EP0485612B1 - Method of and device for producing nitrogen of high purity - Google Patents
Method of and device for producing nitrogen of high purity Download PDFInfo
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- EP0485612B1 EP0485612B1 EP91901554A EP91901554A EP0485612B1 EP 0485612 B1 EP0485612 B1 EP 0485612B1 EP 91901554 A EP91901554 A EP 91901554A EP 91901554 A EP91901554 A EP 91901554A EP 0485612 B1 EP0485612 B1 EP 0485612B1
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- nitrogen
- column
- subrectification
- gas
- heat exchanger
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
- F25J3/04642—Recovering noble gases from air
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
- F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
- F25J3/04254—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using the cold stored in external cryogenic fluids
- F25J3/0426—The cryogenic component does not participate in the fractionation
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
- F25J3/04248—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion
- F25J3/04284—Generation of cold for compensating heat leaks or liquid production, e.g. by Joule-Thompson expansion using internal refrigeration by open-loop gas work expansion, e.g. of intermediate or oxygen enriched (waste-)streams
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J3/00—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification
- F25J3/02—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream
- F25J3/04—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air
- F25J3/04406—Processes or apparatus for separating the constituents of gaseous or liquefied gaseous mixtures involving the use of liquefaction or solidification by rectification, i.e. by continuous interchange of heat and material between a vapour stream and a liquid stream for air using a dual pressure main column system
- F25J3/0443—A main column system not otherwise provided, e.g. a modified double column flowsheet
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2200/00—Processes or apparatus using separation by rectification
- F25J2200/74—Refluxing the column with at least a part of the partially condensed overhead gas
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2200/00—Processes or apparatus using separation by rectification
- F25J2200/90—Details relating to column internals, e.g. structured packing, gas or liquid distribution
- F25J2200/94—Details relating to the withdrawal point
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2210/00—Processes characterised by the type or other details of the feed stream
- F25J2210/42—Nitrogen
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2215/00—Processes characterised by the type or other details of the product stream
- F25J2215/30—Helium
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2215/00—Processes characterised by the type or other details of the product stream
- F25J2215/42—Nitrogen or special cases, e.g. multiple or low purity N2
- F25J2215/44—Ultra high purity nitrogen, i.e. generally less than 1 ppb impurities
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2215/00—Processes characterised by the type or other details of the product stream
- F25J2215/58—Argon
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2220/00—Processes or apparatus involving steps for the removal of impurities
- F25J2220/42—Separating low boiling, i.e. more volatile components from nitrogen, e.g. He, H2, Ne
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2245/00—Processes or apparatus involving steps for recycling of process streams
- F25J2245/02—Recycle of a stream in general, e.g. a by-pass stream
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
- F25J2250/00—Details related to the use of reboiler-condensers
- F25J2250/20—Boiler-condenser with multiple exchanger cores in parallel or with multiple re-boiling or condensing streams
Definitions
- the present invention relates to a method and system for producing high purity nitrogen according to the features of the preamble of claim 1, resp. claim 9.
- Such a method and system is known, for example, from JP-A-62-14 14 85.
- the rectification column is used to separate high-boiling components such as oxygen, monoxide etc from the nitrogen.
- high-boiling components such as oxygen, monoxide etc
- these components cannot be separated in the following subrectification column and no ultra high purity nitrogen can be obtained.
- Fig. 4 is a diagram showing an example of conventional system for producing high purity nitrogen.
- the air including nitrogen and serving as material (hereinafter referred to as material gas) is transported to a molecular sieves adsorption unit 10.
- Impurities included in the material gas are removed by being adsorbed in the molecular sieves adsorption unit 10.
- the material gas is transported to a heat exchanger 14 provided in a cold box 12.
- the material gas is free from water, carbon dioxide (CO2), and the like.
- impurities as hydrogen. helium, and neon are still included in the material gas.
- the material gas is directly introduced to a bottom portion of a fractionating column 16 to be rectified therein.
- Oxygen and hydrocarbon such as methane, which have high boiling points, are removed from the material gas by the rectification effected in the rectification column 16. Consequently, the nitrogen is extracted from the rectification column 16 as product.
