Precautions For Steam Turbine Glands

Steam seal design should take the following factors into consideration:

① The resistance to steam flow within the seal should be maximized to ensure that the energy of any leaking steam is dissipated as fully as possible as it traverses the tortuous flow path and expansion chambers.

② The radial clearance between rotating and stationary components should be minimized, provided that contact and rubbing between them are strictly avoided. Furthermore, the design must incorporate features to mitigate the consequences should rubbing inadvertently occur-specifically, by minimizing the contact area and the resulting frictional heat generation, while simultaneously increasing thermal resistance to prevent heat-induced deformation of the surrounding primary components.

③ The axial clearance between rotating and stationary components must be maintained such that no axial rubbing occurs at any stage throughout the entire turbine unit startup and shutdown cycle; this clearance must also provide sufficient margin to accommodate differential thermal expansion and relative mechanical displacements.

Based on the aforementioned principles, the established and proven steam seal configurations employed in modern large-scale steam turbines include: the early-stage integral seal, the segmental seal, the shoulderless labyrinth seal, the honeycomb seal, and the adjustable seal. In the adjustable seal design, the clearance between the sealing teeth and the rotor decreases as the steam pressure rises, eventually reaching its specified design value. Conversely, during a shutdown sequence-as the steam pressure declines-spring forces act to restore the seal clearance to its maximum value, thereby preventing any contact or rubbing between the rotating and stationary components.

Steam seal performance exerts a significant influence on both the economic efficiency and the operational reliability of a turbine unit. Consequently, in order to minimize steam leakage losses and to enhance both the safety and economic performance of the unit, it is absolutely essential to upgrade existing traditional steam seals through the implementation of advanced steam sealing technologies.