BRPI1100194A2 - Method and mechanism for separating a mixture comprising nitrogen and oxygen - Google Patents

Abstract

METHOD AND MECHANISM TO SEPARATE A MIXTURE THAT UNDERSTAND NITROGEN AND OXYGEN. A method and mechanism for separating a mixture, for example, air, within a cryogenic grinding facility that uses a grouped heat exchanger arrangement. In such an arrangement, a lower pressure heat exchanger is used to cool part of the mixture and an upper pressure heat exchanger is used to heat one or more pumped liquid streams composed of separate nitrogen-rich and oxygen-rich fractions and, thereby producing pressurized product streams. A reinforced pressure stream, which can be part of the air, is used to supply most of the heat exchange performance in the upper pressure heat exchanger. In addition, a heat exchange stream, which can also be part of the mixture, can be partially cooled in the upper pressure heat exchanger and then further cooled in the lower pressure heat exchanger to decrease the temperature difference of the hot end of the higher pressure heat exchanger and therefore the cooling required for the installation.

Description

"METHOD AND MECHANISM TO SEPARATE A MIX UNDERSTANDING NITROGEN AND OXYGEN"

Field of the Invention

The present invention relates to a method and mechanism wherein a mixture comprising nitrogen and oxygen is separated into nitrogen-rich and oxygen-rich fractions by cryogenic rectification and one or more pressurized product streams are produced by pumping and heating a or more liquid streams composed of one of the nitrogen-rich or oxygen-rich product fractions. More particularly, the present invention relates to such a method and mechanism utilizing a pooled arrangement of heat exchangers wherein a heat exchange stream is partially cooled within the upper pressure heat exchanger used in heating one or more liquid streams pumped and then further cooled within the lower pressure heat exchanger to reduce the temperature difference of the hot end within the upper pressure heat exchanger and thus the amount of cooling required to be checked in connection with the rectification. cryogenic.

Background of the Invention

Mixtures containing nitrogen and oxygen, most commonly air, are separated into nitrogen-rich and oxygen-rich fractions and the component fractions found in air, for example argon, by cryogenic rectification. In cryogenic grinding, the mixture is compressed and then purified to remove higher boiling contaminants such as carbon dioxide, water vapor and hydrocarbons. The resulting compressed and purified stream is then cooled to a suitable distillation temperature. Distillation produces nitrogen-rich and oxygen-rich air fractions and potentially other fractions that can be taken as both liquid and gaseous products. There are different distillation column arrangements that are used for such purposes. For example, distillation columns may consist of an upper pressure column and a lower pressure column thermally connected by a heat exchanger to vaporize an oxygen-rich liquid from the bottom stream of the lower pressure column and to condense a nitrogen-rich vapor from the top column of the upper pressure column.

Where there is a demand for large amounts of high pressure oxygen in a gaseous form, for example in gasification, oxygen is often produced by pumping a stream of high oxygen pressure liquid and then a reinforced pressure stream that is typically part of the air to be distilled. In the column arrangement discussed above, the oxygen-rich liquid stream is composed of the oxygen-rich liquid of the upper pressure column bottom stream. Reinforced pressure air will be liquefied as a result of heat exchange and introduced into the upper pressure column, lower pressure column or split between columns after being reduced to a suitable pressure for introduction into such columns. In addition to oxygen, high pressure nitrogen may also be a desirable product, particularly in gasification applications. Such high pressure nitrogen can be produced by pumping a stream of condensed nitrogen rich vapor and heating the resulting liquid by heat exchange with the reinforced pressure stream.

It should be noted that the pumping currents may be heated in a grouped arrangement of heat exchangers having a higher pressure heat exchanger for pumped liquid heating and a lower pressure heat exchanger having a maximum available operating pressure. lower than the upper pressure heat exchanger for cooling at least part of the air. In this regard, although as discussed above, the reinforced pressure stream is commonly composed of air, other fluids may be used. For example, in US Patent No. 4,345,925, a fluid such as argon is compressed and then liquefied as a result of the indirect heat exchange that occurs in the upper pressure heat exchanger. The resulting liquid then serves in various heat exchange functions related to the distillation columns. In particular, fluid is vaporized and overheated in the lower pressure heat exchanger and then compressed again prior to its introduction into the upper pressure heat exchanger. Thus, the fluid circulates in a heat exchange circuit that involves heating the pressurized oxygen rich liquid.

An example of a cryogenic grinding plant in which air serves as the pressure boosting fluid can be seen in United States Patent Application, Publication No. 2008/0307828. In this order, the air is compressed and purified. Part of the resulting purified and compressed air is cooled into the lower pressure heat exchanger and then introduced into the upper pressure column as a main air stream. The upper pressure column is thermally connected to a lower pressure column by a condenser annealing boiler. The condenser annealing boiler condenses the nitrogen-rich steam from the top column of the upper pressure column as opposed to vaporization of the oxygen-rich liquid from the column bottom stream formed in the lower pressure column. Part of an oxygen-rich liquid stream composed of oxygen-rich liquid from the bottom column of the lower pressure column may be pumped to form a pumped liquid oxygen stream and part of the condensed nitrogen-rich steam may also be pumped to produce the pumped liquid nitrogen stream. The pumped liquid oxygen stream and the pumped nitrogen liquid stream are then heated in a higher pressure heat exchanger by indirect heat exchange with the reinforced pressure stream which is formed by compressing another part of the purified compressed air. in a booster compressor. The reinforced current is liquefied, expanded and introduced into the upper and lower pressure columns. A thermal equilibrium current composed of a residual nitrogen stream produced in the lower pressure column is introduced into both the lower pressure heat exchanger and the upper pressure heat exchanger to inhibit the final hot cooling losses by such heat exchangers and also to decrease the difference in temperatures between the reinforced pressure stream and the main air stream at the cold ends of such heat exchangers.

