Claims
- 1. In double fractionation of air at low temperatures in an air separation plant, operating at elevated pressures on a compressed main air feed and producing a nitrogen product, the method for thermodynamically interlinking said air separation plant with a steam generator so that irreversibility of heat transfer within said steam generator is reduced and total efficiency of said interlinked plants is increased, consisting essentially of:
- A. accumulatively and indirectly heating said nitrogen product with said compressed main air feed to form a hot nitrogen product containing a low-grade heat;
- B. indirectly heating said hot nitrogen product with high-grade heat generated by combusting an air-fuel mixture to form combustion products at a high temperature level in connection with said steam generator, without contaminating said nitrogen product with said combustion products, to form a very hot nitrogen product;
- B'. preheating at least a portion of the air of the air-fuel mixture by indirect heat exchange with a portion of said compressed main air feed prior to any further heat exchange;
- C. work-expanding said very hot nitrogen product to obtain energy therefrom and cool said nitrogen product to a lower temperature level;
- D. indirectly cooling said work-expanded nitrogen product to a temperature that is close to ambient by transferring low-grade heat within said steam generator; and
- E. disposing of said cooled nitrogen product, uncontaminated by said combustion products, outside of said interlinked plants.
- 2. The method of claim 1 wherein said high temperature level is above about 1,200.degree.C. and said lower temperature level is at about 880.degree.C.
- 3. The method of claim 2 wherein said low-grade heat is transferred to the water and combustion air which are fed to said steam generator.
- 4. The method of claim 1 wherein said energy obtained by work-expanding said very hot nitrogen product is mechanical energy which is used for compressing said main air feed.
- 5. The method of claim 4 wherein said very hot nitrogen product is work-expanded in a gas turbine which is mechanically connected to a compressor for compressing said main air feed.
- 6. The method of claim 1 wherein said high-grade heat is supplied through a heat exchanger made of heat-resisting material and heated with flue gases.
- 7. The method of claim 6 wherein said hot nitrogen product is at about 280.degree.C. and said very hot nitrogen product is at about 950.degree.C.
- 8. The method of claim 7 wherein said heat-resisting material is a ceramic and said flue gases are supplied from the superheater region of said steam generator.
- 9. In double fractionation of air at low temperatures in an air separation plant, comprising a fractionating column with a high pressure zone and an intermediate pressure zone and operating at elevated pressures to produce a relatively pure nitrogen product and a relatively pure oxygen products, wherein said high pressure zone operates at a pressure higher than 9 ata but lower than 25 ata, and said intermediate pressure zone operates at a pressure higher than 1.5 ata but lower than 9 ata, and wherein an incoming air stream is compressed to more than 9 ata as a main air feed before its separation, an improvement consisting essentially of thermodynamically interlinking said air separation plant with a steam generator and thereby carnotizing said steam generator, essentially by means of indirect heat exchanges between said nitrogen product and the heating fluids and the heated fluids of said steam generator, said indirect heat exchanges comprising:
- A. countercurrently and indirectly exchanging low-grade heat from said compressed main air feed to at least part of said nitrogen product;
- B. indirectly exchanging high-grade heat from said heating fluids of said steam generator to said at least part of said nitrogen product;
- C. work-expanding said at least part of said nitrogen product; and
- D. indirectly exchanging low-grade heat from said work-expanded said at least part of said nitrogen product to said heated fluids, thus recovering at least a substantial part of mechanical energy required for the compression of said incoming air stream without substantially impairing the efficiency of said steam generator.
- 10. The improvement according to claim 9, wherein said fractionation column further comprises a feed and a reflux from said high pressure zone to said intermediate pressure zone and wherein said relatively pure oxygen and nitrogen products are obtained by increasing the reflux quantity to said intermediate pressure zone by the following steps:
- A. throttling at least part of said oxygen product in liquid phase from said intermediate pressure to a lower pressure so as to reduce its temperature and form a throttled oxygen product; and
- B. carrying out an indirect heat exchange between said throttled oxygen product and said feed and said reflux from said high pressure zone so as to subcool said feed and said reflux to such an extent that their partial evaporation during said throttling is minimized.
