Abstract

Hydraulic turbochargers are used in sea water reverse osmosis or acid gas removal cycles to recover wasted pressure energy, decrease operating cost, and increase the overall process efficiency. This paper presents rotordynamic analysis of a large hydraulic turbocharger developed for the acid gas removal process (1500 KW output power, shaft diameter of 101 mm, and operating speed of 8,000 rpm). The hydraulic turbocharger has significant advantages when compared to a reverse running pump such as high speed, compact hydraulics, seal-less design and process lubricated bearings. Utilizing a hydraulic turbocharger in acid gas removal cycles results in a much smaller footprint and no external lubrication oil skid and support system for mechanical seals. The turbocharger rotor consists of a hydraulic turbine runner directly coupled to a pump impeller in a back-to-back arrangement. The shaft is supported in the middle by a set of rigid-walled process-lubricated journal bearings resulting in an overhung configuration (bearing span = 180 mm, rotor mass = 50 kg). For a large high-speed rotor-bearing system, the bearing load-carrying capacity and rotordynamic stability are crucial to ensure a stable performance and to avoid catastrophic failure.

In the presented study, rotordynamic performance of a rotor-bearing system is evaluated analytically and experimentally. An analytical model is developed to simulate the rotordynamic performance of a shaft supported by a set of journal bearings. The analytical model simulates the rotor’s orbit in the time domain by solving the rotor’s equation of motion, and solving the transient Reynold equation for each bearing simultaneously. In addition, the model considers the effect of turbulence. An in-house test loop is developed and used to evaluate the turbocharger’s hydraulic and mechanical performance. The test loop runs on a LabView-based control system. The rotor vibration is measured by a set of eddy-current probes, oriented perpendicular to each other. The simulation results from the analytical model are compared against measured experimental data. Comparison of the simulated waterfall and bode plots with experimental data shows that the simulation results agree with the measured data for the frequency and amplitude of vibration. Moreover, the effect of turbulence on the rotordynamic performance of the hydraulic turbocharger is investigated, and it is shown that the turbulence significantly changes the rotordynamic behavior of the system.

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