DELASSALLE ADRIEN (JP)
| WO2014173496A2 | 2014-10-30 | |||
| WO2014173496A2 | 2014-10-30 |
| US20220260312A1 | 2022-08-18 | |||
| DE202018006161U1 | 2019-05-27 | |||
| US20200182543A1 | 2020-06-11 | |||
| JP2001336876A | 2001-12-07 | |||
| EP3327393A1 | 2018-05-30 | |||
| US5711167A | 1998-01-27 | |||
| US20100242537A1 | 2010-09-30 |
| Claims 1. Method applied to an air separation unit comprising: a main heat exchanger (1) into which feed air is introduced; a nitrogen rectification column (2) into which the feed air is introduced; at least one nitrogen condenser (3,4) for condensing nitrogen gas drawn from the nitrogen rectification column; a high-purity oxygen rectification column (5) into which an oxygen-containing liquid drawn from the nitrogen rectification column is introduced; an oxygen vaporizer (6) for vaporizing a high-purity oxygen liquid rectified in the high-purity oxygen rectification column; and a sub-cooler, wherein the method comprises a step in which i) a portion of an oxygen-enriched liquid drawn from the nitrogen rectification column is supplied to the nitrogen condenser after being cooled in the oxygen vaporizer, and the remainder of the oxygen-enriched liquid is supplied to the nitrogen condenser after being cooled in the sub-cooler (7) which uses, as a refrigerant, at least one of nitrogen gas supplied from the nitrogen rectification column and a gas supplied from a refrigerant side of the nitrogen condenser or ii) an oxygen-enriched liquid drawn from the nitrogen rectification column is cooled in the sub-cooler (7) which uses, as a refrigerant, at least one of nitrogen gas supplied from the nitrogen rectification column and a gas supplied from a refrigerant side of the nitrogen condenser, and is cooled in the oxygen vaporizer, then supplied to the nitrogen condenser. 2. Method according to claim 1 , comprising a step in which the oxygen-containing liquid drawn from the nitrogen rectification column (2) is supplied to the high-purity oxygen rectification column (5) after undergoing heat exchange (8) with a gas drawn from the high-purity oxygen rectification column. 3. Method according to claim 1 or 2, comprising a step in which the oxygencontaining liquid drawn from the nitrogen rectification column (2) is supplied to the high-purity oxygen rectification column (5) after being cooled in the oxygen vaporizer (6). 4. Method according to claim 1 , 2 or 3, comprising a step in which the oxygencontaining liquid drawn from the nitrogen rectification column is cooled in the oxygen vaporizer (6), undergoes heat exchange (8) with a gas drawn from the high-purity oxygen rectification column, and is then supplied to the high-purity oxygen rectification column. 5. Method according to any preceding claim comprising a step in which an oxygen-rich liquid drawn from the nitrogen rectification column is cooled in the subcooler (7) which uses, as a refrigerant, at least one of nitrogen gas supplied from the nitrogen rectification column and a gas supplied from a refrigerant side of the nitrogen condenser, and is cooled in the oxygen vaporizer, then supplied to the nitrogen condenser. 6. Air separation unit comprising: • a main heat exchanger (1 ) for subjecting feed air to heat exchange; • a sub-cooler (7) having a different heat exchange function from the main heat exchanger; • a nitrogen rectification column (2) into which the feed air that has passed through the main heat exchanger is introduced; • at least one nitrogen condenser (3,4) into which nitrogen gas drawn from the nitrogen rectification column is introduced to be condensed; • an expansion turbine (92) for expanding a gas after the gas has been drawn from the at least one nitrogen condenser and passed through the sub-cooler and the main heat exchanger; • a compressor (91 ) for compressing a recycled gas which is drawn from the at least one nitrogen condenser and compressed, then passes through the main heat exchanger, and then returns to the nitrogen rectification column; • a high-purity oxygen rectification column (5) which is supplied with an oxygencontaining liquid drawn from the nitrogen rectification column; • an oxygen vaporizer (6)which is installed in a lower portion of the high-purity oxygen rectification column and serves to generate a vapour stream of oxygen gas; • a pipeline (L100a) for feeding an oxygen-enriched liquid drawn from the nitrogen rectification column to the sub-cooler, and feeding same to the nitrogen condenser; • a pipeline (L100b) for feeding the oxygen-enriched liquid drawn from the nitrogen rectification column as a heat source in the oxygen vaporizer, and feeding same to the nitrogen condenser; • a nitrogen gas drawing pipeline (L23) for feeding nitrogen gas drawn from the nitrogen rectification column to the sub-cooler and the main heat exchanger; • a waste gas drawing pipeline (L41 ) forfeeding, to the sub-cooler and the main heat exchanger, a gas drawn from the at least one nitrogen condenser which is passed through the sub-cooler and the main heat exchanger and used in the expansion turbine; and • a recycled gas pipeline (L41 ) for returning, to the nitrogen rectification column, a recycled gas drawn from the at least one nitrogen condenser which is compressed in the compressor (91) and passed through the main heat exchanger. 7. Air separation unit according to claim 6, comprising: • a second heat exchanger (8) for performing heat exchange between the oxygen-containing liquid drawn from the nitrogen rectification column, and a gas drawn from the high-purity oxygen rectification column; and • a pipeline (L101) for feeding the oxygen-containing liquid drawn from the nitrogen rectification column to the high-purity oxygen rectification column via the second heat exchanger. 8. Air separation unit comprising: • a main heat exchanger (1 ) for subjecting feed air to heat exchange; • a sub-cooler (7) having a different heat exchange function from the main heat exchanger; • a nitrogen rectification column (2) into which the feed air that has passed through the main heat exchanger is introduced; • at least one nitrogen condenser (3,4) into which nitrogen gas drawn from the nitrogen rectification column is introduced to be condensed; • an expansion turbine (92) for expanding a gas after the gas has been drawn from the at least one nitrogen condenser and passed through the sub-cooler and the main heat exchanger; • a compressor (91 ) for compressing a recycled gas which is drawn from the at least one nitrogen condenser and compressed, then passes through the main heat exchanger, and then returns to the nitrogen rectification column; • a high-purity oxygen rectification column which is supplied with an oxygencontaining liquid drawn from the nitrogen rectification column; • an oxygen vaporizer (6) which is installed in a lower portion of the high-purity oxygen rectification column and serves to generate a vapour stream of oxygen gas; • a pipeline (L100c) forfeeding the oxygen-enriched liquid drawn from a bottom portion of the nitrogen rectification column to the sub-cooler, feeding same as a heat source in the oxygen vaporizer, and feeding same to the nitrogen condenser; • a waste gas drawing pipeline (L31 ) forfeeding, to the sub-cooler and the main heat exchanger, a gas drawn from the at least one nitrogen condenser which is passed through the sub-cooler and the main heat exchanger and used in the expansion turbine; and • a recycled gas pipeline (L41 ) for returning, to the nitrogen rectification column, a recycled gas drawn from the at least one nitrogen condenser which is compressed in the compressor and passed through the main heat exchanger. 9. Air separation unit according to claim 8, comprising a bypass pipeline (L100c1 ) which does not pass through the oxygen vaporizer and which branches from the pipeline (L100c) forfeeding the oxygen-enriched liquid drawn from the bottom portion of the nitrogen rectification column (2) to the sub-cooler (7), feeding same as a heat source in the oxygen vaporizer -6), and feeding same to the nitrogen condenser (3,4). 