ES2644280T3 - Method and air separation apparatus - Google Patents

Description

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DESCRIPTION

Method and apparatus for air separation Field of the invention

The present invention relates to a method and an apparatus for separating air, in which oxygen and nitrogen products are produced as concurrent products by rectifying compressed and purified air within a main distillation column in order to produce the nitrogen product. , and subjecting raw liquid oxygen formed in the main distillation column into an auxiliary distillation column to produce the oxygen product.

Background of the invention

Nitrogen is usually obtained with high purity by separating nitrogen from the air within a cryogenic air separation plant that often uses a single distillation column. In such a plant, the air is compressed and then purified from pollutants of higher boiling point, in order to produce a stream of compressed and purified air. The stream of compressed and purified air is then cooled to a temperature suitable for cryogenic rectification within a main heat exchanger, and then introduced into a single distillation column that operates at approximately 3 bars or a higher pressure. The air, inside the distillation column, is rectified to produce a nitrogen-rich steam column at the top and a liquid oxygen-rich column at the bottom, known as raw liquid oxygen or boiler liquid. The oxygen-rich liquid is depressurized in an expansion valve and is then introduced into a heat exchanger to condense a stream of the nitrogen-rich vapor column from the top and thereby produce liquid nitrogen to feed as reflux the distillation column. The oxygen-rich liquid that is partially evaporated can be used to generate cooling for the plant, or, alternatively, cooling can be provided to the plant through the addition of liquid nitrogen to the main column or to a stream entering the heat exchanger. main heat

In general, oxygen is not recovered from such nitrogen plants from a single column. However, there is an interest in also recovering oxygen from said plants. For example, the production of float glass usually requires low purity nitrogen and oxygen in a flow ratio of approximately 2: 1. Oxygen is used in the glass oven to promote recovery and is usually necessary at a low purity of between 90 and 95 percent and at a pressure of between 0.6895 bar and 1.3789 bar (between 10 psig-pounds per square inch gauge ["pounds per square inch gauge"] - and 20 psig). While this oxygen can be provided by an independent vacuum pressure oscillating absorption plant or through the vaporization of liquid provided on the ground, the added expense is not justifiable. It should be noted that both oxygen and nitrogen can be produced by a typical double column air separation plant that has high and low pressure columns operatively associated in a heat transfer relationship. However, such a plant is not economical in the event that float glass is produced, for example, due to the need for product compression and the higher initial capital cost. The incremental modification of a small nitrogen plant of a single column to provide both nitrogen and oxygen products can economically satisfy the procedural requirements such as the production of float glass in which the nitrogen and nitrogen products Oxygen is required at a pressure and with a modest flow rate, for example, less than 2,831.68 m3 / h (100 kcfh -kilo cubic feet per hour ["kilo cubic feet per hour"] -) of nitrogen.

In the prior art there are examples of single-column nitrogen plants that have been modified to jointly produce both nitrogen and oxygen products. For example, in US 4,783,210, a stream of the lower part of the crude liquid oxygen column is partially evaporated in a heat exchanger that is used when condensing a stream from the top, or header, of a steam column rich in nitrogen, produced in a distillation column. The resulting nitrogen-rich liquid is used to feed the column as reflux. A stream of the resulting liquid phase produced by the partial evaporation of the crude liquid oxygen is then bubbled into a secondary or auxiliary distillation column in order to produce a lower part of the oxygen-rich column, which can be extracted as an oxygen product. The auxiliary distillation column is evaporated again with another stream of nitrogen-rich steam, which condenses on the re-evaporation and can be extracted as a liquid nitrogen product and also used to feed the distillation column as reflux.

US 5,074,898 discloses a single column nitrogen generator, with an auxiliary distillation column to produce an oxygen product. In this patent, a stream of crude liquid oxygen generated in a main distillation column is bubbled in an auxiliary distillation column. The auxiliary distillation column is reevaporated with a stream from the top of the nitrogen-rich steam column, produced in the main distillation column. This condenses the nitrogen-rich vapor to produce a feed as reflux to the main distillation column. The residual liquid generated in the auxiliary distillation column can be extracted as a liquid product, together with part of the condensed nitrogen vapor.

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In these two patents, the lower part of the column is being used to condense nitrogen, so that there must necessarily be a pressure lower than that of nitrogen to carry out the condensation of nitrogen. As a result, the oxygen product is also at a low pressure. On the other hand, since a portion of the bottom of the column is removed as a product, there will be less fluid from the bottom to condense the nitrogen. Consequently, nitrogen production is limited. As will be explained, the present invention provides a method and an apparatus for producing concurrent nitrogen and oxygen products, which, among other advantages, may allow the oxygen product to be produced at a high pressure. In another aspect of the present invention, the lower part of the auxiliary column is subjected to a vaporization in stages in order to make it possible for a larger fraction of oxygen to be obtained at a lower power compared to the procedures contemplated in the prior art. .

On the other hand, in US 4,560,397 A a method for separating air is disclosed in order to produce concurrent oxygen and nitrogen products, such that said method comprises:

cooling a compressed and purified stream comprising the air;

rectify the compressed and purified stream within a main distillation column in order to produce a vapor column rich in nitrogen at the top and crude liquid oxygen;

produce an oxygen-rich liquid and an upper part of the auxiliary column containing not less than 5.0 percent oxygen by volume within an auxiliary distillation column, by depressurizing, at least in part, a stream of liquid oxygen in raw composed of the crude liquid oxygen, bubble the raw liquid oxygen stream into the auxiliary distillation column with an ascending bubble gas, and partially evaporate the oxygen-rich liquid through indirect heat exchange with a stream of vapor rich in nitrogen, composed of the upper column of steam rich in nitrogen, which produces a stream of liquid nitrogen, bubbling gas and a liquid rich in residual oxygen;

refluxing the main distillation column with at least part of the liquid nitrogen stream;

forming a fraction of oxygen-rich vapor from the liquid rich in residual oxygen by indirect heat exchange between a liquid stream rich in residual oxygen and a gas stream having a nitrogen concentration not less than that of the air, such so that the stream of the liquid rich in residual oxygen is partially evaporated;

form: a stream of nitrogen product from the top of the nitrogen-rich steam column; and a waste stream from the top of the auxiliary column; Y

pass the nitrogen product stream and the waste stream in direct heat exchange with the compressed and purified stream.

