Alignment and rotordynamic optimization of turbine shaft trains using adjustable bearings in real-time operation

Abstract

A study on the use of innovative journal bearings of adjustable geometry/properties in industrial turbines is presented in this paper. The adjustable bearing geometry is investigated in this work as a bearing function which can resolve issues in rotordynamic performance of industrial steam/gas turbines. The rotordynamic issues that the proposed bearing is supposed to resolve are given shortly as (a) rotor–stator contact and eccentric rotor whirling, (b) non-optimum bearing loading, (c) instability (steam or oil whirl) and (d) structural distortions (in casing, pedestal or other component). The functionality of the proposed journal bearing is presented in results of unbalance response obtained through nonlinear transient analysis. The principle of the adjustable bearing is the quasi-static displacement of the bearing pads to locate the journal centre in the desired position and to configure the optimum bearing bore profile achieving the optimum performance regarding key parameters of operation such as concentricity of rotor and stator, optimum bearing loading, power loss, temperature rise, stability characteristics and others. The inner mechanism for applying the bearing pad displacement is not a topic of discussion in this paper, as in the current work, the adjustable bearing operation is studied on its fundamental operations. The journal bearing model concerns nonlinear bearing impedance forces which are assigned in the rotor nodes after solving numerically the Reynolds equation for the two-partial arc journal bearing lubrication of finite length and the configuration of the bearing is similar the bearing type installed in industrial turbine applications (partial arc bearings). The bearing model enables the development of the oil-whirl/whip phenomenon if there is a trend towards instability (e.g. light loaded bearing, high speeds). The study presented in this paper concerns two steam turbine-generator shaft lines of small (∼50 MW) and medium size (∼200 MW) in which the adjustable bearings are demonstrated on resolving different issues.