- Impurity gas such as hydrogen, helium, and neon has a boiling point lower than that of nitrogen (hereinafter referred to as low boiling gas.)
- the low boiling gas ascends in the rectification column 16 without liquefying therein, and are stored in a condenser 161 provided at an uppermost stage of the rectification column 16. If left in the condenser 161, the low boiling gas, which is noncondensable gas, impairs the efficiency of the condenser 161. In addition, there is a likelihood that the noncondensable gas adversely affects the purity of the produced nitrogen to be extracted from the rectification column 16.
- the noncondensable gas stored in the condenser 161 is purged with the use of nitrogen. Further, the nitrogen is extracted from a stage lower than the one where the condenser 161 is provided, maximally preventing the likelihood that the noncondensable gas is mixed into the produced nitrogen. This causes the purity of the produced nitrogen to be greatly improved.
- the low boiling gas such as hydrogen, helium, and neon. be also removed as impurities from the material gas.
- the conventional method by which the noncondensable gas stored in the condenser 161 is purged, and produced nitrogen is extracted from the stage lower than the one where the condenser 161 is provided, may be sufficiently effective in preventing the purity of the produced nitrogen from being reduced due to the noncondensable gas.
- such a conventional method experiences difficulty in substantially reducing the concentration of the low boiling gas in the produced nitrogen.
- the hydrogen one kind of the low boiling gas, it has been known that if the hydrogen is caused to react with the oxygen in the material gas in the presence of catalyst, the hydrogen concentration in the material gas can be reduced to as low as the order of 0.1 ppm. However, the remaining 0.1 ppm hydrogen cannot be removed from the material gas, and therefore the hydrogen concentration cannot be reduced any further.
- a method of the invention comprises the steps as defined in claim 1.
- the gas ascending in the main rectification column includes low boiling gas abundantly. However, only a tiny quantity of low boiling gas is included in the liquid nitrogen extracted from the main rectification column.
- the liquid nitrogen is introduced into the subrectification column to be further rectified therein.
- the low boiling gas included in the liquid nitrogen is heated to evaporate, and the evaporated low boiling gas oozes upward in the subrectification column. Accordingly, produced nitrogen is extracted from a position lower than the position from which the liquid nitrogen is introduced into the subrectification column, thus produced nitrogen has ultra-high purity.
- Fig. 1 is a diagram showing an exemplary system for carrying out a method of the present invention.
- the system is Provided with a molecular sieves adsorption unit 10 and a cold box 12.
- the cold box 12 comprises a main heat exchanger 14, a main rectification column 16, an expansion turbine 18, and a subrectification column.
- Condensers 161, 201 are provided at uppermost stages of the main rectification column 16 and the subrectification column 20 respectively.
- the air is passed through the molecular sieves adsorption unit 10 so as to remove impurities from the material gas.
- the gas is passed through the main heat exchanger 14 through a air gas inlet passage 11.
- the expansion turbine 18 works to adiabatically expand waste gas from the rectification column 16 and the subrectification column 20.
- the adiabatically expanded waste gas is also passed through the main heat exchanger 14.
- the air is cooled to about -170 °C through the heat-exchange with the waste gas in the heat exchanger 14.
- the air is then introduced to the main rectification column 16 with being cooled at this temperature.
- the liquid nitrogen is rectified in the subrectification column 20, and the low boiling gas included in the liquid nitrogen in only small quantities is caused to ascend by the heating.
- Nitrogen gas is extracted from the subrectification column 20 from a position lower than the one from which the liquid nitrogen is introduced thereinto. As a result, it is made possible to produce exceedingly high purity nitrogen.
- the produced nitrogen is transported to the main heat exchanger 14 through a produced nitrogen outlet passage 24.
- the produced nitrogen is heated in the heat exchanger 14 so as to reach a substantially normal temperature through the heat-exchange with the material gas supplied from outside, then brought out of the system.
- the heat of the nitrogen gas present in the top of the rectification column 16 is utilized as heat source to heat the bottom portion of the subrectification column 20, i.e., heat source for a reboiler of the column 20. More specifically, the liquid nitrogen in the bottom portion of the subrectification column 20 is transported to the condenser 161 of the main rectification column 16 through a passage 26. Nitrogen gas evaporated in the condenser 161 is transported to the subrectification column 20 through a passage 27. The passages 26 and 27 constitute a liquid nitrogen circulating passage. Liquid nitrogen which is not evaporated in the condenser 161 may be transported back to the subrectification column together with the evaporated nitrogen gas.
