Overview of Various Strategies for Balancing Salt Cake, Chloride, and Potassium in an ECF Kraft Mill, 1998 International Chemical Recovery Conference Proceedings

As mill closure increases, so does the accumulation of non-process elements in the kraft liquor cycle. The EPA Cluster Rule requires the implementation of best management practices (BMPs) to contain both pulp and liquor spills. This will require the liquor cycle to be closed more than is normally practiced. For the kraft recovery boiler, mill closure causes increased chloride and potassium concentrations in the as-fired liquor, resulting in a lower melting point ash in the boiler. This can lead to accelerated plugging in the upper superheater and boiler bank sections, resulting in downtime for water washing.

Two technologies for removing chloride and potassium from precipitator dust are described in detail. One is an evaporator/crystallize based process, while the other uses ion exchange. The evaporator/crystallizer process is effective for both chloride and potassium removal (90%), whereas the ion exchange process is more efficient at chloride removal (95%) and less selective in removing potassium (5-0%). The latter is more effective at salt cake recovery (95%) compared to the ormer (80%). The best suited technology depends on the requirements of each mill.