DE102010055448A1 - Method and apparatus for the cryogenic separation of air - Google Patents

Abstract

The method and the device are used for the low-temperature separation of air in a distillation column system for nitrogen-oxygen separation, which has a high-pressure column (21) and a low-pressure column (22). Feed air (1) is compressed in a main air compressor (3) to a first pressure which is significantly higher than the operating pressure of the high pressure column (17). The compressed feed air (8) is divided into a first and a second air flow (7,8) and cooled in a main heat exchanger (16) against reverse flows (34,35). The first air stream (7) is post-compressed upstream of the introduction into the main heat exchanger (16) in a post-compressor (10) to a second pressure which is higher than the first pressure. After partial cooling in the main heat exchanger (16), the first air stream is removed (12c) from the main heat exchanger (16) at a first intermediate temperature and recompressed in a cold compressor (113) to a third pressure which is higher than the second pressure. The cold-compressed first air stream (115) is fed back to the main heat exchanger (16) at a second intermediate temperature which is higher than the first intermediate temperature and further cooled and liquefied or pseudo-liquefied in the main heat exchanger (16). The (pseudo) liquefied first air stream (17) is introduced into the distillation column system for nitrogen-oxygen separation. The second air stream (8) is cooled in the main heat exchanger (16) to a third intermediate temperature, is removed from the main heat exchanger (16) below the third intermediate temperature (24, 28) and then expanded to perform work (25, 28). The second air stream (30), which is relaxed during work, is likewise introduced into the distillation column system for nitrogen-oxygen separation. A liquid product stream (31) is removed from the distillation column system, brought to an increased pressure (32) in the liquid state and evaporated or pseudo-evaporated under this increased pressure in the main heat exchanger (16) and finally drawn off as a gaseous pressure product stream (34). The work-related relaxation of the second air stream is carried out in two relaxation machines (25, 28) connected in parallel. The entry pressure of the work relaxation (25, 28) is essentially equal to the first pressure. The mass flow ratio between the first air flow (7) and the second air flow (8) is between 0.38 and 0.67. The pressure ratio at the cold compressor (113) is 1.3 to 2.3.

Description

The invention relates to a method for the cryogenic separation of air according to the preamble of patent claim 1.

Such a procedure is over WO 2004099690 A1 ( 2 ) known.

In such an internal compression process, at least one of the products (for example, nitrogen from the high-pressure column, oxygen from the low-pressure column of a two-column air separator) is taken off liquid from one of the columns of the distillation column system or from a condenser connected to one of these columns, in liquid Condition brought to an elevated pressure, vaporized in indirect heat exchange with feed air in the main heat exchanger or pseudo-evaporated (at supercritical pressure) and finally recovered as gaseous pressure product. In the present method, not only a portion of the feed air, but the total air is compressed to a first pressure which is significantly higher than the operating pressure of the high pressure column. By "significantly higher" is meant here a pressure difference of at least 2 bar, preferably at least 5 bar.

The inventive method with two turbines is fundamentally similar to the process with a turbine that in the older European patent application with the file reference 10002439.7 is described. While that is particularly well suited for pure gas production or for processes with only slight liquid production, the inventive method is suitable for processes with relatively high cooling capacity of about 120 kW or higher, which is usually required at relatively high liquid product proportion (the numerical value 120 kW refers to the turbine power that is released into the heat). The molar total amount of liquid end product in the process is for example more than 10% of the gaseous pressure product (usually the gaseous pressure oxygen)

The invention has for its object to provide a method of the type mentioned above and a corresponding device, which are economically particularly favorable to operate.

This object is achieved in that the mass flow ratio between the first air flow and the second air flow is between 0.38 and 0.67 and the pressure ratio at the cold compressor is 1.3 to 2.3. This results in a particularly efficient process. In a particularly preferred embodiment, the mass flow ratio between the first air flow and the second air flow is between 0.45 and 0.51 and / or the pressure ratio at the cold compressor is 1.6 to 1.8.

Both air streams are preferably introduced into the high-pressure column in the process according to the invention after their (pseudo) liquefaction) or work-performing expansion. Alternatively, at least a portion of the first and / or the second air stream may be introduced into the low-pressure column, in particular after flowing through a separator for phase separation and optionally after supercooling.

The "main heat exchanger" may be formed of one or more parallel and / or serially connected heat exchanger sections, for example one or more plate heat exchanger blocks.

