JPH05302783A - Method for removing hydrogen with cryogenic distillation in manufacturing of high purity nitrogen - Google Patents

Abstract

PURPOSE: To manufacture high purity nitrogen by removing hydrogen with the aid of cryogenic distillation. CONSTITUTION: There is included an impurity comprising a soft product such as air, one kind or more of a heavier component (for example, oxygen and argon), and one kind or more of a softer component (for example, hydrogen and helium). A feedstock flow cooled, compressed, purified, and dried is supplied to heat exchange means 11 through a conduit 10, and is then supplied to a high pressure tower 13 through a conduit 12. A fluid rich in nitrogen is supplied to a low pressure tower 14 through a conduit 16 for supply from the high pressure tower 13, and it is fractionated at low pressure of 0.4 bar or lower. The fluid flow LIN is removed as a liquid production fraction from a bottom of the low pressure tower 14. Hereby, hydrogen contained in air is removed, and high purity nitrogen can be manufactured without the use of a catalyst.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for removing hydrogen by cryogenic distillation in the production of high purity nitrogen.

[0002]

In producing nitrogen by cryogenic distillation of air or any mixture containing oxygen and nitrogen, the hydrogen contained in the air is concentrated in the nitrogen product. Hydrogen contamination is particularly undesirable in electronics applications where very pure nitrogen is required.

[0003]

Presently, contaminated hydrogen in nitrogen is removed by passing compressed feed air through the catalyst bed at temperatures of about 250 to 500 ° F, which causes hydrogen to react with oxygen. Water and carbon dioxide are formed, which are removed by adsorption or reverse ion exchangers in subsequent steps. However, the removal of hydrogen by this method is not desirable due to the cost of the catalyst and the poisoning of the catalyst by other impurities present in the air, such as sulfur-containing compounds. Furthermore, catalytic reactors and the equipment associated therewith are very expensive and represent a substantial part of the overall required cost.

Therefore, it is an object of the present invention to provide a method for removing hydrogen by cryogenic distillation in the production of high purity nitrogen.

It is also an object of the present invention to provide a method for removing hydrogen by cryogenic distillation in the production of high purity nitrogen which avoids the use of catalytic reactors.

It is a further object of the present invention to provide a mixture containing as a seed a light product, one or more heavier components and one or more trace amounts of lighter impurities.
It is to provide a method for removing light impurities.

[0007]

The above objects, and other objects which will be more apparent from the following description, are to remove hydrogen by cryogenic distillation in the production of high-purity nitrogen comprising the steps shown below. Partially provided by the method.

A) The cleaned, dried mixture containing oxygen and nitrogen cooled to about the dew point is fed to a first distillation column, whereby nitrogen is taken off as a liquid at the top of the first distillation column. , A step of recovering an oxygen-rich liquid stream at the bottom of the first distillation column. b) A step of taking out a small fraction of a gas containing lighter impurities at the top of the first distillation column.

C) The liquid nitrogen at the top of the first distillation column is expanded to an intermediate level in the second distillation column operating at a pressure well below that of the first distillation column to provide first and second distillation columns.
Providing a sufficient temperature difference in the condenser-reboiler-located between the distillation columns of

D) The oxygen rich liquid stream is expanded in the top condenser of the second distillation column to form a condensate at the top of the second distillation column, the condensate being used as reflux for the second distillation column. Returning to the top of the.

E) withdrawing a small fraction of the gas containing substantially all remaining light impurity components at the top of the second distillation column.

F) The liquid is vaporized at the bottom of the second distillation column by heat exchange with the condensed gas at the top of the second distillation column, and the liquid fraction, the vaporized liquid fraction or both are
Recovering as a substantially lighter impurity-free product.

[0013]

The present invention provides a method for removing hydrogen by cryogenic distillation in the production of high purity nitrogen without the use of a catalytic reactor containing the catalyst. Basically, the present invention provides a double column process in which a first distillation column recovers a first fraction of nitrogen product in liquid form. Due to the high relative volatility of hydrogen to nitrogen, very small amounts of hydrogen are present in this liquid. This liquid nitrogen is then fed to a second distillation column where it is further purified to give a high purity nitrogen product at the bottom of the distillation column.

More specifically, the present invention provides a method for removing hydrogen by cryogenic distillation in the production of high purity nitrogen, which comprises several steps.