10. Air separation unit comprising: • a main heat exchanger (1 ) for subjecting feed air to heat exchange; • a sub-cooler (7) having a different heat exchange function from the main heat exchanger; • a nitrogen rectification column (2) into which the feed air that has passed through the main heat exchanger is introduced; • at least one nitrogen condenser (3,4) into which nitrogen gas drawn from the nitrogen rectification column is introduced to be condensed; • an expansion turbine (92) for expanding a gas after the gas has been drawn from the at least one nitrogen condenser and passed through the sub-cooler and the main heat exchanger; • a compressor (91 ) for compressing a recycled gas which is drawn from the at least one nitrogen condenser and compressed, then passes through the main heat exchanger, and then returns to the nitrogen rectification column; • a high-purity oxygen rectification column (5) which is supplied with an oxygencontaining liquid drawn from the nitrogen rectification column; • an oxygen vaporizer (6) which is installed in a lower portion of the high-purity oxygen rectification column and serves to generate a vapour stream of oxygen gas; • a pipeline (L100a) for feeding an oxygen-enriched liquid drawn from the nitrogen rectification column to the sub-cooler, and feeding same to the nitrogen condenser; • a pipeline (L100b) for feeding the oxygen-enriched liquid drawn from the bottom portion of the nitrogen rectification column as a heat source in the oxygen vaporizer, and feeding same to the nitrogen condenser; • a pipeline for feeding the oxygen-containing liquid drawn from the nitrogen rectification column as a heat source in the oxygen vaporizer, and feeding same to the high-purity oxygen rectification column; • a nitrogen gas drawing pipeline (L23) for feeding nitrogen gas drawn from the nitrogen rectification column to the sub-cooler and the main heat exchanger; • a waste gas drawing pipeline (L41 ) forfeeding, to the sub-cooler and the main heat exchanger, a gas drawn from the at least one nitrogen condenser which is passed through the sub-cooler and the main heat exchanger and used in the expansion turbine; and • a recycled gas pipeline (L31 ) for returning, to the nitrogen rectification column, a recycled gas drawn from the at least one nitrogen condenser which is compressed in the compressor and passed through the main heat exchanger. 11. Air separation unit comprising: a main heat exchanger (1 ) for subjecting feed air to heat exchange; • a sub-cooler (7) having a different heat exchange function from the main heat exchanger; • a nitrogen rectification column (2) into which the feed air that has passed through the main heat exchanger is introduced; • at least one nitrogen condenser (3,4) into which nitrogen gas drawn from the nitrogen rectification column is introduced to be condensed; • an expansion turbine (92) for expanding a gas after the gas has been drawn from the at least one nitrogen condenser and passed through the sub-cooler and the main heat exchanger; • a compressor (91 ) for compressing a recycled gas which is drawn from the at least one nitrogen condenser and compressed, then passes through the main heat exchanger, and then returns to the nitrogen rectification column; • a high-purity oxygen rectification column (5) which is supplied with an oxygencontaining liquid drawn from the nitrogen rectification column; • an oxygen vaporizer (6) which is installed in a lower portion of the high-purity oxygen rectification column and serves to generate a vapour stream of oxygen gas; • a pipeline (L100a) for feeding an oxygen-enriched liquid drawn from the nitrogen rectification column to the sub-cooler, and feeding same to the nitrogen condenser; • a pipeline (L100b) for feeding the oxygen-rich liquid drawn from the bottom portion of the nitrogen rectification column as a heat source in the oxygen vaporizer, and feeding same to the nitrogen condenser; • a second heat exchanger (8) for performing heat exchange between the oxygen-containing liquid that has undergone heat exchange in the oxygen vaporizer, and a waste gas drawn from the high-purity oxygen rectification column; • a pipeline (L104)for feeding the oxygen-containing liquid drawn from the nitrogen rectification column to the high-purity oxygen rectification column via the oxygen vaporizer and the second heat exchanger. • a nitrogen gas drawing pipeline (L23) for feeding nitrogen gas drawn from the nitrogen rectification column to the sub-cooler and the main heat exchanger; • a waste gas drawing pipeline (L31 ) forfeeding, to the sub-cooler and the main heat exchanger, a gas drawn from the at least one nitrogen condenser which is passed through the sub-cooler and the main heat exchanger and used in the expansion turbine; and • a recycled gas pipeline (L41 ) for returning, to the nitrogen rectification column, a recycled gas drawn from the at least one nitrogen condenser which is compressed in the compressor and passed through the main heat exchanger. |
| AMENDED CLAIMS received by the International Bureau on 20 December 2023 (20.12.2023) 1. Method applied to an air separation unit comprising: a main heat exchanger (1) into which feed air is introduced; a nitrogen rectification column (2) into which the feed air is introduced; at least one nitrogen condenser (3,4) for condensing nitrogen gas drawn from the nitrogen rectification column; a high-purity oxygen rectification column (5) into which an oxygen-containing liquid drawn from the nitrogen rectification column is introduced; an oxygen vaporizer (6) for vaporizing a high-purity oxygen liquid rectified in the high-purity oxygen rectification column; and a sub-cooler (7), wherein at least a portion of an oxygen-enriched liquid drawn from the nitrogen rectification column is cooled in the sub-cooler which uses, as a refrigerant, at least one of nitrogen gas supplied from the nitrogen rectification column and a gas supplied from a refrigerant side of the nitrogen condenser characterized in that the method comprises a step in which i) only a portion of an oxygen-enriched liquid drawn from the nitrogen rectification column is supplied to the nitrogen condenser after being cooled in the oxygen vaporizer, and the remainder of the oxygen-enriched liquid is supplied to the nitrogen condenser after being cooled in the sub-cooler (7) or ii) an oxygen-enriched liquid drawn from the nitrogen rectification column is cooled in the sub-cooler (7) and is then cooled in the oxygen vaporizer, without having been previously vaporized, then supplied to the nitrogen condenser. 2. Method according to claim 1 , comprising a step in which the oxygen-containing liquid drawn from the nitrogen rectification column (2) is supplied to the high-purity oxygen rectification column (5) after undergoing heat exchange (8) with a gas drawn from the high-purity oxygen rectification column. 3. Method according to claim 1 or 2, comprising a step in which the oxygencontaining liquid drawn from the nitrogen rectification column (2) is supplied to the high-purity oxygen rectification column (5) after being cooled in the oxygen vaporizer (6). 4. Method according to claim 1 , 2 or 3, comprising a step in which the oxygencontaining liquid drawn from the nitrogen rectification column (2) is cooled in the oxygen vaporizer (6), undergoes heat exchange (8) with a gas drawn from the high- purity oxygen rectification column, and is then supplied to the high-purity oxygen AMENDED SHEET (ARTICLE 19) rectification column (5). 5. Method according to any preceding claim comprising a step in which an oxygen-rich liquid drawn from the nitrogen rectification column (2) is cooled in the sub-cooler (7) which uses, as a refrigerant, at least one of nitrogen gas supplied from the nitrogen rectification column and a gas supplied from a refrigerant side of the nitrogen condenser, and is cooled in the oxygen vaporizer (6), then supplied to the nitrogen condenser (3,4). 