In any cryogenic grinding installation, cooling should be provided for such reasons as hot final losses in heat exchangers, heat leakage in the installation and to produce liquids. In the upper pressure heat exchanger, the magnitude of the temperature difference of the hot end between the reinforced current being cooled versus the vaporized liquid stream or currents being heated represents a loss of such cooling. In order to overcome such loss of cooling, more cooling must be introduced into the installation. In the published patent application discussed above, this refrigeration can be produced by introducing a further portion of the purified compressed air into a booster compressor which partially cools such air into the upper and lower pressure heat exchanger and then by introducing the partially cooled stream in a turbodilator to generate cooling in a discharge stream that can be fed into the upper or lower pressure column. The greater the degree of cooling that is required for an installation, the greater the energy that will be expanded in the associated booster compressor. Since total energy expenditure is an important consideration in the cost of production in a cryogenic rectification facility, it is desirable to minimize the energy requirements for the facility. As will be discussed, among other advantages, the present invention provides a method and a cryogenic grinding installation for conducting such a method wherein the hot end temperature differences produced in the upper pressure heat exchanger are reduced to decrease the requirements. and therefore the costs involved in operating the facility.

Summary of the Invention

The present invention, in one aspect, provides a method for separating a mixture comprising nitrogen and oxygen. In accordance with this aspect of the present invention, a cryogenic rectification process is conducted which comprises compression, purification, cooling and distillation of the oxygen mixture with nitrogen-rich and oxygen-rich fractions which provides cooling in the cryogenic rectification process and which produces at least one pressurized product stream by pumping and heating at least part of one of the nitrogen-rich and oxygen-rich fractions in a liquid state.

The cryogenic rectification process is conducted to produce a reinforced pressure current and heat exchange current and the cryogenic rectification process utilizes a grouped heat exchanger arrangement having a lower pressure heat exchanger for cooling the hair. less part of the mixture and a higher pressure heat exchanger for heating at least part of one of the nitrogen rich and oxygen rich fractions. Reinforced pressure current and heat exchange current are introduced into the upper pressure heat exchanger in indirect heat exchange with at least part of one of the oxygen-rich and nitrogen-rich fractions. The heat exchange current is partially cooled in the upper pressure heat exchanger, thereby decreasing a temperature difference of the hot end within the upper pressure heat exchanger and thus the cooling required to be imparted to the cryogenic rectification process. The reinforced pressure current is cooled within the upper pressure heat exchanger and the heat exchange current is further cooled in the lower pressure heat exchanger.

Reducing the temperature difference of the hot end within the upper pressure heat exchanger reduces cooling losses to in turn decrease the amount of cooling that is required for the cryogenic grinding process. Reducing the need for cooling translates into a reduction in the energy consumption of the facility due to lower compression needs to generate cooling in the first place. As used herein and in the claims, the term "partially cooled" means cooled to an intermediate temperature the temperatures that can be reached at the hot and cold ends of a heat exchanger. The term "fully cooled" as used herein and in the claims means cooled to a cold end temperature of a heat exchanger and "fully heated" means heated to a hot end temperature of the heat exchanger.

The cryogenic rectification process can generate a nitrogen-rich vapor stream that is divided into two nitrogen-rich steam streams that are completely heated within the upper pressure heat exchanger and the lower pressure heat exchanger to balance the hot end temperatures of the upper pressure heat exchanger and the lower pressure heat exchanger. The mixture may be air and in such a case, a composite air supply stream, after being compressed and purified, is divided into a first subsidiary compressed air stream; a second subsidiary compressed air stream and a third subsidiary compressed air stream. The first subsidiary compressed air stream is completely cooled within the lower pressure heat exchanger, at least part of the second subsidiary compressed air stream is further compressed to form the reinforced pressure stream forming a liquid air stream after it has been completely cooled. cooled within the upper pressure heat exchanger and the heat exchange current is the third subsidiary compressed air stream. A first part of the second subsidiary compressed air stream may be further compressed to produce the reinforced pressure air stream and a second part of the third subsidiary compressed air stream may be further compressed to a pressure below that of the reinforced pressure air stream. and is therefore further compressed, partially cooled into the upper pressure heat exchanger and introduced into a turbodilator to produce the discharge current. The discharge stream is introduced into the distillation column to provide at least part of the cooling in the cryogenic rectification process.

In a specific embodiment of the present invention, the mixture is distilled into an upper pressure column operatively associated in a heat transfer connection with a lower pressure column by an annealing condenser-boiler configured to condense a top current of the upper pressure nitrogen-rich column removed from the upper pressure column by re-boiling a bottom stream of the lower-pressure oxygen-rich liquid column. The first subsidiary compressed air stream and the third subsidiary compressed air stream, after being completely cooled, are introduced into the upper pressure column. The liquid air stream is expanded and fed into at least one of the upper pressure column and the lower pressure column. A gross liquid oxygen stream composed of a bottom column of the upper pressure column bottom stream is subcooled, reduced in pressure to that of the lower pressure column, and introduced into the lower pressure column for further refinement. The first and second parts of a higher pressure nitrogen rich liquid stream formed from the condensation of the upper pressure nitrogen rich column top stream are used for reflux of the upper pressure column and the lower pressure column. respectively. The second of the upper pressure nitrogen-rich liquid stream parts is subcooled, reduced in pressure to that of the lower pressure column before being introduced as reflux within the lower pressure column and the raw liquid oxygen stream and the second. parts of the low pressure nitrogen rich liquid stream are subcooled by indirect heat exchange with a lower pressure nitrogen rich column top stream withdrawn from the lower pressure column. The at least one liquid stream is one of an oxygen enriched stream, composed of the oxygen rich liquid column of the lower pressure column bottom stream and a third part of the upper pressure nitrogen rich liquid stream.

