SIMULATING OPERATIONAL TRANSITIONS IN A NITROGEN RECYCLE LNG PLANT

摘要

For certain floating natural gas liquefaction (FLNG) applications, nitrogen recycle refrigeration technology can provide an attractive alternative to mixed refrigerant technology. Although less efficient than mixed refrigerant cycles, nitrogen refrigeration cycles avoid the use of hydrocarbon refrigerants. This reduces the inventory of flammable hydrocarbons on the ship and provides the benefit of eliminating the need to import refrigerant and provide storage. For FLNG applications, aero-derivative gas turbines are often selected as the drivers for the refrigeration compressors, although motor drivers are also considered. Either will often lead to parallel arrangements such as 2 × 50% refrigeration trains. If aero-derivative drivers are selected, their more frequent inspection and maintenance schedule will require that a refrigeration train be taken offline periodically. The plant will operate at reduced rates during those times. Smooth transitioning between these operating modes for routine inspection reasons or for unscheduled machinery trips is essential to keep the overall plant online and avoid excessive flaring. Using dynamic simulation with Air Products' proprietary models, this paper will discuss an operational transient in the nitrogen recycle process.