Patent Grant
12078415
This application is a § 371 of International PCT Application PCT/CN2019/097997, filed Jul. 26, 2019, which is herein incorporated by reference in its entirety.
The present invention relates to the separation of air by cryogenic distillation.
Production of industrial gases such as oxygen, nitrogen and argon in gaseous form under any pressure or in liquefied form consumes a large amount of energy.
According to requirements, a multitude of process cycles can be used.
The energy used for the production of industrial gases can be split into three parts:
The separation energy is mainly linked to the various columns and set-up of those columns to perform the separation, and is mainly provided by the Main Air Compressor (MAC)
The compression and liquefaction energy is mainly linked to the heat exchanger and various machines such as expanders, gas or liquid, and compressors set-up and arrangement.
Since the OPEX have a large impact on the economics of an air separation unit (ASU), with the constant increase of cost of energy, there are always incentives to make the process more efficient.
The process of
Air is fed to the first column where it is separated to form an oxygen enriched liquid and a nitrogen enriched gas. Nitrogen enriched liquid and oxygen enriched liquid are sent from the first column to the second column. Liquid oxygen is withdrawn from the bottom of the second column.
At least part of the liquid oxygen is pressurized and sent to a heat exchanger 4 to be vaporized to form product oxygen. Gaseous nitrogen from the first and/or second column is also warmed in the heat exchanger 4.
Air from main air compressor 1 is purified in purification unit 2 to remove carbon dioxide and water and is then divided in two. One part passes through the heat exchanger 4 at the outlet pressure of compressor 1 and is sent in gaseous form to first column 31. The rest of the air is sent to a booster compressor 3 in which it is compressed to a higher pressure and then divided in two. The first part is further boosted, in booster 5, without having been cooled in the heat exchanger 4, and is then sent to the warm end of the heat exchanger 4 where it liquefies or becomes a dense fluid, depending on the pressure. The liquefied air or dense fluid removed from the cold end within a cold section CS of the heat exchanger 4 is expanded in an expander 7 and is then sent to the first column.
The second part of the air from the booster 5 is sent to the warm end of the heat exchanger without further compression and is removed from the heat exchanger 4 at an intermediate position. It is then expanded in a Claude turbine 6 and sent to the first column 31 after being mixed with the stream coming directly from the main air compressor 1.
A gaseous nitrogen stream 27 from the column 31 and/or 33 is warmed in the heat exchanger 4 (not shown).
When analyzing the heat exchanger diagram of this process scheme, by doing an exergy analysis of the cold section CS of the main heat exchanger 4, it is found that irreversibilities occur in this cold section.
Certain embodiments of the present invention aims mainly to improve the liquefaction energy and/or the compression energy of the product by reducing the irreversibilities in the cold section of the exchanger.
According to an embodiment of the invention, there is provided a process for the separation of air by cryogenic distillation in which:
According to other optional features, which may be combined in any logical manner:
According to an embodiment of the invention, there is provided an apparatus for the separation of air by cryogenic distillation comprising a column system comprising at least one column, a heat exchanger, a turbine, means for sending compressed and purified air at a first pressure to be cooled at the first pressure in the heat exchanger, means for sending the cooled air in gaseous form from the heat exchanger to the column system, means for sending a gaseous nitrogen stream from the column system to be warmed in the heat exchanger, means for sending a liquid stream enriched in oxygen or nitrogen from the column system to be vaporized and warmed in the heat exchanger, means for sending a first gaseous stream having a nitrogen content at least that of air and at a higher pressure than the first pressure to be cooled and liquefied or pseudo liquefied in the heat exchanger to form a liquefied stream, means for sending at least part of the liquefied stream to be warmed and vaporized in the heat exchanger to a first intermediate temperature of the heat exchanger to form a vaporized stream, means for removing the vaporized stream from an intermediate section of the heat exchanger, a conduit for sending the vaporized stream to be expanded, at least in part, in the turbine to form an expanded stream, a conduit for sending at least part of the expanded stream to the column system, a conduit for sending a second gaseous stream having the same nitrogen content as the first stream to be cooled in the heat exchanger, conduit means for removing at least part of the second gaseous stream from an intermediate section of the heat exchanger at a second intermediate temperature and sending the at least part of the second gaseous stream to the turbine to be expanded with the vaporized stream, conduit means for sending a further stream having a nitrogen content at least that of air to be liquefied or pseudoliquefied in the heat exchanger, expansion means, means for sending the further stream to the expansion means and conduit means for sending the expanded further stream to the column.
The apparatus may further comprise:
The present invention is described here as a modification of various different cryogenic air separation processes.
This invention of course can be used other process scheme without any limitation.
