FR2887612A1 - Method for charging low temperature liquefied gas to cylinder, involves charging liquefied gas to high pressure charging cylinder using pump and insulating pipe for transporting liquefied gas - Google Patents

Abstract

A low temperature liquefied gas is charged into a high pressure charging cylinder using a pump and an insulating pipe for transporting liquefied gas.

Description

The present invention relates to a method of filling a bottle

  of high pressure gas with a low temperature liquefied gas which, at a temperature

  normal, occurs in the gas phase. More particularly, the invention relates to a method of filling a cylinder of high pressure gas with a low temperature liquefied gas, wherein the low temperature liquefied gas is compressed to a desired pressure in a liquid state with the aid of a pump, and then charged in the compressed gas phase into the high-pressure gas bottle.

  In general, a low boiling liquefied gas occurs in a liquid state at or below a critical low temperature, but in a gaseous state above that critical temperature. In the context of the present invention, this gas is called a low temperature liquefied gas. Due to the above characteristics, the liquefied gas is charged in the gaseous state at a pressure of about 2 × 10 6 Pa to 2 × 10 7 Pa in a high pressure bottle. The liquefied gas can be, for example, nitrogen, oxygen or argon, which are widely used for general applications, or nitrogen trifluoride (NF3, boiling point: -129 ° C.), sulfur hexafluoride (SF6), anhydrous hydrochloric acid (AHC1), anhydrous hydrogen bromide (AHBr), carbon tetrafluoride (CF4) or hexafluoroethane (C2F6) which are used in semiconductor industry.

  A conventional method for filling a gas cylinder with a liquefied gas comprises the steps of condensing the gas at low temperature during its production, storing the gas in the liquid state in a storage container, passing the gas through a vaporizer or a heat exchanger for vaporizing it, and then loading the vaporized gas into a cylinder of high pressure gas at the same time as compressing it by means of a compressor.

  The reason why this method, according to which the liquefied gas is vaporized and loaded in this state into the bottle while being compressed by means of a compressor, is frequently adopted to fill gas cylinders with liquefied gas at low temperature. temperature is as follows. If a pump is used with a low temperature liquid that has a low boiling point, cavitation occurs (a phenomenon which makes it impossible for the pump to work normally when a low boiling liquid is vaporized, then loaded into the pump head). However, when the vaporized gas is compressed by a compressor, there is no need to worry about the phenomenon of cavitation.

  However, this method is problematic because the temperature of the charged gas increases because of the heat of compression generated when the gas is compressed by the compressor, and can, in severe cases, result in a decomposition of the product and therefore an increase in impurities, which decreases the purity of the product. Other problems arise, such as maintenance costs that are high due to the abrasion of certain elements and the loading speed which is reduced to high pressure. However, there is no clear plan of action to address this because of the characteristics of the compressor, but complementary measures, such as mitigating compression heat problems by cooling the gas with the help of a refrigeration apparatus disposed on a compressor head or an output member, and removing the impure particles with a filter mounted on the output member. Nevertheless, the essential problems have not been removed.

  In addition, as a result of advances in the semiconductor industry, the demand for higher purity gas used in this field is increasing, and the criteria for the content of gas impurities are becoming more stringent.

  In the conventional method according to which the liquefied gas is vaporized and charged in this state into the bottle while being compressed by the compressor, the energy consumption is important during the vaporization and compression operations, and in the case of a gas requiring a very high purity, such as gaseous nitrogen trifluoride (NF3) which is used as an attack gas in a semiconductor manufacturing process, there is a significant risk of degradation of the gas.

  It is therefore still necessary to develop, in the above field, a method for filling a gas cylinder with a liquefied gas, which allows to reduce the energy consumption and to avoid degradation of the gas during filling.

  The present invention specifically relates to a method of filling a cylinder of high pressure gas with a liquefied gas at low temperature, characterized in that it consists of using a pump and an insulating pipe to transport the liquefied gas at low temperature.

  Preferably, the low temperature liquefied gas is selected from the group consisting of nitrogen trifluoride, nitrogen, oxygen, argon, sulfur hexafluoride, anhydrous hydrochloric acid, hydrobromic acid anhydrous, carbon tetrafluoride and hexafluoroethane.

  According to a particular characteristic of the invention, a liquid compressed by means of the pump is charged directly into the bottle, or is charged in the gas phase into the bottle after having been vaporized by an evaporator or a vaporizer provided on the discharge side. pump.

  The inventors of the present invention have discovered that, contrary to a conventional method according to which a cylinder of high pressure gas is filled with a gaseous gas by means of a compressor, when a liquefied gas, such as the NF3, which must be extremely pure, is loaded into a high-pressure gas cylinder by means of a pump under conditions that do not cause cavitation, it is not degraded during the filling process and the filling can take place. perform with little energy.

