US 3775988 A
The diclosure is directed to methods of gas separation wherein controlled flow vortex tube expansion principles are employed in liquefaction and cold producing processes; a multi-stage low pressure and a multi-stage high pressure process being involved. The vortex tube is introduced in the parent application as being employed in cases with more efficiency than the expansion turbine. Herein, by addition, support figures are supplied for these cases, and also vortex tube separation processes are shown capable of replacing rectification column processes; liquefaction and separation processes using controlled flow vortex tubes with double purpose being submitted herein as new.
Claims available in
Description (OCR text may contain errors)
1 1 Dec. 4, 1973 CONDENSATE WITHDRAWAL FROM VORTEX TUBE IN GAS LIQUIFICATION CIRCUIT  Inventor: Lancelot A. Fekete, 1632 Colquitt, Houston, Tex. 77006  Filed: May 23, 1969  Appl. No.: 828,111
Related US. Application Data  Continuation-impart of Ser. No. 585,213, Oct. 7,
 US. Cl 62/23, 62/5, 62/9, 62/40  Int. Cl. ..L F25j 1/00, F25j 3/02  Field of Search 62/5, 9, 23, 26
 References Cited UNITED STATES PATENTS 2,522,787 9/1950 Hughes 62/5 2,683,972 7/1954 Atkinson.... 62/5 2,741,899 4/1956 Von Linde 62/5 2,861,431 11/1958 Van Deemter 62/5 3,296,807 1/1967 Fekete 62/5 1,804,432 5/1931 Pollitzer.. 62/23 2,894,371 7/1959 Auer 62/5 1,952,281 3/1934 Ranque 62/5 FOREIGN PATENTS 0R APPLICATIONS 803,301 8/1949 Germany 62/5 OTHER PUBLICATIONS Fulton C. D., Ranques Tube Journal ASRE May 1950 pgs. 473-479 Primary Examiner--Norman Yudkoff Assistant Examiner-Arthur F. Purcell Attorney-Bemard A. Reiter  ABSTRACT The diclosure is directed to methods of gas separation wherein controlled flow vortex tube expansion principles are employed in liquefaction and cold producing processes; a multi-stage low pressure and a multi-stage high pressure process being involved. The vortex tube is introduced in the parent application as being employed in cases with more efficiency than the expansion turbine. Herein, by addition, support figures are supplied for these cases, and also vortex tube separation processes are shown capable of replacing rectification column processes; liquefaction and separation processes using controlled flow vortex tubes with double purpose being submitted herein as new.
7 Claims, 18 Drawing Figures vortex tube PATENTED EB 41m 3.775.988
' V sum 1 m 4 vortex Tube H I W 2 I 1 I, isobar 2 53 h 8' w 2b 20 s i 2c F5 2 v Figure 2A 5 I 5% /J ENTROPY S' v Figure 2 5e 5g I 5y 5f 5f J 1 1 s vortex vortex Tube fubes 51 LANCELOT A. FEKETE inventor CONDENSATE WITHDRAWAL FROM VORTEX TUBE IN GAS LIQUIFICATION CIRCUIT This application is a continuation in part of a copending application Ser. No. 585,213, filed Oct. 7, 1966 and now abandoned; adding data thereto and further disclosing as new, the single outlet vortex tube as used instead of the expansion turbine and vortex tube separation processes replacing rectification column processes.
This invention relates to a newinethod of liquefying gases by means of a vortex tube which uses the so called Ranque effect for the cooling of higher pressure gases by expansion and condensation to a liquid when the cooling by expansion reaches the liquefying temperature. It refers also to the apparatus used in this liquefying processes.
The liquefying of gases can be done by various means, of which the most common process uses the Joule-Thompson expansion to obtain the final low temperatures. Thegas is compressed to a high pressure by suitable compressors, then it is cooled at first with water in condensers, then by the expanded gas in heat exchangers to a sufficiently low temperature, the final lowering of the temperature being achieved by passing the high pressure gas through an expansion valve into the separation vessel where part of it is liquefied, most of it is recirculated through the heat exchangers.
The basic principle of this invention is to use, instead of the common expansion, the Ranque effect, which in most cases provides a much more efficient cooling. The Ranque effect transforms the pressure as potential energy of the gas into heat and cold. The vortex tube is a cylindrical tube in which the gas is introduced tangentially at higher pressure so as to create a fast turning vortex of sonic or supersonic velocity. The outer part of the vortex becomes hotter than the inlet gas, and the inner part becomes colder, the temperature difierence for 1:5 pressure ratio being in therange of 120 F. A diaphragm near the inlet is used to draw off the cold stream, the hot strearnbeing discharged at the other end. The hot or cold stream may be split up into a central and a peripheral part by a concentric tube and may be discharged separately. The essential feature of this new liquefying process is that best economies are obtained if the gas pressures arekept low, and multi-stage Ranque expansion is used, the number of stages being dependent on the liquefying temperature. So to liquefy air a three or four stage process is used,each stage with a compression ratio of about 1:3 range If low pressures are to be maintained throughout, then the compression is carried out between stages, each consecutive stage handling a much smaller gas flow. However there is advantage in using an initial higher pressure, cooling the gas in air or water cooled condensers to ambient temperature, and then putting it through a series of vortex tubes of decreasing flowrate. A remarkable advantage of this liquefying process is that the lower temperature stages handle substantially smaller gas flows, which means sizable savings in heat losses and equipment costs. The present application claims both processes.
