Experimental and numerical studies of buffer impulse dry gas seals

For more than 30 years, gas seal technology has been a key factor in ensuring the safety and reliability of centrifugal pumps, compressors, agitators and rotary equipment in the chemical and petrochemical industries. In view of changing environmental regulations, dry gas lubrication ensures the purity of the pumped liquid medium and zero emissions of toxic substances. The non-contact function of the mechanical seal is achieved thanks to the special topography of one of the surfaces of the seal rings, which creates a gasdynamic opening force during shaft rotation, eliminating friction. Buffer dry gas seals use a regulated inert buffer gas at a pressure of 1-2 bars above the process pressure to seal the process fluid from the atmosphere. At the same time, gas seals have a minimal temperature rise and lower energy consumption than liquid seals. And the global spread of non-contact seals with gas lubrication has led to a reduction in parasitic power losses due to friction and significant energy savings.

Among the double gasdynamic seals with radial arrangement of stages, the significant advantages of buffer impulse mechanical seals are distinguished by their non-contact operation mode and hydrostatic opening force provided by the shaft rotation and periodic impulse supplying of the cavities by feeders with the buffer medium. These seals are much easier to manufacture and reliable. Therefore, in these studies, using the CFD simulation, a thermohydrodynamic analysis of a buffer impulse dry gas seals were performed. Laminar air flow was considered as well as ideal gas law, and heat transfer through the solid surfaces of the seal rings. The transient problem of the flow during the circumferential interaction of the rotor and stator gap regions was solved, which made it possible to simulate the dynamic process of supplying the buffer pressure to the cavities of the buffer impulse seal. The validity of the proposed numerical models was verified by the available experimental results on the leakages, the average temperature of the face surface of the floating ring at the exit from the seal and pressure pulsations in the cavities and on the inter-cavity land. An analysis was performed on the influence of the fixed gap size, the depth and number of cavities and the pressure difference between the buffer and sealed medium on the amplitude of pressure pulsations, the magnitude of the gap opening force, leakages and the surface average temperature of the floating ring at the exit from the seal, as well as pressure and temperature distribution along the circumference and radius of the sealing rings. The thermal and mechanical deformations of the rings and the dynamic coefficients of stiffness and damping of the buffer impulse seal were obtained.