JPS6259520A - Apparatus for producing ammonia water - Google Patents

Abstract

PURPOSE:To produce ammonia water having low impurity content, by evaporating liquid ammonia in an evaporator while leaving a part of the liquid or solid impurities in unevaporated state and filtering the solid or liquid particulate impurities entrained to the evaporated ammonia gas with a filter. CONSTITUTION:Liquid ammonia is evaporated by heating with an evaporator and a part of liquid or solid impurity is left in the evaporator. The evaporated ammonia gas is passed through a filter to remove the entrained solid or liquid particulate impurities. The purified ammonia gas is introduced into an ammonia absorption column and dissolved in ultra-pure water and the obtained ammonia water is stored in a storage tank.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an ammonia water production apparatus for producing ammonia water of a constant concentration with few impurities from liquefied ammonia at low cost.

U Prior Art] For example, when forming an integrated circuit on a silicon wafer or the like in a semiconductor factory to make a so-called IC chip,
In order to maintain its quality, measures are taken to strictly control the contamination of impurities, and of course the cleaning agent used to clean the wafers 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, the ammonia water used was commercially available ammonia water sealed in a can or the like, brought into the factory, filtered through a filter, and stored in a tank.

[Problems to be solved by the invention] However, the purity of commercially available ammonia water as described above is not originally high enough to meet the purpose, and furthermore,
When it absorbs dust left in the container during transportation or tank transfer, or when it comes into contact with the air and absorbs the dust, it reacts with carbon dioxide in the air and produces ammonium carbonate. This may further reduce the purity.

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.

On the other hand, producing ammonia by, for example, a synthetic method requires large-scale equipment and is not practical.

Means for Solving Problem F" In order to solve the above problems, the present invention provides an evaporator that raises the temperature of liquefied ammonia to vaporize it, and 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 are provided.

[Function] According to such an ammonia water production device, when liquefied ammonia is evaporated, some of the impurities in the liquid or solid state at this evaporation temperature remain unvaporized and are also evaporated together with ammonia gas. The fine particles of solid or liquid impurities that are exposed are removed by filtration through a fine-mesh filter. This purified ammonia gas is dissolved in and absorbed by ultrapure water in an ammonia absorption tower to produce ammonia water with a constant concentration and high purity.

[Example code] Hereinafter, one embodiment of the present invention will be explained with reference to FIG.

Liquefied ammonia, which is the raw material, is stored in the raw material tank l.
It passes through a control valve 2 and is led to an evaporator 3.

This evaporator 3 is a heating tank a containing hot water or steam.
A meandering pipe 3b is provided inside to efficiently evaporate liquefied ammonia.

In the pipe 3C on the discharge side of the evaporator 3, fine particles of tetrafluoroethylene polymer (particle size 0.1-
A well-known gas filter 4 filled with 0.2 μm) is attached.

In addition, a pressure regulator 5 is provided in the pipe 3C in front of the gas filter 4 to detect the pressure in the pipe 3c and open and close the control valve 2 based on the detected pressure.

” The pipe 4a on the discharge side of the two-legged gas filter 4 is connected to the control valve 6.
Through 1. and transported to the ammonia absorption tower 7. This ammonia absorption tower 7 consists of an upper small-diameter part 7a and a lower large-diameter part 7b, and a gas-liquid contact layer 8 filled with a porous material (Lanhilling, Telleret, etc.) is formed in this small-diameter part 7a. ing.

A pressure regulator 9 is provided above the gas-liquid contact layer 8 to open and close the L control well 6 by detecting the pressure at the top of the tower.

A pump P is provided between the bottom of the large diameter portion 7b and the top of the small diameter portion 7a.
A circulation system is provided to prevent water from being circulated. This circulation line 10 is provided with a cooler 11 after the pump P to cool the ammonia water whose temperature has risen due to the heat of dissolution of ammonia, thereby making the absorption of ammonia efficient.

After the cooler 11, the circulation line 10 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 IO is branched off after the pump P.

A discharge line 15 is provided which is connected to a storage tank 14 via a filter 13. After this branching point, the circulation line 10 and the discharge line I5 are equipped with electromagnetic valves 16 and 17 that open and close them, respectively.
In front of the pump P of the circulation line 10, an automatic switching device 19 that works with a conductivity meter 18 is provided to detect the electrical conductivity of the internal fluid, and when this detected value reaches a predetermined value (
When the concentration of ammonia water reaches a required value), the solenoid valve I6 of the circulation line IO is closed, the solenoid valve 17 of the discharge line 15 is opened, and the ammonia water is automatically discharged into the storage tank 14. It has become.