The two expansion machines are preferably formed by expansion turbines. They are "parallel" switched; that means in the present application that their inlet and outlet pressures and inlet temperatures are each equal in pairs. The inlet pressure of the working expansion is "substantially equal" to the first pressure, that is, the second air flow is not subjected to Nachverdichtungsschritt between the main air compressor and work-performing relaxation; smaller pressure differences caused by the natural pressure loss when flowing through the intermediary apparatus are permitted.

In the method according to the invention, the first pressure, to which the total air is compressed, is "significantly higher" than the operating pressure of the high-pressure column. This means here that the pressure difference between the first pressure and the operating pressure of the high-pressure column not only corresponds to the natural pressure drop through lines, heat exchangers and other apparatus, but at least 1 bar, preferably at least 3 bar, most preferably at least 5 bar.

The pressure difference between the first pressure and the operating pressure of the high-pressure column is, for example, 5 to 25 bar, preferably 7 to 15 bar. (All pressures given here and below are absolute pressures.)

• – Erster Druck (stromabwärts des Hauptluftverdichters): 10 bis 25 bar, vorzugsweise 16 bis 20 bar
• – Betriebsdruck der Hochdrucksäule: 4 bis 8 bar, vorzugsweise 5 bis 7 bar
• – Zweiter Druck stromabwärts des warmen Nachverdichters 12 bis 31 bar, vorzugsweise 19 bis 25 bar
• – Dritter Druck stromabwärts des Kaltverdichters 20 bis 52 bar, vorzugsweise 32 bis 42. bar
• – Erhöhter Druck des Produktdruckstroms 6 bis 50 bar, vorzugsweise 25 bis 35 bar.

For example, the process according to the invention is run with the following pressures:

• - First pressure (downstream of the main air compressor): 10 to 25 bar, preferably 16 to 20 bar
• - Operating pressure of the high pressure column: 4 to 8 bar, preferably 5 to 7 bar
• - Second pressure downstream of the hot booster 12 to 31 bar, preferably 19 to 25 bar
• - Third pressure downstream of the cold compressor 20 to 52 bar, preferably 32 to 42. bar
• - Increased pressure of the product pressure stream 6 to 50 bar, preferably 25 to 35 bar.

In principle, every level of product pressure is possible, in particular also a plurality of pressure levels. For example, liquid oxygen can be brought to 30 bar in an internal compression pump and divided in cold into two partial streams upstream of the main heat exchanger, one of which is throttled to a lower pressure before it is vaporized and heated in the main heat exchanger. Alternatively or additionally, one or more liquid nitrogen streams in the main heat exchanger (pseudo) are evaporated.

When the pressures of the pressurized product stream and the first air stream are subcritical, they are vaporized or liquefied in the main heat exchanger. At supercritical pressure no real phase transition takes place, then the corresponding stream is pseudo-vaporized or pseudo-liquefied.

It is favorable if the entire cold-compressed second air stream in the main heat exchanger (pseudo) is liquefied. Thereby, the entire pressure increase, which is caused by the cold compressor is concentrated on the part of air, which is used for (pseudo) evaporation of the liquid product stream. Thus, the first pressure can be selected correspondingly lower and energy saved.

Preferably, the entire introduced into the main heat exchanger compressed feed air is divided into the first and the second air flow. So there is no third air flow, but the entire feed air is either under the third pressure (pseudo) liquefied (first air flow) or supplied under the first pressure of the working expansion relaxation (second air flow). A smaller portion of the first, second or third pressure compressed air may be diverted upstream of the main heat exchanger as instrument air.

Preferably, one of the two expansion machines is mechanically coupled to the warm booster and the other of the two expansion machines mechanically coupled to the cold compressor. As a result, on the one hand, both boosters can be driven without external energy having to be used; On the other hand, the process heat is removed by the transfer of mechanical energy from the work-relaxing relaxation on the warm booster. For example, between 40 and 60%, preferably 46 to 54%, of the second air flow flow through the expansion machines coupled to the cold compressor, the remainder of the second air flow is introduced into the expansion machine coupled to the warm after-compressor.

The outlet pressure of the work-performing expansion is preferably approximately equal to the operating pressure of the high-pressure column. "About equal to" includes small pressure differences on the order of magnitude of the natural pressure drop between the discharge pressure of the work-performing expansion and the operating pressure of the high-pressure column.

