KR20140103109A - Air separation method and apparatus - Google Patents

Abstract

A method and apparatus for producing a co-product of oxygen and nitrogen, wherein the compressed and purified air stream is cooled, completely or partially condensed and then rectified in a main distillation column to form a nitrogen-rich vapor column overhead and crude liquid oxygen. The crude liquid oxygen stream is depressurized and stripped by a stripping gas in a secondary distillation column to produce an oxygen-rich liquid. The nitrogen product is formed from the main distillation column using a nitrogen-rich vapor column overhead and the crude liquid oxygen is partially vaporized to produce liquid nitrogen reflux into the stripping gas, the residual oxygen-rich liquid and the main distillation column. The oxygen product is formed from the residual oxygen-enriched liquid by providing a heat exchange function to the condensation of the compressed and purified air stream or by condensing the nitrogen-rich vapor used in the reflux of the main distillation column.

Description

Technical Field [0001] The present invention relates to an air separation method and apparatus,

The present invention is directed to a process for producing a crude product which comprises rectifying the compressed and purified air in a primary distillation column to produce a nitrogen product and stripping the crude liquid oxygen formed in the primary distillation column into a secondary distillation column to produce an oxygen product, And more particularly, to a method and apparatus for separating air.

Nitrogen is usually obtained in high purity by separating nitrogen from air in a cryogenic air separation plant employing a single distillation column. In such a plant, air is compressed and high boiling point contaminants are removed to produce a compressed and purified air stream. The compressed and purified air stream is then cooled to a temperature suitable for its cryogenic rectification in the main heat exchanger and then introduced into a single distillation column operating at about 3 bara or more. The air is rectified in a distillation column to produce a nitrogen-rich vapor column overhead and an oxygen-rich liquid column reservoir known as a crude liquid oxygen or kettle liquid. The oxygen-enriched liquid is depressurized in an expansion valve and then introduced into a heat exchanger to condense the stream of nitrogen-rich vapor column overhead to produce liquid nitrogen to reflux the distillation column. The partially vaporized oxygen-enriched liquid may be used to produce cooling for the plant, or the cooling may be provided to the plant through a stream that enters the liquid nitrogen addition to the main column or into the main heat exchanger.

Generally, oxygen is not recovered from such a single column nitrogen plant. However, there is also interest in recovering oxygen from such a plant. For example, float glass production typically requires nitrogen and low purity oxygen at flow rates of about 2: 1. Oxygen is used in glass furnaces for increased recovery, typically requiring a low purity of 90 to 95% and a pressure of 10 to 20 psig. Such oxygen can be provided by a separate vacuum pressure swing adsorption plant or through evaporation of the liquid supplied in the field, but the added cost is not reasonable. It should be noted that both oxygen and nitrogen can be produced by a typical dual column air separation plant having a high pressure column and a low pressure column operatively coupled in a heat transfer relationship. However, such a plant is not economical, for example in the production of float glass, due to product compression requirements and larger starting capital. The gradual deformation of a small single column nitrogen plant for delivering both nitrogen and oxygen products can be achieved by a number of processes including, for example, the requirements of the process, such as the production of float glass where nitrogen and oxygen products are required to have a pressure and a normal flow rate, for example less than 100 kcfh Can be economically satisfied.

In the prior art, there is an example of a single column nitrogen plant modified to produce both nitrogen and oxygen products simultaneously. For example, in US 4,783,210, a stream of crude liquid oxygen column stock is partially vaporized in a heat exchanger used to condense a stream of nitrogen-rich vapor column overhead produced in the distillation column. The resulting nitrogen-rich liquid is used to reflux the column. The liquid phase stream produced by the partial evaporation of the crude liquid oxygen is then stripped in a second or supplementary distillation column to produce an oxygen-rich column reservoir that can take up as the oxygen product. The secondary distillation column is reboiled with another stream of nitrogen-rich vapors that can be condensed in the reboiling process and taken as the liquid nitrogen product and also used to reflux the distillation column.

US 5,074,898 discloses a single column nitrogen generator having a secondary distillation column for producing oxygen product. In this patent, the crude liquid oxygen stream produced in the main distillation column is stripped in the secondary distillation column. The secondary distillation column is reboiled into a stream of nitrogen-rich vapor column overhead produced in the main distillation column. Which condenses the nitrogen-rich vapor to produce reflux of the main distillation column. The residual liquid produced in the secondary distillation column may be taken as a liquid product with a portion of the condensed nitrogen vapor.

In both of these patents, the column reservoir is used to condense nitrogen and must be present at a lower pressure than nitrogen to achieve nitrogen condensation. As a result, the oxygen product is also present at low pressure. In addition, since a portion of the column reservoir is taken as the product, there will be less bottom fluid to condense nitrogen. As a result, nitrogen production is limited. As will be discussed, the present invention provides a method and apparatus for producing a nitrogen and oxygen co-product, among other advantages, that can allow oxygen products to be produced at elevated pressures. In another aspect of the invention, the auxiliary column reservoir is evaporated stepwise, resulting in a fraction of more oxygen at low power compared to the methods considered in the prior art.

The present invention provides an air separation method for producing oxygen and nitrogen co-products. According to this method, the compressed and purified stream containing air is cooled and rectified in a main distillation column to produce nitrogen-rich vapor column overhead and crude liquid oxygen. Depressurizing the crude liquid oxygen stream consisting at least in part of the crude liquid oxygen, stripping the crude liquid oxygen stream into an ascending stripping gas in the secondary distillation column and separating the nitrogen-enriched vapor stream constituted by the nitrogen- By partial evaporation of the oxygen-rich liquid through exchange, an auxiliary column overhead containing an oxygen-rich liquid and at least 5.0 vol% of oxygen is produced in the secondary distillation column. As a result, a liquid nitrogen stream, a stripping gas and a residual oxygen-rich liquid are produced. The main distillation column is refluxed by at least a portion of the liquid nitrogen stream. The phrase "at least partially" is used in the specification and claims to indicate that further treatment may be generated in the secondary distillation column to produce the oxygen-rich liquid and the secondary column overhead. As described below, the supplemental column may only function to strip the steaming liquid oxygen stream, but may also function to rectify the nitrogen and oxygen-containing vapor produced by such stripping to increase oxygen recovery.

