1. Operating Pressure and Temperature

• High Pressure Heater (HP Heater)
  Operates at higher extraction steam pressures, usually in the range of 2.5–8.0 MPa, with feedwater temperatures close to saturation. Due to harsh conditions, the equipment must withstand high pressure and significant thermal stress.

• Low Pressure Heater (LP Heater)
  Works at lower extraction or exhaust steam pressures, typically 0.2–1.0 MPa. The operating temperature is lower, and the structural design is relatively simple compared to HP heaters.

2. Installation Location

• HP Heater
  Installed after the boiler feed pump (at the pump discharge side). It heats the high-pressure feedwater before it enters the boiler, ensuring higher efficiency and stable operation.

• LP Heater
  Installed before or after the condensate pump. It preheats the condensate to reduce the temperature difference and prevent cold water from directly entering the cycle.

3. Structure and Safety Requirements

• HP Heater
  Commonly designed as a shell and tube heat exchanger. Tubes are often made of stainless steel or alloy steel. Thicker walls, safety valves, and relief devices are required to handle high pressure. Welding quality and hydrostatic testing standards are strict.

• LP Heater
  Built with simpler structures and lower material strength requirements. Carbon steel or low-alloy steel is often used, making it easier and cheaper to maintain.

4. Functional Role

• High Pressure Heater: Increases boiler feedwater temperature, improves boiler efficiency, and protects against thermal stress caused by cold water.

• Low Pressure Heater: Increases condensate temperature, reduces pump cavitation risk, and contributes to higher cycle efficiency.

5. How to Distinguish HP Heater from LP Heater

1. Pressure Level: Above 2 MPa is typically a high pressure heater; below 1 MPa is usually a low pressure heater.

2. Installation Position: Located after the feed pump indicates an HP heater; before/after the condensate pump indicates an LP heater.

3. Design and Structure: HP heaters are larger, with thicker walls and more safety devices.

4. Purpose: HP heaters directly improve boiler efficiency, while LP heaters function as preheaters in the cycle.

Conclusion
Both high pressure heaters and low pressure heaters are vital components of feedwater heating systems in power plants. Their differences lie in operating pressure, installation position, structural design, and purpose. By working together, they form a multi-stage heating system that significantly improves thermal efficiency, reduces fuel costs, and ensures safe and reliable turbine operation.