INTEGRATED MULTICOMPONENT REFRIGERANT AND AIR SEPARATION PROCESS FOR PRODUCING LIQUID OXYGEN

BACKGROUND

The following abbreviations are used herein: multicomponent refrigerant (MR), air separation unit (ASU), main air compressor (MAC), booster air compressor (BAC), liquefied natural gas (LNG), oxygen (O2), nitrogen (N2), gaseous oxygen (GOX), liquid oxygen (LOX), liquid nitrogen (LIN), liquid argon (LAR), and liquid air (LAIR).

A simple mass and energy balance around the cold end of an ASU (distillation columns+sub-cooler) indicates that the quantity of liquid leaving must be approximately equal to the quantity of liquid entering. Also, for an efficient distillation it is known in the art that the air entering the bottom of the distillation column should be cold vapor near the dew point. Therefore, a simple energy balance requires that a liquid stream (typically LAIR) enter the columns and has a flowrate approximately equal to the sum of the LOX+LIN products.

Prior art schemes utilize only low-pressure air (4 to 7 bara) from the main air compressor to distillation column. Per the above cold end energy balance, liquid air must be leaving cold end of main exchanger and entering the distillation. Condensing at such low pressure (4 to 7 bara is significantly below the critical pressure of 62 bara) yields very high latent heat of condensation. As the flowrate of the liquid air increases (due to increasing flowrate of LOX+LIN), the heat exchange to produce this LAIR becomes infeasible without vaporizing another stream in the main exchanger to provide additional refrigeration. This is the case particularly when significant quantities of O2 are removed from the process as liquid (LOX) rather than being pumped to higher pressure and vaporized in the main exchanger against the condensing air stream producing high pressure GOX. Note that the flow of vaporizing MR is already compensated by the condensing of the MR.

In the current application significant quantities of O2 ae removed as LOX rather than vaporizing to produce High Pressure GOX such that at least 80% of oxygen in feed air is produced as liquid oxygen. Or the mass flow of LOX+LIN is greater than mass flow of oxygen in feed air.

Referring now to FIG. 1 (which essentially reproduces the schemes from Praxair U.S. Pat. Nos. 6,260,380 and/or 6,112,550), purified feed air stream 101 is cooled by passage through main heat exchanger 102 by indirect heat exchange with return streams and by refrigeration generated by the multicomponent refrigerant fluid circuit as will be more fully described below, and then passed into higher pressure column 103 which is operating at a pressure generally within the range of from 60 to 200 psia. Within higher pressure column 103 the feed air is separated by cryogenic rectification into nitrogen-enriched vapor and oxygen-enriched liquid. Nitrogen-enriched vapor is withdrawn from the upper portion of higher-pressure column 103 in stream 104 and condensed in main condenser 105 by indirect heat exchange with boiling oxygen-rich liquid which is lower pressure column bottom liquid. Resulting nitrogen-enriched liquid 106 is returned to higher pressure column 103 as reflux and a portion 117 is passed from column to sub-cooler 107 wherein it is subcooled and passed into the upper portion of lower pressure column 108 as reflux. If desired, a portion 109 of stream 106 may be recovered as product liquid nitrogen. Stream 106 may comprise up to 50 percent of the feed air provided into the system.

Oxygen-enriched liquid is withdrawn from the lower portion of higher-pressure column 103 in stream 110 and passed to sub-cooler 111 wherein it is subcooled. Resulting subcooled oxygen-enriched liquid is then divided into first portion 112 and second portion 113. First portion 112 is passed into lower pressure column 108 and second portion 113 is passed into argon column condenser 114 wherein it is at least partially vaporized. The resulting vapor is withdrawn from condenser 114 and passed into lower pressure column 108. Any remaining oxygen-enriched liquid is withdrawn from condenser 114 and then passed into lower pressure column 108.

Lower pressure column 108 is operating at a pressure less than that of higher-pressure column 103 and generally within the range of from 15 to 150 psia. Within lower pressure column 108 the various feeds into that column are separated by cryogenic rectification into nitrogen-rich vapor and oxygen-rich liquid. Nitrogen-rich vapor is withdrawn from the upper portion of lower pressure column 108 in stream 115, warmed by passage through heat exchangers 103, 111, and 107, and may be recovered as product gaseous nitrogen having a nitrogen concentration of at least 99 mole percent, preferably at least 99.9 mole percent, and most preferably at least 99.999 mole percent. For product purity control purposes, a waste stream 116 is withdrawn from lower pressure column 108 from a level below the withdrawal point of stream 115, warmed by passage through heat exchangers 103, 111, and 107, and removed from the system. Oxygen-rich liquid is partially vaporized in the lower portion of lower pressure column 108 by indirect heat exchange with condensing nitrogen-enriched vapor in main condenser 105 as was previously described to provide vapor up-flow for lower pressure column 108. If desired, a portion of the resulting oxygen-rich vapor may be withdrawn from the lower portion of lower pressure column 108 in stream 118 having an oxygen concentration generally within the range of from 90 to 99.9 mole percent. Oxygen-rich vapor in stream 118 is warmed by passage through main heat exchanger 102 and recovered as product gaseous oxygen in stream 119. Oxygen-rich liquid is withdrawn from the lower portion of lower pressure column 108 in stream 120 and recovered as liquid oxygen. Stream 120 may comprise all of the oxygen contained in the feed air.

Fluid comprising oxygen and argon is passed in stream 121 from lower pressure column 108 into third or argon column 122 wherein it is separated by cryogenic rectification into argon-richer fluid and oxygen-richer fluid. Oxygen-richer fluid is passed from the lower portion of column 122 in stream 123 into lower pressure column 108. Argon-richer fluid is passed from the upper portion of column 122 as vapor into argon column condenser 114 wherein it is condensed by indirect heat exchange with the aforesaid subcooled oxygen-enriched liquid. Resulting argon-richer liquid is withdrawn from condenser 114. At least a portion of the argon-richer liquid is passed into argon column 122 as reflux and, if desired, another portion is recovered as product liquid argon as shown by stream 124. Stream 124 may comprise all of the argon in the feed air.

