Patent Grant
8826692
This U.S. patent application is a national stage application of PCT/EP2009/000431 filed on 23 Jan. 2009 and claims priority of both European patent document 08009400.6 filed on 19 Jun. 2008 and German patent document 10 2008 006 431.9 filed on 28 Jan. 2008, the entireties of which are incorporated herein by reference.
The invention relates to a method for low-temperature separation of air.
Methods and devices for low-temperature separation of air are known, for example, from Hausen/Linde, Tieftemperaturtechnik [Low-temperature technology], 2nd edition 1985, Chapter 4 (pages 281 to 337).
The distillation column system of the invention comprises a two-column system (for example a classical Linde double-column system) for separating nitrogen/oxygen having a high-pressure column and a low-pressure column which are in a heat-exchange relationship with one another. The heat-exchange relationship between high-pressure column and low-pressure column is generally effected by a main condenser in which overhead gas of the high-pressure column is liquefied against vaporizing bottom liquid of the low-pressure column. In addition to the columns for separating nitrogen/oxygen, the distillation column system can comprise other devices, for example for producing other air components, in particular noble gases, for example an argon production stage which comprises at least one crude argon column, or a krypton-xenon production stage. The distillation column system, in addition to the distillation columns, also comprises the heat exchangers directly assigned thereto, which heat exchangers are generally constructed as condenser-evaporators.
The majority of modern air separation plants are constructed on the basis of what is termed a double column. This system of two coupled columns having differing working pressures enables not only the production of gaseous oxygen-, argon- and nitrogen-containing products, but also liquid fractions. These liquids can be taken off from the air separation plant as liquid end products or are internally compressed (brought to the higher pressure in a pump and warmed), so they are then available as gaseous pressurized products.
If such liquid fractions are taken off from the double-column system, a corresponding amount of air must be preliquefied before being fed into the double column, that is to say some of the air is passed into the double-column system in the gaseous state (feed air to the high-pressure column and, e.g., air from the Lachmann turbine, which is fed directly into the low-pressure column) and some of the air is fed into the double-column system in the liquid state (throttling stream and liquid air from Claude turbine, where present). If many products are taken off in the liquid state, the proportion of preliquefied air increases correspondingly.
Since only the lower sections of both columns are charged with liquid air, the preliquefied air shares only few of the rectification processes in the double column (compared with gaseous air). Therefore, the preliquefaction has an adverse effect on the rectification processes in the double column. With increasing air preliquefaction, the oxygen yield decreases (and also the argon yield, if the system produces argon). The efficiency and economic efficiency of the air separation plant decrease.
In order to intensify the rectification (in particular in the upper sections of both columns), resort is made to measures such as what is termed a “feed compressor” (which compresses some of the product from the upper part of the low-pressure column to the pressure of the high-pressure column and this is fed into the high-pressure column) and/or attempts are made to use what is termed a nitrogen cycle for generating cold (the air in this case is not liquefied upstream of the double column but within the pressure column by liquid nitrogen). These measures, however, mean a higher energy consumption and make the overall plant more expensive as a result of a higher number of heat exchangers and/or machinery.
It is an object of the invention to increase the oxygen yield (and argon yield, if argon is produced) of an air separation plant even in the case of a high preliquefaction (for example greater than 30 mol %, in particular greater than 40 mol %, of the total feed air) without using additional machinery and heat exchangers.
This object is achieved by the features of patent claim 1. In this case an additional third column (“precolumn”) is connected upstream of the conventional double column. At least some of the gaseous air (the “first substream”) is firstly passed into this third column and (similarly to in the high-pressure column of the double column) separated into liquid nitrogen fractions and crude oxygen. This upstream column is cooled by preliquefied air (the “second substream”) by means of a top condenser (generally placed above the column). This liquid is vaporized in this process and fed in the gaseous state into the distillation column system, preferably into the high-pressure column.
The third column is operated at a pressure which is higher than the pressure of the high-pressure column of the double column in order that the air which vaporizes in the top condenser can be introduced into the high-pressure column.
Preferably, the pressure ratio between precolumn and high-pressure column (in each case measured at the top) is at least 1.4 and is in particular between 1.4 and 1.8, preferably between 1.5 and 1.7.
