1. What is an HRSG?

An HRSG is a type of boiler that recovers thermal energy from hot exhaust gases, typically from gas turbines or industrial processes, and converts it into steam. This steam can then be used for power generation, process heating, or district heating. HRSGs significantly improve energy efficiency by making use of waste heat that would otherwise be discharged into the atmosphere.

2. Working Principle

The HRSG operates by transferring heat from exhaust gases to water through a series of heat exchange sections. These typically include:

• Economizer – Preheats the feedwater to improve thermal efficiency.

• Evaporator – Converts water into saturated steam.

• Superheater – Raises the temperature of the steam to the desired level.

• Steam Drum – Separates and stores steam and water.

These sections are arranged to maximize heat recovery and steam production, depending on the thermal characteristics of the exhaust gases.

3. Structural Types

HRSGs come in various configurations depending on pressure levels, space requirements, and operational needs:

• By Pressure Level:

  • Single-pressure HRSG: Simple design, suitable for small-scale applications.

  • Dual-pressure HRSG: Higher efficiency by using two pressure levels (high and low).

  • Triple-pressure HRSG: Offers the highest efficiency, typically used in large combined cycle plants.

• By Layout:

  • Vertical: Compact design, often used when floor space is limited.

  • Horizontal: Easier for maintenance, commonly used in large installations.

• Optional Features:

  • Can be integrated with Selective Catalytic Reduction (SCR) systems for NOx reduction.

  • May include bypass stacks for flexible operation during startup or maintenance.

4. Key Advantages

• High Efficiency: Boosts total system efficiency to over 60% in combined cycle setups.

• Environmental Benefits: Reduces fuel consumption and lowers emissions of pollutants and greenhouse gases.

• Economic Value: Provides significant energy savings and short payback periods.

• Flexible Design: Modular and customizable to suit different industrial needs.

• Broad Compatibility: Works with various gas turbines, industrial furnaces, and other heat sources.

5. Application Fields

HRSGs are widely used across a variety of industries, including:

• Combined Cycle Power Plants: Converts gas turbine exhaust into steam for additional power generation.

• Petrochemical and Refining: Recovers heat from process gas streams.

• Iron and Steel Production: Utilizes heat from blast furnace gas and other high-temperature flows.

• Waste-to-Energy Plants: Captures thermal energy from incineration.

• Marine Power Systems: Reuses engine exhaust heat on ships for onboard steam generation.

6. Future Trends

With global emphasis on carbon neutrality and smart manufacturing, HRSGs are evolving toward higher efficiency, digital integration, and lower emissions. Innovations such as intelligent control systems, digital twins, and carbon monitoring are expected to enhance performance, lifecycle management, and compliance with environmental regulations.

Conclusion

An HRSG is more than just a piece of equipment — it is a strategic energy recovery solution that helps industries maximize thermal efficiency, lower costs, and contribute to a sustainable future. As industries move toward greener practices, HRSGs will continue to be a key enabler of efficient and responsible energy use.