Compendium of the invention

The present invention is a method for separating air in order to produce concurrent oxygen and nitrogen products as defined in claim 1, and an apparatus for separating air in order to produce concurrent oxygen and nitrogen products as defined in the claim 7.

A fraction of oxygen-rich vapor is formed from the liquid rich in residual oxygen by indirect heat exchange between a stream of the liquid rich in residual oxygen and a gas stream having a nitrogen concentration not less than that of the air, of such that the stream of the residual oxygen-rich liquid partially evaporates. A stream of oxygen product is formed from the vapor fraction, a stream of nitrogen product is formed from the nitrogen-rich vapor, and a waste stream is formed from the top of the auxiliary column of the auxiliary distillation column. The oxygen product stream, the nitrogen product stream and the waste stream are passed in indirect heat exchange with the compressed and purified stream.

As can be seen from the above exposure, since the oxygen product stream is formed from a fraction of vapor that is, in turn, produced from the liquid rich in residual oxygen, the production of the oxygen product It is no longer directly coupled to the production of reflux nitrogen to the main distillation column, since the liquid rich in residual oxygen is not used in the condensation of the nitrogen-rich vapor from the main distillation column. Consequently, the extraction of the liquid rich in residual oxygen does not decrease the feed as reflux of the nitrogen towards the main distillation column and, therefore, the production of nitrogen, as in the prior art.

Additionally, since the liquid rich in residual oxygen is not used to condense nitrogen, this liquid can be produced at a higher pressure.

As indicated above, the upper part, or header, of the auxiliary column can only be produced by bubbling the raw liquid oxygen stream into a distillation column.

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assistant. Alternatively, the main distillation column is refluxed with part of the liquid nitrogen stream. In the latter case, the bubbling of the crude liquid oxygen stream takes place within a bubbling section of the auxiliary distillation column, and the bubbling produces a stream of vapor containing nitrogen and oxygen. The steam stream containing nitrogen and oxygen is rectified within the auxiliary distillation column, inside a rectification section of the auxiliary distillation column located above the bubble section, introducing the vapor stream containing nitrogen and oxygen in the rectification section, and by refluxing the auxiliary distillation column and, therefore, the rectification section with an additional part of the liquid nitrogen stream. The effect of this is to increase the recovery of oxygen within the liquid rich in residual oxygen by effectively trapping oxygen that otherwise escapes from the auxiliary column, within the waste stream.

In any of the aforementioned cases, the oxygen-rich liquid is collected within the auxiliary distillation column. The oxygen-rich liquid is partially evaporated by passing a stream of oxygen-rich liquid and the nitrogen-rich vapor stream through a single-pass heat exchanger, to form the bubbling gas and the oxygen-rich liquid residual, which is collected as the bottom of the column in the auxiliary distillation column.

The gas stream is the compressed and purified stream. The compressed and purified stream is partially condensed in a condenser, and the residual oxygen rich liquid stream is collected in a separating vessel. A liquid phase current, formed by a liquid phase produced within the separation vessel, is introduced into the condenser and partially evaporated in the condenser through an indirect heat exchange with the compressed and purified current, whereby It produces a two-phase current from the liquid phase current. The two-phase stream is introduced into the separation vessel, and the liquid and vapor phases of the two-phase stream are separated within the separation vessel to form a fraction of oxygen-rich vapor, and the liquid phase, together with the flow of the liquid rich in residual oxygen, they are collected in the separation vessel. The oxygen product stream is then formed by discharging a stream of the oxygen rich vapor fraction from the separation vessel.

The condenser is located in a lower region of the main distillation column, such that the condensed air is mixed with the descending liquid produced by the rectification, in order to produce, in this way, the crude liquid oxygen as a lower part of column belonging to the main distillation column. On the other hand, the main distillation column can be refluxed with part of the liquid nitrogen stream, and the waste stream exchanges heat indirectly with the raw liquid oxygen stream, such that the liquid oxygen stream in Gross is subcooled before being depressurized.

As an alternative to form the gaseous stream from the compressed and purified stream, the gaseous stream may be composed of the lower part of the nitrogen-rich vapor column. In such an embodiment, the heat is indirectly exchanged between the stream of the liquid rich in residual oxygen and the gas stream by depressurizing a liquid stream enriched in oxygen and the passage of the stream of the liquid rich in residual oxygen in indirect heat exchange with the gas stream inside a thermosiphon reevaporator. This produces the fraction of steam from the partial evaporation of the liquid oxygen-rich liquid stream, and a condensate stream through the condensation of the gas stream. The condensate stream is introduced into the main distillation column as reflux, in conjunction with the liquid nitrogen stream.

In the above-described embodiment, the waste stream can be passed in indirect heat exchange with the raw liquid oxygen stream, before depressurization of the raw liquid oxygen stream, such that the liquid oxygen stream in Gross is subcooled.

In any embodiment of the present invention, the stream of the liquid rich in residual oxygen can be pressurized, such that the stream of oxygen product is also pressurized. On the other hand, a liquid nitrogen cooling stream can be introduced into the main distillation column to impart refrigeration.

The present invention also provides an apparatus for separating air in order to produce the concurrent oxygen and nitrogen products. Such an apparatus includes a main heat exchanger, a main distillation column and an auxiliary distillation column. The main heat exchanger has been configured to cool a compressed and purified stream comprising the air, and the main distillation column has been configured to rectify the compressed and purified stream in order to produce a nitrogen-rich vapor column in the upper part, and crude liquid oxygen. The auxiliary distillation column is connected to the main distillation column and has been configured such that a stream of crude liquid oxygen, composed of the crude liquid oxygen, is bubbled with an ascending bubble gas located within the auxiliary distillation column, and an oxygen-rich liquid and an upper part, or head, of the auxiliary column are produced, which contains not less than 5.0 percent oxygen by volume, at least in part, as a result of bubbling of the stream of crude liquid oxygen. There is an expansion valve located between the main distillation column and an auxiliary distillation column, such that the liquid oxygen stream is depressurized before being introduced into the auxiliary distillation column.

