EP2313724A2

EP2313724A2 - Process and device for cryogenic air fractionation

Info

Publication number: EP2313724A2
Application number: EP09777817A
Authority: EP
Inventors: Alexander Alekseev
Original assignee: Linde GmbH
Current assignee: Linde GmbH
Priority date: 2008-08-14
Filing date: 2009-08-11
Publication date: 2011-04-27
Also published as: WO2010017968A3; US20110214453A1; WO2010017968A2

Abstract

The process and the device serve for cryogenic air fractionation, in particular for supplying an oxygen-enriched product stream to an oxyfuel power plant. The distillation column system for nitrogen/oxygen separation has a high-pressure column (26) and a low-pressure column (32). The high-pressure column (26) and the low-pressure column (32) are thermally coupled via a condenser-evaporator (37). Feed air (1) is compressed in an air compressor (3), cooled at least in a first post-cooler (6) and purified in a purification device (22), cooled in a main heat exchanger (23a, 23b, 23c) and introduced at least in part (25, 29) into the high-pressure column (26). At least one liquid stream (33, 35) is introduced from the high-pressure column (26) into the low-pressure column (32). An oxygen-enriched product stream (41, 45, 46,47, 48) is taken off from the low-pressure column (32). A first nitrogen stream (63, 64, 65, 66) is withdrawn from the high-pressure column (26) and warmed to a temperature of at least 280 K (6). The warmed first nitrogen stream (67) is work-expanded (72) in a first warm expansion engine (68). The first nitrogen stream (70, 71) which is expanded in the first warm expansion engine (68) is work-expanded in a second warm expansion engine (72).

Description

description

Method and apparatus for the cryogenic separation of air

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

The basics of cryogenic separation of air in general and the construction of two-column plants in particular are described in the monograph "Cryogenics" by Hausen / Linde (2nd edition, 1985) and in an article by Latimer in Chemical Engineering Progress (Vol. 63, No.2, 1967, page 35). The thermal coupling between the high pressure column and the low pressure column is usually realized by a designed as a condenser evaporator main condenser, is liquefied in the head gas of the high pressure column against evaporating bottom liquid of the low pressure column.

The feed air for the cryogenic separation is compressed in an air compressor and cleaned in a cleaning device before it is cooled in a main heat exchanger to about dew point. The cleaning device preferably operates with at least two switchable containers which contain an adsorbent, for example a molecular sieve, and have to be periodically regenerated, either by temperature swing (TSA) or by pressure swing adsorption (PSA). When regenerating one of the containers is traversed by a regeneration gas.

The warm relaxation machine is used for the recovery of pressure energy, which can not be used in the air separation itself. Excess energy from the air separation is converted into mechanical energy (work). This can be delivered, for example, to a generator connected to the relaxation machine and converted there into electrical energy.

Methods of the type mentioned are known from FR 2690982 A1 and JP 11063811 A. The invention has for its object to improve this process energetically.

This object is solved by the characterizing feature of claim 1. In addition to the first warm relaxation machine for the first nitrogen flow from the high pressure column, a second warm expansion machine is used, which is serially connected to the first. Such a two-stage warm relaxation has heretofore been considered to be an excessive expense for recovering excess energy. As part of such warm relaxations (often referred to as hot gas turbine processes) was therefore not considered to use two- or multi-stage relaxations. In the context of the invention, however, it has surprisingly been found that in certain processes, in particular those which are used for the oxygen supply of oxyfuel power plants, the energetic advantage outweighs the additional equipment expense.

A "warm relaxation machine" is understood here to mean a relaxation machine whose inlet temperature is 280 K or more, for example 290 K or more, in particular 300 K or more or 320 K or more

The inlet temperature of the first warm expansion turbine is in the invention, for example, 330 to 360 K, preferably 340 to 350 K. The first nitrogen stream is there to an intermediate pressure of 2 to 3 bar, preferably 2.1 to 2.5 bar relaxed and then in the second warm expansion turbine of the intermediate pressure to a final pressure of 1, 1 to 1, 2 bar.