Rich stream of the remaining oxygen-enriched liquid and the stream of residual oxygen-enriched liquid by indirect heat exchange of the gaseous stream having a nitrogen concentration above the nitrogen concentration of air, To form a vapor fraction. Form an oxygen product stream from the vapor fraction, form a nitrogen product stream from the nitrogen-rich vapor, and form a waste stream from the auxiliary column overhead of the secondary distillation column. The oxygen product stream, the nitrogen product stream and the waste stream are passed through indirect heat exchange with the compressed and purified stream.

As can be appreciated from the above discussion, since the oxygen product stream is formed from the vapor fraction produced from the residual oxygen-rich liquid, the residual oxygen-rich liquid is not used to condense the nitrogen-rich vapor from the main distillation column , The production of the oxygen product is no longer directly coupled to the formation of reflux nitrogen into the main distillation column. As a result, the removal of the residual oxygen-rich liquid does not reduce nitrogen reflux to the main distillation column and thus nitrogen production, as in the prior art.

In addition, since the residual oxygen-enriched liquid is not used for nitrogen condensation, such liquid can be produced at high pressure.

As indicated above, the auxiliary column overhead can only be generated by the stripping of the crude liquid oxygen stream in the secondary distillation column. Alternatively, the primary distillation column is refluxed by a portion of the liquid nitrogen stream. In the latter case, the stripping of the crude liquid oxygen stream occurs within the stripping zone of the secondary distillation column, and the stripping produces a nitrogen and oxygen-containing vapor stream. The nitrogen and oxygen-containing vapor stream is introduced into the rectification zone in a secondary distillation column rectification zone disposed above the stripping zone in the secondary distillation column, the nitrogen and oxygen-containing vapor stream is introduced into the rectification zone and the supplementary distillation column, Rectified by refluxing the zone. The effect of this is to increase the recovery of oxygen in the residual oxygen-enriched liquid by virtue of trapping oxygen through the secondary column in the waste stream.

In one of the cases mentioned above, the oxygen-enriched liquid can be collected in the secondary distillation column. The oxygen-rich liquid is partially vaporized by passing the oxygen-rich liquid stream and the nitrogen-rich vapor stream through a flow heat exchanger to form a residual oxygen-rich liquid which is collected as a column reservoir of stripping gas and a secondary distillation column.

The gaseous stream can be a compressed and purified stream. The compressed and purified stream is partially condensed in the condenser and a stream of residual oxygen-enriched liquid is collected in a separation vessel. The liquid phase stream formed in the liquid phase formed in the separation vessel is introduced into the condenser and is partially evaporated through indirect heat exchange with the compressed and purified stream in the condenser to produce a two phase stream from the liquid phase stream. The two-phase stream is introduced into the separation vessel and the liquid and gaseous phases of the two-phase stream are separated in the separation vessel to form the oxygen-rich vapor fraction and the liquid phase together with the stream of residual oxygen-enriched liquid collected in the separation vessel. The oxygen product stream is then formed by venting the stream of oxygen-rich vapor fraction from the separation vessel.

In the embodiment of the invention described above, the condenser is arranged in the region of the main distillation column bottom to produce condensed liquid oxygen as a column reservoir of the main distillation column by allowing the condensed air to mix with the downward liquid produced by the rectification . Additionally, the primary distillation column can be refluxed by a portion of the liquid nitrogen stream, and the waste stream indirectly exchanges heat with the crude liquid oxygen stream to allow the crude liquid oxygen stream to be subcooled prior to decompression.

As an alternative to forming a gaseous stream from a compressed and purified stream, the gaseous stream may consist of a nitrogen-rich vapor column overhead. In such an embodiment, the liquid oxygen-rich stream is depressurized and the stream of residual oxygen-rich liquid is indirectly heat exchanged with the gaseous stream in a thermo-siphon reboiler, The heat is indirectly exchanged between the liquid stream and the vapor stream. This produces a vapor fraction from the partial evaporation of the stream of residual oxygen-enriched liquid and produces a condensate stream through condensation of the gas stream. The condensate stream is introduced into the main distillation column as reflux with a liquid nitrogen stream.

In the embodiment described above, the waste stream may be indirectly heat exchanged with the crude liquid oxygen stream prior to decompression of the crude liquid oxygen stream and allowed to pass, thereby allowing the crude liquid oxygen stream to be sub-cooled.

In certain embodiments of the present invention, the stream of residual oxygen-enriched liquid may be pressurized so that the oxygen product stream is also pressurized. A liquid nitrogen cooled stream can also be introduced into the main distillation column to provide cooling.

The present invention also provides an air separation apparatus that produces simultaneous oxygen and nitrogen products. Such devices include a main heat exchanger, a main distillation column and a secondary distillation column. The primary heat exchanger is configured to cool the compressed and purified stream comprising air and the primary distillation column is configured to rectify the compressed and purified stream to produce nitrogen-rich vapor column overhead and crude liquid oxygen. The secondary distillation column is connected to the main distillation column and the crude liquid oxygen stream composed of the crude liquid oxygen is stripped into the ascending stripping gas in the secondary distillation column and is at least partially stripped of the oxygen- An auxiliary column overhead containing 5 vol% or more of oxygen is produced. The expansion valve is disposed between the main distillation column and the secondary distillation column such that the crude liquid oxygen stream is depressurized before it is introduced into the secondary distillation column.

