Enamel Tube Air Preheater

Enamel Tube Air Preheater

Enameled tube air preheater is a heat exchange device that uses waste heat from flue gas to heat the air. Its core feature is that the heat exchange element is made of "enameled tube"—a composite tube made by coating a metal base (usually steel) with a plastic coating (such as fluoroplastic or epoxy resin) through an enameling process.

It is primarily used in combustion systems such as boilers and industrial furnaces. By recovering heat from the flue gas, it preheats the air entering the combustion chamber, thereby improving combustion efficiency, reducing fuel consumption, and minimizing heat loss from exhaust gas.

Enameled tube air preheaters achieve heat recovery through indirect heat exchange between hot and cold fluids:

On the high-temperature side: High-temperature flue gas (typically 300-600°C) from boilers and other equipment flows through the exterior (or interior) of the enameled tube, releasing heat.

On the low-temperature side: Cold air to be heated (ambient temperature or slightly above) flows in the opposite direction through the interior (or exterior) of the enameled tube, absorbing heat transferred from the tube wall and raising its temperature (typically to 100-300°C).

Heat transfer: Flue gas and air exchange heat through the enameled tube wall, ultimately lowering the flue gas temperature (and thus the exhaust gas temperature). The heated air then enters the combustion chamber and participates in combustion.

The unique design of the enameled tube is the key to this type of air preheater. Its advantages primarily stem from the properties of the plastic coating on the surface:

Strong corrosion resistance: Flue gas often contains sulfur oxides (such as SO₂, SO₃), nitrogen oxides (NOₓ), and water vapor. At low temperatures, these gases easily form acidic corrosive solutions (such as sulfuric acid mist), which can corrode traditional metal pipes (such as carbon steel and ordinary alloy steel). Enamel coatings (such as fluoroplastics) offer excellent chemical resistance, resisting attack by acids, alkalis, and salts. They are particularly well-suited for the corrosive flue gas environments generated by the combustion of high-sulfur fuels (such as high-sulfur coal and heavy oil).

Abrasion and Ash Deposits

Fly ash (such as coal dust and ash) carried in flue gas can cause erosion and wear on the pipe wall. The smooth surface and moderate hardness of the enamel coating reduce direct damage from fly ash. Furthermore, the smooth surface is less prone to ash absorption, reducing ash accumulation and the resulting decrease in heat transfer efficiency, thereby reducing cleaning and maintenance frequency.

Balanced Thermal Conductivity

Although the thermal conductivity of plastic coatings is lower than that of metals, the metal substrate of enamel pipes ensures basic thermal conductivity. Furthermore, the coating thickness is typically thin (less than a few millimeters), minimizing the impact on overall heat transfer efficiency. This provides a balance between corrosion protection, wear resistance, and heat transfer performance. Extending Equipment Life

Compared to traditional metal pipes, spun-tube air preheaters significantly resist corrosion and wear, reducing the risk of leaks due to wall damage, extending the life of air preheaters (typically by 30%-50%), and reducing equipment replacement costs.

The advantages of spun-tube air preheaters make them particularly suitable for harsh operating environments. They are primarily used in:

Coal-fired boilers (especially power plant and industrial boilers burning high-sulfur coal);

Waste incineration boilers (flue gas contains highly corrosive components such as chlorides and heavy metals);

Biomass boilers (flue gas contains alkali metal oxides, which are prone to scaling and corrosion);

Other industrial furnaces with complex flue gas compositions, high corrosiveness, or high fly ash concentrations.