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Means have been provided to partially evaporate the oxygen-rich liquid by indirect heat exchange with a stream of nitrogen-rich steam composed of the upper part of the nitrogen-rich vapor column, whereby a stream is produced of liquid nitrogen, bubbling gas and a liquid rich in residual oxygen. The partial evaporation means of oxygen-rich liquid are connected to the main distillation column such that the main distillation column is refluxed with at least part of the liquid nitrogen stream. The main heat exchanger is connected to the main distillation column and the auxiliary distillation column, such that a stream of nitrogen product formed from the nitrogen-rich vapor, and a waste stream formed from the part upper auxiliary column of the auxiliary distillation column, exchange heat indirectly with the stream of compressed and purified air. Means have also been provided for indirectly exchanging heat between a stream of the liquid rich in residual oxygen and a gas stream having a nitrogen concentration not less than that of the air, such that the stream of the liquid rich in residual oxygen evaporates partially. On the other hand, means have been provided to form a fraction of oxygen rich vapor from the stream of the liquid rich in residual oxygen, after being partially evaporated. The main heat exchanger is connected to the oxygen-rich vapor fraction formation means, the main distillation column and the auxiliary distillation column, such that an oxygen product stream, composed of the vapor fraction rich in oxygen, a stream of nitrogen product, composed of the upper part of the steam column rich in nitrogen, and a waste stream, composed of the upper part of the auxiliary column of the auxiliary distillation column, pass into the exchanger of main heat, in indirect heat exchange with the compressed and purified stream.

The auxiliary column can only be provided with a section undergoing bubbling in which the bubbling of the crude liquid oxygen stream takes place. Alternatively, the auxiliary column may be provided with a bubbling section and a rectifying section, located above the bubbling section. In the latter case, the bubbling of the crude liquid oxygen stream takes place within a bubbling section of the auxiliary distillation column, and the vapor stream with oxygen content occurs in the bubbling section entering the rectification section for the rectification of the steam stream with nitrogen and oxygen content. This rectification is provided to thereby increase the recovery of oxygen within the liquid rich in residual oxygen. The partial evaporation means of oxygen-rich liquid are connected to the main distillation column such that the main distillation column is refluxed with part of the liquid nitrogen stream, and is also connected to the auxiliary distillation column. in such a way, that the auxiliary distillation column and, therefore, the rectification section are refluxed with an additional part of the liquid nitrogen stream. Another expansion valve is placed between the partial evaporation means of oxygen-rich liquid and the auxiliary distillation column, such that the pressure of the additional part of the liquid nitrogen stream is reduced to that of the auxiliary distillation column .

The auxiliary distillation column is provided with means to collect the oxygen-rich liquid. The partial evaporation means of the oxygen-rich liquid consist of a single-pass heat exchanger connected to an auxiliary distillation column and the oxygen-rich liquid collection means, such that the oxygen-rich liquid is partially evaporated. within the one-step heat exchanger, by passing a stream of oxygen-rich liquid, composed of the oxygen-rich liquid, and the residual oxygen-rich liquid is collected as a bottom column of the distillation column assistant. The auxiliary distillation column is connected to the one-step heat exchanger in such a way that the nitrogen-rich vapor stream is condensed into the single-pass heat exchanger.

The gas stream is the stream of compressed and purified air. In such a case, the stream of the heat exchange media of residual oxygen rich liquid and the oxygen rich vapor fraction formation means consist of a condenser and a separation vessel. The condenser is connected to the main heat exchanger in such a way that the compressed and purified current is partially condensed. The separation vessel is connected to the auxiliary distillation column, such that the liquid oxygen-rich liquid stream is collected in the separation vessel. The separation vessel is connected to the condenser in such a way that a liquid phase current, composed of a liquid phase produced within the separation vessel, is partially evaporated in the condenser to produce a two-phase current that is introduced into the vessel from separation. The liquid and vapor phases of the two-phase stream are separated within the separation vessel to form the oxygen-rich vapor fraction and the liquid phase, and the main heat exchanger is connected to the separation vessel in such a manner. , that the oxygen product stream is formed from the fraction of vapor rich in oxygen.

The condenser is located in a lower region of the main distillation column, such that the condensed air is mixed with the descending liquid produced by the rectification of the compressed and purified stream, in order to produce the raw liquid oxygen in form of a lower column part of the main distillation column. On the other hand, the one-step heat exchanger may be connected to the main distillation column such that the main distillation column is refluxed with part of the liquid nitrogen stream. A subcooling heat exchanger is connected to the one-step heat exchanger, the auxiliary distillation column and the expansion valve, such that the current

Waste heat exchanges indirectly with the raw liquid oxygen stream K inside the subcooling heat exchanger, and the raw liquid oxygen stream K is subcooled before it passes through the expansion valve.

As an alternative, the gas stream may be composed of nitrogen-rich steam. In such a case, the stream of the oxygen-rich liquid heat exchange means and the oxygen-rich vapor fraction formation means are constituted by a thermosiphon reevaporator having a housing. The housing is connected to the auxiliary column to receive the current of the liquid rich in residual oxygen, and there is another expansion valve located between the housing and the auxiliary column, such that the current of the liquid rich in residual oxygen is depressurized. The thermosiphon reevaporator is connected to the main distillation column to receive the gas stream and, thereby, condense the gas stream through an indirect heat exchange with the liquid oxygen rich in residual oxygen stream, and thereby form the oxygen-rich vapor fraction inside the housing and discharge a condensate stream to the main distillation column as reflux, together with the liquid nitrogen stream. The main heat exchanger is connected to the housing, the main distillation column and the auxiliary distillation column in such a way that a stream of oxygen product, formed from the vapor fraction, a stream of product from Nitrogen, formed from the top of the steam column rich in nitrogen, a waste stream, formed from the top of the auxiliary column, produced in the auxiliary distillation column, passes, all of them, inside the exchanger of main heat, in indirect heat exchange with the compressed and purified stream.

In the above-described embodiment, the subcooling heat exchanger is located between the auxiliary distillation column, the main distillation column and the main heat exchanger, such that the waste stream passes in indirect heat exchange with the raw liquid oxygen stream, before depressurizing the raw liquid oxygen stream and before heating the waste stream inside the main heat exchanger.

In any embodiment of the present invention, the main distillation column may be provided with a top inlet for the introduction of a liquid nitrogen cooling stream, in order to impart cooling.