Means are provided for producing a liquid nitrogen stream, a stripping gas and a residual oxygen-rich liquid by partially evaporating the oxygen-rich liquid through indirect heat exchange with a nitrogen-rich vapor stream consisting of a nitrogen-rich vapor column overhead. The oxygen-rich liquid portion evaporation means is connected to the main distillation column such that the main distillation column is refluxed by at least a portion of the liquid nitrogen stream. The main heat exchanger is connected to the main distillation column and the secondary distillation column such that the waste stream formed from the nitrogen product stream formed from the nitrogen-rich vapor and the auxiliary column overhead of the secondary distillation column is indirectly heat exchanged with the compressed and purified air stream . Means are also provided for indirectly exchanging heat between the stream of residual oxygen-enriched liquid and the vapor stream having a nitrogen concentration above the nitrogen concentration of air to partially evaporate the stream of residual oxygen-enriched liquid. In addition, means are provided for forming an oxygen-rich vapor fraction from a stream of residual oxygen-enriched liquid after partial evaporation. The main heat exchanger is connected to the oxygen-rich vapor fractionation means, the main distillation column and the secondary distillation column to produce an oxygen product stream comprised of an oxygen-rich vapor fraction, a nitrogen product stream comprised of a nitrogen- rich vapor column overhead, The waste stream, consisting of the column's auxiliary column overhead, is compressed in the main heat exchanger and indirectly exchanges heat with the purified stream.

A stripping zone is provided in which the stripping of the crude liquid oxygen stream occurs only in the auxiliary column. Alternatively, a stripping zone may be provided in the secondary column, and a rectification zone disposed above the stripping zone. In the latter case, stripping of the steaming liquid oxygen stream takes place in the stripping zone of the secondary distillation column and nitrogen and oxygen-containing vapor streams are produced in the stripping zone and enter the rectification zone for rectification of the nitrogen and oxygen-containing vapor stream . This rectification is provided to increase the recovery of oxygen in the residual oxygen-enriched liquid. The partial evaporation means of the oxygen-enriched liquid is connected to the main distillation column so that the main distillation column is refluxed by a portion of the liquid nitrogen stream and is connected to the secondary distillation column so that the secondary distillation column, To be refluxed. Another expansion valve is arranged between the partial evaporation means of the oxygen-enriched liquid and the secondary distillation column so that the pressure of the additional part of the liquid nitrogen stream is reduced to the pressure of the secondary distillation column.

In certain embodiments of the present invention, means for collection of oxygen-rich liquids in the secondary distillation column may be provided. The partial evaporation means of the oxygen-rich liquid is connected to the secondary distillation column and the oxygen-rich liquid collection means such that the oxygen-rich liquid is partially introduced into the flow-through heat exchanger by passage of an oxygen- Is a flow-through heat exchanger that causes the evaporated and residual oxygen-enriched liquid to be collected as a column reservoir of the secondary distillation column. The primary distillation column is connected to a flow heat exchanger to allow the nitrogen-rich vapor stream to condense in the flow heat exchanger.

The gaseous stream may be a compressed and purified air stream. In such cases, the means for heat exchange of the stream of residual oxygen-enriched liquid and the means for forming oxygen-rich vapor fraction are a condenser and a separation vessel. The condenser is connected to the main heat exchanger such that the compressed and purified stream is partially condensed. The separation vessel is connected to the secondary distillation column so that a stream of residual oxygen-enriched liquid is collected in the separation vessel. The separation vessel is connected to a condenser such that the liquid phase stream constituted by the liquid phase produced in the separation vessel is partially vaporized in the condenser to produce a two phase stream introduced into the separation vessel. The liquid and vapor phases of the two phase stream are separated in the separation vessel to form an oxygen-rich vapor fraction and a liquid phase, and the main heat exchanger is connected to a separation vessel such that the oxygen product stream is formed from the oxygen-rich vapor fraction.

In this embodiment of the invention, the condenser is disposed in the bottom region of the main distillation column such that the condensed air is compressed and mixed with the downward liquid produced by the rectification of the purified stream to form a crude liquid as the column reservoir of the main distillation column Oxygen can be generated. A perfusion heat exchanger may also be connected to the main distillation column so that the main distillation column is refluxed by a portion of the liquid nitrogen stream. The supercooling heat exchanger is connected to a flow heat exchanger, a secondary distillation column and an expansion valve such that the waste stream indirectly exchanges heat with the crude liquid oxygen stream in the supercool heat exchanger and the superheated liquid oxygen stream passes through the expansion valve, .

Alternatively, the vapor stream may consist of nitrogen-rich vapor. In such a case, the means for heat exchange of the residual oxygen-enriched liquid stream and the means for forming the oxygen-rich vapor fraction are formed by a thermal siphon boiler with a shell. The shell is connected to the auxiliary column to receive a stream of residual oxygen-enriched liquid, and another expansion valve is disposed between the shell and the auxiliary column to allow the stream of residual oxygen-enriched liquid to be depressurized. The thermal siphon boiler is connected to the main distillation column to receive the gaseous stream thereby to condense the gaseous stream through indirect heat exchange with the stream of residual oxygen-enriched liquid to form an oxygen-enriched vapor fraction in the shell, Is withdrawn as a reflux with a liquid nitrogen stream into the main distillation column. The main heat exchanger is connected to the shell, the main distillation column and the secondary distillation column to produce an oxygen product stream formed from the vapor fraction, a nitrogen product stream formed from the nitrogen-rich vapor column overhead, All of the waste stream is compressed in the main heat exchanger and indirectly exchanges heat with the purified stream.

In the embodiment discussed above, the supercooling heat exchanger is disposed between the secondary distillation column, the main distillation column and the main heat exchanger such that before the reduced pressure of the crude liquid oxygen stream and before the warming of the waste stream in the main heat exchanger, And indirectly exchanges heat with the stream.

In certain embodiments of the present invention, the primary distillation column may be provided with an upper inlet for introduction of a liquid nitrogen cooling stream to provide cooling.