The same liquefying method maybe applied when a gas mixture is liquefied to separate its components, for instance to manufacture, oxygen from-air, the purification method also being the subject of this invention. The vortex tube not only cools andcondenses gases but also separates them. Two distinct processes may take place inside the vortex tubeQGases are separated by kinetic impact energy, which is proportional to the molecular weight, so that the lower molecular weight compounds are enriched in the hot gas stream of the vortex tube and the higher molecular weight compounds are in the cold side, Vapors entering the vortex tube and also the condensed material from the central part of the tube, are thrown to the periphery and are carried out at the hot outlet. It is advantageous to have a separate peripheral outlet on the hot side to carry out the condensed vapors. This condensing effect inside the vortex tube does also part of the work of the rectifying column, so that smaller columns may be used. The separation may be obtained by using the vortex tubes only, as it is claimed in this patent, without any rectifying columns. This liquefying and purification is particularly useful in the manufacture of liquid oxygen at low, nearly atmospheric pressures, and low temperatures. At ambient temperatures, the vapor pressure of oxygen is about22QQ psi so that the liquefying process is substantially different and involves higher pressures. For other similar gases, the use of the vortex tube instead of common expansion, in the liqufying process assures larger cold temperature differences for the same expansion ratio, and in consequence a better economy. The hot gas stream of the vortex tube can be used to advantage when recirculated.
The classical liquefying processes of Linde and Claude are utilizing the Joule-Thompson expansion of gases at high pressures and low temperatures, where for the same pressure ratio the expansion produces a larger temperature difference. At atmospheric temperatures, farther away from the critical point of air, the Joule- Thompson expansion results in only about 2 temperature difference for 1:5 pressure ratio. For the same pressure ratio, the vortex tube expansion produces about cold temperature difference. The new vortex tube liquefying process differs essentially in principle from the method patented by D. W. Hughes, US. Pat. No. 2,522,787 of Sept. 19, 1950, in that the Hughes patent uses one vortex tube ahead of the expansion valve of the classical Linde-Claude process, and most of the cooling is-done in heat exchangers. The new vortex tube liquefying method uses vortex tubes in series as main cooling devices, with relatively low pressure ratios. This is possible only if the flowrate. of the subsequent vortex tube may be controlled, a recent development. Experiments on the new process show that more a vortex tube in series may produce more cooling for the same total pressure ratio than one vortex tube. Other liquefaction processes using the Ranque vortex tube have a low efficiency of liquefaction because the vapors are thrown out to the periphery of the hot side of the tube and recirculated into the compressor. The new process separates the condensed vapors in the vortex tube by taking it out at the peripheral outlet.
As pointed out before, larger temperature differences can be produced with the Joule-Thompson or common expansion near the boiling point of a gas, especially near the critical point. The velocity of sound of gases and vapors is lower near the boilingpoint, and it has a sharp minimum at the critical point. However the experiments have revealed that the Ranque effect includes the Joule-Thomson effect as a special case without circular flow. On the hot side of the vortex tube, the Joule-Thomson expansion and the condensation effect, as shown by experiments with the new vortex tube acts against the heat effect, so that the difference is felt. The Ranque effect produces cold at and beyond the inversion curve where the Joule-Thomson effect cannot produce cold. Experiments with saturated and superheated vapors show that the Ranque effect is also quite efficient in vapors.
An ethane-propane gas mixture was compressed by a compressor to 580 psi pressure, it was introduced into a vortex tube at 1 F in order to liquefy and separate this gas stream at 68 F and 155 psi pressure, the results of the process being shown below:
Composition of the gas streams (volume percent) Inlet Gaszmol. weightliquid: Cold Gas:
Carbon dioxide 2.37%) 0.39 2.85 Methane 0.38 30.5 0.04 0.50 Ethane 73.67 32.93 87.96 Propane 17.25 26.02 6.30 Iso-butane 2.54 8.99 1.12 N-butane 2.09 49.5 9.84 0.65 Iso-pentane 0.73 7.00 0.31 N-pentane 0.45 5.15 0.21 Hexane plus 0.52 6.94 0.10 Molecular weight 39.95 50.91 32.12 Pressure psi 480 155.0 130.0 Temperature "F 170 68.0 52.0
The molecular weight of the liquid and gaseous components are proof of good separation efficiency. The present invention claims to extend its validity to the combined liquefaction process of the vortex tube and common (Joule-Thompson) expansion.
It may be economical to make the initial higher temperature vortex tube stages a low pressure process, because these stages handle more than four times larger gas volumes. These low compression ratios mean less expensive cold exchangers and equipment, and less cold losses.
In contrary, the low temperature stages are of so small volume, that it is simpler to use a higher compression ratio, for instance 1:4 or 1:6 for the last vortex tube. 1f the first stage lowers the gas temperature sufficiently, one second vortex tube with only one intermediate cold exchanger can decrease the gas temperature by as much as 200 to 300 or more, sufficient for liquefying most gases.
