TW201637998A - Method and apparatus for obtaining a compressed nitrogen product - Google Patents

Abstract

The method and apparatus serve to obtain a compressed nitrogen product by low-temperature fractionation of air in a distillation column system having a high-pressure column (10) and a low-pressure column (11) and a main condenser (12) and a low-pressure column top condenser (13), both of which take the form of condenser-evaporators. Bottoms liquid (28, 29) from the low-pressure column is introduced into the evaporation space of the low-pressure column top condenser (13). Gas formed therein is decompressed to perform work as residual gas (30, 31) in a first residual gas turbine (33). The mechanical energy generated is used to drive a cold compressor (36). A first compressed nitrogen product stream (19) is drawn off in gaseous form from the top of the high-pressure column (10) and warmed in the main heat exchanger (8). A further nitrogen stream (37) is drawn off in gaseous form from the top of the low-pressure column (11), compressed in the cold compressor (36) to a pressure which is at least equal to the pressure of the first compressed nitrogen product stream (19) when it is drawn off from the high-pressure column (10), and is then warmed as the second compressed nitrogen product stream (38) in the main heat exchanger (8). The cold compressor (36) overcomes a pressure differential which is at least equal to two thirds of the pressure differential between the top of the high-pressure column (10) and the top of the low-pressure column (11).

Description

Method and apparatus for extracting pressurized nitrogen products

The present invention is directed to a method as set forth in the introduction to claim 1.

A general description of the low-temperature separation of air and a detailed description of the structure of the two-column equipment can be found in Hausen/Linde's monograph "Cryogenic Technology" (2nd edition, 1985) and a paper by Latimer published in Chemical Engineering Progress (1967) Vol. 63, No. 2, p. 35). The heat exchange relationship between the high pressure column and the low pressure column in the double column is usually achieved by passing through a main condenser in which the gas at the top of the high pressure column is liquefied by the evaporation of the bottom liquid from the lower pressure column.

The main condenser and the low pressure column overhead condenser are constructed as condensation evaporators in the present invention. "Condensing evaporator" means a heat exchanger that provides indirect heat exchange between a first condensed fluid stream and a second condensed fluid stream. Each of the condensing evaporators has a liquefaction chamber and an evaporation chamber formed by a liquefaction passage or an evaporation passage, respectively. The first fluid stream condenses (liquefies) in the liquefaction chamber, and the second fluid stream evaporates in the evaporation chamber. The evaporation chamber and the liquefaction chamber are formed by a group of channels having a heat exchange relationship with each other.

Wherein, the two condensers may be formed by a single heat exchanger block, or may be formed by a plurality of heat exchanger blocks disposed in the common pressure vessel. Both condensers can be constructed as single or multi-block bath evaporators, forced flow evaporators or falling film evaporators. Furthermore, the main condenser can be constructed as a cascade evaporator, as described in, for example, EP 1287302 B1=US 6748763 B2.

The “main heat exchanger” is used to cool the indirect heat exchange with the reflux of the distillation column system. Air used (Einsatzluft). It may be formed by a single heat exchanger section or a plurality of parallel and/or series heat exchanger sections (e.g., one or several plate heat exchanger blocks).

A method of the aforementioned type is disclosed in US 4,453,957. Here, the mechanical energy obtained in the residual gas turbine is used only for refrigeration.

It is an object of the present invention to provide a process and a corresponding apparatus which are capable of extracting nitrogen from a low pressure column at least under high pressure column pressure and having a particularly low energy consumption during this period.

The feature of claim 1 is the solution of the invention to achieve this.

The mechanical energy generated in the first residual gas turbine (33) is at least partially used to drive a cold compressor, which is used directly here to compress the nitrogen product, ie the low pressure column, for example, generally reaches the high pressure column pressure or higher. Pressure nitrogen products.

It has surprisingly been found within the scope of the present invention that the process of the present invention allows the low pressure column nitrogen to reach the pressure level of the high pressure column nitrogen and is energy efficient. As a side effect, a relatively simple procedure is thus formed, and equipment investment is also low, especially for the main heat exchanger.