There will now be described in greater detail the operation of the multicomponent refrigerant fluid circuit which serves to generate preferably all the refrigeration passed into the cryogenic rectification plant thereby eliminating the need for any turbo-expansion of a process stream to produce refrigeration for the separation, thus decoupling the generation of refrigeration for the cryogenic air separation process from the flow of process streams, such as feed air, associated with the cryogenic air separation process, It should be understood that this is simply one example of a multicomponent refrigerant system, and any alternative system that is known in the art that is suitable for this application may be substituted by one skilled in the art.

The following description illustrates the multicomponent refrigerant fluid system for providing refrigeration throughout the main heat exchanger 102. Multicomponent refrigerant fluid in stream 125 is compressed by passage through recycle compressor 126 to a pressure generally within the range of from 45 to 81400 psia to produce a compressed refrigerant fluid. The compressed refrigerant fluid is cooled of the heat of compression by passage through aftercooler 127 and may be partially condensed. The resulting multicomponent refrigerant fluid 128 is then passed through main heat exchanger 102 wherein it is further cooled and generally is at least partially condensed and may be completely condensed. The resulting cooled, compressed multicomponent refrigerant fluid 129 is then expanded or throttled through valve 130. The throttling preferably partially vaporizes the multicomponent refrigerant fluid, cooling the fluid and generating refrigeration. For some limited circumstances, dependent on heat exchanger conditions, the compressed fluid 129 may be subcooled liquid prior to expansion and may remain as liquid upon initial expansion. Subsequently, upon warming in the heat exchanger, the fluid will have two phases. The pressure expansion of the fluid through a valve would provide refrigeration by the Joule-Thomson effect, i.e. lowering of the fluid temperature due to pressure expansion at constant enthalpy. However, under some circumstances, the fluid expansion could occur by utilizing a two-phase or liquid expansion turbine, so that the fluid temperature would be lowered due to work expansion.

Refrigeration bearing multicomponent two phase refrigerant fluid stream 131 is then passed through main heat exchanger 102 wherein it is warmed and completely vaporized thus serving by indirect heat exchange to cool stream 128 and also to transfer refrigeration into the process streams within the heat exchanger, including feed air stream 101, thus passing refrigeration generated by the multicomponent refrigerant fluid refrigeration circuit into the cryogenic rectification plant to sustain the cryogenic air separation process. The resulting warmed multicomponent refrigerant fluid in vapor stream 125 is then recycled to compressor 126 and the refrigeration cycle starts anew. In the multicomponent refrigerant fluid refrigeration cycle while the high-pressure mixture is condensing, the low-pressure mixture is boiling against it, i.e. the heat of condensation boils the low-pressure liquid. At each temperature level, the net difference between the vaporization and the condensation provides the refrigeration. For a given refrigerant component combination, mixture composition, flowrate and pressure levels determine the available refrigeration at each temperature level.

The multicomponent refrigerant fluid contains two or more components in order to provide the required refrigeration at each temperature. The choice of refrigerant components will depend on the refrigeration load versus temperature for the specific process. Suitable components will be chosen depending upon their normal boiling points, latent heat, and flammability, toxicity, and ozone-depletion potential.

Alternatively, this cold end refrigeration balance can be managed by LIN assist from an external liquefier. In this case the flowrate of LIN assist is approximately equal to the flow rate of LOX production, as described below in FIG. 2. However, this scheme requires the N2 feed to the liquefier be warmed to ambient. This warming and cooling of the N2 feed to the liquefier consumes energy which makes this process inefficient.

Turning now to FIG. 2, the multicomponent refrigerant cycle includes warm multicomponent refrigerant return steam 201, which is at reduced pressure. Warm multicomponent refrigerant return stream 201 has the pressure increased in multicomponent refrigerant compressor 202, thereby producing pressurized multicomponent refrigerant stream 203. Pressurized multicomponent refrigerant stream 203 enters multicomponent refrigerant cooler 204, thereby producing cooled pressurized multicomponent refrigerant stream 205. Cooled, pressurized multicomponent refrigerant stream 205 is introduced to first phase separator vessel 206, which produces first vapor portion 207 and first liquid portion 208.

After passing through liquefaction heat exchanger 209, first vapor portion 207 exits as warmed first vapor stream 242. Warmed first vapor stream 242 is introduced to second phase separator vessel 243, which produces second vapor portion 244 and second liquid portion 245. Second vapor portion 244 is introduced into liquefaction heat exchanger 411. After passing through liquefaction heat exchanger 209 second vapor portion 244 exits as cooled to form at least partially condensed portion 246. Second liquid portion 245 is introduced into liquefaction heat exchanger 209. After passing through liquefaction heat exchanger 209, second liquid portion 245 exits as warm second liquid portion 247.

After passing through liquefaction heat exchanger 209, first liquid portion 208 exits as warmed first liquid stream 248. At least partially condensed portion 246 is introduced into third phase separator vessel 249. Third phase separator vessel 249 produces third vapor portion 250 and third liquid portion 251. Third vapor portion 250 and third liquid portion 251 are combined to form third combined multicomponent refrigerant stream 252, which is introduced into liquefaction heat exchanger 209. After passing through liquefaction heat exchanger 209, third combined multicomponent refrigerant stream 252 exits as warm combined multicomponent refrigerant steam 253.

