Flue Gas Heat Recovery Finned Tube Heat Exchanger for Boiler

This is an energy-saving device installed in the tail flue of a boiler. It uses finned tubes to expand the heat exchange area, recovering the sensible heat of high-temperature flue gas (typically 200–400°C) to preheat feedwater/combustion air or produce hot water, significantly improving boiler efficiency and reducing flue gas temperature and fuel consumption.

Working Principle: High-temperature flue gas flows horizontally across the fins outside the tubes, while the low-temperature medium (water/air) flows inside. Heat is transferred between the fins and the tube wall, achieving recovery.

The fins expand the heat exchange area to 5–10 times that of bare tubes and enhance flue gas turbulence, resulting in a heat transfer efficiency 30%–50% higher than bare tubes.

Typical Effects: Flue gas temperature drops from 250–350°C to 100–160°C; boiler efficiency increases by 5%–10%; for every 20°C reduction in flue gas temperature, efficiency increases by approximately 1%.

Core Structure (Finned Tube Bundle)

Base Tube: Carbon steel / Alloy steel / Stainless steel (e.g., SA210C, SA213), temperature and pressure resistant.

Finals: High-frequency welded spiral fins, serrated fins, plate fins; material: carbon steel / stainless steel; fin pitch 15–100mm, designed according to dust and corrosion requirements.

Tube Bank: In-line / staggered, staggered arrangement provides stronger heat exchange but slightly higher resistance.

Inlet/Outlet Headers: Distribute and collect media, with drain/vent ports.

Shell: Carbon steel / Stainless steel, equipped with inspection doors and ash cleaning ports (sonic / rapping ash cleaning).

Main Types and Applications

Economizer: Most commonly used for heating boiler feedwater; reduces flue gas temperature to 120–160°C, increasing efficiency by 5%–8%.

Air Preheater: Preheats combustion air to 150–350°C, enhancing combustion and reducing NOₓ; suitable for high-dust flue gas.

Hot Water Heater: Provides industrial/domestic hot water; exhaust gas temperature can be reduced to below 100°C; commonly used in gas-fired boilers.

Key Advantages:

✅ High Efficiency and Energy Saving: Heat recovery efficiency up to 40%, gas saving rate up to 9.14% (inlet water < 45°C).

✅ Compact Structure: 40%–60% smaller than bare tubes under the same load, suitable for retrofit projects.

✅ Anti-clogging and Wear-resistant: Optimized fin spacing and tube bank, optional ash removal device, adaptable to high-dust/corrosive flue gas.

✅ Quick Payback: Investment typically recovered in 6–18 months, long-term reduction in operating costs.

Design and Selection Considerations:

Flue gas conditions: temperature, flow rate, dust content, dew point (for low-temperature corrosion protection). Medium parameters: Inlet and outlet temperature, pressure, flow rate (feedwater/air/water).

Fin selection:

Low dust (gas-fired): High-density fins (10–15 fins/inch).

High dust (coal-fired/biomass): Low density, large fin spacing (4–8 fins/inch), anti-clogging.

Material matching:

Medium temperature (>160°C): Carbon steel/carbon steel fins.

Low temperature/corrosion (<160°C): ND steel/stainless steel fins, anti-dew point corrosion.

VI. Application scenarios

Industrial boilers (gas-fired/oil-fired/coal-fired/biomass)

Waste heat boilers (HRSG)

Kilns/Heating furnace tail sections

Power plants/Waste incineration plant flue gas cooling