Brief description of the drawings

While the present invention concludes with claims that distinctively state the subject matter that these Applicants consider as their invention, it is believed that the present invention will be better understood as taken in connection with the accompanying drawings, in which:

Figure 1 is a schematic illustration of an air separation plant for carrying out a method according to the present invention;

Figure 2 is a schematic illustration of an alternative embodiment of an air separation plant for carrying out a method whose embodiment does not fall within the scope of the claims; Y

Figure 3 is a schematic illustration of yet another alternative embodiment of an air separation plant for carrying out a method according to the present invention.

Detailed description

Referring to Figure 1, there is illustrated an air separation plant 1 that is capable of concurrently producing oxygen and nitrogen products ("N2" and "O2").

A stream of compressed and purified air 10 is cooled in a main heat exchanger 12 to a temperature suitable for rectification at or near saturation. As can be seen, the air separation plant 1 can be part of an installation that requires compressed air and, in this way, the stream of compressed and purified air 10 can be formed from part of the air produced in such an installation. Alternatively, said current can be generated by compressing the air, usually between 4,8263 bar and 6,2053 45 bar (between 70 psia-pounds per square inch absolute ["pounds per square inch absolute"] - and 90 psia), and then purifying the air of pollutants of higher boiling point, which solidify or concentrate at cryogenic temperatures; for example, carbon dioxide, water vapor and hydrocarbons. The main heat exchanger 12 may be of a thin construction of conventional welded aluminum plate. As occurs to those skilled in the art, heat exchanger 12 may be constituted by a plurality of units operating in parallel.

The stream of compressed and purified air 10, once cooled, is introduced into a condenser 14 located in a lower region 16 of a main distillation column 18. The distillation column 18 contains contact elements with mass transfer, such as trays , structured packaging, random packaging or a combination of such elements that is generally indicated by reference number 20. The incoming air 55 is partially condensed inside the condenser 14 to produce a fraction of steam 22 that rises inside the elements 20 of contact with mass transfer in order to contact a phase

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A descending liquid that produces a top 23 of a nitrogen-rich vapor column. The upper part 23 of the nitrogen-rich vapor column will usually be essentially pure nitrogen. The partial condensation of the air produces a liquid fraction 24 that constitutes about 20 percent of the incoming air and that is collected, together with the liquid that has descended inside the elements 20, within the lower region 16 of the column of primary distillation 18, as crude liquid oxygen 26.

It should be appreciated that alternative means for condensing the incoming air consists in placing the condenser 14 outside the main distillation column 18. However, said embodiment does not fall within the scope of the claims. In connection with such means, the liquid fraction 24 and the liquid that would have descended inside the distillation column 20 may be combined separately to form the crude liquid oxygen 26, or they may be subcooled and supplied separately to the column 34. In other such means, the stream of compressed and purified air can be introduced directly into the housing of the main distillation column. The air will be allowed to mix with the steam inside the column and with the steam that has been recirculated 22 from the condenser 14. In such a configuration, the condenser will not have a condensation side head, that is, it will be induced to the gas simply to flow into the exchanger by condensation. As a further alternative, a portion of the cooled air stream 10 can be directed to the housing of the column 18, and a portion, directed directly to the condenser 14. Such a configuration will make possible a modification of the product's oxygen and nitrogen flows. However, this configuration will require additional valves and control means. Additional means consist of using an independent air stream that could be additionally compressed. The independent air stream will be divided, either by the hot end, in the event that it is compressed additionally, or, if not compressed, by the fno end. The current will then be fully condensed inside the condenser 14. The condensed air will then be introduced at a location between stages of the main distillation column 18 through suitable conduits. The condensed air will not be collected in the column sump but instead, liquefied air will be supplied several stages above with respect to the bottom of the main distillation column 14.

A stream of crude liquid oxygen 28 composed of the crude liquid oxygen 26 is then preferably subcooled within a subcooling heat exchanger 30 and depressurized within an expansion valve 32, located between the main distillation column 18 and the auxiliary column 34, up to a pressure of preferably between 1.0342 bar and 1.7237 bar (between 15 psia and 25 psia). The crude liquid oxygen stream 28 is bubbled into an auxiliary distillation column 34 upon contacting said stream with a rising bubble gas stream 52 inside a mass transfer contact element 36 which they can be trays, structured packaging, random packaging or a combination of such elements. The bubbling produces an upper part 38 of the auxiliary column that usually contains between 80 percent and 90 percent by volume of nitrogen, and a liquid rich in residual oxygen 56 that usually contains 85 percent. one hundred to 98 percent by volume of oxygen.

The oxygen-rich liquid 40 may be collected within a collection tray 42 or by similar means in which the descending liquid is collected and the ascending vapor is allowed to pass through it, and into the contact means with transfer of mass 36. A stream 44 of the oxygen-rich liquid, composed of the oxygen-rich liquid 40, is partially evaporated through indirect heat exchange with a stream 46 of nitrogen-rich steam, composed of the nitrogen-rich vapor 23, within a single pass exchanger 48. As a result of indirect heat exchange, a liquid nitrogen stream 50 is produced. The stream of the oxygen-rich liquid 44 is partially evaporated to produce the bubbling gas 52 and a stream of gas and residual liquid 54 which is collected in the lower part of distillation column 34, in the form of a liquid rich in residual oxygen 56. It should be appreciated that, in an alternate embodiment Therefore, a two-phase stream can be extracted from the boiling side of the single-pass heat exchanger, from the auxiliary distillation column 34, and directed to an independent phase separator to produce the oxygen-rich liquid stream residual 68, and a vapor phase will then be conducted back to the auxiliary distillation column 34 to form the bubbling gas 52. While not preferred, this will be equivalent to that shown in the figures.

As alternative means to the one-step heat exchanger 48 and to the collection tray 42, a thermosiphon reevaporator located at the base of the auxiliary column 34 can be used to partially evaporate the oxygen-rich liquid 40 that falls from the contact elements with mass transfer 36 inside the base of the auxiliary column 34. The core of said reevaporator should settle in the residual oxygen-rich liquid and produce the bubbling gas by evaporating the oxygen-rich liquid 40. This, however, it will not be preferable, since such a heat exchanger will not work with the temperature differences of a single pass heat exchanger; and, consequently, the incoming air will have to be compressed at a higher pressure.

