Method and System for Efficient Nonsynchronous LNG Production using Large Scale Multi-Shaft Gas Turbines

A method of producing liquefied natural gas (LNG) in a LNG liquefaction plant, comprising:

• arranging each of first, second, and third refrigeration compression strings to include one or more refrigeration compressors and a multi-shaft gas turbine operationally connected to the one or more refrigeration compressors;
• using the multi-shaft gas turbine in each of the first, second, and third refrigeration compression strings, driving the respective one or more refrigeration compressors at an operating rotational speed that is not always aligned with the frequency of an electrical grid of the LNG liquefaction plant;
• providing compression to a propane refrigerant and to a mixed refrigerant using the first refrigeration compression string;
• providing compression to the propane refrigerant and the mixed refrigerant using the second refrigeration compression string;
• providing compression to a nitrogen refrigerant using the third refrigeration compression string;
• without assistance from electrical motors with drive-through capability or variable frequency drives, using an inherent speed turn-down range of the multi-shaft gas turbine of at least one of the first, second, and third refrigeration compression strings to
• start the one or more refrigeration compressors from rest,
• bring the one or more refrigeration compressors up to an initial operating rotational speed, and
• adjust compressor operating points to maximize efficiency of the one or more refrigeration compressors;
• and
• wherein operation of the multi-shaft gas turbine of only one of the first, second, and third refrigeration compression strings is required for natural gas liquefaction, wherein each multi-shaft gas turbine of the first, second, and third refrigeration compression strings has a rated output capacity of at least 70 megawatts.