by A single shaft turbine is a type of turbine in which multiple turbine modules are mounted on a single shaft. Each module works independently to convert the kinetic energy of fluid (steam, gas or water) into rotational mechanical energy. The torque produced by each module is additive and helps in faster rotation of the single shaft. This arrangement allows single shaft turbines to generate higher power output compared to multiple shaft turbines with same dimensions.
In a single shaft turbine, steam enters the first turbine module where some of its pressure energy is converted into kinetic energy by the rotating blades. The steam then flows to the next module and the process continues till the steam exhausts after passing through all the modules in Single-shaft Turbine. Each module extracts a certain amount of energy from steam and in the process steam pressure and temperature decrease gradually. The single shaft transfers the rotational force from all modules collectively to the generator which is coupled to it.
Advantages of Single Shaft Design
Compact Design These turbines occupy less space compared to multi shaft designs having same power output. All modules are mounted on a single framework thus reducing the overall footprint.
Lower Costs Manufacturing, installation and maintenance costs are lower due to use of single shaft and less auxiliary components like gearboxes.
Higher Efficiency Single shaft arrangement ensures optimum energy transfer between modules. Steam expands through multiple stages extracting maximum work at each stage. Overall cycle efficiency is higher.
Higher Power Output For a given turbine size, these turbines can produce more power. Additional modules can be mounted on same shaft to boost power. Rated capacity can be 500MW or more.
Scalability Modules can be added or removed as per power requirements without major design changes. Output can be upgraded over plant’s lifetime by small modifications.
Applications
Most widely used in thermal power generation Coal, gas, nuclear and combined cycle power plants extensively use single shaft turbines to drive electrical generators. Steam from boilers first expands in high pressure turbine before exhausting into lower pressure module/s. Depending on the power output, single shafts can have 1-3 expansion stages.
Cogeneration plants Industries producing steam/power for their processes and grid also adopt single shaft designs. Exhaust steam is used for process heating after passing through turbine.
Marine propulsion Naval ships and large marine vessels often have steam turbine plants for propulsion and electrical needs. Single shaft arrangements with multiple modules facilitate compact installation in confined spaces.
Desalination Thermal desalination plants co-located with power stations use single shaft extraction turbines. Part of steam is tapped for desalination after high pressure stage.
Challenges with Single Shaft Turbines
Complex Manufacturing Single forgings or castings forming the shaft and mounting multiple modules require intricate machining and quality assurance checks. Small defects can cause shaft failure jeopardizing entire turbine.
Thermal Stresses Difference in temperatures across modules exert differential thermal expansion stresses on single shaft. Careful material selection and engineering is needed to avoid fatigue failures.
Vibrations Ensuring smooth dynamics during acceleration/deceleration with multiple coupled components mounted on same shaft is challenging. Vibration analysis and balancing is critical.
Maintenance Issues Inspections and overhauls involving shaft withdrawals are more laborious and time taking for single shaft compared to modular designs. Downtimes affect plant load factors.
To summarise, these turbine designs have gained prominence in large power generation applications due to advantages like compactness, higher efficiencies and flexible uprating. Continuous technology improvements are addressing the manufacturing and structural challenges to further enhance reliability of single shaft configurations. Their widespread use will continue in fields requiring compact yet high capacity prime movers.
Future Outlook
With growing global energy demands, trends point towards larger thermal and nuclear power plants coming up in future. This naturally benefits the applications of single shaft turbines owing to their intrinsically high capacity features. Advances in material sciences, 3D printing and specialised fabrication techniques will help manufacture increasingly larger single shafts with multiple stages of higher parameters.
Use of advanced alloys and composites will strengthen single shaft designs against high temperatures and stresses. Online condition monitoring technologies will aid condition-based maintenance reducing unexpected breakdowns. Digital twin modelling will aid virtual prototyping and performance predictions, making design iterations more efficient. 3D thermal/structural simulations can optimise shaft profiles balancing strength and dynamics.
The supercritical parameters of newer ultra thermal and advanced ultra supercritical plants necessitates turbines operating at severe conditions. Single shaft configurations equipped with advanced cooling and sealing technologies can handle such extremes of pressure and temperature. Power augmentation solutions like reheating, residual reheat will be commonly used to boost output of single shafts.
Overall with a perfect marriage of latest manufacturing and material technologies along with intelligent monitoring and simulations, future single shaft turbines are set to scale new heights of power ratings and reliability. Their integration with renewable hybrid systems will further proliferate clean power generation globally.
*Note:
1. Source: Coherent Market Insights, Public sources, Desk research.
2. We have leveraged AI tools to mine information and compile it.
