CA2048293A1 - Pumped liquid oxygen air separation cycles - Google Patents
Pumped liquid oxygen air separation cyclesInfo
- Publication number
- CA2048293A1 CA2048293A1 CA002048293A CA2048293A CA2048293A1 CA 2048293 A1 CA2048293 A1 CA 2048293A1 CA 002048293 A CA002048293 A CA 002048293A CA 2048293 A CA2048293 A CA 2048293A CA 2048293 A1 CA2048293 A1 CA 2048293A1
- Authority
- CA
- Canada
- Prior art keywords
- high pressure
- pressure column
- low pressure
- oxygen
- column
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Landscapes
- Separation By Low-Temperature Treatments (AREA)
Abstract
ABSTRACT The present invention relates to a process for producing medium to high pressure oxygen using a liquid oxygen pump, a booster compressor and a high pressure expansion turbine discharging into the high pressure column. In addition to producing oxygen, the process of the present invention can also produce high pressure nitrogen, low pressure nitrogen and/or argon, if desired.
Description
20~8~3 PUMPED LIQUID OXYGEN
AIR SEPARATION CYCLES
FIELD OF THE INVENTION
The present invention relates to a process for the separation of air into its constituent parts, more particularly, the present invention relates to a process for the production of high pressure oxygen.
BACKGROUND OF THE INVENTION
Numerous processes are known in the art for the production of high pressure oxygen by the cryogenic distillation of air into constituent parts. Most of these processes use either an oxygen compressor or a lO liquid oxygen pump to increase the pressure of the oxygen product. The processes which use an oxygen compressor incur a high capital cost due to the high price of such compressors and the associated controls, instrumentation and safety requirements. Typically, processes which util1ze liquid oxygen pumps suffer from power penalties when compared to 15 the oxygen compressor processes. In addition, these liquid oxygen pump processes have capital penalties due to their complexity. An example of a liquid oxygen pump process is discussed below.
U.S. 4,372,764 discusses a pump liquid oxygen process in which the liquid oxygen is vaporized and warmed against a part of the feed air, 20 which is compressed and divided into two substreams, one at a higher pressure and one at a lower pressure. The first substream, which is the higher pressure, is cooled against the vaporizlng oxygen and heat exchanged and then expanded across the valve, thereby liquefy~ng the substream; the produced liquid product is fed to the high pressure 25 column. The second substream, the lower pressure stream, is cooled in heat exchange and then expanded in a generator loaded expander thereby producing pcwer and refrigeration. The produced cold gas of the second substream is then used to cool the first substream in the heat exchanger and is recycled to the compressor.
-:. , , 2 ~ 3 $UMMARY OF THE INVENTIOH
The present invention is an improvement to a process for the production of an oxygen product by the cryogenic distillation of air in a double column distillation system having a high pressure column and a low 5 pressure column. In the process, a feed air stream is compressed, purified of impurities which will freeze out at cryogenic temperatures and divided into two portions. The first portion is fed to the high pressure column for rectification thereby producing a crude llquid oxygen bottoms and high pressure nitrogen overhead. The second portion is further 10 compressed, cooled and expanded to produce work. The crude liquid oxygen bottoms is subcooled, reduced in pressure and fed to the low pressure column for distillation and the high pressure nitrogen overhead is condensed in a reboiler/condenser located in the bottom of the low pressure column. At least a portion of the condensed nitrogen is returned lS to the top of the high pressure column as pure reflux and at least another portion is subcooled, reduced in pressure and fed to the top of the low pressure column as pure reflux. The crude liquid oxygen bottoms fed to the low pressure column is distilled to produce a low pressure nitrogen overhead and a low pressure column, ltquid oxygen bottoms. Finally, a 20 portion of the low pressure column, liquid oxygen bottoms is reboiled in the reboiler/condenser located in the bottom of the low pressure column against the condensing high pressure nitrogen overhead.
The improvement for the production of high pressure oxygen comprises:
(a) feeding the expanded, second portion to the high pressure column; and 25 (b) removing another portion of the liquid oxygen bottoms from the low pressure column, increasing in pressure the removed portion in a liquid oxygen pump, warming and vaporizing the increased pressure, removed portion, and recovering the vaporized, increased pressure, removed portton as the high pressure oxygen product.
The process of the present invention can further comprise dividing the further compressed, cooled, second portion into two substreams prior to expansion; expanding the first substream and feeding the expanded, first substream to the high pressure column; and condensing and reducing in pressure the second substream and introducing the condensed, reduced 35 pressure, second substream to the high pressure column as impure liquid air reflux.
.. .. ~... . .. . ........ . . .. , . .... .. - .. . . . . . ..
-- . .
204829~ :
Compression and expansion of the second portion can be provided by a compressor and an expander which are mechanically linker often referred to as a compander.
