JPH03170785A - Extremely low temperature air separation and its apparatus - Google Patents

Abstract

PURPOSE: To achieve a conservation of energy consumption, by using vaporized and liquefied air as heating and cooling media between high pressure and low pressure towers to allow condensation at a relatively low pressure. CONSTITUTION: Second feed air fraction entering a condenser/reboiler 58 at a base bottom part of a low pressure tower 34 is condensed by indirect heat exchange using an oxygen-enriched liquid at a bottom part of the low pressure tower 34 and with the condensing of the second feed air fraction, the oxygen- enriched liquid is vaporized. The condensed second feed air fraction enters a super cooler 46 via a line 82, and the liquefied air is expanded by a valve 44 to enter the condenser/reboiler 40 of a high pressure tower 32. A first nitrogen-enriched gaseous fraction ascends to the top part of the high pressure tower 32, where it enters the condenser/reboiler 40 and a nitrogen vapor causes an indirect heat exchange in which it contacts the condensed second feed air fraction that enters it through the valve 44 from the condenser/reboiler 58 of the low pressure tower 34. This enables a lower pressure and condensation.

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to the field of air separation processes, in particular where liquefied air is used as a heat exchange medium to a high pressure column condenser;
Energy. The present invention relates to a method and apparatus for producing nitrogen, oxygen, and/or argon from air, providing an effective process.

Prior art standard cryogenic air separation methods involve filtering incoming air to remove particulate matter and then compressing the air to provide energy for separation.

Typically, the incoming air stream is then cooled and passed through an absorbent to remove contaminants such as carbon dioxide and water vapor. The resulting air stream is subjected to cryogenic distillation.

Cryogenic distillation or air separation involves introducing high pressure air into one or more separation columns operated at cryogenic temperatures so that air components, including oxygen, nitrogen, argon, and noble gases, are separated by distillation. Including getting.

Cryogenic separation methods involving contact between vapor and liquid rely on the difference in vapor pressure for each component.

Components with high vapor pressure (meaning more volatile or lower boiling points) have a tendency to concentrate in the gas phase. Components with low vapor pressure (meaning poor volatility or higher boiling point) tend to concentrate in the liquid phase.

A separation process in which the heating of a liquid mixture concentrates the volatile components of the gas phase and the less volatile components of the liquid phase defines distillation. Partial condensation is a separation process in which a vapor mixture is cooled to concentrate volatile components in the gas phase while simultaneously concentrating less volatile components in the liquid phase.

The process of sequentially combining partial evaporation and condensation involving countercurrent treatment of vapor in the liquid phase is called rectification or sometimes continuous distillation.

Countercurrent contact of the gas and liquid phases is adiabatic and may involve total or differential contact between the phases.

The equipment used to achieve separation methods using the rectification principle and to separate mixtures is often called a rectification column, distillation column, or fractionation column.

As used herein and in the claims, the term "column" refers to a distillation or fractionation column or zone. It may also be described as a contacting column or zone in which liquid or gas phases are brought into countercurrent contact to separate fluid mixtures.

For example, this may involve contacting the gas and liquid phases on a series of vertically spaced trays or plates that are often perforated and corrugated and extend across the column and perpendicular to the center sleeve. Probably. Instead of trays or plates, packing elements may be used to pack the column.

As used herein, the term "double column" refers to a high pressure column that has an upper end that exchanges heat with a lower end of the lower pressure column.

"Standard Air Separation Method or Apparatus" as used herein
is meant to describe the methods and apparatus described above, as well as other air separation methods familiar to those skilled in the art.

As used herein and in the appended claims, the term "indirect heat exchange" means that two fluid streams exchange heat without any physical contact or mixing of the fluids with each other.

Traditionally, nitrogen, oxygen, and/or argon are produced by one of two basic process mechanisms, including single column processes and double column processes.

Regarding nitrogen, single column processes produce good quality gaseous and liquid nitrogen at pressures of about 6-10 bar. Nitrogen recovery is limited by equilibrium at the bottom of the column. Typically, this process involves about 50% to 50% of the nitrogen in the initial feed air.
Nitrogen can be produced at a rate of 60%.

