Applications

• HP to cold reheat
• HRH (Hot Reheat) to condenser, also known as:
  • IP/ LP bypass to condenser
  • LP bypass to condenser
• HP to condenser

Purpose : Turbine bypass systems increase the flexibility in operation of steam power plants. They assist in faster start-ups and shutdowns without incurring significant damage to critical and expensive components in the steam circuit due to thermal transients. In some boiler designs, turbine bypass systems are also used for safety function.

Major hardware components of turbine bypass systems are:

• Steam pressure-reducing valve
• Desuperheater
• Spraywater control valve
• Spraywater isolation valve
• Dump tube/sparger (only for bypass to condenser)
• Actuator

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Performance of the turbine bypass system has a strong influence on plant heat rate and capacity, effective forced outage rate (EFOR) and long-term health of critical components such as boiler tubes, headers and steam turbines. Therefore, correct sizing and selection of all components in turbine bypass systems is essential for smooth operation of a steam plant.
The 530D/540D design meets the critical functional requirements of turbine bypass systems which are:

• High reliability - necessary to achieve high plant availability
• Low vibration and noise - for personnel and equipment safety
• Fine control - for smoothness of start-ups and shutdowns, as well as for long-term life of critical high-pressure, high temperature components
• Tight shutoff - necessary to avoid penalty in heat rate and/or reduction in plant output; class V or MSS SP-61 shut-off is available upon request
• Excellent, reliable desuperheating performance - for long-term protection of the downstream equipment
• Ease of maintenance - no welded seat or cage

Turbine bypass systems are generally sized for a specific percent bypass, which depends on the end-users intent and desire for functionality. Common practices for bypass capacity are 30 – 35%, 60 – 70% and 100% of the design flow. Each of these reflects differing intent of how the plant will be operated and/or the functionality desired in operation. Koso 530D/540D bypass systems are configured with pneumatic actuators; electro-hydraulic actuation is available upon request. Electric actuators are generally not used for this application unless slower response is permitted by the steam system design.