WO1991019142A1 - Method of and device for producing nitrogen of high purity - Google Patents

Abstract

Material gas in a cooled state is fed into a main fractionating column so as to be rectified, liquid nitrogen is taken out at a position lower than the uppermost step in the main fractionating column, the liquid nitrogen thus taken out is fed into the sub-rectifier to be rectified, and nitrogen as a product is taken out from the sub-rectifier at a position lower than the position at which liquid nitrogen is introduced.

Description

 Description Method and apparatus for producing high-purity nitrogen Background technology

 The present invention relates to a method and an apparatus for producing high-purity nitrogen in an air separation device or the like.

 In recent years, demand for ultrapure nitrogen gas has been increasing in accordance with advances in semiconductor technology.

FIG. 4 shows an example of a conventional apparatus for producing this nitrogen gas. In this iD device, the raw air containing nitrogen undergoes processing such as compression and cooling, and then is carried into the molecular adsorption adsorption unit 10, where the adsorption and removal processing of impurities is performed, and then it is kept cool. It is carried into the heat exchanger 14 in the box 12. At this point, although the water and C 0 ₂ or the like raw material in the air is removed, hydrogen, helium, impurities neon is remaining in still gas. In such a state, the raw material gas is directly introduced into the bottom of the rectification column 16, and in the rectification column 16, hydrocarbons such as oxygen and methane, which are high-boiling components, are removed from nitrogen by rectification. While being removed, nitrogen is removed from the rectification column 16 as a product.

Here, the above-mentioned impurity gas having a lower boiling point than nitrogen such as hydrogen, helium, and neon (hereinafter referred to as low-boiling gas) does not liquefy even in the rectification column 16, As it rises, it accumulates in the capacitor 16 1 at the top of the rectification column 16. If left untreated, the low-boiling gas will turn into non-coiling gas, degrading the operation of the condenser 161, and may have a negative effect on the purity of the extracted product slag.

 Therefore, conventionally, the non-condensable gas accumulated in the condenser 161 was purged together with nitrogen, and the condenser 161 was also discharged as a product from the lower stage. As a result, measures have been taken to minimize the mixing of the above-mentioned non-condensable gas into the product gas, thereby increasing the purity of the product nitriding as much as possible.

 However, such a conventional technique has the following problems.

 As described above, with the advance of semiconductor technology in recent years, high purity nitrogen gas has been required as a product nitrogen gas, and at present, the above low boiling gas, that is, hydrogen, nitrogen, neon, etc. It is beginning to be necessary to remove such gases as impurities.

However, since these low-boiling gases have a boiling point lower than that of nitrogen, even after being introduced into the distillation column 16, the low-boiling gas remains in the gas rising in the rectification column 16. It is probably contained, and specifically, the concentration of the low-boiling gas in the ascending gas is almost the same as the concentration in the gas introduced into the bottom of the rectification column 16. Therefore, By simply purging the condenser 161 as in the above or removing the product nitrogen from the stage below the condenser 161, the concentration of the low-boiling gas caused by the non-condensable gas can be reduced. Although it can be prevented, it is difficult to actively lower the low boiling point gas concentration in product gas.

 It has been conventionally possible to remove hydrogen from the low boiling point gas to the order of 0.1 ppm by reacting this hydrogen with oxygen in the raw material air using a catalyst. However, the remaining O. lppm of hydrogen cannot be removed, and further reduction of the concentration cannot be expected. Disclosure of the invention

 In order to solve the above problems, the present invention employs the following configuration.

 That is, in the present invention, the raw material gas is cooled and put into the main rectification column for rectification, and liquid nitrogen is taken out from the position below the uppermost stage in the main rectification column, and this liquid nitrogen is converted to the sub-rectification column. In this sub-column, product nitrogen is taken out from a position below the liquid nitrogen introduction position.

In this method, the gas rising in the main rectification column contains a large amount of low-boiling gas, but a small amount of low-boiling gas is dissolved in the liquid nitrogen derived from the rectification column. It's just Moreover, this liquid nitrogen is sub-rectified As the low-boiling gas contained in the liquid nitrogen is introduced into the tower and the rectification proceeds, the low-boiling gas contained in the liquid nitrogen evaporates under heating and escapes above the tower. By extracting nitrogen as a product from a lower position, ultra-high-purity nitrogen gas can be obtained.

