Steam Turbines Technology Applied in Turbines for Geothermal Plants
As geothermal steam contains corrosive gases and impurities such as silica, salt, and gravel, steam turbine design for geothermal plants has to be not only highly efficient, but also highly corrosive-resistant. Hence, the following technologies are applied in all our turbines for geothermal power plants.
- Extra-low Sulfur CrMoV Rotor Material
- Compared to low-pressure rotors used in steam power plants, this rotor material has higher corrosion resistance, resistance against stress corrosion cracking, and higher corrosion fatigue strength. This is achieved by reducing the amount of sulfur and nickel composition and adjusting the rotor quenching temperatures.
- 12Cr/17-4PH Material for blades
- Usually 12% Cr stainless steel is used for the blades, but for long blades where stresses is higher, and for first-stage blades where scaling easily occurs, 17-4PH is used. Compared to 12% Cr stainless steel, 17-4PH steel has better corrosion resistance against elements, such as H2S in geothermal steam, better resistance against stress corrosion cracking, and higher corrosion fatigue strength and durability.
- 3D Blades/Nozzles
- Full 3-dimensional design is used to optimize blade profile so as to minimize secondary losses and fluid frictional losses, thus increasing efficiency.
- ISB Blades/Last Stage Blades
- Integral shroud blades (ISB) are designed such that the root section, profile section and shroud form a single body. This eliminates the need for high accuracy assembly required for blades with sections manufactured separately. During operation, the ISB also connect with each other to increase vibrational damping and reduce tip leakages, thus increasing reliability and efficiency.
- Drain Catcher
To reduce water droplet erosion, drain catchers are designed to remove condensed water droplets in the low pressure stages.
- The following technologies are also applied for particularly corrosive steam conditions.
- 12Cr Rotor Material
- The amount of Cr is increased to improve resistance against stress corrosion cracking and corrosion resistance.
- Titanium Blades
- Used for first-stage blades when Cl (Chlorine)concentration is high in the geothermal steam.
- Inconel Thermal Spraying/Overlaying
- Applied at the gland sections susceptible to corrosion, so as to increase corrosion resistance.
- Casing/Diaphragm Horizontal Flange Surface Stainless Steel Overlaying
- Stainless steel overlaying is applied on the surface to increase corrosion resistance.
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