In liquefaction and refrigeration processes, part of the gas stream is cooled in expansion turbine to produce additional mechanical energy. The vortex tube may be used instead of the expansion turbine to produce heat energy. The literature points out that besides the advantage of its simple construction its efficiency is close, sometimes even better than that of the expansion turbine. The new single outlet vortex tube with spiral diffuser transforms the kinetic energy of the fast turning vortex into pressure; besides the cold outlet is insulated from the rest of the tube so that the new vortex tube has by far a superior cooling effect by comparison to former designs. The present invention claims the use of the single or multiple outlet vortex tube instead of the expansion turbine in refrigeration and Iiquefaction processes, either as the final separation stage, or as an intermediate stage to produce better cooling efficiency.
Experiments have demonstrated that the vortex tube, besides heating and cooling a gas mixture, separates the components by molecular weight. This separation effect helps in the purification of the liquified gases, either as a preliminary separating effect ahead of the rectifying column, or by itself, as a special vortex tube separation process. The first vortex tube of applicant was made with one inlet, two hot and two cold side outlets: one central in the axis of the tube and one peripheral outlet on both ends. The first tests were made with compressed air of psi, which proved the flow controlled vortex tube a successful cooling device of good efficiency on a wide range of flowrates. The separation effect was tested in 1967 on a 6,000 psi natural gas well. A series of experiments were made with a three stage controlled flow vortex tube, having a central cold outlet and two hot side outlets: a central and a peripheral. It was observed that the condensed fluid was thrown to the periphery of the tube and was taken out at the peripheral outlet. Tests were conducted with pressure ratios of 1:2, 1:3, 1:5 and 1:10 for different cold flowrate ratios at different inlet flowrates. Samples were taken and chemical analysis performed on the inlet, the cold outlet, the hot side central outlet and the peripheral outlet. The chemical analysis showed good separation and liquefaction efficiencies, about 3 to 5 times better than the stage separation.
The vortex tube was also tested with one inlet and just one peripheral outlet, the other outlets being shut off. These tests were performed at first with compressed air. It was observed that when air expanded from 100 psi to 20 psi, the temperature at the outlet of the tube was 5 'F lower than at the inlet, about twice as much as could be obtained with simple Joule- Thomson expansion. Later a similar modified vortex tube was tested on a high pressure gas well in the Mississippi delta, however, it had only one central cold outlet and two hot side outlets. Only the inlet and one peripheral outlets were used. The inlet pressure was 3,500 psi and the outlet pressure was 1,200 psi, the inlet temperature was F, and outlet temperatures down to 100 F were tested, so that most of the ethane and much of the methane were separated by liquefaction. It was found that the single outlet vortex tube has substantially more cooling effect than the expansion through a choke or through an expansion valve. The new design of the single outlet vortex tube is shown on FIGS. 7, Sand 9. It has a tangential inlet as usual, with or without controlled flow, and the gas expands into a tube consisting of a short cylindrical part, followed by a double cone to stabilize the vortex flow, and an outlet in the form of a doughnut shaped spiral difiusor. This shape increases the cooling efficiency of the vortex tube. Another new design feature is the thermal insulation between the inlet and the hot outlet which decreases the cold losses.
In modern low pressure liquefaction and gas separation processes the expansion turbine is used instead of the Joule-Thompson expansion valve to transform the pressure energy into cold. It is used either to liquefy the gas or to cool part of the gas stream in order to use it in exchangers or separators as a cooling medium. Experiments with the vortex tube have shown that its cooling efficiency may compete with the expansion turbine. FIG. 16 is a schematic flow diagram of a vortex tube Iiquefying process, in which the single outlet vortex tube is used instead of the expansion turbine, either as the main expansion device to liquefy gas, or in a partial gas stream, to produce cold by expanding the gas and recirculating the gas through cold exchanger sections to obtain efficient cooling of the main gas stream.
The gas liquefying and purification methods are shown by the drawings, schematic process flowsheets and diagrams, in which:
FIG. 1 is a generalized flowsheet of a three-stage low pressure vortex tube liquefying process.
FIGS. 2 and 2A are schematic temperature-entropy diagrams of flowsheet FIG. 1 which explain the thermodynamical relationships of the process.
FIG. 3 is the generalized flowsheet of three-stage highpressure vortex tube liquefying process.
FIGS. 4 and 4A are schematic temperature-entropy diagrams of the gas liquefying process of which the flowsheet is shown in FIG. 3.
FIG. 5 is the generalized flowsheet of a gas separation and purification process using the low pressure vortex tube liquefying method, combined with a single column rectification, to purify the gas. I
FIG. 6 is the generalized flowsheet of a gas separation and purification process using the high pressure vortex tube 'liquefying method combined with a two-column rectification, to purify the gases.
FIG. 7 is the schematic longitudinal section of a single outlet vortex tube.
FIG. 8 is the cross sectional representation of the single outlet vortex tube of FIG. 7, taken at the inlet.
FIG. 9 is the cross sectional diagram of the single out let vortex tube of FIG. 7 taken across the diffusor.
FIG. 10 is the schematic flowsheet of a single outlet vortex tube liquefaction process.
FIG. 11 is the schematic temperature-entropy diagram of the single vortex tube liquefaction and gas separation process.
