US3292381A

US3292381A - Separation of natural gas by liquefaction with an injected hydrate inhibitor

Info

Publication number: US3292381A
Application number: US381064A
Authority: US
Inventors: Joseph E Bludworth
Original assignee: Coastal States Petrochemical Co
Current assignee: Coastal States Petrochemical Co
Priority date: 1964-07-08
Filing date: 1964-07-08
Publication date: 1966-12-20
Anticipated expiration: 1983-12-20

Description

BLUDWORTH SEPARATION OF NATURAL GAS BY LIQUEFACTION WITH Dec. 20, 1966 AN INJECTED HYDRATE INHIBITOR Filed July 8, 1964 4 Sheets-Sheet 1 fi/uawar/fi INVENTOR ATTO/F/VZVJ I 7 Dec. 20, 1966 BLUDWORTH 3,292,381

SEPARATION OF NATURAL GAS BY LIQUEFACTION WITH AN INJECTED HYDRATE INHIBITOR Filed July 8, 1964 4 Sheets-Sheet 2 1966 J. E. BLUDWORTH SEPARATION OF NATURAL GAS BY LIQUEFACTION WITH AN INJECTED HYDRATE INHIBITOR 4 Sheets-Sheet 3 Filed July 8, 1964 NM N MWN v fi/uc/Wo 2% INVENTORS z 0 w w u WQN.

Arrow 5m Filed July 8, 1964 Dec. 20, 1966 J. E. BLUDWORTH 3,292,331

SEPARATION OF NATURAL GAS BY LIQUEFACTION WITH AN INJECTED HYDRATE INHIBITOR 4 Sheets-Sheet 4 INVEN OR. yaw Z2 ATTO/P/VEVJ United 1 States Patent 3,292,381 SEPARATION OF NATURAL GAS BY LIQUE- FACTION WITH AN INJECTED HYDRATE INHIBITOR Joseph E. Bludworth, Corpus Christi, Tex., assignor to Coastal States Petrochemical Company, Corpus Christi, Tex., a corporation of Delaware Filed July 8, 1964, Ser. No. 381,064 26 Claims. (Cl. 62-20) This invention relates to an improved method of separating components of natural gas streams and more particularly to a method of separating (i) methane and varying amounts of ethane, (ii) propane and/or ethane and higher boiling point hydrocarbon constituents, and (iii) water vapor in a natural gas stream under superatmospheric pressure.

Many processes have been developed and numerous plants constructed to accomplish the separation set forth above. These processes principally involve external refrigeration, cooling by expansion of natural gas, and/ or solvent absorption. The processes using external refrigeration or cooling by expansion of natural gas are not as efiicient as solvent absorption but solvent absorption has the objection of both high initial cost and operating cost.

It is a general object of the present invention to provide an economical and efficient method of separating from natural gas streams the various components referred to above and yield a stabilized liquid product of merchantable quality. A plant constructed in accordance with the present invention costs about one-half to three-fourths of the cost of an oil absorption system having the same efficiency.

A more particular object of the present invention is to provide such a method of separation of components of natural gas streams in which no external refrigeration is used and in which the stabilizer is a fractionating tower requiring no external reflux.

Other and further objects, features, and advantages will be apparent from the following description of the presently preferred examples of the present invention, given for the purpose of disclosure and taken in conjunction with the accompanying drawings, where like character references designate like parts throughout the several views and where:

FIGURE 1 is a schematic flow diagram of examples of the present invention,

FIGURE 2 is a schematic flow diagram of other examples of the present invention,

FIGURE 3 is a schematic flow diagram of still other examples of the present invention, and

FIGURE 4 is a schematic flow diagram of another example of this invention.

The present invention is based upon the discovery that (i) methane and varying amounts of ethane, (ii) propane and/ or ethane and higher boiling point hydrocarbon constituents, and (iii) water vapor (if present) in natural gas streams under superatmospheric pressure may be sepa rated from each other with a high degree of efficiency and yet economically by (1) injecting a hydrate inhibitor into the gas stream, (2) cooling the gas stream until a portion of the methane liquefies forming a layer of liquid hydrocarbons and a layer of hydrate inhibitor-water mixture (3) separating from each other the two liquid layers formed in step (2), (4) passing the gas stream remaining from step (2) through a turbo expander to condense a portion of the gas stream to a liquid, (5) passing at least the liquid from the turbo expander to the top of the fractionating zone of a fractionating tower, (6) flashing a portion of the methane and ethane from the liquid hydrocarbons separated in step (3), (7) passing the liquid remaining from step (6) into the fractionating tower,

3,292,381 Patented Dec. 20, 1966 (8) distilling the liquid in the fractionating tower free of external reflux to form methane and/or ethane gas and a stabilized liquid product of ethane and/or propane and higher boiling point constituents, and (9) performing the cooling of step (2) free of external refrigeration with the gas leaving the turbo expander alone or with other hydrocarbon fluids taken from the gas stream.

In the foregoing and in the remainder of this specification and claims the term external refrigeration means the use of a cooling medium or power produced other than by the expansion of gas in the present process or by gas produced in the fractionating tower or flashing of liquids of the present process.

While water vapor is normally present in natural gas streams, if such vapor should not be present in a particular gas stream, then the hydrate inhibitor need not be added and, consequently, would not be separated from the liquid hydrocarbons in step (3). The water vapor is removed, not because it is desirable to recover it as a product, but rather to prevent it from freezing and clogging the equipment.

It is essential that in step (2) the gas stream is cooled until a portion of the methane liquefies. When the methane liquefies, necessarily the water vapor, a large portion of the propane and higher boiling point constituents, and some of the ethane liquefies.

It is necessary to eflicient recovery that the turbo expander produce both a liquid and a gas. The turbo expander can be of any suitable and available type of axial flow or radial flow turbo expander which operates by isentropic expansion with the production of useful work and which must be capable of handling liquids produced during expansion in the turbo expander.

It is necessary that the liquid from the turbo expander be introduced into the fractionating tower at the top of the fractionating zone which, in a bubble cap and plate tower, would be the top plate. The fractionating tower in which the liquid product is stabilized may be any tower containing a reboiler and plates or packing and which is used for the purpose of separating by distillation various components of a stream of fluid.

Example 1 Referring now to FIGURE 1, natural gas stream constituting the feed gas had, in addition to its water vapor content, the following analysis in mol percent:

This feed gas in the feed line 10 had a temperature of 65 F., a pressure of 785 p.s.i.a., and was introduced at the rate of 50,300,000 cubic feet per day measured at 14.65 p.s.i.a. and 60 F. Methyl alcohol was injected into this gas through a line 12 as a hydrate inhibitor or anti-freeze to prevent the moisture in the feed gas from freezing. After the injection of the alcohol the stream was split at the line 14 with part of the stream passing through indirect

heat exchange coolers

16 and 28 and the other part through another indirect heat exchange cooler 18. Within these

coolers

16, 28, and 18 the gas was cooled sufliciently to liquefy a portion of the methane. Cooling the stream this amount also caused liquefaction of all but a trace of the water and alcohol, a small portion of the ethane, carbon dioxide and nitrogen, and a major portion of the propane and higher boiling point hydrocarbons. Gas and liquids left the cooler 18 through a line 20, were mixed with gas and liquids from the cooler 28 at a line 30 and passed to a separator 32 at 65 F. and 775 p.s.i.a.

In the separator 32 the liquid hydrocarbons, the liquid nitrogen, the liquid carbon dioxide, the alcohol and the water collected in upper and lower layers of a liquid hydrocarbon, nitrogen and carbon dioxide mixture and an alcohol-water mixture respectively.

