Investigation on the Seal Structure Design and Rotor Vibration Controller for Back-to-Back Centrifugal Compressor

Abstract

Centrifugal compressors, as the key equipment in process industries such as petroleum refinery and chemical, are faced with the challenges of rotordynamic stability and high efficiency on condition of high pressure ratio and volume flow rate. The back-to-back centrifugal compressor has a reputation of higher efficiency for its smaller balance piston drum and axial thrust bearing than those of through-in-line compressor. However, fluid non-conservation excitation forces at the balance drum seal will prominently affect the stability of rotor; there are risks of rotor-stator rubbing caused by large vibration amplitude at balance drum seal when the rotor loses stability. Aiming at this case, the patented integrated structure of balance drum seal and vibration controller was presented which combines the function of active-magnetic-bearing (AMB) and hole-pattern-seal (HPS). The feasibility of the integrated AMB-HPS was verified by ANSYS, and the effect of the diameter and depth of the hole on the performance of AMB was studied as well. A test rig was built to test the stiffness-parameters of the integrated AMB-HPS. Finally, the rotor vibration controller was investigated focusing on (1) balancing the cross couple force exerted by the seal on the rotor by the control strategy of displacement feedback, and (2) adding additional damping by the control strategy of velocity feedback. Simulation work of an industrial rotor was carried out. The results indicate that: (1) the presented seal structure can provide enough force for controlling the vibration of the rotor; (2) displacement feedback strategy has less energy consumption than the velocity feedback at the same control effect. The work of this paper can provide the foundation for the designing of new centrifugal compressors.