Warmed second liquid portion 247 is introduced into fourth phase separator vessel 254. Warmed first liquid stream 248 is introduced into fourth phase separator vessel 254. And warm combined nitrogen steam 253 are introduced to fourth phase separator vessel 254. Exiting fourth phase separator vessel 254 are fourth vapor portion 255 and fourth liquid portion 256. Fourth vapor portion 255 and fourth liquid portion 256 are combined to form fourth combined multicomponent refrigerant stream 257, which is introduced into liquefaction heat exchanger 209. After passing through liquefaction heat exchanger 209, fourth combined multicomponent refrigerant stream 257 exits as warm multicomponent refrigerant return steam 201.

It is understood, but not shown in FIG. 2, that there will be pressure reducing valves on streams 247, 248, and 246.

Nitrogen refrigeration cycle includes increasing the pressure of first nitrogen recycle stream 210 in LP nitrogen compressor 211, thereby producing warm medium-pressure nitrogen stream 212. Warm medium-pressure nitrogen stream 212 enters first nitrogen cooler 213, thereby producing cooled medium-pressure nitrogen stream 214.

Cooled medium-pressure nitrogen stream 214 is combined with medium-pressure nitrogen stream 240 from ASU 215 and second nitrogen recycle stream 216, thereby producing combined medium-pressure nitrogen stream 217. The pressure of medium-pressure nitrogen stream 217 is increased in MP nitrogen compressor 218, thereby producing warm intermediate-pressure nitrogen stream 219. Warm intermediate-pressure nitrogen stream 219 enters second nitrogen cooler 220, thereby producing cooled intermediate-pressure nitrogen stream 221.

Cooled intermediate-pressure nitrogen stream 221 is then further compressed in HP nitrogen booster 222, thereby producing high-pressure nitrogen stream 223, High-pressure nitrogen stream 223 then passes through liquefaction heat exchanger 209, after which it is removed at two locations. Typically, first nitrogen refrigeration stream 224 will be removed as a vapor stream, and second nitrogen refrigeration stream 225 will be removed as a liquid stream.

The first location is via first nitrogen refrigeration stream 224, which is then introduced into nitrogen expander 226, Nitrogen expander 276 is connected to HP nitrogen booster 273 by a common drive shaft, After having the pressure reduced in nitrogen expander 276, this stream exits as expanded nitrogen stream 227, which is then introduced into liquefaction heat exchanger 411. Expanded nitrogen stream 227 exits liquefaction heat exchanger 209 as second nitrogen recycle stream 216.

The second location is via second nitrogen refrigeration stream 225, which is then introduced third phase separator vessel 228, which produces nitrogen vapor portion 229 and nitrogen liquid portion 230. Nitrogen vapor portion 229 and nitrogen liquid portion 230 are combined to form combined nitrogen stream 231. A portion of combined nitrogen stream 231 is removed as internal liquid nitrogen stream 232, At least a portion 233 of internal liquid nitrogen stream 232 is returned to the ASU, and a portion of internal liquid nitrogen stream 232 may be removed as external LIN product to storage 234. The remaining portion of combined nitrogen stream 231 is introduced into liquefaction heat exchanger 209 as cold nitrogen recycle stream 235. Cold nitrogen recycle stream 235 exits liquefaction heat exchanger 209 as first nitrogen recycle stream 210.

Multicomponent refrigerant cycle and nitrogen refrigeration cycle work together to provide sufficient refrigeration duty to liquefy inlet natural gas stream 236 into liquid natural gas stream 237. In addition, these combined refrigeration streams also provide sufficient additional refrigeration duty via internal liquid nitrogen stream 233, to satisfy the duty requirements of air separation unit 215.

Compressed and purified inlet air stream 238 enters first heat exchanger 239 wherein it exchanges heat with medium-pressure nitrogen stream 240, then enters air separation unit 215. Air separation unit 215 produces at least medium-pressure nitrogen stream 240, and liquid oxygen stream 241. In order to produce the desired flowrate in liquid oxygen stream 241 it is necessary to introduce additional refrigeration duty, in the form of internal liquid nitrogen stream 233,

Medium-pressure nitrogen stream 240 and inlet natural gas stream 236 are introduced into liquefaction heat exchanger 209, as described above. Liquefaction heat exchanger 209 outputs at least liquid natural gas stream 237 and internal liquid nitrogen stream 232. Liquid natural gas stream 237 is then sent to liquid natural gas storage.

To avoid the excessive energy associated with the sensible heat of rewarming and cooling the N2 feed stream t the liquefier, it could be envisioned to send the cold gaseous N2 directly from the MP column to a cold location in the liquefier. (not warming the gaseous N2 in the ASU). However, in this case the ASU main exchanger heat transfer is imbalanced as the flow of the streams is much higher than the flow of cold streams resulting in unparalleled heat exchange lines as indicated in FIG. 3.

Note, that in FIG. 3 and FIG. 5, the line designated “cold composite” represents the aggregate of the various streams into which heat is being transferred (i.e. “cold” streams), and the line designated “hot composite” represents the aggregate of the various streams from which heat is being transferred (i.e. “hot” streams).

SUMMARY

A process for the production of a liquid oxygen stream and a liquid hydrocarbon-rich stream by the cryogenic rectification of an inlet air stream, including dividing the inlet air stream into a first portion, and a second portion. Cooling the first portion, and the second portion against a cooled multicomponent refrigerant circuit, thereby producing a first cooled portion, and a second cooled portion. Condensing the first cooled portion, thereby producing a condensed first portion, then introducing the condensed first portion into one or more distillation columns. Expanding the second cooled portion in a turbo-expander, thereby producing an expanded second portion, then introducing the expanded second portion within the one or more distillation columns. Producing within the one or more distillation columns at least a waste nitrogen stream, a nitrogen enriched stream, and an oxygen enriched stream.

BRIEF DESCRIPTION OF THE FIGURES

For a further understanding of the nature and objects for the present invention, reference should be made to the following detailed description, taken in conjunction with the accompanying drawings, in which like elements are given the same or analogous reference numbers and wherein

FIG. 1 is a schematic representation of a combined multicomponent refrigerant cycle used with an air separation unit, as known in the art.

