Cryogenic liquefier/chiller

Abstract
A system for chilling and/or liquefying a fluid wherein a multicomponent refrigerant in a circuit is compressed, condensed, expanded and warmed to cool one or more portions of the fluid which are then turboexpanded to generate refrigeration and which are then used to provide refrigeration to a remaining portion of the fluid so as to chill and/or liquefy that remaining portion.
Description




TECHNICAL FIELD




This invention relates generally to providing refrigeration to a fluid and is particularly advantageous for use in conjunction with the operation of a cryogenic air separation plant for the production of liquefied industrial gas.




BACKGROUND ART




The production of liquefied industrial gas, such as liquid nitrogen, is very costly. Early liquefiers utilized single fluid mechanical refrigeration to provide forecooling at the higher temperatures with a turboexpander to provide refrigeration at lower temperature levels. The mechanical units provided the refrigeration at a fixed temperature. Later dual turbine liquefier cycles which eliminated the forecooler were introduced.




In view of the continuing demand for chilled or liquefied industrial gases, any improvement in systems for producing chilled or liquefied industrial gases would be highly desirable.




Accordingly, it is an object of this invention to provide an improved system for producing chilled or liquefied industrial gases.




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 providing refrigeration to a fluid comprising:




(A) compressing a multicomponent refrigerant, condensing the compressed multicomponent refrigerant, expanding the condensed multicomponent refrigerant, and warming the expanded multicomponent refrigerant by indirect heat exchange with said condensing compressed multicomponent refrigerant;




(B) compressing a fluid, cooling a first portion of the compressed fluid by indirect heat exchange with said warming expanded multicomponent refrigerant, and turboexpanding the cooled first portion of the fluid to generate refrigeration; and




(C) warming the refrigeration bearing first portion of the fluid by indirect heat exchange with a second portion of the compressed fluid to provide refrigeration to the second portion of the fluid.




Another aspect of the invention is:




Apparatus for providing refrigeration to a fluid comprising:




(A) a multicomponent refrigerant circuit comprising a compressor, an expansion device, means including at least one cooling heat exchanger pass for passing compressed multicomponent refrigerant from the compressor to the expansion device, and means including at least one warming heat exchanger pass for passing multicomponent refrigerant fluid from the expansion device to the compressor;




(B) a turboexpander, a product heat exchanger, means for passing a first fluid portion in indirect heat exchange relation with said warming heat exchanger pass and thereafter to the turboexpander, and means for passing a second fluid portion to the product heat exchanger; and




(C) means for passing the first fluid portion from the turboexpander to the product heat exchanger, and means for withdrawing refrigerated second fluid portion from the product heat exchanger.




As used herein the term “providing refrigeration” means chilling and/or liquefying.




As used herein the terms “turboexpansion” and “turboexpander” mean respectively method and apparatus for the flow of high pressure fluid through a turbine to reduce the pressure and the temperature of the fluid thereby generating refrigeration.




As used herein the term “expansion” means to effect a reduction in pressure.




As used herein the term “expansion device” means apparatus for effecting expansion of a fluid.




As used herein the term “compressor” means apparatus for effecting compression of a fluid.




As used herein the term “multicomponent refrigerant” means a fluid comprising two or more species and capable of generating refrigeration.




As used herein the term “refrigeration” means the capability to reject heat from a subambient temperature system.




As used herein the term “refrigerant” means fluid in a refrigeration process which undergoes changes in temperature, pressure and possibly phase to absorb heat at a lower temperature and reject it at a higher temperature.




As used herein the term “variable load refrigerant” means a mixture of two or more components in proportions such that the liquid phase of those components undergoes a continuous and increasing temperature change between the bubble point and the dew point of the mixture. The bubble point of the mixture is the temperature, at a given pressure, wherein the mixture is all in the liquid phase but addition of heat will initiate formation of a vapor phase in equilibrium with the liquid phase. The dew point of the mixture is the temperature, at a given pressure, wherein the mixture is all in the vapor phase but extraction of heat will initiate formation of a liquid phase in equilibrium with the vapor phase. Hence, the temperature region between the bubble point and the dew point of the mixture is the region wherein both liquid and vapor phases coexist in equilibrium. In the preferred practice of this invention the temperature differences between the bubble point and the dew point for a variable load refrigerant generally is at least 10° C., preferably at least 20° C., and most preferably at least 50° C.