 In addition, the concealment for realizing the above method includes a main rectification column and a sub-rectification column for rectification, and a raw material for introducing a cooled raw material gas into the main box distillation column. A gas introduction passage, a liquid nitrogen transfer passage for extracting liquid nitrogen from a position below the uppermost stage in the main rectification column and introducing the liquid nitrogen into the sub rectification column, It is preferable that the column is provided with a product nitrogen outlet passage for extracting product nitrogen from a position below the liquid nitrogen introduction position in the liquid nitrogen transfer passage in the tower. BRIEF DESCRIPTION OF THE FIGURES

 FIG. 1 is an overall configuration diagram showing an example of a high-purity nitrogen production apparatus for carrying out the method of the present invention, FIG. 2 is an overall configuration diagram showing another example of the apparatus, and FIG. 3 is another example of the apparatus. FIG. 4 is an overall configuration diagram showing an example of a conventional apparatus for producing high-purity nitrogen. BEST MODE FOR CARRYING OUT THE INVENTION

Fig. 1 shows an example of an apparatus for carrying out the method of the present invention. It is shown. This device is equipped with a molecular sieve adsorption unit 10 and a cool box 12 in which the main heat exchanger 1.4, the main rectification tower 16 and the expansion turn 18 are installed. In addition, a secondary rectification tower (helium tower) 20 is installed. At the top of the main rectification tower 16 and the sub-rectification tower 20, condensers (capacitors) 161 and 201 are provided, respectively.

 Next, a method for producing high-purity nitrogen by this apparatus will be described.

 First, raw air is passed through the molecular sieve adsorption unit 10 to adsorb and remove impurities in the air. Thereafter, the air is passed through the main heat exchanger 14 through the raw gas introduction passage 11. On the other hand, in the main exchanger 14, the aerator gas adiabatically expanded by the action of the expansion turbine 18 is passed, and the raw air is reduced to about one by heat exchange between the waste gas and the raw air. It is cooled to 170 and introduced into the bottom of the main rectification column 16 in this low temperature state.

In the rectification column 16, re-rectification is performed by contact between the flowing liquid and the ascending vapor, and low-boiling components are concentrated as they rise to the top, while high-boiling components fall to the bottom. It is concentrated along with. Here, the low-boiling gas (impurities such as hydrogen, helium, and neon) contained in the above-mentioned raw material air has a boiling point lower than that of nitrogen. It is concentrated, but a small amount of low-boiling gas dissolves in the descending liquid nitrogen. It's just that. Therefore, this liquid nitrogen is extracted from a lower stage than the top stage of the rectification column 16 and the liquid nitrogen transfer passage

It is sent to the middle stage of the sub-rectification column 20 through 22.

 In the sub-rectification column 20, the liquid nitrogen is rectified, and the low-boiling gas of minute S contained therein is expelled by heating and rises. Therefore, by extracting nitrogen gas as a product from a position below the liquid nitrogen introduction position in the sub-rectification column 20, it becomes possible to obtain extremely high-purity product nitrogen. This product nitrogen is sent to the main heat exchanger 14 through the product nitrogen outlet passage 24, brought into a state of approximately normal temperature by heat exchange with the raw material air, and then expelled out of the equipment g.

In the above step, it is desirable to use the heat of the nitrogen gas at the top of the main rectification column 16 as the heating source for the sub-rectification column 20, that is, the heat source for the repoiler. That is, the liquid nitrogen at the bottom of the sub-rectification tower 20 is led to the capacitor 16 1 of the main box tower 16 through the passage 26 (which constitutes a liquid nitrogen circulation passage). Through the passage 27 (constituting a liquid nitrogen circulation passage) to introduce the gaseous nitrogen (which may contain unevaporated liquid nitrogen) into the sub-rectification column 20. Heat exchange with nitrogen gas at the top of the main rectification column 16. As a result, the nitrogen gas is condensed, and the heat of condensation is used to evaporate the liquid nitrogen in the sub-rectification column 20. This evaporation removes the low-boiling gas in the sub-rectification column 20. Since the heating can be performed, the rectification can be efficiently performed.