The liquid nitrogen stream 50, in whole or in part thereof, as illustrated, can be introduced into the main distillation column 18 as a reflux stream 58. The remainder, as an additional liquid nitrogen stream 60 (depressurized by means of a valve 63) and a waste stream 62, composed of the upper part 38 of the auxiliary column, can be introduced, firstly, in the subcooling heat exchanger 30, in indirect heat exchange with the current of crude liquid oxygen 28 for purposes

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of subcooling it, and then be passed in indirect heat exchange with the incoming compressed and purified air stream 10, in order to help cool it inside the main heat exchanger 12. Alternatively, stream 60 and the current 62 can be combined and heated. Once heated, the additional liquid nitrogen stream 60 will be discharged from the main heat exchanger 12 as a concurrent gaseous nitrogen product (W), and the waste stream 62 can be used in the regeneration of absorbents used in a purification unit preliminary that is used to preliminary purify the incoming air and is used in association with the air separation plant 1. On the other hand, it is also possible to recycle all or part of said stream by compressing it again and combining it with the incoming air. It should be appreciated that the use of the stream 60 is optional, and the vaporization of the liquid nitrogen stream 60 serves to provide additional subcooling to the stream 28 and, therefore, makes possible a greater production of oxygen.

It should be appreciated that the liquid nitrogen reflux stream 60 can be extracted from an inter-stage position of the column 20, before passing through the valve 63.

It should also be appreciated that the subcooling heat exchanger 30 or 30 'to be explained may be integrated with the main heat exchanger 12. It is also possible that an embodiment of the present invention can be constructed without making use of such heat exchangers. subcooling heat 30 or 30 '. In any case, in the illustrated embodiment, the additional liquid nitrogen stream 60 can be depressurized in an expansion valve 63 before passing through the subcooling heat exchanger 30 and the main heat exchanger 12.

The concurrent nitrogen product is obtained by heating a stream of nitrogen product 64, composed of the top 23 of a nitrogen-rich steam column, within the main heat exchanger 12, through an indirect heat exchange with the incoming stream of compressed and purified air 10, in order to also help cool it. As illustrated, the nitrogen product stream 64 and the nitrogen rich vapor stream 46 are produced by dividing a stream of nitrogen rich vapor 66, extracted from the top of the main distillation column 18, into the two previous streams . However, the nitrogen product stream 64 and the nitrogen rich vapor stream 46 can be extracted separately from the main distillation column 18. It should be appreciated that, since all the liquid nitrogen stream 50 can be introduced into the main distillation column 18 as reflux, the concurrent nitrogen product can be formed only from the heated nitrogen product stream 64.

The concurrent oxygen product is produced by extracting a stream 68 of the liquid enriched in residual oxygen, composed of the liquid enriched in residual oxygen 56, and introducing said stream into a separating vessel 70. A liquid phase stream 72, composed of the liquid phase 74, is partially evaporated in the condenser 14 to produce a two-phase current 76 through an indirect heat exchange with the incoming compressed and purified air stream 10, whereby the compressed and purified air stream is partially condensed 10 The liquid and vapor fractions of the two-phase stream 76 are separated within the separation vessel to form a vapor fraction and a liquid phase 74 produced by the separation with the stream and the addition of the residual oxygen-rich liquid 68 A control valve (not shown) can be used to modulate the operating pressure of vessel 70. The product flow d and oxygen is formed from a vapor phase stream 80 composed of the vapor fraction 78. A drain stream 82 that is passed through a valve 84 may, optionally, be collected as a liquid product (or directed as a polluting drain vaporizer). Alternatively, a portion of stream 68 may be extracted as a liquid product and sent to a suitable storage.

It should be appreciated that the stream of the residual oxygen-rich liquid 68 can be pressurized as a result of the auxiliary distillation column 34 being located a certain height above the main distillation column 18. This results in an oxygen product pressurized Yet another additional alternative is to pressurize the stream of the liquid rich in residual oxygen by means of a mechanical pump, or to use the pump in association with the liquid header that is produced by placing the auxiliary distillation column 34 above the column of main distillation 18.

As illustrated, the capacitor 14 acts as a thermosiphon. As alternative means for forming the oxygen product, it is possible that the separation vessel 70 may have been constructed to house the capacitor 14. In such a case, the two-phase current will leave the condenser to pass into the separation vessel 70. However, it is believed that the illustrated embodiment is more cost effective with respect to such provision. Additionally, if more than about 20 percent of the oxygen product was to be taken as a liquid product by means of the drain stream 82, then it will be possible to reconfigure the condenser 14 as a single-pass heat exchanger, with a potential savings additional energy consumption. In such an embodiment, the stream of the liquid rich in residual oxygen 68 will be conducted directly to the condenser 14. The partially evaporated product will then be separated in a phase separation vessel and there will be no return current, such as the liquid stream enriched in oxygen that enters the condenser 14.

Referring to Figure 2, an alternative embodiment in the form of an air separation plant 2 is illustrated. It should be appreciated that, in the case that the elements illustrated in Figure 2 have the same description

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that in the previous explanation with respect to Figure 1, such elements shown in Figure 2 will employ the same reference numbers as those in Figure 1 and, for the sake of brevity, will not be further explained. The air separation plant 2 has been specifically designed to allow a larger fraction of the nitrogen contained in the air to be recovered as a product. This is achieved through an increase in the reflux of liquid nitrogen K towards the main distillation column 18.

In the air separation plant 2, the compressed and purified air stream 10, after having been cooled inside the main heat exchanger 12 and introduced into the main distillation column 20 and rectified to produce a top 23 of the steam column rich in nitrogen and a bottom 26 'of crude liquid oxygen column. Optionally, a stream of crude liquid oxygen 28 'may be subcooled in a subcooling unit 30', and bubbled into an auxiliary distillation column 34 after it has been depressurized into the expansion valve 32. A first stream of nitrogen-rich vapor 46 is condensed in the one-step heat exchanger 48 to produce a first stream of liquid nitrogen 50 and a liquid rich in residual oxygen 56, in the manner described with respect to the air separation plant 1 . The resulting stream of the residual oxygen-rich liquid 68 produced in the auxiliary distillation column 34 is introduced into a thermosiphon reevaporator 86 after being depressurized in an expansion valve 90. The stream 68 of the residual oxygen-rich liquid is partially evaporated to through an indirect heat exchange with the gas stream 92, which may be composed of the upper nitrogen-rich steam column 23 of the main distillation column 18. The gas stream 92 passes into a core 94 located inside of a housing 96 of the thermosiphon reevaporator 86 to effect heat exchange. The gas stream 92 is condensed to produce a condensate stream 98 which is introduced into the main distillation column 18 as part of the reflux to said column. All liquid nitrogen stream 50 produced in the one-step heat exchanger 48 is introduced into the main distillation column 18 as a reflux feed of the column. This condensation in stages of the nitrogen-rich vapor column of the upper part will increase the liquid nitrogen reflux and, therefore, will ensure the increased capacity of the air separation plant 2 to produce the nitrogen product.

