Cryogenic air separation and gas turbine integration using heated nitrogen

Abstract
An integrated cryogenic air separation gas turbine system wherein heat of compression within the feed air is provided to nitrogen produced in the cryogenic air separation plant and the heated nitrogen is provided to a gas turbine along with combustion reaction products to produce power.
Description




TECHNICAL FIELD




This invention relates generally to cryogenic air separation and, more particularly, to the integration of cryogenic air separation with a gas turbine system.




BACKGROUND ART




Gas turbines are employed to generate power. In a gas turbine system fuel and oxidant are combusted to form pressurized combustion products which are then expanded in the gas turbine to generate power.




Cryogenic air separation plants may be integrated with gas turbine systems. For example, a common compressor may compress air for combustion in the gas turbine system and also for separation in the cryogenic air separation plant. In addition, one or more products from the cryogenic air separation plant may be used in the gas turbine system. Any improvement in the integration of cryogenic air separation and gas turbine systems would be advantageous.




Accordingly, it is an object of this invention to provide an improved cryogenic air separation and gas turbine integration system.




SUMMARY OF THE INVENTION




The above and other objects, which will become apparent to those skilled in the art upon a reading of this disclosure, are attained by the present invention, one aspect of which is:




A method for operating a cryogenic air separation and gas turbine system comprising:




(A) compressing feed air to produce compressed feed air having heat of compression, and cooling the compressed feed air;




(B) passing the compressed feed air into a cryogenic air separation plant and producing nitrogen by the cryogenic rectification of the feed air within the cryogenic air separation plant;




(C) withdrawing nitrogen from the cryogenic air separation plant and heating the withdrawn nitrogen by indirect heat exchange with the compressed feed air having heat of compression to produce heated nitrogen; and




(D) turboexpanding the heated nitrogen in a gas turbine.




Another aspect of the invention is:




Cryogenic air separation and gas turbine apparatus comprising:




(A) a feed air compressor, a high level heat exchanger, means for passing feed air to the feed air compressor, and means for passing feed air from the feed air compressor to the high level heat exchanger;




(B) a cryogenic air separation plant and means for passing feed air from the high level heat exchanger to the cryogenic air separation plant;




(C) means for passing nitrogen from the cryogenic air separation plant to the high level heat exchanger; and




(D) a gas turbine and means for passing nitrogen from the high level heat exchanger to the gas turbine.




As used herein the term “cryogenic air separation plant” means a facility for fractionally distilling feed air by cryogenic rectification, comprising one or more columns and the piping, valving, etc. attendant thereto.




As used herein the term “column” means a distillation or fractionation column or zone, i.e. a contacting column or zone, wherein liquid and vapor phases are countercurrently contacted to effect separation of a fluid mixture, as for example, by contacting of the vapor and liquid phases on a series of vertically spaced trays plates mounted within the column and/or on packing elements such as structured or random packing. For a further discussion of distillation columns, see Chemical Engineer's Handbook, fifth edition, edited by R. H. Perry and C. H. Chilton, McGraw-Hill Book Company, New York, Section 13,


The Continuous Distillation Process.






The term “double column” is used to mean a higher pressure column having its upper portion in heat exchange relation with the lower portion of a lower pressure column. A further discussion of double columns appears in Ruheman “The Separation of Gases”, Oxford University Press, 1949, Chapter VII, Commercial Air Separation.




Vapor and liquid contacting separation processes depend on the difference in vapor pressures for the components. The high vapor pressure (or more volatile or low boiling) component will tend to concentrate in the vapor phase whereas the low vapor pressure (or less volatile or high boiling) component will tend to concentrate in the liquid phase. Distillation is the separation process whereby heating of a liquid mixture can be used to concentrate the more volatile component(s) in the vapor phase and thereby the less volatile component(s) in the liquid phase. Partial condensation is the separation process whereby cooling of a vapor mixture can be used to concentrate the volatile component(s) in the vapor phase and thereby the less volatile component(s) in the liquid phase. Rectification, or continuous distillation, is the separation process that combines successive partial vaporizations and condensations as obtained by a countercurrent treatment of the vapor and liquid phases. The countercurrent contacting of the vapor and liquid phases can be adiabatic or nonadiabatic and can include integral (stagewise) or differential (continuous) contact between the phases. Separation process arrangements that utilize the principles of rectification to separate mixtures are often interchangeably termed rectification columns, distillation columns, or fractionation columns. Cryogenic rectification is a rectification process carried out at least in part at temperatures at or below 150 degrees Kelvin (K).