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 “subcooling” means cooling a liquid to be at a temperature lower than the saturation temperature of that liquid for the existing pressure.











BRIEF DESCRIPTION OF THE DRAWINGS





FIG. 1

is a schematic representation of one preferred embodiment of the cryogenic liquefier/chiller system of this invention.





FIG. 2

is a representation of one preferred embodiment of the multicomponent refrigerant circuit which may be used in the practice of this invention.











DETAILED DESCRIPTION




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

FIG. 1

, fluid


59


which is to be chilled and/or liquefied is combined with stream


58


, which will be described more fully below, to form fluid stream


50


. The fluid in stream


50


which is to be chilled and/or liquefied may be any suitable fluid such as gaseous nitrogen, oxygen, argon, hydrogen, carbon dioxide and methane, as well as mixtures containing one or more such gases such as air and natural gas. One particularly preferred fluid for processing in the practice of this invention is gaseous nitrogen taken from a cryogenic air separation plant.




Fluid stream


50


is passed to recycle compressor


200


wherein it is compressed to a pressure generally within the range of from 250 to 500 pounds per square inch absolute (psia). Resulting compressed fluid


12


is cooled of the heat of compression in cooler


210


and resulting compressed fluid


13


is divided into a first part


20


and a second part


30


. First part


20


is further compressed in warm booster compressor


220


to a pressure generally within the range of from 400 to 800 psia. Boosted first part


22


is cooled of the heat of compression in cooler


230


to form boosted first part


23


. Second part


30


is further compressed in cold booster compressor


240


to a pressure generally within the range of from 500 to 800 psia. Boosted second part


32


is cooled of the heat of compression in cooler


250


to form boosted second part


33


which is combined with boosted first part


23


to form compressed fluid


40


.




Compressed fluid


40


is divided into a first portion


1


and a second portion


41


. Generally first portion


1


will comprise from 5 to 20 percent of compressed fluid


40


. First fluid portion


1


is cooled by indirect heat exchange with warming multicomponent refrigerant as will be more fully described below. In the embodiment of the invention illustrated in

FIG. 1

, this is shown in representational form by element


500


. After the heat exchange with the warming multicomponent refrigerant fluid, the cooled first fluid portion


2


is turboexpanded to generate refrigeration.




Second portion


41


of compressed fluid


40


is passed to a product heat exchanger. In the embodiment of the invention illustrated in

FIG. 1

the product heat exchanger comprises heat exchanger sections


260


,


270


and


280


wherein heat exchanger section


260


is a warm heat exchanger section and heat exchanger section


280


is a cold heat exchanger section. Second portion


41


is cooled by passage through heat exchanger section


260


emerging therefrom as cooled second fluid portion


42


. In the embodiment of the invention illustrated in

FIG. 1

a third portion


43


of the compressed fluid is split off from second portion


42


and remaining second portion


45


is passed on for further cooling in heat exchanger section


270


.




Third portion


43


is passed as stream


3


for cooling by indirect heat exchange with warming multicomponent refrigerant as will be more fully described below. In the embodiment of the invention illustration in

FIG. 1

, this heat exchange is shown in representational form by element


510


from which the cooled third fluid portion emerges as stream


4


. Typically cooled first portion


2


has a temperature within the range of from 200 to 275° K, and cooled third portion


4


has a temperature which is less than that of cooled first portion


2


and generally within the range of from 150 to 200° K. If desired, some of stream


43


may not be used to form stream


3


but rather, as shown in

FIG. 1

, may be combined with cooled first fluid portion


2


for passage to warm turboexpander


290


as stream


44


. Within warm turboexpander


290


the cooled first portion is turboexpanded to generate refrigeration emerging therefrom as refrigeration bearing first fluid portion


51


. Preferably, as shown in

FIG. 1

, warm turboexpander


290


serves to drive warm booster compressor


220


.