First, substantially water and carbon dioxide-free compressed air, or a mixture containing oxygen and nitrogen, cooled to about dew point, at a pressure such that the heavy air component is separated from the nitrogen. It is fed to the bottom of the first distillation column operated. This produces nitrogen as a liquid at the top of the distillation column and an oxygen-rich liquid stream at the bottom of the distillation column.

According to the present invention, the first distillation column is operated at a pressure of about 4 to 12 bar to effectively separate heavy air components such as oxygen and argon from nitrogen. This air typically contains up to about 20 vpm hydrogen. As already indicated, the first distillation column produces a nitrogen-rich product at its top.

As used herein, "heavy air component" refers to any component of air that has a lower volatility than nitrogen, that is, its vapor pressure is lower than that of nitrogen at the same temperature. That is. Similarly, a "light air component" as used herein refers to any component of air that has a higher volatility than nitrogen, that is, its vapor pressure is higher than that of nitrogen at the same temperature. Is. For example, oxygen and argon are examples of heavy air components, and hydrogen and helium are examples of light air components.

Liquid nitrogen is then expanded at the top of the first distillation column and introduced to the intermediate level of the second distillation column, and the second distillation column is well below the pressure of the first distillation column. Operated at pressure, it provides a sufficient temperature difference between the condenser and reboiler located between the two columns.

The oxygen-rich liquid stream is then vaporized in the overhead condenser of the second distillation column to form a condensate of the main fraction of the gas at the top of the second distillation column and then the condensate is refluxed. Return to the top of the second tower as.

Finally, the minor fraction of gas at the top of the second distillation column containing substantially all light air components is
The liquid withdrawn and at the bottom of the second distillation column is
This vaporized liquid, which is vaporized by heat exchange with the condensed gas at the top of the distillation column, and is substantially free of light air components, is recovered as a product.

In general, the second distillation column is operated at a pressure lower than that of the first distillation column in order to provide a sufficient temperature difference for the condenser-reboiler-that separates the two columns. Good. However, it is preferred that the second distillation column be at a pressure at least about 0.4 bar less than the pressure of the first distillation column. However, it is further preferred that the second distillation column is at a pressure at least about 0.6 bar lower than the pressure of the first distillation column.

Further, as used herein, "substantially all light air components" means that at least 99.99% of all light air components are contained therein. As used herein, "substantially free of light air components" means that 0.01% or less of all light air components are contained therein.

The process of the present invention may be implemented with many variations, some of which are described.

First, in addition to the general description above, along with the gaseous product, the liquid product may also be withdrawn at the bottom of the second distillation column. This is shown in FIGS.
Shown in.

Alternatively, a subcooler can be added to pre-cool the bottom of the first distillation column to the effluent gaseous product and the oxygen-rich residual stream. This is shown in FIG.

In addition, the requirement for cooling is by expanding the oxygen-rich stream, or by expanding the gaseous nitrogen product, or by adding liquid to the process in the form of a liquid aid, or by distilling the feed air. This can be achieved by expanding the minutes.

The present invention provides that whenever light product removal from a mixture containing heavier components is required,
It can be used in combination with other processes.

The present invention is also advantageous for use in combination with other other processes where light products are to be removed from a mixture of heavier components. As a special example,
The process of the present invention, from a mixture also containing hydrocarbons heavier, such as methane (CH _4), it may be used to remove carbon monoxide. In general, this process
It is applicable to some hydrocarbon mixtures containing lighter impurities. The present invention, in order to remove light components,
It may be used with any of these.

Beyond petrochemical processes, there are many other types of reaction mixtures containing lighter components and one or more heavier components. In some processes, other components in the reaction mixture may be unreacted feed. In other processes, the lighter component in the reaction mixture may be one of the reaction products. The process of the present invention is advantageously used with any of these processes to remove light components.

However, in general, mainly light products, 1
It is preferred to use the process of the invention with a method of obtaining a light product from a mixture containing one or more heavier components and traces of lighter impurities. It is more preferred if the lighter impurities are present in the mixture in an amount of up to about 1% by volume, most preferably up to about 0.5% by weight.

Thus, according to another aspect of the invention,
Lighter or more volatile, primarily from a mixture containing lighter or more volatile products, heavier or less volatile components, and trace lighter impurities with lighter or higher volatility than lighter products. A process for producing or removing the product of is provided.

More specifically, the present invention obtains a light product by cryogenic distillation mainly from a mixture of light product, one or more heavier components, and traces of lighter impurities. Provide a way. This method includes the following steps.