The current invention may include recycling to the cold section a stream which is vaporized preferably prior to being injected in the turbo expander inlet. This stream being preferably high pressure air, this allows the irreversibilities to be reduced in the cold section of the main heat exchanger, leading in the studied case to an improvement of 1% for the total energy of the ASU
Further features, advantages and possible applications of the invention are apparent from the following description of working and numerical examples and from the drawings. All described and/or depicted features on their own or in any desired combination form the subject matter of the invention, irrespective of the way in which they are combined in the claims or the way in which said claims refer back to one another.
Certain embodiments of the invention will now be described in greater detail with reference to
The scheme of
Air from main air compressor 1 is purified in purification unit 2 to remove carbon dioxide and water and is then divided in two. One part 13 passes through the heat exchanger 4 at the outlet pressure of compressor 1 and is sent in gaseous form to first column 31. The rest of the air is sent to a booster compressor 3 in which it is compressed to a higher pressure and then divided in two. The first part 16 is further boosted, in booster 5, without having been cooled in the brazed aluminium plate fin heat exchanger 4, and is then sent to the warm end of the heat exchanger 4 where it liquefies or becomes a dense fluid, depending on the pressure. The liquefied air or dense fluid removed from the cold end of the heat exchanger 4 is divided in two. One part 17 is expanded in an expander 7 and is then sent to the first column. The other part 9 is expanded in a valve 9 and then sent to the cold end of the heat exchanger 4 in which it is vaporized. The vaporized air is mixed with air stream 15 within the heat exchanger 4 to form stream 35 which is removed from the heat exchanger at an intermediate temperature of the heat exchanger for example between −70° C. and −140° C. and then sent to the turbine 6 at a pressure between 15 and 65 bara without any further cooling or expansion.
The second part 15 of the air from the booster 5 is sent to the warm end of the heat exchanger without further compression, is cooled to between −70° C. and −140° C. and is removed from the heat exchanger 4 at an intermediate position, having already been mixed with stream 10. The mixed stream 35 is then expanded, as already described, in the Claude turbine 6 to the pressure of column 31 and sent to the first column after being mixed with the stream coming directly from the main air compressor.
In this particular case, stream 15 is cooled to an intermediate temperature in the heat exchanger 4 and stream 10 is warmed to the same intermediate temperature.
It is possible for the streams to be warmed and cooled to slightly different temperatures, for example differing by 1 or 2° C.
The streams may be mixed within the heat exchanger, outside the heat exchanger or on reaching the turbine.
The outlet pressure of booster 3 and the outlet pressure of the valve on stream 10 are necessarily substantially equal, allowing for pressure drop within the heat exchanger 4.
The outlet pressure of booster 3 is equal to the inlet pressure of turbine 6, allowing for the pressure drop of stream 15 in the heat exchanger 4.
A liquid oxygen stream 25 from the bottom of column 33 is vaporized in the heat exchanger 4 and warmed to form a product stream, preferably under pressure. The liquid oxygen stream 25 can be replaced by a liquid nitrogen stream withdrawn from column 31 or 33. A gaseous nitrogen stream 27 from the first and/or second column is warmed in the heat exchanger 4.
It can also be envisaged that stream 10 is vaporized and then warms up to the warm end of the heat exchanger 4 before being mixed with the stream 15 going to the turbine 6. It can also be imagined that this stream 10 is removed from the heat exchanger 4 at a lower temperature than that at which the stream 15 is removed.
The valve 9 can be replaced by a dense liquid expander to further improve the plant efficiency.
In the process of
Air from main air compressor 1 is purified in purification unit 2 to remove carbon dioxide and water and is then divided in two. One part 13 passes through the heat exchanger 4 at the outlet pressure of compressor 1 and is sent in gaseous form to first column 31. The rest of the air is sent to a booster compressor 3 in which it is compressed to a higher pressure and then divided in three. The first part 16 is further boosted, in booster 5, without having been cooled in the heat exchanger 4, and is then sent to the warm end of the heat exchanger 4 where it liquefies or becomes a dense fluid, depending on the pressure. The liquefied air or dense fluid removed from the cold end of the heat exchanger 4, is expanded in an expander 7 and is then sent to the first column.
The second part 10 of the air from booster 3 is sent to a further booster 3a where it is further compressed. The further compressed air 10 is cooled by passing from the warm end to the cold end of the heat exchanger. On leaving the heat exchanger, it is expanded in a valve and then sent to the cold end of the heat exchanger 4 in which it is vaporized and warmed to between −70° C. and −140° C. The vaporized air 10 is mixed with air stream 15 to form stream 35 which is then sent to the turbine 6 at a pressure between 15 and 65 bara.
The third part 15 of the air from the booster 5 is sent to the warm end of the heat exchanger without further compression and is removed from the heat exchanger 4 at an intermediate position, having already been mixed with stream 10. The mixed stream 35 is then expanded, as already described, in the Claude turbine 6 and sent to the first column after being mixed with the stream coming directly from the main air compressor.
In this particular case, stream 15 is cooled to an intermediate temperature in the heat exchanger 4 and stream 10 is warmed to the same intermediate temperature.