The further cooled second portion of the compressed fluid emerges from heat exchanger section


270


as stream


46


and is passed for still further cooling to heat exchanger section


280


. In the embodiment of the invention illustrated in

FIG. 1

, a part of stream


46


is split off as stream


48


and combined with cooled third portion


4


to form stream


49


which is passed to cold turboexpander


300


. Within cold turboexpander


300


the cooled third portion is turboexpanded to generate refrigeration, emerging therefrom as refrigeration bearing third fluid portion


52


. Preferably, as shown in

FIG. 1

, cold turboexpander


300


serves to drive cold booster compressor


240


.




Fluid stream


53


serves as the feed stream for the fluid to be processed by the practice of this invention. One particularly preferred source of stream


53


is a cryogenic air separation plant wherein stream


53


comprises gaseous nitrogen. Stream


53


is combined with refrigeration bearing stream


52


to form stream


54


which is warmed in heat exchanger section


280


by indirect heat exchange with cooling second fluid portion as will be further described below. Resulting stream


55


is withdrawn from heat exchanger section


280


and is combined with refrigeration bearing first fluid portion


51


to form stream


56


which is passed to heat exchanger section


270


of the product heat exchanger wherein it is warmed by indirect heat exchange with the aforesaid cooling second fluid portion. In the embodiment of the invention illustrated in

FIG. 1

, the turboexpanded first fluid portion


51


is passed to the product heat exchanger between the cold heat exchanger section


280


and the warm heat exchanger section


260


. The resulting stream


57


is withdrawn from heat exchanger section


270


, further warmed by indirect heat exchange in heat exchanger section


260


of the product heat exchanger by indirect heat exchange with the aforesaid cooling second fluid portion, and withdrawn therefrom as stream


58


which is combined with make up stream


59


to form aforedescribed fluid stream


50


for passage to recycle compressor


200


.




Refrigeration is provided to the second portion of the fluid as it passes through the product heat exchanger by indirect heat exchange with the turboexpanded refrigeration bearing first portion, and in the embodiment of the invention illustrated in

FIG. 1

, the turboexpanded refrigeration bearing third portion of the fluid. The second fluid portion may be chilled, i.e. reduced in temperature though still in gaseous form, or may be both chilled and liquefied by passage through the product heat exchanger. Referring back now to

FIG. 1

, the cooled second fluid portion is passed as stream


47


to heat exchanger section


280


of the product heat exchanger wherein it is chilled and/or liquefied and/or subcooled by indirect heat exchange with aforesaid warming stream


54


, emerging therefrom as refrigerated stream


99


for recovery as product. In the case where feed stream


53


is from a cryogenic air separation plant, some or all of product stream


99


could be returned to the cryogenic air separation plant, or some or all of product stream


99


could be passed to a use point or passed to storage for subsequent use.





FIG. 2

illustrates one embodiment of the multicomponent refrigerant circuit which serves to cool the first portion of the fluid, and in the embodiment of the invention illustrated in the Drawings, the third portion of the fluid, prior to the turboexpansion of these fluid portions. The numerals in

FIG. 2

are the same as those of

FIG. 1

for the common elements. In the embodiment illustrated in

FIG. 2

there is one multicomponent refrigerant heat exchanger


130


rather than the two multicomponent refrigerant heat exchangers


500


and


510


shown with the embodiment illustrated in FIG.


1


.




Referring now to

FIG. 2

, multicomponent refrigerant


100


is compressed by passage through compressor


150


to a pressure within the range of from 75 to 150 psia, and resulting multicomponent refrigerant


101


is further compressed by passage through compressor


110


to a pressure within the range of from 250 to 300 psia. Resulting compressed multicomponent refrigerant


102


is cooled of the heat of compression in cooler


120


and then passed in stream


103


to multicomponent refrigerant heat exchanger


130


which contains cooling pass


160


and warming pass


170


. Typically the multicomponent refrigerant in stream


103


is partially condensed, i.e. the heavier or less volatile component or components of the multicomponent refrigerant are condensed by the cooling in cooler


120


, and the compressed multicomponent refrigerant is completely condensed by passage through cooling pass


160


of heat exchanger


130


by indirect heat exchange with warming multicomponent refrigerant flowing in warming pass


170


of heat exchanger


130


as will be more fully described below.




