GB1572898A

GB1572898A - Process for the liquefaction of natural gas

Info

Publication number: GB1572898A
Application number: GB1611276A
Authority: GB
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1976-04-21
Filing date: 1976-04-21
Publication date: 1980-08-06
Also published as: CA1053568A; AU2442177A; AU506919B2

Description

(54) A PROCESS FOR THE LIQUEFACTION OF NATURAL GAS (71) We, SHELL INTER NATIONALE RESEARCH MAAT SCHAPPIJ B.V., a company organized under the laws of the Netherlands, of 30, Carel van Bylandtlaan, The Hague, the Netherlands, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a method of liquefying a natural gas by cooling it under pressure in stages, comprising cooling a natural gas stream by passing it in heatexchange relationship with at least one refrigerant circulating in at least one circuit.

This patent application is related to the copending divisional patent applications 1545/79 (serial No. 1572899) and 1546/79 (Serial No. 1572900).

A known method of the above kind comprises cooling a natural gas stream by passing it in heat-exchange relationship with a first refrigerant circulating in a first circuit and successively passing the natural gas stream in heat-exchange relationship with at least a second refrigerant circulating in at least a second circuit, wherein the first refrigerant is of a composition which differs from the composition of the second refrigerant.

Although it is possible and sometimes attractive to use a single component refrigerant, such as for example propane, often at least one of the refrigerants is a so called multi-component or mixed refrigerant, for example, a mixture of at least ethane and butane or, for example, a mixture of at least nitrogen, methane and ethane.

It is an object of the invention to separate from the natural gas to be liquified the heavier hydrocarbons, which comprise butane and hydrocarbons heavier than butane, since the presence of these heavier hydrocarbons in the natural gas may disturb the process of the liquifaction of the natural gas.

It is another object of the invention to extract from the natural gas during the liquifaction process valuable hydrocarbon mixtures comprising mainly ethane, propane and a relatively minor quantity of hydrocarbons heavier than propane.

For this purpose, the invention comprises a method of liquefying a natural gas by cooling it under pressure in stages comprising cooling a natural gas stream passing it in heat-exchange relationship with at least one refrigerant circulating in at least one circuit, so that the heavier hydrocarbons, comprising butane and hydrocarbons heavier than butane, present in the natural gas are condensed, separating the condensed heavier hydrocarbons from the natural gas in a first separator, removing from the separator a composition A comprising the condensed heavier hydrocarbons together with some components lighter than butane, passing the composition A via an expansion device to a first demethanizer and introducing it into the latter, removing from the first demethanizer as overhead vapour methane with possibly some ethane and removing from the first demethanizer as a liquid the remaining hydrocarbons, cooling the separated natural gas further by passing it in heat-exchange relationship with a refrigerant so that again some liquid is formed, separating a composition B of condensed hydrocarbons comprising mainly methane, ethane and propane together with a relatively minor quantity of hydrocarbons heavier than propane from the natural gas in a second separator, removing the composition B from the separator, passing the composition B via an expansion device to a second demethanizer and introducing it into the latter, removing from the second demethanizer as overhead vapour methane with possibly some ethane and removing from the second demethanizer as a liquid the remaining hydrocarbons, and cooling the separated natural gas further by passing it in heat-exchange relationship with a refrigerant, so that the natural gas liquefies.

A suitable embodiment of the above process comprises controlling the quantity of composition B to be passed from the second separator to the second demethanizer and introducing any excess quantity of composition B into the stream of natural gas leaving the second separator. In this manner the production of the abovementioned valuable hydrocarbon mixtures comprising ethane propane and a relatively minor quantity of hydrocarbons heavier than propane can be easily adapted to the demand for said mixtures, without disturbing the process of liquefying the natural gas.

Preferably the overhead vapour removed from the first and/or second demethanizer is introduced into the liquefied natural gas.

The liquid hydrocarbons as removed from the first demethanizer may be passed to a refrigerant make-up unit to produce hydrocarbons selected from the group comprising C2-, C3-, C4- and C5hydrocarbons.

Further details and embodiments of the process according to the invention will be explained with reference to the drawing, accompanying the Provisional Specification showing a flow sheet of the process.

Referring to the drawing, natural gas, from which CO2 and water have been removed, is supplied through a line 1.