6. Air separation unit comprising: • a main heat exchanger (1 ) for subjecting feed air to heat exchange; • a sub-cooler (7) having a different heat exchange function from the main heat exchanger; • a nitrogen rectification column (2) into which the feed air that has passed through the main heat exchanger is introduced; • at least one nitrogen condenser (3,4) into which nitrogen gas drawn from the nitrogen rectification column is introduced to be condensed; • an expansion turbine (92) for expanding a gas after the gas has been drawn from the at least one nitrogen condenser and passed through the sub-cooler and the main heat exchanger; • a compressor (91 ) for compressing a recycled gas which is drawn from the at least one nitrogen condenser and compressed, then passes through the main heat exchanger, and then returns to the nitrogen rectification column; • a high-purity oxygen rectification column (5) which is supplied with an oxygencontaining liquid drawn from the nitrogen rectification column; • an oxygen vaporizer (6) which is installed in a lower portion of the high-purity oxygen rectification column and serves to generate a vapour stream of oxygen gas; • a pipeline (L100a) for feeding an oxygen-enriched liquid drawn from the nitrogen rectification column to the sub-cooler, and feeding same to the nitrogen condenser without passing through the oxygen vaporizer; • a pipeline (L100b) for feeding the oxygen-enriched liquid drawn from the nitrogen rectification column as a heat source in the oxygen vaporizer without passing through the nitrogen condenser or the subcooler, and feeding same to the nitrogen condenser; • a nitrogen gas drawing pipeline (L23) for feeding nitrogen gas drawn from the AMENDED SHEET (ARTICLE 19) nitrogen rectification column to the sub-cooler and the main heat exchanger; • a waste gas drawing pipeline (L41 ) forfeeding, to the sub-cooler and the main heat exchanger, a gas drawn from the at least one nitrogen condenser which is passed through the sub-cooler and the main heat exchanger and used in the expansion turbine; and • a recycled gas pipeline (L41 ) for returning, to the nitrogen rectification column, a recycled gas drawn from the at least one nitrogen condenser which is compressed in the compressor (91 ) and passed through the main heat exchanger. 7. Air separation unit according to claim 6, comprising: • a second heat exchanger (8) for performing heat exchange between the oxygen-containing liquid drawn from the nitrogen rectification column, and a gas drawn from the high-purity oxygen rectification column; and • a pipeline (L104) forfeeding oxygen-containing liquid drawn from the nitrogen rectification column to the high-purity oxygen rectification column via the second heat exchanger. 8. Air separation unit according to claim 6 comprising • a pipeline (L100b) for feeding the oxygen-enriched liquid drawn from the bottom portion of the nitrogen rectification column as a heat source in the oxygen vaporizer (6), and feeding same to the nitrogen condenser; • a pipeline (L104) for feeding the oxygen-containing liquid drawn from the nitrogen rectification column as a heat source in the oxygen vaporizer, and feeding same to the high-purity oxygen rectification column (5). 9. Air separation unit according to claim 6, comprising: • a second heat exchanger (8) for performing heat exchange between the oxygen-containing liquid that has undergone heat exchange in the oxygen vaporizer (6), and a waste gas (L53) drawn from the high-purity oxygen rectification column (5); • a pipeline (L104) for feeding the oxygen-containing liquid drawn from the nitrogen rectification column (2) to the high-purity oxygen rectification column via the oxygen vaporizer and the second heat exchanger (8). 10. Air separation unit comprising: • a main heat exchanger (1 ) for subjecting feed air to heat exchange; • a sub-cooler (7) having a different heat exchange function from the main heat exchanger; AMENDED SHEET (ARTICLE 19) • a nitrogen gas drawing pipeline (L23) for feeding nitrogen gas drawn from the column to the subcooler and the main heat exchanger, • a nitrogen rectification column (2) into which the feed air that has passed through the main heat exchanger is introduced; • at least one nitrogen condenser (3,4) into which nitrogen gas drawn from the nitrogen rectification column is introduced to be condensed; • an expansion turbine (92) for expanding a gas after the gas has been drawn from the at least one nitrogen condenser and passed through the sub-cooler and the main heat exchanger; • a compressor (91 ) for compressing a recycled gas which is drawn from the at least one nitrogen condenser and compressed, then passes through the main heat exchanger, and then returns to the nitrogen rectification column; • a high-purity oxygen rectification column which is supplied with an oxygencontaining liquid drawn from the nitrogen rectification column; • an oxygen vaporizer (6) which is installed in a lower portion of the high-purity oxygen rectification column and serves to generate a vapour stream of oxygen gas; • a pipeline (L100c) for feeding the oxygen-enriched liquid drawn from a bottom portion of the nitrogen rectification column to the sub-cooler, feeding same as a heat source in the oxygen vaporizer without having passed through the nitrogen condenser, and feeding same to the nitrogen condenser; • a waste gas drawing pipeline (L31 ) forfeeding, to the sub-cooler and the main heat exchanger, a gas drawn from the at least one nitrogen condenser which is passed through the sub-cooler and the main heat exchanger and used in the expansion turbine; and • a recycled gas pipeline (L41 ) for returning, to the nitrogen rectification column, a recycled gas drawn from the at least one nitrogen condenser which is compressed in the compressor and passed through the main heat exchanger. 11. Air separation unit according to claim 10, comprising a bypass pipeline (L100c1 ) which does not pass through the oxygen vaporizer and which branches from the pipeline (L100c) for feeding the oxygen-enriched liquid drawn from the bottom portion of the nitrogen rectification column (2) to the sub-cooler (7), feeding same as a heat source in the oxygen vaporizer -6), and feeding same to the nitrogen condenser (3,4). AMENDED SHEET (ARTICLE 19) |
Technical Field
The present invention relates to a method and a separation unit for producing high- purity nitrogen and high-purity oxygen by separating air.
Background Art
Because of demand for high-purity nitrogen, there is a process for producing nitrogen by cryogenic air separation, where a main heat exchanger, a nitrogen rectification column, and a nitrogen condenser are provided, an expansion turbine is arranged in order to supply the required cold, and a recycled gas compressor is arranged in order to increase the amount of nitrogen recovered (e.g., see US 5711167).
There is demand for high-purity oxygen at the same time, and it is known for an oxygen-containing liquid drawn from the nitrogen rectification column to be rectified in an oxygen rectification column. In a method which is already known, the oxygencontaining liquid is supplied to an upper portion of the rectification column, and high- purity oxygen is collected in an oxygen rectification column bottom portion by means of a rectifying operation with a vapour stream supplied by an oxygen vaporizer in the rectification column bottom portion. A portion of the feed air or the oxygen-containing liquid (e.g., see Patent Document 2), or an oxygen-rich liquid drawn from the nitrogen rectification column bottom portion (e.g., see Patent Document 3) may be used as a heat medium in the oxygen vaporizer.
The liquid drawn from the nitrogen rectification column, i.e., the oxygen-containing liquid or oxygen-rich liquid, is a saturated liquid at the time when it is drawn from the nitrogen rectification column, so a portion of this liquid evaporates when the liquid is decompressed, which leads to a process loss. It is therefore preferable for the liquid to be cooled before being decompressed in order to reduce the amount of evaporation during decompression. The oxygen-rich liquid may be cooled by means of nitrogen drawn from the nitrogen rectification column, or a waste gas vaporized in the nitrogen condenser, etc. (e.g., see US 5711167 A), or the oxygen-rich liquid may also be cooled by means of the oxygen vaporizer (e.g., see US 2010/0242537 A1 and WO 2014/173496 A23).
The vaporization capacity of the oxygen vaporizer is an important factor in determining the amount of high-purity oxygen which is produced. In US 2010/0242537 A1 , a portion of the feed air is supplied to the oxygen vaporizer, so it would seemingly be possible to freely set the vaporization capacity, but supplying the feed air to the oxygen vaporizer causes a relative reduction in the amount of feed air supplied to the nitrogen rectification column, which is therefore undesirable from the point of view of nitrogen production.
In WO 2014/173496 A2, the oxygen-rich liquid is cooled by means of the oxygen vaporizer, but when there is a reduction in thermal demand in the oxygen vaporizer, the oxygen-rich liquid may be supplied downstream without having been sufficiently cooled, and a portion of the liquid may evaporate during decompression, giving rise to thermal loss.
The present disclosure provides an air separation unit and an air separation method capable of increasing the amount of production of high-purity nitrogen and high-purity oxygen as compared to the conventional systems described above.