FIG. 2 is another schematic representation of a combined multicomponent refrigerant cycle used with an air separation unit, as known in the art.

FIG. 3 is a schematic representation of the heat flow within the main heat exchanger in a system configured as described in FIG. 2.

FIG. 4 is a schematic representation of a combined multicomponent refrigerant cycle used with an air separation unit.

FIG. 5 is a schematic representation of the heat flow within the main heat exchanger in a system configured as described in FIG. 4.

FIG. 6 is a schematic representation of a combined multicomponent refrigerant cycle used with an air separation unit.

FIG. 7 is a schematic representation of a combined multicomponent refrigerant cycle used with an air separation unit to produce both a liquid oxygen stream and liquid hydrocarbon stream, in accordance with one embodiment of the present invention.

FIG. 8 is a schematic representation of an argon column that may be used in combination with the cycle as indicated in FIG. 7, in accordance with one embodiment of the present invention.

FIG. 9 is a schematic representation of a typical heat flow through an independent air separation unit, as is known in the art.

FIG. 10 is a schematic representation of a typical heat flow through an independent liquefaction unit, as is known in the art.

FIG. 11 is a schematic representation of the heat flow through an integrated air separation unit and liquefaction unit, in accordance with one embodiment of the present invention.

ELEMENT NUMBERS

101=purified feed air stream

102=main heat exchanger

103=higher pressure column

184=nitrogen enriched vapor stream

105=main condenser

106=nitrogen-enriched liquid stream

107=sub-cooler

108=lower pressure column

109=product liquid nitrogen stream

110=oxygen enriched liquid stream

111=sub-cooler

112=first portion (of oxygen-enriched liquid)

113=second portion (of oxygen-enriched liquid)

114=argon column condenser

115=nitrogen rich vapor stream

116=waste stream

117=nitrogen enriched liquid (to sub-cooler)

118=oxygen rich vapor stream

119=product gaseous oxygen stream

120=liquid oxygen

121=oxygen and argon containing stream

122=argon column

123=oxygen-richer fluid (from argon column)

124=product liquid argon

125=low pressure multicomponent refrigerant stream

126=multicomponent refrigerant recycle compressor

127=multicomponent refrigerant aftercooler

128=compressed multicomponent refrigerant stream

129=cooled, compressed multicomponent refrigerant stream

130=multicomponent refrigerant stream throttle valve

131=refrigeration bearing multicomponent refrigerant stream

201=warm multicomponent refrigerant return steam

202=multicomponent refrigerant compressor

203=pressurized multicomponent refrigerant stream

204=multicomponent refrigerant cooler

205=cooled pressurized multicomponent refrigerant stream

206=first phase separator vessel

207=first vapor portion (from first phase separator)

208=first liquid portion (from first phase separator)

209=liquefaction heat exchanger

210=first nitrogen recycle stream

211=LP nitrogen compressor

212=warm medium-pressure nitrogen stream

213=first nitrogen cooler

214=cooled medium-pressure nitrogen stream

215=air separation unit

216=second nitrogen recycle stream

217 =combined medium-pressure nitrogen stream

218=MP nitrogen compressor

219=warm intermediate-pressure nitrogen stream

220=second nitrogen cooler

221=cooled intermediate-pressure nitrogen stream

222=HP nitrogen booster

223=high-pressure nitrogen stream

224=first nitrogen refrigeration stream

225=second nitrogen refrigeration stream

226=nitrogen expander

227=expanded nitrogen stream

228=third phase separator vessel

229=nitrogen vapor portion

230=nitrogen liquid portion

231=combined nitrogen stream

232=internal liquid nitrogen stream

233=return portion (of internal liquid nitrogen stream)

234=storage portion (of internal liquid nitrogen stream)

235=cold nitrogen recycle stream

236=inlet natural gas stream

237=liquid natural gas stream

238=compressed and purified inlet air stream

239=first heat exchanger

240=medium-pressure nitrogen stream

241=liquid oxygen stream

242=warmed first vapor stream

243=second phase separator vessel

244=second vapor portion

245=second liquid portion

246=at least partially condensed portion

247=warm second liquid portion

248=warmed first liquid stream

249=third phase separator vessel

250=third vapor portion

251=third liquid portion

252=third combined multicomponent refrigerant stream

253=warm combined nitrogen steam

254=fourth phase separator vessel

255=fourth vapor portion

256=fourth liquid portion

257=fourth combined multicomponent refrigerant stream

301=warm multicomponent refrigerant return steam

302=multicomponent refrigerant compressor

303=pressurized multicomponent refrigerant stream

304=multicomponent refrigerant cooler

305=cooled multicomponent refrigerant stream

306=multicomponent refrigerant stream throttle valve

307=expanded multicomponent refrigerant stream

308=first phase separator vessel

309=first vapor portion (from first phase separator)

310=first liquid portion (from first phase separator)

311=warmed first vapor stream

312=second phase separator vessel

313=second vapor portion

314=second liquid portion

315=second combined multicomponent refrigerant stream

316=warm combined nitrogen steam

317=warmed first liquid stream

318=third phase separator vessel

319=third vapor portion

320=third liquid portion

321=third combined multicomponent refrigerant stream

322=inlet air stream

323=main air compressor

324=inlet air cooler

325
a/b=air purification vessel

326=purified inlet air stream

327=Claude compressor

328=boosted air cooler

329=cooled, boosted air stream

330=cold air stream

331=condensed first portion (of cooled inlet air)

332=second portion (of cooled inlet air)