The process of the present invention can further comprise further 5 compressing the first portion prior to cooling.
The process of the present invention can also further comprise dividing the expanded, second portion into two substreams prior to feeding the expanded, second portion to the high pressure column; feeding the first substream to the high pressure column; and warming the second 10 substream to recover refrigeration and recycling the warmed substream to the compression step of the feed air stream.
The process of the present invention can further comprise removing a ~ -portion of the increased pressure, liquid oxygen from the low pressure column as liquid product prior to vaporization.
The process of the present invention can further comprise removing and warming a portion of the high pressure nitrogen overhead from the high pressure column as a high pressure nitrogen product.
The process of the present invention can further comprise withdrawing a second oxygen product from the low pressure column and warming the 20 withdrawn product to recover refrigeration. The withdrawn, second oxygen product can be withdrawn as either a gas or a liquid.
Figures 1 through 5 are schematic diagrams of several embodiments of 25 the process of the present inventlon.
DETAILED DESCRIPTION OF THE INVENTION
A problem which exists with the prior art process ls how to produce a high pressure oxygen product efflciently. When distilling air to produce 30 oxygen efficiently, the distillation should be performed at the lowest practical pressure, i.e., less than about 5 psig. Unfortunately, this low pressure need is inconsistent with the need to produce a high pressure product. Therefore, the goal is to increase the pressure of the oxygen product to the required level while minimiz~ng the costs in terms of 35 capital and power of performing th~s function. The present invention is the answer to that goal.
' .. - - ' .
2~29'~
The process of the present invention can be understood in reference to several embodiments. These embodiments are illustrated in Figures 1 through 5. With reference to Figure 1, feed air, in line 10, is compressed to about 95 psia in air compressor 12. The compressed feed air 5 is then precooled and directed to mole sieve adsorber 14 to remove water, carbon dioxide and heavy hydrocarbons which may be contained in the feed air and which will freeze out in the process at cryogenic temperatures.
The dry, carbon dioxide-free, compressed feed air is removed from adsorber 14, via line 16, and then split into two portions.
The first and major portion consisting of about 50 to 60X of the total air flow, in line 20, is cooled in heat exchanger 22 to near its dew point.
The second or minor portion consisting of the remaining feed air, in line 30, is further compressed in compressor 32 so that the resultant 15 pressure of the stream is sufficient to cause the air dew point to be above the oxygen bubble point. For example, for 70 psig oxygen product, the second substream should be compressed to about 225 psig. If the - required air pressure is above or near the critical pressure of air, an optimization of air flow and pressure should be performed. Th;s further 20 compressed, second portion from compressor 32 is then cooled to about -100F to -200F in heat exchanger 22.
At this point, a part of the cooled, further compressed, second portion is removed, via line 34, and expanded in expansion turbine 36 to produce work. This expanded part, in line 38, is combined with the 25 cooled, first portion, in line 24, to form a high pressure column feed air stream, in line 26.
The remainder of the cooled, further compressed, second portion, in line 40, is condensed in heat exchanger 22, reduced in pressure and fed to high pressure column 28 as impure liquid air reflux. As an option, a 30 portion of the condensed, second portion can be fed as impure reflux to low pressure column 62 (this option is not shown in Flgure 1).
In high pressure column 28, the high pressure feed air stream, in line 40, is rectified into a high pressure nitrogen overhead and a crude oxygen bottoms liquid.
: . : . . .. .. . .
2~8293 The high pressure nitrogen overhead is removed from high pressure column 28, via line 50, and fed to reboiler/condenser 52 located in the bottom of low pressure column 62, wherein it is condensed and subsequently divided into two substreams. The first substream, in line 54, is fed to 5 the top of high pressure column 28 as pure liquid nitrogen reflux. The second substream, in line 56, is subcooled in heat exchanger 57, reduced in pressure and fed to the top of low pressure column 62 as pure liquid nitrogen reflux. Although not shown, as an option, a portion of the high pressure nitrogen overhead, up to about 20X of the feed air, can be 10 recovered as high pressure nitrogen product.
The crude oxygen bottoms liquid is removed, via line fiO, from high pressure column 28, subcooled in heat exchanger 57, reduced in pressure and fed to an intermediate location of low pressure column 62 for distillation. In low pressure column 62, this crude oxygen is distilled 15 into a low pressure nitrogen overhead and a liquid oxygen bottoms.
A portion of the liquid oxygen bottoms is boiled against the condensing nitrogen in reboiler/condenser 52, thereby producing reboil for low pressure column 62. The remaining liquid oxygen is removed, via line 70, from the bottom of low pressure column 62, increased in pressure in 20 LOX pump 72, warmed to vaporize the liquid oxygen thereby recovering refrigeration and recovered as high pressure oxygen product, in llne 74.