The high-pressure column has a higher operating pressure than the low-pressure column. Typical values (in each case at the top of the columns) are 4.5 to 5.2 bar in the high-pressure column and below 1.4 bar, preferably below 1.25 bar in the low-pressure column.

The first nitrogen stream, which is expanded in the warm expansion machines, is taken from the pressure column in gaseous form, for example from the top of it or from an intermediate point in the upper region of the column. The obtained during the relaxation of the first nitrogen flow mechanical energy can directly to drive a Be used compressor; Preferably, it is converted into electrical energy in a respective generator coupled to the expansion machines.

It is favorable if the warming-up of the first nitrogen stream is carried out at least in part on the first after-cooler and the first nitrogen stream is brought there in indirect heat exchange with the air downstream of the air compressor. As a result, the waste heat of the air compressor is used to heat the nitrogen before work-performing relaxation. This increases energy generated during relaxation. The second stream of nitrogen exits the warm end of the main heat exchanger at about ambient temperature, for example, and is further brought to the elevated temperature of 330 to 360 K, preferably 340 to 350 K in the first aftercooler and fed under this elevated temperature of the first warm expansion machine. The final temperature, ie the outlet temperature of the second expansion machine is then, for example, 283 to 313 K. Alternatively, to heat the first nitrogen stream residual heat from another source can be used, for example, from an adjacent system that supplies such residual heat.

The two-stage expansion according to the invention allows an intermediate heating and thus an increased outlet temperature from the final stage with the same or even higher energy production. As a result, in particular energy can be saved if, in the further use of the first nitrogen stream - such as a regeneration gas - an elevated temperature is needed.

In this case, in particular the first nitrogen stream is warmed up in the first aftercooler and then expanded in the first expansion machine to an intermediate pressure, and the first nitrogen stream relaxed to the intermediate pressure is heated in a second after-compressor and then expanded in a second expansion machine to a final pressure which is lower as the intermediate pressure is. Even if residual heat from another source to

Warming the first nitrogen flow is used, the transfer of this heat can be performed in two stages, which are arranged in front of the first and second expansion machine.

The first and the second aftercooler are preferably connected in parallel on the air side. For interheater so again waste heat of the air compressor is used.

Preferably, the work in the second hot expansion machine relaxed first nitrogen stream is at least partially as a regeneration in the

Cleaning device used. Since the exhaust gas of the second expansion machine in the invention has a relatively high temperature, in this way energy can be saved, which would otherwise be necessary for the heating of the regeneration gas.

It is also advantageous if a second stream of nitrogen withdrawn from the high-pressure column, is warmed in the main heat exchanger to an intermediate temperature, the second nitrogen flow warmed to the intermediate temperature in a cold expansion machine work expanded and then reheated in the main heat exchanger. In this way, the pressure energy contained in the nitrogen from the high pressure column can also be used to generate process refrigeration.

The working expanded second nitrogen stream can - in addition to or as an alternative to the first nitrogen stream - at least partially as a regeneration in the

Cleaning device can be used. Operationally particularly advantageous is to use both nitrogen streams as regeneration gas. The process thus provides two sources of regeneration gas, one of which is independent of refrigeration. This operationally undesirable coupling of Regeneriergasmenge is canceled to the amount of cold generated. Regenerating gas volume and refrigeration can be optimized independently of each other. Overall, the process is technically particularly simple and energetically particularly favorable.

The regeneration gas derived from the first and / or second nitrogen streams may be heated in an electric or steamed regeneration gas heater prior to introduction to the purifier.

Both the first and second streams of nitrogen are preferably made from the high pressure column operating pressure (minus line losses) to some extent superatmospheric pressure working expanded, sufficient to deliver the streams after flowing through the purifier to the atmosphere. The use as a regeneration usually takes place only temporarily when there is a corresponding need of the cleaning device. At the same time, part of the work-performing expanded nitrogen from the cold and / or warm relaxation can be released as a gaseous nitrogen product or released directly into the atmosphere.