FIG. 12 is the schematic fiow diagram of a gas liquefaction and separation process using a two-stage rectifying column.
FIG. 13 is the schematic temperature-entropy diagram of the vortex tube liquefaction and separation process of FIG. 12.
FIG. 14 is the schematic flow diagram of a gas liquefaction and separation process using vortex tubes and regenerative cold exchangers.
FIG. 15 is the schematic temperature-entropy diagram of the gas liquefaction and separation processof FIG. 14.
FIG. 16 is a schematic flow diagram of a gas liquefaction process using single outlet vortex tubes in place of expansion turbines. I
FIG. 1 is a generalized flowsheet of a three-stage low pressure vortex tube liquefaction process. The gas enters at la into the first stage compressor lb, where it is compressed to a pressure ratio of for instance 1:3. The heat of compression is taken out of the gas by a condenser (water cooled or air cooled) and the gas is precooled in heat exchanger 1d by the returning hot stream of vortex tube 1p. The precooled gas is passed into the first vortex tube 1e, where it is separated into a cold stream If and a hot stream la. The cold stream, about 30 to 50 percent of the inlet gas flow which is now at about the inlet pressure, is compressed in compressor lg to a pressure ratio of say 1:3, and the compressed gas is cooled again in the heat exchanger lit to the original temperature. From here it enters into the second vortex tube 1k where it expands again and is separated into a hot and a cold stream. The cold stream which is about 10 to 25 percent of the suction flowrate of the first compressor is compressed again in compressor 11 to a pressure ratio of 1:3 (say 50 psi) and passed into the heat exchanger 1m where it is cooled again to a low temperature. The low temperature stream enters into the third vortex tube 1p where itis separated anew into a cold stream, a peripheral 11 and a central hot stream. The cold stream and the peripheral hot stream are discharged into the condensing vessel lg as liquid gas, the quantity being only 3 to 15 percent of the suction of the first compressor. The pressure of this liquid is about atmospheric, near the suction pressure of the first compressor. The vapor of the liquefied gas passes to the heat exchanger 1m and retums to the suction of one of the compressors. The central hot stream of vor t'ex tube 1p is rather cold so that it can be used in cool ing of exchanger 1h. The hot stream of the first vortex tube is nearly atmospheric; if it is cold enough, it may be used in an exchanger. The path of the hot side streams of the vortex tubes to the heat exchangers may be different. The liquified gas which is taken out at 1r is about one-tenth to one-thirtieth part of the suction of the first compressor lb, and the following compressors and vortex tubes handle rapidly decreasing gas quantities, at lower and lower temperatures. By this means, the scheme of the process is rather favorable and economical. The normally gaseous product is in liquid form at atmospheric pressures and low temperatures, so that substantial insulation; is necessary to prevent evaporation losses.
FIG. 2 is a schematic temperature entropy (T,S) diagram of the process shown on FIG. 1. The initial state of the gas is 2a and it is compressed in the first com pressor to point 2b. An isothermal compression is shown on the drawing, because of clarity; however the compression is not isothermal but rather polytropic as it is shown on FIG. 2A. The compression heat has to be taken out in a condenser. Line 2b-2c represents the cooling in the cold exchanger after the condenser, point 2b the inlet of the first vortex tube. The hot stream of the first vortex tube is 20-21, which is brought back to initial temperature 21-21;. The cold stream of the first vortex tube is 2c-2d which is compressed again in the second compressor 2d-2e, and cooled in an exchanger. The cold exchanger after the second stage compression in reality hasto take out the polytropic compression heat plus the izobaric heat 2e-2f before entering the second vortex tube at 2f. The hot stream of this second vortex tube is 2f-2m1, and this is brought back infthe cold exchanger to ambient temperature m-a. The cold stream of the second vortex tube is Zf-Zg, and this is again compressed to 2g-2h, cooled in cold exchanger to 21, the inlet of the third vortex tube. The hot gas stream of this third vortex tube is 21-2n, and in the cold exchanger it is heated along line 2n-2a to ambient temperature. The cold stream of the vortex tube is 21-2k, and point 2p represents the liquid gas at atmospheric pressure on the boiling point curve. This T-S diagram is rather schematic, and refers to an assumed generalized flowsheet, not a specefic application.
FIG. 3 shows the generalized flowsheet of a threestage high pressure vortex tube liquefaction process. The gas enters at 30 into the first stage of the compressor, it is compressed to about 3 atm. and returns through condenser 3e to the second stage 3c. 1 is compressed to about 10 atm., returns through condenser 3f into the third stage 3d. It is compressed again to about 30 atm., passed through a third condenser to be cooled to ambient temperature and is further cooled in cold exchanger 3g before entering the first vortex tube 3):. From this, the hot gas stream3i is returned to the suction of the third stage 3d. The cold gas stream passes the cold exchanger 3k where it is cooled to a lower tem-.
perature and goes into the second vortex tube 31. Here the gas stream is split up, the central hot gas stream 3v returns through cold exchanger 3g into the suction of the second compressor stage 3c. The cold gas stream 3m of the second vortex tube 31 passes the final cold exchanger 3p where it is cooled again and enters the third vortex tube 3q. The central hot stream of the third vortex tube 3n passes through cold exchanger 3k into the suction of the first compressor stage. The cold stream of the third vortex tube Sr and the peripheral hot stream 30 is a mixture of liquid and gas at atmospheric pressure and low temperature. It is passed into the insulated flash drum 3s, where the liquid gas can be drawn off at 3t. The vapor passes through cold exchanger 3p into the suction of the first compressor stage. In this process the three stages of the compressor handle about the same quantity of gas, at nearly ambient temperatures but successively increasing pressure. The vortex tubes receive decreasing gas flowrates at successively lower temperatures. The gaseous product is in liquid form at atmospheric pressure and low temperature. Evidently the number of stages and vortex tubes may be varied form one to any number, according to the necessities of the gas and the process conditions.
