Effect of pressure fluctuation in oil-gas multiphase pump on cavitation and performance of sealing liquid film

Abstract

During the operation of the oil-gas multiphase pump, due to the variable gas content of the incoming flow, the medium pressure at the high-pressure end fluctuates widely, which is easy to cause the stress change at both ends of the mechanical seal compensation ring and “instability” phenomenon. In this paper, a three-dimensional spiral groove seal film model is established. Considering the cavitation effect of liquid film gap, the variation law of end face cavitation and sealing performance of liquid film seal is explored according to the effect of pressure pulsation in the pump on the inner diameter side (Static mechanical seal, PLAN74 flushing scheme in API 682) and outer diameter side (Rotary mechanical seal, PLAN53A flushing scheme in API 682). The results show that the local pressure drop in the sealing liquid film is the main cause result to cavitation of liquid film. The inner diameter side pressure fluctuation has a great impact on the end face cavitation, and the wave peak is about 100 times that of the outer diameter side pressure. The inner diameter side pressure fluctuation should be avoided in engineering application. There is hysteresis between gas volume fraction (GVF) and boundary pressure fluctuation. The synchronization between sealing performance parameters and outlet pressure fluctuation is good, but there is phase difference with inlet pressure fluctuation. The inner diameter side pressure fluctuation has a great change on the sealing performance. The peak is about 5–20 times that of the outer diameter side pressure, which is easy to cause vibration of the mechanical seal. The amplitude and period of pressure fluctuation have a great impact on the GVF and sealing performance. The larger the fluctuation period is, the less obvious the hysteresis of GVF is, and the closer to the variation law of pressure fluctuation. During the actual operation of the oil-gas multiphase pump, the mechanical seal connected with the medium in the pump is rotary, and the flushing scheme ought to be PLAN53A to ensure the safe and stable operation of the oil-gas multiphase pump.