The invention ends with a claim which clearly indicates what the applicant regards as their invention, but it is believed that the invention will be better understood when read in conjunction with the accompanying drawings, in which:
1 is a schematic diagram of an air separation plant for carrying out the process according to the invention.
2 is a schematic diagram of an alternative embodiment of an air separation plant for carrying out the process according to the invention.
3 is a schematic diagram of a further alternative embodiment of an air separation plant for carrying out the process according to the invention.

Referring to Figure 1, there is shown an air separation plant 1 capable of simultaneous production of oxygen and nitrogen products ("N ₂ " and "O ₂ ").

The compressed and purified air stream 10 is cooled to a temperature suitable for rectification in the main heat exchanger 12 to saturation or near saturation. As can be appreciated, the air separation plant 1 may be part of a facility that requires compressed air, so that the compressed and purified air stream 10 may be formed from a portion of the air produced in such a facility have. Alternatively, such a stream may be generated by compressing air to typically 70 psia to 90 psia and then removing airborne contaminants, such as carbon dioxide, water vapor, and hydrocarbons, that are solidified or concentrated at cryogenic temperatures. The main heat exchanger 12 may typically be a brazed aluminum plate fin structure. As may occur to a person skilled in the art, the main heat exchanger 12 may be formed from a plurality of units operating in parallel.

The compressed and purified air stream 10 is cooled and then introduced into a condenser 14 disposed in the bottom region 16 of the main distillation column 18. The distillation column 18 comprises a mass transfer contact element, generally designated 20, for example a tray, a structured packing, a random packing or a combination of such elements. Preferably, the incoming air is partially condensed in the condenser 14 to form a vapor fraction that rises into the mass transfer contact element 20 to contact the downward liquid phase producing the nitrogen-rich vapor column overhead 23. [ (22). Typically, the nitrogen-rich vapor column overhead 23 can be essentially pure nitrogen. Partial condensation of air constitutes about 20% of the incoming air and is collected in the liquid fraction () collected as crude liquid oxygen 26 with the liquid falling in the element 20 in the bottom region 16 of the main distillation column 18 24).

It should be appreciated that an alternative means for condensing the incoming air is to place the condenser 14 outside the main distillation column 18. [ In such means, the liquid fraction 24 and the liquid descending in the distillation column 20 may be separately combined to form the crude liquid oxygen 26, or may be subcooled and injected into the column 34 separately. In other similar means, the compressed and purified air stream may be introduced directly into the main distillation column shell. The air will be mixed with the vapor in the column and the vapor 22 recycled from the condenser 14. In such a configuration, the condenser will not have condensing-side headering, i.e. the gas will simply be led to flow into the exchanger through condensation. As a further alternative, a portion of the cooled air stream 10 can be sent to the shell of the column 18, and some can be sent directly to the condenser 14 via the pipe. Such a configuration would allow control of the product oxygen and nitrogen flow rates. However, this configuration will require additional valves and control means. An additional measure is to use a separate air stream that can be further compressed. The separate air stream will be split at the warm end when further compressed, or at the cold end if not so compressed. The stream will then be completely condensed in the condenser 14. The condensed air will then be introduced into the interstage location of the main distillation column 18 via a suitable pipe. Condensed air will not be collected in the sump of the column; instead, liquefied air will be injected a few steps above the bottom of the main distillation column 14.

The crude liquid oxygen stream 28 comprised of the crude liquid oxygen 26 is then preferably subcooled within the subcooling heat exchanger 30 and expanded The pressure in the valve 32 is preferably reduced to a pressure of 15 to 25 psia. The steaming liquid oxygen stream 28 is then fed into the secondary distillation column 34 in the mass transfer contact element 36 which may be a tray, a structured packing, a random packing or a combination of such elements, Lt; RTI ID = 0.0 > 52 < / RTI > Stripping typically results in an auxiliary column overhead 38 containing 80 vol% to 90 vol% nitrogen and a residual oxygen-enriched liquid 56 containing typically 85 vol% to 98 vol% oxygen.

The oxygen-enriched liquid 40 can be collected in the collection tray 42 or by similar means to cause the downward liquid to be collected and the rising vapor to pass through the mass transfer contact element 36 into the mass transfer contact element have. The stream of oxygen-enriched liquid 44 comprised of the oxygen-enriched liquid 40 is passed through indirect heat exchange with a nitrogen-rich vapor stream 46 comprised of a nitrogen-rich vapor 23 in a flow-through heat exchanger 48 Partially evaporated. As a result of indirect heat exchange, a liquid nitrogen stream 50 is produced. The stream of oxygen-enriched liquid 44 is partially vaporized to produce a residual gas liquid stream 54 that is collected as the residual oxygen-enriched liquid 56 at the bottom of the stripping gas 52 and the secondary distillation column 34 . In an alternative embodiment, the two-phase stream from the boiling side of the flow heat exchanger is extracted from the secondary distillation column 34 and sent to a separate phase separator to produce a residual oxygen-rich liquid stream 68 In which case the vapor phase will be returned through the pipe to the secondary distillation column 34 to form the stripping gas 52. Although not preferred, this would be equivalent to that shown in the figures.

As an alternative means of the perfusion heat exchanger 48 and the collection tray 42, a thermal siphon boiler disposed at the base of the secondary column 34 is used to transfer the heat from the mass transfer contact element 36 to the base of the secondary column 34 Rich liquid < / RTI > The core of such a reboiler will be installed in the residual oxygen-enriched liquid to produce stripping gas through evaporation of the oxygen-enriched liquid 40. However, this would not be desirable since such a heat exchanger would not operate at the temperature difference of the flow heat exchanger and, consequently, the incoming air would have to be compressed to a higher pressure.

