(138c) Performance Characteristics of LNG Tandem Expanders

In 1996 the first LNG Expanders went into operation at a liquefaction plant in Malaysia and ever since every new liquefaction plant has been equipped with LNG expanders. It is a frequently discussed trend that the size of LNG liquefaction plants is continuously increasing and consequently also the size of each plant component is increasing as well. For the past 10 years the average size of LNG expanders has doubled and the traditional design of the liquid expanders has satisfied the specified performance requirements without major changes. To comply with the further projected increase in the size of liquefaction trains the design of LNG expanders has to be modified. The key objective for the performance of LNG expanders is high efficiency over a wide range of mass flow variations. Further design objectives are reliability, safety, weight and size. These objectives are best achieved with a new design arranging two LNG expanders in a tandem configuration. The paper presents the basic design and the typical performance characteristics of LNG Tandem Expanders and analyzes the differences and advantages compared to currently designed LNG expanders.