Types of Steam Turbines

Steam turbines can be classified into several types based on different design principles and operating conditions. Here are the main types of steam turbines:

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1. Impulse Turbine:

- Working Principle: In an impulse turbine, high-pressure steam is expanded through a nozzle, converting the pressure energy into kinetic energy. This high-velocity steam strikes the turbine blades, causing the rotor to spin.

- Blade Design: The blades are shaped to change the direction of steam flow, resulting in an impulse that rotates the turbine.

- Example: De Laval turbine.

- Application: Primarily used in high-pressure stages in power plants.

2. Reaction Turbine:

- Working Principle: In a reaction turbine, the steam expands as it passes through both the fixed and moving blades, causing the blades to experience a reaction force that rotates the rotor. Here, both pressure and kinetic energy of steam are utilized to drive the turbine.

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- Blade Design: The blades are shaped to allow steam to expand through them, and the reaction force from this expansion drives the rotor.

- Example: Parsons turbine.

- Application: Suitable for low-pressure stages of steam turbines and large power generation systems.

3. Condensing Turbine:

- Purpose: These turbines are designed to maximize energy extraction from the steam by condensing it into water at the end of the process.

- Process: After passing through the turbine, the steam is condensed in a condenser, creating a vacuum that increases the efficiency of the system.

- Application: Primarily used in power plants where maximizing efficiency is critical.

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4. Non-Condensing (Back Pressure) Turbine:

- Purpose: These turbines exhaust steam at a pressure higher than atmospheric pressure, which can then be used for heating or other industrial processes (cogeneration).

- Application: Common in industrial plants where waste heat is reused for processes like district heating, chemical production, or paper mills.

5. Single-Stage Turbine:

- Design: The entire pressure drop of steam occurs in a single set of blades.

- Application: Typically used in small-scale applications or where pressure differences are small, such as small mechanical drives.

6. Multi-Stage Turbine:

- Design: Steam passes through several sets of blades (stages), with pressure and temperature reducing gradually across each stage.

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- Purpose: More efficient than single-stage turbines, especially for large power generation as they extract more energy from the steam.

- Application: Large power plants and industrial applications where high efficiency is required.

7. Extraction Turbine:

- Working Principle: Steam is extracted from an intermediate stage of the turbine for use in industrial processes or heating while the remaining steam continues to expand and generate more power.

- Application: Cogeneration plants where both power and process steam are needed.

8. Reheat Turbine:

- Working Principle: Steam is expanded partially in the turbine, then reheated in the boiler and passed through additional turbine stages. This process increases efficiency by reducing moisture content in the later stages.

- Application: Common in large power plants to improve thermodynamic efficiency.

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9. Back-Pressure Turbine:

- Working Principle: The turbine exhausts steam at higher pressure than atmospheric, typically used in situations where the exhaust steam is required for other processes like heating or industrial use.

- Application: Industries with both power and process steam needs (e.g., sugar mills, paper mills).

10. Radial Flow Turbine:

- Design: In radial flow turbines, steam enters the turbine radially (perpendicular to the shaft) and flows outward or inward through the blades.

- Application: These turbines are less common in large power generation but may be used in smaller-scale applications or special industrial settings.

11. Axial Flow Turbine:

- Design: Steam flows parallel to the axis of the turbine, making it the most common design for large-scale power generation.

- Application: Widely used in power plants due to its high efficiency and capacity for large steam volumes.

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Each of these turbine types has specific advantages depending on the application, pressure, and efficiency requirements. The choice of turbine type significantly impacts the overall efficiency and operational capabilities of power plants and industrial processes.