Gas-to-Gas Shell & Tube Heat Exchanger
Gas-to-gas shell-and-tube exchangers are used in industries where recovering heat from gas streams is critical for energy efficiency or emissions control:
a. Power Generation
Flue gas heat recovery: Transferring heat from boiler flue gas (hot gas) to preheat combustion air (cold gas), reducing fuel consumption.
Turbine exhaust heat recovery: Capturing waste heat from gas turbine exhaust to preheat compressed air entering the turbine.
b. Industrial Processes
Chemical manufacturing: Cooling or heating process gases (e.g., drying gases, refrigerant gases).
Metallurgy: Recovering heat from furnace exhaust gases to preheat incoming air or fuel gases.
c. Waste Treatment
Incineration plants: Cooling hot exhaust gases from waste incineration to recover energy or prepare gases for scrubbing.
Biogas processing: Heating raw biogas (to remove moisture) using waste heat from cleaned biogas.
d. HVAC & Energy Recovery
Air preheaters: In large buildings or industrial facilities, preheating outside air with exhaust air to reduce heating costs.
Design Considerations
To address the challenges of gas-to-gas heat transfer, designers focus on:
Surface area enhancement: Finned tubes are almost universal—external fins (for shell-side gases) or internal fins (for tube-side gases) increase contact area by 3–10x.
Flow velocity: Higher gas velocities (within pressure drop limits) create turbulence, improving heat transfer coefficients.
Material selection:
For clean gases (e.g., compressed air), carbon steel is common.
For corrosive gases (e.g., flue gas with sulfur dioxide), alloys (e.g., 316 stainless steel) or coated tubes (e.g., ceramic coatings) are used.
For high-temperature applications (e.g., turbine exhaust), heat-resistant alloys (e.g., Inconel) may be required.
Fouling prevention:
Smooth tube surfaces or anti-fouling coatings reduce particulate buildup.
Access doors or removable tube bundles simplify cleaning (e.g., for ash-laden flue gases).
Thermal stress relief: Expansion joints in the shell or U-tube designs accommodate thermal expansion from large temperature differences.