The lower pressure nitrogen-rich column top stream can be divided into the two nitrogen-rich steam streams that are used to balance the cold end temperatures of the upper pressure heat exchanger and the lower pressure heat exchanger. The discharge stream is introduced into the upper pressure column and the liquid air stream is expanded into a liquid dilator.

In another aspect, the present invention provides a mechanism for separating a mixture comprising nitrogen and oxygen. In accordance with this aspect of the present invention, the mechanism comprises a cryogenic grinding plant configured to compress, purify, cool and distill the mixture into nitrogen-rich and oxygen-rich fractions. The cryogenic rectifying plant has at least one pump for pumping at least part of a liquid stream composed of one of the nitrogen-rich and oxygen-rich fractions in the liquid state and a grouped heat exchanger arrangement having the heat exchanger of. lower pressure configured to cool at least part of the mixture and an upper pressure heat exchanger in flow communication with the at least one pump for heating at least part of the liquid stream and thereby producing a pressurized product stream. Additionally, a medium is provided for the production of a reinforced pressure stream, a medium is provided for the production of a heat exchange current, and a medium is provided for providing cooling in the cryogenic rectifying facility. The upper pressure heat exchanger is connected to the reinforced pressure current that produces the medium and the heat exchange current that produced the medium and is configured to partially cool the heat exchange current by indirectly changing the heat of the exchange current. with at least part of the liquid stream, thereby decreasing a temperature difference of the hot end within the upper pressure heat exchanger and thus the required cooling to be granted to the cryogenic rectifying facility and to cool the pressure stream. indirectly by indirectly exchanging the heat of the reinforced pressure stream with at least part of the liquid stream. The lower pressure heat exchanger is connected with the upper pressure heat exchanger and is configured to still cool the heat exchange current after it has been partially cooled within the upper pressure heat exchanger.

The cryogenic rectifying facility can also be configured to generate two nitrogen-rich steam streams and the upper pressure heat exchanger and lower pressure heat exchanger are also configured to receive and completely heat the two nitrogen-rich steam streams. nitrogen so that the cold end temperatures of the upper pressure heat exchanger and the lower pressure heat exchanger are balanced. The mixture may be air and in such a case the cryogenic rectifying plant has a main air compressor and a pre-purification unit connected to the main air compressor to purify the air after it has been compressed. The reinforced pressure producing means comprises a booster compressor connected to the pre-purification unit and the lower pressure heat exchanger is also connected to the pre-purification unit such that a feed stream composed of the mixture after it has been compressed into the pre-purification unit. Main and purified air compressor in the pre-purification unit is divided into a first subsidiary compressed air stream which is completely cooled in the upper pressure heat exchanger and a second subsidiary compressed air stream which at least in part is further compressed in the booster compressor to form the reinforced pressure stream and forming a liquid air stream after it has been completely cooled within the upper pressure heat exchanger. The heat exchange stream producing means comprises the upper pressure heat exchanger also connected to the pre-purification unit so that the feed stream after being compressed and purified is further divided into a third subsidiary compressed air stream which forms the heat exchange current. The booster compressor can be a multistage machine. A first part of the second subsidiary compressed air stream is discharged from a final stage of the booster compressor and forms the reinforced pressure air stream. The cooling granting means, at least in part, comprises another booster compressor connected to an intermediate stage of the booster compressor to further compress a second portion of the second subsidiary compressed air stream. The upper pressure heat exchanger is connected to the other booster compressor so that the second portion of the third subsidiary compressed air stream, after being further compressed, is partially cooled within the upper pressure heat exchanger and a turbodilator is connected to the heat exchanger. of higher pressure heat to expand the first part of the second subsidiary compressed air stream and thereby produce a discharge stream. The turbodilator is connected to the distillation column so that the discharge current is introduced into the distillation column.

The cryogenic grinding plant may have an upper pressure column and a lower pressure column to distill the mixture. The upper pressure column is operatively associated in a heat transfer connection to the lower pressure column by an annealing condenser-boiler. at least part of an upper pressure nitrogen rich column top stream discharged from the upper pressure column is condensed by re-boiling an oxygen rich liquid column from the lower pressure column bottom stream. The lower pressure heat exchanger is connected to the upper pressure column so that the first subsidiary compressed air stream and the second subsidiary compressed air stream are introduced into the upper pressure column. The upper pressure heat exchanger is in flow communication with at least one of the upper pressure column and the lower pressure column so that the liquid air stream is fed into at least one of the upper pressure column and the pressure column. lower pressure. An expansion device is positioned between the upper pressure heat exchanger and at least one of the upper pressure column and the lower pressure column to dilate the flow of liquid air. The upper pressure column is connected to the lower pressure column such that a gross liquid oxygen stream composed of the upper pressure liquid bottom column of the upper pressure column is introduced into the lower pressure column to be further refined and The first and second parts of a higher pressure nitrogen rich liquid stream formed from the condensation of the upper pressure nitrogen rich top stream are introduced into the upper pressure column and the lower pressure column respectively as reflux. A subcooler, positioned between the lower pressure column and the lower pressure heat exchanger, or incorporated into the lower pressure heat exchanger, is configured to subcool the raw liquid oxygen stream and the second of the liquid-rich stream parts. higher pressure nitrogen. Expansion valves are located between the subcooler and the lower pressure column to dilate the raw liquid oxygen stream and the second of the upper pressure nitrogen rich liquid stream portions prior to their introduction into the lower pressure column. The sub-cooler is connected to the lower pressure column so that a lower pressure nitrogen-rich column top current discharged from the lower pressure column passes indirect heat with the raw liquid oxygen stream and the second of the parts of the stream. of higher pressure nitrogen-rich liquid and at least one liquid stream is an oxygen-rich stream, composed of the oxygen-rich liquid column of the lower-pressure column column bottom stream or a third part of the liquid stream high pressure nitrogen rich.