It is possible for the streams 10,15 to be warmed and cooled to slightly different temperatures for example differing by 1 or 2° C.
The streams may be mixed within the heat exchanger, outside the heat exchanger or on reaching the turbine.
The outlet pressure of booster 3 and the outlet pressure of the valve on stream 10 are necessarily substantially equal and are chosen to be between 15 and 65 bara.
The outlet pressure of booster 3 is equal to the inlet pressure of turbine 6.
A liquid oxygen stream 25 from the bottom of column 33 is vaporized in the heat exchanger 4 and warmed to form a product stream, preferably under pressure. The liquid oxygen stream 25 can be replaced by a liquid nitrogen stream withdrawn from column 31 or 33. A gaseous nitrogen stream 27 from the first and/or second column is warmed in the heat exchanger 4.
It can also be envisaged that stream 10 is vaporized and then warms up to the warm end of the heat exchanger 4 before being mixed with the stream 15 going to the turbine 6. It can also be imagine that this stream 10 is removed from the heat exchanger 4 at a lower temperature than that at which the stream 15 is removed.
The valve 9 can be replaced by a dense liquid expander to further improve the plant efficiency.
This set-up shows a slight improvement, but has a CAPEX impact due to the additional BAC section 3a.
Stream 79 is removed from the heat exchanger 4 and expanded in nitrogen turbine 34 to form a partially condensed fluid which is sent to phase separator 81. The liquid from the phase separator is sent to the top of the second column 33 as reflux 85. The gas 83 from the phase separator 81 is mixed with the nitrogen 71.
The gas compressed in compressor 33 is fully cooled in the heat exchanger 4, liquefied and expanded in liquid turbine 7 before being sent to the top of the first column 31 as reflux.
The gas 77 compressed in compressor 32 is fully cooled in heat exchanger is sent to the top of column 31 as reflux.
To adapt the process of
A gaseous nitrogen stream 27 from the column 31 and/or 33 is warmed in the heat exchanger 4 (not shown).
The heat exchanger 4 may be split into first and second heat exchange sections (not shown). The compressed and purified air is cooled at the first pressure in the first heat exchange section and the cooled air is sent from the first heat exchange section to the column system comprising at least one distillation column. Gaseous nitrogen 27 from the column system is warmed in the first and/or second heat exchange sections. The liquid stream 25 enriched in oxygen or nitrogen from the column system is vaporized and warmed in the first heat exchange section. The first gaseous stream having a nitrogen content at least that of air and at a higher pressure than the first pressure is cooled and liquefied or pseudo liquefied in the second heat exchange section to form a liquefied stream. At least part of the liquefied stream 10 is warmed and preferably vaporized in the second heat exchange section to the first intermediate temperature of the second heat exchange section to form the vaporized stream. The second gaseous stream 15 having the same nitrogen content as the first stream is cooled in the second heat exchange section. At least part of the second gaseous stream is removed from the second heat exchange section at the second intermediate temperature.
The heat exchanger is preferably comprised of first and second heat exchange sections wherein any warming air stream, cooling air stream or warming stream produced by the column system above a given pressure is cooled or warmed respectively in the first heat exchange section. Other streams may be cooled or warmed in either of the two heat exchange sections. Thus the first section will have a more robust structure than the second section.
All of the
Although in the examples both streams sent to the turbine have the same composition, it is possible for the streams to have different compositions. For example, one may be an air stream and the other a nitrogen stream.
While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.
The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.
“Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.
“Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.
Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.
Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range.
All references identified herein are each hereby incorporated by reference into this application in their entireties, as well as for the specific information for which each is cited.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2019/097997 | 7/26/2019 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2021/016756 | 2/4/2021 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 4705548 | Agrawal | Nov 1987 | A |
| 5735142 | Grenier | Apr 1998 | A |
| 6110980 | Chen | Aug 2000 | A |
| 20050126221 | Ha | Jun 2005 | A1 |
| 20080223075 | Tranier | Sep 2008 | A1 |
| 20110067444 | Alekseev | Mar 2011 | A1 |
| 20200333069 | Dubettier-Grenier et al. | Oct 2020 | A1 |
| Number | Date | Country |
|---|---|---|
| 1 208 847 | Feb 1999 | CN |
| 107 940 896 | Apr 2018 | CN |
| 108 759 308 | Nov 2018 | CN |
| 208 443 098 | Jan 2019 | CN |
| 109 442 867 | Mar 2019 | CN |
| 109 737 690 | May 2019 | CN |
| 3 307 181 | Sep 1984 | DE |
| 0 789 208 | Aug 1997 | EP |
| 3 072 451 | Apr 2019 | FR |
| 0 302 267 | Mar 2003 | GB |
| Entry |
|---|
| International Search Report and Written Report for PCT/CN2019/097997, mailed Apr. 10, 2020. |
| Number | Date | Country | |
|---|---|---|---|
| 20220282914 A1 | Sep 2022 | US |