The multicomponent refrigerant which maybe be used in the practice of this invention preferably comprises at least two species from the group consisting of fluorocarbons, hydrofluorocarbons, hydrochlorofluorocarbons, fluoroethers, atmospheric gases and hydrocarbons, e.g. the multicomponent refrigerant fluid could be comprised only of two fluorocarbons.




One preferred multicomponent refrigerant useful with this invention comprises at least one component from the group consisting of fluorocarbons, hydrofluorocarbons, and fluoroethers, and at least one component from the group consisting of fluorocarbons, hydrofluorocarbons, hydrochlorofluorocarbons, fluoroethers, atmospheric gases and hydrocarbons.




In one preferred embodiment of the invention the multicomponent refrigerant consists solely of fluorocarbons. In another preferred embodiment of the invention the multicomponent refrigerant consists solely of fluorocarbons and hydrofluorocarbons. In another preferred embodiment of the invention the multicomponent refrigerant consists solely of fluorocarbons, fluoroethers and atmospheric gases. Most preferably every component of the multicomponent refrigerant is either a fluorocarbon, hydrofluorocarbon, fluoroether or atmospheric gas. Furthermore, in a particularly preferred embodiment, the multicomponent refrigerant is a variable load refrigerant.




Referring back now to

FIG. 2

, condensed multicomponent refrigerant in stream


104


is expanded by passage through an expansion device such as Joule Thomson valve


140


and then passed as mostly liquid stream


105


to warming pass


170


of heat exchanger


130


. As it passes through warming pass


170


, the multicomponent refrigerant is warmed and vaporized by indirect heat exchange with the aforedescribed condensing multicomponent refrigerant in cooling pass


160


, and also by indirect heat exchange with the aforedescribed cooling first portion


1


and third portion


3


of the compressed fluid, which emerge from heat exchanger


130


as cooled first and third portions


2


and


4


respectively. As will be understood by those skilled in the art, warming pass


170


of

FIG. 2

is analogous to the unillustrated warming multicomponent refrigerant passing through elements


510


and


500


of FIG.


1


. The warmed multicomponent refrigerant emerges from heat exchanger


130


as stream


100


for passage to compressor


150


and the multicomponent refrigerant circuit is completed.




An example of the invention was carried out using the multicomponent refrigerant circuit shown in

FIG. 2

for the liquefaction of gaseous nitrogen taken from a cryogenic air separation plant, and the results are presented in Tables 1 and 2. In Table 1 the stream numbers are those of FIG.


2


and the concentrations of the various components are reported as mole fractions. The designation R


14


stands for carbon tetrafluoride, the designation R


218


stands for perfluoropropane, and the designation HFE-


347


stands for perfluoropropoxymethane. In Table 2, which reports the unit power consumed, the results for the operation of the invention are shown in column B and, for comparative purposes, the results of a comparable liquefaction using a conventional liquefier system are shown in column A, with the difference shown in column C. In Table 2, the power consumed by the compressors of the multicomponent refrigerant circuit is reported as “MGR Comp Power”. The example is presented for comparative purposes and is not intended to be limiting.





















TABLE 1










Flow




Pres.




Temp.




Vapor











Stream




Mcfh




psia




° K.




Frac.