FIG. 4 is a schematic temperature entropy (T,S) diagram of the liquefaction process shown on FIG. 3. The initial state of the gas is represented by 4a at 70 F and 1 atm. pressure. The three compression stages are 4a-4b, 4b-4c and 4c-4d, on the figure drawn as isothermal for the sake of clarity, but in reality they are polytropic and in series with a condenser to eliminate the compression heat as it is shown on FIG. 4A. The line 4d-4e represents the izobaric cooling of the cold exchanger ahead of the first vortex tube. The inlet of the first vortex tube is represented by 4e, and 4e-4f is the hot gas stream of the tube, nearly ambient temperature. The cold gas stream is 4e-4g, which is cooled in the second cold exchanger to 4g-4h. The second vortex tube heating effect is 4h-4j, which is heated to ambient temperature in the heat exchanger 4j-4b. The cooling process of the second vortex tube is 4h-4k, which is cooled to 4k-4l in the third cold exchanger. The third vortex tube 41 hot outlet is'4 l-4n, which is heated to ambient temperature 4n-4a in the cold exchanger. The cold outlet 4m of the third vortex tube is low temperature liquid gas at atmospheric pressure. This T-S diagram is rather schematic and refers to an assumed generalized flowsheet. A real refrigeration process has approximately the same scheme, with possible modifications only in the number of stages, and the values of temperatures and entropies may be established accordingly.
FIG. 5 is a generalized flowsheet of a gas liquefaction and separation-purification process using the low pressure vortex tube method of FIG. 1 and 2. It may be used on a variety of gas mixtures and here an oxygen liquefaction process is described an an exemple. The air is freed from dust in filter 5a and is compressed in compressor 5b to about3 atm. (45 psi) pressure. From the compressor it goes into the wash tower 5c in which it is sprayed with caustic soda to absorb the carbon dioxide. The heat exchanger 5d and absorber 5v eliminate the water vapor and other vapors from the air. The air is precooled in exchanger 5d and passed into the first vortex tube 5e. The hot stream of this vortex tube is returned, through condenser 50, to the suction of the first compressor. The cold gas stream passes into the countercurrent cold exchanger 5 and the silicagel or alumina adsorber 5k and from there into the second vortex tube 51. In the countercurrent cold exchanger the water is liquefied and taken out through 5h. The hot gas stream of the second vortex tube is recirculated through exchanger 5d into the suction of the first compressor. The cold gas stream of the second vortex tube 51 passes through cold exchanger 5m into the compressor 5n, where it is compressed to about 3 atm. After the compressor, the flow splits into two streams, one going to the bottom, the other to the upper part of the recitifi; cation column. The lower stream passes cold exchanger 5p where it is cooled and enters into vortex tube Sq. The central hot stream of the vortex tube is returned, through cold exchanger 5m into the suction of one of the compressors, the cold stream is passed through coil 5: in the bottom of the rectifying column and enters at the top of the tower, as liquid. The peripheral hot gas stream Sr is sent into the column. The other gas stream passes directly into the vortex tube and enters at the middle of the rectifying column as a gas, to help in the process. The gas at the top of the column is returned through cold exchanger 5p as gaseous nitrogen into heat exchanger 5g and may be used up or recirculated. This process is only a schematic example and it is claimed being applied to a large variety of gases, with simple or double rectifying column and other detail flow arrangements.
FIG. 6 is the schematic flowsheet of a gas liquefaction and separation-purification process using the high pressure vortex tube method of FIGS. 3 and 4. It may be applied on a large variety of gas mixtures and in this figure an oxygen production process is shown with atmospheric air as raw material. The air enters through the dust filter 6a into the first stage of the compressor, it is compressed to about 4 atm. pressure, passes through the carbon dioxide eliminator 6c and condenser 6d' to the second stage 6e, where it is compressed to about 16 atm. From here it passes through condenser 6f into the third stage of the compressor where it is compressed to atm. pressure and in condenser 6h is cooled back to ambient temperature. The air passes into cold exchanger 6i where'it is cooled below ambient temperature and enters into the first vortex tube 6j. The ho't'stream of this vortex tube returns to the suction of the first compressor, the cold stream passes through absorber 6.x and exchanger 6k into the second vortex tube 61. Then the hot stream is returned through exchanger 6i to the suction, the cold stream is split into two branches. The lower branch passes through heat exchanger 6m and absorber into the third vortex tube 6v, the cold stream of which goes into the lower part of the two-stage rectifying column through the coil into filter 6n and through exchanger 6v into the middle of the upper column. The central part of the hot stream returns through exchanger 6k into the suction. Eventually it may pass through exchanger 6p to recover more cold. The peripheral part of the hot gas stream is passed into the lower part of rectifying column. The liquid oxygen is extracted at the bottom of the lower rectifying column. From the top of the lower column, the nitrogen-rich mixture is passed through exchanger 62 into the top of the upper column. The vapor, pure nitrogen, from the top of the upper column is passed through exchangers (iv and 6z into the suction. This process is only a schematic exemple of the invention, and a wide range of application is claimed for different gas mixtures.