As can be seen, other means may be employed in place of the thermosiphon reevaporator 86, including a single-pass heat exchanger if the drain current 106 is of sufficient flow. On the other hand, although it is not illustrated, instead of the nitrogen-rich vapor, a stream having a nitrogen concentration not less than that of the air can be introduced into the core 94 of the thermosiphon reevaporator 86. For example, it is possible to compress a stream of air and liquefying said stream within the main heat exchanger 12. After that, it can be introduced into an intermediate position of the main distillation column 18. A gas stream can then be passed through having approximately the same composition as said liquid stream , inside core 94 of thermosiphon reevaporator 86, and condense. The resulting condensate stream will be introduced at a position of the main distillation column in which the composition of the descending column liquid is the same or almost the same as that of such condensate, or it will be introduced into the auxiliary distillation column 34 for bubbling and the production of the concurrent oxygen product.

The partial evaporation of the stream of the liquid rich in residual oxygen 68 creates vapor and liquid fractions that are collected in the housing as a vapor fraction 100 and a liquid phase 102. A vapor phase stream 104, composed of the fraction of steam 100, is passed in indirect heat exchange with the incoming compressed and purified air stream 10, within the main heat exchanger 12, to heat the vapor phase stream 100 in order to produce the oxygen product ("O2 ”) And help cool the stream of compressed and purified air 10. A drain stream 106, composed of liquid phase 102, can be depressurized in a valve 108 and collected as a liquid oxygen product. In such an embodiment, optionally, the waste stream 62 may be passed in indirect heat exchange with the raw liquid oxygen stream 28 ', within the subcooling heat exchanger 30'. The waste stream 62 is also subsequently passed in indirect heat exchange with the stream of compressed and purified air 10, within the main heat exchanger 12, to heat the waste stream 62 and help cool the stream of compressed and purified air 10. The waste stream 62 can be recycled back into the incoming air. This can be done after heating in the exchanger 12, by direct mixing with feed air or after an additional compression. As in the air separation plant 1, the nitrogen product stream 64, composed of the upper part 23 of the nitrogen-rich steam column, is heated within the main heat exchanger 12 by indirect heat exchange with the compressed and purified incoming air stream 10, to also help cool it.

Referring to both Figure 1 and Figure 2, cooling is imparted to one of the air separation plant 1 or the air separation plant 2 by means of a liquid nitrogen stream 110 that is passed through a flow control valve 112 and then is introduced in an upper inlet 114 located at the top of the main distillation column 18. Said current can be obtained from a storage tank on the ground and can be high or low pressure. The addition of such a current compensates for environmental heat leaks as well as losses at the hot end in which the operation of the main heat exchanger is incurred 12. It should be appreciated that liquid current 110 can be introduced directly into one of the steam streams entering the heat exchangers 30 'or 12. As can be seen, a portion of the incoming air can be expanded before it is introduced into the column

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main distillation 18. In this regard, a portion of the stream of compressed and purified air, after partial cooling inside the main heat exchanger 12, can be expanded and then mixed with the waste gas stream 62. Another possibility is to retropresurize the distillation column system of the main distillation column 18 and the auxiliary distillation column 34, and the waste stream 62 can be partially heated within the main heat exchanger 12, expanded in a turboexpansor and further heated inside the main heat exchanger 12. The use of a turboexpansor may allow the possibility of taking a liquid product from the column system. A portion of the liquid nitrogen obtained from condensers 48 or 96 can be sent to a suitable storage. Yet another additional alternative is that a liquid oxygen stream can be introduced into, or combined with, the residual oxygen rich liquid stream 68 and then introduced into the housing 96 of the thermosiphon reevaporator 86.

With reference to Figure 3, an air separation plant 1 'is illustrated therein which constitutes an alternative embodiment to the air separation plant 1 shown in Figure 1. In an air separation plant 1, a auxiliary column 34 'provided with a bubble section 36a that may have been provided with contact elements with mass transfer 36, as explained above with respect to Figure 1. The crude liquid oxygen stream 28 it is subjected to bubbling within said bubbling section 36a as described above, and, instead of directly producing a header or upper part of the auxiliary column, it produces a vapor containing nitrogen and oxygen. The auxiliary column 34a is also provided with a rectification section 36b located above the bubbling section 36a, in order to rectify said vapor with nitrogen and oxygen content and thereby recover some of the oxygen which, otherwise, it has been vented from the plant in the waste stream 62. The rectification section is refluxed by the liquid nitrogen stream 60 'which is introduced into the upper part of the auxiliary column 34' after being depressurized by a valve 63 '. As can be seen, the same modification can be made in the plant shown in Figure 2. In this case, the auxiliary column will be modified in the same way as shown in Figure 3. In the case of the embodiment of Figure 2 , part of the condensed stream 98 will be used to reflux the auxiliary column 34 '.

As can be seen, all that has been contemplated is to recover some of the oxygen that is otherwise lost in the waste, in order to increase the recovery of oxygen. However, a balance must be sought between the increase in oxygen recovery and the fact that liquid nitrogen is being taken from the liquid nitrogen that would otherwise have been used to reflux the main distillation column, and, by Therefore, the production of nitrogen. Any larger rectification will be accompanied by an increase in the flow of liquid nitrogen stream 60 'and, therefore, by a reduction in the available product nitrogen 64, since the reflux flow rate of the main column must be maintained for the purpose. that maintain the purity of the product nitrogen. A more concrete way of establishing such a limitation is that the behavior of the rectification section 36b, when taken in connection with that of the bubble section 36a, must be such that the upper part or header 38 of the auxiliary column, within Auxiliary column 36, must contain no less than 5.0 percent oxygen by volume. To achieve this, the ratio between the flow rate of the liquid nitrogen stream 60 'and the total available nitrogen flow from column 18 (the sum of streams 60 and 64) should usually be between 0.1 and 0.4, and the ratio between liquid and steam in rectification section 36b, between 0.23 or less.

