MECHANISMS OF RING FORMATION IN LIME KILNS

Rings form when lime mud or product lime particles adhere to the kiln wall and subsequently become hard and resistant to the abrasive action of the sliding/tumbling motion of product lime pellets. The adherence of particles to the kiln wall is partially attributed to the melting of Na2CO3 and Na2SO4 in the mud. The hardening of ring deposits is mai nly caused by recarbonation, which occurs when the ring temperature is below the lime mud calcination temperature. For kilns burning high su lphur containing fuel, hardening of the already formed rings may also be caused by sulphation. Impurities in the lime mud and sintering of p articles at higher temperatures have little impact on ring hardening w hen compared to recarbonation. From a practical standpoint, rings occu r mainly due to a combination of high sodium content in the lime mud a nd the instability of kiln operation.