FUNCTION OF LABYRINTH PACKING IN STEAM TURBINE:-
In a turbine, rotor rotates inside the casing. Rotor extended outside the casing at both side and rear side . the portion from where the rotor exists the turbine casing is called a gland . there is chance of steam leakage and atmospheric air ingress to the front and rear gland respectively. So it is required to seal the portion to prevent leakage of steam and atmospheric air ingress. Gland at the front end is called front gland and rear is called the rear gland . to reduce the pressure difference between atmosphere and inside the casing. Sets of labyrinth seals are provided . as discussed earlier . these labyrinth seals causes pressure drop along the rotor . but only labyrinth packing is not sufficient to prevent steam leakage of steam or air. So, gland sealing system is used to prevent leakage . low pressure steam is supplied to final seats of labyrinths. Arrangement is done vent the excess steam. To drain out the condensate producing due to cooling of the gland steam drain are also provided .
Labyrinth-type steam seal, also known as labyrinth steam seal, has the following commonly used structural forms: comb-shaped, D-shaped, and fir tree-shaped.
Labyrinth-type generally has three components: steam seal body, vapor seal ring and sleeve (or a journal with a convex shoulder), such as the steam seal body fixed to the cylinder body, the inner with T-slot groove (Clapboard steam seal generally does not have gas seal, and directly milled T-slot groove on the partitions). Steam seal ring generally is made up of 4 to 6 steam seal blocks, installed inside the T-slot groove of the gas seal body, and suppressed with the spring leaf. On the inner ring and sleeve(or journal), there are synergistic steam seal tooth and shoulder bump (if the steam seal tooth is flat teeth, there is not shoulder bump on the shaft protruding shoulder), and forms a number of circular holes and circular steam room. This can repeatedly cut down,and gradually reduce the pressure and expand. Under the conditiio of the steam seal parameters and the leakage cross-section are fixed, with the increase in number of steam seal teeth, the pressure difference of every port is correspondingly reduced. Thus, the amount of steam flow through the port is also bound to decrease, thereby to achieve the purpose of reducing the amount of steam leakage.
The steam seal inside the steam turbine includs partitions and the surrounding strap seal, high pressure cylinder and low-pressure cylinder endsteam seal. These steam seal effectively prevents steam leakage in each chamber, steam leak out and air leak into.
The front and rear steam seal of the unit and the clapboard seal steam are using comb-type steam seal structure. In this gas seal structure, steam seal high- and low-tooth on the rotor and steam matching the long- and short-tooth of the steam seal ring forms a labyrinth seal steam. The gear strength of the seal ring of this structure is higher, vapor seal performance is good and is easy to maintain and repair.
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