As used herein the term “indirect heat exchange” means the bringing of two fluids into heat exchange relation without any physical contact or intermixing of the fluids with each other.




As used herein the term “feed air” means a mixture comprising primarily oxygen and nitrogen, such as ambient air.




As used herein the term “heat of compression” means thermal energy imparted to a fluid as a result of the compression of that fluid.




As used herein the term “turbine” means a device which converts pressure energy of a fluid into shaft energy by expansion of the fluid. The shaft energy can be utilized in driving a compressor and/or a generator for power generation.




As used herein the term “gas turbine” means a turbine wherein combustion products are expanded.




As used herein the term “nitrogen turbine” means a turbine wherein nitrogen but no combustion products is expanded.




As used herein the term “combustor” means an enclosure wherein fuel and oxidant are combusted to form combustion products.




As used herein the term “humidifier” means a device wherein moisture is added to gas.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a schematic representation of one preferred embodiment of the cryogenic air separation gas turbine integration system of this invention.





FIG. 2

is a schematic representation of another preferred embodiment of the cryogenic air separation gas turbine integration system of this invention wherein the nitrogen is moisturized prior to heating.











DETAILED DESCRIPTION




The invention will be described in detail with reference to the Drawings. Referring now to

FIG. 1

, feed air


7


is compressed in feed air compressor


105


to a pressure generally within the range of from 60 to 450 pounds per square inch absolute (psia). Compressor


105


does not contain intercoolers so that resulting compressed feed air


8


contains the heat of compression resulting from the compression through non-intercooled compressor


105


. Compressed feed air


8


is passed to high level heat exchanger


106


wherein it is cooled by indirect heat exchange with nitrogen produced in the cryogenic air separation plant as will be further described below. Resulting cooled compressed feed air


10


is further cooled in direct contact aftercooler against cooling water and resulting feed air stream


12


is passed to prepurifier


109


wherein it is cleaned of high boiling impurities such as carbon dioxide, water vapor and hydrocarbons to produce cleaned, cooled, compressed feed air stream


16


.




In the embodiment of the invention illustrated in

FIG. 1

, feed air stream


16


is divided into three portions. One portion, referred to as main air, generally comprising from 60 to 75 percent of stream


16


, is sent directly to cryogenic air separation plant


200


as stream


19


. Another portion


17


, referred to a liquid oxygen pumping air, generally comprising from 25 to 30 percent of stream


16


, is compressed further in booster compressor


120


, cooled in aftercooler


60


and sent to plant


200


as stream


20


. Stream


20


is used in liquid oxygen pumping cycles where oxygen liquid is boiled against a condensing high pressure air stream. Another portion


18


, referred to as refrigeration air, is compressed using a compressor


122


that is linked to an expander of plant


200


, cooled in aftercooler


61


and then fed into plant


200


as stream


21


wherein it is expanded to generate refrigeration.




Cryogenic air separation plant


200


may be any cryogenic air separation plant which produces a nitrogen product. Examples of such cryogenic air separation plants include a single column plant for producing nitrogen, a double column plant which produces both nitrogen and oxygen, and a double column plant with an argon sidearm column which produces nitrogen, oxygen and argon. Within cryogenic air separation plant


200


the feed air is separated by cryogenic rectification resulting in the production of nitrogen. In the embodiment illustrated in

FIG. 1

, oxygen is also produced by the operation of cryogenic air separation plant


200


and is withdrawn and recovered in stream


33


.




Nitrogen, produced in cryogenic air separation plant


200


, is withdrawn from plant


200


in stream


22


which has a nitrogen concentration generally of at least 60 mole percent. If plant


200


produces more nitrogen than can be usefully employed in the gas turbine, such excess nitrogen may be used to generate additional power. In the embodiment illustrated in

FIG. 1

, this excess nitrogen is shown as stream


70


which is heated by passage through high level heat exchanger


106


by indirect heat exchange with cooling compressed feed air, and resulting heated excess nitrogen


71


is expanded through nitrogen turbine


126


to recover power such as to drive generator


62


to produce electricity. Resulting expanded excess nitrogen


72


may then be recovered in whole or in part or may be vented.