Preferably, the total amount of liquid-produced products is between 0.05% and 2.0% of the amount of feed air, in particular between 0.1% and 1.0% of the amount of feed air. By "total amount of liquid products" is meant here the molar amount of liquid products such as liquid oxygen, liquid nitrogen and possibly liquid argon, which are obtained in the process as a final product.

The invention also relates to a device for the cryogenic separation of air according to the claims 7 to 9.

The invention and further details of the invention are explained in more detail below with reference to a first embodiment schematically illustrated in the drawing.

Atmospheric air is used as feed air via pipe 1 from a main air compressor 2 sucked, there to a "first pressure" of 10 to 30 bar, preferably brought about 19 bar, in a pre-cooling 3 cooled to about ambient temperature and an adsorptive air cleaning 4 fed. The purified main air flow 5 is at 6 in a first airflow 7 and a second airflow 8th branched.

The first airflow 7 is in a booster heat exchanger 9 warmed to about the cooling water temperature and in a hot-operated booster 10 further compressed to a "second pressure" of 15 to 60 bar, preferably about 25 bar. Subsequently, the heat of compression is at least partially in a first aftercooler 11 away. (Alternatively, the booster heat exchanger 9 also be omitted; In this case, the first air flow occurs below the exit temperature of the air purification 4 in the warm booster 10 one.)

The airflow 12b . 12c is then in the main heat exchanger 16 introduced and at a "first intermediate temperature" of 120 to 180 K, preferably about 48 K again from the main heat exchanger 16 taken ( 12c ) and in a cold compressor to a "third pressure" of 22 to 90 bar, preferably compressed about 40 bar. Downstream of the cold compression 113 becomes the second airflow 115 at a "second intermediate temperature" of 140 to 220 K, preferably about 180 K back into the main heat exchanger 16 is introduced and is cooled and liquefied there, or (at supercritical pressure) pseudo-liquefied. The cold first airflow 17 is relaxed to a pressure of 4 to 10 bar, preferably about 6 bar (in the example in a throttle valve 18 ) and under this pressure in at least partially liquid state via line 19 in the high pressure column 21 a distillation column system for nitrogen-oxygen separation 20 introduced, which also has a low pressure column 22 , a condenser-evaporator, not shown, and a subcooling countercurrent 23 having.

Not compressed is the second air flow 8th , He is under the first pressure in the main heat exchanger 16 introduced and cooled there to a "third intermediate temperature" of 125 to 200 K, preferably about 140 K.

The second air flow is at this intermediate temperature in two partial streams 24 . 27 Branched and work-performing relaxation in two parallel turbines 25 . 28 subjected, both at about the operating pressure of the high pressure column 21 relax. The two relaxed partial flows 26 . 29 will be reunited and lead over 30 essentially in the gas state in the high pressure column 21 initiated.

The "first intermediate temperature" (inlet temperature of the cold compressor 113 ) can be less than or equal to the "third intermediate temperature" (inlet temperature of the turbines 25 . 28 ), it is preferably - contrary to the representation in the drawing - higher. The "second intermediate temperature" (outlet temperature of the cold compressor 113 ) is higher than the turbine inlet temperature.

From the low pressure column 22 the distillation column system for nitrogen-oxygen separation 20 is oxygenated directly or through a liquid tank 31 deducted as a "liquid product stream" by a pump 32 brought in the liquid state to an elevated pressure of 4 to 70 bar, preferably about 40 bar. Under this increased pressure, the liquid or supercritical oxygen 33 in the main heat exchanger 16 vaporized or pseudo-evaporated by indirect heat exchange with the first air stream and warmed to about ambient temperature. The oxygen eventually becomes a gaseous product stream 34 issued. From the distillation column system for nitrogen-oxygen separation 20 may contain one or more additional product or residual streams 35 be deducted via the main heat exchanger. In addition or as an alternative to the internal compression of oxygen shown in the drawings, nitrogen may also be present, for example from the main condenser or from the high-pressure column of the distillation column system for nitrogen-oxygen separation 20 be densified in an analogous manner.

In the embodiment, the first turbine 25 and the warm booster 10 as well as the second turbine 28 and the cold compressor 113 mechanically coupled in pairs via a common shaft.