- the liquid nitrogen exchanges heat with the nitrogen gas at the top portion of the column 16, thereby condensing the nitrogen.
- the liquid nitrogen from the subrectification column 20 is evaporated in the condenser 161 by the heat of condensation.
- the evaporated nitrogen gas transported back to the subrectification column 20 serves to heat the low boiling gas therein. In this way, the rectification in the column 20 can be effectively performed.
- the operating pressure in the subrectification column 20 be set lower than that in the main rectification column 16 by about 0.6 kg/cm2. Accordingly, liquid nitrogen has the pressure thereof reduced while being transported to the subrectification column 20 from the main rectification column 16 through the liquid nitrogen transport passage 22. This causes the saturation temperature of the liquid nitrogen to be reduced.
- high purity liquid nitrogen is extracted from the main rectification column 16 from a stage lower than the uppermost one thereof.
- the extracted liquid nitrogen is then introduced into the subrectification column 20. Consequently, the produced nitrogen is extracted from the subrectification column 20 from a position lower than the liquid nitrogen introducing position. Accordingly, low boiling gas in the material air, such as hydrogen, helium, and neon, can be effectively removed from the air, thereby enabling production of nitrogen having a greatly improved purity.
- Table-1 shows concentrations of helium, neon, and hydrogen in gases 1, 2, and 3 respectively.
- gas 1 is air.
- Gas 2 is nitrogen produced from the material gas according to the conventional method described with reference to Fig. 4.
- Gas 3 is nitrogen produced from the air according to the present method. The concentration of hydrogen in the air is reduced to 0.1 ppm in advance with the use of catalyst.
- the conventional method can remove almost no low boiling gases present in the air.
- the present method can effectively remove the respective low boiling gases.
- the present invention is not limited to the foregoing embodiment, but can be embodied as follows.
- helium gas extracted from the respective rectification columns 16, 20 is directly brought out of the system as shown in Fig. 1.
- the helium gas may be transported to the main heat exchanger 14 from the rectification columns 16, 20 respectively through helium gas transport passages 31, 32. and thereafter recovered.
- the above operation enables the low temperature helium gas to greatly serve as cooling medium for the main heat exchanger 14, thereby improving overall heat efficiency of the system.
- the gas taken from the upper portion of the main rectification column 16 may be transported to the expansion turbine 18 (expansion means) through a gas transport passage 36.
- the gas is adiabatically expanded by the expansion turbine 18, and further transported as it is to the main heat exchanger 14.
- the gas in the upper portion of the main rectification column 16 can serve as cooling medium for the main heat exchanger.
- the gas in the upper portion of the subrectification column 20 can also be used for the same purpose.
- Fig. 3 shows a system for cooling the system with the use of latent heat of evaporation of liquid nitrogen introduced into the upper portion of the main rectification column 16 through a liquid nitrogen inlet passage 34.
- the gas in the upper portion of the column 16 may be transported to the main heat exchanger 14 through the gas transport passage 36, and can be consequently served as cooling medium for the main heat exchanger 14 similar to the above examples.
- the liquid nitrogen may be supplied to the subrectification column 20 instead of the main rectification column 16 so as to take helium gas therefrom. It may also be appropriate that the liquid nitrogen be supplied to both rectification columns 16, 20.
- the present method can be applied not only to an air separator, but also to any system for producing high purity nitrogen from material gas including nitrogen and low boiling gases.
- liquid nitrogen having high purity is extracted from a main rectification column from a position lower than an uppermost stage thereof, and introduced into a subrectification column.
- the liquid nitrogen is further heated so as to evaporate low boiling gases therein in the subrectification column. Consequently, produced nitrogen is extracted from the subrectification column from a position lower than the position from which the liquid nitrogen is introduced thereinto. Accordingly. the low boiling gases can be effectively removed from the material gas, greatly contributing to production of nitrogen having ultra-high purity.
