Q: When the process requires the heater to operate continuously at 850°C and the flue gas has a high dust content, which is more suitable: finned tube or bare tube bundle?
The finned tube heat exchanger consists of base tubes and metal fins wound or fitted onto the outside of the tubes. The fins extend the heat exchange area on the flue gas side, so that under the same volume the heat exchange capacity is higher than that of a bare tube bundle. For high-temperature dust-laden conditions, the fin spacing can be designed at 8–12 mm to reduce ash bridging; the base tubes can use heat-resistant alloy steel, and the design working temperature can reach 850°C, meeting the hot air circulation requirements of the heater package.
The bare tube bundle heat exchanger has a simple structure and high pressure resistance, but its heat exchange area per unit volume is limited, and it requires a larger footprint under the same heat load. The finned tube option expands the outside tube area by 4–8 times through fins, significantly reducing the flue gas side thermal resistance and lowering overall metal consumption, making it suitable for retrofit projects with limited space. It should be noted that the fin side is not suitable for liquid media prone to scaling, and the flow velocity of dust-laden flue gas should also be controlled at 8–12 m/s.
If the finned tube heat exchanger is used with electric heating elements, the wiring should be connected correctly according to the nameplate voltage and reliably grounded. The finned tube bundle should reserve thermal expansion clearance to avoid cracking of the tube sheet at high temperature. For design and selection personnel, it is recommended to calculate the required number of finned tube rows based on flue gas flow rate, inlet temperature, and allowable pressure drop, and then check whether the base tube wall temperature exceeds the allowable range of the material.