  It is an object of the present invention to provide a novel filling technique whereby a low temperature liquefied gas can be bottled with a pump, thereby preventing heat generation problems during a period of time. compression process by a compressor, high energy costs, as well as vibration and noise. This technique is economical and stable and can therefore be applied to the bottling of gases intended for general use and of very high purity gas for semiconductors, such as NF3.

  The above, as well as other objects, features and advantages of the present invention, will become more apparent from the following detailed description of a preferred embodiment, given by way of non-limiting example and taken in conjunction with the accompanying drawings in which: Figure 1 is a schematic representation of an installation for carrying out a method of filling a bottle with a liquefied gas using a pump, according to the present invention; and Figure 2 is a schematic representation of an installation in which is implemented a conventional method of filling a bottle with a liquefied gas using a vaporizer and a compressor.

  In a liquefied gas bottling process using a pump, the liquefied gas can be easily compressed to a desired pressure not in a gaseous state, but in a liquid state, during the compression process. the pump, which allows it to be transported at a practically constant flow rate at high and low pressure, thus reducing the filling time. In addition, since the heat output is very low at a high compression ratio, it is possible to reliably bottle a product, such as NF3, whose reactivity is considerably increased and which is substantially decomposed at high temperature. On the other hand, since the liquid (liquefied gas at low temperature) is charged to a head portion of the pump, where lubrication is ensured, the formation of metal particles due to friction or abrasion is thus avoided. In addition, compared to a compressor compression process, since a small, low-energy apparatus can be used, it is possible to minimize operating costs, reduce maintenance and energy and to obtain a desirable performance due to the reduction of the filling time.

  Since the compressor transports the gas after having compressed it, while the pump transports it directly to the liquid state, the size of the compressor must be at least 10 times greater than that of the pump for the same quantity of liquefied gas.

  The pump is used to transport and bottle the liquid and is typically composed of a head comprising a piston and a check valve, a motor that provides power and a mechanically operated part (a transmission and an active part of the piston) which generates a fluid pressure thanks to the rotational power of the engine.

  In the context of the present invention, it is preferable for a pipe to be mounted between a storage vessel in which the liquefied gas at low temperature is stored in a liquid state, and the suction side of the pump, and a pipe The suction line is either completely insulated or cooled with a low-temperature refrigerant to avoid a cavitation phenomenon due to the vaporization of a low-temperature liquid.

  It is also preferable that the head portion of the pump is completely insulated to avoid cavitation and, if necessary, a cooling coil or a double liner which can be cooled by means of a low temperature cooler is provided on the -this. A pipe connected to the storage tank is connected to a discharge pipe of the pump so that a priming charge of the pump and a residual solution in the discharge pipe can be recycled to the storage tank. During the priming process of the pump, the liquid flows through the above pipe from the storage tank and, when the filling operation is complete, the residual solution and pressure in the discharge pipe are recycled to the storage tank via said pipe to minimize product losses. In addition, a manometer is provided to control the operation of the pump and the discharge pressure, as well as a safety device to prevent overpressure. It should be noted that, if the pipe is completely filled with liquefied gas at low temperature and is airtightly closed, overpressure may occur as a result of expansion due to an increase in temperature; which, in severe cases, may result in damage to the hose. The liquefied gas that is compressed by the pump is transported through the hose, which is connected to filling devices, to a gas cylinder to be filled and can be loaded directly or after having been vaporized at normal temperature. means of a vaporizer or a separate heat exchanger provided on the discharge pipe. If it is loaded directly into the bottle, a valve of the latter is closed after filling is complete, after which the bottle is left at normal temperature to vaporize the charged liquid. The filling quantity is measured by means of a balance, and a manometer is provided on each filling device to control the filling pressure, in order to avoid overfilling. The filling method of the present invention can be applied to both a single filling device and several filling devices.

  The present invention may be better understood on reading the following example and comparative example which are proposed by way of illustration, but not by way of limitation, of the present invention.

EXAMPLE

  A detailed description of a filling process according to the present invention will be given with reference to FIG. 1. Highly pure and low temperature condensed NF3 was used as a liquefied gas for a fill test. A storage tank T was connected to an installation for producing NF3 via a pipe, a double vacuum lining being provided on an outer surface of the storage tank T to isolate the latter. The liquid NF3 stored in the storage tank was transported via a suction pipe S1 into the suction part of a pump P, the suction pipe Si being formed by a double pipe vacuum insulation type. A pressure gauge was provided on the discharge side of the pump to allow control of the normal operation of the pump. The filling cylinder C has been connected to a discharge pipe S2 of the pump and arranged on a balance so that the filling quantity can be controlled. The filling was carried out thanks to the following procedure. In the present example, the pump P used was a low temperature piston pump.