333=Claude expander

334=expanded second portion

335=distillation column

336=liquid nitrogen product

337=liquid oxygen product stream

338=liquid oxygen stream

339=liquid oxygen pump

340=high pressure liquid oxygen stream

341=high-pressure gaseous oxygen product stream

342=waste nitrogen stream

343=warmed waste nitrogen stream

344=waste nitrogen heater

345=hot waste nitrogen stream

346
ab=regeneration waste stream

347=liquefaction heat exchanger

348=multicomponent refrigerant cycle

601=first portion (of purified air stream)

602=cooled feed air stream

603=second portion (of purified air stream)

604=booster air compressor

605=pressurized first portion

701=warm multicomponent refrigerant return steam

702=first multicomponent refrigerant compressor

703=first pressurized multicomponent refrigerant stream

704=first multicomponent refrigerant cooler

705=first cooled multicomponent refrigerant stream

706=first phase separator vessel

707=first vapor portion (from first phase separator)

708=first liquid portion (from first phase separator

709=second multicomponent refrigerant compressor

710=second pressurized multicomponent refrigerant stream

711=second multicomponent refrigerant cooler

712=second cooled multicomponent refrigerant stream

713=second phase separator vessel

714=second vapor portion (from second phase separator)

715=second liquid portion (from second phase separator)

716=warmed first liquid stream

717=warmed second liquid stream

718=warmed combined nitrogen stream

719=fourth phase separator vessel

720=fourth vapor portion (from fourth phase separator)

721=fourth liquid portion (from fourth phase separator)

722=fourth combined multicomponent refrigerant stream

723=warmed first vapor stream

724=third phase separator vessel

725=third vapor portion (from third phase separator)

726=third liquid portion (from third phase separator)

727=third combined multicomponent refrigerant stream

728=supplemental compressor

729=cold inlet stream

730=inlet natural gas stream

731=liquid natural gas stream

732=dense fluid expander

733=Joule Thompson valve

734=dense fluid expander

735=Joule Thompson valve

736=dense fluid expander

737=Joule Thompson valve

801=argon column

802=oxygen-Argon containing stream

803=argon-lean stream

804=argon-rich stream

805=crude argon stream

901=feed air stream

902=cold waste nitrogen stream

903=main heat exchanger

904=liquid air stream

905=warm waste nitrogen stream

1001=natural gas feed stream

1002=cold multicomponent refrigerant stream

1003=main heat exchanger

1004=liquid natural gas stream

1005=warm multicomponent refrigerant stream

1101=main heat exchanger

Description of Preferred Embodiments

Illustrative embodiments of the invention are described below. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure.

Using Claude Turbine Booster (Claude compressor 327 and Claude expander 333) with a condensing air stream at the cold section of main exchanger combined with a multicomponent refrigerant cycle for the warm section of the main exchanger. The MAC outlet is ˜30 to 35 bara and the outlet of the booster is 35 to 45 bara such that the condensing air stream is 34 to 45 bara resulting in low latent heat of condensation.

Prior art integration of MR cycle with an ASU produces at least some oxygen which enters the main heat exchanger for indirect heat exchange with the multicomponent refrigerant fluid, The current application does not have any oxygen enriched stream in main heat exchanger. Nothing greater than air, 21% O2. This provides safer management of flammable multicomponent refrigerants than prior art.

Turning now to FIG. 4, the multicomponent refrigerant cycle 348 includes warm multicomponent refrigerant return steam 301, which is at reduced pressure. Warm multicomponent refrigerant return stream 301 has the pressure increased in multicomponent refrigerant compressor 302, thereby producing pressurized multicomponent refrigerant stream 303. Pressurized multicomponent refrigerant stream 303 enters multicomponent refrigerant cooler 304, thereby producing cooled multicomponent refrigerant stream 305. Cooled multicomponent refrigerant stream 305 is introduced into multicomponent refrigerant stream throttle valve 306, thereby forming expanded multicomponent refrigerant stream 307. Expanded multicomponent refrigerant stream 307 is introduced into first phase separator vessel 308, which produces first vapor portion 309 and first liquid portion 310.

After passing through liquefaction heat exchanger 347, first vapor portion 309 exits as warmed first vapor stream 311. Warmed first vapor stream 311 is introduced to second phase separator vessel 312, which produces second vapor portion 313 and second liquid portion 314. Second vapor portion 313 and second liquid portion 314 are combined to form second combined multicomponent refrigerant stream 315, which is introduced into liquefaction heat exchanger 347. After passing through liquefaction heat exchanger 347 second combined multicomponent refrigerant stream 315 exits as warmed combined nitrogen stream 316.

After passing through liquefaction heat exchanger 347, first liquid portion 310 exits as warmed first liquid stream 317. Warmed first liquid stream 317 and warmed combined nitrogen stream 316 are introduced into third phase separator vessel 318. Third phase separator vessel 318 produces third vapor portion 319 and third liquid portion 320. Third vapor portion 319 and third liquid portion 320 are combined to form third combined multicomponent refrigerant stream 321, which is introduced into liquefaction heat exchanger 347. After passing through liquefaction heat exchanger 347, third combined multicomponent refrigerant stream 321 exits as warm multicomponent refrigerant return steam 301.

Inlet air stream 322 enters main air compressor 323 wherein the pressure is increased, and the pressurized air is cooled in inlet air cooler 324. The cooled, compressed air stream is then directed to one of air purification vessel 325a/b, wherein the inlet air stream is purified, thereby producing purified inlet air stream 326. Purified inlet air stream 325 is then compressed in Claude compressor 327 and cooled in boosted air cooler 328. Cooled, boosted air stream 329 then enters liquefaction heat exchanger 347, thereby forming cold air stream 330. After having the temperature reduced, first portion 331 of cold air stream 330 exits liquefaction heat exchanger 347 and then enters distillation column 335. Second portion 332 of the cold air stream 330 continues through liquefaction heat exchanger 347 and exits liquefaction heat exchanger 347 and then enters Claude expander 333. Expanded second air stream 334 then enters distillation column 335.