- 11. The improvement according to claim 9, wherein part of said incoming air stream is compressed to a pressure higher than 100 ata, cooled, work-expanded, and led to said high pressure zone of said fractionating column as part of said compressed main air feed.
- 12. The improvement according to claim 9, wherein said nitrogen product is heated to well above 600.degree.C. by the flue gases of a pebble heater, and wherein said steam generator, which is interlinked with said air separation plant, is provided with one pressurized and one non-pressurized heating space, said flue gases from said pebble heater and said work-expanded nitrogen product imparting heat to said heated fluids of said steam generator in said pressurized and non-pressurized spaces, respectively.
- 13. The improvement according to claim 10, wherein said nitrogen product is heated to well above 600.degree.C. in a heat exchanger made of heat-resisting material by the flue gases of said steam generator, and wherein said flue gases, before they enter said heat exchanger, impart some of their high temperature heat to the heated fluids of said steam generator.
- 14. The improvement according to claim 10, wherein substantially all the heat which is generated by the compression of said incoming air stream to form said compressed main air feed is imparted to said nitrogen product and to at least one said heated fluid of said steam generator.
- 15. In double fractionation of air at low temperatures and elevated pressures in a high-prssure zone and in an intermediate-pressure zone of an air separation plant to produce a relatively pure oxygen product and a relatively pure nitrogen product, after compression of said air, wherein said high pressure zone operates at a high pressure higher than 9 ata but lower than 25 ata and said intermediate-pressure zone operates at an intermediate pressure higher than 1.5 ata but lower than 9 ata, an improvement to recover most of the energy required for said compression by interlinking said air separation plant with a steam generator using flue gas for steam generation, consisting essentially of the following steps:
- A. forming a compressed main air feed by compressing said air to said high pressure, without intercooling thereof that would remove relatively low-temperature compression heat generated by said compressing, and dividing said compressed main air feed into a major part and a remaining part;
- B. transferring, by indirect heat exchange, said relatively low-temperature compression heat from said major part of said compressed main air feed to said nitrogen product so that the temperature of said nitrogen product is raised to form a hot nitrogen product;
- C. transferring, by indirect exchange therebetween, said relatively low-temperature compression heat from said remaining part of said compressed main air feed to at least one heated fluid feed for said steam generator;
- D. transferring, by indirect exchange therebetween, a quantity of high-temperature heat from said flue gas to said hot nitrogen product, so that the temperature of said hot nitorgen product is raised additionally and a very hot nitrogen product having a temperature well above 600.degree.C. is formed;
- E. work-expanding said very hot nitrogen product in a gas turbine to obtain mechanical energy therefrom and to cool said very hot nitrogen product so that a work-expanded nitrogen product having a lower temperature is formed, said mechanical energy being used for said compressing of said air in step A; and
- F. transferring, by indirect exchange therebetween, heat at said lower temperature from said work-expanded nitrogen product to at least one heated fluid feed to said steam generator to decrease said lower temperature to an exit temperature well below 150.degree.C. and to form a cooled nitrogen product having essentially no other contaminants than said relatively pure nitrogen product and without augmenting the volume of said nitrogen product by admixing it with said flue gas,
- whereby wastage of said relatively low-temperature compression heat generated by said compression is essentially avoided, a quantity of high-temperature heat is borrowed from said flue gas which is at a temperature substantially hotter than the critical temperature of steam, said high-temperature heat is used for production of mechanical energy, and essentially said quantity of heat is returned at said lower temperature to said at least one heated fluid, the efficiency of said steam generator not being substantially reduced.
- 16. The method of claim 15 wherein said high-pressure zone is at a pressure of about 15 ata and said intermediate-pressure zone is at a pressure of about 5 ata.
- 17. The method of claim 16 wherein said intermediate-pressure zone is operated at reflux in order to obtain products of relatively high purity and wherein the reflux ratio therefor is increased by undercooling of feed and reflux from said high-pressure zone to said intermediate-pressure zone.
