Rotary Air Preheaters for Waste Heat Recovery From Boiler Flue Gas in Thermal Power Plants

Air preheaters are key auxiliary equipment in thermal power plants. They are heat exchange devices that utilize the waste heat of flue gas to heat the air needed for boiler combustion. Air preheaters operate in the area of ​​the boiler with the lowest flue gas temperature, recovering heat from the flue gas, reducing exhaust gas temperature, and thus improving boiler efficiency. An air preheater is a heat exchange surface in the boiler's tail flue gas duct that preheats the air entering the boiler to a certain temperature through internal heat exchange fins. It is used to improve the boiler's heat exchange performance and reduce energy consumption. It is generally referred to simply as an air preheater. It is mostly used in coal-fired boilers. In boiler applications, it is generally a three-compartment type.

Rotary air preheaters are a type of regenerative air preheater. Flue gas and air flow alternately through an intermediate heat carrier. This type of air preheater consists of a rotating rotor and a fixed outer shell. A fan-shaped top and bottom plate fixed to the outer shell divides the rotor's flow cross-section into two parts: one part allows flue gas to flow from top to bottom, and the other part allows air to flow from bottom to top. The fan-shaped top and bottom plates are connected to the upper and lower flue gas ducts and air ducts of the outer shell, respectively. In this way, the flue gas heats the corrugated plates as it flows through. When the rotor rotates to the airflow section, the corrugated plates are cooled by the air, which in turn heats the air. Therefore, one rotation of the rotor completes one heat transfer process.

Large-capacity boilers generally use rotary air preheaters, primarily those with rotating heating surfaces (Junker type). Due to their inherent structure, rotary air preheaters commonly experience some problems during operation, with air leakage being a relatively common one. The air leakage rate of rotary air preheaters is generally around 8%, but can reach 20% in severe cases. Solving the air leakage problem is an urgent requirement for power plants.