June 14, 2024
Single Shaft Turbine

Single Shaft Turbine: An Efficient Power Generator

A single-shaft steam turbine refers to a type of steam turbine that has a single shaft running through the turbine which is connected to the generator or other equipment being powered. In a single-shaft steam turbine, there is only one turbine rotor mounted on a common shaft that runs the entire length of the turbine.

Key Components of a Single-shaft Turbine

Turbine Rotor: The turbine rotor is the central rotating component that converts the thermal energy of pressurized steam into mechanical rotational energy. It consists of a shaft with blades or buckets attached that channel and direct the steam flow.
Casing: The turbine casing houses the stationary and rotating components. It contains and directs the steam flow through the turbine. Different casings make up the high-pressure, intermediate pressure and low-pressure sections.
Nozzles: Steam nozzles inject steam into the buckets to make them rotate. Nozzles are stationary and carefully direct the steam to maximize energy transfer to the turbine rotor.
Steam Supply: High-pressure steam is supplied from a boiler to the turbine inlet. After doing work in each section, steam is exhausted to the condenser through the steam exhaust casing.
Generator: The generator is coupled to the common turbine shaft. It converts the rotational mechanical energy of the shaft into electrical energy through electromagnetic induction.

Working Principle of a Single-shaft Steam Turbine

Steam at high pressure and temperature enters the turbine through stationary nozzle rings. The steam is directed at the buckets attached to the rotor blades, causing them to spin due to impulse and reaction. As the steam moves through the buckets, it decreases in pressure and temperature.

After passing through the high-pressure section, the steam is exhausted into the intermediate pressure section casing where more work is extracted from it. It then enters the low-pressure section for the final extraction of work before being exhausted to the condenser.
Each section is designed to efficiently extract work from the steam at progressively lower pressures until it leaves the turbine as low-pressure saturated vapor. A single rotating shaft transmits the mechanical power generated to a generator or other power-absorbing device.

Advantages of a Single-shaft Turbine

Simple design Fewer shafts and couplings means reduced complexity, maintenance needs and vibrations compared to multi-shaft turbines.

High efficiency Steam expands optimally through multiple turbine stages mounted on a common shaft to maximize energy conversion. Overall efficiency can exceed 90%.
Compact The footprint is smaller as all equipment is mounted on a single shaft. This is advantageous where space is limited.
Low cost Manufacturing, installation and operation costs are lower for single-shaft turbines compared to multi-shaft designs.
Reliability Fewer rotating and stationary parts translates to higher reliability and availability. Maintenance needs are also reduced.
Flexibility A single shaft turbine can accommodate varying steam parameters and loads more flexibly than multiple coupled shafts.

Applications of Single-shaft Steam Turbines

Due to their simplicity, efficiency, compactness and cost-effectiveness, single-shaft turbines are well suited for:

Base load power generation Large utility power plants commonly use single-shaft turbines rated from 100-800 MW to generate base power demands.
Cogeneration Capturing waste heat from industrial processes to drive a steam turbine for on-site power and heat.
Combined cycle power plants Used in conjunction with a gas turbine to boost plant efficiency in combined cycle configuration.
Marine propulsion Providing propulsion power for naval vessels and merchant marine applications.
Mechanical drive Directly driving large centrifugal pumps, compressors or gear boxes for oil & gas, petrochemical and other process industries.

Challenges with Single-shaft Turbines

While single-shaft turbines have many advantages, their challenges include:

Large size Very high capacity single-shaft turbines with ratings over 800 MW become highly complex and costly to manufacture due to their enormous size.
Load following issues Single cylinders aren’t very flexible for load fluctuations and may need supplementary firing or multi-valving for better load changes.
Imbalance problems Precise balancing of the long rotating assembly is critical to prevent excessive vibrations at high operating speeds.
Thermal stresses Large temperature differences within the casing and rotor components induce thermal stresses that must be properly managed.
Maintenance difficulties Removing or replacing components on the long shaft like diaphragms, seals becomes quite difficult during overhauls.

The single shaft turbine has proved to be a very efficient design for base load power generation, cogeneration and mechanical drive applications due to its advantages in reliability, compactness, cost and simplicity of operation over multiple shaft arrangements. With ongoing design improvements, it will continue playing a major role in power plants globally.

*Note:
1. Source: Coherent Market Insights, Public sources, Desk research.
2. We have leveraged AI tools to mine information and compile it.