The upper pressure heat exchanger and the lower pressure heat exchanger can be connected to the sub-cooler so that the lower pressure nitrogen rich column top stream divides into the two nitrogen rich steam streams that are used to balance the cold end temperatures of the upper pressure heat exchanger and the lower pressure heat exchanger. Still the turbodilator is connected to the upper pressure column so that the discharge current is introduced into the upper pressure column and the expansion device is a liquid dilator.

Brief Description of Drawing

While the specification is clear from the claims clearly showing the subject matter which the applicant considers with his invention, it is believed that the invention will be better understood when taken in connection with the accompanying single figure illustrating a mechanism for making a method according to the present invention.

Detailed Description

Referring to Figure 1, a cryogenic grinding plant 1 according to the present invention is illustrated which is designed to cryogenically grind air or other mixture containing nitrogen and oxygen into nitrogen and oxygen fractions as discussed below. For example, the feed for a cryogenic grinding facility of the present invention may be derived from another air separation facility and as such, the feed may be richer in oxygen at a concentration that is higher than air. Furthermore, while the present invention is illustrated in connection with a double column system having an upper pressure column operatively associated with a lower pressure column in a heat transfer connection by virtue of an annealing condenser-boiler to condense a Nitrogen-rich vapor column top stream in the upper pressure column against vaporization of an oxygen-rich liquid column from the lower pressure column bottom stream, the invention is not limited to such a column arrangement. In this regard, the present invention has application to any cryogenic grinding plant employing a pooled arrangement of heat exchangers in which a stream of liquid enriched in a separate composition, typically nitrogen and oxygen, is pumped and then heated in a heat exchanger. of higher pressure heat to form a pressurized product as a high pressure vapor or as a supercritical fluid.

A supply air stream 10 is compressed into a main compressor 12. After removal of heat from the compression by a first post cooler 14, the supply air stream 10 is purified within a pre-purification unit 16 to produce It is appropriate to point out that although post-cooler 14 is shown as a separate unit, such compressors as main compressor 12 may be multi-stage machines with intermediate coolers and a post-cooler installed by the compressor. manufacturer as part of the compressor. As such, the aftercooler may not be a separate unit as illustrated and may instead be part of the compressor itself. The foregoing comments should also apply to any of the above discussed compressor and aftercooler arrangements. The pre-purification unit may contain adsorbent beds, for example, alumina or carbon molecular sieve adsorbent to adsorb the high boiling impurities contained in the air and therefore the feed air stream 10. For example, such Also known high boiling impurities should include water vapor and carbon dioxide which will freeze and accumulate at the low rectification temperatures contemplated by mechanism 1. In addition, hydrocarbons may also be adsorbed which may accumulate within oxygen rich liquids. and thereby present a safety hazard.

A first subsidiary compressed air stream 18 is produced from a first part of the purified compressed air stream 17. A booster compressor 20 is in flow communication with the purification unit 16 to compress a second subsidiary compressed air stream 22. formed from a second part of the purified compressed air stream 17 and a second aftercooler 23 is provided which is connected to the booster compressor 20 to remove the compressor heat from the second subsidiary compressed air stream 22 after it has been further compressed. This forms a reinforced pressure stream 24 having a higher pressure than the first subsidiary compressed air stream 18. It should be noted that the main air compressor 10 and the reinforcing compressor 20 are shown as isolated units. However, as is known in the art, two or more compressors may be installed in parallel to form the main air compressor 10 or the booster compressor 20. The two compressors may be of equal size or unequal size. For example, capacity can be split 70/30 or 60/40 to better meet customer demand. Typically, the second subsidiary compressed air stream 22 will have a flow ranging from about 25 percent to about 40 percent of the compressed air stream flow 17.

An upper pressure heat exchanger 26 is connected to the second post coolers 23 and 101 and a lower pressure heat exchanger 28 is in flow communication with the purification unit 16 to receive the first subsidiary compressed air stream 18. Both the upper pressure heat exchanger 26 and the lower pressure heat exchanger 28 are preferably of welded aluminum construction and consist of layers of separating blades separated by side bars to produce flow passages for the currents to be heated and cooled. Each of the flow passages is provided with stabilizers also known in the art for enhancing the surface area with respect to heat transfer within said heat exchangers. The upper pressure heat exchanger 26 is so named due to the fact that it has a higher maximum allowable operating pressure compared to the lower pressure heat exchanger 28. The upper pressure heat exchanger 26 is set to completely cooling the reinforced pressure stream 24 to produce a liquid air stream 30 and the lower pressure heat exchanger 28 is configured to completely cool the first subsidiary compressed air stream 18 to produce a main feed air stream 32. How can Note, other types of heat exchangers may be used, for example, the upper pressure heat exchanger 26 may be spiral, printed circuit or stainless steel plate stabilized construction. Furthermore, although each of the upper pressure heat exchanger and lower pressure heat exchanger 28 is illustrated as isolated units, in practice each may consist of several heat exchangers connected in parallel.