Liquid nitrogen from the precolumn (or from the condensation compartment of the top condenser thereof) is then fed into the high-pressure column, liquid crude oxygen from the lower region of the precolumn into the high-pressure column and/or into the low-pressure column, or alternatively or additionally into the argon part, where present.
By means of these connections the following advantages are achieved:
According to a fundamental concept of the invention, as far as possible all process streams available at high pressure which are suitable for cooling the precolumn are used for cooling thereof (this does not exclude, however, that in individual cases some of these process streams are introduced into the distillation column system at another point). In particular, preferably the entire preliquefied air, in any case more than 80 mol %, or more than 90 mol % of the preliquefied air, is introduced into the vaporization compartment of the top condenser of the precolumn.
The invention additionally relates to a device for low-temperature air separation according to patent claim 12.
The following variants are possible in the scope of the invention and can if appropriate also be combined with one another:
The invention and also further details of the invention will be explained in more detail hereinafter with reference to exemplary embodiments shown in the drawings. In this case, in the drawings:
In
The separation columns for nitrogen/oxygen separation in the example have the following operating pressures (in each case at the top):
A first substream 1 of the feed air comes in the gaseous state from the cold end of the main heat exchanger (which is not shown) or from a turbine. It is at a pressure which is just above the operating pressure of the precolumn 13 and is introduced immediately above the bottom.
The precolumn 10 comprises a top condenser 14, into the evaporation compartment of which a second substream of air in the liquid state is introduced. This “second substream” is formed in the example by two subdivided streams 2a, 2b. Subdivided stream 2a originates from the outlet of a PC Claude turbine, subdivided stream 2b originates from the cold end of the main heat exchanger (which is not shown) and was condensed or (at supercritical pressure) pseudocondensed against a taken off from the distillation column system in the liquid state and subsequently brought to pressure in the liquid state. During the introduction into the evaporation compartment of the top condenser 14, the second substream 2a, 2b consists essentially (85 to 95 mol %) of liquid. The liquid fraction thereof comprises 30 to 50 mol % of the total feed air. The remaining feed air is introduced into the distillation column system in the gaseous state. The gaseous introduction proceeds—except for possible gaseous fractions in the streams 2a and 2b and the turbine stream 3—completely via the first substream 1 into the interior of the precolumn 10.
In the example, furthermore, an additional liquid stream 4 is passed into the vaporization compartment of the top condenser 14. This originates from an intermediate point of the precolumn 10 which is arranged about 8 to 16 theoretical or practical plates above the bottom.
The entire bottom liquid 5 of the precolumn is introduced here into the high-pressure column 11, more precisely immediately at the bottom thereof. Alternatively, or additionally, the bottom liquid 5 of the precolumn or a part thereof—after cooling in the subcooling countercurrent heat exchanger 37, can be fed into the low-pressure column 12 and/or the argon part 15 (which is not shown in the drawing). The liquid 6 generated in the condensation compartment of top condenser 14 from a part 31 of the top nitrogen 30 of the precolumn 10 is fed into the precolumn 10 as a first part as top reflux 7 and as a second part 8 to the top of the high-pressure column 11. Furthermore, a nitrogen-enriched impure fraction 9 can be passed from the precolumn into the high-pressure column; this impure fraction 9 is taken off at an intermediate point of the precolumn 10 which is arranged about 8 to 16 theoretical or practical plates below the top and passed to the high-pressure column 11 at an intermediate point.
The vaporized fraction 16 formed in the evaporation compartment of the top condenser is passed via line 17 to the bottom of the high-pressure column, together with a third substream 18 of the feed air which originates from the outlet of an HPC Claude turbine. The purge liquid 32 from the top condenser 14 of the precolumn 10 is fed to the high-pressure column 10 at an intermediate point in the lower region.
In the example, furthermore, a further liquid stream 4 is passed into the evaporation compartment of the top condenser 14. This further liquid stream originates from an intermediate point of the precolumn 10 which is arranged about 8 to 16 theoretical or practical plates above the bottom.
Otherwise, the double column 11/12/13 and the optional argon part 15 function in the generally known manner.
From the high-pressure column 11, liquid crude oxygen 33 at the bottom, a liquid air fraction 34 at the intermediate point at which the purge liquid 32 is introduced, impure nitrogen 35 from an intermediate point situated further above and liquid pure oxygen from the condensation compartment of the main condenser 13 are cooled in a subcooling countercurrent heat exchanger 37 in indirect heat exchange with backflows and introduced into the low-pressure column 12 via the lines 38, 39, 40 or 41 at the suitable points. Furthermore, gaseous air 42 from a Lachmann turbine and/or liquid air 43 from an HPC Claude turbine can be fed into the low-pressure column 12.
