A PROCESS TO CONTROL THE LIQUEFYING OF A GASEOUS, METHANE-RICH FEED TO OBTAIN LIQUEFIED NATURAL GAS

摘要

Cooling and liquefying a gaseous, methane-rich feed (20) in a main heat exchanger (1) against evaporating refrigerant to get a liquefied stream (23) and passing (80) the liquefied stream (23) to storage as liquefied product. The process comprises adjusting the composition and the amount of refrigerant and controlling the liquefaction process, using an advanced process controller based on model predictive control to determine simultaneous control actions for a set of manipulated variables in order to optimize at least one of a set of parameters whilst controlling at least one of a set of controlled variables, wherein the set of manipulated variables includes the mass flow rate of the heavy refrigerant fraction (52) the mass flow rate of the light refrigerant fraction (59), the amount of refrigerant components make-up (26), the amount of refrigerant removed (54), the capacity of the refrigerant compressor (30, 32) and the mass flow rate of the methane-rich feed (20) wherein the set of controlled variables includes the temperature difference at the warm end (3) of the main heat exchanger (1), a variable relating to the temperature of the liquefied natural gas (23), the composition of the refrigerant entering the separator (45), the pressure in the shell of the main heat exchanger (1), the pressure in the separator (45) and the level of the liquid in the separator (45), and wherein the set of variables to be optimized includes the production of liquefied product (80).