FIGS. 7, 8 and 9 show the schematic longitudinal and cross sections of an improved single inlet and single outlet vortex tube. FIG. 7 is a schematic longitudinal section of a single outlet vortex tube. The gas or gas mixture enters at 7a into the spiral channel of decreasing cross section 7b. The cross section and curvature of the channel are calculated for a linearly increasing tangential and centrifugal acceleration, with a smooth transition to the circular vortex 7c which has supersonic speeds at its peripheral parts. FIG. 8 is a cross section of the vortex tube through the inlet. To stabilize the vortex, the cylindrical entrance section 7d is gradually decreasing to about nine-tenths of its original diameter 7e, and after a short cylindrical section it is increased again to an enlarging cone 7f of about half angle. The end section of the tube is the spiral diffusor 7g, the cross section of which is shown on FIG. 9. It has tangential outlet 7h which may be designed using the same principles as the diffusor of a compressor or pump. The flowrate of the gas mixture through the vortex tube may be controlled at the inlet spiral 7c through a mechanical device the same way as it is described in US. Pat. No. 3,296,807 of Jan. 10, 1967, for single or multiple inlet vortex tubes. It is economical to use a single inlet up to about 2 inches inside diameter and a multiple inlet for larger vortex tubes. The single inlet vortex tube is shown here controlled by a lever and pin system, the control lever being 7j. Eventually the vortex tube may have an additional cold outlet 7m as shown with dotted lines.
The outlet of the vortex tube has a substantially different temperature from the inlet, and to prevent heat losses, it is insulated from the inlet part by an insulating gasket set 7k, which may be ceramic material, teflon or asbestos compound, or similar high strength insulating material. Eventually the insulation may be in the inside of the vortex tube and the diffusor in form of a ceramic coating. No structural details are shown, only the clamp 71 which was used in the experiments and which makes it easy to take apart the vortex tube and assures a tight highpressure seal.
FIG. l0 shows a possible flowsheet of a vortex tube refrigeration and liquefying process. The gas or gas mixture 100 is compressed in compressor 10b to a pressure of 1:3 to 1:5, depending on the gas mixture to be liquefied and the temperature to be obtained. The compression heat is extracted in condenser 10c and the gas mixtureis cooled to a low temperature in the regenerators or reversing cold exchangers 10d and 10e. Instead of the regenerators, special gas to gas cryogenic exchangers may be advantageous. The cold gas enters into the vortex tube 10f at the inlet 10g, and the liquefied gas is discharged at 10h into the heat exchanger l0j where it is cooled by the gas coming from the cold outlet 10k. Part of the liquid goes through the jacket of the vortex tube 101, 10m, the rest through pipe 10p directly into the separator vessel 10q. Here the liquid is drawn off at 10r and the gas returns through the regenerators 10d and 10a to the compressor. The cold gas 10k from the vortex tube is sent through exchanger 10j and pipe 10s into the separator vessel 10q. The gas from the upper central outlet l0t of the vortex tube is regulated by the control valve 10n as it is of higher temperature than the lower outlet, it is sent into a warmer section of the regenerators at 10v.
FIG. 11 shows the thermodynamic relationships of the above process on the temperature-entropy diagram. The gas 11a is compressed along line Ila-11b, it is cooled in the condenser to the initial temperature at constant pressure along line llb-l 1c and in the regenerators it is further cooled at constant pressure alongline llc-l 1d. At 11d it enters into the vortex tube, and it is separated into three streams. The liquefied gas is shown along l1e1lf-l1g is cooled in the heat exchanger, the liquid being shown at 11h and the gas at llj. The gas is returned through the heat exchangers to llj-lla. The cold outlet is shown along lid-11k, and returns through the heat exchangers to the suction of the compressors with the former gas stream along llk-l 1a. The hot side outlet is represented by the line lld-lll and is: returned along line llm-l la through theheat exchanger into the suction of the compressor.