The invention also relates to a device for cryogenic separation of air according to claim 8. Particularly advantageous embodiments are set forth in claims 9 to 14.

Furthermore, the invention relates to oxyfuel power plant and a method for operating an oxyfuel power plant according to claims 15 and 16, respectively

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

Atmospheric air 1 is sucked in via a filter 2 from an air compressor 3 and compressed there to a pressure of 4.8 to 5.0 bar. The compressed feed air 4 is cooled to a first part 5 in a first aftercooler 6, to a second part 7 in a second aftercooler 8 and to a third part 9 in a third aftercooler 10. The air streams from the aftercoolers are then combined, optionally with a fourth part 1 1, which can be passed over a bypass to the aftercoolers. The reunited feed air stream 12 is further cooled in a direct contact cooler 13 in direct heat exchange with cooling water (14, 16). The cooling water comes from a fresh water stream 17, which is fed to a first part 16 directly as cooling water to the direct contact cooler 13 and cooled to a second part 18, 14 previously in an evaporative cooler 15. The accumulating at the bottom of the direct contact cooler 13 water is withdrawn via line 19 and 20. The further cooled feed air is introduced into a cleaning device 22. This consists in the example of two switchable containers which are filled with a molecular sieve as an adsorbent.

The cleaned air flows to the warm end of the main heat exchanger, which in the example is formed by three air-side parallel blocks 23a, 23b, 23c. The feed air 24 cooled to about dew point is for the most part fed to the high-pressure column 26 immediately above its sump. A small portion 27 may be condensed in a secondary condenser 28 and introduced via line 29 liquid at an intermediate point of the high-pressure column 16 and / or passed directly to the low-pressure column 32 via line 30/31.

The operating pressures of the columns (in each case at the top) in the exemplary embodiment are 4.5 bar in the high-pressure column 26 and 1.2 bar in the low-pressure column 32. High-pressure column 26 and low-pressure column 32 are thermally coupled via a main condenser 37 designed as a condenser-evaporator. In the example, they are juxtaposed to form the distillation column system for nitrogen-oxygen separation.

The oxygen-enriched bottoms liquid 33 of the high-pressure column is cooled in a subcooling countercurrent 34 and introduced via line 35 into the low-pressure column 32. A first portion 36 of the gaseous overhead nitrogen of the high-pressure column 26 is introduced into the liquefaction passages of the main condenser 37. This liquid nitrogen obtained is to a first part 38 of the high-pressure column 26 and to a second part 39/40 after flowing through the

Subcooling countercurrent 34 of the low pressure column 32 abandoned as reflux. A portion of the introduced into the low pressure column 32 nitrogen can be discharged via line 80 as a liquid product (LIN - liquid nitrogen).

From the bottom of the low-pressure column, an oxygen 41 is removed with a purity of about 40 mol% liquid and brought by means of a pump 42 to a slightly elevated pressure of about 4 bar. A first portion 43 of the pumped oxygen is conveyed into the evaporation passages of the main condenser 37 and recycled via line 44 as ascending gas in the low-pressure column 32. A second part is introduced via line 45 oxygen-enriched product stream in the evaporation chamber of the The gaseous oxygen-enriched product stream 46 is heated in the main heat exchanger 23c to approximately ambient temperature and further (47) heated in the third aftercooler 9 of the air compressor 3 and finally via line 48 as a gaseous product (GOX -. gaseous oxygen) and in particular fed to the combustion chamber of an oxyfuel power plant. A third portion 81 of the oxygen from the pump 42 may be delivered as a liquid product (LOX).

At the top of the low pressure column 32 gaseous nitrogen 49 is withdrawn, warmed in the subcooling countercurrent 34, fed via line 50 to the cold end of the main heat exchanger 23b, brought there to about ambient temperature and finally fed via line 51 to the evaporative cooler 15 as a dry gas.