The low pressure nitrogen overhead is removed, via line 80, from low pressure column 62, and subsequently warmed in heat exchangers 57 and 22 to recover refrigeration. This nitrogen overhead can be then boosted in 25 pressure, if necessary, to produce a nitrogen product.
In addition, a waste stream can be removed, via line 90, from an upper intermediate location of low pressure column 62, warmed in heat exchanger 22 to recover refrigeration and then vented as waste.
Figure 2 shows another embodiment of the process of the present 30 invent~on which can be used to produce significant quantities of liquid oxygen, nitrogen or argon products. In this embodiment, feed air, in line 10, is compressed in air compressor 12. The compressed feed air is then precooled and directed to mole sieve adsorber 14 to remove water, carbon dioxide and heavy hydrocarbons which may be contained in the feed 35 air and which will freeze out in the process at cryogenic temperatures.
' 2 ~ 9 3 The dry, carbon dioxide-free, compressed feed air is removed from adsorber 14, via line 16, and then split into two portions.
The first portion, consisting of about 30 to 40X of the total air flow, ~n line 20, is further compressed in compressor 120 and cooled in 5 heat exchanger 22 to near its dew point. Compressor 120 can be eliminated if the pressure required to vaporize the oxygen is lower than the pressure required for the liquid refrigeration requirement. For example, for product requirement of 100 T/D of oxygen at 250 psig, the pressure of the air feed to the cold box will be 600 psig. This cooled, fSrst portion ~s 10 then reduced in pressure and fed to a lower intermediate location of high pressure distillation column 28 as impure liquid air reflux.
The second portion, consisting of the remaining feed air, in line 30, is further compressed in compressor 32 and then cooled in heat exchanger 22. This cooled, further compressed, second portion is then expanded in 15 expansion turbine 36 to produce work. Expander 36 and compressor 32 are mechanically linked as a compander unit. This expanded, second portion is fed to the bottom of high pressure column 28 as its primary feed, via line 138.
In high pressure column 28, the feed air streams are rectified into 20 an high pressure nitrogen overhead and a crude oxysen bottoms liquid.
A first portion of the hlgh pressure nitrogen overhead is removed from high pressure column 28, via line 50, and fed to reboiler/condenser 52 located in the bottom of low pressure column 62, wherein it is condensed and subsequently divided into two substreams. The first 25 substream, in line 54, is fed to the top of high pressure column 28 as pure liquid nitrogen reflux. The second substream, in llne 56, is subcooled in heat exchanger 57, reduced in pressure and fed to the top of low pressure column 62 as pure liquid nitrogen reflux. Optionally, a part of stream 56 can be recovered as liquid nitrogen product, via line 156.
30 Also, a second portion of the high pressure n~trogen overhead, line 150, can be recovered as high pressure nitrogen product, line 152.
The crude oxygen bottoms liquid is removed, via line 60, from high pressure column 28, subcooled in heat exchanger 57, reduced in pressure and fed to an intermediate location of low pressure column 62 for 35 distillation. In low pressure column 62, this crude oxygen is distilled into a low pressure nitrogen overhead and a liquid oxygen bottoms.
., ~, . . '- . .
- : . ; , . ~ . . , ~ .~, . . ..
- , ..
-`` 20~8293 A portion of the liquid oxygen bottoms is boiled against the condensing nitrogen in reboiler/condenser 52, thereby producing reboil for low pressure column 62. The remaining liquid oxygen is removed, via line 70, from the bottom of low pressure column 62, increased in pressure in 5 LOX pump 72, warmed to vaporize the liquid oxygen thereby recovering refrigeration and recovered as high pressure oxygen product, in line 74.
Optionally, a liquid oxygen product can be removed from the process, via line 172.
The low pressure nitrogen overhead is removed, via line 80, from low 10 pressure column 62, and subsequently warmed in heat exchangers 57 and 22 to recover refrigeration. This nitrogen overhead can be then boosted in pressure, if necessary, to produce a nitrogen product.
In addition, a waste stream can be removed, via line 90, from an upper intermediate location of low pressure column 62, warmed in heat 15 exchanger 22 to recover refrigeration and then vented as waste.
If additional liquid products are required, a portion of the expanded, second portion, line 138, can be removed, via line 242, warmed in heat exchanger 22, and fed, v~a line 244, to an intermediate stage of main a~r compressor 12 for recompression. This embodiment is illustrated ; 20 in Figure 3.
Refrigeration for the process can be supplied by several alternative methods other than that shown in Figure 1. For example, the plant refrigeration can be supplied by:
(a) expanding nitrogen from the high pressure column;
(b) expanding a portion of the low pressure air stream into the low pressure column;
(c) expanding an air stream at some intermediate pressure into either the high or low pressure column;
(d) expanding the waste stream from the low pressure column, or (e) feeding liquid oxygen or nitrogen to the process.