Abstract
Description
- The present invention relates to a method and system for producing high purity nitrogen according to the features of the preamble of claim 1, resp. claim 9.
- Such a method and system is known, for example, from JP-A-62-14 14 85. In the known method the rectification column is used to separate high-boiling components such as oxygen, monoxide etc from the nitrogen. When the nitrogen contains low-boiling components, these components cannot be separated in the following subrectification column and no ultra high purity nitrogen can be obtained.
- Fig. 4 is a diagram showing an example of conventional system for producing high purity nitrogen. In this system, after passing through such processing as compression and cooling, the air including nitrogen and serving as material (hereinafter referred to as material gas) is transported to a molecular
sieves adsorption unit 10. Impurities included in the material gas are removed by being adsorbed in the molecularsieves adsorption unit 10. Subsequently, the material gas is transported to aheat exchanger 14 provided in acold box 12. At this stage, the material gas is free from water, carbon dioxide (CO₂), and the like. However. such impurities as hydrogen. helium, and neon are still included in the material gas. In this state, the material gas is directly introduced to a bottom portion of a fractionatingcolumn 16 to be rectified therein. Oxygen and hydrocarbon such as methane, which have high boiling points, are removed from the material gas by the rectification effected in therectification column 16. Consequently, the nitrogen is extracted from therectification column 16 as product. - Impurity gas such as hydrogen, helium, and neon has a boiling point lower than that of nitrogen (hereinafter referred to as low boiling gas.) The low boiling gas ascends in the
rectification column 16 without liquefying therein, and are stored in acondenser 161 provided at an uppermost stage of therectification column 16. If left in thecondenser 161, the low boiling gas, which is noncondensable gas, impairs the efficiency of thecondenser 161. In addition, there is a likelihood that the noncondensable gas adversely affects the purity of the produced nitrogen to be extracted from therectification column 16. - In view of this, the following method has been adopted: The noncondensable gas stored in the
condenser 161 is purged with the use of nitrogen. Further, the nitrogen is extracted from a stage lower than the one where thecondenser 161 is provided, maximally preventing the likelihood that the noncondensable gas is mixed into the produced nitrogen. This causes the purity of the produced nitrogen to be greatly improved. - However, the foregoing conventional method presents the following problems.
- As described above, with the advance of the recent semiconductor production technology, there is a great demand for nitrogen having higher purity. Presently, it is beginning to be required that the low boiling gas, such as hydrogen, helium, and neon. be also removed as impurities from the material gas.
- However, having a boiling point lower than that of the nitrogen, the low boiling gas is abundantly included in the gas ascending in the
rectification column 16 even after introduced thereto. Specifically, concentration of the low boiling gas in the ascending gas is substantially equal to that in the material gas when introduced to the bottom portion of therectification column 16. Accordingly, the conventional method, by which the noncondensable gas stored in thecondenser 161 is purged, and produced nitrogen is extracted from the stage lower than the one where thecondenser 161 is provided, may be sufficiently effective in preventing the purity of the produced nitrogen from being reduced due to the noncondensable gas. However, such a conventional method experiences difficulty in substantially reducing the concentration of the low boiling gas in the produced nitrogen. - Concerning the hydrogen, one kind of the low boiling gas, it has been known that if the hydrogen is caused to react with the oxygen in the material gas in the presence of catalyst, the hydrogen concentration in the material gas can be reduced to as low as the order of 0.1 ppm. However, the remaining 0.1 ppm hydrogen cannot be removed from the material gas, and therefore the hydrogen concentration cannot be reduced any further.
- It is an object of the invention to provide such a method and a system for producing high purity nitrogen as to solve the foregoing problems.
- According, a method of the invention comprises the steps as defined in claim 1.
- According to the above method. the gas ascending in the main rectification column includes low boiling gas abundantly. However, only a tiny quantity of low boiling gas is included in the liquid nitrogen extracted from the main rectification column. In addition, the liquid nitrogen is introduced into the subrectification column to be further rectified therein. The low boiling gas included in the liquid nitrogen is heated to evaporate, and the evaporated low boiling gas oozes upward in the subrectification column. Accordingly, produced nitrogen is extracted from a position lower than the position from which the liquid nitrogen is introduced into the subrectification column, thus produced nitrogen has ultra-high purity.
