen gas through a pipe 20 to prevent contamination with dust and reaction of carbon dioxide and oxygen in the air.

The piping and equipment that make up the above manufacturing equipment are made of highly corrosion-resistant stainless steel (SUS304), and the gaskets and filters for maintaining airtightness are made of tetrafluoroethylene polymer. Further, since the pressure regulators 5 and 9 control the line pressure so that it does not greatly exceed normal pressure, the withstand pressure of the line is not set particularly high.

In this manufacturing equipment, not only the discharge of the product from the absorption tower 7, but also the supply of ammonia gas to the absorption tower 7, the temperature control of the temperature raising tank 3a of the evaporator 3, etc. are automated, and batch processing is sequentially performed automatically. It is becoming more common to do so.

Next, the operation of the ammonia water production apparatus configured as described above will be explained.

The liquefied ammonia that is the raw material for this manufacturing equipment is
There is no particular restriction on the amount of impurities, and any commercially available products can be used. Note that pure liquefied ammonia has a boiling point of -33°C and a heat of vaporization of 327 cal/g.

As shown in Figure 2, the ammonia concentration is 5wt%
Since the conductivity reaches a maximum in the vicinity, the previously treated ammonia water is left in the absorption tower 7 so that the initial value of ammonia concentration does not fall below that value.
It is filled with ultrapure water from the supply line 12.

The liquefied ammonia in the sealed raw material tank 1 is sent to the evaporator 3 via the control valve 2 by its own gas pressure, where it is vaporized and sent to the gas filter 4. At this time, liquid or solid impurities contained in the liquefied ammonia are filtered out by the gas filter 4.

The ammonia gas that has passed through the gas filter 4 is guided to the ammonia absorption tower 7, where it is dissolved and absorbed in ultrapure water or aqueous ammonia. At this time,
Ammonia gas is circulation line 10, main line 10
It efficiently contacts and reacts with ultrapure water or aqueous ammonia spouted from the top of the column through a in the gas-liquid contact layer 8.

The temperature of this ammonia water rises due to the heat of dissolution of ammonia gas. For example, if 28wt% ammonia gas is dissolved in ultrapure water at 0°C and no cooling is performed, the temperature of the ammonia water is calculated to be 150°C or higher. reach even. As shown in Fig. 3, the equilibrium vapor pressure of ammonia water increases greatly as the temperature rises, so in order to advance the ammonia dissolution reaction, ammonia gas must be sent into the ammonia absorption tower 7 to compensate for the increase in ammonia gas. The pressure must be increased, and
The pressure resistance of the ammonia absorption tower 7, piping, etc. must also be set higher accordingly. In order to prevent such a temperature rise, the ammonia water is cooled by a cooler 11 installed in the circulation line 10, a part of which is led back to the top of the tower from the main line 10a, and a part of which is absorbed through the bypass line 10b. It is injected into the large diameter section 7b of the column 7.

The water injected from the bypass line 10b lowers the temperature of the ammonia water in the large-diameter portion 7b, and is stirred to make the concentration uniform to make the absorption of ammonia effective. The conductivity meter 18 operates accurately.

Note that the pressure regulator 9 at the top of the absorption tower 7 is configured to close the control valve 6 and restrict the inflow of ammonia gas when the pressure at this portion exceeds a predetermined value. The pressure inside the ammonia absorption tower 7 is negative pressure due to the dissolution of ammonia gas, but if the dissolution reaction progresses and the temperature rises without cooling enough, the ammonia vapor pressure will also rise. Since the dissolution efficiency decreases, the progress of the reaction is controlled by, for example, setting the pressure of the pressure regulator 9 to 0.5 Kg/cm ² to suppress the pressure at the top.

The speed of such ammonia gas absorption reaction decreases as the ammonia concentration in the ammonia water increases, but as a result, the gas pressure in the pipes 3c and 4a increases, and when it reaches a predetermined value, the pressure regulator The control valve 2 is closed by the signal from 5, thereby controlling the supply of ammonia gas.

When the concentration of ammonia water, which has been gradually concentrated in the above process, reaches a predetermined value, the conductivity meter will measure the predetermined value (conductivity is 380μ/cm when the ammonia concentration is 28wt%). Automatic switching device 1
9 closes the solenoid valve 16, and the discharge line 15
The electromagnetic valve 17 leading to is opened, and the ammonia water is conveyed to the storage tank 14 through the filter 13.

According to such an ammonia water production apparatus, the internal liquid is circulated in the ammonia absorption tower 7, and a cooler 11 is provided in the circulation line 10 to absorb the heat of dissolution of ammonia gas, thereby reducing the pressure inside the ammonia absorption tower 7. Ammonia gas is efficiently absorbed without increasing the temperature.

In addition, by adjusting the temperature and pressure inside the column using the pressure regulator 9, the reaction can be carried out smoothly, and the equipment cost can be reduced by not increasing the pressure resistance of the container or piping more than necessary.

The ammonia absorption tower 7 absorbs ammonia gas in a batch manner to stably generate ammonia water, and also detects the concentration of ammonia water and automates its discharge. In addition to keeping the water concentration constant, batch processing is automatically performed sequentially.
The work is labor-saving and more efficient.

The structure of the cooler is not limited to the above example, and the cooler may be installed, for example, inside the ammonia absorption tower.

[Effects of the Invention] As detailed above, the present invention provides an evaporator that raises the temperature of liquefied ammonia to vaporize it, a filter that filters the vaporized ammonia gas and removes impurities, and a filter that removes impurities from the purified ammonia gas. An ammonia absorption tower that dissolves and absorbs gas into ultrapure water and a storage tank that stores ammonia water discharged from this ammonia absorption tower are provided. The structure is equipped with a cooler to cool the purified ammonia gas, so purified ammonia gas can be efficiently absorbed into ultrapure water without increasing the temperature or pressure in the absorption tower. As a result, it is possible to efficiently produce ammonia water with a constant concentration without impurities at a low cost, and there is no need to increase the withstand pressure of equipment such as ammonia absorption towers and piping, so the equipment cost is low. It has excellent effects such as stable operation.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of an ammonia production apparatus according to an embodiment of the present invention, and FIG. 2 is a graph showing the relationship between the concentration of ammonia and the conductivity of ammonia water.
FIG. 3 is a graph showing the relationship between ammonia concentration and equilibrium vapor pressure at various temperatures of ammonia water. 3... Evaporator, 4... Gas filter, 7... Ammonia absorption tower, 11... Cooler.

Claims (1)

[Claims] 1. An evaporator that raises the temperature of liquefied ammonia to vaporize it, a filter that filters the vaporized ammonia gas and removes impurities, and an ammonia absorption tower that dissolves and absorbs this purified ammonia gas in ultrapure water. Equipped with a storage tank that stores ammonia water discharged from this ammonia absorption tower,
An apparatus for producing ammonia water, characterized in that the ammonia absorption tower is provided with a cooler that cools the ammonia water whose temperature has increased due to dissolution of ammonia gas.