- 18. The method of claim 17 wherein a part of said oxygen product is throttled from 5 ata to 1.1 ata to reduce its its temperature and is then heat-exchanged with the feed and reflux streams to said intermediate-pressure zone so that said feed ad reflux zones are respectively subcooled to 98.degree.K and 99.degree.K, thereby substantially eliminating partial evaporation of said feed and reflux during throttling from 15 ata to 5 ata in said intermediate-pressure zone.
- 19. The method of claim 15 wherein said very hot nitrogen product is at approximately 1,290.degree.C.
- 20. The method of claim 15 wherein a small portion of said compressed main air feed, after said heat-exchanging to form said hot nitrogen product, is compressed further to form highly compressed refrigerating cycle air.
- 21. The method of claim 20 wherein said highly compressed refrigerating cycle air is heat-exchanged with combustion air for said steam generator and thereby partially cooled.
- 22. The method of claim 21 wherein said partially cooled air is further cooled, work-expanded, and fed into said high-pressure zone.
- 23. The method of claim 15 wherein a minor portion of said compressed main air feed, prior to said heat-exchanging to form said hot nitrogen product, is heat-exchanged with combustion air, additionally cooled, and combined with the remainder of said compressed main air feed.
- 24. The method of claim 15 wherein said steam generator is combind with a pebble heater having a pressurized heating space in which said hot nitrogen product is indirectly heat-exchanged with flue gases.
- 25. The method of claim 24 wherein said hot nitrogen product enters said pebble heater at approximately 400.degree.C. and is heated to approximately 1,000.degree.C. therein.
- 26. The method of claim 25 wherein said flue gases are used for generating steam in said steam generator.
- 27. In the simultaneous operation of a steam generator and an air separation plant as two separate and distinct closed systems, in which said steam generator has heated fluids as feeds therefor and a source of high-temperature heat generated by combusting an air-fuel mixture to form flue gases as combustion products and in which said air separation plant operates at elevated pressures on a compressed main air feed and produces a relatively pure nitrogen product, the improvement consisting essentially of the thermodynamic interlinking of said steam generator and said air separation plant through solely indirect heaat exchanges to produce mechanical energy by sequentially heating and work-expanding said nitrogen product without substantially impairing the efficiency of said steam generator, said indirect heat exchanges comprising:
- A. transferring, by indirect heat exchange therebetween, a quantity of relatively low-temperature compression heat from said compressed main air feed to said nitrogen product so that the temperature of said nitrogen product is raised to form a hot nitrogen product;
- B. transferring, by indirect heat exchange therebetween, a quantity of said high-temperature heat from said flue gases to said hot nitrogen product, so that the temperature of said hot nitrogen product is raised additionally and a very hot nitrogen product having a temperature well above 600.degree.C. is formed;
- C. after said work expanding said very hot nitrogen product in a gas turbine to obtain said mechanical energy therefrom so that a work-expanded nitrogen product having a lower temperature is formed, transferring, by indirect heat exchange therebetween, a quantity of heat at said lower temperature from said work-expanded nitrogen product to at least one of said heated fluids to decrease said lower temperature to an exit temperature below 150.degree.C. and to form a cooled nitrogen product having essentially no other contaminants than sad relatively pure nitrogen product and without augmenting the volume of said nitrogen product by admixing it with said flue gases.
- 28. The improvement according to claim 27, wherein an incoming air stream is compressed to a pressure higher than 9 ata to form said compressed main air feed and wherein said air separation plant comprises a fractioning column having a high pressure zone, operating at a high pressure higher than 9 ata but lower than 25 ata, and an intermediate pressure zone, operating at an intermediate pressure higher than 1.5 ata but lower than 9 ata, to produce said relatively pure nitrogen product and a relatively pure oxygen product.
Priority Claims (1)
Number |
Date |
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36741 |
Apr 1971 |
IL |
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CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of co-pending application Ser. No. 196,940, filed Nov. 9, 1971, now abandoned.
US Referenced Citations (6)
Non-Patent Literature Citations (1)
Entry |
"Thermodynamics for Chemical Engineers", Weber & Meissner, 2nd Ed., John Wiley & Sons, 1957. |
Continuation in Parts (1)
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Number |
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Parent |
196940 |
Nov 1971 |
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