- Further, a system according to the invention for carrying out the above method comprises the features as claimed in claim 9.
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- Fig. 1 is a diagram showing an entire construction of an exemplary system for producing high purity nitrogen according to the present invention;
- Fig. 2 is a diagram showing an entire construction of another system for producing high purity nitrogen according to the present invention;
- Fig. 3 is a diagram showing an entire construction of still another system for producing high purity nitrogen according to the present invention; and
- Fig. 4 is a diagram showing an explanatory conventional system for producing high purity nitrogen.
- Fig. 1 is a diagram showing an exemplary system for carrying out a method of the present invention. The system is Provided with a molecular
sieves adsorption unit 10 and acold box 12. Thecold box 12 comprises amain heat exchanger 14, amain rectification column 16, anexpansion turbine 18, and a subrectification column.Condensers main rectification column 16 and thesubrectification column 20 respectively. - Next, there will be described a method for producing high purity nitrogen carried out in thus constructed system.
- First, the air is passed through the molecular
sieves adsorption unit 10 so as to remove impurities from the material gas. Subsequently, the gas is passed through themain heat exchanger 14 through a airgas inlet passage 11. Theexpansion turbine 18 works to adiabatically expand waste gas from therectification column 16 and thesubrectification column 20. The adiabatically expanded waste gas is also passed through themain heat exchanger 14. The air is cooled to about -170 °C through the heat-exchange with the waste gas in theheat exchanger 14. The air is then introduced to themain rectification column 16 with being cooled at this temperature. - In the
rectification column 16, flowing down liquid and ascending vapors come into contact with each other, whereby rectification is performed. Low boiling components become more concentrated as ascending to the top of therectification column 16. On the other hand, high boiling components become more concentrated as descending to the bottom of therectification column 16. Any low boiling gas (impurity such as hydrogen, helium, and neon) included in the material gas has a boiling point lower than that of nitrogen. Accordingly, such low boiling gas is abundantly included in the ascending vapors and concentrated at the top of thecolumn 16. However, only a tiny quantity of low boiling gas is included in the liquid nitrogen flowing down therectification column 16. In view of this, the liquid nitrogen is extracted from a stage lower than the uppermost one of therectification column 16. The extracted liquid nitrogen is transported to a middle stage of thesubrectification column 20 through a liquidnitrogen transport passage 22. - The liquid nitrogen is rectified in the
subrectification column 20, and the low boiling gas included in the liquid nitrogen in only small quantities is caused to ascend by the heating. Nitrogen gas is extracted from thesubrectification column 20 from a position lower than the one from which the liquid nitrogen is introduced thereinto. As a result, it is made possible to produce exceedingly high purity nitrogen. The produced nitrogen is transported to themain heat exchanger 14 through a producednitrogen outlet passage 24. The produced nitrogen is heated in theheat exchanger 14 so as to reach a substantially normal temperature through the heat-exchange with the material gas supplied from outside, then brought out of the system. - In the foregoing process, it is preferable that the heat of the nitrogen gas present in the top of the
rectification column 16 is utilized as heat source to heat the bottom portion of thesubrectification column 20, i.e., heat source for a reboiler of thecolumn 20. More specifically, the liquid nitrogen in the bottom portion of thesubrectification column 20 is transported to thecondenser 161 of themain rectification column 16 through apassage 26. Nitrogen gas evaporated in thecondenser 161 is transported to thesubrectification column 20 through apassage 27. Thepassages condenser 161 may be transported back to the subrectification column together with the evaporated nitrogen gas. In this way, the liquid nitrogen exchanges heat with the nitrogen gas at the top portion of thecolumn 16, thereby condensing the nitrogen. The liquid nitrogen from thesubrectification column 20 is evaporated in thecondenser 161 by the heat of condensation. The evaporated nitrogen gas transported back to thesubrectification column 20 serves to heat the low boiling gas therein. In this way, the rectification in thecolumn 20 can be effectively performed. - In order to smoothly effect the aforementioned heat exchange, it is appropriate that the operating pressure in the