The compressed air expanding across Claude expander 333 removes heat from expanded second air stream 334, thereby effectively increasing the amount of refrigeration as it then enters distillation column 335. This allows distillation column 335 to produce additional distillation products such as liquid nitrogen product stream 336, liquid oxygen product stream 337, liquid oxygen stream 338, and/or waste nitrogen stream 342. The cold vapor streams (i.e. waste nitrogen stream 342) then provide (in addition with multicomponent refrigerant cycle 348) additional cooling and liquefaction for the air and hydrocarbon streams.

Distillation column 335 produces at least liquid nitrogen product stream 336, waste nitrogen stream 342, liquid oxygen stream 338, and liquid oxygen product stream 337. In order to produce the desired flowrate in both liquid oxygen stream 338 and liquid oxygen product stream 337, it is necessary to introduce additional refrigeration duty, in the form of expanded second air stream 334. At least a portion of the liquid oxygen from distillation column 335 may be exported as a liquid oxygen product stream 337.

Optionally, liquid oxygen stream 338 may be removed from distillation column 335. Liquid oxygen stream 338 is increased in pressure in liquid oxygen pump 339, thereby producing high-pressure liquid oxygen stream 340. High-pressure liquid oxygen stream 340 is then introduced into liquefaction heat exchanger 347, wherein it is heated and vaporized, thereby producing optional high-pressure gaseous oxygen product stream 341, which then exits the system. One skilled in the art will recognize that liquid oxygen pump 339 may just as easily product low-pressure or medium-pressure liquid oxygen, and therefore the system may produce low-pressure or medium-pressure gaseous oxygen (not shown) in addition to the high-pressure gaseous oxygen system as illustrated. All oxygen product streams may be only liquid. Or a portion may be liquid and additional (optional) portions maybe low-pressure gaseous oxygen and/or high-pressure gaseous oxygen.

After passing through liquefaction heat exchanger 347, warmed waste nitrogen stream 353 is heated in waste nitrogen heater 354, thereby producing hot waste nitrogen stream 355, Hot waste nitrogen stream 355 is then used to regenerate air purification vessels 325a/b as needed, with the resulting regeneration waste exiting in regeneration waste streams 356a/b.

In this case the ASU main exchanger heat transfer is balanced, as indicated in the parallel heat exchange lines as indicated in FIG. 5.

In an alternative embodiment, as illustrated in FIG. 6, the process cycle may utilize a booster air compressor and a LP main air compressor, rather than the above cycle that utilized a HP main air compressor and no booster air compressor. This cycle results in a slightly less overall efficiency of approximately 2%.

Turning now to FIG. 6, the multicomponent refrigerant cycle 348 includes warm multicomponent refrigerant return steam 301, which is at reduced pressure. Warm multicomponent refrigerant return stream 301 has the pressure increased in multicomponent refrigerant compressor 302, thereby producing pressurized multicomponent refrigerant stream 303. Pressurized multicomponent refrigerant stream 303 enters multicomponent refrigerant cooler 304, thereby producing cooled multicomponent refrigerant stream 305. Cooled multicomponent refrigerant stream 305 is introduced into multicomponent refrigerant stream throttle valve 306, thereby forming expanded multicomponent refrigerant stream 307. Expanded multicomponent refrigerant stream 307 is introduced into first phase separator vessel 308, which produces first vapor portion 309 and first liquid portion 310.

First portion 601 enters liquefaction heat exchanger 347 and exits as cooled feed stream 602, which then enters distillation column 335. Second portion 603 enters booster air compressor 604, thereby producing pressurized first portion 605. Pressurized first portion 605 is then compressed in Claude compressor 327 and cooled in boosted air cooler 328, after which it enters liquefaction heat exchanger 347. First portion 331 of the cooled inlet air exits liquefaction heat exchanger 347 and then enters distillation column 335. Second portion 332 of the cooled inlet air exits liquefaction heat exchanger 347 and then enters Claude expander 333. Expanded second air stream 334 then enters distillation column 335. Distillation column 335 produces at least liquid nitrogen product stream 336, waste nitrogen stream 342, and liquid oxygen product stream 337. In order to produce the desired flowrate in liquid oxygen product stream 337, it is necessary to introduce additional refrigeration duty, in the form of expanded second air stream 334. At least a portion of the liquid oxygen from distillation column 335 may be exported as a liquid oxygen product stream 337.

After waste nitrogen stream 342 passes through liquefaction heat exchanger 347, warmed waste nitrogen stream 343 is heated in waste nitrogen heater 344, thereby producing hot waste nitrogen stream 345. Hot waste nitrogen stream 345 is then used to regenerate air purification vessels 346a/b as needed, with the resulting regeneration

Turning now to FIG. 7, a system wherein a gaseous hydrocarbon stream is integrated into the air separation process. By integrating the natural gas liquefaction cooling into the air separation process, it is possible for the excess refrigeration at a cold range in the air separation unit to be utilized. This excess refrigeration is typically created by the air separation unit flow imbalance between the liquid air (low flow warm stream) and the waste nitrogen stream (high flow cold stream). This imbalance tends to arise between about −150 C and about −170 C. It is desirable to pinch the exchange diagram within this region by increasing the flowrate of warm stream into this region. Specifically the liquefied natural gas (warm stream) can be cooled by the waste nitrogen stream without the need for multicomponent refrigerant cooling. This enables the multicomponent refrigerant to be warmed significantly (i.e. from about −167 C to about −150 C). This is described below, and may result in a net efficiency improvement of about 5%.

The process scheme illustrated in FIG. 7 is approximately 7% to 8% more efficient (i.e. uses less power) than a traditional air separation unit integrated with a nitrogen cycle. This is because the nitrogen cycle must be warmed and re-cooled through the entire temperature range to the warm end (typically from −190 C to +40 C) just to provide refrigeration at the cold end.

