The liquefaction process of natural gas often operates at high pressure level, thus the LNG product is of very high pressure and must be reduced to satisfy the technical requirement for storage and transportation. Traditionally, the high-pressure LNG is expanded isenthalpically by means of J-T valves but this introduces an unexpected temperature rise, leading to vaporization of LNG product and subsequently a reduced delivery. An efficient alternative is using the LNG expanders to replace the J-T valves and achieve a near-isentropic expansion and subsequently suppress the cavitation. In the present study, a single stage LNG turbine expander is developed as a replacement of J-T valve for the purpose of cavitation suppression. The cavitating flow behavior is investigated by using a multiphase cavitation model. The effect of impeller geometric parameters on the turbine flow and performance has been identified through sensitivity studies. The following are demonstrated: (1) The predicted turbine overall efficiency is 91.34%, shaft power delivery is 81.16kW, temperature drop is 0.84 K; and the overall vaporization rate is less than a percentage. (2) Cavitation is encountered in the impeller leading edge region and half stream-wise region, resulting respectively from the viscous dissipation and flow separation. (3) At larger than design flow rates, the predicted turbine overall efficiency decreases nonlinearly with the flow rate due to cavitation zone growth in the leading edge region; at lower than design flow rates, the overall efficiency increases with the flow rate, due to cavitation zone decrease in the half streamwise region. (4) Cavitating flow behavior is sensitive to impeller geometry tuning. Variation of the impeller inducer twist angle reduces the trialing edge cavitation and subsequently improves the turbine overall performance. (5) Cavitation flow behavior is also sensitive to the radial gap size of the nozzle and impeller.
- International Gas Turbine Institute
Design and Numerical Flow Analysis of a LNG Power Recovery Turbine
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Li, K, Sun, J, Fu, J, & Song, P. "Design and Numerical Flow Analysis of a LNG Power Recovery Turbine." Proceedings of the ASME Turbo Expo 2013: Turbine Technical Conference and Exposition. Volume 5B: Oil and Gas Applications; Steam Turbines. San Antonio, Texas, USA. June 3–7, 2013. V05BT24A014. ASME. https://doi.org/10.1115/GT2013-94900
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