Means for Solving the Problems
Afirst air separation method according to the present disclosure comprises:
• a method applied to an air separation unit comprising: a main heat exchanger into which feed air is introduced;
• a nitrogen rectification column into which the feed air is introduced; at least one nitrogen condenser for condensing nitrogen gas drawn from a column top portion of the nitrogen rectification column;
• a high-purity oxygen rectification column which has an oxygen-containing liquid drawn from the nitrogen rectification column introduced into a column top portion thereof;
• an oxygen vaporizer (6) for vaporizing a high-purity oxygen liquid rectified in the high-purity oxygen rectification column; and a sub-cooler,
The method above may comprise: i) a portion of an oxygen-enriched liquid drawn from the nitrogen rectification column is supplied to the nitrogen condenser after being cooled in the oxygen vaporizer, and the remainder of the oxygen-enriched liquid is supplied to the nitrogen condenser after being cooled in the sub-cooler (7) which uses, as a refrigerant, at least one of nitrogen gas supplied from the nitrogen rectification column and a gas supplied from a refrigerant side of the nitrogen condenser or ii) an oxygen-enriched liquid drawn from the nitrogen rectification column is cooled in the sub-cooler (7) which uses, as a refrigerant, at least one of nitrogen gas supplied from the nitrogen rectification column and a gas supplied from a refrigerant side of the nitrogen condenser, and is cooled in the oxygen vaporizer, then supplied to the nitrogen condenser.
The method may comprise:
• a step (second heat exchange step) in which the oxygen-containing liquid drawn from a rectifying portion of the nitrogen rectification column is supplied to a column top of the high-purity oxygen rectification column after undergoing heat exchange with a gas drawn from the column top portion of the high-purity oxygen rectification column.
The method above thus may comprise:
• a step (oxygen-containing liquid cooling/supply step) in which the oxygencontaining liquid drawn from the rectifying portion of the nitrogen rectification column is supplied to the column top portion of the high-purity oxygen rectification column after being cooled in the oxygen vaporizer or
• a step (oxygen-containing liquid cooling/heat exchange/supply step) in which the oxygen-containing liquid drawn from the rectifying portion of the nitrogen rectification column is cooled in the oxygen vaporizer , undergoes heat exchange with a gas drawn from the column top portion of the high-purity oxygen rectification column , and is then supplied to the column top of the high-purity oxygen rectification column. The method above may comprise:
• a step (pressurization step) in which a high-purity oxygen liquid drawn from the bottom portion of the oxygen rectification column is fed to the main heat exchanger after being pressurized.
A second air separation method according to the present disclosure constitutes:
• a method applied to an air separation unit comprising: a main heat exchanger into which feed air is introduced;
• a nitrogen rectification column into which the feed air is introduced; at least one nitrogen condenser for condensing nitrogen gas drawn from a column top of the nitrogen rectification column;
• a high-purity oxygen rectification column which has an oxygen-containing liquid drawn from the nitrogen rectification column introduced into a column top portion thereof;
• an oxygen vaporizer for vaporizing a high-purity oxygen liquid rectified in the high-purity oxygen rectification column;
• and a sub-cooler, wherein the method comprises a step (two-stage cooling step) in which an oxygenrich liquid drawn from a bottom portion of the nitrogen rectification column is cooled in the sub-cooler which uses, as a refrigerant, at least one of nitrogen gas supplied from the column top portion of the nitrogen rectification column and a gas supplied from a refrigerant side of the nitrogen condenser, and is cooled in the oxygen vaporizer , then supplied to the nitrogen condenser.
The method above may comprise:
• a step (second heat exchange step) in which the oxygen-containing liquid drawn from a rectifying portion of the nitrogen rectification column is supplied to a column top of the high-purity oxygen rectification column after undergoing heat exchange with a gas drawn from the column top of the high-purity oxygen rectification column.
The method above may comprise:
• a step (pressurization step) in which a high-purity oxygen liquid drawn from the bottom portion of the high-purity oxygen rectification column) is fed to the main heat exchanger after being pressurized.
Afirst air separation unit according to the present disclosure comprises:
• a main heat exchanger for subjecting feed air to heat exchange;
• a sub-cooler having a different heat exchange function from the main heat exchanger;
• a nitrogen rectification column (comprising an intermediate or lower rectifying portion) into which the feed air that has passed through the main heat exchanger is introduced;
• at least one nitrogen condenser (first and second condensers) into which nitrogen gas (vaporized gas) drawn from a column top of the nitrogen rectification column is introduced, the at least one nitrogen condenser condensing (cooling) this gas and returning it to the column top portion;
• an expansion turbine for expanding a gas after the gas has been drawn from the at least one nitrogen condenser (column top portion of the first condenser) and passed through the sub-cooler and (a part of) the main heat exchanger;
• a compressor for compressing a recycled gas which is drawn from the at least one nitrogen condenser (column top portion of the second condenser) and compressed, then partially passes through the main heat exchanger , and then returns to the nitrogen rectification column;
• a high-purity oxygen rectification column (comprising an oxygen rectifying portion or column top) which is supplied with an oxygen-containing liquid (including a gaseous form and a liquid form) drawn from (an intermediate or upper rectifying portion of) the nitrogen rectification column;
• an oxygen vaporizer which is arranged in a lower portion (of the oxygen rectifying portion) of the high-purity oxygen rectification column and serves to generate a vapour stream of oxygen gas;
• a pipeline for feeding (a part of) an oxygen-rich liquid drawn from the bottom portion of the nitrogen rectification column to the sub-cooler , and feeding same to the nitrogen condenser (second condenser);
• a pipeline for feeding (the remainder of) the oxygen-rich liquid drawn from the bottom portion of the nitrogen rectification column as a heat source in the oxygen vaporizer (6), and feeding same to the nitrogen condenser (second condenser);
• a nitrogen gas drawing pipeline forfeeding nitrogen gas (vaporized gas) drawn from the column top portion of the nitrogen rectification column to the sub-cooler and the main heat exchanger;
• a waste gas drawing pipeline for feeding, to the sub-cooler and the main heat exchanger , a gas drawn from the at least one nitrogen condenser (column top portion of the first condenser) which is passed through the sub-cooler and (a part of) the main heat exchanger and used in the expansion turbine; and
• a recycled gas pipeline for returning, to the nitrogen rectification column, a recycled gas drawn from the at least one nitrogen condenser (column top portion of the second condenser) which is compressed in the compressor and partially passed through the main heat exchanger.
The unit may comprise:
• a bypass pipeline which branches from the pipeline and does not pass through the oxygen vaporizer.
The unit may comprise: • a pipeline for feeding the oxygen-containing liquid drawn from the nitrogen rectification column to the column top portion of the high-purity oxygen rectification column.
The unit may comprise:
• a second heat exchanger for performing heat exchange between the oxygencontaining liquid drawn from the nitrogen rectification column, and a gas drawn from the column top portion of the high-purity oxygen rectification column; and
• a pipeline for feeding the oxygen-containing liquid drawn from the nitrogen rectification column (2) to the high-purity oxygen rectification column via the second heat exchanger.
The unit may comprise:
• a pressurization apparatus for pressurizing the high-purity oxygen liquid drawn from the bottom portion of the high-purity oxygen rectification column; and
• an extraction pipeline through which a high-purity oxygen liquid drawn from the bottom portion of the high-purity oxygen rectification column is fed to the sub-cooler and the main heat exchanger via the pressurization apparatus.