N


2






Argon




R14




R218




HFE-347
































1




400.0




652.3




298.1




1.000




1.0000




0.0000




0.0000




0.0000




0.0000






2




400.0




644.1




224.6




1.000




1.0000




0.0000




0.0000




0.0000




0.0000






3




700.0




647.0




224.6




1.000




1.0000




0.0000




0.0000




0.0000




0.0000






4




700.0




645.0




156.7




1.000




1.0000




0.0000




0.0000




0.0000




0.0000






100




549.2




40.0




295.2




1.000




0.0000




0.0316




0.2524




0.4837




0.2323






101




549.2




104.4




326.0




1.000




0.0000




0.0316




0.2524




0.4837




0.2323






102




549.2




271.5




360.0




1.000




0.0000




0.0316




0.2524




0.4837




0.2323






103




549.2




270.0




302.5




0.750




0.0000




0.0316




0.2524




0.4837




0.2323






104




549.2




268.0




153.9




0.000




0.0000




0.0316




0.2524




0.4837




0.2323






105




549.2




42.0




149.9




0.078




0.0000




0.0316




0.2524




0.4837




0.2323



























TABLE 2












A




B




C




























Total Net LN


2






mcfh




452.5




552.6




100.1






Recycle Power




kW




6118




6111






Feed Gas Power




kW




670




800






MGR Comp Power




kW




0




1080






Total Liquefaction Power




kW




6788




7991




1203






Unit Power




kW/mcfh




15.00




14.46




12.02














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.



Claims
  • 1. A method for providing refrigeration to a fluid comprising:(A) compressing a multicomponent refrigerant, condensing the compressed multicomponent refrigerant, expanding the condensed multicomponent refrigerant, and warming the expanded multicomponent refrigerant by indirect heat exchange with said condensing compressed multicomponent refrigerant; (B) compressing a fluid, cooling a first portion of the compressed fluid by indirect heat exchange with said warming expanded multicomponent refrigerant, and turboexpanding the cooled first portion of the fluid to generate refrigeration; and (C) warming the refrigeration bearing first portion of the fluid by indirect heat exchange with a second portion of the compressed fluid to provide refrigeration to the second portion of the fluid.
  • 2. The method of claim 1 wherein the fluid comprises nitrogen.
  • 3. The method of claim 1 wherein the second portion of the fluid is liquefied by the provision of refrigeration to the second portion of the fluid.
  • 4. The method of claim 1 further comprising cooling a third portion of the compressed fluid by indirect heat exchange with said warming expanded multicomponent refrigerant to a temperature less than that of the cooled first portion of the fluid, turboexpanding the cooled third portion of the fluid to generate refrigeration, and warming the refrigeration bearing third portion of the fluid by indirect heat exchange with the second portion of the fluid to provide refrigeration to the second portion of the fluid.
  • 5. The method of claim 1 wherein the warming of the expanded multicomponent refrigerant serves to vaporize the expanded multicomponent refrigerant.
  • 6. Apparatus for providing refrigeration to a fluid comprising:(A) a multicomponent refrigerant circuit comprising a compressor, an expansion device, means including at least one cooling heat exchanger pass for passing compressed multicomponent refrigerant from the compressor to the expansion device, and means including at least one warming heat exchanger pass for passing multicomponent refrigerant fluid from the expansion device to the compressor; (B) a turboexpander, a product heat exchanger, means for passing a first fluid portion in indirect heat exchange relation with said warming heat exchanger pass and thereafter to the turboexpander, and means for passing a second fluid portion to the product heat exchanger; and (C) means for passing the first fluid portion from the turboexpander to the product heat exchanger, and means for withdrawing refrigerated second fluid portion from the product heat exchanger.
  • 7. The apparatus of claim 6 wherein said at least one warming heat exchanger pass is entirely within a single multicomponent refrigerant heat exchanger.
  • 8. The apparatus of claim 6 wherein the product heat exchanger comprises a plurality of heat exchanger sections including a warm heat exchanger section and a cold heat exchanger section.
  • 9. The apparatus of claim 8 wherein the first fluid portion is passed from the turboexpander to the product heat exchanger between the cold heat exchanger section and the warm heat exchanger section.
  • 10. The apparatus of claim 9 further comprising a cold turboexpander, means for passing a third fluid portion in indirect heat exchange relation with said warming heat exchanger pass and thereafter to the cold turboexpander, and means for passing the third fluid portion from the cold turboexpander to the product heat exchanger.
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