The liquid nitrogen stream 50 may be introduced as a reflux stream 58 into the main distillation column 18 as shown in whole or in part. The waste stream 62 consisting of the remainder (as depressurized through the valve 63) as an additional liquid nitrogen stream 60 and the auxiliary column overhead 38 is passed indirectly to the crude liquid oxygen stream 28 for once supercooling Is introduced into a supercooling heat exchanger 30 that exchanges heat and then indirectly exchanges heat with the compressed and purified air stream 10 entering the main heat exchanger 12 to help cool it. Alternatively, stream 60 and stream 62 may be combined and warmed. After warming, the additional liquid nitrogen stream 60 will be discharged from the main heat exchanger 12 as a gaseous nitrogen co-product ("N ₂ "), and the waste stream 62 is used to pre-purify the incoming air Can be used for the regeneration of the absorber used in the preliminary purification unit used with the air separation plant 1. It is also possible to recycle all or a portion of such a stream by recompressing it and recombining it with incoming air. It should be noted that the use of stream 60 is optional and evaporation of liquid nitrogen stream 60 serves to provide additional subcooling to stream 28, thereby allowing for more oxygen production.

It should be noted that the liquid nitrogen reflux stream 60 may be extracted from the interstage location of the column 20 before passing through the valve 63.

It should also be noted that the supercooling heat exchanger 30 or 30 'to be discussed may be included in the main heat exchanger 12. It is equally possible that embodiments of the present invention can be configured without the use of such a subcooling heat exchanger 30 or 30 '. In either case, in the illustrated embodiment, the additional liquid nitrogen stream 60 may be depressurized in the expansion valve 63 before passing through the supercool heat exchanger 30 and the main heat exchanger 12.

The nitrogen co-product is obtained by warming the nitrogen product stream 64 composed of the nitrogen-rich vapor column overhead 23 via indirect heat exchange with the compressed and purified air stream 10 entering the main heat exchanger 12 Which also helps to cool the stream. As shown, the nitrogen product stream 64 and the nitrogen-rich vapor stream 46 are produced by dividing the nitrogen-rich vapor stream 66 removed from the top of the main distillation column 18 into two such streams . However, the nitrogen product stream 64 and the nitrogen-rich vapor stream 46 may be removed independently from the main distillation column 18. All of the liquid nitrogen stream 50 may be introduced into the main distillation column 18 as reflux and the nitrogen co-product may be formed solely from the warmed nitrogen product stream 64.

The oxygen co-product is produced by removing the stream of residual oxygen-enriched liquid 68 composed of the residual oxygen-enriched liquid 56 and introducing such stream into the separation vessel 70. The liquid phase stream 72 comprised of the liquid phase 74 is partially vaporized in the condenser 14 to produce a compressed and purified air stream 10 through indirect heat exchange with the incoming compressed and purified air stream 10, Lt; RTI ID = 0.0 > (76) < / RTI > The liquid and gaseous fractions of the two-phase stream 76 are separated in the separation vessel to form a liquid phase 74 and a gaseous fraction produced by separation from the stream and addition of the residual oxygen-enriched liquid 68. A control valve (not shown) may be used to regulate the operating pressure of the vessel 70. The oxygen product stream is formed from a vapor stream (80) consisting of a vapor fraction (78). The drain stream 82 that has passed through the valve 84 can optionally be collected as a liquid product (or sent to a contaminant drain evaporator). Alternatively, a portion of the stream 68 may be extracted as a liquid product and sent to the appropriate reservoir.

It should be noted that the stream of residual oxygen-enriched liquid 68 may be pressurized as a result of the secondary distillation column 34 being disposed at a height above the main distillation column 18. [ This produces a pressurized oxygen product. A further alternative is to pressurize the stream of residual oxygen-enriched liquid by the use of a mechanical pump or pump associated with the liquid head produced by placing the secondary distillation column 34 over the main distillation column 18. [

As shown, the condenser 14 functions as a thermal siphon. As an alternative means for forming the oxygen product, it is possible to configure the separation vessel 70 to contain the condenser 14 therein. In such a case, the two phase stream will be discharged from the condenser into the interior of the separation vessel 70.

However, the illustrated embodiment is considered more cost effective than such an arrangement. Additionally, if more than about 20% of the oxygen product is taken as liquid product in the drainage stream 82, it will be possible to change the condenser 14 to a perfusion heat exchanger with potential additional savings in power consumption. In such an arrangement, the stream of residual oxygen-enriched liquid 68 will be sent directly to the condenser 14 via the pipe. In this case, the partially evaporated product will be separated in the phase separation vessel, and there will be no return stream, such as the oxygen-rich liquid stream introduced into the condenser 14.

Referring to Figure 2, an alternative embodiment of the present invention is shown as an air separation plant 2. The elements shown in Fig. 2 can be described in the same manner as discussed above with respect to Fig. 1, and those elements shown in Fig. 2 will use the same reference numerals as the elements of Fig. 1, . The air separation plant 2 is designed in particular to allow more fractions of nitrogen contained in the air to be recovered as product. This is accomplished by increasing the liquid nitrogen reflux into the main distillation column 18.

In the air separation plant 2, the compressed and purified air stream 10 after being cooled in the main heat exchanger 12 is introduced into the main distillation column 20 and rectified to form the nitrogen-rich vapor column overhead 23, And a crude liquid oxygen column stock 26 '. The crude liquid oxygen stream 28 'may optionally be subcooled within the subcooling unit 30', depressurized in the expansion valve 32, and then stripped in the secondary distillation column 34. The first nitrogen-enriched vapor stream 46 is condensed in a flow heat exchanger 48 to produce a first liquid nitrogen stream 50 and a residual oxygen-enriched liquid 56 in a manner described for the air separation plant 1 . The stream of residual oxygen-enriched liquid 68 produced in the secondary distillation column 34 is depressurized in the expansion valve 90 and then introduced into the thermal siphon boiler 86. The stream of residual oxygen-enriched liquid 68 is partially vaporized through indirect heat exchange with the gaseous stream 92, which may consist of the nitrogen-rich vapor column overhead 23 of the main distillation column 18. The vapor stream 92 is sent into the core 94 disposed within the shell 96 of the thermal siphon boiler 86 to achieve heat exchange. The gaseous stream 92 is condensed to produce a condensate stream 98 that is introduced into such a column as part of the reflux into the main distillation column 18. The liquid nitrogen stream 50 produced in the flow heat exchanger 48 is all introduced into the main distillation column 18 as column reflux. This stepwise condensation of the nitrogen-rich vapor column overhead will increase liquid nitrogen reflux and thus increase the ability of the air separation plant 2 to produce nitrogen product.