A second air separation unit according to the present disclosure comprises:
• a main heat exchanger for subjecting feed air to heat exchange;
• a sub-cooler having a different heat exchange function from the main heat exchanger;
• a nitrogen rectification column (comprising an intermediate or lower rectifying portion) into which the feed air that has passed through the main heat exchanger is introduced;
• at least one nitrogen condenser (first and second condensers) into which nitrogen gas (vaporized gas) drawn from a column top of the nitrogen rectification column is introduced, the at least one nitrogen condenser condensing (cooling) this gas and returning it to the column top portion;
• an expansion turbine for expanding a gas after the gas has been drawn from the at least one nitrogen condenser (column top portion of the first condenser) and passed through the sub-cooler and (a part of) the main heat exchanger;
• a compressor for compressing a recycled gas which is drawn from the at least one nitrogen condenser (column top portion of the second condenser) and compressed, then partially passes through the main heat exchanger, and then returns to the nitrogen rectification column;
• a high-purity oxygen rectification column (comprising an oxygen rectifying portion or column top) which is supplied with an oxygen-containing liquid (including a gaseous form and a liquid form) drawn from (an intermediate or upper rectifying portion of) the nitrogen rectification column;
• an oxygen vaporizer which is arranged in a lower portion (of the oxygen rectifying portion) of the high-purity oxygen rectification column and serves to generate a vapour stream of oxygen gas; and
• a pipeline for feeding the oxygen-rich liquid drawn from a bottom portion of the nitrogen rectification column to the sub-cooler , feeding same as a heat source in the oxygen vaporizer , and feeding same to the nitrogen condenser (second condenser);
• a waste gas drawing pipeline for feeding, to the sub-cooler and the main heat exchanger, a gas drawn from the at least one nitrogen condenser (column top portion of the first condenser) which is passed through the sub-cooler and (a part of) the main heat exchanger and used in the expansion turbine; and
• a recycled gas pipeline for returning, to the nitrogen rectification column, a recycled gas drawn from the at least one nitrogen condenser (column top portion of the second condenser) which is compressed in the compressor and partially passed through the main heat exchanger.
The unit may comprise:
• a bypass pipeline which branches from the pipeline and does not pass through the oxygen vaporizer.
• The unit may comprise:
• a pipeline for feeding the oxygen-containing liquid drawn from the nitrogen rectification column to the column top portion of the high-purity oxygen rectification column.
The unit may comprise:
• a second heat exchanger for performing heat exchange (cooling) between the oxygen-containing liquid drawn from the nitrogen rectification column, and a waste gas drawn from the column top portion of the high-purity oxygen rectification column; and
• a pipeline for feeding the oxygen-containing liquid drawn from the nitrogen rectification column to the high-purity oxygen rectification column via the second heat exchanger.
The unit may comprise:
• a pressurization apparatus for pressurizing the high-purity oxygen liquid drawn from the bottom portion of the high-purity oxygen rectification column; and
• an extraction pipeline through which a high-purity oxygen liquid drawn from the bottom portion of the high-purity oxygen rectification column is fed to the sub-cooler and the main heat exchanger via the pressurization apparatus.
A third air separation unit according to the present disclosure comprises:
• a main heat exchanger for subjecting feed air to heat exchange;
• a sub-cooler having a different heat exchange function from the main heat exchanger;
• a nitrogen rectification column (comprising an intermediate or lower rectifying portion) into which the feed air that has passed through the main heat exchanger is introduced;
• at least one nitrogen condenser (first and second condensers) into which nitrogen gas (vaporized gas) drawn from a column top of the nitrogen rectification column is introduced, the at least one nitrogen condenser condensing (cooling) this gas and returning it to the column top portion;
• an expansion turbine for expanding a gas after the gas has been drawn from the at least one nitrogen condenser (column top portion of the first condenser) and passed through the sub-cooler and (a part of) the main heat exchanger;
• a compressor for compressing a recycled gas which is drawn from the at least one nitrogen condenser (column top portion of the second condenser) and compressed, then partially passes through the main heat exchanger , and then returns to the nitrogen rectification column;
• a high-purity oxygen rectification column (comprising an oxygen rectifying portion or column top) which is supplied with an oxygen-containing liquid (including a gaseous form and a liquid form) drawn from (an intermediate or upper rectifying portion of) the nitrogen rectification column;
• an oxygen vaporizer which is arranged in a lower portion (of the oxygen rectifying portion) of the high-purity oxygen rectification column and serves to generate a vapour stream of oxygen gas; and
• a pipeline for feeding (a part of) an oxygen-rich liquid drawn from the bottom portion of the nitrogen rectification column to the sub-cooler , and feeding same to the nitrogen condenser (second condenser);
• a pipeline for feeding (the remainder of) the oxygen-rich liquid drawn from the bottom portion of the nitrogen rectification column as a heat source in the oxygen vaporizer , and feeding same to the nitrogen condenser (second condenser);
• a pipeline for feeding the oxygen-containing liquid drawn from the nitrogen rectification column as a heat source in the oxygen vaporizer , and feeding same to the column top of the high-purity oxygen rectification column;
• a nitrogen gas drawing pipeline forfeeding nitrogen gas (vaporized gas) drawn from the column top portion of the nitrogen rectification column to the sub-cooler and the main heat exchanger;
• a waste gas drawing pipeline for feeding, to the sub-cooler and the main heat exchanger , a gas drawn from the at least one nitrogen condenser (column top portion of the first condenser) which is passed through the sub-cooler and (a part of) the main heat exchanger and used in the expansion turbine; and
• a recycled gas pipeline for returning, to the nitrogen rectification column, a recycled gas drawn from the at least one nitrogen condenser (column top portion of the second condenser) which is compressed in the compressor and partially passed through the main heat exchanger.
The unit may comprise:
• a bypass pipeline which branches from the pipeline and does not pass through the oxygen vaporizer
The unit may comprise, instead of the pipeline:
• a second heat exchanger for performing heat exchange between the oxygencontaining liquid that has undergone heat exchange in the oxygen vaporizer , and a waste gas drawn from the column top portion of the high-purity oxygen rectification column; and
• a pipeline for feeding the oxygen-containing liquid drawn from the nitrogen rectification column to the high-purity oxygen rectification column via the oxygen vaporizer and the second heat exchanger.
• The unit may comprise:
• a pressurization apparatus for pressurizing the high-purity oxygen liquid drawn from the bottom portion of the high-purity oxygen rectification column; and • an extraction pipeline through which a high-purity oxygen liquid drawn from the bottom portion of the high-purity oxygen rectification column is fed to the sub-cooler and the main heat exchanger via the pressurization apparatus.
The high-purity oxygen liquid extracted by the extraction pipeline may be passed through the main heat exchanger (vaporized) to form oxygen gas which is then fed to a point of demand.
The air separation units may comprise:
• various measurement instruments such as flow rate measurement instruments, pressure measurement instruments, temperature measurement instruments, and liquid level measurement instruments;
• various valves such as control valves and gate valves; and
• pipes for connecting the components.
The air separation units may comprise:
• a compressor-expander which includes the expansion turbine and the compressor. At least a portion of the power obtained by the expansion turbine is used as power for the compressor, whereby power that can be recovered in the expansion turbine can be efficiently utilized.
“High-purity oxygen” means oxygen having a purity of 99.99% or greater, for example. “High-purity nitrogen” means nitrogen having a purity of 99.99% or greater, for example.
Effects
(1 ) It is possible to increase the amount of production of high-purity nitrogen and high- purity oxygen.
(2) The oxygen-rich liquid drawn from the nitrogen rectification column is cooled in the oxygen vaporizer while at the same time being cooled in the sub-cooler which uses, as a refrigerant, nitrogen gas supplied from the nitrogen rectification column and waste gas supplied from a refrigerant side of the nitrogen condenser, and, as a result, the oxygen-rich liquid can be sufficiently cooled and thermal efficiency can be improved, even if thermal demand in the oxygen vaporizer varies.
(3) The oxygen-containing liquid is further cooled by means of heat exchange with waste gas in the oxygen rectification column which is drawn from the oxygen rectification column, thereby making it possible to further reduce evaporation loss associated with decompression. (4) The oxygen-containing liquid is cooled at the same time as being utilized as a heat medium in the oxygen vaporizer, thereby enabling a reduction in evaporation loss arising as a result of decompression when the oxygen-containing liquid is introduced into the oxygen rectification column, and the amount of vapour produced in the oxygen vaporizer is increased, which therefore also contributes to increasing the amount of production of high-purity oxygen.
