Patent ID: 9709325
Date: 2017-07-18
CPC Classifications: F25J,Y10T

Claim:
1. A method for retrofitting a main LNG plant having a capacity of at least 4 MTPA to expand the capacity of the main LNG plant and operating the expanded capacity plant, wherein the main LNG plant has design parameters including a winter design capacity, an average ambient temperature design capacity, a refrigeration horsepower requirement, a design production of end flash gas, a design production of boil off gas, a design feed flow rate and a design temperature of a gas stream exiting a main cryogenic heat exchanger and wherein the main LNG plant comprises a main cryogenic heat exchanger having a feed gas inlet and a gas outlet, a nitrogen rejection unit having an inlet in fluid communication with the gas outlet of the main cryogenic heat exchanger, an LNG outlet and an end flash gas outlet, an LNG storage unit having an LNG inlet in fluid communication with the LNG outlet of the nitrogen rejection unit, an LNG storage unit outlet and a boil off gas outlet, the method comprising: connecting a small-scale LNG plant having a capacity of less than 2 MTPA and having at least one inlet and an outlet to the end flash gas outlet of the nitrogen rejection unit of the main LNG plant such that an inlet of the small-scale LNG plant and the end flash gas outlet are in fluid communication; installing a first compressor having a first compressor inlet between the end flash gas outlet of the main LNG plant and the inlet of the small-scale LNG plant in fluid communication with the end flash gas outlet for increasing end flash gas pressure prior to being delivered to the inlet of the small-scale LNG plant; passing a natural gas feed stream at a feed flow rate above the design feed flow rate of the main LNG plant through the main cryogenic heat exchanger of the main LNG plant to produce a gas stream exiting the main cryogenic heat exchanger having a temperature between 5° C. and 30° C. higher than the design temperature; sending the gas stream exiting the main cryogenic heat exchanger to a nitrogen rejection unit to produce a nitrogen reduced LNG stream and an end flash gas stream; sending the nitrogen reduced LNG stream to an LNG storage unit; and compressing at least a portion of the end flash gas stream to produce a compressed end flash gas stream and sending the compressed end flash gas stream to the small scale LNG plant to be liquefied, thereby decreasing the refrigeration horsepower requirement such that the expanded capacity plant can be utilized at the winter design capacity above the average ambient temperature design capacity year-round.