The remaining gas left the separator 32 through a line 34 and passed to the inlet side of an 1100 horsepower turbo expander 36. By the time the gas stream reached the turbo expander 36 all but a trace of the water and alcohol and most of the propane and higher boiling point constituents had removed from it.

The turbo expander 36 was operated so that the material leaving it had a temperature of 130 F. and a pressure of 235 p.s.i.a. At this temperature and pressure a portion of the gas was liquefied. This resulting liquid product contained some methane, ethane, carbon dioxide, nitrogen and all but a trace of the propane and higher boiling point constituents of the feed gas. The gas leaving the turbo expander 36 had the remaining nitrogen and carbon dioxide from the feed gas and the balance was, for all practical purposes, methane and ethane.

Both the liquid and gas from the turbo expander 36 were passed through a line 38 onto the top plate 40 of a bubble cap fractionating tower 42 operating as a stabilizer. Liquid on this top plate 40 was at ll F. and the pressure in the tower was 235 p.s.i.a., the same pressure as in the line 38 from the turbo expander 36. The gas entering fractionating tower 42 from the turbo ex pander 36 immediately passed out the top of the fractionating tower 42 through a line 44. This gas and other methane and ethane in the line 44 from the tower 42 and a separator 64 (as later described) passed countercurrently through the

coolers

28 and 16 to cool the feed gas as previously described. It left the cooler 16 at 52 F. and 235 p.s.i.a. and entered a compressor 46 driven by the turbo expander 36 from which compressor 46 the processed gas emerged in line 48 at 90 F. and 300 p.s.i.a.

The alcohol-water mixture in the separator 32 was withdrawn from the bottom of it through the line 52 and passed to a conventional system, not shown, for recovering the alcohol for recycling. The liquefied hydrocarbons, carbon dioxide, and nitrogen in the separator 32 were also withdrawn therefrom through a line 58 and passed through a pressure reducing regulator 60. This reduction in pressure resulting from passing through the pressure reducing regulator 60 caused a flashing of a portion of the liquid hydrocarbons, carbon dioxide, and nitrogen. The resultant gas and remaining liquid were passed through a line 62 to a separator 64 at a temperature of -110 F. and a pressure of 255 p.s.i.a. Under these conditions of temperature and pressure the gas contained methane, ethane, carbon dioxide, nitrogen, and only a trace of propane and higher boiling point constitucuts. The liquids which collected in the lower part of the separator 64 contained only a small percentage of methane, ethane, nitrogen, and carbon dioxide with the balance being propane and higher boiling point constituents.

Gas from the separator 64 was passed through a line 66 and into the line 44 from the top of the fractionating tower 42. The liquids which collected in the lower portion of the separator 64 were flowed through a line 68 and countercurrently through the cooler 18 from which they emerged at 35 F. and 245 p.s.i.a. This liquid was then passed through a line 70 and into the fractionating tower 42 as feed at the point in the column at which the gas temperature in the fractionating tower 42 was ap- 4. proximately the same as the temperature of the liquid in the line 70.

Within the :fractionating tower 42 the liquid feed from lines 38 and 70 flowed downwardly over the plates in countercurrent flow with vapors rising through the tower as a result of liquids in the lower part of the fractionating tower 42 being heated by passing through a conventional reboiler 72 heated by a heat medium supplied to the reboiler 72 through a line 74. The rising vapors were rich in methane, ethane, carbon dioxide, and nitrogen while the descending liquids were rich in propane and higher 'boiling point hydrocarbons. Normally for eflicient operation of a fractionating tower it is necessary to condense a portion of the rising vapors and return them to the tower by external reflux equipment including an external condenser, a reflux separator, a reflux pump, a spare pump, and instrumentation. However, in the present invention the cold liquids entering the top of the fractionating zone through the line 38 are feed and also accomplish the same result as the use of external reflux so that no external reflux is necessary.

Gas. formed by the fractional distillation process in the tower 42 passed out the line 44 together wit-h the gas which entered the fractionating tower 42 through the line 38. The stabilized propane and higher Boiling point constituents formed by the fractionating process in the tower 42 were withdrawn from the bottom of the tower through a line and cooled by passing through a heat exchanger 86.

No further description of the operation of the fractionating tower 42 is necessary as its operation, other than the use of the liquids from the turbo expander 36 as reflux in this combination rather than the use of an external reflux is conventional and well known in the art.

In this example the minimum temperature of the material leaving the turbo expander 36 was F. but because natural gas streams making up the feed gas fluctuate in quality and pressure there would have been produced, especially by increases in pressure, drops in temperature immediately downstream of the turbo expander 36, which would have caused the temperature of the material leaving the turbo expander to drop below this desired minimum and result in more liquid methane than was desired being formed by the expander 36. Therefore, means were provide-d to maintain the temperature immediately downsteam of the turbo expander 36 at the desired minimum temperature. This means was a bypass line 9 for bypassing a portion of the cool- 1ng gas that would normally flow through the cooler 28 thereby raising the temperature of the gas that enters,

Components: Percentages N 0.51 CO 0.77 CH 94.76 C2H5 C H 0.13 C H 0.01

0 C H and higher 0 The stabilized liquid products leaving the heat exchanger 86 had the following analysis:

Example 2 In the previous example nearly all the ethane passed out the top of the fractionating tower 42 as a gas and only a small amount of it was recovered as a liquid. The system of FIGURE 1 may also be operated to recover much of the ethane as a liquid with the other stabilized liquid products leaving the heat exchanger 86. When the system is operated to recover ethane as a liquid it operates essentially the same as in Example 1 except that the fractionating tower 42 is operated at a sufiiciently low enough bottom temperature to leave as a liquid most of that ethane which enters the tower as a liquid. Additionally, the temperatures and pressures throughout the system will change slightly due to a reduction in the volume of residue gas from the top of the fractionating tower 42. There is this reduction in volume because the ethane that enters the fractionating tower 42 as a liquid remains as a liquid and is not changed to a gas.

In the system of FIGURE 1 is operated to recover ethane as explained in the previous paragraph using the feed gas with the same temperature, pressure, constituents, and rate of flow and with the injection of methyl alcohol, the gas will be cooled sufiiciently in the

coolers

16, 28 and 18 to liquefy a portion of the methane, all but a trace of the water and alcohol, a small portion of the ethane, carbon dioxide and nitrogen, and' a portion of the propane and higher boiling point hydrocarbons. The gas and liquids from the coolers 18 and 28 enter the separator 32 at -60 F. and 775 p.s.i.a. In the separator 32 the liquid hydrocarbons, liquid nitrogen, the liquid carbon dioxide, and the alcohol and the water collect in upper and lower layers of a liquid hydrocarbomnitrogen, and carbon dioxide mixture and an alcohol-water mixture, respectively.

The remaining gas leaves the separator 32 and enters the turbo expander 36 which is operated under conditions that the material leaving it has a temperature of 125 F. and a pressure of 235 p.s.i.a. At this temperature and pressure a portion of the gas is liquefied. The resulting liquid product contains some methane, ethane, carbon dioxide, nitrogen and all but a trace of the propane and higher boiling point constituents of the feed gas. The gas leaving the turbo expander 36 has the remaining nitrogen and carbon dioxide from the feed gas and the balance is, for all practical purposes, methane and ethane.