A) Mixtures containing predominantly lighter products, one or more heavier components, and traces of lighter impurities, from lighter products containing lighter impurities to 1
So that the heavier components of the species or more are separated,
Supplying to the first distillation column. Thereby, the light product withdrawn as liquid at the top of the distillation column and 1
One or more heavier components are withdrawn at the bottom of the first distillation column and the lighter impurities are
Accumulated at the top of the column, some of the lighter impurities are soluble in the light product liquid, and some of the lighter impurities remain in the non-condensable vapor fraction stream. Are removed from the column along with the lighter impurities contained therein.

B) expanding the light product containing some of the lighter impurities of the first distillation column and introducing it to the intermediate level of the second distillation column, leaving the light product and a larger portion of it. A process for producing a small amount of gas fraction containing light impurities.

C) The liquid stream rich in one or more heavier components withdrawn from the bottom of the first distillation column is expanded and introduced into the overhead condenser of the second distillation column. Process. There, the liquid stream is vaporized to the condensed gas stream at the top of the second distillation column. This condensate is returned as reflux to the top of the second distillation column.

D) A step of withdrawing the small amount gas fraction at the top of the second distillation column.

E) the liquid at the bottom of the second distillation column is
A step of vaporizing by heat exchange with condensed gas at the top of the first distillation column, and collecting a vaporized liquid fraction substantially free of light air components as a product.

Particularly with regard to step a) above, the lighter impurities accumulate at the top of the first column. Some of the lighter impurities are soluble in the light product liquor, and some of the lighter impurities remain in the vapor fraction called the non-condensable stream. This stream is removed from the column along with the lighter impurities contained therein.

The term "larger part" as used in step b) above means, for example, more than about 50% by volume. However, the larger portion is preferably greater than about 80, more preferably greater than about 99%.

The present invention thus provides an effective means for separating light products, one or more heavier components, and one or more lighter impurities. According to this aspect of the invention, the feed mixture contains primarily light product and one or more heavier components. Generally, the feed mixture will comprise the light product and one or more heavier components of 50 to 99.
Contains 99%. However, the feed mixture contains light product and one or more heavier components of 75 to 9
It is preferable to contain 9.99%.

As indicated above, generally, one or more of the lighter impurities should be present up to about 1% by volume, preferably about 0.5% by volume or less.

In general, as used herein, "light product" means a mixed component that has a higher volatility. By "heavier component" is meant a less volatile admixture component. By "lighter component" is meant an impurity component having intermediate volatility, which is present in amounts up to about 1% by volume.

According to the present invention, a "trace amount" of lighter impurities generally means a small amount of less than 1% by volume. In addition, "non-condensable" means non-condensable under the conditions at the outlet at the top of both columns.

In order to more fully illustrate the present invention, FIG.
-3.

In FIG. 1, a cooled, compressed, cleaned, light product, such as air, containing one or more heavier components and one or more lighter impurities. The dried and dried raw material stream is supplied to the heat exchange means 11 through the conduit 10 and then to the high pressure column 13 through the conduit 11. The liquid rich in nitrogen is the high pressure column 13
Is supplied to the low pressure column 14 through a conduit 16 for supply. The liquid stream (LIN) is also removed from the low pressure column 14 as a liquid product from the bottom of the column.

The non-condensable material is a column condenser-reboiler-
15 and from the low pressure column overhead condenser 80.

Exhaust gas is removed through conduits 21, 22 and optionally through subcooler 18 to heat exchanger 11 where it exits the process through conduit 28. This off-gas is generated from the bottoms stream 17 withdrawn from the higher pressure column, where it is optionally passed through a subcooler 18 and then introduced through conduit 20 into the overhead condenser 80.

In FIG. 2, light products such as air, 1
A cooled, compressed, cleaned, dried, near-dew point feed stream containing one or more heavier components and one or more lighter impurities results in a high pressure column 1
3 intermediate positions. In the high pressure column 13, an oxygen-rich stream separates at the bottom and a nitrogen-rich stream separates at the top. The liquid nitrogen stream is withdrawn at the top of the higher pressure column 13 and fed through conduit 16 to an intermediate position in the lower pressure column 14. Small gas fractions or non-condensables containing some lighter impurities are removed at the top of the higher pressure column 13 via conduit 30.