subrectification column 20 be set lower than that in themain rectification column 16 by about 0.6 kg/cm². Accordingly, liquid nitrogen has the pressure thereof reduced while being transported to thesubrectification column 20 from themain rectification column 16 through the liquidnitrogen transport passage 22. This causes the saturation temperature of the liquid nitrogen to be reduced. - Also, in the above process, a large amount of nitrogen gas is ascending together with low boiling gas in the
subrectification column 20. Accordingly, it is preferable to liquefy the nitrogen gas at the upper portion of thesubrectification column 20 and recover it as liquid nitrogen. In this case, liquid deposited at the bottom of themain rectification column 16 may be transported to the upper portion of thesubrectification column 20 through aliquid transport passage 28 with the pressure thereof being reduced. Thereby, the upper portion of thesubrectification column 20 can be cooled, enabling efficient liquefaction and recovery of the nitrogen gas. Similar effects can be obtained in the case where liquid present in the middle of themain rectification column 16 is transported to the upper portion of thesubrectification column 20 through a passage similar to theliquid transport passage 28 with the pressure thereof being reduced. - As described above, according to the present method, high purity liquid nitrogen is extracted from the
main rectification column 16 from a stage lower than the uppermost one thereof. The extracted liquid nitrogen is then introduced into thesubrectification column 20. Consequently, the produced nitrogen is extracted from thesubrectification column 20 from a position lower than the liquid nitrogen introducing position. Accordingly, low boiling gas in the material air, such as hydrogen, helium, and neon, can be effectively removed from the air, thereby enabling production of nitrogen having a greatly improved purity. - Table-1 below shows concentrations of helium, neon, and hydrogen in gases 1, 2, and 3 respectively.
- In Table-1, gas 1 is air. Gas 2 is nitrogen produced from the material gas according to the conventional method described with reference to Fig. 4. Gas 3 is nitrogen produced from the air according to the present method. The concentration of hydrogen in the air is reduced to 0.1 ppm in advance with the use of catalyst.
-
- The present invention is not limited to the foregoing embodiment, but can be embodied as follows.
- (1) In the process of the foregoing embodiment, helium gas extracted from the
respective rectification columns main heat exchanger 14 from therectification columns gas transport passages main heat exchanger 14, thereby improving overall heat efficiency of the system. - Further, as shown in Figs. 1 and 2, the gas taken from the upper portion of the
main rectification column 16 may be transported to the expansion turbine 18 (expansion means) through agas transport passage 36. The gas is adiabatically expanded by theexpansion turbine 18, and further transported as it is to themain heat exchanger 14. In this way, the gas in the upper portion of themain rectification column 16 can serve as cooling medium for the main heat exchanger. It should be noted that the gas in the upper portion of thesubrectification column 20 can also be used for the same purpose. - Fig. 3 shows a system for cooling the system with the use of latent heat of evaporation of liquid nitrogen introduced into the upper portion of the
main rectification column 16 through a liquidnitrogen inlet passage 34. In this system, the gas in the upper portion of thecolumn 16 may be transported to themain heat exchanger 14 through thegas transport passage 36, and can be consequently served as cooling medium for themain heat exchanger 14 similar to the above examples. Also, the liquid nitrogen may be supplied to thesubrectification column 20 instead of themain rectification column 16 so as to take helium gas therefrom. It may also be appropriate that the liquid nitrogen be supplied to bothrectification columns - (2) The present method can be applied not only to an air separator, but also to any system for producing high purity nitrogen from material gas including nitrogen and low boiling gases.
- As described above, according to the method and the system of the present invention, liquid nitrogen having high purity is extracted from a main rectification column from a position lower than an uppermost stage thereof, and introduced into a subrectification column. The liquid nitrogen is further heated so as to evaporate low boiling gases therein in the subrectification column. Consequently, produced nitrogen is extracted from the subrectification column from a position lower than the position from which the liquid nitrogen is introduced thereinto. Accordingly. the low boiling gases can be effectively removed from the material gas, greatly contributing to production of nitrogen having ultra-high purity.