In double column processes, nitrogen is produced at a pressure of about 1 to 4 bar. It is more effective than single tower process and
Approximately 90% or more of the nitrogen may be recovered from the nitrogen in the initial feed air. Typically, the columns are stacked with a condenser-reboiler separating the two columns. Because this process produces nitrogen at relatively low pressures, further compression of the nitrogen is often required, adding to manufacturing and usage costs.

In a conventional double column process, air is separated by cryogenic distillation or rectification to produce a nitrogen-rich stream or fraction at the top of the high-pressure column and an oxygen-rich stream or fraction at the bottom. The nitrogen-rich stream is sent to the top of the low pressure column to provide reflux for the column. The oxygen-rich flow at the bottom is
It is introduced into a low pressure column for the next separation.

In the low pressure column, the inlet stream is separated by cryogenic distillation into an oxygen-rich stream or fraction at the bottom and a nitrogen-rich stream or fraction at the top. The top stream can then be recovered as nitrogen product.

In a double column arrangement, the high pressure column and the low pressure column are thermally coupled by a condenser-reboiler arrangement.

Thus, in a conventional double column process, the nitrogen-rich fraction of the higher pressure column is condensed against the vaporized oxygen-rich fraction of the lower pressure column.

For a given pressure in the low pressure column, the pressure of the air introduced into the high pressure column will depend on the composition of the vaporized oxygen-rich stream, the temperature difference between the high pressure column condenser and low pressure column reboiler, and to some extent the relative Defined by the composition of the highly pure, condensed, nitrogen-rich stream.

Other conventional process setups are variations of the single or double column processes described above with additions such as additional overhead condensers or bottom reboilers.

SUMMARY OF THE INVENTION The method of this invention can be used for the energy efficient production of nitrogen, oxygen, and argon.

Basically, the invention consists in using vaporized and liquefied air as heating and cooling medium between high pressure and low pressure columns. Traditionally, nitrogen was used.

Although the invention is described in particular detail with respect to nitrogen, it should be understood that the invention is equally applicable to the production of oxygen and argon. It will be clear to those skilled in the art how to optimize the temperature, pressure, and other operating conditions to optimize the production of oxygen and/or argon as the primary products.

A particular advantage of using air as a heating and cooling medium is that condensing air requires less energy than condensing a nitrogen-rich stream. The relatively low pressure required to condense air at a given temperature is less expensive than to condense nitrogen, since the primary energy cost involves compression of the gas.

For example, nitrogen condenses at -180°C and 7 bar. In contrast, only -178°C and 6 bar are required to condense the air. Thus, a temperature difference of 2° C. and a pressure difference of 1 bar provides a reduced energy consumption in the method of the invention.

In conventional methods where nitrogen is used as a heating and cooling medium between high pressure and low pressure columns, it is necessary to compress the inlet air to a higher inlet air pressure as is required with nitrogen. Thus, the first energy savings come from the reduced need for compression of the introduced air.

The method of this invention requires that 9% of the nitrogen contained in the initially introduced air be
This makes it possible to produce high purity nitrogen of approximately 0% or more. It may be manufactured at a pressure within the range of about 3 bar to about 15 bar. Both high pressure and low pressure nitrogen can be produced. This can be done separately or together. Furthermore, this method is more energy efficient than traditional methods.

According to the method of this invention, the incoming air is treated to remove moisture and impurities such as CO2 and methane by passing through molecular sieves, alumina, silica gel, etc.
It is compressed and introduced into a heat exchanger to exchange heat with the effluent product.

According to one embodiment, the introduced air is divided into two fractions, one fraction is introduced at the bottom of the high pressure column and the other fraction is placed in a condenser/reboiler located at the base of the low pressure column. will be introduced in

Although other proportions can be used, good results have been obtained by dividing the introduced air into equal parts.

According to another embodiment, the introduced air is divided into three fractions. Two portions of the incoming air are introduced into the condenser/reboiler at the base of the high pressure column and the low pressure column as described above. The third air fraction is expanded to provide equipment cooling and then introduced into the low pressure column for cryogenic separation.

