Analysis on the startup characteristics of CO2 dry gas seal based on the F-K slip flow model at high pressure

Abstract

The gas film of the carbon dioxide (CO2) spiral groove dry gas seal (S-DGS) is less than 3 μm during the startup process, and its opening stability is directly related to the operating performance of S-DGS. The finite difference method is employed to solve numerically the pressure distribution of S-DGS considering the slip flow and the real gas effect. The influence of both effects on the startup characteristics of S-DGS is discussed at different structural parameters. The results show that the slip flow effect inhibits the opening ability of CO2 S-DGS, whereas the real gas effect enhances its opening ability. Within the range of working conditions investigated, the seal processes a lowest startup rotational speed when the spiral angle is 7.5°, and the highest gas film stiffness occurs at small spiral angle when the film thickness is 0.6 μm. However, the relationship between groove number and gas film stiffness is complex which relates to the balance film thickness of the startup process. A higher opening ability can also be achieved by reasonably increasing the balance coefficient.