Brief Description of the Drawings
[Fig. 1 A] shows an air separation unit according to embodiment 1 .
[Fig. 1 B] shows an air separation unit according to a different mode of embodiment 1 .
[Fig. 2] shows an air separation unit according to embodiment 2.
[Fig. 3A] shows an air separation unit according to embodiment 3.
[Fig. 3B] shows an air separation unit according to a different mode of embodiment 3.
[Fig. 4] shows an air separation unit according to embodiment 4.
[Fig. 5] shows an air separation unit according to embodiment 5.
[Fig. 6] shows an air separation unit according to embodiment 6.
Several embodiments of the present disclosure will be described below. The embodiments described below are given as an example of the present disclosure. The present disclosure is in no way limited by the following embodiments, and also includes a number of variant modes which are implemented within a scope that does not alter the essential point of the present disclosure. It should be noted that not all the constituents described below are necessarily essential to the present disclosure. Upstream and downstream are based on a flow direction of a gas stream.
Embodiment 1
An air separation unitAI according to embodiment 1 will be described with the aid of fig. 1A.
Feed air is introduced into a main heat exchanger 1 where heat exchange is performed.
A sub-cooler 7 has a different heat exchange function from the main heat exchanger 1 . The main heat exchanger 1 and the sub-cooler 7 are depicted as being connected in fig. 1A but their heat exchange functions are separate. In this embodiment, refrigerants in the sub-cooler 7 are at least: nitrogen gas supplied from a column top portion 23 of a nitrogen rectification column 2, and a gas supplied from a column top portion 31 (refrigerant side) of a first condenser 3.
The feed air that has passed through the main heat exchanger 1 is introduced into the nitrogen rectification column 2. The nitrogen rectification column 2 comprises a bottom portion 21 , a rectifying portion 22, and a column top portion 23. A feed air pipeline L1 passes the feed air through the main heat exchanger 1 and introduces the feed air into a lower rectifying portion 221 of the nitrogen rectification column 2. Nitrogen gas (nitrogen-rich gas) drawn from the column top 23 of the nitrogen rectification column 2 is passed, by way of a nitrogen gas pipeline L23, through the sub-cooler 7 and the main heat exchanger 1 , from which it is drawn as product nitrogen.
Nitrogen gas (vaporized gas) drawn from the column top portion 23 of the nitrogen rectification column 2 is introduced into the first condenser 3 which condenses (cools) this gas. The nitrogen gas is fed by means of a pipeline L231 from the column top portion 23 to the first condenser 3 where it is cooled and then returned to the column top portion 23.
Nitrogen gas (vaporized gas) drawn from the column top portion 23 of the nitrogen rectification column 2 is introduced into a second condenser 4 which condenses (cools) this gas. The nitrogen gas is fed by means of a pipeline L232 from the column top portion 23 to the second condenser 4 where it is cooled and then returned to the column top portion 23.
A pressure on the refrigerant side of the first condenser 3 is lower than a pressure on the refrigerant side of the condenser 4. A high-pressure oxygen-rich liquid concentrated in the second condenser 4 is decompressed by a decompression valve and then fed to the first condenser 3 as a low-pressure refrigerant.
A compressor 91 and an expansion turbine 92 function as a compressor-expander 9. The expansion turbine 92 expands a gas drawn from the column top portion 31 of the first condenser 3, after the gas has passed through the sub-cooler 7 and a part of the main heat exchanger 1 . The expanded gas passes through the sub-cooler 7 and the main heat exchanger 1 , and is treated as waste gas. By way of a waste gas pipeline L31 , the gas which is drawn from the column top 31 of the first condenser 3 is passed through the sub-cooler 7 and a part of the main heat exchanger 1 , expanded in the expansion turbine 92, and then passed through the sub-cooler 7 and the main heat exchanger 1 , from which it is drawn.
The compressor 91 compresses the gas drawn from a column top portion 41 of the second condenser 4. The compressed gas passes through a part of the main heat exchanger 1 and is introduced into a gas phase in the bottom portion 21 of the nitrogen rectification column 2. By way of a recycling pipeline L41 , the gas which is drawn from the column top portion 41 of the second condenser 4 is compressed by the compressor 91 , passed through a part of the main heat exchanger 1 , and introduced into the gas phase in the bottom portion 21 of the nitrogen rectification column 2
An oxygen-containing liquid (including a gaseous form and a liquid form) drawn from an intermediate rectifying portion 222 of the nitrogen rectification column 2 is supplied to a high-purity oxygen rectification column 5. The high-purity oxygen rectification column 5 includes a lower portion 51 , a rectifying portion 52, and a column top portion 53. An oxygen vaporizer is installed in the lower portion 51 of the high-purity oxygen rectification column 5 and generates a vapour stream of oxygen gas. A pipeline L22 draws the oxygen-containing liquid from the intermediate rectifying portion 222 of the nitrogen rectification column 2 and feeds the liquid into the column top portion 53 of the high-purity oxygen rectification column 5. A pipeline L53 draws the gas from the column top portion 53 of the high-purity oxygen rectification column 5 and merges into the waste gas pipeline L31 upstream of the main heat exchanger 1. An extraction pipeline L51 is a pipeline for extracting a high-purity oxygen liquid from the bottom portion 51 of the high-purity oxygen rectification column 5.
It should be noted that, in a different embodiment, the extraction pipeline L51 may be a pipeline for feeding the high-purity oxygen liquid to only either one of the sub-cooler 7 or the main heat exchanger 1 , or the pipeline L51 may be a pipeline for feeding to both, or it may function as a pipeline for supplying the high-purity oxygen liquid as a high-purity oxygen gas product. In such a case, a means for increasing the pressure of the high-purity oxygen liquid may be provided before the high-purity oxygen liquid is fed to the sub-cooler 7 or to the main heat exchanger 1 .
Two types of cooling steps for cooling the oxygen-rich liquid
In the two types of cooling steps for cooling the oxygen-rich liquid, a portion of the oxygen-rich liquid drawn from a bottom portion 211 of the nitrogen rectification column 2 is supplied to the second condenser 4 after being cooled in the oxygen vaporizer s, and the remainder of the oxygen-rich liquid is supplied to the second condenser 4 after being cooled in the sub-cooler 7 which uses, as a refrigerant, nitrogen gas supplied from the column top portion 23 of the nitrogen rectification column 2 and a gas supplied from the column top portion 31 (refrigerant side) of the first condenser 3. In embodiment 1 , the high-purity oxygen liquid drawn from the high-purity oxygen rectification column 5 also functions as a refrigerant.
A pipeline L100a is a pipeline for feeding a part of the oxygen-rich liquid drawn from the bottom portion 21 of the nitrogen rectification column 2 by a pipe L100 to the subcooler 7, and feeding same to the second condenser 4.
A pipeline L100b is a pipeline forfeeding the remainder of the oxygen-rich liquid drawn from the bottom portion 21 of the nitrogen rectification column 2 by the pipe L100 as a heat source in the oxygen vaporizer 6, and feeding same to the second condenser 4.
The nitrogen gas drawing pipeline L23 is a pipeline for feeding nitrogen gas (vaporised gas) drawn from the column top portion 23 of the nitrogen rectification column 2 to the sub-cooler 7 and the main heat exchanger 1 .
A control unit 110 determines a flow rate of the oxygen-rich liquid fed to the oxygen vaporizer 6 and controls the flow rate of the oxygen-rich liquid so as to supply a quantity of heat corresponding to a target amount of evaporation in the oxygen vaporizer 6. It should be noted that the target amount of evaporation is set in accordance with a production amount of product high-purity oxygen, and a process balance in the nitrogen rectification column 2 and the high-purity oxygen rectification column 5.
