Methods and configurations for LNG liquefaction

A liquefied natural gas (LNG) liquefaction plant system for liquefying a natural gas stream, comprising:

• a pre-cooling system comprising a pre-cooling compressor operable to compress the natural gas;
• and
• a heat exchanger system comprising:
• a heat exchanger configured to allow flow of a nitrogen refrigerant in a refrigerant stream through the heat exchanger;
• wherein the refrigerant stream is split into a first split refrigerant stream in a first conduit and a second split refrigerant stream in a second conduit after flowing through the heat exchanger;
• a first compressor-expander operable to expand the first split refrigerant stream and wherein the heat exchanger is configured to allow flow of the expanded first split refrigerant stream back through the second heat exchanger;
• wherein the heat exchanger is configured to allow flow of the second split refrigerant stream back through the heat exchanger;
• a second compressor-expander operable to expand the second split refrigerant stream after flowing back through the heat exchanger and wherein the heat exchanger is configured to allow flow of the expanded second split refrigerant stream back through the heat exchanger;
• wherein the second compressor-expander is operable to compress the expanded second split refrigerant stream after flowing back through the heat exchanger and wherein the first compressor-expander is operable to further compress the compressed second split refrigerant stream from the second compressor-expander;
• and
• wherein the system is configured to cool the natural gas to produce a liquefied natural gas (LNG) by flowing the natural gas through the heat exchanger.

A method of LNG liquefaction, comprising:

• flowing a produced natural gas stream through a heat exchanger;
• flowing a nitrogen refrigerant in a refrigerant stream through the heat exchanger;
• splitting the refrigerant stream into a first split refrigerant stream and a second split refrigerant stream after flowing through the heat exchanger;
• expanding the first split refrigerant stream in a first compressor-expander and flowing the expanded first split refrigerant stream back through the heat exchanger;
• flowing the second split refrigerant stream back through the heat exchanger;
• expanding the second split refrigerant stream in a second compressor-expander after flowing back through the heat exchanger and flowing the expanded second split refrigerant stream back through the heat exchanger;
• compressing, after flowing through the heat exchanger, the expanded second split refrigerant stream in the second compressor-expander and then in the first compressor-expander;
• and
• cooling the produced natural gas stream in the heat exchanger to produce a liquefied natural gas (LNG).