This natural gas, which is at a relatively high pressure of, fcr example, 50 bar and at a temperature of, for example, 20 degrees centigrade, is passed through a coil 2 of a heat-exchanger 4. In the coil 2 the temperature of the natural gas is lowered.

The cooled natural gas leaving the coil 2 is passed through a line 3 to a first phase separator 5, wherein condensed heavier hydrocarbon comprising butane and hydrocarbons heavier than butane are separated from the gas. The condensed heavier hydrocarbons are removed from the first phase separator 5 through a discharge line 6. Together with the condensate some hydrocarbons, lighter than butane are removed from the first separator 5 through the discharge line 6. The natural gas leaves the first phase separator 5 as a vapour and is passed through a line 7 to a coil 8 of the heatexchanger 4, wherein the temperature of the natural gas is lowered further. From coil 8 the cooled natural gas, which contains a small quantity of liquid, is passed through a line 9 to a coil 10 of a heat-exchanger 11.In coil 10 the temperature of the natural gas is reduced to a lower value, so that more liquid is formed. From coil 10 the natural gas is passed through a line 12 to a second phase separator 13. In the second phase separator 13 condensed hydrocarbons are separated from the natural gas. The condensed hydrocarbons, which comprise mainly methane, ethane and propane together with a relatively minor quantity of hydrocarbons heavier than propane are removed from the second separator 13 through a line 14.

Natural gas vapour containing mainly methane, ethane and nitrogen leaving the phase separator 13 is passed through a line 15 to a coil 16 of heat-exchanger 11, wherein the temperature of the natural gas is lowered further and the natural gas is fully condensed. From coil 16 the natural gas is passed to an expansion device 17. In expansion device 17 the pressure of the condensed natural gas is reduced, whereafter it is passed via a line 18 to a coil 19 of heat-exchanger 11.

In coil 19 the condensed natural gas is cooled further to a temperature of, for example, minus 147 degrees centigrade.

From coil 19 the liquefied natural gas is passed through a line 20 to a heat-exchanger 22 in a nitrogen stripper 21. In the heatexchanger 22 the liquified natural gas is cooled further. From heat-exchanger 22 the liquefied natural gas is passed to an expansion device 23. In expansion device 23 the liquefied natural gas is expanded to a lower pressure, so that some vapour is formed, and then it is passed through a line 24 to a distribution device 25 in the stripper 21, wherein liquid and vapour are separated.

The liquid natural gas fraction leaving distribution device 25, passes through the stripper 21 to an outlet 26 and from outlet 26 via line 27 to storage. In stripper 21 nitrogen is separated from the liquefied natural gas.

A methane/nitrogen vapour mixture containing some traces of ethane leaves the top of the stripper 21 via a line 29 and is passed to a heat-exchanger 30. In heatexchanger 30 the temperature of this gas mixture is raised and then this gas mixture is passed through a line 31 to a heat-exchanger 32 in which the temperature of the said gas mixture is raised further. Finally, the said gas mixture is passed from heat-exchanger 32 through a line 33 to a suitable location to be used, for example, as a fuel gas.

The condensate leaving the first phase separator 5 is passed via line 6 and an expansion device 150 to a first demethanizer 151 which is provided with a reboiler 152. Methane, possibly with some ethane, leaves the first demethanizer 151 as overhead vapour and is passed through a line 154 to be intermixed with a gas stream flowing in a line 157.

The remaining hydrocarbons comprising ethane and components heavier than ethane are removed as liquid from the bottom of the first demethanizer 151 and are passed to a refrigerant make-up unit (not shown) via a line 153. In the refrigerant make-up,unit hydrocarbons may be produced which are selected from the group comprising C2-, C3-, C4- and C5-hydrocarbons. Part of the liquid leaving the demethanizer 151 through line 153 is recirculated through the reboiler 152.

The C2-hydrocarbons produced in the refrigerant make-up unit are passed via a line 141 to the heat-exchanger 32 to be lowered in temperature. From heat-exchanger 32 the said C2-hydrocarbons are passed via a line 142 to storage. The C2-hydrocarbons produced in the refrigerant make-up unit are passed via a line 143 to the heatexchanger 32. In heat-exchanger 32 the said C3-hydrocarbons are lowered in temperature and then passed via a line 144 to storage.