The booster heat exchanger 9 and the aftercooler downstream of the warm after-compressor 10 are optional. They can be omitted individually or altogether.

Notwithstanding the embodiment, the second air flow upstream of the cold post-compressor 113 even to the cold end of the main heat exchanger 16 It is then slightly throttled, then re-introduced into the cold end of the main heat exchanger, evaporated again and finally up to the inlet temperature of the compressor 113 warmed up, as for example in EP 1067345 B1 is explained in detail.

• 1. Luftverdichter mit Nachkühler, anschließend Wasserabscheider danach direkt zur Reinigungsvorrichtung.
• 2. Luftverdichter mit Nachkühler, anschließend weiterer indirekter Kaltwassernachkühler, der mit Kaltwasser aus einem Verdunstungskühler betrieben wird.
• 3. Luftverdichter ohne Nachkühler, aber mit Direktkontaktkühler (wie in der Zeichnung dargestellt), wobei der Direktkontaktkühler vorzugsweise mit einer Kühlwasseranwärmung von mehr als 10°C betrieben wird.
• 4. Wie Variante 3 mit zusätzlichem Verdunstungskühler für die Erzeugung von Kaltwasser für den Direktkontaktkühler.
• 5. Zusätzlich kann bei allen Varianten eine Kälteanlage zur Vorkühlung der Einsatzluft eingesetzt werden.

Due to the high pressure, here are all the following variations for pre-cooling the air from the air compressor 3 sense:

• 1. Air compressor with aftercooler, then water separator then directly to the cleaning device.
• 2. Air compressor with aftercooler, then another indirect cold water aftercooler, which is operated with cold water from an evaporative cooler.
• 3. air compressor without aftercooler, but with direct contact cooler (as shown in the drawing), wherein the direct contact cooler is preferably operated with a cooling water heating of more than 10 ° C.
• 4. As variant 3 with additional evaporative cooler for the production of cold water for the direct contact cooler.
• 5. In addition, in all variants, a refrigeration system can be used to pre-cool the feed air.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2004099690 A1 [0002]
• EP 10002439 [0004]
• EP 1067345 B1 [0031]

Claims (9)