The process of the invention employs the following pressure ranges: high pressure column (top): for example 12 bar to 17 bar, preferably 13 bar to 16 bar

Low pressure column (top): for example 6bar to 10bar, preferably 7bar to 9bar

In the present invention, the first pressurized nitrogen product stream and the second pressurized nitrogen product stream may be separately heated in the main heat exchanger. Preferably, however, the first pressurized nitrogen product stream and the second pressurized nitrogen product stream are mixed upstream of the main heat exchanger.

An additional third pressurized nitrogen stream may be formed from another portion of the nitrogen product of the lower pressure column as desired, by directing this portion directly into the main heat exchanger and outputting it as a product at low pressure column pressure (without pressure loss).

The first residual gas turbine is mechanically coupled to the cold compressor based on a first energy transfer scheme between the first residual gas turbine and the cold compressor. This point can be transmitted through the shared shaft or Implemented by moving the device.

To generate process cooling, the residual gas turbine can be mechanically coupled to a generator or hydraulic brake.

According to a second energy transfer scheme between the first residual gas turbine and the cold compressor, the first residual gas turbine is mechanically coupled to the generator, and the cold compressor is driven by the electric motor; in this case, the energy generated by the generator It is electrically transmitted to the motor to drive the cold compressor.

Alternatively, the second portion of the residual gas heated to the intermediate temperature may be expanded in the second residual gas turbine, the second residual gas turbine being coupled in parallel with the first residual gas turbine coupled to the cold compressor. In this case, the first residual gas turbine may be coupled to the cold compressor separately, and the second residual gas turbine may be coupled to the generator or the dissipative brake.

In the case where the pressure of the high pressure column is insufficient, the first pressurized nitrogen stream, the second pressurized nitrogen stream, or the second pressurized nitrogen stream may be further compressed in the nitrogen compressor downstream of the main heat exchanger. The two pressurized nitrogen streams preferably together achieve a higher pressure in the nitrogen compressor.

In this case, it is preferable to concentrate the air compression and the nitrogen compression on the only one machine, which is implemented by compressing the air used in the main air compressor, which is the i-stage starting from the n-stage multi-compressor. Form, n 2, i < n. Among them, the nitrogen compressor is formed by the last ni stage of the n-stage multi-compressor. For example, an eight-stage compressor is used, and the last three to four stages are used as nitrogen compressors.

The invention further relates to an apparatus for extracting a pressurized nitrogen product by cryogenically separating air as in claim 14.

The apparatus of the present invention may be supplemented by one, several or all of the features of the independent method request.

The invention and other technical details of the invention are explained in detail below in conjunction with the embodiments shown in the drawings.