  1) A filling pipe S4 and the high-pressure bottle C were connected to each other at the opening M of the bottle and valves V1 and V2 were closed, while valves V3, V4 and V5 were opened to create a vacuum of at most 1,333x102 Pa (1 Torr) to remove air and moisture from the pipe. Previously, moisture had been removed from the high-pressure bottle C which had then been evacuated to be ready for filling.

  2) After completing step 1), the valves V3, V4 and V5 were closed, while the valves V1 and V2 were opened to prime the pump P, and then the pump was started. to make a circulation.

  3) When the temperature of the pump head H was sufficiently low to transport a liquid in good conditions and the pressure rapidly increased, the valve V2 having been closed, the valves V3 and V4 were opened to fill the bottle C of NF3 liquid.

  4) At the end of the filling, the valve V4 was closed, the pump was stopped and the valves V1, V2 and V3 opened to recycle the residual solution of the filling pipe S4 into the storage tank and stabilize the pressure in this latest. All the valves were closed and the C gas bottle was separated from the loading device. The gas cylinder was left at normal temperature for its temperature to rise to this temperature.

  Alternatively, the liquefied gas compressed by the pump P and transported through the discharge pipe S2 was passed through a vaporizer G to be vaporized and then charged in the gas phase into the cylinder C via a filling pipe S3.

COMPARATIVE EXAMPLE

  A detailed description of a conventional method of bottling a liquefied gas using a vaporizer and a compressor will now be given with reference to Figure 2. Liquid NF3 condensed at low temperature a been used as a liquefied gas for the filling test. A storage tank T was connected to an installation for producing NF3 via a pipe, a vacuum liner being disposed on an outer surface of the storage tank T to isolate it. The liquid NF3 stored in the storage tank was transported via a suction pipe S1 into a vaporizer G. The liquid NF3 passed through the vaporizer G which contained a heater was easily vaporized thanks to an increase in temperature to adopt a gaseous phase. Then, the gaseous NF3 was delivered to a compressor E via a discharge pipe S2 was compressed, and the compressed gaseous NF3 was loaded into a C-fill bottle via a pressure hose. S5 filling.

  Measurements were made on the bottled gas in the liquid state using the pump P of the Example and on the gas bottled in the gaseous state using the vaporizer G and the compressor E of the Comparative Example, in order to measure their respective purity and acidity. The measured values were compared to the purity and acidity of the NF3 contained in the storage tank T, and the results are shown in the following Table 1.

TABLE 1

  Category HF Purity HNO3 Number of (%) (ppm) (ppm) fine particles per liter Reservoir 99.998 0.015 0.150 1.9 x 10-3 storage Example 99.997 0.026 0.653 7.7 x 10-2 Comparative Example 99.998 0.017 0, 251 1.7 x 10-2 In the Comparative Example, the purity is substantially unchanged, but the acidity is considerably higher. This seems to be due to the fact that the gas was activated by the heat of compressor compression, which allowed the gaseous NF3 to decompose easily.

  Similarly, the number of fine particles has increased.

  This increase appears to be the result of a mechanical friction generated during compression filling with the compressor.

  In contrast, in the Example, changes in purity and acidity are insignificant.

  In Table 1 above, the impurities were analyzed by gas chromatography, and the results were retrieved to measure the purity of the gas. With respect to acidity analysis, after a specific amount of gaseous product was absorbed into water, neutralization titration was performed using NaOH to measure total acidity. The amount of HNO3 was calculated by subtracting the amount of HF from the total acidity. The amount of HF was obtained by means of an F-ion analyzer, and the presence of HNO3 was confirmed by anionic qualitative analysis with sulfuric acid and FeSO4. Fine particles were measured using a particle measuring device, and only particles smaller than or equal to 0.2 m were considered.

  The process of the present invention is advantageous in that it can fill a cylinder of high pressure gas with a low temperature liquefied gas which must be extremely pure, thanks to a simple process which avoids the degradation of the liquefied gas and which consumes little energy.

  Although the foregoing description has been directed to a preferred embodiment of the present invention, it is of course not limited to the specific example described and illustrated herein, and those skilled in the art will readily understand that it is possible to make many variations and modifications without departing from the scope of the invention.

Claims (3)

  1. A method of filling a cylinder of high pressure gas (C) with a liquefied gas at low temperature, characterized in that it consists in using a pump (P) and an insulating pipe to transport the liquefied gas at low temperature. .   2. Method according to claim 1, characterized in that the liquefied gas at low temperature is selected from a group consisting of nitrogen trifluoride, nitrogen, oxygen, argon, sulfur hexafluoride anhydrous hydrochloric acid, anhydrous hydrobromic acid, carbon tetrafluoride and hexafluoroethane.   3. Method according to claim 1, characterized in that a liquid compressed with the pump (P) is loaded directly into the bottle (C), or is charged in the gas phase therein after being vaporized by an evaporator or vaporizer (G) provided on the discharge side of the pump (P).