The lower pressure heat exchanger 28 will have a larger cross-sectional area for flow and a larger total volume than the upper pressure heat exchanger 26. Typically the average density of the upper pressure heat exchanger 26 will be greater than lower pressure heat exchanger 28 where density is empty weight divided by volume. A typical density is around 1000 kg / m3. A typical operating pressure of upper pressure heat exchanger 26 is around 1200 psig (8.3 MPa) and higher.

An air separation unit 34 is provided which has an upper pressure column 36 operatively associated with a lower pressure column 38 in a heat transfer connection via an annealing condenser-boiler 50. Optionally the Air separation 34 may also include an argon column that is connected to the lower pressure column 38 to produce an argon product. It is understood that each of the upper pressure column 36 and the lower pressure column 38 contains liquid-vapor mass transfer elements such as perforated plates or packages, random or structured. Such elements also known in the art enhance liquid-vapor contact of the liquid-vapor phases of the mixture to be separated in each of such columns for the purpose of rectification. Air rectification within such distillation columns yields nitrogen-rich and oxygen-rich fractions of air such as the nitrogen-rich column of the upper pressure column top stream 36 and a nitrogen-rich column of the column top flow current. lower pressure 38 in the course of a lower pressure than the nitrogen-rich vapor produced in the upper pressure column 36 and an oxygen-rich liquid as a bottom stream liquid column of the lower pressure column 38. How will be discussed , the streams of these fractions can be directly taken as products or condensed and / or pressurized and heated to form products of the cryogenic grinding plant 1.

The liquid air stream 30 is expanded to a pressure suitable for its introduction into the upper pressure column 36 by means of a liquid turbodilator 40. The energy of liquid turbodilator 40 can be recovered and thus the liquid turbodilator can generate Part of the cooling requirements for cryogenic rectification installation 1. Alternatively, an expansion valve may be used (or a combination of both). After being dilated, the liquid air stream 30 is divided into a first subsidiary expanded stream 42 and a second subsidiary expanded stream 44. The second subsidiary expanded stream 44 is expanded by an expansion valve 46 at a pressure suitable for its introduction in. lower pressure column 38 as another expanded stream 47. Thus, both the first and second subsidiary expanded streams 42 and 44 are introduced at intermediate locations of the upper and lower pressure columns 36 and 38, respectively at their points which should equal the composition of the mixture being separated into the columns. It is understood, however, that embodiments of the present invention are possible wherein the liquid air stream 30 is introduced into the upper pressure column 36 or lower pressure column 38.

Air rectification within the upper pressure column 36 produces a raw liquid oxygen column bottom stream and a nitrogen rich vapor column top stream. Part of a nitrogen-rich steam column top stream 48 is condensed in the annealing boiler condenser 50 in the opposite direction of vaporization of an oxygen-rich column bottom stream that is produced by the rectification that occurs in the lower pressure column. . In this regard, such rectification also produces within the lower pressure column 38 a nitrogen-rich vapor column top stream. The resulting condensation produces a nitrogen-rich liquid stream 52. The first part 54 of the nitrogen-rich liquid stream 52 is returned to the upper pressure column 36 as reflux. A second part 56 is subcooled within the subcooling unit 29 which as shown is an integral part of the lower pressure heat exchanger 28 by providing adequate passages therein. However, as should be known to those skilled in the art, the subcooling unit 29 may in fact be a separate heat exchanger or separate parallel heat exchangers. The resulting subcooled liquid nitrogen stream 58 is further optionally further subdivided into parts 60 and 62. Part 60 of the subcooled liquid nitrogen stream 58 is then expanded into an expansion valve 64 to a pressure suitable for its introduction into the column. lower pressure 38 and then introduced into the lower pressure column 38 as reflux. Part 62 of the subcooled liquid nitrogen stream 58 may be taken as an optional liquid product. Distillation of air produces a raw liquid oxygen column bottom stream, also known in the art as boiler liquid, in the upper pressure column 36. A raw liquid oxygen stream 58 composed of the raw liquid oxygen column bottom stream It is also subcooled within the subcooling unit 29 incorporated into the lower pressure heat exchanger 28 and then expanded into an expansion valve 68 to be introduced into the lower pressure column 38 for further refinement.

A nitrogen rich vapor stream 70 may be removed from the lower pressure column top stream 38 which consists of the low pressure nitrogen rich vapor column top stream produced as a result of the swelling occurring within the pressure column. Although not illustrated, as is known in the art, a residual nitrogen stream may also be removed below the top stream of the lower pressure column 38 so as to maintain the purity of the nitrogen rich steam stream 70 if it is. required in a resulting product. Since this was not done in the illustrated embodiment, the nitrogen rich vapor stream 70 is not of typical product purity where it is contaminated with higher amounts of oxygen than a nitrogen product stream. The nitrogen rich vapor stream 70 is then subdivided into two subsidiary nitrogen rich steam streams 71 and 72. The subsidiary nitrogen rich vapor stream 71 is partially heated in the lower pressure heat exchanger subcooling unit part 28. to subcool the second part 56 of the nitrogen-rich liquid stream 56 and the raw liquid oxygen stream 58. The subsidiary nitrogen-rich steam stream 71 is then completely heated within the lower pressure heat exchanger 28 to form a residual nitrogen stream 73. As illustrated, residual nitrogen stream 73 can be used to regenerate adsorbent beds within the pre-purification unit 16 in a manner known in the art. The subsidiary nitrogen-rich vapor stream is completely heated in the upper pressure heat exchanger to form residual nitrogen stream 74. The flow rates of these currents are selected to balance the temperature difference of the cold end of the pressure heat exchanger. 26 and lower pressure heat exchanger 28. In this regard, if the temperature of the liquid air stream 30 is too high, the liquid produced by the liquid turbodilator 40 after expansion in column pressure will produce a lot of steam and as a result , the desired distillation will not occur within the distillation columns.