1‧‧‧Filter

2‧‧‧Main air compressor

3‧‧‧Compressed air

4‧‧‧Precooling device

5‧‧‧Air used for pre-cooling

6‧‧‧purification device

7‧‧‧Air used for compression, pre-cooling and purification

8‧‧‧Main heat exchanger

9‧‧‧ pipeline

10‧‧‧High Voltage Tower

11‧‧‧Low-voltage tower

12‧‧‧Main condenser

13‧‧‧Low-pressure tower top condenser

14‧‧‧ top gas

15‧‧‧Part 1

16‧‧‧Liquid nitrogen

17‧‧‧Part II

18‧‧‧UKG

19‧‧‧Part II / First pressurized nitrogen product stream

20‧‧‧ pipeline

21‧‧‧Hot pressurized nitrogen

22‧‧‧Nitrogen compressor

23‧‧‧Recooler

24‧‧‧ Liquid Oxygen

25

26‧‧‧ top gas

27‧‧‧Liquid nitrogen

28‧‧‧ bottom liquid

29‧‧‧ pipeline

30‧‧‧Residual gas

31‧‧‧Residual gas downstream of UKG 18

32‧‧‧Residual gas at intermediate temperature

33‧‧‧First residual gas turbine

34‧‧‧Expanded residual gas

35‧‧‧heated residual gas

36‧‧‧ Cold compressor

37‧‧‧Nitrate flow

38‧‧‧Second pressurized nitrogen product stream

39‧‧‧ flushing pipeline

40‧‧‧Generator

41‧‧‧Regulator

49‧‧‧Send to

233‧‧‧Residual gas turbine

240‧‧‧Generator

302‧‧‧Multiple Compressor

419‧‧‧heated nitrogen flow/pipeline

438‧‧‧heated nitrogen flow

420

540‧‧‧Motor

619‧‧‧throttle valve / throttling

701‧‧‧ flushing flow

Figure 1 is a first embodiment of the present invention comprising a single residual gas turbine; Figure 2 is a second embodiment comprising two residual gas turbines; Figure 3 is a variant of Figure 1 comprising a dual compressor; Figure 4 is a diagram Another variant of 1 is that the two pressurized nitrogen product streams are heated separately; Figure 5 is an embodiment of electrical energy transfer between the first residual gas turbine and the cold compressor; Figure 6 is a product pressure slightly lower than the high pressure column pressure Variations; Figure 7 is an embodiment similar to Figure 6, but including a forced flow evaporator; and Figure 8 is a system similar to the system of Figure 4, but comprising several juxtaposed towers.

In Fig. 1, the main air compressor 2 draws atmospheric air (AIR) through the filter 1 and compresses it to a pressure of about 15 bar. The compressed air 3 is cooled in the pre-cooling unit 4. This pre-cooling device may comprise a subcooler for indirect cooling or a direct contact cooler, or both. The pre-cooled air 5 is purified in a purification device 6, which is typically formed by a pair of switchable adsorbers. The air 7 used for compression, pre-cooling and purification is substantially cooled to the dew point in the main heat exchanger 8 and introduced into the high-pressure column 10 by the line 9.

The high pressure column 10 is part of a distillation column system which additionally has a low pressure column 11, a main condenser 12 and a low pressure column overhead condenser 13. The first portion 15 of the top gas 14 of the higher pressure column 10 is directed to the liquefaction chamber of the main condenser 12 where it is at least partially condensed. The liquid nitrogen 16 formed in the liquefaction chamber of the main condenser 12 is introduced into the high pressure column 10 and the first portion thereof serves as a reflux there. The second portion 17 of liquid nitrogen is cooled in the UKG 18 and sent to the top of the (49) low pressure column 11.

The second portion 19 of the top gas 14 of the higher pressure column 10 is passed as a first pressurized nitrogen product stream 19 from line 20 to the main heat exchanger 8 where it is substantially heated to ambient temperature. As shown in FIG. 1, the hot pressurized nitrogen 21 can be further improved in the nitrogen compressor 22 including the recooler 23. The pressure can in principle be increased to any desired discharge pressure. The hot pressurized nitrogen is finally extracted as a pressurized nitrogen product (PGAN). The nitrogen compressor 22 and the subcooler 23 can be eliminated if the desired product pressure is not higher than the high pressure column pressure (excluding the pressure loss).

Liquid raw oxygen (Rohsauerstoff) 24 is extracted from the bottom layer of the high pressure column 10, which is cooled in the UKG 18 and introduced into the low pressure column 11 at an intermediate position.

The top gas 26 of the lower pressure column 11 is directed to the liquefaction chamber of the lower condenser 13 of the lower pressure column. The liquid nitrogen 27 formed there is introduced into the low pressure column 11. The bottom liquid 28 of the lower pressure column 11 is cooled in the UKG 18 and introduced by line 29 into the evaporation chamber of the lower condenser 13 of the lower pressure column, which is continuously or intermittently flushed by the flush line 39. The gas generated there is heated as residual gas 30 in the UKG 18. The residual gas 31 downstream of the UKG 18 is sent from the cold end to the main heat exchanger 8 where it is heated to an intermediate temperature. The residual gas 32 at the intermediate temperature is sent to the first residual gas turbine 33 where it expands to perform work. The expanded residual gas 34 is again sent to the main heat exchanger 8 and heated to the hot end temperature. The heated residual gas 35 exits the apparatus generally at ambient temperature. The residual gas turbine 33 is mechanically coupled to the cold compressor 36 via a common shaft or transmission.

A nitrogen stream 37 is extracted from the top of the lower pressure column 11 in a gaseous state, which is generally compressed in a cold compressor 36 to a high pressure column pressure, directed via a regulating valve 41, and then used as a second pressurized nitrogen product stream 38 and a first pressurization The nitrogen product stream 19 is mixed and heated together in the main heat exchanger 8 and finally extracted as a pressurized nitrogen product (PGAN).

