All steam turbines have identical components, depending on the type of turbine, they are assembled differently. In this blog, we attempt to familiarize you with these components and the building of steam turbines.
Steam Turbine Components
The core components of all steam turbines are the same. Each of these components serves a specific purpose and when combined with the others. This results in the final operation and the ultimate goal of the steam turbine; which is the generation of power and kinetic energy.
You will learn about each of these components and their roles in steam turbines in the sections that follow.
The steam chest and its casing:
This section is linked to the higher pressure steam supply line and the low-pressure steam exhaust line. The governor valve and the Overspeed trip valve are housed in the steam chest linked to the casing. The casing houses the rotor and nozzles that expand and direct the steam against the rotating buckets.
Rotor:
The rotor is made up of a shaft and disk assembly with buckets. Through the bearing casings, the shaft extends beyond the casing. The shaft has one end that connects to the driven pump. The other end serves as the speed governor and the overspeed trip system.
The bearing cases:
With the rotor, the bearing cases are connected. It supports the rotor while also assembling the casing and steam chest.
Sealing glands in casings:
Seal the casing and the shaft together. For this, spring-backed segmental carbon rings are used. Augmented by a spring-backed labyrinth portion for increased exhaust steam.
Governor system:
In steam turbines, the governor system functions as a speed-sensitive control system. By altering the steam flow through the turbine, the governor valve controls the turbine speed. A spring-opposed spinning weight, a steam valve, and an interconnected linkage or servo motor system comprise the system.
Labyrinth Seal :
The labyrinth reduces leakage from the high-pressure side to the low-pressure side by allowing a small amount of leakage. Between the labyrinth and the shaft, minimum clearance is maintained.
Assembly of the nozzle ring and reversing blade:
Bolts hold the nozzle ring to the inside bottom part of the steam end housing. The nozzles direct the steam flow from the steam chest to the first row of blades of the Curtis stage. The reversing blade assembly is bolted to the nozzle ring and is situated between the Curtis stage’s blade rows (the Curtis stage has two rows of blades).
The sentinel valve:
This is a warning mechanism installed on the exhaust end turbine casing. It detects high turbine exhaust end casing pressure. When the casing pressure surpasses a predefined level over the usual operating pressure; the valve emits a small amount of visible steam into the atmosphere, resulting in an audible sound. This valve does not function as a relief valve.
Auxiliary steam valves:
When working under changeable load or steam conditions, auxiliary valves are employed to improve efficiency. The valves are located between the steam chest and the nozzle ring in the steam passageway (the lower part of the steam end turbine casing).
Turning Gears:
Large turbines have moving gears that allow the rotors to rotate gently during warm-up and cool-down.
Diaphragms:
Stationary diaphragms separate the inner stages and house the interstage nozzles and seals. The nozzle expands the steam and directs it against the rows of revolving blades that follow.
Over-speed trip system:
In the event of an over-speed condition, the trip mechanism functions independently of the governor-controlled system, closing the trip valve to stop the flow of steam to the turbine. A spring-loaded pin or weight set on a collar in the turbine shaft, a quick-closing valve separate from the governor valve, and an interconnecting linkage. At a given speed, the centrifugal force generated by the rotation of the pin in the turbine shaft exceeds the spring loading.
Turbine Cylinders:
Turbine cylinders must bear steam pressure, so they are of sturdy construction with strong walls. Temperature gradients within rigid components produce significant stresses in the material, which, when combined with mechanical stress caused by pressure, can lead to material failure.
Gas/Steam Turbine Control System
A gas and steam turbine control system has been created to be a fully integrated control, protection, and monitoring system for gas and steam turbine generators, as well as mechanical drive applications. IS210DRTDH1A and IS210DTAIH1A are some examples of GE control system components.
Summary
Temperature gradients become especially severe during heating and cooling because larger components take longer to change temperature than smaller portions. In addition, thick cylinder walls are essential to bear pressure, but to minimize thermal stress, there should be no abrupt changes in thickness or asymmetrical arrangements. This invariably results in smooth, rounded profiles of the stress-bearing components.
In addition to enhancing your technical knowledge of this machine, knowing the components of the steam turbine will familiarize you with the general construction of steam turbines. Consequently, it gives you a clear grasp of how it operates.
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