This last method (option d) will yield a higher pressure nitrogen product from the low pressure column.
The process of the present invention can be used to produce oxygen product at more than one pressure level, if required. Figure 4 shows an 35 embodiment in which gaseous oxygen is removed from low pressure column 62, .-.
.. . .
~ : .............. ~ ......................... . .
.
20~8293 via line 370, warmed in heat exchanger 22 to recover refrigeration, and recovered as a gaseous oxygen product at about 2 to 4 psig.
: Liquid oxygen can be taken from low pressure column 62, via line 70, and vapor~zed in heat exchanger 22 to produce an oxygen product at about 5 15 to 20 psig. This embodiment is shown in Figure 5.
Finally, referring to Figure l but not shown, product oxygen can also be produced at more than one pressure by taking a portion of the liquid from the LOX pump 72 and letting it down in pressure prior to warming in a separate circuit in heat exchanger 22. ~or this option, it would be more lO efficient to supply air at two pressure levels from air booster 32 in order to better match the cooling curves.
- The above described process is useful for the production of oxygen having an oxygen concentration from about 70 to 99.9X oxygen at pressures ranging from lO psi to 250 psi and above. The process also can produce a 15 nitrogen product stream at either high or low pressures. Although not shown in any of the figures, an argon s1de-arm column can be added to low pressure column 62 to produce a crude argon product from the process.
A benefit of the present invention described above is that it has a capital savings of about 5X for small oxygen plants (i.e., less than 200 20 tons per day) when compared to conventional oxygen compressor processes.
Another advantage of the process of the present invention is that the ; feed air is expanded and fed to the high pressure column rather than the low pressure column. As a result of this step, more nitrogen is available at the top of the high pressure column and therefore more nitrogen reflux 25 is available. This increased availability of nitrogen for refluxing aids in nitrogen recovery and provides more boilup for the production of a purer nitrogen stream, if needed.
The present invention has been described wlth reference to several embodiments thereof. These embodiments should not be viewed as a - 30 limitation of the scope of the present invention; the scope which should be ascerta~ned by the attached claims.
. . . : ; ; ~ . ~ . -, . .
AIR SEPARATION CYCLES
FIELD OF THE INVENTION
The present invention relates to a process for the separation of air into its constituent parts, more particularly, the present invention relates to a process for the production of high pressure oxygen.
BACKGROUND OF THE INVENTION
Numerous processes are known in the art for the production of high pressure oxygen by the cryogenic distillation of air into constituent parts. Most of these processes use either an oxygen compressor or a lO liquid oxygen pump to increase the pressure of the oxygen product. The processes which use an oxygen compressor incur a high capital cost due to the high price of such compressors and the associated controls, instrumentation and safety requirements. Typically, processes which util1ze liquid oxygen pumps suffer from power penalties when compared to 15 the oxygen compressor processes. In addition, these liquid oxygen pump processes have capital penalties due to their complexity. An example of a liquid oxygen pump process is discussed below.
U.S. 4,372,764 discusses a pump liquid oxygen process in which the liquid oxygen is vaporized and warmed against a part of the feed air, 20 which is compressed and divided into two substreams, one at a higher pressure and one at a lower pressure. The first substream, which is the higher pressure, is cooled against the vaporizlng oxygen and heat exchanged and then expanded across the valve, thereby liquefy~ng the substream; the produced liquid product is fed to the high pressure 25 column. The second substream, the lower pressure stream, is cooled in heat exchange and then expanded in a generator loaded expander thereby producing pcwer and refrigeration. The produced cold gas of the second substream is then used to cool the first substream in the heat exchanger and is recycled to the compressor.
-:. , , 2 ~ 3 $UMMARY OF THE INVENTIOH
The present invention is an improvement to a process for the production of an oxygen product by the cryogenic distillation of air in a double column distillation system having a high pressure column and a low 5 pressure column. In the process, a feed air stream is compressed, purified of impurities which will freeze out at cryogenic temperatures and divided into two portions. The first portion is fed to the high pressure column for rectification thereby producing a crude llquid oxygen bottoms and high pressure nitrogen overhead. The second portion is further 10 compressed, cooled and expanded to produce work. The crude liquid oxygen bottoms is subcooled, reduced in pressure and fed to the low pressure column for distillation and the high pressure nitrogen overhead is condensed in a reboiler/condenser located in the bottom of the low pressure column. At least a portion of the condensed nitrogen is returned lS to the top of the high pressure column as pure reflux and at least another portion is subcooled, reduced in pressure and fed to the top of the low pressure column as pure reflux. The crude liquid oxygen bottoms fed to the low pressure column is distilled to produce a low pressure nitrogen overhead and a low pressure column, ltquid oxygen bottoms. Finally, a 20 portion of the low pressure column, liquid oxygen bottoms is reboiled in the reboiler/condenser located in the bottom of the low pressure column against the condensing high pressure nitrogen overhead.
