Supersonic Swirling Separator for natural gas heavy fractions extraction: 1D model with real gas EOS for preliminary design

Abstract A Supersonic Swirling Separator (SSS) device could be usefully adopted in the natural gas transmission pipelines in order to condense and separate the heavy hydrocarbons from the gaseous phase without significant pressure losses. In the present work, two models were developed to simulate the phenomena involved in the process: supersonic flow acceleration in a nozzle, flow swirling effect, centrifugal separation of liquid and gaseous phases in the last straight pipe. The model allows a satisfactory first attempt 1D design of the whole separator. A typical Natural Gas mixture was considered and, starting from that, two different simplified mixtures with reduced number of components (three and five) were defined in order to achieve a purpose satisfactory and reliable model with acceptable computational time and resources for a basic design tool. The GERG EOS were adopted in the mixtures modelling, implemented in NIST REFPROP, which are the most accurate currently available. The thermodynamic one dimensional model allowed the calculation of the shock wave axial position in the divergent channel, the main thermodynamic properties distribution along the nozzle and the composition of the liquid and vapor phases. A simplified but sufficiently accurate numerical procedure was developed to evaluate the two phase sound speed. An extended sensitivity analysis was carried out for the typical range of the device boundary conditions. In addition, a model for the simulation of the gas-liquid centrifugal separation was proposed. Joining the two models allowed the basic design of the separator geometry and the check of the expected condensation and separation performance.

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