As can be appreciated, other means of replacing the thermal siphon boiler 86, including a flow-through heat exchanger, may be used when the drainage stream 106 is present at a sufficient flow rate. In addition, although not shown, a stream having a nitrogen concentration above the nitrogen concentration of air can be introduced into the core 94 of the thermal siphon boiler 86 in place of the nitrogen-rich vapors. For example, it is possible to compress the air stream and liquefy it in the main heat exchanger 12. Thereafter, it can be introduced into the middle position of the main distillation column 18. The gaseous stream having approximately the same composition as such liquid stream can then be passed into the core 94 of the thermal siphon boiler 86 and condensed. The resulting condensate stream may be introduced into the location of the main distillation column with the composition of the downstream column liquid being the same or nearly the same as that of the condensate, or introduced into the secondary distillation column 34 for stripping and producing oxygen co- have.

Partial evaporation of the stream of residual oxygen-enriched liquid 68 produces a vapor and liquid fraction that is collected in the shell as vapor fraction 100 and liquid phase 102. The vapor stream 104 composed of the vapor fraction 100 is indirectly passed through and exchanges heat with the compressed and purified air stream 10 entering the main heat exchanger 12 such that the vapor stream 100 is warmed ("O ₂ ") and helps the compressed and purified air stream 10 to cool. A drain stream 106 composed of liquid phase 102 may be reduced in pressure at valve 108 and collected as liquid oxygen product. In such an embodiment, optionally, the waste stream 62 may pass through indirect heat exchange with the crude liquid oxygen stream 28 'in the supercool heat exchanger 30'. The waste stream 62 is then also exchanged and indirectly heat exchanged with the compressed and purified air stream 10 in the main heat exchanger 12 such that the waste stream 62 is warmed and compressed, (10) to cool. The waste stream 62 may be recycled into the incoming air. This can be achieved by direct mixing with the feed air after warming in the exchanger 12 or after further compression. As an air separation plant 1, a nitrogen product stream 64 composed of a nitrogen-rich vapor column overhead 23 is subjected to indirect heat exchange with a compressed and purified air stream 10 entering the main heat exchanger 12 And also helps to cool the stream.

Referring to both Figures 1 and 2, the liquid nitrogen stream 110 that is introduced into the top inlet 114, which is disposed at the top of the main distillation column 18 after passing through the flow control valve 112, (1) or air separation plant (2). Such a stream can be obtained from an on-site storage tank and can be high or low pressure. The addition of such a stream compensates for the high temperature end losses resulting from the operation of the main heat exchanger 12 as well as ambient heat leaks. It should be noted that the liquid stream 110 may be introduced directly into one of the vapor streams entering the heat exchanger 30 'or 12. As can be appreciated, some of the incoming air can be expanded before being introduced into the main distillation column 18. [ In this regard, after partial cooling in the main heat exchanger 12, a portion of the compressed and purified air stream may be mixed with the waste gas stream 62 after it has been expanded. Another possibility is to back-press the distillation column system of the main distillation column 18 and the secondary distillation column 34 and the waste stream 62 is partially warmed in the main heat exchanger 12, Expanded in a turboexpander, and can be further warmed in the main heat exchanger 12. The use of a turboexpander can provide the possibility of obtaining a liquid product from a column system. Some of the liquid nitrogen from the condenser 48 or 96 may be sent to the appropriate reservoir. Another alternative may be that the liquid oxygen stream is introduced or combined with the stream of residual oxygen-enriched liquid 68 and then introduced into the shell 96 of the thermal siphon boiler 86.

Referring to Fig. 3, there is shown an air separation plant 1 'which constitutes an alternative embodiment to the air separation plant 1 shown in Fig. In the air separation plant 1, the auxiliary column 34 'is indicated as being provided with a stripping zone 36a in which the mass transfer contact element 36 can be provided as discussed above with respect to FIG. The steaming liquid oxygen stream 28 is stripped in such a stripping section 36a as described above and produces nitrogen and oxygen containing vapors rather than directly generating the auxiliary column overhead. The auxiliary column 34a is also provided with a rectification zone 36b disposed above the stripping zone 36a to recover some of the oxygen that would have been discharged from the plant in the waste stream 62 by rectifying such nitrogen and oxygen containing vapor. This rectifying zone is refluxed by liquid nitrogen stream 60 'which is depressurized by valve 63' and then introduced into the top of sub-column 34 '. As can be appreciated, the same variant can be created in the plant shown in Fig. In such a case, the auxiliary column will be deformed in a manner similar to that shown in Fig. In the case of the embodiment of FIG. 2, a portion of the condensate stream 98 will be used to reflux the auxiliary column 34 '.

As can be appreciated, all that is considered is to recover some of the oxygen that may have been lost as waste, thereby increasing oxygen recovery. However, there is a trade-off between increased oxygen recovery and the fact that liquid nitrogen is taken from the liquid nitrogen that would have been used to reflux the main distillation column, i.e., between nitrogen production. Any more rectification may be accompanied by an increase in the flow rate of the liquid nitrogen stream 60 ' and hence a decrease in the available product nitrogen 64, which requires that the reflux rate of the main column be maintained to maintain product nitrogen purity . A more specific way of describing such a limitation is that the performance of the rectifying section 36b should be such that the auxiliary column overhead 38 in the sub-column 36, when considered together with the performance of the stripping section 36a, It is. To achieve this, typically, the ratio of the flow rate of the liquid nitrogen stream 60 'to the total available nitrogen flow from the column 18 (sum of the streams 60 and 64) should be 0.1 to 0.4, The ratio of liquid to vapor in zone 36b should be 0.23 or less.