An oxygen-rich liquid stream 75, composed of the oxygen-rich liquid column of the lower pressure column bottom stream 38, may be removed from the lower pressure column 38. A first part 76 of the oxygen-rich liquid stream 75 may be pressurized by a pump 78 to produce a pumped liquid oxygen stream 80. A second part 82 of the oxygen rich liquid stream 75 may optionally be taken as a product. Pumped liquid oxygen stream 80, two nitrogen-rich vapor streams 71 and 72, and as will be discussed, the second subsidiary nitrogen vapor stream 84 and pumped liquid nitrogen stream 92 constitute the return currents of the air separation 34 which are used to cool the incoming air within the upper pressure heat exchanger 26 and the lower pressure heat exchanger 28. As illustrated, optionally the nitrogen rich vapor stream 48 may be split first and second subsidiary nitrogen vapor stream 82 and 84. The first subsidiary nitrogen vapor stream 82 is introduced into an annealing condenser-boiler 50 and the second subsidiary nitrogen vapor stream 84 is fully heated within the pressure heat exchanger. 28 and forms a nitrogen product stream 86. A third part 88 of the nitrogen rich liquid stream 52 may optionally be pumped into a pump 90 to produce a pumped liquid nitrogen stream 92 which is completely heated within the upper pressure heat exchanger 26 to produce a pressurized nitrogen product stream 94. It should be noted that if pressurized nitrogen products If desired at different pressures, the pumped liquid nitrogen stream 92 can be subdivided and pumped at the different pressures. The pumped liquid oxygen stream 80 is similarly completely heated within the upper pressure heat exchanger 26 to produce a pressurized oxygen product stream 96.

As is well known in the art, any cryogenic rectifying plant should be refrigerated for such reasons as overcoming hot end heat exchange losses, heat leakage in the cold box containing the distillation columns and taking into account the production of liquid products. In the cryogenic grinding plant 1, a part 98 of the second subsidiary compressed air stream 22 is extracted from an intermediate stage of the booster compressor 20 and then further compressed into a reinforcing compressor 100. The part 98 of the second subsidiary compressed air stream 22 will typically be between about 5 percent and about 20 percent of the purified compressed air flow being discharged from the pre-purification unit 16. After removal of the heat from compression in a post-cooler 101, such current is partially cooled within the upper pressure heat exchanger 26 to produce a partially cooled current 103 which is introduced into a turbodilator 14 to produce a discharge current 105 which is introduced into the upper pressure column 36 to provide the required cooling in the power plant. cryogenic rectification 1. As should be known in the art, this is only an option for to provide cooling within a cryogenic rectification facility. For example, depending on the desired manufactured product, the discharge stream may be introduced into the lower pressure column 38 or a residual nitrogen stream may be expanded.

As indicated above, the reinforced pressure stream 24 is fully cooled within the upper pressure heat exchanger 26. That said, embodiments are possible where the reinforced pressure stream 24 is removed before the cold end of the heat exchanger. higher pressure 26 and as such has a warmer temperature. In any case, the purpose of the reinforced pressure stream 24 is to provide the major part of the heat transfer rate in heating the pumped liquid oxygen stream 80 and pumped liquid nitrogen stream 92 in producing the pressurized nitrogen product stream 94. and pressurized oxygen stream 96. In this regard, both pumped oxygen and liquid nitrogen streams 80 and 92 may be pressurized to supercritical pressure and upon heating to supercritical temperatures, the resulting pressurized product nitrogen stream 94 and the Pressurized production oxygen stream 96 must be supplied as supercritical fluids. However, the present invention also contemplates that such fluids must be pressurized to supercritical pressures and as such must be vaporized after heating to be supplied as high pressure vapor streams. It should be noted that instead of the reinforced pressure stream 24 being derived from air, other fluids may be used such as argon as shown in US Patent No. 4,345,925, discussed above, wherein the reinforced pressure stream circulates in a circuit. heat exchange closed.

In all cases, however, there is a loss of cooling relative to such reinforced pressure currents having a magnitude that increases with the temperature difference of the hot end. The temperature difference of the hot end in the case of the upper pressure heat exchanger 26 is the difference, as measured at its hot end, between the average temperature of the currents being cooled, ie reinforced pressure current 24 and part 98 of second subsidiary compressed air stream 22 and the average temperature of the currents being heated, that is, pumped oxygen and liquid nitrogen streams 94 and 96 and the subsidiary nitrogen rich vapor stream 72. The greater the degree of such temperature difference of the hot end, the greater the amount of cooling that will be required. Practically, in the case of cryogenic rectification installation 1, the greatest need for refrigeration must be provided by the booster compressor 100 and therefore a higher energy consumption by such compressor. In order to decrease the temperature difference of the hot end, the required degree of cooling and therefore the energy consumption, a third subsidiary compressed air stream 106 is produced from the compressed and purified air stream part 17. Such a stream serves as a heat exchange stream which is partially cooled within the upper pressure heat exchanger 26 and then further cooled within the lower pressure heat exchanger 108 which may be combined with the first subsidiary compressed air stream 18 within the heat exchanger. lower pressure heat 28. The combination of the two currents cannot necessarily be performed within the heat exchanger. They can proceed separately to the lower column. The resulting combined stream 110 may be further combined with the discharge stream 105 and fed into the upper pressure column as a stream 112.

