Exducer turbines, the optimized solution for liquefied gas expanders

摘要

The liquefaction process for natural gas requires LNG expanders with flexible operation regarding mass flow and differential pressure. The first pilot expanders were installed in Malaysia and were designed as hydraulic turbines with variable inlet guide vanes and air-cooled generators. Sealing problems, low reliability and hydraulic efficiency losses due to guide vane clearances resulted in the development of a completely different generation. The second generation of LNG expanders, designed as a variable speed cryogenic turbine generator, eliminates the variable guide vane losses, but requires step-down and step-up transformers and electronic frequency converters. For power generation in the range above 1.5 MW electronic frequency converters are less economical and constant speed cryogenic submerged turbine generators are the preferred solution. LNG expanders require a design that permits the turbine generators to adjust their operation according to a variety of input parameters. The new and advanced LNG expanders use variable pitch Exducer Turbines operating at constant speed thus eliminating expensive transformers and frequency converters and increasing the total power output. Design and performance of the Exducer Turbine, the third generation of LNG expanders, is presented and compared with conventional variable speed cryogenic turbines. Exducer Turbines are the optimised solution for all applications in new liquefaction plants of any size and process, in floating LNG production units, for de-bottlenecking of existing LNG plants, and for two-phase expansion in specialized processes with partial LNG vaporisation.