How does a large turbine balance axial thrust?
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As the title suggests, how can axial thrust be balanced, other than using thrust bearings?
Most of the time it’s a balance drum + balance tube; I’ve never seen one with a balance disk
Reply to 2# 565026033: I know that centrifugal compressors are equipped with balance discs and balance pipes. But I’ve never seen one like this turbine. I guess I didn’t notice it before. Could you describe it in detail? The leakage gas from the high-pressure side of the turbine enters the low-pressure cylinder to do work; is the purpose of this to balance the axial thrust? Is it still just to recover the leaked steam and reduce the leakage from the labyrinth seal?
Leakage is not used to balance axial forces
http://bbs.hcbbs.com/viewthread.php?tid=901572&highlight=%C6%FB%C2%D6%BB%FA%2B%C6%BD%BA%E2 Check out this thread; it contains relevant information
In a steam turbine, the key components are the balance disk, balance piston, balance holes, and thrust bearings. Reaction-type steam turbines also have a balance drum. In a compressor, the main components are the balance disk, back-to-back configuration, and thrust bearings
The force exerted by steam on the turbine rotor can be broken down into two perpendicular components: a tangential force and an axial force. The tangential force is the circumferential force exerted by the steam on the blades at each stage; it is used to drive the rotor to rotate and generate mechanical work. The direction of the axial force is parallel to the turbine axis; it acts on the turbine rotor from the high-pressure side toward the low-pressure side, and is known as axial thrust. The axial thrust of multi-stage turbines can range from several tons to dozens of tons, and it must be balanced; otherwise, the turbine cannot operate properly. In fact, despite the measures taken, it is impossible to completely balance such a large axial thrust; the remaining unbalanced axial thrust is then borne by the thrust bearings. The function of the thrust bearing is to bear the remaining axial thrust and maintain the correct position of the rotor relative to the stationary parts. Common methods used to balance axial thrust in turbines are as follows: 1. Balancing piston: At the high-pressure end of the turbine, the diameter of its shaft seal is increased to create a balancing piston effect on the end face. Different steam pressures act on the annular areas at both ends of the balance piston. Under the action of this pressure difference, an axial balancing force is generated in the direction opposite to that of the steam flow. 2. Balance holes are provided on the impeller to achieve balance or reduce axial thrust.
In steam turbines, a balance hub, also known as a balance piston, along with balance holes and balance pipes, are used to supply air to the front end of the balance hub in order to counteract axial forces; it is still the balance hub that plays the key role, while balance holes are also provided on the impeller. The remaining axial force is borne by the retaining bearing; the force carried by the retaining bearing is generally smaller, and it is essentially balanced by the above two methods.