How does a boiler exhaust condensing waste heat recovery device work?

A boiler exhaust condensing waste heat recovery device works by capturing both sensible heat and latent heat from boiler flue gas that would otherwise be discharged to the atmosphere, significantly improving overall boiler efficiency.

The working principle can be explained in the following steps:

1. Flue Gas Heat Extraction

Hot exhaust gas from the boiler flows through the waste heat recovery heat exchanger. As the flue gas passes over heat transfer surfaces, its sensible heat is transferred to a colder medium, typically boiler feedwater, make-up water, or process water.

2. Cooling Below the Dew Point

As heat is removed, the flue gas temperature is reduced below its dew point (generally 45–60°C, depending on fuel type and moisture content). At this point, water vapor in the flue gas begins to condense on the heat exchanger surfaces.

3. Latent Heat Recovery Through Condensation

When water vapor condenses into liquid water, it releases latent heat. This latent heat represents a significant portion of the energy loss in conventional boilers and is captured by the heat exchanger and transferred to the circulating water.

4. Condensate Collection and Drainage

The condensed water forms acidic condensate due to dissolved flue gas components. The system includes sloped surfaces, drain connections, and condensate piping to safely collect and discharge the condensate. Neutralization systems are often added before disposal or reuse.

5. Reuse of Recovered Heat

The recovered thermal energy is reused for applications such as boiler feedwater preheating, domestic hot water production, space heating, or low-temperature industrial processes. This reduces boiler fuel consumption and improves system efficiency.

6. Low-Resistance Exhaust Discharge

After heat recovery, the cooled flue gas exits the device at a much lower temperature. The heat exchanger is designed to maintain low pressure drop to avoid increasing back pressure on the boiler.

Summary of the Working Principle

By combining sensible heat recovery and latent heat recovery through condensation, a boiler exhaust condensing waste heat recovery device can increase boiler thermal efficiency by 5–15% or more, reduce fuel consumption, and lower emissions, while safely managing condensate and corrosion risks.