Turning again to FIG. 7, the multicomponent refrigerant cycle 348 includes warm multicomponent refrigerant return steam 701, which is at reduced pressure. Warm multicomponent refrigerant return stream 701 has the pressure increased in first multicomponent refrigerant compressor 702, thereby producing first pressurized multicomponent refrigerant stream 703. First pressurized multicomponent refrigerant stream 703 enters first multicomponent refrigerant cooler 704, thereby producing first cooled multicomponent refrigerant stream 705. First cooled multicomponent refrigerant stream 705 is introduced into first phase separator vessel 706, which produces first vapor portion 707 and first liquid portion 708.

First vapor portion 707 has the pressure increased in second multicomponent refrigerant compressor 709, thereby producing second pressurized multicomponent refrigerant stream 710. Second pressurized multicomponent refrigerant stream 710 enters second multicomponent refrigerant cooler 711, thereby producing second cooled multicomponent refrigerant stream 712. Second cooled multicomponent refrigerant stream 712 is introduced into second phase separator vessel 713 which produces second vapor portion 714 and second liquid portion 715,

After passing through liquefaction heat exchanger 347, second vapor portion 714 exits as warmed first vapor stream 723. Warmed first vapor stream 723 is introduced to third phase separator vessel 724, which produces third vapor portion 725 and third liquid portion 726. Third vapor portion 725 and third liquid portion 726 are combined to form third combined multicomponent refrigerant stream 727 which is introduced into liquefaction heat exchanger 347. After passing through liquefaction heat exchanger 347 third combined multicomponent refrigerant stream 727 exits as warmed combined nitrogen stream 718

After passing through liquefaction heat exchanger 347, first liquid portion 708 exits as warmed first liquid stream 716. After passing through liquefaction heat exchanger 347, second liquid portion 715 exits as warmed second liquid stream 717. Warmed first liquid stream 716, warmed second liquid stream 717, and warmed combined nitrogen stream 718 are introduced into fourth phase separator vessel 719. Fourth phase separator vessel 719 produces fourth vapor portion 720 and fourth liquid portion 721. Fourth vapor portion 720 and fourth liquid portion 721 are combined to form fourth combined multicomponent refrigerant stream 722, which is introduced into liquefaction heat exchanger 347. After passing through liquefaction heat exchanger 347, fourth combined multicomponent refrigerant stream 722 exits as warm multicomponent refrigerant return steam 701.

Multicomponent refrigerant cycle and nitrogen refrigeration cycle work together to provide sufficient refrigeration duty to liquefy inlet natural gas stream 730 into liquid natural gas stream 731. Liquid natural gas stream 731 may optionally have the pressure reduced in either dense fluid expander 736 or Joule Thompson valve 737. In addition, these combined refrigeration streams also provide sufficient additional refrigeration duty via internal nitrogen stream 342, to satisfy the duty requirements of air separation unit 215.

Inlet air stream 322 enters main air compressor 323 wherein the pressure is increased, and the pressurized air is cooled in inlet air cooler 324. The cooled, compressed air stream is then directed to one of air purification vessel 325a/b, wherein the inlet air stream is purified, thereby producing purified inlet air stream 326. Purified air stream 326 is then compressed in Claude compressor 327 and cooled in boosted air cooler 328, after which it enters liquefaction heat exchanger 347 as cooled, boosted air stream 329. First portion 331 of cold air stream 330 exits liquefaction heat exchanger 347, is optionally further compressed in supplemental compressor 728, and then enters distillation column 335 as cold inlet stream 729. Cold inlet stream 729 may optionally have the pressure reduced in either dense fluid expander 732 or Joule Thompson valve 733. Second portion 332 of cold air stream 330 exits liquefaction heat exchanger 347 and then enters Claude expander 333. Expanded second air stream 334 then enters distillation column 335. Expanded second air stream 334 may optionally have the pressure reduced in either dense fluid expander 732 or Joule Thompson valve 733

Distillation column 335 produces at least liquid nitrogen product stream 336, waste nitrogen stream 342, optional liquid oxygen stream 338, and liquid oxygen product stream 337. In order to produce the desired flowrate in optional liquid oxygen stream 338 and liquid oxygen product stream 337, it is necessary to introduce additional refrigeration duty, in the form of expanded second air stream 334.

One potential application for this system is the space industry. In the space industry the demand is for liquid natural gas and liquid oxygen for rocket fuels. In such an application, there will be no gaseous oxygen in the main heat exchanger. This is an important feature because this would make it safe to have an integrated exchanger (MR and NG integrated in ASU exchanger) without O2 in the shared exchanger.

Turning now to FIG. 8, an option argon column 801 may be integrated into distillation column 335 as illustrated in FIG. 7. Oxygen-Argon containing stream 802 is introduced into argon column 801, thereby producing argon-lean stream 803, and argon-rich stream 804. Argon-lean stream 803 is returned to distillation column 335. Argon-rich stream 804 is either combined with internal nitrogen stream 342 or exits the system as crude argon stream 805 for export or further purification.

One skilled in the art would recognize that even if crude argon stream 805 is not desired as a product, argon column 801 is useful due to the low reflux flow (argon-lean stream 803) to distillation column 335, which serves to improve oxygen recovery. This oxygen recovery may be improved by as much as 5%.

As used herein, the term “cold stream” is defined as the streams which are having their temperature increased by the described heat exchange. Such streams may include a waste nitrogen stream exiting the distillation column and, after being warmed, being used to regenerate front end purification units. A “cold stream” may also be a stream exiting a multicomponent refrigerant system after being expanded and cooled.

As used herein, the term “hot stream” is defined as the streams which are having their temperature decreased by the described heat exchange. Such streams may include an inlet air stream that is cooled and at least partially liquefied prior to entering the distillation column. A “hot stream” may also be a natural gas stream that is liquefied into liquefied natural gas.