The improvement for the production of high pressure oxygen comprises:
(a) feeding the expanded, second portion to the high pressure column; and 25 (b) removing another portion of the liquid oxygen bottoms from the low pressure column, increasing in pressure the removed portion in a liquid oxygen pump, warming and vaporizing the increased pressure, removed portion, and recovering the vaporized, increased pressure, removed portton as the high pressure oxygen product.
The process of the present invention can further comprise dividing the further compressed, cooled, second portion into two substreams prior to expansion; expanding the first substream and feeding the expanded, first substream to the high pressure column; and condensing and reducing in pressure the second substream and introducing the condensed, reduced 35 pressure, second substream to the high pressure column as impure liquid air reflux.
.. .. ~... . .. . ........ . . .. , . .... .. - .. . . . . . ..
-- . .
204829~ :
Compression and expansion of the second portion can be provided by a compressor and an expander which are mechanically linker often referred to as a compander.
The process of the present invention can further comprise further 5 compressing the first portion prior to cooling.
The process of the present invention can also further comprise dividing the expanded, second portion into two substreams prior to feeding the expanded, second portion to the high pressure column; feeding the first substream to the high pressure column; and warming the second 10 substream to recover refrigeration and recycling the warmed substream to the compression step of the feed air stream.
The process of the present invention can further comprise removing a ~ -portion of the increased pressure, liquid oxygen from the low pressure column as liquid product prior to vaporization.
The process of the present invention can further comprise removing and warming a portion of the high pressure nitrogen overhead from the high pressure column as a high pressure nitrogen product.
The process of the present invention can further comprise withdrawing a second oxygen product from the low pressure column and warming the 20 withdrawn product to recover refrigeration. The withdrawn, second oxygen product can be withdrawn as either a gas or a liquid.
Figures 1 through 5 are schematic diagrams of several embodiments of 25 the process of the present inventlon.
DETAILED DESCRIPTION OF THE INVENTION
A problem which exists with the prior art process ls how to produce a high pressure oxygen product efflciently. When distilling air to produce 30 oxygen efficiently, the distillation should be performed at the lowest practical pressure, i.e., less than about 5 psig. Unfortunately, this low pressure need is inconsistent with the need to produce a high pressure product. Therefore, the goal is to increase the pressure of the oxygen product to the required level while minimiz~ng the costs in terms of 35 capital and power of performing th~s function. The present invention is the answer to that goal.
' .. - - ' .
2~29'~
The process of the present invention can be understood in reference to several embodiments. These embodiments are illustrated in Figures 1 through 5. With reference to Figure 1, feed air, in line 10, is compressed to about 95 psia in air compressor 12. The compressed feed air 5 is then precooled and directed to mole sieve adsorber 14 to remove water, carbon dioxide and heavy hydrocarbons which may be contained in the feed air and which will freeze out in the process at cryogenic temperatures.
The dry, carbon dioxide-free, compressed feed air is removed from adsorber 14, via line 16, and then split into two portions.
The first and major portion consisting of about 50 to 60X of the total air flow, in line 20, is cooled in heat exchanger 22 to near its dew point.
The second or minor portion consisting of the remaining feed air, in line 30, is further compressed in compressor 32 so that the resultant 15 pressure of the stream is sufficient to cause the air dew point to be above the oxygen bubble point. For example, for 70 psig oxygen product, the second substream should be compressed to about 225 psig. If the - required air pressure is above or near the critical pressure of air, an optimization of air flow and pressure should be performed. Th;s further 20 compressed, second portion from compressor 32 is then cooled to about -100F to -200F in heat exchanger 22.
At this point, a part of the cooled, further compressed, second portion is removed, via line 34, and expanded in expansion turbine 36 to produce work. This expanded part, in line 38, is combined with the 25 cooled, first portion, in line 24, to form a high pressure column feed air stream, in line 26.
The remainder of the cooled, further compressed, second portion, in line 40, is condensed in heat exchanger 22, reduced in pressure and fed to high pressure column 28 as impure liquid air reflux. As an option, a 30 portion of the condensed, second portion can be fed as impure reflux to low pressure column 62 (this option is not shown in Flgure 1).
In high pressure column 28, the high pressure feed air stream, in line 40, is rectified into a high pressure nitrogen overhead and a crude oxygen bottoms liquid.
: . : . . .. .. . .
2~8293 The high pressure nitrogen overhead is removed from high pressure column 28, via line 50, and fed to reboiler/condenser 52 located in the bottom of low pressure column 62, wherein it is condensed and subsequently divided into two substreams. The first substream, in line 54, is fed to 5 the top of high pressure column 28 as pure liquid nitrogen reflux. The second substream, in line 56, is subcooled in heat exchanger 57, reduced in pressure and fed to the top of low pressure column 62 as pure liquid nitrogen reflux. Although not shown, as an option, a portion of the high pressure nitrogen overhead, up to about 20X of the feed air, can be 10 recovered as high pressure nitrogen product.