Some or all of the nitrogen produced in cryogenic air separation plant


200


is passed in stream


24


to compressor


114


wherein it is compressed to a pressure generally within the range of from 150 to 600 psia. In the event plant


200


also produces high pressure nitrogen, such high pressure nitrogen may be passed to a downstream stage of compressor


114


as shown by line


23


.




Compressed nitrogen stream


25


is passed to high level heat exchanger


106


wherein it is heated by indirect heat exchange with the cooling compressed feed air


8


having heat of compression to produce heated nitrogen


37


having a temperature generally within the range of from 300 to 900° F. Heated nitrogen


37


is then passed into gas turbine system


100


which comprises gas turbine compressor


101


, combustor


102


and gas turbine


103


.




In the embodiment illustrated in

FIG. 1

, air


1


is compressed in gas turbine compressor


101


to a pressure generally within the range of from b


150


to 450 psia, and resulting compressed air


2


is passed into combustor


102


. If desired, as shown by stream


4


, a portion of compressed air


2


can be extracted and combined with stream


8


. The heat of compression in this combined feed air stream can then be provided to the nitrogen produced from cryogenic air separation plant


200


. Fuel


41


, such as natural gas, syngas or hydrocarbon liquids, is passed into combustor


102


wherein the fuel and oxygen from compressed air


2


combust to form hot pressurized gas containing combustion reaction products such as carbon dioxide and water vapor. The hot pressurized gas is passed from combustor


102


in stream


51


to gas turbine


103


wherein it is expanded to produce power such as to drive generator


63


to produce electricity.




In the embodiment of the invention illustrated in

FIG. 1

heated nitrogen


37


is passed into combustor


102


. Alternatively, heated nitrogen


37


could be combined with compressed air stream


2


for passage into combustor


102


, or could bypass combustor


102


and be passed directly into gas turbine


103


. In whatever arrangement is employed, the heated nitrogen is expanded in gas turbine


103


thereby increasing the amount of power which can be produced by gas turbine


103


. The heat brought into the turboexpansion in gas turbine


103


by the heated nitrogen gainfully employs the heat of compression resulting from the compression of the feed air for the cryogenic air separation plant, increasing the efficiency of the overall cryogenic air separation gas turbine integration system.




The exhaust


52


from gas turbine


103


may be sent to steam cycle stream


400


for generating steam that can be expanded to produce more power such as by driving generator


64


or may be passed in stream


53


for usage in other processes.





FIG. 2

illustrates another embodiment of the invention wherein the nitrogen is moisturized prior to being heated against the compressed feed air in the high level heat exchanger. The numerals in

FIG. 2

are the same as those of

FIG. 1

for the common elements, and these common elements will not be described again in detail.




The embodiment illustrated in

FIG. 2

employs moisturizing system


65


between high level heat exchanger


106


and cryogenic air separation plant


200


. This arrangement further improves the efficiency of the system by effectively utilizing low level heat from the feed air stream. Since compressed feed air stream


8


has a higher flow rate than the combined flows of nitrogen streams


25


and


70


, high level heat exchanger


106


is warm-end pinched, and feed air stream


10


at the cold end still contains some thermal energy.




Referring now to

FIG. 2

, moisturizing system


65


comprises humidifier


116


, typically a humidification tower or saturator. Water


26


is passed into the upper portion of humidifier


116


and the diluent nitrogen


25


is passed into the lower portion of humidifier


116


. Downflowing water within humidifier


116


directly contacts upflowing nitrogen thereby serving to pass water into the upflowing nitrogen gas resulting in moisturized nitrogen which is then passed in stream


36


to high level heat exchanger


106


for further processing as previously described. Preferably moisturized nitrogen


36


is saturated.




Water


27


from humidifier


116


is split into two portions. A first or blowdown portion


29


is removed from the recirculation loop. A second or recirculation portion


28


is mixed with make-up water


30


and pumped to a higher pressure in pump


118


. Resulting pressurized water stream


31


is passed to low level heat exchanger


107


wherein it is heated by indirect heat exchange with further cooling feed air


10


taken from high level heat exchanger


106


. Resulting heated water


26


is passed from low level heat exchanger


107


to humidifier


116


in stream


26


. The heat in stream


26


improves the mass transfer driving force within humidifier


116


. In this way low level heat in the feed air to the cryogenic air separation plant is effectively utilized to increase the mass of the nitrogen stream sent to the gas turbine and thus to increase the power production from the gas turbine. The resulting feed air from low level heat exchanger


107


is passed in stream


11


to direct contact aftercooler


108


and further processed as was previously described.