Both the liquid and gas from the turbo expander 36 passes onto the top plate 40 of the fractionating tower 42. A liquid on this top plate 40 is at l F. and the pressure in the tower is 235 p.s.i.a., the same pressure as in the line 38 from the turbo expander 36. Gas entering the fractionating tower 42 from the turbo expander 36 passes immediately out the top of the fractionating tower 42 through the line 44. This gas and other methane and ethane in the line 44 from the separator 64 passes countercurrently through the

coolers

28 and 16 to cool the feed gas as previously described. It leaves the cooler 16 at 53 F. and 235 p.s.i.a. and leaves the compressor 46 at 90 F. and 300 p.s.i.a.

The alcohol-water mixture in the separator 32 is withdrawn through the line 52 for recovery. The liquid hydrocarbons, carbon dioxide and nitrogen mixture in the separator 32 is Withdrawn through the line 58 and pressure reducing regulator 60 resulting in the flashing of a portion of the mixture. The resultant gas and remaining liquid passes to the separator 64 at a temperature of -105 F. and a pressure of 255 p.s.i.a. Under these conditions of temperature and pressure the gas contains ethane, methane, carbon dioxide, nitrogen and only a trace of propane and higher boiling point constituents. The liquids in the lower part of the separator 64 contain only a small percentage of methane, ethane, nitrogen and carbon dioxide with the balance being propane and higher boiling point constituents.

Gas from the separator 64 passes into the line 44 from the top of the fractionating tower 42. The liquids in the lower portion of the separator 64 flow countercurrently through the cooler 18 from which they emerge at 90 F. and 245 p.s.i.a. This liquid is then passed to the fractionating tower 42 as feed at the point in the column at which the gas temperature in the fractionating tower 42 is approximately the same as the temperature of the liquid in the line 70.

Within the fractionating tower 42 the reboiler 72 is maintained at a sufiiciently low temperature that the rising vapors in the fractionating tower 42 are rich in methane, carbon dioxide, and nitrogen, but not in ethane The stabilized ethane, propane and higher boiling point constituents are withdrawn from the bottom of the tower 42 through the line and cooled by passing through the heat exchanger 86. I

In this example the processed gas leaving the compressor 46 through the line 48 has the following analysis:

Components: Percentages N 0.52 C0 0.66 CH 96.16 c 1 1 2.54 C H 0.12 C4H1Q 0 C H and higher 0 The stabilized liquid products leaving the heat exchanger will have the following analysis:

Components: Percentages N 0 CO 3.68 CH 1.23 C H 40.49 C H 30.37 C H 13.80 C H 4.91 C H and higher 5.52

Example 3 This example with FIGURE .2-uses the same general physical arrangement as FIGURE 1 except with respect to the coolers.

In thisexample, the natural gas stream constituting the feed gas has, in addition to its water vapor content, the

This gas in the feed line 100 has a temperature of 80 F., a pressure of 450 p.s.i.a., and a rate of flow of 50,300,000 cubic feet per day. To this gas through the line 102 is injected methyl alcohol as an anti-freeze. After the injection of the alcohol the stream is passed through an indirect heat exchange cooler 104 Within which it is cooled sutficiently to liquefy a small portion of the methane, ethane, and nitrogen, a larger portion of the other hydrocarbons, and all but a trace of the alcohol and Water vapor. The gas and liquids leaving the cooler 104 are passed through a line 106 to a separator 108 at -30 F. and 445 p.s.i.a. The liquid hydrocarbons, the nitrogen, the alcohol, and the water collect in'the lower portion of the separator 108 in upper and lower layers of liquid hydrocarbon and nitrogen mixture and an alcohol-water mixture respectively while the remaining gas passes from the separator 108 through a line 109 to another indirect heat exchange cooler 110 for further cooling and resulting liquefaction of a small portion of the methane, ethane, and nitrogen, a larger portion of the other hydrocarbons, and any of the alcohol and Water which has not previously condensed in the cooler 104 such as during the time required in commencing operations. Gas and liquid from the cooler 110 pass through a line 112 and enter a separator 114 at 80 F. and 440 p.s.i.a.

The remaining gas leaves the separator 114 through a line 116 and passes to the inlet side of a turbo expander 118. By the time the gas stream reaches the turbo expander 118 all but a trace of the water and alcohol and most of the propane and higher boiling point constituents are removed from it. The turbo expander is operated so that the material leaving it has a temperature of -180 F. and a pressure of 80 p.s.i.a. At this temperature and pressure a portion of the gas is liquefied. This resulting liquid contains some methane, ethane, and nitrogen and all but a trace of the propane and higher boiling point constituents of the feed gas. The gas leaving the turbo expander 118 contains the remaining nitrogen of the feed gas and the remainder is, for all practical purposes, methane and ethane.

Both the liquid and gas from the turbo expander 118 are passed through a line 120 onto the top plate 122 of a bubble cap fractionating tower 124 operating as a stabilizer. Liquid on this top plate 122 is at 70 F. and the pressure is 75 p.s.i.a. The gas entering the fractionating tower 124 immediately passes out the top of it through a line 126. This gas and other methane and ethane in the line 126 from the tower 124 and from a separator 146 (as later described) passes countercurrently through the

coolers

110 and 104 to cool the feed gas as previously described. It leaves the cooler 104 at 60 F. and 75 p.s.i.a. and enters a compressor 128 driven by the turbo expander 118 from which compressor 128 the processed gas emerges in line 130 at 130 F. and 150 p.s.i.a.

The alcohol-water mixture in the separators 108 and 114 is withdrawn from the bottom of each of these separators through the lines 130 and. 132 respectively and passes to a conventional system, not shown, for recovering the alcohol for recycling. The liquid hydrocarbons and nitrogen in the liquid hydrocarbon layer in the sep arator 108 are withdrawn therefrom through the line 134 and pass through a pressure reducing regulator 136. Likewise, liquid hydrocarbons and nitrogen in the liquid hydrocarbon and nitrogen layer in the separator 114 are continuously withdrawn through a line 138 and pass through a pressure reducing regulator 140. The reduction in pressure resulting from passing through the pressure reducing regulators causes flashing of a portion of the liquid hydrocarbons and nitrogen. The resultant gas and remaining liquid are passed through a :line 142 to a separator 146 at a temperature of 135 F. and a pressure of 95 p.s.i.a. Under these conditions of temperature and pressure the gas contains methane, ethane, nitrogen, and only a trace of propane and higher boiling point constituents. The liquids which collect in the lower part of the separator 146 contain only a small percentageof methane, ethane, and nitrogen with the remainder being propane and higher boiling point constituents.

Gas. from the separator 146 is passed through a line 148 into the line 126 from the top of the fractionating tower 124. The liquid hydrocarbons in the lower portion of the separator 146 are passed through a line 150, through an indirect heat exchange cooler 152 as the cooling medium, and from the cooler 152 through a line 154 into the fractionating tower 124 as feed at the point in the tower at which the gas temperature is approximately the same as the temperature of the liquid in the line 154. Within the fractionating tower 124 the liquid feed from the

lines

120 and 154 flow downwardly over the plates in countercurrent fiow with vapors rising through the tower as a result of liquids in the lower part of the fractionating tower 124 being heated by passing through a conventional reboiler 156 heated by heat medium sup plied to the reboiler 156 through a line 158. Stabilizer tion takes place in the fractionating tower 124 in the same manner as in the fractionating tower 42 of Example 1.

Gas formed by the distillation process in the tower 124 passes out the line 126 together with the gas which enters the fractionating tower 124 through the line 120. The stabilized propane and higher boiling point constituents formed by the distillation process in the fractionating tower 124 are withdrawn from the bottom of the tower through a line 160 and cooled by passing through the cooler 152.