The crude oxygen bottoms liquid is removed, via line fiO, from high pressure column 28, subcooled in heat exchanger 57, reduced in pressure and fed to an intermediate location of low pressure column 62 for distillation. In low pressure column 62, this crude oxygen is distilled 15 into a low pressure nitrogen overhead and a liquid oxygen bottoms.
A portion of the liquid oxygen bottoms is boiled against the condensing nitrogen in reboiler/condenser 52, thereby producing reboil for low pressure column 62. The remaining liquid oxygen is removed, via line 70, from the bottom of low pressure column 62, increased in pressure in 20 LOX pump 72, warmed to vaporize the liquid oxygen thereby recovering refrigeration and recovered as high pressure oxygen product, in llne 74.
The low pressure nitrogen overhead is removed, via line 80, from low pressure column 62, and subsequently warmed in heat exchangers 57 and 22 to recover refrigeration. This nitrogen overhead can be then boosted in 25 pressure, if necessary, to produce a nitrogen product.
In addition, a waste stream can be removed, via line 90, from an upper intermediate location of low pressure column 62, warmed in heat exchanger 22 to recover refrigeration and then vented as waste.
Figure 2 shows another embodiment of the process of the present 30 invent~on which can be used to produce significant quantities of liquid oxygen, nitrogen or argon products. In this embodiment, feed air, in line 10, is compressed in air compressor 12. The compressed feed air is then precooled and directed to mole sieve adsorber 14 to remove water, carbon dioxide and heavy hydrocarbons which may be contained in the feed 35 air and which will freeze out in the process at cryogenic temperatures.
' 2 ~ 9 3 The dry, carbon dioxide-free, compressed feed air is removed from adsorber 14, via line 16, and then split into two portions.
The first portion, consisting of about 30 to 40X of the total air flow, ~n line 20, is further compressed in compressor 120 and cooled in 5 heat exchanger 22 to near its dew point. Compressor 120 can be eliminated if the pressure required to vaporize the oxygen is lower than the pressure required for the liquid refrigeration requirement. For example, for product requirement of 100 T/D of oxygen at 250 psig, the pressure of the air feed to the cold box will be 600 psig. This cooled, fSrst portion ~s 10 then reduced in pressure and fed to a lower intermediate location of high pressure distillation column 28 as impure liquid air reflux.
The second portion, consisting of the remaining feed air, in line 30, is further compressed in compressor 32 and then cooled in heat exchanger 22. This cooled, further compressed, second portion is then expanded in 15 expansion turbine 36 to produce work. Expander 36 and compressor 32 are mechanically linked as a compander unit. This expanded, second portion is fed to the bottom of high pressure column 28 as its primary feed, via line 138.
In high pressure column 28, the feed air streams are rectified into 20 an high pressure nitrogen overhead and a crude oxysen bottoms liquid.
A first portion of the hlgh pressure nitrogen overhead is removed from high pressure column 28, via line 50, and fed to reboiler/condenser 52 located in the bottom of low pressure column 62, wherein it is condensed and subsequently divided into two substreams. The first 25 substream, in line 54, is fed to the top of high pressure column 28 as pure liquid nitrogen reflux. The second substream, in llne 56, is subcooled in heat exchanger 57, reduced in pressure and fed to the top of low pressure column 62 as pure liquid nitrogen reflux. Optionally, a part of stream 56 can be recovered as liquid nitrogen product, via line 156.
30 Also, a second portion of the high pressure n~trogen overhead, line 150, can be recovered as high pressure nitrogen product, line 152.
The crude oxygen bottoms liquid is removed, via line 60, from high pressure column 28, subcooled in heat exchanger 57, reduced in pressure and fed to an intermediate location of low pressure column 62 for 35 distillation. In low pressure column 62, this crude oxygen is distilled into a low pressure nitrogen overhead and a liquid oxygen bottoms.
., ~, . . '- . .
- : . ; , . ~ . . , ~ .~, . . ..
- , ..
-`` 20~8293 A portion of the liquid oxygen bottoms is boiled against the condensing nitrogen in reboiler/condenser 52, thereby producing reboil for low pressure column 62. The remaining liquid oxygen is removed, via line 70, from the bottom of low pressure column 62, increased in pressure in 5 LOX pump 72, warmed to vaporize the liquid oxygen thereby recovering refrigeration and recovered as high pressure oxygen product, in line 74.
Optionally, a liquid oxygen product can be removed from the process, via line 172.
The low pressure nitrogen overhead is removed, via line 80, from low 10 pressure column 62, and subsequently warmed in heat exchangers 57 and 22 to recover refrigeration. This nitrogen overhead can be then boosted in pressure, if necessary, to produce a nitrogen product.