The amount of evaporation in the oxygen vaporizer 6 may be obtained from a pressure in the high-purity oxygen rectification column 5, a production amount of the product high-purity oxygen collected in the bottom portion 51 , ora purity of the product high-purity oxygen. The pressure in the high-purity oxygen rectification column 5 may be measured in the column top portion 53, the rectifying portion (intermediate portion) 52, or the lower portion 51 . The production amount of the product high-purity oxygen may be measured by a flowmeter arranged in the extraction pipeline L51 for drawing the product high-purity oxygen, or it may be calculated from a liquid level gauge in the lower portion 51 of the high-purity oxygen rectification column 5. The purity of the product high-purity oxygen may be the measured purity of oxygen liquid collected in the lower portion 51 of the high-purity oxygen rectification column 5, or it may be measured by drawing oxygen gas from the gas phase portion in the lower portion 51 . The flow rate of the oxygen-rich liquid may be determined by means of a heat capacity of the oxygen-rich liquid, and a difference between an inlet temperature (measured by a thermometer) and an outlet temperature (measured by a thermometer) in the oxygen vaporizer 6. The heat capacity of the oxygen-rich liquid may be estimated from temperature-pressure-composition, and an average value in an assumed operating range may be used as a constant. In this embodiment, the flow rate of the oxygen-rich liquid fed to the oxygen vaporizer 6 is measured by a flowmeter F1 provided in the pipeline L101 b. The flowmeter F1 may be a differential pressure flowmeter, a vortex flowmeter, or a mass flowmeter, etc., for example. Furthermore, the flow rate of the oxygen-rich liquid may be calculated from a difference between an indicated value of an oxygen-containing liquid flowmeter (flowmeter provided in the pipe L22) and an indicated value of a flowmeter for waste gas from the high-purity oxygen rectification column 5 (flowmeter provided in the pipe L53).
The control unit 110 controls the flow rate by adjusting a first control valve V1 provided in the pipeline L1 OOb so that the measurement result (flow rate) at the flowmeter F1 enables a quantity of heat corresponding to the target amount of evaporation to be supplied, in other words, the control unit 110 controls the amount of evaporation by adjusting the quantity of heat supplied.
The control unit 110 may also control the flow rate of oxygen-rich liquid circulating through the pipeline L100a by adjusting a second control valve V2 provided in the pipeline L100a, in addition to the first control valve V1.
In this embodiment, the flow rate of the oxygen-rich liquid is controlled once the inlet temperature and the outlet temperature of the oxygen-rich liquid circulating through the oxygen vaporizers have been stabilised. The inlet temperature of the oxygen-rich liquid in the oxygen vaporizer 6 is equal to a saturation temperature in the bottom portion 21 of the nitrogen rectification column 2, and is unaffected by the oxygen-rich liquid in the sub-cooler 7. This means that the remaining oxygen-rich liquid which is not supplied to the oxygen vaporizer 6, out of the oxygen-rich liquid drawn from the bottom portion 21 of the nitrogen rectification column 2, can be fed to the sub-cooler 7 for cooling, while operability of the oxygen vaporizer 6 is maintained.
Different mode of embodiment 1
An air separation unit A1 according to a different mode of embodiment 1 will be described with the aid of fig. 1 B.
This different mode comprises a bypass pipeline L100b1 .
The bypass pipeline L100b1 branches from the pipeline L100b upstream from the oxygen vaporizers and merges with the pipeline L100b downstream from the oxygen vaporizer 6, without passing through the oxygen vaporizer 6. A control valve V11 is provided in the pipeline L100b upstream from the oxygen vaporizer 6, and a control valve V12 is provided in the bypass pipeline L100b1.
The control unit 110 performs control as in embodiment 1. Furthermore, the control unit 110 controls the control valve V11 to close and the control valve V12 to open, and the oxygen-rich liquid is fed to the bypass pipeline L100b1. As a result, even if the amount of evaporation in the oxygen vaporizer 6 is excessive, a part of the oxygenrich liquid is allowed to circulate to the bypass pipeline L100b1 while the oxygen-rich liquid in the sub-cooler 7 is stably cooled, and the amount of evaporation in the oxygen vaporizer 6 can be appropriately regulated as a result.
Embodiment 2
An air separation unit A1 according to embodiment 2 will be described with the aid of fig. 2. The air separation unit A1 of embodiment 2 has a different configuration from that of the air separation unit A1 of embodiment 1 in that a second heat exchanger 8 is provided. Components which are the same as those of embodiment 1 will not be described or will only be briefly described.
The second heat exchanger 8 performs heat exchange between the oxygencontaining liquid drawn from the intermediate rectifying portion 222 of the nitrogen rectification column 2, and a gas drawn from the column top portion 53 of the high- purity oxygen rectification column 5.
A pipeline L101 is a pipeline for feeding the oxygen-containing liquid drawn from the nitrogen rectification column 2 to the column top portion 53 of the high-purity oxygen rectification column 5 via the second heat exchanger 8.
The oxygen-containing liquid is further cooled by the second heat exchanger 8, thereby making it possible to reduce evaporation loss associated with decompression.
Embodiment 3
An air separation unit A2 according to embodiment 3 will be described with the aid of fig. 3A. The air separation unit A2 of embodiment 3 has a different configuration from that of the air separation unitAI of embodiment 1 in that a pipeline L100c is provided, without the pipelines L100a and L100b being provided. Components which are the same as those of embodiment 1 will not be described or will only be briefly described. The pipeline L100c is a pipeline for feeding the oxygen-rich liquid drawn from the bottom portion 21 of the nitrogen rectification column 2 to the sub-cooler 7, then feeding the oxygen-rich liquid as a heat source in the oxygen vaporizer 6, and next feeding same to the second condenser 4. Two-stage cooling step for cooling the oxygen-rich liquid
In the two-stage cooling step for cooling the oxygen-rich liquid, the oxygen-rich liquid drawn from the bottom portion 21 of the nitrogen rectification column 2 is cooled in the sub-cooler 7 which uses, as a refrigerant, nitrogen gas supplied from the column top portion 23 of the nitrogen rectification column 2 and a gas supplied from the column top portion 31 (refrigerant side) of the first condenser 3, then cooled in the oxygen vaporizer s, and then supplied to the second condenser 4.
A control unit 120 determines a flow rate of the oxygen-rich liquid fed to the oxygen vaporizer 6 and controls the flow rate of the oxygen-rich liquid so as to supply a quantity of heat corresponding to a target amount of evaporation in the oxygen vaporizer 6. It should be noted that the target amount of evaporation is set in accordance with a production amount of product high-purity oxygen, and a process balance in the nitrogen rectification column 2 and the high-purity oxygen rectification column 5.
The control unit 120 controls the flow rate of the oxygen-rich liquid so as to stabilize the temperature of the oxygen-rich liquid at the inlet of the oxygen vaporizer 6. In order to stabilize the temperature of the oxygen-rich liquid at the inlet of the oxygen vaporizer 6, the amount of oxygen-rich liquid cooled in the sub-cooler 7 is controlled to a constant level.
The flow rate of the oxygen-rich liquid supplied to the oxygen vaporizers is measured by a flowmeter F2 provided in the pipeline L100c.
The control unit 120 controls the flow rate by adjusting a control valve V3 provided in the pipeline L100c so that the measurement result (flow rate) at the flowmeter F2 enables a quantity of heat corresponding to the target amount of evaporation to be supplied, in other words, the control unit 120 controls the amount of evaporation by adjusting the quantity of heat supplied.
Different mode of embodiment 3
An air separation unit A2 according to a different mode of embodiment 3 will be described with the aid of fig. 3B.
This different mode comprises a bypass pipeline L100c1 .
The bypass pipeline L100c1 branches from the pipeline L100c upstream from the oxygen vaporizers and merges with the pipeline L100c downstream from the oxygen vaporizer 6, without passing through the oxygen vaporizer 6. A valve V4 is provided in the pipeline L100c upstream from the oxygen vaporizer 6, and a valve V5 is provided in the bypass pipeline L100c1.
