Heat Recovery System Generator (HRSG)

The Heat Recovery Steam Generator (HRSG) is an essential component in combined-cycle power plants and other industrial applications that efficiently recovers waste heat from exhaust gases and converts it into steam. This steam can then be used to generate additional power or for other industrial processes. Here are the key features of an HRSG:

1. Heat Recovery Efficiency

• The primary function of an HRSG is to recover heat from exhaust gases, typically from a gas turbine, and convert it into useful steam.
• HRSGs have high thermal efficiency, often between 80% to 90%, depending on design and operational conditions.

2. Modular Design

• Many HRSGs feature modular designs, making them adaptable for various plant sizes and configurations. This allows for easier installation and flexibility in upgrading or expanding power generation capacity.

3. Multiple Heat Exchange Surfaces

• HRSGs include several heat exchange sections, such as economizers, evaporators, superheaters, and reheaters. Each section plays a specific role in recovering heat and producing steam at the desired temperature and pressure.
  • Economizers: Preheat the feedwater using exhaust gases before it enters the boiler.
  • Evaporators: Convert water into steam.
  • Superheaters: Increase the steam temperature to a required level for use in turbines.
  • Reheaters: Increase the steam temperature after partial expansion in the turbine for optimal efficiency.

4. Steam Production

• HRSGs generate steam that can be used for electricity generation in steam turbines or in industrial processes.
• The steam pressure and temperature can be customized based on the plant’s requirements, ranging from moderate pressures (20–30 bar) to high pressures (up to 90 bar or more).

5. Flexible Operating Conditions

• HRSGs are designed to handle variable operating conditions. They are capable of operating efficiently across different load levels, from full load to partial load, which is common in power plants that use gas turbines with fluctuating power demands.

6. Material Durability

• The construction materials of HRSGs are selected to withstand the high temperatures and pressures encountered during operation. Materials such as carbon steel, stainless steel, and sometimes nickel-based alloys are used for components exposed to high heat and corrosion.

7. Stack and Bypass System

• HRSGs are often equipped with a bypass system that allows exhaust gases to bypass the heat recovery process when the HRSG is not needed, such as during plant startup or when operating at low load. This ensures that the gas turbine can still operate efficiently without overloading the HRSG.
• The stack is used for the safe discharge of exhaust gases after the heat recovery process.

8. Integrated Control and Monitoring Systems

• HRSGs are equipped with advanced control and monitoring systems that track parameters such as temperature, pressure, and steam flow rate. These systems optimize performance, ensure safe operation, and can adjust operation to meet varying demands.
• Automated systems can adjust steam production based on load changes, maintaining efficient heat recovery.

9. Reduced Environmental Impact

• By recovering waste heat from exhaust gases, HRSGs reduce fuel consumption and increase the overall efficiency of power generation, thus lowering greenhouse gas emissions.
• HRSGs often incorporate emissions control systems to reduce harmful emissions, including NOx, CO, and particulate matter, meeting environmental regulations.

10. Compact and Space-Efficient

• HRSGs are designed to be compact and space-efficient, making them ideal for installations where space is limited or where there is a need for a modular system.

11. Heat Recovery from Multiple Sources

• HRSGs are capable of recovering heat from multiple sources, including gas turbines, reciprocating engines, or industrial furnaces, depending on the specific design and application.

12. Operational Flexibility

• HRSGs can operate in different modes, including once-through (single pass) and multi-pressure systems, depending on the steam requirements and the configuration of the plant.
• The multi-pressure system can handle different steam pressures at various stages of the steam cycle, improving overall efficiency.

13. Maintenance and Inspection

• HRSGs are designed with accessibility features for maintenance and inspection. Regular maintenance of components like heat exchangers, drums, and water treatment systems is crucial for ensuring long-term operation and preventing efficiency losses due to scaling or corrosion.

14. Condensing and Non-Condensing Options

• HRSGs can be designed for condensing applications (where steam is condensed back to water) or non-condensing applications (where steam is used directly for process or mechanical work).

15. Corrosion and Scaling Protection

• HRSGs include features to protect against scaling and corrosion, which can degrade the heat transfer efficiency. Regular blowdown and water treatment systems help maintain performance.