| 摘要 |
A method and an apparatus for producing liquid natural gas (LNG) from a well head or other source of cool, high pressure natural gas. The natural gas from the source is purified and split into first and second flow portions. The first flow portion is split into two parts passing through first and second heat exchangers. The two parts are thereafter recombined and throttled into a LNG tank wherein part thereof flashes to liquid natural gas and a part thereof constitutes a very cold saturated vapor to be vented from the LNG tank. The vent remainder of the first flow portion is used as a coolant for the second heat exchanger and is then conveyed to a low pressure receiver such as a collection pipeline, the vent remainder having a pressure equal to or greater than the receiver. The second flow portion enters an expander wherein its pressure is lowered below that of the receiver and its temperature is lowered accordingly. The second flow portion is used as a coolant for the first heat exchanger and thereafter enters a compressor run by expander work wherein its pressure is raised to a level equal to or greater than that of the receiver. The second flow portion passes to the receiver. Under some conditions of pressure at the source and efficiency levels of the equipment used, the second heat exchanger can be eliminated and all of the first flow portion flashes to liquid natural gas, as is shown in the second embodiment of the present invention.
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