Patent ID: 8640493

Claim:
A method for offshore liquefaction of natural gas and transport of produced liquefied natural gas to a trading tanker comprising: a. flowing well gas from a well into a primary processing unit mounted on a floating production storage and offloading vessel; b. the floating production storage and offloading vessel performing the steps of: i. separating condensate and water from the well gas forming a high pressure flash gas; ii. sending high pressure flash gas to a gas treatment unit on the floating production storage and offloading vessel; iii. removing acid gas from the high pressure flash gas forming a treated gas; iv. removing water from the treated gas forming a dry gas and sending the dry gas to a dehydration unit; v. removing propane, butane, pentane and heavier hydrocarbon compounds from the dry gas forming a liquefied natural gas inlet quality gas; and vi. compressing the liquefied natural gas inlet quality gas forming a high pressure liquefied natural gas inlet quality gas; c. transferring the high pressure liquefied natural gas inlet quality gas to the disconnectable turret using a first flexible conduit; d. transferring the high pressure liquefied natural gas inlet quality gas from the disconnectable turret to a liquefaction unit on a liquefied natural gas transport vessel and liquefying and expanding a first portion of the high pressure liquefied natural gas inlet quality gas for storage as liquefied natural gas, and cooling, expanding, and recompressing a second portion of the high pressure liquefied natural gas inlet quality gas into a recycle gas stream, wherein the liquefaction unit is powered by a propulsion means from the liquefied natural gas transport vessel, wherein the propulsion means is connected to a dual fuel diesel electric main power plant or a steam turbo-electric main power plant; e. exporting the recycle gas stream through a second flexible conduit from the disconnectable turret to the floating production storage and offloading vessel; f. compressing on the floating production storage and offloading vessel, the recycle gas stream and blending with the high pressure liquefied natural gas inlet quality gas; g. disconnecting the liquefied natural gas transport vessel from the disconnectable turret when sufficiently loaded with liquefied natural gas and allowing the liquefied natural gas transport vessel to travel to a transfer terminal for offloading to the trading tanker; and h. separating wet gas stream to produce a low pressure wet natural gas stream and a plurality of intermediate pressure wet natural gas streams and compressing the low pressure wet natural gas stream and the intermediate pressure wet natural gas streams and comingling the compressed natural gas streams with the high pressure flash gas.