FIG. 12 is a schematic diagram of a liquefaction and purification process for gas mixtures, using the rectifying column as a separation device and two vortex tubes as expansion cooling devices. The gas mixture enters at 12a and together with the recirculated gas stream 12b is compressed in compressor 124 to about to 200 psi pressure, and in aftercooler 12d it is cooled with water to ambient temperature. Moisture and other condensibles are taken out in the knockout drum 12c, but this may be left out if the gas stream :is dried and cleaned before entering the compressor. In heat exchanger 12 the gas mixture is precooled with the recycled hot" gas and the carbon dioxide and other condensibles are eliminated in the drum 12 before passingthe gas into the main cooling devices. The main cooling devices 12h, 121' may be regenerators, reversing exchangers or special cryogenic cold exchangers. The drawing shows reversing exchangers, with inlet reversing valves 12k and outlet reversing valves 121. After these exchangers there is an other separator 12m or absorption vessel, from which the cold gas enters into the first vortex tube 12n. The cold gas from the vortex tube passes into the top part of the lower high pressure section 12p of the rectifying column. The peripheral discharge l2q with the liquefied gas is discharged into the bottom of the high pressure section 12p. The central upper outlet of the'vortex tube is passed at l2q into the second low pressure vortex tube 12r. The lower outlet with the condensates from the peripheral outlet are passed into the lower bottom part of the upper low pressure section 12s of the rectifying column, where the non condensed gas is moving upwards, andthe purified higher molecular weight liquid is drawn off at 12:. The upper central discharge 12a of the low pressure vortex tube is light molecular weight not very cold gas, mixture and is recirculated through exchanger 12f into the suction of the compressor 12b. The bottom condensates of the lower high pressure section of the rectifying column 12p are lifted by the pressure difference at 12v into the middle part of the upper low pressure rectifying column 12s,
where they are separated into gas and condensate. The
condensed highrnolecular weight gases at the top of the high pressure section are sent to the top of the upper low pressure section where they are separated to gas and liquid. The cold gases at the top of the low. pressure column 12s are recirculated through the reversing exchangers 12h or l2j into the suction of the compressor 12b.
Instead of the three outlet vortex tube, one outlet tube may be used in this process, which will only cool the liquid and do not separate and liquefy it. Three outlet tube is shown because they allow to use substantially smaller rectifying columns without increasing the energy requirements.
The thermodynamic relationships of this process are shown schematically on FIG. 13. The gas mixture is compressed along 13a-13b in the compressor, is cooled to ambient temperature in the aftercooler along line 13b-13c, and is cooled in the precooler and the reversing exchangers 13c-13d. At 13d the gas mixture enters into the first vortex tube where it is separated into three streams. The lower outlet cold gas l3d-13c is passed into the high pressure rectifying column and is separated into liquid 13g and gas 13f. The peripheral outlet gas is entered into the same column along line l3h-13i, and is cooled along line 13i13f, so that it is partly condensed. The upper central outlet gas mixture of the first vortex tube is shown on line 13d-13k to enter into the second vortex tube. Here it is separated into three streams, the lower central 131 and the upper peripheral 13p being entered into the low pressure section of the column, where they are separated into liquid along 13l13m and into gas along l3l-l3n. The. gas at the top of the column is returned through the through the regeneratorsalong 13n-13a into the suction of the compressor. The top central outlet of the second vortex is recirculated separately along line 13q-13a into the compressor.
The separating process with rectifying column is a more complicated process and more expensive than the pure vortex tube process, however it may have some advantages, it may be controlled more easily to produce high purity gaseous products. However the liquefaction and separation may be more economically performed without rectifying columns, using only the vortex tube for cooling and separation.
A possible vortex tube liquefaction and separation process without rectifying column is shown schematically on FIG. 14. The inlet gas mixture 14a with the recirculated gas 14b are compressed in compressor 14c to about 80 to 200 psi pressure, and cooled to ambient temperature in the aftercooler 14d. The condensates are taken out in the knockout vessel 14e and the gas is precooled in exchanger 14f. The impurities are eliminated in the absorption vessel 14g and the gas mixture is passed into the reversing exchangers 14h or 14j, through inlet valves 14k. The outlet valves 14l pass the gas mixture into exchanger 14m, where it is cooled to a low temperature by the recirculating gas. Vessel 14n is an absorption vessel, from where the gas mixture passes into the first vortex tube 14p. This vortex tube cools the high molecular weight gases which leave the vortex tube at 14q into a heat exchanger l4r. The warmer low molecular weight gases leave at 14s and are recirculated into the precooler 14f. The gas from exchanger 14! goes into the liquid separator vortex tube 14a, which has one cold and two hot outlets on the figure. The cold gases leave at 14v, and are recirculated through heat exchangers l4: and 14m into the reversing exchangers. The condensed vapors leave at 14z into the liquid separator vessel 14x. A heat exchanger may eventually be positioned between the vortex tube 14a and the separator vessel 14x, as shown on FIG. 10. The gas from the separator vessel and from the hot end of the vortex tube is passed through exchanger 14m into the regenerators. If the condensates at the cold outlet 14v of the vortex tube are a significant quantity, the cold end may have a peripheral outlet in the form of a diffusor, the same as it is shown on the hot outlet and the vapors may be passed into the separator vessel 14x. These multiple outlet vortex tubes were claimed as new inventions in a former patent application of applicant.
