FUNCTION OF GLAND STEAMING IN TURBINE OPERATION
in this article we discussed about the function of gland steaming during the turbine operation. gland steam providing a seal between turbine shaft and turbine casing . so gland steam protect the leakage of steam outside of the turbine and also and suck the ambient air inside .
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.
DIFFERENT TYPE OF STEAM SEALING IN TURBINE
When the steam turbine runs, the rotor rotates with a high speed, while the cylinder, partitions and other parts are fixed and static. In order to avoid the rub between the rotor and the stator, an appropriate gap should be left between them. The existence of a gap will lead to steam leakage (leakage), mainly reflected in:
At the gap of partitions (or the static blade loop) and the main axis; the gap of rotor blades top and the cylinder (or partition sets); point where the turbine spindle piercing out of the cylinder, in the high-pressure side the steam will leaking out from the cylinder, while in the low-pressure side the steam will leaking air into the cylinder.Steam leakage (leakage) can not only reduce the unit’s efficiency, but also affect the safe operation of the unit. In order to reduce steam leakages and to prevent the air leakage, there are often sef with seals at these gaps, and they are usually called steam seal.
Steam seal can be divided into according to the different installation positions:
Shaft steam seal
As the pressure inside the cylinder isn’t equal to the atmospheric pressure outside, it will make the steam inside the cylinder or air outside the cylinder leak out or into along the radial gap between the spindle and the cylinder, resulting in refrigerant loss, deterioration of operating environment, and heating the bearings journal or make steam into the bearing room, causing deterioration of oil quality, air leakage and the destroyment of the vacuum, thereby increasing the pumping load. These will reduce unit efficiency. Therefore, there are gas seal at both ends where the rotor passes through the cylinder. This kind of gas seal is shaft steam seal or shaft seal for short. High-pressure shaft seal is used to prevent steam leakage out of the cylinder while low pressure shaft seal to prevent air leakage into the cylinder.
Clapboard steam seal
Steam seal for the gap of the clapboard inner hole and the spindle. Due to the great pressure difference in the front and at the back of the partition and the gap between the partition and the spindle, there must be a part of the steam passing through from the front part of the partition and leaking into steam room through the gas
between the partition and the impeller. As this part of the steam doesn’t pass through the nozzle, and worsen the mainstream flow of steam, thus creating a partition steam leakage loss. Therefore, there is setting with a clapboard steam seale.
Flow Steam Seal
Steam seal for the gap between rotor cascade and the partition and the cylinder,and it is used to reduce the the axial steam seal for rotor blades root and radial and axial steam seal at dynamic blades surrounding strap.
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 condition 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 includes partitions and the surrounding strap seal, high pressure cylinder and low-pressure cylinder end steam 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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