To compensate for the cold losses of the equipment, the residual gas turbine 33 does not provide all of its mechanical energy to the cold compressor 36, but additionally drives the generator 40, which is mounted on the same shaft or connected to the same transmission. . Instead of the generator 40, a dissipative brake, such as a hydraulic brake, can also be used.

Two parallel residual gas turbines 33, 233 are used in Figure 2, one of which is coupled to the cold compressor 36 and the other to the generator 240 (or dissipative brake).

In FIGS. 1 and 2, the main air compressor 2 and the nitrogen compressor 22 are composed of two independent machines. Formed, while the embodiment shown in Figure 3 uses a duplex compressor 302 that can perform two tasks. In an embodiment, the dual compressor has n = 8 stages, wherein i = 5 stages form the main air compressor 2. The remaining n-i = 3 stages form a nitrogen product compressor. Thereby a PGAN final pressure of about 70 to 100 bar can be achieved.

In the embodiment of Figure 4, the two pressurized nitrogen product streams 19, 38 are heated in separate sets of channels of the main heat exchanger 8. The heated nitrogen streams 419 and 438 meet at 420. Thereby, the second pressurized nitrogen product stream 38 from the cold compressor 36 can be fed to the main heat exchanger 8 at a higher temperature than the first pressurized nitrogen product stream 19. This can slightly improve the program's energy efficiency.

Unlike FIG. 1, the energy transfer between the first residual gas turbine 33 and the cold compressor 36 is performed electrically, rather than mechanically, in FIG. To this end, the first residual gas turbine 33 is mechanically coupled to the generator 40. The electrical energy obtained there is at least partially transmitted to the motor 540 through a wire network that is mechanically coupled to and driven by the cold compressor 36.

Compared to Figure 2, all of the residual gas expands in the generator-turbine 33/40 and thereby also produces the energy required to drive the cold compressor.

The specific features of Figures 2 to 5 can also be combined with one another in any manner, for example to form a channel group comprising two residual gas turbines and a duplex compressor and having two channels for the two pressurized nitrogen streams in the main heat exchanger. system. In all embodiments, the high pressure column (including the frit) and the low pressure column (including the packing or frit) are stacked one on top of the other. As an alternative, the high pressure column and the low pressure column can be built side by side. The invention is also applicable to offshore solutions, such as floating oil recovery (EOR) for use in oil or gas fields.

6 is substantially identical to FIG. 4, but a throttle valve 619 is further provided in the line 419 herein. In the variant shown here, the product pressure was 10.9 bar when the top pressure of the high pressure column was 12.0 bar. Here, the nitrogen stream 37 from the top of the lower pressure column is correspondingly only compressed to 11.1 bar in the cold compressor 36, ie not fully compressed to the high pressure column pressure. The nitrogen flow comes from high The nitrogen stream 419, which is turbulent and throttled by a throttle 619, converges at 420 at a desired pressure of 10.9 bar.

The main point is that the throttle 619 is carried out downstream of the main heat exchanger 8. Thereby, the throttling loss is minimized to an unexpected extent and the air pressure used can be reduced. By selecting a correspondingly higher pressure loss in the main heat exchanger 8, it is also possible to carry out a throttle operation from 12.0 bar to 10.9 bar in whole or in part. Thereby, the main heat exchanger 8 can be constructed particularly tightly.

7 differs from FIG. 6 in that a forced flow evaporator is used instead of a bath evaporator as the main condenser 12 and the low pressure column overhead condenser 13. In this case, the flushing stream 701 (Purge) is extracted from the bottom layer of the high pressure column 10. As an alternative, a falling film evaporator can also be used as the main condenser 12.

In Fig. 8, the high pressure column 10 is juxtaposed with the low pressure column 11, instead of being stacked one above another as shown in Figs. In other respects, Figure 8 is the same as Figure 4 or Figure 5 - depending on whether the nitrogen product is at the pressure of the high pressure column or at a pressure slightly lower than the pressure of the high pressure column (throttle valve 619).

