Steam turbines are one of the most widely utilized power plant-based components for energy generation currently. Steam turbines are useful in multiple types of power plants globally, including solar thermal, nuclear, coal-based, geothermal, and natural gas-filled power plants. Statistically, it is expected that the market value of the steam turbine industry is set to reach $14.9 billion by 2026.
In the context of the higher efficiency rate of steam turbines, it is important to consider the design of the machine. Indeed, the components and design do determine the overall output level and power generation process efficacy of steam turbines. In fact, currently, power plant developers are focusing on expanding the capacity of steam turbines and ensuring more operational availability. Statistically, the over 300 MW capacity segment of steam turbines noticed the highest volume share in 2019 at approximately 60.5%.
What are steam engines?
Steam turbines mainly convert kinetic (movement) or thermal (heat) energy into electric power. This depends on the turbine type, design, and compatible generation technique.
Typically, the steam turbines operate by heating water with natural heat sources (e.g., nuclear/gas) to create steam. Thereafter, the pressurized steam passes through the turbine and turns the blades, creating rotational energy. Specifically, the rotating stator blades in the turbine speed up the pressurized heated steam.
This creates impulse as well as reaction forces against the rotating blades. This energy modifies to mechanical energy via the generators and results in electricity output. To note, power plant operators can select among different sizes and shapes. The design of steam turbines varies in regions based on the requirement, from single-stage to multiple-stage machine alternatives.
How does a steam turbine operate to produce electricity?
Essentially, this is the fundamental operation of steam turbines for optimal electricity output, though there are more detailed steps involved. The generator of a steam turbine heats up the water after getting exposed to extremely high-temperature sources.
Typically, the steam generated in the boiler pressurizes and releases into the turbine. This results in the rotation of the turbine blades. Thereafter, the mechanical energy it releases supports the electricity generation process in an attached generator. Here, a rotating shaft connects the generator and the turbine together. Therefore, the spinning of the steam turbine results in a similar movement in generators.
To note, power plants that employ combustible fossil fuels for this process require an exhaust piper for ridding the steam of pollutants. On the other hand, exhaust pipes are unnecessary in steam turbines with a solar heat source.
During the last stages of the process, the ready cooling tower reduces the temperature of the steam that passes through the turbine. Natural elements like rivers or lakes are also used in particular regions to lower steam temperature. Most of the used cold gas releases into the atmosphere while the remaining steam chills back into the liquid state. In many power plants, this is reused during future power generation cycles.
The basic process that works in steam turbine-based power generation is the Rankine cycle. Notably, power plant operators can utilize different methods to increase the efficiency of the regular steam turbines for optimal electric generation. However, it is important to consider the cost and necessary thermal efficiency improvements to find a balance for the turbine design. For example, more thermal stress in the blades due to higher steam inlet pressure can increase the cost and challenges from the engineering perspective.
How do you increase efficiency in steam turbines?
In the intermediate-pressure and high-pressure steam turbine, manufacturers can increase the height of the short blade. This improves the efficiency as well as capacity. Generally, last-stage blades result in low-pressure blade and exhaust loss; both are examples of the highest losses in steam turbine operations.
Developers focus on creating a reliable turbine design first. Optimizing the blades like the long last-stage blades can improve turbine performance highly. Also, a useful technique for designing an efficient steam turbine structure is handling harmonic and modal analysis to create 3D CFD simulations. Developers must focus on the stacking, length, twist/lean, and material for the blade design optimization.
It is important to consider the factors that affect the operation of steam turbines. Some examples are excessive moisture, thermal transients, low load operation, and axial thrust balancing. To note, all of these factors can result in different harmful issues if they are not detected or fixed early. Therefore, while designing the steam turbine, it is important to consider these problem areas first-hand to reduce the chance of eventual shutdown or damage.
For developers focusing on steam turbine design, they must have a deep understanding of turbine engineering and factors. For example, it is important to make sure that the dryness fraction related to the exhaust steam in bigger machines should stay at 88% or over. The design of the steam turbine can improve its performance and efficiency. So, power plant owners should keep note of their steam turbine parts and how they fit different power plants as well.
Currently, many new advancements and improvements in steam turbine designs are under R&D. It is important to keep up to date about the innovative design components and evaluate the system carefully as well.