Research On The Swirling Supersonic Two-phase Condensing Flow And Experimental Performance

Supersonic condensation separator used as a novel purification device applied in natural gas process combines low temperature condensation with swirling separation and takes the advantages of compact structure, low investment cost and energy consumption and non-pollution. Gas in the supersonic separating section has lower pressure than the outlet pressure, and lower temperature than the refrigerating temperature obtained in turbo expander under the same pressure ratio, resulting in a high iso-entropic efficiency. This paper aims to reduce pressure energy loss and to make the device suitable for low pressure conditions. Furthermore, explorations regarding to structural design of supersonic gas separator, condensation characteristic of wet flue gas in the nozzle, gas-liquid two phase flow and methods to improve the separation performance, were conducted. The main research work and conclusion are as follows.(1) Based on one-dimensional variable cross-section isentropic flow and numerical computation software, a novel supersonic gas separator used for low inlet pressure is designed. Meanwhile, the influence of structural parameters and operating parameters on the inner flow characteristic in the separator is analyzed, realizing the temperature in the diverging section of nozzle is below 250 K with the lowest temperature of 231 K, and without shock wave in the device when the inlet pressure is 0.14 MPa.(2) The Eulerian two-fluid model for non-equilibrium spontaneous condensation of wet flue gas is built and verified, with the consideration of the velocity slip between gas phase and liquid gas. The effect of structural parameters and operating parameters on the condensation characteristic of the gas is investigated. The results indicate that the diameter of condensing liquid formed in the nozzle can reach 1.12?m, with the peak value of nucleation rate is 7.5×1018m3/s when inlet pressure is 0.14 MPa, relative humidity is 0.6 and area ratio of the nozzle is 1.266.(3) Combined with VOF model, the numerical model used to analyze gas-liquid two phase flow process in the supersonic gas separator is established and verified. With this model, the interaction between liquid film and supersonic flow is researched. It is found that under the action of high velocity gas flow, the height of liquid film becomes thinner along the axis of the nozzle, but the surface velocity of the film becomes larger. Meanwhile, the state of supersonic gas flow in the nozzle is destroyed by the thin liquid film.(4) An experimental platform is set up to investigate the separation performance of the supersonic gas separator under different operating and structural parameters. The experimental results show that with the increase in pressure ratio and outlet angle of the separator, the separation efficiency increases first and then decreases, with the maximum of 57.06%. The type of drainage structure has a significant influence on the efficiency of the experimental device. Drainage structure of (a) type is superior to (b) type. With the increase in the angle of the liquid drainage ?, the separating efficiency is decreased.