In addition, a waste stream can be removed, via line 90, from an upper intermediate location of low pressure column 62, warmed in heat 15 exchanger 22 to recover refrigeration and then vented as waste.
If additional liquid products are required, a portion of the expanded, second portion, line 138, can be removed, via line 242, warmed in heat exchanger 22, and fed, v~a line 244, to an intermediate stage of main a~r compressor 12 for recompression. This embodiment is illustrated ; 20 in Figure 3.
Refrigeration for the process can be supplied by several alternative methods other than that shown in Figure 1. For example, the plant refrigeration can be supplied by:
(a) expanding nitrogen from the high pressure column;
(b) expanding a portion of the low pressure air stream into the low pressure column;
(c) expanding an air stream at some intermediate pressure into either the high or low pressure column;
(d) expanding the waste stream from the low pressure column, or (e) feeding liquid oxygen or nitrogen to the process.
This last method (option d) will yield a higher pressure nitrogen product from the low pressure column.
The process of the present invention can be used to produce oxygen product at more than one pressure level, if required. Figure 4 shows an 35 embodiment in which gaseous oxygen is removed from low pressure column 62, .-.
.. . .
~ : .............. ~ ......................... . .
.
20~8293 via line 370, warmed in heat exchanger 22 to recover refrigeration, and recovered as a gaseous oxygen product at about 2 to 4 psig.
: Liquid oxygen can be taken from low pressure column 62, via line 70, and vapor~zed in heat exchanger 22 to produce an oxygen product at about 5 15 to 20 psig. This embodiment is shown in Figure 5.
Finally, referring to Figure l but not shown, product oxygen can also be produced at more than one pressure by taking a portion of the liquid from the LOX pump 72 and letting it down in pressure prior to warming in a separate circuit in heat exchanger 22. ~or this option, it would be more lO efficient to supply air at two pressure levels from air booster 32 in order to better match the cooling curves.
- The above described process is useful for the production of oxygen having an oxygen concentration from about 70 to 99.9X oxygen at pressures ranging from lO psi to 250 psi and above. The process also can produce a 15 nitrogen product stream at either high or low pressures. Although not shown in any of the figures, an argon s1de-arm column can be added to low pressure column 62 to produce a crude argon product from the process.
A benefit of the present invention described above is that it has a capital savings of about 5X for small oxygen plants (i.e., less than 200 20 tons per day) when compared to conventional oxygen compressor processes.
Another advantage of the process of the present invention is that the ; feed air is expanded and fed to the high pressure column rather than the low pressure column. As a result of this step, more nitrogen is available at the top of the high pressure column and therefore more nitrogen reflux 25 is available. This increased availability of nitrogen for refluxing aids in nitrogen recovery and provides more boilup for the production of a purer nitrogen stream, if needed.
The present invention has been described wlth reference to several embodiments thereof. These embodiments should not be viewed as a - 30 limitation of the scope of the present invention; the scope which should be ascerta~ned by the attached claims.
. . . : ; ; ~ . ~ . -, . .
Claims (11)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In a process for the production of an oxygen product by the cryogenic distillation of air in a double column distillation system having a high pressure column and a low pressure column, wherein a feed air stream is compressed, purified of impurities which will freeze out at cryogenic temperatures and divided into two portions; wherein the first portion is fed to the high pressure column for rectification thereby producing a crude liquid oxygen bottoms and high pressure nitrogen overhead; wherein the second portion is further compressed, cooled and expanded to produce work; wherein the crude liquid oxygen bottoms is subcooled, reduced in pressure and fed to the low pressure column for distillation and the high pressure nitrogen overhead is condensed in a reboiler/condenser located in the bottom of the low pressure column; wherein at least a portion of the condensed nitrogen is returned to the top of the high pressure column as pure reflux and at least another portion is subcooled, reduced in pressure and fed to the top of the low pressure column as pure reflux; wherein the crude liquid oxygen bottoms fed to the low pressure column is distilled to produce a low pressure nitrogen overhead and a low pressure column, liquid oxygen bottoms; and wherein a portion of the low pressure column, liquid oxygen bottoms is reboiled in the reboiler/condenser located in the bottom of the low pressure column against the condensing high pressure nitrogen overhead; the improvement for the production of high pressure oxygen comprises:
(a) feeding the expanded, second portion to the high pressure column; and (b) removing another portion of the liquid oxygen bottoms from the low pressure column, increasing in pressure the removed portion in a liquid oxygen pump, warming and vaporizing the increased pressure, removed portion, and recovering the vaporized, increased pressure, removed portion as the high pressure oxygen product.