The first introduced air fraction is separated into a first nitrogen-rich gas fraction and a first oxygen-rich liquid fraction by cryogenic distillation in a high-pressure column. The oxygen-enriched liquid fraction is removed from the base of the high pressure column and sent to the low pressure column. The second inlet air fraction sent to the condenser/reboiler at the base of the LP column is condensed by heat exchange with an oxygen-rich liquid at the bottom of the LP column, whereby the oxygen-rich liquid is vaporized. The condensed and liquefied air thus produced in the condenser/reboiler is then introduced into the top condenser of the high pressure column where it is used with the first nitrogen-rich gas fraction produced in the high pressure column. vaporized by indirect heat exchange. This condenses the nitrogen.

According to one embodiment, a portion of the nitrogen-rich fraction condensed in the higher pressure column is separated and introduced into the lower pressure column to provide excess reflux. The second inlet air fraction, which is vaporized by indirect heat exchange in contact with nitrogen, in particular in the top condenser of the high-pressure column, is then introduced into the low-pressure column for cryogenic use.

In the lower pressure column, the second introduced air fraction along with a portion of the first oxygen-rich fraction from the higher pressure column is then separated into a second nitrogen-rich stream and a second oxygen-rich stream. .

According to other embodiments, a portion of the second nitrogen-rich stream may be removed as a high pressure nitrogen product. Meanwhile, the remaining portion is used to provide reflux for the lower pressure column.

According to another embodiment, a portion of the high pressure nitrogen product is expanded and provided for equipment cooling and added to the low pressure nitrogen product stream.

The second oxygen-rich stream descending to the bottom of the low pressure column is vaporized by indirect heat exchange in contact with the incoming second inlet air fraction, thereby condensing the second inlet air fraction. According to other embodiments, the second oxygen-rich fraction also includes a third introduced air fraction that is expanded before being introduced into the lower pressure column.

A portion of the second oxygen-rich stream is introduced into the top condenser of the low pressure column where it is vaporized by heat exchange in contact with the rising nitrogen, thereby condensing the nitrogen. The second oxygen-rich stream thus vaporized is removed from the top condenser as waste and warmed in the subcooler and heat exchanger by indirect heat exchange with the process air stream and incoming air.

Desirably, the waste oxygen is expanded and provided for equipment cooling. Alternatively, waste oxygen having a purity of about 70% is used as a product in applications that do not require high purity oxygen.

An apparatus for the above method is also provided. This device includes an air compression means for compressing air from an external source, a precision means for removing carbon dioxide and water vapor from the air compressed by the air compression means, and a precision means for cooling the compressed air from the precision means to cryogenic temperatures. Including a combination of heat exchange means. A first distillation column with a top column or top evaporator/condenser is included for cryogenic separation of a portion of the incoming air from the heat exchanger.

A second distillation column comprising a top column condenser and a bottom column reboiler, together with at least a portion of the oxygen-enriched liquid obtained from the first distillation column, the bottom column reboiler of the second distillation column. and the first
separation into a second oxygen-rich fraction and a second nitrogen-rich fraction by fractional distillation of at least a portion of the cooled and compressed inlet air after circulation through a top column condenser of a distillation column of provided for.

withdrawal of oxygenated liquid at the base of the second distillation column for introduction into the top condenser of the second distillation column to provide indirect heat exchange with the rising vapor in the second distillation column; There are means for this.

Expansion means are provided for the expansion of compressed air taken from the top condenser of the second distillation column and prior to the introduction of the κ oxygen into the second distillation column and/or for the expansion of the nitrogen production for cooling. established in

DETAILED DESCRIPTION OF THE INVENTION In the process diagram of FIG. 1, clean, compressed inlet air is introduced by conduit 20 into a heat exchanger 30.

Air is preferably introduced into the heat exchanger 30 at a pressure in the range of about 5 bar to about 20 bar, where the temperature of the air is cooled to cryogenic temperatures by indirect heat exchange with generated waste and products. Ru.

The introduced air is then divided into two fractions.

Good results have been obtained by dividing the inlet air into equal parts or using airflow, but other proportions may be used. The first fraction of the inlet air is sent by lines 22 and 62 to the high pressure column 32 and the inlet air is The remaining second fraction of air is line 2
2 and 60 to reboiler 58 of low pressure column 34.

In the high pressure column 32 the pressure preferably ranges from about 5 bar to 20 bar.