Claims (11)

5 10 fifteen twenty 25 30 35 40 Four. Five fifty 1. - A method for separating air in order to produce concurrent oxygen and nitrogen products, such that said method comprises: cooling a compressed and purified stream (10) comprising the air; partially condense the compressed and purified stream into a condenser (14) located in a lower region (16) of a main distillation column (18); rectify the vapor fraction (22) of the compressed and purified stream, partially condensed, within the main distillation column (18) to produce a nitrogen-rich steam column of upper part (23), and such that the condensed air is mixed with the descending liquid produced by the rectification within the main distillation column, in order to thereby produce a lower portion of the crude liquid oxygen column (26) within the main distillation column (18); produce an oxygen-rich liquid (40) and an upper part (38) of auxiliary column containing not less than 5.0 percent oxygen by volume, within an auxiliary distillation column (34), when depressurizing, at least in part, of a stream of crude liquid oxygen (28) composed of the lower part of the column of raw liquid oxygen (26), bubbling the stream of raw liquid oxygen (28) into the auxiliary distillation column (34), with an ascending bubbling gas (52), and partially evaporating the oxygen-rich liquid (44) by indirect heat exchange with a stream of nitrogen-rich vapor (46) composed of the upper part (23 ) of a nitrogen-rich steam column, whereby a stream of liquid nitrogen (50), the bubbling gas (52) and a liquid rich in residual oxygen (56) are produced; collect the oxygen-rich liquid (40) within the auxiliary distillation column (34); partially evaporate the oxygen-rich liquid (40) by passing a stream of oxygen-rich liquid, composed of the oxygen-rich liquid (40), and the nitrogen-rich vapor stream (46) through a heat exchanger in a single step (48) to form the bubbling gas (52) and the liquid rich in residual oxygen (56) which is collected as a lower part of the column belonging to the auxiliary distillation column (34); refluxing the main distillation column (18) with at least part (58) of the liquid nitrogen stream (50); forming a fraction of vapor rich in oxygen (78) from the liquid rich in residual oxygen (56) by indirect heat exchange between a stream (68) of the liquid rich in residual oxygen (56) and a gaseous stream (76) having a concentration of nitrogen not less than that of air, so that the stream (68) of the liquid rich in residual oxygen (56) partially evaporates, such that the gas stream (76) is the compressed stream and purified (10); forming a stream of oxygen product (80) from the vapor fraction (78); a stream of nitrogen product (64) from the top of the nitrogen-rich vapor column (23), and a waste stream (62) from the top (38) of the auxiliary column; Y passing the oxygen product stream (80), the nitrogen product stream (64) and the waste stream (62) in indirect heat exchange with the compressed and purified stream (10); in such a way that the oxygen rich vapor fraction (78) is formed by: collecting the stream (68) of the liquid rich in residual oxygen (56) inside a separation vessel (70); introducing a liquid phase current (72), formed by a liquid phase produced within the separation vessel (70), into the condenser (14) and partially evaporating the liquid phase current (72) into the condenser (14), by means of an indirect heat exchange with the compressed and purified current (10), whereby a two-phase current (76) is produced from the liquid phase current (72); introduce the two-phase stream (76) into the separation vessel (70) and separate the liquid and vapor phases from the two-phase stream (76) into the separation vessel (70) to form a vapor fraction rich in oxygen (78) and the liquid phase (74) together with the stream (68) of the liquid rich in residual oxygen collected in the separation vessel (70); Y The oxygen product stream (80) is formed by discharging a stream of the oxygen-rich vapor fraction (78) from the separation vessel (70). 2. - The method according to claim 1, wherein the upper part (38) of the auxiliary column is produced only by bubbling the crude liquid oxygen stream (28) into an auxiliary distillation column (34 ). 5 10 fifteen twenty 25 30 35 40 Four. Five fifty 3. - The method according to claim 1, in which: the main distillation column (18) is refluxed with part (58) of the liquid nitrogen stream (50); the bubbling of the crude liquid oxygen stream (28) takes place within a bubbling section (36a) of an auxiliary distillation column (34 '); the bubbling of the crude liquid oxygen stream (28) into the auxiliary distillation column (34 ') produces a stream of vapor containing nitrogen and oxygen; Y the vapor stream containing nitrogen and oxygen is rectified within the auxiliary distillation column, inside a rectification section (36b) of the auxiliary distillation column (34 '), located above the bubbling section (36a), by introducing the steam stream containing nitrogen and oxygen into the rectification section (36b) and the reflux feed of the auxiliary distillation column (34 '), and, therefore, of the section of rectification, with an additional part of the liquid nitrogen stream (50), whereby the recovery of oxygen in the liquid rich in residual oxygen (56) is increased. 4. - The method according to claim 1, in which: the main distillation column (18) is refluxed with a part (58) of the liquid nitrogen stream (50); Y The waste stream (62) exchanges heat indirectly with the raw liquid oxygen stream (28), such that the raw liquid oxygen stream (28) is subcooled before being pressurized. 5. - The method according to claim 1, wherein the stream (68) of the liquid rich in residual oxygen (56) is pressurized, such that the stream of oxygen product (80) is also pressurized. 6. - The method according to claim 1, wherein a liquid nitrogen cooling stream (110) is introduced into the main distillation column (18) to impart refrigeration. 