Claims (16)
- A method for producing high purity nitrogen comprising the steps of:
introducing air into a main rectification column (16) in a cold state;
extracting liquid nitrogen from the main rectification column (16) from a position lower than an uppermost stage thereof;
introducing the extracted liquid nitrogen into a sub rectification column (20); characterized in that:
in the main rectification column (16), nitrogen and component having a boiling point lower than nitrogen are separated from component having a boiling point higher than nitrogen;
in the subrectification column (20), the component having a boiling point lower than nitrogen is separated from the nitrogen; and
separated nitrogen is extracted from the subrectification column (20) from a position lower than a position into which the liquid nitrogen is introduced. - A method as defined in claim 1 further comprising the steps of:
introducing liquid nitrogen deposited at a bottom portion of the subrectification column (20) into a condenser (161) provided at a top portion of the main rectification column (16); and
introducing evaporated nitrogen gas from the condenser into the subrectification column (20). - A method as defined in claim 1 further comprising the step of introducing liquid nitrogen deposited at a bottom portion of the main rectification column (16) into a condenser (161) provided at a top portion of the subrectification column (20).
- A method as defined in claim 1 further comprising the step of introducing liquid present in a middle portion of the main rectification column (16) into a condenser (201) provided at a top portion of the subrectification column (20).
- A method as defined in any of claims 1 to 4 further comprising the steps of:
exchanging heat between the air and the produced nitrogen by using a heat exchanger (14); and
taking gas present in a top portion (161, 201) of at least one of the main rectification column (16) and the subrectification column (20) therefrom; and
passing the gas through the heat exchanger (14). - A method as defined in claim 5 further comprising the step of expanding the gas while transporting the same from the top portion of at least one of the rectification columns (16, 20) to the heat exchanger (14).
- A method as defined in claim 5 further comprising the step of introducing liquid nitrogen into the top portion (161, 201) of at least one of the rectification columns (16, 20) so as to cool the gas therein before taking the gas therefrom.
- A method as defined in any of claims 1 to 4 further comprising the steps of:
exchanging heat between the air and the produced nitrogen with the use of a heat exchanger (14);
taking helium gas from at least one of the main rectification column (16) and the subrectification column (20); and
passing the taken helium gas through the heat exchanger (14). - A system for producing high purity nitrogen comprising:
a main rectification column (16) and a subrectification column (20) for effecting rectification therein;
an inlet passage (11) for introducing air into the main rectification column (16):
a liquid nitrogen transport passage (22) for transporting liquid nitrogen from the main rectification column (16), to the sub rectification column (20), one end of the passage (22) being connected to the main rectification column (16) at a position lower than an uppermost stage thereof and the other end thereof being connected to the subrectification column (20); and
a produced nitrogen outlet passage (24) for extracting produced nitrogen from the sub rectification column (20);
characterized in that:
the main rectification column (16) separates nitrogen and component having a boiling point lower than nitrogen from component having a boiling point higher than nitrogen;
the subrectification column (20) separates the component having a boiling point lower than nitrogen from the nitrogen; and one end of the outlet passage (24) is connected to the subrectification column (20) at a position lower than a position into which the liquid nitrogen is introduced. - A system as defined in claim 9 further comprising:
a condenser (161) provided at a top portion of the main rectification column (16); and
a circulating passage (26) for transporting liquid nitrogen deposited at a bottom portion of the subrectification column (20) to the condenser and a passage (27) for transporting nitrogen gas evaporated in the condenser (161) to the subrectification column (20). - A system as defined in claim 9 further comprising:
a condenser (201) provided at a top portion of the subrectification column (20); and
a liquid transport passage (28) for transporting liquid deposited at a bottom portion of the main rectification column (16) to the condenser (201). - A system as defined in claim 9 further comprising:
a condenser (201) provided at a top portion of the subrectification column (20); and
a liquid transport passage for transporting liquid deposited at a middle portion of the main rectification column (16) to the condenser (201). - A system as defined in any of claims 9 to 12 further comprising:
a heat exchanger (14) for exchanging heat between the air and the produced nitrogen; and
a gas outlet passage (32, 36) for passing gas from top portions of the respective rectification columns (16, 20) through the heat exchanger (14), one end of the outlet passage being connected to the top portions (161, 201) of the respective rectification columns and the other end thereof extending through the heat exchanger (14). - A system as defined in claim 13 further comprising expansion means (18) provided in a specified position along the gas outlet passage between the heat exchanger (14) and the top portions (161, 201) of the respective rectification columns, the expansion means (18) adapted for expanding the gas passing therethrough.