At this time, in order to carry out the heat exchange smoothly, the operating pressure in the sub-rectification column 20 should be reduced by about 0.6 kg / cm ² from the main distillation column 16, that is, the main distillation column The liquid nitrogen supplied from 16 to the sub-rectification column 20 through the passage 22 may be depressurized, thereby lowering its saturation temperature.

Also, in the above process, since nitrogen gas possibly rises together with the low-boiling gas in the sub-rectification column 20, this nitrogen gas is liquefied at the upper part of the sub-rectification column 20 and collected. It is desirable. In this case, the liquid air collected at the bottom of the main rectification tower 16 is sent to the upper part of the sub-rectification tower 20 under reduced pressure through the liquid supply passage 28, whereby the sub-rectification tower 20 If the upper city is cooled, the nitrogen gas can be efficiently liquefied and recovered. The same effect can be obtained by sending the liquid in the middle part of the main rectification column 16 to the upper part of the sub-rectification column 20 under reduced pressure through the same passage as the liquid supply passage 28. Can be As described above, in this method, high-purity liquid nitrogen is extracted from the lower stage than the uppermost stage in the main rectification column 16, and this liquid nitrogen is further separated into the sub-rectification column 20. And the product nitrogen is extracted from a position below this introduction position, so that low boiling gas such as hydrogen and helium in the raw material air can be effectively removed. As a result, the purity of product nitrogen can be greatly improved.

 The table below shows the concentrations of helium, neon, and hydrogen in each gas.

 In the table, gas 1 is the raw air, gas 2 is the product nitrogen gas obtained by treating the raw air by the conventional method described in FIG. 4, and gas 3 is the raw air. The product air obtained by the above treatment is used as the product nitrogen, and the above-mentioned raw material air is prepared using a catalyst whose hydrogen concentration has been reduced to 0.1 ppm in advance.

 As is clear from this table, while the conventional method can hardly remove low-boiling gas contained in the raw material air, this method can effectively remove each low-boiling gas. . table

(Unit: ppm) The present invention is not limited to such an embodiment, and the following embodiments can be taken as examples. (1) In the process of the above embodiment, as shown in FIG. 1, the helium gas extracted from each of the rectification columns 16 and 20 is directly taken out of the apparatus, but as shown in FIG. As described above, the helium gas may be sent to the main heat exchanger 14 through the helium gas outlet passages 31 and 32 and then recovered. By performing such an operation, the low-temperature helium gas can contribute to the generation of cold in the main heat exchanger 14, and the thermal efficiency of the entire equipment S can be further improved.

 Further, as shown in FIG. 1 and FIG. 1, the gas extracted from the upper part of the main rectification tower (or the sub-rectification tower) 16 is supplied to the expansion turbine (expansion means) 1 through the gas outlet passage 36. The gas can also be contributed to the generation of cold by sending it to the main heat exchanger 14 in an adiabatic expanded state through 8.

 In addition, as shown in FIG. 3, in the system for guiding liquid nitrogen through the liquid nitrogen introduction passage 34 above the main distillation column 16 and cooling the latent heat of vaporization, the gas outlet passage 36 is used for the system. Even when the heat is sent to the main heat exchanger 14, the same effect as the above can be obtained. Also, liquid nitrogen may be introduced into the sub-rectification tower 20 instead of the main rectification tower 16 to extract helium gas, or the rectification towers 16 and 20 of both may be introduced. Liquid nitriding may be sent.

(2) As the method of the present invention is applied to an air separation device, Not only that, it is widely applied to the production of high-purity nitrogen from source gases containing nitrogen and low-boiling gases.

 As described above, according to the present invention, high-purity liquid nitrogen is taken out from a position below the uppermost stage in the main rectification column and put into the sub-rectification column. Since the product gas is taken out from the position below the above-mentioned liquid nitrogen introduction position while heating and evaporating the point gas, the low boiling point gas contained in the raw material gas can be effectively removed. This can greatly contribute to the production of ultra-high purity product nitrogen.