The condensed hydrocarbons leaving the second phase separator 13 via line 14 can be passed via a line 158 to an expansion device 159. Another part of said condensed hydrocarbons can be passed via a pump 160 to the gas flowing in line 15 to be intermixed therewith.

In expansion device 159 the liquid is expanded to a lower pressure and then it is passed to a second demethanizer 162 which is provided with a reboiler 163. Methane, possibly with some ethane, leaves the second de-methanizer 162 as overhead vapour and is passed via the line 157 to a coil 165 in heat-exchanger 11. In coil 165 the gas is cooled and condensed and then it is passed via a line 166 to the natural gas flowing in line 18 to be intermixed therewith.

The remaining hydrocarbons comprising mainly ethane, propane and butane are removed as liquid from the bottom of the second demethanizer 162 and are passed as raw natural gas liquid via a line 164 to storage for further treatment. Part of the liquid leaving the second demethanizer 162 through line 164 is recirculated through the reboiler 163.

The quantity of liquid to be passed to the second demethanizer 162 can be controlled at will by manipulating the expansion device 159. In so doing the extraction of natural gas liquids from the natural gas feed stream can be regulated. All condensate from the second separator 13 which is not sent to the second demethanizer 162 is passed via pump 160 to line 15.

In the above natural gas liquefaction system two separate cooling circuits are used. In the first cooling circuit a so-called mixed refrigerant, for example a suitable mixture of methane, ethane, propane, butane and pentane, is supplied in gaseous condition through a line 34 to a compressor 35. In compressor 35 the pressure of the mixed refrigerant is raised. From compressor 35 the mixed refrigerant is passed through a line 36 to a heat-exchanger 37, which is cooled for example by water. In heat-exchanger 37 the mixed refrigerant is cooled to such a degree that partial condensation of the mixture occurs. From heat-exchanger 37 the partially condensed mixed refrigerant is passed through a line 38 to a phase separator 39 in which condensed mixed refrigerant is separated from gaseous mixed refrigerant.The gaseous mixed refrigerant is passed from phase separator 39 through line 40 to a compressor 41. In compressor 41 the pressure of the gaseous mixed refrigerant is raised further. From compressor 41 said gaseous mixed refrigerant is passed through a line 42 to a heat-exchanger 43.

The condensed mixed refrigerant leaves the phase separator 39 via outlet 44 and is passed to a pump 45. In pump 45 the pressure of the condensed mixed refrigerant is raised to such a level that it can be passed through a line 46 to line 42 and be added to the gaseous mixed refrigerant leaving the compressor 41. In the heat-exchanger 43, which is, for example, cooled by water, the mixed refrigerant is cooled and partially condensed and from heat-exchanger 43 the cooled mixed refrigerant is passed through a line 47 to a phase separator 48.

The condensed mixed refrigerant leaving the phase separator 48 is passed through a line 49 to a coil 50 of the heat-exchanger 4.

The gaseous mixed refrigerant leaving the phase separator 48 is passed through a line 51 to a coil 52 of the heat-exchanger 4.

In coil 50 the condensed mixed refrigerant is cooled and is then passed from coil 50 via a line 53 to an expansion device 54. In expansion device 54 the cooled liquid refrigerant is expanded to a lower pressure.

The liquid, possibly together with a small portion of vapour, is passed from expansion device 54 through a line 55 and is injected through a distribution device 56 into heatexchanger 4, wherein it combines with a mixed refrigerant stream which enters heatexchanger 4 via a distribution device 64.

The combined mixed refrigerant stream flows downward over the coils 50, 52, 100 and 2 to cool the contents of these coils.

During this process the largest part of the mixed refrigerant evaporates. The mixed refrigerant, which is largely in gaseous condition and contans only a small portion of liquid, leaves the heat-exchanger 4 via a line 57 to be passed to a phase separator 58.

In phase separator 58 liquid mixed refrigerant is separated from gaseous mixed refrigerant. The separated liquid mixed refrigerant is removed from phase separator 58 via an outlet 76 to be injected, after its pressure has been raised, into, for example, line 36, or into, for example, separator 39.

Via a line 59 so-called "make-up refrigerant" is added to the refrigerant passing through line 57 to compensate for refrigerant lost during the process. Gaseous refrigerant is passed from phase separator 58 via line 34 to compressor 35 to repeat the cycle as described in the above.