As may be known, there are other possibilities for the formation of such a heat exchange current. For example, a portion of the residual nitrogen stream 73 may be compressed and then partially cooled within the upper pressure heat exchanger 26 instead of the illustrated heat exchange stream 106. Such a stream may then be further cooled within the heat exchanger. pressure 28 and then introduced at an intermediate location of the upper pressure column 36.

The following table is a summary of current derived from a calculated example of the operation of the cryogenic rectifying plant 1.

Table

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As would be appreciated by those skilled in the art, although the present invention has been discussed with respect to a preferred embodiment, numerous changes, addition and omissions to such embodiment may be made in accordance with the spirit and scope of the present invention as set forth. in the attached claims.

Claims (12)

Method for separating a mixture comprising nitrogen and oxygen, comprising: conducting a cryogenic rectification process comprising: compression, purification, cooling and distillation of the oxygen mixture with nitrogen rich and oxygen rich fractions , which provides cooling in the cryogenic rectification process and which produces at least one pressurized product stream by pumping and heating at least part of one of the nitrogen-rich and oxygen-rich fractions in a liquid state; the cryogenic rectification process being conducted to produce a reinforced pressure current and a heat exchange current and the cryogenic rectification process utilizing a grouped heat exchanger arrangement having a lower pressure heat exchanger for the cooling of at least part of the mixture and a higher pressure heat exchanger for heating at least part of one of the nitrogen-rich and oxygen-rich fractions after pumping; introducing the reinforced pressure current and the heat exchange current in the upper pressure heat exchanger into indirect heat exchange with at least part of one of the nitrogen rich and oxygen rich fractions; partially cooling the heat exchange current in the upper pressure heat exchanger, thereby decreasing a temperature difference of the hot end within the upper pressure heat exchanger and thus the cooling required to be imparted to the cryogenic rectification process; cooling of the reinforced pressure stream within the upper pressure heat exchanger; and further cooling of the heat exchange current in the lower pressure heat exchanger after it has been partially cooled in the upper pressure heat exchanger. Method according to claim 1, characterized in that the cryogenic rectification process generates a nitrogen-rich vapor stream which is divided into two nitrogen-rich vapor streams which are completely heated within the pressure heat exchanger. upper and lower pressure heat exchanger to balance the cold end temperatures of the upper pressure heat exchanger and the lower pressure heat exchanger. Method according to claim 1 or claim 2, characterized in that: the mixture is air; a composite air supply stream after it has been compressed and purified is divided into a first subsidiary compressed air stream; a second subsidiary compressed air stream and a third subsidiary compressed air stream; the first subsidiary compressed air stream is completely cooled within the lower pressure heat exchanger; at least part of the second subsidiary compressed air stream is further compressed to form the reinforced pressure stream and forms a liquid air stream after it has been completely cooled within the upper pressure heat exchanger; and the heat exchange stream is the third subsidiary compressed air stream. Method according to claim 3, characterized in that: a first part of the second subsidiary compressed air stream is further compressed to produce the reinforced pressure air stream; a second portion of the third subsidiary compressed air stream is further compressed to a pressure below that of the reinforced pressure air stream and is therefore further compressed, partially cooled into the upper pressure heat exchanger and introduced into a turbodilator to produce a discharge current; The discharge stream is introduced into the distillation column to provide at least part of the cooling in the cryogenic rectification process. Method according to claim 4, characterized in that: the mixture is distilled into an upper pressure column operatively associated in a heat transfer connection with a lower pressure column by an annealing condenser-boiler configured to condensing an upper-pressure nitrogen-rich column top stream removed from the upper-pressure column by re-boiling an oxygen-rich liquid column from the lower-pressure column bottom stream; the first subsidiary compressed air stream and the third subsidiary compressed air stream, after being completely cooled, are introduced into the upper pressure column; the liquid air stream is expanded and fed into at least one of the upper pressure column and the lower pressure column; a gross liquid oxygen stream composed of one bottom column liquid stream from the upper pressure column is subcooled, reduced in pressure to that of the lower pressure column and introduced into the lower pressure column for further refinement; The first and second parts of a higher pressure nitrogen-rich liquid stream formed from the condensation of the upper pressure nitrogen-rich column top stream are used for reflux of the upper pressure column and the lower pressure column. respectively; the second part of the upper pressure nitrogen-rich liquid stream is subcooled, reduced in pressure to that of the lower pressure column before being introduced as reflux within the lower pressure column; the raw liquid oxygen stream and the second of the upper pressure nitrogen-rich liquid stream parts are subcooled by indirect heat exchange with a lower pressure nitrogen-rich column top stream withdrawn from the lower pressure column; at least one liquid stream is that of an oxygen enriched stream composed of the oxygen rich liquid column of the lower pressure column bottom stream and a third part of the upper pressure nitrogen rich liquid stream. Method according to claim 5, characterized in that: the top stream of the lower pressure nitrogen-rich column is divided into the two nitrogen-rich steam streams which are used to balance the cold end temperatures of the exchanger. upper pressure heat exchanger and lower pressure heat exchanger; the discharge current is introduced into the upper pressure column; and the liquid air stream is expanded into a liquid dilator. 