Claims

The scope of the claims  The raw material gas is also put into the soil rectification tower with cooling in mind, and liquid nitrogen is taken out from the position below the top in the main rectification tower for rectification, and this liquid nitrogen is put into the sub-rectification tower to perform rectification. A method for producing pure nitrogen, characterized in that product nitrogen is removed from the sub-rectification column from a position below the liquid nitrogen introduction position.  2.The method for producing high-purity nitrogen according to claim 1, wherein a condenser is provided at the top of the main rectification column, and liquid nitrogen at the bottom of the sub-rectification column is guided to the condenser. A method for producing high-purity nitrogen, comprising introducing gaseous nitrogen evaporated from a parenthesis condenser into a sub-rectification column.  3. The high-purity nitrogen production method according to claim 1, wherein the liquid collected at the bottom of the main rectification column is sent to a condenser at the top of the sub-rectification column. Nitrogen production method.  4. The method for producing high-purity nitrogen according to claim 1, wherein the liquid in the middle part of the main rectification column is sent to a condenser at the top of the sub-rectification column. Production method. 5. The method for producing high-purity nitrogen according to any one of claims 1 to 4, wherein heat is exchanged between the raw material gas and the product nitrogen using a heat exchanger, and at least one refinement is performed. The gas at the top of the distillation tower is led out and passed through the heat exchanger. Production method.  6. The method for producing high-purity nitrogen according to claim 5, wherein gas introduced from at least one rectification column is expanded and then introduced into the heat exchanger. A method for producing high-purity nitrogen.  7In the method for producing high-purity nitrogen according to claim 5, liquid nitrogen is introduced into at least the top of one rectification column, a cooled gas is extracted, and introduced into the heat exchanger. A method for producing pure nitrogen.  8. The method for producing high-purity nitrogen according to any one of claims 1 to 4, wherein heat is exchanged between the raw material gas and the product nitrogen by using a heat exchanger, and at least one of A method for producing pure nitrogen, comprising passing helium gas extracted from a rectification tower through the heat exchanger.  9. Main rectification column and sub-rectification column for rectification, source gas introduction passage for introducing raw material gas in a cooled state into the main rectification column, top stage in the main rectification column A liquid nitrogen transfer passage for drawing liquid nitrogen from a position below and introducing the liquid nitrogen into the sub-rectification column; and introducing liquid nitrogen through the liquid nitrogen transfer passage in the sub-rectification column. An apparatus for producing high-purity nitrogen, comprising a product nitrogen outlet passage for introducing product nitrogen from a position below the position. 10. The high-purity nitrogen production apparatus described in claim 9 In addition, a condenser is provided above the main rectification tower, and liquid nitrogen at the bottom of the sub-rectification tower is led to the condenser, where it is evaporated into the sub-rectification tower from the bracket condenser An apparatus for producing high-purity nitrogen, which is provided with a liquid nitrogen circulation passage for introducing the gaseous nitrogen.  11. The high-purity nitrogen producing apparatus according to claim 9, wherein a liquid supply passage for feeding the liquid collected at the bottom of the main rectification column to the condenser at the top of the sub-rectification column is provided. An apparatus for producing high-purity nitrogen, comprising:  1 2. In the production and concealment of high-purity nitrogen described in the scope of claim 9, the liquid supply for sending the liquid in the middle part of the main rectification tower to the upper clarifier of the sub-rectification tower装置 Purity nitrogen production equipment characterized by having a communication path.  13. The apparatus for producing pure nitrogen according to any one of claims 9 to 12, wherein a heat exchanger for performing heat exchange between the raw material gas and the product nitrogen, and an upper part of each rectification column. A high-purity nitrogen producing apparatus, comprising: a gas lead-out passage for leading out a gas from the heat exchanger and passing the gas through the heat exchanger.  14. The high-purity nitrogen producing apparatus according to claim 13, wherein an expansion means for expanding gas passing through the gas outlet passage is provided in the gas outlet passage. Manufacturing equipment. 15. The high-purity nitrogen producing apparatus according to claim 13, wherein the regas is discharged through the gas discharge passage. A high-purity nitrogen production system, which is equipped with a liquid nitrogen guide passage for introducing liquid nitrogen at the top of the rectification column.  16. The apparatus for producing high-purity nitrogen according to any one of claims 9 to 12, further comprising: a heat exchanger for performing heat exchange between the raw material gas and the product nitrogen; An apparatus for producing high-purity nitrogen gas, the apparatus comprising a helium gas outlet passage for extracting the helium gas and passing the helium gas through the heat exchanger.