The mixed refrigerant passing through coil 52 is lowered in temperature and condensed in said coil and is then passed to a further coil 60 of heat-exchanger 4.

In coil 60 the condensed mixed refrigerant is cooled further and then it is passed via a line 61 to an expansion device 62. In expansion device 62, the refrigerant is expanded to a lower pressure so that some vapour is formed and then it is passed via a line 63 to a distribution device 64. From distribution device 64 the refrigerant, which is largely in liquid condition, flows downward over the coils 60, 101 and 8 to cool the contents of these coils and further downward over the coils 50, 52, 100 and 2 to cool the contents of these coils until it reaches the bottom of the heat-exchanger.

During this process the refrigerant evaporates largely. Finally, the refrigerant leaves the heat-exchanger 4 via the line 57 to be passed to phase separator 58.

Some of the condensed refrigerant leaving the phase separator 48 via the line 49 is branched off and is passed through a line 65 to an expansion device 66. In expansion device 66 the refrigerant is expanded to a lower pressure so that some gas is formed and is then passed through a line 67 to a distribution device 68 of a heat-exchanger 69 which is provided with a coil 70. The refrigerant, which is largely in liquid condition, leaving the distribution device 68 flows downward over the coil 70 to cool the contents of the coil 70. During this process the refrigerant evaporates largely and finally leaves the heat-exchanger 69 through a line 71.

Via line 71 the refrigerant is passed to an expansion device 72 in which the refrigerant is expanded to a lower pressure. Then the refrigerant, which is largely in gaseous condition, is passed from the expansion device 72 to the phase separator 39 via a line 73 to be combined with the refrigerant arriving from the compressor 35. In heatexchanger 69 natural gas to be liquefied is precooled in order to remove a quantity of water which is present in the natural gas.

For this purpose the natural gas is supplied through a line 74 to the coil 70 and passed through coil 70. The natural gas precooled in coil 70, leaves the coil 70 via a line 75 and is passed to a phase separator (not shown) in which condensed water is removed from the natural gas. Then the partly dried natural gas is passed to a conventional drier (not shown) to remove the remaining water from the natural gas. This conventional drier is, for example, of the kind containing a suitable desiccant. From the conventional drier the natural gas is passed to line 1 in order to be liquefied in the manner as described in the above.

In the second cooling circuit a so-called mixed refrigerant is circulating as well. The composition of the mixed refrigerant circulating in the second cooling circuit is, however, different from the mixed refrigerant circulating in the first cooling circuit.

The mixed refrigerant circulating in the second cooling circuit is, for example, a mixture of ethane, methane and nitrogen.

In the second cooling circuit gaseous mixed refrigerant is supplied through a line 80 to a compressor 81.

In the compressor 81 the pressure of the mixed refrigerant is raised and then it is passed through a line 82 to a heat-exchanger 83, which is cooled, for example, by water.

In heat-exchanger 83 the mixed refrigerant is cooled and then it is passed via a line 84 to a knock-out vessel 85 in which liquid components, if any, can be removed in conventional manner. From knock-out vessel 85 the mixed refrigerant is passed via a line 86 to a compressor 87.

In compressor 87 the pressure of the mixed refrigerant is raised further and then it is passed via a line 88 to a heat-exchanger 89 which is cooled, for example, by water.

From heat-exchanger 89, the mixed refrigerant is passed via a line 90 to a coil 100 of the heat-exchanger 4. In coil 100 the temperature of the mixed refrigerant is lowered. From coil 100, the mixed refrigerant is passed to a coil 101 in which it is cooled further and partially condensed.

From coil 101 the cooled mixed refrigerant is passed through a line 102 to a phase separator 106. In the phase separator 106 the gaseous refrigerant is separated from liquid refrigerant. From phase separator 106, the liquid refrigerant is passed through a line 110 to a coil 111 of the heat-exchanger 11. In coil 111 the refrigerant is cooled further and then it is passed through a line 112 to an expansion device 113. In expansion device 113 the refrigerant is expanded, whereafter it is passed through a line 114 and is injected through a distribution device 115 into the heat-exchanger 11, wherein it combines with a mixed refrigerant stream which enters heat-exchanger 11 via a distribution device 132.