If the plant does not have an argon part, the following products can be withdrawn:
The plant can, but need not, generate all of these products simultaneously.
The gaseous product streams are warmed in a main heat exchanger which is not shown in indirect heat exchange with feed air. The main heat exchanger can consist of a block or of two or more parallel and/or serially connected blocks. The liquid oxygen can be produced as a liquid product; alternatively, or additionally, at least a part of the oxygen withdrawn in the liquid state from the low-pressure column is brought to pressure in the liquid state and subsequently vaporized or (at supercritical pressure) pseudo-vaporized in the main heat exchanger and warmed and subsequently withdrawn as gaseous pressurized product (what is termed internal compression).
In a variant of the exemplary embodiment of
From the exemplary embodiment of
In
Additionally or alternatively, one or two nitrogen products 296, 297 can be produced at very high pressure in a similar manner by internal compression by bringing the liquid high-pressure nitrogen 52 in a nitrogen pump 295 to a correspondingly high pressure and, at this pressure (and if appropriate in part at a somewhat lower intermediate pressure), (pseudo-)vaporizing and warming it in the main heat exchanger 260.
The exemplary embodiment of
In the exemplary embodiment of
In
The feed air is here brought in a main air compressor 601 to a pressure of, for example, 5.5 to 24 bar, fed at this pressure to a precooler 602 and further to prepurification 603 which is constructed, for example, as a molecular sieve adsorber station. The total purified feed air is subsequently further compressed in a recompressor 604 to a pressure of, for example, up to 40 bar. The resultant high-pressure air 605 is divided into a first branch stream 606 and a second branch stream 607.
The first branch stream 606 is brought in a further recompressor 661 which is driven by the PC Claude turbine 361 to a still higher pressure and serves as throttle stream 2b. The second branch stream 607 is introduced into the main heat exchanger 260 at the exit pressure of the recompressor 604 and expanded in the PC Claude turbine 361.
All of the processes and plants shown are to be understood as exemplary. The drawings are intended primarily to illustrate the functional relationships. Although high-pressure column and low-pressure column are shown one above the other and with an integrated main condenser, in the context of the invention, however, any other known arrangement of columns and condensers is also possible.
The columns can be equipped with sieve trays, structured packings or non-structured packings or else contain combinations of said types of mass-transfer elements.
The main condenser is constructed as falling film or bath evaporator. In the case of a bath evaporator, it can be constructed as a single storey or multistorey (cascade condenser). The top condenser of the precolumn is preferably constructed as a bath condenser.
Some streams or column sections can be absent in the actual connection. In terms of the process this means that the amount of the corresponding stream is equal to zero or the number of theoretical plates in the relevant section is equal to zero. With respect to the device this generally means that the corresponding line or the corresponding column section is absent.
The main heat exchanger can in each case be constructed in an integrated or split manner, the drawings show only the unit function of the exchanger—warm streams are cooled by cold streams.
In all exemplary embodiments of the invention no pump is used to transport a liquid from one column to another column.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2008 006 431 | Jan 2008 | DE | national |
| 08009400 | Jun 2008 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2009/000431 | 1/23/2009 | WO | 00 | 10/25/2010 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2009/095188 | 8/6/2009 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5730004 | Voit | Mar 1998 | A |
| 20020189281 | Pompl | Dec 2002 | A1 |
| 20060075779 | Higginbotham | Apr 2006 | A1 |
| Number | Date | Country |
|---|---|---|
| 11 45 649 | Mar 1963 | DE |
| 199 33 558 | Sep 2000 | DE |
| 2 831 250 | Apr 2003 | FR |
| WO 0060294 | Oct 2000 | WO |
| Entry |
|---|
| English Abstract of FR 2 831 250. |
| English Abstract of WO 0060294. |
| English Abstract of DE 199 33 558. |
| Response to International Search Report and First Written Opinion by the International Search Authority, International application No. PCT/EP2009/000431, dated Jun. 2, 2010. |
| Number | Date | Country | |
|---|---|---|---|
| 20110023540 A1 | Feb 2011 | US |