Although the invention has been described in detail with reference to certain preferred embodiments, those skilled in the art will recognize that there are other embodiments of the invention within the spirit and the scope of the claims. For example, hot water or steam from the steam cycle system may be used to supply additional heat to increase the saturation level of the nitrogen stream. In another embodiment a portion of the nitrogen may be used for acid gas, e.g. carbon dioxide, removal in an acid gas removal system prior to being sent to the gas turbine. In another embodiment a portion of compressed feed air


8


may be passed to combustor


102


rather than being passed to the high level heat exchanger. In yet another embodiment, oxygen from the cryogenic air separation plant, which may be heated in a manner similar to that of the nitrogen heating, may be used in a gasification plant to produce synthesis gas, e.g. hydrogen and carbon monoxide, from the partial combustion of dirty fuel such as coal, petroleum coke, refinery residual oil, etc., and the resulting clean syngas may be used as the fuel in the combustor of the gas turbine system.



Claims
  • 1. A method for operating a cryogenic air separation and gas turbine system comprising:(A) compressing feed air in a non-intercooled feed air compressor to produce compressed feed air having heat of compression, and cooling the compressed feed air; (B) passing the compressed feed air into a cryogenic air separation plant and producing nitrogen by the cryogenic rectification of the feed air within the cryogenic air separation plant; (C) withdrawing nitrogen from the cryogenic air separation plant and heating the withdrawn nitrogen by indirect heat exchange with the compressed feed air having heat of compression to produce heated nitrogen; (D) turboexpanding the heated nitrogen in a gas turbine; and (E) compressing air in a gas turbine compressor and passing at least some of the resulting compressed air into a combustor.
  • 2. The method of claim 1 wherein the heated nitrogen is passed to the combustor prior to being turboexpanded.
  • 3. The method of claim 1 further comprising adding water to the withdrawn nitrogen prior to the heating of the withdrawn nitrogen.
  • 4. The method of claim 3 wherein the water added to the withdrawn nitrogen is first heated by indirect heat exchange with compressed feed air.
  • 5. Cryogenic air separation and gas turbine apparatus comprising:(A) a non-intercooled feed air compressor, a high level heat exchanger, means for passing feed air to the feed air compressor, and means for passing feed air from the feed air compressor to the high level heat exchanger; (B) a cryogenic air separation plant and means for passing feed air from the high level heat exchanger to the cryogenic air separation plant; (C) means for passing nitrogen from the cryogenic air separation plant to the high level heat exchanger; (D) a gas turbine and means for passing nitrogen from the high level heat exchanger to the gas turbine; and (E) a gas turbine compressor, a combustor, means for passing air to the gas turbine compressor, and means for passing air from the gas turbine compressor to the combustor.
  • 6. The apparatus of claim 5 wherein the means for passing nitrogen from the high level heat exchanger to the gas turbine includes the combustor.
  • 7. The apparatus of claim 5 further comprising a low level heat exchanger wherein the means for passing feed air from the high level heat exchanger to the cryogenic air separation plant includes the low level heat exchanger.
  • 8. The apparatus of claim 5 further comprising a humidifier wherein the means for passing nitrogen from the cryogenic air separation plant to the high level heat exchanger includes the humidifier.
  • 9. The apparatus of claim 5 further comprising a low level heat exchanger and a humidifier wherein the means for passing feed air from the high level heat exchanger to the cryogenic air separation plant includes the low level heat exchanger and the means for passing nitrogen from the cryogenic air separation plant to the high level heat exchanger includes the humidifier, and further comprising means for passing water to the low level heat exchanger and means for passing water from the low level heat exchanger to the humidifier.
  • 10. The apparatus of claim 5 further comprising a nitrogen turbine, means for passing excess nitrogen from the cryogenic air separation plant to the high level heat exchanger, and means for passing excess nitrogen from the high level heat exchanger to the nitrogen turbine.
  • 11. The method of claim 1 wherein a portion of the air compressed in the gas turbine compressor is passed into the cryogenic air separation plant.
  • 12. The apparatus of claim 5 further comprising means for passing air from the gas turbine compressor to the cryogenic air separation plant.
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