Acoustic analysis of recovery boiler dissolving tank operation and smelt shattering efficiency

The interaction of molten smelt and water inside a recovery boiler dissolving tank produces loud noise and can be violent even during normal boiler operation. Inadequate shattering of the smelt stream leads to even more violent interaction, as evidenced by an increased acoustic intensity of the dissolving tank. On rare occasions, a violent dissolving tank can explode, causing equipment damage and even injury to personnel. To warn operators of changes in dissolving tank conditions, an acoustics-based monitoring system could be developed. To assess the feasibility of such a system, acoustic observations were recorded at three pulp mills. Analysis of the recordings indicates that when a smelt stream is not being shattered, the intensity of the dissolving tank soundscape increases significantly and the frequency spectrum changes. We also observed a large variation between different mills both in average intensity and in signal variance. The results of this study suggest that the development of a monitoring system is feasible.