(a) feeding the expanded, second portion to the high pressure column; and (b) removing another portion of the liquid oxygen bottoms from the low pressure column, increasing in pressure the removed portion in a liquid oxygen pump, warming and vaporizing the increased pressure, removed portion, and recovering the vaporized, increased pressure, removed portion as the high pressure oxygen product.
2. The process of Claim 1 which further comprises dividing the further compressed, cooled, second portion into two substreams prior to expansion;
expanding the first substream and feeding the expanded, first substream to the high pressure column; and condensing and reducing in pressure the second substream and introducing the condensed, reduced pressure, second substream to the high pressure column as impure liquid air reflux.
expanding the first substream and feeding the expanded, first substream to the high pressure column; and condensing and reducing in pressure the second substream and introducing the condensed, reduced pressure, second substream to the high pressure column as impure liquid air reflux.
3. The process of Claim 1 wherein compression and expansion of the second portion is provided by a compressor and an expander which are mechanically linked (compander).
4. The process of Claim 1 which further comprises further compressing the first portion prior to cooling.
5. The process of Claim 1 which further comprises dividing the expanded, second portion into two substreams prior to feeding the expanded, second portion to the high pressure column; feeding the first substream to the high pressure column; and warming the second substream to recover refrigeration and recycling the warmed substream to the compression step of the feed air stream.
6. The process of Claim 1 which further comprises removing a portion of the increased pressure, liquid oxygen from the low pressure column as liquid product prior to vaporization.
7. The process of Claim 5 which further comprises removing a portion of the increased pressure, liquid oxygen from the low pressure column as liquid product prior to vaporization.
8. The process of Claim 1 which further comprises removing and warming a portion of the high pressure nitrogen overhead from the high pressure column as a high pressure nitrogen product.
9. The process of Claim 1 which further comprises withdrawing a second oxygen product from the low pressure column and warming the withdrawn product to recover refrigeration.
10. The process of Claim 9 wherein the withdrawn, second oxygen product is liquid.
11. The process of Claim 9 wherein the withdrawn, second oxygen product is gaseous.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US56480390A | 1990-08-08 | 1990-08-08 | |
| US07/564803 | 1990-08-08 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2048293A1 true CA2048293A1 (en) | 1992-02-09 |
Family
ID=24255956
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002048293A Abandoned CA2048293A1 (en) | 1990-08-08 | 1991-08-01 | Pumped liquid oxygen air separation cycles |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2048293A1 (en) |
-
1991
- 1991-08-01 CA CA002048293A patent/CA2048293A1/en not_active Abandoned
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4715873A (en) | Liquefied gases using an air recycle liquefier | |
| US4615716A (en) | Process for producing ultra high purity oxygen | |
| US4702757A (en) | Dual air pressure cycle to produce low purity oxygen | |
| US4433989A (en) | Air separation with medium pressure enrichment | |
| EP0645595B1 (en) | Air separation schemes for oxygen and nitrogen co-production as gas and/or liquid products | |
| EP0147460B1 (en) | Cryogenic triple-pressure air separation with lp-to-mp latent-heat-exchange | |
| US5351492A (en) | Distillation strategies for the production of carbon monoxide-free nitrogen | |
| CA2228799C (en) | Air separation with intermediate pressure vaporization and expansion | |
| US4783210A (en) | Air separation process with modified single distillation column nitrogen generator | |
| EP0646755B1 (en) | Cryogenic air separation process and apparatus producing elevated pressure nitrogen by pumped liquid nitrogen | |
| US5373699A (en) | Process for the production of nitrogen by cryogenic distillation of atmospheric air | |
| EP0962732B1 (en) | Multiple column nitrogen generators with oxygen coproduction | |
| US5129932A (en) | Cryogenic process for the separation of air to produce moderate pressure nitrogen | |
| US4704147A (en) | Dual air pressure cycle to produce low purity oxygen | |
| EP0381319A1 (en) | Apparatus and method for separating air | |
| US5077978A (en) | Cryogenic process for the separation of air to produce moderate pressure nitrogen | |
| CA2211767C (en) | Process to produce nitrogen using a double column plus an auxiliary low pressure separation zone | |
| CA2070498C (en) | Cryogenic process for producing ultra high purity nitrogen | |
| US5682762A (en) | Process to produce high pressure nitrogen using a high pressure column and one or more lower pressure columns | |
| EP0807792B1 (en) | Air separation method and apparatus | |
| EP0343421B1 (en) | Ultra pure liquid oxygen cycle | |
| JP2000346547A (en) | Cryogenic distillation for separating air | |
| CA2049519A1 (en) | Cryogenic nitrogen generator with bottom reboiler and nitrogen expander | |
| CA2068065C (en) | Process to produce oxygen and nitrogen at medium pressure | |
| US5768914A (en) | Process to produce oxygen and argon using divided argon column |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Discontinued | ||
| FZDE | Discontinued |
Effective date: 19940201 |