A first introduced air fraction is introduced at the bottom of the column 32 as indicated at 36 below the bottom distillation tray. Here, the first introduced air fraction is separated into a first nitrogen-rich gas fraction that rises to the top of column 32 and a first oxygen-rich liquid fraction that descends to the bottom of column 32.

At least a portion of the first oxygen-rich liquid is recovered from the bottom 38 of the high pressure column. It contains about 35% to 40% oxygen. It is approximately the same proportion as the prior art method.

The first oxygen-rich liquid removed from the bottom of the high pressure column 32 by line 54 is passed to a subcooler 46 where the product nitrogen exits from the top of the low pressure column 34 by line 48 and to the top condenser of the low pressure column 34. /The temperature is further reduced by indirect heat exchange with the waste leaving the evaporator.

The cooled first oxygen-enriched liquid from subcooler 46 is then introduced into low pressure column 34 above the bottom tray after expansion through valve 76 .

A second condenser/reboiler 58 at the base of the low pressure column
The introduced air fraction is condensed at the bottom of the low pressure column 34 by indirect heat exchange with an oxygen-enriched liquid. This condenses the second introduced air fraction and vaporizes the oxygen-rich liquid.

The condensed second inlet air fraction leaves the condenser/reboiler of low pressure column 34 and enters subcooler 46 via line 82. Liquefied air exits subcooler 46 via line 84 and is expanded by valve 44 into condenser/reboiler 40 of high pressure column 32. If necessary, a portion of the condensed second inlet air fraction is expanded by valve 92 and then introduced into the low pressure column 34 via line 90 to control the balance of air between the high and low pressure columns. Can be done.

The first nitrogen-rich gas fraction rises to the top of high pressure column 32 where it enters condenser/reboiler 40.

Here, the nitrogen vapor is transferred to the condenser/reboiler 58 of the low pressure column 34.
indirect heat exchange occurs in contact with the condensed second condensed large air fraction passing through valve 44.

This vaporizes the liquefied air and condenses the nitrogen vapor. As shown in FIGS. 3 and 4, some or all of the condensed nitrogen portion is returned to high pressure column 32 to provide reflux as needed.

Any nitrogen vapor that is not condensed by indirect heat exchange with the condensed second introduced air fraction is recovered as high pressure nitrogen from the top of high pressure column 32 by removal, e.g., by line 67 as shown in FIG. obtain.

If high pressure nitrogen flow is small or not needed, a portion of the condensed nitrogen can be sent to lower pressure column 34 for extra reflux. This portion of the condensed nitrogen is shown in Figures 1 and 3.
It is removed from the top of high pressure column 32 by line 68 as shown. The condensed nitrogen is then passed to a subcooler 66 to create an indirect heat exchange in contact with the nitrogen products and waste generated therein. From the subcooler 66, the condensed nitrogen passes through a continuous line 68 and is introduced into the low pressure column 34 after expansion through a valve 78.

．． At the same time, the vaporized air leaving the condenser/reboiler 40 at the top of the high pressure column 32 via line 56 is at about the same level as for the introduction of the first oxygen-rich limb by line 64, entering by line 54. It is separated by introduction into the low pressure column 34.

The first oxygen-rich limb removed from the base of column 32 and the vaporized air removed by line 56 from the condenser/reboiler 40 at the top of high pressure column 32 are transferred to the second oxygen-rich limb at the exit of column 34. It is further separated into a nitrogen-rich gas fraction and a second oxygen-rich fraction.

The second nitrogen-rich gaseous fraction rises to the top of the low pressure column 34, while the second oxygen-rich fraction falls to the bottom of the low pressure column 34.

A portion of the second oxygen-rich liquid fraction at the bottom of the low pressure column 34 is removed by line 74 and passed to the first subcooler 46 . Here, the second oxygen-rich liquid is in the lower pressure column 3
Further cooling is provided by indirect heat exchange with nitrogen gas removed from the top of column 4 by line 48 and waste air stream exiting by line 52 from the top condenser 70 of low pressure column 34.

The second oxygen-rich liquid is continuously cooled for further cooling by indirect heat exchange with nitrogen gas removed from the top of high pressure column 32 by line 68 and waste oxygen stream exiting by line 52 from top condenser 70. A line 74 leads to the second subcooler 66 .

