Compact, modular method and apparatus for liquefying natural gas

A compact and modular apparatus for refrigerating and liquefying a gas such as pure methane or a natural gas stream rich in methane, the apparatus comprising:

• a. a means for cooling a compressed main feed stream entering at a pressure between about 1500 psig to about 3500 psig and at near ambient temperature to a temperature of between about −10° F. to about −100° F.;
• b. a turboexpander configured to expand the cooled, compressed feed stream to form a first bi-phase stream comprising a first refrigerated vapor component and a first liquid component;
• c. a primary separation tank configured to separate the first refrigerated vapor component and the first liquid component;
• d. a means configured to expand the separated first liquid component to form a second bi-phase stream comprising a second refrigerated vapor component and a second liquid component;
• e. a secondary separation tank configured to separate the second refrigerated vapor component and the second liquid component;
• and
• f. a means configured for storage and transport of the separated second liquid component.

A compact and modular apparatus for refrigerating and liquefying a gas such as pure methane or a natural gas stream rich in methane, the apparatus comprising:

• a. a multistage compressor configured for receiving and compressing a main stream gas at a pressure of about 85 psig and at near ambient temperature to a pressure of between about 1500 psig to about 3500 psig;
• b. an after-cooler configured to cool the compressed feed stream to near ambient temperature immediately after each compression stage in the multistage compressor;
• c. a heat exchanger configured to cool the compressed feed stream to a temperature of between about −10° F. to about −100° F., typically between about −20° F. to about −60° F., and more typically about −30° F.;
• d. a turboexpander configured to expand the compressed and cooled feed stream to a pressure of between about 15 to about 135 psig, typically between about 80 to about 105 psig, and more typically to between about 90 to about 95 psig, to form a first refrigerated vapor component and a first liquid component having a temperature of between about −155° F. to about −240° F., typically about −190° F. to about −215° F., and more typically about −200° F. to about −205° F.;
• e. a primary separation tank configured to separate the first refrigerated vapor component and the first liquid component;
• f. a throttle valve configured to expand the first liquid component to a pressure of between about 3 psig to about 7 psig, and more typically to about 5 psig to form a second refrigerated vapor component and a second liquid component having a temperature of between about −250° F. to −265° F., and typically between about −252° F. to about −258° F.;
• g. a secondary separation tank configured to separate the second refrigerated vapor component and the second liquid component;
• h. a means configured for storage and transport of the separated second liquid component;
• and
• i. a means to place the separated first refrigerated vapor component and the separated second refrigerated vapor component into fluid communication with the compressed main feed stream.