Although the present invention has been described with reference to preferred embodiments, many variations, additions and deletions may be made without departing from the spirit and scope of the invention as set forth in the appended claims, as may occur to those of ordinary skill in the art.

Claims (21)

Cooling the compressed and purified stream comprising air;
Rectifying the compressed and purified stream in a primary distillation column to produce a nitrogen-rich vapor column overhead and a crude liquid oxygen;
The crude liquid oxygen stream consisting at least in part of the crude liquid oxygen is depressurized and the crude liquid oxygen stream is stripped in a secondary distillation column with rising stripping gas to form an oxygen-enriched liquid and an oxygen- The liquid nitrogen stream, the stripping gas and the residual oxygen-enriched liquid are removed by partial evaporation through indirect heat exchange with the nitrogen-rich vapor stream constituted by the nitrogen-rich vapor column overhead, ;
Refluxing the main distillation column with at least a portion of the liquid nitrogen stream;
Rich stream is partially vaporized by indirect heat exchange between the stream of residual oxygen-enriched liquid and the gaseous stream having a nitrogen concentration above the nitrogen concentration of air to produce an oxygen-enriched vapor fraction ;
Forming an oxygen product stream from the vapor fraction, a nitrogen product stream from the nitrogen-rich vapor column overhead, and a waste stream from the auxiliary column overhead;
Passing the oxygen product stream, the nitrogen product stream and the waste stream through indirect heat exchange with the compressed and purified stream
≪ / RTI > wherein the oxygen and nitrogen co- The method of claim 1, wherein the auxiliary column overhead is generated by stripping of the crude liquid oxygen stream only in the auxiliary distillation column. The method according to claim 1,
The main distillation column is refluxed by a portion of the liquid nitrogen stream;
Stripping the crude liquid oxygen stream occurs within the stripping zone of the secondary distillation column;
Stripping the crude liquid oxygen stream in the secondary distillation column produces a nitrogen and oxygen containing vapor stream;
The nitrogen and oxygen containing vapor stream is introduced into the rectification zone of the secondary distillation column disposed above the stripping zone in the secondary distillation column by introducing a nitrogen and oxygen containing vapor stream into the rectification zone and a further portion of the liquid nitrogen stream, Thereby rectifying the rectification zone by refluxing, thereby thereby increasing the recovery of oxygen in the residual oxygen-rich liquid. The method according to claim 1,
The oxygen-rich liquid is collected in a secondary distillation column;
The oxygen-rich liquid is partially vaporized by passing the oxygen-rich liquid stream and the nitrogen-rich vapor stream comprised of the oxygen-rich liquid to a perfusion heat exchanger to remove the remaining oxygen-rich liquid stream, which is collected as a column reservoir of the stripping gas and the secondary distillation column, A method for forming an abundant liquid. 5. The method of claim 4,
The gaseous stream is a compressed and purified stream;
The compressed and purified stream is partially condensed in the condenser;
The oxygen-rich vapor fraction
Collecting a stream of residual oxygen-enriched liquid in a separation vessel;
Phase stream from the liquid phase stream by introducing a liquid phase stream formed in the liquid phase formed in the separation vessel into the condenser and partially evaporating the liquid phase stream through indirect heat exchange with the compressed and purified stream in the condenser, ;
The two-phase stream is introduced into a separation vessel and the liquid and vapor phases of the two-phase stream are separated in a separation vessel to form an oxygen-rich vapor fraction and a liquid phase together with a stream of residual oxygen-enriched liquid collected in the separation vessel ≪ / RTI >
Wherein the oxygen product stream is formed by withdrawing a stream of oxygen-rich vapor fraction from a separation vessel. 6. The method of claim 5, wherein the condenser is disposed in the region of the main distillation column bottom region so that condensed air is mixed with the downward liquid produced by the rectification, thereby producing the crude liquid oxygen as a column reservoir of the main distillation column. The method according to claim 6,
The main distillation column is refluxed by a portion of the liquid nitrogen stream;
Wherein the waste stream indirectly exchanges heat with the crude liquid oxygen stream such that the crude liquid oxygen stream is subcooled prior to decompression. 5. The method of claim 4, wherein the gaseous stream comprises a nitrogen-rich vapor column overhead;
The liquid oxygen-rich stream is depressurized and the stream of the remaining oxygen-rich liquid is indirectly heat-exchanged with the gaseous stream in a thermo-siphon reboiler and passed through a stream of residual oxygen- By indirectly exchanging heat between the gaseous streams, a vapor fraction is produced from the partial evaporation of the stream of residual oxygen-enriched liquid and a condensate stream is produced through condensation of the gaseous stream;
And introducing the condensate stream into the main distillation column as reflux with the liquid nitrogen stream. 10. The method of claim 8, wherein the waste liquid stream is indirectly heat exchanged with the crude liquid oxygen stream prior to decompression of the crude liquid oxygen stream, thereby allowing the crude liquid oxygen stream to subcooled. The method of claim 1 wherein the stream of residual oxygen-enriched liquid is pressurized so that the oxygen product stream is also pressurized. The method of claim 1, wherein the liquid nitrogen cooling stream is introduced into the main distillation column to provide cooling. A main heat exchanger configured to cool the compressed and purified stream comprising air;
A primary distillation column configured to rectify the compressed and purified stream to produce nitrogen-rich vapor column overhead and crude liquid oxygen;
Wherein the crude liquid oxygen stream connected to the main distillation column is stripped of the riser stripping gas in the secondary distillation column and is at least partially stripped of the oxygen-rich liquid and at least 5 vol% as a result of the stripping of the crude liquid oxygen stream A secondary distillation column configured to produce an auxiliary column overhead containing oxygen;
An expansion valve disposed between the main distillation column and the secondary distillation column such that the crude liquid oxygen stream is depressurized before it is introduced into the secondary distillation column;
Means for producing a liquid nitrogen stream, a stripping gas and a residual oxygen-rich liquid by partially evaporating the oxygen-rich liquid through indirect heat exchange with a nitrogen-rich vapor stream consisting of a nitrogen-rich vapor column overhead;