The resulting cooled second oxygen-enriched liquid is passed to an extending line 74 where the liquid, after expansion by a valve 72, is introduced into a top condenser 70 at the top of the low pressure column 34 where a second oxygen-enriched liquid is passed. Cooling streams rich in

A major portion of the second nitrogen-rich stream is recovered as nitrogen product from the top of the lower pressure column 343 via line 48. The gaseous nitrogen stream passes through subcoolers 66 and 46 before exiting the system;
It is also heated by passing through a heat exchanger 30.

The remaining portion of the second nitrogen-rich stream in low pressure column 34 is
It is condensed by heat exchange with the second oxygen-rich liquid in the top evaporator/condenser 70 of the low pressure column 34, vaporizing the second oxygen-rich liquid. Condensation of nitrogen provides reflux for low pressure column 34. The vaporized oxygen-rich liquid exits the top evaporator/condenser 70 via line 52 and is subsequently warmed by passage through subcoolers 46 and 66 and heat exchanger 30.

After warming in heat exchanger 30, the waste oxygen stream is passed to turboexpander 78 where it can be expanded and provided for equipment cooling.

It will be appreciated that the method described above uses air as a heating and cooling medium between the high pressure and low pressure columns. In conventional methods, a nitrogen-rich stream is used to transport heat to the bottom of the low pressure column. For a given nitrogen recovery, i.e., nitrogen recovery with the same composition of oxygen-rich stream, more energy is required to condense the nitrogen-rich stream than to condense air. should be kept in mind. What this means is that for a given nitrogen recovery using air as the heat transport medium, high pressure columns can operate at lower pressures than prior art methods. Also, according to the invention, the low pressure column can function at a higher pressure for the same pressure in the high pressure column.

Table 1 below shows the first
Figure 3 illustrates the expected performance of the invention as illustrated in the figures and above description.

Total introduced air flow Introduced air pressure Nitrogen product stream Nitrogen pressure Nitrogen purity Disposal tV (#subenriching) stream i Qin material pressure Compressed air tower 32 1i132 j! 32 Oxygen Enriched Liquid 1 Condensed Second Inlet Air Fraction Condensed Second Inlet Air Fraction M1 Condensed Second Inlet Air Fraction Table 1 Line 20 Line 20 Line 48 Line 18 Line 52 Line 16 line 22 top bottom line 38 line 82 line 82 line 84 154Ei2Nm3 /h 10.2 pearl abs 10514Nm' /b 5.5 bar abs. 18vpm 02 4948NII1' /h 1,3 bar abs. -l80°C lO, 2 pearl abs. -170°C -160°C -1 [35. G°C -l [i7.5°C -187.5°C - t7t'c Condenser/) Second vaporized inlet air fraction from I boiler 40 Nitrogen discharge column 32 H nitrogen removal Supercooler 66 Tower 34 From tower 34! Nitrogen product exiting from column 34 Nitrogen product exiting column 34 Oxygen from condenser 70! I waste air flow line 56 line 68 line 68 line 74 line 74 #72 line 48 line 48 line 52 -172.8°C -170.6°C -174.4°C 5.5 bar abs, -168.8°C - 174.4°C -179°C -177.8°C 5 bar abs. −178.9° C. When following the embodiment shown in FIGS. 3 and 4, 21 bar abs. The introduced air pressure in the high pressure column 32 is approximately 2
0 bar abs. A pressure of about 14 bar abs. pressure will be generated.

Various modifications of the method and apparatus of the invention as described above will be apparent to those skilled in the art and may be relied upon without departing from the spirit and scope of the invention as defined by the claims.

[Brief explanation of the drawing]

FIG. 1 is a schematic process diagram of the method and apparatus of the present invention in which low pressure nitrogen is produced; FIG. 2 is the same method of the invention as in FIG. 1 except that air expansion is provided instead of waste expansion; and a schematic process flow diagram of the apparatus; FIG. 3 is a schematic process flow diagram of the method and apparatus of the present invention in which high-pressure and low-pressure nitrogen is produced; FIG. FIG. 4 is a schematic process flow diagram of the method and apparatus of the present invention, which is the same as FIG. 3; 30... Heat exchanger, 32... High pressure column, 34... Low pressure column, 40... Condenser/reboiler, 46.66... Supercooler, 58... Reboiler , 7 0...Top condenser, 7 8...Turbo expander