Process for the cryogenic separation of air in a distillation column system ( 20 ) for nitrogen-oxygen separation, which is a high-pressure column ( 21 ) and a low pressure column ( 22 ), in which - feed air ( 1 ) in a main air compressor ( 2 ) is compressed to a first pressure which is significantly higher than the operating pressure of the high-pressure column ( 21 ), - the compressed feed air ( 5 ) into a first and a second air stream ( 7 . 8th ) and in a main heat exchanger ( 16 ) against backflow ( 34 . 35 ), - the first air stream ( 7 ) upstream of the introduction into the main heat exchanger ( 16 ) in a warm booster ( 10 ) is recompressed to a second pressure which is higher than the first pressure, - the first air flow after partial cooling in the main heat exchanger ( 16 ) at a first intermediate temperature from the main heat exchanger ( 16 ) ( 12c ) and in a cold compressor ( 113 ) is recompressed to a third pressure which is higher than the second pressure, - the cold-compressed first air flow ( 115 ) at a second intermediate temperature, which is higher than the first intermediate temperature, the main heat exchanger ( 16 ) and in the main heat exchanger ( 16 ) is further cooled and liquefied or pseudo-liquefied, - the (pseudo) liquefied first air stream ( 17 ) is introduced into the distillation column system for nitrogen-oxygen separation, - the second air stream ( 8th ) in the main heat exchanger ( 16 ) is cooled to a third intermediate temperature, below the third intermediate temperature from the main heat exchanger ( 16 ) ( 24 . 27 ) and then work-relaxed ( 25 . 28 ), - the work-performing relaxed second air flow ( 30 ) is also introduced into the distillation column system for nitrogen-oxygen separation, - a liquid product stream ( 31 ) taken from the distillation column system, brought in the liquid state to an elevated pressure ( 32 ) and under this increased pressure in the main heat exchanger ( 16 ) is vaporized or pseudo-evaporated and finally as a gaseous pressure product stream ( 34 ) and - the work-performing expansion of the second air stream in two parallel relaxation machines ( 25 . 28 ), the inlet pressure of the working expansion ( 25 . 28 ) is substantially equal to the first pressure, characterized in that - the mass flow ratio between the first air flow ( 7 ) and the second air stream ( 8th ) is between 0.38 and 0.67 and - the pressure ratio at the cold compressor ( 113 ) Is 1.3 to 2.3. A method according to claim 1, characterized in that the entire cold-compressed second air stream ( 115 ) in the main heat exchanger ( 16 ) (pseudo-) liquefied. A method according to claim 1 or 2, characterized in that the whole in the main heat exchanger ( 16 ) introduced compressed feed air to the first and the second air flow ( 7 . 8th ) is divided. Method according to one of claims 1 to 3, characterized in that one of the two expansion machines ( 25 ) mechanically with the warm booster ( 10 ) and the other of the two relaxation machines ( 28 ) mechanically with the cold compressor ( 113 ) is coupled. Method according to one of claims 1 to 4, characterized in that outlet pressure of the work-performing expansion ( 25 . 28 ) approximately equal to the operating pressure of the high-pressure column ( 21 ). Method according to one of claims 1 to 5, characterized in that the total amount of liquid products produced between 0.05% and 2.0% of the amount of feed air, in particular between 0.1% and 1.0% of the amount of feed air. Device for the cryogenic separation of air - with a distillation column system ( 20 ) for nitrogen-oxygen separation, which is a high-pressure column ( 21 ) and a low pressure column ( 22 ), - with a main air compressor ( 2 ) for compressing feed air ( 1 ) to a first pressure which is significantly higher than the operating pressure of the high-pressure column ( 21 ), - with means for dividing the compressed feed air ( 8th ) into a first and a second air stream ( 7 . 8th ), - with means for feeding the first and the second air stream into a main heat exchanger ( 16 ) for cooling against return streams ( 34 . 35 ), - with a warm booster ( 10 ) for recompressing the first air stream ( 7 ), upstream of the introduction into the main heat exchanger ( 16 ) to a second pressure which is higher than the first pressure, - with means for removing ( 12c ) of the first air stream after partial cooling to a first intermediate temperature from the main heat exchanger ( 16 ), - with a cold compressor ( 113 ) for recompressing the extracted first air stream to a third pressure, - with means for supplying the cold-compressed first air stream ( 115 ) to the main heat exchanger ( 16 ) at a second intermediate temperature higher than the first intermediate temperature for the purpose of its further cooling and liquefaction or pseudo-liquefaction in the main heat exchanger ( 16 ), - with means for introducing the (pseudo) liquefied first air stream ( 15 ) in the distillation column system for nitrogen-oxygen separation, - with means for removal ( 24 . 27 ) of the second air stream after partial cooling to a third intermediate temperature from the main heat exchanger ( 16 ), - with means for work-relaxing ( 25 . 28 ) of the extracted second air stream ( 24 . 27 ) from the first pressure, - with means for introducing the working expanded second air stream ( 30 ) in the distillation column system for nitrogen-oxygen separation, - with means for removing a liquid product stream ( 31 ) from the distillation column system, - with resources ( 32 ) to increase the pressure to an elevated pressure of the liquid product stream ( 31 ), - with means for introducing the liquid product stream under this increased pressure into the main heat exchanger ( 16 ) for evaporation or pseudo-evaporation, and - means for stripping the (pseudo) vaporized product stream as a gaseous stream of pressurized product ( 34 ), - with means for transferring a first part of the work-performing relaxation ( 21 ) generated mechanical energy to the cold compressor ( 13 ), Whereby the means for work-performing relaxation are two parallel relaxation machines ( 25 . 28 ), characterized by control means which - the mass flow ratio between the first air flow ( 7 ) and the second air stream ( 8th ) in the normal operation of the plant to be between 0.38 and 0.67, and - the pressure ratio at the cold compressor ( 113 ) during normal operation of the system so that it is 1.3 to 2.3. Apparatus according to claim 7, characterized in that the means for supplying the cold-compressed first air flow ( 12b ) to the main heat exchanger ( 16 ) are formed so that during operation of the device, the entire cold-compressed second air stream ( 12c ) in the main heat exchanger ( 16 ) (pseudo-) liquefied. Apparatus according to claim 7 or 8, characterized in that all means for guiding feed air are formed so that during operation of the device, the entire in the main heat exchanger ( 16 ) introduced compressed feed air ( 5 ) to the first and second air streams ( 7 . 8th ) is divided.

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