An oxygen-rich liquid portion evaporation means coupled to the main distillation column to cause the main distillation column to be refluxed by at least a portion of the liquid nitrogen stream;
Connected to the main distillation column and the secondary distillation column to allow the waste stream formed from the nitrogen product stream comprised of the nitrogen-enriched vapor column overhead and the secondary column overhead of the secondary distillation column to indirectly exchange heat with the compressed and refined air stream A main heat exchanger;
Means for indirectly exchanging heat between the stream of residual oxygen-enriched liquid and the vapor stream having a nitrogen concentration above the nitrogen concentration of air to partially evaporate the stream of residual oxygen-enriched liquid, Means for forming an oxygen-rich vapor fraction from a stream of oxygen-enriched liquid; And
An oxygen-rich vapor fractionation apparatus, an oxygen product stream connected to the main distillation column and the secondary distillation column, the oxygen product stream comprising an oxygen-rich vapor fraction, a nitrogen product stream comprised of a nitrogen-rich vapor column overhead, The waste stream consisting of overhead is compressed in the main heat exchanger and indirectly exchanges heat with the purified stream and passes through the main heat exchanger
Wherein the oxygen and nitrogen co- 13. The apparatus of claim 12, wherein a stripping zone is provided in which only stripping of the crude liquid oxygen stream occurs in the auxiliary column. 13. The method of claim 12,
The secondary column has a stripping zone and a rectification zone disposed above the stripping zone;
Stripping of the steaming liquid oxygen stream occurs in the stripping zone of the secondary distillation column and the nitrogen and oxygen containing vapor stream is produced in the stripping zone and enters the rectification zone for rectification of the nitrogen and oxygen containing vapor stream, The recovery of oxygen in the liquid is increased;
The partial evaporation means of the oxygen-enriched liquid is connected to the main distillation column so that the main distillation column is refluxed by a portion of the portion of the liquid nitrogen stream and is connected to the secondary distillation column so that the secondary distillation column and thus the rectification zone, To be refluxed by a portion of the additional;
Another expansion valve is disposed between the partial evaporation means of the oxygen-enriched liquid and the secondary distillation column such that the pressure of the further portion of the liquid nitrogen stream is reduced to the pressure of the secondary distillation column. 13. The method of claim 12,
The secondary distillation column has means for collecting the oxygen-rich liquid;
The partial evaporation means of the oxygen-rich liquid is connected to the secondary distillation column and the oxygen-rich liquid collection means such that the oxygen-rich liquid is partially introduced into the flow-through heat exchanger by passage of an oxygen- Wherein the vaporized and residual oxygen-rich liquid is collected as a column reservoir of the secondary distillation column;
Wherein the primary distillation column is connected to a flow heat exchanger such that the nitrogen-rich vapor stream is condensed in the flow heat exchanger. 16. The method of claim 15,
The gaseous stream is a compressed and purified air stream;
The means for heat exchange of the residual oxygen-enriched liquid and the means for forming the oxygen-rich vapor fraction are a condenser connected to the main heat exchanger so that the compressed and purified stream is partially condensed, and a separation vessel;
The separation vessel is connected to the secondary distillation column so that a stream of residual oxygen-enriched liquid is collected in the separation vessel;
The separation vessel is connected to a condenser to produce a two phase stream in which the liquid phase stream constituted by the liquid phase produced in the separation vessel is partially vaporized in the condenser and introduced into the separation vessel and the liquid phase and the vapor phase of the two phase stream are separated To separate in the vessel to form an oxygen-rich vapor fraction and a liquid phase;
The main heat exchanger is connected to the separation vessel so that the oxygen product stream is formed from the oxygen-rich vapor fraction. 17. The method of claim 16, wherein the condenser is disposed in the bottom region of the main distillation column such that the condensed air is mixed with the downward liquid produced by the compression of the compressed stream and the rectification of the purified stream to produce crude liquid oxygen as the column reservoir of the main distillation column Lt; / RTI > 18. The method of claim 17,
The flow heat exchanger is connected to the main distillation column so that the main distillation column is refluxed by a portion of the liquid nitrogen stream;
The supercooling heat exchanger is connected to a flow heat exchanger, a secondary distillation column and an expansion valve such that the waste stream indirectly exchanges heat with the crude liquid oxygen stream in the supercool heat exchanger and the superheated liquid oxygen stream passes through the expansion valve, . 16. The method of claim 15,
The gaseous stream is composed of nitrogen-rich vapor;
The means for heat exchange of the residual oxygen-enriched liquid stream and the means for forming the oxygen-rich vapor fraction are thermal siphon boilers with shells;
The shell is connected to the secondary column to receive a stream of residual oxygen-enriched liquid;
Another expansion valve is disposed between the shell and the subcolumn such that the stream of residual oxygen-enriched liquid is depressurized;
The thermal siphon boiler is connected to the main distillation column to receive the gaseous stream thereby to condense the gaseous stream through indirect heat exchange with the stream of residual oxygen-enriched liquid to form an oxygen-rich vapor portion within the shell, With a liquid nitrogen stream as reflux to a main distillation column;
The main heat exchanger is connected to the shell, the main distillation column and the secondary distillation column to produce an oxygen product stream formed from the vapor fraction, a nitrogen product stream formed from the nitrogen-rich vapor column overhead, Wherein the waste stream is compressed in the main heat exchanger and indirectly passes heat through the purified stream. 20. The method of claim 19, wherein the subcooling heat exchanger is disposed between the secondary distillation column, the main distillation column and the main heat exchanger such that the waste stream before the reducing pressure of the crude liquid oxygen stream and before the warming of the waste stream in the main heat exchanger, And indirectly through the heat exchange. 13. The apparatus of claim 12, wherein the primary distillation column has an upper inlet for introduction of a liquid nitrogen cooling stream to provide cooling.

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