The lighter impurities are then removed at the top of the lower pressure column 14 via the non-condensable stream, the bottom fraction being substantially free of lighter impurities, ie about 0.5.
It only contains less than volume%.

The nitrogen product is transferred to the liquid (L
IN) is taken from the bottom of the low pressure column. The gaseous nitrogen product is withdrawn from the column via conduit 19 and reheated in exchanger 11. A portion of this product is
The remaining part is compressed by the compressor 60. This compressed stream fraction is recovered as product via conduit 57. The remaining fraction is sent via conduit 51 to a high pressure column reboiler-52 where it is condensed to provide reboil for the high pressure column.

The condensed recycle stream is then fed from the reboiler via conduit 53 to the top of the high pressure column to provide a special reflux for the high pressure column.

The oxygen-rich stream is sent from the bottom of the higher pressure column 13 via conduit 17 to the condenser 80 of the lower pressure column, where it is vaporized, passed through exchanger 11 and reheated. The reheated stream is then fed to an expander, which in turn is fed to an exchanger, where it is used to provide the required cooling and then discharged as an exhaust.

In FIG. 3, the cooled, compressed, cleaned and dried feed stream is fed via conduit 73 to the reboiler 52 of distillation column 13 where it is liquefied and the liquefied feed stream is Then, it is supplied to the high-pressure column 13.
The other part of the cooled, compressed, cleaned and dried feed stream is expanded by the expander 71 and introduced into the high pressure column 13, where pure nitrogen and lighter impurities are introduced at the top of the high pressure column 13. Is withdrawn and at the bottom of it an oxygen-rich liquid is withdrawn. Some lighter impurities are removed via conduit 30.

The liquid nitrogen fraction is withdrawn at the top of the higher pressure column and sent via conduit 16 to the intermediate stage of the lower pressure column. The gaseous nitrogen fraction formed at the top of the higher pressure column is condensed in the reboiler 15 to provide reboil for the lower pressure column.

The low pressure column 14 further purifies the liquid nitrogen feedstock and the lighter, impurity-free liquid product is provided in conduit 24.
Is recovered at the bottom of the low pressure column via. Conduit 19 provides recovery of lighter, impurity-free gaseous nitrogen.

The remaining lighter impurities are removed via conduit and exit the top of the lower pressure column.

Oxygen-rich liquid from the bottom of the higher pressure column is transported via conduit 17 to the lower condenser 80 at the top of the lower pressure column where it is vaporized and via conduits 21, 22, 28, and optionally. It exits the process through subcooler 10 and then through exchanger 11.

Gaseous nitrogen exits the column via conduit 19, and optionally through subcooler 18, via conduit 23 and then through exchanger 11. The process then exits via conduit 29.

By vaporizing the oxygen-rich liquid, the gaseous nitrogen at the top of the low pressure column condenses and is returned as reflux in the low pressure column.

Thus, according to the present invention, the above-described method and apparatus are provided.

Although the present invention has been described above, it will be apparent to those skilled in the art that the above-described aspects of the present invention can be subjected to many variations and modifications without departing from the spirit and scope of the present invention.

[Brief description of drawings]

1 is a flow chart for the removal of hydrogen by cryogenic distillation in the production of high-purity nitrogen, in which the liquid product as well as the gaseous product is withdrawn at the bottom of the second column.

FIG. 2 is a flow chart for the removal of hydrogen by cryogenic distillation in the production of high-purity nitrogen in which the nitrogen cycle promotes the recovery of nitrogen.

FIG. 3: Hydrogen expansion by cryogenic distillation in the production of high purity nitrogen, where the necessary cooling is achieved by expanding a portion of the compressed air in a turbine before it is fed to the first distillation column. Flow chart for removal.

[Explanation of symbols]

10 ... Conduit, 11 ... Heat exchange means, 13 ... High pressure column, 14 ...
Low pressure column, 15 ... Condenser-reboiler-, 16 ... Conduit, 17
... bottom stream, 18 ... subcooler, 80 ... top condenser.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (71) Applicant 591181403 Liquid Air Engineering Corporation LIQUID AIR ENGINEER ING CORPORATION Canada 3H / 1H, Quebec, Montreal, Sherbrooke Street West 1155 (72) Inventor Bao Her, California 94688, Berkaville, USA Weatherfield Drive 807 (72) Inventor Wilfried Petrier France, 75003 Paris, Rue de Tample 129 (72) Inventor Francois Bune United States, California 94594, Walnut Creek, Kamino Birde Circle 1075

