ABOUT LEAKS

Reducing air leaks to the flue gas is the main goal of most of the modernizations of the Rotary Air Preheaters. Better sealing of the rotor reduces heat loss, causes smaller power consumption by fans, improves the efficiency of electrostatic precipitators and reduces the annual cost of overhauls for preheaters.

Large rotor diameters (up to several meters) and big differences in temperature between the cold and the hot end (up to ~ 400°C) cause significant dynamic thermal distortion of the rotor, reaching up to a few cm on the perimeter and varying along with the changing of the boiler load. In addition, there is a large pressure differential between the flowing air (at overpressure) and flowing flue gas (at a vacuum), which is the main cause of leaks occurring in Rotary Air Preheaters. For this reason, it is extremely difficult to seal this type of preheater, there is no technology that allows to 100% avoid leaks.

The figure shows unwanted gas flow directions:

1. Ambient air sucked into the flue gas outlet channel through radial seals under the radial wings – increases the amount of air in the flue gas, reduces flue gas temperature, increases the amount of gas volume.

2. Preheated air after passing through the rotor sucked into the inlet flue gas channel by radial seals under the radial wings – as above.

3. The air bypasses the rotor around the ZK air channel and enters the space between the rotor and circumferential seals, part of the flow bypasses the circumferential seals on the GK and goes directly to the boiler, another part takes the direction of the rotation of the rotor and through the gaps between the axial wings and rotor is sucked in to the exhaust channel and mixes with the flue gas – increases the amount of air in the flue gas, reduces flue gas temperature, a part of it bypasses the rotor and does not take part in the balance of power.

4. Flue gas bypasses the rotor around the GK exhaust channel and enters into the space between the rotor and the circumferential seals – it does not transfer heat to the heating elements and increases the undesirable volume of the flue gas before entering the electrostatic precipitator.