Process for producing ultrapure nitrogen

Details Process for producing ultrapure nitrogen Process for producing ultrapure nitrogen

1999-11-10

2001-08-21

Doerrler, William (Department: 3744)

Refrigeration

Cryogenic treatment of gas or gas mixture

Separation of gas mixture

C062S920000

Reexamination Certificate

active

06276172

ABSTRACT:

The invention relates to a process for producing ultrapure nitrogen by lowtemperature fractionation of air in a rectification system having at least one rectification column, in which process compressed and purified feed air is conducted into a pressure column (synonymously termed a “high pressure” column in the United States), an oxygen-free pressurized nitrogen fraction is produced from the pressure column, conducted into a low-pressure column and in the low-pressure column carbon-monoxide-free low-pressure nitrogen is produced as overhead gas.
BACKGROUND OF THE INVENTION
German Patent Application DE 198 06 576 A1 published Aug. 6, 1998 discloses a process wherein an oxygen-free pressurized nitrogen fraction is taken off from a pressure column. In order for the nitrogen to be also carbon-monoxide-free, the pressure column has at least 160 theoretical plates. However, the energy requirement for this, despite the 160 theoretical plates, is still very high. It is also a disadvantage that most of the ultrapure nitrogen is produced in the gaseous state.
SUMMARY OF THE INVENTION
It is therefore an object of one aspect of the invention to avoid this disadvantage and to decrease the energy requirement.
A further object of an aspect of the invention is to provide a process which is optionally operated with a liquid pressurized nitrogen fraction directly from the pressure column or from a tank containing liquid pressure-column nitrogen.
Upon further study of the specification and appended claims, other aspects of the invention will become apparent. In brief, the invention comprises a process for producing ultrapure nitrogen by low-temperature fractionation of air in a rectification system having at least one rectification column, in which process compressed and purified feed air is conducted into a pressure column, an oxygen-free pressurized nitrogen fraction is produced from the pressure column, conducted into a low-pressure column and in the low-pressure column carbon-monoxide-free low-pressure nitrogen is produced as overhead gas, characterized in that the oxygen-free pressurized nitrogen fraction is either taken off in the liquid state from the upper 50% of the pressure column or is provided from a liquid tank containing stored oxygen-free nitrogen and in that the oxygen-free pressurized nitrogen fraction is expanded into the bottom-heated low-pressure column, ascending vapour being formed in the low-pressure column and being freed from carbon monoxide using a reflux of ultrapure nitrogen applied at the top of the low-pressure column, being taken off at the top of the low-pressure column as carbon-monoxide-free overhead gas and after a pressure increase being partly liquefied and the liquefied part being expanded into a bottom-heated He—Ne—H
2
column from which the ultrapure nitrogen is taken off in the liquid state.
It is characteristic of the invention that the oxygen-free pressurized nitrogen fraction is either taken off in the liquid state from an upper region of the pressure column or is provided from a liquid tank containing stored oxygen-free nitrogen. (By “upper region” is meant the upper 50%, preferably the upper 15% of the pressure column.) The oxygen-free pressurized nitrogen fraction is expanded into the bottom-heated low-pressure column, ascending vapour being formed in the low-pressure column and being freed from carbon monoxide using a reflux of ultrapure nitrogen applied at the top of the low-pressure column. At the top of the low-pressure column, carbon-monoxide-free overhead gas is withdrawn, and after a pressure increase, is partly liquefied. The liquefied part is then expanded into a bottom-heated He—Ne—H
2
column from which the ultrapure nitrogen is taken off in the liquid state.
By means of the process according to the invention the ultrapure nitrogen is produced in the liquid state and can in this form be more readily transported and therefore more simply distributed to customers. The process, furthermore, is universally useable. This is because it can be used in connection with an air fractionation plant (with or without liquid nitrogen tank) or only with a liquid nitrogen tank (with spatial separation from the air fractionation plant). At an air fractionation plant having a liquid nitrogen tank, in addition, the ultrapure liquid nitrogen can also be produced without the air fractionation plant being in operation.
In an embodiment of the process of the invention, the carbon-monoxide-free overhead gas and an overhead gas of the He—Ne—H
2
column can be combined to form a carbon-monoxide-free cold gas stream.
Alternatively, the carbon-monoxide-free overhead gas can be partially liquefied in a condenser/evaporator against a liquid refrigerant which is simultaneously vaporized and a gas stream which is produced in the vaporization of the liquid refrigerant and an overhead gas of the He—Ne—H
2
column can be combined to form a carbon-monoxide-free cold gas stream.
Advantageously in both cases, the carbon-monoxide-free cold gas stream is warmed in a heat exchanger, compressed and cooled again in countercurrent in the same heat exchanger and one part is used in the low pressure column and another part is used in the He—Ne—H
2
column for heating the bottoms and is liquefied in the course of this, except for residual streams remaining in the gaseous state, and is fed as the liquid refrigerant to the condenser/evaporator.
The streams which are liquefied in the heating of the He—Ne—H
2
column and the low-pressure column can be fed as reflux to the He—Ne—H
2
column.
In the case of the use of a condenser/evaporator which is described above as an alternative, using the streams which are liquefied in the heating of the He—Ne—H
2
column and the low-pressure column, the carbon-monoxide-free overhead gas of the low-pressure column can be liquefied in the evaporator/condenser of the low-pressure column, except for a residual stream, and can be fed at least in part as reflux to the He—Ne—H
2
column. Counteracting the disadvantage of an additional capital cost of the condenser/evaporator is then the advantage, which is not to be underestimated, that in the case of air leaks during the compression of the carbon-monoxide-free gas stream, no contamination of the ultrapure liquid nitrogen can occur.
Ultrapure nitrogen can be withdrawn in the liquid state from the He—Ne—H
2
column and produced in part as the reflux for the low-pressure column and in part as liquid ultrapure nitrogen product.
The ultrapure liquid nitrogen product can be fed to a product tank.
The ultrapure liquid nitrogen product can also be pressurized using a pump, vaporized utilizing the cold content in the production of the oxygen-free pressurized nitrogen fraction, warmed and fed as gaseous pressurized product for use. In this case, gaseous ultrapure nitrogen product can also be produced by the process for producing ultrapure liquid nitrogen product and the cold of the originally present liquid product can be utilized efficiently.
In general, the ultrapure nitrogen has impurities below 1 mol ppm, preferably between 100 and 10
−3
mol ppb for each of the components CO, O
2
, Ar, H
2
, Ne and He, with the most preferred being between 10 and 10
−2
mol ppb. In practice the CO concentration is kept below such a maximum tolerated value resulting in O
2
and Ar concentrations far below this value.
The same occurs with H
2
and He if Ne is kept below such tolerated values. The use of the process according to the invention is not limited, in principle, to the above stated values.


REFERENCES:
patent: 4464188 (1984-08-01), Rakesh
patent: 5123947 (1992-06-01), Agrawal
patent: 5167125 (1992-12-01), Rakesh
patent: 5170630 (1992-12-01), Stern
patent: 5351492 (1994-10-01), Agrawal et al.
patent: 5421164 (1995-06-01), Brugerolle
patent: 5638699 (1997-06-01), Yamamoto et al.
patent: 5906113 (1999-05-01), Lynch et al.
patent: 198 06 576 A1 (1998-08-01), None
patent: 0 569 310 (1993-11-01), None
patent: 0 834 711 (1998-04-01), None

Affiliated with

Also associated with

Rating

Process for producing ultrapure nitrogen does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Process for producing ultrapure nitrogen, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for producing ultrapure nitrogen will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2515341