In this example the desired minimum temperatureof the material leaving the turbo expander 118 is 180 F. A bypass line 113 for feed gas is provided across the cooler 110. Flow of gas through this bypass line 113 is controlled by the temperature controlled throttling valve which valve is open when the temperature in line immediately downstream of the turbo expander 118 drops below 180 F. Opening this valve 115 causes the temperature at the downstream side of the turbo expander 118 to rise to the desired minimum.

In the example just given theprocessed gas leaving the compressor 128 through the line has the following analysis:

The stabilized liquid products leaving the heat exchanger 152 have the following analysis:

Components: Percentages N 0 CH 0 C H 0.34 C H 38.07 C H 32.49 C H 11.30 C H and higher 17.80

Example 4 In the previous example nearly all the ethane passed out the top of the fractionating tower as a gas and only a small amount of it was recovered as a liquid. The system of FIGURE 2, like the system of FIGURE 1, may also be operated to recover much of the ethane as a liquid with other stabilized liquid products leaving the heat exchanger 152 by operating the fractionating tower 124 at a sutliciently low bottom temperature to leave as a liquid the ethane which enters the tower 124 as a liquid.

To recover ethane in the manner previously described with the system of FIGURE 2, if the same feed gas having the same temperature, pressure, and rate of flow also is injected with methyl alcohol, it is cooled in the cooler 104 sufficiently to liquefy a portion of the methane, ethane, and nitrogen, a larger portion of the other hydrocarbons, !and all but a trace of the alcohol and water vapor. The gas and liquids leaving the cooler 104 enter the separator 108 at -25 F. and 445 p.s.i.a. The liquid hydrocarbons, the nitrogen, the alcohol, and the water collect in the lower portion of the separator 108 in :upper and lower layers of liquid hydrocarbon and nitrogen mixture and an alcohol-water mixture respectively. The remaining gas passes from the separator 108 and through the cooler 110 resulting in liquefaction of a small portion of the methane, ethane and nitrogen, '21 larger portion of the remaining hydrocarbons, and any of the alcohol and water which is not previously condensed. Gas and liquid from the cooler 110 enter the separator 114 at 70 F. and 440 p.s.i.a.

The remaining gas leaves the separator 1 14 and passes to the inlet side of the turbo expander 118. By this time all but a trace of the Water and alcohol and most of the propane and higher boiling point constituents are removed. Turbo expander 118 is operated so that the material leaving it has a temperature of 170 F. and a pressure of 80 p.s.i.a. At this temperature and pressure a portion of the gas is liquefied. This resulting liquid contains some methane, ethane, nitrogen and all but a trace of the propane and higher boiling point constituents of the feed gas. The gas leaving the turbo expander 118 contains the remaining nitrogen of the feed gas and the remainder is, for all practical purposes, methane and ethane.

Both liquid and gas from the turbo expander 118 enter onto the top plate 122 of the fractionating tower 124 which top plate is at .155 F. and the pressure is 75 p.s.i.a. The gas entering the fractionating tower 124 immediately passes out the top of it through a line 126.

This gas and other methane from the tower 124 and from the separator 146 pass countercurrently through the

coolers

110 and 104 to cool the feed gas previously described. The gas leaves the cooler 104 at 60 F. and 75 p.s.i.a. and leaves the compressor 128 at 130 F. and 150 p.s.i.a.

The alcohol water mixture in each of the separators 108 and 114 and the liquid hydrocarbons and nitrogen in the same separators are withdrawn and treated identically as in Example 3. The gas and liquid after a flashing of a portion of the liquid enters the separator 146 at a temperature of 125 F. and a pressure of 95 p.s.i.a. Under these conditions of temperature and pressure the gas in the separator 146 contains methane, ethane, nitrogen and only a trace of propane and higher boiling point constituents. The liquids which collect in the lower portion of the separator 146 contain only a small percentage of methane, ethane, and nitrogen with the remainder being propane and higher boiling point constituents.

Gas from the separator 146 passes through the line 148 to the line 126 from the top of the fractionating tower 124 while liquid hydrocarbons pass through the indirect heat exchange cooler 152 as a cooling medium and from there into the fractionating tower 124 as feed at the point in the tower at which the gas temperature is approximately the same as the temperature of the liquid in the line from the cooler 152.

Within the fractionating tower 124 the liquid feed from the

lines

120 and 154 flows downwardly with a reboiler being operated at 'a sufficiently low temperature that the condensed ethane is not vaporized. Stabilization takes place in the fractionating tower 124 in the same manner as in the fraotionating tower 42 of Example 2. Gas formed by the distillation process in the tower 124 passes out the line 126 together with the gas that enters the fractionating tower 124 through the line 120. The stabilized ethane, propane, and higher boiling point constituents formed by the distillation process are withdrawn from the bottom of the tower and cooled by the cooler 152.

In the example just given the processed gas leaving the compressor 128 has the following analysis:

Components: Percentages N 1.29 CH 97.31 C H 1.37 C H 0.03 C H Trace C5H12 O C H and higher 0 The stabilized liquid products leaving the heat exchanger have the following analysis:

Components: Percentages N 0 CH 1.41 C H 39.32 C H 22.99 C H 19.15 C H 6.65 C H and higher 10.48

Example 5 This example of FIGURE '3 uses the same general arrangement as FIGURE 1 except principally with respect to the coolers.

In this example, the natural gas stream constituting Gas in the feed line 200 is at a temperature of 70 F., a pressure of 67 p.s.i.a., and flows at the rate of 50,300,000 cubic feet per day. To this gas through the line 202 methyl alcohol is injected as an anti-freeze. After the injection of the alcohol the stream is split at a line 204 with a portion :of the stream passing through an indirect heat exchange cooler 206 and the other portion passing through another indirect heat exchange cooler 208, through a line 210, through another heat exchange cooler 212, through a line 214, and through another heat exchange cooler 2'16. Within these

coolers

206, 208, 212, and 216 the gas stream is cooled sufficiently to liquefy a small portion of the methane and ethane, a large portion of the propane and higher boiling point constituents, and all but a trace of the alcohol and water. Gas and liquids leave the cooler 206 through a line 218 and are joined with gas and liquids from the cooler 216 in a line 220 and passed to a separator 222 at F. and 65 p.s.i.a. The liquid hydrocarbons, the alcohol, and the water collect in the lower portion of the separator 222 in upper and lower layers of liquid hydrocarbon and an alcohol-water mixture respectively.

The gas remaining leaves the separator 222' through a line 223 and passes to the inlet side of a turbo expander 224 driving an electric generator 226. By the time the gas stream reaches the turbo expander 224 all but a trace of the water and alcohol and most of the propane and higher boiling point constituents are removed from it. The turbo expander 224 is operated so that the material leaving it has a temperature of 200 F. and a pressure of 20 p.s.i.a. At this temperature and pressure a portion of the gas is liquefied. This resulting liquid contains some methane and ethane and all but a trace of the propane and higher boiling point constituents. The gas leaving the turbo expander 224 contains, for all practical purposes, only methane and ethane.

Boththe liquid and gas from the turbo expander 224 are passed through a line 228 into a separator 230. Gas from the separator 230 is passed through a line 232 to a line 234 from the top of a fractionating tower 236. The liquid hydrocarbons which collect in the lower portion of the separator 230 are withdrawn therefrom through a line 1235 and are pumped by a pump 238 (powered by the generator 226) to a pressure of 230 p.s.i.a. to force them int-o the fractionating tower 236 and onto the top plate 240. The liquid flowing into the tower 236 is at -200 F. but the liquid on the top plate 240 is only 130 F. as a result of being warmed by the rising vapors in the tower 236.