- A system as defined in claim 13 further comprising liquid nitrogen inlet passages (34) for introducing liquid nitrogen to the top portions (161, 201) of the respective rectification columns (16, 20).
- A system as defined in any of claims 9 to 12 further comprising:
a heat exchanger (14) for exchanging heat between the air and the produced nitrogen; and
a helium gas outlet passage (31, 32) for passing helium gas from the respective rectification columns (16, 20) through the heat exchanger (14), one end of the helium gas outlet passage being connected to the respective rectification columns and the other end thereof extending through the heat exchanger (14).
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP14376190 | 1990-05-31 | ||
JP143761/90 | 1990-05-31 | ||
PCT/JP1990/001710 WO1991019142A1 (en) | 1990-05-31 | 1990-12-26 | Method of and device for producing nitrogen of high purity |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0485612A1 EP0485612A1 (en) | 1992-05-20 |
EP0485612A4 EP0485612A4 (en) | 1993-03-10 |
EP0485612B1 true EP0485612B1 (en) | 1995-10-18 |
Family
ID=15346410
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP91901554A Expired - Lifetime EP0485612B1 (en) | 1990-05-31 | 1990-12-26 | Method of and device for producing nitrogen of high purity |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP0485612B1 (en) |
DE (1) | DE69023141T2 (en) |
WO (1) | WO1991019142A1 (en) |
Families Citing this family (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5205127A (en) * | 1990-08-06 | 1993-04-27 | Air Products And Chemicals, Inc. | Cryogenic process for producing ultra high purity nitrogen |
US5170630A (en) * | 1991-06-24 | 1992-12-15 | The Boc Group, Inc. | Process and apparatus for producing nitrogen of ultra-high purity |
JP2983393B2 (en) * | 1991-10-15 | 1999-11-29 | レール・リキード・ソシエテ・アノニム・プール・レテュード・エ・レクスプロワタシオン・デ・プロセデ・ジョルジュ・クロード | Method for removing hydrogen by cryogenic distillation in the production of high purity nitrogen |
JP2893562B2 (en) * | 1992-09-22 | 1999-05-24 | 日本エア・リキード株式会社 | Ultra high purity nitrogen production method and apparatus |
FR2774753B1 (en) * | 1998-02-06 | 2000-04-28 | Air Liquide | AIR DISTILLATION SYSTEM COMPRISING MULTIPLE CRYOGENIC DISTILLATION UNITS OF THE SAME TYPE |
Family Cites Families (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS5439343B2 (en) * | 1971-09-21 | 1979-11-27 | ||
JPS5864478A (en) * | 1981-10-15 | 1983-04-16 | 日本酸素株式会社 | Device for manufacturing nitrogen having high purity |
JPS62141485A (en) * | 1985-12-16 | 1987-06-24 | 日本酸素株式会社 | Manufacture of nitrogen having high purity |
JPS63176986A (en) * | 1987-01-14 | 1988-07-21 | 株式会社神戸製鋼所 | High-pressure nitrogen production unit |
JP2685523B2 (en) * | 1988-08-24 | 1997-12-03 | 株式会社日立製作所 | Method and apparatus for producing ultra-high purity nitrogen |
-
1990
- 1990-12-26 WO PCT/JP1990/001710 patent/WO1991019142A1/en active IP Right Grant
- 1990-12-26 EP EP91901554A patent/EP0485612B1/en not_active Expired - Lifetime
- 1990-12-26 DE DE69023141T patent/DE69023141T2/en not_active Expired - Lifetime
Non-Patent Citations (1)
Title |
---|
L. Clarke, R.L. Davidson, Manual for process engineering calculations, McGraw-Hill, pages 404-408 * |
Also Published As
Publication number | Publication date |
---|---|
DE69023141T2 (en) | 1996-04-04 |
WO1991019142A1 (en) | 1991-12-12 |
EP0485612A4 (en) | 1993-03-10 |
DE69023141D1 (en) | 1995-11-23 |
EP0485612A1 (en) | 1992-05-20 |
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