Claims (9)

[Claims] 1. A) a cleaned, dried mixture containing oxygen and nitrogen cooled to about dew point is fed to a first distillation column, whereby nitrogen is a liquid at the top of the first distillation column. Withdrawing and recovering an oxygen-rich liquid stream at the bottom of the first distillation column, b) removing a small fraction of the gas containing lighter impurities at the top of the first distillation column, c) The liquid nitrogen at the top of the first distillation column is expanded to an intermediate level in the second distillation column operating at a pressure well below that of the first distillation column, between the first and second distillation columns. Providing a sufficient temperature difference in the condenser-reboiler located, d) expanding the oxygen-rich liquid stream in the overhead condenser of the second distillation column and condensing the condensate at the top of the second distillation column. Formed and used this condensate as reflux at the top of the second distillation column E) withdrawing a small fraction of the gas containing substantially all residual light impurity components at the top of the second distillation column, and f) condensing gas at the top of the second distillation column. Heat vaporizing the liquid to vaporize the liquid at the bottom of the second distillation column and recover the liquid fraction, the vaporized liquid fraction or both as a substantially lighter impurity-free product. , A method of removing hydrogen by cryogenic distillation in the production of high-purity nitrogen. 2. The process according to claim 1, wherein the second distillation column is operated at a pressure at least 0.4 bar lower than the first distillation column. 3. The process according to claim 1, wherein the first distillation column is operated at a pressure of about 4 to 12 bar. 4. The process according to claim 1, wherein the second distillation column is operated at a pressure at least 0.4 bar lower than the first distillation column. 5. A) predominantly a light product, a mixture containing one or more heavier components and traces of lighter impurities, one or more of a lighter product containing lighter impurities. The lighter product and the one or more heavier products withdrawn to the top of the distillation column as a liquid are fed so that the above heavier components are separated. Components are withdrawn at the bottom of the first distillation column, the lighter impurities accumulate at the top of the first column, and some of the lighter impurities are soluble in the light product liquor, Some of the lighter impurities remain in the non-condensable vapor fraction stream, and the non-condensable vapor fraction stream is removed from the column along with the lighter impurities contained therein, b) the first distillation column. Of lighter products containing some lighter impurities of And introducing it to the intermediate level of the second distillation column to produce a light product and a small gas fraction containing a larger portion of residual light impurities, c) withdrawing from the bottom of the first distillation column. The liquid stream enriched in the one or more heavier components formed is expanded and introduced into the overhead condenser of the second distillation column, where the liquid stream is
Vaporizing the condensed gas stream at the top of the distillation column, and returning the condensate to the top of the second distillation column as reflux, d) withdrawing the small gas fraction at the top of the second distillation column. And e) vaporizing the liquid at the bottom of the second distillation column by heat exchange with condensed gas at the top of the first distillation column,
Comprising a step of recovering, as a product, a vaporized liquid fraction substantially free of a light air component, mainly a light product, one or more heavier components, and a trace amount of one or A method of removing light products from a mixture containing more lighter impurities. 6. Double fractionation means having high pressure fractionation means in fluid connection with a feed stream containing oxygen and nitrogen and withdrawing a first fraction of a nitrogen producing liquid; and said liquid nitrogen from said high pressure fractionation means. Apparatus for removing hydrogen by cryogenic distillation in the production of high purity nitrogen, comprising separation conduit means for feeding the low pressure fractionating means for further purification of the product. 7. An indirect heat exchange of the oxygen-rich liquid at the bottom of the first column in fluid communication with the bottom reboiler of the high pressure fractionation means, whereby the compressed nitrogen cycle is in contact with said reboiler. 7. The apparatus of claim 6 wherein the compressed nitrogen cycle stream, which has been vaporized by, is condensed and expands at the top of the first column to increase its reflux and reboil. 8. A turbine further fluidly connected to the first distillation column, wherein a part of the compressed air in the turbine is expanded before being supplied to the first distillation column. An apparatus according to claim 6 or 7, wherein the required cooling is achieved. 9. A bottom reboiler of the high pressure fractionation means is further provided, whereby the compressed feed stream is condensed against an oxygen-rich liquid that is vaporized by indirect heating, and the condensed feed stream is 9. The apparatus according to claim 8, which is supplied to one fractionating means.