Large base-load natural gas liquefaction (LNG) facilities with optional capability for high ethane, propane or mixed LPG recovery.
Feedstock: Naturally occurring hydrocarbon gas pretreated to remove contaminants such as moisture, H2S, CO2, mercaptans and mercury.
The process uses three predominantly pure component refrigerants: propane, ethylene and methane. The first refrigerant is a multiple-stage closed-loop propane system (1). The second is a closed-loop ethylene system (2) consisting of two or more stages. Ethane may be substituted for ethylene. A combination of brazed aluminum and core-in-kettle exchangers are utilized for heat exchange. Feed is routed successively through each stage of propane and ethylene. Air or cooling water removes process heat and condenses propane, while propane removes heat and condenses ethylene.
Heavier products are typically removed (3) after one or more stages of ethylene refrigeration. Fractionation design is highly dependant on feed composition and desired product recovery. Efficient designs with high ethane and propane (>95%) recovery are available. The resulting methane-rich feed is routed to methane refrigeration.
Methane refrigeration (4) is a multiple-stage open- or closed-loop system. A recycle methane stream is used to help balance refrigeration loads and improve efficiency. Propane and ethylene are used to remove process heat. With the open-loop configuration, fuel gas is drawn off to prevent inerts from building in the refrigerant. For feeds with high nitrogen or helium, an inerts rejection system is integrated into the design.
Economics: The process offers a well-established, reliable, efficient and low-cost LNG solution. Overall facility EPC costs utilizing the technology have been at or under $200 per mtpy. Thermal efficiency of the process is high with designs that exceed 93%, including utilities, feed pretreatment and the remaining facility. Large train sizes of over 7.5 mtpy are available in multiple turbine/driver configurations with even larger train sizes in development.