A second part 52 of the gaseous nitrogen head of the high-pressure column 26 is fed as a "second nitrogen flow" the cold end of the main heat exchanger 23c, removed again at an intermediate temperature of 133 K via line 53 and in a cold expansion machine 54 work to 1, 2 bar relaxed. The expanded second nitrogen stream 56 is returned to the cold end of the main heat exchanger 23c, heated to approximately ambient temperature and at least partially supplied via the lines 58 and 59 of the cleaning device 33 as a regeneration gas, optionally after further heating in a steam-powered Regeneriergaserhitzer 60. Laden Regeneriergas 61 becomes delivered the atmosphere.

A portion of the gas from line 58 - or if there is no temporary need for regeneration gas, even the total amount - can be vented via line 62 into the atmosphere.

A third part 63 of the gaseous nitrogen head of the high-pressure column 26 is heated as "first nitrogen flow" in the main heat exchanger 23 a to about ambient temperature and at least partially via the lines 64, 65 and 66 to the first aftercooler 6 and heated there to about 340 K. The first heated first nitrogen stream 67 is working in a first warm expansion machine 68 to an intermediate pressure of about 2.3 bar and a temperature of about 288 K working relaxed. The first nitrogen stream 70, which is under the intermediate pressure, is heated a second time to approximately 340 K in the second aftercooler 8. The first nitrogen stream 71, which has been heated for the second time, is expanded in a second warm expansion machine 72 to a final pressure of about 1.15 bar and a temperature of about 287 K. The first nitrogen stream 74, which has been expanded to the final pressure, is mixed via lines 75, 76 with the expanded and warmed second nitrogen stream 57 and likewise at least partially used as regeneration gas for the cleaning device 22. By way of a bypass line 76, at least part of the gas from line 65 can be led past the two warm expansion turbines 69, 72.

A portion 83 of the pressurized nitrogen 83 warmed in the WT 23a may be discharged as a gaseous pressure product (PGAN - pressurized gaseous nitrogen).

A portion of the feed air 23 can be used as equalizing flow 77, 78, 79 between the second block 23b and the third block 23c of the main heat exchanger.

All relaxation machines of the embodiment are designed as a turboexpander and are braked by generators 55, 69, 73.

Claims

claims

A process for the cryogenic separation of air in a distillation column system for nitrogen-oxygen separation, comprising a high pressure column (26) and a low pressure column (32), wherein - the high pressure column (26) and the low pressure column (32) via a

Condenser-evaporator (37) are thermally coupled,

- Compressed air (1) in an air compressor (3) compressed, at least in a first aftercooler (6) and cleaned in a cleaning device (22) cooled in a main heat exchanger (23a, 23b, 23c) and at least partially into the high pressure column (26 ) (25, 29),

- at least one liquid stream (33, 35) is introduced from the high-pressure column (26) into the low-pressure column (32),

- the low-pressure column (32) an oxygen-enriched product stream (41, 45, 46, 47, 48) is removed, - a first nitrogen stream (63, 64, 65, 66) withdrawn from the high-pressure column (26) and to a temperature of at least 280 K warmed up (6) will and

- The warmed first nitrogen stream (67) in a first warm expansion machine (68) work expanded, 72), characterized in that

- The first in the first warm relaxation machine (68) relaxed first nitrogen flow (70, 71) in a second warm expansion machine (72) is working expanded.

2. The method according to claim 1, characterized in that for heating the first nitrogen stream residual heat is used, wherein in particular the warming of the first nitrogen stream at least partially carried out in the first aftercooler (6) and the first nitrogen stream (66) there in indirect heat exchange with Feed air (5) downstream of the air compressor (3) is brought.

3. The method according to claim 2, characterized in that the first

Nitrogen stream (66, 67) heated upstream of the first warm expansion machine (68) in the first aftercooler (6), then in the first Relaxation machine (68) is relaxed to an intermediate pressure, and the relaxed to the intermediate pressure first nitrogen stream (70) in a second aftercooler (8) is heated and then relaxed in the second warm expansion machine (72) to a final pressure which is lower than the intermediate pressure is.