The combined mixed refrigerant stream is passed over the coils 111, 127, 165, 16 and 10 which causes cooling of the contents of these coils. During the passage of the refrigerant over the coils 111, 127, 165, 16 and 10 the refrigerant evaporates at least partly.

Finally, the refrigerant reaches the lower part of the heat-exchanger 11 and then it is passed through a line 116 to a heatexchanger 117.

In heat-exchanger 117, the refrigerant cools the contents of a coil 109 of the heatexchanger 117. Then the refrigerant is passed through a line 118 to a knock-out vessel 119. Finally, the refrigerant, which is in gaseous condition, is passed from knockout vessel 119 through the line 80 to the compressor 81 to repeat the cycle.

Gaseous refrigerant leaves the phase separator 106 through a line 125. From line 125 part of the said gaseous refrigerant is passed through a line 126 to a coil 127 in the heat-exchanger 11 in which it is cooled and condensed. From coil 127 the condensed refrigerant is passed to a coil 128 in which it is cooled further. From coil 128 the refrigerant is passed via a line 129 to an expansion device 130 in which the refrigerant is expanded to a lower pressure.

From expansion device 130, the refrigerant, which is now largely in liquid condition is passed via a line 131 to a distribution device 132. From distribution device 132, the refrigerant is passed downward over the coils 19, 128, 16, 165, 10, 127 and 111 to the bottom part of the heat-exchanger 11.

During the passage of the refrigerant, the latter cools the contents of the said coils.

Finally, the refrigerant leaves the heatexchanger 11 through the line 116.

Part of the gaseous refrigerant leaving the phase separator 106 via the line 125 is branched off and is passed via a line 135 to the heat-exchanger 30. In heat-exchanger 30 the refrigerant is cooled against gaseous mixture leaving the nitrogen stripper via the line 29. From heat-exchanger 30 the refrigerant is passed via a line 136 to an expansion device 137.

In expansion device 137 the refrigerant is expanded to the pressure of the refrigerant leaving the expansion device 130. Finally, both streams of refrigerant are mixed and led via line 131 to the distribution device 132 to be injected into the heat-exchanger 11.

Part of the mixed refrigerant passing through line 90 is recycled. For this purpose, part of the gas stream is branched off and is passed via a line 138 to the coil 109 of the heat-exchanger 117. In coil 109 the temperature of the mixed refrigerant is lowered and then it is passed from coil 109 through a line 139 to line 102 to be intermixed with the mixed refrigerant passing through line 102 to be passed to the phase separator 106.

At 120 make-up refrigerant is added to the refrigerant circuit to compensate for losses of refrigerant circulating in the circuit.

WHAT WE CLAIM IS: 1. A method of liquefying a natural gas by cooling it under pressure in stages, comprising cooling a natural gas stream by passing it in heat-exchange relationship with at least one refrigerant circulating in at least one circuit, so that the heavier hydrocarbons, comprising butane and hydrocarbons heavier than butane, present in the natural gas are condensed, separating the condensed heavier hydrocarbons from the natural gas in a first separator, removing from the separator a composition A comprising the condensed heavier hydrocarbons together with some components lighter than butane, passing the composition A via an expansion device to a first demethanizer and introducing it into the latter, removing from the first demethanizer as overhead vapour methane with possibly some ethane and removing from the first demethanizer as a liquid the remaining hydrocarbons, cooling the separated natural gas further by passing it in heat-exchange relationship with a refrigerant so that again some liquid is formed, separating a composition B of condensed hydrocarbons comprising mainly methane, ethane and propane together with a relatively minor quantity of hydrocarbons heavier than propane from the natural gas in a second separator, removing the composition B from the separator, passing the composition B via an expansion device to a second demethanizer and introducing it into the latter, removing from the second demethanizer as overhead vapour methane with possibly some ethane and removing from the second demethanizer as a liquid the remaining hydrocarbons, and cooling the separated natural gas further by passing it in heat-exchange relationship with a refrigerant, so that the natural gas liquefies.

2. The method as claimed in claim 1, comprising controlling the quantity of composition B to be passed from the second separator to the second demethanizer and introducing any excess quantity of composition B into the stream of natural gas leaving the second separator.