FIG. 15 is a schematic temperature-entropy diagram of the liquefaction and separation process shown on FIG. 14. The incoming gas, with part of the returning gas is compressed in the compressor along line 15a-15b, it is cooled in the intercooler and aftercooler along line l5b-15c, it is further cooled in the regenerators along line 15c-15d, and enters at 15d into the first vortex tube. The gas is separated in 3 streams. The heaviest parts leave through the central orifice expanding along line 15d-1Se and they are introduced into the second vortex tube. The light gas leaves at the hot end along line 15e-l5f, it is expanded along line 15f-15g and it transfers its heat along line 15g-15h to the heat exchangers and returns to the suction of the compressor. The gas in the second vortex tube is separated into 3 streams. The heavy gaseous part leaves through the central orifice along line 1511-15 j and by passing through heat exchangers it returns to the compressor along line l5j-1Sk-15a. The vapors with some gas leave on-the peripheral outlet along line l5h-'l5a, where they are cooled in the vessel along 151-15- m-15n, so that part of it is condensed to liquid along line l5n-15p, part'of it returns as gas through the heat exchangers into the compressor. The hot central outlet gas leaves along line 15h-15q, it is expanded along lSq-15k and returns to the suction of the compressor through heat exchangers along line 15k-15a.
FIG. 16 is a schematic flow diagram of a liquefaction process which uses the single outlet vortex tube of FIGS. 7, 8 and 9 instead of an expansion turbine. Two different uses of the vortex tube are shown. One as an expansion device (dotted lines) in a partial gas stream which uses the cold energy of the expanded gas in the heat exchanger to precool the main gas stream. The second vortex tube is used as a main expansion device which discharges the partially liquefied gas into the separator vessel. The process starts with the incoming gas stream 16a, which is compressed in compressor 16b to a high pressure, the high pressure gas is cooled in heat exchangers 16c, 16d and 16e with the returning cold gas which was not liquefied, and passes into the vortex tube 16f where it expands, cools down and is partly liquefied, and passes into the separator vessel 163, where the level control acting on valve 16h discharges the liquefied phase. The gas of the separator vessel 16g returns at l6j through exchangers 16c, 16d and 16e into the suction of the compressor. Part of the lean gas mixture is bled off at 16k. Additional cooling may be obtained by expanding a partial gas stream and sending it through a heat exchanger into the compressor. The partial stream at 161 is passed into the vortex tube expansion device 16m, where it is cooled by expansion to a substantially lower temperature than in an expansion valve, and the cold gas is used in exchangers 16d and 16c to precool the compressed gas. An expansion valve 16p is shown with dotted lines, as an alternate to vortex tube 16f.
Already in 1946, it was pointed out that the Ranque effect seems to contradict the second law of thermodynamics, since it creates heat without external heat source. The temperature difference developed in the vortex tube as deducted from the classical thermodynamic theory of ideal gas flow is;
T, gas temperature at the inlet p gas pressure at the inlet p gas pressure at the outlet K adiabatic exponent of the gas 1 constant dependent of the construction of the vortex tube A more recent equation based on the dynamic heat exchange theory for the temperature difference in the vortex tube is:
x cold stream fraction g /G d: (A/B)St 1.95 for optimum design vortex tubes A surface area available for heat transfer B cross sectional area of the stream St tb/C, pV AT (l/b) (l m) the Stanton number w p /p pressure ratio through the vortex tube f F /F inlet nozzle area/diaphragm cross sectional area a (t'q/ot FTJ'l, where a, and a are the orifice coefficients for the inlet nozzle and for the diaphragm B (K l)(2/K 1)"* thermodynamic constant 8 K l/K Though my invention has been described in terms of particularly useful embodiments, it is limited only by the scope of the appended claims, wherein the terms gas is used in its broadest sense and includes, for instance, gas mixtures, natural gas, and gas-vapor mixtures.
1. A method of separating the components of a gaseous mixture by use of a vortex tube comprising the steps of: injecting the mixture under pressure tangentially into the vortex tube, developing a gaseous stream following and outer peripheral pattezm of flow about an axis, withdrawing the said peripherally flowing gas axially into a zone of larger diameter, so as to cause gaseous vapors to be thrown to the periphery, resulting in condensation and separation of the vapors as they encounter a larger diameter section of the tube, and removing the condensed vapors from the tube through a tangential (peripheral) outlet therein.
2. The separation method of claim 1 wherein the condensed vapors are conducted through a tangential (peripheral) outlet, shaped as a spiral diffusor of increasing diameter, so as to produce an aerodynarnically advantageous velocity distribution, thus obviating sharp changes in velocity, so as to enhance good separation efficiency, and to convert the kinetic energy of the fluid into pressure and thus increase the efficiency of the process.
3. A method for liquefying gases utilizing vortex tubes which produce hot and cold stream effluent as the prime cooling device which comprises partially expanding a compressed gas through a series of at least two vortex tubes wherein the low temperature effluent from the first and subsequent vortex tubes is separated from the high temperature effluent from each vortex tube; cooling this low temperature effluent from each vortex tube and conducting sequentially each low temperature effluent to the subsequent vortex tube until effluent containing liquid is obtained.
4. The method of claim 3 wherein the minimum pressure ratio across each vortex tube stage is about 2:1.
5. The method of claim 3 wherein the said hot stream effluent of subsequent vortex tube stages is employed to cool the inputs to prior vortex tube stages.
6. The method of claim 3 wherein a single polytropic compression of the gas sufficient to produce at least a 2:1 pressure ratio through all the vortex tube stages is effected prior to the first vortex tube stage.
7. The method of claim 3 wherein the gas is compressed and cooled prior to each vortex tube stage to provide at least a pressure ratio of 2:1 through each vortex tube stage.