7. Mechanism for separating a mixture comprising nitrogen and oxygen, characterized in that it comprises: a cryogenic grinding plant configured to compress, purify, cool and distill the mixture into nitrogen-rich and oxygen-rich fractions; the cryogenic rectifying plant having at least one pump for pumping at least part of a liquid stream composed of one of the nitrogen-rich and oxygen-rich fractions in the liquid state, a grouped heat exchanger arrangement having the heat exchanger of lower pressure configured to cool at least part of the mixture and a higher pressure heat exchanger in flow communication with the at least one pump for heating at least part of the liquid stream and thereby producing a pressurized product stream, medium for producing a reinforced pressure stream, means for producing a heat exchange stream, and means for providing cooling in the cryogenic rectification facility; the upper pressure heat exchanger connected to the reinforced pressure stream producing the medium and the heat exchange stream that produced the medium and configured to partially cool the heat exchange stream by indirectly exchanging heat from the heat exchange stream with at least part of the liquid stream, thereby decreasing a temperature difference of the hot end within the upper pressure heat exchanger and thus the required cooling to be granted to the cryogenic rectifying facility and to cool the pressure stream reinforced by indirectly exchanging the heat of the reinforced pressure stream with at least part of the liquid stream; and the lower pressure heat exchanger connected with the upper pressure heat exchanger and configured to further cool the heat exchange current after it has been partially cooled within the upper pressure heat exchanger. Mechanism according to Claim 7, characterized in that the cryogenic rectifying plant is also configured to generate two nitrogen-rich steam streams and the upper pressure heat exchanger and the lower pressure heat exchanger are also provided. configured to receive and completely heat the two nitrogen-rich steam streams so that the cold end temperatures of the upper pressure heat exchanger and the lower pressure heat exchanger are balanced. Mechanism according to Claim 8, characterized in that: the mixture is air; the cryogenic rectification facility has a main air compressor and a pre-purification unit connected to the main air compressor to purify air after it has been compressed; the reinforced pressure stream production means comprises a reinforcing compressor connected to the pre-purification unit; the lower pressure heat exchanger is also connected to the pre-purification unit so that a feed stream composed of the mixture after it has been compressed in the main air compressor and purified in the pre-purification unit is divided into a first supply stream. subsidiary compressed air which is completely cooled in the upper pressure heat exchanger and a second subsidiary compressed air stream which at least in part is further compressed in the reinforcing compressor to form the reinforced pressure stream and which forms a liquid air stream after having been completely cooled within the upper pressure heat exchanger; and the heat exchange stream producing means comprises the upper pressure heat exchanger also connected to the pre-purification unit so that the feed stream after being compressed and purified is further divided into a third subsidiary compressed air stream. forming the heat exchange current. Mechanism according to Claim 9, characterized in that: the booster compressor is a multistage machine; a first part of the second subsidiary compressed air stream is discharged from an end stage of the booster compressor and forms the reinforced pressure air stream; and the cooling medium at least in part comprises another booster compressor connected to an intermediate stage of the booster compressor to further compress a second portion of the second subsidiary compressed air stream, the upper pressure heat exchanger connected to the other. booster compressor so that the second part of the third subsidiary compressed air stream, after being further compressed, is partially cooled within the upper pressure heat exchanger, a turbodilator connected to the upper pressure heat exchanger to dilate the first part of the second subsidiary compressed air stream and thus produce a discharge stream and the turbodilator connected to the distillation column so that the discharge stream is introduced into the distillation column. Mechanism according to Claim 10, characterized in that: the cryogenic rectifying plant has an upper pressure column and a lower pressure column for distilling the mixture, the upper pressure column operatively associated with the pressure column. in a heat transfer connection by an annealing condenser-boiler configured to condense at least part of a higher pressure nitrogen-rich column top stream discharged from the upper pressure column by re-boiling a oxygen-rich liquid from the bottom stream of the lower pressure column; the lower pressure heat exchanger is connected to the upper pressure column so that the first subsidiary compressed air stream and the second subsidiary compressed air stream are introduced into the upper pressure column; the upper pressure heat exchanger is in flow communication with at least one of the upper pressure column and the lower pressure column so that the liquid air stream is fed into at least one of the upper pressure column and the pressure column. lower pressure; an expansion device positioned between the upper pressure heat exchanger and at least one of the upper pressure column and the lower pressure column for expanding the liquid air stream; the upper pressure column is connected to the lower pressure column such that a gross liquid oxygen stream composed of the upper pressure liquid background column of the upper pressure column is introduced into the lower pressure column to be further refined and the first and second parts of a higher pressure nitrogen rich liquid stream formed from the condensation of the upper pressure nitrogen rich top stream are introduced into the upper pressure column and the lower pressure column respectively as reflux; a subcooler, positioned between the lower pressure column and the lower pressure heat exchanger, or incorporated into the lower pressure heat exchanger, configured to subcool the raw liquid oxygen stream and the second of the nitrogen rich liquid stream parts higher pressure; expansion valves located between the subcooler and the lower pressure column to dilate the raw liquid oxygen stream and the second of the upper pressure nitrogen rich liquid stream portions prior to their introduction into the lower pressure column; the subcooler is connected to the lower pressure column so that a lower pressure nitrogen rich column top stream discharged from the lower pressure column passes indirect heat with the raw liquid oxygen stream and the second of the parts of the stream. of nitrogen-rich liquid of higher pressure; and the at least one liquid stream is an oxygen rich stream, composed of the oxygen rich liquid column of the lower pressure column bottom stream and a third part of the upper pressure nitrogen rich liquid stream. Mechanism according to Claim 11, characterized in that: the upper pressure heat exchanger and the lower pressure heat exchanger are connected to the subcooler so that the lower pressure nitrogen-rich column top current divides into the two nitrogen-rich steam streams that are used to balance the cold end temperatures of the upper pressure heat exchanger and the lower pressure heat exchanger; the turbodilator is connected to the upper pressure column so that discharge current is introduced into the upper pressure column; and the expansion device is a liquid dilator.