4. The method according to claim 3, characterized in that the first and the second aftercooler (6, 8) are connected in parallel on the air side.

5. The method according to any one of claims 1 to 4, characterized in that in the second warm expansion machine (72) performing work-relaxed first nitrogen stream (74) at least partially as a regeneration gas (58, 59) in the cleaning device (22) is used.

6. The method according to any one of claims 1 to 5, characterized in that

a second stream of nitrogen (52) is withdrawn from the high pressure column (26), heated in the main heat exchanger (23c) to an intermediate temperature,

- The heated to the intermediate temperature second nitrogen flow (53) in a cold expansion machine (54) work expanded and then reheated in the main heat exchanger (23 c).

7. The method according to claim 6, characterized in that the work-performing expanded second nitrogen stream (57) at least partially as a regeneration gas (58, 59) in the cleaning device (22) is used.

8. Apparatus for cryogenic separation of air

with a distillation column system for nitrogen-oxygen separation, which has a high-pressure column (26) and a low-pressure column (32),

wherein the high-pressure column (26) and the low-pressure column (32) are thermally coupled via a condenser-evaporator (37),

- With an air compressor (3) for compressing feed air (1), a first aftercooler (6) for cooling compressed feed air (4), a downstream of the first aftercooler (6) arranged cleaning device (22) for feed air, a main heat exchanger (23a. 23b, 23c) for cooling purified feed air (23) and a main air line (25) for introducing cooled feed air into the high-pressure column (26),

- means for removing at least one liquid stream (33, 35) from the high pressure column (26) and introducing it into the low pressure column (32), - having an oxygen product line for withdrawing an oxygenated product stream (41, 45, 46, 47, 48) from the low pressure column,

- With a first nitrogen line for removing a first nitrogen stream (63) from the high pressure column (26), - with means (6) for heating the first nitrogen stream (65, 66) to a

Temperature of at least 280 K and

- With a first warm relaxation machine (68) for work-performing expansion of the warmed first nitrogen flow (67), characterized by a second warm relaxation machine (72) for work-relaxing the relaxation in the first warm relaxation machine

(68) relaxed first nitrogen stream (70, 71).

9. The device according to claim 8, characterized in that the means for heating the second nitrogen stream comprise the first aftercooler (6), and this for the indirect heat exchange between the first nitrogen stream

(66) and compressed feed air (5) is formed.

10. The device according to claim 9, characterized in that between the first warm expansion machine (68) and the second warm expansion machine (72), a second aftercooler (8) is arranged, for the indirect heat exchange between the second nitrogen flow (70) and compacted Feed air (7) is formed.

11. The device according to claim 10, characterized in that the first and the second aftercooler (6, 8) are connected in parallel on the air side.

12. Device according to one of claims 8 to 11, characterized by means for supplying in the second warm relaxation machine (72) performing work-relaxed first nitrogen stream (74) as a regeneration gas (58, 59) to the cleaning device (22).

13. Device according to one of claims 8 to 12, characterized by a second nitrogen line for removing a second nitrogen stream (52) from the high-pressure column (26), wherein the second nitrogen line through the main heat exchanger (23 c) leads, at an intermediate point of the

Main heat exchanger (23 c) emerges and further through a cold expansion machine (54) and again through the main heat exchanger (23 c) leads.

14. The apparatus according to claim 13, characterized by means for supplying the working expanded second nitrogen stream (57) as a regeneration gas (58, 59) to the cleaning device

15. oxy-fuel power plant with a combustion chamber and a cryogenic air separation plant, the cryogenic air separation plant as

Device according to one of claims 8 to 14 is executed and the oxygen product line (48) is connected to the combustion chamber.

A method of operating an oxyfuel power plant comprising a combustor and a cryogenic air separation plant wherein the cryogenic air separation plant of any one of claims 1 to 7 is operated and the oxygen-enriched product stream (48) is at least partially supplied to the combustor.

(22)