| 摘要 |
<p>A process for liquefying a gaseous methane-rich feed (20) to obtain liquefied natural gas, wherein a gaseous methane-rich feed at elevated pressure is conducted through a heat exchanger (1), where it is cooled, liquefied and sub-cooled against evaporating refrigerant. The liquefied product (21) is discharged from the heat exchanger. The refrigerant cycles in a closed loop, wherein the evaporated refrigerant (22) is removed from the heat exchanger, and is compressed (30) to get high pressure refrigerant which is cooled (31,32) and divided into a liquid (heavy) portion (24) and a gaseous (light) portion (25), which are conducted to the heat exchanger for sub-cooling and liquefying the gaseous methane-rich feed. The sub-cooled refrigerant portions (35,37) are introduced into the shell of the heat exchanger at respective positions for being evaporated. The process is controlled by two separate process controllers, wherein the mass flow of the methane-rich feed is controlled by using a first process controller, and the loop of the refrigerant is controlled by a second controller using a model predictive control.</p> |