The methane and ethane released in the fractionating tower 236, as later described, leave the top of the fractionating tower 236 at 30 F. and a pressure of 200 p.s.i.a. through the line 234. A pressure reducing regulator 242 in the line 234 ahead of its connection with the line 232 from the separator 230 reduces the pressure in line 234 to 20 p.s.i.a. with a corresponding drop in temperature. This gas in line 234 from the separator 230 and the fractionating tower 236 together with other methane and ethane from

separators

248 and 254 pass countercurrently through the cooler 206 to cool a portion of the feed gas as previously described. The gas leaves the cooler 206 at 60 F. and 15 p.s.i.a.

The alcohol-water mixture in the separator 222 is withdrawn through a line 242 and passed to a conventional system, not shown, for recovering the alcohol for recycling. The liquid hydrocarbons in the separator 222 are removed and pass through a line 244 at 65 p.s.i.a. and 150 F. to the cooler 216 as the cooling medium. Within the cooler 216 pressure is reduced slightly on the liquid hydrocarbons and then they are warmed to 130 F. by the feed gas. At these conditions of pressure and temperature a portion of the methane and ethane in the liquid hydrocarbons is changed from liquid to gas and the heat of vaporization needed for this change of state comes from the gas which is passed through the cooler 216 for cooling.

The gases and liquids used as a cooling medium in the cooler 216 are passed through a line 246 to a separator 248 in which the pressure is maintained at 50 p.s.i.a. In this separator 248 the gas formed in the cooler 216 is separated from the liquid hydrocarbons and passed through a line 250 to the line 234. The liquids remaining in the separator 248 are passed through a line 251 to the cooler 212 as the cooling medium. Here the pressure on liquid hydrocarbons is dropped slightly and the liquid hydrocarbons warmed to 60 F. by the feed gases flowing through the cooler 212. At these conditions of temperature and pressure a portion of the methane and ethane in the liquid hydrocarbons is vaporized and the heat to supply the heat of vaporization is taken from the feed gas. This cooling material is then passed from the cooler 212 through a line 252 and enters a separator 254 in which the pressure is maintained at 35 p.s.i.a. The gas formed by the cooling medium passing through the cooler 212 separates from the remaining liquids and is passed through a line 256 into the line 234.

The liquid remaining in the separator 254 is passed through a line 258 to the cooler 208 as the cooling medium. Again conditions are adjusted to permit vaporization of the cooling medium within the cooler 208. Pressure on this liquid in the cooler 208 is reduced slightly and then it is warmed to 30 F. by the feed gas. This allows the methane and ethane and a portion of the propane in the liquid hydrocarbons to vaporize with the heat of vaporization being supplied by the feed gas. From the cooler 208 the cooling medium is passed through a line 260 to a separator 262 in which the pressure is maintained at 20 p.s.i.a.

Because the gas in the separator 262 contains propane in addition to methane and ethane both the gas and the liquid hydrocarbons in the separator 262 are sent to the fractionating tower 236. The liquids from the separator 262 are passed through a line 264 to a pump 266 powered by the electric generator 226 which pump 266 develops 220 p.s.i.a pressure on the liquids and forces them into the .tractionating tower 236 at a point at which the temperatue of the gas in the tower 236 is l0 F. which is approximately the same as that of the liquids in the line 264 at that point.

The gases in the separator 262 are compressed by a compressor 268 powered by the electric generator 226, passed through a line 280, cooled in a fan cooled heat exchanger 282 (powered by the generator 226) to remove the heat of compression and liquefy a portion, joined with the liquids in the line 264, and passed to the fractionating tower 236.

Within the fractionating tower 236 the liquid feed from the

lines

235 and 264 flow downwardly over the plates in countercurrent flow with vapors rising through the tower as a result of liquids in the lower portion of the fractionating tower 236 being heated by passing through a conventional reboiler 266 heater by a heat medium supplied to the reboiler 266 through a line 268. Stabilization in the fractionating tower 236 takes place in the same manner as in the fractionating tower 42 of Example 1.

Gas formed by the distillation process in the fractionating tower 236 passes out the line 234 as previously described. The stabilized propane and higher boiling point constituents formed by the distillation process in the tower 236 are withdrawn from the bottom of the tower through a line 270 and cooled by passing through a fan cooled heat exchanger 272 powered by the generator 226.

A bypass line 207 bypasses feed gas to the cooler 206.:

downstream of line 256 has the following analysis:

Components: Percentages CH 98.84 C H 5.01 C H 0.14 C H 0.01 C5H12 0 C H and higher 0 The stabilized liquid products leaving the heat exchanger 272 will have the following analysis:

Components: Percentages CH 0 C H 0.51 C H 54.40 C H 29.91 C H 9.36 C6H14 and higher 13 Example 6 In the previous example nearly all the ethane passed out the top of the fractionating tower 236 as gas and only a small portion of it was recovered as a liquid. The system of FIGURE 3, like the systems of FIGURES 1 and 2, may be operated to cover much of the ethane as a liquid by lowering the bottom temperature in the fractionating tower 236.

If the system of Example 5 is operated to recover ethane as a liquid using this same feed gas with the same temperature, pressure, and rate of flow with a similar injection of methyl alcohol the gas stream will be cooled in the

coolers

206, 208, 212, and 216 sufficiently to liquefy a small portion of the methane and ethane, a large portion of the propane and higher boiling point constituents, and all but a trace of the alcohol and Water. Gas and liquids enter the separator 222 at 148 F. and 65 p.s.i.a. The

liquid hydrocarbons, the alcohol, and the water collect in the lower portion of the separator 222 as previously described with resrzect to Example 5.

The gas which leaves the separator 222 and passes to the turbo expander 224 has all but a trace of the water and alcohol and most of the propane and higher boiling point constituents removed from it. The turbo expander 224 is operated so that the material leaving it has a temperature of 198 F. and a pressure of p.s.i.a. At this temperature and pressure a portion of the gas is liquified. The resulting liquid contains methane and ethane and all but a trace of the propane and higher boiling point constituents. The gas leaving the expander 224 contains, for all practical purposes, only methane and ethane. p

The liquid and gas from the turbo expander 224 enter the separator 230 with gas from the separator 230 passing to the line 234 from the top of. the fractionating tower 236 and the liquid hydrocarbons collecting in the lower portion of the separator 230 being pumped by the pump 238 at a pressure of 230 p.s.i.a. into the 'fractiona-ting tower 236 and onto the top plate 240. The liquid flowing into the tower 236 is at 198 F. but the liquid on the top plate 240 is at --130 F. as a result of being warmed by rising vapors in the tower 236.

The methane and a small amount of ethane released in the fractionating tower 236 leave the top of the tower at -l F. and a pressure of 200 p.s.i.a. through the line 234 and pass through the pressure regulator 242 which reduces the pressure to 20 p.s.i.a. with a corresponding drop in temperature. The gas in the line 234 from the separator 230 and the fractionating tower 236 together with methane and ethane from the

separators

248 and 254 pass through the coolers 206 to cool that portion of the feed gas previously described. The gas leaves the cooler 206 at 60 F. and 15 p.s.i.a.

The alcohol water mixture in the separator 222 is withdrawn and treated in the same manner as described with respect to Example 5. The liquid hydrocarbons in the separator 222 are removed and passed through the line 244 at 65 p.s.i.a. and 160 F. to the cooler 216 as a cooling medium. Within the cooler 216 the pressure is reduced slightly and the hydrocarbons are warmed to l F. by the feed gas. At these conditions of pressure and temperature a portion of the methane and ethane in the liquid hydrocarbons is changed from liquid to gas as in Example 5.