The control unit 120 performs control as in embodiment 3. Furthermore, the control unit 120 controls the valve V4 to close and the valve V5 to open, and the oxygen-rich liquid is fed to the bypass pipeline L100c1. As a result, even if the amount of evaporation in the oxygen vaporizer 6 is excessive, the oxygen-rich liquid is allowed to circulate to the bypass pipeline L100c1 while the oxygen-rich liquid in the subcooler 7 is stably cooled, and the amount of evaporation in the oxygen vaporizer 6 can be appropriately regulated as a result.
Embodiment 4
An air separation unit A3 according to embodiment 4 will be described with the aid of fig. 4. The air separation unit A3 of embodiment 4 has a different configuration from that of the air separation unit A1 of embodiment 1 in that a pipeline L103 is provided, without the pipeline L22 being provided. Components which are the same as those of embodiment 1 will not be described or will only be briefly described.
The pipeline L103 is a pipeline for drawing the oxygen-containing liquid from the intermediate rectifying portion 222 of the nitrogen rectification column, feeding this liquid as a heat source in the oxygen vaporizer 6, then feeding the liquid to the column top portion 53 of the high-purity oxygen rectification column 5. This configuration utilises two types of liquids as the heat source in the oxygen vaporizer 6, namely the oxygen-rich liquid and the oxygen-containing liquid.
By this means, the oxygen-containing liquid is utilized as a heat medium and cooled in the oxygen vaporizer s, thereby enabling a reduction in evaporation loss arising as a result of decompression when the oxygen-containing liquid is introduced into the oxygen rectification column 5. That is to say, the amount of vapour produced in the oxygen vaporizers is increased, which therefore contributes to increasing the amount of production of high-purity oxygen.
Embodiment 5
An air separation unit A3 according to embodiment 5 will be described with the aid of fig. 5. The air separation unit A3 of embodiment 5 has a different configuration from that of the air separation unit A3 of embodiment 4 in that a pipeline L104 is provided, without the pipeline L103 being provided. Components which are the same as those of embodiment 4 will not be described or will only be briefly described.
The second heat exchanger 8 performs heat exchange between the oxygencontaining liquid drawn from the intermediate rectifying portion 222 of the nitrogen rectification column 2 and utilized as a heat medium in the oxygen vaporizers, and a gas drawn from the column top portion 53 of the high-purity oxygen rectification column 5.
The pipeline L104 is a pipeline for feeding the oxygen-containing liquid drawn from the nitrogen rectification column 2 to the oxygen vaporizer 6, then feeding this liquid to the column top portion 53 of the high-purity oxygen rectification column 5 via the second heat exchanger 8.
The oxygen-containing liquid is further cooled by the second heat exchanger 8, thereby making it possible to reduce evaporation loss associated with decompression.
Embodiment 6
An air separation unit A3 according to embodiment 6 will be described with the aid of fig. 6. The air separation unit A3 of embodiment 6 has a different configuration from that of the air separation unit A3 of embodiment 5 in that a pressurization apparatus 65 is provided. Components which are the same as those of embodiment 5 will not be described or will only be briefly described.
The pressurization apparatus 65 pressurizes the high-purity oxygen liquid drawn from the bottom portion in the lower portion 51 of the high-purity oxygen rectification column 5.
The pressurized high-purity oxygen liquid is fed to the sub-cooler 7 and the main heat exchanger 1 via the extraction pipeline L51 , from where it can be extracted as high- pressure, high-purity oxygen gas.
Embodiment 1 , example in fig. 1
A simulation example of embodiment 1 will be described.
Feed air is supplied to a warm end of the main heat exchanger 1 at 10.86 barA, a temperature of 55°C, and a flow rate of 1065 Nm 3 /h, cooled to -162°C, and then supplied to the nitrogen rectification column 2.
Nitrogen gas is drawn from the column top portion 23 of the nitrogen rectification column 2 at 575 Nm 3 /h, warmed in the sub-cooler 7 and the main heat exchanger 1 , and then drawn out.
An oxygen-rich liquid comprising 39% oxygen is drawn at 836 Nm 3 /h from the bottom portion 21 of the nitrogen rectification column 2, and 621 Nm 3 /h thereof is fed to the sub-cooler 7 and cooled to -171°C, then supplied to the second condenser 4. The other 215 Nm 3 /h is cooled to -177°C in the oxygen vaporizer 6 then supplied to the second condenser 4.
Recycled air is generated in the second nitrogen condenser 4 at 6.5 barA and 417 Nm 3 /h, and the pressure is boosted to 10.8 barA in the compressor 91 , after which the recycled air is cooled in the main heat exchanger 1 then returned and recycled to the nitrogen rectification column 2.
Waste gas is generated in the first condenser 3 at 5.1 barA and 419 Nm 3 /h, warmed to -137°C in the sub-cooler 7 and the main heat exchanger 1 , and then cooled while simultaneously being expanded in the expansion turbine 92, once again warmed in the sub-cooler 7 and the main heat exchanger 1 , and then treated as waste gas.
In order to produce high-purity oxygen, an oxygen-containing liquid comprising 19% oxygen is drawn at 71 Nm 3 /h, decompressed to 1.5 barA, and then supplied to the column top portion 53 of the high-purity oxygen rectification column 5. A high-purity oxygen liquid is drawn at 4.3 Nm 3 /h from the bottom portion in the lower portion 51 of the high-purity oxygen rectification column 5. Waste gas is drawn from the column top portion 53 at 66.7 Nm 3 /h, mixed with the waste gas supplied from the expansion turbine 92, then warmed in the sub-cooler 7 and the main heat exchanger 1 and treated as waste gas.
As a comparative example, an oxygen-rich liquid drawn from the bottom portion of the nitrogen rectification column 2 is fed to the oxygen vaporizer 6 and then fed to the second condenser 4, without the sub-cooler 7 of embodiment 1 being provided. The configuration comprises only the pipeline L100b, without the pipeline L100a.
The amount of high-purity oxygen liquid produced by the high-purity oxygen rectification column of the example was confirmed to be between 1.1 and 1.3 times that of the comparative example.
Other embodiments
(1) In the embodiments above, the refrigerants in the sub-cooler 7 were at least: nitrogen gas supplied from the column top portion 23 of the nitrogen rectification column 2, and a gas supplied from the column top portion 31 (refrigerant side) of the first condenser 3, but as another embodiment, a pipeline by which the pipeline L31 feeds to the main heat exchanger 1 without passing through the sub-cooler 7, or a bypass pipe for feeding to the main heat exchanger 1 without passing through the sub-cooler 7 may further be provided. Furthermore, as another embodiment, a pipeline by which the nitrogen gas pipeline L23 feeds to the main heat exchanger 1 without passing through the sub-cooler 7, or a bypass pipe for feeding to the main heat exchanger 1 without passing through the sub-cooler 7 may further be provided.
(2) The pressurisation apparatus 65 was provided in embodiment 6, but the pressurisation apparatus may equally be provided in the other embodiments 1 to 5.
(3) The bypass pipeline of embodiment 1 may equally be provided in embodiments 5 and 6.
(4) Although not explicitly stated, pressure regulators and flow rate controllers, etc. may be installed in each pipeline in order to regulate pressure and regulate flow rate.
(5) Although not explicitly stated, control valves and gate valves, etc. may be installed in each line.
(6) Although not explicitly stated, pressure regulators and temperature measurement devices, etc. may be installed in each column in order to regulate pressure and regulate temperature.
Key to Symbols
1 Main heat exchanger
2 Nitrogen rectification column
3 First condenser
4 Second condenser
5 High-purity oxygen rectification column
6 Oxygen vaporizer
7 Sub-cooler
8 Second heat exchanger
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