Chloride Removal from The Kraft Recovery Boiler Dust Using the Precipitator Dust Purification (PDP) System, 1998 International Chemical Recovery Conference Proceedings

As kraft mills gradually incorporate system closure, there is increasing concern about the accumulation of a number of non-process elements in the recovery cycle, chloride in particular. High levels of chloride lower the range of temperatures at which sticky deposits are produced on the superheater and the generating bank tubes of the kraft recovery boiler, leading to plugging of the flue gas passages. Plugging problems can cost a mill millions of dollars in lost pulp, steam, and electricity production. The precipitator dust purification (PDP) system was developed to address these problems. It removes sodium chloride from an aqueous solution of the electrostatic precipitator (ESP) dust of the recovery boiler. ESP dust from two inteior Canadian mills was dissolved in water at 55 °C, and filtered to remove suspended solids. It was then introduced into a fixed-resin bed which retained sodium chloride in preference to sodium sulphate and carbonate. Chloride removal efficiency of 97% was achieved, while the recovery of sodium sulphate and sodium carbonate was as high as 98%. The chloride-free ESP dust solution can then be returned to the kraft recovery cycle. A computer simulation indicated that treating the ESP dust using the PDP system would result in an increase in the melting point temperature of the superheater deposits.