The gas and liquids used as a cooling medium in the cooler 216 are passed to the separator 248 in which the pressure is maintained at p.s.i.a. In this separator 248 gas and liquids are separated with the gas passing to the line 234. The liquids are passed to the cooler 212 as the cooling medium. Here the pressure on the hydrocarbons is dropped slightly and the liquid hydrocarbons warmed to 100 F. by the feed gases flowing through the cooler 212. At these conditions at temperature and pressure a portion 'of the methane and ethane in "the liquid hydrocarbons is vaporized and the heat to supply the heat of vaporization is taken from the feed gas. This cooling material is then passed to the separator 254 which is maintained at 35 p.s.i.a. The gas formed while the cooling medium passes through the cooler 212 passes to the line 234.

The liquid remaining in the separator 254 is passed to the cooler 208 as the cooling medium. Again, temperatures are adjusted to permit vaporization of the cooling medium within the cooler 208. Pressure on this liquid in the cooler 208 is reduced slightly and then it is warmed to F. by the feed gas. This allows the methane and ethane and a portion of the propane in the liquid hydrocarbons to vaporize with the heat of vaporization being supplied by the feed gas. From the cooler 208 the cooling medium is passed to the separator 262 in which the pressure is maintained at 20 p.s.i.a. 7

Because the gas in the separator 262 contains propane in addition to methane and ethane, both the gas and liquid hydrocarbons in the separator 262 are sent to the fractionating tower 236. The liquid from the separator 262 is pumped by the pump 266 at 220 p.s.i.a to the fractionating tower 236 at a point at which the temperature of the gas on the tower 236 is 55 F. -which is approximately the same as that of the liquids entering the tower ,at that point. The gas in the separator 262 is compressed by the compressor 260 and joined with liquids in the line 264 and. passed to the fractionating tower 236. The fan cooled heat exchanger 282 need not be operated here.

Within the fractionating tower 236 stabilization takes .place in much the same manner as in Example 2 under conditions at which only a small portion of the liquid ethane entering the fractionating tower 236 is vaporized.

Gas formed by the distillation process in the tower passes vout to the line 234 aspreviously described. The stabilized ethane and higher boiling point constituents formed in the tower are withdrawn from the bottom of the tower and passed through the fan cooled heat exchanger 272.

In the example just given the processed gas in the line 234 downstream of line 256 has the following analysis:

Comp onents Percentages CH 97.5 1 C H 2.45 C H 0.04 C Hm Trace C H 0 C H and higher 0 The stabilized liquid products leaving the heat exchanger have the following analysis:

Components: Percentages CH 0.30 C H 38.49 C H 34.09 0 H 18.03 C H 5.61 C l-I and higher 3.48

Example 7 drocarbons.

If the system of FIGURE 4 is operated to recover much of the ethane as a liquid together with other liquid stabilized products, and thereafter to separate the ethane from those other liquid products, using the same feed gas at line 310 with the same temperature, constituents, rate of flow and with injection of methyl alcohol at line 312 as in Example 2, but with an inlet pressure of 865 p.s.i.a., the gas will be cooled sufficiently in

coolers

316 and 328 to liquefy a portion of the methane, all but a trace of the water and alcohol, a small portion of the ethane, carbon dioxide and nitrogen, and a portion of the propane and higher boiling point hy- The gas and liquids from the cooler 328 enters the separator 332 at 60 F. and 860 p.s.i.a. In the separator 332 the liquid hydrocarbons, liquid nitrogen, the liquid carbon dioxide, and the alcohol and the water collect in upper and lower layers of a liquid hydrocarbon, nitrogen, and carbon dioxide mixture and an alcohol-water mixture, respectively.

The remaining gas leaves the separator 332 and enters the turbo expander 336 which is operated under conditions that the material leaving it has a temperature of 135 F, and a pressure of 235 p.s.i.a. At this temperature and pressure a portion of the gas is liquefied. The resulting liquid product contains some methane, ethane, carbon dioxide, nitrogen and all but -a trace of the propane and higher boiling point constituents of the feed gas. The gas leaving the turbo expander 336 has the remaining nitrogen and carbon dioxide from the feed gas and the balance is, for all practical purposes, methane and ethane.

Both the liquid and gas from the turbo expander 336 pass onto the top plate 340 of the fractionating tower 342. Liquod on this top plate 340 is at 1l5 F. and the pressure in the tower is 235 p.s.i.a, the same pressure as in the line 338 from the turbo expander 336. Gas entering the fractionating tower 342 from the turbo expander 336 passes immediately out the top of the fractionating tower 342 through the line 344. This gas and other methane and ethane in the line 344 from the separator 364 passes countercurrently through the

coolers

328 and 316 to cool the feed gas as previously described. It leaves the cooler 316 at 55 F. and 235 p.s.i.a. and leaves the compressor 346 at 93 F. and 300 p.s. i.a.

In this example the desired minimum temperature of the material leaving the turbo expander 336 is 135 F. A bypass line 301 for cooling gas is provided across the cooler 328. Flow of gas through this bypass line 301 is controlled by the temperature controlled throtttling valve 302, which valve is open when the temperature in the line 338 immediately downstream of the turbo expander 336 drops below 135 F. Opening this valve 302 causes the temperature at the downstream side of the turbo expander 336 to rise to the desired minimum.

The alcohol-water mixture in the separator 332 is withdrawn through the line 352 for recovery. The liquid hydrocarbons, carbon dioxide and nitrogen mixture in the separator 332 is withdrawn through the line 358 and pressure reducing regulator 360 resulting in the flashing of a portion of the mixture. The resultant :gas and remaining liquid pass to the separator 364 at a temperature of -l25 F. and a pressure of 255 p.s.i.a. Under these conditions of temperature and pressure the gas contains ethane, methane, carbon dioxide, nitrogen and only a trace of propane and higher boiling point constituents. The liquids in the lower part of the separator 364 contain only a small percentage of methane, ethane, nitrogen and carbon dioxide with the balance being propane and higher boiling point constituents.

Gas from the separator 364 passes into the line 344 from the top of the fractionating tower 342. The liquids in the lower portion of the separator 364 flow through line 370 and countercurrently through a cooler 308 from which they emerge at 90 F. and 245 p.s.i.a. This liquid is then passed 10 the fractionatin-g tower 342 as teed at the point in the column at which the gas temperature in the fractionating tower 342 is approximately the same as the temperature of the liquid in the line 371.

Within the fractionating tower 342 the re-boiler 372 is maintained at a sufiiciently low temperature that the rising vapors in the vfra-ctionating tower 342 are rich in methane, carbon dioxide, and nitrogen, but not in ethane. The stabilized ethane, propane and higher boiling point constituents are withdrawn from the bottom of the tower 342 through the line 380 and forced by pump 311 into a conventional de-ethanizing tower 315.

Tower 315 is a conventional fractionating tower operated to separate the ethane from the propane and higher boiling point constituents received from the fractionating 5 t-ower 342. The refrigeration requirement for condensing the necessary reflux is supplied at a heat exchange.

cooler 308 which is cooled by excess refrigeration from exchange with liquids from the separator 364 before they are fed into the tower 342. The condensed reflux liquids and the ethane rich vapors are transferred through a line 309 to a separator 317 operating at 415 p.s.i.a. and 40 F. from which the liquids are pumped back to the tower 315 through a line 313 by a pump 319 and the vapors are removed through a line 321. The propane and higher.

boiling point constituents are withdrawn from the bottom of the tower 315, a reboiler 320, a line 322 and cooled by a heat exchanger 325.