Claims (21)

[Claims] (1) A process for the cryogenic separation of air by rectification in at least one column to produce at least one vapor fraction, at least one liquid fraction, and at least one product nitrogen stream, the method comprising: providing an inlet air stream in a compressed vapor state, condensing at least a portion of the inlet air stream to vaporize the liquid fraction by indirect heat exchange contact of the at least one liquid fraction; and vaporizing a portion of the condensed incoming air stream by indirect heat exchange contact with one of the vapor fractions. 2. The method of claim 1, wherein said vaporized inlet air stream is further introduced into one of said distillation columns as inlet air for cryogenic separation by rectification. (3) performing cryogenic distillation of air in a high-pressure distillation column to produce a first oxygen-enriched fraction and a first nitrogen-enriched liquid fraction; at least a portion of the first oxygen-enriched fraction; is introduced into a low-pressure distillation column to produce a second oxygen-enriched fraction and a second nitrogen-enriched fraction, the method comprising: A method for cryogenic separation of air comprising the step of thermally coupling a column. (4) a second inlet air fraction that causes indirect heat exchange between the first inlet air fraction and the second oxygen-enriched fraction that are introduced into the high pressure column for cryogenic separation of the inlet air; vaporizing at least a portion of the second oxygen-enriched fraction; condensing at least a portion of the second introduced air fraction; condensing the first nitrogen-enriched fraction and vaporizing the condensed second introduced air fraction through indirect heat exchange with a first nitrogen-enriched fraction; 4. The method of claim 3, further comprising introducing an incoming air fraction of 200 to the low pressure column for cryogenic separation. (5) (A) cooled substantially free of moisture and impurities;
dividing the compressed inlet air into a first inlet air fraction and a second inlet air fraction; (B) introducing the first inlet air fraction into a high pressure column with a top condenser; (C ) separating the first introduced air fraction in the high pressure column into a first nitrogen-enriched fraction and a first oxygen-enriched fraction by cryogenic distillation; (E) removing at least a portion of the first oxygen-enriched fraction from a second oxygen-enriched fraction;
(F) into a low pressure column equipped with a bottom condenser/reboiler and a top evaporator/condenser for cryogenic separation into a nitrogen-enriched fraction and a second oxygen-enriched fraction; (G) introducing a second introduced air fraction into the condenser/reboiler of the low pressure column; condensing an inlet air fraction thereby vaporizing at least a portion of the second oxygen-enriched fraction; (H) transferring at least a portion of the condensed second inlet air fraction to the high pressure column; (I) condensing the second in the top condenser of the high pressure column by indirect heat exchange with at least a portion of the first nitrogen-enriched fraction in the high pressure column; (J) vaporizing at least a portion of the first oxygen-enriched fraction into a second nitrogen-enriched fraction and a second oxygen-enriched fraction; the second nitrogen-enriched fraction vaporized by indirect heat exchange contact with the first nitrogen-enriched fraction in the top condenser of the high pressure column for the cryogenic separation of
(K) removing at least a portion of the second nitrogen-enriched fraction as a product from the low pressure column; (L) removing at least a portion of the second nitrogen-enriched fraction as a product from the low pressure column; (M) introducing at least a portion of the removed oxygen-enriched fraction into the top condenser of the low pressure column; N) vaporizing at least a portion of the second oxygen-enriched fraction in the top condenser by indirect heat exchange with at least a portion of the ascending second nitrogen-enriched fraction in the lower pressure column; (O) thereby condensing the second nitrogen-enriched fraction and providing reflux for the lower pressure column, and (O) discharging the vaporized second fraction as waste from the top condenser.
A method of producing nitrogen from air comprising removing at least a portion of an oxygen-enriched fraction of. 6. The method of claim 5, further comprising: (6) removing at least a portion of the condensed first nitrogen-enriched fraction from the high pressure column as a high pressure nitrogen product. (7) removing at least a portion of the condensed first nitrogen-enriched fraction from the high pressure column; and transferring at least a portion of the removed and condensed first nitrogen-enriched fraction to the low pressure column. 6. The method of claim 5, further comprising introducing. (8) further dividing the compressed inlet air into a third inlet air fraction, expanding and cooling at least a portion of the third inlet air fraction, and 6. The method of claim 5 further comprising introducing at least a portion into the low pressure column. 7. The method of claim 6, further comprising: (9) expanding at least a portion of the waste oxygen removed from the top condenser. 