In addition, the conductivity of ammonia water and ammonia a! 'T, there is a relationship as shown in Figure 2, and the concentration or 5w
Since there is a nearly linear one-to-one correlation when the conductivity exceeds t%, the ammonia concentration can be detected by measuring this conductivity.

The filter 13 is provided to remove relatively large pieces of dirt that have suddenly been mixed in.

Furthermore, the storage tank 14 is hermetically sealed, and inside is a pipe 2.
It is filled with inert gas such as high-purity nitrogen gas to prevent contamination with dust and reactions with carbon dioxide in the air.

The piping and equipment constituting 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 regulator 5.9 controls the line pressure so that it does not greatly exceed normal pressure, the withstand pressure of the line is not set particularly high.

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

Liquefied ammonia, which is a raw material for this production equipment, is not particularly regulated in terms of impurities, and any commercially available liquefied ammonia can be used. Note that pure liquefied ammonia has a boiling point of 133° C. and a heat of vaporization of 327 cal/g.

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

The liquefied ammonia in the sealed raw material tank 1 is sent by its own gas pressure to the evaporator 3 via the control valve 2, where it is vaporized, and then sent to the gas filter 4.

At this time, solid or liquid 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, the ammonia gas efficiently contacts and reacts in the gas-liquid contact layer 8 with ultrapure water or ammonia water spouted from the top of the column through the main line 10a of the circulation line IO1. The temperature of this ammonia water rises due to the heat of dissolution of the ammonia gas, but it is cooled by the cooler It from the large diameter section 7b of the absorption tower 7 through the circulation line 10, and a part of it is led back to the top of the tower from the main line lOa. , a part is injected into the large diameter section 7b of the absorption tower 7 via the bypass line 10b.

The water injected from this bypass line 10b is transferred to the large diameter portion 7b.
By lowering the temperature of the ammonia water and stirring, the concentration of the ammonia water is made uniform to make absorption of ammonia more effective, and to ensure accurate operation of the conductivity meter 18 of the automatic switching device 19.

Note that the pressure regulator 9 at the top of the absorption tower 7 closes the control valve 6 to regulate the inflow of ammonia gas when the pressure at this portion exceeds a predetermined value. The pressure inside the 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 vapor pressure of the ammonia water will rise. However, since the dissolution efficiency decreases, the progress of the reaction is controlled by, for example, setting the pressure of the pressure regulator 9 at 0.5 kg/cm'' 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 Control valve 2 is activated by the signal from 5.
is closed, 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 measures the predetermined value (when the ammonia concentration is 28 wt%, the conductivity is 380μ7).
J/am), and the automatic switching device 19 switches on the solenoid valve 1.
6 is closed, the solenoid valve 11 leading to the discharge line I5 is opened, and the ammonia water is conveyed through the filter 13 to the storage tank I4.

When the impurities in the ammonia water produced in this way were analyzed, they were found to be AI, B, Ca, Cu, Fe, and Mg.

Mn, Na, Pb, Sn, and Zn are all 0.
It was 0.01 ppm or less. .

According to such an ammonia water production apparatus, the internal liquid is circulated in the ammonia absorption tower 7 to efficiently absorb ammonia gas, and the 1 temperature in the tower is adjusted by cooling it, the bypass line tab, and the pressure adjustment device 9. ,
By adjusting the pressure, the reaction can be carried out smoothly, and secondly, the equipment cost can be reduced by not increasing the pressure resistance of containers and piping more than necessary.

In addition, the absorption of ammonia gas in the ammonia absorption tower 7 is performed batchwise (batch type) to stably generate ammonia water, and the concentration of ammonia water is detected and its discharge is automated. The concentration of ammonia water is kept constant, and the work is labor-saving and efficient.

[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. The structure includes an ammonia absorption tower that dissolves and absorbs gas in ultrapure water, and a storage tank that stores the ammonia water discharged from this ammonia absorption tower, so it can be used at low cost using commercially available liquefied ammonia as a raw material. ,? This method has an excellent effect of being able to stably produce aqueous ammonia at a constant concentration.

[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. 3... Evaporator, 4... Gas filter,
7... Ammonia absorption tower, 14... Storage tank.

Claims (1)

[Claims] 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. An ammonia water production device comprising: a storage tank for storing ammonia water discharged from an ammonia absorption tower.