In this example the processed gas leaving the com- The ethane rich vapors withdrawn through line 321 will have the following composition:

Components: Percentages 2 0 CO 8.1 1 CH 2.71 C H 87.22 0 H 1.96 C H 0 C H 0 G l-I and higher 0 The propane and higher boiling point constituents withdrawn through line 322 will have the following analysis:

Components: Percentages C H 25.27 C H 8.99

661-114 and higher 7 In the schematic illustrations in FIGURES l, 2, 3, and

4, there is not shown the various accessories and miscellaneous equipment such as valves, liquid level controls,

- miscellaneous controls, instruments, etc. as such items are conventional, are well known in the art, and need not be here illustrated. Additionally, the construction and pressor 346 through the line 348 has the following anal- 17 method of operation under various conditions of the individual separators, heat exchangers, pumps, and turbo expanders are conventional and well known in the art and need no further explanation.

From the foregoing discussions, examples, and description of the invention it is apparent that the objects set forth herein as well as others have been achieved. Those skilled in the art will recognize that the principles of this invention may be applied in several ways, only a few of which have been exemplified herein specifically. Accordingly, the invention is to be limited only by the spirit thereof and the scope of the appended claims.

What is claimed is:

1. The method of separating methane and ethane from propane and higher boiling point constituents in a natural gas stream under superatmospheric pressure, said process comprising:

(a) cooling the gas stream until a portion of the methane, ethane, and other gaseous hydrocarbons are changed to liquid hydrocarbons.

(-b) passing the gas stream remaining after step (a) through a turbo expander to condense a portion of the gas stream to a liquid,

(c) passing the liquid from the turbo expander to the top of the fractionating zone of a fractionating tower,

(d) flashing a portion of the methane and ethane from the liquid hydrocarbons separated in step (a),

(e) passing the liquid hydrocarbons remaining from step (d) to the fractionating tower,

(f) distilling the liquid in the fractionating tower free of external reflux to form ethane and methane gas and a stabilized liquid product of propane and higher boiling point constituents, and

(g) performing the cooling of step (a) free of external refrigeration with the gas from the turbo expander.

2. The method of claim 1 including performing a portion of the cooling of step (a) of claim 1 by vaporizing at least a portion of the liquid hydrocarbons formed in step (a) in heat exchange relationship with the gas stream.

3. The method of claim 1 including performing a portion of the cooling of step (a) of claim 1 with the gas formed in step (f) of claim. 1.

4. The method of separating (i) methane and ethane, (ii) propane and other higher boiling point hydrocarbon constituents, and (iii) water vapor in a natural gas stream under superatmospheric pressure, said process compris- (a) injecting a hydrate inhibitor into the gas stream,

(b) cooling the gas stream until the water vapor and the hydrate inhibitor and a portion of the methane, ethane, and other gaseous hydrocarbons are liquefied forming a layer of liquid hydrocarbons and a layer of hydrate inhibitor-water mixture,

() separating from each other the two liquid layers formed in step (b),

(d) passing the gas stream remaining from step (b) through a turbo expander to condense a portion of the gas stream to a liquid,

(e) passing the liquid from the turbo expander to the top of the fractionating zone of a fractionating tower, I

(f) flashing a portion of the methane and ethane from the liquid hydrocarbons separated in step (c),

(g) passing the liquid remaining from step (f) into the fractionating tower,

(h) distilling liquid in the fractionating tower free of external reflux to form ethane and methane gas and a stabilized liquid product of propane and higher boiling point constituents, and

(i) performing the cooling of step (b) free of external refrigeration with gas from the turbo expander.

5. The method of claim 4 including performing a por- 18 tion of the cooling of step (b) of claim 4 by vaporizing at least a portion of the liquid hydrocarbons formed in step (b) in heat exchange relationship with the gas stream.

6. The method of claim 4 including performing a portion of the cooling of step (b) of claim 4 with the gas formed in step (h) of claim 4.

7. The method of separating methane and some ethane from propane, the remaining ethane, and higher boiling point constituents in a natural gas stream under superatmospheric pressure, said process comprising:

(a) cooling the g asstream until a portion of the methane, ethane, and other gaseous hydrocarbons are changed to liquid hydrocarbons,

(b) passing the gas stream remaining after step (a) through a turbo expander to condense a portion of the gas stream to a liquid,

(f) distilling the liquid-in the fractionating tower free of external reflux to form methane gas and a stabilized liquid product of ethane and higher boiling point constituents, and

8. The method of claim 7 including performing a portion of the cooling of step (a) of claim 7 by vaporizing at least a portion of the liquid hydrocarbons formed in step (a) in heat exchange relationship with the gas stream.

9. The method of claim 7 including performing a portion of the cooling of step (a) of claim 7 with the gas formed in step (f) of claim 7.

'14 The method of separating (i) methane and some ethane, (ii) propane, the remaining ethane, and higher boiling point hydrocarbon constituents, and (iii) water .vapor in a natural gas stream under superatmospheric pressure, said process comprising:

(a) injecting .a hydrate inhibitor into the gas stream,

(b) cooling the gas stream until the water vapor and the hydrate inhibitor and a portion of the methane,

j ethane, and other gaseous hydrocarbons are liquefied forming a layer of liquid hydrocarbons and a layer 'of hydrate inhibitor-water mixture,

(c) separating from each other the two liquid layers formed in step ('b),

'(d) passing the gas stream remaining from step (b) through a turbo expander to condense a portion of the gas stream to a liquid,

(e) passing the liquid from the-turbo expander to the top of the fractionating zone of a fractionating tower,

( f) flashing a portion of the methane and ethane from the liquid hydrocarbons separated in step (c),

(g) passing the liquid remaining from step (f) into the fractionating tower,

(h) distilling liquid in the fractionating tower free of external reflux to form methane gas and a stabilized liquid product of ethane. and higher boiling point constituents, and

(i)- performing the cooling of step (b) free of external refrigeration with gas from the turbo expander.

. 11. The method of claim 10 including performing a portion of the cooling of step (b) of claim 10 by vaporizing at least a portion of the liquid hydrocarbons formed in step (b) in heat exchange relationship with the gas stream.

12. The method of claim 10 including performing a portion of the cooling of step (b) of claim 10 with the gas formed in step (h) of claim 10.

13. The method of separating methane and ethane from propane and higher boiling point constituents in a natural gas stream under superatmospheric pressure, said process comprising:

(a) cooling the gas stream until a portion of the methane, ethane, and other gaseous hydrocarbons are changed to liquid hydrocarbons,

(c) maintaining the temperature of material leaving the turbo expander above a predetermined minimum,

(d) passing the liquid from the turbo expander to the top of the fractionating zone of a fractionating tower,

(e) flashing a portion of the methane and ethane from the liquid hydrocarbons separated in step (a),

(f) passing the liquid hydrocarbons remaining from step (e) to the fractionating tower,

(g) distilling the liquid in the fractionating tower free of external reflux to form ethane and methane gas and a stabilized liquid product of propane and higher boiling point constituents, and

(h) performing the cooling of step (a) free of external refrigeration with the gas from the turbo expander.

14. The method of claim 13 including performing a portion of the cooling of step (a) of claim 13 by vaporizing at least a portion of the liquid hydrocarbons formed in step (a) in heat exchange relationship with the gas stream.