7. The method of claim 6, further comprising: (10) expanding at least a portion of the high pressure nitrogen product prior to discharging the low pressure nitrogen product. (11) cooling the inlet air by indirect heat exchange in contact with waste and product Kiryu, and compressing the inlet air to provide a pressure in the high pressure column in the range of about 2 bar to about 20 bar; 6. The method of claim 5, comprising: (12) the first introduced air fraction in step (B) is introduced into the lower half of the high pressure column, and the first oxygen enriched fraction in step (D) is introduced from the base of the high pressure column; 6. The method of claim 5, wherein (13) the first oxygen-enriched fraction of step (E) is introduced into the bottom half of the low pressure column, and the second oxygen-enriched fraction of step (N) is introduced into the bottom half of the low pressure column; 6. The method of claim 5, taken from. (14) cooling the waste oxygen obtained in step 0 through a turboexpander and warming the cooled waste oxygen from the turboexpander by indirect heat exchange contact with the inlet air, such that the inlet air 6. The method of claim 5, further comprising cooling. (15) a top column condenser for cryogenic separation by rectification of a portion of the cooled compressed inlet air into a first nitrogen-enriched fraction and a first oxygen-enriched fraction; obtained from the first distillation column after circulation through the first distillation column, the bottom column reboiler of the second distillation column and the top column condenser of the first distillation column. separation into a second oxygen-enriched fraction and a second nitrogen-enriched fraction by precision of at least a portion of the cooled and compressed introduced air together with at least a portion of the first oxygen-enriched fraction; a second distillation column with a top column condenser and a bottom column reboiler for and conduit means in the first and second distillation columns for the introduction and withdrawal of liquid and vapor; conduit means communicating between the first and second distillation columns for the introduction and withdrawal of liquid and vapor; and the bottom of the second distillation column for the introduction of cooled and compressed inlet air. conduit means in communication with a column reboiler, for transporting condensed inlet air from the reboiler in the second distillation column to the top column condenser in the first distillation column; conduit means communicating the bottom column reboiler of the second distillation column with the top column condenser of the first distillation column; the top column condenser of the first distillation column and the second distillation column for removal of air and introduction into the second distillation column for cryogenic separation;
conduit means in communication with a distillation column and the removal of at least a portion of the first oxygen-enriched fraction from the first distillation column and introduction into the second distillation column for cryogenic separation; apparatus for producing nitrogen from cooled compressed air, comprising conduit means communicating said first distillation column and said second distillation column. (16) using the vapor rising in the second distillation column by removing the oxygen-enriched fraction from the second distillation column and introducing it into the top column condenser of the second distillation column; conduit means communicating the second distillation column with the top column condenser of the second distillation column to provide indirect heat exchange; conduit means communicating with the top column condenser of the second distillation column for removal of the first nitrogen-enriched fraction from the first distillation column and the second distillation column; 16. The apparatus of claim 15, further comprising conduit means communicating said first distillation column and said second distillation column to provide reflux for said second distillation column upon introduction to said second distillation column. (17) compression means for compressing air from an external source; precision means for removing carbon dioxide, water, and other impurities from the air compressed by the air compression means; and precision means for removing the compressed air from the precision means. heat exchange means for cooling to cryogenic temperatures, and said second
conduit means communicating with the top column condenser of the distillation column; and communicating with the heat exchanger and the first distillation column and the second distillation column for the introduction of cooled and compressed inlet air. 17. The apparatus of claim 16, further comprising conduit means. 18. The apparatus of claim 15 further comprising conduit means communicating said first distillation column and said heat exchange means for removal of nitrogen product. 19. The apparatus of claim 18 further comprising expansion means communicating with said conduit means for expanding and cooling at least a portion of the nitrogen product. 20. The apparatus of claim 15, further comprising expansion means for expansion of the oxygen waste. (21) The apparatus according to claim 15, further comprising expansion means for expanding the cooled and compressed air before it is introduced into the second distillation column and cooled.