7. - An apparatus for separating air in order to produce concurrent oxygen and nitrogen products, such that said apparatus comprises: a main heat exchanger (12), configured to cool a compressed and purified stream (10) comprising the air; a condenser (14), located in a lower region (16) of a main distillation column (18), and configured to partially condense the compressed and purified current (10); such that the main distillation column (18) is configured to rectify the vapor fraction (22) of the compressed and purified stream, partially condensed, in order to produce an upper part of the nitrogen rich vapor column (23) , and so that the condensed air is mixed with the descending liquid produced by the rectification in the main distillation column (18), in order to thereby produce a lower portion of the crude liquid oxygen column (26); an auxiliary distillation column (34), connected to the main distillation column (18) and configured such that a stream of crude liquid oxygen (28), composed of the lower part of the liquid oxygen column, is bubbled in the rough (26), with an ascending bubble gas (52) located within the auxiliary distillation column (34), and an oxygen-rich liquid (40) and an upper part (38) of auxiliary column are produced containing not less than 5.0 percent oxygen by volume, at least in part as a result of the bubbling of the crude liquid oxygen column (28), the auxiliary distillation column (34) having means for collecting the oxygen-rich liquid ; an expansion valve (32), located between the main distillation column (18) and the auxiliary distillation column (34), such that the flow of crude liquid oxygen (28) is depressurized before being introduced into the auxiliary distillation column; means (48) for partially evaporating the oxygen-rich liquid (44) by indirect heat exchange with a stream of nitrogen-rich steam, composed of the upper part of the nitrogen-rich vapor column (23), whereby produces a stream of liquid nitrogen (50), bubbling gas (52) and a liquid rich in residual oxygen (56); such that the partial evaporation means (48) of the oxygen-rich liquid consist of a single-pass heat exchanger, connected to an auxiliary distillation column (34) and to the oxygen-rich liquid collection means, of such that the oxygen-rich liquid (40) is partially evaporated into the one-step heat exchanger (48) by the passage of a stream of oxygen-rich liquid, composed of the oxygen-rich liquid (40), and the liquid rich in residual oxygen (56) is collected as the lower part 12 5 10 fifteen twenty 25 30 35 40 Four. Five fifty column of the auxiliary distillation column (34); Y The main distillation column (18) is connected to the one-step heat exchanger (48), such that the nitrogen-rich vapor stream (46) condenses inside the single-step heat exchanger (48) and so that the main distillation column is refluxed with at least a portion (58) of the liquid nitrogen stream (50); The main heat exchanger (12) is connected to the main distillation column (18) and to the auxiliary distillation column (34) such that a stream of nitrogen product (64), composed of the top column of nitrogen-rich steam (23), and a waste stream (62) formed from the upper part (38) of the auxiliary column, belonging to the auxiliary distillation column (34), exchange heat indirectly with the compressed air stream and purified (10); means (70) for exchanging heat indirectly between a stream (68) of the liquid rich in residual oxygen (56) and a gaseous stream (76, 92) having a nitrogen concentration not less than that of the air, such that the stream (68) of the residual oxygen rich liquid (56) is partially evaporated, and means for forming a fraction of oxygen rich vapor (78) from the stream of the residual oxygen rich liquid, after being partially evaporated, of such that the gas stream (76) is the stream of compressed and purified air (10); in which: The heat exchange means with the residual oxygen rich liquid are the condenser (14), and the oxygen rich vapor fraction formation means are a separating vessel (70); The separation vessel (70) is connected to the auxiliary distillation column (34) such that the current (68) of the liquid rich in residual oxygen (56) is collected in the separation vessel (70); The separation vessel (70) is connected to the condenser (14) in such a way that a liquid phase current (72), composed of a liquid phase produced within the separation vessel, is partially evaporated in the condenser (14) to produce a two-phase stream (76) that is introduced into the separation vessel (70), such that the liquid and vapor phases of the two-phase stream are discharged into the separation vessel to form the fraction of oxygen-rich vapor (78) and the liquid phase (74); the main heat exchanger (12) is connected to the separating vessel (70) such that the oxygen product stream (80) is formed from the oxygen rich vapor fraction (78); Y The main heat exchanger (12) is connected to the means (70) for forming the oxygen-rich vapor fraction, the main distillation column (18) and the auxiliary distillation column (34), such that a stream of oxygen product (80), composed of the fraction of vapor rich in oxygen (78), a stream of nitrogen product (64), composed of the top of a column of vapor rich in nitrogen (23), and A waste stream (62), composed of the upper part (38) of the auxiliary column, belonging to the auxiliary distillation column (34), passes through the interior of the main heat exchanger (12), in indirect heat exchange with the compressed and purified stream (10). 8. - The apparatus according to claim 7, wherein the auxiliary column (34 ') is only provided with a bubbling section (36a) in which the bubbling of the crude liquid oxygen stream (28) takes place. ). 9. - The apparatus according to claim 7, in which: the auxiliary column (34 ') has a bubbling section (36a) and a rectifying section (36b), located above the bubbling section (36a); the bubbling of the crude liquid oxygen stream (28) takes place within the bubbling section (36a) of the auxiliary distillation column (34 '), and a vapor stream is produced in the bubbling section (36a) with nitrogen and oxygen content, which enters the rectification section (36b) for the rectification of the vapor stream with nitrogen and oxygen content, thereby increasing the recovery of oxygen within the residual oxygen-rich liquid (28); The partial vaporization means (48) of the oxygen-rich liquid are connected to the main distillation column (18) such that the main distillation column is refluxed with part (58) of the liquid nitrogen stream ( 50), and they are also connected to the auxiliary distillation column (34 ') such that the auxiliary distillation column and, therefore, the rectification section (36b) are refluxed with an additional part (60') of the liquid nitrogen stream (50); Y there is another expansion valve (63 '), located between the partial evaporation means (48) of the oxygen-rich liquid and the auxiliary distillation column (34'), such that the pressure of the additional part (60 ') of the liquid nitrogen stream (50) is reduced to that of the auxiliary distillation column (34 '). 10. - The apparatus according to claim 7, in which: The one-step heat exchanger (48) is connected to the main distillation column (18) such that the main distillation column is refluxed with part (58) of the liquid nitrogen stream (50) ; Y there is a subcooling heat exchanger (30), connected to the single step heat exchanger 5 (48), to the auxiliary distillation column (34) and to the expansion valve (32) such that the flow of waste (62) indirectly exchanges heat with the crude liquid oxygen stream (28) inside the subcooling heat exchanger (30), and the crude liquid oxygen stream (28) is subcooled before passing through the expansion valve (32). 11. The apparatus according to claim 7, wherein the main distillation column (18) has a top inlet (114) for the introduction of a liquid nitrogen cooling stream (110) intended to impart refrigeration.