1‧‧‧Filter

2‧‧‧Main air compressor

3‧‧‧Compressed air

4‧‧‧Precooling device

5‧‧‧Air used for pre-cooling

6‧‧‧purification device

7‧‧‧Air used for compression, pre-cooling and purification

8‧‧‧Main heat exchanger

9‧‧‧ pipeline

10‧‧‧High Voltage Tower

11‧‧‧Low-voltage tower

12‧‧‧Main condenser

13‧‧‧Low-pressure tower top condenser

14‧‧‧ top gas

15‧‧‧Part 1

16‧‧‧Liquid nitrogen

17‧‧‧Part II

18‧‧‧UKG

19‧‧‧Part II / First pressurized nitrogen product stream

20‧‧‧ pipeline

21‧‧‧Hot pressurized nitrogen

22‧‧‧Nitrogen compressor

23‧‧‧Recooler

24‧‧‧ Liquid Oxygen

25

26‧‧‧ top gas

27‧‧‧Liquid nitrogen

28‧‧‧ bottom liquid

29‧‧‧ pipeline

30‧‧‧Residual gas

31‧‧‧Residual gas downstream of UKG 18

32‧‧‧Residual gas at intermediate temperature

33‧‧‧First residual gas turbine

34‧‧‧Expanded residual gas

35‧‧‧heated residual gas

36‧‧‧ Cold compressor

37‧‧‧Nitrate flow

38‧‧‧Second pressurized nitrogen product stream

39‧‧‧ flushing pipeline

40‧‧‧Generator

49‧‧‧Send to

Claims (14)