15. The method of claim 13 including performing a portion of the cooling of step (a) of claim 13 with the gas formed in step (g) of claim 13.

16. The method of separating (i) methane and ethane, (ii) propane and other higher boiling point hydrocarbon constituents, and (iii) water vapor in a natural gas stream under superatmospheric pressure, said process comprismg:

(a) injecting a hydrate inhibitor into the gas stream,

(c) separating from each other the two liquid layers formed in step (b),

(e) maintaining the temperature of material leaving the turbo expander above a predetermined mini-.

mum,

(f) passing the liquid from the turbo expander to the top of the fractionating zone of a fractionating tower,

(g) flashing a portion of the methane and ethane from the liquid hydrocarbons separated in step (c),

(h) passing the liquid remaining from step (g) into the fractionating tower,

(i) distilling liquid in the fractionating tower free of external reflux to form ethane and methane gas and a stabilized liquid product of propane and higher boiling constituents, and

(j) performing the cooling of step (b) free of external refrigeration with gas from the turbo expander.

17. The method of claim 16 including performing a portion of the cooling of step (b) of claim 16 by vaporizing at least a portion of the liquid hydrocarbons formed in step (b) in heat exchange relationship with the gas stream.

18. The method of claim 4 including performing a portion of the cooling of step (b) of claim 16 with the gas formed in step (i) of claim 16.

19. The method of separating methane and some 20 ethane from propane, the remaining ethane, and higher boiling point constituents in a natural gas stream under superatmospheric pressure, said process comprising:

(g) distilling the liquid in the fractionating tower free of external reflux to form methane gas and a stabilized liquid product of ethane and higher boiling point constituents, and

20. The method of claim 19 including performing a portion of the cooling of step (a) of claim 19 by vapor izing at least a portion of the liquid hydrocarbons formed in step (a) in heat exchange relationship with the gas stream.

21. The method of claim 19 including performing a portion of the cooling of step (a) of claim 19 with the gas formedin step (g) of claim 19.

22. The method of separating (i) methane and some ethane, (ii) propane, the remaining ethane, and higher boiling point hydrocarbon constituents, and (iii) water vapor in a natural gas stream under superatmospheric pressure, said process comprising:

(a) injecting a hydrate inhibitor into the gas stream,

(c) separating from each other the two liquid layers formed in step (b),

(e) maintaining the temperature of material leaving the turbo expander above a predetermined minimum,

(h) passing the liquid remaining from step (g) into the fractionating tower,

(i) distilling liquid in the fractionating tower free of external reflux to form methane gas and a stabilized liquid product of ethane and higher, boiling point constituents, and

23. The method of claim 22 including performing a portion of the cooling of step (b) of claim 22 by vaporizing at least a portion of the liquid hydrocarbons formed in step (b) in heat exchange relationship with the gas stream.

24. The method of claim 22 including performing a portion of the cooling of step (b) of claim 22 with the gas formed in step (i) of claim 22.

25; The method of separating methane and some ethane from propane, the remaining ethane, and higher boiling point constituents in a natural gas stream under superatmospheric pressure, said process comprising:

(c) passing the liquid from the turbo expander to the top of the fractionating zone of a first fractionating tower,

(e) passing the liquid hydrocarbons remaining from step (d) to the first fractionating tower,

(f) distilling the liquid in the first fractionating tower free of external reflux to form methane gas and a stabilized liquid product of ethane and higher boiling point constituents,

(g) performing the cooling of step (a) free of external refrigeration with the gas from the turbo expander,

(h) passing the stabilized liquid product formed in the first fractionating tower to a second fractionating tower,

(i) distilling the liquid product in the second fractionating tower to form ethane gas and a stabilized liquid product of propane and higher boiling point constituents, and

(j) using cold liquid formed upstream of the first fractionating tower to form reflux for the second fractionating tower.

26. The method of separating (i) methane and some ethane, (ii) propane, the remaining ethane, and higher boiling point hydrocarbon constituents, and (iii) water vapor in a natural gas stream under superatmospheric pressure, said process comprising:

(a) injecting a hydrate inhibitor into the gas stream,

(b) cooling the gas stream until the water vapor and the hydrate inhibitor and a portion of the methane, ethane, and other gaseous hydrocarbons are liquefled forming a layer of liquid hydrocarbons and a layer of hydrate inhibitor-water mixture,

(c) separating from each other the two liquid layers formed in step (b),

(d) passing the gas stream remaining from step (b) through a turbo expander to condense a portion of the gas stream to aliquid,

(e) passing the liquid from the turbo expander to the top of the fractionating zone of a first fractionating tower,

(g) passing the liquid remaining from step i (f) into the fractionating tower,

(h) distilling liquid in the first fractionating tower free of external reflux to form methane gas and a stabilized liquid product of ethane and higher boiling point constituents,

(i) performing the cooling of step (b) free of external refrigeration with gas from the turbo expander, (j) passing the stabilized liquid product formed in the first fractionating tower to a second fractionating tower,

(k) distilling the liquid product in the second fractionating tower to form ethane gas and a stabilized liquid product of propane and higher boiling point constituents, and

(1) using cold liquid formed upstream of the first fractionating tower to form reflux for the second fractionating tower.

References Cited by the Examiner UNITED STATES PATENTS 2,151,248 3/ 1939 Vaughan.

2,230,619 2/ 1941 Katz.

2,265,558 12/1941 Ward et al 6239 X 2,433,604 12/ 1947 Dennis 6 238 X 2,552,451 5/ 1951 Patterson 6239 X NORMAN YUDKOFF, Primary Examiner.

V. W. PRETKA, Assistant Examiner.

Disclaimer and Dedication 3,292,38L-J0seph E. Bludworth, Corpus Christi, Tex. SEPARATION OF NATURAL GAS BY LIQUEFACTION WITH AN INJECTED HYDRATE INHIBITOR. Patent dated Dec. 20, 1966. Disclaimer and dedication filed May 1, 1970, by the assignees, Garrett Tucker, Sidneg Johnson and M ekn'n Fina-Ice. Hereby disclaim and dedicate said patent to the Public.

[Ofiiaz'al Gazette July 7, 1.970.]

Claims

1. THE METHOD OF SEPARATING METHANE AND ETHANE FROM PROPANE AND HIGHER BOILING POINT CONSTITUTES UB A NYATURAL GAS STREAM UNDER SUPERATMOSPHERIC PRESSURE, SAID PROCESS COMPRISING: (A) COOLIING THE GAS STREAM UNTIL A PORTION OF THE METHANE, ETHANE, AND OTHER GASEOUS HYDROCARBONS ARE CHANGED TO LIQUID HYDROCARBONS. (B) PASSING THE GAS STREAM REMAINING AFTER STEP (A) THROUGH A TURBO EXPANDER TO CONFENSE A PORTION OF THE GAS STREAM TO A LIQUID, (C) PASSING THE LIQUID FROM THE TURBO EXPANDER TO THE TOP OF THE FRACTIONATING ZONE OF A FRACTIONATING TOWER, (D) FLASHING A PORTION OF THE METHANE AND ETHANE FROM THE LIQUID HYDROCARBONS SEPARATED IN STEP (A), (E) PASSING THE LIQUID HYDROCARBONS REMAINING FROM STEP (D) TO THE FRACTIONATING TOWER, (F) DISTILLING THE LIQUID IN THE FRACTONATING TOWER FREE OF EXTERNAL REFLUX TO FORM ETHANE AND METHANE GAS AND A STABILIZED LIQUID PRODUCT OF PROPANE AND HIGHER BOILING POINT CONSTITUENTS, AND