Air Preheater Enhancement – Shentou Power Station, China

Air preheaters at Shentou Power Station were permitting excessive amounts of leakage, due to erosion of the sealing surfaces. Conversion to the Howden VN sealing system reduced leakage from 17% to 6%. Shentou No 2 power station, consists of 2x500MW units firing local coal. The high quantity of ash in the flue gas was a major cause of erosion, which resulted in the leakage in the two quad-sector regenerative airpreheaters being significantly higher than the design value. In addition, it was identified that the parallel sector plate arrangement did not fully provide effective sealing.

It was decided that many features of the Howden VN design should be fitted to the existing air preheaters. The radial and axial sector-plates separating primary and secondary air had to be replaced because of erosion, it was therefore decided to widen the sector-plates in conjunction with increasing the number of radial plates in the rotor to achieve double sealing along the full radius. The reduction in free rotor area due to the widening was not significant. The effect of double sealing is to reduce the pressure drop across each seal, which in turn lowers the velocity of the particles hitting the sector-plates and other components, thus significantly reducing wear. Erosion of the drive rack on the rotor rim was also a problem. To alleviate this the heater was converted to the Howden centre drive system.

With this configuration, all drive components are located on the top of the shaft, outside the gas stream. A further benefit is that the axial seals can run the full length of the rotor, which improves the overall sealing.

Air to gas leakage was reduced from 17% to less than 6%. Primary air to secondary air leakage was reduced by 25%, which was reflected in the reduction of motor current from 320 to 240A per fan. This was equivalent to savings of 1200kW per boiler, and when the FD and ID fans were also considered, the power savings totalled 1600kW.

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