Air Preheater Europe Design

Low Maintenance Cost and Low Leakage Rates with

Advanced Sealing System

Package APH with leaf seals and swivel type soot blower
Lower radial sealing plate
Radial seal adjusting device

The pressure differential between the air and flue gas streams requires that the Ljungström® APH be equipped with a sealing system to keep the flows separate. The sealing system comprises radial and axial seals that define the air and gas sections and also minimise the air-to-gas leakage to an acceptable level. A circumferential throttle ring prevents the flue gas and air flows from by-passing the rotor.


For small APH sizes, up to 8 m diameter, the most economical solution is a packagetype design with fixed radial sealing plates attached to the housing structure and leaf seals bolted to the edges of the radial walls of the rotor. The package radial sealing system cannot be adjusted from outside during operation.

Depending on the application and the customer’s requirements, an adjustable axial sealing system can also be installed.


Our large APHs always have adjustable radial and axial sealing plates. All seals can be adjusted from outside during operation. Semi- and fully automatic control systems are available for adjusting the radial and axial seals directly to the rotor diaphragm without any contact. Basically, three variants are available:



Standard Sealing System
Electro-Mechanical Sealing System
High-Tech Sealing System

Standard Sealing System

e.g. for oil- and brown coal-fired (bi-sector) units, with manually pre-set sealing plates and – for larger air preheaters – with an ON/OFF automatic adjustment at the hot side.



Electromechanical Sealing System

e.g. for hard coal (mill APH) units which have an ON/OFF automatic adjustment at the hot side or a sensor control system for large rotor diameters.



High-Tech Sealing System

e.g. for fluidised bed boilers, where all sector plates automatically follow the thermal deformation of the rotor by using our proven sensor technology for gap measurements. By increasing the number of diaphragms under the sealing plates (labyrinth) we can obtain very low leakage rates (ΔO2 < 1%) irrespective of the high pressure differential which is characteristic for FBC plants.

The selection of the sealing system is made taking into consideration the rotor diameter and the operating conditions of the boiler. Based on Air Preheater Europe design concept of a controlled and wear-resistant sealing system we can assure you that our low leakage rate will not increase between two boiler maintenance periods.

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