3. The method as claimed in any one of the claims 1 or 2, comprising introducing the overhead vapour removed from the first and/or second demethanizer into the liquefied natural gas.

4. The method as claimed in any one of the claims 1 to 3, comprising passing the liquid hydrocarbons as removed from the first demethanizer to a refrigerant make-up unit to produce hydrocarbons selected from

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. Finally, the refrigerant reaches the lower part of the heat-exchanger 11 and then it is passed through a line 116 to a heatexchanger 117. In heat-exchanger 117, the refrigerant cools the contents of a coil 109 of the heatexchanger 117. Then the refrigerant is passed through a line 118 to a knock-out vessel 119. Finally, the refrigerant, which is in gaseous condition, is passed from knockout vessel 119 through the line 80 to the compressor 81 to repeat the cycle. Gaseous refrigerant leaves the phase separator 106 through a line 125. From line 125 part of the said gaseous refrigerant is passed through a line 126 to a coil 127 in the heat-exchanger 11 in which it is cooled and condensed. From coil 127 the condensed refrigerant is passed to a coil 128 in which it is cooled further. From coil 128 the refrigerant is passed via a line 129 to an expansion device 130 in which the refrigerant is expanded to a lower pressure. From expansion device 130, the refrigerant, which is now largely in liquid condition is passed via a line 131 to a distribution device 132. From distribution device 132, the refrigerant is passed downward over the coils 19, 128, 16, 165, 10, 127 and 111 to the bottom part of the heat-exchanger 11. During the passage of the refrigerant, the latter cools the contents of the said coils. Finally, the refrigerant leaves the heatexchanger 11 through the line 116. Part of the gaseous refrigerant leaving the phase separator 106 via the line 125 is branched off and is passed via a line 135 to the heat-exchanger 30. In heat-exchanger 30 the refrigerant is cooled against gaseous mixture leaving the nitrogen stripper via the line 29. From heat-exchanger 30 the refrigerant is passed via a line 136 to an expansion device 137. In expansion device 137 the refrigerant is expanded to the pressure of the refrigerant leaving the expansion device 130. Finally, both streams of refrigerant are mixed and led via line 131 to the distribution device 132 to be injected into the heat-exchanger 11. Part of the mixed refrigerant passing through line 90 is recycled. For this purpose, part of the gas stream is branched off and is passed via a line 138 to the coil 109 of the heat-exchanger 117. In coil 109 the temperature of the mixed refrigerant is lowered and then it is passed from coil 109 through a line 139 to line 102 to be intermixed with the mixed refrigerant passing through line 102 to be passed to the phase separator 106. At 120 make-up refrigerant is added to the refrigerant circuit to compensate for losses of refrigerant circulating in the circuit. WHAT WE CLAIM IS:

1. A method of liquefying a natural gas by cooling it under pressure in stages, comprising cooling a natural gas stream by passing it in heat-exchange relationship with at least one refrigerant circulating in at least one circuit, so that the heavier hydrocarbons, comprising butane and hydrocarbons heavier than butane, present in the natural gas are condensed, separating the condensed heavier hydrocarbons from the natural gas in a first separator, removing from the separator a composition A comprising the condensed heavier hydrocarbons together with some components lighter than butane, passing the composition A via an expansion device to a first demethanizer and introducing it into the latter, removing from the first demethanizer as overhead vapour methane with possibly some ethane and removing from the first demethanizer as a liquid the remaining hydrocarbons, cooling the separated natural gas further by passing it in heat-exchange relationship with a refrigerant so that again some liquid is formed, separating a composition B of condensed hydrocarbons comprising mainly methane, ethane and propane together with a relatively minor quantity of hydrocarbons heavier than propane from the natural gas in a second separator, removing the composition B from the separator, passing the composition B via an expansion device to a second demethanizer and introducing it into the latter, removing from the second demethanizer as overhead vapour methane with possibly some ethane and removing from the second demethanizer as a liquid the remaining hydrocarbons, and cooling the separated natural gas further by passing it in heat-exchange relationship with a refrigerant, so that the natural gas liquefies.

the group comprising C2-, C2-, C4- and C5- hydrocarbons.

5. A method of liquefying a natural gas as claimed in any one of claims 1--4, substantially as hereinbefore described with reference to the drawings accompanying the provisional specification.