A method for extracting a pressurized nitrogen product by cryogenically separating air in a distillation column system, the distillation column system having a high pressure column (10) and a low pressure column (11) and a main condenser (12) and a low pressure column overhead condenser (13) The second condenser is constructed as a condensing evaporator, wherein the air (7) used for compression, pre-cooling and purification is cooled in the main heat exchanger (8) and at least partially introduced into the high-pressure column (10), The top gas (14, 15) of the high pressure column is introduced into the liquefaction chamber of the main condenser (12), and at least a portion of the liquid nitrogen (16) formed in the liquefaction chamber of the main condenser (12) is introduced into the high pressure column (10), the top gas (26) of the low pressure column (11) is introduced into the liquefaction chamber of the lower condenser (13) of the low pressure column, and the liquid nitrogen formed in the liquefaction chamber of the condenser (13) at the top of the low pressure column ( At least a portion of 27) is introduced into the lower pressure column (11), and the bottom liquid (28, 29) of the lower pressure column (11) is introduced into the evaporation chamber of the lower condenser (13) of the lower pressure column, resulting in condensation at the top of the lower pressure column. The gas in the evaporation chamber of the device (13) is heated as a residual gas (30, 31) in the main heat exchanger (8) to an intermediate temperature, at least A portion (32) is expanded in the first residual gas turbine (33) for work, again sent to the main heat exchanger (8) and heated to the hot end temperature of the main heat exchanger (8), from the low pressure tower (11) a top gaseous extraction nitrogen stream (37), and extracting a first pressurized nitrogen product stream (19) from the top of the high pressure column (10) and heating it in the main heat exchanger (8), characterized in that The mechanical energy generated by the first residual gas turbine (33) is at least partially used to drive the cold compressor (36), The nitrogen stream (37) extracted from the top of the lower pressure column (11) is compressed in the cold compressor (36) to a pressure at least equal to the first pressurized nitrogen product stream (19) being extracted from The high pressure column (10) is subtracted from the pressure after 2 bar, and then the nitrogen stream is heated as a second pressurized nitrogen product stream (38) in the main heat exchanger (8) and the gaseous state is extracted from the lower pressure column (11) The nitrogen stream (37) at the top is compressed in the cold compressor (36) to a pressure at least equal to the first pressurized nitrogen product stream (19) being extracted from the high pressure column (10) The pressure after 2 bar is subtracted, and then the nitrogen stream is heated as a second pressurized nitrogen product stream (38) in the main heat exchanger (8), wherein the cold compressor (36) overcomes a pressure differential The pressure difference is at least equal to two-thirds of the pressure difference between the top of the high pressure column (10) and the top of the low pressure column (11). The method of claim 1, wherein the first pressurized nitrogen product stream (19) and the second pressurized nitrogen product stream (38) are mixed upstream of the main heat exchanger (8). The method of claim 1 or 2, wherein the first residual gas turbine (33) is mechanically coupled to the cold compressor (36) via a common shaft or transmission. The method of claim 3, characterized in that the first residual gas turbine (33) is also mechanically coupled to a generator (40) or a hydraulic brake. The method of claim 1 or 2, wherein the first residual gas turbine (33) is mechanically coupled to a generator (40) that is driven by the electric motor (540) and is The energy of the generator (40) is at least partially electrically transmitted to the motor (540). The method of any one of claims 1 to 5, characterized in that the second portion of the residual gas (32) heated to the intermediate temperature is in a second residual gas in parallel with the first residual gas turbine (33) The expansion work is performed in the turbine (233). The method of claim 6 characterized in that the first residual gas turbine (33) is mechanically coupled to the cold compressor (36) and the second residual gas turbine is mechanically coupled to the generator (240) or the dissipative brake . The method of any one of claims 1 to 7, characterized in that the first pressurized nitrogen stream, the second pressurization is further compressed in a nitrogen compressor (22) downstream of the main heat exchanger (8) A stream of nitrogen or a stream of the two pressurized nitrogen. The method of claim 8, characterized in that the used air is compressed in a main air compressor (2) formed by an i-stage beginning with an n-stage multi-compressor (302), n 2, i < n, and the nitrogen compressor (22) is formed by the last ni stage of the n-stage duplex compressor (302). The method of any one of claims 1 to 9, wherein the nitrogen stream (37) extracted from the top of the lower pressure column (11) is compressed to a pressure in the cold compressor (36), The pressure is at least equal to the pressure at which the first pressurized nitrogen product stream (19) is extracted from the higher pressure column (10). The method of any one of claims 1 to 10, wherein the first pressurized nitrogen product stream (19) and the second pressurized nitrogen product stream (38) are heated in separate channels, and The specific words then merge. The method of any one of claims 1 to 11, characterized in that at least one, several or all of the following measures are employed: the main condenser (12) is constructed as a forced flow evaporator, the main condensation The reactor (12) is constructed as a falling film evaporator, and the low pressure column top condenser (13) is constructed as a forced flow evaporator. The method of any one of claims 1 to 12, wherein the low pressure column (11) is juxtaposed with the high pressure column (10), the main condenser (12) is disposed above the high pressure column (10), and The lower pressure column top condenser (13) is disposed above the low pressure column. An apparatus for extracting a pressurized nitrogen product by cryogenic separation of air, comprising: a distillation column system having a high pressure column (10) and a low pressure column (11) and a main condenser (12) and a low pressure column overhead condenser (13), The two condensers are constructed as a condensing evaporator, a main heat exchanger (8) for cooling the air (7) used for compression, pre-cooling and purification, wherein the liquefaction chamber of the main condenser (12) and the high pressure The top of the tower (10) is connected by a flow connection (14, 15, 16), and the liquefaction chamber of the top condenser (13) of the low pressure column is connected to the top of the low pressure column (11) (26, 27), and the low pressure The evaporation chamber of the top condenser (13) of the column is connected to the bottom layer of the low pressure column (11) (28, 29), and includes: a gas for generating an evaporation chamber of the condenser (13) at the top of the low pressure column. a means for extracting residual gas (30, 31) for heating the residual gas (31) to an intermediate temperature in the main heat exchanger (8) for causing the partially heated residual gas ( 32) a first residual gas turbine (33) for expanding work, means for introducing the expanded residual gas (34) into the main heat exchanger (8), and for Means for extracting the heated residual gas from the hot end of the main heat exchanger (8), using the mechanical energy generated by the first residual gas turbine (33) to drive the cold compressor (36), and Extracting a gaseous first pressurized nitrogen product stream (19) from the top of the higher pressure column (10) and a first pressurization for heating the first pressurized nitrogen product stream (19) in the main heat exchanger (8) a nitrogen product line characterized by Means for extracting a gaseous nitrogen stream (37) from the top of the lower pressure column (11), means for introducing the gaseous nitrogen stream (37) to the cold compressor (36), and for cold compression The nitrogen stream is introduced as a means for introducing a second pressurized nitrogen product stream (38) into the main heat exchanger (8), wherein the cold compressor (36) is designed to overcome a pressure differential that is at least equal to the high pressure column (10) Two-thirds of the pressure difference between the top and the top of the low pressure column (11).