As used here, the term “hot composite” or “hot stream” is defined as collectively including cooled, boosted air stream 329 and natural gas feed stream 730. As used herein, the term “hot collective flow rate” is defined as the total mass flowrate of cooled, boosted air stream 329 and natural gas feed stream 730.

As used here, the term “cold composite” or “cold stream” is defined as collectively including high-pressure liquid oxygen stream 340, waste nitrogen stream 342, cold multicomponent refrigerant stream 708, cold multicomponent refrigerant stream 714, cold multicomponent refrigerant stream 715, fourth combined multicomponent refrigerant stream 722, and third combined multicomponent refrigerant stream 727. As used herein, the term “cold collective flow rate” is defined as the total mass flow rate of high-pressure liquid oxygen stream 340, waste nitrogen stream 342, cold multicomponent refrigerant stream 708, cold multicomponent refrigerant stream 714, cold multicomponent refrigerant stream 715, fourth combined multicomponent refrigerant stream 722, and third combined multicomponent refrigerant stream 727

Turning now to FIG. 9, the heat flow within the main heat exchanger 903 of a generic system comprising an independent air separation unit is shown. Such a system is not integrated into a multicomponent refrigerant system or any other cryogenic system. Feed air stream 901 enters main heat exchanger 903 and exchanges heat with cold waste nitrogen stream 902, which may be arriving from the distillation column (not shown). As a result of this heat transfer, liquid air stream 904 and warm waste nitrogen stream 905 are produced. As is indicated in the heat flow diagram, in this particular simulation, there is a significant temperature difference between the “hot stream” and the “cold stream” above −155 C. This is because of the low liquid air flow relative to the waste nitrogen flow yielding small temperature differential at the cold end and a large temperature differential at the warm end. One skilled in the art would recognize these diverging lines as an indication of less efficient heat transfer having taking place as compared to ideal efficient process of parallel lines.

Turning now to FIG. 10, the heat flow within the main heat exchanger 1003 of a generic system comprising an independent natural gas liquefaction unit is shown. Such a system utilizes a multicomponent refrigerant system but no other cryogenic system. Natural gas feed stream 1001 enters main heat exchanger 1003 and exchanges heat with cold multicomponent refrigerant stream 1002, Cold multicomponent refrigerant stream 1002 is coming directly from the cold end of the multicomponent refrigerant system (not shown). As a result of this heat transfer, liquid natural gas stream 1004 and warm multicomponent refrigerant stream 1005 are produced. As is indicated in the heat flow diagram, in this particular simulation, there is a significant temperature difference between the “hot stream” and the “cold stream” during the entire process. This is because of the small temperature differential at the warm end and the large temperature differential at the cold end. One skilled in the art would recognize these diverging lines as an indication of less efficient heat transfer having taking place. as compared to ideal efficient process of parallel lines,

Turning now to FIG. 11, the heat flow within the main heat exchanger 1101 of an integrated system comprising an air separation unit and a natural gas liquefaction unit is shown. As this is a slightly simplified representation of the system described above in FIG. 7, element numbers from FIG. 7 are being used for clarity.

Feed air stream 329 enters main heat exchanger 1101 and exchanges heat with waste nitrogen stream 342, natural gas feed stream 730, and cold multicomponent refrigerant stream 708/714/715, As a result of this heat transfer, liquid air stream 331, liquid natural gas stream 731, warm waste nitrogen stream 343, and warm multicomponent refrigerant stream 701 are produced. As is indicated in the heat flow diagram, in this particular simulation, the temperature difference between the “hot stream” and the “cold stream” at all points between −150 C and −170 C are closer to one another. One skilled in the art would recognize this as an indication of more efficient heat transfer having taking place.

One of ordinary skill in the art will recognize that when the flow of composite “hot streams” is less than the flow of composite “cold streams” and in the heat exchange zone the cold inlet temperature is colder than the liquefied hydrocarbon withdraw temperature, the resulting exchange diagram will tend to pinch at the cold end and tend to open up (i.e. exhibit a larger temperature differential) at the warm end of this zone. Because of this design inefficiency, the larger temperature differential at the point of liquid hydrocarbon withdrawal means that there is excess refrigeration available at the hydrocarbon withdrawal temperature. Thus, the mixed refrigerant stream can be warmed up. For example, the multicomponent refrigerant inlet temperature is warmer than hydrocarbon outlet. This is in stark contrast to the prior art where the refrigerant must be colder than the stream to be cooled.

The object of the current invention is the optimization of the heat transfer at the cold end of liquefaction heat exchanger 347 when the natural gas liquefaction process is integrated with the air separation process. This is preferentially accomplished with no oxygen-rich stream also in liquefaction heat exchanger 347. The “hot stream” (i.e. the liquid air composite streams) has a lower mass flowrate than the “cold stream” (i.e. the waste nitrogen flow), and excess refrigeration capacity exists in the region of liquefaction heat exchanger 347 where liquid natural gas stream 731 is withdrawn. This allow multicomponent refrigeration cycle 348 to be warmed significantly, saving a considerable amount of energy. The inlet multicomponent refrigerant stream is warmer than the natural gas stream that it is cooling. It should be noted that in the prior art, the mixed refrigerant stream is colder than the natural gas stream that it is intended to cool.

It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.

	Number	Date	Country
	63223410	Jul 2021	US
	63287558	Dec 2021	US

INTEGRATED MULTICOMPONENT REFRIGERANT AND AIR SEPARATION PROCESS FOR PRODUCING LIQUID OXYGEN

Information

Publication Number

Date Filed

Date Published

Inventors

Original Assignees

CPC

International Classifications

Abstract

Description

Claims

CROSS REFERENCE TO RELATED APPLICATIONS

Provisional Applications (2)